- Email: [email protected]
The non-marine Lower Cretaceous Wealden strata of southern England
Proceedings of the Geologists’ Association 123 (2012) 235–244
Contents lists available at SciVerse ScienceDirect
Proceedings of the Geologists’ Association journal homepage: www.elsevier.com/locate/pgeola
The non-marine Lower Cretaceous Wealden strata of southern England Jonathan D. Radley a,*, Percival Allen b,1 a b
School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Postgraduate Research Institute for Sedimentology, The University of Reading, PO Box 227, Whiteknights, Reading RG6 6AB, UK
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 November 2011 Accepted 6 January 2012 Available online 8 March 2012
The non-marine Lower Cretaceous Wealden strata of the Wessex-Weald Basin (southern England) are introduced, with reference to the depositional model developed by Professor Percival Allen FRS (Allen, 1975). To demonstrate this model and the development of Wealden palaeoenvironments through time, Wealden sites have been selected for the Geological Conservation Review programme. Site selection rationale is briefly outlined. ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Geological Conservation Review Wealden Lower Cretaceous Wessex-Weald Basin Southern England
1. Introduction to the Wealden Following Martin (1828) and other nineteenth century workers, geologists use the term ‘Wealden’ for non-marine sandstone and mudstone-dominated successions of Lower Cretaceous age, that have been documented through north-west Europe (Allen, 1967a) and further afield. The name derives from the Weald, a picturesque area of south-east England where Wealden rocks outcrop. In southern England as a whole, Wealden strata are found in both the largely onshore Weald Sub-basin of south-east England, and the northern part of the partly offshore Wessex Sub-basin of southern and south-west England. These depocentres are effectively separated by the Purbeck-Isle of Wight structure (Allen, 1981; Gale, 2000) and collectively make up the Wessex-Weald Basin (Figs. 1 and 2). The Wealden strata of the Weald Sub-basin outcrop in the counties of Kent, Sussex, Surrey and Hampshire; the Wealden type-area (Topley, 1875; Allen, 1975). The Wessex Subbasin successions are seen on the Isle of Wight and in south Dorset (White, 1921; Arkell, 1947a; Fig. 1). Scattered, poorly exposed patches of Lower Cretaceous strata of Wealden aspect occur along the north-western margin of the Wessex-Weald Basin in the English South Midlands (Arkell, 1947b; Casey and Bristow, 1964; Horton et al., 1995; Fig. 1). In north-eastern England, the coeval Lower Cretaceous strata are wholly marine in origin (Rawson, 1992a,b, 2006).
* Corresponding author. E-mail address: [email protected] (J.D. Radley). 1 Deceased.
The Wealden successions preserved within the Weald and Wessex sub-basins (Fig. 2) differ to varying extents in terms of their relative age, styles of facies architecture, and their enclosed fossil assemblages. To a degree, these differences reflect contrasting tectonic contexts and perhaps their differing climatic histories (Allen, 1981, 1998). Taken as a whole, the southern English Wealden ranges in age from upper Berriasian to lower Aptian, equating to approximately 15 million years of Earth history (Allen and Wimbledon, 1991). Broadly, the Wealden comprises two major facies associations as developed in both southern English sub-basins. These are (a) largely oxidised mudstones, siltstones and fine to coarse-grained sandstones indicating distal meanderplain to proximal braidplain and possible fan settings (arenaceous formations), and (b) relatively fossiliferous mudstone-dominated successions deposited in lakes, channels, coastal lagoons and on mudflats of fluctuating but mainly low salinities (argillaceous formations; Allen, 1981, 1989). In the Weald Sub-basin, the arenaceous formations that typify the lower part of the Wealden succession (the Berriasian – Valanginian Hastings Beds Group; Allen and Wimbledon, 1991; Callomon and Cope, 1995; Fig. 3) generally coarsen upwards, overall. Typically they have a relatively high content of kaolinite amongst the clay minerals. Fossils tend to be sparse and/or localised in these formations, but include remains of land plants, freshwater molluscs, fish and dinosaurs (Topley, 1875; Allen, 1975, 1998). The argillaceous formations generally have lower kaolinite content and amongst their relatively abundant fossil biotas there are many ostracods, small, fresh to brackish-water molluscs and fish, together with remains of aquatic and land plants, reptiles including dinosaurs (Allen, 1975, 1989, 1998),
0016-7878/$ – see front matter ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.pgeola.2012.01.001
236
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 1. Outcrop of Wealden (non-marine Lower Cretaceous) strata in the Weald and Wessex sub-basins, southern England. (a) Location of southern English Weald and Wessex sub-basins. (b) Location of significant growth faults. P-W: Purbeck – Wight faults. Pn: Portsdown, Hampshire. HB: Hog’s Back structure, Surrey.
Fig. 2. Non-marine Early Cretaceous basins and source massifs in north-west Europe, and outline of major stratigraphic units. After Allen (1998, fig. 1). 1. Dorset (palaeolatitude c. 348N), 2. Swindon, Wiltshire, 3. Hartwell, Buckinghamshire, 4. Shepherd’s Chine, Isle of Wight, 5. Sandown Bay, Isle of Wight, 6. West Hoathly, West Sussex (palaeolatitude c. 298N), 7. Mussey, France.
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
237
Fig. 3. Biostratigraphic interpretation of non-marine Lower Cretaceous strata, Weald Sub-basin, south-east England. Incorporating data from Allen and Wimbledon (1991) and Callomon and Cope (1995, fig. 34).
238
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 4. Diagrammatic process model and palaeogeographic context for the Wealden (non-marine Lower Cretaceous) of the Weald Sub-basin, southern England. Adapted from Allen (1975, fig. 8; 1989, fig. 8). (a) Location of the southern English Weald and Wessex sub-basins in relation to influential Early Cretaceous source massifs. (b) Principal detrital sources. (c) Arenaceous formations. Uplift of the London massif (Londinia) enhances stream-flow. Braided alluvial sandplains spread from the north. Water drains north-west towards the Boreal sea. (d) Argillaceous formations. Downfaulting and erosion of London massif (Londinia) reduces relief, streamflow and sedimentation rates. Sub-basin reverts to freshwater-brackish lake-lagoon-mudswamp. Boreal sea encroaches on the sub-basin round west end of Londinian relic hills. During Weald Clay times (Hauterivian up to Barremian or early Aptian), Armorican-Cornubian uplift phases allow western detritus to reach the sub-basin. (e) Known extent of detritus in the Weald Sub-basin: north-eastwards from Armorica; eastwards from Cornubia; southwards from Boreal sea.
insects (Jarzembowski, 1995; Jarzembowski et al., 2010) and many ichnofossils (Allen, 1975; Goldring et al., 2005). Interpretation of the alternating arenaceous and argillaceous formations that make up the Hastings Beds Group was fundamental to pioneering sedimentological and palaeoenvironmental modelling of the Wealden undertaken by one of us (Percival Allen) during the 1950s and 1960s. Following initial work in the field and laboratory during the 1930s and 1940s (e.g. Allen, 1938, 1946, 1949a,b), P. Allen developed a model that invoked an overall eustatic control on Wealden deposition, facies architecture and palaeoecology (Allen, 1959). Petrographic studies of the Ashdown Beds and Lower Tunbridge Wells Sand formations (Fig. 3) confirmed them as alluvial detritus derived from a London massif (termed ‘Londinia’) to the north of the Weald Sub-basin and to a lesser degree from a south-western Armorican massif (‘Armorica’; Fig. 4). Thus, these formations were ascribed to the predominantly southward progradation of deltas and associated fans into a lacustrine basin. At that time, the intervening argillaceous formations were taken to indicate delta abandonment and transgression, due to lake-level rise. However, this model was substantially weakened by evidence of shallow-water, locally emergent conditions throughout
Fig. 5. Model for Wealden (non-marine Lower Cretaceous) argillaceous formations in the Wessex – Weald Basin, southern England. Asterisk (lower right) indicates inferred direction of possible Tethyan marine influxes. After Allen (1981, Fig. 11).
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Wealden times, notably the Equisetites (‘horsetail’) soil beds in the supposedly transgressive argillaceous formations (Allen, 1941, 1946, 1959). Other unresolved issues included the detrital petrographic evidence for multiple detrital sources, and indications of both lagoonal and alluvial incursions from similar directions. Following some experimentation with palaeogeographies (Allen, 1964, 1967b), P. Allen developed a new model in the early 1970s, published in these Proceedings (Allen, 1975). In this revised model, the arenaceous, alluvial formations of the Hastings Beds Group were attributed to brief phases of Londinian upfaulting, superseded by longer intervals equating to downfaulting, reducing clastic supply and grain-size of sediment in the sub-basin below (Figs. 4–6). This model neatly explained the expansion of very shallow water-bodies in the Weald depocentre, producing a shifting mosaic of fresh to slightly brackish pools, lakes, mudbanks and sluggish channels, as now represented by the argillaceous formations (Fig. 5). Amongst the fossils of the argillaceous formations, invertebrates indicating the brackish-water conditions (Allen and Keith, 1965; Allen et al., 1973; Allen, 1989) were taken to indicate seawater leakage into the sub-basin as coastal barriers decayed, possibly influenced by minor sea-level fluctuations. As previously (Allen, 1959), Allen’s new model recognised up to three ‘megacycles’, making up the Hastings Beds Group and lower part of the overlying Hauterivian possibly up to early Aptian Weald Clay
239
Group. Each megacycle comprises an arenaceous formation (Ashdown Beds, Lower Tunbridge Wells Sand, Upper Tunbridge Wells Sand) equating to Londinian uplift, overlain by an argillaceous formation (Wadhurst, Grinstead and basal Weald clays; Fig. 3) that correspond to the ‘normal’ Wealden scene of reduced massif relief (Figs. 4 and 5). In the new model, pebble beds capping the Ashdown Beds and Lower Tunbridge Wells Sand formations of the Hastings Beds Group were interpreted as residues of braidplain gravel reworked in transgressive strandline settings, following downfaulting of the London massif. The argillaceous lacustrine-lagoonal lithofacies that dominate the younger Weald Clay Group indicate a tectonically inactive and increasingly eroded London massif, from Hauterivian times onwards. Tourmaline-rich sand intercalations within the Weald Clay of the western Weald were derived from a western massif (termed Cornubia), occupying the general region of Devon, Cornwall and the Scilly Isles (Allen, 1975, 1981; Figs. 4 and 5). The situation in the Wessex Sub-basin (Figs. 1 and 4) is simpler. There, the succession is dominated by the alluvial Wessex Formation (early Valanginian possibly up to lower Aptian; Allen and Wimbledon, 1991; Fig. 7) which generally coarsens and thins westwards from the Isle of Wight into Dorset (Arkell, 1947a; Allen, 1981; Stewart, 1978). Petrographic studies of the Wessex Formation sands confirm a Cornubian source as also identified
Fig. 6. Model for Wealden (non-marine Lower Cretaceous) arenaceous formations in the Wessex – Weald Basin, southern England. The Cornubian massif (Cornubia) lies to the west of the basin; the London massif (Londinia) to the north-east and the Armorican massif (Armorica) to the south. After Allen (1981, Fig. 8).
240
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 7. Chronstratigraphic interpretation of Wealden strata (Valanginian up to Aptian) in the Wessex Sub-basin, southern England. Incorporating data from Allen and Wimbledon (1991) and Callomon and Cope (1995, fig. 34).
in the Weald Clay Group of the western Weald (see above; Figs. 4 and 5). Through much of the Wessex Sub-basin outcrop, the Wessex Formation is overlain by a relatively thin argillaceous lacustrine-lagoonal formation; the Barremian up to early Aptian Vectis Formation (Allen and Wimbledon, 1991; Stewart et al., 1991). 2. The Geological Conservation Review The identification of Great Britain’s most important Earth science sites commenced in the 1950s. In the late 1970s the Nature Conservancy Council initiated a systematic review of the sites, known as the Geological Conservation Review (GCR). This review was completed in 1990. Since then, a major programme has resulted in publication of Geological Conservation Review accounts for a scientific readership (Ellis et al., 1996; Ellis, 2008, 2011). Nearly forty years since publication, Allen’s seminal ‘new model’ (Allen, 1975) still provides the basis of modern Wealden interpretative studies. Our account of the southern English Wealden is essentially an expanded and updated version of this model, illustrated by Geological Conservation Review (GCR) sites throughout the southern English outcrops (Table 1). The initial site selection and documentation for the Wealden ‘Block’ of the Geological Conservation Review (Ellis et al., 1996; Ellis, 2008, 2011) was undertaken by P. Allen and W.A. Wimbledon. This account is the combined work of P. Allen and J.D. Radley, with much support provided by W.A. Wimbledon. Building upon P. Allen’s investigations spanning seven decades, additional fieldwork in both sub-basins was undertaken by J.D. Radley between
1997 and 1999, together with laboratory work at the Postgraduate Research Institute for Sedimentology, University of Reading. Over the following few years the site reports were refined by P. Allen and J.D. Radley. Sadly, Percival (‘Perce’) Allen died in 2008, before the work could be completed. The Geological Conservation Review account was therefore completed by J.D. Radley and is dedicated to Perce Allen’s memory and the body of work that he contributed to northwest European Wealden studies over many decades (Fig. 8). J.D. Radley would like to point out that his status as senior author is an editorial protocol. Indeed, a large proportion of this work is very much Perce’s vision of the Wealden scene – his ‘dreamland terrain’ (Allen, 1975, p. 437). Batten (1996) provided a list of Perce Allen’s publications up to the mid-1990s. The Geological Conservation Review sites described and interpreted in these papers were originally selected as the best examples to demonstrate the sedimentological, palaeobiological and stratigraphic development of Wealden successions in both southern English sub-basins (Table 1). They comprise a range of extant and disused stone quarries and brick pits, road, lane and rail cuttings, natural exposures in inland settings and coastal cliffs. Sites in the Weald Sub-basin are presented in broad accordance of their stratigraphic range. Those in the Wessex Sub-basin are documented in order of their location from east (Isle of Wight) to west (Dorset). Sites along the northern margin of the WessexWeald Basin in the South Midlands are arranged in accordance of location from south-west to north-east. Most of the sites are now protected and conserved under British law as Sites of Special Scientific Interest. Further insight into the objectives of the
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
241
Table 1 Wealden (non-marine Lower Cretaceous) Geological Conservation Review sites: locations and selection criteria. GCR site
National Grid Reference
Units
Selection criteria
Weald Sub-basin Hastings–Pett Level, East Sussex
TQ 828093–TQ 888132
Ashdown Beds Formation, Wadhurst Clay Formation
Extensive coastal exposures of fluvial, lacustrine and lagoonal sediments; many fossiliferous. Demonstrates Wealden sedimentary cyclicity on a range of scales and provides an important reference section for inland sites.
Winchelsea, East Sussex
TQ 90231691
Ashdown Beds – Wadhurst Clay Formation boundary
Demonstrates the Ashdown–Wadhurst alluvial-lacustrine transition towards the south-eastern margin of the Weald Sub-basin.
Brede, East Sussex
TQ 83151845–TQ 83241834
Ashdown Beds – Wadhurst Clay Formation boundary
Type section for the Ashdown–Wadhurst alluvial-lacustrine transition. Fundamental to the development of the currently accepted Wealden model (Allen, 1975, 1981, 1989).
Waldron, East Sussex
TQ 552187
Ashdown Beds Formation
Exposes the Waldron Soil Bed within the alluvial Top Ashdown Sandstone.
Hadlow Down, East Sussex
TQ 523259
Ashdown Beds – Wadhurst Clay Formation boundary
A site with considerable potential for detailed sedimentological interpretation of the Top Ashdown Sandstone.
Iden, East Sussex
TQ 931224–TQ 931225
Cliff End Sandstone Member of the Wadhurst Clay Formation
Exposes fan delta-top deposits, allowing comparison with nearby sites exposing the Cliff End Sandstone.
Fairlight, East Sussex
TQ 857115–TQ 859115, TQ 859119
Cliff End Sandstone Member of the Wadhurst Clay Formation
Leached and plant-colonised development of the top Cliff End Sandstone.
Battle, East Sussex
TQ 769142
Wadhurst Clay Formation
Richly fossiliferous Telham Pebble (Bone) Bed.
