Skillicore Member

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Skillicore Member (SKIL), Carboniferous, Northern England Province[edit]

Skillicore Member is a member of theDerbyhaven Formation and part of the Great Scar Limestone Group

Name[edit]

Derived from Lough Skillicore and defined by Chadwick et al. (2001[1]), the member was formerly named the Upper Michelinia Beds by Lewis (1930[2]).

Lithology[edit]

Argillaceous limestone, with common interbedded claystone and siltstone and subordinate sandstone. The limestones are packstone, grey, bioclastic, bioturbated and pyritic, with wave ripple cross-lamination. The claystones and siltstones are grey, forming beds up to 1 m thick. They are generally unfossiliferous, though some are burrowed. The sandstones are fine-grained, cross-laminated and wave rippled.

Genetic interpretation[edit]

The unit is interpreted as an upper-ramp, shallow-water carbonate facies.

Stratotype[edit]

A partial type section, exposing the lower part of the member, occurs at Lough Skillicore (SC 2914 6831 to 2921 6838) in an embayment of the sea on the foreshore east of Ronaldsway Airport (see Dickson et al., 1987[3]).

Lower and upper boundaries[edit]

The base of the member is poorly defined. It overlies the limestones of the Sandwick (Isle of Man) Member with a gradational contact, taken at the appearance and increasing occurrence of fine-grained sandstone, together with an increase in siltstone and a more tabular bedding style.

The top of the member is also poorly defined. It is overlain by the Knockrushen Formation, with the boundary taken as immediately above a bryozoan-bearing limestone bed, which is exposed at Port St Mary (SC 212 672) and Ballasalla (SC 276 700) (Dickson et al., 1987[3]). No thickness is given by Dickson et al. (1987[3]) for this bed, but the top surface is figured in their publication (see Dickson et al., 1987, fig. 7[3]).

Thickness[edit]

Between 21 and 46 m.

Distribution and regional correlation[edit]

The member occurs in the southern part of the Isle of Man, in the Castletown area, from Ballasalla (SC 2857 7017) to Derbyhaven (SC 2798 6754). Visean rocks in the northern part of the island are entirely concealed and hence it is unknown whether it is present in the north.

Age and biostratigraphical characterisation[edit]

Arundian. The limestones have crinoids and corals (including Michelinia megastoma), the claystones and siltstones have some Chondrites burrows.

References[edit]

  1. 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.
  2. Lewis, H P.1930.The Avonian succession in the south of the Isle of Man.Quarterly Journal of the Geological Society of London, Vol. 86, 234–290.
  3. 3.0 3.1 3.2 3.3 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.