Scottish Middle Coal Measures Formation

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Scottish Middle Coal Measures Formation (MCMS), Carboniferous, Midland Valley of Scotland[edit]

Scottish Middle Coal Measures Formation is part of the Scottish Coal Measures Group

Name[edit]

The epithet ‘Scottish’ is applied to the Middle Coal Measures to distinguish them from the formation in England and Wales (Waters et al., 2007[1]).

Lithology[edit]

The Scottish Middle Coal Measures comprise similar lithologies to the Scottish Lower Coal Measures (see Section 4.6.1 above).

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 non-marine faunas), river and delta distributary channel (thick sandstones) and wetland forest and soils (coal and seatrock). Marine bands resulted from marine transgressions.

Stratotype[edit]

The type section of the upper part of the Scottish Middle Coal Measures (from the base of ‘Skipsey’s Marine Band’ marking the top of the formation, to the Drumpark Marine Band) is from 9.5 to 26.0 m depth in the Dalzell Works, Motherwell Bore No. 4 (BGS Registration Number NS75NE/316) (NS 7571 5672). For the lower part of the formation (from the Drumpark Marine Band to the ‘Queenslie Marine Band’ at the base) the type section is from 18.29 to 187.50 m depth in the Clyde Bridge, Motherwell Borehole (BGS Registration Number NS75NW/68) (NS 7380 5622). A section containing a full development of the Vanderbeckei (Queenslie) Marine Band (VDMB) is present from 15.24 to 37.49 m depth in the Moffat Mills Water Bore (BGS Registration Number NS76SE/77A) (NS 7898 6499) east of Airdrie. All three of these sections are 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 Middle Coal Measures is taken at the base of the Vanderbeckei (Queenslie) Marine Band (VDMB) or its local equivalent, overlying cyclical sedimentary rocks of the Scottish Lower Coal Measures (Figure 6, Column 4). Where this horizon cannot be established, the closest approximation based on nonmarine bivalve faunas is taken. In North Ayrshire this is the top of the Shale Coal.

The top of the Scottish Middle Coal Measures is drawn at the base of the Aegiranum (Skipsey’s) Marine Band (AGMB), forming the base of the Scottish Upper Coal Measures.

Thickness[edit]

The maximum thickness of the formation is about 350.m based on the dip corrected section of the Sealab No. 1A Borehole (BGS Registration Number NT38NW/31) (NT 3230 8568) in the Firth of Forth from about 32 to 340 m depth, and exposures on the Fife Coast between West Wemyss (NT 321 947) and Buckhaven (NT 351 976). Generalised thicknesses were given of about 50 m on Arran (BGS, 1987a[3]) and 95 m in the main coalfield area at Machrihanish (BGS, 1996[4]).

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 the Solway).

Age and biostratigraphical characterisation[edit]

Westphalian B (Duckmantian). NJ Miospore Zone of Clayton et al. (1977)[5]. The most abundant fauna of the formation is the non-marine bivalves of the upper Modiolaris and Lower Similis-Pulchra chronozones (see Trueman and Weir, 1946[6]; Calver, 1969[7]). Genus Anthracosia dominates and includes, for example, in the upper Modiolaris Chronozone A. ovum and A. phrygiana, and in the Lower Similis-Pulchra Chronozone A. caledonica and A. atra (see Cameron and Stephenson, 1985, fig. 29[8]). The Vanderbeckei Marine Band at the base of the formation attains ‘goniatite-pectenoid’, ‘productoid’ and Lingula facies. Its varied fauna may include in places the ammonoid Anthracoceras sp. with the bivalve Dunbarella sp., brachiopods (including productoids), or just Lingula (see Calver, 1969[7]). A group of up to four marine bands occurs in the Lower Similis-Pulchra Chronozone, usually only with Lingula, but with bivalves present in a few areas.

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. 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.1987a.Arran. Scotland Special Sheet, 1:50.000 Series. Bedrock. (Southampton: Ordnance Survey for the British Geological Survey.)
  4. British Geological Survey.1996.Campbeltown. Scotland Sheet 12, Provisional Series. Solid and Drift 1:50.000. (Keyworth, Nottingham: British Geological Survey.)
  5. 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.
  6. Trueman, A E, and Weir, J.1946.A monograph of British Carboniferous nonmarine lamellibranchia.Palaeontographical Society, London, monograph
  7. 7.0 7.1 Calver, M A.1969.Westphalian of Britain.6e Congres Internationale Stratigraphie et Geologie Carbonifere. Sheffield 1967. Compte Rendu, Vol. 1, 233–254.
  8. Cameron, I B, and Stephenson, D.1985.British regional geology: The Midland Valley of Scotland. (London: HMSO for the British Geological Survey.)