Paralic sedimentology of the Mussentuchit Member coastal plain, Cedar Mountain Formation, central Utah, U.S.A.

Abstract

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 δ18O, and distinct shifts in relative humidity (ε); 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.

An early-diverging iguanodontian (Dinosauria: Rhabdodontomorpha) from the Late Cretaceous of North America

“…dossi were recovered from brackish water estuarine environments of the Twin Mountains Formation, overlain by deltaplain channels [ 62 ]. In a similar vein, the holotype skeleton of Iani derives from paralic sediments of the Mussentuchit Member, Cedar Mountain Formation, capturing life on an evolving deltaplain [ 130 ]. The lower Mussentuchit Member represents a wet, humid environment inundated by a high base level of brackish groundwater and minor tidal influences [ 130 ].…”

“…In a similar vein, the holotype skeleton of Iani derives from paralic sediments of the Mussentuchit Member, Cedar Mountain Formation, capturing life on an evolving deltaplain [ 130 ]. The lower Mussentuchit Member represents a wet, humid environment inundated by a high base level of brackish groundwater and minor tidal influences [ 130 ]. This is comparable with paleoenvironmental interpretations of Tenontosaurus -bearing strata of the Twin Mountains and Antlers formations.…”

“…We omitted character 111 because of problematic homologies. We followed Poole [32] in considering the following characters additive: 22,31,48,69,70,72,81,91,96,103,105,109,120,123,124,127,129,130,136,137,150,151,153,162,172,186,200,204,205,216,218,228,248,262,263,271,278,301, 321 and using Eocursor as the outgroup.…”

“…Locality and horizon. NCSM 29373 was recovered from the lower Mussentuchit Member, upper Cedar Mountain Formation, Emery County, Utah, USA ("Fortunate Son" NCPA-LEOUT14; Fig 1) approximately 1.0 m above the contact with the underlying Ruby Ranch Member and ±7.0 m below MAZ1 (99.490 +0.057/-0.050 Ma) [59]. A Bayesian depositional age estimation and age-depth modelling yielded an estimated age for emplacement for NCSM 29373 that is no later than 99.652 +0.413/-0.094 Ma [59: Figs 3 and 4].…”

“…Stratigraphic range of Thescelosauridae based on Zephyrosaurus (first occurrence)(middle of the Little Sheep Member, Cloverly Formation[122], mean age ~116.5 Myr[109]) and Thescelosaurus (last occurrence)(Hell Creek Formation, youngest age 66 Ma[123]). Stratigraphic range of Styracosterna based on Uteodon (first occurrence)(Brushy Basin Member, Morrison Formation, mean age ~151 Ma[124]) and Edmontosaurus (last occurrence)(Hell Creek Formation, youngest age 66 Ma[123]) and the nested clade Hadrosauromorpha based on first Eolambia (first occurrence)(Mussentuchit Member, Cedar Mountain Formation, oldest age ~99.5 Ma[59]) and Edmontosaurus (last occurrence)(Hell Creek Formation, youngest age 66 Ma[123]). Phylogenetic topology and clade composition follow[125,126].…”