The BGS Lexicon of Named Rock Units — Result Details

Hake Mudstone Member

Computer Code: HAMU Preferred Map Code: notEntered
Status Code: Full
Age range: Guadalupian Epoch (PUG) — Lopingian Epoch (PUL)
Lithological Description: The Hake Mudstone Member is easily distinguished within the Turbot Anhydrite Formation by its high-gamma, low-velocity, and low-resistivity, blocky log responses. The member is generally composed of grey, greenish grey, yellow or reddish brown mudstone, but locally includes one or more thin beds of white or pale grey anhydritic dolomite or sandstone. Its mudstones are variably dolomitic, anhydritic and micaceous, and they are locally carbonaceous. Where present, dolomite beds contain laminae of clay and nodular anhydrite. In parts of the Outer Moray Firth, the member is composed entirely of fine or medium grained, argillaceous sandstone.
Definition of Lower Boundary: The base of the Hake Mudstone Member is defined by a downward transition from terrigenous sediments to anhydrite or, in some sections, from dolomite to anhydrite. These transitions are marked by a sharp downward decrease in gamma-ray values and increase in velocity and resistivity.
Definition of Upper Boundary: The top of the Hake Mudstone Member is defined by a downward change from anhydrite to mudstone or, locally, argillaceous sandstone, marked by a sharp downward increase in gamma-ray values and decrease in velocity and resistivity.
Thickness: The member is generally between 4 and 15 m thick.
Geographical Limits: The Hake Mudstone Member is restricted to those areas beyond the margins of the Shearwater Salt Formation in which a complete Upper Permian section has been preserved from post-Permian erosion. Thus it is absent at Auk and Argyll but is otherwise widespread in southern Quadrants 29 and 30. It occurs in the South Halibut Basin, is widespread in northeastern parts of the Outer Moray Firth, and has been proved on the eastern flank of the Forties-Montrose High.
Parent Unit: Turbot Anhydrite Formation (TBAN)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 20/04- 1: 3377.5-3385.5 m (11081-11107 ft) below KB (Cameron, 1993). 
Reference Section  North Sea well 14/15- 1: 2299-2311.5 m (7543-7583 ft) (Cameron, 1993). 
Reference Section  North Sea well 15/13- 2: 2379.5-2388.5 m (7807-7836 ft) (Cameron, 1993). 
Reference(s):
Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. The geology of the southern North Sea. United Kingdom offshore regional report. (London: HMSO for the British Geological Survey.) 
Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. 
Taylor, J C M. 1990. Upper Permian-Zechstein. In: Glennie, K W (ed.) Introduction to the petroleum geology of the North Sea, 153-190. Blackwell Scientific Publications, Oxford. 
Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable