Paper No. 9
Presentation Time: 8:00 AM-6:00 PM
STRATIGRAPHY AND DEPOSITIONAL FACIES IN THE NEOPROTEROZOIC FORMATION OF RED CASTLE, MOUNT POWELL QUADRANGLE, HIGH UINTAS WILDERNESS, UTAH
OSTERHOUT, Shannon L., Idaho State University, Pocatello, ID 83204, LINK, Paul K., Department of Geosciences, Idaho State University, Pocatello, ID 83209 and DEHLER, Carol M., Department of Geology, Utah State Univ, 4505 Old Main Hill, Logan, UT 84322, osteshan@isu.edu
New 1:24,000 scale mapping of the Neoproterozoic Uinta Mountain Group in the Mount Powell quadrangle of the High Uinta Wilderness, shows that the informal formation of Red Castle can be divided into three members. The fluvial lower unit (20-185m thick) is arkosic arenite with lesser mudstone intervals containing lenticular, wedgeform, and channelform geometries, and thins westward. West of The Red Castle, the lower Red Castle member contains three (meter to decimeter scale) tongues of marine mature quartzose sandstone, each with a sharp basal contact (a flooding surface) above fluvial arkosic arenite. The middle unit (100–400 m) is a tidally- influenced deltaic facies containing cyclic tabular to gently-inclined couplets (sub m to m scale) of arkosic arenite and mudrock with abundant crossbedding indicating bidirectional flow. The marine upper unit (220-340m thick) contains mudrock , submature arkosic arenite, and mature quartz arenite. These lithologies form channelforms and erosive geometries. Southwest-dipping clinoforms present in the cirque wall at the head of the Smith’s Fork represent southward offlap of marine bars.
The erosional contact below the lowest mudrock interval in the upper Red Castle unit is the same surface as the stratigraphic sequence boundary at the base of the overlying quartz-rich Dead Horse Pass Formation in the Kings Peak quadrangle directly to the east. This sequence boundary can be traced down section into the upper Red Castle unit in a northwest direction until it is at the contact between the middle and upper Red Castle members.
This work verifies conclusions of C.A. Wallace (1972) that the quartzose marine Dead Horse Pass and Mount Agassiz strata do not crop out on the north limb of the Uinta anticline. Instead they are replaced by a north-derived arkosic arenite mapped as the upper Red Castle unit. As predicted by sequence stratigraphic principles, above the basal sequence boundary of the Dead Horse Pass Formation, the transgression can be traced shoreward into the fluvially-influenced arkosic arenites of the upper Red Castle member.
