Depositional History of Jurassic Rocks in the Area of the Powder River Basin, Northeastern Wyoming and Southeastern Montana (Chapter J).

摘要

During the Jurassic, a complex active margin existed along the western edge of the North American plate. The topographically positive Western Cordillera bounded this margin on the east, forming the western side of the topographically lower Western Interior, and the central part of the North American craton was exposed east of the Western Interior. During the Middle through early Late Jurassic, the middle Western Interior intermittently contained a large epeiric seaway composed of a deep retro-arc basin on the west and a shallow marine shelf on the east. In the area of the Powder River Basin, five marine events resulted in a complex sequence of craton-wedge deposits separated by surfaces of erosion. Southern and eastern source areas contributed sediments to the seaway during the first through third events, but uplift of the Cordillera during the Late Jurassic provided a western source for the fourth and possibly fifth marine events and for the nonmarine deposition that followed.