Ediacaran Large Acanthomorphic Acritarchs from the Zavkhan Terrane of Mongolia: Implications for Palaeogeography and Biostratigraphy

The Neoproterozoic paleogeographic affinity of the Zavkhan Terrane in western Mongolia remains debated, with competing models proposing a Siberian connection, a peri-Siberian location, or an isolated intra-oceanic position. Here we report a diverse large acanthomorphic acritarch (LAA) assemblage (24 species) from chert nodules of the lower Shuurgat Formation. Key taxa include Asterocapsoidessinensis, Cavaspinaacuminata, C. basiconica, Cymatiosphaeroidesforabilatus, Membranospinosphaeraformosa, Tanariumconoideum, and T. tuberosum. The cooccurrence of T. conoideum and C. basiconica places this assemblage within the T. conoideum–C. basiconica Zone, and negative δ¹³Ccarb excursions correlate with the EN2 excursion of the lower Doushantuo Formation (Yangtze block) and Krol A Formation (Lesser Himalaya), indicating an early Ediacaran age. Quantitative bioprovincial analysis of a global LAA database (232 species, seven regions) shows that the Zavkhan assemblage clusters most closely with those of the Yangtze block and Lesser Himalaya. Notably, several taxa previously considered endemic to South China including Membranospinosphaeraformosa, Knollisphaeridiumlongilatum, and Ericiasphaerafibrilla are now documented in Zavkhan. These results, together with comparable stratigraphic successions and detrital zircon age spectra, support a close palaeogeographic affinity between Zavkhan, South China, and northern India during the Ediacaran, challenging models that favor a Siberian connection. This study demonstrates that Ediacaran LAAs may serve as powerful tools for palaeogeographic reconstruction.