calibrating the end permian mass extinction the end permian mass extinction was the most severe biodiversity crisis in earth history to better constrain the timing and ultimately the causes of this event we collected a suite of geochronologic isotopic and biostratigraphic data on several well preserved sedimentary sections in south china high precision u pb dating reveals that the extinction peak occurred just before 252 28 0 08 million years ago after a decline of 2 per mil in 13c over 90 000 years and coincided with a 13c excursion of 5 that is estimated to have lasted 20 000 years the extinction interval was less than 200 000 years and synchronous in marine and terrestrial realms associated charcoal rich and soot bearing layers indicate widespread wildfires on land a massive release of thermogenic carbon dioxide and or methane may have caused the catastrophic extinction

anomalous early triassic sediment fluxes due to elevated weathering rates and their biological consequences analysis of 16 marine permian triassic boundary sections with a near global distribution demonstrates systematic changes in sediment fluxes and lithologies in the aftermath of the end permian crisis sections from continent margin and platform settings exhibit higher bulk accumulation rates bars and more clay rich compositions in the griesbachian earliest triassic relative to the changhsingian latest permian these patterns which largely transcend regional variations in tectonic setting sequence stratigraphic factors and facies are hypothesized to have resulted from a substantial average 7 increase in the flux of eroded material from adjacent land areas owing to accelerated rates of chemical and physical weathering as a function of higher surface temperatures increased acidity of precipitation and changes in landscape stability tied to destruction of terrestrial ecosystems this sediment surge may have been a contributory factor to the latest permian marine biotic crisis as well as to the delayed recovery of early triassic marine ecosystems owing to the harmful effects of siltation and eutrophication contemporaneous deep sea sections show no increases in sediment flux across the permian triassic boundary owing to their remoteness from continental siliciclastic sources and location below the paleo carbonate compensation depth

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

87sr 86sr stratigraphy from the early triassic of zal iran linking temperature to weathering rates and the tempo of ecosystem recovery recovery from the late permian mass extinction was slowed by continued environmental perturbations during the early triassic rapid fluctuations of the early triassic marine carbonate carbon isotope record indicate instability in the global carbon cycle and recent 18 o apatite studies link elevated temperatures to the prolonged biotic recovery high temperatures potentially caused enhanced continental weathering that was detrimental to marine ecosystems but linking weathering rates to temperature has proven difficult one proxy for weathering is the 87 sr 86 sr of marine carbonate we present here an 87 sr 86 sr record from an upper permian lower triassic succession near zal iran that is coupled to a 13 c carbonate record an increase in the rate of 87 sr 86 sr rise from the dienerian to the smithian may be linked to elevated continental weathering rates caused by warming during the smithian

a new model for the indochina and south china collision during the late permian to the middle triassic article i nfo a comparative analysis of indochina and south china during the early paleozoic indicates the former may be extended to include north vietnam part of the qinzhou tectonic zone and southern hainan island these three regions were traditionally regarded as parts of south china separated from indochina by the song ma suture in central north vietnam a new suture called the dian qiong suture is proposed here approximately along the southern margin of the present nanpanjiang basin this suture is linked to its eastern counterpart in hainan island through a nne trending dextral transform fault zone along the eastern margin of the nanpanjiang basin the conventional song ma suture originally constitutes its western extension and was translated to its present location by sinistral displacement along the red river fault zone during the tertiary upper paleozoic deep water turbidites and associated mid oceanic ridge basalts along the suture in the nanpanjiang basin illustrate a coeval ocean between indochina and south china the ocean was consumed by south directed subduction beneath indochina during the late permian to the middle triassic this suture zone was finally re shaped by the indentation between the active margin of indochina and the irregular passive continental margin of south china during the late triassic as well as displacement along the red river fault zone during the cenozoic

magnesium isotope fractionation in biogenic and abiogenic carbonates implications for paleoenvironmental proxies abstract geochemical variations in marine biogenic carbonates that are preserved in the geological record serve as proxies of past environmental change however interpreting most proxies is complicated by biologically mediated vital effects highlighting the need to develop new tools for reconstructing paleoenvironmental change recently magnesium mg isotope variability in carbonates has been explored extensively to determine its utility as a paleoenvironmental proxy we review the results of these works which have yielded valuable information on the factors affecting mg isotope fractionation between carbonates and solution 26mgcarb sol in biogenic and abiogenic carbonate minerals strong evidence exists for a mineralogical control on 26mgcarb sol with the negative offset from 0 following the sequence aragonite 3 mol mol and saturation states 3 that are similar to seawater suggest that 26mgcarb sol has a temperature dependence of 0 01 c 1 and is insensitive to precipitation rate in contrast a significant precipitation rate dependence is observed in calcites precipitated from solutions with relatively low mg ca ratios

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

early triassic productivity crises delayed recovery from world s worst mass extinction the recovery of life after the latest permian extinction was protracted over early triassic time detailed geochemistry of marine sections along northwest pangea indicates that upwelling ceased at the extinction event nitrogen stable isotope data suggest that this was associated with progressive increase in nutrient stress throughout the early triassic coincident with a significant decrease in organic carbon content despite pervasive anoxic to euxinic conditions we argue that the early triassic hothouse both reduced marine productivity and deepened the nutricline reducing the overall rate of nutrient delivery to the photic zone creating an early triassic nutrient gap when oceans finally cooled by middle triassic time renewed nutrient upwelling and onset of organic rich shale deposition occurred across northwest pangea marking the final return of global marine productivity

