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C-CORE, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X5
Observation of sub-surface deformation structures beneath modern oceanic iceberg scours is impossible, but Quaternary scours exposed above sea or lake level on land provide this opportunity. Well developed iceberg scours which are clearly visible on the former bed of glacial Lake Agassiz in southeastern Manitoba were chosen for detailed studies of sub-scour deformation.
Partial burial of the scour troughs and the absence of bioturbation of the clay sediments have preserved the surface morphology and sub-scour deformation structures in pristine condition. Shallow-angle faults and sub-horizontal thrust faults are developed below the scour trough, the former extending to at least 3 m beneath the deepest part of the scour incision surface. These faults formed in response to vertical and horizontal loading of the lake bed by the encroaching keel. High-angle normal faults developed outside the scour margin represent gravity collapse of sediment blocks that were piled up on the scour berms as a result of lateral displacement of material away from the axis of the scour. Definition of deeply penetrating faults has significant engineering implications for the burial depths required to protect oil and gas production pipelines in areas of active scouring today.
Remnant pods and lenses of tightly folded laminated sediments, in places carrying a well developed fracture cleavage, are all that remain of original primary layering in the severely reworked sub-scour sediments. Based on our findings, criteria for the recognition of scours and of ice keel turbates exposed in argillaceous sediments are proposed.
