monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

provenance of neoproterozoic and early paleozoic siliciclastic rocks of the tepla barrandian unit bohemian massif evidence from u pb detrital zircon ages abstract new la icp ms u pb detrital zircon ages from ediacaran and paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the tepla barrandian unit tbu in the centre of the bohemian massif central europe czech republic the samples taken span the period from 635 ma to 385 ma and permit recognition of provenance changes that reflect changes in geotectonic regime detrital zircon age spectra of two ediacaran one lower cambrian and three upper ordovician samples resemble the ages known from the nw african proportion of gondwana particularly the trans saharan belt while three rocks from higher lower cambrian to lowermost ordovician strata contain detritus that may have been derived exclusively from local sources the age spectrum of the devonian rock is a combination of the nw gondwanan and local features these new findings in combination with a wide range of published data are in agreement with a neoproterozoic subduction related setting at the margin of gondwana followed by a cambrian early ordovician rifting stage and an ordovician passive margin setting furthermore the data are in favour of a position of the tbu at the gondwanan margin throughout pre variscan times

evidence for denitrification regulated by pyrite oxidation in a heterogeneous porous groundwater system abstract denitrification is an important natural attenuation process that has been observed in many fissured and porous aquifers however an important factor limiting denitrification in aquatic systems is the microbial availability of electron donors pyrite as the most abundant sulfide mineral in nature represents one of the potential electron sources for denitrifiers to reduce nitrate but the reaction mechanisms coupling denitrification processes to pyrite oxidation are still questionable we utilized hydrochemical data and stable isotopes of nitrate and sulfate in groundwater isotope ratios of sulfur compounds in aquifer sediments and tritium based groundwater dating for assessing denitrification processes in a pyrite bearing porous groundwater system the oxic part of the aquifer with mean water transit times of approximately 60 years was characterized by nitrate concentrations of around 15 mg l and 15 n values were similar to those typical for nitrification in contrast in the anoxic part with mean water transit times of up to 100 years low nitrate concentrations accompanied by elevated 15 n values were observed furthermore isotope data of groundwater sulfate and sulfur compounds in the aquifer sediment suggest that pyrite oxidation is the dominant source of sulfate in the aquifer the trend of increasing 15 n values and decreasing nitrate concentrations in concert with depleted 34 s values of groundwater sulfate similar to 34 s values of pyrite fes 2 suggests that denitrification is coupled to pyrite oxidation particularly when water mean transit time is elevated

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

early jurassic carbon isotope excursion in the qiangtang basin tibet the eastern tethys implications for the toarcian oceanic anoxic event abstract the early jurassic was characterized by a global disturbance of the carbon cycle known as the toarcian oceanic anoxic event t oae this event is recorded by a large negative carbon isotope excursion cie in marine carbonates and marine organic matter as well as fossil wood here we present new high resolution carbonate 13 c carb and organic 13 c org carbon isotope records and total organic content from the bilong co section in the qiangtang basin the eastern tethys this section is high in organic carbon and black shale facies are also identified the bilong co section shows heavy 13 c org values compared to other reported marine organic carbon isotope values for the t oae this is explained by variable mixing of terrestrial and marine organic matter compared to european sections the magnitude of the negative cie in the bilong co section is slightly different which could be explained by different local paleoenvironmental conditions and strata missing although these the carbon isotope profile from the bilong co area displays a similar trend to those in contemporaneous strata in the western tethyan and boreal realms of nw europe which is characterized by a distinct negative excursion in the early toarcian our new data from the bilong co section in n tibet provide the first high resolution record of the early toarcian oceanic anoxic event in the eastern tethys

early jurassic carbon and oxygen isotope records and seawater temperature variations insights from marine carbonate and belemnite rostra pieniny klippen belt carpathians abstract new carbon and oxygen isotope records and discussion of the main variations in seawater temperature through the sinemurian aalenian of the pieniny klippen basin northern tethys ocean are presented herein comparison of the recorded changes in stable isotope compositions of bulk carbonate and belemnite rostra from an open marine environment with previously documented predominantly restricted epicontinental data enables determination of major climatic events that were most likely of worldwide extent a slight positive 13c shift is recorded in the lowermost upper pliensbachian a significant positive excursion in carbonate carbon isotope values is documented in the lower toarcian serpentinum zone furthermore the 13c values display a falling trend in the lower upper toarcian and relatively constant values in the aalenian temperatures inferred from the 18o values of well preserved belemnite rostra suggest rather cool seawater conditions 10 13 c in the pieniny klippen basin during the late sinemurian warming by 4 c in the early pliensbachian and then cooling by 8 c in the late pliensbachian the seawater temperature rose once more in the early toarcian and began to fall again during the middle toarcian in the middle late aalenian seawater temperatures oscillated between 10 and 13 c

warm and wet conditions in the arctic region during eocene thermal maximum 2 several episodes of abrupt and transient warming each lasting between 50 000 and 200 000 years punctuated the long term warming during the late palaeocene and early eocene 58 to 51 myr ago epochs1 2 these hyperthermal events such as the eocene thermal maximum 2 emt2 that took place about 53 5 myr ago2 are associated with rapid increases in atmospheric co2 content however the impacts of most events are documented only locally86 here we show on the basis of estimates from the tex 86 proxy that sea surface temperatures rose by 3 5 c in the arctic ocean during the emt2 dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters which resulted in euxinia in the photic zone the presence of palm pollen implies5 that coldest month mean temperatures over the arctic land masses were no less than 8 c in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6 in light of our reconstructed temperature and hydrologic trends we conclude that the temperature and hydrographic responses to abruptly increased atmospheric co2 concentrations were similar for the etm2 and the better described palaeocene eocene thermal maximum7 8 55 5 myr ago 2009 macmillan publishers limited all rights reserved

sediment accumulation rate in the lakes of kumaun himalaya india using 210 pb and 226 ra the rate of sedimentation and the source of sediments in the lake basins of nainital region kumaun himalaya have been estimated employing210pb and210ra methods this has yielded a rate of sedimentation of 11 5 4 70 3 72 and 3 00 mm yr in nainital bhimtal naukuchiyatal and sattal lakes respectively the higher rate of sedimentation in nainital lake compared to other lakes is related to faster erosion in the catchment aided by greater anthropogenic activity while the slowest rate in sattal lake is due to less erosion and more input of soil derived material involving a slow rate of accumulation

toarcian carbon isotope shifts and nutrient changes from the northern margin of gondwana high atlas morocco jurassic palaeoenvironmental implications the early toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes these coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial and culminate in the so called toarcian oceanic anoxic event it is believed that the environmental crisis was triggered by the activity of the karoo ferrar large igneous province in order to further document the early toarcian palaeoenvironmental perturbations carbon isotope total organic matter calcareous nannofossils and phosphorus content of the amellago section in the high atlas rift basin of morocco were investigated this section is extremely expanded compared to the well studied european sections its position along the northern margin of the gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western tethyan realm the carbon isotope curve shows two negative excursions of equal thickness and amplitude at the pliensbachian toarcian boundary and at the transition from the polymorphum to the levisoni zone this confirms the supra regional nature of these shifts and highlights the possible condensation of the first boundary shift in european sections phosphorus content is used to trace palaeo nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels confirming that these episodes are related to enhanced continental weathering probably due to elevated greenhouse gases in the atmosphere in the high atlas basin the increase in nutrient levels at the pliensbachian toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the saharan carbonate platform a middle toarcian event centered on the boundary between the bifrons and gradata zones characterized by a positive carbon isotope excursion and nutrient level rise is documented in the amellago section

dynamics of a stepped carbon isotope excursion ultra high resolution study of early toarcian environmental change abstract in the toarcian early jurassic 183 myr ago the ocean atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 myr known as the toarcian oceanic anoxic event t oae this event was accompanied by a 6 negative carbon isotope excursion cie caused by massive injection of isotopically light carbon into the ocean atmosphere system possibly from destabilisation of gas hydrates this study reveals the pacing and sequence of events leading up to the cie and to widespread deposition of organic rich sediments the very high resolution isotopic record from exceptionally well preserved carbonate and organic matter from the paris basin enables recognition of increased co 2 levels 130 kyr in advance of the major negative cie an accelerated increase in the p co 2 is registered 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the paris basin undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface dwelling calcifiers these environmental perturbations representing precursor phases of co 2 injection predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to karoo ferrar magmatism this negative shift was registered slightly earlier in terrestrial carbon than marine carbonate subsequent global warming is credited with liberating isotopically light carbon and ultimately fostered anoxia in the paris basin the response of these cumulative inputs of carbon to the earth system isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative cie suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation 45 kyr after the first step of the cie this re establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon

assessment of nutrients and heavy metals in the surface sediments of the artificially lake water reservoir karla thessaly greece in this research the sediment quality of the recently reconstructed lake karla central greece was evaluated by monitoring the nutrient loadings and heavy metal concentrations in 16 sites during the initial period of the lake s rehabilitation the results indicated that lake sediments exhibited a high nutrient status as manifested by the high loadings of organic carbon oc total nitrogen tn and available phosphorus ap comparison of metal ni cr co zn cu and pb levels with sediment quality guidelines showed that ni and cr were found in concentrations well above the pel probable effect level values no correlations were found between the nutrients and the measured heavy metals multivariate analysis results implied that ni cr co cu and zn were controlled by natural geological sources whereas pb might have an anthropogenic origin the bioavailability ratios of metals followed a decreasing order of pb cu co zn ni cr based on results obtained by a single 0 5 m hcl leach total and bioavailable concentrations of metals demonstrated significant seasonal variations but trends could not be generalized for all the elements on the contrary the nutrients did not show significant seasonal differences indicating that the lake sediments record the history of contamination with regard to nutrient status

carbon isotope records of the early jurassic toarcian oceanic anoxic event from the valdorbia umbria marche apennines and monte mangart julian alps sections palaeoceanographic and stratigraphic implications the toarcian oceanic anoxic event ca 183 ma coincides with a global perturbation marked by enhanced organic carbon burial and a general decrease in calcium carbonate production probably triggered by changes in the composition of marine plankton and elevated carbon dioxide levels in the atmosphere this study is based on high resolution sampling of two stratigraphic successions located in valdorbia umbria marche apennines and monte mangart julian alps italy which represent expressions of the toarcian oceanic anoxic event in deep water pelagic sediments these successions are characterized by the occurrence of black shales showing relatively low total organic carbon concentrations compared with coeval strata in northern europe generally 2 and low hydrogen indices on this basis they are similar to other toarcian black shales described from the tethyan region the positive and negative carbon isotope records from the two localities permit a high resolution correlation such that ammonite biostratigraphy information from valdorbia can be transferred to those parts of the monte mangart section that lack these fossils spectral analyses ofd 13 corg values and of caco3 percentages from the sedimentary records of both the valdorbia and monte mangart sections reveal a strong cyclic pattern best interpreted as an eccentricity signal which hence implies a duration of ca 500 kyr for the negative carbon isotope excursion based on the carbon isotope curves obtained the high resolution correlation between the italian successions and a section in yorkshire northern europe confirms the supposition that the apparent mismatch between the dating of the toarcian oceanic anoxic event in the boreal and tethyan realms is an artefact of biostratigraphy

organic matter variations and links to climate across the early toarcian oceanic anoxic event t oae in toyora area southwest japan abstract marked climate warming during the early toarcian oceanic anoxic event t oae 182 ma has been shown to have had a significant effect on the global carbon cycle and biosphere there is also emerging evidence that a primary short term consequence of this warming was a marked increase in hydrological cycling in this study we have investigated local environmental responses to t oae climate change by conducting a palynofacies analysis through an expanded panthalassic margin record of the event exposed in southwestern japan nishinakayama formation toyora area palynomorphs are poorly preserved and rare in the studied interval a pronounced increase in terrestrial phytoclast abundance coeval with the peak of the t oae can be linked to increased fluvial supply driven by enhanced hydrological cycling that occurred in response to early toarcian warming broader scale trends in phytoclast abundance through the studied interval may be linked to longer term sea level changes nitrogen isotopes commonly used to elucidate basin redox changes are found to correlate with changes in the relative abundance of phytoclasts in contrast carbon isotope data are probably not significantly influenced by changes in organic matter type through the succession however thermal maturity indicators demonstrate that the succession is overmature and this likely suppresses the magnitude of the well known t oae carbon isotope excursion in this succession

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

controls on weathering and provenance in the amazonian foreland basin insights from major and trace element geochemistry of neogene amazonian sediments abstract miocene and pliocene deposits from the ecuadorian bolivian and peruvian amazonian foreland basin north and south amazonian foreland basin nafb and safb were analyzed for major and trace element geochemistry 97 and 104 samples respectively neogene deposits are well homogenized and have an overall paas like composition they are mainly derived from a granodioritic crust in the nafb chemical weathering increases from miocene to pliocene to cia values 100 physical sorting seems to have played a minor role in the chemical composition of these sediments chemical ratios such as cr th and th u and eu anomaly vary within each formation and from one formation to another in the safb sediments have a paas like composition with recycling increasing toward the distal part of the foreland basin in the nafb the neogene formations have various provenances basic andesitic sediments originated from the ecuadorian andes these sediments were trapped in the subsiding ecuadorian foredeep during the miocene and reached the iquitos forebulge to join the paleo amazon near iquitos amazon formation during the pliocene other miocene formations have paas like affinities but are enriched in zr and hf relative to the paas suggesting that they are derived from a recycled and differentiated upper continental crust uplift of the iquitos forebulge may have been responsible for dividing drainage networks originating from the andes and the craton the quaternary floodplain deposits of the amazon river resemble paas with depletion in trace elements and enrichment in zr and hf which indicate that they are derived from a recycled differentiated upper continental crust overall the transition from tidal sedimentation in the miocene to fluvial sedimentation in the late miocene pliocene related to a change with foreland basin dynamics have caused increasing silicate weathering that could have had consequences on climate and global carbon cycle during the neogene

continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle toarcian in the paris basin abstract lower toarcian strata lower jurassic have been extensively studied with a view to understanding the oceanographic climatic and biological processes that drove the earth s system into an oceanic anoxic event oae for this time period the evolution of the european marine seaways is now relatively well constrained owing to multiple geochemical studies but investigations regarding climatic trends in the continental realm remain sparse in the present study we test the clay mineralogy as a continental climate sensitive proxy in the well documented sancerre core southern paris basin we compare variations in the kaolinite content with p co 2 fluctuations derived from paired carbon isotopes 13 c 13 c carb 13 c org taking advantage of the detailed chemostratigraphic palaeoenvironmental and sequence stratigraphy frameworks established for this core material the results indicate a substantial decrease in kaolinite abundance at the end of the pliensbachian which is compatible with a long term diminution in continental weathering and an inferred temperature decrease the early toarcian prior to the carbon cycle perturbation and deposition of black shale facies remained relatively cold with minima in both the proportion of kaolinite and reconstructed p co 2 the mineralogical and geochemical responses across the prominent negative carbon isotope excursion cie itself are not univocal the first of four steps that compose the negative limb of the cie at sancerre is associated with decreased kaolinite and p co 2 and increased carbonate oxygen isotope ratios taken together these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition conversely the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in yorkshire providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the cie relaxation in the intensity of continental weathering as suggested by resumed low kaolinite abundance is seen immediately after the cessation of co 2 input after the fourth step of the cie the interval spanning the upper portion of the early toarcian and the middle toarcian records a subsequent long term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment continued greenhouse conditions even after the recovery from the carbon isotope perturbation and regional black shale deposition are likely related to sustained co 2 emission by karoo ferrar volcanism through the considered interval

water and sediment geochemistry of major kumaun himalayan lakes india four major himalayan lakes in kumaun region in india namely nainital bhimtal sattal and naukuchiatal have been studied to understand water and sediment geochemistry the lakes are characterised by varying degrees of natural and human influences the nainital is intensively used and is a major tourist destination whereas the other three lakes have attracted much attention lately the lakes have a tectonic origin and are characterised by dolomites limestones shales and silicate rocks the water chemistry is dominated by ca mg and hco3 an indication of a carbonate lithology source for the water composition about 55 80 of na and only 30 40 of ca in the lakes are derived from silicate lithology the nainital lake is also characterised by a high chemical index of alteration which is reflected in its high carbonate and the clay mineral content of the sediments model calculations show that 33 and 67 of nitrate in sattal lake is contributed by agriculture and cultural effects respectively the 87sr 86sr ratios in the lakes are very high 0 72 with samples from sattal lake being extremely radiogenic 0 82 similar to many himalayan rivers the 1 sr 87sr 86sr in sediments show two major sources for sr silicates and carbonates the contributions of sr from carbonate and silicate lithology is estimated to be 25 and 60 respectively in bhimtal lake

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

palaeoceanography methane release in the early jurassic period reply wignall 1 suggest that the abrupt negative 13corg shifts that we recognize in our data set2 could be localized features caused by recycling of isotopically light marine carbon this overlooks two important lines of evidence2 that the early toarcian negative 13c excursion is present in several sections around the world3 4 5 and that the excursion is recorded in terrestrial plant material4 these crucial observations together preclude the possibility that the event was restricted to a localized marine environment

late quaternary climate changes in central africa as inferred from terrigenous input to the niger fan time series of terrigenous source elements al k ti zr from core geob4901 8 recovered from the deep sea fan of the niger river record variations in riverine sediment discharge over the past 245 000 yr although the flux rates of all the elements depend on physical erosion which is mainly controlled by the extent of vegetation coverage in central africa element al ratios reflect conditions for chemical weathering in the river basin maximum sediment input to the ocean occurs during cold and arid periods when precipitation intensity and associated freshwater runoff are reduced high carbonate contents during the same periods indicate that the sediment supply has a positive effect on river induced marine productivity in general variations in the terrestrial signals contain a strong precessional component in tune with changes in low latitude solar radiation however the terrestrial signal lags the insolation signal by several thousand years k al ti al and zr al records reveal that african monsoonal precipitation depends on high latitude forcing we attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of african climate to primary orbital configurations which may be caused by a complex interaction of the secondary control parameters such as surface albedo and or thermohaline circulation

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

pliensbachian environmental perturbations and their potential link with volcanic activity swiss and british geochemical records abstract the mechanisms leading to environmental and climate change prior to and anticipating the well studied toarcian oceanic anoxic event are not completely understood specifically the role of the continuing break up of pangea associated palaeogeographic rearrangements and the influence of volcanic activity are less well known therefore we studied the pliensbachian interval in the open marine hemipelagic section of the breggia gorge in southern switzerland to elucidate the potential impact of these major changes on the environment and climate we identified carbon isotope excursions towards lower values in whole rock carbonates dated from the sinemurian pliensbachian boundary davoei margaritatus and spinatum zones and possibly from the pliensbachian toarcian boundary using the whole rock oxygen isotope record and phosphorus content we associated these events with phases of increased runoff possibly related to climate warming we also established the first mercury hg record for the entire pliensbachian and in order to verify its validity we analysed an additional section located along the dorset coast in southern england the presence of hg spikes common in both sections may indicate the influence of episodes of increased volcanic activity the hg spike during the earliest pliensbachian may coincide with a late phase of the central atlantic magmatic province and or increased rifting linked with the opening of the hispanic corridor further significant maxima in hg contents are observed within the davoei and margaritatus zones and both phases may correspond to early volcanic activity of the karoo ferrar large igneous province further analyses are however needed to corroborate this interpretation and evaluate the importance of organic matter scavenging and detrital input in comparison to volcanic activity

pacing of the toarcian oceanic anoxic event early jurassic from astronomical correlation of marine sections abstract the early toarcian oceanic anoxic event oae in the early jurassic period is associated with a major negative carbon isotope excursion cie mass extinction marine transgression and global warming the toarcian oae is thought to have been caused by flood basalt magmatism and may have been a trigger for mass extinction however these proposed causes of the toarcian oae and associated biotic crisis are not adequately resolved by a precise chronology the duration of the toarcian oae has been estimated to be anywhere from 0 12 to 0 9 myr most recently 0 74 to 3 26 myr from u pb dating the cie associated with the toarcian oae has a similar pattern at numerous localities and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals here we estimate a duration of 620 kyr for the main negative cie 860 kyr for the polymorphum zone and 1 58 myr for the levisoni zone based on 405 kyr astronomical eccentricity tuning of the marine section at peniche portugal this 405 kyr tuned series provides a 2 5 myr continuous high resolution chronology through the early toarcian there are 6 or possibly 7 short eccentricity cycles in the main cie interval at peniche to confirm this astronomically based estimate we analyzed three other sections at yorkshire uk dotternhausen germany and valdorbia italy from marine carbon isotopic series these four stratigraphic sections from early jurassic western tethys record the toarcian oae with 6 prominent carbon isotope cycles in the cie that span a 600 100 kyr duration the peniche 405 kyr tuned series indicates that the pre and post cie intervals experienced strong precession eccentricity forced climate change whereas the cie interval is marked by dominant obliquity forcing these dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the early toarcian paleoclimate system that was directly linked to the global carbon cycle

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

ocean oxygen depletion due to decomposition of submarine methane hydrate global warming could decompose submarine methane hydrate and cause methane release into the ocean the released methane causes oxygen depletion via oxidation however its global impact is yet to be quantitatively investigated we have projected the potential impact of oxygen depletion due to methane hydrate decomposition via numerical modeling we find that the global methane hydrate inventory decreases by approximately 70 35 under four times twice the atmospheric co2 concentration and is accompanied by significant global oxygen depletion on a timescale of thousands of years in particular we demonstrate the great expansion of suboxic and hypoxic regions having adverse impact on marine organisms and ocean biogeochemical cycles this is because hydrate decomposition primarily occurs in the pacific ocean where present day seawater has low oxygen concentration besides the decrease in oxygen solubility and reduced ventilation associated with global warming the process described in this study is also important in oxygen depletion

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

geochemical fractionation of heavy metals in chilka lake east coast of india a tropical coastal lagoon chilka lake the largest coastal lagoon of asia is one of the most dynamic ecosystems along the indian coast historically the lagoon has undergone a considerable reduction in surface area due in part to input from natural processes but mostly due to human activities the purpose of this investigation is to document the heavy metals affinity for specific geochemical phases in the recently deposited sediments in the lagoon thirty three samples were collected and analyzed for different geochemical phases of fe mn cu cr ni pb and zn utilizing a sequential extraction scheme in the nonlithogenous fraction the exchangeable fraction was not geochemically significant having 2 of the total metal concentration for all the elements however the carbonate fraction contained the following percentages of the total concentration 1 fe 13 mn 6 cu 4 cr 8 ni 13 pb and 12 zn suggesting the detrital origin of the sediments reducible and organic matter bound fractions were the significant phases in the nonlithogenous fraction containing 9 fe 16 mn 15 cu 16 cr 16 ni 14 pb and 14 zn in the former and 4 fe 3 mn 17 cu 3 cr 14 ni 15 pb and 14 zn in the latter the phenomenon has been attributed to the scavenging affinity of fe mn oxides and affinity for sorption into organic matter of the lagoon sediments the lithogenous residual fraction generally considered as a guide for natural background values was determined to contain 87 fe 67 mn 61 cu 77 cr 61 3 ni 56 pb and 60 zn of the total concentrations

environmental pollution impact on water and sediments of kumaun lakes lesser himalaya india a comparative study a study of the water and sediment chemistry of the nainital bhimtal naukuchiyatal and sattal lakes of kumaun has shown that the water of these lakes are alkaline and that electrical conductivity total dissolved solid and bicarbonate hco 3 are much higher in nainital than in the other three lakes the weathering of limestone lithology and anthropogenic pollution the latter due to the very high density of population in the nainital valley are the primary sources of enhanced parameters the low ph of nainital lake water is due to low photosynthesis and enhanced respiration increasing co2 in the water and the consequent enhancement of ca2 and hco 3 the dissolved oxygen in nainital lake is less compared to other lakes indicating anoxic conditions developing at the mud water interface at depth the po 4 3 content in nainital is higher 124 g l showing an increasing trend over time leading to eutrophic conditions the trace metals cu co zn ni mn and sr are present in greater amounts in the water of nainital lake than in the other three lakes though fe and cr are high in bhimtal and fe in naukuchiyatal the higher abundance is derived from the leaching of fe mg from metavolcanic and metabasic rocks most of the heavy metals cr ni cu mn fe sr and zn significantly enrich the suspended sediments of the lakes compared to the bed sediments which due to their adsorption on finer particles and owing to multiple hydroxide coating and organic content except for fe which is enriched in the bed sediments the high rate of sedimentation 11 5 mm year in nainital compared to bhimtal with 4 70 mm year naukuchiyatal with 3 72 mm year and sattal with 2 99 mm year has resulted in shorter residence time poor sorting of grains and lesser adsorption of heavy metals leading consequently their depletion in the bed sediments of nainital lake

the palynological response to the toarcian oceanic anoxic event early jurassic at peniche lusitanian basin western portugal abstract the uppermost pliensbachian and lower toarcian lower jurassic succession exposed at peniche in the central part of the lusitanian basin western portugal was examined for palynomorphs the 45 samples span the emaciaticeras emaciatum dactylioceras polymorphum and hildaites levisoni ammonite biozones abs and the succession includes the global boundary stratotype section and point gssp for the toarcian stage and the toarcian oceanic anoxic event t oae a low diversity dinoflagellate cyst flora typical of the sub boreal realm was recovered from the emaciaticeras emaciatum and dactylioceras polymorphum abs the dominant element is the cold water species luehndea spinosa which is an index for the pliensbachian to earliest toarcian and is thought to have migrated from the more northerly boreal realm prior to the t oae dinoflagellates thrived in the lusitanian basin except during a brief warm period in the earliest toarcian despite the latter the recovery from this event was relatively rapid and was characterised by a return to relatively cool temperatures the hildaites levisoni ab at peniche represents the t oae and the overlying strata and is characterised by a profound reduction in dinoflagellate cyst relative abundances this dinoflagellate cyst blackout and the associated rise of prasinophytes reflects significant environmental stress such as marine anoxia elevated temperatures and reduced salinity with the former two probably being most important the low proportions of dinoflagellate cysts following the t oae indicates a protracted recovery phase from the bottom and water column anoxia developed throughout the lusitanian basin

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

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

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

high precision geochronology links the ferrar large igneous province with early jurassic ocean anoxia and biotic crisis abstract apparent synchrony between eruption emplacement of large igneous province lip magmas and mass extinction has led to the implication of magmatism as a primary trigger of global scale environmental change evaluating the efficacy of magmatism as a driver of global change depends on the relative timing of magmatism and environmental change and the magma effusion intrusion rate both of which can be constrained by high precision geochronology early jurassic pliensbachian toarcian global ocean anoxia and acidification carbon isotope perturbations and biotic crisis have been linked to synchronous eruption and emplacement of the karoo and ferrar lips to better constrain the timing and duration of ferrar magmatism we apply the single crystal chemical abrasion u pb id tims method to zircon crystals isolated from twenty ferrar lip sills and lavas and the dufek intrusion dates suggest that both intrusive and extrusive ferrar magmatism occurred over an interval of 349 49 kyr beginning with intrusive magmatism as early as 182 779 0 033 ma lava eruption was synchronous with and in some cases postdates intrusion when coupled with existing geochronology on the karoo province our dates confirm broad synchrony between karoo and ferrar magmatism though karoo magmatism began demonstrably prior to ferrar magmatism starting as early as 183 246 0 045 ma the short lived magmatic history of the ferrar lip makes it a plausible trigger for early jurassic environmental change

sediment and hydro biogeochemistry of lake nainital kumaun himalaya india the picturesque nainital lake in the uttarakhand state of india is one of the major tourist attractions in the northern part of india the increasing tourism and population around these lakes are a major concern for the ecology and good sustenance of the lakes the present study is aimed to understand the behaviour of nutrients and metals in the sediment and their association with chemical forms in the lake the study was accomplished by studying the water interstitial water and sediments for major oxides nutrients and metals in the lake the different chemical forms of phosphorus and metals in the sediments were done using sequential extraction procedures the water chemistry ca mg na k and the sediment chemistry cia and al2o3 k2o show that the rocks in the catchment area play an important role in the geochemistry of the lake the metals in the water also show that the tallital basin is more polluted than the mallital basin may be due to the influence of bus station the high concentration of chloride nh4 so4 and metals in the sediment water interface and the interstitial water shows denitrification sulfidisation and sulfide oxidation in the anoxic bottom water the sediment composition shows that the phosphorus in the water is sequestered as carbonate flour apatite and the metals precipitate as carbonate the geo accumulation index shows that the metals zinc cobalt and nickel show moderate polluted nature than other metals in general the lake is less affected by anthropogenic activities the chemical processes undergoing within the lake like sulfidisation and sulfide oxidation oxide dissolution and denitrification and organic matter degradation play an important role in the remobilization of the metals from the lake sediments

polar record of early jurassic massive carbon injection abstract the toarcian oceanic anoxic event t oae ca 182 myr early jurassic represents one of the best recognized examples of greenhouse warming decreased seawater oxygenation and mass extinction the leading hypothesis to explain these changes is the massive injection of thermogenic or gas hydrate derived 13 c depleted carbon into the atmosphere resulting in a 3 per mil negative carbon isotope excursion cie accelerated nutrient input and dissolved oxygen consumption in the oceans nevertheless the lack of a precisely dated record of the t oae outside low latitudes has led to considerable debate about both its temporal and spatial extent and hence concerning its underlying causes here we present new isotopic and lithological data from three precisely dated n siberian sections which demonstrate that mass extinction and onset of strong oxygen deficiency occurred near synchronously in polar and most tropical sites and were intimately linked to the onset of a marked 6 negative cie recorded by bulk organic carbon rock eval pyrolysis data from siberia and comparisons with low latitudes show that the cie cannot be explained by the extent of stratification of the studied basins or changes in organic matter sourcing and suggest that the negative cie reflects rapid 13 c depleted carbon injection to all exchangeable reservoirs sedimentological and palynological indicators show that the injection coincided with a change from cold abundant glendonites and exotic boulder sized clasts to exceptionally warm conditions dominance of the thermophyllic pollen genus classopollis in the arctic which likely triggered a rapid possibly partly glacioeustatic sea level rise comparisons with low latitude records reveal that warm climate conditions and poor marine oxygenation persisted in continental margins at least 600 kyr after the cie features that can be attributed to protracted and massive volcanic carbon dioxide degassing our data reveal that the t oae profoundly affected arctic climate and oceanography and suggest that the cie was a consequence of global and massive 13 c depleted carbon injection

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

a review of the broad pattern of jurassic sea level changes and their possible causes in the light of current knowledge abstract an assessment is made of the current state of research into jurassic sea level changes based on new insights into depositional patterns in relation to these changes and new stratigraphic information from several widely separated regions across the world the bearing of this information on alternative models respectively involving sea level rise interrupted by stillstands or falls is then evaluated the gross pattern appears to be one of more or less gradual rise of sea level through the period interrupted by episodes of comparative stillstand rather than eustatic fall and several episodes of significant regression are shown to be the result of regional tectonics major episodes of eustatic rise took place in the early hettangian early sinemurian early pliensbachian early toarcian early and late bajocian middle callovian and late oxfordian to kimmeridgian a significant episode of rapid and very extensive regression possibly global took place at the end of the triassic but other regressive episodes in the late aalenian bathonian late oxfordian kimmeridgian and tithonian are clearly only regional in extent there is no evidence for glacioeustasy and most if not all of the regional or global changes recognised can readily be related to plate tectonics the events at the triassic jurassic boundary seem to be the result of mantle plume activity centred on the central atlantic region

expression of the early toarcian negative carbon isotope excursion in separated carbonate microfractions jurassic paris basin abstract the causes of the pronounced negative excursion in carbon isotope values that was recorded during the early toarcian oceanic anoxic event t oae are still under debate particularly with regard to the local versus global pattern of the excursion and the extent to which recorded signals are under a diagenetic control in this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a toarcian section recovered from the sancerre couy borehole southern paris basin beyond the recognition of a 6 13 c excursion in the bulk carbonate content our data also demonstrate that biogenic particles such as coccoliths and inorganic grains precipitated as early diagenetic phases including dolomite both record the excursion with the same magnitude although several black shales occur through the paris basin toarcian section it is only that associated with the onset of the oae that coincides with a large negative carbon isotope excursion taken together these observations indicate that during this event the entire water column was characterized by homogeneous carbon isotope values such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re mineralized organic carbon cf the kuspert model since this would have required a strong vertical gradient in the water column additionally the paris basin data show that the decrease in carbonate 13 c values during the oae occurred in several discrete steps each of some 2 as has previously been found for organic carbon substrates in other european sections the stepped nature of the isotopic profile which is part of a stratigraphic signature previously ascribed to milankovitch forcing is compatible with regular pulsed input of light carbon into the whole atmosphere ocean system from a climatically sensitive source such as gas hydrate or from thermal methanogenesis of organic rich sediments in the karoo ferrar large igneous province contrasts in the amplitude of the negative carbon isotope excursion on a regional scale remain an important unexplained aspect of the toarcian record

isotope records c o sr of late pliensbachian early toarcian environmental perturbations in the westernmost tethys majorca island spain the late pliensbachian early toarcian early jurassic was a time of major environmental changes that culminated with the early toarcian oceanic anoxic event t oae ca 183 ma this period is marked by significant disturbances in the carbon cycle and rapid climatic changes to improve the understanding of the expression of these events in westernmost tethyan domains this study provides new belemnite and bulk carbonate c and o stable isotope records of a 5 myr upper pliensbachian to middle toarcian marine succession of the balearic basin es cosconar section majorca time resolution has been improved by combination of biostratigraphic ammonoids and brachiopods and geochronologic 87sr 86sr methods seawater paleotemperatures derived from 18o belemnite records reveal cooler paleotemperatures in the upper part of the spinatum zone the uppermost spinatum zone is characterized by the onset of a warming event that crosses the pliensbachian toarcian boundary culminating with the warmer temperatures up to 10 c of warming for the serpentinum zone of the lower toarcian this warming event has been detected contemporaneously in many other european and tethyan basins and is interpreted to represent generalized raised seawater temperatures linked to the t oae four significant 13c events have been recorded in belemnite and bulk carbonate records the first is a negative carbon isotope excursion cie around the pliensbachian toarcian boundary which is best represented in the belemnite record soon after the bulk carbonate record shows a positive shift in the lower tenuicostatum zone concomitant with a return to background values in the belemnite record suggesting strong water stratification or decoupling probably related with export of neritic carbonate to the basin the third is a negative cie represented in bulk carbonate across the tenuicostatum serpentinum zonal transition which could be correlated with the negative excursion characterizing the onset of the t oae in other sections the position of this excursion corresponds with a gap in the belemnite record finally in the lower toarcian both the bulk carbonate and belemnite carbon isotope records show pronounced positive cies in the lower middle part of the serpentinum zone these cies testify the impact of the t oae in the balearic basin

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

environmental isotope study on hydrodynamics of lake naini uttar pradesh india environmental isotopes 18o d and 3h were used to understand the hydrodynamics of lake naini in the state of uttar pradesh india the data was correlated with the in situ physico chemical parameters namely temperature electrical conductivity and dissolved oxygen the analysis of the data shows that lake naini is a warm monomictic lake i e in a year the lake is stratified during the summer months march april to october november and well mixed during the remaining months the presence of a centrally submerged ridge inhibits the mixing of deeper waters of the lake s two sub basins and they exhibit differential behaviour the rates of change of isotopic composition of hypolimnion and epilimnion waters of the lake indicate that the water retention time of the lake is very short and the two have independent inflow components a few groundwater inflow points to the lake are inferred along the existing fractures fault planes and dykes in addition to poor vertical mixing of the lake due to the temperature induced seasonal stratification the lake also shows poor horizontal mixing at certain locations of the lake the lake groundwater system appears to be a flow through type also a tritium and water balance model was developed to estimate the water retention time of well mixed and hydrologically steady state lakes the model assumes a piston flow of groundwater contributing to the lake the developed model was verified for a finger lakes new york b lake neusiedlersee austria and c blue lake australia based on literature data the predicted water retention times of the lakes were close to those reported or calculated from the hydrological parameters given in the references on application of this model to lake naini a water retention time of 2 years and age of groundwater contributing to the lake 14 years is obtained copyright 2001 john wiley sons ltd

palaeoceanography methane release in the early jurassic period arising from d b kemp a l coe a s cohen l schwark nature 437 396 399 2005 kemp et al reply dramatic global warming triggered by release of methane from clathrates has been postulated to have occurred during the early toarcian age in the early jurassic period1 kemp et al 2 claim that this methane was released at three points as recorded by three sharp excursions of 13corg of up to 3 magnitude but they discount another explanation for the excursions namely that some perhaps all of the rapid excursions could be a local signature of a euxinic basin caused by recycling of isotopically light carbon from the lower water column this idea has been proposed previously see ref 3 for example and is supported by the lack evidence for negative 13c excursions in coeval belemnite rostra4 kemp et al dismiss this alternative claiming that each abrupt shift would have required the recycling of about double the amount of organic carbon that is currently present in the modern ocean however their measurements are not from an ocean but from a restricted epicontinental seaway and so would not require whole ocean mixing to achieve the excursions

astronomical forcing and chronology of the early toarcian early jurassic oceanic anoxic event in yorkshire uk 1 during the early toarcian 183 ma ago a high rate of organic carbon burial globally over a brief interval of time has led to the recognition of a major oceanic anoxic event oae a pronounced negative excursion in the carbon isotope composition of marine organic matter marine carbonate and terrestrial plant material is a key feature of this event but the precise timescale and cause s of this isotopic anomaly are debated associated with the negative carbon isotope excursion is evidence for a coeval rise in seawater palaeotemperature an increase in continental weathering rates and the mass extinction of marine invertebrate species the early toarcian oae provides evidence for the earth s response during rapid climate change and critical to our understanding of the event is a high resolution timescale that allows us to quantify the rates duration and lead lag times of environmental processes in this study we present 2743 new high resolution organic carbon sulphur and carbonate concentration data from samples of well preserved organic rich mudrocks spanning the early toarcian oae in yorkshire uk we have used these data to document the geochemical changes and significantly extend and refine the astronomical timescale across this event our detailed analysis of the relationship between astronomical forcing and carbon isotope changes in both yorkshire and a section from peniche portugal indicates that astronomical forcing paced the timing of major shifts in 13c and hence climate in both sections our analyses also demonstrate that there was a marked increase in the relative strength of astronomical forcing recorded at the onset of the oae and that the recorded nature of astronomical forcing changed during the event both the yorkshire and peniche cyclostratigraphies suggest that one astronomical forcing parameter paced environmental change through the 13c event and that this parameter was obliquity or precession

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

stepwise atmospheric carbon isotope excursion during the toarcian oceanic anoxic event early jurassic polish basin abstract during the mesozoic 250 64 ma intervals of about 0 5 myr were subject to severe environmental changes including high sea surface temperature and very low oxygen content of marine water these oceanic anoxic events or oaes occurred simultaneously with profound disturbance to the carbon cycle the carbon isotope anomaly in the early jurassic that marks the toarcian oceanic anoxic event t oae at 182 ma is characterized in marine sections by a series of dramatic steps towards lighter values herein we present new carbon isotope data from terrestrial organic matter phytoclast separates collected through a late pliensbachian middle toarcian coastal and marginal marine succession in the polish basin a setting where hinterland climate and sea level change are well recorded the results show that the shift to light carbon isotope values in the woody organic matter and therefore also in atmospheric carbon dioxide similarly occurred in major steps the steps are here correlated with those identified from marine organic matter where they have previously been attributed to 100 kyr eccentricity forcing of climate the results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean atmosphere system in a series of rapid bursts additionally a link between the carbon isotope steps and shoreline movements can be demonstrated individual peaks of the negative excursion are mostly associated with facies indicative of sea level rise flooding surfaces however at the same time inferred higher atmospheric carbon dioxide content may be expected to have resulted in increased rainfall and temperature leading to accelerated weathering and erosion and consequently increased sediment supply progradation and regression causing some mismatches between isotope shifts and inferred sea level changes enhanced abundance of megaspores derived from hydrophilic plant groups and marked increase in kaolinite are coincident with the overall development of the negative isotope excursion the combined data suggest that each 100 kyr cycle in carbon isotope values was characterized by increasingly severe palaeoclimatic change culminating in extremely hot and humid conditions co incident with the peak of the final most negative carbon isotope excursion the chemostratigraphic correlation allows very precise dating of the late pliensbachian middle toarcian coastal and marginal marine sedimentary succession in the polish basin

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

denitrification and mixing in a schist aquifer influence on water chemistry and isotopes nitrate concentrations in groundwater close to the water table in the upper weathered zone of the coet dan catchment brittany france reach 200 mg l with intensive agriculture covering 86 5 of the catchment area the pollution results principally from the spreading of livestock manure the rapid decrease of no3 concentrations with depth in the fractured part of the aquifer is partly the result of dilution by older groundwater that was probably never polluted as deduced from the isotopic data of water 3h 2h 18o and sulphate 34s 18o molecules however the extent of denitrification is demonstrated by n2 concentrations as well as by mass balance calculations showing that denitrification may contribute to a loss of at least 50 70 mg l 1 of no3 just below the upper zone of the aquifer several electron donors may be involved in the denitrification reactions for example ferrous iron and sulphides of the pyrite and organic matter with at least the last two processes being aided by the presence of bacteria autotrophic denitrification is considered to be the predominant process in the unweathered schist whereas heterotrophic processes may occur in the overlying weathered zone autotrophic reactions tend to liberate so4 but concentrations of sulphate are probably controlled by precipitation of sulphate amorphous phases and also minerals such as jarosite

sedimentary evidence for enhanced hydrological cycling in response to rapid carbon release during the early toarcian oceanic anoxic event abstract a pronounced excursion in the carbon isotope composition of biospheric carbon and coeval seawater warming during the early toarcian 183 ma has been linked to the large scale transfer of 12c enriched carbon to the oceans and atmosphere a european bias in the distribution of available data means that the precise pattern tempo and global expression of this carbon cycle perturbation and the associated environmental responses remain uncertain here we present a new cm scale terrestrial dominated carbon isotope record through an expanded lower toarcian section from japan that displays a negative excursion pattern similar to marine and terrestrial carbon isotope records documented from europe these new data suggest that 12c enriched carbon was added to the biosphere in at least one rapid millennial scale pulse sedimentological analysis indicates a close association between the carbon isotope excursion and high energy sediment transport and enhanced fluvial discharge together these data support the hypothesis that a sudden strengthening of the global hydrological cycle occurred in direct and immediate response to rapid carbon release and atmospheric warming

the significance of an early jurassic toarcian carbon isotope excursion in haida gwaii queen charlotte islands british columbia canada abstract during the early toarcian there was a significant disruption in the short term active carbon reservoir as revealed by carbon isotope records which show a broad positive shift that is interrupted by a large 5 7 negative excursion 13 c org carbon isotope excursion co occurs with the deposition of organic rich shales in many areas this perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia the two leading hypotheses as to the cause of this event invoke either global or regional controls here we present carbon isotope data from haida gwaii british columbia canada showing a significant perturbation within a temporally constrained early toarcian succession that was deposited in the northeastern paleo pacific ocean these data reinforce the concept that the short term active carbon reservoir was affected globally and assist with the correlation of ammonite zonal schemes between western north america and europe the 13 c org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7 8 5 in 13 c wood in the early toarcian kanense zone this negative excursion also coincides with increasing total organic carbon toc from 0 4 to 1 2 these data suggest that the early toarcian carbon isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle deep marine shallow marine atmospheric

globally enhanced mercury deposition during the end pliensbachian extinction and toarcian oae a link to the karoo ferrar large igneous province the mesozoic era featured emplacement of a number of large igneous provinces lips formed by the outpouring of millions of cubic kilometres of basaltic magma the radiometric ages of several mesozoic lips coincide with the dates of oceanic anoxic events oaes as a result of these coincidences a causal link has been suggested but never conclusively proven this study explores the use of mercury as a possible direct link between the karoo ferrar lip and the coeval toarcian oae t oae mercury is emitted to the atmosphere as a trace constituent of volcanic gas and may be distributed globally before being deposited in sediments modern marine deposits show a strong linear correlation between mercury and organic matter content results presented here indicate departures from such a simple linear relationship in sediments deposited during the t oae and also during the pliensbachian toarcian transition an event that saw elevated benthic extinctions and carbon cycle perturbations prior to the t oae a number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events suggesting a rise in the depositional flux of this element complications to this relationship may arise from very organic rich sediments potentially overprinting any hg toc signal whereas environments preserving negligible organic matter may leave no record of mercury deposition however the global distribution of coevally elevated hg rich levels suggests enhanced atmospheric mercury availability during the early toarcian potentially aided by the apparent affinity of hg for terrestrial organic matter although the relative importance of aquatic vs terrestrial fixation of hg in governing these enrichments remains uncertain a perturbation in atmospheric hg is most easily explained by enhanced volcanic output it is suggested that extrusive igneous activity caused increased mercury flux to the early toarcian sedimentary realm supporting the potential of this element as a proxy for ancient volcanism this interpretation is consistent with a relationship between lip formation and a perturbed carbon cycle during the pliensbachian toarcian transition and t oae the recording of these two distinct hg excursions may also indicate that the karoo ferrar lip released volatiles in temporally distinct episodes due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile rich lithologies

bacterial magnetite in lake sediments late glacial to holocene climate and sedimentary changes in northern norway magnetic properties of sediments retrieved from a small lake in northern norway spanning the last f14500 cal years have been analyzed in detail the high resolution core with its ability to detect sub centurial variability records the rapid retreat of the fennoscandian ice sheet fis in northern lyngen and subsequently the establishment of a stable allerod to younger dryas watershed from early holocene and to the present magnetotactic bacteria mb producing stable single domain ssb magnetite become the dominating magnetic carrier the small low relief catchment area with its quartzite bedrock scattered till and vegetated surface generates a negligible contribution of detrital magnetic minerals this allows for the opportunity to follow the presence and changes of the magnetosomes during the last 10000 years a strong positive statistical relationship r 2 0 83 between the anhysteretic remanent magnetisation susceptibility varm and loss on ignition loi suggests an environmental control over the bacteria magnitude quart int 88 2002 13 that most likely is related to summer climate a comparison between the magnetic mineralogy as evident from the s ratio jirm100mt jsirm3t and the reconstructed summer temperatures from a nearby lake shows a close covariation between cooler summers and harder s ratios for a series of climatic events intervariability of loi data and other proxies such as august sea surface temperatures sst from the nordic sea suggests land ocean connections during converging phases of cooler climate where the most prominent in phase periods are approximately 1 6500 5000 2 3500 2400 and 3 1700 1000 cal years bp the most significant change in the holocene magnetic signal is initiated at f3700 cal years bp which we refer to here as the holocene turnover d 2004 elsevier b v all rights reserved

long term resilience decline in plant ecosystems across the danian dan c2 hyperthermal event boltysh crater ukraine mass balance calculations indicate that a massive amount of 13 c depleted carbon was released into the early danian atmosphere in volumes comparable with the younger paleocene eocene thermal maximum petm this danian hyperthermal event the dan c2 has been documented from the fill of the boltysh meteorite crater ukraine palynofloras recovered from the boltysh crater fill show a trend from mesic forest to savannah ecosystem dominance on a millennial scale across the hyperthermal inception with no abrupt compositional shift this longer term trend is overprinted by moisture availability oscillations reflecting orbital forcing forcing is not directly tracked by the oscillations which are composed of mesic forest and savannah palynofloras separated by rapid critical transitions the absence of an ecological collapse at the dan c2 indicates that plant ecosystems experienced dominant forcing from orbital cyclicity rather than a stochastic temperature rise

distribution of clay minerals in early jurassic peritethyan seas palaeoclimatic significance inferred from multiproxy comparisons article i nfo a set of published unpublished and new clay mineral data from 60 european and mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the pliensbachian toarcian period early jurassic by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution in order to discuss their palaeoclimatic meaning a compilation of low latitude belemnite 18 o 13 c mg ca and 87 sr 86 sr values is presented for the first time for the whole pliensbachian toarcian period once diagenetic and authigenic biases have been identified and ruled out kaolinite content variation is considered as a reliable palaeoclimatic proxy for the early jurassic major kaolinite enrichments occur during times of low 18 o high mg ca and increasing 87 sr 86 sr implying warm climates and efficient runoffs during the davoei falciferum and bifrons zones conversely cooler and drier times such as the late pliensbachian or the late toarcian are characterized by low hydrolysis of landmasses and correspond to kaolinite depleted intervals secondary factors as modifications of sources or hydrothermalism may sporadically disturb the palaeoclimatic signal e g in the bakony area during the late pliensbachian in addition a spatial comparison of clay assemblages displays significant kaolinite enrichments towards northern parts of the peritethyan realm probably related to the latitudinal zonation of hydrolyzing conditions this implies enhanced runoffs on northern continental landmasses that reworked kaolinite rich

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

seasonal variability in phosphorus speciation and deposition in a calcareous eutrophic lake abstract settling particulate matter was collected in sediment traps from the major depositional basin of onondaga lake a calcareous eutrophic lake in syracuse new york u s a sediment traps were deployed at three depths from july to november and for a brief period under ice cover in february to investigate both vertical and seasonal variations in sedimentation a sequential chemical extraction fractionation method was applied to the collected material to quantify the following phosphorus p fractions or forms loosely bound p sorbed p caco3 associated p and fe and al bound p extractable biogenic p easily degradable organic p and biogenic inorganic poly phosphates calcium mineral p e g apatite and refractory organic p extractable biogenic p and refractory organic p were strongly correlated suggesting a common autochthonous origin in plankton calcium mineral p appears to be of terrigenous origin a dramatic increase in the loosely bound p content of the particulate matter was observed during fall turnover when dissolved fe2 which had accumulated in the anoxic hypolimnion mixed with the surface waters and oxidized with attendant adsorption of p we estimate that the labile or exchangeable p i e loosely bound and extractable biogenic p forms content of the settling particulates constitutes 50 of the total p influx to the sediments over the period of study the labile p flux over the july november study period was 11 mg p m 2 day 1 and the labile p flux estimated from sediment traps deployed under ice cover was 6 mg p m 2 day 1 from these values the annual average labile p flux to the sediments was estimated to be 9 mg p m 2 day 1 only slightly less than the estimated annual average sediment p release rate of 10 mg p m 2 day 1 this indicates that the sediments are approximately at steady state with respect to current external p loadings to the lake

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments