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==Three Yard Limestone Member [http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=TYL (TYL)], Carboniferous, Northern England Province ==
Three Yard Limestone Member is part of the [[Alston Formation]]
=== Name ===
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)<ref name="MandH">Mills, D A C, and Hull, J H.1976.Geology of the country around Barnard Castle.''Memoir of the Geological Survey of Great Britain'', Sheet 32 (England and Wales).</ref>; Burgess and Holliday (1979)<ref name="BandH">Burgess, I C, and Holliday, D W.1979.Geology of the country around Brough-under-Stainmore.''Memoir of the Geological Survey of Great Britain'', Sheet 31, parts 25 and 30 (England and Wales)</ref>; Chadwick et al. (1995)<ref name="Chadwick">Chadwick, R A, Holliday, D W, Holloway, S, and Hulbert, A G.1995.The structure and evolution of the Northumberland–Solway Basin and adjacent areas.''Subsurface Memoir of the British Geological Survey''. (Keyworth, Nottingham: British Geological Survey.)</ref>; Day (1970)<ref name="Day70">Day, J B W.1970.Geology of the country around Bewcastle.''Memoir of the Geological Survey of Great Britain'', Sheet 12 (England and Wales)</ref>; Dunham (1990)<ref name="Dunham90">Dunham, K C.1990.Geology of The Northern Pennine Orefield: Volume 1, Tyne to Stainmore (2nd edition).''Economic Memoir of the British Geological Survey'', Sheets 19 and 25, parts 13, 24, 26, 31 and 32 (England and Wales)</ref>; Dunham and Wilson (1985)<ref name="DandW">Dunham, K C, and Wilson, A A.1985.Geology of the Northern Pennine Orefield: Volume 2, Stainmore to Craven.''Economic Memoir of the British Geological Survey'', Sheets 40, 41 and 50, parts 31, 32, 51, 60 and 61(England and Wales)</ref>; Eastwood et al. (1968)<ref name="Eastwood">Eastwood, T, Hollingworth, S E, Rose, W C C, and Trotter, F M.1968.Geology of the country around Cockermouth and Caldbeck.''Memoir of the Geological Survey of Great Britain'', Sheet 23 (England and Wales).</ref>; Frost and Holliday (1980)<ref name="FandH">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)</ref>; Gunn (1900)<ref name="Gunn">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).</ref>; Johnson et al. (1962)<ref name="Johnson62">Johnson, G A L, Hodge, B L, and Fairbairn, R A.1962.The base of the Namurian and the Millstone Grit in north-east England.''Proceedings of the Yorkshire Geological Society'',Vol. 33, 341–362</ref>; Johnson and Nudds (1996)<ref name="JandN">Johnson, G A L, and Nudds, J R. 1996.Carboniferous biostratigraphy of the Rookhope Borehole, County Durham.''Transactions of the Royal Society of Edinburgh: Earth Sciences'', Vol. 86, 181–226</ref>; Lumsden and Wilson (1961)<ref name="LandW">Lumsden, G I, and Wilson, R B.1961.The stratigraphy of the Archerbeck Borehole, Canonbie, Dumfriesshire.''Bulletin of the Geological Survey of Great Britain'', No. 18, 1–89.</ref>; Young and Boland (1992)<ref name="YandB">Young, B, and Boland, M P.1992.Geology and land-use planning: Great Broughton–Lamplugh area, Cumbria.</ref>.

=== Lithology ===
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<ref name="BandH"></ref>; Dunham and Wilson, 1985<ref name="DandW"></ref>); a thin coal is shown at a similar horizon in the Barnard Castle district to the east (Mills and Hull, 1976<ref name="MandH"></ref>).

=== Stratotype ===
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<ref name="MandH"></ref>).

=== 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.

=== Thickness ===
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<ref name="Eastwood"></ref>; Young and Boland, 1992<ref name="YandB"></ref>). 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<ref name="LandW"></ref>), the Rookhope Borehole (BGS Registration Number NY94SW/1) (NY 9375 4278) (Johnson and Nudds, 1996<ref name="JandN"></ref>), 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.

=== Age ===
Brigantian. A goniatite indicative of the ''Lyrogoniatites georgiensis'' P2c Subzone has been recorded from mudstones above the Three Yard Limestone (Johnson et al., 1962<ref name="Johnson62"></ref>).

== References ==
<references/>
[[Category:Carboniferous lithostratigraphical nomenclature]]

Three Yard Limestone Member - Revision history

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Geosource>Volunteer 01 at 10:15, 5 August 2015