Cottonshope Volcanic Formation

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Cottonshope Volcanic Formation (COVO), Carboniferous, Midland Valley of Scotland[edit]

Cottonshope Volcanic Formation is part of the Inverclyde Group

Name[edit]

Previously known as the Cottonshope Lavas (Taylor et al., 1971[1]).

Lithology[edit]

Basalt lavas, olivine-phyric, tholeiitic; several sheets of intensely fractured, dark blue-grey basalt, each passing up into highly amygdaloidal, scoriaceous and pillow-like tops which contain infills of overlying sedimentary rock. The upper part of formation is intercalated with dark grey and greenish grey sandstone and argillaceous dolostone (‘cementstone’) of the overlying Ballagan Formation.

Stratotype[edit]

The type section is Cottonshope Head Quarry and adjacent Cottonshope Burn, Upper Redesdale, Northumberland (NT 803 058) (see Millward in Stephenson, et al., 2003[2]; Miller, 1887[3]; Tomkeieff, 1931[4]; Taylor et al., 1971[1]). Here the volcanic succession comprises three sheets of basalt. The lowest one is 12 m thick and has an undulating pillow-like to ‘slaggy’, scoriaceous top with sedimentary infills. This is overlain by a 6 m-thick vesicular basalt. The uppermost basalt, also 6 m thick, is separated from the underlying ones by 6 m of bedded mudstones, flaggy sandstones and ‘cementstones’ (Millward in Stephenson, et al. (2003, p..136)[2].

Lower and upper boundaries[edit]

The lower boundary is taken at the broadly conformable base of the lowest basalt sheet that sharply overlies a sequence of red and grey flaggy sandstones with ochreous brown spots, interbedded with purple, red, lilac and green mudstone containing ochreous concretions, and thin concretionary carbonate (‘cornstone’) beds (the Lower Freestone Beds of Taylor et al., 1971[1]). This is possibly part of the Kinnesswood Formation.

The upper boundary of the formation is taken at the base of the overlying interbedded sandstone, mudstone and argillaceous dolostone sequence of the Ballagan Formation (formerly the Cementstone Group). The upper contact is intercalated.

Thickness[edit]

Up to 24 m.

Distribution and regional correlation[edit]

South-west flanks of the Cheviot Block: exposed in Cottonshope Burn, Spithope Burn, Hungry Law, and between the Bareinghope Burn and the Chattlehope Burn, Northumberland.

Age[edit]

Tournaisian.

References[edit]

  1. 1.0 1.1 1.2 Taylor, B J, Burgess, I C, Land, D H, Mills, D A C, Smith, D B, and Warren, P T.1971.British regional geology: northern England (4th edition). (London: HMSO for Institute of Geological Sciences.)
  2. 2.0 2.1 Stephenson, D, Loughlin, S C, Millward, D, Waters, C N, and Williamson, I T.2003.Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front.Geological Conservation Review Series, No. 27. (Peterborough: Joint Nature Conservation Committee.)
  3. Miller, H.1887.The geology of the country around Otterburn and Elsdon.Memoir of the Geological Survey of Great Britain, Sheet 8 (England and Wales)
  4. Tomkeieff, S.1931.Lower Carboniferous igneous rocks.Proceedings of the Geologists’ Association, Vol. 42, 259–261.