Meta-analysis of the DOUNCE event (Shuram/Wonoka excursion): Pattern, variation, causal mechanism, and global correlation

Abstract

The DOUNCE (DOUshantuo Negative Carbon isotope Excursion) was marked by a significant shift in δ¹³C_carb from ∼ + 5 ‰ down to ∼ − 12 ‰ in the upper part of the Ediacaran Doushantuo Formation of South China. As an equivalent event of the Shuram/Wonoka anomaly, the DOUNCE event is the largest negative δ¹³C_carb excursion in geological history and denotes a global ocean oxygenation event. Consequently, it has been widely used as a chemostratigraphic tool for correlating the Ediacaran strata globally. Nonetheless, the DOUNCE exhibits variable stratigraphic expressions across sections and depositional environments, raising questions about its representation as a primary indicator of the Ediacaran seawater δ¹³C value. Such variability casts doubt on the reliability of the DOUNCE for global correlation, and its implications for the carbon cycle, oceanic oxygenation, and biological evolution during the Ediacaran period. To elucidate the DOUNCE event as a synchronous global occurrence and a chemostratigraphic tool, we have compiled the “DOUNCEraq”, a global-scale database comprising 9375 valid δ¹³C_carb analyses from 156 sections/boreholes documenting the DOUNCE/Shuram/Wonoka event. Our meta-analysis of DOUNCEraq highlights the global scope of the DOUNCE event and reveals the presence of an instant rise stage post the abrupt δ¹³C_carb decline as an inherent feature of the DOUNCE pattern. Moreover, it also emphasizes the impacts of palaeolatitude, palaeocontinent, water depth, and lithology on the DOUNCE's pattern and variability: (1) lower pre-DOUNCE δ¹³C_carb values and smaller shift magnitudes within 30–0°N compared to the southern hemisphere; (2) compared to the shallower sections, deep-water sections exhibit lower pre-DOUNCE and DOUNCE nadir δ¹³C_carb values with smaller shift magnitudes relative to shallower sections; (3) dolostones demonstrate lower pre-DOUNCE values, higher values at the DOUNCE nadirs, and smaller shift magnitudes compared to limestones. Such local impacts on the DOUNCE pattern provide important constraints on the causes of the DOUNCE event and could be explained within the DOC-oxidation hypothesis via regulating oxidants supply. Overall, the present meta-analysis enhances our understanding of the DOUNCE's global stratigraphic expressions and provides important constraints on the DOUNCE causes.