The 5th International Conference of Geobiology

Carbonate carbon isotopes (δ¹³C_carb) have long been used in global stratigraphic comparisons and paleoceanographic environmental reconstruction studies, in which at least three significant negative carbon isotope excursions have been identified in the Ediacaran Doushantuo Formation (~635-551 Ma). However, previous studies have mostly focused on shallow-water platforms, and there is a lack of systematic knowledge of carbon isotope features in deep-water basins. In this study, we systematically reveal the carbon isotope characteristics in deep-water environments through high-precision carbon (δ¹³C_carb, δ¹³C_org) and oxygen isotope (δ¹⁸O) analyses of drilling samples from the Ediacaran Doushantuo Formation in northern Guangxi, South China. The results show that two distinct negative δ¹³C_carb excursions are identified: (1) negative δ¹³C_carb excursion in basal dolostones, with δ¹³C_carb values ranging from -4.07‰ to -6.26‰, which can be compared with the negative δ¹³C_carb excursion in the cap carbonate of Doushantuo Formation in South China. (2) Negative δ¹³C_carb excursion in the central part of the Doushantuo Formation, with δ¹³C_carb values ranging from -4.81‰ to -14.55‰, which can be correlate with both the EN3/DOUNCE interval in South China and global Shuram Excursion (SE) records, further confirming the global nature of the SE event. Notably, the observed δ¹³C_carb-δ¹³C_org covariation at the termination of the second excursion suggests that oxidising conditions may have extended into deep marine environments during the mid-Ediacaran. Compared with previously published data, the SE profiles in this study are relatively more complex and longer in duration, which may be related to the enhanced DOC reservoirs and efficiency of microbial activities in deep-water basins. These findings not only provide deep-water phase evidence for the global nature of the SE, but also reveal the potential coupling between the dynamic evolution of the oceanic DOC reservoir during the Neoproterozoic oxidation event (NOE) and the early eukaryotic radiation, offering new perspectives on biosphere-geosphere co-evolution.

Carbonate carbon isotopes; Shuram Excursion; Doushantuo Formation; Basin facies.