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Geology of the country around Tewkesbury. Memoir for 1:50 000 geological sheet 216 (England and Wales)

B C Worssam, R A Ellison and B S P Moorlock

Bibliographical reference: Worssam, B C, Ellison, R A and Moorlock, B S P. 1989. Geology of the country around Tewkesbury. Memoir of the British Geological Survey, Sheet 216 (England and Wales).

British Geological Survey

• Authors
• B C Worssam, R A Ellison And B S P Moorlock
• Contributors
• A J M Barron R J Wyatt

London: Her Majesty's Stationery Office 1989. © Crown copyright 1989 First published 1989. ISBN 0 11 884426 1. Printed in the United Kingdom for Her Majesty's Stationery Office. Dd 240426 C10 9/89

• Authors
• B C Worssam, BSc R A Ellison, BSc B S P Moorlock, BSc, PhD British Geological Survey, Keyworth
• Contributors
• A J M Barron, BSc R J Wyatt, MBE British Geological Survey, Keyworth

Other publications of the Survey dealing with this district and adjoining districts

Books

• Memoirs
• Geology of the country between Hereford and Leominster, Sheet 198, 1989
• Geology of the country around Stratford upon Avon and Evesham, Sheet 200, 1974
• Geology of the country around Monmouth and Chepstow, Sheets 233 and 250, 1961
• British Regional Geology
• Central England, 3rd Edition, 1969

Maps

• 1:1000 000
• Pre-Permian geology of the United Kingdom (South), 1985
• 1:625 000
• Geological map of the United Kingdom (Solid Geology), 3rd Edition, 1979, South Sheet
• Quaternary map of the United Kingdom, 1st Edition, 1977, South Sheet
• Aeromagnetic map of Great Britain, South Sheet, 1st Edition, 1965
• Bouguer anomaly map of the British Isles, Southern Sheet, 1986
• Hydrogeological map of England and Wales, 1st Edition, 1977
• 1:250 000
• 51N 04W Bristol Channel: Sea bed sediments and Quaternary, 1986
• 51N 04W Bristol Channel: Solid Geology, 1988
• 51N 04W Bristol Channel:Aeromagnetic anomaly, 1980
• 51N 04W Bristol Channel:Bouguer gravity anomaly, 1986
• 52N 04W Mid Wales and Marches: Solid Geology, in press
• 52N 04W Mid Wales and Marches: Aeromagnetic anomaly, 1980
• 52N 04W Mid Wales and Marches: Bouguer gravity anomaly, 1986
• 1:63360
• Sheet 235 Cirencester, Drift (1933) 1:50 000
• Sheet 198 Hereford, Solid and Drift (1989)
• Sheet 200 Stratford-upon-Avon, Solid and Drift (1974)
• Sheet 216 Tewkesbury, Solid and Drift (1989)
• Sheet 217 Moreton-in-Marsh, Drift (1981)
• Sheet 233 Monmouth, Solid and Drift (1974)
• Sheet 234 Gloucester, Solid and Drift (1972)

(Front cover)

(Rear cover)

Preface

The district covered by the Tewkesbury (216) Sheet of the 1:50 000 geological map of England and Wales was originally surveyed on the one-inch scale as Old Series Sheets 43SE by D Williams, J Phillips, H H Howell and A C Ramsey, published in 1845 (revised 1855); 43NE by J Phillips and H H Howell, published in 1845 (revised in 1855); and 44 by E Hull and H H Howell, published in 1856 (revised 1879 to include a survey of the Penarth Group by H W Bristow). A memoir by Phillips describing the geology of the Malvern Hills and surrounding area was published in 1848.

The north-east corner of the Tewkesbury Sheet was surveyed on the six-inch scale by A Whittaker in 1966. The remainder of the sheet was surveyed on the 1:10 000 scale by B C Worssam, R A Ellison, B S P Moorlock, R J Wyatt and A J M Barron between 1979 and 1982.

This memoir is a summary account of the geology depicted on the published 1:50 000 Solid and Drift edition of the Tewkesbury Sheet. Dr S G Molyneux has reported on acritarchs from the Fowlet Farm Borehole. Cambrian invertebrates have been identified by Dr A W A Rushton and Silurian invertebrates by Dr D E White. Dr G Warrington has identified Triassic miospores, and Dr H C Ivimey-Cook faunas from the Lias Group. Dr M J Simms has kindly allowed the use of his collection of Lias Group fossils. Where possible, fossil names quoted from earlier publications have been updated. Photographs, a list of which is in Appendix 2, were taken by C J Jeffery in 1980 and 1981 and by J Rhodes in 1950. The text figures were drawn in the BGS drawing office, Keyworth. British Coal has provided reports on the coals of the Newent Coalfield. This account has been edited by J E Wright.

Grateful acknowledgement is made to numerous organisations and individuals, including landowners, quarry operators, consulting engineers and public and local authorities, for generous help during the survey.

F G Larminie, Director, British Geological Survey, Keyworth, Nottinghamshire NG12 5GG. 11 April 1989

Data held by BGS

Geological maps at 1:10 000 scale

The survey gives complete coverage of the Tewksbury district. Geological National Grid 1:10 000 maps included wholly or in part in Sheet 216 are listed below together with the initials of the surveyors and the dates of the survey. The surveyors were A J M Barron, R A Ellison, B S P Moorlock, A Whitaker, B C Worssam and R J Wyatt. All maps are available for consultation or for purchase as dyeline prints. Those maps marked * have been surveyed only in part.

Geological notes and local details

BGS Land Survey Open File Reports

Each 1:10 000 map has an accompanying open file report. These are in two series. Authors' names are abbreviated as for maps.

Geology with special emphasis on potential resources of sand and gravel

BGS open file reports from specialist departments

Petrography of Triassic sediments from the Eldersfield Borehole. Petrology Unit Internal Report No. 215, 1981. Phosphate mineralisation in a carbonate mudstone from Lower House No. 2 Borehole. Petrology Unit Internal Report PE/LD/84/2 and 84/3.

Consultation of data

Enquiries relating to the district should be addressed to the Manager, National Geosciences Data Centre, Keyworth.

Geology of the country around Tewkesbury—summary

The area described in this memoir is one of great geological diversity, ranging from Precambrian igneous rocks to river gravels of Quaternary age.

The Malvern Hills and the country to the west is an unspoiled area of natural beauty favoured by tourists. The broad lowlands of the River Severn valley occupy the central part of the area, with the expanding conurbations of Gloucester and Cheltenham to the south and the rising ground of the Cotswold escarpment to the east.

The Malvern axis, a major north–south geological structure, divides the district. To the west of the axis lie Lower Palaeozoic rocks of Cambrian to Devonian age, including the Silurian inliers at Ledbury and May Hill. The Precambrian rocks of the Malvernian Complex and the Warren House Volcanics lie at the core of the structure and their outcrops form the Malvern Hills. Farther south, inliers of Coal Measures rocks form the small, fault bounded Newent Coalfield where coal was won in the last century. East of the axis, the rocks beneath the Severn valley occupy a depositional basin, the Worcester Basin, containing more than 2 km of Permo-Triassic continental sediments overlain by Jurassic marine rocks. The basement rocks beneath the Permian succession in the basin are largely unknown but consist, in part, of Precambrian volcaniclastics.

Small patches of glacial deposits in the west are relics of an ice sheet which advanced from the north and probably terminated close to the Malvern Hills. Later Quaternary sediments include the sand and gravel of the Severn and Avon river terraces.

In this account the petrology of the Precambrian rocks, the stratigraphy of the sedimentary rocks and the geological structure are described and interpreted. New information regarding the stratigraphy was obtained during the course of the survey from boreholes put down through parts of the Cambrian, Silurian, Carboniferous, Triassic and early Jurassic sequences, and from seismic reflection surveys. These new data have led to an advance in our understanding of the form and origin of the Worcester Basin.

(Geological succession) Geological succession in the Tewkesbury district.

Geological succession in the Tewkesbury District

Chapter 1 Introduction and geological setting

This memoir describes the geology of the area covered by the Tewkesbury 1:50 000 geological sheet, extending from Tewkesbury to the Malverns in the north and from Cheltenham to May Hill in the south. The survey was conducted at a scale of 1:10 000, mainly between 1979 and 1982, although a small area around Bredon Hill was surveyed in 1966–67. The surveyors' geological notes and local details for each 1:10 000 sheet are available in BGS as Open File Reports; so are the 1:10 000 geological maps. There is also available a set of reports with special emphasis on potential resources of sand and gravel. These are all tabulated in the data lists (p. viii). This account lacks the full local details of the geology traditionally found in memoirs; for this type of information, the reader is referred to the Open File Reports described above.

The Tewkesbury district covers part of the lower Severn valley, the town of Tewkesbury being situated at the confluence of the River Severn and its tributary the Avon. Much of the area is pleasant agricultural country, of moderate relief. The southern end of the north–south Malvern Hill range, terminating at Chase End Hill [SO 761 354], occurs in the north-west of the district and other prominent physical features are May Hill, in the south-west, and Bredon Hill, in the north-east. In the west are the small market towns of Ledbury and Newent, while in the southeast the district includes the western half of the large residential town of Cheltenham, with its fringe of light industries.

The Malvern Hills, with their core of late Precambrian igneous rocks (Figure 1), lie along one of the major structural lineaments of southern Britain. This lineament has governed the trend of fold axes and of faults from early Palaeozoic times onwards, and its effect can be seen in the mainly north–south trend of present-day outcrops. A northwesterly structural trend is present locally, notably in the May Hill pericline and the adjacent Glasshouse Fault, which lie on the Woolhope–May Hill Axis.

Following the Hercynian compressive movements, Permo-Triassic crustal extension resulted in the formation of the Worcester Basin, a north–south graben, with a width of 30 km between the Malvern Hills in the west and the Vale of Moreton Axis in the east, and with a floor up to 2 km below OD. North of Chase End Hill the western boundary of the basin is formed by a single major fault along the east side of the Malvern Hills, and south of there by several lesser faults.

The basin is filled largely with thick Permo-Triassic continental sediments, overlain by marine Jurassic formations of a shallow-water shelf facies. These sediments show faulting and minor folding but, apart from undergoing uplift and erosion, appear not to have been affected by Tertiary (Alpine) earth movements.

There are no deposits within the district representative of the Cretaceous and Tertiary periods but there are scattered patches of glacial material from the Quaternary and more extensive river terraces and solifluction deposits belonging to the late Quaternary.

Chapter 2 Precambrian

Previous research

Precambrian rocks form the 13 km-long chain of the Malvern Hills, of which only the southernmost 5 km lie within the present district. The complexity of the geology was noted by Horner (1811) who concluded from banding present in many of the rocks that they were originally sediments. Holl (1865) considered that most of the rocks were metamorphosed sediments, but mapped a separate group of rocks north-east of Swinyard Hill as 'post primordial trap'. The volcanic nature of these rocks was later confirmed by Callaway (1880), and Green (1895), who named them after Warren House. This name is retained in the present account.

Callaway (1889) concluded that: a) all the crystalline rocks of the Malvern chain are of igneous origin; b) the gneisses and schists were produced from igneous rocks by secondary action; and c) the chief mineral and chemical changes have taken place in bands of rock (shear zones). He also introduced the name 'Malvernian' to include the rocks other than those of the Warren House Formation. Despite some disagreement with Callaway's conclusions (e.g. Rutley, 1887, Brammall, 1940) recent work on the Malvernian supports a magmatic origin for most of the Malvernian Complex.

Malvernian Complex (MvC)

Swinyard Hill [SO 763 385], Midsummer Hill [SO 759 375], Hollybush Hill [SO 762 375], Ragged Stone [SO 759 364], and Chase End Hill [SO 761 355] are all composed of Malvernian rocks. Exposures adjacent to Pink Cottage [SO 763 390] confirm Malvernian rocks to the south of the Warren House Formation outcrop, as shown by Holl (1865) and Groom (1900) (cf. the maps of Blyth, 1952 and Phipps and Reeve, 1969).

Within the chain of hills, depressions extend southwards from The Gullet [SO 760 380] to beyond Hollybush. In some of these, there is evidence of outliers of Cambrian or Silurian rocks. In the depression just north of Chase End Hill, Groom (1899) recorded loose blocks of Cambrian rocks but none were found during the present survey.

The Malvernian is composed mainly of diorites and tonalites. Granites occur in lesser proportion and ultramafic rocks are also present, but mainly north of the present district. The above rocks are cut by microdiorite dykes and pink granite pegmatites. Many of the rocks are so extensively sheared that they resemble gneisses and schists, and locally they have been converted to phyllonites and mylonites. Garnetiferous rocks have been recorded at several localities, but most commonly at Swinyard Hill. The presence of garnet has led to the suggestion that metasediments may be present within the Complex, but most of the garnets appear to be confined to shear-veins or to sheared granites, except for the garnets in a schist-like rock on Swinyard Hill.

The petrography of the Malvernian Complex was studied by Lambert and Holland (1971) and about 100 rock samples were examined during the present survey. Thin sections show that most of the ultramafic rocks of the southern Malverns consist of coarse-grained aggregates of green-brown amphibole. In some specimens the amphibole is a pale green 'actinolitic' type formed of interlocking grains. Diorites and tonalites make up some 75 per cent of the Malvernian outcrop. They contain green hornblende and blocky oligoclase or andesine, these minerals probably being primary. The less mafic diorites and tonalites contain highly sericitised plagioclase and the hornblende is in places replaced by epidote. Accessory minerals include sphene and apatite.

In Gullet Quarry [SO 762 382], there are massive mafic rocks which Lambert and Holland (1971) referred to as 'epidiorites'. These rocks possess a distinct 'metamorphic' texture and consist of about 50 per cent green hornblende, with partly sericitised oligoclase, subsidiary chlorite, epidote, quartz, and opaque oxide. Lambert and Holland suggested that these rocks originally crystallised as dykes under conditions of high water pressure, with primary hornblende and plagioclase; the country rock at the time of emplacement was hot.

Pink, leucocratic granites are common on the north side of Swinyard Hill. They contain tabular microcline and oligoclase, and biotite, together with small amounts of muscovite, epidote, chlorite, and iron oxides which make up less than 10 per cent of the rock. Garnet has been found in some samples. Pegmatites range from large, dyke-like bodies to indistinct, diffuse streaks and may contain albite or microcline. Muscovite is usually present, together with small quantities of biotite and secondary chorite. Epidote is locally common.

Three petrographically distinct types of sheared rock were recognised by Lambert and Holland (1971):

1. rocks in narrow, sharp-sided, discontinuous fracture zones, containing quartz, iron oxides, and hydrolysed silicates;
2. schistose rocks in shear zones of centimetre and upwards scale, containing chlorite, muscovite, epidote, plagioclase, and quartz; and
3. irregularly banded rocks containing alternating felsic and chloritic layers of millimetre scale.

They considered that the first type formed by brittle deformation at a moderate temperature, probably during the final stages of magma consolidation, in an environment where alkalis were highly soluble. The second type shows variations from weakly schistose diorites to highly chloritic, schistose rocks. Alkali solubility again appears to have been important in their formation. The third type includes the weakly foliated pink granites; these have a strong lineation but weak foliation produced by their micas. The lineation probably formed by stress during the latter part of crystallisation.

Dykes occur throughout the Malvernian but in the south, most are deformed and schistose. The main types are a hornblende microdiorite (Ivy Scar microdiorite) found mainly in the northern hills, and a granophyric textured, quartz microdiorite, commonly referred to as a dolerite, which is more widespread. The latter contains andesine laths poikilitically enclosed in clinopyroxene or secondary hornblende; these minerals have commonly been hydrolysed to sericite and chlorite respectively. Micrographic intergrowths of quartz and feldspar occur interstitially. The mineralogy demonstrates that the dykes were emplaced prior to the main hydrolysis of the complex, but their chemistry suggests that the dykes are unrelated to the main mass of Malvernian rocks (Lambert and Holland, 1971). The Ivy Scar microdiorites have a non-ophitic texture with highly zoned andesine and green hornblende which shows alteration to chlorite. Chemically these dykes are similar to the Malvernian diorites (Lambert and Holland, 1971).

It is still uncertain whether metasediments are present within the Malvernian. Garnet-bearing assemblages found at several localities have been cited as evidence for the presence of metasediments, but the garnets are generally very small (0.2 to 0.5 mm), mostly highly corroded, and altered to chlorite. In many instances, the rocks containing garnets appear to be sheared granites or granite veins, but at Swinyard Hill they contain muscovite, biotite and garnet, the last largely altered to chlorite.

On the western slopes of Ragged Stone Hill, bands of a pale-coloured rock can be traced across the hillside. This rock has the appearance of a sheared quartzite, but is perhaps a sheared granite.

Deformation of the Malvernian

The rocks of the Malvernian Complex have been strongly deformed by multidirectional shearing. Two main events can be recognised. The first produced a weak foliation, probably during final crystallisation of the complex. A later event, producing extensive brittle shearing, must have taken place in cooler rocks. As the adjacent Lower Cambrian sediments are relatively undeformed, both deformation events must be Precambrian in age.

Age of the Malvernian

The highly deformed nature of the Malvernian compared with the overlying Lower Cambrian sediments led many workers to believe that the Malvernian is of great antiquity. For example Fitch and others (1969) concluded that the Malvernian had undergone many metamorphic events, including at least one of garnet-amphibolite facies, associated with migmatisation, followed by several episodes of retrograde metamorphism which reduced both amphibolites and granites to banded mylonites. K/Ar dates of around 600 million years obtained by them were interpreted as being related only to the last deformation. The same writers suggested a similarity between the less-sheared Malvernian and the Laxfordian rocks of South Harris in the Outer Hebrides.

