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Little is known regarding characteristics and evolution of radiolarian fossils in the early Cambrian due to its rarity and poor preservation. Here we report a new radiolarian fauna from the Cambrian Shuijingtuo Formation corresponding to the Chiungchussuan Stage (Cambrian Series 2) in western Hubei, China. It contains over 300 radiolarian tests and these fossils belong to 4 morphotypes, including Paraantygopora porosa gen.et sp. nov., Braunosphaera sinensis gen.et sp. nov., Tetrasphaera? sp. and incertae spherical radiolarians. In taxonomy, Spumellaria predominates in the fauna and comprises 92% of the total. In shell structure, about 73% of all specimens are similar to the early Ordovician radiolarian fossils, with the shell walls characterized by perforated plate structures. The spherical radiolarians with latticed shells constitute another feature of the early Cambrian radiolarian fauna. The radiolarian fauna reported here contains many fossil specimens and covers different taxonomical taxa. These specimens usually consist of distinctive concentric multi-layers with complex structure. These characteristics indicate that Radiolaria had already thrived during the Cambrian Chiungchussuan Stage (Series 2, Stage 3), which may have occurred synchronously with the explosion and prosperity of macrobiota recorded in the strata deposited in shallower water condition. [ABSTRACT FROM AUTHOR]

Diverse and well-preserved latest Permian phytoplankton assemblages are described from four sections of the Yangtze Block, South China from localities in Zhongzhai (Guizhou Province), Shangsi (Sichuan Province), Xiakou (Hubei Province) and Dongpan (Guangxi Province). Most of the species have been reported previously from other upper Permian sections worldwide. The South Chinese phytoplankton taxa are generally very small in size, usually displaying diameters of about 20 μm and commonly include the generaMicrhystridium,VeryhachiumandLeiosphaeridia. However, larger taxa with vesicles often exceeding 80 μm in diameter, such asDictyotidium, are also abundant in the Shangsi section. Due to the presence of large populations ofMicrhystridiumandVeryhachium, a simple classification scheme for theMicrhystridium/Veryhachiumcomplex is proposed, based on the geometrical shape of the vesicle. We propose dividing the complex into five groups: theVeryhachium cylindricumgroup, representing all ellipsoidal specimens; theVeryhachium trispinosumgroup, all with triangular-shaped vesicles; theVeryhachium lairdiigroup, all with rectangular forms; theMicrhystridium pentagonalegroup, all with pentagonal specimens; and theMicrhystridium brevegroup, which includes all spherical forms. [ABSTRACT FROM PUBLISHER]

Abundant metazoans phyla made their first appearances in the fossil record during a relatively short time span in the Ediacaran-Cambrian interval (560–520 Ma) and rapidly expanded ecologically during the early Cambrian, leading to the establishment of metazoan-dominated ecosystems accompanied by widespread biomineralization. This unique evolutionary event was known as the 'Cambrian Explosion'. Although a significant amount of work has been undertaken to understand the evolution of life during this time interval, previous studies have mainly focused on fossil records from the Cambrian fine-grained clastic rocks deposited in shallow-water environments. However, fossil records from marlstones and mudstones formed in deep-water basins were poorly understood. In this study, we focus on fossil records from the black thin-bedded marl and calcareous mudstones of the lower Cambrian Shuijingtuo Formation in the Three Gorges area, Hubei Province. A total of 9059 fossil specimens, including both microfossils and megafossils belonging to 45 species and 14 major taxonomic groups were recovered from the Shuijingtuo Formation at the Luojiacun section. Four palaeoecological assemblages were recognized based on fossil composition and ecological characteristics. The oldest assemblage (Assemblage A) features an Isoxys -dominated planktonic community with only one benthic group of bradoriids and exhibits the highest fossil abundance and lowest species diversity. Assemblage B is characterized primarily by highly diverse benthic groups, which in decreasing order of abundance include bradoriids (27.4%), sponge spicules (9.8%), cnidarians (5.7%) and hyoliths (2.0%). The third assemblage (Assemblage C) introduces the predominant role of sponge spicules, which compose 44.8% of the community. In contrast, Assemblage D is predominated by phytoplankton featuring the lowest fossil abundance and low diversity. Integration with geochemical and sedimentary data indicates that these biotic assemblages and their evolution were mainly controlled by environmental redox variations and changes in terrestrial fluxes and water depth, subsequently suggesting a significant role of these factors on biotic evolution in the early Cambrian deep-water environment. This study provides support for the importance of oxygen levels in the evolution of life during the early Cambrian. • Four palaeoecological assemblages were recovered from the Shuijingtuo Formation. • Redox, terrestrial fluxes and sea level change were considered the main controls. • Significance of oxygen content were implied on the evolution of early life. [ABSTRACT FROM AUTHOR]

From the wake of the Marinoan glaciations to the early Cambrian, the global ocean experienced progressive but likely nonuniform and nonlinear oxygenation to levels that, although still low with respect to the modern ocean, and might be therefrom triggered the ecological expansion of animals. In this study, integrated palaeontological and geochemical analyses were conducted on the upper Shuijingtuo Formation (Cambrian Series 2, Stage 3) which outcrops western Yichang City, Hubei Province, South China, in order to assess the influence of oxygen on Cambrian ecosystem diversification in the local environment. To better understand the oxygen fluctuations in the water column over the Yangtze Block and their correlation with the spatial distributions of marine biota during the early Cambrian, three sections representing different environmental settings are investigated: from the carbonate epicontinental platform (Changkan section) to the intra-platform basin (Luojiacun and Qiaojiaping sections). The semi-quantitative analysis shows that the assemblages from the epicontinental platform are dominated by eodiscoid trilobites and brachiopods. Assemblages from the intra-platform basin differ in being dominated by articulated sponges and possible cnidarians, while brachiopods and trilobites are rare. Diagenetic effects on these observed patterns are assessed by SEM-coupled EDS analysis: they indicate that although such effects cannot be definitely discarded, the observed faunal distribution and relative abundance most probably reflect variations in environmental settings. The geochemical analysis (Mo-EF vs. U-EF) furthermore provides evidence of an oxygen gradient from the edge of the platform down to the intra-platform basin. Variations in palaeo-redox conditions between the different studied settings can be observed, which undoubtedly influenced the observed differentiation of benthic communities. Frequent anoxic events in the intra-platform basin were fatal for benthic communities, but dysoxic environments could have favored the persistence and even prosperity of metazoans such as sponges and possible cnidarians that can endure lower dissolved oxygen in the water column than other groups. • Two fossil assemblages with overturned biodiversity found in the upper Shuijingtuo Fm. • Sponges, ?cnidarians in deeper, trilobites, brachiopods dominated in shallower water. • An oxygen gradient from epicontinental sea down to intra-platform basin is detected. • Sponges, ?cnidarians prospering in deep water due to their oxygen deplete endurances. [ABSTRACT FROM AUTHOR]