geochemical evidence for a catastrophic biotic event at the frasnian famennian boundary in south china a strong delta sup 13 c anomaly coincides with a weak ir anomaly at the frasnian famennian f f boundary exposed at xiangtian guangxi south china the maximum whole rock ir abundance is 0 23 ppb 0 35 ppb on a carbonate free basis compared with averages of 0 016 and 0 044 ppb above and below the boundary interval the delta sup 13 c in carbonate abruptly shifts from a late frasnian level of about 1 per thousand to minus 2 49 per thousand in the boundary interval and then abruptly returns to pre boundary levels suggesting a temporary reduction of surface water biomass a widely distributed over at least several hundred kilometers limestone breccia unit of possible wave deposit origin is present directly below the boundary in south china enrichments of al v cr as and u and a dip in the mn abundance in the boundary interval indicate that reducing conditions might have been associated with the element enrichment however an alternative hypothesis is that oceanic impact s at the f f boundary near south china provided the excess ir and caused the biotic crisis and the formation of breccia deposits observed in the late devonian south china sea

quantitative conodont based approaches for correlation of the late devonian kellwasser anoxic events we present the trends of absolute conodont abundance relative genera abundance and conodont morphometrics across the late devonian kellwasser horizons at three northern gondwanan epicontinental seaway locations at three contrasting depositional settings the kellwasser events are characterized by a decrease in conodont abundance high percentage of the conodont genus icriodus and morphological change of the conodont genus palmatolepis these changes can be identified in sections where the events are expressed as interbedded anoxic and oxic deposits as well as in settings characterized by continuous anoxic sediment accumulation hence these changes are interpreted as global and synchronous and can be thus used for event correlation the paradox of these results is that despite quite similar isotopic signals faunal change during the lower kellwasser event was less than during the upper kellwasser event we interpret that this discrepancy is due to an unconformity including topmost frasnian to earliest famennian at several f f sections which removed the record of peak paleoenvironmental change

stratigraphy and paleoenvironmental analysis of the frasnian famennian upper devonian boundary interval in tioga north central pennsylvania abstract two pulses of extinction in the late frasnian late devonian the lower and upper kellwasser lkw and ukw events coincided with the deposition of organic rich strata in many parts of the world including the appalachian basin here we describe two stratigraphic sections from tioga north central pennsylvania that span the frasnian famennian f f boundary interval the f f boundary and ukw equivalent strata are probably located in the covered interval between the two sections but the lkw equivalent pipe creek formation is well exposed we propose several stratigraphic revisions including raising the lock haven formation to group status and dividing it into formations as well as redefining the base of the canaseraga formation and subdividing it into members paleoenvironments at tioga range from offshore outer shelf to middle shoreface a regression follows the lkw transgression as evidenced by the sharp superposition of middle shoreface sands on outer shelf mudstones similar to large facies changes associated with the lkw in other settings the lkw is typically interpreted as representing deposition under dysoxic anoxic conditions and trace and body fossil content suggest that the pipe creek formation represents dysoxic but not permanently anoxic conditions these stratigraphic revisions and records of environmental change will provide the framework for more detailed studies of the lkw and ukw extinction events in the appalachian basin

carbon isotope excursions and sea level change implications for the frasnian famennian biotic crisis new carbon and oxygen isotope data from carbonates spanning the frasnian famennian f f boundary in the guilin area south china show a broad positive 13 c rise and fall with sharp short lived negative 13 c events this pattern is comparable to that in europe and north america the integration of the isotope stratigraphy with high resolution sequence stratigraphy corroborates the onset of the positive 13 c excursion during a third order sea level fall in the latest frasnian this can best be explained through increased burial of c org during the sea level fall brought about by increased organic productivity caused by increased continent derived nutrient flux to the ocean due to enhanced weathering through the proliferation of land plants in the devonian this scenario would have resulted in anoxic and eutrophic conditions over epicontinental seas and blooms of cyanobacteria creating a highly stressful and fragile ecosystem for oligotrophic normal marine benthic organisms and leading to their massive decline the global third order sea level fall near the end of the frasnian may have led to gas hydrate dissociation giving the negative 13 c events and caused wild climatic fluctuations the subsequent short term events of sea level rise anoxia and eutrophication in the latest part of the f f transition would have placed additional environmental stresses on the already weakened biota leading to their further demise

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

upper devonian conodont zonation sea level changes and bio events in offshore carbonate facies lali section south china abstract the lali section guangxi province south china is composed of quiet water carbonates containing abundant conodonts which allowed recognition of 12 frasnian and 20 famennian biozones the kellwasser and annulata events are characterized by transgressive black carbonates while the hangenberg event is represented by black shale deposits other transgressive events recognized at lali include the middlesex nehden enkeberg and dasberg as well as the strunian transgression four regressive events were recognized on the basis of lithological and microfacies changes i e the linguiformis regression condroz event velifer regression and the derwer regression these sea level change events were of short duration and globally isochronous based on conodont correlations microfacies analyses and the abundance of palmatolepis indicate that the highest frasnian sea level lies in fz 12 13 upper rhenana zone whereas the highest famennian sea level was in the utahensis zone

frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

influence of palaeoweathering on trace metal concentrations and environmental proxies in black shales the mineralogical and chemical compositions of lower carboniferous tournaisian marine black shale from the kowala quarry the holy cross mountains poland were investigated this study focuses on disturbances in palaeoenvironmental proxies caused by palaeoweathering which progressively changed the major and trace element abundances palaeomagnetic investigations reveal that the devonian carboniferous succession was weathered during the permian triassic by the infiltration of oxidizing fluids related to karstification following post variscan exhumation the weathering process led to vermiculitization of chlorite partial dissolution of calcite and replacement of pyrite by hematite and goethite moreover the concentrations of some trace metals including co cu pb mo ni as and u significantly decreased consequently some elemental abundance ratios that are used as environmental proxies including u th ni co and v cr were altered elements that are bound to iron sulphides e g mo appear to be especially prone to mobilization by even a lightly weathered black shale the documented weathering including changes in elemental concentrations can potentially create misinterpretations of the original palaeoenvironmental conditions in addition the palaeoweathering of the studied samples appears to have substantially changed the carbon oxygen nitrogen and molybdenum stable isotope values the nitrogen and molybdenum stable isotope ratios in particular appear to be most sensitive to the effects of weathering and therefore are good indicators of palaeo weathering processes the major cause of these changes is the decay of organic matter and pyrite for the organic carbon stable isotopes ratios the main factor that controlls this process appears to be the preferential degradation of labile organic matter a combination of the total organic carbon toc total sulphur ts content mo concentration and stable isotope compositions seems to be the most useful for identify palaeo weathering our results suggest that reductions in ts and mo in tandem with diminished mo stable isotope values in the absence of obvious changes to the toc content provide the most compelling evidence of palaeo weathering

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

eutrophication by decoupling of the marine biogeochemical cycles of c n and p a mechanism for the late devonian mass extinction the late devonian mass extinction was unusually protracted and ecologically selective with preferential diversity losses among reefbuilding organisms and tropical shallow water faunas in general we have investigated the link between the extinction s unique characteristics and changes in biogeochemical cycling through analyses of the 13 c and c n p atomic ratios of organic matter buried across the kellwasser horizons in western new york state each horizon is characterized by 1 a long term 4 5 excursion in 13 c 3 of which occurs within the horizon and 2 a dramatic increase in the burial ratios of c n p from values of 100 15 1 to an average of 5000 170 1 on the basis of these results we propose that 1 increased efficiency of biolimiting nutrient recycling resulting from cyclic water column stratification and mixing promoted eutrophication during kellwasser deposition in new york and 2 the isotope excursions represent the composite effect of long term global organic c burial and local changes in photosynthetic c isotope fractionation related to nutrient availability this eutrophication model forges a mechanistic link between proposed late devonian climatic cooling and the selective demise of taxa likely to have been narrowly adapted to oligotrophic conditions

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

comment on the kaiho et al paper a forest fire and soil erosion event during the late devonian mass extinction palaeogeography palaeoclimatology palaeoecology 392 2013 272 280 abstract kaiho et al 2013 palaeogeography palaeoclimatology palaeoecology 392 2013 272 280 interpreted the occurrence of elevated concentrations of high molecular weight polycyclic aromatic hydrocarbons and dibenzofuran as indicators of wildfires and enhanced run off near the frasnian famennian f f boundary we argue that other processes including weathering or hydrothermal oxidation not discussed by kaiho et al led to the observed increase in the concentration of these compounds and also changed their distribution kaiho et al s evidence for soil erosion and eutrophication induced euxinia is also weak in the case of the investigated belgian sections finally kaiho et al rather unfortunately omitted a great wealth of important data published elsewhere choosing instead to include only those which support their ideas and interpretations

large sulphur isotopic perturbations and oceanic changes during the frasnian famennian transition of the late devonian the frasnian famennian transition of the late devonian was one of the most critical intervals in the phanerozoic sulphur isotopic pairs of carbonate associated sulphate and pyrite sulphide from coeval sections in south china and poland reveal frequent perturbations of sulphur cycling during this time interval these data suggest a sudden oceanic overturn during a rapid sea level fall probably induced by jerky block tilting in the latest frasnian this event was followed by long lasting photic zone euxinia during a rapid sea level rise in the earliest famennian large increases in continental nutrient fluxes and subsequent primary productivity and organic burial could have greatly enhanced bacterial sulphate reduction producing excessive sulphide through the water columns owing to iron depletion subsequently rapid ventilation of oceanic basins occurred dur ing which direct aerobic oxidation of sulphide into sulphate predominated in bottom waters and even surface sediments with minimal fractionation this oxygenation was probably induced by intensive climatic cooling and or large scale sea level fall the temporal coincidence of two extinction phases with the oceanic overturn and succeeding photic zone euxinia suggests that these extreme oceanic events played an important role in the severe biotic crisis furthermore photic zone euxinia coupled with subsequent climatic cooling may have delayed post extinction recovery of some taxa

carbon isotope geochemistry of the frasnian famennian transition abstract carbon isotope records for inorganic and total organic carbon toc as well as for individual organic biomarkers show two positive excursions in the late frasnian with comparable shape and amplitude in 13c the positive shifts in 13c can be correlated with the deposition of the kellwasser horizons the inorganic carbon isotope excursions are explained by an enhanced organic carbon burial that is expected to lower the concentration of oceanic dissolved co2 toc 13c values do not exhibit a larger shift than that recorded by inorganic carbon 13c values this is unexpected since a decrease in the dissolved co2 concentration should result in lower carbon isotope fractionation during photosynthesis ep 13c values of presumed algal biomarkers low molecular weight n alkanes pristane phytane although offset by 2 5 exhibit essentially identical records as toc and confirm this unexpected result it is proposed that high atmospheric and oceanic co2 concentrations during the devonian resulted in maximum photosynthetic fractionation any change in the co2 concentration would thus not affect ep as such 13c of primary organic carbon and 13ccarb will exhibit parallel excursions the data imply that carbon isotopes and the relationship between ep and co2 will not be effective to study changes in pco2 levels during the devonian since co2 concentrations were too high

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

prediction of spring elbe discharge based on stable teleconnections with winter global temperature and precipitation abstract the predictability of elbe streamflow anomalies during spring is examined using previous winter sea surface temperature sst temperature over land tt and precipitation pp anomalies based on running correlation analysis the authors identify several regions where the spring streamflow anomalies are stable correlated with sst tt and pp anomalies from the previous winter during the period 1902 71 the elbe spring streamflow is stable correlated with previous winter pp anomalies from its catchment area with tt anomalies from the black sea caspian sea region northwestern europe and northern canada as well as with sst anomalies from the tropical pacific the indian ocean and several regions of the north pacific and the north atlantic an index based on winter sst tt and pp anomalies from these regions is highly significantly correlated with spring streamflow anomalies during this period based on sst tt and pp anomalies from stable correlated regions a forecast scheme is developed an

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

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

size reduction of conodonts indicates high ecological stress during the late frasnian under greenhouse climate conditions in south china abstract the late frasnian mass extinction lfme during extreme greenhouse conditions had a serious impact on biotic evolution herein based on detailed size measurements of 1783 elements of the conodont genera polygnathus and palmatolepis at the lali and duan sections in south china conodont animals underwent significant size reduction at the genus level during the late frasnian the bergmann s rule controlled the evolution of frasnian conodont animals and their size reduction during the late frasnian may have resulted from long term global warming and indicated high ecological stress before the frasnian famennian boundary ffb this phenomenon can explain why the decline of benthic faunas such as corals brachiopods or metazoan reefs predated the extinction of pelagic faunas such as conodonts in the upper kellwasser ukw event and at the ffb

physico chemical environment of pedogenic carbonate formation in devonian vertic palaeosols central appalachians usa the morphology and geochemistry of pedogenic carbonate found in vertic claystone palaeosols in the devonian catskill formation in central pennsylvania preserve a record of the physical and chemical environment of carbonate precipitation the carbonate is characterized by three distinct petrographic generations pedogenic rhizoliths and nodules are the earliest precipitated generation and typically consist of dull red brown luminescent micrite clear equant calcite spar cement fills voids in the centres of rhizoliths as well as circumgranular cracks and septarian voids in nodules early spar cements are nonluminescent to dull luminescent whereas later spar cements exhibit bright yellow orange luminescence late stage pedogenic fractures are always occluded with very bright yellow orange luminescent spar cements the incorporation of progressively higher concentrations of mn up to 34 000 ppm into successively younger calcite spar cements without concomitant increases in fe suggests carbonate precipitation from an evolving meteoric water in which mn2 became increasingly mobile over time the increased mobility is possibly due to decreasing eh resulting from oxidation of organic matter after rapid soil burial on the floodplain the amount of fe2 available for incorporation into calcite was limited because most iron was immobile having been earlier oxidized and bound to the palaeosol clay matrix as a poorly crystallized ferric oxide or oxyhydroxide mineral carbon isotope compositions of pedogenic carbonate correlate with the inferred depth of carbonate precipitation rhizoliths preserved below the lowest stratigraphic occurrences of pedogenic slickensides are consistently depleted in 3c relative to nodules which formed stratigraphically higher within the zone of active soil shrink and swell processes nodular carbonate precipitated in proximity to deep cracks in the soil is enriched due to increased gas exchange with isotopically heavy atmospheric c02 accordingly rhizolith compositions will most accurately estimate palaeoatmospheric levels of c02 the use of nodule compositions may result in overestimation of pco by as much as 30

zinc and strontium isotope evidence for climate cooling and constraints on the frasnian famennian 372 ma mass extinction abstract the frasnian famennian f f mass extinction is one of the big five biotic crises during the phanerozoic whereas the cause of this catastrophic event still remains debated here we present for the first time high resolution zn and sr isotope data obtained by a sequential leaching procedure for carbonate rocks across the f f boundary from the fuhe section in south china both 66zn and 87sr 86sr values rapidly increase in the lower and upper kellwasser horizons and palmatolepis delicatula platys to p minuta minuta conodont zones and the positive isotope shifts are exactly located in the same horizons characterized by low 13c values equivalent to low atmospheric pco2 level reflecting climate cooling and sea level fall stages the strong temporal coupling of 66zn values raise with elevated 87sr 86sr ratios is most likely to have been caused by input of isotopically heavy zn and radiogenic sr from carbonate dominated weathering and or uptake of isotopically light zn into primary producers during climate cooling climate cooling could cause relative sea level falls resulting in widespread exposure of carbonate platform enhance carbonate influx proportion through differential weathering of carbonate and silicate rocks and cause greater productivity by promoting oceanic thermohaline circulation and enhancing upwelling of bio limiting nutrients all of these processes would have contributed to the positive shifts of 66zn as observed this proposed scenario is in accordance with the fact that the f f mass extinction was almost limited to the shallow water tropical stenothermal faunas whereas the high latitude and deep water faunas were less affected our data support and represent the composite effect of a series of events linked to climate cooling which may have induced this catastrophic event

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

osmium isotopic evidence against an impact at the frasnian famennian boundary two sections across the frasnian famennian boundary were analyzed for re and os concentrations and 187os 188os ratios to evaluate evidence for a meteoritic input coincident with this boundary and its associated mass extinction these sections are from a siltstone and shale sequence at irish gulf in new york us and a calcareous shale and ferromanganese oxide sequence at la serre in france the irish gulf section with an initial 187os 188os of about 0 49 does not show the characteristic meteoritic os imprint with an 187os 188os of about 0 13 the integrity of the section with regard to re and os retention is indicated by the construction of an isochron with an age of 388 41 ma consistent with independently determined ages for the frasnian famennian boundary although the la serre section with os concentrations as high as 33 ppb and re concentrations ranging from 1 4 to 7 4 ppb might be expected to show excellent evidence for a meteoritic contribution the highly radiogenic isotopic composition 187os 188os 2 42 3 61 instead suggests recent massive re loss or addition of radiogenic os these possibilities prevent the reconstruction of an initial 187os 188os value for the boundary for this site assuming reasonable re concentrations prior to loss the os isotopic composition is inconsistent with a large meteoritic component this inconsistency emphasizes that platinum group element pge concentrations are not reliable indicators of extraterrestrial addition

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

record of climate driven morphological changes in 376 ma devonian fossils the lower and upper kellwasser horizons represent two anoxic events that mark the mass extinction at the frasnian famennian f f boundary among other groups conodont animals were severely affected but the genus palmatolepis survived with a complete turnover at the f f boundary here the fine morphological variations of the genus palmatolepis and the sea surface temperature evolution are quantified in two f f boundary sections using morphometrics and oxygen isotopic composition of apatite respectively in accordance with other f f sections the isotope records show two positive excursions of 1 during the lower and upper kellwasser anoxic events the conodont shape and the oxygen isotopic composition of the genus palmatolepis are significantly correlated within the frasnian and famennian stages suggesting a strong environmental influence on the morphology of the feeding apparatus of the conodont animal we propose that the morphological differences are linked to changes in the trophic position of palmatolepis enhanced organic carbon burial which is supported by global positive carbon isotope excursions in inorganic and organic carbon during both the lower and upper kellwasser events altered the primary biomass production and thus the subsequent nutrient supply to higher trophic levels while the carbon and oxygen isotopic shifts are of similar amplitude during lower and upper kellwasser events the variation of the shape of palmatolepis during the upper kellwasser i e the f f boundary is more pronounced than during the lower kellwasser

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

the influence of the late devonian kellwasser events on deep water ecosystems evidence from palaeontological and geochemical records from south china abstract the late devonian frasnian famennian f f event consisting of the lower and upper kellwasser events had a severe impact on shallow water ecosystems while the effect on deep water ecosystems is ambiguous in order to recognize the kellwasser events and to evaluate their influences on the deep water ecosystems a newly refined conodont biostratigraphic framework spanning the lower palmatolepis rhenana zone to the pa delicatula platys zone has been established in the nandong section basinal facies guangxi south china the upper devonian lower and upper kellwasser horizons lkh and ukh have been recognized in the deep water facies on the basis of lithological variations biological turnovers and positive carbon isotope 13ccarb excursions the lkh is characterized by the enrichment of marine nektonic communities e g conodonts homoctenids and entomozoacean ostracods whereas the top of the ukh is barren of fossil organisms suggesting that the upper kellwasser event had a more severe effect on nekton than the lower kellwasser event the upper kellwasser uk 13ccarb positive excursion lags behind the enrichment of cu ni mo and v indicating that the uk 13ccarb positive excursion was probably related to elevated primary productivity which induced oxygen depletion in the water column the uk 13ccarb positive excursion peak prior to the f f boundary indicates a more limited effect of riverine influx on the deep water setting which suggests that the regional palaeogeographic configuration played an important role in the carbon cycle

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

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

carbon and sulfur isotope anomalies across the frasnian famennian extinction boundary alberta canada stable isotopes of carbonate and organic carbon from two upper devonian sections in alberta canada indicate a heavy carbon event across the frasnian famennian f f boundary and a negative 13 c shift at the boundary at cinquefoil mountain 13 c values in carbonate are anomalously high 3 5 to 4 5 pdb peedee belemnite within an interval 10 m below to 23 m above the f f boundary representing about 1 m y two standard conodont zones compared to background values of 1 above and below this interval superimposed on this positive excursion is a marked 13 c decrease of about 1 at precisely the f f boundary at medicine lake a similar 13 c excursion in organic carbon from a background of 29 to a high of 26 5 is recorded across the f f boundary the 34 s data for iron sulfide in these sections show unusually high values as much as 15 to 20 cdt canon diablo troilite in the f f boundary interval these data together with those from other areas indicate a period of major global changes e g greenhouse and marine anoxia that took place well before and after the sudden biomass killing event at the f f boundary existing evidence suggests that the f f mass extinction was probably caused by a large extraterrestrial impact on earth at a time when the global ecosystem was already severely stressed

the late devonian frasnian famennian event in south china patterns and causes of extinctions sea level changes and isotope variations abstract the frasnian famennian f f event may be recognized in various facies areas in south china in the pelagic cherty basin facies both lower and upper kellwasser events can seemingly be recognized in the deeper water carbonate facies the f f event level is well controlled in light of conodont biostratigraphy in the shallow water carbonate and mixed carbonate shale facies the f f boundary may be defined by clear taxonomic distinction in benthic fossils articulate brachiopods and corals as well as evidence from minor pelagic fossils post extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups in open shallow water platform to inter platform depression areas brachiopods seem to recover quickly probably in the middle pa triangularis zone benthic ostracodes seem to recover at a later stage recovery of rugose corals did not happen until the uppermost famennian three steps of the f f mass extinction are postulated 1 extinction of diverse brachiopods including most atrypids 2 extinction of pelagic conodonts 3 extinction of both benthic faunas very abundant and diverse rugose corals and ostracodes and pelagic conodonts evidence of an end frasnian regression in south china is clear particularly in shallow water settings however in deeper water settings the picture is complicated with evidence of both sea level rise and fall in the latest frasnian it may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic hydrothermal activities may have mainly caused frequent and rapid climatically warming cooling alterations and sea level changes as well as marine ecologic collapse eutrophication microbial blooming seawater acidification and anoxia which may explain the f f extinction pattern in south china

strontium isotope stratigraphy potential resolution and event correlation abstract a new generation 87sr 86sr isotope curve for the phanerozoic seawater based on a compilation of 3635 stratigraphically well defined and well preserved skeletal components results in a substantially narrower band with some discrepancies if compared to the curve of burke et al 1982 which is based mostly on whole rock samples the results obtained from low mg calcite shells foraminifers belemnites brachiopods and oysters are mostly superior to those from phosphatic skeletal components such as conodonts even if the latter are exceptionally well preserved cai 1 5 at this stage the phanerozoic data set based on fossils is patchy for the cambrian upper ordovician lower devonian and upper carboniferous triassic intervals the major practical constraint that precludes delineation of an unequivocal sr isotope curve for the phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples as a result the curve is in reality a band this is a reflection of the limitations of biostratigraphy and geochronology that are inherited by any derivative correlation and dating technique including isotope stratigraphy it is therefore unlikely that in the near future the sr isotope stratigraphy will surpass the resolution capability of biostratigraphy as a global correlation tool on the other hand if complemented by lithostratigraphy it is potentially a valuable tool for correlation of sequences on intrabasinal and regional scales taking into account the above limitations careful consideration must be given to assignment of higher order isotope peaks to specific events within a biozone and to the use of such events as a global correlation tool

carbon isotope lateral variability in a middle frasnian carbonate platform belgium significance of facies diagenesis and sea level history abstract carbon isotopic variations of frasnian shallow water carbonates from belgium are related to facies and major sea level trends the influence of the diagenetic overprint was assessed in order to determine the primary signal of the frasnian carbonates shallow water microfacies are characterized by biostromes with stromatoporoids and lagoonal deposits dominated by carbonate mud and calcareous algae with subaerial exposure surfaces the diagenetic history was controlled by three main events early meteoric diagenesis short term subaerial exposure during deposition late meteoric diagenesis major famennian regression and burial diagenesis the oxygen isotopic values are almost constant with respect to facies original material carbonate mud and cement and sedimentological units no differences before or after the main regression this homogeneity is related to resetting during late meteoric diagenesis the carbon isotopic values are related to facies with the more negative values for the shallowest facies and to major sea level variations most negative values after the main regression this pattern is interpreted as being related to primary signals this trend was enhanced by early meteoric diagenesis and the influence of more negative values from paleosols the carbon isotope patterns reflect the influence of sea level and water circulation on shallow water deposits and this influence implies that shallow water carbonates are not necessarily good material for assessing the primary isotopic values of the ocean because of the influence of long residence time aging of the platform top water and because of early diagenesis

did climate changes trigger the late devonian kellwasser crisis evidence from a high resolution conodont δ18opo4 record from south china abstract the impact of climate change on biodiversity has been the focus of studies on the phanerozoic biotic crises however it is still controversial whether climate change has caused the frasnian famennian f f biotic crisis since there is no unequivocal view on the global climate change during this critical period in order to reconstruct palaeotemperatures during the f f transition in south china eastern palaeotethys a high resolution oxygen isotope 18 o po 4 record was obtained based on 104 measurements of conodont apatite from the yangdi section the oxygen isotope record based on mono generic samples reveals an increase in 18 o po 4 by 0 7 in the lower kellwasser horizon lkh and 1 4 in the upper kellwasser horizon ukh translating into low latitude surface water cooling of 3 c and 6 c respectively these two 18 o po 4 shifts agree well with the time equivalent 18 o po 4 records from the western palaeotethys suggesting that two climate cooling pulses in conjunction with the deposition of the kellwasser horizons are a global signal during the f f transition the positive shift of 18 o po 4 coincides with positive excursion in carbon isotope of carbonates 13 c carb in the ukh indicating that enhanced burial of organic carbon resulted in a drop in atmospheric p co 2 and thus global climate cooling cooling started immediately before the upper kellwasser biotic crisis with the lowest temperature documented at the top of the ukh climate cooling during the deposition of the lkh is observed in conjunction with the sharp decline in metazoan reefs the coincidence of cooling and the kellwasser biotic crisis suggests that global cooling played a major role in the collapse of ecosystems

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

a silicate weathering mechanism linking increases in marine 87sr 86sr with global glaciation the 87sr 86sr ratio of sea water is generally regarded as a proxy for the rate of chemical weathering of the continents interpretation of the 87sr 86sr record in marine limestones requires an understanding of how changes in this quantity are linked to climate and tectonic events a connection between the strontium isotope record and the extent of global glaciation has been proposed1 8 but without a well established mechanism glaciation may influence marine 87sr 86sr by changing global riverine sr fluxes that is rock weathering rates and or 87sr 86sr ratios that is relative mineral weathering rates here we investigate how the 87sr 86sr release from silicate weathering is affected by glaciation using the sr isotope systematics of granitoid soils on alpine glacial moraines in the wind river range wyoming we observe a negative correlation between the 87sr 86sr ratio of exchangeable sr in soils and the soil age indicating that the 87sr 86sr ratio of sr released in the early stages of weathering is significantly higher than in later stages we estimate that this mechanism can increase global riverine 87sr 86sr by an average of 0 0002 during periods of glacial interglacial cycling when superimposed on long term trends controlled by tectonic processes2 7 9 10 this shift can account for the correlation between the rate of change of marine 87sr 86sr and the intensity of glaciation over at least the past 10 myr

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

a forest fire and soil erosion event during the late devonian mass extinction abstract the late devonian mass extinction occurred in a stepwise manner and culminated close to the frasnian famennian f f boundary 372 million years ago organic molecular indices from marine sedimentary rocks at the sinsin section belgium indicate that the sequence of combustion of land vegetation soil erosion and anoxia euxinia occurred close to this boundary the increased concentrations of biomarkers indicating forest fire and soil erosion measured in the sinsin section suggest that fire became widespread at this time leading to various damaging consequences increased runoff and oceanic anoxia that caused marine extinctions magnetic susceptibility data in the sinsin section indicate a relatively dry climate spanning the f f boundary which would have encouraged forest fires the study of organic biomarkers presents several lines of evidence to link forest fire and soil erosion to the late devonian mass extinction

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

biogeochemical controls on black shale deposition during the frasnian famennian biotic crisis in the illinois and appalachian basins usa inferred from stable isotopes of nitrogen and carbon abstract the frasnian famennian biotic crisis is marked by two distinct intervals known as the lower and upper kellwasser events kwes that in many locations are associated with deposition of organic rich shales sedimentary nitrogen and carbon isotopes offer insight into the biogeochemical processing of nutrients production of organic matter and palaeoceanographic conditions during the kwes here we present new bulk nitrogen 15nbulk and organic carbon 13corg isotope data from the late devonian appalachian and illinois basins ab and ib with a focus on intervals encompassing the kwes black shales from the ib and ab including the kwes are 15n depleted 1 0 2 0 and have significantly lower 15nbulk than interbedded grey shales 0 5 4 0 a trend consistent with many instances of black shale deposition in the phanerozoic organic carbon isotopes exhibit the broad positive excursions 3 5 from background that are typical of the kwes globally superimposed over these positive excursions in 13corg are sharp decreases of up to 3 0 within the black shale beds to as low as 30 5 the pattern of 15nbulk and 13corg values suggests that the depth of the chemocline and the degree of water column stratification exert a primary control on both 15nbulk and 13corg during black shale deposition in the context of the frasnian famennian biotic crisis the oscillating redox state and changing temperatures would have likely placed extreme stress on organisms within the marine environment of the ab and ib and may potentially have been a contributing factor to diversity loss over this time period

carbon dioxide in the paleozoic atmosphere evidence from carbon isotope compositions of pedogenic carbonate stable carbon isotope compositions of pedogenic carbonate occurring in three clay rich vertic paleosols within paleozoic red bed successions in central pennsylvania provide a record of past pedogenic environments and can be used to estimate co sub 2 pressure p sub co sub 2 of the paleozoic atmosphere the delta sup 13 c values of carbonate nodules from paleosols in the deltaic lower bloomsburg formation upper silurian reflect the contribution of carbon from marine groundwater or fossils coupled with low biological activity the delta sup 13 c values of carbonate rhizocretions from stratigraphically high paleosols in the bloomsburg formation and in the alluvial catskill upper devonian and mauch chunk upper mississippian formations suggest an extensive c sub 3 flora and significant contribution of atmospheric co sub 2 paleozoic atmospheric co sub 2 levels inferred from delta sup 13 c of pedogenic carbonate are significantly higher than present levels

synchronous changes in seawater strontium isotope composition and global climate the 87sr 86sr ratio of sea water has increased gradually over the past 40 myr suggesting a concomitant increase in global chemical weathering rates1 6 recently dia et al 7 analysed a 250 kyr 87sr 86sr record and found superimposed on this gradual increase higher frequency 87sr 86sr variations which appeared to follow a 100 kyr cycle this periodicity corresponds to one of the prominent cycles in the earth s orbital parameters which are known to modulate the patterns of solar insolation and hence climate8 10 the resolution of this record was however insufficient to establish the phase relationship between the 87sr 86sr variations and global climate cycles here we present a high resolution seawater 87sr 86sr record spanning the past 450 kyr we find that maxima and minima in 87sr 86sr coincide with minima and maxima respectively in continental ice volume from the specmap oxygen isotope record20 apparently suggesting that there was less chemical weathering in arid glacial periods than in the more humid interglacials during glacial interglacial transitions however seawater 87sr 86sr changes at a rate of 1 p p m kyr 1 approximately three times that evaluated by dia et al 7 mass balance calculations illustrate that simple changes in modern chemical weathering regimes cannot fully account for such rapid changes suggesting that we need to revise current ideas about strontium reservoirs and the mechanisms for exchange between them

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

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

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

links between central greenland stable isotopes blocking and extreme climate variability over europe at decadal to multidecadal time scales the link between central greenland stable oxygen isotopes atmospheric blocking frequency and cold temperature extremes at decadal to multidecadal time scales is investigated using observed and proxy data as well as model experiments a composite analysis reveals that positive stable isotope anomalies in central greenland are associated with enhanced blocking activity in the atlantic european region several indices of blocking activity in the atlantic european region are higher correlated with central greenland stable isotope time series than with the north atlantic oscillation indices both in observations and model simulation furthermore the blocking frequency anomaly pattern associated with central greenland stable isotope variability is similar to the blocking anomaly pattern associated with the atlantic multidecadal oscillation a composite analysis reveals that stable isotope variations in central greenland are related to a large scale pattern in the frequency of extreme low temperature events with significant positive anomalies over europe and a southwest to northeast dipolar pattern over asia during observational period central greenland isotope records blocking and extreme temperature indices over europe show enhanced variability 10 30 and 50 70 years similar quasi periodicities dominate the spectrum of central greenland isotope variability during the last millennium we argue that long term variations of climate extreme indices over europe and asia as derived from observational data can be put into a long term perspective using central greenland stable isotope ice core records

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

estimating greenland surface melt is hampered by melt induced dampening of temperature variability he positive degree day pdd model provides a particularly simple approach to estimate surface melt from land ice based solely on air temperature here we use a climate and snow pack simulation of the greenland ice sheet modele atmospherique regional mar as a reference to analyze this scheme in three realizations that incorporate the sub monthly temperature variability differently i by local values ii by local values that systematically overestimate the dampened variability associated with intense melting or iii by one constant value local calibrations reveal that incorporating local temperature variability particularly resolving the dampened variability of melt areas renders model parameters more temperature dependent this indicates that the negative feedback between surface melt and temperature variability introduces a non linearity into the temperature melt relation to assess the skill of the individual realizations we hindcast melt rates from mar temperatures for each realization for this purpose we globally calibrate greenland wide constant parameters realization i exhibits shortcomings in the spatial representation of surface melt unless temperature dependent instead of constant parameters are calibrated the other realizations perform comparatively well with constant parametrizations the skill of the pdd model primarily depends however on the consistent calibration rather than on the specific representation of variability

large scale climatic fluctuations in the latest ordovician on the yangtze block south china likely under warm and humid conditions low cia values however indicate the near absence of chemical weathering thereby refl ecting cool and or arid conditions in this paper the paleo climatic changes during the ordovician silurian transition were reconstructed in the light of cia values derived from the chemical composition of fi ne grained siliciclastic rocks in the mid upper yangtze river region china the infl u ences of paleoclimatic changes on biota are also discussed abstract the ordovician silurian transition was a critical interval in earth s history marked by dramatic climatic oceanic and biological turnovers here we present the chemical index of alteration cia as a proxy of changes in intensity of chemical weathering and its varia tions across the ordovician silurian boundaries wufeng through guanyinqiao to longmaxi formations from wangjiawan and nanbazi on the yangtze block south china in order to explore the climatic changes our data show that the cia values of sediments commonly range from 75 to 90 in the wufeng and longmaxi formations indicating a high degree of chemical weathering and thus a hot and humid climate during deposition in contrast a sharp drop in cia values most 60 70 in the guanyinqiao formation or hirnantian suggests an overall cold and arid climate interrupted by several intervals of warm climate when deposited the temporal coincidence of two phases of massive biotic extinctions with the beginning and end of the cold climate epoch respectively suggests that the large climatic changes could be one of the main controls on the mass extinctions although other factors may also have played a role

the southern oscillation part i global associations with pressure and temperature in northern winter abstract we describe the global correlations between a measure of the southern oscillation and sea level pressure and surface air temperature in the northern winter the stability of these correlations were tested on the northern hemisphere for an 80 year period and it turned out that most stable correlation coefficients were found over india the north pacific ocean the rocky mountains and the central and western north atlantic ocean on the southern hemisphere most records are too short for a similar test but the following may tentatively be said about the southern oscillation in middle and high southern latitudes when pressure is low in lower latitudes over the south pacific ocean it tends to be high at higher latitudes of that ocean high over east antarctica and low in the belt of westerlies in the indian and south atlantic oceans in the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitud

depositional environment of the paleoproterozoic yuanjiacun banded iron formation in shanxi province china the paleoproterozoic 2 38 2 21 ga yuanjiacun banded iron formation bif located in shanxi province is a superior type bif in the north china craton this bif is within a metasedimentary rock succession of the yuanjiacun formation in the lower luliang group which has undergone lower greenschist facies metamor phism iron oxide magnetite and hematite carbonate and silicate facies are all present within the iron rich layers the eastward transition from carbonate into oxide facies iron formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite ankerite and magnetite stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east these distinct lateral facies are also observed vertically within the bif i e the iron mineral assemblage changes upsection from sider ite through magnetite into hematite rich iron formation the oxide facies bif formed near shore whereas carbonate siderite and silicate facies assemblages formed in deeper waters based on detailed analyses of these variations on a basinal scale the bif precipitated during a transgressive event within an environment that ranged from deep waters below storm wave base to relatively shallow waters the bif samples display distinctively seawater like rees y profiles that are characterized by positive la and y anomalies and hrees enrichment relative to lrees in post archean australian shale normalized diagrams consistently positive eu anomalies are also observed which are typical of reduced high temperature hydrothermal fluids in addition slightly negative to positive ce anomalies and a large range in ratios of light to heavy rees are present in the oxide facies bif these characteristics in combination with consistently positive 56fe values suggest that deposition of the bif took place along the chemocline where upwelling of deep anoxic iron and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater the ankerite displays highly depleted 13c values and the carbonate rich bif has a high content of organic carbon suggesting dissimilatory fe iii reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column that same biomass was likely tied to the original oxidation of dissolved fe ii the fact that the more ferric bif facies formed in shallower waters suggests that river sourced nutrients would have been minimal thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory fe iii reduction by contrast in deeper waters more proximal to the hydrothermal vents nutrients were abundant and high biomass productivity was coupled to increased carbon burial leading to the deposition of iron rich carbonates the deposition of the yuanjiacun bif during the onset of the great oxidation event goe ca 2 4 2 2 ga confirms that deep marine waters during this time period were still episodically ferruginous but that shallow waters were sufficiently oxygenated that fe ii oxidation no longer needed to be tied directly to proximal cyanobacterial activity

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

a global biogeochemical perturbation across the silurian devonian boundary ocean continent biosphere feedbacks abstract the large scale global biogeochemical perturbation across the silurian devonian s d boundary recorded in the major positive excursion of the 13c time curve klonk event of an amplitude of 2 5 to 3 0 max 4 0 in europe and up to 5 0 in north america reflects a unique combination of palaeogeographic biogeochemical and evolutionary processes in the late caledonian geodynamic setting the steady sulfur isotopic ratios show an overall stability of the s d oceanic geochemical system as a whole and do not indicate any synchronous changes in anoxic deep oceanic and sediment processes therefore this led us to a hypothesis that the crucial changes that contributed to the recorded carbon cycling turnover are related to rapidly evolving ocean continent biosphere feedback coastal zones of the latest silurian epicontinental seas accumulated considerable quantities of organic carbon from early vascular vegetation which explosively expanded to inhabit vast near coastal shallows and deltas large primary production of these early terrestrial plants and rapidly enhanced sedimentary burial of organic carbon were also responsible for co2 drawdown which have resulted in reversed greenhouse effect and a global climatic cooling tendency this feedback was blocked when the sea level gradually dropped and led to shrinking of the silurian epicontinental seas and the growing climatic deterioration during the s d transition limited primary production furthermore continued processes of regressive abrasion and erosion limited the storage of organic carbon as well as the efficiency of the carbonate factory during the following early devonian greenhouse interval marine regression and active latest caledonian tectonism promoted progressive weathering of the sedimentary organic matter the oxidation of c rich deposits caused the subsequent growth of co2 levels in the early devonian culminating in the warming of global climate

carbon isotopic evidence for the associations of decreasing atmospheric co2level with the frasnian famennian mass extinction 1 a perturbation of the global carbon cycle has often been used for interpreting the frasnian famennian f f mass extinction however the changes of atmospheric co2 level pco2 during this interval are much debatable to illustrate the carbon cycle during f f transition paired inorganic 13ccarb and organic 13corg carbon isotope analyses were carried out on two late devonian carbonate sequences dongcun and yangdi from south china the larger amplitude shift of 13corg compared to 13ccarb and its resultant 13c 13c 13ccarb 13corg decrease indicate decreased atmospheric co2level around the f f boundary the onset ofpco2 level decrease predates that of marine regressions which coincide with the beginning of conodont extinctions suggesting that temperature decrease induced by decreased greenhouse effect of atmospheric co2might have contributed to the f f mass extinction

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

high resolution bio and chemostratigraphic framework at the frasnian famennian boundary implications for regional stratigraphic correlation between different sedimentary facies in south china abstract as one of the big five mass extinctions in phanerozoic the frasnian famennian f f boundary event records the extinction of 40 of marine invertebrate genera the f f boundary is defined by the first appearance of conodont palmatolepis subperlobata as well as the abundant occurrences of pa ultima at the base of the lower pa triangularis zone the f f boundary is also broadly coincident with a positive excursion in carbon isotopes suggesting the possible linkage between the perturbation of marine carbon cycle and the biotic crisis however the correlation between conodont biostratigraphy and carbon isotope chemostratigraphy has not been established yet preventing the high resolution regional stratigraphic correlation among different sedimentary facies in this study we studied the conodont biostratigraphy and analyzed carbonate carbon 13 c carb and organic carbon 13 c org isotopes of the baisha section in the guangxi province south china the first appearance of index conodont fossil pa subperlobata for the lower pa triangularis zone i e the f f boundary is coincident with the onset of a 3 positive excursion in 13 c carb while pa triangularis and pa subperlobata occur nearly simultaneously but predate the disappearances of pa linguiformis and other typical frasnian elements in addition a positive excursion in 13 c org is associated with the decline of 13 c carb near the base of the middle pa triangularis zone which is marked by the first appearance of pa delicatula another important famenian element pa minuta the index fossil for the upper pa triangularis zone first appears when 13 c org starts to decline the offset between 13 c org and 13 c carb excursions could be attributed to the oceanic anoxia the kellwasser event near the f f boundary followed by the mixing of surface and deep water in earliest famenian the high resolution bio and chemostratigraphic framework can be used as the standard for regional stratigraphic correlation and identification of the f f boundary in different depositional environments in south china we propose that the f f boundary can be identified from a conodont poor carbonate section by the onset of the positive excursion in 13 c carb whereas the f f boundary in a non fossiliferous siliciclastic section might be placed slightly below the positive excursion in 13 c org

strontium isotopic composition of mid cretaceous seawater the 87sr 86sr ratio in fish teeth separated from mid cretaceous marl and black shale from the northeastern apennines and venetian alps italy define three periods of low 87sr 86sr ratio at 121 to 124 million years ago ma 110 to 115 ma and 89 to 91 ma the 87sr 86sr excursions correspond to oceanic anoxic events represented by the livello selli livello 113 livello urbino and livello bonarelli black shale marker beds and probably reflect an increase in the low 87sr 86sr hydrothermal strontium flux associated with the emplacement of the ontong java and kerguelen plateaus 120 to 110 ma and the caribbean plateau 89 to 91 ma the modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed cretaceous crustal production rates of 50 to 100 percent greater than modern

facies and geochemistry across the early middle frasnian transition late devonian on south china carbonate shelf comparison with the polish reference succession abstract dongcun and longmen are two important reference sections for the study of the frasnian carbonate platform of guangxi southern south china at the dongcun section conodonts recovered in the present study provide a robust biostratigraphic framework for the lower middle frasnian interval the studied interval uppermost givetian to middle frasnian basal palmatolepis hassi zone is characterized by repeated shallower and deeper water deposits but the cyclic depositional trend was mainly deepening upward carbon isotopic investigation of bulk samples recognizes a major four step perturbation across the lower middle frasnian boundary which is also evident in the holy cross mountains poland the pattern is reinforced by correlative organic carbon isotopic secular trends from the reference polish sections a prominent long lasting increase in 13ccarb up to 4 5 event iii is evident in the palmatolepis punctata zone but is preceded and followed by rapid negative shifts events ii and iv respectively to ca 0 a weak incipient positive excursion event i is recognized in carbonate carbon only in the upper part of the palmatolepis transitans zone in chinese sections different background isotopic values indicate decoupled isotopically dissimilar hydrothermally affected and mostly oxygenated water masses over the carbonate shelf as shown by trace and rare earth elements the shallower water upslope diagenetically unaltered dongcun succession reveals lighter carbon isotopic ratios on the order of 2 while the less densely sampled and less certainly dated mostly muddy siliceous longmen downslope succession shows 13ccarb levels similar to those recorded worldwide the onset of the bipartite event iii is marked by 13c enrichment of 4 3 at dongcun event iv a light carbon excursion is especially well recorded in the shallow water facies by a 2 5 negative shift the event i excursion in the transitans zone is obscured as in some polish successions but is probably recorded in organic carbon trends slight differences in timing and magnitude of the 13ccarb oscillations may originate from geochemical decoupling between the open ocean and the tectonically active morphologically differentiated epeiric basins nevertheless a global extent for this major punctata event is clear from the similar biogeochemical signals recorded on the distantly separated south laurussian and south china shelves