Post-LGM sedimentation history and deglaciation processes in the southern Gulf of St. Lawrence, Canada

Abstract

Highlights • Significant influence of the Bølling-Allerød and Younger Dryas on sedimentation. • Buried sediment basins and channels filled by late Pleistocene sediments. • Sedimentation rates >0.4 cm a−1 during deglaciation. • Erosional truncation possibly related to the Holocene RSL lowstand. • Marine sedimentation close to the coast of PEI as early as ∼13.6 ka BP. Abstract During the last glacial period, continents and surrounding shelves in high latitude regions of the Northern Hemisphere were covered by ice sheets. Their retreat after the Last Glacial Maximum resulted in isostatic adjustments of the previously glaciated landmass and post-glacial changes in relative sea level during the late Pleistocene and Holocene. Many questions, however, remain about the timing and impact of the ice retreat and of short-lived climatic events on continental shelf environments. This study aims to reconstruct the sedimentation and deglaciation processes on the continental shelf of the southern Gulf of St. Lawrence (Canada) over the past 14 ka by investigating changes in the sedimentation patterns and paleo-environments. Using information from sub-bottom profiles, sediment cores, and multibeam bathymetry, this study finds that most of the continental shelf was flooded 13.6 ka ago, as evidenced by the presence of Bølling-Allerød marine sediments at a water depth of ∼50 m and ∼15 km off the modern coastline, which also suggests an earlier retreat of the Laurentide Ice Sheet than suggested by previous studies. We estimate sedimentation rates for the Bølling-Allerød of ∼0.4 cm a−1, which increased up to 1 cm a−1 during the Younger Dryas cooling event, likely associated with increased storm-wave activity and sea ice development caused by deteriorating climatic conditions. The presence of an erosional truncation atop Younger Dryas sediments indicates a late Pleistocene-early Holocene relative sea level fall and associated lowstand. Based on our new data, we established a geological model that highlights sedimentation processes since the Last Glacial Maximum and demonstrate the potential impact of short-lived climatic events on the former ice margin during deglaciation