Three Yard Limestone Member
Three Yard Limestone Member is part of the Alston Formation
Formerly the Acre Limestone of Northumberland, and the Third Limestone of north of the Lake District. The Three Yard Limestone bed now has member status. See Mills and Hull (1976); Burgess and Holliday (1979); Chadwick et al. (1995); Day (1970); Dunham (1990); Dunham and Wilson (1985); Eastwood et al. (1968); Frost and Holliday (1980); Gunn (1900); Johnson et al. (1962); Johnson and Nudds (1996); Lumsden and Wilson (1961); Young and Boland (1992).
Limestone, packstone, fine-grained, mid and dark grey, thickly bedded; fissile and nodular in part, with styolites; thin mudstone partings, particularly in north Northumberland. Crinoid debris and foraminifers are typically characteristic, but the member is not particularly fossiliferous on the Alston Block. On the Askrigg Block, the limestone is split into two leaves by a ganister-like sandstone which thickens to up to 8 m westwards (Burgess and Holliday, 1979; Dunham and Wilson, 1985); a thin coal is shown at a similar horizon in the Barnard Castle district to the east (Mills and Hull, 1976).
The type area is coastal exposures at Saltpan Rocks (NU 026 493 to 026 481), about 3 km south-east of Berwick-upon-Tweed, Northumberland where Fowler (1926, p..25) described the limestone exposed on the shore below tide-mark as pale grey, dipping eastward at about 12°, folded, and with marine fossils (including Saccamminopsis) about 4.5 m thick. The type section is in the River Greta at Scotchman’s Stone (NY 0807 1245), about 8 km east of Bowes, Co. Durham where the limestone is 3.66 m thick and includes shale partings and a 3.5 cm coal (see Mills and Hull, 1976, p. 15).
Lower and upper boundaries
The lower boundary is taken at the generally conformable, sharp base of the first bed of limestone that overlies measures of the Alston Formation. On the Alston Block, it usually lies above a major sandstone body referred to as the Six Fathom Hazle. This typically displays a seatearth below the limestone, and in north Northumberland there is typically a coal; also, a few tens of centimetres of mudstone may intervene locally.
The upper boundary of the member is taken at the top of the uppermost limestone bed that is overlain by a sequence of dark grey mudstones and siltstones, in north Northumberland containing ironstone nodules locally.
Between 1.8 and 4.6 m on the Alston Block; 3–10.m in the Whitehaven to Gilcrux district, north of the Lake District; an average of 2.7 m on the Askrigg Block; 5–6.m in Northumberland.
Distribution and regional correlation
Widespread limestone member occurring throughout northern England and the Scottish Borders within the Alston Formation, stratigraphically lying below the Four Fathom Limestone and above the Five Yard Limestone on the Alston Block (Figure 11, Column 1; Figure 14, Columns 2, 3; Figure 15, Columns 1–3) or the Eelwell Limestone in Northumberland (Figure 11, Column 3; Figure 12, Columns 1–4; Figure 13, Column 4). This definition incorporates its other local names of Acre Limestone in Northumberland and Third Limestone of Cumbria (Eastwood et al., 1968; Young and Boland, 1992). Geographical distribution therefore includes Cumbria, Northumberland, Durham and North Yorkshire. The member has been seen in numerous deep boreholes throughout the region including the Archerbeck Borehole (BGS Registration Number NY47NW/14) (NY 4160 7820) (Lumsden and Wilson, 1961), the Rookhope Borehole (BGS Registration Number NY94SW/1) (NY 9375 4278) (Johnson and Nudds, 1996), the Barrock Park Borehole (BGS Registration Number NY44NE/28) (NY 4613.4660), the Throckley Borehole (BGS Registration Number NZ16NW/45) (NY.1456.6762), the Harton Borehole (BGS Registration Number NZ36NE/80) (NZ 3966 6563), the Woodland Borehole (BGS Registration Number NZ02NE/4) (NZ 0910 2769) and the Seal Sands Borehole (BGS Registration Number NZ52SW/308) (NZ 538 239). The member has also been widely seen on the Alston Block in many mine shafts and workings.
Brigantian. A goniatite indicative of the Lyrogoniatites georgiensis P2c Subzone has been recorded from mudstones above the Three Yard Limestone (Johnson et al., 1962).
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- Young, B, and Boland, M P.1992.Geology and land-use planning: Great Broughton–Lamplugh area, Cumbria.