Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 119, Issue 13, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2025606119
Keywords
atmospheric oxygenation; quadruple sulfur isotope; mass-independent S-isotope fractionation; Transvaal Basin
Categories
Funding
- NSF under the Frontiers in Earth System Dynamics initiative Dynamics of the Earth System Oxygenation [NSF-1138810]
- Simons Collaboration on the Origin of Life [290361FY18]
- Chinese National Natural Science Foundation [41821001]
- Strategic Priority Research Program of Chinese Academy of Sciences [XDB26000000]
- MIT International Science & Technology Initiative Global Seed Award
- US NSF [EAR-2004618]
- University of Wisconsin-Madison
- European Research Council [856555]
- European Research Council (ERC) [856555] Funding Source: European Research Council (ERC)
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This study uses a new bulk quadruple S-isotope record to investigate support for atmospheric oxygen oscillations in the Rooihoogte Formation in the South African Transvaal Basin. The study finds coexistence of different sulfur pools and extreme spatial variability.
The disappearance of mass-independent sulfur isotope fractionation (S-MIF) within the c. 2.3-billion-year-old (Ga) Rooihoogte Formation has been heralded as a chemostratigraphic marker of permanent atmospheric oxygenation. Reports of younger S-MIF, however, question this narrative, leaving significant uncertainties surrounding the timing, tempo, and trajectory of Earth's oxygenation. Leveraging a new bulk quadruple S-isotope record, we return to the South African Transvaal Basin in search of support for supposed oscillations in atmospheric oxygen beyond 2.3 Ga. Here, as expected, within the Rooihoogte Formation, our data capture a collapse in Delta(3x) S values and a shift from Archean-like Delta S-36/Delta S-33 slopes to their mass-dependent counterparts. Importantly, the interrogation of a Delta S-33-exotic grain reveals extreme spatial variability, whereby atypically large Delta S-33 values are separated from more typical Paleoproterozoic values by a subtle grain-housed siderophile-enriched band. This isotopic juxtaposition signals the coexistence of two sulfur pools that were able to escape diagenetic homogenization. These large Delta S-33 values require an active photochemical sulfur source, finger-printing atmospheric S-MIF production after its documented cessation elsewhere at similar to 2.4 Ga. By contrast, the Delta S-33 monotony observed in overlying Timeball Hill Formation, with muted Delta S-33 values (<0.3) and predominantly mass-dependent Delta S-36/Delta S-33 systematics, remains in stark contrast to recent reports of pronounced S-MIF within proximal formational equivalents. If reflective of atmospheric processes, these observed kilometer-scale discrepancies disclose heterogenous S-MIF delivery to the Transvaal Basin and/or poorly resolved fleeting returns to S-MIF production. Rigorous bulk and grain-scale analytical campaigns remain paramount to refine our understanding of Earth's oxygenation and substantiate claims of post-2.3 Ga oscillations in atmospheric oxygen.
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