Triassic-Jurassic Boundary Research Articles

New Insights on the Upper Triassic Silves Group in Algarve Basin, Portugal: Palynological, paleophytogeography and paleoclimatology advances

This paper presents the results of palynostratigraphic studies in the Silves Group in the Algarve Basin, Portugal. From bottom to top comprises the Silves Sandstones, the Silves Marl-Carbonate Evaporitic Complex, and the Volcano-Sedimentary Series. This study aims to detail the age of the Silves Group, bracketing the Triassic-Jurassic transition, using palynology. For this purpose, 250 samples were collected from 14 main sections. Previous results from a section above the Variscan unconformity, enabled to date the base of the Silves Sandstones and the onset of the Mesozoic sedimentary cycle in the Algarve Basin to lower Carnian. In this work, the top of the Silves Sandstones, containing Camerosporites secatus, Enzonalasporites vigens, Granuloperculatipollis rudis, Lagenella martinii, Patinasporites densus, Samaropollenites speciosus, and Vallasporites ignacii, is dated to the upper Carnian. The base of the Silves Marl-Carbonate Evaporitic Complex, consisting of Alisporites sp., Araucariacites australis, Classopollis meyerianus, Classopollis torosus, Paracirculina quadruplicis and Triadispora sp., indicates an upper Carnian age. The presence of Alisporites diaphanus, Araucariacites australis, Cerebropollenites macroverrucosus, Classopollis meyerianus, Classopollis torosus, Perinopollenites elatoides, Calamospora mesozoica, and Kraeuselisporites reissingeri allows to date the top of the Silves Marl-Carbonate Evaporitic Complex as upper Rhaetian-lower Hettangian. This study allows to date the Silves Group in the Algarve Basin from the lower Carnian to lower Hettangian (Triassic-Jurassic boundary) for the first time. The Carnian microflora provides new insights of the Onslow Microflora in the Western Tethys.

Late Triassic carbon isotope anomalies in the Canadian Cordillera: Paleoenvironmental disturbances associated with the Norian/Rhaetian boundary and end-Triassic mass extinction event

The Late Triassic was a particularly turbulent interval of the geologic past, marked by repeated paleoenvironmental instability culminating in the end-Triassic mass extinction (ETME). These episodes of disturbance are associated with enhanced volcanism, harbinger of the eventual break-up of Pangea. As evidenced by geochemical signals in the marine carbon isotope record, these events were often significant enough to disrupt the global carbon cycle. However, the duration and extent of ETME-associated disturbances leading up to the Triassic/Jurassic boundary (TJB) remain contentious. The present study investigates eight stratigraphic sections from across British Columbia to create a comprehensive Panthalassan carbon isotope record spanning the Norian to early Hettangian. Three distinct negative excursions are observed: an excursion proximal to the Norian/Rhaetian boundary (NRB), another excursion within the Rhaetian, and a final excursion coinciding with the TJB. This is generally consistent with prior studies, but suggests there may be no clear distinction between the negative excursion associated with the NRB, and the oldest Rhaetian “precursor” excursion proposed to be associated with the TJB. Several of the excursions observed in the present study are too large in magnitude to plausibly reflect global ocean water chemistry (∼10 ‰ compared to the expected ∼3 ‰), indicating some local mechanism was amplifying these carbon isotope excursions. A potential explanation is increased organic carbon respiration in restricted marine environments, triggered during episodes of paleoenvironmental disturbance. Regardless, this evidence for repeated carbon isotope excursions supports paleontological data suggesting that the ETME is not a singular and geologically instantaneous event at the TJB, but is instead the amalgamation of several turnovers beginning as early as the NRB.

Patterns of extinction and recovery across the Triassic–Jurassic boundary interval in three resilient Southern Tethyan carbonate platforms

During the end-Triassic extinction (ETE), carbonate platform biocalcifiers suffered high extinction rates that have been linked to volcanically-induced global changes in climate and carbon cycle. Most studies have been focused on the classical sections of the Northern Calcareous Alps (NCA, Austria) and Lombardy Basin (Italy), where the extinction of the aragonitic Dachstein-type biota (involutinid foraminifera and megalodontid bivalves) coincides with the demise of the carbonate platform and with the initial negative carbon isotope excursion (CIE) of the reference sections for the Triassic/Jurassic Boundary (TJB).In this study, we present a detailed facies analysis, bio- and carbon-isotope stratigraphy of three Southern Tethyan carbonate platform sections, Mt. Messapion (Greece), Valle Agricola and Mt. Sparagio (southern Italy) that instead show persisting carbonate productivity across the TJB and potentially preserve the most detailed record of timing and patterns of the ETE in these ecosystems.In the studied sections, the disappearance of the Dachstein-type biota is observed within a positive δ13Ccarb excursion that, according to our study, correlates with that documented in the Schattwald beds (NCA) and Malanotte Fm (Lombardy Basin) above the initial CIE. This level represents the true extinction of the Dachstein-type biota, while the disappearance in the Northern Tethyan sections of the NCA and Lombardy Basin represents a pseudoextinction coinciding with the carbonate platform demise. Above the ETE, Southern Tethyan carbonate platform sections are characterized either by microbial laminites or ooid and oncoid limestones and low-diversity associations.This study reveals a possible paleogeographic and/or latitudinal control on the response of biocalcifiers and carbonate platform ecosystems during the ETE. The Dachstein-type biota was resilient to the environmental perturbations associated with the initial CIE in Southern Tethys, but probably failed to survive subsequent and/or prolonged stress. Despite extinctions, Southern Tethyan carbonate platforms adapted to environmental disturbances through a shift of the dominant carbonate production style from aragonitic biocalcification to chemical and microbially-mediated CaCO3 precipitation. The ecosystem recovery was slow and aragonitic biocalcifiers (dasycladacean algae) reappeared during the early Sinemurian.

Climate-forced Hg-remobilization associated with fern mutagenesis in the aftermath of the end-Triassic extinction

The long-term effects of the Central Atlantic Magmatic Province, a large igneous province connected to the end-Triassic mass-extinction (201.5 Ma), remain largely elusive. Here, we document the persistence of volcanic-induced mercury (Hg) pollution and its effects on the biosphere for ~1.3 million years after the extinction event. In sediments recovered in Germany (Schandelah-1 core), we record not only high abundances of malformed fern spores at the Triassic-Jurassic boundary, but also during the lower Jurassic Hettangian, indicating repeated vegetation disturbance and stress that was eccentricity-forced. Crucially, these abundances correspond to increases in sedimentary Hg-concentrations. Hg-isotope ratios (δ202Hg, Δ199Hg) suggest a volcanic source of Hg-enrichment at the Triassic-Jurassic boundary but a terrestrial source for the early Jurassic peaks. We conclude that volcanically injected Hg across the extinction was repeatedly remobilized from coastal wetlands and hinterland areas during eccentricity-forced phases of severe hydrological upheaval and erosion, focusing Hg-pollution in the Central European Basin.

Marine Strontium Isotope Evolution at the Triassic‐Jurassic Transition Links Transient Changes in Continental Weathering to Volcanism of the Central Atlantic Magmatic Province

AbstractThe end‐Triassic extinction (ETE) is one of the most severe biotic crises in the Phanerozoic. This event was synchronous with volcanism of the Central Atlantic Magmatic Province (CAMP), the ultimate cause of the extinction and related environmental perturbations. However, the continental weathering response to CAMP‐induced warming remains poorly constrained. Strontium isotope stratigraphy is a powerful correlation tool that can also provide insights into the changes in weathering regime, but the scarcity of 87Sr/86Sr data across the Triassic‐Jurassic boundary (TJB) hindered the use of this method. Here we present new high‐resolution 87Sr/86Sr data from bulk carbonates at Csővár, a continuous marine section that spans 2.5 Myrs across the TJB. We document a continuing decrease in 87Sr/86Sr ratio from the late Rhaetian to the ETE, terminated by a 300 kyr interval of a flat trend and followed by a transient increase in the early Hettangian that levels off. We suggest that the first in the series of perturbations is linked to the influx of non‐radiogenic Sr from the weathering of freshly erupted CAMP basalts, leading to a delay in the radiogenic continental weathering response. The subsequent rise in 87Sr/86Sr after the TJB is explained by intensified continental crustal weathering from elevated CO2 levels and reduced mantle‐derived Sr flux. Using Sr flux modeling, we also find support for such multiphase, prolonged continental weathering scenarios. Aggregating the new data set with published records employing an astrochronological age model results in a highly resolved Sr isotope reference curve for an 8.5 Myr interval around the TJB.

Substrate control in track registration and preservation: insights across the Triassic–Jurassic boundary in southern Africa

Tracks registration is influenced by the dynamic interplay between the pedal anatomy of the trackmaker, its behaviour, and the substrate conditions it interacts with. Differences in substrate conditions, especially those linked to grain size and moisture content, often result in the most dramatic variations in track morphology. In the upper Stormberg Group, main Karoo Basin of southern Africa, diverse trace fossils, primarily comprising Late Triassic–Early Jurassic dinosaur tracks, are preserved. Numerous studies have extensively documented individual ichnosites, investigating variations between sites over time, with recent studies suggesting that track abundance and anatomical fidelity increase up-stratigraphy. Despite the well-established link between substrate and track morphology, past studies have not specifically focused on substrate conditions, often emphasizing macro-sedimentary features instead. Here, we examine the micro-sedimentary features of track-bearing units in the upper Stormberg Group using petrographic techniques to better understand the palaeosubstrate and its effect on fossil track registration and preservation. The analysis revealed that very fine-grained sandstones and substrates modified by microbial activity tend to preserve tracks with greater abundance and/or higher anatomical fidelity. Furthermore, the prevalence of very fine-grained and microbially modified strata, and their associated track trends increases in younger stratigraphic units. Across the Triassic – Jurassic boundary in southern Africa, a boom in dinosaur track abundances is observed and credited to the proliferation of dinosaur populations during the Early Jurassic. Our findings, however, suggest that the observed local increase in track abundance (and anatomical fidelity) up-stratigraphy may be linked to substrate composition differences, which were ultimately controlled by large-scale changes in the palaeoenvironment from high-energy meandering fluvial to lower-energy aeolian-lacustrine settings in the Late Triassic and Early Jurassic, respectively. These findings have implications for global macroevolutionary patterns, palaeo-geographical reconstructions, and biostratigraphic correlations in the early Mesozoic.

Plant-insect interactions across the Triassic–Jurassic boundary in the Sichuan Basin, South China

Plants and insects are the most diverse and ecologically important organisms in the terrestrial biosphere. Their interactions are also among the richest biotic relationships, and offer significant insights into the evolution of terrestrial ecosystem complexity through the geological record. This investigation of the late Rhaetian Xujiahe and the earliest Jurassic Zhenzhuchong floral assemblages provides the first data on foliar herbivory generated by terrestrial arthropods across the Triassic–Jurassic transition in the eastern Tethys (East Asia) region. The damage types from two fossil assemblages are collectively attributed to seven functional feeding and egg-laying categories (i.e., hole feeding, margin feeding, surface feeding, skeletonization, piercing and sucking, oviposition, and galling). Most feeding strategies are spread across the major plant groups and persist through the Triassic–Jurassic boundary, with the exception of skeletonization (a category of external foliage feeding), which was restricted to the latest Triassic within dipteridacean ferns. The survey reveals that the respective frequency and diversity of interactions between plants and insects prior to and following the end-Triassic mass extinction event are almost the same, despite a substantial turnover of floral components. This suggest that insect herbivores were largely able to transfer to alternative (but commonly related) plant groups during the dramatic floristic turnover and environmental changes at the end of the Triassic. Sporadic occurrences of foliar modifications, such as marginal cusps on pinnules of Pterophyllum and prominent ridges on the rachises of some ferns and bennettites are interpreted as adaptations for defense against insect herbivores. A few differences in taxonomic composition and herbivory representation between the latest Triassic Xujiahe flora and the earliest Jurassic Zhenzhuchong flora are more likely to be related to collection and preservational biases rather than reflecting palaeoecological changes. We encourage further investigations exploring the distribution of insect damage in fossil floras from other palaeolatitudinal zones and spanning other major extinction events to develop a better understanding of terrestrial ecosystem responses to major crises in Earth’s history.

