Diverse organic-walled microfossils from the basal Cambrian Yanjiahe Formation in the eastern Three Gorges area

Acritarchs and cyanobacteria, as critical primary producers, are essential for our understanding of marine ecosystem during the Ediacaran-Cambrian interval. This study investigates cherts from the Yanjiahe Formation in eastern Three Gorges area to elucidate the components of primary producers of the basal Cambrian recorded in chert Lagerstätten. High-resolution sampling revealed abundant organic-walled microfossils in thin sections, including eight genera, eight species assigned to acritarchs, coccoidal microfossils and cyanobacteria: the AHC assemblage (Asteridium tornatum, Heliosphaeridium ampliatum, Comasphaeridium annulare), Yurtusia uniformis, Dictyotidium? sp., Archaeophycus yunnanensis, Myxococcoides sp., and Megathrix longus. These diverse microfossils indicate a gradual diversification of phytoplankton following the end-Ediacaran extinction. Their proliferation not only enriches the primary producer composition of the Yanjiahe biota but also implies their potential contribution to fueling metazoan radiation within the Cambrian marine ecosystem.