The BGS Lexicon of Named Rock Units — Result Details
Brae Formation
| Computer Code: | BRAE | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Kimmeridgian Age (JD) — Tithonian Age (JI) | ||
| Lithological Description: | Grey-brown, medium- to coarse-grained sandstone and conglomerate interbedded with fine-grained sandstone, mudstone and mud-matrix supported breccia. Six major facies have been recognised (Turner et al., 1987; Richards et al., 1993). 1. Sand-matrix conglomerate facies: fine to coarse grained sandstone matrix with clasts up to boulder grade (up to 2 m across) of ?Devonian sandstone and quartz pebbles. Clasts are of variable angularity, poorly sorted and unorientated with respect to bedding. Locally shelly and woody. 2. Mud-matrix breccia facies: angular pebble to boulder grade clasts of quartzo-feldspathic sandstone in a variably sandy mudstone matrix. 3. Medium to thick bedded sandstone facies: Very fine to very coarse grained sandstone, sometimes pebbly, with laminations and cross-bedding. Local mudstone clasts and bioclastic material present. Interbedded mudstone occurs (up to 20% of the facies). 4. Alternated thin-bedded sandstones and interlaminated sandstone-mudstone facies: Sandstone laminae and thin beds (50-80% of the facies) with mudstone. (informally termed 'tiger stripe' deposits). 5. Interlaminated mudstone-sandstone facies: Mudstone (up to 80%) with thin beds of sandstone. 6. Laminated mudstone facies: Planar laminated, dark grey to black, micaceous and carbonaceous mudstones. | ||
| Definition of Lower Boundary: | The base of the formation has been penetrated only locally. In the South Viking Graben, sandstones pass down into mudstones. The boundary is usually taken at a downward change from sandstone with minor mudstone to a more complex succession of interbedded sandstone and mudstone. On geophysical logs this is shown as a downward change from relatively consistent, low gamma response to a more variable gamma-ray response. | ||
| Definition of Upper Boundary: | The upper boundary is defined by a downward change from mudstone with sporadic interbedded sandstone (Kimmeridge Clay Formation, Offshore) to sandstone or interbedded sandstone, conglomerate and mudstone. Gamma values decrease down-section and velocity increases. | ||
| Thickness: | The formation reaches a maximum drilled thickness of c. 760 m but wedges out eastwards. | ||
| Geographical Limits: | South Viking Graben and parts of the East Shetland Basin. North Sea quadrants 9 and 16. | ||
| Parent Unit: | Humber Group (HMBG) | ||
| Previous Name(s): | East Thelma Member
(-5082)
Tiffany Conglomerate Member (-5083) Upper Jurassic Sand Formation (-5084) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | North Sea well 16/07a- 8 at 3679.5-4271 m depth below KB (Turner et al., 1987; Richards et al., 1993). | ||
| Reference Section | North Sea well 9/09b- 5 at 3920-4253.5 m depth (Richards et al., 1993). | ||
| Reference Section | North Sea well 16/07a- 16 at 3768-4139 m depth (Richards et al., 1993). | ||
| Reference Section | North Sea well 16/08- 1 at 3859-4023 m depth (Richards et al., 1993). | ||
| Reference(s): | |||
| 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.) | |||
| 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. | |||
| Turner, C.C., Cohen, J.M., Connell, E.R. & Cooper, D.M. 1987. A depositional model for the South Brae Oilfield. In Brooks, J. & Glennie, K.W. (eds) Petroleum Geology of North West Europe, 853-864. [Graham & Trotman, London] | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||