Subglacial deforming bed conditions recorded by late Quaternary sediments exposed in Vineland Quarry, Ontario, Canada

There has been considerable interest in recent years in the development of theoretical models of subglacial transport and deposition of sediment, but relatively few studies report field documentation of the resultant sediment stratigraphies. This paper presents detailed sedimentological description and analysis of a succession of late Quaternary deposits interpreted to record subglacial overriding and deformation of previously deposited lacustrine sediments exposed in the Vineland Quarry that sits close to the crest of the Niagara Escarpment within the Lake Ontario basin. The predominately fine-grained sediments record deposition under glaciolacustrine conditions followed by deformation and deposition by overriding glacial ice. Laminated silt and clay deposits overlie the striated bedrock surface and were deposited within a lake that formed as the Ontario Lobe of the Laurentide Ice Sheet advanced during the Port Huron stadial and ponded water against the Niagara Escarpment. The laminated silt and clay facies show increasing amounts of deformation up-section, passing from planar through ductile to brittle deformation. This succession of deformed facies is overlain by a macroscopically massive clay-rich diamict that caps the section. This pattern of sediment deposition and deformation is consistent with that proposed by current models of subglacial sediment deformation with the disrupted laminated silts and clays representing 'glacitectonites' resulting from downward penetrating stresses imparted by an overriding ice sheet. The uppermost massive diamict unit represents full macroscopic homogenization of the overridden sediment and is classified as a subglacial 'traction till'. The gradual transition from undisturbed laminated deposits through increasingly deformed sediment to structureless, diamict suggests that these deposits record a single episode of ice advance across the region. This ice advance was probably the short-lived advance of the Ontario Lobe of the Laurentide Ice Sheet that occurred at approximately 13,000 ybp.