A more recent Rb/Sr isochron age (Beckinsale and others, 1981) of 681 ± 53 million years is interpreted as being associated with the initial cooling of the magmatic complex, as the low initial Sr⁸⁷/Sr⁸⁶ ratio precludes a prolonged crustal history.

Warren House Formation (WHF)

The Warren House Formation crops out along Broad Down [SO 765 393] in the extreme north of the district, and extends for a short distance into the adjoining Worcester district. It consists mainly of sodic basalts and rhyolites, together with less abundant keratophyres and pyroclastic rocks. The volcanic rocks are intruded by dolerite dykes.

The conclusion of French and Winchester (personal communication to Lambert and Holland, 1971) that the formation occurs in an easterly-plunging syncline with basaltic rocks to the west, overlain by rhyolites and pyroclastic rocks farther east, may be broadly correct, but the situation is more complex. Excavations at the British Camp Reservoir [SO 765 399] (Acland, 1894; Green, 1895) showed a sequence of interbedded basalts, rhyolites and tuffs, the easterly dip ranging from 45° to near vertical.

The petrography of the rock types making up the formation was described by Platt (1933). Thorpe (1972; 1974) found that the chemistry of the Warren House rocks suggests that they represent a magmatic series with features found in 'island arc' and 'abyssal' tholeiites. He concluded (1974) that the basalts could be of 'ocean floor' type. More recent work on the chemistry of the Warren House, Charnian and Uriconian volcanic rocks suggests (Pharaoh and others, 1987) that the late Proterozoic basement of central England comprises a heterogenous mosaic of geochemically distinct volcanic terrains, formed in separate volcanic arc/marginal basin environments, tectonically brought together during the Avalonian/Cadomian Orogeny since c.700 Ma. The Warren House lavas, they suggest, may represent relicts of marginal-basin basalt trapped and uplifted along a Proterozoic Malvern suture between the Uriconian and Charnian terrains. Probable pillow structures in the basalts (Plate 2) suggest that at least part of the formation was deposited subaqueously, which accords with Thorpe's findings, but one anomalous factor is the relatively high proportion of acid rocks which, together with pyroclastic rocks, are more characteristic of island arc environments.

No radiometric dates have been published for the Warren House Formation but it has generally been regarded as Precambrian, mainly on the evidence of pebbles of volcanic rocks within the Malvern Quartzite. The Warren House Formation has been correlated with the Uriconian of Shropshire (Callaway, 1880; Earp and Hains, 1971) though Wright (1969) argued that the Eastern Uriconian underlies structurally deformed Longmyndian rocks, and therefore is likely to be older than the Warren House Formation.

Fitch and others (1969) considered the formation to have been subjected to a Precambrian greenschist facies metamorphism, which they correlated with a major retrogressive metamorphism of the Malvernian. The mineral changes noted by Fitch and his co-authors may perhaps be alternatively the product of intense hydrothermal alteration (propylitisation).

Some workers consider the junction between the Warren House Formation and the Malvernian to be a fault but others favour an unconformity. Pocock and Whitehead (1948) and Wright (1969) favoured the latter and believed they could detect a weathered top to the Malvernian adjacent to the junction, though their observations were not confirmed during the present survey. The mapping south of Hangman's Hill is important to any interpretation of the junction. In this area Blyth (1952) mapped the Warren House Formation as terminating against May Hill Sandstone, the line of junction being a north-west–south-east wrench fault. Phipps and Reeve (1969) incorporated this fault in their Herefordshire Beacon Thrust, and concluded that the Malvernian and the Warren House rocks are bounded at depth by a single thrust.

Earlier mapping of the area to the south of Hangman's Hill by Holl (1865) and Groom (1900), showing a strip of Malvernian between the Warren House rocks and the May Hill Sandstone, has been confirmed during the present survey. Phipps and Reeve (1969) showed the junction between the Warren House Formation and the Malvernian to the west of Broad Down and Hangman's Hill to be a fault dipping east at 60°, older than, and truncated at depth by the Herefordshire Beacon Thrust. Structure contours show, however, that the junction dips east at much less than 60°; in fact, the dip is about 35°, as suggested by Groom (1900). The dip is thus only slightly greater than that of the underlying Herefordshire Beacon Thrust, and the junction is probably another thrust of similar orientation and age.

The Warren House rocks are less deformed than the Malvernian. While this may indicate that the former are the younger, it need not do so, if the main deformation of the Malvernian was associated with its uplift to higher crustal levels.

Chapter 3 Cambrian

The main outcrop of Cambrian rocks lies to the west of Midsummer Hill [SO 759 375], Ragged Stone Hill [SO 759 364], and Chase End Hill [SO 761 355]; and there are also several small outliers within the Malvernian outcrop. Groom's (1899; 1902; 1910) subdivision of the Cambrian into Malvern Quartzite, Hollybush Sandstone, and White-leaved Oak Shale is followed here, together with the inclusion of the Bronsil Shale of Tremadoc age, placed at the time of his writing in the Ordovician.

The Cambrian succession has been intruded by a number of basic dykes, sills and small bosses of presumed Ordovician age.

Malvern Quartzite (MQ)

The Malvern Quartzite crops out to the south-west of Gullet Quarry [SO 7598 3799], in Hollybush Quarry [SO 7600 3710] and at Winter Coombe [SO 7600 3665]. It has been reported from a quarry, now untraceable, on the west side of Ragged Stone Hill (Symonds, 1880), where loose debris was found by Groom (1899). Groom mentioned loose blocks of Malvern Quartzite at several other localities, but Butcher (in Jones and others, 1969) has suggested that these may be debris from prehistoric fortifications.

The Malvern Quartzite consists of pale grey, hard, quartz-cemented sandstones and interbedded conglomerates. The conglomerates consist mainly of rounded quartz pebbles, usually less than 1 cm in diameter, set in a matrix of quartz sand. Other common pebbles include material derived from the Malvernian Complex. In addition, pebbles of rhyolite, andesite, and basalt were noted by Groom (1910). The conglomerates are particularly well cemented and break across individual pebbles when struck with a hammer.

At Hollybush Quarry, the Malvern Quartzite is unconformable on rocks of the Malvernian Complex, although there has been slight shearing along the contact. South-west of Gullet Quarry, the present survey interprets this junction as a fault and a similar interpretation was made for the junction in Winter Coombe [SO 760 367], based on evidence of dip from the mapping of Groom (1899).

Because its base is faulted in all but one section, the thickness of the Malvern Quartzite is difficult to estimate. At Hollybush Quarry a maximum thickness of only some 10 m can be accommodated between the Malvernian and the Hollybush Sandstone, but the junction with the latter is unexposed and could also be a fault. South-west of Gullet Quarry up to 60 m may be present at outcrop.

The fauna of the Malvern Quartzite is sparse; the inarticulate brachiopod Micromitra phillipsii (Holl) has been recorded by Groom (1910) and Jones and others (1969); Groom also recorded Obolella(?)groomii and 'Hyotithes'primaevus. Stubblefield (1966) reported Paterina rhodesi, found elsewhere only from the lowest fossiliferous Cambrian strata of Shropshire.

Lambert and Rex (1966) implied that there is insufficient palaeontological evidence to conclude that the Malvern Quartzite is Lower Cambrian, but Stubblefield (1966) argued that the doubt, if any, is whether or not Middle Cambrian sediments are present in the Malverns area.

The Malvern Quartzite is interpreted as having formed along a shoreline, adjacent to a landmass on which rocks of Malvernian type were being eroded. The pebbles of volcanic rocks in the conglomerates may be from the Warren House Formation or, equally possibly, from some more distant source.

Hollybush Sandstone (HoS)

The main outcrop of the Hollybush Sandstone stretches from just south of The Gullet [SO 758 379], along the western flank of the Malvern Hills, to White-leaved Oak, with small outliers at Hollybush Quarry [SO 760 371], and Winter Coombe [SO 760 367].

The sandstone, estimated to be about 300 m thick, is flaggy, micaceous and of a distinctive, dark green colour caused by an abundance of chlorite and glauconite. Groom (1910) also noted grey and black sandstones, quartzites, thin conglomerates and impure limestones. He considered the lower part of the sandstone to be more shaly and flaggy than the upper. Within the sandstone, ripple marks and various sole structures are common with trails and burrows at some localities. The main fossils are Micromitra phillipsii, 'Hyolithes' primaevus, and 'H.'malvernensis. Groom (1910) regarded the Hollybush Sandstone as Middle Cambrian, but the formation is here classed, following Stubblefield (1966), as Lower Cambrian. The conditions of deposition of the Hollybush Sandstone are envisaged as shallow marine, but slightly deeper than those prevailing during the formation of the underlying Malvern Quartzite. The presence of much mica in the sandstone is consistent with derivation from the Malvernian.

White-Leaved Oak Shale (WOa)

The outcrop of the White-leaved Oak Shale trends northwest–south-east through the hamlet of White-leaved Oak [SO 760 358]. The formation consists predominantly of dark grey to black, fissile mudstone. Exposures are uncommon, but the formation was proved in the Fowlet Farm Borehole [SO 7546 3595] from 9.4 m below surface level to a depth of 58 m where a reverse fault brought in the younger Bronsil Shale. In its top 4.98 m, the borehole encountered weathered mudstones with the silver-grey colour characteristic of Bronsil Shale. Although these could also be White-leaved Oak Shale bleached by intrusion of dolerite sills (cf. Groom, 1901), the White-leaved Oak Shale deeper in the borehole showed no evidence of such bleaching, and classification of the beds near the surface as Bronsil Shale is preferred.

The thickness of the White-leaved Oak Shale is difficult to estimate as the top and base of the formation are generally faulted but a figure between 150 and 250 m may be realistic. In the lower beds of the White-leaved Oak Shale the crustacean Cyclotron lapworthi is abundant; originally thought to be of late Middle Cambrian age, Taylor and Rushton (1971) showed that an early Upper Cambrian age is more probable for these beds. Beds higher in the sequence have yielded the trilobites Lotagnostus trisectus and numerous olenids including Ctenopyge pecten, C. bisulcata, Peltura scarabaeoides, Sphaerophthalmus humilis and S. major. Conditions of sedimentation are likely to have been slow in a reducing environment.

Bronsil Shale (BSh)

The Bronsil Shale, a very fissile, silver-grey mudstone, crops out around Bronsil [SO 750 374], and farther south to the west of the White-leaved Oak Shale outcrop. Exposures are few as the area is partly covered by Head deposits. Silver-grey mudstones proved in the top 5 m of the Fowlet Farm Borehole are presumed to be Bronsil Shale. The formation was brought in again in the borehole by a reverse fault at 58 m beneath White-leaved Oak Shale and was seen to a depth of 116 m. The thickness of the formation cannot be estimated with accuracy, as it is affected by faulting, but is probably between 250 and 350 m.

The fauna of the Bronsil Shale includes acrotretid brachiopods and Broeggeria salteri, trilobites such as Acanthopleurella grindrodi, Boeckaspis mobergi and Platypeltoides croftii, and the early Tremadoc graptolite Dictyonema flabelliforme sociale. A sample from the Fowlet Farm Borehole (77.5 to 79.0 m below surface level) contained poorly preserved acritarchs indicative of an early Tremadoc age. Dr Molyneux reports that the acritarchs are grey to black in colour indicating a high degree of thermal alteration, presumably related to the intrusion of adjacent dykes and sills.

The Bronsil Shale was deposited under less reducing conditions than the underlying White-leaved Oak Shale.

Chapter 4 Post-Cambrian igneous intrusions

Basic intrusions cut all the Cambrian rocks, except the Malvern Quartzite, though their absence from the latter may be apparent and arise only from its small outcrop. They are not found in the May Hill Sandstone or younger rocks and thus are presumed to be Ordovician in age. Most are dykes or sills which form ridges trending .north-west–south-east but intrusions with circular or more irregularly shaped outcrops also occur. Blyth's (1935) classification of the intrusions into three main types based on mineralogy and texture is followed below. All three types are characterised by sodic plagioclase which led Blyth to regard the rocks as members of the spilite suite. Their distribution is shown in (Figure 2).

Type A (Spilitic andesites)

Intrusions of this type form most of the circular and irregular outcrops, and also the dyke which is crossed by the Ledbury–Tewkesbury road at Hollybush [SO 757 368]. They are fine-grained, purplish grey, commonly porphyritic rocks with a microcrystalline groundmass of zoned oligoclase, or less commonly albite, together with chlorite, apatite, magnetite, ilmenite and pyrite.

Type B (Amygdaloidal spilites)

Rocks of this group occur near Bronsil and near White-leaved Oak (Plate 3). They are porphyritic and vesicular with a trachytic-textured groundmass of small oligoclase or albite crystals. Chlorite pseudomorphs after amphibole or pyroxene and after olivine are present. Vesicles are filled with calcite, chlorite and zeolite.

Type C (Spilitic olivine diabases)

Rocks of this type form the broad ridge which extends northwest from the Malvernian outcrop of Chase End Hill, and are also present north of the Ledbury–Tewkesbury road [SO 751 366]. The margins of these intrusions are porphyritic with small phenocrysts of oligoclase-andesine in a cryptocrystalline matrix of albite-oligoclase with chlorite, epidote, pyrite and leucoxene. In the central parts, oligoclase and secondary chlorite are ophitic and serpentine replaces original olivine.

Chapter 5 Silurian

Ordovician sediments do not crop out in the Tewkesbury district and the earliest Silurian rocks rest unconformably on the Cambrian. Silurian and Devonian rocks crop out extensively west of a line joining the Malvern Hills and May Hill. Their classification is shown in (Table 1).

For many years the Silurian/Devonian boundary was taken at the base of the Ludlow Bone Bed (Holland, 1965a;b) which lies at the base of the Downton Castle Sandstone in this district and marks a change from marine to continental conditions of deposition. Following a decision to base the international boundary stratotype on the marine succession in Czechoslovakia (Chlupae" and Kukal, 1977), the boundary in the Welsh Borderland and adjacent areas must now be taken at a level above the Ludlow Bone Bed. Allen and Williams (1981) proposed that the boundary be taken at the Townsend Tuff Bed, an ash-fall deposit and a good chronostratigraphical marker, about 100 m below the top of the Raglan Mudstone throughout much of South Wales and parts of the Welsh Borderland. This bed has yet to be identified in the present district, however, and the local position of the Silurian/Devonian boundary thus remains uncertain. In this account, the Lower Old Red Sandstone sediments are described together, even though the lower part of the succession is now considered to be of Silurian age.

Following uplift of the area during the Ordovician, the district remained part of a landmass, bounded by the Welsh sea to the west of Shropshire, until the early Silurian. This sea spread eastwards during the late Llandovery reaching the west of the Tewkesbury district in Aeronian times. Brachiopod communities in the May Hill Sandstone (Ziegler, Cocks and McKerrow, 1968) indicate deposition in a shallow, but generally deepening, sea although with some evidence of periodic shallowing.

May Hill Sandstone (MHS)

In the Malverns, the May Hill Sandstone (Sedgwick, 1853) has been divided (Groom, 1910) into the Cowleigh Park Beds and the overlying Wych Beds, although these are not shown separately on the 1:50 000 geological map. In the May Hill area, a broadly similar, two-fold division has been made into Huntley Hill Formation and Yartleton Formation (Gardiner, 1920). For the shaly beds directly underlying the Woolhope Limestone, Symonds and Lambert (1861) introduced the name Woolhope Shales. This formation was never properly defined, however, and as the type section in the Malvern railway tunnel is unavailable for further study, we follow Zeigler and others (1968) in rejecting the name and the beds are included within the May Hill Sandstone.

To the west of the Malvern Hills, the May Hill Sandstone forms a high escarpment which rises steeply above the Cambrian outcrop. On the east side of the Malverns, the Sand- stone is restricted to a small outcrop on the eastern flank of Swinyard Hill. The maximum thickness of the sandstone is estimated to be about 200 m. In the south Malverns the May Hill Sandstone completely oversteps the Cambrian succession to rest unconformably on the Malvernian Complex.

West of Bronsil, where the oldest beds of the May Hill Sandstone overlie the highest Cambrian strata, the basal beds, exposed in a temporary section, consist (Ziegler and others, 1968) of up to 5 m of red, micaceous mudstone interbedded with several green sandstones less than 10 cm thick. Above are some 30 m of brown siltstones and sandstones, followed by a similar thickness of pink to purple, coarse-grained sandstones, grits, and conglomerates. These beds are overlapped in an easterly direction by beds higher in the formation. These are poorly exposed except at the Gullet Quarry, where they rest unconformably on the Malvernian, although some (Phipps and Reeve, 1964; Whitworth, 1962) regard the junction as a major fault. Here, the basal bed of the sandstone is a conglomerate less than 1 m thick containing pebbles and cobbles of Malvernian rocks in a matrix ranging from grey clay to grey-green sandstone, locally iron-stained and red-brown. Reading and Poole (1961) recorded corals and brachiopods in the conglomerate in a position of growth and also recognised small sea-stacks rising from the irregular Malvernian surface. Above the conglomerate, several metres of brownish grey, interbedded siltstones, sandstones and subordinate limestones are exposed dipping west at about 60°.

In Eastnor Park Borehole [SO 7437 3809] (Figure 3), 58.58 m of May Hill Sandstone are proved. The top 8 m are grey, calcareous mudstones with thin nodular limestones; below are purple mudstones and siltstones which characteristically contain Costistricklandia lirata. A lack of purple colour in loose blocks at the surface suggests that it is lost during weathering.

The lower part of the May Hill Sandstone contains a sparse fauna, including Lingula spp., Stegerhynchus decemplicatus and bivalves. Higher beds yield a much more diverse fauna dominated by Costistricklandia lirata, and including Eocoelia curtisi and Pholidostrophia salopiensis. In the uppermost beds corals such as favositids, halysitids and solitary rugose forms are also common, and from this level Pocock (1930) has recorded the stratigraphically important crinoid, Petalocrinus.

The Llandovery–Wenlock Series boundary in the Eastnor Park Borehole is placed at the first appearance of Costistricklandia lirata, at 49.96 m, 5.64 m below the top of the May Hill Sandstone. This boundary cannot be precisely placed on the basis of conodonts (Aldridge, 1986) since the amorphognathoides Zone, which in the stratotype section spans the boundary (Mabillard and Aldridge, 1985), embraces several tens of metres in the borehole.

Huntley Hill Formation (HH)

The Huntley Hill Formation is restricted to the May Hill area, and consists mainly of grey and brown, feldspathic sandstones and conglomerates with subordinate mudstones. The conglomerates consist mainly of poorly sorted, rounded clasts of quartzite and pink felsite. In addition, angular fragments of Malvernian rocks and andesite porphyry have been recorded (Ziegler and others, 1968). The sandstones are locally gritty and are composed of moderately well-rounded quartz grains with subrounded to subangular fragments of pink felsite. At the top of the formation, these sandstones are interbedded with flaggy, laminated, fine-grained sandstones to form a transition into the overlying Yartleton Beds. Mudstones probably less than 5 m thick occur locally in the upper part of the formation.

The uppermost 150 m or so of the formation crop out in this district, out of an estimated total thickness of between 180 m (Lawson, 1954) and 280 m (Ziegler and others, 1968). The Huntley Hill Formation is poorly fossiliferous, the most commonly recorded fossils being species of Eocoelia and Lingula.

Yartleton Formation (Yt)

The Yartleton Formation succeeds the Huntley Hill Formation conformably. Above the basal transition zone, the beds are mainly grey-brown to pale yellow-brown, well-bedded, flaggy, fine-grained sandstones and siltstones with subordinate mudstones in the upper part of the formation. The sandstones and siltstones are typically finely laminated, micaceous, and locally very fossiliferous. The upper beds contain calcareous siltstones and impersistent grey, massive, crystalline limestones.

The formation is estimated to be about 200 m thick. The most characteristic fossils are Costistricklandia lirata, Eocoelia sulcata, Pentameroides sp. and solitary corals.

Woolhope Limestone (WoL)

The Woolhope Limestone conformably succeeds the May Hill Sandstone and in the Eastnor Park Borehole [SO 7437 3809] comprises 14.22 m of alternating pale grey, nodular limestone and darker grey, calcareous mudstone. The base of the formation is taken at the first appearance of significant nodular limestone (Figure 3). At outcrop, the beds weather to buff and olive-grey. The formation thickens northwards and a few kilometres to the north, at North Malvern, it consists of an upper and lower limestone, each up to 9 m thick, separated by up to 60 m of calcareous mudstone (Phipps and Reeve, 1967).

At May Hill, the Woolhope Limestone is up to 30 m thick in the west, thickening eastwards to about 60 m at Glasshouse Hill [SO 711 205] and to 75 m at Glasshouse [SO 710 213]. At the base of the formation at some localities, a mudstone up to 15 m thick is present; at others, a 10 m-thick mudstone occurs about 5 m above the base.

The fauna of the Woolhope Limestone is restricted in both species and individuals, the commonest fossils being corals and brachiopods. Tabulate corals include favositids, halysitids and heliolitids, and the characteristic rugose coral is Schlotheimophyllum patellatum. Brachiopods include Coolinia pecten, Dalejina phellodra, Dicoelosia paralata, Eoplectodonta duvalii, Leptaena oligistis and Streptis grayii.

The presence of much comminuted shell debris in the Woolhope Limestone suggests deposition in a high energy environment–such as a shallow sea with vigorous wave action. The thicker development of mudstone and siltstone around May Hill, compared with the southern Malverns, may be attributable to increased clastic input and greater subsidence.

Wenlock Shale (WSh)

West of the Malverns and at May Hill, the outcrop of the Wenlock Shale is characterised by relatively low-lying, poorly drained ground. The formation is poorly exposed and a detailed stratigraphy is known only for the basal 30 m proved in the Eastnor Park Borehole. This revealed an interbedded sequence of dark grey, calcareous mudstones and siltstones with subordinate, paler grey limestones generally less than 10 cm thick. The latter occur at intervals of about 1 m near the base of the formation and become less common upwards. Ten bentonite bands, each up to several centimetres thick, were encountered in the basal 17 m of the formation. On weathering, the Wenlock Shale becomes buff to olive. In the southern Malverns the formation is estimated to be about 200 m thick decreasing to 170 m or less at May Hill.

The common fossils are mainly brachiopods and include Anastrophia deflexa, Atrypa reticularis, Coolinia pecten, Cyrtia exporrecta, Dalejina hybrida, Dicoelosia biloba, Eoplectodonta duvalii, Eospirifer radiatus, Gypidula galeata, Howellella elegans, Resserella canalis, and Strophonella euglypha. Fragments of Dalmanites spp. are also locally abundant, as are small solitary corals, but compound corals are rare.

The Wenlock Shale marks an increase in the deposition of terrigenous sediments, compared to the underlying Woolhope Limestone, and also perhaps increased basin subsidence (Phipps and Reeve, 1967).

Wenlock Limestone (WeL)

The outcrop of the Wenlock Limestone west of the Malverns forms prominent wooded ridges, the most impressive of which, the Ridgeway, extends northwards from Eastnor. Farther west, the limestone crops out in the cores of several periclines near Ledbury. The outcrops around May Hill are much disjointed by faulting. At Gorsley, the limestone is unconformably overlain by Upper Ludlow Shale and was formerly regarded as Aymestry Limestone until Lawson (1954) put forward strong lithological and palaeontological evidence of its Wenlock age.

In the southern Malverns, the Wenlock Limestone is estimated to be between 70 and 90 m thick. Limestones predominate, but locally, for example just north of Eastnor, mudstones increase in importance. In the May Hill area, the formation is between 85 and 100 m thick and a three-fold division can be made into an upper and lower limestone separated by a predominantly mudstone sequence.

Because of extensive quarrying, the Wenlock Limestone is the best exposed and perhaps the best known of the Silurian formations. Several lithologies can be recognised; the most common, seen in most quarries, is a grey to blue-grey, nodular limestone with individual nodules ranging from a few centimetres up to several tens of centimetres across, set in a matrix of calcareous mudstone or siltstone. Also common are bioclastic limestones formed of well sorted, sand-grade shell particles together with complete valves of brachiopods and fragments of corals, crinoids and trilobites. Pisolitic limestones occur in both the May Hill and Malvern areas, but are of limited extent and thickness. The Wenlock Limestone contains an abundant, diverse fauna of brachiopods, corals, crinoids, and trilobites; gastropods, bivalves and cephalopods are less common. The faunas at May Hill and the southern Malverns are similar and include Favosites gothlandicus, Halysites catenularius, Amphistrophia funiculata, Coolinia pecten, Dalejina hybrida, Gypidula galeata, Howellella elegans, Leptaena depressa, Leptostrophia filosa, Meristina obtusa, Plectatrypa imbricata, Resserella canalis, Rhynchotreta cuneata, Sphaerirhynchia wilsoni, Strophonella euglypha, and Dalmanites spp.

Pisolitic and bioclastic limestones within the Wenlock Limestone indicate a return once more to shallower conditions above wave base. Mudstones within the formation, especially at May Hill, may reflect local changes in depth or an increase in clastic sediment supply.

Ludlow Shale, Undivided (Lu)

In the May Hill area, rocks of Ludlow age form a predominantly mudstone and siltstone sequence and the Aymestry Limestone is not developed. Lawson's (1955) sixfold division of these rocks was mainly biostratigraphical; for lithostratigraphical purposes, the sediments have been mapped as undivided Ludlow Shale.

The Ludlow Shale is a coarsening-upwards sequence of sparsely fossiliferous, buff and olive-grey, blocky mudstones overlain by laminated siltstones and fine-grained sandstones which at certain horizons are very fossiliferous. South-west of May Hill, an impersistent limestone about 10 m thick occurs approximately 30 m below the top of the formation and several limestone-conglomerates and phosphatised pebble beds reflect breaks in sedimentation.

The Ludlow Shale at May Hill is estimated to be 100 to 120 m thick and is thus markedly thinner here than deposits of a similar age in the south Malverns, although at Gorsley, 4 km north-west of May Hill, only 3.5 m of these sediments are present.

In the area west of the Malverns, the Ludlow sequence has been divided into Lower Ludlow Shale, Aymestry Limestone and Upper Ludlow Shale.

Lower Ludlow Shale (LLu)

The outcrop of the Lower Ludlow Shale forms relatively low-lying ground between the wooded ridges of the Wenlock Limestone and Aymestry Limestone between Ledbury and the Malvern Hills. The formation is a sequence of buff-brown to olive-grey, calcareous siltstones and mudstones containing much comminuted shell material, alternating with thin limestones; the limestones are more common near the base and top of the formation where the shale grades into the underlying Wenlock Limestone and into the overlying Aymestry Limestone. In the Bradlow area [SO 718 389], corn-minuted shell material is absent and the siltstones contain well-preserved brachiopod valves.

The formation is estimated to be about 120 m thick in the southern Malverns, with a rather thicker development around Bradlow. It thins southwards and at Gorsley, 13 km south-west of the Malverns, its position in the Silurian sequence is marked by an unconformity.

The fauna consists mainly of brachiopods, together with common trilobites, solitary corals and cephalopods. Species include Aegiria grayi, Atrypa reticularis, Craniops implicatus, Cyrtia exporrecta, Dicoelosia biloba, Glassia obovata, Howellella elegans, Isorthis orbicularis, Microsphaeridiorhynchus nucula, Plectatrypa imbricata, Protochonetes minimus, Shagamella minor, Skenidioides lewisii, Cypricardinia subplanulata, Kionoceras angulatum, Michelinoceras ibex, Dalmanites spp., Encrinurus spp., and Proteus (s.l.) spp.

Aymestry Limestone (AL)

The outcrop of the Aymestry Limestone, repeated by folding and faulting, forms several wooded ridges north-east and east of Ledbury. The formation is a sequence of grey, nodular limestones interbedded with olive to grey, calcareous mudstones, the latter becoming thicker towards the south. Overall the formation thins southwards from about 40 m in the north to just under 15 m at Woodfields Farm [SO 7259 3546] (White and others, 1984). At Gorsley, no beds of this age are preserved and Upper Ludlow Shale rests directly on Wenlock Limestone.

In the southern Malverns, the solitary coral Phaulactis sp.is common in the lower half of the formation. Gypidula lata is common near the base, and Coolinia pecten, Leptostrophia filosa, and Strophonella euglypha occur in the lower half of the formation. In the upper half, Shaleria aff. ornatella, Microsphaeridiorhynchus nucula, and the button coral Rhabdocyclus sp. are characteristic. The brachiopods Atrypa reticularis, Howellella elegans, Leptaena cf. depressa and Sphaerirhynchia wilsoni occur throughout.

Upper Ludlow Shale (ULu)

The Upper Ludlow Shale crops out between Ledbury and the Malvern Hills, and also farther south at Gorsley. It consists of grey to olive, fossiliferous, silty mudstones with thin, nodular limestones and, near the base of the formation, intraformational conglomerates containing bored pebbles. Similar conglomerates elsewhere in the Welsh Borderlands have been interpreted as hardgrounds (Cherns, 1980).

The present survey confirms the southerly thinning of the Upper Ludlow Shale suggested by Phipps and Reeve (1967) but not their conclusion that south of Eastnor, in the Clencher' s Mill [SO 732 351] area, the formation is composed only of about 12 m of conglomeratic beds. Instead, in this area, the conglomeratic beds are restricted to the lower part of the formation and are overlain by mudstones and siltstones. At nearby Woodfields Farm (White and others, 1984), several thin conglomerates occur near the base of the formation which is about 25 m thick.

At Gorsley, the Upper Ludlow Shale has thinned to only 3.5 m; a succession of calcareous siltstones is currently exposed in three disused quarries and in several stream banks. The siltstones can be divided at a phosphatised pebble bed which marks a break in sedimentation (Lawson, 1954).

In the southern Malverns, brachiopods are well represented in the lower part of the formation, especially Dayia navicula, Microsphaeridiorhynchus nucula, Sphaerirhynchia wilsoni, along with molluscs (mainly bivalves), and Saetograptus leintwardinensis. In the upper part, M. nucula, Protochonetes ludloviensis, and Salopina lunata are numerous at some levels. Also present is the characteristic late-Ludlow ostracod Calcaribeyrichia torosa. A similar distribution was noted by Lawson (1955) at Gorsley.

A shelf sea prevailed over the southern Malverns area during the Ludlow. Intraformational conglomerates at the base of the Upper Ludlow Shale reflect minor breaks in local sedimentation due to emergence or perhaps just winnowing by waves and currents. These episodes were related to gentle uplift of the area along the Gorsley axis which locally resulted in the non-deposition of the Lower Ludlow Shale and the Aymestry Limestone. This uplift also resulted in several breaks in the sequence in the May Hill area (Lawson, 1955).

Chapter 6 Silurian and Devonian (Lower Old Red Sandstone)

As described in the previous chapter, the recently revised boundary between the Silurian and the Devonian is now placed higher than the Ludlow Bone Bed and falls within the lower part of the Lower Old Red Sandstone, possibly close to the horizon of the Townsend Tuff, somewhere within the higher beds of the Raglan Mudstone. The tuff has not been identified in the Tewkesbury district, however, and the position of the boundary remains uncertain. The division of the Lower Old Red Sandstone is outlined in (Table 1).

Downton Castle Sandstone (DCS)

The Downton Castle Sandstone is steeply dipping in the Ledbury area and has a narrow outcrop, but at Gorsley [SO 674 265], where it is disposed in the core of an anticline, its outcrop is more extensive. At May Hill, its outcrop is much broken by faulting and locally near Appletree Grove [SO 7015 2445] it is absent.

In the Gorsley and May Hill areas, the Downton Castle Sandstone was previously named the Clifford's Mesne Beds (Lawson, 1954, 1955); broadly equivalent beds are the Rushall Beds (Squirrell and Tucker, 1960) in the nearby Woolhope Dome and the Rushall Formation of the Hereford district (Brandon, 1989).

At the base of the formation in the present district is the local equivalent of the Ludlow Bone Bed, which in the southern Malverns consists (White and others, 1984) of small lenses (2 cm X1 cm) of fine-grained sandstone containing numerous fragments of fish. The sandstone lenses occupy troughs in the underlying mudstones. In the Gorsley area, the basal bed (Lawson, 1954) is less than 2 cm thick and contains phosphatised pebbles of siltstone and mudstone, but fossils are rare. At May Hill, the basal bed has revealed Thelodus scales, fish spines and broken valves of Ludlow brachiopods (Lawson, 1955).

The basal bed is generally overlain by 4 to 10 m of pale buff to pale brown, hard, indurated sandstone with small, dark orange or dark brown spots but at Clifford's Mesne [SO 701 233] the sandstone thickens to about 25 m and was formerly worked in many small quarries. At Gorsley, a yellowish brown, shaly siltstone, up to 1.4 m thick, containing Lingula minima, eurypterids, and plant remains, occurs beneath the sandstone. At Newent Woods [SO 704 220], numerous ostracods including Londinia sp. and Frostiella groenvalliana, which are diagnostic of an early Přídolí age (Bassett, Lawson and White, 1982), occur just above the base of the formation. Lingula is present throughout the sandstone.

Gentle uplift of the region at the end of Ludlow times resulted in a change from marine to continental conditions of deposition. The Ludlow Bone Bed probably resulted (Allen, 1974a) from a shallowing of the sea accompanied by vigorous wave action producing a winnowing affect on the clastic sediments. The overlying sandstone lithologies of the Downton Castle Sandstone compare well with upper shoreface and beach sands in modern environments. The formation shows a vertical sequence of lithofacies similar to the regressive sequences found on present-day sandy, accretionary coasts.

Raglan Mudstone Formation (Rg)

The Raglan Mudstone crops out extensively west of Led-bury and May Hill, where it directly overlies the Downton Castle Sandstone; the Temeside Shale Formation, which intervenes throughout much of the Welsh Borderlands, is not developed in the present district.

The Raglan Mudstone, estimated to be 700 to 900 m thick, comprises red-brown, micaceous mudstones and siltstones with subordinate sandstones and concretionary limestones known as cornstones. These occur in fining-upwards rhythms, each usually commencing with a coarse-grained sandstone with an erosional base, which is overlain by siltstone and mudstone, and then by concretionary limestone.

The sandstones occur mainly within the lower two-thirds of the formation, are mostly less than 2 m thick, coarse to fine grained, and vary from grey-green to purple and red-brown. The concretionary limestones are also usually less than 2 m thick and are formed from concentrations of limestone nodules within a mudstone matrix. Individual nodules range in size from a few millimetres up to several centimetres across, and are usually elongated normal to the bedding. The base of each limestone is gradational but the top is usually sharp and is commonly eroded by the basal sandstone of the succeeding rhythm. At the top of the formation is the Bishop's Frome Limestone (BFL), consisting of 2 to 4 m of concretionary limestone, apparently formed by the coalescence of small limestone nodules into irregularly shaped masses up to 0.3 m in diameter.

The greater part of the Raglan Mudstone probably accumulated on an alluvial plain, for the fining-upwards cycles are generally comparable with the deposits of modern, mature fluvial environments, with sinuous streams flowing across broad alluvial deposits. The concretionary limestones (Allen, 1974b) are very similar to modern deposits of known pedogenic origin. The conditions required for the formation of present-day, pedogenic limestones (caliche) include high mean annual temperatures, an arid to semi-arid environment, and a markedly seasonal rainfall.

