The BGS Lexicon of Named Rock Units — Result Details

Wadhurst Clay Formation
Computer Code: WDC Preferred Map Code: WdC
Status Code: Full
Age range: Valanginian Age (KV) — Valanginian Age (KV)
Lithological Description: Comprises soft, dark grey thinly-bedded mudstones ("shales") and mudstones with subordinate beds of pale grey siltstone, fine-grained sandstone (locally calcareous where it is known as Tilgate Stone or colloquially "Hastings Granite"), shelly limestone, clay ironstone and rare pebble beds. The top metre or so of the Wadhurst Clay often comprises stiff clay stained red by penecontemporaneous weathering. Thin beds of shelly limestone, rich in Neomiodon and Viviparus, are present throughout. Nodular clay-ironstone occurs particularly in the lower part of the formation, but also near the top. Thicker beds of siltstone and lenticular calcareous sandstone units are also present. In the Tunbridge Wells district a thicker sand in the lower part of the formation has been named Hog Hill Sand Member (Allen, 1959; Bristow and Bazley, 1972) but this does not appear on BGS maps. Rare Equisetities fossil soils have been described. The base of the formation is commonly a thicker siltstone and in some areas a basal pebble bed, the Top Ashdown Pebble Bed is present.
Definition of Lower Boundary: The base is sharp and marked by the top of the Top Ashdown Pebble Bed locally but where this is absent the boundary is transitional, and placed in siltstones between the underlying fine-grained sandstones of the Ashdown Formation and the mudstones of the Wadhurst Clay Formation. Up-section change from sandstones (Ashdown Formation) into nodular clay-ironstone, silty mudstone and siltstone (Wadhurst Clay Formation).
Definition of Upper Boundary: The upper boundary is marked by a sharp change from siltstones of the Wadhurst Clay Formation up into fine-grained silty sandstones of the Tunbridge Wells Sand Formation. The top of the Wadhurst Clay is commonly red-stained at this junction.
Thickness: The formation thickens westward from 30m at Rye to 70m at Cuckfield and 78m at Worth.
Geographical Limits: Occurs at outcrop in the Weald and at subcrop westward in the Wessex Basin where the succession is imperfectly known. Thins against the London Brabant Ridge to the north and the Hampshire-Dieppe High to the south. The Wadhurst Clay Formation is widespread beneath the Weald, having been recorded in boreholes. It also crops out on several geological sheets in the Weald. Sevenoaks and Tonbridge (287): southern quarter of the sheet from Dry Hill, east of Dormans Land, eastwards across the sheet south of Tonbridge to Brenchley. Maidstone (288): South eastern corner of the district near Castle Hill to the east of Mount Easy. Horsham (302): Eastern part of the sheet, south of East Grinstead to Horsted Keynes. Tunbridge Wells (303): Extensive. East Grinstead to Tunbridge Wells and Lamberhurst-Rotherfield and Wadhurst areas. In the south of the district it is seen in the Danehill, Cackle Street and Buxted to Burwash areas. Tenterden (304): Extensive in southern half of the sheet. Goudhurst-Benenden-Rolvenden-Tenterden areas; Ticehurst-Etchingham-Sandhurst-Newenden areas; and Staple Cross-Northiam-Peasmarsh-Iden areas. Brighton and Worthing (318/333): Confined to a very small area on the very northeastern margin of the district, north of Burgess Hill. Lewes (319): southwest of the Newick, Ridgewood, Framfield and Horam areas to the Dalington, Bodle Street, Green Street and Boreham Street areas. Hastings and Dungerness (320/321): extensive in the western part of the sheet, west of a line drawn from Rye, Winchelsea and Fairlight.
Parent Unit: Wealden Group (W)
Previous Name(s): Wadhurst Formation (-3123)
Wadhurst Clay (-1267)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Sharpthorne Brickworks, West Hoathly. Gallois and Worssam, 1993. 
Reference Section  High Brooms Brickworks, Southborough. Bristow and Bazley, 1972. 
Reference Section  Cuckfield No.1 Borehole, TQ22NE/2, between 219.46 and 283.53m depth. Lake and Thurrell, 1974; Gallois and Worssam, 1993. 
Reference Section  Freshfield Lane Brickworks. Gallois and Worssam, 1993. 
Reference Section  Quarry Hill Brickworks, Tonbridge. Bristow and Bazley, 1972. 
Reference Section  Wadhurst Park Borehole. Anderson et al., 1967; Bristow and Bazley, 1972. 
Reference(s):
Dines, H G, Buchan, S and Bristow, C R. 1969. Geology of the country around Sevenoaks and Tonbridge. Memoir of the Geological Survey of Great Britain, Sheet 287, 183pp. 
Gallois, R W and Worssam, B C. 1993. Geology of the country around Horsham. Memoir of the British Geological Survey, Sheet 302 (England and Wales). 130pp. 
Lake, RD & Shephard-Thorn, ER 1987. Geology of the country around Hastings and Dungeness. Memoir of the British Geological Survey, Sheets 320 and 321 (England and Wales). 
Lake, R D and Thurrell, R G. 1974. The sedimentory sequence of the Wealden Beds in boreholes near Cuckfield, Sussex. Report of the Institute of Geological Sciences, No. 74/2. 
Lake, R D, Young, B, Wood, C J and Mortimore, R N. 1987. Geology of the country around Lewes. Memoir of the British Geological Survey, Sheet 319 (England and Wales). 
Shephard-Thorn, E R, Smart, J G O, Bisson G and Edmonds, E A. 1966. Geology of the country around Tenterden. Memoir of the British Geological Survey, Sheet 304 (England and Wales). 
Young, B and Lake, R D. 1988. Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey, Sheets 318 and 333 (England and Wales). 
Allen, P. 1949. Wealden Petrology: The Top Ashdown Pebble Bed and the Top Ashdown Sandstone. Quarterly Journal of the Geological Society of London, Vol.104, 257-321. 
Allen, P. 1976. The Wealden of the Weald. Proceedings of the Geologists' Association, Vol.86, 389-437. 
Anderson, F W, Bazley, R A B and Shephard-Thorn, E R. 1967. The sedimentary and faunal sequence of the Wadhurst Clay (Wealden) in boreholes at Wadhurst Park, Sussex. Bulletin of the Geological Survey of Great Britain, No.27, 171-235. 
Worssam, B C. 1963. Geology of the country around Maidstone. Memoir of the Geological Survey of Great Britain, Sheet 288 (England and Wales). 
Bristow, C R and Bazley, R A. 1972. Geology of the country around Royal Tunbridge Wells. Memoir of the Geological Survey of Great Britain, Sheet 303. 
Allen, P. 1962. The Hastings Beds deltas: Recent progress and Easter field meeting report. Proceedings of the Geologists' Association, Vol.73, 219-243. 
Topley, W. 1875. The geology of the Weald. Memoir of the Geological Survey of England and Wales. 
Drew, F. 1861. On the succession of the beds in the Hastings Sand in the Northern portion of The Weald. Quarterly Journal of the Geological Society, London, Vol.17, 271-286. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E287 E288 E302 E303 E304 E305 E306 E318 E319 E320 E321 E333
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