Provenance of Conglomerate and Sandstone from Early Permian Shoushangou Formation in Xi Ujimqin,Inner Mongolia:Implications for Understanding Paleo-Asian Ocean Subduction

During the Late Carboniferous to Early Permian,a rift was formed by post-collisional extension after ocean closure or an island arc-related basin formed by Paleo-Asian Ocean(PAO)subduction in the Xi Ujimqin area.Nevertheless,the closure time of the PAO is still under debate.Thus,to identify the origin of the PAO,the geochemistry and U-Pb age of zircons were analyzed for the extra-large deep marine,polymict clastic boulders and sandstones in the Shoushangou Formation within the basin.The analyses revealed magmatic activity and tectonic evolution.The conglomerates include megaclasts of granite(298.8±9.1 Ma)and granodiorite porphyry(297.1±3.1 Ma),which were deposited by muddy debris flow.Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I-type granite,characterized by low Zr+Nb+Ce+Y and low Ga/Al values.The granitoid boulders were formed in island arc setting,indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction-related granitoid in southern Xi Ujimqin.Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc-related felsic rocks.Detrital zircon U-Pb age cluster of 330–280 Ma was obtained,indicating input from granite,ophiolite,Xilin Gol complex,and Carboniferous sources to the south.The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc.The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO.The backarc basin and intrusive rocks,in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol,confirm the presence of an Early Permian trencharc-basin system in the region,represented by the Baolidao arc and Xi Ujimqin backarc basin.This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin.

Early Jurassic Soft-Sediment Deformation Interpreted as Seismites in the Wuqia Pull-Apart Basin and the Strike-Slip Talas-Ferghana Fault, Xinjiang, China

The early Jurassic soft-sediment deformation occurring within lacustrine sandstone is distributed mainly in the Wuqia region of SW Tianshan Mountains, Xinjiang, western China. Triggered by earthquakes, such deformation was found to occur in three beds overlying the lower Jurassic Kangsu Formation. The main styles of deformation structures comprise load cast, ball-and- pillow, droplet, cusps, homogeneous layer, and liquefied unconformity. The deformation layers reflect a series of three strong earthquakes at the end of early Jurassic in the Wuqia region. The differences of deformation mechanisms undergone might represent the varying magnitudes of the earthquake events. During the early Jurassic, the Wuqia region was located in a pull-apart basin controlled by the significant Talas-Ferghana strike-slip fault in central Asia, which initiated the soft-sediment deformation induced by earthquakes. Our research suggests that the paleoseismic magnitudes could have ranged from Ms 6.5 to 7.

Braincase Anatomy of the Basal Theropod Sinosaurus from the Early Jurassic of China

The neuroanatomy of the mid-sized theropod Sinosaurus triassicus from the Lower Jurassic Lufeng Formation, Lufeng Basin in Yunnan Province, China was studied using X-ray computed tomography. The braincase is characterized by a large supraoccipital knob that is capped by a posterior projection of the parietal and two external foramina for the caudal middle cerebral vein, which is completely enclosed by the supraoccipital. The basicranium has well defined, short basipterygoid processes that project ventral to the basal tubera. The basisphenoid is expanded, projects posteroventrally, and is pierced by four pneumatic recesses. The endocranial morphology resembles that observed in other basal theropods—in particular some allosauroids—and has a strongly marked pontine flexure and a large dorsal expansion. The inner ear morphology is also similar to that observed in other basal theropods, with slender semicircular canals. The anterior semicircular canal is 20% larger than the posterior semicircular canal, and the angle formed between them is less than 90° when seen in dorsal view.

Early Jurassic Flora and Stratigraphy from Shansonggang of Southern Jilin,China

More than 35 species belonging to 22 genera of fossil plants are recognized by the authors from the Shan-songgang flora in the Shansonggang Basin of Jilin, China. Among them, the coexistence of Coniopteris and Cycadocarpi-dium demonstrates that the present flora possesses the characters of the early assemblage of Early Jurassic floras in Eura-sia. Therefore, the age of the Shansonggang flora is considered the Early Jurassic.This study would be beneficial for bet-ter understanding the paleoecological and paleoclimatic characteristics of the Shansonggang Basin. Based mainly on the characters of the flora, the authors suggest that the Lower Jurassic coal-bearing strata, the Shansongang Formation, should namely be renewed.

Subsidence Analysis and Burial History of the Late Carboniferous to Early Jurassic Soutpansberg Basin,Limpopo Province,South Africa

The subsidence history of the Soutpansberg Basin was reconstructed by a tectonic subsidence analysis coupled with backstripping calculations based on data of newly interpreted sequence boundaries. Furthermore, burial and time plots were constructed in order to understand the burial and thermal history of the basin. Input data were based on facies, lithostratigraphic models and tectonic interpretations. The studied succession is up to 1000 m and is underlain by the Achaean Limpopo Mobile Belt. The subsidence within the basin supports the primary graben system which must have been centred within the present basins, and later became a region of faulting. The subsidence and burial history curves suggests two phases of rapid subsidence during the Early-Late Permian （300–230 Ma） and Middle Triassic （215–230 Ma）. The areas of greater extension subsided more rapidly during these intervals. Two slow subsidence phases are observed during the Late Triassic （215–198 Ma） and Early Jurassic （198–100 Ma）. These intervals represent the post-rift thermal subsidence and are interpreted as slow flexural subsidence. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion （300 Ma） is therefore recognised as the first stage of the Soutpansberg Basin formation.

Late Jurassic and Early Cretaceous Radiolarians from Zhilong,Gyangse,Tibet

Abundant well-preserved Late Jurassic-Early Cretaceous radiolarian fossils were extracted from 31 bedded green chert samples collected from Zhilong section,Gyangse,southern Tibet.This

New Evidence of Sauropod Dinosaurs from the Early Jurassic Period of Thailand

The oldest dinosaur assemblages of Thailand deposit in continental sedimentary rocks of the Nam Phong Formation. Not only Isanosaurus attavipatchi was discovered but at least two more species of basal sauropods were found. A partial skeleton from Phu Hin Tan locality refers to sauropod taxon A. It is different from Isanosaurus and shares some characteristics with basal sauropods in the Early Jurassic. The sauropod taxon B was found in Non Sra Ard locality. Base on postcranial skeleton, sauropod taxon B shares some characteristics of the family Vnlcanodontidae. Moreover, several fragments of the sauropods specimen are also found in Pha Khok Wang Yang and Phu Noi localities. All of the evidences above indicate that there are a highly diversity of sauropods in the Nam Phong Formation. At least three sauropod species （including Isanosaurus） were found in the Nam Phong formation. The issue about the age of the Nam Phong has been debated for a long time between the Triassic and Jurassic age. All of sauropodomorphs, in this study, are more likely the Early Jurassic period dinosaurs than the Triassic period dinosaurs. And they have deposited in the upper part of Nam Phong Formation.

Discovery of Fossil Charophytes from the Late Triassic Xujiahe Formation and Early Jurassic Lower Yimen Formation, Sichuan Province, and Its Significance

This paper describes the fossil charophytes collected from the Late Triassic Xujiahe Formation in Dazuand Early Jurassic Lower Yimen Formation in Xichang, Sichuan Province, and their significance. Up to now,papers dealing with fossil charophytes of the Late Triassic, especially of the Early Jurassic, have been rarelypublished. The description of the two new species of Porochara, P. dazuensis and P. xichangensis, and theirfossil assemblage not only provides an important basis for classification and correlation of red beds insouthwestern China but reveals for the first time the features of the charophyte flora of the Late Triassic-EarlyJurassic in the area, thus offering valuable data for the establishment of Triassic and Jurassic charophyte fossilzones in China.

Early Jurassic Coleopterans from the Mintaja Insect Locality,Western Australia

Beetles （Coleoptera） are the most common insects recovered from the Lower Jurassic Mintaja insect locality of Western Australia, with over half of the fossils recorded from this site being isolated coleopteran elytra. A range of partial beetle bodies and other isolated beetle sclerites have also been recovered from the locality; much of this material is taxonomically unidenitifiable due to its disarticulation and poor preservation. A number of the Mintaja coleopterans are assigned to the archostematan family Ommatidae, including Zygadenia westraliensis （Riek, 1968） comb. nov, previously placed in the morphogenus Mesothoris, and an unnamed species of Tetraphalerus. Also recorded is a new species of elaterid, Lithomerus wunda sp. nov., along with other fragments likely attributable to the same family. The remaining material is assigned into morphospecies, separated primarily on preserved body parts - specifically, there are three morphospecies based on partially articulated coleopteran bodies, two morphospecies based on isolated head capsules, three morphospecies based on isolated thoracic sclerites, three morphospecies based on isolated abdominal sclerites, and 13 morphospecies based on isolated elytra. Overall, the ecology of these fossils is difficult to interpret due to poor preservation, although some of the beetles were likely aquatic, and the Ommatidae and Elateridae were both likely xylophilous. There is a strong similarity between the Mintaja coleopterans and those from the Late Triassic Denmark Hill locality of Queensland, though many of these similarities are based on morphotaxa and may be superficial in nature. Of the species that have been assigned to named taxa, all are generally typical of the Late Mesozoic worldwide, with Zygadenia, Tetraphalerus and Lithomerus all long-ranging, cosmopolitan genera.

Late Jurassic-Early Cretaceous Erg Deposits in the Mengyin Basin, Western Shandong Province, China: Inferences about the Wind Regime and Paleogeography

The Late Jurassic-Early Cretaceous Santai Formation, sporadically distributed in western Shandong Province, comprises terrestrial alluvial-eolian successions, which records regional wind patterns and paleogeography in eastern North China. This paper conducts an analysis of eolian stratification, bounding surfaces, facies architecture and paleowind direction of the Santai Formation in the east of the Mengyin Basin, western Shandong Province. Three basic types of eolian stratification are recognized in the Santai Formation, including grainflow strata, wind ripple strata and adhesion strata, and have been grouped into eolian dune and interdune facies associations. The occurrences of reactivation surfaces and superimposition surfaces within eolian dune deposits indicate active compound dunes or draas. The association of adhesion strata with grainflow or windripple strata is the development of a wet eolian system. Cross-strata dip direction indicates different paleowind directions from the lower to the upper part of the Santai paleoerg. The lower part of the paleoerg was characterized by paleowinds blowing from northwest to northeast, whereas the upper part was under the influence of paleowinds consistently towards east to northeast. The identified changes in wind directions possibly suggest wind regime shifts from monsoon circulation to westlies of planetary wind system, which may be related with the collapse of the East China Plateau during the Late Jurassic to Early Cretaceous.

Petrogenesis of the Early Jurassic Longtang and Menglong Peraluminous Granites in Tengchong Terrane,and their Tectonic Implication

A comprehensive study of zircon U-Pb geochronology,in situ Hf isotopes,whole-rock major and trace element geochemistry,and Nd isotopes was carried out for two Early Jurassic two-mica granites(Longtang and Menglong)in the southern part of the Tengchong terrane,which is in the northern part of the larger Sibumasu terrane.We assess the origin of the granites and explore their possible genetic relationship to the Paleo-Tethyan regime.LA-ICP-MS zircon U-Pb dating shows that they were simultaneously emplaced in the Early Jurassic(ca.199 Ma).They have SiO2 contents of 69.7–75.1 wt%and are mainly strongly peraluminous with alumina saturation index(ASI)values ranging from 1.06 to 1.46.They show similar Mg#(0.29–0.42)to experimental partial melts of metasedimentary rocks under continental pressuretemperature(P-T)conditions.They are enriched in light rare earth elements(LREEs)relative to heavy rare earth elements(HREEs),with moderately negative Eu anomalies and flat HREEs patterns.They show negativeεNd(t)values(−9.0 to–12.4)andεHf(t)values(−8.0 to−9.1).Elemental and isotopic data suggest that they most likely to formed by muscovitedehydration melting of a metapelitic source at lower temperatures in the range of 700℃to 750℃.The granites might represent a post-collisional tectonic setting response to Paleo-Tethyan regime.

Identification of the Early Jurassic mylonitic granitic pluton and tectonic implications in Namling area,southern Tibet

A number of studies revealed that the Gangdese magmatic belt of southern Tibet was closely related to the northward subduction of the Neo-Tethys oceanic lithosphere and Indo-Asian collision.However,pre-Cretaceous magmatism is still poorly constrained in the Gangdese magmatic belt,southern Tibet.Here,we conducted systematically geochronology and geochemistry studies on a newly-identified granitic pluton in the middle Gangdese magmatic belt(Namling area),southern Tibet.Zircon SHRIMPⅡU-Pb dating for one representative sample gives a weighted age of 184.2±1.8 Ma(MSWD=±1.11),corresponding to emplacement and crystallization age of the granitic pluton in the Early Jurassic(Pliensbachian).High SiO2(68.9-72.1 wt.%)contents and intermediate Mg#values(35-38)together suggest that the newly-identified granitic pluton was probably formed by partial melting of crustal material with minor injection of mantle-derived magma,precluding an origin from melting of metasedimentary rocks that are characterized by low Mg#and high zirconδ^18O values(>8‰).Geochemically,the newly-identified granitic pluton belongs to typical I-type granitic affinity,whereas this is inconsistent with aluminium saturation index(ASI=A/CNK ratios)and geochemical signatures.This suggests that zircon oxygen isotopes(4.30‰-5.28‰)and mineral features(lacking Al-rich minerals)are reliable indicators for discriminating granitic origin.Significantly depleted whole-rock Sr-Nd-Hf isotopic compositions and zirconεHf(t)values indicate that the granitic pluton was derived from partial melting of depleted arc-type lavas.In addition,the granitic pluton shows zirconδ^18O values ranging from 4.30‰to 5.28‰(with a mean value of 4.77‰)that are consistent with mantle-derived zircon values(5.3‰±0.6‰)within the uncertainties,indicating that the granitic pluton might have experienced weak short-living high-temperature hydrous fluid-rock interaction.Combined with the Sr-Nd-Hf-O isotopes and geochemical signatures,we propose that the newly-identified granitic pluton was originated from partial melting of depleted mafic lower crust,and experienced only negligible wall-rock contamination during ascent.Integrated with published data,we also propose that the initial subduction of the Neo-Tethys oceanic lithosphere occurred no later than the Pliensbachian of the Early Jurassic.

Geochemistry and Geochronology of OIB-type Early Jurassic Magmatism in the Zhangguangcai Range, NE China, as a Result of Continental Back-arc Extension

The Zhangguangcai Range in the Xing’an(Hinggan) Mongolian Orogenic Belt, NE China, contains Early Jurassic(c. 188 Ma) Dabaizigou(DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have(87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive εNd(t) values of 2.3–3.2 and positive εHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet-to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia.

Comparison of Early Jurassic flora from South Primorye of Russia with its main coeval floras of China

The Early Jurassic flora,with over 42 species of 26 genera and documented in age by sandwiched marine beds,from the Lower Jurassic Schitukhe Formation of South Primorye,Russia,is further reported.The flora is dominated by cycadophytes,ferns and conifers,with some of ginkgoales and czekanowskiales,and characterized by occurrence of Cycadocarpidium,with very rare Coniopteris.A comparison of this flora with its coeval Early Jurassic floras of China is discussed.The Russian flora is considered as the early assemblage of Early Jurassic flora,and more similar to the Early Jurassic floras from the Shansonggang-and Yihe formations of Jilin,Beipiao Formation of Liaoning,and lower-middle Guanyintan Formation of Hunan in China.

Changes of taxonomical composition of Late Jurassic-Early Cretaceous palynofloras of Bureya Basin,Russia

The changes of taxonomical composition of the Late Jurassic-Early Cretaceous palynofloras are revealed,in the upper stream of Bureya River in Bureya Basin.The palynofloras are dominated as follows:the Berriasian one by ferns(Cyatheaceae,Dicksoniaceae,Osmundaceae),Classopollis and bisaccate pollen;the Valanginian-Hauterivian one by ferns(Cyatheaceae,Dicksoniaceae),Ginkgocycadophytus and bisaccate pollen;the Barremian one by ferns(Cyatheaceae,Dicksoniaceae);the Aptian one by ferns(Cyatheaceae,Dicksoniaceae,Gleicheniaceae) and Ginkgocycadophytus;and the Albian one by ferns(Schizaeaceae) and bisaccate pollen.In the Albian the floral diversity raises with the angiosperms appearing.

Geochemical Characteristics and Geological Significance of Early Permian Baya'ertuhushuo Gabbro in South Great Xing'an Range

Field geological investigation and geochemical analysis are carried out on Baya＇ertuhushuo Gabbro in South Great Xing＇an Range. Field investigation reveals that the gabbro is a magmatic intrusion rather than a component of an ophiolite suite as previously thought. Zircon laser ablation inductively coupled plasma mass spectroscopy （LA-ICP-MS） U-Pb dating indicates the gabbro was formed in 274-275 Ma, just as the widespread volcanic rocks of Dashizhai Formation （P1d）, monzogranites and miarolitic alkali-feldspar granites in the study area. The gabbro has SiO2 content between 47.23 wt% and 50.17 wt%, high MgO and FeOT contents of 6.95-11.29 wt% and 7.32- 12.24wt%, respectively, and it belongs to low-K tholeiitic series in the SiO2-K2O diagram. The Chondrite-normalized rare earth element （REE） patterns and primitive mantle-normalized spider diagrams of the gabbro are similar to those of Normal Mid-Ocean Ridge Basalt （N-MORB） except for the enrichment of large ion lithophfle elements （LILE）, such as Rb, Ba and K. In trace element tectonic discriminative diagrams, the samples are mainly plotted in the N-MORB field, and Zircon in situ Lu-Hf isotopic analysis also indicates the gabbro originated from depleted mantle. Through synthetic studies of the geochemical characteristics and petrogenesis of Baya＇ertuhushuo gabbro, volcanic rocks of Dashizhai Formation and granitoids in the area, it is suggested that the early Permian magmatism in the Xilinhot-Xiwuqi area formed in the tectonic setting of asthenosphere upwelling, which was caused by breaking-off of the subducted Paleo-Asian Ocean slab.

Compaction Rate of an Early Permian Volcanic Tuff from Wuda Coalfield, Inner Mongolia

Compaction rates of sediments or volcaniclastic material are needed to reconstruct original thickness of a bed, which in turn is required to reconstruct subsidence rates, sea-level rise, or in the case of volcanielastic, the location or direction of the eruption site. The knowledge of compaction rates can also aid in the reconstruction of deformed fossils. The known shape of deformed fossils can allow the determination of the compaction they experienced. Here we report the compaction rate in an early Permian volcanic tuff from Wuda, Inner Mongolia, determined from the deformation of standing tree fern stems of known anatomy. The compaction rate has been found to be 0.56 in this case, indicating that 44% of original thickness remains.

Progress,Problems and Prospects on the Stratigraphy and Correlation of the Kungurian Stage,Early Permian (Cisuralian) Series

The Kungurian Stage is one of the three remaining stages of the Permian that is not yet defined at the base by a Global Stratotype Section and Point （GSSP）. The candidate section at the Yuryuzan＇River in the Urals yields few conodonts, and contains non-marine sediments near the boundary. The search for a suitable, continuous marine succession is a principal task for the Subcommission on Permian Stratigraphy. The Leonardian, with its type area in the southwest United States, and in objective stratigraphic succession directly beneath the basal Guadalupian Roadian Stage,has priority to serve as a subseries of the Lower Permian. However, distinct provincialism limits the correlation of Leonardian fossil zones with the fusuline-based Tethyan timescale. Conodonts can be correlated in many important regions on opposite sides of Pangea, yet contradictions arise when relating conodont zones with fusuline and ammonoid zones. The different taxonomic philosophies are highly suspected for the cause of the conflicts, but also there are different conodonts from the type Roadian in West Texas. Given that the Pamir and Darvaz in central Asia are difficult to access, further investigations should focus on South China, where abundant fusulines and ammonoids facilitate correlation throughout the Tethyan region, and where conodonts permit correlation with North America.

The Early Permian Woniusi Flood Basalts from the Baoshan Terrane, SW China: Petrogenesis and Geodynamic Implications

The Woniusi flood basalts from the Baoshan terrane,SW China,represent a significant eruption of volcanic rocks which were linked to the Late Paleozoic rifting of the Cimmeria from the northern margin of East Gondwana.However,the precise mechanism for the formation and propagation of the rifting is still in debate.Here we report 40 Ar/39 Ar dating,whole-rock geochemistry,and Sr-Nd-Pb isotopes for the Woniusi basalts from the Baoshan terrane of SW China,with the aim of assessing if a mantle plume was related to the formation of the continent Cimmeria.40 Ar/39 Ar dating of the Woniusi basalts yielded ages of 279.3±1.1 Ma and 273.9±1.5 Ma,indicating they were emplaced during the Early Permian.Whole-rock geochemistry shows that these basalts have subalkaline tholeiitic affinity,low Ti O2(1.2-2.2 wt%),and fractionated chondrite-normalized LREE and nearly flat HREE patterns[(La/Yb)N=2.86-5.77;(Dy/Yb)N=1.21-1.49]with noticeable negative Nb and Ta anomalies on the primitive mantle-normalized trace element diagram.Theε(Nd)(t)values(-4.76 to+0.92)and high(206 Pb/204 Pb)i(18.40-18.66)along with partial melt modeling indicates that the basalts were likely derived from a sub-continental lithospheric mantle(SCLM)source metasomatized by subduction-related processes.On the basis of a similar emplacement age to the Panjal basalts and Qiangtang mafic dykes and flood basalts in the Himalayas,combined with a tectonic reconstruction of Gondwana in the Early Permian,we propose that the large-scale eruption of these basalts and dykes was related to an Early Permian mantle plume that possibly initiated the rifting on the northern margin of East Gondwana.

Petrogenesis of Early Permian Intrusive Rocks from Southeastern Inner Mongolia, China: Constraints on the Tectonic Framework of the Southeastern Central Asian Orogenic Belt

The late Paleozoic tectonic framework of the southeastern Central Asian Orogenic Belt is key to restricting the accretion orogeny between the Siberia Craton and the North China Craton. To clarify the framework, petrogenesis of early Permian intrusive rocks from southeastern Inner Mongolia was studied. Zircon U-Pb dating for bojite and syenogranite from Ar-Horqin indicate that they were emplaced at 288–285 Ma. Geochemical data reveal that the bojite is highly magnesian and low-K to middle-K calc-alkaline, with E-MORB-type REE and IAB-like trace element patterns. The syenogranite is a middle-K calc-alkaline fractionated A-type granite and shows oceanic-arc-like trace element patterns, with depleted Sr-Nd-Hf isotopes,(~(87)Sr/~(86)Sr)I = 0.7032–0.7042, ε_(Nd)(t) = +4.0 to +6.6 and zircon ε_(Hf)(t) = +11.14 to +14.99. This suggests that the bojite was derived from lithospheric mantle metasomatized by subducted slab melt, while the syenogranite originated from very juvenile arc-related lower crust. Usng data from coeval magmatic rocks from Linxi-Ar-Horqin, the Ar-Horqin intra-oceanic arc was reconstructed, i.e., initial transition in 290–280 Ma and mature after 278 Ma. Combined with regional geological and geophysical materials in southeastern Inner Mongolia, an early Permian tectonic framework as ‘one narrow ocean basin of the PAO', ‘two continental marginal arcs on its northern and southern' and ‘one intra-oceanic arc in its southern' is proposed.