Geology of the Isle of Wight : a brief explanation of the Isle of Wight Geological Sheet. Parts of sheets 330, 331, 344 and 345 Isle of Wight (England and Wales)

P M Hopson and A R Farrant

With contributions by A J Newell, K A Lee, J Thompson, M A Woods, I P Wilkinson, L B Bateson, G K Lott, C Dashwood, G O Jenkins, D G Cameron, D Beamish and C James

Bibliographic reference: Hopson, P M, and Farrant, A R. 2015. Geology of the Isle of Wight—a brief explanation of the geological sheet. Sheet Explanation of the British Geological Survey. Parts of 1:50 000 sheets 330 (Lymington), 331 (Portsmouth), 344 (Chale) and 345 (Ventnor) (England and Wales).

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Keyworth, Nottingham: British Geological Survey

Notes

Acknowledgements

The authors, Peter Hopson and Andy Farrant, would like to thank all of our colleagues who have contributed to this Sheet Explanation whilst the Integrated Isle of Wight Project was in existence. They include Andrew Newell, Kathryn Lee, Joanna Thompson, Luke Bateson, Gareth Jenkins, Claire Dashwood, Graham Lott, Ian Wilkinson, Mark Woods, Ceri James, Dave Evans, Andy Hulbert, Don Cameron and Lee Jones. Thanks go also to the BGS Drilling crew who completed four campaigns on various sites throughout the island under the guidance of Steve Thorpe and Chris Slater; and to Sheila Myers, Henry Holbrook, Tony Clifton, Niall Spencer, Bob Cooper and Jerry Hodgson in cartography who contributed so much with the published maps and illustrations throughout the life of the project. Early drafts of the explanation were reviewed by Don Aldiss. Finally, the BGS Editor, Joanna Thomas, and other reviewers are acknowledged without whom this Sheet Explanation would not be published.

Considerable assistance to the project has been forthcoming from a number of people whose help was freely given. We would like to thank, in no particular order, Professor Andy Gale (Portsmouth), Professor Rory Mortimore (Brighton), Professor Steve Hesselbo (Oxford), Professor Malcolm Hart (Plymouth), Professor Ian Jarvis (Kingston), Dr Becky Briant, Dr Rob Scaife, Dr Peter Montgomery, Dr Francis Wenban-Smith, Dr Chris King, Dr Adrian Palmer and lastly Dr Rebecca Loader (Senior Archaeologists IoW) who kindly reviewed the section on the human occupation of the island.

Thanks are extended to Graham Heard and Jerry Field of Northern Petroleum, Neil Anderton and UKOGL for permission to use the seismic line shown in (Figure 4) herein (website: www.ukogl.org.uk); Steve Burton and Alan Bulpin of Aggregate Industries (UK) Ltd (Bardon Vectis) for access to St Georges Down; Mike Packman (Southern Water); representatives in various departments of the Isle of Wight Council; Dr Martin Munt formerly Curator of Geology Museum of Isle of Wight, Isle of Wight Council and now with The Natural History Museum, London; Robin Lang of the National Trust for the considerable help in access to NT land and for accommodating our drilling rig at various sites; Mr O Hoskyns (Hobbits Farm), Mr R Morgan (Knighton Sand Pit), Dr K Ballard (RSPB, Brading), Mr D Lovegrove (Hill Farm) who all permitted access to our drilling rig.

We would also like to thank Mr Mike Forsyth-Caffrey of the Maritime and Coastguard Agency, The Freshwater Bay Independent Lifeboat Crew who saw us safely to Scratchell’s Bay, Mr Bill Webb of the Isle of Wight Geological Society, Edwin and Sally Burt who put up with the team over many weeks at their West Standen Farm. Lastly all our thanks go to the land owners and the many interested residents and tourists who we met throughout the survey.

Chapter 1 Introduction

This sheet explanation provides a summary of the geology of the Isle of Wight district (Special Sheet) arising from the British Geological Survey’s Isle of Wight Integrated Project. This project, commenced in September 2007 and completed in 2013, sought to improve the understanding of the near-surface geology, and create representational models of the 3D structure. This will provide essential framework information for use by the geological community operating in this classic area of British geology.

This sheet explanation and accompanying 1:50 000 scale geological map special sheet are principally aimed at users in academia, local authorities and statutory bodies, but also at the large number of ‘geotourists’ that are such an important part of the island’s economy. A Special Issue of the Proceedings of the Geologists’ Association (Geologists’ Association, 2011) introduced by Hopson (2011) gives further detailed accounts of the recent work by BGS on the island.

The Isle of Wight (Figure 5). Deep boreholes (see also (Figure 9): 1. Norton 1, SZ38NW18; 2. Wilmingham 1, SZS38NE9; 3.Bouldnor Copse 1, SZ39SE1; 4. Sandhills 1, SZ49SE3; 5. Sandhills 2, SZ48NE55; 6. Cowes1 (Bottom Copse), SZ59SW17; 7. Arreton 1, SZ58NW2; 8. Arreton 2, SZ58NW1; 9. Chessell 1, SZ48NW11." data-name="images/P937077.jpg">(Figure 1), the largest island in England at 384 km2, is separated from the mainland by the Solent. This body of water is essentially the drowned lower reaches of an extensive Quaternary river system draining much of southern central England. The island’s protective presence offshore of the south coast within the English Channel strongly influences the tidal regime within the Solent system and led directly to the development of Southampton and Portsmouth as major ports. Large parts of the island form Areas of Outstanding Natural Beauty (ANOBs) and a considerable length of the coastline in the south-west and north-west of the island is designated as Heritage Coast (Figure 45)." data-name="images/P937078.jpg">(Figure 2).

Topographically the diamond shape of the island is the direct result of the presence of a central, east–west orientated ridge, of complex tectonic origins, founded on the steeply dipping, moderately hardened, Chalk Group (Figure 3). The softer sediments of the Palaeogene forming lower-lying ground within the northern, mainland-facing, part of the island are protected from extensive tidal erosion by this Chalk ridge. To the south-west of the central ridge, sediments of the Early Cretaceous, forming low cliffs, suffer extensive erosion from Atlantic storms funnelling up the Channel. The south-eastern coast, eastward of St Catherine’s Point, is protected by a capping of more durable, essentially horizontal Upper Greensand and Chalk strata forming the Southern Downs but here an extensive, deeply seated landslide (the largest in north-west Europe) considerably modifies the coastal geomorphology.

Geological setting and history of research

The island has long been regarded as one of the most significant of the classic areas of British geology. It has been of interest for geological studies since the early 19th century. This interest had spawned an industry of competing geotourist guides and pamphlets. Many of the earliest are no more than descriptions of leisurely tours, locations to visit, as well as describing selected views and geomorphological features. All of them offer something of a social commentary of their times, for example in Mill (1832), Ware (1871) and the Ward Lock and Co. series—‘Illustrated Guide to the Isle of Wight’—first published in 1880 and almost annually thereafter (e.g. Ward Lock, 1920) until the 1970s. Many, however, carry the reader through the spectacularly exposed rocks on the coast and their inland occurrences in great detail. Pre-eminent amongst these are perhaps Englefield (1816) and Mantell Mantell (1847); Mantell, (1851, 1854—editions that also carry one of the earliest published geological maps). In terms of volume of publications, the many-editioned Brannon’s Pictures of the Isle of Wight (e.g. Brannon, 1848a, b) distributed from his home in Wootton Common on the island are important. There are, in addition, many other notable tour guides and geological reviews, for example: Nelson (1859), Wilkins (1859), Venables (1860), Norman (1887), Colenutt (in Morey, 1909); Clinch, (1921), and Hughes, (1922) to name just some of the more readable.

There were many notable Victorian geological treatises, such as the Memoirs of the Geological Survey (Bristow, 1862; Forbes, 1856; Reid and Strahan, 1889; White, 1921) and articles in the then fledgling scientific publications such as the Journal of the Geological Society, (e.g. Prestwich, 1846 and Fitton, 1847) and in the Transactions (Webster, 1814), in the Geological Magazine (e.g. Jukes-Browne, 1877; Reid, 1887) and the Proceedings of the Geologists’ Association (e.g. Rowe, 1908).

The island is, and has been, very popular for geological field excursions to satisfy all levels of academic attainment from primary and secondary school levels through to academic research studies, and by industry as onshore exploration analogues. Indeed this long-term interest is illustrated by the numerous field meetings run by the Geologists’ Association. Excursion reports, describing various aspects of the geology in the Isle of Wight, were published, under the excursion directors name, at regular intervals within the Proceedings up to the present day including 1864, reported in the Geological and Natural History Reportory for 1866; 1882; 1892; 1896; 1906; 1919; 1933; 1948; 1954; 1957; 1962; 1964; 1971; 1974; 1979; and 1994. The Geologists’ Association also published a Guide (No. 25) on the geology of ‘The Isle of Wight’ (Curry and Wright, 1958) that was subsequently revised (Curry et al., 1972; Curry et al., 1966; Daley and Insole, 1984) before being reissued, later, as Guide No. 60 (Insole et al., 1998). The Association also featured the island in its 50th Jubilee Volume (Herries, 1909), wherein a comprehensive review of the complete geological succession was given. In addition, there are a great number field guides written for professional organisations dedicated to various aspects of the island’s geology, for example Wach and Ruffell (1991) and Briant et al. (2009). There are also a large number of PhD theses devoted to the geology of the island e.g. Daley (1969); Swiecicki (1980); Laurie (2006) and many more, and, of course, perhaps the largest number of learned papers for any area of the British Isles of this size. The bibliography within the 5th impression of White’s Memoir (1994) is extensive, but by no means comprehensive, given the upsurge in interest in the island’s geology within both PhD theses and papers since the 1980s. Many newer references and the revised terminology for the Chalk and the Lower Cretaceous strata on the island, used throughout this explanation, are set out in two research reports of the British Geological Survey (Hopson, 2005; Hopson et al., 2008) that can be downloaded free from the BGS website.

With the exception of the Jurassic strata (proven at depth in hydrocarbon exploration boreholes) the island is a microcosm of the later Mesozoic and Cenozoic strata that are found widely across south-eastern England. This succession is laid bare in spectacular sea cliffs, stretching for a total of 98 km that provide essential viewing for both the amateur and professional geologist. Indeed it is true to say that the cliff sections around the island have been the focus of the greater part of previous geological study to the detriment of the description of some equally illuminating inland sections and exposures.

These coastal cliffs provide significant exposures of the terrestrial Wealden strata with their sauropod remains (e.g. Martill and Naish, 2001). They were the subject of some of the earliest comprehensive descriptions of this succession by eminent geologists (e.g. Fitton, 1847), and of the change from terrestrial to fully marine deposition within the Early Cretaceous (e.g. Wach and Ruffell, 1991). They also provide near-vertical exposures of the Chalk succession seen elsewhere in the south of England (e.g. Mortimore et al., 2001). The Chalk forms the central topographical spine of the island (Figure 3) and is a very visible manifestation of part of the structural development of the island. The northern part of the island comprises the most complete Palaeogene succession in north-west Europe (e.g. Forbes, 1856; King, 2006; King, in press). It includes many type sections within the coastal exposures, including the internationally renowned sections at Alum Bay and Whitecliff Bay (e.g. Curry 1954, 1957) at the western and eastern ends of the island, respectively. The geology of the island has been imaged in many ways (e.g. photography, aerial photography, seismic surveys) since the earliest years of investigation, each providing a new insight into the make-up of the island. Most recently, the HiRES airborne survey has provided new sets of data (high-resolution magnetic, electrical conductivity, radiometric) that add significant detail to earlier national surveys (White and Beamish, 2011; Beamish and White, 2011a, b, 2012; Beamish, 2013).

The steeply dipping strata that make up the central spine of the island, are testimony to a significant tectonic event—the Alpine Orogeny. This formed the many east–west mountain chains of southern Europe around 23 to 14 million years ago (Ziegler, 1981, 1990). The geological structure of the island (Underhill and Paterson, 1998; Evans et al., 2011) results from reversal of the extensional tectonic events that created the Wessex Basin during the preceding Mesozoic (Stoneley, 1982; Chadwick, 1986, 1993). This Wessex Basin story itself has its origins within the Palaeozoic and carries a history of Variscan continental collision and division that offers an insight into the development of the major continental masses through time.

Overlying these bedrock strata is a patchy spread of Quaternary superficial deposits that hold keys to unlock our understanding of the ancient Solent River. This fluvial/estuarine/marine system has formed a significant feature in the landscape for at least the last 600 000 years (Bates and Briant, 2009). The onshore Quaternary sequence, and that in the immediate offshore, carries a signature of numerous cold–warm climate cycles, widely fluctuating sea levels and some of the earliest glimpses of the hominin occupation of the British Isles.

Structure and basin development

Structurally, the Isle of Wight falls within the Wessex Basin (Stoneley, 1982; Chadwick, 1986, 1993), which extends over most of southern England south of the London Platform and Mendip Hills (Figure 4). This sedimentary basin preserves a thick succession of Permian/Triassic to Cretaceous rocks and is underlain at great depth by Palaeozoic strata in the Variscan fold belt (Penn et al., 1987).

The Palaeozoic (or Variscan) basement preserves an imprint of deep-seated structures that were initiated when the continental masses of Gondwana and Laurussia collided (i.e. the Variscan Orogeny) to create the supercontinent of Pangaea (Holdsworth et al., 2006). This period of deformation culminated at about 299 Ma at the end of the Carboniferous Period. As a consequence of this collision, the rocks of the Variscan basement were weakly metamorphosed and are cut by several major, shallow southward-verging, northward-compressing thrust zones and north-west-oriented wrench faults that have been identified principally from seismic reflection data. These thrusts form an important feature in the subsequent tectonic development of the region.

A major period of stability, erosion and, eventually, continental red-bed deposition ensued through the Permian into the Triassic Period. The first stages of the break-up of the supercontinent of Pangaea commenced during the Jurassic Period. In the southern England (Wessex) region the break-up process was effectively related to the opening (extension) of the Central Atlantic Ocean between the supercontinents of Laurasia and a dividing southern continent (South America and Africa plates). This Jurassic–Cretaceous crustal extension was accommodated on faults developed above the Variscan basement thrusts as a series of generally southward-throwing normal faults, creating half-graben-like structures (Chadwick, 1986; Penn et al., 1987). The largest of these faults divides the Wessex Basin into a series of sub-basins and within this district the Weald and Channel sub-basins are separated by the Hampshire–Dieppe High (also known as the Cranborne–Fordingbridge High) (Figure 4) inset. This high is effectively represented by the northern part of the Isle of Wight and the immediately adjacent mainland. The northern boundary of the high lies along the Portsdown–Middleton faults on the mainland, with the southern margin represented by the monoclinal structure (Purbeck–Wight Structure or Isle of Wight Monocline) that forms the spine of the island. During the Cretaceous Period, the break-up of Laurasia into the North American and Eurasia continental masses resulted in further extension as the early North Atlantic Ocean opened from the south (Holdsworth et al., 2006).

The early development of half-graben structures in the south-west of the Wessex Basin (the Dorset Sub-basin), outside of the area described herein, preserves thick Permian (298.9 to 252.2 Ma) red-bed facies strata. Further extension developed these half-graben structures towards the north-east and younger Triassic (252.2 to 201.3 Ma) red-bed facies strata are preserved more widely beneath southern England and the Isle of Wight (Ruffell and Shelton, 2000, and references therein).

As basin extension continued into the Jurassic (201.3 to 145 Ma), coupled with a progressive, but cyclical, rise in relative sea level, marine successions were widely developed within the Wessex Basin as greater accommodation space became available. This extension continued throughout the Early Cretaceous (145 to 100.5 Ma) although an early phase of low relative sea level resulted in terrestrial deposition (the Wealden Group) prior to a return to marine deposition. Throughout this long period of extension, the intervening structural highs and some of the larger extensional faults became more influential on sedimentation. Stratigraphical units experienced thickness attenuation or even severe erosion at various times depending on the relative sea level, the degree of movement on individual faults and the accommodation space available. By the Early Cretaceous, separate successions had developed within the Weald and Channel sub-basins (see for example Chadwick, 1986; Penn et al., 1987; Gale, 2000a; Hopson et al., 2008). Onlap, particularly on to the London Platform and the Hampshire–Dieppe High, can be demonstrated within the Wealden, Lower Greensand, Gault, and Upper Greensand successions of the Early Cretaceous.

A further period of regional subsidence, but apparently with considerably less fault movement, and a sustained relative sea level rise within the Late Cretaceous (100.5 to 66 Ma) resulted in the highest relative sea level in Earth’s history. This high sea level, coupled with a greenhouse Earth, saw a relatively uniform and thick Chalk Group deposited widely in this region and across the continental shelf areas adjacent to the ever-widening North Atlantic (see Gale, 2000b and references therein). However, there is a growing weight of evidence (e.g. Mortimore and Pomerol, 1997; Evans and Hopson, 2000; Evans et al., 2003 and references therein; van der Molen et al., 2005; Duperret et al., 2012) to show that some variations in chalk lithology and thickness within the Chalk Group can be attributed to local tectonic influence and not just to eustasy as previously supposed. Global sea-level fall at the end of the Cretaceous resulted in erosion of parts of the uppermost Chalk and the development of a pre-Cenozoic unconformity. This was effectively the end of the Wessex Basin as a major structural and depositional unit. However, structural disharmonies preserved in the succession within the Wessex Basin continued to influence sedimentation and tectonics through to the present day.

Marine and fluviatile deposition in Paleocene to Oligocene times took place on the shallow margin of a subsiding Palaeogene (66 to 23 Ma) or ‘Tertiary’ North Sea Basin (King, 2006). It was followed by a compressive tectonic regime during the Early to Mid Miocene (Alpine Orogeny, about 23 to 14 Ma), although there is evidence that the Isle of Wight structural uplift was initiated by earlier Palaeogene compression as exemplified in Daley and Edwards (1971), Gale et al. (1999) and Newell and Evans (2011). The major Miocene thermal re-equilibriation in the lower crust/upper mantle following rifting and the Alpine compressional event effectively reversed the sense of movement on the major bounding faults of the older Wessex Basin resulting in the structural inversion of earlier basins and highs. Compression was essentially from the south-east for this region, a direction at a slight angle to the preserved structures of the Wessex Basin. This slight obliquity led to differential movement along each of these major faults. These pressures also emphasised the north-west-orientated wrench faulting inherent in the underlying strata and there is evidence of block and ‘scissor’ faulting particularly associated with the most significant structures (e.g. the Purbeck–Wight or Isle of Wight Structure).

The Alpine inversion event effectively separated the onshore area of Palaeogene deposition in southern England into two geographically isolated areas, known as the London and Hampshire basins. The event created the reverse-faulted monoclinal structures best exemplified by the Hog’s Back in Surrey and its westward extension south of the London Platform, and the Purbeck–Wight Structure that extends westward through the Isle of Wight into the Ballard Down and Isle of Purbeck structures of Dorset (King, 2006). Between these two easily recognised structures, the compression also formed a series of regularly spaced, roughly east–west-trending strongly asymmetric anticlines and synclines that are somewhat less striking topographically. The northern margin of the Wessex Basin is the London Platform, which is a long-term feature, founded on the stable basement block of the East Midlands Microcraton. Maximum uplift during the Alpine Orogeny, exemplified by the Weald Anticline, is estimated at about 1500 m (Simpson et al., 1989).

The structure of the island (Figure 4) is most spectacularly represented by the ridges of vertical Chalk at the eastern (Culver Down and Whitecliff Bay) and the western end of the island (Scratchell’s Bay, The Needles and Alum Bay). These represent a continuation of the Purbeck–Wight Structure, which on the island, is termed the Isle of Wight Monocline. This is effectively two en echelon monoclinal features—the strongly asymmetric Brighstone and Sandown anticlines, commonly referred to variously as monoclines, structures, or flexures in the literature—separated by flatter-lying chalk downland, central to the island, that is now regarded as a classic fault-ramp area (Evans et al., 2011; Mortimore, 2011b). The monoclinal structures have been regarded as simple, if extreme, examples of folding, at least extreme in terms of southern England. The observations of the surveying team and a reinterpretation of the available seismic data have indicated that the two monoclines of Sandown and Brighstone are not simple structures; they are now reinterpreted as ‘failed’ monoclines with significant reverse faulting on the northern limb. A new interpretation and evolution of the Isle of Wight Monocline is given by Evans, et al. (2011) and an example from that paper showing the structural complexity of the Sandown Anticline is given in (Figure 5). The reverse fault complexes or zones (the faulted steeply dipping northern limbs of the Sandown and Brighstone anticlines) are shown as simple single or at most double reverse faults on the map face and within the more detailed 1:10 000 scale primary mapping. In reality there are likely to be many small interconnecting, limited-throw, generally strike-parallel, normal and reverse faults within those zones essentially in areas of steeply dipping strata. Numerous small quarries, particularly within the more commonly excavated Chalk Group strata, show small faults that cannot be traced with any certainty outside of the exposures themselves. The survey has also demonstrated that there are blocks of the steeply dipping zone separated one from another by generally north to north-westerly trending faults that must have been contemporary with the reverse fault failure of the monocline. This block faulting and perhaps localised rotation being a consequence of the slight obliquity between the maximum compressional forces of the Alpine tectonic event and the structural grain imposed by the extensional fracturing during the creation of the Wessex Basin.

The Isle Of Wight HiRES Survey (High Resolution Environmental and Resource Survey)

A separately funded part of the Integrated Isle of Wight Survey provided a huge dataset of magnetic, radiometric (gamma-ray spectroscopy) and electromagnetic (EM, conductivity) geophysical data across the whole island. This spectacular low-fly airborne survey, at 200 m north–south line spacing and 60 m altitude, was completed in 2008. It covered a grid 36 by 22 km including the whole island and a small part of the mainland around Lymington. The data adds significantly more spatial detail to the UK national magnetic baseline surveys completed in the past. It provides the first modern results in southern England on the gamma-ray flux typically held within the upper 30 cm of the surface and a suite of four electromagnetic frequency (0.9, 3, 12 and 25 kHz) results that indicate different ranges of penetration up to about 100 m depth. Examples of the interpreted baseline results derived from this new survey are shown here but much of this data is still to be fully interpreted. Initial results were presented in the Proceedings of the Geologists’ Association Special Isle of Wight Issue (2011, Vol. 122) and other papers (Beamish, 2013; Beamish and White, 2012).

The magnetic data (Total Magnetic Intensity, TMI) obtained by the 36 by 22 km HiRES survey is shown in (Figure 6). Overlying the magnetic basement, the sedimentary sequence is largely nonmagnetic. The data have been processed in a number of ways to summarise the magnetic basement features and to delineate faults in the sedimentary package. The latter are observed as subtle gradients enhanced by the shaded-relief component of (Figure 6). The data provides a reinforced interpretation of the location and depth of a magnetic body to the south of the Isle of Wight, suggesting that this body is at a shallower depth and probably younger in age than previously envisaged. A more complete interpretation is provided by White and Beamish (2011).

The radiometric data obtained by the survey are shown in (Figure 7) as a ternary (three-way colour stretch) image using the three common radioisotopes of potassium (%K in red), thorium (eTH, in green) and uranium (eU, in blue). The image is confined to onshore locations since the water response is a null. The bedrock exerts a strong control on the distribution of the radioisotopes and the low ternary response (dark colours) of the Chalk outcrop is very evident. Data of this type is commonly interpreted to provide a focus to environmental, health and soil science (parent material) issues. Additional detailed analysis of this data can be found in Beamish and White (2011b).

The four-frequency electromagnetic data obtained by the survey has been converted to estimates of apparent conductivity. ((Figure 8) shows the data at the lowest frequency (deepest penetrating) and highest frequency (shallowest penetrating) using the same conductivity scale. Urban areas are blanked using a black colour. It is very evident that the younger Palaeogene rocks and Gault Formation are highly conductive while the Chalk Group and Lower Greensand Group appear persistently resistive. These results provide the first comprehensive baseline data on the electromagnetic properties of some of the geologically youngest lithologies ever assessed in the UK. They provide a significant contribution whose detailed appraisal is relevant widely over the southern mainland. A preliminary geological and hydrogeological assessment of the data and a detailed appraisal of the Lynnbottom Landfill site (to the east of Newport) are provided by Beamish and White (2011a).

Chapter 2 Geological description

Concealed strata

There are nine deep boreholes (Norton 1, Wilmingham 1, Bouldnor Copse, Sandhills 1 and 2, Cowes 1 ( Bottom Copse), Arreton 1 and 2, and Chessell 1) that prove the strata concealed at depth beneath the island (see (Figure 5). Deep boreholes (see also (Figure 9): 1. Norton 1, SZ38NW18; 2. Wilmingham 1, SZS38NE9; 3.Bouldnor Copse 1, SZ39SE1; 4. Sandhills 1, SZ49SE3; 5. Sandhills 2, SZ48NE55; 6. Cowes1 (Bottom Copse), SZ59SW17; 7. Arreton 1, SZ58NW2; 8. Arreton 2, SZ58NW1; 9. Chessell 1, SZ48NW11." data-name="images/P937077.jpg">(Figure 1) and (Figure 9) for location of these boreholes. Each was drilled in the hope of finding a hydrocarbon reservoir similar to that at Wytch Farm to the west in Dorset. While some showed hydrocarbon traces none proved sufficiently productive to develop further. However, each provides important clues to the nature of the strata at depth and together they demonstrate the differences between the preserved sequences on the Hampshire–Dieppe High and the Channel Basin. They also offer an insight into the development of the Purbeck–Wight Structure (Isle of Wight Monocline) and the timing of oil migration. Of the nine boreholes, seven are north of the monocline and only Arreton 1 and 2 are south of that structure. A summary of the strata encountered in each of these boreholes is given in (Figure 9), and a generalised vertical section in (Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present." data-name="images/P937086.jpg">(Figure 10).

Devonian

The pre-Permian basement map of Smith (1985) shows the island to be underlain in the north by Devonian rocks with the basement in the area south of the Isle of Wight Monocline interpreted as Devonian to Carboniferous in age. The closest known occurrences of Carboniferous strata to the Isle of Wight are the Culm Basin of Devon, the Ferques Inlier in the Pas de Calais in northern France, and at depth elsewhere in south-east England (e.g. the Kent Coalfield). There is, however, no direct evidence of rocks of Carboniferous age being present beneath the island or offshore to the south of the island where commercial hydrocarbon wells prove only Devonian strata in the basement (Hamblin et al., 1992).

The nature of the Palaeozoic basement is revealed in five of these boreholes which penetrate Devonian strata. A maximum of 388.3 m is proven in the Arreton 2 Borehole but seismic data suggests that considerably more Devonian strata are present at depth. Over 900 m of Lower Devonian strata were proven in boreholes in the Southampton area to the north (Hamblin et al., 1992) implying that at least this thickness is present beneath the 388 m of Mid Devonian age (around 380 to 390 Ma) found at Arreton. Further afield, up to 1500 m of Upper Devonian strata are known from southern Devon and similar metasediments are known in the Boulonnais in France, so strata of this age and thickness may well be present beneath parts of the island. Purplish red to red claystone, siltstone and fine-grained sandstone are preserved in four of the boreholes north of the monocline, whilst Arreton 2 proved purplish ortho-quartzite to the south. All are weakly metamorphosed. Descriptions of the lithologies present in the boreholes suggest that deposition took place in a continental fluvial plain environment. Other than at Arreton, none of the sequences has so far yielded reliable age information but comparison of the lithologies encountered with other successions at outcrop and in boreholes indicates a Devonian age.

Triassic

A succession of Triassic strata overlies the Devonian in the deep boreholes. These occurrences represent the easternmost margins of the thicker Triassic successions found in the Wytch Farm hydrocarbon reservoir and the Dorset Basin to the west. The thickest and stratigraphically most complete development of the Triassic and Permian strata within the Wessex Basin is seen on the coast between Torbay and Sidmouth (Edwards and Scrivener, 1999; Edwards and Gallois, 2004). Seismic evidence suggests that Permian strata are absent beneath all but the southernmost part of the island and therefore the depth to the pre-Permian basement contours across the island ((Figure 11), based on Smith, 1985) represent the base of the Triassic strata.

Additional insights into the concealed strata beneath the island have been obtained from remotely sensed geophysical data. UK baseline magnetic and gravity surveys of the island were carried out in the 1970s and in 2008 a low-level airborne HiRES survey was undertaken with magnetic, radiometric and conductivity measurements obtained. White and Beamish (2011) compared the UK baseline magnetic dataset with that obtained from the HiRES survey. Their reinterpretation of the results from the southern extremity of the island and within the offshore area some distance to the south, indicates that significant magnetic bodies originally thought to be between 2 and 5 km depth (and therefore within the Variscan basement succession), may be at shallower depths of about 2 km within Permian to Triassic strata. They may therefore be equivalent to the scattered outcrops of the ‘Exeter Volcanics’ of Permian age in the Dorset Basin (Knill, 1969; Cornwall et al., 1990). Knill regards these olivine basaltic and highly potassic lavas as explosive fissure eruptions from a shallow sill-like magma body associated with rapid subsidence and active normal faulting during the Early Permian.

Seven of the nine deep boreholes prove Triassic strata and up to 450 m is known. Representatives of the Sherwood Sandstone Group, Mercia Mudstone Group and the Penarth Group are all present in varying thicknesses. Very earliest Triassic strata are known in offshore boreholes to the west and south-west of the island, and are equated to the Aylesbeare Mudstone Formation of Dorset and Devon. The Triassic represents a long period of arid continental red-bed deposition over a low-relief desert plain. Early fluviatile sandstone-dominated successions characterised by the Sherwood Sandstone Group (SSG) give way upwards to clay- and silt-dominated and generally red strata of the Mercia Mudstone Group (MMG), which also includes significant evaporite units within the lower part of full successions (as in Norton 1 Borehole). The MMG represents deposition in distal alluvial and playa-lake environments with thin sandstones representing a variety of channel and crevasse splay deposits (Hounslow and Ruffell, 2006). The Blue Anchor Formation (BAn) is distinguished at the top of the MMG within the Bouldnor Copse, Norton and Chessell boreholes where 21 m, 36.6 m and 20.7 m respectively are described as green marls. These are considered regionally to represent lacustrine conditions. The formation is not distinguished in the other deep boreholes on the island.

The close of the Triassic saw the widespread Rhaetian transgression (the Cimmerian II unconformity of Ziegler, 1990) and the deposition of the Penarth Group (PnG) which is represented in this area by a relatively thin shallow marine succession. There are major worldwide environmental changes in the transition from the latest Triassic into the earliest Jurassic and this represents a major extinction event in Earth history. The Penarth Group is divided in this region into the Westbury Formation, characterised by dark grey to black shaly mudstone with minor calcareous siltstone and concretionary limestone, overlain by the Lilstock Formation (comprising the Gotham and Langport members) dominated by a variety of shallow-water calcareous mudstones and shallow-water peloidal limestones. Thin representatives of these same units have been identified from chipping samples and from their characteristic geophysical downhole log signature in the deep boreholes beneath the island.

Jurassic

A representative sequence (Figure 9) and (Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present." data-name="images/P937086.jpg">(Figure 10) of the entire Jurassic succession was proven in the Arreton wells south of the Hampshire–Dieppe High where a maximum thickness of 1188.4 m of strata (Arreton 2) is encountered. At depth, in the north of the district, over the Hampshire–Dieppe High itself, the Aptian/Albian Lower Greensand basal unconformity cuts out or oversteps the Wealden and Purbeck groups, which were, perhaps, never deposited over the high. This unconformity also cuts down deeply through the Jurassic succession, such that the youngest unit of the Lower Greensand (Monks Bay Sandstone Formation, Hopson et al., 2011b) is known to rest, with some discordance, on units down to the Middle Jurassic Cornbrash Formation, for example in the Sandhills 1 Borehole. The evidence from the deep boreholes suggests that up to 610 m of Jurassic strata are absent beneath the Lower Greensand unconformity (Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present." data-name="images/P937086.jpg">(Figure 10) across the northern half of the island.

A suite of lithostratigraphical units within the Jurassic is present beneath the island and can be closely correlated with the successions at depth across the Wessex Basin and at outcrop in Dorset and the Cotswolds. The Jurassic succession of limestone, lime-mudstone and mudstone demonstrates a return to fully marine conditions following the red-bed deposition of the Triassic. For the most part, sedimentation rates throughout the Jurassic kept pace with the rising sea level and the new accommodation space made available during the tectonic extensional phases that created the Wessex Basin. The palaeoenvironment was maintained in broad shallow- to intermediate-depth shelf-sea platforms. Notwithstanding this general uniformity of deposition, each of the units within the Jurassic thins significantly or is absent within the deep boreholes that overlie the Hampshire–Dieppe High. This points to the fact that the southern bounding fault(s) to that structure had a direct influence on each unit as the basin developed, i.e. the thicker representatives of each unit are on the downthrown side of these structures. Regionally, variable stratal thickness patterns against these extensional faults demonstrate that the timing of individual fault movements was not uniform basin-wide (Penn et al., 1987 and references therein).

The Purbeck Group, which spans the Jurassic–Cretaceous boundary, is characterised by shallow lagoonal limestone, shell detrital limestone and palaeosols together with significant anhydrite beds indicating the gradual change of palaeoenvironment towards peritidal and terrestrial deposition of the Wealden Group as relative sea level fell during the latest Jurassic and earliest Cretaceous.

Lias Group (Li)

The most complete succession known beneath the island was described in the Arreton 2 Borehole, south of the Hampshire–Dieppe High, where 383.4 m of strata have been divided into the traditional units of Lower, Middle and Upper Lias. However thinner successions in boreholes on the structural high in the north of the district are variously correlated with older terms (see Hallam, 1992) attributed to successions seen to the west in Dorset and these reflect the vintage of the borehole completion. These older terms may be equated to the modern lithostratigraphical framework exemplified in Cope (2006). The group is principally composed of dark grey mudstone and siltstone with thin subordinate argillaceous limestone units in parts. The basal unit (Lower or Blue Lias) is widespread in the Wessex Basin with characteristically interbedded limestone, marl and shale that demonstrate a decimetre-scale rhythmicity reflecting widely variable oxygenation states of deposition. This unit has been identified in the Arreton 2 Borehole.

The uppermost part of the Lias identified in the deep boreholes is consistently described as a conspicuous calcareous sandy siltstone to sandy argillaceous limestone and has been equated with the Bridport Sand Formation.

The Lias was deposited in a broad seaway, of variable depth, between the low-lying islands of Cornubia, to the west, Anglo–Brabant to the east and further afield in western Ireland and Scotland.

Inferior Oolite Group (Ino)

The thickest succession attributed to the Inferior Oolite Group is found in the Arreton boreholes (52 and 70 m), with only thinner representatives to the north upon the Hampshire–Dieppe High. The group is undivided in the borehole records and comprises principally, microcrystalline limestone, wackestone, sandy, silty limestone and calcareous mudstone, each with varying amounts of shell debris and glauconite. Deposition was generally in shallow-water lagoonal, reef, and forereef settings with consequently fairly rapid lateral variation in facies. Localised differential subsidence related to tectonic events is probably the main influence on facies type and the frequency of omissions in the sequence.

The Inferior Oolite was deposited over a relatively long period of time in relation to the thickness of the unit, in a narrowing shelf sea between the expanded landmasses of Cornubia, Anglo–Brabant and a newly emergent Welsh/northern England landmass to the north and north-west. At this time the central North Sea region experienced up-doming and volcanic activity.

Great Oolite Group (Gto)

The Great Oolite Group is generally divided in the deep boreholes records with the thickest succession within the inclined Chessell Borehole. However a general maximum of about 145 m seems to be preserved beneath the island. This is one of the horizons regarded as having significant hydrocarbon potential and the succession is generally divided into a lowest unit of the Fuller’s Earth Formation that is followed by the Great Oolite Limestone (often divided into ‘units’ depending on the permeability of the rocks), Forest Marble Formation (including the Frome Clay which is now considered a formation in its own right) and Cornbrash Formation (undivided in the deep boreholes beneath the island).

Lithologically the group comprises calcareous mudstone and argillaceous limestone overlain by variable-porosity wackestone limestone, a further unit of variable calcareous mudstone and surmounted by microcrystalline limestone.

Deposition was in a slightly broader shallow sea than that seen during the development of the preceding Inferior Oolite.

Kellaways Formation (Kys)

This generally thin unit (13 to 30 m) comprises interbedded, grey, calcareous, fine-grained sandstone and mudstone but is absent in the Sandhills 1 Borehole where much of the Jurassic has been removed beneath the basal Lower Greensand unconformity.

This formation marks the start of the expansion of the Jurassic sea with the landmasses of Cornubia, Anglo–Brabant and Wales/northern England diminishing as relative sea level rose.

Oxford Clay Formation (Oxc)

The formation, undivided in boreholes, is known to be about 130 to 140 m thick generally but its presence is limited north of the Purbeck–Wight Structure (i.e. the Hampshire–Dieppe High) by erosion beneath the basal Lower Greensand unconformity. The formation comprises finely bedded mudstone, siltstone and carbonaceous mudstone.

Deposition was in expanding and deepening seas and the formation is fairly uniform in its constituent lithologies and sedimentary breaks throughout southern Britain and into the North Sea region.

Corallian Group (Cr)

Generally the group is up to 69 m thick and is undivided in the borehole records. It is absent in Sandhills 1 and 2 boreholes. Lithological descriptions within the boreholes show that the group comprises a lower, variably calcareous, siltstone and oolitic limestone overlain by dark grey calcareous finely bedded mudstone. These two major units may well represent the lower and upper Cornbrash described in Dorset and into the Cotswolds, where a number of different formation names are applied to the lithologies present, depending on correlations over the major extensional faults in this part of the Wessex Basin. This medial dividing boundary within the group is a significant nonsequence and transgression surface in the Dorset and Cotswolds outcrops and is known to be widespread in the subcrop across the Wessex Basin.

Regionally this group represents a relatively short-term, Mid to Late Oxfordian, return to shallower-water deposition caused by widespread uplift.

Kimmeridge Clay Formation (Kc)

Generally thin or absent north of the Isle of Wight Monocline (i.e. on the Hampshire–Dieppe High) due to erosion beneath the basal Lower Greensand unconformity, up to 337 m of finely bedded fossiliferous, in part calcareous, mudstone with thin calcareous siltstone and limestone is encountered in the Arreton boreholes to the south of that structure.

Regionally the formation comprises rhythmically bedded, decimetre-scale alternations of organic-rich and relatively carbonate-rich mudstone. The formation contains significant oil-shale and bituminous-rich horizons, and whilst generally not mature onshore in the UK, it is still regarded as a principal hydrocarbon source rock.

The formation was deposited in a broad sea reflecting renewed deepening from the latest Oxfordian through to the latest Kimmeridgian sensu anglico times.

Portland Group (PL)

This group is only present in the Chessell and Arreton boreholes. The group is generally between 26 and 30 m and comprises sandy, glauconitic, bituminous fine- to very fine-grained calcareous sandstone overlain by shelly, weakly glauconitic argillaceous limestone.

The group represents a time of rapid regression with the shallow marine Wessex Basin area now separated from the North Sea area by a significant landmass.

Lower Cretaceous

The Lower Cretaceous strata known from the island include the greater part of the Purbeck Group, the Wealden Group, the Lower Greensand Group and the Selborne Group, and offer one of the most complete successions of this age in southern England ((Figure 9), (Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present." data-name="images/P937086.jpg">(Figure 10), (Figure 12) and (Figure 13). The Purbeck Group and the lower part of the Wessex Formation in the Wealden Group are only known from boreholes south of the Isle of Wight Monocline (south of the Hampshire–Dieppe High).

Purbeck Group (Pb)

The Purbeck Group is only fully preserved south of the bounding structures of the Hampshire–Dieppe High (Purbeck–Wight Structure), where it is 99.7 m and 113.7 m thick respectively, within the Arreton 2 and Arreton 1 boreholes. It is also present in the Chessell Borehole where a reduced thickness of 31.1 m of the group is represented closely associated with the Purbeck–Wight Structure. The unit contains the Jurassic–Cretaceous boundary low in the succession.

At the type site in Dorset, the group is now formally divided into the Lulworth Formation, below and the Durlston Formation above, with the base of the Durlston Formation placed at the base of the Cinder Bed. This formation-level terminology can now be applied extensively in the outcrop and subcrop of the group including the Isle of Wight. The Cinder Bed, and therefore the base of the Durlston Formation, has been identified within the Arreton 1 Borehole between 708.05 to 709.57 m on the basis of abundant Ostrea distorta. Thus a thickness of 42.06 m can be attributed to the Durlston Formation with 71.63 m assigned to the Lulworth Formation. The Cinder Bed was not recognised in the Chessell Borehole and the limestone encountered overlying anhydrite cannot be divided below the group level.

The Durlston Formation in the Arreton 1 Borehole comprises grey shelly limestone with green staining including abundant gastropods, bivalves and ostracods overlying shelly recrystallised limestone and grey finely bedded calcareous mudstone with some shell debris with the Cinder Bed at its base.

The Lulworth Formation in this borehole comprises interbedded shelly limestone and bituminous calcareous mudstone with ooids towards the base, overlying anhydritic limestone and anhydrite with increasing bituminous finely bedded calcareous mudstone and sandy limestone towards the base.

It is not possible from the generalised descriptions in the Arreton boreholes to divide the formations with any confidence into their constituent members and therefore the base of the Cretaceous (base Berriasian), known to be stratigraphically low within the Lulworth Formation and within the Mupe Member, cannot be recognised.

The Purbeck Group was deposited in a limited basin broadly equivalent to the Wessex Basin. The limestone, algal limestone, calcareous mudstone and evaporitic deposits were laid down in short-lived, restricted shallow-marine, lagoonal and variable-salinity to fresh-water environments.

Wealden Group (W)

Regionally the Wealden Group is represented by sequences in two depositional centres, the Weald and Channel basins, divided by the upstanding Hampshire–Dieppe High. The deposits seen on the Isle of Wight represent deposition in the Channel Basin. In both areas the depositional environment was a low-lying terrestrial alluvial plain with significant rivers, freshwater lakes and shallow brackish lagoons.

The full thickness (620 m) of the Wealden Group (Figure 9) and (Figure 13) is present in the Arreton boreholes but only the upper third (about 180 m; Radley, 2006) is represented at outcrop along the spectacular south-west coast and in the deeply cut chines in the immediate hinterland. Even less of the succession is visible within Sandown Bay in the east, north of the termination of the seawall. While the group covers about 9 km2 and 4 km2 of outcrop inland of Brighstone–Compton Bay and Sandown Bay respectively, there are no significant exposures still clearly visible. The group is divided into two formations but the division between these is only vaguely identifiable in either of the Arreton boreholes. The Wessex Formation and the Vectis Formation, as defined by Daley and Stewart (1979), replace the terms Wealden Marls and Wealden Shales, respectively, that were adopted in the earlier survey memoirs (White, 1921). The group, particularly the Wessex Formation, is internationally famous for its included saurian remains, including some forms unknown from anywhere else in the world (Martill and Naish, 2001; Insole and Hutt,1994).

Wessex Formation (Wx)

The Wessex Formation has no formal subdivision on the island (Figure 9) and (Figure 13), and it is not fully exposed, although a number of named beds (principally the dividing sandstone units) are described from the continuous coastal section (Figure 14) in Compton Bay and Brighstone Bay (Daley and Stewart, 1979; Stewart, 1981a, b; Insole and Hutt, 1994). The type section of the formation is at Bacon Hole and Mupe Bay on the coast in Dorset to the west.

Lithologically, at outcrop, the formation comprises varicoloured (mainly red) mudstone with subordinate unconsolidated sand and indurated sandstone (generally white or pale yellow as well as red) and some ironstone (Plate 1). The highest bed of red sand and mudstone, immediately below the White Rock (basal Vectis Formation), contains a significant fauna of dinosaur debris and is called the Hypsilophodon Bed. Sandstone units generally fine upwards from basal conglomerate grading up into mudstone. The sandstone units, which usually exhibit large-scale trough or planar cross-bedding, pass up into climbing ripple-laminated sandstone and are surmounted by interbedded sand and mud. Throughout the succession are plant-rich horizons (including large logs) and Upper Jurassic clasts. The latter represent erosion of nearby fault scarps (the southern margin of the Hampshire–Dieppe High) marking the northern limit of the Channel Basin. Westward, on the mainland through Dorset, and where the lowest part of the formation can be examined, sandstone units thicken and some significant coarse sand, grit and pebble beds act as markers locally.

The formation represents deposition in a complex broad alluvial floodplain (characteristic of a Mediterranean-type climate) with high-sinuosity river channels, ephemeral ponds, and lakes that all experienced significant major flooding events and desiccation. Mudstones are regarded as principally the result of vertical accretion of suspended load from ponded flood waters, with original laminations being consistently destroyed by bioturbation and by pedogenesis. The sandstones are generally considered as point bar accretions in a strongly meandering river (e.g. the Brighstone Sandstone Member) but others (e.g. the Ship Ledge Sandstone) are interpreted as a crevasse-splay unit built-out onto the floodplain where the channel margin has been breached.

The base of the formation is not seen on the Isle of Wight at outcrop but identified in the Arreton 2 Borehole at the upward change from gastropod- and bivalve-rich, green-stained limestone into fluviatile light grey mottled dark green, calcareous mudstone with calcareous pebbles. The top of the formation on the Isle of Wight is placed at the abrupt colour change from the predominantly red mudstone of the Wessex Formation up into the dull grey finely bedded mudstone and sandstone of the Vectis Formation. The unit spans the Late Berriasian through to Barremian stages.

Vectis Formation (Vs)

The continuous exposure of the formation in Brighstone Bay (Figure 15)a on the south-west coast of the island provides the type section (west from Atherfield Point) for the Vectis Formation. Its constituent three members are defined at this locality (from the base, these are the Cowleaze Chine, Barnes High Sandstone and Shepherd’s Chine members) and can be easily traced on this coastline (Daley and Stewart, 1979; Stewart, 1981b; Stewart et al., 1991; Wach and Ruffell, 1991) in the high cliffs. The Compton Bay outcrop, to the north-west on this coastline, is poorly exposed being heavily landslipped but outline sequences are described in Radley and Barker (1998). In Sandown Bay (Figure 15)b the formation is less well exposed in low cliffs but a thinner sandstone unit attributed to the Barnes High Sandstone is still present. An outline correlation of the formation is given in (Figure 15)c and bed-by-bed descriptions are given in White (1921).

There are limited exposures of this formation away from the three significant coastal sections. The sandstone shown within the Vectis Formation in the hinterland of Sandown Bay, and equated to the Barnes High Sandstone Member, was formerly exposed in the road south of Yaverland [SZ 614 546]. Historically this unit was also seen in a pit [SZ 596 488] and in the adjacent railway cutting near Foxes Bridge where about 6.1 m of yellow sandstone was described (White, 1921). The mudstone within the higher part of the Vectis Formation above the sandstone was also formerly seen in the Streetend Brickworks nearby [SZ 595 484] but this area is now completely built over with houses.

Cowleaze Chine Member

The Cowleaze Chine Member (7 to 10 m thick) comprises finely interlaminated dark grey mudstone (often described as shale or paper shale) and pale grey silt/fine-grained sandstone. In places these beds are arranged into thin fining-upwards units but commonly the mudstone is intensely bioturbated. A 1 m-thick white fine sandstone (the White Rock) occurs at the base in places (Plate 2) as does the underlying ‘Hypsilophodon Bed’ that contains significant saurian/reptilian bone remains and is the topmost unit of the Wessex Formation.

Barnes High Sandstone Member

The Barnes High Sandstone Member is a single unit of principally medium-grained yellow to grey sandstone, between 6 and 7 m thick, at the type site between Atherfield Point and Barnes Chine. Elsewhere the member is divided by thin intervening mudstones, for example in Compton Bay the member comprises three coarsening-upwards, fine- becoming medium-grained, sandstones separated by laminated mudstone. The thin topmost bed of the member usually comprises a thin mudstone and bivalve conglomerate. Inland exposures are rare as mentioned above.

Shepherd’s Chine Member

The Shepherd’s Chine Member, up to 49 m thick, comprises light grey fine-grained sandstone, siltstone and dark grey mudstone, arranged in up to 65 thin, rhythmically bedded fining-upward units. Each unit comprises a light grey fine-grained sandstone or siltstone with a sharp and erosional contact at the base, passing up into dark grey mudstone. Several thin muddy limestones comprising bivalve and other shell concentrates occur in the higher parts of the succession together with a ‘beef bed’ (fibrous calcite commonly with cone-in-cone structures) (White, 1921).

The Vectis Formation shows considerably more evidence than the preceding Wessex Formation of very shallow lacustrine or lagoonal deposition with fluctuating salinities. Although mainly freshwater, interbeds representing short-lived marine incursions occur commonly towards the top of the succession and provide an early glimpse of the return to fully marine conditions within the overlying Lower Greensand Group. This changing environment and the ostracoda present demonstrate that the top of the formation spans the Barremian–Aptian boundary.

Lower Greensand Group (LGS)

The Lower Greensand Group (Figure 13) has its own local nomenclature, at formation level and below, developed from the exposures on the island (principally in Chale Bay) and those sections that partially repeat the succession to the west in Dorset. The principal type exposures are within the low cliffs in Compton Bay [SZ 370 850] (although this is much obscured by landslides) and Chale Bay from Atherfield Point [SZ 453 792] to Blackgang [SZ 490 760]. These coastal sections are comprehensively described bed by bed in the short account (White, 1921) and the Chale Bay locality illustrated in the Geologists’ Association Guide (Insole et al., 1998; White, 1921, fig. 6) (Plate 4)." data-name="images/P937092.jpg">(Figure 16). Inland the group underlies a relatively narrow strip of well-featured ground south of the Chalk escarpment through Hulverstone [SZ 400 840] and Yafford [SZ 445 820]. It also underlies the broad interfluve areas of the Medina and Eastern Yar catchments between the Central Chalk Downs and the Southern Chalk Downs, where featuring of the individual sand beds becomes subtle or nonexistent. The group forms the low cliffs on the south-east coast of the island between Luccombe Bay [SZ 585 795] and Sandown Pier [SZ 597 839] (see Insole et al., 1998 fig. 11) and again in a narrow steeply dipping exposure from Red Cliff [SZ 620 853] towards Whitecliff Ledge [SZ 630 854] in the northern part of Sandown Bay (Insole et al., 1998). Correlations of the formations within the group between the Chale Bay type site and exposures on the south-east coast are relatively clear-cut, but correlation of the constituent members, particularly within the Ferruginous Sands Formation, are not readily determined. Inland sections of the group are present, most notably the sandpit at Knighton [SZ 574 866] (see below). Other exposure locations are noted in the individual sections below.

The original classification of the group was by Fitton (1847) who divided the ‘Lower Greensand’ into a large number of beds and ‘groups’ that he amalgamated into six ‘divisions’. That scheme was simplified in later survey memoirs (Bristow, 1862; Reid and Strahan, 1889; White, 1921) where the four units of Atherfield Clay, Ferruginous Sands, Sandrock and Carstone were defined by reference to the units of Fitton. It must be noted that the south-west coast that formed the type sections for Fitton’s classification suffers rapid coastal erosion and the original sections are no longer present. The current exposures are between 70 and 100 m further inland. The best descriptions of the succession, as currently seen, are summarised (Plate 4)." data-name="images/P937092.jpg">(Figure 16), from various authors (see below), in the Geologists’ Association Guide No. 60 by Insole et al. (1998), whilst the biostratigraphy of the group is described for the island, and correlated more widely in Casey (1961).

The four units have been given formal formation status but the Carstone Formation has subsequently been renamed the Monk’s Bay Sandstone Formation (Hopson et al., 2008; and formally defined in Hopson et al., 2011b) from its parastratotype on the island. The group represents a return to predominantly shallow-marine conditions following the major early Aptian transgression (Simpson, 1985; Wach and Ruffell, 1991; Dike, 1972a, b) and overall the palaeoenvironment represents deposition in mainly shallow seas with increasingly strong tidal influences through time. The shallow shelf seas with slow sedimentation rates and storm-scouring are characteristic of the Atherfield Clay Formation. The Ferruginous Sands Formation demonstrates deposition over an ever-shallowing shelf with coastal sand waves and troughs together with localised omission surfaces and common firm-ground development. Further regression during the deposition of the Sandrock Formation is characterised by estuarine conditions cross-cut by subtidal channels. A further period of erosion, followed quickly by transgression that deposited the iron-rich coarse sandstone of the Monk’s Bay Sandstone Formation, represents, essentially, the basal member of the Albian transgression.

Atherfield Clay Formation (AC)

The formation was named after Atherfield Point on the Isle of Wight by Fitton (1847) and the unit was formalised as the Atherfield Clay Formation in Rawson (1992). The type section is in Chale Bay (Shepherd’s Chine to Whale Chine) [SZ 4466 7982] to [SZ 4684 7825] (Plate 4)." data-name="images/P937092.jpg">(Figure 16). The formation, which is up to 53 m thick, is divided into five units referred to as members in Simpson (1985) (see below). These members have not proved possible to distinguish, other than in the cliff sections in Chale Bay and Sandown Bay [SZ 622 854] (Plate 3). Even here the lower part of the formation is heavily landslipped and only the Perna Member and the Crackers Member can be distiguished with certainty. They have therefore not been adopted for mapping purposes. At Compton Bay [SZ 369 850] the greater part of the formation is concealed by vegetated mudslides and the constituent members are difficult to distinguish.

The ‘members’ are in ascending order the Perna Member, Chale Clay Member, Lower Lobster Member, Crackers Member and Upper Lobster Member. These members equate to the lowest three divisions (Perna Mulleti, Atherfield Clay and The Crackers) of Fitton (1847) although he reserved the term Atherfield Clay (essentially the Chale Clay Member) for his second division only. Subsequently in the work of the Survey, the use of the term Atherfield Clay was extended to include Fitton’s Perna ‘Bed’ and the Lower Lobster ‘Bed’, and in other works now includes all of his third division (The Crackers). The five members in Simpson (1985) are further divided into 19 numbered beds.

On the Isle of Wight the lower boundary of the formation is placed at the sharp nonsequence where the dark grey mudstone of the Vectis Formation is overlain by the gritty fossiliferous mudstone of the ‘Atherfield Bone Bed’ (see below). The upper boundary is placed at the change from interbedded mudstone with subordinate sandstone of the Upper Lobster Member (Simpson, 1985) and the fine-grained ferruginous sandstone of the Ferruginous Sand Formation.

The predominant lithology is blue grey mudstone, variably sandy and with calcareous concretions. The formation also includes beds of sandstone, clay ironstone and phosphatic nodules. The Perna Member (1.5 m at Atherfield Point and 1.8 m in Sandown Bay) is a grey brown to dark blue, sandy mudstone with bivalves, overlain by greenish, calcareous, coarse-grained sandstone. These two beds are fossiliferous throughout and the lower includes basal coarse-grained quartz ‘grit’ with bone fragments, fish teeth, phosphatic nodules and rolled ammonites. The whole member is Bed 1 of Simpson (1985) which is also termed the Atherfield Bone Bed. The Chale Clay Member (19 m in Chale Bay) comprises predominantly pale bluish grey mudstone. At the base of the member a ‘chocolate’ brown mudstone (Bed 3) has a gritty base (Bed 2) overlain by pale blue sandy mudstone with fragments of pyritised wood, bivalves and clay-ironstone nodules (Bed 4). Bed 5 is a brown mudstone with a ‘cementstone’ at its base overlain by the major part of the member which comprises pale bluish, poorly laminated grey mudstone with irregular small nodules and red clay-ironstone nodules (Bed 6). The Lower Lobster Member (11.6 m in Chale Bay) is a pale blue-grey mudstone with brown nodules (Bed 7) passing up into thin dark blue micaceous mudstone with yellow sand lenses (Bed 8), then into brown sandy mudstone (Bed 9), dark blue micaceous mudstone with yellow sandy lenses (Bed 10), laminated and sporadically glauconitic brown sandy mudstone (Bed 11) and dark blue argillaceous sandstone (Bed 12). The Crackers Member (6 m in Chale Bay) is dark blue densely packed sandstone (Bed 13), overlain by harder brown sandstone (Bed 14) with seams of phosphatic nodules near the base and top of the member. Both beds contain a single discontinuous seam of fossiliferous large doggers. The Upper Lobster Member (14.5 m in Chale Bay) comprises alternations of dark grey sandy mudstone (Beds 15, 17 and 19) and medium to dark grey firm sandstone (Beds 16 and 18) with flat nodules present in beds 15 and 16.

Whilst the outcrop of the Atherfield Clay Formation can be traced in the south and east of the island there are no significant inland exposures. Thus there is little information on any likely lateral facies changes within the formation as the depositional on-lap margin, represented by the contemporaneous early development of the Hampshire–Dieppe High, is approached towards the north.

Ferruginous Sands Formation (FrS)

The term was first used by Reid and Strahan (1889) based on the work of Fitton (1847). The type section of the formation is in the coastal cliffs between Chale Bay [SZ 453 791], south-east of Atherfield Point, to Rocken End [SZ 489 761], where at least 140 m of strata are seen see (Plate 4).

The formation forms much of the inland outcrop of the Lower Greensand Group. The unit forms a multi-element low escarpment in places with the sand–sandstone units forming a number of small scarps where they become relatively harder than the surrounding beds. This is particularly well developed in the Mottistone and Brighstone areas and south-eastward towards Chale. It is less evident east of the Medina catchment perhaps resulting from a less well-developed contrast in bed hardness and reflecting a northward lateral change in the formation as exemplified in the cliffs around Shanklin and Sandown.

The type succession at Chale Bay [SZ 453 791] is divided into eleven units of member status whose numbering follows on from the original ‘members’ of the preceding Atherfield Clay Formation, i.e. the ‘Groups’ I, II and III of Fitton (1847). The members are difficult to recognise and trace laterally away from the type site of Chale Bay and must therefore be regarded as informal terms. The members, in ascending order, are Member IV, Member V, Member VI, Whale Chine Member, Member VIII, Ladder Chine Member, Member X, Member XI, Old Walpen Chine Member, New Walpen Chine Member, Member XIV and Member XV.

The Lower Greensand succession to the west in Compton Bay [SZ 370 850] is more steeply dipping and considerably thinner than at the type site, with only 76.7 m of strata attributed to the Ferruginous Sand. This thinning, and increased ferruginous content similar to that at Sandown Bay, perhaps reflects onlap onto a developing Hampshire–Dieppe High at this time.

The formation is seen again in the northern limb of the Sandown Anticline within Sandown Bay [SZ 6225 8540] to [SZ 6260 8550]. Here a reduced (105 m), though apparently complete succession, is visible in the Red Cliff, but by comparison with the type site only the lithological characteristics of Members XII to XIV can be recognised with any certainty at the northern end of the cliff exposure. On the southern limb of the Sandown Anticline, south of Sandown Esplanade [SZ 596 838] southward to Yellow Ledge [SZ 586 798], only the middle to uppermost part of the formation (Members VI to XIV) is seen.

The formation comprises a number of heavily bioturbated coarsening-upward units each comprising dark grey sandy mud or muddy sand passing up into fine- to medium-grained grey to green glauconitic sand. Weak cementation occurs at the top of many of the units producing discontinuous calcareous, phosphatic or pyritic concretions that are generally fossiliferous. The middle of the formation contains plant debris. Full lithological descriptions for each of the members as seen in Chale Bay are given in Insole et al. (1998, pp. 65 to 68).

The lower boundary of the formation is marked by a downsection change from ferruginous sand and sandstone with concretions of Member IV, via a narrow transition to silty clay of the upper Atherfield Clay Formation (the Upper Lobster Member). The top of the formation is marked by the change from dark green and brown sand of Member XIV and XV up into a thick band of black mud at the base of the Sandrock Formation. In places this surface is burrowed.

Inland exposures are relatively common with many small roadside cuttings showing clear sections of sand and sandstone. Notable examples are in the cutting for the A3055 (Military Road) at [SZ 3743 8489], in the Mottistone ‘Ravine’ (White, 1921) [SZ 405 838], near Yafford Mill [SZ 447 821], in the cuttings at Kingston [SZ 482 811] in the west, and to the east around Horringford [SZ 543 852], Newchurch [SZ 561 855] and near Adgestone [SZ 593 861]. Numerous other sites are given in White (1921).

Sandrock Formation (Sr)

The Sandrock ‘term’ was first used by Reid and Strahan (1889) and was later formalised as a formation. The type section is in Chale Bay between Rocken End [SZ 4908 7554] and Blackgang Chine [SZ 4850 7692]. Reference sections are at Compton Bay [SZ 370 850], Luccombe Bay and Luccombe Chine [SZ 583 793], and north of Red Cliff [SZ 619 853] in Sandown Bay.

There is no formal division of the formation but the Sandrock comprises up to four upward coarsening sedimentary rhythms. Although rarely complete, a full cycle comprises a basal pebble bed overlying a scoured surface, overlain by a very dark grey mudstone, passing up through bioturbated finely laminated, fine-grained sand and silt into well-sorted, commonly cross-bedded, fine- to coarse-grained sand the top of which is scoured (Plate 7), [SZ 57471 86575]. P683935." data-name="images/P683935.jpg">(Plate 5). The sands with small-scale cross-bedding are believed to have been deposited as migrating shoals in shallow water, estuarine conditions, whereas the large-scale cross-bedded sands are considered to be subtidal channels (Wach and Ruffell, 1991; Insole et al., 1998; Ruffell and Wach, 1998a, b).

The base is described above within the Ferruginous Sands Formation section. The top of the formation is an eroded surface where there is a change from rhythmically bedded fine to coarse-grained, generally large- and small-scale cross-bedded sand, dark grey mudstone and pebble beds below, up into gritty, reddish brown sandstone with pebbles and phosphatic nodules (the Monks Bay Sandstone Formation). This depositional break is called the ‘Mid tardefurcata break’ by Casey (1961).

Inland the Sandrock Formation forms a generally narrow outcrop on the southern side of the Purbeck–Wight Structure from Compton Bay in the west through to Sandown Bay in the east. There is a wider outcrop around the northern margin of the Southern Downs. The outcrop is generally identified by the clean white sand soils commonly developed between regular shallow exposures in road cuttings. There are many small inland sections, the most notable being the Knighton Sandpit shown in (Plate 7), [SZ 57471 86575]. P683935." data-name="images/P683935.jpg">(Plate 5) (Hopson et al., 2011b). Many of these exposures are described in White (1921) including the road cutting at Rock [SZ 425 839], the now much-overgrown long section known as Marvel Wood Sand Pit [SZ 499 868], the numerous old degraded sand pits east of Standen House [SZ 507 871] and small exposures around Kern [SZ 578 864]. The Marvel Wood Sand Pit exposes up to 10 m of pure white current-bedded sand with thin grey clay seams overlain by one of the better inland exposures of the Monk’s Bay Sandstone Formation (see below). South of Blackwater a local pebble bed is developed [SZ 507 856] in the lower part of the Sandrock probably marking a subtidal channel. Around the northern slopes of the Southern Downs many of the exposures mentioned in White (1921) are now degraded but there are still some exposures along the cuttings for the old railway lines north of Whitwell [SZ 521 784] and east of Winstone [SZ 551 811].

Monk’s Bay Sandstone Formation (MBS)

The Monk’s Bay Sandstone Formation is a new name for the Carstone of the Isle of Wight. It was first proposed in Hopson et al. (2008) and subsequently ratified by the Stratigraphy Commission of the Geological Society. The term ‘Carstone’ was first applied to the Isle of Wight succession by Reid and Strahan (1889), who regarded it as a correlative of the Carstone of Norfolk. Whilst the two units are of similar age and lithology they are not contiguous.

The Monk’s Bay Sandstone Formation consists of interbedded units of highly ferruginous, generally coarse-grained, weakly consolidated quartz-rich sandstone (‘gritstone’), fine-grained pebbly sandstone and ironstone that form the upper part of the Lower Greensand Group of the Isle of Wight. It equates to the upper part of Fitton’s (1847) Group XVI.

The type site is defined as the Monk’s Bay cliff section [SZ 579 780] (Hopson et al., 2011b) where 10.5 m of ferruginous and pebbly sandstone and grit characteristic of the unit are exposed (Plate 6). The unit thickens towards the north-east across the island from as little as 1.8 m at Compton Bay, 3.7 m at Blackgang, 9.1 m at Bonchurch and up to 21.9 m at Red Cliff [SZ 627 856] in Sandown Bay where brown sandstone and argillaceous gritstone are visible high in the cliff face. Inland the formation is at least 4.6 m thick in the degraded section at Marvel Wood [SZ 4988 8690]. It was reported to be at least 9 m thick at Rookley Brickworks [SZ 5133 8395] (Dike, 1972a) and is between 5.5 m and 9.4 m in the Ventnor 2 and Ventnor 3 boreholes respectively. An estimated 9.5 m thickness was found in the sequence of boreholes drilled by BGS at Hobbit’s House Farm, Whitwell [SZ 521 786], an estimated 6 m in a series of boreholes at Mottistone [SZ 409 843] but only a metre in thickness within Compton Chine Borehole SZ38NE/30 [SZ 36935 85182].

The lower boundary of the formation is erosional (Plate 7) while the upper boundary is gradational. At this boundary the reddish brown ferruginous coarse-grained sandstone of the Monk’s Bay Sandstone Formation passes up into dark greenish grey gritty mudstone and dark grey mudstone of the Gault Formation.

From a palaeogeographical perspective the formation represents the earliest Albian transgressive succession that overlapped the younger formations of the Lower Greensand Group against the margin of the Hampshire–Dieppe High. As transgression proceeded the contemporary land surface developed on various Jurassic strata over the High was inundated. The presence of abundant iron within the formation is the result of incorporation of significantly iron-rich waters from that contemporary land surface into the transgressive depositional environment and the weathering of any glauconite originally present in the formation.

Selborne Group

The Selborne Group (Figure 13) is the formal term adopted by the BGS (Hopson et al., 2008) to include the Middle and Upper Albian strata throughout southern England. It also reintroduces the concept of Jukes-Browne and Hill (1900) of a Selbornian Stage (Selbornian Beds in White, 1921) albeit modified with the group epithet, as the lithological counterpart. On the island the group is represented by the Gault Formation and the Upper Greensand Formation. The boundary between the two formations is represented by a variable thickness of sandy clay and silty sand across much of southern England, and the unsatisfactory term Passage Beds has been utilised widely for this intermediate unit.

On the Isle of Wight these intermediate beds are considered to be the lower part of the Upper Greensand Formation (equivalent to unit A of Jukes-Browne and Hill, 1900; (Figure 17); (Plate 8) but this is not necessarily the case within the deep boreholes where the thicknesses quoted may well reflect a different approach to the boundary depending on the views of the logging geologists. Comparison of the group with successions on the mainland in Wiltshire and Dorset and around the western closure of the Weald Anticline, as described for example in Bristow et al. (1995), Bristow et al. (1999), Hopson et al. (2001) and Wilkinson et al. (In Press), demonstrate distinct similarities with the succession on the island. The group is fully marine in origin, with the Gault representing mid- or outer-shelf deposition and the Upper Greensand representing eastward-prograding shallower-water deposition. At this time the influence of the Hampshire–Dieppe High waned as relative sea levels rose once more and fully representative successions of the group are found at outcrop across the southern part of the island and at depth in the north of the island. Aspects of the foraminiferal biostratigraphy of this succession and the basal part of the overlying Chalk Group derived from examination of core and samples from the Ventnor 2 Borehole are discussed in Wilkinson and Hopson (2011).

The group has a significant influence on the landscape and built environment over the southern part of the island. For example the Gault commonly provides a medium within which a significant number of slip planes develop, and on which many landslides incorporating the formation are initiated, hence its old local name of ‘blue slipper’ (Jenkins et al., 2011). In addition, parts of the Upper Greensand are the most significant locally derived building stone used on the island (Lott, 2011).

Gault Formation (G)

The Gault is generally sandier than its equivalents described from around the Weald and is considered to have been the result of slow sedimentation below wave base at water depths of about 100 to 200 m (Gale et al., 1996). Detailed descriptions of the succession at Redcliff have been given by Gale et al. (1996) expanding upon the interpretations for the more widespread occurrences of the formation known from elsewhere on the island in Owen (1971).

In general the formation is a monotonous succession of grey and dark blue-grey mudstone, with varying relative proportions of silt and clay, with thin lamellae of very fine-grained pale sand. Towards the south and west of the island the formation is generally fine sand throughout with few thin distinct sand beds. The deposit is commonly heavily bioturbated and trace fossils such as Chondrites are common at some horizons. There are distinct glauconite-rich levels commonly associated with thin brown and dark grey phosphatic nodule horizons. The unit is generally micromicaceous, pyritic, and in unweathered samples, weakly calcareous from disseminated shell debris.

The formation varies generally from about 28 to 36 m in thickness across the island but exceptionally with up to 46.9 m being attributed to this formation in the Sandhills 2 Borehole.

For the most part, the Gault Formation is principally attributed to the ‘Lower Gault’ (spanning the H. dentatus to E. lautus zones of the Mid Albian) across the island. The great majority of the coastal sections demonstrate considerable land slippage and the best and most accessible section is within the cliffs of Compton Bay [SZ 366 853] where about 95 feet (29 m) are described in Jukes-Browne and Hill (1900).

Upper Greensand Formation (UGS)

The Upper Greensand is the coarser unit of the Selborne Group and is regarded as forming within shallow offshore shelf and lower shoreface zones related to a prograding shoreline.

The formation is lithologically variable and the geological map of the island depicts the base of an unnamed chert-rich unit within the succession that essentially corresponds to a Unit E (within units A to F) as defined in Jukes-Browne and Hill (1900).

The Upper Greensand (Figure 17) contains a lowest unit of pale grey to bluish grey silty and sandy micaceous clay becoming clayey sand towards the top including some calcareous nodules. This is the ‘Passage Beds’ or ‘A Bed’ of earlier authors. Overlying this basal unit is a series of greenish grey fine- to medium-grained sandstone, weakly indurated sand and sandy siltstone with varying proportions of glauconite and mica together with small phosphatic nodules and fragments. Siliceous and calcareous concretions are known throughout but are generally concentrated in the middle and top of the succession enclosing a unit characterised by significant numbers of large bedded cherts in grey glauconitic sandstone (the ‘Chert Beds’ of Jukes-Browne and Hill (1900).

The most complete succession described in White (1921) is at Gore Cliff [SZ 492 763] (Plate 49)." data-name="images/P201734.jpg">(Plate 9), (Figure 17) and along the back scar of The Undercliff landslide where the six units (A to F) were recognised. There are 115 feet (35.05 m) of beds recognised at Gore Cliff beneath the Glauconitic Marl Member of the overlying Chalk Group. The ‘Passage Beds’ are here represented by four beds (together making up Unit A) that is 28.5 feet (8.7 m) thick.

The most significant inland exposure of the Upper Greensand is in the road cutting north of Brook Church [SZ 396 848] (the Brook Hill cutting) where much of the middle and upper part of the formation can be seen when the section is clear of vegetation (Plate 10). The Passage Beds are not seen and the beds equivalent to the Chert Beds contain little chert. A similar lack of chert is noted at the exposure [SZ 366 854] in Compton Bay.

Upper Cretaceous

The Late Cretaceous is commonly described as a greenhouse world and was characterised by high global temperatures, high concentrations of atmospheric carbon dioxide and high relative sea levels with little evidence of polar ice caps. The Chalk of the Isle of Wight is described in terms of the Southern Province lithostratigraphical succession whose constituent units, type sections and regional context are defined, for example, in Hopson (2005). The spectacular coastal exposures on the island provide a number of the type sites and many reference sections for these constituent units.

Chalk Group (Ck)

The Chalk Group (Figure 13), (Figure 18) can be said to be the most impressive and for many, the most memorable aspect of the Isle of Wight’s geology, with the steeply dipping chalk cliffs of Culver Down (Plate 11) in the east and the spectacular, much photographed Needles promontory to the west (Plate 12). These cliffs are the most significant manifestations of the Purbeck–Wight Structure. In the east, Culver Down forms the headland from Sandown Bay northward through Whitecliff Ledges into Whitecliff Bay (the GCR site of Mortimore et al., 2001). It provides the finest continuous section of the group (traversable with great care at the lowest spring tides) in southern England. The much described succession can be correlated with equally spectacular cliffs between Beachy Head and Brighton on the mainland (see Mortimore, 1986b; Mortimore et al., 2001 and references therein). The Culver Down section is mirrored in the west of the island from Compton Bay through to Alum Bay. This western section is continuous for over 8 km, but large parts (most notably below the long stretch of Tennyson Down to West High Down) are impossible to visit, other than by boat, even during the lowest tides. In the far west, at The Needles promontory, it is possible to visit the higher part of the Chalk succession by boat to Scratchell’s Bay. The Scratchell’s Bay succession has been the subject of numerous PhD theses, as indeed has the Culver Down headland, each thesis characterising a particular aspect of the Chalk succession (e.g. Montgomery, 1994; Swiecicki, 1980). The Scratchell’s Bay section is fully described in Hopson et al. (2011a).

While these coastal sections are the most studied because of their continuity there are many inland sections that provide an equal amount of lithological detail from the individual formations encountered. They are not discussed in detail herein but a summary map of their occurrence is given in (Figure 20). Over 300 major sites in quarries, erosional bluffs and along roadways present themselves throughout the Chalk outcrop and these together with smaller exposures in animal burrows, fallen tree roots and temporary excavations provide a comprehensive cover across the island to delimit the outcrop of individual formations. The most notable inland exposures are the quarries on Brading Down e.g. The Mall Quarry [SZ 60204 86693] and Morton Manor Quarry [SZ 60223 86504], at Downend [SZ 53435 87395], at Cheverton Down [SZ 44891 84215] and adjacent to the Shalcombe to Brook road (B3399) [SZ 39442 08508]. Brief details of these and other notable exposures are given in the relevant formation entries below.

The seminal works of Jukes-Browne and Hill (1903, 1904), Rowe (1908) and White (1921) formed the basis for the description of the chalk on the island for decades, and still provide a great deal of important detail. The upsurge in interest in Chalk lithostratigraphy across southern England particularly in the 1980s (e.g. Mortimore, 1979, 1986b; Robinson, 1986) has led to a comprehensive reappraisal of the Chalk Group, in which it is divided into two subgroups and nine formations (e.g. Rawson et al., 2001; Hopson, 2005; Mortimore, 2011a, Aldiss et al., 2012; (Figure 18), (Figure 19) and (Figure 21). This reappraisal can be readily applied to the Isle of Wight (Mortimore et al., 2001: Mortimore, 2011b; Farrant et al., 2012) developing earlier works such as that by Hancock (1975), Jefferies (1963) and Kennedy (1969). The development of Chalk terminology is illustrated in (Figure 18).

The finer lithostratigraphical subdivision of the Chalk Group used by BGS since the early 1990s has enabled the geological structure to be mapped at a higher resolution on the island and more widely on the mainland (e.g. Mortimore and Pomerol, 1991, 1997). Evidence for considerably more faulting (both cross-cutting and parallel to the Chalk outcrop), than previously recognised (Evans et al., 2011) has been identified during the most recent survey. The survey has also re-appraised and in part corroborated the existence of faults identified by Nowell (1987, 1995) and Mortimore (2011b). The fault and structural control of outcrop is further demonstrated when making geomorphological interpretations of the subtle crest-orientation changes, that mimic the underlying bed strike, along the steeply dipping ridges to the east and west of the island.

The Culver Down section and that around The Needles have provided internationally important reference sections for the study of various aspects of the Chalk Group. Particular attention has been paid to biostratigraphy (Hart et al., 1987, 1989; Prince et al., 1999, 2008; Swiecicki, 1980), geochemistry (Jarvis et al., 2001), carbon and oxygen isotope studies (Jarvis et al., 2006; Jenkyns et al., 1994), sequence stratigraphy (Gale, 1996; Grant et al., 1999), magnetostratigraphy (Montgomery, 1994; Montgomery et al., 1998), studies of Milankovitch cyclicity (Gale,1989; Ditchfield, 1990), and global stage-boundary correlation Gale et al. (1995).

Across the Isle of Wight, the Chalk Group spans the chronostratigraphical stages of the Cenomanian to Campanian (Figure 18) and (Figure 19). In Cenomanian times, emergent landmasses were present in south-west England, Brittany, Wales, and farther afield in Scotland, Northern Ireland, the Vosges, the Ardennes and the Baltic Shield. In general, relative sea level rose throughout the Late Cretaceous, until a marked fall after the Campanian (Hancock and Kaufman, 1979). However, short-term, possibly isochronous reversals to this progression produced regionally correlative changes in deposition. The maximum transgression in Campanian times probably only left the highest parts of the Welsh Massif above sea level. Southern Britain lay approximately 10 degrees of latitude farther south than at present. Chalk accumulated on the outer shelf of an epicontinental subtropical sea of normal salinity and with little terrigenous input. The chalk that makes up most of the group consists of predominantly soft white to off-white very fine-grained and very pure, microporous limestone with subordinate hardgrounds and beds of marl, calcarenite and flint. The lowest part of the succession comprises alternations of marl and marly limestone. The bulk lithology is composed largely of the microscopic calcareous remains of planktonic algae (coccoliths). Other coarser carbonate material is present, some in rock-building proportions; this includes foraminifera, ostracods and calcispheres, together with entire and finely comminuted echinoderm, bryozoan, coral and bivalve remains including disaggregated prisms of inoceramids (Rawson, 2006 and references therein).

Other, generally minor, constituents of a depositional and early diagenetic origin are present.

Mud-grade material, consisting chiefly of the clay minerals illite, smectite and kaolinite, in varying relative amounts, forms an appreciable proportion (30 to 40 per cent, Destombes and Shephard-Thorn, 1971) of the marly parts of the Lower Chalk and of thin marl seams elsewhere in the White Chalk Subgroup (see below). Throughout the main body of the Chalk, above the West Melbury Marly Chalk, the proportion of argillaceous material falls progressively, until in the White Chalk Subgroup it does not exceed five per cent. The geochemical signature of individual marl seams in the White Chalk Subgroup is proving to be sufficiently characteristic to correlate the basinal sequences of Sussex and Kent (Wray and Gale,1993).

A coarser silt and fine- to medium-grade sand fraction, predominantly of detrital quartz, forms less than one per cent of the Chalk overall. Certain beds, most notably the Glauconitic Marl Member in this district, contain other stable mineral species such as mica, zircon, rutile and tourmaline (Jukes-Browne and Hill, 1903). Another minor siliceous element is derived from skeletal material such as sponge spicules and radiolaria. These are commonly replaced by secondary calcite or pyrite. The authigenic minerals glauconite and calcium phosphate occur throughout the Chalk succession, but are most conspicuous in winnowed and condensed horizons such as the Glauconitic Marl and Jukes-Browne Bed 7 (lying above a possible nonsequence within the Zig Zag Chalk) and within the Chalk Rock Member of the Lewes Chalk Formation. The phosphate occurs most commonly as reworked nodules within these winnowed levels. Hardgrounds within the chalk commonly have concentrations of glauconite and phosphate as impregnations and coatings. Much of this material is the product of early diagenesis. Finely disseminated pyrite is a common authigenic mineral in the more argillaceous parts of the succession and pyrite nodules and burrow fills are a conspicuous feature of much of the Chalk.

For parts of the White Chalk Subgroup, the most important noncarbonate constituent is flint, which occurs in nodular and tabular form in seams that parallel the bedding, and also along cross-cutting joints and fissures. The formation of flint is related to the diagenetic history of the Chalk.

The diagenesis of the Chalk occurred in two distinct phases. An early phase, associated with interruptions in sedimentation, affected unconsolidated sediment at or just below the sea floor. A late phase was associated with deeper burial, compaction, silicification and carbonate dissolution. Early diagenesis of the Chalk in response to changing water depth, deposition rates and erosion gave rise to a variety of bedding surfaces and associated lithologies. These range from simple omission surfaces, demonstrating nondeposition, to complicated scoured, burrowed and mineralised surfaces (hardgrounds) overlying lithified chalk (chalkstone). They provide a framework of lithological markers within the Chalk Group. The fact that many of these surfaces and lithologies are the result of basin-wide changes in depositional conditions has permitted detailed regional correlations (Mortimore, 1986b, 1987; Bromley and Gale, 1982; Robinson, 1986). The progression in the development of hardgrounds is given in Kennedy and Garrison (1975). Late-stage diagenesis modified the framework of Chalk lithostratigraphy created during early sedimentation. Carbonate dissolution as the result of deep burial and compaction has produced a variety of effects. In hard chalks, microstylolites are common, but in the softer chalks stylolites are absent and anastomosing residual clay seams are widespread. Where dissolution has been extensive, the softer chalk takes on a ‘flaser’ appearance with ‘augen’ of white chalk enveloped by greyish marl (Kennedy and Garrison, 1975), a texture described as ‘griotte’ chalks by Mortimore (1979).

The most conspicuous diagenetic process in the Chalk is silicification. The major product of this silicification is flint which is considered to have resulted from the segregation of silica (SiO2) in layers, parallel to the sea floor. Flint is a type of chert, with a particularly well-developed, conchoidal fracture, which is composed of an aggregate of ultramicroscopic quartz crystals only a few microns across. It is generally present in pure white chalks with little clay content and is thus most prevalent in the White Chalk Subgroup. The silica was presumably derived from dissolution of original biogenic sponge material and skeletons of other siliceous organisms, notably radiolarians and diatoms. Clayton (1986) suggests that this precipitation was a multistage process, initiated by dissolution of host carbonate and occurred 5 to 10 m below the sediment surface, at the oxic–anoxic boundary. Noncarbonate grains, textures and fabrics in the original chalk are commonly preserved in detail during this process. Local porosity in excess of 75 to 80 per cent and permeability variations, particularly in response to burrowing (trace fossils are mainly Thalassinoides and Zoophycos), produced the characteristic burrow-fill form of most flint nodules. Layers where a uniform permeability occurs give rise to tabular flint bands. The most strongly developed of the horizontal flint beds can be traced over large distances amounting to many kilometres across the depositional basin. Even later-stage silicification and remobilisation of silica is demonstrated by cross-cutting and near-horizontal, sheet-like flint bodies which line open joints and faults.

Eustatic changes in sea level, subsidence and variable sediment accumulation rates influenced the deposition of the Chalk, but these factors did not have a uniform effect over the whole British Chalk basin. Thick successions accumulated in basinal areas and incomplete or condensed successions on adjacent highs, but through time the different areas of deposition migrated in response to these changes in environment and local tectonic control. Evidence of small-scale cyclical deposition occurs in the West Melbury and lower Zig Zag Chalk formations (Gale, 1989, 1995). Elsewhere in the succession, a lack of suitable markers or colour variations precludes the identification of these cycles. The cyclicity reflects a linkage with the Earth’s orbital cycles (Milankovitch Cycles) (Gale, 1989) of variable periodicy.

Marl seams in some parts of the Chalk Group appear unrelated to sedimentary rhythms and are therefore regarded as episodic. Some at least may represent volcanic ash accumulations analogous to the contemporaneous tuffs identified in the north German chalk succession. The origin of other marl seams is not clearly understood, but Wray and Gale (1993) regard them as representing an increased supply of detrital material, at times of falling sea level.

Historically there has been a wide range of estimates for the depth of the ‘Chalk Sea’ (e.g. Cayeux, 1897; Jukes Browne and Hill,1904; Reid, 1973; Kennedy and Garrison, 1975). Winnowed hardground developments suggest a near-storm-base water depth of 50 m or less while Rawson (2006) quotes a ‘normal’ depth of 100 to 500 m. It follows, therefore, that typical white chalk is neither deep oceanic ooze nor a deposit of shallow-water origin.

Grey Chalk Subgroup (GCk)

The Grey Chalk Subgroup is made up of the older West Melbury Marly Chalk and the younger Zig Zag Chalk formations and approximates (with the exclusion of the younger Plenus Marls Member) to the old division of the Lower Chalk. The two formations are present throughout the island but remain undivided in the deep boreholes (Figure 9) where between 58 and 88 m are recognised. These thicknesses were originally determined for the Lower Chalk and so generally include a short interval for the Plenus Marls Member at the top. At outcrop the subgroup shows a decrease in thickness towards the west from about 61 m at Culver Cliffs to about 48 m at Compton Bay.

West Melbury Marly Chalk Formation (WMCk)

The formation is divided into two unequal parts and ranges in thickness between 15 and 19 m on the island. A thin basal unit, comprising calcareous glauconitic sand and glauconitic sandy silty chalk with phosphatic nodules is called the Glauconitic Marl Member. It ranges in thickness between 1.8 and 3.6 m and rests on the heavily bored surface of the underlying Upper Greensand Formation. The nonsequence represented by this surface has been estimated at 1 to 2 million years in duration by Insole et al. (1998) but may well be of considerably shorter duration. This member was described as the Chloritic Marl of the Isle of Wight in White (1921) and by Jukes-Browne and Hill (1903).

The remainder of the formation comprises interbedded buff, pale to dark grey and off-white, soft, marly chalk and hard pale grey limestone arranged in couplets each generally in the range of 0.5 to 1.5 m in thickness. The formation, as defined, is in part equivalent to a large portion of the traditionally termed Chalk Marl. The top of the formation is marked by the burrowed erosion surface immediately below the Cast Bed (Bed C1 of Gale, 1995). In full successions the uppermost bed equates to the Tenuis Limestone or Bed B 42/43 of Gale (1995).

The two principal exposures of the formation are at Compton Bay [SZ 350 855] (Plate 13) (Mortimore et al., 2001, p.179) and in the northern part of Sandown Bay [SZ 628 855] where it forms part of Bembridge–Culver Down cliff and the Ledges beneath Bembridge Down (Figure 21) (Kennedy, 1969; Jarvis, 1980, written communication, 2011). White (1921) includes numerous other sections within the Southern Downs and inland including sections at St Boniface Down [SZ 570 781], Gore Cliff [SZ 494 761] and Brook Shute [SZ 3965 8485]. The Brook Shute locality provides an almost continuous roadside exposure, though obscured in places, of the progression from the Upper Greensand through to the lower Zig Zag Chalk (Woods, 2009) including the Glauconitic Marl Member at the base of the Chalk succession. A similar section from Upper Greensand to low in the Zig Zag Chalk is seen on the Southern Downs along St Lawrence Shute [SZ 53421 77168] to [SZ 53495 76715] (Woods, 2008b). The upper part of the Glauconitic Marl Member is seen in a clear section at West Standen [SZ 50582 87619]. A section in a trackway at Garstons Down [SZ 477 858] near Gatcombe includes the Cast Bed at the base of the succeeding Zig Zag Chalk Formation. An old pit on the Downend road [SZ 53100 87070] is in the middle of the formation and includes several examples of the ammonites Schloenbachia varians and Hyphoplites sp. (Woods, 2008a).

Zig Zag Chalk Formation (ZCk)

The Zig Zag Chalk is composed typically of medium-hard greyish to white blocky chalk. The lower part is generally marlier and contains some thin limestones; it equates with the upper part of the ‘Chalk Marl’ of the traditional scheme (Figure 18), (Plate 14).

The base of this formation is taken at the Cast Bed (Bristow et al., 1997), a very fossiliferous silty chalk immediately above the Tenuis Limestone where this is present. Other conspicuous units are a pale grey hard splintery limestone with conspicuous Sciponoceras about 3 to 4 m from the base and a calcarenite bed with phosphatic nodules equivalent to the Jukes-Browne Bed 7 (JB7) in the middle of the succession above which regular limestone–marl couplets become less distinct. The JB7 bed marks the base of the ‘Grey Chalk’ in the traditional nomenclature for the ‘Lower Chalk’. The top of the formation is taken at the base of the Plenus Marls. The base of the formation is in the Acanthoceras rhotomagense Zone, Turrilites costatus Subzone and the top within the Metoicoceras geslinianum Zone.

The formation is exposed in the Compton Bay section [SZ 350 855] (Mortimore et al., 2001) and in the section on the foreshore (Whitecliff Ledge) and cliffs below Bembridge Down/Culver Down in the northern Sandown Bay area (Figure 21). Both localities are described in Kennedy (1969). There are numerous exposures inland described in White (1921) and the majority were visited during the recent survey although many of these are now degraded and offer poor sections. The most notable, where clear sections can be seen currently, are the Brook Shute, Garstons trackway (Plate 14) and St Lawrence Shute roadside exposures mentioned above. The old Morton Manor quarry [SZ 60242 86504] near Brading includes strata from the mid Zig Zag Chalk up-sequence into the Holywell Nodular Chalk Formation including the Plenus Marls Member (Woods, 2007). The entrance to this quarry provides a poor section but includes the arenitic chalk with common brachiopods that is attributed to the Cast Bed at the base of the Zig Zag Chalk Formation. Much of the Zig Zag Chalk succession can be seen northward along Pumpfold Lane [SZ 437 836] and again in the road traversing the Brighstone escarpment north of Rock [SZ 424 842].

White Chalk Subgroup (WCk)

The White Chalk Subgroup is most fully represented onshore in southern England by the strata preserved on the Isle of Wight. The subgroup is divided into seven formations. A number of members and many named beds help to define the individual formations and act as important markers for regional correlation (Hopson, 2005). The criteria for the identification of these units during geological surveying are given in Aldiss et al. (2012).

Holywell Nodular Chalk Formation (HCk)

The Holywell Nodular Chalk is composed of medium hard to very hard and nodular chalk with flaser marls throughout. It is generally shelly to very shelly and has a gritty texture. The Melbourn Rock Member near its base is a very hard nodular chalk but generally lacks significant shell debris whilst the oldest unit of the formation is the Plenus Marls Member characterised by a thin succession of interbedded coloured marl and white chalk (Jefferies, 1963; (Plate 15).

Including the Plenus Marls and Melbourn Rock, which are about 5 m thick, this formation is between 25 and 35 m thick based on field estimates. At Culver up to 32 m (Figure 21) of the formation is present and this reduces westward to 25 m at Compton Bay. The formation spans the Cenomanian–Turonian boundary close to the top of the Melbourn Rock (Figure 14).

Widely, throughout southern England, the very hard nodular chalk of the Melbourn Rock gives rise to a strong positive feature at the base of the Chalk scarp. On the island, however, this feature is not readily apparent where the Chalk dips steeply but has been identified on the northern margin of the Southern Downs where the dip is low. However, the distinctive hard nodular brash of the Melbourn Rock can be traced throughout the district. Above the Melbourn Rock, the remainder of the Holywell Nodular Chalk is characteristically nodular with common shells of the inoceramid bivalve Mytiloides, locally in rock-building proportions (Plate 16). The higher part of the Holywell Chalk is conspicuously more shelly than the lower part. In hand specimen the rock has a grainy rough texture, a feature that, in the absence of significant shell debris, helps distinguish these beds from the chalk above and below. The sequence also contains thin interbedded flaser and plexus marls, but these are only readily apparent in exposures. The upper limit of this formation is at the top of the highest shell-detrital nodular chalk bed.

The formation is exposed in the section at Compton Bay in the west (Mortimore et al., 2001) and again along the eastern end of Whitecliff Ledges, Sandown Bay (Figure 21) (Kennedy, 1969; Jarvis 1980, written communication, 2011). Inland the formation is seen along many track and road sections, including some of those mentioned previously, and notably in the quarry north of Morton Manor [SZ 60242 86504] (Plate 15) and in the Mersley Down Limekiln Quarry [SZ 55783 87168].

New Pit Chalk Formation (NPCk)

The New Pit Chalk comprises medium-hard, massive-bedded, pure white chalk with regularly spaced pairs or groups of marls, each up to 15 cm thick, for example in the Compton Bay section. It is sparsely fossiliferous with brachiopods dominant. In this district small flints are confined to the uppermost part of the succession. The formation is 27 m thick in the Culver Cliff section (Jarvis 1980; written communication, 2011; (Figure 21) but there is a significant westward reduction and only 14 m of strata are seen in Compton Bay (Mortimore et al., 2001).

The Compton Bay foreshore (which is safely accessible only during falling tides) and Compton Down Military Road (Mortimore et al., 2001; called the Afton Down road cutting in White, 1921) are the principal easily accessible exposures of this formation on the island. The section in the east below Culver Cliff (Figure 21) is difficult to access because of the large boulder scree along the foreshore and the tides. Inland the large exposure at Cheverton Quarry [SZ 451 843] (Plate 17) shows the whole of the formation where 20 m of strata are preserved below the Lewes Nodular Chalk Formation (Mortimore, 2011b).

The Castle View Marl Pit (also known as the Nunnery Pit) [SZ 49043 87752] near to Carisbrooke is described in Rowe (1908, Pit 51) and in White (1921). The fossil collections from here, including those made during the current survey (Woods, 2008a), from a much degraded section, indicate that the whole of New Pit Chalk Formation is present.

Lewes Nodular Chalk Formation (LeCk)

The Lewes Nodular Chalk comprises interbedded hard to very hard nodular chalk, with soft to medium-hard chalk and marl. The first persistent seams of flint appear near the base. The flints are typically burrow-form, medium to large, black or bluish black with a thick white cortex. On the island the formation is consistently between 40 and 45 m thick.

Biostratigraphically, the Lewes Nodular Chalk includes the topmost part of the Terebratulina lata Zone and all of the succeeding Plesiocorys (S.) plana (formerly Sternotaxis plana) and Micraster cortestudinarium zones. On the island the lithological boundary with the New Pit Chalk Formation is placed immediately below the distinct nodular chalk of the Ogborne Hardground (Bromley and Gale, 1982), that is equivalent to the Spurious Chalk Rock of older literature, at about the horizon of the Glynde Marls as seen in Sussex (Mortimore et al., 2001).

The Lewes Nodular Chalk is divided into two units by the Lewes Marl and the underlying Lewes Tubular Flints, which comprise an extensive system of black cylindrical burrow-form flints. The lower unit consists of medium- to high-density chalk and conspicuously iron-stained hard nodular chalk. The upper unit is mainly low- to medium-density chalk with regular thin nodular beds; it yields the bivalve Cremnoceramus (Mortimore, 1986b).

A lengthy exposure is visible along Compton Down Military Road. The corresponding section in Compton Bay is difficult to visit due to the boulder-strewn nature of the foreshore and the tides. The uppermost part of the formation is exposed in Freshwater Bay, below Fort Redoubt [SZ 3446 8553] and in Watcombe Bay [SZ 3426 8550] immediately to the west, and within the cliffs below Tennyson Down. Both Watcombe Bay and the long cliff exposure below Tennyson Down towards Sun Corner [SZ 2982 8458] can only be accessed by boat and landing is difficult against a boulder scree at the base of the cliff. The top of the formation is again visible at Sun Corner in Scratchell’s Bay but the magnificent water- and wind-worn cliff exposure is inaccessible, forming a sheer drop to a rock platform that is rarely exposed, even during the lowest spring tides.

The whole of the lower part of the formation up to the Lewes Marl (Mortimore 2011b, fig. 4) is exposed inland at Cheverton Quarry (Plate 17). A significant part of the upper Lewes Nodular Chalk is exposed in a faulted block within the western end of this quarry (Mortimore, 2011b, fig. 10).

At the eastern end of Brook Down [SZ 3943 8510] (Plate 18) a section from the topmost New Pit Chalk Formation (about 3 m) into the lower part of the Lewes Nodular Chalk (7 m) includes the Ogbourne Hardground at the base of the formation and the dark plastic-textured Fognam Marl some 2.5 m higher in the succession (Woods, 2007). The topographically highest pits adjacent to the road north of Rock [SZ 4234 8440] currently show beds high within the New Pit Chalk Formation but formerly also exposed the junction with the Lewes Nodular Chalk (White, 1921; Rowe, 1908, Pit 77).

Numerous other exposures of the lower part of the formation are present throughout the island, indicating the value of this hard nodular chalk for road metal. Notable examples are adjacent to the Adgestone Road [SZ 5989 8668] west of Brading (White, 1921, fig. 15) and the Castle View Marl Pit [SZ 49043 87752]. The Lewes Nodular Chalk forms much of the crag upon which Carisbrooke Castle was built.

The whole formation is visible in Culver Cliffs from Sandown Bay to the Nostrils (Figure 21) but this area is difficult to visit because of the bouldery nature of the foreshore and the tides (Jarvis 1980, written communication, 2011). In comparison to Compton Bay and most other mainland successions, the section at the Nostrils [SZ 6380 8544] demonstrates a significant attenuation, with only 6 to 7 m present, above the Hope Gap Hardground in the uppermost part of the Lewes Chalk. This is one of the first signs up-sequence of the unique nature of the Culver–Whitecliff section that may be related to early tectonic/eustatic influences on deposition in this part of the Chalk outcrop.

Seaford Chalk Formation (SCk)

The Seaford Chalk is composed primarily of soft white chalk with seams of large nodular and semitabular flint. Within the steeply dipping zones, the formation can become variably tectonically hardened. Near the base, thin harder nodular chalk seams also occur associated with seams of carious flints giving this formation a similar appearance to the upper part of the Lewes Nodular Chalk; the boundary is not clear-cut in mapping terms (Aldiss et al., 2012). Higher in the sequence the flints are large, black and bluish black, mottled grey, with a thin white cortex, and they commonly contain shell fragments. Typically, brash from the lower part of the Seaford Chalk contains an abundance of fragments of the bivalves Volviceramus and Platyceramus; brash from the upper part contains Cladoceramus and Platyceramus (Mortimore, 1986b). In the absence of these bivalves, the flaggy-bedded nature and pure whiteness of the soft chalk serves to distinguish it from the Lewes Nodular Chalk below.

The formation is about 73 m thick in the cliff at Culver Down (Whitecliff) (Plate 19) in the east and as much as 95 m within the fully developed succession exposed at Scratchell’s Bay (Figure 22)a in the west.

Biostratigraphically, the Seaford Chalk is co-extensive with the Micraster coranguinum Zone. The formation crosses the Coniacian–Santonian boundary which is placed at the Michel Dean Flint (Mortimore, 1986b). This boundary is also marked by the appearance of Cladoceramus. It correlates with the strata from Shoreham Marl 2 to the base of Buckle Marl 1 of Mortimore (1986b).

The principal exposures of this formation are within Compton Bay and Scratchell’s Bay (Figure 22)a, in the cliffs below Tennyson Down see also (Plate 43), Watcombe Bay and around Freshwater Bay (Plate 20) in the west. The Freshwater Bay site, comprising cliffs to both the west and east of the sea wall, represent the most easily accessible exposure of this unit on the island. Here the junction with the underlying Lewes Chalk can be seen at low tides by traversing around the headland adjacent to the sea stack called Stag Rock. The junction with the overlying Newhaven Chalk is where the crinoid Uintacrinus first appears as you travers westward and where significant marl seams appear in the section.

The formation is also present from the Nostrils into Horseshoe Bay below Culver Down (Figure 21), (Plate 19) in the east but this is only accessible at the lowest spring tides. Here the basal part of the Seaford Chalk, with up to 25 m of beds from the Shoreham Marl up to the Seven Sisters Flint, is expanded in comparison to the same unit on the mainland. The belts of Platyceramus and Volviceramus, typical of this part of the succession, are strongly developed. However, the youngest part of the formation in Horseshoe Bay [SZ 6384 8548] contains two distinctive glauconitised hardgrounds suggesting condensation of the sequence locally.

Inland exposures, usually only exposing parts of this thick unit, are known for example at The Mall Chalk pit [SZ 60204 86693] west of Brading that has beds including Platyceramus and Cladoceramus on its clear southern face indicating a position within the middle of the formation and equivalent to the Cuckmere and Haven Brow beds of Mortimore (1986b). Similarly the Downend Quarry [SZ 53435 87395] near Arreton contains beds with Cladoceramus on its southern side, indicating that this extensive quarry exposes White Chalk Subgroup beds from the middle of the Seaford Chalk Formation upwards. The Shide Quarry [SZ 50578 88003] near Newport commences, in its south-west corner, within the lower part of the Seaford Chalk and Volviceramus is common.

Newhaven Chalk Formation (NCk)

The Newhaven Chalk is composed of soft to medium hard, smooth, white chalks with numerous marl seams (Plate 21) and flint bands; it is commonly tectonically hardened on the Isle of Wight. Typically, the marls vary between 20 and 70 mm thick. They are much attenuated or absent locally where differentiation between the Seaford and Newhaven formations is difficult to judge, other than by the incoming of a ‘mesofauna’ typified by oysters and crinoids particularly Uintacrinus. Channels with hardgrounds and phosphatic chalks have been recorded widely but in limited areas across the mainland (Hopson, 1994; Mortimore, 1986a) with one such occurrence being seen in the Culver cliff section (Mortimore et al., 2001; Gale et al., 2013). There is an argument as to whether these hardgrounds are the result of channelling, tectonism or most likely a combination of both. The formation is up to 67 m thick on the island with the section in Scratchell’s Bay slightly thicker due to repetition of the sequence.

The brash is composed of smooth, angular flaggy fragments of white chalk very similar in appearance to that of the Seaford Chalk. The incoming of abundant Zoophycos flints near the base of the member serves as a useful marker for mapping the lower boundary.

Biostratigraphically the Newhaven Chalk covers the whole of the Uintacrinus socialis, Marsupites testudinarius and the Uintacrinus anglicus zones and the greater part of the Offaster pilula Zone. The Santonian–Campanian stage boundary lies within this formation at the Friars Bay Marl (Mortimore, 1986b). The formation was originally correlated with the strata from the base of Buckle Marl 1 to the base of the Castle Hill Marl of Mortimore (1986b), but recently Bristow et al. (1997) placed the top of the member slightly higher in thick basinal sequences at the Pepper Box Marls. Individual thecal plates of the zonal index Marsupites testudinarius can be found in numerous small pits and track-side exposures, but otherwise macrofossils are rare.

The full succession of the Newhaven Chalk Formation is present in Scratchell’s Bay (Figure 22)a, b and in the cliffs below Culver Down (see (Plate 19), (Figure 21). Numerous inland sections are known, many in old degraded sites where the exposure has become limited. The formation is fully represented at the Downend Quarry [SZ 53435 87395] (Woods, 2007; White, 1921, p.72, fig. 16; Rowe, 1908, Pit 21) and the large pit complex at Shide [SZ 50578 88003] (Woods, 2008b; Rowe, 1908, Pit 105) near Newport. Partial sections are present at the quarry south of Duxmore Farm [SZ 55172 87437] (Woods, 2008b; White, 1921) and at Ashengrove quarry [SZ 44561 87200] (Woods, 2009; Rowe, 1908, Pit 99; Mortimore, 2011b).

Culver Chalk Formation (CCk)

The Culver Chalk is composed of soft white chalks without significant marl seams, but with some very strongly developed nodular and semitabular flints. A particular concentration of large flints, the Castle Hill Flints, occurs near the base of the unit as defined (at the Castle Hill Marls) by Mortimore (1986b) that is just above the level of the Arundel Sponge Bed (Mortimore, 1986b). In mapping terms (following Bristow et al., 1997) the boundary is placed in the late Offaster pilula Zone perhaps as low as the Telscombe/Meeching Marls of the standard Sussex succession (Mortimore, 1986b). The formation is 77 m thick at Culver Cliffs and estimated to be as much as 83 m elsewhere. The section in Scratchell’s Bay is much reduced with only 38 m identified in the recent survey (Figure 22)b.

In parts of Dorset and Sussex, the Culver Chalk Formation can be divided into a lower Tarrant Chalk and an upper Spetisbury Chalk. These were regarded formations in Bristow et al. (1997) but current practice treats these as members of the Culver Chalk (Rawson et al., 2001). These members are not identified during mapping within the formation on the island but Mortimore et al. (2001, fig. 3.72) separates the members in the Culver section at a bed named the Whitecliff Wispy Marls. Thus the Tarrant and Spetisbury members are 46 m and 31 m thick respectively in this section. Correlation (Hopson et al., 2011, fig. 5a) suggests that it is principally the Spetisbury Chalk Member, and therefore a considerable part of the Gonioteuthis quadrata Zone, principally the so-called ‘overlap zone’ with Bellemnitella mucronata, that is absent in Scratchell’s Bay.

Biostratigraphically, the Culver Chalk mostly or entirely lies within the Gonioteuthis quadrata Zone, with the base possibly extending downwards into the Offaster pilula Zone in some areas outside this district. It is entirely within the Campanian stage (Mortimore, 1986b; Bristow et al., 1997).

The formation is exposed within Scratchell’s Bay (Figure 22)b; (Plate 22) and in the cliffs below Culver Down (Figure 21) and there are numerous small exposures in the steeply dipping chalk along both the Brighstone and Sandown anticlines inland. The most notable of these include the large quarry, although now much degraded, at Ashey [SZ 57469 87869] (Woods, 2007; Rowe, 1908, Pit 46), where a logged section shows 15 m of semiporcellanous white chalk with many regularly spaced flint seams and a single thin marl on which a dip of 62° to the north can be measured. They also include the Duxmore Farm pit, mentioned above, where a complex faulted section shows the base of the formation and about 45 m of strata up to a fault that limits the stratigraphical extent of the formation, and the northern part of the Downend Quarry (above) where the lower to middle part of the formation is identified. To the west beyond Newport the top of the formation and basal Portsdown Chalk is identified on Apes Down [SZ 45822 87595], about 8 to 10 m of strata attributed to the Culver Chalk is seen at a pit near Newbarn Farm [SZ 43244 86719] (Woods, 2009; Rowe, 1908, Pit 95; Mortimore, 2011b, fig. 18) and a 2 m section of very flinty chalk at the top of a largely degraded quarry [SZ 41940 84994] within the middle of the formation (Woods, 2009; Rowe, 1908, Pit 69). On Wellow Down a fauna from a mostly degraded pit [SZ 38556 85612] again indicates the middle of the formation characterised by the Applinocrinus cretaceus Subzone fauna; similar faunas were identified in Woods (2009) at [SZ 35426 85854]; Rowe (1908) at Pit 3 [SZ 33232 85712]; and Rowe (1908) at Pit 10.

Portsdown Chalk Formation (PCk)

The formation consists of white flinty chalk with common marl seams, the base of which is taken at the Portsdown Marl (Mortimore, 1986b; Bristow et al., 1997) as defined at Farlington on the mainland outcrop around Ports Down itself. On the island much of the formation is tectonically hardened within the steeply dipping zones of the Purbeck–Wight Structure; marl seams are commonly streaked-out and slickensided, and flints are shattered in situ. The highest part of the formation as used herein is reasonably free of conspicuous marls and was given the name of the Alum Bay Beds by Mortimore (1979, 1983) but was formally described as the Studland Chalk Member in Gale et al. (1987). It is considered as a member of the Portsdown Chalk Formation in BGS usage. The top of Portsdown Chalk on the Isle of Wight is controlled by the sub-Palaeogene erosion surface. In general about 110 m of Portsdown Chalk is estimated to be present in the outcrop and in deep wells. About 63 m are present in the Culver Down cliff section into Whitecliff Bay with an estimated 95 m interpreted for the Scratchell’s Bay and contiguous Alum Bay sections from manuscript details provided by Professor Gale.

Biostratigraphically the Portsdown Chalk Formation on the island is within the Belemnitella mucronata Zone of the Late Campanian. The principal exposures of the formation are from Scratchell’s Bay around The Needles (Plate 23) into Alum Bay (Figure 22)b, and above the Whitecliff Ledges into Whitecliff Bay (Figure 21) beneath Culver Down.

There are numerous small exposures in the steeply dipping chalk along both the Brighstone and Sandown structures inland adjacent to the Palaeogene outcrop. All are attributed to the Belemnitella mucronata Zone. The majority are partly degraded but the most notable commonly provide a small section. A large pit south of Longlands on Bembridge Down has obviously been expanded at some point after the visit of Rowe (1908, Pit 15) as it now exposes a significant succession of steeply dipping hard flinty chalk with well-developed marl seams and is attributed to the B. mucronata Zone (Woods, 2007). A small pit [SZ 59217 87235] near Nunwell House exposes about 10 m of steeply dipping hard chalk with flint and marl seams that demonstrate a pair of high-angle almost bed-parallel faults. Further west a pit [SZ 57329 87848] near to the main exposure on Ashey Down (see above) exposes about 17 m of strata with regular flint seams that include a zone of shattered chalk about 4 m thick that parallels the strike of the beds. The Portsdown Chalk Formation is present to the north of a near strike-parallel fault at Duxmore Farm Pit (see above). The fauna, within a succession with regular marl seams, indicates a level above the basal part of the formation (Woods, 2008b).

The enormous degraded Shide Quarry (see above) contains many small sections with those in the north-east proving the Portsdown Chalk and the junction with the underlying Culver Chalk. This occurs a little below a pair of marls in inoceramid-rich chalk attributed to the Farlington Marls, marking the base of the B. mucronata Zone (Woods, 2008b).

West of Newport, pits at Newbarn Farm [SZ 43047 86880] and Apesdown [SZ 45589 87570] provide significant exposures of the lower part of the Portsdown Chalk (Woods, 2007, 2009; Mortimore, 2011b, fig. 23 and fig. 26). In the former, the Farlington Marls are identified. The old partly degraded quarry at Shalcombe Manor [SZ 39444 85503] includes examples of Belemnitella together with abundant Echinocorys subconicula and E. subglobosus indicating a position within the lower part of the Portsdown Chalk.

There are frequent quarries along the Palaeogene margin west of Shalcombe Down through to West High Down revealing faunas that confirm both Culver and Portsdown Chalk. The most significant is the quarry [SZ 32471 85562] south of Nodewell Farm, which includes many small sections. The southern and central part of the quarry exposes hard flinty chalks with regular marl seams and a fauna including E. conica and many inoceramid fragments attributed to Cataceramus. The northernmost exposures yield the brachiopods Magus chitoniformis and Cretirhynchia woodwardi. Taken together the fauna indicates that the Portsdown Chalk here is representative of the lower part of the formation and of the stratigraphically higher Studland Chalk Member.

Palaeogene

There is a significant unconformity see (Figure 23), (Figure 24), representing a time-gap of about 15 million years, between the youngest known Chalk on the island and the basal beds of the overlying Reading Formation. It is assumed that chalk deposition continued from the Late Campanian (the youngest Portsdown Chalk Formation is perhaps about 72 Ma on the island) up until at least the youngest Maastrichtian as there is evidence of chalk of this age being present beneath the English Channel (Hamblin et al., 1992). It is still unclear as to whether chalk sedimentation continued into the Danian in this area (as in the North Sea Basin) as the Channel Basin (Figure 4) was affected by minor episodes of Early Palaeogene inversion at this time as precursors to the major inversion in the Mid Miocene (as discussed in Chapter 1). Evidence that the area of the Isle of Wight was land for a short time is provided by the sea-level fall in the Selandinian and Early Thanetian (Figure 25); and the absence in southern England of sediments representative of the Early and much of the Late Paleocene. Basin-wide peneplanation of the Chalk and progressive overstep of the Reading Formation over younger chalk is demonstrated on the Isle of Wight by the absence from the Culver Down succession of 25 m of the topmost Portsdown Chalk that is present in Alum Bay. The greenhouse climate continued into the Paleocene and through into the Mid Eocene with a marked thermal maximum identified at the Paleocene–Eocene boundary (PETM). From the beginning of the Mid Eocene the climate began to cool through to the Terminal Eocene Cooling Event (TECE) marked by the Eocene–Oligocene boundary (King, 2006 and references therein). These major climatic events can be studied in the rocks exposed on the Isle of Wight.

The outcrop and exposures of the Palaeogene of the Isle of Wight offer the most extensive and complete succession (Figure 23) available in the UK and the island is a principal site for Palaeogene investigation in north-west Europe. The strata represent about 20 million years of deposition covering the Paleocene to Early Oligocene in the western margins of a basin that extended into the North Sea, and at times may have been connected with the North Atlantic to the south-west (Chapter 1). The succession on the island is characterised by strata laid down on the margins of a shallow sea in a fluctuating transgressive–regressive cyclic regime that has resulted in complications in the correlation of strata over the width of the island.

Historically Palaeogene exposures on the Isle of Wight have received a great deal of attention. These works are the source of many of the terms, adjusted and revised, that have resulted in the present nomenclature.

The lithostratigraphical classification of the Palaeogene used until the 1970s in the Hampshire Basin and the Isle of Wight was based principally on studies by Prestwich (1846, 1850, 1852, 1854), Forbes (1856), Fisher (1862) and Gardner (e.g. Gardner et al., 1888). Their terms were modified into a basin-wide stratigraphical scheme utilised by the Geological Survey, for example in Bristow (1862), Reid and Strahan (1889) and White (1921) for the Isle of Wight. Curry et al. (1958) summarised and defined the commonly used lithostratigraphical units up to that time and provided an extensive bibliography. Stinton (1975) proposed a reclassification using Hedbergian principles, and introduced many new terms that were partly followed by Curry et al. (1978). Cooper (1976) published a similar scheme for the Palaeogene of the London and Hampshire basins. King (1981) formalised terminology for the London Clay Formation and associated deposits. However both the Stinton and Cooper schemes were criticised soon after their publication (e.g. Daley et al., 1979; King,1981) for their lack of formal definitions of each new unit proposed.

Edwards and Freshney (1987) provided a comprehensive reappraisal for the Hampshire Basin Palaeogene and this was partly revised for the western part of the basin by Bristow et al. (1991). Minor lithostratigraphical revisions of parts of the Bracklesham Group in the central and eastern Hampshire Basin were made by Todd (1990) and Freshney et al. (1990). King (1996) summarised recent stratigraphical studies on the Bracklesham Bay section.

Recently, Daley (1999a) and Daley and Balson (1999) have provided comprehensive summaries of previous literature on the Isle of Wight incorporating details of the minor stratigraphical units within each formation. The Cenozoic strata are comprehensively described in King (2006). The classification of these deposits continues to provoke differing views, with a unified classification for the Hampshire and London basins being given in King (in press). Herein the scheme promulgated by Insole et al. (1998) is the principal source used during the current work as this formed the most up-to-date appraisal available during the field survey (Figure 23). The relationship between the terms used herein and those adopted by King (in press) are shown in (Figure 24).

The rocks contain evidence of many environments from shallow marine (neritic), beach, tidal flat (littoral), coastal marsh and lagoon, estuarine, river (fluvial) and lake/marsh (lacustrine and paludal) reflecting the relative position of the fluctuating shoreline through time. On the Isle of Wight the succession has been described and interpreted at length within the literature with the texts of Daley and Edwards (1974, 1990), Edwards and Freshney (1987), Insole and Daley (1985), King (1981), and Plint (1982, 1983) being most prominent. These are summarised in the GA Guide to the Isle of Wight (No. 60) by Insole et al. (1998). There is evidence that Early Palaeogene inversion has affected the successions of the Palaeogene in terms of local emergence and erosion adjacent to the Isle of Wight Monocline. From within the Mid Eocene one such minor uplift and erosion event adjacent to the Sandown Anticline is discussed by Gale et al. (1999), but further evidence is presented by Newell and Evans (2011) for a younger inversion event that affected the Headon Hill Formation in the north-west of the island.

Biostratigraphy

The Hampshire Basin, including the important exposure in Whitecliff Bay, provides the principal laboratory for Palaeogene biostratigraphical study (Figure 25) in the UK. However, this area is not without its problems, mainly as a consequence of the predominantly nearshore to marginal marine depositional environments providing an imperfect record of planktonic microfossil groups. Consequently there are problems in the biostratigraphical correlation with the deeper marine environments of the central North Sea Basin.

With the exception of the middle of the London Clay Formation, planktonic foraminiferids are rare or absent and calcareous nannofossils are generally of low diversity (Aubry, 1983). Many of the lithostratigraphical units have suffered postdepositional decalcification, particularly in surface exposures, resulting in poor preservation or absence of calcareous fossils. The dinoflagellate record is more complete but as assemblages are generally environmentally controlled they are difficult to correlate with the open-marine assemblages preserved in the North Sea Basin. The dinoflagellate assemblage zones introduced by Bujak et al. (1980) across southern England are imprecise and not currently clearly tied to the known lithostratigraphical units.

In the Solent Group, the marginal-marine and nonmarine environments carry a significant terrestrial mammal fossil fauna that is important for correlation with other areas in Western Europe (Hooker et al., 2005).

Magnetostratigraphy

As a potential aid to correlation the magnetostratigraphy of much of the Isle of Wight Palaeogene has been studied, principally at Whitecliff Bay. Early application of the technique by Townsend (1982) to the interval from the Reading Formation to the lower Barton Clay Formation provides data for both Alum Bay and Whitecliff Bay. These results were summarised by Townsend and Hailwood (1985), and interpreted in terms of the standard geomagnetic scale by Aubry et al. (1986). The Whitecliff Bay section was resampled by Ali (1989), who reinterpreted some of the Early Eocene data presented by Townsend (Ali et al., 1993). The magnetostratigraphy of the Headon Hill Formation, Bembridge Limestone Formation and lower Bouldnor Formation at Whitecliff Bay was analysed by Gale et al. (2006). Brief summaries of the magnetostratigraphy are given in each lithostratigraphical section below, these being derived from the interpretations of earlier authors given in King (in press). The relationship of the magnetostratigraphy to the chronological stages and the lithostratigraphical units are given in (Figure 25).

Across-island correlations

There are still some problems with correlation of the Palaeogene strata across the island, particularly in the steeply dipping and faulted outcrops close to the Isle of Wight Monocline, where individual units are difficult to trace in the field. There is a general paucity of significant inland exposures between the two extensive exposures presented by Whitecliff Bay and Bembridge Foreland (Figure 26) in the east and by Alum, Totland and Colwell bays in the west (Figure 27), (Figure 28) and (Plate 24). The full suite of Headon Hill Formation members seen in the cliffs at Totland (Figure 29) and Colwell bays is not apparent east of Freshwater through lateral change and erosion and the rapid eastward failure of the Hatherwood and Lacey’s Farm Limestone members. The intermittent coastal cliff and foreshore exposures along the north-west coast (Bouldnor Cliff, Hampstead Cliff, Thorness Bay and Gurnard Bay) provide the only localities where the Bouldnor Formation can be examined, including the thin Bembridge Insect Bed with its extensive flora and insect content. The coastal sections of the Headon Hill Formation in the north-east, from East Cowes through Wotton and Ryde to Bembridge, are very limited with generally relatively restricted exposures in the foreshore and low cliffs, and commonly within landslide blocks.

However the surface information is supplemented by geophysical logs and lithological interpretations that enable some correlations to be demonstrated (Figure 28).

Lambeth Group

Within the London and Hampshire basins the Lambeth Group includes the Upnor, Reading and Woolwich formations. On the Isle of Wight only the Reading Formation is recognised and the thin nonglauconitic sand previously identified as the ‘Bottom Bed’ at Alum Bay (White 1921; Edwards and Freshney 1987), and attributed as an Upnor Formation equivalent, is now regarded as a basal unit of the Reading Formation.

Reading Formation (RB)

The Reading Formation is principally varicoloured (mainly red, brown, purple and grey) and colour-mottled (pedogenically modified) clay and silt, with lenticular, channel-fill units of fine- to coarse-grained sand. A thin basal sand unit, with some flint pebbles, is commonly present where the Reading Formation overlies the White Chalk Subgroup. This basal unit is characteristically smectite rich. Edwards and Freshney (1987) suggested that the smectite has been reworked from the ‘Bottom Bed’ of the Upnor Formation which occurs further north within the Hampshire Basin. The Reading Formation at Alum Bay and Whitecliff Bay has reverse polarity, interpreted as Chron C24r (King, in press) and is therefore slightly older than equivalent beds in the London Basin.

The formation is 35 to 40 m thick in the east of the island where its principal exposure is at Whitecliff Bay [SZ 638 858] and is between 26 and 35 m thick in the west where it is best seen in Alum Bay [SZ 306 852] (Figure 26) and (Figure 27). The formation is generally well exposed at the Alum Bay site which provides a reference section for the unit (Edwards and Freshney, 1987).

In Whitecliff Bay the karstified, subaerial erosion surface at the base of the formation is generally poorly exposed on the foreshore but may be visible higher up the cliffs where landslides occasionally expose the surface. Immediately overlying this surface is a thin grey pebbly bed with angular and well-rounded flints for which Insole et al. (1998) used the term Reading Formation Bottom Bed. At Alum Bay this palaeosurface is clearly seen immediately behind the beach shingle and on the south side of the short valley to the top of the cliffs to the east (Plate 25). This valley suffers considerable creep and slippage during wet conditions and can be dangerous to traverse. Where the surface is visible, a thin conglomerate comprising greenish grey to grey fine- to medium-grained sand with rounded flint, fresh nodular flint and rounded blocks of chalk is present as a bed and within solution features (penetrating up to 3 m into the chalk) on the strongly karstified chalk surface. It has been estimated that the sands are some 15 Ma younger than the underlying chalk.

The Reading Formation was formerly well exposed during the construction of the railway cutting south of Brading Station [SZ 609 868] to [SZ 607 866] and was reported upon in the memoir of Reid and Strahan (1889, fig. 17) and repeated in White (1921). Inland, the Reading Formation is generally very poorly exposed, and is commonly obscured by superficial slope deposits derived from the adjacent Chalk downlands.

Thames Group

The Thames Group includes the Harwich Formation and the London Clay Formation. Only a basal thin unit attributed to the Harwich Formation is present on the Isle of Wight and this is not distinguished on the geological maps where it is included within the London Clay Formation outcrop.

Harwich Formation

This formation is identified at Whitecliff Bay (2.3 m) (Figure 26), above a sharp contact, and at Alum Bay (4.3 m) (Figure 27), above a burrowed erosion surface, with the Reading Formation. This basal unit comprises a thin pebble bed of silty sand with well-rounded flint, chalk and Reading Formation mud pebbles, overlain by glauconitic sandy silt and silty sand with shelly lenses.

This unit is called the London Clay Basement Bed by Edwards and Freshney (1987), a term originally used by Prestwich (1850), and this usage was followed by Insole et al. (1998). King (1981) uses the term Tilehurst Member (Division A1) within the Harwich Formation (formerly Oldhaven Formation) for this basal unit on the island and reports (King, in press) that it has reverse polarity, interpreted as Chron C24r.

London Clay Formation (LC)

The London Clay Formation was formally defined by King (1981, see below), with a composite type section in London; a reference section for the Hampshire Basin was designated at Whitecliff Bay (Figure 26). The ‘Bagshot Sands’ identified on the old geological map and discussed in the memoir (White, 1921) have been re-interpreted (e.g. King, 1981, 1991; Edwards and Freshney,1987). The sequence of heterogeneous sand units present in Whitecliff Bay was divided between the London Clay Formation and the overlying Bracklesham Group. Consequently, in the Hampshire Basin the lower (see above in Harwich Formation) and upper boundaries of the London Clay Formation were modified. The upper London Clay–Bracklesham boundary was moved up-succession, to include units of ‘London Clay’ facies which had previously been assigned to the Bracklesham Group (King, 1981, 1991; Edwards and Freshney, 1987).

In the Hampshire Basin the London Clay Formation is overlain by the Wittering Formation (Bracklesham Group) in the east and by the Poole Formation (Bracklesham Group) in the west with the Isle of Wight district straddling this change. Regionally the upper boundary of the London Clay Formation is a deeply incised erosion surface with the formation more truncated from east to west.

The London Clay Formation of the Hampshire Basin and the Isle of Wight was originally divided by King (1981) into four Divisions (A to D) and smaller-scale units (e.g. A1, A2 etc.). Later emendation excluded the Tilehurst Member (formerly A1) and included the lower part of the ‘Bracklesham Beds’ at Whitecliff Bay, which were correlated with ‘Divisions’ D2 and E of the London Basin (Edwards and Freshney, 1987; King, 1991). The lettered divisions (A to E) are retained in King (in press) with the addition of some named sand members. Divisions A to D are recognised in both Alum Bay and Whitecliff Bay (Figure 26) and (Figure 27). Only in Whitecliff Bay is the Division E recognised having been considered as the lower part of the ‘Bracklesham Beds’ in White (1921) (formerly the Bagshot Sands). On the Isle of Wight the formation is about 150 m in the east and around 70–73 m in the west at Alum Bay.

Lithologically the formation on the island can be described using the characteristic units that define the divisions of King. The base of each division is at the base of thin pebble beds that rest on interburrowed transgressive omission surfaces (Plate 26). Ideally each division comprises three successive units. Above the basal glauconitic clay or pebble bed an interval characterised by coarsening-upward silty clay becoming very fine sand is surmounted by locally developed incised channels (King, 1981; Plint, 1988) of fine- to coarse-grained cross-stratified sand and pebble gravel. Regionally the middle coarsening-upward unit demonstrates a general westward increase in grain size indicating a westward proximity to source.

Five lithologically distinctive incised channel-sand ‘members’ of the formation were named by King (1981), however other sand units and most of the finer-grained units remain unnamed. Some of these names were modified by Edwards and Freshney (1987), who also added an additional unit on the mainland (Durley Sand Member).

Regionally the Portsmouth Sand Member fills erosional channels at the top of Division C2 whilst the Whitecliff Sand Member, likewise filling channels, represents practically all of the Division D of King (1981) at Whitecliff Bay (Plate 27). These two sand members were formerly assigned to the ‘Bagshot Sands’ (e.g. White, 1921). Both have their type sites [SZ 640 860] at Whitecliff Bay but are also seen widely on the mainland.

At Whitecliff Bay Division E commences with a pebble bed and has a top positioned where the mud lithologies typical of the London Clay give way to heterolithic silt-rich, finely bedded sediments of the Bracklesham Group. This level is recognised as Plint’s (1983) second transgressive surface (T2) that can be correlated with the succession exposed in Alum Bay.

In respect of magnetostratigraphy, the London Clay Formation on the island ranges from Chron C24r at Whitecliff Bay and Alum Bay (Divisions A2 and A3) through to Chron C23n (Division E) at Whitecliff Bay. A full discussion of the placement of chron boundaries is given in Ali et al. (1993) and King (in press).

Whitecliff Sand Member and Portsmouth Sand Member Undivided (LC(sa))

At Whitecliff Bay, the Portsmouth Sand Member and Whitecliff Sand Member (Plate 27) are both represented but separated only by a thin interval of sandy clay. This thin sandy clay has not been identified during surveying inland and hence the sand unit at the top of the London Clay is designated as ‘sand in the London Clay’ undifferentiated. Throughout the island this sand unit at the top of the London Clay is at most between 30 and 38 m thick.

The Portsmouth Sand Member is mainly medium- to coarse-grained cross-stratified sand with some pebbly levels and is about 10 m thick. The member fills erosional channels at the top of Division C2.

The Whitecliff Sand Member attains 15 m or more in thickness at Whitecliff Bay and fills deeply incised channels at the top of Division D1. It comprises medium- to coarse-grained generally cross-bedded sand with some pebble lenses.

Bracklesham Group (BrB)

The lithostratigraphical terminology of the Bracklesham Group has been derived largely from two areas: Whitecliff Bay (Figure 26) on the Isle of Wight and Bracklesham Bay on the mainland. These areas include the type and reference sections of the Wittering, Earnley, Marsh Farm and Selsey formations, which are mainly marine and marginal marine in origin. (Curry et al., 1977; Fisher, 1862; Edwards and Freshney, 1987 and references therein; Huggett and Gale, 1997). The Poole, Branksome and Boscombe formations (originally assigned to a Bournemouth Group) are defined with type sections in the Bournemouth area (Plint, 1982, 1983; Bristow et al., 1991 and references therein) but these units extend to the western Isle of Wight and Alum Bay (Figure 27). They are mainly marginal marine and nonmarine in origin. A broad correlation of the units represented in these areas was only established relatively recently, by a combination of sedimentology, magnetostratigraphy, sequence stratigraphy, and dinoflagellate assemblages. The Alum Bay section lies between Whitecliff Bay and the Bournemouth area, and carries units common to both; a complete correlation is still not entirely resolved across the island although geophysical log correlations (Figure 28) provide a reasonable interpretation.

The group is shown undivided on the map and ranges in thickness from up to 173 m in the east to between 220 and 230 m in the west.

Hooker (1986) redefined the upper limit of the Bracklesham Group, assigning the highest part (his Huntingbridge Division) to the overlying Barton Clay Formation, which he also formally defined (see Barton Group). Edwards and Freshney (1987) followed this revision and also reassigned the lower part of the Wittering Division to the London Clay Formation (see above), as proposed by King (1981). These revisions established the Bracklesham Group as a well-defined unit bounded by regional erosion surfaces.

Wittering Formation

The type section of this unit is the cliffs and foreshore at Whitecliff Bay (Figure 26) [SZ 640 860] with a reference section defined on the foreshore at Bracklesham Bay (in West Sussex) [SZ 765 984] to [SZ 808 961].

The formation is mainly laminated clay and heterolithic sediments, with subordinate lithologies including bioturbated glauconitic sand, cross-stratified sand and glauconitic clay. On the Isle of Wight the formation is generally between 76 and 90 m thick (exceptionally about 53 m at Whitecliff) in the east whilst its lower and upper parts in the west, where it interdigitates with the Poole Formation, are 45 and 23 m thick respectively. Near the top in the east, the formation includes the Whitecliff Bay Bed (Edwards and Freshney, 1987) comprising a lignite bed overlying a paleosol with rootlets.

The Wittering Formation is represented mainly in the eastern and central Hampshire Basin. It grades laterally westwards into the Poole Formation. The base of the Wittering Formation is an erosion surface, incised into the underlying London Clay Formation. In most sections a variable thickness of Division E of the London Clay Formation is preserved beneath the erosion surface.

The depositional environment is inner neritic (sublittoral) shelf to marginal marine. The age of the formation is Mid to Late Ypresian (NP12 NP14 where NP is the calcareous nannoplankton Zone, (Figure 25)) and possibly earliest Lutetian. In terms of magnetostratigraphy the base of the formation is within the lower part of Chron 23n whilst the top is low within Chron 21r.

At Alum Bay (Figure 27), (Plate 29) the Wittering Formation is divided into two by a lower leaf of the Poole Formation unit. The lower unit of the Wittering Formation is equivalent to Beds 1 to 3 of Plint (1983) and is about 45 m thick. The basal contact is an interburrowed omission surface, overlain by a thin bed of clayey sand with wood fragments and (probably reworked) glauconite. The upper leaf is equated to Bed 7 of Plint (1983), is about 23 m thick, and comprises dominantly heterolithic sediments (lenticular- and thin-bedded sand and clay) and laminated clay, with large-scale channelling. The base is marked by sandy mud with rootlets.

At Whitecliff Bay the formation is considered to be about 53 m thick and includes the top part (about 24 m) of a unit termed Cycle 1 in Insole et al. (1998) comprising heterolithic laminated mud and sand with lignite and some glauconite. Above a strongly burrowed surface the succeeding Cycle 2 unit (29 m) comprises heterolithic, thin-bedded mud, silt and sand with lignite. Near the base of this cycle are two prominent thin shell beds that make up the Cardita Bed and about 7 m from the top of the cycle a 1 m-thick lignite with underlying rootlet bed is termed the Whitecliff Bay Bed. Equivalents to the Whitecliff Bay Bed have been found widely within the Hampshire Basin and it is an important horizon with palaeogeographical significance and marks an emergent period where a supratidal marsh environment was established.

Poole Formation (western Wight only)

On the Isle of Wight this formation is confined to the west where it interdigitates with the upper leaf of the Wittering Formation (see above). It is only seen within Alum Bay (Figure 27), (Plate 29) and cannot be traced separately inland from this exposure.

The formation comprises two parts. The lower leaf of the formation, equivalent to Plint’s (1983) Bed 4 to 6, is up to 23 m thick and comprises fine- to medium-grained, partly planar, partly cross-bedded sand, fining upwards from a sharply defined base. This is overlain by a distinctive unit of fine-grained bioturbated sand and ferruginous sandstone with rounded flint and quartz pebbles that was formerly glauconitic (now oxidised to limonite). It marks a marine transgressive event (the T2 transgression of Plint, 1983). It can probably be correlated with the strongly bioturbated horizon at the base of Cycle 2 in the Wittering Formation at Whitecliff Bay which also includes quartz pebbles. This bed is a key marker in correlations across the island and between the western and eastern Hampshire Basin. A heterolithic unit including fine- to medium-grained sand with lenticular beds of kaolinitic clay forms the top of the succession and includes the Lower Alum Bay Leaf Bed (Prestwich, 1846). The base of this upper heterolithic unit is sharp, with coarse sand at the base. Plint (1983) identified a rooted lignite bed at the top of this unit, largely cut out by an erosion surface at the base of the upper leaf of the Wittering Formation, which Edwards and Freshney (1987) interpreted as a correlative of the Whitecliff Bay Bed.

The upper leaf of the Poole Formation is 25 m thick and equivalent to Beds 8 and 9 of Plint (1983). It comprises fine- to coarse-grained sand that is partly cross-bedded and has small quartz pebbles at several levels. The basal contact is sharp, and is probably an erosion surface.

Earnley Sand Formation

The cliffs and foreshore at Whitecliff Bay [SZ 640 860] (Figure 26) form the type section for this unit with a closely allied reference section being on the foreshore at Bracklesham Bay [SZ 808 961] to [SZ 823 950] on the other side of the Solent.

The Earnley Sand Formation is represented in the eastern and central Hampshire Basin but thins progressively westwards due to truncation beneath the erosion surface at the base of the overlying Marsh Farm Formation. The formation is not present at Alum Bay.

The Earnley Sand Formation is principally bioturbated, silty glauconitic fine-grained sand (‘greensand’) and is up to 22 m thick in eastern Wight. The contact with the underlying Wittering Formation is an interburrowed omission surface that is regarded as a transgressive horizon (T3) by Plint (1983). The formation carries an abundant marine fauna and a low diversity foraminiferal fauna. The upper 4.5 m of the member carries abundant remains of the large foraminiferid Nummulites laevigatus (the Nummulites laevigatus Bed of White, 1921) indicating a contemporary connection with the warm waters of the North Atlantic. The formation represents deposition in marine, inner neritic (sublittoral) environments.

In terms of its magnetostratigraphy the lowest part of the Earnley Formation has reverse polarity, assigned to Chron C21r on the basis of its biostratigraphical context. The change to normal polarity between the ‘Cardita Bed’ and ‘Turritella Bed’ at Bracklesham Bay, and at a similar level at Whitecliff Bay, therefore represents the base of Chron C21n. The formation is of Early Lutetian (NP14) age.

Marsh Farm Formation

The formation has its type section within the cliffs and extending onto the foreshore at Whitecliff Bay [SZ 640 860] (Figure 26). A reference section is defined on the foreshore at Bracklesham Bay (West Sussex) [SZ 823 950] to [SZ 825 946].

The Marsh Farm Formation overlies the Earnley Formation in the central and eastern Hampshire Basin. The basal contact is an erosion surface that to the west entirely cuts out the underlying Earnley Formation (e.g. Edwards and Freshney, 1987). In the western Hampshire Basin on the mainland, the Marsh Farm Formation grades laterally into the Poole Formation but can be distinguished separately in Alum Bay (Figure 27).

The Marsh Farm Formation is mainly laminated clay, heterolithic sediments and units of medium- to coarse-grained, sparsely glauconitic sand, partly as channel-filling units, with high lateral variability. There is a unit of glauconitic shelly sandy clay within the formation at Whitecliff Bay that has not been identified elsewhere. In the east of the island the formation is about 18 m thick but up to 35 m is found in the west at Alum Bay (Figure 27). The formation was deposited in a marginal marine and inner neritic (sublittoral) environment. The upper Alum Bay Leaf Bed forms lenticular masses at the base of the formation at Alum Bay.

Both Nummulites laevigatus (s.s.) and N. variolarius occur in the glauconitic unit at Whitecliff Bay (Blondeau and Curry, 1963). In the Paris Basin this association occurs within the lower part of NP15.

Chron C21n is represented within the lower and middle Marsh Farm Formation at Whitecliff Bay. The upper part has not been analysed. The age is regarded as Mid Lutetian.

Branksome Sand Formation (western Wight only)

The Branksome Sand Formation is identified in the west of the island and is present at Alum Bay (Figure 27) where between 65 and 70 m of the unit is seen.

The formation comprises a lower and thicker unit of fine- to medium-grained sand, partly bioturbated with Ophiomorpha, which contains several pebbly layers and occasional thin clay seams. This is overlain by a thinner unit (about 15 m) of interbedded blocky massive clay, rooted lignite, silt and very fine-grained sand, which includes several bioturbated levels.

The formation is equivalent to beds 14 to 17 in Plint (1983) and the erosive base represents his T4 transgressive surface. The lower part of this interval has reverse polarity and the middle part normal polarity, indicating that the formation includes the Chron C20r–C20n boundary.

No biostratigraphical data has been obtained from this or the overlying Boscombe Sand Formation. Their classification is based on lithostratigraphical comparison with the succession in the Bournemouth area.

The Branksome Formation has been interpreted as a proximal lateral correlative of the Selsey Sand Formation, based on its relative stratigraphical position (Plint 1983; Edwards and Freshney, 1987). In petroleum exploration wells in the western Isle of Wight and the adjacent area of Hampshire (e.g. Bouldnor Copse 1 Borehole) the Selsey Sand Formation underlies a unit of grey and brown clay and lignite that can be correlated with Plint’s Beds 15 to 17 at Alum Bay. There is, however, no evidence for any transition or interfingering between the Branksome Formation and Selsey Formation in this western area of the island, although these units are represented in sections only 5 km apart (Alum Bay and Norton 1 Borehole). The dinoflagellate cyst data indicate that the highest part of the Branksome Formation is not older than the upper Selsey Formation, tending to confirm the lateral equivalence of the two units.

Selsey Sand Formation

The type section of the formation is within the cliffs and on the foreshore at Whitecliff Bay [SZ 640 860] (Figure 26) with a reference section on the foreshore at Bracklesham Bay [SZ 825 946] to [SZ 845 926]. It is represented throughout the eastern and central Hampshire Basin but is not present at Alum Bay in the west of the island.

The lithological qualifier in the formation name, retained herein, has been rejected by Todd (1990) and King (1996; in press) as a high proportion of the formation is represented by silt and clay, in some areas. The Selsey Sand Formation in the type section corresponds to the ‘Selsey Division’ of Curry et al. (1977). Its upper boundary, as originally defined by Edwards and Freshney (1987) in the type section, was placed at a lower level than the base of the Selsey Division of Curry et al. (1977), but was later emended to correspond to the limits of the ‘Selsey Division’. The Selsey Sand Formation overlies the Marsh Farm Formation.

The Selsey Sand Formation was interpreted by Edwards and Freshney (1987) as interfingering westwards into the Branksome Sand Formation, but available data indicate a rather abrupt boundary, more suggestive of an erosional contact (see above). Everywhere it underlies the Barton Clay Formation whose base is a regional unconformity surface, as demonstrated by Todd (1990) and this erosional surface progressively truncates the Selsey, Branksome and Boscombe sand units from west to east.

The formation is dominantly shelly, bioturbated, fine-grained sand, silty sand, silt and clay, and is sparsely glauconitic at most levels. In the east of the island the formation is up to 43 m thick. The basal contact is an interburrowed omission surface. At the type section in Whitecliff Bay the formation includes the Cerithium giganteum Bed at the base and the large foraminiferid Nummulites variolarius [Nummulina variolaria] is commonly encountered and forms the Nummulites variolarius Bed at the top (Wilkinson and Farrant, 2011). The formation represents deposition in a marine, inner neritic (sublittoral) environment and is considered to be Mid to Late Lutetian (NP15 and NP16) in age.

Boscombe Sand Formation (western Wight only)

The Boscombe Sand Formation is equivalent to Bed 18 of Plint (1983). The type section for the formation is within the cliffs east of Bournemouth, between Boscombe Pier and Hengistbury Head in Dorset [SZ 112 911] to [SZ 170 907]. Regionally the formation is restricted to the Bournemouth–Lymington area on the mainland and the western end of the Isle of Wight, and is present at Alum Bay (Figure 27). This formation was included by Edwards and Freshney (1987) in the Barton Group, on the assumption that it was the lateral correlative of the lower part of the Barton Clay Formation (Hooker 1986; Edwards and Freshney, 1987), but this is not supported by any published data. The basal surface of the Barton Clay Formation is a combined erosion surface and transgressive surface, and marks a major lithological and environmental break that can be traced across the Hampshire Basin (Todd, 1990). Since the Boscombe Sand Formation lies below this surface it is now (King, in press) re-assigned to the Bracklesham Group, on the basis of its lithology and stratigraphical relationships.

At Alum Bay the formation comprises 14 m of fine- and medium-grained sand, partly cross-bedded, with occasional Ophiomorpha that indicate a marginal marine depositional environment. The base is gradational from the underlying Branksome Sand Formation. The formation is markedly coarsening-upward and a thin pebble bed of large rounded and chatter-marked flint pebbles forms a narrow ridge in the degraded cliffs south of the chair lift. The formation is considered to be of Late Lutetian age.

Barton Group (Ba)

Most lithostratigraphical subdivisions of the Barton Group are based on the type section between Highcliff and Barton-on-Sea in Christchurch Bay (Dorset and Hampshire) (Daley, 1999b). This is commonly referred to as the Barton or Barton Cliffs section, but in the 19th century literature it was sometimes cited as Hordwell. At Barton, Gardner et al. (1888) divided the ‘Barton Beds’ into Lower, Middle and Upper intervals. The Lower and Middle Barton Beds correspond to the ‘Barton Clay’ and the Upper Barton Beds to the ‘Barton Sand’. The ‘Barton Beds’ in the Barton cliffs section were divided by Burton (1929, 1933) into lettered ‘faunal horizons’ (A1–A3 to L) or ‘Beds’. Beds A1 to B correspond to the Lower Barton Beds, C to G to the Middle Barton Beds, H to L to the Upper Barton Beds of Gardner et al. (1888). The ‘Bed’ limits were lithologically defined and they can be regarded as lithostratigraphical units although for the most part they are unmappable other than in cliff sections. Hooker (1986) differentiated three depositional sequences (‘cyclothems’), with their boundaries at the base of Beds A1, B and J.

The Barton Group is redefined in King (in press) and comprises a lower clay-dominated interval (the Barton Clay Formation) and an upper sand-dominated interval (the Becton Formation) (Figure 24). In practice an intermediate Charma Sand Formation can be mapped between the Barton Clay and Becton Sand on the mainland although this Chama Sand is considered as an informal unit or ‘Bed’ within the Becton Formation by King (in press).

For mapping purposes on the Isle of Wight, the Barton Group is divided into a Barton Clay Formation and an overlying Barton Sand unit that corresponds to the undivided Becton Sand and Chama Sand formations (the redefined Becton Formation of King, in press). At Alum Bay and Whitecliff Bay (White, 1921 p. 99 and 100) the Chama Sand is differentiated within the cliff sections shown in Insole et al. (1998) but this division within a thick sand unit could not be maintained inland due to the steep dip, possible bed-parallel faulting and poor exposure. However, the distinction between the Barton Clay Formation and Barton Sand (Becton Sand and Chama Sand formations undivided) can be maintained over much of the outcrop.

The Group is up to 124 m thick in the east of the Isle of Wight and up to 118 m in the west where the Boscombe Sand Formation is excluded from the group (see above).

Barton Clay Formation (BaC)

The Barton Clay Formation is preserved over a wide area of the central Hampshire Basin and the whole of the Isle of Wight where it overlies the Selsey Formation or the Boscombe Sand Formation. The basal contact is an interburrowed omission surface which marks a regional unconformity (Todd, 1990).

The Barton Clay Formation comprises the upper part of the former Bracklesham Beds/Group (‘Huntingbridge Division’) and the former ‘Barton Clay’ (Lower and Middle Barton Beds) (King, in press). In the original definitions of the formation, the top was taken in the middle of Bed H (‘Chama Bed’) of Burton (1929, 1933) at the upward change from sandy clay to silty sand, but this boundary is transitional and cannot be clearly defined. King (in press) places the boundary at the base of Bed H, defined at an abrupt upward change from silty clay to coarser-grained sediments. These coarser-grained sediments are the Chama Sand Formation of BGS usage (Edwards and Freshney, 1987), and the informally ‘ranked’ Chama Bed of the Becton Formation (King, in press).

The type section is within the cliffs between Mudeford and Barton-on-Sea (‘Barton Cliffs’) [SZ 194 927] to [SZ 242 927] on the mainland. The formation is formally divided in King (in press) with a lower Elmore Member, an intermediate Highcliff Member and an upper Naish Member. None of these have proved to be mappable inland over the Isle of Wight but the Elmore Member has its type section on the foreshore at Whitecliff Bay (Gale et al., 1999) and is also present at Alum Bay. The Highcliffe Member has its type section within the cliffs at Highcliffe in Dorset and has a reference section in Alum Bay. The Naish Member is absent at Whitecliff, where the Becton Formation of King (Chama and Becton sand formations undivided) rests on the Highcliffe Member, but it is present at Alum Bay.

Generally the formation comprises interbedded, bioturbated, silty clay, silt and sandy clayey silt, which is highly glauconitic at some levels. The formation was deposited in a marine inner to mid neritic (sublittoral) environment.

Up to 45 m of the formation is present in the cliff and on the foreshore at Whitecliff Bay (Figure 26) but is poorly exposed other than when the foreshore has been stripped of its beach deposits. The formation comprises principally bluish grey silty clay. Two beds in the middle of the succession contain abundant Nummulites; the thin lower glauconitic sand contains Nummulites prestwichianus and about 6 m higher N. rectus occurs commonly in a stiff blue-grey mud.

The formation is represented by up to 83 m in the west at Alum Bay (Figure 27). Immediately above the pebble bed at the top of the Boscombe Sand, the formation comprises lignitic and sandy mud that passes up through laminated mud into brown and green mud. At about 14 m from the base, a glauconitic sandy mud with abundant Nummulites prestwichianus is present. The following succession comprises mud and sandy mud with glauconite-rich beds and ironstone bands and contains a rich molluscan fauna. The formation is Late Lutetian and Early Bartonian in age. The nannoplankton zone NP16–NP17 boundary is located low in the succession around the N. prestwichianus Bed.

Barton Sand (B+C) (Chama and Becton sand formations undifferentiated)

The ‘Barton Sand(s)’ as originally defined comprise the sand-dominated interval designated Beds H to K at Barton-on-Sea (Burton, 1929; 1933). The Becton Sand Formation was introduced by Hooker as a formal name for approximately the same interval, but with its base taken at a level in the middle of Bed H. However, as Hooker (1986) noted, the junction is difficult to recognise. Edwards and Freshney (1987) independently introduced the same term, but restricted its use to Beds J and K. They introduced an additional older unit, the Chama Sand Formation, for the ‘Chama Bed’ (Bed H) and its presumed lateral equivalents.

King (in press) considers the Chama Sand as insufficiently lithologically distinctive to be differentiated at formation level and considers it as an informal ‘Bed’ at the base of his Becton Formation. He points out that there is a sharply defined boundary between Bed F (clay) and the lower part of Bed H (sandy clay) and this can be identified in all sections (Bed G is a limited local unit and not identified on the Isle of Wight). This clay to sand change is clearly recognisable on gamma-ray logs and King chooses this as the base of his Becton Formation. The ‘sand’ qualifier he regarded as inappropriate, as in some areas the formation includes thick units of sandy silt and sandy clay.

For clarity the Chama Sand and Becton Sand formations as mapped by the Survey on the mainland, and identified at Alum Bay and Whitecliff Bay, are defined below. However these have proved indivisible in mapping terms across the island. This undivided unit is equivalent to the Becton Formation of King (in press). The members of the Becton Formation as defined by King (in press) are not delimited on the map but some can be identified in the Alum Bay and Whitecliff Bay sections.

The age of the Chama Sand and Becton Sand formations undivided is not well-constrained, partly due to the limited biostratigraphical data available. The Bartonian/Priabonian stage boundary has not yet been identified in the Hampshire Basin. Dinoflagellate cyst data indicates that the interval up to (and including ) the Becton Bunny Member, a silty sandy clay unit of limited distribution low in the undivided unit on the mainland (Barton Cliffs), predates the first occurrence of the dinoflagellate cyst Rhombodinium perforatum and is thus Bartonian or earliest Priabonian in age. Mammalian data indicates that the base of the overlying Headon Hill Formation is probably Priabonian (King, in press and references therein).

Chama Sand Formation (C)

As originally defined, this unit was characterised primarily palaeontologically, by the common occurrence of the bivalve Chama squamosa (but this may not be a unique feature as the overlying interval at Barton-on-Sea is decalcified). The type section, as defined by Edwards and Freshney (1987) is within the Barton Cliff section on the Hampshire–Dorset border [SZ 243 927] where the unit comprises mainly sandy clayey silt and silty glauconitic sand. It is considered to be the lowest and informal unit of the Becton Formation at Barton-on-Sea by King (in press). It is recognisable elsewhere in south-west Hampshire, but its lithological differentiation from overlying sands is not clear-cut. The formation is considered to have been deposited in a marine, inner neritic (sublittoral) environment.

At Alum Bay (Figure 27) the unit is characterised by about 7 m of blue-grey sandy silty clay with abundant C. squamosa, and gastropod Turritella.

In the east at Whitecliff Bay the formation is poorly exposed and the estimated 15 m of deposit north of the ‘zigzag path’ is principally made up of intensely bioturbated muddy sand.

Becton Sand Formation (B)

The Becton Sand Formation is represented in the New Forest and adjacent areas of Hampshire, and in the Isle of Wight.

The formation comprises very fine- to coarse-grained sand and silty sand, partly glauconitic, interbedded in some areas with units of sandy clayey silt, sandy clay and clayey silt. The formation is considered to have been deposited in a marginal-marine (beach to upper shoreface) to inner-neritic (sublittoral) environment.

The Becton Sand Formation at Whitecliff Bay comprises three lithological units (Gale et al., 1999). A thin glauconitic sand (50 mm thick) with clasts including fossils reworked from the Chalk and younger Palaeogene formations is overlain by a thick (about 30 m) unit of interbedded very silty clay and thin beds of fine-grained sand with sparse glauconite grains. The top of this unit marks a lithological change to the fine-grained bioturbated sand, sparsely glauconitic, with silt/clay flasers at most levels that makes up the rest of the formation. Subangular flint pebbles occur at several levels.

At Alum Bay the formation is represented by about 33 m of white and pale yellow fine-grained sand with Ophiomorpha burrows preserved in places.

Solent Group (Solt)

The Solent Group comprises all of the strata above the Barton Group, including the Headon Hill (Figure 29), Bembridge Limestone and Bouldnor formations. Forbes (1853) divided the ‘Fluvio-Marine Series’ into the Headon, Osborne, Bembridge and Hempstead [Hamstead] Series. These units (as Headon Beds etc.) and their subdivisions were adopted by subsequent Geological Survey publications, and remained in use until 1985. Insole and Daley (1985) replaced them by a formal scheme, retaining most of Forbes’ subdivisions, but with modified terminology, and naming some more geographically restricted units. Edwards and Freshney (1987) independently introduced formal names for units in the lower part of the Solent Group, but these have failed to find acceptance.

Insole and Daley’s (1985) Solent Group terminology is largely followed by King (in press), but with significant proposed modifications (Figure 24). King (in press) considers the Headon Hill Formation as unwieldy and proposed splitting the succession into three formations. He proposes abandoning the Headon Hill Formation in preference to upgrading the Totland Bay and Colwell Bay members to formation status and proposed a younger Ryde Formation to include all of the remaining strata of the Headon Hill Formation. He considered this to be justified on the basis of the stratigraphical complexity of the Headon Hill Formation, and the wish to see some units raised to member status (e.g. Brockenhurst ‘Bed’, How Ledge Limestone) since they have well-defined boundaries, and the presence of ‘unconformities’ between some beds in some areas. King also considered that the Hamstead Member and maybe the ‘Bembridge Marls Member’, within the currently defined Bouldnor Formation, should also be given formation status, on a similar basis, but this will require consensus on the significance of units such as the ‘Black Band’. None of these proposals have been adopted on the new Isle of Wight Special Geological Sheet.

The Group is divided into three formations. The lower Headon Hill Formation is separated from the younger Bouldnor Formation by the Bembridge Limestone Formation. The full succession is principally of nonmarine, freshwater to brackish water, fluvial/terrestrial clastic deposition with freshwater limestone. Only two units, the Brockenhurst Bed, a unit at the base of the Colwell Bay Member (Headon Hill Formation), and the Corbula Beds at the top of the Cranmore Member (Bouldnor Formation) represent fully marine deposition.

A magnetostratigraphical record for the Solent Group outcropping at Whitecliff Bay (Gale et al., 2006), has been proposed to aid correlation, but its interpretation has been disputed by Hooker et al. (2009).

The whole group amounts to between 193 and 200 m in thickness across the island. A cross-island correlation based on interpretation of boreholes is shown in (Figure 30).

Headon Hill Formation (HH)

The Headon Hill Formation of Insole and Daley (1985) essentially formalises the earlier Headon Beds and Osborne Beds adopted in White (1921). Edwards and Freshney (1987) independently introduced the term Headon Formation, which corresponds exactly to the former Headon Beds. The suggestion in King (in press) that the Headon Hill Formation should be split into the Totland Bay, Colwell Bay and Ryde Formations is not adopted herein as it postdates the survey activity on the island and consequently the proposed formations have not been tested as mappable units. In general the constituent members of the Headon Hill Formation cannot be identified consistently other than in coastal exposures and over the Headon Hill area (Figure 29), (Plate 30) where significant limestone units form distinct back scars of landslides. Hence the formation is generally shown undivided on the map. There is still controversy over the position of the Nettlestone Grits (Seagrove Bay Member on the north-east coast) with the work of Gale et al. (2006) indicating that these beds are effectively lateral equivalents to the Lacey’s Farm Limestone Member and therefore predate the Fishbourne and Osborne members.

The formation varies between 85 m in the west and up to 90 m in the east and represents deposition in mainly coastal plain, nonmarine fluviatile, lacustrine and palustrine environments with only limited brackish or very marginal marine deposition.

Totland Bay Member

Insole and Daley (1985) introduced the Totland Bay Member, which is equivalent to the Lower Headon unit of Forbes (1853, 1856), and the Lower Headon Beds and the Headon Hill Member of Edwards and Freshney (1987). The Totland Bay Member is represented in the Isle of Wight and in adjacent areas of south-west Hampshire, overlying the Becton Sand Formation. The contact between the two is sharp but apparently conformable.

The type section is at Headon Hill (Isle of Wight) [SZ 306 860], with reference sections at Totland Bay [SZ 320 867] to [SZ 324 876] and Whitecliff Bay [SZ 640 862]. In general the member comprises interbedded green clay, silt and sand, with several thin freshwater limestone beds and lignites. The sand units are commonly channel filling and there are several palaeosols represented.

The member has a series of named beds as subdivisions best seen on the mainland at Hordle Cliffs. These include from the base upwards; the Lignite Bed (Horizon L of the Barton Beds of Burton, 1929, 1933), Mammal Bed, Leaf Bed, Crocodile Bed, Chara Bed, Unio Bed and Rodent Bed [Limnaea Marl] (Tawney and Keeping, 1883; Edwards and Daley, 1997; Daley, 1999b).

Reid and Strahan (1889, after Forbes, 1853; 1856) identified the Cyrena cycladiformis Bed, a sandy green clay unit near the base of the member, and the Cyrena pulchra Bed and a green carbonaceous clay unit in the middle of the member at Headon Hill. The How Ledge Limestone (Bed) (Keeping and Tawney, 1881), close to the top of the Totland Bay Member, crops out at Headon Hill and adjacent coastal sections in the Isle of Wight and the Warden Ledge Limestone (Daley 1999b), within the middle of the Totland Bay Member, crops out between Totland Bay and Colwell Bay (Plate 30).

On the Isle of Wight the member is represented in the east at Whitecliff Bay where up to 8.2 m of green mud, lignitic mud and muddy sand strata are poorly exposed. A sandy ironstone bed in the middle of the succession contains a freshwater molluscan fauna which in its uppermost part contains brackish-water-tolerant forms. In the west, on the slopes below Headon Hill and into Totland Bay, the member is poorly exposed but comprises about 27 m of silty mud, calcareous mudstone, some thin sands and pale brown shelly limestone. The limestone contains freshwater molluscs whilst the bulk of the member indicates freshwater to brackish water deposition within a marginal marine and nonmarine, coastal plain environment. The How Ledge Limestone at about 2 m thick forms a prominent unit near the top of the member (Plate 30).

Mammals from the lower Totland Bay Member at Hordle Cliff (including the Mammal Bed and Crocodile Bed) and in the Isle of Wight are assigned to the Early Headonian stehlini–depereti Zone. Mammals from the Rodent Bed, How Ledge Limestone and similar levels (highest Totland Bay Member) are assigned to the early Headonian vectensis–nanus Zone (Hooker et al., 2005). These all indicate a Priabonian age.

Colwell Bay Member

Insole and Daley (1985) introduced the name Colwell Bay Member, which is equivalent to the middle Headon unit of Forbes (1853), the middle Headon Beds (White, 1921) and the Lyndhurst Member (Edwards and Freshney, 1987). The Colwell Bay Formation is represented in the Isle of Wight and in adjacent areas of south-west Hampshire. The contact with the Totland Bay Formation is an interburrowed omission surface penetrated by Thalassinoides burrows.

The type section is in Colwell Bay on the north-west coast of the Isle of Wight [SZ 330 883] with reference sections on Headon Hill [SZ 306 860] and in Whitecliff Bay [SZ 640 862]. In general the member is mainly silt, clayey silt and silty clay, with thin sand beds and locally a thin freshwater limestone. The beds indicate a dominantly marine (inner neritic–sublittoral) and marginal marine environment of deposition.

The member has a number of named units including the Brockenhurst Bed, Roydon Bed (Keeping and Tawney, 1881), Venus Bed (Wright, 1851) and Neritina Bed (Wright 1851). The basal Brockenhurst Bed (shelly glauconitic clayey sand) and the overlying Roydon Bed (sandy and silty clay) are represented in the western Isle of Wight and the adjacent mainland by marginal-marine units, including the Neritina Bed. The overlying Venus Bed is present in almost all sections. The Colwell Oyster Bed (Reid and Strahan, 1889) (the Ostrea Bed of Wright, 1851) is a localised channel-filling shell bed in the Venus Bed at Colwell Bay.

At the type site in Colwell Bay the member is 9 m thick and can be seen in the small embayment north of Hatherwood Point where the basal Neritina Bed, comprising dark brown clayey sand, is overlain by blue-green, grey and brown, shelly, silty clay and muddy sand. The Venus and Colwell Oyster beds can be seen when the section is clear of slipped debris. The uppermost bed of the member, comprising greenish interbedded fine-grained sand and silty clay with shell seams, is the Batillaria Bed.

A greatly expanded succession of about 30 m attributed to the member in Whitecliff Bay contains three transgressive cycles. The basal dark brown, shelly, sandy, silty clay is the Brockenhurst Bed. The major part of the succession is generally yellow muddy fine-grained sand overlain by green sandy silty clay with shells, which comprise the Venus Bed. The youngest part of the member is a bed of bright green silty clay with only a sparse shelly fauna.

Charophytes and dinoflagellate cysts within this member indicate a Mid Priabonian age and the magnetostratigraphy indicates a general normal polarity, interpreted as Chron C15n by Gale et al. (2006).

Linstone Chine Member

Insole and Daley (1985) introduced this term for the 4 m of fine- to medium-grained sand with plant debris identified at the type section in Linstone Chine, Colwell Bay (Isle of Wight) [SZ 331 886]. The unit is localised, interpreted as marginal marine channel fill incised into the Colwell Bay Member. It is not present on the southern part of Headon Hill itself and in the east at Whitecliff Bay has been tentatively recognised as a single thin sand bed by Daley (1999b). The Microchoerus Bed has a limited occurrence on the northern part of Headon Hill where clayey sand with wood debris and mammal remains forms the basal bed of the Linstone Chine Member (Hooker et al., 2005).

Hatherwood Limestone Member (Hath)

Insole and Daley (1985) introduced the term to formalise the term Headon Hill Limestone introduced by Blake (1881). The type section is on Headon Hill [SZ 4306 0860] where the unit forms the prominent scar towards the top of the western facing cliff face (Plate 30). The member has a lateral extent limited to Headon Hill itself.

The member comprises about 9 m of fossiliferous limestone at the type section with numerous thin laminated marls, dessication crusts that are derived from subaerial exposure, and calcretes. A more irregular surface about 2 m from the base is overlain by a discontinuous lignitic mud that contains vertebrate remains including those of turtles (the Lignite Bed). The included molluscs indicate a freshwater depositional environment for the greater part of the member but brackish water forms become dominant towards the top. Northward into Colwell Bay the member is apparently absent although there may be a thin representative of it comprising 0.5 m of buff shelly limestone that is truncated by a significant erosion surface.

There are named beds within the limestone on Headon Hill. Other than the Lignite Bed the member also includes the Nystia polita Bed and Theodoxus planulatus Bed named by Jackson (1925).

Cliff End Member (Clen)

Insole and Daley (1985) introduced the term and designated the type section of Cliff End at the northern end of Colwell Bay [SZ 330 890] together with reference sections at Linstone Chine, Colwell Bay [SZ 331 886] and Whitecliff Bay [SZ 643 864]. The member is up to 9 m thick on the flanks of Headon Hill, over 10 m at the type site in Colwell Bay and up to 15 m at Whitecliff Bay.

The member comprises dominantly grey-green and brown mud, shaly in part; clay with thin shell layers, mainly dominated by the bivalve Potamomya and gastropod Viviparus; and some thin sand beds. A thin brown limestone occurs at the type site about 3.5 m from the erosional base of the member. King (in press) separates colour-mottled clays at the top of the unit as the Fort Albert Member within a Ryde Formation but this designation is not followed here. The lithology and the included fauna indicate deposition in a nonmarine coastal plain environment.

The lowest part of the Cliff End Member at Whitecliff Bay has normal polarity, interpreted as Chron C15n. The remainder has predominantly reversed polarity, interpreted as Chron C13r (Gale et al., 2006).

Lacey’s Farm Limestone Member (LaF)

The member was introduced by Insole and Daley (1985) as part of the Headon Hill Formation and they defined its type area on Headon Hill [SZ 307 859] and the type section within Lacey’s Farm Quarry [SZ 3220 8616]. This type section is now poorly exposed. King (in press) considers this unit to be a member within his newly defined Ryde Formation.

The member at its type section comprises about 5.5 to 6.5 m of nonmarine, lacustrine, pale brown, sandy, calcareous, nodule-rich mudstone that passes up into white rubbly limestone with interbedded green marl. Northward into Colwell Bay the member grades laterally into interbedded marl and limestone and eventually dies out. At Whitecliff Bay the member comprises 6.7 m of green to white, mottled, calcareous mud and muddy limestone with a distinctive creamy white, 0.30 m-thick, limestone bed (the One Foot Bed of White, 1921) in the middle of the succession.

King (in press) considers the lower part of the member to comprise mainly colour-mottled marls, with occasional thin and diffuse marly limestone beds as the Fort Albert Member (Ryde Formation) overlying the Cliff End Member. He restricted the Lacey’s Farm Member to the type area around Headon Hill.

Recent investigations point to this member being laterally equivalent to the Nettlestone Member (Grits) (Gale et al., 2006; King, in press) of the north-east coastal area of the island.

The assemblage from Headon Hill and the Lacey’s Farm Quarry indicates the Headonian pseudolithicus–thaleri zone (MP18) (Hooker et al., 2005).

Fishbourne Member

This member is defined by Insole and Daley (1985) from the foreshore between Fishbourne and north-westwards to King’s Quay on the north-east coast of the island [SZ 562 932] to [SZ 538 941]. It was formerly called the Fish and Plant Beds by Colenutt (1888).

The member comprises about 7 m of brown and blue-grey thin-bedded clay with thin shell beds. At Colwell Bay the member is reduced to only 3 m in thickness but up to 10.7 m are attributed to it at Whitecliff Bay. The lithologies and fauna indicate deposition in a marginal marine to nonmarine setting.

The Fishbourne Member includes the Chapelcorner Fish Bed as defined in Gamble (1982).

Osborne Member

Insole and Daley (1985) used the term Osborne Marls Member to cover the unit called the Osborne Beds by Reid and Strahan (1889). The Osborne Beds were formerly well exposed in cliff sections [SZ 522 958] near Osborne House but successive landslides have significantly destroyed this exposure. Insole and Daley (1985) defined a new type section in Whitecliff Bay [SZ 643 864] where up to 10.7 m of the member are seen. The member is represented by about 13.5 m in Colwell Bay on the north-west coast. Both lower and upper boundaries are sharp or rapidly transitional. King (in press) considered the colour-mottled mud defined by Insole and Daley (1985) as the Seagrove Bay Member at Whitecliff Bay to be the upper part of his extended Osborne Member (Ryde Formation).

The member comprises red and green colour-mottled calcareous clay and silt representing an unfossiliferous nonmarine fluviatile environment.

Seagrove Bay Member

Insole and Daley (1985) defined the Seagrove Bay Member from the type site at Horestone Point in Seagrove Bay [SZ 634 907]. They describe an extremely variable succession of sand, sandstone, sandy limestone and marl with few muds all capped by a lignitic mud immediately below the overlying Bembridge Limestone. This member has a distribution between East Cowes and Whitecliff Bay and a thickness of 0 to 15 m. They considered this variable succession as a single unit and by implication included the two calc-arenitic units of Forbes (1856) (i.e. the lower Nettlestone Grits and the upper St Helen’s Sands). King (in press) considers the succession defined by Insole and Daley (1985) as two distinct units each of member status and distinct lateral associations, and abandons the term Seagrove Bay Member. These newly defined units are the younger St Helen’s Member (St Helen’s Sands of Forbes, 1856) and the older Nettlestone Member (Gale et al., 2006; the Nettlestone Grits of Forbes, 1856). King (in press) also considers much if not all of the Seagrove Bay Member defined within Whitecliff Bay to be part of the Osborne Member (see above).

King (in press) utilises the definition of the Nettlestone Member in Gale et al. (2006) with a type section on the foreshore and low cliffs at Nettlestone Point, Seaview [SZ 4629 0918] (see (Figure 24)). The member comprises about 7 m of fine sand, locally calcareous sandstone, with local shell-fragment coquinas, grading up to sandy limestone and shell-fragmental limestone (the Binstead Stone or ‘Feather Bed’). The member is a localised unit, apparently restricted to the Seaview area and underlies both the Fishbourne and Osborne members. Following King (in press) the Nettlestone Member probably fills channels incised into his Fort Albert Member (a redefined upper part of the Cliff End Member of Insole and Daley, 1985).

The St Helen’s Member is defined in King (in press) from the type section of the cliffs at Nodes Point [SZ 638 900] and Priory Bay, and comprises 10 m of fine- to coarse-grained partly calcareous sand with flint pebbles grading up into sandy calcareous clays (marl). It overlies the Osborne Member above an erosional base. King’s definition includes beds 1 to 6 as defined by Forbes (1856) for the area between St Helen’s and Ryde. These beds are principally described from the section at Nodes Point (Watch House Point of Forbes) where the contact with the overlying Bembridge Limestone Formation is exposed, i.e. the type section of the Seagrove Bay Member (Insole and Daley, 1985).

The interval at Whitecliff Bay included in the Seagrove Member (Insole and Daley, 1985; Gale et al., 2006) is dominantly colour-mottled marl, with several thin silt to very fine sand beds and is considered by King (in press) to be part of the Osborne Member.

The Nettlestone Member, Fishbourne Member, Osborne Marls Member and St Helen’s Member have predominantly reverse polarity, interpreted as Chron C13r by Gale et al. (2006).

Bembridge Limestone Formation (BeL)

The formation is defined at the type section in the cliffs at the northern end of Whitecliff Bay, Isle of Wight [SZ 645 865], where up to 9 m of beds are seen (Plate 31), (Figure 31). These beds are arranged in three cycles with each commencing with an erosive base overlain by a thin intraformational conglomerate and succeeded by marl and marly limestone that passes upwards into massive hard limestone. This exposure extends northwards into Bembridge Ledges and is seen from there intermittently in offshore reefs and onshore in degrading low cliffs, such as Priory Bay [SZ 635 903] and Seagrove Bay [SZ 632 910], on the north-eastern coast of the island. Elsewhere the formation includes peloidal limestone (Prospect Quarry) and calcrete, with clay interbeds.

The unit is known throughout the northern Isle of Wight with seaweed-covered exposures at Hamstead Ledge [SZ 405 920] at the north-eastern end of Hamstead cliff, at Gurnard Ledge (Figure 31), where 6.7 m of the member is present [SZ 467 953] and elsewhere to the south-west in Thorness Bay, and at the inland Prospect Quarry [SZ 385 866] where up to 4 m of principally peloidal limestone is exposed. The member is also seen in part in the Tapnell Farm Quarry [SZ 380 864].

At the type section Insole and Daley (1985) included about 2 m of marl and clay above the highest limestone bed, with brackish mollusc faunas, in the Bembridge Limestone Formation. These were reassigned to the overlying Bouldnor Formation by Armenteros et al. (1997).

The basal contact is gradational or sharp. Locally the upper surface represents a channel truncation by the overlying Bembridge Marls (Reid and Strahan, 1889) and was interpreted by Daley and Edwards (1971) and Hooker et al. (2009) as evidence for contemporaneous tectonics, but could also be interpreted as a simple erosion surface.

The formation is nonmarine to marginal. The term palustrine limestone is used to denote essentially pedogenically modified, very shallow-water, lacustrine deposition.

A unit of brown clay with a corbiculid shell bed (up to 3 m thick) is represented within the Bembridge Limestone Formation at most localities. It was designated the ‘middle muds’ by Hooker et al. (2009).

At Whitecliff Bay the Bembridge Limestone Formation has predominantly reverse polarity. The highest part has normal polarity. These were interpreted as Chrons C13r and C13n by Gale et al. (2006).

Bouldnor Formation

The Bouldnor Formation was used by Insole and Daley (1985) to denote those beds above the Bembridge Limestone Formation and limited by the sub-Quaternary erosion surface. The formation comprises the Bembridge Marls Member, the Hamstead Member and the Cranmore Member (not shown separately on the map). The formation has a wide outcrop across much of the north of the island and is about 100 m thick.

The Bembridge Series, as originally defined by Forbes (1853) comprised the Bembridge Limestone(s), the Bembridge Oyster Bed, Lower Bembridge Marl and the Upper Bembridge Marl. The latter three units were grouped as the Bembridge Marls by Bristow (1862). The younger Hempstead Series (Forbes, 1853) was originally divided into Lower, Middle and Upper Hempstead divisions, overlain by the Corbula Beds. The series was renamed the Hamstead Beds by Reid and Strahan (1889), and subdivided into Lower and Upper Hamstead beds. Insole and Daley (1985) renamed the Lower Hamstead Beds as the Hamstead Member, and the Upper Hamstead Beds (equivalent to the Corbula Beds) as the Cranmore Member.

King (in press) has proposed the name Gurnard Member to replace the Bembridge Marls Member with a wish to avoid homonymy with the Bembridge Limestone Formation but the name is retained herein and on the map face. He proposes the exposure at Thorness Bay as the type section (Daley, 1999b).

Bembridge Marls Member (BM)

Bembridge Marls Member (Insole and Daley, 1985) is the formal term used to cover the Bembridge Marls (Forbes, 1853, 1856).

As defined currently the type section is within the cliffs at the northern end of Whitecliff Bay [SZ 645 865] with a reference section within the Hamstead Cliff and foreshore [SZ 400 918] (Daley, 1999b) (Figure 32), (Plate 32). The member is present throughout the northern part of the island and comprises marginal-marine to nonmarine, varicoloured clay and silt with shell seams. It is between 22 and 34 m thick. The basal contact is an interburrowed omission surface but in some areas the contact is markedly erosional.

The member is partially subdivided with named units of bed status. These are in ascending order the Bembridge Oyster Bed, Insect Limestone and Nystia Band (a shell bed near the top of the member).

Forbes (1853) described the Bembridge Oyster Bed from its type locality, at the north end of Whitecliff Bay. The ‘Bembridge Oyster Beds’ were more precisely redefined by Curry (1958) who included the lowest 4 m of the Bembridge Marls Member (up to the base of the Insect Limestone). Subsequent authors (e.g. Daley, 1999b) restricted the term to a thin sand unit within this interval that includes a hyposaline mollusc assemblage dominated by the oyster Ostrea vectensis. This bed comprises fine- to medium-grained shelly sand and clayey sand, partly indurated to a calcareous sandstone unit that includes scattered flint pebbles.

Reid and Strahan (1889) described the unit named the Insect Limestone which was formalised as the Bembridge Insect Bed by Daley (1999b). This lagerstätte is a tabular bed of micritic limestone, locally with insects and plant debris and up to 0.6 m thick. This unit is about 4 m above the base of the member. It is somewhat impersistent, and has been identified mainly in sections on the north-west coast of the Isle of Wight and at Whitecliff Bay. The lithology of the bed is described and its included fauna well documented in McCobb et al. (1998) and in references therein particularly Jarzembowski (1980).

The lowest 4 m of the Bembridge Marls Member has normal polarity at Whitecliff Bay, as has the underlying Bembridge Limestone (the ‘Bembridge normal polarity zone’), interpreted as Chron C13n by Gale et al. (2006). Higher levels, at Whitecliff Bay and at the Hamstead cliff, have reverse polarity, interpreted as Chron C12r by Gale et al. (2006).

The member is Late Priabonian to Early Rupelian in age.

Hamstead Member (Hams)

The Hamstead Member is defined by Insole and Daley (1985) and equates to the Lower Hamstead Beds of Reid and Strahan (1889). Its type section is within the cliffs and on the foreshore between Bouldnor and Hamstead Ledge [SZ 4375 0902] to [SZ 4404 0920], north-east of Yarmouth (Figure 33).

The member is predominantly marginal-marine and nonmarine, colour-mottled clay and silt with organic-rich clay beds and thin shell beds. It is between 58 and 69 m thick and is present throughout much of the north of the island. The basal contact is an omission surface, overlying a paleosol at the top of the Bembridge Marls Member (Hooker et al., 2004). The member contains four named marker horizons, some of which can be traced across the outcrop. These are in ascending order (Figure 33) the Black Band (at the base), Nematura Bed (10 m above the base), White Band (about 20 m above the base) and the thin, laminated, carbonaceous mud of the Water-Lily Bed (about 44 m above the base) (Reid and Strahan, 1889). The first three are described separately below.

A main turnover of palynofloral assemblages appears between the Black Band and the Nematura Bed (Brown, 1988). The major turnover in mammal faunas at the Headonian–Suevian boundary was originally identified within the Lower Hamstead Member (Hooker, 1987). Further refinement places the youngest mammal records immediately below the Nematura Bed (Hooker et al., 2004). The youngest atavus zone mammals (early Suevian, MP21) occur 4 m higher in the succession (Hooker et al., 2004), and continue upward to above the White Band (Hooker, 1987, 1992; Hooker et al., 2004, 2005, 2006).

The lowest 6 m of the Hamstead Member has reverse polarity, interpreted as Chron C12r by Gale et al. (2006). Higher levels have not been analysed.

The member is Late Priabonian to Early Rupelian in age. The lowest marine Rupelian biostratigraphical indicators are known from the White Band. The age of the underlying interval is still in dispute.

The Black Band of Forbes (1853, 1856) has its type section within Bouldnor Cliff [SZ 380 903] to [SZ 392 910]. It is a distinctive and widespread unit throughout the outcrop and subcrop over the north of the island. Its occurrence, at an otherwise poorly defined horizon in terms of surface topography was interpreted by Reid from a significant number of shallow boreholes and augering to define the interpreted outcrop line between the Bembridge Marls Member and the Hamstead Member. This interpretation, with modifications based on new field evidence and 3D modelling, has been retained to divide the Bouldnor Formation on the current map.

The Black Band comprises dark brown to black shelly organic-rich clay with widely scattered angular flint pebbles, is about 0.4 m thick and contains a freshwater fauna and flora. It overlies an apparent rooted paleosol, with calcareous concretions interpreted as calcretes, this being the highest unit of the underlying Bembridge Marls Member. This contact has been variously interpreted but its significance is a matter of debate (Gale, 2007; Gale et al., 2006; Hooker et al., 2004; Hooker et al., 2009; Pomerol, 1989; Vandenberghe et al., 2003).

The Nematura (pupa) Bed was described in Reid and Strahan (1889) from its type site within Bouldnor Cliffs [SZ 380 903] to [SZ 392 910]. The bed comprises marginal marine, shell-rich grey and organic-rich clay (about 1 m). The Nematura Bed contains brackish mollusc and ostracod assemblages, contrasting with the freshwater environments of overlying and underlying units.

Widespread at outcrop and subcrop in the northern Isle of Wight (Reid and Strahan, 1889), it is about 10 m above the base of the Hamstead Member in the type section. In the type section the base is an erosion surface, overlying thin clayey sand with water-escape structures and large coniferous logs (the ‘log bed’ of Hooker et al., 2004, 2009).

The basal contact of the bed has been interpreted as a hiatus representing a sequence boundary (Hooker et al., 2004, 2009), although its significance has been disputed by Hooker et al. (2006).

The White Band was described by Forbes (1856) from the type section within Bould-nor Cliff [SZ 380 903] to [SZ 392 910] and is only definitely known from this locality. It occurs about 20 m above the base of the Hamstead Member. The bed comprises about 2 m of marginal marine, very shelly green clay with abundant corbiculid bivalves in diffuse layers. It contains brackish molluscs and marine dinoflagellates. The base is apparently an omission surface, with burrowing bivalves in life position (Reid and Strahan, 1889).

A fine sand unit ‘on or about the same horizon’ is widespread in the eastern Isle of Wight (Reid and Strahan, 1889), and can be traced by augering. It is shown on the map face as ‘sand in the Hamstead Member’. This is probably an overbank flood deposit but local abrupt thickening may indicate the position of contemporary channels, with a maximum thickness of about 12 m. Only freshwater molluscs are recorded. It may represent an incised valley fill immediately preceding the transgressive event represented elsewhere by the White Band. King (in press) suggests that the unit should have member status and states that the unit is ‘often regarded as a lateral correlative of the White Band’ (e.g. Hooker et al., 2009).

Cranmore Member

Insole and Daley (1985) introduced the term to cover those beds previously described as the Upper Hamstead Beds (Bristow, 1862; Reid and Strahan, 1889). The member is not shown separately on the map but is known to be present in two small areas at Bouldnor Cliffs and around Staplers Hill [SZ 517 893].

The type section is at the top of Bouldnor Cliff (Figure 33), north of Cranmore [SZ 386 906] where about 9 m of the member is present. The member comprises variably shelly brown-weathering, blue-grey and black silty clay containing brackish to marine mollusc forms. The basal contact is sharp but apparently conformable above bright green clay. The unit is considered to have been deposited in a marginal-marine to marine, inner neritic (sublittoral) environment. The Cranmore Member is the youngest Palaeogene unit preserved in the Hampshire Basin. This unit is about 5.8 m thick on the cliffs at Cranmore where it is truncated by Quaternary gravels.

The member has been divided (e.g. Insole and Daley, 1985) into two successive named, but not strictly lithostratigraphical, units, the Cerithium Beds and the overlying Corbula Beds. The division of the member is based on their included mollusc assemblages. At Cranmore in the top of Bouldnor Cliff the two units are 3.4 m and a truncated 5.8 m thick, respectively.

Similar names, in various informal guises, have been used from the earliest descriptions. Forbes (1853) used the term ‘Upper Hempstead freshwater and estuary marls’ for the Cerithium Beds, whilst Reid and Strahan (1889) used ‘Cerithium plicatum Beds’ and White (1921) ‘Cerithium Beds’. The modern term for this cerithid mollusc is Pirenella monilifera (Cerithium plicatum) which is restricted to this unit. The ‘Corbula Beds’ are described in Reid and Strahan (1889) and are equivalent to the Corbula Beds of Forbes (1853, 1856).

Quaternary

The cover of Quaternary superficial deposits on the Isle of Wight comprises a rather patchily distributed, incomplete succession with many enigmatic gravel deposits occurring across the island. Until recently, few reliable dates were obtained from these deposits. Compared to the more extensive deposits on the adjacent mainland to the north, the outcrops on the Isle of Wight have received scant investigation and the succession of events is only really discernible by reference to the mainland successions. There is considerable debate as to the age of the units, and correlations still carry considerable doubt. Notwithstanding this, there are several important sites that help to unravel the story of the island’s Quaternary deposits, their relationship to the evolution of the Solent River system and to the British Quaternary stratigraphy as a whole. A broad interpretation of the classification of the succession and its relationship to the more widespread Solent River deposits on the mainland is summarised on (Figure 34) and (Figure 35). This interpretation forms the basis of the classification shown on the Special Geological Sheet that carries considerably more detailed outcrop patterns and a more appropriate interpretation of the superficial deposits than previous editions. An outline appraisal (Figure 34) and (Figure 36), as seen from the perspective achieved during the recent survey, is presented here, incorporating current knowledge and based also on a simple appreciation of relative elevation, the lithologies of the deposits and their artefact content. Even this outline, briefly expanded upon below, will be open to considerable debate, but hopefully will stimulate further research on the Quaternary successions encountered on the island.

The general concept of terrace aggradation as propounded in the works of Bridgland (1994, 1995, 1996, 2006) and Bridgland et al. (2004) provides a clear method of development for each terrace cycle and points to a complex relationship of fluviatile deposits and environments through cold, then temperate and back into cold climatic cycles. A complication, only briefly touched upon in the ‘Bridgland model’ (e.g. Bridgland, 2006, 2010), is the interplay of periglacial remobilisation and slope deposition particularly during the downcutting events as the rivers respond to relative base-level fall. Periods of lower sea level related to the onset of northern hemisphere glaciations trigger a complicated response in the lower reaches of fluvial systems including that of the Solent River catchment. Initial incision is followed by a phase of aggradation as sediments transported from the upper part of the catchment arrive creating a stack of sediment in the lower part of the catchment. This is a period in each cycle during which exposed slopes are in their most unstable condition and periglacial (active layer) processes are at their most active. This issue particularly seems to be reflected in the deposits encountered on the Isle of Wight. A further complication is related to the position of the Isle of Wight within the Solent River system in respect to its contemporary estuarine and marine deposits. At times of sea-level highstand the lower-level parts of the Isle of Wight and the Sussex coastal plain were inundated, while at periods of lowstand, deep trenches and fluviatile aggregation were the norm offshore (e.g. Antoine et al., 2003; (Figure 37)). Whilst not clearly understood, or indeed enumerated, the role of spatially variable uplift during neotectonic phases during the Neogene and Pleistocene adds a further complication to deposit correlation where topographical height alone is used. This seems particularly true when considering correlation between deposits in the north-eastern part of the island and with mainland occurrences.

The island contains a wide range of Pleistocene and Holocene deposits. Many of these were classified into four simple groups on the 1976 published map: plateau gravel, marine gravel, gravel terraces and alluvium, and the discussion here includes these terms for comparison with the new terms adopted on the current map (Figure 36). Clearly these earlier designations are an oversimplification and the gravels were considered simply as river terrace deposits (undifferentiated) within the digital map dataset (DiGMap 50) to reflect the dominant depositional process. This is, in itself, an obvious simplification if topographical height, alone, is considered. The recent survey has demonstrated even within individual outcrops, that the history of deposition is difficult to unravel. Many of the fluvial river terrace deposits, which commonly demonstrate a complicated depositional history with multiple channel fills, have often been either partially or completely remobilised during one or more gelifluction events during Pleistocene cold stages. The new map recognises this complexity with a significant number of new terms replacing the original simple scheme (Figure 36). However there is still a great deal of investigation of individual outcrops required to achieve a complete Quaternary history for the island as a whole.

Three sites, Priory Bay [SZ 635 900], Great Pan Farm [SZ 507 886] and Bleak Down [SZ 512 810] to [SZ 512 831] can be regarded as of national importance because of the abundant Palaeolithic artefacts derived from them that indicate periods of human occupation. The deposits at Priory Bay, Great Pan Farm, Bembridge Raised Beach [SZ 647 888] to [SZ 653 871] and at Steyne Wood [SZ 642 866] provide specific dates that act as a skeletal framework within which the relative age and context of other deposits can be placed.

The island of Wight—when and how

It is widely postulated that throughout the Quaternary and possibly before that time into the Late Neogene, the Solent area was crossed by a segment of a major axial river system known as the Solent River. This formed the major fluvial system into which flowed the ‘proto’ Frome, Piddle, Stour, Avon, Test, Itchen and other minor streams, including northward-flowing streams crossing the area of the Isle of Wight. There is an overriding presumption in the Solent River story through time that the Isle of Wight was previously connected to the mainland by a ridge of steeply dipping Chalk that connected the Isle of Wight through The Needles area with the chalk cliffs of Ballard Down (Handfast Point) north of Swanage in Dorset. The ridge forms the southern limb of the principal asymmetrical syncline of the Hampshire Basin whose inception was resultant upon the far-field tectonic effects of the Alpine Orogeny during the Mid Miocene (e.g. Jones, 1980; Allen and Gibbard, 1993, and references therein).

This chalk ridge, and the uplands across the Isle of Wight, separated the eastward-flowing Solent River from the trunk stream of the Channel River which flowed south-westward down the axis of what is now the English Channel. The ridge was regarded as ‘in place’ for the greater part of the time from the Solent River’s inception through to the Late Devensian and Holocene although its width and height can only be guessed at. The confluence of the two major river systems was offshore to the south-east of the island. Through time, channel configurations and terrace aggradations relating to the valleys of these two major river systems must have migrated widely in the area offshore of Bembridge to St Catherine’s Point in relation to the extreme sea level variations throughout the Pleistocene. In the absence of sufficient interpreted shallow offshore seismic data and confirmatory boreholes in this area, the definition of estuary positions, terrace correlations offshore and the position of the confluence through time is not possible with any degree of certainty.

The timing of the breaching of the chalk ridge between Ballard Down and The Needles, to isolate the Isle of Wight, is discussed in Velegrakis et al. (1999), citing new evidence derived from bathymetric and shallow seismic surveys in Christchurch Bay. This evidence led the authors to conclude that three significant palaeovalleys irreversibly breached the chalk ridge prior to the Flandrian transgression (possibly during the Late Devensian sea-level lowstand). This event must have divided the upper reaches of the Solent River system with the Frome/Piddle system and probably the Avon/Stour system diverted to flow southward through the breaches. Whether the breaching was an entirely fluvial process related to the downcutting of the rivers to a sea-level lowstand is unclear. Perhaps, the breach was polycyclic in nature initiated from both the northern and southern sides of the chalk ridge and involving an element of river capture by back-cutting streams confluent with the Channel River system to the south, and even tectonism. Notwithstanding these questions it is true that the youngest Devensian terraces of the Frome and Avon/Stour have significantly higher gradients than similarly dated deposits within the main Solent River valley to the east; thus indicating that they were deposited in reaction to a lower base level.

Velegrakis et al. (1999) also suggest that, following the breaching of the chalk ridge, rising sea levels inundated the lower reaches of the Frome/Piddle and Avon river systems creating Poole Bay at an early stage of the Flandrian transgression, as there is evidence offshore of transgressive facies sequences. Christchurch Bay was submerged somewhat later in the same transgressive event when a seaway link was created into the western Solent thus finally isolating the Isle of Wight around 7000 to 7500 BP during the Mesolithic period of human occupation (see section below). A slightly contradictory view regarding the final separation of the island from the mainland is given in Momber et al. (2011) where a Late Mesolithic (i.e. 5500 BP) date is given as the earliest possible timing of this event.

Clay-with-flints and related periglacial deposits (regolith domain)

The oldest Quaternary deposit on the island is the clay-with-flints. The term ‘Angular Flint Gravel of the Chalk Downs’ (used on the old geological map and in White, 1921) is essentially a local facies of the clay-with-flints as defined by Hodgson et al. (1967, and references therein) on the mainland. Consequently the term clay-with-flints is applied to the new geological sheet. The deposit on the island is assumed to have a similar mode of formation over an extended period in the Late Neogene and Early Pleistocene, with its internal variability and close associations demonstrating that it was probably formed through a number of climatic phases. The clay-with-flints sensu stricto (Hodgson et al., 1967) is a residual rubified stony clay deposit created by the modification of the original Palaeogene cover and progressive, possibly phased, dissolution of the underlying Chalk. The basal surface of the deposit approximates to the sub-Palaeogene unconformity but this is much modified by dissolution of the underlying Chalk with karstic features in evidence in most exposures. There is evidence from the new survey that relatively intact, although not in-situ, Palaeogene sediment, generally completely concealed by the clay-with-flints, may well be preserved in solution features on this sub-Palaeogene surface. One example, exposed in a new forestry road cutting, was cleared and logged during the survey (Plate 33) on Brighstone Down [SZ 431 849].

Part of the deposit has been remobilised in cold phases during the Late Neogene and Early Pleistocene and this has been mapped widely on the mainland and described by others (Hodgson et al., 1967) as clay-with-flints sensu lato. It shares many characteristics with clay-with-flints sensu stricto but is found at levels adjacent to or below the sub-Palaeogene surface and the contained flints are predominantly angular rather than nodular. These deposits are shown as the Head 1 on the new map. This remobilised unit may include cryoturbated, aeolian sand units, as observed on the mainland (e.g. Frenchen et al., 2003; Hopson, 1995). Perhaps by their presence they imply a correlation with more extensive Early Pleistocene wind-blown deposits that are a feature of coeval successions on the continent.

In addition, further remobilisation, as the landscape was denuded throughout the Pleistocene, has developed an ‘apron’ of angular gravelly, sandy clays at lower topographical levels. This is commonly closely associated with, and potentially remobilises, fluvial terrace gravels. These ‘late-stage’ remobilised materials are generally preserved on steeper slopes well below the base level of the clay-with-flints and were mapped as separate slope deposits during the new survey. They have been designated as Gravelly Head 1, present within all of the catchments on valley slopes, and the ridge-topping Gravelly Head 2 present within the Medina catchment only. They are considered to be predominantly periglacial in origin and are likely to have a polyphase development during successive cold phases, with each phase extending the deposits further downslope as valley incision continued. Consequently individual occurrences may well be related in age terms to other deposits differentiated, on the basis of their geomorphology, as fluvial terrace aggradations (see below for further discussion).

Terrace gravel aggradations (formerly the plateau gravel, marine gravel and valley gravel)

On the mainland to the north, the term plateau gravels was originally applied to the ‘staircase’ of gravel-rich deposits within the New Forest and adjacent to Southampton Water. These are all now considered as fluvial aggradations of a long-lived and extensive Pleistocene Solent River Catchment (the proto-Solent) that drained much of the western and central Hampshire Basin, into east Dorset (see Briant et al., 2006; Bates and Briant, 2009 and references therein). The main stream drained eastward and migrated southward over time, presumably reworking much of the south-bank aggradations of each terrace cycle. This proto-Solent stream graded to very variable contemporary sea levels that range from 46 m or more below to about 40 m above current sea level during the more extreme climatic oscillations. It is likely that the downcutting and regrading of each terrace cycle may be ‘incomplete’ being overtaken by the next climatic cycle before the streams could fully remobilise the previous terrace aggradations. This is perhaps most true in the headwater areas of each successive proto-Solent river and within the steeper gradient contemporary tributary streams.

Similarly, on the Isle of Wight, fluvial deposits, previously classified as plateau gravel and terrace deposits, show a topographical relationship with the four principal river systems currently crossing the landscape. These are, the proto-Solent, which is the principal drainage system across the north of the island, and three contemporary northward-flowing streams that were confluent with that principal stream through time, namely, the Western Yar, Medina and Eastern Yar. The individual outcrops within each river system are classified together at formation level within the Solent River Formation, Western Yar River Formation, Medina River Formation and Eastern Yar River Formation, including its tributary Wroxall Brook, respectively.

It must be said that the designation of a terrace order to the deposits indentified in each formation is based solely on topographical height and gradient, and by implication their chronology. While this provides a framework for classification, correlation between river systems is not readily achievable without considerably more investigation. This is due to their very patchy nature, the lack of significant exposure, and the absence or rarity of datable sediments, artefacts, faunas and floras. Significantly the Solent Basin does not have the benefit of extra-basin exotic clast influxes, such as is seen within the Thames Basin terraces, and consequently there are no significant lithological variations between terrace aggradations that would enhance correlation. The primary descriptions of deposits related to the northward flowing confluent streams indicate that they have a very limited variety in clast types indicating a limited range of bedrock lithologies in those catchments. In addition, as already pointed out for the clay-with-flints, the gravel-rich outcrops are each associated with significant spreads of remobilised material (the ‘gravelly heads’). These rework the original well-bedded fluviatile sand and gravel to lower topographical levels as sheets of relatively structureless material. Indeed, these sheet deposits, where they spread over a significant height range, may well disguise other topographically distinct terrace aggradations or platforms. This is demonstrated for example by Farrant et al. (2011) describing the high-level (about 70 to 100 m OD) gravels identified as the St George’s Down Gravel Member.

In general, across the island, these fluvial deposits are between 3 and 5 m thick but may become considerably thicker where they are associated with channelling or where remobilised material is also present.

Solent River Formation

Gravel aggradations in the north of the Isle of Wight, which were formerly allocated to plateau gravel and marine gravel are now considered as terrace aggradations within the lower reaches of a proto-Solent River catchment (Wenban-Smith et al., 2009) with some earlier authors suggesting that they also include contemporaneous beach gravels at their eastern end (e.g. White, 1921).

The higher-level gravel deposits within the Solent River Formation, including the Twenty Acre Gravel Member (about 80 to 85 m OD), Knight’s Cross Gravel Member (65 to 70 m OD) and Bouldnor Copse Gravel Member (about 50 to 55 m OD) (also designated as plateau gravel on previous geological sheets) occur as isolated outcrops on the high ground around Newport through to the north-west coast near Cranmore. Their relationships to the deposits along the coast and to the younger river terraces have received scant investigation since the compilation of the old geological map and memoir (White, 1921). These outcrops all show evidence of being formed as bedded fluvial gravels, but each is now known to be associated with a variable ‘apron’ of mass-movement material that commonly disguises the true base level of the fluvial component(s) or indeed may have remobilised such fluvial components completely. It is presumed that the fluvial element of these outcrops can be related to proto-Solent terrace deposition (either within the main stream itself or within northward-flowing south-bank tributaries of that major stream). By comparison to the Priory Bay site (see below), they must be attributable to one of the higher-level terraces on the mainland and thus be of pre-MIS 13 age. They are potentially correlatable with the Tiptoe to Whitefield Hill terrace aggradations of the western Solent River (Bridgland, 2001; Bates et al., 2007; Bates et al., 2004; Westaway et al., 2006; summarised in Bates and Briant, 2009; and references therein).

The Steyne Wood Clay Member (Holyoak and Preece, 1983; Preece and Scourse, 1987; Preece et al., 1990) at the eastern end of the island at Bembridge is at about 38 to 40 m OD. Originally discovered in a trench dug for a sewer pipe (Jackson, 1924; Reid and Chandler, 1924), a borehole reinvestigation in 1983 demonstrated a pebbly mottled silty clay (head) overlying 1.95 m of organic, dark greyish brown becoming olive-grey, clay, that was shelly and sandy in its lower portion. The contained fauna and flora indicate deposition in an estuarine environment in a post-temperate climatic stage of an interglacial of some antiquity and a correlation with the Goodwood–Slindon Raised Beach of youngest Cromerian Complex age (MIS 13) is widely accepted.

Along the north and north-east coast between Thorness [SZ 447 928] and St Helens [SZ 625 895], a series of gravel-rich outcrops are mapped between 50 and 28 m above OD. These probably represent more than one fluvial aggradation. They comprise a succession of pebbly sands and sandy gravels with associated lateral gravelly head deposits. Within the topographically lower, coastward, portion of these outcrops a consistent sand unit between gravel-rich units has been identified. Boreholes and trial pits across the outcrops suggest a variable composition but generally between 5 and 6 m of deposit. These are termed the Wootton Gravel Complex Member on the map. They are shown as both Plateau Gravel and Marine Gravel on earlier editions of the geological map.

The best descriptions within this member are from the Priory Bay site [SZ 635 900], on the cliffs adjacent to the hotel (Wenban-Smith et al., 2009), at the lower topographical level (about 29 m OD) within the member (Figure 38). These deposits are likely to be both in situ representatives of the member and the associated gravelly head derived from them. The descriptions of the deposits at Priory Bay include evidence of contemporary hominin occupation, as well as interbedded, polyphase mass-flow material. The presence of artefacts (Loader, 2001, fig. 7.3 and fig. 7.5) at the topographically lowest level in the cliffs adjacent to Priory Bay (Figure 38) and the availability of optically stimulated luminescence (OSL) dating at this cliff-top site provide keys to the age of this part of the complex deposit that is placed between MIS 11 and 9 (367 ka to 216 ka). Comparison with the western Solent River successions on the mainland suggest equivalence with the Old Milton to Mount Pleasant Gravel terrace interval in the western Solent Valley and between Terrace 9 and 10 in the east Solent Valley (Bridgland, 2010). Based on the preponderance of artefacts, the deposit may also be in part equivalent to the artefact-rich Taddiford Terrace (Terrace 7). The complex of deposits at Priory Bay provides a baseline to help interpret deposits occurring at a higher level (including conjoined gravelly spreads up to 50 m OD inland from Priory Bay itself) and indicate that the very highest deposits within and above this member throughout the island are likely to be early Mid Pleistocene (i.e. older than the Anglian) or even Early Pleistocene in age.

Wenban-Smith et al. (2009) suggests that the abraded artefacts in the lowest stratigraphical levels at Priory Bay may be derived from the conjoined deposits that rise to approximately 50 m OD immediately inland of that site. On the basis of height alone these ‘50 m’ deposits are considered to be contemporaneous with or older than the Steyne Wood Clay. Thus it is hypothesised that the in situ gravels on the platform above Priory Bay and north-westward towards Cowes, at the height of up to 50 m OD, may also be of the same age.

As a second line of evidence, it has long been noted that these Wootton Gravel Complex outcrops contain an interbedded sand unit with beach pebbles that was regarded as marine in derivation, though this unit is completely devoid of shell material. It was equated to the ‘Portsdown–Goodwood range of raised beaches’ (White, 1921), i.e. the Goodwood–Slindon Raised Beach of modern literature and by inference with the Steyne Wood Clay Member. It is believed that the presence of this sand unit and ‘beach-pebble’ occurrences were originally used on the geological map to differentiate these outcrops into Plateau Gravel and Marine Gravel. However, this sand was observed, during the recent survey, further to the west in temporary excavations in the outcrop around Palmer’s Farm, Wootton [SZ 536 925] and field evidence shows that it is also present around Cowes—it is mentioned at Ruffins Copse [SZ 482 941] west of the Medina in the memoir (White, 1921).

The Bembridge Raised Beach Member (Plate 34) at the eastern extremity of the island is well exposed from Bembridge Point [SZ 647 888] to Howgate Bay [SZ 653 871] (Codrington, 1870; Preece and Scourse, 1987; Preece et al., 1990; Wenban-Smith et al., 2005). The member comprises two units. A lower unit of well-rounded flint gravel with some sand lenses interpreted as a high energy beach deposit and possibly representing a spit. It is overlain by an upper unit, only rarely seen in current exposures, comprising a pale bed of yellow matrix-supported gravel with a poorly sorted clay, silt and sand matrix, and characterised by poorly defined contorted bedding and clast imbrications. This is interpreted as a periglacial solifluction deposit. A thermoluminescence date of 115 000 BP (Preece et al., 1990) obtained from a sandy lens within the lower unit indicates the raised beach is of Ipswichian age. By implication the upper periglacial unit was considered to be of Devensian age. Later work (Wenban-Smith et al., 2005), based on OSL dating and pollen records, attributed the lower gravel unit to the high sea-level event of MIS 5e centred on a range of 120 000 to 130 000 BP. The upper unit was dated to between 82 000 and 115 000 BP, corresponding to MIS 5d to 5b.

Overlying these gravels is a variable thickness of well-sorted silt with pebble stringers that has some characteristics of an aeolian deposit but has suffered significant remobilisation by hillwash or downslope creep.

At topographically lower levels and associated with the many minor streams that cross the northern coastal plain are a number of gravelly deposits that comprise part of the Solent River Formation. These have been attributed to Undifferentiated terrace deposits in the north-west of the island where their correlation is not clearly understood, and to the Great Wood Gravel Member and Dunnage Copse Gravel Member associated with the Blackbridge Brook in the north-east of the island where each member is distinct topographically. Their age is likely to be very Late Devensian or Early Holocene based on their topographical height and close association with thin alluvium spreads in the base of these minor streams.

Western Yar River Formation

In the west the Western Yar breaches the Chalk ridge at Freshwater and related terrace deposits are mapped from there northwards towards Yarmouth. The Kings Manor Gravel Member is closely associated with, and topographically a few metres above, the alluvial and tidal river deposits, and has the widest distribution. At Freshwater, the King’s Manor Gravel Member comprises about 6 m of fairly structureless clayey sand gravel with some sand lenses as a lower unit. This is overlain by a variable thickness of sandy silty clay formerly considered to be a brickearth and with supposed aeolian affinities. The clayey gravels exposed in a well-marked channel on the west side of Freshwater Bay (Plate 35) are attributed to the King’s Manor Gravel Member.

The next highest unit, the Backet’s Copse Gravel Member, is about 10 m above the floodplain at between 15 and 20 m OD. The Freshwater Gravel Member forms the two outcrops around Norton Green at about 30 to 40 m OD. There are no exposures in the higher units. There are no dates available for this group of three terraces but the King’s Manor Gravel Member contains remains of the woolly mammoth Elephas primigenius indicating cold climatic conditions and thereby suggestive of a Late Devensian age.

Along the south-western coast, headwater deposits related to the Western Yar Catchment are also delimited but their exact relationship to the terrace levels of the main stream are difficult to elucidate because the confluent areas between the tributaries and the contemporary main stream of the Western Yar have been removed by coastal erosion as the south-west coast has retreated. The Downton Farm Gravel Member forms the terrace closely associated with the alluvial tract and may be considered as roughly equivalent to the King’s Manor Gravel Member in the main stream. The Sudmoor Point Gravel Member, up to 2.5 m thick, forms the caps of the cliff south-east of Brookgreen [SZ 386 834] and is some 5 to 10 m above the lower terrace. Approximate height relationships suggest that this gravel is equivalent to the Backet’s Copse Gravel Member. Remains of a dubiously located Elephas primigenius were reported at about 29 m OD east of Brook Chine (p. 166, White, 1921), this together with the periglacial contortions evident in the sandy clayey flint gravels, indicate a cold climate for these gravels.

The outcrop of the Headon Warren Sand and Gravel Member at Headon Warren [SZ 315 859] is quite isolated. Previously it has been interpreted as being a ‘fan of rock waste’ (i.e. a ‘head deposit’) derived from former higher ground to the south (Warren, 1900; White, 1921) but the recent survey regards the deposit as of fluvial origin although much disturbed in places (Plate 36). The base level of this complex of fluvial deposits is at around 90 to 100 m OD. Wenban-Smith and Loader (2007, Appendix 1) note a single flake discovered at this site. The deposit must be of considerable antiquity but any correlation more widely would be speculative.

Medina River Formation

St George’s Down Gravel Member: The complex of deposits around St George’s Down [SZ 515 865] comprise in-situ fluvial gravels at around 100 m OD (Plate 37) and long periglacial ‘tails’ spreading down interfluves to the north (Plate 38) to levels of 70 and 60 m OD respectively (Farrant et al., 2011). The in-situ fluvial gravels have long been considered as being part of a very early proto-Medina, i.e. a south bank tributary of the proto-Solent. It is difficult to date the in-situ, high-level fluvial part of the St George’s Down gravels as there is little evidence of a northward gradient suggesting a potential confluent height with the contemporary proto-Solent River. Thus a correlation of the high-level fluvial deposits (100 m OD+) within the St George’s Down Gravels with a western Solent Terrace succession cannot be achieved with any confidence at present. However, none of the in-situ gravels within the higher-level St George’s Down Member have produced artefacts, and this single line of evidence suggests they are older than the gravels on the north-east coast. By analogy with the mainland they must therefore equate to terraces tentatively assigned to MIS stages 14 and older.

The associated periglacial deposits (shown as Gravelly Head 2 on the map) are also devoid of artefacts but in this case the deposits are considered to have a very long history of development, potentially represent periglacial deposition during a number of cold climate phases as the landscape was denuded to successively lower levels (Farrant et al., 2011). A strongly cryoturbated palaeosurface is intimately associated with the Gravelly Head 2 at the western end of St George’s Down (Pan Down adjacent to the Shide Quarry) where it is found between two massive structureless clayey gravel units that make up the bulk of this deposit (Plate 38).

Even younger periglacial deposits (Gravelly Head 1) form a further ‘apron’ adjacent to and at lower topographical levels around the St George’s Down Gravel Member and Gravelly Head 2 outcrops. These younger head deposits completely cover bedded fluvial gravels on the northward facing slope [SZ 532 878] of Arreton Down nearby. These buried fluvial gravels and the gravels themselves are only exposed at the Combeley Farm Quarry (Plate 39) where they are intimately associated with a significant cryoturbated deposit (the Robins Hill Palaeosol Member). Farrant et al. (2011) regard the bedded gravels as representing a cold stage event laterally equivalent to the high-level in-situ St Georges Down Gravel and the cryoturbated unit as likely to be a temperate soil. The whole sequence represents one of the oldest deposits on the island.

The Bleak Down Gravel Member outcrop has long been regarded as a high-level northward-flowing proto-Medina terrace aggradation with a base level of about 80 m to 70 m OD, and is also noted for its high content of artefacts. The flint-rich gravels, known to be up to 2.4 m thick in old, now degraded, pits (White, 1921) and whose base is some 35 m above the Medina alluvial tract, were described in Poole (1934) and he recognised a ‘higher terrace’ and a ‘lower terrace’ both with complex internal architecture. He also determined that the artefacts were of considerable variety, state of preservation and type, indicating both in-situ deposition and reworking from now nonexistent deposits. Wenban-Smith and Loader (2007) consider that the deposit may be as old as pre-Anglian in age and this would imply that the deposits at the highest level on St George’s Down are of even greater antiquity. Quite how these gravels fit within the Quaternary story is difficult to judge. A natural correlation, on the basis of the high content of rolled and in-situ artefacts, with the Priory Bay deposits (Wootton Gravel Complex Member) on the north-east coast, would seem possible although highly speculative.

The deposit rests on the interfluve between the headwaters of the Medina River and the western headwater arm of the Eastern Yar west of Godshill [SZ 525 820] and as such could be considered as either a Medina or Yar catchment deposit. Herein they are grouped with the terraces associated with the Medina on the basis of their similar gradient to the current stream and other lower terrace aggradations (such as the Blackwater Hollow Gravel Member). The exact relationship of the Medina headwater stream and that of the western arm of the Eastern Yar headwaters is complicated by timing of potential river capture in the Merstone [SZ 526 850] and Budbridge [SZ 532 838] area north of Godshill (see Merstone Clay Member below).

The Blackwater Hollow Gravel Member occurs between Rookley [SZ 508 841] and Whitecroft [SZ 495 860], where small outcrops of flint- and chert-rich gravels rest on the interfluve at 60 and 65 m OD, between the Medina headwaters and the Blackwater Brook tributary and at about 25 m above the current Medina headwater floodplain. These areas were formerly described (White, 1921) as a continuation of the Bleak Down Gravel Member but they form a separate group of outcrops with their own gradient mirroring that of the Blackwater valley. They have a greater chert pebble content than the gravels on Bleak Down and in consequence have been given a separate name.

The Bridge Farm Gravel Member is closely associated with, and forms a terrace flat 2 to 3 m above the alluvial tract of the western arm of the Eastern Yar River south of Bohemia Corner [SZ 520 836], and the Merstone Clay Member that forms the infill to the valley draining north-westward into the Medina catchment at Blackwater [SZ 507 860]. It is possible to envisage this western arm of the eastern Yar as a former headwater tributary of the Medina River. A ridge of the Ferruginous Sand Formation is postulated to have originally connected Godshill, through Kennerley Farm [SZ 525 835] to Redway [SZ 534 847] and northward to Arreton, and was breached in the Budbridge area at some time in the Late Devensian. This river capture is alluded to in (White, 1921) with the statement that there was a fall from the Blackwater ‘old valley’ of ‘barely 25 feet [7.6 m] above the recent alluvium of the Yar’. The almost continuous terrace is up to about 3 m in thickness and comprises variably clayey and sandy flint with chert gravel.

The Merstone Clay Member (older alluvium), forming the base of the Blackwater Brook branch of the Medina catchment, was renamed to differentiate this area of peat and alluvial clay from the lower tracts of alluvium associated with the Medina and the Eastern Yar. It emphasises the understanding of the potential river capture of the old Blackwater stream (now the headwaters of the Yar). The member comprises a sequence of finely interbedded mottled clay, silt, sand and peaty silty sandy overbank deposits resting on a thin basal flint- and chert-rich loose gravel. Up to 5.7 m of deposit has been proven in Merstone Manor water well above the Ferruginous Sands Formation.

The Seaclose Park Gravel Member flanks the tidal stretch of the Medina River from the river gap in Newport northward for a distance of 4.5 km to Werrar Farm [SZ 503 827]. Topographically it forms a terrace flat about 5 m above the estuarine alluvium and must be correlatable to the lowest level terraces associated with the current streams elsewhere on the island. It is thereby probably of Late Devensian to Early Holocene in age.

In Newport an outcrop of the Seaclose Park Gravel is closely associated with the internally complex head deposits and concealed gravels at Great Pan Farm [SZ 506 886]. This area has been investigated in detail for proposed development and the sloping head deposit mapped there disguises a staircase of three terrace gravel aggradations between 5 and 22 m above the adjacent floodplain. The higher two of these have no expression outside the head outcrop but the lowest concealed terrace is relatable to the Seaclose Park Gravel Member. The Great Pan site (Poole, 1924; Shackley, 1973, 1981; Wymer, 1996, 1999) has provided a large collection of flakes and hand axes including bout coupé hand axes and Levalloisian material (Poole, 1924) in the lowest terrace level. The most modern interpretation gives the middle of the three terraces identified here (11 to 14 m above floodplain level) an OSL dating of 50 000 BP, placing that deposit in the Mid Devensian (Oxford Archaeology, 2005). Exposures of this lower terrace are present along the eastern banks of the Medina estuary where 2 m of angular flint gravel can be seen.

Eastern Yar River Formation including Wroxall Brook

The terrace gravels (plateau gravels and valley gravels) delimited to the south and east of the Eastern Yar at levels between 60 and 20 m OD, may be considered, simply, as the higher-level terrace aggradations of a larger proto-Eastern Yar stream system and are likely to contain significant amounts of material derived directly from the southern downs. On the basis of height alone they must all postdate the in-situ Bleak Down deposits. Thus the speculative correlation of Bleak Down with Priory Bay would place these Eastern Yar terraces at post MIS 9 or much younger (MIS 6) and lower levels topographically may therefore potentially be equivalent to the Bembridge Storm Beach deposits that have an OSL date of 120 000 to 130 000 (MIS 5e) at a site on the Foreland (Wenban-Smith et al., 2005).

The terraces associated with the Eastern Yar Catchment have been divided into two groups: a series of terraces associated with the main stream from Budbridge to Brading (Cockerel Gravel, Hale Common Gravel and Langbridge Gravel members), and another series associated with the tributary stream of Wroxall Brook (Froghill Farm Gravel, Whiteley Bank Gravel and Bobberstone Farm Gravel members). The exact relationship between these two series is uncertain.

The thickness of each terrace aggradation varies between 2 and 5 m and all comprise sandy, flint- and chert-rich gravels set in a variable orange-brown clayey silt matrix; generally, the older the terrace, the higher the silt and clay content. Although frequently dug on a local basis in the past there are now few exposures.

A further isolated terrace on the northern margin of the estuarine alluvium that forms Brading Marshes is named the Carpenters Farm Gravel Member after the nearby farmhouse.

The most extensive outcrops between Budbridge and Alverstone [SZ 577 855] are represented by the Langbridge Gravel Member, which forms a terrace flat between 2 and 5 m above the Yar floodplain. It was well exposed during the survey in workings at Horringford (Plate 40). The Hale Common Gravel Member crops out principally around Hale Common [SZ 546 843] and as limited outcrops south of Alverstone. The terrace flat, essentially an alluvial fan deposit, is about 10 to 15 m above the Yar floodplain and forms one of the principal glasshouse horticulture areas on the island. The highest terrace, the Cockerel Gravel Member, between 20 and 25 m above the main floodplain, underlies the interfluves around Newchurch [SZ 560 855] and the Queen’s Bower to Branstone area adjacent to Winford [SZ 567 844].

Within the tributary catchment of Wroxall Brook three terrace levels have been delimited based on their height above the local stream. The Bobberstone Farm Gravel Member has a single outcrop south of that farm on the west side of the valley and is between 1 and 5 m above the thin alluvial strip in the base of the valley. The Whiteley Bank Gravel Member is represented by three outcrops to the east of the valley and between 5 to 10 m above the floodplain. The highest terrace deposit, about 15 to 20 m above the floodplain, is represented by two outcrops of the Froghill Farm Gravel Member on the interfluves to the west of the stream. There is no dating evidence available for these three deposits and the relationship to the terraces of the main Yar stream is unknown.

A single outcrop with a distinct 2 to 4 m- high bluff adjacent to the estuarine alluvium of Brading Marshes is termed the Carpenters Farm Gravel Member. The relationship of this deposit to the gravels buried beneath the estuarine alluvium and its correlation with other terrace successions is not known.

Unattributed deposits

Three types of head deposits have been recognised across the island. Those closely associated with fluvial terrace deposits (Gravelly Head 1 and 2) have been discussed above and reflect a long spasmodic depositional history throughout much of the Pleistocene. Most of the generally dry headwater valleys, characteristically over the Chalk and Lower Greensand bedrocks, but also elsewhere, carry a valley bottom head deposit. These deposits do not demonstrate a marked ‘valley flat’ geomorphology, characteristic of a flowing stream, and whilst they may contain bedded material are also made up of soil and slope creep deposits. The deposits are generally thin and grade downvalley into both terrace and alluvial deposits. Lithologically they comprise a variable mix of clay, silt, sand and gravel whose relative proportions closely reflect the available materials in the local bedrock units. It is presumed that most of these deposits are relatively young and related to the last downcutting event in each valley and are likely to be latest Devensian to Holocene in age.

Isolated outcrops, shown as undifferentiated river terrace deposits are not attributed to any of the river formations. A distinct group of these outcrops, previously designated as plateau gravel, has been identified on the Palaeogene outcrop in the north-west of the island (see Solent River Formation discussion above). Various depositional processes were attributed to these deposits in the past such as the ‘coombe out-washes’ around Calbourne described by White (1921, p. 158). Some may equally be mass-movement slope deposits derived from a range of original in-situ deposits or even remnants of far-travelled low-density periglacial mudslide debris emanating from the Chalk ridge to the south. However, there is a distinct lineation and gradient to these deposits and an equally viable derivation could be as thin terrace aggradations related to a stream confluent with the Western Yar around Yarmouth draining east to west from the Calbourne area.

Other outcrops occur in the hinterland behind Shanklin and Sandown in the east of the island around Adgestone [SZ 586 860], associated with Scotchell’s Brook and headwater valleys to the south. Although generally presenting a terrace flat to their upper surface they show no pattern in respect of relative height above the local stream and have not been allocated to named deposits associated with the Eastern Yar catchment. Their generally gravelly and sandy soil brash and apparent bedding suggest fluvial deposition but they may represent isolated periglacial mass movement material.

A single occurrence regarded as a first river terrace deposit is delimited adjacent to Whale Chine [SZ 470 783] on the south-west coast of the island. This deposit has a base level between 5 and 10 m above the adjacent alluvial tract within the deeply eroded chine itself. The relationship to other fluvial deposits locally is unknown but it is likely to be related to the headwaters of the Western Yar River Formation. The gravels are overlain by blown sand that caps the cliffs for a distance of 800 m to the south-east of Whale Chine (Plate 41).

The alluvium and tidal river deposits associated with the present streams and drowned valleys are all considered to be of Holocene age and to represent an infill of valleys that were cut down to a Late Devensian sea-level lowstand below current sea level. In general the deposits are relatively thin, up to 5 m, beneath narrow floodplains, but where the freshwater alluvial deposits interdigitate with the more extensive tidal flat and tidal river deposits downstream, up to 15 m of sediment have been proven in boreholes.

Boreholes, completed during the survey in the Eastern Yar succession beneath Brading Marshes near Yarbridge, demonstrate a succession of grey soft silty clay with significant peat units resting on a chalky flint gravel and in-situ Chalk. These are classified as tidal river deposits. The deepest borehole at Yarbridge proved an unbottomed 13 m of sediment but a series of boreholes 2 km farther inland proved up to 15 m of deposit with a basal gravel unit resting on bedrock. Initial dating results from peat in the BGS boreholes at Yarbridge give 14C dates from 7140 BP to 4120 BP. These results accord reasonably with infill chronologies of other coastal alluvial sites on the mainland and with those envisaged for the Western Yar (Devoy, 1987).

The exact position where the river alluvium gives way to that of the tidal river is not clearly defined. The present upper limit to tidal influence on the major rivers is commonly an artificial barrier. At depth within the alluvial/estuarine successions it is likely that salt-water influence migrated up and down the valleys in response to quite minor fluctuations in the contemporary sea level. Shell beds within the successions vary between those of an entirely freshwater aspect to those of a fully marine type.

The principal lithology of the alluvium is soft to very soft grey and yellow brown, humic, sandy silty clays, although interbedded lenses and thin beds of peat, thin gravel and calcareous tufa deposits also occur. Thick units of extremely soft organic mud, commonly misidentified as peat are present within the lower reaches of alluvial tracts. Where these related lithological units become sufficiently extensive at outcrop they are shown separately on the map.

Peat deposits are shown within the upper Medina and Eastern Yar valleys closely associated with the present-day streams. Other thin occurrences are also known for example at Shippards Chine [SZ 375 844] on the south-west coast where many logs and hazelnuts have been recorded in a sequence up to 3.9 m thick (White, 1921).

Within the Medina valley the three principal outcrops are identified at the Wilderness [SZ 505 824], near Gatcombe [SZ 498 850] and in the Blackwater Brook north-west of Merstone. These have not been described other than ‘the alluvial deposits are generally marsh clay and silt, with a black peaty soil on top’ (White, 1921) but the recent survey identified a mixture of both reed- and osier-dominated facies and marginal alder carr-type peat deposits. These types have not been differentiated. In general at Gatcombe there is between 0.5 and 1 m of fibrous peat or highly organic silt overlying soft alluvial clays proven in boreholes but elsewhere no borehole data is available to give thicknesses of the peat units present.

Peat is delimited in the headwaters of the Eastern Yar, north-east of Godshill and the distinct change in character between these valleys and that to the east of Godshill (the old Blackwater headwaters) perhaps substantiates the river capture hypothesis of this stream at Budbridge discussed earlier. Again both reed and osier peats and marginal alder carr peats are known downstream to Alverstone and within the Scotchell’s Brook tributary. The thickness of the peat units is not well known, and reports of significant thicknesses cannot be substantiated by the available boreholes in the headwater areas. Downstream of Alverstone, a significant number of boreholes show the alluvial succession to be up to 15 m thick (see above) but individual peat units are generally thin and in the range 0.5 to 2 m thick.

Tidal flat and beach deposits are represented around the island. Generally the beach deposits range from muddy sand and sand to gravel or cobble strewn gravel strands and berms. Where the cliffs above are steep, the ‘beach’ is commonly little more than stranded cobbles and large boulders on a wave-cut platform. This is particularly true of the south-west, south-east and part of the north-west coasts that experience considerable sediment transport. In places very limited amounts of mobile sediment are present over wave-cut platforms for example at The Needles, beneath Tennyson Down from Sun Corner to Freshwater Bay both in the far west, and at Culver Cliff in the east where a wide chalk platform is exposed at lowest tides. This situation is also found at Bembridge Ledges and offshore of Nettlestone Point where exposures of Palaeogene limestone are generally swept clear of sediment.

From Newtown Bay on the north-west coast around the Cowes Roads and eastward through to Bembridge there is a variable width of tidal flat deposits. These vary from narrow pebbly sand beaches and offshore flats to the expansive mobile sand platforms offshore of Ryde and Priory Bay. A great deal of data on these mobile sediments is carried in the SCOPAC (Standing Conference On Problems Associated with the Coastline) reports and the Isle of Wight Shoreline Management Plan 2 (Isle of Wight Council, 2010).

Landslide deposits and the mitigation of their effects on the natural and built environment are particularly important on the island, and so they are discussed in the following applied geology section.

Chapter 3 Applied geology

Landslides

The Cretaceous and Palaeogene sedimentary rocks that crop out on the Isle of Wight are mainly composed of relatively soft, commonly poorly lithified sedimentary rocks, the nature of which makes them highly susceptible to landsliding. The island offers an important field laboratory where a number of the different types of failure can be investigated. Many of these landslides represent a significant engineering hazard, with several urban areas requiring remedial work and planning constraints on both new developments and extant buildings (e.g. The Undercliff and Seagrove Bay) to aid development. Slope instability is exacerbated at the coast where marine erosion removes material from the shoreline leading to cliff failure and sequential failure within existing landslides. Extensive landslides occurring inland, for example on the slopes of the southern chalk downs, are the result of a complex interrelationship between the strata, geomorphological development, past and present climate, and groundwater.

The studies of landslides affecting The Undercliff in Ventnor, Luccombe, and Seagrove Bay (Hutchinson, 1991; Hutchinson et al., 1991a, b; Jenkins et al., 2011; Moore et al., 2010; Moore et al., 2007; Winfield et al., 2007) have significantly improved the understanding of the nature and mechanisms of these landslides. However, until recently (Jenkins et al., 2011, fig. 1), little data was published on other important landslides on the island. An outline of the results of that study is given below. As a consequence of the detailed geotechnical work completed over a number of years, principally in The Undercliff area along the south-east coast, there are a considerable number of local planning constraints applied by the Isle of Wight Council to developments in landslipped areas.

Both the Wessex and Vectis formations within the Wealden Group are highly susceptible to landslide failures, particularly where they are exposed to storms on the south-west coast. The character of the failure is determined by the presence and thickness of sandstone units within the generally red and grey mudstone and siltstone strata. Three basic types of failure were identified (Zones A to C) along the south-west coastal area associated with the group (Jenkins et al., 2011), as illustrated in (Figure 39). Within the outcrop in Sandown Bay, the landsliding is characterised by Zone C-type failures.

Within the Lower Greensand Group the principal unit involved with rock-mass failure is the Atherfield Clay Formation at the base of the succession and landslides in this unit are significantly larger than those in the underlying Wessex Group. Failures are common along the south-west coast and within the northern part of Sandown Bay. The dip of the beds and the relationship to higher cliffs can result in the basal Atherfield Clay failure incorporating the Ferruginous Sands and Sandrock formations through translational and rotational failure. The major landslide at Blackgang is complex and not related to the Atherfield Clay Formation but to significant clay aquitards within the otherwise sand/sandstone dominant lithologies of the Ferruginous Sands and Sandrock formations (Insole et al., 1998). Each minor failure within successive Lower Greensand Group aquitards creates bench-like features with overlying sand or sandstone bluffs that suffer foundering or toppling failure. This major landslide is further complicated eastward towards Rocken End and Gore Cliff where the Gault Clay is present (see below).

The Selborne Group is the controlling geological factor in the landsliding of The Undercliff at Ventnor (Plate 42). Between Gore Cliff [SZ 492 763] in the south and Dunnose [SZ 581 790,] north of Ventnor, multiple deep-seated rotational landslides are essentially founded on the interface between the Gault and the overlying Upper Greensand where groundwater pore pressures are high. This is an area that has become internationally renowned as an example of good practice in landslide investigation and remediation. The area has been the subject of three large conferences to demonstrate best practice in dealing with landslide problems (Chandler, 1991; McInnes and Jakeways, 2002; McInnes et al., 2007); each conference has provided a large volume of documentation.

The extensive landslide at Luccombe Chine (essentially the northernmost part of The Undercliff) and those inland around the Southern Downs are also founded on the Selborne Group and similar failure mechanisms are invoked. However, unlike those along the coast, there is little removal of debris from the fronts of the inland landslides and the majority of them are mature having reached a stable angle of repose.

The age of initiation of the larger landslide features within the Selborne Group is open to speculation but they probably fall in the ‘ancient landslide’ category (old landslides that are essentially stable unless reactivated by new events) adopted by Lee and Moore (1989). Very similar landslides occur in the same geological setting (e.g. Hopson, 1999) near the Hampshire/Sussex border around the western closure of the Weald and here they are considered to be Late Devensian or immediately post-Devensian in age. They are considered to have resulted from remobilisation of groundwater during the climatic amelioration at the end of the Devensian. This resulted in high moisture content and pore pressures as well as spring-head erosion at the base of the Upper Greensand.

The White and Grey Chalk subgroups form the steep, high cliffs between Compton Bay and The Needles [SZ 28965 84840], in the west, and also at Culver Cliff [SZ 63710 85395], at the east of the island. These cliffs are subject to toppling falls of material. Some sliding is controlled by the presence of well-developed bedding and joint planes and their attitude relative to the foreshore and erosion.

At Afton Down [SZ 36075 85580] in the west, failures in the 70 m-high chalk sea cliff have required a major realignment of the A3055 Military Road. Here the chalk beds dip steeply inland. Widely spaced (1 to 2 m), low-angled joints that are orthogonal to bedding and so parallel to the sloping cliff promote fissuring in the weathered chalk at the cliff face. The fissures run roughly parallel to the cliff edge. Failure occurs by translational movement along the appropriate seaward-sloping joint planes, leading to toppling failures. Marine erosion at the site is also a significant factor leading to undercutting of the cliff and failure of material by falling. Similar fissures are found on the southern margins of Culver Cliff where it abuts Sandown Bay [SZ 6350 8550]. Photographs acquired during an airborne geophysics survey by the BGS in September 2008 reveal the presence of similar large fissure cracks above Tennyson Down at the western end of the island, suggesting that further failures along this section are also likely (Plate 43).

The influence of the lithologies within the Chalk Group, on failure types in chalk cliffs, has not been studied on the island. However, an association between lithology, fracture patterns and failure types has been recognised on the Sussex Coast (Mortimore et al., 2004). It is envisaged that these associations will relate to the Chalk Group on the Isle of Wight particularly within the Southern Downs and on inland steep scarps. However, the influence of the tectonic hardening of the Chalk formations within the steeply dipping zone, and the way this modifies the concepts examined in Mortimore et al. (2004), has not been specifically investigated across the Isle of Wight.

The chalk that forms the north side of The Needles headland in the south of Alum Bay [SZ 30000 85000] has a steep (70 to 75°) northerly dip into the bay. Here undercutting by wave action results in failure of the strata along bedding planes rather than along joints. Typically rock slides occur where the dip of the beds is approximately parallel to the topographical slope, which is about 60° to the north (Plate 44). It is possible that the movement includes both translational failures and toppling.

Landsliding of varying type, activity and age is present along the northern coastal fringe of the island and is associated with all of the Palaeogene units present. Shallow rotations, mudslides and gullying are commonplace. On the island the Solent Group, particularly, exhibits major failures along the north-western and northern coasts. Inland landsliding is uncommon within the Palaeogene.

Mudsliding is common along cliffs and where bedding is steep (Plate 45). This form of failure is most active during winter and early spring when the cliffs become saturated due to higher rainfall levels. It results in the formation of lobes extending onto the beach. The toe of the mudslide is subject to marine erosion and is commonly eroded back to the cliff line during the summer months, when rainfall levels are generally lower and the slide is less active.

An overview of the landslides on the Isle of Wight may be found in Jenkins et al. (2011) but a brief outline is given below in tabular form (Figure 40).

Examples of the types of landslide present within the Solent Group are given below but there is a need for further study to provide a comprehensive appraisal of this group throughout the island. Outcrops of the Headon Hill Formation are subject to active erosion and landsliding, especially along the coastline from Fort Albert [SZ 33010 89090] to Yarmouth [SZ 34715 89750]. Landslides of various sizes including mudslides and flows are currently eroding the cliffs at Fort Victoria [SZ 33615 89630], forming embayments and lobes. In the lower sections of the cliff, landsliding is occurring through failure at relatively shallow depth whilst higher in the cliff, deep-seated rotational landslides result in recession of the cliff line. Within the wooded areas of Fort Victoria Country Park [SZ 33630 89580] there is a conspicuous landslide topography of degraded hummocks and ridges. These relict features indicate that there has previously been a more pervasive period of landsliding along this section of coastline and that it was more deep-seated than the shallow failures that are currently active within the cliff. It is likely that these ancient landslides formed when sea level was lower (Lambeck, 1997) than at the present day, and their slip planes are thought to propagate beneath current beach level. Evidence for this larger-scale ancient activity is present in the beach in front of the cliff. The Fishbourne and Osborne members of the Headon Hill Formation, seen as horizontally bedded units in the mid-cliff section, are also found on the beach platform as steeply dipping, back-tilted, rotated blocks indicating a buried slip plane at depth. Hutchinson and Bromhead (2002) also described a raft of Headon Hill Formation with vertical strata near to this site at Bouldnor Cliff [SZ 38810 90955].

Rotational landslides and mudslides are a feature of the Bouldnor and Hamstead cliffs [SZ 39845 91630] on the north-west coast. The cliffs along this section of coastline are composed entirely of the Bouldnor Formation, which is weak and susceptible to marine erosion. The mudslides are thought to have been initiated at the turn of the 20th century and are seasonal (White, 1921). They appear to be controlled by high precipitation, high groundwater levels and associated elevated pore-water pressures (Bromhead, 1979). Denness (1970) suggested that the presence of a syncline behind Hamstead Cliffs plunging toward the sea provides a directed pathway for groundwater toward the cliff, resulting in increased activity at this site. Another control on the type and activity of landsliding along this section of coastline is the presence and height of the resistant Bembridge Limestone Formation beneath the Bouldnor Formation. To the east of Bouldnor, the Bembridge Limestone crops out at beach level. The increased resistance provided by the limestone at the base of the cliff reduces the rate of recession and decreases the activity and scale of mudsliding in the overlying Bouldnor Formation (Hutchinson, 1983). To the west of Bouldnor, the limestone is not exposed in the beach and this leads to increased marine erosion of the soft mud. The rate of erosion at the toe is greater than the rate of mudsliding, leading to an oversteepening of the cliffs. This leads in turn to the formation of deeper-seated rotational landslides (Bromhead, 1979).

Landsliding of varying type, activity and age is present on the coast between Cowes [SZ 49580 96380] and Gurnard [SZ 47240 95455]. Large, deep-seated, ancient, degraded landslides form many of the coastal slopes in this area. Evidence for modern landsliding is also apparent in both the developed and undeveloped areas. Houses show evidence of displacement and settlement and cracks commonly appear in roads. Heaving of the landslide toe is evident along the Esplanade. Further inland along the coastal slope, benches and fresh scarps provide evidence for more recent movement (Halcrow Group Ltd, 2000). Erosion rate at the toe exceeding the cliff-fall material replenishment rate in this area has led to active recession of the back scar, as indicated by the loss of part of a garden from a private residence on the cliff at Gurnard during the winter of 2007/2008. Landslide activity at Seagrove Bay [SZ 63130 91070], on the north-east coast presents a significant hazard to local infrastructure. There is a long history of property damage due to ground movement (Winfield et al., 2007). The whole of the slope behind the bay is critically stable: it is close to failure and has a factor of safety very close to one. A change in the environmental conditions, such as an increase in the level of the local water table, or removal of support from the toe of the landslide by beach erosion, could result in failure of the slope.

Inland, there are many small mudslides in the Bouldnor Formation, usually where stream erosion has oversteepened valley slopes or where the formation is associated with spring lines developed in thin sandy horizons within the formation.

Hydrogeology

The hydrogeology of the Isle of Wight has been reviewed by Maurice et al. (2011). This, with the references therein, provides the most up-to-date appraisal.

Around 50 to 60 percent of public water supply on the island is derived from groundwater resources, with a further 20 to 25 per cent abstracted from surface water. Since the 1980s, a considerable proportion of the total supply (20 to 25 per cent) has been imported by pipeline across the Solent but this supply is itself potentially under threat as the demands throughout southern England increase, particularly from Chalk groundwater resources. Licensed abstraction of groundwater resources is also used for small private supplies and small-scale irrigation, although little is now used for industrial supply (Environment Agency, 2004).

The main source of groundwater for both public and private supplies is the Chalk Group and the underlying Upper Greensand Formation, which are in hydraulic continuity throughout the island. The Chalk–Upper Greensand aquifer has good water quality but yields are generally lower than on the mainland because the strata dip steeply and the recharge area is small; therefore the amount of available water is limited. Seasonal demand means that some groundwater resource sites suffer from reduced yields as the groundwater level is drawn down.

Groundwater is also abstracted from the more marginal Lower Greensand Group. Development of this aquifer has provided an additional source of water for both direct supply and river augmentation in the Eastern Yar and Medina rivers, where subsequent abstraction occurs downstream. However this resource is not without problems. Water obtained from the Lower Greensand Group requires treatment prior to use because of the high iron concentrations. Borehole yields become compromised with time because of iron precipitation and the resultant bacterial encrustation and, to a lesser extent, because of the ingress of fines from the aquifer into graded filter packs.

Sands within the Palaeogene and Quaternary deposits are classified as minor aquifers and were previously exploited for groundwater, especially for small private and agricultural supplies.

Surface drainage is predominantly via three major northward flowing rivers, the Medina, the Eastern Yar and the Western Yar, although there are a number of smaller streams. Springs commonly occur within the Upper Greensand Formation at the contact with the underlying low-permeability Gault Formation. The surface drainage and springs are used to a limited extent. Spring flow is commonly augmented by adits and boreholes.

The Isle of Wight provides an unusual example of an ‘island aquifer’ in which the exploitation of its groundwater resources is close to its maximum potential with little saline intrusion because low-permeability strata around much of the coastline protect the main aquifers. As a small island with a relatively dense population, and one that increases significantly during the long holiday season, the Isle of Wight was one of the first areas of the UK in which water became scarce. Pressure on the finite resources is likely to increase as populations rise, large-scale infrastructure development occurs and individual household demands develop. There will also be constraints on the aquifers themselves such as climate variations affecting recharge rates and surface resources. Consequently the island instituted one of the first mandatory water metering schemes to help conserve supply. Innovative solutions were sought to promote the sustainable development of its limited water resources both to meet demand and reduce negative environmental impacts. It may be possible that some limited groundwater supplies could be obtained from the Palaeogene deposits, as a result of improved borehole design and construction.

There are more data available for the Lower Greensand Group, because these strata were intensively investigated from the late 1970s to the early 1990s, when water resource pressures led to the need to explore previously underdeveloped aquifers. It was also clear that there was a greater resource potential in the Lower Greensand Group than the already heavily exploited Chalk–Upper Greensand aquifer. Outline porosity, permeability, transmissivity and water chemistry are given in Maurice et al. (2011) and in the reviews on UK major (Allen et al., 1997) and minor (Jones et al., 2000) aquifers.

Chalk–Upper Greensand aquifer

The Chalk is predominantly a pure, microporous limestone in which groundwater flow is predominantly through fractures, some of which may be enlarged by solution to form fissures, or small karst conduits (Plate 46). Generally, surface karst features (stream sinks and dolines) are relatively uncommon on the island, although subsurface, sediment-filled dissolution features can be observed at the Chalk–Palaeogene contact and beneath the clay-with-flints in both coastal and inland quarry exposures. The Chalk contains common marl, flint and hardgrounds seams, which are known to concentrate flow (Allen et al., 1997). The Chalk has a high porosity of about 30 to 45 per cent and therefore storage is in the matrix, as well as in fractures and fissures. Many small springs occur along the northern margin of the Chalk outcrop where the group dips beneath Palaeogene strata, for example at Carisbroke Castle.

The Upper Greensand Formation is up to 46 m thick on the island and comprises loose sand, sandstone and chert, overlying clays and sandy clays known as the Passage Beds. The lower beds make up, at most, 12 to 15 m of the formation and effectively form the base of the aquifer. The formation carries many vertical joints and groundwater flow and storage is predominantly via fractures, with any intergranular flow and storage restricted to the more weakly cemented calcareous sandstone and loose sand. The chert beds and silicified sandstone at the top of the Upper Greensand Formation have low permeability and may restrict groundwater flow.

Water levels proven within boreholes in the Chalk–Upper Greensand aquifer have seasonal ranges of between 2 and 36 m with a mean of 14 m. Many fissures feeding abstraction boreholes are only seasonally saturated, therefore transmissivity reduces during summer periods. Peak water levels generally occur between December and February, whereas low water levels occur between July and November. These water level fluctuations suggest that storage may be limited.

Chalk (and Upper Greensand) ground-waters on the island have similar chemistry to the Chalk on the mainland and are dominated by calcium and bicarbonate ions.

Lower Greensand Group aquifer

The Lower Greensand Group on the Isle of Wight varies in thickness from 128 m in the west to 250 m in the south. It comprises four formations with the basal Atherfield Clay Formation forming an aquiclude. The Lower Greensand Group forms a major aquifer on the mainland (Allen et al., 1997), but on the island the sediment is generally much finer and it is best regarded as a marginal aquifer. It is a complex multilayered aquifer with locally extreme vertical and lateral variations in lithology, with variable hydrogeological characteristics, although it can generally be divided into a shallow, unconfined aquifer and a deeper, confined or semiconfined aquifer. Groundwater flow and storage is predominantly intergranular.

There is a high density of surface drainage on the Lower Greensand Group, suggesting that infiltration is limited. There are no large springs in the Lower Greensand Group on the island although small springs and seepages occur throughout the aquifer and provide base flow to the main rivers. Five springs in the Lower Greensand Group are recorded in the National Groundwater Archive (Centre for Ecology and Hydrology, 2009) as having been used to provide a water supply for up to three or four houses. Three emanate from the Ferruginous Sands Formation, one from the Sandrock Formation and one from the Monk’s Bay Sandstone Formation.

Water levels in the Lower Greensand Group are monitored in 26 boreholes by the Environment Agency and records extend back to the early 1980s. Patterns are complex and affected by pumping tests and abstractions as well as climate. A number of boreholes are artesian (overflowing), whereas in others water-level variations are between 1 and 14 m with a mean of 5 m.

The water chemistry of the Lower Greensand Group on the island is fairly similar to that on the mainland (Shand et al., 2003). On the Isle of Wight, calcium concentrations are slightly lower and magnesium, sodium, potassium and chloride concentrations are slightly higher than on the mainland. Dissolved iron concentrations in the Lower Greensand Group on the Isle of Wight range from 0.4 to 28 mg l-1 (Packman, 1996), and exceed the European Union maximum acceptable concentration in drinking water (0.2 mg l-1). Water therefore requires treatment prior to use as drinking water and iron encrustation of boreholes, together with siltation, causes initially high yields to decline with time. Groundwater discharges from the Lower Greensand on the Isle of Wight for stream augmentation must not exceed 3 mg l-1 of iron, as recommended by Montgomery (1982) and confirmed by a condition of the Discharge Order. Radiocarbon data for the water from the confined Lower Greensand aquifer give ages in the range of 2000 to 4500 years from three samples.

Palaeogene aquifers

The Palaeogene succession crops out in the north of the island and is the thickest onshore in the UK (Figure 9) and (Figure 23). Some of the Palaeogene formations are classified as minor aquifers and were used together with river terrace deposits (formerly known as plateau gravel deposits) to provide small-scale supplies in the past. In the mid to late nineteenth century, loose-laid shallow pipes drained groundwater from river terrace deposits in the Cowes and West Wight areas to surface reservoirs. However, the shallow groundwater was susceptible to contamination and loss of yield during drought conditions.

Towards the end of the nineteenth century additional water was obtained from deep boreholes drilled to the Barton Sand Formation at depths of up to 200 m. Yields were originally up to 1 Ml day-1 but declined with time because of borehole clogging due to the fine sand of the aquifer and the elevated iron in the groundwater (Entec, 2006). Small domestic supplies were obtained from the Hamstead Member of the Bouldnor Formation, the Bembridge Limestone Formation, the Headon Hill Formation, and to a lesser extent the Becton Sands. Although there are no records of boreholes abstracting from the Bracklesham Group on the island, there are small springs in these strata (White, 1921; Jones et al., 2000), and freshwater was obtained from the Bracklesham Group at Horse Sand and No Man’s Land forts in the Solent between the mainland and the island. There are no records of boreholes obtaining water from the fine sand beds that are present within the London Clay Formation. These sands may have limited yields because the steep dip results in a very small recharge area (White, 1921).

Water levels in the Palaeogene on the island are often shallow and many boreholes are either artesian (overflowing) or have water levels within 10 m of the surface. However, a disused deep borehole at Cowes that abstracted only from the highly confined Barton Sands had a groundwater level nearly 50 m below ground level, when clearance-pumped in 2004.

Bulk minerals

The occurrence of bulk mineral resources of the Isle of Wight was examined in a report (McEvoy et al., 2004) for the then Office of the Deputy Prime Minister. This report gives outline information on the potential for resource availability and informs this section, although the base map (British Geological Survey, 1976) utilised in that report predates the new special sheet. The island holds resources of chalk, sand and gravel, limestone, flint, peat, sandstone, clay and historically used building stone. The island imports considerable quantities of marine-dredged sand and gravel. These and other more ‘exotic’ minerals have been won historically from deposits on the island. Many sites where small-scale extraction has taken place have been identified across the island (Figure 41) but modern practice throughout the bulk minerals industry is to concentrate extraction on fewer, larger sites to maximise the economies of scale, reliable long-term resource availability and consistency. Consequently, current extraction is limited to a few larger sites. The island is a now net importer of cement, bricks and some aggregate.

The mineral resources on the island are limited by planning constraints including statutory designations. These include the Isle of Wight Area of Outstanding Natural Beauty (ANOB), the Heritage Coastline, national nature reserves, sites of special scientific interest, special areas of conservation, special protection areas and those with a Ramsar designation and, within the built environment, scheduled monuments. There may be many other locally defined constraints on extraction outwith these nationally defined areas.

The Isle of Wight Council commissioned Entec UK Ltd to make an assessment of the potential for mineral sites throughout the island. The assessment, which included the identification of existing and potential sites together with outline information on safeguarding areas concentrated on the commodities brick clay, sand and gravel, limestone and chalk, (Entec, 2010). The report informs the Core Strategy Development Plan and the Minerals and Waste Development Plan documents being prepared for the island.

Brick clay

All of the argillaceous deposits throughout the island have been used historically as a resource for brick, tile and pipe making. There is currently no production on the island although some locally derived clay material supports artisan potters.

A list of former brick and tile manufacturing sites across the island is available in an article on Isle of Wight brickmaking on the website of the Isle of Wight Industrial Archaeology Society site www.iwias.org.uk. Much of this data has been derived from old maps and local knowledge but much of the infrastructure of the industry has been removed with only place names or overgrown depressions remaining to attest to the extensive industry. The data has been used to update and enhance the information held within the British Geological Survey’s national BritPits database. The great majority of the known sites are from the 18th and 19th century, providing building materials of variable quality and durability. Few of these sites survived into the 20th century as demand for better-quality products increased, and the availability of better transport and supporting infrastructure improved.

The last production on the island, providing a wide variety of products using the clays in the Gault Formation, was from the Rookley Brickworks (now a country leisure park) which ceased production in 1974.

Sand and gravel

Sand resources are won from both bedrock and superficial deposits. The former are principally in the Lower Greensand Group and to a lesser extent some units within the Palaeogene. The latter are principally derived from the widely spaced patchy outcrops in the Quaternary succession as unwashed material or as beneficiated grades of sand and gravel. Most production presently comes from aggregate quarries on St George’s Down and at Hale Manor near Arreton. The offshore resources dredged under licence from the Solent River deposits to the north-east and east of the island are landed in Cowes.

The principal end uses of sand are as fine aggregate in concrete and asphalt and as mortar sand. Coarse aggregate, derived principally from the Quaternary deposits and from offshore dredging is used principally in concrete manufacture.

Lime and cement

The principal resource for lime and cement is within the Chalk Group and the succession was quarried widely especially for agricultural lime. Numerous small disused quarries occur concentrated along the northern edge of the Chalk outcrop and spread more thinly elsewhere. Many of these quarries also had kilns to burn the chalk for lime used in plaster and lime mortar. Cement manufacture on the island ceased in 1939. The Medina Cement Works based around the Shide Quarry [SZ 505 880] in Newport, which closed in 1939, and the West Ashey site [SZ 575 878], both quarried and mined the Culver Chalk and Portsdown Chalk formations. Chalk is still extracted from a site on the north side of Arreton Down and at Cheverton Quarry, principally as a low-grade fill material and for agricultural liming.

At Brading the Bembridge Limestone was sporadically made into cement from 1884 through to 1915.

Building stones

The principal review reference for the building stones of the Isle of Wight is that by Lott (2011). The Isle of Wight has a diverse stone-built heritage that has received relatively little attention, with the exception of the important study of the local vernacular architecture by Brinton et al. (1987). Local guidebooks commonly tend to focus on the picturesque in terms of building stone usage (e.g. Brighstone village; Winkle Street, Calbourne; Appuldurcombe House) rather than on the rich stone-built heritage that exists in towns and villages throughout the island.

The relative isolation of the island historically has meant that almost all the building stone used in the Isle of Wight, from at least Roman times, has been locally sourced. In the Medieval period the island was an important exporter, supplying stone for many major buildings on the adjacent mainland (e.g. Quarr Stone see below). Currently the Isle of Wight has no commercially significant building stone resources.

There are few parts of the island’s diverse geological succession that have not supplied local stone for construction purposes. They comprise a wide variety of sandstones, limestones and ironstones together with assorted chert and flint nodules and cobbles derived from the Upper Greensand and Chalk succession, or from the coarse superficial gravel deposits that cover parts of the island. However, much of the character of the stone buildings in the Isle of Wight is not due entirely to the variety of stone, but also to the distinctive local construction styles which are used in the houses.

The almost ubiquitous occurrence of coursed Cretaceous sandstones, chalks and Cenozoic limestones, and galleting is particularly characteristic of the island.

Wealden Group (Wessex and Vectis formations)

Although the succession is dominantly clay it does yield harder, thin limestone and coarser fossiliferous and conglomeratic beds. These provided a local source of rubblestone, for building and decorative materials in the villages of Brook, Mottistone, Brighstone and Yafford in the west, and which are occasionally evident in Sandown and the village of Yaverland on the eastern outcrop. Some of the thin, coarsely fossiliferous, brown, freshwater lagoonal limestone slabs (containing Filosina sp. or Viviparus infracretacicus), which are common on the beach at Sandown, were locally used as paving stone. They are very similar in character to the fossiliferous ‘Paludina’ limestone of the Wealden Group in the Weald area of south-east England.

Lower Greensand Group (Ferruginous Sands, Sandrock and Monk’s Bay Sandstone formations)

The ferruginous units of the Lower Greensand Group provide one of the most distinctive building stone resources in the southern part of the Isle of Wight. Most of the group is composed of poorly cemented fine-grained sand. However stones taken from the more durable beds of both the Ferruginous Sands and Sandrock formations and the distinctive ‘ironstones’ extracted from the hard Monk’s Bay Sandstone Formation are found throughout the villages in the southern part of the island.

The finer-grained sandstone is used both as uncoursed rubblestone blocks and as dressed ashlar (square-hewn stone), but the Monk’s Bay Sandstone lithologies are most commonly seen as large, irregularly coursed, rubblestone blocks.

Upper Greensand Formation

This formation was the most important source of building sandstone on the island (Plate 47). It comprises pale greenish grey, fine-grained, glauconitic, calcareous and siliceous sandstone with spicular chert, which has been the source of the large ashlar stone blocks used for many houses in the island. The principal worked bed, historically known as the ‘freestone’ bed, is only about 1.2 to 1.8 m in thickness but can be traced in the cliff and quarry sections along much of its outcrop (e.g. Jukes-Browne and Hill, 1900; White, 1921). Historically the coastal location of the quarries facilitated export of the stone to the mainland. Former quarries at Vayres Farm and Gat Cliff have been identified as important sources of local building sandstone since pre-Norman times. The Upper Greensand was also commonly used in historically significant buildings outside the outcrop with Appuldurcombe House, Arreton Manor and Yaverland Manor being prime examples. The Upper Greensand Formation was also used for the construction of Carisbrooke Castle.

A particularly distinctive facies variant of the sandstone from this group was quarried between Bonchurch and Ventnor in the south and was termed Green Ventnor Stone because of the higher concentration of green glauconite grains present in the sandstone at this particular location. The principal quarries were developed along the area known as The Undercliff, some of which were still active in 1921, and even appear to have extended their workings underground in places. Subsequently the railway station and sidings at Ventnor occupied some of these quarries. Large blocks of Green Ventnor ashlar are common in houses in the town and in surrounding villages.

The sandstone generally comprises a cemented framework of fine- to medium-grained quartz, with subordinate glauconite and bioclastic debris. Where the cement is siliceous the resulting building stone is commonly termed firestone or hearthstone because of its resistance to high temperatures. Concentrations of siliceous sponge spicules have led to the development of extensive chert (siliceous) lenses and laterally continuous, undulating thin beds, particularly in the upper part of the unit. Occasionally, isolated lenses and nodules of chert, and some siliceous burrowfills can be seen in some Upper Greensand wall fabric blocks, but in general the thicker chert beds are only rarely used as wall stones with the softer, glauconitic sandy facies preferred as a general building stone.

Chalk Group

The hard, white chalk limestone of the Upper Cretaceous Chalk Group is one of the most distinctive and easily recognised building stones of the island. Much of the Chalk within the steeply dipping zones is secondarily hardened due to recementation during tectonism and this has promoted the use of chalk as a building stone on the island. Houses, barns, farms and churches on and adjacent to the central and southern Chalk outcrops were commonly partly constructed using chalk blocks (Plate 48). There is some marked variability in Chalk usage with random rubble and polygonal chalk rubblestone patterns common in some cottages, while in others coursed and squared ashlar chalk blocks were preferred. In addition to the importance of the group as a source of this hard white Chalk building stone, the younger units also yield flint nodules which are a common feature in some houses in parts of the outcrop. Rounded flints were also derived either directly from the Palaeogene strata or hand picked from Quaternary units and beach gravels. There are many examples of the use of these reworked, rounded or dressed flint nodules around the island, most notably at Ventnor and Calbourne.

One unusual use for these pure white hardened chalks was as tesserae in Roman mosaic floors, presumably as a substitute for expensive Italian marbles, and examples of their use are seen at Brading Roman villa and many other sites on the mainland. This usage indicates that the Isle of Wight was likely to have been a principal exporter (Tasker et al., 2011).

Palaeogene building stones

The principal building stone resources of the Palaeogene succession are the pale grey, fossiliferous, freshwater limestone beds of the Bembridge Limestone and Headon Hill formations. These limestone developments (which have a maximum thickness about 9 m in the Bembridge Limestone Formation) are unique to the island. The beds were extensively quarried east of Alum Bay at Headon Hill and also at Quarr, Binstead, Gurnard (Cowes) and St Helen’s near Bembridge (Colvin et al., 1982). In the latter area the worked limestone beds form a series of ledges at sea level. The quarrying of Bembridge Limestone at Gurnard (west of Cowes) and St Helen’s for construction of fortifications at Portsmouth is documented from 1562 (Colvin et al., 1982).

A range of different lithologies was quarried from these limestone beds and are best seen in the town buildings of Binstead, West and East Cowes, Ryde, and in villages such as Calbourne, Shalfleet, Newtown, Newbridge and Totland. Numerous other historic buildings on the island also used Bembridge Limestone in their construction (Yarmouth Castle, Quarr Abbey and Arreton Church). The quarries in the Binstead area were briefly mentioned by Mantell (1847) who noted several active quarries varying in depth from 10 to 20 feet [3 to 6.1 m].

Perhaps the most famous of these ‘Bembridge limestones’ is the so-called Quarr Stone (or Featherbed Limestone) which was taken from a lithologically very distinctive unit composed of layers of closely packed, bioturbated, broken and abraded mollusc shells—shell brash or ragstone—within the Headon Hill Formation. The distinctive fabric of the rock and its durability made it an excellent freestone and it was often preferred for use in decorative mouldings and quoins rather than for general walling stone (Robinson, 1998; Tatton-Brown, 1980). There is no exposure of this facies in the Binstead area today. It is likely that the heavily quarried ‘hills and holes’ area east of Quarr Abbey and encompassed by Binstead, Quarr Wood and Holy Cross Church was the principal source area of the Quarr Stone. The surviving walls of the abbey grounds and the local church contain significant proportions of the Quarr Stone, but in general its use in the island as a whole does not compare with the volumes exported and used on the mainland, most notably in the facade of Winchester Cathedral (Tatton-Brown, 1993), Chichester Cathedral and sporadically at both the cathedral and castle at Canterbury (Tatton-Brown, 1990). Quarr Stone has also been identified widely in numerous Hampshire churches.

The most common building limestone quarried from the Bembridge Formation is known as the Binstead or Bembridge Stone (named according to the vicinity from which it was quarried) with its distinctive open vuggy layers and fossil casts. This lithology is particularly common in the older 19th century stone buildings of Ryde and East Cowes. Norris Castle (1799), for example, has a mixture of both Bembridge Limestone and cross-bedded Palaeogene sandstone stonework. The mortar work of the castle also has an unusual but very distinctive fine flint-shard galleting within the mortar work.

The use of the limestone of the Bembridge Limestone Formation on the mainland is known to date back to Roman times and was recorded at, for example, Fishbourne Palace near Chichester (Williams, 1971). Archaeological studies of the roofing materials used in several Roman villa sites on the island suggest that Bembridge Limestone was also used for the production of roofing slates and examples can be seen on display at the Brading Roman Villa site on the island (Tomalin, 1987).

Pleistocene building stones

The generally unconsolidated Pleistocene successions of the island were an important local source of flint and/or chert pebbles and cobbles for building purposes. Flint walling is a common feature in some villages and towns. The flint was used either as cobbles in the round, or as fractured cobbles in which the paler grey-brown, lustrous, internal face is revealed. The flints are commonly bedded in mortar in coursed or random patterns.

Occasionally ferruginous, cemented blocks (ferricretes) from these local gravels (elsewhere in Hampshire commonly termed ‘Heathstones’) can be seen in some wall fabrics.

Imported building and decorative stones

Until comparatively recent times, the import of building stone from the mainland for use on the island appears to have been very limited. Despite the proximity of the Portland quarries, surprisingly little Portland Stone is known on the island, with the exception of a number of banks (e.g. Ryde HSBC), war memorials and sculptural objects. The heavy fossiliferous limestone known as Purbeck Roofing Slate can be seen in Mottistone Manor, Wolverton Manor, West Court Manor, King James Grammar School in Newport, Brighstone Church and at Carisbrooke Castle. The ‘Purbeck Marble’ is used in some churches (e.g. in the Norman church at Shalfleet) and alabaster, probably imported from Nottinghamshire, is known from the tomb effigies of Sir William Worsley at Godshill Church.

Although many of the great houses of the Isle of Wight are characterised by the use of local building materials well into the 19th century, there is one prominent exception—Queen Victoria’s Osborne House, which was designed and constructed between 1845 and about 1851 by Prince Albert and Thomas Cubitt. This Victorian house, in Italianate style, is an architectural curiosity on the island. Some of the latest building techniques were used in its construction but only limited use was made of local materials. The house is constructed of brick with an iron framework and smooth, plaster ‘stucco’ facade and although the island has a long local brickmaking tradition there is no clear evidence that locally made bricks were much used in the construction of the house. There are several brickmaking pits surrounding the estate in the Bembridge Marls, but these appear to have been principally used to provide drainage pipework.

The future of the Isle of Wight’s stone buildings

Today, as elsewhere in the UK, most if not all of the local building stones once quarried in the Isle of Wight are no longer produced. This has resulted in significant concerns for both heritage conservation and new build programmes in the island. The need for replacement stone for conservation repair will inevitably grow over time. This applies not only to its better known heritage buildings such as Mottistone Manor and Carisbrooke Castle, but also to the hundreds of smaller stone buildings in its towns and villages. Even the best quality building stones can eventually decay and fail and will need to be replaced. The Isle of Wight’s local character and distinctiveness is unique, and is very much a combination of its spectacular landscapes and distinctive built environments. New indigenous sources of stone for conservation repair and, equally importantly, for new build projects, need to be safeguarded to retain the character of the built environment on the island.

Hydrocarbons

Considerable effort has been expended on the Isle of Wight in the search for hydrocarbons. Nine deep exploration boreholes have been drilled, the most recent being those at Bouldnor Copse and Sandhills 2 (together with its inclined offset) (Figure 9). None have encountered viable resources of hydrocarbons. The hydrocarbons encountered in these boreholes have been of insufficient quantity. This perhaps demonstrates migration through potential traps but with loss during erosional or tectonic events where the enclosure has been breached, or where the hydrocarbons have suffered biological degradation and are essentially residual tars. However, prospecting still continues with recent licences granted to Northern Petroleum in the onshore (Bouldnor Copse and Sandhills 2 boreholes) and immediate offshore area to the south-west of the island associated with the continuation of the Brighstone Anticline.

Stoneley (1992) reviewed the occurrence of hydrocarbons within the Wessex Basin including the Isle of Wight. Underhill and Stoneley (1998) investigated the development and evolution of the Wessex Basin, and Bray et al. (1998) investigated the preservation potential and prospectivity across the same area. Other articles in the Geological Society of London Special Publication 133 edited by Underhill (1998) describe additional data. A pdf format summary of the current understanding of the prospectivity for the English Channel Region is available on the Department of Energy and Climate Change website.

In terms of hydrocarbon prospectivity the Isle of Wight and the surrounding offshore area can be divided into the structurally defined Wessex Basin and the Central English Channel Basin, separated by the Purbeck–Wight Structure. The source rocks are considered to be the Lias Group, and the Oxford Clay and the Kimmeridge Clay formations but hydrocarbon development from these organic-rich clay units relies on significant burial and maturation and the serendipitous association with one of the potential reservoir rocks. Potential traps across the region may have been affected by intra-Cretaceous tilting or erosion or Palaeogene tectonic inversion, or both, allowing hydrocarbons to migrate and dissipate. Essentially two trap types are recognised across the region. Most common are those associated with Mesozoic tilted fault blocks and horsts that to succeed need to be near potential source rocks of sufficient maturity, and importantly are not later affected by Palaeogene inversion and breaching. Others are within Cenozoic inversion anticlines that accept a secondary migration of hydrocarbon resources but cease movement before inversion breaches the seal.

In both the Wessex and Channel basin areas, hydrocarbons are associated with five potential reservoirs or ‘plays’:

So far on the Isle of Wight, noncommercial hydrocarbons have been encountered within the Sherwood Sandstone and Great Oolite plays with the Bridport Sandstone, Corallian and Portland plays being either absent (north of the dividing structure) or developed in a lithological facies that reduces their reservoir potential.

Currently commercially important hydrocarbon discoveries are restricted to the Wessex Basin north of the Purbeck–Wight Structure. The largest of these is the Wytch Farm oilfield located in the Wareham–Poole Harbour area, west of the Isle of Wight. The principal reservoir is within the Sherwood Sandstone, which is known to have an extension offshore in well 98/11-2. Whilst the Sherwood Sandstone has been encountered widely across the island, no commercially important hydrocarbon resources have been encountered, although hydrocarbon migration is indicated. The lack of significant accumulations is possibly a consequence of intra-Cretaceous erosion and tectonic tilting that has removed the seals to potential traps.

The Great Oolite Group has significant lateral facies changes. Its reservoir potential is not only affected by the development of significant clay units within the succession, but also by the variable recrystalisation within the limestone that generally forms the reservoir rocks. The Great Oolite encountered at depth across the island is substantially clayey in its lower part, and increasingly so offshore to the south-west, where some limestone is argillaceous. The best reservoir quality within this unit is found on the mainland around Horndean to the north-east of the island, where vuggy and open-framework ooidal limestone is best developed within a nearshore shallow-water, reef environment.

Geotechnical considerations

The important geotechnical considerations in relation to the widespread occurrence of landslides on the island are discussed above. Areas of landslipped ground are common in the Isle of Wight district and failures can be spectacular as shown in the historic example captured in (Plate 49).

For other geotechnical considerations on the island, the following statements should be taken only as a guide to likely or possible problems and should not replace site-specific studies. The main constraints for each of the units or groups of units identified on the map face are summarised in (Figure 42). The extent of ground susceptible to these geohazards is indicated within the BGS Geosure dataset at www.bgs.ac.uk/products/geosure/.

The Chalk is locally affected by solution phenomena causing the fractures naturally occurring in the Chalk to be enlarged and a very irregular rockhead surface to be created. Solution can result in the formation of surface sink holes (dolines) that range in size up to some 50 m across, and up to 6 m deep. These generally overlie pipes filled with Palaeogene materials, clay-with-flints or, in some places, head (Plate 50). Such depressions continue to act as sumps for surface drainage, and may be liable to further subsidence. Differential compaction under load can occur across such structures. Either phenomenon can create difficulties during or following construction. Localised dissolution phenomena are also present in the Bembridge Limestone Formation across the broad outcrop to the west-north-west of Shalcombe.

Thin deposits of head are much more widespread than indicated by the geological map. In particular, large parts of the Palaeogene, White Chalk and Lower Greensand outcrops, which are shown with no overlying superficial deposit, actually carry a thin and extensive, but discontinuous, blanket of head. Head, especially where clay rich, can contain gently dipping shear planes that can fail when loaded.

Planning for future construction should allow for the possible existence of small areas of made ground, infilled ground or landscaped ground. Such areas might be liable to differential settlement. Commonly the nature of the fill is unknown. In the case of landfill sites the presence of gas derived from the breakdown of the buried wastes may present a problem.

Peat is a compressible material that will compact when loaded. It may give rise to differential settlement when partially built over. Care should be taken to identify peat units that may exist within the major floodplains, although not indicated by surface mapping, for example within the Blackwater Valley, and within the headwater areas of both the River Medina and the Eastern Yar.

Excavations within units comprising unconsolidated sand are liable to failure if unsupported particularly where groundwater is present. Such sand occurs, for example, within the Lower Greensand Group, the Upper Greensand Formation and most of the sand units present throughout the Palaeogene and Quaternary strata.

Geodiversity

Geology and geodiversity have received more interest in recent years particularly with the focus on the effects of climate change on our environment. Many local authorities are now publishing geodiversity action plans (Burek and Potter, 2006) and DEFRA has provided various policies, guidance and measures such as the Aggregate Levy Sustainability Fund, to reduce the impact of activities such as aggregate extraction (Defra, 2006). The Isle of Wight produced a first-issue plan (based on earlier consultation drafts) in 2010 for English Nature (Price and Jakeways, 2010), although this is a formalisation of a long-standing policy of landscape and resource management on the part of the County Council over many years. The local authority supports both the Dinosaur Island Museum in Sandown and The Isle of Wight Centre for the Coastal Environment, both of which do much to monitor, conserve and promote the geodiversity on the island.

Much of the island is designated as an area of outstanding natural beauty (AONB) and a large part of the south-western and north-western coasts have heritage coastline status (Figure 45)." data-name="images/P937078.jpg">(Figure 2). The island has many important SSSIs (sites of special scientific interest), reflecting a government policy, backed by legislation, which was first used on the island in 1951. These SSSI designations protect 42 localities, 17 of which are specifically designated for their geological/geomorphological interest (Figure 43). Some wetland areas have been proposed as Ramsar sites, which have international importance. There are many more RIGS (regionally important geological/geomorphological sites), which have a lesser legal protection but add to and expand upon the SSSIs. In addition there are a number of nature reserves that not only protect the biota identified but also the geological setting of that area.

The value of outreach for both geology and geodiversity has been comprehensively reviewed in Anderson and Brown (2010) (see also Booth and Brayson, 2011), which concentrates on the Quaternary aspects of geology although their reasoning and assumptions can readily apply to all areas of geology. Munt (2008) reviewed the history of geological conservation for the Isle of Wight.

The island’s spectacular geology is perhaps more varied than any other area of comparable size in southern England. The surface geology records a history from about 125 Ma, in the Early Cretaceous, through to the present day. But in its structure and geology at depth, it also records a significant history of continental drift and collision that takes the geological story back to the Late Palaeozoic Carboniferous and Devonian epochs (some 390 Ma).

The Isle of Wight presents a huge geological resource for teaching and study but also presents a spectacular landscape to be enjoyed by the tourist whether on foot, cycle, vehicle or boat. The geological story begins with any of the ferry crossings from Portsmouth, Southampton or Lymington over the Solent.

The island is noted as the best site in Europe for the study and collection of dinosaur remains, it contains the largest landslide complex in northern Europe, it offers sea cliffs (notably at Alum Bay and the adjacent world famous Needles promontory, Whitecliff Bay and Culver Down), and carries a story of human occupation related to the development of the ancient Solent River that stretches back half a million years. The island exposes one of the most complete Cretaceous successions onshore in the UK: the stratigraphical extent of the Chalk Group is only surpassed by less readily studied exposures in East Anglia and Yorkshire. The Palaeogene succession is the most complete in the UK and north-west Europe and in the Insect Bed of the Bouldnor Formation contains an important lagerstätte unit (a deposit with exceptionally high-quality fossil preservation) as well as a significant mammalian fauna providing strong correlations with the continent.

Chapter 4 Human occupation of the Isle of Wight

There is of evidence for hominin (modern humans, extinct human species and our direct ancestors) occupation of the island from the Palaeolithic period through to the Iron Age and into Roman and later historic times (Figure 44), covering at least 500 000 years (see the web-delivered Archaeological Resource Assessments for the Isle of Wight, Solent Thames Research Framework, Oxford Archaeology, dated 2010).

The Vectis Report (Basford, 1980) gives a broad assessment of the archaeology of the island although much new data and changing theories of human occupation have been presented in the subsequent 30 years.

The island was not permanently settled until the Mesolithic period and this was essentially the start of a pastoral economy that lasted well into historical times. The great expansion in population and modern urbanisation did not really occur until the Georgian, Victorian and Edwardian eras with the upsurge in popularity of the island as a holiday destination, prompted by the patronage of the monarchy and aristocracy.

For the great majority of the time that hominins have been present in the British Isles, they can be regarded as hunter-gatherers. They effectively lived within the constraints presented by their contemporary environment rather than significantly modifying it and their lifestyle can be imagined as very mobile, using only basic shelters. As such these societies left little behind in terms of dwellings or occupation sites other than natural features in the landscape that were used for shelters. However, they did leave a rich heritage of artefacts, which together with their geological associations are important in developing chronologies in the Quaternary. Artefact types or ‘industries’ that are represented during the Lower and Middle Palaeolithic phases (known as the Clactonian, Acheulian, Levallois and Mousterian) were once considered to be indicative of age because of their apparent increase in sophistication as time progressed. This concept has now been almost entirely discredited as a means of dating deposits, as the ranges of the different types overlap significantly, and instead are thought to point to population migrations and technological interchange through time. However there are characteristic patterns to these flint industries that still present a fascinating insight into the lifestyles of the populations.

These early phases of human occupation are considered to be representative of early hominin species with modern man, Homo sapiens sapiens, not arriving in Europe and Britain until about 40 000 years ago. There is evidence in nearby Europe that early human species and modern humans coexisted for a period. A comprehensive review of the Palaeolithic archaeology of the Solent River is given in Wenban-Smith and Hosfield (2001) and papers cited therein.

Palaeolithic

In the British Isles, this phase of the Pleistocene was dominated climatically by periods of glacial and interglacial climates and human occupation was strongly influenced by these changes. The deposits within the area of the Isle of Wight carry no glacial signature but rather indicate that during glacial periods the area was cold tundra with severe winters and very low summer temperatures. It probably supported a fauna and flora that was directly modified to deal with these climatic extremes such as the mammoth and woolly rhinoceros roaming a treeless landscape with herds of herbivores migrating over much of southern Europe and into southern Britain across a rich summer grass and shrub steppe environment. During the interglacial periods the island supported a woodland environment with stands of typical broadleaved forest such as hazel, oak, ash and elm with yew and a fauna of deer, bison, horse and their carnivorous hunters. Amongst these hunters were early humans who followed the herds and left behind their flint tools but little else. These people were truly hunter-gatherers and collected nuts, plants, herbs and fish, and other foods from the dense woodland. Like the animal herds, they probably used the rivers as natural routeways to cross the land. Many of the Lower and Middle Palaeolithic sites on the island are represented by only single finds. Three sites at Bleak Down [SZ 512 810] to [SZ 512 831], Priory Bay [SZ 635 900] and Great Pan Farm [SZ 507 886] have produced a great many artefacts through a long period of collecting from the late 19th century to the present day (e.g. Codrington, 1870; Poole, 1924, 1930, 1934, 1936, 1937, 1939). A significant review of the Lower and Middle Palaeolithic for the island is given by Wenban-Smith and Loader (County Resource Assessment, Wenban-Smith and Loader, 2006, 2011). Whilst is was thought that there was semicontinuous human occupation in Britain since MIS 13, there is growing evidence that significant periods in the Pleistocene saw no human occupation of the British Isles (Ashton and Lewis, 2002) with a suggested absence for at least part of the period from MIS 6 to MIS 4 (Late Wolstonian to Early Devensian).

The earliest occupation on the island probably dates to about 425 000 BP or perhaps a little earlier but whilst the Steyne Wood Clay [SZ 642 866] (about 40 m OD) at Bembridge is reliably dated to the pre-Anglian (MIS 13), it has produced no artefacts. The earliest occupation with artefacts is probably represented by the Bleak Down site at about 80 m OD in the centre of the island. Here a rich assemblage, but of crude typology (Poole, 1924, 1934) and with no firm dating evidence, is regarded as being deposited during or immediately after the Anglian because of the number of lower terraces elsewhere. The abraded nature of the artefacts may also indicate that they were derived from an earlier deposit that is now absent. Earlier eoliths (supposed early artefacts) associated with the St Georges Down site [SZ 515 865] at around 105 m OD (Poole, 1939) are now considered as naturally abraded stones.

Perhaps the most significant site on the island is that at Priory Bay (Loader, 2001; Wenban-Smith et al., 2009) on the north-east coast. Here, the Wootton Gravel Complex Member produces artefacts from a number of levels in both fresh and abraded condition and at various topographicalal levels around 34 to 29 m OD. The main artefact-bearing horizons are regarded as representing fluvial deposition dated to MIS 11–9 (Hoxnian to Mid Wolstonian) with OSL dating giving a range of 367 000 to 216 000 BP.

The Great Pan Farm site, in Newport, is one of the most important Mousterian flint implement industry sites in the British Isles with both bout-coupé and Levalloisian technologies identified. A related OSL date of 50 000 BP in a deposit slightly higher topographically at the site confirms human occupation during the last Devensian glaciation.

West High Down [SZ 308 851] in the extreme south-west of the island produced a number of hand axes and flakes but all are abraded suggesting that the assemblage is a mixed concentration of derived artefacts. The Bembridge Foreland [SZ 655 875] has a number of find spots with hand axes but none in context. Other information indicates a date of about 125 000 BP (Ipswichian) for the raised beach deposits here.

There is no unequivocal evidence for Late Palaeolithic occupation on the island and this may well point to a period when humans were absent from the British Isles following the breaching of the Straits of Dover. However the presence of sites of this age in the offshore zone north of the island is thought to have some potential.

Mesolithic

The Mesolithic and younger occupational phases approximately correspond to the Holocene (Flandrian) stage and the various terms utilised to discuss these phases and the immediate Late Devensian are shown in (Figure 45).

Mesolithic sites with hearths and a more sophisticated flint technology, represented by heavy tranchet axes, picks, gravers, arrowheads and microliths, are concentrated on the north coast, within the Medina River catchment and over the Lower Greensand landscape of the island. The date of the severance of the island from the mainland is still a matter of debate (see discussion on pp.101–104). With latest thinking placing it in the Late Mesolithic at the earliest (Momber et al., 2011), coastal and river transport would have been an important aspect of survival and communication throughout the Mesolithic.

One of the most significant sites of this period was first identified at Werrar Farm [SZ 503 927] in the Medina valley south of Cowes. This was during the extraction of clay for brickmaking within Quaternary saltmarsh deposits associated with the tidal river deposits and Seaclose Park Terrace Member passing into the underlying Hamstead Formation. Hubert Poole (1936) recorded an old land surface into which hearths had been dug, associated with flint implements including tranchet axes, a microlith, burins, scrapers and debitage. More recent pollen analysis has confirmed Poole’s interpretation of a palaeosol from which flints were recovered overlain by a transgressive peat (Scaife, unpublished report, Isle of Wight Historic Environment Record, Isle of Wight Council).

A similar occupation surface containing worked flint and burnt flint was noted by Poole (1936) in tidal river deposits within the eastern spit at the mouth of the Newtown Estuary [SZ 418 919].

A number of hearth sites associated with the fluvial deposits of the Western Yar River are known from the eroding cliffs along the south-west coast. These were assumed by antiquarians to be of Mesolithic date but none have been securely dated to this period although a radiocarbon date of about 8500 to 8250 BP has been obtained for organic deposits of the old Western Yar.

An extensive shoreline survey between Wootton Creek [SZ 555 932] and Ryde [SZ 594 929] has revealed a large collection of tranchet axes and picks together with scatters of burnt and worked flints including numerous microliths. These were associated with palaeochannels crossing the foreshore and overlain by organic silts/peats that have been radiocarbon dated to 4645 ± BP (Tomalin et al., 2012).

In the offshore zone at Bouldnor [SZ 368 900], on the north-west coast of the island, evidence of Mesolithic occupation has been investigated by divers to depth of -7 to -11 m OD. Finds include worked and burnt flint, charred hazelnuts, cordage, and timbers with indications of woodworking. Radiocarbon and dendrochronological dating places this activity in the late seventh to early sixth millennium BC (Momber et al., 2011).

Neolithic

The earliest surviving standing monuments on the Isle of Wight date from the Neolithic. There are two long barrows, at Longstone [SZ 407 842] and Afton Down [SZ 352 857], both in west Wight, and an oval earthwork [SZ 336 855] on Tennyson Down. The latter was confirmed as a Neolithic mortuary enclosure following radiocarbon dating of charcoal recovered from its ditch. The environment was then still essentially thickly forested and settlements, mostly evidenced by scatters of burnt and worked flint, are closely associated with the three major rivers and coastal estuary sites, much as with earlier occupational evidence. Indeed some sites show an occupation chronology from the Mesolithic through to the early Bronze Age e.g. Newtown estuary, Black Pan Farm [SZ 582 835] near Sandown and at Redcliff [SZ 620 854] near Yaverland. Fieldwork on the north-east coast of the island between Wootton Creek and Ryde has produced evidence of coastal exploitation in the Neolithic in the form of trackways, possible fishing structures and scatters of burnt and worked flint including arrowheads and scrapers (Tomalin et al., 2012).

Bronze Age

The most striking evidence that survives from the Bronze Age takes the form of the numerous burial mounds, which are highly visible on the island’s central chalk ridge and southern downs. The remains of more than 300 Bronze Age burial mounds have been recorded. Bowl barrows are the most common form, although there are also bell and disc barrows. Many no longer survive as earthworks, the mounds having been destroyed by ploughing and other activities, but take the form of ring ditches, which are particularly visible from the air. The presence of these ceremonial burial sites perhaps indicates a more open aspect to the landscape with phases of tree clearance that accelerated into the late Bronze Age and Iron Age and probably gave rise to the distinctive chalk downland scenery seen today. Field systems are a significant feature attesting to the increasing importance of agriculture. During the later Bronze Age, cremation became the favoured funerary rite and the cremated remains were placed in pottery urns and buried in cemeteries. At least four such cemeteries have been recorded from the island.

The Bronze Age sees the first use of metal on the island. Hoards of metalwork containing numerous implements and weapons have been found; the first found whilst quarrying chalk on Arreton Down, is the named type site for metalwork of this period. Other implements have been recovered during excavation of burial mounds.

There is a continuum of occupation that can be demonstrated from the late Neolithic into the early Bronze Age and further into the Iron Age but there is still only sparse evidence of dwellings from these periods.

Iron Age

On the neighbouring mainland, large hillforts are a prominent feature of the Iron Age landscape. However, there are only two unconfirmed hillforts on the Isle of Wight—on Chillerton Down and at Yaverland. A late Iron Age enclosed farmstead was excavated in the 1960s at Knighton to the south of the central chalk ridge, and there is evidence of Iron Age occupation predating some of the island’s Roman villas, for example at Combley, (unpublished report, Isle of Wight Historic Environment Record, Isle of Wight Council IWHER) and Brading (Cunliffe, 2013).

There is considerable evidence for trade in the late Iron Age continuing into the Roman period, both with mainland Britain and with the Continent. The importance of the role of the island in the Iron Age to maritime trade is discussed in Trott and Tomalin (2003).

Roman Wight

The most obvious signs of the Roman occupation of the island are the numerous villas, essentially stone-built farmsteads of varying sophistication which may have been remodelled at various times during their lifetime. Brading Villa with its mosaic floors is perhaps the most celebrated but other sites are known at Gurnard, Combley, Carisbrooke, Shide, Rock, Clatterford, and Bowcombe. There is no known evidence for Roman fortifications or roads on the island.

Modern interpretations suggest that many of these villa sites are Romano-British settlements with the high-ranking families from the late Iron Age cultures taking-up the imposed Roman administration. They prospered from this association as regular trade across the Roman Empire increased. The fertility of the island’s soils was the basis for agricultural trade. Locally made coarse pottery is found at all of the island’s Roman sites and there is evidence for salt-making on coastal sites including at Wootton Creek, Quarr, Grange Chine, Springvale and Redcliff. Bembridge Limestone and Quarr Stone were exported to mainland Britain, being used for example in the construction of the Roman palace at Fishbourne near Chichester. Exports even included such simple things as the hard chalk tesserae derived from the tectonised chalk that are found in many villa sites throughout southern Britain including the Brading site on the island.

Early Medieval

The Isle of Wight is mentioned in early accounts such as the Anglo-Saxon Chronicles and Bede’s Ecclesiastical History, although these cannot be regarded as entirely reliable. The Anglo-Saxon Chronicle suggests that the Isle of Wight was ‘invaded’ by the West Saxons around AD 530 but this is contradicted by evidence recovered from a number of late fifth to early sixth century cemeteries, which have been excavated on the island. It seems likely that the economy was still based on the rural estates that had developed around the earlier Roman villas, but little is known about settlement on the island during this period.

The Norman Domesday Book indicates a pre-existing Anglo-Saxon settlement pattern with ten churches and over 100 manors being recorded on the island, although place-name evidence suggests that many settlements unrecorded in Domesday Book originated in the early Medieval period. From the 11th century the manorial estates achieved, in some part, the parish structure that survives until the present day.

Medieval

Following the Norman Conquest, the military significance and status of the Isle of Wight was reflected in its donation to William Fitz Osbern, a trusted kinsman of William the Conqueror, and Carisbrooke Castle was developed to become a powerful and symbolic residence of the ruler of the island.

The Medieval period saw the laying out of the first planned towns on the island, at Newport, Yarmouth, Newtown and Brading in the late 12th to 13th century, but none were very prosperous and French raids in the 14th century were particularly damaging to Yarmouth, Newport and Newtown.

Many of the island’s parish churches, although extensively altered particularly in the Victorian period, date from the 12th to 13th century. Quarr Abbey was founded in 1131 and became a significant land owner with maritime contacts in the south-west and along the east coast of England and on the Continent. Limestone quarried from sites adjacent to the abbey was an important export which was shipped as far afield as Kent and London, and was used in many significant mainland buildings including Romsey Abbey and the cathedrals of Chichester and Winchester, although the abbey never controlled the quarries. It is believed that the distinctive Quarr Featherbed Limestone was exhausted by the early 13th century.

Post-Medieval and modern Wight

The strategic importance of the Isle of Wight became particularly pertinent during the 16th century when the country was faced with the threat of attack from France and Spain. The island was seen as a potential base from which the mainland could be attacked. Fortifications including Yarmouth Castle, Sandown Fort and blockhouses at the mouth of the River Medina at East and West Cowes were constructed. The threat of invasion again reared its head during the Napoleonic Wars, when several barracks were constructed along the island’s coast, none of which survive. The next major phase of improvements to the island’s coastal defences took place in the mid 19th century. The Royal Commission on the Defence of the United Kingdom was set up, again as a response to the threat of French invasion, and recommended the construction of a ring of forts to guard the dockyard at Portsmouth, including fortifications along the island’s coast, between Freshwater Bay in the west and Sandown in the east. Many of these fortifications continued to play an important role through to the Second World War.

The rural landscape was developed through a number of large landed estates but this period saw the greatest expansion of the towns. The growing popularity of the island as a tourist destination in the 19th century led to the development of seaside resorts which was hastened by the coming of the railways. East and West Cowes became important shipbuilding centres and retained their industrial heritage well into the late twentieth century.

The island’s vernacular architecture uses many locally won stones which give a distinctive character to the surviving grand houses, farmsteads and villages (see Building Stones, p.129).

Information sources

Sources of further geological information held by the British Geological Survey relevant to the Isle of Wight district and adjacent areas are listed here. Information on BGS publications is given in the current BGS Catalogue of Geological Maps and Books, available on request and at the BGS website (www.bgs.ac.uk). BGS maps, memoirs, books, and reports relevant to the district may be consulted at BGS and some other libraries. They may be purchased from the BGS Sales Desk, or via the bookshop on the BGS website. This website also provides details of BGS activities and services, and information on a wide range of environmental, resource and hazard issues. Searches of indexes to some of the materials and documentary record collections can be made on the BGS website.

Geological enquiries, including requests for geological reports on specific sites, should be addressed to the BGS Enquiry Service at Keyworth. The addresses of the BGS offices are given on the back cover and at the end of this section.

Maps

Books

Technical reports relevant to the district, including biostratigraphical reports, may be consulted at the BGS library or purchased from the BGS Sales Desk.

Documentary records collections

1:10k tile km2 Name Geologist
SZ28NE* 0.1 Alum Bay South PMH
SZ28SE* 0.1 Scratchell’s Bay PMH
SZ39SE* 3 Bouldnor and Hampstead AJN
SZ38NW* 13 Totland and Freshwater AJN, PMH
SZ38NE* 24 Yarmouth AJN, PMH
SZ38SW* 0.4 Tennyson Down West PMH
SZ38SE* 5 Brook KAL, PMH
SZ49NE* 4 Cowes West AJN
SZ49SW* 12 Newtown AJN
SZ49SE* 23 Parkhurst AJN
SZ48NW 25 Calbourne AJN, ARF
SZ48NE 25 Newport West ARF
SZ48SW* 19 Brighstone KAL, PMH
SZ48SE 25 Shorwell KAL, ARF
SZ47NW* 0.2 Atherfield KAL, PMH
SZ47NE* 13 Chale KAL, PMH
SZ59NW* 3 Cowes East AJN
SZ59SW* 23 Wootton Bridge ARF, AJN
SZ59SE* 15 Ryde ARF
SZ58NW 25 Newport East ARF
SZ58NE 25 Ashey Down PMH, ARF
SZ58SW 25 Godshill KAL
SZ58SE* 21 Shanklin JB, PMH
SZ57NW* 20 Whitwell JB
SZ57NE* 9 Ventnor JB
SZ69SW* 7 Nettlestone PMH, ARF
SZ68NW* 23 Brading PMH
SZ68NE* 1.5 Bembridge PMH
SZ68SW* 0.5 Sandown PMH

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Winfield, P, Moses, E, and Woodruff, M. 2007. Combining slope stability and coast protection at Seagrove Bay on the Isle of Wight. 365–376 in Landslides and climate change: challenges and solutions. Proceedings of the International Conference on Landslides and Climate Change. Ventnor, Isle of Wight, May 21–24, 2007. McInnes, R G, Jakeways, J, Fairbank, H, and Mathie, E (editors). (London: Thomas Telford.)

Woods, M A. 2007. Upper Greensand and Chalk Group macrofossils from the Isle of Wight. British Geological Survey Internal Report, IR/07/104.

Woods, M A. 2008a. Cretaceous macrofossils from the Isle of Wight: Spring 2008. British Geological Survey Internal Report, IR/08/056.

Woods, M A. 2008b. A biostratigraphical review of old BGS macrofossil collections from the Chalk Group of the Isle of Wight. British Geological Survey Internal Report, IR/08/002.

Woods, M A. 2009. Macrofossils from the Upper Greensand Formation and Chalk Group of the Isle of Wight: Spring 2009. British Geological Survey Internal Report, IR/09/056.

Wray, D S, and Gale, A S. 1993. Geochemical correlation of marl bands in Turonian chalks of the Anglo-Paris Basin. 211–226 in High Resolution Stratigraphy. Hailwood, E A, and Kidd, R B (editors). Geological Society of London Special Publication, No. 70.

Wright, T. 1851. A stratigraphical account of the section at Hordwell, Beacon and Barton Cliffs, on the coast of Hampshire. Annals and Magazine of Natural History, Vol. 72, 433–446.

Wymer, J J. 1996. The English Rivers Palaeolithic Survey. 7–22 in The English Palaeolithic Reviewed. (Salisbury: Wessex Archaeology for English Heritage.)

Wymer, J J. 1999. The Lower Palaeolithic Occupation of Britain. No. 1 and 2. (Salisbury: Wessex Archaeology and English Heritage.)

Ziegler, P A. 1981. Evolution of sedimentary basins in north-west Europe. 3–39 in Petroleum geology of the continental shelf of north-west Europe. Illing, L V, and Hobson, G D (editors). (London: Heydon.)

Ziegler, P A. 1990. Geological atlas of western and central europe (Maatschappij BV, The Hague: Shell International Petroleum.) ISBN 9066441259.

Uncited Excursion Guide References

Barnard, T. 1948. Whitsun field meeting to the Isle of Wight: 23rd–26th June, 1947. Proceedings of the Geologists’ Association, Vol. 59, 229–233.

Blake, J F, and Leighton, T. 1892. Excursion to the Isle of Wight, March 26th–31st, 1891. Proceedings of the Geologists’ Association, Vol. 12, 145–173.

Colenutt, G W, and Hooley, R W. 1919. Excursion to the Isle of Wight: Whitsuntide, 1919. Proceedings of the Geologists’ Association, Vol. 30, 133–138.

Colenutt, G W, Hooley, R W, and Young, G W. 1906. Excursion to the Isle of Wight. Proceedings of the Geologists’ Association, Vol. 19, 357–366.

Hall, S. 1933. Field meeting in the Isle of Wight, Whitsun May 23–26, 1931. Proceedings of the Geologists’ Association, Vol. 44, 184–186.

Herries, R S, and Monckton, H W. 1896. Excursion to the Tertiary beds of the Isle of Wight, Easter 1895. Proceedings of the Geologists’ Association, Vol. 14, 99–111.

Middlemiss, F A, and Bromley, R G. 1962. Field meeting on the Lower Greensand and Chalk in the Isle of Wight. Proceedings of the Geologists’ Association, Vol. 73, 449–454.

Radley, J D. 1994. Field meeting, 24–25th April, 1993: the Lower Cretaceous of the Isle of Wight. Proceedings of the Geologists’ Association, Vol. 105, 145–152.

Stinton, F C. 1964. Field meeting in the Oligocene of north-west Isle of Wight. Proceedings of the Geologists’ Association, Vol. 75, 87–92.

Stinton, F C. 1971. Easter field meeting in the Isle of Wight; Thursday, 26 March to Tuesday, 31 March 1970. Proceedings of the Geologists’ Association, Vol. 82, 403–411.

Tawney, E B. 1882. Excursion to the east end of the Isle of Wight: Whit Monday, June 6th, and two following days, 1881. Proceedings of the Geologists’ Association, Vol. 7, 185–189.

Figures and plates

Figures

(Frontispiece 1) Geological succession in the Isle of Wight Palaeogene–Quaternary.

(Frontispiece 2) Geological succession in the Isle of Wight Devonian–Cretaceous.

(Figure 5). Deep boreholes (see also (Figure 9): 1. Norton 1, SZ38NW18; 2. Wilmingham 1, SZS38NE9; 3.Bouldnor Copse 1, SZ39SE1; 4. Sandhills 1, SZ49SE3; 5. Sandhills 2, SZ48NE55; 6. Cowes1 (Bottom Copse), SZ59SW17; 7. Arreton 1, SZ58NW2; 8. Arreton 2, SZ58NW1; 9. Chessell 1, SZ48NW11." data-name="images/P937077.jpg">(Figure 1) The outline topography, principal towns and locations of the principal deep boreholes on the Isle of Wight. The line of section shown is illustrated in (Figure 5). Deep boreholes (see also (Figure 9): 1. Norton 1, SZ38NW18; 2. Wilmingham 1, SZS38NE9; 3.Bouldnor Copse 1, SZ39SE1; 4. Sandhills 1, SZ49SE3; 5. Sandhills 2, SZ48NE55; 6. Cowes1 (Bottom Copse), SZ59SW17; 7. Arreton 1, SZ58NW2; 8. Arreton 2, SZ58NW1; 9. Chessell 1, SZ48NW11.

(Figure 45)." data-name="images/P937078.jpg">(Figure 2) The Isle of Wight Areas of Outstanding Natural Beauty and designated Heritage Coastline. The SSSI sites are indicated by a symbol (see (Figure 45).

(Figure 3) The topography of the Isle of Wight as demonstrated in a shaded-relief digital terrain model. This image has been created from the NEXTMap Britain TM Elevation dataset and has been produced by exaggerating the terrain by a factor of two.

(Figure 4) The structural setting of the Isle of Wight within the broader Wessex Basin (inset), and a generalised view of the surface structures based on the currently available geological map.

(Figure 5) An example of the interpretation of seismic data from the Isle of Wight. Based on fig. 4 in Evans et al. (2011). Calibration and interpretation of a seismic reflection line tying the Sandhills 1 Borehole. The interpretation is of a large reverse fault cutting the northern limb of the Sandown Anticline and arising from reversal of movement on an underlying major syndepositional normal fault. The reverse fault propagated upwards from the normal fault in the overlying post-rift strata during inversion. Possible minor reverse faulting propagating to the north from the main fault is also indicated.

(Figure 6) The decultured HiRES TMI anomaly data shown as a shaded-relief image with a linear colour scale. Shading from the north-east.

(Figure 7) Ternary colour plot of the relative contributions made by the percentage of potassium (K), thorium (eTh) and uranium (eU) components of the dataset. The most striking geological control is illustrated by the almost null response (black) of the high purity calcium carbonate Chalk Group outcrop, with higher concentrations of all three radioisotope elements showing as white where clays predominate.

(Figure 8) Images of apparent conductivity data obtained for the (a) 0.9 kHz and (b) 25 kHz frequency bands.

(Figure 9) Stratal thicknesses encountered in the nine deep hydrocarbon exploration boreholes on the Isle of Wight. Notes. *These thicknesses represent an undivided Upper Palaeogene above the Barton Group. The thickness shown is likely to include representatives of the Headon Hill, Bembridge Limestone and Bouldnor formations.

(Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present." data-name="images/P937086.jpg">(Figure 10) (Opposite) A composite of the concealed bedrock strata encountered beneath the Isle of Wight. North of the Isle of Wight Monocline, the Monk’s Bay Sandstone Formation of the Lower Cretaceous Lower Greensand Group (Figure 13) cuts down to the Cornbrash Formation, whilst to the south the full succession is present.

(Figure 11) The depth to the pre-Permian basement beneath the Isle of Wight (modified from Smith, 1985, red contours in hundreds of metres). The fault traces are interpreted on the Variscan basement surface. Low angle extensional faults are shown with a window of the fault plane itself (in grey) between the footwall and hanging-wall blocks. Thickness contours for the Sherwood Sandstone Group, and the Mercia Mudstone and Penarth groups (undifferentiated), are indicated by lines in blue (modified from Hamblin et al., 1992).

(Figure 12) Outline of the Early Cretaceous timechart based on Gradstein et al. (2012). Lithostratigraphical correlation derived from various sources.

(Figure 13) The Cretaceous strata at outcrop in the Isle of Wight. A further 430 m of the Wessex Formation are present in the subcrop (see (Figure 9)).

(Figure 14) Generalised coastal section of the Wessex Formation in Compton Bay to Brighstone Bay (modified after Insole et al., 1998) incorporating an outline lithological log for the section east of Sudmoor Point modified after Stewart (1981a) and Martill and Naish (2001).

(Figure 15) A summary of the Vectis Formation: a. The section in Brighstone Bay between Barnes Chine and Atherfield Point on the south-west coast. b. The section within Sandown Bay on the east coast. c. A correlation of the formation between its three outcrops on the island (modified after Radley and Barker, 1998, 2000; and Martill and Naish, 2001).

(Plate 4)." data-name="images/P937092.jpg">(Figure 16) The coastal outcrop of the Lower Greensand Group between Atherfield Point and Rocken End, and outline lithostratigraphical section. Modified after White (1921, fig. 6) and Insole et al. (1998). See also (Plate 4).

(Figure 17) The classification of the Upper Greensand Formation within The Undercliff, Ventnor, after Jukes-Browne and Hill (1900). Outline graphic log for the Upper Greensand section exposed in Gore Cliff (modified from descriptive section in Jukes-Browne and Hill, 1900; White, 1921).

(Figure 18) The Chalk Group terminology for the Southern Chalk Province (JB7 = Jukes-Browne Bed 7).

(Figure 19) Outline of the Late Cretaceous timechart after Gradstein et al. (2012). Correlation of the UK Chalk lithostratigraphical units is based on Jarvis et al. (2006) and Jenkyns et al. (1994).

(Figure 20) The distribution of localities from which details of the Chalk Group were derived during the survey.

(Figure 21a) The Chalk Group succession exposed in the coastal cliffs between Culver Cliff and Whitecliff Bay. The outline correlation of the succession is plotted against the carbon isotope curve of Jarvis et al. (2006).

(Figure 21b) The outline lithostratigraphical log of the Culver Down succession based on the sections presented in Jarvis (written communication, 2011), Jarvis et al. (2006), Mortimore et al. (2001) and BGS interpretations. Note: For the zone names in a. refer to (Figure 18).

(Figure 22) The full succession of the Seaford Chalk to Portsdown Chalk visible within Scratchell’s Bay (Hopson et al., 2011a).

(Figure 23) The Palaeogene strata at outcrop on the Isle of Wight.

(Figure 24) The terminology used herein compared to that in King (in press).

(Figure 25) The Palaeogene Period, with an outline correlation of the strata present on the Isle of Wight.

(Figure 26) a. The Palaeogene coastal exposure within Whitecliff Bay (after White, 1921 and Insole et al., 1998). b. Outline graphic log of the London Clay Formation to Becton Sand Formation within Whitecliff Bay. Modified from Daley (1999a) after Huggett and Gale (1997). Divisions A to E of the London Clay after King (1981).

(Figure 27) a. The Palaeogene exposure in Alum Bay modified after White (1921) and Insole et al. (1998). b. The outline lithostratigraphical log modified from Daley (1999a) and earlier authors (King, 1981; Plint, 1983; Edwards and Freshney, 1987).

(Figure 28) A correlation based on an interpretation of the gamma log signatures of selected boreholes linked to the Alum Bay and Whitecliff Bay coastal sections. (Written communication, A J Newell, 2013).

(Figure 29) a. The Headon Hill Formation exposure between Hatherwood Point and Totland Bay (after Daley and Insole, 1984; Insole et al., 1998). b. Graphic logs for the three principal exposures of the Headon Hill Formation based on Daley (1999a) after Edwards (1967), Insole and Daley (1985) and various other authors.

(Figure 30) A correlation based on a lithofacies interpretation of selected borehole logs for the Palaeogene strata younger than the Becton Sand Formation from west to east across the Isle of Wight. (A J Newell, written communication, 2013).

(Figure 31) Outline graphic logs of the type section of the Bembridge Limestone Formation in Whitecliff Bay and the two partial exposures in Gurnard Bay (north-west coast) and inland at Prospect Quarry (west Wight). Modified after Armenteros et al. (1997).

(Figure 32) The principal exposures of the Bembridge Marls at Whitecliff, Gurnard and Hamstead Cliffs. Modified after Daley (1973, 1999a).

(Figure 33) Outline log of the Hamstead and Cranmore members of the Bouldnor Formation within the cliffs at Bouldnor/Hamstead. Modified after Daley (1999a).

(Figure 35) Outcrops of the Quaternary strata on the Isle of Wight derived from the currently available digital dataset with an interpretation of the relative correlation.

(Figure 34) (Opposite) The outline of the Quaternary succession on the Isle of Wight and its relationship to the Solent River story. Left-hand columns derived from Lugowski and Ogg (2011) without revision (note the younger Devensian and younger Ipswichian boundaries are slightly too old).

(Figure 36) Quaternary lithostratigraphy applied to the new geological map with the relationship to the older survey terms indicated.

(Figure 37) The offshore bathymetry in the area around the Isle of Wight.

(Figure 38) The Priory Bay Section [SZ 635 900], within the Wootton Gravel Complex Member (after Wenban-Smith et al., 2009). This section shows a complex of interbedded sand, gravel and clay that contains many Palaeolithic artefacts. The basal Units III have been OSL dated at 367 ± 49 ka BP whilst those within the Unit IV have a date of 284 ± 29. This indicates an age range from MIS 11 or 10 to MIS 8 with the unit immediately beneath the local soil horizon being much younger with an OSL date of 41.3 ± 2.7 ka BP indicating MIS 3. The basal bedded gravel unit is considered as a fluvial or nearshore marine deposit with the later units IV and V being a soliflucted deposit under cold climatic conditions. Interpretations of abraded artefacts correlate the basal Unit III with the Slindon–Goodwood Raised Beach on the mainland or derived directly from such contemporaneous deposits.

(Figure 39) Diagrammatic representation of the landslide susceptibility ‘zones’ within the Wealden Group on the south-west coast (after Jenkins et al., 2011).

(Figure 40) Outline landslide types related to lithostratigraphy in the Palaeogene.

(Figure 41) Mineral extraction sites on the Isle of Wight 2013. a. Working status b. Commodity extracted c. End uses. Source BGS Britpits database www.bgs.ac.uk/products/minerals/BRITPITS.html.

(Figure 42) Potential geotechnical constraints of the strata encountered in the district.

(Figure 43) The designated Sites of Special Scientific Interest (SSSI) on the Isle of Wight.

(Figure 44) The terminology of the human occupation of the British Isles. *Vectis is an old term for the Isle of Wight. MIS = Marine Isotope Stage, a notation based on alternating warm and cold periods within the Quaternary palaeoclimate deduced from oxygen isotope data from core samples. MIS 1 is the present with odd numbers indicating other warmer interglacial intervals.

(Figure 45) Terms commonly used to distinguish subdivisions of the Flandrian (Holocene) Stage and the latest Devensian Stage. * Blytt-Sernander classification based on the work of Blytt (1876) and Sernander (1908).

Plates

(Plate 1) Top of Brighstone Sandstone Member at beach level, overlain by grey and red mudstone typical of the Wessex Formation in the coastal section between Chilton Chine and Cowleaze Chine. The upper part of the cliff is being cut back by landsliding, [SZ 41521 81930]. P774638.

(Plate 2) The Vectis Formation in the coastal section between Chilton Chine and Cowleaze Chine. The thick massive sandstone bed in the upper cliff is the Barnes High Sandstone Member. A thin succession of grey mudstone belonging to the Shepherd’s Chine Member is present in the upper cliff above the Barnes High Sandstone Member that itself overlies grey mudstone of the Cowleaze Chine Member. The lower cliff comprises a prominent pale yellowish grey sandstone (the ‘White Rock’) overlying red and grey mudstone of the Wessex Formation, [SZ 44218 80204]. P774666.

(Plate 3) The Red Cliff in Sandown Bay on the northern limb of the Sandown Anticline (Figure 4). The yellow-brown sandstone of the Ferruginous Sandstone Formation overlie the grey silty clay of the Atherfield Clay Formation to the left of the photograph, [SZ 62360 85367]. P683596.

(Plate 4) A panorama of the Lower Greensand Group in Chale Bay on the south-west coast looking south-eastward towards St Catherine’s Point. The grey silty clay of the Atherfield Clay Formation forms the lowest slopes at the base of the cliff in the near view with the Ferruginous Sands Formation forming the eastward-dipping succession of yellow-brown sands and pale grey-brown silty clays to Blackgang Chine and Rocken End near the Point. The Sandrock Formation forms the mid-cliff pale yellow buttresses in the far distance with the Monks Bay Sandstone Formation immediately above. The Gault and Upper Greensand formations form the upper cliff at Blackgang Chine up to the steep buttress of Gore Cliff on the horizon in the right third of the image. This stretch of the cliffs forms the principal exposure of the Ferruginous Sands Formation, [SZ 45580 79071]. P774554.

(Plate 7), [SZ 57471 86575]. P683935." data-name="images/P683935.jpg">(Plate 5) Knighton Sand Quarry exposes about 45 m of the Lower Greensand Group on the northern limb of the Sandown Anticline and is the principal inland exposure of the Sandrock Formation and the overlying Monk’s Bay Sandstone Formation. This part of the Sandrock Formation is represented here by a coarsening-upward succession of dark grey laminated silty clay that passes up (middle of lower face) into trough and tabular cross-bedded fine- to medium-grained yellow sand. A sharp contact with a pale grey-brown laminated and finely bedded very fine sandy silty clay, representing the lower unit of another truncated coarsening-upwards cycle is the youngest unit present in the formation and can be seen in the middle of the upper face. Overlying this laminated unit, above the dark overhang representing an erosional transgressive surface, is the dark orange-brown coarse gritty ferruginous sandstone of the Monk’s Bay Sandstone Formation (see also (Plate 7), [SZ 57471 86575]. P683935.

(Plate 6) The type locality of the Monk’s Bay Sandstone Formation on the south-east coast near Ventnor. The bright yellow sand of the Sandrock Formation is overlain by the indurated ferruginous gritty sandstone (steeper upper cliff) of the Monk’s Bay Sandstone Formation (formerly Carstone Formation). The basal Gault Formation forms the shallow capping to the cliff, [SZ 58099 78122]. P732203.

(Plate 7) The basal unit of the Monk’s Bay Sandstone at Knighton Quarry. The well-bedded dark yellow-brown, coarse gritty sandstone rests above an erosional transgressive surface above a laminated unit at the top of the Sandrock Formation. This part of the Monk’s Bay Sandstone is characterised by indurated ferruginous gritty sandstone with a framework of concretionary ironstone and weakly bedded ferruginous medium-grained sandstone. Units are about 30 cm thick in this image, [SZ 57476 86654]. P683918.

(Plate 8) The characteristic dark clay of the Gault Formation and pale interbedded silt and clays of the ‘Passage Beds’ (the basal Upper Greensand Formation) on the south-west coastal section just west of Compton Chine, [SZ 36715 85243]. P774480.

(Plate 49)." data-name="images/P201734.jpg">(Plate 9) The Upper Greensand Formation exposed at Gore Cliff about 2 km south-west of Niton. The informal units of the ‘Chert Beds’ (6.7 m) in the upper part of cliff slightly overhang the ‘Freestones’ (1.8 to 2.4 m) immediately below them. The lower cliff exposes sandstone with concretions of the lower part of the Upper Greensand with the talus slope covering the Gault Formation and the ‘Passage Beds’. The West Melbury Marly Chalk Formation with the Glauconitic Marl Member at its base and a variable thickness of chalky Quaternary talus forms the sloping ground above the ‘Chert Beds’ [SZ 49500 75500]. P201734 (A01783). Compare with (Plate 49).

(Plate 10) The road cutting in the Upper Greensand Formation on the B3399 north of Brook Hill Church, [SZ 39639 84830]. P732205 to P732209.

(Plate 11) Oblique aerial view of Culver Cliff and Culver Down looking north-westward (see (Figure 21). The steeply dipping monoclinal northern limb of the Sandown Anticline exposes the full Chalk Group succession in Sandown Bay and around this headland. The cliffs in this view expose the upper part of the Lewes Nodular Chalk Formation — on the left of the image at the two sea caves known as the Nostrils. The Seaford Chalk and Newhaven Chalk are seen in Horseshoe Bay, and the Culver Chalk and Portsdown Chalk formations are on the right of the image above Whitecliff Ledges. The highest part of the Portsdown Chalk, beyond the cliff-fall debris cone, is exposed in Whitecliff Bay below the caravan site at the top of the image. The grid reference for this site [SZ 63790 85470] is the position of the marked angle in the coastal fence left centre of the image. P680972.

(Plate 12) Oblique aerial view of The Needles, Scratchell’s Bay and West High Down to Tennyson Down. Scratchell’s Bay and The Needles expose the White Chalk Subgroup from the upper Lewes Nodular Chalk through to the Portsdown Chalk. The cliffs on the right of the image, below West High Down and Tennyson Down (in the distance), are in the Seaford Chalk, Lewes Nodular Chalk and uppermost New Pit Chalk formations. The point, known as Sun Corner, below the triangular grass field is at [SZ 29840 84620]. P681055.

(Plate 13) The West Melbury Marly Chalk Formation passing up into the basal part of the Zig Zag Chalk Formation exposed in the cliffs in Compton Bay. The formation comprises thin dark grey marly chalk and hard off-white chalk limestone in couplets demonstrating a cyclicity controlled by Milankovitch orbital cycles, [SZ 36220 85450]. P692145. Compare fig. 3.59 of Mortimore et al. (2001).

(Plate 14) (Below) View of the limestone–marl couplets within the lower part of the Zig Zag Chalk Formation. Hammer 30 cm long. Exposure in the track leading south-westward from Garstons. Gatcombe, Isle of Wight, [SZ 47780 85770]. P612400.

(Plate 15) Exposure of the Holywell Nodular Chalk Formation in the more southerly (Morton Manor) of two large quarries at Brading, Isle of Wight. The contact of Plenus Marls Member and the Melbourn Rock Member above is marked by the hammer (35 cms), [SZ 60239 86496]. P692239.

(Plate 16) Mytiloides-rich, grainy, detrital chalk characteristic of the upper part of the Holywell Nodular Chalk Formation. Sandown Bay, north, on the foreshore below Culver Down, [SZ 63380 85420]. P692044.

(Plate 17) Cheverton Quarry in the valley east of Cheverton Down. The typical large blocky, white, moderately hard chalk with well-developed conjugate joint sets of the New Pit Chalk Formation is overlain on the upper terrace by the intensely hard, nodular chalks of the Lewes Nodular Chalk Formation [SZ 45093 84301]. P692233.

(Plate 18) Exposure of the Lewes Nodular Chalk Formation at the eastern end of Brook Down. Steeply dipping chalk in this small pit shows the New Pit Chalk (mainly concealed in the talus in this image) and the overlying Lewes Nodular Chalk formations. A good exposure of nodular and phosphatic nodular chalk equivalent to the Ogbourne Hardground is indicated by a hammer (right lower centre of image), [SZ 39430 85106]. P774500.

(Plate 19) Horseshoe Bay beneath Culver Down. This view shows the steeply northward-dipping middle and upper part of the Seaford Chalk Formation on the left with its characteristic regularly spaced large nodular flint seams, with the Newhaven Chalk Formation on the right. The grassed platform to the left of the image is at the White Horse Marl with about 30 m of the highest Seaford Chalk represented in the vertical cliff above, [SZ 63930 85540]. P692108.

(Plate 20) Freshwater Bay East—the most accessible Seaford Chalk Formation exposure on the island. Characteristic nodular flint seams, spaced regularly throughout the formation, highlight the steep dip on the northern limb of the Brighstone Structure, [SZ 34814 85663]. The top of the cliff shows an exposure of a fluvial sequence associated with the Western Yar River Formation and shows examples of dissolution pipes filled with Quaternary sediments. P683646.

(Plate 21) A typical anastomosing marl seam within the Newhaven Chalk Formation exposed in Scratchell’s Bay, [SZ 29675 84767]. Hammer 28 cms. P699960.

(Plate 22) A typical view of the Culver Chalk Formation in Scratchell’s Bay, with its large blocky structure and consistent large nodular flint seams, [SZ 29595 84795]. P700032.

(Plate 23) The Needles at the western end of Scratchell’s Bay. All three of the Needles and the immediate Needles Promontory are made of the Portsdown Chalk Formation. The white smooth chalk, nodular flint seams and air-weathered thin marl seams typical of the lower to middle Portsdown Chalk are clearly visible, [SZ 29490 84835]. P700021.

(Plate 24) A general view of the Palaeogene exposure at Alum Bay. View looking east from The Needles approach road. The highest part of the steeply dipping Portsdown Chalk forms the steep cliff on the right (south) of the image with the reddish brown clay of the Reading Formation in the shaded valley immediately to the left. The London Clay Formation (greyish brown) and the brightly coloured sand and clay of the Bracklesham Group form the steeply dipping units northward to the landing stage in the left centre of the photograph. Further north the Barton Group units form the minor valley (Alum Bay Chine) that carries the chairlift and steps to the beach and also contains a major reverse fault (mostly obscured) that divides the steeply dipping strata to the south from the low-angle northerly dipping Headon Hill Formation (Solent Group) strata towards Hatherwood Point. The promontory in the left background is Cliff End with the large white Fort Albert building at sea level [SZ 29619 84888]. P683972 to P683974.

(Plate 25) The Chalk–Reading Formation contact at Alum Bay [SZ 30680 85230]. This palaeokarst surface, with a local topography of between 1 and 3 m, separates the Portsdown Chalk Formation and the brightly coloured Reading Formation clay. P691977.

(Plate 26) The lower part of the London Clay Formation at Whitecliff Bay [SZ 63882 85855]. Top of Division A is marked by the paler sand unit and indistinct basal pebble bed within the pinnacle. North, and succession ‘younging’, is to the right of the image. P683844.

(Plate 27) The Whitecliff Sand and Portsmouth Sand members at Whitecliff Bay, [SZ 63902 85939]. P692056.

(Plate 28) The middle part of the Wittering Formation (Bracklesham Group) exposed at Whitecliff Bay [SZ 63929 86053]. The hammer is estimated to be approximately at the 176 m marker on the section presented as fig. 2 in Huggett and Gale (1997). P683861.

(Plate 29) The Bracklesham Group at Alum Bay taken from West High Down [SZ 30417 85069]. The greater part of the group is visible and gives rise to the famous ‘coloured sands’. The top of the lower leaf of the Wittering Formation is on the extreme right of the photograph succeeded northward by the lower leaf of the Poole Formation, and the upper leaves of the Wittering and the Poole formations. The Marsh Farm grey clays and the pale yellow to dark grey Branksome Sand Formation form the prominent ridge from the cable car gantry on the cliff top to the foreshore. The bright yellow Boscombe Sand Formation (topmost Bracklesham Group) comes to the foreshore at the landing stage on the extreme left. P683972 to P683974.

(Plate 30) Aerial view looking towards the south-east of Hatherwood Point and Alum Bay Chine. The cliff section exposes the whole of the Headon Hill Formation with the three prominent limestone members marked by steep bluffs that correspond up-sequence to the How Ledge Limestone, the Hatherwood Limestone and the Lacey’s Farm Limestone (Figure 29). The underlying softer clay and sand of the Barton Group form the chine on the right of the landing stage and the lower part of the cliffs are founded in the undivided Becton and Chama sands (Becton Sand Formation). P681038.

(Plate 31) View of the Bembridge Limestone outcrop in Whitecliff Bay, looking north towards the point at Black Rock, [SZ 64150 86280]. P692084.

(Plate 32) Small coastal section between Whitecliff Bay and the Bembridge Foreland [SZ 64492 86477]. Image shows the top of Bembridge Limestone overlain by the basal beds of the Bembridge Marls including a prominent limestone rib above the Oyster Bed. P774710

(Plate 33) The Palaeogene succession preserved in a solution hollow beneath clay-with-flints in Brighstone Down [SZ 431 849]. Auger 2.3 m. P774472.

(Plate 34) The Bembridge Raised Beach Deposit. Looking east-north-east from the coastal path south of the Coastguard Station [SZ 65305 97226]. P774688.

(Plate 35) The King’s Manor Gravel Member in the exposure on the west side of Freshwater Bay [SZ 34514 85610]. P683653.

(Plate 36) One of a number of gravel pits [SZ 30881 85847] at the summit of Headon Hill, south of Totland. The Headon Hill Sand and Gravel Member river terrace deposits comprise alternations of variably clayey flint gravel, gravelly sand and sand, commonly with extensive iron oxide cementation. Irregular and impersistent bedding characterises the whole deposit. Ruler 25 cm. P875783.

(Plate 37) Crag of well-cemented coarse angular flint gravel of the in-situ fluvial St Georges Down Gravel Member, 450 m south-east of Standen House [SZ 51000 86830], Newport. P692170.

(Plate 38) Cryoturbated gravels at the western end of St Georges Down and associated soil horizons within the Gravelly Head 2 deposits closely associated with the St George’s Down Gravel Member [SZ 50634 87855]. P699976.

(Plate 39) Combeley Farm Quarry [SZ 53761 88848] exposing the Gravelly Head 1 and the associated Robins Hill Palaeosol (below figure) Member. P774721.

(Plate 40) A 3 m exposure of the Langbridge Gravel Member at Hale Manor Farm near Horringford [SZ 5413 8468]. P875640.

(Plate 41) The first river terrace deposit overlain by blown sand on the cliff to south-east of Whale Chine [SZ 47266 77920]. The Quaternary deposits overlie the grey laminated shales of the Old Walpen Chine Member of the Ferruginous Sand Formation. P774540.

(Plate 42) Aerial view of The Undercliff at Ventnor, looking north-north-west. Massive rotational slides underlie the whole town. The degraded back scar forms the hinterland to the residential area. P681156.

(Plate 43) Tennyson Down looking westward towards The Needles. Cliff-top fissure cracks in the northward-dipping White Chalk Subgroup indicate potential failure of cliffs. Cliff face shows remnant debris from earlier failures [SZ 31603 85028]. P769938.

(Plate 44) Portsdown Chalk Formation exposed on the southern side of Alum Bay [SZ 30260 85013], dips steeply towards the camera. P769937.

(Plate 45) Recently active mudflow in the Reading Formation at Alum Bay [SZ 30580 85240]. P691968.

(Plate 46) Small phreatic dissolutional conduit within the Newhaven Chalk Formation at Downend Quarry near Arreton. [SZ 55058 87530]. P875565.

(Plate 47) Barn at Yaverland Manor with a variety of stone types incorporated into the wall including limestones and sandstones from the Upper Greensand, Monk’s Bay Sandstone, Chalk, Bembridge Limestone and other Early Cretaceous and Palaeogene units [SZ 61440 85860]. P699926.

(Plate 48) Stone Barn at Adgestone Farm made out of partially dressed Chalk blocks [SZ 59500 86260]. P699928.

(Plate 49) Gore cliff landslide 1928. This picture is taken whilst the landslide of the 26th July 1928 was occurring. It is estimated that 100 000 tonnes of rock was involved in this slide. The road from Niton to Blackgang was blocked and never reopened. This fall triggered another landslide below the cliff in the following September. Compare (Plate 49)." data-name="images/P201734.jpg">(Plate 9) that predates this image.

(Plate 50) Large solution features into the Seaford Chalk Formation beneath the St George’s Down Gravel Member. Chalk pinnacles (in the foreground), once encountered, generally limit extraction of the sand and gravel [SZ 50758 87925]. P875526.

Figures

(Figure 9) Stratal thicknesses encountered in the nine deep hydrocarbon exploration boreholes on the Isle of Wight. Notes.

*These thicknesses represent an undivided Upper Palaeogene above the Barton Group. The thickness shown is likely to include representatives of the Headon Hill, Bembridge Limestone and Bouldnor formations.

1 Strata Norton 1 Wilmingham 1 Bouldnor Copse 1 Sandhills 1 Sandhills 2 Cowes 1 (Bottom Copse) Arreton 1 Arreton 2 Chessell
2 Borehole number SZ38NW/18 SZ38NE/9 SZ39SE/1 SZ49SE/3 SZ48NE/55 SZ59SW/17 SZ58NW/2 SZ58NW/1 SZ48NW/10
3 Grid reference [SZ 34006 89098] [SZ 36620 87790] [SZ 38537 90179] [SZ 45700 90850] [SZ 46129 89840] [SZ 50036 94161] [SZ 53070 85640] [SZ 53200 85800] [SZ 40912 85023]
4 OD 43.5 ft (13.26 m) 31 ft (9.45 m) 125.5 ft (38.25 m) 74 ft (22.56 m) 96.31 ft (32.53 m) 24 ft (7.32 m) 125 ft (35.1 m) 105 ft (32 m) 263 ft (80.16 m)
5 Bouldnor Formation 88.4 46.4 74.1 - - - -
6 Bembridge Limestone Formation 10.1 2.4 6.1 - - - -
7 Headon Hill Formation 53.6 167.9" 53.1 83.6 81.0 189.9" - - -
8 Barton Group 126.2 82.3 178.3 185.4 188.6 33.8 - - -
9 Bracklesham Group 239.3 169.2 161.8 161.5 171.6 202.7 - - 146.9
10 Thames Group 68.3 71.6 129.0 119.5 124.1 94.8 - - 74.4
11 Lambeth Group 35.1 25.9 42.4 53.3 51.8 39.0 - - 55.5
12 White Chalk Subgroup 313.6 323.1 273.7 287.4 299.0 285.9 - - 376.7
13 Grey Chalk Subgroup 58.2 68.0 63.7 68.9 87.8 68.9 - - 59.1
14 Upper Greensand Fm 45.5 24.7 29.6 21.0 28.0 22.3 - - 33.5
15 Gault Formation 16.1 32.0 27.7 33.8 46.9 36.3 - - 27.4
16 Lower Greensand Gp 4.0 10.4 3.0 5.2 7.9 4.9 64.0 57.9 21.3
17 Wealden Group - - - - - - 615.7 619.4 54.6
18 Purbeck Group - - - - - - 113.7 99.7 31.1
19 Portland Group - - - - - - 26.5 27.4 15.8
20 Kimmeridge Clay Fm - 23.5 - - - 5.2 337.4 336.8 67.3
21 Corallian Group 24.1 29.0 - - - 30.8 65.8 68.9 32.6
22 Oxford Clay Formation 118.9 114.3 41.5 - 8.2 134.7 137.2 132.3 146.0
23 Kellaways Formation 13.4 20.7 12.8 - 16.5 18.0 30.2 23.8 20.4
24 Great Oolite Group 118.3 146.2 117.0 119.2 127.1 129.9 142.3 145.4 167.6
25 Inferior Oolite Group 12.2 34.7 10.4 9.8 - 31.7 52.4 70.4 24.1
26 Lias Group 131.2 80.2 51.2 41.4 - 207.9 - 383.4 149.0
27 Penarth Group 16.8 15.8 7.9 15.5 - 18.0 - 25.0 19.8
28 Mercia Mudstone Gp 246.4 244.8 205.1 157.0 - 173.4 - 135.3 203.9
29 Sherwood Sandstone Gp 53.9 - 33.5 14.3 - - - 291.4 104.9
30 Devonian - - 10.7 33.2 - 51.2 - 388.3 93.3

(Figure 17) The classification of the Upper Greensand Formation within The Undercliff, Ventnor, after Jukes-Browne and Hill (1900). Outline graphic log for the Upper Greensand section exposed in Gore Cliff (modified from descriptive section in Jukes-Browne and Hill, 1900; White, 1921).

Bed Description Thickness m
F Sand with layers of calciferous concretions often partly phosphatised 1.8
E Chert beds 6.7–7.3
D Firestone and freestone (2.4–5.5 m) 9.1–12.1
C Sandstone with phosphatic nodules and courses of large calcareous doggers
B Rough sandstone with irregular concretions 9.1–12.1
A Bluish sandy clay or micaceous silt (Passage Beds) 13.1–15.2

(Figure 24) The terminology used herein compared to that in King (in press)

Special sheet and this sheet explanation

King (in press)
Whitecliff Bay and east IoW Alum Bay and west IoW Whitecliff Bay and east IoW Alum Bay and west IoW

Solent Group

Bouldnor Formation

 Cranmore Member Hamstead Member Bembridge Marls Mbr.

Solent Group

Bouldnor Formation

 Cranmore Member
Hamstead Member
Gurnard Member

Bembridge Limestone Formation

Bembridge Limestone Formation

Headon Hill Formation

 Seagrove Bay Member

Osborne Member

Fishborne Member Lacy's Farm Member Cliff End Member Hatherwood  Limestone Member

Linstone Chine Member

Ryde Formation

 St Helens Member Osborne Member Fishborne Member Nettlestone Member Fort Albert Member Lacy's Farm Limestone Mbr. Cliff End Member Hatherwood Limestone Mbr. Linstone Chine
Member
Colwell Bay Member

Colwell Bay Formation
Totland Bay Member

Totland Bay Formation

Barton Group

Becton Sand Formation

Chama Sand Formation

Becton Formation

 Chama Bed

Barton Clay Formation

Barton Clay Formation
Boscombe Sand Fm.

Bracklesham Group

Bracklesham Group

 Boscombe Sand Fm.
Selsey Sand Fm. Branksome Sand Fm. Selsey Formation Branksome Formation

Marsh Farm Formation

Marsh Farm Formation
Poole Fm. (upper) Poole Fm. (upper tongue)
Wittering Fm. (upper) Wittering Fm. (upper tongue)
Earnley Sand Fm. Poole Fm. (lower) Earnley Fm Poole Fm. (lower tongue)
Wittering Fm. Wittering Fm. (lower) Wittering Fm Wittering Fm. (lower tongue)

Thames Group

 London Clay Portsmouth Sand and Whitecliff Sand mem- bers

Thames Group

 London Clay Fm Whitecliff (Sand) Member Portsmouth (Sand) Member
Formation Undivided on map Divisions A to E
'London Clay Basement Bed' Harwich Fm Tilehurst Member
Lambeth Group Reading Fm. Lambeth Group Reading Fm.

(Figure 36) Quaternary lithostratigraphy applied to the new geological map with the relationship to the older survey terms indicated

New map term Formation Sub- group Group Age Term used within old surveys
Clay-with-flints

Residual Deposits Group

 ?Pliocene to Early Pleistocene Angular flint gravel of the Chalk downs
Head 1 Early to Mid Pleistocene Not mapped
Kings Manor Gravel Member

Western Yar River Formation

Solent Catchments Subgroup

Britannia Catchment Group

Mid Pleistocene to Late Pleistocene

 Gravel terrace
Downton Farm Gravel Member Gravel terrace
Backet's Copse Gravel Member Plateau gravel
Sudmoor Point Gravel Member Plateau gravel
Freshwater Gravel Member Plateau gravel
Headon Warren Sand and Gravel Member Plateau gravel
Bembridge Raised Beach Member

Solent River Formation

 Bembridge Raised Beach
Wootton Gravel Complex Member Plateau gravel and marine gravel
Steyne Wood Clay Member Brickearth
Bouldnor Copse Gravel Member Plateau gravel
Knight's Cross Gravel Member Plateau gravel
Twenty Acre Gravel Member Plateau gravel
Dunnage Copse Gravel Member Not mapped
Great Wood Gravel Member Not mapped
Merstone Clay Member

Medina River Formation

 Alluvium
Seaclose Park Gravel Member Not mapped
Bridge Farm Gravel Member Gravel terraces
Blackwater Hollow Gravel Member Plateau gravel
Robins Hill Palaeosol Member Brickearth
Bleak Down Gravel Member Plateau gravel
St George's Down Gravel Member Plateau gravel
Carpenters Farm Gravel Member

Eastern Yar River Formation

 Not named
Langbridge Gravel Member Gravel terraces
Hale Common Gravel Member Gravel terraces
Cockerel Gravel Member Gravel terraces
Bobberstone Farm Gravel Member (Wroxall Brook) Gravel terraces
Whiteley Bank Gravel Member (Wroxall Brook) Gravel terraces
Froghill Farm Gravel Member (Wroxall Brook) Gravel terraces
Gravelly Head 2 Medina Catchment Not mapped
Gravelly Head 1 Present in all formations above Not mapped
River terrace deposits undifferentiated

Stand alone
terms

Holocene

 Gravel terraces
Head Not mapped
Peat Peat
Alluvium Alluvium
Estuarine alluvium undifferentiated

Includes informal Yarmouth, Newtown, Medina and Brading members

 Included in alluvium
Beach deposits Not mapped
Tidal flat deposits Not mapped
Blown sand deposits Blown sand shingle

(Figure 40) Outline landslide types related to lithostratigraphy in the Palaeogene

Group Basic lithology Failure types Notable localities
Lambeth Group Mottled unctious clay with a basal sand and pebble unit Mudslides Alum Bay, Whitecliff Bay
Thames Group Interbedded clay and silt with sand Mudslides Alum Bay, Whitecliff Bay
Bracklesham Group Glauconitic sand and clay at the base, succeeded by interbedded clay, silt, and sand and also lignite Not generally susceptible to widespread landsliding, but are susceptible to shallow rotations, mudslides and gullying erosion. Alum Bay, Whitecliff Bay
Barton Group Clay and silty clay - Sand with clay and silt Not generally susceptible to widespread landsliding, but are susceptible to shallow rotations, mudslides and gullying erosion Alum Bay to Hatherwood Point
Solent Group Clay, sandy clay and limestone
-
Limestone and marly limestone
-
Shelly clay black organic sediments Grey-green clay and sandy clay		 Shallow mudslides, landsliding through failure at relatively shallow depth, deep- seated rotational landslides

Rotational landslides and mudslides		 Hatherwood Point to Totland Bay Fort Albert to Yarmouth




Bouldnor and Hamstead cliffs on the NW coast; Cowes and Gurnard; Priory Bay to Seagrove Bay

(Figure 42) Potential geotechnical constraints of the strata encountered in the district.

Geological unit Potential ground constraints

Worked ground

 Variable foundation conditions
Unstable sides on old workings

Made ground

 Variable foundation conditions
Leachate and methane production from waste
Infilled ground As above

Landslide-affected ground 

 Slope instability
Variable foundation conditions

Head

 Variable foundation conditions
Ground heave

Peat

 Compressible strata
Risk of flooding

Alluvium

 Compressible strata
Risk of flooding
Variable foundation conditions

River terrace deposits

 High water table
Possibility of undocumented and filled former pits

Palaeogene formations

 Variable foundation conditions
Ground heave
Potential shrink-swell in clay horizons
Sink holes close to contact with Chalk
Perched water tables sumps and springs in sand layers

Chalk Group

 Slightly elevated natural radon emissions
Groundwater protection requirement
Possibility of undocumented and infilled former pits
Dissolution cavities and sinkholes
Potential for high frequency of flint
Irregular bedrock surface

Upper/Lower Greensand formations

 Variable foundation conditions
Potential for running sand in excavations

Gault Formation

 Potential shrink-swell in clay horizons
Potential for reduced residual strength and relict shear surfaces caused by ancient landslide events
Wealden Group Potential shrink-swell in clay horizons

(Figure 43) The designated Sites of Special Scientific Interest (SSSI) on the Isle of Wight

SSSI name NGR* Notification year and revisions Interest protected Subsidiary interest
Alverstone Marshes [SZ 572 859] 1951 Biological, wet land alluvial Holocene environment
America Wood [SZ 567 820] 1986 Biological, wet land flora Lower Greensand
Arreton Down [SZ 540 872] 1979 (part), 1987 Biological, Chalk grassland Chalk quarries
Bembridge Down [SZ 628 856] 1951, 1984 Geological, Cretaceous Grassland flora, birdlife
Bembridge School and Cliffs [SZ 647 869] - 658 878 and [SZ 643 866] 1999 Geological, Quaternary, Hoxnian Steyne Wood Clays and Bembridge Raised Beach
Bonchurch landslips [SZ 582 785 1977, 1984 Geomorphological, Upper Greensand cliff and Gault Biological
Bouldnor and Hamstead cliffs [SZ 390 910 1951, 1987 Geological Oligocene, Hamstead Member Fossil floras and faunas
Brading Marshes to St Helens Ledges [SZ 635 883] 1951, 1971, 1977, 1984, 1988 Geological, Palaeogene Coastal habitats, rare floras and faunas
Briddlesford Copses [SZ 549 904] 2003 Biological diverse broadleaved woodland Butterflies, bats and mammals
Calbourne Down [SZ 429 858] 1989 Biological, Chalk grassland Rich flora and butterflies
Clowell Bay [SZ 323 873] - [SZ 330 887] 1959, 1995 Geological, Palaeogene Headon Hill Formation Fossil flora and fauna
Compton Chine and Steephill Cove [SZ 489 763] 2003 Geological, Wealden and Lower Greensand groups Coastal
geomorphology and biology
Compton Down [SZ 365 856] 1951, 1984 Geological Chalk reference section Chalk Grassland biota
Cranmore [SZ 393 901] 2002 Biological flora and fauna Bouldnor formation landscape
Cridmore Bog [SZ 495 815] 1985 Biological bogland flora and fauna Holocene
Eaglehead and Bloodstone Copses [SZ 584 877] 1987 Biological , woodland flora, grassland fauna Chalk grassland
Freshwater Marshes [SZ 344 866] 1951, 1986 Biological marsh and fen flora and fauna Holocene
Garston's Down [SZ 475 855] 1971, 1985 Biological, Chalk grassland flora Chalk Down geomorphology
Greatwood and Cliff Copses [SZ 56 80]–[SZ 57 80] 1986 Biological, woodland flora Upper Greensand and Gault, landslide geomorphology
Headon Warren and West High Down [SZ 316 852] 1951, 1984 Geological, geomorphological Chalk to Palaeogene with Quaternary Coastal geomorphology, Alum Bay and the Needles, heathland biota
King's Quay Shore [SZ 536 935] 1951, 1987 Geological and biological, estuary to freshwater marsh, Palaeogene Holocene
Lacy's Farm Quarry [SZ 323 862] 1993 Geological, Headon Hill Formation Type site of Lacy's Farm Limestone Member
Lake Allotments [SZ 586 838] 1988 Biological Unique for Fumaria martini UK site
Lock's Farm Meadow [SZ 449 908] 1988 Biological, unimproved hay meadow Orchids
Medina Estuary [SZ 508 924] 1977, 1995 Biological intertidal mudflats, wetlands Holocene, proposed Ramsar site
Mottistone Down [SZ 414 846] 1971, 1984 Biological, grassland biota Cretaceous downland and Quaternary cover
Newton Harbour [SZ 425 915] 1951, 1984, 1986 Biological, estuarine mudflats and saltmarsh Holocene, proposed Ramsar site
Northpark Copse [SZ 435 885] 1986 Biological, unique woodland pasture Hamstead Member
Parkhurst Forest [SZ 473 915] 1986 Biological, mixed woodland Hamstead Member, Quaternary
Priory Woods [SZ 635 900] 1998 Geological, Pleistocene gravels and hominid Palaeogene Bembridge Marls Pleistocene
Prospect Quarry [SZ 385 866] 1971, 1986 Geological, Bembridge Limestone parastratotype Biological limestone grassland
Rew Down [SZ 550 775] 1977, 1985 Biological, grassland flora and fauna Chalk and
Pleistocene gravels
Rowridge Valley [SZ 454 864] 1951, 1987 Biological, woodland flora and fauna Chalk
geomorphology
Ryde Sands and Wootton Creek [SZ 548 920] -[SZ 634 908] 1993, 1995 Biological, intertidal mudflats and sands, birds Holocene
Shide Quarry [SZ 506 881] 1971, 1984 Geological and biological, Chalk flora and fauna Bat roosting site
St Lawrence Bank [SZ 536 768] 1951, 1986 Biological, ungrazed chalk grassland Chalk
The Wilderness [SZ 505 824] 1951, 1984 Biological,wet unmanaged woodland Holocene
Thorness Bay [SZ 455 935] 1966, 1987 Geological and biological, undisturbed coast and Bembridge Limestone Holocene
Ventnor Downs [SZ 575 786] 1951, 1987 Biological, Chalk, clay-with- flints, grassland biota Chalk
geomorphology and Pleistocene
Whitecliff Bay and Bembridge Ledges [SZ 657 872] 1955, 1986 Geological, Chalk and Palaeogene Many Palaeogene types sites
Watcombe Bay [SZ 343 855] 1971 Geological Chalk stratigraphy Holocene coastal geomorphology
Yar Estuary [SZ 353 886] 1977, 1995 Biological estuarine and coastal biota habitats Holocene

(Figure 44) The terminology of the human occupation of the British Isles

Occupation phases Subdivisions Age Notes
Palaeolithic c. MIS 17 and before to MIS 9 Lower Palaeolithic c. 800 000 to 325 000 BP Earliest occupation of the UK around 813 ka at Pakefield in Suffolk. Boxgrove in West Sussex at around 500 000 BP. Hunter-gatherer societies
MIS 9 to MIS 3 Middle Palaeolithic c. 325 000 to 45 000 BP Hunter-gatherer societies
MIS 3 to MIS 1 Upper Palaeolithic c. 45 000 to 10 000 BP Hunter-gatherer societies
Mesolithic c. 10 000 to 5500 BP Hunter-gatherer societies
Mesolithic -Neolithic transition c. 5500 to 4000 BP Farming and animal domestication and land clearance
Neolithic c. 4000 to 2200 BC Long-term site occupation and evidence of dwellings. Farming, animal domestication and forest clearance. The earliest pottery
Bronze Age Early Bronze Age c. 2200 to 1200 BC Beaker pottery appears in the record around 2475 BC. Arreton metal-working c. 1500 BC
Late Bronze Age c. 1200 to 750 BC Sparse dwelling indicators. Pottery including and bronze working provide evidence of trading
Iron Age c. 750 BC to 200 BC Round houses, trade more widespread with the first 'coinage'
Late Pre- Roman Iron Age c. 200 BC to 43AD Vectis* an important trading hub for the Atlantic margin and Europe
Historic Britain Roman c. 43 AD to 400 AD Villas and other occupation sites. Large-scale cereal cultivation and livestock rearing for trade. Widespread European trade. Vectis pottery ware. Brick and tile firing, building stone quarrying. Trading centres (emporia) at Fishbourne Beach and Yarmouth Roads, also Brading Haven. International coinage (the first Euros!)
Medieval c. 400 AD to 1500 AD Evidence of Roman influence into early 5th century. Anglo-Saxon 'invasion' and settlement. First signs of urbanisation. First written histories. Domesday book records 10 churches and c. 100 'manors' on the island. Norman fortification at Carisbrooke
Post- Medieval to Modern c. 1500 AD to present Significant political and socio-economic changes and industrialisation. Urban nucleation

(Figure 45) Terms commonly used to distinguish subdivisions of the Flandrian (Holocene) Stage and the latest Devensian Stage

Zones (after Blytt and Sernander) Pollen zones (after Godwin, 1956) Stage Substage Years BP (approx) Human occupation (approx)
Sub-Atlantic VIII

Flandrian Mid

Late Flandrian

 2500 to present

Neolithic to present
Sub-Boreal Vim 5000 to 2500
Atlantic VIIa Flandrian 7000 to 5000

Mesolithic

Boreal

 VI

Early Flandrian

 9000 to 7000
V 9500 to 9000
Pre-Boreal IV 10 000 to 9500
Younger Dryas III

Late Devensian

Late Glacial

 11 000 to 10 000

Upper Palaeolithic (pars)
Allerod II 12 100 to 11 000
Older Dryas I Late Glacial/ Glacial 14 200 to 12 100