The BGS Lexicon of Named Rock Units — Result Details

Irchester Member

Computer Code: IRCH Preferred Map Code: BwL
Status Code: Full
Age range: Bathonian Age (JN) — Bathonian Age (JN)
Lithological Description: A pale grey to off- white or yellowish limestone with thin marls and mudstones, fossiliferous, bioturbated peloidal, ooidal and shell-fragmental more or less argillaceous packstones and wackestones, with subordinate cross-bedded, ooidal, shell-fragmental grainstones, containing a fauna mainly of bivalves, and locally brachiopods, such as Digonella digonoides, described as the Digonoides Beds of Torrens, 1967.
Definition of Lower Boundary: Generally a sharp boundary with the underlying Roade Member comprising ofsimilar limestones generally containing K sharpi, or else a marl or mudstone bed at this level, which may prove a reliable marker, such as the mudstone at the base of the equivalent Ardley Member of the White Limestone Formation in Bucks-Oxon.
Definition of Upper Boundary: Generally a sharp boundary of the limestones with mudstones of the Blisworth Clay Formation.
Thickness: Typically from 5 m to 7 m thick, measured as 6.15 m in type section.
Geographical Limits: The Towcester district to Kettering district, Northants, passings outh-west into the equivalent Ardley Member of the White Limestone Formation, and passing north into the equivalent Longthorpe Member of the Blisworth Limestone Formation.
Parent Unit: Blisworth Limestone Formation (BWL)
Previous Name(s): Great Oolite Limestone [Obsolete Name And Code: Use BWL, GOG or CFDO] (GOL)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Irchester Country Park, a comparable section is located in the adjacent ironstone quarry. See Torrens, 1967; Cripps, 1986; and Cox, B M, and Sumbler, M G. 2002; for additional reference sections. 
Type Section  Irchester Old Lodge Pit, which is now entirely infilled. Cripps,1986; Cox, B M, and Sumbler, M G. 2002. 
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.] 
Torrens, H S, 1967. The Great Oolite Limestone of the Midlands. Transactions of the Leicestershire Literary and Philosophical Society, Vol.61, 65-90. 
Cripps, D W. 1986. A facies analysis of Upper Great Oolite Group in Central and Eastern England. (University of Aston in Birmingham: Unpublished PhD thesis.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E171 E185 E186 E202 E203