Northiam, East Sussex
TQ 829253
Northiam Sand Member of the Wadhurst Clay Formation
Potentially important site for sedimentological modelling of a minor Wadhurst Clay sand-body.
West Hoathly (Sharpthorne), West Sussex
TQ 374328–TQ 375329
Wadhurst Clay Formation
Sections through the lacustrine lower Wadhurst Clay, with special reference to palaeontological and sedimentological investigations.
Horsted Keynes, West Sussex
TQ 381266, TQ 386265
Wadhurst Clay Formation up to Upper Tunbridge Wells Sand Formation
Important site for the Hastings Beds Group, clearly demonstrating Hastings Beds ‘megacycles’.
Southborough, Kent
TQ 59254170, TQ59444200– TQ59564186
Wadhurst Clay Formation, Lower Tunbridge Wells Sand Formation
Reference section for the Wadhurst Clay–Lower Tunbridge Wells Sand lacustrine-alluvial transition.
Pembury, Kent
TQ 615416, TQ 613414, TQ 613415
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Well-preserved fluvial channels and scours, close to the southern margin of the London massif.
Tunbridge Wells, East Sussex
TQ 558382–TQ 562384
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Extensive and easily accessible sections through the fluvial Ardingly Sandstone, preserving a wealth of sedimentary structures.
East Grinstead, West Sussex
TQ 380348–TQ 381348
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Clear sections through the fluvial Ardingly Sandstone, preserving a wealth of sedimentary structures.
West Hoathly (Philpots Quarry), West Sussex
TQ 35563228
Lower Tunbridge Wells Sand Formation, Grinstead Clay Formation
Investigations spanning several decades have resulted in detailed sedimentological and palaeobiological interpretation of the Ardingly Sandstone and overlying lower Grinstead Clay, contributing importantly to the currently accepted Wealden model (Allen, 1975, 1981, 1989).
West Hoathly (Hook Quarry), West Sussex
TQ 355313
Lower Tunbridge Wells Sand Formation, Grinstead Clay Formation
Detrital petrographic studies of the marginal-lacustrine Top Lower Tunbridge Wells Pebble Bed have allowed detailed reconstruction of Londinian palaeogeology.
Turners Hill, West Sussex
TQ 339354
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Provides three-dimensional sections within ‘festoon-bedded’ lithofacies of the Ardingly Sandstone.
Scaynes Hill, East Sussex
TQ 391228
Cuckfield Stone Member of the Grinstead Clay Formation
A reference section of the Cuckfield Stone, with much potential for sedimentological analysis.
Horsham (Warnham Mill Pond outfill), West Sussex [Potential GCR Site]
TQ 164318
Upper Tunbridge Wells Sand Formation
A reference section within the Upper Tunbridge Wells Sand, demonstrating meanderplain deposition at the close of Hastings Beds times.
Slinfold, West Sussex
TQ 125312–TQ 124319, TQ 127318
Lower Weald Clay (Horsham Stone Member: BGS Bed 1)
Reference sections within the Horsham Stone, demonstrating alluvial/lacustrine deposition, a range of sedimentary structures and a Cornubian detrital signature.
Warnham, West Sussex
TQ 179352–TQ182354
Lower Weald Clay (in range of BGS Bed 2)
Richly fossiliferous mudstone-dominated succession demonstrating lacustrine/lagoonal environments, small-scale sedimentary cyclicity and fluctuating salinities.
242
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Table 1 (Continued ) GCR site
National Grid Reference
Units
Selection criteria
Capel, Surrey
TQ 176387–TQ 177387
Lower – Upper Weald Clay boundary beds
Richly fossiliferous mudstone-dominated succession demonstrating a vertical transition from offshore to marginallacustrine deposition.
Billingshurst, West Sussex
TQ 078276–TQ 079277
Upper Weald Clay (Okehurst Sand Member: BGS Bed 3a)
Section within Okehurst Sand, currently taken as the base of the Barremian Stage in the Weald Sub-basin. Indicates meanderplain deposition, sourced ultimately from Cornubia.
Coneyhurst Common, West Sussex
TQ 10112441– TQ10072452
Upper Weald Clay (BGS Bed 4)
Representative exposure of a large-Viviparus limestone bed, demonstrating marginal lacustrine deposition.
Ockley, Surrey
TQ 112372–TQ114375
Upper Weald Clay below BGS Bed 5c
Richly fossiliferous mudstone-dominated succession demonstrating a range of palaeoenvironmentally and palaeoclimatically significant features including marginallacustrine pedogenesis and dinoturbation. An outstanding site for palaeontological discoveries.
Chiddingfold, Surrey
SU 942338–SU 944343
Upper Weald Clay (Netherside Sand Member: BGS Bed 7f)
Demonstrates plant colonisation of a fluvial sand body.
Fernhurst, West Sussex
SU 89152873–SU 89222880
Upper Weald Clay (Netherside Sand Member: BGS Bed 7f)
Representative exposure of the Netherside Sand, thought to represent a fluvial sand-bar.
Cranleigh (Bookhurst Tileworks), West Sussex [Potential GCR Site]
TQ 076395
Upper Weald Clay above BGS Bed 8a
Richly fossiliferous mudstone-dominated succession demonstrating lacustrine/lagoonal deposition in latest Wealden times.
SZ 611849–SZ 621853
Wessex Formation, Vectis Formation
Demonstrates replacement of meanderplain environments by muddy coastal lakes and lagoons, towards the close of Wealden times. An important site for modelling late Wealden climates and palaeogeography, and for palaeobiological studies.
Compton Bay – Brighstone Bay, Isle of Wight
SZ 369851–SZ 452792
Wessex Formation, Vectis Formation
Extensive coastal sections through the upper part of the distal alluvial Wessex Formation, overlain by the lacustrine/lagoonal Vectis Formation. Of outstanding importance for sedimentological and palaeobiological studies.
Swanage, Dorset
SZ 031795–SZ 039809
Wessex Formation, Vectis Formation
Extensive coastal sections through the upper part of the alluvial Wessex Formation, overlain by a thin development of the lacustrine/lagoonal Vectis Formation. Particularly significant for demonstrating westward-coarsening alluvial facies gradients and for chronostratigraphic studies.
Steeple, Dorset [Potential GCR Site]
SY 911809
Wessex Formation
Significant for sedimentological studies of the Coarse Quartz Grit, thought to be a Cornubian flood deposit.
Mupe Bay and Worbarrow Bay, Dorset
SY 843797–SY 843801, SY 871796–SY 868801
Wessex Formation
Extensive sections through the Wessex Formation, occupying a key position within the lateral transition from distal to medial floodplain environments towards Cornubia, and demonstrating a range of features including a floodplain oil seep and the chronostratigraphically significant Coarse Quartz Grit.
Lulworth Cove, Dorset
SY 824798–SY824797, SY 828798–SY828797
Wessex Formation
Extensive sections through the Wessex Formation, demonstrating features indicative of the lateral transition from distal to medial floodplain environments.
Durdle Door, Dorset
SY 805802–807802
Wessex Formation
Extensive sections through the Wessex Formation, demonstrating thinning and coarsening of alluvial strata towards Cornubia, and preserving a thick development of the chronostratigraphically significant Coarse Quartz Grit.
Upwey/Bincombe, Dorset
SY 672854
Wessex Formation
Cuttings within the westernmost development of the Wessex Formation. Significant for sedimentological and palaeobiological studies.
Marginal Wealden Dinton, Wiltshire
SU 006309–SU 010310
Muswell Hill, Buckinghamshire
SP 640153
Whitchurch Sands Formation
Cuttings (presently overgrown) through ironstones (some fossiliferous), sandstones and mudstones. The site has considerable potential for critical chronostratigraphic, sedimentological and palaeobiological studies.
Stone, Buckinghamshire
SP 780126
Whitchurch Sands Formation
The site of former sand pits that exposed a unique development of highly quartzose fluvial ‘glass sands’.
Wessex Sub-basin Sandown Bay, Isle of Wight
Formerly exposed poorly dated sands and mudstones of Wealden aspect. The site is potentially significant for reconstructing regional stratigraphy and palaeogeography near the northern margin of the Wessex-Weald Basin.
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
243
(formerly Countryside Council for Wales) and David Skevington (former GCR editor for the Jurassic-Cretaceous boundary beds block). Sincere gratitude is also expressed to Jim Rose for his patience, advice and editorial expertise, to Jenny Kynaston for her technical drawing skills and to Lisa Gordon for her assistance. The Curry Fund of the Geologists’ Association is acknowledged for the production of illustrations.
References
Fig. 8. Professor Percival (‘Perce’) Allen FRS amongst the ‘lifts’ (Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation) at Philpots Quarry, West Hoathly, West Sussex (West Hoathly (Philpots Quarry) GCR site).
Geological Conservation Review programme, site selection procedures and rationale were provided by Ellis et al. (1996) and Ellis (2008, 2011). 3. Palaeontological conventions Authors of fossil species are omitted from the texts for purposes of brevity. Details of those authors can be found within palaeontological works cited within the accounts, and are documented in full within the recently published Palaeontological Association Field Guide to English Wealden fossils (Batten, 2011). 4. Copyright The British Geological Survey (BGS) data are used with permission of the Executive Director, British Geological Survey (NERC). The copyright of materials derived from the British Geological Survey’s work is vested in the Natural Environment Research Council (NERC). Ordnance Survey topographic data incorporated within BGS publications are reproduced by permission of the Ordnance Survey. Illustrations originally published by the Palaeontological Association and Geological Society are reproduced with permission of those organisations. Illustrations previously published in Elsevier journals are reproduced by permission of Elsevier. Acknowledgements Amongst those who assisted in the preparation of this introduction we would especially like to thank Neil Ellis (Joint Nature Conservation Committee, Peterborough), Bill Wimbledon
Allen, P., 1938. Ashdown Sand – Wadhurst Clay junction. Geological Magazine 75, 560–561. Allen, P., 1941. A Wealden soil bed with Equisetites lyelli (Mantell). Proceedings of the Geologists’ Association 52, 362–374. Allen, P., 1946. Notes on Wealden fossil soil-beds. Proceedings of the Geologists’ Association 57, 303–331. Allen, P., 1949a. Wealden petrology; the Top Ashdown Pebble Bed and the Top Ashdown Sandstone. Quarterly Journal of the Geological Society, London 104, 257–321. Allen, P., 1949b. Notes on Wealden bone-beds. Proceedings of the Geologists’ Association 60, 275–383. Allen, P., 1959. The Wealden environment: Anglo-Paris Basin. Philosophical Transactions of the Royal Society Series B 242, 283–346. Allen, P., 1964. Sedimentological models. Journal of Sedimentary Petrology 34, 289– 293. Allen, P., 1967a. Origin of the Hastings facies in North-Western Europe. Proceedings of the Geologists’ Association 78, 27–106. Allen, P., 1967b. Strand-line pebbles in the Mid-Hastings Beds and the geology of the London Uplands. Old Red Sandstone, New Red Sandstone and other pebbles. Conclusion. Proceedings of the Geologists’ Association 78, 241–276. Allen, P., 1975. Wealden of the Weald: a new model. Proceedings of the Geologists’ Association 86, 389–437. Allen, P., 1981. Pursuit of Wealden models. Journal of the Geological Society, London 138, 375–405. Allen, P., 1989. Wealden research – ways ahead. Proceedings of the Geologists’ Association 100, 529–564. Allen, P., 1998. Purbeck-Wealden (early Cretaceous) climates. Proceedings of the Geologists’ Association 109, 197–236. Allen, P., Keith, M.L., 1965. Carbon isotope ratios and palaeosalinities of PurbeckWealden carbonates. Nature 208, 1278–1280. Allen, P., Keith, M.L., Tan, F.C., Deines, P., 1973. Isotopic ratios and Wealden environments. Palaeontology 16, 607–621. Allen, P., Wimbledon, W.A., 1991. Correlation of NW European Purbeck-Wealden (nonmarine Lower Cretaceous) as seen from the English type-areas. Cretaceous Research 12, 511–526. Arkell, W.J., 1947a. The Geology of the Country Around Weymouth, Swanage, Corfe and Lulworth, Memoir of the Geological Survey of Great Britain. HMSO, London, xxvii+386 pp. Arkell, W.J., 1947b. The Geology of Oxford. Clarendon Press, Oxford, vi+267 pp. Batten, D.J., 1996. Editorial. Cretaceous Research 17, 2–4. Batten, D.J. (Ed.), 2011. English Wealden fossils. Palaeontological Society Field Guides to Fossils Series, No. 14. Palaeontological Association, London, p. 769. Callomon, J.H., Cope, J.C.W., 1995. The Jurassic Geology of Dorset. In: Taylor, P.D. (Ed.), Field Geology of the British Jurassic. Geological Society, London, pp. 51– 103. Casey, R., Bristow, C.R., 1964. Notes on some ferruginous strata in Buckinghamshire and Wiltshire. Geological Magazine 101, 116–128. Ellis, N., 2008. In: Burek, C.V., Prosser, C.D. (Eds.), A history of the Geological Conservation Review. The History of Geoconservation. Geological Society, London, Special Publication 300, pp. 123–135.
244
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Ellis, N., 2011. The Geological Conservation Review (GCR) in Great Britain – Rationale and methods. Proceedings of the Geologists’ Association 122, 353– 362. Ellis, N., Bowen, D.Q., Campbell, S., Knill, J.L., McKirdy, A.P., Prosser, C.D., Vincent, M.A., Wilson, R.C.L., 1996. An Introduction to the Geological Conservation Review. Geological Conservation Review Series, No. 1. Joint Nature Conservation Committee, Peterborough, viii+131 pp. Gale, A.S., 2000. Early Cretaceous: rifting and sedimentation before the flood. In: Woodcock, N., Strachan, R. (Eds.), Geological History of Britain and Ireland. Blackwell Science, pp. 339–355. Goldring, R., Pollard, J.E., Radley, J.D., 2005. Trace fossils and pseudofossils from the Wealden strata (nonmarine Lower Cretaceous) of southern England. Cretaceous Research 26, 665–685. Horton, A., Sumbler, M.G., Cox, B.M., Ambrose, K., 1995. Geology of the Country Around Thame. Memoir for 1:50,000 Geological Sheet 237 (England and Wales). HMSO, London, x+169 pp. Jarzembowski, E.A., 1995. Early Cretaceous insect faunas and palaeoenvironment. Cretaceous Research 16, 681–693. Jarzembowski, E.A., Siveter, D.J., Palmer, D., Selden, P.A., 2010. Fossil Arthropods of Great Britain. Geological Conservation Review Series, No. 35. Joint Nature Conservation Committee, Peterborough, xvi+294 pp.
Martin, P.I., 1828. A Geological Memoir on a Part of Western Sussex; With Some Observations Upon Chalk-basins, the Weald-denudation, and Outliers-by-protrusion. John Booth, London, x+100 pp. Rawson, P.F., 1992a. Cretaceous. In: Duff, P., Mc, L.D., Smith, A.J. (Eds.), Geology of England and Wales. The Geological Society, London, pp. 355–388. Rawson, P.F., 1992b. Early Cretaceous. In: Cope, J.C.W., Ingham, J.K., Rawson, P.F. (Eds.), Atlas of Palaeogeography and Lithofacies. Geological Society, London, Memoir 13, pp. 131–137. Rawson, P.F., 2006. Cretaceous: sea levels peak as the North Atlantic opens. In: Brenchley, P.F., Rawson, P.F. (Eds.), The Geology of England and Wales. 2nd edition. The Geological Society, London, pp. 365–393. Stewart, D.J., 1978. The sedimentology and palaeoenvironment of the Wealden Group of the Isle of Wight, southern England. PhD thesis, Portsmouth Polytechnic, Portsmouth, UK. Stewart, D.J., Ruffell, A., Wach, G., Goldring, R., 1991. Lagoonal sedimentation and fluctuating salinities in the Vectis Formation (Wealden Group, Lower Cretaceous) of the Isle of Wight, southern England. Sedimentary Geology 72, 117–134. Topley, W., 1875. The Geology of the Weald. Memoir of the Geological Survey, England and Wales. HMSO, London, xiv+503 pp. White, H.J.O., 1921. A Short Account of the Geology of the Isle of Wight, Memoirs of the Geological Survey of Great Britain. HMSO, London, viii+201 pp.
