T80 Global Change: Evolution and Extinctions in the Triassic

Monday, 5 November 2018
8:00 AM - 12:00 PM
Room 136-137

IS MERCURY FROM “BACKGROUND” VOLCANISM PRESERVED IN THE SEDIMENTARY RECORD? A TEST USING FLUVIO-LACUSTRINE STRATA FROM THE UPPER TRIASSIC OF ARGENTINA

Paper number: T80-11
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM

Authors

Abstract

High concentrations of mercury (Hg) in the sedimentary record are an emerging proxy for large igneous province (LIP) volcanism, based on the observation that extant volcanism is a major source of Hg to the modern natural environment. Previously, most geologic studies of Hg have focused only on very large eruptions (such as LIPs), which are assumed to produce greater Hg flux that is more likely to be capable of affecting the global Hg inventory, and therefore be widely preserved in the geologic record. However, these assumptions have not been empirically tested in deep time, so there is little understanding of how smaller-scale “background” eruptions might affect the sedimentary Hg record, particularly at local to regional scales. To examine the effect of local volcanism on Hg concentration in sediments, we studied Upper Triassic fluvio-lacustrine strata in the Ischigualasto-Villa Unión rift basin of northwestern Argentina. Here, the lacustrine Los Rastros Formation (Carnian) and overlying fluvial Ischigualasto Formation (upper Carnian-lower Norian) preserve multiple tuff horizons (<1 cm to >1 m thick) derived from local volcanic eruptions. From both formations, we analyzed samples of the tuffs as well as underlying and overlying siliciclastic sediments (claystone, siltstone, and sandstone) for Hg concentration, total organic carbon content (TOC), and organic carbon stable isotope (δ13Corg) values. These data reveal multiple spikes in Hg concentration (normalized against TOC) and dynamic changes in the sources of organic carbon. Consequently, these investigations provide important new insights into whether LIP eruptions are the only volcanic events that can perturb the Hg cycle (as largely assumed), or whether smaller-scale “background” volcanism must also be considered when interpreting Hg anomalies in the non-marine sedimentary record.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-325054

© Copyright 2018 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.