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The Changning-Menglian suture zone is a critical tectonic belt pivotal to the evolution of the Paleo-Tethys. The Wenquan Formation, characterized as turbidite deposited on the western side of the Changning-Menglian suture zone as well as the eastern edge of the Baoshan Block. Analysis of detrital zircons from the Wenquan Formation reveals two significant age peaks approximately at 440 and 980 Ma, with additional age populations around 600, 780, and 2 500 Ma. The major age peak at about 440 Ma is come from the andesitic-dominant volcanic arc within the Lancang Block and the western Simao Block, corroborated by the presence of andesite fragments in thin section studies. Meanwhile, the zircons that form the secondary age peak at ∼980 Ma and other older age groups probably originate from the Baoshan Block. Deposited on the western side of the Paleo-Tethyan ophiolites, the Wenquan Formation received detrital materials from the continental margin on the opposite side. Thus, the main Paleo-Tethyan Ocean basin was not sufficiently broad enough to cut off the transference of detrital materials. It was a relatively narrow basin in the Early Devonian. [ABSTRACT FROM AUTHOR]

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]

The Permian radiolarian zones and their correlations with conodont zones or other chronostratigraphic schemes are still under debate. In this study, four genera, 21 species and two subspecies of radiolarians together with one genus and six species of conodonts were recovered from the Linghao Formation cropping out at the Longwangpo (LWP) section, northwestern Guangxi, South China. Six radiolarian interval zones and one abundance zone are recognized in the section, namely in ascending order, the Follicucullus scholasticus, Albaillella cavitata, A. protolevis, A. levis, A. excelsa, A. triangularis Interval zones and A. yaoi Abundance Zone. They are correlated with the Clarkina dukouensis, C. guangyuanensis and C. orientalis conodont zones recognized at the same section. Based on our data, the F. scholasticus Interval Zone and the lowermost part of A. cavitata Interval Zone are recognized to be upper Capitanian age, whereas the four Albaillella Interval zones are of Lopingian age (Wuchiapingian to the late Changhsingian). Two previously known Changhsingian radiolarian zones, namely the A. triangularis and A. yaoi Interval zones, should be extended down to the uppermost Wuchiapingian in this studied section. [ABSTRACT FROM AUTHOR]

Sponges have great significance for understanding the origin and evolution of metazoans. Biomarker fossil and molecular clock studies suggest a Precambrian origin of sponges, but no unambiguous fossil of sponge spicules have been recovered from units older than the early Cambrian to date. Here, we report abundant siliceous spicules from Ediacaran-Cambrian transition strata, representing a deep-slope setting on the southeastern margin of the Yangtze Block in South China. The first appearance of monaxon spicules in the Sifangjing section is in the lower Liuchapo Formation (uppermost Ediacaran), from below the Basal Cambrian Carbon isotope Excursion (BACE), which is consistent with the timing of their initial appearance in shallow-platform settings (e.g., the Three Gorges area). These spicules are monaxons that are isolated or aggregated as spiculate bundles, the latter having a structural arrangement consistent with construction by demosponges. Polyaxial spicules first appear in phosphatic nodules of the basal Jiumenchong Formation (early Cambrian Stage 2). Relative to shallow-water settings, the appearance of polyaxial spicules in deep-water slope settings was delayed (∼10 Ma). Oxygenation of anoxic deep watermasses and increasing concentrations of dissolved Si in seawater during Cambrian Stage 2 may have facilitated the expansion of the Hexactinellida into deep-water settings. The triaene spicules from the basal Jiumenchong Formation are the oldest (∼522 to 525 Ma) Tetractinellida spicule fossils identified to date. • Sponge spicules were recovered from the Liuchapo Formation at Sifangjing section. • The first appearance of monaxons is near the Ediacaran-Cambrian boundary. • Polyaxial spicules appear in Cambrian Stage 2, marking evolution of Tetractinellida. • Siliceous sponges had an evolutionary tendency from monaxon to triaxon spicules. [ABSTRACT FROM AUTHOR]

• Spherical ministromatolite clumps in Mesoproterozoic dolostone. • Abundant microfossils within the organic matter surround the ministromatolite. • The unique silicification process favors the preservation of microfossils. • Biogenic and chemical process together contributes the formation of ministromatolite. Although the biogenicity of the very common millimeter-sized ministromatolites in the Proterozoic has been noted, direct biotic evidence is missing, leading to the discussion of a chemical origin that differs from that of the cyanobacteria-related stromatolites in the Phanerozoic. Distinctive ministromatolites were recently discovered in a microbial dolostone interval of the Mesoproterozoic Wumishan Formation, at Lingyuan, North China. Thin section examination of the ministromatolites reveals the presence of abundant coccoidal microfossils ranging 10–30 μm in diameter. Petrofabric analysis shows that the ministromatolites experienced three periods of diagenetic silicification, and that the microfossils are exclusively preserved within early diagenetic chert. This supports the view that silicification penecontemporaneous with mat growth is the key to unique preservation of microfossils. In contrast, the absence of microfossils in most Precambrian carbonate stromatolites may well be interpreted as the lack of hydrochemical conditions favorable for early silicification. Although chemically-formed fibrous carbonate minerals are the dominant components of these ministromatolites, the presence of abundant microfossils indicates that the role of microorganisms in the formation of ministromatolites has previously been underestimated. Therefore, this research suggests that Mesoproterozoic ministromatolites were not solely chemical products but consist of complex associations of both biotic and chemical fabrics. [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]

Ordovician-Silurian transition (OST) sections of South China contain extremely high mercury (Hg) concentrations (>1000 ppb) of uncertain provenance. The main hypotheses concerning their origin are: (1) contemporaneous elevated seawater Hg concentrations (e.g., due to volcanogenic inputs) combined with normal Hg-uptake processes by marine sediments, and (2) normal seawater Hg concentrations combined with enhanced Hg uptake by marine sediments (e.g., due to strong adsorption by sulfides). Here, we investigate Hg isotopes, which are a promising tool to track the sources of Hg in sediments, in OST strata of the Jiaoye drillcore from the Yangtze Platform of South China. Black shales and pyritic beds exhibit mass-independent fractionations of odd Hg isotopes (odd-MIF, i.e., Δ 199 Hg) of + 0.13 ± 0.05 ‰ and + 0.13 ± 0.03 ‰ , respectively. These values are similar to those of modern and ancient marine sediments, supporting a seawater source of Hg in the study units and providing evidence against a volcanic source. We infer that the extreme Hg enrichment of the OST beds was due to elevated rates of Hg uptake from seawater through adsorption to pyrite. Local environmental conditions (e.g., intense euxinia and microbial sulfate reduction) played a dominant role in Hg enrichment of OST strata in South China. • Hg isotope data for highly Hg-enriched Ordovician-Silurian boundary strata, China. • (Chalcophilic) Hg taken up by pyrite under anoxic bottomwater conditions. • Hg peaks around OSB were sourced from seawater, not from volcanic inputs. • Mass-independent fractionation (Δ 199 Hg = + 0.13 ± 0.03 ‰) supports seawater source. [ABSTRACT FROM AUTHOR]

The late Ediacaran Shuram Excursion (SE) records the most prominent negative δ 13C excursions (δ 13C = −12‰) during Earth's history. It has been hypothesized to have resulted from oxidation of dissolved organic matter, diagenetic or authigenic precipitates. However, the origin of the SE remains enigmatic; current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions. Here, we show that the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the SE event, contains mineralogical and geochemical signatures related to igneous processes. Both the occurrence of ankerite, feldspar, moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source. In particular, the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks. These observations suggest that the deep cycle of ancient carbonate rocks, which were subjected to decarbonation during subduction, melting and eruption related to the breakup of the Rodinia supercontinent, contributed to the SE. This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth. [ABSTRACT FROM AUTHOR]

• Major magmatic episodes in southwestern Yangtze at ca. 3.08, 2.85 and 2.36–2.32 Ga. • Northern and southwestern domains of the Yangtze show differences in crustal growth. • The two domains have independent evolutionary histories prior to mid-Paleoproterozoic. • The two domains share a common history during and after Nuna assembly. New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]

The Ediacaran-Cambrian (E-C) transition was a critical stage for the origin and evolution of early complex life on Earth. Because studies of E-C biotas and environments are relatively fewer for deep-water than for shallow-water facies, we undertook a systematic paleontological analysis of the E-C transition in the deep-water Liuchapo Formation at Longbizui, South China. Two sequential but distinct assemblages were recovered, namely the Lower Liuchapo Assemblage (LLA) and the Upper Liuchapo Assemblage (ULA). The LLA consists mainly of soft-bodied fossils, including Longbizuiella hunanensis gen. et sp. nov., Nenoxites jishouensis sp. nov., Nenoxites irregularis sp. nov., Nenoxites sp., Helanoichnus sp., Shaanxilithes ? sp. and tiny-sized spherical fossils. The ULA is dominated by skeletal organisms comprising the small shelly faunas (SSFs, mainly protoconodonts, hyoliths and Cambroscleritida), sponge spicules, and the first reported Poratusiramus xiangxiensis gen. et sp. nov. Biostratigraphic correlation support a latest Ediacaran age for the LLA, whereas the majority of the ULA belongs to the early Cambrian—thus the change from the LLA to the ULA coincided with the E-C transition. Our results suggest that, during the E-C transition, a biological revolution may have occurred in deep-water settings synchronously with the well-studied faunal turnover in shallow-water environments. At Longbizui, fossil abundance and diversity decreased gradually during the latest Ediacaran and recovered stepwise after the E-C transition. The deep-water fauna, including both benthic and pelagic members, developed a biomineralization ability during the E-C transition. As calcareous and possibly phosphatic skeletal organisms began to flourish in shallow-water environments, siliceous skeleton-forming organisms, represented by the spicule-bearing sponges, colonized the deep seafloor in great abundance. In addition, the siliceous spicules documented in this study record fast evolutionary development during the early history of sponges, one of the earliest-branching metazoan phyla. The evolution of spicules from monaxon to diaxon-triaxon and then to tetraxon and polyactinal forms, as well as their considerable increase in diameter and length, was achieved during the first SSF biozone. • First detailed study of deep-water fossil assemblages of Ediacaran-Cambrian age. • Deep-water fauna may have experienced a turnover during the E -C transition. • Patterns of biodiversity and abundance paralleled those of shallow-marine habitats. • Record of diversification of earliest sponges and other siliceous biomineralizers. • Utility of evolutionary sequence of sponge spicule types as biostratigraphic index. [ABSTRACT FROM AUTHOR]

• Accumulations of Cloudina are described from the topmost Dengying Formation in the Three Gorges. • An updated SIMS 206Pb/238U age of 540.6 ± 3.4 Ma is obtained from the upper Dengying Fm. • Bio-, chemo- and chronostratigraphical evidences suggest that the E-CB should be placed in the Yanjiahe Fm. Numerous issues remain concerning palaeobiology, palaeoecology, and biostratigraphy of Cloudina , an iconic tubular organism of the Ediacaran period. In this study, accumulations of Cloudina are described from the topmost bed of the Dengying Formation in the Baiguotang section of the eastern Three Gorges area, South China. The massive occurrence of Cloudina refutes any possibility of setting the Ediacaran-Cambrian boundary (E-CB) beneath the lithological transition between Dengying and Yanjiahe formations in this area. The age of the Cloudina aggregates is younger than 540.6 Ma based on a concordia 206Pb/238U age of 540.6 ± 3.4 Ma obtained from underlying upper part of the Baimatuo Member (Baiguotang section), which is consistent with the 539 Ma E-CB reported from southern Namibia. Combining fossil evidence provided by Asteridium–Heliosphaeridium–Comasphaeridium acritarchs and Anabarites trisulcatus–Protohertzina anabarica small shelly fossil assemblages and the Basal Cambrian Carbon isotope Excursion (BACE), we tentatively place the E-C boundary within the lower part of the Yanjiahe Formation, close to the BACE excursion located in the lower part of the Yanjiahe Formation in the southern Huangling Anticline. [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]