Dun Limestone Member
Dun Limestone Member is part of the Tyne Limestone Formation
Previously referred to as the Ladies Wood Limestone (obsolete) in the Bellingham district, and the Lamberton Limestone (obsolete) in the Eyemouth district. See Frost and Holliday (1980); Greig (1988); Gunn (1900).
A dark grey, argillaceous, crinoidal, shelly limestone with algal nodules, weathering to a rusty ochreous colour.
Of marine origin
The type area is the north side of Huds Head, Spittal, near Berwick-upon-Tweed, Northumberland (NU 010 510 to 015 506) (see Scrutton, 1995).
Lower and upper boundaries
At the lower boundary, the Dun Limestone is generally underlain conformably by a thin marine mudstone that overlies a thin coal or seatearth of the Tyne Limestone Formation (Figure 12, Columns 1–4).
The upper boundary of the member is generally a conformable change from limestone to overlying marine mudstone that passes up into deltaic arenaceous deposits of the Tyne Limestone Formation (or Alston Formation, where the normal boundary at the base of the limestone that marks the base of the Brigantian Stage has not or cannot be mapped).
Between 1.2 and 1.6 m in the Eyemouth and north Berwickshire districts. 5–8 m in Northumberland (Frost and Holliday 1980).
Distribution and regional correlation
Confined to Berwickshire and north Northumberland in the Tyne Limestone Formation, Yoredale Group, the Dun Limestone is widely correlatable throughout the Northumberland Trough (Frost and Holliday, 1980). The contained fauna and flora is equivalent to the MacGregor Marine Bands of the Midland Valley of Scotland (Wilson, 1974; Neves et al., 1973).
Age and biostratigraphical characterisation
Asbian. An NM Zone miospore assemblage was reported by Neves et al. (1973) in the Dun Limestone Member in the Marshall Meadows Borehole (BGS Registration Number NT95NE/5) (NT 9797 5685), and an Asbian age is supported by the presence of the coral Siphonodendron junceum (see Fowler, 1926).
- Frost, D V, and Holliday, D W.1980.Geology of the country around Bellingham.Memoir of the Geological Survey of Great Britain, Sheet 13 (England and Wales)
- Greig, D C.1988.Geology of the Eyemouth District.Memoir of the British Geological Survey, Sheet 34 (Scotland).
- Gunn, W.1900.The geology of Belford, Holy Island, and the Farne Islands, Northumberland.Memoir of the Geological Survey of Great Britain, Sheet 4 (England and Wales)
- Scrutton, C (editor).1995.Northumbrian Rocks and Landscape: a Field Guide. (Maryport: Ellenbank Press for the Yorkshire Geological Society.)
- Wilson, R B.1974.A study of the Dinantian marine faunas of South-East Scotland.Bulletin of the Geological Survey of Great Britain, No. 46, 35–65.
- Neves, R, Gueinn, K J, Clayton, G, Ioannides, N S, Neville,R S W, and Kruszewska, K.1973.Palynological correlations within the Lower Carboniferous of Scotland and northern England.Transactions of the Royal Society of Edinburgh,Vol. 69, 23–70.
- Fowler, A.1926.The geology of Berwick on Tweed, Norham and Scremerston.Memoir of the Geological Survey of Great Britain, Sheets 1 and 2 (England and Wales)