Dynamics of sediments on a glacially influenced, sediment starved, current-swept continental margin: The SE Grand Banks Slope off Newfoundland

摘要

The SE Grand Banks Slope is unusual on the glaciated eastern Canadian margin in that it was remote from ice stream and glacial ice of the Laurentide Ice Sheet (LIS). It thus allows an analysis of the role of contour currents and landslides in sculpting the continental margin, processes that are largely masked where downslope pro-glacial sediment supply dominated. Detailed oxygen isotope, geotechnical, pXRF, and bulk sediment geo-chemical analyses were made on seven piston cores and were placed in context using multi-beam bathymetry and high-resolution seismic reflection profiles. Cores have a record of sedimentation back to MIS6 preserved in autochthonous sediment and slide blocks, contourites and mass-transport deposits (MTDs). Detrital-carbonaterich Heinrich layers (H) are present throughout the succession, but red mud layers of glacial meltwater origin from ice-streams in the SE sector of the LIS are identified only during MIS2 and late MIS3. Both layers allowed high-resolution correlation between cores. Sediments on the upper slope above H2 are condensed and the section above H1 is 50 cm thick, indicating that the powerful Labrador Current winnowed the section above H2. In contrast to the upper slope, approximately 3 to 5 m sediments were recorded in the mid-slope above H2 suggesting that the Labrador Current was weaker. Regional stratigraphic variations compared to Flemish Pass and Orphan Basin to the north suggest that NE Newfoundland sources of sediment played an important role and may have been previously underestimated. This study demonstrates that across-margin thickness variations reflect the character and distribution of the Labrador Current sediment transport system through time.