Geological Society of America

T223 Radiogenic Isotopes as Tracers of Geologic Processes: Dates, Rates, and Proxies I

Wednesday, 12 October 2022
8:00 AM - 12:00 PM
502

ESTABLISHING A ROBUST TEMPORAL FRAMEWORK FOR THE PALEOPROTEROZOIC LOMAGUNDI-JATULI CARBON ISOTOPE EXCURSION IN THE FRANCEVILLIAN BASIN, GABON

Paper number: T223-7
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Sally M. Stevens
University of Wisconsin-Madison, Madison, WI
Karen Bakakas Mayika
Université des Sciences et Techniques de Masuku, Franceville
Annie Bauer Presenting Author
University of Wisconsin-Madison, Madison, WI
Kalle Kirsimäe
University of Tartu, Tartu
Mathieu Moussavou
Université des Sciences et Techniques de Masuku, Franceville
Aivo Lepland
Geological Survey of Norway, Trondheim, Sør-Trøndelag county
Anthony R. Prave
University of St Andrews, St Andrews, N/A
Alan Rooney
Yale University, New Haven, NC
Athena Eyster
University of Wisconsin-Madison, Madison, WI
Michael Tappa
University of Wisconsin-Madison, Madison, WI

Abstract

The initial rise of atmospheric oxygen levels in the Paleoproterozoic and ensuing fluctuations may have profound implications for the trajectory of biological evolution and global nutrient cycling. We are working to improve our understanding of the trajectory of atmospheric oxygen during the ~2.3-2.0 Ga Lomagundi-Jatuli positive carbonate carbon isotope (δ¹³C_carb) excursion and associated negative organic carbon isotope excursion in the Lastoursville sub-basin of the Francevillian Basin, Gabon. A more accurate temporal framework is necessary to understand if atmospheric oxygenation and marine carbon cycle disturbances are coupled in this interval. We present petrographic, isotopic, and geochronologic constraints to resolve these interpretations. LA-ICP-MS imaging reveals a heterogeneous distribution of redox-sensitive elements within the organic-rich sediments and no significant remobilization of these elements into pyrobitumen or silica veins. Homogeneous Nd isotope stratigraphy confirms no major changes in clastic provenance through this interval. We have obtained a Re-Os age constraint for the transition from positive to near-zero δ¹³C_carb values in the Lastoursville sub-basin. This new age constraint excludes subsamples with negative initial ¹⁸⁷Os/¹⁸⁸Os, which we attribute to post-depositional Os loss. Radiogenic initial ¹⁸⁷Os/¹⁸⁸Os suggests the transport of oxidized Os to the oceans through oxidative weathering. Our new robust geochemical characterization of these rocks allows for global correlations and will result in novel insights into the rise of oxidative weathering and global carbon cycling at the termination of what may have been the most dramatic disturbance to the carbon cycle in Earth history.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381933

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