The BGS Lexicon of Named Rock Units — Result Details
Senni Formation
| Computer Code: | SB | Preferred Map Code: | notEntered |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Pragian Age (DP) — Emsian Age (DE) | ||
| Lithological Description: | Mainly green and green-grey (locally red-brown and purplish green), very fine to medium-grained, micaceous sandstones, mainly channelised, cross-bedded and parallel-laminated, with green and red-brown siltstone and mudstone interbeds, some calcretes and intraformational conglomerates; characterised by the presence of vascular fossil plant remains. | ||
| Definition of Lower Boundary: | In Black Mountains, at base of green sandstones, which overlie cyclic red-brown sandstones and mudstones of the underlying St Maughans Formation. Where mature calcretes at the top of the St Maughans Formation are present (the Ffynnon Limestones), the base of the formation is placed at the top of the uppermost calcrete. | ||
| Definition of Upper Boundary: | In Black Mountains, where red sandstones of the Brownstones Formation overlie the green sandstones of the Senni Beds Formation, the junction being gradational. | ||
| Thickness: | 300 to 450 m in the Brecon Beacons and Black Mountain, 150 to 200 m in the Black Mountains. | ||
| Geographical Limits: | Carmarthen Bay eastwards to the Black Mountain, Brecon Beacons and Black Mountains, and from there southwards to Abergavenny, wedging out north of Pontypool. | ||
| Parent Unit: | Cosheston Subgroup (COB) | ||
| Previous Name(s): | Clee Sandstone Formation
(CFO)
Senni Beds [Obsolete Name and Code: Use SB] (-2409) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Type Section | Glyn Senni, Powys, south central Wales (type area); waterfall exposures in tributary of the Avon Senni (Nant Ystwyth) above Tyleglas [SN 930 209]. Cantrill, 1904. | ||
| Reference Section | Heol Senni Quarry, Powys; about 40 m of grey-green sandstones, with minor siltstones, mudstones and intraformational conglomerates [SN 9145 2210]. Dineley, 1999; Loeffler and Thomas, 1980; Barclay, 2004. | ||
| Reference(s): | |||
| Allen, J R L. 1974. The Devonian rocks of Wales and the Welsh Borderland. 47-84 in The Upper Palaeozoic and post-Palaeozoic rocks of Wales. Owen, T R (editor). (Cardiff: University of Wales Press.) | |||
| Cantrill, T C. 1904. In Strahan, A, Gibson, W and Cantrill, T C. The geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil. Memoir of the the Geological Survey of Great Britain. | |||
| Barclay, W J. 2004. Heol Senni Quarry. In Barclay et al. Old Red Sandstone rocks of Great Britain. Joint Nature Conservation Review Series. | |||
| Dineley, D L. 1999. Heol Senni Quarry. Pp. 142-144 in Dineley, D L and Metcalf, S J. Fossil Fishes of Great Britain. Geological Conservation Review Series. | |||
| Edwards, D E, Richardson, J B and Thomas, R G. 1978. Heol Senni Quarry, Powys. Pp. 77-78 in Friend, P F and Williams, B P J (editors). A field guide to selected outcrop areas of the Devonian of Scotland, the Welsh Borderland and South Wales. International Symposium on the Devonian System (PADS) September 1978. | |||
| Loeffler, E J. and Thomas, R G. 1980. A new pteraspid ostracoderm from the Devonian Senni Beds Formation of South Wales and its stratigraphical significance. Palaeontology, Vol. 23, 287-296. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E232 E231 E230 E229 E212 E213 E214 | |||