Recent geochemical data from Oman, Newfoundland, and the western United States suggest that long-term oxidation of Ediacaran oceans resulted in progressive depletion of a large dissolved organic carbon (DOC) reservoir and potentially triggered the radiation of acanthomorphic acritarchs, algae, macroscopic Ediacara organisms, and, subsequently, motile bilaterian animals. However, the hypothesized coupling between ocean oxidation and evolution is contingent on the reliability of continuous geochemical and paleontological data in individual sections and of intercontinental correlations. Here we report high-resolution geochemical data from the fossil- acritarchs ͉ isotopes ͉ redox ͉ Neoproterozoic ͉ early animals T he Ediacaran (635-542 Ma) Earth witnessed profound changes in the aftermath of widespread and potentially global ice ages, including the evolution and radiation of complex megascopic life and major perturbations of the global carbon cycle that accompanied oxygenation of the deep ocean (1-9). These biological and environmental events have been speculatively linked, yet their temporal relationships have not been accurately documented in relatively continuous and fossil-rich sections that span a range of well-documented depositional settings. For example, geochemical data from siliciclasticdominated Ediacaran successions in Newfoundland (5) and the western United States (7) are incomplete, and those from the early Ediacaran interval in Oman (4) are of low stratigraphic resolution. Furthermore, paleontological data from these successions are limited to macroscopic Ediacara fossils and the biomineralizing animal Cloudina (10).To further test the proposed linkages between redox changes and biological evolution (4, 5), we carried out a high-resolution chemostratigraphic and biostratigraphic investigation of the fossiliferous Doushantuo Formation in the Yangtze Gorges area, South China. Our data reveal pulsed oxidation events that coincide with the origination and diversification of acanthomorphic acritarchs and other multicellular life forms in the basin. In combination with available data from other Ediacaran successions, our results indicate that oxidation of terminal Proterozoic oceans may have been episodic (4), with the final and permanent oxidation occurring Ϸ551 Ma. Sedimentological, Paleontological, and Geochemical DataThe Doushantuo Formation in the Yangtze Gorges area, constrained between 635.2 Ϯ 0.6 and 551.1 Ϯ 0.7 Ma (11), is divided into four lithostratigraphic members (Fig. 1). At the Jiulongwan section [supporting information (SI) Fig. 3], member I represents an Ϸ5-m-thick cap dolostone overlying the Nantuo glacial diamictite and contains a suite of enigmatic sedimentary structures and textures (12, 13). Member II is characterized by Ϸ70 m of alternating organic-rich shale and dolostone beds with abundant pea-sized chert nodules. Member III is Ϸ70 m thick and is composed of dolostone and bedded chert in the lower part that passes up-section into alternating limestone-dolostone ''ribbon rocks.'' Me...

The deep-water Avalon biota (about 579 to 565 million years old) is often regarded as the earliest-known fossil assemblage with macroscopic and morphologically complex life forms. It has been proposed that the rise of the Avalon biota was triggered by the oxygenation of mid-Ediacaran deep oceans. Here we report a diverse assemblage of morphologically differentiated benthic macrofossils that were preserved largely in situ as carbonaceous compressions in black shales of the Ediacaran Lantian Formation (southern Anhui Province, South China). The Lantian biota, probably older than and taxonomically distinct from the Avalon biota, suggests that morphological diversification of macroscopic eukaryotes may have occurred in the early Ediacaran Period, perhaps shortly after the Marinoan glaciation, and that the redox history of Ediacaran oceans was more complex than previously thought.

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 robustusn. sp.,Knollisphaeridium?bifurcatumn. sp.,Megasphaera cymbalan. sp.,Megasphaera patellan. sp.,Megasphaera puncticulosan. sp.,Mengeosphaera eccentrican. gen. n. sp.,Papillomembrana boletiformisn. sp.,Sinosphaera variabilisn. sp.,Tanarium victorn. sp.,Tianzhushania raran. sp.,Variomargosphaeridium gracilen. sp., andWeissiella brevisn. sp. The Weng'an microfossil assemblage is dominated byMegasphaeraandMengeosphaerabut shares some taxa that are characteristic of theTianzhushania spinosabiozone and theTanarium conoideum–Hocosphaeridium scaberfacium–Hocosphaeridium anozosbiozone 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. spinosaandH. anozosemerges 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.