The BGS Lexicon of Named Rock Units — Result Details

Tresham Rock Formation

Computer Code: TRR Preferred Map Code: TR
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Limestone, calcilutite, pale grey, bioturbated, silici-muddy, poorly fossiliferous; passing up into whitish grey, less silici-muddy calcilutite. Lenses of ooidal limestone occur in places, at the base (Hen's Cliff Oolite of Arkell and Donovan, 1952) and in the upper part. Subordinate calcareous mudstone beds occur in places. Passes laterally by interdigitation southwards into the predominantly mudstone sequence of the Fuller's Earth Formation, and by increase in ooid content northeastwards into the Athelstan Oolite Formation.
Definition of Lower Boundary: Sharp change up from grey mainly calcareous mudstone of the Fuller's Earth Formation (locally known as theHawkesbury Clay) or, where absent, erosive non-sequence, with a sharp upward change from bioclastic limestone of the Dodington Ash Rock Member (Fuller's Earth Formation) into fine-grained limestone.
Definition of Upper Boundary: Rapid passage up from calcilutite with ooidal limestone lenses into massive ooid-limestones of the Athelstan Oolite Formation or, locally, where that formation is absent, well-bedded ooid-limestone of the Chalfield Oolite Formation, or in the south, a sharp upward change into grey mudstone of the Lansdown Clay (Fuller's Earth Formation).
Thickness: 0 to about 17m.
Geographical Limits: Outcrop: Dodington, Gloucestershire, where the Tresham Rock passes into the Fuller's Earth Formation, to Kingscote, Gloucestershire, where it passes into the Athelstan Oolite Formation. Subcrop: Biddestone to Milbourne (Malmesbury), Wiltshire (Wyatt, 1996).
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Tresham Rock (-4937)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Tresham to Kingscote, Gloucestershire. Cave, 1977. 
Reference Section  Hullavington borehole, ST88SE/16. Full thickness between 34.59 and 48.55m depth, dominated by fine-grained limestone with median calcareous mudstone unit, underlain by the Fuller's Earth Formation (Hawkesbury Clay), overlain by typical Athelstan Oolite Formation. Samples held by BGS. Wyatt, 1996. 
Type Section  Foxley No.1 borehole, ST98NW/14A. Full thickness between 47.80 and 64.50m depth, dominated by limestone with a median mudstone unit, underlain by the Dodington Ash Rock Member (Fuller's Earth Formation), overlain by the Athelstan Oolite Formation. Samples held by BGS. Wyatt, 1996. 
Reference(s):
Wyatt, R J. 1996. A correlation of the Bathonian (Middle Jurassic) succession between Bath and Burford, and its relation to that near Oxford. Proceedings of the Geologists' Association, Vol. 107, 299-322. 
Arkell, W J and Donovan, D T. 1952. The Fuller's Earth of the Cotswolds and its relation to the Great Oolite. Quarterly Journal of the Geological Society of London, Vol.107, 227-253. 
Cave R. 1977. Geology of the Malmesbury District. Memoir of the Geological Survey of Great Britain, Sheet 251 (England and Wales). 
Cox, B M and Sumbler, M G. in press. Bathonian-Callovian Correlation chart. in Wright, J K and Cox, B M (editors), A correlation of Jurassic rocks in the British Isles: Middle and Upper Jurassic. Special report of the Geological Society of London. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E251 E265