Coupling of shallow marine redox change and multi-stage animal radiations during the early Cambrian

Abstract

Marine redox variations are widely accepted as an environmental driver for the Cambrian explosion, yet relative changes in shallow marine dissolved oxygen levels during the Ediacaran–Cambrian transition have long remained unconstrained. Here we present compiled nitrogen and organic carbon isotope data from shallow-water deposits in four sections, including new record from the Meishucun and Zhujiaqing sections, on the Yangtze Platform. The results reveal that nitrogenous environments with active denitrification prevailed in shallow ocean during the Terreneuvian, which may have been sufficient only for ecological successes of lophotrochozoans with relatively low O2 demands. In contrast, the diversification of ecdysozoans and deuterostomes with higher O2 demands was possibly suppressed and delayed until a rise of dissolved oxygen concentrations during the Cambrian Age 3. Our findings provide crucial support for a causal link between marine oxygen availability and rapid diversification of metazoans during the Cambrian explosion.