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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 Tethys orogenic belt in SW Yunnan constitutes a critical part of the expansive Tethys-Himalayan tectonic domain. The abundant, well-preserved geologic records make it an ideal area for studying the tectonic evolution of Proto- and Paleo-Tethys. In this paper, we focus on several major tectonic units in SW Yunnan and reconstruct the Tethyan evolution from the early Paleozoic to the early Mesozoic, based on stratigraphic, sedimentologic, and magmatic evidences. The recently discovered early Paleozoic Yunxian-Menghai ophiolitic belt in the Lincang Terrane situated east of the Changning-Menglian Belt represents the suture zone of the Proto-Tethys. The oceanic basin of Proto-Tehtys opened in the latest Neoproterozoic and subsequently began subducting in the late Miaolingian of the Cambrian (about 505 Ma). From the late Late Ordovician to the ealiest Silurian (about 450–442 Ma), the Proto-Tethys basin gradually closed resulting in the collision of the continental plates on both sides of the Proto-Tethyan ocean. The main collision stage occurred in the early Silurian (about 442–430 Ma) and the post-collision stage lasted from the mid-Silurian to the early Carboniferous (430–355 Ma). The earliest record of Paleo-Tethyan oceanic crust was generated in the late Devonian, and the ocean was then subducted in an eastward direction in the middle Late Carboniferous (about 310 Ma). The initial collision stage in the Paleo-Tethys took place at the end of the Permian (about 253 Ma), and the main stage of the collision persisted into the early Ladinian (about 253–238 Ma). This was followed by post-collision extension from the late Ladinian to the early Jurassic (ca. 238–196 Ma). We suggest that the opening of Paleo- Tethyan Ocean in SW Yunnan was a result of the extensional rift basin of the Proto-Tethys. Additionally, the activity of the Manxin mantle plume was likely a crucial factor in the rapid expansion of the Paleo-Tethyan Ocean. [ABSTRACT FROM AUTHOR]

The Huai Hin Lat Formation has a high-potential resource, and the Ban Nong Sai part was researched and sampled. To achieve this goal, petrographic analysis (kerogen types), geochemical analysis (total organic carbon content, TOC), vitrinite reflectance (Ro), and Rock–Eval (RE) pyrolysis were carried out in this study. According to the findings, types II, III, and IV were identified using a modified Van-Krevelen diagram because the higher mature source rock showing hydrogen index (HI) and oxygen index (OI) are continuously depleted and raised. However, microscopic observation describes macerals as primarily sapropelic amorphinite, therefore, type I is important. The TOC was determined to be between 1.90% and 7.06%, which is considered very good to excellent. The original total organic carbon (TOCo) was decided to use its maceral components to determine how to convert extremely mature TOC to TOCo. It varies between 5.13% and 10.74% and reaches a maximum of 57.21% which is comparable to TOC. At 0.82%–1.04%, 443–451 °C, 0.50%–38.10%, and 69.00%–99.59% are the vitrinite reflectance (Ro), maximum temperature (Tmax), production index (PI), and transformation ratio (TR), respectively. Late peak maturity refers to a mixture of oil and gas, whereas most TR ratios refer to the main gas phase. Similarly, the petroleum residual shows no indication of gas trapped at a volume of 6309.50 mcf/ac-ft. In summary, source rock potential was assessed within a suitable risk range defined by Tmax (445.70 °C), Ro (0.91%), TR (90.63%), TOC (8.15%), shale thickness (46 m), and kerogen type (type I). [ABSTRACT FROM AUTHOR]

The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock. However, hydrocarbon-forming organisms of these organic-rich shales was poorly understood. In this paper, the results of palynofacies analysis and hydrocarbon-forming organism characteristics of the Niutitang Formation from the Yangtze Block are reported for the first time, and the sedimentary environment is discussed in combination with geochemical data. Palynofacies analysis show that the organic matter (OM) of the Niutitang Formation is mainly composed of amorphous organic matter (AOM), with a small amount of structural organic matter (STOM) and palynomorphs (PL). The results of CONISS (stratigraphically constrained incremental sum of squares) cluster analysis show that the PL can be divided into three zones in the ascending order: Leiosphaeridia-Micrhystridium-fungal zone, algal bloom zone and fungal development zone, corresponding to three stages: transgression, high-stand and regression, respectively. The principal component analysis (PCA) shows that the main hydrocarbon-forming organisms include planktonic green microalgae or dinoflagellates that are related to Leiosphaeridia and Microcystidium. Palynofacies analysis and geochemical data show that the Niutitang Formation was deposited under anoxic or dysoxic condition which was favorable to the enrichment of organic matter. [ABSTRACT FROM AUTHOR]

The beginning of the Phanerozoic was marked by abundant phytoplankton, the occurrence of animals and a newly established ecosystem structure, which in turn, resulted in different modes of organic matter (OM) cycling and preservation. In this study, we present an integrated paleontological and geochemical study of the Lower Cambrian Yanjiahe and Shuijingtuo formations in the Three Gorges area, South China. Rock samples were analyzed for major and trace elements, in order to evaluate the marine productivity. Fossil samples were recovered using palynological methods, destructive analytical techniques, SEM analysis and thin section microscopy. The organic-walled microfossils in the investigated sections include marine microphytoplankton, linings of sponge spicules, small shelly fossils and some unnamed sheet-like and net-like microfossils (animal parts). Additionally, fecal structures and coprolites fossils were found. Three intervals in the Luojiacun Section were proposed to discuss the links among microfossil assemblages and their influence on OM cycling and preservation. We found that the marine microphytoplankton was the main source of OM in the investigated sections. The appearance of fecal structures groups and massive appearance of animals in the pelagic zone indicate a higher transfer efficiency of OM aggregates through the water column. Oxygenated conditions in the water-column would have led to a moderate to low preservation of OM, an effect which would have been further enhanced by the potential presence of bioturbators. Overall, our study reveals the contribution of various organisms to the sedimentary OM and highlights the links and feedbacks among microfossil assemblages, OM recycling efficiency and OM preservation in the tipping point of the Phanerozoic "new world". [ABSTRACT FROM AUTHOR]

Petrography and geochemistry analyzing Dat Yai section can describe paleoproductivity and past-redox condition. Paleoproductivity proxies consisted of AOM, phytoclast, TOC, excess SiO2, Ba/Al, and P/Al as high values through sections which similarly indicate high productivity. High productivity in Beds 3 and 27 showed lower peak TOC which is explained by poorer preservation. Lower productivity of Bed 18 showed a high TOC peak indicating good preservation. Paleoredox condition was evaluated using Ni/Co, U/Th, V/Cr, V/(V+Ni), Ni/V, and (Cu+Mo)/Zn. Values for V/(V+Ni) ranged from 0.67 to 0.85 exceeding the cutoff value of 0.46 for a reducing environment. The average value of V/Cr (2.07) exceeded 2.0 of anoxic. Bed 9 consisted of the highest peak of TOC that does not reflect the excellent preservation resulting from dominantly high paleoproductivity. Bed 21 exhibited lower productivity and lowest TOC which indicated a poverty-reducing effect. AOM and phytoclasts were supplied and kept in the benthic floor by extreme redox. Sediments became black shale which expelled oil and some gas. [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]

Radiolarians form an important part of the planktonic realm in the ocean of Early Paleozoic, but their origin and evolutionary processes has long been enigmatic. The ancestral representatives of radiolarians have been considered to belong to the order Archaeospicularia, whose unquestionable fossil records were dated back to the Middle Cambrian. Here we report ?Blastulospongia and unnamed spherical radiolarians in the Terreneuvian from the Yanjiahe Formation in Hubei Province, South China. Blastulospongia is an enigmatic siliceous microfossil genus, with affinities proposed amongst the radiolarian, sphinctozoan-grade sponges and uncertain protists. As for the newly discovered unnamed radiolarians, morphologically they possess latticed shell, spherical shape and are all small in size. Our discoveries support the idea that spherical radiolarians is an ancient representative, whose origin and diversification was probably much earlier than generally accepted. The hypothesis that the oldest radiolarians belong to the order Archaeospicularia needs to be re-examined. [ABSTRACT FROM AUTHOR]

The relationship between metazoan evolution and ocean-atmosphere oxygen levels has been extensively debated. Similarly, there is no consensus on the factors controlling the evolution of the marine redox landscape. The early Cambrian is a particularly critical time interval to examine, as there is a marked increase in metazoan body plan diversity and increased ecosystem complexity, but few constraints on marine redox conditions during this seminal interval. We present an assessment of early Cambrian marine redox conditions from the Luojiacun section in west Hubei Province (the upper Yangtze platform). There are low trace elements enrichments (U, Mo) in the Yanjiahe Formation followed by an abrupt increase in the overlying Shuijingtuo Formation. U-Mo systematics in the most metal-enriched samples suggest deposition under a weakly restricted offshore basin, which is consistent with previous studies. There is correlation between excess Ba (Ba xs ) and total organic carbon (TOC), suggesting a strong production control on organic matter concentration. Further, higher Ba excess in the Shuijingtuo Formation than the Yanjiahe Formation indicates dysoxic-oxic conditions in the Yanjiahe Formation is linked to lower productivity, and anoxic conditions in the Shuijingtuo Formation are linked to higher productivity. Although strong productivity controls on Proterozoic and Paleozoic marine redox conditions have been commonly invoked, we provide some of the first empirical evidence for this control on marine redox structure. More broadly, we find that excess barium coupled with redox proxies may provide useful constraints on the interplay between preservation and production controls on organic matter abundances in the Paleozoic successions. [ABSTRACT FROM AUTHOR]

On the basis of expanded documentation of complex fossils, early Mesoproterozoic has already been proven as an important Era for eukaryotic evolution. In order to portray the biological community of this critical era, we studied a new silicified microbiota from the ∼1560 Ma Gaoyuzhuang Formation in the classic Jixian section, Tianjin, China. In total, eighteen species have been recognized, four species have been identified informally and five species have been identified in open nomenclature. Similar to other Proterozoic microbial mat biota, the new microbiota is dominated by cyanobacteria filaments and coccoids as well. Potential eukaryotic microfossils, such as ornamented coccoids, filaments with flanges and terminal cell, were firstly recovered. Amongst them, filaments with flanges and conidia-like terminal cell probably were the earliest unidirectional growing multi-cellular organisms as well as the earliest phylogeny-resolved multicellular eukaryotes. Combined with increasing records of Proterozoic eukaryotes, these microfossils indicated that eukaryotes have evolved into a new level in Early Mesoproterozoic. [ABSTRACT FROM AUTHOR]

Relatively high-resolution clay mineralogical and chemical index of alteration (CIA) analyses were conducted on the terrestrial Lubei section in southwestern China, to gain a better understanding of the paleoclimatic/paleoenvironmental evolution on land during the Permian-Triassic transition (P-Tr transition). Clay-mineral species include illite-smectite mixed layers (I/S), illite, irregular chlorite-expandable mixed layers (C/E), chlorite, kaolinite, vermiculite, hydroxyl-interlayered mineral (HIM), and corrensite. CIA values are as high as approaching 100 in the Permian and show a gradual and subtle decrease towards the lowermost Triassic, where a sudden decrease to persistently < 60 occurs with only periodic positive excursions. Diagenetic alteration is important at the study section and include chloritization, illitization of smectite in the Permian-lowest Triassic, transformation of smectite to corrensite in the upper sampled Triassic and potassium-addition induced decrease of CIA values throughout the section. However, with the integration of climate-sensitive sedimentary features, paleoclimatic/paleoenvironmental information was extracted from both clay-mineral composition and CIA. The dominance of precursor smectite together with the occurrence of kaolinite, Gigantopteris -type flora and coal seams, indicates an overall warm and semi-humid to semi-arid climate for the Permian part, and a general drying-out trend is suggested by the gradual decrease and final disappearance upsection of kaolinite, Gigantopteris -type flora and coal seams, as well as decreasing CIA values. Chemical weathering decrease is minor up to the lowest Triassic, which is mainly manifested by the subtle decrease of CIA values and which is probably partly due to the augmentation by acidification as indicated by the presence of vermiculite and HIM clay minerals. The short-term lingering (preliminarily estimated as < 0.08 Myr) of relatively intense chemical weathering after the extinction event was followed by an abrupt drop of CIA values to < 60, which indicates the onset of a rapid and enhanced dry-out condition unfavorable for chemical weathering. In association with the general drying-out trend is an increase in climate periodicity and/or seasonality, which is manifested by increasingly prominent laminations, lithological alternation and intermittent large excursions of CIA values, suggesting a more complicated climate condition during the Early Triassic than previously recognized. While drying-out rather than acidification is suggested in this study to have been a killer agent to land plant at the Lubei section, the real relationship between environmental deterioration and the end-Permian mass extinction is still enigmatic and needs further investigation. This is the first relative high-resolution clay mineralogical and CIA investigation on a well-preserved and continuous terrestrial Permian-Triassic section. [ABSTRACT FROM AUTHOR]

A set of new U–Pb geochronological, elemental and Sr–Nd–Hf isotopic data is presented to constrain the formation age and petrogenesis of granites in SE Thailand, which are significant for understanding eastern Paleotethyan tectonic evolution and regional correlation in SE Asia. Six granite samples from the Chonburi, Rayong–Bang Lamung and Chanthaburi plutons yielded similar crystallization ages of 222–218 Ma. These granites can be geochemically classified into S-type (Group 1) and I-type (Group 2) granites. Both groups have similar chondrite-normalized REE and primitive mantle-normalized multi-element patterns but distinctly different Sr–Nd–Hf isotopic compositions. Group 1 is characterized by more enriched initial 87 Sr/ 86 Sr (i) ratios (0.7101–0.7272) and lower ε Nd (t) values (− 12.0 to − 13.2) compared with those of Group 2 with 87 Sr/ 86 Sr (i) of 0.7027–0.7053 and ε Nd (t) of − 0.6 to − 1.2. Consistently, zircons from Group 1 yield negative ε Hf (t) values of − 7.3 to − 27.4 and Mesoproterozoic or older Hf model ages (T DM = 1.53–2.63 Ga), distinct from those of Group 2 with positive ε Hf (t) values (+ 5.0–+11.3) and younger T DM (0.42–0.67 Ga). Group 1 granites mainly originated from ancient greywackes but Group 2 from juvenile mafic crust with the input of meta-sedimentary component. These data, along with available observations, synthetically indicate that these granites formed in the post-collisional gravitational collapse setting of the thickened crust in response to the assemblage of the Indochina with Sibumasu blocks. They linked northerly and easterly to the Late Triassic granitoids in NW Thailand and East Malay Peninsula related to the Paleotethyan tectonic regime, respectively. [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 Openness based on DEM emphasizes the terrain convexity and concavity. It facilitates the interpretation of detailed landforms on the Earth's surface. Compared with the layer stacking of ETM+ with less three-dimensionality and visualizability and with indefinite details of linear images in the deep cutting or deep covered region, the Openness is used for accurate interpretation of tectonic geomorphic units and linear structures. In this paper, the ETM+ images (741 RGB) and RRIM based on Openness combined with the field geological investigation are used to trace the escaping structure in SE Asia. The east boundary is Ailaoshan shear zone and the west boundary is Uttaradit-Dien Bien Phu fault, which together form the southwards extruding wedge block. The arc boundary surface of the southern Khorat Plateau is jutted to the north. The NW and NE sides of Khorat Plateau are traversed by Uttaradit-Dien Bien Phu fault and Thakhek-Da Nang fault, respectively, resulting in a blocked escaping structure. The SE margins of Truong Son structure belt and Song Ma structure belt are both arcs jutting to SE. These arc structures clamped by faults or related to the fault on one side indicating the material flow direction obviously, are the most specific manifestation of escaping structures. Moreover, these push units are extruded from south to north successively. [ABSTRACT FROM AUTHOR]

The Permian planktonic distribution is not well known, in contrast to other fossil distributions of nekton and benthos. Radiolaria are representative microfossils of plankton in the Permian palaeocean. This study compares both correlated radiolarian occurrences ( Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston) in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China. Pseudotormentus distributions are concentrated in the Panthalassa, whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys. The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins, indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys. In other words, this study infers the provincialism of Permian planktonic microorganisms. The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current. [ABSTRACT FROM AUTHOR]

Pyrite morphology, iron speciation, and pyrite sulfur isotope data from the Xiakou section (Hubei Province, South China) were integrated to explore oceanic environmental variations through the Permian–Triassic transition and their possible relations to the largest mass extinction in Earth history. High ratios of highly-reactive iron to total iron (Fe HR /Fe T > 0.6) and pyrite iron to highly-reactive iron (Fe Py /Fe HR > 0.7) together with a high abundance of small (mean diameter <5 μm) framboidal pyrite show that euxinic conditions existed in the late Permian (pre-extinction interval). High ratios of Fe HR /Fe T (mostly >0.6) along with lower values of Fe Py /Fe HR (<0.7) and more variable framboid content among samples indicate anoxic but dominantly ferruginous conditions punctuated by episodic euxinic events in the latest Permian to earliest Triassic (post-extinction interval). The largest fluctuations of these redox proxies are observed in the ∼1.0 m of strata directly overlying the first (latest Permian) extinction horizon, indicating unsettled marine environmental conditions marked by frequent perturbations during the ∼60-kyr interval immediately following the mass extinction. The two largest redox events at Xiakou coincided with deposition of volcanic ash layers that have been correlated with Beds 25 and 28 of the Meishan D section, each of which was associated with an extinction pulse (the first and second extinction horizons of latest Permian and earliest Triassic age, respectively). Thus, our observations document two pulses of oceanic environmental change during the Permian–Triassic transition, each associated with a faunal crisis and possibly triggered by contemporaneous volcanic activity. [ABSTRACT FROM AUTHOR]

The volcanic rocks from the Sayabouli area in northwestern Laos have been poorly studied. These volcanic rocks are traditionally mapped as the Permian-Early Triassic sequences on the geological map. One basaltic-andesite from the Sayabouli area yields a zircon U-Pb age of 237.7±1.7 Ma, suggesting a Middle Triassic origin. All basalt and basaltic-andesite samples from the Sayabouli area show depletions in HFSEs (e.g., Nb, Ta, Ti) and have high LILE/HFSE ratios, and exhibit the geochemical affinity to the continental arc volcanic rocks and are geochemically similar to the continental arc volcanic rocks from the Phetchabun belt in northeastern Thailand, suggesting a Late Permian-Middle Triassic continental margin in the Sayabouli area of northwestern Laos and Phetchabun area of northeastern Thailand. Our data indicate that the Phetchabun arc volcanic belt through the western Loei sub-belt can be linked to the Sayabouli area in northwestern Laos. [ABSTRACT FROM AUTHOR]

Radiolarians are usually abundant in chert sequences and they have thus been widely used for the biostratigraphy of deep-water sediments. However, there are many difficulties in the correlation of radiolarian biostratigraphic schemes with the standard conodont zones. In this study, 21 radiolarian species were extracted from the Gufeng Formation that crops out in the Luojiaba (LJB) section (western Hubei, China), together with 5 co-occurring conodont species. In this way, it is the first time that the Pseudoalbaillella globosa , Follicucullus monacanthus and F. scholasticus radiolarian zones can be directly correlated with the Jinogondolella nankingensis gracilis , J. aserrata and J. postserrata conodont zones. Accordingly, the 3 radiolarians zones are now firmly correlated with the Roadian to middle Capitanian interval (Middle Permian). [ABSTRACT FROM AUTHOR]

The Tibetan Plateau and western Yunnan are known to have formed by the amalgamation of Gondwana-derived continental blocks and arc terranes as a result of Tethyan subduction followed by continental collisions during the Paleozoic, Mesozoic and Cenozoic. The Devonian and the southern Lancangjiang zone, western Yunnan is a critical period and key region for studying the transformation between the “Proto-Tethyan” and Paleo-Tethyan oceanic systems. New geochemical data and LA-ICPMS U–Pb zircon ages of the Late Devonian volcanogenic sediments from the southern Lancangjiang zone in western Yunnan, SW China, are presented. The studied sedimentary rocks of the Nanguang Formation are volcaniclastic rocks with high volcanic lithic content (55–65%, mostly andesite, dacite, with some rhyolite and tuffs). Whole rock geochemistry, zircon trace elements and detrital modal analyses indicate derivation from a subduction-related magmatic arc. Three tuff samples yield Late Devonian weighted mean 206 Pb/ 238 U ages of 378 ± 4 Ma, 366 ± 5 Ma and 382 ± 8 Ma, suggesting a Late Devonian depositional age. 104 zircon U–Pb analyses on 104 zircon grains from two sandstone samples present extremely tight age clusters, mostly ranging from 380 Ma to 360 Ma. This indicates a single Late Devonian igneous source. A short transport distance and a high rate of denudation and deposition within an arc-related basin are considered likely for the tuffs and volcaniclastic rocks in this study. This implies the presence of an as yet unidentified Late Devonian magmatic arc in the southern Lancangjiang zone. The cryptic Late Devonian arc is likely to represent either a continuation of Late Ordovician–Late Silurian “Proto-Tethyan” subduction or the initial stage of the Paleo-Tethyan Lincang Arc and indicates that subduction of the Changning-Menglian ocean beneath the Simao/Indochina Block occurred in the Late Devonian. [ABSTRACT FROM AUTHOR]

The key to gaining a better understanding of Paleotethyan tectonic evolution is to determine the tectonic setting of the main suture/tectonic zones and their relationships in SE Asia. The Luang Prabang tectonic zone in NW Laos lies in the area that aligns with the Jinshajiang–Ailaoshan suture zone to the north and the Nan suture zone to the south. Correlations among them have been debated. Samples from a diabase dyke and coarse-grained basalt in the Luang Prabang tectonic zone yield zircon U–Pb weighted mean ages of 335.5 ± 3.3 Ma and 304.9 ± 3.9 Ma, respectively, suggesting that these mafic rocks formed in the Carboniferous rather than in the Permian, as previously inferred. The zircon in-situ ε Hf (t) values range from 11.6 to 13.3. Their initial 87 Sr/ 86 Sr ratios range from 0.70318 to 0.70522, and ε Nd (t) ranges from + 5.16 to + 6.93. The diabase samples have E-MORB-like characteristics with an addition of a subduction-related component, and the basalt samples were derived from the same type of source as N-MORB magmas newly modified by a slab-derived component. The ages of the mafic rocks along the Luang Prabang tectonic zone are similar to the mafic rocks from the Jinshajiang–Ailaoshan, Song Ma and Nan suture zones in SE Asia. A synthesis of available data suggests the development of a Carboniferous continental back-arc basin separating the Sukhothai Terrane and the Indochina Block. The Luang Prabang tectonic zone represents a remnant of a series of synchronous back-arc basins to the northeast of the Paleotethyan Main Ocean. It is proposed that the Luang Prabang tectonic zone links with the Nan suture zone to the southwest and with the Jinshajiang–Ailaoshan suture zone to the north. [ABSTRACT FROM AUTHOR]

The Middle Permian is a critical period when a possible cooling regime prevailed and massive deep-water cherty sediments were deposited in the South China Craton. An integration of radiolarian paleoecologic and geochemical studies from the Middle Permian Gufeng cherty succession of western Hubei Province, South China tests the relationships among oceanic productivity, redox conditions, and radiolarian responses as well as origin of the cherts. A total of 21 species and six undetermined species in 10 radiolarian genera are identified from the Gufeng Formation in the northern margin basin of the Yangtze Platform of the South China Craton. Three radiolarian Pseudoalbaillella globosa , Follicucullus monacanthus , and Follicucullus scholasticus zones were established and constrained the Gufeng Formation as Roadian to Middle Capitanian in age. The Gufeng cherts embrace a biologic and hydrothermal origin in the northern marginal basin and southern margin basin (the Nanpanjiang Basin) of the South China Craton, respectively. The high oceanic primary productivity in surface oceans resulted in the widespread reducing conditions in the bottom water column. Such high oceanic productivity event slightly predated the Middle Permian Kamura cooling event of the Panthalassian Ocean. Both the elevated continent weathering due to pre-eruptive crustal uplift of the Emeishan flood volcanism and active oceanic upwelling may have stimulated high oceanic productivity and facilitated the deposition of the Gufeng cherts. All radiolarians bloomed in relatively oxic conditions. Only shallow-water radiolarians, mainly spherical forms, proliferated in the reducing conditions, which also coincided with an enhanced oceanic productivity. The abundance of spherical radiolarians therefore is an ideal proxy indicating oceanic primary productivity. [ABSTRACT FROM AUTHOR]

The ~ 90% biodiversity loss among marine invertebrate species during the end-Permian mass extinction, the most severe Phanerozoic biocrisis, has been attributed to widespread oceanic anoxia (“superanoxia”). Recent studies of the lithofacies, inorganic geochemistry, and biomarkers of Permian–Triassic boundary (PTB) sections have yielded an inferred pattern of oceanic redox changes that is complex and sometimes inconsistent. In this contribution, we review the ecology of radiolarians, an important microzooplankton group during the Permo–Triassic transition, and consider its implications for contemporaneous changes in paleoceanographic conditions. Our analysis shows that (1) Late Permian radiolarian faunas were cosmopolitan with different orders having specific depth preferences, i.e., albaillellarians favoring deeper waters and spherical forms (entactinarians and spumellarians) shallower waters; (2) deep-water taxa declined earlier than shallow-water taxa; (3) many Paleozoic-type taxa survived into the Early Triassic but went extinct during a second crisis in the Dienerian (“dead clade walking”), followed by the appearance or expansion of Mesozoic-type taxa during the Olenekian; and (4) the survival of Paleozoic-type taxa during the Early Triassic was greater at higher paleolatitudes than in the tropics. These observations are consistent with a first-order redox control on radiolarian faunal distributions, specifically a shallowing and poleward expansion of the oceanic oxygen-minimum zone during the PTB crisis. The consequent adaptation of some deepwater taxa to shallower environments resulted in Early Triassic radiolarian faunas in continental basins becoming more similar to those in pelagic settings. Enhanced survival of Paleozoic-type taxa in high-latitude regions indicates that the main stressor on Permo-Triassic radiolarian communities was reduced oceanic oxygen levels (stronger in the tropics) rather than climatic warming (stronger at the poles). [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]

