Late Triassic Intracontinental Deformation of South Tianshan,Central Asia:Evidence from Syn-tectonic Sedimentation and Detrital Zircon Provenances of the Kuqa Depression

The Tianshan range,a Paleozoic orogenic belt in Central Asia,has undergone multiple phases of tectonic activities characterized by the N-S compression after the early Mesozoic,including the far-field effects of the Cenozoic Indian-Asian collision.However,there are limited reports on the tectonic deformation and initiation of Triassic intracontinental deformation in the Tianshan range.Understanding this structural context is crucial for interpreting the early intracontinental deformation history of the Eurasian continent during the early Mesozoic.Growth strata and syn-tectonic sediments provide a rich source of information on tectonic activities and have been extensively used in the studies of orogenic belts.Based on detail fieldwork conducted in this study,the middle-late Triassic Kelamayi Formation of the northern Kuqa Depression in the southern Tianshan fold-thrust belt has been identified as the typical syn-tectonic growth strata.The youngest detrital zircon component in two lithic sandstone samples from the bottom and top of the Kelamayi growth strata yielded U-Pb ages of 223.4±3.1 and 215.5±2.9 Ma,respectively,indicating that the maximum depositional age of the bottom and top of the Kelamayi growth strata is 226-220 and 218-212 Ma.The geochronological distribution of detrital samples from the Early-Middle Triassic and Late Triassic revealed abrupt changes,suggesting a new source supply resulting from tectonic activation in the Tianshan range.The coupling relationship between the syn-tectonic sedimentation of the Kelamayi Formation and the South Tianshan fold-thrust system provides robust evidence that the Triassic intracontinental deformation of the South Tianshan range began at approximately 226-220 Ma(during the Late Triassic)and ended at approximately 218-212 Ma.These findings provide crucial constraints for understanding the intraplate deformation in the Tianshan range during the Triassic.

Geochronology and Geochemistry of the Xingxingxia Triassic A-type Granites in Central Tianshan,NW China:Petrogenesis and Tectonic Implications

The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt.In this study,we present SHRIMP zircon U-Pb ages,Hf isotopic and geochemical data on the Xingxingxia biotite granite,amazonite granite and granitic pegmatite in Central Tianshan,NW China.Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite.These granitoid rocks have high K_(2)O with low MgO and CaO contents.They are enriched in Nb,Ta,Hf and Y,while being depleted in Ba and Sr,showing flat HREE patterns and negative Eu anomalies.They have typical A-type granite geochemical signatures with high Ga/A_(1)(8–13)and TFeO/(TFeO+MgO)ratios,showing an A_(2) affinity for biotite granite and an A_(1) affinity for amazonite granite and granitic pegmatite.Zircon ε_(Hf)(t)values of the granitoids are 0.45–2.66,with Hf model ages of 0.99–1.17 Ga.This suggests that these A-type granites originated from partial melting of the lower crust.We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.

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).

Characteristics and control factors of feldspar dissolution in gravity flow sandstone of Chang 7 Member,Triassic Yanchang Formation,Ordos Basin,NW China

To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.

LA-ICP-MS zircon U-Pb dating of tuffites in the Sachakou Pb-Zn mining area, Karakorum, Xinjiang and its establishment of Early Triassic strata

1.Objective In the past decade,a group of medium to giant lead-zinc deposits,represented by Huoshaoyun,Sachakou,and Yuanbaoling,have been discovered in the Aksai Chin region of Karakoram,Xinjiang.They are all located in the Mesozoic carbonate and clastic rock formations.The Sachakou leadzinc mining area is adjacent to the northwest of the Huoshaoyun lead-zinc mining area and is in the same stratigraphic layer as Huoshaoyun.Although many scholars have been arguing about the type and age of Huoshaoyun lead-zinc mineralization,few scholars have paid attention to the classification of the ore-bearing strata in the area.The stratigraphy of the Lower Permian Shenxianwan Group to the Upper Cretaceous Tielongtan Group is exposed in the Sachakou area of Karakorum,Xinjiang,however,the Late Permian-Early Triassic stratigraphy is missing(Fig.1a).Due to the harsh natural conditions in the area and the low level of work,the stratigraphic delineation is not exhaustive,and the regional lithology is dominated by carbonates and clastic rocks,which makes it difficult to identify the age of the regional lithology and causes problems for the exploration and research of lead-zinc in the area.

Discovery and Significance of the Triassic–Late Paleozoic Double-layered Basement in the Songliao Basin:Based on the Complete Coring Data from ICDP Borehole SK2

The Songliao Basin(SLB)covers an area of approximately 260,000 km2in northeastern Asia and preserves a continuous and complete Cretaceous terrestrial record(Wang et al.,2021).The region is the most important petroliferous sedimentary basin in China because of its continual annual oil and gas equivalent production of tens of millions of tons(ca.220–440 million barrels per year)since 1959.The SLB was previously thought to have developed on Hercynian basement and accumulated continuous sedimentary deposits during the Late Jurassic and Cretaceous(Wan et al.,2013;Wang et al.,2016).

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.

Review of the Triassic Curvicubitidae(Insecta:Hemiptera),with Description of New Material from China

The Curvicubitidae is a Triassic cicada family with some taxa systematically debatable.Here a new curvicubitid species,Beaconiella tongchuanensis sp.nov.,is established from the Middle Triassic Tongchuan Entomofauna in NW China.Restudy of the two Australian species of Beaconiella Evans,1963(B.fennahi and B.multivenata)confirms that they are different species and first reveals the hindwing venation of B.multivenata.A detailed restudy of Curvicubitus triassicus Hong,1984 confirms the treatment of Curvicubitus as a junior synonym of Beaconiella.A key to all the six species of Beaconiella in Curvicubitidae is first given.Although reported from only three sites,the family Curvicubitidae potentially was globally distributed during the Middle-Late Triassic,implying that this family probably originated as early as the Early Triassic or even the Permian.

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.

Hydrocarbon Potential of the Triassic-Jurassic Sediments in Southeast Sulawesi, Indonesia, Based on Lithofacies and Geochemical Analysis

Triassic-Jurassic carbonates widely distributed in Eastern Indonesia are believed as oils source rock. The Mesozoic Tokala Formation exhibit source rock potential, as evidenced by high contents of organic matter. Recent exploration has been conducted in southeastern Sulawesi, targeting the Mesozoic intervals. Therefore, in this study, we attempted to determine source rock potential of Tokala Formation outcropped in southeastern Sulawesi area and its capability to generate hydrocarbon. Five distinct lithofacies were delineated, emphasizing lithological and mineralogical features: foraminifera wackestone (FW), lime mudstone (LM), massive bioturbated calcareous-argillaceous shale (MBCAS), weakly laminated argillaceous-calcareous shale (WLACS), and strongly laminated calcareous-argillaceous shale (SLCAS). Subsequent analyses showed that carbonate-rich samples (FW and LM facies, >50% CaO) had poor source rock potential. Conversely, shale facies with moderate carbonate content (WLACS, MBCAS, and SLCAS, 15% - 50% CaO) had good to excellent source rock characteristics, qualifying them as preferable source rock. In addition, levels of SiO2 and Al2O3 should not be neglected, as these constituents play important roles in clay mineral adsorption. Laminated shale facies with moderate CaO content tended to be more promising as source rock than bioturbated facies. The shale facies of Tokala Formation indicate prospective source rock horizon.

布青山-阿尼玛卿山两侧三叠纪盆地沉积特征及其对布青山-阿尼玛卿洋关闭时限的约束

位于布青山-阿尼玛卿山两侧的共和盆地和巴颜喀拉山盆地,三叠纪时其沉积特征与古特提斯洋的分支洋———布青山-阿尼玛卿山洋的演化密切相关。前人对盆地东部进行了大量研究工作,但对盆地中-西部的研究较为薄弱。本文选取共和盆地隆务河群和巴颜喀拉山盆地巴颜喀拉山群为研究对象,通过对二者的沉积序列、古流向、沉积物源和原型盆地类型等综合分析研究,结合已有的区域地质资料,探讨布青山-阿尼玛卿洋的闭合时限。研究认为:①共和盆地三叠纪时为弧后盆地,接受不同的物源区,玛沁以北,共和、贵南、泽库、河南以西物源区为东昆仑和柴达木,玛曲以北,共和、贵南、泽库、河南以东物源主要来源于东北部的祁连山,玛沁、玛曲以南物源来源于南部布青山-阿尼玛卿山;②巴颜喀拉盆地三叠纪时为残留洋盆地,主要物源来源于北侧的布青山—阿尼玛卿山;③布青山-阿尼玛卿山地区在三叠系沉积之前已经隆升并成为剥蚀区,为两侧盆地体提供主要物源。

北秦岭南召盆地太山庙组下部凝灰岩锆石U-Pb年龄及其地质意义

晚三叠世卡尼期全球古气候发生明显转变,全球降水量增加,海水温度上升了6~8℃,大量陆源碎屑物质输入海洋,导致海洋中出现碳酸盐生产危机。北秦岭南召盆地太山庙组可能记录了卡尼期洪水事件。目的为精确限定太山庙组沉积时代,凸显其地质意义,方法采用激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)对太山庙组下部凝灰岩进行锆石U-Pb同位素定年分析。结果结果表明:凝灰岩锆石颗粒呈粒状、短柱状,无磨圆;阴极发光图像显示振荡环带结构明显;根据阴极发光图像和Th/U,认为太山庙组下部凝灰岩中18颗锆石均为火山来源,剔除轻稀土富集的锆石后,选择其中15颗锆石进行计算,得到其加权平均年龄为(241.4±1.3)Ma(1σ;MSWD=0.27),代表凝灰岩中锆石的结晶年龄;结合前人研究成果,计算出太山庙组下部平均沉积速率为20.6 m/Ma,太山庙组底界年龄约246 Ma,因此,太山庙组至少自中三叠世安尼期就开始沉积,至晚三叠世卡尼期末结束;根据南召盆地遗迹化石组合演化规律和植物孢粉变化,认为太山庙组沉积时期古气候发生了明显转变,由干旱炎热气候转变为温暖、湿润气候。结论研究结果对北秦岭南召盆地三叠纪地层划分产生了新认识,有助于研究探讨南召盆地对卡尼期洪水事件的沉积响应。

黔南Ladinian-Carnian期海侵与碳酸盐岩台地演化

位于扬子地块西南缘的黔南地区在中三叠世晚期(相当于Ladinian-Carnian期)出现了一次大规模的海侵,使从晚元古代至中三叠世末期(约从850～236Ma)以浅水相碳酸盐岩沉积为主的扬子碳酸盐岩台地被海水淹没,形成了一套深水相的瘤状暗色灰泥岩和代表最大海泛面的黑色页岩沉积,之后扬子台地被以陆相碎屑岩为主的沉积所覆盖,从此结束了其长达约630my的碳酸盐岩台地生长演化历史。研究表明,黔西南地区Ladinian-Carnian期海侵与全球海平面变化同步,是一次全球性的海平面变化。

阿拉善地区二叠纪-三叠纪构造变形环境与属性:问题与争论

【研究目的】二叠纪—三叠纪是中亚造山带演化的关键阶段,形成了一系列不同性质、机制和时代的变形,可能代表了古亚洲洋俯冲-碰撞-陆内3个重要演化阶段的产物。近年来的工作在中亚造山带中段的阿拉善地区识别出大量的二叠纪—三叠纪变形,但是对这些变形的解释和认识存在很多争论,导致对古亚洲洋关闭时限产生不同认识。【研究方法】系统介绍目前已知阿拉善不同地区二叠纪—三叠纪变形,厘定了该时期阿拉善地区的构造序列和特点。【研究结果】中二叠世晚期(270~260 Ma),在阿拉善北部形成广泛分布的线性褶皱与逆冲构造。晚二叠世末—三叠纪初,形成卷入整个阿拉善地块与中亚造山带的大型韧性剪切变形;晚三叠世,形成了切割造山带的大型左行走滑变形。以上3期变形的切割关系在阿拉善东北部狼山、中部杭乌拉、西部霍布哈尔等地区最典型。系统分析碰撞阶段和陆内阶段的变形特点,认为晚二叠世变形代表了古亚洲洋关闭碰撞阶段的变形,晚二叠世末—三叠纪初的变形代表了造山带形成之后,Pangea超大陆形成的巨型剪切变形,是中亚造山带形成后经历的第一期陆内变形,而晚三叠世变形代表了受控于板块周缘陆陆碰撞的远程效应。【结论】古大洋消失后的碰撞阶段变形与陆内变形有一定的差异,从变形角度可以有效限定古亚洲洋不同阶段的演化。以阿拉善地区为代表的中亚造山带在洋陆转换阶段内连续经历不同性质、不同方向变形的叠加,也是增生型造山带的重要特征。

鄂尔多斯盆地延安地区三叠系长7页岩源储配置及油气富集规律

鄂尔多斯盆地三叠系长7段陆相页岩油气资源丰富,勘探开发潜力较大。通过岩心观察及测井、录井资料分析,综合地球化学数据、X射线衍射分析及现场解析气体数据等,对鄂尔多斯盆地延安地区三叠系长7段3个亚段页岩的源储特征进行了分析,并对不同源储组合特征及其与油气富集相关性进行了解剖。研究结果表明:①鄂尔多斯盆地延安地区三叠系延长组长7段有机质类型以Ⅱ1型和Ⅱ_(2)型为主,Ⅰ型次之,自上而下3个亚段的总有机碳(TOC)质量分数平均值分别为3.39%,4.35%,5.57%,镜质体反射率(Ro)分别为0.69%,0.97%,1.31%,分别处于低成熟、成熟、高成熟演化阶段,分别为差烃源岩、中等烃源岩、优质烃源岩。②研究区长7_(3)亚段泥页岩矿物组分具有富黏土矿物特征,长7_(2)亚段黏土矿物含量高于长7_(1)亚段,3个亚段的孔隙类型分别以溶蚀孔、粒间孔—溶孔、粒间孔为主,储层可划分为Ⅰ类(优)、Ⅱ类(中)和Ⅲ类(差)。③研究区主要发育优质烃源岩-差储层、中等烃源岩-优质储层、差烃源岩-中等储层、中等烃源岩-中等储层、优质烃源岩-中等储层、差烃源岩-优质储层6种源储配置特征,长7_(3)亚段油气富集程度最高,长7_(2)亚段次之,长7_(1)亚段不利于页岩油气的富集成藏。④高有机质丰度、高有机质成熟度的泥页岩具有较好的生烃潜力,高黏土矿物含量、较好的孔隙连通性有利于油气运移聚集成藏,源储配置特征控制着页岩油气的富集部位。

西昆仑稀有金属成矿带成矿大地构造背景:来自琅达板岩体的地球化学制约

琅达板岩体位于西昆仑造山带西端康西瓦构造带南侧的木吉地区,该岩体主要岩性为石英二长岩,锆石LA-ICP-MS U-Pb定年结果显示,^(206)Pb/238U加权平均年龄为214.3±0.8 Ma,表明其侵位于晚三叠世。琅达板石英二长岩是钾玄质岩石且具有强过铝质的组分;轻、重稀土元素分异明显,稀土元素配分模式呈轻稀土元素富集的右倾型,重稀土元素分异不明显(Dy_(N)/Yb_(N)=1.24~1.66),具有中等Eu负异常(δEu=0.59~0.77);微量元素蛛网图呈现显著的Ba、Nb、Sr、P和Ti负异常。琅达板岩体具有显著的弧岩浆特征,其形成可能与乔尔天山古特提斯洋的北向俯冲有关。西昆仑稀有金属伟晶岩成矿带的侵位时间为209~204 Ma,稍晚于琅达板岩体,也比麻扎-康西瓦古特提斯洋盆闭合时间晚,但早于乔尔天山古特提斯洋盆闭合时间。结合成矿带的大地构造位置以及前人研究成果,认为西昆仑稀有金属伟晶岩成矿带可能形成于麻扎-康西瓦古特提斯洋盆闭合以后的后碰撞和乔尔天山古特提斯洋北向俯冲的复合大地构造环境。

库车坳陷上三叠统黄山街组沉积特征及地质意义

塔里木盆地库车坳陷三叠系黄山街组为一套源、储、盖共生的地层,是未来潜在的油气勘探目标。但目前缺乏其详细沉积特征与演化方面的研究,不利于对古地理演化的理解。故基于多条露头剖面,详细分析沉积特征并揭示其地质意义,结果表明:①黄山街组一段与二段构成向上变深的下旋回,三段构成向上变深但不完整的中旋回,四段构成浅→深→浅的上旋回;②由砾质粗碎屑构成的黄山街组一段与三段是物源区在印支运动中两幕强烈隆升的沉积响应;③黄山街组中发育有洪水、地震等所致的事件沉积;④黄四段发育的暗色泥岩是高可容纳空间下充足物源的快速沉积;⑤黄三段沉积之后发生了区域性的构造抬升及构造—沉积转换,源区也呈准平原化;⑥黄四段与下伏黄三段及上覆塔里奇克组之间均存在一定的沉积间断。

川中地区三叠系须家河组二段致密气储层特征及主控因素

为了明确川中地区三叠系须家河组二段(须二段)致密气优质储层特征、成因及分布特征,综合利用铸体薄片、扫描电镜、核磁共振、高压压汞试验和CT测试等资料,明确了储层质量的主控因素,优选多种宏观和微观参数,通过Q型聚类对储层进行了定量划分,并对各类别储层的分布特征进行了分析。研究结果表明:①川中三叠系须二段为岩屑长石砂岩和长石岩屑砂岩,平均孔隙度和平均渗透率分别为6.58%和0.21 mD,为特低孔—低孔、低渗致密气储层;储集空间以残余粒间孔和粒内溶孔为主,其次为粒间溶孔和裂缝,孔隙和喉道半径分别为1.31~55.00μm和0.05~1.04μm,为微米孔隙和微米-亚微米喉道组合。②研究区沉积作用控制了岩石粒度和泥质含量,是决定初始孔隙度形成和后期演化的基础条件;强烈的机械压实和胶结作用分别破坏了14.6%~20.1%和9.8%~15.1%的原始孔隙,是造成储层致密化的主要原因;次生溶蚀、绿泥石包膜等建设性成岩作用形成了次生溶孔且对原生孔隙具有一定保护作用,挤压破裂形成的裂缝进一步扩大了次生溶蚀范围,是将致密砂岩改造成优质储层的关键。③研究区须二段储层可分为4类,不同类型储层的物性和微观结构差异较大,Ⅰ,Ⅱ类储层物性好、试气产能高,是主要的“甜点”储层和有利开发目标,主要分布于区域中部H1,H3井区和东部H125井区,纵向上集中在须二上亚段。

Late Triassic sedimentary records in the northern Tethyan Himalaya:Tectonic link with Greater India

The Upper Triassic flysch sediments(Nieru Formation and Langjiexue Group)exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen.This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area.The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances.The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust.These rocks have relatively low Chemical Index of Alteration values(with an average of 62)and Index of Compositional Variability values(0.69),indicating that they experienced weak weathering and were mainly derived from a mature source.The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidicintermediate igneous source.Furthermore,hornblende and feldspar experienced decomposition in the provenance,and the sediment became enriched in zircon and monazite during sediment transport.The detrital zircons in the strata feature two main age peaks at 225-275 Ma and 500-600 Ma,nearly continuous Paleoproterozoic to Neoproterozoic ages,and a broad inconspicuous cluster in the Tonian-Stenian(800-1200 Ma).The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300-325 Ma(characteristic of the Lhasa block)and 1150-1200 Ma(characteristic of the Lhasa and West Australia blocks).Therefore,neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata.Newly discovered Permian-Triassic basalt and mafic dikes in the Himalayas could have provided the 225-275 Ma detrital zircons.Therefore,Indian and Himalayan units were the main provenances of the flysch strata.The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous.This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.

First Record of Protorosaurid Reptile (Order Protorosauria) from the Middle Triassic of China

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.