Regional studies of the cross-bedding in the sandstones indicate that the direction of sediment transport was from the north-west (Ball and others, 1961; Allen, 1962; Brandon, 1989). This, combined with a high proportion of detrital garnet (Fleet, 1925; 1926) in the sandstones, suggests derivation from a metamorphic terrain.

The Bishop's Frome Limestone at the top of the Raglan Mudstone probably represents a prolonged interval of emergence and soil formation.

St Maughans Formation (SMg)

Steeply dipping beds of the St Maughans Formation crop out west of Gorsley, and are well exposed in cuttings along the M50 motorway. The formation is estimated to be about 650 m thick in this area. The basal few metres are also preserved in a small outlier just west of Ledbury.

Within the St Maughans Formation, the mudstones and siltstones closely resemble those in the Raglan Mudstone; the sandstones, however, are more abundant, generally finer-grained and less micaceous. Another notable difference is the presence of conglomerates formed by the reworking of concretionary limestones. These conglomerates have yielded (Allen and Dineley, 1976) fragments of Pteraspis, Traquairaspis cf. symondsi, a cephalaspid perhaps similar to Cephalaspis lyellii, and Tesseraspis?.

In the St Maughans Formation garnet is present in much smaller amounts than in the Raglan Mudstone, indicating that sediment was no longer derived from the metamorphic province. It has been suggested (Allen, 1974a) that this might be due to river capture or a reversal of drainage, perhaps initiated (Allen and Crowley, 1983) by epeirogenic uplift following the intrusion of the Irish granites.

Brownstones Formation (Brs)

The Brownstones Formation is estimated to be at least 900 m thick, of which the lowest 750 m crop out in the present district to the west of May Hill. It is well exposed in motorway cuttings just west of the district where, in the lower part of the formation, fine-grained sandstones with basal intraformational conglomerates alternate with equal proportions of red-brown mudstone. Higher in the formation the mudstones decrease in importance and fine- to medium-grained sandstones predominate, with coarser-grained sandstones in the highest levels. Conglomeratic beds in the higher levels (Allen and Dineley, 1976) contain clasts of vein quartz, assorted sandstones (some fossiliferous), greywackes, tuffs and acid lavas.

Trace fossils within the formation include Diplocraterion sp., Planolites?, and Annelidichnium?.

Chapter 7 Carboniferous

Carboniferous rocks have a narrow outcrop (Figure 4) in the vicinity of Newent, fringing the Bromsgrove Sandstone outcrop between Stallion Hill [SO 715 238] in the south and Welsh House [SO 719 303] in the north. They rest unconformably on, or are faulted against, the Raglan Mudstone and are overlain unconformably by the Bromsgrove Sandstone. The Stallion Hill Sandstone, the lowest formation in the succession, is estimated to be up to 80 m thick, and has been identified for the first time in the present survey. The Carboniferous age of the Stallion Hill Sandstone has not been proved, though alternative ages, such as Upper Devonian, seem less likely on lithological grounds. The overlying Upper Coal Measures were formerly worked for coal. A stratigraphical thickness of 210 m has been proved by boring, and the total thickness may be over 300 m.

Stallion Hill Sandstone (Stn)

This formation lies unconformably on the Raglan Mudstone and crops out between Stallion Hill and Boulsdon Lea [SO 7083 2422], and in a small area [SO 705 247] 500 m east of Briery House. In addition, a pebble bed a metre or two thick at the base of the Upper Coal Measures [SO 702 251] south-east of Kilcot, and pebbly sandstone exposed to 1.5 m in a small disused quarry [SO 7150 2995] near Little Woodend near the northern extremity of the Coal Measures outcrop, may be part of the formation. On the basis of a 10° average northeasterly dip, about 80 m of strata come to crop on Stallion Hill, and 18 m south-west of Knapper's Farm.

At the base of the formation at Stallion Hill is an estimated 10 m-thick loosely cemented, poorly sorted conglomerate with a red-brown, sandy matrix. The clasts are up to 15 cm in diameter and include subrounded, weathered igneous rocks, quartzite, sandstone and limestone. There is no evidence of a basal conglomerate in the outcrop east of Briery House. The pebble bed 500 m farther to the northwest includes pebbles, up to 10 cm in diameter, of Malvernian granite and of purple-stained, fine-grained sandstone. The sandstone in the pit near Little Woodend includes cobbles of quartzite and possible Malvernian rocks up to 15 cm in diameter.

At Stallion Hill the bulk of the formation consists of sandstone, with some interbedded mudstones. The sandstone is fine to coarse grained, mainly grey, friable, cross-bedded and slightly micaceous. The mudstones, rarely seen in section, are buff, purple and red-brown mottled, and weather to a sticky clay. A section behind a barn at Stallion Hill [SO 7151 2405] exposed 5.7 m of sandstone; sandstone with thin (less than 10 cm) mudstone bands is exposed in the stream [SO 7122 2429] south-east of Boulsdon Croft and in the roadside [SO 7167 2380] south-east of Stallion Hill.

No macrofossils have been seen in the Stallion Hill Sandstone and a sample examined for palynomorphs proved bar ren. Direct evidence of age is therefore lacking, but the beds could possibly be correlated with sandstones in the Trenchard Formation (Westphalian C–D) of the Forest of Dean. A Carboniferous rather than an Upper Devonian age would also seem likely in view of the proximity of the outcrop of the formation to that of the Upper Coal Measures.

Upper Coal Measures (UCM)

Upper Coal Measures were proved to a depth of 262 m without the base being reached in two adjacent BGS boreholes (Figure 5) west of Newent, Lower House No. 1 and No. 2 [SO 6988 2629]. Abstract logs have been published (British Geological Survey, 1984). The dip averaged 30° down to 190 m and 50° below that level and the true thickness penetrated by the holes is estimated to be 208 m. Coal seams in the higher part of the sequence, above 130 m, have high sulphur and ash contents, but the lowest coal proved, LH 19, has a moderately low sulphur content of 1.38 per cent and low ash (2.8 per cent) (National Coal Board reports, 1984a;b). Smith and Spriggs (1984) report that spore assemblages of the coals are characterised by species generally found in seams of Westphalian D age.

Lithologically, the red mudstones proved in the highest part of Lower House No. 1 Borehole down to 20.6 m resemble mudstones typical of the Keele Formation of the Midlands (Figure 6). The beds from 20.6 m to about 130 m, including the Spirorbis limestones at 67.10 m and 67.50 m, not hitherto recorded from the Newent Coalfield, are comparable in facies with the Highley Beds (Mitchell and others, 1961) of the Wyre Forest Coalfield, commonly correlated with the Halesowen Formation of the Midlands. Between about 130 and 150 m in Lower House No. 2 Borehole, the beds are predominantly brown and grey mottled mudstone, and from 150 to 173 m they are grey mudstone, with seat-earths but no coal seams. From 173 m downwards, apart from some yellowish brown and grey mottled blocky mudstone between 206 and 214 m, the beds are of the grey facies usual in the Coal Measures, comprising cycles composed typically in upward succession of mudstone, thin sandstones, seatearth and coal. Apart from burrows at the base of a cycle at 233.70 m, no trace of any fauna was obtained from those beds below 173 m that were cored.

Smith and Spriggs (1984) favour a correlation between seams 16 to 19 of the boreholes and the Yorkley to Trenchard seams of the lower part of the Pennant Formation and the Trenchard Formation in the Forest of Dean (Figure 6). Assuming, however, that the red beds at the top of the Lower House succession are higher than any strata present in the Forest of Dean, this correlation would imply that the thick Pennant sandstones of the Forest of Dean are represented by mudstones with only thin sandstones at Lower House. An alternative correlation, between seams 16 to 19 of the boreholes and the lower part of the Supra-Pennant Formation of the Forest of Dean, has more to commend it from a lithofacies point of view, and cannot be excluded on palynological grounds, for previous published work in the Forest of Dean (Smith and Butterworth, 1967) has not included palynological examination of the Supra-Pennant seams below the Woorgreen seams.

Smith and Spriggs (1984) also point to the broadly similar pattern in the ranges of selected spores (Thymospora perverrucosa, Vestispora magna, Schopfites dimorphus and Punctatosporites granifer) at Lower House and in Oxfordshire, which suggests correlation between seams LH 16 to 19 and the Witney Coal Formation and between seams LH 3 to 14 and the Burford Coal and Crawley formations. Near the top of the Burford Coal Formation in the Upton and Apley Barn boreholes in Oxfordshire are Spirorbis limestones, containing ostracods and resting on seatearths, which resemble the Spirorbis limestone beds just below seam LH 1 at Lower House, and this supports the correlation.

The Newent Coalfield was mainly worked between about 1760 and 1810 and a brief account of the mining is given in Section 12.

Chapter 8 Permian and Triassic

The Hercynian earth movements, which brought Carboniferous deposition to an end, resulted in the formation of a 'super-continent', Pangaea. The hot desert climate of Permian and Triassic times resulted from the position of Britain near the middle of this continent, and at low northern latitudes.

The Permian and Triassic outcrop lies east of a line from the Malverns to May Hill. The sediments rest unconformably on rocks from Precambrian to Carboniferous in age and make up the major part of the fill of the Worcester Basin, where they are more than 1500 m thick. The generalised succession of strata and their classification are shown in (Table 2).

The Permian–Triassic boundary is arbitrarily placed at the top of the Bridgnorth Sandstone. From the study of palynomorphs, occurring mainly in rare intercalations of grey or green strata in the succession of red beds, Warr ington (1970) has achieved a broad but indirect correlation of the Triassic rocks with the marine stages (Table 2). Current usage (Warrington and others, 1980) places the base of the overlying Jurassic System at the incoming of the ammonite Psiloceras planorbis, which in this district is in the basal part of the Lias Group.

Haffield Breccia (HBr)

The Haffield Breccia, at the base of the Permo-Triassic succession, was termed the Haffield Conglomerate by Phillips (1848) and the name Haffield Breccia was introduced by Groom (1902). The breccia lies with strong unconformity on Silurian and Malvernian rocks and forms a pronounced ridge between The Vineyard [SO 7182 3344] and the Glynch Brook valley [SO 7315 3480]. It also occupies the lower slopes to the east of the ridge rising to Howler's Heath [SO 748 353]. The best exposures are around Haffield House [SO 7245 3369] where the breccia has been quarried. It attains a probable maximum thickness of 75 m at outcrop. Measured dips are 18° to 25° to the south or south-east but, as the regional dip is closer to 10° to the south-south-east, there is a substantial depositional dip.

The most common lithology comprises poorly sorted, hematite-coated, subangular clasts of Malvernian rocks (mainly sheared, pinkish brown granite and dark green diorite) and greenish grey and purple-brown May Hill Sandstone and siltstone in a matrix of purple to dark red-brown, sandy siltstone and mudstone (Plate 4). The clasts are mostly less than 10 cm across, but blocks up to 1 m in diameter have been recorded (Blackith, 1956). The sediments are generally well bedded, some beds having erosive bases scouring down as much as 30 cm into the underlying sediments. In some of the southernmost exposures, the beds are less than 8 cm thick, many consisting of a thin basal breccia fining upwards into coarse-grained sandstone with only a few small clasts.

No flora or fauna has been recorded from the Haffield Breccia, but by analogy with the Clent Breccia in the West Midlands (Mitchell and others, 1961), which lies unconformably on Upper Carboniferous strata, it is tentatively assigned to the Lower Permian.

Bridgnorth Sandstone (Bri)

The dune-bedded Bridgnorth Sandstone, formerly the Lower Mottled Sandstone or the Dune Sandstone, which overlies the Haffield Breccia, is regarded largely as Lower Permian in age (Smith and others, 1974).

The Bridgnorth Sandstone crops out in a tract bounded by faults to east and west between The Vineyard and Bromsberrow [SO 747 341]. It rests with apparent conformity on the Haffield Breccia with no evidence, at least at outcrop, of lateral passage from one to the other. The formation generally gives rise to subdued topography, but it is exposed in two building-sand quarries at Bromsberrow Heath [SO 73 23] (Plate 5) and in numerous small roadside exposures. The probable thickness at outcrop, assuming a regional dip of 8° to 10° to the south or south-east, is about 420 m; measurements of the true dip are generally impracticable because cross-bedding is so common. The lithology is remarkably uniform and consists of well-sorted, red-brown, medium- to coarse-grained sandstone with moderately well-rounded quartz grains. Large-scale cross-bedding,. interpreted as aeolian dune bedding, occurs in beds up to 15 to 20 m thick with foreset beds up to 4 m thick. It is particularly well displayed in the Bromsberrow quarries and in the road cutting [SO 7485 3480] 1 km north-east of Bromsberrow church, where the depositional dip of the foreset laminae is up to 30°. Foresets dip consistently to the south or south-west, indicating winds from the north during deposition. The reddish brown colour of the rock is caused by a coating of hematite around each sand grain, but there is little interstitial cement and consequently the sandstone is soft and friable and readily weathers to a sandy soil which forms a thick colluvial wash in valleys.

The junction with the overlying Bromsgrove Sandstone is sharp. It shows little sign of discordance despite an inferred non-sequence between the two formations, with both the Kidderminster Formation and the Wildmoor Sandstone missing. Correlation of the sands at Bromsberrow with the Bridgnorth Sandstone rather than the Wildmoor Sandstone is supported by dipmeter measurements from the Kempsey Borehole (Whittaker, 1980) just south of Worcester which indicate dune-bedding in the Bridgnorth Sandstone but not in the Wildmoor Sandstone. In this borehole the Bridgnorth Sandstone is 938 m thick and dips are high, ranging up to 30°

The Bridgnorth Sandstone has been penetrated to 91 m depth in a borehole [SO 7385 3326] at Bromsberrow Pumping Station, starting an estimated 60 m below the top of the formation, and farther down-dip, in a borehole south of Lintridge [SO 7441 3175], and probably in one at Oxenhall [SO 7092 2644]. A 0.7 m pebbly bed at an estimated 100 m below the top of the formation in the Bromsberrow Pumping Station Borehole indicates that in addition to aeolian sandstone, there are other lithologies within the sequence, probably of fluvial origin.

Sherwood Sandstone Group

Kidderminster Formation (Kdm)

The Kidderminster Formation (Warrington and others, 1980), formerly the Bunter Pebble Beds, does not crop out in the Tewkesbury district but its concealed presence at depth within the Worcester Basin was deduced from a prominent reflector on seismic lines. This was considered by Chadwick (1985), on evidence from the Kempsey Borehole and from seismic profiles, to mark the top of the formation. The thickness between this reflector and the sub-Permian floor is estimated at 500 to 800 m in the central part of the basin. In the Kempsey Borehole, the corresponding interval is 1066 m, the Kidderminster Formation occupying the top 150 m and the Bridgnorth Sandstone the lower part. Assuming similar relative thicknesses, the concealed Kidderminster Formation may be 80 to 130 m in thickness between the Malverns and the River Severn.

The formation consists of yellow-brown, compact sandstones with lenticular beds of pebble-conglomerate, the latter characteristically including white vein quartz and liver-coloured quartzite pebbles. The beds are considered (Audley-Charles, 1970) to be the deposits of a large braided river that flowed northwards from the northern France–English Channel region through the Worcester Basin.

Wildmoor Sandstone (WrS)

In the West Midlands the Kidderminster Formation is succeeded by the Wildmoor Sandstone (Warrington and others, 1980), formerly called the Upper Mottled Sandstone (Wills, 1970;1976), which consists of dark reddish brown, fine-grained, soft sandstones with a few pebbles. The formation is 285 m thick at Kempsey and the seismic evidence shows that it is present and of similar thickness at depth in the Tewkesbury district, although it does not crop out.

Dune-bedding is absent from the Wildmoor Sandstone at its type locality in the Droitwich district (Audley-Charles, 1970), where its sedimentary structures suggest fluvial deposition, albeit from a slower-flowing river than that which deposited the Kidderminster Formation. At Kempsey (Whittaker, 1980), the sandstones are trough cross-bedded and interlaminated with siltstones and mudstones.

Bromsgrove Sandstone (BmS)

The Bromsgrove Sandstone (Warrington and others, 1980), formerly the Keuper Sandstone, crops out south of Bromsberrow Heath [SO 741 329]. In the north of the district it rests with sharp unconformity on the Bridgnorth Sandstone, but to the west it is partly unconformable on, and partly faulted against, Coal Measures, Raglan Mudstone and Silurian rocks. To the east the Mercia Mudstone Group conformably overlies the Bromsgrove Sandstone near Newent although the junction is faulted elsewhere. The thickness is estimated to be about 150 m near Oxenhall [SO 711 267], increasing to 400 m near Redmarley d'Abitot [SO 752 313]. Seismic evidence indicates about 900 m of strata between the top of the Bromsgrove Sandstone and the top of the Kidderminster Formation at depth in the vicinity of Eldersfield [SO 800 311]. The lower part of this interval is presumed to consist of the Wildmoor Sandstone, and a thickness of about 600 m for the Bromsgrove Sandstone seems likely. This compares with 560 m in the Kempsey Borehole.

The Bromsgrove Sandstone consists of reddish brown to yellowish brown conglomerates, pebbly sandstones, sandstones and thin (less than 1 m) red-brown mudstones in fining-upwards, fluvial cycles each about 2 m to 10 m or more in thickness. The sandy conglomerates, rarely more than 1 m thick, are composed of subrounded quartz and quartzite pebbles, 5 m or less in diameter, and red mudstone clasts, locally with a calcite cement. Fine- to medium-grained, cross-bedded sandstones form the bulk of the formation. Carbonate nodules of pedogenic origin are common in sandstone beds near the top of each cycle.

A particularly persistent mudstone has been traced for 6 km from west of Newent northwards to near Payford Bridge [SO 749 300]. Close above it, between Newent and The Scarr [SO 726 280] is a well-developed conglomerate lens. The succeeding 30 m of the sequence contains fine-grained sandstones. Above this are fine-grained micaceous sandstones which are about 3 m thick at outcrop near Brand Green [SO 741 281] and are similar to the former 'Waterstones' of Shropshire and Cheshire. In the BGS Eldersfield Borehole [SO 7891 3221], which penetrated the top 58 m of the Bromsgrove Sandstone (348.47 to 407.06 m depth), the top 20.71 m of the formation are of this facies and comprise interbedded, laminated, muddy siltstones and fine- to medium-grained sandstones, commonly with concentrations of biotite mica flakes on bedding planes. Below 369.18 m, cross-bedded sandstones with thin beds of red-brown mudstone or siltstone were proved. Middle Triassic miospores occurred at 351.2 and 376.7 m.

A strongly-flowing fluvial regime is indicated by the pebbly sands of the lower part of the Bromsgrove Sandstone. The 'Waterstones' facies represents lower energy deposition, possibly in estuarine water influenced by a marine incursion from the north, which seems just to have reached as far south as Worcestershire (Warrington, 1970, p.205).

Mercia Mudstone Group (MMG)

The Mercia Mudstone, formerly the Keuper Marl (Warrington and others, 1980), crops out across the broad lowland between the Malverns and the Penarth Group escarpment. The group is about 550 m thick in the north thinning to about 250 m in the south-west. Seismic profiles indicate that thickness is maintained close to the Eastern Boundary Fault of the Malverns.

The group consists largely of rather massive, red-brown, silty mudstone commonly with scattered, green-grey spots up to 1 cm or so in diameter and irregular green-grey patches up to 10 cm across. Beds of laminated, silty mudstone up to 0.5 m thick occur at intervals. Anhydrite and gypsum occur as small nodules, 10 cm or less in diameter, and as secondary veins of satin-spar up to several centimetres wide; throughout the middle part of the group. The nodules are best developed in the laminated beds. The evaporites are usually leached out by weathering within 20 to 30 m of the ground surface. The mudstones weather to red, clayey soils and the weathered mudstone, close to the surface, is commonly slightly calcareous and was formerly dug from small 'marl' pits as lime for top-dressing the land. Impersistent beds of hard, blocky, red and green mottled siltstone or silty mudstone, or of thinly bedded, green-grey sandstone, are known as skerries and are 0.3 to 1 m thick.

The Arden Sandstone is the thickest of the sandstones; it is 2 to 7 m thick and lies 100 to 180 m below the top of the Mercia Mudstone sequence. Its thickness makes it a useful marker bed within an otherwise monotonous, lithological succession. Another useful marker bed is the Blue Anchor Formation, formerly known as the Tea Green Marl in the Tewksbury district, which comprises the uppermost 3 to 10 m of the Mercia Mudstone succession. The Arden Sandstone and the skerries form escarpments, and the Blue Anchor Formation usually occupies a steep slope at the foot of the Penarth Group escarpment.

A composite but complete section of the group was provided by the BGS Twyning [SO 8493 3664] and Eldersfield [SO 7891 3221] boreholes, the former proving strata from the top down to 7 m below the Arden Sandstone (190 m in all), the latter from the base of the Arden Sandstone downwards (348 m). The Droitwich Halite Formation, which probably lies at an horizon just below the Arden Sandstone, is believed not to extend as far south as the Tewkesbury district. It was not present in the Eldersfield Borehole or in a borehole (Richardson, 1930) at Upton-on-Severn in the Worcester district, to the north of Twyning.

Several skerries are mapped in the lower part of the Mercia Mudstone at Taynton [SO 730 217] and Cobb's Cross [SO 764 334], but it has not proved possible to correlate them with the Eldersfield Borehole sequence. Common sedimentary features of the laminated beds in the Eldersfield Borehole are desiccation cracks, ripple lamination, convoluted lamination and mudstone breccias. The blocky mudstone is mainly structureless, but in that part of the sequence about 140 m or more below the Arden Sandstone are faintly outlined breccias consisting of irregular-shaped mudstone clasts separated by narrow irregular veins of silty mudstone which may be paler or darker-coloured than the clasts.

The Arden Sandstone forms a prominent escarpment along most of its outcrop and there are numerous small exposures in the vicinity of Eldersfield, Pendock [SO 786 331] and Longdon [SO 837 362]. It is 7 m thick at Eldersfield and Pen-dock but 2 m or less south of Staunton; 4.5 m were proved in the Twyning Borehole. The Arden Sandstone is typically a finely interbedded sequence of coarse-grained, cross-bedded, grey sandstone and greenish grey dolomitic limestone and mudstone; sandstone makes up about one third of the total thickness. In the Twyning Borehole, the Arden Sandstone was largely dark greenish grey, silty mudstone with subordinate siltstones; thin sandstones, each less than 5 cm thick, are restricted to the lowermost 0.3 m. Sedimentary structures include ripple lamination, desiccation polygons, mudflake breccias, load casts and convolute lamination. Fossils in the Arden Sandstone include plant remains, the crustacean Euestheria minuta, and fish remains (Symonds, 1855). Bioturbation is common, with individual burrows up to 3 mm in diameter; in some sandstones this has completely destroyed the primary lamination. Between Tibberton [SO 765 218] and Hartpury [SO 795 253], a hard, blocky, red-brown and green siltstone about 1 m thick lies 20 m above the Arden Sandstone, and near Oridge Street [SO 788 278] and west of Forthampton [SO 856 326], there are skerries between 20 and 40 m above the Arden Sandstone. In the Twyning Borehole, finely laminated beds occur between 68 and 100 m below the top of the Blue Anchor Formation, where the concentration of nodular gypsum/anhydrite is greatest. Nodules and gypsum veins are absent in the top 60 m of the Group.

The Blue Anchor Formation comprises 7 m of greenish grey siltstones and silty mudstones in the Wainlode river cliff [SO 8455 2575]. In the outlier at Berrow Hill [SO 794 336] Richardson (1905a;c) recorded a total thickness of only 3.5 m. In the Twyning Borehole it was 9.75 m thick; the uppermost beds yielded isolated fish scales and desiccation cracks were common. The beds are more resistant to weathering than is usual in the Mercia Mudstone Group, possibly owing to slight induration by a dolomitic cement.

The blocky mudstones and silty mudstones that make up the greater part of the Mercia Mudstone accumulated during the progressive development of a flat arid plain or inland sabkha which was subjected to local flooding. They are interpreted (Wills, 1970, Arthurton, 1980), as being partly aeolian in origin, the lack of primary sedimentary structures resulting from the breaking up and mixing of the sediments prior to consolidation. Gypsum crystals growing close below the sediment surface may have been a cause of this reordering, a mechanism which could also account for the breccias observed in the blocky mudstones of the Eldersfield Borehole.

The laminated beds, characterised by sedimentary structures typical of a low-energy aqueous environment, are interpreted as deposits of shallow playa lakes. Ripple-laminated, dolomitic siltstones and sandstones and mudstone breccias indicate short periods of flood-generated currents, and the associated desiccation cracks, load casts and water-release structures represent periodic emergence and oscillation of the water table. Anhydrite/gypsum nodules were produced by interstitial growth close beneath the sediment surface in the emergent conditions (Arthurton, 1980) of the sabkha plain. They are concentrated in those parts of the sequences where the frequency of laminated beds is relatively high, presumably because the water table was highest during those intervals. In the subaqueous conditions when laminated siltstones were laid down, the more soluble chlorides and sulphates remained in solution and dolomite was precipitated in the matrix around the silt grains.

A widespread change in environment, perhaps with a humid climate in the source area (Wills, 1970), occurred during deposition of the Arden Sandstone. The Sandstone correlates with the Schilfsandstein of Germany (Warrington, 1970: Wills, 1970) and has yielded Carnian (late-Triassic) miospores at Longdon and at a depth of 314 m in the Twyning Borehole.

Penarth Group (PnG)

The Penarth Group, formerly the 'Rhaetic' (Warrington and others, 1980), includes marine deposits, and resulted from an inundation that led to the establishment of widespread shelf seas over Britain during the Jurassic. The outcrop of the group lies just below the crest of a sinuous escarpment between Murrell's End [SO 790 222] and Tewkesbury. The outcrop is cut out by faulting to the south of Murrell's End and from Tewkesbury northwards for 6 km to Stratford [SO 884 385]. Outliers occur at Rodway Hill [SO 785 205], Grey Hill [SO 852 270], to the west and north-west of Tewkesbury, and at Berrow Hill [SO 794 337].

The Penarth Group ranges from 8 to 10 m in thickness and comprises the Westbury Formation, about 5 m thick, overlain by the Lilstock Formation, represented locally by the Cotham Member, 3 to 5 m thick. The two divisions are not mappable separately in the Tewkesbury district. The Westbury Formation consists of dark grey to black, finely laminated mudstone and silty mudstone with thin layers of fine-grained, pale grey, yellow-weathering sandstone near the base. Fossils are abundant, in particular the bivalves Rhaetavicula contorta and Protocardia rhaetica. Within 0.5 m of the base is a thin sandstone crowded with fish remains, the local representative of the 'Rhaetic Bone Bed'. The Cotham Member consists of pale, greenish grey, calcareous mudstone with some thin layers of fine-grained limestone. The mudstone weathers to a soft grey clay.

Individual beds within the Penarth Group can be traced for long distances. Wainlode Cliff [SO 845 255] on the River Severn provides a good exposure of the lower part of the group (Plate 6), but the higher beds there are rather obscured. Richardson (1903) measured a detailed section on this cliff. He also (1903) recorded details of sections, now overgrown, in a lane cutting [SO 8678 2457] at Prior's Norton and in another [SO 8880 2707] at Coombe Hill. He gave the thickness of the Westbury Formation ('Lower Rhaetic') as 4.75 m at Prior's Norton and 4.37 m at Coombe Hill. Only the base of the Cotham Member ('Upper Rhaetic') was exposed in the Prior's Norton section but the upper part was recorded by Richardson at Coombe Hill, at Grey Hill and in a road cutting [SO 8205 2768] near Hill Farm, Hasfield. Richardson (1903), quoting earlier authors, also gave details of Penarth Group beds exposed in a cutting [SO 8633 3341], now overgrown, on the Tewkesbury–Ledbury road near Bushley.

The Twyning Borehole proved a thickness of 9.9 m for the Penarth Group, the Cotham Member being 4.39 m thick. Greenish grey mudstone at its base rested with a sharp, slightly discordant junction on dark grey, laminated, silty mudstone at the top of the Westbury Formation; the latter totalled 5.51 m. On Berrow Hill Richardson (1905a; c) recorded the Westbury Formation as 2.74 m thick, overlain by 2.74 m of Cotham Member marls. He commented that the Westbury Formation was unusually thin, and considered that the lowest three beds of the Wainlode Cliff section, including the Bone Bed, were not represented.

Lias Group (part)

At the base of the Lias Group are alternating beds of shelly limestone and mudstone or shale with bivalves (notably Liostrea and Modiolus), termed by Richardson (1904; 1905b) the 'Ostrea-beds' . They are mapped as limestone in Lower Lias Clay. Together with the lowest beds of the Jurassic, the alternating limestone and shales with Psiloceras planorbis of the lower part of the planorbis Zone, they form the crest and dip-slope of the Penarth Group escarpment. Near Ashleworth [SO 812 255], the dip-slope is nearly 1 km wide but elsewhere it rarely exceeds 100 to 200 m in width. The limestone bands were formerly dug for building or paving stone or for lime burning and numerous small quarries, now overgrown, occur along the outcrop.

In a railway cutting [SO 797 215], now disused, at Lassington, Woodward (1893) recorded 3.51 m of the Ostrea beds; the Twyning Borehole proved 3.07 m of these beds. Richardson (1904; 1905b) recorded a 3 m section in 'Ostrea beds' in a quarry on Sam Hill [SO 860 340], a 1.2 m section in a quarry (exact site uncertain) on Heath Hill [SO 850 375], and a 1.7 m section on Berrow Hill.

Chapter 9 Jurassic

Jurassic rocks, dipping gently eastwards, crop out in, and to the east of, the Severn Valley. They belong mainly to the Lias Group and are Hettangian to Toarcian in age (Table 3), although beds of the Inferior Oolite Group of Aalenian age cap Bredon Hill. The succession was deposited in a shelf sea on the western side of the London–Ardennes land mass. Deposition of the Lias Group took place under open-water, low-energy conditions but a change to very shallow-water, almost emergent, conditions was marked by the Aalenian carbonate sediments. The climate was warm, in latitudes of, perhaps, 40 to 45°N.

Lias Group (part)

The Lias Group was formerly divided (Table 3) into Lower, Middle and Upper Lias. These terms, however, are essentially biostratigraphical and the boundary between Lower and Middle Lias in particular, defined at the top of the davoei Zone, has always presented difficulty in mapping. Near Cheltenham, it lies within the Dyrham Silts. The name Lower Lias Clay is used for beds between the Penarth Group and the Dyrham Silts, and corresponds to the bulk of the former Lower Lias. Cope and others (1980) used the name 'Lower Lias Clays' for beds of Sinemurian age above the Blue Lias in some southern England localities, but the Blue Lias is here treated as a part of the Lower Lias Clay. The term Upper Lias Clay is used for beds of clay between the Marlstone Rock Bed and the base of the Lower Inferior Oolite.

Lower Lias Clay (LLi)

This formation consists largely of grey silty mudstone but the Blue Lias comprises interbedded mudstone and argillaceous limestone. Ammonites occur at many levels and provide the basis for subdivision of the strata into biostratigraphical zones and subzones (Dean, Donovan and Howarth, 1961). The succession of zones is shown in (Table 3). The thicknesses of the planorbis to bucklandi zones inclusive are based on the Twyning Borehole record, and those of higher zones on thicknesses proved in the Scarborough Cottages [SO 9643 3788] (Whittaker, 1972a) and Stowell Park [SP 084 118] (Green and Melville, 1956) boreholes. Although the boundaries between zones are independent of changes in lithology, it has proved possible from the wide scatter of localities that have yielded fossils, both during the recent survey and to previous investigators, to construct a map showing approximately the extent of the strata in each zone (Figure 7).

The incoming of the ammonite Psiloceras planorbis in the lower part of the formation marks the base of the Jurassic System (Cope and others, 1980). In the Twyning Borehole the lowest beds of the planorbis Zone comprise alternating thin limestones and mudstones. In mapping, it has not proved possible to separate the lowest Jurassic beds from the similar interbedded thin limestones and mudstones of the topmost Triassic.

Richardson (1904;1905b) used the term 'planorbis-beds' for deposits of the planorbis Zone. He gave details of a 4.5 m section in alternating limestone and shale beds with P. planorbis in a quarry at Sarn Hill [SO 860 340], 'a little to the north' of one exposing 'Ostrea-beds'(Triassic), and of a 4.3 m section in a quarry 'at the southern end of the Heath Hill outlier'. Limestone with P. planorbis is exposed in another small quarry [SO 8460 3826] in the same outlier.

Thin limestones in the upper part of the planorbis Zone have been recorded in a temporary excavation [SO 880 265] near Barrow and in a river-bank exposure [SO 8985 2950] at Tredington. The Twyning Borehole proved 27 m of clays with a few thin limestone bands between the top of the planorbis Zone and the base of the Blue Lias.

The Twyning Borehole proved 58 m of Blue Lias, extending from the upper part of the liasicus Zone to the lower part of the bucklandi Zone. Through much of the Blue Lias the limestone beds average 0.1 m thick, alternating with mudstone beds around 0.6 m thick. The outcrop is not marked by any topographical feature comparable with the escarpment produced by the basal limestones of the Lias Group, presumably because the Blue Lias limestones are softer and more easily weathered. There is also little sign of the beds having been quarried in the past, perhaps because of their poor quality.

The Blue Lias crops out west of the Severn north of Maisemore [SO 810 210], with outliers west of Hasfield at Barrow Hill [SO 821 268] and Hill Farm [SO 815 276]. Richardson (1906) recorded a 7.5 m section of Blue Lias in a river cliff [SO 8178 2168] near Maisemore. East of the Severn the broad outcrop between Sandhurst [SO 830 230] and Staverton [SO 890 235] is mostly low-lying ground where scattered exposures show low dips of variable direction. From Staverton northwards there is a steady easterly dip and the outcrop is a band about 1 km wide, though its exact limits are uncertain. Between Staverton and Boddington [SO 895 255] the outcrop is distinguished by low ridges trending north–south. There is a small outlier at Tewkesbury Park [SO 882 312].

The outcrop of Lower Lias Clay above the Blue Lias is mainly low-lying and characterised by heavy clay soils. North of Stoke Orchard [around 915 295] slight ridges formed by limestone or Gryphaea shell beds can be traced for short distances.

Dyrham Silts (DyS)

This formation consists of grey silt and silty clay. Its outcrop, on the western slope of Bredon Hill [SO 941 392], is largely covered by landslip. A thickness of about 60 m of silts in the margaritatus Zone and upper part of the davoei Zone was estimated from mapping in the adjoining Stratford-on-Avon district (Williams and Whittaker, 1974).

Marlstone Rock Bed (MRB)

In the Lalu Barn Borehole [SO 9577 3996] (Whittaker, 1972a) the Marlstone Rock Bed, 6.0 m thick, comprises sandstone with some beds of light grey, sandy limestone. The outcrop forms a shelf on the western side of Bredon Hill for 200 m southward from the northern boundary of the district; farther south, to the Bredon Hill Fault on the south side of the hill, the outcrop is covered by landslip.

