The BGS Lexicon of Named Rock Units — Result Details
Rannoch Formation
| Computer Code: | RANN | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Aalenian Age (JA) — Bajocian Age (JB) | ||
| Lithological Description: | Northern East Shetland Basin: The formation comprises an upward coarsening succession from mudstone (informally the 'Rannoch Mudstone unit' of Richards et al., 1993) to very fine- or fine-grained sandstone. Southern East Shetland Basin: Upward coarsening sandstones (the 'Rannoch Mudstone unit' is absent). Sandstones are often parallel laminated and hummocky cross-stratified, micaceous, and carbonaceous along the laminations. Individual beds have sharp bases and may show an upward succession from laminated or hummocky cross-stratified sandstone to ripple laminated sandstone. Bioturbation is extensive. Locally calcite-cemented. The 'Ranoch Mudstone unit' comprises a heterolithic succession of interbedded mudstones, siltstones and sandstones. Mudstones and siltstones are dark grey, carbonaceous, micaceous and laminated. Low angle scours truncate laminations in places. Sandstones are thin, very fine-grained and micaceous. Bioturbation is locally intense. South-western East Shetland Basin: Fine-grained, locally medium-grained sandstone. | ||
| Definition of Lower Boundary: | East Shetland Basin: In the southern part of the East Shetland Basin the boundary is placed at a downward change from very fine-grained, micaceous sandstone to coarser sandstones (Broom Formation). In the northern part of the East Shetland Basin the boundary is marked by a downward change from micaceous mudstones ('Rannoch Mudstone unit') to coarse sandstone (Broom Formation). In both areas there is a down-section decrease in gamma values. South-western part of the East Shetland Basin: downward transition from fine-grained- to medium-grained, micaceous, laminated sandstones (Rannoch Formation) to coarse grained sandstone (Broom Formation). This corresponds to the base of an interval of increased gamma-ray values. North eastern part of East Shetland Basin: micaceous mudstones ('Rannoch Mudstone unit') overlie poorly micaceous mudstones of the Drake Formation (Dunlin Group). This corresponds with a slight down-section decrease in gamma values and increase in velocity. | ||
| Definition of Upper Boundary: | The boundary is defined by a sharp downward change from coarser, less micaceous, generally structureless sandstones (Etive Formation) to finer, micaceous, laminated sandstones. It coincides with a downward increase in gamma values and and often a downward increase in velocity. | ||
| Thickness: | Up to c. 100 m. | ||
| Geographical Limits: | East Shetland Basin and into the Viking Graben. North Sea quadrants 2, 3, 210, 211. | ||
| Parent Unit: | Brent Group (BRNT) | ||
| Previous Name(s): | Micaceous Sand
(-5198)
Micaceous Sand Bed (-5199) Rannoch Mudstone Unit (-5200) Rannoch Shale (-5201) Rannoch Sub-Unit (-5202) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | North Sea well 211/29- 3 between 2783 and 2819 m below KB (Deegan and Scull, 1977). | ||
| Reference Section | North Sea well 211/13- 7 between 3695.5 and 3798.5 m (Richards et al., 1993). | ||
| Reference Section | North Sea well 211/18- 7 between 3311.5 and 3360 m (Richards et al., 1993). | ||
| Reference Section | North Sea well 211/27- 10 between 3597.5 and 3620.5 m (Richards et al., 1993). | ||
| Reference Section | North Sea well 3/01- 2 between 3783.5 and 3801 m (Richards et al., 1993). | ||
| Reference(s): | |||
| 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. | |||
| Bowen, J M. 1975. The Brent Oil-Field. 353-361 in Petroleum and the continental shelf of North-West Europe. Woodland, A W (editor). (Heyden and Son, London.) | |||
| 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. | |||
| Giles, M R, Stevenson, S, Martin, S V, Cannon, S J C, Hamilton, P J, Marshall, J D and Samways, G M. 1992. The reservoir properties and diagenesis of the Brent Group: a regional perspective. In: Morton, A C, Haszeldine, R S, Giles, M R and Brown, S (eds.) Geology of the Brent Group. Special Publication of the Geological Society, London, No.61, 289-327. | |||
| 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.) | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| none recorded or not applicable | |||