| Computer Code: |
CRRC |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Aptian Age (KP)
— Albian Age (KA) |
| Lithological Description: |
Central and Northern North Sea: The Carrack Formation comprises essentially non-calcareous, carbonaceous, pyritic, micaceous mudstones and siltstones with local sandstones. Mudstones are medium to dark grey and black (locally red-brown: e.g. Well 14/4-1), firm to hard and blocky to fissile. They have a low average sonic velocity. Thin greenish white tuffaceous layers correspond to high gamma-ray spikes (e.g. Well 15/21a-7 at 3142 m) and broader peaks (e.g. Well 14/20-8 at c. 2698 m) on wire line logs. Thin beds of white to buff, microcrystalline, argillaceous limestones, dolomitic limestones and chalky mudstones are interbedded with the mudstones and produce relatively high velocity spikes (e.g. Well 14/19-13). Local sandstones are fine- to coarse-grained and each sandstone unit usually displays upward fining. One of these sandstone units has been given member status (Skiff Sandstone Member).
Southern North Sea: The fomation comprises poorly calcareous, occasionally sandy, dark-grey to red-brown and variagated mudstones. Sonic velocity is low. Thin sandy beds and phosphatic pebbles produce occasional high gamma peaks. |
| Definition of Lower Boundary: |
Central and Northern North Sea: The base is normally taken at the downward change from dark grey-black, non-calcareous and carbonaceous mudstone (Carrack Formation) to chestnut brown, brick red, reddish grey or pale calcareous mudstones and chalky mudstones (Valhall Formation). It is marked on wireline logs by a sharp downward increase in velocity and density. Locally in the Central and Northern North Sea the formation rests on the Wick Sandstone and Britannia Sandstone formations.
Southern North Sea: There is a sharp downwards change from dark, poorly calcareous mudstones to paler, harder, chalky mudstone (Valhall Formation) and a corresponding downward increase in velocity and decrease in gamma values. |
| Definition of Upper Boundary: |
The top of the formation is normally marked by a downward change from pale to dark grey and red brown calcareous mudstones, chalky mudstones and thin, interbedded limestones (Rødby Formation) to dark grey and black, non-calcareous (or poorly calcareous in the Southern North Sea) mudstones. It is marked by a downward increase in gamma-ray values and a downward decrease in velocity and density. Where the Rødby Formation is absent, the Chalk Group rests unconformably on the Carrack Formation. |
| Thickness: |
Up to 100 m. |
| Geographical Limits: |
Central and Northern North Sea: Quadrants 6-9, 12-16, 19-23, 26-30.
Southern North Sea: Quadrants 35-39, 41-44, 47-49, 51-54. |
| 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 14/20- 8 2670.5-2771.5 m below KB (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 15/16- 14 between the depths 2670.5 and 2771.5 m (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 20/08- 1 at 2251-2350 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 29/09a- 1 at 4003-4091 m depth (Johnson and Lott, 1993). |
| Reference Section |
North Sea well 44/24- 1 at 1393-1402 m depth (Lott and Knox, 1994). |
| Reference Section |
North Sea well 47/09b- 6 at 666-680 m depth (Lott and Knox, 1994). |
| Reference Section |
North Sea well 48/22- 3 at 420.5-430 m depth (Lott and Knox, 1994). |
| Reference Section |
North Sea well 49/25a- 5 at 1812-1853 m depth (Lott and Knox, 1994). |
| 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. |
| Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. |
| Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. |
| Hesjedal, A, and Hamar, G P. 1983. Lower Cretaceous stratigraphy and tectonics of the south-southeastern Norwegian offshore. In: Kaasschieter, J P H, and Reijers, T G A (eds) Petroleum geology of the southeastern North Sea and the adjacent onshore areas (The Hague, 1982) Geologie en Mijnbouw, 62, 135-144. |
| 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.) |
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. |
| Lott, G K and Knox, R W O'B. 1994. 7. Post-Triassic of the Southern 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 |
