Rhizocorallium and turtle tracks: a late Cretaceous proximal distributary channel trace-fossil assemblage, central Utah

Abstract

A proximal distributary channel deposit in the Turonian Ferron Sandstone of central Utah contains a trace-fossil assemblage comprised of turtle tracks (Chelonipus), vertebrate swim trace fossils (Characichnos), repichnial traces of mollusks (Archaeonassa), Rhizocorallium, and Teredolites. Mayflies are abundant producers of horizontal, spreiten, U-shaped burrows in modern freshwater channels, but rarely ascribed as producers of Rhizocorallium in the rock record. The in situ trace fossils studied are interpreted as a freshwater assemblage. Teredolites occurs within allochthonous debris reworked from stratigraphically lower brackish-water deposits. This Ferron Sandstone assemblage provides an example of the juxtaposition of freshwater ichnocoenose with exhumed brackish-water clasts. Caution must be exercised in environmental interpretation when taking into consideration both adjacent floodplain and the sedimentary structures surrounding the clasts. Complex trace-fossil relationships such as these may play a role in the scarcity of Rhizocorallium reports from freshwater deposits in the rock record, and may be more common than presently recognized. This study illustrates the importance of addressing the detailed ichnology above and below the base of channel deposits in progradational environments (e.g., delta plain), where reworked, brackish-water deposits (and bored clasts) may be entrained within overlying lower salinity facies.

Keywords:

• Channel
• Rhizocorallium
• turtle
• mayfly
• Cretaceous
• Chelonipus
• Characichnos
• Ferron
• ichnofacies
• Teredolites

Acknowledgements

We would like to thank Rares Bistran, Tara Allman, Bob King, and Tina King for their help in the field. Fieldwork work was conducted in cooperation with the Bureau of Land Management (Utah; M.R. King, Permit #UT08-024S), as well as the Utah Geological Survey. The assistance from personnel in both of these offices was greatly appreciated. Thanks to editor Dr. Luis Buatois and reviewer Dr. Dirk Knaust for their insight, which helped to improve the quality of this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Financial support for this project was provided by a grant from The Jurassic Foundation to M. Ryan King and funding from a Discovery Grant awarded to S. George Pemberton from the National Sciences and Engineering Research Council of Canada (NSERC).