The BGS Lexicon of Named Rock Units — Result Details

Stamford Member

Computer Code: STAM Preferred Map Code: St
Status Code: Full
Age range: Bajocian Age (JB) — Bathonian Age (JN)
Lithological Description: A pale greenish grey to yellowish and white, generally massive, fine-grained, generally friable, quartzose, unfossiliferous sandstone or siltstone, interpreted as mainly swamp and lacustrine, seen particularly in the upper part of the succession and in thicker successions as a sandy silty mudstone with plant debris, rootlets and thin lignite lenses, especially near the top, locally including interpreted lacustrine carbonaceous mudstones in hollows at the base and at the top.
Definition of Lower Boundary: In the north, this junction is identified by a sandstone/siltstone/mudstone lithology, sharply and unconformably overlying an uneven channelled surface of marine ooidal limestones of the Lincolnshire Limestone Formation, commonly marked by a secondary limonitic 'Ironstone Junction Bed', and in a presumed narrow zone beyond the limit of the Lincolnshire Limestone-Kettering-Peterborough by similar sandstone, siltstone and mudstone sediments of the Grantham Formation, although in most of Northants, this boundary is seen as an ironstone or ferruginous sandstone of the Northampton Sand Formation or mudstones of the Lias Group, and across the London Platform subcrop the sediments overlie Palaeozoic strata.
Definition of Upper Boundary: The top of the sandstone/siltstone/mudstone as above, often strongly rootletted or with more or less well-developed mudstone seatearth, generally sharply and erosively overlain by marine beds of typically mudstone or sandy mudstone of the succeeding rhythm.
Thickness: Up to 12m, but typically 4m to 5m thick, measured as 4.5 m in the type section.
Geographical Limits: North Lincolnshire,arbitrarily taken at the northern margin of 1:50 000 Sheet 102 where the unit passes northward into the Thorncroft Sand Member of the Rutland Formation, which is more sandy and includes marine intercalations, with an additional sedimentary cycle at the base, south and south-westwards to Bucks, approximating to the southern boundary of Sheet 202, and in subcrop, the western boundary of Sheet 220, where the unit passes into the Horsehay Sand Formation, which is more sandy, interpreted to be of deltaic facies.
Parent Unit: Rutland Formation (RLD)
Previous Name(s): Lower Freshwater Sequence (-3049)
Lower Freshwater Bed of Thompson, 1930 (LFRSH)
White Sands (-976)
Brackish Water Beds (-4345)
Freshwater Beds (-1201)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Stamford, South Lincolnshire, Rutland, north Northants. See Bradshaw (1978) for additional reference sections. 
Reference Section  Ketton Quarry. Aslin, in Torrens,1968; Bradshaw,1978; Cox, B M, and Sumbler, M G. 2002. 
Type Section  Williamson Cliff Brickyard,Stamford. Thompson,1930;Bradshaw,1978. 
Reference(s):
Cox, B M and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series No.26. [Peterborough: Joint Nature Conservation Committee.] 
Bradshaw, M J. 1978. A facies analysis of the Bathonian of eastern England. (University of Oxford: Unpublished PhD thesis.) 
Thompson, B. 1930. The Upper Estuarine Series of Northamptonshire and north Oxfordshire. Quarterly Journal of the Geological Society of London. Vol.86, p.430-462. 
Sharp, S. 1870. The Oolites of Northamptonshire, Part 1. Quarterly Journal of the Geological Society of London, Vol. 26, 354-391. 
Torrens, H S. 1968. The Great Oolite Series. 227-263 in Sylvester-Bradley, P C and Ford, T D (editors), The geology of the East Midlands. (Leicester: Leicester University Press.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E171 E102 E114 E127 E143 E157 E158 E170 E172 E185 E186 E202