Upper Lias Clay (ULi)

This formation consists of mudstones with subordinate silts and siltstones. The outcrop lies north of the Bredon Hill Fault and is covered by landslip. The Lalu Barn Borehole [SO 9577 3996] proved 110 m and Whittaker (1972a) suggested a thickness of more than 122 m beneath the centre of Bredon Hill, but that this diminishes westwards to 76 m in the Tewkesbury district.

Inferior Oolite Group

Lower Inferior Oolite (LIO)

The following lithological divisions of the Lower Inferior Oolite, in ascending order, have been recorded on Bredon Hill: Scissum Beds (sandy limestones); Lower Limestone (oolitic limestones); Pea Grit (coarse oolitic limestones with pisolitic layers); and Lower Freestone (soft oolitic limestones). Probably 30 m of beds are present.

About 9.1 m of massive, oolitic, shell-fragmental limestones are exposed in an old quarry [SO 946 392], recorded by Richardson (1902) as showing Lower Limestone overlain by Pea Grit. The beds in a disused quarry 1 km north-east of Westmancote [SO 9474 3872] dip at up to 50°, probably the result of cambering (Whittaker, 1972a). Richardson (1902), who gave the locality as a mile to the north-west of Overbury church, recorded faulted Scissum Beds, estimated at 8.5 m thick, overlain in turn by 10.5 m of Lower Limestone, up to 4.3 m of Pea Grit, and Lower Freestone.

Chapter 10 Structure and tectonic history

The most important structural element of the Tewkesbury district is the Malvern Axis, an ancient north–south belt of crustal weakness. In the north this is marked by the Malvernian outcrops which separate folded and faulted Lower Palaeozoic rocks to the west from the gently dipping, less strongly faulted, Mesozoic rocks of the Worcester Basin to the east. The Malvern Axis has repeatedly given rise to up-folding along north–south lines through successive episodes of earth movement. Other lines of basement weakness are the north-west–south-east Woolhope–May Hill Axis in the south-west of the district and a north–south axis, here named the Tewkesbury Axis, responsible for a belt of faults and folds in Triassic and Jurassic rocks through Twyning and Tewkesbury. The major structural elements are outlined in a diagram marginal to the 1:50 000 geological map.

The Worcester Basin (Figure 8) is a graben that originated in Permian times (Whittaker, 1975). It lies between the Malvern Hills and the Vale of Moreton Axis, 30 km to the east, and is divided by the north–south Inkberrow–Haselor Hill Axis into two roughly equal subbasins, one in the west centred on Worcester and the other centred near Winchcombe (Smith and Burgess, 1984). The floor of the basin in the Tewkesbury district may consist of Precambrian volcaniclastics similar to those proved in the Kempsey Borehole near Worcester (Whittaker, 1980). South of the Malvern Hills, the Worcester Basin extends a few kilometres farther west, and the Permo-Triassic fill overlies and abuts against folded and faulted Carboniferous and older rocks.

Precambrian tectonic history

The age of the Malvernian igneous complex is 681 ± 53 Ma (Beckinsale and others, 1981). The nature of the rocks into which it was emplaced is not clear, but they were presumably part of a micro-continent that developed between 900 Ma and 450 Ma (late Ordovician), by accretion of island arcs and associated accretionary prisms, and which now constitutes the crust of southern Britain south of the Iapetus suture (Anderton, 1982; Thorpe and others, 1984).

The Malvernian pluton is inferred (Thorpe and others, 1984) to have resulted from south-easterly-directed subduction of oceanic lithosphere, at a time coeval with deposition of the Mona Complex in Anglesey.

The Warren House Formation, probably in faulted contact with the Malvernian, may represent relicts of marginal basin basalts trapped and uplifted along the Malvern lineament, a Proterozoic suture between Uriconian and Charnian terraines (Pharaoh and others, 1987).

Lower Palaeozoic tectonic history

By early Cambrian times Malvernian rocks were exposed at the surface, for pebbles of Malvernian rocks occur in the basal Cambrian quartzites. The thick (up to c. 1 km) Cambrian succession was deposited continuously across the Malvern Axis so far as is known. Basic dykes were intruded during the Ordovician, which locally was a period of uplift and erosion. At the end of the Ordovician, Malvernian rocks were exposed along the western edge of a broad up-faulted tract that included Tortworth and the Birmingham area (Ziegler, 1964). Deposition was resumed in the Llandovery (Silurian) and, on the west side of the Malvern Hills, the basal May Hill Sandstone unconformably oversteps the whole Cambrian sequence to rest on Malvernian at a former shoreline, exposed at the Gullet Quarry [SO 762 382] (Brooks, 1970; Reading and Poole, 1961; Ziegler, 1964).

At May Hill the base of the May Hill Sandstone Group is not exposed, but it probably rests on Huntley Quarry Beds of possible Precambrian age (Callaway, 1900; Gardiner, 1920), brought to the surface by the Ordovician movements that exposed Malvernian rocks in the Malverns.

The Silurian rocks are mainly of shelf facies, succeeded conformably by late Silurian and early Devonian (Lower Old Red Sandstone) continental fluvial deposits. Minor intra-Silurian movements are indicated by thickness variations, notably a thinning of Ludlow rocks near Gorsley (Lawson, 1954) on the Woolhope–May Hill Axis.

The unconformity between Lower and Upper Old Red Sandstone, to be seen in neighbouring districts (Cave, 1977; Welch and Trotter, 1961), is the local expression of the final closing of the Iapetus Ocean, which brought the Caledonian Orogeny to an end.

Carboniferous (Hercynian) tectonic history

The effects of the Hercynian orogeny in the Tewkesbury district are represented mainly by movements of probable Carboniferous age. Dextral crustal shearing to the south of the district caused movement on the Malvern and Woolhope–May Hill axes, which led to the development of open folds and reverse faults west of the Malvern Axis, accompanied, or perhaps followed, by sinistral movement along the Woolhope–May Hill Axis and along the north-north-west–south-south-east Ledbury Fault. Overfolding and thrusting on the Malvern Axis probably represent the culmination of the movements.

In the May Hill area, many of the structures associated with wrench faulting (Wilcox and others, 1973) are present. There are en-échelon periclines at May Hill [SO 695 215], Aston Ingham [SO 688 230] and Gorsley [SO 670 265]. The May Hill pericline is asymmetrical with a locally overturned western limb, and the Aston Ingham pericline is bounded by the steep, reverse New House Fault. The sinistral Glasshouse Fault is interpreted as an antithetic fault with the numerous north-east–south-west trending faults terminating against the Glasshouse Fault being synthetic fractures. The theoretical model is distorted, in the May Hill area, by movement on the Malvern Axis which formed the north–south Clifford's Mesne [SO 700 235] and Black House [SO 716 225] anticlines, and probably caused the bend in the New House Fault at Aston Ingham [SO 685 230].

Phipps and Reeve (1969) suggested that the Ledbury folds, which comprise several north-east–south-west periclines which plunge south-west into the Ledbury Fault, formed as a result of the sinistral shear along the line of the fault.

In the Newent area, the Stallion Hill Formation of probable Carboniferous age, may have been deposited in a relatively local basin within an area of general uplift close to the Malvern Axis. Later movements of Westphalian age could have given rise to the more extensive basin in which were deposited the Westphalian D Coal Measures of the Newent Coalfield. Similar movements of intra-Carboniferous age have been recorded from the Forest of Dean area to the south-west (Sullivan, 1964) and from the Wyre Forest Coalfield to the north (Mykura, 1951).

Cessation of localised earth movement during Westphalian D, and its replacement by more-widespread subsidence, is suggested by the resemblance, both in thickness and in facies, between the Upper Coal Measures of Newent and those of the Forest of Wyre and of the more-distant Oxfordshire Coalfield.

The general subsidence was brought to an end by more intensive late Carboniferous earth movements which may have been responsible for the low-angle overthrusts of Chase End Hill [SO 761 355] and Herefordshire Beacon in the Malverns. These movements presumably also caused inversion of the area now occupied by the Worcester Basin, and subsequent erosion removed the Upper Coal Measures before the deposition of the Permo-Triassic fill. Seismic profiles clearly illustrate the structure of the Permo-Triassic rocks of the Worcester Basin but show little detail of the basement, and the structure of any Malvernian rocks east of the overthrusts of the Malvern Hills can only be conjectured. Farther south, buried Malvernian rocks may be the cause of a magnetic high east of Newent, centred under Highleadon [SO 780 235]. On the assumption that it is caused by a vertical-sided basement structure, Brooks (1968) calculated a depth of 2.1 km to its top. That the anomaly is not related to basement relief, is illustrated by seismic line 82–01 WB. Where it crosses the anomaly the Permo-Triassic base is at about 1 km depth in the west, descending to 2 km at its eastern margin, which coincides approximately with the western side of a small Permo-Triassic graben under Maisemore. The base of the Permo-Triassic on the seismic trace is poorly defined west of the magnetic anomaly, perhaps because it is underlain by Lower Palaeozoic rocks (Chadwick, 1985). The better definition of the base above the magnetic anomaly may perhaps indicate the existence of a wedge of Precambrian sediments or tuffs over Malvernian.

Permo-Triassic and later tectonic history

The Worcester Basin developed as a result of crustal stretching. Its western boundary as shown by BGS seismic lines 02BK1–6 (Malvern 1980) (Greenwood, 1982; Chadwick, 1985) and 82–01 WB (Figure 9) (Chadwick, 1985), is defined by major syndepositional normal faults, throwing down to the east and active throughout Permo-Triassic times. Farther east, other faults within the basin moved at various times and affected local patterns of deposition. Chadwick (1985) explained the subsidence history of the basin in terms of two phases of crustal extension, the first in the Permian and the second early in the Triassic. Each phase produced rapid, fault-controlled subsidence which was followed by a period of more gradual subsidence. The Bridgnorth Sandstone is interpreted as having been deposited under conditions of gradual subsidence in the first phase, while the coarser-grained nature of the Kidderminster Formation points to more rapid subsidence and elevation of basin margins at the onset of the second phase. The rate of subsidence probably lessened through the deposition of the Wildmoor Sandstone, increased during the deposition of the coarser Bromsgrove Sandstone, and thereafter became relatively low.

Seismic line 02BK1–6 (Figure 9) shows a single normal fault with a throw of more than 2 km on the east side of the Malverns, whereas in the south of the district on line 82–01 WB the same cumulative throw is produced by a number of smaller faults over a tract about 8 km wide. The continuation of the East Malverns Fault south of the Malvern Hills throws Mercia Mudstone against Bromsgrove Sandstone. Farther west the listric Donnington Fault marks the western margin of the Worcester Basin. The tract between these two faults forms a relatively shallow westward extension of the Worcester Basin. Cook and Thirlaway (1955) estimated from Bouguer gravity anomaly contours that the depth to pre-Permo-Trias basement under Newent is 0.9 km cf. (Figure 4), compared to 1.8 km east of the line of the Malverns. At the northern end of the tract the basal Haffield Breccia rests with strong unconformity on pre-Permian rocks and this basin floor is presumed to dip gently to the south-south-west or be progressively step-faulted down in that direction. It is limited south-west of Newent however, by north-west–south-east faults controlled by the Woolhope–May Hill Axis. It is considered that the fault south of the Malverns, the Donnington Fault and those south-west of Newent were all active from the early Permian onwards.

In the early Triassic these more westerly faults were probably inactive while subsidence continued in the main part of the Worcester Basin. In assessing the displacement of faults much depends on the identification of the outcrop around Bromsberrow [SO 745 340], between the Haffield Breccia and the Bromsgrove Sandstone, as Bridgnorth Sandstone. The identification is made on the basis of dune bedding which occurs in the Bromsberrow outcrop and in the Bridgnorth Sandstone of the Kempsey Borehole, but not in the lithologically similar Wildmoor Sandstone of the borehole. A thick sand development reported beneath the Bromsgrove Sandstone in the Oxenhall water borehole [SO 709 265] is taken to be Bridgnorth Sandstone.

It is thus inferred that the. Kidderminster Formation and the Wildmoor Sandstone are not present within the tract beneath Newent. If this is the case, early Triassic crustal stretching would have been accommodated by the fault along the Malvern line, east of which seismic profiles indicate the presence of the Kidderminster Formation. Only with the commencement of deposition of the Bromsgrove Sandstone did movement resume on the Donnington Fault and on the faults at the southern end of the Newent tract.

Structure contours on the base of the Arden Sandstone (see structural diagram marginal to geological map) show that much differential movement took place even from relatively late in the Triassic. The main structures, superimposed on a gentle regional easterly dip, include i) a synclinal belt extending south-south-east from Berrow Hill [SO 793 338] to Corse Wood Hill [SO 817 290] and thence south through Maisemore; ii) a north-north-west–south-south-east synclinal belt between Holdfast Hill [SO 848 377] and Southwick Park [SO 890 308]; iii) a belt of faults along a north–south, east-facing monocline connecting a small north-northwest–south-south-east pericline at Towbury Hill [SO 881 368] with a north-north-east–south-south-west pericline between Notcliffe House [SO 880 286] and Leigh [SO 870 262]. In addition there are indications that a syncline underlies Bredon Hill in the north-east corner of the district.

The north–south synclinal tract through Maisemore overlies a pronounced Permo-Triassic graben, the Maisemore Fault Trough (Figure 9), while commercial seismic evidence suggests that the Notcliffe House–Leigh pericline is developed over a basement ridge. The belt of structures running north from this pericline marks the Tewkesbury Axis, while the syncline under Bredon Hill lies between this and the Inkberrow–Haselor Hill Axis.

The age of the structures shown by the Arden Sandstone contours is not known, but comparable structures involve rocks as high as the Inferior Oolite Group and the movements probably continued intermittently through the Triassic and Jurassic (cf. Whittaker, 1972a;b), perhaps into the early Cretaceous.

Chapter 11 Quaternary

The oldest drift in the district (Table 4) is of glacial origin, dating from a pre-Devensian glaciation traditionally attributed to the Wolstonian cold stage (Shotton and others, 1977). An alternative view (Bowen and others, 1986) questions the stratigraphical basis of the Wolstonian and supports the theory that the main glaciation to affect the Midlands is of Anglian age. During this glaciation an ice sheet is presumed to have moved down the vale between the Malverns and the Cotswold scarp, against which it emplaced the Camden Tunnel Drift (Shotton, 1953), to terminate somewhere near Tewkesbury (Figure 10). Prior to the glaciation a large part of the Midlands, from the vicinity of Bredon Hill north-eastwards, may have drained northwards through Leicestershire into the River Trent via the valley of the River Soar. The Avon came into existence (Shotton, 1953) following the retreat of the ice in the Severn Valley. From that event until the late Devensian, about 25 000 years ago, the Avon drainage basin was as large, if not larger than that of the Severn, which then rose north of Kidderminster. During the late-Devensian glacial advance, at some time between 25 000 and 13 000 years ago, the upper part of the present-day Severn, which had previously flowed north into the Irish Sea, was diverted into its present lower valley, cutting the Ironbridge Gorge, north of Bridgnorth, in the process (Wills, 1924). The gravels deposited in the lower valley at that time are those of the Third or Main Terrace of the Severn.

Glacial deposits

Boulder Clay

Boulder Clay has been mapped in the Glynch Brook valley at Dyke House [SO 7318 3371] and in the Severn Valley [SO 847 380] near Longdon Heath and on Sandhurst Hill [SO 836 246] (Figure 10). The Dyke House deposit was proved in 1981 in a trial pit [SO 7316 3365] which showed, at 0.9m below the ground surface, 2.1 m of unbedded red-brown clay containing quartzite pebbles generally less than 1 cm in diameter, some Wenlock Limestone boulders (up to 20 cm) and fragments of coal. This rested on coarse glacial or fluvioglacial gravel, seen for 0.3 m. The boulder clay is part of a spread that Hey (1959, 1963) named the Eastnor Boulder Clay, describing it as deposited by an ice tongue that formed a westerly offshoot from a large glacier in the Severn Valley. On entering the Glynch Brook valley the ice tongue acted as a dam, causing a lake to form on the west side of the Malverns, in which the glacial lake deposits north of Eastnor [SO 732 372] were laid down. The boulder clay at Dyke House has a surface level of 85 m above OD. Hey (1959) reported scattered exposures of till to the north of this vicinity between about 82 m and (near the Hollybush Pass [SO 760 369]) 140 m above OD. Hey (1959) considered that the ice tongue crossed the Malvern Hills by way of the Hollybush Pass but Adlam (1972) thought that the pass was too high for this, and that the ice entered the Glynch Brook valley by rounding the southern end of the Malverns. An alternative interpretation can be made on the evidence of extensive glacial deposits further north in the Glynch Brook valley (Brandon, 1988) and outliers to the north-west (Brandon, 1989). They indicate a much larger ice sheet west of the Malvern Hills than was recognised by Hey (1959).

The age of the boulder clay near Longdon is uncertain. A small overgrown limestone quarry [SO 8460 3826] exposed 2 m of a typical Trias-derived till comprising small angular clasts (10 to 20 mm) of red-brown mudstone, siltstone and fine-grained sandstone in a red-brown clay matrix. With a surface height near 30 m above OD the deposit is intermediate in height between the Main and Kidderminster terraces of the Severn but despite this low elevation, the Longdon till could be of pre-Ipswichian age and owe its preservation to being lodged on relatively resistant strata. It is situated in a col with low hills to north and south and may occupy a hollow that was originally an east–west subglacial channel.

Wills (1938) reported a red till-like material overlying 5th/6th Terrace deposits at Bushley Green [SO 862 347] but this deposit, exposed recently (Bridgland and others, 1986), is probably a slope deposit. It may have resembled red clayey gravel overlying Sixth Terrace Deposits at Apperley [SO 863 280] which, although also suggested as a boulder clay by Wills (1938), is probably only a weathered, cryoturbated river gravel. The deposit on Sandhurst Hill is a red-brown sandy clay which in places appears to underlie the Fluvioglacial Sand and Gravel.

Glacial Lake Deposits

Glacial Lake Deposits are mapped at Compton Green, where brown plastic clay with scattered erratics, seen in a roadside section [SO 7343 2862], forms a flat-surfaced spread adjacent to a patch of fluvioglacial gravel. The deposit is isolated on a hilltop and its original extent is unknown.

Hey (1959) described laminated clay and silt, proved in a borehole [SO 7277 3890] to a depth of 26.5 m, as the deposits that filled a glacial lake west of the Malverns, dammed by an ice tongue in the Hollybush Pass. The deposits, seen in the approach cutting [SO 7265 3862] to the Ledbury railway tunnel, are assumed to underlie much of the Glynch Brook valley north of Eastnor, though they are obscured by a veneer of pebbly clay which covers the valley floor (see also Brandon, 1988).

Fluvioglacial Sand and Gravel

Deposits mapped as Fluvioglacial Sand and Gravel correspond broadly to the Woolridge Terrace of Wills (1938) and include the Woolridge Gravels and the Upleadon Gravels of Hey (1958; 1959; 1963) (Figure 11). The Woolridge Gravels cap high ground on the Lias Group outcrop at Corse Wood Hill [SO 814 286] and at about 1 km to the south-east [SO 824 282], at Sandhurst Hill [SO 839 248] and near Woolridge [SO 804 236]. The Upleadon Gravels occur in a belt extending from near Clencher's Mill [SO 732 351] in the Glynch Brook valley south towards Upleadon [SO 752 270] and thence south-eastwards to Limbury Hill [SO 777 253] and Catsbury Hill [SO 790 246]. Both gravels consist predominantly of 'Bunter' quartzite pebbles, but the Woolridge Gravels contain 5 to 10 per cent of flints, and the Upleadon Gravels up to 20 per cent of Silurian fragments, some Malvernian fragments, and very few flints. The Woolridge Gravels, at 80 to 85 m above OD, are higher than the nearby Upleadon gravels (75 m at Limbury Hill and Catsbury Hill) and are therefore presumed to be older.

Hey (1963) saw the Woolridge Gravels as the outwash of a chalky boulder clay ice sheet that extended into the Severn Valley from the Vale of Moreton, and the Upleadon Gravels as the outwash released from the Glynch Brook valley with the melting of the ice tongue in the Hollybush Pass.

River Terrace Deposits

The numbering of the Severn terraces (Figure 11) is based on the work of Wills (1938) and that of the Avon terraces on Tomlinson (1925). The Severn terraces slope seawards at slightly more than the gradient of the present-day floodplain, having been graded to the lower sea levels of glacial times. The Severn Valley appears to have no equivalent to the Third Terrace of the Avon, and the Third Terrace of the Severn corresponds in level to the Second Terrace of the Avon. The lowest terrace of the Severn in the Tewkesbury district is the Second (Worcester) Terrace. This corresponds with the First Terrace of the Avon. The First (Power House) Terrace of the Severn passes beneath the floodplain north of Worcester.

The terraces of the River Leadon and its tributaries are numbered to correspond with those of the Severn.

Sixth and Fifth (Bushley Green) terraces

The highest two terraces (the Sixth and Fifth) correspond to the upper and lower parts of the Bushley Green Terrace of Wills (1938).

Shotton (1977) recorded that the Avon Fifth Terrace was not known to be fossiliferous until recently when a temporary exposure, 43 m above the river at Pershore (Sheet 199), yielded to P F Whitehead a fauna of mammal bones, ostracods and molluscs. Shotton noted that the indicated climate was temperate and certainly not extreme in either direction.

The largest outcrop of Sixth Terrace deposits in the Tewkesbury district is at Hill End [SO 897 380] where a motorway cutting exposed 7.2 m of sands with some gravelly bands, the gravels being composed largely of 'Bunter' pebbles, with some flints and Liassic cementstones.

A gravel pit [SO 8620 3508] at Bushley Green formerly showed (Wills, 1938) about 9.5 m of terrace deposits, mainly grey to yellow sands and gravels, including a 0.15 m loam containing vole teeth and 10 species of land snails, none indicative of a cool temperate climate (Bridgland and others, 1986). About 2 km to the south-east, near Bushley Park, another small gravel pit (Wills, 1938) showed about 1.5 m of gravel composed principally of Malvernian clasts, presumably derived from long-since eroded sheets of solifluction gravels, similar to the Fan Gravel that now flanks the east side of the Malverns.

Other Fifth and Sixth Terrace deposits occur at Apperley [SO 860 280] (Wills, 1938) and on Lassington Hill [SO 802 205].

In the Leadon valley are some small patches of Fifth Terrace gravel derived from erosion of Fluvioglacial Sand and Gravel spreads, notably near Laughton's Farm [SO 797 229], in Carswall's Wood [SO 7435 2690] and at The Heath [SO 766 305].

Fourth (Kidderminster) Terrace

Wills (1938) described the Kidderminster Terrace as extending up the Severn as far as Bewdley, and its deposits as consisting of sands and gravels, the latter composed mainly of 'Bunter' material, with Irish Sea erratics conspicuously absent. In the Avon valley in the Tewkesbury district, Fourth Terrace gravels are estimated to be 4 to 5 m thick, but are probably 1 m or so thicker north of Bredon village [SO 929 377]. The terrace shows gravelly soils in which 'Bunter' pebbles predominate, but which also contain many flints and small amounts of Jurassic limestones; a few pebbles of gneissic rocks (?Malvernian) have also been recorded.

The BGS Twyning Borehole [SO 8943 3664] proved 4.1 m of sandy gravel of this terrace. A gravel pit south of the borehole site, in work in the early 1970s, had been backfilled at the time of the geological survey, but Shotton (1977) and Whitehead (in Shotton, 1977) recorded that it showed, beneath the characteristic 'Bunter' and flint gravel, a deposit of irregular thickness in which a much more local component of Jurassic material predominates. This lower gravel yielded fossils of bison, horse, mammoth and reindeer together with 10 species of molluscs (identified by B W Sparks) which included one specimen of Pisidium vincentianum, now a non-British species and found in cold Quaternary environments. The conditions obtaining at the time of the Fourth Terrace were inferred as cold and probably treeless. Shotton (1977) further reported that Twyning and other Fourth Terrace sites in the Avon Valley had produced several scores of Palaeolithic implements, all fashioned from pebbles and all derived. Hand axes are prominent and typologically the artefacts range from Mid-Acheulian to Levalloisian.

Below the Avon–Severn confluence Fourth Terrace gravels occur at Redhouse Farm [SO 888 292], near Tirley [SO 835 285], at Maisemore [SO 811 213] and around Lassington [SO 796 210], where the Severn apparently swung in a loop around the western side of Lassington Hill.

The Leadon valley contains scattered patches of Fourth Terrace deposits as far upstream as Highbridge Farm [SO 705 354]. In the Ell Brook valley relicts of Fourth Terrace deposits cap hill tops as far upstream as the vicinity of Cleeve Mill [SO 732 262].

Third Terrace of the Avon

In the Tewkesbury district, Avon Third Terrace deposits are confined to small patches at Bredon [SO 920 370] and Bredon's Hardwick [SO 913 355]. Higher up the Avon, deposits assigned to the Third Terrace have yielded warm-climate mollusca and vertebrates (Tomlinson, 1925) pointing to an Ipswichian Interglacial age. Shotton, (1968; 1977) holds that these deposits are older than those of the Fourth Terrace even though they are at a lower level. Recent work (Maddy, personal communication) indicates, however, that the Fourth Terrace deposits are older. No deposits of Ipswichian age are known from the Severn Valley.

Third (Main) Terrace of the Severn and Second Terrace of the Avon

The Third Terrace of the Severn consists of material carried into the lower Severn Valley after the southward diversion of the upper part of the river through the Ironbridge Gorge. The terrace level is about the same as that of the Second Terrace of the Avon, but the deposits of the two terraces may not be of exactly the same age.

In the Avon valley the geological survey distinguished a higher (2b) and a lower (2a) terrace, resting upon separate benches cut into Lias clays. At the time of the survey, Terrace 2b deposits (sandy limestone-pebble gravels) were well exposed in the Aston Mill Gravel Pit [SO 944 355]. They result from re-sorting by the Carrant Brook of material contributed by the Fan Gravel of the lower slopes of Bredon Hill. Their thickness varies between 2 m and 6 m. Analyses of particle size, clast composition and heavy mineral composition are given by Briggs (1975) and Briggs and others (1975). Radiocarbon dates of 26 000, 29 500 and 31 900 years BP have been obtained from plant material from silt pockets at the base of the gravel (Shotton and others, 1974; 1975). The mammal fauna obtained by Whitehead from this pit (Shot-ton and others 1974; 1975) is similar to that found in the Beckford Gravel Pit in the same gravel spread, about 4 km to the east. The fossils include remains of mammoth, horse, bison and reindeer, and Whitehead commented that the fauna indicated a cold tundra environment. He also noted that the Carrant gravels had yielded about 65 Palaeolithic tools and flakes, mostly not in situ.

In the Severn Valley below Tewkesbury the Main Terrace is represented by scattered patches of sand and gravel. Along the Leadon and its tributaries this is the principal terrace. It is marked S3 on the maps to indicate its equivalence in level with the Main Terrace of the Severn, though it is likely that the deposits accumulated over a long period of time, like those of the Avon Second Terrace.

In the upper part of the Leadon valley, upstream from Callow Farm [SO 721 312], the terrace gravels are composed largely of local Raglan Mudstone cornstone fragments less than 2 cm in diameter in a matrix of variably sandy, clayey silt. They have been worked in the past in small pits. Some small patches of gravel occur on the Bromsgrove Sandstone outcrop, and more extensive, though thin, deposits occur on the Mercia Mudstone. In the Glynch Brook valley the Third Terrace is traceable upstream into a wide area of Head between Lowbands [SO 776 316] and Redmarley Park [SO 764 326]. The solifluction material seems to have been the source of supply for the terrace deposits.

In the Ell Brook valley downstream from Cleeve Mill a well-marked bench is present at 5 m above the present floodplain surface. Coarse detritus was in short supply, however, and only locally do the deposits on the bench reach a thickness of 1 m or more.

Second (Worcester) Terrace of the Severn and First Terrace of the Avon

Wills (1938) described the Worcester Terrace as forming a prominent feature rising to about 3 m above the floodplain, near Ripple [SO 869 379]. Farther downstream the deposits are closer to the level of the alluvium. They form gravel banks at Rye Court Farm [SO 859 302], at Deerhurst [SO 870 300] and at Haw Bridge [SO 844 280]. Wills (1938) described a pit at Town Street, Tirley [SO 843 292] as showing 0.5 m of false-bedded sand and shingle with broken Gryphaea shells overlain by 1.8 m of coarse gravel of 'Bunter' pebbles, occasional flints and igneous erratics. Much of the gravel under the Severn floodplain is probably of this age.

In the Avon valley the First Terrace fringes the floodplain. In 1982 a gravel pit [SO 908 358] at Bredon's Hardwick showed 3 m of sandy gravel overlain by 0.9 m of reddish brown medium-grained sand. The gravel is medium to coarse grained with a dominance of 'Bunter' pebbles but also some oolitic limestone and Liassic cementstone, derived Liassic ammonites, and Gryphaea shells.

Fan Gravel

The term Fan Gravel is used for solifluction detritus that originated on high ground, of the Malverns and Bredon Hill in the north, the Cotswold escarpment to the east, and to a smaller extent May Hill in the south-west of the area. It was re-sorted by water action and deposited as fan-shaped spreads on gentler lower slopes. The deposits are mostly 1 to 2 m in thickness, and may locally attain 3 to 4 m. Those flanking Bredon Hill and the Cotswolds incorporate quartz sand, perhaps of wind-blown origin under cold climatic conditions. The deposits originating on the Malvern Hills have previously been described as 'Malvernian gravels' (Wills, 1938) or Castlemorton Gravels (in BGS open-file reports) and those flanking the Cotswolds as 'Oolite gravels' (Wills, 1938) or 'Jurassic gravels' (Tomlinson, 1940).

Some of the deposits merge downslope into river terraces. Others have been separated by subsequent erosion from spreads of river terrace deposits at comparable levels. Where the separation is not great, as between Fan Gravel at Wingmoor Farm [SO 938 272] and the Avon Second Terrace at Tredington, a correlation is straightforward, but the ages of some more isolated, higher-level patches of Fan Gravel remain doubtful.

The most extensive spreads of Fan Gravel coincide in level with the Avon Second Terrace, which represents perhaps 15 000 years of tundra-like climate. Fan Gravel spreads of comparable extent may have developed during the deposition of the Fourth (Kidderminster) Terrace, while the preponderance of Malvernian detritus recorded by Wills (1938) in a section of Fifth Terrace gravels at Bushley Park suggests extensive Fan Gravel deposition still earlier in the Quaternary.

The best section of Fan Gravel at the time of survey (1981) was provided by a gravel pit near Wingmoor Farm. The gravel was 0.6 m thick at the south end of the main face of the pit [SO 9430 2705] but increased to 1.5 m at the north end [SO 9430 2743]. Deposition in the slightly meandering channel of a fast-flowing stream of about the same width as the present deposit (300 to 400 m) is suggested. In this pit, as in most other sections of Fan Gravel derived from the Jurassic escarpment, the gravel is overlain by 0.5 m or so of brown sandy loam which is largely a product of decalcification (Tomlinson, 1940) but which may incorporate a weathered residue of alluvial clay originally deposited on top of the gravel. In 1984, continued working of the pit revealed two east–west channels close to the base of the gravel, filled with organic silts and clays with plant fragments and mollusca (Briggs, 1984). Preliminary results of pollen studies (Hunt, 1984) suggest open vegetation, probably interspersed with areas of disturbed ground.

Cheltenham Sand

The Cheltenham Sand has the same constituents as the Fan Gravel, but consists mainly of quartz sand, with few oolitic limestone and ironstone pebbles. It is medium grained, well sorted, and quartzose with rounded grains and contains small proportions of calcium carbonate, mainly as ooliths or small angular limestone fragments (Briggs, 1975). Gravel commonly occurs as thin stringers or lenses in the sand. It is best developed in the valley of the River Chelt, where it is 6 m thick under much of Cheltenham and over 15.2 m thick in a borehole in Monson Avenue [SO 9492 2283]. It also occurs at the head of the Hatherley Brook valley [around 940 209] and east of the district at the head of the Swilgate valley, but is not developed in the Dean Brook valley [SO 940 288] or northwards. Briggs (1975) described a 'Cheltenham Sand and Gravel' comprising a lower 'Cheltenham Gravel' and an upper Cheltenham Sand, but the geological survey did not confirm this division. Instead, the Fan Gravel and Cheltenham

Sand, though locally in contact, are considered to have originated at different times and, on the whole, in different areas.

The Cheltenham Sand was apparently wind-derived from glacial sands in the Midlands (Richardson, 1912; Tomlinson, 1940) and fluvially re-distributed late in the Devensian. There appear to have been two main episodes of deposition. The earlier is represented by two elongate spreads sloping down from about 80 m above OD in south Cheltenham to between 70 and 65 m in the vicinity of The Park [SO 940 208], where they are at the level of Fan Gravel forming a terrace on either side of the Hatherley Brook at about 60 m above OD. Scattered patches of sand between Hardwicke [SO 906 272], and Swindon [SO 935 251], and also at Leigh End [SO 863 258], may be the dissected remains of an early spread comparable with the Avon Second Terrace in the Swilgate valley.

The later episode of sand deposition is represented by the main outcrop of Cheltenham Sand, in the Chelt valley. Contours on its base, based on numerous boreholes, show that in the east of Cheltenham the sand fills two valleys, which joined and followed a broad hollow along the present Chelt valley under the Chelt alluvium. This suggests an episode of active down-cutting quite late in the Pleistocene, probably during the Severn Third to Second Terrace interval. Windblown sand that might have been derived from these terrace deposits (Briggs, 1975) then choked the Chelt valley but not the valleys of the River Swilgate or the Dean Brook.

North-west of Cheltenham is a terrace-like spread of Cheltenham Sand which thins and peters out [SO 904 258], as if no more sand were available for spreading farther down-valley. If this view is correct it suggests derivation from the south-east by fluvial reworking of the wind blown deposits.

Head

Downwash or colluvial deposits of late Devensian to Flandrian age have been mapped as Head. They are composed of locally derived material and vary from clay to clayey sand and gravel. Most Head lies on slopes, though some has been mapped in valley bottoms on the Raglan Mudstone outcrop. Head is particularly extensive on the Bridgnorth Sandstone around Bromsberrow, and on the Mercia Mudstone in the vicinity of Lowbands [SO 776 315].

Alluvium

Alluvium is the floodplain deposit of the present-day streams and is everywhere a stiff grey to brownish grey clay, exposed to a thickness of 1 to 2 m or more in river banks. In the Severn and Avon valleys the alluvium overlies local deposits of silt and peat, and more extensive deposits of gravel. The gravels are probably mainly of Worcester Terrace (Avon First Terrace) age. The Severn floodplain conceals a buried channel with its floor descending from 1 m below OD at the bridge at Queenhill [SO 870 370] to 5.2 m below OD at Maisemore Ham [SO 8196 2031] (Beckinsale and Richardson, 1964).

An average thickness of about 10 m of alluvium (including 2 to 4 m of basal gravel) was proved by trial boreholes for the Queenhill bridge, and southwards from Chaceley [SO 855 305]. The thickest recorded suballuvial gravel is 7.9 m, underlying 6.3 m of sand, silt and clay, in a borehole on Maisemore Ham.

