The Pangaea Megamonsoon records: Evidence from the Triassic Mungaroo Formation,Northwest Shelf of Australia |
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| Institution: | 1. Key Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, China;2. School of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. Bureau of Economic Geology, The University of Texas at Austin, Austin, TX 78713, USA;4. China National Offshore Oil Corporation Research Institute, Beijing 100028, China;1. Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA;2. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA;3. Dipartimento di Scienze della Terra ‘Ardito Desio’, Università degli Studi di Milano, via Mangiagalli 34, I-20133 Milan, Italy;1. Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK;2. Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA;3. Department of Biology, University of Washington, Box 351800, Seattle, WA 98195, USA;4. Burke Museum, University of Washington, Box 351800, Seattle, WA 98195, USA;1. Department of Geology, University of Jaén, Spain;2. Department of Botanic and Geology, University of Valencia, Spain;3. Museum of Natural Sciences of Valencia, Spain;4. Museum of Natural History, University of Valencia, Spain;5. Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Spain;6. School of Earth Sciences, University of Bristol, United Kingdom |
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| Abstract: | An integrated analysis in this study of paleogeographic, paleontologic, seismic and sedimentologic data has been used to explain the effect of the Pangaean megamonsoon on the whole Triassic (especially the Middle–Late Triassic Mungaroo Formation) in the North Carnarvon Basin, Northwest Shelf of Australia. Our results show that the three Triassic formations from bottom to top (Locker Shale, Mungaroo Formation and Brigadier Formation) comprise a complete depositional cycle and correspond to an undeveloped, strong, and weak monsoon periods, respectively. During the strong monsoon period of the Mungaroo Formation, the palynological evidences exhibited mixture spore-pollen characteristics of the hygrophytic assemblage (spore-pollen from the pteridophyte spores, seed ferns and cycads pollen in humid environment of lowlands and coastal plain) and the xerophytic assemblage (pollen from the drought tolerant plants of the interior mountainous areas). The sedimentary evidences of the Mungaroo Formation show low-angle shingled progradational seismic reflection configuration. The highly seasonal variations in precipitation during deposition of the Mungaroo Formation exhibited typical “sandwiched” depositional characteristics of coarse channels sandstone (fining-upward fluvial aggradational cycles (FACs) with poor to moderately sorting and angular to subangular roundness), organic mudstone and coal seam interbedded. Finally, in contrast to today's typical examples of Poyang Lake Delta, a shallow-water braided delta conceptual depositional model of the Mungaroo Formation is formed with a large proximal and distal delta plain, and small delta front. The model results serve mainly to indicate the importance of various climate-forming factors (climate, topography, eustatic), whereas tectonic activity unlikely played any significant role in this process. |
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