biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

surface area control of shallow cratonic to deep marine carbonate accumulation sites of calcium magnesium carbonate accumulation have been shifting from shallow shelf to deep marine settings since the late cretaceous during this time total area of flooded epicratonic shelf has decreased about 50 and areas of shelf carbonate deposition have declined from 27 106 km to present areas of 1 4 106 km while the maximum extent of platform carbonate accumulation has decreased from about 50 to 28 north latitude in terms of cratonic carbonate this decrease in tropical shelf area has resulted in a sixfold reduction in shoal water limestone accumulation from a cretaceous rate of 0 6 km m y to a present value of about 0 1 106 km m y over the same time period the global carbonate compensation depth has deepened by about 1 5 km attendant with a threefold areal increase of calcite ooze depositionn 40 to 130 106 km this expansion has resulted in an eightfold increase in pelagic limestone accumulation from a cretaceous rate of 0 05 106 km m y to a present rate of about 0 4 106 km m y transfer of accumulation from shallow cratonic to deep marine depositional settings records the central role of sedimentary environment surface area in predicating the differential partitioning of finite carbonate fluxes to phanerozoic global oceans

did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

macroevolutionary history of the planktic foraminifera planktic foraminifera are an abundant component of deep sea sediment and are critical to geohistorical research primarily because as a biological and geochemical system they are sensitive to coupled bio hydro lithosphere interactions they are also well sampled and studied throughout their evolutionary history here we combine a synoptic global compilation of planktic foraminifera with a stochastic null model of taxonomic turnover to identify statistically significant increases in macroevolutionary rates there are three taxonomic diversifications and two distinct extinctions in the history of the group the well known cretaceous paleogene extinction is of unprecedented magnitude and abruptness and is linked to rapid environmental perturbations associated with bolide impact the eocene oligocene boundary extinction occurs due to a combination of factors related to a major reorganization of the global climate system changes in ocean stratification seawater chemistry and global climate recur as primary

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

whole layer convection in a heterogeneous planetary mantle 1 geochemical observations demonstrate that earth s mantle is heterogeneous but the sizes forms and characteristics of its reservoirs are not constrained using laboratory experiments we have systematically studied a simple nonhomogeneous system where two layers of miscible fluids with different densities depths and viscosities are subjected to a destabilizing temperature contrast when the buoyancy number b i e the ratio of the stabilizing chemical density anomaly to the destabilizing thermal density anomaly is lower than 0 3 0 5 the whole layer regime develops with a deformed interface and convective patterns over the whole tank depth the system systematically evolves toward one fluid rayleigh benard convection because of stirring however the two isolated fluids can persist for very long time compared to the characteristic timescale of thermal convection and give rise to numerous transient behaviors of particular interest for planetary mantles are the pulsatory dynamics where the interface between the two layers deforms in large domes moving up and down quasiperiodically according to the scaling laws derived from the experiments such a mechanism could indeed provide a simple and single physical explanation for the superswells observed at present on earth and more generally for the long term episodicity in planetary interiors observed in geological records

sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

ecological succession palaeoenvironmental change and depositional sequences of barremian aptian shallow water carbonates in northern oman barremian and aptian shallow water carbonate facies uppermost lekhwair kharaib and shuaiba formations are described from outcrops in northern oman based on facies analysis and bedding pattern three orders of depositional sequences are defined third to fifth order and correlated between sections over the course of three third order sequences covering the barremian to lower aptian a third order depositional pattern is documented that consists of a succession of three distinct faunal assemblages discoidal orbitolinids and calcareous algae were deposited during early transgression microbialites and microencrusters dominate the late transgressive to early highstand facies and a rudist and miliolid dominated facies is typical of the highstand this ecological succession was controlled largely by palaeoenvironmental changes such as trophic level and clay influx rather than sedimentological factors controlled by variations in accommodation space orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow water carbonate response to global changes affecting late barremian to aptian palaeoclimate and palaeoceanography

geochemistry of atmospheric aerosols generated from lava seawater interactions 1 trace elements were measured in the aerosol plume produced by lava seawater interactions along the shoreline of kilauea volcano hawaii plume concentrations were normalized relative to hawaiian basalt composition and showed a linear log log covariation with their emanation coefficient an indicator of element volatility normalized aerosol concentrations also consistently covaried with corresponding normalized concentrations in dilute fumarolic gas from kilauea volcano and fumarolic gas condensates from kudryavy and merapi volcanoes despite different mechanisms of element volatilization conservatively estimated regional ocean deposition rates of cu cd ni pb mn zn fe and p were 50 times background rates thus upper ocean volcanism may be an important source of both toxic and nutrient elements to the surrounding ocean it appears unlikely however that shallow ocean volcanism can exert a significant impact on the global ecosystem even during massive lava emplacements

late cretaceous paleosols as paleoclimate proxies of high latitude southern hemisphere mata amarilla formation patagonia argentina abstract although there is general consensus that a global greenhouse climate characterized the mid cretaceous details of the climate state of the mid cretaceous southern hemisphere are less clearly understood in particular continental paleoclimate reconstructions are scarce and exclusively derived from paleontological records using paleosol derived climofunction studies of the mid to upper cretaceous mata amarilla formation southern patagonia argentina we present a reconstruction of the mid cretaceous climate of southern south america our results indicate that at 60 south paleolatitude during the cenomanian santonian stages the climate was subtropical temperate warm 12 c 2 1 c and humid 1404 108 mm yr with marked rainfall seasonality these results are consistent with both previous estimations from the fossil floras of the mata amarilla formation and other units of the southern hemisphere and with the previous observations of the displacement of tropical and subtropical floras towards the poles in both hemispheres the data presented here show a more marked seasonality and slightly lower mean annual precipitation and mean annual temperature values than those recorded at the same paleolatitudes in the northern hemisphere

supercontinents and superplume events distinguishing signals in the geologic record abstract simultaneous supercontinent and superplume events may reinforce or cancel signals preserved in the geologic record alternatively one signal may overwhelm the other for instance relatively low sea level during a 2 7 ga superplume supercontinent event may reflect direct hits of superplumes beneath the supercontinent although both supercontinent formation and superplume events occurred at 0 28 1 9 and 2 7 ga global warming at these times indicates the dominance of superplume events in controlling climate enhanced deposition of black shales correlates with superplume events and with supercontinent breakup carbon isotopes in seawater however show positive excursions during supercontinent breakup at 2 2 2 1 and 0 8 0 6 ga but show mixed signals or no signal during other supercontinent or superplume events probably due to negative feedbacks peaks in marine organism originations at 100 280 and 480 ma correlate with possible superplume events whereas an overall decrease in origination rate in the early paleozoic correlates with the growth of pangea and destruction of shallow marine environments increased production rates of juvenile crust correlate with formation of supercontinents and with superplume events there may be two types of superplume events catastrophic events which are short lived

equatorial convergence of india and early cenozoic climate trends india s northward flight and collision with asia was a major driver of global tectonics in the cenozoic and we argue of atmospheric co2 concentration pco2 and thus global climate subduction of tethyan oceanic crust with a carpet of carbonate rich pelagic sediments deposited during transit beneath the high productivity equatorial belt resulted in a component flux of co2 delivery to the atmosphere capable to maintain high pco2 levels and warm climate conditions until the decarbonation factory shut down with the collision of greater india with asia at the early eocene climatic optimum at 50 ma at about this time the india continent and the highly weatherable deccan traps drifted into the equatorial humid belt where uptake of co2 by efficient silicate weathering further perturbed the delicate equilibrium between co2 input to and removal from the atmosphere toward progressively lower pco2 levels thus marking the onset of a cooling trend over the middle and late eocene that some suggest triggered the rapid expansion of antarctic ice sheets at around the eocene oligocene boundary

crustal volumes of the continents and of oceanic and continental submarine plateaus global topographic data and the assumption of airy isostasy have been used to estimate the crustal volumes of the continents and the oceanic and continental submarine plateaus the calculated crustal volumes are 7182 x lo6 km3 for the continents 242 x lo6 km3 for continental submarine plateaus and 369 x lo6 km3 for oceanic plateaus the falkland plateau and the lord howe rise are the two largest continental submarine plateaus with volumes of 48 x lo6 km3 and 47 x lo6 km3 respectively total continental crustal volume is 7581 x lo6 km3 including the volume of continental sediments on the ocean floor 160 x lo6 km3 in good agreement with previous estimates continental submarine plateaus on the seafloor comprise 3 2 of the total continental crustal volume the largest oceanic plateaus in order of decreasing size are the ontong java plateau the kerguelen plateau the caribbean the chagos laccadive ridge the ninetyeast ridge and the mid pacific mountains together they comprise 54 of the total anomalous crustal volume in oceanic plateaus an upper bound to the continental crust addition rate by the accretion of oceanic plateaus is 3 7 km3 yr a value that assumes accretion of all oceanic plateaus with a total volume of 4 9 of the continental crustal volume on a 100 myr time scale even if a substantial fraction of the crustal volume in oceanic plateaus is subducted accretion of oceanic plateaus could make a contribution to continental growth since the upper bound to the addition rate exceeds recent estimates of the island arc addition rate subduction of continental submarine plateaus with the oceanic lithosphere on a 100 myr time scale gives an upper bound to the continental crustal subtraction rate of 2 4 km3 yr much larger than recent estimates of crustal subtraction by subduction of seafloor sediments effective subduction of all oceanic plateaus implies equally effective subduction of continental submarine plateaus a potentially important way to recycle continental crust back into the mantle may be the break off of small fragments from the continents entrapment of the continental fragments in the seafloor and subduction of the fragments with the oceanic lithosphere this process may be occurring in the mediterranean for corsica and sardinia

modelling oceanic carbon and phosphorus fluxes implications for the cause of the late cenomanian oceanic anoxic event oae2 a two box ocean model with a coupled carbon and phosphorus cycle is used to test which processes can realistically generate a rapid positive 2 13c excursion in the global carbon reservoir internal oceanic processes enhanced preservation of organic matter under anoxic conditions enhanced upwelling cannot produce a substantial 13c excursion under the assumption that burial rates of c and p are coupled loss of nutrients to the sediment acts as a negative feedback mechanism that prevents a substantial perturbation of the carbon cycle a large and renewable source of nutrients is needed either from increased continental weathering or from enhanced regeneration of sedimentary organic phosphorus under anoxic conditions measurements of total phosphorus and organic carbon in sediments from the tarfaya basin morocco suggest that a large decrease in p burial occurred relative to organic carbon at the base of the cenomanian turonian oceanic anoxic event oae2 with the right magnitude to quantitatively explain a 2 shift in 13c it is concluded that the main underlying mechanism that allowed and sustained enhanced carbon burial during the mid cretaceous was a perturbation of the oceanic phosphorus cycle

carbon dioxide emissions from deccan volcanism and a k t boundary greenhouse effect a greenhouse warming caused by increased emissions of carbon dioxide from the deccan traps volcanism has been suggested as the cause of the terminal cretaceous extinctions on land and in the sea we estimate total eruptive and noneruptive co2 output by the deccan eruptions from 6 to 20 1016 moles over a period of several hundred thousand years based on best estimates of the co2 weight fraction of the original basalts and basaltic melts the fraction of co2 degassed and the volume of the deccan traps eruptions results of a model designed to estimate the effects of increased co2 on climate and ocean chemistry suggest that increases in atmospheric pco2 due to deccan traps co2 emissions would have been less than 75 ppm leading to a predicted global warming of less than 1 c over several hundred thousand years we conclude that the direct climate effects of co2 emissions from the deccan eruptions would have been too weak to be an important factor in the end cretaceous mass extinctions

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

quantitative analysis of calcareous microfossils across the albian cenomanian boundary oceanic anoxic event at dsdp site 547 north atlantic nannofossil and planktonic and benthic foraminiferal assemblages were studied quantitatively in an expanded albian to cenomanian section at dsdp site 547 in the eastern north atlantic the section spans a 0 5 positive 13c excursion across the albian cenomanian boundary representing one of the mid cretaceous oceanic anoxic events oae1d the base of the carbon excursion at site 547 coincides with a major faunal turnover in planktonic foraminifera including extinctions and first appearances of several species as well as geographic entries in contrast nannofossil assemblage composition which reflects conditions in the photic zone shows little variation related to the carbon excursion arguing against a noticeable change in surface water productivity during the event benthic foraminifera which represent a paleowaterdepth of around 1 km show that there was no change in environmental conditions at that water depth and offer no support for increased deep water anoxia combined with published data microfossils at site 547 suggest that improved preservation of organic matter due to a decrease in oxygen content in a shallow oxygen minimum zone is a more likely cause for the albian cenomanian boundary anoxic event than an increase in productivity

ontogeny and habitat change in mesozoic cephalopods revealed by stable isotopes δ18o δ13c abstract stable isotope 18 o and 13 c ratios were measured in successive aragonitic shell sequences of ammonoids class cephalopoda to determine whether their depth distributions changed within ontogeny and whether stable isotope values differ in various morphological groups e g leiostraca vs trachyostraca we concentrate mainly on 18 o for temperature results and added 13 c data to obtain information on the ontogenetic history for which full spiral measurements were undertaken for the first time to obtain valid stable isotope data from ammonoid shells we measured ontogenetic sequences full shell within different genera data sets from the jurassic cadoceras and cretaceous hypacanthoplite s nowakites were chosen due to the pure primary aragonitic shell preservation the study was designed to extract better information on the habitat and life cycle of fossil cephalopods e g ammonoids in comparison with recent cephalopods e g nautilus spirula sepia possessing equivalent or comparable hard parts the data from three genera suggest different modes of life in at least two morphological groups we detected and established two main groups with different ontogenetic strategies based on the 18 o data the wcw type warm cool warm type of cadoceras resembles strategies in nautilus and sepia which migrate from shallow into deeper environments and back in ontogeny wc type warm cool type and the cw type cool warm type of hypacanthoplites resembling the first two migration phases of spirula cwc type which migrates from deeper into shallower and back again into deeper habitats the main three phases revealed by both 18 o and 13 c data sets most probably reflect diet changes in juvenile to mid aged individuals followed by a habitat change for spawning adults in cadoceras the temperatures range from 21 2 c for juveniles down to 12 1 c for mid aged individuals and back up 16 9 c in adults the cw type strategy of hypacanthoplites involves a temperature range of 22 8 c to 28 9 c the respective mean values are 24 2 c juveniles 25 8 c middle phase and 27 8 c adults the 13 c values also revealed three ontogenetic stages in cadoceras and hypacanthoplites including two major shifts from positive to negative and from negative to positive values which probably correspond to sexual maturation the initiation of reproduction and concomitant changes in diet the presented data combined with previous ontogenetic studies e g stable isotopes on spirula nautilus and sepia can be used as proxies to directly correlate the habitats and ontogeny of recent and fossil cephalopods

microfacies biostratigraphy and geochemistry of the hemipelagic barremian aptian in north central tunisia influence of the oae 1a on the southern tethys margin upper barremian lower upper aptian hemipelagic deposits of the hamada formation in the djebel serdj area north central tunisia were studied in detail with regard to microfacies biostratigraphy 13 c stratigraphy and geochemistry our data provide insights into the palaeoenvironmental evolution and sea level fluctuations of the tunisian shelf the unusually expanded deposits consist of mud wacke and packstones which reflect mid and outer ramp depositional environments planktonic foraminifer and 13 c stratigraphy allowed us to establish a detailed time frame and the recognition of the lower aptian oceanic anoxic event 1a oae 1a as well as time equivalent deposits of shallowmarine carbonate platform drowning based on our microfacies studies we subdivide the studied sections into four genetic intervals a pre oae 1a interval an oae 1a and platform drowning equivalent interval and a post platform drowning interval we present a 3rd order sea level curve for the tunisian shelf deriving from the results of our microfacies studies deposits of the oae 1a in the sections investigated are characterised by bioclastic wacke and packstones with high abundances of poorly preserved radiolarians and moderately to well preserved planktonic foraminifers suggesting a transgression and an eutrophication of the upper water column scarceness of benthic macrofossils low abundances of small benthic foraminifers and ostracods possibly suggest dysoxic conditions at the seafloor mudstones of the platform drowning time equivalent deposits directly overlying the oae 1a are partly showing a pronounced drop in carbonate content and are scarce of macrofossils 2008 elsevier b v all rights reserved

