The BGS Lexicon of Named Rock Units — Result Details

Bowland Shale Formation
Computer Code: BSG Preferred Map Code: BSh
Status Code: Full
Age range: Asbian Age (CR) — Yeadonian Sub-age (CY)
Lithological Description: Mainly dark grey fissile and blocky mudstone, weakly calcareous, with subordinate sequences of interbedded limestone and sandstone, fossiliferous in more-or-less discrete bands. Furness and Settle areas: thick-bedded, blocky to sub-fissile, dark grey and black, organic-rich mudstone, with subordinate beds of dark grey siltstone, sandstone and pale brown dolomitic limestone. Marine bands are also present. Shows an upwards decrease in carbonate turbidites and a concomitant increase in siliciclastic sandstone turbidites. South Isle of Man: Black claystone with localized deposition of carbonate turbidites, debris flows, olistoliths, volcaniclastic deposits and lavas. At the base of the formation, the Scarlett Point Member comprises cherty and pyritous tabular beds of pale wackestone and lime-mudstone (dolomitized in places), which display gradational boundaries with interbedded black, fissile, blocky claystone. The limestone is burrowed and has inadunate crinoidal lags and scattered ammonoids. At the top of the formation, the Scarlett Volcanic Member is dominated by a series of volcaniclastic debris flows and gravity slides. Claystone rafts and megaclasts are entrained within the volcaniclastic rocks, and carbonate olistoliths and pillow lavas also occur. Between the members, where the formation oversteps the Balladoole Formation (Great Scar Limestone Group), coarse-grained detrital carbonates and debris beds are common. These include erosively based, graded packstone beds, conglomerate, megaclasts and large olistoliths (with reef limestone and ammonoid faunas) derived from the Balladoole Formation. The middle part of the exposed formation comprises black, calcareous, platy claystone with subordinate beds (up to 2 m thick) of dark wackestone, and dark detrital packstone debris. North Isle of Man: Siltstone, claystone and ironstone dominate, but includes two marine bands and five palaeosols.
Definition of Lower Boundary: The conformable base upon the Pendleside Limestone Formation in the Craven Basin, on the Widmerpool Formation in the East Midlands, and the Pentre Chert and Cefn-y-Fedw Sandstone Formation in North Wales, on the Hodderense Limestone Formation in the south of the Isle of Man, is taken at the first appearance of black mudstone above variegated mudstones or fine-grained limestones. In south Cumbria the lower boundary of the formation is taken at the base of the Cravenoceras leion Marine Band, where the dark grey to black marine mudstone rests upon thinly interbedded limestones, mudstones and subordinate sandstones of the Alston Formation. The Bowland Shale Formation onlaps onto and eventually, by Pendleian times, extends over the carbonates of the Central Lancashire High (Trawden Limestone Group). In the Craven Reef Belt, in the Malham Cove/Gordale Scar area, the fissile mudstones with nodules and thin beds of ironstone and limestone of the Bowland Shale Formation, rest unconformably and diachronously on the Malham Formation (Great Scar Limestone Group), or Yoredale Group.
Definition of Upper Boundary: The top of the formation is taken at the base of the Millstone Grit Group over most of the Pennine Basin and at the base of the Morridge Formation in Staffordshire and the East Midlands. The formation shows complex intertongueing with the Morridge and Cefn-y-Fedw Sandstone formations. It is seen as a conformable boundary defined by the base of the lowermost thick feldspathic sandstone of the Millstone Grit Group, or quartzitic sandstone of the Morridge and Cefn-y-Fedw formations, above thick dark grey mudstone of the Bowland Shale Formation.
Thickness: Generally between 120m and 620m. The formation thickens northeastwards along the axis of the Central Lancashire High, from about 22m in the Roddlesworth Borehole (SD62SE/6), 68m thick in the Holme Chapel Borehole (SD82NE/68), and 102m in the Boulsworth Borehole (SD93SW/14). The underlying Trawden Limestone Group shows a thinning in the same direction (Evans and Kirby, 1999), suggesting the thickening of the Bowland Shale Formation reflects available accommodation space. In the Craven Reef Belt the Bowland Shale Formation is perhaps 30m to 200m thick (see Arthurton et al., 1988, figure 22). In south Cumbria, the Roosecote Borehole (see above) proved the formation to be 130m thick (see Johnson et al., 2001; Rose and Dunham, 1977). On the Isle of Man, the Bowland Shale Formation might be at least 186m thick. In the north Isle of Man, the Shellag Point Borehole [NX 4565 9965] proved only a part of the formation, reaching 27.55m in thickness.
Geographical Limits: Widespread in the Craven Basin, including the Lancaster, Garstang, Settle, Clitheroe and Harrogate districts, south Cumbria and the Isle of Man; also in North Wales, Staffordshire and the East Midlands.
Parent Unit: Craven Group (CRAV)
Previous Name(s): Edale Shales (-1397)
Holywell Shale Formation (-1398)
Lower Bowland Shale Formation [Obsolete Name And Code: Part Of BSG] (LBS)
Bowland Shales (-730)
Halkyn Formation (-731)
Holywell Shales (-2643)
Halkyn Formation [Obsolete Name And Code: See Revision Data] (HAF)
Upper Bowland Shale Formation [Obsolete Name And Code: See BSG] (UBS)
Edale Shale Group [Obsolete Name And Code: Use BSG] (ESH)
Holywell Shale Formation [Obsolete Name And Code: Use BSG] (HSH)
Cawdor Group [Obsolete Name And Code: See Revision Data] (CW)
Bowland Shale Formation (Offshore) [Obsolete Code: Use BSG] (BWSF)
Bowland Shale Group (-2027)
Edale Shale Group (-1396)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Little Mearley Clough, 400m to 1100m southeast and upstream from Little Mearley Hall. Earp et al., 1961, pp 89-91; Fewtrell and Smith, 1980. 
Reference Section  Roosecote Borehole, Barrow-in-Furness (SD26NW/19), includes an entire thickness of the formation from 158.13 to 613.31m depth. Rose and Dunham, 1977; Johnson et al., 2001 
Reference Section  Shellag Point Borehole, north Isle of Man cored from 100.60m to 128.15m, with neither the base nor top proved. Chadwick et al., 2001 
Reference Section  River Ribble at Dinckley, on the south bank of the River Ribble between Dinckley Hall and the suspension footbridge, about 300m to the west downstream. (Earp et al., 1961, pp 85-87) 
Reference Section  Coed Pen-y-Maes stream section at Holywell, Clwyd, North Wales. Intermittent exposures of the Formation showing mudstone lithologies typical for the North Wales region; base and top not seen. Davies et al., 2004 
Reference Section  Duffield Borehole, near Derby (SK34SW/5), from 0.86m to 405.78m depth, from the H1a marine band to the base od the Formation. Aitkenhead, 1977. 
Reference(s):
Aitkenhead, N, 1977. The Institute of Geological Sciences borehole at Duffield, Derbyshire. Bulletin of the Geological Survey of Great Britain, No.59, 1-38. 
Whittard, W F and Simpson, S. 1960. Lower Carboniferous. 54-55 in Whittard, W F and Simpson, S (editors), Lexique Stratigraphique International, Part 3a VII, Vol.1. 
Earp, J R and others, 1961. Geology of the country around Clitheroe and Nelson. Geological Survey of Great Britain Memoir, Sheet 68. 
Aitkenhead, N, Chisholm, J I and Stevenson, I P. 1985. Geology of the country around Buxton, Leek and Bakewell. Memoir of the British Geological Survey, England and Wales Sheet 111. 
Davies, J R, Wilson, D and Williamson, I T, The geology of the country around Flint. Memoir of the British Geological Survey, Sheet 108. 
Fewtrell, M D and Smith, D G, 1980. Revision of the Dinantian stratigraphy of the Craven Basin, N. England. Geological Magazine, Vol.117, p.37-49. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E108 E123 E059 E060 E067 E069 E096
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