| Computer Code: |
WOEV |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
| Lithological Description: |
The West Orkney Evaporite Formation comprises sandstones, anhydritic mudstones, variably anhydritic siltstones and halites. The mudstones and siltstones are red to brown or purple to grey, hard, mostly anhydritic, micaceous and calcareous, and occasionally dolomitic. The sandstones are red-brown or rarely grey to orange, very fine to fine or occasionally medium or coarse, argillaceous, moderately to well sorted, calcareous, arkosic, micaceous, and well cemented. The halites are clear to white, occasionally sandy, and occur as discrete thin beds, veins or disseminated masses. |
| Definition of Lower Boundary: |
The base of the West Orkney Formation has only been penetrated in well 205/27a-l on the Solan Bank High, where it is marked by a downward transition from sandstones and anhydritic mudstones, to Solan Bank Formation sandstones. On wireline logs, this change is represented by a marked downward decrease in gamma-ray log values and a slight increase in velocity. |
| Definition of Upper Boundary: |
The top of the West Orkney Evaporite Formation is marked by a downward change from Otter Bank Formation mudstones to siltstones on the Solan Bank High (205/27a-l) or Shoal High Bank Formation siltstones, to interbedded mudstones, anhydrites, sandstones and halites (202/19-1) in the West Orkney Basin. On wireline logs, the former transition shows a downward increase in gamma-ray log values and a sharp increase in velocity whereas in case of the latter, a decrease in gamma-ray log values and a sharp increase in velocity is recorded. |
| Thickness: |
A maximum unbottomed thickness of 1432 m has been recorded from well 202/19-1. |
| Geographical Limits: |
The West Orkney Evaporite Formation has only been encountered in well 202/19-1 within the West Orkney Basin and in well 205/27a-l on the Solan Bank High. The formation may well be present at depth to the west within the North Rona Basin and to the southwest in the North Lewis and North Minch basins (Stoker et al., 1993). |
| Parent Unit: |
Zechstein Group (ZG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 202/19- 1: 1757-3189 m TD (5764-10462 ft) (Ritchie et al., 1996). |
| Reference Section |
North Sea well 205/27a- 1: 1738-2203 m (5702-7228 ft) (Ritchie et al., 1996). |
| Reference(s): |
| Stoker, M S, Hitchen, K, and Graham, C C. 1993. United Kingdom offshore regional report: the geology of the Hebrides and West Shetland shelves and adjacent deep-water areas. (London: HMSO for the British Geological Survey.) |
| Ritchie, J D, Gatliff, R W and Riding, J, 1996. 1. Pre - Tertiary lithostratigraphy. In: Stratigraphic Nomenclature of the UK North West Margin. British Geological Survey, Nottingham. |
| Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
