EDIACARAN ACANTHOMORPHIC ACRITARCHS AND OTHER MICROFOSSILS FROM CHERT NODULES OF THE UPPER DOUSHANTUO FORMATION IN THE YANGTZE GORGES AREA, SOUTH CHINA

摘要

Silicified microfossils preserved in chert nodules of the Doushantuo Formation in the Yangtze Gorges area of South China have great potential to improve the biostratigraphic subdivision and correlation of the Ediacaran System. This potential can be realized only if solid taxonomy is available. However, a systematic treatment of these microfossils (particularly acanthomorphic acritarchs) is lacking, greatly limiting their biostratigraphic potential. This paper presents the systematic paleontology of silicified microfossils from upper Doushantuo Formation (Member III) chert nodules at three sections in the Yangtze Gorges area. More than 90 species of microfossils are described, including 66 named taxa of acanthomorphs, seven named taxa of sphaeromorphs, 12 taxa of cyanobacterial filaments and coccoids, four taxa of algal thalli, and two species of tubular microfossils. Several acritarch species, including Appendisphaera clava n. sp., Mengeosphaera grandispina n. sp., M. stegosauriformis n. sp., Leiosphaeridia, and possibly Sinosphaera rupina, are shown to be multicellular organisms, consistent with the proposition that some Ediacaran acritarchs may be diapause eggs of early animals. This study supports the view that the Tianzhushania spinosa acanthomorph biozone is unique to the lower Doushantuo Formation in South China (and perhaps its equivalent in northern India) and that Ediacaran acanthomorph assemblages from Australia, Siberia, and East European Platform are younger than the Tianzhushania spinosa biozone. It is proposed that the first occurrence of Hocosphaeridium anozos, a species with easily recognizable morphology and wide taphonomic and geographic distributions, be used to define the second Doushantuo acanthomorph biozone succeeding the Tianzhushania spinosa biozone. New taxa described in this paper include three new genera (Bispinosphaera n. gen.; Yushengia n. gen.; and Granitunica n. gen.) and 40 new species: Appendisphaera? brevispina n. sp., A. clava n. sp., A.? hemisphaerica n. sp., A. longispina n. sp., A. setosa n. sp., Bispinosphaera peregrina n. gen. n. sp., Crinita paucispinosa n. sp., Ericiasphaera densispina n. sp., Hocosphaeridium dilatatum n. sp., Knollisphaeridium denticulatum n. sp., K. longilatum n. sp., K. obtusum n. sp., K. parvum n. sp., Mengeosphaera angusta n. sp., M. bellula n. sp., M. cf. bellula n. sp., M. constricta n. sp., M.? cuspidata n. sp., M.? gracilis n. sp., M. grandispina n. sp., M. latibasis n. sp., M. minima n. sp., M. spicata n. sp., M. spinula n. sp., M. stegosauriformis n. sp., M. triangularis n. sp., M. uniformis n. sp., Sinosphaera asteriformis n. sp., Tanarium acus n. sp., T. elegans n. sp., T. longitubulare n. sp., T.? minimum n. sp., T. obesum n. sp., T. varium n. sp., Urasphaera fungiformis n. sp., U. nupta n. sp., Yushengia ramispina n. gen. n. sp., Granitunica mcfaddeniae n. gen. n. sp., Osculosphaera arcelliformis n. sp., and O. membranifera n. sp.