Teffichthys wui sp. nov., a new perleidid fish from the Early Triassic of Jiangsu and Anhui, China

Perleididae is a group of stem neopterygian fishes known only from the Triassic.Here,we report the discovery of a new perleidid,Teffichthys wui sp.nov.,based on six well-preserved specimens from the late Smithian(Olenekian,Early Triassic)marine deposits of Jurong,Jiangsu and Chaohu,Anhui,China.This new discovery documents the third and youngest species of Teffichthys,which is slightly younger than the Dienerian(Induan)T.elegans from Guizhou and the early Smithian T.madagascariensis from Madagascar.The new species shows diagnostic features of Teffichthys(presence of a spiracular,38-41 lateral line scales,and no more than three epaxial rays in the caudal fin)but differs from T.madagascariensis and T.elegans in some autapomorphies(e.g.,a horizontal opercle/subopercle contact and smooth scales with a nearly straight posterior margin).The diagnostic features for the genus Teffichthys and the family Perleididae are emended based on detailed comparisons of the new taxon with other perleidids.The phylogenetic relationships of perleidids with other stem neopterygians are discussed using a cladistic approach,and the results provide new insights into the phylogeny and classification of main stem neopterygian clades.

Early Triassic Volcanic Rocks in the Western Yarlung Zangbo Suture Zone:Implications for the Opening of the Neo-Tethys Ocean

In this study,zircon U-Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone(YZSZ)in southern Xizang(Tibet)yielded an age of 247±3 Ma.According to whole rock geochemical and Sr-NdPb isotopic data,the Early Triassic samples could be divided into two groups:Group 1 with P-MORB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70253–0.70602,ε_(Nd)(t)values of 4.2–5.3,(^(206)Pb/^(204)Pb)_(t)ratios of 16.353–18.222,(^(207)Pb/^(204)Pb)_(t)ratios of 15.454–15.564,and(^(208)Pb/^(204)Pb)_(t)ratios of 35.665–38.136;Group 2 with OIB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70249–0.70513,ε_(Nd)(t)values of 4.4–4.9,(^(206)Pb/^(204)Pb)_(t)ratios of 17.140–18.328,(^(207)Pb/^(204)Pb)_(t)ratios of 15.491–15.575,and(^(208)Pb/^(204)Pb)_(t)ratios of 36.051–38.247.Group 2 rocks formed by partial melting of the mantle source enriched by a former plume,and assimilated continental crustal material during melt ascension.The formation of Group 1 rocks corresponds to the mixing of OIB melts,with the same components as Group 2 and N-MORBs.The Zhongba Early Triassic rocks belong to the continental margin type ophiolite and formed in the continental–oceanic transition zone during the initial opening of the Neo-Tethys in southern Xizang(Tibet).

Late Olenekian Radiolarians from Bedded Chert of Ashio Terrane, Northeast Japan, and Faunal Turnovers in Western Panthalassa during Early Triassic

Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Anisian faunas, respectively, and is herein named the Minowa fauna. Study of the literature indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic. The first turnover is the Paleozoic type radiolarian extinction at the Permian Triassic boundary, the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic type radiolarian faunas that are characterized by multi segmented Nassellaria.

Application of R-Mode Cluster Analysis to Multielement Taxonomy of Early Triassic Conodonts

The multivariate statistical analysis is profitably applicable to the study of conodont multielement taxonomy.R- mode duster analyses of quantitative and 0-1 data are carried out here to classify more than 6000 discrete Lower Triassic conodont specimens belonging to 108 kinds of conodont elements from Western Guangxi . The results of R-mode cluster analysis reveal more directly the relationship among many isolated conodont elements , and they also prove that the results of the logical inference are basically correct,i.e. 108 kinds of conodont elements can be identified into 32 species belonging to 11 genera of conodonts . The application of R- mode duster analysis multielement taxonomy by the method . has brought about 4 significant conclusions , which can be used by conodont researchers as reference .

The Early Triassic Helongshan Formation in Anhui,China:Record of the Triassic Biotic Recovery in the Lower Yangtze Region

The Lower Triassic is well outcropped in central and southern Anhui Province,East China,and it consists of the Yinkong,Helongshan and Nanlinghu Formations in an ascending order.The Helongshan Formation belonging to the Smithian has been well studied in this project because of the typical sedimentary features and different fossil types which are not similar to the lower Yinkeng Formation or

Detrital Zircon Geochronology of Early Triassic Strata in the West Qinling Orogen:Implications for the Tectonic Evolution of the Paleo-Tethyan Ocean

The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.

