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The Stretton Group is a group of rocks associated with the Longmyndian Supergroup of Ediacaran age,〔http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=YST BGS lexicon of named rock units〕 in Shropshire, England. The rocks are located within the tract between two elements of the Welsh Borderland Fault System, 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 Stretton 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. Turbidites are observed and deltas form latterly with alluvial plains with occasional marine washovers. This creeps up into the Wentnor Group where alluvial plains 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 Isles〕〔〔W. 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 present oldest to youngest as it makes much more sense in this way. One should read the Wentnor Group stratigraphy as well 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). ==Ragleth Tuff Formation== This is a unit of coarse epiclastic sediments that may pass upward into the Helmeth Grit. Its position is stratigraphically tentative.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stretton Group」の詳細全文を読む スポンサード リンク
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