The BGS Lexicon of Named Rock Units — Result Details

Gorse Mudstone Member

Computer Code: GORS Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Oxfordian Age (JO) — Oxfordian Age (JO)
Lithological Description: Brownish black, paralic mudstones with locally abundant coal fragments.
Definition of Lower Boundary: The basal boundary of the Gorse Member (and Heather Formation) may be conformable or unconformable. It is defined by a down-section passage from mudstones to thinly bedded sandstones, mudstones and coals (Stroma Member, Pentland Formation). It is marked by a sharp down-section decrease in gamma-ray and velocity values. In some sections, the member is seen to rest unconformably on Triassic reddish and grey-brown mudstones (Smith Bank Formation).
Definition of Upper Boundary: The top is defined by a down-section change from grey mudstone (Heather Formation) to brownish black mudstones; a down-section increase in resisitivity, a decrease in velocity and, often, a temporary increase in gamma.
Thickness: Up to c. 60 m.
Geographical Limits: Witch Ground Graben and South Halibut Basin (Outer Moray Firth) (Quadrants 14, 15 and 20).
Parent Unit: Heather Formation (HTHE)
Previous Name(s): Skene Member (-5143)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 20/8-1 between depths 2764 and 2783.5 m below KB (Richards et al. 1993). 
Reference Section  North Sea well 15/21-4 between depths 2556.5 and 2569.5 m (Richards et al., 1993). 
Reference(s):
Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G. Lithostratigraphic nomenclature of the UK North Sea. [British Geological Survey, Nottingham] 
Harker, S D, Mantel, K A, Morton, D J and Riley, L A. 1993. The stratigraphy of Oxfordian-Kimmeridgian (Late Jurassic) reservoir sandstones in the Witch Ground Graben, UK North Sea. American Association of Petroleum Geologists Bulletin, 77, 1693-1709. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable