U-Pb calcite age of the Late Permian Castile Formation, Delaware Basin: a constraint on the age of the Permian-Triassic boundary (?)

Organic-rich calcite laminated with gypsum in the evaporitic, non-fossiliferous Castile Formation of the Delaware Basin, southwest USA, yields a Total Pb/U isochron age of 251.5±2.8 Ma (MSWD=1.3). The Castile Formation is almost certainly Late Permian based on its ⁸⁷Sr/⁸⁶Sr value of 0.706923, identical to the distinct minimum in the late Permian Sr curve. In this paper we explore the potential for using U-Pb calcite ages to date traditionally undatable sections and show how this southern-midcontinent USA (far west Texas and southeast New Mexico) deposit can be correlated to the type section in China. We accept that diagenetic alteration can bias U-Pb results, but the data set we present shows no evidence for such alteration. Clearly with alteration the age we present would represent a minimum age for the Castile Formation. If the age actually dates the Castile Formation then it requires the Permian-Triassic boundary to be younger than 251.5±2.8 Ma.     

The Permian-Triassic boundary event: a geochemical study of three Chinese sections

Trace elements were determined in two well-documented Chinese Permian-Triassic (P/Tr) boundary sections (Meishan and Shangsi) and in a new section (Liangfenya). Iridium concentrations range from 3 to 87 pg/g, at or below levels in common sedimentary rocks. The results contrast with previous reports of high Ir concentration in the Meishan and Shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the Permian. A notable feature in each of these widely separated P/Tr sections (500–1500 km) is the existence of 2–5 light-colored clay layers at and near the boundary. These clay layers are strongly enriched in Cs, Zr, Hf, Ta, and Th and depleted in Cr, Co, and Ir, indicating that they are altered ash, apparently from the same massive silicic volcanic eruptions. We estimate the magnitude of these eruptions to be a few thousand km³ of magma, a volume comparable to the great Toba eruption.     

Microbial influences on paleoenvironmental changes during the Permian-Triassic boundary crisis

The biosphere interacts and co-evolves with natural environments.Much is known about the biosphere’s response to ancient environmental perturbations,but less about the biosphere’s influences on environmental change through earth history.Here,we discuss the roles of microbes in environmental changes during the critical Permian-Triassic(P-Tr)transition and present a perspective on future geomicrobiological investigations.Lipid biomarkers,stable isotopic compositions of carbon,nitrogen and sulfur,and mineralogical investigations have shown that a series of microbial functional groups might have flourished during the P-Tr transition,including those capable of sulfate reduction,anaerobic H2S oxidation,methanogenesis,aerobic CH4oxidation,denitrification,and nitrogen fixation.These microbes may have served to both enhance and degrade the habitability of the Earth-surface environment during this crisis.The integrated microbial roles have enabled the Earth’s exosphere to be a self-regulating system.     

Absence of extraterrestrial He in Permian-Triassic age sedimentary rocks

Helium concentration and isotopic composition were measured in a suite of samples across the Permian-Triassic boundary at Opal Creek, Canada, to determine whether high extraterrestrial helium concentrations are associated with a possible extinction-inducing impact event at this time. No extraterrestrial ³He was detected, implying that neither fullerene-hosted nor IDP-hosted He is present at or near the boundary. This observation is consistent with similar studies of some Permian-Triassic sections, but contrasts sharply with reports of both fullerene- and IDP-hosted extraterrestrial ³He at other sections.Step-heat experiments indicate rapid diffusion of extraterrestrial helium from sediments heated to temperatures above ∼ 70 °C. Given the likelihood of burial and associated heating in Permian-Triassic age rocks, the initially unexpected absence of IDP-hosted ³He likely indicates thermally induced diffusive loss. Indeed one of the key sections (Graphite Peak, Antarctica) from which extraterrestrial ³He has been reported at and near the Permian-Triassic boundary has been sufficiently heated that the reported preservation of extraterrestrial helium, in both IDPs and fullerenes, is inexplicable. Recent contamination provides a plausible explanation for extraterrestrial ³He in these samples.While no extraterrestrial ³He was detected at Opal Creek, there is a sharp increase in nucleogenic ³He very close to or at the Permian-Triassic boundary. This presumably arises from the major lithologic change at this time, from cherts in the Permian to shales and siltstones in the Triassic. Increased nucleogenic ³He is associated with increases in both lithium and organic carbon content into the Triassic. Either the production rate or the retention of this ³He is higher in the shales and siltstones than in the cherts. Care must be taken to eliminate such artifacts before interpreting changes in ³He concentration in terms of fluctuations in the delivery of ³He from space.     

Geochemical characteristics of pelagic chert sequences across the Permian-Triassic boundary in southwest Japan

Abstract Geochemical characteristics, mainly of major and trace elements and REE (rare earth elements) of bedded chert and shale/mudstone sequences, across the Permian/Triassic boundary in southwest Japan are examined. The boundary is characterized by the disappearance of bedded cherts, and the interval between the Upper Permian cherts and Lower Triassic (probably Smithian) cherts comprises siliceous shales and organic black mudstones. Bedded cherts are characterized by a gradual depletion of chemical elements from Middle to Upper Permian. However, overlying siliceous shales exhibit a clear enrichment in some elements, especially alkaline metals (such as K, Rb and Cs) and Ti, Th, Y, P₂O₅, and REE in comparison with elements of the PAAS (post Archean Australian shales). This indicates that average components of the upper continental crust were transported in the boundary interval, possibly caused by volcanic activity. Ce-negative shifting in NASC (North American Shales Composite)-normalized REE patterns is characteristic of this interval, and could be related to the deposition of siliceous rocks in Ce-depleted seawater. This was probably caused by an invasion of water mass with a Ce-negative anomaly into the previously existing water mass of the Paleo-Tethys. Weak negative Eu-anomalies in this interval are suggestive of plagioclase fractionation caused by acid volcanisms and the LREE/HREE ratios in the interval show a slightly light-REE enrichment. Organic black mudstones are characteristically intercalated in the interval. These rocks are usually regarded as a product of oceanic deterioration, but in pelagic conditions, organic materials were formed by high primary production that resulted from the active upwelling of ocean floor water currents with rich nutrients. This may have been caused by the inferred mixing of water masses of the Paleo-Tethys and of the Panthalassa in Early Triassic time which was regarded as an event synchronous with an increase in volcanic activity on highly matured island arcs and/or continents.     

Timing of the terrestrial Permian-Triassic boundary biotic crisis: Implications from U-Pb dating of authigenic zircons

The Late Permian to Early Triassic transition represents one of the most important Phanerozoic mass extinction episodes. The cause of this event is still in debate between catastrophic and gradual mechanisms. This study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic clay deposits at Chahe (Guizhou Province, SW China) to examine time constraints for this event. The results of both this and previous studies show that the ages of Bed 68a and 68c (the upper clay bed of the terrestrial Permian-Triassic boundary (PTB)) respectively are 252.6±2.8 and 247.5±2.8 Ma. This age (within the margin of error) almost accords with the upper clay bed (Bed 28) age of Meishan and the eruption age of Tunguss Basalt, and is so far the most accurate age obtained from terrestrial PTB. The claystone of Bed 68 was formed in the earliest Triassic. The biotic crisis occurred at nearly the same time in terrestrial and marine environments during Permian-Triassic interval; however the extinction patterns and processes are different. The extinction pattern of the terrestrial plants shows a major decline at the PTB after long-term evolution, followed by a retarded extinction of the relicts in the earliest Triassic.     

Paleo-redox conditions across the Permian-Triassic boundary in shallow carbonate platform of the Nanpanjiang Basin,South China

Ocean anoxia has been widely implicated in the Permian-Triassic extinction.However,the duration and distribution of the ocean anoxia remains controversial.In this study,the detailed redox changes across the Permian-Triassic boundary(PTB)in the shallow platform interior at Great Bank of Guizhou(GBG)has been reconstructed based on the high-resolution microfossil composition and multiple paleo-redox proxies.The shallow platform is characterized by low sulfur(total sulfur(TS)and pyrite sulfur(Spy))concentrations,low Spy/TOC ratios,and low DOP values before the mass extinction,representing oxic conditions well.Following the mass extinction,the shift of multiple geochemical proxies,including high Spy/TOC ratios and DOP values,indicates dysoxic-anoxic conditions in shallow ocean.Furthermore,we reconstruct the transition of the redox conditions of Nanpanjiang Basin:the intense volcanic eruptions,which release huge CO2 and SO2 before the mass extinction,provoke the temperature rising and the collapse of terrestrial ecosystem.As a result,the increased weathering influx causes the carbon isotopic negative excursion and the expansion of the ocean oxygen minimum zone(OMZ).When the OMZ expanded into the photic zone,the episodic H2S release events enhance the pyrite burial at Dajiang section.Thus,intense volcanic eruptions,temperature increase,and oceanic hypoxia together lead to the PTB extinction.Recent studies show high temperature might be the key mechanism of the PTB extinction.In addition,this study confirms that the microbialites were formed in the dysoxicanoxic shallow water.     

The shift of biogeochemical cycles indicative of the progressive marine ecosystem collapse across the Permian-Triassic boundary: An analog to modern oceans

Global warming, the most severe faunal mass extinction and the shift of biogeochemical cycles were observed in the ocean across the Permian-Triassic boundary about 252 million years ago, providing an analog to understanding the modern oceans. Along with the progressive global warming, the biogeochemical cycle was documented to show a shift from the decoupled processes of carbon, nitrogen and sulfur prior to the mass extinction to the coupled biogeochemical processes during faunal mass extinction. The coupled biogeochemical cycle was further observed to shift from the coupled C-N processes during the first episode of the faunal mass extinction to the coupled C-N-S processes during the second episode, diagnostic of the progressive development of more deteriorated marine environmental conditions and the more severe biotic crisis across the Permian-Triassic boundary. The biogeochemical cycles could thus be an indication to the progressive collapse of marine ecosystems triggered by the global warming in Earth history. In modern oceans, the coupled C-N cycle triggered by the global warming was observed in some regions. If these local C-N processes develop and expand to the global oceans, the coupled C-N-S processes might be brought into existence and the marine ecosystems are inevitable to suffer from complete collapse as observed at 252 million years ago.     

The age of the Miocene-Pliocene boundary in the Capo Rossello area (Sicily)

Detailed correlations of magnetostratigraphy, biostratigraphy and lithostratigraphy reveal that the basal Pliocene is equally complete in the Eraclea Minoa and Capo Rossello sections (Sicily) and the Singa section (Calabria), and that, in accordance with the model of the Pliocene flooding event in the Mediterranean, the deposition of the pelagic marls of the Trubi Formation started synchronously on Sicily and in adjacent Calabria. In addition, the data obtained from the Trubi in the Eraclea Minoa section allows the age of the Miocene-Pliocene boundary to be adjusted slightly from 4.83–4.84 [1] to 4.86 Ma because downward extrapolation of both sedimentation rate and average duration of small-scale sedimentary cycles in the Trubi yields this age for the boundary in this section. Linearly interpolated ages for the top of the Sphaeroidinellopsis acme and the first substantial increase in Globorotalia margaritae (the FOD of this species is non-existent in the Mediterranean Pliocene) at Eraclea Minoa arrive at 4.74 and 4.63 Ma respectively.Because of the detailed magnetostratigraphy and the very accurate dating of the Miocene-Pliocene boundary, it is preferable to select the Eraclea Minoa section as the boundary stratotype rather than the Capo Rossello section.Finally, this age of 4.86 Ma for the Miocene-Pliocene boundary suggests that the beginning of the Pliocene is connected with the termination of a series of latest Miocene glaciations and that the re-establishment of open marine conditions in the Mediterranean might be of glacio-eustatic origin.     

Ostracod fauna across the Permian-Triassic boundary at Chongyang, Hubei Province, and its implication for the process of the mass extinction

Thirty species of 10 ostracod genera were identified from 440 fossil specimens isolated through the hot acetolysis of the rock samples collected across the Permian-Triassic boundary at Chongyang section. Twenty species of 6 genera are found to occur in the limestone of Changxing Formation, and 11 species of 7 genera above the main faunal mass extinction horizon. The os-tracod assemblages identified at the Chongyang section are obviously different from those previously reported in the contem-poraneous microb...     

Paleo-productivity evolution across the Permian-Triassic boundary and quantitative calculation of primary productivity of black rock series from the Dalong Formation,South China

The change of the primary productivity across the Permian-Triassic boundary(PTB)remains controversial.In this study,records from two deep-water sections in South China(Xiakou and Xinmin sections)show the primary productivity decreased gradually from the latest Permian to the earliest Triassic,and five evolutionary stages Increase-Decrease-Recovery-RecessionStagnation)can be observed from Clarkina changxingensis-C.deflecta to Hindeodus parvus-Isarcicella isarcica zones.Primary productivity decreased abruptly from the base of C.meishanensis zone.Besides,for adjusting to the deterioration of the oceanic environment,the primary producers in the oceanic surface had changed to acritarch and cyanobacteria,which were more tolerant of stressful environment.Then the producers were under huge stagnation in the H.parvus-I.isarcica zone.The values of quantitative calculation of the primary productivity from the black rock series in the Dalong Formation were very high,corresponding to that of an upwelling area in modern ocean,which shows that the strata of the Dalong Formation in the study region are potential hydrocarbon source-rocks.This result may come from the fact that South China craton was located at the equatorial upwelling area during the Permian-Triassic transitions.But organic matter contents were different in various sections because they could be affected by redox conditions and diagenesis process after burial.     

An accurately delineated Permian-Triassic Boundary in continental successions

The Permian-Triassic Boundary Stratigraphic Set (PTBST), characteristic of the GSSP section of Meishan and widespread in marine Permian-Triassic Boundary (PTB) sequences of South China, is used to trace and recognize the PTB in a continental sequence at Chahe (Beds 66f―68c). Diversified Permian plant fossils extended to the PTBST, and a few relicts survived above that level. Sporomorphs are dominated by fern spores of Permian nature below the PTBST, above which they are replaced by gymnosperm pollen of Triassic aspect. In the nearby Zhejue Section, the continental PTBST is charac- terized by the fungal 'spike' recorded in many places throughout the world. The boundary claybeds (66f and 68a,c) of the PTBST are composed of mixed illite-montmorillonite layers analogous with those at Meishan. They contain volcanogenic minerals such as β quartz and zircon. U/Pb dating of the upper claybed gives ages of 247.5 and 252.6 Ma for Beds 68a and 68c respectively, averaging 250 Ma. In con- trast to the situation in Xinjiang and South Africa, the sediment sequence of the Permian-Triassic tran- sition in the Chahe section (Beds 56―80) become finer upward. Shallowing and coarsening upward is not, therefore, characteristic of the Permian-Triassic transition everywhere. The occurrence of relicts of the Gigantopteris Flora in the Kayitou Fm. indicates that, unlike most marine biota, relicts of this pa- leophytic flora survived into the earliest Triassic. It is concluded that Bed 67 at Chahe corresponds to Bed 27 at Meishan, and that the PTB should be put within the 60-cm-thick Bed 67b④, now put at its base tentatively. This is the most accurate correlation of the PTB in continental facies with that in the marine GSSP.     

SIMS U-Pb zircon age of a tuff layer in the Meishucun section,Yunnan, southwest China: Constraint on the age of the Precambrian-Cambrian boundary

Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out closely following the guidance of cathodoluminescence images, and the majority of analyses were conducted on the oscillatory zircon grains. Thirteen measurements yield a highly reliable Concordia U-Pb age of 536.7 ± 3.9 Ma for the Bed 5 horizon. A grand mean of 206Pb/238U age of 535.2± 1.7 Ma (...     

Geological event sequences of the Permian-Triassic transition recorded in the microfacies in Meishan section

The microfacies sequence in the key interval of Beds 24―29 of the Meishan section comprehensively recorded the geological events during the Permian-Triassic transition, including the anoxia, storm disturbance, hard-ground/firm-ground form, volcanic eruption, weathering input, and microbialite development. This investigation of event sequences on the microfacies provided synthetically some clues to clarifying the previously proposed mechanisms of the end-Permian extinction. The deposit succession in Bed 24 o...     

The age of the inner core

The energy conservation law, when applied to the Earth’s core and integrated between the onset of the crystallization of the inner core and the present time, gives an equation for the age of the inner core. In this equation, all the terms can be expressed theoretically and, given values and uncertainties of all relevant physical parameters, the age of the inner core can be obtained as a function of the heat flux at the core–mantle boundary and the concentrations in radioactive elements. It is found that in absence of radioactive elements in the core, the age of the inner core cannot exceed 2.5 Ga and is most likely around 1 Ga. In addition, to have an inner core as old as the Earth, concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds.     

