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The end-Triassic mass extinction (ETME; c. 201.6 Ma), one of the so-called “big-five” mass extinctions in the Phanerozoic era, is associated with widespread marine anoxia, ocean acidification, global warming, carbon cycle perturbations (δ13C) and an extinction of diverse marine and terrestrial groups. This extinction is frequently linked to the volcanic activity in the Central Atlantic Magmatic Province (CAMP) which is often cited to explain e.g., the correlative negative carbon excursions across many sections, mutagenesis of land plants by Hg-toxicity, and enrichment of Hg/TOC. Despite this, the exact identification of a volcanic signal in many of these sections is not well constrained. In this study we present high-precision platinum group element (PGE: Ir, Ru, Pt, Pd) and Re data for the Triassic-Jurassic boundary succession at the Kuhjoch section (Austria). These are the first results from our new analytical setup using high-pressure asher digestion, isotope dilution and multi-collector inductively-coupled plasma mass spectrometry for precise determination in low concentration (e.g. ppt) samples such as sediments. The PGE and Re concentrations and patterns vary significantly with stratigraphy. The c. 13 m of clayey sediments above the onset of the extinction (marked by the c. 16 cm thick T-bed) show pronounced enrichment in Pt, Pd and Ir concentrations relative to the under- and overlying carbonate dominated stratigraphy. Their PGE patterns are non-chondritic with Pd/Ir and Pt/Ir similar to CAMP basalts. Normalised for lithology (Al2O3), however, there are no significant variations in Pt, Pd and Ir values below, within and above the clayey sediments. Re and Ru are, however, depleted compared to the other PGEs in the clayey interval, something also observed in some CAMP basalts. One possibility is therefore to interpret the PGE-rich, clayey sediments, including the main extinction interval in the basal portion, as recording increased weathering of CAMP basalts. As the PGE enrichment increases up through the T-bed, this could show that the onset of CAMP weathering and mass extinction would have therefore coincided. However, further work is needed to identify the relative role of CAMP volatile emission during volcanic activity versus post-eruption weathering of basalts.

Fossilised fibrous skeletons of non-spicular demosponges have been reported in carbonates throughout the Phanerozoic and recently from rocks dated back to 890 Ma ago. These records expanded our understanding of metazoans in multiple aspects, including their early evolution, the cryptic ecology in fossil reefs, and recovery after mass extinction events. However, debates and confusion persist on the differentiation of these fossils from other biogenic or abiotic structures. Here we propose six identification criteria based on established taphonomical models and biological characteristics of these sponges (“Keratosa”sensuMinchin, 1900). Besides, sponge fossils of this kind from the lowermost Triassic of Chanakhchi (Armenia) are described with a 3-D reconstruction to exemplify the application of these criteria in the recognition of such organisms. Subsequently, the state-of-the-art understanding of the taxonomy and evolution of these fossil sponges, a previously poorly addressed topic, is summarized. The morphology of the Triassic Chanakhchi fossils indicates an affinity with Verongimorphs, a group that may have evolved by the Cambrian Age 3. Other than that, more efforts are still required to explore the taxonomic diversity and evolutionary details in the accumulating data of these fossil non-spicular demosponges.

The Norian Stage is the longest stage in the Phanerozoic, and some members of the boundary working group have been evaluating suitable Carnian-Norian boundary sections for roughly two decades. This has identified two possible candidate boundary sections, at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). After a formal voting procedure within the working group, ending on the 26th July, 2021, the Pizzo Mondello section was selected as the global stratotype section and point for the base of the Norian. We evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and the ‘flat-clam’ Halobia austriaca. Secondary markers were also evaluated around these boundary datums for correlation potential, and the veracity of the proposed sections for GSSP status. Data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in voting, conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the base of the Norian. A secondary biotic marker for this boundary is the first occurrence of Primatella (Carnepigondolella) gulloae, in sample NA43, ca. 0 m below FNP135A, and the FA of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating the first subzone of the Jandianus Zone). The best physical secondary marker is the magnetozone PM5n with the proposed boundary ca.40% through the thickness of PM5n. Strengths of the chosen datum are: 1) it also maintains historical priority for ammonoid zonations, which had placed the base Norian near to this level in Europe, North America and probably NE Asia; 2) Halobia austriaca is widely distributed in all paleolatitudes and is a long-established taxon.

Geobiology, 19 (6), ISSN:1472-4677, ISSN:1472-4669

The end-Permian mass extinction was the most severe biotic crisis in Earth’s history. In its direct aftermath, microbial communities were abundant on shallow-marine shelves around the Tethys. They colonized the space left vacant after the dramatic decline of skeletal metazoans. The presence of sponges and sponge microbial bioherms has largely gone unnoticed due to the sponges’ size and the cryptic method of preservation. In addition to sponge dominated facies recently described in South Armenia and Northwestern Iran, we describe here sponge-microbial bioherms cropping out in two well-known Permian-Triassic boundary localities: the Kuh-e Hambast section, south-east of Abadeh city and the more distal Shahreza section, near Isfahan. In both sections, the extinction horizon is located at the top of an upper Changhsingian ammonoid-rich nodular limestone, calledParatiroliteslimestone. At Kuh-e Hambast, the overlying decimetric thick shale deposit called “boundary clay,” the latest Permian in age, is conformably overlain by well-dated transgressive basal Triassic platy limestone containing four successive levels of decimeter to meter scale, elongated to form cup-shaped mounds made of branching columnar stromatolites. Sponge fibers from possibly keratose demosponge, are widely present in the lime mudstone matrix. At the Shahreza section, above the extinction level, the boundary clay is much thicker (3 m), with thin platy limestone intervals, and contains two main levels of decimeter to meter scale mounds of digitate microbialite crossing the Permian-Triassic boundary with similar sponge fibers. Three levels rich in thrombolite domes can be seen in the overlying 20 m platy limestone of earliest Triassic age. Sponge fibers and rare spicules are present in their micritic matrix. These sponge fibers and spicules which are abundant in the latest Permian post-extinction boundary clay, followed microbial buildups during the Griesbachian time.

Three small-scale extinctions occurred in the Early Triassic with one of them recognized close to the Smithian-Spathian boundary. In the last two decades, the end-Permian mass extinction as well as the subsequent recovery have been intensively studied throughout the Tethys region, but correlations within the Lower Triassic are difficult due to conodonts endemism. Here we use paleontological and geochemical methods to document a high-resolution biostratigraphy of the Smithian-Spathian boundary interval from two sections of Oman. In combination with previously published data from both South-Central Europe and South China, a quantitative stratigraphic correlation has been achieved with 7 conodont UA Zones recognized using the unitary association method. Based on conodonts and carbonate carbon isotope data, the Smithian-Spathian boundary is identified in the interval from UAZ4 to UAZ5 close to the last occurrence of Nv. pingdingshanensis in Oman and South China, and within the range of P. inclinata, Ns. planus, Pl. regularis, and Pl. corniger in South-Central Europe. UAZ7 fauna displays a clear diachronism as it starts from South China, arrives a bit later in Oman and even later in western Tethys. Foliella gardenae and Icriospathodus zaksi are reported from Oman for the first time and thus expand the geographical distribution of these rarely reported species.

Sedimentary deposits of the Lower Cretaceous Xiagou Formation form the most significant potential hydrocarbon reservoirs in the Qingxi Sag, Jiuquan Basin (NW China). Zircon U-Pb ages of the dated basalts at the top of the Xiagou Formation give an isochron age of 115.6 Ma, and the sedimentation interval of the Xiagou Formation was speculated to range from about 125/124 Ma to 115 Ma based on paleontological research and stratigraphic correlation analysis. Here we use GR logging data as a palaeoenvironmental and palaeoclimatic proxy to conduct a detailed cyclostratigraphic study of five selected wells. Power spectra, evolutionary fast Fourier transformation and wavelet analysis all reveal significant sedimentary cycles in the Xiagou Formation. The ratios of cycle wavelengths in these stratigraphic units are 33.82 m : 7.91 m : 3.06 m : 1.79 m, which is similar to the ratio of orbital targets of 20 : 5 : 2 : 1. The ratio of 20 : 5 : 2 : 1 is interpreted as Milankovitch cycles of 405 kyr long eccentricity, 100 kyr short eccentricity, 37 kyr obliquity, and 22 kyr precession cycles respectively. A high-resolution astronomical time scale is constructed by tuning the stratigraphy into target curves of orbital cycles respectively. Based on the astronomical time scale, the absolute ages of 55 samples were estimated, which are used for subsequent stable carbon and oxygen isotope stratigraphy analysis. The analysis results of the five studied wells in the Qingxi Sag indicate: (1) a negative trend of δ 13 C values upwards in the Xiagou Formation, and (2) negative δ 18 O values with a positive trend upwards. Both relatively heavy values and pronounced covariances of δ 13 C values and δ 18 O values indicate an arid-evaporation-controlled climate during the sedimentary period of the Lower Cretaceous Xiagou Formation, Qingxi Sag, Jiuquan Basin. Moreover, positive covariances of SQK 1 g 2+3 indicate extremely high temperature, and negative covariances of SQK 1 g 1 indicate a relatively low temperature.

Late Permian mass extinction (LPME) research has focused primarily on Tethyan sections because it is believed that these successions are more complete than those from other localities, and provide a more comprehensive record of the largest, most devastating extinction event in Earth history. The Kisejin section, a previously undocumented mid-Tethyan, Upper Permian-Lower Triassic succession located in the Central-Iran Plate. The Kisejin section contains a continuous Permian-Triassic sequence with only small breaks in sedimentation and was examined in order to determine sedimentologic, biostratigraphic, and carbon isotopic trends across the Permian-Triassic transition. Abnormal (anachronistic) carbonates developed in the study area following the LPME, and include microbialites, edgewise conglomerates, sparitic microspheres, and microbially-coated grains; microbialites occur as thrombolites, stromatolites, and as agglutinated forms. Renalcis-type calcimicrobes are documented for the first time from Permian-Triassic boundary microbialites (PTBMs) of Iran. Coated grains fall into two groups, and include pre-PTBM ooids, which are dense and cloudy, and possibly microbial in origin, and post-PTBM cortoids with destructive and constructive micrite envelopes. Latest Permian conodonts (H. praeparvus, M. ultima), coupled with carbon isotopic values, place the Permian-Triassic boundary within the lowermost thrombolite unit, about 2.1 m above the boundary between the Nessen Formation and the Elika Formation, and indicate that microbialite growth began during the latest Permian. Our study of this previously unknown section shows that, unlike other well-known PTB sections from Iran, the microbialite pattern is complicated, and is more similar to PTBM successions from Turkey. In addition, we note a similarity between the unusual facies of the Kisejin section and those of eastern Tethyan sections from China (i.e. sparry microspheres and Renalcis-type calcimicrobes); these unusual facies have not been previously reported from other well-known Iranian sections, including Julfa and Abadeh, which are thick and have been extensively studied.

The End-Triassic Mass Extinction (ETME) is one of the five major mass extinctions of the Phanerozoic. The deposition of ooids is atypically high in the direct aftermath of major extinction events, including the ETME. Ooids were intensively investigated both petrographically and sedimentologically in the past decades; but only recently their potentialities as archives for the original chemical composition of the oceans where they formed, have gained awareness. Here we present stratigraphical, sedimentological and geochemical aspects for a mid-Norian-Hettangian section from the Emirates.Petrographic analyses provided a detailed morphological classification of post-ETME coated grains, supported by point counting of two isochronous geological sections. FE-SE-EDX imaging unraveled peculiar µm-scale features linked to morphology, diagenesis and biotic interaction in the cortex. LA-ICP-MS analyses were performed for specific major and trace elements. Post-extinction oolites show high variability in size and development of the cortex. They range from small (~ 300 µm) and superficial coating, to bigger (up to 800 µm) and well developed. The degree of micritization highlights different oxic conditions in the diagenetic environment. LA-ICP-MS analyses give insights into seawater redox conditions during ooids formation, siliciclastic contamination, diagenetic processes and the role of bacterial strain in shaping the ooids. Petrographical and geochemical data point out to a calcitic deposition of these ooids as odd with the general consideration that the Late Triassic to Early Jurassic was part of the Aragonite sea. This has major implication on the understanding of the carbonate saturation in the oceans just after the mass-extinction and on the interpretation of several proxies as the C and Ca isotope-system.

International audience; The establishment of the Late Triassic time scale has given rise to considerable controversy, particularly regarding the Rhaetian duration and the inferred absolute age models. In this respect the astronomical polarity time scale (APTS) established from the continental successions of the Newark Basin (eastern North America) is considered as a reference record, although its completeness is questioned. Numerous magnetostratigraphic correlation schemes have been proposed between the APTS and biostratigraphically well-constrained Tethyan marine sections. This has led to two main contrasting options: a "short" Rhaetian duration (about 4-5 myr), and a "long" one (about 8-9 myr). Astronomical calibration of the Tethyan Rhaetian and estimate of its duration is necessary to help advance this debate. We have undertaken a cyclostratigraphic analysis of a Rhaetian composite record built from four overlapping Austrian reference sections. Magnetic susceptibility variations of the 131.5 m thick record are astronomically paced by the precession and 405-kyr orbital eccentricity cycles. 405-kyr orbital tuning allows to establish a floating time scale, and thus to suggest a minimum duration of 6.69 myr of the Rhaetian stage. Given the well-established radioisotopic age of the Rhaetian-Hettangian boundary of 201.36 Ma, an age no younger than 208.05 Ma for the Norian-Rhaetian boundary can be proposed. This result will contribute to the refinement of the Late Triassic time scale, but it does not solve the long-standing debate on bio-magnetostratigraphic correlations between the continental Newark APTS and the Tethyan marine sections, nor the question of the completeness of the Rhaetian Newark Basin.

During the earliest Triassic microbial mats flourished in the photic zones of marginal seas, generating widespread microbialites. It has been suggested that anoxic conditions in shallow marine environments, linked to the end‐Permian mass extinction, limited mat‐inhibiting metazoans allowing for this microbialite expansion. The presence of a diverse suite of proxies indicating oxygenated shallow sea‐water conditions (metazoan fossils, biomarkers and redox proxies) from microbialite successions have, however, challenged the inference of anoxic conditions. Here, the distribution and faunal composition of Griesbachian microbialites from China, Iran, Turkey, Armenia, Slovenia and Hungary are investigated to determine the factors that allowed microbialite‐forming microbial mats to flourish following the end‐Permian crisis. The results presented here show that Neotethyan microbial buildups record a unique faunal association due to the presence of keratose sponges, while the Palaeotethyan buildups have a higher proportion of molluscs and the foraminifera Earlandia. The distribution of the faunal components within the microbial fabrics suggests that, except for the keratose sponges and some microconchids, most of the metazoans were transported into the microbial framework via wave currents. The presence of both microbialites and metazoan associations were limited to oxygenated settings, suggesting that a factor other than anoxia resulted in a relaxation of ecological constraints following the mass extinction event. It is inferred that the end‐Permian mass extinction event decreased the diversity and abundance of metazoans to the point of significantly reducing competition, allowing photosynthesis‐based microbial mats to flourish in shallow water settings and resulting in the formation of widespread microbialites., After the end‐Permian mass extinction, microbialites filled the ecological niche previously occupied by metazoan reefs. The factors that allowed microbialite‐forming microbial mats to flourish are, however, hotly debated. By investigating the faunal composition and depositional setting of Permian/Triassic boundary microbialites, we propose that the impact of the extinction event on the abundance of metazoans suppressed the biological controls that were previously excluding microbialite development from subtidal environments.

The Carnian Humid Episode is an interval of prominent climatic changes in the Late Triassic. We studied the carbon isotope (δ13C) geochemistry of carbonates from sections in southwestern China and northern Oman. δ13C records from the Yongyue section (western Guizhou, South China) show a progressive positive shift from 1.4 to 2.8‰ in the early to middle Julian 1 substage. This positive trend is followed by a swift negative shift of c. 4.2‰ from 2.8 to −1.4‰ in the Julian 2 substage. δ13C from the Wadi Mayhah section (northern Oman) shows a positive shift from 2.2 to 2.8‰ in the Julian 1 substage, followed by a negative shift of c. 3.2‰ from 2.8 to −0.3‰ in the Julian 2 substage. The δ13C records from the two study sections generally correlate well with each other as well as with published records, pointing to a considerable input of isotopically light carbon starting in the late Julian 1 substage. Such a large amount of light carbon probably derived from direct degassing and the sediment–sill contact metamorphism of the Panthalassan Wrangellia Large Igneous Province and contemporary Tethyan volcanism. The voluminous volcanogenic greenhouse gases probably contributed to the warming pulse in the middle Carnian. Thus the dry–wet climatic transition during the Carnian Humid Episode is best interpreted as a warm climate-driven intensification of the activities of the atmospheric circulation and hydrological cycle.

After the latest Permian mass extinction event, microbial mats filled the ecological niche previously occupied by metazoan reefs, resulting in widespread microbialites. This study focuses on the lipid biomarker (molecular fossil) and invertebrate fossil records from Neotethyan platform margin sections to understand microbial-metazoan bioherm formation. Here, we find that early Griesbachian thrombolitic and stromatolitic microbialites from Curuk Dag (Turkey) and Kuh e Surmeh (Iran) contain abundant lipid biomarkers, representing input from cyanobacteria, anoxygenic phototrophic bacteria, sulfate-reducing bacteria, and halophilic archaea. The biomarker inventory suggests that the microbialites were constructed by cyanobacteria-dominated microbial mats. Biomarkers of halophilic archaea are interpreted to reflect input from the water column, suggesting that the Neotethys experienced at least episodically hypersaline conditions. We also demonstrate that bacteria, possible keratose sponges (up to 50% of the carbonate is represented by the possible sponges), and microconchids lived synergistically to form microbial-metazoan bioherms in the immediate aftermath of the extinction along the western margin of the Neotethys. Abundant fossils of oxygen-dependent invertebrates (i.e. microconchids, bivalves, gastropods, brachiopods, and ostracods) and foraminifers were also found within these bioherms. The presence of invertebrates in conjunction with abundant molecular fossils of cyanobacteria indicates an oxygenated water column. Even though the presence of the biomarker isorenieratane in microbialites may considered as evidence for euxinic conditions in the water column, its absence in the background sediments rather points to a source organism belonging to the mat community. The new finding of bioherms built in part by metazoans suggests that reef ecosystems underwent a major turnover across the extinction event, and shortens the ‘metazoan reef gap’ to just the uppermost Changhsingian. During the Early Triassic, therefore, reefal ecosystems were able to recover in oxygenated settings since the earliest Griesbachian, albeit in an impoverished state.

Serpentinite-hosted ecosystems are potential sites where life may first have evolved on Earth. Serpentinization reactions produce strongly reducing and highly alkaline fluids that are typified by high concentrations of molecular hydrogen (H2) and methane (CH4), which can be used as an energy source by chemosynthetic life. Low-temperature serpentinization at slow-spreading mid-ocean ridges provides an ideal environment for rich microbial communities. Similar environments have also been discovered on land, where present-day low temperature serpentinization occurs during the circulation of groundwater through exposed ophiolites, triggering the production of CH4 and H2, as well as the precipitation of secondary carbonate minerals. The rock samples analyzed here are from the Chimaera seeps in Turkey, representing serpentinized peridotites that are cross-cut by veins composed of brucite and hydromagnesite. Hydromagnesite features a mean δ13C value of −19.8‰ caused by kinetic isotope fractionation during air-groundwater exchange of CO2, followed by CO2 hydroxylation to bicarbonate within the groundwater. Geochemical modeling revealed that mixing of Mg- and Ca-rich groundwaters is required for hydromagnesite formation at the expense of brucite. Within the carbonate-hydroxide veins the lipid biomarkers pentamethylicosane (PMI) and squalane with δ13C values of +10‰ and +14‰, respectively, and unsaturated derivatives thereof were identified. Archaeol, sn2-hydroxyarchaeol, and sn3-hydroxyarchaeol are other prominent archaeal biomarkers in the veins, also revealing high δ13C values from +6 to +13‰. These isotope patterns combined with the absence of crocetane – a biomarker for methanotrophic archaea – reveal that the microbial communities of the Chimaera seeps performed methanogenesis from a CO2-limited pool rather than methanotrophy. Moreover, bacterial dialkyl glycerol diethers (DAGEs) with unusually high δ13C values (−9 to −2‰) and minor monoalkyl glycerol monoethers (MAGEs) were identified, suggesting that bacterial sulfate reduction is also active at the Chimaera site. This study reveals that archaeal methanogenesis and bacterial sulfate reduction may be prominent at onshore peridotite-hosted sites, and that biogenic CH4 may contribute to abiotic CH4 emissions from terrestrial seeps. (Less)

Conodonts have been a key tool for biostratigraphical, evolutionary and palaeobiogeographical studies, and the Germanic Basin has been one of the most important regions for these studies. However, ...

A negative shift in the calcium isotopic composition of marine carbonate rocks spanning the end-Permian extinction horizon in South China has been used to argue for an ocean acidification event coincident with mass extinction. This interpretation has proven controversial, both because the excursion has not been demonstrated across multiple, widely separated localities, and because modeling results of coupled carbon and calcium isotope records illustrate that calcium cycle imbalances alone cannot account for the full magnitude of the isotope excursion. Here, we further test potential controls on the Permian-Triassic calcium isotope record by measuring calcium isotope ratios from shallow-marine carbonate successions spanning the Permian-Triassic boundary in Turkey, Italy, and Oman. All measured sections display negative shifts in δ44/40Ca of up to 0.6‰. Consistency in the direction, magnitude, and timing of the calcium isotope excursion across these widely separated localities implies a primary and global δ44/40Ca signature. Based on the results of a coupled box model of the geological carbon and calcium cycles, we interpret the excursion to reflect a series of consequences arising from volcanic CO2 release, including a temporary decrease in seawater δ44/40Ca due to short-lived ocean acidification and a more protracted increase in calcium isotope fractionation associated with a shift toward more primary aragonite in the sediment and, potentially, subsequently elevated carbonate saturation states caused by the persistence of elevated CO2 delivery from volcanism. Locally, changing balances between aragonite and calcite production are sufficient to account for the calcium isotope excursions, but this effect alone does not explain the globally observed negative excursion in the δ13C values of carbonate sediments and organic matter as well. Only a carbon release event and related geochemical consequences are consistent both with calcium and carbon isotope data. The carbon release scenario can also account for oxygen isotope evidence for dramatic and protracted global warming as well as paleontological evidence for the preferential extinction of marine animals most susceptible to acidification, warming, and anoxia.

The end-Permian mass extinction was the most severe biotic crisis in Earth's history. In its direct aftermath microbial communities colonized some of the space left vacant after the severe decline of skeletal metazoans. The Permian-Triassic boundary microbialites were peculiarly abundant on low-latitude shallow-marine carbonate shelves of central Tethyan continents. Armenia features particularly well preserved and diverse basal Triassic sponge-microbial build-ups (BTSMBs), which were not studied in detail to date. Here, the Chanakhchi section in southern Armenia is described petrographically and by means of stable isotope analyses. The Armenian BTSMBs formed in a distally open marine setting on a pelagic carbonate ramp in the course of two phases of microbial growth during the Induan (Lower Triassic). The BTSMBs are represented by predominantly thrombolitic but also dendrolitic and digitate stromatolite biostromes and mounds that vary in height between 5 cm to 12 m. The digitate stromatolites are associated with calcium carbonate crystal fans (CCFs). Microfacies analyses revealed that the BTSMBs exhibit a number of different growth forms and internal fabrics. The formation of CCFs was apparently not devoid of biological influence and took place above the sediment surface. The abundance of sponges in the BTSMBs reveals that ecologically complex metazoan-microbial reefs have been present already early after the end-Permian mass extinction. However, the formation of biostromes and mounds did not depend on sponges or other metazoans. BTSMBs that formed during the second microbial growth phase revealed similar δ13C-values like the surrounding sediment. In contrast, the δ13Cmicrobialite and δ13Csediment values from the BTSMBs and CCFs of the first growth phase show a difference of up to + 2.3‰, suggesting a significant influence of photoautotrophy during microbially induced carbonate precipitation.

The occurrence of a series of thin but persistent early Cambrian (Cambrian Age 4) brachiopod shell concentrations extending along a transect of some 150 km in NE Greenland, indicates the ability of the group to form widespread, skeletal pavements very early in the history of the phylum, its gregarious behaviour and ability to harness available nutrients. These extensive shell pavements within the Bastion Formation mark biological events within the basin, the abundance of shells perhaps associated with oscillating redox conditions prompting the dissolution of phosphate and its spread across the shelf. The shells were subsequently reworked and deposited by episodic distal storm surges with some winnowing.

6 pages; International audience

In this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate – siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (δ13Ccarb) show an increase from −2.6 to 0‰ from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to −3‰ in the Smithian substage and a large positive excursion from −3.0 to 3.5‰ across the Smithian-Spathian boundary. A short negative shift to −1.0‰ occurred in the early Spathian substage, and is followed by a positive trend from ~−1.0 to 1.0‰ in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (δ13Corg) co-vary with δ13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian–Spathian boundary. Thus, in the Spiti area, the positive δ13Ccarb excursion across the Smithian–Spathian boundary is recorded in generally well‑oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian–Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.

Conodont ecology of the Early Triassic Smithian–Spathian transition is still poorly understood. Here we use oxygen isotope ratios of monogeneric conodonts from Omani samples to reveal the differences of oxygen isotopic composition between different taxa. Oxygen isotope analyses from Oman reveal that Neogondolella inhabited a deeper part of the water column relative to neospathodids and Icriospathodus. This indicates that species of Neogondolella lived in an environment ca. 1.7 °C cooler than where neospathodids lived. The investigation of conodonts from these Smithian and Spathian sections has also enabled the first recovery of some rarely reported species (e.g., Icriospathodus zaksi, Paullella omanensis sp. nov. Chen and Gladigondolella laii sp. nov. Chen) from Oman. Paullella omanensis sp. nov. was further recovered from Plavno, Croatia, indicating a large geographic distribution, and its value for biostratigraphic correlations. The discovery of these species in both Oman and Croatia expands their geographical distribution.

The Triassic in the “Medianes rigides” Nappe of the Swiss Prealps, belonging to the Brianconnais realm of the Western Alps, consists of a several hundred meters thick carbonate succession. At the localities Wiriehorn and Rothorn, 650 m above sequence base, the Costatoria goldfussi limestone, a remarkable coquina and widespread transgressive marker bed, yields the key conodont Sephardiella truempyi (HIRSCH), a proxy for the Curionii - lower Gredleri ammonoid Zones (Early Ladinian). This new discovery has deep implications on the age of the different Triassic formations in the Swiss Prealps and for its correlation with other tectonic units. The newly established Pralet Formation in the Swiss Prealps comprises the Balmi Member with the Lower Ladinian Costatoria goldfussi limestone at its base, followed by the dolomitic breccias of the Ladinian Erpilles Member. Below the S. truempyi level, both the mighty platform carbonate sequence of the Wiriehorn Formation in the Swiss Prealps, and of the coeval Champcella Formation in the Brianconnais realm, are reassigned here to the Late Anisian. In our revised correlation, the Costatoria goldfussi limestone corresponds to the main flooding surface (MFS) of the large marine transgression that correlates biostratigraphically the now well dated Upper Muschelkalk transgression in Provence, Sardinia and Spain with the basal Ladinian type locality at Bagolino in the Southern Alps.

Conodonts are a clade of chordates and are valuable indicator fossils for biostratigraphy. The segminiplanate (neogondolelliform) conodonts represent a major morphological group ranging from upper Carboniferous to Upper Triassic marine sediments. However, the morphological similarity of segminiplanate P 1 elements generates problems for taxonomy, especially in the Permian and Triassic clades. This paper represents the first study of morphological variation in Triassic segminiplanate conodonts using a geometric morphometric approach. The laminar microstructures observed in conodont cross-sections indicate that, within our analysed specimens, smaller conodonts with fewer laminae are generally from an earlier ontogenetic stage while larger conodonts with more laminae are from a later stage of ontogeny. Using linear regressions between relative warp scores from both upper and lateral views and conodont length, we demonstrate strongly allometric growth patterns for the species Paragondolella bifurcata Budurov & Stefanov. Our results indicate that the species-group taxon Pg. praeszaboi bystrickyi (Kovacs et al.) is an early growth stage of Pg. bifurcata and thus synonymous. We suggest that the allometry of conodonts should be considered seriously, especially when there are numerous transitional morphologies between large- and small-sized conodonts. Reconstructing the ontogenetic series and using larger-sized conodonts within the numerous transitional morphologies in the population of a rock sample for the definition of new species are suggested for future studies.

Samples from strata spanning the Triassic–Jurassic boundary at the GSSP at Kuhjoch and at Kendlbachgraben were studied by NAA, XRF and combustion analysis to determine Ir levels and associated geochemistry. The results are compared to previously determined carbon isotope stratigraphy at these sections. Ir concentrations in the limestones of the Kossen Formation at Kuhjoch are very low (

We present new data on the structure and age of the upper Permian strata in the basin of the Setorym River (tributary of the Vostochnaya Khandyga River) in the South Verkhoyansk region, represented by the Imtachan Formation and the lower part of the Nekuchan Formation. Based on the new findings of bivalve fossils from the Intomodesma costatum Zone, as well as on the study of carbon isotopes in the shells and carbon isotopes of the organic matter of the host mudstones, we have for the first time proved the completeness of the Permian section. The detailed description of the contact between the Imtachan and Nekuchan Formations bears evidence for a certain continuity of the lithologic characteristics of the sandstones. The sharp lithologic contact between the formations reflects not a regional sedimentation hiatus but a shift of depositional settings from the upper parts of a delta to the deep shelf, caused by forced marine transgression. It is concluded that there was no long-term hiatus between the accumulation of the Imtachan and Nekuchan Formations. Images of the most characteristic species of bivalves and crinoids from the Imtachan Formation are presented.

The taxonomy, diversity, evolutionary lineages, and stratigraphical distributions of Middle and early Late Triassic conodonts are reviewed and re-evaluated. Twenty-five genera are recognized in the Middle and early Late Triassic, including a new genus cited in open nomenclature. Of these, 24 genera are assigned to two families and seven subfamilies. The family Gondolellidae consists of the subfamilies Cornudininae, Epigondolellinae, Neogondolellinae, Novispathodinae, Paragondolellinae and Pseudofurnishiinae. The family Gladigondolellidae is monotypic, consisting of the subfamily Gladigondolellinae. The genus Neostrachanognathus is not assigned to any family or subfamily as its origin is unclear. Conodont provincialism was low in the early Anisian, but from the late Anisian faunistic differences started to increase and became stronger during the early Ladinian, reaching a peak around the mid-Ladinian. Provincialism remained strong until the earliest Carnian and changed to an all-Triassic low in the early Tuvalian. The provincialism between North America and Tethys rebounded on the specific level during the late Tuvalian. Diversities on generic and specific levels have been established, and two major conodont diversity cycles are recognized: the first ranges from the Bithynian (early Anisian) to the Julian (late early Carnian), and the second is restricted to the Tuvalian (late Carnian).

The recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity. The pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors. Here, we present an analysis of changes in marine conditions following the end-Permian mass extinction with the objective of evaluating the role of environmental factors in the protracted (~ 5-Myr-long) recovery of marine ecosystems during the Early Triassic. Specifically, our study examines changes in weathering, productivity, and redox proxies in three sections in South China (Chaohu, Daxiakou, and Zuodeng) and one in northern India (Mud). Our results reveal: 1) recurrent environmental perturbations during the Early Triassic; 2) a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early Griesbachian, late Griesbachian, mid-Smithian, and (more weakly) the mid-Spathian; 3) increases in marine productivity during the aforementioned intervals except for the early Griesbachian; and 4) stronger and more temporally discrete intervals of environmental change in deepwater sections (Chaohu and Daxiakou) relative to shallow and intermediate sections (Zuodeng and Mud). Our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity, within-community (alpha) diversity, infaunal burrowing, and ecosystem tiering. We infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the Early Triassic. These perturbations were associated with elevated weathering and productivity fluxes, implying that nutrient and energy flows were key influences on recovery. More regular secular variation in deepwater relative to shallow-water environmental conditions implies that perturbations originated at depth (i.e., within the oceanic thermocline) and influenced the ocean-surface layer irregularly. Finally, we compared patterns of environmental disturbance and ecosystem recovery following the other four “Big Five” Phanerozoic mass extinctions to evaluate whether commonalities exist. In general, the pace of ecosystem recovery depends on the degree of stability of the post-crisis marine environment.

The Late Triassic time interval witnessed several important biological turnovers, extinctions and onset of new life forms. Therefore, it is crucial to better constrain the tectonic, climatic and oceanographic framework at this time. The radiogenic strontium isotopic composition (87Sr/86Sr) of seawater, recorded in marine carbonates is sensitive to variations in continental weathering and oceanic spreading rates. This makes it a powerful proxy for palaeo-environmental reconstructions and an excellent global stratigraphic correlation tool of marine sediment records. In this study, we present a new and extended 87Sr/86Sr dataset across the late Norian - Hettangian interval, established from carbonate successions in Austria and Turkey. The well-established biostratigraphy and high sampling resolution allow evaluating changes in the 87Sr/86Sr record with a better time constraint than in previous studies. An exceptionally sharp trend towards unradiogenic values has been observed in the latest Norian and in the early Rhaetian from 0.70800 to 0.70779. Considering Late Triassic climate change, updated tectonic models and actual dating of magmatic events, possible explanations for the observed trend in the 87Sr/86Sr record are: (i) enhanced dissolution of pre-Norian carbonates, (ii) dissolution of widespread Late Triassic evaporites and (iii) tectonic reorganization of sedimentary basins due to the break-up of the supercontinent Pangea. At the very end of the Choristoceras marshi Zone, in the late Rhaetian, the unradiogenic 87Sr/86Sr trend is reversed. This is likely related to environmental changes due to the continental emplacement of the Central Atlantic Magmatic Province.

In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick (927.5 m) Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The δ13C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the +8‰ amplitude around the Dienerian-Smithian boundary (DSB), followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary (SSB) a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary (SAB). Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated: 1) the dolostone member (Early Griesbachian) ; 2) the siliciclastic member (red-coloured shale, siltstone, sandstone with oolitic/bioclastic grainstone intercalations), which can be further divided into lower, middle and upper intervals (Late Griesbachian, Dienerian and Smithian) ; and 3) the mudstone member (grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods-Spathian). The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.

Jiarong (Huishui County, Guizhou Province, South China) is a key locality for the study of the Early Triassic recovery after the end-Permian mass extinction. The size reduction of conodonts at the Smithian/Spathian transition was first documented in Jiarong, and it is also a locality that contributes to the documentation of the Early Triassic paleo-seawater temperatures. In the Jiarong sections, thirteen conodont zones were identified for the Early Triassic; in ascending order, they are Hindeodus parvus Zone, Hindeodus sosioensis Zone, Clarkina krystyni Zone, Neoclarkina discreta Zone, Neospathodus cristagalli–Eurygnathodus costatus assemblage zone, Novispathodus waageni eowaageni Zone, Novispathodus waageni waageni Zone, Discretella discreta Zone, Pachycladina–Parachirognathus assemblage zone, Novispathodus pingdingshanensis Zone, Icriospathodus collinsoni Zone, Triassospathodus homeri Zone, Triassospathodus triangularis Zone. These conodont zones in the Jiarong sections improve the global correlation of Early Triassic sections and also provide better regional age constraints in an area that is important for studies of recovery from the extinction. Based on the first appearance of Nv. waageni eowaageni, the Induan/Olenekian boundary is recognized at 3.6 m above the base of the Jiarong III Section. The dominance of blade-shaped (segminate) conodonts was replaced by gondola-shaped (segminiplanate) conodonts twice; the first time was in the late Griesbachian, and the second time was in the early Spathian. The dominance of segminiplanate conodonts probably indicates that the deeper seawater environment became more oxygenated during the late Griesbachian and early Spathian for short time intervals, as it is believed that the Griesbachian segminiplanate conodonts favored deeper oxygenated water habitats. A new genus, Spathogondolella gen. nov., and a new species, Spathogondolella jiarongensis sp. nov., have been recognized.