Advance and retreat glacigenic deformation at Williams Lake, British Columbia

Abstract

Glacigenic deformation structures at Williams Lake, British Columbia, occur within stratified Quaternary sediments that both overlie and underlie lodgement till of the last (Fraser = Late Wisconsinan) glaciation. The main structures in sediments below the lodgement till are faults, joints, and clastic dikes produced by glacier overriding during Late Wisconsinan time. The orientation of these structures is closely related to the direction of glacier flow at Williams Lake. Their character and stratigraphic position suggest that the substrate in this area was partly frozen and partly unfrozen when covered by ice during the Fraser Glaciation.A different suite of glacigenic deformation structures is found in sediments above the lodgement till. These include complex folds, load casts, and high-angle faults formed during deglaciation as a result of loss of ice support and collapse. These structures yield information on the local pattern of ice decay, but bear no relationship to the regional direction of Late Wisconsinan glacier flow.