Jurassic Research Articles

Petrology of Jurassic and Cretaceous basaltic formations from the Parnaíba Basin, NE Brazil: correlations and associations with large igneous provinces

Petrology of Jurassic and Cretaceous basaltic formations from the Parnaíba Basin, NE Brazil: correlations and associations with large igneous provinces

Systematic Revision of Symbiodiniaceae Highlights the Antiquity and Diversity of Coral Endosymbionts

The advent of molecular data has transformed the science of organizing and studying life on Earth. Genetics-based evidence provides fundamental insights into the diversity, ecology, and origins of many biological systems, including the mutualisms between metazoan hosts and their micro-algal partners. A well-known example is the dinoflagellate endosymbionts ("zooxanthellae") that power the growth of stony corals and coral reef ecosystems. Once assumed to encompass a single panmictic species, genetic evidence has revealed a divergent and rich diversity within the zooxanthella genus Symbiodinium. Despite decades of reporting on the significance of this diversity, the formal systematics of these eukaryotic microbes have not kept pace, and a major revision is long overdue. With the consideration of molecular, morphological, physiological, and ecological data, we propose that evolutionarily divergent Symbiodinium "clades" are equivalent to genera in the family Symbiodiniaceae, and we provide formal descriptions for seven of them. Additionally, we recalibrate the molecular clock for the group and amend the date for the earliest diversification ofthis family to the middle of the Mesozoic Era (∼160 mya). This timing corresponds with the adaptive radiation of analogs to modern shallow-water stony corals during the Jurassic Period and connects the rise of these symbiotic dinoflagellates with the emergence and evolutionary success of reef-building corals. This improved framework acknowledges the Symbiodiniaceae's long evolutionary history while filling a pronounced taxonomic gap. Its adoption will facilitate scientific dialog and future research on the physiology, ecology, and evolution of these important micro-algae.

Geoheritage and advanced training for the oil industry: The Lusitanian Basin case study (Portugal)

The Lusitanian Basin (central Portugal) is a recurring subject of study within different disciplines of earth sciences, mainly because of the excellent stratigraphical and paleontological records, as well as the world-class quality of outcropping elements of petroleum systems and salt tectonics geometries. In fact, in the Lusitanian Basin, three global stratigraphic references were defined for the Jurassic System—the Toarcian Global Stratotype Section and Point (GSSP), the Bajocian GSSP, and the Bathonian Auxiliary Stratigraphic Section and Point—but the sedimentary record of the Lusitanian Basin includes a set of geosites that provide favorable conditions for educational activities, in the frame of the Portuguese educational system, which are increasingly being sought for the development of advanced training activities in the context of the hydrocarbon exploration models. This paper presents the main reasons that attract this particular public, which includes geospecialists and geoexperts, to the Lusitanian Basin outcrops, as well as the geosites that are currently visited for advanced training purposes by different oil companies. As such, the geological heritage of the Lusitanian Basin represents a paradigmatic example of the relevance of enlarging the traditional vision that confines technical applications of geoconservation to scientific research, education, and geotourism, the last of which is considered in the sense of an activity intended exclusively for geoamateurs and/or people who are either unaware of or interested in learning about geological issues.

Characterisation of carbon components and their isotopic composition in gas shales

Shales are an important reservoir of both organic and inorganic carbon that can be decoupled by incremental stepwise combustion without acid treatment. The study of shales from various depths of three cores of Haynesville-Bossier formation of Jurassic period indicates the presence of organic and inorganic carbon with comparable δ13C and nitrogen/carbon (N/C) ratios in all three. Both the isotopic and elemental ratios predominantly indicate a continental source but a minor N/C fraction corresponding to a marine/lacustrine source is also seen. This indicates either mixing from different sources and/or fractionation, perhaps due to preferential loss of nitrogen during organic matter degradation. Because some of the organic component is released at a high temperature of 1000-1200 °C although ungraphitised, it may be locked up in minerals like sulphides and K-feldspars, incorporated during diagenesis and hydrothermal alteration. Carbon locked in these minerals can be isolated from the carbon cycle for a longer period of time.

The different sources and petrogenesis of Jurassic intrusive rocks in the southern Lhasa subterrane, Tibet: Evidence from the trace element compositions of zircon, apatite, and titanite

ABSTRACT The Jurassic magmatism distributed in the southern Lhasa subterrane (SLT) has been recognized as a record of the early-stage evolution of the Neo-Tethys ocean; however, the magma compositions and detailed crystallization histories remain an enigma. Zircon, apatite, and titanite in igneous rocks can serve as effective petrogenetic indicators. In this paper, we present the whole-rock geochemical, zircon U Pb data, zircon Hf isotopic analyses, and major and trace elemental compositions of zircon, apatite, and titanite from Baiga granite porphyry (EGP), Shanba granodiorite (EGD), Pengcuolin granodiorite porphyry (MGP), and Dazhuqu monzonite (LM) rocks in the SLT to constrain their source and petrogenesis. The results from this study show that a combination of zircon Ti, Th/U, Hf, and rare earth element (REE) contents, apatite halogen, REE and Sr contents, and titanite REEs can be used to track the detailed magmatic crystallization histories. Higher Sr contents are found in apatite (SrAp) from EGP (ca. 192 Ma) and EGD (ca. 176 Ma) than those in their host rocks (SrWR), indicating that their magma genesis may have involved some mafic magma. The magma genesis of LM (ca. 159 Ma) may have involved more reduced mafic (or least evolved) magma, as evidenced by the higher Th/U but lower Yb/Gd ratios, higher zircon saturation and Ti-in-zircon temperatures in zircon, highest SrAp/SrWR ratios, and large positive Eu anomalies in titanite from LM. The lower Cl contents and higher (La/Sm)N values in apatite from MGP (ca. 172 Ma) are inherited from the low-Cl melts. The MGP rocks have higher zircon Ce4+/Ce3+ and EuN/EuN* ratios, a greater apatite SO3 content, and a higher titanite total REE content, which indicates that MGP has a higher oxidation state than do EGP, EGD, and LM. The MGP also exhibits a higher H2O content (>11 wt%) dissolved in the melt, greater Ba/La and Nb/Ta ratios in whole rock, and higher Nb/Ta ratios in zircon. However, MGP demonstrates lower zircon saturation and Ti-in-zircon temperatures, which suggest that MGP was generated by fluid-fluxed melting below 750 °C. The low Ti-in-zircon temperatures but high La/Yb and Sr/Y ratios of MGP indicate that a local thickened crust likely existed in the Middle Jurassic period in the SLT due to mafic magma underplating during this time.

Особливості просторового розподілу території Хорольського ботанічного саду

Викладено умови та проектне рішення просторового розподілу 18 га території новоствореного Хорольського ботанічного саду, висвітлено головні чинники, що вплинули на особливості розподілу. Показано значення функціонального зонування території, у результаті якого створено наукову (0,58 га), експозиційну (17,24 га) та адміністративно-господарську (0,18 га) зони. Зазначено, що проектом організації території Хорольського ботанічного саду (2014 р.) повною мірою обґрунтовано використання ботаніко-географічного, систематичного, флористичного, екологічного та декоративного принципів улаштування колекційно-експозиційних ділянок. Повідомляється, що Хорольський ботанічний сад новостворена установа (Указ Президента України від 11.12.2009 р. № 1041 «Про створення Хорольського ботанічного саду»), що розпочала функціонувати лише в кінці 2011 року (Наказ Міністерства екології та природних ресурсів України від 18.10.2011 р. № 395 «Про затвердження положення про Хорольський ботанічний сад»), проте на сьогодні вже реконструйовано ділянку дубового гаю та закладено науково-дослідну ділянку саду субтропічних плодових культур, ділянку парку юрського періоду, частково – ділянку горіхового саду, готується земельна ділянка для закладки райського саду. Підкреслено, що резервом для примноження плодових культур у лісостеповій зоні України є окремі субтропічні види, адже за низкою господарських показників вони відповідають вимогам сучасного плодівництва, бо володіють підвищеною стійкістю до хвороб і мало вражаються шкідниками, мають високу регенеративну здатність, а отже, швидко відновлюються в разі пошкоджень, рано вступають у репродуктивну фазу розвитку. Указуємо, що вагомим аргументом є й такий фактор, як глобальне потепління клімату, оскільки інтродукція субтропічних видів здійснюється з півдня на північ. Показано, що Хорольський ботанічний сад – територія, призначена для вирощування та вивчення різних рослинних організмів і їх угрупувань у типових для Лісостепу України екологічних умовах. Створені ботанічні колекції нових, рідкісних та екзотичних рослин наочно демонструють розвиток просторового розподілу території ботанічного саду й вирішують питання збереження біорізноманіття й генофонду рослин, теоретичних і практичних питань інтродукції й акліматизації рослин, ландшафтної архітектури та пропаганди природоохоронних знань.

AT THE BEGINNING OF THE BIOSTRATIGRAPHY (TO THE 250TH ANNIVERSARY OF THE BIRTHDAY OF WILLIAM SMITH)

The main side of the W. Smith’s work — geological mapping — has been shown to be expressed in the series of maps, created by him, and first of all in the «Map of layers of England and Wales». The layers represented for Smith an object for mapping. His stratigraphic tables constitute the lists of stratons, systemized in the order of their bedding and origin. W. Smith discovered a general sequence of 34 layers ofEnglandandWales, in more detailes separated the deposits, substracted later in the Jurassic system. Fossils were considered by W. Smith as specific features of layers, being mapped. The very combination of the characteristics of talented geologist — map-maker und collector of fossils — allowed making the famous conclusion that every layer contained the fossils, typical exactly for it. W. Smith showed the specifics and continuity of paleontological characteristics of different layers, predefined the oportunity of their recognition and identification and designed the base for the development of biostratigraphic method and historical geology in a whole. The short biographic data for Smith has been given.

Geochronology of Ashidani Formation in the Hida Gaien Belt at Kuzuryu, Central Japan

Previously a mystery, era in which the Ashidani Formation was formed in the Hida Gaien Belt at Kuzuryu is determined. The detrital zircon SHRIMP U–Pb age of Ashidani Formation sandstone is found to be within the range of 280 and 220 Ma. The most recent generation noted in samples collected is 224.2 ± 5.4 Ma (between the Carnian and Norian stages of the late Triassic Period). The metamorphic muscovite K–Ar age of sandstone schist is 182.6 ± 3.9 Ma (between the Pliensbachian and Toarcian stages of the Early Jurassic Age). There are no previous reports on metamorphic age values of 180 Ma in the Hida Gaien Belt. According to these dating results, geological development of the Ashidani Formation was limited to between the latter part of the late Triassic period and the start of the early Jurassic period, and can be compared to the Chizu metamorphic belt in the Chugoku region. Geological development of the Ashidani Formation is limited to the start of the early Jurassic period. Ashidani Formation Rocks were deposited in the forearc region of the eastern margin of the China craton at the beginning of the early Jurassic period. They then underwent high-pressure metamorphism alongside protoliths of the Chizu metamorphic belt in the middle part of the early Jurassic period due to subduction of the oceanic plate.

A long-lived Indian Ocean slab: Deep dip reversal induced by the African LLSVP

A slab-like high seismic velocity anomaly (referred as SEIS) has been inferred beneath the central-southern Indian Ocean in a recent tomographic inversion. Although subduction has previously been suggested regionally by surface observations, the new inversion is consistent with a north-dipping slab extending from the upper mantle to the core mantle boundary (CMB). We propose that SEIS anomaly originated from an oceanic plate in the Paleo-Tethys that was consumed by a south-dipping intra-oceanic subduction zone during the Triassic and Jurassic periods. SEIS challenges traditional concepts of the dynamics of slab descent by its relatively shallow depths and a present-day polarity opposite to the geometry of subduction. Geodynamic models show the upwelling mantle flow exerted by a thermochemical pile can hold and stagnate the descending SEIS slab at shallow depths for more than 100 Myr. The spatial distribution of resistance from the upwelling mantle flow can reverse the slab dip, producing a structure consistent with seismic inversions as well as with our proposed tectonic scenario and geology constraining the Tethyan tectonic domain. The results suggest that slabs can descend through the lower mantle at rates substantially lower than 1 cm/yr, and even reverse their polarity through interactions with background mantle flow.

An Early Cretaceous eutherian and the placental-marsupial dichotomy.

Molecular estimates of the divergence of placental and marsupial mammals and their broader clades (Eutheria and Metatheria, respectively) fall primarily in the Jurassic period. Supporting these estimates, Juramaia-the oldest purported eutherian-is from the early Late Jurassic (160 million years ago) of northeastern China. Sinodelphys-the oldest purported metatherian-is from the same geographic area but is 35 million years younger, from the Jehol biota. Here we report a new Jehol eutherian, Ambolestes zhoui, with a nearly complete skeleton that preserves anatomical details that are unknown from contemporaneous mammals, including the ectotympanic and hyoid apparatus. This new fossil demonstrates that Sinodelphys is a eutherian, and that postcranial differences between Sinodelphys and the Jehol eutherian Eomaia-previously thought to indicate separate invasions of a scansorial niche by eutherians and metatherians-are instead variations among the early members of the placental lineage. The oldest known metatherians are now not from eastern Asia but are 110 million years old from western North America, which produces a 50-million-year ghost lineage for Metatheria.

The pore structure of tight limestone—Jurassic Ziliujing Formation, Central Sichuan Basin, China

The pore structure of the tight limestone in the Daanzhai Member of the Ziliujing Formation, Jurassic System, in central Sichuan Basin, China, is complex but essential to the exploration and development of tight oil. The pore structure of the tight limestone is studied by using scanning electron microscopy (SEM), nitrogen adsorption, high-pressure mercury intrusion, and nuclear magnetic resonance (NMR). The experimental results suggest that the pores are mainly slit pores and mesopores and macropores contribute to the pore volume and specific surface. The displacement pressure, average pore size, and homogeneity coefficient correlate with porosity and permeability and can be used to evaluate the pore structure. The full pore-size distribution was obtained by combining nitrogen adsorption and high-pressure mercury intrusion. We find that the limestone mainly contains mesopores with diameter of 2−50 nm. The T2 distribution was converted into pore-size distribution, well matching the full pore-size distribution. The relation between T2 and pore size obeys a power law and the geometric mean of T2 correlates with the pore structure and can be used in the pore structure evaluation.

Cuticles and Spores in Situ of Coniopteris hymenophylloides from the Middle Jurassic in Gansu, Northwestern China

Coniopteris was a ubiquitous plant of the Jurassic and Cretaceous periods and played an important role in the flora of the time. However, its anatomical structure is relatively poorly known. The specimens of Coniopteris hymenophylloides (Brongniart) Seward described here were collected from the Yaojie Formation in Gansu Province, northwestern China. The sterile fronds are characterized as being at least bipinnate with alternate arranged linear pinnae covered by thin cuticles. Fertile fronds are linear‐lanceolate, with single sorus at the margin of each fertile pinnule. In situ spores are typically trilete, triangle to subcircular in polar view, cap‐shaped in equatorial view, and 37 μm in average diameter. The trilete marking is straight and narrow, generally extends to 4/5 of the spore radius. The spore surface is smooth, and parts of the exine are granulated. The epidermal cells of cuticles are irregular in shape, approximately 40–60 μm long and 10–20 μm wide. The elliptical stomatal complexes are paracytic, approximately 30 μm long and 19 μm wide, and irregularly distributed. On the basis of its epidermal structures and comparisons with extant ferns, we consider that Coniopteris displays combined features of the related extant genera.

Evidence for niche partitioning among ground-height browsing sauropods from the Upper Jurassic Morrison Formation of North America

Two tooth-bearing snout fragments from a diplodocid sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic) excavated from the Mygatt-Moore Quarry in Rabbit Valley, Colora­do are described. The Mygatt-Moore Quarry has produced thousands of vertebrate fossils from the Brushy Basin Member, with the diplodocid Apatosaurus cf. louisae and the tetanuran Allosaurus fragilis dominat­ing the assemblage. Additionally, remains of another diplodocid, Diplodocus sp., have been found near the quarry within Rabbit Valley. Both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (CT) scans. This is inconsistent with the genus Diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. The presence of eight replacement teeth per alveolus has previously only been reported in the Cretaceous rebbachisaurid Nigersaurus taqueti, which has been interpreted to have occupied a similar ground-height browsing feeding strategy to both Diplodocus and Apatosaurus. This is the first report of this type of high-count replacement teeth in a diplodocid sauropod from the Morrison Formation. The high number of replacement teeth in a close relative to the contemporaneous Diplodocus provides evidence for niche partitioning among the contemporary ground-height browsing diplodocid sauropods of the Late Jurassic Period in North America.

De novo assembly of English yew (Taxus baccata) transcriptome and its applications for intra- and inter-specific analyses.

We provide novel genomic resources for Taxus baccata in the form of a reference transcriptome, SSR and SNP markers, and orthologous single-copy genes, useful for phylogenomic and population genomic applications. English yew (T. baccata) is the only European representative of the Taxaceae family, a conifer group originated in the Jurassic period. The wide extent of environmental heterogeneity within the species' range, together with its long presence in Europe, make English yew an ideal species to investigate adaptive evolution in conifers. To enlarge the genomic resources available for this species, we used Illumina short read sequencing followed by de novo assembly to build the transcriptome of English yew. In addition to a fully annotated transcriptome as well as large sets of new potential SSR and SNP markers for T. baccata, we provide a data set of orthologous single-copy genes across three Taxus species using Picea sitchensis as outgroup, and discuss ortholog uses and limitations for phylogenomic and population genomic applications.

Metamorphic P–T evolution of the Gotsu blueschists from the Suo metamorphic belt in SW Japan: Implications for tectonic correlation with the Heilongjiang Complex, NE China

In the Gotsu area of the c. 200 Ma high-P/T Suo metamorphic belt in the Inner Zone of southwest Japan, blueschists occur as lenses or layers within pelitic schists. Prograde, peak, and retrograde stages are distinguished in the blueschists, and the prograde and the peak metamorphic conditions are determined using pseudosection modelling in the NCKFMASHO system. The prograde metamorphic stage is defined by inclusions in porphyroblastic epidote and glaucophane, such as phengite, chlorite, albite, epidote and glaucophane/winchite, and the estimated metamorphic conditions are <325 °C and < 4–5 kbar at the boundary between the glaucophane schist facies and the greenschist facies. The peak metamorphic stage is well-defined by the schistosity-forming minerals, i.e. epidote, glaucophanic amphibole, phengite, and chlorite, suggesting the glaucophane schist facies conditions of 475–500 °C and 14–16 kbar. Actinolite/magnesiohornblende, chlorite, and albite replacing the peak stage minerals suggest the retrograde metamorphism into the greenschist facies. The metamorphic facies series of the Suo belt is defined by pumpellyite–actinolite facies to epidote–blueschist facies, and it has a relatively lower-P/T compared with the c. 300 Ma Renge belt in the Inner Zone of southwest Japan, which is defined by a sequence of lawsonite–blueschist facies to glaucophane–eclogite facies. The P– $$ {M}_{{\mathrm{H}}_2\mathrm{O}} $$ pseudosection and water isopleth show that the rocks were dehydrated during the initial stage of the exhumation and remained in water-saturated conditions. Similarities of the detrital zircon and peak metamorphic ages of the blueschists from the Suo metamorphic belt in southwest Japan and the Heilongjiang Complex in northeast China suggest that both metamorphic belts were probably formed in the same Paleo-Pacific subduction system in the Late Triassic to Jurassic period.

Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana.

Haramiyida was a successful clade of mammaliaforms, spanning the Late Triassic period to at least the Late Jurassic period, but their fossils are scant outside Eurasia and Cretaceous records are controversial1-4. Here we report, to our knowledge, the first cranium of a large haramiyidan from the basal Cretaceous of North America. This cranium possesses an amalgam of stem mammaliaform plesiomorphies and crown mammalian apomorphies. Moreover, it shows dental traits that are diagnostic of isolated teeth of supposed multituberculate affinities from the Cretaceous of Morocco, which have been assigned to the enigmatic 'Hahnodontidae'. Exceptional preservation of this specimen also provides insights into the evolution of the ancestral mammalian brain. We demonstrate the haramiyidan affinities of Gondwanan hahnodontid teeth, removing them from multituberculates, and suggest that hahnodontid mammaliaforms had a much wider, possibly Pangaean distribution during the Jurassic-Cretaceous transition.

Gas-condensate potential of the middle-Jurassic petroleum system in Abadan plain, Southwest Iran: Results of 2-D basin modeling

ABSTRACTThe Jurassic petroleum system has been proven as prolific oil and gas prospects in the southwestern of Iran. During this study, 2-D regional modeling was done on two selected sections (north-south and east-west); furthermore, 1-D models were reconstructed on 7 deeply drilled wells in order to evaluate petroleum generation and source rock maturity histories in the Abadan Plain area in southwest Iran. The results revealed that the Middle Jurassic Sargelu Formation with average present-time TOC and HI values of 2.65wt% and 151 mgHC/gTOC, respectively, can be classified as good to excellent type II source rock. The initial TOC and HI values regarded for modeling are 5wt% and 620 mgHC/gTOC, respectively. The geochemical maturity parameters indicate a wet gas window for the Sargelu Formation. The modeling results show that the maximum temperature and vitrinite reflectance in the Sargelu Formation has reached 150 oC and 1.3%VRo. Generation of hydrocarbon in the Sargelu commenced during the Early Cretaceous, while the main expulsion happened in the Paleogene. 2-D models show that the Jurassic source rock has already reached a high transformation ratio within the studied area and, due to lack of intense tectonic activity, the maturity is the same throughout the studied area. Oil and gas migrated mostly vertically to the overlying traps which are existed in the Jurassic and Cretaceous succession. The results predict the existence of gas-condensate in the Jurassic petroleum system of the studied area.

The Dynamic Topography of Eastern China Since the Latest Jurassic Period

AbstractSome changes in the topography of eastern China since Late Jurassic times cannot be well explained by lithospheric deformation. Here we analyze global mantle flow models to investigate how mantle‐driven long‐wavelength topography may have contributed to shaping the surface topography of eastern China. Paleodrainage directions suggest that a southward tilted topography once existed in eastern north China in the latest Jurassic Period, which is different from that at present day (southeastward tilting). Our model dynamic topography reveals a southward tilting topography between 160 and 150 Ma, followed by southeastward tilting and rapid subsidence, which is compatible with paleodrainage directions and tectonic subsidence of the Ordos Basin. The Cretaceous anomalous subsidence of the Songliao and North Yellow Sea basins, as well as the Cenozoic anomalous subsidence of the East China Sea Shelf Basin, can also be explained by dynamic topography. An apatite fission track study in the Taihang Mountains reveals four stages of evolution: Late Jurassic fast unroofing, Cretaceous slow unroofing, early Cenozoic fast unroofing, and late Cenozoic slow unroofing. We propose that mantle flow influenced this surface unroofing because the model predicts Late Jurassic dynamic uplift, Cretaceous dynamic subsidence, early Cenozoic dynamic uplift, and late Cenozoic dynamic subsidence. Apatite fission track data from northern south China are also in reasonable agreement with predicted dynamic topography between 80 and 30 Ma. The spatial and temporal agreement between geological observations and model dynamic topography indicates that mantle flow has had a significant influence in shaping the surface topography of eastern China.

Evidence for niche partitioning among ground-height browsing sauropods from the Upper Jurassic Morrison Formation of North America

Two tooth-bearing snout fragments from a diplodocid sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic) excavated from the Mygatt-Moore Quarry in Rabbit Valley, Colora­do are described. The Mygatt-Moore Quarry has produced thousands of vertebrate fossils from the Brushy Basin Member, with the diplodocid Apatosaurus cf. louisae and the tetanuran Allosaurus fragilis dominat­ing the assemblage. Additionally, remains of another diplodocid, Diplodocus sp., have been found near the quarry within Rabbit Valley. Both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (CT) scans. This is inconsistent with the genus Diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. The presence of eight replacement teeth per alveolus has previously only been reported in the Cretaceous rebbachisaurid Nigersaurus taqueti, which has been interpreted to have occupied a similar ground-height browsing feeding strategy to both Diplodocus and Apatosaurus. This is the first report of this type of high-count replacement teeth in a diplodocid sauropod from the Morrison Formation. The high number of replacement teeth in a close relative to the contemporaneous Diplodocus provides evidence for niche partitioning among the contemporary ground-height browsing diplodocid sauropods of the Late Jurassic Period in North America.

Detrital zircon geochronology and geochemistry of Jurassic sandstones in the Xiongcun district, southern Lhasa subterrane, Tibet, China: implications for provenance and tectonic setting

AbstractJurassic sandstones in the Xiongcun porphyry copper–gold district, southern Lhasa subterrane, Tibet, China were analysed for petrography, major oxides and trace elements, as well as detrital zircon U–Pb and Hf isotopes, to infer their depositional age, provenance, intensity of source-rock palaeo-weathering and depositional tectonic setting. This new information provides important evidence to constrain the tectonic evolution of the southern Lhasa subterrane during the Late Triassic – Jurassic period. The sandstones are exposed in the lower and upper sections of the Xiongcun Formation. Their average modal abundance (Q21F11L68) classifies them as lithic arenite, which is also supported by geochemical studies. The high chemical index of alteration values (77.19–85.36, mean 79.96) and chemical index of weathering values (86.19–95.59, mean 89.98) of the sandstones imply moderate to intensive weathering of the source rock. Discrimination diagrams based on modal abundance, geochemistry and certain elemental ratios indicate that felsic and intermediate igneous rocks constitute the source rocks, probably with a magmatic arc provenance. The detrital zircon ages (161–243 Ma) and εHf(t) values (+10.5 to +16.2) further constrain the sandstone provenance as subduction-related Triassic–Jurassic felsic and intermediate igneous rocks from the southern Lhasa subterrane. A tectonic discrimination method based on geochemical data of the sandstones, as well as detrital zircon ages from sandstones, reveals that the sandstones were most likely deposited in an oceanic island-arc setting. These results support the hypothesis that the tectonic background of the southern Lhasa subterrane was an oceanic island-arc setting, rather than a continental island-arc setting, during the Late Triassic – Jurassic period.