Norian Research Articles

Late Triassic (Norian) strontium and oxygen isotopes from the Baoshan block, southwestern China: Possible causes and implications for climate change

The Norian Stage (Late Triassic) has long been regarded as an interval of stable climates, but, in fact, there are only sparse studies of the paleoclimate variations during this longest (>20 Myr) stage of the Phanerozoic. Here, oxygen and strontium isotopes have been measured on conodont apatite from the open-marine shelf succession at the Xiquelin section (Baoshan block, Yunnan Province, China). Magnetostratigraphy linked to conodont biostratigraphy indicates that the succession was deposited during the Sevatian substage, upper Norian. The δ18Oapatite values from conodonts indicate that low-latitude average sea-surface temperatures in eastern Tethys were ∼32 °C during the earliest Sevatian, cooled to ∼25 °C through the middle Sevatian, and then increased again to ∼29 °C by the late Sevatian. The seawater 87Sr/86Sr values maintained a high plateau through the entire Sevatian, with very little variation between inferred warm and cool episodes. The possible explanation for the observed trends in sea-surface temperature and 87Sr/86Sr during Sevatian is an enhanced weathering of silicates exposed during the closure of the Paleo-Tethys Ocean at the zenith of Pangea supercontinent assembly.

A revision of the Carnian/Norian boundary radiolarian assemblages: Insight from the biostratigraphic record of the Norian GSSP, Pizzo Mondello section (Sicily, Italy)

The Triassic was a critical period for a significant increase in the generic diversity of radiolarians after the disappearance of >80% of radiolarian genera during the Permian-Triassic mass extinction. In particular, the Upper Triassic radiolarian fauna is rich and has been documented in several world regions, such as North America, Western Europe, the Mediterranean area, Japan, the Philippines, Timor, and Far East Russia. In this study, a well-preserved and high-diversity fauna from a continuous pelagic-hemipelagic section deposited in western Tethys (Sicily, Italy) provides one of the most detailed radiolarian records of the Carnian-Norian boundary interval, which can be correlated worldwide, from high to low-latitude, from both sides of the Pangea and both Hemispheres. The 99 species belonging to 50 genera from this time interval have been collected from the Pizzo Mondello section (Sicanian Basin, Western Sicily), the selected GSSP for the base of the Norian stage, and then compared to the radiolarian associations documented in other coeval regions. Based on the occurrences of characteristic radiolarian species, we defined and proposed a new radiolarian biozonation across the Carnian-Norian boundary, which consists of five new assemblages (PM assemblage 1–5) that are correlated and calibrated to the already well-defined biozonation of bivalves, ammonoids, and conodonts.

Magnetostratigraphy of the Mercia Mudstone Group (Devon, UK): implications for regional relationships and chronostratigraphy in the Middle to Late Triassic of Western Europe

Global synchronization of environmental change in terrestrial successions in deep time is challenging owing to the paucity of dating methods, a case also applicable to the Middle to Upper Triassic Mercia Mudstone Group in Britain. Using coastal cliff sections, magnetostratigraphy was evaluated at 263 horizons, defining 53 magnetozones. Magnetozones from the lower 140 m of the group demonstrate correspondence to those from the mid-Ladinian to early Carnian polarity timescale, dating that is compatible with magnetostratigraphy from the underlying Sherwood Sandstone Group. Magnetostratigraphy of the Dunscombe Mudstone Formation, and associated palynological data, suggest a late Carnian to earliest Norian age, and a dramatically lower accumulation rate than for adjacent formations. The polarity record demonstrates coeval flooding events, evaporite deposits and intervals of sand supply between the Wessex Basin and the Central European Basin in the Carnian. This is the result of linked climatic and eustatic changes between these separate basins, related to aeolian dust supply and the shrinkage of hyper-arid source regions for the fine material. Magnetostratigraphy from the Branscombe Mudstone and Blue Anchor formations demonstrates their Norian and early Rhaetian age. These and other data suggest an alternative synchronization of marine and non-marine polarity records for the Norian polarity timescale. Supplementary material : Section details and detailed logs of the sampled sections and inferred sequence boundaries, magnetic mineralogy data, demagnetization behaviour and mean directions, summary of virtual geomagnetic pole data and a comparison with other European poles, construction of other composite reference sections and revised polarity scales, an Excel sheet of magnetic data, statistically evaluated correlation models and age models are available at https://doi.org/10.6084/m9.figshare.c.6613788

Siliciclastic input controlling carbonate deposition on a low-angle ramp system: New insight from the Upper Triassic Luning Formation (Western-Central Nevada)

Although more than one century has passed since the first studies, knowledge about the Upper Triassic shallow-water carbonates from the Panthalassa Ocean remains lower than their Tethyan counterparts. Characterising these sedimentary rocks represents a unique way to deepen our understanding of the biosphere's evolution and recovery after the major Permian–Triassic biological crisis. The Triassic Luning Formation in Western–Central Nevada is a crucial sedimentary succession due to its considerable thickness and areal extent. Among the three members forming the Luning Formation, the present study has only described the upper one in detail due to the minor areal distribution of the Lower Member and the pure siliciclastic nature of the middle Member. All accessible localities in this region, 21 in total, have been extensively sampled for facies and micropalaeontological analyses, including conodonts and poorly preserved foraminifera, leading to new insights about the depositional conditions and exact age of the Luning Formation's Upper Member. A depositional model is proposed for the first time, corresponding to a low-angle ramp with homogeneous bathymetric and hydrodynamic conditions subjected to frequent siliciclastic input from the continent. The regular terrigenous influx causes a significant cyclicity in this portion of the formation, comprising heterogeneously thick limestone beds. The environment-diagnostic fauna is characterised by pioneer organisms that regenerate carbonate production after the main break related to the pure siliciclastic Middle Member's deposition. Numerous conodont specimens indicate that the entire Upper Member is middle Norian in age. Identifying the observed organisms, tied to a reliable stratigraphic interval, allows comparing the Luning Formation with other Upper Triassic carbonates from the Panthalassa Ocean, now cropping out at different latitudes on the eastern and western coasts of the Pacific Ocean. Despite some faunal affinities, especially with carbonate build-ups developed at middle-palaeolatitudes, the Luning Formation differs from most other East Panthalassa carbonates because of its short palaeo-distance from the continent (i.e. the American craton), being deposited near the mainland coast instead of on an isolated volcanic arc.

A New Rhynchosaur Taxon from the Popo Agie Formation, WY: Implications for a Northern Pangean Early-Late Triassic (Carnian) Fauna

New discoveries in the lower Popo Agie Formation (lower carbonate unit) of central Wyoming necessitated a reevaluation of USNM 494329 from the same unit, the only known hyperodapedontine rhynchosaur in western North America. Well known from Gondwanan deposits, hyperodapedontines appear to be restricted to the Carnian age (Late Triassic), with the exception of Teyumbaita in the earliest Norian age (Late Triassic) of Brazil. Initially assigned to c.f. ‘Hyperodapedon’ sanjuanensis, our phylogenetic analyses reject this hypothesis, in support of a sister relationship between USNM 494329 (Beesiiwo cooowuse, gen. et. sp. nov.) and Oryctorhynchus bairdi forming an early-diverging clade that is only distantly related to ‘H.’ sanjuanensis. Five additional specimens recovered from the lower Popo Agie are described. Three are referred to B. cooowuse, and another two are placed closer to Hyperodapedon and the remainder of Hyperodapedontinae. Our analysis demonstrates potential temporal distinction between a grade of earliest-diverging hyperodapedontines (including all Wyoming taxa) and a exclusively Late Carnian, Southern Pangaean hyperodapedontine clade (including ‘H.’ sanjuanensis). We consider the lower Popo Agie Formation to represent the first nonmarine Late Triassic unit of Western North America that can be confidently restricted to the Carnian age.

Paleoenvironmental interpretation of the Late Triassic Norian – Rhaetian boundary interval in the Whitehorse Trough (Stikine Terrane, northern Canadian Cordillera)

The Norian – Rhaetian boundary (NRB) is associated with significant faunal turnover in a wide variety of groups. Following the relative stability of the Norian Stage, this boundary potentially marks the beginning of a protracted and continuous episode of elevated extinction rates, which culminated with the end-Triassic mass extinction. Despite the importance of the NRB to paleontological trends in the Late Triassic, much about this event remains enigmatic, including potential causal mechanisms as well as the characteristics of the resulting paleoenvironmental changes. Fossiliferous limestone of the Sinwa Formation occurs in extensive outcrops throughout northwestern British Columbia and provides an exceptional record of Upper Triassic stratigraphy that represents a paleogeographic region largely uninvestigated prior. The present study integrates lithostratigraphic, paleontological, and geochemical data to reconstruct the shallow marine paleoenvironments recorded by the Sinwa Formation in two sections on Mount Sinwa, south of Atlin, within the Stikine Terrane. The progression of lithological facies observed in these sections suggests a gradual base level rise throughout the late Norian. Following this steady facies progression is a prominent shift from coral reef boundstone to shale near the top of both sections. This facies change approximately coincides with the NRB interval as evidenced by the first occurrence of the latest Norian – Rhaetian conodont species Mockina mosheri morphotype B, as well as by Re – Os isochron ages of organic-rich limestone. Although the base level rise observed at the NRB interval could be due to regional tectonics, it could also potentially be recording eustatic sea level rise given the lack of consensus around sea level change at the NRB. Measurements of late Norian 87Sr/86Sr ratios on Mount Sinwa are consistent with those recorded in Tethyan studies, but the Panthalassan record overall does not replicate the same drop across the NRB observed in the Tethys. The lithological facies shift is also immediately preceded by a negative excursion in the δ13C values of carbonate, indicating that the NRB interval on Mount Sinwa is associated with coral reef collapse as well as the globally observed disruption of carbon cycling.

A new phytosaur species (Archosauriformes) from the Upper Triassic of Jameson Land, central East Greenland

ABSTRACT Herein we describe phytosaurs from thin fluvial overbank sandstones of the Upper Triassic Malmros Klint Formation of the Fleming Fjord Group (central East Greenland). The new sample includes more than 150 disarticulated bones and teeth from small to large specimens belonging to at least four individuals. The fossils mostly consist of teeth and postcranial elements and permit the recognition of a new species of Mystriosuchus, M. alleroq, diagnosed by an L-shaped quadratojugal whose anterior suture trends anterodorsally and a tripartite degree of heterodonty. Humeral diaphyseal histology of one specimen reveals a fairly compact cortex that surrounds a cancellous medullary region followed by a remodeling zone containing scattered secondary osteons. Primary bone tissue is parallel-fibred with a moderate to low vascular density. The cortex is cyclically interrupted by distinct growth marks indicating a seasonal environment. A change in growth rate from moderate to low is documented within the outer cortex, indicating that at least this individual was close to somatic maturity. Mystriosuchus has formerly been known as an exclusively European taxon. The new findings support the European faunal influence in East Greenland during the Late Triassic inferred from other taxa such as temnospondyls and archosaurs. The mid-late Norian age of European Mystriosuchus suggests an additional age constraint for the vertebrate-bearing portion of the Malmros Klint Formation.

Hydrothermal-bacterial structures with a brachiopod fauna on the surface of Tessel paleovolcano (South coast of Crimea)

Research subject. For the first time, the results of a study of hydrothermal-bacterial carbonate structures and a shell bank of brachiopods on the surface of the effusive sequence of the Late Triassic Tessel paleovolcano are presented. Methods. Petrographic thin sections were studied using an Olympus BX 5 microscope with an Olympus DP 12 camera. Geochemical investigations were performed according to the conventional methodology by an inductively coupled plasma mass spectrometer (ICP-MS). The isotopic composition of carbon was determined by isotope ratio mass spectrometry (IRMS) by a Deltaplus Advantage instrument. The mass spectrometer was paired with an EA Flash1112 analyzer and a TC/EA convector. When measuring, the NBS-19, NBS-18, and IAEA-C-3 standards were used. Results. The data obtained on the geology, geochemistry, and isotopic composition of the studied materials confirm the existence of a symbiosis between brachiopods and protozoa. The primary formation of organic matter and carbonate of bacterial structures occurred due to the processing of paleofluids by the community of bacteria and archaea. These organisms created carbonate, sulfide and organic matter in a suboxide environment of hydrogen sulfide and methane. The biocenosis of the shell bank of brachiopods was characterized by a poor taxonomic composition and a high biological productivity. The formation of a shell bank of brachiopods with bacterial carbonate edifices took place during the period of volcanic activity and continued during breaks in eruptions. The results of geochemistry and the carbon isotopic composition of the carbonate of bacterial buildups confirm the deep nature of the paleofluids. The Norian age of paleovolcanism was determined from finds on the surface of the terrigenous- volcanic sequence of brachiopods Worobiella ex gr. caucasica Dagys and ammonite Megaphyllites insectus (Mojsisovics). Conclusions. According to geological features, the material of the shell bank of brachiopods with bacterial carbonate structures on the surface of the Tessel paleovolcano belongs to the ancient hydrocarbon seeps-carbonate. Based on their genesis and formation material, these formations should be referred to as Triassic methanoliths. Signs of allocation of similar formations in other time intervals and regions are given. Emissions of fluids with hydrogen sulfide and methane by the Tessel paleovolcano in the Late Triassic may have been related to the causes of the “global extinction”.

Carbon-isotope excursions in the Norian stage (Upper Triassic) of the Baoshan terrane, western Yunnan, China

The biostratigraphy and carbon stable isotopes of the Norian Stage (Upper Triassic) are well studied in the western Tethys, but little information is available from the eastern Tethys. Therefore, we studied the Hongyan-B (HYB) section in the Baoshan terrane, western Yunnan Province, SW China, which was located in the eastern Tethys during the Late Triassic. The HYB section was investigated for conodonts, radiolarians, total organic carbon, carbonate carbon and oxygen stable isotopes (δ13Ccarb and δ18Ocarb), and carbon isotopes of organic matter (δ13Corg). The Mockina slovakensis and Mockina bidentata conodont biozones proposed in the HYB section are associated with two radiolarian zones of the Sevatian substage, the Praemesosaturnalis multidentatus and Praemesosaturnalis pseudokahleri zones (TR8A and TR8B Sugiyama zones). This biostratigraphy places the Alaunian-Sevatian substage boundary (middle-upper Norian) at meter 23 of the HYB section. Unfortunately, the δ13Ccarb and δ18Ocarb values suggest that they might have been influenced by diagenesis. However, the δ13Corg record preserves multiple carbon-isotope excursions across the Alaunian-Sevatian boundary that can be correlated with other coeval global sections. The carbon-isotope excursions registered at this middle-upper Norian boundary are perhaps related to the major outgassing of light carbon during the emplacement of Angayucham flood basalts.

The dawn of the flying reptiles: first Triassic record in the southern hemisphere

AbstractPterosaurs were the first vertebrates to evolve powered flight. The timing of their origin is still debated, and hypotheses range from the end of the Permian Period, to the lower Mesozoic Era, and through to the Middle–Late Triassic epochs. Regardless of when they originated, the oldest records are restricted to the Upper Triassic Norian Stage in the northern hemisphere (Europe, USA and Greenland). We report two new raeticodactylid pterosaurs, Yelaphomte praderioi gen. et sp. nov. and Pachagnathus benitoi gen. et sp. nov. from the upper Norian to Rhaetian Quebrada del Barro Formation in north‐western Argentina. The new specimens (an isolated dentary symphysis, partial rostrum, and distal half of ulna) are the first unequivocal Triassic records of pterosaurs in the southern hemisphere, confirming that the absence of pterosaurs outside north‐western Pangaea during the Late Triassic was the result of poor sampling rather than true absence. These new discoveries provide evidence of a greater diversity of pterosaurs living in terrestrial habitats and a wider global distribution of pterosaurs from the beginning of their evolution on Earth.

Lost Norian fluvial tracks: Sedimentology and stratigraphy of the Upper Triassic coarse-grained deposits in Kamienica Śląska (Upper Silesia, southern Poland)

In the Triassic‒Jurassic boundary profiles of the Upper Silesian region, there are locally developed coarse clastic deposits, commonly known as the Połomia Gravels, Połomia Beds or “Połomia Formation’’ (informal name). Due to the lack of reliable stratigraphic tools, the chronostratigraphic position of these deposits remains one of the most controversial aspects of the Triassic‒Jurassic lithostratigraphy in the region. Sparse biostratigraphic data from the overlying and underlying deposits indicate a wide range of ages, from the Late Triassic to Early Jurassic. This paper presents the results of sedimentological, petrographical and palynological analyses of the coarse-grained deposits from the Kamienica Śląska gravel pit, which is currently one of the biggest facilities of this type in Upper Silesia. The outcrop section, with a total thickness of up to 20 m, is dominated by friable, light grey to beige and locally dark grey, large-scale planar to trough cross-stratified conglomerates and coarse-grained sandstones with subordinate thin interbeds of grey and reddish brown mudstones. Three facies associations have been distinguished, representing a main channel belt, secondary channels and floodplains subenvironments. Facies analysis points to a braided river tract with localised floodplain sediments. The grain composition of the Kamienica Śląska gravel/conglomerate is less diversified than that of the polymictic typical Połomia Beds of the Myszków area and resembles oligomictic conglomerates known from the Grabowa Formation of the Norian age and/or conglomerates of the Gorzów Beds of Rhaetian age, which also occur on the studied region. Palynological analysis of mudstone interbeds within the conglomeratic deposits shows the presence of miospores guiding and characteristic for subzone c of the Corollina meyeriana zone of the late Norian‒early Rhaetian age. The appearance of the coarse-grained deposits in late Norian could be associated with the development of a long-reach braided fluvial tract, draining the S and SE part of the Sudetian-Malopolska-Lublin land (S-M-L land) in response to the tectonic rearrangement in the source area and gradual climatic change from semi-arid to humid in the Rhaetian.

The Upper Triassic deposits of the west Bangong-Nujiang suture zone and their paleogeographic implications

The Bangong-Nujiang Suture Zone (BNSZ) of Tibet (Xizang) has been interpreted to represent a relic of the Bangong-Nujiang Ocean. However, the existence of this ocean during Triassic time remains a point of contention. A sedimentary succession spanning the Upper Permian through Triassic described from the central BNSZ suggests that the Lhasa and South Qiangtang terranes were contiguous thus negating the existence of a terrane-separating ocean during Triassic time. However, the apparent lack of Triassic deposits in the west BNSZ has called into question the existence of Triassic deposits in the central region of the BNSZ. Our biostratigraphic work in the Wuga Formation of the Gaize area has yielded abundant Norian conodonts thus confirming the existence of Upper Triassic deposits in the west BNSZ. The clastic deposits of the Wuga Formation are herein interpreted to be of Rhaetian age. Moreover, intercalated limestone and chert are termed the Dongnale Formation of Norian age. The Norian to Rhaetian succession can be correlated with strata of the central BNSZ as well as with deposits of the Lhasa Terrane and the South Qiangtang Terrane. Similar stratigraphies among these regions through the Late Triassic suggests a shared depositional setting and that the BNSZ was not an ocean in Norian and Rhaetian time.

New sphenodontian (Reptilia: Lepidosauria) from a novel Late Triassic paleobiota in western North America sheds light on the earliest radiation of herbivorous lepidosaurs

AbstractHerbivory is a common ecological function among extant lepidosaurs, but little is known about the origin of this feeding strategy within Lepidosauria. Here we describe a sphenodontian (Lepidosauria) from the Late Triassic of western North America,Trullidens purgatoriin. gen. n. sp., that reveals new aspects of the earliest radiation of herbivorous lepidosaurs. This taxon is represented by an isolated lower jaw with robust structure bearing transversely widened dentition and extensive wear facets, suggesting a masticatory apparatus specialized for herbivory. An unusual ‘incisor-like’ tooth is present at the anterior end of the jaw; a unique feature among lepidosaurs, this tooth is convergent with the incisors of extant rodents and lagomorphs. Phylogenetic analyses support the placement of this taxon within opisthodontian sphenodontians, a group sharing derived cranio-dental morphologies specialized for herbivory. The new taxon was recovered in a recently discovered and unnamed series of Upper Triassic strata in southeastern Colorado, USA, exposed in Canyons incised by the Purgatoire River and its tributaries. These strata comprise a dominantly red-bed sequence of conglomerates, sandstones, and siltstones deposited in a fluvio-lacustrine setting, preserving a Late Triassic biota of invertebrate and vertebrate ichnofossils, plant macrofossils, bony fish, temnospondyl amphibians, and reptiles. We use aetosaur osteoderms as biostratigraphic links to the nearby Chinle Formation of Arizona, USA, establishing a middle Norian age for these strata. The presence of an opisthodontian from western equatorial Pangaea in the Norian Stage reveals a near-global radiation of this clade across the Pangaean supercontinent during the Late Triassic.UUID:http://zoobank.org/A737c03f-863a-488e-a860-5cc914548774.

Late Triassic rifting and volcanism on the northeastern Indian margin: A new phase of Neo-Tethyan seafloor spreading and its paleogeographic implications

The stratigraphic record of the northern Indian margin documents tectonic extension and magmatic activity during the Late Triassic. The geodynamic process and the paleogeographic implications of this event remain, however, incompletely understood. This study presents new stratigraphic, petrographic, geochronologic and geochemical data from a mixed carbonate-clastic Upper Triassic succession of the Tethys Himalaya in southern Tibet (Tela Formation). The new finding of volcanic detritus with bimodal mafic/felsic composition in the Tela Formation indicates nearby volcanic activity constrained by detrital zircon UPb dating as latest Carnian to early Norian in age (229–223 Ma). The alkalic signature of mafic volcanic rock fragments, showing LREE enrichment and HREE depletion, indicates a within-plate extensional setting. The igneous activity in northeastern India compares with coeval volcanism in northwestern Australia, suggesting that a rift-related volcanic belt developed along the northern margin of eastern Gondwana in the Late Triassic. This volcanic belt controlled the accumulation of thick turbidites of the Langjiexue Group in northeastern India and induced accelerated tectonic subsidence and increased sedimentation rates all along the Tethys Himalayan zone as far west as the Zanskar-Spiti Synclinorium. This major rifting phase is suggested to have initiated a new phase of sea-floor spreading in the Neo-Tethys Ocean that torn off the Lhasa Block from eastern Gondwana.

Microfacies and biostratigraphy of an Upper Triassic Dachstein limestone fore-reef block in the Jurassic Sirogojno carbonate-clastic Mélange (Zlatibor Mt., SW Serbia)

In the late Middle to early Late Jurassic carbonate-clastic Sirogojno Melange in the Zlatibor Mountain there is one roughly 35 m thick overturned block with an intact Late Triassic fore-reefal Dachstein Limestone succession studied for its biostratigraphic age, content and microfacies characteristics. The succession starts with coarse-grained rudstones followed by meter-sized reefal blocks intercalated in partly layered resedimented grainstones and packstones with abundant reef-building organisms like calcareous sponges, corals and encrusting organisms. Inside this part of the succession open-marine influenced layers are rare. The succession continues with a partly turbiditic sequence and chaotic rudstones, densely packed with reef-derived material like broken reefbuilding organisms and shallow-water material like gastropods, bivalves and foraminifers. Grainstones with clear open-marine influence (e.g., thin-shelled bivalves, crinoids, conodonts) appear in between those rudstones, in cases lumachelle layers be composed of halobiids were deposited. To the end of the succession some layers show turbiditic bedding with mixed shallow-water and deep-marine grains and organisms, i.e. filaments and crinoids. On base of conodonts, foraminifers, calcareous algae, holothurians and halobiids throughout the whole studied succession, a middle Norian (Alaunian) to Rhae tian 1, most probably a late Norian (Sevatian) age can be assigned to this fore-reefal Dachstein Limestone succession, with a similar sedimentation pattern like Late Triassic Dachstein fore-reef limestone facies, e.g., in the Northern Calcareous Alps or the eastern Southern Alps. The study of this block in the Sirogojno Melange closes an important gap in knowledge about the extent, facies and stratigraphy of the Dachstein Carbonate Platform evolution in the Dinarides.

New dinosauromorph specimens from Petrified Forest National Park and a global biostratigraphic review of Triassic dinosauromorph body fossils

Dinosauromorph specimens from Petrified Forest National Park have been recovered from four major collecting efforts since 1982, including the most recent paleontological inventory of new park lands acquired in 2011. Additionally, an emphasis on understanding the stepwise acquisition of character traits along the dinosaurian lineage has helped identify previously collected specimens in museum collections. Here we briefly describe and use apomorphies to identify 32 additional dinosauromorph specimens found at Petrified Forest National Park, bringing the total number of dinosauromorph specimens presently known from the park to 50, a 600% increase since the year 2000. These specimens are all Norian in age and come from the Blue Mesa Member, Sonsela Member, and Petrified Forest Member of the Chinle Formation. These include the proximal end of a tibia that represents the oldest unambiguous dinosaur specimen from the Chinle Formation. We then contextualize these specimens with the dinosauromorph assemblages from the Norian of Utah, Colorado, New Mexico, and Texas, as well as the Carnian and Norian dinosauromorph assemblages from South America, Africa, and Europe. Despite increased sampling we still find no evidence for sauropodomorph and ornithischian dinosaurs in Western North America. An increase in sampling, combined with the use of apomorphies to identify collected specimens, will continue to improve the global dinosauromorph fossil record that can be used to answer questions on biochronology and the evolutionary history of the avian lineage.

The Sedimentary Evolution During Late Triassic‐Jurassic Period and the Hydrocarbon Exploration Direction in the Eastern Part of the Qiangtang Basin, Tibet

AbstractBased on the field outcrops surveyed, combined with recent published the regional tectonic evolution and geochronology data, we analyzed the lithologies and rock associations of strata, identified the sedimentary facies types, and discussed the distribution sedimentary facies and the hydrocarbon accumulation in the eastern Qiangtang basin during the Late Triassic – Jurassic. Marked by regional unconformities, there are two tectono‐stratigraphic units (from the Carnian to the Norian and from the Rhaetian to the Kimmeridgian, respectively) in the eastern part of Qiangtang basin. We systematically described the distribution range, thickness variation and lithological characteristics of different formations in the tectono‐stratigraphic units. The Late Triassic‐Jurassic is dominated by marine facies and marine ‐ continental transitional facies. The marine ‐ continental transitional facies include deltaic and tidal‐lagoon facies. Marine facies including gentle carbonate slope, evaporative platform, restricted platform, littoral, neritic, bathyal and abysmal facies. The Carnian stage is dominated by littoral–neritic–bathyal–abysmal facies in the north Qiangtang depression otherwise the littoral–neritic facies in the south Qiangtang depression. The early Norian stage is dominated by carbonate gentle slope‐mixed continental shelf facies. The late Norian, Bajocian, Callovian and Kimmeridgian stage are dominated by tidal flat‐delta facies in the north Qiangtang depression and littoral‐neritic facies in the south Qiangtang depression. The Bathonian and Oxfordian stage are dominated by evaporative platform‐ restricted platform‐ mixed continental shelf facies. The sedimentary facies formed zones from north to south and extended in an E–W direction. The Eastern Lower Uplift (ELU) played an important role in the division zones of sedimentary facies from north to south. During the Bathonian and Oxfordian, the ELU developed below the sea level and controlled the distribution of restricted platform, evaporative platform and platform margin. We analyzed 20 source rock samples from the upper Triassic‐Jurassic. The total organic carbon (TOC) value from Qoimaco, Buqu and Adula Formations. of late Triassic‐Jurassic in the eastern Qiangtang basin are ranges from 0.17∼0.33% (average 0.28%), 0.05∼0.25% (average 0.15%) and 10.32∼28.78% (average 19.33%), respectively. Obviously, the Adula Fm. developed good source rocks. The values of Tmax and S1+S2 in the Adula formation are 459–461°C (average 460°C) and 6.75‐28.55 mg/g (average 18.18mg/g), indicating that the Adula source rock has reached high‐over‐maturity stage. The bathyal, gentle slop and platform facie belts of the Upper Triassic can configurate the good hydrocarbon prospects in the northeastern area of the Qiangtang basin.

U-Pb zircon geochronology and depositional age models for the Upper Triassic Chinle Formation (Petrified Forest National Park, Arizona, USA): Implications for Late Triassic paleoecological and paleoenvironmental change

AbstractThe Upper Triassic Chinle Formation is a critical non-marine archive of low-paleolatitude biotic and environmental change in southwestern North America. The well-studied and highly fossiliferous Chinle strata at Petrified Forest National Park (PFNP), Arizona, preserve a biotic turnover event recorded by vertebrate and palynomorph fossils, which has been alternatively hypothesized to coincide with tectonically driven climate change or with the Manicouagan impact event at ca. 215.5 Ma. Previous outcrop-based geochronologic age constraints are difficult to put in an accurate stratigraphic framework because lateral facies changes and discontinuous outcrops allow for multiple interpretations. A major goal of the Colorado Plateau Coring Project (CPCP) was to retrieve a continuous record in unambiguous superposition designed to remedy this situation. We sampled the 520-m-long core 1A of the CPCP to develop an accurate age model in unquestionable superposition by combining U-Pb zircon ages and magnetostratigraphy. From 13 horizons of volcanic detritus-rich siltstone and sandstone, we screened up to ∼300 zircon crystals per sample using laser ablation–inductively coupled plasma–mass spectrometry and subsequently analyzed up to 19 crystals of the youngest age population using the chemical abrasion–isotope dilution–thermal ionization mass (CA-ID-TIMS) spectrometry method. These data provide new maximum depositional ages for the top of the Moenkopi Formation (ca. 241 Ma), the lower Blue Mesa Member (ca. 222 Ma), and the lower (ca. 218 to 217 Ma) and upper (ca. 213.5 Ma) Sonsela Member. The maximum depositional ages obtained for the upper Chinle Formation fall well within previously proposed age constraints, whereas the maximum depositional ages for the lower Chinle Formation are relatively younger than previously proposed ages from outcrop; however, core to outcrop stratigraphic correlations remain uncertain. By correlating our new ages with the magnetostratigraphy of the core, two feasible age model solutions can be proposed. Model 1 assumes that the youngest, coherent U-Pb age clusters of each sample are representative of the maximum depositional ages and are close to (<1 Ma difference) the true time of deposition throughout the Sonsela Member. This model suggests a significant decrease in average sediment accumulation rate in the mid-Sonsela Member. Hence, the biotic turnover preserved in the mid-Sonsela Member at PFNP is also middle Norian in age, but may, at least partially, be an artifact of a condensed section. Model 2 following the magnetostratigraphic-based age model for the CPCP core 1A suggests instead that the ages from the lower and middle Sonsela Member are inherited populations of zircon crystals that are 1–3 Ma older than the true depositional age of the strata. This results in a model in which no sudden decrease in sediment accumulation rate is necessary and implies that the base of the Sonsela Member is no older than ca. 216 Ma. Independent of these alternatives, both age models agree that none of the preserved Chinle Formation in PFNP is Carnian (>227 Ma) in age, and hence the biotic turnover event cannot be correlated to the Carnian–Norian boundary but is rather a mid-Norian event. Our age models demonstrate the powers, but also the challenges, of integrating detrital CA-ID-TIMS ages with magnetostratigraphic data to properly interpret complex sedimentary sequences.

A New Prozostrodontian Cynodont (Eucynodontia, Probainognathia) from the Upper Triassic of Southern Brazil

ABSTRACT Probainognathian cynodonts are well represented in the fossil record from the Middle and Upper Triassic of South America, especially in Brazil and Argentina. In this contribution, we describe a new genus and species of non-mammaliaform prozostrodontian cynodont from southern Brazil. The new taxon comes from the Niemeyer Site, a locality in which the traversodontid cynodont Siriusgnathus niemeyerorum is numerically dominant, whereas probainognathians and other tetrapods are comparatively scarce. The fauna from the Niemeyer Site was putatively assigned to the Riograndia Assemblage Zone (Norian age) recently, although none of the index fossils for that biozone (e.g., Riograndia, Clevosaurus, Jachaleria) have so far been discovered at this locality. The new cynodont taxon is based on a left lower jaw with the canine and six (pc2–pc7) well-preserved postcanines (CAPPA/UFSM 0262, holotype), and a second referred specimen (CAPPA/UFSM 0208, paratype), which includes a right lower jaw with incisors, canine, and seven (pc1–pc7) postcanines, with pc6–pc7 being the best preserved. These specimens have a robust dentary, a long and dorsoventrally tall Meckelian groove, unserrated canines, and unserrated, sectorial postcanine teeth with posteriorly inclined cusps and a poorly developed lingual cingulum. This combination of features is unknown in other Carnian and Norian non-mammaliaform cynodonts. The new taxon contributes to our knowledge of the evolutionary radiation of small prozostrodonts that occurred in western Gondwana during the Late Triassic and led to the emergence of several important cynodont groups, including Mammaliaformes. http://zoobank.org/urn:lsid:zoobank.org:pub:FDC21881-532B-490A-96A1-A65EA5F62737

STRATIGRAFIA E SEDIMENTOLOGIA DEI "CALCARI E MARNE A <em>RHAETAVICULA CONTORTA</em> AUCTT. (NORICO-RETICO) DELLA TOSCANA NORD-OCCIDENTALE - NUOVA SUDDIVISIONE FORMAZIONALE

Nine sections from the "Limestones and marls with Rhaetavicula contorta" Auctt. (Norian-Rhaetian) of the Tuscan Nappe in eastern Liguria and northwestern Tuscany, have been examined for their stratigraphic and sedimentological characteristics. The results obtained have been integrated with data pertaining to the previously studied Pania di Corfino section.
 Two formations were identified and studied in detail: that of Pania di Corfino and that of La Spezia.
 Where present, the Pania di Corfino Formation accounts for the lower portion of the sections. It consists mainly of thick beds and massive layers of dolomites, dolomitic limestones and limestones. Thinly-bedded dark limestones appear less frequently, while layers rich in clay are rare. The top of the formation is surely of Rhaetian age, in some sections, as indicated by the presence of Triasina hantkeni Majzon; in the others, it is Norian-Rhaetian. The age of the bottom portion can be regarded as Norian-Rhaetian in all the sections; the presence of considerably thick deposits beneath the established Rhaetian layers in some sections, however, suggests an Early Rhaetian or even Late Norian age.
 The depositional environment of the Pania di Corfino Formation may be envisaged as an epicontinental carbonate platform with predominantly restricted water circulation on which fine carbonate sediments are deposited beneath the wave base; features suggesting a tidal flat are rare. The environment of deposition was, for brief periods only, that of a platform with open circulation in which the effects of wave-motion were prominent; features strictly relatable to a true platform edge have not been found.