Phylogenetic reconstruction of Corydioidea (Dictyoptera: Blattodea) provides new insights on the placement of Latindiinae and supports the proposal of the new subfamily Ctenoneurinae

AbstractRepresentatives of the cockroach superfamily Corydioidea are less sampled than members of the two other cockroach superfamilies (Blaberoidea and Blattoidea) due to the difficulty of collecting them in the field, accentuated by a general lack of knowledge on their biology. Their evolutionary relationships have not yet been investigated with a relevant sampling and are therefore poorly known. Here, we assess the phylogenetic relationships of 35 Corydioidea species with mitochondrial genomes and two nuclear gene fragments. Our sampling for Corydiidae comprises Corydiinae and Euthyrrhaphinae representatives, whereas our sampling for the remaining Corydioidea includes species belonging to genera Beybienkonus Qiu, Wang and Che, Compsodes Hebard, Ctenoneura Hanitsch and Nocticola Bolívar. We further infer their divergence times with molecular dating analyses relying on five fossil calibrations. We also carry out reconstructions of ancestral character states for 11 phenotypic and one biological traits. Our results recover two major Corydioidea clades, one consisting solely of Corydiidae (except Latindiinae) and the other of all remaining Corydioidea taxa. Based on the results of phylogenetic analyses, an updated classification of extant Corydioidea is proposed, where Latindiinae Handlirsch stat.rev. and Ctenoneurinae Qiu and Che, subfam.nov. are assigned to the family Nocticolidae Bolívar sensu nov. A new genus Pseudoeupolyphaga Qiu and Che, gen.nov. is also established within Corydiinae. Both the origin of crown Corydioidea and the divergence of the two major lineages are estimated to have occurred during the Triassic–Jurassic boundary. Ancestral character state reconstruction analyses also suggest an adaptive relationship between phenotypic characteristics and habitat preferences.

A possible Norian–Rhaetian boundary in the high-latitude continental Junggar Basin indicated by the δ 13 C org record

Abstract In contrast to the Triassic–Jurassic boundary, there is no consensus on the definition and age of the Norian–Rhaetian boundary (NRB), which hampers the global correlation of Rhaetian strata and thus interpretation of the patterns and driving mechanism of the end-Triassic mass extinction. Recent works show that a significant negative carbon isotope excursion (N-CIE) occurs in the NRB interval ( c. 205.7 Ma), which probably provides a physical marker for the NRB. However, no such records have so far been reported from high-latitude continental deposits. Here we present high-resolution bulk organic carbon isotope data from the Upper Triassic continuous lacustrine-to-fluvial deposits in the Haojiagou section of the high-latitude continental Junggar Basin in northwestern China. A significant N-CIE is shown at an age of c. 205 Ma, which is most probably the expression of the NRB N-CIE in the Junggar Basin owing to their very close occurrence times. The NRB is thus probably along the N-CIE in the Haojiagou section, and a short Rhaetian stage is then supported. The Late Triassic climate in the high-latitude Junggar Basin was consistent with the global changes in climate, characterized by a long-sustained cooler and humid climate interrupted by the late Norian and latest Rhaetian warm events.

Valvaeodinium hymenosynypha (Morbey) comb. nov., a dinoflagellate cyst from the uppermost Triassic and lowermost Jurassic (Rhaetian and Hettangian) of Europe

Cymatiosphaera hymenosynypha Morbey 1975, previously recorded from the Rhaetian Westbury Formation in the United Kingdom, occurs in Triassic–Jurassic boundary strata from Denmark. From the present study it is clear that this small, finely reticulate, ellipsoidal, two-layered palynomorph is not a prasinophyte, but a dinoflagellate cyst with a combination apical/intercalary archaeopyle (type tAtI) which involves three apical plates plus one intercalary plate. This cavate cyst is morphologically similar but not identical to Valvaeodinium hanneae Piasecki 2001 from the uppermost Bathonian to lower Callovian of East Greenland, and it is therefore here transferred to Valvaeodinium, as Valvaeodinium hymenosynypha (Morbey) Lindström comb. nov. The appearance of Valvaeodinium hymenosynypha in Rhaetian strata in the Danish Basin suggests that the lineage of cavate Valvaeodinium cysts originated in the Late Triassic alongside a chorate species of the genus. Valvaeodinium hymenosynypha seems to have survived just barely past the end-Triassic mass extinction as it is also present in the earliest Hettangian.

Biological extinction and photic-zone anoxia across the Triassic–Jurassic transition: insights from the Qiangtang Basin, eastern Tethys

The end-Triassic mass extinction (ETME) is one of the five catastrophic extinction events. However, the driving mechanisms of biodiversity loss during this interval remain controversial. In this study, we investigate the marine sediment geochemistry and fauna across the Triassic–Jurassic boundary in the Wenquan section of Qiangtang Basin, and the triggering mechanism of the Late Triassic extinction in the eastern Tethys Ocean. Our study shows that the main pulse of the ETME occurred in Bed 8, manifesting as the disappearance of four brachiopod species, a significant decrease of other faunas, and the ‘Lilliput effect’ on bivalves. Analyses of pyrite framboids and redox-sensitive trace elements suggest the development of photic zone anoxia near the T/J boundary and coincident with the Late Triassic extinction. Thus, the development of abrupt and intense photic-zone anoxia could play an important role in the end-Triassic extinction. Supplementary material: Supplementary tables giving element contents and palaeontological data are available at https://doi.org/10.6084/m9.figshare.c.6771606

Geological and chronostratigraphic overview of the Upper Triassic and Jurassic successions of the Junggar Basin, NW China

Abstract The vast, widely exposed terrestrial (lacustrine to fluvial) Upper Triassic–Jurassic (except Tithonian) successions of the Junggar Basin not only record most of the stratigraphic boundaries of the Upper Triassic and Jurassic, including the Triassic–Jurassic boundary and the Hettangian–Sinemurian, Sinemurian–Pliensbachian, Pliensbachian–Toarcian, Lower–Middle Jurassic, Middle–Upper Jurassic and Oxfordian–Kimmeridgian boundaries, but also record a range of geological, organic, palaeogeographic and palaeoclimatic events known to have happened globally in the Late Triassic and Jurassic. The Triassic–Jurassic boundary is placed in the stratigraphic interval of the first occurrence of Retitriletes austroclavatidites and Callialasporites dampieri and the last occurrence of Lunatisporites rhaeticus . The end-Triassic mass extinction is characterized by the disappearance of most of the sporomorph and macro-plant taxa. The end-Triassic mass extinction occurred before the first occurrence of the sporomorph Cerebropollenites thiergartii , and ended after its appearance when life began to revive. The Junggar Basin was situated at a high latitude during the Late Triassic–Early Jurassic Pliensbachian ‘hothouse’ and ‘greenhouse’ periods. The Late Triassic–Mid Jurassic Bajocian was humid and warm, and rich in coal swamps, except the Toarcian, which yields little coal because it was relatively warmer and drier. It became arid from the early Late Jurassic Oxfordian.

Detrital zircon and apatite U-Pb provenance and drainage evolution of the Newark Basin during progressive rifting and continental breakup along the Eastern North American Margin, USA

Abstract Mesozoic rift basins of the Eastern North American Margin (ENAM) span from Florida in the United States to the Grand Banks of Canada and formed during progressive extension prior to continental breakup and the opening of the north-central Atlantic. The syn-rift strata from all the individual basins, lumped along the entire margin into the Newark Supergroup, are dominated by fluvial conglomerate and sandstone, lacustrine siltstone, mudstone, and abundant alluvial conglomerate and sandstone lithofacies. Deposition of these syn-rift sedimentary rocks was accommodated in a series of half grabens and subsidiary full grabens situated within the Permo-Carboniferous Appalachian orogen. The Mesozoic ENAM is commonly depicted as a magma-rich continental rift margin, with magmatism (Central Atlantic magmatic province [CAMP]) driving continental breakup. However, the southern portion of the ENAM shows evidence of magmatic breakup (e.g., seaward-dipping reflectors), and rifting and crustal thinning appeared to start ~30 m.y. prior to CAMP emplacement in the Jurassic. This study provides extensive new detrital zircon and apatite U-Pb provenance data to determine the provenance and reconstruct the paleodrainages of the Newark Basin during progressive rifting and magmatic breakup and the implications for the overall rift configuration and asymmetry during progressive rifting along the ENAM rift margin. Detailed new detrital zircon (N = 21; n = 3093) and apatite (N = 4; n = 559) U-Pb results from sandstone outcrop and core samples from the Newark Basin indicate a distinct provenance shift, with relatively older Carnian syn-rift strata predominately sourced from the hanging wall of the basin bounding fault in the east while relatively younger Norian strata were regionally sourced from both the hanging wall and footwall. The syn-rift strata at the Triassic-Jurassic boundary were sourced from the hanging wall before a transition to local footwall terranes. These results suggest two major provenance changes during progressive rifting—the first occurring during Carnian crustal necking and rift flank uplift as predicted by recent numerical models and the second occurring at the onset of the Jurassic due to regional and local thermal uplift during CAMP magmatism as seen along other magma-rich margins, such as the North Atlantic and the southern portion of the South Atlantic margin.

Palynology of the Triassic–Jurassic transition of the Danish Basin (Denmark): a palynostratigraphic zonation of the Gassum–lower Fjerritslev formations

The Upper Triassic–Lower Jurassic succession in the Danish Basin is penetrated by many deep wells that were drilled during former hydrocarbon exploration campaigns, but it is today targeted for geothermal energy and storage of CO2. The Stenlille salt dome on Sjælland sandstones of the Gassum Formation, sealed by the overlying Fjerritslev Formation mudstones, has been used for decades as a seasonal storage for natural gas. With its comprehensive dataset of seismics, geophysical well logs and conventional core data from 20 wells, the Stenlille succession serves as a model for other salt domes currently being evaluated as potential CO2 storage sites in the basin. Over the last decade the cored Triassic–Jurassic boundary succession has contributed to the understanding of environmental and palynological events during the end-Triassic mass extinction. Core, sidewall core and cutting samples from several of the closely situated Stenlille wells are here used to establish a high-resolution palynostratigraphic zonation scheme covering the entire Rhaetian to Sinemurian succession by integrating new analyses with previously published data. The palynological dataset has allowed the recognition of nine formally described spore-pollen zones, of which eight are new, while two previously described dinoflagellate cyst zones are subdivided into three informal subzones each. The palynological zonation is integrated with a sequence stratigraphic framework and will form the basis for the dating of future well sections in the Danish Basin and other basins and for correlation to outcrops. The large palynological dataset further shows that the vegetation around the Danish Basin was remarkably stable during the early to middle Rhaetian, but that events related to the emplacement of the Central Atlantic Magmatic Province accelerated ecosystem changes for c. 175 ky in the late Rhaetian and earliest Hettangian, including ∼25 ky of successional recovery before the terrestrial ecosystem had again stabilised.

