The BGS Lexicon of Named Rock Units — Result Details

Mousa Formation

Computer Code: MOUS Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Eocene Epoch (GE) — Eocene Epoch (GE)
Lithological Description: The Mousa Formation consists predominantly of poorly consolidated, variably glauconitic, locally shelly, fine to coarse grained sandstone. In some sections, the sandstones are massively bedded (e.g. 15/21-1), whereas in others they are interbedded with thin mudstones (e.g. 9/16-1). Most sections include at least one relatively thick unit of glauconitic, grey to grey-brown or grey-green silty mudstone or siltstone. Individual sandstone units mostly show blocky gamma-ray and resistivity log signatures, indicating little vertical variation in grain size. However upward-coarsening trends are often displayed in the basal unit of each major sandstone package (e.g. 15/4-1), and small-scale, discrete upward-coarsening units are often present in the uppermost part of the formation.
Definition of Lower Boundary: In the Northern North Sea, the Mousa Formation overlies the Balder Formation, the boundary being defined by a gamma-ray peak and by a downward change to grey, tuffaceous mudstone. In the Outer Moray Firth, it overlies either the Dornoch Formation (e.g. 15/4-1) or the Balder Formation (e.g. 15/21-1). In both cases, the base of the Mousa Formation is marked by a unit of high-gamma glauconitic mudstone resting on sandstone, lignite, or grey, non-glauconitic mudstone.
Definition of Upper Boundary: The top of the Mousa Formation is marked by a downward change from highly glauconitic silty mudstone or siltstone to sandstone with a significantly lower glauconite content. A marked gamma-ray peak is commonly present at the base of the overlying Skade Formation (e.g.15/4-1).
Thickness: The Mousa Formation is commonly between 200 to 300 m thick.
Geographical Limits: The Mousa Formation is restricted to western parts of the North Sea Basin, but appears to have a northern limit within Quadrant 3 and a southern limit within Quadrant 27.
Parent Unit: Stronsay Group (STRY)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 15/4-1: 504-942 m (1653-3090 ft) below KB. 
Reference Section  North Sea well 9/7-1: 880-1052 m (2887-3452 ft). 
Reference Section  North Sea well 9/16-1: 474.5-1067.5 m (1557-3502 ft). 
Reference Section  North Sea well 15/21-1: 629-1100 m (2064-3608 ft). 
Reference(s):
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