The BGS Lexicon of Named Rock Units — Result Details
Helmeth Grit Member
| Computer Code: | HLG | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Ediacaran Period (AD) — Ediacaran Period (AD) | ||
| Lithological Description: | Massive, coarse-grained, buff, brown or blue-grey tuffaceous sandstones in at least four beds, interbedded with greenish grey and purple mudstones. | ||
| Definition of Lower Boundary: | Uncertain. Considered by Greig et al (1968) to rest unconformably on the Ragleth Tuff Formation, but Cobbold and Whittard (1935) and Pauley (1991) suggested a conformable contact based on lithological similarities with the underlying rocks. The base is marked by a sharp transition from lithic tuffs and interbedded purple mudstones of the Ragleth Tuff Formation, the boundary being taken at the base of the first massive sandstone bed. | ||
| Definition of Upper Boundary: | Uncertain. Pauley (1991) considered the possibility of an unconformity with the overlying Stretton Shale Formation at this level on the basis of variations in dip between the two units. Accordingly he placed the Helmeth Grit as a Member in the upper part of the Ragleth Tuff Formation. The boundary is therefore taken at the top of the highest coarse-grained sandstone bed beneath the pale greenish grey mudstones of the Stretton Shale Formation. | ||
| Thickness: | At least 30 m. | ||
| Geographical Limits: | The Welsh Borderlands in Shropshire, and the Church Stretton area. | ||
| Parent Unit: | Ragleth Tuff Formation (RT) | ||
| Previous Name(s): | Helmeth Grits [Obsolete Name and Code: Use HLG]
(-3469)
Helmeth Grit [Obsolete Code: Use HLG] (YSHH) |
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| Alternative Name(s): | Watling Shales |
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| Stratotypes: | |||
| Type Area | The northwest flanks of the Ragleth, Hazler and Helmeth hills. Greig et al., 1968. | ||
| Reference(s): | |||
| Pauley J C. 1991. A revision of the stratigraphy of the Longmyndian Supergroup, Welsh Borderland, and of its relationship to the Uriconian volcanic complex. Geological Journal, Vol. 26, 167-183. | |||
| Greig D C, Wright, J E, Hains, B A and Mitchell, G H. 1968. Geology of the country around Church Stretton, Craven Arms, Wenlock Edge and Brown Clee. Memoir of the Geological Survey, Sheet 166 (England and Wales). (London: H.M.S.O.). 379pp. | |||
| Cobbold, E S and Whittard, W F, 1935. The Helmeth Grits of the Caradoc Range, Church Stretton; their bearing on part of the Pre-Cambrian succession of Shropshire. Proceedings of the Geologists' Association, Vol.46, 348-359. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E166 | |||