Triassic Boundary Research Articles

Structural reconstructions effect on oil and gas formation of the Yenisei-Khatanga trough eastern part

The article presents the results of research on the influence of structural reconstructions on the hydrocarbon systems evaluation in the eastern part of the Yenisei-Khatanga trough. Based on seismic data interpretation and paleoprofiles construction, several stages of structural reconstructions in the geological evolution of the basin are established: at the Middle and Late Triassic boundary, Late Triassic and Jurassic boundary, in the Bathonian-Callovian time, Tithonian-Valanginian time, in the Barremian-Aptian time, in the Aptian-Albian time, in the Cenomanian time, and powerful reconstructions in the Cenozoic era. Based on interpretation of geochemical information of the well-core and outcrops, the characterization of the type of organic matter, the amount of initial organic carbon, the oil and gas source potential for the Late Triassic, Lower Jurassic, Middle Jurassic, Upper Jurassic, Lower Cretaceous oil and gas source rocks is given. The results of exploration of the geological structure of the region, the geochemical features of oil and gas source rocks became the basis for building a 2D basin model, which made it possible not only to identify generation kitchen, migration routes and accumulation zones of hydrocarbon fluids, but also to estimate the start time of generation and emigration of hydrocarbons, as well as the moments of interruption of these processes during periods of uplifting of the territory. Changes of the structural plan transformed the configuration of the basin, which led, on the one hand, to the formation of areas where rich in organic matter interlayers accumulated, and, on the other hand, to the interruption of hydrocarbon systems evaluation, reconfiguration and even destruction of deposits.

Palaeoenvironments and elemental geochemistry across the Permian–Triassic boundary at Ursula Creek, British Columbia, Canada, and a comparison with some other deep‐water Permian–Triassic boundary shelf/slope sections in western North America

The Permian–Triassic boundary sediments at Ursula Creek accumulated in a continental shelf basin, or on the continental slope of the western Canadian passive margin, at 30°N palaeolatitude along the eastern Panthalassic Ocean margin. The area lay within the cold northerly ocean currents at the junction of westerly and north-easterly trade wind belts, the latter causing summer coastal upwelling. The shift from uppermost Permian grey radiolarian cherts and grey shales to lowermost Triassic grey and black shales and fine-grained dolomites is typical of deep-water Panthalassic sediments. The palaeogeographical situation and palaeoenvironments are comparable to those of the present Canadian north-western Pacific margin. The Ursula Creek section reveals the progressive decline of seafloor oxygen values in the Changhsingian Stage), followed by the persistent development of euxinic conditions in the latest Changhsingian and throughout the Early Triassic; a transition that coincides with the disappearance of a siliceous sponge fauna and the loss of diverse radiolarian populations. Much of the detrital sediment was supplied by summer north-east Trade winds from the deserts of western North America, although variable amounts may have come across the Panthalassic Ocean as dust from contemporary volcanic eruptions. Relative palaeoproductivity changes show no consistent change in productivity across the Permian–Triassic boundary producing results that are comparable with those from the similar Opal Creek section to the south-east. The Ni/Co, Cu/Zn, U/Al and Th/U ratios indicate variable redox conditions in all sections, but with a tendency for oxic conditions to change to dysoxic across the Permian–Triassic boundary. The lack of consistent element geochemical changes across the boundary accompanied by significant isotopic changes, here and elsewhere, suggests that atmospheric and oceanic chemistry rather than physical changes, like provenance and sea-level changes, drove Permian–Triassic environmental changes and extinctions.

Late Permian–Middle Triassic magnetostratigraphy in North China and its implications for terrestrial-marine correlations

A detailed magnetostratigraphic study, linked to a new latest Permian U–Pb ID-TIMS age, was undertaken on the continental Shichuanhe section (SCH) in North China in order to provide a magnetic polarity scale for the Late Permian–early Middle Triassic interval. Tilt-corrected mean directions of the characteristic remanent magnetization pass the reversal test and correspond to a site paleolatitude of 18.1°N during the Early Triassic, consistent with previous results from the North China Block. The magnetostratigraphy shows close similarity with previous studies, allowing interregional correlations with both marine and non-marine records. Normal magnetozone SCH3n, constrained by an absolute age of 252.21±0.15 Ma from an ash bed 3.5 m below its base, is unambiguously correlated to the earliest Triassic normal magnetochron LT1n. Our newly established magnetostratigraphic framework and published carbon-isotope chemostratigraphy, indicate that the Permian–Triassic Boundary is ca. 8 m above the base of SCH3n (within the middle part of the Sunjiagou Formation) at SCH. The overlying reverse polarity dominated interval (SCH3r–SCH5r) ranges to the middle Liujiagou Formation, and straddles an interval from the mid-Griesbachian to mid-Smithian. The base of the Olenekian is provisionally located in the lower part of the Liujiagou Formation, near the base of magnetozone SCH5n. The succeeding thick normal magnetozone SCH6n persists into the upper Heshanggou Formation, with the inferred Smithian–Spathian boundary located in the upper part of the Liujiagou Formation. The transition from reverse magnetozone SCH6r to the overlying normal magnetozone SCH7n, coincides with a clear erosional contact with the base of the Ermaying Formation. Consequently, magnetozone SCH7n is matched to the Early Anisian magnetochron MT3n, with the Olenekian–Anisian boundary interval missing. Our new timescale provides additional magnetostratigraphic constraints on the timing of the terrestrial ecological crisis in North China, which is found to lie within reverse magnetozone SCH2r (equivalent with reverse magnetochron LP3r), a level some 270±150 kyrs before the main marine extinction, that falls in the overlying normal magnetochron LT1n.

Marine invertebrate fossils from the Permian–Triassic boundary beds of two core sections in the northern Perth Basin, Western Australia

Marine macroinvertebrate fossils from two petroleum exploration cores, Apium-1 and Redback-2, are described, and found to contain two separate assemblages. The assemblage from the Apium-1 core was recovered from an ca 5-m-thick interval (2756.35–2751.28 m) in the basal Hovea Member (‘inertinitic interval’) of the Kockatea Shale and includes the following forms: ?Spinomarginifera sp., Cimmeriella sp., ?Etherilosia sp., Elivina sp., Cleiothyridina sp., and Paeckelmanelloidea gen. et. sp. indet. (all brachiopods). The age of this assemblage is interpreted as Changhsingian, as constrained by its association with the palynofloral Dulhuntyispora parvithola Zone. The assemblage from the Redback-2 core was recovered from the ‘sapropelic interval’ of the Hovea Member of the Kockatea Shale between 3806 m and 3786 m and comprises the following forms: Lingulidae gen. et sp. indet. (brachiopod), Claraia perthensis Dickins & McTavish, Crittendenia cf. australasiatica (Krumbeck), ?Paralledon sp. (bivalves), ?Otoceras sp. (ammonoid), Microconchus utahensis Zatoń, Taylor & Vinn (microconchid) and Magniestheria mangaliensis (Jones) (spinicaudatan). Among these, the first local appearances of the lingulid species, ?Otoceras sp. and M. mangaliensis are associated with the palynofloral Protohaploxypinus microcorpus Zone and are interpreted as latest Changhsingian in age. Other occurrences of the Redback-2 fossil assemblage overlap with the palynofloral Kraeuselisporites saeptatus Zone and are considered to be of earliest Triassic (Griesbachian) age. G.R. Shi [guang@uow.edu.au] and Sangmin Lee [sangminlee76@gmail.com], School of Earth, Atmospheric and Life Sciences, University of Wollongong, Northfields Ave, Wollongong, NSW 2522, Australia; Ian Metcalfe [imetcal2@une.edu.au], Earth Sciences, Earth Studies Building C02, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia; Daoliang Chu [chudl@cug.edu.cn], State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, PR China; Huiting Wu [ht_wu415@163.com], College of Geoscience and Surveying Engineering, China University of Mining & Technology, Beijing, PR China; Tinglu Yang [yang@geology.hk], Faculty of Geosciences, East China University of Technology, Nanchang 330013, PR China; Yuri D. Zakharov [yurizakh@mail.ru], Far East Geological Institute, Far East Branch, Russian Academy of Sciences, Vladivostok, 690022 Russia.

Environmental crises at the Permian–Triassic mass extinction

The link between the Permian–Triassic mass extinction (252 million years ago) and the emplacement of the Siberian Traps Large Igneous Province (STLIP) was first proposed in the 1990s. However, the complex cascade of volcanically driven environmental and biological events that led to the largest known extinction remains challenging to reconstruct. In this Review, we critically evaluate the geological evidence and discuss the current hypotheses surrounding the kill mechanisms of the Permian–Triassic mass extinction. The initial extrusive and pyroclastic phase of STLIP volcanism was coeval with a widespread crisis of terrestrial biota and increased stress on marine animal species at high northern latitudes. The terrestrial ecological disturbance probably started 60–370 thousand years before that in the ocean, indicating different response times of terrestrial and marine ecosystems to the Siberian Traps eruptions, and was related to increased seasonality, ozone depletion and acid rain, the effects of which could have lasted more than 1 million years. The mainly intrusive STLIP phase that followed is linked with the final collapse of terrestrial ecosystems and the rapid (around 60 thousand years) extinction of 81–94% of marine species, potentially related to a combination of global warming, anoxia and ocean acidification. Nevertheless, the ultimate reasons for the exceptional severity of the Permian–Triassic mass extinction remain debated. Improved geochronology (especially of terrestrial records and STLIP products), tighter ecological constraints and higher-resolution Earth system modelling are needed to resolve the causal relations between volcanism, environmental perturbations and the patterns of ecosystem collapse. At the Permian–Triassic boundary (252 million years ago), a series of environmental crises triggered by the Siberian Traps eruptions caused the extinction of 81–94% of marine species and 70% of terrestrial vertebrate families. This Review discusses the relationships between volcanism, environmental perturbations and ecosystem collapse at the Permian–Triassic boundary.

The Anisian continental-marine transition in Sardinia (Italy): state of the art, new palynological data and regional chronostratigraphic correlation

The scarce evidence of paleontological records between the upper Permian and the Anisian (Middle Triassic) of Western Europe could reflect (1) large stratigraphic gaps in the continental successions and/or (2) the persistence of disturbed conditions after the Permian–Triassic Boundary extinction event and the succession of ecological crises that occurred during the Early Triassic. In this context, the study of palynological associations, integrated with the stratigraphical and sedimentological data, plays a key role in dating and correlating the successions of the Western European domain and improves our understanding of environmental and paleoclimatic conditions. In some cases, pre-Anisian paleontological evidence is lacking, as in Sardinia (Italy), where a long gap encompasses the middle Permian (pars) to late Lower Triassic successions. Although fragmented and disseminated, the continental Lower-Middle Triassic sedimentary successions (Buntsandstein) of Sardinia have proved crucial to our understanding of the evolution of the southern edge of the Paleo-Europe and the different timings of the Tethys transgression (Muschelkalk facies) in some of these areas. Various paleogeographic reconstructions were attempted in previous works, without providing any consensus on the precise position of Sardinia and its surrounding seaways in the Western Tethys domain during this time interval. At present, the configuration and distribution of the subsiding and emerging landmasses and the temporal development of the transgressions of the Western Tethys during the Middle Triassic remain unclear. This work focuses on the stratigraphical, sedimentological and palynological aspects of three Middle Triassic continental-marine sedimentary successions in Sardinia, with particular attention to the analysis of the palynological associations sampled there, and it also provides a detailed review of all previous palynological publications on the Sardinian Anisian. The studied successions are: Su Passu Malu section (Campumari, SW Sardinia), Arcu is Fronestas section and Escalaplano section (Escalaplano, Central Sardinia). These sections were also correlated to other significant sections in the SW (Scivu Is Arenas) and NW (Nurra) parts of the island.

Latentifistularia and other radiolarian species from the lower Smithian (Lower Triassic) Lang Son Formation, NE Vietnam

Well-preserved Early Triassic radiolarians were recovered from lower Smithian (lower Olenekian) beds in NE Vietnam. The radiolarian assemblage consists only of Paleozoic relict species of Latentifistularia and some entactinarians. Three latentifistularian species, Ruzhencevispongus vietnamensis nov. sp., Tetragregnon chilangensis nov. sp., and Tetragregnon langsonensis nov. sp., belonging to the families Ruzhencevispongidae Kozur and Tetratormentidae Nestell and Nestell are erected herein. The entactinarian family Triassothamnidae nov. fam. and one new genus and two new species of Langsonsphaera pseudocubica nov. gen. nov. sp. and Stigmosphaerostylus amabilis nov. sp. are also described. In this region, the Paleozoic-type radiolarian groups Latentifistularia and Entactinaria survived across the Permian–Triassic boundary and were present during the Induan–early Olenekian interval. Thus, in the eastern Tethyan seaway near the equator, the true extinction of some Paleozoic radiolarian groups took place at the middle of the Early Triassic, immediately after the Smithian, rather than during the Permian–Triassic crisis.

On Traces of Non-Equilibrium States in the Evolution of Terrestrial Vertebrate Communities across the Paleozoic–Mesozoic Boundary

Evolutionary change in a living system starts with a disturbance to its equilibrium and an increase in its internal disorderliness. Typical manifestations of this process are exemplified by the transformation of the tetrapod faunas across the Permian–Triassic boundary. These are seen both at the end of the transition to a new equilibrium (in the pioneer Triassic faunas) and at its beginning (in the terminal Permian communities). In the first case, the most distinct manifestations are: unfinished state of structural changes within some new groups; a high degree of endemism of regional pioneer communities, and the heterogeneity of their change with time. In the second case, as can be seen from analysis of the early-crisis (Vyaznikovian) biota of Eastern Europe, the observed events primarily include the “precocious” appearance of some future dominants; the “return” of a number of relics to the fossil record; and examples of explosive group variability in some taxa close to extinction. Actual or probable traces of non-equilibrium changes, similar to those noted in the Vyaznikovian biota, can also be partly traced in other Late Permian faunas of Eurasia and in coeval communities of southern and northern Gondwana.

ПЕТРО- И ПАЛЕОМАГНЕТИЗМ МАФИТОВЫХ ДАЕК СЕРГЕЕВСКОГО ТЕРРЕЙНА (ЮЖНЫЙ СИХОТЭ-АЛИНЬ)

The paper presents the results of paleomagnetic and rock magnetic studies of rocks from the mafic dikes of the Sergeevka terrane that intruded the basement rocks. Currently, they are widespread in coastal outcrops of the eastern part of the Peter the Great Bay of the Sea of Japan between Anna and Priboinaya bays in the south of Primorsky Krai. Structural information allows us to conclude that dikes of both the eastern (Srednyaya Bay-Priboinaya Bay) and the western (Anna Bay-Cape De Livron) clusters intruded from the igneous centers of the same strike. Rocks of the dikes have undergone significant secondary alterations. Inverse magnetic fabric in the dikes is the result of high-temperature decomposition and granulation of primary titanomagnetites during postmagmatic deformations and metamorphism, traces of which are clearly visible in the microscopic and microprobe study of secondary alteration products. All this testifies to a significant secondary change in the rocks of the dikes after their intrusion. This is the secondary heating of the dikes above a temperature of 600 °C, that is, above the Curie point of magnetite (578 °C). The nature of the isolated high-temperature NRM component of the dikes is not primary, but secondary, that is, metachronous. The paleomagnetic data constrained the time of the metamorphic event leading to the remagnetization of mafic dikes of the Sergeevka terrane to ca. 250 Ma. The calculated paleolatitude of the Sergeevka terrane at the time of acquisition of the metachronous NRM component by mafic dikes (21.8 ± 4.2° N) is consistent with the paleolatitudes of the northeastern edge of the North China Craton at the Late Permian/Early Triassic boundary.

Palynological Dynamics Across the Permian–Triassic Boundary in Southwestern China

Palynological Dynamics Across the Permian–Triassic Boundary in Southwestern China

Two pulses of increasing terrestrial input to marine environment during the Permian–Triassic transition

The destruction of both terrestrial and marine ecosystems generally shows a process of rapid extinction followed by the wipe out of the Permian-type relics in the Permian–Triassic mass extinction, but the relationship between the terrestrial and marine ecosystem collapses is not clear until now. The terrestrial input from the land to marine system is an important link between them. Previous study has demonstrated a substantial increase of terrestrial influx to the marine water most likely corresponding to the Permian–Triassic mass extinction. Our new geochemical data from the Laolongdong section in the shallow marine carbonate platform of South China, reveal that the elevated terrestrial input nearby the Permian–Triassic Boundary (PTB) is actually marked by a two-pulse scenario. The first pulse represents a ~ 3- to ~ 6-fold increase of the terrestrial flux. The onset of the increase took place in the extinction horizon at the basal part of microbialites at Laolongdong, basically corresponding to Bed 24a of Meishan section and prior to the end-Permian mass extinction zenith; then the increase continued and spanned the extinction zenith. The second pulse is characterized a ~ 21- to ~ 35-fold increase in the terrestrial flux, equivalent to the widespread, abundant presence of mudstones in the earliest Triassic and roughly corresponding to the stage where the Permian-type survivors were thoroughly wiped out. A two-pulse terrestrial input is also clearly recorded at Cili, Shangsi and Meishan of South China, western Australia and Arctic Canada. Two episodes of the enhanced terrestrial input provide strong evidence for the devastation of the terrestrial ecosystem and insights into the reasonable explanation for the relationship between terrestrial and marine ecosystem collapses nearby the PTB. • Geochemical data reveal a two-pulse terrigenous input nearby the PTB. • The first pulse was linked to the end-Permian terrestrial mass extinction, as a prelude of the marine mass extinction. • The second pulse terminated microbialite, linked to the devastating of vegetation and soil erosion in the Early Triassic. • The enhanced terrestrial inputs provide insights into the relationship between terrestrial and marine ecosystem collapses.

THE OLENEKIAN-ANISIAN/EARLY-MIDDLE TRIASSIC BOUNDARY, AND ASSESSMENT OF THE POTENTIAL OF CONODONTS FOR CHRONOSTRATIGRAPHIC CALIBRATION OF THE TRIASSIC TIMESCALE

The conodont Chiosella timorensis (Nogami, 1968) has for a long time been considered to be a suitable biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. The recently acquired ammonoid record around that boundary clearly shows that the FAD of this conodont is located well below the boundary, i.e., in the late Spathian. In the present paper, it is underlined that the conodont Chiosella timorensis was promoted as a proxy for the nominated boundary in the early 1980s when the ammonoid record around the boundary was not yet well established. On the other side, until the mid 1990s the taxonomic definition and the lineage of the conodont Chiosella timorensis were not well stated, and even now there are still controversial interpretations of the taxonomic content of this conodont species. The new data achieved from the ammonoid/conodont record around the nominated boundary, especially in the western USA, and also in the Deşli Caira section in Romania, firmly demonstrate that the conodont Chiosella timorensis is a defunct proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. As a consequence, the present data on the ammonoid-documented Olenekian-Anisian/Early-Middle Triassic boundary requires the recalibration of all physical events that have been tied to the FAD of the conodont Chiosella timorensis. The case of the Albanian Kçira-section, for which the chronostratigraphic interpretation of the ammonoid record is proved incorrect, definitely makes the conodont Chiosella timorensis a defunct proxy for the nominated boundary. Also, the case of the two Chinese sections recently proposed as being “exceptional” GSSP candidates for the Early-Middle Triassic boundary, which is based on an inconsistent ammonoid/conodont biochronology, fully strengthens this conclusion. The history of the controversial usage of the conodont species Chiosella timorensis in defining the Olenekian-Anisian boundary justifies a discussion about the usefulness of conodonts in the chronostratigraphic calibration of the standard Triassic timescale. One may conclude that the conodonts are not qualified, and have not a reasonable potential, to be used to define or to redefine the boundaries of chronostratigraphic units in the standard Triassic timescale, which have been basically defined on ammonoid biochronology.

Late Palaeozoic‐Mesozoic palaeontology and stratigraphy in China: A tribute to the achievements of Professor Zhuoting Liao

As one of the pioneer palaeontologists, Professor Zhuoting Liao has contributed his lifetime to promoting palaeontological and stratigraphical research in China for 60 years, and he passed away in the field excursion in South China on June 20, 2020. In his palaeontological career, Liao has worked on Late Palaeozoic to Mesozoic palaeontology and stratigraphy of almost all regions across China, and his interests have also extended to the Permian–Triassic (P‐Tr) boundary and mass extinction. He has worked on palaeontology, palaeobiogeography, biostratigraphy, tectonostratigraphy, and their implications in mineral and oil‐gas industries. Liao has established 22 new genera and 172 new species of brachiopods, and, together with his colleagues, proposed 11 new genera and 25 new species of echinoderms. He dedicated his lifetime to work on Late Palaeozoic palaeontology and stratigraphy of the previously remote and tectonically complex Xinjiang and adjacent regions, north‐west China, and established integrated stratigraphical frameworks for the Carboniferous to Permian strata, providing fundamental basis for mineral and hydrocarbon exploration in the poorly understood Central Asian terranes. In addition, he has mentored many young palaeontologists and stratigraphers in various ways. This volume assembles 30 papers addressing the Late Palaeozoic to Mesozoic palaeontology and stratigraphy of China and adjacent regions, which pays tribute to the achievement of Professor Zhuoting Liao.

Faunal composition and paleoenvironmental reconstruction of a Middle–Late Triassic boundary assemblage in the Pyrenean basin (Catalonia, NE Spain)

AbstractThe Ladinian–Carnian transition in the Tethys domain was accompanied by an important environmental change representing a milestone in the climate evolution of the Triassic. However, estimations on paleodiversity composition and paleoenvironmental conditions across this interval are scarce in marine settings due to the lack of fossil-bearing successions. In this work, a refined paleontological and sedimentological study has allowed us to better characterize a well-preserved marine ?Ladinian–Carnian carbonate succession in the South Central Pyrenees (Odèn site, Catalonia, NE Spain). Vertebrate faunas include numerous actinopterygian specimens, forming an assemblage composed of at least four taxa: Peltopleurus cf. P. nuptialis Lombardo, 1999, Saurichthys sp., Colobodus giganteus (Beltan, 1972), and an indeterminate halecomorph. Specimens belonging to the genus Peltopleurus are dominant; the long-snouted Saurichthys, the halecomorph, and the large-bodied Colobodus giganteus are less abundant. Tetrapod remains are scarcely present and are assigned to sauropterygians. Invertebrate faunas include bivalves (Pseudocorbula gregaria [Münster in Goldfuss, 1838]) and brachiopods (Lingula sp.). The fossil assemblage was recovered from organic-rich laminated silty mudstone layers. Sedimentological and textural analyses suggest that fossil biotas were deposited below the fair-weather wave base in shallow subtidal coastal settings. These environments were sporadically sourced by silt/clay. The age of the Odèn site, on the basis of the recovered fauna, is assigned to the ?late Ladinian–middle Carnian (Middle–Late Triassic), which is in agreement with previously published ages based on palynomorph data.The refined integration of paleontological, sedimentological, and biostratigraphic data from the Odèn site and other vertebrate-bearing localities in the Tethys domain can help better constrain the paleoenvironmental conditions and paleogeographical configuration impacting ecosystem diversity during the late Ladinian–Carnian interval.

The Permian–Triassic boundary section at Baghuk Mountain, Central Iran: carbonate microfacies and depositional environment

Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.

Paleo-oil reservoir pyrolysis and gas release in the Yangtze Block imply an alternative mechanism for the Late Permian Crisis

The causes of the global mass extinction that occurred around the Permian–Triassic boundary have been widely studied through the geological record and in various locations. The results show that volcanic activity was a key factor in initiating the crisis during the Late Permian. Compared to other thermal events triggered by volcanic activity, pyrolysis of petroleum in Pre-Permian reservoirs has rarely been suggested as a significant source of the greenhouse gases that caused the mass extinction. In this study, geochemical analysis is carried out of a huge paleo-oil reservoir in the Yangtze Block (YB), South China. The detection of mineral inclusions and pyrobitumens is evidence of rapid pyrolysis of accumulated oil in the Ediacaran reservoir. New evidence from hydrothermal minerals and the presence of domain mesophase in the pyrobitumen suggest that the pyrolysis process occurred abruptly and that greenhouse gases were rapidly released through venting pipes. The dating of such a complex geological event in this old and deeply buried reservoir is inevitably difficult and potentially unreliable. However, cross-validation of the multiple evidence sources, including hydrothermal minerals and domain mesophase, indicates that the rapid oil pyrolysis must have been driven by a major thermal event. Reconstruction of burial and thermal histories suggests that the thermal event was most likely to have been triggered by the Emeishan Large Igneous Province (ELIP), which was in a period of significant volcanic activity during the Late Permian. Massive volumes of gases, including methane, carbon dioxide, and possibly hydrogen sulfide, were released, causing a significant increase in greenhouse gases that may have contributed to global warming and the resulting mass extinction during the Late Permian Crisis (LPC).

Nonmarine Mass Extinctions

A critical review of putative nonmarine mass extinctions associated with the so-called “Big 5 mass extinctions” of marine invertebrates (Late Ordovician, Late Devonian, end Permian, end Triassic and end Cretaceous) as well as a likely sixth mass extinction in the marine realm, the end-Guadalupian extinction, reveals little evidence of coeval marine and nonmarine mass extinctions. Little lived on land during the Ordovician other than a bryophyte-like flora that appears to have been diversifying, not going extinct, during the Late Ordovician. No case can be made for mass extinctions on land coeval with the marine extinctions of the Late Devonian-land plant diversity increased into the Carboniferous, and the tetrapod fossil record is inadequate to identify any mass extinctions. A case can be made for coeval plant/tetrapod extinctions and the end-Guadalupian marine extinctions, so this may be the first coeval marine-nonmarine mass extinction. However, problems of timing and questions about the extent of the nonmarine late/end-Guadalupian extinctions indicate that further research is needed. There were no mass extinctions of land plants, insects or tetrapods across the Permo–Triassic boundary. The Late Triassic was a time of low origination and high extinction rates on land and in the seas; there was no single end-Triassic mass extinction in either realm. The end-Cretaceous provides the strongest case for coeval land–sea mass extinctions, but there is no mass extinction of land plants, evidence of insect extinction is based on assumption-laden analyses of proxies for insect diversity and the tetrapod extinction was very selective. So, whether the nonmarine extinction at the end of the Cretaceous was a mass extinction is worth questioning. Part of the inability to identify nonmarine mass extinctions stems from taphonomic megabiases due to the relatively poor quality and uneven sampling of the nonmarine fossil record. Extinction resistance and resilience of terrestrial organisms is also a likely factor in the dearth of nonmarine mass extinctions, and this merits further investigation.

Calcilobes wangshenghaii n. gen., n. sp., microbial constructor of Permian\u2013Triassic boundary microbialites of South China, and its place in microbialite classification

Permian–Triassic boundary microbialites (PTBMs) that formed directly after the end-Permian extinction in the South China Block are dominated by one structure, a lobate-form calcium carbonate construction that created extensive very thin (ca. 2–20 m thick) framework biostromes in shallow marine environments, effectively occupying the ecological position of the prior pre-extinction Permian reefs and/or associated carbonates. In the field, vertical sections show the microbialite is dendrolite (branched) and thrombolite (clotted), but because thrombolite may include branched portions, its structure is overall best classed as thrombolite. In the field and in polished blocks, the microbial material appears as dark carbonate embedded in lighter-coloured micritic sediment, where details cannot be seen at that scale. In thin section, in contrast to the largely unaltered micritic matrix, the microbial constructor is preferentially partly to completely recrystallised, but commonly passes gradationally over distances of a few mm to better-preserved areas comprising 0.1–0.2 mm diameter uneven blobs of fine-grained calcium carbonate (micrite to microsparite). The lobate architecture comprises branches, layers and clusters of blobs ca. 1–20 mm in size, and includes constructed cavities with geopetal sediments, cements and some deposited small shelly fossils. Individual blobs in the matrix may be fortuitous tangential cross sections through margins of accumulated masses, but if separate, may represent building blocks of the masses. The lobate structure is recognised here as a unique microbial taxon and named Calcilobes wangshenghaii n. gen., n. sp. Calcilobes reflects its calcium carbonate composition and lobate form, wangshenghaii for the Chinese geologist (Shenghai Wang) who first detailed this facies in 1994. The structure is interpreted as organically built, and may have begun as separate blobs on the sea floor sediment (that was also composed of micrite but is interpreted as mostly inorganic), by microbial agglutination of micrite. Because of its interpreted original micritic–microsparitic nature, classification as either a calcimicrobe (calcified microbial fossil) or a sedimentary microbial structure is problematic, so C. wangshenghaii has uncertain affinity and nature. Calcilobes superficially resembles Renalcis and Tarthinia, which both form small clusters in shallow marine limestones and have similar problems of classification. Nevertheless, Calcilobes framework architecture contrasts both the open branched geometry of Renalcis, and the small tighter masses of Tarthinia, yet it is more similar to Tarthinia than to Renalcis, and may be a modification of Tarthinia, noting that Tarthinia is known from only the Cambrian. Calcilobes thus joins Renalcis, Tarthinia and also Epiphyton (dendritic form) and others, as problematic microbial structures. Calcilobes has not been recognised elsewhere in the geological record and may be unique to the post-end-Permian extinction facies. C. wangshenghaii occurs almost exclusively in the South China Block, which lay on the eastern margin of Tethys Ocean during Permian–Triassic boundary times; reasons for its absence in western Tethys, except for comparable fabrics in one site in Iran and another in Turkey, are unknown.

Shell microstructures of latest Permian Rugosochonetidae (Brachiopoda): evidence from SEM‐ and CT‐scanned shell materials

Microscopic perforations in brachiopod shells, such as endopunctae, pseudopunctae, extropunctae, aditicules and epipunctae, have various biological functions. Based on excellently preserved material, aditicules are found to be widely developed in the Fusichonetes and Neochonetes, and setae-bearing aditicules are shown to exist in rugosochonetid brachiopods for the first time. SEM and Micro-CT images show that aditicules obliquely insert into the primary layer and are arranged in a single column along the crest of a costellae. The setae are supposed to play a role in triggering the closure of shells by sensing dangers, preventing large particles from entering the inner cavity and helping to increase the water pressure by forming a functional siphon. The SEM and Micro-CT images also show that papillae are solid cones on the inner surface of the shell, and the density of papillae varies over different regions of the shell surface, and with environment. The variation in density of the papillae is most likely related to diverse functions in the ‘filtering system’. In the marginal area, the small and densely spaced papillae can prevent intermediate and fine particles from entering the mantle cavity, whereas the large and sparse papillae in the mid-valve can trap fine particles. In this study, these two microstructures are interpreted as a sediment ‘filtering system’ in Fusichonetes and Neochonetes, which is corroborated by the predominant occurrence of these genera in shallow-water clastic shelves and deep-water siliceous basins across the Permian–Triassic boundary interval in South China.

Drainage and environmental evolution across the Permo–Triassic boundary in the south‐east Germanic Basin (north‐east Bavaria)

AbstractThe identification of the factors triggering continental environmental changes at the Permian–Triassic transition is of general interest as they allow a better understanding of the most controversial mass extinction of the Phanerozoic. This study investigates the environmental response to external forcings on continental successions at the south‐east‐margin of the Central European Basin System in Germany. Studies from this area are scarce, and its evolution is poorly understood. This work integrates high‐resolution core‐logging and quantitative sedimentary petrography of Middle Permian–Early Triassic successions recovered from the wells Obernsees‐1 and Lindau‐1. The sedimentological investigation reveals major vertical variations in the depositional settings marked by changes in grain‐size trends and facies associations: (i) the progradation of mass flow/fluvial fans over sandflat environments denotes the Guadalupian–Lopingian; (ii) sabkha to shallow‐marine conditions occur during the uppermost Permian; (iii) the onset of braided fluvial sequences marks the Permian–Triassic boundary; (iv) changes in fluvial style, reflecting increased river sinuosity, and aeolian deposition characterize the remaining Triassic. Environmental changes are accentuated by variations in sediment composition. Proximal deposits (for example, alluvial fan) are lithic arkoses, while more distal associations reveal arkosic composition. Detrital modes point to: (i) a high‐grade metamorphic source feeding the drainage of Lindau‐1 (metamorphic index, MI 441–500); and (ii) a mixed low‐grade and high‐grade metamorphic source (MI 277–395) feeding the Permian of Obernsees‐1, passing upward to high‐grade metamorphic (MI 441–500) and subordinate granitoid sources. Compositional signatures and environmental changes suggest distinct drainage evolutions regulated by upstream climate and tectonic controls. The higher plutonic clast content coeval to the onset of fluvial sedimentation and coarse‐grained influxes reflects local tectonic perturbations attributed to the Early Triassic reactivation of Variscan faults. The evidence of perennial fluvial systems during the lowermost Triassic reflects wetter climate conditions in the upstream catchment area, which contradicts the common view of increased aridity at the Permian–Triassic boundary.