silicification and dolomitization of anhydrite nodules in argillaceous terrestrial deposits an example of meteoric dominated diagenesis from the triassic of central spain cauliflower shaped nodules are widespread in a single red mudstone bed in the buntsandstein triassic facies of the iberian range they consist mostly of quartz dolomite and calcite but other minerals such as barite kaolinite and iron oxyhydroxides are also present the nodules are spherical ovoid or elongate in shape and range from 1 to 8 cm across the surface of the nodules is irregular and some show a pedogenic coating of microspar the sedimentological and petrographic data suggest that the initial anhydrite nodules formed through a progressive increase in the porewater concentration of ca2 and so4 2 in a vadose environment occasionally under the influence of pedogenic processes partial replacement of the anhydrite by megaquartz occurred under more dilute conditions in the same type of setting as indicated by the presence of organic filaments on the quartz crystal surfaces in type a nodules the dissolution of the innermost anhydrite was complete and different types of quartz cement filled the porosity fracturing and meteoric cementation by calcite and minor amounts of kaolinite were the latest processes affecting these nodules in type b nodules the dissolution of the anhydrite was incomplete inhibiting quartz cementation and enabling later dolomitization of the anhydrite dolomitization appears to have been driven by sulphate reduction as indicated by the presence of bacterial bodies within the dolomite crystals dedolomitization and precipitation of barite kaolinite and calcite spar cements occurred later under the influence of meteoric solutions the nodules may mark the former locations of the water table and provide evidence for an episode of highly evaporitic conditions throughout wide areas of the basin their occurrence reveals not only a complex diagenetic history but is also indicative of palaeogeographic and palaeoclimatic conditions

reactive transport modelling of reflux dolomitization in the arab d reservoir ghawar field saudi arabia it has long been recognized that the arab d reservoir in ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir previous studies indicated that dolomite occurs with either a stratigraphic or non stratigraphic distribution when mapped dolomite tends to form several parallel linear trends across the field although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits non stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below this study focuses primarily on these non stratigraphic dolomites and proposes that i these dolomites initially formed via seepage reflux but were reinforced by late stage hydrothermal dolomitization and ii reflux is also responsible for the formation of parallel linear trends of dolomite the reflux model hypothesizes that an evaporative lagoon which is the source of dolomitizing fluids formed during the falling stage systems tract of a depositional sequence and that with continuing sea level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the ghawar field leaving behind lines of dolomite bodies along a series of temporary coastlines two dimensional reactive transport models have been built to test this hypothesis and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non stratigraphic dolomite as well as the mapped lateral distribution of the dolomite trends in addition the major ion compositions of late jurassic seawater are calculated based on fluid inclusion data in the literature using jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over dolomitization than using modern seawater

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

dolomites and dolomites in mesozoic platform carbonates of the southern apennines geometric distribution petrography and geochemistry abstract a multidisciplinary study of the dolomitized bodies present among the late triassic to late cretaceous carbonate deposits of the monti lattari belt southern apennines of italy compares the different dolomitization styles present within this succession of these mesozoic platform carbonates and furnishes an overview of their formative genetic models the revealing traces of the diverse modes of diagenesis in this region include both surface and subsurface mechanisms utilizing a geometric reconstruction of the dolomitized bodies an integrated facies and petrographic analysis of the components and a geochemical characterization of the sediments including detailed mineralogy and associated stable isotope values the data presented demonstrate that some intervals are characterized by surface related dolomitization processes middle late triassic and cretaceous while others latest triassic to lower middle jurassic and are mainly dominated by later large scale subsurface dolomitization processes all of the middle late triassic norian successions are pervasively dolomitized exhibit fabric preserving textures and have a distinctly heavy stable isotope signature their origin has been related to diagenesis due to particular climatic and palaeoceanographic conditions leading to the formation of extended blankets of shallow warm saline seawater this setting was terminated by climatic and palaeoceanographic changes during the latest triassic which dramatically reduced the significance of surface related dolomitization on a regional scale the overlying latest triassic rhaetian outcrops consist of a widespread coarse fabric destructive massive dolomite with a lighter isotopic signature these dolomites seem genetically related to the ones of the lower middle jurassic which share the same geometrical petrographic and geochemical characteristics caused by large scale fluid circulation this diagenetic pattern apparently started in the early jurassic during burial driven by thermal convection due to the different temperatures between the oceanic waters and the warmer carbonate platform the middle upper jurassic units feature local episodes of early dolomitization that partially replaced the muddy carbonate facies due to tidal pumping and reflux mechanisms dolomitization is not a pervasive feature during this phase of deposition in the cretaceous portion of the succession dolomites have a totally different and distinct character and are generally related to bedding and show variability in textures and mg ca ratios local association with evaporites geometry of dolomitized bodies and stable isotope geochemistry suggest processes comprising evaporative pumping and reflux all related to the surface environment this evidence points to a renewal of a climatic context more favorable for early dolomitization thus this study permits recognition of the presence of three quite different dolomitization styles within the carbonate platform succession of the southern apennines fold thrust belt one ascribed to the norian one to the rhaetian lower jurassic and one to the cretaceous

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

origin and modification of early dolomites in cyclic shallow platform carbonates yeongheung formation middle ordovician korea abstract the middle ordovician yeongheung formation korea consists of numerous metre scale shallowing upward cycles which were deposited on a shallow marine carbonate platform depositional sequences developed on the inner platform were completely dolomitized regardless of constituting lithology whereas those developed on the outer platform were partially dolomitized the amount of replacement dolomite within a metre scale shallowing upward peritidal cycle decreases downward from the peritidal cycle cap in the partially dolomitized depositional sequences the cross platform distribution of dolomites and their stratigraphic position in the sequences suggest that the yeongheung dolomite formed syndepositionally the common existence of pseudomorphs of evaporite minerals and nodules in the yeongheung formation indicates that dolomitization of the yeongheung formation occurred in a sabkha type tidal flat environment it also occurred during each cycle of deposition influenced by high frequency sea level oscillations the present day yeongheung replacement dolomites are characterized by near stoichiometric to stoichiometric composition 49 9 to 52 1 caco3 mole and low strontium concentration 52 to 133 ppm the 18o value of the replacement dolomites ranges from 7 7 to 5 2 pdb this is much depleted relative to that of contemporary sabkha type dolomites these geochemical characteristics of yeongheung dolomite indicate significant post depositional modification the common existence of oomolds leached skeletal grains and dissolved evaporites in the yeongheung formation illustrates invasion of meteoric water into the sediments recrystallization of yeongheung dolomites in the infiltrated meteoric water at slightly elevated temperatures during shallow burial resulted in lighter 18o values and lower strontium concentration

code numbers for cenozoic low latitude radiolarian biostratigraphic zones and gpts conversion tables abstract code numbers for the radiolarian zonation for the tropical pacific indian and atlantic oceans rp1 rp22 for the paleogene and rn1 rn17 for the neogene are standardized and introduced thirty nine zones are recognized from the lower paleocene to the holocene revision of previously separate upper neogene zonations for the pacific and indian oceans in which the same zonal names were applied to different stratigraphic intervals resulted in a single tropical zonation we change four upper neogene indian ocean zones to subzones and refer to them simply by their code numbers rn12b pterocanium prismatium rn12a anthocyrtidium jenghisi rn11b stichocorys peregrina rn11a phormostichoartus fistula we introduce the name lychnodictyum audax interval zone rn11 for the interval stratigraphically equivalent to the combined stichocorys peregrina and phormostichoartus fistula zones in the indian ocean and to the anthocyrtidium jenghisi zone in the pacific ocean two paleocene zones bekoma bidartensis rp7 and b campechensis rp6 and two subzones stylotrochus nitidus pterocodon poculum rp6c and orbula discipulus rp6b are emended each zone is formally defined and we include a stratigraphically ordered list of radiolarian events falling within each zone mean numerical ages for zonal boundary events were culled from previous literature and converted to the geomagnetic polarity time scale gpts references to the original description and concept herein applied of all included taxa and tables which allow for accurate conversion in simple increments between the different published gptss are included in this paper

