PHOSPHATIZED ACANTHOMORPHIC ACRITARCHS AND RELATED MICROFOSSILS FROM THE EDIACARAN DOUSHANTUO FORMATION AT WENG'AN (SOUTH CHINA) AND THEIR IMPLICATIONS FOR BIOSTRATIGRAPHIC CORRELATION

The Doushantuo Formation at Weng'an in Guizhou Province, South China, is best known for animal embryo-like microfossils preserved in phosphorites. However, this unit also contains a diverse assemblage of three-dimensionally phosphatized acanthomorphic acritarchs, which are useful in the biostratigraphic subdivision and correlation of the lower middle Ediacaran System. These acritarchs can be studied using both thin sectioning and acid maceration techniques, thus have the potential to resolve taxonomic inconsistencies between acritarchs preserved in cherts and shales. This paper presents a systematic treatment of acanthomorphs (and related spheroidal microfossils) from the Doushantuo Formation at Weng'an. More than 40 distinct species are described, including the following new species: Asterocapsoides robustus n. sp., Knollisphaeridiuni? bifurcatum n. sp., Megasphaera cymbala n. sp., Megasphaera patella n. sp., Megasphaera puncticulosa n. sp., Mengeosphaera eccentrica n. gen. n. sp., Papillomembrana boletiformis n. sp., Sinosphaera variabilis n. sp., Tanarium victor n. sp., Tianzhushania rara n. sp., Variomargosphaeridium gracile n. sp., and Weissiella brevis n. sp. The Weng'an microfossil assemblage is dominated by Megasphaera and Mengeosphaera but shares some taxa that are characteristic of the Tianzhushania spinosa biozone and the Tanarium conoideum-Hocosphaeridium scaberfacium-Hocosphaeridium anozos biozone recognized in the Yangtze Gorges area. It may represent a transitional assemblage between these two biozones. The Weng'an microfossil assemblage also shares some elements with Ediacaran acanthomorph assemblages from Australia, Siberia, and East European Platform, indicating at least partial biostratigraphic overlap with those assemblages. Among the taxa described here, T. spinosa and H. anozos emerges as easily recognizable and widely distributed acanthomorph species whose first appearance may be used to define acanthomorph biozones for regional and global biostratigraphic correlation of lower-middle Ediacaran successions.