characteristics of wall deflections and ground surface settlements in shanghai the characteristics of wall deflections and surface ground settlements at six deep multi strutted excavations in shanghai soft soils were studied and compared with those of similar case histories reported worldwide particularly in taipei and singapore the measured wall deflections at the six metro stations of the pearl ii circle line show a typical bulging profile or deep seated shape at the end of the excavation the ratio between the measured maximum wall deflection and the depth of the excavation hm h in shanghai was 0 007 which was similar to the ratio measured in taipei but it was substantially smaller than the peck bounding limit of 0 01 at each station the measured maximum displacement was 0 45 of the final excavation depth because of the large aspect ratios of the underground excavations no significant three dimensional effects or corner effects were observed the measured maximum settlements of the six metro excavations fell within zone i of the peck classical normalized settleme

oceanic redox evolution across the end permian mass extinction at shangsi south china abstract the end permian mass extinction epme was the most severe extinction event of the phanerozoic to investigate oceanic redox conditions around the epme we conducted a series of geochemical analyses including iron speciation trace element geochemistry total organic carbon toc and nitrogen isotopes of kerogen 15nkero around the epme at the shangsi section south china three intervals with different redox conditions can be distinguished based on iron speciation during the first interval early and middle changhsingian bottom waters were pervasively euxinic in the second interval late changhsingian and the epme bottom water fluctuated between oxic and anoxic but non sulfidic conditions with the oxic mode becoming increasingly predominant over time during the third interval following the epme bottom waters appeared to have been consistently anoxic although again not pervasively euxinic this redox history is supported by enrichments in the authigenic fraction of redox sensitive elements these relatively high 15nkero values 1 0 corresponding with changhsingian euxinia suggest reducing bottom waters did not impinge on the photic zone the shift to values near 0 within and above the epme indicates an ecological expansion of diazotrophs stratigraphic trends of nixs cdxs pxs and toc indicate that primary productivity was highest in the first interval coinciding with euxinic bottom water then decreased during the lower part of interval 2 and remained at low level through the remainder of the studied section the temporal relationship between redox condition and primary productivity suggests that euxinia was supported by high productivity and carbon export in the early changhsingian the expansion of n2 fixation coincides closely with the previously documented warming of the ocean surface at shangsi and may be related to reduced oceanic circulation and suppressed vertical mixing the temporal distribution of deepwater anoxia and euxinia suggests that they were not primary causes for the extinction of benthos at shangsi

molecular records of microbialites following the end permian mass extinction in chongyang hubei province south china abstract by using gas chromatograph gc and gc mass spectrometry a series of biomarkers were identified in the aliphatic fractions of extracts from microbialites following the end permian faunal mass extinction in chongyang section hubei province south china the dominance of lower molecular weight n alkanes in the samples from the section suggests that algae and bacteria were the dominant contributors to the organic fraction preserved in this marine section with bacteria particularly enhanced within the stromatolite the end permian biotic crisis coincided with a short term suppression of autotrophs indicated by the ratio of pristane pr and phytane ph to c 17 and c 18 n alkanes and proliferation of heterotrophs shown by the ratio of branched to normal c 17 alkanes the biotic crisis also may have been associated with a transient oxygenation event in the shallow marine indicated by elevated pr ph ratios and lowered c 27 18 h 22 29 30 trisnorneohopane ts to c 27 17 h 22 29 30 trisnorhopane tm and gammacerane to c 31 homohopane c 31 hp ratios subsequently three short term episodes of intensified anoxia or enhanced salinity at chongyang are recorded by decreases in pr ph ratios in conjunction with lithological boundaries in the section

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

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

composition and structure of microbialite ecosystems following the end permian mass extinction in south china after the end permian mass extinction microbialites were widespread in the shallow marine environments in south china diverse microbialites are characteristic of the early triassic carbonate sequences their stratigraphic range is rather short just across the permian triassic p tr boundary and defined by conodonts n meishanensis h changxingensis and h parvus zones thus the p tr microbialites grew immediately after the first episode of the end permian mass extinction coinciding with the beginning of the conodont n meishanensis zone and ceased their growth at the beginning of the conodont i staeschei zone which occurred just before the second episode of the end permian crisis at meishan they include three main types stromatolites thrombolites and dendrites in south china the presence of abundant microbial remains of coccoid type and renalcis like microbes strengthens the previous view that the p tr microbialites are biogenic both cyanobacteria and other microbes have participated to construct the microbial ecosystems the thrombolite communities are dominated by the renalcis like microbes and foraminifers and also contain ostracods microgastropods and microconchids the stromatolite communities are dominated by coccoidal microbes with minor constituents of other undetermined microbes metazoans are rare the dendrolite assemblage contains few identifiable microfossils most of microbialite communities have a high abundance low diversity community structure characteristic of marine communities after the end permian mass extinction some metazoans of either opportunists or disaster forms dwelled in this special ecosystem the microbialite builders formed the primary producer communities and constructed the lowest level ecosystem structure the lower level ecosystem proliferated due to the collapse of the higher level of ecosystem structure characterized by benthic shelly and predator communities in the end permian crisis

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

molybdenum isotopic evidence for oxic marine conditions during the latest permian extinction the latest permian extinction lpe ca 252 ma represents the most severe extinction event in earth s history the cause is still debated but widespread marine anoxic to euxinic h2s rich conditions from deep to shallow water environments are commonly suggested as a proxy for marine oxygen levels we analyzed 98 95mo of two lpe sections that represent a gradient in water depth on the northwest margin of pangea results from deep water slope environments show a large shift in 98 95mo values from 2 02 to 2 23 at the extinction horizon consistent with onset of euxinic conditions in contrast sub storm wave base shelf environments show little change in the molybdenum isotopic composition 1 34 to 0 05 indicating ongoing oxic conditions across the lpe these results indicate that areas of the continental shelf of northwest pangea underwent mass extinction under oxic conditions throughout the lpe event and that shallow water anoxia was therefore not a global phenomenon

lipid biomarker and stable isotopic profiles through early middle ordovician carbonates from spitsbergen norway abstract one of the most dramatic episodes of sustained diversification of marine ecosystems in earth history took place during the early to middle ordovician period changes in climate oceanographic conditions and trophic structure are hypothesised to have been major drivers of these biotic events but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain this study examines well preserved carbonate rich strata spanning the tremadocian through upper dapingian stages from the oslobreen group in spitsbergen norway abundant bacterial lipid markers elevated hopane sterane ratios average 4 8 maximum of 13 1 detection of chlorobi markers in organic rich strata and bulk nitrogen isotopes 15ntotal averaging 0 to 1 for the open marine facies suggest episodes of water column redox stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone near absence of the c30 sterane marine algal biomarker 24 n propylcholestane 24 npc in most samples supports and extends the previously observed hiatus of 24 npc in early paleozoic late cambrian to early silurian marine environments very high abundances of 3 methylhopanes average 9 9 maximum of 16 8 extends this biomarker characteristic to early ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia anoxia extending into the photic zone of the water column

changes in marine nitrogen fixation and denitrification rates during the end devonian mass extinction abstract the end devonian was a critical interval in earth history recording the transition from the early paleozoic greenhouse climate to the late paleozoic icehouse climate a mass extinction at this time the hangenberg extinction eliminated 21 of genera and 16 of families of marine invertebrates although its causes remain poorly understood the marine nitrogen cycle is intimately related to the nutrient status of seawater microbial community composition and the redox condition of the oceans and thus it may provide insights into the mechanism s of the end devonian mass extinction and climate change here we analyzed high stratigraphic resolution bulk sediment nitrogen isotope variation 15 n bulk in three sections from south china 1 long an an isolated carbonate platform section 2 qilinzhai a shallow water carbonate platform section between the yangtze oldland and the youjiang trough and 3 malanbian a shallow water carbonate platform section between the yangtze and cathaysia oldlands and distant from deep water areas our 15 n bulk records show a major perturbation to the marine nitrogen cycle in the middle siphonodella praesulcata zone which is marked by a decline in 15 n bullk from 4 to 0 at long an and from 4 5 to 2 5 at malanbian this perturbation coincided with the main end devonian mass extinction as well as with a negative shift in carbonate carbon isotopes 13 c carb the shift to lower 15 n values suggests locally enhanced nitrogen fixation possibly as a consequence of increased denitrification in response to globally expanded marine anoxia thus these 15 n bulk data are consistent with the hypothesis that intense anoxia was the immediate cause of the end devonian mass extinction the 15 n bulk records generated in this study suggest that there was significant spatial and temporal variation in the nitrogen isotope composition of seawater nitrate in the yangtze marginal sea during the latest devonian this variation may have been related to the complex paleogeography of the south china craton which contained numerous isolated and continent attached platforms and deep water basins that influenced watermass circulation nutrient inventories and primary productivity levels and watermass ventilation and redox conditions

gas hydrate contribution to late permian global warming abstract rapid gas hydrate release the clathrate gun hypothesis has been invoked as a cause for the rapid global warming and associated negative carbon isotope excursion observed during the latest permian extinction lpe we modeled the stability of gas hydrates through a warming middle to late permian world considering three settings for methane reservoirs 1 terrestrial hydrates 2 hydrates on exposed continental shelves during glacial sea level drop and 3 hydrates in deep marine settings model results show that terrestrial hydrates would rapidly destabilize over 400 ky after deglaciation for moderate heatflow 40 mw m2 and more rapidly for higher heat flow values exposed continental shelves would lose hydrates even more rapidly after being flooded due to loss of ice storage on land these two major hydrate reservoirs would thus have destabilized during the middle to late permian climate warming well prior to the lpe event however they may have contributed to the 2 negative c isotopic shift during the late middle permian deep marine hydrates would have remained stable until lpe time rapid warming of deep marine waters during this time could have triggered destabilization of this reservoir however given the configuration of one super continent pangea hydrate bearing continental slopes would have been less extensive than modern day this suggests that any potential gas hydrate release would have had only a minor contributing impact to the runaway greenhouse during the latest permian extinction

contrasting microbial community changes during mass extinctions at the middle late permian and permian triassic boundaries abstract microbial communities are known to expand as a result of environmental deterioration during mass extinctions but differences in microbial community changes between extinction events and their underlying causes have received little study to date here we present a systematic investigation of microbial lipid biomarkers spanning 20 myr middle permian to early triassic at shangsi south china to contrast microbial changes associated with the guadalupian lopingian boundary glb and permian triassic boundary ptb mass extinctions high resolution analysis of the ptb crisis interval reveals a distinct succession of microbial communities based on secular variation in moretanes 2 methylhopanes aryl isoprenoids steranes n alkyl cyclohexanes and other biomarkers the first episode of the ptb mass extinction me1 was associated with increases in red algae and nitrogen fixing bacteria along with evidence for enhanced wildfires and elevated soil erosion whereas the second episode was associated with expansions of green sulfur bacteria nitrogen fixing bacteria and acritarchs coinciding with climatic hyperwarming ocean stratification and seawater acidification this pattern of microbial community change suggests that marine environmental deterioration was greater during the second extinction episode me2 the glb shows more limited changes in microbial community composition and more limited environmental deterioration than the ptb consistent with differences in species level extinction rates 71 vs 90 respectively microbial biomarker records have the potential to refine our understanding of the nature of these crises and to provide insights concerning possible outcomes of present day anthropogenic stresses on earth s ecosystems

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

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

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

variations of the relative palaeointensity of the geomagnetic field in western europe in the interval 25 10 kyr bp as deduced from analyses of lake sediments summary two independent methods have been applied on late glacial and glacial homogeneous lacustrine sediments in order to obtain an evaluation of the geomagnetic field palaeointensity in the interval 10 000 95 000 yr bp the anhysteretic remanent magnetization arm normalization method and the stirred remanent magnetization strm normalization method yield relative palaeoiiitensity curves which can be critically compared the st rm normalization curve considered as the most reliable shows successive oscillations with periods ranging from 1500 to 1 1 000 yr the lowest values of the field intensity occur at 10000 and 31 000 yr bp and the highest value occurs at 15 000 yr bp

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

high resolution variation in ostracod assemblages from microbialites near the permian triassic boundary at zuodeng guangxi region south china abstract after the end permian mass extinction epme the marine environment was considered extremely toxic mainly due to anoxic and high temperature conditions and ocean acidification consequently the ecosystem contained few organisms this paper describes a new ostracod fauna from the microbialite bearing permian triassic p tr strata at zuodeng guangxi region china one thousand and seventy ostracod specimens were extracted from forty eight samples fifty three species belonging to fourteen genera were identified ostracods primarily from the family bairdiidae were extremely abundant in the microbialites which suggests that ostracods were opportunists that could survive the epme within this special microbial ecosystem with sufficient food and scarce competitors and predators rather than undergoing a rapid and early recovery after the epme event ostracods having simultaneous paleozoic and meso cenozoic affinities coexisted in this fauna the similarities and differences among the ostracod faunas in the microbialite sections of the p tr boundary around the paleo tethys indicate that there was a long distance dispersal of ostracods but the faunas maintained endemism at the species level previous studies have regarded microbialites as whole units and it is difficult to detect environmental changes within a microbialite interval based on paleoecological groups of super families in this study high resolution sampling was applied to identify changes in the ostracod abundance diversity assemblages and proportion of five dominant species in the section which exhibited an evolutionary trend from the bairdia group to the liuzhinia antalyaensis bairdiacypris ottomanensis group furthermore the transition of the ostracod fauna could be divided into six stages according to changes in the dominant species groups suggesting that the microbialite environment was not entirely monotonous but fluctuated during the postextinction interval

the interplay between massive volcanism and the local environment geochemistry of the late permian mass extinction across the sydney basin australia abstract the isotopic geochemical and physical characteristics of the late permian mass extinction have been identified and assessed from terrestrial sections across the sydney basin eastern australia these new data are used to both correlate the extinction event across the basin and elucidate its cause two stratigraphically well constrained cores were examined one each from the northern and southern regions of the sydney basin both sections show uninterrupted transitions from the last permian coal to a carbonaceous shale overlain by siltstones mudstones sandstones and shales whose mineralogical and physical characteristics are consistent with non marine origins these non marine origins are also broadly supported by elemental data carbon isotopic data were the primary means for identifying the stratigraphic position of the late permian mass extinction across the basin the data show that the mass extinction occurred as an interval with the form of a closely spaced double negative 13corg excursion within 1 m of the top of the last permian coal a feature previously unrecognised in the basin this result is supported by coincident excursions in 15n and 34spyrite the first measurements of their kind for the late permian mass extinction in the sydney basin the interrelationships between the c n and s isotopic data concentrations and elemental ratios together with major trace and rare earth element concentrations ratios and statistical analyses show severe environmental disruption occurred at the time of the extinction event with die off of terrestrial vegetation and the injection of sulphate into the water column consistent with massive volcanism geochemical evidence also shows however that local conditions have the potential to disrupt the late permian mass extinction signature and hence the data need to be interpreted carefully

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

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

shift in limiting nutrients in the late ediacaran early cambrian marine systems of south china abstract the ediacaran to cambrian periods are characterized by the diversification and extinction of metazoans carbon cycle perturbation and ocean oxygenation ocean nutrient cycles play a major role in the primary production and productivity driven shallow water anoxia that was responsible for mass extinction in some phanerozoic intervals however the relationships between these cycles and primary production and biological events during the ediacaran to cambrian periods have not previously been well explored this study presents stratigraphic profiles of nitrogen and organic carbon isotopes for sections belonging to the shelf and deep basin regions of the yangtze platform south china the nitrogen isotope profiles for these two regions share a similar trend showing 1 relatively stable 15n values of 5 6 in the early middle ediacaran 635 ma ca 560 ma and 2 a shift towards lower 15n values 3 4 since the shuram 13ccarb excursion the 15n values in the shelf section experienced a two stage decrease from the late ediacaran to cambrian stage 2 of the terreneuvian series down to 1 and then an increase from 1 to 4 across the cambrian stage 2 3 boundary i e the terreneuvian cambrian series 2 boundary at 521 ma these data in combination with previously reported nutrient profiles 15n p and mo allow the following new conclusions to be drawn 1 the early middle ediacaran ocean was characterized by n mo colimitation of primary production on a geological timescale that is different from the p limitation on long term primary production in the modern ocean 2 a shift in the ultimate limiting nutrient from n and mo to p likely occurred in late ediacaran early cambrian marine systems this shift may have been a prerequisite for the extinction of small shelly fossils in response to the development of photic zone anoxia for several million years in cambrian stage 2 which was followed by the third and most prominent phase of metazoan diversification

nitrogen isotope evidence for redox variations at the ediacaran cambrian transition in south china abstractnitrogen isotope 15n analyses of the early cambrian ca 542 520 ma strata in the yangtze gorges area south china reveal a prominent positive 15n excursion 8 concurrent with a negative shift in organic carbon isotopes 13corg at the early nemakit daldynian or early fortunian stage this positive 15n excursion in combination with the previously reported paired 13ccarb 13corg at this interval can be interpreted as resulting from denitrification with large isotopic fractionation subsequent 15n from early nemakit daldynian to early tommotian stage 2 are dominated by stable values fluctuating between 2 and 2 close to that of atmosphere n2 0 accompanied by the low and stable 13corg 33 and decoupled 13ccarb 13corg we argue that the relatively low and invariant 15n values from this interval likely resulted from enhanced n fixation with limited isotopic fractionation enhanced n fixation is generally associated with significant nutrient n loss mainly through denit

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

oceanic redox evolution around the end permian mass extinction at meishan south china abstract the end permian marine extinction epme eliminated 80 of species globally making it the most severe extinction of the phanerozoic anoxia and euxinia are potential kill mechanisms that may have contributed to this biotic crisis however redox changes in the atmosphere ocean system are likely to have been complex with both the vertical location of the oxic anoxic boundary in the water column or sediments and the total area or volume of anoxic and euxinic water in the global ocean changing over time in this study we generated iron speciation and major and trace element data from 141 samples of the meishan 1 core which was drilled at a site 550 m to the west of the meishan d section iron speciation results in combination with authigenic concentrations and enrichment factors of redox sensitive metals mo v and u and previously published macrofossil trace fossil and bioturbation evidence suggest that 1 beds 21 24d were deposited beneath a predominantly oxic water column 2 beds 24e 28 were deposited under a persistently anoxic watermass with intermittently euxinic bottom water and 3 beds 29 34 were deposited under primarily ferruginous conditions excess fractions and enrichment factors of u v and mo in the anoxic and euxinic intervals of the meishan 1 core suggest that authigenic precipitation of redox sensitive trace metals mainly occurred before and during the epme with nearly no detectable authigenic u v or mo accumulating after the epme our results along with published u v and mo concentrations from across the neotethys paleotethys and panthalassic ocean basins indicate that oceanic trace metal reservoirs were depleted before and during the main extinction interval this depletion of oceanic trace elements suggests a spatial expansion of both anoxic and euxinic watermasses prior to and during the epme the apparent coincidence in timing between the mass extinction and the areal expansion of anoxic and euxinic watermasses suggests that these factors played important roles in the loss of marine biota around the permian triassic boundary ptb through oxygen deprivation and h2s toxicity

ocean redox structure across the late neoproterozoic oxygenation event a nitrogen isotope perspective abstract the end of the neoproterozoic era 1000 to 541 ma is widely believed to have seen the transition from a dominantly anoxic to an oxygenated deep ocean this purported redox transition appears to be closely linked temporally with metazoan radiation and extraordinary perturbations to the global carbon cycle however the geochemical record of this transition is not straightforward and individual data sets have been variably interpreted to indicate full oxygenation by the early ediacaran period 635 to 541 ma and deep ocean anoxia persevering as late as the early cambrian because any change in marine redox structure would have profoundly impacted nitrogen nutrient cycling in the global ocean the n isotope signature of sedimentary rocks 15 n sed should reflect the neoproterozoic deep ocean redox transition we present new n isotope data from amazonia northwest canada northeast svalbard and south china that span the cryogenian glaciations 750 to 580 ma these and previously published data reveal a n isotope distribution that closely resembles modern marine sediments with a mode in 15n close to 4 and range from 4 to 11 no apparent change is seen between the cryogenian and ediacarian data from earlier proterozoic samples show a similar distribution but shifted slightly towards more negative 15 n values and with a wider range the most parsimonious explanation for the similarity of these n isotope distribution is that as in the modern ocean nitrate and hence o2 was stable in most of the middle late neoproterozoic ocean and possibly much of proterozoic eon however nitrate would likely have been depleted in partially restricted basins and oxygen minimum zones omzs which may have been more widespread than in the modern ocean

nitrogen isotope chemostratigraphy across the permian triassic boundary at chaotian sichuan south china abstract nitrogen isotopic compositions of upper permian to lowermost triassic rocks were analyzed at chaotian in northern sichuan south china in order to clarify changes in the oceanic nitrogen cycle around the permian triassic boundary p tb including the entire changhsingian late late permian prior to the extinction the analyzed ca 40 m thick interval across the p tb at chaotian consists of three stratigraphic units the upper wujiaping formation the dalong formation and the lowermost feixianguan formation in ascending order the upper wujiaping formation ca 10 m thick is mainly composed of dark gray limestone with diverse shallow marine fossils such as calcareous algae and brachiopods deposited on the shallow shelf in contrast the overlying dalong formation ca 25 m thick is mainly composed of thinly bedded black mudstone and siliceous mudstone containing abundant radiolarians deposited on the relatively deep slope basin absence of bioturbation substantially high total organic carbon contents up to 15 and abundant occurrence of pyrite framboids in the main part of the dalong formation indicate deposition under anoxic condition the lowermost feixianguan formation ca 5 m thick is composed of thinly bedded gray marl and micritic limestone with minor fossils such as ammonoids and conodonts deposited on the relatively shallow slope 15ntn values are in positive values around 1 to 2 in the upper wujiaping formation implying denitrification and or anammox in the ocean 15ntn values gradually decrease to 1 in the lower dalong formation and are consistently low around 0 in the middle dalong to lowermost feixianguan formation no clear 15ntn shift is recognized across the extinction horizon the consistently low 15ntn values suggest the enhanced nitrogen fixation in the ocean during the changhsingian at chaotian composite profiles based on previous and the present studies demonstrate the substantial 15n variation on a global scale in the late permian to earliest triassic a systematic 15n difference by low and high latitudes is particularly clarified although the enhanced nitrogen fixation throughout the changhsingian at chaotian was likely a regional event in northwestern south china the composite 15n profiles imply that the sea area in which fixed nitrogen is depleted has gradually developed worldwide in the changhsingian possibly acting as a prolonged stress to shallow marine biota

water mass denitrification during the latest permian extinction in the sverdrup basin arctic canada late permian early triassic bulk sedimentary nitrogen isotope 15 n and biomarker data have been generated from the northwest margin of pangea sediments from the buchanan lake section arctic canada deposited prior to the latest permian extinction lpe event are characterized by positive 15 n values of 9 associated with the presence of lycopane implying upwelling of denitrified waters from an expanded oxygen minimum zone the data show that anoxic bottom water conditions were not developed in northeastern panthalassa during the late permian promoted by dispersing coal ash from siberian traps volcanics as marked by an abrupt rise in c n ratios 20 prior to the lpe event euxinic conditions first developed at the lpe pronounced differences in the nitrogen inventory across the lpe event however suggest that while unfavorable conditions prevailed for aerobiosis in the paleo tethys persistent upwelling of deoxygenated denitrified waters occurred in the sverdrup basin across the lpe excluding the prevalence of photic zone euxinia along the northwest margin of pangea

the tice event perturbation of carbon nitrogen cycles during the mid tournaisian early carboniferous greenhouse icehouse transition abstract carbonate carbon 13ccarb and bulk nitrogen 15n isotopic variation during the mid tournaisian was analyzed in the malanbian and long an sections of south china their c isotope profiles document a large positive excursion herein termed the mid tournaisian carbon isotope excursion tice during the siphonodella isosticha conodont zone although its magnitude differed between the two sections 6 at malanbian versus 3 at long an the tice event coincided with sedimentologic and oxygen isotopic evidence of climatic cooling and glaciation during the mid tournaisian it was probably triggered by an increase in organic carbon burial rates linked to changes in global ocean circulation the study sections also document a large positive shift in 15n from 1 7 to 4 2 at malanbian and from 1 5 to 3 8 at long an the n isotope shift shows no termination within the study sections and is likely to mark the onset of an extended interval of 15n enriched marine nitrate that lasted for the duration of the late paleozoic ice age its initiation coincided with tice and thus may have been linked to ocean circulation changes that resulted in intensified upwelling and an increase in water column denitrification the continuation of the n isotope shift over millions of years may have been linked to glacio eustatic fall and a long term shift in the locus of denitrification from continental shelf sediments to continent margin oxygen minimum zones the tice event thus marks the onset of sustained continental glaciation during the late paleozoic ice age

perturbation of the marine nitrogen cycle during the late ordovician glaciation and mass extinction abstract the late ordovician was a critical interval in geologic history during which both the biosphere and marine environments underwent severe perturbations including one of the big five phanerozoic mass extinctions and the massive but short term 0 5 myr hirnantian glaciation the onset and termination of the hirnantian glaciation have been widely accepted as the triggers for the two extinction pulses that comprise the late ordovician biocrisis but the mechanisms that caused the hirnantian glaciation itself remain poorly known here we analyze the nitrogen isotope composition 15 n of two sections in south china wangjiawan and nanbazi in order to better understand nitrogen cycle perturbations in the late ordovician ocean and their relationship to contemporaneous climatic and biogeochemical changes low 15 n 1 in the upper katian and lower rhuddanian of both sections suggests intensive i e near quantitative denitrification and thus nitrogen fixation as the main source of biologically available nitrogen for primary producers a positive 15 n excursion in both sections during the hirnantian indicates weaker i e non quantitative denitrification possibly as a result of more vigorous thermohaline circulation and improved ocean ventilation weaker denitrification would have reduced the flux of n 2 o an intermediate product of denitrification to the atmosphere n 2 o is a potent greenhouse gas and a major decline in its production would have led to cooler climatic conditions and ultimately the hirnantian glaciation a global survey of published nitrogen isotope records suggests that similar processes operated broadly within the late ordovician global ocean

vertical δ13corg gradients record changes in planktonic microbial community composition during the end permian mass extinction abstract the global carbon cycle experienced a major perturbation during the permian triassic transition reflected inter alia in a large increase in the vertical shallow to deep gradient of carbonate 13c 13ccarb in early triassic seas however the effect of this perturbation on the vertical gradient of organic matter 13c in seawater 13corg is less known to date here we examine geographic and secular variations in 13corg in late permian early triassic seas of the south china craton and their implications for contemporaneous changes in microbial community composition and paleoredox conditions vertical 13corg gradients document the existence of a narrow and relatively shallow oxygen minimum zone omz within the open ocean northern deepwater basin ndw and a deeper and thicker omz within the semi restricted nanpanjiang basin npjb for the pre extinction interval 13corg gradients between the shallow and intermediate watermasses of the ndb and between the shallow and deep watermasses of the npjb record contributions to the sediment of organic matter from bacteria living below the ocean surface layer these bacteria were mainly anaerobic chemoautotrophs that inhabited suboxic to anoxic waters of an omz and that produced more strongly 13c depleted organic matter than surface water eukaryotic algae thus increasing 13corg for the post extinction interval a reversed 13corg in the ndb is attributed to blooms of green sulfur bacteria or other anaerobic photoautotrophic bacteria that were resident in a deep chlorophyll maximum layer and that had smaller carbon isotopic fractionation than surface water algae although quantitatively important in intermediate to deep water areas during the early triassic such bacteria were absent in coeval shallow water sections reflecting water depth controls on microbial community composition a concurrent flatting of the 13corg gradient in the npjb was caused by a return of oxic conditions and or a decline of primary productivity in the surface ocean

two episodes of environmental change at the permian triassic boundary of the gssp section meishan abstract high resolution stratigraphic records through the permian triassic boundary ptb interval of the global stratotype section and point gssp at meishan zhejiang province china reveal that the ptb crisis was not a single abrupt catastrophe a bed by bed analysis of environmental and biotic changes makes clear that the crisis can be resolved into two discrete episodes each consisting of three stages a unstably oscillating conditions b peak crisis conditions and c ameliorating conditions the first crisis episode commenced in bed 23 peaked in beds 24e 26 and ameliorated in beds 27 and 28 while the second crisis episode commenced in bed 29 peaked in beds 34 38 and ameliorated in beds 39 and higher the macroscopic mass extinctions happened not at the beginning nor the end of each cycle but at times when the crisis or perturbation of environments began these extinction events do not show detectable feedbacks to concurrent environmental changes in each episode cyanobacteria proliferation postdated the macroscopic extinction while proliferation of green sulfur bacteria predated the environmental crisis causational analysis between environmental and microbial changes show that geomicrobial functional groups exercised pronounced effects on the marine c n s cycles and ocean redox conditions during the ptb crisis it is possible thus that the microbial crises played an important role in strengthening or evening triggering the environmental crisis

carbon isotopic evidence for chemocline upward excursions during the end permian event abstract a negative shift in marine inorganic carbon isotope composition 13 c carb during the end permian mass extinction has been used as evidence for several different extinction mechanisms changes to the 13 c of organic matter and the difference between it and 13 c carb 13 c 13 c carb 13 c org have been examined at few locations with conflicting interpretations we examine the changes to both organic and inorganic carbon isotopes across the permian triassic boundary at two marine sections from south china meishan and shangsi and compare these to data from other previously published sections through these analyses we demonstrate that a decrease in 13 c occurred during the extinction event throughout the paleo tethys ocean the extent and intensity of the decrease varies by location averaging a negative shift of 5 several possibilities as to the cause of this shift exist including siberian trap volcanism a change in the terrestrial marine organic carbon input to the system or a change in the dominant marine biota brought about through environmental changes such as widespread ocean anoxia euxinia the decrease in 13 c observed at many of these sections across the event horizon is here interpreted to represent a shift from algae cyanobacteria to less fractionating phototrophic sulfur bacteria in marine shelf environments resulting from upward excursions of the chemocline these chemocline upward excursions would release euxinic water to the photic zone allowing phototrophic sulfur bacteria to thrive the limited available biomarker data are consistent with this interpretation

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

migration controls extinction and survival patterns of foraminifers during the permian triassic crisis in south china abstract the permian triassic mass extinction the greatest biotic crisis in earth history triggered the complete replacement of ecosystems with the 5 10 surviving species giving rise to the mesozoic fauna despite a long history of systematic studies on permian triassic foraminifera there have been few investigations into spatial and temporal patterns of survivorship and evolution during this critical interval we interrogate a high resolution data set comprising newly obtained and previously published foraminiferal data including 13 422 specimens in 173 species in 62 genera from seven well studied permian triassic successions that record a transect of platform to basin facies in south china shallow water settings seen at the cili and dajiang sections suffered a single pulse sudden extinction with high extinction rates at the end of the palaeofusulina sinensis zone deeper water and slope environments seen at liangfengya and meishan experienced a two pulse extinction in the clarkina yini and isarcicella staeschei zones basinal settings seen at shangsi gujiao and sidazhai record a single less devastating extinction pulse in and slightly above the c yini zone in the late permian foraminiferal diversity was greatest on the shallow platforms where 76 4 of species recorded in our study lived the two pulses of the permian triassic extinction prompted this foraminiferal diversity hotspot to move to deeper slope settings comprising 75 6 of contemporary species and finally basinal settings comprising 88 8 of species we propose that foraminifera migrated to deeper water to avoid overheating and toxicity in shallow waters that were driven by the emplacement of the siberian traps and coeval volcanic activities around the paleotethys ocean this study provides a methodological framework for investigating survival mechanisms for foraminifers and other taxonomic groups during mass extinction events

darriwilian carbon isotope stratigraphy in the taebaeksan basin korea and its implications for middle ordovician paleoceanography abstract the middle darriwilian carbon isotope excursion mdice event is first documented from central eastern korea taebaeksan basin the eastern part of the sino korean block and is well correlated with global carbon isotope chemostratigraphy the korean mdice record shows three broad positive peaks and complements records from the middle ordovician peri gondwanan epeiric seas showing incomplete records due to disconformity this study reconstructed paleoceanographic conditions with nitrogen isotopic compositions and clay mineral compositions to understand the causes of carbon isotope excursions the heavier excursion in nitrogen isotopic curve and abrupt increase of kaolinite in the early mdice interval are interpreted as a result of epeiric sea denitrification associated with strong seawater stratification and the main cause of those conditions was likely increased precipitation in the adjacent land subsequent sea level rise caused an anti estuarine circulation in the taebaeksan sea and increased the organic carbon burial in the adjacent basin setting which might have sustained the mdice the documentation of the mdice event in this study supports the view that the mdice occurred globally this study provides not only information on the regional paleoceanographic conditions that occurred in the middle ordovician epeiric seas during the course of mdice but also reports that the mdice event occurred as a response to seawater circulation associated with global sea level rising in the middle ordovician

changes in productivity and redox conditions in the panthalassic ocean during the latest permian the gujo hachiman section in central japan provides a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 251 ma the section is characterized by a sharp transition from green gray organicpoor cherts to black siliceous shales in the uppermost permian normalization to the clay fraction demonstrates that apparent increases in the concentrations of organic matter and trace metals above this transition were due primarily to the loss of a diluent biogenic radiolarian silica fl ux and only secondarily to a small shift toward more reducing bottom waters in the black shale pyrite abundance increases by a factor of 30 and is dominated by framboidal grains of probable syngenetic origin these observations suggest that the expansion of lowoxygen conditions within the panthalassic ocean was focused within the oxygen minimum zone rather than at the seafl oor such a pattern implies that 1 changes in nutrient fl uxes and primary productivity rates rather than stagnation of oceanic circulation were a key factor infl uencing oceanic redox conditions around the permian triassic boundary and 2 large regions of the panthalassic ocean underwent only limited redox changes providing potential refugia for marine taxa that survived into the triassic

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

sulfur isotopic evidence for chemocline upward excursions during the end permian mass extinction the latest permian was a time of major change in ocean chemistry accompanying the greatest mass extinction of the phanerozoic to examine the nature of these changes samples from two well studied marine sections that span the permian triassic boundary have been analyzed the meishan and shangsi sections located in southern china isotopic analysis of the carbonate associated sulfate in these samples provides a detailed record of several isotopic shifts in 34scas approaching and across the ptb ranging from 30 to 15 vcdt with repeated asynchronous fluctuations at the two locations we interpret the patterns of isotopic shifts in conjunction with other data to indicate a shallow unstable chemocline overlying euxinic deep water which periodically upwelled into the photic zone these chemocline upward excursion events introduced sulfide to the photic zone stimulating a bloom of phototrophic sulfur oxidizing bacteria we hypothesize that elemental sulfur globules produced by these organisms and 34s depleted pyrite produced in the euxinic water column were deposited in the sediment later oxidation led to incorporation as cas this created the large changes to the 34scas observed in the latest permian at these locations

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

stepwise and large magnitude negative shift in δ13ccarb preceded the main marine mass extinction of the permian triassic crisis interval abstract large perturbations to the global carbon cycle occurred during the permian triassic boundary mass extinction the largest extinction event of the phanerozoic eon 542 ma to present controversy concerning the pattern and mechanism of variations in the marine carbonate carbon isotope record of the permian triassic crisis interval ptci and their relationship to the marine mass extinction has not been resolved to date herein high resolution carbonate carbon isotope profiles 13ccarb accompanied by lithofacies were generated for four sections with microbialite taiping zuodeng cili and chongyang in south china to better constrain patterns and controls on 13ccarb variation in the ptci and to test hypotheses about the temporal relationship between perturbations to the global carbon cycle and the marine mass extinction event all four study sections exhibit a stepwise negative shift in 13ccarb during the late permian early triassic with the shift preceding the end permian crisis being larger 3 than that following it 1 2 the pre crisis shifts in 13ccarb are widely correlatable and hence represent perturbations to the global carbon cycle the comparatively smaller shifts following the crisis demonstrate that the marine mass extinction event itself had at most limited influence on the global carbon cycle and that both late permian 13ccarb shifts and the mass extinction must be attributed to some other cause their origin cannot be uniquely determined from c isotopic data alone but appears to be most compatible with a mechanism based on episodic volcanism in combination with collapse of terrestrial ecosystems and soil erosion

global warming leads to early triassic nutrient stress across northern pangea the largest extinction in earth history in the latest permian was followed throughout most of the early triassic by a prolonged period of ecologic recovery what factors delayed biotic recovery are still under debate and partly revolve around impacts of global warming on primary marine productivity we examined n isotope records from the festningen section on spitsbergen to examine changes in nutrient availability through the early to middle triassic along the northern margin of pangea our results show progressive decline in n availability throughout the griesbachian leading to severe nutrient limitations through the remainder of the early triassic until returning to a highly productive continental margin in middle triassic time these results are consistent with other studies from northern and western pangea and thus show regional nutrient limitations occurred in what should have been the main zone of marine primary productivity such nutrient limitation likely stressed primary production and consequently contributed to prolonged marine recovery we suggest this was driven by high ocean temperatures depressing the marine nutricline

nitrogen isotope compositions of the upper triassic chang 7 shale ordos basin north china implications for depositional redox conditions abstract nitrogen isotope 15n analysis has been used to evaluate depositional redox conditions in well preserved sedimentary systems however fewer n isotope studies have been performed to reconstruct the redox conditions in lacustrine shales in this paper we report the 15n data from the upper triassic chang 7 shale of the ordos basin north china sedimentary 15n values are significantly higher in the chang 73 and the lower part of the chang 72 submembers zone a average 9 4 1 3 than in the upper part of the chang 72 and the chang 71 submembers zone b average 5 4 1 5 previous geochemical measurements i e u and toc p of both zones show wide redox variation however the average values of these redox proxies are relatively higher in zone a than those of zone b combined with lithological aspects of the chang 7 shale our study suggest that zone a was mainly deposited under suboxic bottom water conditions whereas zone b deposits accumulated within an oxygenated water column stable organic carbon isotopes 13corg and total nitrogen tn values of the two zones display little variation that could be attributed to changing organic matter sources and or post depositional alteration of 15n thus we suggest that variations in 15n throughout the chang 7 shale primarily reflect differences in depositional redox conditions and 15n values of the shale that can provide important details regarding the depositional history of unconventional resource plays

ammonium ocean following the end permian mass extinction abstract the aftermath of end permian mass extinction was marked by a 5 million year interval of poorly understood extreme environments that likely hindered biotic recovery contemporary nitrogen isotope variations are considered using a new conceptual model to support a scenario that shows intensive nitrate removal processes gradually depleted the global oceanic nitrate inventory during long lasting oceanic anoxia enhanced nitrogen fixation shifted the oceanic nitrogenous nutrient nutrient n inventory to an ammonium dominated state ammonium is toxic to animals and higher plants but fertilizes algae and bacteria this change in ocean chemistry could account for the intense and unexplained losses of nektonic taxa and the proliferation of microbial blooms in the early triassic the transition from a nitrate ocean to an ammonium ocean was accompanied by a decrease in respiration efficiency of organisms and a shrinking oceanic nutrient n inventory ultimately leading to generally low productivity in the early triassic oceans these unappreciated nutrient changes during episodes of prolonged ocean anoxia may be the key life limiting factor at such times

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

photic zone euxinia during the permian triassic superanoxic event carbon and sulfur isotopic data together with biomarker and iron speciation analyses of the hovea 3 core that was drilled in the perth basin western australia indicate that euxinic conditions prevailed in the paleowater column during the permian triassic superanoxic event biomarkers diagnostic for anoxygenic photosynthesis by chlorobiaceae are particularly abundant at the boundary and into the early triassic similar conditions prevailed in the contemporaneous seas off south china our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery

paleoredox biotic and sulfur isotopic changes associated with the end permian mass extinction in the western tethys abstract detailed cm scale s toc total organic carbon 34ssulfide and pyrite morphological analysis of the permian triassic boundary beds at the bulla section northern italy suggests that marine waters at this site saw the influx of two dysoxic euxinic intervals that mark the end permian extinction event this suggests reduced oxygen conditions and the presence of h2s is the cause of the end permian extinction the bulla section also shows three troughs in 34ssulfate of which the latter two coincide with the dysoxic euxinic intervals this suggests that the latter two 34ssulfate troughs are the result of h2s oxidation in surface waters but the first trough is the result of a different mechanism we propose that h2s was oxidized in another region either to low 34ssulfate water or elemental s which then moved to the bulla area at the balvany section hungary there are two 34ssulfate troughs near the extinction and no evidence of euxinia a similar mechanism to the first bulla 34ssulfate trough is proposed with the suggestion that these waters were also depleted in oxygen in order to effect the extinction at balvany

organic geochemistry of the early toarcian oceanic anoxic event in hawsker bottoms yorkshire england a comprehensive organic geochemical investigation of the hawsker bottoms outcrop section in yorkshire england has provided new insights about environmental conditions leading into and during the toarcian oceanic anoxic event t oae 183 ma rock eval and molecular analyses demonstrate that the section is uniformly within the early oil window hydrogen index hi organic petrography polycyclic aromatic hydrocarbon pah distributions and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the t oae and across a lithological transition unlike other ancient intervals of anoxia and extinction biomarker indices of planktonic community structure do not display major changes or anomalous values depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the t oae in addition to carotenoid biomarkers for green sulfur bacteria gsb we report the first occurrence of okenane a marker of purple sulfur bacteria psb in marine samples younger than 1 64 ga based on modern observations a planktonic source of okenane s precursor okenone would require extremely shallow photic zone euxinia pze and a highly restricted depositional environment however due to coastal vertical mixing the lack of planktonic okenone production in modern marine sulfidic environments and building evidence of okenone production in mat dwelling chromatiaceae we propose a sedimentary source of okenone as an alternative lastly we report the first parallel compound specific c13 record in marine and terrestrial derived biomarkers across the t oae the c13 records of short chain n alkanes acyclic isoprenoids and long chain n alkanes all encode negative carbon isotope excursions cies and together they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs to date molecular c13 records of the t oae display a negative cie that is smaller in magnitude compared to the bulk organic c13 excursion although multiple mechanisms could explain this observation our molecular petrographic and rock eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic c13 records of the t oae

biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end permian mass extinction event article i nfo the permian triassic boundary event at 252 2 ma marks the largest extinction of marine fauna in the phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic anoxic event thestratotypeofthechanghsingianstage preciselyconstrainedbytheptbglobalstratotypesectionandpoint gssp and the gssp for the wuchiapingian changhsingian boundary both at meishan in southern china is well documented in respect to geochronology and the pattern of extinction here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the ptb and through the entire changhsingian interval our analysis of these data viewed in the context of relative sea level change and strontium isotopes reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event specifically patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late wuchiapingian middle changhsingian and early griesbachian stages secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria chlorobiaceae identify periods when euxinic conditions extended into the photic zone during the entire changhsingian stage here also the 15

enhanced nitrogen fixation in the immediate aftermath of the latest permian marine mass extinction the carbon 13 c org and nitrogen 15 n isotopic compositions of bulk organic matter were analyzed in two high resolution permian triassic transitional sections containing microbialite in south china the results from these shallow marine sections show that an abrupt negative shift in 15 n from 3 to 0 occurred immediately after the latest permian mass extinction lpe in both sections concurrent with a distinct negative shift in 13 c org the persistently low values of 15 n suggest that following the lpe microbial nitrogen fixation became the main source of biologically available nitrogen in the nanpanjiang basin and perhaps over a broader region of the eastern paleotethys ocean enhanced n fixation is probably indicative of the prevalence of stratified anoxic water masses characterized by intense denitrification and or anaerobic ammonium oxidation at the time perturbation of the marine nitrogen cycle might have contributed to high temperatures following the main marine mass extinction through the release of the greenhouse gas n 2 o the sharp declines in 15 n and 13 c org may be ascribed to an abrupt change in shallow water microbial communities which differed in composition from contemporaneous deep water communities

geobiology of microbial carbonates metazoan and seawater saturation state influences on secular trends during the phanerozoic abstract microbial carbonates are long ranging essentially bacterial aquatic sediments their calcification is dependent on ambient water chemistry and their growth is influenced by competition with other organisms such as metazoans in this paper these relationships are examined by comparing the geological record of microbial carbonates with metazoan history and secular variations in caco3 saturation state of seawater marine abundance data show that microbial carbonates episodically declined during the phanerozoic eon past 545 myr from a peak 500 myr ago this abundance trend is generally inverse to that of marine metazoan taxonomic diversity supporting the view that metazoan competition has progressively limited the formation of microbial carbonates lack of empirical values concerning variables such as seawater ionic composition atmospheric partial pressure of co2 and ph currently restricts calculation of caco3 saturation state for the phanerozoic as a whole to the use of modeled values these data together with palaeotemperature data from oxygen isotope analyses allow calculation of seawater caco3 saturation trends microbial carbonate abundance shows broad positive correspondence with calculated seawater saturation state for caco3 minerals during the interval 150 545 myr ago consistent with the likelihood that seawater chemistry has influenced the calcification and therefore accretion and preservation of microbial carbonates these comparisons suggest that both metazoan influence and seawater saturation state have combined to determine the broad pattern of marine microbial carbonate abundance throughout much of the phanerozoic in contrast for the major part of the precambrian it would seem reasonable to expect that seawater saturation state together with microbial evolution was the principal factor determining microbial carbonate development interrelationships such as these with feedbacks influencing organisms sediments and the environment are central to geobiology

global and regional variations in tropical marine environments of gondwana as revealed by a multi stable isotope study middle triassic anisian israel levant basin abstract the world during the early middle triassic anisian was characterized by a distinct recovery of the carbonate factory after the permian triassic crisis this recovery seems to have passed over the anisian environment on the tropical northern margin of gondwana israel levant basin and to have resulted in the low diversity of barren horizons of carbonate secreting organisms four anisian successions the ramon 1 hameishar 1 nafha 1 and david 1 boreholes were studied to decode the factors preventing regional recovery a multi proxy analysis was performed on these boreholes including the carbonate siliciclastic ratio total organic carbon toc carbon nitrogen c n ratio and inorganic carbon 13ccarb oxygen 18ocarb and nitrogen 15n isotopic compositions the aim of assessing the combination of these proxies was to characterize the geochemical conditions in the regional basins these successions record two c cycle perturbation events characterized by negative shifts in 13ccarb values and recognized in most successions indicating the land marine teleconnection effect on the c cycle perturbation the 18ocarb excursions revealed similar oscillation trends with global warming evidenced by increasing circumtropical precipitation and terrestrial influxes whereas global cooling was reflected by increased carbonate factory production the low 15n values in all of the studied successions indicated the presence and flourishing of n fixers the absence or scarcity of carbonate secreting organisms suggests that these n fixers were the source of the carbonate fraction in the sediments episodic events with high 15n values suggest an accumulation of terrestrial organic matter om or oxygenation events allowing short term colonization by benthic fauna at the marine sites