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The BGS Lexicon of Named Rock Units — Result Details

Breadstone Shale Formation

Computer Code: BDSH Preferred Map Code: notEntered
Status Code: Full
Age range: Tremadoc Series (O1) — Tremadoc Series (O1)
Lithological Description: Fissile, micaceous, grey to bluish grey or greenish grey mudstone, with bands of fine-grained sandstone and rare thin calcareous beds with cone-in-cone concretions.
Definition of Lower Boundary: Not seen. Strata beneath the Breadstone Shale Formation are not exposed in the Tortworth Inlier.
Definition of Upper Boundary: Overlain by the Micklewood Beds (Tremadoc). Contact not seen but probably conformable and gradational. The Micklewood Beds are distinguished from the Breadstone Shale Formation by the more common occurrence of flaggy sandstone and siltstone beds.
Thickness: Estimated to be about 1500 thick.
Geographical Limits: The northern end of the Lower Palaeozoic Tortworth Inlier, between Purton (SO 691 042) and Newport (ST 699 977).
Parent Unit: Not Applicable (-)
Previous Name(s): Breadstone Shales (-4449)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Around Breadstone in the Tortworth Inlier. Smith & Stubblefield 1933; Curtis, 1968. 
Reference(s):
Smith, S and Stubblefield, C J. 1933. On the occurrence of Tremadoc Shales in the Tortworth Inlier (Gloucestershire), with notes on the fossils. Quarterly Journal of the Geological Society of London, Vol. 89, 357-378. 
Cave R. 1977. Geology of the Malmesbury District. Memoir of the Geological Survey of Great Britain, Sheet 251 (England and Wales). 
Curtis M L K. 1968. The Tremadoc rocks of the Tortworth Inlier, Gloucestershire. Proceedings of the Geologists' Association, Vol. 79, 349-362. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E234 E251