The Athabasca fluting field, Alberta, Canada: implications for the formation of large-scale fluting (erosional lineations)

Abstract

Current drumlin and fluting hypotheses, centred on processes of formation, erosion and deposition by subglacial deformation, accretion by lodgement, glacial erosion, and meltwater erosion and deposition, rarely receive comprehensive field testing. This paper documents the morphology, internal structure, and landscape associations of the Athabasca fluting field, Alberta, and discusses how well these characteristics are explained by postulated fluting forming processes. Fluting hypotheses are comprehensively tested by this approach and their rejection or acceptance are firmly based on field observation and knowledge of processes. Using multiple criteria, fluting is shown to be erosional and not to be a product of pervasive subglacial deformation or accretion by lodgement. Morphology, landscape associations, bed truncation, plus glaciofluvial lags and gravel on fluting ridges are inferred to support erosion by meltwater. Intact primary bedding, synsedimentary faults and injection structures very close to the landsurface, showing no sign of shear deformation, are used to reject erosion by subglacial deformation. Fluting is shown to be closely associated with tunnel channels and indicates that these channels were overtopped by broad floods that formed the fluting field and eroded anabranching tracts over the length of the Alberta Plains. Prior to fluting formation, sequences with melt-out and lodgement till, conduit sediment and boulder lags record net deposition over an extended time period. Diapirism prior to fluting formation marks a period of extreme pressure gradients which are related to bed separation. Following fluting formation, there was only minimal landscape modification, dominated by glaciofluvial and glaciolacustrine deposition, not glacial processes. This progression is presented as evidence for two very different glacial regimes separated by a short period with diapirism and extensive landscape modification by meltwater erosion. We note that the study area was glaciated only once, during the Late Wisconsinian, and it follows that glacial sedimentation and landscape modification were confirmed to this single glacial episode.