Geological Society of America

392 D37. Volcanology (Posters)

Wednesday, 25 October 2017
9:00 AM - 6:30 PM
Halls 4EF

TRACING OF VOLCANISM DURING JURASSIC AND CRETACEOUS OCEANIC ANOXIC EVENTS (OAES) USING MERCURY ISOTOPES

Paper number: 392-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Xin-Yuan Zheng Presenting Author
University of Wisconsin-Madison, Madison, WI
Hugh C. Jenkyns
University of Oxford, Oxford
Runsheng Yin
Institute of Geochemistry, Chinese Academy of Sciences, Guiyang
Runsheng Yin
The Hong Kong Polytechnic University, China, Hongkong
Lawrence M.E. Percival
University of Lausanne, Lausanne
Lawrence M.E. Percival
University of Oxford, Oxford
Chuanwei Zhu
Institute of Geochemistry, Chinese Academy of Sciences, Guiyang
Aisha Al-Suwaidi
The Petroleum Institute, a part of Khalifa University of Science and Technology, Abu Dhabi
Rich Barclay
Smithsonian Institution, Edgewater, MD
Zunli Lu
Syracuse University, Syracuse, NY
Xiangdong Li
The Hong Kong Polytechnic University, China, Hongkong
Stephen P. Hesselbo
University of Exeter, Penryn

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-305506

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