Long-lived Doushantuo-Pertatataka acritarchs during the Ediacaran Shuram carbon isotope excursion: Evidence from the Kheseen Formation in northwest Mongolia

The Ediacaran Shuram carbon isotope excursion (CIE; 573−568 Ma) is widely recorded on many paleocontinents. The Doushantuo-Pertatataka acritarchs have long been considered to occur exclusively or predominantly in pre-Shuram Ediacaran strata. The absence of precise age constraints and uncertainty in the stratigraphic relationship of the fossil occurrences with the Shuram CIE greatly hindered the global correlation and our understanding of the coevolution of Ediacaran biotas and environment. We report, for the first time, the occurrence of the Shuram excursion on the Tuva-Mongolia terrane and correlate it with those of South China and Siberia cratons, thus indicating an Ediacaran age for the phosphorites of the Kheseen Formation. A new acritarch assemblage with a high diversity is recovered from the Kheseen Formation of the Murun section that is well exposed in the Khuvsgul basin, northwest Mongolia. Diverse acritarchs occur in the horizon recording the Shuram excursion, suggesting that their last appearances are younger than previously thought. New paleontological and chemostratigraphic data at the Murun section extend the spatial and temporal distributions of Ediacaran acritarchs, facilitating stratigraphic correlation with South China and Siberia cratons, and other paleocontinents, and lessening the role of environmental drivers in the evolution of Ediacaran acritarchs.