New microfossils from the neoproterozoic (Sinian) Doushantuo Formation, Wengan, Guizhou Province, southwestern China

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Abstract
Well-preserved, three-dimensional microfossils are reported from a 3.7 m thick black phosphorite bed in the Sinian Doushantuo Formation at Wengan Phosphate Mine, Guizhou Province, southwest China. The diverse assemblage, observed in thin sections, comprises planktonic acritarchs, benthic cyanobacteria, bacteria, and thallophytes. Twenty one taxa are recognized, including 1 new genus and 4 new species. Acritarchs include Baltisphaeridium rigidum sp. nov., Vulcanisphaera phacelosa sp. nov., Comasphaeridium magnum Zhang 1984, Cymatiosphaeroides yinii sp. nov., Dicrospinasphaera zhangii gen. et sp. nov., Echinosphaeridium maximum (Yin, 1987) Knoll, 1992, Ericiasphaera sp., ?Ericiasphaera sp., Hocosphaeridium scaberfacium Zang & Walter, 1992, Meghystrichosphaeridium sp., Meghystrichosphaeridium wenganensis Chen & Liu, 1986, Polyhedrosphaeridium sp. The cyanobacteria and bacteria comprise Paratetraphycus giganteus Zhang, 1984, Gloeodiniopsis lamellosa (Schopf, 1968) Knoll & Golubic, 1979, Globophycus sp., Myxococcoides sp., type A, Siphonophycus rugosum (Maithy, 1975) Hofmann & Jackson, 1994, Siphonophycus robustum (Schopf, 1968) Knoll, Swett & Mark, 1991, Gunflintia sp., and a rod-like bacterium (type B). At least 6 distinctive acritarch taxa from the black phosphorite bed are also represented in the Pertatataka assemblage reported by Zang & Walter (1992) in the Amadeus Basin of central Australia, suggesting a biostratigraphic correlation with the Pertatataka Formation, which underlies strata containing Ediacaran metazoans and overlies Varangerage glacial sediments. Abundant bacteria-like coccoids and filaments preserved in the vesicles of many acritarch specimens attest to the presence of a thriving microbiota of decomposers within dead acritarchs, and a specimen of Thallophyca ramosa Zhang 1989 has well-preserved reproductive structures that comparable with those of the modern rhodophyte Bangia and the phaeophyte Fucus.