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Neoproterozoic Uinta Mountain Group of Kings Peak Quadrangle, Utah: A Marine-Fluvial Interface?

Kingsbury, Esther M.1, Paul K. Link1, Carol M. Dehler2, and C. Mark Fanning3
1Idaho State University, Pocatello, ID
2Utah State University, Logan, UT
3Australian National University, Canberra, Australia

     The Neoproterozoic Uinta Mountain Group (UMG) is a wellknown but little studied unit that occupies the core of the Uinta Mountains. Traditionally the UMG has been referred to as “Mesoproterozoic”, but this is incorrect: three samples of siltstone from the lower and middle UMG contain detrital zircons of about 770 Ma (Fanning and Dehler, 2005, GSA National Meeting Abstract, v. 37, no. 7, p. 42).
     New 1:24,000 scale mapping in the Kings Peak quadrangle of the High Uintas Wilderness indicates that the central part of the UMG represents a marine shoreline and estuary system sourced from the east. These eastern coarse-grained sandstones represent a rapidly aggrading west-flowing braided river system, containing Mesoproterozoic- and Grenville-aged Laurentian detrital zircons that filled a half-graben south of a boundary fault along the reactivated Cheyenne Belt.
     Spectacularly exposed stratigraphic relationships in cirque walls display an incised valley with tens of meters of relief, cut into a marine(?) sandstone of the formation of Deadhorse Pass and filled with onlapping siltstone of the Gilbert Peak shale member. These relationships suggest a shoreface to fluvial plain stratigraphic interface. The <770 Ma age constraint, plus Neoproterozoic microfossil assemblages, supports the ChUMP (Chuar-Uinta Mountain- Pahrump) correlation, which hypothesizes the existence of a Neoproterozoic interior seaway. The UMG contains the eastern fluvial-marine transition into this seaway. These sediments may record brackish geochemical and paleobiological conditions just prior to the Sturtian glaciations. Geologic mapping and stratigraphic analysis are ongoing.


AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah