simulation of modern and middle cretaceous marine δ18o with an ocean atmosphere general circulation model 1 we have developed a coupled ocean atmosphere general circulation model the genesis mom model with the ability to transport and fractionate water isotopes in the ocean and atmosphere the model is used to predict modern and cretaceous precipitation and seawater 18o the model reproduces the large scale modern day isotopic distribution in the zonal mean the difference between simulated and observed seawater 18o is within 0 2 in the low and middle latitudes and within 1 at high latitudes in comparison to modern simulated cretaceous surface seawater 18o is systematically depleted by 0 3 at low and middle latitudes these differences are attributed to equilibrium fractionation during surface evaporation at low latitudes and an increased partitioning of 18o from the surface into the deep ocean due to intermediate and deep water formation in subtropical basins in the cretaceous we also find that regional seawater 18o is significantly influenced by the paleobathymetry and the resolution of oceanic gateways boundary conditions that are not well known for the past our simulation of cretaceous seawater 18o has major implications for oxygen isotope paleothermometry we conclude that conventional assumptions of past seawater 18o may lead to an overestimate of cretaceous sea surface temperatures especially at middle and high latitudes

changes in streamflow components following logging and regeneration in the southern forest of western australia two small experimental catchments were established in the south west of western australia to study the effects of logging and subsequent regeneration on the mechanism of streamflow generation following a six year pre treatment calibration period 1976 1981 one catchment march road was logged and reforested in 1982 and the other april road south remained as a control logging resulted in an increase in groundwater levels and subsequently groundwater discharge area the deep permanent groundwater levels in the valley and upslope areas rose until 1986 and then began to decline the maximum rise was 5 m in the upslope areas the duration of shallow intermittent groundwater system perched on underlying clay was extended from 2 3 months in winter before logging to 5 6 months after logging the shallow groundwater level rose in the valley and began to discharge at the ground surface in 1986 logging resulted in an increase in streamflow the maximum increase 18 of annual rainfall was in 1983 one year after logging the increase in streamflow was due to a substantial decrease in interception and evapotranspiration increased recharge to the shallow groundwater system decreased soil moisture deficit and consequently an increase in throughflow the increase in base flow was about twice that of quick flow the changes in streamflow and its components in the subsequent years were closely related to the groundwater discharge area most of the quick flow was generated as saturation excess overland flow from the groundwater discharge area in the valley the expansion of the groundwater discharge area increased soil moisture content higher groundwater level and the presence of the shallow groundwater system for the extended periods were responsible for the process of streamflow generation

drowning unconformities palaeoenvironmental significance and involvement of global processes abstract drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms they mostly consist in the deposition of deep marine facies on top of shallow marine limestones although large scale depositional geometries mimic lowstand systems track architecture these sedimentary turnovers are developed in relation with major sea level rise inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up this so called paradox of carbonate platform drowning implies that parameters other than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems worldwide and at different times during earth history in depth studies of drowning unconformities revealed that changes in nutrient input clastic delivery temperature or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers the examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities this is complemented by new data from early cretaceous successions from the helvetic alps during this time period the helvetic carbonate platform developed along the northern tethyan margin using both photozoan and heterozoan communities phases of healthy production were interrupted by several drowning episodes the latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation from the earliest valanginian to the early to late barremian three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions which first induced a switch from photozoan to heterozoan communities and then to long lasting drowning phases the latter encompass several sea level rise and fall cycles and may be linked to strengthened upwelling currents with the return to more oligotrophic conditions during the late barremian photozoan urgonian type communities took up again their development has been abruptly stopped at the end of the early aptian by a major emersion phase the subsequent drowning is documented in various peritethyan areas this initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the cenomanian this long term trend in the evolution of the helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena in particular the progressive opening of the northern and equatorial atlantic may have impacted sea level by creating new oceanic basins the emplacement of submarine volcanic plateaus may have triggered sea level rise and fertilized deep oceanic waters through hydrothermal processes drowning unconformities thus record the interplay of local with long term processes and constitute regional sedimentary archives of global phenomena

evidence for a complex valanginian nannoconid decline in the vocontian basin south east france the early cretaceous is punctuated by widespread biocalcification crises these are characterized by decrease in the carbonate platform growth and in the pelagic realm by a decline in nannoconus relative abundance in the calcareous nannofossil assemblages the valanginian nannoconus decline started before the positive 13c excursion characterizing the weissert event the nannoconid decline is investigated in two sections of the vocontian basin la charce and vergol which are biostratigraphically well constrained and contain wellpreserved calcareous nannofossils absolute and relative abundances of nannoconus show a polyphased decline with a first decrease in the interval from the campylotoxus to the verrucosum ammonite subzones before the positive 13c shift and a second decrease from the end of the peregrinus to the base of the radiatus ammonite zones concomitant with the long term decrease in 13c these two declines are separated by an important increase in the nannoconus abundance from the verrucosum to the peregrinus ammonite subzones concomitant with a slight short term decrease of 13c biometric analysis shows size changes of n steinmannii and n kamptneri along the nannoconid decline the patterns of abundances and size changes seem to be related to paleoenvironmental changes mainly characterized by a temperature decrease and variable nutrient supply the described valanginian nannoconid recovery seems to occur during the most intense phase of the cooling event and is recorded in the vocontian basin as well as in the atlantic and tethys oceans these spatial correlations suggest a supra regional character for the valanginian nannoconid recovery event best recorded in the vocontian basin and at low latitudes

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

instability in tropical pacific sea surface temperatures during the early aptian the cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric co2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events oaes yet the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained here we present a ighresolution record of sea surface temperatures ssts reconstructed using the tex86 paleothermometer for a sequence of early aptian organic rich sediments deposited during the first cretaceous oae oae1a at shatsky rise in the tropical pacific ssts range from 30 to 36 0c and include two prominent cooling episodes of 4 0c the cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter sst instability recorded during the early aptian in the pacific is comparable to that reported for the late albian early cenomanian in the atlantic suggesting that such climate perturbations may have recurred during the cretaceous with concomitant consequences for biota and the marine environment

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

design and application of a constant head well permeameter for shallow high saturated hydraulic conductivity soils a new constant head well permeameter has been designed to measure saturated hydraulic conductivities ks ranging from 10 6 to 10 3 ms 1 application to shallow soils of western australia in this ks range highlighted problems with different aspects of the borehole discharge response firstly steady state borehole discharge was only reached in 13 out of 50 tests conducted this was a consequence of the constraint placed on the volume of water storage 40 l of the permeameter for some non steady state cases techniques of estimating steady state discharge from the available data are examined secondly borehole discharge was observed to increase with time in 34 per cent of cases a satisfactory physical explanation of this phenomenon is not presently available other limitations in the application of the constant head well permeameter are noted examination of a number of recent theoretical developments in the determination of ks led to a preference of saturated unsaturated flow solutions by philip 1985 and reynolds et al 1985 these solutions involve the sorptive number to which the solutions were sensitive but not critically sensitive the theory was used to establish design criteria for the permeameter and to identify an optimum application strategy in terms of well dimensions and heads error estimation indicated that the designed permeameter was a practically useful field instrument

extensional fault control on the sedimentation patterns in a continental rift basin el castellar formation galve sub basin spain in the galve sub basin the sedimentary record of the upper hauterivian lower barremian el castellar formation is divided into two stages by a marlstone interval with gypsum stage 1 shows a great variety of subenvironments and facies alluvial palustrine and lacustrine whereas in stage 2 an extensive shallow carbonate lake developed sedimentation was controlled by a system of south dipping ene wsw listric normal faults laterally bounded by nnw sse steeper transfer faults faults controlled sedimentation from a basin scale basin margins and main characteristics and evolution of sediments to a regional and a local scale thickness and facies distribution of the synrift series as well as the location and evolution of lakes and minor alluvial fans the changes between stages 1 and 2 are related to the passing from an independent movement of faults to the movement of all the extensional faults as a whole at a sole detachment level the interval with gypsum was caused by underground water flow changes associated with the interrelation and connection of the faults in the transition period these changes have been correlated with the transition from the rift initial stage to the rift climax stage which took place in the hauterivian barremian transition

calcite twinning constraints on stress strain fields along the mid atlantic ridge iceland calcite veins and amygdule fillings within basalts older than 0 7 ma are mechanically twinned and preserve a subhorizontal shortening strain that resulted from compression and shortening normal to the mid atlantic ridge on both sides of the plate boundary our sample suite includes 19 specimens 7 from the north american plate 4 veins 3 amygdule fillings and 12 from the european plate 9 veins 3 amygdule fillings 18 of which record ridge normal subhorizontal shortening five of the strain analyses two from the north american plate and three from the european plate have a high percentage of negative expected values and these secondary strain results record a ridge parallel shortening strain with plunges that vary parallel to the ridge axis averaged shortening strain magnitudes for the twinned calcite 2 5 european plate 6 02 north american plate and inferred differential stresses 48 mpa that caused the twinning are modest and are thought to represent regional tectonic conditions i e ridge push not local e g hotspot or glacial loading phenomena

atlantic cooling associated with a marine biotic crisis during the mid cretaceous period most of the marine biotic crises that occurred during the hot mesozoic era have been linked to episodes of extreme warmth 1 2 others however may have occurred during cooler intervals that interrupted cretaceous greenhouse warmth 3 5 there are some indications of cooling in the late aptian 6 8 116 114 myr ago but it has not been definitively linked to biotic crisis here we assess the timing and magnitude of late aptian cooling and its association with biotic crises using a suite of geochemical and micropalaeontological assessments from a marine sediment core from the north atlantic ocean as well as global biogeochemical modelling sea surface temperatures derived from the tex86 proxy suggest that surface waters cooled by about 5 degrees c during the two million years coincident with a positive delta c 13 excursion of approximately 2 parts per thousand in carbonates and organic carbon surface productivity was enhanced during this period but the abundance of planktonic foraminifera and nannoconid phytoplankton declined our simulations with a biogeochemical model indicate that the delta c 13 excursion associated with the cooling could be explained by the burial of about 812 000 gigatons of carbon over 2 5 million years about 50 of the this carbon burial occurred in the atlantic southern and tethys ocean basins we conclude that global cooling during greenhouse conditions can cause perturbations to marine ecosystems and biogeochemical cycles at scales comparable to those associated with global warming

