A new species of Gladiopycnodus (Coccodontoidea,Pycnodontomorpha) from the Cretaceous of Lebanon provides new insights about the morphological diversification of pycnodont fishes through time

The Coccondontoidea is a distinctive superfamily of pycnodont fishes characterized by a series of derived characters, including thick and well-ossified cranial bones supporting horns and spines and a hypertrophied pectoral girdle sutured to the skull forming a sort of cephalo-torax. A new distinctive coccodontoid species, Gladiopycnodus byrnei n. sp., is described from the Cenomanian locality of Hjoûla, Lebanon. This new species exhibits a unique combination of features that clearly support its inclusion within the coccodontoid family Gladiopycnodontidae, including an extremely elongate snout forming a sword-shaped rostrum, thick dermal bones ornamented with rounded tubercles, large supracleithrum and cleithrum extensively sutured to the skull, and irregularly imbricated scales covering the entire body. The new taxon differs from type species G. karami by having different meristic counts and body proportions, dermal bones strongly ornamentated, skull roof with partially fused bones, scales ornamented with small tubercles, and rounded scales covering the caudal peduncle absent. The presence of pectoral fins in our exquisitely well-preserved specimen allowed us to redefine the morphology of the genus Gladiopycnodus, also modifying the diagnosis of the family. In order to interpret the patterns of morphospace occupation and quantify the morphological diversification of pycnodonts through time, the geometric morphometric approach was used. The morphospace analysis revealed that a significant increase in morphological disparity of pycnodonts during the Late Cretaceous was related, at least in part, to the appearance of the representatives of the superfamily Coccodontoidea. The rapid evolutionary radiation of these well-armored pycnodonts was interpreted as an adaptive solution in response to the large predatory-prey escalation in the context of the Mesozoic Marine Revolution.     

Palynological assemblages of non-marine rocks at the Permian–Triassic boundary, western Guizhou and eastern Yunnan, South China

Marine and non-marine facies of the Permian–Triassic boundary stratigraphic set (PTBST) are well developed in South China. Palynological assemblages enable subdivision and correlation of the Permian–Triassic boundary (PTB) rocks. Three palynological assemblages are recognized across the PTBST in two terrestrial PTB sections in western Guizhou and eastern Yunnan, South China. Assemblage 1 (Xuanwei Formation) is a Late Permian palynological assemblage dominated by ferns and pteridosperms, with minor gymnosperms. Most taxa are typical long-ranging Paleozoic forms, but the appearance of Lueckisporites confirms a Late Permian age for this assemblage. Assemblage 2 (PTBST) is marked by an abrupt decrease in palynomorph abundance and diversity, and thriving fungal/algal(?) spores. Assemblage 2 is still dominated by ferns and pteridosperms, with a few gymnosperms, but is characterized by a mixed palynoflora containing both Late Permian and Early Triassic elements. Most taxa are typical Late Permian ones also found in Assemblage 1, however, some taxa of Early Triassic aspect, e.g. Lundbladispora and Taeniaesporites, appeared for the first time. In Assemblage 3 (top Xuanwei Formation and Kayitou Formation), the proportion of gymnosperm pollen increases rapidly, exceeding that of ferns and pteridosperms, but the abundance of palynomorphs is still low. Typical Early Triassic taxa (such as Lundbladispora, Aratrisporites and Taeniaesporites) are present in greater abundance and confirms an Early Triassic age for this assemblage.     

云南鲁史三合洞组地层时代讨论

云南兰坪盆地三合洞组的时代存在争议,有早古生代和中生代两种观点。本文通过对云南鲁史上三叠统三合洞组和挖鲁八组岩石地层、古生物化石、微体化石及碎屑锆石U-Pb年代学研究,认为三合洞组时代为晚三叠世。本区三合洞组生物碎屑灰岩、泥晶灰岩及白云质灰岩与挖鲁八组炭质板岩呈整合接触关系,与歪古村组砂质板岩呈逆断层接触关系,整体表现为倒转地层。挖鲁八组炭质板岩中采获叉皱海燕蛤、虚海燕蛤等晚三叠世化石,而三合洞组灰岩中的小欣德牙形刺、奥泽克刺、滑梯螺、长卵形槽花介等微体化石时代也为晚三叠世。笔者从挖鲁八组粉砂岩中获得碎屑锆石U-Pb年龄,其最小年龄为218 Ma,指示挖鲁八组的最晚沉积时代为晚三叠世。综合生物化石和同位素年代学资料,认为兰坪盆地三合洞组的时代为晚三叠世。     

First Late Triassic Record of a Paleoentomofauna from South America(Malargüe Basin,Mendoza Province,Argentina)

<正>Late Middle Triassic to early Late Triassic insects from Argentina have been previously described from the Bermejo and Cuyana Basins where they have been recovered from the Ischichuca-Los Rastros and Potrerillos-Cacheuta Formations,respectively.The insect fauna discussed herein was collected during field studies in 1986/1987 from the Llantenes section(Norian to Rhaetian? Late Triassic),which is situated in the Malargue Basin in southern Mendoza province.The insect remains were found in the upper part of the Llantenes section (Llantenes Formation),which is built up of two coarsening-upwards cycles reflecting a deltaic progradation of a fluvial into a lacustrine environment(lower part),succeeded by repeated progradations into a floodplain-dominated environment(upper part;with finds of insects,conchostracans,fish remains,plant fragments,and drifted logs).The new finds represent the youngest Triassic insect records described from Argentina and even from South America in its entirety.There is only one contemporaneous fossil assemblage in Gondwana:in the Clarence/Moreton Basin(Aberdare Conglomerate;Late Norian)in Australia.The new Triassic insects include an impression of an isolated Mecopterida-like wing(Mendozachorista volkheimeri gen.et sp.nov.; Mendozachoristidae fam.nov.),coleopteran elytra of the Permosynidae(Ademosyne rosenfeldi sp.nov.and Ademosyne llantenesensis sp.nov.)and other isolated body fragments.This new Late Triassic entomofauna from Argentina is of considerable importance in the reconstruction of the biotic recovery of continental environments in Gondwana after the catastrophic mass extinction at the P/T boundary.     

Zircon ages and Hf isotopic compositions of Permian and Triassic A-type granites from central Inner Mongolia and their significance for late Palaeozoic and early Mesozoic evolution of the Central Asian Orogenic Belt

ABSTRACT

This work presents zircon ages and Hf-in-zircon isotopic data for Permian and Triassic A-type granitoids and reviews the evolution of central Inner Mongolia, China, during the early Permian and Late Triassic. SHRIMP U–Pb dating of zircons of peralkaline granites yielded ²⁰⁶Pb/²³⁸U ages of 294 ± 4 Ma and 293 ± 9 Ma that reflect the time of Permian magmatism. Zircon ages were also obtained for Late Triassic granites (226 ± 4 Ma, 224 ± 4 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia.

The Permian peralkaline granites show typical geochemical features of A-type granites, which also have highly positive zircon ε_Hf(t) values (+4.9 – +17.1), indicating a significant contribution of an isotopically depleted source, likely formed from mantle-derived magmas. Late Triassic A-type granitoids, however, in central Inner Mongolia show large variations and mostly positive in zircon ε_Hf(t) values (?1.3 – +13.5), suggesting derivation from a mixture of crust and mantle or metasomatized lithospheric mantle with crustal contamination. The geochemical characteristics of the Permian peralkaline granites and Late Triassic A-type granitoids are consistent with a post-collisional setting and were likely related to asthenosphere upwelling during the evolution of the Northern Block and Central Asian Orogenic Belt (CAOB).     

Stratigraphy, biostratigraphy and C-isotopes of the Permian–Triassic non-marine sequence at Dalongkou and Lucaogou, Xinjiang Province, China

Measured lithostratigraphic sections of the classic Permian–Triassic non-marine transitional sequences covering the upper Quanzijie, Wutonggou, Guodikeng and lower Jiucaiyuan Formations at Dalongkou and Lucaogou, Xinjiang Province, China are presented. These measured sections form the framework and reference sections for a range of multi-disciplinary studies of the P–T transition in this large ancient lake basin, including palynostratigraphy, vertebrate biostratigraphy, chemostratigraphy and magnetostratigraphy. The 121 m thick Wutonggou Formation at Dalongkou includes 12 sandstone units ranging in thickness from 0.5 to 10.5 m that represent cyclical coarse terrigenous input to the lake basin during the Late Permian. The rhythmically-bedded, mudstone-dominated Guodikeng Formation is 197 m and 209 m thick on the north and south limbs of the Dalongkou anticline, respectively, and 129 m thick at Lucaogou. Based on limited palynological data, the Permian–Triassic boundary was previously placed approximately 50 m below the top of this formation at Dalongkou. This boundary does not coincide with any mappable lithologic unit, such as the basal sandstones of the overlying Jiucaiyuan Formation, assigned to the Early Triassic. The presence of multiple organic δ¹³C-isotope excursions, mutant pollen, and multiple algal and conchostracan blooms in this formation, together with Late Permian palynomorphs, suggests that the Guodikeng Formation records multiple climatic perturbation signals representing environmental stress during the late Permian mass extinction interval. The overlap between the vertebrates Dicynodon and Lystrosaurus in the upper part of this formation, and the occurrence of late Permian spores and the latest Permian to earliest Triassic megaspore Otynisporites eotriassicus is consistent with a latest Permian age for at least part of the Guodikeng Formation. Palynostratigrahic placement of the Permian–Triassic boundary in the Junggar Basin remains problematic because key miospore taxa, such as Aratrisporites spp. are not present. Palynomorphs from the Guodikeng are assigned to two assemblages; the youngest, from the upper 100 m of the formation (and the overlying Jiucaiyuan Formation), contains both typical Permian elements and distinctive taxa that elsewhere are known from the Early Triassic of Canada, Greenland, Norway, and Russia. The latter include spores assigned to Pechorosporites disertus, Lundbladispora foveota, Naumovaspora striata, Decussatisporites mulstrigatus and Leptolepidites jonkerii. While the presence of Devonian and Carboniferous spores and Early Permian pollen demonstrate reworking is occurring in the Guodikeng assemblages, the sometimes common occurrence of Scutasporites sp. cf. Scutasporites unicus, and other pollen, suggests that the Late Permian elements are in place, and that the upper assemblage derives from a genuine transitional flora of Early Triassic aspect. In the Junggar Basin, biostratigraphic data and magnetostratigraphic data indicate that the Permian–Triassic boundary (GSSP Level) is in the middle to upper Guodikeng Formation and perhaps as high as the formational contact with the overlying Jiucaiyuan Formation.     

Geochronology and geochemistry of Late Triassic bimodal igneous rocks at the eastern margin of the Songnen–Zhangguangcai Range Massif,Northeast China: petrogenesis and tectonic implications

Abstract

New zircon laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectroscopy U–Pb ages, and Hf isotope and whole-rock geochemical data are reported for Mesozoic igneous rocks from the eastern margin of the Songnen–Zhangguangcai Range Massif, Northeast China, in order to document the petrogenesis of the igneous rocks and reconstruct the early Mesozoic tectonic setting of the region. Zircons from five representative igneous rocks are euhedral–subhedral and display oscillatory growth zoning or striped absorption in cathodoluminescence images, suggesting a magmatic origin. The dating results indicate that granite, gabbro, and rhyolite from the eastern Songnen–Zhangguangcai Range Massif formed during Late Triassic (204–211 Ma). The Late Triassic granitoids and rhyolites have an affinity to A-type granites or rhyolites. Their zircon ε_Hf(t) values and Hf two-stage model ages range from –3.8 to +3.8 and from 999 to 1485 Ma, respectively, indicating that their primary melts were derived from the partial melting of the Meso-Proterozoic crust. The geochemistry of coeval gabbros, which reflects primary magma composition, shows a significant large ion lithophile element (e.g. Ba and Sr) enrichment and high field strength element (i.e. Zr, Hf, Nb, Ta, and Ti) depletion. Based on zircon ε_Hf(t) values (–4.2 to +2.8) and Hf single-stage model ages (746–1031 Ma), we conclude that the mafic magma is the product of partial melting of lithospheric mantle that was metasomatically enriched by fluids derived from the subducted oceanic crust. The Late Triassic magmatism along the eastern margin of the Eurasian continent has bimodal magma compositions, indicating an extensional setting after the final closure of the Palaeo-Asian Ocean rather than being related to subduction of the Palaeo-Pacific Plate beneath the Eurasian continent. The occurrence of Late Triassic igneous rocks on the eastern side of the Mudanjiang Fault suggests that this fault does not represent the suture zone between the Songnen–Zhangguangcai Range and Jiamusi massifs.     

Guanling Biota: A Marker of Triassic Biotic Recovery from the end-Permian Extinction in the Ancient Guizhou Sea

After a slow recovery from the end-Permian extinction during the Early Triassic and rapid radiation in the Middle Triassic, evolution of organisms reached a new peak phase in the Late Triassic. The Guanling Biota from the Wayao Member （conodont Paragondolella polygnathiformis Zone）, Falang Formation, Xinpu, Guanling County, Guizhou Province, southwestern China corresponds to this peak that marks the full recovery from the end-Permian extinction of marine ecosystems. The biota is of high diversity, containing well preserved and completely articulated skeletons of vertebrates comprising marine reptiles, fishes, and invertebrates including crinoids, ammonites, bivalves, and other fossils, and is one of the best examples of marine ecosystem records in life history. The fossil marine reptiles and crinoids are most significant in this biota, especially the marine reptiles, which provide an important link between the Triassic Pacific and Tethys, and between Triassic basal forms and the Jurassic-Cretaceous marine top predators. The most remarkable fossils are the large completely articulated ichthyosaur skeletons up to and more than 10 m, and the first recorded thalattosaurs and placodonts in China. Following our review, of the 17 named reptilian taxa the eight listed here are considered to be valid： three ichthyosaurs （Qianichthyosaurus zhoui Li, 1999; Guizhouichthyosaurus tangae Cao and Luo in Yin et al., 2000, Guanlingsaurus liangae Yin in Yin et al., 2000）, three thalattosaurs （Anshunsaurus huangguoshuensis Liu, 1999, Xinpusaurus suni Yin in Yin et al., 2000, Xinpusaurus kohi Jiang et al., 2004）, and two placodonts （Sinocyamodus xinpuensis Li, 2000, Psephochelys polyosteoderma Li and Rieppel, 2002）. Mixosaurus guanlingensis Cao in Yin et al., 2000 might be a junior synonym of Qianichthyosaurus zhoui Li, 1999, and Cymbospondylus asiaticus Li and You, 2002 and Panjiangsaurus epicharis Chen and Cheng, 2003 might be junior synonyms of Guizhouichthyosaurus tangae Cao and Luo in Yin et al., 2000. It needs to re-describe the holotypes after a complete preparation for clarifying the taxonomic status of Typicusichthyosaurus tsaihuae Yu in Yin et al., 2000, Xinpusaurus bamaolinensis Cheng, 2003, Neosinosaurus hoangi （Zhou in Yin et al., 2000）, Wayaosaurus geei Zhou in Yin et al., 2000, Wayaosaurus bellus Zhou in Yin et al., 2000 and Placochelys ？ minutus Yin and Luo in Yin et al., 2000.     

藏北羌塘中部上二叠统—下三叠统天泉山组的建立及意义——对龙木错-双湖-澜沧江洋构造演化的指示

藏北羌塘中部改则县以北天泉山、屏风岭等地区大面积分布一套浅变质岩系,岩性以变质杂砂岩、千枚岩为主,夹变质玄武岩、变质安山岩等火山岩夹层,因缺乏化石依据时代不明。通过LA-ICP-MS锆石U-Pb同位素定年测得安山岩的~(206)Pb/~(238)U年龄为251.4±2.4Ma,同时结合该地区已测得的254Ma的~(206)Pb/~(238)U年龄,证实这套浅变质岩系的时代应属于晚二叠世—早三叠世,并非传统意义的展金组。在剖面测制和区域对比的基础上,将天泉山、屏风岭一带的浅变质岩系重新厘定为上二叠统—下三叠统天泉山组。天泉山组的发现和建立不仅进一步完善了该区的地层系统,而且是龙木错-双湖-澜沧江洋首次发现的晚二叠世—早三叠世洋盆地层记录,为进一步丰富和研究龙木错-双湖-澜沧江洋的演化提供了重要的地层证据。     

西藏仲巴中－晚三叠世放射虫化石特征及其地质意义

在1∶25万霍尔巴幅区域地质调查中,在雅鲁藏布江结合带穷果群上部及修康群中发现了较多的硅质板岩,其内含有较丰富的放射虫化石,共有48属35种,可识别为Cenosphaera-Phormocyrtis,Capnuchosphaera-Angulobracchia和Parahsuum-Citriduma 3个组合,时代为中—晚三叠世。厘定修康群的形成时代为晚三叠世,穷果群的形成时代为中三叠世。这一发现为确定蛇绿岩的时代提供了重要的古生物依据,表明该区蛇绿岩的形成时代应早于中三叠世。结合区域地质特征,修康群应形成于大陆斜坡-深海沉积环境,位于南带特提斯洋盆区的边部地带。     

西藏打加错晚三叠世安山质岩浆作用的锆石U-Pb年代学和Hf同位素

青藏高原南部拉萨地体晚三叠世-早侏罗世时期岩浆活动的地球动力学背景仍是尚待解决的一个重要科学问题。本文报道了南部拉萨地体西部打加错地区新发现的安山玢岩的锆石U-Pb年代学、Hf同位素和全岩地球化学数据。打加错安山玢岩主要由蚀变细粒斜长石、辉石和角闪石组成。2件样品的LA-ICP-MS锆石U-Pb定年结果分别为204±4Ma和203±2Ma,表明打加错地区在晚三叠世发生了安山质岩浆活动。结合近期报道的打加错地区辉石角闪二长闪长岩的年龄(207.3±3.6Ma)记录,表明南部拉萨地体西部打加错地区发生了晚三叠世岩浆活动。2件安山玢岩的锆石εHf(t)值多为正值(分别为-2.2~+8.8和-2.0~+10.7),可比于南部拉萨地体中东部其它地区同期岩浆记录的Hf同位素成分(如:工布江达南部203Ma正长花岗岩的锆石εHf(t)为-4.9~+2.7;日喀则东部约205Ma二长花岗岩的锆石εHf(t)为+11.9~+15.8),这表明南部拉萨地体晚三叠世岩浆活动从东工布江达向西延伸到打加错一带,东西延伸约800km。打加错地区2件安山玢岩样品(SiO2=56.1%~59.0%)以较低Mg#(45.8~48.7)和Al2O3含量(16.4%~17.0%)为特征,属于偏铝质钾玄质-高钾钙碱性火山岩。本文获得的新数据,结合最近报道的早侏罗世桑日群岩浆活动记录以及打加错地区上三叠统地层研究新进展,本文更赞成打加错地区和南部拉萨地体其它地区的晚三叠世岩浆活动形成于与班公湖-怒江洋壳南向俯冲有关的弧后环境。     

New Insights into the Late Triassic Nadigangri Formation of Northern Qiangtang,Tibet, China: Constraints from U‐Pb Ages and Hf Isotopes of Detrital and Magmatic Zircons

We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5–225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma(Norian-Rhaetian), including three predominant groups of 220–225 Ma, 210–217 Ma and 201–205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive εHf(t) value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1–1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.     

澜沧江南带三叠纪火山岩岩石学、地球化学特征、Ar-Ar年代学研究及其构造意义

滇西三江地区澜沧江南带广泛发育三叠纪火山岩。在北部云县一带,中晚三叠世火山岩出露齐全,自下而上可划分为中三叠统忙怀组(T₂m),上三叠统小定西组(T₃x)和上三叠统芒汇河组(T₃mh)。忙怀组以酸性火山岩为主,为一套流纹岩夹火山碎屑岩组合;小定西组发育为中基性火山熔岩夹火山碎屑岩;芒汇河组具有流纹质火山碎屑岩与玄武岩共存的"双峰式"火山岩特征。地球化学特征表明,南澜沧江带三叠纪火山岩具有弧火山岩与大陆板内火山岩的双重属性,推测其形成环境为过渡型的大陆边缘造山带环境。对南澜沧江带南部景洪附近采集到的石英安山岩样品进行Ar-Ar年龄测试,得到的坪年龄为236.7±2.2Ma,为中三叠世。结合火山岩年代学结果,推测澜沧江洋主碰撞期为早三叠世,中三叠世与晚三叠世早期分别为碰撞后的应力松弛阶段与洋盆继续俯冲期,到晚三叠世末期,俯冲作用结束,澜沧江洋关闭。     

Isotopic constraints on crustal architecture and Permo‐Triassic tectonics in New Guinea: Possible links with eastern Australia

New U–Pb zircon ages and Sr–Nd isotopic data for Triassic igneous and metamorphic rocks from northern New Guinea help constrain models of the evolution of Australia's northern and eastern margin. These data provide further evidence for an Early to Late Triassic volcanic arc in northern New Guinea, interpreted to have been part of a continuous magmatic belt along the Gondwana margin, through South America, Antarctica, New Zealand, the New England Fold Belt, New Guinea and into southeast Asia. The Early to Late Triassic volcanic arc in northern New Guinea intrudes high‐grade metamorphic rocks probably resulting from Late Permian to Early Triassic (ca 260–240 Ma) orogenesis, as recorded in the New England Fold Belt. Late Triassic magmatism in New Guinea (ca 220 Ma) is related to coeval extension and rifting as a precursor to Jurassic breakup of the Gondwana margin. In general, mantle‐like Sr–Nd isotopic compositions of mafic Palaeozoic to Tertiary granitoids appear to rule out the presence of a North Australian‐type Proterozoic basement under the New Guinea Mobile Belt. Parts of northern New Guinea may have a continental or transitional basement whereas adjacent areas are underlain by oceanic crust. It is proposed that the post‐breakup margin comprised promontories of extended Proterozoic‐Palaeozoic continental crust separated by embayments of oceanic crust, analogous to Australia's North West Shelf. Inferred movement to the south of an accretionary prism through the Triassic is consistent with subduction to the south‐southwest beneath northeast Australia generating arc‐related magmatism in New Guinea and the New England Fold Belt.     

The Late Triassic microvertebrate fauna of Tytherington,UK

The Late Triassic fissure fills from the region of Bristol, SW England and S Wales, preserve unique assemblages of small vertebrates derived from an archipelago of palaeo-islands that document aspects of a critical transition in the history of terrestrial ecosystems. Tytherington Quarry, in south Gloucestershire, is the site of several fossiliferous fissures, all dated as Rhaetian (terminal Triassic), and source of abundant remains of the ‘Bristol dinosaur’, Thecodontosaurus antiquus. In addition, the fissure sediments have yielded previously unreported microvertebrate assemblages, including over 400 jaw remains from three genera of sphenodontians and 100 archosaur teeth assigned to 15 morphotypes. The land fauna is dominated by sphenodontians, with Diphydontosaurus by far the most common form, followed by Clevosaurus, then the sauropodomorph dinosaur Thecodontosaurus, and then the sphenodontian Planocephalosaurus. There are, in addition, rare remains of contemporaneous bony fishes, as well as fossils apparently reworked from the Carboniferous limestones, namely conodonts, holocephalian (chimaeroid) teeth, and a shark tooth. Many typical latest Triassic animals, such as temnospondyls, phytosaurs, aetosaurs, rauisuchians, plateosaurids and dicynodonts are not represented at Tytherington, perhaps because these generally larger animals did not live on the palaeo-island, or because their carcasses could not fit into the fissures. The absence of tritylodonts and early mammals is, however, less easy to explain on the basis of size, although it is known that these forms were abundant here by the Early Jurassic.     

Euthycarcinoids

The euthycarcinoids are a mysterious group of extinct, possibly amphibious, arthropods. Like many groups of arthropods their affinities remain enigmatic. They comprise 15 species known mainly from the Late Carboniferous Coal Measures of Europe and North America, although they have been found in older rocks in Argentina and Australia. The oldest known euthycarcinoid is Apankura machu, from the Late Cambrian of Argentina, and the youngest is Euthycarcinus kessleri, from the Middle Triassic of France.     

Carbon isotope evidence for CAM photosynthesis in the Mesozoic

Crassulacean acid metabolism (CAM) photosynthesis, a flexible adaptation to water‐stress, has not been shown to occur before the Pleistocene, despite suggestions that CAM first evolved in the Mesozoic or earlier. Here we report on multiple (≥7) positive organic carbon isotope excursions (δ¹³C_org > ?20 ‰ ) in Late Triassic and Early Jurassic (c. 200 Ma) sedimentary rocks from an arid terrestrial ecosystem in South Africa. These excursions are interpreted as evidence of the episodic dominance of CAM plants in response to heightened aridity in the heartland of Gondwana, and hint at climatic instability in a greenhouse world.     

Episodic Late Palaeozoic to Cenozoic denudation of the southeastern highlands of Australia: Evidence from the Bogong High Plains,Victoria

The Bogong High Plains of eastern Victoria occur as plateau remnants in a highly dissected region of the Australian Alps. Results from apatite fission track analyses indicate that the Bogong region experienced multiple episodes of rapid low‐temperature cooling, most of which can be tentatively linked to a tectonic cause. Early episodes of cooling occurred during the Middle to Late Devonian (ca 400–370 Ma) and Late Carboniferous to Early Permian (ca 310–290 Ma), presumably during different stages of deformation associated with the development of the Lachlan Fold Belt and glacial erosion. Rapid cooling occurred during the Late Permian to Early Triassic (ca 260–240 Ma), presumably in response to the Hunter‐Bowen orogenic event along the eastern Australian continental margin. Since the Triassic, two major episodes of fault reactivation have further displaced fission track ages between sample groups on different structural blocks. The first episode occurred during the middle Cretaceous at ca 110–90 Ma, probably in response to initial extension and denudation along the eastern Australian passive margin prior to breakup. Subsequently during the Early to mid‐Tertiary at ca 65–45 Ma, large‐scale fault reactivation occurred along the Kiewa Fault, possibly in response to changes in intraplate stresses which occurred during the middle Tertiary.     

Petrogenesis and tectonics of late Permian felsic volcanic rocks,eastern Qiangtang block,north-central Tibet: Sr and Nd isotopic evidence

The Palaeo-Tethyan tectonic evolution of central Tibet remains a topic of controversy. Two Permian to Late Triassic arc-like volcanic suites have been identified in the eastern Qiangtang (EQ) block of north-central Tibet. Three competing models have been proposed to explain the formation of these volcanic suites, with two models involving a single stage of long-lived subduction but with opposing subduction polarities, while the other model involves a two-stage subduction process. Here, we present new whole-rock geochemistry, including Sr–Nd isotope data, for late Permian felsic volcanics of the Zaduo area. These volcanics are mainly low to middle K calc-alkaline felsic tuffs and rhyolites with SiO₂ concentrations up to 73 wt.%. In primitive mantle-normalized diagrams, the volcanics are typified by large ion lithophile element enrichment and high-field-strength element (e.g. Nb, Ta, P, and Ti) depletion, with slightly negative Eu anomalies. They have initial Sr ratios (⁸⁷Sr/⁸⁶Sr) _i of 0.70319–0.70547, and ?Nd(t) values of +3.4 to +3.5, suggesting derivation by the partial melting of a depleted mantle wedge, followed by assimilation of crustal material. The available geochemical data indicate the presence of two distinctive igneous evolution trends within the Permian to Late Triassic volcanics of the EQ block, consistent with a two-stage subduction model. Permian to Early Triassic arc-like volcanics are formed during northward (present-day orientation) subduction, whereas the Late Triassic volcanics are related to southward (present-day orientation) subduction of mafic crust of the Garze–Litang Ocean.     

Triassic stratigraphy,facies and evolution of the Arabian shelf in the northern United Arab Emirates

This study provides a reconstruction of the Late Permian and Triassic depositional history of the Arabian shelf in the northern United Arab Emirates based on facies analysis and foraminiferal biostratigraphy. The presented data show that sedimentation occurred in three major sequences. From the Late Permian to Olenekian carbonates and evaporites were deposited in restricted lagoons and tidal flats. After a hiatus, sedimentation resumed and continued until the Late Ladinian/Carnian, leading to the deposition of a carbonate platform dominated by peritidal dolostones. A period of shelf exposure and erosion, spanning from the Carnian to Norian, was followed by the third major sequence with sedimentation into the Early Jurassic. During this third depositional sequence sedimentation changed from pure carbonate into mixed carbonate–siliciclastic deposits. This transition reflects the global regression of the sea in the Late Triassic (Triasina hantkeni Zone) and the increased erosion of large parts of the Arabian hinterland. A comparison of the evolution of the Arabian shelf in the study area with chronostratigraphic reference schemes for the Arabian Plate reveals remarkable differences in the distribution of Middle and Upper Triassic sequences. These are most likely the result of poor biostratigraphic control on previously studied formations in the region.