Mass extinction and Pangea integration during the Paleozoic-Mesozoic transition

The greatest Phanerozoic mass extinction happened at the end-Permian to earliest Triassic.About 95%species,82%genera,and more than half families became extinct,constituting the sole macro-mass extinction in geological history.This event not only caused the great extinction but also destroyed the 200 Myr-long Paleozoic marine ecosystem,prompted its transition to Mesozoic ecosystem,and induced coal gap on land as well as reef gap and chert gap in ocean.The biotic crisis during the Paleozoic-Mesozoic transition was a long process of co-evolution between geospheres and biosphere.The event sequence at the Permian-Triassic boundary(PTB)reveals two-episodic pattern of rapidly deteriorating global changes and biotic mass extinction and the intimate relationship between them.The severe global changes coupling multiple geospheres may have affected the Pangea integration on the Earth’s surface spheres,which include:the Pangea integration→enhanced mountain height and basin depth,changes of wind and ocean current systems;enhanced ocean basin depth→the greatest Phanerozoic regression at PTB,disappearance of epeiric seas and subsequent rapid transgression;the Pangea integration→thermal isolation effect of continental lithosphere and decrease of mid-ocean ridges→development of continental volcanism;two-episode volcanism causing LIPs of the Emeishan Basalt and the Siberian Trap(259–251 Ma)→global warming and mass extinction;continental aridification and replacement of monsoon system by latitudinal wind system→destruction of vegetation;enhanced weathering and CH4emission→negative excursion ofδ13C;mantle plume→crust doming→regression;possible relation between the Illawarra magnetic reversal and the PTB extinction,and so on.Mantle plume produced the Late Permian LIPs and mantle convection may have caused the process of the Pangea integration.Subduction,delamination,and accumulation of the earth’s cool lithospheric material at the"D"layer of CMB started mantle plume by heat compensation and disturbed the outer core thermo-convection,and the latter in turn would generate the mid-Permian geomagnetic reversal.These core and mantle perturbations may have caused the Pangea integration and two successive LIPs in the Permian,and probably finally the mass extinction at the PTB.     

Timing of the terrestrial Permian-Triassic boundary biotic crisis: Implications from U-Pb dating of authigenic zircons

The Late Permian to Early Triassic transition represents one of the most important Phanerozoic mass extinction episodes. The cause of this event is still in debate between catastrophic and gradual mechanisms. This study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic clay deposits at Chahe (Guizhou Province, SW China) to examine time constraints for this event. The results of both this and previous studies show that the ages of Bed 68a and 68c (the upper clay bed of the terrestrial Permian-Triassic boundary (PTB)) respectively are 252.6±2.8 and 247.5±2.8 Ma. This age (within the margin of error) almost accords with the upper clay bed (Bed 28) age of Meishan and the eruption age of Tunguss Basalt, and is so far the most accurate age obtained from terrestrial PTB. The claystone of Bed 68 was formed in the earliest Triassic. The biotic crisis occurred at nearly the same time in terrestrial and marine environments during Permian-Triassic interval; however the extinction patterns and processes are different. The extinction pattern of the terrestrial plants shows a major decline at the PTB after long-term evolution, followed by a retarded extinction of the relicts in the earliest Triassic.     

Extinction pattern and process of siliceous sponge spicules in deep-water during the latest Permian in South China

Diverse and abundant siliceous sponge spicules were found in the latest Permian beds, Dongpan and Ma'anying sections, South China, including 52 types and 85 forms. Further investigation on these spicules allows us to understand extinction patterns and processes of deep-water sponges. These sponge spicules rapidly decreased below the Permian/Triassic boundary (PTB), and the extinction rates reach up to 88%-90% for types and 88%-92% for forms. Their extinction pattern is a gradual one that consists of two stages: the first is characterized by a gentle and slow extinction speed and low extinction rate, and the second by sharp and fast extinction speed and high extinction rate. The morphological extinction process is involved in the disappearance first of the triaxons and tetraxons, then of the polyaxons and demas, and last of monaxons. In exterior structure extinction, the complex spicules with branches and spines became extinct more easily than did smooth spicules. After the end-Permian mass extinction, only five common and smooth forms survived: Oxeas A, Oxeas B, Strongles B, Oxy-orthpentactines and Oxy-orthohexactines A.     

The microfacies and sedimentary responses to the mass extinction during the Permian-Triassic transition at Yangou Section,Jiangxi Province,South China

A Permian-Triassic (P-Tr) boundary section of continuous carbonate facies, which well recorded the biotic and environmental processes through the great P-Tr transition in the shallow non-microbialite carbonate facies, has been studied in Yangou, Leping County, Jiangxi Province. The P-Tr sequence is well correlated with the Meishan section according to the conodont biostratigraphy and the excursion of carbon isotopes. A series of high-resolution thin-sections from the P-Tr boundary carbonate rocks at the Yangou section are studied to explore the interrelation between environmental change and biological evolution during the transitional time. Six microfacies have been identified based upon the observation of the thin-sections under a microscope on the grains and matrix and their interrelation. Combined with the data of fossils and carbon isotopes, Microfacies 4 (MF-4), coated-grain-bearing foraminifer oolitic sparitic limestone, and Microfacies 6 (MF-6), dark shelly micritic limestone, should be the different responses to the two episodes of mass extinction and environmental events that can be correlated throughout South China and even over the world. The oolitic limestone of MF-4 is the first finding from the latest Permian strata in South China and it might be a proxy of an unusual environmental condition of high pCO₂, low sulfate concentration and of microbial blooming in the aftermath of the latest Permian mass extinction. The micritic limestone of MF-6 containing rich micro-gastropods and ostracods probably represents the blooming event of disaster taxa in the earliest Triassic environment. The microfacies analysis at the Yangou section can well reveal the episodic process of the biological evolution and environmental change in the shallow non-microbialite carbonate facies throughout the great P-Tr transition, thus the Yangou section becomes an important complement to the Meishan section.     

Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time

The end-Permian mass extinction not only severely distressed the Paleozoic ecosystems but also dramatically changed the sedimentary systems, resulting in a peculiar Early Triassic ecosystem and submarine environment during the recovery time following the mass extinction. The Lower Triassic is characteristic of the wide occurrence of various distinctive sediments and related sedimentary structures, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thin-bedded limestone and zebra limestone-mudstone. These sediments were common in the Precambrian to Early Ordovician marine settings, and then they occurred only in some extreme and unusual environments with the expansion of metazoan faunas. However, the Early Triassic witnessed an "anachronistic" reappearance of some distinctive sedimentary records in normal shallow marine settings. The study of these anachronistic facies should be of great importance for the understanding of the unique ecosystem and marine environment through the great Paleozoic-Mesozoic transition. The anachronistic facies characterized by vermicular limestone have been documented in many localities in South China and occur at various horizons of the Lower Triassic. Most types of re- ported distinctive sediments over the world have been observed in the Lower Triassic of South China. This provides an excellent opportunity for understanding the Early Triassic environment and its co- evolution with the biotic recovery. Among the anachronistic facies the vermicular limestone is the most characteristic and common distinctive sediments in the Lower Triassic of South China but has received relatively few investigations. Taking it as a case study, we will detail the variation of vermicular limestone and its stratigraphic distribution in the Three Gorges area, Hubei Province. The investigation on the vermicular limestone and other distinctive sediments from the Lower Triassic of South China further indicates that the appearance of anachronistic facies immediately following the mass extinction and the elimination from normal shallow marine facies with the radiation of Mesozoic marine faunas imply the natural response of the sedimentary systems and ecosystems to the great Paleozoic-Mesozoic transitional events and their induced harsh environments. Therefore, the ups and downs of the anachronistic facies may act as a proxy for the evolution of ecosystems independent of fossil analyses.     

Size variation of the end Permian conodont <Emphasis Type="Italic">Neogondolella</Emphasis> at Meishan Section,Changxing, Zhejiang and its significance

This study is based on both a generic and species level investigation of the individual size of the latest Permian conodont Neogondolella Pa elements collected from Meishan Section A, Changxing, Zhejiang Province. In this study, an obvious size reduction of Neogondolella Pa elements within bed 24e of the upper Changxing Limestone is recognized. The size variation of the Neogondolella occurs simultaneously with some important events including the negative shift of δ ¹³C, change in the ratio of the abundance of cyanobacterial biomarkers versus that of other general bacterial biomarkers and the shallowing of the sea water. Through the investigation of the paleoenvironmental changes and the analysis of the paleoecology of the conodont genus Neogondolella, the authors propose that the major factors for the size reduction of species of the conodont genus Neogondolella are food shortages caused by the mass extinction, the shallowing of the sea water as well as the increase in opacity of the sea water during the end Permian. The same phenomenon of Neogondolella size reduction is also observed in preliminary research from the same horizon at Shangsi Section, Sichuan Province. All the evidence suggests that there was a mass extinction that occurred at the horizon of bed 24e, and the evidence supports the viewpoint of a multi-phase mass extinction during the Permian and Triassic transition in South China.     

Two episodes of C-depletion in organic carbon in the latest Permian: Evidence from the terrestrial sequences in northern Xinjiang, China

New analyses reveal two intervals of distinctly lower δ¹³C values in the terrestrial organic matter of Permian–Triassic sequences in northern Xinjiang, China. The younger negative δ¹³C_org spike can be correlated to the conspicuous and sharp δ¹³C drops both in carbonate carbon and organic carbon near the Permian–Triassic event boundary (PTEB) in the marine section at Meishan. The geochemical correlation criteria are accompanied by a magnetic susceptibility pulse and higher abundances of distinctive, chain-like organic fossil remains of Reduviasporonites.The older negative δ¹³C_org spike originates within a latest Permian regression. Significant changes in organic geochemical proxies are recorded in the equivalent interval of the marine section at Meishan. These include relatively higher concentrations of total organic carbon, isorenieratane, C₁₄–C₃₀ aryl isoprenoids and lower ratios of pristane/phytane that, together, indicate the onset of anoxic, euxinic and restricted environments within the photic zone. The massive and widespread oxidation of buried organic matter that induced these euxinic conditions in the ocean would also result in increased concentrations of ¹³C-depleted atmospheric CO₂. The latest Permian environmental stress marked by the older negative δ¹³C_org episode can be correlated with the distinct changeover of ostracod assemblages and the occurrences of morphological abnormalities of pollen grains. These observations imply that biogeochemical disturbance was manifested on the land at the end of the Permian and that terrestrial organisms responded to it before the main extinction of the marine fauna.     

Paleo-redox conditions across the Permian-Triassic boundary in shallow carbonate platform of the Nanpanjiang Basin,South China

Ocean anoxia has been widely implicated in the Permian-Triassic extinction.However,the duration and distribution of the ocean anoxia remains controversial.In this study,the detailed redox changes across the Permian-Triassic boundary(PTB)in the shallow platform interior at Great Bank of Guizhou(GBG)has been reconstructed based on the high-resolution microfossil composition and multiple paleo-redox proxies.The shallow platform is characterized by low sulfur(total sulfur(TS)and pyrite sulfur(Spy))concentrations,low Spy/TOC ratios,and low DOP values before the mass extinction,representing oxic conditions well.Following the mass extinction,the shift of multiple geochemical proxies,including high Spy/TOC ratios and DOP values,indicates dysoxic-anoxic conditions in shallow ocean.Furthermore,we reconstruct the transition of the redox conditions of Nanpanjiang Basin:the intense volcanic eruptions,which release huge CO2 and SO2 before the mass extinction,provoke the temperature rising and the collapse of terrestrial ecosystem.As a result,the increased weathering influx causes the carbon isotopic negative excursion and the expansion of the ocean oxygen minimum zone(OMZ).When the OMZ expanded into the photic zone,the episodic H2S release events enhance the pyrite burial at Dajiang section.Thus,intense volcanic eruptions,temperature increase,and oceanic hypoxia together lead to the PTB extinction.Recent studies show high temperature might be the key mechanism of the PTB extinction.In addition,this study confirms that the microbialites were formed in the dysoxicanoxic shallow water.     

An accurately delineated Permian-Triassic Boundary in continental successions

The Permian-Triassic Boundary Stratigraphic Set (PTBST), characteristic of the GSSP section of Meishan and widespread in marine Permian-Triassic Boundary (PTB) sequences of South China, is used to trace and recognize the PTB in a continental sequence at Chahe (Beds 66f―68c). Diversified Permian plant fossils extended to the PTBST, and a few relicts survived above that level. Sporomorphs are dominated by fern spores of Permian nature below the PTBST, above which they are replaced by gymnosperm pollen of Triassic aspect. In the nearby Zhejue Section, the continental PTBST is charac- terized by the fungal 'spike' recorded in many places throughout the world. The boundary claybeds (66f and 68a,c) of the PTBST are composed of mixed illite-montmorillonite layers analogous with those at Meishan. They contain volcanogenic minerals such as β quartz and zircon. U/Pb dating of the upper claybed gives ages of 247.5 and 252.6 Ma for Beds 68a and 68c respectively, averaging 250 Ma. In con- trast to the situation in Xinjiang and South Africa, the sediment sequence of the Permian-Triassic tran- sition in the Chahe section (Beds 56―80) become finer upward. Shallowing and coarsening upward is not, therefore, characteristic of the Permian-Triassic transition everywhere. The occurrence of relicts of the Gigantopteris Flora in the Kayitou Fm. indicates that, unlike most marine biota, relicts of this pa- leophytic flora survived into the earliest Triassic. It is concluded that Bed 67 at Chahe corresponds to Bed 27 at Meishan, and that the PTB should be put within the 60-cm-thick Bed 67b④, now put at its base tentatively. This is the most accurate correlation of the PTB in continental facies with that in the marine GSSP.     

Geochemical characteristics of pelagic chert sequences across the Permian-Triassic boundary in southwest Japan

Abstract Geochemical characteristics, mainly of major and trace elements and REE (rare earth elements) of bedded chert and shale/mudstone sequences, across the Permian/Triassic boundary in southwest Japan are examined. The boundary is characterized by the disappearance of bedded cherts, and the interval between the Upper Permian cherts and Lower Triassic (probably Smithian) cherts comprises siliceous shales and organic black mudstones. Bedded cherts are characterized by a gradual depletion of chemical elements from Middle to Upper Permian. However, overlying siliceous shales exhibit a clear enrichment in some elements, especially alkaline metals (such as K, Rb and Cs) and Ti, Th, Y, P₂O₅, and REE in comparison with elements of the PAAS (post Archean Australian shales). This indicates that average components of the upper continental crust were transported in the boundary interval, possibly caused by volcanic activity. Ce-negative shifting in NASC (North American Shales Composite)-normalized REE patterns is characteristic of this interval, and could be related to the deposition of siliceous rocks in Ce-depleted seawater. This was probably caused by an invasion of water mass with a Ce-negative anomaly into the previously existing water mass of the Paleo-Tethys. Weak negative Eu-anomalies in this interval are suggestive of plagioclase fractionation caused by acid volcanisms and the LREE/HREE ratios in the interval show a slightly light-REE enrichment. Organic black mudstones are characteristically intercalated in the interval. These rocks are usually regarded as a product of oceanic deterioration, but in pelagic conditions, organic materials were formed by high primary production that resulted from the active upwelling of ocean floor water currents with rich nutrients. This may have been caused by the inferred mixing of water masses of the Paleo-Tethys and of the Panthalassa in Early Triassic time which was regarded as an event synchronous with an increase in volcanic activity on highly matured island arcs and/or continents.     

Geochemical evidence for the origin of Late Triassic melange units in the Oman Mountains as a small ocean basin formed by continental rifting

A useful tool to elucidate past tectonic environments is the geochemistry of volcanic and sedimentary rocks when used together.The regional structural setting of the Oman Mountains indicates that deep-water sediments and volcanic rocks formed adjacent to the rifted Arabian margin in the Late Triassic near the axis of a narrow ocean basin of Red Sea-type. Tholeiitic to trachytic extrusives formed seamounts associated with Late Triassic reefal build-ups. “Immobile” trace element compositions point to a within-plate origin. The interbedded and overlying Late Triassic deep-sea sedimentary cover comprises ribbon radiolarites and both distal siliclastic and calcareous turbidites that accumulated on an abyssal plain at least ca. 180 km northeast of the Arabian continent. Associated ferromanganiferous oxide-sediments are interpreted as chemical precipitates derived from high-temperature vents in the spreading axis of the young ocean basin. Pervasive regional subsidence took place during end Triassic/Early Jurassic time.Later, in the Cretaceous, oceanic crust was consumed in a northeast-dipping subduction zone. MORB-type crust was subducted while Late Triassic volcanic edifices and sedimentary cover were accreted. During eventual trench-margin collision the Semail ophiolite split into blocks allowing sub-ophiolite melange rocks to be expelled upwards through corridors, creating the Batinah Melange. As the ophiolite nappe ploughed inboard over already thrust-assembled abyssal plain sediments (Hawasina Complex), some duplexes were uplifted, oversteepened, overturned and then slid backwards onto the ophiolite to form the Batinah Sheets.     

Size variation of the end Permian conodont Neogondolella at Meishan Section,Changxing,Zhejiang and its significance

Recent works reveal that the size reduction of or- ganisms during the Permian-Triassic transition is of great importance for research on biotic mass extinction and recovery in this period[1,2]. Initially, Urbanek (1993) observed a decrease in the size of Silurian graptolites during the biotic crisis, and used the term “Lilliput Effect” to define the size reduction in sur- viving animal taxa[3]. Subsequently, researchers re- ported a decrease in size of late Devonian conodonts[4], heart urc…     

Multiple sulfur isotope chemostratigraphy across the Permian–Triassic boundary at Chaotian,China: Implications for a shoaling model of toxic deep-waters

Previous studies on multiple sulfur isotopes (³²S, ³³S, and ³⁴S) in sedimentary pyrite at the end-Permian suggested a shoaling of anoxic/sulfidic deep-water contributing to the extinction. This scenario is based on an assumption that the sedimentary sulfur cycle was largely controlled by benthos activity, though a stratigraphic correlation between the sulfur records and ichnofabrics of the sediments at the end-Permian has not yet been examined. We report the multiple sulfur isotopic composition of pyrite in the Permian–Triassic boundary interval at Chaotian, South China. Our data can be generally explained by a mixing of sulfur in sulfide from two different sources: one produced via sulfate reduction in an open system with respect to sulfate and the other produced in a closed system. In particular, the former with the substantially low δ³⁴S (<−40 ‰) and high ∆³³S (up to +0.100 ‰) values was likely produced via water-mass sulfate reduction or via sulfate reduction in oxic sediments with common burrows. The frequent occurrence of small pyrite framboids (mostly <5 μm in diameter) in the Lopingian (Late Permian) Dalong Formation of deep-water facies supports the enhanced water-mass sulfate reduction in an anoxic deep-water mass. The negative ∆³³S values are observed only in the oxic limestones, and no substantial ∆³³S change is observed across the extinction horizon despite of the disappearance of bioturbation. Our results are apparently inconsistent with the previous shoaling model. We expand the model and infer that, when the deep-water was sulfidic and its shoaling rate was high, a substantial amount of hydrogen sulfide (H₂S) was supplied onto the shelf via the shoaling; that resulted in the positive ∆³³S value of the bulk sediments. The observed ∆³³S variation on a global scale suggests a substantial variation in H₂S concentration and/or in upwelling rate of shoaling deep-waters during the Permian–Triassic transition.     

Depositional model of Early Permian reef-island ocean in Eastern Kunlun

Many fusulinid fossils have been found in thin- to middle-bedded limestones which are distributed between the Early Permian limestone hills and formerly considered as Early Triassic. The fusulinid fossils, identified asNeoshwagerina sp.,Verbeekina sp. andSchwagerina sp., can also be found in massive limestone hills. At the same time, Early Permian radiolarian chert of deep basin facies was discovered in Animaqing. All the above show that the massive limestone hills, thin- to middle-bedded limestones and radiolarian chert belong to syndeposits in Early Permian ocean. The sediments in the study area can roughly be divided into three types: shallow facies, basin facies and transitional facies. The carbonate buildup can be subdivided into massive bioclastic limestone and reef framestone. Basin facies contains thin- or middle-bedded limestone, abyssal red mudstone or ooze, blue-green mudstone and radiolarian chert. Transitional facies includes reef talus and platformal skirt facies. The Early Permian ocean in Eastern Kunlun is recognized as a kind of reef-island ocean environment according to distribution and composition of different facies. The reef-island ocean in Eastern Kunlun is characterized by reef islands (or carbonate buildups) alternating with basins, complicated sea-floor topography, sharp facial change and well-developed reefs.     

Detrital heavy minerals from Lower Jurassic clastic rocks in the Joetsu area,central Japan: Paleo‐Mesozoic tectonics in the East Asian continental margin constrained by limited chloritoid occurrences in Japan

Detrital chloritoids were extracted from the Lower Jurassic sandstones in the Joetsu area of central Japan. The discovery of detrital chloritoids in the Joetsu area, in addition to two previous reports, confirms their limited occurrence in the Jurassic strata of the Japanese islands. This finding emphasizes the importance of the denudation of chloritoid‐yielding metamorphic belts in Jurassic provenance evolution, in addition to a change from an active volcanic arc to a dissected arc that has already been described. Possible sources for the detrital chloritoids from the Jurassic sandstones are the Permo–Triassic chloritoid‐yielding metamorphic rocks distributed in dispersed tectonic zones (Hida, Unazuki, Ryuhozan and Hitachi Metamorphic Rocks), which are in fault contact with Permian to Jurassic accretionary complexes in the Japanese islands. This is because all of these pre‐Jurassic chloritoid‐yielding metamorphic rocks have a Carboniferous–Permian depositional age and a Permo–Triassic metamorphic age, whereas a Permian–Triassic metamorphic age on the Hitachi Metamorphic Rocks remains unreported. In addition, most metamorphic chloritoids imply a former stable land surface that has evolved into an unstable orogenic area. Therefore, the chloritoid‐yielding metamorphic rocks might form a continuous metamorphic belt originating from a passive continental margin in East Asia. Evidence from paleontological and petrological studies indicates that the Permo–Triassic metamorphic belt relates to a collision between the Central Asian Orogenic Belt and the North China Craton. The evolution of the Permian–Jurassic provenance of Japanese detrital rocks indicates that the temporal changes in detritus should result from sequences of collision‐related uplifting processes.     

The timing and extent of the eruption of the Siberian Traps large igneous province: Implications for the end-Permian environmental crisis

We present new high-precision ⁴⁰Ar/³⁹Ar ages on feldspar and biotite separates to establish the age, duration and extent of the larger Siberian Traps volcanic province. Samples include basalts and gabbros from Noril'sk, the Lower Tunguska area on the Siberian craton, the Taimyr Peninsula, the Kuznetsk Basin, Vorkuta in the Polar Urals, and from Chelyabinsk in the southern Urals. Most of the ages, except for those from Chelyabinsk, are indistinguishable from those found at Noril'sk. Cessation of activity at Noril'sk is constrained by a ⁴⁰Ar/³⁹Ar age of 250.3 ± 1.1 Ma for the uppermost Kumginsky Suite.The new ⁴⁰Ar/³⁹Ar data confirm that the bulk of Siberian volcanism occurred at 250 Ma during a period of less than 2 Ma, extending over an area of up to 5 million km². The resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates, or is synchronous with, the end-Permian mass extinction, further strengthening an association between volcanism and the end-Permian crisis. A sanidine age of 249.25 ± 0.14 Ma from Bed 28 tuff at the global section and stratotype at Meishan, China, allows us to bracket the P–Tr boundary to 0.58 ± 0.21 myr, and enables a direct comparison between the ⁴⁰Ar/³⁹Ar age of the Traps and the Permo–Triassic boundary section.Younger ages (243 Ma) obtained for basalts from Chelyabinsk indicate that volcanism in at least the southern part of the province continued into the Triassic.     

Jianshangou Bed of the Yixian Formation in West Liaoning,China

The Jianshangou fossil locality was first found byChang Zhenglu and his colleagures in 1962, now thearea of Jianshangou, Sihetun and Huangbanjigou be-comes famous all over the world for its yielding feath-ered dinosaurs, Confuciusornis and Archaefructus. Thename of Jianshangou Bed was proposed by the firstauthor of present paper as an informal suggesting unitduring the research on Jehol fossils of western Liaon-ing in 1963 and 1964. The unit was named then asJianshan Bed[1], indicating th…     

High‐resolution lithostratigraphy and organic carbon isotope stratigraphy of the Lower Triassic pelagic sequence in central Japan

After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian–Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high‐resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ¹³C_org) was carried out. Stratigraphic variation of the δ¹³C_org value shows large‐amplitude fluctuations between ?34.4 and ?21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ¹³C_org records in the Inuyama area with high‐resolution isotopic profiles of carbonate carbon (δ¹³C_carb) from shallow‐marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high‐resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site.     

Chronology and geochemistry of the volcanic rocks in Woruo Mountain region,northern Qiangtang depression: Implications to the Late Triassic volcanic-sedimentary events

A suite of sedimentary-volcaniclastic rocks intercalated with the volcanic rocks unconformably overlies the Triassic Xiaochaka Formation in the Woruo Mountain region, Qiangtang Basin, northern Tibet. The vitric tuff from the base of these strata gives a SHRIMP zircon U-Pb age of 216 ± 4.5 Ma, which represents the age of the Late Triassic volcanic-sedimentary events in the Woruo Mountain region, and is consistent with that of the formation of the volcanic rocks from the Nadi Kangri Formation in the Nadigangri-Shishui River zone. There is a striking similarity in geochemical signatures of the volcanic rocks from the Woruo Mountain region and its adjacent Nadigangri-Shishui River zone, indicating that all the volcanic rocks from the Qiangtang region might have the same magmatic source and similar tectonic setting during the Late Triassic. The proper recognition of the Late Triassic large-scale volcanic eruption and volcanic-sedimentary events has important implications for the interpretation of the Late Triassic biotic extinction, climatic changes and regressive events in the eastern Tethyan domain, as well as the understanding of the initiation and nature, and sedimentary features of the Qiangtang Basin during the Late Triassic-Jurassic.     

Paleo-productivity evolution across the Permian-Triassic boundary and quantitative calculation of primary productivity of black rock series from the Dalong Formation,South China

The change of the primary productivity across the Permian-Triassic boundary(PTB)remains controversial.In this study,records from two deep-water sections in South China(Xiakou and Xinmin sections)show the primary productivity decreased gradually from the latest Permian to the earliest Triassic,and five evolutionary stages Increase-Decrease-Recovery-RecessionStagnation)can be observed from Clarkina changxingensis-C.deflecta to Hindeodus parvus-Isarcicella isarcica zones.Primary productivity decreased abruptly from the base of C.meishanensis zone.Besides,for adjusting to the deterioration of the oceanic environment,the primary producers in the oceanic surface had changed to acritarch and cyanobacteria,which were more tolerant of stressful environment.Then the producers were under huge stagnation in the H.parvus-I.isarcica zone.The values of quantitative calculation of the primary productivity from the black rock series in the Dalong Formation were very high,corresponding to that of an upwelling area in modern ocean,which shows that the strata of the Dalong Formation in the study region are potential hydrocarbon source-rocks.This result may come from the fact that South China craton was located at the equatorial upwelling area during the Permian-Triassic transitions.But organic matter contents were different in various sections because they could be affected by redox conditions and diagenesis process after burial.