STRATIGRAPHIC INVESTIGATIONS OF THE NEOPROTEROZOIC UINTA MOUNTAIN GROUP: COMBATING “THE CURSE OF THE PROTEROZOIC SANDSTONES”
The undivided UMG facies include: thickly-bedded to massive sandstone (Zut); low-angle cross-bedded and trough cross-bedded sandstone (Zul); interbedded Zut and Zul facies (Zui); and fine-grained facies (Zuf). Facies analysis to the south, where the eroded top of the UMG is exposed, shows similar facies trends with predominantly Zut interbedded with intervals of Zuf. The sandstone facies (Zut, Zul, Zui) are fine to coarse-grained quartz arenites (~90-95% quartz, ~1-5% feldspar, ~0.2-5% fine grained micaceous matrix, n=8) and represent a braided river system. The fine-grained facies (Zuf) comprises fine grained subarkosic arenite (~80% quartz, ~18% feldspar, ~2% micaceous matrix, n=2) to shale and represents a lower energy deposit that may have a different sediment source, likely representing delta plain/shoreline deposition.
The lowermost Zuf unit is mapped westward for 10s of kms and allows correlation of the undivided UMG from the SCQ area to the UMG westward in the Flaming Gorge area. Further stratigraphic mapping will facilitate regional correlation of the UMG between the eastern and western Uinta Mountains, and continued characterization may also lead to linkage with Neoproterozoic strata in the Wasatch Mountains and beyond.