The BGS Lexicon of Named Rock Units — Result Details
Downend Member
| Computer Code: | DN | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Bolsovian Substage (CC) — Asturian Substage (CAS) | ||
| Lithological Description: | Sandstone with some conglomerate and pebbly sandstone and sporadic fissile mudstone beds. Some workable coal seams are also present. Sandstone is typically a coarse-grained lithic arenite of 'Pennant' type. The sandstones formed in channels and floodplains within a broad alluvial tract. The lower part of the member is Bolsovian in age. This is constrained in the Somerset Coalfield with the base of the member occurring between the Aegiranum and Cambriense marine bands, whereas in the Bristol Coalfield it occurs above the Cambriense Marine Band. At Bickley Wood [ST 644 703] plant fossils have been interpreted as indicating a lower or middle Asturian age (Cleal and Thomas, 1996). | ||
| Definition of Lower Boundary: | Base of member is the base of the lowest mappable lithic sandstone of 'Pennant' type above the grey and red mudstone-dominated succession of the Winterbourne Formation. The base is diachronous; In the Somerset Coalfield the base of the member occurs between the Aegiranum and Cambriense marine bands, wheras in the Bristol Coalfield it occurs above the Cambriense Marine Band. | ||
| Definition of Upper Boundary: | The top of the Downend Member is defined at the top of the Mangotsfield Coal and associated thin fissile mudstone, overlain by the sandstone-dominated succession of the Mangotsfield Member. | ||
| Thickness: | About 120 m thick in the northern part of the Bristol Coalfield [ST 78], broadly thickening southward to about 660 m in the Somerset Coalfield [ST 75]. About 275 m in the type area. | ||
| Geographical Limits: | Bristol and Somerset coalfields. | ||
| Parent Unit: | Pennant Sandstone Formation (PES) | ||
| Previous Name(s): | Downend Group [Obsolete Name and Code: Use DN]
(*144)
Downend Formation [Obsolete Name and Code: Use DN, WINT] (-4001) |
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| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | The sandstone quarry at Frenchay Bridge [ST 639 771]: about 30 m of massive sandstone, from below the stinking Coal [NE Bristol] (Kellaway and Welch, 1993). | ||
| Type Area | Downend, Avon [ST 65 77]. | ||
| Reference Section | Harry Stoke C (Downend) borehole (ST67NE/1) [ST 6504 7677] from 317.1 m to 10.4 m (Kellaway and Welch, 1993). | ||
| Reference(s): | |||
| Kellaway, G A. 1969. The Upper Coal Measures of South-West England compared with those of South Wales and the Southern Midlands. Compe Rendu 6e Congres Internationale Stratigraphie et Geologie Carbonifere, Sheffield, 1967, Vol. 3, 1039-1055. | |||
| Kellaway, G A and Welch, F B A. 1993. Geology of the Bristol district. Memoir of the British Geological Survey Special Sheet [England and Wales]. | |||
| 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: | |||
| E250 E251 E264 E281 E280 | |||