facies outcrop gamma ray and c o isotopic signature of exposed miocene subtropical continental shelf carbonates north west cape western australia abstract exposed uplifted miocene carbonate sequences of the cape range north west cape western australia provide outcrop analogues of seismic sequences from offshore parts of the shelf facies include deep shelf marls very fine and fine packstone larger foram wackestone floatstone and muddy rudstone foram coralline algal skeletal fragment packstone wackestone shallow seagrass facies lagoonal wackestone mudstone with scattered corals and tidal flat laminites the exposed early miocene units include the mandu highstand a sequence in the tulki and one in the middle miocene trealla limestone sequences contain decameter scale 5 20 m thick 4th order parasequences evident on gamma ray logs and by facies stacking that shallow and coarsen up they appear to be due to eccentricity driven sea level changes which may have been up to 50 m higher frequency meter scale parasequences of deep water marl up into larger foram rudstone floatstone perhaps precession obliquity are evident at the base of the exposed mandu section these parasequences are not merely random storm deposits this is indicated by the covariance of c and o isotopes with the lighter values associated with deepening and deposition of deep shelf marls and the heavier values being associated with shallowing and deposition of larger foram facies the uplifted miocene continental shelf sediments of the north west cape preserve a record of eustasy paleoclimate and paleoceanography and thus provide a window into factors affecting the shelf that can be compared with coeval better studied deep sea cores

reconstruction of early triassic ocean redox conditions based on framboidal pyrite from the nanpanjiang basin south china abstract widespread oceanic anoxia has been implicated as an important factor in the ptb permian triassic boundary mass extinction and the delayed recovery of early triassic marine ecosystems an investigation of framboidal pyrite in the bianyang section nanpanjiang basin south china suggests that euxinia dysoxia peaked during the induan late smithian to earliest spathian and late spathian these anoxic episodes show a relationship albeit imperfect to major episodes of climatic warming during the early triassic that were associated with intensified oceanic stratification reduced marine productivity and organic carbon sinking fluxes as well as diminished burial fluxes of organic carbon and reduced sulfur in contrast intervals of better oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle smithian and mid spathian the degree of ventilation of the thermocline region in particular had a profound effect on marine biotas with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the nanpanjiang basin these observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of early triassic marine ecosystems and specifically that episodic expansion of oceanic oxygen minimum zones omzs resulted in repeated setbacks to the recovery process a pattern that persisted until the late spathian

thermal imprint of rift related processes in orogens as recorded in the pyrenees 19 the extent to which heat recorded in orogens reflects thermal conditions inherited from 20 previous rift related processes is still debated and poorly documented as a case study we 21 examine the mauleon basin in the north western pyrenees that experienced both extreme 22 crustal thinning and tectonic inversion within a period of 30 myrs to constrain the time 23 temperature history of the basin in such a scenario we provide new detrital zircon fission 24 track and u th sm he thermochronology data the role of rift related processes in 25 subsequent collision is captured by inverse modeling of our thermochronological data using 26 relationships between zircon u th sm he ages and uranium content combined with 27 thermo kinematic models of a rift orogen cycle we show that the basin recorded significant 28 heating at about 100 ma characterized by high geothermal gradients 80 c km our 29 thermo kinematic modeling and geological constraints support the view that subcontinental 30 lithospheric mantle was exhumed at that time below the mauleon basin such a high 31 geothermal gradient lasted 30 myr after onset of convergence at 83 ma and was relaxed 32 during the collision phase from 50 ma this study suggests that heat needed for ductile 33 shortening during convergence is primarily inherited from extension rather than being only 34 related to tectonic and or sedimentary burial this should have strong implications on tectonic 35 reconstructions in many collision belts that resulted from inversion of hyper extended rift 36 basins

testing for causal relationships between large pyroclastic volcanic eruptions and mass extinctions the permo triassic mass extinction the most extensive of all phanerozoic extinctions erwin 1990 has been correlated with both massive pyroclastic eruptions yang and yin 1987 yin et al 1989 jinwen 1989 and flood basalts rampino and strothers 1988 more tentatively the end cretaceous mass extinction has also been linked with massive volcanic events officer et al 1987 rampino and strothers 1988 however the nature of the connection between volcanism and either mass extinction remains uncertain rather than study volcanic events at known extinction horizons another approach is to identify extremely large 1000 km3 pyroclastic eruptions with well constrained age determinations and evaluate the fossil record for evidence of significant regional or global extinctions we selected the largest best constrained pyroclastic events known toba tuff huckleberry ridge tuff tuff of blacktail and the elkhorn mountain volcanics neither global marine diversity nor global or regional terrestrial vertebrate diversity exhibit any biological effect from these extremely massive pyroclastic eruptions we conclude that massive pyroclastic eruptions are unlikely to have been an effective cause of mass extinctions

palaeoclimatic and biotic changes during the aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain the uppermost toarcian lowermost bajocian deposits have been studied in 10 sections located in the western part of the basque cantabrian basin northern spain the studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale the foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for c and o isotope facies and thickness distribution of the aalenian sediments suggest that deposition took place in a nearly symmetrical sub basin included into an intraplate shallow platform developed over continental crust on which flexure was the main control responsible for subsidence and basin evolution noteworthy negative 13cbel excursions coinciding with seawater temperature changes were recorded during the bradfordensis biochron around the concavum limitatum biochron boundary and around the aalenian bajocian boundary a close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced during the comptum biochron the 18obel based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15 7 c this cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the basque cantabrian basin as a consequence a strong increase in the diversity of the foraminiferal assemblages 28 5 of first appearances occurred this interval also coincides with the highest ammonoid abundance recorded during the aalenian a notable increase in temperature with peak values up to 24 3 c was measured during the bradfordensis biochron this warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids however the increase in the relative abundances of some foraminiferal taxa such as the genus spirillina during the warming phase is remarkable some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from nw europe that arrived during the comptum cooling interval and that did not survive to rise of the seawater temperature another drop in temperature was recorded during the late gigantea and the early concavum biochrons coinciding with this cooling interval nearly 20 of the foraminiferal species disappeared while the ammonoid abundance increased a new and significant warming episode occurred during the latest aalenian limitatum biochron extending to the earliest bajocian discites biochron biotic response to this new t of 2 5 c is remarkable marking one of the most important crises of the aalenian more than 30 of the foraminiferal species disappeared and no new appearances were recorded ammonoids show a decrease in the specimen abundance during the limitatum discites warming preceding a drastic decrease in the species abundance the remarkable biotic changes linked to the variations of seawater temperature recorded in the basque cantabrian basin during the aalenian open the possibility that some of these faunal turnovers specially marked in the benthic foraminifers were of global extent and mainly forced by climate changes

carbon isotope record of the p t boundary and the lower triassic in the southern alps evidence for rapid changes in storage of organic carbon abstract the carbonate carbon isotope record of lower triassic shelf sediments was investigated in the pufels and l om picol uomo sections of the western central dolomites to derive a complete record from the permian triassic transition to the uppermost lower triassic from the western tethys the carbon isotope record shows the well studied decrease at the permian triassic boundary ptb followed by an increase to about 1 5 at the dienerian smithian boundary the 13c values increase to a pronounced 6 maximum a steady rapid drop until the upper smithian below 2 follows this 13c peak at the smithian spathian transition a steep rise to positive values is documented the positive carbon isotope peak is interpreted to reflect an interval of enhanced burial of organic carbon whereas the isotopic minima provide evidence of periods of oxidation of organic matter and or release of isotopically light carbon this may be ascribed to quickly changing environmental conditions which have already been postulated by paleontologists due to the delayed biotic recovery from the permian triassic extinction event because of the short time interval these positive isotope excursions represent their generation by burial of organic carbon in periods of high productivity and or anoxia appears plausible concurrent carbon isotopic excursions are reported from iran pakistan and oman as well as from southern china which indicate an at least tethys wide event if the excursion proves to be of global significance dark shale deposited in the pelagic panthalassa ocean may have acted as sink for organic carbon supporting the hypothesis of a periodically stratified ocean in the lower triassic

a chemostratigraphic overview of the late cryogenian interglacial sequence in the adelaide fold thrust belt south australia within the neoproterozoic sequence of the adelaide fold thrust belt south australia two of the most severe ice ages in earth history sturtian and marinoan are recorded in the glacigenic rocks which mark the base and top of the 4 5 km thick umberatana group the focus of the present chemostratigraphic study rock units from three drillholes and ten measured outcrop sections located in the southern and central flinders ranges and on the stuart shelf were sampled for isotopic analysis of their co existing calcite 13ccal dolomite 13cdol and kerogen 13corg strontium and sulphur isotopic analyses were also run on selected samples the sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen the resulting data when integrated with the lithostratigraphy of the umberatana group yield one of the most complete records of secular variation in the c isotope signature of the late cryogenian ocean between 750 and 680 ma its composite 13ccarb curve begins with a sharp positive excursion 3 to 1 5 in the dolomitic tindelpina shale which caps sturtian glacial diamictites wilyerpa formation then follows a steady climb through the shoaling upward tapley hill formation reaching 4 in the brighton limestone and culminating in a plateau of 13c enrichment within the platformal carbonates of the etina formation 8 to 10 the upper part of the temporal trend shows a decline to 6 to 7 in the stromatolite reef facies of the enorama shale and a dramatic drop to 8 to 9 5 followed by a recovery to 3 in the youngest carbonate unit trezona formation beneath the marinoan glacigenic elatina formation the latter is capped by a thin dolostone the nuccaleena formation which records a consistent up section decrease in 13c 1 to 3 superimposed on this overall pattern of c isotopic variation are second and third order fluctuations attributable to eustatic sea level change pyritic sulphur in the lower tapley hill formation 34s 9 to 40 is distinctly heavier than that in the underlying wilyerpa formation 4 to 20 minimum 87sr 86sr values obtained from the brighton limestone 0 7071 and etina formation 0 7076 are consistent with their late cryogenian age this sturtian to marinoan interglacial succession is more complete than equivalent sequences elsewhere and thus provides a useful reference for global chemostratigraphic correlation notable features of its c isotope curve are the strong post wilyerpa positive excursion also seen in key sections from svalbard and western mongolia the etina plateau of 13c enrichment which is remarkably similar to maxima in the terminal proterozoic c isotope records of western mongolia north western canada and brazil and the spectacular depletion of 13c in the lower trezona relative to similar carbonate facies in the underlying etina formation and enorama shale a preglacial offset in 13ccarb values of such proportions 14 is almost unprecedented except perhaps for that recently documented in the upper ombaatjie formation beneath tillites of the ghaub formation otavi group namibia it represents a key piece of evidence in the case presented by the proponents of a neoproterozoic snowball earth

new geochemical constraints on the paleocene eocene thermal maximum dababiya gssp egypt the paleocene eocene thermal maximum petm shows an extraordinary drop in the 13c of carbonate and organic matter across the globe suggesting massive release of 13c depleted carbon dioxide into the ocean and atmosphere over a very short time interval probably 20ky we report a geochemical and mineralogical study of 106 samples spanning the most expanded petm at the dababiya global stratotype standard section and point gssp near luxor egypt the field and laboratory observations reveal that the deposition occurred in a submarine channel extended laterally about 200 m with the deepest part 0 88 m at the designated gssp although all bio zones are present stable isotope records of both carbonate and organic carbon show decreases starting 0 6 m below the paleocene eocene boundary peb and culminating at the erosion surface a persistent shift in 15norg values to near zero reflects a gradual increase in bacterial activity high ti k and zr and low si contents at the peb coincide with increased kaolinite contents which suggests intense chemical weathering under more humid conditions at the petm onset two negative ce anomalies indicate intervals of anoxic conditions during the lower and middle petm base and top of zone e1 the first anoxic event is represented by a negative ce anomaly high v c rand v v ni ratios negative mn and an abundance of idiomorphic pyrite crystals that indicate anoxic to euxinic conditions the anoxic event middle petm is marked by high u mo v fe and abundant small sized 2 5 m pyrite framboids increased cu ni and cd at the same level suggesting anoxic conditions linked to high surface water productivity above this interval oxic conditions returned as indicated by the precipitation of phosphorus and barium these data reveal an expanded petm interval marked by intense weathering as a crucial parameter during the recovery phase

carbon isotopic profile across the bilara group rocks of trans aravalli marwar supergroup in western india implications for neoproterozoic cambrian transition abstract the rocks of marwar supergroup in the trans aravalli sector in western india are presumed to span the time interval between neoproterozoic and early cambrian this predominantly unfossiliferous marine sedimentary sequence is characterized by a lower arenaceous facies jodhpur group middle carbonate facies bilara group and upper argillaceous arenaceous facies nagaur group rocks the sedimentation has been essentially in a shallow basin described either as the fore land slope of the rising aravalli mountains or a sag basin which developed and evolved due to subsidence of the updomed crust during neoproterozoic malani magmatism that failed to open rifts the carbon isotopic profile for the bilara group carbonate rocks in the lower part shows marked oscillations and broadly negative 13 c character with negative anomalies as low as pdb observed near the base of dhanapa formation lower unit and pdb in the overlying gotan formation middle unit the upper part of the profile shows a gradual positive shift the carbon isotopic signatures of the bilara group rocks can be correlated with the end neoproterozoic early cambrian vendian tommotian carbon isotopic evolution curve extremely low 13 c values indicate the glaciation related cold climatic postulates of the end neoproterozoic followed by the warmer climatic conditions as indicated by the positive shift the carbon isotopic data for gotan formation carbonates at variance with the globally observed 13 c trends for early tertiary do not support the recently proposed tertiary age for the bilara group

carbon isotopic evidence for biomass burning at the k t boundary a new interpretation of existing carbon isotopic data combined with results from a biogeochemical model suggests that burning of terrestrial biomass occurred on a global scale at the cretaceous tertiary k t boundary carbon isotopic ratios from planktonic and benthic microfossils across the k t boundary reveal not only a breakdown in the normal surface water to deep water gradient of 13 c 12 c but also a reversal at the boundary this reversal cannot be explained by the cessation off primary production alone we propose that combustion of terrestrial biomass with subsequent transfer of isotopically light carbon to surface waters is the most likely cause of this anomaly a biogeochemical model is used to quantify the extent of burning at the boundary combustion of roughly 25 of the above ground biomass at the end of the cretaceous is necessary to account for the observed isotopic signal

high resolution c isotope chemostratigraphy of the uppermost cambrian stage stage 10 in south china implications for defining the base of stage 10 and palaeoenvironmental change the wa9ergang section in south china has been proposed as a potential global stratotype section and point gssp for the base of stage 10 the uppermost stage of the cambrian system in this study high resolution c isotopic compositions are reported and we identified three large negative 13 c excursions namely n1 n2 and n3 at wa9ergang the n1 is located just above the first appearance datum fad of lotagnostus americanus corresponding to the possible base of the proconodontus posterocostatus conodont zone the n2 was identified within the micragnostus chuishuensis trilobite zone and the proconodontus muelleri conodont zone the n3 is located in the lowermost part of the leiagnostus cf bexelli archaeuloma taoyuanense trilobite zone or eoconodontus conodont zone the n1 and n2 can be correlated with the negative 13 c excursions preceding the top of cambrian carbon isotope excursion toce observed globally the n3 can be correlated with the toce or the hellnmaria red tops boundary herb event the inter basinal correlation of n1 and l americanus strongly supports that the base of stage 10 may be best defined by the fad of l americanus we also used a box model to quantitatively explore the genesis of the negative 13 c excursions from south china our numerical simulations suggest that weathering of the organic rich sediments on the platform probably driven by intermittent sea level fall and or the oxygenation of the dissolved organic carbon doc reservoir in seawater may have contributed to the generation of the negative 13 c excursions observed in the stage 10 at wa9ergang in south china

geochemical events documented in inorganic carbon isotopes abstract screening of sampling and analytical data is crucial for the detection of real global shifts in marine 13c against the noise of diagenesis the real global shifts of 13c are of two types 1 long term secular shifts caused by changes in the fractional burial of organic carbon and 2 transient shifts caused by abrupt changes of biological productivity in the surface photic zone both are applicable to stratigraphic correlation but differ in their application to modelling of changes in oceanographic or atmospheric composition a recent compilation found 34 carbon isotope events in the phanerozoic and neoproterozoic equally distributed among positive and negative shifts this in itself attests to a variety of proximate causes of the shifts

interpreting carbon isotope excursions strangelove oceans large negative excursions in marine carbonate delta sup 13 c are commonly associated with period boundaries and mass extinctions explanations for these events must be consistent with limitations imposed by carbon isotope mass balance at steady state i e for excursions lasting more than 10 sup 5 yr the surface ocean delta sup 13 c is set by the organic fraction of the total carbon burial rate and the magnitude of the photosynthetic isotope effect the delta sup 13 c of the deep ocean and the surface to deep isotope gradient are set by both the organic fraction of the ocean s remineralized particulate flux and the magnitude of the isotope effect thus it is the carbon isotope composition of the deep ocean that is most reflective of internal oceanic processes the surface ocean records changes in the longer term throughput of carbon in the system the cessation of organic export from the surface ocean such as is presumed to have caused the strangelove ocean condition of the cretaceous tertiary k t boundary leads to an isotopically homogeneous ocean in decades to centuries if this condition persists the ocean s isotopic composition approaches that of the riverine weathering input in 10 sup 5 yr failure to approach this value during the k t event suggests continued production andmore burial of organic carbon dominantly in either terrestrial or shallow marine environments less

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

carbon isotopes across the eocene oligocene boundary sequence of kutch western india implications to oceanic productivity and pco2 change 1 analyses of foraminiferal 18o 18ocarb 13c 13ccarb and bulk organic matter 13corg across a tropical eocene oligocene boundary eob section from kutch basin western india show that the ocean cooling at least 3 c is coincident with a rapid enrichment 3 in 13corg but depletion 1 5 in 13ccarb the decrease in pco2 in ocean atmosphere system across the boundary possibly resulting from enhanced silicate weathering in rising himalayas and accompanied organic carbon burial in ocean caused the cooling and 13corg enrichment the end eocene climatic stress decreased the oceanic productivity and 13ccarb eventually causing extinction of larger benthic foraminiferal community the data suggest a critical role of tropical ocean and direct forcing of co2 on global climate change at least for this crucial cenozoic transition

thermochronology constraints for the propagation sequence of the south pyrenean basement thrust system france spain 1 in this work we combined apatite fission track and biotite k feldspar 40ar 39ar ages with tectonic data in the west central part of the axial zone of the pyrenees we discuss the exhumation ages and rates of the neouvielle bordere louron and bielsa variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the pyrenean orogenic prism the 40ar 39ar ages on k feldspars from the neouvielle massif sample nv7 seem to indicate tectonic movements on the eaux chaudes thrust during the early middle eocene fission track results suggest that the exhumation of the neouvielle massif occurred around 35 ma and exhumation of the bordere louron massif around 32 ma in relation to thrusting on the gavarnie thrust the bielsa massif was exhumed from around 19 ma by out of sequence movements on the bielsa thrust we thus show that whereas most of the pyrenean basement thrust faults here the eaux chaudes gavarnie and guarga thrusts were active in sequence toward the southern foreland from the early eocene to the earliest miocene some of them here the bielsa thrust were activated out of sequence in the hinterland later than the generally accepted aquitanian age for the end of the pyrenean compression finally the apatite fission track modeling indicate a last cooling episode starting around 5 ma which is most certainly related to the pliocene reexcavation of the southern and northern flanks of the pyrenees

