Abstract

The Hulett Sandstone Member of the Sundance Formation (Callovian and Oxfordian, Jurassic) exposed along the eastern flank of the Bighorn Basin, Wyoming, occurs as lenticular and discontinuous units of oolitic calcarenite, whose dominant internal structure is trough cross-stratification. This crossbedding type indicates that the units may have formed as large-scale, asymmetrical sand waves. The near north-south bipolar distribution of crossbed inclination directions at individual localities suggests that tidal current action, probably in the subtidal zone, was responsible for the formation of the units. The primary mode of the directions measured perpendicular to small-scale symmetrical ripple marks is aligned near north-south and corresponds with crossbed data. An exhumed calcarenite body of the Hulett Sandstone that appears to be a composite fossil sand wave was found. The length of this body is roughly transverse to the local bipolar crossbed modes. The shape and structure of the body supports the view that it and other less well exposed bodies of the Hulett Sandstone are large-scale, composite sand waves.

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