The BGS Lexicon of Named Rock Units — Result Details

Great Scar Limestone Group

Computer Code: GSCL Preferred Map Code: GScL
Status Code: Full
Age range: Tournaisian Stage (CT) — Pendleian Substage (CE)
Lithological Description: The Great Scar Limestone Group (George et al., 1976; see also Waters et al., 2007) of open marine, platform and ramp carbonates facies comprises many formations with distinct formation nomenclature for the isolated horst and tilt-block highs: The Alston Block includes the Melmerby Scar Limestone Formation (see Dunham, 1990); The Stainmore Trough has the Coldbeck Limestone, Scandal Beck Limestone, Brownber, Breakyneck Scar Limestone, Ashfell Sandstone, Ashfell Limestone, Potts Beck Limestone and Knipe Scar Limestone formations (see Dunham and Wilson, 1985); The Askrigg Block includes the Tom Croft Limestone, Ashfell Sandstone, Fawes Wood Limestone, Garsdale Limestone and Danny Bridge Limestone formations (see Dunham and Wilson, 1985); The Askrigg Block-Craven Basin Transition Zone includes the Kilnsey, Chapel House Limestone, Malham and Cracoe Limestone formations (see Arthurton et al., 1988); South Cumbria has the Martin Limestone, Red Hill Limestone, Dalton, Park Limestone and Urswick Limestone formations (see Rose and Dunham, 1977; Johnson et al., 2001); North and west Cumbria includes the Frizington Limestone and Eskett Limestone formations (see Akhurst et al., 1997). It therefore includes the lower part of the now obsolete Chief Limestone Group; The south Isle of Man includes the Derbyhaven, Knockrushen and Balladoole formations (see Chadwick et al., 2001); The north Isle of Man includes undifferentiated strata assigned to either the Great Scar Limestone Group or the Yoredale Group (see Chadwick et al., 2001); The succession comprises limestone, typically well washed, bioclastic, highly bioturbated with crinoid banks, shelly or coral biostromes and algal (Girvanella) bands. The group, common to other Visean platform areas in the British Isles, shows a trend from dark grey Arundian to Holkerian carbonates to pale grey Asbian to Brigantian limestones with eight major palaeokarstic bedding surfaces overlain by thin mudstones (Waltham, 1971). Apron knoll reefs are developed along the southern margin of the Askrigg Block. In the Stainmore Trough the limestone succession locally includes numerous intercalated sandstone beds, presumably derived from upstanding areas of lower Palaeozoic rocks. The lower part of the group, present in the Stainmore Trough (Coldbeck Limestone Formation) and South Cumbria (Martin Limestone Formation), was deposited in a carbonate dominated, nearshore to peritidal, restricted marine environment with common stromatolites and oncolites. Younger strata, dominated by thick bioclastic limestones, were deposited in an open, shallow marine environment. Palaeokarst surfaces indicate periodic emergence. The alluvial Brownber and fluviodeltaic Ashfell Sandstone formations represent brief incursions of siliciclastic deposits into the Stainmore Trough that encroached from the north. They may have been a distal extension of the Fell Sandstone Formation of the Border Group. In the north of the Isle of Man undifferentiated strata assigned to either the Great Scar Limestone Group or the Yoredale Group comprise massive, stylolitised, fractured and sucrosic dolomite (see Chadwick et al. 2001).
Definition of Lower Boundary: In the Stainmore Trough the base of the group is taken at the base of the Coldbeck Limestone Formation where the Algal Nodular Beds of the underlying Ravenstonedale Group are conformably overlain by carbonate-dominated strata. On the Askrigg Block the base of the group is taken at the base of the Tom Croft Limestone Formation where a nodular dolostone bed with rhizoliths, indicative of emergence (Burgess, 1986), is locally developed at the top of the underlying Penny Farm Gill Formation (Ravenstonedale Group). This boundary is disconformable and marks a low sea-level stand. On the Alston Block the base of the group is taken at the base of the Melmerby Scar Limestone Formation where the conglomerates of the underlying Marsett Formation (Ravenstonedale Group) are unconformably overlain by the onset of platform carbonate strata. In north and west Cumbria the base of the group is taken at the base of the Frizington Limestone Formation where the conglomerates of the Marsett Formation (Ravenstonedale Group) are disconformably overlain by bioturbated peritidal limestones with rhizoliths, lime muds and sandstones. This disconformity represents nondeposition during Chadian to Arundian times. In south Cumbria the base of the group is not exposed, but it is taken to be at the base of the Martin Limestone Formation where limestone becomes dominant over shale in the conglomeratic Marsett Formation (Ravenstonedale Group). In the south Isle of Man the base of the group is taken at the base of the Derbyhaven Formation where the conglomerates (some of which are apparently reworked) of the Langness Conglomerate Formation (Ravenstonedale Group) are directly overlain by limestones.
Definition of Upper Boundary: In most places, the base of the Yoredale Group (mixed shelf carbonate and deltaic ('Yoredale') facies) defines the top of the Great Scar Limestone Group. The exceptions include the north Isle of Man where the Millstone Grit Group (fluviodeltaic ('Millstone Grit') facies) defines the top of what may be either the Great Scar Limestone Group or the Yoredale Group, and the south Isle of Man where the Craven Group defines the top of the Balladoole Formation.
Thickness: The group is about 107 m thick on the Alston Block. It gains a maximum thickness of about 800 m in the Stainmore Trough. On the Askrigg Block it is about 400 m thick. In Cumbria, up to about 740 m of strata are present, and in the south Isle of Man the group is up to about 157 m thick. In the north Isle of Man approximately 7.3 m of what may be either Great Scar Limestone Group or Yoredale Group strata are at the base of the Ballavaarkish (Shellag North) Borehole.
Geographical Limits: The Great Scar Limestone Group is widespread across Northern England.
Parent Unit: Carboniferous Limestone Supergroup (CL)
Previous Name(s): Main Limestone Group (Cumbria) [Obsolete Name and Code: Use GSCL] (MALG)
Chief Limestone Group [Obsolete Name and Code: Use GSCL, AG] (CHFL)
Great Scar Limestone [Obsolete Name and Code: Use GSCL] (-295)
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
Dean, M T, Browne, M A E, Waters, C N and Powell, J H. 2011. A lithostratigraphical framework for the Carboniferous successions of northern Great Britain (onshore). British Geological Survey Research Report, RR/10/007. 165pp. 
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.) 
Arthurton, R S, Johnson, E W and Mundy, D J C. 1988. Geology of the country around Settle. Memoir of the British Geological Survey, Sheet 60 (England and Wales). 
Burgess, I C. 1986. Lower Carboniferous sections in the Sedbergh district, Cumbria. Transactions of the Leeds Geological Association, Vol.11, 1-23. 
Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M and Roberts, D H. 2001. Geology of the Isle of Man and its offshore area. British Geological Survey Research Report, RR/01/06. 
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). 
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). 
George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottam, W H C, Sevastopulo, G D and Wilson, R B. 1976. A correlation of the Dinantian rocks of the British Isles. Special Report of the Geological Society of London, No 7. 
Johnson, E W, Soper, N J, Burgess, I C, Ball, D F, Beddoe-Stephens, B, Carruthers, R M, Fortey, N J, Hirons, S, Merritt, J W, Millward, D, Roberts, B, Walker, A B and Young, B. 2001. Geology of the country around Ulverston. Memoir of the British Geological Survey, England and Wales, Sheet 48. 
Waters, C N, Browne, M A E, Dean, M T and Powell, J H. 2007. Lithostratigraphical framework for Carboniferous successions of Great Britain (Onshore). British Geological Survey Research Report, RR/07/01. 
Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, Young, B, Ambrose, K, Auton, C A, Barclay, W J, Barnes, R P, Beddoe-Stephens, B, James, J C W, Johnson, H, Jones, N S, Glover, B W, Hawkins, M P, Kimbell, G S, MacPherson, K A T, Merritt, J W, Milodowski, A E, Riley, N J, Robins, N S, Stone, P, and Wingfield, R T R. 1997. The geology of the west Cumbria district. Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales). 138pp. 
Rose, W C C, and Dunham, K C. 1977. Geology and hematite deposits of South Cumbria. Economic Memoir of the Geological Survey of Great Britain, Sheet 58, part 48 (England and Wales). 
Waltham, A C. 1971. Shale units in the Great Scar Limestone of the southern Askrigg Block. Proceedings of the Yorkshire Geological Society, Vol. 38, 285-292. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E050 E041 E040 E031 E049 E400 E039