Vanadium isotope evidence for expansive ocean euxinia during the appearance of early Ediacara biota

For reasons that remain unclear, the initial appearance of large, morphologically complex life on Earth seems to have taken place in deep-marine environments. We provide new perspective on this topic by applying for the first time the vanadium (V) isotope paleoredox-proxy. We use shales in two different sections that preserve Doushantuo Member IV (South China) to reconstruct a global seawater V isotope composition (delta V-51=similar to-0.23 +/- 0.06 parts per thousand) during the late-Ediacaran (similar to 567 to >= 560 million years ago) that is much lighter than today. A mass-balance model informed by this composition is only reconciled by a global ocean in which hydrogen sulfide-rich ('euxinic') conditions were commonly present on continental shelves. Higher surface temperatures are a known driver of widespread euxinia in Earth's past, and if this was also the case during the late-Ediacaran, then relegation of large complex life to deep-marine settings at this time was probably driven to some extent by the persistently cooler and sulfide-poor conditions offered by this refuge. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The research on vanadium isotopes indicates that during the late-Ediacaran period, global seawater was hydrogen sulfide-rich mainly on continental shelves, which may have been one of the reasons for the relegation of large, complex life to deep-marine settings during that time.