Difference between revisions of "Scottish Lower Coal Measures Formation"

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Scottish Lower Coal Measures Formation (LCMS), Carboniferous, Midland Valley of Scotland[edit]

Scottish Lower Coal Measure Formation is part of the Scottish Coal Measures Group

Name[edit]

The epithet ‘Scottish’ is applied to the Lower Coal Measures to distinguish them from the formation in England and Wales on account of the different definition of the base of the formation (and group) (Waters et al., 2007[1]).

Lithology[edit]

The Scottish Lower Coal Measures comprise sandstone, siltstone and mudstone in repeated cycles, which most commonly coarsen-upwards, but also fine-upwards, with seatearth and coal at the top. The mudstones and siltstones are usually grey to black, while the sandstone is fine- to medium-grained and off-white to grey. Coal seams are common and many exceed 0.3 m in thickness. Minor lithologies include cannel and blackband and clayband ironstone, the latter nodular as well as bedded. Bands composed mainly of nonmarine bivalves, the characteristic ‘musselbands’, usually occur in mudstone or ironstone. Upward-fining parts of the succession, dominated by fine- to coarse-grained sandstone, are widely developed and thick multistorey sandstones are a feature.


Genetic interpretation[edit]

Fluviodeltaic (‘Coal Measures) facies. The depositional environments include prograding deltas (upward-coarsening sequences), floodplain (planty or rooted siltstone and mudstone), shallow lakes (mudstones with nonmarine faunas), river and delta distributary channel (thick sandstones) and wetland forest and soils (coal and seatrock). Marine bands will have resulted from marine transgressions.

Stratotype[edit]

The type section of the formation is between 187.50 and 301.19 m depth in the Clyde Bridge, Motherwell Borehole (BGS Registration Number NS75NW/68) (NS 7380 5622) in the west Central Coalfield (see Browne et al., 1999, fig..7, col. 4[2]).

Lower and upper boundaries[edit]

The base of the Scottish Lower Coal Measures is taken at the base of the Lowstone Marine Band (LOMB), its local correlative, or at a plane of disconformity. It is underlain by cyclical sedimentary rocks of the Passage Formation (Figure 6, Column 4). This is at a slightly higher stratigraphical level than in England and Wales (see Section 4.6 above).

The top of the formation lies at the base of the Vanderbeckei (Queenslie) Marine Band (VDMB), or its local equivalent, at the base of the Scottish Middle Coal Measures.

Thickness[edit]

The maximum thickness of the formation is between 220 and 240 m in the Sealab No. 2 Borehole (BGS Registration Number NT38SW/1) (NT 3272 8449) in the Firth of Forth from about 220 to 500 m depth. The variation in thickness is a function of correction for stratal dip (see Browne et al., 1999, p..18[2]). Generalised thickness were given of about 65.m on Arran (BGS, 1987a) and 67.5 m in the main coalfield area at Machrihanish (BGS, 1996[3]).

Distribution and regional correlation[edit]

The Midland Valley of Scotland, on the Isle of Arran, at Machrihanish, and in the small basins of the Southern Uplands (excluding Solway).

Age and biostratigraphical characterisation[edit]

Westphalian A (Langsettian). SS to RA Miospore zones of Clayton et al. (1977)[4]. The most abundant fauna of the formation is the nonmarine bivalves of the upper Lenisulcata, Communis and lower Modiolaris chronozones (see Trueman and Weir, 1946[5]; Calver, 1969[6]). Genus Carbonicola dominates and includes, for example, in the upper Lenisulcata Chronozone C. extenuata, in the Communis Chronozone C. polmontensis, C. pseudorobusta and C. oslansis, and in the lower Modiolaris Chronozone C. venusta (see Cameron and Stephenson, 1985, fig. 29[7]). The Lowstone Marine Band at the base of the formation is commonly developed as a Lingula band as too is the small group of up to three marine bands present near the top of the Lenisulcata Chronozone.

References[edit]

  1. 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
  2. 2.0 2.1 Browne, M A E, Dean, M T, Hall, I H S, McAdam, A D, Monro, S K, and Chisholm, J I.1999.A lithostratigraphical framework for the Carboniferous rocks of the Midland Valley of Scotland.British Geological Survey Research Report, RR/99/07
  3. British Geological Survey.1996.Campbeltown. Scotland Sheet 12, Provisional Series. Solid and Drift 1:50.000. (Keyworth, Nottingham: British Geological Survey.)
  4. Clayton, G, Coquel, R, Doubinger, J, Gueinn, K J, Loboziak, S, Owens, B, and Streel, M.1977.Carboniferous miospores of western Europe: illustration and zonation.Mededelingen. Rijks Geologische Dienst, Vol. 29, 1–71.
  5. Trueman, A E, and Weir, J.1946.A monograph of British Carboniferous nonmarine lamellibranchia.Palaeontographical Society, London, monograph.
  6. Calver, M A.1969.Westphalian of Britain.6e Congres Internationale Stratigraphie et Geologie Carbonifere. Sheffield 1967. Compte Rendu, Vol. 1, 233–254
  7. Cameron, I B, and Stephenson, D.1985.British regional geology: The Midland Valley of Scotland. (London: HMSO for the British Geological Survey.)