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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]

Sedimentary organic matter (OM) is a major reservoir of organic carbon in the global carbon cycle. Despite many studies, there still exist many debates on the mechanism of OM accumulation and preservation in marine sediments. We present a new field study of a Lower Cambrian shallow marine shelf sequence in the northern edge of the Yangtze Plate, China. Our results show that palynological OM and biogenic silica (Bio-Si) could be used alongside more conventional redox and paleo-productivity proxies to study the distribution of OM in marine sediments. The qualitative and quantitative study of palynological OM provides more detailed information on the nature of sedimentary organic carbon, which can be helpful in the assessment of primary productivity and OM preservation. In addition, the presence of Bio-Si stimulates the physical preservation of OM. Further analysis indicates that an increase in Bio-Si can promote OM preservation. This case-study provides insight into the intertwined factors controlling OM accumulation in the Early Cambrian. [ABSTRACT FROM AUTHOR]

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]

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]

Sponges are the earliest metazoans, and according to molecular-clocks, have a deep history back into the Cryogenian. However, the record of their biomineralized elements below the Ediacaran-Cambrian Boundary has been controversial. Here we present the first and earliest indisputable record of hexactinellid spicules in the lowest Cambrian, Terreneuvian, below the small shelly fossil Anabarites trisulcatus – Protohertzina anabarica assemblage zone (Zone I). Spicules recovered from cherts of the lowest Yanjiahe Formation in the Yichang, Hubei province, South China, include monaxons, diaxons, triaxons, and that are all siliceous in composition. This earliest record of silica biomineralization by filter feeding metazoan suggests sponges have contributed to the cycling of silica in the oceanic system as early as the beginning of the Phanerozoic. These results, along with a review of previously reported sponge occurrences, suggest a two-step evolution on sponges of the early Cambrian. [ABSTRACT FROM AUTHOR]

The Changning-Menglian belt, distributed over southwestern Yunnan Province in Southwest China, contains oceanic rocks that are considered to be remnants of the Paleotethys. This study observed Triassic siliceous rocks of the Muyinhe Formation in the Changning-Menglian belt and analyzed their geochemistry. The samples have high concentrations of SiO (81.65 wt.%-88.38 wt.%; average: 84.99 wt.%±2.14 wt.%). Most of the samples were plotted in the non-hydrothermal field on the Al-Fe-Mn diagram. Most of the samples were plotted in the continental margin field on the FeO/TiO-AlO/(AlO+FeO) and (La/Ce)N-AlO/(AlO+FeO) diagrams. Moreover, the samples show a flat REE (rare earth element) pattern normalized to NASC (North America shale composite). These geochemical results, in addition to the lack of rhythmical bedding of the siliceous rocks, strongly suggest that the siliceous rocks are unlikely to represent pelagic deposits. Although previous studies have suggested that the siliceous rocks are pelagic deposits, the present results indicate that the extent of the pelagic ocean basins in the Paleotethys during the Triassic is probably less than previously believed. These non-pelagic deposits may represent the closure stage of the Paleotethys. [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]

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]

The Ediacaran-Cambrian transition was one of the most significant intervals in geological history, witnessing the origin of the metazoans and major environmental changes. Establishing a precise chronostratigraphic framework for the Ediacaran-Cambrian transition has great significance for understanding the geological and evolutionary processes during this transition. An integrated study on carbonate carbon isotopes and U-Pb zircon dating was conducted within the Liuchapo Formation in the Sifangjing section in northeastern Guizhou Province, South China to recognize the Ediacaran-Cambrian boundary in slope facies of the Yangtze Block. A substantial negative carbonate carbon isotope excursion was recognized within the lower part of the Liuchapo Formation. Moreover, a weighted-mean U-Pb zircon age of 540.7 ± 3.8 (±6.6) Ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion. The carbon isotope and age-dating results indicate that the Ediacaran-Cambrian boundary within the Sifangjing section should be placed in the lower part of the Liuchapo Formation. Additionally, in the Sifangjing section, a distribution of Horodyskia minor extends up to the basal Cambrian, while the last appearance datum (LAD) of Palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the Liuchapo Formation. This relationship indicates that the LAD of the Palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the Ediacaran-Cambrian boundary successions in slope and deep-water basin settings of the Yangtze Block. • New carbonate δ13C dataset from slope facies of the Yangtze Block • The δ13C dataset shows a negative excursion within the Liuchapo Formation. • The absolute age of the negative δ13C excursion is about 540.7 ± 3.8(±6.6) Ma. • The Palaeopascichnus jiumenensis can be used to identify the E-C boundary. [ABSTRACT FROM AUTHOR]

Biogenic silica is a powerful palaeoproductivity proxy in palaeomarine environments and is significant within shale gas reservoirs, demonstrating the association of marine hydrocarbon source rocks with the abundance of micro-siliceous fossils, yet detailed studies that investigate this strong alliance in the Ordovician-Silurian transition are still lacking. The bulk of TOC in marine sediments is commonly assumed to have been derived predominantly from marine phytoplankton, with modern ocean surveys indicating good correspondence between silica content and primary productivity. This study discovers a strong positive correlation between biogenic silica (Bio-Si) and TOC in the Upper Ordovician-Lower Silurian Wufeng and Longmaxi formations of South China in the Jiaoye 41-5 (R = +0.68, p(α) < 0.01, n = 69) and Jiaoye 51-2 (R = +0.68, p(α) < 0.01, n = 48) cores, implying that enhanced marine productivity has a strong effect on organic carbon enrichment. Geochemical and palaeontological analyses revealed that silica within these shales generally had a biogenic origin in Jiaoye 41-5 and Jiaoye 51-2, subsequently modified by silica dissolution and re-crystallization of radiolarians and sponge spicules. Palaeoproductivity proxies, including biogenic silica, barium, phosphorous, copper and nickel, were applied, together with the occurrence of pyritized or "ghost" radiolarians, to confirm high palaeoproductivity in the O-S transition. Synchronous OCAR and Bio-SiAR profiles imply that silica originating from siliceous organisms (Bio-Si) served as a likely vector for organic carbon enrichment in the Palaeozoic Wufeng-Longmaxi marine siliceous source rock, providing two possibilities: (i) the abundance of radiolarians was linked to algal proliferation, and consequently, high productivity resulted in a large organic carbon flux and/or (ii) radiolarians contributed to TOC (supported by studies revealing that modern radiolarians exhibit lipid contents of up to 47%). • Wufeng-Longmaxi marine shales display five stages on the basis of TOC enrichment. • Stage II- upper Wufeng and Stage IV- lower Longmaxi exhibit large amounts of TOC. • Established evidence of biogenic origin of silica in the studied area. • High R co-efficient confirms a significant link between Bio-Si and TOC enrichment. • Radiolarians unconventionally contribute to TOC enrichment along with phytoplanktons. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) mass extinction, the most severe biocrisis in Earth's history, is thought to have been triggered by catastrophic volcanic activity. PTB sections in South China contain numerous volcanic ash beds, the source of which is inferred to have been either the Siberian Traps Large Igneous Province (STLIP) or intraregional subduction-zone arc volcanism. In this study, the provenance of these ash beds is determined through a comprehensive analysis based on the geochronological and geochemical signatures of zircons from four PTB sections (Dongpan, Xinmin, Ganxi and Shangsi). Inherited zircons yielded U–Pb ages of 250–3521 Ma with major age clusters in the Permian, Carboniferous to Silurian, early Cambrian to Neoproterozoic, early Neoproterozoic to late Mesoproterozoic, and early Paleoproterozoic. The age spectrum of these zircons is similar to those of detrital zircons from sedimentary and magmatic rocks of the South China and Indochina cratons but different from those of the Siberian Craton, providing evidence for an intraregional source of the volcanic material. The trace-element, εHf(t), and δ18O signatures of syn-depositional magmatic zircons are consistent with an arc-related/orogenic setting. PTB sections in South China can be assigned to sectors based on the number and cumulative thickness of ash beds and the length of zircon crystals. Sector I (South) includes the Dongpan and Xinmin sections, which have cumulative ash-bed thicknesses of 0.86–1.14 m and average zircon lengths of 151–217 μm. Sector II (North) includes the Ganxi, Shangsi and Daxiakou sections, which have cumulative ash-bed thicknesses of 0.17–0.33 m and average zircon lengths of 82–104 μm. Sector III (Northeast) includes the Niushan and Meishan sections, which have cumulative ash-bed thicknesses of 0.1–0.14 m and average zircon lengths of 71–73 μm. Systematic trends toward fewer and thinner ash beds and as well as smaller zircon sizes from Sector I to Sector III indicate a paleo-northward or -northeastward direction of ash transport. Collectively, our findings provide evidence that the source of volcanic ash in South China PTB sections was intraregional subduction-zone arc volcanism along the convergent margin between the South China and Indochina cratons. Highlights • Investigation of source(s) of volcanic ash in Permian-Triassic Boundary beds of 4 deepwater sections across South China • Geochemical signatures of syn-depositional magmatic zircons indicate an arc-related/orogenic setting. • Zircon U–Pb age distributions consistent with ash sourced from South China or Indochina cratons but not the Siberian Craton • Spatial variation in total ash bed number and thickness and in zircon crystal size indicates ash sourced from paleo-south. • Most likely ash source was subduction-zone volcanism along the South China-Indochina convergent plate margin. [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]

• Microbial mats from the Jixian Group, North China were systemically investigated and three types of them were recognized. • Five kinds of sedimentary structure which were built by or related to microbial mat were recovered. • Bottleneck structures and bubble structures have been recovered and studied for the first time. Microbial mats were well established and widespread during the Proterozoic eon, playing a pivotal role in atmospheric oxygen content. In this study, microbial mats were systematically investigated from the 1600 Ma to 1400 Ma Jixian Group, North China. Three types of microbial mats were recognized, including Microbial Mat dominated by Filaments (MMF), Microbial Mat dominated by Coccoids (MMC), Microbial Mat dominated by Filaments and Coccoids (MMFC). These microbial mats were mainly built by Siphonophycus kestron , Siphonophycus solidum , Myxococcoides sp. and Coniunctiophycus majorinum. Due to in situ preservation, five sedimentary structures related to photosynthesis and oxygen release were discovered in these microbial mats. The alternating light-dark laminae and bottleneck structure may be caused by immediate mineralization and phototropism of filaments in a hypersaline environment. Bubble structure, fenestrae structure and hourglass structure probably were related to oxygen release, and their emergence fill the gap between oxygenic photosynthesis of microbial mat and atmospheric oxygen content in Proterozoic eon. [ABSTRACT FROM AUTHOR]

The Ediacaran-Cambrian (E-C) transition witnessed significant ecosystem perturbations of the oceanic environment (e.g., oxygen concentrations of seawater) and biological evolution. However, in spite of abundant Ediacara-type megafossils, trace fossils, small shelly fossils (SSFs), macroscopic algae and metazoans recovered from shallow-water E-C transition strata throughout South China, the manifestation of geological events in deep-water settings remains elusive. Here, we present new paleontological and geochemical evidence from the ~38-m-thick deep-water Liuchapo Formation (ca. 551–523 Ma) of the Yangtou section, northeastern Guizhou Province, China, which consists mainly of chert through the E-C transition. The Liuchapo Formation can be divided into two members based on biostratigraphy and redox proxies. The lower member (0–32 m) is characterized by low Mo/Al (0.15–1.82 ppm/%) and U/Al (0.47–2.51 ppm/%) values that suggest deposition under suboxic conditions. These deposits are dominated by Horodyskia minor , Paleopascichnus jiumenensis , spherical cyanobacteria (? Myxococcoides) and random acritarchs. The upper member (32–38 m) records a transition to anoxic (non-sulfidic) conditions as suggested by marked increases in Mo/Al (5–47 ppm/%) and U/Al (8–810 ppm/%). The upper member contains SSFs, sponge spicules, filamentous cyanobacteria, multicellular algae and sheet-like fossils. The survival of diverse organisms under strongly reducing conditions reflected in the upper member suggests that, marine redox fluctuations may limit the growth of Late Ediacaran organisms and provide the living space and elevated nutrients for early Cambrian biota. • Organismal shifts and redox condition variations during the Ediacaran-Cambrian transition • Flourishing multicellular organisms are reported from the upper Liuchapo Formation. • Geochemical proxies confirm the studied chert is of seawater origin. • Diverse organisms may have survived under oxygen-depleted condition. • Marine redox fluctuation was important for the biotic turnover. [ABSTRACT FROM AUTHOR]

In recent years, significant progress has been made in organic-walled microfossil research from the Paleozoic of China. In the present study, all palynological investigations from the Cambrian of China, including thin sections, are reviewed and a synthesis of the organic-walled microfossil record is presented. The stratigraphic ranges of the organic-walled microfossils for each geographical region of China are listed in chronological order according to the most recent international stratigraphic chart. The compilation reveals that 99 genera and 276 species of organic-walled microfossils have been documented so far. The localities of the investigated areas are mostly on the Cambrian Jiangnan slope and basin and the north continental shelf of the Yangtze plate, where the Ediacaran–Cambrian transition has been largely discussed. The compilation points out that some geographical areas and some stratigraphical intervals remain relatively unstudied. Further research on these intervals and areas needs to be carried out to fill some of the gaps in the record. The data from the literature on organic-walled microfossils in China are added to the previously published dataset of global acritarch diversity. The higher diversities in the early Cambrian Fortunian stage and Stage 2 in China point to a global diversification up to a diversity peak around the late early/early middle Cambrian reported in previous studies. The latest Cambrian diversification rise in China confirms the onset of the Ordovician plankton revolution. • All data on Cambrian organic-walled fossils from China have been reviewed. • All stratigraphic ranges are made in chronological order and for each region. • Most data are reported from the South China Plate. • The data complete the formerly published dataset of global acritarch diversity. • The Chinese Cambrian data were largely ignored in former international studies. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations. Highlights • Eight genera and twenty-five species (belong to four forms) of acritarchs were record from eight sections in South China. • Two extinction events for the acritarchs across the Permian-Triassic transition. • The second event were more severe than the first one. This may result from the different causes for the two events. [ABSTRACT FROM AUTHOR]

Lower Cambrian assemblages of phosphatic and chitinous tubular fossils of probable cnidarian affinities were recovered from the Yanjiahe, Shuijingtuo and Shipai formations in the Three Gorges area, South China. Terreneuvian Cambrorhytium cf. C . major co-occur with an unnamed taxon in the Yanjiahe Formation. They can be compared with specimens from the Ediacaran Miaohe Fauna in the Three Gorges area. The most abundant and diversified cnidarian assemblages, including Cambrorhytium gracilis n. sp., Cambrorhytium cf. major , Cambrorhytium minor , Sphenothallus songlinensis , Sphenothallus taijiangensis ?, Sphenothallus kozaki , ? Sphenothallus sp., ? Byronia sp., and ? Mackenzia sp. are reported from the overlying, Cambrian Stage 3–4, Shuijingtuo and Shipai formations. These new fossils show previously unknown evidence for cnidarian affinities, such as an attachment disk, clonal clusters and probable budding structures. These diversified assemblages of probable cnidarian fossils further fill major gaps in the Cambrian record of stem metazoans and document associated early evolutionary patterns. In addition, our discovery suggests that along with sponges, these tubular fossils represent another important component of benthic ecosystems that colonized often dysoxic, deep-settings during the Cambrian explosion. The observed increases of average body-size and biomineralization among these probable cnidarians are tentatively linked to oxygenation of deep oceanic settings and appearance of predatory pressure during the Ediacaran–Cambrian transition, respectively. [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]

Records of more than 20 Permian-Triassic Boundary (PTB) sections from South China show that widespread end-Permian regression took place in whole South China. Timing of the low ebb of this regression was pinpointed to the Clarkina meishanensis and Hindeodus changxingensis zones. Biostratigraphic and paleogeographic studies at conodont zonation level reveal that the Yangtze Carbonate Platform and isolated small carbonate platforms in the Hunan–Guizhou–Guangxi (HGG) Basin experienced sedimentary hiatus during these two zones which lasted about 50–100 kya. Meanwhile the basinal areas, namely the Northern Marginal Basin of Yangtze Platform and the Hunan–Guizhou–Guangxi Basin, have continuous conodont zonation with silicious and ashbed deposits. The basinal areas show two negative δ 13 C shifts during the PTB interval from Clarkina yini zone to Isarcicella isarcica zone, while on the platforms there is usually only one negative shift because the early shift at C. meishanensis zone was lost during hiatus. The end-Permian regression and successive rapid transgression taking place at the PTB casted important effects to the pattern and process of the PTB mass extinction. The depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction. [ABSTRACT FROM AUTHOR]

Abstract: The Late Paleoproterozoic to Early Mesoproterozoic (from ∼1700 Ma to ∼1300 Ma) was highlighted by the assembly of the Nuna supercontinent, expansion of euxinic marine environments and apparent stasis in the diversity of eukaryotes. The isotopic composition of carbonate carbon (δ 13Ccarb) was surprisingly constant during this interval, but little is known about the secular variation in the organic carbon isotopic composition (δ 13Corg). Here we report δ 13Corg data from the latest Paleoproterozoic (>1650 Ma) to Early Mesoproterozoic (∼1300 Ma) succession in North China. The δ 13Corg values range from −25‰ to −34‰, and are dependent on sedimentary facies. In subtidal and deeper environments δ 13Corg values are low and constant, ca. −32‰, but relatively enriched and more variable in shallower intertidal and supratidal environments. We attribute the facies-dependent variation in δ 13Corg to the presence of a shallow chemocline. A probable result of a shallow chemocline is that it supported significant contributions of organic matter produced by chemoautotrophic and/or anaerobic photoautotrophic microbes in relatively deep environments from the latest Paleoproterozoic to Early Mesoproterozoic continental shelf of North China. [Copyright &y& Elsevier]

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]

Our understanding of the early Cambrian bioradiation is largely driven by the contrasting information obtained from small skeletal fossils (SSF) and various types of exceptionally preserved fossils from different parts of the world. In this study, a new 'Orsten'-type fossil Lagerstätte is reported from the Cambrian Series 2 upper Shuijingtuo Formation in the eastern Three Gorges area, South China. The Shuijingtuo Formation yielded a range of microscopic fragments of metazoan cuticles as well as fragments of possible epithelial tissue. Seventeen different types of micro-ornamentation patterns are recognized on the surface of these cuticular fragments. Based on comparisons with fossil organisms recorded from coeval strata elsewhere, as well as extant relatives, possible affinities with arthropods, palaeoscolecids, acrotretid brachiopods and mollusks are discussed. This 'Orsten'-type fossil assemblage was deposited in offshore environments, and the lack of evidence for long-distance transportation indicates that a highly diverse fauna was present in, or very close to, the relatively deep shelf settings in the Three Gorges area during the early Cambrian (Epoch 2, Age 3). The invasion of metazoans into deeper, offshore environments could have closely followed, or even been coeval, with their radiation in relatively shallow water settings. Thus, albeit highly fragmented, such cuticular fossils can aid in providing a more complete picture of the Cambrian bioradiation. [Display omitted] • 'Orsten'-type fossilisation is reported from the Cambrian Shuijingtuo Formation, China. • Seventeen types of micro-ornamentation patterns are recognized. • Large scale metazoan invasion of offshore environments already started by Cambrian Age 3. [ABSTRACT FROM AUTHOR]

• Fe-S-C-trace elemental analysis was conducted for Tonian Luotuoling Fm. • Redox proxies yielded conflicting redox signals for fossil-bearing intervals. • Redox interpretations are contrasting for fossil- and non-fossil-bearing intervals. • The unique redox data can be best explained by benthic oxygen oasis hypothesis. • Our findings inform Neoproterozoic biogeochemistry and eukaryote evolution. Benthic oxygen oases linked to photosynthetic mats have been reported in modern anoxic aquatic systems. Benthic macroalgal blooms were common in stratified, anoxic Neoproterozoic oceans, leading us to hypothesize the existence of benthic oxygen oases at that time. This hypothesis has significant implications regarding the bioavailability of transition metals (e.g., Cu, Zn, Ni, Mo, V) and the distribution of aerobic eukaryotes in these oceans. However, little research has been directed toward testing the benthic oxygen oasis hypothesis in ancient anoxic marine systems. In this contribution, we report on an integrated investigation of iron speciation, trace elements, and carbon–sulfur-δ34S py for the Tonian Longfengshan Biota-bearing versus non-fossil-bearing shales of the Luotuoling Formation in the Longfengshan section of the Yanshan Basin (North China). Typical marine B/Ga values (6.5–7.3) suggest that the Yanshan Basin was fully marine and well connected with the open ocean. The low Fe HR /Fe T ratios of the non-fossiliferous intervals (mean 0.14) suggest oxic water-column conditions during their deposition, and their Fe HR pool contains significant amounts of pyrite and siderite (up to 44%), implying their formation in underlying reducing sedimentary porewaters. In contrast, the fossil-bearing layers show high and oscillating Fe HR /Fe T ratios (mean 0.39; up to 0.51) and systematically low Fe py /Fe HR (mean ~0), suggesting dominantly ferruginous water-column conditions with redox oscillation. Furthermore, lack of redox sensitive trace-metal and sulfide enrichments and dominance of the Fe HR pool by ferric oxide and magnetite (96–100%) indicate substantially oxidative power in the reducing water-column and underlying surface sediments. In combination with coexisting sedimentological and paleontological data, these conflicting and contrasting redox signals can be best interpreted by the development of benthic oxygen oases in deeper reducing waters, regulated by the Neoproterozoic benthic macroalga Longfengshaniaceae most likely in association with microbial/cyanobacterial mats, which contributed the oxidative power in the reducing environments. Our findings provide new insights into early Neoproterozoic oceanic redox conditions, iron cycling and the evolution of early aerobic eukaryotes, including animals. [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]

