The BGS Lexicon of Named Rock Units — Result Details

Lansdown Clay Formation

Computer Code: LDN Preferred Map Code: notEntered
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: Mudstone, grey, bedded, calcareous, shell detrital, with subordinate fine grained, shell detrital and ooidal limestone beds.
Definition of Lower Boundary: Sharp change up from fine-grained limestone of the Tresham Rock Formation, locally (seen in Biddestone borehole) a non-sequence with a hardground, or massive ooid-limestone of the Athelstan Oolite Formation (where present) into mudstone of Lansdown Clay.
Definition of Upper Boundary: Sharp change up from mudstone of Lansdown Clay into ooid-limestone or coarse-grained shelly ooidal limestone ('Grickstone Beds'), locally with limestone pebbles, of Chalfield Oolite Formation. May be a non-sequence.
Thickness: Up to about 10 m. 3.9 m in Biddestone borehole (ST87SE 1) [ST 8609 7282].
Geographical Limits: South Cotswolds: at outcrop from the southern limit of the underlying Tresham Rock Formation near Dyrham [ST 74 74] to the pinch-out/passage of the Lansdown Clay Formation into the Athelstan Oolite Formation at Grickstone Farm [ST 776 829], Little Sodbury. At depth seen from Biddestone borehole (ST87SE 1) [ST 8609 7282] near Corsham to boreholes at Hullavington (ST88SE 16) [ST 8894 8249] (Wyatt, 1996) and Sherston (ST88NW 1) [ST 8474 8542] (Wyatt and Cave, 2002), near Malmesbury.
Parent Unit: Great Oolite Group (GOG)
Previous Name(s): Upper Fuller's Earth Member (UFE)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  South Cotswolds, Tormarton area [ST 75 78], Gloucestershire. 
Type Section  Cutting on M4 motorway at Dodington Ash where it is fully exposed, and comprises about 9 m of calcareous mudstone with thin limestone beds (Torrens, 1968). 
Reference Section  Biddestone borehole (ST87SE 1) [ST 8609 7282], full thickness at 52.19 to 56.05 m depth. Samples held by BGS (Wyatt, 1996). 
Reference(s):
Torrens, H S. 1968. Some Fuller's Earth sections in the south Cotswolds. Proceedings of the Bristol Naturalists' Society, Vol. 31, 429-438. 
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. 
Barron, A J M, Lott, G K, and Riding, J B. 2012. Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report RR/11/06. 
Wyatt, R J and Cave, R. 2002. The Chalfield Oolite Formation (Bathonian, Middle Jurassic) and the Forest Marble overstep in the south Cotswolds, and the stratigraphical position of the Fairford Coral Bed. Proceedings of the Geologists' Association, Vol.113, 139-152. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable