controls of eustasy and diagenesis on the 238u 235u of carbonates and evolution of the seawater 234u 238u during the last 1 4 myr using a leaching protocol designed for the study of u isotopes in recent carbonates we measured the u isotope composition both 238 u 235 u and 234 u 238 u of modern and ancient corals n 6 a limestone and a dolostone as well as 43 shallow water carbonate sediments from the odp leg 166 site 1009 drill core on the slope of the bahamas platform although bulk corals record the seawater 238 u value within 0 02 differences of up to 0 30 in the 238 u of individual leachates suggest a control of the coral structure and a more positive 238 u 235 u ratio in the centers of calcification the drill core 238 u data shows that the 238 u 235 u ratio of shallow water carbonates is controlled mainly by 1 variations in sea level through the mixing of different amounts of platform derived sediments with 238 u 0 50 0 60 heavier than seawater and pelagic sediments with seawater like 238 u values 2 authigenic u enrichment via pore watercirculation and u reduction both on the platform and down to 5 m below the surface mbsf after deposition of the sediment and to a lesser extent by 3 early diagenetic processes i e carbonate dissolution and or recrystallization during sediment burial the global effect of these processes leaves the 238 u values of shallow water carbonates offset relative to that of seawater by carbonates sw 0 24 0 06 95 ci including all samples this shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow water platform shelf and slope environments i e most of the carbonate sedimentary record prior to the mesozoic to account for the average effect of carbonate diagenesis assuming that the 238 u 235 u ratio of carbonate platform sediments directly records the seawater 238 u 235 u ratio would underestimate the extent of ocean seafloor anoxia by at least a factor 10 the rapid fluctuations in 238 u values due to sea level changes i is a factor that should be considered before interpreting 238 u variations as reflecting changes in oceanic paleoredox conditions and ii reinforces the need for statistically meaningful data sets the 234 u data suggest that the 234 u 238 u ratio of the seawater has remained within 20 of the modern seawater value during the last 1 1 4 myr furthermore we find that small scale 1 15 variations in seawater 234 u mirror sea level changes during the penultimate glacial interglacial period 140 to 200 ka thus confirming the record of lower 234 u sw during periods of low sea level stand and expanding it to at least the last two glacial interglacial events i e 0 23 ma such fluctuations in 234 u initial values should be taken into account when screening carbonate sediments u th ages on the basis of the initial 234 u 238 u ratios of the samples

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

uranium stable isotope fractionation in the black sea modern calibration of the 238 u 235 u paleo redox proxy abstract the isotopic compositions of redox sensitive metals including uranium u in marine sediments have recently emerged as powerful diagnostic tracers of the redox state of the ancient ocean atmosphere system reliable interpretation of sedimentary isotopic information requires a thorough understanding of the environmental controls on isotopic fractionation in modern anoxic environments before being applied to the paleo record in this study the relationship between ocean anoxia and the isotopic fractionation of u was investigated in the water column and sediments of the black sea the world s largest anoxic basin paired measurements of 238 u 235 u and u concentration supported by other redox parameters were obtained for water column and sediment samples collected during the 2013 ga04n geotraces expedition to the black sea removal of u from the water column occurs during the redox transition of soluble u vi to relatively insoluble u iv resulting in up to 43 of u being removed from solution in euxinic bottom waters uranium reduction and removal is accompanied by a progressive shift in 238 u 235 u towards isotopically light values in the water column as heavier 238 u is preferentially exported to sediments over lighter 235 u this gives rise to apparent isotope enrichment factors of e 0 63 0 09 and e 0 84 0 11 when u removal is modelled by rayleigh and closed system equilibrium isotope fractionation respectively these e values fall within the range determined for bacterial u reduction experiments and together with a striking correlation between the distributions of u and h 2 s implicate microbially mediated u vi u iv reduction as the primary mechanism controlling u isotopic shifts in the black sea the 238 u 235 u of underlying sediments is related to the the 238 u 235 u of black sea bottom waters through the isotope enrichment factor of the u reduction reaction but the relationship between sedimentary and water column 238 u 235 u is complicated by mass transport processes and the modelled e values may underestimate the true isotope enrichment factors these new results for the black sea provide important constraints on the use of 238 u 235 u as a proxy of the redox state of ancient oceans

hydrogen sulphide and methane emissions on the central namibian shelf abstract hydrogen sulphide occurs frequently in the waters of the inner shelf coastal upwelling area off central namibia the area affected coincides with hatching grounds of commercially important pelagic fish whose recruitment may be severely affected by recurring toxic sulphidic episodes both episodic biogenic methane gas driven advective and molecular diffusive flux of hydrogen sulphide have been implicated as transport mechanisms from the underlying organic matter rich diatomaceous mud to test hypotheses on the controls of hydrogen sulphide transport from the sediments on the inner namibian shelf water column and sediment data were acquired from four stations between 27 and 72 m water depth over a 3 year long period on 14 cruises temperature salinity dissolved oxygen nitrate methane and total dissolved sulphide were determined from water column samples and pore water dissolved methane total dissolved sulphide biomass of benthic sulphide oxidising bacteria beggiatoa and thiomargarita and bacterial sulphate reduction rates were determined from sediment cores superimposed on a trend of synchronous changes in water column oxygen and nutrient concentrations controlled by regional hydrographic conditions were asynchronous small scale variations at the in shore stations that attest to localized controls on water column chemistry small temporal variations in sulphate reduction rates determined with 35 s labeled sulphate do not support the interpretation that variable emissions of sulphide and methane from sediments are driven by temporal changes in the degradation rates of freshly deposited organic matter the large temporal changes in the concentrations of hydrogen sulphide and the co occurrence of pore water sulphate and methane support an interpretation of episodic advection of methane and hydrogen sulphide from deeper sediment depths possibly due to gas bubble transport effective fluxes of hydrogen sulphide and methane to the water column and methane and sulphide concentrations in the bottom waters were decoupled likely due to the activity of sulphide oxidising bacteria while the causal mechanism for the episodic fluctuations in methane and dissolved sulphide concentrations remains unclear this data set points to the importance of alternating advective and diffusive transport of methane and hydrogen sulphide to the water column

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

late mesozoic gravity sliding and oxfordian hydrocarbon reservoir potential of the northern yucatan margin abstract the stratigraphy and structural evolution of the western florida margin is much better understood than its northern yucatan conjugate because previous hydrocarbon exploration has been more extensive on the florida margin in the deep water northeastern gom the post salt section records late jurassic cretaceous gravity sliding of rafted blocks along a basinward dipping layer of callovian salt this study uses approximately 31 000 line km of 2d seismic data to describe a coeval area of widespread gravity sliding along the less studied northern yucatan margin we define three structural domains based on their distinctive salt structures and associated deformation 1 a region in the northeastern study area consists of relatively undeformed late jurassic cretaceous section underlain by 0 300 m thick salt 2 areas in the central and southwestern study area contain late mesozoic gravity slides defined by 300 600 m thick salt rollers and normal faults rooted onto a 1 4 basinward dipping salt detachment and 3 the distal margin of the western and central study area exhibits large salt diapirs up to 6 km tall that deform quaternary stratigraphic units in the central yucatan study area containing late mesozoic gravity slides a stratigraphic unit equivalent to the productive oxfordian norphlet sandstone of the deep water northeastern gom is identified based on its similar seismic character reconstructing the extent of this norphlet equivalent unit along the yucatan margin to its location during oxfordian deposition places it adjacent to an extensive area of norphlet sandstone mapped in the deep water northeastern gom by previous authors our reconstruction suggests a 48 000 km2 fairway of potential aeolian late jurassic reservoirs on the yucatan and campeche margins that includes productive reservoirs in the southeastern bay of campeche which previous authors correlated with the norphlet formation

causes of the marine productivity and oxygen changes associated with the permian triassic boundary a reevaluation with ocean general circulation models widespread anoxic and dysoxic deposition in marine sediments has been associated with a stagnant ocean at the permian triassic p tr boundary this p tr boundary is also associated with one of the largest mass extinctions of species of the paleozoic marking the transition to the mesozoic here we review recent three dimensional numerical model studies that have investigated possible circulation patterns at the p tr boundary in addition we conduct new sensitivity experiments with a coupled ocean atmosphere model of intermediate complexity including marine chemistry to study changes of the deep sea oxygen distribution associated with 1 a significant change in the hydrological cycle and 2 a massive release of methane gas hydrates from marine sediments freshening of sea surface water masses by a strong freshwater source along the west coast of south polar pangea produces a significant local minimum in oxygen in the eastern tropical panthalassa ocean at intermediate depth and at the sea floor the methane release experiment with an atmospheric co2 concentration of 18 times the preindustrial co2 level simulates a strong increase in sea surface temperature about 4 5 8c and a vigorous deep sea circulation in contrast to the conclusions drawn from previous studies this reanalysis of the ocean circulation at the p tr boundary favors a strong ventilation in most parts of the deep sea thus a significant change in the oceanic carbon inventories and a reorganization of the marine productivity associated with a stronger biological pump may be required to explain the anoxic sedimentary deposits d 2005 elsevier b v all rights reserved

global ocean redox variations across the smithian spathian boundary linked to concurrent climatic and biotic changes abstract the smithian spathian boundary ssb was an interval characterized by a major global carbon cycle perturbation climatic cooling from a middle late smithian boundary hyperthermal condition and a major setback in the recovery of marine necto pelagic faunas from the end permian mass extinction although the ssb has been linked to changes in oceanic redox conditions key aspects of this redox variation e g duration extent and triggering mechanisms and its relationship to coeval climatic and biotic changes remain unresolved here we report a high resolution middle smithian to middle spathian u isotope 238u record based on marine carbonates of the zuodeng south china and jesmond british columbia sections to investigate the timing and global extent of ocean redox variation across the ssb our 238u record reveals values similar to or slightly heavier than modern seawater 0 39 during the middle smithian a rapid negative shift to highly negative values during the early late smithian a positive shift at the ssb and a rapid shift back to more negative values in the early middle spathian a simple u isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late smithian and the early middle spathian covering 11 of total seafloor area but that it contracted sharply during the ssb 2 the redox pattern documented by our 238u record shows a good first order correspondence to tropical sea surface temperature sst data for the smithian spathian in particular peak anoxia coincided with the middle late smithian boundary hyperthermal event and diminished anoxia with a pronounced decline in ssts at the ssb the temporal correlation between anoxia and low biodiversity levels of many marine clades e g conodonts and ammonoids during the late smithian indicates that oceanic anoxia may have played a role in the ssb biocrisis

biogeochemical controls on photic zone euxinia during the end permian mass extinction geochemical biomarker and isotopic evidence suggests that the end permian was characterized by extreme oceanic anoxia that may have led to hydrogen sulfide buildup and mass extinction we use an earth system model to quantify the biogeochemical and physical conditions necessary for widespread oceanic euxinia and hydrogen sulfide release to the atmosphere greater than threefold increases in ocean nutrient content combined with nutrient trapping ocean circulation cause surface water h 2 s accumulation in the paleo tethys ocean and in areas of strong upwelling accounting for the presence of sulfide oxidizing phototrophs in the model suppresses but does not prevent widespread release of h 2 s to the atmosphere evidence from the geologic record is consistent with modeled geochemical distributions of widespread nutrient induced euxinia during the end permian suggesting h 2 s toxicity and hypercapnia may have provided the kill mechanism for extinction

environmental instability prior to end permian mass extinction reflected in biotic and facies changes on shallow carbonate platforms of the nanpanjiang basin south china abstract shallow carbonate platforms exhibit major changes in faunal composition and facies types during the latest permian and earliest triassic although the microbialites that developed following the latest permian mass extinction lpme have attracted wide attention temporal variations in shallow platform facies and faunas prior to the lpme have been less thoroughly studied here we analyze diversity patterns and variation in skeletal composition in three upper permian sections from isolated carbonate platforms of the nanpanjiang basin in addition to the well known transition from fossil rich upper permian limestones to fossil poor permian triassic boundary ptb microbialites these sections exhibit several distinct changes that predate the lpme first foram faunas show a shift from non fusulinid dominated to fusulinid dominated communities in the

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

global seawater redox trends during the late devonian mass extinction detected using u isotopes of marine limestones abstract the late devonian extinction ranks as one of the big five phanerozoic extinctions affecting up to 80 of marine species and is characterized by two major extinction events that are separated by 238 u across a 7 my interval of well dated upper devonian marine limestones from the devil s gate formation in nevada usa the measured 238 u curve shows no co variation with local sediment derived redox trends water depth dependent facies changes redox sensitive metals toc or diagnostic elemental ratios from these relationships we infer that the 238 u curve represents global seawater redox conditions two negative 238 u excursions indicating more reducing seawater are observed with durations of 3 8 my late frasnian and 1 1 my early famennian respectively steady state modeling of the observed 0 2 to 0 3 shifts in 238 u points to a 5 15 increase in the total area of anoxic seafloor during these excursions the late frasnian negative excursion is broadly coincident with the first extinction event late rhenana zone or lower kellwasser event whereas the early famennian negative excursion lower middle triangularis zones occurs after the most intense frasnian famennian boundary f f extinction event upper kellwasser event compilations of local sediment redox conditions from upper devonian marine deposits with conodont zone level age control indicates that the extinction events were coincident with widespread anoxic deposits accumulating in subtropical epeiric sea and some open ocean settings supporting previous interpretations that widespread marine anoxia had an important influence on the late devonian extinctions the temporal relationships between global ocean redox trends represented by the 238 u curve and the newly compiled subtropical marine redox sediment trends indicates that local epeiric seawaters carried a similar u isotopic composition as the open ocean for the majority of the studied interval except for a brief interval

temporal variations in air permeability and soil co2 flux in volcanic ash soils island of vulcano italy air permeability is a major physical factor affecting the advective transport of a gas through the soil and variations in this parameter can strongly influence the emission of endogenous gases from the soil to the atmosphere in this paper we illustrated a new and simple method for measuring in situ air permeability based on the measurement of air pressure inside a special probe inserted into the soil the method was designed and developed primarily to study the relationship between air permeability and the soil co2 flux in an active volcanic area the method was used for continuous monitoring of the air permeability at two different locations on the island of vulcano at the same time the values of the atmospheric pressure temperature rain and volumetric water content of the soil were also acquired to investigate their effect on soil air permeability and soil co2 flux the results showed that during the monitoring period soil air permeability exhibited minor variations at each site while larger variations in the soil co2 flux were recorded the effect of soil air permeability on soil co2 flux was negligible at both sites whereas a strong dependence of soil co2 flux on volumetric water content and on atmospheric pressure was found furthermore the variation in air permeability recorded at both sites was much lower than that predicted using some well known predictive models showing that the relationship among different soil transport parameters is more complex in real field conditions than would be expected by semiempirical models

u th pb isotope data indicate phanerozoic age for oxidation of the 3 4 ga apex basalt abstract the occurrence of ferric oxides in archean rocks has played an important role in discussions on the amount of free oxygen in the atmosphere of the ancient earth recognizing that post archean weathering may also produce oxide minerals drill cores have been used to obtain samples beneath the depth of phanerozoic weathering the first core of the archean biosphere drilling project abdp 1 documented hematite as alteration products in 3 4 ga basalts from the marble bar area of the pilbara craton nw australia and this has been used to infer the presence of an o2 bearing atmosphere in the archean it is possible however that despite recovery of samples from 100 m depth oxidation of the basalts occurred much younger than the depositional age in this study the age of oxidation of the apex basalt from the abdp 1 drill core at marble bar is constrained by u th pb geochronology lead and u concentrations of the basalts from the abdp 1 drill core vary greatly between

u mo ratios and δ98 95mo as local and global redox proxies during mass extinction events abstract when used in conjunction with trace metal redox proxies the use of u mo ratios and 98 95 mo values can considerably enhance the interpretation of ocean oxygenation trends both locally and globally this is illustrated with studies from two biogenic chert dominated records of mass extinction the ordovician silurian boundary and the late permian in sections from the yangtze block in south china the latest ordovician mass extinction is well known to coincide with oxygenation episode in the hirnantian stage here revealed by trace metal proxies v v ni v cr ni co that show it sandwiched between anoxic euxinic black shales the predominantly anoxic euxinic ordovician silurian strata provide a record of seawater 98 95 mo values that are seen to gradually rise during the interval from 0 5 to 1 0 the exception to the 98 95 mo stability is the datum of the slight negatively 98 95 mo associated with decreasing of v cr and v v ni ratio suggesting the hirnantian oxygenation event the upper permian chert succession at shangsi reveals an overall better ventilated record in which the best oxygenated strata show the highest u mo values that is interpreted as relative enrichment of u in suboxic conditions at a few levels anoxic euxinic conditions show the 98 95 mo values to be 2 close to modern values implying that latest permian oceans were as well ventilated as those today the well known end permian oceanic anoxic event is therefore suggested to only develop at the end of this period

controls on regional marine redox evolution during permian triassic transition in south china abstract although oceanic anoxia is regarded as a leading cause of the permian triassic boundary ptb mass extinction its timing extent and underlying causes remain unclear here we conducted a high resolution fe s c mo geochemical study of the entire changhsingian and lowermost induan succession in a carbonate ramp setting at ganxi western hubei province south china six stratigraphic units representing discrete redox intervals were identified based on integrated fe s c mo data units i iii are of latest wuchiapingian to early changhsingian age with units i and iii characterized by euxinia and unit ii by uncertain redox conditions unit iv of mid changhsingian age records a gradual transition from euxinic to ferruginous conditions units v and vi spanning the latest permian mass extinction lpme to earliest triassic interval were deposited under dominantly ferruginous conditions punctuated by both euxinic and oxic episodes redox variations at ganxi were controlled by contemporaneous oceanographic changes in the upper oceanic thermocline region i euxinia in units i and iii may record elevated marine productivity as suggested by mean organic carbon accumulation rates or ocar of 6 5 and 5 1 mg cm2 kyr respectively that was possibly related to upwelling ii the euxinic to ferruginous transition from unit iv to units v vi can be attributed to a combination of reduced sulfate availability and rising terrigenous iron inputs mean fe of 1 7 and 3 9 respectively for units v iv and vi compared to 1 0 for units i iii and iii transient intervals of euxinia in units v and vi were facilitated by enhanced sulfate fluxes related to episodic volcanism during this interval an integration of the redox data from ganxi with previously published data from the shangsi and xiakou sections suggests that enhanced weathering fluxes were most likely the key factor controlling the marine redox transition from euxinic to ferruginous conditions during the latest permian across the south china region

the phanerozoic δ88 86sr record of seawater new constraints on past changes in oceanic carbonate fluxes the isotopic composition of phanerozoic marine sediments provides important information about changes in seawater chemistry in particular the radiogenic strontium isotope 87sr 86sr system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric co2 concentrations however the 87sr 86sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium sr output flux which is primarily controlled by the burial of calcium carbonate caco3 at the ocean floor the sr budget of the phanerozoic ocean including the associated changes in the amount of caco3 burial is therefore only poorly constrained here we present the first stable isotope record of sr for phanerozoic skeletal carbonates and by inference for phanerozoic seawater 88 86srsw which we find to be sensitive to imbalances in the sr input and output fluxes this 88 86srsw record varies from 0 25 to 0 60 vs srm987 with a mean of 0 37 the fractionation factor between modern seawater and skeletal calcite 88 86srcc sw based on the analysis of 13 modern brachiopods mean 88 86sr of 0 176 0 016 2 standard deviations s d is 0 21 and was found to be independent of species water temperature and habitat location overall the phanerozoic 88 86srsw record is positively correlated with the ca isotope record 44 40casw but not with the radiogenic sr isotope record 87sr 86sr sw a new numerical modeling approach which considers both 88 86srsw and 87sr 86sr sw yields improved estimates for phanerozoic fluxes and concentrations for seawater sr the oceanic net carbonate flux of sr f sr carb varied between an output of 4 7x1010mol myr and an input of 2 3x1010mol myr with a mean of 1 6x1010mol myr on time scales in excess of 100myrs the f sr carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the aragonite and calcite sea episodes on time scales less than 20myrs the f sr carb seems to be controlled by variable combinations of carbonate burial rate shelf carbonate weathering and recrystallization ocean acidification and ocean anoxia in particular the permian triassic transition is marked by a prominent positive 88 86srsw peak that reflects a significantly enhanced burial flux of sr and carbonate likely driven by bacterial sulfate reduction bsr and the related alkalinity production in deeper anoxic waters we also argue that the residence time of sr in the phanerozoic ocean ranged from 1myrs to 20myrs

enhanced recycling of organic matter and os isotopic evidence for multiple magmatic or meteoritic inputs to the late permian panthalassic ocean opal creek canada abstract the geochemical record for the permian triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on earth we present inorganic and organic geochemical data and re os isotope systematics in a critical stratigraphic interval of pre and post extinction upper permian lower triassic sediments from opal creek western canada paleolatitude of 30 n we document significant and long lived changes in panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to late permian seawater evidenced by notable decreases of os isotopic ratios upsection geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the late permian euxinic signals are most prominent in the upper permian sediments with low organic carbon and high sulfur contents and gradually wane in the lower triassic the observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and or water column providing hydrogen sulfide to form pyrite this scenario requires nearly complete anaerobic decomposition of predominantly labile marine organic matter om without the necessity for a complete collapse of primary marine productivity similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the late permian both scenarios could have provided similar kill mechanisms for the latest permian mass extinction despite the moderate thermal maturity of the section om in all studied samples is dominantly terrestrial and or continentally derived recycled and refractory ancient om we argue that as such the quantity of the om in the section mainly reflects changes in terrestrial vegetation and or weathering and not in marine productivity at opal creek a pyrite layer and

turnover of organic matter in differently textured soils i physical characteristics of structurally disturbed and intact soils abstract soil type effects on organic matter turnover are most often ascribed directly to differences in soil clay content since soil texture determines the physical characteristics of soil aggregation and water holding capacity may be more relevant to address in the search for controls of organic matter turnover most studies of microbial processes in soils are based on structurally disturbed soil where the abiotic conditions for the microbial activity may be quite different from those in intact soils in this study basic physical characteristics were determined for structurally disturbed and intact soil samples from differently textured soils bulk soil was retrieved from 0 20 cm depth at six locations along a textural gradient in an arable field on weichselian morainic deposits in denmark the samples na1 to na6 ranged in clay from 11 to 45 and in silt from 7 to 15 clay and silt sized organomineral complexes were isolated from na2 soil by ultrasonic dispersion and sedimentation in water the clay and silt fractions were added individually and in varying proportions to na1 soil providing three clay amended cl2 cl4 and cl6 and three silt amended si2 si4 and si6 soils all 12 soils were crushed in air dry state to 100 m air diffusivity and permeability measurements showed disturbed soils to have a less continuous and more tortuous pore system than undisturbed reference samples water filled pore space at a critical level of air diffusion potential was significantly higher for undisturbed than for disturbed samples especially in soils high in clay drop cone measurements showed disturbed soils to be structurally weaker than undisturbed ones intact and structurally disturbed soils were found to differ significantly in physical properties even after 17 months of soil structure regeneration water filled pore space seems to reflect the potential of available water and aeration status to regulate aerobic microbial activity of structurally disturbed soil but not of intact field soil

factors controlling carbonate platform asymmetry preliminary results from the great bank of guizhou an isolated permian triassic platform in the nanpanjiang basin south china abstract a well exposed isolated carbonate platform the great bank of guizhou in the nanpanjiang basin of south china developed from the latest permian to the earliest late triassic platform strata are dissected by a faulted syncline exposing a complete cross section through the interior margins and flanks enabling a detailed assessment of depositional controls previous studies portrayed the platform as having a relatively symmetrical architecture even though much of the former work was focused on the platform interior and northern margin basin transition our research reveals five aspects of the southern margin facies and stratigraphy that are significantly different from those of the northern margin 1 subaerial exposure and unconformity developed on top of the upper permian sponge boundstone and in the overlying lower triassic strata 2 permian and triassic clasts chaotically admixed within early triassic breccias 3 lower triassic strata remarkably thinner on the southern margin 4 a much narrower tubiphytes reef facies preserved along the southern margin in the middle triassic and 5 large scallop shaped reentrants at the southern margin evident in satellite images three end member models may explain the asymmetry 1 antecedent topography of the underlying upper permian reef rimmed margin coupled with eustatic sea level fluctuation 2 differential tectonic uplift and 3 large scale submarine collapse of the platform margin subaerial exposure and admixing of permian and triassic clasts observed at yungan section is best explained by the tectonic uplift model however the submarine collapse model also explains several of the observations if it is associated with uplift s or sea level fall s submarine collapse is supported by large concave erosional reentrants scallops visible in satellite images taken together our observations suggest that a combination of tectonic uplift and margin collapse contributed to platform asymmetry further work promises to further constrain the details and timing of processes that contributed to the asymmetry

the influence of seawater carbonate chemistry mineralogy and diagenesis on calcium isotope variations in lower middle triassic carbonate rocks abstract the geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks as a result calcium ca isotope ratios 44ca 40ca expressed as 44 40ca can help to constrain ancient carbon cycle dynamics if ca cycle behavior can be reconstructed however the 44 40ca of carbonate rocks is influenced not only by the 44 40ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation in this study we investigate the dominant controls on carbonate 44 40ca in upper permian to middle triassic limestones ca 253 to 244 ma from south china and turkey this time interval is ideal for assessing controls on ca isotope ratios in carbonate rocks because fluctuations in seawater 44 40ca may be expected based on several large carbon isotope 13c excursions ranging from 2 to 8 parallel negative 13c and 44 40ca excursions were previously identified across the end permian extinction horizon here we find a second negative excursion in 44 40ca of 0 2 within lower triassic strata in both south china and turkey however this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the 44 40ca of global seawater additionally 44 40ca values from turkey are consistently 0 3 lower than contemporaneous samples from south china providing further support for local or regional influences by measuring 44 40ca and sr concentrations sr in two stratigraphic sections located at opposite margins of the paleo tethys ocean we can determine whether the data represent global conditions e g secular variations in the 44 40ca of seawater versus local controls e g original mineralogy or diagenetic alteration the sr and 44 40ca data from this study are best described statistically by a log linear correlation that also exists in many previously published datasets of various geological ages using a model of early marine diagenetic water rock interaction we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate 44 40ca values the relationship between sr and 44 40ca holds potential for reconstructing first order secular changes in seawater 44 40ca composition

the sureste super basin of southern mexico the sureste basin of southern mexico has all the components to be classed as one of the world s super basins for hydrocarbon exploration and production this is because of its endowment with one of the world s great source rock systems namely the late jurassic edzna formation in combination with stacking of multiple potential reservoirs in a highly structural salt basin this paper discusses the hydrocarbon play potential of the sureste basin within a tectono stratigraphic context and outlines the key risks uncertainties and opportunities for future exploration surface oil seepage and seismic mapping clearly show that many prospective structures extend into the underexplored deeper water basin area key risks are related to charge with substantial migration required from deeply buried late jurassic source rocks into shallower carbonate and clastic reservoirs in particular deep charge focus and hydrocarbon charge versus trap timing are key risk elements two key uncertainties are the deep reservoir quality of the lithic sandstones in paleogene reservoirs and column height prediction for high relief traps the highly structured nature of the underexplored deep water campeche slope in combination with extensive hydrocarbon seepage to the seabed bodes well for a prolific exploration future in expanding the proven reservoir systems further taking advantage of established deep water drilling practices and advanced wide azimuth three dimensional 3 d seismic imaging it is also likely that with expanding high quality 3 d seismic coverage around shallow water and onshore existing discoveries additional reservoir targets and additional fault blocks will become visible

uranium isotope evidence for limited euxinia in mid proterozoic oceans abstract reconstructing earth s oxygenation history is key to deciphering environmental controls on early biospheric evolution during the mid proterozoic eon low but potentially variable atmospheric po2 led to highly heterogeneous marine redox conditions with most studies indicating a relatively shallow depth of oxygen penetration the relative proportion of oxic anoxic and iron rich ferruginous and anoxic and sulfide rich euxinic conditions on the global seafloor is difficult to quantify however due to a general reliance on local redox proxies applied to the temporally discontinuous black shale record it is particularly important to constrain the global prevalence of euxinic bottom waters because sulfide toxicity has been implicated as a primary constraint on evolution in mid proterozoic oceans and limits the solubility of bioessential trace metals such as copper zinc and molybdenum here we present a suite of new uranium u isotope data from marine carbonate rocks that span the entire mid proterozoic interval 1 8 to 0 8 ga u isotopes in well preserved carbonate rocks represent a powerful new proxy that can be used to quantitatively constrain the global extent of marine euxinia the median 238 u value for mid proterozoic carbonate samples is 0 43 which is lower than the median value for modern post depositional carbonate sediments from the bahamas yet significantly higher than carbonate 238 u values recorded during other times of expanded anoxia in earth history such as during the end permian mass extinction when paired with a three sink isotope mass balance model our data indicate that no more than 7 of the global seafloor was euxinic during the mid proterozoic eon although transient pulses of expanded euxinia are recorded although these results challenge early expectations of a sulfide rich mid proterozoic ocean they are consistent with more recent inferences from the black shale trace metal record evidence therefore indicates that euxinic bottom waters were relatively limited in their spatial extent in the mid proterozoic oceans

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

palynology and vegetation dynamics across the permian triassic boundary in southern tibet abstract the end permian mass extinction epme is regarded as the most severe biotic crisis in earth history which is particularly well documented in the marine fossil record despite compelling evidence that dramatic global environmental changes probably drove this extinction event its effects on terrestrial plants are still highly controversial here we present changhsingian latest permian to late smithian latest early triassic composite palynological successions from the lagoonal to open marine qubu and tulong sections in southern tibet quantitative analyses of palynomorph distributions range charts and relative abundance data allow us to differentiate five distinct informal palynofloral assemblages in ascending order the scheuringipollenites ovatus vitreisporites pallidus op assemblages the reduviasporonites catenulatus assemblage the endosporites papillatus pinuspollenites thoracatus pt assemblages the lundbladispora brevicula densoisporites nejburgii bn assemblages and the falcisporites nuthallensis alisporites landianus nl assemblages these palynological assemblage intervals and the associated ammonoid and conodont biostratigraphy resolve vegetation changes across the permian triassic boundary ptb on the northern tethyan margin of gondwanaland in great detail and high resolution principal component analysis pca of palynological data indicates that the op assemblages which are dominated by non taeniate bisaccate pollen represent a vegetation in a cool and dry climate during the changhsingian in the qubu section the palynological turnover from the op assemblages to the c assemblage 0 81 m below the ptb coincides with abrupt sea level fluctuations in the latest permian as this turnover further coincides with an extreme negative 13corg shift a great abundance of amorphous organic matter aom and marine acritarchs as well as the frequent occurrence of reduviasporonites catenulatus the c assemblage is tentatively interpreted to represent the fungal spike reported worldwide at the onset of the epme in southern tibet the epme appears to result only in a short term disturbance and range contraction of land plant communities surprisingly the early dienerian pt assemblages postdating the epme by about 500kyrs closely resemble the late changhsingian op assemblages suggesting a resurgence of those land plant groups that were dominant during the late changhsingian this recovery was disrupted with the onset of the late dienerian bn assemblages in the qubu section which is represented by a peak abundance of cavate trilete spores reflecting large scale deforestation for nearly one million years the regional vegetation appears to have been dominated by pioneer communities of quillworts and spike mosses only towards the end of the smithian bisaccate gymnosperm pollen regained dominance with the onset of the nl assemblages in the tulong section integrating the results of the principal component analysis on our new palynological data and conodont apatite oxygen isotope data from neighbouring sections in pakistan the contraction of gymnosperm forests during the early dienerian smithian in southern tibet is interpreted to be accompanied by an abrupt change to an episode with a warmer and more humid climate this observation supports the hypothesis that the secondary eruptions of the siberian large igneous province during the induan led to long term global warming and as a side effect to more humid conditions in the southern temperate zone as a result of altered precipitation and evaporation patterns

shallow water redox conditions from the permian triassic boundary microbialite the rare earth element and iodine geochemistry of carbonates from turkey and south china redox sensitive elements serve as useful proxies of the oxygenation state of ancient environments but their interpretation may not always be straightforward to evaluate the inherent complexities rare earths and yttrium rey iodine and major element concentrations are determined in two carbonate sections spanning the permian triassic p tr transition in demirtas turkey and cili south china we use major oxides to identify non seawater rey sources such as siliciclastics fe oxides phosphates and diagenetic fluids additionally we employ y ho ratio la anomaly and light rare earth element depletion to identify which samples preserve a seawater like reysn distribution in contrast to past interpretations we find that the p tr boundary microbialites in both sections contain rey signatures indicative of deposition in an oxic environment these boundary microbialites have their base at the extinction horizon and are widespread within the tethyan region in the cili section the underlying permian limestone also preserves a seawater like rey signature with a negative ce anomaly this indicates that the water column was oxygenated both before and after the extinction event the permian limestone in the demirtas section does not preserve a seawater like reysn distribution so the absence of a ce anomaly cannot be used to distinguish prevailing redox conditions during deposition however in these samples we find the presence of a diverse permian benthic community sufficient to identify deposition in an oxic environment the geochemical evidence for a continuously oxic environment during the deposition of the boundary microbialite presented in this study strongly supports work done using ostracods as redox indicators within the boundary microbialite in south china the microbialite has been proposed as a disaster facies in part resulting from the exclusion of grazers although anoxia is one of the suggested mechanisms for the exclusion of grazers we find that it is not supported by geochemical and biotic evidence

global enhancement of ocean anoxia during oceanic anoxic event 2 a quantitative approach using u isotopes during the mesozoic greenhouse world the oceans underwent several oceanic anoxic events oaes characterized by intervals during which organic rich black shales were deposited indicating strong oxygen depletion in the marine realm the cenomanian turonian oae2 ca 93 ma represents one of the most prominent events of the cretaceous with significant perturbations of the global carbon cycle although oae2 likely reached a global scale the spatial extent of seawater anoxia during this oae is poorly constrained here we demonstrate that variations in the 238u 235u isotope ratio 238u a newly developed paleoredox proxy can be used to quantify the extent of marine anoxia for black shales from the mid cretaceous oae2 we find a systematic shift toward lighter 238u and lower u concentrations as compared to modern equivalent organic rich sediments from the black sea this shift translates to a global increase of oceanic anoxia during oae2 by at least a factor of three as compared to the present day or to periods before and after oae2 the constant offset in u concentrations and isotope compositions of black shales throughout oae2 compared to modern black sea sediments indicates an enhancement of oceanic anoxic conditions already prior to the onset of oae2

uranium isotopes distinguish two geochemically distinct stages during the later cambrian spice event a b s t r a c t anoxic marine zones were common in early paleozoic oceans 542 400 ma and present a potential link to atmospheric po2 via feedbacks linking global marine phosphorous recycling primary production and organic carbon burial uranium u isotopes in carbonate rocks track the extent of ocean anoxia whereas carbon c and sulfur s isotopes track the burial of organic carbon and pyrite sulfur primary long term sources of atmospheric oxygen in combination these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million year time scales here we report high precision uranium isotopic data in marine carbonates deposited during the late cambrian spice event at ca 499 ma documenting a well defined 0 18 negative 238 u excursion that occurs at the onset of the spice event s positive 13

prediction of vertical soil organic carbon profiles using soil properties and environmental tracer data at an untilled site abstract soil organic carbon soc has considerable spatial and temporal variability both at the hillslope and catchment scale as well as down the soil profile in recent years the distribution of soc down the soil profile has become an area of interest in the understanding of the carbon sequestration potential of soils most studies however have concentrated on highly disturbed agricultural sites with little data available for untilled locations in this study the vertical distribution of soc is examined at a grassland site in the young river area of western australia that has remained undisturbed by human activity for 50 years soil physical properties texture rock content as well as the distribution of the environmental tracers 137 cs and 210 pb were assessed with the aim of better understanding the transport processes which produce the observed vertical distribution of soc while no consistent relationship was found between soc and soil physical properties significant relationships were found between the distribution of soc and the environmental tracers 137 cs and 210 pb finite element simulations based on a diffusion convection decay model showed that the transport of 137 cs and 210 pb down the soil profile is likely to be driven by the same primarily diffusive processes the same model used in conjunction with plant input and decay data generated from the rothc 26 3 soil carbon model revealed that transport of soc down the soil profile while also a diffusion process was significantly slower indicating that different processes and or pathways are involved in soc transport at this site

iron depleted pelagic water at the end permian mass extinction inferred from chemical species of iron and molybdenum in deep sea sedimentary rocks abstract this study determined chemical species of iron fe and molybdenum mo in a pelagic deep sea permian triassic boundary section that records redox variations across the severe mass extinction event we applied x ray diffraction xrd and extended x ray absorption fine structure exafs at the fe k edge and x ray absorption near edge structure xanes at the mo k edge to silicic sedimentary rock samples for analysis of the studied section according to the exafs and xrd analyses pyrite was the dominant fe bearing mineral in most samples whereas ferric minerals such as hematite were absent throughout the permian triassic transition this result supports those of previous studies of other deep sea japanese permian triassic boundary ptb sections the fe in pyrite mineral quantified by exafs spectra displayed synchronous variation with sulphide sulphur ssulphide but with total organic carbon content which revealed the fe limited conditions for pyrite formation in the pelagic panthalassa region the xanes analysis indicated the presence of tetrahedral and octahedral configurations of mo bonded to oxygen o and sulphur s which were referred to as moo42 moo3 as a possible alternative reference material of mo in organic ligands moo2 and mos2 the mos2 species dominated in the end permian horizons coinciding with high abundances of total mo which suggests a sulphidic depositional environment the mos2 and moo3 species were the main contributors to these high mo abundances in the end permian strata the presence of the molybdenite mos2 species in the studied section indicates that the samples were subjected to alteration under high temperatures with sufficiently sulphidic and limited reactive fe availability conditions for mos2 formation during late diagenesis the fe in pyrite decreased across the mass extinction boundary which coincided with the highest total mo amount with the mos2 and moo3 species these trends reflected a decrease in reactive fe in the sediments and contemporaneous seawaters under sulphidic conditions the low reactive fe condition could be due to massive pyrite formation under prolonged sulphidic water conditions in the pelagic and ambient continental margin regions in the end permian

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

structural geometry and evolution of the ku zaap and maloob structures campeche bay mexico the ku zaap and maloob structures consist of an arcuate series of fold thrust structures which change orientation from approximately east west to north northwest south southeast along a structural salient in the offshore campeche bay mexico the structures are related to a series of thrust faults which merge into the maloob thrust the ku zaap and maloob fields located on these structures together constitute an important complex of fields with proven remaining reserves of approximately 1850 mmboe the structures formed during three main periods of deformation 1 a jurassic cretaceous extensional episode 2 a miocene compressive phase during which the main trap forming structures were formed and 3 a pliocene to holocene extensional episode resulting in several listric growth faults three dimensional 3 d models of the main reservoir unit upper cretaceous breccia and other prospective reservoir units eocene and kimmeridgian constructed by integrating 3 d seismic interpretation well data and a series of balanced structural cross sections provide an understanding of the geometry and evolution of the structures the zaap maloob and sub maloob structures are interpreted as a series of faulted detachment folds detaching within salt and other jurassic ductile units the front limbs of these structures are typically cut by thrust faults with small displacements terminating in the lower tertiary section the ku and pakal structures also originated as a detachment fold but was faulted relatively early in its deformational history the frontal zone of this structure is marked by a closely spaced thrust system consisting of the ku pakal 1 and maloob thrusts the 3 d models provide an accurate picture of the structural geometry of the principal reservoir units which will be useful for future production from the fields and for exploration in adjacent areas in the basin

inverse correlation between the molybdenum and uranium isotope compositions of upper devonian black shales caused by changes in local depositional conditions rather than global ocean redox variations abstract coupled mo u isotope data from the upper devonian kettle point formation ontario canada provide a cautionary tale regarding interpretation of global ocean redox conditions using data from euxinic black shales in the gore of chatham core the kettle point black shales have high mo concentrations 48 473 g g and consistently high mo u ratios 3 times the mo u ratio of modern seawater suggesting a euxinic depositional environment these shales yield an inverse correlation r 0 89 p

petrologic and geochemical evidence for the formation of organic rich siliceous rocks of the late permian dalong formation lower yangtze region southern china abstract black shales are economically and scientifically important because they are commonly associated with high quality hydrocarbon source rocks and metal accumulations formed during periods of abrupt environmental change organic rich siliceous rocks of the late permian dalong formation developed extensively within middle upper yangtze region western yangtze platform however the formation mechanism of its formation in the lower yangtze region eastern yangtze platform remains a subject of debate due to a lack of outcrop exposure petrologic mineralogic and geochemical data are presented for three sections of the dalong formation within the lower yangtze region geochemical ratios including v v ni v cr ni co u th and v sc suggest that the dalong formation was deposited in an oxygen poor environment the elevated concentration of mo 100 ppm further suggests that free h2s existed in the bottom water which was favorable for the accumulation of large amounts of organic matter mo toc ratios reveal that water flow in the lower yangtze basin was moderately to strongly restricted during deposition of the dalong formation flow within the upper middle parts of the yangtze basin was also restricted suggesting that northern marginal basins on the yangtze platform formed part of a single ocean during the late permian i e changhsingian cherts of the dalong formation reflect high primary productivity similar to that of modern day upwelling zones which increased the amount of organic matter these results combined with previous work suggest that the long term oxygen poor conditions during deposition of the dalong formation were caused by restricted water circulation in a unique paleogeographic environment characterized by low latitude and submarine paleo highlands such settings of low latitude characterized by tropical climate favored the growth of siliceous zooplankton in the zones with submarine paleo highlands having created topographic barriers to water circulation restricted bottom water flow and oceanic anoxia during the late permian were likely the main controls on the accumulation of organic rich rocks elevated nutrient levels caused by frequent oceanic upwelling along the western margin of the south china craton and global volcanism at this time facilitated siliceous organism productivity

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

conodont biostratigraphy across the permian triassic boundary at the dawen section great bank of guizhou guizhou province south china implications for the late permian extinction and correlation with meishan several continuous permian triassic boundary ptb sections are well exposed in the interior of the great bank of guizhou gbg on the east limb of the bianyang syncline luodian county guizhou province south china fourteen conodont taxa are identified including clarkina kazi clarkina lehrmanni n sp clarkina taylorae clarkina zhejiangensis hindeodus eurypyge hindeodus inflatus hindeodus sxlatidentatus hindeodus parvus erectus hindeodus parvus parvus hindeodus postparvus hindeodus praeparvus hindeodus typicalis isarcicella staeschei and merrillina ultima based on a detailed study of the permian triassic interval at the dawen section the first occurrence fo of h parvus parvus in the lower daye formation at about 7 45 m above the contact surface between the upper permian skeletal packstone and a calcimicrobial framestone unit is correlated with the permian triassic boundary the occurrence of h eurypyge h praeparvus and m ultima immediately below and h postparvus above the interval supports this interpretation a morphometric analysis of 31 hindeodus specimens helped distinguish h parvus erectus from h parvus parvus and h postparvus correlation with the meishan section ptb gssp using both conodont biostratigraphy and carbon isotopes indicates that the major extinction at the two localities is simultaneous and coincides with the top of the skeletal packstone at dawen the contact between the skeletal packstone and the calcimicrobialite is very irregular and has previously been interpreted as a dissolution surface and correlated with a surface in the lower part of bed 27 at meishan our results confirm this interpretation and reveal that the dissolution event postdated the extinction

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

rapid expansion of oceanic anoxia immediately before the end permian mass extinction tive of an expansion of oceanic anoxia and higher th u ratios from 0 06 to 0 42 indicative of drawdown of u concentrations in seawater using a mass balance model we estimate that this isotopic shift represents a sixfold increase in the flux of u to anoxic facies implying a corresponding increase in the extent of oceanic anoxia the intensification of oceanic anoxia coincided with or slightly preceded the eh and persisted for an interval of at least 40 000 to 50 000 y following the eh these findings challenge previous hypotheses of an extended period of whole ocean anoxia prior to the end permian extinction

three dimensional structural model of the cantarell and sihil structures campeche bay mexico the cantarell and sihil fields are located in a complex system of compressive structures in the offshore campeche bay province in mexico the geometry of the cantarell sihil structure varies along trend from a simple fault related structure in the south to a duplex consisting of the cantarell and sihil structures in the central part to a more complex system consisting of compressive blocks separated by tertiary normal faults in the north the cantarell sihil structures formed during three main episodes of deformation 1 jurassic to early cretaceous extension resulting in the formation of normal faults that displace tithonian kimmeridgian and lower cretaceous units 2 miocene compression during which the cantarell sihil thrust system was formed and 3 pliocene to holocene extension during which several of the preexisting jurassic normal faults were reactivated the cantarell field produces out of three separate fault bounded allochthonous blocks the akal nohoch and kutz blocks the main field is located in the akal structure secondary fields in the allochthonous block include kutz which formed on the crest of a downthrown fault block and nohoch which formed above a west vergent backthrust the recently discovered sihil field is located in a subthrust compressive structure and consists of two structural lobes formed above the sub sihil fault the chac structure is formed at the updip edge of a tilted fault block in the autochthonous block the detailed three dimensional structural model is being used for future production of the remaining reserves in the cantarell field as well as for the delineation of the sihil field

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

constituents of some widely distributed soils in denmark abstract the results presented in this paper follow from investigations of the constituents of some danish soils during the last 5 6 years the data are considered in the context of the geomorphological and climatic conditions in the country the results indicate that the dominant soil group on the saale glacial deposits 100 000 years consists of haplorthods whereas the main group on glacifluvial deposits related to the terminal moraines of the weichselian glacial stage 16 000 to 20 000 years seems to be haplohumods hapludults are commonly found on the more coarse textured parts of these terminal moraines hapludalfs are dominant on the moraines and agrudalfs are commonly found on till plains of the later phases of the weichselian glacial stage inceptisols and entisols are also commonly present but due to differences in origin and age their constituents also differ substantially those soils are not considered in details only average figures from the widely distributed soil groups are included in this paper the formation of haplorthods and haplohumods and to a certain extent of hapludults has resulted in relative accumulations of quartz in the upper horizons disappearance of chlorite reductions in kaolinite and vermiculite formation of poorly crystalline 2 1 layer silicate clay minerals in the a and e horizons and accumulations of oxy hydroxides of fe and al in the bh and bs horizons in both hapludalfs and agrudalfs transformation of illite into vermiculite and smectite seems to have occurred in the upper horizons furthermore some smectite has accumulated in the bt horizons of soils of these two groups the contents of quartz feldspars kaolinite and oxy hydroxides of fe and al stay almost constant with depth in soils of the two groups

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

diagenetic effects on uranium isotope fractionation in carbonate sediments from the bahamas abstract uranium isotope variations 238u recorded in sedimentary carbonate rocks are a promising new proxy for the extent of oceanic anoxia through geological time however the effects of diagenetic alteration on the u isotopic composition in carbonate sediments which are crucial to understand the accurate reconstruction of marine 238u are currently poorly constrained here we examine the effects of the aragonite to calcite transition in the pleistocene key largo limestone of south florida and assess the effects of vadose meteoric phreatic meteoric and phreatic marine diagenesis on u isotope fractionation in carbonate sediments from the bahamas transect including the well studied clino unda and odp site 1006 drill cores our results suggest that early diagenetic processes in bahamas carbonate sediments fractionate u isotopes by an average of 0 27 0 14 1 sd heavier than contemporaneous seawater downcore variations of 238u in slope and basin sediments display little if any correlation with u concentration and common geochemical indicators of diagenesis 13c 18o mn sr mg ca sr ca enrichments of redox sensitive elements or rare earth elements anomalies we propose two possible mechanisms to interpret the positive change in the 238u during carbonate diagenesis authigenic enrichment of isotopically positive u iv in carbonates and preferential incorporation of isotopically positive aqueous u vi species into carbonates these processes likely operate during early syndepositional diagenesis on the banktop further diagenesis during deeper burial is limited by the low solubility of u iv under reducing pore water conditions the early diagenetic behavior of u isotopes in bahamas carbonate sediments is likely broadly representative of carbonate diagenesis in the geological past we suggest that the mean diagenetic offset determined in this study be applied when reconstructing seawater 238u from ancient carbonates furthermore early diagenesis induces significant statistical variability in sediment 238u values pointing to the need for large high resolution data sets in order to average out stochastic variations in individual bulk sediment samples

uranium isotope compositions of biogenic carbonates implications for u uptake in shells and the application of the paleo ocean oxygenation proxy abstract the application of u isotopes in carbonates as a paleo ocean oxygenation proxy is based on the critical assumption that the carbonaceous shell building organisms incorporate u into their shells without fractionating the u isotopic composition of the ambient seawater recent studies claim a small but resolvable isotopic offset during abiotic and biogenic aragonite precipitation whereas no isotope fractionation has been recorded during calcite precipitation although aragonite is meta stable and not preserved over geological timescales 1 myr and u precipitates during diagenesis the u isotope composition of biogenic aragonite is important because aragonite precipitation is an important u flux to carbonate sediments in contrast low magnesium calcite is preserved over geological timescales and may provide a reliable fingerprint of ancient ocean chemistry therefore a more general study is needed that compares u isotope compositions of primary marine biogenic carbonate precipitates we report the u isotope compositions of 32 modern samples from geographically distinct localities in the atlantic oceans including corals scleractinia octocorallia brachiopods articulata molluscs tellina listeri codahia obicularis and barnacles as well as one fossil mollusc these samples reflect variable primary minerals water temperatures water depths ph values of ambient water and u concentrations several seawater samples have also been measured to compare our methods with those of previously published studies the analyzed modern corals and brachiopods display u isotopic compositions that are indistinguishable from modern seawater this suggests that these carbonates have the potential to faithfully record the u isotopic composition of the surrounding seawater in which they form the analyzed brachiopods are of particular interest as they are composed of the calcium carbonate polymorph low mg calcite lmc that is stable over geological timescales while this study shows for the first time that lmc phases are robust targets in ancient samples their low u abundance presents analytical challenges for precise u isotope analyses we also show that two barnacle shells collected with ambient seawater have u isotopic compositions that are both lighter and heavier than the ambient seawater the mechanism to explain this offset is not determined but it demonstrates that at least barnacle shells are not representative of the seawater in which they last lived two of three partially fossilized mollusc shells also show resolvable offsets from seawater likely indicating secondary processes that are known to shift or fractionate u isotopes collectively our new data indicate that 1 aragonite delivers u with seawater composition to carbonate sediments and 2 lmc shells of brachiopods that are stable over geological timeframes may be more suitable for reconstructing the u isotope composition of ancient oceans

uranium depletion across the permian triassic boundary in middle east carbonates signature of oceanic anoxia we present a geochemical profile through a 445 m 1459 9 ft section of shallow water carbonate platform strata in the upper part of the khuff formation the permian triassic boundary ptb is recognized in this section based on the immediately preceding negative shift in bulk rock carbonate carbon isotope composition equivalent to the end permian extinction horizon combined with biostratigraphic control from nearby wells these strata show an abrupt and long lasting decrease in bulk rock uranium u content coincident with the carbon isotope shift because of low siliciclastic content and the consequently low potassium and thorium of these carbonates the decrease in u is clearly reflected in the total gamma ray gr profile recorded by wire line logging published log curves show similar distinctive gr profiles throughout a large area of the middle east indicating that u depletion across the ptb is a regional characteristic this feature cannot be explained as diagenetic and is not related to the organic matter content of the host sediments but it is suggested to reflect the global depletion of u in earliest triassic seawater caused by the abrupt onset of deep ocean anoxia and the resulting increase in u precipitation in oxygen poor sediments this explanation carries the implication that similar u depletion should be characteristic of lowermost triassic carbonates from shallow water oxygenated settings worldwide analogous signatures of u depletion should also have developed in shallow water carbonates deposited contemporaneously with episodes of deep ocean anoxia during other periods of geological time these predictions can be tested by high accuracy u profiling of other well characterized carbonate successions potentially yielding a new approach for tracking the degree of oceanic circulation throughout earth s history

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

paleoclimate proxies for cyclostratigraphy comparative analysis using a lower triassic marine section in south china abstract multiple proxies for paleoclimatic and paleoenvironmental change within sedimentary sequences have been developed but understanding their relationships and their relative strengths or weaknesses are required to access a wealth of untapped paleoclimate information we propose two main criteria for multiple proxy datasets to estimate their individual signal to noise levels and to decipher the relationship between multiple proxies first for proxies affected by similar processes then their time dependent changes should be similar second a paleoclimate proxy that is more sensitive to an external forcing such as astronomical forcing is more useful than those that do not have such a response we introduce two methods to evaluate these criteria 1 hierarchical cluster analysis hca probes the relationships among multiple proxies based on similarities of their oscillation patterns and 2 power decomposition analysis pda tests proxy sensitivity to external climate forcing we evaluate 16 high resolution paleoclimate proxies in detail for their applications in paleoclimatology from the marine lower triassic daye formation at the daxiakou section in the three gorges region of south china which has carbonate claystone cycles deposited on an outer ramp the proxies are spectral gamma ray gamma ray intensity potassium uranium thorium thorium uranium and thorium potassium rock color lightness l redness a and yellowness b magnetic susceptibility measured in both laboratory and outcrop anhysteretic remanent magnetization arm lithologic rank simplified lithologic rank and non carbonate fraction carbonate thickness and couplet thickness hierarchical cluster analysis hca gathers these proxies into groups likely affected by the same process the arm and thorium uranium proxies seem to reflect the hinterland weathering process during the early triassic gamma ray potassium uranium thorium magnetic susceptibility and non carbonate fraction proxies refer to terrestrial input the l a and lithologic rank proxies indicate the productivity the redox state and the relative sea level respectively at this section this case study contributes to the understanding of the sensitivity of these types of proxies within marine strata for deep time paleoclimate and astronomical tuned time scales

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

zinc isotope evidence for intensive magmatism immediately before the end permian mass extinction the end permian extinction is typically ascribed to massive volcanic eruptions but direct geochemical evidence linking the two independent events is generally lacking zinc is an important micronutrient of marine phytoplanktons and zn isotope 66zn ratios of seawater are markedly higher than those of volcanic rocks and riverine waters we conducted high resolution zn concentration and zn isotope analyses on carbonate rocks across the permian triassic boundary ptb in the meishan section of south china an abrupt increase of zn concentration and a concomitant 0 5 decrease in 66zn occur 35 k y before the mass extinction and carbon isotope 13c minima mass balance calculation demonstrates that a 0 5 negative shift in 66zn within thousands of years requires rapid and massive input of isotopically light zn from volcanic ashes hydrothermal inputs and or extremely fast weathering of large igneous provinces a positive 66zn shift of as much as 1 0 following the mass extinction demonstrates that primary productivity recovered and reached a maximum in fewer than 360 k y our finding provides insights into the marine zn cycling across the ptb and clarifies the temporal relationship and duration of events including intensive volcanism carbon isotope excursion mass extinction and widespread ocean anoxia

geochemical and multi isotopic 87sr 86sr 143nd 144nd 238u 235u perspectives of sediment sources depositional conditions and diagenesis of the marcellus shale appalachian basin usa abstract we investigate sediment sources depositional conditions and diagenetic processes affecting the middle devonian marcellus shale in the appalachian basin eastern usa a major target of natural gas exploration multiple proxies including trace metal contents rare earth elements ree the sm nd and rb sr isotope systems and u isotopes were applied to whole rock digestions and sequentially extracted fractions of the marcellus shale and adjacent units from two locations in the appalachian basin the narrow range of end values from 7 8 to 6 4 at 390 ma is consistent with derivation of the clastic sedimentary component of the marcellus shale from a well mixed source of fluvial and eolian material of the grenville orogenic belt and indicate minimal post depositional alteration of the sm nd system while silicate minerals host 80 of the ree in the shale data from sequentially extracted fractions reflect post depositional modifications at the mineralogical scale which is not observed in whole rock ree patterns limestone units thought to have formed under open ocean oxic conditions have 238u values and ree patterns consistent with modern seawater the 238u values in whole rock shale and authigenic phases are greater than those of modern seawater and the upper crust the 238u values of reduced phases the oxidizable fraction consisting of organics and sulfide minerals are 0 6 greater than that of modern seawater bulk shale and carbonate cement extracted from the shale have similar 238u values and are greater than 238u values of adjacent limestone units we suggest these trends are due to the accumulation of chemically and more likely biologically reduced u from anoxic to euxinic bottom water as well as the influence of diagenetic reactions between pore fluids and surrounding sediment and organic matter during diagenesis and catagenesis

global ocean redox variation during the middle late permian through early triassic based on uranium isotope and th u trends of marine carbonates uranium isotopes 238u 235u in carbonates a proxy for global ocean redox conditions owing to their redox sensitivity and long residence time in seawater exhibit substantial variability in the daxiakou section of south china from the upper middle permian through the mid lower triassic 9 m y middle and late permian ocean redox conditions were similar to that of the modern ocean and were characterized by improving oxygenation in the 2 m y prior to the latest permian mass extinction lpme countering earlier interpretations of sustained or gradually expanding anoxia during this interval the lpme coincided with an abrupt negative shift of 0 5 in 238u that signifies a rapid expansion of oceanic anoxia intensely anoxic conditions persisted for at least 700 k y griesbachian lessening somewhat during the dienerian th u concentration ratios vary inversely with 238u during the early triassic with higher ratios reflecting reduced u concentrations in global seawater as a consequence of large scale removal to anoxic facies modeling suggests that 70 100 of marine u was removed to anoxic sinks during the early triassic resulting in seawater u concentrations of 5 that of the modern ocean rapid intensification of anoxia concurrent with the lpme implies that ocean redox changes played an important role in the largest mass extinction event in earth history

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

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

mo ni and organic carbon isotope signatures of the mid late mesoproterozoic oxygenation abstract this study performed a redox sensitive trace element rste and organic carbon isotope investigation on the shallow section of 1 2 ga bijaigarh shale kaimur group vindhyan supergroup the results demonstrate that unlike the coeval deeper section in which mo and ni concentrations are several folds higher compared to the upper continental crust ucc the shallow section contains mo and ni equivalent to the upper continental crust ucc this spatially heterogeneous burial of mo and ni is very similar to the modern stratified basins i e black sea and cariaco basin where ni and mo composition of the sediments underlying a shallow oxic water column is comparable to the ucc however the deeper sediments underlying the anoxic euxinic contains several folds higher mo and ni compared to the ucc bulk precipitation of mo in a hydrosphere is mainly controlled by sulphide present in the anoxic euxinic layers of the water column on the other hand ni precipitation is generally controlled by oxygenic primary productivity though the shallow section of the bijaigarh shale is depleted in ni a significant correlation between ni and toc is still relevant and indicates an oxygen rich surface water layer for the respective palaeohydrosphere furthermore 13c org values between 32 0 and 30 4 from the shallow section suggests that the organic carbon exported into the sediments during the bijaigarh shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers

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

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

complete biotic and sedimentary records of the permian triassic transition from meishan section south china ecologically assessing mass extinction and its aftermath abstract the meishan section south china is the global stratotype section and point gssp for the permian triassic boundary ptb and is also well known for the best record demonstrating the permian triassic mass extinction ptme all over the world this section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest phanerozoic biocrisis of life on earth many important scenarios interpreting the great dying have been proposed on the basis of data from meishan nevertheless debates on biotic extinction patterns and possible killers still continue this paper reviews all fossil and sedimentary records from the permo triassic p tr transition based on previously published data and our newly obtained data from meishan and assesses ecologically the ptme and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis eight updated conodont zones clarkina yini clarkina meishanensis hindeodus changxingensis clarkina taylorae hindeodus parvus isarcicella staeschei isarcicella isarcica and clarkina planata zones are proposed for the ptb beds at meishan major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between bed 24e 5 and bed 24e 6 suggesting an extinction horizon in a thin stratigraphic interval the irregular surface in the middle of bed 27 is re interpreted as a firmground of glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface both fossil fragment contents and ichnodiversity underwent dramatic declines in beds 25 26a coinciding with metazoan mass extinction fossil fragment content ichnodiversity and all ichnofabric proxies including burrow size tiering level bioturbation level indicate that the p tr ecologic crisis comprises two discrete stages coinciding with the first and second phases of the ptme in meishan ecologic crisis lagged behind biodiversity decline during the ptme pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest changhsingian became euxinic in beds 25 26a turned dysoxic in bed 27 then varied from euxinic to anoxic through most of the griesbachian the 9 c increase in seawater surface temperature from bed 24e to bed 27 at meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in beds 25 26a but had little effect on all ecologic proxies both metazoans and infauna seem not to have been affected by the pre extinction anoxic euxinic condition the anoxic event associated with the ptme may have occurred in a much shorter period than previously thought and is only recorded in beds 25 26a at meishan fossil fragment contents ichnofaunas ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in bed 27 the early griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower yinkeng formation in which the ichnofauna is characterized by small simple horizontal burrows of planolites and metazoan faunas are characterized by low diversity high abundance opportunist dominated communities the rapid increase of 9 c in sea surface temperature and a short anoxia or acidification coincided with the first pulse biocrisis while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second pulse ptme marine ecosystems started to recover coupled with environmental amelioration in the late griesbachian

the effects of diagenesis on geochemical paleoredox proxies in sedimentary carbonates abstract metal and metal isotope records in carbonates have the potential to provide novel insights into ancient ocean atmosphere redox conditions paleoenvironmental conditions and biogeochemical cycling however trace element geochemical signatures in carbonates can record either diagenetic or depositional signatures here we explore the variability in uranium isotopes trace metal and rare earth element yttrium rey concentrations in carbonate successions that have undergone several common types of diagenetic alteration case studies include the cryogenian balcanoona reef australia marine dolomitization neomorphism the devonian canning basin reefs australia burial dolomitization karstification the paleozoic of the great basin usa high temperature and regional burial dolomitization and the carboniferous waulsortian limestone ireland pb zn mineralization in all of the examined cases there are significant heavier and or lighter shifts in u isotope values between the most petrographically pristine marine depositional components and altered or late stage diagenetic phases although we also found that rey patterns can be overprinted during diagenesis normalized rey profiles appear to be commonly retained through diagenetic recrystallization consistent with previous studies the direction and magnitude of the change in metal isotope systems during diagenesis cannot be generalized between case studies consistent with carbonate alteration being controlled by a wide range of factors including the composition and source of the alteration fluids in this light we build on framework developed from traditional isotope systems and support the view that future work on metal and metal isotope compositions of carbonates should include integrated sedimentological and petrographic analysis petrographic work not only represents a screening procedure for sedimentary geochemical work but can also significantly enhance the paleo environmental interpretation of metal isotope data

ek balam field a structure related to multiple stages of salt tectonics and extension the ek balam field is a major oil and gas field in the offshore campeche bay mexico the structure was formed as a result of multiple episodes of salt tectonics and associated extension salt movement into the core of the structure initiated in the jurassic early cretaceous and continued until the miocene the most prominent normal faults are of jurassic early cretaceous age and detach in the jurassic salt these faults mostly dip to the west although in the vicinity of the ek balam structure some east dipping faults are also present some of these faults were subsequently reactivated in the late cretaceous and tertiary separating the ek and balam structures is a set of upper cretaceous faults which drop the eastern part of the structure down tertiary faults are related to continued uplift of the salt and are symmetrically distributed with respect to the central uplift seismic time maps three dimensional depth models of the top of the cretaceous breccia and the kimmeridgian and balanced structural cross sections provide accurate details of the structural geometry and fault patterns in the ek balam structure at the level of the cretaceous breccia many of the faults have small throws and are discontinuous along trend the top of the kimmeridgian however is cut by faults of different ages many of which have significant throw and extend for longer distances the detailed structural geometry and fault patterns will be useful for identifying compartments within the ek balam field and for identifying secondary traps within kimmeridgian and oxfordian reservoirs