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Van Tuyl Lecture: Matthew Malkowski, Stanford University
October 24, 2019 @ 4:00 pm - 5:00 pm
Matthew Malkowski, Stanford University
Berthoud 241, 4-5PM
Sediment Transport and Geomorphology along the U.S. Beringian Margin, Bering Sea, Alaska
Abstract: The resource-rich Bering Sea (Aleutian Basin) is situated between Alaska and Far-East Russia and represents one of the key mission areas for the United States Extended Continental Shelf Project aimed at establishing the outer limits of the U.S. economic borders. These limits are contingent upon a geological interpretation of the sea floor as defined by the United Nations Convention on the Law of the Sea – Article 76. In addition to the political and economic ramifications, the Bering Sea serves as a remarkable natural laboratory for investigating sediment transport dynamics across continental shelves in response to climatic and sea level fluctuations. Despite this, the region remains insufficiently researched and poorly-constrained, geologically. The Bering Sea is characterized by a broad (up to 900 km-wide by 1000 km-long) shallow-marine continental shelf that abruptly descends into the deep-marine Aleutian Basin along the Beringian Margin. Here, the continental slope is deeply incised by several large and now mostly inactive submarine canyons, including the largest in the world. However, during sea-level low-stands the canyons may have been active sediment fairways that connected to deltaic systems and terrestrial sediment sources. To investigate the controls on sediment transfer from terrestrial sources, across an expansive continental shelf, and into the deep sea, we use U-Pb detrital zircon geochronology from piston core sediment samples and dredged submarine canyon wall-rock. We interpret the modern Aleutian Basin sediment provenance to be dominantly the result of passive or relict sediment transport from Alaska’s Yukon–Kuskowkim Delta prograding during low-stands, and to a lesser extent from sea ice, aeolian transport, storms, and slope-failure instigated debris flows. During low-stands these passive transport processes probably serve as background sediment supply to otherwise well-connected sediment routing systems. Thus, during both low-stand and high-stand sea level conditions, Aleutian Basin sediment is dominantly Alaskan-derived and transported to the deep-sea via Beringian shelf-and-slope margin processes.