Academic literature on the topic 'Triassic (P/Tr) boundary'

Newly obtained foraminifer faunas from the Permian-Triassic (P-Tr) transition at the Dajiang and Bianyang sections in the Nanpanjiang Basin, South China, comprise 61 species in 40 genera. They belong to thePalaeofusulina sinensisZone, the youngest Permian foraminifer zone in South China. Quantitative analysis reveals that the last occurrences of more than a half of species (28/54) fall into a 60-cm-interval at the uppermost Changhsingian skeletal packstone unit and thus calibrate the end-Permian extinction to the skeletal packstonecalcimicrobial framestone boundary. About 93% (54/58) of species of the latest Permian assemblage became extinct in the P-Tr crisis. Four major foraminiferal groups, the Miliolida, Fusulinida, Lagenida, and Textulariina, have extinction rates up to 100%, 96%, 92%, and 50%, respectively, and thus experienced selective extinctions. BothHemigordius longusand ?Globivalvulina bulloidestemporarily survived the end-Permian extinction event and extended into the earliest Triassic but became extinct soon after. The post-extinction foraminifer assemblage is characterized by the presence of both disaster taxa and Lazarus taxa. Foraminifer distribution near the P-Tr boundary also reveals that the irregular contact surface at the uppermost Permian may be created by a massive submarine dissolution event, which may be coeval with the end-Permian mass extinction. A new species,Rectostipulina hexamerata,is described here.

The morphographic characters of fossil saccate pollen and their evolutionary sequence through the span of Gondwana formations play a vital role in the biohorizon stratigraphy. Based on evolutionary changes in the morphology of the pollen group, their FADs (First Appearance Datums) and LADs (Last Appearance Datum) and the cluster levels, eleven biohorizons and ten inter-biohorizon Zones (Interval-zones) have been identified. The model of alliance among the prime morphographies has been acquired through simple character state analysis. By extrapolation of lineages, four unique monosaccate and one simple disaccate organizations could be identified to have their origin in the early Upper Carboniferous stock of Australia, which, in turn, were related with the Devonian progymnospermopsida complex. The five outgroup stocks continued as such into the late Early Asselian Talchir Formation of India and sprouted in the subsequent Permian time. A gap in the sequence has been identified during Upper Carboniferous of Australia and the lowermost Permian in India. The sixth major lineage of striate pollen branched off from the simple disaccate pollen lineage to appear in the Late Asselian. Cladistic analysis supports the applicability of the proposed biohorizons as important stratigraphic parameter. The congruence of derived and ancestral states of internally compatible and persimonically harmonious characters in pollen organizations has been used in drawing relationship trees. Thus, the cladograms and stralograms (nested diagrams of stratigraphic occurrences) together depict the maximum diversification at the lower Upper Talchir and the P/Tr boundary. The major extinction of monosaccates at the Lower Permian-Upper Permian boundary and that of the striate-disaccates in the basal Triassic have also been brought to light. The reasons of such a behaviour is attributed to environmental stresses caused by massive glaciations during Early Permian Talchir Formation, climatic changes towards warmer-drier situation at Lower/Upper Permian passage and global cooling and regression at the permo-Triassic level. Pollen features, like striations, taeniae, girdling monosaccus, clefts and remnant of germinal marks, etc. of the Permian and Triassic have perished completely by the end of Triassic. Most of the Jurassic palyno-assemblages contain the fag-end organizations of simple disaccate lineages; the experimentation seems to have attained a more simple state in the morphography of saccate pollen which continued thereafter.

High-resolution palynological data sets from shallow marine Triassic-Jurassic (Tr/J) boundary beds of two principal sections in Europe (Hochalplgraben in Austria and St. Audrie's Bay in the United Kingdom) were analyzed to reconstruct changes in vegetation, biodiversity, and climate. In Hochalplgraben, a hardwood gymnosperm forest with conifers and seed ferns is replaced by vegetation with dominant ferns, club mosses and liverworts, which concurs with an increased diversification of spore types during the latest Rhaetian. Multivariate statistical analysis reveals a trend to warmer and wetter conditions across the Tr/J boundary in Hochalplgraben. The vegetation changes in St. Audrie's Bay are markedly different. Here, a mixed gymnosperm forest is replaced by monotonous vegetation consisting mainly of Cheirolepidiaceae (80–100%). This change is caused by a transition to a warmer and more arid climate. The observed diversity decrease in St. Audrie's Bay affirms this interpretation. Although both sections show major vegetation changes, neither of them demonstrates a distinctive floral mass extinction. A compilation of Tr/J boundary sections across the world demonstrates the presence of Cheirolepidiaceae-dominated forests in the Pangaean interior and increases in abundance of spore-producing plants adjacent to the Tethys Ocean. We propose that the non-uniform vegetation changes reflected in the Tr/J palynological records are the result of environmental changes caused by Central Atlantic Magmatic Province volcanism. The increase in greenhouse gases caused a warmer climate and an enhanced thermal contrast between the continent and the seas. Consequently, the monsoon system got stronger and induced a drier continental interior and more intensive rainfall near the margins of the Tethys Ocean.

A Permian-Triassic palynofloral transition is recorded in Borehole TP-8, Talcher Coalfield, Orissa, India. The change of palynoflora from Late Permian to Early Triassic is gradual and not abrupt. The variation in the pattern of changeover of the palynomorph distribution at P/Tr transition in Talcher Coalfield, Mahanadi Basin and Raniganj Coalfield, Damodar Basin is discussed.

AbstractThe Order Spiriferinida spanning the latest Ordovician to Early Jurassic is a small group of brachiopods overshadowed by other taxon-rich clades during the Paleozoic. It diversified significantly after the end-Permian extinction and became one of the four major clades of Triassic brachiopods. However, the phylogeny and recovery dynamics of this clade during the Triassic still remain unknown. Here, we present a higher-level parsimony-based phylogenetic analysis of Mesozoic spiriferinids to reveal their evolutionary relationships. Ecologically related characters are analyzed to indicate the variances in ecomorphospace occupation and disparity of spiriferinids through the Permian–Triassic (P-Tr) transition. For comparison with potential competitors of the spiriferinids, the pre-extinction spiriferids are also included in the analysis. Phylogenetic trees demonstrate that about half of the Mesozoic families appeared during the Anisian, indicating the greatest phylogenetic diversification at that time. Triassic spiriferinids reoccupied a large part of the ecomorphospace released by its competitor spiriferids during the end-Permian extinction; they also fully exploited the cyrtiniform region and developed novel lifestyles. Ecomorphologic disparity of the spiriferinids dropped greatly in the Early Triassic, but it rebounded rapidly and reached the level attained by the pre-extinction spiriferids in the Late Triassic. The replacement in ecomorphospace occupation between spiriferids and spiriferinids during the P-Tr transition clearly indicates that the empty ecomorphospace released by the extinction of Permian spiriferids was one of the important drivers for the diversification of the Triassic spiriferinids. The Spiriferinida took over the empty ecomorphospace and had the opportunity to flourish.

ABSTRACTRecent stratigraphic revisions of the Upper Triassic Chinle Formation of Petrified Forest National Park, in conjunction with precise and accurate documentation of fossil tetrapod occurrences, clarified the local biostratigraphy, with regional and global implications. A significant overlap between Adamanian and Revueltian faunas is rejected, as is the validity of the Lamyan sub-land vertebrate faunachron. The Adamanian–Revueltian boundary can be precisely placed within the lower Jim Camp Wash beds of the Sonsela Member and thus does not occur at the hypothesised Tr-4 unconformity. This mid-Norian faunal turnover, may coincide with a floral turnover, based on palynology studies and also on sedimentological evidence of increasing aridity. Available age constraints bracketing the turnover horizon are consistent with the age of the Manicouagan impact event. The rise of dinosaurs in western North America did not correspond to the Adamanian–Revueltian transition, and overall dinosauromorph diversity seems to have remained at a constant level across it. The paucity of detailed Late Triassic vertebrate biostratigraphic data and radioisotopic dates makes it currently impossible to either support or reject the existence of globally synchronous Late Triassic extinctions for tetrapods.

