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The alleged subaqueous sliding of large sheets of sediment in the silurian rocks of north wales
Author(s) -
Boswell P. G. H.
Publication year - 1952
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350010202
Subject(s) - geology , transgressive , paleontology , hiatus , zoning , series (stratigraphy) , scale (ratio) , fauna , sedimentary depositional environment , structural basin , law , geography , cartography , political science , ecology , biology
Since reference is made from time to time to examples of supposed subaqueous sliding on a large scale in the Silurian rocks (Salopian Series) of Denbighshire, North Wales, for the purpose of supporting inferences about the mode of origin of certain intraformational disturbances, the stratigraphical evidence in Denbighshire is reviewed. On the basis of zoning by means of graptolites (or shelly faunas where available), the boundaries of the alleged sheets of slipped material prove to be transgressive. In particular, the largest ‘contemporaneously‐disturbed’ sheet includes parts of the undisturbed succession ranging in age from the nilssoni zone to the tumescens zone. Its supposed base would have to cross its supposed surface, so that it would appear to have a negative thickness—of minus 1,000 feet or more. Acceptance of the hypothesis of large‐scale sliding on the sea‐floor in this area is thus incompatible with a belief in the value of graptolites as zonal indices in the Salopian rocks.