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

the valanginian isotope event a complex suite of palaeoenvironmental perturbations abstract the valanginian records a severe crisis of carbonate systems both on platforms and in the pelagic realm this crisis is roughly concomitant with the weissert event characterized by a positive 13c excursion of about 2 in marine carbonates however it is unclear if the response of these two carbonate systems to the global perturbations is contemporaneous or if they react differently for this purpose accumulation rates of pelagic carbonates produced by nannofossils and of platform derived carbonates have been quantified in a hemipelagic environment the vocontian basin se france that has the potential to record the reaction of both shallow water and pelagic carbonate production to a major perturbation of the carbon cycle testified by the isotope excursion also changes through time of clay input have been measured in order to evaluate variations in continental weathering rates and thus in continent derived nutrient input and climatic conditions in terms of humidity aridity accumulation rates of pelagic carbonates of platform derived carbonates and of clays were calculated on the basis of nannofossil absolute abundance and species specific masses of weight percent carbonate content of rocks and a high resolution timescale given by cyclostratigraphy the onset of the positive 13c excursion and the demise of the platforms testify for a synchronous but inverse response of the shallow water and pelagic carbonate systems to an increase in nutrient influx to marine waters as carbonate production by nannofossils decreased during the late valanginian in time of still low platform production the low temperature of marine waters coeval to a still high nutrient input recorded in the latest late valanginian possibly could explain that both platform and pelagic carbonate production contemporaneously decreased

reconstructing estuarine conditions oyster shells as recorders of environmental change southwest florida abstract live collected shells of the oyster crassostrea virginica contain geochemical records of modern temperature and salinity so records of prehistoric conditions may be obtained from subfossil shells restoration of channelized watersheds in florida is receiving much attention and plans for targeted watersheds require information about estuarine conditions before channelization lack of historical records necessitates alternative methods to understand pre disturbance conditions a 14c calibrated amino acid geochronology based on racemization of glutamic acid yielded ages ranging from 190 1220 ad and from 1270 1860 ad for subfossil oysters from blackwater river near natural watershed and for faka union bay channelized watershed respectively 18o and 13c values of subfossil shells from blackwater river indicate salinity and summer temperatures similar to present winter temperatures recorded in shells from 190 590 720 and 1050 ad appear 1 5 c colder than present winter temperatures whereas the shell from 1220 ad records winter temperatures similar to modern winter temperatures these temperature shifts may indicate change in climate or natural seasonal variation of winter temperature from year to year subfossils from faka union bay may reflect a complicated hydrology which cannot be evaluated by isotopic compositions alone and demonstrates the need for development of independent elemental proxies for temperature and salinity decreases in 13c from subfossil to modern shells may in part result from co2 added to the atmosphere from fossil fuel burning the suess effect subfossil 13c that is 1 more positive than modern shells suggest a change in the dominant carbon sources from terrestrial c4 or aquatic plants to c3 plants mangroves

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

cool episode and platform demise in the early aptian new insights on the links between climate and carbonate production the early aptian encountered several crises in neritic and pelagic carbonate production major perturbations in the carbon cycle and an oceanic anoxic event oae1a yet the causal links between these perturbations and climate changes remain poorly understood partly because temperature records spanning the early aptian interval are still scant we present new 18o data from well preserved bivalves from a carbonate platform of the galve subbasin spain that document a major cooling event postdating most of oae1a our data show that cooling postdates the global platform demise and cannot have triggered this event that occurred during the warmest interval the warmest temperatures coincide with the time equivalent of oae1a and with platform biotic assemblages dominated by microbialites at aliaga as well as on other tethyan platforms coral dominated assemblages then replace microbialites during the subsequent cooling nannoconids are absent during most of the time equivalent of the oae1a probably related to the well known crisis affecting this group yet they present a transient recovery in the upper part of this interval with an increase in both size and abundance during the cool interval portion that postdates oae1a an evolution toward cooler and drier climatic conditions may have induced the regional change from microbial to coral assemblages as well as nannoconids size and abundance increase by limiting continent derived input of nutrients

a volcanic co2 pulse triggered the cretaceous oceanic anoxic event 1a and a biocalcification crisis the aptian oceanic anoxic event 1a oae1a ca 120 ma ago is one of the most prominent of a series of geologically brief intervals in the cretaceous characterized by the deposition of organic carbon rich sediments oaes reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records however the triggering mechanisms for oaes remain controversial here we present a bulk rock and molecular marine and terrestrial bio markers c isotope record at unprecedented time resolution from the cismon section of northern italy that shows that oae1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle the documented sequence of events is most compatible with a trigger associated with increased co 2 emissions possibly leading to a doubling of p co 2 which in turn caused larger c isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the oae1a carbon cycle perturbation

progressive palaeoenvironmental change during the late barremian early aptian as prelude to oceanic anoxic event 1a evidence from the gorgo a cerbara section umbria marche basin central italy abstract during oceanic anoxic event 1a oae 1a 120 ma li et al 2008 organic carbon rich layers were deposited in marine environments under anoxic conditions on a global scale in this study palaeoenvironmental conditions leading to this event are characterised by studying the upper barremian to the lower aptian succession of the gorgo a cerbara section central italy for this an integrated multi proxy approach 13ccarb 13corg 18o phosphorus total organic carbon toc bulk rock mineralogy as well as redox sensitive trace elements rstes has been applied during the late barremian thin organic rich layers occur episodically and associated corg ptot ratios indicate the presence of intermittent dysoxic to anoxic conditions coarse correlations are observed between toc p and biogenic silica contents indicating links between p availability productivity and toc preservation however the corresponding 13ccarb and 18o records remain quite stable indicating that these brief periods of enhanced toc preservation did not have sufficient impact on the marine carbon reservoir to deviate 13c records around the barremian aptian boundary toc enriched layers become more frequent these layers correlate with negative excursions in the 13ccarb and 13corg records possibly due to a warming period as indicated by the 18o record during the earliest aptian this warming trend is reverted into a cooling trend which is then followed by an important warming step near the onset of oceanic anoxic event 1a oae 1a during this time period organic rich intervals occur which are characterised by the progressive increase in rste the warming step prior the onset of oae 1a is associated with the well known negative spike in 13ccarb and 13corg records an important peak in p accumulation rste enrichments and corg ptot ratios indicating the prevalence of anoxic conditions the selli level itself may document a cooling phase rste enrichments and corg ptot ratios confirm the importance of anoxic conditions during oae 1a at this site the gorgo a cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the ontong java plate basalt plateau which started already around the barremian aptian boundary and culminated into oae 1a

sea surface water temperatures over the period 1884 1983 reconstructed from oxygen isotope ratios of a bivalve mollusk shell arctica islandica southern north sea although climate system modeling cannot be imagined without long sea surface temperature sst records observational data is spatiotemporally incomplete and inhomogeneous prior to about 1950 moreover almost no high resolution sst proxies exist from temperate and boreal marine settings here we present a temporally equidistant high resolution sst proxy record of the southern north sea during the period 1884 1983 calculated from oxygen isotope ratios 18oaragonite of arctica islandica l a bivalve mollusk shell arctica islandica produces daily growth increments which enable precise intraannual dating the growing season of specimens from about 25 m water depth upper well mixed layer of the ocean started in february and ended in september observational coads etc and 18oaragonite derived sst data during february through september compare well to each other especially after 1950 apart from similar overall sst trends we found north atlantic oscillation type cycles of 7 9 years in our proxy sst record and in various different instrumentally determined sst chronologies no vital effects exist so that 18oaragonite ratios determined across the shell i e throughout lifetime of the studied specimen reflect ambient water temperatures that occurred during shell growth results of our study demonstrate that a islandica provides long independent and high resolution sst proxy chronologies from higher latitudes such records can complement and further validate observational sst data and help improving climate system models

the vertebrates of the anisian ladinian boundary middle triassic from bissendorf nw germany and their contribution to the anatomy palaeoecology and palaeobiogeography of the germanic basin reptiles abstract systematically excavated bones are described from bissendorf osnabrucker bergland north western germany the bone bed in the compressus zone of the ceratitenschichten meisner fm upper muschelkalk anisian ladinian boundary middle triassic was dated by ceratites sedimentologically it is a bioclastic rudstone built mainly from coenothyris vulgaris brachiopods which were heavily compressed into a 3 mm thin layer parts of the bone bed and the following 15 cm of autochthonous mud were partially eroded synsedimentary by the compressus storm event the material of the not rich bone bed in the germanic upper muschelkalk consists of isolated teeth or fin spines from five well known shark species hybodus longiconus agassiz 1843 acrodus lateralis agassiz 1837 acrodus gaillardoti agassiz 1837 palaeobates angustissimus agassiz 1838 and polyacrodus polycyphus agassiz 1837 teeth and scales from the teleosteans gyrolepis sp dollopterus sp colobodus maximus quenstedt 1835 c frequens dames dames w 1888 die ganoiden des deutschen muschelkalkes palaeontologische abhandlungen 4 133 180 and saurichthys sp have been proved found were mostly vertebra centra and ribs but also teeth and some other postcranial bones from the small pachypleurosaurs anarosaurus sp as well as mostly neusticosaurus sp these originated from adult and juvenile animals which indicates the primary habitat and populations of this region large marine nothosaur reptiles found include nothosaurus cf mirabilis munster 1834 and n giganteus munster 1834 proof of two placodonts is given thanks to placodus gigas agassiz 1833 and cyamodus sp finally a tooth from the terrestrial lepidosaur tanystrophaeus longibardicus bassani 1866 is the northerly most sample found the recorded fauna is well known with complete skeletons of the described species from the northern tethys mte san giorgio switzerland the reptile skeletons are presented here in reconstruction the bone bed composition in bissendorf shows differences in the younger and more terrestrial mixed as well as the age difference in bone beds of northern enodis posseckeri zone and southern germany dorsoplanus zone at bissendorf only nearly complete marine vertebrates occur within the maximum high stand high marine ichthyosaurs seem to be absent indicating a shallow marine position in the western germanic basin

