Permian-Triassic Research Articles

The impact of frequent wildfires during the Permian–Triassic transition: Floral change and terrestrial crisis in southwestern China

Wildfires are considered to have played an important role in the land plants crisis during the Permian–Triassic (P–T) transition. However, the nature and impact of wildfires in the P–T terrestrial crisis remains unclear. Organic petrology data from a terrestrial sequence from southwestern China show that the inertinite content ranges from 21.3% to 80.9% (mean 44.5%), suggesting that wildfires were a frequent phenomenon in low-latitude tropical rainforests during the P–T transition. Abundant inertinite and Hg/TOC peaks in earliest Triassic strata support the co-existence of wildfires and volcanism at that time. Volcanic emissions were potentially lethal for plants and adjacent arc volcanism represents a possible source of ignition. Inertinite reflectance values are used to estimate wildfire combustion temperatures, which themselves are a function of wildfire type. Inertinite with reflectances higher than 4.5% have concentrations between 47% and 65% in the P–T transitional strata. Crown fires with high combustion temperatures were prevalent in wetland settings in the latest Permian. However, surface fires with lower combustion temperatures became dominant during the major terrestrial extinction phase as a result of the sparse, scrubby vegetation that dominated at that time. The subsequent spread of gymnosperms in the earliest Triassic resulted in the re-establishment of high-temperature crown fires. Wildfires associated with the onset of volcanism in the late Permian likely contributed to ecological disturbance in terrestrial settings, which occurred notably earlier than that seen in marine environments. Thus, enhanced wildfire activity destabilised wetlands and increased ecological stress in the late Permian. Wildfire activity on land potentially had devastating consequences for late Permian marine environments via a complex cascade of terrestrial denudation, runoff, and nutrient flux.

Large durophagous fish from the Spathian (late Early Triassic) of Romania hints at earlier onset of the Triassic actinopterygian revolution

AbstractFossil evidence suggests that ray‐finned fishes (Actinopterygii) diversified greatly after the largest mass extinction event at the Permian–Triassic boundary. This radiation resulted in a diversity peak in the Middle Triassic, which is manifested in diverse feeding specializations, especially among small‐bodied Neopterygii. We present new material from an early Spathian (Early Triassic) outcrop in northern Dobrogea, southeast Romania. The material includes isolated jaw and palatal bones that evidently belong to a single individual, a durophagous actinopterygian, and isolated scales referred to the same taxon. A systematic evaluation of this material indicates affinities with †Polzbergiidae, and provides a first glimpse of internal aspects of the feeding apparatus of that group. A pair of ectopterygoids with crushing dentition show a well‐developed lateral process, a feature that was previously proposed to be a synapomorphy uniting Cladistia (bichirs) with the Triassic †Scanilepiformes. The recognition of this structure in various Triassic ray‐fins (summarized herein) indicates that it was probably widespread among stem neopterygians. The new material belongs to a large individual with a heterodont dentition, therefore representing the earliest large, specialized, durophagous neopterygian. It increases the group's morphological diversity in the Spathian, and hints at an earlier trophic diversification after the mass extinction. Based on new data, we analyse changes in body size of bony fishes through the Early and Middle Triassic. Current evidence suggests that body size distribution remained skewed towards larger sizes in the late Early Triassic, and that the diversification of small‐bodied stem neopterygians had not yet been in full swing.

Discovery of Permian–Triassic eclogite in northern Tibet establishes coeval subduction erosion along an ~3000-km-long arc: COMMENT

Discovery of Permian–Triassic eclogite in northern Tibet establishes coeval subduction erosion along an ~3000-km-long arc: COMMENT

Discovery of Permian–Triassic eclogite in northern Tibet establishes coeval subduction erosion along an ~3000-km-long arc: REPLY

Discovery of Permian–Triassic eclogite in northern Tibet establishes coeval subduction erosion along an ~3000-km-long arc: REPLY

Deep Dive into the factors influencing acoustic velocity in the Dalan-Kangan formations, the central Persian Gulf

The propagation of acoustic waves in rocks is directly influenced by the rocks’ elastic properties. To evaluate petrophysical properties from acoustic data, it is essential to understand the factors that influence the variations in acoustic velocity of sedimentary rocks. Carbonate reservoirs are heterogeneous, and their evaluation is complicated. A closer look at the factors affecting the elastic properties of these rocks is essential because they reveal important information about the reservoir properties and their formation evaluation. Rock physics modeling relies on laboratory-measured acoustic data. This study, however, employs acoustic logs to elucidate the key factors influencing sonic velocity, offering a more comprehensive and field-applicable perspective. Samples were prepared from the Permian–Triassic Upper Dalan and Kangan formations. Porosity, permeability, sedimentary textures, mineralogy, and pore types were investigated. Furthermore, compressional, shear, and Stoneley well-logs data were recorded and converted to acoustic velocity in the sampled interval. Porosity-velocity modeling based on the differential effective medium (DEM) theory was performed for different values of equivalent pore aspect ratio (EPAR). The results show that there is a strong inverse relationship between acoustic velocities and porosity. Acoustic velocities also exhibit an inverse correlation with permeability, but the strength of these relationships is relatively weak. Acoustic velocities are not affected by carbonate textures. A specific texture may exhibit different velocities due to the influence of diagenetic processes. Mineralogy has only a minor influence on acoustic velocities. Dolostones have a slightly higher velocity than limestones, but the difference is insignificant. Stoneley log values are slightly different in limestone and dolostone, because this wave propagates along the mud-borehole interface. The velocities were affected by the variations in pore types within the studied formations. Therefore, in carbonate rocks, porosity, and the pore types play a significant role in controlling acoustic velocities. The value of EPAR = 0.15 can be considered as the boundary between stiff pores (moldic and vuggy) and soft pores (interparticle, intercrystalline, micro-intercrystalline, and microporosity). The lower EPAR value of interparticle pores in limestones compared to dolostones can be attributed to diagenetic processes such as dolomitization and compaction. The findings of this study can help to better understand what factors affect acoustic velocity in carbonate rocks. This study also shows that acoustic logs data can be effectively used in rock physics modeling and pore type identification. By identifying the pore types, it is possible to recognize diagenetic processes and determine the rock types to control the heterogeneity and estimate reservoir quality.

Applying integrated Triassic biostratigraphy in Timor-Leste to unlock an under-sampled Gondwanan sector of the Tethys puzzle

The contribution to Tethyan and global Triassic studies from the Australian sector of southeastern Tethys is limited relative to that from the Himalayan sector. Whilst many of the Triassic successions from the Australian sector are located offshore, one succession is exposed on the island of Timor. This marine succession, dismembered during collision between the Australian continent and the volcanic Banda Arc, has been investigated for over 100 years but has also made limited modern contributions to Tethyan and global Triassic studies. To address this a new integrated Triassic biostratigraphic microfossil database (conodonts, palynomorphs and radiolarians) from Timor-Leste is presented here that compliments published foraminiferal data. This integrated data set 1) supports application in Timor of the endemic palynomorph zonal scheme from the North West Shelf of Australia whilst providing additional ties for this to the Geological Time Scale (GTS), 2) provides paleobiogeographic support for accumulation of the Timor-Leste Triassic succession within a southeast Tethyan Gondwanan basin and informs discussions about Tethyan paleobiogeography, 3) calibrates over 300 outcrops to the GTS enabling an improved reconstruction of the dismembered succession that will facilitate enhanced regional and local paleogeographic and tectonostratigraphic assessments, and 4) provides independent GTS calibration for published basinal foraminiferal assemblages which will assist understanding the biostratigraphic utility of these assemblages. This database identifies key outcrops, such as the first outcropping Permian-Triassic Boundary section from this sector of southeastern Tethys, that will facilitate targeted studies addressing a range of Tethyan and global Triassic issues unlocking insights from an under-sampled Gondwanan sector of Tethys.

The terrestrial end-Permian mass extinction in the paleotropics postdates the marine extinction.

The end-Permian mass extinction was the most severe ecological event during the Phanerozoic and has long been presumed contemporaneous across terrestrial and marine realms with global environmental deterioration triggered by the Siberian Traps Large Igneous Province. We present high-precision zircon U-Pb geochronology by the chemical abrasion-isotope dilution-thermal ionization mass spectrometry technique on tuffs from terrestrial to transitional coastal settings in Southwest China, which reveals a protracted collapse of the Cathaysian rainforest beginning after the onset of the end-Permian marine extinction. Integrated with high-resolution geochronology from coeval successions, our results suggest that the terrestrial extinction occurred diachronously with latitude, beginning at high latitudes during the late Changhsingian and progressing to the tropics by the early Induan, spanning a duration of nearly 1 million years. This latitudinal age gradient may have been related to variations in surface warming with more degraded environmental conditions at higher latitudes contributing to higher extinction rates.

Biogeographic response to major extinction events: The case of Triassic bivalves

Mass extinctions decimate the biota causing the disappearance of existing palaeobiogeographical patterns, which is not surprising given that palaeobiogeographical units are usually established on the basis of endemic taxa and these are the most affected in global crisis events. This paper deals with the evolution of the biogeographic pattern shown by bivalve genera in response to the end-Permian extinction event. From a network analysis (based on Simpson's and Bray-Curtis' similarity indices) and an Occurrence Ratio Profile, the Early Triassic is recognized as a time of general biogeographic homogeneity. The Middle Triassic shows a clear differentiation, with the evolution of many new genera, and an increase in endemicity, which reaches a maximum by the Carnian. During the Norian-Rhaetian the main biogeographic biochoremas appear well differentiated. Unlike other invertebrates, like brachiopods, bivalves show generally high similarity values between biogeographic units, and in this particular case study, Early Triassic biogeographic units appear more related to each other than to the corresponding Middle or Late Triassic units.

Did gorgonopsians survive the end-Permian “Great Dying”? A re-appraisal of three gorgonopsian specimens (Therapsida, Theriodontia) reported from the Triassic Lystrosaurus declivis Assemblage Zone, Karoo Basin, South Africa

Gorgonopsians were the dominant carnivores of the late Permian (Lopingian) and it is widely accepted that the clade became extinct at the Permian-Triassic boundary, almost 252 million years ago. However, South African collections house three historically-collected gorgonopsian specimens listed as Early Triassic in age, based on their discovery at localities producing the index fossil Lystrosaurus. Initial reports suggested that these specimens had been reworked from underlying Permian strata, but this possibility was never thoroughly addressed. The possible survival of gorgonopsians into the Triassic would significantly alter our understanding of the end-Permian mass extinction and post-extinction ecosystem dynamics. Here we use Synchrotron X-ray micro-computed microtomography to confirm the identifications and investigate the taphonomic histories of these three specimens. We also relocated the original localities to determine their stratigraphic position. We confirm that all three specimens are indeed gorgonopsians, belonging to the small-bodied genus Cyonosaurus, and that taphonomic assessments do not support reworking. Two of them can be confidently assigned to the latest Permian Lystrosaurus maccaigi-Moschorhinus Subzone of the Daptocephalus Assemblage Zone. In contrast, at the locality listed for the third specimen, NMQR 389, the lowermost outcropping strata belong to the upper Palingkloof Member of the Balfour Formation, which is Early Triassic in age. Despite the evident absence of Permian-aged rocks, other Permian fossils were reported from the same locality, thus casting doubts about the age of NMQR 389. Additionally, differences in preservation style between this skull and the newly collected material at the site cast doubt on its provenance. Although not supporting gorgonopsian survival into the Triassic, these new occurrences expand the range of the genus Cyonosaurus higher up in the extinction zone, increasing the complexity of the ecological turmoil that carnivores endured during “The Great Dying”.

Geochemistry and geochronology of early Triassic tephra from SW China: implications for biological evolution and tectonics

ABSTRACT Late Permian to middle Triassic volcanic activities were very strong, however, volcanic records in the early Triassic strata are less reported than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary in the Yangtze plate, especially within the Sichuan basin. We conduct zircon U-Pb dating and geochemical analysis of the tephra which was first found in the early Triassic Jialingjiang Formation from the Maliuping section, Hechuan, Chongqing. The volcanic ash in the paper yields the new 248.5 ± 0.7 Ma U-Pb age consistent with those of volcanic ashes in these contemporaneous strata in the Yangtze plate. Geochemical characters of whole-rock samples show lower contents in SiO2, K2O and higher components in Al2O3, CaO, MgO, relatively enriched LREE and depleted HREE with distinct negative Eu anomaly, and conspicuous Ba, Nb, Ta, Sr, P, Ti depletion and Th, U, K, Nd enrichment, which is similar to those of the Mung Bean rock of the Triassic Olenekian-Anisian boundary, and those of acidic volcanics from the Sanjiang orogenic belt and Shiwandashan-Qiangfang suture zone during the Early-Middle Triassic. Trace elements of whole rock and analysed zircons of the tuff imply its primary magma derived from Rhyodacite/Dacite and its tectonic setting of volcanic arc granite with continental crust affinity. The early Triassic volcanism during the syn-collision stage of the Paleo-Tethys evolution was less active than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary, while the volcanic event may have a crucial effect on prolonging fully biotic recovery and entirely ecosystem turnover soon after the Permian-Triassic mass extinction.

Interrelationships among Early Triassic faunas of Western Gondwana and Laurasia as illuminated by a new South American benthosuchid temnospondyl.

The End-Permian Mass Extinction marked a critical turning point in Earth's history, and the biological recovery that followed the crisis led to the emergence of several modern vertebrate and invertebrate taxa. Even considering the importance of the Early Triassic biotic recovery for the evolution of modern faunas and floras, our knowledge of this event is still hindered by the sparse sampling of crucial geological formations. This leaves our understanding of Early Triassic ecosystems fundamentally biased toward productive and historically well-explored geological units. Recent surveys in poorly known Gondwanan localities, such as those within the Sanga do Cabral Formation in southern Brazil, have unveiled insights into Early Triassic terrestrial ecosystems, shedding light on a diverse and previously unknown tetrapod fauna. Here, we report the discovery of a new temnospondyl genus and species in the Lower Triassic Sanga do Cabral Formation. The new taxon can be confidently assigned to the Benthosuchidae, a stereospondyl clade with a distribution previously restricted to the East European Platform. Phylogenetic analysis confirms the relationship of the new genus to the trematosaurian lineage, being closely related to the genus Benthosuchus. Our results raise questions about the biogeographical history of stereospondyls after the End-Permian Mass Extinction and suggest a potential connection between Russian and South American Early Triassic faunas. Further investigations are needed to thoroughly explore the potential dispersal routes that may explain this seemingly unusual biogeographical pattern.

Atmospheric ozone destruction and the end-Permian crisis: Evidence from multiple sulfur isotopes

The end-Permian mass extinction (EPME) is considered the largest biotic crisis of the Phanerozoic. To explain the worldwide destruction and mutation of land plants, previous work has emphasized the role of enhanced UV irradiation linked to volcanism-induced disruption of the ozone shield. However, direct evidence for a link between volcanic SO2 emission and stratospheric ozone deterioration is missing. Previous bulk analysis (i.e., SF6 method) found no Mass-Independent Fractionation of sulfur isotopes (MIF-S, noted Δ33S). However, possible grain scale sulfur isotope anomaly can be easily overlooked during bulk analysis. To detect possible sulfur isotope anomaly in grain scale, we applied in-situ multiple sulfur isotope analysis of the sulfide using secondary ion mass spectrometry (SIMS). We found a marked positive shift (higher than +0.30‰ and up to +0.94‰) just before the end-Permian extinction in the Meishan section. Modelling shows that these positive Δ33S anomalies cannot be explained by Mass Dependent Fractionation (MDF) processes alone, rather by UV-induced photolysis of volcanic SO2. The formation and preservation of MIF-S anomalies in the atmosphere and subsequent transport to the oceans require intense and prolonged irradiation of the Earth's surface with solar UV, thus fingerprinting severe disruption of the atmospheric ozone balance at the onset of Earth's largest mass extinction.

Paleomagnetism of the Permian-Triassic Boundary of the Orenburg Region (East European Platform, Volga-Ural Anteclise)

This article presents the results of a detailed paleomagnetic study of five sections of the Permian-Triassic sedimentary rocks from the southeastern part of the Volga-Ural anteclise in the East European Platform (Orenburg region, Russia): Boevaya Gora, Vyazovka, Sambulak, Krasnogor, and Vozdvizhenka. The magnetic fabric determined by magnetic susceptibility anisotropy indicates that the rocks accumulated under the conditions of intense hydrodynamic activity. This makes it possible to reconstruct a predominantly submeridional transport of detrital material. The rocks of the Boevaya Gora section have a bipolar distribution of the characteristic component of their remanent magnetization, while other sections show a reversed polarity. In the Vyazovka section, the E/I method was used to calculate the inclination shallowing coefficient of the rocks (f = 0.79). The regional fold test yielded positive results, suggesting that the rocks of the studied sections were displaced after the deposition. For each section, paleomagnetic poles were calculated, with the poles of the Boevaya Gora and Vyazovka sections being the most reliable. The mean paleomagnetic pole coordinates of the studied sections, except the Sambulak section, are as follows: slat = 51.7°, slong = 55.8°, n = 4, plat = 48.5°, plong = 173.4°, α95 = 3.4°, paleolat = 23.4°.

A new pachypleurosaur (Reptilia: Sauropterygia) from the Middle Triassic of southwestern China and its phylogenetic and biogeographic implications

After the devastating Permo-Triassic Mass Extinction, several new groups of large reptilian predators invaded the sea in the early part of the Triassic. Among these predators, sauropterygians, consisting of placodonts, pachypleurosaurs, nothosaurs and pistosaurs (including the iconic plesiosaurs), displayed the greatest diversity at both the generic and species levels, and persisted from the Early Triassic to the Late Cretaceous. Here, we report a new species of Pachypleurosauria, Dianmeisaurus mutaensis sp. nov., from a recently discovered Lagerstätte in the Upper Member of the Anisian Guanling Formation. The only known specimen of the new species was collected from a quarry near Muta village, Luxi County, Yunnan Province, South China. Our new phylogenetic analysis based on a novel data matrix recovered the new taxon as a sister group to Dianmeisaurus gracilis—a small pachypleurosaur from the Middle Triassic Luoping biota. The new phylogenetic analysis also collapsed the monophyly of the traditionally recognized Eusauropterygia. Pistosauroidea, Majiashanosaurus, and Hanosaurus comprise the consecutive sister groups to a new clade including Pachypleurosauria and Nothosauroidea. A monophyletic Pachypleurosauria, within which the clade consisting of Dianmeisaurus and Panzhousaurus occupies the basal-most position, is recovered by this study. The clade consisting of Dawazisaurus and Dianopachysaurus forms the sister group to the remaining pachypleurosaurs included in this study. Since Dianmeisaurus, Panzhousaurus, Dawazisaurus, and Dianopachysaurus are all exclusively known from South China, our study provides further evidence to the hypothesis that pachypleurosaurs had a palaeobiogeographic origin in the eastern Tethys.

Extremely high resolution XRF core scanning reveals the Early Triassic depositional history of the Montney Formation in northeastern British Columbia, Canada

The Montney Formation is a laterally extensive, fine-grained sedimentary unit in western Alberta and northeastern British Columbia, and a major target of hydrocarbon exploration. It also retains a complete record of the Early Triassic epoch, a time when the biosphere was recovering from the effects of the end-Permian mass extinction. An industry well provides a full-diameter core of the complete distal Montney Formation in northeastern British Columbia (over 350 m thick), with stratigraphic age control provided by conodont biostratigraphy and regional correlations. For this study, the core was scanned using an ITRAX X-ray fluorescence spectrometer, at centimeter-scale resolution. The resulting dataset (over 37,000 individual measurements) provides an extremely high level of resolution for a deep-time geochemical study. While the data generated by this instrument are semiquantitative, they can be calibrated by correlating them with more conventional ICP-MS and XRF measurements of select samples. Using this method, we assessed the reliability of each of the elemental data series, and where possible converted them to quantitative geochemical measurements. These calibrated measurements serve as the basis for our detailed reconstruction of the Montney Formation's depositional history.The distal Montney depositional basin, including the location of the c-65-F core, was euxinic immediately following the end-Permian mass extinction, and accumulated sediments from the rapidly eroding margin of western North America. Conditions stabilized somewhat in the Dienerian, with oxic bottom water and a trend toward more compositionally mature sediment, but conditions of widespread euxinia and rapid erosion of the North American craton recurred in the early Smithian, earlier than this global crisis has been recognized elsewhere. Above the middle-upper Montney sequence boundary, in the overlying Spathian succession, local effects predominate. Coastal upwelling resumed in the basal Spathian, though the Montney depositional basin was soon cut off from the global ocean by uplift of the Yukon-Tanana arc bounding the basin to the west. Restricted conditions, with euxinic bottom water, were punctuated by oxic intervals, when rising sea level allowed the basin to freely exchange water with the open ocean. Intervals of restriction became progressively less acute in the upper Spathian.

The oldest teleosts (Teleosteomorpha): their early taxonomic, phenotypic, and ecological diversification during the Triassic

As the fossil record reveals, neopterygians had a major diversification after the great mass extinction at the Permian-Triassic boundary, including the appearance of the major clade Teleosteomorpha. Detailed studies of new taxa (Pseudopholidoctenus germanicus, Barschichthys ruedersdorfensis, and Ruedersdorfia berlinensis) from the lower Anisian (middle Muschelkalk) of Germany and their comparisons with other Triassic relatives are presented, including new information concerning size, shape, and diet. Two families, Pholidophoridae and Marcopoloichthyidae, made a modest appearance during the Anisian of Europe and Asia almost simultaneously, with Pseudopholidoctenus (and the teleosteomorphs Barschichthys and Ruedersdorfia) from the Germanic Basin, being the oldest stem teleosts (244 Ma), followed shortly by Marcopoloichthys ani from Italy. The early teleostean diversification was fast—already in the late Ladinian three lineages were present: Prohalecitiidae (Europe), Pholidophoridae (Asia, Europe), and Marcopoloichthyidae (Asia, Europe), with ca. 20 species inhabiting the Tethys Ocean during the Middle–Late Triassic. Most Triassic teleosteomorphs were small, ca. 50 mm standard length, and a few as possibly miniature, with torpedo or oblong shapes, and suction feeders—probably a plankton based-diet. These first Triassic radiations were replaced during the early Sinemurian of marine ecosystems of Europe with two major groups: (a) non-monophyletic ‘pholidophoriforms’ and (b) proleptolepids and leptolepids, having an average size (ca. 100 mm SL) longer than Triassic forms, with oblong and fusiform shapes. A fast dispersion from the Tethys to the Paleo-Pacific followed, as demonstrated by the presence of small (ca. 50 mm SL) suction feeder proleptolepids in the early Sinemurian of Chile.

ТЕРМИНАЛЬНЫЙ КОМПЛЕКС ПЕРМСКИХ БРАХИОПОД ВЕРХОЯНЬЯ, СЕВЕРО-ВОСТОК РОССИИ

Brachiopods from the upper Khalpirkian Regional Stage of the Tiryakh-Kobyume section of the Kobyume structural-facies zone of Southern Verkhoyan were studied. The collection is dominated by Strophalosia? vollossovitschi (Fredericks) and Cancrinella? sp. Single spiriferids are assigned to Crassispirifer monumentalis Abramov et Grigorjeva and Cr. aff. monumentalis Abramov et Grigorjeva, which indicate that the host deposits belong to the Crassispirifer monumentalis beds. These beds were previously established by us only in the lower part of the Khalpirkian Regional Stage. A review of reliable finds of brachiopods of the terminal assemblage, confined to the Khalpirkian regional stage of the Upper Permian, is given. The assemblage is dominated by strophalosiids represented by Wyndhamia gijigensis (Zavodowsky), Marginalosia? magna Abramov et Grigorjeva, Subtaeniothaerus lungersgauzeni Solomina, and Strophalosia? aff. vollossovitschi (Fredericks). «Magadania» sp. and Cancrinella? sp. identified from linoproductids. An important element of the terminal assemblage are the spiriferids Crassispirifer monumentalis. Athyridids of the Khalpirkian Regional Stage, known only in its lower part, are represented by Cleiothyridina nikolaevi Grunt, Cleiothyridina sp., and Bajtugania sp. In the studied regional stage are also finds of terebratulids attributed to Marinurnula? aff. mantuanensis (Campbell) and M.? aff. chivatschense (Zavodowsky). No brachiopods are known at the top of the Khalpirkian Regional Stage, while the rhynchonellids Piarorhynchia sp. appear at the base of the Regional Stage. At the beginning of the Khalpirkian time, the brachiopod community had an extended area in the shelf zone of the Verkhoyan Sea along the coastline of Angaraland. Subsequently, this area was reduced, initially dividing into two independent subareas confined to the East Kharaulakh and South Verkhoyan sectors. In the late Khalpirkian time, the brachiopod community concentrated only in the Kobyume zone, where it ended its existence during the end-Permian mass extinction. Some taxa of the identified brachiopod assemblage have been traced in the Okhotsk region, the Ayan-Yuryakh anticlinorium, and the Omolon massif.

Thermal evolution and sediment provenance of the Cooper–Eromanga Basin: Insights from detrital apatite

AbstractThe prolific hydrocarbon and geothermal potential of the Cooper–Eromanga Basin has long been recognised and studied, however, the thermal history which underpins these resources has largely remained elusive. This study presents new apatite fission track and U–Pb data for eight wells within the southwestern domain of the Cooper–Eromanga Basin, from which thermal history and detrital provenance reconstructions were conducted. Samples taken from sedimentary rocks of the upper Eromanga Basin (Winton, Mackunda and Cadna‐owie Formations) yield dominant Early‐Cretaceous and minor Late‐Permian–Triassic apatite U–Pb ages that are (within uncertainty) equivalent to corresponding fission track age populations. Furthermore, the obtained Cretaceous apatite ages correlate well with the stratigraphic ages for each analysed formation, suggesting (1) little time lag between apatite exposure in the source region and sediment deposition, and (2) that no significant (>ca. 100°C) reheating affected these formations in this region following deposition. Cretaceous apatites were likely distally sourced from an eastern Australian volcanic arc, (e.g. the Whitsunday Igneous Association), and mixed with Permian–Triassic sediment sources from the New England and/or Mossman Orogens. Deeper samples (>2000 m) from within the southwestern Cooper Basin yielded partially reset fission track ages, indicative of heating to temperatures exceeding ca. 100–80°C after deposition. The associated thermal history models are broadly consistent with previous studies and suggest that maximum temperatures were reached at ca. 100–70 Ma as a result of hydrothermal circulation correlating with high rates of sedimentation. Subsequent Late‐Cretaceous–Palaeogene cooling is interpreted to reflect post magmatic thermal subsidence and cessation of hydrothermal activity, as well as potential modified rock thermal conductivity as a response to fluid flow. Five of the seven modelled wells record a Neogene heating event, the geological significance of which remains tentative but may suggest possible reactivation of the Cooper Hot Spot and associated hydrothermal circulation.

Geochemical and Isotopic Compositions of Fluorites from the Yama Fluorite Deposit in the Qilian Orogen in Northwest China, and Their Metallogenic Implications

The Yama area is characterized by numerous large-scale fluorite–quartz veins that are located along faults within the widespread Late Devonian–Late Silurian syenogranites in the Tataleng granitic batholith, Qilian Orogen, Northwest China. These fluorite–quartz veins contribute to an important fluorite reserve, but their ore genesis remains unresolved so far. In this study, trace elements, rare earth elements (REEs), and hydrogen, oxygen, and strontium isotopic compositions of fluorites are analyzed. The studied fluorite samples have similar chondrite-normalized REEs, including Y patterns, with relatively strong enrichment in heavy REEs, negative Eu anomalies, strongly positive Y anomalies, and comparably invariable Y/Ho ratios of 41.43–73.79, suggesting a unique hydrothermal genesis. The relatively variable values of δD and δ18O are −77.4‰ to −102.4‰ and −12.7‰ to −4.3‰, respectively, close to the meteoric water line. These fluorites yield relatively invariable analytical 87Sr/86Sr ratios of 0.749089−0.756628 (except for an anomalously high ratio), and their calculated initial 87Sr/86Sr ratios, based on the ore-forming ages provided, are apparently higher than the calculated initial 87Sr/86Sr ratios of syenogranite wall rocks. Collectively, the geochemistry of trace elements, REEs, and stable isotopes (H, O, and Sr) suggests that the ore-forming fluids were of meteoric origin and that the Sr sources were directly derived from the ore-forming fluids themselves rather than syenogranite wall rocks. Finally, it was considered that the Yama fluorite deposit is a fault-controlled hydrothermal vein-type deposit which was possibly related to the evolution of the Paleo-Tethys Ocean in the Permian–Triassic.

Tectonic evolution of a sequence of related late Permian transtensive coal-bearing sub-basins, Mongolia: A global wrench tectonics portrait

During the late Permian in Mongolia, inertia-driven transtensive reactivation of primordial fracture zones gave rise to the development of a sequence of related, but isolated, fault-bounded sub-basins; some of these became the locus of substantial peat accumulation that evolved into economically important coal deposits. The present study focuses on late Permian coal measures in two widely separated areas: Area 1: located in central Mongolia, developed along the southern margin of the Mongol-Transbaikalian Seaway. The late Permian coal sequence forms a c. 420 m thick middle part of a Permo-Triassic succession which spans c. 2,600 m. The V-shaped, fault-bounded NE oriented sub-basin evolved under transtensive conditions. The thick infill records a transition from shallow marine and humid coal forming depositional environments during the late Permian to relatively arid desolate terrestrial conditions during early Triassic times, considered here to mark the dramatic drainage of the Mongol-Transbaikalian Seaway across the Permo-Triassic boundary. Area 2: situated in southern Mongolia, is a NE oriented elongate sub-basin, bounded by two wrench faults, which formed under transtensive conditions. Thickness of the late Permian coal-bearing strata is c. 650 m. The sedimentary strata record a transition from a humid coal-bearing environment to predominantly marine conditions. Both study areas are located proximal to two controversial suture zones. However, the zones do not show the presumed shortening, major thrusting, regional metamorphism and given the complete absence of tuffs within the studied Permo-Triassic successions it could be argued that the sutures are not only cryptic but non-existent.