Geological Society of America

T56 New Advances in Geobiology

Sunday, 22 September 2024
1:30 PM - 5:30 PM
208A

THE SHURAM EXCURSION: NOVEL ISOTOPIC AND BIOLOGICAL CONSTRAINTS ON AN ENDURING EDIACARAN ENIGMA

Paper number: T56-4
Program: Technical Sessions
Time: 2:05 PM – 2:25 PM

Authors

Alan Kaufman Presenting Author
University of Maryland, College Park, MD
Vadim Maximenko
Trofimuk Institue of Petroleum Geology and Geophysics, Novosibirsk
Dmitriy Grazhdankin
Trofimuk Institute of Petroleum Geology and Geophysics, Novosibirsk, N/A
Tian Gan
University of Maryland, College Park, MD
Tian Gan
George Mason University, Fairfax, VA
Matthew Pedersen
University of Maryland, College Park, College Park, MD
Andrew Doerrler
University of Maryland, College Park, MD
Philip M. Piccoli
University of Maryland-College Park, College Park, MD
Geoffrey Gilleaudeau
George Mason University, Fairfax, VA
Lucien Nana Yobo
Texas A&M University, College Station, TX
Natalia Bykova
Columbia, MO
Shuhai Xiao
Virginia Polytechnic Institute and State University, Blacksburg, VA

Abstract

Widespread continental collision and repeated global glaciations, likely reflecting wide oscillations in greenhouse gas concentrations, enhanced both physical and chemical weathering rates in the Neoproterozoic Era. The combination of these weathering forces may have reached a crescendo during the Shuram Excursion, a profound negative carbon isotope anomaly recognized worldwide in thick mid-Ediacaran carbonate-dominated successions. Our novel analyses of well-preserved limestones deposited at the nadir of Shuram δ¹³C compositions in both central Siberia and South China reveal near crustal δ⁷Li values, suggesting a high degree of intense congruent weathering and the rapid formation of authigenic clay in ocean sediments. This interval in central Siberia is characterized by rapid seafloor cementation and the growth of crystal fans in lower shoreface environments and preserves low δ⁸⁸Sr values suggesting elevated carbonate saturation of seawater and rapid precipitation rates. High carbonate saturation may additionally explain the depletion and covariance of carbon and oxygen isotope compositions of Shuram carbonates, as well as the sudden appearance of biomineralized animal shells near the end of the oceanographic phenomenon. Multiple lines of elemental and isotopic evidence suggest widespread ocean oxygenation during the Shuram Excursion that is linked to enhanced inputs of oxidants (like sulfate) and nutrients (including phosphorous) from terrestrial weathering. The long-term elevated flux of these inputs would have stimulated shallow marine photosynthesis and organic carbon sequestration by sponge-grade animals and their presumed symbionts, analogous to sulfide oxidizing bacteria in modern sponges that concentrate phosphorous from seawater. By soaking up photosynthetic organic matter, sponge-grade animals may have promoted global oceanic ventilation, revealed in δ²³⁸U compositions of Shuram carbonates worldwide, and the rise of the soft-bodied Ediacara biota.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404283

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