Abstract: Late Wisconsinan glacial history of Placentia Bay, Newfoundland, as interpreted from seabed geomorphology and stratigraphy

This thesis reconstructs the glacial history of Placentia Bay, Newfoundland through the integration of seabed data and existing terrestrial records. Multibeam sonar data, augmented by seismic and coring data revealed a range of flow-parallel and flow-transverse glacial landforms on the Placentia Bay seabed. Flow-parallel landforms include drumlins, flutes, megaflutes and crag-and-tails. These landforms show a general trend of convergent flow, interpreted to represent fast-flowing ice converging into an ice stream down the axis of Placentia Bay. Flow-parallel landforms and striations from the surrounding land areas demonstrate that the convergent flow can be traced up-ice to regional ice dispersal centres. Flow-transverse landforms include De Geer moraines and grounding-line moraines. De Geer moraines occur in several fields throughout the bay marking the intermittent retreat of grounded ice up the bay. Radiocarbon ages from glaciomarine silt suggest that ice became ungrounded and glaciomarine sedimentation started ca. 16.1 cal ka BP and ended after 12.0 cal ka BP. This glacial landsystem is consistent with a conceptual model showing Late Wisconsinan ice advance to shelf edges with rapid calving retreat along deepwater channels and slower retreat of ice margins grounded in shallow water. The integrated approach used in this study represents an important development in mapping palaeo ice flows and the understanding of ice sheet behaviour during the transition from largely marine-based to land-based glacial conditions which may reflect deglacial scenarios in other bays in Newfoundland and elsewhere.