T134 New Advances in Geobiology

Monday, 16 October 2023
1:30 PM - 5:30 PM
325

SEQUENTIAL SULFUR EXTRACTION AND ISOTOPIC ANALYSIS OF EARLY EDIACARAN PHOSPHORITE FROM THE DOUSHANTUO FORMATION AT WENG'AN, SOUTH CHINA

Paper number: T134-8
Program: Technical Sessions
Time: 3:15 PM – 3:30 PM

Authors

Abstract

The Ediacaran Doushantuo Formation hosts some of the largest phosphorus reserves in the world and preserves extraordinary fossils that can illuminate our understanding of biological evolution and environmental change. However, the origin of phosphorite and depositional environment of the Doushantuo Formation is not entirely resolved. Here, we conducted sequential extraction of different sulfur species present in both black and gray phosphorite of the Doushantuo Formation at Weng’an. Sulfur species were extracted using dichloromethane (for elemental sulfur, ES), sodium chloride solution (for water-soluble sulfates, WSS), acetic acid (presumably for carbonate-associated sulfate or CAS), hydrochloric acid (for phosphate-associated sulfate or PAS), diethylenetriamine pentaacetate and sodium hydroxide solution (for barite), chromium reduction (for pyrite), and combustion of final residual (for kerogen sulfur). The sequential extraction products were analyzed for sulfur isotope compositions. The results show that, in general, δ34SPAS and δ34Skerogen have the highest values of 30–35‰ VCDT, and these are interpreted to have recorded the sulfur isotope composition of sulfate in seawater and porewaters. In contrast, δ34SWSS, δ34Sbarite, and δ34SCAS are mostly 10–20‰ VCDT, similar to δ34Spyrite, likely compromised by pyrite oxidation on the outcrop or in the laboratory. δ34SES is also mostly 10–20‰ VCDT, but with greater variability, in part due to the instability of elemental sulfur at geological time scale. The data indicate that kerogen and early diagenetic phosphorite can be valuable archives of seawater sulfate δ34S, and that pyrite oxidation can be pervasive and poses a considerable challenge in sequential sulfur extraction and isotopic analysis. Thus, careful quantification of sulfur species and their isotopic compositions is important to understand sulfur cycles, redox conditions, and phosphogenesis in Ediacaran oceans.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-393696

© Copyright 2023 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.