The Wentnor Group is a group of rocks associated with the

Longmyndian Supergroup The Longmyndian Supergroup is a sequence of Late Precambrian rocks that outcrop between the Pontesford–Linley Fault System and the Church Stretton Fault System in the Welsh Borderland Fault System. The supergroup consists of two major geol ...

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

age in present-day

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

, U.K. The rocks are located within the confines between the Church Stretton Fault and the Pontesford-Lindley 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 as time goes a coarsening occurs with increased terrigenous input from the continent.

Turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

s 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 The information below is presented oldest to youngest as it makes much more sense in this way. One should read the Stretton Group stratigraphy first in order to get a sense of continuity. The progradational Longmyndian Sequence from oldest to youngest is: Ragleth Tuff Formation; Stretton Shale Formation; Burway Formation; Synalds Formation; Lightspout Formation; Portway Formation; Bayston-Oakswood Formation; Bridges Formation. The latter two units belong to the Wentnor Group. Below we carry on from the underlying Portway Formation (Stretton Group).

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 subrounded lithic clasts and subangular sedimentary clasts. These are interpreted as braided fluvial deposits. (Unit is barren of fossils).

Bridges Formation

This is the top most formation of the Wentnor Group and viz. the

. 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.

References

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External links

Shropshire Geology
Geology of Shropshire Geology of Wales Precambrian Europe