Petroliferous Lithosomes in the Moenkopi Formation, Southern Utah

Abstract

Recent stratigraphic studies of the Triassic Moenkopi Formation suggest the possibility of important petroleum potential within the unit in southeastern and central Utah. Potential reservoir rocks include shoreline sandstone in the Black Dragon Member, carbonates in the Sin bad Limestone Member, and delta-front and delta-slope sandstone in the Torrey Member. Significant tar sand deposits have been mapped in the Moenkopi Formation in the San Rafael Swell and Circle Cliffs, and small oil and gas fields produce from the Moenkopi at the Grassy Trail and Last Chance fields respectively. These occurrences plus the large areas of bleached, nonred Moenkopi indicate that large amounts of hydrocarbons have moved through the formation. The most favorable source rocks for the Moenkopi hydrocarbons were probably the thick, dark, Paleozoic and Lower Triassic rocks west of the Cordilleran Hingeline (Wasatch Line). Thick Jurassic rocks deposited west of the Ancient Ephraim Fault may also have been important source rocks. Future successful exploration in the Moenkopi will involve locating an area where reservoir rocks and favorable structure coincide. Previous exploration involving surface structure has been rather disappointing, but recent exploration in the Rocky Mountain Region has indicated that many existing oil fields occur along major lineaments and their intersections. Major linear features are located throughout the area of study and may provide the most promising areas for future exploration.