Abstract

The Copper River has prograded a marine dominated fan-delta onto the deep, tectonically active northern shelf of the Gulf of Alaska. The morphology and internal stratigraphy of the delta system are products of the sporadic influx of great volumes of bed load sediment into a basin characterized by a high wave, tide, and current energy flux. Subaerial morphology and processes of the delta are typical of humid region alluvial fans. The fan margin is, however, completely reworked and modified by wave and tidal action, and marine portions are skewed westward by longstore drift and marine currents. Major environments of the delta include (1) the subaerial deltaic plain, consisting of marsh and swamp organic muds, and braided to estuarine distributary channel fills; (2) the tidal lagoon, composed of tidal sand and mud flat sequences interlaced with a complex of tidal channel fills; and (3) the shoreface, which consists of marginal island, breaker bar, and middle shore face sands, lower shoreface sand and mud, and prodelta/shelf mud. Marine influenced tidal lagoon and shoreface facies are volumetrically dominant components of the system. The Copper River fan-delta is a working depositional model for tectonic clastic wedges prograded into an open marine basin.

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