The BGS Lexicon of Named Rock Units — Result Details
Claymore Sandstone Member
| Computer Code: | CYSA | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Kimmeridgian Age (JD) — Tithonian Age (JI) | ||
| Lithological Description: | Well sorted, non-graded, generally structureless sandstones with rare interbedded mudstone. Boote and Gustav (1987) recognised three main facies: 1. Medium-grained, generally internally structureless (but with rare graded bedding) sandstones with rare thin mudstone beds, commonly arranged in sets up to c. 5 m thick. 2. Medium- to thin bedded fine to medium-grained sandstones with common, interbedded, locally highly carbonaceous, mudstones. Sandstones are massive or have planar or ripple lamination. 3. Medium to thick bedded, medium-grained sandstones in amalgamated sets, with beds of finely laminated and sporadically bioturbated mudstones. Further facies were described by Turner (1984): 1) coarse- to very coarse-grained sandstones with matrix-supported sandstone pebbles up to 6 mm across and 2) Bioturbated, very fine to fine-grained sandstone with oblique burrows and U-shaped burrows. Turner (1984) also noted load casts, flame structures, dish structures, small slump structures, soft sediment faults and water escape structures in otherwise massive sandstones. Matrix-supported, angular mudstone clasts (up to 2 cm in size) are locally common. In the Claymore Field, the sandstones are subarkose and, locally, carbonate concretions occur (Maher and Harker, 1987). In the lower (early Volgian) part of the member in the Galley Field, sandstones are quartz-arenitic, but higher sandstones (Mid Volgian) there are feldspathic. The thick bedded and amalgamated sandstones produce a 'blocky' gamma-ray log and the thin-bedded sandstones produce a 'ratty' log. | ||
| Definition of Lower Boundary: | The base is defined by a down-section change from sandstone or interbedded sandstone and mudstone, to mudstone (Kimmeridge Clay Formation). It is marked by a down-section increase in gamma-ray values and decrease in velocity. Where interbedded mudstones are present in the lower part of the formation, there is a change to consistently high gamma values. NB. In some areas there are thin sandstones in the underlying Kimmeridge Clay, including a 3 m thick turbidite at its base. These are not included within the Claymore Sandstone Member. | ||
| Definition of Upper Boundary: | The top is recognised by the down-section change from organic-rich, dark grey mudstone (Kimmeridge Clay) to sandstones. The boundary is also marked by down-section decrease in gamma-ray values and an increase in velocity. Locally, on highs in the Claymore Field, calcareous mudstones of the Lower Cretaceous Valhall Formation unconformably rest on the Claymore Sandstone Member (Maher and Harker, 1987). | ||
| Thickness: | Commonly between 50 and 250 m, but the thickest record is 372.5 m in well 15/21-2. | ||
| Geographical Limits: | Witch Ground Graben (quadrants 14 and 15). | ||
| Parent Unit: | Kimmeridge Clay Formation (KC) | ||
| Previous Name(s): | Galley Sands
(-5162)
High Gamma-Ray Sands Unit (-5163) Hot Lens A Member (-5164) Hot Lens B Member (-5165) Low Gamma-Ray Sands Unit (-5166) Silt Unit (-5167) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | North Sea well 14/19- 4 between 2484 and 2566.5 m below KB (revised depths) (Turner et al., 1984; Richards et al., 1993). | ||
| Reference Section | North Sea well 14/19- 2 between 2483 and 2569.5 m (Richards et al., 1993). | ||
| Reference Section | North Sea well 15/17- 8A between 3781.5 and 3891 m (Richards et al., 1993). | ||
| Reference Section | North Sea well 15/23- 4B between 4133.5 and 4419.5 m (Richards et al., 1993). | ||
| Reference(s): | |||
| Turner, C C, Richards, P C, Swallow, J L and Grimshaw, S P. 1984. Upper Jurassic stratigraphy and sedimentary facies in the Central Outer Moray Firth Basin, North Sea. Journal of Marine and Petroleum Geology, 1, 105-117. | |||
| Boote, D R D, and Gustav, S H. 1987. Evolving depositional systems within an active rift, Witch Ground Graben, North Sea. 819-833 in Petroleum Geology of North West Europe. Brooks, J, and Glennie, K W (editors). [Graham and Trotman, London.] | |||
| Coward, R N, Clark, N M and Pinnock, S J. 1991. The Tartan Field, Block 15/16, 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, 377-384. | |||
| Richards, P C, Lott, G K, Johnson, H, Knox, R W O'B. and Riding, J B. 1993. 3. Jurassic 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. | |||
| O'Driscoll, D, Hindle, A D and Long, D C. 1990. The structural controls on Upper Jurassic and Lower Cretaceous reservoir sandstones in the Witch Ground Graben, UK North Sea. In: Hardman, R F P and Brooks, J (eds.) Tectonic events responsible for Britain's oil and gas reserves. Special Publication of the Geological Society, London, No.55, 191-205. | |||
| 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 and Maher, C E. 1988. Late Jurassic sedimentation and tectonics, main area Claymore reservoir, North Sea. In: Giant oil and gas fields. SEPM Core Workshop No.12, 395-458. | |||
| 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. | |||
| Maher, C E and Harker, S D. 1987. Claymore OIlfield. In: Brooks, J and Glennie, K W (eds.) Petroleum Geology of North West Europe, 835-845. [Graham & Trotman, London] | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||