Difference between revisions of "Sandwick (Isle of Man) Member"
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Dickson et al. (1987) divided the singular Sandwick Member (as defined by Chadwick et al., 2001) into a lower unit, the ‘Sandwick Member’, and an upper unit, the ‘Ronaldsway Member’. See also Lamplugh (1903). The epithet (Isle of Man) is added to distinguish the Sandwick (Isle of Man) Member from the Sandwick Fish Bed Member (Orkney).
Limestone, with interbedded subordinate claystone and siltstone. The limestones are packstone and wackestone, grey, bioclastic (including crinoids and corals), bioturbated, sharp based, graded beds with hummocky cross-bedding. The grey, bioclastic claystones and siltstones form thin, discontinuous beds.
The member is interpreted as a mid-ramp carbonate facies with storm deposit limestones, and quiet water mudstones. It represents a period of maximum flooding.
A partial type section occurs in natural foreshore exposures 700 m to the south-south-east of Derbyhaven (SC 2827 6699). Discontinuous poorly exposed outcrops are present through the lower half of the member (SC 2831 6718 to 2825 6669) (see Dickson et al., 1987). A reference section is provided on the foreshore east of Ronaldsway Farm (SC 2924 6822 to 2941 6859). Here about 24 m of discontinuous exposures in the lower part of the Sandwick (Isle of Man) Member are present (see Dickson et al., 1987).
Lower and upper boundaries
The base of the Sandwick (Isle of Man) Member is poorly defined. It is poorly exposed on the foreshore at Derbyhaven (SC 2835 6653) where it overlies the Turkeyland Member. The boundary is gradational, taken at the change from limestone to limestone with interbedded claystones.
The top of the member is also poorly defined as it is overlain by limestones, sandstones and siltstones of the Skillicore Member, with a gradational contact. It is taken at the appearance and increasing occurrence of fine-grained sandstone, together with an increase in siltstone and a more tabular bedding style in the Skillicore Member.
Some 46 m.
Distribution and regional correlation
The member occurs in the southern part of the Isle of Man, in the area east of Castletown (SC 2970 6913 to 2822 6677). Visean rocks in the northern part of the island are entirely concealed and hence it is unknown whether it is present in the north.
- Dickson, J A D, Ford, T D, and Swift, A.1987.The strati-graphy of the Carboniferous rocks around Castletown, Isle of Man.Proceedings of the Yorkshire Geological Society, Vol. 46, 203–229.
- Chadwick, R A, Jackson, D I, Barnes, R P, Kimbell, G S, Johnson, H, Chiverrell, R C, Thomas, G S P, Jones, N S, Riley, N J, Pickett, E A, Young, B, Holliday, D W, Ball, D F, Molyneux, S G, Long, D, Power, G M, and Roberts, D H.2001.The geology of the Isle of Man and its offshore area.British Geological Survey Research Report, RR/01/06.
- Lamplugh, G W.1903.The geology of the Isle of Man.Memoir of the Geological Survey of Great Britain.