Timing and magnitude of tetrapod extinctions across the Permo-Triassic boundary

A review of the tetrapod (amphibian and amniote) record across the Permo-Triassic boundary (PTB) indicates a global evolutionary turnover of tetrapods close to the PTB. There is also a within-Guadalupian tetrapod extinction here called the dinocephalian extinction event, probably of global extent. The dinocephalian extinction event is a late Wordian or early Capitanian extinction based on biostratigraphic data and magnetostratigraphy (the extinction precedes the Illawara reversal), so it is not synchronous with the end-Guadalupian marine extinction. The Russian PTB section documents two tetrapod extinction events, one just before the dinocephalian extinction event and the other at the base of the Lystrosaurus assemblage. However, generic diversity across the latter extinction remains essentially the same despite a total evolutionary turnover of tetrapod genera. The Chinese and South African sections document the stratigraphic overlap of Dicynodon and Lystrosaurus. In the Karoo basin, the lowest occurrence of Lystrosaurus is in a stratigraphic interval of reversed magnetic polarity, which indicates it predates the marine-defined PTB, so, as previously suggested by some workers, the lowest occurrence of Lystrosaurus cannot be used to identify the PTB in nonmarine strata. Correlation of the marine PTB section at Meishan, southern China, to the Karoo basin based primarily on magnetostratigraphy indicates that the main marine extinction preceded the PTB tetrapod extinction event. The ecological severity of the PTB tetrapod extinction event has generally been overstated, and the major change in tetrapod assemblages that took place across the PTB was the prolonged and complex “replacement” of therapsids by archosaurs that began before the end of the Permian and was not complete until well into the Triassic. The tetrapod extinctions are not synchronous with the major marine extinctions at the end of the Guadalupian and just before the end of the Permian, so the idea of catastrophic causes of synchronous PTB extinctions on land and sea should be reconsidered.     

Composition and similarity of global anomodont-bearing tetrapod faunas

Anomodont synapsids represent the dominant herbivores of Permian and Triassic terrestrial vertebrate ecosystems. Their taxonomic diversity and morphological disparity in combination with their cosmopolitan distribution makes them an ideal study object for macroevolutionary patterns across the most devastating extinction event in earth history. This study provides a thorough review of anomodont-bearing tetrapod faunas to form the basis for a faunal similarity analysis and future studies of anomodont diversity. The stratigraphic correlation and composition of all known anomodont assemblages is revisited, including a discussion of the validity of the globally distributed anomodont species. The similarity analysis of anomodont faunas is performed on the basis of presence–absence data of anomodont taxa, using explorative methods such as cluster analysis (UPGMA) and non-metric multidimensional scaling (NMDS). The recovered faunal groupings indicate a common biostratigraphic age and furthermore reflect biogeographic patterns. Even though endemism and faunal provinciality was a constant element in anomodont faunas of the Permian and Triassic, the available evidence indicates that the end-Permian extinction resulted in a distinct uniformity that was unique to Early Triassic anomodont faunas. This is in particular characterized by the global distribution and overwhelming abundance of the disaster taxon Lystrosaurus. In contrast, cosmopolitan anomodonts also existed in the Late Permian (e.g., Diictodon) and Middle Triassic (e.g., Shansiodon), but those taxa coexisted with endemic faunal elements rather than dominated the fauna as Lystrosaurus did.     

Permian-Triassic vertebrate footprints from South Africa: Ichnotaxonomy,producers and biostratigraphy through two major faunal crises

The fossil record of mid to late Permian terrestrial vertebrates in the South African Karoo Basin is regarded as the most abundant and diverse in the world. Despite the extensive research on body fossils, to-date the vertebrate footprint sites have not been subjected to an anatomy-consistent ichnotaxonomic investigation. Here we present a comprehensive ichnotaxonomic revision of Permian-Early Triassic tracksites in the main Karoo Basin of South Africa. Furthermore, a track-trackmaker correlation for all Permian synapsid groups is provided for the first time, based on the analysis of the functional morphology of potential producers. The following ichnotaxa and their proposed trackmakers are recognized: Brontopus giganteus (dinocephalians), cf. Capitosauroides isp. (therocephalians), cf. Dicynodontipus isp. (cynodonts), Dolomitipes accordii (small dicynodonts), Dolomitipes icelsi n. comb. (large dicynodonts), Karoopes gansfonteinensis n. igen. n. isp. (gorgonopsids), Procolophonichnium nopcsai (procolophonids) and Rhynchosauroides isp. (non-archosauriform diapsids). Three different footprint assemblages (FA I–III) are proposed for footprint biostratigraphy: FA I (lower Tapinocephalus AZ), a Guadalupian assemblage dominated by dinocephalian tracks; FA II (topmost Tapinocephalus-Cistecephalus AZ), a latest Guadalupian-Wuchiapingian assemblage dominated by gorgonopsid and dicynodont tracks in association with subordinate therocephalian tracks and FA III (lower Lystrosaurus AZ), an Induan assemblage with dicynodont, cynodont, procolophonid and diapsid tracks. The lower FA II includes the earliest ichnofauna with Lopingian affinity all over the world (topmost Tapinocephalus-Pristerognathus AZ, ~260–259 Ma) and could indicate an early recovery phase after the end-Guadalupian mass extinction, because of the high abundance of large gorgonopsid tracks and absence of dinocephalian tracks. This footprint record may also predate the body fossil record, suggesting an earlier gorgonopsid radiation. FA III represents the earliest and most complete post end-Permian extinction ichnofauna, which includes an early phase of abundant small dicynodont tracks, potentially indicating a stressed post-event community. Nevertheless, this ichnofauna looks very similar to pre-extinction ichnofaunas from Europe, in agreement with the skeletal record at the Daptocephalus-Lystrosaurus AZ transition.     

An anatomy-consistent study of the Lopingian eolian tracks of Germany and Scotland reveals the first evidence of the end-Guadalupian mass extinction at low paleolatitudes of Pangea

The poor preservation and apparent monospecifity of Permian tetrapod footprints from eolian paleoenvironments have thus far hampered their reliable interpretation. This study clarifies how this is due to distinct and repeated ichnotaphonomic effects on trackway pattern and footprint morphology on originally inclined planes. Once these effects are excluded, the anatomy-consistent ichnotaxobases useful for ichnotaxonomy can be recognized. Several nomina dubia are identified, among these the ichnogenus Chelichnus, here considered a taphotaxon. The eolian ichnoassociations from the Lopingian of Scotland and Germany include six different ichnotaxa: cf. Capitosauroides isp. (?eutheriodont therapsid), Dicynodontipus geinitzi (cynodont therapsid), Dolomitipes isp. (dicynodont therapsid), Pachypes loxodactylus n. comb. (pareiasaurian parareptile), Procolophonichnium isp. (small parareptile) and Rhynchosauroides isp. (non-archosauriform neodiapsid). This is completely different from the interpretations of the last 20 years, which postulated that these paleoenvironments comprised monospecific associations of synapsid tracks. These ichnoassociations are instead moderately diverse, similar to low-latitude marginal marine to floodplain ichnoassociations and belong to the Lopingian Paradoxichnium footprint biochron. The Cornberg Formation of Germany, being constrained between the Illawarra reversal and the mid-Wuchiapingian Kupferschiefer at the Rotliegend/Zechstein transition, constitutes the earliest evidence of Lopingian tetrapod faunas at low paleolatitudes and the first evidence of low-paleolatitude faunal turnover related to the end-Guadalupian mass extinction from both the skeleton and the track record. This suggests a global extension of the dinocephalian extinction event, which occurred at high-mid (South Africa and Russia) and low (Western Europe) paleolatitudes of Pangea about 259–260 Ma and was probably triggered by the eruption of the Emeishan Large Igneous Province of SW China, which considerably changed global environmental conditions in both marine and continental settings.     

Rapid vertebrate recuperation in the Karoo Basin of South Africa following the End-Permian extinction

The mass extinction that occurred at the end of the Permian Period approximately 251 Mya is widely accepted as the most devastating extinction event in Earth’s history. An estimated 75–90% of global diversity from both marine and terrestrial realms disappeared synchronously within at most one million and perhaps as little as 100,000 years. To date, most research has focused on the marine record and it is only recently that a few fully preserved terrestrial Permo-Triassic boundary sequences have been discovered. The main Karoo Basin of South Africa hosts several well-preserved non-marine Permo-Triassic boundary sequences that have been the focus of intensive research into the nature of the extinction and its possible causes. This study uses sedimentological and biostratigraphic data from boundary sequences near Bethulie in the southern Karoo Basin to make assumptions about the rates and timing of recovery of the terrestrial fauna in this portion of southern Gondwana after the extinction event. The biostratigraphic data gathered from 277 in situ vertebrate fossils allows us to define more accurately the temporal ranges of several taxa. These data also confirm a more precise extinction rate in this part of the basin of 54% of latest Permian vertebrate taxa, followed by the onset of a relatively rapid recovery, within an estimated 40–50 thousand years (based on the calculation of floodplain aggradation rates and compaction ratios) that included the origination of at least 12 new vertebrate taxa from amongst the survivors.     

A Review on the Global Stratotype Section and Point of the Permian-Triassic Boundary

1 Introduction The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary (PTB) has been ratified by IUGS in 2001 (Yin et al., 2001). It is defined at the base of the Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan Section D, Changxing County, Zhejiang Province, South China. The PTB is important because it is not only an erathem boundary but also a great turning point of geological history symbolized by profound global changes and the strongest …     

Global climate perturbations during the Permo-Triassic mass extinctions recorded by continental tetrapods from South Africa

Several studies of the marine sedimentary record have documented the evolution of global climate during the Permo-Triassic mass extinction. By contrast, the continental records have been less exploited due to the scarcity of continuous sections from the latest Permian into the Early Triassic. The South African Karoo Basin exposes one of the most continuous geological successions of this time interval, thus offering the possibility to reconstruct climate variations in southern Laurasia from the Middle Permian to Middle Triassic interval. Both air temperature and humidity variations were estimated using stable oxygen (δ¹⁸O_p) and carbon (δ¹³C_c) isotope compositions of vertebrate apatite. Significant fluctuations in both δ¹⁸O_p and δ¹³C_c values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution. In terms of air temperature, oxygen isotopes show an abrupt increase of about + 8 °C toward the end of the Wuchiapingian. This occurred during a slight cooling trend from the Capitanian to the Permo-Triassic boundary (PTB). At the end of the Permian, an intense and fast warming of + 16 °C occurred and kept increasing during the Olenekian. These thermal fluctuations may be related to the Emeishan (South China) and Siberian volcanic paroxysms that took place at the end of the Capitanian and at the end of the Permian, respectively. Vertebrate apatite δ¹³C_c partly reflects the important fluctuations of the atmospheric δ¹³C values, the differences with marine curves being likely due to the evolution of local humidity. Both the oxygen and carbon isotope compositions indicate that the PTB was followed by a warm and arid phase that lasted 6 Ma before temperatures decreased, during the Late Anisian, toward that of the end-Permian. Environmental fluctuations occurring around the PTB that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release.     

Large Tetrapod Burrows from the Permian Naobaogou Formation of the Daqingshan Area,Nei Mongol,China

Two new tetrapod burrow casts from the Naobaogou Formation （Middle or Late Permian） of Nei Mongol,China are described.It marks the first pre-Cenozoic tetrapod burrow from China,and one of the earliest records of tetrapod burrows.Comparison to other Permian and Triassic burrows suggests that these burrows were created by tetrapod slightly smaller than Lystrosaurus.Deduced from the morphology and sizes of two burrows and known tetrapods of the Naobaogou Formation,the burrow should be the production of a therapsid,most likely a dicynodon.These burrows indicate a seasonal climate and this area was semiarid or arid during that time.     

Molecular carbon isotope variations in core samples taken at the Permian–Triassic boundary layers in southern China

Stable carbon isotope composition (δ¹³C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian–Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian–Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C₁₅ to C₄₀, steranes (C₂₇ dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C₂₅, and squalane, are depleted in δ¹³C by up to 8–10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian–Triassic boundary.     

Late Permian–Early Triassic environmental changes recorded by multi-isotope (Re-Os-N-Hg) data and trace metal distribution from the Hovea-3 section,Western Australia

The temporal coincidence between the Late Permian mass extinction (LPME) and the emplacement of Siberian Trap basalts suggests a causal link between the two events. Here, we discuss stratigraphic changes of organic and inorganic (including isotopic) geochemical properties of marine sediments across the Permian–Triassic boundary (PTB) in the Hovea-3 core, Western Australia, a key PTB section in the southern Neo-Tethys ocean. These data are compared with published data from the Meishan section, southern China, and from the Opal Creek section in western Canada, providing a view of Tethys and Panthalassa changes at the PTB. Trace metal and N-isotopic data, together with organic matter properties suggest that anoxic conditions were established prior to the LPME, intensified close to the LPME, and continued with photic-zone euxinia into the Early Triassic. For the Hovea-3 section, Re-Os ages confirm Changhsingian (253.5 ± 1.4 Ma) deposition of the dated interval sampled immediately below the stratigraphic level characterized by major lithological and isotopic changes. Evaluation of Re-Os, N, and Hg elemental and isotopic data for Hovea-3 suggests that anoxic conditions in the latest Permian were generally unrelated to direct magmatic contributions. A major increase in the initial Os isotopic ratio of Lower Triassic shales suggest an ~8× increase in the Early Triassic continental runoff, based on moderately conservative assumptions for end-members contributing Os to the Permian–Triassic ocean. Comparison to other PTB sections confirms a global signal of increasing Re/Os ratios in the Late Permian, and major and long-lived changes in the isotopic composition of the post-extinction ocean. A distinct peak in Hg concentrations carrying a volcanic isotopic signature, also identified in other PTB sections, likely represents a major pulse of Siberian Trap volcanism. This Hg peak in the Hovea-3 section, however, is detected above the stratigraphic level containing multiple other widely recognized and more permanent geochemical changes. Therefore, direct volcanic inputs to the Permian–Triassic Ocean likely post-date the LPME in this Western Australian section.     

湖北秭归吴家坪组—长兴组界线氧化还原条件及其意义

二叠纪发生了两次重大生物灭绝事件，一次是位于吴家坪初期即瓜德鲁普世末生物灭绝事件，另一次是位于长兴末期即晚二叠世末生物灭绝事件。在这两次生物灭绝事件之间的大约八百万年时间里，其环境变化研究相对较少，古海洋的氧化还原条件变化目前尚未清楚。通过分析湖北秭归县杨林剖面的黄铁矿形态来探讨吴家坪组-长兴组界线氧化还原条件及其意义。研究结果表明:吴家坪组与长兴组石灰岩沉积时期的古海水主要是贫氧至氧化环境。在吴家坪组上部至长兴组下部地层沉积时期古水体出现间歇性硫化现象。该硫化缺氧事件不仅出现在秭归地区，还广泛分布于鄂西盆地、扬子台地南缘南盘江盆地、阿拉伯地台以及东格陵兰盆地地区。这说明吴家坪-长兴组界线沉积时期的间歇性硫化缺氧事件有可能是一个全球性事件。该事件可能与二叠末事件有一定的关联。     

Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) revisited

As integral parts of du Toit’s (1927) “Samfrau Geosyncline”, the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) share similar paleoclimatic, paleogeographic, and paleotectonic aspects related to the Late Paleozoic tectono-magmatic activity along the Panthalassan continental margin of Gondwanaland. Late Carboniferou-earliest Permian glacial deposits were deposited in the Sauce Grande (Sauce Grande Formation) and Karoo (Dwyka Formation) basins and Falkland–Malvinas Islands (Lafonia Formation) during an initial (sag) phase of extension. The pre-breakup position of the Falkland (Malvinas) Islands on the easternmost part of the Karoo basin (immediately east of the coast of South Africa) is supported by recent paleomagnetic data, lithofacies associations, paleoice flow directions and age similarities between the Dwyka and the Lafonia glacial sequences. The desintegration of the Gondwanan Ice Sheet (GIS) triggered widespread transgressions, reflected in the stratigraphic record by the presence of inter-basinally correlatable, open marine, fine-grained deposits (Piedra Azul Formation in the Sauce Grande basin, Prince Albert Formation in the Karoo basin and Port Sussex Formation in the Falkland Islands) capping glacial marine sediments. These early postglacial transgressive deposits, characterised by fossils of the Eurydesma fauna and Glossopteris flora, represent the maximum flooding of the basins. Cratonward foreland subsidence was triggered by the San Rafael orogeny (ca. 270 Ma) in Argentina and propogated along the Gondwanan margin. This subsidence phase generated sufficient space to accommodate thick synorogenic sequences derived from the orogenic flanks of the Sauce Grande and Karoo basins. Compositionally, the initial extensional phase of these basins was characterized by quartz-rich, craton-derived detritus and was followed by a compressional (foreland) phase characterized by a paleocurrent reversal and dominance of arc/foldbelt-derived material. In the Sauce Grande basin, tuffs are interbedded in the upper half of the synorogenic, foldbelt-derived Tunas Formation (Early–early Late? Permian). Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late Early Permian (260?Ma) age. Silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) peaked between the late Early Permian and Late Permian. A link between these volcanics and the consanguineous airborne tuffs present in the Sauce Grande and Karoo basins is suggested on the basis of their similar compositions and ages.     

Landscape ecological shift at the Permian‐Triassic boundary in Antarctica

Palaeosols across the Permian‐Triassic boundary in Antarctica provide evidence of a marked change in ecosystems at this greatest of all extinctions in the history of life on Earth. The boundary can now be recognised from evidence of carbon isotopic (δ¹³C) stratigraphy, reptiles of the earliest Triassic Lystrosaurus zone, and Late Permian glossopterid fructifications and pollen. The boundary is a profound change in palaeosols, with very different suites of pedotypes in Permian compared with Triassic sequences. Permian palaeosols include coals, rooted lithic sandstones and rooted tuffaceous silt‐stones. Triassic palaeosols in contrast are largely rooted, green‐red‐mottled claystones. These palaeosols represent a shift from Late Permian cold temperate broadleaf deciduous swamp woodlands to Early Triassic cool temperate conifer forests. Indications of more intense weathering during the earliest Triassic confirm a significantly warmer palaeoclimate in the earliest Triassic than in the latest Permian. Palaeoclimate remained humid with low evapotranspiration in both Permian and Triassic, but Triassic ecosystems were more oligotrophic, humus‐poor and more oxidised than Permian ones. Yet both Permian and Triassic palaeosols were unpodzolised, unlike soils today under such climates and vegetation. Palaeosols in Antarctica confirm several peculiarities of the earliest Triassic: (i) a global coal gap; (ii) a high‐latitude greenhouse; and (iii) a Gondwanan tuff gap. Palaeosols support evidence from fossil plants and reptiles and from carbon isotopic studies for a shift toward oligotrophic, low‐productivity ecosystems, dominated by opportunistic and stress‐tolerant organisms in the earliest Triassic. Life was difficult on land as well as in the sea following the terminal Permian mass extinction.     

The plant fossil record reflects just two great extinction events

Five great taxonomic extinctions (the so‐called ‘Big Five Mass Extinctions’) are widely recognized in life history, at the end of the Ordovician, Frasnian (Late Devonian), Permian, Triassic and Cretaceous. All of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes. Previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events, but it is unknown whether they suffered the same level of large‐scale taxonomic disruption as marine organisms. Here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events, one through the Carboniferous‐Permian transition, the other during middle‐late Permian times. This differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes.     

Ocean Chemistry Revealed by Mineralogical and Geochemical Evidence at the Permian–Triassic Mass Extinction, Offshore the Persian Gulf, Iran

The Upper Permian Dalan Formation and the Lower Triassic Kangan Formation in the Persian Gulf area are mainly composed of shallow marine facies limestone and dolomite. Two subsurface-cored intervals were investigated in order to understand the original mineralogy and paleoceanic conditions. The decreasing trend of Sr concentration in these deposits shows that aragonite was precipitated during the Late Permian and then gradually changed to calcite toward the Permian–Triassic boundary (PTB). The dissolution rate of aragonite decreased from 60 m below the PTB toward the boundary, with the only exception at 10 m below the Permian-Triassic Boundary (PTB) due to the Permian–Triassic unconformity in this region. The increasing trend of Mg/Ca ratio in a global scale at the end-Permian time shows that the interpreted variation of mineralogy does not result from the change of this ratio. The increasing pCO2 and decreasing pH are considered to be the main controlling factors. The increase of Ca2+ at the end-Permian time due to the input of meteoric waters is too little to fully compensate this effect. A local maximum of the Si content just at the PTB confirms the input of runoff waters.     

Magnetostratigraphic correlations of Permian–Triassic marine-to-terrestrial sections from China

We have studied three Permian–Triassic (PT) localities from China as part of a combined magnetostratigraphic, ⁴⁰Ar/³⁹Ar and U–Pb radioisotopic, and biostratigraphic study aimed at resolving the temporal relations between terrestrial and marine records across the Permo-Triassic boundary, as well as the rate of the biotic recovery in the Early Triassic. The studied sections from Shangsi (Sichuan Province), Langdai (Guihzou Province), and the Junggar basin (Xinjiang Province), span marine, paralic, and terrestrial PT environments, respectively. Each of these sections was logged in detail in order to place geochronologic, paleomagnetic, geochemical, conodont and palynologic samples within a common stratigraphic context. Here we present rock-magnetic, paleomagnetic and magnetostratigraphic results from the three localities.At Shangsi, northern Sichuan Province, we sampled three sections spanning Permo-Triassic marine carbonates. Magnetostratigraphic results from the three sections indicate that the composite section contains at least eight polarity chrons and that the PT boundary occurs within a normal polarity chron a short distance above the mass extinction level and a reversed-to-normal (R-N) polarity reversal. Furthermore, the onset of the Illawarra mixed interval lies below the sampled section indicating that the uppermost Permian Changhsingian and at least part of the Wuchiapingian stages postdate the end of the Kiaman Permo-Carboniferous Reversed Superchron.At Langdai, Guizhou Province, we studied magnetostratigraphy of PT paralic mudstone and carbonate sediments in two sections. The composite section spans an R-N polarity sequence. Section-mean directions pass a fold test at the 95% confidence level, and the section-mean poles are close to the mean PT pole for the South China block. Based on biostratigraphic constraints, the R-N transition recorded at Langdai is consistent with that at Shangsi and demonstrates that the PT boundary occurred within a normal polarity chron a short distance above the mass extinction level.In the southern Junggar basin, Xinjiang Province, in northwest China, we determined the magnetostratigraphy of three sections of a terrestrial sequence. Normal and reversed polarity directions are roughly antipodal, and magnetostratigraphies from the three sections are highly consistent. Combined bio- and magneto-stratigraphy used to correlate this sequence to other PT sequences suggests that the previously-proposed biostratigraphic PT boundary in the Junggar sections was most likely misplaced by earlier workers suggesting that further work is necessary to confidently place the PT boundary there.     

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.     

贵州罗甸二叠纪末生物大灭绝事件后沉积的微生物岩时代和沉积学特征

二叠纪末期发生的显生宙以来最大的生物绝灭事件,使海洋生态系统和陆地生态系统均受到重创之后,微生物岩广泛分布于全球正常浅海地区。研究认为,扬子地台在二叠纪末期存在一次海平面降低的事件,造成研究区二叠纪地层与早三叠世微生物岩之间存在沉积间断或剥蚀,并使三叠纪牙形石混入二叠纪末期的沉积物中。二叠-三叠系界线位于微生物岩层的底界;微生物岩形成于早三叠世最早期,相当于Hindeodus parvus带,是早三叠世最早期开始的海侵事件为其提供生长所需的可容纳空间。在Isarcicella staeschei带-I. isarcica带早期再次发生相对海平面降低事件,之后海平面开始快速上升。研究区早三叠世早期的微生物岩以凝块构造发育为特征,具有斑状、层状、枝状和网状凝块构造4种典型中型构造。结合前人的工作,认为微生物群落通过生物沉积和物理沉积作用形成球状体,球状体汇聚形成不同的中型凝块构造。研究扬子地台早三叠世凝块石的确切时代和结构、构造类型特征,为准确恢复生物大灭绝事件前后的环境变迁以及生物演化事件与环境变化的相互作用关系提供重要的证据。     

湖北黄石二门二叠系/三叠系界线剖面长兴阶牙形刺分带及有机碳同位素的变化

湖北黄石二门二叠系/三叠系界线剖面出露完好,原始沉积连续,由乐平统龙潭组保安段灰黑色硅质岩、大隆组黑色硅质岩—硅质泥岩和下三叠统大冶组黑灰色泥岩以及泥岩夹灰岩组成,为介于典型浅水碳酸盐岩型与深海硅质岩型二叠系/三叠系界线剖面之间的半深海剖面。长兴阶可划分为Clarkinasubcarinata—Clarkinawangi及Clarkinachangxingensis两个牙形刺带。后者又可划分为3个亚带,自下而上依次为Clarkinachangxingensischangxingensis—Clarkinadeflecta亚带、Clarkinameishanensis亚带及Waning—Clarkina亚带,完全可以与二叠系/三叠系界线的全球层型剖面与点进行对比。另外,二叠纪末牙形刺的生态演化呈阶段性绝灭模式;有机碳同位素值在二叠纪/三叠系界线处出现明显的负偏移,指示了二叠纪/三叠纪之交生物绝灭后海水表层水原始产率的降低以及大气和海水中CO2含量的增加。     

Effects of the Permian–Triassic boundary on reservoir characteristics of the South Pars gas field,Persian Gulf

The Permian–Triassic boundary (PTB) is a world‐wide event characterized by the most extensive mass extinction in the history of life. In the Persian Gulf, the rock record of this time interval host one of the most important hydrocarbon reserves in the world: the South Pars Gas Field and its southern extension, the North Dome (or North Field). These carbonate and evaporite successions were sampled in eight wells for petrographic, geochemical and porosity–permeability studies. An important characteristic of the Dalan and Kangan formations is the centimetre‐scale lithological heterogeneities caused by facies changes and diagenetic imprints that led to the compartmentalization of these reservoirs. These Permian–Triassic (P‐T) sediments were deposited in a shallow marine homoclinal ramp. The PTB in this hydrocarbon field is represented by a reworked coarse‐grained intraclastic/bioclastic grainstone facies deposited during a marine transgression. Prolonged subaerial exposure in the P‐T transition caused hypersaline and meteoric diagenesis, including extensive cementation, dolomitization and some dissolution, influencing reservoir characteristics of bordering units. Both δ¹⁸O and δ¹³C values in this succession mirror worldwide excursions typical of other P‐T sections, with some variations due to diagenetic alterations. A pronounced decline in ⁸⁷Sr/⁸⁶Sr values, reflective of global seawater geochemistry for most of the Permian is evident in our data. Reservoir quality declines through the late Permian, as a result of facies change and diagenesis. The Late Permian is succeeded by a Triassic transgressive facies and decline in reservoir quality. Copyright © 2009 John Wiley & Sons, Ltd.