The BGS Lexicon of Named Rock Units — Result Details

Hobbyhorse Bay Limestone Formation

Computer Code: HBL Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Chadian Substage (CI) — Chadian Substage (CI)
Lithological Description: Grey, thick-bedded, coarsely crinoidal packstones. Locally dolomitized. Deposited in a distal ramp setting.
Definition of Lower Boundary: Taken at a sharp junction between the dark limestones, cherts and mudstones of the Linney Head Formation and the overlying thick-bedded coarsely crinoidal limestones of the Formation.
Definition of Upper Boundary: Taken at sharp junction between dolomitised crinoidal packstones at the top of the Formation and the crinoidal packstones with mudstone partings of the overlying Pen-y-holt Limestone Formation. This boundary is unsatisfactory but has not been changed as it defines the base of the Arundian Stage and needs further work.
Thickness: 17m at type locality in southwest Pembrokeshire.
Geographical Limits: Castlemartin area [SR 95 98], south west Pembrokeshire. Relationship to coeval Gully Oolite Formation to the north unknown.
Parent Unit: Pembroke Limestone Group (PEMB)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  East side of Hobbyhorse Bay, 500m east of Linney Head, Castlemartin area, South Pembrokeshire. Entire unit seen and compromises thick bedded coarse crinoidal packstones. Contacts with underlying Linney Head Formation and overlying Pen-y-holt Limestone Formation seen. 
Reference(s):
Dixon, E E L, 1921. The Geology of the South Wales Coalfield, Part XIII , the country around Pembroke and Tenby, being an account of the region comprised in sheets 244 and 245. Memoir of the Geological Survey of Great Britain (HMSO). 
Simpson, J and Kalvoda, J. 1987. Sedimentology and foraminiferal biostratigraphy of the Arundian [Dinantian] stratotype. 226-237 in Micropalaeontology of carbonate enviroments. Hart, M B [editor]. British Micropalaeontological Society series. [Chicester: Ellis Horward Ltd.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E244 E245