The BGS Lexicon of Named Rock Units — Result Details

Conybeare Group

Computer Code: CNYB Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Westphalian Stage (CW) — Westphalian Stage (CW)
Lithological Description: The term Conybeare Group is introduced here for Westphalian coal measures and primary red beds of the Southern North Sea. The top of the Conybeare Group is a regionally angular unconformity. The Conybeare Group generally rests on 'Millstone Grit' facies of the Whitehurst Group, but oversteps the latter to onlap Dinantian carbonates and Lower Paleozoic basement along the northern flank of the London-Brabant Massif. The Group is divided into four formations. Boundaries between these formations are diachronous, and in some cases strongly so. The base of the Conybeare Group is defined by the lowest Westphalian coal seam, which occurs up to 100 m above the Namurian/Westphalian boundary in those few wells with good biostratigraphic control. The term Caister Coal Formation is introduced for sandy Westphalian A to early Westphalian B coal measures; these are limited to the north of the UK Southern North Sea. They are overlain by, and pass southwards by lateral transition into, argillaceous coal measures, here termed the Westoe Coal Formation. The term Schooner Formation is introduced for a composite unit that incorporates these sandy coal measures together with overlying primary red mudstones and sandstones of Westphalian C age (Ketch Member). Farther south, primary red beds are also preserved in Variscan synclines along the flank of the London-Brabant Massif, but are largely Westphalian D in age there (Besly et al. 1993). They are underlain by a thin, condensed unit of late Westphalian C or Westphalian D coal measures which is believed to be separated from the underlying Westoe Coal Formation by an intra-Westphalian unconformity (refer to Tubb et al. 1986). The term Brig Formation is introduced for the composite unit incorporating the coal measures and red beds above this unconformity.
Definition of Lower Boundary: The Conybeare Group generally rests on 'Millstone Grit' facies of the Whitehurst Group, but oversteps the latter to onlap Dinantian carbonates and Lower Paleozoic basement along the northern flank of the London-Brabant Massif. The base of the Conybeare Group is defined by the lowest Westphalian coal seam, which occurs up to 100 m above the Namurian/Westphalian boundary in those few wells with good biostratigraphic control.
Definition of Upper Boundary: The top of the Conybeare Group is a regionally angular unconformity.
Thickness: 1500 m +
Geographical Limits: none recorded or not applicable
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
Cameron, T D J. 1993. Carboniferous and Devonian of the Southern North Sea. In: Knox, R W O'B & Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. (British Geological Survey, Nottingham). 
Tubb, S R, Soulsby, A and Lawrence, S R. 1986. Palaeozoic prospects on the northern flanks of the London-Brabant Massif. In: Brooks, J, Goff, J C and Van Hoorn, B (eds.) Habitat of Palaeozoic gas in NW Europe. Geological Society, London, Special Publication No.23, 55-72. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable