Vanadium isotope evidence for widespread marine oxygenation from the late Ediacaran to early Cambrian

Abstract

Early animals experienced multiple-phase radiations and extinctions from the late Ediacaran to early Cambrian. Oxygen likely played an important role in these evolutionary events, but detailed marine redox evolution during this period remains highly debated. The emerging vanadium (V) isotope system can better capture short-term perturbations to global ocean redox conditions. In this study, we analyzed V isotope compositions (δ51V) of organic-rich cherts and black shales deposited from the late Ediacaran to early Cambrian (ca. 560–518 Ma) in the Yangtze Block, South China. The robust positive correlation between the δ51V values and previously reported δ98Mo values validates V isotope system as a paleo-oxybarometer. The continuously temporal open-ocean seawater δ51V variation is reconstructed from the sedimentary δ51V records. The results suggest that the ocean experienced a rapid transition from expansive euxinia at ca. 560–553 Ma to widespread oxygenation likely reaching the modern level at ca. 552–551 Ma, and kept extensively oxygenated approaching the modern oxygenation level from ca. 551 Ma to 521 Ma and reaching the modern level again at ca. 521–518 Ma. The prolonged and widespread oceanic oxygenation may have been beneficial to the ecological radiation of early animals from the late Ediacaran to early Cambrian, ultimately leading up to the “Cambrian Explosion”.