| Computer Code: |
STRR |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Eifelian Age (DI)
— Givetian Age (DV) |
| Lithological Description: |
The Strath Rory Formation encompasses a range of alluvial-fan and alluvial plain Middle Devonian deposits. Fanglomerates have been encountered at seven sites in the southern Inner Moray Firth. Their principal clast types are of quartzite and gneiss, derived from the metamorphic basement, but dolerite clasts have also been recorded in Quadrant 12, and granitic clasts occur near the South Halibut Granite, in Quadrant 13. The alluvial-plain sediments consist mainly of fine to medium or coarse grained, white and grey sandstones with minor beds of grey and reddish brown, commonly micaceous siltstone and mudstone. These beds include highly radioactive horizons in Quadrant 13 that are presumed to be rich in organic detritus. Sand-dominated sections up to 250 m thick have been proved beneath, within, and above fanglomerates at different sites. Well 12/29-2 also encountered a 67 m-thick section of reddish brown, greyish brown and grey lacustrine siltstones and mudstones of mid Eifelian to early Givetian age above fanglomerates. |
| Definition of Lower Boundary: |
The Strath Rory Formation rests unconformably on mainly lacustrine Lower Devonian sediments or on metamorphic or granitic basement. |
| Definition of Upper Boundary: |
Regional unconformities separate the Strath Rory Formation from overlying Upper Devonian or Lower Permian fluvial sandstones or Mesozoic sediments. In most sections, the boundary is marked by a clearly defined wireline-log break. Where Middle Devonian and Lower Permian sandy sections are juxtaposed, the latter can be distinguished by a higher proportion of mudstone beds, and the boundary is generally marked by a sharp downward increase in velocity. |
| Thickness: |
The formation has a maximum drilled thickness of 987 m offshore, but equivalent sequences are more than 3 km thick in parts of northeast Scotland (Mykura, 1991). |
| Geographical Limits: |
Middle Devonian fanglomerates and alluvial-plain deposits of the Strath Rory Formation are widespread across the southern Inner Moray Firth, and have been proved beneath the Halibut Horst at 13/24-1. From there, they may continue south of proven contemporary lake sediments at the Claymore Field to the South Viking Graben. |
| Parent Unit: |
Middle Old Red Group (MIOR)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
North Sea well 12/29- 2: 1985-2972 m (6513-9750 ft) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 12/27- 2: 2678-3064.5 m (8786-10054 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 13/24- 1: 1924-2277 m TD (6313-7471 ft TD) (Cameron, 1993). |
| Reference(s): |
| Armstrong, M. 1977. The Old Red Sandstone of Easter Ross and the Black Isle. In Gill, G (editor). The Moray Firth area - geological studies. Inverness Field Club. |
| Mykura, W. 1991. Old Red Sandstone. 297-346 in Geology of Scotland (3rd edition, revised). Craig, G Y (editor). Geological Society of London. |
| Andrews, I J, Long, D, Richards, P C, Thomson, A R, Brown, S, Chesher, J A, and McCormac, M. 1990. The geology of the Moray Firth. (London: British Geological Survey.) |
| 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.) |
| Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
