Geological Society of America

T331 Mercury in the Geologic Record

Wednesday, 25 October 2017
1:30 PM - 5:30 PM
Room 607

HG ISOTOPES AS TRACERS OF DEPOSITIONAL ENVIRONMENTS IN MARINE SEDIMENTS FROM THE PRECAMBRIAN TO THE PHANEROZOIC

Paper number: T331-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Alyson M. Thibodeau Presenting Author
Dickinson College, Carlisle, PA
Shuhei Ono
Massachusetts Institute of Technology, Cambridge, MA
Bridget A. Bergquist
University of Toronto, Toronto, ON
Frank Corsetti
University of Southern California, Los Angeles, CA
Joyce A. Yager
University of Southern California, Los Angeles, CA
A. Joshua West
University of Southern California, Los Angeles, CA
David Bottjer
University of Southern California, Los Angeles, CA
Will Berelson
USCEarth Sciences, Los Angeles, CA
Linda C. Kah
University of Tennessee, Knoxville, TN
Robert M. Hazen
Carnegie Institution for Science, Washington, DC

Abstract

Mercury (Hg) is a volatile, chalcophilic, photochemically-active, redox-sensitive metal with complex biogeochemistry that displays a wide range of mass-dependent (MDF) and mass-independent (MIF) stable isotopic fractionation. Throughout geologic time, there have been many events and environmental shifts capable of modifying the global Hg cycle, including the eruption of large igneous provinces (LIPs), variations in atmospheric and oceanic redox conditions, and changes in the biosphere (e.g. the evolution of terrestrial flora). Here, we use Hg isotopes (in particular, the Hg-MIF signatures) to investigate how and if such changes are reflected in the isotopic composition marine sediments through time. In the Phanerozoic, we focus on marine sediments deposited during periods of massive volcanism (e.g., before, during, and after the emplacement of the Central Atlantic Magmatic Province, coincident with the end-Triassic mass extinction). The Precambrian sediments span in age from 600 Ma to ~3.3 Ga and represent a wide variety of depositional environments and Earth surface conditions. Our results indicate Phanerozoic successions do record isotopic shifts in response to the eruption of LIPs, with a reduction in Hg-MIF consistent with an overwhelming igneous source. Phanerozoic sediments (deposited prior to, or following LIPs) and Precambrian sediments tend preserve small amounts of odd-isotope Hg-MIF and have ∆¹⁹⁹Hg/∆²⁰¹Hg ratios consistent with the production of MIF via the magnetic isotope effect. The direction of MIF appears correlated with depositional environment, with deep water successions generally having odd isotope excesses (e.g. positive ∆¹⁹⁹Hg values) and sediments deposited in shallower, near shore environments generally having odd-isotope deficits (e.g. negative ∆¹⁹⁹Hg values). These signatures are consistent with sediments dominated by Hg inputs from atmospheric Hg²⁺ deposition versus terrestrial runoff, respectively. The similar Hg-MIF signatures of Precambrian and Phanerozoic sediments also suggest that the pathways and sources of Hg to marine sediments (i.e., atmospheric deposition and terrestrial runoff) may have remained similar over much of Earth history.

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

doi: 10.1130/abs/2017AM-306035

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.