Although intensified work on the volcaniclastic-rich sediments of the fossil-bearing Mussentuchit Member (uppermost Cedar Mountain Formation, Utah) has provided a refined chronostratigraphic framework, paleoenvironmental interpretations remain cryptic. To resolve this, we performed facies analysis and architectural reconstruction on exposed Mussentuchit Member outcrops south of Emery, central Utah, USA. Contrary to previous interpretations (fluvial, lacustrine), we identified a broad suite of facies that indicate that deposition occurred on the landward part of a paralic depocenter, influenced by both distal alluvial and proximal coastal systems. We conclude that the Mussentuchit Member was a sink for suspension-settling fines with most undergoing pedogenic alteration, analogous to the modern coastal plain of French Guiana (Wang et al. 2002; Anthony et al. 2010, 2014). However, this landward paralic depocenter was not uniform through time. Sedimentological evidence indicates landscape modification was ongoing, influenced by an altered base-level (high groundwater table, long residency of water in sediments, shifts in paleosol types, heavier to lighter d18O, and distinct shifts in relative humidity (e); common in coastal settings). If the above data is coupled with recent age data, we interpret that the Mussentuchit Member correlates to the S.B. 4 Greenhorn Regression (Thatcher Limestone) of the adjacent Western Interior Seaway to the east. As a landward paralic depocenter, the Mussentuchit would have been sensitive to base-level conditions in response to ongoing tectonic processes pushing the foredeep east, and lower paleo-CO2 levels coupled with a minor global sea-level fall (brief glacial phase) just before to the Cenomanian–Turonian Thermal Maximum. Altogether, our results not only strengthen linkages in the central Western Interior Seaway, but simultaneously results in novel linkages to near-coeval paralic depocenters across mid-Cenomanian North America.
Bibliographical noteFunding Information:
We thank staff, students, and volunteers of the 2015–2019 expeditions for repeated explorations of the Mussentuchit Member: M. Leschin, S. Foss, G. McDonald, R. Anderson, R. Hunt-Foster, J. Kirkland, M. Hayden, J. Krishna, R. Irmis. The staff of the Price Field Office, the Bureau of Land Management, Utah State Office, the Natural History Museum of Utah, and the Utah Geological Survey are thsnked for permitting and expedition support. Financial support was provided by Stellenbosch University’s Department of Earth Sciences, North Carolina Museum of Natural Sciences, the Canyonlands Natural History Association, Field Museum of Natural History, the DRD, and National Science Foundation awards FRES 1925884, 1925973, and 1925915. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Finally, we wish to thank editor K.M. Marsaglia, the generous reviewers W.W. Little and P. Flaig, associate editor G. Ludvigson, and corresponding editor J.B. Southard, along with anonymous persons for their feedback and improvements to this manuscript.
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