The BGS Lexicon of Named Rock Units — Result Details
Dark Grey Mudstone Member [Obsolete: use MSW]
Computer Code: | DMM | Preferred Map Code: | notEntered |
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Status Code: | Index Level | ||
Age range: | Aeronian Age (SA) — Aeronian Age (SA) | ||
Lithological Description: | [Obsolete: use MSW] Comprises dark grey anoxic mudstone. Pyritous. Generally sandstone and siltstone poor. Graptolitic hemipelagic mudstone is dominant. | ||
Definition of Lower Boundary: | The member is underlain by the dominantly oxic mudstones and siltstones of the Derwenlas Formation. Generally a sharp boundary. | ||
Definition of Upper Boundary: | The member is overlain by oxic sandstones, siltstones and mudstones of the remainder of the Cwmsymlog Formation. Generally a sharp boundary. | ||
Thickness: | (i) Up to 18-20 metres thick. (ii) 18-20 metres thick in the type section. | ||
Geographical Limits: | The unit is located in the south-east and north-east parts of Sheet 149. It is present on the Aberystwyth Sheet 163 as the "Dark Grey Mudstone". | ||
Parent Unit: | none recorded or not applicable | ||
Previous Name(s): | Monograptus-Sedgwicki Shales [Obsolete Name and Code: Use DMM]
(-4000)
Dark Grey Mudstone [Obsolete Name and Code: Use DMM] (-4612) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Reference Section | The type section is fully representative of the member. | ||
Type Section | Type locality provides type section. Old coach road, Derwenlas, 335m due west of the old National School. | ||
Reference(s): | |||
Jones, O T, and Pugh, W J, 1916. The geology of the district around Machynlleth and the Llyfnant Valley. Quarterly Journal of the Geological Society, Vol.71, p. 343-385. | |||
Cave, R and Hains, B A. 1986. Geology of the country between Aberystwyth and Machynlleth. Memoir of the British Geological Survey, Sheet 163 [England and Wales]. [London: HMSO.]. 148pp. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
none recorded or not applicable |