Abstract: The origin of radiolarians and their early evolution are of great interest for paleontologists and biologists. The needle-like or spicular construction of radiolarians represented by Order Archaeospicularia has been considered as an ancestor of radiolarians until Braun et al. (2007) discovered some radiolarians with latticed shells from the Early Cambrian in South China. The two radiolarian tests reported here were collected from the Shuijingtuo Formation corresponding to the basal part of Cambrian Series II, in South China. One of them is spherical, latticed, and similar to the radiolarians described by Braun et al. (2007). The other is grouped within the genus Kalimnasphaera formerly reported only from the Ordovician. The result indicates that the oldest known radiolarian fauna does not belong to Order Archaeospicularia. The hypothesis that Archaeospicularia is the representative of the oldest radiolarian group needs to be reexamined. Further investigation of early forms of radiolarians in the Early Cambrian or older strata is warranted. [Copyright &y& Elsevier]

The Yanshan Basin, located in northern North China, underwent three primary stages in the Mesoproterozoic, and corresponding biotas have been summarized for each stage in the present study. The three stages are stage A (the lower part of the Changcheng Group which dominated by clastic sediments), stage B (the upper part of the Changcheng Group to the Jixian Group which characterized by carbonate sediments), and stage C (the upper part of the Jixian Group which dominated by clastic sediments). This paper will focus on the evolution of biota during stage B. Microbiota of the stage B exhibits a high level of diversity and abundance. Planktonic microfossils have various forms and complex decorations. Most microfossils are generally small. In stage B, there was great variation in the biotic abundance and diversity, the average diameter of spherical benthic microfossils, and the maximum diameter of the spherical microfossils. We analyzed these parameters and identified two typical biotic events, and both biotic events were corresponded with geological events. The first event occurred in the third member of the Dahongyu Formation. In this era, the maximum diameter of the silicified microfossils significantly increased, and large, spherical planktonic specimens are abundant. The flourishing of large organisms in the strata is presumably related to volcanic activity. The second event occurred in the third member of the Gaoyuzhuang Formation. During this era, the microfossil assemblage changed significantly. The changes correspond with a decline in stromatolites as well as the transformations of the carbon isotope ratios and the elemental geochemistry. [ABSTRACT FROM AUTHOR]

Abundant siliceous micro-fossils were found from the Dalong Formation, Xinmin section, Guizhou, which include nine species of radiolarians belonging to seven genera as well as nine types of siliceous spongy spicules. The radiolarian fauna consists of all spherical radiolarians, without any species of Albaillellaria and Latentifistularia, indicating a relative shallow water sedimentary environment. The high relative co-efficient between the radiolarian abundance and total organic carbon (TOC) shows that the radiolarian assemblage represented by Copicyntra and Paracopicyntra can be used as a proxy to the paleo-productivity. However, the relative co-efficient between biogenic silica and the radiolarian and sponge spicule abundances is low. A possible explanation is that an oceanic circulation has changed the biogenic silica content after radiolarian test and siliceous spongy spicule were dissolved. [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]

Late Permian-Early Triassic (P-T) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO and KO and high AlO and NaO. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone. [ABSTRACT FROM AUTHOR]

On the basis of the petrographic characteristics, rock assemblages, petrochemistry, REEs, trace elements and geotectonic settings, the authors described the characteristics of continental marginal arc-volcanic rocks in the Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of the ocean-ridge/oceanic island basalts in the Chiang Mai belt. The volcanic rock assemblage is basaltic andesite-andesite-rhyolite. The volcanic series is dominated by the calc-alkaline series, with the tholeitic series coming next. The chemical composition of the volcanic rocks is characterized by high Al2O3; the REE distribution patterns are of the LREE-enrichment rightward incline type; the large cation elements are highly enriched, and the volcanic rocks are generally enriched in U and Th and depleted in Ti, Cr and P. The petrochemical plot falls within the field of island-arc volcanic rocks, in consistency with the projected points of continental marginal arc-volcanic rocks in the Lancangjiang belt. These continental marginal arc-volcanic rocks, together with ocean-ridge/oceanic island-type volcanic rocks in the Chiang Mai belt, constitute the ocean-ridge volcanic rock-arc magmatic rock belts distributed in pairs, indicative of eastward subduction of the oceanic crust in the Chiang Mai belt. This result is of great importance in exploring the evolution of the paleo-Tethys in the Chiang Mai belt. [ABSTRACT FROM AUTHOR]

Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extremely silicified serpentinite), cumulates (pyroxenolite, gabbro, and gabbro-diorite), ocean-ridge basalt, oceanic-island basalt and radiolarian silicalite, and it was formed during D3-P. The rock series, rock types and petrogeochemical characteristics of metamorphic tholeiites in the Nan area of the Nan-Uttaradit zone are similar to those of ocean-ridge basalts (C1) in China's Ailaoshan zone. As for the Hawaiites in the Nan area of the Nan-Uttaradit zone, their major elements, REEs and trace elements are similar to those of oceanic-island basalts in China's Jinshanjiang zone (P1¹). In the Uttaradit area of this zone the metamorphic alkaline basalts show transitional petrogeochemical characteristics between ocean-ridge basalts and oceanic-island basalts, which were still formed in oceanic-island environments. The above-described basalts are all oceanic volcanic rocks and they are the most important part of the Paleo-Tethys oceanic crust in the Nan-Uttaradit zone. [ABSTRACT FROM AUTHOR]

Abstract: During the Triassic, the Bayan Har Basin is a huge triangular basin surrounded by the North China Platform, South China Platform and Qingtang Terrane. It is filled by a Triassic turbidite sequence, the Bayan Har Group. For a long time, the series of Bayan Har Group in the eastern part of the basin were considered to be a Lower to Upper Triassic sequence, and in the western part, was attributed to the Upper Triassic. A well-preserved diversified radiolarian fauna was recovered from radiolarian chert and tuffite interbeds of the Bayan Har Group turbidites and adjacent stratigraphic units in the Hoh Xil area, northern Tibet. Sixty-seven species are identified and subdivided into two assemblages: late Anisian and early Carnian. Combined with the discovery of the Late Permian and Early Triassic turbidite in the Bayan Har Group in this area by Huang et al., it proves that all the Triassic is also present in the Bayan Har Group sequence in the western part. The evolution of the Bayan Har Basin may be traced back to the Late Permian. The massive sequence of the Bayan Har Group and its provenance indicate that the Kunlun and Qinling orogenic belts rapidly rise during the Middle-Late Triassic. The basin extended to the end of the Triassic, possibly locally to the Jurassic. [Copyright &y& Elsevier]

The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt being the main rock types. The alkaline series is dominant with sub-alkaline series occurring in few cases. The geochemical characteristics are described as follows: the major chemical compositions are characterized by high TiO2, high P2O5 and medium K2O; the rare-earth elements are characterized by right-inclined strong LREE-enrichment patterns; the trace element patterns are of the upward-bulging K-Ti enrichment type; multi-component plots falling within the fields of oceanic island basalts and alkali basalts, belonging to the oceanic island-type volcanic rocks, which are similar to the equivalents in Deqin and Gengma (the Changning-Menglian zone) of Yunnan Province, China. [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]

Free specimens of small foraminifers are not commonly reported from Permian strata. A foraminiferal fauna with free tests accompanied by abundant radiolarians has been discovered from uppermost Permian, upper Changhsingian strata in the Liuqiao Section, southwestern Guangxi Zhuang Autonomous Region, South China. SEM microphotography and thin sections of free specimens were both used for the study of external and internal morphological features. In most cases the wall structure is not preserved because of recrystallization, however, most species could be identified based on test morphology. Twenty species (six new) of fourteen genera (one new) have been identified. The new genus and new species are: Dalongella n. gen., Dalongella fusiformis n. gen. n. sp., Glomospirella? mamilla n. sp., Glomospirella? curva n. sp., Hemigordius? yini n. sp., Geinitzinita changhsingensis n. sp. and Pseudolangella costata n. sp. The composition of this fauna is quite different from similar age small foraminiferal faunas reported from South China. Furthermore, the presence of radiolarians and cool-water brachiopods probably implies that the fauna is from a deep-water environment. [ABSTRACT FROM AUTHOR]

This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied. [ABSTRACT FROM AUTHOR]

Abstract: Investigations on the Upper Changhsingian radiolarian fauna in South China allow us to trace, in detail, extinction processes and to research relations between the Permian and Triassic radiolarian faunas. Evolution of the radiolarian fauna is divided into three stages: radiation, extinction and survival intervals. In the radiation interval (10.28–2.68 m below the PTB), the radiolarian fauna consists of 137 species belonging to 50 genera and includes 8 representative Triassic genera. Two crises are recognized in the extinction interval (2.68–0.77 m below the PTB). The first crisis is characterized by extinction at species level and the second crisis, by disappearance of many genera. In the survival interval (0.77 m below the PTB to lower Lower Triassic), the radiolarian fauna includes only Paleozoic-type taxa and its diversity and abundance are unusually low. The first crisis corresponds to the extinction located at the top of Bed 24d in Meishan Section D and the second crisis, to the extinction located at the top of Bed 24e of Meishan Section D. [Copyright &y& Elsevier]

Abstract: The Permo-Triassic crisis was a major turning point in geological history. Following the end-Guadalupian extinction phase, the Palaeozoic biota underwent a steady decline through the Lopingian (Late Permian), resulting in their decimation at the level that is adopted as the Permian–Triassic boundary (PTB). This trend coincided with the greatest Phanerozoic regression. The extinction at the end of the Guadalupian and that marking the end of the Permian are therefore related. The subsequent recovery of the biota occupied the whole of the Early Triassic. Several phases of perturbations in δ 13Ccarb occurred through a similar period, from the late Wuchiapingian to the end of the Early Triassic. Therefore, the Permian–Triassic crisis was protracted, and spanned Late Permian and Early Triassic time. The extinction associated with the PTB occurred in two episodes, the main act with a prelude and the epilogue. The prelude commenced prior to beds 25 and 26 at Meishan and coincided with the end-Permian regression. The main act itself happened in beds 25 and 26 at Meishan. The epilogue occurred in the late Griesbachian and coincided with the second volcanogenic layer (bed 28) at Meishan. The temporal distribution of these episodes constrains the interpretation of mechanisms responsible for the greatest Phanerozoic mass extinction, particularly the significance of a postulated bolide impact that to our view may have occurred about 50,000 Myr after the prelude. The prolonged and multi-phase nature of the Permo-Triassic crisis favours the mechanisms of the Earth''s intrinsic evolution rather than extraterrestrial catastrophe. The most significant regression in the Phanerozoic, the palaeomagnetic disturbance of the Permo-Triassic Mixed Superchron, widespread extensive volcanism, and other events, may all be related, through deep-seated processes that occurred during the integration of Pangea. These combined processes could be responsible for the profound changes in marine, terrestrial and atmospheric environments that resulted in the end-Permian mass extinction. Bolide impact is possible but is neither an adequate nor a necessary explanation for these changes. [Copyright &y& Elsevier]

Geochemical characteristics of the Upper Permian (P2) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks; the volcanic rocks are characterized by high Al2O3 and low TiO2, with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc, volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt. [ABSTRACT FROM AUTHOR]

Abstract: Based on our extensive fieldwork in southwestern Yunnan and northern Thailand, followed by detailed stratigraphic and paleontological studies, we propose that the Triassic Simao Basin in Yunnan can be correlated with the Triassic Lampang–Phrae Basin in Thailand. Strata equivalent to those in the southern Lancangjiang sub-basin have not been identified in northern Thailand. We consider that during the Triassic the Simao and the Lampang–Phrae Basins belonged to the same tectonopaleogeographic unit. The orogenic belt to the east of this unit includes the Nan–Uttaradit and Ailaoshan sutures. The ‘Shan–Thai Block’ in northern Thailand, can be divided from east to west into the Sukhothai, the Inthanon, and the Shan terranes. According to tectonopaleogeographic correlation, our results support the idea that the Sukhothai Terrane, including the Lampang–Phrae Basin, belongs to the Cathaysian domain and not to Gondwana domain, and that the geosuture corresponding to the Changning–Menglian Suture in Yunnan must lie to the west of the Sukhothai Terrane in Thailand. [Copyright &y& Elsevier]

Moderately well-preserved radiolarian assemblages are described from bedded cherts south of Mae Hong Son, north-west Thailand. Twenty species and subspecies are identified, including one new species ( Archocyrtium sashidai Feng sp. nov.). The assemblages belong to the middle Early Carboniferous Albaillella indensis and Eostylodictya rota zones. The new data suggest that there was a pelagic basin between the Shan-Thai terrane and Gondwana during the Early Carboniferous. This implies, contrary to previous interpretations, that the Shan-Thai terrane had already rifted apart from Gondwana during the Early Carboniferous. [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]

• Sediment Hg can be hosted by the organic, sulfide or clay fractions. • Hg uptake by sulfide fraction favored under strongly euxinic conditions. • TS > 1.0% and TS/TOC > 0.35 linked to dominant sulfide host phase. • Dominant host phase must be determined for correct normalization of Hg volcanic proxy. Mercury (Hg) concentration enrichments have become a widely used proxy for volcanic inputs to sediments, especially for investigation of ancient large igneous province (LIP) eruptions. Its application for this purpose requires normalization to an element representing the dominant host phase of Hg–generally total organic carbon (TOC) for the organic fraction, but occasionally total sulfur (TS) or aluminum (Al) for the sulfide or clay fractions, respectively. Hg studies generally assume an organic matter host, but recent work has demonstrated that sulfide or clay fraction host phases are not uncommon, making it essential to determine formation-specific Hg host phases. Here, we investigate Hg concentrations and their relationships to TOC, TS, and Al in four modern marine settings (Black Sea, Japan Sea, Saanich Inlet, and Peru Margin) and six ancient marine formations (from Lower Cambrian to Lower Jurassic). Multiple regression analysis (MRA) shows that the organic fraction is the dominant host of Hg in all of the modern marine sediments examined here, as well as in many ancient marine units, although in some of the latter Hg resides primarily in the sulfide fraction (i.e., lower Cambrian and Upper Ordovician units) or partly in the clay mineral fraction (Middle Permian) of the sediment. A sulfide host phase is more likely in strongly euxinic depositional facies, as reflected in high TS concentrations (>1.0%) and TS/TOC ratios (>∼0.35). This study thus demonstrates the importance of determining Hg host phases in sediments prior to normalization and use of Hg as a volcanic proxy. [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]

Cherts, radiolarites, and radiolarian cherts are one of the most important components of accretionary complexes, and much used in the reconstruction of imbricated sections of ocean plate stratigraphy, and of the palaeogeographic and tectonic settings of ophiolitic mélanges. There has been little research on radiolarian cherts in the Kyrgyz South Tianshan, and the tectonic setting and temporal framework of the South Tianshan ocean are controversial. Here, we report well‐preserved radiolarians in ribbon‐bedded cherts in an ophiolitic mélange of the Atbashi accretionary complex (South Tianshan, Kyrgyzstan), which provide key evidence of ambient Palaeozoic oceanic conditions. The hydrofluoric acid technique was used to extract from the cherty rocks siliceous radiolarian, which yielded an age of late Early Carboniferous. Analyses of major, trace, and rare‐earth elements of four cherts indicate they are biogenic and deposited with little hydrothermal influence in a hemipelagic to continental margin environment. Our fossil ages and geochemical results of the radiolarian cherts from the Atbashi accretionary complex indicate that the South Tianshan ocean was still open in the Late Carboniferous, implying that it was a wide, long‐lived, major ocean that closed by northward subduction. [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]

The Pagoda Formation is a lithologically and biologically distinctive unit among the Upper Ordovician. The strata are characterized by a nodular limestone, which yields fossil assemblages of high diversity. Conodonts of 14 genera 20 species (6 undetermined species) and ostracods of 14 genera 26 species (16 undetermined species) are identified. In addition, spherical radiolarians and minute-walled foraminifers were first reported from this formation in South China. The conodont assemblage is attributed to the Hamarous europaeus Zone, which indicates the Early Katian Age. The conodont HDS biofacies, along with thin-shelled ostracods, spherical radiolarians and foraminifers, suggest relatively deep and quiet water depositional environment. Accordingly, these fossil materials not only enrich the diversity of the Pagoda biota, but also provide evidence for discussions of depositional environments and stratigraphic correlations for the Pagoda Formation. [ABSTRACT FROM AUTHOR]