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The Mesozoic and Cainozoic beds of the Gulf of Alaska sedimentary province were deposited respectively in an active trough and on a rapidly subsiding shelf at the Pacific margin of the North American continent. They have been deformed by repeated oceanwards thrusting and folding, which decrease in intensity towards the ocean away from a currently active dextral strike-slip fault at the inner edge of the basin: it is estimated that a lateral shortening of the order of 10 miles in the Cainozoic sediments alone is represented by this thrusting. The processes whereby these structures could have developed are examined: it is concluded that they have resulted essentially from a continuous movement of the Pacific Ocean floor relatively towards, and perhaps underneath, the continental margin, with two culminations of intensity during which the sedimentary layers above were stripped off and thrust back towards the ocean. This movement took place simultaneously with an independent dextral displacement on the bounding strike-slip fault-system, which may have contributed to the lateral shortening in the sedimentary province to the south and was at least strong enough to influence the strike-directions of the late Cainozoic structures.
