The BGS Lexicon of Named Rock Units — Result Details

Sele Formation

Computer Code: SELE Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Paleocene Epoch (GP) — Eocene Epoch (GE)
Lithological Description: The Sele Formation is characterized by medium to dark grey, carbonaceous, pyritic, fissile mudstone, commonly with fine-scale colour lamination. Locally, the mudstone is pale grey, siliceous and blocky, though still finely laminated. Sporadic, thin, altered tuff layers are present, especially in the lower and upper parts. Sandstone units are developed at various levels within the mudstone succession. These are fine to coarse grained and are sharply differentiated from the associated mudstones. The thicker and more continuous sandstone units are given formal member status within the Sele Formation.
Definition of Lower Boundary: Where the Sele Formation overlies the Lista Formation, the boundary is normally defined by a downward change from dark grey, fissile mudstone to the grey-green and green-grey, blocky, bioturbated claystones of the Lista Formation. This is commonly associated with a downward decrease in gamma-ray values and by a downward change from well-oriented to scattered dips. The sonic response varies from area to area, though the base of the formation commonly lies at or shortly below a downward decrease in velocity. Where the lower part of the Sele Formation is sandy, the characteristic downward change in log signature may not be displayed (e.g. 22/6-1). In many mudstone-dominated sections, a high-gamma peak is present near the base, e.g. 29/6a-1, and marks a downward change from fissile, well-laminated mudstone to somewhat less fissile, poorly laminated mudstone. Over much of the North Sea Basin, the lower mudstone unit is less than 10 m thick, and where its identification is hampered by poor sample control or a lack of clear wireline-log signatures, the base of the high-gamma spike may provide the most practicable pick for the base of the formation (e.g. 30/24-6).
Definition of Upper Boundary: Where the Balder Formation is present, the top of the Sele Formation is marked by a rapid downward decrease in the proportion of tuff layers, represented by a marked downward increase in gamma-ray values. A progressive downward decrease in velocity also occurs across the boundary, but the sharpest change normally occurs a few metres below the gamma marker, reflecting the downward continuation of pale to medium grey silica-cemented mudstone into the uppermost part of the Sele Formation. Where the Balder Formation is absent, as in parts of Quadrant 21 (e.g. 21/25-6), the top of the Sele Formation is taken at a marked downhole incoming of grey, carbonaceous, fissile mudstone.
Thickness: Where the mudstone facies is dominant, thicknesses are typically in the range 30 to 50 m, increasing to over 200 m where the Forties Sandstone is most fully developed.
Geographical Limits: The Sele Formation is present throughout the basinal areas of the Central and Northern North Sea but passes westwards into the siltstones and sandstones of the Dornoch Formation. Lott & Knox (1994) extended the geographical range of the Sele Formation in the Southern North Sea area.
Parent Unit: Moray Group (MORA)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 21/10-1 (Deegan & Scull 1977, p.33, fig.36): 2100-2321.5 m (6890-7617 ft) below KB (revised depths). 
Reference Section  North Sea well 16/12a-2: 2195.5-2280 m (7203-7480 ft). 
Reference Section  North Sea well 22/6-1: 2158-2277 m (7080-7470 ft). 
Reference Section  North Sea well 22/1Oa-4: 2476-2636.5 m (8124-8650 ft). 
Reference Section  North Sea well 29/6a-1: 2563.5-2627 m (8410-8618 ft). 
Reference(s):
Knox, R W O'B and Holloway, S. 1992. 1. Paleogene 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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable