STRATIGRAPHIC COMPONENTS AND CORRELATION OF THE JUANA LOPEZ MEMBER TO PROXIMAL MARINE FACIES IN THE SEVIER FORELAND BASIN, MANCOS SHALE, UINTA BASIN, UTAH

Across the Colorado Plateau the Mancos Shale is a widespread silty mudstone recording over fifteen million years of Late Cretaceous deposition into the foreland basin of the Sevier fold and thrust belt. Within the Lower Mancos, the Juana Lopez Member is a natural laboratory to study mudstone variety, as it is muddy and organic-rich, yet highly heterolithic. The Juana Lopez is coeval with lowstand deposits of the Ferron Sandstone, but does not fit the model of basin floor sand deposition concurrent with lowstand deltas. This study investigates the facies and stratigraphy of the Juana Lopez Member, specifically the drivers of deposition and preservation of organic-rich, heterolithic deposits. Detailed core description, thin section examination, SEM analyses, x-ray fluorescence analyses, and programmed pyrolysis were completed in order to accurately identify and describe the Juana Lopez. Basin-wide correlations have been made in order to document the lateral and vertical distribution of stratigraphic packages and their relationship to updip marginal marine facies. Aggregates and mud rip-ups, normally and inversely graded beds, and rippled and scoured laminae observed in core and thin section indicate high energy deposition of biogenic calcareous and detrital siliceous material. Interbedded organic-rich mudstone and rippled siltstone and fine sandstone suggest various modes of sediment dispersal. A counter-clockwise gyre in the seaway periodically delivered biogenic calcareous material from the shallow eastern ramp to the foredeep via storm-driven flows. Clastic sediments were sourced from shore-parallel geostrophic currents, with smaller clastic volumes distributed across the shelf. Restricted circulation due to an embayment in the coastline of the Western Interior Seaway known as the Utah Bight may have led to accumulation of both terrestrial and marine organic matter that was subsequently distributed to the distal realm. Recognition of a genetic relationship between the Juana Lopez and the Ferron Sandstone aids in understanding the transition between nearshore and offshore marine systems, as well as elucidates the combination of paleo-oceanographic conditions that allows for deposition and preservation of organic carbon.

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Session No. 23

T191. Mud, Mud, Glorious Mud: Advances in Stratigraphic, Sedimentologic, Geochemical, and Geomechanical Analyses of Fine-Grained Lithologies

Sunday, 25 September 2016: 8:00 AM-12:00 PM

Room 401 (Colorado Convention Center)

Geological Society of America Abstracts with Programs. Vol. 48, No. 7
doi: 10.1130/abs/2016AM-287139

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