Garsdale Limestone Formation
Garsdale Limestone Formation (GAL), Carboniferous, Northern England Province
Garsdale Limestone Formation is part of the Great Scar Limestone Group
Name
The name is derived from Garsdale (SD 73 90), Yorkshire (see Dunham and Wilson, 1985 and references therein[1]).
Lithology
The Garsdale Limestone Formation comprises dark grey biomicrosparites to porcellanous micrites (wackestone with bands of porcellaneous calcilutite) with interbedded sandstone and siltstone, numerous thin mudstone beds and rare thin coals. Three coal seams, up to 0.07 m thick, occur in the Beckermonds Scar Borehole (see below). Minor fenestral and palaeokarst surfaces occur. The formation contains the equivalent of Garwood’s (1913[2]) ‘Bryozoa Band’.
Genetic interpretation
Shallow marine carbonates (with some intertidal deposits).
Stratotype
The type section is the River Clough (SD 6977 9128 to 6967 9129) in Garsdale, comprising a variety of limestones with interbedded sandstones and siltstones, and a thin coal (see Burgess, 1986, pp. 11–12[3]). Reference sections include the Beckermonds Scar Borehole (BGS Registration Number SD88SE/1) (SD 8636 8016) from about 101 to 143 m depth, including dark grey wackestones with beds of calcilutite, three thin coal seams, and beds of mudstone concentrated near the top of the unit (see Wilson and Cornwell, 1982[4]), and the BGS Raydale Borehole (BGS Registration Number SD98SW/1) (SD 9626 8474) from about 103 to 158 m depth. Dunham and Wilson (1985, p. 28, see also fig. 5 cols. 5 and 7[1]) described the formation as comprising dominantly dark grey, fine-grained wackestone with many interbeds of siltstone and mudstone, and one to four thin coal seams and seven to ten beds of calcilutite up to 1.22 m thick.
Lower and upper boundaries
The conformable base of the formation overlies the mid to dark grey limestones of the Fawes Wood Limestone Formation (Figure 9, Column 17; Figure 15, Column 3).
The top of the formation is conformable beneath the pale to mid grey limestone of the Danny Bridge Limestone Formation.
Thickness
The formation is 41–58 m thick (Dunham and Wilson, 1985[1]).
Distribution and regional correlation
Askrigg Block and Wharfedale.
Age and biostratigraphical characterisation
Late Holkerian to early Asbian. The equivalent of Garwood’s (1913[2]) ‘Bryozoa Band’ includes Pleuropugnoides pleurodon, Productus garwoodi, Punctospirifer scabricosta, Leiopteria lunulata and ostracods. Dunham and Wilson (1985[1]) considered that the Holkerian–Asbian boundary should occur within the Garsdale Limestone Formation as defined at Little Asby Scar (see George et al., 1976[5]). As such it has no direct lithological, or time equivalent, correlative within the nearby Holkerian/Asbian succession of Ravenstonedale.
References
- ↑ Jump up to: 1.0 1.1 1.2 1.3 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, parts 31, 32, 51, 60 and 61(England and Wales).
- ↑ Jump up to: 2.0 2.1 Garwood, E J.1913.The Lower Carboniferous succession in the north-west of England.Quarterly Journal of the Geological Society, Vol. 68, 449–596.
- ↑ Burgess, I C.1986.Lower Carboniferous sections in the Sedbergh district, Cumbria.Transactions of the Leeds Geological Association, Vol. 11, 1–23.
- ↑ Wilson, A A, and Cornwell, J D.1982.The Institute of Geological Sciences Borehole at Beckermonds Scar, North Yorkshire.Proceedings of the Yorkshire Geological Society,Vol. 44, 59–88.
- ↑ George, T N, Johnson, G A L, Mitchell, M, Prentice, J E, Ramsbottom, W H C, Sevastopulo, G D, and Wilson, R B.1976.A correlation of Dinantian rocks in the British Isles.Geological Society of London Special Report, No.7.