The BGS Lexicon of Named Rock Units — Result Details

Peak Limestone Group

Computer Code: PKLM Preferred Map Code: PKLM
Status Code: Full
Age range: Tournaisian Age (CT) — Brigantian Substage (CX)
Lithological Description: Platform and ramp carbonate facies. Across the East Midlands during Tournaisian to early Visean times there was a slow onlap of marine ramp carbonates, with some evaporites, onto an irregular palaeorelief, evident as the Rue Hill Dolomite Formation. At this time there is a distinction in the carbonate succession from comparatively massive and dolomitic, shallower water limestones of the northern part of the Peak District inlier (Buxton to Matlock) recognised as the Woo Dale Limestone Formation and relatively deeper water limestones with mud-mounds present within the south-western part of the inlier (Dovedale and Manifold Valley), the Milldale Limestone Formation. Bridges and Chapman (1988) suggest that the mud-mounds accumulated in water depths of 220 to 280 m. As the latter subfacies occurs as a belt extending north-west of the north-west-trending half-graben of the Widmerpool Gulf, it is tempting to recognise a structurally induced palaerelief influencing deposition. On the Nottingham Shelf, the Milldale Limestone Formation is overlain, possibly unconformably, by the Belvoir Limestone Formation, in turn overlain, possibly unconformably, by the Plungar Limestone Formation. By Asbian times a sea-level rise and syn-rift subsidence led to a clear differentiation between a shelf province, fringed by apron-reefs, and off-shelf facies (Craven Group). The shelf province includes the Hopedale Limestone Formation, Bee Low Limestone Formation, Monsal Dale Limestone Formation, Fallgate Volcanic Formation, and Eyam Limestone Formation. The Monsal Dale Limestone Formation includes a complex stratigraphy of lavas and tuffs. The remainder of the shelf is largely known from subsurface borehole and seismic data. Chadian mud-mounds or bioherms and Asbian shelf-edge reefs are described by Strank (1987). Localised tectonic uplift resulted in disconformities, particularly during the Chadian and Brigantian. Subaerial palaeokarstic dissolution hollows are common, particularly during the Asbian and Brigantian of Derbyshire (Walkden, 1974). In Derbyshire these surfaces are locally associated with subaerial and subaqueous basaltic lava flows and tuffs (Waters, 2003). A thick sequence of pale to dark grey, thinly to thickly bedded biosparite and cherty micritic limestone units displaying knoll-reefs, comprising fossiliferous, massive micrite with localised common spar-filled cavities, and grey-brown to dark grey dolomitic limestones. Subordinate partings and thin beds of calcareous mudstone and siltstone, basaltic lava, sills and pyroclastic rocks including tuff and volcanic breccia are common in the upper part of the Group, as well as pedogenic crusts, palaeokarstic surfaces and thin bentonite partings (known locally as "wayboards"), notably in Matlock [SK 20 60 to 30 60], and the Millers Dale to Buxton [SK 06 72 to 16 74] areas of the Peak District.
Definition of Lower Boundary: The group generally rests unconformably upon deformed Lower Palaeozoic strata, or locally upon alluvial or peritidal facies strata.
Definition of Upper Boundary: The top of the group is typically a conformable boundary marked by the transition into basinal mudstones and siltstones of the Craven Group, though is locally truncated beneath Westphalian strata.
Thickness: More than 500 m thickness of Peak Limestone Group is present on the East Midlands Platform.
Geographical Limits: The main area of exposure is within the Peak District of Derbyshire, which during the Visean formed a promontory of the East Midlands Platform. It is present in the subsurface elsewhere in the East Midlands.
Parent Unit: Carboniferous Limestone Supergroup (CL)
Previous Name(s): Carboniferous Limestone Series [Obsolete Name and Code: Use CLWYD, PKLM] (-2703)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Peak District of Derbyshire and Staffordshire - see component formations for reference sections. Aitkenhead and Chisholm, 1982. 
Reference(s):
Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. 
Carney, J N, Ambrose, K, Brandon, A, Royles, C P, Lewis, M A, and Sheppard, H. 2004. Geology of the country around Melton Mowbray. Sheet Description of the British Geological Survey, 1:50 000 Series Sheet 142 Melton Mowbray (England and Wales). 
Strank, A R E. 1987. The stratigraphy and structure of Dinantian strata in the East Midlands, UK. In: Miller, J, Adams, A E and Wright, V P (eds.) European Dinantian environments, 157-175. John Wiley & Sons, Chichester. 
Waters, C N. 2003. Carboniferous and Permian igneous rocks of central England and the Welsh Borderland. In: Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front. (editors Stephenson D, Loughlin S C, Millward D, Waters C N, and Williamson I T.), pp. 279-316, Geological Conservation Review Series, No. 27 (JNCC). 
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. 
Bridges, P H, and Chapman, A J. 1988. The anatomy of a deep water mud-mound complex on the SW margin of the Dinantian platform in Derbyshire. Sedimentology, Vol. 35, 139-162. 
Walkden, G M. 1974. Palaeokarstic surfaces in upper Visean (Carboniferous) Limestones of the Derbyshire Block, England. Journal of Sedimentary Petrology, Vol. 44, 1232–1247. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
Aitkenhead, N, and Chisholm, J I. 1982. A standard nomenclature for the Dinantian formations of the Peak District of Derbshire and Staffordshire. Report of the Institute of Geological Sciences, No. 82/8. 
Carney, J N, Ambrose, K and Brandon, A. 2001. Geology of the country between Burton, Loughborough and Derby. Description of 1:50k Sheet 141 (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E099 E111 E124 E125 E141 E112