T204 New Voices in Geobiology II

Tuesday, 6 November 2018
1:30 PM - 5:30 PM
Room 243

SULFUR ISOTOPE HETEROGENEITY IN FRAMBOIDAL PYRITES FROM A STRATIFIED EUXINIC LAKE

Paper number: T204-3
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

Sulfur isotope measurements of pyrite and calcite-associated sulfate in sedimentary rocks are used to interpret the evolution of the global sulfur cycle and the history of ocean redox change. However, recent work suggests that local depositional and diagenetic processes can obscure relevant environmental information recorded in δ34S. One difficulty in interpreting sedimentary δ34Spyrite records may result from the presence of both syngenetic and diagenetic sources in a traditional bulk δ34S measurement. In this study, we examine the relationship between pyrite framboid diameter and δ34S of framboids in a modern euxinic analog to examine the extent to which sedimentary δ34Spyrite reflects water column versus sedimentary sulfur cycling. We used density separation techniques to isolate pyrites from surface sediments collected from depths at and below the chemocline in meromictic Fayetteville Green Lake (FGL), NY. We measured framboid diameter via SEM and δ34S of individual framboids via SIMS. Framboidal pyrites isolated from a single sample have a range of up to 40 permil in δ34S with no clear relationship to framboid diameter. This is greater than the range of δ34S reported in bulk pyrite and sulfide samples from FGL, but similar to other high-resolution studies of pyrite. We suggest that that these measurements capture both pyrites formed in the water column and in the sediments. Isotopically enriched pyrites may reflect closed system behavior, either within particles in the water column or within the sediments. This high-resolution S isotope approach may improve our understanding of pyrite formation and preservation in FGL as well as in euxinic intervals of the rock record.

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

doi: 10.1130/abs/2018AM-320236

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