Content and licensing view original scan buy a printed copy

Geology of the Wells-next-the-Sea district — a brief explanation of the geological map Sheet 130 Wells-next-the-Sea

B S P Moorlock, S J Booth, R J O Hamblin, S J Pawley, N J P Smith and M A Woods

Bibliographic reference: Moorlock, B S P, Booth, S J, Hamblin, R J O, Pawley, S J, Smith, N J P, and Woods, M A. 2008. Geology of the Wells-next-the-Sea district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey.1:50 000 Sheet 130 Wells-next-the-Sea (England and Wales).

Keyworth: British Geological Survey, 2008.

Copyright in materials derived from the British Geological Survey's work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, email ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

Your use of any information provided by the British Geological Survey (BGS) is at your own risk. Neither BGS nor the Natural Environment Research Council gives any warranty, condition or representation as to the quality, accuracy or completeness of the information or its suitability for any use or purpose. All implied conditions relating to the quality or suitability of the information, and all liabilities arising from the supply of the information (including any liability arising in negligence) are excluded to the fullest extent permitted by law.

(Front cover) The Harbour, Wells- next-the-Sea. The Dutch ketch Albatros at the Quay, with the old Granary behind [TF 917437]. Photograph: Paul Witney (P694831).

(Rear cover)

Notes

The word 'district' refers to the area covered by geological Sheet 130. National Grid references are given in square brackets; unless otherwise specified they lie within 100 km square TF; specific locations and boreholes are accompanied by their National Grid reference at their first mention within the text. Lithostratigraphical symbols shown in brackets in the text are those shown on the published map. Colour is described using Munsell® colour names and notations e.g. yellowish brown (10YR 5.5/6). The serial number given with the plate captions is the registration number in the National Archive of Geological Photographs, held at BGS.

Acknowledgements

This Sheet Explanation was compiled by B S P Moorlock. S M Pawley and R J O Hamblin contributed information on the glacigenic deposits, M A Woods on the Chalk Group, S J Booth on the Holocene deposits, and N J P Smith on the concealed strata; edited by D T Aldiss and A N Morigi. J Rose and J R Lee (now BGS) of the Department of Geography, Royal Holloway, University of London collaborated extensively on the glacigenic deposits. The authors' thanks are due to the many landowners, local authorities, utilities and site investigation companies for access to land and provision of geological information.

Geology of the Wells-next-the-Sea district (summary from rear cover)

(Rear cover)

Building developments require accurate geological information in order to identify resources and ensure that foundations are adequate. Commercial agriculture also requires knowledge of the underlying geology. This Sheet Explanation and the geological map that it describes provide valuable information on a wide range of earth science issues. A substantial list of references is provided for further geological information about the district.

The small commercial port and holiday resort of Wells-next-the-Sea is situated on the north coast of Norfolk. The district also includes a number of attractive small villages, several situated along the coast, and very popular with the sailing community. Much of the coast is fringed by marshland, which forms an internationally important wetlands habitat for large numbers of over-wintering migratory birds. Inland this predominantly rural district rises to just under 100 m OD, and includes some of the highest land in Norfolk. The fertile soils developed on glacial tills are well suited to a wide range of arable crops that include wheat, barley, sugar beet, oil seed rape and potatoes.

Much of the area to the south of the coastal marshes is underlain by Pleistocene tills and associated outwash sands and gravels. The youngest of these deposits, the Holderness Formation, extends only a short distance inland, and is Devensian in age. The more extensive glacigenic deposits to the south, the Sheringham Cliffs and Briton's Lane formations, are older and may result from more than one glaciation, but their precise ages are still the subject of debate. The Chalk Group forms bedrock throughout the entire district. The outcrop of the older Grey Chalk Subgroup is restricted to the extreme west of the district, with the gentle easterly dip bringing the younger White Chalk Subgroup to crop farther east. The deeper concealed geology is known from two hydrocarbon exploration boreholes within the district at North Creake and South Creake, and other boreholes, including the BGS Hunstanton and Trunch boreholes, in adjacent districts.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the geology of the area covered by the geological 1:50 000 Sheet 130 Wells-next- the-Sea, including the offshore area. It also provides directions to further geological information about the district. It is written for the professional user, and those who may have limited experience in the use of geological maps.

The district takes its name from the small holiday resort and commercial port of Wells-next-the-Sea in north Norfolk. The town has a resident population of about 3000, which swells to about 13 000 with tourists during the summer months. Nearby, there are several interesting villages including the coastal settlements of Brancaster and Holme next the Sea, with Burnham Market and Little Walsingham inland. Holkham Hall, built in the 18th century, and its extensive agricultural estate occupy much of the central part of the district. Cereals, sugar beet and potatoes are the main crops; the rarity of late frosts in this coastal area enables lucrative early crops of the latter to be grown. The coastal marshes provide an internationally important wetlands habitat. The Royal Society for the Protection of Birds reserve at Titchwell attracts large numbers of visitors, both avian and human.

The plateau area in the southern part of the district, which rises to just under 100 m OD, is underlain by chalk-rich till and locally by overlying sand and gravel. Northwards, towards the coast, the plateau becomes dissected, with Chalk cropping out on the lower ground. In the north, marshes, sand-dunes and gravel spits fringe the coast. The landward edge of the marshes is notable for its linearity between Hunstanton and Cromer, possibly marking the approximate position of a major east–west fault that may have controlled sedimentation as far back as the Carboniferous and Permian.

Boreholes within and adjacent to the district indicate the presence of concealed Cambrian and Ordovician rocks, but Silurian and Devonian rocks appear to be absent. Precambrian rocks have not been proved but are assumed to be present. Gravimetric lows have been modelled as granites within the basement, but these lie deeper than any boreholes. The Precambrian and Early Palaeozoic rocks form the northern part of the London Platform, a positive area which periodically became partially inundated during the Late Palaeozoic and completed submerged by the Mid Cretaceous. Carboniferous strata are probably preserved in the offshore part of the Wells-next-the- Sea district, but are absent in onshore bore-holes. Likewise, Permian strata appear to be restricted to the offshore part of the district. Sedimentation during the Triassic occurred across the entire district with representatives of the Sherwood Sandstone Group and the overlying Mercia Mudstone Group both present. At the time of their deposition Britain was at a similar latitude to the Sahara Desert at the present day which resulted in the formation of red sediments. During the ensuing Rhaetian a shallow sea spread over the region and was followed during the Jurassic by a sequence of near-shore environments, with condensed deposition, and erosion at several levels which becomes more marked southwards towards the middle of the London Platform. During the Early Cretaceous, shallow marine sedimentation continued, culminating in the deposition of the famous Red Chalk, now known as the Hunstanton Formation. The Early Cretaceous strata are well exposed in The Wash and King's Lynn districts to the west.

Within the Wells-next-the-Sea district the bedrock geology at outcrop is restricted to formations within the Late Cretaceous Chalk Group. The older GreyChalk Subgroup crops out in the extreme west, with the gentle easterly dip bringing the youngest rocks of the overlying White Chalk Subgroup to crop in the east.

During the Quaternary, ice from Scotland and northern England covered the area at times and left a variety of glacigenic deposits which mask much of the Chalk outcrop, particularly in the south and east of the district. The oldest of these deposits is the Sheringham Cliffs Formation which comprises both off-white, very chalky till and brown sandy till. Locally, outwash sand and gravel is present both within and at the base of the formation. In places, particularly on the higher ground, the Sheringham Cliffs Formation is overlain by the Briton's Lane Formation, a glaciofluvial outwash sand and gravel, comprised of predominantly flint gravel and sand with erratics derived from northern England and Scotland (and Scandinavia in the Cromer district to the east). The Sheringham Cliffs Formation and the Briton's Lane Formation both predate the Devensian, but there is still debate as to whether they formed during the Anglian or intervening cold periods between the Anglian and the Devensian.

Extensive areas of the Holderness Formation are present along the lower ground adjacent to the coast. These reflect the maximum southerly extent of the Devensian ice in East Anglia. This formation mainly comprises two tills, the red-brown Holkham Till Member and the more localised off-white and chalk-rich Red Lion Till Member. A third component, the Ringstead Sand and Gravel Member, represents the glaciofluvial outwash from the ice-sheet.

A variety of shallow marine Holocene deposits fringe the coast. Onshore, these include tidal river deposits, tidal flat deposits, shoreface or beach deposits, and storm beach deposits. Dunes of blown sand are associated with these sediments along much of the coast. In several places such as Scolt Head Island, West Sands and in the extreme east of the district (part of Blakeney Head), the Holocene deposits have developed into excellent examples of re-curved spits. Offshore much of the Chalk bedrock is obscured by extensive sandbanks and sheet deposits together with large areas of tidal flats sands nearer the land.

Chapter 2 Geological description

Precambrian–Carboniferous

Precambrian and Palaeozoic rocks occur at depth in the district and their presence is known only from deep boreholes and geophysical data. A deep borehole, North Creake (TF83NE/24) (drilled by D'Arcy in 1945) [TF 8566 3863] lies within the district and another, South Creake (TF83SE/65) (drilled by BP in 1969) [TF 8573 3402], is outside the district. There are about six deep boreholes adjacent to the district. Seismic reflection profiles were acquired prior to drilling South Creake, and more recent seismic data, of improved quality, lie just outside the district to the west, south-east and offshore to the north. Seismic reflection profiles were acquired locally prior to drilling South Creake, and lines of more recent seismic data, of better quality, lie just outside the district to the west and south-east, and offshore to the north.

No Precambrian rocks have been proved within the district but there is no reason to doubt their existence at depth.

The North Creake Borehole reached recrystallized ash-flow tuff below Triassic strata. Noble et al. (1993) obtained a U-Pb age of 449 ± 13 Ma, a similar age to that of other Ordovician rocks in East Midlands boreholes, and suggested that this was evidence of Caradocian calc-alkaline arc magmatism. Only the basement rocks proven within borehole (TF47/29A-1) offshore (about 25 km to the north-north-east of Hunstanton) [TF 7459 6461] have been biostratigraphically dated, yielding chitinozoa of early Ordovician, probably Llanvirn, age.

Interbedded siltstones and sandstones were encountered within (TF47/29A-1), and within boreholes at Halton Holegate (Lincolnshire) and Saxthorpe (south-east of the district). These rocks have high seismic velocities, distinguishing them from Late Palaeozoic strata, but there is evidence from seismic reflection profiles that they are younger than the Caradoc.

Silurian rocks appear to be absent from a large area of the Midlands Microcraton (Smith, 1987) and the seismic and aeromagnetic evidence suggests that Silurian strata are probably absent from this district also. Persistent north-dipping basement reflectors in the offshore seismic profiles may be indicative of sedimentary rocks rather than faulting. The dip of reflectors beneath (TF47/29A-1) is towards the south-west suggesting it is unlikely that Silurian rocks could be present in the Wells district.

The strike of the Precambrian and Early Palaeozoic rocks follows a Charnian (north–west to south–east) trend. There are gravimetric lows (GA3 and GA4) respectively south of Hunstanton and south-east of North Creake ((Figure 1); Lee et al., 1990). GA3 has been modelled as a Palaeozoic sedimentary basin (Allsop, 1983) and interpretation of more recent seismic reflection data from the east coast of the Wash has shown that deeply-buried sedimentary strata, possibly of Carboniferous age, may account for part of this gravity low. GA4 has been modelled by Chroston and Sola (1982) as a granite intrusion, supported by evidence of a high velocity refractor, and alternatively as a sedimentary basin. A sedimentary basin younger than the Caradocian basement found at North Creake here seems equally likely; Silurian strata are present to the south-east of the GA4 anomaly and the regional dip in the basement south-east of the Wells district is to the east.

A positive aeromagnetic anomaly that lies to the south of the district (MH6;( Figure 2)) is probably the south-east extension of the Wash–Askrigg aeromagnetic anomaly (Lee et al., 1990). It passes south of the district along a west–north–west to east–south–east trend and is bounded to the south by a west–north–west–trending gravity gradient ('28GM' of Lee et al.,1990), which Cornwell and Walker (1989) identified as extending to the vicinity of the Barkston Fault in the East Midlands. As both the (TF47/29A-1) and North Creake boreholes contain Ordovician strata, which include magnetic rocks in Wales and elsewhere, the top of the magnetic basement is interpreted as Ordovician (Caradoc) in age. Overlying Silurian strata in England and Wales are generally not magnetic.

Offshore, to the north of the Wells district, a south-westerly-dipping imbricate structure and 'mid-crustal reflectors' dipping northwards have been identified on seismic profiles (Cameron et al., 1992). These 'mid-crustal reflectors' represent dipping strata with a thickness of at least 2500 m. They reach the Variscan unconformity in the mouth of The Wash, but have not produced faults in the overlying sequence.

Devonian strata are probably absent from the district. Carboniferous rocks have been proved in the (TF47/29A-1) borehole, but are absent from onshore boreholes. Carboniferous strata may occur within the northern part of the district, offshore, but it is probable that they wedge out entirely just to the north of the coastline.

Permian–Triassic

In the (TF47/29A-1) borehole a thick sequence of Permian strata was proved, comprising sandstone, limestone, mudstone and anhydrite resting on Carboniferous rocks. Permian strata thin southwards onto the London Platform and within the district occur only as far south as the coast. The pre-Permian surface slopes northwards from about 600 to 1100 m below sea level. The rapid northward increase in the depositional thickness of Carboniferous and Permian sediments appears to have occurred across an east–west line just north of the present-day Norfolk coast. The deposition may have been fault-controlled, and it is possible that this structure subsequently gave rise to the markedly straight Pleistocene coastline between Hunstanton and Cromer.

Both the Sherwood Sandstone Group and the Mercia Mudstone Group of the Triassic are present within the district (Whittaker, 1985). The former was proved in both the North Creake and South Creake boreholes, lying unconformably on the Early Palaeozoic basement. Mercia Mudstone strata may overlap the Sherwood Sandstone, as they do further west, to lie unconformably on the basement between the South Creake and Lexham [TM 850 180] boreholes.

Strata of the Sherwood Sandstone Group range in thickness from about 45 m in the south to nearly 200 m in the north-east, offshore. Within the Hunstanton No. 1 Borehole [TF 6923 4270] the uppermost 80 m of this group comprises sandstone that overlies a thin 'Bunter Shale'. To the south in the South Creake Borehole only shale was proven.

Isopachs for the Mercia Mudstone Group (and the laterally equivalent Haisborough Group offshore) show a thickening from about 115 m in the south to about 225 m in the north-east, offshore. The sequence is dominated by grey, green and red mudstones and argillaceous siltstones with sandstones. An anhydrite marker bed is present toward the top of the sequence. The basal beds are non-porous sandstones ranging from 20 to 35 m thick, which overlie the Sherwood Sandstone Group within the district.

Strata of the overlying Penarth Group, predominantly limestone with mudstone, are present between 524 to 530.7 m depth in the Hunstanton No 1 Borehole (Gallois, 1994), which may correlate with the sandstone at 521 to 526 m depth in the South Creake Borehole.

Jurassic

The Jurassic sequence beneath the western part of the Wells-next-the-Sea district is almost complete, including representatives of all the major divisions that crop out in the East Midlands (Figure 3). However, the sequence is thinner than at outcrop because of attenuation against the London Platform.

Late, Mid and Early Jurassic sediments have been proved in the North Creake and South Creake boreholes within the district, and also in the Hunstanton No. 1 Borehole just west of the district. Proven thicknesses are variable, particularly in the Mid Jurassic.

The sequence contains evidence of near-shore environments, condensed deposition and erosion at several levels. The more important stratigraphical breaks are at the base of the Lias (late Sinemurian on Rhaetian), the base of the middle Jurassic (Bajocian on early Toarcian) and the base of the Sandringham Sands (late Volgian/Portlandian on Kimmeridgian). All these erosion surfaces become more marked in the south, in thedirection of the London Platform.

Latest Jurassic–Early Cretaceous

Sandringham Sands Formation

The Sandringham Sands Formation (Figure 4) comprises up to about 50 m of predominantly arenaceous material which can be divided into the Roxham, Runcton, Mintlyn and Leziate members (Casey and Gallois, 1973). These deposits represent slow and intermittent sedimentation in a shallow sea that extended across the East Midlands Shelf in the Late Jurassic and Early Cretaceous. There is a major erosion surface at the base of the Sandringham Sands. The Sandringham Sands has a small subcrop that does not extend far beyond its outcrop. It was proved in the deep boreholes at Hunstanton, North Creake and South Creake, but appeared to be absent from the Great Ellingham [TM 0262 9847] and Lexham boreholes. When traced northwards into The Wash, the formation becomes more clayey and pebbly and the members identified on land can no longer be recognised (Gallois, 1994). A detailed account of the Sandringham Sands Formation in the adjacent King's Lynn district is given by Gallois (1994).

In the adjacent King's Lynn district the Roxham Member consists of 3 to 6 m of poorly consolidated grey and yellowish green, locally glauconitic sands. Disseminated pyrite and pyrite nodules are also present at some levels.

The Runcton Member, which unconformably overlies the Roxham Member, consists, in the adjacent King's Lynn district, of up to 1.5 m of dark green, clayey, highly glauconitic sands with phosphatic nodule and phosphatic pebble beds at several horizons. The sands are intensely bioturbated and no other sedimentary features have been recorded at exposures or in boreholes. The Runcton Member (0.27 m thick) was proved in the BGS Hunstanton Borehole just north-west of the district [TF 6857 4078], but was absent at Marham [TF 707 097] and Gayton [TF 724 192] to the south of the district. It is uncertain whether it extends into the western margin of the present district.

The Jurassic/Cretaceous boundary lies at the top of the Runcton Member within the lower part of the Sandringham Sands Formation.

The Mintlyn Member rests unconformably on and oversteps the Runcton Member. It consists of grey, greyish green and green glauconitic sands and clayey sands with thin beds of doggers of clay ironstone (sideritic mudstone), and thin (mostly less than 15 cm thick) beds of green glauconitic clay. In the Hunstanton Borehole the Mintlyn Member is 11.4 m thick, but its easterly extent into the present district is unknown.

The Leziate Member consists of loose, fine-grained, cross-bedded sands; these are yellow, green, orange-brown or red in places, but mostly clean grey or white, with subordinate beds of silt and clay. Locally the sands are lithified to form a friable sandrock. Pyrite nodules are common throughout the formation, but above the water table become oxidised to form limonitic concretions, geodes or ferruginous stains. Glauconite is abundant in some areas, but absent in others. In the Hunstanton area just north-west of the present district, the Leziate Member is about 22 m thick.

Dersingham Formation

The overlying Dersingham Formation comprises a laterally variable sequence of thinly bedded fine-grained sands, ferruginous sandstones, silts and clays. In the Hunstanton Borehole just west of the present district, the Dersingham Formation is 11.6 m thick and comprised of silts, clays and silty, sandy and oolitic (chamositic) clays that form a complex rhythmic sequence. The upper part of the Dersingham Formation appears to be the lateral equivalent of the Snettisham Clay, seen at Heacham [TF 678 364], in the adjacent King's Lynn district (Gallois, 1994).

The term 'Roach' was first used by Jukes-Browne (1887) for a formation of oolitic and pebbly sandy clays in the upper part of the Lincolnshire Early Cretaceous sequence. Swinnerton (1935) divided the formation into a lower and upper member separated by a calcareously cemented sandstone with ferruginous ooliths which he called the 'Roach Stone'. Thurrell (in Owen and Thurrell, 1968) subsequently used Roach Stone for any hard bed that gave rise to a topographical feature at about the middle part of the Roach outcrop, irrespective of lithology. In the Hunstanton Borehole, 16.6 m of Roach Formation were proved. No 'Roach Stone' was recognised in the borehole, although thin calcareously or ferruginously cemented beds occur at several horizons. The base of the formation is taken at a minor erosion surface that separates the predominantly oolitic and pebbly clays of the formation from the predominantly argillaceous, sparsely pebbly Dersingham Formation. The fauna in the Hunstanton Borehole is dominated by small marine bivalves. The eastwards extent of the Roach Formation within the present district is unknown.

Carstone Formation

The Carstone Formation typically comprises rusty brown, massive, ferruginous sandstone, but where fresh and unweathered, it is a greenish brown sandstone in which common Arenicolites and Skolithos burrows can be seen. The extent of the subcrop of the Carstone Formation in north Norfolk is poorly known. About 17.7 m of the formation was proved in the North Creake Borehole (Kent, 1947), a similar thickness in the South Creake Borehole, 18.9 m in the Hunstanton Borehole, and 6.8 m in the more distant Great Ellingham Borehole [TM 0262 9847] to the south (Cox et al., 1989). The formation was not recorded in the Saxthorpe [TG 1226 3013], Somerton [TG 4607 2120] and East Ruston [TG 3530 2680] boreholes, but this could have been due to problems of recognition. A few sand grains and pebbles in poorly recovered samples from the Trunch Borehole [TG 2933 3455], in the north-east of Norfolk, were assigned to the Carstone (Gallois and Morter, 1976).

Hunstanton Formation

The Hunstanton Formation (formerly known as the Red Chalk) has an extensive subcrop in Norfolk. It has been proved within the district in the North Creake and South Creake boreholes and is presumed to underlie the entire county north of a line from Sandringham to Great Yarmouth (Gallois, 1994). In the cliff sections at Hunstanton, the Hunstanton Formation is 1.1 m thick and comprised of pink sandy limestone with red marl wisps. Wiltshire (1859, 1869) and Seeley (1864) divided the Hunstanton Formation at Hunstanton into three beds of limestone separated by two prominent seams of red sandy marl. This five-fold division can be recognised throughout the cliff exposure. The limestones contain a range of sedimentary structures that includes burrows, borings, and probable stromatolitic laminations, but many of these have been modified by lithification, cementation and mineral migration (Jeans, 1980; Gallois, 1994). The Hunstanton Formation appears to lie conformably on the Carstone Formation. The Hunstanton Formation has yielded a rich and diverse marine fossil fauna including brachiopods, bivalves, echinoderms, ammonites and polyzoans. More detailed accounts of the Hunstanton Formation (Red Chalk) are given by Gallois (1994) and Owen (1995). Southwards from Hunstanton, the formation becomes progressively more argillaceous and in the Fakenham district it is replaced laterally by the Gault Formation.

Late Cretaceous

Rocks of the Late Cretaceous Chalk Group crop out throughout the entire district. The Chalk bedrock has a very shallow general dip to the east so that in a west to east traverse progressively younger Chalk formations come to crop. Local small variations in dip and strike may occur. Following Rawson et al. (2001), the Chalk of the Wells district has been subdivided into Grey Chalk Subgroup and White Chalk Subgroup, but extensive cover of Quaternary strata has prevented the mapping of most formational boundaries. Nevertheless, a more detailed understanding of the succession can be gleaned from the sparse exposures and boreholes, and from archival data.

Chalk is typically a very fine-grained white limestone, predominantly composed of the disaggregated remains (coccoliths) of tiny planktonic algae that flourished in the seas of the Late Cretaceous. The Chalk Group is composed of almost pure calcium carbonate in the form of low-magnesian calcite, except the lower part, which contains up to 30 per cent clay. Flint nodules, clay-rich layers (marls), beds of indurated mineralised chalk (hardgrounds), and coarsely bioclastic chalk horizons also occur, and some of these are geographically extensive markers.

The Chalk of north Norfolk, including the Wells district, in part belongs to the 'Northern Province' of Mortimore et al. (2001). This designation recognises differences in lithology and fauna of the Chalk of Yorkshire, Lincolnshire and northern East Anglia compared to that of southern England (the 'Southern Province'); differences that appear gradually in the Chalk extending north-eastwards from the Berkshire Downs into central East Anglia (the 'Transitional Province'). In general, the Chalk of the Northern Province is more indurated; a consequence of the secondary infilling of pore spaces by calcite, although the mechanism by which this has occurred is still unclear. Flints occur at lower stratigraphical levels in Northern Province Chalk compared to equivalent sequences in southern England, and are more commonly of tabular form. However, only the lower part of the north Norfolk Chalk succession is of Northern Province type, and it seems likely that the boundary between the Northern Province and Transitional Province changed with time (Mortimore et al., 2001).

Separate lithostratigraphical classifications are used in the Chalk of the Northern and Southern provinces (Rawson et al., 2001; (Figure 5)), and as yet the extent to which each is applicable in the Transitional Province remains undecided.

In the presence of the extensive Quaternary cover, biostratigraphy has historically been the key to understanding the Chalk of north Norfolk. The work of Peake and Hancock (1970) showed that macrofossil collections from more than 200 localities could be used to construct a biozonal map of the Chalk for the northern part of East Anglia. This work provides a more detailed picture of stratigraphical variation in the Chalk than can be achieved by conventional geological mapping in this region, and is a guide to correlation with successions to the north and south, and with the BGS Trunch Borehole [TG 2933 3455], a key reference borehole for the Chalk of north Norfolk (Wood et al., 1994). (Figure 6) shows the occurrence and biozonal classification of localities in the Wells district, including those used in the construction of Peake and Hancock's biozonal map. The biozonal classification used by Peake and Hancock (1970), and in part employed on (Figure 6), differs from the standard macrofossil scheme; its relationship to current nomenclature is shown in (Figure 5).

Microfossil samples from some of the localities on (Figure 6) (numbered 1 to 10) were examined for biostratigraphically significant foraminifera (Wilkinson, 2004). The results generally confirm previous biozonal assignments by Peake and Hancock (1970), except for the Titchwell Parish Pit [TF 762 433] (Locality 2 of (Figure 6)). This was assigned by Peake and Hancock (1970) to the Plesiocorys (Sternotaxis) Zone, but actually belongs to the Micraster coranguinum Zone on the basis of microfossil (Wilkinson, 2004) and macrofossil data (Mortimore et al., 2001).

Fossil evidence from localities near Stiffkey and Warham show that the youngest Chalk in the Wells district equates with the basal part of the Portsdown Chalk of southern England (Wilkinson, 2004), an interval in which marl seams typically occur. It is not known whether marl seams are present at this level in the Wells district, although they have been recorded in the slightly younger Basal mucronata Zone equivalent of the Portsdown Chalk in the Trunch Borehole (Wood et al., 1994).

Boreholes at South Creake and North Creake, in the southern and central parts of the Wells district, show the Chalk Group to be between 140 and 160 m thick thereabouts. Younger Chalk Group strata occur farther east, making the maximum thickness of the Group about 300 m based on biozonal thickness data (Peake and Hancock, 1970; Wood et al., 1994).

Grey Chalk Subgroup (GyCk)

In the Bircham Borehole [TF 7567 3329], just to the south of the Wells district, the Grey Chalk Subgroup is about 13 m thick (Figure 7), compared to about 50 m in southern East Anglia (Bristow, 1990), and more than 70 m in southern England (Mortimore et al., 2001). A similarly thin Grey Chalk Subgroup occurs in the Trunch Borehole, and represents a regional trend of increasing condensation and induration of this interval in north Norfolk. The Grey Chalk here comprises hard, marly chalk with stylolites, hardgrounds and shell-rich intervals. Its lithology is typical of the Ferriby Chalk Formation which comprises the Grey Chalk Subgroup in the Northern Province (Figure 5). Several regionally developed marker beds can be recognised within it.

The basal part of the Grey Chalk Subgroup in the Bircham Borehole includes very hard, nodular and glauconitised chalk. This probably represents the Paradoxica Bed, named for the abundance of burrows of Thalassinoides paradoxica (Woodward) and seen at the base of the Chalk Group in the cliffs at Hunstanton, just west of the Wells district (Gallois, 1994). Above this, the Bircham Borehole contains a few metres of shell-rich chalk that probably represent the Lower and Upper Inoceramus beds, seen at Hunstanton and traceable into the Lincolnshire succession north of The Wash (Gaunt et al., 1992; Gallois, 1994). These bioclastic beds are largely made of the fragmental remains of the bivalve Inoceramus ex gr. crippsi Mantell, but may include other forms.

The Totternhoe Stone is a widespread marker in the Grey Chalk Subgroup of northern, eastern and parts of southern England. In the Bircham Borehole it is represented by 0.3 m of grey, marly and silty chalk with glauconitised pebbles overlying a glauconitised hardground. The Totternhoe Stone is 0.7 m thick at Hunstanton, and just over a metre thick in the Trunch Borehole (Gallois, 1994; Wood et al., 1994). The base of the Totternhoe Stone marks the junction of the West Melbury Marly Chalk and Zig Zag Chalk formations in southern England.

The higher part of the Grey Chalk Subgroup in the Northern Province contains the Nettleton Stone, an indurated unit of slightly gritty chalk with an oyster-rich marl at its base. In the Bircham Borehole, a 0.2 m-thick marl containing oyster remains occurs less than a metre above the inferred Totternhoe Stone, and might represent the base of the Nettleton Stone. The Nettleton Stone has been described at several localities in the King's Lynn district, including Dersingham [TF 7013 3092] and Heacham [TF 688 368], just to the west of the Wells district (Gallois, 1994), and it is widely developed in the Chalk north of The Wash (Whitham, 1991; Gaunt et al., 1992).

White Chalk Subgroup (WhCk)

The White Chalk Subgroup probably has a maximum thickness of about 285 m in the Wells district, based on borehole and biozonal data. Although poorly exposed in the district, data from abandoned chalk pits and borehole records from adjacent areas provide some insight into the details of its stratigraphy.

The base of the Subgroup is the base of the Plenus Marls, a member which typically includes characteristic beds of clay-rich chalk. In north Norfolk, this member is much attenuated compared to the several metres that is typical of the unit in southern England. In the King's Lynn district, the Plenus Marls is just a few centimetres thick, and has been recorded at Barrett Ringstead [6787 3979] and in the former pit at Heacham [688 368], just to the west of the Wells district (Gallois, 1994). In the Bircham Borehole, the Plenus Marls is not clearly visible in the core samples. However, its horizon is inferred from a small inflection on the resistivity log, coincident with a downward change from shelly, coarse-textured chalk to smooth-textured chalk (Figure 7).

Hard, nodular, shell-rich chalk occurs above the inferred Plenus Marls in the Bircham Borehole. This interval is just over 20 m thick, contains sporadic nodular flints, and is clearly represented by a distinctive high resistivity interval on resistivity logs for this borehole and the nearby Manor Farm Borehole [TF 7525 3597] at Docking (Figure 7). The same interval was also recognised by Barker et al. (1984) as forming the lower part of the Welton Chalk Formation in the Killingholme Borehole DG1 [TA1498 1908] in Lincolnshire (Figure 7). The lower part of this shell-rich interval at Bircham probably corresponds with the similarly bio- clastic Holywell Nodular Chalk of southern England. However, the higher part of the shelly chalk at Bircham contains Inoceramus cuvieri and Conulus subrotundus, fossils that are typical of the New Pit Chalk of southern England. Biostratigraphical and geophysical evidence thus indicate that in the Wells district it is no longer possible to separate the Holywell and New Pit Chalk formations of the southern England classification. Instead, the best correlation is with the Northern Province Welton Chalk Formation, equivalent to the combined Holywell, New Pit and basal Lewes Nodular Chalk of southern England (Figure 5).

The higher part of the core in the Bircham Borehole is poorly bioclastic. It contains a thick (c.50 mm) grey marl seam about 10 m above the top of the shell-rich interval, and in the highest part of the borehole a thick (c.0.3 m) flint bed. This part of the sequence is probably similar to that described in the Swaffham and Thetford districts by Mortimore and Wood (1986). These authors recorded a succession of named marker-marls (based on the work of Ward et al., 1968) in strata equivalent to the middle and higher part of the Welton Formation, capped by thick flints. There are four principal marl seams, comprising (in ascending stratigraphical order): the Pilgrims Walk Marl, the Mount Ephraim Marl, the Twin Marl and the Grimes Graves Marl (Figure 7). The lowest two of these probably occur in the Manor Farm and Bircham boreholes, and most have been identified in the Trunch Borehole. The marls can be recognised by distinctive inflections on borehole resistivity and gamma logs and form an easily correlatable framework (Figure 7). The succession is very similar to the higher part of the Welton Chalk Formation and the basal Burnham Chalk Formation described by Whitham (1991) in east Yorkshire, and marl seam correlations have been established with this and the southern England succession (Mortimore and Wood, 1986; (Figure 7)). The thick flint in the higher part of the Bircham core may relate to the flint-rich interval that occurs in the Thetford area, named the Brandon Flint Series, which correlates with the junction of the Welton and Burnham Chalk formations in Lincolnshire and Yorkshire (Mortimore and Wood, 1986).

The remainder of the White Chalk mostly equates with the Upper Chalk of traditional classification (Figure 5); an interval that is largely masked by Quaternary deposits in the Wells district. Historically, recognition of the base of the Upper Chalk in north Norfolk has been problematic because of poor surface expression of the indurated horizon (the Chalk Rock) traditionally used to map this boundary (Whitaker et al., 1893; Whitaker and Jukes-Browne, 1899). However, a topographic feature believed to be broadly coincident with the Chalk Rock was traced during the present survey and this line is shown on the map as a horizon within the lower part of the White Chalk Subgroup.

Poor exposure has meant that biostratigraphical subdivisions have formed the basis for previous lithological discussion of strata equivalent to the middle and higher parts of the White Chalk Subgroup within the district (Jukes-Browne and Hill, 1904; Peake and Hancock, 1970; Wood et al., 1994), and in the absence of any current means of systematic lithological subdivision, this method is adopted herein. Thickness estimates for zones are based on data from Peake and Hancock (1970) for the whole of north Norfolk, and from the Trunch Borehole (Wood et al., 1994).

Chalk of the Plesiocorys (Sternotaxis) plana Zone is 25 to roughly 37 m thick. Exposures occur at several localities in the western part of the Wells district (Figure 6). At Bircham Newton [TF 7695 3390] Jukes-Browne and Hill (1904) recorded hard, white chalk with grey, nodular and tabular flints at regular intervals and larger, Paramoudra-like flints. In the Trunch Borehole, the plana Zone succession compares closely with the Burnham Chalk of north-east England and many of the key flints and marls can be correlated between the successions. In places in the Wells district, the Plesiocorys (Sternotaxis) plana Zone is coincident with the feature thought to be formed by the Chalk Rock. North and north-east of Sedgeford, this feature is only 20–30 m above the base of the White Chalk Subgroup, but there is probably at least 40 –50 m of the White Chalk Subgroup below the Plesiocorys (Sternotaxis) Zone in the Bircham and Manor Farm boreholes (Figure 7). Evidence from the Trunch Borehole suggests that this discrepancy might possibly be explained by rapid north-westward thinning in the lower part of the White Chalk Subgroup.

The Micraster cortestudinarium Zone chalk is about 20 m thick. There are no known exposures in the Wells district, but the fauna from this interval in the Trunch Borehole shares features with the succession to the north, in Lincolnshire and Yorkshire (Wood et al., 1994).

Mortimore et al. (2001) records that the chalk of the Micraster coranguinum Zone (here 51 to c.76 m thick) resembles the Seaford Chalk Formation of southern England, and that flinty chalk with marl seams, equivalent to the basal part of the Seaford Chalk, occurs in the Titchwell Parish Pit [TF 762 433] in the north-western part of the Wells district. Chalk belonging to the coranguinum Zone mostly occurs in the central part of the Wells district (Figure 6), and at South Creake [8553 3625] is 'rather hard chalk with layers of flint' (Jukes- Browne and Hill, 1904). The moderately high diversity of the fauna recorded at South Creake might suggest assignment to the higher (Santonian) part of the coranguinum Zone. In the Trunch Borehole there are possible correlatives of named flint marker beds in southern England. This record of flint in the higher part of the coranguinum Zone, and its known occurrence in superjacent zones in north Norfolk, contrasts with the complete absence of flint in the partly coeval Flamborough Chalk Formation in north-east England (Whitham, 1993).

In north Norfolk the Uintacrinus socialis Zone is represented by soft chalk, mainly lacking flint (Peake and Hancock, 1970, (Figure 3). There is a record of the occurrence of this zone near East Barsham, just south of the present district (Figure 6).

The Marsupites testudinarius Zone and the Uintacrinus socialis Zone are together 28 to 42 m thick. There are at least four localities in the eastern part of the Wells district where chalk belonging to this zone has been recorded (Figure 6). The chalk is apparently similar to that belonging to the socialis Zone (Peake and Hancock, 1970), but Jukes-Browne and Hill (1904) noted rather hard testudinarius Zone chalk at Houghton St Giles [TF 9235 3542]. Faunas from Houghton St Giles include common oysters, especially Pseudoperna boucheroni, suggesting that the oyster-rich bioclastic facies that overlies the testudinarius Zone in the Trunch Borehole might here also occur within this zone.

There is no record of the Uintacrinus anglicus Zone in north Norfolk, although it probably occurs in the southern part of East Anglia and definitely occurs in east Yorkshire (Mitchell, 1995). Any strata that do equate with this zone were presumably included in the basal part of their overlying 'Zone of Gonioteuthis' by Peake and Hancock (1970).

The chalk (78 to c.97 m thick) assigned to the 'Zone of Gonioteuthis' by Peake and Hancock (1970) equates with the (?Uintacrinus anglicus Zone), O. pilula Zone, and the greater part of the G. quadrata Zone of southern England (Figure 5). The highest part of the quadrata Zone, assigned to the 'Basal mucronata Chalk' by Peake and Hancock (2000), occurs outside the Wells district. In the eastern part of the Wells district, 14 localities are assigned to the 'Zone of Gonioteuthis' (Figure 6), the best exposure being the former quarry at Wells-next-the-Sea [928 428]. Here, nearly 40 m of succession was visible, equating with the upper O. pilula Zone and lower G. quadrata Zone of southern England. The succession contains flint and marl seams, suggesting similarity to the Newhaven Chalk Formation of southern England (Peake and Hancock, 1970, 2000; Mortimore et al., 2001). A strongly developed marl in the Wells succession has previously been correlated with the Old Nore Marl in the Newhaven Chalk of southern England (Wood et al., 1994), but may in fact be younger, and closer to the top of the pilula Zone (Mortimore et al., 2001). In the Trunch Borehole, coarse-grained bioclastic chalk occurs in the lower part of the pilula Zone, and this facies, characterised by common oyster remains, occurs at several localities near Wells and also at Great and Little Walsingham. Microfossil data from localities near Warham and Stiffkey show that the chalk there equates with the [basal part of the Portsdown Chalk of southern England (Wilkinson, 2004; (Figure 5)).

Quaternary

Most of the Wells-next-the-Sea district is underlain by Quaternary deposits. Much of the higher ground is underlain by till of the Sheringham Cliffs Formation. There is no evidence to indicate the presence of the Lowestoft Till, which is present to the west and south of the district, and which characteristically has numerous chalk clasts and a significant clay content derived from the Jurassic mudstone formations, and is dark grey when unweathered. The Sheringham Cliffs Formation is overlain extensively by sand and gravel of the Briton's Lane Formation. On the lower ground in the north of the district, there is a further development of till. This has been assigned to the Holkham Till Member of the Holderness Formation and is of Devensian age. Post-glacial deposits include head, peat and alluvium and a variety of shore deposits along the coastal strip. Sands are present in the offshore area. The thickness of the Holocene sediments along the coastal margin is constrained by the presence of an underlying glacial and post-glacial erosion surface which cuts into the underlying glacial sediments and Chalk (Funnell and Pearson, 1989; Andrews and Chroston, 2000). Coring and shallow seismic reflection surveys indicate that the Holocene and glacial sediments occur in an east–west trough (Figure 8) defined by the surface of the Chalk and interpreted as a palaeovalley (Chroston et al., 1999). The trend of the valley may have been influenced by east-west faulting of the bedrock along the northern margin of the London Platform. At its deepest the base of the channel lies at just below −16 m OD (Andrews and Chroston, 2000; and references therein).

No pre-glacial marine or fluvial deposits that could be attributed to either the Crag Group (Rose et al., 2001) or the deposits of the Ancaster River were found during the survey of the Wells-next-the-Sea district. It is probable that the Ancaster River, which brought Pennine material into the Crag Basin, followed an easterly course just north of the district (Rose et al., 2002), whereas the western margin of the marine Crag basin lay just west of Weybourne about 11 km to the east, in the Cromer district.

Glacial deposits

Sheringham Cliffs Formation

This formation crops out extensively across much of the higher ground of the district and locally descends to lower levels in the north. The formation comprises mainly till, but also includes sand and gravel. The till comprises two distinct lithologies, an extremely chalk-rich till which is pale buff to off-white in colour, and a brown sandy till which contains much less chalk. It has not been possible to map the two till lithologies separately. The chalk-rich till has often been referred to informally as the 'marly drift'. The 'marly drift' in this part of north Norfolk has generally been considered a variant of the Anglian Lowestoft Till (Perrin et al., 1979; Ehlers and Gibbard, 1991; Lunkka, 1994; Lewis, 1999), although Straw (1965, 1973) argued that it was deposited by a younger post-Anglian–pre-Devensian glaciation.

The stratotype for the Sheringham Cliffs Formation is the coastal exposures between West Runton [TG 18 43] and Skelding Hill [TG 14 43] in the adjacent Cromer district. In the present district the formation is very well exposed in the upper part of the large disused quarry [TF 928 428] to the south-east of Wells-next-the-Sea where it directly overlies Chalk bedrock.

The chalk-rich till is a pale buff to off white diamicton with a silt-rich particle size distribution (40–50% silt) and an extremely high carbonate content (80–90% CaCO₃). The particle size and clast lithological properties are much more uniform than within the associated brown till. However, there is a slight increase in sand content towards the east. The chalk-rich till exhibits large-scale glaciotectonic deformation in the Wells- next-the-Sea Pit and at other sites in the adjacent Cromer district, indicating an ice flow direction from the south-west.

The brown till comprises a yellowish brown sandy (34–45% sand) diamicton that is well exposed in pits at Wells-next-the-Sea, Barrow Common [TF 7901 4293] and Whin Hill [TF 871 380]. The diamicton is generally stratified with tectonic laminations of chalk mud. The sand content of the till increases towards the east, whereas chalk, carbonate and the incidence of far-travelled erratics increase westwards. The brown till was deposited by British ice flowing from the north-west.

Both till lithologies and the basal sand and gravel are well exposed in a scoured depression in the Chalk bedrock at the south-west margin at the Wells-next-the-Sea Pit (Plate 1). The lowermost unit is 0.5 m thick, and comprised of clast-supported gravel which rests directly on the Chalk bedrock at 7 m OD. The gravel is coarse and includes cobbles of rounded and chatter-marked flints. Clast lithologies are dominated by flint (62.9% of the 8–16 mm size fraction), and chalk (31% of the 8–16 mm size fraction), but traces of red chalk (Hunstanton Formation), glauconitic sandstone, Jurassic calcareous and micaceous sandstone, crystalline limestone, granite, acid porphyry, basic porphyry, and quartz schist are also present. The overlying unit is the brown till which here is a clast-rich sandy facies (c.35% sand). The till is a stratified diamicton consisting of 10–20 cm-thick massive or laminated beds, and 0.1–5 cm-thick layers of chalk silt with some highly attenuated boudins and tectonic microstructures. The till contains abundant chalk (67.3%) and flint (31.5%) with trace amounts of Jurassic limestone, shale and calcareous sandstone, which indicates a north-west–south-east ice flow path. The brown till is overlain by the chalk-rich till which is here a highly chalk-rich (89% CaCO₃), clast-rich (7.3%), silty diamicton (9.2% sand). The till is white except for some decalcification pipes and iron staining along the lower contact. The base of this till is also tectonically banded with some laminations of silty to sandy diamicton, remoulded from the underlying brown till. The till contains mostly chalk clasts (93%) with small amounts of flint and quartzose rocks. Fold geometry and clast fabrics indicate that the stress direction was from the south-west, as found by Ehlers et al. (1987).

Sections in the Sheringham Cliffs Formation at Whin Hill demonstrate a transition from glaciolacustrine to subglacial and glaciofluvial conditions. The sequence comprises glaciolacustrine fine-grained chalk sands and massive laminated muds, overlain by clast-poor diamicton. This part of the sequence is poorly exposed and the stratigraphic context cannot be fully determined. In several pits, for example at Barrow Common, there are small patches of till incorporated into the overlying Briton's Lane Formation, probably representing blocks reworked from the underlying Sheringham Cliffs Formation.

A pit at Telegraph Plantation [TF 7889 4253] reveals a highly deformed melange within the Sheringham Cliffs Formation, overlying Chalk bedrock at 35 m OD. Three lithofacies are present: coarse flint and chalk gravels, chalky laminated silts and clays, and chalk-rich diamicton. This assemblage is deformed by a complicated series of large recumbent folds that are intruded by gravel-filled clastic dykes up to a few metres long, formed as water escape structures (Plate 2).

The gravels are composed almost exclusively of chalk and flint with only traces of porphyry and other crystalline clasts. They directly overlie the Chalk bedrock and almost certainly formed as outwash from the ice-sheet that deposited the diamicton. They are generally massive and coarse-grained but poorly sorted, with large flint cobbles, except where they fine 'up-flow' in the water escape structures.

The gravels also form a large folded raft within the melange. The gravels are generally overlain by a thick (2–6 m) unit of massive or thickly laminated chalk muds. The muds are mostly silt-rich (about 50% silt) with rare clay-rich units. They represent deposition in standing water, most probably a local lake basin, perhaps a small proglacial lake.

The chalk-rich diamicton is pale yellow in colour and is silt-rich (c.45%) and clast-rich. Clast lithologies are dominated by chalk (91.7% of the 8–16 mm fraction) and flint (7.1% of the 8–16 mm fraction) with trace amounts of acid porphyry and metaquartzite. The diamicton contains layers of chalk mud and pods of flint gravel.

The injection of such coarse-grained gravel to form clastic dykes must have required both extremely high pore-water pressures, caused by rapid loading by a large mass of relatively impermeable diamicton, and the wide range of grain sizes in the underlying gravels, enabling inter-granular movement. The interlayering of diamicton, silt and gravel, the abundant water escape structures and the presence of laminated silts and clays indicates that the folding occurred while the sediments were still water-saturated. The folding may have been caused either by slumping of diamict into a glaciolacustrine basin, or by compressive stresses as the ice-margin pushed into the subaqueously-deposited sediments.

Briton's Lane Formation

The Briton's Lane Sand and Gravel was previously regarded as a member of the Overstrand Formation in the adjacent Cromer district (Moorlock et al., 2002), but it has since been raised to formation status. The stratotype for the Briton's Lane Formation is the Briton's Lane Quarry [TG 168 415] at Beeston Hill, Sheringham.

Throughout the present district, small outcrops of sand and gravel form raised features above the till of the Sheringham Cliffs Formation. The sand and gravel is typically up to several metres thick but locally, especially where developed on valley sides, up to about 10 m may be present. The gravel, which ranges from fine to coarse-grained with cobbles, is composed predominantly of flint, but contains significant amounts of sandstone and lesser amounts of granite, dolerite, gabbro and gneiss. The sand and gravel is locally draped down hillsides over a pre-existing topography, which suggests that at least some of it was deposited directly from ice rather than in a sandar environment.

A proglacially-thrust complex of Briton's Lane Formation sand and gravel and brown till is exposed at Barrow Common [TF 7901 4293]. Proximal outwash from the Briton's Lane Formation ice-sheet deposited a succession of coarse-grained sand and gravel typically comprising clast-supported coarse gravels, locally interbedded with thin horizontally-bedded sand units that are more prevalent towards the top of the succession. Extremely poorly sorted cobble beds also occur, representing very high velocity outwash events. The gravels here have a relatively low flint content (66.5% of the 8–16 mm fraction) and are relatively rich in far-travelled material. Indicator rocks include Devonian sandstone, Jurassic mudstone, oolitic limestone and sandstone, glauconitic sandstone, carstone and red chalk. A significant crystalline rock component (3% of the 4–8 mm fraction) includes granite, acid and basic porphyry, quartz schist and greenschist.

Holderness Formation

Lewis (1999) includes the Devensian tills and associated outwash deposits of north-west Norfolk within the Hunstanton Formation. However, the term 'Hunstanton Formation' has previously been assigned to the Red Chalk at Hunstanton, and is therefore inappropriate for these Devensian deposits. Lewis (1999) uses the term Holderness Formation for Devensian deposits at Holderness and in Lincolnshire; the use of this formational name has been extended by Moorlock et al. (2002) to include the Devensian deposits of north Norfolk. The Holderness Formation here includes three local members; the Holkham Till Member, the Red Lion Till Member and the Ringstead Sand and Gravel Member.

Further geochronological research is required before the Holderness Formation can be assigned unequivocally to the Early (Marine Isotope Stage 4) or the Late Devensian (Marine Isotope Stage 2) although the younger age is currently favoured.

The Holkham Till Member (known previously as the Hunstanton Till) has been described since the work of Woodward (1884) and Whitaker and Jukes-Browne (1899) as a distinctive reddish brown till containing a wide range of sedimentary and crystalline clast lithologies. Its type section is a large, now partially overgrown former brickpit [TF 863 428] within the grounds of Holkham Hall. A comprehensive review of the till and associated deposits is given by England and Lee (1991). The distribution of the Holkham Till was originally mapped by Straw (1960); it has been revised during the recent survey with new evidence redefining the southernmost extent of the Devensian glaciation in north Norfolk. In particular, the remapped distribution of the Holkham Till confirms that several small ice-lobes, previously postulated by Straw (1965) on the basis of geomorphological evidence, encroached into the valleys between Stiffkey and Wells-next-the-Sea (Brand et al., 2002; Riding et al., 2003).

The thickness of the till is commonly less than 1 m, but it may locally reach a maximum of about 10 m. Its presence is marked by red-brown soils developed on the lower ground and locally on north-facing flanks of the coastal 'upland'. On these upland slopes, a distinct break of slope commonly marks the junction of the till with the Chalk bedrock occurring higher up the slope. Northwards, at the marsh edge, the till disappears beneath Holocene deposits of the coastal zone.

Lithologically, the Holkham Till is a stiff, red-brown, variably sandy and silty clay, which contains a relatively high percentage (around 12%) of matrix-supported clasts. Characteristically, the clast components tend to comprise small fragments of red, green and 'mustard-coloured' fine to medium-grained sandstone and micaceous sandstone (probably Triassic in age) with coal. In places locally-derived chalk clasts are common. Other characteristic lithologies include dark grey Carboniferous limestone (including crystalline limestone) and mudstone, red mudstone and ironstone. An abundant igneous and metamorphic fraction includes fragments of basalt, dolerite, porphyry, granite, schist, and gneiss (Gallois, 1979; Lewis, 1999).

The Red Lion Till Member is restricted to the area around Stiffkey where it caps the hillside overlooking the river. In the car park [TF 9687 4335] of the Red Lion public house at Stiffkey, a now-degraded section, about 4 m high, exposes a chalk-rich diamicton overlying a heavily disturbed Chalk surface. This exposure was noted by England and Lee (1991) and by Hoare and Connell (2003). The latter authors described the succession as comprising three diamictons differentiated on the basis of their colour, which ranges from reddish brown (5YR 4/4) to yellowish brown (10YR 5.5/6).

The most obvious characteristic of this Stiffkey exposure is the dominance of chalk in the matrix; the deposit was initially interpreted by BGS as locally derived, soliflucted head. Hoare and Connell (2003) showed that the yellowish brown facies has a heavy mineral signature indistinguishable from that of the Holkham Till and Skipsea Till. They interpreted the sequence as 'fresh' deposits rather than material reworked as head.

The Ringstead Sand and Gravel Member was deposited from the Devensian ice-sheet that just impinged on the north coast of Norfolk (Plate 3). It has a discontinuous outcrop along the lower ground in the northern part of the district and to the north is overlain by Holocene coastal deposits. The thickness of the sand and gravel is very variable, but is estimated to be generally less than 3 m. Soils developed on the sand and gravel are flint-rich but also contain common clasts of dolerite and other igneous rocks, and less abundant schist and gneiss. Landforms associated with meltwater deposition include the Hunstanton esker in Old Hunstanton Park [TF 694 340] (Straw, 1960), just west of the present district, and also probable kame terraces which extend along the valley at Ringstead Common (between [TF 725 404] and [TF 711 402]) shown as head on the map. Excavations in one of the latter [TF 7254 4053] have revealed a degraded terrace comprising 2.5 m of sand and fine-grained gravel (Plate 5) resting on Chalk. It is suggested that these sediments represent lake margin deposits, formed by traction current activity with high rates of suspended sediment deposition forming climbing ripple beds and draped lamination in the sands. Ripple drift lamination indicates flow towards the west. The interbedded muddy granular gravels represent deposition from slightly higher velocity currents but with suspended sediment deposition forming the mud-rich matrix. The lake margin sediments at this site could be fed by fluvial input from the surrounding hill slopes although a direct glacial input into the lake is indicated by the presence of coal fragments. As the terrace surface is at 21 m OD, which is approximately 6 m above the base of the Ringstead Downs Channel in the adjacent district to the west (Figure 8), these deposits provide some support for the presence of a glacial lake in the Ringstead valley that overflowed and caused incision of the Ringstead Downs Channel.

Glaciofluvial sand and gravel of uncertain age has been mapped at several localities. It is uncertain whether these deposits are of Devensian age, or older.

Spoil from excavations for an irrigation reservoir just east of Beacon Hill [TF 742 417] revealed a deposit beneath head comprised of boulders, cobbles and very coarse gravel. The clasts consist of chalk or flint. The deposit was not seen in situ, it has no topographic expression and both its extent and age are unknown.

Mass movement deposits

Head

Head comprises poorly sorted and poorly stratified deposits formed by the mass movement of surficial materials on sloping ground. Mass movement processes that have been active in the district include modern hillwash and soil creep (giving rise to deposits often referred to as Colluvium) as well as solifluction, an important mode of sediment transport under former periglacial conditions. It is probable that many of the head deposits formed during the Devensian cold period, with accumulation continuing through the Flandrian.

On the 1:50 000 map, two types of head deposit are distinguished; the most extensive spreads predominantly comprise sandy silt and clay and (depending on source) can be gravelly. Head gravel comprises clayey gravel and is found on the lower slopes of the northward draining valleys of the Rivers Stiffkey and Burn.

In the area between Titchwell [TF 75 43] and Brancaster [TF 77 43] several northward- draining narrow valleys containing head have cut into the Chalk. These valleys die out and cannot be traced northwards across the Devensian Holkham Till. This would suggest that the valleys pre-date the Devensian glaciation and were subsequently blocked by Holkham Till. The head deposits have a maximum thickness of several metres.

Landslides

Several small landslides affecting the Chalk have been mapped along the steep valley sides of the River Stiffkey [TF 97 42] near the village of Stiffkey. The age of the landsliding is unknown.

Fluvial deposits

Alluvium

Alluvium, comprised of silt, clayey silt, and silty sand underlies the floors of most of the main valleys; peats may occur within these deposits, and gravel may locally be present at the base of the sequence. Most of the alluvium is likely to be less than 3 m thick but, locally, thicker accumulations may be present. Alluvium is likely to be intercalated with head deposits (hill-wash) in many places.

Peat

Peat has been mapped extensively along the lower reaches of the River Burn (which flows north-eastwards between the villages of Burnham Market and Burnham Overy) and is also present offshore in Holkham Bay [TF 865 465]. This submerged occurrence must have formed within the valley of the River Burn at a time when the coastline was in a more northerly position. Peat is also present on the foreshore north of Titchwell in Brancaster Bay [TF 755 455]. According to Bridges (1998, p.25), 'a lower peat bed, 0.45 m thick, has its base between 0.75 m and 1.7 m below OD and a thinner peat occurs higher up the beach at 2.5–3 m above OD passing beneath the dunes. At low tide, the lower of these peats can be seen to have tree stumps remaining in situ'.

Peat may also be expected within deposits mapped as alluvium.

The coast and coastal deposits

One of the remarkable features of this district is the pre-Holocene coastline, which runs from west to east in an almost straight line across the district. The cause of this unusual natural feature is unknown but it is suspected to be controlled by as yet unproven faulting in the Chalk bedrock. The coastal fringe includes a west to east buried channel probably associated with a still stand position of the former Devensian ice-sheet (Figure 8). The straightness may reflect the presumed course of a pre-glacial valley associated with the Ancaster River (Clayton, 2000; Rose et al., 2001).

The coastal area, part of the most extensive low-barrier beach system in Britain, has a distinct geomorphological character. On the seaward side there are low-lying shingle banks (including barrier spits and islands), usually capped by sand dunes (Plate 4). Behind them lies a zone of sheltered salt-marsh and tidal flats up to 2.5 km wide which is flanked on the south side by a subdued-relief 'upland' (see schematic section on 1:50 000 map). Much of the system is marine-influenced, with freshwater inflows restricted to small rivers and streams.

The relationships within these deposits are complex so that, on the map, it has not always been possible to differentiate them. For example, storm beach deposits are included in bank deposits at Scolt Head Island [TF 790 464].

Tidal river or creek deposits

Several occurrences of tidal river or creek deposits are depicted on the 1:50 000 scale map, but there are many intricate networks of smaller creeks that are too narrow to be shown clearly at this scale. These rivers and creeks are the natural channels for tidal ebb and flow. As such they are an essential element of sediment transport and accretion over the marshland, enabling the marsh surface to keep pace with rising sea level. Water flow depends very much on the state of the tide; it can be rapid, so deepening the channels, causing bank failure and extending the overall creek length or width. Deposition occurs as the tidal current slackens at high water leaving sediment on the surface of the tidal flats and marshes. As currents increase on the ebb tide they do not exceed the threshold for erosion of the deposited sediment and net accretion occurs.

Due to higher velocities within the channels, the deposits within most of the tidal channels consist predominantly of sand, for example in Blakeney Harbour [TF 98 46], along The Run [TF 91 46] to the north of Wells-next- the-Sea and south [TF 79 45] of Scolt Head Island.

Tidal Flat Deposits (including 'salt-marsh deposits')

A combination of a high tidal range and a shallow gently-inclined seabed has allowed the development of extensive intertidal areas covered by tidal flat deposits. These wide intertidal areas comprise sand-dominated flats on the seaward side of the barrier spits and islands; on the landward side the flats are clay-dominated back barrier marshes and creeks. The former merge, commonly imperceptibly, into shoreface and beach deposits — the distinction in places is arbitrary. The maximum thickness of the marshland sequence is in the order of 10 metres thick.

The marsh surface appears to be silt to clay-rich ('muddy'). However, in creek sections and auger borings the sediments are seen to comprise alternating layers of silt and sand with local channels or other depressions infilled with coarser material up to gravel grade.

The marsh is a low-energy environment in which accretion tends to occur with every significant inundation. Where marshes have been reclaimed and protected within sea embankments, ground levels are lower and commonly below mean sea level. This is partly the result of land reclamation drainage and sediment consolidation but also because there is no new deposition.

Approximately half the former salt-marshes are enclosed by sea-flood defences, have been drained and are used for grazing and cultivation (as at Holkham, Burnham Deepdale and Holme next the Sea). Of the remaining marshes, a few are in their natural condition (e.g. Brancaster Marsh) whilst other managed marshes have been allowed to revert to salt-marsh or modified to include lagoons and reed-beds as part of nature reserves (e.g. Titchwell, RSPB Nature Reserve).

On topographic maps, the relatively higher parts of the tidal flats, which are inundated by only the highest of tides and thus able to support a range of halophytic plants, are often referred to as salt-marshes. There is no readily observable compositional difference between the sediments 'salt-marsh' and of the 'tidal flat environment'; they are both part of the same element of the back-barrier sediment-sink and no geological distinction is made between them.

To the north of Holkham and also north of Stiffkey, localised berms of gravel, sand and silt are included in the tidal flat deposits. These features are known as the Holkham Meals (or Meols) [TF 892 453] and the Stiffkey Meals (or Meols) [TF 966 447] and [TF 982 447], respectively. They are overlain by blown sand.

Shoreface and beach deposits

The shoreface and beach deposits thin seawards and may extend up to 2 km seaward of the low water mark as, for example, in the area between Wells-next-the-Sea and Blakeney Point. Where the beach sediments are thin, Holocene peat and estuarine deposits may be exposed in the intertidal or shallow subtidal zone, as in Brancaster and Holkham bays (Plate 5).

Shoreface and beach deposits are moved by swash and backwash across the beach prism as part of a generally westwards long-shore drift process strongly influenced by the prevailing east to west wave-induced currents (see also storm beach deposits).

The present-day shoreface and beach deposits comprise sand and pebbly sand, with subordinate gravel; those on the backshore may intercalate with blown sand. Deposition is ephemeral; periods of sediment accretion are interrupted by storm events that result in the major seaward removal of sediment. The relative proportions of sand and gravel on the foreshore differ from place to place and also with time. Typical foreshore profiles are sand- dominated in their upper parts, with gravel increasing towards the low water mark. The gravel fraction is dominated by sub-rounded to rounded flint pebbles, although rounded quartz and quartzite pebbles are also present.

Storm beach deposits

Extensive, narrow, coast-parallel ridges (or bars) of storm beach deposits are present along much of the coastline. At the easternmost ends of the bars e.g. at Blakeney Spit [TF 990 458], near West Sands [TF 891 457] and Scolt Head Island [TF 790 464] (Plate 4), the shoreface and beach deposits tend to be recurved or cuspate, aligned north-east to south-west. There are numerous relict examples of this preserved in the present Scolt Head Island e.g. at [TF 817 463], [TF 805 465] and [TF 790 460] providing supporting evidence of the westwards-accreting and landward-migrating development of the spit. Another example is present on the onshore/near- shore part of Holkham Bay [TF 855 460]. These gravel bars may have been formed along a more open foreshore when sea levels were lower than at present. Storm beach deposits also fringe the seaward sides of many of the dunes e.g. [TF 885 455].

Storm beach deposits are composed predominantly of flint gravel with subordinate sand. The storm beach deposits are of recent age and are still accreting.

Blown sand

Blown sand can occur anywhere in the barrier beach — marshland complex; whilst it forms a veneer on the beach deposits throughout the district, it is the pronounced dune-field occurrences that have been mapped. These form coast-parallel, mobile and semi-fixed dune ridges with intervening dune slacks; the sand usually capping gravel-rich storm beaches, so forming the barrier spits and islands. This combination occurs (with a few breaks associated with the larger creek outfalls) from Holme next the Sea in the west to Wells-next-the-Sea in the east. The most extensive dune-fields occur to the north of Holme next the Sea [TF 70 44] and Brancaster [TF 78 45], on Scolt Head Island [TF 81 46], to the north-east of Burnham Overy Staithe [TF 86 45] and north of Holkham [TF 89 45].

Blown sand, which is generally yellowish brown and fine-grained, attains a maximum thickness of about 5 m.

The offshore area and associated marine deposits

The offshore area is relatively shallow with water depths of generally less than 10 m. The area of shallow water continues northwards beyond the district boundary as a submerged plateau known as Burnham Flats and Docking Shoal. This extends for over 30 km north of Scolt Head Island. The deepest water found offshore in this district is just over 20 m below OD in an area between Blakeney Overfalls and Blakeney Point.

The coast is macrotidal, with spring tidal ranges increasing from east to west. Spring tidal range is 4.4 m at Cromer (22 km to the east of this district) and 6.5 m at Hunstanton (5 km to the west of this district). At low tide an area of Gore Middle may become exposed. Tidal currents increase from west to east up to a maximum of approximately 1.1 metres/second on spring tides and 0.6 metres/second on neap tides.

Offshore currents tend to flow from to the east in contrast to the wave-induced littoral currents, which flow from to the west.

The offshore Chalk platform is locally overlain by thin, discontinuous Pleistocene deposits comprising possible glacial till or glaciofluvial sand and gravel, as in the north-to-south channel north of Wells-next- the-Sea [TF 92 50]. Shallow depressions may contain Holocene peat and intertidal silt deposited during a period of lower sea level. The Chalk bedrock may be exposed (or very thinly covered by marine sand) in depressions such as Brancaster Road [TF 805 485].

Tabular and sheet deposits

Tabular and sheet deposits cover much of the sea bed and may exhibit small sand waves and other bed forms. Most of these deposits directly overlie Chalk bedrock, but locally in the west and east, thin sheets overlie discontinuous Holocene and Pleistocene deposits.

The sand waves mostly have heights of around 1 metre but are up to 2.5 metres high south of Stiffkey Overfalls; they are mostly asymmetrical with a steeper eastern face indicating a dominant eastward direction of sand transport, following the prevailing offshore current direction.

Tabular and sheet deposits comprise mainly medium and coarse-grained quartz sand with local shell-rich debris accumulations.

Bank deposits

Several extensive areas of bank deposits are present within the district. They typically form low elongate, coast-parallel, features and overlie older Holocene or more locally Pleistocene deposits e.g. [TF 92 50]. Locally they directly overlie Chalk. Those forming Gore Middle in the west and Stiffkey Overfalls, to the north of Holkham Bay, are up to 10 m thick, and those in Blakeney Overfalls in the north-east corner of the district may be over 12 m thick.

The bank deposits consist mainly of fine to medium-grained sand, but little is known of their grading.

Artificially modified ground

Worked ground is shown where natural materials have been removed, for example from quarries and pits, and road and rail cuttings. Within the district there are large numbers of small pits commonly only a few metres across and up to several metres deep. Many of these have been dug in calcareous till or chalk to obtain material for 'liming' or 'marling' adjacent acidic sandy and gravelly soils. Most of these pits and many of the cuttings are too small to depict on the 1:50 000 scale map but they are shown on the component 1:10 000 scale maps. Made ground is shown on the map where excavated or waste material has been deposited upon the natural land surface. Such areas may include spoil from sand and gravel workings, flood protection embankments, and road and rail embankments. On the 1:50 000 scale map, small embankments have generally been omitted for clarity, but they are depicted on the component 1:10 000 scale maps. Infilled ground comprises areas where the natural ground has been removed, and the void so created has been wholly or partially back-filled with natural or waste materials. In the present district these areas are restricted to former small sand and gravel, chalk, and clay pits. Landscaped ground has been remodelled with areas of cut and fill too small to be identified separately. It is of restricted extent in the district, but includes sewage farms and some ancient earthworks. Extensive areas of former tidal mud-flats (and salt-marshes), e.g. Holme [TF 715 445], Burnham Norton [TF 820 445] and north of Holkham [TF 885 445], have been enclosed by sea defence embankments and drained. These are shown as reclaimed ground on the map. Such areas are typically used for summer pasture. The underlying deposits are similar to those in the adjacent areas of undrained tidal flats.

Chapter 3 Applied geology

Geological factors have an influence on ground conditions and hence the planning and nature of future developments. By giving consideration to geological conditions at an early stage in the planning process, it may be possible to mitigate some of the problems commonly encountered during construction work. The diverse local geology gives rise to variable ground conditions and some significant aspects of this are discussed here. Other important factors are water resources, mineral workings, gas emissions and the risk of flooding.

Mineral resources

Building stone

A variety of local rocks including ironstones and ferruginous sandstones from just west of the district, chalk and flint have been used for building purposes. A traverse from west to east across the northern part of the district reveals a change from houses and walls built of carstone (Early Cretaceous ferruginous sandstone) to houses built predominantly of chalk (Plate 6) and flint reflecting the local supply of materials. The chalk used in the buildings appears to be derived from the Grey Chalk Subgroup and in particular the harder horizons of the Paradoxica Bed, Inoceramus Bed and the Totternhoe Stone. Chalk is also being used for present-day buildings, but this is now brought into the district from elsewhere. The chalk is susceptible to frost and care is required to keep it as dry as possible.

Chalk

Chalk has been worked in a number of pits in the district, mostly for agricultural needs. The large pit [TF 928 428] just south-east of Wells-next-the-Sea has been worked for resources from both the Chalk and the overlying very chalk-rich tills of the Sheringham Cliffs Formation.

Marl

Many fields within the outcrop of the Sheringham Cliffs Formation contain degraded small pits, commonly only a few metres across. These are shown on the 1:10 000 scale maps but many are omitted from the 1:50 000 scale map. These pits were dug to obtain calcareous alkaline material for spreading on adjacent acidic soils developed on the sands and gravels of the Briton's Lane Formation, a process known as 'marling'.

Aggregate, ballast and building sand

Within the district there are a number of small pits in the glacigenic deposits that have been worked for sand or gravel; several of these still provide materials for individual farm or estate use. Some of the larger disused pits probably provided materials for the construction of local airfields and defences during the Second World War. The Early Cretaceous formations which crop out just west of the district provide a more extensive source of aggregate and building sand.

Spoil from excavations for an irrigation reservoir about 800 m east of Beacon Hill [TF 742 417] revealed a deposit comprised of boulders, cobbles and very coarse gravel. The clasts consist of both chalk and flint. At the time of survey (2004) a stockpile of the deposit was being screened on site and transported for use as fill.

Water resources

The Chalk is the main aquifer in the district. Groundwater within the Chalk may be stored both in the intergranular pores and also within microfissures and macrofissures, although groundwater movement relies on flow within fissures. The density of the fissures tends to be greatest in valleys and other low-lying areas, where stress release from the removal of overburden and the enlargement of fissures by solution offer the best hydraulic conditions for high-yielding boreholes.

Groundwater in the Chalk is of the calcium bicarbonate type. The aquifer is vulnerable to diffuse pollution, particularly where there is no cover of till. It should also be noted that the tills within the Sheringham Cliffs and Holderness formations are typically more permeable than the tills within the Lowestoft Formation, which is derived from Jurassic mudstones and has a much higher clay content.

Over-pumping of water adjacent to the coast may lead to the ingress of saline water to the aquifer.

Many farms now have their own reservoirs, in which pumped water collected during the wetter winter months is stored for irrigation during the drier summer months.

Geological hazards and engineering properties

Chalk dissolution

Chalk is prone to dissolution because of the action of acidic rainwater and groundwater, particularly in the near-surface vadose zone. This may result in the formation of cavities and pipes that typically become infilled with overlying material. In rural areas such as the Wells-next-the-Sea district, this may cause particular problems with lined irrigation reservoirs constructed on either chalk or very chalk-rich till. Movement of sand or other material within dissolution pipes may ultimately lead to failure of the liner and loss of water.

Landslides

Landslides appear to be restricted to a small area [TF 97 42] near Stiffkey, where steep valley sides in Chalk have suffered minor sliding resulting in areas of uneven ground. The age of the landsliding is unknown.

Coastal 'erosion' and marine-induced flooding

The coastline is still responding to changes in the coastal system due to the rise in sea level since the last glaciation, when sea level stood at some 65 m below its present level. During the early Holocene the expanding North Sea rapidly moved the coastline southwards to its present position, creating broad expanses of intertidal flats, barrier beaches and marshland. The present shoreline complex is therefore relatively young and low-lying (mostly below +5 m OD).

Much of the seaward-facing part of the coastline is in its natural state with little or no artificial protection; essentially the barrier spits and islands form an almost continuous flood bank. Human intervention has been mostly at the local level, such as establishing preferred channels for shipping and the construction of local embankments to enclose and drain marshland for agriculture.

The 1953 North Sea storm surge and associated widespread flooding, which resulted in many deaths, costly property damage and saline contamination of farmland, had a marked impact on this district and adjoining neighbourhoods. Modern concerns about local coastal erosion and marine flooding are driven by national and global concerns about climate change and climatic impacts.

Numbers of rising sea level scenarios have been modelled for south-east England, typically predicting a rise in the order of 1 m in 1000 years. If sea level rise alone is considered, the amount of landward encroachment by the sea is determined not only by the rise itself but also by the seaward slope of the coastal area. Coastlines with steeper slopes will experience less landward transgression than those with gentle slopes.

The offshore ramp between Scolt Head Island and Burnham Flats slopes at around 1:3000. Projected onshore a 1 mm/year rise in sea level would result in a landward displacement of the coastline by 3 m/year; a 5 mm rise would result in a 15 m/year transgression (Clayton, 2004). This is a simplistic model; in reality there is a complex relationship between factors such as the non-uniform loss of wave/current-induced erosive energy across this shallow ramp (the slope is variable across the district), longshore drift and unpredictable rates of sediment supply from distant cliff sources, weather conditions and the frequency of storm surges.

Other hazards

Radon is a naturally occurring radioactive gas that is produced by the progressive decay of uranium, which is found in small but variable quantities in all soils and rocks. Radon released from rocks and soils normally quickly disperses in the atmosphere and does not present a hazard. However, radon that enters poorly ventilated spaces such as basements may become potentially hazardous, leading to increased risk of serious illness, including lung cancer.

Engineering properties

There are no published engineering data for the Chalk bedrock within the district, but its indurated nature, particularly that of the Grey Chalk Subgroup (Lower Chalk), suggest that it is stronger, in its unweathered state, than Chalk at the same stratigraphical level elsewhere in southern England. Within the Chalk the Paradoxica Bed and the Inoceramus Bed form significantly harder bands. However, the near-surface bulk properties are largely governed by the degree of weathering and fracturing.

The broad engineering characteristics of the most extensive onshore superficial deposits are described in (Figure 9).

Information sources

Sources of further geological information held by the British Geological Survey relevant to the Wells-next-the-Sea 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 records 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.

Books

British Regional Geology Guides
East Anglia and adjoining areas (Fourth edition), 1961
Memoirs
Geology of the country around King's Lynn and The Wash (Sheets 145 and part of 129), 1994
Sheet explanations
Geology of the country around Cromer (Sheet 131), 2002

Maps

Geological maps
1:1 500 000
Tectonic map of Britain, Ireland and adjacent areas, 1996
1:1 000 000
Pre-Permian geology of the United Kingdom (South), 1985
1:625 000
Bedrock geology of the United Kingdom: South Map (2007)
Quaternary geology: South sheet (1977)
1:250 000
East Anglia: Solid Geology, 1986 East Anglia: Seabed sediments, 1988
East Anglia: Quaternary Geology, 1991
1:50 000
Sheet 129 The Wash (Solid and Drift), 1997
Sheet 131 Cromer (Solid and Drift), 2003
Sheet 145, 129 King's Lynn and The Wash (Solid and Drift), 1978
Sheet 146 Fakenham (Solid and Drift) Provisional, 1999
1:10 000
Details of the original geological surveys are listed on editions of the 1:50 000 scale or 1:63 360 scale geological sheets. Relevant parts of the component 1:10 000 scale maps for the Wells-next-the-Sea district were surveyed between 1997 and 2003 by the following BGS geologists: S J Booth, R J O Hamblin, H Kessler, and B S P Moorlock.
Copies of maps from these and earlier large-scale surveys are available for reference in the BGS Libraries at Keyworth and Edinburgh, and at the BGS London Information Office in the Natural History Museum Earth Galleries. Copies for purchase are produced on a print-on-demand basis and are available from the BGS Sales Desk.
Digital geological map data
In addition to the printed publications, many BGS geological maps are available in digital form. Details are given on the BGS website. National coverage of digital geological map data (DiGMapGB) is derived from geological maps at scales of 1:625 000, 1:250 000 and 1:50 000. Selected areas also have digital geological data derived from 1:10 000 scale geological maps. Digital geological data for offshore areas is derived from 1:250 000 scale geological maps.
Geophysical maps
1:1 000 000
Coloured shaded-relief gravity anomaly map of the Low Countries, 2001
Coloured shaded-relief magnetic anomaly map of the Low Countries, 2005
1:625 000
Gravity anomaly map of the UK: South sheet (2007)
Magnetic anomaly map of the UK: South sheet (2007)
Geochemical maps
1:625 000
Methane, carbon dioxide and oil susceptibility, Great Britain — South, 1995
Radon Potential based on solid geology, Great Britain — South, 1995
Distribution of areas with above national average background concentrations of potentially harmful elements (As, Cd, Cu, Pb and Zn), Great Britain — South, 1995
Hydrogeological maps
1:625 000
Hydrogeological map of England and Wales, 1977
1:125 000
Hydrogeological map of Northern East Anglia, 1981
Groundwater vulnerability maps
1:100 000
West Norfolk, 1990
East Norfolk, 1990
Mineral Maps
1:1 000 000
Industrial minerals resource map of Britain, 1996
Mineral Resource Planning maps and reports
Norfolk: report and map

Documentary records collections

Detailed geological survey information, including large scale geological field maps, is archived at the BGS. Enquiries concerning unpublished geological data for the district should be addressed to the Manager, National Geoscience Data Centre (NGDC), BGS Keyworth.

Borehole and trial pit records

Borehole records for the district are catalogued in the NGDC at BGS Keyworth. Index information, which includes site references, names and depths for these boreholes, is available through the BGS website. Copies of records in the public domain can be ordered through the same website, or can be consulted at BGS Keyworth.

Hydrogeological data

Records of water wells, springs, and aquifer properties held at BGS Wallingford can be consulted through the BGS Hydrogeology Enquiry Service.

Geophysical data

These data are held digitally in the National Gravity Databank and the National Aeromagnetic Databank at BGS Keyworth. Seismic reflection data from coal and hydrocarbon exploration programmes is available for the north of the district. Indexes can be consulted on the BGS website.

BGS Lexicon of named rock units

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Sheet 130 (Wells-next-the-Sea) are held in the BGS Stratigraphic Lexicon database, which can be consulted on the BGS website. Further information on the database can be obtained from the Lexicon Manager at BGS, Keyworth.

BGS photographs

The National Archive of Geological Photographs, held at BGS in Keyworth and Edinburgh, includes a number of photographs from the Wells-next-the-Sea district. Part of the collection can be viewed at BGS libraries at Keyworth and Edinburgh, and on the BGS website. Copies of the photographs can be purchased from BGS.

Other relevant collections

Groundwater licensed abstractions, Catchment Management Plans and landfill sites

Information on licensed water abstraction sites, groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, detail of aquifer protection policy and extent of Washlands and licensed landfill sites are held by the Environment Agency.

References

Most of the references listed here can be consulted at the BGS Library, Keyworth. Copies of BGS publications can be obtained from the sources described in the previous section. The BGS Library may be able to provide copies of other material, subject to copyright legislation. Links to the BGS Library catalogue and other details are provided on the BGS website.

Allsop, J M. 1983. Geophysical appraisal of two gravity minima in the Wash district. Report of the Institute of Geological Sciences, No. 83/1.

Andrews, J, and Chroston, N. 2000. Holocene evolution of the north Norfolk barrier coastline in the Holkham–Cley area. 131–148 in The Quaternary of Norfolk and Suffolk. Lewis, S G, Whiteman, C A, and Preece, R (editors). (London: Quaternary Research Association.)

Barker, R D, Lloyd, J W, and Peach, D W. 1984. The use of resistivity and gamma logging in lithostratigraphical studies of the Chalk in Lincolnshire and South Humberside.Quarterly Journal of Engineering Geology and Hydrogeology, Vol. 17, 71–80.

Brand, D, Booth, S J, and Rose, J. 2002. Late Devensian glaciation, ice-dammed lake and river-diversion, Stiffkey, north Norfolk, England. Proceedings of the Yorkshire Geological Society, Vol. 54, 35–46.

Bridges, E M. 1998. Classic landforms of the North Norfolk Coast. (Sheffield: The Geographical Association.)

Bristow, C R. 1990. Geology of the country around Bury St Edmunds. Memoir of the British Geological Survey, Sheet 189 (England and Wales).

Cameron, T J D, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. United Kingdom offshore regional report: the geology of the southern North Sea. (Keyworth, Nottingham: British Geological Survey.)

Casey, R, and Gallois, R W. 1973. The Sandringham Sands of Norfolk. Proceedings of the Yorkshire Geological Society, Vol. 40, 1–22.

Chroston, P N, Jones, R, and Makin, B. 1999.Geometry of Quaternary sediments along the north Norfolk coast, U K: a shallow seismic study. Geological Magazine, Vol. 136, 465–474.

Chroston, P N, and Sola, M. 1982. Deep boreholes, seismic refraction lines, and the interpretation of gravity anomalies in Norfolk. Journal of the Geological Society, London, Vol. 139, 255–264.

Clayton, K M. 2000. Glacial erosion of the Wash and Fen basin and the deposition of the chalky till of eastern England. Quaternary Science Reviews, Vol. 19, 811–822.

Clayton, K M. 2004. Adjustment to greenhouse gas induced sea level rise on the Norfolk Coast — a case study. 310–321 in Climate and sea level change: observations, projections and implications. Warrick, R A, Barrow, E M, and Wigley, T M L (editors). (Cambridge: Cambridge University Press.)

Cornwell, J D, and Walker, A S D. 1989. Regional geophysics. 25–51 in Metallogenic models and exploration criteria for buried mineral deposits — a multidisciplinary study in eastern England. Plant, J A, and Jones, D G (editors). (Nottingham: British Geological Survey.)

Cox, F C, Gallois, R W, and Wood, C J. 1989.Geology of the country around Norwich. Memoir of the British Geological Survey, Sheet 161 (England and Wales).

Ehlers, J, and Gibbard, P L. 1991. Anglianglaciation and glacial deposits in Britain and the adjoining offshore regions. 17–24 in Glacial deposits in Great Britain and Ireland. Ehlers, J, Gibbard, P L, and Rose, J (editors). (Rotterdam: Balkema.)

Ehlers, J, Gibbard, P L, and Whiteman, C A. 1987. Recent investigations of the Marly Drift of northwest Norfolk, England. 39–54 in Tills and glaciotectonics. Van der Meer, J J M (editor). (Rotterdam: Balkema.)

England, A C, and Lee, J A. 1991. Quaternary deposits of the eastern Wash margin. Bulletin of the Geological Society of Norfolk, Vol. 40, 67–99.

Funnell, B M, and Pearson, I. 1989. Holocene sedimentation on the North Norfolk barrier coast in relation to relative sea-level change. Journal of Quaternary Science, Vol. 4, 23–36.

Gallois, R W. 1979. The Pleistocene history of west Norfolk. Bulletin of the Geological Society of Norfolk, Vol. 30, 3–38.

Gallois, R W. 1994. Geology of the country around King's Lynn and The Wash. Memoir of the British Geological Survey, Sheet 145 and part of 129 (England and Wales).

Gallois, R W, and Morter, A A. 1976. The Trunch Borehole. Report of the Institute of Geological Sciences, No. 76/10.

Gaunt, G D, Fletcher, T P, and Wood, C J. 1992.Geology of the country around Kingston-upon-Hull and Brigg. Memoir of the British Geological Survey, Sheets 80 and 89 (England and Wales).

Hoare, P G, and Connell, E R. 2003. Drift deposits at the 'Red Lion', Stiffkey, north Norfolk. Quaternary Newsletter, Vol. 101, 52–54.

Jeans, C V. 1980. Early submarine lithification in the Red Chalk and Lower Chalk of eastern England: a bacterial control model and itsimplications. Proceedings of the Yorkshire Geological Society, Vol. 4, 81–157.

Jukes-Browne, A J. 1887. Geology of east Lincolnshire. Memoir of the Geological Survey of Great Britain.

Jukes-Browne, A J, and Hill, W. 1904. The Cretaceous rocks of Britain. Vol. III. The Upper Chalk of England. Memoir of the Geological Survey of the United Kingdom.

Kent, P E. 1947. A deep boring at North Creake, Norfolk. Geological Magazine, Vol. 84, 2–18.

Lee, M K, Pharaoh, T C, and Soper, N J. 1990.Structural trends in central Britain from images of gravity and aeromagnetic fields. Journal of the Geological Society, London, Vol. 147, 241–258.

Lewis, S G. 1999. Eastern England. 10–27 in A revised correlation of Quaternary deposits in the British Isles. Bowen, D Q (editor). Geological Society of London Special Report, No. 23.

Lunkka, J P. 1994. Sedimentation and lithostratigraphy of the North Sea Drift and Lowestoft Till Formations in the coastal cliffs of northeast Norfolk. Journal of Quaternary Science, Vol. 9, 209–233.

Mitchell, S F. 1995. Uintacrinus angelicus Rasmussen from the Upper Cretaceous Flamborough Chalk Formation of Yorkshire: implications for the position of the Santonian-Campanian boundary. Cretaceous Research, Vol. 16, 745–756.

Moorlock, B S P, Hamblin, R J O, Booth, S J, and Kessler, H. 2002. Geology of the Cromerdistrict — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey, 1:50 000 Sheet 131 Cromer (England and Wales).

Mortimore, R N, and Wood, C J. 1986. The distribution of flint in the English Chalk, with particular reference to the 'Brandon Flint Series' and the high Turonian flint maximum. 7–20 in The Scientific Study of Flint and Chert: Proceedings of the Fourth International Flint Symposium held at Brighton Polytechnic, 10–15 April 1983. Sieveking, G de G, and Hart, M B (editors). (Cambridge: Cambridge University Press.)

Mortimore, R N, Wood, C J, and Gallois, R W.2001. British Upper Cretaceous Stratigraphy. Geological Conservation Review Series. No. 23. (Peterborough: Joint Nature Conservation Committee.)

Noble, S R, Tucker, R D, and Pharaoh, T C.1993. Lower Palaeozoic and Precambrian igneous rocks from eastern England and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes. Geological Magazine, Vol. 130, 835–846.

Owen, E F, and Thurrell, R G. 1968. British Neocomian rhynchonellid brachiopods.Bulletin of the British Museum (Natural History) Geology, Supplement 8, 1–164.

Owen, H G. 1995. The upper part of the Carstone and the Hunstanton Red Chalk (Albian) of the Hunstanton Cliff, Norfolk. Proceedings of the Geologists' Association, Vol. 106, 171–181.

Pawley, S M, Candy, I, and Booth, S J. 2006. The Late Devensian terminal moraine ridge at Garret Hill, Stiffkey valley, north Norfolk, England. Proceedings of the Yorkshire Geological Society, Vol. 56, 31–39.

Peake, N B, and Hancock, J M. 1970. The Upper Cretaceous of Norfolk [reprinted with corrigenda and addenda]. 293–339 and 339A–339J in The Geology of Norfolk. Larwood, G P, and Funnell, B M (editors). (Norwich: The Geological Society of Norfolk.)

Peake, N B, and Hancock, J M. 2000. The Chalk of Norfolk I: 1961–2000. 22–26 in The Geological Society of Norfolk 50th anniversary volume. Dixon, R G (editor). (Norwich: Geological Society of Norfolk.)

Perrin, R M S, Rose, J, and Davies, H. 1979. The distribution, variation and origins of pre-Devensian tills in eastern England. Philosophical Transactions of the Royal Society of London, Vol. B287, 535–570.

Rawson, P F, Allen, P, and Gale, A. 2001. The Chalk Group a revised lithostratigraphy. Geoscientist, Vol. 11, 21.

Riding, J B, Rose, J, and Booth, S J. 2003.Allochthonous and indigenous palynomorphs from the Devensian of the Warham Borehole, Stiffkey, north Norfolk, England; evidence for the sediment provenance. Proceedings of the Yorkshire Geological Society, Vol. 54, 223–237.

Rose, J, Candy, I, Moorlock, B S P, Wilkins, H, Lee, J A, Hamblin, R J O, Lee, J R, Riding, J B, and Morigi, A N. 2002. Early and early Middle Pleistocene river, coastal and neotectonic processes, southeast Norfolk, England. Proceedings of the Geologists' Association, Vol. 113, 47–68.

Rose, J, Moorlock, B S P, and Hamblin, R J O. 2001. Pre-Anglian fluvial and coastal deposits in eastern England: lithostratigraphy andpalaeoenvironments. Quaternary International, Vol. 79, 5–22.

Seeley, H G. 1864. On the fossils of the Hunstanton Red Rock. Annual Magazine of Natural History Series 3, Vol. 14, 276–280.

Smith, N J P. 1987. The deep geology of central England: prospectivity of the Palaeozoic rocks. 217–224 in Petroleum geology of north west Europe. Brooks, J, and Glennie, K W (editors). (London: Graham and Trotman.)

Straw, A. 1960. The limit of the 'Last' Glaciation in north Norfolk. Proceedings of the Geologists' Association, Vol. 71, 379–390.

Straw, A. 1965. A reassessment of the Chalky Boulder Clay or Marly Drift of north Norfolk. Zeitschrift für Geomorphologie, Vol. 9, 209–221.

Straw, A. 1973. The glacial geomorphology of central and north Norfolk. The East Midland Geographer, Vol. 5, 333–354.

Swinnerton, H H. 1935. The rocks below the Red Chalk of Lincolnshire and their cephalopod faunas. Quarterly Journal of the Geological Society, London, Vol. 91, 1–46.

Ward, W H, Burland, J B, and Gallois, R W. 1968. Geotechnical assessment of a site at Mundford, Norfolk, for a large proton accelerator. Géotechnique, Vol. 18, 399–431.

Whitaker, W, and Jukes-Browne, A J. 1899.Geology of the borders of the Wash: including Boston and Hunstanton. Memoir of the Geological Survey of Great Britain.

Whitaker, W, Skertchley, S B J, and Jukes-Browne, A J. 1893. Geology of south-western Norfolk and northern Cambridgeshire. Memoir of the Geological Survey of Great Britain.

Whitham, F. 1991. The stratigraphy of the Upper Cretaceous Ferriby, Welton and Burnham formations north of the Humber, north-east England. Proceedings of the Yorkshire Geological Society, Vol. 48, 227–255.

Whitham, F. 1993. The stratigraphy of the Upper Cretaceous Flamborough Chalk Formation north of the Humber, north-east England. Proceedings of the Yorkshire Geological Society, Vol. 49, 235–258.

Whittaker, A (editor). 1985. Atlas of onshore sedimentary basins in England and Wales. (Glasgow: Blackie.)

Wilkinson, I P. 2004. Chalk biostratigraphy of the Wells-next-the-Sea district (1:50K Sheet 130) based on foraminifera. British Geological Survey Internal Report, I R/04/123.

Wiltshire, T. 1859. On the Red Chalk of England. The Geologist, Vol. 2, 261–278.

Wiltshire, T. 1869. On the Red Chalk of Hunstanton. Quarterly Journal of the Geological Society, London, Vol. 25, 185–192.

Wood, C J, Morter, A A, and Gallois, R W. 1994. Appendix 1: Upper Cretaceous stratigraphy of the Trunch Borehole. 105–110 in Geology of the country around Great Yarmouth. Memoir of the British Geological Survey, Sheet 162 (England and Wales).

Woodward, H B. 1884. Geology of the country around Fakenham, Wells and Holt. Memoir of the Geological Survey of Great Britain.

Index to the 1:50 000 Series maps of the British Geological Survey

The map shows the sheet boundaries and numbers of the 1:50 000 Series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased.

(Index map)

The area described in this sheet explanation is indicated by a solid block.

British geological maps can be obtained from sales desks in the Survey's principal offices, through the BGS London Information Office at the Natural History Museum, and from BGS-approved stockists and agents.

Figures and plates

Figures

(Figure 1) Colour shaded relief Bouguer gravity anomaly map in milligals (mGals) calculated against the Geodetic Reference System 1967, referred to the National Gravity Reference Net, 1973. Contour interval 1 mGal.

(Figure 2) Colour shaded relief magnetic anomaly map. Total field magnetic anomalies in nanotesla (nT) relative to a local variant of IGRF90. Contour interval 10 nT.

(Figure 3) Lithostratigraphy of the Jurassic strata within the district.

(Figure 4) Lithostratigraphy of the Lower Cretaceous strata within the district. N.B. The Jurassic/Cretaceous boundary lies at the top of the Runcton Member.

(Figure 5) The stratigraphy of the Chalk Group in the Wells district, and its relationship to lithostratigraphical subdivisions in southern England and north-east England.

(Figure 6) Occurence of Chalk Group biozones in the Wells district. Based on data from N B Peake (BGS archives) and I P Wilkinson.

(Figure 7) Correlation and stratigraphical interpretation of key boreholes on the Chalk Group west Norfolk and Lincolnshire. Log interpretations for North Pickenham follow Mortimore and Wood (1986); log interpretation for Killingholme follow Barker et al. (1984).

(Figure 8) Features associated with the Devensian ice sheet.

(Figure 9) Engineering characteristics of the Chalk Group and selected superficial deposits.

Plates

(Geological succession) Summary of the geological succession in the Wells-next-the-Sea district.

(Index map) Index to the 1:50 000 Series maps of the British Geological Survey

(Front cover) The Harbour, Wells- next-the-Sea. The Dutch ketch Albatros at the Quay, with the old Granary behind [TF 917437]. Photograph: Paul Witney (P694831).

(Rear cover) Geology of the Wells-next-the-Sea district. An explanation of sheet 130 (England and Wales) 1:50 000 series map

(Plate 1) The two common till lithologies within the Sheringham Cliffs Formation, Wells-next-the-Sea Pit. The trowel is 22 cm long. Photograph © S M Pawley.

(Plate 2) Clastic dyke structures within Sheringham Cliffs Formation, Telegraph Plantation Pit. View is about 0.75 cm across. Photograph © S M Pawley.

(Plate 3) Trial pit in Ringstead Sand and Gravel Member, Ringstead Common. The sand units are fine-grained and carbonate- rich. Chalky gravel with a mud-rich matrix and coal fragments forms horizontal and tabular beds. The deposits are banked against the Chalk bedrock of the valley sides. Photograph © S M Pawley.

(Plate 4) Holocene deposits of Scolt Head Island [TF 810 460], viewed from the west. Photograph © Mike Page Aerial Photography.

(Plate 5) Holocene peat and estuarine mud exposed in the intertidal zone at Brancaster Bay [TF 755 453] (P694749).

(Plate 6) Chalk used as building stone (P667881).

Figures

(Geological succession) Summary of the geological succession in the Wells-next-the-Sea district.

Period	Series/Epoch	Group	Formation or lithogenetic units	Members	Thickness (m)
QUATERNARY	HOLOCENE	Flandrian	Artificial (man-made) deposits Alluvium, Peat, Blown sand Marine and coastal deposits
	PLEISTOCENE	Devensian (Marine Isotope Stage 2) to post- Anglian (Marine Isotope Stage 10?)	Head
			Holderness Formation	Ringstead Sand and Gravel Member
				Holkham Till Member
				Red Lion Till Member
			Briton's Lane Formation
			Sheringham Cliffs Formation
CRETACEOUS	LATE CRETACEOUS	Chalk Group	White Chalk Subgroup		c.285
			Grey Chalk Subgroup		c.13
	EARLY CRETACEOUS		Hunstanton Formation		c.1
			Carstone Formation		17–19
			Roach Formation		c.17
			Dersingham Formation		c.12
			Sandringham Sands Formation	Leziate Member	Up to c.50
				Mintlyn Member
JURASSIC	LATE JURASSIC			Runcton Member
				Roxham Member
		Ancholme Group	Kimmeridge Clay Formation		140 to 201
			Ampthill Clay Formation
			West Walton Formation
	MID JURASSIC		Oxford Clay Formation
			Kellaways Formation
		Great Oolite Group	Cornbrash Formation		6–40
			Undivided
	EARLY JURASSIC	Lias Group			170–182
TRIASSIC		Penarth Group			4–7
		Mercia Mudstone Group			115 to 225 offshore 156 to 198 onshore
		Sherwood Sandstone Group			45 to 200 offshore 40–107 onshore
PERMIAN		Present offshore only
PALAEOZOIC	CAMBRIAN, ORDOVICIAN and CARBONIFEROUS (offshore only)
PRECAMBRIAN	Undifferentiated

(Figure 3) Lithostratigraphy of the Jurassic strata within the district.

	Lithostratigraphy		Lithology	Thickness (m)
Late Jurassic	Ancholme Group	Kimmeridge Clay Formation	mainly mudstone	49–116
		Ampthill Clay Formation	mudstone with interbedded limestone	26–58
		West Walton Formation	calcareous mudstone and limestone	14
		Oxford Clay Formation	mainly mudstone	31–42
Mid Jurassic		Kellaways Formation	mudstone, sandstone and limestone	6–16
	Great Oolite Group	Cornbrash Formation	limestone	c.1
	Great Oolite Group	undifferentiated	mudstone, sandstone and limestone	0–30
Early Jurassic	Lias Group	undifferentiated	mudstone, siltstone, sandstone and limestone	170–182

(Figure 4) Lithostratigraphy of the Lower Cretaceous strata within the district. N.B. The Jurassic/Cretaceous boundary lies at the top of the Runcton Member.

Formation	Member	Lithology	Thickness in BGS Hunstanton Borehole
Hunstanton Formation (previously Red Chalk)		nodular pink and white limestone interbedded with brick-red calcareous clay	1.12
Carstone Formation		greenish grey, 'chamositic', clayey, pebbly sandstone weathering to rusty brown sand	18.90
Roach Formation		grey and brown, pebbly, oolitic (limonitic), soft mudstone	16.56
Dersingham Formation		rhythmic alternations of sand and soft pebbly mudstone passing northwards into mudstone and pebbly mudstone	11.60
Sandringham Sands Formation	Leziate Member	loose white and grey fine and medium-grained sands, glauconitic in part	22.00
	Mintlyn Member	green glauconitic sands with thin beds of glauconitic mudstone and tabular bands of sideritic mudstone	9.80
	Runcton and Roxham Members	loose green glauconitic sand with calcareously cemented phosphatic pebble bed at base	?

(Figure 9) Engineering characteristics of the Chalk Group and selected superficial deposits.

Engineering geological unit	Geological unit	Geotechnical characteristics	Trench stability	Use as fill	Natural slope stability
Non-cohesive soil (coarse)	Sheringham Cliffs Formation sand and gravel Ringstead Sand and Gravel Member	Medium-dense to dense, sand and gravel. May contain lenses of clay and silt	Moderately stable, less stable below water table	Suitable	Areas of natural unstable slopes unlikely
Cohesive soil	Sheringham Cliffs Formation till Holkham Till Member	Firm to stiff, fissured, overconsolidated sandy clay and clayey sand with flint and chalk clasts	Generally stable but running sand from lenses possible.'Peeling-in' risk	Suitable	Unstable slopes are possible if saturated, loaded or undercut
Mixed (cohesive and non-cohesive soils)	Alluvium	Variable composition, mainly very soft to firm clay and silt, loose to dense sand, with peat and underlying gravel; high moisture content. Compressible with uneven settlement	Moderately stable; decreasing with increasing moisture content. Possibly running sand below water table	Generally suitable except peat and organic soils	Areas of natural unstable slopes are unlikely except for banks of streams and drainage channels, which may be sensitive to loading or undercutting
	Head	Highly variable. Weak/ loose cohesive and non-cohesive soil and clasts covering lower slopes and at foot of slopes	Unstable	Poor to moderate	Highly unstable. Contains relict shear planes capable of reactivation if slopes are saturated, loaded or undercut
	Made Ground	Very variable grain size, compaction and composition	Moderate to unstable	Determine on site-specific basis	Determine on site-specific basis
	Infilled Ground	Potential contamination
Very weak to weak limestone	Chalk Group	Very weak to weak limestone with flints (predominantly in upper part). May be highly fractured and is commonly reduced to soft to firm soil in near-surface zone. Possibility of karstic weathering with solution pipes and more irregular areas	Generally good dependant on weathering grade and fracture spacing	Suitable for general fill	Not generally prone to slope failure, but some failure noted in the Stiffkey area. Rock fall may occur on steep slopes. Very weak limestone of the Grey Chalk Subgroup may be subject to instability if saturated, loaded or undercut