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