environmental impact of volcanic margin formation late rift stage uplift and subsequent massive transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere hydrosphere and thus biosphere on regional and global scales the early tertiary north atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls and that extrusive complexes influenced paleogene oceanic and continental margin circulation and sedimentation temporal correspondence with the terminal paleocene deep sea extinction event and the earliest eocene greenhouse suggests a global impact possibly by enhanced atmospheric co 2 levels leading to polar warming and thereby changing patterns of deep water formation in this context transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

influence of oceanic anoxic events on the evolution of mid cretaceous radiolaria in the north atlantic and western tethys abstract mid cretaceous aptian turonian extinction radiation events of radiolaria from the north atlantic and western tethys are summarized in relation to oceanic anoxic events oae from investigations of radiolarian faunas black shales and stable carbon isotopes extinction and radiation events of radiolaria can be observed from the late early aptian the earliest albian the latest albian and the cenomanian turonian boundary these events correlate well with organic carbon rich sediments that contain type ii kerogen and show positive 13c excursions they correspond to the oceanic anoxic events oae in the early aptian oae 1a selli level early albian oae 1b late albian oae 1d and latest cenomanian oae 2 bonarelli level detailed investigations of the two most significant events the selli and the bonarelli level in the umbria marche basin of central italy show that extinctions coincide with the first occurrence of marine black shales type ii kerogen and the most prominent rise of 13corg values stepwise extinctions and continuous radiations precede and follow the events similar patterns are evident for the oae 1b and 1d black shales dominated by terrestrial organic matter type iii kerogen e g oae 1c are not characterized by isotopic excursions or by radiolarian extinction radiation events contemporaneous drowning events documented from carbonate platforms around the investigated basins provide a link to a model where flooding of lowlands and leaching of nutrients during a relative rise of sea level lead to an increased productivity and an expansion of the oxygen minimum zone omz because of the loss of deep habitats deeper dwelling forms become extinct shallower dwelling radiolarians survive a narrowing of the omz during highstands and relative sea level falls together with a coupled decrease of the nutrient supply leads to the development of new niches and therefore to radiation

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

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

a note on the use of a nomogram for self potential anomalies a nomogram has been devised for situations in which the source of a self potential anomaly can be approximated by an obliquely polarized sphere or horizontal cylinder embedded in a homogeneous half space the nomogram can be used for rapid determination of three parameters of the target 1 depth to the centre 2 angle between the axis of polarization and the horizontal 3 shift of the point vertically above the centre of the body from zero potential value the nomogram has been tested and the parameters determined for sp results obtained over ore bodies weiss and suleymankoy in the ergani copper district turkey the curves computed for the estimated parameters match the field curves well

the ischia volcanic island southern italy inferences from potential field data interpretation abstract in this paper we present a study of the structural setting of the volcanic island of ischia by the analysis and interpretation of high resolution aeromagnetic and self potential data recently acquired over the island the magnetic data allowed us to locate the main anomaly sources and lineaments of the island and its offshore surroundings while the self potential sp data provided information on both the structural pattern of the resurgent caldera and the high temperature fluid circulation an inversion of the acquired magnetic and sp data and a joint modelling of the magnetic data and of a previous gravity data set along a sw ne profile allowed us to build a model of the island the model is characterized by the presence of an igneous very likely trachytic structure whose top is located at 1200 1750 m b s l such a body possibly formed by several neighbouring intrusions has a density contrast with the pyroclastic cover of about 0 4 gr cm 3 and its central western part below mt epomeo seems to be demagnetized the demagnetization should be connected to the high geothermal gradient measured in this portion of the island and may be due to hydro chemical alteration processes and or to the possible presence of partially melted spots within the intrusion our outcome is consistent with the results of previous geophysical geo volcanological and geothermal studies

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

the mid cretaceous super plume carbon dioxide and global warming carbon dioxide releases associated with a mid cretaceous super plume and the emplacement of the ontong java plateau have been suggested as a principal cause of the mid cretaceous global warming the authors developed a carbonate silicate cycle model to quantify the possible climatic effects of these co sub 2 releases utilizing four different formulations for the rate of silicate rock weathering as a function of atmospheric co sub 2 they find that co sub 2 emissions resulting from super plume tectonics could have produced atmospheric co sub 2 levels from 3 7 to 14 7 times the modern pre industrial value of 285 ppm based on the temperature sensitivity to co sub 2 increases used in the weathering rate formulations this would cause a global warming of from 2 8 to 7 7c over today s global mean temperature altered continental positions and higher sea level may have been contributed about 4 8c to mid cretaceous warming thus the combined effects of paleogeographic changes and super plume related co sub 2 emissions could be in the range of 7 6 to 12 5c within the 6 to 14c range previously estimated for mid cretaceous warming co sub 2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20 of the mid cretaceous increase in atmospheric co sub 2

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

oceanic crust production and climate during the last 100 myr in order to evaluate the possible influence of oceanic crust production on climatic changes during the past 100myr variations in total oceanic crust for this period including production at mid ocean ridges oceanic plateaus and back arc basins were calculated using the most recent and accurate time scales the rates presented here differ from those of larson 1991a b on cenozoic fluctuations and show that 1 maximum production values occurred during the cenomanian palaeocene and late oligocene early miocene and 2 minimum values occurred in campanian maastrichtian late eocene and middle miocene significantly variations of oceanic crust production correspond with variations in the 18o of deep water benthic foraminifera maximum values of oceanic crust production correspond with minimum values of 18o and minimum production values with maximum values of 18o this latter synchronism suggests that changes in land sea relationships and atmospheric co2 related to major fluctuations in oceanic crust production were the main cause of mid cretaceous warming and late cretaceous cooling and of climatic quasi cycles having a periodicity of 33 38 million years over the last 100 myr this is the first report showing variations of ocean crust production synchronized with the cenozoic climate changes

natural polarization studies at balcova geothermal field contrasting resistivity temperature pressure porosity and fluid migrations are the main causes of ion accumulations along the discontinuities which create coupling induced natural current flow which is observed as the natural polarization potential npp on the surface natural polarization electric field npe variations were recorded along 13 profiles about 2 5 km each in a north south direction interpretation of the coincident anomalies of the npp and the npe field resulted in determination of the polarization angle polarization focal depth and the azimuths of the polarized interfaces considerable agreement between faults delineated by previous geological and geophysical investigations and polarization discontinuities was observed the polarization plane was observed to be horizontal in high temperature areas but steepened gradually in relatively colder regions in the northern costal area from the polarization depth distribution two depression zones were observed separated by an uplifted section elongated in a north south direction the basin at the eastern side had an estimated polarization depth of 1 1 km and was limited by the agamemnon 2 and 1 faults while the western basin had an estimated depth of 1 3 km and extended in the east west direction not previously reported the eastern basin extends on the north side around the town of inciralti more the western basin appeared to be elongated towards the town of cesme less

paleoceanography and paleoclimatology an earth system perspective abstract the purpose of this paper is to provide an overview of paleoceanography and paleoclimatology as a framework for other papers dealing with the earth system geochemical perspectives an introduction to both paleoceanography and paleoclimatology is followed by examples of the temporal changes through the phanerozoic the important and interactive role of the biosphere is emphasized many important changes in the earth system have affected the coupled ocean atmosphere system and many in turn have been reflected in biotic events many such changes can be tracked through time using geochemical signatures as proxy indicators whereas the scale of past paleoceanographic and paleoclimatic changes have been generally appreciated for some time the recognition of periodic rapid change in the ocean climate state and the ability to study and measure these precisely is only a recent accomplishment the potential for such rapid change in the ocean climate biosphere of the earth system raises concerns for events in the near future that may be forced by anthropogenic activities that enhance natural variability

modelling the effect of salinity on radium desorption from sediments abstract the desorption of the four naturally occurring radium isotopes 223 ra 224 ra 226 ra and 228 ra from estuarine sediments is investigated these isotopes are created within sediments by the radioactive decay of insoluble thorium parents due to competition from other ions for the occupation of adsorption sites on the sediment grains radium desorption is a function of salinity a model is developed to describe radium desorption as it is affected by salinity grain size and sediment concentration it is shown that to model the desorption of radium for a particular sediment requires the estimation of two independent parameters one of these parameters is the concentration of radium available for exchange on the sediment the other depends on major ion and radium exchange coefficients desorption experiments performed on sediments from the bed of the bega river australia are used to validate the model and to evaluate the parameters needed for model application

late tertiary history of hydrothermal deposition at the east pacific rise 19 s correlation to volcano tectonic events commonly it is assumed that the intensity of mid ocean ridge hydrothermal activity should correlate with spreading rate since high spreading rates are an indication of large subcrustal heat sources needed for intense hydrothermal activity we have tested this hypothesis by modeling the deposition of hydrothermal precipitates from cores from deep sea drilling project leg 92 taken on the west flank of the east pacific rise at 19 s although spreading rates at the east pacific rise and its predecessor the mendoza rise have varied by only 50 in the last 30 million years we found certain episodes at about 25 18 14 and 9 million years ago of hydrothermal manganese deposition as much as a factor of 20 higher than equivalent holocene accumulation these eposides do not correlate with spreading rate changes and instead seem to occur at times of major tectonic reorganizations we propose that ridge jumps and changes of ridge orientation may substantially increase hydrothermal activity by fracturing the ocean crust and providing seawater access to deep seated heat sources

ra and th adsorption coefficients in lakes lake kinneret sea of galilee natural experiment the adsorption rate constants of ra and th were estimated from empirical data from a freshwater lake and its feeding saline springs we utilized the unique setting of lake kinneret sea of galilee northern israel in which most of the ra and th nuclides are introduced into the lake by saline springs with high 226 ra activities and a high 224 ra 228 ra ratio of 1 5 the mixing of the ra enriched saline waters and freshwater in the lake causes the 224 ra 228 ra ratio to drop down to 0 1 in the kinneret due to preferential adsorption of 228 th these conditions constitute a natural experiment for estimating adsorption rates we developed a simple mass balance model for the radionuclides in lake kinneret that accurately predicted the ra isotope ratios and the 226 ra activity in the lake the model is comprised of simultaneous equations one for each radionuclide the equations have one input term supply of radionuclides from the saline springs and three output terms adsorption on particles in the lake radioactive decay and outflow from the lake the redundancy in the analytical solutions to the mass balance equations for the relevant nuclides constrained the values of ra and th adsorption rate constants to a very narrow range our results indicate that the adsorption rate constant for ra is between 0 005 d 1 and 0 02 d 1 the rate constant for th is between 0 5 d 1 and 1 d 1 about fifty to a hundred times higher the estimated desorption rate coefficient for ra is about 50 100 times larger than its adsorption rate constant the mass balance equations show that the residence times of all ra isotopes 226 ra 228 ra 223 ra 224 ra and of 228 th in the lake are about 95 92 14 6 and 1 d respectively these residence

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

major episodes of geologic change correlations time structure and possible causes abstract published data sets of major geologic events of the past 250myr extinction events sea level lows continental flood basalt eruptions mountain building events abrupt changes in sea floor spreading ocean anoxic and blackshale events and the largest evaporite deposits have been synthesized with estimated errors these events show evidence for a statistically significant periodic component with an underlying periodicity formally equal to 26 6 myr and a recent maximum close to the present time the cycle may not be strictly periodic but a periodicity of 30myr is robust to probable errors in dating of the geologic events the intervals of geologic change seem to involve jumps in sea floor spreading associated with episodic continental rifting volcanism enhanced orogeny global sea level changes and fluctuations in climate the period may represent a purely internal earth pulsation but evidence of planetesimal impacts at several extinction boundaries and a possible underlying cycle of 28 36 myr in crater ages suggests that highly energetic impacts may be affecting global tectonics a cyclic increase in the flux of planetesimals might result from the passage of the solar system through the central plane of the milky way galaxy an event with a periodicity and mean phasing similar to that detected in the geologic changes

thorium isotopes in the western mediterranean sea an insight into the marine particle dynamics we present a detailed view of the 230 th 232 th systematics in the western mediterranean sea in order to constrain water and particle fluxes the conclusions obtained at the regional scale are also relevant at a more global scale although they may be more difficult to establish in the open ocean 230 th and 232 th were analyzed in size fractionated seawater and marine particle samples collected in the ligurian alboran and ionian seas the 230 thxs 230 th produced by the radioactive decay of 234 u in seawater profiles at dyfamed and in the alboran sea site are not linear due to the formation of deep waters the difference of 230 thxs concentration between these two sites is related to the aging of the water masses and to different scavenging conditions the 230 th 232 th ratio is used as a tracer during mixing processes to provide information on the pathways followed by the matter in the water column at dyfamed filtered 6 0 2 wm and ultrafiltered 6 1 kda solutions have similar 230 th 232 th ratios suggesting that an equilibrium exists between truly dissolved and colloidal th the change of the th flux and of the 230 th 232 th ratio of trapped particles observed in august between 200 m and 1000 m is best explained by aggregation of filtered large particles on the trapped particles the residence time of filtered large particles with respect to aggregation on trapped particles is of the order of 8 80 days the combined budget of 230 th and 232 th inputs to the western mediterranean sea requires the dissolution of 3 5 of the th associated with all the continental particulate inputs including particles sequestered in margins suggesting that eolian inputs are not the only source of refractory elements to the mediterranean sea and may be to the whole ocean fl 2002 elsevier science b v all rights reserved

the warm cretaceous climate role of the long term carbon cycle an annual energy balance model is coupled to a steady state formulation of the long term co sub 2 cycle to investigate the possible sources of the global warming at the cretaceous it is found that paleogeography solely is an insufficient factor but that the different latitudinal distribution of continental masses 100 my ago influenced the co sub 2 cycle and favored a larger content of the atmospheric co sub 2 level a larger rate of tectonic activity and the possible influence of the vegetation in a co sub 2 richer atmosphere provide further sources of atmospheric carbon dioxide increase the combination of these factors together with a more vigorous poleward heat transport provides co sub 2 levels 5 to 15 times larger than today and a global surface warming within the 6 12c estimated from paleoindicators

precambrian superplumes and supercontinents a record in black shales carbon isotopes and paleoclimates prominent maxima in black shale abundance and in black shale total shale ratio occur at 2 0 1 7 ga with less prominent peaks in the late neoproterozoic 800 600 ma and in the late archean 2 7 2 5 ga peaks in chemical index of alteration cia of shales at the same times suggest corresponding warm paleoclimates the peaks in cia and black shale abundance are correlated in time at a 94 confidence level the black shale and cia peaks may reflect the combined effects of mantle superplume events and supercontinent formation at 2 7 and 1 9 ga mantle superplume events may have introduced large amounts of co2 into the atmosphere ocean system increasing depositional rates of carbon and increasing global warming increased black shale deposition may reflect some combination of 1 increased oceanic hydrothermal fluxes introducing nutrients 2 anoxia on continental shelves and 3 disrupted ocean currents the apparent absence of carbon isotope anomalies at these times reflects an increase in the deposition and burial rate of both reduced and oxidized carbon peaks in black shale abundance at 2 1 ga and 800 600 ma correlate with peaks in 13 c in marine carbonates increases in atmospheric oxygen and with high cia values in shales these are all consistent with higher rates of organic carbon burial in black shales at these times these peaks may record the breakup of supercontinents at 2 2 2 0 ga and again at 800 600 ma which resulted in increased numbers of partially closed marine basins disruption of ocean currents and increased hydrothermal vents at ocean ridges all of which led to widespread anoxia 2001 elsevier science b v all rights reserved

climate change during the last 150 million years reconstruction from a carbon cycle model variations of the atmospheric co2 level and the global mean surface temperature during the last 150 ma are reconstructed by using a carbon cycle model with high resolution input data in this model the organic carbon budget and the co2 degassing from the mantle both of which would characterize the carbon cycle during the cretaceous are considered and the silicate weathering process is formulated consistently with an abrupt increase in the marine strontium isotope record for the last 40 ma the second order variations of the atmospheric co2 level and the global mean surface temperature in addition to the first order cooling trend are obtained by using high resolution data of carbon isotopic composition of marine limestone seafloor spreading rate and production rate of oceanic plateau basalt the results obtained from this model are in good agreement with the previous estimates of palaeo co2 level and palaeoclimate inferred from geological biogeochemical and palaeontological models and records the system analyses of the carbon cycle model to understand the cause of the climate change show that the dominant controlling factors for the first order cooling trend of climate change during the last 150 ma are tectonic forcing such as decrease in volcanic activity and the formation and uplift of the himalayas and the tibetan plateau and to a lesser extent biological forcing such as the increase in the soil biological activity the mid cretaceous was very warm because of the high co2 level 4 5 pal maintained by the enhanced co2 degassing rate due to the increased mantle plume activities and seafloor spreading rates at that time although the enhanced organic carbon burial would have a tendency to decrease the co2 level effectively at that period the variation of organic carbon burial rate may have been responsible for the second order climate change during the last 150 ma

integrated depositional model for the cenomanian turonian organic rich strata in north africa abstract during the late cenomanian early turonian c t oceanic anoxic event oae2 organic rich strata was deposited in rift shelf basins and slopes across north africa and in deep sea basins of the adjacent oceans based on a review of published and unpublished information this paper documents the distribution and organic richness of c t strata across the whole region within a palaeogeographic framework and systematically analyses the conditions and processes which controlled their deposition previously the c t in north africa has been most intensively studied in southern morocco tarfaya and tunisia only little data is availabe for other parts of north africa namely algeria libya and egypt because distribution of c t corg strata there becomes more patchy a general decrease in peak organic richness and black shale thickness occurs from west to east partly as a result of upwelling along the moroccan atlantic coast and the absence of upwelling in the eastern mediterranean area furthermore in the confined central atlantic the oxygen minimum zone omz in many places reached down to the deep sea floor 3 4 km while the lower limit of the omz along the north african tethys was much shallower and underlain by oxic water masses as documented by high resolution biostratigraphic and chemostratigraphic data c t black shale deposition in most areas outside the upwelling zone are restricted to a strong eustatic latest cenomanian transgressive phase triggered by this sea level rise the omz impinged onto the north african continental shelf and the margins of intrashelf basins which mostly formed during the early cretaceous as halfgrabens important units containing c t organic rich strata in the region are the atlantic tarfaya black shales morocco western sahara black shales and phtanites in the moroccan and algerian atlas the bahloul fm in the se constantine basin and in northern and central tunisia the etel fm in the sirte basin the al hilal fm in cyrenaica libya the abu roash fm in the abu gharadig and fayium basins western desert egypt the daliyya fm along the ne sinai palestine isreal coast and the shueib fm in west central jordan

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

increased terrigenous influx but no drowning palaeoenvironmental evolution of the tunisian carbonate platform margin during the late aptian during the aptian some carbonate platforms of the sub tropical realm for example on the northern tethys margin or in the gulf of mexico were affected repeatedly by severe perturbations in the carbonate production factory and drowning preferentially during global warming events such as the early aptian oceanic anoxic event 1a and a prominent mid late aptian warming interval these platform growth crises have been explained mainly by strongly increased coastal runoff for example siliciclastics and nutrients in combination with pronounced eustatic sea level rises in the last few years increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events this raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas in this study upper aptian middle gargasian to uppermost clansayesian inner tropical carbonate ramp deposits of the serdj formation at djebel serdj north central tunisia are studied in detail with regard to microfacies lithology biostratigraphy and chemostratigraphy these data allow reconstruction of the palaeoenvironmental evolution of the tunisian carbonate platform margin and investigation of its response to the prominent mid late aptian warming interval the unusually expanded 600 m thick serdj formation consists of limestones marlstones and siltstones suggesting deposition within mid ramp to inner ramp palaeoenvironments deposits of the mid late aptian are represented by quartz rich platform carbonates and siltstones probably resulting from increased coastal runoff on the tunisian shelf as a response to global warming and accelerated water cycling the siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae carbonate platform drowning during the mid late aptian as reported from the sub tropical realm has not been identified a comparison with other tropical river influenced platforms suggests that none of them drowned during the mid late aptian one important reason might be widespread arid to semi arid climatic conditions within lower latitudes during that time promoting platform growth due to comparably low nutrient runoff

the cenomanian turonian boundary mass extinction late cretaceous new insights from ammonoid biodiversity patterns of europe tunisia and the western interior north america major biological crises are attributed to a variety of factors whose respective contributions and interactions are often difficult to disentangle the cenomanian turonian boundary was a period of high organic matter burial coupled with a high positive excursion in the carbon isotope record this event has been widely recognized to reflect anoxic conditions the oceanic anoxic event 2 and is concomitant with one of the major mass extinctions of the phanerozoic it has been considered a typical example of global extinction caused by the spreading of anoxic waters however recent studies question this anoxia kill mechanism in europe both from palaeontological and sedimentological arguments hence this study analyzes the biodiversity patterns of ammonoids from three major areas europe tunisia and the western interior in order to better understand the relationships between ammonoid biodiversity patterns and abiotic factors during the cenomanian turonian interval the biodiversity patterns of ammonoids species richness origination extinction turnover poly cohort survivorship and taxonomic distinctness highlight that the mass extinction of the cenomanian turonian boundary is restricted to europe when considering only ammonoids only europe documents an actual decrease of species richness during the late cenomanian which results mainly from decreasing origination in tunisia where the onset of anoxic waters is synchronous with europe species richness increases during the late cenomanian and reaches its highest values in the lower turonian the western interior records relatively high species richness during the late cenomanian with only a single minor extinction event furthermore major changes in biodiversity patterns of ammonoids occurred around the middle upper cenomanian boundary i e ca 0 75 myr before the onset of the oae2 although there is extensive evidence for widespread anoxia during the cenomanian turonian boundary interval in deep sea environments the biodiversity patterns of ammonoids in europe tunisia and the western interior rule out global anoxia as a direct causal mechanism for changes in ammonoid diversity these biodiversity patterns also question the global scale character of the so called cenomanian turonian mass extinction observed biodiversity patterns of ammonoids strongly support the global warming of the late cenomanian as evidenced by the northward migration of the tethyan realm changes in ammonoid diversity are compatible with the exceptional high sea level occurring at that time and with concomitant regional climate changes

middle cretaceous greenhouse hydrologic cycle of north america we present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid latitude north america based on the oxygen isotopic composition of sphaerosiderites found in middle cretaceous wetland paleosols our reconstructed middle cretaceous d 18 o values of precipitation are 4 less than values from comparable modern low elevation coastal settings free of monsoons the data fit a conceptual model in which the precipitation source for the eastern margin of the cretaceous western interior seaway of north america is an 18 o enriched oceanic coastal jet in this subtropical tropical setting midcretaceous precipitation rates are interpreted to range from 2500 to 4100 mm yr

kimberlite eruptions as triggers for early cenozoic hyperthermals 1 the early cenozoic experienced at least three short but major hyperthermals associated with disruptions of the global carbon cycle the largest among those the paleocene eocene thermal maximum was associated with a negative carbon isotopic excursion of 2 5 that appears to be best explained by the thermal dissociation of methane hydrates due to an initial period of warming the cause of the initial warming has been attributed to a massive injection of carbon co2 and or ch4 into the atmosphere however the source of the carbon is as yet unknown the emplacement of a large cluster of kimberlite pipes at 56 ma in the lac de gras region of northern canada may have provided the carbon that triggered early warming in the form of exsolved magmatic co2 our calculations indicate that the estimated 900 1100 pg of carbon required for the initial 3 c of ocean water warming associated with the paleocene eocene thermal maximum could have been released during the emplacement of a large kimberlite cluster the coeval ages of two other kimberlite clusters in the lac de gras field and two other early cenozoic hyperthermals indicate that co2 degassing during kimberlite emplacement is a plausible source of the co2 responsible for these sudden global warming events

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels

early cenomanian hot greenhouse revealed by oxygen isotope record of exceptionally well preserved foraminifera from tanzania the search into earth s mid cretaceous greenhouse conditions has recently been stimulated by the tanzania drilling project tdp which has recovered exceptionally well preserved biogenic carbonates from subsurface pre neogene marine sediments in the eastern margin of central africa published tanzanian oxygen isotope records measured on exquisitely preserved foraminiferal tests dating to as old as 93ma provided evidence for a turonian hot greenhouse with very high and stable water column temperatures we have generated a comparable data set of exceptionally well preserved foraminifera from a lower cenomanian interval of tdp site 24 spanning 99 9 95 9ma planktonic foraminiferal thalmanninella globotruncanoides zone nannofossil corollithion kennedyi to lithraphidites eccentricus zones thereby extending the age coverage of the tanzanian foraminiferal o record back by 7 million years throughout the interval analyzed the new foraminiferal o data are consistently around 4 3 for surface dwelling planktonic taxa and 1 9 for benthic lenticulina spp which translate to conservative paleotemperature estimates of 31 c at the surface and 17 c at the sea floor upper bathyal depths considering the 40 s cenomanian paleolatitude of tdp site 24 these estimates are higher than computer simulation results for accepted normal greenhouse conditions those with up to 4x preindustrial pco2 level and suggest that the climate mode of the early cenomanian was very similar to the turonian hot greenhouse taking account of other comparable data sources from different regions the hot greenhouse mode within the normal mid cretaceous greenhouse may have begun by the latest albian but the precise timing of the critical transition remains uncertain

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

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

uranium thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the salton sea geothermal field southeastern california naturally occurring u and th series radionuclides have been analyzed in high temperature brines 300 c 25 wt dissolved solids and associated rocks from two deep geothermal wells located on the northeastern margin of the salton sea geothermal field ssgf these data are part of a study of the ssgf as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds and permit evaluation of some characteristics of water rock interaction in the ssgf rock brine concentration ratios rc dpm g rock dpm g brine were found to vary from near unity for isotopes of ra pb and rn to about 5 105 for 232th the high sorptivity of 232th is closely followed by that of 238u and 234u rc 5 104 suggesting that u is retained in the 4 oxidation state by the reducing conditions in the brines the relatively high solubility of 210pb and 212pb is attributed to formation of chloride complexes while the high ra solubility is attributed to chloride complexing a lack of suitable adsorption sites due to the high brine salinity and temperature and the reducing conditions that prevent mno2 and raso4 from forming the 228ra226ra ratios in the brines are approximately equal to those of their parents 232th230th in associated rocks indicating that ra equilibration in the brine rock system is achieved within the mean life of 228ra 8 3 years the 224ra228ra ratios in these brines are about 0 7 indicating that either 1 brine composition is not homogeneous and 224ra decays in fracture zones deficient in ra and th as the brine travels to the wellhead or 2 ra equilibration in the brine host rock system is not complete within the mean life of 224ra 5 2 days because the desorption of 224ra from the solid phase is impeded the 228ac228ra activity ratio in the ssgf brines studied is 0 1 and from this ratio the residence time of 228ac in the brine before sorption onto solid surfaces is estimated to be 70 minutes indicating the potential for rapid removal of reactive isotopes fom brines the brine is greatly enriched in 226ra 2 3 dpm g about 104 105 times that of its parent 230th while reservoir rocks are about 10 deficient in 226ra relative to 230th material balance calculations for 2226ra and 18o suggest that brines reside in the reservoir for 102 103 years that the ssgf formed 10 000 40 000 years b p and that porosity cannot be more than 20