The BGS Lexicon of Named Rock Units — Result Details

Thorncombe Sand Member

Computer Code: TCSA Preferred Map Code: TS
Status Code: Full
Age range: Pliensbachian Age (JE) — Pliensbachian Age (JE)
Lithological Description: Yellow-weathering silty very fine-grained sands, locally bioturbated and with hummocky cross-bedding. Impersistent 0.3m limestone in middle. At base 'Blue Band' - 1.8m of blue-grey mudstone - overlies Margaritatus Stone. At top 2.3m of grey mudstone occurs between the Thorncombiensis Bed and the Beacon Limestone Formation
Definition of Lower Boundary: Top of the Margaritatus Stone.
Definition of Upper Boundary: Base of Beacon Limestone Formation (formerly termed Junction Bed).
Thickness: 23m
Geographical Limits: Southwest Dorset. Mapped on Sheet 327 (Bridport). Northern limit not yet proved.
Parent Unit: Dyrham Formation (DYS)
Previous Name(s): Thorncombe Sands (-563)
Alternative Name(s): none recorded or not applicable
Type Section  Seacliffs between Seatown and Eype Mouth. Howarth, M K, 1957. 
Howarth, M K, 1957. The Middle Lias of the Dorset coast. Quarterly Journal of the Geological Society of London, Vol.113, 185-204. 
Buckman, S S, 1922. Jurassic Chronology: II - Preliminary studies. Certain Jurassic strata near Eypesmouth (Dorset): the Junction-Bed of Watton Cliff and associated rocks. Quarterly Journal of the Geological Society of London, Vol.78, 378-436. 
Day, E C H, 1863. On the Middle and Upper Lias of the Dorsetshire Coast. Quarterly Journal of the Geological Society of London, Vol.19, 278-297. 
Arkell W J, 1933. The Jurassic System in Great Britain [Oxford: Clarendon Press.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E327 E341 E342 E343