Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published December 15, 2015 | Supplemental Material
Journal Article Open

Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata

Abstract

Carbonate Associated Sulfate (CAS) is trace sulfate incorporated into carbonate minerals during their precipitation. Its sulfur isotopic composition is often assumed to track that of seawater sulfate and inform global carbon and oxygen budgets through Earth's history. However, many CAS sulfur isotope records based on bulk-rock samples are noisy. To determine the source of bulk-rock CAS variability, we extracted CAS from different internal sedimentary components micro-drilled from well-preserved Late Ordovician and early Silurian-age limestones from Anticosti Island, Quebec, Canada. Mixtures of these components, whose sulfur isotopic compositions vary by nearly 25‰, can explain the bulk-rock CAS range. Large isotopic variability of sedimentary micrite CAS (^(34)S-depleted from seawater by up to 15‰) is consistent with pore fluid sulfide oxidation during early diagenesis. Specimens recrystallized during burial diagenesis have CAS ^(34)S-enriched by up to 9‰ from Hirnantian seawater, consistent with microbial sulfate reduction in a confined aquifer. In contrast to the other variable components, brachiopods with well-preserved secondary-layer fibrous calcite—a phase independently known to be the best-preserved sedimentary component in these strata—have a more homogeneous isotopic composition. These specimens indicate that seawater sulfate remained close to about 25‰ (V-CDT) through Hirnantian (end-Ordovician) events, including glaciation, mass extinction, carbon isotope excursion, and pyrite-sulfur isotope excursion. The textural relationships between our samples and their CAS isotope ratios highlight the role of diagenetic biogeochemical processes in setting the isotopic composition of CAS.

Additional Information

© 2015 Elsevier B.V. Received 18 June 2015; Received in revised form 30 September 2015; Accepted 4 October 2015. Funding for this work was provided by the American Chemical Society Petroleum Research Fund New Directions grant #53994-ND2, NSF Division of Earth Sciences award EAR-1349858, and the Agouron Institute grant AI-GC17.09.3. We thank David Jones and Benjamin Gill for thoughtful reviews. We thank David Fike and Seth Finnegan for helpful input and field context for the Anticosti Island specimens. We thank Renata Cummins for instruction on how to prepare brachiopod secondary-layer fibrous calcite, and Lindsey Hedges, Fenfang Wu, and Nathan Dalleska for analytical support. We thank Joe Kirschvink for help interpreting rock magnetic data. Thank you to Kristin Bergmann for providing the T. transversa specimen, and Nivedita Thiagarajan for help preparing deep-sea coral samples. Ion chromatography was done at the Caltech Environmental Analysis Center.

Attached Files

Supplemental Material - mmc1.pdf

Supplemental Material - mmc2.pdf

Supplemental Material - mmc3.pdf

Supplemental Material - mmc4.xlsx

Supplemental Material - mmc5.xlsx

Supplemental Material - mmc6.xlsx

Files

mmc1.pdf
Files (7.9 MB)
Name Size Download all
md5:353f53e69e1d1598fbca9b2ad8f99edc
5.5 MB Preview Download
md5:56023da2acd29de45ab2d61a18718ee6
1.6 MB Preview Download
md5:7d85e81457a0367a6e52d4c1d7f7939a
17.7 kB Download
md5:042b9c3b170bc516726d907b27e0f2a5
29.6 kB Download
md5:cfba1767ab745affa7f6e89d85aae4ee
789.5 kB Preview Download
md5:0f52d144b978f780774c351e43dc7a5b
13.4 kB Download

Additional details

Created:
August 22, 2023
Modified:
October 25, 2023