| Computer Code: |
CRGR |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Oxfordian Age (JO)
— Oxfordian Age (JO) |
| Lithological Description: |
Light grey to buff limestone, sandstone and thin mudstone in the Southern North Sea Basin. Limestones are calcite spar cemented oolites with occasional pisolite horizons and abundant bioclastic debris. Sandstones are fine- to medium-grained and variably cemented. 'Raxella' sponge spicules are common. On geophysical logs, the formation forms a funnel-shaped profile where massive limestone are overlain by interbedded, cemented and poorly cemented sandstone.
A westerly facies change to fine sandstone-, siltstone- and mudstone- dominated deposits (Seeley Formation) takes place on the East Midland Shelf. |
| Definition of Lower Boundary: |
The lower boundary is characterised by a downward change from carbonate-cemented sandstone (Corallian Formation, Offshore) to mudstone (Seeley Formation) and a downward increase in gamma values and decrease in velocity values. |
| Definition of Upper Boundary: |
The upper boundary is defined by a downward change from mudstones (Woodward and Kimmeridge Clay formations) to the massive, oolitic limestones of the Coralline Formation (Offshore). Geophysical logs show a downward decrease in gamma values and an increase in velocity. |
| Thickness: |
Variable in thickness up to a maximum of c. 100 m (in UK wells 47/9-2 and 47/9-3). |
| Geographical Limits: |
Southern North Sea; Quadrants 41, 42, 43, 47 and 48. |
| Parent Unit: |
Humber Group (HMBG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 47/15- 1X; 919-995 m depth (Rhys, 1974, p.7; Lott and Knox, 1994). |
| Reference Section |
North Sea well 42/28- 1; 727-816 m depth (Lott and Knox, 1994). |
| Reference Section |
North Sea well 48/11b- 8; 1264-1337 m depth (Lott and Knox, 1994). |
| Reference Section |
North Sea well 48/17b- 3; 1102-1152 m depth (Lott and Knox, 1994). |
| Reference(s): |
| 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. |
| 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. |
| 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. |
| Lott, G K. 1992 Jurassic. In: Cameron, T D J, Crosby, A, Balson, P S, Jeffrey, D J, Lott, G K, Bulat, J and Harrison, D J. United Kingdom offshore regional report: the geology of the southern North Sea. pp.67-79. [HMSO, London, for the British Geological Survey] |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
