Late Wisconsinan glacial landsystems on Atlantic Canadian shelves: New evidence from multibeam and single‐beam sonar data

Abstract

Multibeam sonar surveys in the past decade, augmented by single‐beam data from the OLEX charting system, reveal landsystems on Atlantic Canadian shelves that are diagnostic of Late Wisconsinan ice‐sheet dynamics. Four landsystems are described. (1) The Bay of Fundy landsystem comprises two contrasting sets of bedforms, and is interpreted as evidence of topographically controlled fast‐flowing ice adjacent to slower‐moving ice. (2) The German Bank landsystem off southwest Nova Scotia is comprised of glacially fluted terrain overprinted by De Geer moraines and arcuate recessional moraines. We infer that a flow of grounded glacial ice out of the Bay of Fundy was followed by steady retreat, punctuated by at least one major re‐advance. (3) The Placentia Bay landsystem consists of a convergent field of streamlined landforms with superimposed De Geer moraines, overprinted in one area by flutings. We infer that this landsystem was formed in the onset zone of fast‐flowing ice, and that overprinting was due to a re‐advance of ice from offshore. (4) The south coast of Newfoundland landsystem, which includes arcuate, fjord‐mouth moraines and a coast‐parallel, fluted moraine, indicates strong topographic control on a retreating marine ice margin as it reached a fjord coastline. These submarine glacial landsystems are not inconsistent with a conceptual model showing Late Wisconsinan ice advance to shelf edges, rapid calving retreat along deepwater channels and slower retreat of ice margins grounded in shallow water. The re‐advances documented two of the study areas have parallels in the Last British Ice Sheet, confirming that the reorganization of marine‐based ice sheets, caused by calving in embayments, led to internally forced re‐advances.