A new small baurioid therocephalian from the Lower Triassic Jiucaiyuan Formation, Xinjiang, China

Several therocephalian species,mainly represented by cranial material from the late Permian,have been reported from China in recent years.Here we describe a tiny new baurioid therocephalian,Jiucaiyuangnathus confusus gen.et sp.nov.,from the Jiucaiyuan Formation,Xinjiang,China.The new taxon is represented by a partial snout with occluded partial lower jaw and two postcranial skeletons.Although juvenile in stage,the new species is diagnosed by the following features:round pit in middle of lateral surface of maxilla;lacrimal contact nasal;fossa for dentary tooth on the posterior end of the premaxilla,lateral to the anterior choana;two small vertical triangular ridges extending dorsally and ventrally on the vomerine anterior portion,and bordering a thin vomerine foramen laterally;anterior projection of the lateral part of the frontal on the nasal;symphyseal region of the dentary projected anteriorly;5 upper premaxillary teeth,upper and lower canines absent,diastema between the last premaxillary upper incisor and first maxillary tooth present,no diastema separating anterior from posterior dentition in the mandible,10 maxillary teeth and 12 dentary teeth,posterior postcanine expands mesiodistally,having a main large cusps and tiny anterior and posterior accessory cusps in line;neural arches of the atlas fused by the neural spine,neural spine of the axis projected posteriorly,procoracoid foramen lies between procoracoid and scapula.Features of the dentition resembles those of the small baurioid Ericiolacerta parva from South Africa and Silphedosuchus orenburgensis from Russia.The specimens provide the rare opportunity to know in detail the postcranial skeleton of baurioids.

Conodont Biostratigraphy and Age of the Early Triassic Fish-Bearing-Nodule Levels from Nanjing and Jurong, Jiangsu Province, South China

Fish-bearing-nodules are found in Early Triassic marine strata in many regions, including East Greenland, East Spitsbergen, Northwest Madagascar, Canada, Angola, and South China. A new Olenekian(Early Triassic) conodont biostratigraphic study for stratum that contains fish-bearing-nodule levels is conducted based on the Longtan(LT) Section of Nanjing City and the Qingshan(QS) Section of Jurong County, Jiangsu Province, South China. A total of 101 samples were collected at the two sections and three conodont zones were recognized: in ascending order, they are Scythogondolella(Sc.) milleri Zone, Novispathodus(Nv.) pingdingshanensis Zone, and Triassospathodus(Tr.) aff. homeri Zone. The Scythogondolella milleri Zone is globally recognized as the uppermost conodont zone of the Smithian and the base of the Novispathodus pingdingshanensis Zone was previously suggested as the marker of the Smithian-Spathian boundary in the Yangtze region. The fish-bearing-nodule levels of Nanjing and Jurong are within the conodont Scythogondolella milleri Zone, laterally correlated well with the upper part of the Novispathodus waageni Zone in Chaohu of Anhui Province that also contains fish-bearing-nodule levels. The conodont biostratigraphic correlation confirms the Early Triassic fish-bearing-nodule levels in the Lower Yangtze region are coeval, with an end-Smithian in age.

A Griesbachian(Early Triassic) Mollusc Fauna from the Sidazhai Section, Southwest China, with Paleoecological Insights on the Proliferation of Genus Claraia(Bivalvia)

After the end-Permian mass extinction, genus Claraia （Bivalvia） was the most abundant and most noticeable fossil during the survival and recovery stage. However, the reasons for the proliferation of Claraia are still debated. This paper describes a new Griesbachian （Early Triassic） mollusc fauna from deep-water settings in South China in the aftermath of end-Permian mass extinction. This fauna yielded five bivalve species in two genera （Claraia griesbachi, C. wangi, C. stachei, C. radialis, and Promyalina putiatinensis） and two ammonoid species （Ophiceras sp. and Ussuridiscus sp.） and could be assigned to the Claraia wangi-C, griesbachi assemblage zone, indicating a Middle-Late Griesbachian Age. The bivalves were dominated by Claraia griesbachi and were featured by articulated Claraia fossils. As Claraia was epibyssate, it was an excellent autochthonous fauna. While the shallow and deep marine water became dysoxic to anoxic globally, as indicated by recent studies of the early Early Triassic, we suggest the genus Claraia could tolerate dysoxic and/or anoxic conditions and its proliferation could be attributed to its physiological features which were adapted to the stressed environment. The wide distribution of Claraia was probably related to its planktonic larval stage. Where the larva of Claraia could have been transported by ocean flow and increased its potential for long-distance dispersal. In addition, Claraia was a significant disaster and opportunistic taxon during the Early Triassic based on observations in South China.

There was no “Great Bank of Guizhou” in the Early Triassic in Guizhou Province, South China

In the 1990s, some geologists named the Early Triassic isolated carbonate platform in the Luodian area of southern Guizhou Province in South China as the ＂Great Bank of Guizhou＂. During the past twenty years, this term ＂Great Bank of Guizhou＂ was used in more than 300 articles in foreign countries. In the 1990s, the authors have studied the lithofacies palaeogeography of the Early and Middle Triassic in South China. In June 2014, we went to the Luodian area and studied the Early Triassic Bianyang section again. According to the geological data we acquired, in the Early Triassic of the Luodian area of southern Guizhou Province, there was only an isolated ＂Luodian Carbonate Platform＂, while no bank existed, not to mention the ＂Great Bank of Guizhou＂. It is worth further discussion.

Western Tethyan Epeiric Ramp Setting in the Early Triassic： An Example from the Central Dinarides (Croatia)

In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick （927.5 m） Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The 613C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the ＋8%0 amplitude around the Dienerian-Smithian boundary （DSB）, followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary （SSB） a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary （SAB）. Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated： 1） the dolostone member （Early Griesbachian）; 2） the silicielastic member （red-coloured shale, siltstone, sandstone with oolitic/bioclastie grainstone intercalations）, which can be further divided into lower, middle and upper intervals （Late Griesbachian, Dienerian and Smithian）; and 3） the mudstone member （grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods- Spathian）. The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.

Taphonomy of Early Triassic fish fossils of the Vega-Phroso Siltstone Member of the Sulphur Mountain Formation near Wapiti Lake,British Columbia,Canada

Abstract The taphonomy of fishes living in lacustrine environments has been extensively studied in both the laboratory and the fossil record;the taphonomy of marine fishes,however,is poorly known.Triassic marine fishes with heavy ganoid and cosmoid scales,which provided protection from rapid taphonomic loss,offer a means to examine marine fish taphonomy in the fossil record.Four genera of Early Triassic fishes(the ray-finned actinopterygians Albertonia,Bobasatrania,Boreosomus,and the lobe-finned coelacanth(sarcopterygian),Whiteia)from the Wapiti Lake,British Columbia locality of the Lower Triassic Sulphur Mountain Formation were examined in order to gain a better understanding of the taphonomy of fish in marine environments,determine ambient environmental conditions in the region during the Early Triassic,and ascertain the habitat and mode of life of the fish.Results indicate that environmental conditions that contributed to the preservation of the fossil fishes of the current study included deposition in deep,quiet waters,which reduced the odds of disarticulation,colder waters under higher pressure,which slowed decay and limited postmortem floatation,and waters that were anoxic,which discouraged predators and scavengers.In addition,the thickness of the primitive ganoid and cosmoid scales of the fossil fishes also increased their preservation potential.Taphonomic,physiological and environmental indicators suggest that Whiteia,Albertonia,and possibly Bobasatrania lived in deep,cold waters near the oxygen minimum zone,while Boreosomus lived higher in the water column.While the anatomical and physiological characteristics of modern fishes will likely continue to inhibit marine taphonomy studies,examination of ancient fish,particularly those with ganoid or cosmoid scales,may provide future avenues of research to gain a better understanding of marine fish taphonomy and provide a powerful tool to examine ancient fish behavior and their environment.

Discovery of Early Triassic conodonts in western Gangdisê and the establishment of the Tangnale Formation

Most geologists believe that there are no Early and Middle Triassic strata in the W. Gandisê stratigraphic subregion, but the present authors have found Early Triassic conodonts for the first time in the Shiquanhe area, including five conodonts genera (Form genera): Pachycladina, Neohindeodella, Cornudina, Hadrodontina and Hibbardella sp. etc. Then we affirm that Early Triassic deposits exist in the Gandisê stratigraphic subregion, and establish the Tangnale Formation. The conclusion is new important complementary basal data for Triassic stratigraphy division of Gangdisê, reconstructing palaogeography and studying Gangdisê from Paleozoic to Mesozoic island-arc evolution and transi-tion.

Paleomagnetic study on the Early Triassic red beds from Jiaocheng, Shanxi Province ——Local rotation and tectonic significance

Paleomagnetic and rock magnetic study has been conducted on the Early Triassicred beds of Liujiagou Formation from Jiaocheng, Shanxi Province. Hematite was shown as themain magnetic mineral. After eradicating an initial viscous component at room temperature to～100℃-200℃, thermal demagnetization shows that most samples contain two remanencecomponents, intermediate-temperature remanence component at 250℃-500℃ and high-tem-perature component at 500℃-680℃. The intermediate-temperature component has a negativefold test at the 95% confidence level. And the pole position of the intermediate-temperaturecomponent in geographic coordinates is correlated with the Middle Jurassic reference pole of theNorth China Block (NCB) within the 95% confidence, suggesting that it might be a remagnetiza-tion component acquired during the Yanshanian period. The high-temperature component con-tains both reversal and normal polarities with positive fold test and C-level positive reversal test atthe 95% confidence level, which suggests that this high-temperature component can be regardedas primary magnetization. Comparison of this newly obtained Early Triassic paleopole with thecoeval mean pole of the Ordos Basin suggests that a locally relative rotation may have happenedbetween the Ordos and the Jiaocheng area of Shanxi Province. This rotation may be related withtwo faults: one is Lishi big fault separating Ordos from Shanxi and the other is Jiaocheng big fault,which is situated in the southeast of sampling locality and was still in motion during the Cenozoic.

Early Triassic microbialites from the Changxing Region of Zhejiang Province,South China

Microbialites, often considered as a signal of extreme marine environment, are common in the Lower Triassic strata of South China where they flourished in the aftermath of the end-Permian mass extinction. Early Triassic microbialite facies are known to vary palaeogeographically, perhaps due to differing climates, ocean chemistry, and water depths. This paper provides the first record of a brief, but spectacular development of microbialites in the aftermath of the end-Permian mass extinction at Panjiazhuang section, Changxing Region of Zhejiang Province (eastern South China). Here, the Upper Permian Changxing Formation comprises typical shallow platform facies rich in calcareous algae and foraminifera, the development of which was terminated by the major end-Permian regression. A 3.4-m-thick microbialite began to form at the onset of the transgression in the earliest Triassic. The microbialite at Panjiazhuang section is composed of thrombolite that contains abundant calcified cyanobacteria, small gastropods, microconchid tubes and ostracods, representing a low-diversity shallow marine community in the aftermath of the end-Permian crisis. The microbialites are succeeded by thin-bedded micrites bearing thin-shelled bivalves, which record a rapid sea-level rise in the Early Triassic. Abundant populations of small pyrite framboids are observed in the upper part of the microbialites and the overlying thin-bedded micrites, suggesting that dysoxic water conditions developed at that time. The appearance of microbialites near the Permian-Triassic boundary (PTB) at Panjiazhuang section was the result of peculiar marine conditions following the end-Permian regression, whilst their disappearance was due to the increasing water depth and the development of dysoxia.

Evolution of strontium isotopic composition of sea-water from Late Permian to Early Triassic based on study of marine carbonates,Zhongliang Mountain,Chongqing,China

Collected from a Late Permian to Early Triassic sedimentary section in the Zhongliang Mountain of Chongqing, Southwest China, sixty marine carbonate samples were measured for the 87Sr/86Sr ratios, and corresponding evolution curve was constructed. The concentrations of SiO2, CaO, MgO, Mn and Sr are used to evaluate reservation of strontium isotopic composition for original seawater and the credi-bility of the dissolution method for sample preparation. The results show that most of the samples (except seven samples with the Mn/Sr ratios higher than 2) contain the original geochemistry signa-tures of ancient seawater. Compared to the published 87Sr/86Sr ratios from the Late Permian to Early Triassic, our database reported here is the largest and the curve constructed is the most complete. The strontium isotopic curve from Late Permian to Early Triassic is consistent globally and exhibits a gen-eral trend of steady increase during this period. The minimum of 87Sr/86Sr ratios (0.707011) occurs in the Late Permian (30 m in thickness below the Permian-Triassic boundary), and the maximum (0.708281), near the Early-Middle Triassic boundary. The lack of land plants and the rapid continental weathering result in the increase of 87Sr/86Sr ratios during the interval. The Permian-Triassic boundary in Zhongli-ang Mountain Section has been accepted internationally. The 87Sr/86Sr ratios of six samples near the boundary vary from 0.70714 to 0.70715 with an average of 0.70714, which is consistent with the value of 0.70715 (samples are from articulate brachiopod shells) from Korte et al. published in 2006 (within the error range in experiment). Accordingly, the strontium isotope composition in the Permian-Triassic boundary in this paper is of global significance. It can be confirmed that the 87Sr/86Sr ratios of the sea-water in the Permian-Triassic transition are in the range of 0.70714―0.70715.

Carbon isotopic composition of Early Triassic marine carbonates, Eastern Sichuan Basin, China

As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates.However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood.A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin.The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C.The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected.By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic.The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately -2‰ to the extremely high value of 8‰ within a period of about 5 Ma.The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around -6‰ to the maximum near 4‰).The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates.This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic.The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.

Sedimentary Facies Architectures of Third-Order Sequences from Early to Middle Triassic in Nanpanjiang Basin

There are complex and regular changes on sedimentary facies from the Early to the Middle Triassic in the Nanpanjiang basin. After the obvious drowned event of carbonate platforms in the transitional period between Permian and Triassic, carbonate platforms have evolved into the ramp type from the rimmed shelf type. The differentiation of sedimentary facies becomes clearer in space, which are marked by the changes from an attached platform to a turbidity basin and several isolated platforms in the basin. The striking characteristics are the development of oolitic banks on isolated platforms in Nanning and Jingxi and the reef and bank limestones in the margin of the attached platform in the Early Triassic. Despite the difference of the time span and the architecture of facies succession of third order sedimentary sequences, the process of the third order relative sea level changes reflected by the sedimentary facies succession of the third order sequences is generally synchronous. Therefore, six third order sequences could be discerned in the strata from the Early to the Middle Triassic in the Nanpanjiang basin. Using two types of facies changing surfaces and two types of diachronisms in stratigraphic records as the key elements, the sedimentary facies architectures of the third order sequences that represent sequence stratigraphic frameworks from the Early to the Middle Triassic in the Nanpanjiang basin could be constructed.

Sedimentary-volcanic tuffs formed during the early Middle Triassic volcanic event in Guizhou Province and their stratigraphic significance

The sedimentary-volcanic tuff (locally called “green-bean rock”) formed during the early Middle Triassic volcanic event in Guizhou Province is characterized as being thin, stable, widespread, short in forming time and predominantly green in color. The green-bean rock is a perfect indicator for stratigraphic division. Its petrographic and geochemical features are unique, and it is composed mainly of glassy fragments and subordinately of crystal fragments and volcanic ash balls. Analysis of the major and trace elements and rare-earth elements (REE), as well as the related diagrams, permits us to believe that the green-bean rock is acidic volcanic material of the calc-alkaline series formed in the Indosinian orogenic belt on the Sino-Vietnam border, which was atmospherically transported to the tectonically stable areas and then deposited as sedimentary-volcanic rocks there. According to the age of green-bean rock, it is deduced that the boundary age of the Middle-Lower Triassic overlain by the sedimentary-volcanic tuff is about 247 Ma.

Study of the Early and Middle Triassic Lower Yangtze Sea Basin

The Early and Middle Triassic primary lower Yangtze sea basin was formed before the Yangtze and Sino. Korean blocks collided and were assembled. showing the characteristics of an open continental shelf.continental margin sea. In order to provide evidence useful for oil and gas exploration in the studied region, this paper centres on the features of the sediments and their facies framework in the basin and the sedimentation parameters such as the deposition rate, palaeotemperature, palaeosatinity, palaeodepth of water and palaeocurrents of the basin.