A peat layer from near Haw Bridge [SO 845 278] at 4.2 to 5.1 m above OD (about 6 m below the floodplain surface), has been dated from its pollen content to Zone VIIa (Atlantic period, c.7500 to 5000 years ago) (Beckinsale and Richardson, 1964).

In the Avon valley [around 914 370] trial boreholes for the motorway crossing the floodplain proved up to 8 m of alluvial clay, overlying up to 4.7 m of sand and gravel, on Lias clay bedrock.

The wide floodplains of the lower parts of the valleys of the Hatherley Brook and the River Chelt were probably formed during the Flandrian rise of sea level following late Devensian downcutting of the River Severn.

A wide floodplain (Tibberton Meadows) is developed in the valley of a tributary of the Leadon [SO 762 230]. A temporary excavation [SO 7642 2295] proved alluvial clay to 4.3 m, at which depth it included fossil tree trunks and the skull of an aurochs. Both this tract, and the much more extensive spread of alluvium at Longdon Marsh [SO 820 360], probably formed by the silting up of hollows that developed on the Mercia Mudstone in valleys with restricted outlets through the Arden Sandstone outcrop.

Peat

Peat has been mapped near Arle, on the Chelt floodplain [SO 9335 2370] to [SO 9390 2323], and at Leckhampton [SO 9424 2014], where it seems to have formed at springs issuing from the base of the Cheltenham Sand. Both occurrences were noted by Richardson (1912; 1913).

Chapter 12 Economic geology

Agriculture and soils

Agriculture is one of the main industries of this predominantly rural district. Detailed soil surveys have been carried out in the area within the grid square SO 82 (Cope, 1973) and to the north of the district (Palmer, 1976; 1982). The results of these surveys, and conclusions based on them, regarding land use capability and farm management are applicable to much of the Tewkesbury district.

Broadly speaking, eight main physiographic regions can be distinguished, in each of which the predominant soil type is dependent on the underlying geological formations. The solid rocks and steep slopes of the Malvern Hills produce soils which support limited areas of rough grazing (Palmer, 1976). On the Raglan Mudstone, the characteristic soil type is a fertile, moderately heavy, silty clay-loam. Soil drainage is good, owing partly to the relief provided by ridges developed along sandstone and limestone outcrops. On Wenlock and Ludlow formations soils are predominantly grey clays. The Bromsgrove Sandstone and Bridgnorth Sandstone tract between Newent and Bromsberrow has light sandy soils, well adapted to market gardening and, partly because the strong relief gives many frost-free locations, to modern fruit-growing techniques. There is a large area of greenhouse cultivation north of Newent, and apple orchards are extensive. The largest region is that underlain by Mercia Mudstone. Soils are moderately well drained fertile red clays, well adapted both to pasture and arable cultivation, the latter particularly where lightened by thin gravelly drifts. Soils on the Lower Lias Clay and Blue Lias are heavy grey clays, poorly drained under natural conditions, partly because of the low relief. Soils on the Fan Gravel and Cheltenham Sand contrast sharply with those on Lias clays in being light, well drained and easily cultivated. Market gardening is well developed on the Cheltenham Sand at Uckington. The last main group of soils comprises those on the extensive floodplains. Present-day river management practice is to maintain the floodplains of the Severn and Avon to accommodate excess flood water and the alluvial tracts are in consequence almost entirely under permanent pasture.

Sand and gravel

The main mineral industry of the district, and the one with the greatest potential for future development, is that of quarrying for sand and gravel. The resources lie in River Terrace Deposits (including sand and gravel beneath the alluvium of the Severn and the Avon), in the Fan Gravel and Cheltenham Sand, and in the Bridgnorth Sandstone.

The extent of currently available information on resources is described in seven BGS open-file reports dealing with potential resources of sand and gravel (see list of BGS Land-survey Open File Reports, p. viii).

Not all the spreads of sand and gravel shown on the geological map are of current economic value, some being too limited in extent, thickness or quality, though they may have been worked on a small scale in the past. Examples are provided by the terrace deposits of the River Leadon on the Raglan Mudstone outcrop, and by the apron of Fan Gravel east of the Malverns, which though of wide extent is, so far as is known, thin and of poor quality. Sand and gravel deposits, moreover, commonly underlie agricultural soils of good quality, so that even where deposits are of sufficient thickness and extent to interest gravel operators, planning considerations may dictate their retention for agricultural use.

An indication of where larger-scale working has been or is being carried out is given by the distribution on the map of worked-out gravel areas. Quarries in operation in 1984 and their products are as follows:

• Aston Mill Pit, [SO 944 355], in Avon Second Terrace; sand, gravel and ballast
• Wingmoor Farm Pit, [SO 943 272], in Fan Gravel; sand, gravel and ballast
• Bredon's Hardwick Pit, [SO 908 358], in Avon First Terrace; sand and gravel
• Bromsberrow Heath Pit, [SO 7385 3285], in Bridgnorth
• Sandstone and Bromsgrove Sandstone; red building sand
• Bromsberrow Heath Sand Pit, [SO 7385 3305], in Bridgnorth Sandstone; red asphalt sand

Roadstone, building stone, limestone, brick-clay

These materials are not worked at present but there are resources which might be workable in the appropriate economic circumstances.

The principal source of roadstone has been the Malvernian rocks of the Malvern Hills. The large quarries at Hollybush [SO 760 371] and The Gullet [SO 762 382] attest the former scope of the industry, but working ceased in about 1970 as a result of local opposition on amenity grounds.

Most of the harder rock formations have been quarried for local building stone and have contributed to the attractive appearance of the vernacular architecture. In the north-west, Malvernian rocks were much used for building stone as well as for roadstone. Here and in the south-west of the district stone quarries are numerous on outcrops of the Wenlock Limestone but somewhat less so on that of the Woolhope Limestone. Many of these contain remains of limekilns, but building stone and roadstone together may have accounted for about half the output of the quarries. In the south-west, the May Hill Sandstone has been quarried around May Hill, and the Downton Castle Sandstone at Gorsley Common.

There are numerous small building stone quarries on the Bromsgrove Sandstone outcrop. The less pebbly sandstones in the upper part of the formation, being thickly bedded and even-grained, were particularly suitable for building. The Haffield Breccia was quarried and used as a rough walling stone around Haffield House [SO 724 337]. The Arden Sandstone locally includes massive beds well suited for building, for example in Pendock church [SO 817 336]. The tower, of 14th century date, is built largely of squared blocks of this stone, some of them from beds 0.8 m thick. Old quarries adjoin the churchyard and may have been the source of the stone.

Limestone beds at the base of the Lias Group were formerly much quarried, partly for lime burning and partly as a building stone. The Blue Lias outcrop has few quarries however and it may be inferred that the limestones were too easily weathered for use in building. In the Inferior Oolite on Bredon Hill there are some large old quarries from which walling stone and freestone would have been obtained for local use.

There are old flooded brickworks on the Severn floodplain, for example near Sandhurst [SO 817 232] and Apperley [SO 858 290], at locations that suggest that the alluvial clay was dug as the raw material and that river transport was used to bring coal to the works and carry away the finished products.

Coal

The Newent Coalfield flourished briefly in the late 18th and early 19th centuries, until about 1810 (see Bick, 1971; 1979a) when mining seems to have been brought to a halt largely by difficulties of geological structure. There followed sporadic attempts at working during the mid-19th century, culminating in the formation in 1876 of the Newent Colliery Company which sank three shafts at a site [SO 699 267] near White House by 1879, but was forced to close in 1880.

The steep dip and evidence for numerous faults in the BGS Lower House Nos.1 and 2 Boreholes (BGS, 1984) confirm early accounts of difficult geological structure. The underground extent of the Coal Measures can only be surmised, but if the beds are indeed preserved in a narrow syncline (Figure 4) then the concealed eastern limb, being closer to the Malvern Axis, may be steeper than the beds exposed to the west.

No thickness of Upper Coal Measures as great as the 262 m proved in the Lower House boreholes was previously recorded from Newent, though some of the early workings were of such depth as to suggest that they may have penetrated much of the succession. Thus an unpublished 1833 manuscript record by Murchison noted that 'at Bowsden the shaft was 250 yards (228 m) deep through a thick covering of New Red'. Phillips (1848) recorded pits and borings near White House being sunk 'to depths from 20 to 100 and, it was said, even 200 yards'. A diagram in an unpublished notebook of De la Beche shows a trial shaft near Boulsdon [at about 7110 2442] sunk to 183 m (200 yards) in 'shales with thin seams of coal and some sandstones' without reaching their base.

The workings of the 1760–1810 period were mainly in the vicinity of Boulsdon (Boulsdon collieries) and of Lower House (Lower House and Hill House collieries). William Smith (in Phillips, 1844; 1848), Maclauchlan (1837), Murchison (1839) and De la Beche (1846) referred to shafts in these areas about 40 m deep, working a thick (1.7 to 2.1 m) main seam overlying a group of thinner seams, within a total thickness of about 10 m of strata (Figure 4). The coals were sulphurous and can be recognised as corresponding broadly to seams 3 to 10 of the Lower House boreholes. None of the old records give precise locations for the shafts and boreholes that they describe, so they throw little light on the detailed geological structure of the coalfield. However, it is probable that the dip near Boulsdon, around 5° to 10°, on the axis of the inferred coalfield syncline, made for easier working of the coal than the 30° dip in the Lower House vicinity recorded by Maclauchlan (1837) and confirmed by the Lower House boreholes. Faults were numerous in both areas; Murchison (unpublished manuscript notes of 1833; 1839) recorded that coal-working at Boulsdon was brought to a halt in about 1810 by an outburst of water 'which not [only] filled the works but actually rushed to the top of a 50 yard shaft and overflowed the adjoining meadow'.

Remains of old shafts are particularly numerous in the Boulsdon vicinity, but signs of workings, including small filled-in shafts which may have been no more than bell-pits, as well as adits, are to be found along the length of the Upper Coal Measures outcrop. Details, giving reference to published records, are included in the relevant Open File Reports (sheets SO62NE, 72SW, 72NW, and 73SW). Some of these small workings in the 18th century must have encountered the lower seams (LH17 to 19) proved at Lower House, and possibly still lower seams not reached by Lower House No.2 Borehole. If these latter are of as good quality as LH19 they may have encouraged the favourable view of the coalfield's prospects that led to the construction in 1795 of a special branch of the Hereford and Gloucester Canal (Bick, 1979b) to convey its products, as well as to the opening of the deeper but ultimately disappointing collieries near Boulsdon and Lower House.

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Appendix 1 BGS boreholes and key sections

Boreholes drilled by BGS during the survey of the sheet and their terminal depths in metres are listed below under the appropriate National Grid 1:10 000 quarter sheet. The borehole numbers are those of the BGS records system.

Consultation of data

Enquiries relating to the district should be addressedd to the Manager, National Geosciences Data Centre, Keyworth.

Specimens collected from the above boreholes are avalable for examination from the registered collections held in the National Geosciences Data Centre at Keyworth. Logs of numerous other boreholes drilled within the Tewksbury district are also held at the centre and are available for consultation.

Key sections

• Malvernian Complex: [SO 7620 3820] Gullet Quarry
• Malvernian Complex: [SO 7600 3710] Hollybush Quarry
• Warren House Formation: [SO 7625 3937] Clutter's Cave (Plate 2)
• Malvern Quartzite [SO 7598 3800] beside track 130–m west of Gullet Quarry
• Malvern Quartzite [SO 7600 3713] Hollybush Quarry, west side
• Hollybush Sandstone [SO 7600 3713] Hollybush Quarry, west side
• White-leaved Oak Shale [SO 7594 3613] small exposures along hedge 200–m north west of White-leaved Oak
• Bronsil Shale: [SO 7565 3565] steep bank 500–m west of Chase End Hill
• Intrusions in Cambrian: [SO 757 368] road cutting 500 m west of Hollybush
• May Hill Sandstone: [SO 7609 3820] north end of Gullet Quarry
• Huntley Hill Formation: [SO 6972 2220] small quarry south of Hay Farm
• Yartleton Formation: [SO 6870 2240] Old Oaks Quarry 400 m south-west of New House Farm
• Woolhope Limestone: [SO 7463 3851] small quarry 1.7 km north east of Eastnor
• Woolhope Limestone: [SO 6874 2124] small quarry south of Yartleton Farm
• Wenlock Shale: [SO 7411 3829] stream bank 1 km north east of Eastnor
• Wenlock Limestone: [SO 7350 3635] quarry 500 m south of Eastnor
• Wenlock Limestone: [SO 6775 2570] Linton Quarry, Gorsley
• Ludlow Shale undivided: [SO 7135 2309] small pit in beds 100–m from top of the formation about 500 m east of Woodgate
• Lower Ludlow Shale: [SO 7151 3858] Cut Throat Lane, Ledbury
• Lower Ludlow Shale:[SO 7259 3456] Woodfields Farm
• Aymestry Limestone: [SO 7259 3456] Woodfields Farm
• Upper Ludlow Shale: [SO 7171 3983] The Firth
• Upper Ludlow Shale:[SO 7259 3456] Woodfields Farm
• Downton Castle Sandstone: [SO 7259 3456] Woodfields Farm
• Downton Castle Sandstone: [SO 6775 2570] Linton Quarry, Gorsley
• Raglan Mudstone: [SO 6685 2636] Motorway cutting in Linton Wood
• Bishop's Frome Limestone: [SO 6804 2075] disused railway cutting 150–m north east of Upper Boxbush
• St Maughans Formation: [SO 663 260] west of Tewkesbury district in motorway cutting
• Brownstones Formation: [SO 6576 2571] west of district in motorway cutting Stallion Hill Sandstone:
• Brownstones Formation: [SO 7151 2405] exposure behind barn on Stallion Hill
• Haffield Breccia: [SO 7245 3369] quarries at Haffield House
• Bridgnorth Sandstone: [SO 7385 3285] Bromsberrow Heath Pit
• Bromsgrove Sandstone: [SO 7385 3285] Bromsberrow Heath Pit
• Mercia Mudstone Group: [SO 8880 3410] Mythe Bridge; north bank of River Severn
• Mercia Mudstone Group: [SO 8455 2575] Wainlode Cliff
• Arden Sandstone: [SO 837 362] public house car park, Longdon
• Arden Sandstone: [SO 7807 3167] road cutting south east of Dobshill Farm
• Blue Anchor Formation (Tea Green Marl): [SO 8455 2575] Wainlode Cliff (Plate 6)
• Penarth Group: [SO 8455 2575] Wainlode Cliff (Plate 6)
• Lias Group: [SO 8460 3826] small quarry 700 m south east of Longdon Heath

Appendix 2 List of Geological Survey photographs

Copies of these photographs may be seen in the Library of the British Geological Survey, Keyworth, Nottingham NG12 5GG. Prints and lantern slides may be bought. National Grid References, all in 100 km square SO, are those of the viewpoints. The photographs belong to Series A, those marked with an asterisk are available in black and white only.

Precambrian

Palaeozoic

Permian and Triassic

Quaternary

General views

Figures, plates and tables

Figures

(Figure 1) Generalised geology of the Tewkesbury district.

(Figure 2) Distribution of intrusions in the Cambrian.

(Figure 3) Simplified log of Eastnor Park Borehole [SO 7437 3809].

(Figure 4) Outcrop and inferred structure of the Coal Measures of the Newent Coalfield.

(Figure 5) Comparative sections in the Coal Measures of the Newent Coalfield.

(Figure 6) Comparison of the Newent Coalfield sequence with neighbouring areas.

(Figure 7) Ammonite zones in the Lower Lias near Tewkesbury.

(Figure 8) Structure of the Worcester Basin related to geology and gravity anomalies.

(Figure 9) Geological interpretation of BGS seismic lines.

(Figure 10) Present river courses and inferred Anglian palaeogeography.

(Figure 11) Surface levels of Fluvioglacial and River Terrace deposits in relation to the long profile of the River Severn. The deposits of each terrace are likely to have originally had a height-range corresponding to that of the deposits beneath the present-day flood plain (stippled). Existing deposits, particularly of the higher terraces, therefore give only an approximate guide to the surface-height of former river-profiles.

Plates

(Front cover)

(Rear cover)

(Geological succession) Geological succession in the Tewkesbury district.

(Plate 1) Frontispiece. View of the Malvern Hills from the Penarth Group escarpment at Wainlode Hill; Norton. (A14146).

(Plate 2) Pillow structures in lavas of the Warren House Formation; Clutter's Cave [SO 7628 3935]. (A13617).

(Plate 3) White-leaved Oak and Ragged Stone Hill from Chase End Hill. (A13618).

(Plate 4) Poorly sorted subangular and subrounded clasts of Malvernian and Lower Palaeozoic rocks; Haffield Breccia, Haffield House near Ledbury [SO 7245 3369]. (A14126).

(Plate 5) Dune cross bedding; Brignorth Sandstone, Bromsberrow quarry. (A14132).

(Plate 6) Mercia Mudstone Group and Penarth Group; Wainlode Cliff [SO 847 259]. (A13628) 1 Mercia Mudstone Group 2 Blue Anchor Formation 3 Westbury Formation 4 Cotham Member 5 Lower Lias Group.

Tables

(Table 1) Stratigraphical correlation of Silurian and Devonian rocks of the Tewkesbury district Graptolites above the bohemicus Zone have not been recorded in the UK.

(Table 2) Permian and Triassic stratigraphy of the Tewkesbury district.

(Table 3) Divisions of the Lias Group.

(Table 4) Quaternary deposits of the Tewkesbury district.

Tables

(Table 2) Permian and Triassic stratigraphy of the Tewkesbury district

(Table 4) Quaternary deposits of the Tewksbury district