Global marine redox changes drove the rise and fall of the Ediacara biota

Abstract

The role of O2 in the evolution of early animals, as represented by some members of the Ediacara biota, has been heavily debated because current geochemical evidence paints a conflicting picture regarding global marine O2 levels during key intervals of the rise and fall of the Ediacara biota. Fossil evidence indicates that the diversification the Ediacara biota occurred during or shortly after the Ediacaran Shuram negative C-isotope Excursion (SE), which is often interpreted to reflect ocean oxygenation. However, there is conflicting evidence regarding ocean oxygen levels during the SE and the middle Ediacaran Period. To help resolve this debate, we examined U isotope variations (δ238U) in three carbonate sections from South China, Siberia, and USA that record the SE. The δ238U data from all three sections are in excellent agreement and reveal the largest positive shift in δ238U ever reported in the geologic record (from ~ −0.74‰ to ~ −0.26‰). Quantitative modeling of these data suggests that the global ocean switched from a largely anoxic state (26%–100% of the seafloor overlain by anoxic waters) to near-modern levels of ocean oxygenation during the SE. This episode of ocean oxygenation is broadly coincident with the rise of the Ediacara biota. Following this initial radiation, the Ediacara biota persisted until the terminal Ediacaran period, when recently published U isotope data indicate a return to more widespread ocean anoxia. Taken together, it appears that global marine redox changes drove the rise and fall of the Ediacara biota.

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Keywords

Life Sciences & Biomedicine, Physical Sciences, Biology, Environmental Sciences, Geosciences, Multidisciplinary, Life Sciences & Biomedicine - Other Topics, Environmental Sciences & Ecology, Geology, early animals, Neoproterozoic, ocean oxygenation, Shuram negative carbon isotope excursion, uranium isotopes, CARBON-ISOTOPE EXCURSION, YANGTZE GORGES AREA, SOUTH CHINA IMPLICATIONS, URANIUM ISOTOPE, JOHNNIE FORMATION, OCEAN OXYGENATION, DEATH-VALLEY, DOUSHANTUO FORMATION, 1ST APPEARANCE, SHURAM, 0402 Geochemistry, 0403 Geology, 0602 Ecology, Geochemistry & Geophysics

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