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The Origin of late Devensian sands and gravels, southeast Anglesey, N. Wales
Author(s) -
Helm D. G.,
Roberts B.
Publication year - 1984
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.3350190104
Subject(s) - geology , outwash plain , carboniferous , glacial period , meltwater , paleozoic , clastic rock , fluvial , paleontology , geochemistry , granulometry , streams , geomorphology , sedimentary rock , structural basin , sediment , computer network , computer science
The Lleiniog Sand and Gravel Formation, of late Devensian age, has been divided into four Members. The sediments are interpreted as the sequential products of the wasting of a single ice lobe. Member I formed where subglacial streams debouched into a pro‐glacial lake and is noteworthy for the occurrence of a bedform, hitherto undescribed but which may be common in many outwash sequences; Member 2 consists of channel sands and gravels deposited by pro‐glacial streams; Member 3 has the characters of a melt‐out till deposited after a readvance; and Member 4 accumulated in pools of meltwater on the irregular surface of Member 3. Clasts above granule grade are dominantly of locally‐derived Carboniferous rocks although a far travelled component from northern England and southern Scotland can be distinguished as well as a small but constant input of Lower Palaeozoic rock types from the Conwy area. The sand grade is dominated by quartz grains released from Permo‐Triassic sandstones. Clay grade material has been derived from Carboniferous shales.