MicroS · Micro-scale δ34S variation of sulfide species
Horizon 2020 — Marie Skłodowska-Curie Actions
- Duration
- 2020-10-01 → 2023-09-30
- EU contribution
- €254,363
- Participants
- 2
- Scheme
- MSCA-IF
Lines connect the coordinator with its partners.
Results in brief
Micro-scale δ34S variation of sulfide species
Life exerts significant influence on the redox landscape of Earth; however, to what extent environmental factors, i.e., background oxygen levels and bio-essential nutrient availability, influenced the early diversification of eukaryotes remains debated. To solve this conundrum, accurate reconstructions of redox landscapes from critical junctions in Earth’s history are necessary. The often-compared metasedimentary rocks from the ca. 2.0 billion-year-old Onega Basin (Karelia, Russia) and Francevillian Basin (Gabon) have been central to reconstructing Earth’s early oxygenation and following environmental change. However, a growing body of conflicting interpretations of paleoredox conditions from ancient sedimentary rocks has complicated such efforts. One of the most debated paleoredox proxies is the sulfur (δ34S) isotope record. The MicroS project addresses the uncertainties under which (bio)geochemical sulfur cycling occurred during periods of significant change in Earth’s atmosphere-ocean evolution, the degree to which geochemical signals reflect local or global processes, and how these signatures are ultimately preserved in the rock record. To better understand the environmental information in the ancient Onega and Francevillian rocks, the project investigates the generation and transfer of geochemical signals under modern depositional conditions in structurally similar basins such as the Gulf of California (e.g., semi-restricted bathymetry, tectonic activity, hydrocarbon seepage).
Data: CORDIS, © European Union
Project objective
Sedimentary sulfur (S) isotope systematics (δ34S) has been widely used in paleoredox reconstruction of early Earth’s environments. Large-scale variations in the δ34S record are typically interpreted to reflect fluctuations in the global S cycle. However, the expression of S isotope fractionation is sensitive to open- vs. closed-system conditions and heterogeneous micro-scale δ34S patterns can form in S-bearing phases that precipitate over time in evolving pore-water conditions. Such intra-sample δ34S variability is undetectable in traditional bulk analyses, which has been the conventional approach in time-series δ34S compilations. Moreover, early- and late-stage interactions between organic matter and inorganic sulfide (thermochemical sulfate reduction) can impact δ34S signatures at different stages of sulfide formation leading to sulfide species with distinct δ34S compositions. Therefore, the existing stratigraphic bulk-rock pyrite δ34S compilations possibly integrate a whole spectrum of δ34S variability that may not reflect the depositional isotope composition. MicroS project will take advantage of high-resolution in situ analytical methods (SIMS, synchrotron-based X-ray spectroscopy) to investigate the micro-scale variability in organic-rich sedimentary rocks and its applicability to key intervals of Earth’s history. The project focuses on three organic-rich sedimentary basins: ~2.0 Ga Onega, ~2.1 Ga Francevillian and the modern Guaymas Basins, that share several characteristics, such as a semi-restricted rift environment, syndepositional magmatism and hydrocarbon seepage. By examining the δ34S composition of the co-existing sulfide species (e.g., pyrite, pyrrhotite, organic sulfur) and placing them into the geologic context of the individual basins, the project aims to decipher the current gap in understanding processes that govern S isotope fractionations, the transfer of δ34S to the rock record and its preservation over geologic time.
Original text from CORDIS.
Participants
- TARTU ULIKOOL · TartuCoordinatorEstonia
- THE WASHINGTON UNIVERSITY CORPORATION · St LouisUnited States
Links
Data: CORDIS, © European Union