| Computer Code: |
LOOR |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Early Devonian Epoch (DL)
— Early Devonian Epoch (DL) |
| Lithological Description: |
Well 26/14-1, in the Forth Approaches Basin, encountered a complete, 70 m thick Lower Devonian section comprising pink, red, grey and green, fine to coarse grained, poorly sorted sandstone with beds of greenish grey, micaceous shale and reddish brown calcareous mudstone. Nearby well 26/12-1 terminated after penetrating 24 m of weathered olivine-basalts and reddish brown mudstones. Similar volcanic sequences in the Scottish Midland Valley are mainly Gedinnian in age (Gatliff, 1994).
The steeply dipping Lower Devonian section drilled in well 20/9-1, in the South Halibut Basin, comprises reddish grey, greenish grey, pink and white siltstones, with sporadic thin beds of reddish brown mudstone and fine or very fine grained sandstone. |
| Definition of Lower Boundary: |
In well 26/14-1, which lies along strike from the Southern Uplands of Scotland, the Lower Old Red Group rests on steeply dipping Lower Paleozoic turbidites. The base of the Devonian has not been penetrated in the South Halibut Basin. |
| Definition of Upper Boundary: |
The top of the Lower Old Red Sandstone is an angular unconformity throughout Scotland (Mykura, 1991), except at the centre of the Orcadian Basin where there is a conformable transition to Middle Old Red Sandstone. In the Forth Approaches and South Halibut basins, Lower Devonian sediments generally subcrop Permian strata. However, in well 26/12-1, Upper Silurian or Lower Devonian volcanics are unconformably overlain by Upper Devonian strata. |
| Thickness: |
Lower Devonian sediments are up to 9000 m thick along the northern flank of the Midland Valley of Scotland (Mykura, 1991), but it is unlikely that they are so thick offshore. |
| Geographical Limits: |
Palaeogeographic reconstructions by Ziegler (1982) suggest that Lower Devonian sediments continue offshore from eastern Scotland between the continuation of the Highland Boundary and Southern Uplands faults. Their northeastward extent beyond the Forth Approaches and South Halibut basins is unknown. |
| Parent Unit: |
Not Applicable (-)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
North Sea well 20/09- 1: 2616-3353 m TD (8582-11000 ft TD) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 26/14- 1: 1136-1206.5 m (3728-3958 ft) (Cameron, 1993). |
| Reference(s): |
| 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. |
| Gatliff, R W, Richards, P C, Smith, K, Graham, C C, McCormac, M, Smith, N J P, Long, D, Cameron, T D J, Evans, D, Stevenson, A G, Bulat, J, and Ritchie, J D. 1994. United Kingdom offshore regional report: the geology of the central North Sea. (London: HMSO for the British Geological Survey.) |
| Mykura, W. 1991. Old Red Sandstone. 297-346 in Geology of Scotland (3rd edition, revised). Craig, G Y (editor). Geological Society of London. |
| Bluck, B J. 1984. Pre-Carboniferous history of the Midland Valley of Scotland. Transactions of the Royal Society of Edinburgh 75, 275-295. |
| Richards, P C. 1985. A Lower Old Red Sandstone lake in the offshore Orcadian basin. Scottish Journal of Geology 21, 381-383. |
| Ziegler, P A. 1982. Geological atlas of Western and Central Europe. Shell Internationale Petroleum Maatschappij, Amsterdam. |
| 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 |
