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Geology of the country around Norwich. Memoir of the British Geological Survey, sheet 161 (England and Wales)

F C Cox R W Gallois and C J Wood

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

British Geological Survey

London: Her Majesty's Stationery Office 1989. © Crown copyright 1989 First published 1989. ISBN 0 11 884410 5. Printed in the United Kingdom for HMSO Dd 240413 C20 5/89

• Contributors
• Geophysics:J D Cornwell,  E A Howell
• Geochemistry: T C Pharaoh
• Engineering geology: T P Gostelow
• Sand and gravel resources: E F P Nickless
• Hydrogeology: A C Benfield
• Pleistocene palaeontology: D M Gregory
• Authors
• F C Cox, BSc, PhD formerly of British Geological Survey
• R W Gallois, BSc, PhD British Geological Survey, Edinburgh
• C J Wood, BSc formerly of British Geological Survey
• Contributors
• J D Cornwell, BSc, PhD, T P Gostelow, BSc, PhD, T C Pharaoh, BSc, PhD British Geological Survey, Keyworth
• E F P Nickless, BSc Natural Environment Research Council, Swindon
• A C Benfield, BSc, D M Gregory, BSc, E A Howell, BSc formerly of British Geological Survey

(Front cover)

(Rear cover)

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

Books

• British Regional Geology
• East Anglia and adjoining areas (4th edition)
• Institute of Geological Sciences Report Series
• Assessment of British Sand and Gravel Resources
• Sand and gravel resource sheet TG 10 (Hethersett)
• Sand and gravel resource sheet TG 11 (Attlebridge)
• Sand and gravel resource sheet TG 20 (south-east of Norwich)
• Well catalogue
• Records of wells in the area of the New Series one-inch Geological Sheet 161 (Norwich)

Maps

• 1:625 000
• Solid geology (south sheet)
• Quaternary geology (south sheet)
• 1:250 000
• East Anglia Solid geology
• Aeromagnetic anomaly
• Bouguer gravity anomaly
• 1:125 000
• Northern East Anglia Hydrogeology
• 1:50 000 (Solid and Drift)
• Sheet 145 and part sheet 129 King's Lynn and The Wash
• Sheet 173 Ely
• Sheet 189 Bury St Edmunds

Notes

• The word 'district' used in this memoir means the area included in the 1:50 000 Geological Sheet 161 (Norwich).
• National Grid references are given in square brackets throughout the memoir.
• Numbers preceded by A refer to photographs in the Survey's collection.

List of six-inch maps

The following is a list of six-inch (1:10 560) geological maps included wholly, or in part, in the area of the 1:50 000 Norwich (161) Geological Sheet, with the initials of the surveying officers and the date of the survey for each six-inch map; the surveyors were: F C Cox, E G Poole and M C McKeown.

Manuscript copies of these maps have been deposited for public reference in the library of the British Geological Survey, Keyworth, Nottingham and in the British Geological Survey Information Point at the Geological Museum, Exhibition Road, South Kensington, London. They contain more detail than appears on the 1:50 000 map.

Preface

This Memoir is intended as a brief guide to the geological history of the district. It does not purport to provide detailed descriptions but such details are available for inspection at the National Geosciences Data Centre at Keyworth, Nottinghamshire.

Much of northern East Anglia was mapped originally in the 1870's and 1880's and published in the Old Series One-inch Geological Map Series, with accompanying memoirs. Two maps in that series, sheets 66 NE and SE, incorporate much of the area represented on the Norwich (161) Sheet; they were surveyed by H B Woodward between 1875 and 1880 and his explanatory memoir was published in 1882. Primary survey at the six-inch (1:10 560) scale was undertaken in 1965–1969 mainly by Mr E G Poole and Dr F C Cox, with smaller tracts by Mr M C McKeown, under the direction of Mr S C A Holmes as District Geologist. The 1:50 000 Geological Map was published in 1975. Subsequently, a Regional Geological Survey of East Anglia was mounted. Many new data relevant to the geology of the Norwich Sheet were acquired, and the results are summarised here. The regional study was a collaborative project involving external workers as well as officers of the Geological Survey. We gratefully acknowledge in particular, the assistance given in dating Quaternary pollen assemblages by Dr C Turner of the Open University as well as by Dr L Phillips and Dr S Peglar, of Cambridge University, and in the identification of Pleistocene molluscs by Rev. P E P Norton. Mr C J Wood and Miss D M Gregory, both formerly of the Geological Survey, identified the Cretaceous faunas and the Pleistocene ostracods respectively.

Of the rocks older than the Pleistocene, only the Upper Chalk, of Cretaceous age, is exposed within the district. The basement rocks below the Mesozoic have been the subject of much research since the completion of the survey in 1969 and this work is reviewed in the present account. The history of the Pleistocene of East Anglia continues as a subject of debate and the Regional Geological Survey was largely directed towards the solution of some of the associated problems. Again, the results bearing on the geology of the Norwich Sheet are reviewed.

The memoir incorporates accounts by Dr Cox both on the marine Pleistocene represented by the Norwich Crag and also on the complex series of superficial deposits of Pleistocene and Recent ages, by Dr R W Gallois on the concealed strata and by Mr C J Wood on the Upper Cretaceous rocks. Geophysical data were reviewed originally by Mrs E A Howell and have been revised by Dr J D Cornwell to incorporate fresh results, whilst new geochemical information has been summarised by Dr T C Pharaoh. The sections of the Economic Chapter relating to both the brick clays and the Chalk and flints were written by Dr Cox, whilst the supplementary information on the occurrence of chalk mines and subsidences was compiled by Dr T P Gostelow. Mr E F P Nickless prepared the section on sand and gravel resources and Mr A C Benfield that on water supply. The explanation has been edited by Mr D A Gray, CBE.

We are particularly grateful to Mr N B Peake and Professors J M Hancock, B M Funnell and R G West for valuable discussions in their respective fields of research. During the course of the field studies access to both property and records were provided by many organisations: thanks are due in particular to the Anglian Water Authority, the City Architect and City Engineer of the Norwich City Council, the Frettenham Lime Co. Ltd., the Howes Lime Co. Ltd., the Longwater (Gravel) Co. Ltd., RMC Atlas Aggregates Ltd., the Superior Oil Company and the Norris Oil Company. The work of the surveyors was also greatly eased by the generous assistance of landowners and tenants in providing access to their properties.

F G Larminie, OBE Director, British Geological Survey Keyworth, Nottingham NG12 5GG. 1st February 1989

Geology of the country around Norwich—summary

This memoir describes part of Norfolk extending from East Dereham to Norwich and Attleborough. Deep boreholes and geophysical data have been interpreted in new models of the regional deep structure. The outcrop of Upper Chalk is redescribed and new palaeontological data are presented. Marine early Pleistocene deposits, the Norwich Crag, are succeeded by Pleistocene fluvial and glacial deposits, the latter being widespread at the surface. Several important interglacial sites are described that shed light on the sequence of events. Past and present quarrying and mining activities and the groundwater potential of the district are also considered.

(Geological succession) Geological sequence in the Norwich district.

Geological sequence in the Norwich district

Chapter 1 Introduction

This memoir describes the district covered by the 1:50 000 Norwich (161) Geological Sheet, which lies within the county of Norfolk, largely to the south and west of the City of Norwich (Figure 1). The gently rolling countryside ranges in elevation from a metre or so above Ordnance Datum (OD) in the valley of the River Yare east of Norwich, to more than 60 m above OD in the south and west of the sheet. Most of the country, however, forms a plateau lying between 30 and 60 m above OD and composed of glacial deposits. The rivers around Norwich have cut through these deposits to expose the underlying Norwich Crag and Chalk (Figure 2). The principal river valleys are characterised by terrace features on their flanks and by flat alluvial floors, in which the alluvium caps a variety of concealed glacial, interglacial and periglacial deposits.

The glacial deposits of the higher ground consist of Boulder Clay and Glacial Sand and Gravel, each giving rise to a distinctive landscape. The boulder clay plateau to the south and west of Norwich is predominantly an area of arable farming, particularly for cereals, sugar beet and, in recent years, oil-seed rape, whilst to the north and east the extensive spreads of sandy deposits support woodland and heath. The rivers Yare and Wensum, and their tributaries the Tas, Tiffey and Tud, drain most of the district and, downstream of their confluence at Norwich, flow eastwards to the coast at Great Yarmouth. A small sector of the district around Attleborough and along the western boundary of the district south of Scoulton Mere is drained westwards via the River Wissey into the River Great Ouse and thence into the Wash.

The district is rich in evidence of man's occupation since Palaeolithic times. Flint tools recovered from various deposits indicate that early hunters established camps along the river valleys, as at Whitlingham where tools of Acheulian type have been recorded. The Mesolithic is not well represented, but there is ample evidence of Neolithic occupation within the district, as illustrated, for example, by the earthworks of the Henge Monument at Arminghall. Neolithic pillar-and-stall galleries, excavated for flints into the sides of the Wensum valley, continued to be worked until the Roman era.

Records of artefacts from the Bronze Age are fairly common. Iron Age tools are less so, however, due to their destruction by corrosion in acid soils, although pottery and earthworks have been recorded. Evidence of Roman settlement is provided by the walled town at Caistor St Edmund, 5 km south of Norwich, and one of only two towns existing in Norfolk during Roman times. Norwich was not established as a settlement until the 9th century, but the City expanded greatly during the Middle Ages and continues in its predominant position as the cultural and commercial centre of northern East Anglia.

Outline of geology

The geological structure of the solid rocks exposed in the present district is simple, but the Pleistocene and Recent (Quaternary) history is complex and still the subject of debate in several respects. The Superficial Deposits of Pleistocene age are fragmentary and scattered so that the local sequence of events which they represent has to be inferred, at least in part, from evidence outside the Norwich Sheet. The geological history summarised in this section refers only to the solid rocks and superficial deposits at outcrop.

Upper Chalk (Cretaceous) underlies the district represented on the Sheet but its outcrop is restricted to the flanks of a few valleys around Norwich, being elsewhere overlain by Quaternary deposits (Figure 2). The Upper Chalk is a soft, white limestone which was formed in warm, clear late Cretaceous seas; flints abound in the formation as lines of nodules, as tabular sheets and also in giant, vertical cylindrical forms known as paramoudras (Plate 1).

The early post-Cretaceous history of northern East Anglia is not known in detail, but extensive erosion must have taken place. Eocene formations have been recorded in boreholes near Great Yarmouth, but none occurs within the area of the Norwich Sheet. Neither are deposits of the succeeding Neogene (Miocene and Pliocene) now recognised within the present Sheet boundaries, although parts of the Crag sequence immediately to the east may be of Pliocene age. Around Norwich the Chalk is overlain by the marine, shelly sands, silts and clays of the Norwich Crag, which were deposited during the Lower Pleistocene and so record the only post-Cretaceous marine transgression of the district. These intertidal sediments, together with a near-shore sandy and pebbly facies, indicate the presence of a Lower Pleistocene coastline west of Norwich and trending roughly north to south.

The succeeding Pleistocene deposits are of pre-Anglian age. They consist of fluviatile gravels incorporating quartz, white quartzite and volcanic pebbles, and were included in the Glacial Sand and Gravel depicted on the 1:50 000 Norwich Sheet. A period of major climatic change, during the Anglian Stage, was accompanied by the arrival of ice sheets which deposited the Norwich Brickearth (Plate 3) and the (Chalky) Boulder Clay or Lowestoft Till (Plate 4).

The climatic conditions during the several glacial, pre-glacial and interglacial episodes of the Pleistocene modified the preglacial drainage considerably. Locally, the valleys were over-deepened, only to be infilled subsequently by a variety of deposits, including outwash gravels formed by torrents draining and eroding the new glacial materials, solifluxion deposits, and by interglacial lacustrine sediments, laid down during warm phases. The ice sheet associated with the succeeding and final (Devensian) glacial phase is thought not to have crossed the north Norfolk coast.

The geological formations proved within the district are shown in the table inside the front cover of this memoir: the rocks older than the Upper Chalk have been encountered only in boreholes. The re-classification of the Jurassic strata, as well as the changes in the thicknesses of the Norwich Crag and the pre-Pleistocene formations, compared with those shown in the generalised vertical section on the 1:50 000 Norwich Sheet, follow research completed after the publication of the Map in 1975.

History of research

Charlesworth (1957) considered it difficult in East Anglia to decide which was the more complex, its geology or its Quaternary literature! The present district is no exception, having a long history of geological research, which can only be summarised here. Though few are now available for examination, quarries and pits abounded in the 19th century and a lucrative source of income for the quarrymen was the sale of the best fossil specimens to museums and collectors. The earliest workers include Taylor (1824), who studied both the Crags and the Chalk, and Rose (1835, 1836) who worked on the Chalk. The first comprehensive account of the geology of Norfolk was by Samuel Woodward (1833) and it was his grandson, H B Woodward, who compiled two of the Geological Survey maps of the area around Norwich (Sheets 66 NE and SE at the scale of one inch to the mile) between 1875 and 1880 and wrote an accompanying Memoir, published in 1882. This work was part of a comprehensive study of northern East Anglia by the Geological Survey, and several other maps and memoirs relating to adjoining areas, some overlapping the boundaries of the Norwich Sheet, were produced at about that date (Reid, 1882; Bennett, 1884; Whitaker and Dalton, 1887; Blake, 1888, 1890).

The Crags and glacial deposits of East Anglia were the particular interest of F. W. Harmer who published a strati-graphical classification for the Crags (1899), as well as accounts of the post-Cretaceous period (1902, 1910a, b, c). The final part of his revision of Wood's Monograph of the Crag Mollusca was issued posthumously in 1924. Other workers (e.g. Baden-Powell, 1948) continued research into the distribution and lithology of tills (boulder clays). Subsequently, little was published on the relationships between the Quaternary deposits until the mid-1950's. However, publication by West of the results of his research into the Quaternary sediments of Hoxne (1956), and his review of British Pleistocene stratigraphy (1963), stimulated a renascence of Quaternary studies in Britain and particularly in East Anglia. Woodward (1882) had described a tripartite glacial sequence of two tills separated by the 'Middle Sands'. That simple division has been revised by several workers, particularly in relation to the stratigraphical significance of the Middle Sands, now recognised as the Corton Sands. Study of the field relations led Cox and Nickless (1972) to introduce a more complex classficiation which was used by Bristow and Cox (1973) in proposing major revisions to the glacial stratigraphy of East Anglia.

The development of the glacial and post-glacial valley systems of the region was described by Woodland (1970) in a classic paper on tunnel-valleys. Detailed investigations into the stratigraphy of sites in two valleys within the Norwich Sheet boundaries and of others elsewhere in the region (Cox, 1985a, b) led to the conclusion that the present valleys have been fluvial channels since the retreat of the Crag sea. Such debates on the Pleistocene and Recent history of the region continue, particularly in relation to the significance of its geomorphology, and can be followed in the writings of Shot-ton and others (1977), Perrin and others (1979), Straw (1979), Hey (1980), Cox (1983, 1985a, b); Bridge and Hopson (1985) and Hopson and Bridge (1987).

So far as the exposed pre-Pleistocene rocks are concerned, the early workers collected extensively from the highly fossiliferous, well exposed 'Norwich Chalk'. A valuable collation of their collections was compiled by Woodward (1882). Relatively few of the former pits were available to the early 20th century workers such as A W Rowe, whose unpublished notebooks are a valuable source of information, and R M Brydone, who published several significant papers (1930, 1932, 1933, 1938). Even fewer pits are now accessible and more recent work owes much to the earlier records. Augmenting this previous research by further extensive studies, Peake and Hancock (1961, 1970) have published comprehensive studies of the Chalk of Norfolk, including a zonal map of the formation and much biostratigraphical detail.

Information concerning the Mesozoic, Permian and basement rocks of the region has been increased in recent years by new drilling and geophysical data arising from hydrocarbon exploration. The results of much of the associated research have been published, including papers by Wills (1951, 1973, 1978), Thurrell (1961), Linssler (1968), Kent (1947, 1968), Chroston and Sola (1982), Allsop and Jones (1981), Allsop (1984); Chroston (1985); Smith and others (1985) and (Pharaoh and others, 1987).

Chapter 2 Deep geology

Regional stratigraphy and structure

The proximity of Norfolk to the gasfields of the southern North Sea and the associated onshore exploration for oil and gas, has resulted in the drilling of a number of deep boreholes in East Anglia, as well as in the acquisition of much new geophysical data relating to the region. Two of the boreholes occur within the present district and permit the local stratigraphy and structure of the concealed strata to be determined and, taken in conjunction with other data, placed in a regional setting (Figure 3) and (Figure 4).

The most complete section through these concealed rocks is the sequence proved in the borehole drilled in 1965 at Great Ellingham [TM 0262 9847] by the Superior Oil Company ((Table 1), (Figure 3), Borehole H and Appendix 1). The borehole was sited at an elevation of 53.3 m above OD on glacial deposits overlying Upper Chalk of the Marsupites Zone. The depth intervals from 269.14 to 373.99 m and from 395.94 to 398.98 m were cored continuously and rock-bit samples were collected from the remainder of the borehole. A suite of geophysical logs was obtained and these provide some control on the physical properties of the main rock types encountered within the district. A closely similar sequence was found in Rocklands No. 1 Borehole at a site some 4 km to the west-south-west [TL 995 966] which was drilled in 1969 by the Norris Oil Company ((Table 1) and (Figure 3), Borehole J). The site was at an elevation of 45.7 m above OD and was also on glacial deposits overlying Upper Chalk of the Uintacrinus Zone. The borehole was rock-bitted throughout, but the geophysical logs permit correlation of the strata with those in the Great Ellingham Borehole. The partial re-classification of the strata in the Rocklands No. 1 Borehole, compared with that shown on the 1:50 000 map has been referred to above (see inside front cover). One other borehole, drilled in 1862 at the Carrow works of Messrs J J Colman in Norwich (Appendix 1), has penetrated to below the Chalk and is thought to have stopped in the Gault (Whitaker, 1921). Section 2 shown on the 1:50 000 Norwich Sheet is based, so far as the concealed rocks are concerned, on the evidence provided by those three boreholes. The line of section extends from Rockland All Saints [TL 987 963] in the south-west, through Ketteringham [TG 168 033] to Drayton [TG 187 145] in the north.

Table for (Figure 3) Contours on the pre-Permian surface in northern East Anglia (a) in metres below OD

Table for (Figure 3) Contours on the pre-Permian surface in northern East Anglia(b) with the base of the Aptian–Albian as datum

Table for (Figure 4) (a) Occurrence of Jurassic rocks

Table for (Figure 4) (b) thickness of Permo-Triassic rocks in northern East Anglia

The available geological information concerning the ages and distribution of the pre-Permian strata beneath the region is summarised in (Figure 3)a. Kent (1968) and Wills (1978) proposed the existence in the pre-Devonian subcrop of an east-west trending belt of Precambrian basement extending from Charnwood to the Wash, overlain to the north and south by Lower Palaeozoic rocks. This interpretation is based on petrographical comparison of concealed felsic volcanic rocks encountered in the boreholes at North Creake (Phemister in Kent, 1947), Glinton (Kent, 1962), and else where, with the exposed Charnian (Late Proterozoic) volcanic suites. This view has been challenged by Le Bas (1972) and Evans (1979) who infer the presence of a north-west–south-east trending Caledonide fold-belt in this region. Support for this latter view is provided by the data of Pharaoh and others (1987), which indicate an Ordovician age (448 ± 32 Ma) for the Glinton volcanic rocks and demonstrate the geochemical dissimilarity of the concealed volcanic suites to the Charnian rocks.

A lobe of undifferentiated Precambrian–Silurian strata, having this approximate north-west–south-east trend, is shown by Smith and others (1985), following Wills (1973, 1978), as extending from the Wash towards Norwich possibly to beneath the north-west corner of the Sheet. Indurated, commonly steeply dipping and poorly cleaved mudstones have been found beneath the Mesozoic strata over much of the remainder of the region. On the basis of the limited palaeontological evidence available from several boreholes, and on the geochemical evidence advanced by Pharaoh and others (1987), these have been assigned variously to the Ordovician, Silurian, undifferentiated Lower Palaeozoic or Devonian. Beneath most of the Norwich district the sub-Mesozoic rocks are at present thought to be of Silurian age, except in small sectors in the south-west floored by Devonian (see below) and in the north-east probably underlain by Carboniferous rocks (Smith and others, 1985). The evidence for the presence of Carboniferous strata has been obtained from boreholes at East Ruston and Somerton, where they overlie Lower Palaeozoic (Ordovician–Silurian) strata. Geophysical data suggest that representatives of the Carboniferous rocks may extend southwards and westwards to impinge upon the northeastern corner of the present district (Allsop, 1984).

Diagrams illustrating the local aeromagnetic and Bouguer gravity anomalies are shown on the 1:50 000 Norwich Sheet and these are placed in their regional settings in (Figure 5)a and (Figure 5)b of this account. The anomalies in both figures indicate that the structural trend of the basement rocks in the Norwich district, and regionally, is WNW–ESE. Not only does this accord approximately with the orientation of the lobe of Precambrian–Silurian rocks referred to above, but also with many of the structures affecting Mesozoic rocks offshore, suggesting that both may be controlled by the same suite of faults. Linsser (1968) concluded that the Bouguer gravity and magnetic anomalies are not caused by the same bodies, although they are both due to faulted horst and graben structures within the basement.

None of the Mesozoic rocks gives rise to magnetic anomalies and the variations in the total magnetic field shown in (Figure 6)a are therefore due to the distribution of magnetic rocks in the basement; possible to the volcanic assemblages encountered in the North Creake and South Creake boreholes and lying at maximum depths of 4.5 km. Alternative models for the magnetic anomalies along the profile AA′ (Figure 5)a and b) are shown in (Figure 6). In Model B the anomalies are explained in terms of magnetic rocks, possibly volcanics, in the basement. For Model A the effect is assumed to be due partly to the presence at the northern boundary of the district of a granite in the basement, as suggested by Chroston and Sola (1982) and Chroston (1985).

The Bouguer anomalies reflect variations in the densities of the underlying rocks. The most significant density contrast occurs between the pre-Permian rocks, densities typically 2.60–2.75 Mg/m³, and the Permian and younger sediments (2.10–2.45 Mg/m³). The gravity effect of the lower density sediments can be calculated and added to the observed values to produce a profile ((Figure 6)b) which largely reflects variations within the basement rocks. The systematic northward increase in the background anomaly to be seen in (Figure 6)b is due to a deep-seated change, probably a decrease in the thickness of the crust. Two of many possible interpretations of the Bouguer anomaly variation superimposed on the background change are shown in (Figure 6). The first ((Figure 6)c) assumes that the gravity low is due to a concealed granite, while the second ((Figure 6)d), derived using slightly different background values, assumes that there is a northward thickening of Palaeozoic sediments. Additional geophysical evidence is provided by the results of a seismic refraction line (Chroston and Sola, 1982; Chroston, 1985) which extends across East Anglia and through the present district. These results suggest that the Palaeozoic rocks are less than 1.5 km thick and rest on high velocity crystalline rocks, possibly volcanic rocks comparable with those encountered in the North and South Creake boreholes. However, the data are insufficiently definitive to resolve the ambiguity as to the cause of the gravity low north of the district.

In middle to late Upper Devonian times the Lower Palaeozoic rocks of East Anglia were much affected by the latest phase of the Caledonian earth movements (the Svalbardic phase of Wills, 1951). Between late Devonian and late Cretaceous times the Lower Palaeozoic and earlier Devonian rocks of the region formed part of a stable block, the London Platform. Locally this was partially submerged to give rise to islands throughout much of the Upper Palaeozoic and Mesozoic, but during the Cretaceous the stable block including the present district, was finally overstepped by the successive marine transgressions represented by the Carstone, the Gault and the Chalk.

Contours on the pre-Permian surface of Norfolk suggest that the Norwich district lies close to the north-eastern margin of the London Platform ((Figure 3)a). However, this surface contains a component of post-Cretaceous folding that manifests itself as the gentle eastward dip of the Lower Cretaceous, Chalk and Tertiary deposits. When allowance is made for this regional tilt ((Figure 3)b), the district can be seen actually to border the north-western margin of the Platform. The isopachyte map of the Permo-Trias ((Figure 4)b) shows how these rocks thicken northwards into the North Sea basin of deposition. The Jurassic rocks similarly thicken away from the London Platform towards the Midlands.

Local stratigraphy

Precambrian

Neither of the two hydrocarbon exploratory boreholes on the Norwich Sheet, Great Ellingham and Rocklands ((Figure 3), boreholes H and J), reached Precambrian rocks, but reference has been made above to the possible presence of a lobe of Precambrian–Silurian beneath the north-west corner of the district. The Lexham Borehole, some 15 km to the west-north-west of the sheet boundary ((Figure 3), Borehole L), encountered metamorphic rock immediately below the Jurassic strata. Pharaoh and others (1987) consider this to be ?Cambrian in age.

Palaeozoic

The Mesozoic rocks of most of the district are thought to be underlain by poorly cleaved and silty mudstones of Lower Palaeozoic, probably late Silurian, and early Devonian age, except for the small area in the north-east where Carboniferous strata may be present. At Great Ellingham, steeply dipping, poorly cleaved mudstones were proved beneath the Triassic rocks. No fauna was obtained from the mudstones, but a sparse assemblage of poorly preserved spores suggests a mid-Devonian age. Comparison of the rock cuttings and geophysical logs of the Rocklands Borehole with the cores and logs from Great Ellingham, indicates that the basement rocks at Rocklands are of similar lithology. Similarly, the basement in the Breckles Borehole, some 4 km south-west of the district boundary ((Figure 3), Borehole K), has also been classified as Devonian.

Permo-Trias

No strata of Permian age have been recorded from boreholes drilled within the Norwich Sheet, but Triassic rocks are present and their regional distribution and thickness are summarised in (Figure 4)b. Compared with the sequences further north, the Trias of Norfolk is attenuated and, especially in the areas adjacent to the London Platfctrm, consists predominantly of soft sandstones, siltstones and marls of late Triassic age. Beneath the Norwich Sheet the Trias is thought to thicken irregularly northwards from about 30 m to over 100 m ((Figure 4)b). At Great Ellingham 29.3 m of soft, white and greenish grey, partially dolomitised sandstones and silt-stones and red and green mottled mudstones were recorded. They contained a sparse microflora indicative of a late Triassic age. The rock-cuttings and geophysical logs from the Rocklands Borehole indicate a similar thickness of the same lithologies.

Jurassic

Throughout East Anglia, the Jurassic sequence is attenuated in comparison with that in adjoining regions. The formations are particularly thin adjacent to the London Platform where evidence of erosion, condensed deposition and near-shore environments has been found at a number of horizons. The complexities of the erosional and depositional history are reflected in the occurrence of laterally variable sequences around the edge of the Platform.

In the Great Ellingham Borehole, only the upper part of the Lower Lias (Lower Jurassic) and a thin development of the Estuarine 'Series' (Middle Jurassic) are present, the remainder of the Jurassic sequence having been removed during the erosional-phase. The pale grey silty mudstones of the Lower Lias are sparsely fossiliferous but worm burrows and seams of phosphatic pebbles suggest deposition in a near-shore environment. The overlying alternating siltstone/mudstone sequence of the Estuarine 'Series' contains carbonised plant traces, but bivalves become plentiful enough to form a shell-fragmental limestone, the Blisworth Limestone, immediately underlying the Carstone.

In the Trunch Borehole (Gallois and Morter, 1976), about 25 km north-north-east of Norwich, a similarly attenuated sequence is present ((Figure 4)a, Borehole S) and it seems likely that representatives of the Lower and Middle Jurassic are everywhere present within the district, except in the extreme south-east. Much thicker and more complete sequences have been recorded in north-west Norfolk, for example in the Hunstanton Borehole ((Figure 4)a, Borehole Q), and it is probable that the Jurassic succession beneath the north-west sector of the district is more complete than in the south and east.

Cretaceous

Late in Lower Cretaceous time the London Platform was submerged by a series of transgressions and by the late Albian it had been completely inundated. In the present district, near the northern edge of the Platform, the earliest Cretaceous deposits are diachronous and consist of limonitic and chamositic, pebbly sands of the Carstone, here of Albian age. The Carstone and the mudstones of the succeeding Gault (Gallois and Morter, 1982), also Albian, are well developed at Great Ellingham and Rocklands: in these boreholes the lower part of the Carstone contains pebbly sands reminiscent of the Lower Greensand outcrop around Cambridge. It is uncertain whether this material is Lower Greensand in situ, or Lower Greensand incorporated into the basal beds of the Carstone. An early account of the drilling record at the Carrow Works in Norwich indicates that Lower Greensand was present. However, the reliability of that version is discounted by Whitaker (1921) in favour of the report by Crompton (1862), in which the borehole is recorded as stopping in the Gault, penetrating 36 ft (10.97 m) of that formation (Appendix 1). Both the Carstone and the Gault probably occur everywhere within the district.

Few samples are preserved from the Chalk in any borehole within the present district and, except for the exposed parts of the Upper Chalk; the formation is known only from the boreholes at Great Ellingham, Rocklands and the Carrow Works in Norwich (Whitaker, 1921). Drilling records from the Carrow Works suggest that the Lower Chalk is separated from the Gault by a thin development of Upper Greensand (Whitaker, 1921). References to Greensand in the Carrow well were also made by Kitton (1872, 1874). The thickness of the Lower and Middle Chalk has been determined by comparing the geophysical logs of the Rocklands Borehole with those from other wells in East Anglia in which the Chalk has been cored.

The Lower Chalk of the southern part of the district is probably similar lithologically to that of the Cambridgeshire outcrop. The Plenus Marl is developed at the top of the formation, which is estimated to vary in thickness from 32 m at Norwich to 38 m in the Rocklands Borehole. The Middle Chalk of the district may be similar to the Welton Chalk of Lincolnshire and Yorkshire. Although there is a lack of data in the Norwich area, the Lincolnshire succession is known to extend, with minor modifications, as far south as Thetford. Although open to other interpretations, the balance of the evidence from the geophysical logs indicates that the top of the Middle Chalk occurs in the Rocklands Borehole at a depth between 143 and 146 m. The base of the formation in this borehole is taken at 214 m at the junction of the Plenus Marl below and 3 m of Melbourn Rock above, to give a Middle Chalk thickness of 68–71 m.

Chapter 3 Solid geology at outcrop (Cretaceous and early Pleistocene)

Cretaceous: Upper Chalk

Chalk everywhere underlies the district, although outcrops are confined to the river valleys in the vicinity of Norwich (Figure 2). The Chalk is a soft, white, friable limestone consisting principally of the microscopic, calcareous remains of coccoliths (planktonic algae). The formation appears rather uniform throughout its thickness, but in fact a wide variety of distinct lithologies is present. Differences in lithology are thought to reflect changes in the depth of the Cretaceous seas in which the Chalk was deposited, and some of the distinctive `hardgrounds' and nodular chalks were probably formed during periods of temporary shallowing. Flint (cryptocrystalline silica) is common at many levels in the sequence above the Lower Chalk, which is flintless. It occurs in bands and as irregular nodules, commonly incorporating fossil remains. Giant, vertical, cylindrical flints termed `paramoudras', the origin of which is discussed in Bromley and others (1985), characterise the top of the Upper Chalk sequence. An example of such a structure, photographed in 1969 at Colman's (Whitehouse) Pit, Whitlingham [TG 2678 0766] is shown in (Plate 1).

The formation was famous in the 19th century as a source of fossils, particularly from the many pits in the vicinity of the City. A comprehensive review of the history of research, the biostratigraphy, the structure and the lithology of the Chalk of Norfolk, including a regional zonal map, was published by Peake and Hancock in 1961 and revised by them in 1970. Both the litho- and the biostratigraphy have been further updated by Wood (1988).

The record of the borehole at the Carrow Works (Appendix 1), referred to above, shows a combined thickness for all of the Chalk and 'Upper Greensand' (see section two) of 1141 ft (348 m). Allowing for the extra thickness of the Chalk between the ground surface at the works and the base of the Norwich Crag nearby, the total thickness at Norwich for the preserved Chalk and 'Upper Greensand' is 365–370m. To the east of the City, higher zones of the Upper Chalk are present, and at the eastern boundary of the district the total thickness of the Chalk may be 375–385 m. Allowing for the Middle and Lower Chalk, this implies a maximum thickness for the Upper Chalk of some 285 m.

The surface of the Chalk is generally planar with an elevation of between 20 and 30 m above OD: generalised contours on this surface are shown (in red) on the 1:50 000 Norwich Sheet. However, glacial and post-glacial erosion has resulted in steep-sided valleys being cut into the Chalk and, locally, these valleys are overdeepened to as much as 40 m below OD (Figure 7). Thus, the subdrift topography of the Chalk surface can have a maximum relief of some 70 m over relatively short distances. Early workers (e.g. Woodward, 1882) recorded many sections in the Chalk along the Yare and Wensum valleys around Norwich which exhibited evidence of glacial tectonics. Additional occurrences continue to be reported; for example chalk has been observed overlying Chalky Boulder Clay at the Whitlingham Sewage Works [TG 278 976]. Following the recent survey it is suspected that some of the Chalk outcrops in the east of the district constitute one or more glacially-emplaced rafts. For example, this condition may apply to much of the area east of Trowse [TG 247 066] in which disturbed chalk has been described (Woodward, 1882; Wood, 1988). Around Drayton [TG 180 136] and Ringland [TG 138 140], much of the chalk shows evidence of reconstitution resulting from the action of permafrost, with only the flints providing evidence of the original bedding. The results of both phenomena can be seen at Bawburgh Rookery [TG 1610 0906] where both reconstituted and glacially disturbed chalk have been recognised.

Biostratigraphy

The stratigraphical terminology applied to the exposed Chalk and the key sections available during the Sheet survey, are shown in (Table 2). The Chalk in the Norwich district dips to the east so that progressively younger zones appear at outcrop in that direction. The oldest beds occur in the south-west of the district and probably belong to the Uintacrinus socialis Zone, but these are hidden byuperficial deposits; the oldest exposed Chalk is of the Gonioteuthis Zone and the youngest of the Belemnitella mucronata Zone. Immediately to the east of the district the Belemnella lanceolata Zone (indicative of the Lower Maastrichtian Substage) has been recorded at Bramerton [TG 2956 0609] in the banks of the River Yare. Maastrichtian Chalk may be present in the district, but is not exposed.

The Chalk of the district can be conveniently considered under the headings given below:

• Gonioteuthis Zone (Lower Campanian Substage).
• Belemnitella mucronata Zone (Upper Campanian Substage).

The distribution of the subdivisions of the Chalk and the principal localities referred to in the text are shown in (Figure 8).

Gonioteuthis Zone

This poorly exposed zone, originally named by Brydone (1933) the 'Zone of granulated Actinocamax' [i.e. Gonioteuthis],corresponds to the combined Offaster pilula and Gonioteuthis quadrata zones of the southern England zonal scheme. The name was first used in Norfolk by Peake and Hancock (1961), who considered the two zones not to be readily distinguishable in the county. More recently, however, they have recognised both zones (1970, p.339C), but because of the paucity of present exposures, it remains convenient to refer the beds between the underlying Marsupites and overlying Belemnitella mucronata zones to an undivided Gonioteuthis Zone.

The chalk of this zone is generally soft with a tendency to break along bedding planes. The lower part is very white with flints common, generally in bands, while the upper part may be yellowish and with the flints more scattered. They are commonly spindle-shaped, but also occur as hollow, round nodules containing sponge debris. The majority of the pits in the district located in this zone belong to the higher part of the succession, i.e. equivalent to the quadrata Zone of southern England; a former pit near Carlton Forehoe [TG 092 055] was probably in the pilula Zone. The thickness of the Gonioteuthis Zone is thought by Peake and Hancock (1961) to range between 180 ft (55 m) and 260 ft (79 m).

Belemnitella mucronata Zone

The six-fold, essentially palaeontological, scheme of subdivision of the Norfolk mucronata Zone established by Peake and Hancock (1961; 1970) derived much from the researches of earlier workers, notably Rowe and Brydone. In recent years fossils collected from temporary sections in critical parts of the zone, together with studies of Micraster assemblages from the top of the zone, or correlative succession, in Germany, have enabled eleven faunal belts to be recognised provisionally by Wood (1988). Their relation to the Peake and Hancock scheme is shown in (Table 2).

The term 'Pre-Weybourne Chalk' has been introduced by Wood to include the Eaton Chalk and Basal mucronata Chalk of the Peake and Hancock classification. Its use helps to resolve the discrepancies between Brydone's (implied) concept of these subdivisions and the concepts subsequently adopted by Peake and Hancock. The Pre-Weybourne Chalk is relatively poorly exposed, but it is considered that five faunal belts can be recognised within it, at least in the present district.

Pleistocene: Norwich Crag

Distribution and lithology

The outcrops and probable sub-drift distribution of the Norwich Crag are shown in (Figure 9), together with the principal localities at which the formation is exposed. A small area adjoining the district to the east is included to show the position of the type section at Bramerton. The sub-drift Chalk/Crag boundary is conjectural.

Although the Norwich Crag succession varies in detail, a broad sequence of lithological units, generally totalling 10–15 m thick, can be recognised in the district. The lower member is a basal stone bed with overlying cross-bedded, shelly sands (Plate 2); it is generally followed by flaserbedded sands accompanied by thin green and brown clays. An upper bed of quartz and quartzite-rich flint gravels, commonly included in the Norwich Crag, is now regarded as a separate deposit. Criteria for its separation were discussed by Funnell (1961, p.359), while Cox (198513) described more than one quartz-rich deposit above the Crag. This latter interpretation is taken further by Bridge and Hopson (1985) who recognised a quartz/quartzite outwash suite related to the Anglian North Sea Drift and derived from the Norwich Brickearth.

The basal stone bed of the Crag is composed mostly of large, angular, iron-stained and glauconite-coated flints; it rests on an undulating Chalk surface which slopes gently eastwards. The flints are set in a clayey or sandy matrix which locally contains shells and commonly includes small, black, well rounded flints. Mollusc borings filled with sand are also found penetrating the irregular chalk surface. The stone bed, which is similar to the residual flint bed on the wave-cut platform of the Chalk of the present Norfolk coast, is widespread around Norwich City and Caistor St Edmund. The ripples that gave rise to the cross-bedding in the overlying sands do not show any preferred direction of current flow and were probably cuased by wave action in shallow water.

The succeeding flaser-bedded sands with clays contain distinctive iron-stained nodules and geodes and have been equated by some workers (Wood, 1880; Harmer, 1902; Cambridge, 1977) with the Chillesford Beds of Suffolk. However, the concept of such widespread continuous horizons of finely bedded sands ignores the nature of the tidal, estuarine depositional environment in which they were laid down and which are characterised by shifting facies depending upon the changing coastal conditions. Woodward (1882) had reservations concerning the correlation with Suffolk, and Downing (1959) demonstrated that there is more than one clay horizon within the Norwich Crag of East Anglia. The correlation was discounted by West (1977), and Funnell, Norton and West (1979) included the Chillesford Clay as a member of the Norwich Crag (Bramertonian).

South of Norwich at the Caistor St Edmund Pit [TG 239 046], the Crag sequence begins with a rounded-flint gravel resting on the Chalk. A similar gravel was recorded at the same elevation on the Chalk at Flordon [TG 192 968]. This marginal facies most probably represents the former shoreline. At Flordon the gravel is overlain by a rounded-flint and quartzite gravel similar to the Westland Green Gravels described by Hey (1980) and referred to above, as well to the Bure Valley Beds (Wood, 1866). This is not so at Caistor St Edmund where the gravels are overlain by indurated, shelly Crag which has been reworked by braided stream action under conditions of permafrost. This braided stream complex is capped by marine sands with rare shells and many burrows. At Catton Grove [TG 233 099], to the north of Norwich City, a rounded-flint gravel is again seen resting directly upon Chalk and, like its equivalent at Flordon, is also thought to be a deposit of the Crag shoreline.

The general coarsening of the sediments from east to west (Nickless, 1971) and the gentle eastward slope ofthe Chalk surface below the Crag, together with the position of the shoreline referred to above, all suggest that the coastline lay to the west of the present outcrop. However, much of the Norwich Crag of the district has been eroded by glacial action and its western limit remains uncertain.

Norton (1970) postulated that separate deposition and facies development took place in a 'Southern Basin' around the Chillesford, Aldeburgh and Sizewell area and in a much larger 'Northern Basin', which included the present district, and which was separated from the south by a chalk ridge. Part of the Northern Basin, excluding the Norwich district, was a depositional basin in Pre-Ludhamian and Ludhamian times. Both basins, except for the area of the present Norfolk Coast, then subsided to receive sediments during the Thurnian, Antian, Baventian and Bramertonian and became linked during the Pastonian Stage. Funnell and others (1979) recognised faunal communities and facies assemblages within the Norwich Crag, which vary laterally to accord with the conditions of deposition.

Regional stratigraphy

The successive terminologies applied to the stratigraphy of the Crags are summarised in (Table 3). For the purpose of this account the Norwich Crag exposed in the district is regarded as being Bramertonian in age and is therefore within the Lower Pleistocene (after Mitchell and others, 1973). It should be noted however, that Funnell (in Curry and others, 1978, p.56) recognised that ' ...possibly part but probably not all of the Norwich Crag Formation...' should be considered as of Pliocene age.

The oldest Pliocene/Pleistocene sediments recorded in East Anglia are marine sands and intertidal silts and clays, which have been recovered from near the base of the Stradbroke Trough in Suffolk. These sediments, of 'Pre-Ludhamian' age (West, 1961a), are correlated with the Red Crag of East Suffolk, which flanks the Pliocene 'Coralline Crag' at the surface. The first detailed description of the Red Crag was by Charlesworth (1835), who named the deposits on the basis of their highly oxidised appearance.

Drilling to the east of the Norwich Sheet at Ormesby St Margaret has proved intertidal silts of similar age at a depth of 70 m (Cox, 1985a). During these early Crag times the coastline was located close to the eastern boundary of the Sheet but it transgressed westwards into the district during the deposition of the Norwich Crag.

The term 'Norwich Crag' was first introduced by Lyell (in Buckland, 1840). Harmer (1900, 1902) included the Norwich Crag, Chillesford Beds, and the Weybourn Crag in the `Icenian Crag' and subdivided the Red Crag into Waltonian, Newbournian and Butleyan (Table 3). He regarded the Crags as reflecting a progressive deterioration of the climate which culminated in the glaciation of East Anglia. The evidence for this deterioration was the increasing proportion of fossil molluscs which he considered indicative of a cold climate, but this view was not accepted by Cambridge (1977, p.42). Funnell (1961) and West (1961a) studied foraminifera and pollen from the Crags and related their occurrence to alternating temperate and. cold stages. They regarded Harmer's Butleyan, Newbournian, and Waltonian subdivisions as having a strictly local significance and recommended that they should not be used in a stratigraphical sense. A number of authors have extended the pollen-based zonal scheme (Funnell and West, 1962; Norton, 1970; Norton and Beck, 1972; Norton and Spaink, 1973; West and Norton, 1974; Funnell, Norton and West, 1979),. but the precise field relations of some of the deposits so correlated remain undetermined.

Funnell (1961, pp.348–349) regarded the Ludhamian and Thurnian deposits found in the Ludham Pilot Borehole, east of the present district, as climatically distinct from the Norwich Crag, in which he included the Antian, Baventian and Pastonian stages. The Norwich Crag sequence recorded in the Ludham Borehole is only partly represented in the vicinity of Norwich. The subsequent stratigraphical classification of the Crags (Table 3) proposed by Funnell and West in 1977 was modified by them in a paper with Norton (1979), in which they define the Crag at Bramerton as the Type Section of the 'Bramertonian' Stage (Norwich Crag). Both the Westleton Beds (sensu Hey, 1967) and the Chillesford Beds of Suffolk are now regarded as correlatives of the Bramertonian Norwich Crag.

Hey (1980, p.287) correlated high-level, quartzite-rich fluvial gravels — the 'Westland Green Gravels' Member of the Kesgrave Sands and Gravels — with a marine conglomerate of Pre-Pastonian age at Beeston described by West (1980). Hey listed six localities (1980, table 1) in the present district at which these gravels are represented, implying that the marine conditions of the. Norwich Crag gave way to terrestrial deposition of fluvial gravels.

Chapter 4 Superficial Deposits or Drift (Pleistocene and Recent)

Pleistocene chronology in Britain is the subject of much debate and the classical stages enumerated by Mitchell and others (1973) continue to be modified, the evidence from East Anglia being critical to many of the arguments. To understand the history of the post-Crag deposits of the district it is necessary to examine the regional stratigraphical relations. Various interpretations have been placed on these relations due to the occurrence of some of the sediments in a complex system of deep 'buried' channels. These have been proved to be a feature of the district by the records of the many wells and boreholes sunk for water supply and other purposes and are illustrated in (Figure 7). The unconformable contacts between the various sediments infilling the channels represent gaps in the sedimentary record which are commonly of uncertain stratigraphical significance.

Subsequent to the completion of the survey of the Norwich Sheet, a Regional Geological Survey of East Anglia (Institute of Geological Sciences, 1985) was mounted and supplemented the earlier work. The combined research has resulted in the recognition that the sedimentary sequence described below is representative of the post-Crag Pleistocene period. The descriptions of the distribution and lithologies of the sediments are given in the ascending order of deposition determined from their field relations (Figure 10). For convenience, the deposits have been grouped into pre-Anglian, Anglian and post-Anglian (Hoxnian–Flandrian) categories. The relationship between the members of this sequence and the drift deposits depicted on the 1:50 000 Norwich Sheet is shown in the footnotes to the table shown on the inside front cover.

Pre-Anglian

Fluvial deposits

These widespread fluvial gravels contain quartz, quartzite and flint pebbles in a medium-grained, quartz sand with sparse igneous pebbles. A rich literature is associated with them and their relations with other Pleistocene deposits have been debated extensively. It is now thought that their deposition may extend from the pre-Pastonian through the Beestonian to the Cromerian Stage, although it may have ceased at the end of the Beestonian (Table 3).

Wood (1866) separated a suite of quartz-rich gravels from the Norwich Crag, regarding them as a discrete formation which he termed the `Bure Valley Beds'. This separation was maintained by Prestwich (1871) who introduced the name `Westleton Beds' for strata in Suffolk which he correlated with the Bure Valley Beds. However, some subsequent workers (including Woodward, 1882; Reid, 1882; Whitaker and Dalton. 1887) were not convinced by Prestwich's correlation and used non-committal terms such as 'Pebbly Gravel' and 'Pebble Series' to describe the formation. Woodward (1882) equated the Bure Valley Beds with a shelly sequence at Wroxham [TG 2721 1602], some 2 km north of the district. However, the lithology at Wroxham differs from other 'Pebbly Gravel' deposits and generally resembles the lowest beds of the Norwich Crag, of Bramertonian age, although the fossil molluscs from Wroxham do not provide sufficient evidence to correlate the Wroxham and Bramerton deposits (Funnell and others, 1979).

The stratigraphy of these gravels has been further complicated by the introduction to East Anglia of the term `Westland Green Gravels' (Hey, 1980). In addition to a preponderance of quartz and quartzite in that formation, Hey records rhyolites and other leucrocratic igneous rocks. Gravels containing pebbles of that petrology have been recognised in the vicinity of Norwich at Eaton Golf Course [TG 215 059] and at Swardeston to the south-west, at Caistor St Edmund [TG 239 046] and Flordon [TM 192 968] to the south, at Catton Brickpit [TG 234 130] to the north, at Colman's (Whitehouse) Whitlingham Pit [TG 267 076] in the east, and in the Rackheath area [TG 270 145] to the north-east.

More recently, Bridge and Hopson (1985) have shown that quartz/quartzite gravels occur at several levels within the Pleistocene sequence. By analysing the fine-grained component ( + 4 – 8 mm) of this group of gravels which precede the Lowestoft Till but post-date the marine Crags, they have divided them into an early pre-Anglian sand and gravel — probably equivalent to the `Kesgrave Formation' of Rose and Allen (1977)—and a younger (Anglian) outwash group associated with the advancing ice sheet of the North Sea Drift. The outwash deposits differ only in their minor component of Scandinavian indicator pebbles. Bridge and Hopson (1985) concluded that these deposits probably derived a large proportion of their coarse gravel fraction directly from the pre-Anglian sediments; they saw the local occurrence in them of stable detrital mineral grains, which are characteristic of the older sands and gravels, as supporting this supposition.

The lower, rounded-flint gravels at Flordon [TM 177 975] are probably of Bramertonian age, whilst the content of the quartzite-rich gravel overlying them appears, according to the criteria of Bridge and Hopson, to be consistent with that of the pre-Anglian sand and gravel. The gravels at Caistor St Edmund [TG 239 046] similarly comprise a ?Bramertonian beach deposit and an overlying fluvial sequence of pre-Anglian age.

The provenance of this distinctive suite of gravels has long been in dispute. Prestwich (1890) suggested that the quartz and quartzite pebbles came from Belgium and the rounded flints from the Tertiary rocks of Kent, Belgium and northern France: Harmer (1910b) considered that the source was hidden beneath the North Sea. However, offshore surveys in the North Sea have not revealed an adequate source of similar rocks and Harmer's view should now probably be discounted. Hey (1980) has interpreted the deposits as originating from a proto-Thames which extended from the London Basin across Essex, Suffolk and Norfolk. More recently Hopson and Bridge (1987) have suggested that a river system draining the East Midlands is the source. Insufficent evidence is yet available to warrant endorsement of either suggestion. It is clear, however, that at least two periods of quartz/quartzite pebble gravel deposition followed the Bramertonian and that one of these is represented by widespread braided-stream deposition over much of the eastern half of the present district.

At the time of the field survey the fluvial quartz/quarzite gravels were either included as a part of the Norwich Crag, or mapped as Glacial Sand and Gravel and are shown as such on the 1:50 000 Norwich Sheet. It is now recognised that these latter may also include a component of outwash material from the Anglian North Sea Drift.

Anglian

Norwich Brickearth

The distribution of the Norwich Brickearth is limited to the north-eastern quadrant of the district (Figure 2). The base of the formation is planar, although small channels and washouts may be present. The formation suffered considerable erosion by the action of the ice sheet which emplaced the Chalky Boulder Clay and in the past may have been considerably more extensive than now. The type section of the formation at Catton Old Brickpit (Plate 3) is no longer exposed but the Norwich Brickearth can be seen in excavations in the north and east of Norwich City. At the surface the deposit appears as a brown, decalcified sandy clay with small, scattered, ochreous and Triassic-derived quartz pebbles and quartzite fragments, as well as a small component of chalk. Laminations are common and are associated with cross-bedded, sandy layers and lenses. Seen in excavations above the water table, the sandy clay is oxidised to a rusty brown and contains thin stringers and lenses of sand and scattered, well rounded pebbles of flint, quartz and some chalk. Funnell recorded (in West, 1961b) that below the water table the formation is grey in colour.

The Norwich Brickearth within the district occurs as a single sheet ranging from 3 to 6 m in thickness. Cross-bedding and wash-outs have been recorded in this Brickearth at Upper Hellesdon [TG 2200 1150] and Old Catton [TG 2337 1304], whereas to the north-east of Norwich, sections in the formation show a structureless loam containing scattered erratics. Boswell (1916) recognised a variety of igneous erratics of Scandinavian origin as being diagnostic of the Brickearth; these included rhomb-porphyries, mica-schists, gneisses and granitic rocks. Pipe-trenches excavated from north-east of Norwich towards the Norfolk coast at Bacton showed that the erratic content, which increases towards the coast, also includes chalk pebbles. Bridge and Hopson (1985) found the + 4–8 mm gravel fraction to contain flint (54 per cent), vein quartz (24 per cent) and quartzite (8 per cent), with small amounts of chalk, shell debris and igneous materials.

Harmer (1902) considered that the Norwich Brickearth was formed in a glacial lake impounded by the ice that deposited the Cromer Till. Whilst the laminated Brickearth with its cross-bedding and wash-outs may have formed in a temporary pro-glacial lake, it is generally supposed that most of the deposition was directly from ice as a virtually structureless, lodgement till.

West of Norwich the relationship between the Chalky Boulder Clay (Boulder Clay of the 1:50 000 Norwich Sheet) and the Norwich Brickearth is obscured by spreads of thick outwash deposits (Glacial Sand and Gravel) up to 5 km wide. To the east of the City this outwash is considerably reduced in both thickness and extent until, at the confluence of the Yare and the Wensum, the outcrops of the Chalky Boulder Clay and Norwich Brickearth are separated only by the 1 km width of the Yare valley. Within the district these two formations have not been recorded in the same section.

Corton Sands

These well sorted, medium- and fine-grained quartz sands occur only in the east of the district and are at their thickest (up to 10 m) in the Rackheath area. They are shown on the 1:50 000 map as Glacial Sand and Gravel and are not distinguished from the Lowestoft Till Outwash described below. The sands were termed 'Middle Glacial' by Woodward (1882), who regarded them as older than the Chalky Boulder Clay and younger than the Norwich Brickearth. In the cliff section at Corton, north of Lowestoft, the sands do indeed lie between the Chalky Boulder Clay and the Brickearth (Banham, 1971), but recent comparative studies of the heavy mineral content and the fine gravel component led Bridge and Hopson (1985) to conclude that the Corton Sands were derived as outwash from the Norwich Brick-earth.

As well as around Rackheath, representatives of the Corton Sands are present at Longdale [TG 155 114] near Bas-ton, where well sorted, cross-bedded sands are overlain by angular flint gravels; also at Caistor St Edmund [TG 239 046]. At the latter site `U'-shaped burrows are present in ripple-drifted, medium-grained sand, indicating a possible marine or brackish environment. Locally, thin clays have been recorded within the sand sequence. One such clay in a gravel pit south of Ringland [TG 150 123] contained carbonaceous matter and roots, but no pollen. Temporary exposures were seen during the construction of the Norwich Ring-road west of Mile Cross [TG 207 106]. Two metres of well sorted, medium-grained, strongly cross-bedded sand overlay a quartzose gravel which had been deposited in the shallow channels of a braided stream. The quartzite gravel was possibly derived from the Norwich Brickearth which is present at the surface 0.5 km north-east of this locality.

Chalky Boulder Clay or Lowestoft Till

The name 'Chalky Boulder Clay' was introduced by Harmer (1902) and, as a descriptive term, can be applied to the deposit cropping out over some three quarters of the district: the formation is now generally equated with the Lowestoft Till and is depicted on the 1:50 000 Norwich Sheet simply as Boulder Clay. Much of the west, centre and south of the district comprises a gently dissected, undulating, boulder clay plain, broken only by small patches of Glacial

Sand and Gravel and forming part of the Chalky Boulder Clay plateau of East Anglia (Bristow and Cox, 1973, fig.1). `Marl' pits are common on this plateau, especially near the more extensive spreads of sand and gravel, where the excavated chalky clay was used to give both 'body' and lime to the 'hungry' sandy soils.

Drilling records indicate that the Chalky Boulder Clay is commonly about 30 m thick. At the surface this till varies from a deeply weathered, sandy, reddish brown, flinty clay in which chalk fragments occur only below the main zone of weathering (Plate 4), to a slightly weathered, stiff, brownish grey, flinty clay, with chalk fragments extending almost to the surface and commonly exposed by shallow ploughing. In an unoxidised, unweathered state the colour can vary from bluish grey, through greenish grey to black. Weathered or unweathered, the clay is tenacious and poorly permeable. Chalk and flint of various colours, including pale grey, brown, black and red, are the most common pebbles.

The sandy variety of till is most common in the north and north-east of the district, adjoining its boundaries with the main outcrops of Glacial Sand and Gravel. Sections exposed in pipeline trenches commonly showed up to 0.5 m of soil on 0.1 –1.0 m of rusty-brown, decalcified sandy clay resting upon brownish-grey, mottled clay, with abundant chalk fragments ranging in size from less than a millimetre to large rounded blocks. Locally, cryoturbation appears to have resulted in mixing of the sand and clay. The contact between the decalcified, sandy clay and the stiff, unweathered, chalky clay can be highly irregular, due partly to uneven advance of the leaching front and partly to cryoturbation. The lower surface of the leached zone can be lobate, with pebbles aligned parallel to the margins of the lobes. Cryoturbation structures affecting the Chalky Boulder Clay and the top of the underlying Upper Chalk are exposed in a pit at Keswick (Plate 6).

The bluish grey matrix of the stiff Chalky Boulder Clay was thought by earlier workers (e.g. Harmer, 1902), to have originated from the Jurassic clays traversed by the ice sheet whose lodgement till it represents. Recent research, however, indicates that the mechanical composition of the matrix of the till is unlike that of the Mesozoic clays, and Perrin and others (1973) suggest that the source is to be found in the sediments beneath the North Sea. Most of the quartz and quartzite pebbles in the till, and the included brown-stained sand, are probably derived directly from the Triassic outcrops of eastern England or from similar material on the floor of the North Sea and the Wash.

Other erratics, ranging up to 30 cm in size, include fragments of Carstone, Kimmeridge Clay, Jurassic limestones and ironstone, Jurassic fossils including belemnites and Gryphaea incurva, indeterminate sandstones (some probably Carboniferous in age), and deeply weathered igneous and metamorphic rocks. Locally chalk becomes the dominant constituent of the boulder clay and the deposit then forms a mass of re-constituted chalk with rare erratics of other rock types.

Lowestoft Till Outwash

These coarse, outwash gravels, classified on the 1:50 000 Norwich Sheet as Glacial Sand and Gravel, are commonly crudely stratified, with the appearance of torrent gravels (Plate 5). Flint is the dominant constituent, with only minor quanitities of quartz and quartzites. Large flints may appear completely unweathered but there is great variation in the colour, size and degree of weathering of the constituents. Sands associated with the gravels are commonly pebbly and cross-stratified. The main outwash gravels are generally about 25 m thick, but there are also smaller masses of sand and gravel, believed to be of englacial origin, that rarely exceed 12 m in thickness. These latter masses are also cross-bedded and may contain chalk blocks up to 30 cm long, although most of the pebbles are medium-sized flints. Patches of laminated clays and of fine, chalk gravel have also been recorded in these supposed englacial masses.

Hoxnian–Flandrian

Hoxnian Interglacial deposits

Immediately following the retreat of the ice sheet which deposited the Chalky Boulder Clay, the drainage in the region is thought to have developed along hollows formed on the surface of the newly-deposited boulder clay which reflected the subglafial topography. Laminated, silty clays with thin layers of peat, now indurated, were deposited in small lakes in these hollows. At Dunston Common in the valley of the Tas [TG 227 027] 16.2 m of such deposits have been recorded (Figure 12), and 8.1 m of similar material have been recovered from a borehole south of Barford in the Tiffey valley [TG 1114 0692] (Cox and Nickless, 1972, fig.7) (Appendix 1).

The geological setting of these deposits has been described elsewhere (Cox and Nickless, 1972; Phillips, 1976; Cox, 1985a). Comparison of the pollen assemblages of the Dunston Common and Barford deposits with those from Hoxne (West, 1956) and Marks Tey (Turner, 1970), led Phillips (1976) to describe them as of Hoxnian type. The relevant zonal sequences are summarised in (Table 4).

The gravels form a wedge stretching north-westwards from Keswick, through Cringleford, Colne and Easton to Ringland. That line, extended north-eastwards from Keswick to Thorpe St Andrew, is thought to define the maximum northward extent of the Chalky Boulder Clay ice sheet in this district (Cox and Nickless, 1972; Cox, 1985a). Boulton and others (1984), following Nickless (1971) and Cox and Nickless (loc cit), have suggested that these outwash gravels were deposited in a zone situated between the two penecontemporaneous ice sheets they envisaged as responsible for the emplacement of the Chalky Boulder Clay and the Norwich Brickearth. A possible sequence of events leading to this development is illustrated in (Figure 11).

Coarse, cobble-sized, orange-brown, 'cannon shot' gravels occur at a few localities in layers up to 6 m thick. They are poorly sorted, with many fresh flint fragments and much clay in their matrix. A distinctive 'cannon shot' gravel is overlain by Chalky Boulder Clay at Wymondham [TG 115 014], but rests on the same formation at Attleborough [TM 045 956]. Locally, these gravels form north-east-trending elongate spreads on top of the main outwash deposits, as at Wymondham.

Solifluxion deposits and First Terrace

The flora from the lacustrine clays indicate a return to polar conditions at the end of the Hoxnian Interglacial, but few localities have been identified at which deposits can be assigned to this period with any confidence. However, Cox (1985a, b) has described solifluxion deposits thought to have been formed during this cold phase and recovered from below Ipswichian Interglacial silts at Intwood Hall (Figure 13) and referred to in more detail below. Extensive gravel spreads having terrace form (depicted on the 1:50 000 Norwich Sheet as River Gravels of the First Terrace) flank the present valleys and may also have been deposited in this period. However, the evidence is equivocal, as, for example, the uncertain age of the angular flint gravels and sands at Dunston Common, which may be partly outwash materials.

Ipswichian Interglacial deposits

At Intwood Hall [TG 199 043], in the valley of a minor tributary of the Yare, some 8–9 m of peaty silts are associated with both shelly and clean sands lying beneath gravels and alluvium (Figure 13). Similar deposits occur at Elsing in the Wensum valley, 4 km north of the sheet boundary. The silts appear to infill earlier channels within the present day valleys and, at Elsing, were some 20 m thick. Samples from the boreholes at Intwood Hall were analysed for pollen assemblages which indicated an Ipswichian age (Dr S Peglar, personal communication).

River gravels

These poorly sorted gravels, rarely more than 13 m thick in-fill all the major modern valleys. They are thought to have been deposited at a time of greatly increased surface run-off when an ice sheet covered much of Britain, but not this part  of Norfolk during the Devensian. These gravels are not distinguished on the 1:50 000 Norwich Sheet.

Head

The effects of weathering, including that during a period of permafrost, have caused a widespread pebbly, sandy clay, about 1 m thick, to blanket much of the region. A large element of wind-blown material is incorporated into the deposit, which is not depicted on the published map.

Alluvium

Alluvium is present in the valleys of all the rivers and their tributaries, locally forming ill-drained, reedy tracts in the flood plains. It is generally composed of silt or clay, although locally it includes peat or fine gravel. In the higher reaches of the streams the alluvium may be just over 1 m thick, whereas around Norwich up to 5 m may occur. The alluvium, still forming at the present day, is commonly underlain by gravels, the deposition of which may have begun in the late Devensian.

Chapter 5 Economic geology

Industrial minerals and engineering geology

Brick clays

Brick-making has not been a major industry in the district, although the Norwich Brickearth, as its name implies, has been used in the manufacture of bricks, tiles and agricultural pipeware. The variable sand content in the formation precluded its development as a major resource. The last brickpit to use the Norwich Brickearth as raw material was at Catton, where the brickearth was made into a distinctive red brick for a specialist market by Messrs Ryump: the work ceased in 1969.

The Chalky Boulder Clay of the district has also been used, with added straw, to make porous bricks and blocks which provided a useful construction material for barns and other agricultural purposes, as, for example, at Shotesham [TM 242 993]. From Medieval times, loosely-woven hazel laths plastered with weathered chalky boulder clay (`Wattle and daub') have been used in the district for the construction of walls in timber-framed cottages, made weather-proof with tar wash.

Sand and gravel

Several of the Superficial Deposits described above are important sources of aggregate for the construction industry. The resources are considered briefly below, but fuller details may be obtained from three reports (Nickless, 1971, 1973a, b), which record the results of investigations into the resources of construction aggregates in those parts of of the district lying north and east of Wymondham, but excluding the Norwich urban area.

At the time of the investigations, four assessment criteria had to be met before a deposit was considered as a potential source of aggregate: the average thickness of the deposit had to be at least 1 m, the ratio of overburden to aggregate could not exceed 3:1, the proportion of fine material ( < 0.063 mm) could not exceed 40 per cent and the aggregate had to be within 25 m of the surface. On that basis, the major resources were in the Glacial Sand and Gravel as depicted on the 1:50 000 geological map, with a small potential in the Norwich Crag and the River Gravels, including the First Terrace gravels and some of the gravels beneath the flood-plain deposits.

Collating the results of the investigations given in the three assessment reports, it is estimated that within the 225 km² examined, the total resources amount to 1400 million cubic metres (2100 million tonnes). Of that, well over 90 per cent —1300 million cubic metres (2000 million tonnes) — are found in the Glacial Sand and Gravel and the Norwich Crag, the remainder in the River Gravels. These estimates preclude consideration of non-geological factors which might inhibit the development of resources.

Chalk and flint

The soft white limestone of the Chalk has been worked at many localities in the district and the valleys of the Yare and the Wensum are pitted with disused, overgrown chalk quarries. Large tonnages of the limestone were formerly burnt to make lime for agricultural dressing. Woodward (1882) recorded the use of the Chalk for the manufacture of whiting and linseed-oil putty, and in the cement industry — practices likely to have continued into the present century. In recent times the local lime trade has diminished considerably so far as the number of working pits is concerned, and at the time of the survey of the Norwich Sheet (1965–69) only the pits at Keswick and Caistor St Edmund were operating. The chalk is no longer burnt, but is merely crushed and dried before being bagged for use.

The low strength characteristics of the chalk enable it to be excavated by mechanical diggers, but the numerous flints which occur in the Upper Chalk have to be separated by screening. Today, the flints are used chiefly for hard core, although small quantities meet a demand for decorative purposes. In the past, flints derived directly from the Chalk and indirectly from the Superficial Deposits, were used extensively for building stone and many fine examples of the flint knapper's art can be seen in the historic buildings, particularly the churches, in Norwich and its surrounding villages. Small amounts of flint may have been exported from the district for use in the ceramics industry, but better documented is the local manufacture of gun-flints at Attoe's Pit, Catton [TG 230 110], so interestingly described by Skertchley (1879, pp.10–11.)

A common method of extracting Chalk and flints from beneath Norwich City was by means of mines and underground tunnels. At several sites headings were con-structured from within a quarry, and individual galleries were excavated on a grid pattern extending into the hillside; the 'pillar and stall' method of working was usual. Although many of these cavities have been opened up and surveyed, it is by no means certain that others do not exist. The mines are of various ages, and probably range from Neolithic to Roman.

In some parts of Norwich the mines pose a continuing subsidence hazard. In particular, during or after phases of housing and road development, parts of the old tunnels have collapsed causing considerable damage to services and buildings. The most serious event occurred in 1936, when a complete house in Merton Road subsided into a cavity and two people were killed. The localities at which mines are known to be present, or at which subsidences have been recorded, are shown in (Figure 14). It is emphasised that mines other than those shown may exist, and also that the total areal extent of the recorded workings is riot known accurately. The map was compiled largely from records of the Norwich City Engineer's Department and from Woodward (1882). Subsidences and underground workings have been recorded from areas outside that shown on (Figure 14).

Hydrogeology and water supply

Groundwater contributes significantly to the water supply of the district and licensed abstraction of groundwater from permeable rocks totals some 15–20 megalitres (million litres) per year. This constitutes approximately 30 per cent of the total licensed abstraction, the balance being extracted directly from rivers, principally the Wensum and the Yare. These in turn rely for their base-flows on the natural discharge of groundwater from permeable formations such as the Chalk, the Norwich Crag and the Glacial Sand and Gravel. Accordingly, the presence of these formations is doubly important for water supply. No surface reservoirs within the district are used for public water supply.

Previous published information on the hydrogeology of the region is contained in Taylor and Morant (1870), Woodward (1882), Whitaker (1921), Woodland (1946), meson (1962), Anon. (1963), Anon. (1971), Harvey and others (1973), Moseley and others (1976). The water supply potential of the various formations is described briefly below, but the reader is referred to Harvey and others (1973) for the details of approximately 600 wells and boreholes registered within the district and to Moseley and others (1976) for information on the regional occurrence of groundwater and its chemical quality.

River gravels and Alluvium

In the past, domestic supplies were obtained from shallow shafts in the terrace gravels, a'•luvium and suballuvial gravels present in the river valleys. Such wells are prone to contamination and failure and are generally no longer used.

Chalky Boulder Clay (Lowestoft Till)

This formation is depicted on the 1:50 000 Norwich Sheet as Boulder Clay. Although it incorporates irregular masses and lenses of sand and gravel, the boulder clay is essentially only semi-permeable and it confines groundwater in the underlying Chalk and Norwich Crag under artesian pressure. Nevertheless, it has been estimated that the mean annual infiltration to the Chalk is 64 mm (Anon. 1971): this constitutes 32 per cent of the residual rainfall (precipitation minus evapo-transpiration).

As a source of water supply the Chalky Boulder Clay is now of minor importance, although historically it was significant in the rural areas. Shafts, generally about 1.5 m in diameter, yield small-scale supplies which are probably derived from sandy intercalations within the boulder clay. Domestic supplies were generally derived from shafts 6–8 m deep, but those for agricultural or horticultural purposes were sunk to depths of 25 m to obtain yields of up to 45 m³/-day. The water is generally hard and commonly ferruginous.

Glacial Sand and Gravel

These arenaceous sediments are highly permeable and it has been estimated (Anon. 1971) that they may permit over 90 per cent of the residual rainfall to infiltrate to the underlying Chalk or Norwich Crag (where no Boulder Clay intervenes). The formation has been little used for water supply, probably due to the difficulties of sinking and completing wells in such unconsolidated sediments.

Norwich Brickearth

These sandy clays are poorly permeable, but are thought to constitute only a partial barrier to infiltration into the Norwich Crag and Chalk. In general the formation lies within the unsaturated zone and does not constitute a source of water supply.

Norwich Crag

Despite the high permeability of the sands and gravels of the Norwich Crag, the formation has not been used as a source of supply within the district, again probably due to the problem of constructing wells in such poorly consolidated material.

Chalk

The Chalk is the principal aquifer in the region. Although the formation is highly porous with primary porosity generally greater than 30 per cent, its intergranular permeability is low (generally less than 10⁻³m/d), and groundwater flow takes place dominantly through fissures in the rock. The bulk of the flow to wells is thought to occur within the upper 60 m of the formation.

The configuration of the minimum groundwater level in the Chalk aquifer within the region is broadly similar to the topography (Harvey and others, 1973, fig.3; Moseley and others, 1976). Groundwater levels are highest in the west and south-west, where they generally exceed 40 m OD, and fall to the north-east to less than 5 m OD in the Wensum valley. Seasonal fluctuations in the groundwater levels are greatest in the south and west of the sheet, but are still less than 2 m. Overflowing artesian conditions may be encountered at a number of low-lying localities. Yields to wells in the Chalk are generally greatest at river sites (Ineson, 1962), while, in areas covered by glacial drift, maximum yields commonly occur along the lines of buried channels. Generally, however, most sites in the interfluve areas yield only small supplies, ranging from 0.5 to 1.01/s from a borehole of 100 mm diameter to 8.0l/s from one of 250 mm diameter.

The chemical quality of the groundwater in the Chalk of the Norwich district is generally satisfactory for most pur poses, although the water is hard and locally ferruginous. Recent problems associated with nitrate contamination of groundwater have been investigated at Colney, as part of a larger national programme (Foster and others, 1986). Supplies derived from the Chalk beneath boulder clay have carbonate hardness values ranging between 250 and 350 mg/l, but elsewhere values are generally less than 200 mg/l. Non-carbonate hardness is generally in the range 20–100 mg/l. Anomalously high values for both carbonate and non-carbonate hardness, as well as for the chloride and sulphate ions, have been recorded from some riverside wells in Norwich.

References

ANON. 1963. East Anglian Rivers Hydrological Survey. Ministry of Housing and Local Government. (London: HMSO.)

ANON. 1971. Water Resources Act 1969-First Survey of Water Resources and Demands. East Suffolk and Norfolk River Authority.

ANON. 1976. Production of aggregates in Great Britain, 1975. Department of the Environment. (London: HMSO.)

ARKELL, W J. 1933. The Jurassic System in Great Britain. (Oxford: Clarendon Press.)

ALLSOP, J M. 1984. Geophysical appraisal of a Carboniferous basin in north-east Norfolk, England. Proc. Geol. Assoc. , Vol. 95, 175–180.

ALLSOP, J M. and JONES, C M. 1981. A pre-Permian paleogeological map of the East Midlands and East Anglia. Trans. Leicestershire Lit. Philos. Soc., Vol. 75, 28–33.

BADEN-POWELL, D F W. 1948. The chalky boulder clays of Norfolk and Suffolk. Geol. Mag., Vol. 85, 279–296.

BANHAM, P H. 1971. Pleistocene beds at Corton, Suffolk. Geol. Mag., 108, 281–285.

BENNETT, F J. 1884. The geology of the country around Attleborough, Watton and Wymondham. Mem. Geol. Surv. G.B.

BLAKE, H. 1888. Geology of the country around East Dereham. Mem. Geol. Surv. G.B.

BLAKE, H. 1890. The geology of the country near Yarmouth and Lowestoft. Mem. Geol. Surv. G.B.

BOSWELL, P G H. 1916. The petrology of the North Sea Drift and Upper Glacial brick-earths in East Anglia. Proc. Geol. Assoc. , Vol. 27, 79–98.

BOULTON, G S, COX, F C, HART, J, and THORNTON, M 1985. The glacial geology of Norfolk. Bull. Geol. Soc. Norfolk, Vol. 34, 103–122.

BRIDGE, D, McC, and HOPSON, P M. 1985. Fine gravel, heavy mineral and grain-size analyses of Mid-Pleistocene glacial deposits in the lower Waveney valley, East Anglia. Modern Geol., Vol. 9, 129–144.

BRITISH GEOLOGICAL SURVEY. 1987. Directory of mines and quarries. (Keyworth, Nottingham: British Geological Survey.)

BRISTOW, C R, and Cox, F C. 1973. The Gipping Till: a reappraisal of East Anglian glacial stratigraphy. J. Geol. Soc. London, Vol. 129, 1–37.

BROMLEY, R G, SCHUTZ, M G, and PEAKE, N B. 1975. Paramoudras: giant flints, long burrows and the early diagenesis of chalks. K. Danske Vidensk. Selsk. Biol. Skr., No. 20.

BRYDONE, R M. 1906. Further notes on the stratigraphy and fauna of the Trimmington Chalk. Geol. Mag. , Vol. 43, 13–22, 72–78, 124–131, 289–300.

BRYDONE, R M. 1930. The 'Norwich Chalk'. Trans. Norfolk & Norwich Nat. Soc. , Vol. 13, 47–49.

BRYDONE, R M. 1932. The course of Marsupites and Uintacrinus across Norfolk (with a note on the Basal Norwich Chalk). Trans. Norfolk & Norwich Nat. Soc., Vol. 13, 115–118.

BRYDONE, R M. 1933. The zone of granulated Actinocamax in East Anglia. Trans. Norfolk & Norwich Nat. Soc. , Vol. 13, 285–293.

BRYDONE, R M. 1938. On correlation of some of the Norfolk exposures of Chalk with Belemnitella Mucronata. (London.)

BUCKLAND, W. 1840. Address to the Geological Society. Proc. Geol. Soc. London, Vol. 3, 210–268.

CAMBRIDGE, P G. 1977. Whatever happened to the Boytonian? A review of the marine Plio-Pleistocene of the southern North Sea basin. Bull. Geol. Soc. Norfolk, Vol. 29, 23–45.

CHARLESWORTH, E. 1835. Observations on the Crag-formation and its organic remains: with a view to establishing a division of the Tertiary strata overlying the London Clay in Suffolk. Philos. Mag. , (3), Vol. 7, 81–94.

CHARLESWORTH, E. 1837. A notice of the remains of vertebrated animals found in the Tertiary beds of Norfolk and Suffolk. Br. Assoc. Adv. Sci., Rep. for 1836 (Bristol).

CHARLESWORTH, J K. 1957. The Quaternary era with special refernce to its glaciation. (London: Edward Arnold.)

CHROSTON, P N. 1985. A seismic refraction line across Norfolk. Geol. Mag., Vol. 122, 397–401.

CHROSTON, P N. and SOLA, M. 1975. The sub-Mesozoic floor in Norfolk. Bull. Geol. Soc. Norfolk, Vol. 27, 3–19.

CHROSTON, P N. and SOLA, M.  1982. Deep boreholes, seismic refraction lines, and the interpretation of gravity anomalies in Norfolk. J. Geol. Soc. London, Vol. 139, 255–264.

COX, F C. 1983. The Gipping Till revisited. 32–42 in The Quaternary in Britain. (Oxford: Pergamon Press.)

COX, F C. 1985a. The East Anglia Regional Geological Survey: an overview. Modern Geol., Vol. 9, 103–115.

COX, F C. 1985b. The tunnel-valleys of Norfolk, East Anglia. Proc. Geol. Assoc. , Vol. 96, 357–369.

COX, F C. and NICKLESS, E F P. 1972. Some aspects of the glacial history of central Norfolk. Bull. Geol. Surv. G.B., No. 42, 79–88.

COX, F C., POOLE, E G, and MCKEOWN, M C. 1975. 1:50 000 Geological Sheet 161 (Norwich). (Institute of Geological Sciences.)

CROMPTON, J. 1862. Notes on deep or artesian wells at Norwich. The Geologist, Vol. 5, 460–462.

CURRY, D, ADAMS, C G, BOULTER, M C, DILLEY, F C, EAMES, F E, FUNNELL, B M, and WELLS, M K. 1978. A correlation of Tertiary rocks in the British Isles. Spec. Rep. Geol. Soc. London, No. 12.

DOWNING, R A. 1959. A note on the Crag in Norfolk. Geol. Mag., Vol. 96, 81–86.

EVANS, A M. 1979. The East Midlands aulacogen of Caledonian age. Mercian Geologist, Vol. 7, 31–42.

FOSTER, S S D, BRIDGE, L R, GEAKE, A K, LAWRENCE, A R, and PARKER, J M. 1986. The groundwater nitrate problem: a summary of research on the impact of argicultural land-use practices on groundwater quality between 1976 and 1985. Hydrogeol. Rep. Br. Geol. Surv. , No. 842.

FUNNELL, B M. 1961. The Palaeogene and early Pleistocene of Norfolk. Trans. Norfolk & Norwich Nat. Soc. , Vol. 19, 340–364.

FUNNELL, B M. and WEST, R G. 1962. The early Pleistocene of Easton Bavents, Suffolk. Q. J. Geol. Soc. London, Vol. 118, 125–141.

FUNNELL, B M. and WEST, R G. 1977. Periglacial Pleistocene deposits of East Anglia. 247–265 in British Quaternary Studies, recent advances. SHOTTON, F W, (editor). (Oxford: Clarendon Press.)

FUNNELL, B M., NORTON, P E P, and WEST, R G. 1979. The Crag at Bramerton, near Norwich, Norfolk. Philos. Trans. R. Soc. London, Series B, Vol. 287, 489–534.

GALLOIS, R W, and MORTER, A A. 1976. The Trunch Borehole. 8–10 in IGS Boreholes 1975. Rep. Inst. Geol. Sci., No. 76/10.

GALLOIS, R W, and MORTER, A A. 1982. The stratigraphy of the Gault of East Anglia. Proc. Geol. Assoc. , Vol. 93, No. 4, 351–368.

HARMER, F W. 1899. On a proposed new classification of the Pliocene deposits of the East of England. Rep. Br. Assoc. Adv. Sci. (Dover) Trans. Sec. C., 751–753.

HARMER, F W.1900. The Pliocene deposits of the East of England-Part II: The Crag of Essex (Waltonian) and its relation to that of Suffolk and Norfolk. Q. J. Geol. Soc. London, Vol. 56, 705–738.

HARMER, F W.1902. A sketch of the later Tertiary history of East Anglia. Proc. Geol. Assoc., Vol. 17, 416–439.

HARMER, F W.1910a. The Pleistocene period in the eastern counties of England. Proc. Geol. Assoc. , Jubilee Volume, 103–123.

HARMER, F W.1910b. The glacial deposits of Norfolk and Suffolk. Trans. Norfolk & Norwich Nat. Soc., Vol. 9, 108–133.

HARMER, F W.1910c. The Pliocene deposits of the eastern counties of England. Proc. Geol. Assoc., Jubilee Volume, 86–102.

HARMER, F W. 1924. The Pliocene molluscs of Great Britain. Vol. II, Pts I-IV, Mon. Palaeontol. Soc. London.

HARVEY, B I, and others. 1973. Records of wells in the area around Norwich: Inventory for one-inch Geological Sheet 161, New Series. Well Inventory Ser. [Metric Units] Inst. Geol. Sci.

HEY, R W. 1967. The Westleton Beds reconsidered. Proc. Geol. Assoc. , Vol. 78, 427–445.

HEY, R W. 1980. Equivalents of the Westland Green Gravels in Essex and East Anglia. Proc. Geol. Assoc. , Vol. 91, 279–290.

HOPSON, P M, and BRIDGE, D McC. 1987. Middle Pleistocene stratigraphy in the Lower Waveney valley, East Anglia. Proc. Geol. Assoc. , Vol. 98, 171–185.

INESON, J. 1962. A hydrogeological study of the permeability of the Chalk. J. Inst. Water Engrs. , Vol. 16, 449–463.

INSTITUTE OF GEOLOGICAL SCIENCES. 1985. Annual report for 1984–85. (Keyworth, Nottinghamshire: British Geological Survey.)

KENT, P E. 1947. A deep boring at North Creake, Norfolk. Geol. Mag, Vol. 84, 2–18.

KENT, P E. 1962. A borehole to basement rocks at Glinton, near Peterborough, Northants. Proc. Geol. Soc. London, No. 1595, 40–42.

KENT, P E. 1968. The buried floor of Eastern England. In The geology of the East Midlands. SYLVESTER-BRADLEY, P C, and FORD, T D (editors). (Leicester: Leicester University Press.)

KITTON, F. 1872. On the spongeous origin of flints. Trans. Norfolk & Norwich Nat. Soc. , Vol. 1, 51–60.

KITTON, F. 1874. Further notes on the spongeous origin of flints. Trans. Norfolk & Norwich Nat. Soc. , Vol. 1, 81.

LE BAS, M J. 1972. Caledonian igneous rocks beneath central and eastern England. Proc. Yorkshire Geol. Soc. , Vol. 39, 71–86.

LINSSER, H. 1968. Transformation of magnetomatic data into tectonic maps by digital template analysis. Geophys. Prospect. , Vol. 16, 170–207.

MITCHELL, G F, PENNY, L F, SHOTTON, F W, and WEST, R G. 1973. A correlation of Quaternary deposits in the British Isles. Spec. Rep. Geol. Soc. London, No. 4.

MOSELEY, R, WOODWARD, C M, DAY, J B W, and LANGSTON, M J. 1976. Hydrogeological Map of Northern East Anglia, Sheets 1 and 2. Hydrogeological Map Series. (Institute of Geological Sciences.)

NICKLESS, E F P. 1971. The sand and gravel resources of the country south-east of Norwich, Norfolk: Description of 1:25 000 resource sheet TG20. Rep. Inst. Geol. Sci. , No. 71/20.

NICKLESS, E F P. 1973a. The sand and gravel rsources of the country around Hethersett, Norfolk: Description of 1:25 000 resource sheet TG10. Rep. Inst. Geol. Sci. , No. 73/4.

NICKLESS, E F P. 1973b. The sand and gravel resources of the country around Attlebridge, Norfolk: Description of 1:25 000 resource sheet TG11. Rep. Inst. Geol. Sci. , No. 73/15.

NORTON, P E P. 1970. The Crag Mollusca-a conspectus. Bull. Soc. Beige Geol. (Paleontologie Hydrologie), Vol. 79, 157–166.

NORTON, P E P. and BECK, R B. 1972. Lower Pleistocene molluscan assemblages and pollen from the Crag of Aldeby (Norfolk) and Easton Bavents (Suffolk). Bull. Geol. Soc. Norfolk, Vol. 22, 4 31

NORTON, P E P. and SPAINK, G. 1973. The earliest occurrence of Macoma Balthica (L.) as a fossil in North Sea deposits. Malacolagia, Vol. 14, 33–37.

PEAKE, N B, and HANCOCK, J M. 1961. The Upper Cretaceous of Norfolk. Trans. Norfolk & Norwich Nat. Soc. , Vol. 19, 293–339.

PERRIN, R M S, DAVIES, H, and FYSH, M D. 1973. Lithology of the Chalky Boulder Clay. Nature, London, Phys. Sci. , Vol. 245, 101–104.

PERRIN, R M S, ROSE, J, and DAVIES, H. 1979. The distribution, variation and origins of pre-Devensian tills in eastern England. Philos. Trans. R. Soc. London, Series B, Vol. 287, 535–550.

PHARAOH, T C, MERRIMAN, R J, WEBB, P C, and BECKINSALE, R D. 1987. The concealed Caledonides of eastern England: preliminary results of a multi-disciplinary study. Proc. Yorkshire Geol. Soc., Vol. 46, 355–369.

PHILLIPS, L. 1976. Pleistocene vegetational history and geology in Norfolk. Philos. Trans. R. Soc. London, Series B, Vol. 275, 215 - 286.

PHILLIPS, L. 1871. On the structure of the Crag-beds of Suffolk and Norfolk, with some observations on their organic remains. Part III-The Norwich Crag and Westleton Beds. Q. J. Geol. Soc. London, Vol. 27, 452–496.

PHILLIPS, L. 1890. On the relation of the Westleton Beds or Pebbly Sands of Suffolk, to those of Norfolk, and of their extension inland; with some observations on the period of the final elevation and denudation of the Weald and of the Thames Valley etc. Q. J. Geol. Soc. London, Vol. 46, 120–154.

REID, C. 1877. On the succession and classification of the beds between the Chalk and the Lower Boulder Clay in the neighbourhood of Cromer. Geol. Mag., Vol. 4, 300–305.

REID, C. 1882. The geology of the country around Cromer. Mem. Geol. Surv. G.B.

ROSE, C B. 1835. A sketch of the geology of west Norfolk. Philos. Mag., Vol. 7, 171–182, 274–279, 370–376.

ROSE, C B. 1836. A sketch of the geology of west Norfolk. Philos. Mag. , Vol. 8, 28–42.

ROSE, J, and ALLEN, P. 1977. Middle Pleistocene stratigraphy in south-east Suffolk. J. Geol. Soc. London, Vol. 133, 83–102.

SHOTTON, F W, (editor). 1977. British Quaternary studies: recent advances. (Oxford: Clarendon Press.)

SKERTCHLEY, S B J. 1879. On the manufacture of gun-flints, the methods of excavating for flint, the age of Palaeolithic Man and the connection between Neolithic art and the gun-flint trade. Mem. Geol. Surv. G.B.

SMITH, N J P, JACKSON, D I, ARMSTRONG, E J, MULHOLLAND, T, JONES, 5, AULD, H A, BULAT, J, SWALLOW, J L, QUINN, N F, OATES, N K, and BENNETT, J R P. 1985. Map 1: Pre-Permian Geology of the United Kingdom (South). Scale 1:1 000 000. (Keyworth, Nottinghamshire: British Geological Survey.)

STRAW, A. 1979. The geomorphological significance of the Wolstonian glaciation of eastern England. Trans. Inst. Br. Geogr., Vol. 4, 540–549.

TAYLOR, R C. 1824. On the Crag strata at Bramerton, near Norwich. Trans. Geol. Soc. London, 2nd ser., Vol. 1, 371–373.

TAYLOR, J E, and MORANT, A W. 1870. The water-bearing strata in the neighbourhood of Norwich. Geol. Mag. , Vol. 4, 119–122.

THURRELL, R G. 1961. The sub-Cretaceous rocks of Norfolk. Trans. Norfolk & Norwich Nat. Soc. , Vol. 19, 271–292.

TURNER, C. 1970. The Middle Pleistocene deposits at Marks Tey, Essex. Philos. Trans. R. Soc. London, Series B, Vol. 257, 373–437.

WEST, R G. 1956. The Quaternary deposits at Hoxne, Suffolk. Philos. Trans. R. Soc. London, Series B, Vol. 239, 265–356.

WEST, R G. 1961a. Vegetational history of the Early Pleistocene of the Royal Society Borehole at Ludham, Norfolk. Proc. R. Soc. London, Series B, Vol. 155, 437–543.

WEST, R G. 1961b. The glacial and interglacial deposits of Norfolk. Trans. Norfolk & Norwich Nat. Soc., Vol. 19, 365–375.

WEST, R G. 1963. Problems of British Quaternary. Proc. Geol. Assoc., 74, 147–186.

WEST, R G. 1970. The glacial and interglacial deposits of Norfolk (2nd edition, with addenda). Trans. Norfolk & Norwich Nat. Soc., Vol. 19, 365–376.

WEST, R G. 1977. Pleistocene geology and biology (2nd edition.) (London: Longman.)

WEST, R G. 1980. The pre-glacial Pleistocene of the Norfolk and Suffolk coasts. (Cambridge: Cambridge University Press.)

WEST, R G. and NORTON, P E P. 1974. The Icenian Crag of the Norfolk and Suffolk coasts. Philos. Trans. R. Soc. London, Series B, Vol. 269, 1–28.

WHITAKER, W, and DALTON, W G. 1887. The geology of the country around Halesworth and Harleston. Mem. Geol. Surv. G.B.

WEST, R G. 1921. The water supply of Norfolk from underground sources. Mem. Geol. Surv. G.B.

WILLS, L J. 1951. A palaeogeographical atlas. (Glasgow: Blackie and Son.)

WEST, R G. 1973. A palaeogeographical map of the Palaeozoic floor below the Upper Permian and Mesozoic formations. Mem. Geol. Soc. London, No. 7.

WEST, R G. 1978. A palaeogeographical map of the Lower Palaeozoic floor below cover of Upper Devonian, Carboniferous and later formations. Mem. Geol. Soc. London, No. 8

WOOD, C J. 1988. The stratigraphy of the Chalk of Norwich. Bull. Geol. Soc. Norfolk, Vol. 38. p. 3 et seq.

WOOD, S V. 1866. On the structure of the Red Crag. Q. J. Geol. Soc. London, Vol. 22, 538–552.

WOOD, S V, (junior). 1880. The New Pliocene period in England. Q. J. Geol. Soc. London, Vol. 36, 457–528.

WOODLAND, A W. 1946. Water supply from underground sources of Cambridge-Ipswich District. (Quarter-inch Geological Sheet 16), Pt X-general discussion. Wartime Pamph. Geol. Surv. G.B., No. 20.

WOODLAND, A W. 1970. The buried tunnel-valleys of East Anglia. Proc. Yorkshire Geol. Soc., Vol. 37, 521–578.

WOODWARD, H B. 1882. Geology of the country around Norwich. Mem. Geol. Surv. G.B. (1881 on title page.)

WOODWARD, S. 1833. An outline of the geology of Norfolk. Norwich.

Appendix 1 Abstracts of selected borehole logs

Boreholes are identified by their registered numbers in the Survey's 1:10 000 sheet registration system.

Barford Borehole (TG10NW/2) [TG 1114 0692] Drilled in 1970 Logged by F C Cox Surface level unrecorded

Carrow Works Borehole (TG20NW/121) [TG 2414 0753] Drilled in ?1862 Logged by Rev. J Crompton (in Whitaker, 1921) Surface level unrecorded

Dunston Common (TG20SW/20) [TG 2270 0267] Drilled 1969 Logged by F C Cox Surface level + 9.6 m

Great Ellingham Borehole (TM09NW/1) [TM 0262 9847] Drilled in 1965 Logged by R W Gallois Surface level + 53.3 m

Rocklands No. 1 Borehole (TL99NE/1) [TL 995 966] Drilled in 1969 Surface level c. + 45.7 m Synopsis given in (Table 1)

Home Farm, Saxlingham Green (TM29NW/18) [TM 2415 9671] Drilled 1951 Surface level + 37.8 m

Fylands Cottages (Dawson's Farm) (TM29NE/5) [TM 2601 9625] Drilled 1950 Surface level + 41.2 m

Appendix 2 List of Geological Survey photographs

Copies of these photographs are deposited for reference in the libraries of the Geological Museum, South Kensington, London SW7 2DE, and of the British Geological Survey, Keyworth. Black and white prints and slides can be supplied, and in addition colour prints and transparencies are available for all the photographs with 5-figure numbers. All numbers belong to Series A. Numbers A5641–A5653 taken by J Rhodes, A11124–A11172 by P E Baker and A11173 by J W Pulsford.

Figures, plates and tables

Figures

(Figure 1) Physical features of the Norwich district.

(Figure 2) Generalised geological map of the Norwich district.

(Figure 3) Contours on the pre-Permian surface in northern East Anglia a) in metres below OD and b) with the base of the Aptian–Albian as datum.

(Figure 4) a) Occurrence of Jurassic rocks and b) thickness of Permo-Triassic rocks in northern East Anglia.

(Figure 5) a) Aeromagnetic and b) Bouguer anomaly maps of northern East Anglia.

(Figure 6) Aeromagnetic and Bouguer anomaly profiles and models for lines shown in (Figure 5).

(Figure 7) Contours on the sub-Drift surface of the Chalk.

(Figure 8) Map showing subdivisions of the Upper Chalk in the eastern part of the district.

(Figure 9) Map showing distribution and key localities of the Norwich Crag in the eastern part of the district.

(Figure 10) Schematic section illustrating relationships within the Superficial Deposits of the district.

(Figure 11) Stages in the glaciation of Norfolk indicating the deposition of outwash sands and gravels (after Cox and Nickless, 1972).

(Figure 12) Borehole sections through Hoxnian Interglacial deposits at Dunston Common (adapted from Cox, 1985).

(Figure 13) Borehole sections through Ipswichian Interglacial deposits at Intwood Hall.

(Figure 14) Approximate locations of known chalk mines and subsidences in central Norwich.

Plates

(Front cover)

(Rear cover)

(Geological succession) Geological sequence in the Norwich district.

(Plate 1) A paramoudra flint 2 m high in Upper Chalk at Colman's Pit, Whitlingham [TG 2678 0766]. (A11127).

(Plate 2) The Norwich Crag Stone Bed; the junction of the shelly Crag sands with the underlying Chalk is marked by a bed of large flints; Colman's Pit, Whitlingham [TG 268 075]. (A11131).

(Plate 3) Norwich Brickearth at Catton Old Brick Pit [TG 233 130]. The deposit consists of pebbly, sandy clay with lenses and laminae of fine sand. (A11136).

(Plate 4) Weathered Chalky Boulder Clay at Intwood Pits [TG 196 043], Intwood Hall. (A11168).

(Plate 5) Cross-bedded Glacial Sand and Gravel (Lowestoft Till Outwash) in a pit at Long Dale [TG 155 110]. (A11140).

(Plate 6) Cryoturbation structures affecting Chalky Boulder Clay and Upper Chalk in a pit at Keswick [TG 212 049]. (A11173).

Tables

(Table 1) Summary of strata penetrated in the Great Ellingham and Rocklands boreholes.

(Table 2) The stratigraphical terminology of the exposed Upper Chalk in the Norwich district.

(Table 3) The stratigraphical terminology of the Pleistocene Crags.

(Table 4) Zones of the Hoxnian Interglacial present at Dunston Common and Barford.

Tables

(Table 1) Summary of strata penetrated in the Great Ellingham and Rocklands boreholes

(Table 2) The stratigraphical terminology of the exposed Upper Chalk in the Norwich district

(Table 4) Zones of the Hoxnian Interglacial present at Dunston Common and Barford