Neoarchean atmospheric chemistry and the preservation of S-MIF in sediments from the Sao Francisco Craton

Author(s)

Bosco-Santos, Alice ; Gilhooly III, William Patrick ; de Melo-Silva, Paola ; Fouskas, Fotios ; Bouyon, Amaury ; Motta, Joao Gabriel ; Baldim, Mauricio Rigoni ; Fabricio-Silva, Wendell ; Philippot, Pascal ; Oliveira, Elson Paiva

• Document type: Journal article
• Source: GEOSCIENCE FRONTIERS; v. 13, n. 5, p. 20-pg., 2022-08-26.

Abstract

Sulfur mass-independent fractionation (S-MIF) preserved in Archean sedimentary pyrite is interpreted to reflect atmospheric chemistry. Small ranges in Delta S-33 that expanded into larger fractionations leading up to the Great Oxygenation Event (GOE; 2.45-2.2 Ga) are disproportionately represented by sequences from the Kaapvaal and Pilbara Cratons. These patterns of S-MIF attenuation and enhancement may differ from the timing and magnitude of minor sulfur isotope fractionations reported from other cratons, thus obscuring local for global sulfur cycling dynamics. By expanding the Delta S-33 record to include the relatively underrepresented Sao Francisco Craton in Brazil, we suggest that marine biogeochemistry affected S-MIF preservation prior to the GOE. In an early Neoarchean sequence (2763-2730 Ma) from the Rio das Velhas Greenstone Belt, we propose that low delta C-13(org) (<-30 parts per thousand) and dampened Delta S-33 (0.4 parts per thousand to -0.7 parts per thousand) in banded iron formation reflect the marine diagenetic process of anaerobic methane oxidation. The overlying black shale (TOC up to 7.8%) with higher delta C-13(org) (-33.4 parts per thousand to -19.2 parts per thousand) and expanded Delta S-33 (2.3 parts per thousand +/- 0.8 parts per thousand), recorded oxidative sulfur cycling that resulted in enhance preservation of S-MIF input from atmospheric sources of elemental sulfur. The sequence culminates in a metasandstone, where concomitant changes to more uniform delta C-13(org) (-30 parts per thousand to -25 parts per thousand), potentially associated with the RuBisCO I enzyme, and near-zero Delta S-33 (-0.04 parts per thousand to 0.38 parts per thousand) is mainly interpreted as evidence for local oxygen production. When placed in the context of other sequences worldwide, the Rio das Velhas helps differentiate the influences of global atmospheric chemistry and local marine diagenesis in Archean biogeochemical processes. Our data suggest that prokaryotic sulfur, iron, and methane cycles might have an underestimated role in pre-GOE sulfur minor isotope records. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). (AU)

• FAPESP's process: 15/16235-2 - The co-evolution of life and oxygen on early Earth: a South American perspective
• Grantee: Pascal Andre Marie Philippot
• Support Opportunities: Research Projects - SPEC Program
• FAPESP's process: 12/15824-6 - Evolution of archaean terranes of the São Francisco Craton and the Borborema Province, Brazil: global environmental and geodynamic implications
• Grantee: Elson Paiva de Oliveira
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 16/02933-2 - Isotope geochemistry and biomarkers in Archaean terranes and in their modern analogues systems: environmental constraints and ecology of early Earth life
• Grantee: Alice Bosco Santos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral