The BGS Lexicon of Named Rock Units — Result Details

Letham Silt Member

Computer Code: LESI Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Holocene Epoch (QH)
Lithological Description: Very fine- to coarse-grained sand, silt and clay, grey and brownish grey, well laminated to thin-bedded, some pebbles up to 4cm, finely micaceous, rooty near top below sub-Carse Peat (where developed), depending on location within the palaeo-estuary, the dominant material varies from sand to clay. The deposit forms a series of buried raised beaches/terraces related to transgressive and regressive cycles of sea-level change.
Definition of Lower Boundary: Unconformable and transgressive base on older units including the Bothkennar Gravel, Abbotsgrange Silt and Kinneil Kerse Silt members of the Forth Clay Formation and the Errol Clay Formation.
Definition of Upper Boundary: Overlain unconformably by the sub-Carse Peat (where present) and transgressive estuarine clay, silt and sand of the Carse of Stirling Clay Member.
Thickness: Up to 9m
Geographical Limits: Forth valley west of Aberfoyle to the Forth estuary at Grangemouth.
Parent Unit: Carse Clay Formation (CARCL)
Previous Name(s): Letham Beds (-1650)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  M876 13/1 Borehole, BGS Ref. NS88SE/SE2567 13/1, from 6.20m to 11m depth. 
Reference(s):
Cameron, I B, Aitken, A M, Browne, M A E and Stephenson, D. 1998. Geology of Falkirk District. Memoir of the British Geological Survey Sheet 31E (Scotland). 
Paul, M A, Peacock, J D and Wood, B F. 1992. The engineering geology of the Carse Clay at the SERC Soft Clay Research Site, Bothkennar. 
Paul, M A, Peacock, J D and Barras, B F. 1995. Flandrian Stratigraphy and Sedimentation in the Bothkennar-Grangemouth area, Scotland. Quaternary Newsletter, February 1995, No.75, 22-35 
Browne, M A E, Graham, D K and Gregory, D M 1984. Quaternary estuarine deposits in the Grangemouth area, Scotland. Report of the Institute of Geological Sciences, No.16/3. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S038 S039 S031 S032 S038