The BGS Lexicon of Named Rock Units — Result Details
Upper Tunbridge Wells Sand
| Computer Code: | UTW | Preferred Map Code: | UTW |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Valanginian Age (KV) — Valanginian Age (KV) | ||
| Lithological Description: | The unit comprises a complex succession of interbedded deposits with both upward-fining and upward-coarsening cycles. Thinly bedded silty mudstones, siltstones, silty sandstones and fine-grained sandstones are laterally persistent over long distances. Sandstones, which form prominent scarp and dip slope features, are typically fine-grained and quartzose, weathering to a pale yellowish grey or brown colour. They are locally ferruginous in the St Leonard's Forest area where three sandstone beds are sufficiently persistent to be named Shelly Plain Sandstone, Colgate Sandstone and Roffey Park Sandstone (Gallois and Worssam, 1993). Clay ironstone occurs locally, notably in the Horsham-Crawley area (Worssam, 1972). In the Cuckfield area, silt is the dominant component (Lake and Thurrell, 1974). Here, grey and greenish grey silty mudstones and siltstones, red-mottled in part, dominate in the lower part of the unit, whereas pale grey to yellowish grey sandstone mostly appear in the upper part. Channel and slump structures, together with cross-bedding occur in the sandstones. Siltstones are commonly bioturbated. | ||
| Definition of Lower Boundary: | The base is marked by an up-section change from mudstone (Grinstead Clay Member) up into fine-grained sandstones and siltstones (Upper Tunbridge Wells Sand). In some areas the boundary is sharp (e.g. Scayne's Hill, in the Horsham district, where a thick basal sandstone unit occurs). | ||
| Definition of Upper Boundary: | The upper boundary is generally transitional. The fine-grained sandstone and siltstones pass up into mudstone of the Weald Clay Formation. The boundary is shown in the resistance log in the Cuckfield No1 Borehole (Lake and Thurrell, 1974). In the Crawley area, at outcrop, "silty and clayey sediments with rare thin sandstone beds" (Upper Tunbridge Wells Sand) are overlain by "clayey sediments without sandstones" (Weald Clay Formation)(Gallois and Worssam, 1993). The boundary is placed at the top of the highest sandstone. However, in the southern part of the Horsham district and the northern part of the Brighton district, the top of the Upper Tunbridge Wells Sand is marked by a thick sandstone unit, locally capped by "very ferruginous, ripple marked sandstone" or by clay ironstone. The top is also a persistent sandstone bed in the Crawley-Lingfield area of the Tunbridge Wells district (Bristow and Bazley, 1972). 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 maps. | ||
| Thickness: | Up to c.100m (possibly up to 128m according to Gallois and Worssam, 1993). | ||
| Geographical Limits: | The unit is informal and widespread in the Weald of southeastern England, although where the Grinstead Clay and Ardingly Sandstone are missing, it is not possible to distinguish the Lower and Upper Tunbridge Wells Sand units (which are incorporated into the Tunbridge Wells Sand Formation). The Upper Tunbridge Wells Sand unit can be traced across the Sevenoaks-Tonbridge sheet (287), Horsham sheet (302) and Tunbridge Wells sheet (301) where it is seen only in boreholes, and Tenterden sheet (304). It is again present in the northern part of the Brighton and Worthing district sheet (316/333) and can be traced onto the northwestern part of the Lewes sheet (319), but it is again undifferentiated Tunbridge Wells Sand Formation in much of the Lewes district and in the adjoining Hastings district (sheet 320/321). | ||
| Parent Unit: | Tunbridge Wells Sand Formation (TWS) | ||
| Previous Name(s): | Upper Tunbridge Wells Sand
(UTW)
Upper Tunbridge Wells Sand Formation [Obsolete Name and Code: Use UTW] (-4954) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | 550m southsouthwest of Burstow Church. Gallois and Worssam, 1993. | ||
| Reference Section | Hundred Acreas Wood Brickworks, Turners Hill. Bristow and Bazley, 1972. | ||
| Reference Section | Hammond Farm. Gallois and Worssam, 1993. | ||
| Reference Section | Wanham Mill Pond, Horsham. Gallois and Worssam, 1993. | ||
| Reference Section | Stream section, Tinsley Green. Gallois and Worssam, 1993. | ||
| Reference Section | Cuckfield No 1 Borehole TQ22NE2 the Upper Tunbridge Wells Sand is encountered between 65.43 and 166.04m depth. Lake and Thurrell, 1974; Bristow and Bazley, 1972. | ||
| Reference Section | Haywards Heath railway cutting and tunnel. Gallois and Worssam, 1993. | ||
| Reference Section | Freshfield Lane Brickworks. Bristow and Bazley, 1972. | ||
| Reference(s): | |||
| 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. | |||
| 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. | |||
| Hopson, P M, Wilkinson, I P and Woods, M A. 2008. A stratigraphical framework for the Lower Cretaceous of England. British Geological Survey. British Geological Survey Research Report, RR/08/03. | |||
| 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. | |||
| 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. | |||
| 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). | |||
| 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). | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E286 E287 E302 E303 E318 E319 E333 | |||