TY - JOUR
T1 - Testing the global significance of the sulfur isotope record of the ca. 2.0 Ga Zaonega Formation
T2 - A micro-scale S isotope investigation
AU - Paiste, K.
AU - Fike, D. A.
AU - Kirsimäe, K.
AU - Jones, C.
AU - Lepland, A.
N1 - Funding Information:
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 894831. K.K. acknowledges the Estonian Science Agency project PRG 447 and D.A.F. acknowledges support from the McDonnell Center for the Space Sciences at Washington University. S. Ono is thanked for editorial handling and three anonymous reviewers for constructive feedback that helped to improve the manuscript. We are grateful to A. R. Prave for proof-reading of the manuscript and we acknowledge the late A. E. Romashkin, who will be dearly missed.
Funding Information:
This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 894831. K.K. acknowledges the Estonian Science Agency project PRG 447 and D.A.F. acknowledges support from the McDonnell Center for the Space Sciences at Washington University. S. Ono is thanked for editorial handling and three anonymous reviewers for constructive feedback that helped to improve the manuscript. We are grateful to A. R. Prave for proof-reading of the manuscript and we acknowledge the late A. E. Romashkin, who will be dearly missed.
Publisher Copyright:
© 2022 The Authors
PY - 2022/8/15
Y1 - 2022/8/15
N2 - The Paleoproterozoic metasedimentary rocks of the Zaonega Formation (Onega Basin, NW Russia) are important archives of inferred global environmental change following the initial oxygenation of the Earth's atmosphere and oceans. However, the geochemical signals preserved in these exceptionally organic-and pyrite-rich metasedimentary rocks and their environmental meaning remain contested. In particular, the Zaonega Formation's unusually high pyrite sulfur isotope ratios (δ34S) have been explained by either global or local forcings acting on sulfur cycling processes. We tested former interpretations of the Zaonega Formation's sedimentary pyrite record by integrating bulk and micro-scale δ34S analysis to discriminate the isotopic signatures of different generations of pyrite and determine the underlying mechanisms contributing to δ34S variability. We show that the prolonged genesis of pyrite occurred via multiple stages and included precipitation from early diagenetic fluids, organic matter pyritization, and late-stage alteration fluids. Our results demonstrate that early-stage pyrite typically carries more variable and lower δ34S values than late-stage pyrite. Although the early pyrite captures pore water S isotope signatures least evolved from the seawater, their contribution to the bulk δ34S results can be dwarfed by the greater volume of late-stage coarse pyrite. Consequently, determining the sequence of pyrite precipitation and δ34S characteristics of individual generations in any given sample are fundamental to interpreting bulk δ34S records. Our micro-scale results suggest that previous estimates based on bulk pyrite data (ca. 6 to 18‰) should not be related to the original seawater sulfate's isotopic composition. These results demonstrate that a thorough understanding of the geological context and mechanisms associated with S-cycling, and pyrite formation is necessary to interpret bulk δ34S records accurately.
AB - The Paleoproterozoic metasedimentary rocks of the Zaonega Formation (Onega Basin, NW Russia) are important archives of inferred global environmental change following the initial oxygenation of the Earth's atmosphere and oceans. However, the geochemical signals preserved in these exceptionally organic-and pyrite-rich metasedimentary rocks and their environmental meaning remain contested. In particular, the Zaonega Formation's unusually high pyrite sulfur isotope ratios (δ34S) have been explained by either global or local forcings acting on sulfur cycling processes. We tested former interpretations of the Zaonega Formation's sedimentary pyrite record by integrating bulk and micro-scale δ34S analysis to discriminate the isotopic signatures of different generations of pyrite and determine the underlying mechanisms contributing to δ34S variability. We show that the prolonged genesis of pyrite occurred via multiple stages and included precipitation from early diagenetic fluids, organic matter pyritization, and late-stage alteration fluids. Our results demonstrate that early-stage pyrite typically carries more variable and lower δ34S values than late-stage pyrite. Although the early pyrite captures pore water S isotope signatures least evolved from the seawater, their contribution to the bulk δ34S results can be dwarfed by the greater volume of late-stage coarse pyrite. Consequently, determining the sequence of pyrite precipitation and δ34S characteristics of individual generations in any given sample are fundamental to interpreting bulk δ34S records. Our micro-scale results suggest that previous estimates based on bulk pyrite data (ca. 6 to 18‰) should not be related to the original seawater sulfate's isotopic composition. These results demonstrate that a thorough understanding of the geological context and mechanisms associated with S-cycling, and pyrite formation is necessary to interpret bulk δ34S records accurately.
KW - Paleoproterozoic
KW - Pyrite
KW - SIMS
KW - Sulfur isotopes
KW - Zaonega formation
UR - http://www.scopus.com/inward/record.url?scp=85132712334&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2022.05.021
DO - 10.1016/j.gca.2022.05.021
M3 - Article
AN - SCOPUS:85132712334
SN - 0016-7037
VL - 331
SP - 86
EP - 104
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -