Ediacaran Acanthomorphic Acritarchs and Other Microfossils from Chert Nodules of the Upper Doushantuo Formation in the Yangtze Gorges Area, South China

Abstract

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, includingAppendisphaera clavan. sp.,Mengeosphaera grandispinan. sp.,M. stegosauriformisn. sp.,Leiosphaeridia, and possiblySinosphaera 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 theTianzhushania spinosaacanthomorph 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 theTianzhushania spinosabiozone. It is proposed that the first occurrence ofHocosphaeridium anozos, a species with easily recognizable morphology and wide taphonomic and geographic distributions, be used to define the second Doushantuo acanthomorph biozone succeeding theTianzhushania spinosabiozone. New taxa described in this paper include three new genera (Bispinosphaeran. gen.;Yushengian. gen.; andGranitunican. gen.) and 40 new species:Appendisphaera?brevispinan. sp.,A. clavan. sp.,A.?hemisphaerican. sp.,A. longispinan. sp.,A. setosan. sp.,Bispinosphaera peregrinan. gen. n. sp.,Crinita paucispinosan. sp.,Ericiasphaera densispinan. sp.,Hocosphaeridium dilatatumn. sp.,Knollisphaeridium denticulatumn. sp.,K. longilatumn. sp.,K. obtusumn. sp.,K. parvumn. sp.,Mengeosphaera angustan. sp.,M. bellulan. sp.,M.cf.bellulan. sp.,M. constrictan. sp.,M.?cuspidatan. sp.,M.?gracilisn. sp.,M. grandispinan. sp.,M. latibasisn. sp.,M. miniman. sp.,M. spicatan. sp.,M. spinulan. sp.,M. stegosauriformisn. sp.,M. triangularisn. sp.,M. uniformisn. sp.,Sinosphaera asteriformisn. sp.,Tanarium acusn. sp.,T. elegansn. sp.,T. longitubularen. sp.,T.?minimumn. sp.,T. obesumn. sp.,T. variumn. sp.,Urasphaera fungiformisn. sp.,U. nuptan. sp.,Yushengia ramispinan. gen. n. sp.,Granitunica mcfaddeniaen. gen. n. sp.,Osculosphaera arcelliformisn. sp., andO. membraniferan. sp.

Acanthomorphic acritarchs of the Doushantuo Formation from an upper slope section in northwestern Hunan Province, South China, with implications for early–middle Ediacaran biostratigraphy

“…The specimen is broadly similar to Briareus borealis, whose processes are also distally and basally expanded (Knoll, 1992). However, as pointed out by Liu et al (2014b), the processes of Briareus borealis are shorter, much more closely spaced, and have a weakly developed waist.…”

“…7I). Considering their high abundance in the Doushantuo Formation chert nodules in the Yangtze Gorges area (Liu et al, 2014b;Zhang et al, 1998), the rare occurrence of filamentous cyanobacteria at Lujiayuanzi may be related to paleoecological or taphonomical factors.…”

“…In total 26 specimens of spiny acritarchs have been recognized, and 23 of them are identifiable at least to the genus level (Table 1). These spiny acritarchs represent 5 genera and 8 species, according to taxonomic treatments of Grey (2005), Liu et al (2014b), Moczydłowska (2005), Moczydłowska and Nagovitsin (2012), and Xiao et al (2014).…”

“…1A) (Liu et al, 2014a,b;McFadden et al, 2009;Xiao, 2004a;Xiao et al, 2014;Zhang et al, 1998;. Phosphatized microfossils have been reported from many places on the Yangtze block, including Weng'an in central Guizhou Province Yuan and Hofmann, 1998;Zhang et al, 1998), Chadian in southern Shaanxi Province , Zhangcunping (McFadden et al, 2009, and references therein) and Baizhu (Zhou et al, 2001(Zhou et al, , 2004 in western Hubei Province, and Chaoyang in eastern Jiangxi Province (Zhou et al, 2002) ( from the Doushantuo chert nodules in the Yangtze Gorges areas of western Hubei Province (Liu et al, 2014b;Xiao, 2004b;Zhang et al, 1998;. Compared with the phosphatized assemblages that are mostly preserved in reworked clasts and restricted within specific phosphorite horizons, silicified DPAs are generally preserved in situ and thus have greater potential in Ediacaran acritarch biostratigraphy (Liu et al, 2013a(Liu et al, , 2014aMcFadden et al, 2009;.…”

“…Compared with the phosphatized assemblages that are mostly preserved in reworked clasts and restricted within specific phosphorite horizons, silicified DPAs are generally preserved in situ and thus have greater potential in Ediacaran acritarch biostratigraphy (Liu et al, 2013a(Liu et al, , 2014aMcFadden et al, 2009;. For example, in the Yangtze Gorges area, two acanthomorph assemblage zones have been recognized-the Tianzhushania spinosa assemblage zone in the lower Doushantuo Formation and the Hocosphaeridium anozos assemblage zone in the middle-upper Doushantuo Formation (Liu et al, 2013a(Liu et al, , 2014bMcFadden et al, 2009;Xiao et al, 2016;Yin et al, 2011a). The Tianzhushania spinosa assemblage zone is absent from early Ediacaran successions in many other continents such as Australia and Siberia (Grey et al, 2003;Liu et al, 2013aLiu et al, , 2014aMoczydłowska and Nagovitsin, 2012;Narbonne et al, 2012;Xiao et al, 2014).…”