A glacial landform assemblage in Placentia Bay, Newfoundland, eastern Canada

Abstract

Placentia Bay, located on the south coast of the island of Newfoundland, is bounded to the west by Burin Peninsula and to the east by Avalon Peninsula (Fig. 1a). At the Last Glacial Maximum (LGM) the Laurentide Ice Sheet extended south of the bay, reaching the edge of the continental shelf (Shaw et al. 2006). Placentia Bay was an onset region for fast-flowing ice in Halibut Channel, a cross-shelf trough beyond the bay. The bay became ice free at c. 14 ka, by which time retreat of Laurentide ice had isolated a Newfoundland ice cap. Placentia Bay has been mapped with multibeam sonar and surveyed with sub-bottom profilers. Results from these activities are contained in 1:50 000 scale shaded-relief maps, backscatter strength maps, a ‘seascape’ map (Shaw et al. 2011) and in various papers (e.g. Brushett et al. 2007; Shaw et al. 2009). The landform assemblage includes: (1) glacially overdeepened troughs; (2) streamlined sedimentary landforms; (3) rock drumlins; (4) flutes overprinting sedimentary drumlins; (5) De Geer moraines superimposed on streamlined landforms; (6) a complex landform suite comprising coast-parallel moraines, drumlins and megaflutes, eskers and hummocky moraine; (7) transverse moraines; (8) submarine slides; and (9) paraglacially modified terrain. Fig. 1. Multibeam sonar bathymetry from Placentia Bay, Newfoundland, eastern Canada (Fig. 2g). ( a ) Sun-illuminated multibeam sonar bathymetric image, with a cross-section across the bay. Acquisition systems Kongsberg EM1002 and EM300. Frequency 12 kHz. Grid-cell size 5 m. ( b ) Backscatter strength. White line indicates area of seafloor erosion (megaflutes). ( c ) Streamlined glacial-sedimentary landforms. ( d ) Rock drumlins. ( e ) Drumlins (top) overprinted by flutes (bottom), illustrating a readvance from the SW. The inner bay includes three narrow channels (Fig. 1a): Western Channel (maximum depth 450 m), Central Channel (265 m), and Eastern Channel (333 m). The outer bay has lower relief and encompasses …