Latest Smithian (Early Triassic) ammonoid assemblages in Utah (western USA basin) and their implications for regional biostratigraphy,biogeography and placement of the Smithian/Spathian boundary |
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| Affiliation: | 1. Biogéosciences, UMR6282, CNRS, Université Bourgogne Franche-Comté, 6 Boulevard Gabriel, 21000 Dijon, France;2. 1134 Johnson Ridge Lane, West Jordan, UT 84084, USA;3. 140 South 700 East, Spanish Fork, UT 84660, USA;4. Université Clermont Auvergne, CNRS, Laboratoire Magmas et Volcans, 63000 Clermont-Ferrand, France;5. Department of Earth Science, Utah Valley University, 800 West University Parkway, Orem, UT 84058, USA;6. Univ Lyon, Université Claude Bernard Lyon 1, CNRS, ENTPE, UMR 5023 LEHNA, F-69622 Villeurbanne, France;1. State Key Laboratory of Continental Dynamics and Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi’an 710069, China;2. Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden;3. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;1. A.A. Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya str., 123, Moscow 117647, Russia;2. Zoological Institute, Russian Academy of Sciences, Universitetskaya emb., 1, St. Petersburg 199034, Russia;3. National Research Centre ‘Kurchatov Institute’, Kurchatov Square, 1, Moscow 123182, Russia;1. Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, 07749 Jena, Germany;2. Geology Department and Albany Museum, Rhodes University, Makhanda/Grahamstown 6140, South Africa;1. Université d’Oran 2 Mohamed Ben Ahmed, Laboratoire de Géodynamique des Bassins et Bilan Sédimentaire, B.P. 1524, El M''Naouer, 31000, Oran, Algeria;2. Faculty of Natural and Life Sciences, Mustapha Stambouli-Mascara University, 29000, Mascara, Algeria;3. Institute of Ecology and Earth Sciences, University of Tartu, Ravila 14A, 50411, Tartu, Estonia;4. 2 Rue Guy de Maupassant, F-76800 Saint Étienne du Rouvray, France;1. University of Yaounde I, Department of Earth Sciences, P.O. Box. 812, Yaounde, Cameroon;2. Institute of Geological and Mining Research, P.O. Box. 4110, Yaoundé, Cameroon;3. University of Liège, Palaeobiogeology-Palaeobotanic-Palaeopalynology Unit, B18, P.O. Box 4000, Liège, Belgium;4. University of Cocody, UFR-STRM, 22 BP. 582 Abidjan, Côte d’Ivoire;5. University of Douala, Department of Earth Sciences, P.O. Box 24157, Douala, Cameroun;1. Eberhard Karls University of Tübingen, Department of Geoscience, Sigwartstr. 10, 72076 Tübingen, Germany;2. Senckenberg Centre for Human Evolution and Paleoenvironment (HEP Tübingen), Sigwartstr. 10, 72076 Tübingen, Germany |
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| Abstract: | The late Smithian extinction represents a major event within the Early Triassic. This event generally corresponds to a succession of two, possibly three successively less diverse, cosmopolitan ammonoid assemblages, which when present, provide a robust biostratigraphic framework and precise correlations at different spatial scales. In the western USA basin, known occurrences of latest Smithian taxa are rare and until now, have only been documented from northeastern Nevada. Based on these restricted basinal occurrences, a regional zone representing the latest Smithian was postulated but not corroborated, as representative taxa had not yet been reported from outside Nevada. Here we document two new ammonoid assemblages from distant localities in northern Utah, overlying the late Smithian Anasibirites beds and characterized by the unambiguous co-occurrence of Xenoceltites subevolutus and Pseudosageceras augustum. The existence of a latest Smithian zone in the western USA basin is therefore validated, facilitating the identification of the Smithian/Spathian boundary and intra-basin correlation. This zone also correlates with the latest Smithian zone recognized from southern Tethyan basins. Additionally, these new data support other observed occurrences of Xenoceltites subevolutus throughout most of the late Smithian. |
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| Keywords: | Late Smithian Early Triassic Ammonoids Utah Biostratigraphy |
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