The BGS Lexicon of Named Rock Units — Result Details

Dovey Valley Formation

Computer Code: DOVEY 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 Dovey (Afon Dyfi) and its tributaries. Includes contemporaneous head, colluvium and pedigenic deposits within the catchment area. Clasts principally consist of local, Lower Palaeozoic turbidites. Aggradational river terraces and major alluvial fans are dominated by pebble cobble gravels and medium- to coarse-grained sand; the modern floodplain is dominated by silt and clay, and locally includes lenses of peat.
Definition of Lower Boundary: Sharp, unconformable and locally channelised on bedrock and Late Devensian head deposits and Welsh glacigenic deposits (including Eryri and Plynlimon till formations). 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.
Geographical Limits: The valley of the River Dovey and its tributaries (Gwynedd, Powys and Dyfed), west Wales.
Parent Unit: West Wales Catchments Subgroup (WWACA)
Previous Name(s): Alluvial Fan Deposits (ALF)
River Terrace Deposits (RTD)
Lacustrine Deposits (LDE)
Head (HEAD)
Alluvium (ALV)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Dovey valley between Mallwyd and Cemmaes Road. This reach contains numerous well developed alluvial fans, a staircase of terraces and a broad floodplain, mostly developed on glaciofluvial deposits; the ages of several of the post-glacial alluvial deposits (surfaces) are well constrained (Sheppard and Davies, 2004). Wilby et al., 2005 
Reference(s):
Cave, R and Hains, B A. 1986. Geology of the country between Aberystwyth and Machynlleth. Memoir of the British Geological Survey, Sheet 163 [England and Wales]. [London: HMSO.]. 148pp. 
Wilby, P R, Wilson, D and Davies, J R. 2005. A geological investigation of the Quaternary fill of the Dyfi valley, Mid Wales. British Geological Survey Commissioned Report CR/05/072. 
Thomas, G S P, Summers, A J and Dackombe, R V. 1982. The Late Quaternary deposits of the middle Dyfi Valley, Wales. Geological Journal, Vol.17, 297-309. 
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp 
Sheppard, T H and Davies, J R. 2004. Predictive and investigative modelling of flood risk within Welsh river catchments: a co-funded pilot. A preliminary report, February 2004. IR/04/068, British Geological Survey. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable