DEPOSITIONAL ENVIRONMENT OF THE WANAKAH FORMATION IN THE WESTERN COLORADO REGION: AN ANALOG STUDY FOR LACUSTRINE PETROLEUM SYSTEMS

The Jurassic Wanakah Formation is exposed in western Colorado and functions as a seal that overlies the permeable Entrada Sandstone. Previous studies assign either a marine or lacustrine depositional environment to the unit; this study tests the hypothesis of a hypersaline lake origin. Petrography, QEMSCAN, XRD, whole rock analysis and stable isotopes are used to evaluate the petrography, mineralogy, and geochemistry to document lateral lithofacies variability and construct a regional stratigraphic cross-section. Sedimentary and petrophysical properties within the Wanakah Formation in western Colorado suggest a hypersaline lake system that records subaqueous deposition, meters-thick horizons of gypsum precipitation, saturated and exposed paleosol development and fluvial and shoreline sandstones. Lateral variability on an outcrop-scale within the Wanakah Formation suggests that any petroleum system that includes lacustrine units must be evaluated on a fine scale to ensure a comprehensive picture of the system.