- 1 Derbyhaven Formation (DBH), Carboniferous, Northern England Province
- 2 References
Derbyhaven Formation is part of the Great Scar Limestone Group
The formation comprises limestone, with interbedded, subordinate claystone and siltstone. The limestones vary from packstone, to wackestone and grainstone. They are typically grey, bioclastic (including crinoids and corals) and bioturbated. Sedimentary structures vary but include cross-bedding, wave ripples and hummocky cross-bedding. The claystones and siltstones are grey, bioclastic, and form thin, discontinuous beds. The formation includes three members, the Turkeyland, Sandwick (Isle of Man), and Skillicore members.
The sequence is interpreted as representing a carbonate ramp facies.
Dickson et al. (1987; see also Chadwick et al., 2001) compiled the type section from the constituent members along the eastern coastline of the Isle of Man. They referred to exposures of the Turkeyland Member 16.7 m thick at Derbyhaven (SC 289 678), where dolomitisation has destroyed much of the primary rock fabric; exposures of the Sandwick (Isle of Man) Member, apparently 46 m thick at Sandwick Bay (SC 282 671), and on the foreshore east of Ronaldsway Airport (SC 294 684), where there are limestones with shale partings; and exposures of the Skillicore Member, 21 m thick on the foreshore north-east of the airport (SC 292 682) comprising mainly argillaceous limestones with abundant shale intercalations.
Lower and upper boundaries
The base of the formation (taken at the base of the typically ooidal and bioclastic grainstones of the Turkeyland Member) is poorly defined. It rests directly on conglomerates of the Langness Conglomerate Formation, Ravenstonedale Group, on the foreshore at Derbyhaven (SC 2820 6607) (Figure 8, Column 8), although outcrops are discontinuous and poorly exposed. It was formerly exposed at the now infilled Turkeyland Quarry (SC 2950 6940), where it rests directly on conglomerates of the Langness Conglomerate Formation.
The top of the formation is poorly defined. It is overlain by the limestones with interbedded subordinate claystone of the Knockrushen Formation, with the boundary taken immediately above a byozoan bed, which is exposed to the north-east of the airport light gantry at Ronaldsway at about (SC 28 68), at Port St Mary at about (SC 21 67), and at Ballasalla at about (SC 28 70) (see Dickson et al., 1987 who quoted no grid references for these localities).
The formation is more than 90 m thick (Chadwick et al., 2001).
Distribution and regional correlation
The southern part of the Isle of Man, in the Castletown area.
Age and biostratigraphical characterisation
Arundian. The Skillicore Member includes the coral Michelinia megastoma.
See also Appendix 1. Members of the Derbyhaven Formation in ascending stratigraphical order include:
- 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.
- 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.
- 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.