Abstract

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement.

Cretaceous deep-water sedimentary rocks are discontinuously exposed or have been dredged along 1,650 km of the outer continental margin of the Alaska Peninsula–Bering Sea Shelf; these rocks have been studied intensively in the outer Shumagin and Sanak Islands, located on the continental shelf near the southwestern end of the Alaska Peninsula. Here, the sequence is comprised of monotonous sections of thin (4 cm) to thick (10 m) bedded sandstone and mudstone, showing grading, convolute lamination, and groove and flute casts. Petrographic studies indicate that the sandstone beds are lithic arenite with greater than 40 percent volcanically derived framework grains. The rocks have been subject to mild zeolite-grade metamorphism. Over 500 measurements of sole markings in the Shumagin and Sanak Islands show maxima to the southwest and west-northwest respectively, with minor lateral feed from the north. The data indicate turbidity current deposition in an elongate trough confined to the crescent trend of the 1,650 km belt of exposure. These ponded deep-water sediments occurring in an arcuate basin at a continental margin are interpreted to have been deposited in an ancient oceanic trench that bordered a Cretaceous volcanic arc. The deep-water rocks, a flysch deposit, comprise the central part of a Triassic to early Tertiary eugeosyncline exposed along the Shumagin-Kodiak Shelf.

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