| Computer Code: |
BUHN |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Frasnian Age (DR)
— Frasnian Age (DR) |
| Lithological Description: |
The Buchan Formation in well 38/3-1 is largely composed of fine, and fine to medium grained, reddish brown and white sandstones; these are anhydritic near the top, and locally dolomitic towards the base of the formation. Beds of sandy conglomerate are interbedded with sandstone in the basal 85 m, and sporadic thin beds of reddish brown and greenish grey mudstone and siltstone occur throughout. Principal clast types in the basal conglomerate are white microcrystalline dolomite, phyllite, and vein quartz.
Eleven thin coal seams have been reported between 2880 and 3345 m in well 38/3-1. However, these are not interbedded within typical coal measures, and are interpreted as beds of detrital coal. Two thin beds of pale grey to green 'porphyritic' tuff have been reported in the well at 3587 m and 3590 m. |
| Definition of Lower Boundary: |
In well 38/3-1, the Buchan Formation rests conformably on mid-Devonian marine beds of the Kyle Group, and the boundary is defined by the sharp downward transition from interbedded reddish sandstones, sandy conglomerates and minor volcanics to dark grey mudstones. Beyond the limits of the Kyle Group, the Buchan Formation is likely to rest on Lower Paleozoic strata. |
| Definition of Upper Boundary: |
The Buchan Formation is known to be unconformably overlain by Lower Permian (Auk Formation) sandstones in well 38/3-1, although the precise position of the boundary is open to question. Where Devonian sandstones are overlain by Lower Permian sandstones in the Central North Sea, the boundary is often marked by a significant downhole increase in sonic velocity (Cameron, 1993), but this is not displayed in well 38/3-1. The highest recorded Frasnian palynomorphs occur at 2591 m, but the most likely position of the boundary is at the downhole decrease in gamma-log response at 2528.5 m. The alternative position favoured by the well operators is at 2240 m, although there is no wireline-log break at this level. |
| Thickness: |
In well 38/3-1, the formation is at least 1081 m, and perhaps as much as 1371 m thick. |
| Geographical Limits: |
The formation is widespread in the Central North Sea (Cameron, 1993); it may continue beneath the Tayport Formation south and west of 38/3-1. |
| Parent Unit: |
Upper Old Red Group [Offshore] (UPOR)
|
| Previous Name(s): |
Buchan Formation [Obsolete Code: Use BUHN]
(BUCH)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North Sea well 21/01- 6 (Cameron, 1993, p.136): 2685-3360 m TD (8809-11023 ft TD) below KB. |
| Reference Section |
North Sea well 38/03- 1: 2528.5-3611 m (8296-11848 ft) (Cameron, 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.) |
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. |
| 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. |
| Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. United Kingdom offshore regional report: the geology of the southern North Sea. (London: HMSO for the British Geological Survey.) |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
