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Drumlin sedimentology in a hard‐bed, lowland setting, Connemara, western Ireland: implications for subglacial bedform generation in areas of sparse till cover
Author(s) -
EVANS DAVID J. A.,
ROBERTS DAVID H.,
COFAIGH COLM Ó
Publication year - 2015
Publication title -
journal of quaternary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.142
H-Index - 94
eISSN - 1099-1417
pISSN - 0267-8179
DOI - 10.1002/jqs.2801
Subject(s) - drumlin , geology , meltwater , geomorphology , sedimentology , bedform , glacier , ice sheet , sediment , ice stream , geochemistry , paleontology , sediment transport , oceanography , sea ice , cryosphere
Cores of coastal drumlins in Connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites. The diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice‐contact fans, whose strata were being syn‐depositionally over‐steepened by glacitectonic deformation. The localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans/wedges. These depo‐centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre‐existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full‐depth till deformation processes (e.g. instability mechanisms) within the same drumlin field. Till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins. This zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial (esker) and subaqueous (grounding line) sediments in an otherwise marginal‐thickening till sheet.