Late Wisconsinan grounding-zone wedges, northwestern Gulf of St Lawrence, eastern Canada

Abstract

Grounding-zone wedges (GZWs) are formed on high-latitude continental shelves by the accumulation of subglacial sediments from fast-flowing ice at the grounding zone of an ice sheet during temporary stillstands (e.g. Mosola & Anderson 2006; Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). GZWs are therefore recognized to record phases of episodic ice-sheet retreat (Dowdeswell et al. 2008). The morphology and distribution of a series of GZWs mapped using high-resolution multibeam sonar and airgun seismic data in the northwestern Gulf of St Lawrence, eastern Canada, are described here (Fig. 1a–d). These ice-contact submarine landforms were deposited when the marine-based southeastern margin of the Laurentide Ice Sheet stabilized for a few decades to centuries during its rapid retreat through the Gulf of St Lawrence. Fig. 1. Grounding-zone wedges (GZW) in the northwestern Gulf of St Lawrence, eastern Canada. ( a ) Location of study area (red box; map from GEBCO_08). ( b ) Oblique view of grounding-zone wedge at 180 m water depth (GZW 1) illustrating circular depressions along its steeper down-ice slope. ( c ) Seismic-reflection profile with two GZWs. Seismic profile shows bedrock surface which consists of gently dipping monoclinal Middle Ordovician sedimentary rocks of the St Lawrence Platform (Sanford 1993). Profile is located …