Multiple ocean oxygenation events during the Ediacaran Period: Mo isotope evidence from the Nanhua Basin, South China

Abstract

The Ediacaran Period (ca. 635–539 Ma) was an eventful interval in Earth history, during which a succession of biological and environmental changes, including episodic ocean oxygenation events (OOEs), may have paved the way for the Cambrian radiations of animal life. To better understand the evolution of ocean redox conditions and to estimate the extent of seafloor oxygenation during this period, we analysed molybdenum (Mo) isotope compositions and redox sensitive element (RSE) concentrations from a continuous, mid-slope section of the Doushantuo Formation (ca. 635–560 Ma) of the Nanhua Basin on the South China Craton. Alongside an updated compilation of published Mo isotope and RSE data, our new data show that three OOEs occurred within a generally anoxic Ediacaran ocean, with the last, particularly extensive event occurring during deposition of Doushantuo Member IV. Here, these findings suggest that the global balance of redox-related Mo sinks shifted dynamically in response to these transient OOEs, which correlate well with the first appearance of Ediacaran fossil groups and so may have triggered or stimulated biotic innovations and radiations. Moreover, the spatial distribution of the Mo data from multiple sections supports episodic expansion of a euxinic wedge on the slopes of the Nanhua Basin, consistent with pyrite burial as a potential cause of the OOEs.

Implications of new geochronological constraints on the Aberfeldy stratiform barite deposits, Scotland, for the depositional continuity and global correlation of the Neoproterozoic Dalradian Supergroup

“…The paucity of sulfides in the Ben Lawers Schist, and in barite beds M6 and M7 in the uppermost part of the Ben Eagach Schist (Fig. 2b and 4a), is consistent with increased oxygenation of the sea bed at this time, possibly corresponding to one of the episodic ocean oxygenation events that occurred in the Ediacaran (Yuan et al, 2022).…”