A local rather than a global oxidation in the early Ediacaran deep ocean: Evidence from the Doushantuo Formation in East Guizhou Province, South China

After the end of the Cryogenian Snowball Earth glaciations, the Ediacaran Ocean experienced rapid oxidation and a subsequent increase in marine sulfate concentration. This led to a significant negative excursion in pyrite sulfur isotope values, particularly observed in the Doushantuo Formation of the slope facies in the South China. However, the extent of this oxidation event remains unclear. In order to address this, we carried out geochemical analysis of the Doushantuo Formation in the Cenpiaokou section of the Jiangkou County, Guizhou Province. In the Cenpiaokou section, the pyrite is mainly euhedral-subhedral and framboidal in crystal morphology. The pyrite contents are highest at the base of the Doushantuo Formation and decrease towards the middle and upper parts. Similarly, the proportion of framboidal pyrite also decreases upward, ranging from 93 % at the bottom to 9 % in the upper part of the Doushantuo Formation. Additionally, the sulfur isotope of pyrite (δ³⁴S) shows significant differences compared to other slope facies sections. There is no negative excursion in δ³⁴S at the base of the Doushantuo Formation. The lower part of the Doushantuo Formation exhibits frequent oscillations with generally high δ³⁴S values (+6.6 ‰ ∼ +37.3 ‰), while the upper part shows a decreasing trend. The organic carbon isotope (δ¹³C_org) displays an inverse correlation with δ³⁴S, with stable values in the lower part and gradually heavier values in the upper part. The nitrogen isotopes (δ¹⁵N) range from -1.6 ‰ to +2.1 ‰, suggesting a generally anoxic state with strong nitrogen fixation at the Cenpiaokou section. These findings suggest that the deep ocean oxidation during the early Ediacaran was not a global event, but rather a regional event, with anoxia still dominant overall.