The rise of siliceous organisms is generally considered to have driven the abrupt decrease of silica in the ocean during the Ediacaran-Cambrian (E-C) interval, even if the exact timing and biological triggers of this event are still debated. Although Ediacaran-Cambrian chert depositions are widely distributed, multiple evidences converge to support their hydrothermal origin. In this study, we provide petrographic study supplemented by elemental concentration, SEM and Raman spectral data on the siliceous rocks from the Yanjiahe Formation (the Three Gorges area, South China), in order to ascertain the origin of included silica and discuss the involved processes of silica deposition. Contrary to most previous studies, our analyses suggest that studied cherts mainly resulted from biogenic silica, and subsidiary from abiotic precipitation influenced by surrounding hydrothermal activity and from detrital input. The deposition model of silica includes direct deposition of siliceous bioclasts, secondary replacement of carbonate by dissolved biosilica, and microbial induced silicification from seawater. The sink of silica recorded in the Yanjiahe Formation was characterized of a transition from typical Precambrian to Phanerozoic process. In addition, micropalaeontological and taphonomical analyses of the Yanjiahe Formation revealed two pulses of microfossil abundance and diversity in the Fortunian and Stage 2, respectively. They can be correlated with a regression and an enrichment in dissolved phosphate that probably derived from enhanced detrital flux. • Silica source in chert of the Yanjiahe Formation is mainly biogenic. • Silicification process was discussed in the Yanjiahe Formation. • Two pulses of blooming of microfossils are recognized in the studied chert. • Varied sources of silica from different settings in the Yangtze Block are discussed. [ABSTRACT FROM AUTHOR]

• We document sponge spicules from Ediacaran-Cambrian boundary interval. • Earliest spiculites are reported here in the lower Yanjiahe Formation. • Geochemical signal confirms the studied chert is mainly of biogenic origin fixed by sponges. • Ecosystem engineering by sponges was probably an important trigger for the first establishment of modern-type ecosystems. • Taphonomy may have affected morphology of spicules and their scarcity in Precambrian. The lack of unequivocal sponge fossils before the Cambrian despite their probable deep origin during the Cryogenian period has been a conundrum to geologists. Their impact on the dramatic evolution of ecosystems and the seawater silica cycle during the Ediacaran-Cambrian (E-C) transition is also speculative. In this study, abundant sponge spicules and spicule-like structures that probably represent original sponge fossils were recovered from four sections of the E-C boundary interval in the Yangtze Gorges, South China. The paleontological and geochemical data presented herein provides evidence for a continuous distribution of relatively abundant sponge spicules, some even forming spiculites, as well as the earliest biogenic deposition of silica by metazoans in the Ediacaran-Cambrian boundary interval. These results further confirm that a biological takeover of oceanic dissolved Si co-occurred with the evolution of silica biomineralization in the E-C interval, resulting in the widespread deposition of biogenic chert. Hydrothermal input in spicule-bearing cherts is also observed. Such hydrothermal activity might have favored the blooming of sponges through significant nutrient supply. These results provide the first conjunction of geochemical and paleontological proxies in support of previous models considering that sponges, by ventilation, filtration and oxygenation of seawater, were important ecosystem engineers of the E-C bioradiation event and of the related establishment of modern-type ecosystems. [ABSTRACT FROM AUTHOR]