Difference between revisions of "Martin Limestone Formation"
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Martin Limestone Formation is part of the Great Scar Limestone Group
The Martin Limestone Formation comprises grey or greenish grey carbonate mudstones (commonly with fenestrae), pelletoid and bioclastic grainstones (locally with small oncoliths) and ooidal limestones. The limestone is extensively dolomitised locally, and there is a calcareous or dolomitic nodular band with algal structures at the base (Johnson et al., 2001; Rose and Dunham, 1977).
The formation was deposited in a carbonate-dominated, nearshore to peritidal, restricted marine environment, with barrier beach complexes, tidal flats and restricted lagoons (Johnson et al., 2001). A more open marine platform carbonate facies developed in the upper part of the succession (Rose and Dunham, 1977).
The type section is at the partly filled in Martin (now Marton) Quarry (SD 2434 7688) near Dalton-in-Furness. Leviston (1979, p. 12, fig. 2) referred to 14 m of bioclastic calcite mudstone with common micaceous shales and a well-developed oncolitic limestone being present 5 m above the base. A reference section is at Meathop Quarry (SD 4316 7928), Grange-over-Sands. Leviston (1979, p. 8–10, fig. 2) referred to about 4.5 m of dolomitised bioclastic limestone with interbedded grey micaceous shale and common algal beds, being overlain by 21.7 m of slightly dolomitised pelletic bioclastic limestone with common beds of black micaceous shale and common dolomitised stromatolitic limestone, beneath 19.5 m of bioclastic limestone (a higher proportion being highly dolomitised) without shale beds. A further reference section occurs in the Kendal Quarry Borehole (BGS Registration Number SD59SW/25) (SD 5022 9250) at Kendal from 84.8 to 159.75 m depth. Here, 29.14 m of limestone with sporadic corals overlie 27.51.m of dolomitised limestone and 12.3 m of dolostone with interbedded siltstone. 6 m of siltstone with beds of dolostone occur at the base.
Lower and upper boundaries
The base of the formation in Furness (South Cumbria) is not exposed, but it is taken to overlie the Marsett Formation (Ravenstonedale Group) (Figure 9, Column 14) where limestone becomes dominant over shale (Rose and Dunham, 1977, p. 28). In practice, the base is taken in boreholes at the first significant shale parting.
The upper boundary of the formation is a non-sequence below the grainstones of the Red Hill Limestone Formation, the base of which may be marked by the ‘Algal Band’ of Rose and Dunham (1977).
The formation is 25–135 m thick in Furness. The variable thickness is attributed to onlap on to irregular ridges in the early Palaeozoic basement topography (see Johnson et al., 2001, p. 58).
Distribution and regional correlation
South Cumbria and north Lancashire, including the Furness and Cartmel, Kendal, Arnside, Carnforth and Kirkby Lonsdale areas, separated from the Stainmore Trough by the Howgills ‘axis’. In west Cumbria a 6–12 m thick shallow marine succession proved in boreholes at Sellafield was assigned to the Martin Limestone Formation by Barclay et al. (1994) and Akhurst et al. (1997). This may prove unwarranted if the succession is later considered to be part of the Marsett Formation. In the Kendal area, there is a transitional passage from conglomerate and shale of the Marsett Formation (which in the Stainmore Trough is of a mostly fluvial but locally reworked shallow marginal marine facies), to the lower part of what is considered to be a local equivalent of the Martin Limestone Formation (of carbonate-dominated, near shore to peritidal, restricted marine facies). The inclusion of interbedded fluvial facies in the lower part of the Martin Limestone Formation, suggests that the formation is more typical of the Ravenstonedale Group of continental and peritidal facies, and this appears to be further supported by the striking similarity noted in field characteristics between the lower part of the Martin Limestone Formation and the Stone Gill Limestone Formation. However, the upper part of the Martin Limestone Formation, at Kendal and elsewhere, contains a more open marine platform and ramp carbonates facies, typical of the Great Scar Limestone Group.
Age and biostratigraphical characterisation
Tournaisian to late Chadian. Fossils, which are more numerous in the upper part of the formation, include the coral Dorlodotia pseudovermiculare and foraminifer Eoparastaffella sp. (Eoparastaffella Cf4 Zone).
- Rose, W C C, and Dunham, K C.1977.Geology and hematite deposits of South Cumbria.Economic Memoir of the Geological Survey of Great Britain, Sheet 58, part 48 (England and Wales).
- Johnson, E W, Soper, N J, and Burgess, I C.2001.Geology of the country around Ulverston.Memoir of the British Geological Survey, Sheet 48 (England and Wales).
- Leviston, D.1979.A study of four localities, the Martin Limestone (Lower Carboniferous, Dinantian) of Furness and Grange-over-Sands.Proceedings of the Cumberland Geological Society, Vol. 4, 3–20.
- Barclay, W J, Riley, N J, and Strong, G E.1994.The Dinantian rocks of the Sellafield area, West Cumbria.Proceedings of the Yorkshire Geological Society, Vol. 50, 37–49.
- Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, and Young, B.1997.Geology of the west Cumbria district.Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales).