The BGS Lexicon of Named Rock Units — Result Details

Black Metals Member

Computer Code: BKME Preferred Map Code: BKME
Status Code: Full
Age range: Pendleian Substage (CE) — Pendleian Substage (CE)
Lithological Description: A distinctive thick, laterally persistent dark grey mudstone (Read, 1965), distinguished by one or morebeds, termed "Black Metals Marine Bands" [not to be confused with the Black Metals Marine Band of Cumberland, of Duckmantian age], containing a varied shelly fauna indicative of a marine depositional environment (Wilson, 1967). The member also includes beds with Lingula and beds with a shelly fauna, including Naiadites, indicative of non-marine depositional conditions. Read (1965) describes a commonly recorded sequence within the member of mudstone with Lingula at the base, overlain by mudstone with non-marine bivalves or unfossiliferous mudstone, overlain by mudstone with a varied marine fauna comprising the middle part of the member and overlain by mudstone containing non-marine bivalves. The characteristic lithologies of the member vary laterally within the Midland Valley of Scotland. On the western side of the Central Coalfield in the Glasgow district, strata that comprise the member are described and illustrated by Hall et al. (1997, fig.11) as black and dark grey, carbonaceous mudstones and silty mudstones with characteristic development of brownish grey clayband ironstone nodules (California Clayband Ironstone). Sandstones are restricted to thin beds and comprise two or three metres thickness in a total interval thickness of about 32m. Eastwards from the Central Coalfield the member includes siltstone and sandstone beds that increase progressively in number and thickness to become the predominant lithology; seatearth and coal also appear (Read, 1965). In the western coastal Irvine district, the Logans Bands, thin beds of ironstone in a laterally persistent mudstone sequence containing Lingula and Naiadites or non-marine bivalves (Monro, 1999), have been correlated with the unit in southern and central Ayrshire by Simpson and MacGregor (1932) or Eyles et al. (1949).
Definition of Lower Boundary: In the Central Coalfield, mudstone of this unit alternates (is interbedded) with sandstone of the overlying Limestone Coal Formation. The boundary is picked at the base of the lowermost bed of coarse siltstone or sandstone (Read, 1965). Locally, the erosive base of the sandstone has cut down into the member or is abruptly overlain by lavas in the Bo'ness area of the Livingston district (Read, 1965). In the Glasgow district the upper boundary of the unit is just below (within about 5m) of the Knott Coal horizon (Hall et al., 1998, fig.11).
Definition of Upper Boundary: In the Central Coalfield, the lower boundary of the unit is picked at the top of the Black Metals Basal Coal (Forsyth and Read, 1962). Eastwards the base is picked at the top of a laterally equivalent seatearth and correlated to a thin coal above the Torrance Four-inch Coal farther east in Fife (Read, 1965), fig. 2). Westwards, in the Glasgow district, marine fossils are recorded just above the lower boundary of the Black Metals Member, which is picked at the roof of the Upper Garscadden Coal (Hall et al., 1997, fig.11), where instead blackband ironstone (Upper Garscadden Ironstone) may be developed (Forsyth and Read, 1962).
Thickness: The thickness of the unit is described by Read (1965) as exceeding that of the fining-upward cycles, otherwise typical of the Limestone Coal Formation, that are approximately 3m to 10m (10 feet to 30 feet) thick. In the Cardowan No.2 borehole, north of Glasgow on the western side of the Central Coalfield, the full development of the unit is 32.3m thick, from 470m to 502.3m depth (Hall et al., 1997, fig.11). The thickness of the member is similar in the Kincardine basin and the Fife-Midlothian basin. However, in the Kincardine basin in west Fife, the thickness of the member increases eastwards from 33m to a maximum of 66m, associated with the lateral change to an increasingly sandstone-bearing succession (Francis et al., 1970, p.190 and plate VIII).
Geographical Limits: Central Scotland.
Parent Unit: Limestone Coal Formation (LSC)
Previous Name(s): Black Metals (-4469)
Alternative Name(s): none recorded or not applicable
Reference Section  Monckton House Borehole NT37SW/43, Midlothian. Tulloch and Walton, 1958, plate III. Includes interbedded sandstone and coal-bearing strata within the unit. 
Type Section  No. 2 Pit, Cardowan NS66NE/67. Pit section; 297 fathoms, 4 feet (544.37m) to 315 fathoms, 4 feet, 5 inch, (577.42m). 
Reference Section  Kincardine Bridge Bore NS98NW/40, Borehole section; 617 fathoms, 2 feet, 5 inches (1129.11m) to 631 fathoms, 5 feet, 1 inch (1155.52m). 
Type Section  Cardowan No.2 borehole NS66NE/66, north of Glasgow. 
Reference Section  Borehole NT19SE/550, at Dora opencast coal site, Area G, Fife. Includes interbedded sandstone and coal-bearing strata within the unit. 
Richey, J E, Anderson, E M, and Macgregor, A G. 1930.The geology of north Ayreshire. Memoir of the Geological Survey of Great Britain. 
Eyles, V A, Simpson, J B and Macgregor, M C. 1949. Geology of Central Ayrshire. Memoir of the Geological Survey of Scotland, British Geological Survey, Sheet 14 (Scotland). 
Francis, E H, Forsyth, I H, Read, W A and Armstrong, M. 1970. The geology of the Stirling district. Memoir of the Geological Survey of Great Britain, Sheet 39 (Scotland). 
Hall, I H S, Browne, M A E and Forsyth, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland). 
Tulloch, W and Walton, H S. 1958. The geology of the Midlothian Coalfield. Memoir of the Geological Survey, Scotland. 
Monro, S K. 1999. Geology of the Irvine District. Memoir of the British Geological Survey, Sheet 22W and part of 21E (Scotland). 
Simpson, J B and MacGregor, A G. 1932. The economic geology of the Ayrshire coalfields, Area IV. Memoir of the Geological Survey, Scotland. 
Clough, C T, Hinxman, L W, Wright, W B, Anderson, E M, Carruthers, R G. 1916. The economic geology of the Central Coalfield of Scotland. Area V. Memoir of the Geological Survey of Scotland. 
Read, W A. 1965. Shoreward facies changes and their relation to cyclical sedimentation in part of the Namurian east of Stirling, Scotland. Scottish Journal of Geology, Vol.1, 69-92. 
Forsyth, I H and Read, W A. 1962. The Correlation of the Limestone Coal Group above the Kilsyth coking coal in the Glasgow-Stirling region. Bulletin of the Geological Survey of Great Britain No.19, 29-52. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S031 S031 S030 S022 S023 S032 S032 S039 S040 S040 S022