The BGS Lexicon of Named Rock Units — Result Details

Lamba Formation

Computer Code: LMBA Preferred Map Code: notEntered
Status Code: Full
Age range: Selandian Age (GS) — Thanetian Age (GT)
Lithological Description: The Lamba Formation consists of mudstones with substantial developments of sandstone in the thicker, basinal sections. The mudstones are typically pale to medium grey in colour, silty and of generally monotonous lithology. In some sand-free marginal sections (e.g. 207/1-2) the upper part of the formation consists of cream and pale grey-green to green mudstones. Sandy aggregates associated with the tests of agglutinated foraminifera are commonly seen in cuttings from the upper part of the formation. The sandstones largely occur in units consisting of a succession of discrete beds separated by mudstones, producing a distinctly serrated appearance on wireline logs (e.g. 214/27-1 and 208/17-1). Bed thicknesses as recorded on wireline logs are mostly between one and five metres thick, but reach 10 to 15 metres thick in some instances. Medium to coarse grained, locally pebbly, sandstones also occur higher in the succession in some marginal sections (e.g. 204/23-1; 208/19-1), with thicker sections displaying an overall upward-fining profile. Units of tuffaceous siltstone or tuffite (reworked tuff) occur at the base of the more basinal sections in central parts of the area, where they constitute the Kettla Member (e.g. 214/27-1). The tuffaceous material is dark grey to green- grey and is distinguished on wireline logs by low gamma values associated with high resistivity, high density and high velocity.
Definition of Lower Boundary: The base of the Lamba Formation is defined in some basinal sections by a downward change from tuffaceous mudstone (Kettla Member) to mudstones of the Vaila Formation (e.g. 214/27-1). Where the Kettla Member is absent, the boundary is placed at a sustained downward increase in gamma-ray values (e.g. 204/19-1; 208/17-1). Cuttings examination indicates that this change is associated with subtle downward change from pale to medium grey mudstones to medium to dark grey mudstones with a higher proportion of carbonaceous material.
Definition of Upper Boundary: In more distal sections, the top of the Lamba Formation is defined by a downward change from lithologically varied facies of the Flett Formation, represented by erratic log signatures, to uniform mudstone facies (Lamba Formation), represented by consistent wireline-log signatures. A small gamma- ray peak commonly occurs at the base of the Flett Formation (e.g. 214/27-1). In more proximal sections, the basal beds of the Flett Formation are generally more sandy, and the uppermost sediments of the Faroe Group are more variable in lithology, rendering the boundary more difficult to define on lithology alone. In all sections where the top of the Faroe Group is in mudstone facies, the boundary is marked by a major increase in the abundance of foraminifera, particularly the distinctive agglutinated Bathysiphon/Rhabdammina type. Some sections also show a downward change from grey or variegated mudstones to more consistent pale grey-green mudstones. No such change in mudstone colour is displayed in more distal sections, however.
Thickness: It reaches a maximum thickness of c. 720 m in well 208/17-1.
Geographical Limits: UK north west margin. The Lamba Formation is present throughout the region except where removed by erosion in marginal sections.
Parent Unit: Faroe Group (FARO)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 214/27- 1: 2776-3402 m (9108-11161 ft) (Knox et al., 1997). 
Reference Section  North Sea well 206/01- 1A: 2390-2596 m (7841-8517 ft) (Knox et al., 1997). 
Reference Section  North Sea well 204/19- 1: 1821-2376.5 m (5974-7797 ft) (Knox et al., 1997). 
Reference Section  North Sea well 208/17- 1: 2613-3331 m (8572-10929 ft) (Knox et al., 1997). 
Reference(s):
Knox, R W O'B, Holloway, S, Kirby, G A and Baily, H E. 1997. Stratigraphic nomenclature of the UK North West Margin. 2. Early Paleogene lithostratigraphy and sequence stratigraphy. British Geological Survey, Nottingham. 
Mitchell, S M, Beamish, G W J, Wood, M V, Malacek, S J, Armentrout, M J, Damuth, J E, and Olson, H C. 1992. Paleogene sequence stratigraphic framework of the Faroe Basin. In: Parker, J R (ed.) Petroleum geology of Northwest Europe: proceedings of the 4th conference, 1011-1023. The Geological Society, London. 
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