Scottish Upper Coal Measures Formation

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Scottish Upper Coal Measures Formation (UCMS), Carboniferous, Midland Valley of Scotland[edit]

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

Name[edit]

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

Lithology[edit]

The Scottish Upper Coal Measures comprise sandstone, siltstone and mudstone in repeated cycles, which most commonly fine-upwards. The mudstone occurs most commonly as structureless beds and seatearth. The sequences are usually reddish brown and purplish grey. Coal seams are not common, are normally less than 0.3 m thick and may be replaced, totally or in part, by red (haemetitic) and dark grey carbonaceous diagenetic limestone. Brecciation textures may occur and nodular pedogenic carbonate is present in some clay/silt grade rocks in Fife.

Genetic interpretation[edit]

Fluviodeltaic (‘Coal Measures) facies. The reddish brown and purplish grey colours are due to oxidation of originally grey strata beneath the Permian unconformity, but some reddening may be primary, related to periods of lowered water table during deposition.

Stratotype[edit]

The partial type section of the Scottish Upper Coal Measures is from surface to 285 m depth in the Hallside Borehole (BGS Registration Number NS65NE/66) (NS 6693 5974) south-east of Glasgow in the west Central Coalfield (see Browne et al., 1999, fig. 7, col. 4[2]). Reference sections are provided by the Killoch No. 1 Bore (BGS Registration Number NS42SE/7) (NS 4756 2023) from the sub-Permian unconformity at 39.9 m depth to an ‘ashy conglomerate’ at 123.6 m depth (the strata at 63.9 m depth including Anthraconaia pruvosti of the undifferentiated Phillipsii and Tenuis chronozones), and the Killoch No. 1A Bore (BGS Registration Number NS42SE/8) (NS 4758 2024) which continues the section from 123.6 m depth at the ‘ashy conglomerate’ mentioned above, to the Aegiranum (Skipsey’s) Marine Band at 481.3 depth.

Lower and upper boundaries[edit]

The base of the formation is drawn at the base of the Aegiranum (Skipsey’s) Marine Band (AGMB) (Forsyth et al., 1996[3]; Browne et al., 1999, p.19[2]), which is underlain by cyclical sedimentary rocks of the Scottish Middle Coal Measures (Figure 6, Column 4). In Fife and Lothian this bed has been tentatively recorrelated with the ‘Buckhaven Planolites Band’ and the Montague Bridge Marine Band (see Browne et al., 1999, and references therein[2]). The Aegiranum Marine Band is at a lower stratigraphical level than the Cambriense Marine Band, the top of which marks the base of the Pennine Upper Coal Measures.

The top of the Scottish Upper Coal Measures is marked by an erosional unconformity of regional extent beneath Permian strata.

Thickness[edit]

Based on the interpretation of commercial seismic data the maximum thickness of the formation probably exceeds 1200 m under the Firth of Forth. Up to 460 m in central Ayrshire. A generalised thickness of 280 m in the main coalfield area at Machrihanish was given by BGS (1996)[4].

Distribution and regional correlation[edit]

The Midland Valley of Scotland, Machrihanish and the small basins of the Southern Uplands (excluding Solway).

Age and biostratigraphical characterisation[edit]

Westphalian C–D (Bolsovian–Asturian). The fauna of the formation includes, in its lower parts, nonmarine bivalves of the Upper Similis-Pulchra and the combined Phillipsii and Tenuis chronozones. Anthraconaia adamsi, A. spathulata and Naiadites hindi may, for example, occur in the Upper Similis-Pulchra Chronozone, and A. pruvosti, Anthraconauta phillipsii and An. tenuis in Phillipsii/Tenuis strata (see Trueman and Weir, 1946[5]; Mykura, 1967[6]; Calver, 1969[7]; Cameron and Stephenson, 1985, fig. 29[8]). The Aegiranum Marine Band at the base of the formation has a rich and varied ‘benthonic and cephalopod’ fauna with calcareous brachiopods, ammonoids and nautiloids (see Calver, 1969[7]). There is no evidence of marine conditions above the Upper Similis-Pulcra Chronozone. In the upper part of the Upper Coal Measures only scarce plant remains and the annelid Spirorbis sp. are found (Cameron and Stephenson, 1985[8]). Floras indicative of the Bolsovian and Asturian stages have been identified (Scott, 1976[9]).

Plant impressions from a sedimentary intercalation in the Mauchline Volcanic Formation exposed in the River Ayr near Stairhill (NS 4521 2423) were formerly regarded as being characteristic of an Asturian (Westphalian D) or more likely late Stephanian age (see Wagner, 1966[10]; Mykura, 1967, pp. 25, 27, 80[6]; Ramsbottom et al., 1978, fig. 14:4, p. 62[11]). However, with further evidence, including the presence of Lobatopteris geinitzii (von Gutbier, emend. Sterzel) comb. nov., Wagner (1983[12]; see also Brand, 1983, p. 175 and references therein[13]) was able to compare the assemblage with lower Rotliegend floras of central Europe and give it a probable early Permian (early Autunian; Asselian) age, which is still accepted (see Cleal and Thomas, 1995, pp. 229–233[14]). However, biostratigraphical problems associated with geologically long-lived plant genera, phylogenic variation, climate change and the potential of mixed diachronous and refugial floral assemblages at the Carboniferous–Permian boundary make desirable an independent reinterpretation of the fossil flora and palynology at the Stairhill site (Hilton in Dean, 2002[15]).

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 2.2 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. Forsyth, I H, Hall, I H S, and McMillan, A A.1996.Geology of the Airdrie district.Memoir of the British Geological Survey, Sheet 31W (Scotland).
  4. British Geological Survey.1996.Campbeltown. Scotland Sheet 12, Provisional Series. Solid and Drift 1:50.000. (Keyworth, Nottingham: British Geological Survey.)
  5. Trueman, A E, and Weir, J.1946.A monograph of British Carboniferous nonmarine lamellibranchia.Palaeontographical Society, London, monograph.
  6. 6.0 6.1 Mykura, W.1967.The Upper Carboniferous rocks of south-west Ayrshire.Bulletin of the Geological Survey of Great Britain, No. 26, 23–98
  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. 8.0 8.1 Cameron, I B, and Stephenson, D.1985.British regional geology: The Midland Valley of Scotland. (London: HMSO for the British Geological Survey.)
  9. Scott, A C.1976.Environmental control of Westphalian plant assemblages from northern Britain. Unpublished PhD thesis, University of London.
  10. Wagner, R H.1966.On the presence of probable Upper Stephanian beds in Ayrshire, Scotland.Scottish Journal of Geology, Vol. 2, 122–123
  11. Ramsbottom, W H C, Calver, M A, Eagar, R M C, Hodson, F, Holliday, D W, Stubblefield, C J, and Wilson, R B.1978.A correlation of Silesian rocks in the British Isles.Geological Society of London Special Report, No. 10
  12. Wagner, R H.1983.A lower Rotliegend flora from Ayrshire.Scottish Journal of Geology, Vol. 19, 135–155
  13. Brand, P J.1983.Stratigraphical palaeontology of the Westphalian of the Ayrshire Coalfield, Scotland.Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 73, 173–190
  14. Cleal, C J, and Thomas, B A.1995.British Upper Carboniferous stratigraphy.Geological Conservation Review Series, No. 11. (London: Chapman and Hall.)
  15. ean, M T.2002.The Carboniferous macropalaeontology and biostratigraphy of Ayr and Mauchline (Scotland Sheet 14).British Geological Survey Internal Report, IR/02/006