Global correlations of mid Early Triassic events: The Induan/Olenekian boundary in the Dolomites (Italy) |
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| Institution: | 1. Earth and Environmental Sciences, Department of Earth Sciences, University of Geneva, rue des Maraîchers 13, CH-1205 Geneva, Switzerland;2. Institute and Museum of Paleontology, University of Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland;3. Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, N-0318, Norway;4. Guangxi Bureau of Geology and Mineral Resources, Jiangzheng Road 1, 530023 Nanning, China;5. Laboratoire de Géologie de Lyon, Université Claude Bernard, Lyon, F-69622 Villeurbanne, France;6. Holcim Technology Ltd, Geological Investigations, CH-5113 Holderbank, Switzerland;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Biogéosciences, UMR 6282, CNRS, Université de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France;3. Museum für Naturkunde, Otto-von-Guericke-Straße 68–73, 39104 Magdeburg, Germany;4. Institute of Geology and Paleontology, Linyi University, Linyi 276000, China;1. Institute of Geology and Paleontology, Tohoku University, Sendai 980-8578, Japan;2. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;3. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;1. Department of Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8551, Japan;2. Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan;3. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8550, Japan;4. Laboratory of Ocean-Earth Life Evolution Research (OELE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan;5. Department of Geology, The University of Leicester, Leicester LE1 7RH, UK |
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| Abstract: | The Dolomites (Southern Alps, Italy) are a reference-area for research on the end-Permian mass extinction and its Early Triassic aftermath. The effects on shallow marine benthic biota are recorded in the Werfen Formation, a thick mixed carbonate-siliciclastic sedimentary succession. Only in its lower (Griesbachian) and upper (Spathian) parts, this formation is bio-chronologically constrained by means of conodonts and ammonoids, whilst no significant bioevent occurs in its middle part. This represents an impediment to the biochronologic recognition of the Induan/Olenekian boundary (IOB).The Bulla/Pufels (Val Gardena) succession is a key-section for the P/T boundary and Early Triassic for global correlation due to the abundance of studies on biostratigraphy (mostly on conodonts), magnetostratigraphy and chemostratigraphy carried out there by stratigraphers of various nationalities. Recent chemostratigraphic studies have permitted the recognition of some carbon isotope positive peaks, the strongest of which is considered to approximate the IOB. However, various authors have reached different conclusions on the position of the maximum peak and thus on the IOB location. This leads to important stratigraphic consequences for the calibration of conodont biostratigraphy. The critical revision of the traditional stratigraphic units (litho- and biostratigraphy), under-evaluated in most of the recent literature, and magneto-, chemo- and sequence stratigraphic units allowed herein an integrated stratigraphic scale for the Bulla/Pufels section to be proposed. This contribution highlights the mid Early Triassic Dolomites record for regional and global correlations.The most significant results attained herein regard the different lithostratigraphic subdivisions of the middle Werfen Formation and its consequences on the position of the IOB with respect to the conodont and bivalve biostratigraphy and sequence stratigraphic units. The upper part of the section is attributed herein to the Gastropod Oolite Member, which is represented by the lithozone A, a predominant supratidal episode, and the lower part of the subtidal lithozone B. Between the lithozones A and B, a sequence boundary of 3th order (Sc2/Sc3) is located. The maximum carbon isotope excursion is near this boundary, which therefore approximates the IOB in the Dolomites. This proposal suggests a Dienerian age for the FO of the conodont Pachycladina obliqua, which occurs about 60 m below the stage boundary. No significant biotic event, either for molluscs or conodonts, occurred across this stage boundary. |
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