| Computer Code: |
CPSA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Aptian Age (KP)
— Albian Age (KA) |
| Lithological Description: |
Sandstones with minor interbedded siltstone and mudstones. Sandstones are poorly sorted, very fine- to coarse- grained, sometimes pebbly and locally argillaceous. They are grey-brown to pale grey and quartzose with common glauconite, carbonaceous debris and pyrite. Sandstones are usually poorly consolidated, but locally calcareous nodules are present (high velocity spikes on wireline logs). Interbedded mudstones and siltsones are mainly calcareous, pale to dark grey, sometimes red-brown and variegated, micromicaceous, glauconitic and typical of the Valhall Formation. However, locally, they are fissile and non-calcareous, with low sonic velocity on wireline logs and typical of the Carrack Formation (Johnson and Lott, 1993). |
| Definition of Lower Boundary: |
The base of the Captain Sandstone Member is taken at a downward change from sandstones and siltstones, with interbedded mudstones, to argillaceous lithologies of the Valhall Formation. It is not necessarily taken at the base of the lowest sandstone within the Aptian sequence, but at the base of the sandstone-rich section (e.g. well 13/17-1). On wireline logs it is marked by a downward increase in gamma-ray values and a decrease in velocity. (Johnson and Lott, 1993). |
| Definition of Upper Boundary: |
The top of the member is normally a downward change from dark grey, carbonaceous, non-calcareous, low velocity mudstones (Carrack Formation) to sandstones with interbedded mudstones (e.g.13/17-1). Locally the Captain Sandstone Member is enclosed within relatively high velocity mudstones (Valhall Formation) (e.g. Well 13/13-1). The boundary is not necessarily taken at the top of the highest Aptian/Albian Sandstone or siltstone bed, but at the top of the sandstone/siltstone-rich section (e.g. Well 12/30-1). It is normally marked on wireline logs by a sharp downward decrease in gamma-ray values and increase in velocity. |
| Thickness: |
Generally up to 100 m, but locally up to 200 m. |
| Geographical Limits: |
Inner Moray Firth (North Sea Quadrants 12-14). |
| Parent Unit: |
Wick Sandstone Formation (WISA)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 13/17- 1 at 992.5-1183.5 m below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 12/30- 1 at 962-991 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 13/14- 1 at 1378-1442 m (Johnson and Lott, 1993). |
| Reference(s): |
| Johnson, H and Lott, G K. 1993. 2. Cretaceous 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 |
