Scottish Coal Measures Group
The ‘Coal Measures’ were regarded as a lithostratigraphical group by Forsyth et al. (1996). The epithet ‘Scottish’ was proposed by Waters et al. (2007) to distinguish the ‘Coal Measures’ of Scotland from those of England and Wales to account for the different definitions of the base of the Upper Coal Measures and the base of the groups.
The Scottish Coal Measures Group (Figure 5; Browne et al., 1999, fig. 7) (fluviodeltaic (‘Coal Measures’) facies) is divided, in ascending sequence, into Scottish Lower, Middle and Upper Coal Measures formations. Lithologically the group comprises repeated cycles of sandstone and mudstone with coal and seatearth, arranged in both upward-fining and upward-coarsening units. The strata are generally grey in colour but are extensively reddened towards the top. A wide range of alluvial and lacustrine environments of deposition is represented. These include wetland forest and soils (coal and seatrock), floodplain (planty or rooted siltstone and mudstone), river and delta distributary channel (thick sandstones), prograding deltas (upward-coarsening sequences) and shallow lakes (mudstones with nonmarine faunas). Marine bands are rare but provide important stratigraphical markers. Economically important coal seams are common in the Lower and Middle Coal Measures, some of which can be correlated between coalfields.
The base of the group in the Midland Valley of Scotland is now taken at the base of the Lowstone Marine Band, its local correlative, or at a plane of disconformity. This is at a slightly higher stratigraphical level than in England and Wales, where the lower boundary lies at the base of the Subcrenatum Marine Band at the base of the Langsettian (Westphalian A) Stage. This horizon has not been recognised in Scotland though it may correlate with one of the higher marine bands of the Passage Formation (No. 6) and with the Porteous Marine Band of the Douglas Coalfield. An unconformity of regional extent beneath Permian strata marks the top of the Scottish Coal Measures Group in the Midland Valley of Scotland.
The Scottish Coal Measures Group occurs in the Midland Valley of Scotland and adjacent areas including Sanquhar, Thornhill, Machrihanish, Arran, Stranraer and Morvern. Probably exceeding 1790 m in the Midland Valley of Scotland, it is Langsettian to Asturian (Westphalian D) in age. It is considered that no Stephanian rocks have been identified in the Midland Valley of Scotland. However, see Wagner (1983), details provided below.
- 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).
- 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.
- 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.
- Wagner, R H.1983.A lower Rotliegend flora from Ayrshire.Scottish Journal of Geology, Vol. 19, 135–155.