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

Allan A Ekdale,Marjorie A Chan,Takashi Sato

doi:10.31711/giw.v5i0.27

Abstract

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 assemblages. 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.

Highlights

The concept of ichnofacies, which was originally proposed by Seilacher (1967), has been expanded by many subsequent workers (e.g., Frey and Pemberton, 1984; Bromley and Asgaard, 1993; Smith and others, 1993; Buatois and Mángano, 1995; Genise and others, 2000; Ekdale and others, 2007; Genise and others, 2010).Initially Seilacher (1967) proposed a single continental ichnofacies that has been developed into six continental ichnofacies: Scoyenia, Mermia, Corprinisphaera, Entradichnus, Termitichnus, and Celliforma ichnofacies (Buatois and Mángano, 2011)
This study focuses on late-stage basin-fills of the uppermost Uinta and Duchesne River Formations, which generally comprise coarser-grained deposits than the underlying, renowned petroleum source rock of the Green River Formation
This paper documents remarkable changes in continental trace fossil assemblages according to fluctuations in the relative water-table level

Summary

Introduction

The concept of ichnofacies, which was originally proposed by Seilacher (1967), has been expanded by many subsequent workers (e.g., Frey and Pemberton, 1984; Bromley and Asgaard, 1993; Smith and others, 1993; Buatois and Mángano, 1995; Genise and others, 2000; Ekdale and others, 2007; Genise and others, 2010).Initially Seilacher (1967) proposed a single continental ichnofacies that has been developed into six continental ichnofacies: Scoyenia, Mermia, Corprinisphaera, Entradichnus, Termitichnus, and Celliforma ichnofacies (Buatois and Mángano, 2011) (figure 1). The concept of ichnofacies, which was originally proposed by Seilacher (1967), has been expanded by many subsequent workers (e.g., Frey and Pemberton, 1984; Bromley and Asgaard, 1993; Smith and others, 1993; Buatois and Mángano, 1995; Genise and others, 2000; Ekdale and others, 2007; Genise and others, 2010). The mostly shallow marine Skolithos ichnofacies has been documented in coastal lacustrine environments (e.g., Buatois and Mángano, 1995, 2007). T., Chan, M.A., and Ekdale, A.A., 2018, Trace fossils and fluvial-lacustrine ichnofacies of the Eocene Uinta and Duchesne River Formations, northern Uinta Basin, Utah: Geology of the Intermountain West, v. Trace Fossils and Fluvial-Lacustrine Ichnofacies of the Eocene Uinta and Duchesne River Formations, Northern Uinta Basin, Utah Sato, T., Chan, M.A., and Ekdale, A.A T., Chan, M.A., and Ekdale, A.A., 2018, Trace fossils and fluvial-lacustrine ichnofacies of the Eocene Uinta and Duchesne River Formations, northern Uinta Basin, Utah: Geology of the Intermountain West, v. 5, p. 209–226.

Methods

Discussion

Conclusion