| Computer Code: |
OTBA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Early Triassic Epoch (TE)
— Early Triassic Epoch (TE) |
| Lithological Description: |
The Otter Bank Formation is made up of a mixture of mudstones, siltstones and sandstones. The mudstones are brown to red or grey, occasionally green to purple, hard, sometimes laminated or blocky, micaceous, variably calcareous and slightly anhydride, whereas the siltstones are red to brown and generally very calcareous and micaceous. The sandstones are brown to red, argillaceous, mostly fine grained, moderately well sorted, occasionally micaceous, calcareous and cemented. |
| Definition of Lower Boundary: |
The base of the Otter Bank Formation is marked by a downward change from mudstones, siltstones and sandstones, to either variably anhydride siltstones, mudstones and sandstones of the West Orkney Evaporite Formation (205/27a-1) or limestones and siltstones of the Bosies Bank Formation (220/26-2). On wireline logs, the transition between the Otter Bank Formation and the Bosies Bank Formation is represented by a marked downward decrease in gamma-ray log values and an increase in velocity, whereas the transition to West Orkney Evaporite Formation is marked by increases in velocity and gamma-ray log values. |
| Definition of Upper Boundary: |
The top of the Otter Bank Formation is represented by a downward transition from mainly sandstones of the Cormorant Formation in the Møre Basin (220/26-2) or Foula Formation on the Solan Bank High (205/27a-l), to mudstones, siltstones and sandstones. On wireline logs, these changes are marked by a downward increase in gamma-ray log values and a decrease in velocity. The velocity log values decrease only slightly downwards from Foula Formation sandstones to Otter Bank Formation mudstones, probably due to the clean and porous nature of the sandstones within the former formation. |
| Thickness: |
It reaches a maximum drilled thickness of 56 m in well 205/27a-1. |
| Geographical Limits: |
The Otter Bank Formation only occurs in well 220/26-2 within the Møre Basin and in well 205/27a-1 on the Solan Bank High. |
| Parent Unit: |
Heron Group (HERO)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 205/27a- 1: 1682-1738 m (5518-5702 ft) (Ritchie et al., 1996). |
| Reference Section |
North Sea well 220/26- 2: 3782-3807 m (12408-12490 ft) (Ritchie et al., 1996). |
| Reference(s): |
| Booth, J, Swiecicki, T, and Wilcockson, P. 1993. The tectono-stratigraphy of the Solan Basin, west of Shetland. 987-998 in Petroleum Geology of Northwest Europe: Proceedings of the 4th Conference. Parker, J R (editor). (The Geological Society, London.) |
| 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 |
