| Computer Code: |
SPSA |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Valanginian Age (KV)
— Hauterivian Age (KH) |
| Lithological Description: |
Interbedded calcareous sandstones, conglomerates, mudstones and chalky mudstones with thin limestone beds and concretions. Sandstones are fine- to medium- grained, mainly massive to poorly laminated and both non-graded and upward fining sandstone occur. Clasts of micrite and mudstone, comminuted carbonaceous debris and broken shelly material are dispersed throught the sandstones. Laminated sandstone very fine- to very coarse- grained. Pebbly sandstone and thin bioturbated, well sorted sandstones present. Sandstones friable to tightly cemented by calcite. Conglomerates are matrix supported, with poorly sorted, pebble to boulder sized clasts. Matrix is grey-green sandy mudstones to coarse sandstones or conglomerates. Mudstones are typical of the Valhall Formation: generally pale to dark grey, locally red and green calcareoous mudstones and chalky mudstones and pale to dark grey, laminated sandy mudstones. Limestone beds are hard to soft, microcrystalline to argillaceous and pale grey to white.
The member has a variety of wireline log responses reflecting the range of lithofacies. Massive sandstones produce relatively uniform and low gamma-ray values and high velocity. Interbedded thin sandstones, conglomerates, mudstones and limestones produce a more variable serrated log response. Calcite-cemented sandstone produce spikes on the sonic log. (Revised by Johnson and Lott, 1993). |
| Definition of Lower Boundary: |
The base is normally marked by a downward change from sandstones and conglomerates (Scapa Sandstone Member) into dominantly argillaceous strata (Valhall Formation). It does not necessarily coincide with the base of the lowest sandstone in the Valhall Formation, but is marked by an overall downward increase in gamma-ray values (e.g.14/19-15). The sonic log response is variable. Locally the Scapa Sandstone Member rests directly on dark grey-brown, organic-rich, non-calcareous mudstones of the Kimmeridge Clay Formation (e.g. 14/19-9). (Revised Johnson and Lott, 1993). |
| Definition of Upper Boundary: |
The top boundary is marked by a downward change from argillaceous lithofacies (Valhall Formation) to interbedded sandstones, conglomerates, siltstones and mudstones. On wireline logs there is a downward decrease in gamma-ray values and an increase in velocity. The sonic log response is variable in character. The top of the Scapa Sandstone Member is not necessarily placed at the highest sandstone bed within the informal Valhall unit 3 (Johnson and Lott, 1993), but rather at a log break that marks the top of a sandstone- or conglomerate-rich succession. (Revised Johnson and Lott, 1993). |
| Thickness: |
Commonly 50 to 150 m. |
| Geographical Limits: |
NW Witch Ground Graben (North Sea Quadrants14-15). |
| Parent Unit: |
Valhall Formation (VALH)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 14/19- 15 at 2540.5 to 2599.5 m below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 14/19- 9 at 2498 to 2893 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 14/19- 17 at 2727.5-2883 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 14/20- 8 at 2914.5 to 3004 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. |
| Riley, L A, Harker, S D, and Green, S C H. 1992. Lower Cretaceous palynology and sandstone distribution in the Scapa Field, UK North Sea. Journal of Petroleum Geology, 15, 97-110. |
| Harker, S D, Gustav, S H and Riley, L A. 1987. Triassic to Cenomanian stratigraphy of ther Witch Ground Graben. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 809-818. [Graham & Trotman, London] |
| Harker, S D, Green, S C H and Romani, R S. 1991. The Claymore Field, Block 14/19, UK North Sea. In: Abbotts, I L (ed.) United Kingdom oil and gas fields, 25 years commemorative volume. Memoir of the Geological Society, London, 14, 269-278. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
