The BGS Lexicon of Named Rock Units — Result Details

Cromarty Sandstone Member

Computer Code: CROS Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Eocene Epoch (GE) — Eocene Epoch (GE)
Lithological Description: The Cromarty Sandstone Member mostly consists of clean, unconsolidated, very fine to fine grained sandstone interbedded with grey, carbonaceous mudstone. In westernmost sections, the lower part of the formation is more argillaceous, with frequent interbedded mudstones.
Definition of Lower Boundary: The base of the Cromarty Sandstone Member is taken at a downward change from sandstone to dark grey mudstone, associated with an increase in gamma-ray values and decrease in velocity. The underlying Sele mudstone (Sele unit 2a, refer to Sele Formation) commonly displays a profile of upward increasing gamma and decreasing sonic velocity.
Definition of Upper Boundary: The top of the Cromarty Sandstone Member is taken at a sharp downward change from dark grey mudstone to sandstone, associated with a decrease in gamma-ray values and increase in velocity.
Thickness: Maximum thickness of about 120 m.
Geographical Limits: The Cromarty Sandstone Member is restricted to northern and western parts of the UK Central Graben.
Parent Unit: Sele Formation (SELE)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Type Section  North Sea well 21/2-1 (Mudge & Copestake, 1992, fig.7): 1612-1764 m (5288-5788 ft) below KB (revised depths). 
Reference Section  North Sea well 21/10-3A: 2108-2172 m (6916-7126 ft). 
Mudge, D C and Copestake, P. 1992a. Revised Lower Palaeogene lithostratigraphy of the Outer Moray Firth, North Sea. Marine and Petroleum Geology 9, 53-69. 
Knox, R W O'B and Holloway, S. 1992. 1. Paleogene 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