did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

cretaceous tertiary and permian triassic boundary events compared abstract the cretaceous tertiary k t and permian triassic p tr events differ in many more aspects than they are similar this alone makes it unlikely that they are parts of a common web of periodic mass extinction events mee unlike the k t most mee have no ir anomalies and where in the comparatively complete section of the p tr at gartnerkofel austria weak ir concentrations are found their ratios to siderophile elements co ni cr are far less than chondritic in contrast ratios to chalcophile elements as sb zn never approach chondritic even in k t peaks and locality differences suggest local depositional processes that may also affect the siderophiles profiles of isotopes 13ccarb 87 sr 86 sr and possibly 18ocarb across these boundaries also differ radically whereas the k t profile of surface ocean 18ocarb has been shown to be mainly a drop in primary productivity the p tr profile is interpreted at least in part to be a consequence of a large and accelerating oxidation of previously stored corg with greatly differing consequences for climate these and other differences of proximate forcings for these two mee lead us to a hypothesis that such external exigencies were ever intermittently and severally with us but were effective only when the biotic web had already internally unravelled in some crucially strained patch gaia became antigaia

sedimentary host phases of mercury hg and implications for use of hg as a volcanic proxy abstract mercury hg concentration enrichments have become a widely used proxy for volcanic inputs to sediments especially for investigation of ancient large igneous province lip eruptions its application for this purpose requires normalization to an element representing the dominant host phase of hg generally total organic carbon toc for the organic fraction but occasionally total sulfur ts or aluminum al for the sulfide or clay fractions respectively hg studies generally assume an organic matter host but recent work has demonstrated that sulfide or clay fraction host phases are not uncommon making it essential to determine formation specific hg host phases here we investigate hg concentrations and their relationships to toc ts and al in four modern marine settings black sea japan sea saanich inlet and peru margin and six ancient marine formations from lower cambrian to lower jurassic multiple regression analysis mra shows that the organic fraction is the dominant host of hg in all of the modern marine sediments examined here as well as in many ancient marine units although in some of the latter hg resides primarily in the sulfide fraction i e lower cambrian and upper ordovician units or partly in the clay mineral fraction middle permian of the sediment a sulfide host phase is more likely in strongly euxinic depositional facies as reflected in high ts concentrations 1 0 and ts toc ratios 0 35 this study thus demonstrates the importance of determining hg host phases in sediments prior to normalization and use of hg as a volcanic proxy

new 40ar 39ar dating of the antrim plateau volcanics australia clarifying an age for the eruptive phase of the kalkarindji continental flood basalt province the kalkarindji flood basalt province of northern australia erupted in the mid cambrian today the province consists of scattered volcanic and intrusive suites the largest being the antrim plateau volcanics apv in northern territory accurate dating of the kalkarindji flood basalt province has proved challenging with previous studies focused on minor volcanic rocks and intrusive dykes in northern territory and western australia these previously published data corrected to the same decay constants range from 512 8 to 509 6 2 5 ma 2 placing the kalkarindji flood basalt province in apparent synchronicity with the cambrian stage 4 5 biotic crisis at 510 1 ma this study utilizes 40ar 39ar dating of basalts from the apv to accurately date the major volcanic eruptions in this province the results yield an age of 508 0 498 3 5 5 ma 2 indicating that the apv is younger than the intrusive rocks these dates allude to a relative timing discrepancy where intrusive activity in the north australian craton preceded the eruption of the apv as the last magmatic activity in the region the determination of these largest eruptions to be later than 510 ma effectively disassociates the kalkarindji lavas from being a major cause of the 510 ma biotic crisis but cannot definitively discount any deleterious effects on the fragile cambrian ecosystem supplementary material 40ar 39ar analysis data tables xrf geochemical data alteration study and photomicrographs of all five samples are available at https doi org 10 6084 m9 figshare c 4176674

intraplate extension prior to continental extrusion along the ailao shan red river shear zone left lateral movement of the ailao shan red river shear zone lends support to the hypothesis of continental extrusion resulting from the collision of india with asia our new observations from northwestern yunnan china and northwestern vietnam on different sides of the shear zone demonstrate that the sinistral offset was 600 km according to correlations of permian triassic flood basalt successions and late paleogene highly potassic mafic magmas we conclude that the shear was propagating on the south china continental margin and does not correspond to a suture between south china and indochina furthermore the highly potassic magmas were emplaced from ca 40 to 30 ma before the shear movement which was caused by the late oligocene to early miocene ca 27 22 ma extrusion activity this suggests that a late eocene to early oligocene intraplate extension possibly induced by delamination of thickened continental lithosphere took place in northwestern yunnan or eastern tibet as a response to the india asia collision this extension and sea floor spreading of the south china sea that began ca 30 ma could have accounted for the initiation of the ailao shan red river shear zone

40ar 39ar geochronological constraints on the age and evolution of the permo triassic emeishan volcanic province southwest china abstract the biostratigraphically constrained permo triassic emeishan volcanic province evp extending over wide areas in southwest china has been recently considered as a large igneous province contemporaneous with the siberian traps and the siliceous tuffs at the p t boundary in south china we report the first 40ar 39ar ages on this igneous province minimum ages have been obtained on phenocrystic plagioclase of the emeishan basalt which has undergone a pervasive metamorphism most likely during subsequent tectonization as a consequence of terrane amalgamation comparison between the ar release spectra obtained on clear vs cloudy plagioclase indicates a 40 30 ma sericite resetting time a minimum apparent age of 246 4 ma for plagioclase from a plagiogranite a late differentiate of the panzhihua layered complex and an age of 254 5 ma for phlogopite from a pyroxenite near lake erhai provide the first absolute age constraint on this igneous province additional ar ar age measurements on post emeishan alkaline and mafic magmatism yielded 104 2 and 100 2 ma for an alkaline complex near panzhihua and 42 1 ma for a gabbro sill emplaced near the ertan dam further study is still needed to determine the age of the emeishan volcanic emission accurately and to test the validity of the assumed short duration of the eruption

intercalibration of 40ar39ar dating standards a number of standards used for k ar and 40ar39ar dating have been intercalibrated multiple splits 15 40 mg each of mmhb 1 sb 3 biotite lp 6 biotite 40 60 ga1550 biotite fish canyon tuff 3 biotite taylor creek rhyolite sanidine bern 4 muscovite bern 4 biotite and pennsylvania state university orthoclase 1a were irradiated in capsules fused and analyzed in replicate analyses most of these standards proved to be homogeneous in 40ar 39ark ratio age k ca and 36ar contents mmhb 1 is inhomogeneous in age at the 15 mg level indicating it is unsuitable for use as an interlaboratory standard using material taken straight from the bottle the orthoclase sample is also inhomogeneous at the 30 mg level quoted relative to an age of 162 9 ma for the sb 3 biotite standard total fusion ages are lp 6 biotite 40 60 128 1 ma ga1550 biotite 97 8 ma fish canyon tuff 3 biotite 27 95 ma taylor creek rhyolite sanidine 28 0 ma bern 4 muscovite 18 51 ma bern 4 biotite 17 21 ma these ages are in good agreement with the absolute k ar ages of these minerals different preparations of biotite and sanidine standards from a welded tuff such as the fish canyon tuff may not be of identical ages tests on submilligram splits reveals that sb 3 biotite ga1550 biotite fish canyon tuff 3 biotite and taylor creek rhyolite sanidine are suitable for use as monitors in laser work the sanidine specimen appears to be the most suitable for use as the primary monitor for 40ar39ar dating

mercury as a proxy for volcanic emissions in the geologic record abstract large igneous province lip eruptions are increasingly considered to have driven mass extinction events throughout the phanerozoic however uncertainties in radiometric age dating of lip materials along with difficulty in accurate age dating of sedimentary rocks that record the environmental and biological history of our planet create inherent uncertainties in any linkage as such there is interest in using geochemical proxies to fingerprint periods of major volcanism in the sedimentary record termed here lip marks the use of sedimentary mercury hg contents has been suggested to be the best tool to accomplish this goal and recent work is reviewed here studies to date show that most extinction events ocean anoxic events and other environmental crises through the phanerozoic have an associated sedimentary hg anomaly it remains unclear though if each hg anomaly is truly a signature of massive volcanism or if it is controlled by local or regional processes as hg has a strong affinity to organic matter om normalisation with total organic carbon toc has been used to assess anomalies the measurement of toc has been fraught with error throughout many studies leaving some claimed hg toc anomalies questionable normalisation by other elements that can affect hg sequestration such as al and s are less common but warrant further investigation stable isotope systematics of hg have helped to further clarify the origin of hg spikes and clearly show that not all hg anomalies are directly related to volcanism although a promising tool the hg proxy requires more refinement to accurately understand the nuances of an hg anomaly in the rock record

sedimentary mercury enrichments as a marker for submarine large igneous province volcanism evidence from the mid cenomanian event and oceanic anoxic event 2 late cretaceous oceanic anoxic event 2 oae 2 during the cenomanian turonian transition 94 ma was the largest perturbation of the global carbon cycle in the mid cretaceous and can be recognized by a positive carbon isotope excursion in sedimentary strata although oae 2 has been linked to large scale volcanism several large igneous provinces lips were active at this time e g caribbean high arctic madagascan ontong java and little clear evidence links oae 2 to a specific lip the mid cenomanian event mce 96 ma identified by a small 1 positive carbon isotope excursion is often referred to as a prelude to oae 2 however no underlying cause has yet been demonstrated and its relationship to oae 2 is poorly constrained here we report sedimentary mercury hg concentration data from four sites three from the southern margin of the western interior seaway and one from demerara rise in the equatorial proto north atlantic ocean we find that in both areas increases in mercury concentrations and hg toc ratios coincide with the mce and the oae 2 however the increases found in these sites are of a lower magnitude than those found in records of many other mesozoic events possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events combined the new mercury data presented here are consistent with an initial magmatic pulse at the time of the mce with a second greater pulse at the onset of oae 2 possibly related to the emplacement of lips in the pacific ocean and or the high arctic

the permian triassic boundary event a geochemical study of three chinese sections abstract trace elements were determined in two well documented chinese permian triassic p tr boundary sections meishan and shangsi and in a new section liangfenya iridium concentrations range from 3 to 87 pg g at or below levels in common sedimentary rocks the results contrast with previous reports of high ir concentration in the meishan and shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the permian a notable feature in each of these widely separated p tr sections 500 1500 km is the existence of 2 5 light colored clay layers at and near the boundary these clay layers are strongly enriched in cs zr hf ta and th and depleted in cr co and ir indicating that they are altered ash apparently from the same massive silicic volcanic eruptions we estimate the magnitude of these eruptions to be a few thousand km3 of magma a volume comparable to the great toba eruption

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

climatic and oceanic changes during the middle late ordovician transition in the tarim basin nw china and implications for the great ordovician biodiversification event abstract the middle late ordovician transition darriwilian to sandbian age witnessed a major pulse of the great ordovician biodiversification event gobe and distinctive oceanic geochemical fluctuations such as coeval negative c and sr isotope excursions in this study investigations into geochemical variations notably the hg abundance or hg toc have been carried upon the organic rich black shale of the middle upper ordovician saergan formation to unravel the causes of this pulse based on these data three phases were identified phase 1 0 to 3 m is characterized by rising hg toc up to 138 ppb wt and ti al values as well as high ciacorr corrected chemical index of alteration values 68 9 72 3 with negligible enrichment of redox sensitive elements rse and nutrient elements e g u 5 2 ppm v 153 ppm mo 1 8 ppm p2o5 0 2 suggesting intensified volcanism which could have emitted significant amounts of greenhouse gases thereby leading to climate warming in contrast phase 2 3 to 11 m is characterized by decreasing hg toc and ti al ratios relatively low though slightly fluctuating ciacorr values generally depleted in rse except moderately enriched u up to 14 6 ppm and increased p al and ba al ratios implying weakening volcanic activity and subsequent climate cooling and the potential for improved seawater ventilation as a result of oceanic upwelling phase 3 sandbian age 11 13 m witnessed continuous decrease in hg toc ratio an increase in ti al and ciacorr values fairly low values of rse enrichment and p al and ba al ratios indicating recurrent climate warming and the potential for slowed oceanic circulation and attenuated upwelling of nutrient rich deep waters onto the shallow shelf these changes could have diminished bioproductivity and organic output onto the seafloor this study offers insights into volcanic climatic oceanic interactions during a major pulse of the gobe around the middle late ordovician transition while black shales were extensively deposited

carbon and sulfur isotope geochemistry of the hirnantian late ordovician wangjiawan riverside section south china global correlation and environmental event interpretation detailed geochemical analyses 13ccarb 13corg 34ssulfide and abundance of sulfide carbonate and organic carbon were performed on samples from the wangjiawan riverside section close to the gssp global stratotype section and point for the hirnantian stage of the ordovician new data show two increases in carbonate content coincident with two glacial pulses that reduced detrital input the new 34ssulfide data show distinct changes in this section with relatively high values in the kuanyinchiao formation a pattern observed throughout the yangtze platform however there is no consensus on the cause of these changes the new 13ccarb data show a sharp rise and peak in the extraordinarius zone below the previously published 13corg peak in the persculptus zone a compilation of the new results with other sections indicates the hirnantian carbon isotope excursion starts near the pacificus extraordinarius boundary and elevated values remain until the end of the excursion in the persculptus zone for both 13corg and 13ccarb the controversy over correlating hirnantian graptolite zones with chitinozoan zones can also be addressed the new 13ccarb data also allow direct comparison with hirnantian 13ccarb data from anticosti island and the baltic region which are zoned by chitinozoan fossils this comparison favors a correlation of the taugourdeaui and scabra chitinozoan zones with the extraordinarius graptolite zone

magnetostratigraphic investigations on an emeishan basalt section in western guizhou province china abstract a magnetostratigraphic investigation has been conducted on a late permian emeishan basalt section at duge in western guizhou province china the characteristic remanent magnetization chrm directions resolved at high temperatures from the basalts pass the fold test with dual polarity and define a normal magnetozone of five sixths of the total thickness in the lower part and a reversed magnetozone of one sixth of the thickness in the top part of the section the chrm directions from the basalt clasts of pyroclastic rocks fail the conglomerate test but the direction and polarity of the chrm of the clasts from the upper reversed zone are consistent with those of the basaltic lavas in the reversed zone and the normal directions also dominate the chrm of the clasts taken from the lower normal zone this suggests that either the original remanence of the clasts was reset by cementing basaltic lavas or the chrm of the basalts was acquired late but not beyond a field reversal the magnetostratigraphic pattern n r observed at duge is as simple as that observed from some major continental flood basalt provinces in the world where very few magnetic polarity zones were observed from volcanic sequences of great thickness the emplacement of the emeishan basalts in western guizhou is estimated to be less than two million years the normal polarity magnetozone observed indicates that the extrusion of the emeishan basalts in western guizhou postdates the permo carboniferous reversed superchron pcrs the apparent shortness of the reversed magnetozone explains why far fewer reverse directions than normal ones have been so far reported from the emeishan basalts

a minimum upb age for siberian flood basalt volcanism abstract establishing an accurate and precise age for siberian flood basalt volcanism is of great importance in evaluating causes for the unequaled mass extinction of flora and fauna at the permian triassic boundary we report a new minimum u pb age obtained from zircon and baddeleyite from the mineralized noril sk i intrusion that cuts the lower third of this rapidly deposited 3500 m thick volcanic sequence near noril sk this 251 2 0 3 2 ma age is within analytical error of the shrimp u pb age for zircon from the permian triassic boundary at meishan south china 251 1 3 6 ma 2 and confirms siberian basaltic volcanism as a possible contributor to the mass extinction

extinction intensity during ordovician and cenozoic glaciations explained by cooling and palaeogeography a striking feature of the marine fossil record is the variable intensity of extinction during superficially similar climate transitions here we combine climate models and species trait simulations to explore the degree to which differing palaeogeographic boundary conditions and differing magnitudes of cooling and glaciation can explain the relative intensity of marine extinction during greenhouse icehouse transitions in the late ordovician and the cenozoic simulations modelled the response of virtual species to cooling climate using a spatially explicit cellular automaton algorithm we find that palaeogeography alone may be a contributing factor as identical changes in meridional sea surface temperature gradients caused greater extinction in late ordovician simulations than in cenozoic simulations differences in extinction from palaeogeography are significant but by themselves are insufficient to explain observed differences in extinction intensity however when simulations included inferred changes in continental flooding and interval specific models of sea surface temperature predicted differences in relative extinction intensity were more consistent with observations from the fossil record our results support the hypothesis that intense extinction in the late ordovician is partially attributable to exceptionally rapid and severe cooling compared to cenozoic events high extinction intensity during late ordovician but not cenozoic transitions to glacial conditions can be attributed to both temperature and palaeogeography according to analysis combining climate models and simulations of virtual species

weathering history and landscape evolution of western ghats india from 40 ar 39 ar dating of supergene k mn oxides laterites preserved on both sides of the western ghats escarpment of peninsular india have formed by long term lateritic weathering essentially after india seychelles continental break up following deccan traps emplacement c 63 ma ago supergene manganese ores of the western ghats were formed on late archean manganese protores among mn oxides composing the ores cryptomelane k rich mn oxide was characterized and dated by 40ar 39ar geochronology measured ages complement those previously obtained in other south indian manganese ores from the hinterland plateau bonnet et al 2016 and further document three major weathering periods c 53 44 ma c 39 22 ma and c 14 10 ma the later being documented for the first time in india these periods coincide with global paleoclimatic proxies and date the lateritic weathering of three successive paleolandscapes of the western ghats that evolved under slow denudation c 8 m myr over the last 44 myr and were mostly incised during the neogene 22 ma that indicates the western ghats are a relict of a south indian plateau preserved at the headwaters of very long east flowing river systems and above the western ghats escarpment topography and denudation history of this landscape do not require neogene tilt of the peninsula as recently proposed

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

selective environmental stress from sulphur emitted by continental flood basalt eruptions several biotic crises during the past 300 million years have been linked to episodes of continental flood basalt volcanism and in particular to the release of massive quantities of magmatic sulphur gas species flood basalt provinces were typically formed by numerous individual eruptions each lasting years to decades however the environmental impact of these eruptions may have been limited by the occurrence of quiescent periods that lasted hundreds to thousands of years here we use a global aerosol model to quantify the sulphur induced environmental effects of individual decade long flood basalt eruptions representative of the columbia river basalt group 16 5 14 5 million years ago and the deccan traps 65 million years ago for a decade long eruption of deccan scale we calculate a decadal mean reduction in global surface temperature of 4 5 k which would recover within 50 years after an eruption ceased unless climate feedbacks were very different in deep time climates acid mists and fogs could have caused immediate damage to vegetation in some regions but acid sensitive land and marine ecosystems were well buffered against volcanic sulphur deposition effects even during century long eruptions we conclude that magmatic sulphur from flood basalt eruptions would have caused a biotic crisis only if eruption frequencies and lava discharge rates had been high and sustained for several centuries at a time

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

age of the emeishan flood magmatism and relations to permian triassic boundary events the permian triassic p t mass extinction the greatest biological mortality event in the earth s history was probably caused by dramatic and global forcing mechanisms such as the siberian flood volcanism here we present the first set of high precision 40 ar 39 ar dating results of volcanic and intrusive rocks from the emeishan traps south china which define a main stage of the flood magmatism at v251 253 ma and a subordinate precursory activity at v255 ma this time span is generally coeval with or slightly older than the age of the p t boundary estimated by the ash beds in the meishan stratotype section and the main eruption of the siberian traps our data reinforces the notion that the eruption of the emeishan traps rather than eruption of the siberian traps accounted for the formation of the p t boundary ash beds in south china the emeishan flood magmatism which occurred in the continental margin comprising thick marine limestone formations moreover may have triggered rapid release of large volumes of methane and carbon dioxide that could have been responsible for the global n 13 c excursion and associated environmental crisis leading to the mass extinction at the p t boundary fl 2002 elsevier science b v all rights reserved

marine redox variability from baltica during extinction events in the latest ordovician early silurian abstract it is well documented that upper ordovician and silurian successions record multiple marine turnover events including the second largest mass extinction in the phanerozoic widespread glaciation and multiple global carbon cycle perturbations whereas causal mechanisms for the late ordovician major mass extinction event involving climate paleoceanographic variation and 13c records have been published similar records remain poorly constrained for subsequent extinction events in the early silurian here we present new organic matter carbon isotope 13corg chemostratigraphy and corresponding paleoredox proxies fe speciation mn v mo and pyrite sulfur isotopes from two organic rich drill core sections in sweden and latvia that span the upper katian through lower wenlock stages 446 431 ma pyritized fe and bulk sedimentary mn concentrations from upper ordovician strata in southern sweden suggest a local redox shift to more reducing conditions in the late hirnantian possibly including euxinic anoxic and sulfidic water column conditions that coincide with the second mass extinction pulse the new high resolution 13corg and 34spyr datasets from the late aeronian early silurian interval within both drill cores show positive excursions that are broadly coincident with the associated sandvika and sedgwickii extinction events independently fe speciation and bulk sedimentary trace metal data from this late aeronian interval record locally euxinic conditions in both the deep basinal sweden and distal shelf latvia settings before and during the late aeronian positive 13c excursion this multiproxy paleoredox dataset provides the first direct evidence for local to regional expansion of reducing marine conditions coincident with this early silurian late aeronian biotic event and positive 13c excursion additionally new 34spyr values spanning the llandovery wenlock boundary interval in the latvia core show a positive excursion coincident with fe speciation and trace metal enrichments that imply a local redox perturbation with intermittently euxinic bottom waters during the rising limb of the ireviken positive 13c excursion the combination of these geochemical data for local to regional scale more data required for global interpretations changes in marine redox conditions with paleobiological records and evidence for eustatic sea level rise indicate that environmental stresses related to an expansion of anoxic to euxinic conditions were a probable driver for several extinction events during the latest ordovician early silurian

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

globally enhanced hg deposition and hg isotopes in sections straddling the permian triassic boundary link to volcanism abstract mercury hg toc spikes from eight permian triassic boundary ptb sections in this study display patterns similar to each other across the so called extinction interval as well as strong variation in sedimentation rates from section to section mercury may have been originated from the synchronous magmatism of the siberian traps large igneous province stlip at the gssp in meishan china hg toc peaks were observed in the latest permian mass extinction interval lpme and early triassic mass extinctions etme the successions at hovea 3 australia ursula creek canada idrijca slovenia rizvanusa croatia exhibit hg toc peaks at the lpme and ptb the rizvanusa section displays one peak at the etme horizon zal and abadeh iran successions at the lpme and etme horizons while misci seres tyrol italy section shows an enrichment at the lpme the largest hg toc peaks at the lpme ptb and etme are perhaps linked to the beginning of stage 2 extrusive hiatus of the siberian traps lip the meaning of the hg toc spike between the lpme event and the ptb in seven of these sections is fuzzy in the 202hg mdf vs 201hg mif cross plot the majority of samples from the extinction interval appear within the volcanic emission box and a few samples plot in the sediment soil peat box hg isotope signatures resulted from mixing processes of volcanic and normal marine sediment hg generating four horizontal trends whose 201hg shows negligible to no variation less terrigenous hg influx was noticed in the sections closer to the stlip rizvanusa idrijca and seres misci all in europe in which 201hg mif is close to zero marked influence occurs in sections far distant from the stlip meishan ursula creek and hovea 3 that exhibit negative 201hg mif the two sections from iran at intermediate distance from the stlip exhibit the highest positive 201hg values abadeh section and the lowest negative 201hg values zal section a 199hg mif vs hg n ng 1 cross plot suggests that volcanic hg has been contaminated by normal marine source hg influx in these sections helping to shape two major curved trends the negative c isotope excursions and hg toc enrichments in the studied sections are nearly coeval and this supports the hypothesis of synchronism between the permian triassic transition biotic crises lpme and etme and the start of the stage 2 of the siberian traps sill intrusion style of magmatism

high 3he plume origin and temporal spatial evolution of the siberian flood basalts an olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the siberian flood basalt province sfbp yielded a 40ar 39ar plateau age of 253 3 2 6 million years distinctly older than the main tholeiitic pulse of the sfbp at 250 0 million years olivine phenocrysts of this rock showed 3he 4he ratios up to 12 7 times the atmospheric ratio these values suggest a lower mantle plume origin the neodymium and strontium isotopes rare earth element concentration patterns and cerium lead ratios of the associated rocks were also consistent with their derivation from a near chondritic primitive plume geochemical data from the 250 million year old volcanic rocks higher up in the sequence indicate interaction of this high 3he sfbp plume with a suboceanic type upper mantle beneath siberia

carbon isotope stratigraphy and correlation of depositional sequences in the upper ordovician ely springs dolostone eastern great basin usa abstract shallow water carbonate shelf strata of the ely springs dolostone accumulated on the western laurentian margin as relative sea level fluctuated during the late ordovician icehouse the ely springs dolostone is divided into four upper katian depositional sequences and one hirnantian sequence here we present new carbon isotope data from the ely springs in the context of the sequence stratigraphic architecture these data derive from a shelf transect of five stratigraphic sections exposed in the eastern great basin usa and provide records of carbon cycling on the laurentian margin prior to and during the hirnantian glacial maximum the 13 c values range between 2 and 4 at each section and chemostratigraphic tie points occur in all sections of the transect intrabasinal correlations based on the 13 c records are consistent with correlations derived from sequence stratigraphy and conodont biostratigraphy the ely springs dolostone carbon isotope curve can also be correlated with the late katian cincinnatian composite derived from epicontinental deposits of the laurentian midcontinent the globally documented hirnantian positive carbon isotope excursion commonly referred to as hice occurs within the uppermost depositional sequence immediately below a regional unconformity coinciding with peak glacial conditions on gondwana the late katian elkhorn and waynseville 13 c excursions are also present in the ely springs dolostone carbon isotope record the peak value of the hirnantian carbon excursion increases from 2 6 to 3 8 across the shallow shelf and reaches 7 3 in coeval limestones of the hanson creek formation deposited in a deep dysoxic setting this lateral gradient is not the result of changes to the 13 c of weathered carbon supplied by rivers as previously proposed it may be instead related to authigenic carbonate cement precipitation during early diagenesis of the hanson creek strata that these pervasively dolomitized shallow water carbonates retain 13 c signatures useful for regional and global stratigraphic correlation indicates that 13 c chemostratigraphy may be an appropriate correlation tool for dolostones with few biostratigraphically useful fossils

a volcanic trigger for the late ordovician mass extinction mercury data from south china and laurentia the late ordovician mass extinction lome one of the five largest phanerozoic biodiversity depletions occurred in two pulses associated with the expansion and contraction of ice sheets on gondwana during the hirnantian age it is widely recognized that environmental disruptions associated with changing glacial conditions contributed to the extinctions but neither the kill mechanisms nor the causes of glacial expansion are well understood here we report anomalously high hg concentrations in marine strata from south china and laurentia deposited immediately before during and after the hirnantian glacial maximum that we interpret to reflect the emplacement of a large igneous province lip an initial hg enrichment occurs in the late katian age while a second enrichment occurs immediately below the katian hirnantian boundary which marks the first pulse of extinction further hg enrichment occurs in strata deposited during glacioeustatic sea level fall and the glacial maximum we propose that these hg enrichments are products of multiple phases of lip volcanism while elevated hg concentrations have been linked to lip emplacement coincident with other phanerozoic mass extinctions the climate response during the lome may have been unique owing to different climatic boundary conditions including preexisting ice sheets our observations support a volcanic trigger for the lome and further point to lip volcanism as a primary driver of environmental changes that caused mass extinctions

high resolution early paleozoic ordovician silurian time scales for much of the geologic time scale resolving power appears to be limited by the duration of biostratigraphic zones and subzones yet these zones exploit the appearance and disappearance events of only a small fraction of the species they span computer algorithms can sequence an order of magnitude more events and make explicit the uncertainties that arise when calibrating the resulting time line an illustrative case history builds an ordovician and silurian time scale from the geologic record of the entire graptolite clade over 1900 species from more than 400 localities and sections worldwide the same approach can be applied to any stratigraphic interval with detailed biostratigraphic observations it provides the foundation for time scales and paleobiologic time lines using logic similar to graphic correlation optimizing algorithms search for a composite sequence of species first and last appearance events that minimizes the implied shortcomings of all the field observations the algorithms minimize the number of species coexistences that are implied but never observed and the net adjustments needed to bring local range charts into agreement with a single composite sequence of events after total section thicknesses have been rescaled to help normalize for variation in depositional rate mean stratigraphic thicknesses are used to scale the intervals between adjacent events in the composite sequence the resulting scaled composite sequence is converted to a relative geologic time scale by identifying stage and zone boundaries within the sequence of graptolite events this relative scale is in turn calibrated by dated volcanic ash beds that were incorporated in the search for the optimal sequence these dated events are also used to test for linearity of the scaled composite the final time scale has a potential resolving power of 0 02 0 1 m y more than ten times better than can be achieved by traditional zones graptolite zones vary widely in duration from as short as 0 1 m y to nearly 5 0 m y the mean duration of zones or zonal groupings calibrated here is 1 44 m y in the ordovician and 0 91 m y in the silurian the average uncertainty in locating zone boundaries in a single composite sequence is about one fourth of the mean zone duration the variance resulting from differences in time scales developed from differing numbers of field observations and in response to changes in the optimization criteria gives a very conservative measure of the overall robustness of the method these differences indicate an average uncertainty in the age of graptolite zone boundaries that is more nearly equal to the mean zone duration for zone duration the mean uncertainty amounts to about one half of the length of an average zone

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

mercury enrichments and the frasnian famennian biotic crisis a volcanic trigger proved the frasnian famennian f f global event one of the five largest biotic crises of the phanerozoic has been inconclusively linked to rapid climatic perturbations promoted in turn by volcanic cataclysm especially in the viluy large igneous province lip of siberia conversely the triggers of four other phanerozoic mass extinction intervals have decisively been linked to lips owing to documented mercury anomalies shown as the diagnostic proxy here we report multiple hg enrichments in the two step late frasnian kellwasser crisis interval from paleogeographically distant successions in morocco germany and northern russia the distinguishing signal 1 ppm hg in the domain of closing rheic ocean was identified in different lithologies immediately below the f f boundary and approximately correlated with the onset of the main extinction pulse this key hg anomaly comparable only with an extreme spike known from the end ordovician extinction was not controlled by increased bioproductivity in an anoxic setting we suggest therefore that the global chemostratigraphic pattern near the f f boundary records a greatly increased worldwide hg input controlled by the center hill eruptive pulse of the eovariscan volcanic acme but likely not manifested exclusively by lip s consequently all five major biotic crises of the phanerozoic have now been more reliably linked to volcanic cataclysms

effect of intense weathering and postdepositional degradation of organic matter on hg toc proxy in organic rich sediments and its implicationsfor deep time investigations

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

δ13c depth profiles from paleosols across the permian triassic boundary evidence for methane release stable carbon isotopic analyses of organic carbon 13 c in individual paleosol profiles from permian triassic sequences of antarctica reveal systematic isotopic variations with profile depth these variations are in many cases analogous to those in modern soils which are functions of redox conditions soil development and degree and type of microbial decay in modern soils these isotopic depth functions develop independently from vegetation changes c 3 versus c 4 vegetation and can be diagnostic of soil orders this study shows that soil intrinsic functions can be preserved in the 13 c values of paleosols as old as 260 ma and constitute valuable data for paleoecological interpretations a large carbon isotopic offset of as much as 10 in whole paleosol profiles across the permian triassic boundary indicates significant changes in the soil biogeochemistry and the soil atmosphere system early triassic paleosols are distinctive in their extremely low 13 c values to 42 and often show an anomalous 13 c depth distribution compared to both permian paleosols and modern soils highly depleted 13 c values as the ones in early triassic paleosols are suggested to be associated with microbial methane oxidation methanotrophy this hypothesis implies increased methane concentrations in the early triassic soil atmosphere system increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the permian triassic boundary

cascading trend of early paleozoic marine radiations paused by late ordovician extinctions the greatest relative changes in marine biodiversity accumulation occurred during the early paleozoic the precision of temporal constraints on these changes is crude hampering our understanding of their timing duration and links to causal mechanisms we match fossil occurrence data to their lithostratigraphical ranges in the paleobiology database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high resolution time slices in addition we apply capture recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates our method reveals a stepwise biodiversity increase with distinct cambrian and ordovician radiation events that are clearly separated by a 50 million year long period of slow biodiversity accumulation the ordovician radiation is confined to a 15 million year phase after which the late ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years based on a first differences approach on potential abiotic drivers controlling richness we find an overall correlation with oxygen levels with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present day levels during the middle ordovician darriwilian age contrary to the traditional view of the late ordovician extinctions our study suggests a protracted crisis interval linked to intense volcanism during the middle late ordovician katian age as richness levels did not return to prior levels during the silurian a time of continental amalgamation we further argue that plate tectonics exerted an overarching control on biodiversity accumulation

mercury enrichments provide evidence of early triassic volcanism following the end permian mass extinction abstract oceanic environments and biotas were in a state of near continuous perturbation during the early triassic the 5 million year interval following the latest permian mass extinction lpme but the underlying cause s remain uncertain the role of episodic volcanic or intrusive magmatic activity in triggering global scale perturbations during this interval is suspected but has not been strongly evidenced to date here we investigate the record of volcanism through the early triassic with a focus on the smithian spathian boundary or ssb using mercury hg concentrations in marine sediments as a proxy this study examines five marine sections from three paleo oceans paleo tethys neo tethys and panthalassa representing a range of depositional settings from shallow platform to deep slope our results suggest that volcanic and magmatic activity of the siberian traps large igneous province stlip was most intense during the first 1 3 million years following the lpme and that termination of its most active stage was responsible for a sharp cooling event at the ssb variations in the intensity of stlip activity are thus likely to account for the large 8 fluctuations of 13ccarb and related changes in oceanic redox and environmental conditions that characterized the griesbachian to smithian substages of the early triassic in marine sections globally we hypothesize that a strong reduction or cessation of stlip activity at the ssb set the stage for the recovery of marine biodiversity and ecosystems in the spathian and later

mercury anomaly deccan volcanism and the end cretaceous mass extinction reply the contribution of the deccan traps west central india volcanism in the cretaceous paleogene kpg crisis is still a matter of debate recent u pb dating of zircons interbedded within the deccan lava flows indicate that the main eruptive phase 1 1 106 km3 of basalts initiated 250 k y before and ended 500 k y after the kpg boundary however the global geochemical effects of deccan volcanism in the marine sedimentary record are still poorly resolved here we investigate the mercury hg content of the bidart france section where an interval of low magnetic susceptibility ms located just below the kpg boundary was hypothesized to result from paleoenvironmental perturbations linked to the paroxysmal deccan phase 2 results show hg concentrations 2 orders of magnitude higher from 80 cm below to 50 cm above the kpg boundary maximum 46 6 ppb and coincident with the low ms interval increase in hg contents shows no correlation with clay or total organic carbon contents suggesting that the hg anomalies resulted from higher input of atmospheric hg species into the marine realm rather than organic matter scavenging and or increased runoff the hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera suggesting correlative changes in marine biodiversity this discovery represents an unprecedented piece of evidence of the nature and importance of the deccan related environmental changes at the onset of the kpg mass extinction

oceanic environment changes caused the late ordovician extinction evidence from geochemical and nd isotopic composition in the yangtze area south china the ordovician silurian o s transition was a critical interval in geological history multiple geochemical methods are used to explore the changes in oceanic environment the nd isotopic compositions in the yangtze sea are controlled by two sources the continental erosion and the panthalassa ocean high end t values during the katian late hirnantian and rhuddanian intervals are associated with the high sea level which resulted in less terrestrial input based on the low ti al and zr al ratios in contrast low end t values during the early hirnantian interval are related to the sea level fall in this case the exposure of submarine highs and the growth of yangtze oldlands could lead to more continental materials being transported into the yangtze sea based on high ti al and zr al ratios in addition the negative end t excursion can also be attributed to the weak circulation between the yangtze sea and panthalassa ocean when sea level was low furthermore the sea level eustacy plays a significant role in the changes in redox water conditions the redox indices mainly uef ce ce and corg pt across the o s transition show a predominance of anoxic ocean over the yangtze sea during the katian late hirnantian and rhuddanian intervals and an oxygenated episode was briefly introduced during the early hirnantian period because of the fall in sea level the late ordovician biotic crisis was marked by two phase extinction events and the change in sea level and redox chemistry may be the important kill mechanisms

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

latest permian mercury anomalies a sedimentary record from the buchanan lake section canadian high arctic shows anomalous high levels of mercury hg during the latest permian extinction lpe on northwest pangea significant influx of hg progressively overwhelmed the marine system major disruption of the organic matter mediated hg drawdown process resulted in accumulation of dissolved hg to maximum levels at the lpe boundary affecting an already stressed global ecosystem a switch to euxinic marine conditions at the lpe boundary led to chemical drawdown of hg sulfides as marked by progressive hg mitigation this allowed self recovery from toxic hg conditions and ultimately led to reestablishment of the internal hg organic matter drawdown process we hypothesize that anomalous hg levels may be attributed to the significant natural atmospheric emissions caused by catastrophic siberian traps volcanic eruptions

conodont survival and low iridium abundances across the permian triassic boundary in south china the permian triassic sedimentary sequence of china includes one of the most complete and fossiliferous paleozoic mesozoic boundaries known closely spaced sampling across the boundary which is an important extinction event for most organisms has produced good conodont faunas that show little diversity change a drop in conodont abundance is the only apparent response to the extinction event a low concentration of iridium in the boundary clay 0 002 part per billion 20 percent as well as in samples immediately below and above that range from 0 004 to 0 034 part per billion do not support the proposal of an extraterrestrial impact event at this boundary in china

the end ordovician mass extinction a single pulse event abstract the end ordovician mass extinction eome is widely interpreted as consisting of two pulses associated with the onset and demise of the gondwana glaciation respectively with the second pulse eradicating the distinctive glacially related hirnantian benthic biota hbb a global review of occurrence data of latest ordovician benthic marine organisms reveals that virtually all warm water benthic assemblages previously assigned to the hbb comprise two distinct and clearly postglacial faunas both younger middle and late hirnantian respectively than the cool water hirnantia fauna latest katian to early hirnantian the newly recognised three transitional benthic faunas i e tbfs 1 3 can be closely tied to graptolite conodont and chitinozoan biozonations the hirnantian isotope carbon excursion hice and the glaciation thereby providing an integrated much higher resolution timescale for understanding the tempo and nature of the eome at this finer resolution we postulate a more profound impact of the first pulse of the eome than hitherto envisaged as evidenced by opportunistic expansion of the hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath we also argue based on high quality data from well documented benthic groups in south china i e brachiopods tabulate and rugose corals trilobites and sponges that the magnitude of the second pulse of the eome caused by the deglaciation has been overestimated because the two postglacial faunas i e tbfs 2 3 were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline thus it is more plausible to reinterpret the eome as a single pulse rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the hirnantian prior to the onset of a progressive reestablishment of marine ecosystems during the early silurian rhuddanian and aeronian associated with an overall amelioration of climatic conditions

new late middle to early late ordovician u pb zircon ages of extension related felsic volcanic rocks in the eastern pyrenees ne iberia tectonic implications pre variscan basement rocks from the pyrenees provide evidence of several magmatic episodes with complex geodynamic histories from late neoproterozoic to palaeozoic times one of the most significant episodes consisting of several granitic and granodioritic bodies and volcanic rocks mostly pyroclastic in nature dates from the late ordovician period in the eastern pyrenees this magmatism is well represented in the ribes de freser and nuria areas here the nuria orthogneiss and the ribes granophyre both dated at c 457 460 ma seem to form a calc alkaline plutonic suite emplaced at different crustal levels the presence of numerous pyroclastic deposits and lavas interbedded with upper ordovician sandbian lower katian formerly caradoc sediments intruded by the ribes granophyre suggests that this magmatic episode also generated significant volcanism moreover the area hosts an important volume of rhyolitic ignimbrites and andesitic lavas affected by alpine deformation these volcanic rocks were previously attributed to late variscan volcanism extensively represented in other areas of the pyrenees here we present the first five laser ablation u pb zircon dates for this ignimbritic succession and two new ages for the ribes granophyre the ages of the ignimbrites overlapping within error are all 460 ma suggesting a genetic relationship between the plutonic and volcanic rocks and indicating that the sandbian katian magmatism is much more voluminous than reported in previous studies and possibly includes mega eruptions linked to the formation of collapse calderas

duration evolution and implications of volcanic activity across the ordovician silurian transition in the lower yangtze region south china abstract volcanism provides a reliable record of local and global tectonic events and substantially influences both modern and ancient environments climates and the evolution of life the ordovician silurian o s transition is a special period because intensive volcanism occurred globally including in the yangtze region of south china volcanic events during this period are a symptom of plate tectonic behaviour and are thought to be responsible for the remarkable changes in climate in the early palaeozoic though the relationships between these events remain unclear and controversial coeval igneous rocks and volcanic sediments vs are primarily used to resolve this issue however limited studies have been performed on vs from the o s transition in south china recently a typical vs bearing section was found in the lower yangtze region which contains 100 thin interbedded volcanic ash layers across the o s transition detailed petrographic and geochemical analyses of the volcanic ashes were conducted to determine their isotopic ages magma sources evolutionary processes and tectonic settings our preliminary results suggest that volcanic eruptions in south china lasted for more than 22 ma across the o s boundary from 449 3 3 6 to 427 6 4 1 ma where 445 14 ma is the lowermost graptolite biozone for metabolograptus extraordinarius as well as the initiation of the late ordovician mass extinction lome event in the yangtze region the evolutionary history of the parental magma was constructed from a depleted mantle source in the early stage and from a crustal source in the late stage with several transitional features in the middle the mantle source and arc related geochemical indicators for the volcanic ashes support the disputed subduction collision orogeny model we propose that the strong volcanism in south china accompanied by volcanism in numerous other regions worldwide was an important trigger for the lome and was likely responsible for oceanic 87sr 86sr fractionation and other climatic changes during the o s transition

emeishan basalts sw china and the end guadalupian crisis magnetobiostratigraphic constraints abstract a magnetostratigraphic investigation of the permian emeishan lip large igneous province was carried out on a composite section in ebian county close to the type area in sichuan sw china the main succession of twelve flows 175 m thick carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity the data enable a correlation to be proposed with an emeishan basalt sequence in western guizhou c 400 km to the se from our knowledge of the geomagnetic field9s reversal behaviour during the permian it suggests that the main lava pile along the eastern half of the emeishan basalt outcrop belt was erupted within a half to one million years using magnetobiostratigraphic data from the adjacent south china platform the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the maokou limestones constrained by conodont data the main emei basalts appear to be at least two biozones older 1 1 5 ma than the mid late permian boundary it is possible however that the emei basalt waning zone sequence which represents an explosive volcanic phase might be coeval with the end guadalupian biotic crisis thus arguments implicating emei basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative age constraints

sulfate controlled marine euxinia in the semi restricted inner yangtze sea south china during the ordovician silurian transition abstract conflicting published interpretations of marine redox conditions during the ordovician silurian transition ost may have been linked to spatial redox heterogeneity during this interval however details of the pattern of redox heterogeneity and its underlying causes remain unclear here we present a high resolution geochemical study of a drillcore section pengye 1 from pengshui county chongqing municipality southwestern china that was located in the semi restricted inner yangtze sea during the ost we analyzed fe speciation redox sensitive trace elements major elements and pyrite 34s compositions 34spy and then compared these data with published results from coeval sections at datianba and shuanghe in the same basin the integrated dataset demonstrates pronounced spatiotemporal heterogeneity of redox conditions especially the local development of euxinic conditions in the inner yangtze sea during the ost integrated data further suggest that high primary productivity and ample fe fluxes in the inner yangtze sea may have depleted dissolved sulfate through microbial sulfate reduction msr and subsequent pyrite formation except in areas with enhanced sulfate supply from continental weathering or open ocean exchange which varied as a function of both tectonic i e the regional kwangsian orogeny and eustatic changes i e the global hirnantian glaciation limited sulfate availability thus likely prevented the development of euxinic conditions in some regions of the inner yangtze sea as reflected in spatial variation of 34spy our study highlights the potential role of sulfate availability on the development of watermass euxinia in semi restricted marginal marine basins during the ost

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

permian carboniferous and permian triassic magmatism in the rift zone bordering the tethyan margin of southern pangea magma was emplaced in the india australia rift zone along the tethyan margin during permian carboniferous and permian triassic time permian carboniferous alkalic granite and basaltic and rhyolitic lava flows and tuffs formed at the same time as right lateral transtension of pangea as recorded by the magmatic rocks of neocratonic post variscan europe and post kanimblan eastern australia permian triassic tholeiitic basalt in india alkalic magmatic rocks in oman and rhyolite dolerite and undersaturated alkalic volcanic rocks in western australia preceded and accompanied the early opening of the neo tethys ocean coeval magmatism included the voluminous mid plate siberian traps the emeishan basalt of south china and the peak activity of the magmatic arc along the convergent panthalassan margin the background magmatism probably permitted the siberian traps to trigger the environmental catastrophe at the permian triassic boundary

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

factors controlling organic matter accumulation in the upper ordovician lower silurian organic rich shale on the northeast margin of the upper yangtze platform evidence from petrographic and geochemical proxies abstract organic rich shales are widespread in the upper ordovician lower silurian wufeng longmaxi formations on the northeastern margin of the upper yangtze platform and these shales have been recognized to be the hydrocarbon source rocks and shale gas reservoirs with the greatest development potential in china however organic matter accumulation in these shales needs further research especially in the areas which experienced an extensive upwelling and volcanism here this work integrates detailed petrographic and geochemical proxies namely redox sensitive trace elements rstes and ratios of si al ti al from two ordovician silurian sections on the northeast margin of upper yangtze platform in order to understand the depositional environment and identify the major factors controlling the organic matter accumulation during the ordovician silurian transition data of si al and ti al ratios indicate that the deposition of black gray siliceous mudstones in the lower wufeng formation commenced with a transgression triggered by the boda warming event which led to a reduced detrital input based on rstes the black carbonaceous shales of the upper wufeng formation are organic rich owing to an elevated primary productivity caused by seasonal upwelling driven by the vigorous thermohaline circulation abundant nutrients supplied by the post glacial transgression and a mass biotic recovery of marine microorganisms stimulated productivity and further strengthened the depletion of oxygen in the water column which lead to high concentrations of organic matter in lower longmaxi formation although the water column conditions were not conducive to the accumulation of organic matter it was possible that the increased productivity from upwelling resulted in relatively high organic matter contents in the middle longmaxi formation the rstes especially cd mo co mn reveal that the organic matter accumulation of the wufeng longmaxi formation during ordovician silurian transition may have been primarily controlled by the preservation conditions and also influenced by the marine primary productivity and the detrital input

new u pb zircon age and carbon isotope records from the lower silurian longmaxi formation on the yangtze platform south china implications for stratigraphic correlation and environmental change abstract the ordovician silurian o s transition was a period of dramatic climatic environmental and biological change numerous studies have documented the late ordovician glacial or mass extinction interval but the early silurian has received significantly less attention this study presents a u pb zircon age data and organic carbon isotope 13corg records from the upper ordovician to lower silurian succession of south china to better constrain carbon isotope perturbations and to evaluate their possible causes and relationships to paleoenvironmental change during early silurian time a volcanic ash bed located at the top of the organic rich lower silurian longmaxi formation yields a 206pb 238u zircon age of 440 3 ma mswd 1 4 which is consistent with the rhuddanian aeronian r a boundary age the newly acquired age is similar to that documented an ash bed in scotland 439 57 1 13 ma perhaps indicating synchronous volcanism the 13corg values show a negative excursion in the organic rich lower longmaxi formation that is interrupted by a positive excursion in the organic lean upper part of the unit the positive excursion begins immediately above the dated ash bed thus assigning it to the r a boundary the documented 13corg trend is comparable to those of other sections throughout the world and is suggestive of a global perturbation of carbon cycle the negative 13corg excursion of the rhuddanian stage was coeval with deposition of organic rich shale under anoxic euxinic conditions whereas the subsequent positive 13corg excursion coincided with a change to suboxic conditions that could have diminished organic matter preservation we propose that the negative 13corg excursion could be considered as the defining isotopic characteristic of the rhuddanian oceanic anoxic event rhuddanian oae results of the present study in tandem with published age data from the guanyinqiao bed immediately below the base of the longmaxi formation suggest that the negative 13corg excursion and associated rhuddanian oae persisted for approximately 3 myr this relatively long lived event reflects a sustained addition of isotopically light carbon into the atmosphere ocean system possibly related to the release of volcanic co2 the enhanced burial of organic carbon in association with the rhuddanian oae could have removed the substantial 12c from the carbon reservoir and lowered atmospheric pco2 thus resulting in a subsequent positive 13c excursion and global cooling at the r a boundary

glacial onset predated late ordovician climate cooling the ordovician glaciation represents the acme of one of only three major icehouse periods in earth s phanerozoic history and is notorious for setting the scene for one of the big five mass extinction events nevertheless the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained here using an earth system model with an innovative coupling method between ocean atmosphere and land ice accounting for climate and ice sheet feedback processes we report simulations portraying for the first time the detailed evolution of the ordovician ice sheet we show that the emergence of the ice sheet happened in two discrete phases in a counterintuitive sequence of events the continental ice sheet appeared suddenly in a warm climate only during the second act and set against a background of decreasing atmospheric co2 followed steeply dropping temperatures and extending sea ice the comparison with abundant sedimentological geochemical and micropaleontological data suggests that glacial onset may have occurred as early as the middle ordovician darriwilian in agreement with recent studies reporting third order glacioeustatic cycles during the same period the second step in ice sheet growth typified by a sudden drop in tropical sea surface temperatures by approximate to 8 degrees c and the further extension of a single continental scale ice sheet over gondwana marked the onset of the hirnantian glacial maximum by suggesting the presence of an ice sheet over gondwana throughout most of the middle and late ordovician our models embrace the emerging paradigm of an early paleozoic ice age

mercury in marine ordovician silurian boundary sections of south china is sulfide hosted and non volcanic in origin abstract mercury hg enrichment in stratigraphic successions is now widely used as a proxy for volcanic inputs often for the purpose of documenting a relationship between large igneous province lip magmatism and ecosystem perturbations earlier studies of hg in ordovician silurian boundary osb sections in south china and laurentia identified transient spikes in hg toc ratios on the basis of which a link between volcanism and the late ordovician mass extinction lome was claimed however hg enrichments must be tested based on normalization to their main host phase and hg toc is a suitable proxy only if hg is mainly complexed by organic matter in the sediment here we demonstrate that hg in three osb sections in south china qiliao yanzhi and jiaoye is overwhelmingly associated with pyrite as shown by r hg ts 0 9 versus r hg toc 199 hg values 0 11 0 03 that are inconsistent with volcanic inputs we therefore infer that previous reports of hg enrichments in osb sections were due to the presence of hg rich sulfides and that hg data from both the present and earlier studies provide no evidence of any volcanic influences on the lome the results of the present study highlight the need for caution in applying the hg proxy for volcanic inputs and the importance of evaluating the main host phase of hg in paleo marine sediments

late ordovician mass extinction caused by volcanism warming and anoxia not cooling and glaciation the ordovician saw major diversification in marine life abruptly terminated by the late ordovician mass extinction lome around 85 of species were eliminated in two pulses 1 m y apart the first pulse in the basal hirnantian has been linked to cooling and gondwanan glaciation the second pulse later in the hirnantian is attributed to warming and anoxia previously reported mercury hg spikes in nevada usa south china and poland implicate an unknown large igneous province lip in the crisis but the timing of hg loading has led to different interpretations of the lip extinction scenario in which volcanism causes cooling warming or both we report close correspondence between hg mo and u anomalies declines in enrichment factors of productivity proxies and the two lome pulses at the ordovician silurian boundary stratotype dob s linn scotland these support an extinction scenario in which volcanogenic greenhouse gases caused warming around the katian hirnantian boundary that led to expansion of a preexisting deepwater oxygen minimum zone productivity collapse and the first lome pulse renewed volcanism in the hirnantian stimulated further warming and anoxia and the second lome pulse rather than being the odd one out of the big five extinctions with origins in cooling the lome is similar to the others in being caused by volcanism warming and anoxia