the carbon isotope excursion on gssp candidate section of lopingian guadalupian boundary an isotopic stratigraphically well documented outcrop in penglaitan guangxi province south china has been proposed as a candidate gssp for the lopingian guadalupian boundary correlatable outcrops from the west wing tieqiao section and east wing penglaitan section of the laibin syncline exhibit synchronous excursions in carbon isotopes the isotopic excursions 13c show the best placement of the boundary may lie at the base of bed 6k which coincides with the clarkina postbitteri conodont zone and with eustatic change 13c increases during the uppermost guadalupian jinogondolella granti conodont zone from the top of 3c to the base of 6i a 13c peak value of 5 is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression a gradual depletion of carbon isotopes occurs in the c postbitteri zone from bed 6e to 7b and this gradual 13c excursion also suggests the sequences around the guadalupian lopingian boundary at the candidate section are conformable during the middle later c postbitteri zone a 3 5 dramatic 13c depletion is recorded at the tieqiao section but only a 2 depletion at the deeper facies penglaitan section synchronous with conodont zones that mark eustatic changes

insights from isotope stratigraphy a symposium on precambrian isotope stratigraphy was heldwithintheframeofthe33rdigcheldatoslo norway august2008 this symposium spawned the idea for a special issue on this themeand ultimately to the ten papers assembled here this special issueprovides the results of some of the latest cutting edge research ontraditional c sr s isotopechemostratigraphyandintroducesomenewer isotope systems ree ca and hg chemostratigraphy as apotential tracer for glacial events and estimate of the buildup ofvolcanicgases includingco

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

observations of near surface wind and temperature structures and their variations with topography and latitude in east antarctica received 10 december 2008 revised 30 march 2009 accepted 5 june 2009 published 15 september 2009 1 the first multiyear surface meteorological observations over dome a the highest ice feature in the entire antarctica continent are analyzed to understand the surface wind temperature and stability climatology over dome a and how it differs from the surface climatology at two lower latitude lower elevation sites along similar longitude in east antarctica the climatology is also compared with that over dome c in contrast to the surface winds at lower sites where moderate to strong northeasterly winds prevail with a distinct diurnal oscillation in wind speed in response to the diurnal change in katabatic forcing summertime surface winds over dome a are very weak are variable in direction and show little diurnal variation although both temperature and temperature gradient oscillate diurnally the gradient over dome a remained positive all day long indicating a persistent surface inversion while at the two lower sites as well as over dome c sufficient insolation leads to the breakup of inversion and the development of a convective boundary layer in the afternoon wavelet analysis of near surface stability revealed that besides the strong diurnal signal the near surface stability also exhibits annual semiannual and interseasonal period 50 days oscillations at all locations these oscillations in near surface stability are linked to the same peaks in the 500 hpa geopotential height spectra and therefore are believed to be caused by variations of synoptic conditions

garnet compositions in scottish and norwegian basement terrains a framework for interpretation of north sea sandstone provenance detrital garnets have proved to be useful discriminators of north sea sandstone provenance because they show a wide range of potential compositions and are relatively stable during burial diagenesis it has been less easy to use garnet data to provide a direct link between sediment and source because of the lack of a comprehensive database of garnet compositions in basement terrains forming the north sea hinterland this paper presents garnet compositional data from river sediments sourced from northern scotland and norway and demonstrates the presence of marked variations in garnet compositions from different regions related to fundamental differences in basement lithology the value of the river sediment database is demonstrated by comparing it with garnet compositions in paleocene sandstones from the north sea and more basins enabling the establishment of direct links between source and sediment paleocene sandstones in the gannet field area on the southwestern margin of the central north sea were derived from the dalradian of the grampian highlands those in the northern north sea were derived from the moine dalradian rocks of shetland and those along the more basin margin were derived from western norway by contrast paleocene sandstones in the nelson field central north sea and in the beryl embayment northern north sea have a garnet component that cannot be readily traced back to any basement terrain in either scotland or norway this component which was ultimately derived from granulite facies metasediments or charnockites is interpreted as being recycled from triassic sandstones which were themselves derived from an exotic source probably to the west of the british isles q 2004 elsevier ltd all rights reserved

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

provenance of the sardona flysch eastern swiss alps example of high resolution heavy mineral analysis applied to an ultrastable assemblage abstract the sardona flysch of eastern switzerland was deposited in the northern sector of the embryonic alpine foreland basin the so called north penninic trough during the late cretaceous early tertiary the flysch sediments consist of quartz arenites sublitharenites and arkosic arenites plus polygenic pebble to boulder conglomerates the sardona flysch was sourced by a single petrologic province composed of plutonic variscan granitoids gneisses and low grade quartzo feldspathic schists plus associated cover sediments throughout its sedimentary history its heavy mineral suite principally comprises zircon tourmaline rutile and varying amounts of apatite whose distribution cannot be used to characterise the various lithostratigraphic units however recording the diagnostic varieties of ultrastable heavy minerals using a high resolution heavy mineral analysis hrhma yielded conclusive results the varietal distribution of zircon proved especially informative demonstrating that changes in its distributional trends coincide remarkably well with lithostratigraphic subdivisions and reveal subtle variations in the provenance of the flysch the limited number of heavy mineral species was predetermined by the low diversity of parent rock lithologies in the hinterland rather than resulting from high sediment maturity or progressive removal of unstable species during diagenesis the basin was structurally confined by the south helvetic and north penninic prattigau swells which defined its northern and southern margins respectively these structural highs may represent mesozoic normal fault blocks reactivated under compressive stresses within the european foreland they provided detritus to the sardona flysch basin and prevented the influx of material from the orogenic thrust wedge hence garnet and unstable heavy minerals recycled from medium grade metamorphic rocks within the mineralogically more diverse austroalpine thrust wedge are absent from the flysch sediments

a numerical study of strong katabatic winds over antarctica abstract certain coastal sections of antarctica most notably adelie land and terra nova bay experience anomalously intense persistent katabatic winds the forcing of such katabatic outflow is believed to originate several hundred kilometers upslope in the interior of the continent where cold air drainage currents from a large area converge into a relatively narrow zone focused on the steeply sloping ice terrain near the coastline numerical simulations with a three dimensional hydrostatic model incorporating terrain features representative of adelie land reveal a significant topographical channeling of the surface airflow katabatic wind speeds as depicted by the model are greatly enhanced downslope of the convergence channel these results emphasize the importance of topography in the continental interior in shaping the character of coastal katabatic flow

slope winds and the axisymmetric circulation over antarctica abstract an axisymmetric model of the flow over antarctica is used to study the circulation induced by cooling of the air at the slopes of the continent it is found that the resulting circulation with southeasterly surface winds and westerlies in the free troposphere agrees qualitatively quite well with the observed circulation the profiles of wind and temperature obtained above the slope are compared to the results from a simple one dimensional model of flow over sloping terrain the agreement is quite good near the surface but not at upper levels the reasons for this discrepancy are discussed it is found that the two dimensional flow does not settle down to a satisfactory steady state it is argued that the surface easterlies at the slopes of antarctica provide a source of westerly angular momentum in the atmosphere three dimensional eddies can export momentum to lower latitudes whereas the flow in the model cannot dispose of the momentum this points to the limitations of the two dimensional app

new magnetostratigraphic dating of the palaeogene syntectonic sediments of the west central pyrenees tectonostratigraphic implications financial support to develop this investigation was provided by projects cgl2009 08969 cgl2010 21968 c02 02 cgl2009 14214 cgl2010 17479 and cgl2014 55900 p of the former spanish ministry of science and innovation micinn

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

δ13c and δ18o values of triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature abstract a dataset of 160 isotope 13c and 18o values from anisian ladinian carnian and rhaetian articulate brachiopod shells complemented by 158 carbon and oxygen isotope values from whole rock carbonates define the first continuous stable isotope baseline trends for the triassic seawater the carbon isotope data suggest the existence of several short term high amplitude excursions in the early triassic followed by a predominance of values around 0 5 1 during the middle triassic a rise to 3 5 during the carnian plateau at this level during the late carnian to early norian and a 1 5 decline in the middle norian to values around 2 during the late norian rhaetian interval the causation scenarios for these rapid oscillations are at present equivocal but may in part reflect a biological instability of the carbon cycle following the recovery from the end permian extinction event and or an input of mantle derived co2 from enhanced volcanic activity the 18o values from well preserved brachiopods from the tethyan realm range from 3 9 to 0 6 v pdb these values require open marine triassic seawater 18o values close to 0 v smow for the calculated temperatures to be within the range of tolerance of the coexisting reef building corals a 2 18o increase within the uppermost cordevolian and early julian suggests either a distinct temperature decline in the southern alps during that time interval an increase in seawater salinity or their combination oxygen isotope values for the muschelkalk brachiopods range between 6 2 and 2 0 and likely reflect a strong influx of meteoric waters into the germanic basin that shifted the oxygen isotopes to more negative values

record of environmental changes in the triassic jurassic boundary interval in the zliechov basin western carpathians abstract the fatra and kopieniec formations in the zliechov basin comprise a record of several environmental crises that may have contributed to the global triassic jurassic t j boundary events the diversity of the benthic fauna decreases at the base of the transition beds the uppermost member of the fatra formation this assemblage comprises many species that do not appear in younger strata in cycle 13 of the fatra formation stable isotope excursions correspond to significant lithological changes in the sequence the negative 13 c excursion is correlated with a positive 18 o peak and the beds containing the excursion are overlain by a thin layer with unusual lithological and mineral composition this layer is composed of small calcitized microspheres showing complex alteration during diagenesis the origin of this layer traceable over tens of kilometres is problematic impact ejecta volcanic glass or altered aragonitic particles an increase in terrigenous sediment recorded by sandy beds in the uppermost part of the fatra formation indicates increased run off a sharp lithological boundary between the fatra and the kopieniec formations marks a sudden termination of carbonate sedimentation followed by deposition of the boundary clay the negative 13 c anomaly recognized in this succession may correspond to the isotopic signature at the t j boundary which has been described from many sections in the world

a critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for late cretaceous global correlation abstract climate variability is driven by a complex interplay of global scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter regional correlation which in most cases cannot be obtained with biostratigraphic methods alone chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high resolution correlation over large distances but complications arise from a multitude of possible influences from local differences in biological diagenetic and physico chemical factors on individual 13c records that can mask the global signal to better assess the global versus local contribution in a 13c record it is necessary to compare numerous isotopic records on a global scale as a contribution to this objective this paper reviews bulk sediment 13ccarb records from the late cretaceous in order to identify differences and similarities in secular 13c trends that help establish a global reference 13c record for this period the study presents a global scale comparison of twenty 13c records from sections representing various palaeo latitudes in both hemispheres and different oceanic settings from the boreal tethys western interior indian ocean and pacific ocean and with various diagenetic overprinting the isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute 13c values and variation in amplitude between the sites these differences reflect the varying local influences e g from depositional settings bottom water age and diagenetic history whereas the concordant patterns in 13c shifts might represent 13c fluctuations in the global seawater dissolved inorganic carbon the latter is modulated by variations in organic matter burial relative to re mineralization in the global scale formation of authigenic carbonate and in partitioning of carbon between organic carbon and carbonate sinks these variations are mainly controlled by changes in climate and eustasy additionally some globally synchronous shifts in the bulk 13ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and thus can be globally synchronized by fluctuations in eustasy atmospheric and oceanic oxygen levels or in large scale oceanic circulation because the influence of early diagenetic cements on the bulk 13ccarb signal can but need not be synchronized chemostratigraphy should not be used as a stand alone method for trans continental correlation and especially minor isotopic shifts have to be interpreted with utmost care nevertheless the observed consistency of the 13c correlations confirms global scale applicability of bulk sediment 13c chemostratigraphy for the late cretaceous including sediments that underwent lithification and burial diagenesis such as the sediments from the himalayan and alpine sections limitations arise from increased uncertainties 1 in sediments with very low carbonate content 2 from larger 13c variability in sediments from very shallow marine environments 3 from unrecognized hiatuses or strong changes in sedimentation rates and 4 in sections with short stratigraphic coverage or with few biostratigraphic marker horizons the combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes facies or provincialism of key fossils by using an iterative approach to stepwise increase precision of the correlations isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested which helps to improve biostratigraphic zonations to assess zonal boundary ages and to identify useful criteria for defining late cretaceous stage boundaries many of which are still not formally defined the presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid cretaceous sea level high whereas diachroneity appears to be more pronounced during the late campanian and maastrichtian global sea level fall a similar pattern is observed for trans continental consistency in the 13c shifts graphic correlation of isotopic shifts magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo and magnetostratigraphy finally an attempt of a global average 13c stack is presented for the turonian through maastrichtian

upper kellwasser carbon isotope excursion pre dates the f f boundary in the upper devonian lennard shelf carbonate system canning basin western australia abstract here we report four high resolution carbon isotope records in addition to trace element data for the frasnian famennian f f boundary interval in the lennard shelf carbonate system of the canning basin western australia this region lacks the characteristic black shale horizons associated with the global late devonian kellwasser extinction events yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world two positive 13c excursions with 3 4 amplitudes enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity given the continuous and stratigraphically expanded nature of lennard shelf sections together with high density sampling constrained by both conodont biostratigraphy and magnetostratigraphy we observe that the upper kellwasser isotope excursion maximum 13c values and associated trace element enrichments occur distinctly lower than the f f boundary level these results have implications for the paleoenvironmental conditions leading up to the late devonian mass extinction in terms of ocean chemistry and circulation patterns this data set allows for a rare detailed look at the temporal relationship between the kellwasser events and the f f boundary and constrains the pattern of carbon isotope perturbations at the intra zonal scale

the sis palaeovalley a record of proximal fluvial sedimentation and drainage basin development in response to pyrenean mountain building the sis conglomerate body represents the middle eocene to oligocene transfer zone trunk palaeovalley fill of the sis fluvial system a drainage system established within the pyrenees during late palaeocene times the spatial stability of the fluvial transfer zone active for at least 38 my and hence the longevity of its aggradational palaeovalley component 19 5 my was controlled by its location between long lived pre existing structures coarse grained fluvial facies dominate the palaeovalley fill with alluvial fan facies shed from its defining marginal structures the detailed sedimentology of very proximal fluvial facies deposited within the dominantly erosional realm of an active mountain belt has rarely been documented before because of their poor preservation potential the sis conglomerate body contains a robust internal stratigraphy with stratigraphic units defined by distinct bounding surfaces across which there are pronounced changes in facies and provenance these mark the reorganization of the headward portions of the sis fluvial system during the evolution of the pyrenean axial zone antiformal stack major changes in discharge resulted demonstrating the highly variable nature of even mountain belt scale fluvial systems when viewed on timescales of several to tens of millions of years provenance details indicate that initial unroofing of hercynian granitoids situated within the pyrenean axial zone occurred around 54 5 ma early ypresian immediately before the first significant exhumation event within the drainage basin of the sis fluvial system this is earlier than previously constrained by apatite fission track studies rock uplift accelerated in the lutetian and bartonian with the initial aggradation of the palaeovalley fill the cajigar and cornudella formations and sis one and two members this became marked in the priabonian sis three and four members with significant activity on local structures including the morreres backthrust an increase in basement derived clasts and a headwater decapitation event also indicate pronounced axial zone antiformal stack development at this time axial zone development intensified further in the oligocene with the deposition of the collegats formation and the switch in the main depositional loci of the system from the tremp graus thrust sheet top basin to the ebro basin to the south

carbon chemostratigraphy of the cambrian ordovician transition in a midlatitude mixed platform montagne noire france the cambrian drumian carbon isotope excursion dice and the steptoean positive carbon isotope excursion spice have been so far reported in subtropical platforms the dice event is a large negative excursion in 13ccarb record that nearly coincides with the beginning of the drumian cambrian series 3 whereas the spice event is a large positive shift in 13ccarb identified close to the base of the paibian furongian series the chemostratigraphic excursions have been recognized in carbonate dominated platforms and their application to mid and high latitude siliciclastic dominated platforms has been problematic this paper offers for the first time a high resolution stratigraphic analysis of this time span in a temperate water platform montagne noire france that recorded episodes of carbonate productivity in nearshore environments two sections were analyzed in detail a complete cambrian series 3 tremadocian succession devoid of carbonate interbeds and paleogeographically located in the distal part of the platform pardailhan nappe and a furongian tremadocian succession which has limestone interbeds and represents the proximal part of the platform minervois nappe the lower part of the la gardie formation in the pardailhan nappe displays background 13corg values of 22 punctuated by a large negative middle languedocian regional substage shift peaking at 24 5 this negative excursion is similar to the dice event reported close to the base of the drumian although the latter is exclusively based on 13ccarb values stable isotopes of 13ccarb and 13corg from both sections also indicate a common chemostratigraphic shift at the onset of the furongian in nearshore deposits of the minervois nappe the 13ccarb background values for the interbedded limestone strata of the val d homs formation gradually increase from 3 to 1 and are punctuated by a sharp increase in 13ccarb values to 3 0 by contrast in basinal shales of the la gardie formation in the pardailhan nappe the 13corg background values decrease from 22 to 27 1 this trend is directly controlled by total organic carbon toc contents and is interpreted to have been initiated by changes in the degree of biodegradation of organic matter sulfate reduction and methanogenesis before or soon after burial despite this overprinting and the very low degree of metamorphism reached by the shales the 13corg background trend is also punctuated by a sharp positive shift in 13corg values to 4 0 similar to the spice event in addition the asymmetric shape of the spice excursion in the montagne noire shows evidence for the herb event a late furongian negative carbon isotope excursion not yet accepted as a worldwide chemostratigraphic anomaly the recognition of both chemostratigraphic shifts in mixed and clayey strata opens new possibilities of chemostratigraphic correlation in mid and high latitude platforms where carbonate factories did not widely develop and strata only contain endemic fauna this implication has a major consequence because the global stratotype section and point gssp of the drumian and paibian stages occurs near the base of both excursions

high primary productivity during the ediacaran period revealed by the covariation of paired c isotopic records from south china abstract remarkable carbonate carbon isotope 13ccarb excursions accompanied by invariant organic carbon isotope 13corg values have been observed in many late neoproterozoic successions this decoupled relationship between 13ccarb and 13corg in the precambrian differs from most phanerozoic records which have been substantially imprinted by aqueous photosynthesis and it has been tentatively interpreted as resulting from exotic organic matter inputs or diagenesis in this study we present high resolution 13corg records in combination with previously published 13ccarb data from a continuous drill core from the yangtze platform of south china the studied interval spans the cryogenian nantuo formation the ediacaran doushantuo and dengying formations and the base of the cambrian yanjiahe formation the 13ccarb profile of this drill core can be reliably correlated with contemporaneous sequences and it reveals multiple negative 13ccarb excursions associated with phosphorite deposits intriguingly the 13corg profile exhibits a co varying trend with the 13ccarb profile and the coupled relationship between 13ccarb and 13corg is rare in geological records of the precambrian the 13corg values of the drill core vary from 22 13 to 34 12 and the overall isotopic difference 13ccarb org between 13ccarb and 13corg ranges between 19 61 and 34 58 most of the 13corg and 13ccarb org data can be interpreted in terms of oxygenic photosynthesis probably mainly by eukaryotic algae however it is possible that exotic organic matter most likely doc from the deep ocean may also have contributed to the sedimentary organic matter composition of specific intervals studied herein moreover high primary productivity in shallow water may have been sustained for a long period in phosphate rich conditions and the organic matter generated by photosynthesis may have been quantitatively sufficient to overwhelm the doc buffering effect in the total 13corg signal throughout the ediacaran period the enhanced burial of organic matter in sediments would gradually result in the accumulation of oxygen both in the ocean and atmosphere which would likely have paved the way for macroscopic animal evolution

new records of ediacaran acraman ejecta in drillholes from the stuart shelf and officer basin south australia new occurrences of the acraman impact ejecta layer were recently discovered in two south australian drillholes scyw 79 1a stuart shelf and munta 1 officer basin using lithostratigraphy acritarch biostratigraphy carbon isotope stratigraphy and biomarker anomalies to predict the stratigraphic position the ejecta layer is conspicuous because it consists of pink sandsized angular fragments of volcanic rock distributed along the bedding plane surface of green marine siltstone in scyw 79 1a it forms a layer 5 mm thick in munta 1 the ejecta layer is thin and discontinuous because of its distance 550 km from the impact structure palynological biomarker and carbon isotope anomalies can now be shown to coincide with the ejecta layer in scyw 79 1a and munta 1 suggesting the acraman impact event may have had far reaching influences on the rapidly evolving ediacaran biological and geochemical cycles

carbon isotope record of late cambrian to early ordovician carbonates of the argentine precordillera a more than 2000 m thick cambrian ordovician carbonate platform succession developed on the exotic argentine precordillera terrane during rifting from laurentia and drifting towards gondwana on base of these carbonates a carbon isotope curve could be developed for the cambrian ordovician we measured 13ccarb and 13corg values on bulk rocks selected components and diagenetic cements whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis most subtidal carbonates exhibit primary marine values we can report reliable curves for the middle late cambrian transition and for the latest cambrian to earliest middle ordovician the 13c curve matches well with the published data from global cambrian ordovician boundary sections excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy this indicates the interdependence on sea level which rules the productivity and or preservation of organic carbon and therefore the partition between corg and ccarb burial

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

the variscan geology of the pyrenees abstract the main outlines of the geology of the variscan part of the pyrenees are discussed rocks involved in this cycle are high grade basement gneisses palaeozoic sediments and their metamorphic equivalents late intrusive granodiorites and early pre variscan granites the main features of the stratigraphy of the palaeozoic are given structures fall into two domains a low grade suprastructure essentially with steep folds and cleavages and a high grade infrastructure with dominantly low dipping foliations an important phase of early pre cleavage folding occurs in low grade rocks mainly along the southern border of the axial zone in high grade rocks most structures and the metamorphism postdate the main cleavage phase in low grade rocks the influence of the alpine orogeny on the variscan structures consists mainly of faults steep reverse faults in the northern and south directed thrusts in the southern part of the pyrenees metamorphism took place under high geothermal gradients and low pressures as indicated by the abundant occurrence of andalusite and cordierite

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

depositional setting and paleoenvironment of an alatoconchid bearing middle permian carbonate ramp sequence in the indochina terrane abstract a middle permian carbonate sequence at khao somphot in the south of the khao khwang platform has been measured and analyzed this sequence is characterized by prolific fossil content and large bizarre alatoconchid bivalves nine major microfacies types are differentiated and consist of algal foram facies fusuline facies alatoconchid facies lime mudstone wackestone facies laminated bindstone facies fine grained cortoid grainstone facies coral biostrome facies crinoidal packstone facies and carbonate breccia conglomerate facies laminated bindstone lime mudstone with fenestral fabric and algal foram facies represent loferites deposited in a restricted intertidal zone of an inner ramp fusuline grainstone and cortoid grainstone facies indicate sand shoals of an inner ramp the fusuline wackestone packstone and alatoconchid facies were deposited in a subtidal below fair weather wave base environment in the mid ramp the crinoidal facies which overlies collapse breccia possibly accumulated during transgression in the deeper part of the mid ramp storm deposits are prevalent throughout as thin accumulates and as alatoconchid floatstone rudstone coquinite layers and are common in mid ramp setting the khao khwang platform probably evolved from a rimmed platform in the early permian to a ramp in the middle permian the general trend of 13c composition from both brachiopod shell and rock matrix from the lower part of the study section wordian is significantly high moreover the 13c signature from this interval is up to 8 vpdb which suggests high productivity on the tropical tethyan shelf of the indochina terrane an abrupt negative shift in 13c in the late wordian and late capitanian indicating significant changes in paleoenvironment productivity and the carbon cycle is probably contemporaneous with the kamura event recorded from sediments of the mid panthalassa ocean in japan and elsewhere related to global cooling and a sea level lowstand

bathymetry and productivity of the southern great basin seaway nevada usa an evaluation of isotope and trace element chemistry in mid carboniferous and modern brachiopods abstract the stable isotope and trace element chemistry of brachiopods from stratigraphically paleontologically and geochemically three coeval intervals about the mid carboniferous boundary in the bird spring formation were evaluated for their potential of serving as proxies of bathymetry and productivity of the southern great basin seaway an eastern arm of the panthalassa ocean oxygen isotopes delineate both spatial and temporal differences in values of brachiopods from the three coeval mid carboniferous sections based on pristine brachiopod 18 o values and supported by paleoecological information water depth increased from apex to kane springs wash east to arrow canyon in addition there is also an increase in values from the latest mississippian to the earliest pennsylvanian suggesting a water temperature cooling a water depth increase and or change in both of the habitat of the penecontemporaneous brachiopods analogous to values and trends observed in modern brachiopods the fe mn ratio of fossil counterparts may be a potential proxy of seawater productivity related to the micronutrient iron overall the high ratios of fe mn suggest highly productive waters for the southern great basin seaway with somewhat reduced productivity during the earliest pennsylvanian in contrast the carbon isotope values of the coeval material are relatively invariant with respect to productivity trends similar to observations on modern carbonate allochems based on habitat and paleogeography the antler orogenic highlands west of the foreland basin are considered a potential source for the micronutrient iron enrichment of the carbonate platform shelf edge environment it is further postulated that upwelling currents in part which weakened from the latest mississippian through to the earliest pennsylvanian may have transported the micronutrient iron onto the shelf basin environments of the bird spring formation of the southern great basin

seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the toarcian early jurassic in central and northern spain comparison with other european sections the early toarcian mass extinction marks one of the critical events in the history of the earth many of these events have been linked to important climate changes two sections of the toarcian showing high resolution ammonite based biostratigraphy are studied in central and northern spain stable isotope datasets based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates allowed the construction of 13c curves and a 18o based palaeotemperature comparison of the extinction pattern with other sections in europe and northern africa shows that the early toarcian mass extinction boundary occurred at the tenuicostatum serpentinum transition and that the organic rich facies linked to the oceanic anoxic event and the associated negative 13c excursion are diachronous from a latest pliensbachian cooling interval a first increment of seawater temperature averaging about 4 5 c started around the pliensbachian toarcian boundary and developed during the earliest toarcian tenuicostatum biochron marking the beginning of the main extinction interval from the tenuicostatum serpentinum transition up to the bifrons biochron a rise in seawater temperature averaging 5 7 c to 7 8 c was recorded this warming interval which started rapidly and which seems to be synchronous at least in western europe is considered one of the main factors responsible for mass extinction for some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere but it does not seem to be recorded in belemnite calcite and the origin of these possible gases is largely debated in the literature additional isotope excursions were found in the studied sections in spain during the middle and late toarcian a negative 13cbel excursion has been recorded at the latest bifrons biochron above this shift the illustris vitiosa subzones thermal peak which represents a 2 3 c t could be linked to one of the tectonomagmatic activity peaks recorded in the karoo basin a renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in nw europe and western tethys an interesting thermal peak has also been detected in belemnites of the insigne subzone t is in the order of 3 c and in both sections the thermal peak is included into a 13cbel negative excursion of about 1 5 relative synchrony with the new age for the karoo main magmatic activity 178 180 ma indicates that the 13c negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases at this short interval noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of nw europe and tethys are observed the uppermost levesquei subzone thermal peak has only been recognized in the deposits of the section located in central spain and coincides with a positive 13c excursion

the significance of garnet in the permo carboniferous volcanic rocks of the pyrenees garnet occurs within rhyolitic to dacitic lavas ignimbrites and volcaniclastic sediments of the pyrenean calc alkaline permo carboniferous volcanic rocks on the basis of texture and major and trace element composition the garnet is interpreted as having a phenocrystal as opposed to a xenocrystal or restite origin the pyrenean silicic volcanics are strongly peraluminous consistent with derivation as a partial melt from a sedimentary source they were erupted contemporaneously with the hercynian thermal anomaly which produced regional granulite facies metamorphism and anatectic granites the late hercynian granodiorites were also intruded at about this time geochemical data suggest that the petrogenesis of the volcanic rocks differed from that of the granodiorites ree garnet matrix partition coefficients for garnets from a welded rhyolitic ignimbrite are similar to those reported for other phenocrystal garnets in rhyolites ree abundances imply that the garnets crystallized from a hree depleted melt and this is considered to reflect the effects of garnet in the restite experimental constraints suggest that the garnet crystallized at pressures 4 5kb implying that the rhyolites originated from 14 17km depth and were erupted rapidly from these depths in order for the garnet to survive these figures place constraints on the thermal regime prevailing in the late stages of the hercynian orogeny

intraseasonal variability of katabatic wind over east antarctica and planetary flow regime in the southern hemisphere the intraseasonal variation 30 to 50 day period of katabatic wind has been found at mizuho plateau east antarctica as a predominant mode of the subseasonal time scale variability the atmospheric circulation in the southern middle and polar latitudes associated with this fluctuation of katabatic wind has been deduced by using the nmc gridded 500 mbar zonal wind and geopotential height field the axisymmetric circulation pattern to antarctica is noticeable in the anomalous zonal wind and height field that is the strong weak katabatic wind phase corresponds to the shallower and broadened deepened and narrowed tropospheric circumpolar vortex with weaker stronger westerlies over the surrounding oceans these results strongly suggest that the intraseasonal variation of katabatic wind regime over east antarctica is part of the modulation of planetary flow regime and meridional circulation in the southern middle and high latitudes i e part of the index cycle of the southern hemisphere

local controls on carbon cycling in the ordovician midcontinent region of north america with implications for carbon isotope secular curves abstract the carbon isotope record from ancient epicontinental seas may contain much more of a local scale carbon cycling signal than is generally appreciated a unique opportunity exists to examine this issue in the case of the late ordovician mohawkian sea of eastern laurentia where the millbrig k bentonite stratigraphic framework has been used to delineate a time slice at 454 ma extending over 1 500 000 km2 of the eastern united states across the time slice carbonate and organic carbon 13c vary by 4 5 and 7 5 respectively a spatial variation that is as large as temporal secular changes in epeiric sea 13c that have been reported in the past these new data are considered in the context of geographic variations in lithological biological and other geochemical sediment characteristics collectively these sediment properties distinguish regions of the mohawkian sea which likely differed in terms of the nature and relative importance of carbon cycling processes water column depth and structure and barriers to free exchange of water across the mohawkian sea may have been overarching factors in the development of these regions raising the possibility that changes in circulation patterns such as those caused by sea level change played a role in driving secular carbon isotope excursions by changing the rate of exchange of dissolved inorganic carbon between water masses if the observed effects of local carbon cycling on the distribution of mohawkian sea 13c were commonplace in ancient epicontinental marine environments it would imply that local scale carbon cycling may have left a nontrivial imprint on epeiric sea records of secular variations in 13c in addition to the imprint left by changes in the global carbon cycle this may have contributed to the broad scatter in 13c values observed in the paleozoic portion of the global carbon isotope secular curve

uranium depletion across permian triassic boundary in persian gulf and its implications for paleooceanic conditions abstract high resolution uranium analyses as well as oxygen carbon and strontium isotopes data through permian triassic boundary ptb in the marine sections of three offshore wells in persian gulf are illustrated in this paper a decreasing trend in u content from upper permian strata toward the ptb is recorded in all wells such a trend could not be adequately explained by the facies changes diagenetic events salinity variations dolomitization or total organic carbon toc content of the samples distinct and negative uranium anomalies coincide with the onset of the carbon isotope shifts which might indicate influx of anoxic waters the th u ratios below the ptb in the studied sections are mainly less than 2 reinforcing this possibility reducing conditions associated with the anoxia would have gradually increased the rate of u fixation on the deep sea floor resulting in low u concentration in the shallow water carbonates a negative 18o shift of about 4 could be seen at the ptb in all studied wells such excursion indicates a meteoric diagenesis below the boundary also abnormally higher 87sr 86sr ratios below the ptb indicate significant input of radiogenic 87sr during subaerial exposures at the end of permian this palaeoexposure surface is also reflected in depleted oxygen isotope values of this interval biostratigraphic studies also show that some important guide forms of late permian are absent in studied wells that could be due to several factors including non sedimentation subaerial exposure and erosion thus a near surface meteoric realm or emergent surface could be considered for the ptb in studied wells

pacific miocene carbon isotope stratigraphy using benthic foraminifera abstract seven miocene pacific ocean deep sea drilling project sites from four different water masses planktonic foraminiferal biogeographic regions have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal 13c records in dsdp site 289 the correlations are based on the assumption that there are global or at least pacific wide controls on the 13c of deep water hco3 each of the individual 13c records is correlated to site 289 based on the shape of the curves in a manner analogous to that used to correlate sea floor magnetic anomaly patterns the results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to 100 000 years correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than 200 000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized globally applicable correlation tool with an interregional precision of 100 000 years or better as more continuous and undisturbed deep sea sections become available as a result of the hydraulic piston coring program

geochemical record of late devonian to early carboniferous events palaeozoic of graz eastern alps austria the late famennian mass extinction has been associated with a worldwide anoxic event evidenced at many sites by the accumulation of organic rich shales starting prior to the devonian carboniferous d c boundary environmental reconstructions are hampered by the fact that only a few d c boundary sections exist in carbonate facies one of these is the palaeozoic steinberg section eastern alps austria based on detailed geochemical investigations and correlation with previously investigated sections we propose a succession of events from the late famennian to the tournaisian both the low total rare earth element ree contents and the normalized ree distribution patterns indicate low terrigenous input from the praesulcata zone to the typicus zone the dc do ds and total organic content toc show a shift towards higher values which correlates well with the late famennian isotopic trends that are related to a period of active ocean circulation cooling and increased productivity two isotopic shifts are present in the section the older isotopic shift of the dc values is situated at the level of the lower to middle praesulcata zone while the younger one is found at the level of the upper praesulcata zone in the sulcata zone a sharp decrease in do values and a shift in the ce anomaly follow concomitantly a drop in the dc and ds values highly variable toc values and the main and secondary element concentrations are interpreted to be related to a drop in primary productivity with the recovery continuing in the crenulata zone in this context the variations towards lower cao sr rb and ba values probably correlate with biomass variations and a transition from cooler towards warmer conditions the mass extinction that occurred prior to the devonian carboniferous d c boundary was the sixth largest extinction of the phanerozoic sepkoski 1996 it mainly affected pelagic and hemipelagic organisms e g conodonts ammonoids echinoderms trilobites ancient agnathan and placodermian fishes continental plant communities and to a lesser extent shallow marine ostracods foraminifera and corals paproth streel 1984 flajs et al 1988 becker paproth 1993 simakov 1993 becker 1994 sepkoski 1996 streel et al 2000 a short time after the extinction there was a phase of radiation and biotic innovations caplan bustin 1999 streel et al 2000 this phase was characterized by the diversification of certain groups of organisms such as tetrapods walliser 1996 subsequent palaeontological advances have shown that changes in different groups of marine organisms and terrestrial plants are not synchronous streel et al 2000 the late famennian is characterized by the occurrence of a grey shale level and sometimes black shales known as hangenberg shale after a locality in the rheinisches schiefergebirge germany schmidt 1924 the hangenberg shale shows variable lithology with the black shale not always occurring at the base bless et al 1988 worldwide the d c sections display similar lithoand biostratigraphy consisting of a lower cephalopod limestone shale and an upper cephalopod limestone walliser 1984 although there is little agreement on the estimation of the absolute age of the d c boundary gradstein et al 2004 and references therein the shales appear even when the famennian strata occur in carbonate ramp settings or are situated at lower latitudes walliser 1984 caplan et al 1996 the position of the d c global boundary stratotype has been defined at the first appearance of the conodont siphonodella sulcata within the evolutionary lineage from from g siewicz a slowakiewicz m eds palaeozoic climate cycles their evolutionary and sedimentological impact geological society london special publications 376 http dx doi org 10 1144 sp376 15 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on september 20 2013 http sp lyellcollection org downloaded from

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

the south pyrenean eocene carbonate megabreccias revisited new interpretation based on evidence from the pamplona basin abstract the south pyrenean foreland basin contains numerous units of eocene carbonate megabreccias intercalated with siliciclastic turbidites and derived by resedimentation of shallow marine carbonate platforms previous studies were limited mainly to the foreland eastern part known as the jaca basin the present study from the pamplona basin a western part of the foreland trough sheds new light on the origin and regional significance of these south pyrenean eocene carbonate megabreccias specms the number of the specm units in the foreland basin is higher than previously recognized and their age is somewhat older than originally assumed the specm units appear to occur as time stratigraphic clusters which can be correlated with the relative sea level lowstands and linked with phases of tectonic activity the megabreccias were derived from a carbonate platform system hosted by the foreland basin s southern passive margin the episodic instability and mass wasting were triggered by phases of structural steepening forebulge uplift accompanied by high magnitude earthquakes with the former causing platform emergence increased load stresses and excess pore water pressure in the carbonate ramp the specm deposits were emplaced by cohesive debris flows evolving into high density turbidite currents an ideal specm unit consists of 1 an immature homogeneous debrite in the proximal part 2 a differentiated bipartite debrite and turbidite in the medial part and 3 an incomplete base missing debrite overlain by turbidite or a turbidite alone in the distal part the debrite component volumetrically predominates in the specm units and the original terms megaturbidite and seismoturbidite thus seem to be inappropriate for these deposits

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

anoxia as a cause of the permian triassic mass extinction facies evidence from northern italy and the western united states facies faunal and geochemical evidence from the permian triassic boundary sediments of the dolomites and idaho indicates a major anoxic event in the earliest triassic in both regions the basal beds consist of finely laminated micrites with common syngenetic pyrite the only fauna consists of occasional bedding plane assemblages of lingula or clacaria a typical lower dysaerobic assemblage this is a level where previous studies have shown a major negative carbon isotope excursion and a cerium anomaly in the dolomites the pyritic micrite directly overlies strata containing a diverse and typically permian marine fauna of algae foraminifers including fusulinids and articulate brachiopods implying an abrupt extinction in contradiction to many previous views sequence stratigraphic analysis of the dolomite boundary sediments reveals a minor sequence boundary in the late permian followed by extremely rapid transgression leading to the development of the relatively deep water pyritic micrite a maximum flooding surface at the permo triassic boundary a further pulsed deepening in the lower griesbachian recorded in both the dolomites and idaho lead to the widespread establishment of dysaerobic facies it is clear that most of the extinctions occurred at the erathem boundary although the subsequent failure of the marine benthos to fill the empty ecospace in the ensuing griesbachian may have been due to the widespread development of dysaerobic conditions

isotopic chemostratigraphy across the early middle frasnian transition late devonian on the south polish carbonate shelf a reference for the global punctata event abstract the coupled high resolution carbon isotope data from whole rock limestone and organic matter samples of the transitans early frasnian punctata and the earliest hassi zones middle frasnian from the south polish carbonate shelf successions reveal the presence of a large multi part 13 c excursion one of the largest known carbon cycle disturbance of devonian period this early middle frasnian e mf 13 c perturbation consists of two positive excursions a minor event i and a major event iii and two negative shifts events ii and iv the major positive excursion up to 5 begins near the e mf boundary and the onset of middlesex transgressive anoxic event the latter broader scale positive 13 c perturbation correlates with the worldwide punctata event documented across eastern and western laurussia as well as northern gondwana the large magnitude of the punctata isotopic event paired with negligible biotic effects is similar to the silurian biogeochemical perturbations but contrasts markedly with the younger kellwasser events the distinctive protracted about 1 ma e mf 13 c variations may be only partly explained by escalated sea water exchange between epeiric seas and the anoxic open ocean during successive transgressive pulses very high 13 c plateau values of the punctata event correspond to a positive 87 sr 86 sr shift as well as elevated clastic input proxies and magnetic susceptibility suggesting altogether that delivery of tectonically promoted land derived nutrients to marine basins was a key factor stimulating the biogeochemical perturbation extreme increases in primary productivity and enhanced organic matter burial in restricted deeper basinal settings would promote a gradual drawdown in surface water as well as atmospheric p co 2 and consequently a climatic cooling by 5 c as indicated by the high resolution 18 o phosphate record

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

paleoenvironmental and paleoecological implications of permian guadalupian radiolarian and geochemical variations in the lamar limestone delaware basin west texas usa abstract geochemical proxies integrated with well preserved radiolarian data from the lamar limestone and lower part of the reef trail member of the bell canyon formation provide insights into paleoceanographically and climatically driven controls on radiolarian distribution in the northern part of the delaware basin of west texas during late guadalupian time data from a section of the lamar limestone 8 9 m 500 kyr interval indicate that major variations between sphaerellarian dominated and follicucullus dominated faunas appear to be controlled by fluctuations in nutrient supply and salinity geochemical parameters of bulk carbonate carbon and oxygen isotopes 13 c carb and 18 o carb organic carbon isotope 13 c org and total organic carbon toc were analyzed and show variations on two scales on a fine scale sphaerellarian dominated beds are associated with a relatively siltier lithology higher toc and higher radiolarian richness but lower diversity and are interpreted as the result of a rise in productivity stimulated from increased terrestrial input the radiolarian variations and geochemical evidence imply that the permian spongiose spumellarians are more opportunistic than follicucullus albaillellids in response to eutrophication on a broad scale 18 o carb variations in limestone samples are interpreted mainly as a proxy for paleosalinity in response to changes in basin circulation mg ca ratios from the carbonate fraction co vary with 18 o carb and are used as an additional paleosalinity proxy in this basin the limestone beds in the middle part of the section have lighter 18 o carb values compared to limestone beds above and below and likely represent the interval when the delaware basin was less restricted and had relatively normal marine salinity impacts of diagenesis are mild but are likely the cause for systematically light 18 o carb values in silty limestone beds in the middle interval the mg ca ratios and 18 o carb values in the limestone samples both increase from the middle to the top of the section implying a gradually enhanced evaporitic environment coupled with increased salinity towards the top section collectively these data paint a picture of intermittent restriction in the delaware basin prior to the change to a dominantly evaporative regime in the late permian and on a finer scale show pronounced and frequent ecological fluctuations that appear to be driven by fluxes in terrestrial input and to some extent paleoproductivity

a new middle to late eocene continental chronostratigraphy from ne spain abstract the calibration of the european paleogene mammal biochronology with the international reference geochronological scale is unconstrained due to the lack of direct marine continental correlations and insufficient robust magnetostratigraphic data for mammal fossil bearing sequences the currently accepted european continental biochronology argues for a correlation of the paleogene mp14 to mp16 mammal reference levels with the bartonian stage and of the mp17 to mp20 levels with the priabonian however new magnetostratigraphic data of the continental sediments of the south central pyrenees substantially challenge this chronology our new results from the la pobla de segur basin and sierra de sis have been integrated into the framework of previous marine continental stratigraphic correlations and magnetostratigraphic data of the south central pyrenees in this new chronology mp14 and mp15 reference levels correspond to the lutetian whereas mp16 and early mp17 correlate with the early bartonian this calibration represents a significant revision of currently accepted marine continental correlations in europe but is not in conflict with the available biostratigraphic data of the south pyrenean ebro foreland basin and other western european reference basins

chemostratigraphy and magnetic susceptibility of the late devonian frasnian famennian transition in western canada and southern china implications for carbon and nutrient cycling and mass extinction we investigate the late devonian frasnian famennian extinction interval in western alberta and south china to shed light on the palaeoecological and palaeoceanographic conditions that characterize this biotic crisis both the lower and upper kellwasser events are documented in western canada only the upper kellwasser event has been evaluated in south china our multi proxy geochemical approach reveals that these events are characterized by positive d 13 c and d 15 n excursions and increasing magnetic susceptibility canada china and increases in detrital al si ti zr productivity cu ni zn and redox mo u v elemental proxies canada we interpret these trends as part of a systemic palaeoecological shift associated with the development of wide spread terrestrial forests and their alteration of chemical mechanical weathering patterns increase in detrital proxies is thus interpreted as resulting from pedogenically driven weathering on the con tinents that nutrified epeiric and continental margin seas high biological productivity led to eutro phication and development of suboxic to anoxic conditions during both events and probably euxinic conditions during the upper kellwasser event in western canada positived 13 c excursions are the telltale signature of excessive carbon burial while redox proxies and d 15 n records indicate

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

a unique geochemical record at the permian triassic boundary a 330 metre core drilled through the marine permian triassic boundary in the carnic alps of austria allows closely correlated studies of geochemistry petrography and palaeontology across the boundary the isotope shifts and metal concentrations are extended multiple and complex and do not resemble those seen at the cretaceous tertiary boundary both the carbon isotope shifts and the chemical events including an indium anomaly may have causes related to a major regression of the sea

carbon oxygen isotope signal of mississippian slope carbonates appalachians usa a complex response to climate driven fourth order glacio eustasy abstract mississippian chesterian ramp slope muds in virginia deposited on the margin of a rapidly subsiding foreland basin were not significantly reset isotopically by regional meteoric aquifer systems that affected units on the adjacent platform carbon and oxygen isotopic ratios of these muds tend to covary at the scale of the twelve 4th order sequences that dominate the platform succession the 13 c values of the slope muds range from 0 5 to 4 pdb and lie in the range of least altered contemporaneous brachiopods from north america indicating little resetting of carbon isotopes by diagenesis there is an approximately 1 to 2 decrease in 13 c in the maximum flooding zone relative to the lowstand followed by a positive shift upward in the highstand before becoming more negative toward 4th order correlative conformities meteoric diagenesis might have reset some sediments just beneath a sequence boundary to lighter values it cannot account for the observed shifts evident throughout the sequences the 13 c enriched values in 13 c profiles could be due to increased productivity during glacial stages the increased productivity during glacial stages was probably due to increased ocean circulation coupled with shallowing which brought the ramp top into waters with more 13 c enriched dissolved inorganic carbon with the opposite effects occurring during deglaciation the 18 o values of muds range from about 2 2 to about 4 6 pdb falling within and beyond the lighter part of the range of contemporaneous north american brachiopods mii h s grossman e l yancey t e 1999 carboniferous isotope stratigraphies of north america implications for carboniferous paleoceanography and mississippian glaciation geol soc am bull 111 960 973 these values likely have been reset by burial diagenesis and perhaps by some meteoric diagenesis just beneath correlative conformities the sequences show negative excursions of 1 to 2 in 18 o in the maximum flooding zone relative to the lowstand and then become more positive upward in the highstand then decrease toward the correlative conformities some of the preserved signal could reflect ice volume changes although this would account for only 0 5 to 1 change the ice volume effect during lowstands plus cooling of ramp top waters and small increases in salinity due to increased aridity in the appalachian basin could account for the remaining 0 5 to 1 5 of oxygen isotope excursions with the opposite effect occurring during high sea levels the 18 o and 13 c of the appalachian ramp slope facies lack the strong 3rd order trends of the mid continental united states and europe the remnant 4th order carbon and oxygen isotope signal is similar in structure to cenozoic deep sea isotope profiles that are due in large part to 4th order glacio eustasy this would be compatible with onset of late paleozoic glaciation of gondwana

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

carboniferous permian carbon isotope stratigraphy of successions from china yangtze platform usa kansas and russia moscow basin and urals abstract the pennsylvanian and early permian were times of extreme sea level changes of 100 to perhaps up to 200 m for example glacio eustatic sea level changes are well documented from the us midcontinent moscow basin and yangtze platform where more than 100 stacked subtidal to supratidal sequences have been described in contrast carbonates developed in the ural mountains and south guizhou of the yangtze platform were deposited in ramp and slope settings 13c values of whole rock samples from the us midcontinent and moscow basin were intensively affected by diagenesis only well preserved brachiopod shells maintained their original carbon isotope ratios in contrast limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios mean 13c values of slope carbonates of the yangtze platform increase from about 3 during the visean and serpukhovian to 5 at the carboniferous permian boundary and decrease to values around 2 in the early kungurian this positive 13c excursion coincides with low 13c values in the yangtze platform successions which were reset by meteoric diagenesis the highest 13c values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea level lowstands short lived but significant negative 13c excursions in the chinese slope succession are interpreted to reflect changes in ocean circulation due to sea level rises which caused enhanced production and or preservation of organic matter which influenced the subsequent early diagenetic cementation

continental scale simulation of the antarctic katabatic wind regime abstract katabatic winds are a common feature of the lower antarctic atmosphere although these drainage flows are quite shallow there is increasing evidence that the low level circulations are an important component in establishing large scale tropospheric motions in the high southern latitudes three dimensional numerical simulations of the antarctic katabatic wind regime and attendant tropospheric circulations have been conducted over the entire continent to depict the topographically forced drainage patterns in the near surface layer of the atmosphere results of the simulation enable a mapping of katabatic wind potential and identification of coastal regions which may experience anomalously intense katabatic winds a large upper level cyclonic circulation forms rapidly in response to the evolving katabatic wind structure in the lower atmosphere suggesting that the drainage circulations are an important component in prescribing the resulting resulting circumpolar vortex these results imply that som

does sedimentary organic δ13c record variations in quaternary ocean co2 aq ocean surface water co2 aq variations based on glacial interglacial changes in sediment delta 13corg are shown to compare favorably with reconstructions based on ice core co2 in particular an approximate 80 microatmospheres increase in atmospheric pco2 during the last glacial interglacial transition is calculated to correspond to a 3 4 micromolar increase in ocean surface water co2 aq at atmospheric equilibrium a widespread marine delta 13corg decrease of 1 2 accompanied this event and was not preceded by an equivalent isotopic change in surface water total dissolved inorganic carbon these observations support the hypothesis that co2 aq influences photosynthetic isotope fractionation between marine inorganic and organic carbon pools and therefore that plankton sediment delta 13corg may serve as a proxy for surface water co2 aq

stable isotope δ13ccarb and org δ15norg and trace element anomalies during the late devonian punctata event in the western canada sedimentary basin late devonian marine deposits in the western canada sedimentary basin were analyzed for 1 accumulations of bioproductivity and paleoredox trace element proxies and for 2 variations of 13c carb and org and 15norg in order to understand and interpret the regional history of the global yet short term punctata event geochemical perturbation statistical correlations suggest that changes in detrital input and associated micronutrient delivery were the main driver of a eutrophication event noted early and possibly also late in the punctata zone around the isolated miette platform manifested by increased toc positive 13c excursions and concurrent enrichments of all elemental proxies evaluation of data within a regional sequence stratigraphic perspective revealed a eustatic sea level influence with proxy accumulations associated mostly with early transgression iic1 deposition and preservation of organic matter rich facies occurred during conditions of enhanced primary production and facilitated bottom water suboxia anoxia following eutrophication lower 15norg and 13corg values predominated and persisted throughout much of the punctata zone before rebounding toward its close suggesting a time interval of environmental stagnation and lower overall productivity during which n2 fixing autotrophs may have had an ecological advantage under nitrate limited conditions the punctata event approximately coincided with the advent of archaeopterid forest expansion beginning around mid frasnian time which fundamentally altered the nature of continental weathering through extensive soil formation and increased nutrient delivery to the oceans this evolutionary event may have amplified the detrital influx already elevated by sea level lowstand and early transgression and increased denudation of rising mountain ranges in near equatorial regions

geochemical and organic carbon isotope studies across the continental permo triassic boundary of raniganj basin eastern india abstract organic carbon isotope and geochemical changes across a continental interior permo triassic boundary section from the raniganj basin india indicate a 9 drop in organic carbon 13c in the early triassic and synchroneity of this event throughout the pangea the study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes a global sea level fall and oxidation of marine gas hydrates possibly increased the 12co2 input in the ocean atmosphere system which caused a climatic shift from humid to warm semi arid type and consequent extinction of land plants simultaneous increase in erosion from near barren lands change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate no extraterrestrial source therefore is needed to explain this eu anomaly the response of the terrestrial plant community to this perturbation of the carbon reservoir was however sluggish and the 13c drop took place slowly being maximal in the early triassic only

contrasting sterane signatures in neoproterozoic marine rocks of australia before and after the acraman asteroid impact abstract organic matter preserved in marine mudstones from three late neoproterozoic depocentres the officer and amadeus basins and the adelaide fold belt was examined using standard microscopic and geochemical methods including gas chromatography mass spectrometry gc ms total organic carbon toc contents of these sediments are typically low

carbon isotope stratigraphy of lochkovian to eifelian limestones from the devonian of central and southern europe lower to middle devonian carbonates of the prague syncline the carnic alps the montagne noire and the cantabrian mountains were investigated for 13ccarb and 13corg these values were measured on bulk rocks selected components and cements many carbonates exhibit primary marine values but some are altered by diagenesis a 13c curve can be presented for the latest pridolian to emsian time interval several sharp or broad positive excursions are obvious in the woschmidti postwoschmidti sulcatus kitabicus late serotinus and kockelianus conodont zones the excursion at the silurian devonian boundary is known worldwide and therefore considered global in nature some of the others are described for the first time from central and southern europe and their global nature has to be verified by further investigations in other regions most excursions relate to and or started during major regressions whereas sea level highstands correspond to minimal 13c values similar relationships between sea level changes and 13c have been observed from other early palaeozoic intervals the transgressive chotec and kacak events are marked by positive isotope excursions this type of combination is usually observed in late palaeozoic to cenozoic black shale events

silurian records of carbon and sulfur cycling from estonia the importance of depositional environment on isotopic trends abstract the llandovery wenlock carbonate marl succession of the baltoscandian basin has been analyzed in the viki drill core western estonia for carbonate carbon 13 c carb organic carbon 13 c org carbonate associated sulfate 34 s cas and pyrite 34 s pyr isotopes along with trace element concentrations following the end ordovician glaciation and the hirnantian carbon isotope excursion 13 c carb values rise to an early llandovery carbon isotope maximum 2 subsequently 13 c carb and coeval 13 c org record a large 4 5 excursion in the early wenlock associated with a regression and biotic turnover known as the ireviken bioevent ibe overall 34 s cas values generally fall within a range 25 to 35 similar to that reported in other sections of comparable age two distinct trends are observed low and stable 34 s cas values are associated with deep water facies while 34 s cas becomes higher and more variable in the shallow water facies similarly 34 s pyr values are low and invariant 15 in deep water facies but become higher and more variable ranging between 35 and 16 in shallow water deposits despite abundant recrystallization no obvious evidence for large scale alteration of proxies is apparent in concentrations of fe sr mn and mg or in isotopic correlations although increased variability and lower values of 34 s cas are observed where cas abundance is low a large well resolved positive excursion in 34 s cas observed during the ibe from a time correlative section on gotland sweden is absent in the data presented here this difference demonstrates that counter to general understanding local environmental variations can give rise to divergent 34 s cas profiles in coeval sections the s isotope fluctuations in cas and pyrite in the viki drill core can be explained by local processes involving facies changes early diagenetic processes and associated open vs closed system behavior that can overprint and potentially mask basin or global signals

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

the influence of antarctica on the momentum budget of the southern extratropics the antarctic plateau acts as a strong heat sink for the global climate cooling the atmosphere and radiating energy to space a cold dense atmospheric boundary layer is formed strong surface winds are formed as the boundary layer drains off the plateau these drainage winds and the eddy fluxes necessary to maintain them are analysed in a general circulation model gcm the drainage flow is well represented in the gcm the associated mean meridional circulation is analysed in isentropic coordinates the momentum budget over antarctica reveals a balance between the eliassen palm flux convergence and the coriolis torque exerted by the mean meridional mass flux both vertical and horizontal components of the eliassen palm flux contribute the vertical component being the greater

carbon isotope composition of upper cambrian to lower ordovician carbonate in korea and its bearing on the cambrian ordovician boundary and lower ordovician paleoceanography abstract this study presents an example of locating cambrian ordovician boundary in the lower paleozoic carbonate succession in korea using carbon isotope stratigraphy the yeongweol unit of the lower paleozoic joseon supergroup comprises the upper cambrian wagok formation and the lower ordovician mungok formation in the cambrian ordovician transition interval conventionally the boundary was placed at the lithostratigraphic boundary between the two formations this study reveals that the boundary is positioned in the basal part of the mungok formation based on the carbon isotope stratigraphy coupled with biostratigraphic information of conodont and trilobite faunas the 13c curve of the lower ordovician mungok formation shows a similar trend to that of the coeval stratigraphic interval of argentine precordillera buggisch et al 2003 suggesting that the 13c curve of the mungok formation reflects the early ordovician global carbon cycle

late early triassic climate change insights from carbonate carbon isotopes sedimentary evolution and ammonoid paleobiogeography the late early triassic sedimentary facies evolution and carbonate carbon isotopemarine record 13ccarb of ammonoid rich outer platform settings show striking similarities between the south china block scb and the widely distantnorthern indianmargin nim the studied sections are located within the triassic tethyshimalayan belt losar section himachal pradesh india and the nanpanjiang basin in the south china block jinya section guangxi province respectively carbon isotopes from the studied sections confirm the previously observed carbon cycle perturbations at a time of major paleoceanographic changes in the wake of the end permian biotic crisis this study documents the coincidence between a sharp increase in the carbon isotope composition and the worldwide ammonoid evolutionary turnover extinction followed by a radiation occurring around the smithian spathian boundary based on recent modeling studies on ammonoid paleobiogeography and taxonomic diversity we demonstrate that the late early triassic smithian and spathian was a time of a major climate change more precisely the end smithian climate can be characterized by a warm and equable climate underlined by a flat pole to equator sea surface temperature sst gradient while the steep spathian sst gradient suggests latitudinally differentiated climatic conditions moreover sedimentary evidence suggests a transition froma humid and hot climate during the smithian to a dryer climate fromthe spathian onwards by analogywith comparable carbon isotope perturbations in the latedevonian jurassic andcretaceouswe propose that high atmosphericco2 levels could have been responsible for the observed carbon cycle disturbance at the smithian spathian boundary we suggest that the end smithian ammonoid extinction has been essentially caused by a warm and equable climate related to an increased co2 flux possibly originating froma short eruptive event of the siberian igneous province this increase in atmospheric co2 concentrations could have additionally reduced the marine calcium carbonate oversaturation and weakened the calcification potential of marine organisms including ammonoids in late smithian oceans