QUATERNARY SEDIMENTARY PROCESSES ALONG THE U.S. ATLANTIC CONTINENTAL MARGIN FROM THE SHELF TO THE ABYSSAL PLAIN

Along the U.S. Atlantic continental margin, as with other passive margins, down-slope and along-slope processes interact to form complex seafloor morphology. This morphology reflects patterns of short- and long-term margin growth, through overprinting of instantaneous destructive modification (landslides, turbidity flows) preceded and followed by pervasive along-slope and hemipelagic/pelagic transport and deposition. Shifting fluvial and glacial sediment inputs along the Atlantic margin during and after the Last Glacial Maximum associated with global and local climate variations add further complexity to developing a regionally consistent understanding of the margin’s recent geologic history.

As part of marine geohazard and UN Convention on the Law of the Sea studies, we have been reexamining the sedimentary processes responsible for the recent evolution of the U.S. Atlantic continental margin. Open-slope and confined submarine landslides and submarine canyon/channel/fan systems have been identified and/or entirely remapped along the margin from the shelf edge down to abyssal depths (using multibeam bathymetry, backscatter/sidescan, and seismic reflection data). Submarine landslides and debris flows are ubiquitous along the margin, with some transporting more than 100 km³ per event and modifying tens of thousands of square kilometers of seafloor. Shelf-breaching and slope confined canyons dissect the U.S. Atlantic margin from the shelf to abyssal depths (>4000 m), coalescing at depth into a number of discrete canyon systems (e.g., Oceanographer-Lydonia, Hudson, Wilmington-Baltimore, Norfolk-Washington, Hatteras) that eventually transition into broad, low-relief submarine fans. Deep-water contour currents have also been active along the U.S. Atlantic margin since the Oligocene and continue to actively shape the region today. The Hatteras, Blake-Bahama and now buried Chesapeake contourite drift systems are the clear manifestation of the along-slope processes, but we also find evidence of bottom-current influence on seafloor morphology and sedimentation at almost all depths, and various scales, along the margin. New interpretations arising from this work will provide the basis for comprehensive reevaluation of latitudinal and temporal drivers of margin evolution.