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GSA Connects 2024 Meeting in Anaheim, California

Paper No. 56-9
Presentation Time: 3:50 PM

GLOBAL RECORDS REVEAL A STEEP OCEANIC DIC δ13C DEPTH GRADIENT DURING THE HIRNANTIAN GLACIATION


YANG, Shengchao, State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China; Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing, Jiangsu 210023, China, FAN, Junxuan, Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing, Jiangsu 210023, China; State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China; Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, Beijing 100029, China, ALGEO, Thomas, Department of Geosciences, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221-0001; State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, Hubei 430074, China; State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei 430074, China and LI, Chao, State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation & Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China; Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications of Ministry of Natural Resources & International Center for Sedimentary Geochemistry and Biogeochemistry Research, Chengdu University of Technology, Chengdu, Sichuan 610059, China

The Hirnantian carbon isotopic excursion (HICE) was characterized by a global positive δ13C excursion (up to ~ + 7‰ in excursion magnitude) during the Ordovician-Silurian (O/S) transition, while its mechanism remains controversial, hampering our understanding of this global event and its environmental significance. In this study, we compiled a dataset of global carbon isotope records, including 65 paleogeographically widely distributed sections (4,612 carbon isotope data in total), which documents a steep oceanic δ13C water-depth gradient (e.g., a 4.6‰ offset in the HICE excursion magnitude within Laurentia and 3.3‰ within South China) during the Hirnantian Stage. We propose a hybrid hypothesis that the HICE records a shift towards more positive values due to a large glacio-eustatic fall (up to ~150 m) under the herein-identified steep oceanic δ13C water-depth gradient, with potential contributions from global-ocean δ13CDIC changes and authigenic carbonates. This study provides the first large-data evidence for a steep oceanic DIC δ13C water-depth gradient and widely density-stratified ocean during the Hirnantian Glaciation, which has implications for reconstructions of the carbon cycle and ocean circulation during the Early Paleozoic.

Keywords: Ordovician; HICE; carbon cycle; dissolved inorganic carbon

Recorded Presentation

Session No. 56

T29. New Advances in Geobiology
Sunday, 22 September 2024: 1:30 PM-5:30 PM
208A (Anaheim Convention Center)
Geological Society of America Abstracts with Programs. Vol. 56, No. 5
doi: 10.1130/abs/2024AM-404059
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