The BGS Lexicon of Named Rock Units — Result Details

Stronsay Group

Computer Code: STRY Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Eocene Epoch (GE) — Eocene Epoch (GE)
Lithological Description: The Stronsay Group is characterized by greenish mudstones, often glauconitic in proximal locations. These mudstones contrast with the predominantly grey mudstones of the underlying Montrose Group and with dominantly brown mudstones of the overlying Westray Group. The Stronsay Group is also characterized by a relatively sharp differentiation between a sandstone and siltstone dominated shelf succession and a mudstone-dominated basinal succession. On this basis, two formations are recognised: the Mousa Formation and the Horda Formation. In the Viking Graben area, however, the succession is more complex, with the presence of an extensive basal sandstone sheet along the eastern margin of the East Shetland Platform. This sandstone possesses a clear basinward limit and is geographically separated from equivalent deep-water sandstones (Frigg Sandstone Member, Skroo Sandstone Member).
Definition of Lower Boundary: The base of the Stronsay Group is marked by a downward change from greenish mudstones to predominantly grey mudstones of the underlying Montrose Group.
Definition of Upper Boundary: The top of the Stronsay Group is marked by a downward change from dominantly brown mudstones of the Westray Group to greenish mudstones.
Thickness: The Stronsay Group reaches over 700 m in parts of Quadrant 9, thinning to less than 50 m in the centre of the North Sea Basin.
Geographical Limits: The Stronsay Group extends throughout the North Sea area (Knox & Holloway 1992; Lott & Knox 1994). Knox et al. (1997) extended the geographical range of the Stronsay Group to include the West of Shetland area.
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
Knox, R W O'B, Holloway, S, Kirby, G A and Baily, H E. 1997. Stratigraphic nomenclature of the UK North West Margin. 2. Early Paleogene lithostratigraphy and sequence stratigraphy. British Geological Survey, Nottingham. 
Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. [British Geological Survey, Nottingham]. 
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