Stratigraphy and structure of part of the Fish Lake Plateau, Sevier County, Utah

Graduation date: 1965Presentation date: 1965-05-14Over 3,000 feet of nonmarine Late Cretaceous sedimentary rocks are exposed within the northern Fish Lake Plateau. The Cretaceous\ud strata are overlain by over 2,000 feet of Early Tertiary nonmarine sedimentary rocks and volcanics. Landslide deposits cover over one-half of the area. The Late Cretaceous Blackhawk Formation, the oldest formation\ud exposed, was deposited in fluvial, swamp, coastal lagoon, and possibly shallow marine environments during the eastward retreat of\ud the Mancos sea. This formation is overlain disconformably by the Late Cretaceous Price River Formation which is composed largely of\ud quartz arenites derived from Paleozoic and Mesozoic sedimentary rocks exposed to the west. The sediments were carried into the area by streams and were deposited under piedmont and flood plain conditions. The Late Cretaceous and Early Tertiary North Horn formation conformably overlies the Price River Formation. The lower part is composed largely of fluvial sandstones but, in the upper part, lacustrine mudstones and siltstones predominate. The latter were\ud deposited in the Uinta Lake which persisted until late middle Eocene. In this lake the Early Tertiary Flagstaff, Colton and Green River Formations were deposited in succession. After an interval of erosion, the Eocene Gray Gulch Formation was deposited and, later, lavas of Oligocene age. Two periods of folding are reflected by structures within the area. The Early Laramide orogeny caused the disconformity between the Blackhawk and Price River Formations, and a later period of folding, between the late Eocene and Miocene, formed the Wasatch and Gates Creek monoclines. Late Tertiary normal faulting has been superimposed on the earlier structures. There do not appear to be favorable structures for the accumulation of oil and gas. However, stratigraphic conditions exist for both the formation and accumulation of oil and gas. The Mancos Shale, a known source rock for oil and gas farther to the east, is present in the sub-surface. Sand pinchouts in Late Cretaceous strata are believed to exist in the subsurface. Potential production in this\ud area will depend on the presence of these updip sand pinchouts