SEDIMENTOLOGY OF JURASSIC OOLITIC SAND BODIES IN THE MIDDLE SUNDANCE FORMATION, BIGHORN BASIN, WYOMING

The Jurassic Sundance Formation was deposited in a sea that covered a large area of the western interior of North America. In the Bighorn Basin, Wyoming lenticular oolitic sand bodies of the Sundance Formation roughly two square kilometers in area have come under debate as to their origins. Traditionally these sand bodies have thought to have been deposited in a marine environment; however, new theories suggest that these sand bodies are reworked marine sands deposited through aeolian processes. Research was conducted during the summer of 2012 at a three-dimensionally exposed outcrop near Lovell, Wyoming with a focus on the sedimentology of the sand bodies. Asymmetrical climbing ripple cross-stratification with inverse grading form well-consolidated, well-cemented layers. Grain-fall and sand-flow cross-stratification form poorly consolidated, poorly cemented layers. Adhesion warts occur at the base of the sand body while high crested symmetric ripples occur at the top. Current directions are similar to those in the aeolian Entrada Formation of Utah, which was deposited contemporaneously. Based on the presence of sand flow, grain fall, and climbing ripple cross-stratification it is likely that the ooids were exposed to a subaerial environment where it was reworked by aeolian processes. Periods of relative stability allowed the climbing ripple cross-stratification to form. The presence of adhesion warts indicate that these dunes formed over wet sediment. Then, based on the preservation of aeolian features and the presence of interstitial micrite, the oolitic sand bodies were gently submerged such that cross-stratification was not reworked by submarine processes.