Extinction, the irreversible loss of species, is perhaps the most alarming symptom of the ongoing biodiversity crisis. Some of the most significant changes in evolution throughout Earth’s history have coincided with extinction boundary events. In this thesis various organic geochemical (biomarker and stable isotopes) and geological (sedimentology and palaeontology) approaches have been undertaken to examine one of the most significant mass extinction events that occurred during the Late Permian (252 My ago) near to the Permian/Triassic (P/Tr) boundary. In the marine realm 49% of invertebrate families became extinct (equivalent to 80–96% of species loss). However, identifying an ecological crisis and associated extinction interval in any given extinction boundary section can often be difficult.Many different hypotheses have been proposed to explain the end-Permian extinction. The coincidence in timing of the extinction with the massive volcanic eruptions in Siberia has been established. The release of methane and possibly other gases during the volcanic event could have led to global warming. The oceans were oxygen deficient leading to euxinic conditions (with H[subscript]2S as a toxic agent) possibly triggering the extinction. Further, the selectivity of the extinction suggests hypercapnia (high CO[subscript]2) as a kill mechanism. It is widely accepted that the extinction is a “tangled web of causality” with several mechanisms contributing to the biotic crisis.Analyses of molecular fossils (biomarkers) and their stable isotopic compositions provide an alternative tool for identifying mass extinction intervals complimenting bulk stable isotopic data (δ[superscript]34Spyrite, δ[superscript]13Ccarbonate, δ[superscript]13Corg), sedimentological and fossil record data. Only recently have biomarker abundances (and δ[superscript]13C) and changes associated with the end-Permian extinction attracted significant attention. For example, biomarkers ultimately derived from pigments of organisms carrying out anoxygenic photosynthesis (Chlorobiaceae) have been recently reported in several P/Tr sections, providing evidence for widespread photic zone euxinic conditions.The aims of this PhD thesis were (i) to establish the palaeoenvironmental conditions associated with the P/Tr mass extinction event using an integrated biomarker, isotopic (including δD of biomarkers) and sedimentological approach for one section from the northern hemisphere and (ii) to establish whether the biomarker and isotopic signals (including δD of bulk kerogen) observed in several sections from about the globe represent localised environments of deposition and/or are related to global depositional conditions.In Chapter 2 for the first time an integrated study including sedimentological data, biomarker distributions/abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes (δ[superscript]34Spyrite, δ[superscript]13Ccarbonate, δ[superscript]13Corg) for a Late Permian section from Lusitaniadalen, Spitsbergen, Norway has been conducted. These data support a marine transgression and collapse of the marine ecosystem in the Late Permian. Strong evidence for waxing and waning of photic zone euxinic conditions throughout the Late Permian section is provided by Chlorobiaceae-derived biomarkers (including δ[superscript]13C data) and δ[superscript]34Spyrite, suggesting several events of H[subscript]2S outgassing and potentially several pulses of extinction. A rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event suggests a decline in terrestrial organisms during the Late Permian and/or increasing distance from the palaeoshoreline as an effect of sea level rise. Changes in δD of biomarkers also indicate a change in source of OM, microbial diversification and sea level rise. Further, compound specific isotope analysis (CSIA) data of algal and land-plant derived biomarkers, δ[superscript]13Ccarbonate and δ[superscript]13Corg provide strong evidence for synchronous changes in δ[superscript]13C of marine and atmospheric CO[subscript]2, attributed to a [superscript]13C-depleted source. The source could either be associated with isotopically depleted methane released from the melting of gas clathrates and/or from respired OM, due to the collapse of the marine ecosystem.In Chapter 3 δD of kerogen (δDkerogen) for three P/Tr sequences (Hovea#3, Perth Basin, Western Australia; Schuchert Dal section, Jameson’s Land, East Greenland and Lusitaniadalen, Spitsbergen) have been measured and compared with δ[superscript]34S of total reduced inorganic sulfur (δ[superscript]34Spyrite) of all three sections and for one sample set δ[superscript]13C of carbonate (δ[superscript]13Ccarbonate) to establish (i) similarities between the sections and (ii) evaluate whether these signals are local or global. Stable isotope shifts occur for all localities either at the P/Tr transition (Western Australia) or coinciding with the marine ecosystem collapse (Spitsbergen and East Greenland). δDkerogen reflects OM/kerogen type. Reliable palaeoenvironmental information in terms of the use of δD can therefore only be obtained for the P/Tr transition from hydrogen compound-specific isotope analyses of biomarkers (Chapter 2). The negative shifts in δ[superscript]13Ccarbonate (primary) and δ[superscript]13Ckerogen are attributed to the release of [superscript]13C-depleted carbon into the atmosphere, whereas the isotopic excursions in δ[superscript]34Spyrite relate to global palaeoredox changes. However, the global synchronous shifts in δDkerogen, δ[superscript]34Spyrite and δ[superscript]13Ckerogen for all sections suggest a relation between the sulfur, carbon and hydrogen cycles.In Chapter 4 the abundances of several polycyclic aromatic hydrocarbons (PAHs) throughout three P/Tr sections from the Global Stratotype Section and Point (GSSP) in Meishan (South China), Kap Stosch Area (East Greenland) and Peace River Basin (Western Canada) were evaluated. The PAHs dibenzothiophene and dibenzofuran were found to decrease in abundance just before or shortly after the P/Tr boundary in all three sections, supporting the hypotheses of a worldwide decrease in preservation of terrestrial OM. Perylene was observed in high abundance at the onset of the main extinction horizon (at bed 25) in Meishan and has been attributed to a wood degrading fungal source, consistent with the demise of land plants. Frequently occurring forest fire events are also evident from the abundance of several combustion-derived PAHs showing independent patterns in all sections. The coincidence of high abundances of combustion markers occurring simultaneous with ash beds in Meishan section indicates an origin related to the Late Permian and Early Triassic volcanic eruptions in Siberia and China.In Chapter 5 an evaluation of selected biomarker maturity parameters [methylnaphthalene ratio (MNR), methylphenanthrene index (MPI-1), C27 diasterane/sterane ratio and Ts/(Ts+Tm) ratio] has been conducted for a number of P/Tr samples (Western Australia, East Greenland and Spitsbergen). Differences in these parameters have been observed between freely extractable bitumens from sedimentary rocks (Bitumen I) and bitumens comprising hydrocarbons closely related to the kerogen/mineral matrix (Bitumen II). Further, a distinct connection between these differences and the clay/TOC ratio of the sediments has been made. The information on thermal maturity that is preserved within Bitumen II could be of significance in petroleum exploration studies, as the original thermal maturity signal of Bitumen I may be overprinted by migrated bitumen.