Mercury Enrichment in the Sedimentary Record Associated with Local Volcanism: A Triassic example

WHITESIDE; IRMIS, RANDALL B.; BENAVENTE, CECILIA ANDREA; PERCIVAL; MANCUSO, ADRIANA CECILIA; NAYEE; MATHER

Congreso; Goldschmidt; 2019

Mercury (Hg) enrichment in the deep time sedimentary record is often used as a proxy for large igneous province (LIP) volcanism, because extant volcanism is one of the few non-anthropogenic sources of Hg in the modern environment, and the residence time of Hg is very short. However, existing studies are equivocal as to whether Hg enrichment from smaller-scale, non-LIP eruptions can also be preserved, with very few studies examining time intervals in the geologic record when no LIPs were known to be active. To address whether local volcanism can affect the sedimentary Hg record, we studied a Triassic fluvio-lacustrine sequence with multiple tuff horizons from the Ischigualasto-Villa Unión rift basin of northwestern Argentina. This allowed us to determine: a) whether any Hg enrichment was present; b) if these enrichments are directly associated with volcanic events (i.e., tuff layers); and c) whether depositional style played a role in Hg preservation in the lacustrine Los Rastros Fm. versus the overlying fluvial Ischigualasto Fm. We analyzed siliciclastic sediments and tuffs for Hg concentration, total organic carbon content (TOC), and organic carbon stable isotope (δ13Corg) values. Our data demonstrate multiple Hg enrichments (normalized against TOC) directly associated with tuffs in the Los Rastros Fm. In contrast, there was no evidence for Hg enrichment associated with volcanism in the Ischigualasto Fm., where sediments typically had very low TOC. These data suggest that local small-scale volcanism can be preserved as Hg enrichment in non-marine sediments as long as enough organic matter is present. As such, precise and age constraints may be necessary to confidently associate sedimentary Hg spikes with penecontemporaneous LIPs in the geologic record.