T26 Comings and Goings of Proterozoic Global Glaciations (Posters)

Sunday, 9 October 2022
9:00 AM - 1:00 PM
Exhibit Hall F

AN OCEAN VENTILATION EVENT RECORDED BY URANIUM ISOTOPES IN THE TONIAN SHORIKHA FORMATION (BITTER SPRINGS-EQUIVALENT), SIBERIA

Paper number: T26-2
Program: Technical Sessions
Time: 9:00 AM – 1:00 PM

Authors

Abstract

The Neoproterozoic Era is characterized by large swings in the δ13C composition of marine carbonates, often associated with extreme changes in global climate, ocean redox, and biological innovation. Uranium isotopes (δ238U) provide a promising tool to link the δ13C record to changes in ocean oxygenation because of the sensitivity of the δ238U composition of seawater (which can be recorded in marine carbonates) to the global extent of anoxic and/or euxinic marine environments. Uranium isotopes have previously provided evidence for ocean ventilation coincident with the Ediacaran Shuram negative δ13C excursion, with associated increases in complexity of the marine biosphere. Little is known, however, about the redox context of earlier Neoproterozoic δ13C excursions, which also may have had profound biological consequences. Here, we present new δ238U data from the late Mesoproterozoic to early Neoproterozoic Turukhansk Uplift succession in Siberia, with particular focus on the Tonian-aged Shorikha, Miroyedikha, and Turukhansk formations. Newly measured sections and δ13C profiles reveal a major negative δ13C excursion from ~0‰ down to −5‰ in the Shorikha Formation, which is interpreted as equivalent to the Tonian Bitter Springs anomaly previously identified in Australia, Canada, Svalbard, and Ethiopia. This is followed by a recovery to δ13C values between 0 and +4‰ in the overlying Miroyedikha and Turukhansk formations. Our δ238U profile shows evidence for strongly anoxic oceans during deposition of the lower Shorikha and underlying formations (median δ238U value = −0.74‰), analogous to low δ238U values recently reported in early Tonian carbonates from North China. This is followed, however, by a shift to near-modern carbonate δ238U values in the upper Shorikha and lower Miroyedikha formations, coincident with the Bitter Springs-equivalent negative δ13C excursion. This can be interpreted as a major Tonian ocean ventilation event associated with the first significant Neoproterozoic carbon cycle perturbation. Ocean ventilation associated with the Bitter Springs anomaly adds to a growing body of evidence that the Neoproterozoic oceans were characterized by pulsed oxygenation events against a backdrop of widespread anoxia, and that this redox pattern is a primary cause of observed δ13C variability.

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

doi: 10.1130/abs/2022AM-382416

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