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The Ediacaran to Cambrian transition witnessed great biological and environmental turnovers from the Precambrian to Phanerozoic. These changes are also reflected by the fossil records during that time. However, the fossil distribution was highly heterogenous. While diverse fossils were constantly found from the shallow shelf including restricted basins, reports from deep-water areas, which are characterized by chert-dominated formations straddling the Ediacaran-Cambrian boundary, were scarce. Among them was the Liuchapo Formation that has been considered barren. In this study, a fossiliferous assemblage was found from the Liuchapo Formation in east Guizhou Province, South China. This assemblage comprises Palaeopascichnus jiumenensis, Horodyskia minor, multicellular algae that possibly related with red algae, cyanobacteria, sponge spicules, small shelly fossils, membrane structures of uncertain affinity, and fossils with structures resemble the Ediacaran Megasphaera. Palaeopascichnus and Horodyskia have been widely reported and abundant in the Liuchapo Formation and equivalents, while the others have seldomly, or never, been found from this formation or, more widely, the deep-water chert of transitional interval. The discovery not only contributes to the rare paleontological records preserved in deep-water sediments, but also expanded the geographic distribution of the fossils, providing new materials of biological diversity during this critical interval. [ABSTRACT FROM AUTHOR]

Small shelly fossils (SSFs) are widely utilized for Cambrian biostratigraphy of shallow-water carbonates. The apparent linkage of SSFs to carbonate facies reflects an observational bias. Our study on the deeper siliceous facies of the Yangtze Craton in Zhejiang and Hunan provinces (China) reveals that SSFs also can be extracted from cherts. For this purpose a quick-etching method with weak hydrofluoric acid is applied. SSFs extracted from cherts are comparable with those from carbonates. Energy-dispersive X-ray spectroscopy analyses indicate a primary composition of SSFs of organic carbon and apatite. Hydrofluoric acid-processing can provide valuable biostratigraphic data of SSFs that are complementary to standard methods. [ABSTRACT FROM AUTHOR]

• The oldest radiolarian fossils were recovered. • Most of the radiolarians are related with the order Spumellaria. • Early morphology of radiolarians is multilayered spherical without spicule(s). • Molecular appearance of radiolarian was estimated deep in Neoproterozoic. • Advent of radiolarians brought biogenetic influence into silica cycle and sediment. Radiolarian, as a group of siliceous skeleton-bearing heterotrophic protist, has a long history from modern ocean back to the Cambrian. The earliest stage in the evolution of radiolarians, although poorly understood, is important not only for itself but also with respect to the development of the global silica cycle and biogenetic siliceous sediments. It has been hypothesized that radiolarians evolved from an ancestral form constructed by spicules, although this is not without controversy since origin and their early morphology is still in dispute. However, the record of Cambrian radiolarians, especially the early Cambrian, is still sparse. Here we report a research in chert of the Liuchapo Formation from the latest Ediacaran to early Cambrian in South China that yielded the most probable oldest radiolarians from deep-water settings. Accompanied fossils and stratigraphic correlation indicate a Fortunian age. Judging by the prominent concentric multilayered shell and absence of spicules, the fossils were classified into the order Spumellaria according to the advance of radiolarian taxonomy and phylogeny. They can be compared with radiolarians from Series 2 to Furongian of the Cambrian. Molecular study conducted here also supports the existence of spumellarian during the Cambrian. Together with other reports of Cambrian radiolarians in recent years, the occurrence of non-spicule forms predates the ones constructed by spicules, which do not support the previous assumption about primitive radiolarian. The discovery not only added to the sparse fossils record of the Cambrian radiolarian, but also demonstrated their contribution to silica cycle and siliceous sediments. Evolution of early radiolarians still subjects to open discussion and awaits more evidence. [ABSTRACT FROM AUTHOR]

The Early Phanerozoic witnessed one of the most important events in Earth history - the Cambrian Explosion. There is also a consensus that at roughly the same time oceanic dissolved silicon (DSi) concentrations decreased from close to saturation to somewhere below saturation. Yet the timing and magnitude of the putative DSi decrease, and any relationship with biological innovations, remain poorly known. Here, we study the widespread chert formed during the Ediacaran-Cambrian transition (ca. 551-522 Ma) on the Yangtze Block, South China. Major and trace element geochemistry suggest the silicon for the chert is predominantly sourced from seawater, and most likely precipitated via adsorption on organic matter and uptake by silica-secreting organisms. New and compiled silicon isotope data from seven sections spanning the E-C boundary show an increase in divergence of δ 30 Si values at ca. 533 Ma. Using mass-balance arguments, we interpret this as evidence that the radiation of siliceous sponges and radiolarians contributed to a substantial (ca. 80%) decrease in oceanic DSi concentrations, which is corroborated by fossil records and simple box-models. Reduced oceanic DSi may reduce the effort needed to maintain intracellular Si concentrations below the level at which harmful Si precipitation in organismal cytoplasm occurs. This energy can be reallocated to other metabolic pathways of new functional types, potentially the establishment of suspension-feeding communities that triggered Phanerozoic-type mixground ecology. Therefore, the early appearance of silicifiers (∼540-530 Ma) may have made conditions more favorable for the main stage (∼520 Ma) of Cambrian Explosion in functional and ecological diversification. • Silica for the Ediacaran-Cambrian cherts derives mainly from seawater. • Silicon isotopes suggest the radiation of biosilicifiers drove a decline in ocean dissolved silicon in the early Cambrian. • A box-model suggests the degree of the dissolved silicon drawdown is high (ca. 80%). • The removal of silicon toxicity may have promoted the main stage of Cambrian Explosion. [ABSTRACT FROM AUTHOR]