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

strontium and carbon isotope chronostratigraphy of barremian aptian shoal water carbonates northern tethyan platform drowning predates oae 1a abstract a widely accepted hypothesis proposes that the early aptian demise of carbonate platforms in the northern tethyan realm reflects the impact of environmental changes that eventually led to the deposition of organic rich basinal sediments during oceanic anoxic event oae 1a in fact the temporal correlation of oceanic anoxia and platform drowning has not been rigorously tested and evidence indicating causality is debated the present paper provides a high resolution carbon and strontium isotope chronostratigraphy combined with detailed sedimentological analysis applied to the barremian aptian urgonian carbonate platform development at the northern rim of the tethys subalpine chains haute savoie ese france a characteristic barremian aptian carbon and strontium isotope pattern below the onset of oae 1a interval permits precise platform to basin correlation with the barremian stratotype locality of angles se france this chemostratigraphic pattern equally allows for a correlation with well studied shoal water and pelagic records of the northern and central tethys strontium isotope stratigraphy provides a high resolution numerical age data set indicating an earliest aptian age

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

a volcanically induced climate warming and floral change preceded the onset of oae1a early cretaceous the aptian oceanic anoxic event 1a oae1a is preceded by a prominent negative c isotope excursion ncie attributed to major volcanism on the ontong java plateau that is supposed to lead to a pco2 increase and a climate change lower aptian sporomorph assemblages in two pelagic sections from the southern tethys margin n italy were analysed in order to test if the postulated climate changes affected the terrestrial vegetation at the base of the ncie the sporomorph assemblages comprise abundant bisaccate pollen reflecting a warm temperate climate several tens of kiloyears ka after the start of the ncie decreasing bisaccate pollen and increasing classopollis spp and araucariacites spp suggest the beginning of a long term temperature rise palynomorphs indicate that maximum temperatures were reached several tens of ka after the end of the ncie and the onset of oae1a the highest temperatures coincide with arid conditions which could reflect a northward shift of the hot arid northern gondwana floral province as a result of an increasing pco2 over 200 ka after the onset of oae1a reduced volcanic activity and or increased black shale deposition allowed for a drawdown of most of the excess co2 and a southward shift of floral belts

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

stable isotope sclerochronology of rudist bivalves growth rates and late cretaceous seasonality the almost complete translation of shell accretion to vertical growth was a successful morphogenetic adaptation of rudist bivalves which replaced coral algal hydrozoan communities in most tethyan shallow marine environments during the cretaceous growth rates of rudist shells are therefore important in reconstructions of cretaceous shallow marine benthic communities carbon and oxygen isotopic compositions were analyzed in sclerochronological profiles through the shells of two late cretaceous rudist bivalves from greece and turkey values of 13 c vary between 0 8 and 2 2 in the hippuritid vaccinites ultimus and between 0 8 and 2 6 in the radiolitid gorjanovicia cf costata ranges in 18 o are 5 3 to 2 9 and 4 6 to 2 1 respectively a distinct cyclicity of 13 c and 18 o in both shells reflects late cretaceous seasonality and indicates annual vertical growth increments of 45 mm in v ultimus and 54 mm in gorjanovicia the concentrations of minor elements are similar to those of extant bivalves with low mg calcite shells

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

response of input and output of water and chloride to clearing for agriculture five small forested catchments in the collie river basin in southwest western australia were instrumented to quantify the changes in the input and output of salt and water when land use changed from forest to agriculture the paired catchment approach was used with two adjacent catchments located in high rainfall 1200 mm yr 1 and a group of three located in a lower 800 mm yr 1 rainfall area the treatment of complete clearing was applied to one catchment in the high rainfall zone and to about half of one catchment in the lower rainfall zone after three years of calibration with the uncleared control catchments strategies of partial clearing were applied to the third catchment in the lower rainfall zone the catchment pairs were found to be well matched the yield of water and salt increased immediately after clearing in the higher rainfall catchment streamflow increased about four times to 48 of rainfall salt load increased to fifteen times the mean saltfall measured as chloride ion of 7 g m 2 yr 1 direct runoff increased fourfold to 16 of yearly streamflow due partly to the progressive increase in the area of soil saturated to the surface the perched groundwater system was the major source 77 in 1983 of streamflow though it was the route rather than the source of increased salt to the stream the mottled and pallid clay profile was the dominant source of salt transported by the deep groundwater system into the perched aquifer streamflow became perennial in the first postclearing year absolute increases in streamwater and salt output from partially cleared catchments in the lower rainfall location were about an order of magnitude less than for the higher rainfall catchment though the relative increases were similar the three catchments were found to be accumulating salt in the cleared catchments the rising potentiometric surface would establish a saline groundwater discharge zone in the valley and a net export of salt in all treated catchments reduced interception results in increased water availability at the soil surface for stormflow and infiltration the reduction in transpiration had an added effect in increasing recharge to groundwater a new equlibrium for water had not been achieved eight years after clearing but was estimated to precede the new salt equilibrium

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

early aptian algal bloom in a neritic proto north atlantic setting harbinger of global change related to oae 1a pervasive growth of microencrusters lithocodium bacinella characterizes short lived stratigraphic intervals in lower aptian shallow water carbonate platform settings of the central and southern tethys although a causal relationship between this peculiar shallow water facies and the early aptian oceanic anoxic event oae 1a seems likely the temporal and spatial distributions of lithocodium and bacinella mass occurrences in the rock record point to a rather complex pattern possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event oae 1a slightly pre or postdating the deposition of dark organic rich black shales in pelagic basins this study presents evidence for a punctuated and well expressed early aptian bloom of the ulvophycean green algae lithocodium aggregatum observed at the proto north atlantic margin lusitanian basin portugal similar to southern and central tethyan sections a lithocodium dominated interval temporally replaces the rudist dominated platform ecosystem this lithocodium rich horizon is composed of oncoidal floatstones and boundstones including a well exposed biohermal level and reaches a thickness of up to 6 m high resolution carbon isotope stratigraphy shown here clearly argues for lithocodium to represent a biotic harbinger of environmental change in the run up of oae 1a chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto north atlantic was coeval with an early aptian carbonate platform drowning episode observed in the northern tethys prior to oae 1a a regionally enhanced nutrient level and a relative sea level rise are suggested to have triggered the transient mass occurrence of lithocodium microencrusters which also may have been influenced by elevated atmospheric co2 concentrations related to the emplacement of the ontong java large igneous province upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients which tentatively diminished and finally interrupted the metazoan carbonate platform factory

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

a mechanism for brief glacial episodes in the mesozoic greenhouse 1 the mesozoic perhaps the longest period of warmth during the phanerozoic earth history has been repeatedly affected by short lived cold interludes lasting about one million years while the origin of these cold snaps has been classically attributed to a temporary atmospheric co2 drawdown quantified mechanisms explaining these instabilities of the carbon cycle are still lacking based on a climate carbon cycle model we show that the general demise of carbonate platforms accompanying these short lived cold interludes is a powerful mechanism capable of generating a fast atmospheric co2 decrease and a moderate sea level drop associated with ice sheet buildup the temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning

absence of major vegetation and palaeoatmospheric pco2 changes associated with oceanic anoxic event 1a early aptian se france the deposition of organic rich sediments during the late early aptian oceanic anoxic event oae 1a has been interpreted to result in a major decrease of palaeoatmospheric co2 concentrations accompanied by significant changes in the terrestrial flora in order to test this hypothesis the oae 1a interval in the vocontian basin se france has been studied with a combined approach including stable carbon isotopes organic geochemistry and palynology to estimate changes in palaeoatmospheric co2 levels across the oae 1a the 13c composition of presumed algal biomarkers low molecular weight n alkanes steranes and of bulk carbonate carbon are used our results yield estimated early aptian carbon dioxide partial pressure pco2 values three to four times the preindustrial level and only a moderate drop across the black shale event this moderate drop in pco2 is supported by palynological results the frequency patterns of climate sensitive sporomorphs incl pteridophyte spores bisaccate pollen and classopollis spp display only minor fluctuations throughout the studied section and indicate relatively stable patterns of terrestrial vegetation during and after formation of the oae 1a black shale the occurrence of a characteristic early aptian carbon isotope pattern across the oae 1a interval permits accurate chemostratigraphic correlation with the well studied livello selli interval of the cismon record n italy the contemporaneous formation of individual black shale layers at both sites indicates that transient episodes of dysoxic anoxic bottom waters prevailed over large areas in the w tethys ocean independent of depositional setting comparison of the palynological data from the two locations displays significant differences in the frequency patterns of bisaccate pollen the contrasting pollen spectra are interpreted to reflect prominent changes in the palaeoceanographic current patterns and or selective sorting due to sea level rise rather than latitudinal shifts of the major floral belts

stable isotope fractionation between mollusc shells and marine waters from martinique island abstract forty nine aragonitic and calcitic shells from 14 species of marine tropical molluscs bivalvia gastropoda polyplacophora and ambient waters from martinique have been analyzed for their carbon and oxygen isotope compositions mineralogy of shells was systematically determined by raman spectroscopy that reveals composite shell structures and early processes of diagenetic alteration in mangrove brackish waters result from the mixing between 89 1 of seawater and 11 1 of freshwater a hydrological budget quantified by both oxygen isotope and salinity mass balance calculations mollusc shells from the mangrove environment s 31 18 o 0 5 are characterized by mean 13 c values 1 2 lower than those 2 6 living in the open sea s 35 18 o 1 these low carbon isotope compositions result from the oxidation of organic matter into bicarbonate ions used in the building of mollusc shells the oxygen isotope compositions of the studied mollusc species are mainly controlled by the temperature and composition of seawater whereas the role of the so called vital effects is negligible contrasting with carbon isotopes variability in the 18 o values among and within species of mollusc shells is very low 1 0 15 for a given littoral environment using ambient temperatures of seawater 28 30 c oxygen isotope fractionations between all studied living species and environmental waters match those extrapolated from the fractionation equation established for molluscs by grossman and ku chem geol isot geosci sect 59 1986 59 in the range 3 20 c by analyzing calcite and aragonite layers from the same shell or by comparing shells from different species living in the same environment there is no evidence that oxygen isotope fractionation between aragonite and water differs from that between calcite and water on the basis of these results we conclude that the oxygen isotope compositions of shells from most fossil mollusc species are suitable to estimate past seawater temperatures at any paleolatitude

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

unraveling environmental histories from skeletal diaries advances in sclerochronology high resolution proxy archives from aquatic settings are essential to better understand processes and mechanisms of global change during the last decade it has become increasingly evident that calcified tissues of bivalve mollusks and cold water corals in particular can significantly increase our knowledge of seasonal to multi decadal paleoclimate and paleoenvironmental variability in the extratropical oceans and coastal marine settings daily tidal fortnightly and annual growth patterns of periodically formed skeletal hard parts provide a means to place the proxy record in a precise temporal context their extreme longevity coupled with the running similarity between growth increment time series of contemporaneous bivalves opens the possibility of constructing stacked chronologies covering centuries to millennia which provide information on decadal climate and environmental variability and magnitudes of climate variability through time a current major research focus is on how to translate geochemical properties of the skeletons into quantifiable environmental proxy data and how to eliminate the adverse influence of vital effects on the proxy records this special issue presents the most recent advances in the field of sclerochronology specifically calcified tissues of bivalve mollusks cold water corals and tropical shallow water corals the majority of the contributions deal with the potential reconstruction of temperature ph and productivity through the analysis of variable growth rates sr ca mg ca ba ca u ca li ca 13c 18o and 44 40ca four papers present composite chronologies of two long lived bivalve species and discuss inherent decadal climate variability and one study demonstrates that sclerochronology can shed light on socioeconomic patterns of past human populations as well as resource use and resource management by people

late cenozoic sedimentation in california continental borderland basins as revealed by seismic facies analysis the california continental borderland began to form during late miocene time only the latest miocene and younger sediments are ponded in the contemporary basins upper miocene strata are characterized by widespread diatomaceous deposits that conformably drape all of the underlying topographic irregularities the pliocene quaternary sediments occur as flat lying ponded clastic sequences that fill the contemporary basins a seismic facies analysis has defined facies patterns in the pliocene quaternary basin fill sequences of each basin in the offshore basins patton tanner santa cruz and san nicolas fine grained mass flow and hemipelagic sediments derived from the local insular sources dominate the basin fill sequences santa catalina basin is a transitional basin filled with fine grained turbidites and hemipelagic sediments derived from both continental and local insular sources the nearshore basins santa barbara santa monica and san pedro basins and san diego trough are filled by thick sequences of continental sediments that form prominent deep sea fans the borderland was dominated by biogenic pelagic sedimentation in the late miocene and by detrital sediment gravity flow deposition in the pliocene and quaternary accumulation rates estimated from pliocene quaternary sediment thickness for each basin show that in the offshore basins as well as in san diego trough rates have remained fairly constant since the pliocene in contrast the nearshore basins exhibit an increasing rate of accumulation versus time that is related to the progradation of continent derived sediments outer and intermediate basin accumulation data indicate decreasing contributions with time from offshore highs because of erosion and regional subsidence intermediate basins show an increase in mass wasting deposits slope facies with time which is the result of increasing fine suspension slope deposition and eventual failure

effects on catchment water balance from the management of pinus plantations on the coastal lowlands of south east queensland australia a paired catchment study was conducted over a 10 year period on the hydrology of an exotic pinus plantation in the coastal lowlands of south east queensland australia each catchment was instrumented with a stream monitoring station tipping bucket rain gauge and a network of piezometers to monitor the shallow perched water table after a 6 year calibration period a harvest treatment was imposed on one catchment review clearfelling approximately 90 of the catchment area which contained a mature 44 year old pinus elliottii plantation this subsequently was re established with a second rotation plantation of a hybrid of p elliottii p caribaea var hondurensis the control catchment crayfish contained a p elliottii plantation similar to that clearfelled at review the post harvest period was monitored for a further 4 years evapotranspiration was found to be the major output flux with stream flow only a minor component of the study catchments water budget areas with gleyed podzolic soils were found to remain waterlogged for periods up to 7 months following the seasonally high summer rainfall period with other soils having water logging periods of only a few months little change was observed in waterlogging characteristics following harvesting in contrast to stream flow which increased for 3 years but with evidence of a decline after 5 years the perched watertable piezometric surface indicated that its lateral drainage differs from that of surface flows the perched watertable drainage fluxes from the study catchments seem minor and off site movement of solutes e g nutrients and contaminants via them would be limited it was identified that the interaction between the perched and deep aquifers was poorly understood as well as the relative importance of the soil moisture storage of the aquitard clay layer between them it was concluded that there is a need to undertake more detailed analysis using modelling and to obtain additional field data on soil layer properties and piezometric levels of the deep aquifer copyright 2002 john wiley sons ltd

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

reconstruction of short term palaeoceanographic changes during the formation of the late albian niveau breistroffer black shales oceanic anoxic event 1d se france the niveau breistroffer black shale succession in the vocontian basin se france is the regional equivalent of the widely distributed late albian oceanic anoxic event 1d the studied black shale rich interval at the col de palluel section is 6 28 m thick and comprises four black shale units with up to 2 5 wt total organic carbon toc intercalated with marlstones calcareous nannofossil palynomorph planktic foraminifera and stable isotopic data from the niveau breistroffer succession suggest that short term climate changes influenced its deposition with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition an increase in the terrigenous marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation a nutrient index based on calcareous nannofossils and the abundance pattern of small 63 125 m hedbergellid foraminifera show short term changes in the productivity of the surface water surface water productivity was reduced during black shale formation and increased during marlstone deposition a calcareous nannofossil temperature index and bulk rock oxygen isotope data indicate relative temperature changes with warmer surface waters for black shale samples at these times warm humid climate and reduced surface water productivity were accompanied by greater abundances of subsurface dwelling calcareous nannofossils nannoconids and planktic foraminifera rotaliporids these taxa presumably indicate more stratified surface water conditions we suggest that the formation of the niveau breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation this in turn caused a decrease in low latitude deep water formation and probably an increase in surface water stratification the combination of these two mechanisms caused depleted o 2 concentrations in the bottom water that increased the preservation potential of organic matter

interactions between environmental change and shallow water carbonate buildup along the northern tethyan margin and their impact on the early cretaceous carbon isotope record 1 the evolution of the early cretaceous northern tethyan carbonate platform was not only influenced by changes in sea level detrital influx and surface water temperature but also by changes in trophic levels we distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder water heterozoan communities superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy the initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general on the basis of a comparison between the temporal changes in an early cretaceous ammonite calibrated d 13 c record from southeastern france and coeval changes in the platform record we suggest that the history of carbon fractionation along the northern tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir but it was also influenced by the above mentioned changes in the ecology and geometry of the adjacent carbonate platform phases of photozoan carbonate production induced positive trends in the hemipelagic carbonate d 13 c record phases of heterozoan carbonate production pushed the d 13 c system toward more negative values platform drowning episodes implied an initial increase in d 13 c values followed by a longerterm decrease in d 13 c values

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

episodes of high productivity and cooling in the early aptian alpine tethys a palynological and organic geochemical study of the early aptian selli unit oceanic anoxic event 1a of the western tethys provides new information about paleoceanography and documents pronounced changes in the regional climate pattern it also emphasizes the role of oxic degradation of organic matter even at horizons with the highest rates of organic carbon corg accumulation the absence of anoxia indicates that enhanced primary production is the main reason for these organic carbon accumulations and variations in preservation are related to pulses in primary production and nutrient recycling despite the high productivity character of the selli unit black shales the 13ccarb values are not marked by a positive shift but by an interval of unchanged values warm climatic conditions for deposition of the selli unit are inferred from the presence of southern provenance pollen and low 18o values for the interval above the selli unit changes in the pollen spectrum and an increase in 18o values reflect a hitherto undocumented late early aptian cooler and more humid climate and or a reorganization of the tethyan oceanographic circulation pattern

community replacement of neritic carbonate organisms during the late valanginian platform demise a new record from the provence platform abstract the valanginian is marked by a major platform demise inducing a hiatus in the northern tethyan neritic carbonate record from the top of the lower valanginian to the lower hauterivian new biostratigraphic and chemostratigraphic data from the ollioules section provence platform southern france are presented here demonstrating that a large part of the upper valanginian is preserved in an inner platform environment the thick upper valanginian aggrading carbonate succession is observed in an aborted rift domain implying relatively low subsidence in this context a relatively long term sea level rise was required to sustain a keep up style of carbonate production like the apulian platform the remarkable preservation of the provence platform may have been favored by its remoteness from terrigenous source areas as suggested by the low clastic inputs and low p accumulation rates two main biotic community replacements are observed in ollioules the first saw the development of abundant microbialites and algae at the onset of the late valanginian a tubiphytes concentration occurred during the coolest climatic conditions and the transition towards arid conditions whereas the subsequent lithocodium bacinella and orbitolinids assemblages developed under low nutrient conditions during a warmer interval both assemblages may have been triggered by increased alkalinity the second community replacement saw the installation of coral and rudist dominated communities during the latest valanginian to early hauterivian they indicate a change to oligotrophic open marine conditions six medium scale sequences have been defined in ollioules indicating short term transgressive regressive trends superimposed on a long term transgression low nutrient inputs and relatively low subsidence in an aggradational context may explain the survival of the isolated provence carbonate platform during a time of widespread drowning episodes and platform demise in the northern tethyan domain

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes