Browsing by Author "Jonk, Louis"

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    Palaeoenvironmental and sedimentological context for dinosaurian assemblages in the Mussentuchit Member, Cedar Mountain Formation, central Utah (USA)
    (Stellenbosch : Stellenbosch University, 2018-12) Jonk, Louis; Tucker, Ryan T.; Zanno, Lindsay Elizabeth; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The Cretaceous-aged sediments of the Western North America Interior preserve the geological and biological signatures of notable tectonic events in Earth’s history, such as the formation of the Western Interior Basin and Beringian Land Bridge. The Mussentuchit Member of the Cedar Mountain Formation is a fossiliferous sedimentary succession that preserves a key portion of the geological and biological evolution of the North American Western Interior Basin. The geological and temporal context for this unit, however, remains limited. This study, therefore, attempts to place recently opened fossil quarries within the Mussentuchit Member near Cathedral Valley, Utah into a rigorous geological framework via stratigraphic, palaeoenvironmental, and temporal analysis. This study identified fifteen facies and seven architectural elements, which were combined into six representative facies associations. Further, this study concludes that these sediments were deposited within a fluctuating, distal deltaic, or tidal mudflat. Stratigraphic reconstructions place the Mussentuchit Member near Cathedral Valley, Utah as the uppermost member of the Cedar Mountain Formation, with notable variations in sedimentation patterns between the lower and upper Mussentuchit. The change in sedimentation illustrates the gradation from a, supra-tidal zone (lower Mussentuchit), to inter tidal to sub-tidal zone (upper Mussentuchit) of the tidal delta. Geochronological results from radiometric dating of detrital zircon assemblages indicate that these environments developed in response to multiple tectonic events. Specifically, these include thin-skinned thrusting, subsequent internal breakup, and duplexing of the Pavant Sheet of the Sevier Orogeny. These tectonic events are respectively estimated to have occurred during the Albian (±110.92 Ma), Cenomanian (±96.00 Ma) and Turonian (±93.00 Ma), with actual sedimentation of the member estimated to have occurred from the Cenomanian (±98.00 Ma) to Turonian (±93.00 Ma). This change in thrusting mechanisms resulted in the respective deposition of the lower Mussentuchit and upper Mussentuchit within the late-underfilled stage and filled to overfilled stage of the Sevier Foredeep; the depositional low within the Western Interior basin closest to the orogenic highlands. Results from this study added geological context to the fossil quarries on the western flank of the San Rafael Swell, near Cathedral Valley, Utah. Sediments from the lower Mussentuchit and quarries preserved there were dated at a maximum age of deposition of ±105.00 Ma (Albian), though a younger depositional age of ±98.00 Ma is suspected. The Fortunate Son fossil quarry, positioned within the lower Mussentuchit, was placed within the supra-tidal portion of a tidal delta. Detrital zircons from the Mini Troll and Suicide Hill fossil quarries of the upper Mussentuchit were radiometrically dated at a Cenomanian age of ±93.95 Ma and ±93.45 Ma, respectively, and placed within the intertidal to intertidal-subtidal transition zone of a tidal delta. This study provides a more robust understanding of the Mussentuchit sedimentation and enables more meaningful comparisons with regional-scale geological and faunal evolution.