The BGS Lexicon of Named Rock Units — Result Details

Drake Formation

Computer Code: DRKE Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Toarcian Age (JT) — Aalenian Age (JA)
Lithological Description: The formation typically comprises medium to dark grey, variably silty and sandy, variably calcareous mudstone. Mudstone clasts, floating sand grains or thin beds of sandstone occur at the top of the formation. A thin bed of coarse-grained sandstone is developed 0.15-0.20 m below the top of the formation in some sections. Thin beds of oolitic ironstone (iron silicate and siderite), sometimes containing belemnites, occur in some sections.
Definition of Lower Boundary: The lower boundary is defined by a downward change from mudstones to siltstones with subordinate sandstones (Cook Formation). It coincides with a down-section decrease in gamma values and an increase in velocity.
Definition of Upper Boundary: The upper boundary is usually marked by a downward change from sandstone (Broom Formation) to mudstones (although thin Broom-like sandstones occur within the highest part of the Drake Formation). The boundary coincides with a sharp down-section increase in gamma values. In the north-eastern part of the East Shetland Basin (e.g. Well 211/13-7), mudstones of the Rannoch Formation overlie mudstones of the Drake Formation. Here the boundary is placed at the downward change from micaceous to poorly micaceous mudstones and a weak downward decrease in gamma values and increase in velocity.
Thickness: Up to 65 m, but absent on some structural highs.
Geographical Limits: East Shetland Basin and Viking Graben, North Sea quadrants 2, 3, 210, and 211.
Parent Unit: Dunlin Group (DUNL)
Previous Name(s): Drake Sub-Unit (-5186)
Dunlin Shale Member (-5187)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea Well 211/29-3 between 2829.5 and 2887 m below KB (Deegan and Scull, 1977). 
Reference Section  North Sea Well 211/13-7 between 3798.5 and 3822 m (Richards et al., 1993). 
Reference Section  North Sea Well 211/27-4A between 3730 and 3743.5 m (Richards et al., 1993). 
Reference(s):
Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. 
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] 
Bowen, J M. 1975. The Brent Oil-Field. In: Woodland, A W (ed.) Petroleum and the contineental shelf of North-West Europe, 353-361. [Heyden & Son, London] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable