The BGS Lexicon of Named Rock Units — Result Details
Loggerheads Limestone Formation
| Computer Code: | LGHL | Preferred Map Code: | LoL |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Asbian Substage (CR) — Asbian Substage (CR) | ||
| Lithological Description: | Thickly bedded, massive, pale grey shelly limestones (packstones and grainstones), locally mottled and pseudobrecciated, arranged in shoaling upwards cycles capped by calcretes, hummocky palaeokarstic surfaces and associated thin bentonitic clay seams (palaeosols) and rare coals. Locally dolomitised and with scattered chert nodules. The Loggerheads Limestone Formation records late Asbian platform carbonate deposition on the North Wales Dinantian shelf. Each cyclic sequence records a shoaling upwards unit developed in response to transgressive and regressive movements in sea level. Many regressions culminated in emergence of the platform surface and the formation of calcrete and karstic dissolution features. During these periods of emergence, wind blown volcanic ash accumulated on the platform surface to form thin bentonitic soils. | ||
| Definition of Lower Boundary: | Top of highest porcellanous limestone of underlying Leete Limestone Formation. | ||
| Definition of Upper Boundary: | Base of lowest sequence of thinly interbedded dark-grey limestones and mudstones of overlying Cefn Mawr Limestone Formation. | ||
| Thickness: | To 275m | ||
| Geographical Limits: | North Wales between Anglesey [SH5080] and Oswestry [SJ2723]; including the Corwen Outlier [SJ0542]. | ||
| Parent Unit: | Clwyd Limestone Group (CLWYD) | ||
| Previous Name(s): | White Limestone, Middle [Obsolete Name And Code: Use LGHL]
(MDWL)
Great Orme Limestone Formation [Obsolete Name And Code: Use LGHL] (ORL) Penmon Limestone Formation [Obsolete Name And Code: Use LGHL] (PEL) Treborth Formation [Obsolete Name And Code: Use LGHL] (TREB) Llandulas Limestone Formation [Obsolete Name And Code: Use LGHL] (LNDL) Middle White Limestone [Obsolete Name and Code: Use LGHL] (-2900) Llandulas Limestone [Obsolete Name and Code: Use LGHL] (*419) Eglwyseg Limestone [Obsolete Name and Code: Use LGHL] (*73) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Partial Type Section | Base exposed in scarp east of River Alyn, in the Leete Country Park at Loggerheads; taken above highest porcellanous limestone of the underlying Leete Limestone Formation. Somerville, 1979. | ||
| Reference(s): | |||
| Davies, J R, Wilson, D and Williamson, I T. 2004. Geology of the country around Flint. Memoir for 1:50 000 Geological Sheet 108. | |||
| Wedd, C B, Smith, B and Wills, L J. 1927. The geology of the country around Wrexham, Part 1. Lower Palaeozoic and Lower Carboniferous rocks. Memoir of the Geological Survey of Great Britain. [London: HMSO.] 179pp. | |||
| Warren, P T, Price, D, Nutt, M J C and Smith, E G. 1984. Geology of the country around Rhyl and Denbigh. Memoir for 1:50 000 geological sheets 95 and 107 and parts of sheets 94 and 106. | |||
| Somerville, I D, 1979. Cyclotherms in the early Brigantian (lower D2) limestones east of the Clwydian Range, North Wales. Geological Journal, Vol.14, 69-87. | |||
| Morton, G H 1876-8. The Carboniferous Limestone and Millstone Grit of North Wales. Proceedings of the Liverpool Geological Society. Vol.3, 190-201. | |||
| Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E108 E096 E093 E094 E095 E107 E120 E121 E137 | |||