The BGS Lexicon of Named Rock Units — Result Details

Lower Tunbridge Wells Sand

Computer Code: LTW Preferred Map Code: LTW
Status Code: Index Level
Age range: Valanginian Age (KV) — Valanginian Age (KV)
Lithological Description: The unit comprises: (i) A lower unit of thinly interbedded silty fine-grained sandstones and common, though subordinate, siltstone and rare beds of clay or silty clay; (ii) An upper unit of largely massive or thickly bedded, fine- and medium-grained sandstone (Ardingly Sandstone Member of the Tunbridge Wells Sand Formation). It is cross-bedded and festoon-bedded in part. In much of the Horsham district it is composed of "sandrock", a clean white or greyish white, soft quartzose sandstone that forms crags. It becomes finer-grained towards the south of the Horsham district. Locally, in the East Grinstead area, stringers of quartz and quartzite pebbles are common. The pebbles become larger towards Tunbridge Wells.
Definition of Lower Boundary: The lower boundary is taken where interbedded silty sandstones and subordinate siltstones of the unit rest with a sharp contact on red stained mudstones of the Wadhurst Clay Formation. Commonly a spring line is associated with the junction.
Definition of Upper Boundary: The upper boundary is taken at the base of the Top Tunbridge Wells Pebble Bed, which is situated at the base of the mudstones of the Grinstead Clay Member. Where the pebble bed fails, as in the Tunbridge Wells district, the base is placed at the junction between the Grinstead Clay Member above the Ardingly Sandstone Member below. Locally ripples of coarse-grained sand separate these two members. In some districts, however, such as Tenterden (304) Hastings (320/321) and Lewes (319) where the Ardingly Sandstone Member and the Grinstead Clay Member thin out, the sands between the Wadhurst Clay Formation and the Weald Clay Formation are undifferentiated and called the Tunbridge Wells Sand Formation in BGS Memoirs and on BGS maps.
Thickness: Up to 33m.
Geographical Limits: The unit is widespread in the Weald of southeastern England, although where the Grinstead Clay Member and Ardingly Sandstone Member are missing, it is not possible to distinguish the informal Lower and Upper Tunbridge Wells Sand units, which have been incorporated into the "Tunbridge Wells Sand". The informal unit can be traced across the Sevenoaks-Tonbridge (sheet 287), Maidstone (sheet 288), Horsham (sheet 302) and Tunbridge Wells (sheet 303) districts, but the Tunbridge Wells Sand Formation is undifferentiated on the Tenterden sheet (304). The informal unit is again present in the northern part of the Brighton and Worthing district (sheet 318/333) and onto the Lewes sheet (319), but it is again undifferentiated Tunbridge Wells Sand Formation in the Eastern part of the Lewes district and in the Hastings district (sheet 320/321).
Parent Unit: Tunbridge Wells Sand Formation (TWS)
Previous Name(s): Lower Tunbridge Wells Sand Formation (-2926)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Stream gorge, west of Ditton Place, Handcross. Gallois and Worssam, 1993. 
Reference Section  Stream section, 550m southsoutheast of Monks. Gallois and Worssam, 1993. 
Reference Section  High Grove. Gallois & worssam, 1993. 
Reference Section  Sunken Road at Brook House Gallois and Worssam, 1993 
Reference Section  Kelsey's Culverden Brewery. Bristow and Bazley, 1972. 
Reference Section  East Grinstead Church Bristow & Bazley, 1972 
Reference Section  Railway cutting north of Stoneland's Farm. Bristow and Bazley, 1972. 
Reference Section  High Brooms Brickworks, Southborough. Bristow and Bazley, 1972. 
Reference Section  Cuckfield No.1 TQ22NE/2 [TQ 2961 2731] Borehole where the full succession is encountered between 192.94 and 219.46m depth. Gallois and Worssam, 1993. 
Reference Section  Philpotts Quarry. Gallois and Worssam, 1993 
Reference Section  Old pit near Kingscote House. Gallois & Worssam, 1993. 
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 (England and Wales), 183pp. 
Young, B and Lake, R D. 1988. Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey, Sheet 318 and 333 (England and Wales). 
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. 
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. 
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 (England and Wales). 
Gallois, R W. 1964. In: Summary of Progress of the Geological Survey of Great Britain, for 1964, p.47. 
Lake, R D and Thurrell, R G. 1974. The sedimentary sequence of the Wealden Beds in boreholes near Cuckfield, Sussex. Report of the Institute of Geological Sciences, No.74/2. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E287 E288 E302 E303 E318 E333