The BGS Lexicon of Named Rock Units — Result Details
Gamlan Formation
| Computer Code: | GN | Preferred Map Code: | Gn |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | St David's Series (ED) — St David's Series (ED) | ||
| Lithological Description: | Grey, green and purple colour-banded, locally pyritic mudstones and thin, coarse-grained turbiditic sandstones. Upper part of Formation manganiferous, with thin mudstone beds near the top. | ||
| Definition of Lower Boundary: | Conformable, sharply overlain by turbiditic siltstones of the Barmouth Formation. | ||
| Definition of Upper Boundary: | Conformable and transitional with overlying black mudstones of the Clogau Formation (Mawddach Group). | ||
| Thickness: | 150 to 240m | ||
| Geographical Limits: | Northern, eastern and southern flanks of Harlech Dome. | ||
| Parent Unit: | Harlech Grits Group (HGG) | ||
| Previous Name(s): | Gamlan Shale Group [Obsolete Name And Code: Use GN]
(GMSH)
Gamlan Black Shales [Obsolete Name and Code: Use GMSH, GN] (-288) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Partial Type Section | Afon Gain northwest of Mynydd Bach. Tuffitic mudstones near the top of the Formation. Allen, P M and Jackson, A. 1985. | ||
| Partial Type Section | Manganese mine, a short distance north of Frith Farm [SH6123 3047] (manganiferous horizons). Dewey, H and Dines, H G. Tungsten and manganese ores. Memoir of the Geological Survey of Great Britain, 83. | ||
| Reference(s): | |||
| Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 (England and Wales). (London: HMSO.) 112 pp. | |||
| Matley, C A and Wilson, T S. 1946. The Harlech Dome, North of the Barmouth Estuary. Quarterly Journal of the Geological Society of London, Vol.102, 1-40. | |||
| Dewey, H and Dines, H G. 1923. Tungsten and manganese ores. Memoir of the Geological Survey of Great Britain. [London: HMSO.] | |||
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E119 E149 E135 | |||