Abstract

Mesozoic eolian oolitic carbonates are rarely documented in the Western Interior of North America, despite the ample presence of exposed carbonate strata spanning the Paleozoic through the Quaternary. This study reinterprets a distinct 15-meter-thick deposit in the Middle Jurassic lower Sundance Formation, located in Wyoming’s Bighorn Basin, traditionally interpreted as high-energy subtidal deposits. These large-scale cross-stratified oolitic strata are interpreted to be eolian deposits, attributed to the deflation of emergent oolitic shoals following structural uplift and sea level fall during the late Callovian. Evidence of an eolian origin is supported by the presence climbing trans-latent stratification produced by migrating wind ripples, composed of alternating laminations of ooids and silt-sized quartz grains. Additional evidence consists of coarsening-upward sequences of fragmented and abraded ooid grains, and evidence of vadose diagenesis. The cross-stratified oolitic bodies’ relationship with surrounding lithofacies also supports the eolian hypothesis, suggesting these oolitic limestones were deposited as isolated bedforms on an emergent deflation surface during a regression of the Jurassic Sundance Sea. The exceptional preservation of these eolian carbonates, was facilitated by low-energy conditions during a subsequent transgression.

Key Words: Eolian, Carbonates, Sundance, Jurassic, Bighorn Basin, Wyoming