a new contribution to the geology of the egyptian red sea shelf using geophysical data abstract the study examines the egyptian red sea shelf and throws more light on the structural set up and tectonics controlling the general framework of the area and nature of the crust herein an integrated study using gravity and magnetic data with the available seismic reflection lines and wells information was carried out along the offshore area the bouguer and reduced to pole aeromagnetic maps were processed and reinterpreted in terms of rifting and plate tectonics the qualitative interpretation shows that the offshore area is characterized by positive gravity everywhere that extremely increases towards the centre of the graben supporting the presence of an intrusive zone below the axial main trough the gravity data were confirmed by the presence of high magnetic amplitudes magnetic linearity and several dipoles concentrated along the rift axis for at least 250 km the lineament analysis indicates widespread of the erythrean red sea trend that was offset cut by transform faults in the ne direction aqaba the tectonic model suggests the presence of one tensional n65 e and two compressional n15 w n30 w phases of tectonism resulted in six cycles of deformations classified into three left lateral n35 e n15 e and n s and three right lateral n85 w n45 w and n60 w the basement relief map reveals a rough basement surface that varies in depth between 1 and 5 6 km it outlines several offshore basins separated from each other by ridges the models show that the basement consists of tilted fault blocks which vary greatly in depth and composition and slopes generally to the west they indicate that the coastal plain is underlain by acidic basement blocks continental crust with no igneous activity while suggesting elevated basic materials oceanic crust below the rift axis the study suggests that northern red sea forms an early stage of seafloor spreading or at least moved past the late stage of continental rifting

massive magnesium depletion and isotope fractionation in weathered basalts abstract magnesium isotopes have been shown to fractionate significantly during continental weathering however the degree and direction of fractionation varies from one study to the next and the main factors that control mg isotope fractionation during weathering have yet to be delineated here we report mg contents and isotopic compositions for two 10 m deep drill cores through bauxites developed on columbia river basalts crbs samples from these two drill cores have very low mgo contents 0 12 0 25 wt and variable but high 26mg values from 0 1 to up to 1 8 the heaviest isotopic composition ever reported for mg relative to the average values of fresh crbs 26mg 0 23 0 07 and mgo 5 9 wt these features reflect the near complete loss of mg in the isotopically heavy regolith the most highly weathered bauxites at the tops of the profiles have the lowest 26mg values reflecting the addition of isotopically light eolian dust excluding these samples 26mg in bauxites displays a weak positive correlation with gibbsite abundance suggesting that gibbsite preferentially retains 26mg in the bauxites the integrated mg isotopic fractionation factors between bauxite and fluid 26mgbauxite fluid inferred from rayleigh fractionation calculations vary from 0 05 to 0 4 which is similar to the range inferred from previous studies of igneous rock weathering profiles though none of these previous studies found the extremely heavy 26mg and massive mg depletion seen here collectively studies of weathering profiles suggest loss of isotopically light mg from the continents which must contribute to the very light 26mg seen in river water and seawater

the influence of weathering processes on riverine magnesium isotopes in a basaltic terrain this study presents major trace element and mg isotope data for the dissolved load and suspended particulates of icelandic rivers draining dominantly basaltic catchments including both glacier fed and direct runoff rivers these samples provide the opportunity to understand the behaviour of mg isotopes during chemical weathering where variations due to lithology are not extant given the significant role of mg in the carbon cycle such variations may provide important information on the regulation of earth s climate hydrothermal waters groundwater precipitation glacial ice basalt glass olivine and representative soils have also been analysed the dissolved load shows a wide range of 26mg compositions compared to the parent basaltic glass 26mg 0 29 ranging from 0 96 to 0 64 while precipitation and hydrothermal waters possess 26mg values of 0 83 and 0 85 respectively with lower mg concentrations than the dissolved load biomass activity in vegetation and organic material in soils and rivers colloids appear to have little effect on the mg isotope compositions rather the data suggest that mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions in some samples seawater in the form of direct precipitation or glacial runoff also appears to be an important source of mg glacier fed rivers groundwaters and some direct runoff rivers with a high ph have higher 26mg than basalt which is most likely due to the incorporation of light mg isotopes in secondary minerals in contrast those direct runoff rivers which have a relatively low ph have low 26mg relative to basalt consistent with preferential incorporation of heavy mg isotopes into secondary phases although it is not possible to rule out some contribution from precipitation riverine suspended particulates are depleted in mobile elements and have 26mg compositions values both higher and lower than unweathered basalt in the glacier fed and direct runoff rivers where the 26mg of the dissolved phase is heavy due to the formation of secondary phases the suspended load is light because it contains more of those phases the opposite is true for the remainder of the direct runoff rivers which have low ph this could be due to dissolution of secondary minerals enriched in light mg which are unstable at low ph or the formation of new secondary phases

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

positive correlation between li and mg isotope ratios in the river waters of the mackenzie basin challenges the interpretation of apparent isotopic fractionation during weathering during chemical weathering magnesium mg is released by the dissolution of both carbonate and silicate sources the degree to which solute concentrations and isotopic compositions of rivers reflect the relative proportions of these two inputs or cycling by a series of processes associated with weathering is poorly constrained in the river waters of the mackenzie basin canada the mg content is high and mg isotope ratios 26mg 24mg expressed as mg 26 show in excess of one per mil variability part of this variability is attributed to the 3 range in the carbonate and silicate rocks drained despite this inherent lithological control on river water mg 26 values there is also evidence for a fractionation control a linear positive covariation between lithium 7li 6li expressed as li 7 and mg isotope ratios in the river waters of the mackenzie basin is reported this covariation is not expected because previously reported fractionation related to physicochemical processes associated with clays or oxides should induce a negative covariation with mg isotope ratios

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

magnesium isotope geochemistry in the han river south korea abstract magnesium mg isotopes can be a proxy for directly constraining the sources of riverine mg but the dominant controls on riverine mg isotope ratios are still uncertain here we report mg isotope ratios for river waters experimental leachates and digestions bulk rocks and fertilizers in the han river hr south korea the hr is composed of two lithologically distinct tributaries the north han river nhr that flows over only silicate rocks and the south han river shr that flows over silicate and carbonate rocks the lithological differences between the nhr and shr are reflected in major ion 87sr 86sr and 26mg geochemistry in particular the nhr has lower major ion concentrations but higher 87sr 86sr ratios and 26mg values than the shr simple mass balances and mixing equations indicate that if the riverine 26mg values in the hr system are mainly controlled by conservative mixing between silicate and carbonate weathering the average carbonate end member 26mg value should be unlikely lower than what are measured in this study although multiple process related fractionations occur in the hr system the enrichment of 24mg in river waters relative to silicate rocks they drain could be mostly controlled by either fractionation or mixing between isotopically distinct reservoirs such as minerals or fractions labile and structural mg during dissolution while the little depletion of 24mg in the shr waters relative to carbonate rocks they drain could be likely due to the input of groundwater with lower 26mg value rather than fractionation however it is difficult to identify the contribution of anthropogenic inputs to riverine 26mg because their effects are little this study suggests that the potential of mg isotopes for constraining mg sources in a lithologically varied river basin can be enhanced with a better understanding of process related fractionation

end permian mass extinction in the oceans an ancient analog for the twenty first century the greatest loss of biodiversity in the history of animal life occurred at the end of the permian period 252 million years ago this biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of earth s largest continental flood basalt provinces the siberian traps volatile release from basaltic magma and sedimentary strata during emplacement of the siberian traps can account for most end permian paleontological and geochemical observations climate change and perhaps destruction of the ozone layer can explain extinctions on land whereas changes in ocean oxygen levels co2 ph and temperature can account for extinction selectivity across marine animals these emerging insights from geology geochemistry and paleobiology suggest that the end permian extinction may serve as an important ancient analog for twenty first century oceans

mg rich clay mineral formation associated with marine shallow water hydrothermal activity in an arc volcanic caldera setting abstract shallow water hydrothermal activity represented by venting of hydrothermal fluid around 200 c occurs in the wakamiko submarine crater at 200 m water depth in kagoshima bay southwest japan the crater is the center of large eruptions that formed a volcanic caldera which is semi submerged at present the crater is covered with thick volcanic sediments of felsic composition we studied the distribution and chemical composition of hydrothermal clay minerals that are abundant in the sediment collected by piston coring we also conducted chemical analysis of pore fluids squeezed from the sediment to understand hydrothermal interactions that resulted in formation of these clay minerals the pc 2 core 340 cm in length collected in the vicinity of a high temperature fluid venting site was characterized by abundant mg saponite that is limited to a layer between 270 and 300 centimeters below the seafloor cmbsf and montmorillonite throughout the core below 55 cmbsf vertical profiles of pore fluid chemistry suggest that saponite formation is related to the interface between the seawater and the hydrothermal component in the sediment layer formation temperatures of the montmorillonite were estimated to be 118 163 c based on oxygen isotope thermometry formation of the montmorillonite is attributed to hydrothermal interaction between seawater dominant pore fluid and volcanic glass the formation temperature of the saponite was estimated to be 164 c based on oxygen isotope thermometry formation of the saponite is attributed to hydrothermal interaction between seawater dominant pore fluid and the montmorillonite which had been formed at a prior stage the pc 1 core 240 cm in length collected from a relatively low temperature fluid shimmering site was characterized by the occurrence of kerolite in the lower section 210 240 cmbsf vertical profiles of pore fluid chemistry suggest that the kerolite formation occurred at the interface between seawater and the hydrothermal component of the sediment layer formation temperature of the kerolite was estimated to be about 211 c based on oxygen isotope thermometry formation of the kerolite is attributed to precipitation from a fluid that was a mixture of a hydrothermal component and seawater this study revealed the occurrence of mg rich clay minerals saponite and kerolite beneath a submarine hydrothermal field that developed within sediment of felsic composition during hydrothermal interactions that formed these clay minerals seawater penetrated into the sediment and was an important mg source formation of mg rich clay minerals saponite and kerolite are controlled by pore fluid chemistry which varies from a seawater dominant to hydrothermal dominant component exclusive formation of mg rich clay minerals at different sites could be explained by different water rock ratios of the hydrothermal interaction saponite formation at low water rock ratio and kerolite precipitation at high water rock ratio occurrence of mg rich clay minerals provides clues to the hydrological structure in sediment covered hydrothermal systems in an arc volcanic caldera setting

evidence for recurrent early triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations abstract carbon cycle disturbance associated with mass extinction at the end of the permian period continued through the early triassic an interval of approximately 5 million years coincidence of carbon cycle stabilization with accelerated middle triassic biotic recovery suggests a link between carbon cycling and biodiversity but the cause of early triassic carbon isotope excursions remains poorly understood previous modeling studies have focused exclusively on the initial negative excursion in 13c across the permian triassic boundary and have not addressed the cycles of positive and negative excursions observed through the early triassic this study uses a simple carbon cycle box model to investigate potential causes underlying the series of early triassic carbon isotope excursions and to assess possible relationships between isotope excursions and coeval patterns of carbonate deposition according to the model introduction of carbon with the isotope composition of volcanic co2 produces small negative carbon isotope excursions followed by larger and more protracted positive excursions positive excursions result because increased pco2 causes warming enhancing marine anoxia and associated regeneration of phosphate and thus allowing greater productivity in addition carbonate weathering is more sensitive than organic carbon weathering to changes in atmospheric pco2 and climate causing an increase in the overall 13c composition of weathered carbon therefore the full early triassic record of negative and positive carbon isotope excursions can only be accounted for within the model by several pulses of carbon release characterized by varying mixtures of organic and mantle isotope compositions thermal metamorphism of coal and carbonate rocks in the crust of the siberian craton during eruption of the siberian traps flood basalts provides the most plausible mechanism for such a carbon release scenario if multiple episodes of co2 release account for early triassic carbon cycle instability regardless of their precise trigger then cessation of co2 release is likely to explain acceleration of biotic recovery early in the middle triassic

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

discerning primary versus diagenetic signals in carbonate carbon and oxygen isotope records an example from the permian triassic boundary of iran abstract sedimentary successions across the permian triassic boundary ptb are marked by a prominent negative carbon isotope excursion this excursion found in both fossil e g brachiopod and bulk carbonate at many sites around the world is generally considered to be related to a global carbon cycle perturbation oxygen isotopes also show a negative excursion across the ptb but because 18o is more prone to diagenetic overprint especially in bulk carbonate these data are often not used in palaeoenvironmental analyses in the present study bulk rock and brachiopod 13c and 18o as well as conodont 18o were analyzed in ptb successions at kuh e ali bashi and zal nw iran in order to evaluate diagenetic overprints on primary marine isotopic signals the results show that the use of paired c o isotopes and mn sr concentrations is not sufficient to identify diagenetic alteration in bulk materials because 13c 18o covariation can be due to environmental factors rather than diagenesis and sr ca and mn ca ratios can vary as a function of bulk rock lithology comparison of 13c profiles shows that all bulk carbonate is altered to some degree although the general bulk rock trend mimics that of the brachiopod data with a systematic offset of 1 2 0 4 this suggests that the first order 13c trend in bulk carbonate is generally robust but that the significance of small scale carbon isotope fluctuations is uncertain especially when such fluctuations are linked to lithologic variation the ptb interval which is marked by a low carbonate boundary clay in the study sections may be especially prone to diagenetic alteration e g via late stage dolomitization comparison of oxygen isotope profiles for bulk rock and well preserved fossils both brachiopods and conodonts shows that the former are offset by 2 1 0 4 diagenetic modeling suggests that these offsets were the product mainly of early diagenesis at burial temperatures of 50 80 c and water rock ratios of

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

recovery tempo and pattern of marine ecosystems after the end permian mass extinction high resolution sampling of more than 10 000 microfossils from seven late permian middle triassic paleoequatorial sections in south china refutes claims for a 5 m y recovery delay after the end permian mass extinction we show that level bottom seafloor diversity began to recover in the early smithian little more than 1 m y after the mass extinction while recovery of reef building metazoans began 4 m y later in the anisian a further mass extinction in the late smithian identified in the pelagic fossil record is weakly manifest as a temporary pause in diversification among benthic communities in the early triassic of south china the offshore diversity increase began before then in shallower settings the recovery from the end permian mass extinction in south china was therefore significantly more rapid and environmentally more complex than hitherto known

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

using mg isotope ratios to trace cenozoic weathering changes a case study from the chinese loess plateau abstract the magnesium isotope system is a useful tracer of weathering processes due to its sensitivity to secondary mineral formation we present elemental and isotopic data in bulk loess and paleosol sediments from the luochuan profile in the chinese loess plateau clp due to a relatively constant pre weathering mineralogy changes in the sediment chemistry with depth can be interpreted to reflect changes in weathering processes that are ultimately controlled by climate we find that the luochuan sediments are all enriched in light mg relative to the upper continental crust ucc 0 22 the isotopically light signature is a result of three way mixing between mg sourced from silicate calcite and dolomite changes in 26 mg between loess and paleosol reflect the higher weathering intensities during pedogenesis and corresponding loss of easily leachable calcite enriched in light mg isotopes from the loess layers this is confirmed by the results of a simple leaching procedure in which the leachate phase contains high ca concentrations and isotopically light 26 mg values of up to 2 any isotopic fractionation of mg imparted by isotopically heavy clay mineral formation appears to be insignificant and is obscured by the presence of detrital dolomite that is resistant to acid leaching and is isotopically light the isotopic composition of mg at luochuan broadly follows the magnetic susceptibility record in that loess layers are relatively isotopically light and have lower magnetic susceptibilities than their adjacent paleosol as such the changes in 26 mg values with depth do correspond to changes in chemical weathering however the driving factor behind these changing 26 mg values is carbonate preservation which in itself is not a highly sensitive paleoclimate proxy from a global perspective the 26 mg value of luochuan loess is similar to other loess sediments which are often isotopically light relative to the ucc we have recalculated the average 26 mg value of global loess sediments to be 0 58 1 18 this reflects the fact that 26 mg values in loess are highly heterogeneous and are generally enriched in 24 mg compared to typical ucc rocks due to preservation of high amounts of isotopically light carbonate minerals for this reason loess sediments cannot be used to approximate the isotopic composition of mg in the earth s crust

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

intensified chemical weathering during early triassic revealed by magnesium isotopes abstract marine ecosystem recovery after the latest permian mass extinction lpme was a protracted process during the early triassic 252 247 ma owing to repeated climatic and environmental perturbations chemical weathering can supply nutrients to the ocean and may have played an important role in the early triassic carbon cycle and biological recovery however only limited geochemical records of chemical weathering during the early triassic have been presented to date and the relationship between changes in weathering intensity and the slow recovery of marine ecosystems is effectively unknown here we report magnesium mg isotopic compositions of the siliciclastic components from shallow marine carbonates in two well studied upper permian lower triassic sections in iran and south china to track changes in chemical weathering intensity after the lpme both sections display a wide range of 26mg values 2 09 to 1 10 at zal 2 30 to 0 33 at zuodeng we identified two distinct stages i and ii in each section based on 26mg values and major elemental ratios variations of 26mg values in stage i changhsingian to mid dienerian are mainly controlled by mineralogical composition that can obscure weathering signals by contrast 26mg variations in stage ii upper dienerian to upper spathian are independent of lithology and inferred to reflect control by chemical weathering intensity the trends in chemical weathering intensity within stage ii correspond to first order variations in climate and carbon cycling marine ecosystem recovery during the early triassic may have been linked to recurrent episodes of intense chemical weathering caused by co2 degassing and climate warming this study demonstrates the potential utility of the mg isotopic compositions of the silicate fraction in marine carbonates as a proxy for chemical weathering intensity laying the groundwork for general applications of this method to deep time earth systems

clay mineralogical characteristics at the permian triassic shangsi section and their paleoenvironmental and or paleoclimatic significance abstract high resolution clay mineralogical investigations were conducted on the permian triassic p tr carbonate and siliceous rocks from the shangsi section south china the clay mineralogy is dominated by illite and illite smectite mixed layers i s throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 approaching the end permian mass extinction horizon epme onwards positive correlations of clay fraction with mainly land derived tio2 and magnetic susceptibility ms indicate a primary continental origin of the clay minerals rock eval pyrolysis analysis palynomorph coloration scanning electron microscope sem and transmission electron microscope tem observations all suggest that the rocks experienced thermal diagenesis which mainly promotes illitization processes of smectite clay minerals while discrete clay minerals are merely affected despite this diagenetic effect clay minerals still carry valuable paleoenvironmental and paleoclimatic information in the shangsi section the overall illitic composition of the clay minerals and nearly absence of kaolinite suggest a general semi arid condition during the p tr interval appearance of chlorite from bed 24 onwards suggests further aridification compared to the late permian occurrence of vermiculite from beds 24 28 in association with abundant volcanogenic materials most negative 13ccarb values as well as enhanced soil derived moretane abundance suggests catastrophic soil erosion and likely soil acidification during the p tr transition in the source area s in relation with the active volcanism in that time further decrease of chemical weathering and increase of physical weathering are indicated by increased input of primary clay minerals such as chlorite a better illite crystallinity and increase of al2o3 tio2 ratios a climate cooling period corresponding to the clarkina changxingensis clarkina deflecta conodont zone to the lower clarkina zhangi conodont zone is indicated by higher abundance of illite lower terrigenous tio2 ms and al2o3 tio2 in comparison with the overlying uppermost permian strata

geometry conditions and timing of off axis hydrothermal metamorphism and ore deposition in the solea graben the recent discovery of fossil spreading axes along the northern margin of the troodos ophiolite1 provides a unique opportunity to compare a fossil seawater hydrothermal system with systems of modern oceanic spreading centres2 6 whereas previous accounts of ophiolite hydrothermal systems7 13 including troodos14 16have elucidated many aspects of sea floor hydrothermal metamorphism earlier workers have not placed ophiolite hydrothermal features within any specific spreading centre structural framework most ophiolites exhibit complex histories of post accretion deformation that mask or obliterate early structures related to seafloor spreading the troodos ophiolite is apparently still in the process of being emplaced 17 and most structural elements at troodos appear to have originated beneath a cretaceous sea floor1 we have discovered an extensive area of intense seawater hydrothermal alteration within the sheeted dyke complex of the solea graben fig 1 the metamorphic petrology and oxygen isotope geochemistry of 100 dyke samples from this graben reveal the size and three dimensional geometry of the hydrothermal system and yield estimates of temperature salinity oxygen isotope composition and recharge discharge geometry for fluids that transported the constituents of massive sulfide orebodies geometric discordance between the trends of the hydrothermally altered area and of earlier seafloor spreading structures compels us to consider a post spreading off axis origin for the orebodies of the solea graben

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

smithian spathian boundary event evidence for global climatic change in the wake of the end permian biotic crisis one of the most important carbon cycle perturbations following the end permian mass extinction event straddles the smithian spathian boundary ssb olenekian early triassic this anomaly is characterized by a prominent positive carbon isotope excursion known from tethyan marine rocks its global signifi cance is established here by a new high paleolatitude record spitsbergen paleontological evidence such as boreal palynological data barents sea norway and global patterns of ammonoid distribution indicates a synchronous major change in terrestrial and marine ecosystems near the ssb the reestablishment of highly diverse plant ecosystems including the rise of woody gymnosperms and decline of the formerly dominating lycopods is interpreted as an effect of a major climate change this hypothesis is supported by modeling of ammonoid paleobiogeography the distribution patterns of which are interpreted as a proxy for sea surface temperatures sst the latest smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator sst gradient in contrast the steep spathian sst gradient suggests latitudinally differentiated climatic conditions we propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end smithian co2 injection the ssb event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end permian biotic crisis

extreme magnesium isotope fractionation at outcrop scale records the mechanism and rate at which reaction fronts advance isotopic fractionation of cationic species during diffusive transport provides a novel means of constraining the style and timing of metamorphic transformations here we document a major 1 decrease in the mg isotopic composition of the reaction front of an exhumed contact between rocks of subducted crust and serpentinite in the syros melange zone this isotopic perturbation extends over a notable length scale 1 m implicating diffusion of mg through an intergranular fluid network over a period of 100 kyr these novel observations confirm models of diffusion controlled growth of reaction zones formed between rocks of contrasting compositions such as found at the slab mantle interface in subduction zones the results also demonstrate that diffusive processes can result in exotic stable isotope compositions of major elements with implications for mantle xenoliths and complex intrusions

investigating the behaviour of mg isotopes during the formation of clay minerals abstract we present elemental and isotopic data detailing how the mg isotope system behaves in natural and experimentally synthesized clay minerals we show that the bulk mg isotopic composition 26 mg of a set of natural illite montmorillonite and kaolinite spans a 2 range and that their isotopic composition depends strongly on a balance between the relative proportions of structural and exchangeable mg after acid leaching these natural clays become relatively enriched in isotopically heavy mg by between 0 2 and 1 6 results of exchange experiments indicate that the mg that has adsorbed to interlayer spaces and surface charged sites is relatively enriched in isotopically light mg compared to the residual clay the isotopic composition of this exchangeable mg 1 49 to 2 03 is characteristic of the isotopic composition of mg found in many natural waters further experiments with an isotopically characterized mgcl 2 solution shows that the clay minerals adsorb this exchangeable mg with little or no isotopic fractionation although we cannot discount the possibility that the uptake of exchangeable mg does so with a slight preference for 24 mg to characterize the behaviour of mg isotopes during clay mineral formation we synthesized brucite mg oh 2 which we consider to be a good analogue for the incorporation of mg into the octahedral sheet of mg rich clay minerals or into the brucitic layer of clays such as chlorite in our experiment the brucite mineral becomes enriched in the heavy isotopes of mg while the corresponding solution is always relatively enriched in isotopically light mg the system reaches a steady state after 10 days with a final fractionation factor solid solution of 1 0005 at near neutral ph this result is consistent with the general consensus that secondary clay minerals preferentially take up isotopically heavy mg during their formation however our results also show that exchangeable mg is an important component within bulk clay minerals and can have an important influence over the bulk clay 26 mg value modeling shows that in certain soils or sediments where the percentage of exchangeable mg is 30 and the isotopic composition of the exchangeable mg is around 2 the generation of bulk 26 mg values of 26 mg values that are closer in composition to the ucc despite this results of modeling together with experimental observation suggests that the uptake of exchangeable mg into these clay rich sediments could cause a decrease in the bulk 26 mg value by up to 0 3 0 4 this should be accounted for when assessing the 26 mg value of sediments on a crustal scale

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

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

adsorption and desorption controlled magnesium isotope fractionation during extreme weathering of basalt in hainan island china magnesium isotopic compositions of a set of clay rich saprolites developed on the neogene tholeiitic basalt from hainan island in southern china have been measured in order to document the behavior of mg isotopes during continental weathering compared with unaltered basalts 26mg 0 36 the overlying saprolites are strongly depleted in mg i e th mg 99 1 to 92 9 and display highly variable 26mg ranging from 0 49 to 0 40 magnesium concentration and 26mg value of the saprolites display a general increasing trend upwards in the lower part of the profile but a decreasing trend towards the surface in the upper part the variations of mg concentration and isotopic composition in this weathering profile can be explained through adsorption and desorption processes 1 adsorption of mg to kaolin minerals kaolinite and halloysite with preferential uptake of heavy mg isotopes onto kaolin minerals and 2 desorption of mg through cation exchange of mg with the relatively lower hydration energy cations in the upper profile evidence for adsorption is supported by the positive correlation between 26mg and the modal abundance of kaolin minerals in saprolite of the lower profile while negative correlations between 26mg and concentrations of lower hydration energy cations e g sr and cs in the upper profile support the desorption process our results highlight that adsorption and desorption of mg on clay minerals play an important role in behavior of mg isotopes during extreme weathering which may help to explain the large variation in mg isotopic composition of river waters

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

constraining magnesium cycling in marine sediments using magnesium isotopes abstract magnesium concentrations in deep sea sediment pore fluids typically decrease down core due to net precipitation of dolomite or clay minerals in the sediments or underlying crust to better characterize and differentiate these processes we have measured magnesium isotopes in pore fluids and sediment samples from ocean drilling program sites 1082 1086 1012 984 1219 and 925 that span a range of oceanographic settings at all sites magnesium concentrations decrease with depth at sites where diagenetic reactions are dominated by the respiration of organic carbon pore fluid 26mg values increase with depth by as much as 2 because carbonates preferentially incorporate 24mg low 26mg the increase in pore fluid 26mg values at these sites is consistent with the removal of magnesium in mg carbonate dolomite in contrast at sites where the respiration of organic carbon is not important and or weatherable minerals are abundant pore fluid 26mg values decrease with depth by up to 2 the decline in pore fluid 26mg at these sites is consistent with a magnesium sink that is isotopically enriched relative to the pore fluid the identity of this enriched magnesium sink is likely clay minerals using a simple 1d diffusion advection reaction model of pore fluid magnesium we estimate rates of net magnesium uptake removal and associated net magnesium isotope fractionation factors for sources and sinks at all sites independent estimates of magnesium isotope fractionation during dolomite precipitation from measured 26mg values of dolomite samples from sites 1082 and 1012 are very similar to modeled net fractionation factors at these sites suggesting that local exchange of magnesium between sediment and pore fluid at these sites can be neglected our results indicate that the magnesium incorporated in dolomite is 2 0 2 7 depleted in 26mg relative to the precipitating fluid assuming local exchange of magnesium is minor at the rest of the studied sites our results suggest that magnesium incorporated into clay minerals is enriched in 26mg by 0 to 1 25 relative to the precipitating fluid this work demonstrates the utility of magnesium isotopes as a tracer for magnesium sources sinks in low temperature aqueous systems

the major ion δ44 40ca δ44 42ca and δ26 24mg geochemistry of granite weathering at ph 1 and t 25 c power law processes and the relative reactivity of minerals abstract we dissolved boulder creek granodiorite in a plug flow reactor for 5794 h at ph 1 and t 25 c the primary purpose of the experiment was to identify controls on dissolved 44 40ca 44 42ca and 26 24mg values during granite weathering herein we also examine the origin of ca and mg isotopic variability among minerals composing the boulder creek granodiorite and we constrain fundamental characteristics of granite weathering important for quantifying the elemental and isotopic geochemistry of the reactor output nine ca bearing minerals display an 8 80 range of 44 40ca values and a 0 51 range of 44 42ca values three mg bearing minerals display a 1 53 range of 26 24mg values these ranges expressed at the mineralogical scale are higher than the ranges thus far reported for bulk igneous rocks most of the 44 40ca variability reflects 40ca enrichment in k feldspar and to a lesser extent biotite due to the radioactive decay of 40k over the 1 7 ga age of the rock whereas the entire range of 44 42ca values reflects mass dependent isotope fractionation during igneous differentiation and crystallization the range of 26 24mg values may represent either fractionation during the chloritization of biotite or interaction of the boulder creek granodiorite with mg rich metamorphic fluids having low 26 24mg values the elemental and isotopic composition of the reactor output varied substantially during the experiment we synthesize the mineralogical and fluid data using coupled mass conservation equations solved at non steady state model calculations reveal an intricate balance between increasing specific surface area and decreasing mineral concentrations while surface area normalized dissolution rate constants were time invariant specific surface area increased as a power law function of time through positive feedbacks between mechanical disaggregation chemical dissolution and mineral depletion variations in dissolved 44 40ca 44 42ca and 26 24mg values reflect conservative mixing rather than fractionation apatite and calcite initially control 44 40ca and 44 42ca values followed by biotite titanite epidote hornblende and plagioclase the release of radiogenic 40ca clearly defines the period where biotite dissolution dominates the brucite layer of chlorite initially controls 26 24mg values followed by biotite the tot layer of chlorite and hornblende through direct isotopic tracking these results demonstrate that trace minerals such as apatite and calcite in the case of ca and brucite in the case of mg dominate elemental release during the incipient stages of granite weathering the results further show that biotite dissolution dominates the middle stages of granite weathering and that plagioclase dissolution only becomes important during relatively late stages the ca and mg isotope variations associated with these stages are distinct and potentially resolvable in soil mineral weathering studies

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

the effects of diagenesis and dolomitization on ca and mg isotopes in marine platform carbonates implications for the geochemical cycles of ca and mg abstract the ca mg o and c isotopic and trace elemental compositions of marine limestones and dolostones from odp site 1196a which range in depth 58 to 627 mbsf and in depositional age 5 and 23 ma are presented the objectives of the study are to explore the potential for non traditional isotope systems to fingerprint diagenesis to quantify the extent to which geochemical proxies are altered during diagenesis and to investigate the importance of diagenesis within the global ca and mg geochemical cycles the data suggest that ca which has a relatively high solid to fluid mass ratio can be isotopically altered during diagenesis in addition the alteration of ca correlates with the alteration of mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks bulk carbonate 44 ca values vary between 0 60 and 1 31 srm 915a scale the average limestone 44 ca is 0 97 0 24 1sd identical within error to the average dolostone 1 03 0 15 1sd magnesium isotopic compositions 26 mg dsm 3 scale range between 2 59 and 3 91 and limestones 3 60 0 25 and dolostones 2 68 0 07 are isotopically distinct carbon isotopic compositions 13 c pdb scale vary between 0 86 and 2 47 with average limestone 1 96 0 31 marginally offset relative to average dolostone 1 68 0 57 the oxygen isotopic compositions 18 o pdb scale of limestones 1 22 0 94 are substantially lower than the dolostones measured 2 72 1 07 the isotopic data from 1196a suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories numerical modeling supports the contention that such trends can be interpreted as diagenetic and suggests that the appropriate distribution coefficient k mg associated with limestone diagenesis is 1 to 5 10 3 distinctly lower than those values 0 015 reported in laboratory studies with respect to mg isotopes the modeling also suggest that diagenetic fractionation factors of 0 9955 4 5 and 0 9980 2 are appropriate for limestone diagenesis and dolomitization respectively

a conodont based revision of the 87 sr 86 sr seawater curve across the permian triassic boundary abstract based on analyses of 565 conodonts from meishan liangfengya and daijiagou south china and abadeh central iran we propose a revision of the seawater 87 sr 86 sr curve for the time period spanning 200 kyr prior to the permian triassic boundary ptb to 330 kyr after the ptb with carefully designed sample cleaning conodonts faithfully record seawater 87 sr 86 sr seawater 87 sr 86 sr was 0 707030 10 200 kyr prior to the ptb rose to 0 707070 10 approximately 39 kyr prior to the ptb at the marine extinction horizon the top of bed 24e at meishan to 0 707080 10 at the ptb and to 0 707120 20 at 330 kyr after the ptb the rate of change of seawater 87 sr 86 sr was 0 0000185 myr from the capitanian minimum to 100 kyr before the ptb and was 0 00020 7 5 myr between 100 kyr before and 330 kyr after the ptb over 6 myr this rate of change would result in a maximum 87 sr 86 sr of 0 70825 at the end of the early triassic compared with a model value of 0 7080 the sr data are consistent with the interpretation that the rise in marine 87 sr 86 sr was due primarily to an increase in the continental weathering and erosional flux and that soil binding vegetation was not re established during most of the early triassic the rapid rise in seawater 87 sr 86 sr began at least 30 kyr prior to the marine extinction at meishan indicating that the terrestrial extinction preceded that in the oceans

magnesium isotope fractionation during shale weathering in the shale hills critical zone observatory accumulation of light mg isotopes in soils by clay mineral transformation abstract magnesium isotopic ratios have been used as a natural tracer to study weathering processes and biogeochemical pathways in surficial environments but few have focused on the mechanisms that control mg isotope fractionation during shale weathering in this study we focus on understanding mg isotope fractionation in the shale hills catchment in central pennsylvania mg isotope ratios were measured systematically in weathering products along geochemical pathways of mg during shale weathering from bedrock to soils and soil pore water on a planar hillslope and to sediments stream water and groundwater on a valley floor significant variations of mg isotopic values were observed 26mg values 0 6 to 0 1 of stream and soil pore waters are about 0 5 to 1 lighter than the shale bedrock 26mg values of 0 4 consistent with previous observations that lighter mg isotopes are preferentially released to water during silicate weathering dissolution of the carbonate mineral ankerite depleted in the shallow soils but present in bedrock at greater depths produced higher mg2 concentrations but lower 26mg values 1 1 in groundwater 1 5 lighter than the bedrock 26mg values 0 2 to 0 4 of soil samples on the planar hillslope are either similar or up to 0 2 lighter than the bedrock hence a heavy mg isotope reservoir complementary to the lighter mg isotopes in soil pore water and stream water is missing from the residual soils on the hillslope in addition soil samples show a slight but systematic decreasing trend in 26mg values with increasing weathering duration towards the surface we suggest that the accumulation of light mg isotopes in surface soils at shale hills is due to a combined effect of i sequestration of isotopically light mg from soil water during clay dissolution precipitation reactions and ii loss of isotopically heavy particulate mg in micron sized particles from the hillslope as suspended sediments this latter mechanism is somewhat surprising in that most researchers do not consider physical removal or particles to be a likely mechanism of isotopic fractionation stream sediments 26mg values of 0 3 to 0 5 accumulated on the valley floor are 0 2 heavier than the bedrock and are thus consistent with that mobile particulates are the heavy mg isotope reservoir our study provides the first field evidence that changes in clay mineralogy lead to accumulation of lighter mg isotopes in residual bulk soils this example also demonstrates that transport of isotopically distinct fine particles from clay rich systems could be a new and important mechanism to drive the mg isotope compositions of silicate weathering residuals this mechanism drives fractionation in an opposite direction as might be expected from previous studies i e residual soils are driven to lighter mg values and sediments become isotopically heavier

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

integrated sr isotope variations and global environmental changes through the late permian to early late triassic new 87sr 86sr data based on 127 well preserved and well dated conodont samples from south china were measured using a new technique la mc icpms based on single conodont albid crown analysis these reveal a spectacular climb in seawater 87sr 86sr ratios during the early triassic that was the most rapid of the phanerozoic the rapid increase began in bed 25 of the meishan section gssp of the permian triassic boundary ptb and coincided closely with the latest permian extinction modeling results indicate that the accelerated rise of 87sr 86sr ratios can be ascribed to a rapid increase 2 8 of riverine flux of sr caused by intensified weathering this phenomenon could in turn be related to an intensification of warming driven runoff and vegetation die off continued rise of 87sr 86sr ratios in the early triassic indicates that continental weathering rates were enhanced 1 9 times compared to those of the late permian continental weathering rates began to decline in the middle late spathian which may have played a role in the decrease of oceanic anoxia and recovery of marine benthos the 87sr 86sr values decline gradually into the middle triassic to an equilibrium values around 1 2 times those of the late permian level suggesting that vegetation coverage did not attain pre extinction levels thereby allowing higher runoff

convergent continental margin volcanic source for ash beds at the permian triassic boundary south china constraints from trace elements and hf isotopes abstract volcanic activity around the time of the permian triassic boundary ptb has been proposed as a trigger for the associated biocrisis multiple claystone beds are prominent near the ptb sections in south china twenty one ptb ash beds from three sections at shangsi jianshi and meishan in south china were sampled and analyzed volcanic ash geochemistry indicate dacite and rhyolite compositions zircons from the ash layers yield comparatively low nb hf and high th nb ratios falling in the range of arc orogenic related settings zircon hf isotope compositions show that ehf t values vary from 11 7 to 1 8 indicating involvement of both juvenile and ancient crustal components the ash beds ss27a js129 js130 js133 ms25 ms26 near the biotic extinction horizon display a large variation in ehf t and relatively positive average values indicating input of juvenile mantle or crust and implying rapid transit through the older basement of the south china craton spatial and temporal distribution of ash beds from thirty one ptb sections worldwide reveal that volcanic ash beds occur mainly in or proximal to the tethys region and were sourced locally integration of hf isotope and trace element compositions from magmatic zircons suggests that the ptb volcanism occurred along the convergent continent margin in or near southwestern south china as a result of the closure of the paleo tethys ocean

the time scale of river sediment source to sink processes in east asia abstract knowledge of river sediment recycling provides important constraints on continent weathering and earth surface processes in this study we estimate the comminution age of sediments from the changjiang yangtze river and two small mountainous rivers in taiwan based on their lithogenic 234u 238u ratio the 234u 238u distributions in the changjiang catchment are overall related to sediment grain size and chemical weathering regime while 234u 238u ratios in taiwan rivers mainly depend on erosion denudation processes the comminution age constrains the time scale of sediment source to sink processes in catchments from sediment weathering denudation to transportation and finally deposition our results indicate that the comminution ages vary from 250 to 600 kyr for the changjiang sediments and 110 kyr for the taiwan sediments different comminution ages are associated with contrasting erosion and weathering regimes and diverse topography between the large changjiang catchment and small mountainous taiwan basins the longer comminution age of the changjiang sediment is an interacting effect of a longer erosion weathering history and sediment trapping effect and thus slow transfer rate created by broad floodplains and lakes in the middle and lower reaches the shorter comminution age of the taiwan sediment results from fast sediment denudation and transport associated with strong tectonic uplift typhoon climate and steep topography as these two major river systems dominate the sedimentology in east asia continent margin the distinct geological and topographical settings between the changjiang and taiwan river systems result in different sediment source to sink transport processes this work presents a systematic and quantitative constraint on the time scale of river sediment transfer process in east asia and also provides new insight into weathering regimes and sediment transport in monsoon climate dominated continent and island

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

mechanisms of magnesium isotope fractionation in volcanic soil weathering sequences guadeloupe magnesium mg stable isotopes are increasingly used as a weathering proxy in soils and rivers but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure a better understanding of the behaviour of mg isotopes during weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone here we investigate isotopic variations in 26mg in bulk soils and clay fractions relative to their parent andesite in three soilweatheringsequences from guadeloupe formed under contrasting climatic conditions soils formed in drier conditions low precipitation contain smectite whereas soils formed under wet conditions high rainfall are characterized by halloysite and fe oxides or kaolinite all clay fractions have mg isotopic compositions 26mg 0 41 to 0 10 similar to or heavier than their parent andesite 26mg 0 47 supporting the preferential incorporation of heavy mg isotopes in secondary mg bearing clay minerals with the first direct measurements on clay fractions soils with lighter mg isotope compositions have greater quantities of exchangeable mg the data support a contribution from sea spray to the exchangeable mg pool correlated to the soilweathering degree this study highlights for the first time that the soil 26mg not only depend on 26mg of the parent rock and on any fractionation that might occur but also on the mg retention on the exchange complex which could in turn be controlled by external inputs such as sea spray

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