effect of dolomitization on isotopic records from neoproterozoic carbonates in southwestern mongolia abstract carbon isotope values from shallow marine carbonate rocks including those from many dolomitized successions are the primary lens through which we interpret the ancient carbon cycle carbon isotopes are typically regarded as being robust to alteration during dolomitization due to the high carbon content of the rock compared to the fluid however chemostratigraphic studies of the neoproterozoic tsagaan olom group in southwestern mongolia exhibit 3 12 differences in carbon isotopes between stratigraphically equivalent limestone and dolomitized successions to understand the origins of this geochemical variation we conducted detailed geological mapping petrographic isotopic 13c 18o 44 40ca and 26mg and fluid inclusion analyses of carbonates in the taishir ol and shuurgat formations of the tsagaan olom group stratigraphic and textural constraints distinguish fabric retentive early dolomitization dolomitization event 1 that occurred in the taishir and ol formations during and soon after deposition of the ca 635 ma marinoan cap dolomite of the ol formation and fabric destructive dolomitization that occurred after the deposition of the younger shuurgat formation dolomitization event 2 either prior to or during early cambrian foreland basin formation the dolomitizing fluids moved through porous stratigraphic units bound by impermeable shale of the khongor and zuun arts formations dolomitization homogenized the isotopic records of all neoproterozoic tsagaan olom group dolomites undolomitized successions show more extreme negative excursions from more positive background values the salinity and isotopic values of seawater the dolomitizing fluids and the original platform carbonate were estimated from fluid inclusion data and a numerical model of diagenetic dolomitization these results demonstrate that both early and late dolomitization can have a profound effect on carbon isotopic records of carbonates however with a multi isotope approach the original carbon isotopic composition of platform top carbonate can be distinguished from that of seawater and other dolomitizing fluids

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

chemostratigraphy indicates a relatively complete late permian to early triassic sequence in the western united states although the latest permian mass extinction and associated 13 c excursion are well documented from the tethys ocean carbonate rocks preserving these events in the eastern panthalassic ocean western pangea are unknown we present 13 c carb from the gerster and thaynes permian and triassic formations in the western united states and document a negative excursion with no evidence for major breaks in continuity to further constrain the age of the 13 c carb excursion in the absence of index fossils we analyzed the same samples for 87 sr 86 sr when examining our new carbon and sr data in the context of biostratigraphy and sequence stratigraphy we conclude that parts of the western united states may preserve carbonate successions that span the latest permian extinction

intrabasin variability of the carbon isotope record across the permian triassic transition sverdrup basin arctic canada abstract a major late paleozoic depocentre the sverdrup basin canadian high arctic has been largely left out of the latest permian extinction debate as early workers presumed middle to late permian strata were absent basin scale sequence stratigraphic and chemostratigraphic correlations indicate late permian strata are only missing on the basin margins where they were removed by sub triassic erosion whereas continuous deposition is recorded in the basin centre the varying degree of sub triassic erosion has significant impact on the carbon isotope record across the latest permian extinction event where both the apparent rate and magnitude of carbon isotope shift vary as a function of basin position the intrabasin variability in apparent 13corg shift across the event is equivalent to that observed globally in contrast to the abrupt isotope shifts recorded on the basin margin similar to many records reported globally the basin centre section shows a systematic shift associated with the latest permian extinction the earth likely underwent a prolonged period of increasing environmental stress leading up to the event

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

ultrapotassic magmas along the flanks of the oligo miocene rio grande rift usa monitors of the zone of lithospheric mantle extension and thinning beneath a continental rift

phosphorites glass ramps and carbonate factories the evolution of an epicontinental sea and a late palaeozoic upwelling system phosphoria rock complex this is the peer reviewed version of the following article matheson e j and frank t d 2020 phosphorites glass ramps and carbonate factories the evolution of an epicontinental sea and a late palaeozoic upwelling system phosphoria rock complex sedimentology doi 10 1111 sed 12731 which has been published in final form at https doi org 10 1111 sed 12731 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

garnet and pyroxenes in the mantle a test of the majorite fractionation hypothesis experimental data are reported for the compositions of garnets and pyroxenes that coexist with liquid in the system cao mgo al2o3 sio2 cmas at 80 160 kbar all experiments were run using the uniaxial split sphere apparatus at stony brook our data have permitted a refinement of gasparik s 1990a thermodynamic analysis of garnets and pyroxenes that occur at arid below the solidus our results should provide precise estimates of the temperature pressure conditions at which peridotite and garnet xenoliths equilibrated in the mantle an examination is also made of the composition of garnet that crystallizes as a liquidus phase it is demonstrated to be a function of both composition and pressure pressure has the effect of changing the composition of garnet from pyropic at around 80 kilobars to pyroxene like majorite at pressures in excess of 140 kbar changes that mirror those seen for garnets in the subsolidus failure to consider the effects of pressure on the composition of liquidus garnet can result in an erroneous test of the hypothesis that garnet fractionation occurred in early earth history it is shown that primitive mantle peridotite could have formed as a liquid by 35 majorite garnet fractionation from a cv chondrite like allende at 200 260 kbar these results support the hypothesis that extensive or possibly total melting occurred during the growth of the earth by accretion of planetesimals e g davies 1985 abe and matsui 1985 stevenson 1987 wetherill 1990 and that majorite fractionation could have occurred during this time ohtani and sawamoto 1987 removal of majorite to the lower mantle during the crystallization of a magma ocean is a successful way of explaining differences in mgo sio2 and cao al2o3 between mantle peridotite and chondrite

ti phlogopites of the shaw s cove minette a comparison with micas of other lamprophyres potassic rocks kimberlites and mantle xenoliths the two generations of micas in the shaw s cove minette mica potash feldspar lamprophyre of northern new brunswick canada are tio2 rich phlogopites with variable but low silica and potash contents low soda and efectively all their aluminum in tetrahedral sites a majority of the micas have an excess of y cations and a deficiency of x cations there are positive correlations between excess y ions and number of al ions in z sites between k2o and sio2 contents and between k2o and volatile free totals yet the micas optically appear fresh do not respond to hydration or glycolation and x ray diffraction patterns show none of the peaks of talc montmorillonites vermiculite or 7 or l4 a chlorites this suggests that some normally octahedrally coordinated cations and water or hydronium ions are located in the interlayer x sites phenocryst micas are sharply zoned cores are paler colored and have high mg atomic ratio mg mg fe 2 0 810 88 cr2o3 i 0 88 wt vo and nio i 0 08 wt but relatively low tio2 2 93 wt and negligible bao phenocryst rims and groundmass micas are darker reddish brown and have lower mg 0 68 0 79 nil crzor and nio but high tio2 x 5 40 wt and bao x 0 38 wt micas in minettes from other localities 62 analyses are frequently richer in silica and potash than the shaw s cove samples but otherwise are generally chemically comparable chemical zoning or bimodalism is nearly universal in minette micas though the boundary between high zg low tioz phenocryst and low mghigh tioz groundmass groups varies from province to province and even from minette to minette within a swarm comparison of analyses of minette micas with 353 analyses of micas from other mafic largely potassic rocks indicates that micas chemically indistinguishable from those of minettes can be found within some other lamprophyres ultra potassic rocks kimberlites and high pressure xenoliths in alkaline volcanic rocks and kimberlites though each ofthese groups also contains micas unlike those in minettes those kimberlite phlogopites that match minette micas are predominantly secondary rims of phenocrysts or megacrysts or groundmass crystals mainly type ii but some are unzoned pre fluidization phenocrysts while primary primary metasomatic and uaruo suite phlogopites of mantle xenoliths are unlike minette micas higher mg and sioz lower tio2 and alzor some of the secondary metasomatic phlogopites in sheared garnetiferous mantle xenoliths are wholly minettelike the chemical identity of minette mica phenocryst cores and some phenocrysts of diverse mantle derived rocks implies crystallization under similar conditions by analogy with the chemistry of phlogopites produced experimentally in potassic systems at high pressures and studies of equilibration conditions of natural phlogopites it is concluded that phenocrystic phlogopites in minettes may form at temperatures and pressures up to at least 1250 c and 40 kbar and probably under o conditions between the nno and hm buffers higher o than for primary primary metasomatic and uanto suite micas in kimberlites and their included xenoliths

characterization and comparison of structural and compositional features of planetary quadrilateral pyroxenes by raman spectroscopy this study reports the use of raman spectral features to characterize the structural and compositional characteristics of different types of pyroxene from rocks as might be carried out using a portable field spectrometer or by planetary on surface exploration samples studied include lunar rocks martian meteorites and terrestrial rocks the major structural types of quadrilateral pyroxene can be identified using their raman spectral pattern and peak positions values of mg mg fe ca of pyroxene in the mg fe ca quadrilateral can be determined within an accuracy of 0 1 the precision for ca mg fe ca values derived from raman data is about the same except that corrections must be made for very low ca and very high ca samples pyroxenes from basalts can be distinguished from those in plutonic equivalents from the distribution of their mg mg mg fe and wo values and this can be readily done using point counting raman measurements on unprepared rock samples the correlation of raman peak positions and spectral pattern provides criteria to distinguish pyroxenes with high proportions of non quadrilateral components from mg fe ca quadrilateral pyroxenes

high pressure minerals in mafic microgranular enclaves evidences for co mingling between lamprophyric and syenitic magmas at mantle conditions mafic microgranular enclaves composed of diopside and rare magnesium biotite phenocrysts in a groundmass of diopside biotite apatite fe ti oxides and alkali feldspar are associated with neoproterozoic piquiri potassic syenite in southern brazil co genetic mica and clinopyroxene cumulates present inclusions of pyrope rich garnet in diopside phenocrysts textural evidence as well as the chemical and mineralogical composition suggest that enclaves crystallized from a lamprophyric magma and co mingled with the host syenitic magma the contrasting temperature between both magmas and the consequent chilling was important for the preservation of some early crystallized minerals in the mafic magma diopside groundmass grains contain micro inclusions of k rich augite and phlogopite and some clinopyroxene phenocrysts and elongate groundmass crystals have potassium rich cores the pyrope rich garnet have high mg number 67 68 with appreciable amounts of na2o and k2o comparable to pyrope synthesized at 5 gpa the extremely high k2o contents of k rich augite micro inclusions suggest non equilibrium with the parental magma whereas the other k rich clinopyroxenes are similar to k clinopyroxenes produced at 5 6 gpa k clinopyroxene and garnet in mafic microgranular enclaves suggest that lamprophyric magma started its crystallization at upper mantle conditions and chilled clinopyroxenes with measurable amounts of k2o are taken as evidence that co mingling began still at mantle pressures

evidence for recurrent changes in lower triassic oceanic circulation of the tethys the δ13c record from marine sections in iran abstract stable carbon isotope curves derived from lower triassic carbonate rocks from three iranian sections are established to investigate changes in the carbon cycle during the early triassic in this area the sections are located in the south center abadeh north amol and northwest zal of iran all three curves show a similar pattern starting out with high 13 c values in the uppermost permian decreasing across the permian triassic boundary an increase toward more positive values during the griesbachian that slowly increase further up during the dienerian followed by a positive excursion to values as high as 8 near the dienerian smithian boundary during the smithian values return to below 0 whereas second positive excursion to values higher than 3 is recorded at the smithian spathian boundary again followed by a drop in 13 c into the spathian and a final excursion to positive values at the spathian anisian boundary the results from these iranian sections are consistent with previous studies from italy and china thus strongly suggesting that the recorded 13 c variability represents at least tethys wide geochemical signals moreover the new curves reveal evidence of high amplitude frequent oscillations pointing toward rapid and profound changes in the global carbon cycle during the lower triassic stratification of the ocean interrupted by episodic overturning transporting deep water to the ocean surface is a viable mechanism to account for the recorded isotope variations provided that the 13 c curve is representative of the global lower triassic ocean it has high potential for accurately dating sedimentary successions via chemostratigraphy

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

plagioclase xenocrysts and mafic magmatic enclaves in some granitoids of the sierra nevada batholith california plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts an oscillatory locally patchy zoned andesine or more calcic core a ring with dusty calcic plagioclase and a normally zoned rim of sodic plagioclase although aspect of the calcic rings and width and zoning of the rims may slightly vary from the enclaves to the hosts cores of both phenocrysts and large plagioclase crystals show similar zoning and composition the andesine or more calcic cores are interpreted to have crystallized in the felsic or the mafic magma respectively and been incorporated into the coeval magma when the two magmas mixed introduction of the xenocrystic cores into a magma where they were not in equilibrium resulted in partial dissolution development of abundant patchy zoning and coating with dusty calcic plagioclase in both granitoids and mafic magmatic enclaves composition and zoning contrast between cores and rims of the plagioclase crystals reflect drastic changes in conditions of crystallization before and after the mechanical mixing event mixing of two magmas with contrasted compositions is suggested to be the major mechanism for generating complexly zoned plagioclase xenocrysts in granitoids and mafic magmatic enclaves this hypothesis is consistent with many recent models in which mixing of two contrasting components is proposed to play a fundamental part in the generation of calc alkaline granitoids and mafic magmatic enclaves of the sierra nevada batholith plagioclase xenocrysts may also provide information on the timing of the different mixing processes and on the magmatic evolution of the plutons

subduction related shoshonitic and ultrapotassic magmatism a study of siluro ordovician syenites from the scottish caledonides syenites are important or predominant components of several plutonic complexes emplaced between 456 and 415 ma along the nw margin of the caledonian orogenic belt adjacent to the lewisian foreland in w and nw scotland although there are in detail chemical differences between the syenites from each centre they form a well defined compositional group overall ratios amongst their trace elements especially very high values of la nb are quite different from those trachytes and syenites formed by fractional crystallisation of ocean island basalts and their continental equivalents emplaced in regions of anorogenic crustal tension instead the scottish caledonian syenites closely resemble chemically the fractional crystallisation residua of potassic subduction related magmas such as the shoshonitic series a comendite minor intrusion from a swarm associated with the loch borralan and loch ailsh syenitic complexes is remarkably similar in composition to recent obsidian from the shoshonitic volcano of lipari in the aeolian arc published sr and pb isotopic ratios preclude a significant component of either upper proterozoic moine schists or lower crust granulite facies archaean lewisian or proterozoic grenvillian gneisses in all these syenites except in local syenitic facies of the glenelg ratagain complex fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas the phases involved in this process may have included plagioclase alkali feldspar pyroxene amphibole biotite garnet fe ti oxide sphene allanite apatite zircon and zirconolite and therefore all the ratios amongst even the so called incompatible elements may have changed during the evolution of the leucocratic magmas nevertheless a detailed study of the glen dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas these appear to be picritic shoshonite mgo 15 ni 400ppm la yb 20 la nb 5 for the glen dessarry loch borralan and loch ailsh syenites and picritic ultrapotassic magmas mgo 15 ni 400 ppm la yb 60 la nb 7 such as would crystallise to minettes for the loch loyal and glenelg ratagain syenites mafic shoshonites were erupted amongst the 410 ma lome lavas of this region and also occur as widespread approximately contemporaneous volcanic feeder plugs minettes of similar age are also common as dykes in nw scotland numerous large tonalite granite complexes with minor diorites and gabbros were emplaced in w and nw scotland between 435 and 400 ma these are generally acknowledged to be mixtures of magmas from crustal and mantle sources their more mafic members show compositional features such as very high ba and sr which group them with the rare syenites and the lorne lavas of the same region into a distinctive geochemical province within which shoshonitic and allied magmas were the mantle derived component two models are presented to account for the generation of strongly potassic subduction related magmas several hundred km behind a nw directed subduction zone or during the period immediately following continental collision

conodont diversity and evolution through the latest permian and early triassic upheavals abstract a study of latest permian and early triassic multielement conodonts identifies eight steps in their evolutionary history during an interval when earth s biosphere was highly stressed these steps are 1 gradual decline of families and genera through the changhsingian up to the late griesbachian 2 conodont biofacies change and extinction of tethyan endemic species close to the permian triassic boundary ptb 3 faunal turnover with extinction and origination in the late griesbachian 4 initial radiation in gondolellids and diversification in apparatuses during the dienerian 5 explosive radiation in the early middle smithian 6 major extinction in the late smithian 7 major radiation early in the spathian 8 gradual turnover and decline in the late spathian through early anisian conodontophorids were reduced from five families at the beginning of the changhsingian to three by the ptb and to two late in the griesbachian from the changhsingian to the late griesbachian there was a single multielement apparatus represented in the gondolellidae whereas by the olenekian there were at least twelve given absolute age constraints the conodont recovery in the aftermath of the ptb was extraordinary conodont evolution during the dienerian remains obscure but was very significant in terms of changes in multielement apparatuses in spite of induan extinctions generic diversity generally increased from the ptb up to the late smithian in terms of species genera and multielement apparatuses the acme of triassic conodonts was in the middle smithian and the biggest extinction was in the late smithian after this extinction generic and apparatus diversity quickly returned to high levels marking a significant spathian recovery gradual decline characterized the late spathian and persisted into the early anisian a synthetic summary of the temporal distribution and proposed relationships amongst all known lower triassic conodonts provide an improved foundation for biostratigraphic and biochronologic studies extinction and radiation trends correlate well with sea level changes and sequence boundaries faunal turnovers correspond to lowstands in the late griesbachian late smithian and late spathian and radiations correspond to transgressions in the early griesbachian early smithian and early spathian the trends also correlate with perturbations in the carbon cycle with lower triassic 13c minima corresponding to extinction and faunal turnover and positive values generally occurring during radiations however middle triassic recovery of marine benthos follows a positive maxima and an overall decline in conodont diversity new taxa borinella chowadensis b megacuspa neogondolella griesbachensis and n mongeri are described

melting of pyrope mg3al2si3o12 up to 10 gpa possibility of a pressure induced structural change in pyrope melt the melting of pyrope mg3al2si3o12 has been determined experimentally at pressures up to 10 gpa pyrope melts congruently in the pressure range 3 5 10 gpa at pressures below 7 gpa aluminous enstatite of pyrope composition crystallizes during quenching whereas quench pyrope appears at higher pressures moreover the slope of the melting curve of pyrope decreases significantly at pressures above 7 gpa these changes in both the nature of the quench phase and the slope of the melting curve suggest a pressure induced coordination change for al3 in pyrope melt at around 7 gpa this pressure induced coordination change of al3 probably occurs even in magmatic liquids generated in the deep upper mantle and should affect some of their physical properties

a permian triassic boundary section at quinn river crossing northwestern nevada and implications for the cause of the early triassic chert gap on the western pangean margin the upper permian lower triassic quinn river formation in northwestern nevada was previously thought to represent an incomplete permian triassic boundary sequence owing to an inferred disconformable relationship between permian radiolarian and spicule rich chert and overlying triassic siltstone petrographic and geochemical studies demonstrate that the siltstone is in fact a radiolarian bearing early authi genic dolomicrite with both the chert and dolomicrite deposited conformably in deep water chert production declined or ceased in the late permian and reappeared in the spathian forming a widespread chert gap in permian triassic sequences given the conformable lithofacies relationships deep water depositional setting new radiolarian data extending ranges of key taxa and the presence of the global chert gap sedimentation in the quinn river formation was apparently continuous across the permian triassic boundary this represents the first permian triassic boundary section in the united states portion of the north american cordillera and one of the few deep water sections worldwide organic carbon isotope stratigraphy of the quinn river formation displays multiple excursions through sediments of wuchiapingian anisian age with a negative excursion 1 54 m above the chert shale transition likely representing the permian triassic boundary the multiple excursions in the organic carbon record verify studies of the carbonate carbon record in china that suggest instability in the isotopic record throughout the early triassic and demonstrate that the permian triassic boundary isotope excursion was not an isolated event stratigraphic variation in redox sensitive trace metals indicates that seawater became less oxic slightly before the chert shale transition in turn impacting siliceous sponge communities and creating the widespread chert gap the distinctive dolomicrites in the quinn river formation represent a widespread lithofacies deposited in many localities during the late permian early triassic and express early authigenic formation of dolomite via microbial sulfate reduction in organic rich low oxygen environments

large perturbations of the carbon cycle during recovery from the end permian extinction high resolution carbon isotope measurements of multiple stratigraphic sections in south china demonstrate that the pronounced carbon isotopic excursion at the permian triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the early triassic before ending abruptly early in the middle triassic the unusual behavior of the carbon cycle coincides with the delayed recovery from end permian extinction recorded by fossils suggesting a direct relationship between earth system function and biological rediversification in the aftermath of earth s most devastating mass extinction

the survival recovery and diversification of metazoan reef ecosystems following the end permian mass extinction event abstract the triassic period records important ecological transitions in the aftermath of the end permian mass extinction and is a key interval in the evolution of modern coral reefs there have been several critical developments in our understanding of triassic reef evolution over the past decade the timing of events and duration of stages have changed dramatically the discovery of metazoan reefs in the early triassic details about the environmental perturbations that drove the extinction the relationship between tectonic activity and platform margin reef proliferation and additional proxy evidence for the co evolution of coral reef builders and their photosymbionts here we provide an up to date synthesis of reef collapse and recovery dynamics following the end permian extinction specifically integrating recent discoveries the evolution of reef ecosystems can be divided into five phases based on their composition 1 microbial metazoan reefs represent survival communities that characterize the immediate extinction aftermath 2 the re establishment of reefs built by metazoans small sponge biostromes and bivalve buildups is observed in oxygenated settings in the olenekian early triassic 3 towards the end of the olenekian and into the anisian middle triassic low diversity tubiphytes dominated reefs formed which represent the first triassic platform margin reefs platform margin reefs however are not widespread until the late anisian 4 late anisian reefs also record a composition change and increase in species richness with sponges and tubiphytes as the main reef builders 5 the first scleractinian corals which are the main reef builder in modern marine reef ecosystems evolved during the anisian but are not reported as dominant reef builders until the late triassic the radiation of coral reefs is posited to be coupled to the acquisition of photosymbionts e g zooxanthellae there is clearly a stepwise evolution of reef types during the triassic however once each reef type appears it persists throughout the remainder of the triassic the survival recovery and diversification of reef ecosystems is therefore more complex than previously outlined particularly with respect to the earliest post extinction ecosystems these recent advances highlight the need to thoroughly document the faunal compositions of understudied reef systems as well as to continue the exploration of triassic ecosystems in underrepresented regions

carbon and conodont apatite oxygen isotope records of guadalupian lopingian boundary sections climatic or sea level signal abstract the guadalupian lopingian g l boundary 260 4 ma is one of the major extinction events in earth history that coincides with the emeishan large igneous province and palaeoclimatic changes carbon isotopes of whole rock samples were studied in order to document changes in the global carbon cycle in contrast to earlier studies we observe no major negative excursion in 13 c in the middle capitanian a positive 13 c excursion is observed in the latest capitanian with a 1 5 increase registered in the j xuanhanensis zone to c postbitteri hongshuiensis subzone followed by a decrease of 1 within the c postbitteri postbitteri subzone and a 2 decrease in the c dukouensis to c asymmetrica zone oxygen isotopes of conodonts from two g l boundary sections were measured in order to reconstruct conodont habitat and potential changes in water temperature oxygen isotope ratios of gondolellid conodonts are higher in comparison to oxygen isotope ratios measured on hindeodid conodonts suggesting that gondollelids lived in cooler and thus deeper waters compared with hindeodids the oxygen isotope record reconstructed from gondollelid conodonts suggests warming of water temperatures of about 4 c in the late capitanian j postserrata to j granti zone cooling of about 6 to 8 c across the g l boundary and in the earliest wuchiapingian and again significant warming in the wuchiapingian c dukouensis to c liangshanensis zone the temperature increase can be correlated with the main phase of emeishan volcanism suggesting that climatic warming may have resulted in an intensified hydrological cycle fertilisation of the oceans and enhanced primary productivity the latter documented in the positive late capitanian carbon isotope excursion however changes in sea level seem to parallel reconstructed water temperatures suggesting that changes in water depth in combination with superimposed climatic changes may be responsible for the observed temperature changes this study documents that oxygen isotope studies on permian conodonts should be performed on mono generic conodont samples and that oxygen isotopes not only provide valuable palaeoclimatic information but also may help to constrain the life habitat of conodonts

new u pb constraints identify the end guadalupian and possibly end lopingian extinction events conceivably preserved in the passive margin of north america implication for regional tectonics the discovery and dating of a volcanic ash bed within the upper phosphoria formation in se idaho usa is reported the ash occurs 11 m below the top of the phosphatic meade peak member and yielded a 206 pb 238 u date of 260 57 0 07 0 14 0 31 ma i e latest capitanian guadalupian the stratigraphic position of this ash near the top of the meade peak phosphatic member of phosphoria formation indicates plausible completeness of the sedimentation within the guadalupian lopingian and probably at the permo triassic p t transitions the new radiometric age reveals that the regional biostratigraphy and palaeontology of phosphoria and park city formations requires serious reconsideration particularly in cool water conodonts bryozoans and brachiopods the new age proposes that the guadalupian lopingian boundary glb coincides with the meade peak rex contact and consequently with the end guadalupian extinction event the lack of a major unconformity at the p t transition suggests that the effects of the sonoma orogeny were not as extensive as has been assumed

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

sources and settings of ediacaran post collisional syenite monzonite diorite shoshonitic magmatism from southernmost brazil abstract the arroio do silva pluton comprises quartz rich syenite monzonite diorite rocks with subordinate lamprophyre as enclaves compositional and textural variations lead to the identification of three main varieties i quartz monzonite to syenite ii quartz monzonite to monzodiorite and iii quartz diorite the transition between all rock types is gradational and marked mostly by the increase of mafic mineral phases especially biotite and by the k feldspar content which is characteristically euhedral in the quartz monzonite to syenite variety and becomes subhedral to anhedral towards diorite compositions geochemical features corroborate field relations and both point to magma mingling as the main differentiation process syenite is considered to be the felsic endmember whilst the mafic one has dioritic composition different degrees of interaction between these magmas result in hybrid varieties represented by quartz monzonite to monzodiorite a third magma type is observed as ultrapotassic lamprophyric enclaves but its influence in the mixing processes seems to have been minor both mafic and felsic magmas have k2o na2o ratios between 1 and 2 compatible with their shoshonitic affinity whilst ratios slightly above 2 characterize lamprophyric enclave magmas as ultrapotassic the source of shoshonitic and ultrapotassic magmas according to trace element and isotope evidence is probably a phlogopite bearing mantle which was affected by previous subduction of paleoproterozoic or neoproterozoic age the variation of ultrapotassic to shoshonitic magmas is probably controlled by variation of phlogopite contents in the mantle source u pb zircon crystallization age of 578 ma la mc icp ms determined for the asp quartz monzonite to syenite variety is in agreement with the neoproterozoic post collisional period of the dom feliciano belt this age value is also in agreement with that of other syenitic associations from south brazil such as the piquiri syenite massive that records similar chemical signatures therefore these syenitic associations are taken to represent previously metasomatized mantle sources in late post collisional setting from the brasiliano pan african cycle in southermnmost brazil

global oolite deposits across the permian triassic boundary a synthesis and implications for palaeoceanography immediately after the end permian biocrisis abstract the permian triassic mass extinction ptme is not only a dramatic loss in biodiversity and major change in ecosystem structures but also coincided with the formation of abundant unusual sedimentary structures of these ooids were widespread in shallow marine carbonate settings during the permian triassic p tr transition and giant ooids occurred more frequently at this critical period than any time during the phanerozoic global review of 43 oolite bearing permian triassic boundary ptb sections with reliable biostratigraphic controls indicates that ooids occurred mostly in coincidence with the latest permian extinction lpe and its immediate aftermath ooids became widespread over extensive regions just after the lpe during the interval corresponding to the conodont hindeodus changxingensis zone they persisted into the earliest triassic until the conodont isarcicella isarcica zone in addition oolites are often found in association with microbialites in low latitude shallow marine settings proliferation of ooids over the p tr transition indicates an extensive range of warm waters with high level of carbonate saturation state that prevailed in the oceans during that time the latest permian ooids were usually small 0 3 to 0 7 mm in diameter aragonitic poorly preserved and recrystallized while moderately to well preserved morphology bimineralic and oversized forms usually occurred in the i isarcica zone of the earliest triassic and afterwards widespread aragonitic ooids in the end of the permian reinforce the scenario that an aragonite sea period may have resulted in the dramatic losses of skeletal organisms that precipitated low mg calcite and hampered their recovery in the aftermath the anomalous primary mineralogy of lower triassic ooids implies that previously assumed stable seawater composition during the early triassic needs to be revaluated

the mid capitanian middle permian mass extinction and carbon isotope record of south china abstract conodont c isotope and fossil and facies data are presented for the capitanian middle permian mass extinction record seen in platform carbonates maokou and wuchiaping formations of south china where limestones interdigitate with the volcanic succession of the emeishan large igneous province the maokou formation provides an extinction record marked by the loss of keriothecal walled fusulinaceans and a turnover in calcareous algae in sections within the emeishan province this crisis occurs at the base of the oldest record of volcanism from the jinogondolella altudaensis conodont zone of mid capitanian age around the periphery of the emeishan province this extinction level lies within the upper part of the maokou formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events the assemblages of the uppermost maokou formation are characterised by typical late permian taxa although these levels still lie within the middle permian guadalupian series disaster taxa such as earlandia and diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction the crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts therefore a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate a composite 13ccarb curve calibrated against a high resolution conodont biostratigraphy reveals a major intra capitanian negative excursion of 5 superimposed on typically heavy 4 5 middle permian values this curve can also be recognised in panthalassan seamount carbonates of japan although this requires reassignment of apparently upper permian limestones to the middle permian in both china and japan the capitanian mass extinction occurs during the early stage of this major intra capitanian negative excursion assuming typical platform carbonate accumulation rates the records of the maokou formation suggest 13ccarb values fell at 0 01 kyr suggesting a catastrophic origin such as gas hydrate destabilisation is unlikely although a volcanic source is possible

dispersed remnants of a northeast pacific fringing arc upper paleozoic terranes of permian mccloud faunal affinity western u s two fragmentary subparallel belts of terranes within the western north american cordillera contain upper paleozoic rocks and are characterized by contrasting lithotectonic assemblages and contrasting permian faunal affinity these two belts are a volcanic arc related successions of permian mccloud faunal affinity mccloud belt and b subduction related accretionary complexes of permian tethy an faunal affinity cache creek belt this paper supports the hypothesis that the fragmentary terranes of the mccloud belt once constituted parts of a northeast pacific fringing arc system and in constrast to some earlier interpretations concludes that the volcanic arc evolved above an eastward dipping subduction zone the absolute distance between this arc and western north america during the late paleozoic cannot be constrained however there is little evidence to suggest closure of a major 10 km ocean basin or protracted periods of westward dipping subduction parts of devonian to permian volcanic island arc sequences of the western u s cordillera are represented in the northern sierra eastern klamath bilk creek grindstone and chilliwack terranes these scattered volcanic arc remnants share several fundamental characteristics 1 the sequences were constructed across continental affinity basement assemblages 2 they underwent similar tectonic evolution during late paleozoic time such as coeval pulses in volcanism and related depositional histories 3 they contain early permian mccloud type fauna of distinctive biogeographic affinity 4 mccloud belt terranes are spatially and possibly genetically related to westward lying accretionary complexes of the cache creek belt which contain fragments of upper triassic blueschist and permian limestone blocks bearing tethyan permian fusulinids and corals based on the presence of distinctive early permian mccloud fauna the island arc remnants discussed in this paper are referred to as the mccloud belt the similarities between mccloud belt terranes suggest that they were once parts of a long lived late paleozoic volcanic arc complex the stratigraphy of these terranes records the tectonic evolution of the volcanic arc volcanism within the paleozoic arc began as early as the early devonian and was succeeded or accompanied by carbonate and epiclastic sedimentation during the middle and late devonian an influx of detritus derived from sedimentary and metasedimentary rocks during the late devonian and mississippian records the uplift and erosion of arc basement sequences an event that was at least locally accompanied by ongoing volcanism a pulse in volcanism during the pennsylvanian and coeval uplift led to the establishment of shallow marine and deltaic volcanogenic and carbonate sedimentation and locally subaerial exposure which persisted into the early early permian elsewhere during the early permian shallow water carbonate deposition was established with only minor influx of volcanogenic debris during the late permian and locally as early as late early permian a major pulse in volcanism occurred and is now represented by voluminous sequences of volcanogenic debris and lavas most of these sequences are overlain by upper triassic carbonate platformal sequences arc volcanism was recorded at least locally until the middle jurassic paleomagnetic data are used to constrain a schematic pre cretaceous reconstruction of these volcanic arc sequences and their associated subduction assemblages the inferred paleogeography of island arc sequences and the adjacent accretionary terranes suggests that volcanism occurred above an east dipping subduction zone with a long lived paleogeographic relation to north america the current structural position of these terranes is largely the result of mesozoic and locally younger deformation

petrography and geochemistry of the permian triassic boundary interval yangou section south china implications for early griesbachian seawater δ 13 c dic gradient with depth abstract the carbon isotopic composition 13 c carb recorded in shelf carbonates has been widely used as a proxy for the isotopic composition 13 c dic of surface ocean water to establish paleocean chemistry and circulation patterns however 13 c carb values do not necessarily preserve the 13 c dic due to post depositional diagenetic alteration in order to examine the early griesbachian surface to deep 13 c dic gradient with depth the diagenetic features of the permian triassic boundary interval beds 18 to 35 from yangou section located in the yangtze carbonate platform interior south china are delineated to compare with those of the slope gssp meishan section the petrographic and geochemical observations show that the early griesbachian carbonates in the yangou section underwent pervasive dolomitization in its early diagenetic history three types of early replacement dolomites and one type of dolomite cement are present the dolomite crystals display internal zonation with high ca calcian dolomite hcd core being encased successively by calcite and an outermost fe rich hcd cortex the initial dolomitization took place in anoxic seawater and underwent subsequent diagenetic system involved with meteoric water the two most negative 13 c values in claystones of beds 21 3 and 35 are probably related to meteoric diagenesis above and or below the meteorically influenced beds the dolomite and calcite have uniformly positive 13 c values the primary carbon isotopic compositions are probably preserved in the early griesbachian carbonate from the platform yangou section which could probably be related to the poor formation of the outermost fe rich hcd cortex compared to the slope carbonate from the meishan section the platform carbonate from the yangou section has lower primary 13 c carb values it is estimated that the 13 c dic gradient with depth between yangou and meishan is less than the previously suggested the results highlight the need for evaluation of local 13 c carb as record of 13 c dic in paleoseawater and carry important implications for understanding the permian triassic carbonate successions throughout the world

low temperature alteration of monazite fluid mediated coupled dissolution precipitation irradiation damage and disturbance of the u pb and th pb chronometers abstract low temperature alteration of monazite is documented in three centimeter sized monazite crystals from norway arendal madagascar ambato and sri lanka the three crystals have different chemical compositions especially in their u th y and pb contents and have 208 pb 232 th ages ranging from 491 to 900 ma optical microscope om scanning electron microscope sem and transmission electron microscope tem images and electron microprobe analyses epma show that all three preserve a similar patchy texture this texture is interpreted as resulting from an alteration reaction in which unaltered monazite mnz1 reacts to form a secondary th u y depleted high th u monazite mnz2 accompanied by thorite huttonite thsio 4 thorianite tho 2 and xenotime ypo 4 the proportions of which are dependent upon the initial composition of the monazite mnz1 images reveal variably intense internal fracturing with cracks filled with th rich fe rich phases monazite xenotime thermometry demonstrates that the pristine monazites mnz1 interacted with a low temperature fluid the alteration process is interpreted to follow a mechanism of fluid mediated coupled dissolution precipitation chemical dating with the electron microprobe shows no th u pb age differences between primary and secondary monazites except in the case of the ambato monazite in which altered domains yield older 750 ma apparent ages than the pristine mnz1 domains u pb and th pb isotope dating using la icp ms yields ages consistent with electron probe dates for pristine mnz1 zones however disturbance of these systems in the altered monazite domains leads to variable age results for these depending on sample in the case of sri lanka and arendal only 208 pb 232 th dates provide a reasonable estimate of the age of alteration which are constrained to be 450 and 864 ma respectively u pb systems are disturbed due to common pb contamination up to 40 and u fractionation relative to th during alteration responsible for depletion of u in altered monazites and increase of th u in contrast for the ambato monazite both the u pb and th pb systems were affected and yield inconsistent older dates for altered zones this is attributed to significant common pb contamination up to 80 which affects all pb isotopes and explains why electron probe ages are erroneous th u silicate contamination during measurement resulting from the presence of a numerous nano phases and nano fractures filled with th u silicates that are visible only under tem also contributes to the anomalously old ages for these disturbed mnz2 domains these results demonstrate the important role of radiation damage effects in particular swelling induced fracturing and the essential role of porosity and cracks which allow fluid charged with elements migration through monazite during low temperature alteration

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

chemostratigraphy and biostratigraphy of devonian carboniferous and permian sediments encountered in eastern saudi arabia an integrated approach to reservoir correlation abstract the following study was completed on inorganic geochemical data acquired from 850 core and cuttings samples taken from devonian carboniferous and permian sediments encountered in six wells in the arabian gulf eastern saudi arabia the principal objective of the study was to employ chemostratigraphy to produce a robust high resolution correlation scheme a secondary aim was to integrate this with existing biostratigraphic data as part of a multidisciplinary approach to reservoir correlation data were derived for 50 elements using icp oes inductively coupled plasma optical emission spectrometry and icp ms inductively coupled plasma mass spectrometry but definition of chemostratigraphic boundaries are based on changes in the following key element ratios cr p th nb th ta zr th zr p nb ti and nb p variations in these parameters are largely dependent on changes in source provenance which affects the relative concentrations of detrital heavy minerals to avoid geochemical variations relating to changes in grain size lithology separate frameworks were constructed for data derived from sandstone and mudrock lithologies both comprise a hierarchical order of zones subzones and divisions with subdivisions also being identified in the sandstone dataset the schemes are considered to be robust as chemozones general term used to refer to any zone subzone division or subdivision are clearly defined using geochemical profiles and binary diagrams and most are correlative between three or more wells given the similarities in definitions of zones subzones and divisions in the two schemes and the fact that these chemozones are considered to be roughly time equivalent both were combined to produce a final chemostratigraphy scheme in a further stage of interpretation the correlation was refined by integrating the interpretations of this chemostratigraphy study with lithostratigraphic markers identified by significant trends in gr that exist in two or more wells and an existing correlation based on biostratigraphy in the tawil and jauf formations there are obvious inconsistencies between the placement of chemostratigraphic and biostratigraphic boundaries with some subzones occurring within different palynozones in adjacent wells such disparities may be explained by the existence of separate fluvio deltaic shallow marine sandstones having a similar source provenance but being deposited in different parts of the study area at different times this interpretation is supported by the available seismic data showing that the jauf and to a lesser extent the tawil formations take the form of laterally discontinuous sandstones by contrast the chemozones associated with the overlying jubah formation berwath formation unayzah group juwayl and nuayyim formations and base khuff clastics member show a very close match with the placement of palynozones in each well and were probably deposited at a similar time on both field and subregional scales

erosional truncation of uppermost permian shallow marine carbonates and implications for permian triassic boundary events comment payne et al 2007 1 suggest that there is widespread evidence for a carbonate dissolution surface at the level of the end permian mass extinction and that this crisis was at least partly due to ocean acidification that preferentially affected heavily calcified marine invertebrates these ideas

the permian triassic boundary at nhi tao vietnam evidence for recurrent influx of sulfidic watermasses to a shallow marine carbonate platform the permian triassic boundary at nhi tao cao bang province vietnam was sampled in a 7 5 m thick outcrop section at high resolution 5 cm intervals for chemostratigraphic and magnetic susceptibility analysis the section consists entirely of slightly argillaceous limestone representing shallow marine facies of the jinxi platform one of several large carbonate platforms within the nanpanjiang basin located on the southern margin of the south china craton upper permian strata beds 1 7 are mainly dark gray cherty fossiliferous wackestones and packstones containing a diverse open marine fauna whereas uppermost permian and lower triassic strata beds 9 and higher are medium gray calcimicrobial framestones containing rare macrofossils these facies are separated by a 12 cm thick oolitic pisolitic grainstone bed 8 that coincides with the disappearance of most late permian faunal elements as well as with the first appearance of various geochemical anomalies that continue into the lower triassic part of the section this late permian event horizon is characterized by 1 an abrupt decline in total organic carbon to near zero values 2 the onset of a sustained decline in carbonate 13c and 3 the first of eight concentration peaks in pyrite sulfur significantly each sulfide peak is associated with lower pyrite 34s values as well as with the onset of a negative carbonate 13c excursion or the acceleration of an excursion already in progress these chemostratigraphic relationships are consistent with multiple episodes of upwelling of sulfidic 34s and 13c depleted deep ocean waters onto the jinxi platform the first upwelling event was the most intense and caused a drastic reduction in primary productivity and the demise of the late permian fauna subsequent episodes were less intense but may have contributed to a delay in recovery of early triassic marine ecosystems a ten fold increase in magnetic susceptibility in bed 9 may record the influx of fine detrital particles following destruction of terrestrial ecosystems and massive soil erosion the terrestrial signal of the end permian catastrophe thus follows the marine signal with a 12 cm lag which may reflect the time of transit of soil derived particles across the nanpanjiang basin suggesting that the marine and terrestrial crises in the nhi tao region occurred more or less synchronously these observations suggest a model in which renewal of global ocean overturn followed a prolonged interval of deep ocean stagnation during the late permian with upwelling intensity modulated by short term 20 kyr climate cyclicity

stable carbon isotope signature in mid panthalassa shallow water carbonates across the permo triassic boundary evidence for 13 c depleted superocean the jurassic accretionary complex in southwest japan contains exotic blocks of the permo triassic limestone primarily deposited on ancient mid oceanic seamounts in an ancient pacific ocean or superocean panthalassa this study examines stable carbon isotope compositions 13ccarb and 13corg of such open ocean shallow water limestone across the permo triassic boundary ptb at kamura and taho in southwest japan the results show an almost identical secular change in 13ccarb values with a remarkable negative spike across the ptb in both sections this confirms for the first time that the mid panthalassa shallow water carbonates are bio and chemo stratigraphically correlated not with previously studied ptb sections from the peripheries of pangea the negative shift in 13ccarb occurs parallel to that of 13corg in both sections and the difference 13c 13ccarb 13corg remains nearly constant throughout the sections this implies that the 13c depleted water should have developed widely probably in a global extent throughout the superocean panthalassa across the ptb these findings suggest that a large input of 12c enriched carbon into the ocean atmosphere system has occurred and may have caused a global environment change probably relating to the greatest mass extinction in the phanerozoic

strontium isotope 87sr 86sr stratigraphy of ordovician bulk carbonate implications for preservation of primary seawater values the present study on bulk carbonate 87 sr 86 sr stratigraphy represents a companion work to earlier research that presented a conodont apatite based ordovician seawater 87 sr 86 sr curve for the tremadocian katian stages 485 445 ma here we directly compare the curve based on conodont apatite including some new data not published in earlier work with a new curve based on 87 sr 86 sr results from bulk carbonate from the tremadocian sandbian stages we sampled eight lower to upper ordovician carbonate successions in north america to assess the reliability of bulk carbonate to preserve seawater 87 sr 86 sr and its utility for 87 sr 86 sr chemostratigraphy a high resolution 87 sr 86 sr curve based on 137 measurements of bulk conodont apatite is used as a proxy for seawater 87 sr 86 sr 87 sr 86 sr seawater in total 230 bulk carbonate samples that are paired to conodont samples were measured for 87 sr 86 sr in order to determine the conditions under which 87 sr 86 sr seawater is preserved in bulk carbonate results indicate that well preserved bulk carbonate can faithfully record the 87 sr 86 sr seawater trend but that its 87 sr 86 sr values are commonly more variable than those of conodont apatite on average bulk carbonate samples of the same age vary by 10 20 10 5 compared to 5 10 10 5 for conodont apatite the amount of isotopic alteration of bulk carbonate from seawater 87 sr 86 sr 87 sr 86 sr was determined by taking the difference between 87 sr 86 sr values of bulk carbonate and the approximated seawater trend based on the least radiogenic conodont 87 sr 86 sr values cross plots comparing 87 sr 86 sr values to bulk carbonate sr concentration sr and conodont color alteration indices cai an estimate of the thermal history of a rock body indicate that bulk carbonate is most likely to preserve 87 sr 86 sr seawater minimally altered when either 1 bulk carbonate sr is greater than 300 ppm or 2 carbonate rocks experienced minimal thermal alteration with burial temperatures less than 150 c carbonates with intermediate sr e g between 130 and 300 ppm can also yield 87 sr 86 sr seawater values but results are less predictable and local diagenetic conditions may play a greater role modeling results support the argument that seawater 87 sr 86 sr can be preserved in bulk carbonates with low sr if pore water rock ratios are low 87 sr 86 sr is similar to the seawater 87 sr 86 sr value preserved in limestone bulk carbonate samples that meet these criteria can be useful for high resolution measurements of 87 sr 86 sr seawater with a sample variation on par with fossil materials 5 particularly for successions where well preserved fossil material i e conodonts or brachiopods is not available such as precambrian strata sequences recording mass extinction events or otherwise fossil barren facies these criteria and model predictions based on bulk carbonate sr must be considered in the context of whether a limestone accumulated under calcite seas e g ordovician with relatively high seawater sr ca or aragonite seas in which case the diagenetic transformation of aragonite to calcite may result in incorporation of non seawater sr

potassium rich clinopyroxene in the mantle an experimental investigation of a k rich lamproite up to 60 kbar clinopyroxenes with up to 1 6 7 wt k2o occur in high pressure 50 60 kbar and temperature 1200 1500 c experiments using an armalcolite phlogopite lamproite compsition these p t conditions are considered to approximate those of the early stages in the evolution of kimberlite and olivine lamproitic magmas with progressively decreasing temperatures from 1500 1200 c at these pressures the clinopyroxene coexist with garnet garnet coesite garnet coesite phlogopite rutile liquid occurs in all assemblages potassium contents of clinopyroxene systematically decrease with temperature and increase with pressure as does the kd cpx melt comparable trends occur with ca and na whereas mg increases with temperature and decreases with pressure similarly fe contents of these clinopyroxenes decrease with pressure but show no systematic relationship to temperature aluminum in sixfold coordination also has a trend similar to that of k na and ca at 60 kbar but not at 50 kbar where lower al vi occurs these results suggest that k is incorporated within clinopyroxene by complex coupled substitution mechanisms such as mg fe al vi k na ca with charge balance involving incorporation of al vi cr fe 3 and ti in the clinopyroxene structure in octahedral sites the k contents of these clinopyroxenes are greater than those reported for most clinopyroxenes in deep seated diamondiferous inclusions in eclogites and kimberlites but are comparable to those of some clinopyroxenes from diamond inclusions and from other high pressure experiments the presence of the large amounts of k2o in the clinopyroxene may be attributed to the high compressibility of k as well as the high k2o in the bulk composition the paucity of high k enriched compositions in nature may be due to the fact that most olivine lamproite and kimberlite magmas have not been subjected to the lower temperature ranges 1250 1300 c at the high pressures 50 60 kbar necessary for the incorporation of k into the clinopyroxene structure clinopyroxene that can form under p t conditions comparable to those of this study may be an important mantle reservoir for k

field evidence for successive mixing and mingling between the piolard diorite and the saint julien la vetre monzogranite nord forez massif central france recent mapping of the nord forez region massif central france reveals a variety of complex field relationships along contacts between a large enclave of diorite and its enclosing monzogranite field relations hybrid rocks and a wide variety of mafic magmatic enclaves can be explained by a succession of processes between coexisting mafic and felsic magmas that either prevent or promote exchanges the large volume of mafic magma and consequently the large amount of heat it brought with it favored exchange processes because the distribution of heat varied with both time and place the nature and intensity of the compositional exchange processes also varied most of the features attributed to exchange are related to processes that occurred at the level of emplacement and after the beginning of crystallization of the two magmas these processes affected both the granitic and dioritic magmas already thoroughly hybridized by nearly similar processes that took place earlier at depth

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

strontium isotope evolution of late permian and triassic seawater the 87sr 86sr values based on brachiopods and conodonts define a nearly continuous record for the late permian and triassic intervals minor gaps in measurements exist only for the uppermost brahmanian lower part of the upper olenekian and middle norian and only sparse data are available for the late permian these 219 measurements include 67 brachiopods and 114 conodont samples from the tethyan realm as well as 37 brachiopods and one conodont sample from the mid european middle triassic muschelkalk sea the late permian lower triassic interval is characterized by a steep 1 3 10 3 rise from 0 7070 at the base of the dzhulfian to 0 7082 in the late olenekian a rate of change comparable to that in the cenozoic in the mid triassic anisian and ladinian the isotope values fall to 0 7075 followed again by a rise to 0 7081 in the middle late norian the 87sr 86sr values decline again in the late norian sevatian and rhaetian to 0 7076 the sharp rise in the 87sr 86sr values during the late permian early triassic was coincident with widespread clastic sedimentation because of the paucity of tectonic uplifts the enhanced erosion may have been due to intermittent humid phases during mainly an arid interval coupled with the absence of a dense protective land plant cover following the mass extinction during the latest permian the apex of the 87sr 86sr curve at the olenekian anisian boundary coincides with cessation of the large scale clastic sedimentation and also marks the final recovery of land vegetation as indicated by the renewed onset of coal formation in the middle triassic the rising 87sr 86sr values from the middle carnian to the late norian coincide with the uplift and erosion of the cimmeride indosinian orogens marking the closure of the palaeotethys the subsequent rhaetian decline that continues into jurassic pliensbachian toarcian boundary on the other hand coincides with the opening of the vardar ocean and its eastern continuation in the izmir ankara ophiolitic belt samples from the upper muschelkalk are more radiogenic than the global trend this may reflect separation of the basin from the open ocean due to strong meteoric influx from a large land mass in the north the germanic basin became increasing brackish up section in the north and east but because of the high evaporation rates the salt content was not much reduced in the southern and central basin where a rich but increasingly endemic marine fauna survived

substitution mechanisms and solubility of titanium in phlogopites from rocks of probable mantle origin previously proposed substitution mechanisms for ti in phlogopites based on experimental studies and crystal chemistry have been examined using data for 81 phlogopites from mantle derived rocks primarily as nodules in kimberlites and also from alkali basalts lamprophyres and carbonatites 49 phlogopites from high k rocks with basaltic affinities and from 32 phlogopites crystallized in high pressure experiments mainly on high k rock compositions for the majority of phlogopites from the kimberlite group and for all those crystallized in the experimental studies the substitution of ti can be represented by a combination of the mechanisms represented by 2mg vi ti vi vi and mg vi 2si iv ti vi 2al iv some phlogopites in ultrapotassic rocks have only the former substitution mechanism the ti contents of phlogopites generally increase with decreasing octahedral site occupancy and decreasing si al vi for the phlogopites crystallized in the experiments on high k rocks the solubility of ti increases with increasing fo2 and temperature and possibly with decreasing pressure at constant fo2 the effect of the composition of the liquids used in the experimental studies from which these phlogopites have crystallized has only minor effect on either the substitution mechanism or the solubility of ti in phlogopites this suggests that phlogopite in high k rocks may be a potential geothermometer and possibly a geobarometer

archean lamprophyre dykes and gold mineralization matheson ontario the conjunction of lile enriched mafic magmas deep crustal structures and au concentration at the canadian arrow deposit matheson separate base and precious metal bearing fracture arrays are associated with a trondhjemitic stock transected by lamprophyre dykes peripheral to the stock high fe tholeiitic pillow basalts fe2o3 17 8 wt tio2 2 4 wt al2o3 tio2 13 7 with interbedded felsic units experienced amphibolite facies hydrothermal or regional metamorphism and intense ductile deformation focussed within mylonite zones at the interflow horizons the trondhjemite stock experienced pervasive reaction with marine water at temperatures that diminished to 150 c this was accompanied by conversion of plagioclase of igneous origin to albite concomitant enrichment of sodium na2o 8 32 1 16 wt 1 and shifts of albite up to 18o 14 with attendent variably negative quartz albite fractionations galena dominated veins were precipitated at 220 255 c from hypersaline cacl2 nacl hydrothermal fluids with 22 34 equivalent wt nacl 18o 0 6 to 2 5 these were of evolved mar