The BGS Lexicon of Named Rock Units — Result Details

Four Fathom Limestone Member

Computer Code: FFL Preferred Map Code: FFL
Status Code: Full
Age range: Brigantian Substage (CX) — Brigantian Substage (CX)
Lithological Description: Limestone, packstone, fine-grained, medium and dark grey, thick bedded and wavy-bedded, with few mudstone partings; somewhat argillaceous, particularly at the top. Typically contains layers of nodules and lenses of black chert. Crinoidal but not particularly fossiliferous on the Alston Block; contains conspicuous coral biostromes to the north and south of the Alston Block. Goniatites indicative of the P2c biozone have been found in mudstones above the Four Fathom Limestone in the Mount Pleasant Borehole [NZ034 152] near Barnard Castle (Johnson et al, 1962).
Definition of Lower Boundary: Taken at the generally conformable, sharp base of the first bed of limestone that overlies measures of the Alston Formation. On the Alston Block, usually overlies less than 2m of dark grey seatearth mudstone and mudstone with abundant plants that overlies as a prominent sandstone referred to there as the Natrass Gill Hazle. In the Bellingham district a coal underlies the limestone.
Definition of Upper Boundary: Taken at the top of the uppermost limestone bed that is overlain by a sequence of dark grey mudstones, the lowermost of which are calcareous and fossiliferous. On the Askrigg Block the limestone member is overlain by a dark grey or almost black chert referred to as the Underset Chert.
Thickness: 7-10m north of the Lake District and in Northumberland; 5 to 12m on the Alston Block; about 9m on the Askrigg Block, but locally up to 25m.
Geographical Limits: Occurs throughout northern England and the Scottish borders, lying below the Great Limestone near the top of the Alston Formation.
Parent Unit: Alston Formation (AG)
Previous Name(s): Four Fathom Limestone (-904)
Second Limestone (-905)
Eight Yard Limestone (-2799)
Low Dean Limestone [Obsolete Name And Code: Use FFL] (LDL)
Sandbanks Limestone [Obsolete Name And Code: Use FFL] (SBKL)
Buccleuch Limestone [Obsolete Name And Code: Use FFL] (BUCC)
Underset Limestone [Obsolete Name And Code: Use FFL] (UNL)
Alternative Name(s): none recorded or not applicable
Type Section  Stream section, Middlehope Burn, Westgate, Upper Weardale. 
Reference Section  Rookhope Borehole (BGS Reg No NY94SW1), Rookhope, Weardale, Co. Durham. Johnson and Nudds (1996). 
Type Area  Coastal exposures of Near Skerr, Middle Skerr and Far Skerr, about 4km southeast of Berwick upon Tweed. 
Chadwick, R A, Holliday, D W, Holloway, S and Hulbert, A G. 1995. The structure and evolution of the Northumberland-Solway Basin and adjacent areas. Subsurface Memoir of the British Geological Survey. 
Johnson, G A L, Hodge, B L and Fairbairn, R A. 1962. The base of the Namurian and the Millstone Grit in northeast England. Proceedings of the Yorkshire Geological Society, Vol.33, 341-362. 
Young, B and Boland, M P. 1992. Geology and land-use planning: Great Broughton-Lamplugh area, Cumbria. BGS Technical Report WA/92/54. 
Dunham, K C, and Wilson, A A. 1985. Geology of the Northern Pennine Orefield. Volume 2 Stainmore to Craven. Economic Memoir of the British Geological Survey, Sheets 40, 41 and 50, and parts of Sheets 31, 32, 51, 60 and 61(England and Wales). 
Burgess, I C and Holliday, D W. 1979. Geology of the country around Brough-under-Stainmore. Memoir for 1:50 000 geological sheet 31 and parts of sheets 25 and 30. Geological Survey of Great Britain (England and Wales). [London: HMSO.] 131pp. 
Dunham, K C. 1990. Geology of the Northern Pennine Orefield, Vol.1. Tyne to Stainmore, (2nd edition) Economic Memoir of the British Geological Survey, Sheets 19 and 25, parts of 13, 24, 26, 31, 32 (England and Wales). 
Frost, D V and Holliday, D W. 1980. Geology of the country around Bellingham. Memoir of the British Geological Survey, Sheet 13 (England & Wales). 
Gunn, W. 1900. The geology of the Belford, Holy Island and the Farne Islands, Northumberland. Memoir of the Geological Survey of Great Britain, Sheet 4 (England and Wales). 
Lumsden G I and Wilson R B. 1961. The stratigraphy of the Archerbeck Borehole, Canonbie Dumfriesshire. Bulletin of the Geological Survey of Great Britain, No.18, 1-89. 
Eastwood,T, Hollingworth, S E, Rose, W C C and Trotter, F M. 1968. Geology of the country around Cockermouth and Caldbeck. Memoir of the Geological Survey of Great Britain, England and Wales, Sheet 23. 
Johnson, G A L and Nudds, J R. 1996. Carboniferous biostratigraphy of the Rookhope Borehole, Co. Durham. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol.86, 181-226. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E032 E031 E025 E024 E020 E018 E023 E026 E014 E013 E019 E011 E001 E002 E003 E004 E006 E009 E030 E040