The boundary layer of the residence time field

The residence time of a tracer in a control domain is usually computed by releasing tracer parcels and registering the time when each of these tracer parcels cross the boundary of the control domain. In this Lagrangian procedure, the particles are discarded or omitted as soon as they leave the control domain. In a Eulerian approach, the same approach can be implemented by integrating forward in time the advection–diffusion equation for a tracer. So far, the conditions to be applied at the boundary of the control domain were uncertain. We show here that it is necessary to prescribe that the tracer concentration vanishes at the boundary of the control domain to ensure the compatibility between the Lagrangian and Eulerian approaches. When we use the Constituent oriented Age and Residence time Theory (CART), this amounts to solving the differential equation for the residence time with boundary conditions forcing the residence time to vanish at the open boundaries of the control domain. Such boundary conditions are likely to induce the development of boundary layers (at outflow boundaries for the tracer concentration and at inflow boundaries for the residence time). The thickness of these boundary layers is of the order of the ratio of the diffusivity to the velocity. They can however be partly smoothed by tidal and other oscillating flows.     

The formation age of the Brachina meteorite

Nuclear particle tracks were studied in various phases from the Brachina meteorite, which was classified until recently as a chassignite. Fission tracks due to the decay of²⁴⁴Pu(T₁₂ = 82m.y.) were observed and indicate that Brachina formed ～ 4.5 b.y. ago in a parent body which was most probably asteroidal in size. Contrary to what has been previously suggested [7], there is no need to postulate a Martian origin for this meteorite. This conclusion is supported by independent evidence obtained by other groups.     

Microbialite of anoxic condition from Permian-Triassic transition in Guizhou,China

Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,and are evenly scattered in micritic matrix. Their abundance makes the rock as-signed to microbialites. The accompanied organisms include ostracods and algal mat,but no gastro-pods or bivalves. Presence of small (<7 μm) pyrite framboids indicates that this bed formed in anoxic conditions. In some sections,this bed is overlain and underlain by tidal-flat micritic limestone with microgastropods and small burrows. Occurrence only in deposits on reef top indicates that the micro-bial organism was benthic,and needed sunlight in life. The size of the microbial fossil exceeds that of any bacteria or cyanobacteria. Thus,it does not belong to these two phyla. It may belong to lower green algae,and is assigned to a new species in a new genus,Ziyunosphaeridium sinensis gen. et sp. nov. Up to now,the rocks described as microbialites from the Permian-Triassic transition include six types: (1) porous micritic limestone such as that descried from Japan by Sano and Nakashima (1997),(2) limestone with rich globular microfossils such as that described from the Nanpanjiang Basin in China by Lehrmann (1999),(3) dendroidal limestone such as that described from the vicinity of Chongqing by Kershaw et al. (1999),(4) spherical microbial limestone adapted to anoxic environments described from Ziyun,Guizhou reported in this paper,(5) limestone with cyanobacterial fossils such as that described by Wang et al. (2005),and (6) stromatolites. All these microbialites are not reefs in the proper sense,and the argument that Permian reef ecosystems extended into the Mesozoic is incorrect.     

Secular geomagnetic variations and volcanic pulses in the Permian-Triassic traps of the Norilsk and Maimecha-Kotui provinces

Detailed paleomagnetic studies have shown that the effusive Permian-Triassic traps in the Kotui River valley were formed as the result of volcanic activity, which occurred in the form of volcanic pulses and individual eruptions with net duration of at most 7000–8000 years, excluding the periods of volcanic quiescence. According to the analysis of the paleomagnetic data earlier obtained by Heunemann and his coauthors [2004b] on the Abagalakh and Listvyanka sections in the Norilsk region, those geological units were formed during 25 volcanic pulses and separate eruptions, which all lasted up to 8000 years altogether, whereas the total time of formation (including the periods of volcanic quiescence) exceeded 10000–100000 years for the Norilsk section and was probably a bit shorter for the Kotui section. Comparison of the positions of virtual geomagnetic poles calculated for the Norilsk and the Kotui sections provides no grounds to suggest that these sections were formed at different geological times. The scatter in the positions of the virtual geomagnetic poles (VGP) for the directional groups and individual directions (58 altogether) jointly for the two sections (more than 160 lava flows) indicates that the secular geomagnetic variations at the Permian-Triassic boundary had similar amplitudes to those that occurred in the past 5 Ma.