| Computer Code: |
BTSA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Barremian Age (KB)
— Aptian Age (KP) |
| Lithological Description: |
The formation comprises sandstones with interbedded mudstones. Sandstones are pale grey or tan and mainly fine- to medium-(locally coarse) grained. They vary from hard to friable, with patchy calcareous cement. Interbedded mudstones are typical of the Valhall and Carrack formations, into which they laterally pass. The thick, massive sandstones display a blocky wireline log signature; the thinly interbedded sandstones and mudstones are characterised by serrated motifs and the upward fining units have gradually upward increasing gamma values. In the Kilda Field (Block 16/26), the formation has been divided into six informal sandstone facies (Guy, 1992), but Johnson and Lott (1993) informally subdivide the formation into two (Upper and Lower). |
| Definition of Lower Boundary: |
The base is usually marked by a downward change from sandstones (Britannian Formation) to mudstones and chalky mudstones (Valhall Formation). On wireline logs it corresponds with a downward increase in gamma-ray values and a decrease in velocity. Locally (e.g. Well 16/27a-2), the Britannia Sandstone Formation rests unconformably on the Valhall Formation. |
| Definition of Upper Boundary: |
The upper boundary is normally defined by the downward change from mudstones (Carrack Formation) to sandstones (Britannia Sandstone Formation). On wireline logs this is shown by low velocity of the mudstones to higher velocities of the sandstone and a downward decrease in gamma-ray values. Locally the Britannia Sandstone Formation is overlain by the Valhall Formation (e.g.22/1a-3). |
| Thickness: |
Up to 180 m. |
| Geographical Limits: |
Outer Moray Firth, Glen Horst, Fisher Bank Basin (Quadrants 15-16, 21-22). |
| Parent Unit: |
Cromer Knoll Group (CRKN)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 15/30- 9 at 4027-4124.5 m below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 16/26- 16 at 3995-4195.5 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 21/02- 6 at 3342-3450 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 22/03a- 1 at 4140-4200 m (Johnson and Lott, 1993). |
| Reference(s): |
| Andrews, I J, Long, D, Richards, P C, Thomson, A R, Brown, S, Chesher, J A, and Mccormac, M. 1990. The geology of the Moray Firth. British Geological Survey United Kingdom offshore regional report (London). |
| Bisewski, H. 1990. Occurrence and depositional environment of the Lower Cretaceous sands in the Southern Witch Ground Graben. 325-338 in Tectonic events responsible for Britain's oil and gas reserves. Hardman, R F P, and Brooks, J (editors). Geological Society, London, Special Publication, 55. |
| Crittenden, S, Cole, J, and Harlow, C. 1991. The early to 'middle' Cretaceous lithostratigraphy of the Central North Sea (UK Sector). Journal of Petroleum Geology, 14, 387-416. |
| Guy, M. 1992. Facies analysis of the Kopervik Sand interval, Kilda Field, Block 16/26, UK North Sea. In: Hardman, R F P (ed.) Exploration Britain: Geological insights for the next decade. Geological Society, London, Special Publication, 67, 187-220. |
| 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 |
