| Computer Code: |
COSA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Hauterivian Age (KH)
— Barremian Age (KB) |
| Lithological Description: |
Sandstones with interbedded siltstone and mudstone. Sandstones are quartzose, very fine- to coarse- or very coarse- grained, pale grey to white and sporadically glauconitic. Generally calcareous, although commonly friable. Interbedded mudstones and siltstones are pale to dark grey, calcareous, micromicaceous and locally carbonaceous. Sporadic white to pale grey and tan, microcrystalline and argillaceous, hard to soft limestone concretions produce high velocity spikes (e.g. well 12/30-1). |
| Definition of Lower Boundary: |
The base is taken at a downward change from sandstones and siltstones with interbedded mudstones to dominantly argillaceous strata (Valhall Formation). On wireline logs there is a downward increase in gamma-ray values and, commonly, an increase in velocity (e.g. 12/30-1). |
| Definition of Upper Boundary: |
The top is taken at a downward change from pale to dark grey, calcareous mudstones (Valhall Formation) to pale grey sandstones and siltstones with interbedded mudstones. On wireline logs, it is normally a downward decrease in gamma-ray values and an increase in velocity. |
| Thickness: |
Up to 400 m. |
| Geographical Limits: |
Inner Moray Firth, extending on to the Halibut Shelf and Halibut Horst (North Sea quadrants 12-13). |
| 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 1291.5-1504 m below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 12/30- 1 at 1366-1405 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 |
