Refinement of the Quaternary seismic stratigraphy and analysis of buried glacial channels on the Labrador Shelf

Abstract

The Laurentide Ice Sheet covered vast areas of North America during the Wisconsinan, including the Labrador Shelf, off the coast of eastern Canada. The shelf is characterized by glacial cross-shelf troughs, which have been considered as predominantly eroded by the last ice advance. Nevertheless, these cross-shelf troughs contain substantial sedimentary infill that has not yet been thoroughly explored and elucidated. Therefore, we hypothesize that older, potentially non-glacial, sediments are preserved within these cross-shelf troughs on the Labrador Shelf. In this study, we investigate the stratigraphic infill of three major trough systems on the Labrador Shelf using 2D seismic reflection data to refine the erosional and depositional processes that produce the geomorphology and stratigraphy of the shelf. The results of the study present an updated Quaternary stratigraphy of the Labrador Shelf, comprising eight seismic units. For the first time, we interpret glaciomarine and open marine deposits between glacial till layers. Additionally, we identified sets of elongated depressions, at three different depth intervals. Some of them are classified as subglacial meltwater channels and some others as ice stream troughs. Finally, we propose a stratigraphic evolution model consisting of 10 phases and spanning two glacial–interglacial cycles. The results support our hypothesis and suggest that the deeper sediment layers on the shelf contain evidence of older glacial–interglacial cycles. They also lend support to the hypothesis of a multiphase origin over multiple glacial cycles for the cross-shelf troughs. Consequently, new opportunities are provided for the reconstruction of ice-sheet dynamics and associated oceanographic conditions on the Labrador Shelf, as the sedimentary succession provides an archive to reconstruct dynamics of ice sheets during at least two Quaternary glacial–interglacial cycles.