SEDIMENTOLOGY, STRATIGRAPHY, AND ICHNOLOGY OF THE CATHEDRAL BLUFFS TONGUE OF THE WASATCH FORMATION

Strata of the Cathedral Bluffs Tongue of the Wasatch Formation record latest Early Eocene (earliest Bridgerian – Gardnerbuttean) deposition in the South Pass area, Wyoming. These strata were deposited within braided to meandering fluvial systems that coarsen northwards towards the flank of the Wind River Mountains. Cathedral Bluffs successions in the northern part of the study area are dominated by clast- and matrix-supported conglomerate with subordinate pedogenically-altered sand- and gravel-rich siltstone intervals. To the south and southwest the study interval is dominated by variegated sandy mudstone beds (interpreted as paleosols) which are bisected by common laterally restricted fluvial channel sandstone and laterally extensive crevasse splay sandstone beds. Limestone beds and oil shale intervals become increasingly common to the southwest where the Wasatch Formation interfingers with the Green River Formation.

Although rapid lateral facies changes and intraformational unconformities render correlation within the Cathedral Bluffs Tongue difficult , detailed facies analysis has allowed stratigraphic subdivision of the study interval. Analysis of the paleosols, including ichnological characterization, has proven to provide invaluable evidence about the local position of the water table and has aided in assessing proximity to Paleolake Gosiute. Intervals with higher proportions of channelized conglomerate and conglomeratic sandstone reflect episodes of uplift in the source area in the Wind River Mountains. Displacement along the Wind River Thrust Fault, and concomitant uplift of the Wind River Mountains, played a dominant role in the stratigraphic evolution of the study area. Thin limestone and oil shale interbeds in the study interval record short duration shifts to lacustrine deposition on the basin margin and record a complex interplay between climatic and tectonic influences.