DETRITAL ZIRCON GEOCHRONOLOGY OF THE BERING SEA, SHELF TO DEEP BASIN: CLIMATIC AND EUSTATIC INFLUENCE ON SEDIMENT TRANSPORT PATHWAYS

This investigation explores how climate and eustacy influenced shallow- to deep-marine sediment transport and connectivity in the Bering Sea over the past 2 m.y. The northern Bering Sea is characterized by a broad (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 eroded by several large and now mostly inactive submarine canyons. During sea-level lowstands the canyons may have been active sediment fairways that connected to deltaic systems and terrestrial sediment sources. To test this hypothesis, we compare U-Pb geochronology of detrital zircons from Holocene sediment collected in the deep-marine Aleutian Basin with that of the shallow-marine Bering shelf (Yukon Delta) and candidate non-marine sources. Detrital zircon age spectra from the Yukon Delta are characterized by primary age peaks of 108, 94, and 57 Ma with secondary age peaks at 38 and 10 Ma. Detrital ages in the Yukon–Kuskokwim Delta match closely with the Alaska Range, which also has peak populations of 94, 60, and 37 Ma. A compilation of 2,703 new ages from 18 deep-water sediment samples in the Aleutian Basin yield age peaks at 97, 59 and 38 Ma, similar to the Yukon Delta and Alaska Range signatures. These results indicate that surficial sediment of the deep Aleutian Basin is derived from the Alaska Range suggesting that sand-sized sediment transport across the Bering shelf was achieved. Because there are no known active channels for sand-sized sediment dispersal to the deep Aleutian Basin, we interpret the modern Aleutian Basin provenance signature to be the result of Yukon Delta pro-gradation during sea level lowstands. These results highlight that (1) at >1 m.y. time scales, provenance signatures of the deep-water “sink” match closely with their terrestrial source, and (2) at <1 m.y. time scales, climatic and eustatic sea-level fluctuations may play an important role in the connectivity of sources and sinks in submarine environments with broad continental shelves.