The BGS Lexicon of Named Rock Units — Result Details

Neath Valley Formation

Computer Code: NEATH Preferred Map Code: notEntered
Status Code: Full
Age range: Holocene Epoch (QH) — Holocene Epoch (QH)
Lithological Description: Unconsolidated, stratified gravels, sands, silts and clays forming the alluvial deposits of the River Neath (Afon Nedd) and its tributaries. Includes contemporaneous head, colluvium and pedogenic deposits within the catchment area. Clasts consist exclusively of Old Red Sandstone and Carboniferous limestone, sandstone and coal sourced either directly from the bedrock or via the reworking of Late Devensian glacigenic deposits (e.g. Brecknockshire Formation). Aggradational river terraces and major alluvial fans are dominated by pebble cobble gravels and medium- to coarse-grained sand (Strahan et al., 1932); the modern floodplain is dominated by silt and clay, or poorly sorted gravel (Barclay et al., 1988, p.39). Locally the deposits include lenses of peat.
Definition of Lower Boundary: Sharp, unconformable and locally channelised, predominantly on bedrock and Late Devensian head and glacigenic deposits (e.g. Brecknockshire Formation). Interdigitates in a complex manner with Tidal Flat Deposits (Gwynllwg Formation of Bowen, 1999) in the estuary.
Definition of Upper Boundary: Generally the present ground surface or, locally, overlain by peat.
Thickness: Generally to around 10m; 6m of (fluvial) gravel over 15m (?glaciofluvial) sand were recorded in a borehole near Resolven at [SN 8346 0313] (Strahan et al., 1932).
Geographical Limits: The valley of the River Neath and its tributaries (west Glamorgan, mid Glamorgan and Powys), Wales.
Parent Unit: West Wales Catchments Subgroup (WWACA)
Previous Name(s): River Terrace Deposits (RTD)
Alluvial Fan Deposits (ALF)
Lacustrine Deposits (LDE)
Head (HEAD)
Alluvium (ALV)
Alternative Name(s): none recorded or not applicable
Type Area  Neath Valley between Pontneddfechan and Cwmgwrach. Anderson and Owen, 1979. This reach contains numerous well developed alluvial fans, a laterally continuous terrace and a broad floodplain, mostly developed on glacigenic deposits (components of the Brecknockshire Formation). The thickness of the valley deposits has been documented by Anderson and Owen (1979); they considered the fans and the terrace to potentially represent the glacial to post-glacial lake terraces. 
Anderson, J G C and Owen, T R. 1979. The Late Quaternary history of the Neath and Afon valleys, South Wales. Proceedings of the Geologists' Association, Vol.90(4), 203-211. 
Barclay, W J, Taylor, K and Thomas, L P, 1988. Geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil. Third Edition. Memoir of the British Geological Survey, Sheet 231 (England and Wales). 
Strahan, A, Gibson, W and Cantrill, T C. 1932. The geology of the South Wales Coalfield, Part V, the country around Merthyr Tydfil. HMSO. 
Bowen, D Q, 1999. Wales. Chapter 7 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No.23. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable