The depositional facies types of the fourth member of the Middle Triassic Leokoupo Formation(Lei-4 Member)in western Sichuan Basin are examined through the methods of sedimentology,lithology and analysis of well-loggi...The depositional facies types of the fourth member of the Middle Triassic Leokoupo Formation(Lei-4 Member)in western Sichuan Basin are examined through the methods of sedimentology,lithology and analysis of well-logging data,as well as the special lithofacies indicators such as microbialite,gypsum-salt rock and tempestites,using the data of about 400 wells and 11 outcrop sections.The distribution and evolution and its hydrocarbon geological significances of the bay facies have been discussed.The Lei-4 Member in western Sichuan Basin has an ocean–bay–flat depositional model,with the presence of evaporated tidal flat,restricted tidal flat and paleo-bay facies from east to west.The subfacies such as bay margin,subtidal bay and bay slope are recognized within the paleo-bay,with microbial reef and grain bank microfacies in the bay margin,microbial flat,deep-water spongy reef and hydrostatic mudstone microfacies in the subtidal bay,and tempestites and collapsed deposits in the upper bay slope.The bay boundary covered the Guangyuan-Zitong-Dujiangyan area in the period of the first submember of the Lei-4 Member(Lei-4-1)with falling sea level,regressed westward into the Shangsi-Jiangyou-Dujiangyan area in the period of Lei-4-2,and expanded to the Shangsi-Zitong-Langzhong-Wusheng-Yanting-Chengdu area in the northern part of central Sichuan Basin in the period of Lei-4-3 along with a small-scale transgression.The topographic pattern of“one high and two lows”is confirmed in the Lei-4 Member,corresponding to a configuration of source rocks and reservoir rocks alternated horizontally and superimposed vertically.Two efficient source-reservoir configuration models,i.e.side source&side reservoir,and self-generating&self-storing,are available with the microbial reef and grain bank reservoirs at the bay margin and the high-quality source rocks within the sags on both sides of the bay.The research findings will inevitably open up a new situation for the hydrocarbon exploration in the Leikoupo Formation.展开更多
The Middle Triassic Panxian fauna is a physical marker and representative record of the rapid recovery of the Triassic marine ecosystem following the Early Triassic stagnant stage after the end-Permian mass extinction...The Middle Triassic Panxian fauna is a physical marker and representative record of the rapid recovery of the Triassic marine ecosystem following the Early Triassic stagnant stage after the end-Permian mass extinction. Ten marine reptile taxa have been found from the 1.82-2.10 m-thick fossiliferous level in the Upper Member of the Guanling Formation, which can be subdivided into three marine reptile beds through the analysis on the stratigraphic distributions of fossil reptiles. The Lower Reptile Bed yields the sauropterygians Placodus inexpectatus Jiang et al., 2008 and Lariosaurus hongguoensis Jiang et al., 2006, the ichthyopterygians Xinminosaurus catactes Jiang et al., 2008 and Phalarodon cf. Phalarodon fraasi Merriam, 1910, associated with Mixosaurus panxianensis Jiang et al., 2006, representing a stage of predominance of durophagous taxa. In this bed, the large complete skeletons may reach up to 2.3 m in length, and lithofacies and chemostratigraphic analyses indicate a relatively deep carbonate platform with an oxic water environment near the bottom, as well as a rising sea level The Middle Reptile Bed yields the sauropterygian Nothosaurus yangjuanensis Jiang et al., 2006 and the archosaur Qianosuchus mixtus Li et al., 2006, associated with Mixosaurus panxianensis Jiang et al., 2006. The fossils in this bed are characterized by its pincering dentition and large overall body size, with the largest possibly exceeding 3 m in length. This bed might represent a time of deepest basin with relatively anoxic condition near the bottom. The Upper Reptile Bed yields the sauropterygians Wumengosaurus delicatomandibularis Jiang et al., 2008, Keichousaurus sp., the protorosaur Dinocephalosaurus orientalis Li, 2003, and the ichthyopterygian Mixosaurus panxianensis Jiang et al., 2006. In this bed, reptilian taxa characterized by suction feeding appeared, and most are less than 1 m long. This bed corresponds to a period of decreasing water depth.展开更多
A new genus and species of the family Tanystropheidae, Dinocephalosaurus orientalis gen. et sp. nov., is described based on a nearly complete skull. This is the first record of the order Protorosauria from China. It a...A new genus and species of the family Tanystropheidae, Dinocephalosaurus orientalis gen. et sp. nov., is described based on a nearly complete skull. This is the first record of the order Protorosauria from China. It also represents the only known occurrence of Tanystropheidae outside Europe, the Middle East and North America. Dinocephalosaurus is quite similar to Tanystropheus from Monte San Giorgio, Switzerland. Primarily it is distinguished from Tanystropheus in the shape of the premaxilla, maxilla, jugal and parietal. Although the family Tanystropheidae is now referred to the order Protorosauria, the new material from China indicates that the archosauromorph affinities of tanystropheids need further investigation. The discovery of Dinocephalosaurus provides new clues for the study of the evolution and radiation of Protorosauria and Tanystropheidae. It is also important for the study of the eastern Tethyan Fauna and the paleobiogeographical relationship between Europe and southern China in the Triassic.展开更多
Two complete specimens from the Pelsonian （Middle Anisian, Middle Triassic） of Luoping, Yunnan Province, South China are referred to a new actinopterygian genus, Luopingichthys gen. nov., and ascribed to the perleid...Two complete specimens from the Pelsonian （Middle Anisian, Middle Triassic） of Luoping, Yunnan Province, South China are referred to a new actinopterygian genus, Luopingichthys gen. nov., and ascribed to the perleidiform family Polzbergidae based especially on a typical synapomorphy of a peculiar premaxillary-maxillary complex, i.e., the fusion between premaxillary and maxillary along the antero-dorsal margin of the maxillary. The new taxon differs from other deep-bodied representatives of the family, Felberia and Stoppania, in its fusiform or deep fusiform body shape; sickle-shaped preopercular with short infraorbital process; lack of modified scales at the base of the anal fin; the short-based dorsal fin; scarcely ornamented scales; and thin anterior teeth. Based on a redescription of the holotype of the taxon Ctenognathichthys hattichi from the Middle Triassic （Ladinian） Prosanto Formation, Canton Graubiinden, eastern Switzerland, the only known specimen, which shows the same fusion between premaxillary and maxillary, the systematic position of the species is clarified and the taxon is proposed to be a further representative of the family Polzbergidae, and is transferred to the new genus.展开更多
Sedimentary response to an orogenic process is important for determining whether South China had compressional or extensional orogeny during the period from the Late Permian to the Middle Triassic besides the tectonic...Sedimentary response to an orogenic process is important for determining whether South China had compressional or extensional orogeny during the period from the Late Permian to the Middle Triassic besides the tectonic and magmatologic evidence. An intracontinental collision event took place between the Yangtze and Cathaysia blocks in the Late Permian. Beginning at the Late Triassic, the tectonic movement was completely changed in nature and entered a post-collisional extensional orogenic and basin-making process. This paper presents sedimentological evidence from the Late Permian to the Middle Triassic in the Shiwandashan basin at the southwestern end of the junction zone between the Yangtze and Cathaysia blocks.展开更多
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-ande...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.展开更多
Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizonta...Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.展开更多
Saurichthys dawaziensis sp. nov., from the third member of the Gejiu Formation （Anisian of Middle Triassic） in the vicinity of Luoping, Yunnan Province, is a small to mediumsized saurichthyid fish. It is characteriz...Saurichthys dawaziensis sp. nov., from the third member of the Gejiu Formation （Anisian of Middle Triassic） in the vicinity of Luoping, Yunnan Province, is a small to mediumsized saurichthyid fish. It is characterized by the efferent pseudobranchial arteries penetrating on the parasphenoid and the mandible sensory canal with a branch in the angular. The new species is more derived than the Lower Triassic species in having a relatively narrow postorbital region, short preopercular, single ossification of the sclerotic ring, small haemal arches between the pelvic fins and the anal fin without ossified spines, and in the absence of quadratojugal. It is more primitive than the Middle and Upper Triassic Saurichthys in having fringing fulcra and numerous segments in the unpaired fins, and the presence of both prae- and post-zygapophyses in the neural arches. Some anatomic changes related to the vertebral column and unpaired fins of the genus are also discussed.展开更多
The Luoping Biota discovered from the early Middle Triassic （Anisian） Guanling Formation of southwestern China represents a fully recovered shallow marine ecosystem, marking the end point of Early Triassic biotic re...The Luoping Biota discovered from the early Middle Triassic （Anisian） Guanling Formation of southwestern China represents a fully recovered shallow marine ecosystem, marking the end point of Early Triassic biotic recovery following the end-Permian mass extinction. Contemporaneously preserved are prolific trace fossils, which offer good opportunities to understand the palaeoecology of marine invertebrates from a fully recovered shallow marine ecosystem. Here we present a newly discovered sinuous branching burrow from the fossil-bearing unit in Member II of the Guanling Formation. Several features, including the horizontal regular sinuous nature, the branching pattern, typical H-junction, and the small wavelength/amplitude ratio of these sinuous structures within the burrow systems justify assignment of these traces as Sinusichnus sinuosus, a trace possibly produced by decapod crustaceans. Close association ofS. sinuosus with Rhizocorallium commune suggests a deposit-feeding strategy of these trace makers. The newly reported Anisian material from the Guanling Formation in Luoping represents first report of Sinusichnus from South China. The global record of Sinusichnus occurrence suggests that these burrows might have an older history than Early Middle Triassic.展开更多
Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes pl...Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be resolved.Herein we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province,southwestern China.Morphological features,together with previous geobiological investigations,suggest that the laminated lime mudstones represent the former presence of microbial mats.These lime mudstones consist mainly of calcite,dolomite and quartz,with clay minerals and pyrites as subordinate components.In particular,micro-analysis shows copious nano-globules(65–878 nm)and capsule-shaped nano-rods in laminations.These low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances(EPS).Nano-sized globules coalesce to form semi-euhedral micrite crystals.We suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local micro-environment.As an intermediate,these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.展开更多
Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bos...Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazariste were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.展开更多
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 Per...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.展开更多
Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of...Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.展开更多
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 mar...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.展开更多
Affected by the Indosinian movement, the sediments in the main part of South China, Yangtze platform, started to transform from marine to continental during the Middle Triassic. In the meantime, a noticeable paleogeog...Affected by the Indosinian movement, the sediments in the main part of South China, Yangtze platform, started to transform from marine to continental during the Middle Triassic. In the meantime, a noticeable paleogeographic and sedimentary facies differentiation occurred in the marginal regions of the platforms and produced completely different lithologic and paleontologic sequences in various paleogeographic gradients and sedimentary facies areas, which brought about the difficulties for the stratigraphic correlation based on the traditional stratigraphies. This paper proposes to use some characteristic environmental events as the markers of the stratigraphic correlation across various paleogeographic sedimentary facies, considering that some distinctive regional environmental events should have affected at the same time on the entire basin or the connected sedimentary regions and produced some closely related sedimentary records in the stratigraphic sequences though the affected intensity and recorded pattern might be different among the regions. The change of violent relative sea level (generally water depth) and the alteration of tectonic activity summarized from the dynamic mechanism of sedimentation are the best markers of environmental events for stratigraphic correlation. Based on the analysis and recognition of some significant environmental events at the typical stratigraphic sequences from various paleogeographic sedimentary facies and combined with the consideration of the variations in expressed form and strength of the events among different paleogeographic gradients and sedimentary facies, the stratigraphic sequences from different sedimentary facies can be easily correlated directly. Furthermore, the evolutionary history of the whole sedimentary basin can be clearly established.展开更多
Kannemeyeriiformes were dominated tetrapods in the Middle Triassic terrestrial faunae of China.Although abundant materials of Sinokannemeyeria have been collected, their postcranial morphology information is not well ...Kannemeyeriiformes were dominated tetrapods in the Middle Triassic terrestrial faunae of China.Although abundant materials of Sinokannemeyeria have been collected, their postcranial morphology information is not well studied, especially the juveniles. This paper presents a description of an articulated Sinokannemeyeria skeleton from the Middle Triassic Ermaying Formation and reports the histological microstructure of its femur. This specimen represents a late-stage juvenile based on the histological information. For the first time, this specimen offers insights into the postcrania information of juvenile Sinokannemeyeria.展开更多
The Nanpanjiang Basin is a key area for paleontological and biostratigraphical study of the Middle Triassic.Herein we studied Middle Triassic conodonts from a well-exposed section,the Shaiwa Section,which is located a...The Nanpanjiang Basin is a key area for paleontological and biostratigraphical study of the Middle Triassic.Herein we studied Middle Triassic conodonts from a well-exposed section,the Shaiwa Section,which is located at the northwest end of the Nanpanjiang Basin.A total of six Anisian conodont zones are recognized;in ascending order,they are:the Nicoraella germanica Zone,the Nicoraella kockeli Zone,the Paragondolella bulgarica Zone,the Neogondolella constricta Zone,the Neogondolella cornuta Zone,and the Paragondolella excelsa Zone,respectively.The first occurrence of Nicoraella kockeli defines the Bithynian-Pelsonian boundary.The Pelsonian-Illyrian boundary is defined by the first occurrence of Neogondolella constricta.The Anisian-Ladinian boundary cannot be recognized at the Shaiwa Section due to the absence of conodont indicative of the Ladinian.However,the new conodont data indicate that the uppermost strata could be very close to the boundary.The abrasion of conodont surfaces provides evidence for demonstrating reworking at the Shaiwa Section,which makes some conodonts possess a longer stratigraphic range than previously recorded.The variation in relative abundance between blade-shaped conodonts and platform conodonts indicates that segminiplanate elements probably preferred deeper and oxygenated environments whereas a restricted marine environment is more suitable for segminate elements.展开更多
The Middle Triassic was the great turning period of South China from marine sedimentary basins to continental deposits or erosion. This paper summarizes the distribution and variation of the stratigraphic sequences, l...The Middle Triassic was the great turning period of South China from marine sedimentary basins to continental deposits or erosion. This paper summarizes the distribution and variation of the stratigraphic sequences, lithofacies and biotas in various Middle Triassic depositional basins of South China. The close relationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies, thus the paleogeography, is demonstrated. The process of the transition from the depositional paleogeography and its relation to the tectonic settings is concluded.展开更多
Zircon LA-ICP-MS U-Pb geochronology and geochemical analyses are undertaken for the garnet-bear-ing muscovite monzogranite in Yitong area, central Jilin Province. The formation age and petrogenesis of the granite are ...Zircon LA-ICP-MS U-Pb geochronology and geochemical analyses are undertaken for the garnet-bear-ing muscovite monzogranite in Yitong area, central Jilin Province. The formation age and petrogenesis of the granite are determined, and the regional tectonic background is discussed. Zircons from the granite are euhe-dral-subhedral in shape, and display fine-scale oscillatory growth zoning, indicating a magmatie origin. LA- ICP-MS zircon U-Pb dating result indicates that the garnet-bearing muscovite monzogranites formed in the mid-dle Triassic （243 Ma ）. The garnet-bearing muscovite monzogranites have high SiO2 （SiO2 = 74.1%- 76.49% ）, rich aluminum （A1203 = 14.47%-14.68% ） and alkali （ NazO ＋ K20 = 4.31%-7.9% ）, low Fe203T and MgO （MgO =0.1%-0. 13% , Fe203T =0.46%-1.02% ）. The ratio of CaO/Na20 is between 0.17--0. 21. The garnet-bearing muscovite monzogranites in Yitong region are relatively enriched in light rare earth elements （LREEs） and large ion lithophile elements （LILEs） , and depleted of heavy rare earth elements （HREEs） and high field strength elements （HFSEs）. They are characterized by high Sr and Ba, poor Rb and Y, and negative Eu abnormally （δEu =0.48-0.62） , with Rb/Sr 〈 1. The εHf（t） values and TDM2 of zircons range from ＋ 6. 10 to ＋ 8.00 and from 725 Ma to 814 Ma, respectively. The above features indicate that gar- net-bearing muscovite monzogranites in Yitong area were derived from partial melting of metasedimentary rock. These granites have high Sr/Y ratios, which suggest they formed in a thickened continental crust. Combined with the coeval granitic rocks in central Jilin Province, we suggested that a significant eollisional and thickening event took place during the Middle Triassic.展开更多
The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion res...The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.展开更多
基金Supported by the General Project of National Natural Science Foundation of China(41872150)Major Project of National Natural Science Foundation of China(42230310)Enterprise Innovation and Development of National Natural Science Foundation of China(U19B6003)。
文摘The depositional facies types of the fourth member of the Middle Triassic Leokoupo Formation(Lei-4 Member)in western Sichuan Basin are examined through the methods of sedimentology,lithology and analysis of well-logging data,as well as the special lithofacies indicators such as microbialite,gypsum-salt rock and tempestites,using the data of about 400 wells and 11 outcrop sections.The distribution and evolution and its hydrocarbon geological significances of the bay facies have been discussed.The Lei-4 Member in western Sichuan Basin has an ocean–bay–flat depositional model,with the presence of evaporated tidal flat,restricted tidal flat and paleo-bay facies from east to west.The subfacies such as bay margin,subtidal bay and bay slope are recognized within the paleo-bay,with microbial reef and grain bank microfacies in the bay margin,microbial flat,deep-water spongy reef and hydrostatic mudstone microfacies in the subtidal bay,and tempestites and collapsed deposits in the upper bay slope.The bay boundary covered the Guangyuan-Zitong-Dujiangyan area in the period of the first submember of the Lei-4 Member(Lei-4-1)with falling sea level,regressed westward into the Shangsi-Jiangyou-Dujiangyan area in the period of Lei-4-2,and expanded to the Shangsi-Zitong-Langzhong-Wusheng-Yanting-Chengdu area in the northern part of central Sichuan Basin in the period of Lei-4-3 along with a small-scale transgression.The topographic pattern of“one high and two lows”is confirmed in the Lei-4 Member,corresponding to a configuration of source rocks and reservoir rocks alternated horizontally and superimposed vertically.Two efficient source-reservoir configuration models,i.e.side source&side reservoir,and self-generating&self-storing,are available with the microbial reef and grain bank reservoirs at the bay margin and the high-quality source rocks within the sags on both sides of the bay.The research findings will inevitably open up a new situation for the hydrocarbon exploration in the Leikoupo Formation.
基金supported bygrants from the National Natural Science Foundation ofChina(no.:40672002 and 40302009)the Program for NewCentury Excellent Talents in University(no.:NCET-07-0015)+1 种基金the Committee for Research and Exploration ofthe National Geographic Society of USA(no.:7886-05)Peking University,and was a contribution to the IGCP-572 project
文摘The Middle Triassic Panxian fauna is a physical marker and representative record of the rapid recovery of the Triassic marine ecosystem following the Early Triassic stagnant stage after the end-Permian mass extinction. Ten marine reptile taxa have been found from the 1.82-2.10 m-thick fossiliferous level in the Upper Member of the Guanling Formation, which can be subdivided into three marine reptile beds through the analysis on the stratigraphic distributions of fossil reptiles. The Lower Reptile Bed yields the sauropterygians Placodus inexpectatus Jiang et al., 2008 and Lariosaurus hongguoensis Jiang et al., 2006, the ichthyopterygians Xinminosaurus catactes Jiang et al., 2008 and Phalarodon cf. Phalarodon fraasi Merriam, 1910, associated with Mixosaurus panxianensis Jiang et al., 2006, representing a stage of predominance of durophagous taxa. In this bed, the large complete skeletons may reach up to 2.3 m in length, and lithofacies and chemostratigraphic analyses indicate a relatively deep carbonate platform with an oxic water environment near the bottom, as well as a rising sea level The Middle Reptile Bed yields the sauropterygian Nothosaurus yangjuanensis Jiang et al., 2006 and the archosaur Qianosuchus mixtus Li et al., 2006, associated with Mixosaurus panxianensis Jiang et al., 2006. The fossils in this bed are characterized by its pincering dentition and large overall body size, with the largest possibly exceeding 3 m in length. This bed might represent a time of deepest basin with relatively anoxic condition near the bottom. The Upper Reptile Bed yields the sauropterygians Wumengosaurus delicatomandibularis Jiang et al., 2008, Keichousaurus sp., the protorosaur Dinocephalosaurus orientalis Li, 2003, and the ichthyopterygian Mixosaurus panxianensis Jiang et al., 2006. In this bed, reptilian taxa characterized by suction feeding appeared, and most are less than 1 m long. This bed corresponds to a period of decreasing water depth.
基金This work is supported by the Natural Science Foundation of China grants 40072010 and J9930095.
文摘A new genus and species of the family Tanystropheidae, Dinocephalosaurus orientalis gen. et sp. nov., is described based on a nearly complete skull. This is the first record of the order Protorosauria from China. It also represents the only known occurrence of Tanystropheidae outside Europe, the Middle East and North America. Dinocephalosaurus is quite similar to Tanystropheus from Monte San Giorgio, Switzerland. Primarily it is distinguished from Tanystropheus in the shape of the premaxilla, maxilla, jugal and parietal. Although the family Tanystropheidae is now referred to the order Protorosauria, the new material from China indicates that the archosauromorph affinities of tanystropheids need further investigation. The discovery of Dinocephalosaurus provides new clues for the study of the evolution and radiation of Protorosauria and Tanystropheidae. It is also important for the study of the eastern Tethyan Fauna and the paleobiogeographical relationship between Europe and southern China in the Triassic.
基金supported by Peking University and NSFC(grant 40702001)by a grant from UNIMI Chancellorand FIRST funds for the Italian team
文摘Two complete specimens from the Pelsonian （Middle Anisian, Middle Triassic） of Luoping, Yunnan Province, South China are referred to a new actinopterygian genus, Luopingichthys gen. nov., and ascribed to the perleidiform family Polzbergidae based especially on a typical synapomorphy of a peculiar premaxillary-maxillary complex, i.e., the fusion between premaxillary and maxillary along the antero-dorsal margin of the maxillary. The new taxon differs from other deep-bodied representatives of the family, Felberia and Stoppania, in its fusiform or deep fusiform body shape; sickle-shaped preopercular with short infraorbital process; lack of modified scales at the base of the anal fin; the short-based dorsal fin; scarcely ornamented scales; and thin anterior teeth. Based on a redescription of the holotype of the taxon Ctenognathichthys hattichi from the Middle Triassic （Ladinian） Prosanto Formation, Canton Graubiinden, eastern Switzerland, the only known specimen, which shows the same fusion between premaxillary and maxillary, the systematic position of the species is clarified and the taxon is proposed to be a further representative of the family Polzbergidae, and is transferred to the new genus.
基金Financial support of the National Natural Science Foundation of China(Grants 40272092 and 40334039)the Chinese Academy of Sciences(Grant KZCX2-102)China Postdoctoral Science Foundation(200333418)is gratefully acknowledged.
文摘Sedimentary response to an orogenic process is important for determining whether South China had compressional or extensional orogeny during the period from the Late Permian to the Middle Triassic besides the tectonic and magmatologic evidence. An intracontinental collision event took place between the Yangtze and Cathaysia blocks in the Late Permian. Beginning at the Late Triassic, the tectonic movement was completely changed in nature and entered a post-collisional extensional orogenic and basin-making process. This paper presents sedimentological evidence from the Late Permian to the Middle Triassic in the Shiwandashan basin at the southwestern end of the junction zone between the Yangtze and Cathaysia blocks.
基金supported by the National Natural Science Foundation of China(Nos.41172202,41190073,41302178)the China Geological Survey(No.1212011121256)the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences in Wuhan(No.MSFGPMR201202)
文摘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.
基金supported by the National Natural Science Foundation of China (No. 41072003)the Fostering Foundation of Henan Polytechnic University for the Excellent Ph. D Dissertation (No. 2011011001)
文摘Fluvial deposits from the Middle Triassic Youfangzhuang Formation in Henan Province, China contain a low-diversity trace fossils. Vertical dwelling burrows of opportunists dominate in active channel, whereas horizontal deposit-feeding, grazing, and vertical dwelling burrows occur in overbank deposits. Seven recurrent ichnofabrics were distingushed. The Palaeophycus tubularis ichnofabric pre- serves below scour interface between two fluvial cycles. The Skolithos linearis ichnofabric forms in middle to high-energy, soft substrates in the middle and upper parts of active channel deposits under semi-arid climate. The Skolithos linearis-Planolites montanus ichnofabric occurs in the sediments just a little above the Skolithos linearis ichnofabric and is formed in middle-energy, soft substrates in the up- per part of active channel deposits. The Planolites montanus ichnofabric is mostly preserved in associa- tion with medium- to thick-bedded brown-red silty mudstones or siltstones in low-energy, perennial muddy bottom ponds in overbank settings. The Taenidium barretti ichnofabric is interpreted as peri- odically exposed ephemeral ponds or low-energy distal floodplain. The Skolithos isp. ichnofabric com- monly occurs in middle to high-energy firm ground of proximal foodplain or crevasse-splay deposits. The root trace iehnofabric occurs in the crevasse splay deposits. The presence of thin palaeosols and the abundance of calcretization in mudstones indicate a seasonal climate ranging from humid to semi-arid, with high temperature, rainfall, and well-defined dry and wet seasons.
基金supported by theNSFC(grants no.40572004 and 40702001)
文摘Saurichthys dawaziensis sp. nov., from the third member of the Gejiu Formation （Anisian of Middle Triassic） in the vicinity of Luoping, Yunnan Province, is a small to mediumsized saurichthyid fish. It is characterized by the efferent pseudobranchial arteries penetrating on the parasphenoid and the mandible sensory canal with a branch in the angular. The new species is more derived than the Lower Triassic species in having a relatively narrow postorbital region, short preopercular, single ossification of the sclerotic ring, small haemal arches between the pelvic fins and the anal fin without ossified spines, and in the absence of quadratojugal. It is more primitive than the Middle and Upper Triassic Saurichthys in having fringing fulcra and numerous segments in the unpaired fins, and the presence of both prae- and post-zygapophyses in the neural arches. Some anatomic changes related to the vertebral column and unpaired fins of the genus are also discussed.
基金partly supported by the ARCDP discoverygrant to G. R. Shi (No. DP150100690)supported by a CAS Pioneer Hundred Talents Program (to ML)+2 种基金supported by a grant from the State Key Laboratory of Biogeology and Environmental Biology (No. GBL21410 to ML), China University of Geosciences (Wuhan)a grant from the National Natural Science Foundation of China (No. 41502013)supported by for China Geological Survey projects (Nos. DD20160020, 1212011140051, 12120114030601, and 1212010610211)
文摘The Luoping Biota discovered from the early Middle Triassic （Anisian） Guanling Formation of southwestern China represents a fully recovered shallow marine ecosystem, marking the end point of Early Triassic biotic recovery following the end-Permian mass extinction. Contemporaneously preserved are prolific trace fossils, which offer good opportunities to understand the palaeoecology of marine invertebrates from a fully recovered shallow marine ecosystem. Here we present a newly discovered sinuous branching burrow from the fossil-bearing unit in Member II of the Guanling Formation. Several features, including the horizontal regular sinuous nature, the branching pattern, typical H-junction, and the small wavelength/amplitude ratio of these sinuous structures within the burrow systems justify assignment of these traces as Sinusichnus sinuosus, a trace possibly produced by decapod crustaceans. Close association ofS. sinuosus with Rhizocorallium commune suggests a deposit-feeding strategy of these trace makers. The newly reported Anisian material from the Guanling Formation in Luoping represents first report of Sinusichnus from South China. The global record of Sinusichnus occurrence suggests that these burrows might have an older history than Early Middle Triassic.
基金supported by the Chinese Academy of Sciences(No.XDB26000000)the CAS Pioneer Hundred Talents Program(No.2018-039)+2 种基金the CAS Open Fund(No.193110)the National Natural Science Foundation of China(Nos.41830323,41930322)the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSWDQC023)。
文摘Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be resolved.Herein we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province,southwestern China.Morphological features,together with previous geobiological investigations,suggest that the laminated lime mudstones represent the former presence of microbial mats.These lime mudstones consist mainly of calcite,dolomite and quartz,with clay minerals and pyrites as subordinate components.In particular,micro-analysis shows copious nano-globules(65–878 nm)and capsule-shaped nano-rods in laminations.These low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances(EPS).Nano-sized globules coalesce to form semi-euhedral micrite crystals.We suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local micro-environment.As an intermediate,these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.
基金financed by the Croatian Ministry of Science and EducationUniversity of Zagreb financial support founds
文摘Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazariste were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.
基金ThestudyisjointlysupportedbytheChinaPetroleumCorporation (No .NPJ- 10 0 19)andalsobytheMinistryofScienceandTechnology (SSER)
文摘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.
文摘Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.
文摘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.
基金the National Natural Science Foundationof China!(Nos.49502022and49632070) .
文摘Affected by the Indosinian movement, the sediments in the main part of South China, Yangtze platform, started to transform from marine to continental during the Middle Triassic. In the meantime, a noticeable paleogeographic and sedimentary facies differentiation occurred in the marginal regions of the platforms and produced completely different lithologic and paleontologic sequences in various paleogeographic gradients and sedimentary facies areas, which brought about the difficulties for the stratigraphic correlation based on the traditional stratigraphies. This paper proposes to use some characteristic environmental events as the markers of the stratigraphic correlation across various paleogeographic sedimentary facies, considering that some distinctive regional environmental events should have affected at the same time on the entire basin or the connected sedimentary regions and produced some closely related sedimentary records in the stratigraphic sequences though the affected intensity and recorded pattern might be different among the regions. The change of violent relative sea level (generally water depth) and the alteration of tectonic activity summarized from the dynamic mechanism of sedimentation are the best markers of environmental events for stratigraphic correlation. Based on the analysis and recognition of some significant environmental events at the typical stratigraphic sequences from various paleogeographic sedimentary facies and combined with the consideration of the variations in expressed form and strength of the events among different paleogeographic gradients and sedimentary facies, the stratigraphic sequences from different sedimentary facies can be easily correlated directly. Furthermore, the evolutionary history of the whole sedimentary basin can be clearly established.
基金jointly supported by Department of Natural Resources of Shanxi Provincethe Strategic Priority Research Program of Chinese Academy of Sciences (XDB26000000)。
文摘Kannemeyeriiformes were dominated tetrapods in the Middle Triassic terrestrial faunae of China.Although abundant materials of Sinokannemeyeria have been collected, their postcranial morphology information is not well studied, especially the juveniles. This paper presents a description of an articulated Sinokannemeyeria skeleton from the Middle Triassic Ermaying Formation and reports the histological microstructure of its femur. This specimen represents a late-stage juvenile based on the histological information. For the first time, this specimen offers insights into the postcrania information of juvenile Sinokannemeyeria.
基金funded by the National Natural Science Foundation of China(Nos.41972033,41830320,41572324)。
文摘The Nanpanjiang Basin is a key area for paleontological and biostratigraphical study of the Middle Triassic.Herein we studied Middle Triassic conodonts from a well-exposed section,the Shaiwa Section,which is located at the northwest end of the Nanpanjiang Basin.A total of six Anisian conodont zones are recognized;in ascending order,they are:the Nicoraella germanica Zone,the Nicoraella kockeli Zone,the Paragondolella bulgarica Zone,the Neogondolella constricta Zone,the Neogondolella cornuta Zone,and the Paragondolella excelsa Zone,respectively.The first occurrence of Nicoraella kockeli defines the Bithynian-Pelsonian boundary.The Pelsonian-Illyrian boundary is defined by the first occurrence of Neogondolella constricta.The Anisian-Ladinian boundary cannot be recognized at the Shaiwa Section due to the absence of conodont indicative of the Ladinian.However,the new conodont data indicate that the uppermost strata could be very close to the boundary.The abrasion of conodont surfaces provides evidence for demonstrating reworking at the Shaiwa Section,which makes some conodonts possess a longer stratigraphic range than previously recorded.The variation in relative abundance between blade-shaped conodonts and platform conodonts indicates that segminiplanate elements probably preferred deeper and oxygenated environments whereas a restricted marine environment is more suitable for segminate elements.
基金This study is supported by the National Natural Science Foundation of China( No.4963 2 0 70 )
文摘The Middle Triassic was the great turning period of South China from marine sedimentary basins to continental deposits or erosion. This paper summarizes the distribution and variation of the stratigraphic sequences, lithofacies and biotas in various Middle Triassic depositional basins of South China. The close relationship between the biotic paleoecology and the lithofacies as well as the sedimentary facies, thus the paleogeography, is demonstrated. The process of the transition from the depositional paleogeography and its relation to the tectonic settings is concluded.
基金Supported by National Basic Research Program of China(No.41572043)
文摘Zircon LA-ICP-MS U-Pb geochronology and geochemical analyses are undertaken for the garnet-bear-ing muscovite monzogranite in Yitong area, central Jilin Province. The formation age and petrogenesis of the granite are determined, and the regional tectonic background is discussed. Zircons from the granite are euhe-dral-subhedral in shape, and display fine-scale oscillatory growth zoning, indicating a magmatie origin. LA- ICP-MS zircon U-Pb dating result indicates that the garnet-bearing muscovite monzogranites formed in the mid-dle Triassic （243 Ma ）. The garnet-bearing muscovite monzogranites have high SiO2 （SiO2 = 74.1%- 76.49% ）, rich aluminum （A1203 = 14.47%-14.68% ） and alkali （ NazO ＋ K20 = 4.31%-7.9% ）, low Fe203T and MgO （MgO =0.1%-0. 13% , Fe203T =0.46%-1.02% ）. The ratio of CaO/Na20 is between 0.17--0. 21. The garnet-bearing muscovite monzogranites in Yitong region are relatively enriched in light rare earth elements （LREEs） and large ion lithophile elements （LILEs） , and depleted of heavy rare earth elements （HREEs） and high field strength elements （HFSEs）. They are characterized by high Sr and Ba, poor Rb and Y, and negative Eu abnormally （δEu =0.48-0.62） , with Rb/Sr 〈 1. The εHf（t） values and TDM2 of zircons range from ＋ 6. 10 to ＋ 8.00 and from 725 Ma to 814 Ma, respectively. The above features indicate that gar- net-bearing muscovite monzogranites in Yitong area were derived from partial melting of metasedimentary rock. These granites have high Sr/Y ratios, which suggest they formed in a thickened continental crust. Combined with the coeval granitic rocks in central Jilin Province, we suggested that a significant eollisional and thickening event took place during the Middle Triassic.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC0602704)the National Natural Science Foundation of China(Grant No.U20B6001 and 91755211).
文摘The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.
