Seismic stratigraphy of the Bering Trough, Gulf of Alaska: Late Quaternary history of Bering Glacier dynamics
Abstract:Sedimentary architecture of the cross-shelf Bering Trough is studied using 5 high resolution seismic profiles integrated with the drilling data acquired during Integrated Ocean Drilling Program (IODP) Expedition 341. The objectives of this work are to constrain the number of advance-retreat cycles that have occurred through the Late Quaternary, examine the impact of the Bering Glacier on the continental shelf and slope, and reconstruct Bering Glacier dynamics. By tying these sequences with δ18O stratigraphy, we can test the Bering Glacier’s relation to global ice sheet evolution and better understand the degree to which the glacial advance-retreat cycles were in phase with global events.
Our results show that: (1) Identification of erosional surfaces and glacigenic landforms that record positions of stillstand events and diagnose the style of retreat allow us to distinguish nine phases of glacial advances and subsequent retreats. (2) Mapping shows that glacier pathways and flow directions through time are influenced by the occurrence of thick grounding-zone deposits and shifting foci of erosion. (3) Continuous buildup of glacigenic sediment fills tectonically created accommodation space and allows the glacier to advance seaward for the last three advances. Discovery of systematic, prominent deposition of glacial diamict and ice-rafted debris (IRD) during phases of glacial retreat is supported by the drilling data and suggests reconsideration of IRD impact on slope sedimentation. (4) The trough mouth fan started its development during marine isotope stage (MIS) 6, progressively advancing to the position of present shelf edge during the subsequent MIS 4 and MIS 2 and is recognized by evidence of extensive deposition of glacigenic debris flows on the slope. (5) Sedimentation rates in the depocenter are exceptionally high and are estimated to be 1-2 m/k.y. through the middle Pleistocene on the shelf and 4-5 m/k.y. average through MIS 6 on the slope.