Glacially influenced submarine-channel sedimentation in the Yakataga Formation, Middleton Island, Alaska

The Yakataga Formation (Miocene to Recent) is a 5-km sequence of marine and glaciomarine sediments underlying a large area of the Gulf of Alaska continental shelf. The upper, early Pleistocene part of the formation, some 1.25 km thick, is exposed on Middleton Island. A 200-m-thick sequence of channelized sand and gravel lithofacies at the base of the exposed succession outcrops on extensive wave-cut platforms. These facies fill channels up to 500 m wide and 70 m deep and are associated with lenticular units of diamict. Eight major facies types are identified within the channel infills: chaotic gravel/diamict, massive gravels and sands, inversely and normally graded gravels and sands, and massive diamict. Channelized gravel and sand facies were deposited by different types of sediment-gravity flows, including debris flows, turbidity currents, and density-modified grain flows; lenticular diamict units probably formed by the passive infilling of abandoned channels by marine muds and ice-rafted debris. The facies described in this paper infill a broad submarine-channel complex, cutting the Alaskan continental shelf edge and upper slope. The complex was fed by glacial meltstreams draining a grounded or partially floating ice sheet extending out onto the continental shelf. This paper provides the first detailed descriptions of extensive outcrops of glacially influenced submarine-channel-fill facies and provides important data as to the infills of large sea valleys and submarine canyons in both glacially influenced and nonglacial settings elsewhere.