A Composite Ediacaran Acritarch Biostratigraphic Sequence in South China Constructed by Constrained Optimization (conop)

The Ediacaran Period witnessed a transition in Earth's habitability from the “Snowball Earth” of the Cryogenian to the Cambrian Explosion. The Ediacaran strata in South China provide a relatively complete fossil record of biotic evolution after the “Snowball Earth” event. In particular, the Doushantuo Formation (~635–551 Ma) in South China preserves abundant acritarchs, which serve as valuable material for revealing evolutionary patterns in the early Ediacaran and also play an important role in global biostratigraphic subdivision and correlation. Previous biostratigraphic investigations of the Doushantuo Formation largely relied on compiling fossil records of acritarchs from different stratigraphic sections. Such approaches are easily biased by incomplete fossil preservation and the Signor-Lipps effect. Therefore, whether the previously published biozones can be consistently recognized across sections requires further verification. In this study, we apply constrained optimization (CONOP) to integrate acritarch occurrences and geological events from 20 sections of the Doushantuo Formation, South China, thereby constructing a composite biostratigraphic sequence and deriving a species-level diversity curve. Our results indicate that acritarch diversity peaked in the middle of the Doushantuo Formation, and that the stratigraphic ranges of multiple taxa in the composite section are longer than previously recognized. Furthermore, the fossil assemblages in the composite sequence, while consistent with some of the existing biozones, show discrepancies with the others, suggesting a reappraisal of the remaining biozones. This study provides an important reference for establishing a more robust and reliable acritarch biozonation for the early Ediacaran Period.