Late Early Triassic climate change: Insights from carbonate carbon isotopes,sedimentary evolution and ammonoid paleobiogeography |
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| Institution: | 1. AIRIE Program, Colorado State University, Fort Collins, CO 80523-1482, USA;2. Geological Survey of Norway, 7491 Trondheim, Norway;3. CEED, University of Oslo, 0316 Oslo, Norway;4. SINTEF Petroleum Research, NO-7465 Trondheim, Norway;5. Norwegian University of Sciences and Technology, NO-7491 Trondheim, Norway;6. Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482, USA;7. Norwegian Petroleum Directorate, NO-4003 Stavanger, Norway;1. Department of Geosciences and Earth System Science Center, Pennsylvania State University, University Park, PA 16802, United States;2. School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK;1. Institute of Earth Sciences, University of Graz, Nawi Graz, Heinrichstraße 26, 8010 Graz, Austria;2. Geological Survey of Slovenia, Dimi?eva ulica 14, SI-1000 Ljubljana, Slovenia;3. University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10 000 Zagreb, Croatia;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), Wuhan 430074, China;2. Department of Earth, Atmosphere and Environment, Monash University, Victoria 3800, Australia;3. Department of Earth Sciences, University of St Andrews, KY16 9AL, UK;4. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), Wuhan 430074, China;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;3. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;4. Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL 32306-4520, USA;5. Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, China;6. Wuhan Institute of Geology and Mineral Resources, Wuhan 430205, China;7. Department of Earth Sciences, University of California, Riverside, CA 92521, USA |
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| Abstract: | The late Early Triassic sedimentary–facies evolution and carbonate carbon-isotope marine record (δ13Ccarb) of ammonoid-rich, outer platform settings show striking similarities between the South China Block (SCB) and the widely distant Northern Indian Margin (NIM). The studied sections are located within the Triassic Tethys Himalayan belt (Losar section, Himachal Pradesh, India) and the Nanpanjiang Basin in the South China Block (Jinya section, Guangxi Province), respectively. Carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end-Permian biotic crisis. This study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover (extinction followed by a radiation) occurring around the Smithian–Spathian boundary.Based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity, we demonstrate that the late Early Triassic (Smithian and Spathian) was a time of a major climate change. More precisely, the end Smithian climate can be characterized by a warm and equable climate underlined by a flat, pole-to-equator, sea surface temperature (SST) gradient, while the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. Moreover, sedimentary evidence suggests a transition from a humid and hot climate during the Smithian to a dryer climate from the Spathian onwards. By analogy with comparable carbon isotope perturbations in the Late Devonian, Jurassic and Cretaceous we propose that high atmospheric CO2 levels could have been responsible for the observed carbon cycle disturbance at the Smithian–Spathian boundary. We suggest that the end Smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased CO2 flux possibly originating from a short eruptive event of the Siberian igneous province. This increase in atmospheric CO2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms, including ammonoids, in late Smithian oceans. |
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