Tethyan ocean acidification triggered the end-Triassic mass extinction: New Ca isotopic constraints from the Qiangtang Basin

Oceanic acidification has long been suggested as a potential environmental trigger of marine ecosystem collapse in the Earth’s history. However, evidence for oceanic acidification as an important controlling mechanism of the end-Triassic mass extinction is still limited. Here, the first coupled carbon- and calcium-isotope records across the Triassic-Jurassic transition are provided. The calcium isotope (δ44∕40Ca) profile from the Qiangtang Basin, eastern Tethys exhibits a prominent negative excursion of ∼0.3‰ at the Triassic-Jurassic (T-J) boundary, which is consistent with the onset of negative δ13C excursion, suggesting a possible relationship between large-scale volcanic eruption and calcium isotopic composition. The Ca isotope perturbation during the T-J boundary is interpreted to be triggered by a significant decrease in CaCO3 burial related to CO2-induced ocean acidification. The coupled δ13C and δ44/40Ca records reveal that the carbon cycle perturbations controlled oceanic acidification and decreased carbonate burial. This provides robust evidence for the causal link between oceanic acidification, carbon cycle perturbation in response to Central Atlantic Magmatic Provence (CAMP), and the T-J boundary mass extinction.

Constraining the Triassic–Jurassic boundary carbon cycle perturbations using high-resolution δ 13 C org records from the Haojiagou section in northwestern China

Abstract Large magnitude and rapid negative carbon isotope (δ 13 C) excursions in the Triassic–Jurassic boundary (TJB) interval have been proposed as critical evidence for the hypothesis that the emplacement of the Central Atlantic Magmatic Province (CAMP) triggered global carbon cycle perturbations and the end-Triassic mass extinction (ETE). However, the pattern and timing of δ 13 C variations during the ETE remain poorly constrained. Here I present high-resolution organic carbon isotope (δ 13 C org ) records from a terrestrial TJB succession continuously exposed along the Haojiagou valley on the southern margin of the Junggar Basin, northwestern China. The δ 13 C chemostratigraphic correlations, combined with the palynological data, indicate that the position of the TJB should be placed at the base of bed 53. Importantly, the results show that two rapid negative carbon isotope excursions at the end Triassic roughly coincide with two episodes of variations in the palynological records. This observation supports the hypothesis that two pulses of biotic crisis during the ETE may have been triggered by two major episodes of CAMP magmatic activity. In addition, the data in this study support an early start for CAMP magmatic activity in the early Rhaetian, which may have led to a global carbon cycle perturbation and the related biotic crisis or turnover.

Early Jurassic orthopteran insects from the southern Junggar Basin, NW China, with discussion of biodiversity changes of Orthoptera across the Triassic–Jurassic boundary

Abstract Orthoptera constitutes an important ecological component of the global fauna, but the order's Early Jurassic record is limited in China and its evolution is poorly understood after the end-Triassic mass extinction. Several orthopterans are described herein from the Lower Jurassic Badaowan and Sangonghe formations of the southern Junggar Basin, Xinjiang, NW China. From the Badaowan Formation, a new species, Parahagla cheni sp. nov., is established and assigned to Chifengiinae (Hagloidea: Prophalangopsidae), which represents the oldest record of this subfamily. From the Sangonghe Formation, a forewing fragment is attributed to Sinagryllus xinjiangensis Wang et al. , 2019 (Grylloidea: Baissogryllidae); another forewing fragment and a metathoracic leg without attribution are also described. The discovery of these fossils increases the biodiversity of Orthoptera in the Early Jurassic, and further indicates that orthopterans probably flourished in the Junggar area during the Early Jurassic. An analysis of orthopteran biodiversity at generic and species levels reveals an extinction in Orthoptera in the Late Triassic, especially for the superfamilies Hagloidea and Oedischioidea, which suffered a substantial extinction. This extinction occurred in the Late Triassic, earlier than the mass extinction of marine animals at the end of the Triassic.

Uncertainties surrounding the oldest fossil record of diatoms

Molecular clocks estimate that diatom microalgae, one of Earth’s foremost primary producers, originated near the Triassic–Jurassic boundary (200 Ma), which is close in age to the earliest, generally accepted diatom fossils of the genus Pyxidicula. During an extensive search for Jurassic diatoms from twenty-five sites worldwide, three sites yielded microfossils initially recognized as diatoms. After applying stringent safeguards and evaluation criteria, however, the fossils found at each of the three sites were rejected as new diatom records. This led us to systematically reexamine published evidence in support of Lower- and Middle-Jurassic Pyxidicula fossils. Although Pyxidicula resembles some extant radial centric diatoms and has character states that may have been similar to those of ancestral diatoms, we describe numerous sources of uncertainty regarding the reliability of these records. We conclude that the Lower Jurassic Pyxidicula fossils were most likely calcareous nannofossils, whereas the Middle Jurassic Pyxidicula species has been reassigned to the Lower Cretaceous and is likely a testate amoeba, not a diatom. Excluding the Pyxidicula fossils widens the gap between the estimated time of origin and the oldest abundant fossil diatom record to 75 million years. This study underscores the difficulties in discovering and validating ancient microfossils.

Uranium isotope evidence for extensive seafloor anoxia after the end-Triassic mass extinction

The end-Triassic extinction (ETE) ranks as one of the ‘Big Five’ biotic crises of the Phanerozoic and is thought to be triggered by volcanism of the Central Atlantic Magmatic Province (CAMP). However, the proximal causes of the extinction and the factors responsible for the delayed biotic recovery remain debated. Here we use uranium isotopes and geochemical models to constrain the evolution of global seafloor anoxia during the latest Triassic and earliest Jurassic. We document a major negative uranium isotope anomaly from carbonates in a western Tethyan continuous marine Triassic-Jurassic boundary section. The onset of the δ238U anomaly is coincident with the initial negative carbon isotope anomaly that is correlative with the extinction horizon and a major pulse of intrusive CAMP volcanism. The U isotope values remain low throughout most of the Hettangian indicating persistent, widespread anoxia. Our coupled C-P-U Earth system and U-cycle box model results show that the maximum extent of anoxia (∼13%) was reached 200–250 kyr after the extinction, probably as a consequence of extrusive CAMP pulses. The anoxic extent remained high (1–6%) throughout the Hettangian. We suggest that the continuing volcanic activity, recorded by the successive negative carbon isotope anomalies and Hg peaks in the section, inhibited any rapid recovery from anoxia. Our results indicate that the spread of marine anoxia and the ETE have a common cause rather than a cause-and-effect relationship but anoxia played a key role in hindering the biotic recovery of benthic ecosystems following the extinction.

Latest Triassic and Early Jurassic Spiriferinida (Brachiopoda) of Zealandia(New Zealand and New Caledonia).

The Late Triassic spiriferinides of Zealandia include the endemic or Austral genera Rastelligera, Psioidea and Psioidiella, and the cosmopolitan Zugmayerella. Mentzelia kawhiana is revised and placed in Callospiriferina. It appears in the late Rhaetian and is found in the Téremba Terrane in New Caledonia and throughout the Murihiku Terrane in New Zealand. The spiriferinides were severely affected at the Triassic-Jurassic boundary in Zealandia as elsewhere, but a moderately diverse fauna developed in the Early Jurassic. This has strong links to South America, and affinities with southern Europe and North Africa. In this study, a total of six species of Jurassic spiriferinides are recognised. Callospiriferina ongley is present in middle and late Hettangian and Sinemurian faunas. It is succeeded in the Pliensbachian and early Toarcian by Callospiriferina radiata. Two species of Spiriferina are recognised. S. sophiaealbae n. sp. first appears in the Middle Hettangian and is present in the Southland and Kawhia Synclines until the early Toarcian. S. arakiwa n. sp. is found mainly on the southwest limb of the Southland Syncline in the Pliensbachian and early Toarcian. The non-costate European genus Cisnerospira is represented in Zealandia by the small C. antipoda n. sp. This species ranges from Hettangian to early Toarcian. Two specimens of a spiriferinide with a costate sulcus are tentatively identified as Dispiriferina sp. cf. D. chilensis. The highest stratigraphic level at which Zealandian spiriferinides have been found is that of the Dactylioceras band at Kawhia, which is correlated with the Crassum Subzone of the Bifrons Zone (highest Early Toarcian) and includes three species of spiriferinide. This suggests that the Zealandian spiriferinides survived the Toarcian Event, only to meet their demise slightly later.