CHARACTERIZATION OF THE RED PINE SHALE, UINTA MOUNTAIN GROUP: MID-NEOPROTEROZOIC PALEOGEOGRAPHY OF NE UTAH

Ongoing stratigraphic, sedimentologic, and geochemical studies add insight into local and regional paleogeography, and age, of the Neoproterozoic(?) Red Pine Shale, Uinta Mountain Group, NE Utah. Measured sections include the type section (~600 m thick) and a section along the north fork of the Duchesne River (~900 m thick) (western Uinta Mountains), and a new section along Ashley Creek (~450 m thick) (eastern Uinta Mountains). The western sections include three main facies: shale facies, shale-and-sandstone facies, and sandstone facies. The shale facies (organic-rich, gray-to-black siltshale) is parallel- to ripple-laminated and found in intervals £100 meters thick. The shale-and-sandstone facies (organic-rich, gray-to-black siltshale interbedded with quartz arenite to feldsarenite in thin beds) shows graded beds, hummocky-cross stratification (HCS), and parallel to ripple laminations in intervals £10's of meters thick. The sandstone facies (thickly bedded quartz arenite to feldsarenite) shows graded beds, HCS, cut-and-fill structures, ripplemarks, ripple laminations, and planar-tabular foresets with rare associated topsets. d¹³C_org analysis of organic-rich shales from these sections reveals 9‰ (PDB) variability (values range from -21.7 to -30.7‰ PDB). TOC values range from 0.32 to 5.9 %. Chuaria are present in these sections, and vase-shaped microfossils are present in the type section. The eastern section includes two main facies: variegated mudrock and fine-grained sandstone. The former facies is laminated green-gray-red mudshales and siltstones in intervals £10's of meters thick. The latter facies is fine-grained, thinly bedded sandstone with ripplemarks in meter-scale intervals. Sandstone petrology, major element abundances, and shale petrographic data from the three sections will also be presented. Facies characteristics and paleontology are suggestive of marine deposition below and near fairweather wavebase, likely in a deltaic setting.

Paleoenvironmental interpretations, C-isotope variability, and fossils allow comparison to mid-Neoproterozoic marine successions such as the ³742 Ma Chuar Group, Grand Canyon, and other regional and global successions. The Red Pine Shale may be an important unit for interpreting Neoproterozoic Earth systems.