Abstract: Holocene Sediment Volume and Modern Sediment Yield, Northeast Gulf of Alaska

Bruce F. Molnia, Paul R. Carlson, William P. Levy

The volume of Holocene sediment on the continental shelf of the northeast Gulf of Alaska between Montague Island and Yakutat is 3,000 cu km. If uniformly distributed, this sediment would cover the entire shelf area (55,900 sq km) to a thickness of about 55 m; however the distribution is not uniform. West of Kayak Island, where 38% of the 30,300-sq km area of the shelf is bare of Holocene sediment, the average thickness of Holocene sediment is 65 m. East of Kayak Island, where 23% of the 25,600-sq km area of the shelf is bare of Holocene sediment, the average thickness of Holocene sediment is 90 m. East of Kayak Island, much of the noncovered surface is at the shelf edge in water depths near 200 m, seaward of the growing wedge of Holocene sediment. This contrasts markedly ith the western area, where most of the noncovered surface is in 100 m of water or less. In the west, Holocene sediment apparently has been scoured and resuspended by strong bottom currents and storm waves which prevent its accumulation on the shelf and which presumably transport it beyond the shelf break.

Sediment yields from the Malaspina Glacier drainage systems and the Copper River are calculated at 0.1 cu km/year and 0.05 cu km/year, respectively; together these sources appear to contribute between one-third and one-half of the sediment input to the Gulf of Alaska. If these rates are projected back for the 10,000 years since deglaciation of the shelf, the Copper and Malaspina systems could account for about 1,500 cu km, or half of the sediment now on the shelf. If other sources, including the Bering Glacier and Alsek River systems, are assumed to be about equal in sediment yield to the Copper and Malaspina, all the Holocene sediment on the northeast Gulf of Alaska shelf can be accounted for. If these other sources yield more sediment, or if the inputs of the Malaspina and Copper sy tems are lower now than in the past, then substantial quantities of sediment must have bypassed the shelf.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma