Trace fossils and fluvial-lacustrine Ichnofacies of the Eocene Uinta and Duchesne River Formations, northern Uinta Basin, Utah

Takashi Sato, Marjorie A. Chan, Allan A. Ekdale
2018 Geology of the Intermountain West  
Trace fossil assemblages in a fluvial-lacustrine sequence stratigraphic context hold significant poten-tial for expanding our understanding of environmental controls and continental basin-fill history. The succession of the Eocene Uinta Formation and four members of the Duchesne River Formation is ex¬tremely well-exposed in the Uinta Basin of northeastern Utah, revealing a robust stratigraphic framework to document broad-scale fluvial-lacustrine facies architectures and associated trace fossil
more » ... ssemblages. Greenish- and gray-colored mudstone beds with interbedded tabular sandstone representing lacustrine environments contain the trace fossils Arenicolites and Gordia (= Haplotichnus). In contrast, red mudstone beds with interbedded channelized sandstone representing upstream fluvial and alluvial environments contain a variety of insect trace fossils, including Scoyenia, Ancorichnus, and nest structures. Transitional, interfingering lithologies of wetland or shallow, short-lived lacustrine environments on the alluvial plain contain the trace fossil Steinichnus. Although there are many small-scale (bed-scale) physical sedimen¬tary structures and trace fossils from continental subenvironments, this study focuses on the large-scale (member-scale) change in trace fossil assemblages, with results indicating that the ichnofacies corroborate continental sequence stratigraphic interpretations in a fluvial-lacustrine setting.
doi:10.31711/giw.v5i0.27 fatcat:wdrnk5uwzjhnviiwxhkmbizhiq