Sulfur isotopic values (δ34S) in sedimentary organic matter and pyrite provide essential information about the global S cycle. The measurement of δ34S values is commonly used to reconstruct paleo-environmental conditions of sediment deposition. In petroleum geochemistry, δ34S values are used to trace relationships between disparate elements of petroleum systems. However, the determination of organic and pyrite δ34S values requires a tedious and time-consuming (weeks) stepwise procedure. Here we used the latest version of the Rock-Eval® 7S analyzer, which can quantify different S-fractions in sedimentary rocks. We have coupled the Rock-Eval® pyrolysis cycle with a multi-collector inductively coupled plasma mass spectrometer (RE/MC-ICPMS). The analysis requires a small sample size (5 to 90 mg), and minimum sample preparation of acid treatment to avoid the carbonate effect on the pyrolyzed pyrite-S. The RE/MC-ICPMS system allows for measuring the pyrolysable organic-S and pyrite-S and directly determining δ34S values from a decarbonated rock. The new method was applied to a set of immature sedimentary rocks of various paleoenvironmental origins and geographic locations. The rapid analysis by the RE/MC-ICPMS, which takes only 20 min per sample, achieved an average precision of 0.5‰, for peaks above 5 nanomole of S. Accuracy was determined relative to a common wet chemistry method followed by an offline EA-IRMS analysis and reached an agreement of <1‰.
Bibliographical noteFunding Information:
We thank Vinci Technologies for the collaboration in this project and for providing the Rock-Eval ® 7S prototype and financial support. A special thanks to Nicolas Bouton and Leonardo Freitas for the technical support. Geoffrey Ellis of the U.S Geological Survey is appreciated for providing the rock samples. A.A and Y.O.R thank to the Ministry of National Infrastructures Energy and Water Resources of Israel for the research grant (No. 15/16 ). A.A. thank the Israeli Science Foundation grant # 3195/19 for partial support of this study. H.C.S. is grateful for the Ph.D. scholarships provided by the Ministry of National Infrastructures Energy and Water Resources of Israel and by the Yael Pitoun Environmental Research Fund. We appreciate the detailed and constructive comments by the four anonymous reviewers and the associate editor.
© 2023 Elsevier B.V.
- MC-ICPMS, δS
- Organic sulfur
- Rock-Eval® 7S
- Sedimentary rocks
- Source rocks