Paper No. 392-2
Presentation Time: 9:00 AM-6:30 PM
TRACING OF VOLCANISM DURING JURASSIC AND CRETACEOUS OCEANIC ANOXIC EVENTS (OAES) USING MERCURY ISOTOPES
ZHENG, Xin-Yuan, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, University of Wisconsin, Madison, WI 53706, YIN, Runsheng, State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, China, Hongkong, China, PERCIVAL, Lawrence M.E., Institute of Earth Sciences, University of Lausanne, Geopolis, Lausanne, 1015, Switzerland; Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom, ZHU, Chuanwei, State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China, AL-SUWAIDI, Aisha, Department of Petroleum Geosciences, The Petroleum Institute, a part of Khalifa University of Science and Technology, PO BOX 2533, Abu Dhabi, United Arab Emirates, BARCLAY, Richard S., National Museum of Natural History, Smithsonian Institution, P.O. Box 28, Edgewater, MD 21037, LU, Zunli, Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, LI, Xiangdong, Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, China, Hongkong, China, HESSELBO, Stephen P., Camborne School of Mines and Environment and Sustainability Institute, University of Exeter, Tremough Campus, Penryn, TR10 9EZ, United Kingdom and JENKYNS, Hugh C., Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom, xzheng75@wisc.edu
Oceanic anoxic events (OAEs) that occurred during the early Toarcian (T-OAE, ~183 Ma) and the Cenomanian-Turonian boundary (OAE 2, ~94 Ma) were associated with widespread marine anoxia/euxinia, and major perturbations of the global carbon cycle. Volcanism interpreted as coeval with the two OAEs have been suggested to play a crucial role in the feedbacks that initiated and sustained these events, but evidence that unequivocally supports a causal link remains limited. Volcanism is a major source of Hg, and mass-dependent (MDF) and mass-independent (MIF) fractionations of stable Hg isotopes make them potentially useful proxies for Hg sources and pathways. Such information is not readily available from Hg concentrations or Hg/TOC ratios alone.
We present the first effort to use Hg isotopes, preserved in organic-rich sediments, as proxies for volcanism across the T-OAE and OAE 2. Hg isotopes were measured for two sections for OAE 2, one from Demerara Rise (equatorial Atlantic) and one from Tarfaya (Morocco), and for one section from Yorkshire (UK) for the T-OAE. For the OAE 2 sections, δ202Hg values (-3.2‰ to -0.3‰) are relatively variable across the event, suggesting variable and regional controls (e.g., adsorption) on MDF of Hg isotopes. Interestingly, Δ199Hg from both sections decreased from moderately positive values of ~0.2‰ to ~0‰ during OAE 2, indicative of enhanced volcanic input of Hg. For the Yorkshire section, δ202Hg values range from ~-2‰ to 0‰, and show a ~0.5‰ positive excursion during the T-OAE. A ~0.2‰ negative excursion in Δ199Hg was also observed during the T-OAE, but the measured values (between ~-0.35‰ to -0.15‰) are different from the positive values analyzed from the two OAE 2 sections, suggesting different Hg sources. Further analyses on sections differing in regional redox conditions, type of organic matter, and proximity to potential volcanic sources for the two OAEs are underway to further deconvolve the implications carried by Hg isotopes. However, our preliminary results show that Hg isotopes represent promising tracers for volcanism and Hg sources/pathways during Mesozoic OAEs.
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