The Wentnor Group is an assemblage of two geological formations associated with the Longmyndian Supergroup of Precambrian age in present-day Wales, U.K.
The rocks are located between the Church Stretton Fault and the Pontesford-Linley Lineament.P. J. Brenchley, P. F. Rawson The Geology of England and Wales, 2006, 2nd ed. The Wentnor Group is a predominantly sedimentary group with a range of facies attributable to that of a closing ocean.J. N. Carney, J. M. Horak, et al., Precambrian Rocks of England and Wales, Joint Nature Conservation Committee. Geological Conservation Review Series 20 The Wentnor Group overlies the Stretton Group of rocks and although the units are separate, together they show a good geological progression. At the base of the Stretton Group the rocks are of basinal oceanic facies and over time a coarsening occurs with increased terrigenous input from the continent. Turbidites are observed and deltas form latterly with alluvial plains with occasional marine washovers. This creeps up into the Wentnor Group where alluvial plains occur latterly with fluvial and alluvial deposits noted in the uppermost (youngest) Bridges Formation.Pharaoh, T. C., Gibbons, W., Precambrian Rocks in England and Wales south of the Menai Strait Fault System, 1987 A Revised Correlation of the Precambrian Rocks in the British IslesW. Compston, A. E. Wright, P. Toghill, "Dating the Late Precambrian volcanicity of England and Wales". 2002, Journal of the Geological Society of London. 159 323-339.J. C. Pauley, “A revision of the stratigraphy of the Longmyndian Supergroup, Welsh Borderland, and its relationship to the Uriconian Volcanic Complex”, 1991, Geological Journal. 26 167-183
Bridges Formation This is the topmost formation of the Wentnor Group and viz. the Longmyndian Supergroup. The unit grades up from the underlying Bayston-Oakswood Formation. The massive and cross-bedded sandstones of the underlying unit become interbedded with purple siltstones and thin ripple cross laminated sandstones. Thick cross-bedded sandstones are recorded with sharp erosional bases and are interpreted as fluvial channels running upon mud rich alluvial plain deposits.
Bayston-Oakswood Formation This is made up of fine to medium grained cross-stratified sandstone with mudstone rip-up clasts and sub-rounded lithic clasts. There are interbeds of cross-laminated finer grained sandstones with apparent upward fining successions. The formation also contains matrix and clast supported conglomerate members with sub-rounded lithic clasts and sub-angular sedimentary clasts. These are interpreted as braided fluvial deposits. (Unit is barren of fossils).
References
External links Shropshire Geology