Abstract

Small and large scale trough cross-bedding as defined by McKee and Weir is very common in the Cretaceous Newcastle Sandstone of the Black Hills area of Wyoming and South Dakota. Similar large scale trough cross-bedding occurs in the Paleocene Fort Union Formation of Wyoming. Based on the grain size of the Newcastle Sandstone, the minimum current velocity necessary to erode the troughs was about 20 cm/sec; deposition of the cross-beds probably occurred in current velocities of less than 3 cm/sec. The troughs were probably eroded by tidal currents and filled by sediments deposited from slow-moving delta distributaries.

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