STRATIGRAPHIC, MINERALOGICAL AND GEOCHEMICAL ANALYSIS OF THE RED PINE SHALE, UINTA MOUNTAIN GROUP, NE UTAH

High-resolution stratigraphic, mineralogical and geochemical analysis of the Neoproterozoic Red Pine Shale, Uinta Mountain Group, NE Utah provides paleogeographic information and allows correlation with other Neoproterozoic marine successions of the western US (the Chuar Group of Grand Canyon and the Pahrump Group, Death Valley).

Petrologic data from two locations (~600 m from the type locality at Red Pine Creek and ~700 m from a new measured section along the north Fork of the Duchesne river) are presented. A tentative correlation between the new and type sections resulted in a 1300-m-thick composite section showing two cycles of shale facies grading upward into sandstone facies. These cycles represent delta retrogradation and progradation along a wave-dominated shoreline. This interpretation is consistent with previous work regarding the overall paleogeographic setting proposed for the western Uinta Mountain Group. Organic-rich shales of the Red Pine Shale, which contain Chuaria and Melanocyrillium, show d¹³Corg variability in on the order of 10‰.

Sandstone petrology, major element (Si, Al, Fe, Mg, Ti) abundances and shale petrographic data (BSEM) confirm textural (grain size and sorting) and mineralogical (abundant biotite) characteristics consistent with a proximal derivation. Elevated Ni and Cr abundances, compared to Chuar Group mudrocks, suggest a source with a greater juvenile crustal component. The detrital mineral components (biotite, muscovite, plagioclase) suggest a significant plutonic and metamorphic provenance. Bulk chemistry (Si, Al and Fe/Ti, Mg/Ti) is controlled primarily by detrital mineral composition despite diagenetic alteration of micas and plagioclase.