Basement Control of Sediment Routing in the Gulf of Alaska

New seismic reflection data from the June 2011 R/V Marcus G. Langseth cruise MGL1109 reveal that sediment routing throughout the vast Gulf of Alaska is profoundly shaped by basement structure, even after the primary basement topography has been completely buried. This control by basement topography is true for elements of the Surveyor and Baranof fan systems on a regional scale over millions of years as evidenced by stacked channel systems whose placement was originally controlled by the locations of fracture zone ridges and troughs and by irregular barriers within now-buried groups of seamounts. The new seismic reflection data show that the Kodiak-Bowie seamount chain is considerably broader and more voluminous than is evident from a bathymetric map. Sediments immediately landward of the central part of the chain are generally thinner compared to seaward sediments; the landward basement is shallower than previously recognized, and many significant seamounts (with original elevations > 1 km) are buried just beneath the sediment surface. Major submarine channels of the Baranof fan were historically diverted abruptly to the southeast by elevated topography connecting some of the larger volcanic edifices of the Kodiak-Bowie seamounts. Today those volcanic septa are completely buried yet the channels retain their previous routing. Similarly, the underlying presence of the ridges and troughs of the Aja fracture zone drive the prominent westward bend in the Surveyor channel. The new observations suggest that the routing of these major channel systems is largely self-perpetuating, and therefore the morphology of the now-buried Pacific oceanic basement continues to be an important factor in the sedimentary development of the southeastern Alaska margin.