Contents lists available at SciVerse ScienceDirect
Proceedings of the Geologists’ Association journal homepage: www.elsevier.com/locate/pgeola
The non-marine Lower Cretaceous Wealden strata of southern England Jonathan D. Radley a,*, Percival Allen b,1 a b
School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Postgraduate Research Institute for Sedimentology, The University of Reading, PO Box 227, Whiteknights, Reading RG6 6AB, UK
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 November 2011 Accepted 6 January 2012 Available online 8 March 2012
The non-marine Lower Cretaceous Wealden strata of the Wessex-Weald Basin (southern England) are introduced, with reference to the depositional model developed by Professor Percival Allen FRS (Allen, 1975). To demonstrate this model and the development of Wealden palaeoenvironments through time, Wealden sites have been selected for the Geological Conservation Review programme. Site selection rationale is briefly outlined. ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved.
Keywords: Geological Conservation Review Wealden Lower Cretaceous Wessex-Weald Basin Southern England
1. Introduction to the Wealden Following Martin (1828) and other nineteenth century workers, geologists use the term ‘Wealden’ for non-marine sandstone and mudstone-dominated successions of Lower Cretaceous age, that have been documented through north-west Europe (Allen, 1967a) and further afield. The name derives from the Weald, a picturesque area of south-east England where Wealden rocks outcrop. In southern England as a whole, Wealden strata are found in both the largely onshore Weald Sub-basin of south-east England, and the northern part of the partly offshore Wessex Sub-basin of southern and south-west England. These depocentres are effectively separated by the Purbeck-Isle of Wight structure (Allen, 1981; Gale, 2000) and collectively make up the Wessex-Weald Basin (Figs. 1 and 2). The Wealden strata of the Weald Sub-basin outcrop in the counties of Kent, Sussex, Surrey and Hampshire; the Wealden type-area (Topley, 1875; Allen, 1975). The Wessex Subbasin successions are seen on the Isle of Wight and in south Dorset (White, 1921; Arkell, 1947a; Fig. 1). Scattered, poorly exposed patches of Lower Cretaceous strata of Wealden aspect occur along the north-western margin of the Wessex-Weald Basin in the English South Midlands (Arkell, 1947b; Casey and Bristow, 1964; Horton et al., 1995; Fig. 1). In north-eastern England, the coeval Lower Cretaceous strata are wholly marine in origin (Rawson, 1992a,b, 2006).
* Corresponding author. E-mail address: [email protected] (J.D. Radley). 1 Deceased.
The Wealden successions preserved within the Weald and Wessex sub-basins (Fig. 2) differ to varying extents in terms of their relative age, styles of facies architecture, and their enclosed fossil assemblages. To a degree, these differences reflect contrasting tectonic contexts and perhaps their differing climatic histories (Allen, 1981, 1998). Taken as a whole, the southern English Wealden ranges in age from upper Berriasian to lower Aptian, equating to approximately 15 million years of Earth history (Allen and Wimbledon, 1991). Broadly, the Wealden comprises two major facies associations as developed in both southern English sub-basins. These are (a) largely oxidised mudstones, siltstones and fine to coarse-grained sandstones indicating distal meanderplain to proximal braidplain and possible fan settings (arenaceous formations), and (b) relatively fossiliferous mudstone-dominated successions deposited in lakes, channels, coastal lagoons and on mudflats of fluctuating but mainly low salinities (argillaceous formations; Allen, 1981, 1989). In the Weald Sub-basin, the arenaceous formations that typify the lower part of the Wealden succession (the Berriasian – Valanginian Hastings Beds Group; Allen and Wimbledon, 1991; Callomon and Cope, 1995; Fig. 3) generally coarsen upwards, overall. Typically they have a relatively high content of kaolinite amongst the clay minerals. Fossils tend to be sparse and/or localised in these formations, but include remains of land plants, freshwater molluscs, fish and dinosaurs (Topley, 1875; Allen, 1975, 1998). The argillaceous formations generally have lower kaolinite content and amongst their relatively abundant fossil biotas there are many ostracods, small, fresh to brackish-water molluscs and fish, together with remains of aquatic and land plants, reptiles including dinosaurs (Allen, 1975, 1989, 1998),
0016-7878/$ – see front matter ß 2012 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.pgeola.2012.01.001
236
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 1. Outcrop of Wealden (non-marine Lower Cretaceous) strata in the Weald and Wessex sub-basins, southern England. (a) Location of southern English Weald and Wessex sub-basins. (b) Location of significant growth faults. P-W: Purbeck – Wight faults. Pn: Portsdown, Hampshire. HB: Hog’s Back structure, Surrey.
Fig. 2. Non-marine Early Cretaceous basins and source massifs in north-west Europe, and outline of major stratigraphic units. After Allen (1998, fig. 1). 1. Dorset (palaeolatitude c. 348N), 2. Swindon, Wiltshire, 3. Hartwell, Buckinghamshire, 4. Shepherd’s Chine, Isle of Wight, 5. Sandown Bay, Isle of Wight, 6. West Hoathly, West Sussex (palaeolatitude c. 298N), 7. Mussey, France.
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
237
Fig. 3. Biostratigraphic interpretation of non-marine Lower Cretaceous strata, Weald Sub-basin, south-east England. Incorporating data from Allen and Wimbledon (1991) and Callomon and Cope (1995, fig. 34).
238
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 4. Diagrammatic process model and palaeogeographic context for the Wealden (non-marine Lower Cretaceous) of the Weald Sub-basin, southern England. Adapted from Allen (1975, fig. 8; 1989, fig. 8). (a) Location of the southern English Weald and Wessex sub-basins in relation to influential Early Cretaceous source massifs. (b) Principal detrital sources. (c) Arenaceous formations. Uplift of the London massif (Londinia) enhances stream-flow. Braided alluvial sandplains spread from the north. Water drains north-west towards the Boreal sea. (d) Argillaceous formations. Downfaulting and erosion of London massif (Londinia) reduces relief, streamflow and sedimentation rates. Sub-basin reverts to freshwater-brackish lake-lagoon-mudswamp. Boreal sea encroaches on the sub-basin round west end of Londinian relic hills. During Weald Clay times (Hauterivian up to Barremian or early Aptian), Armorican-Cornubian uplift phases allow western detritus to reach the sub-basin. (e) Known extent of detritus in the Weald Sub-basin: north-eastwards from Armorica; eastwards from Cornubia; southwards from Boreal sea.
insects (Jarzembowski, 1995; Jarzembowski et al., 2010) and many ichnofossils (Allen, 1975; Goldring et al., 2005). Interpretation of the alternating arenaceous and argillaceous formations that make up the Hastings Beds Group was fundamental to pioneering sedimentological and palaeoenvironmental modelling of the Wealden undertaken by one of us (Percival Allen) during the 1950s and 1960s. Following initial work in the field and laboratory during the 1930s and 1940s (e.g. Allen, 1938, 1946, 1949a,b), P. Allen developed a model that invoked an overall eustatic control on Wealden deposition, facies architecture and palaeoecology (Allen, 1959). Petrographic studies of the Ashdown Beds and Lower Tunbridge Wells Sand formations (Fig. 3) confirmed them as alluvial detritus derived from a London massif (termed ‘Londinia’) to the north of the Weald Sub-basin and to a lesser degree from a south-western Armorican massif (‘Armorica’; Fig. 4). Thus, these formations were ascribed to the predominantly southward progradation of deltas and associated fans into a lacustrine basin. At that time, the intervening argillaceous formations were taken to indicate delta abandonment and transgression, due to lake-level rise. However, this model was substantially weakened by evidence of shallow-water, locally emergent conditions throughout
Fig. 5. Model for Wealden (non-marine Lower Cretaceous) argillaceous formations in the Wessex – Weald Basin, southern England. Asterisk (lower right) indicates inferred direction of possible Tethyan marine influxes. After Allen (1981, Fig. 11).
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Wealden times, notably the Equisetites (‘horsetail’) soil beds in the supposedly transgressive argillaceous formations (Allen, 1941, 1946, 1959). Other unresolved issues included the detrital petrographic evidence for multiple detrital sources, and indications of both lagoonal and alluvial incursions from similar directions. Following some experimentation with palaeogeographies (Allen, 1964, 1967b), P. Allen developed a new model in the early 1970s, published in these Proceedings (Allen, 1975). In this revised model, the arenaceous, alluvial formations of the Hastings Beds Group were attributed to brief phases of Londinian upfaulting, superseded by longer intervals equating to downfaulting, reducing clastic supply and grain-size of sediment in the sub-basin below (Figs. 4–6). This model neatly explained the expansion of very shallow water-bodies in the Weald depocentre, producing a shifting mosaic of fresh to slightly brackish pools, lakes, mudbanks and sluggish channels, as now represented by the argillaceous formations (Fig. 5). Amongst the fossils of the argillaceous formations, invertebrates indicating the brackish-water conditions (Allen and Keith, 1965; Allen et al., 1973; Allen, 1989) were taken to indicate seawater leakage into the sub-basin as coastal barriers decayed, possibly influenced by minor sea-level fluctuations. As previously (Allen, 1959), Allen’s new model recognised up to three ‘megacycles’, making up the Hastings Beds Group and lower part of the overlying Hauterivian possibly up to early Aptian Weald Clay
239
Group. Each megacycle comprises an arenaceous formation (Ashdown Beds, Lower Tunbridge Wells Sand, Upper Tunbridge Wells Sand) equating to Londinian uplift, overlain by an argillaceous formation (Wadhurst, Grinstead and basal Weald clays; Fig. 3) that correspond to the ‘normal’ Wealden scene of reduced massif relief (Figs. 4 and 5). In the new model, pebble beds capping the Ashdown Beds and Lower Tunbridge Wells Sand formations of the Hastings Beds Group were interpreted as residues of braidplain gravel reworked in transgressive strandline settings, following downfaulting of the London massif. The argillaceous lacustrine-lagoonal lithofacies that dominate the younger Weald Clay Group indicate a tectonically inactive and increasingly eroded London massif, from Hauterivian times onwards. Tourmaline-rich sand intercalations within the Weald Clay of the western Weald were derived from a western massif (termed Cornubia), occupying the general region of Devon, Cornwall and the Scilly Isles (Allen, 1975, 1981; Figs. 4 and 5). The situation in the Wessex Sub-basin (Figs. 1 and 4) is simpler. There, the succession is dominated by the alluvial Wessex Formation (early Valanginian possibly up to lower Aptian; Allen and Wimbledon, 1991; Fig. 7) which generally coarsens and thins westwards from the Isle of Wight into Dorset (Arkell, 1947a; Allen, 1981; Stewart, 1978). Petrographic studies of the Wessex Formation sands confirm a Cornubian source as also identified
Fig. 6. Model for Wealden (non-marine Lower Cretaceous) arenaceous formations in the Wessex – Weald Basin, southern England. The Cornubian massif (Cornubia) lies to the west of the basin; the London massif (Londinia) to the north-east and the Armorican massif (Armorica) to the south. After Allen (1981, Fig. 8).
240
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Fig. 7. Chronstratigraphic interpretation of Wealden strata (Valanginian up to Aptian) in the Wessex Sub-basin, southern England. Incorporating data from Allen and Wimbledon (1991) and Callomon and Cope (1995, fig. 34).
in the Weald Clay Group of the western Weald (see above; Figs. 4 and 5). Through much of the Wessex Sub-basin outcrop, the Wessex Formation is overlain by a relatively thin argillaceous lacustrine-lagoonal formation; the Barremian up to early Aptian Vectis Formation (Allen and Wimbledon, 1991; Stewart et al., 1991). 2. The Geological Conservation Review The identification of Great Britain’s most important Earth science sites commenced in the 1950s. In the late 1970s the Nature Conservancy Council initiated a systematic review of the sites, known as the Geological Conservation Review (GCR). This review was completed in 1990. Since then, a major programme has resulted in publication of Geological Conservation Review accounts for a scientific readership (Ellis et al., 1996; Ellis, 2008, 2011). Nearly forty years since publication, Allen’s seminal ‘new model’ (Allen, 1975) still provides the basis of modern Wealden interpretative studies. Our account of the southern English Wealden is essentially an expanded and updated version of this model, illustrated by Geological Conservation Review (GCR) sites throughout the southern English outcrops (Table 1). The initial site selection and documentation for the Wealden ‘Block’ of the Geological Conservation Review (Ellis et al., 1996; Ellis, 2008, 2011) was undertaken by P. Allen and W.A. Wimbledon. This account is the combined work of P. Allen and J.D. Radley, with much support provided by W.A. Wimbledon. Building upon P. Allen’s investigations spanning seven decades, additional fieldwork in both sub-basins was undertaken by J.D. Radley between
1997 and 1999, together with laboratory work at the Postgraduate Research Institute for Sedimentology, University of Reading. Over the following few years the site reports were refined by P. Allen and J.D. Radley. Sadly, Percival (‘Perce’) Allen died in 2008, before the work could be completed. The Geological Conservation Review account was therefore completed by J.D. Radley and is dedicated to Perce Allen’s memory and the body of work that he contributed to northwest European Wealden studies over many decades (Fig. 8). J.D. Radley would like to point out that his status as senior author is an editorial protocol. Indeed, a large proportion of this work is very much Perce’s vision of the Wealden scene – his ‘dreamland terrain’ (Allen, 1975, p. 437). Batten (1996) provided a list of Perce Allen’s publications up to the mid-1990s. The Geological Conservation Review sites described and interpreted in these papers were originally selected as the best examples to demonstrate the sedimentological, palaeobiological and stratigraphic development of Wealden successions in both southern English sub-basins (Table 1). They comprise a range of extant and disused stone quarries and brick pits, road, lane and rail cuttings, natural exposures in inland settings and coastal cliffs. Sites in the Weald Sub-basin are presented in broad accordance of their stratigraphic range. Those in the Wessex Sub-basin are documented in order of their location from east (Isle of Wight) to west (Dorset). Sites along the northern margin of the WessexWeald Basin in the South Midlands are arranged in accordance of location from south-west to north-east. Most of the sites are now protected and conserved under British law as Sites of Special Scientific Interest. Further insight into the objectives of the
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
241
Table 1 Wealden (non-marine Lower Cretaceous) Geological Conservation Review sites: locations and selection criteria. GCR site
National Grid Reference
Units
Selection criteria
Weald Sub-basin Hastings–Pett Level, East Sussex
TQ 828093–TQ 888132
Ashdown Beds Formation, Wadhurst Clay Formation
Extensive coastal exposures of fluvial, lacustrine and lagoonal sediments; many fossiliferous. Demonstrates Wealden sedimentary cyclicity on a range of scales and provides an important reference section for inland sites.
Winchelsea, East Sussex
TQ 90231691
Ashdown Beds – Wadhurst Clay Formation boundary
Demonstrates the Ashdown–Wadhurst alluvial-lacustrine transition towards the south-eastern margin of the Weald Sub-basin.
Brede, East Sussex
TQ 83151845–TQ 83241834
Ashdown Beds – Wadhurst Clay Formation boundary
Type section for the Ashdown–Wadhurst alluvial-lacustrine transition. Fundamental to the development of the currently accepted Wealden model (Allen, 1975, 1981, 1989).
Waldron, East Sussex
TQ 552187
Ashdown Beds Formation
Exposes the Waldron Soil Bed within the alluvial Top Ashdown Sandstone.
Hadlow Down, East Sussex
TQ 523259
Ashdown Beds – Wadhurst Clay Formation boundary
A site with considerable potential for detailed sedimentological interpretation of the Top Ashdown Sandstone.
Iden, East Sussex
TQ 931224–TQ 931225
Cliff End Sandstone Member of the Wadhurst Clay Formation
Exposes fan delta-top deposits, allowing comparison with nearby sites exposing the Cliff End Sandstone.
Fairlight, East Sussex
TQ 857115–TQ 859115, TQ 859119
Cliff End Sandstone Member of the Wadhurst Clay Formation
Leached and plant-colonised development of the top Cliff End Sandstone.
Battle, East Sussex
TQ 769142
Wadhurst Clay Formation
Richly fossiliferous Telham Pebble (Bone) Bed.
Northiam, East Sussex
TQ 829253
Northiam Sand Member of the Wadhurst Clay Formation
Potentially important site for sedimentological modelling of a minor Wadhurst Clay sand-body.
West Hoathly (Sharpthorne), West Sussex
TQ 374328–TQ 375329
Wadhurst Clay Formation
Sections through the lacustrine lower Wadhurst Clay, with special reference to palaeontological and sedimentological investigations.
Horsted Keynes, West Sussex
TQ 381266, TQ 386265
Wadhurst Clay Formation up to Upper Tunbridge Wells Sand Formation
Important site for the Hastings Beds Group, clearly demonstrating Hastings Beds ‘megacycles’.
Southborough, Kent
TQ 59254170, TQ59444200– TQ59564186
Wadhurst Clay Formation, Lower Tunbridge Wells Sand Formation
Reference section for the Wadhurst Clay–Lower Tunbridge Wells Sand lacustrine-alluvial transition.
Pembury, Kent
TQ 615416, TQ 613414, TQ 613415
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Well-preserved fluvial channels and scours, close to the southern margin of the London massif.
Tunbridge Wells, East Sussex
TQ 558382–TQ 562384
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Extensive and easily accessible sections through the fluvial Ardingly Sandstone, preserving a wealth of sedimentary structures.
East Grinstead, West Sussex
TQ 380348–TQ 381348
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Clear sections through the fluvial Ardingly Sandstone, preserving a wealth of sedimentary structures.
West Hoathly (Philpots Quarry), West Sussex
TQ 35563228
Lower Tunbridge Wells Sand Formation, Grinstead Clay Formation
Investigations spanning several decades have resulted in detailed sedimentological and palaeobiological interpretation of the Ardingly Sandstone and overlying lower Grinstead Clay, contributing importantly to the currently accepted Wealden model (Allen, 1975, 1981, 1989).
West Hoathly (Hook Quarry), West Sussex
TQ 355313
Lower Tunbridge Wells Sand Formation, Grinstead Clay Formation
Detrital petrographic studies of the marginal-lacustrine Top Lower Tunbridge Wells Pebble Bed have allowed detailed reconstruction of Londinian palaeogeology.
Turners Hill, West Sussex
TQ 339354
Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation
Provides three-dimensional sections within ‘festoon-bedded’ lithofacies of the Ardingly Sandstone.
Scaynes Hill, East Sussex
TQ 391228
Cuckfield Stone Member of the Grinstead Clay Formation
A reference section of the Cuckfield Stone, with much potential for sedimentological analysis.
Horsham (Warnham Mill Pond outfill), West Sussex [Potential GCR Site]
TQ 164318
Upper Tunbridge Wells Sand Formation
A reference section within the Upper Tunbridge Wells Sand, demonstrating meanderplain deposition at the close of Hastings Beds times.
Slinfold, West Sussex
TQ 125312–TQ 124319, TQ 127318
Lower Weald Clay (Horsham Stone Member: BGS Bed 1)
Reference sections within the Horsham Stone, demonstrating alluvial/lacustrine deposition, a range of sedimentary structures and a Cornubian detrital signature.
Warnham, West Sussex
TQ 179352–TQ182354
Lower Weald Clay (in range of BGS Bed 2)
Richly fossiliferous mudstone-dominated succession demonstrating lacustrine/lagoonal environments, small-scale sedimentary cyclicity and fluctuating salinities.
242
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Table 1 (Continued ) GCR site
National Grid Reference
Units
Selection criteria
Capel, Surrey
TQ 176387–TQ 177387
Lower – Upper Weald Clay boundary beds
Richly fossiliferous mudstone-dominated succession demonstrating a vertical transition from offshore to marginallacustrine deposition.
Billingshurst, West Sussex
TQ 078276–TQ 079277
Upper Weald Clay (Okehurst Sand Member: BGS Bed 3a)
Section within Okehurst Sand, currently taken as the base of the Barremian Stage in the Weald Sub-basin. Indicates meanderplain deposition, sourced ultimately from Cornubia.
Coneyhurst Common, West Sussex
TQ 10112441– TQ10072452
Upper Weald Clay (BGS Bed 4)
Representative exposure of a large-Viviparus limestone bed, demonstrating marginal lacustrine deposition.
Ockley, Surrey
TQ 112372–TQ114375
Upper Weald Clay below BGS Bed 5c
Richly fossiliferous mudstone-dominated succession demonstrating a range of palaeoenvironmentally and palaeoclimatically significant features including marginallacustrine pedogenesis and dinoturbation. An outstanding site for palaeontological discoveries.
Chiddingfold, Surrey
SU 942338–SU 944343
Upper Weald Clay (Netherside Sand Member: BGS Bed 7f)
Demonstrates plant colonisation of a fluvial sand body.
Fernhurst, West Sussex
SU 89152873–SU 89222880
Upper Weald Clay (Netherside Sand Member: BGS Bed 7f)
Representative exposure of the Netherside Sand, thought to represent a fluvial sand-bar.
Cranleigh (Bookhurst Tileworks), West Sussex [Potential GCR Site]
TQ 076395
Upper Weald Clay above BGS Bed 8a
Richly fossiliferous mudstone-dominated succession demonstrating lacustrine/lagoonal deposition in latest Wealden times.
SZ 611849–SZ 621853
Wessex Formation, Vectis Formation
Demonstrates replacement of meanderplain environments by muddy coastal lakes and lagoons, towards the close of Wealden times. An important site for modelling late Wealden climates and palaeogeography, and for palaeobiological studies.
Compton Bay – Brighstone Bay, Isle of Wight
SZ 369851–SZ 452792
Wessex Formation, Vectis Formation
Extensive coastal sections through the upper part of the distal alluvial Wessex Formation, overlain by the lacustrine/lagoonal Vectis Formation. Of outstanding importance for sedimentological and palaeobiological studies.
Swanage, Dorset
SZ 031795–SZ 039809
Wessex Formation, Vectis Formation
Extensive coastal sections through the upper part of the alluvial Wessex Formation, overlain by a thin development of the lacustrine/lagoonal Vectis Formation. Particularly significant for demonstrating westward-coarsening alluvial facies gradients and for chronostratigraphic studies.
Steeple, Dorset [Potential GCR Site]
SY 911809
Wessex Formation
Significant for sedimentological studies of the Coarse Quartz Grit, thought to be a Cornubian flood deposit.
Mupe Bay and Worbarrow Bay, Dorset
SY 843797–SY 843801, SY 871796–SY 868801
Wessex Formation
Extensive sections through the Wessex Formation, occupying a key position within the lateral transition from distal to medial floodplain environments towards Cornubia, and demonstrating a range of features including a floodplain oil seep and the chronostratigraphically significant Coarse Quartz Grit.
Lulworth Cove, Dorset
SY 824798–SY824797, SY 828798–SY828797
Wessex Formation
Extensive sections through the Wessex Formation, demonstrating features indicative of the lateral transition from distal to medial floodplain environments.
Durdle Door, Dorset
SY 805802–807802
Wessex Formation
Extensive sections through the Wessex Formation, demonstrating thinning and coarsening of alluvial strata towards Cornubia, and preserving a thick development of the chronostratigraphically significant Coarse Quartz Grit.
Upwey/Bincombe, Dorset
SY 672854
Wessex Formation
Cuttings within the westernmost development of the Wessex Formation. Significant for sedimentological and palaeobiological studies.
Marginal Wealden Dinton, Wiltshire
SU 006309–SU 010310
Muswell Hill, Buckinghamshire
SP 640153
Whitchurch Sands Formation
Cuttings (presently overgrown) through ironstones (some fossiliferous), sandstones and mudstones. The site has considerable potential for critical chronostratigraphic, sedimentological and palaeobiological studies.
Stone, Buckinghamshire
SP 780126
Whitchurch Sands Formation
The site of former sand pits that exposed a unique development of highly quartzose fluvial ‘glass sands’.
Wessex Sub-basin Sandown Bay, Isle of Wight
Formerly exposed poorly dated sands and mudstones of Wealden aspect. The site is potentially significant for reconstructing regional stratigraphy and palaeogeography near the northern margin of the Wessex-Weald Basin.
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
243
(formerly Countryside Council for Wales) and David Skevington (former GCR editor for the Jurassic-Cretaceous boundary beds block). Sincere gratitude is also expressed to Jim Rose for his patience, advice and editorial expertise, to Jenny Kynaston for her technical drawing skills and to Lisa Gordon for her assistance. The Curry Fund of the Geologists’ Association is acknowledged for the production of illustrations.
References
Fig. 8. Professor Percival (‘Perce’) Allen FRS amongst the ‘lifts’ (Ardingly Sandstone Member of the Lower Tunbridge Wells Sand Formation) at Philpots Quarry, West Hoathly, West Sussex (West Hoathly (Philpots Quarry) GCR site).
Geological Conservation Review programme, site selection procedures and rationale were provided by Ellis et al. (1996) and Ellis (2008, 2011). 3. Palaeontological conventions Authors of fossil species are omitted from the texts for purposes of brevity. Details of those authors can be found within palaeontological works cited within the accounts, and are documented in full within the recently published Palaeontological Association Field Guide to English Wealden fossils (Batten, 2011). 4. Copyright The British Geological Survey (BGS) data are used with permission of the Executive Director, British Geological Survey (NERC). The copyright of materials derived from the British Geological Survey’s work is vested in the Natural Environment Research Council (NERC). Ordnance Survey topographic data incorporated within BGS publications are reproduced by permission of the Ordnance Survey. Illustrations originally published by the Palaeontological Association and Geological Society are reproduced with permission of those organisations. Illustrations previously published in Elsevier journals are reproduced by permission of Elsevier. Acknowledgements Amongst those who assisted in the preparation of this introduction we would especially like to thank Neil Ellis (Joint Nature Conservation Committee, Peterborough), Bill Wimbledon
Allen, P., 1938. Ashdown Sand – Wadhurst Clay junction. Geological Magazine 75, 560–561. Allen, P., 1941. A Wealden soil bed with Equisetites lyelli (Mantell). Proceedings of the Geologists’ Association 52, 362–374. Allen, P., 1946. Notes on Wealden fossil soil-beds. Proceedings of the Geologists’ Association 57, 303–331. Allen, P., 1949a. Wealden petrology; the Top Ashdown Pebble Bed and the Top Ashdown Sandstone. Quarterly Journal of the Geological Society, London 104, 257–321. Allen, P., 1949b. Notes on Wealden bone-beds. Proceedings of the Geologists’ Association 60, 275–383. Allen, P., 1959. The Wealden environment: Anglo-Paris Basin. Philosophical Transactions of the Royal Society Series B 242, 283–346. Allen, P., 1964. Sedimentological models. Journal of Sedimentary Petrology 34, 289– 293. Allen, P., 1967a. Origin of the Hastings facies in North-Western Europe. Proceedings of the Geologists’ Association 78, 27–106. Allen, P., 1967b. Strand-line pebbles in the Mid-Hastings Beds and the geology of the London Uplands. Old Red Sandstone, New Red Sandstone and other pebbles. Conclusion. Proceedings of the Geologists’ Association 78, 241–276. Allen, P., 1975. Wealden of the Weald: a new model. Proceedings of the Geologists’ Association 86, 389–437. Allen, P., 1981. Pursuit of Wealden models. Journal of the Geological Society, London 138, 375–405. Allen, P., 1989. Wealden research – ways ahead. Proceedings of the Geologists’ Association 100, 529–564. Allen, P., 1998. Purbeck-Wealden (early Cretaceous) climates. Proceedings of the Geologists’ Association 109, 197–236. Allen, P., Keith, M.L., 1965. Carbon isotope ratios and palaeosalinities of PurbeckWealden carbonates. Nature 208, 1278–1280. Allen, P., Keith, M.L., Tan, F.C., Deines, P., 1973. Isotopic ratios and Wealden environments. Palaeontology 16, 607–621. Allen, P., Wimbledon, W.A., 1991. Correlation of NW European Purbeck-Wealden (nonmarine Lower Cretaceous) as seen from the English type-areas. Cretaceous Research 12, 511–526. Arkell, W.J., 1947a. The Geology of the Country Around Weymouth, Swanage, Corfe and Lulworth, Memoir of the Geological Survey of Great Britain. HMSO, London, xxvii+386 pp. Arkell, W.J., 1947b. The Geology of Oxford. Clarendon Press, Oxford, vi+267 pp. Batten, D.J., 1996. Editorial. Cretaceous Research 17, 2–4. Batten, D.J. (Ed.), 2011. English Wealden fossils. Palaeontological Society Field Guides to Fossils Series, No. 14. Palaeontological Association, London, p. 769. Callomon, J.H., Cope, J.C.W., 1995. The Jurassic Geology of Dorset. In: Taylor, P.D. (Ed.), Field Geology of the British Jurassic. Geological Society, London, pp. 51– 103. Casey, R., Bristow, C.R., 1964. Notes on some ferruginous strata in Buckinghamshire and Wiltshire. Geological Magazine 101, 116–128. Ellis, N., 2008. In: Burek, C.V., Prosser, C.D. (Eds.), A history of the Geological Conservation Review. The History of Geoconservation. Geological Society, London, Special Publication 300, pp. 123–135.
244
J.D. Radley, P. Allen / Proceedings of the Geologists’ Association 123 (2012) 235–244
Ellis, N., 2011. The Geological Conservation Review (GCR) in Great Britain – Rationale and methods. Proceedings of the Geologists’ Association 122, 353– 362. Ellis, N., Bowen, D.Q., Campbell, S., Knill, J.L., McKirdy, A.P., Prosser, C.D., Vincent, M.A., Wilson, R.C.L., 1996. An Introduction to the Geological Conservation Review. Geological Conservation Review Series, No. 1. Joint Nature Conservation Committee, Peterborough, viii+131 pp. Gale, A.S., 2000. Early Cretaceous: rifting and sedimentation before the flood. In: Woodcock, N., Strachan, R. (Eds.), Geological History of Britain and Ireland. Blackwell Science, pp. 339–355. Goldring, R., Pollard, J.E., Radley, J.D., 2005. Trace fossils and pseudofossils from the Wealden strata (nonmarine Lower Cretaceous) of southern England. Cretaceous Research 26, 665–685. Horton, A., Sumbler, M.G., Cox, B.M., Ambrose, K., 1995. Geology of the Country Around Thame. Memoir for 1:50,000 Geological Sheet 237 (England and Wales). HMSO, London, x+169 pp. Jarzembowski, E.A., 1995. Early Cretaceous insect faunas and palaeoenvironment. Cretaceous Research 16, 681–693. Jarzembowski, E.A., Siveter, D.J., Palmer, D., Selden, P.A., 2010. Fossil Arthropods of Great Britain. Geological Conservation Review Series, No. 35. Joint Nature Conservation Committee, Peterborough, xvi+294 pp.
Martin, P.I., 1828. A Geological Memoir on a Part of Western Sussex; With Some Observations Upon Chalk-basins, the Weald-denudation, and Outliers-by-protrusion. John Booth, London, x+100 pp. Rawson, P.F., 1992a. Cretaceous. In: Duff, P., Mc, L.D., Smith, A.J. (Eds.), Geology of England and Wales. The Geological Society, London, pp. 355–388. Rawson, P.F., 1992b. Early Cretaceous. In: Cope, J.C.W., Ingham, J.K., Rawson, P.F. (Eds.), Atlas of Palaeogeography and Lithofacies. Geological Society, London, Memoir 13, pp. 131–137. Rawson, P.F., 2006. Cretaceous: sea levels peak as the North Atlantic opens. In: Brenchley, P.F., Rawson, P.F. (Eds.), The Geology of England and Wales. 2nd edition. The Geological Society, London, pp. 365–393. Stewart, D.J., 1978. The sedimentology and palaeoenvironment of the Wealden Group of the Isle of Wight, southern England. PhD thesis, Portsmouth Polytechnic, Portsmouth, UK. Stewart, D.J., Ruffell, A., Wach, G., Goldring, R., 1991. Lagoonal sedimentation and fluctuating salinities in the Vectis Formation (Wealden Group, Lower Cretaceous) of the Isle of Wight, southern England. Sedimentary Geology 72, 117–134. Topley, W., 1875. The Geology of the Weald. Memoir of the Geological Survey, England and Wales. HMSO, London, xiv+503 pp. White, H.J.O., 1921. A Short Account of the Geology of the Isle of Wight, Memoirs of the Geological Survey of Great Britain. HMSO, London, viii+201 pp.