Breakyneck Scar Limestone Formation

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Breakyneck Scar Limestone Formation (BRE), Carboniferous, Midland Valley of Scotland[edit]

Breakyneck Scar Limestone Formation is part of the Great Scar Limestone Group

Name[edit]

The name is derived from Breakyneck Scar, Scandal Beck, Ravenstonedale and was proposed by Pattison (1990)[1]. It replaces such terms as the Blea Tarn and Tarn Sike limestones of Garwood (1913)[2], and the ‘Michelinia grandis Beds’ of George et al. (1976)[3]. Similar in lithology and identical in age range to the Tom Croft Limestone Formation of the Askrigg Block (see below), it may be argued that either one or the other of these formation names be deemed redundant. However, whilst BGS is not actively working on these successions rationalisation must be deferred.

Lithology[edit]

The Breakyneck Scar Limestone Formation comprises dark grey, unevenly (commonly rubbly) bedded, fine- to coarse-grained fossiliferous packstone or grainstone with dark grey mudstone/siltstone interbeds.

Genetic interpretation[edit]

Shallow marine–transgressive carbonates.

Stratotype[edit]

The type section is exposed in the valley of Scandal Beck, Ravenstonedale, Cumbria, where there is an estimated 150 m thickness of mainly limestones with interbedded mudstones (see Pattison, 1990[1]). The contact with the underlying Brownber Formation is exposed near Orton (NY 6103 0923 to 6125 0925). A locality in the Appleby district is Ravensworth Fell (NY 597 098) where calcarenites of the Brownber Formation are overlain by coarse-grained fossiliferous limestone (see McCormac, 2001[4]).

Lower and upper boundaries[edit]

The formation unconformably overlies the interbedded sandstone, limestone and dolostone of the Brownber Formation within the Stainmore Trough.

The top of the formation, beneath the overlying Ashfell Sandstone Formation cannot be described precisely due to poor exposure (see Pattison, 1990[1]).

Thickness[edit]

Up to 150 m thick in the east of Ravenstonedale the formation thins westwards, pinching out along the line of the Anne’s Well Fault at (NY 584 115) (McCormac, 2001[4]). It is about 75.m thick north of Newbiggin-on-Lune, and about 25.m thick near Howe Nook, Orton.

Distribution and regional correlation[edit]

Ravenstonedale, Stainmore Trough.

Age and biostratigraphical characterisation[edit]

Early Arundian (George et al., 1976[3]; Mitchell, 1978[5]; Millward et al., 2003[6]). The limestones contain a rich fauna including the corals Siphonodendron martini, Palaeosmilia murchisoni and Syringopora sp., the productoid Linoprotonia sp. and costate spiriferoids.

References[edit]

  1. 1.0 1.1 1.2 Pattison, J.1990.Geology of the Orton and Sunbiggin Tarn districts: 1:10 000 sheets NY60NW and NE.British Geological Survey Technical Report, WA/90/12
  2. Garwood, E J.1913.The Lower Carboniferous succession in the north-west of England.Quarterly Journal of the Geological Society, Vol. 68, 449–596.
  3. 3.0 3.1 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
  4. 4.0 4.1 McCormac, M.2001.The Upper Palaeozoic rocks of the Shap and Penrith district, Edenside, Cumbria.British Geological Survey Research Report, RR/01/10
  5. Mitchell, M.1978.Dinantian.168–177 in The geology of the Lake District. Moseley, F (editor).Occasional Publication of the Yorkshire Geological Society, No. 3
  6. Millward, D, McCormac, M, Hughes, R A, Entwistle, D C, Butcher, A, and Raines, M G.2003.Geology of the Appleby district.Sheet explantion of the British Geological Survey,Sheet 30 (England and Wales)