global distribution of late paleogene hiatuses six global late paleogene hiatuses pha to phe have been identified from deep sea sequences these hiatuses occurred at the middle late eocene boundary late eocene eocene oligocene boundary late early oligocene late oligocene and oligocene miocene boundary horizons paleodepth distribution of hiatuses shows hiatus maxima characterized by major mechanical erosion below 4800 m at mid depth between 2000 and 3000 m and in shallower water above 1600 m paleodepth the geographic distribution and paleodepth of these hiatus maxima suggest that flow paths of major water masses and currents are the principal cause widespread short hiatuses due to carbonate dissolution or nondeposition occurred primarily during global cooling trends or climatic instability and appear to correlate to sea level transgressions or onlap sequences these hiatuses may have been caused by basin shelf fractionation of carbonates

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

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

planktonic foraminiferal biostratigraphy and mechanisms in the extinction of morozovella in the late middle eocene the muricate planktonic foraminiferal genera morozovella and acarinina were abundant and diverse during the upper palaeocene to middle eocene and dominated the tropical and subtropical assemblages a significant biotic turnover in planktonic foraminifera occurred in the latest middle eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids these genera are extensively employed as palaeoclimatic and biostratigraphic markers and therefore this turnover episode is an important event in the record of the cenozoic planktonic foraminifera sediments from the western north atlantic ocean drilling program site 1052 were examined in order to investigate these extinction events in terms of both timing and mechanisms biostratigraphic events of the middle and late eocene have been examined with a sampling resolution of approximately 3 kyr these have been calibrated to the magneto and astrochronology to accurately define the timing of key biostratigraphic events particularly the extinction of morozovella spinulosa which is a distinct biomarker for late middle eocene sediments high resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form the large acarininids acarinina praetopilensis terminate 10 kyr prior to the extinction of m spinulosa and small acarininids acarinina medizzai and acarinina echinata continue into the upper eocene high resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western north atlantic to reconstruct sea surface temperatures ssts and deep water temperatures and the structure of the water column around this major biotic turnover whilst the extinctions of m spinulosa and a praetopilensis occur during a long term cooling trend the biotic turnover in the muricate group does not appear to be related to significant climatic change sea surface temperatures decrease slowly prior to the extinction events and there is no evidence for a large temperature shift associated with the faunal changes the turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae d 2003 elsevier b v all rights reserved

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

radiolarian responses to paleoceanographic events of the southern south china sea during the pleistocene abstract a quantitative radiolarian study at core 17957 2 from the south china sea scs allows reconstructing two paleoceanographic events occurring during the last 1500 ka based on the abundance variations of siliceous microfossils radiolarian diatom and sponge spicule the definitions of the productivity and thermocline indexes dar diatom accumulation rate and tsr thermocline surface radiolarian indexes as indicators for productivity and thermocline changes as well as changes in the species composition two distinct changes at 900 ka and 600 ka could be detected being related to the multiple transition phenomena of the mid pleistocene revolution mpr the change in the species composition at 900 ka indicated by an increase in subtropical radiolarians and a decrease in tropical radiolarians exhibits a lowering of the sea surface temperatures in the scs that can be related to a southward shift of the north equatorial current induced by variations in the northern trade wind system increasing subsurface and intermediate species and dar and tsr indexes at 700 600 ka may reflect higher sea surface productivity and shallowing thermocline caused by stronger upwelling and nutrient supply the comparison of the radiolarian signal recovered from core 17957 2 with the magnetic susceptibility signal obtained from the chinese loess plateau reveals the close connection of the climatic transitions at 700 600 ka in the southern scs to strengthening of the east asian summer monsoon circulation the spectral analyses indicate that ice mass fluctuations oxygen isotope record have clear 100 ka eccentricity dominated and processional signals after the mpr but with a more significant obliquity related response before the mpr the surface productivity e g dar and thermocline depth e g tsr index show the 100 ka dominant cyclicity before the mpr the 32 ka significant regional cyclicity for the last 1500 ka responds to the surface productivity e g dar and thermocline depth e g tsr index signals

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

high sea surface temperatures during the early cretaceous epoch the early cretaceous epoch about 145 100 million years ago is generally thought of as a greenhouse period with high atmospheric co2 concentrations1 and high global mean temperatures2 but evidence for episodes of cooler conditions and even transient glaciations has been proposed3 4 5 6 7 8 9 here we present sea surface temperature records spanning the period from 142 to 128 million years ago berriasian barremian ages from low and mid latitudes reconstructed using the tex86 palaeotemperature proxy during this period we find sea surface temperatures exceeding 32 c at 15 20 n and averaging 26 c at 53 s these temperatures substantially exceed modern temperatures at equivalent latitudes and are incompatible with the notion of consistently cooler conditions in the earliest cretaceous moreover we find little variability in the sea surface temperature records even during the valanginian carbon isotope excursion 138 135 million years ago which was thought to be associated with marked temperature fluctuations5 we conclude that the earliest cretaceous was characterized by a warm stable climate with a lower meridional temperature gradient than today

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less

comparison of radiolarian and sedimentologic paleoproductivity proxies in the latest miocene recent benguela upwelling system abstract estimating past ocean productivity from ocean sediments often gives different results depending on the measurement used we have examined a suite of paleoproductivity proxies in latest miocene recent sediments from dsdp site 532 and odp site 1084 two deep sea sections underlying the benguela upwelling system off the atlantic coast of southern africa the productivity history of this system has been previously established via organic carbon concentration diatom floras and alkenone based estimates of surface water temperature and shows a change from low productivity in the early pliocene to sustain high productivity in the late pliocene recent each of our samples was split and simultaneously analysed for several proxies of ocean productivity including organic carbon toc carbonate abundance of opaline radiolarians accumulation rate of benthic foraminifera bfar the radiolarian faunal composition indices upwelling radiolarian index uri and the water depth ecology index wade other proxies for opal and carbonate dissolution plus stable isotopes of benthic foraminifera comparisons between proxies in the same measured samples between sites in downcore plots and to the published productivity record for this region suggest that toc and radiolarian faunal composition particularly the wade index are good indicators of past productivity albeit with different sensitivities log linear correlation wade toc r 0 78 n 65 p

replacement of evaporites within the permian park city formation bighorn basin wyoming usa the permian park city formation consists of cyclically bedded subtidal to supratidal carbonates cherts and siltstones early diagenesis of park city formation carbonates occurred under the influence of waters ranging from evaporative brines to dilute meteoric solutions and resulted in evaporite emplacement syndepositional nodules and cements as well as dolomitization silicification and leaching of carbonate grains major differences are seen however in the diagenetic patterns of subsurface and surface sections of park city formation rocks subsurface samples are characterized by extensively preserved evaporite crystals and nodules and preserve evidence of significant silicification chert chalcedony and megaquartz and minor calcitization of evaporites in outcrop sections the evaporites are more poorly preserved and have been replaced by silica and calcite and also leached the resultant mouldic porosity is filled with widespread very coarse blocky calcite spar these replacements appear to be multistage phenomena field and petrographic evidence indicates that silicification involved direct replacement of evaporites and occurred during the early stages of burial prior to hydrocarbon migration siliceous sponge spicules provided a major source of silica and the fluids involved in replacement were probably a mixture of marine and meteoric waters a second period of replacement and minor calcitization is inferred to have occurred during deep burial under the influence of thermochemical sulphate reduction although the presence of hydrocarbons probably retarded most other diagenetic reactions during this time interval the major period of evaporite diagenesis however occurred during late stage uplift the late stage replacement and pore filling calcites have 13c values ranging from 0 5 to 25 3 and 18o values of 16 1 to 24 30 pdb reflecting extensive modification by meteoric water vigorous groundwater flow associated with mid tertiary block faulting led to migration of meteoric fluids through the porous carbonates to depths of several kilometres these waters reacted with the in situ hydrocarbon rich pore fluids and evaporite minerals and precipitated calcite cements the tosi chert appears to have been an even more open system to fluid migration during its burial and has undergone a much more complex diagenetic history as evidenced by multiple episodes of silicification calcitization ferroan and non ferroan and hydrocarbon emplacement the multistage replacement processes described here do not appear to be restricted to the permian of wyoming similarly complex patterns of alteration have been noted in the permian of west texas new mexico greenland and other areas as well as in strata of other ages thus multistage evaporite dissolution and replacement may well be the norm rather than the exception in the geological record

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

atlantic eocene planktonic foraminiferal historical biogeography and paleohydrographic indices abstract analysis of a quantitative and synoptic data base of eocene atlantic planktonic foraminifera has illuminated many facets of foraminiferal faunal structure and composition reflective of bioprovince and useful for empirical establishment of ecologic and paleohydrographic indices tropical indigenes such as the morozovellids turborotaliids subquadrate acarininids and some globigerinathekids dissolve most rapidly along with juveniles of most species tropical faunas are high in diversity and dominance include oxygen minimum indices such as the biserial heterohelicids only in high productivity times such as the middle eocene are dominated by genera with high numbers of species and species consistently typical of warm water regions until the late eocene when faunas include a higher number of middle than lower latitude types truly tropical genera are replaced by subtropical eutrophic indicators such as the globigerinathekids and contract to the florida current region prior to their extinctions at the end of the middle eocene atlantic late paleogene tropical forms first appear in the gulf of mexico at the end of the middle eocene middle latitude faunas include high numbers of chiloguembelinids pseudohastigerinids small and biconvex morozovellids round and globigerinid form acarininids low spired subbotinids in the late middle eocene high spired subbotinids large and typical globigerinids in the late eocene these forms have intermediate dissolution susceptibilities middle latitude faunas are often high in diversity in midddle latitude frontal regions dominance is low even in warm intervals when tropical indigenes increase in number in middle latitude faunas especially in boundary currents low latitude species penetrate temperate areas also during cool eutrophic periods of vigorous circulation such as the late middle eocene typical of temperate slope faunas are high abundances of high spired subbotinids and small sized catapsydracids high latitude faunas are usually low in diversity except in the middle to late eocene when frontal regions were located in the southern labrador sea and over rockall bank typical forms are the low spired subbotinids until the late middle eocene globorotaloids catapsydracids tenuitellids and in the late eocene the biserial heterohelicids indigenous species are the most solution resistant and many are mesopelagic during warmings rare low latitude indices penetrate high latitudes subpolar faunas have greatest affinities with middle latitude faunas at these times

middle eocene to late oligocene antarctic glaciation deglaciation and southern ocean productivity during the eocene oligocene transition earth cooled significantly from a greenhouse to an icehouse climate nannofossil assemblages from southern ocean sites enable evaluation of paleoceanographic changes and hence of the oceanic response to antarctic ice sheet evolution during the eocene and oligocene a combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes a cooling trend started in the middle eocene was interrupted by warming during the middle eocene climatic optimum and by short cooling episodes the cooling episode at 39 6 ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from 39 1 to 36 2 ma we suggest that oligotrophic conditions were associated with increased water mass stratification low nutrient contents and high efficiency of the oceanic biological pump that in turn promoted sequestration of carbon from surface waters which favored cooling after 36 2 ma we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance this turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient antarctic ice sheet and or to iron delivery to the sea surface eutrophic conditions were maintained throughout the oligocene which was characterized by a nannofossil assemblage shift toward cool conditions at the eocene oligocene transition finally a warm nannofossil assemblage in the late oligocene indicates a warming phase

middle eocene regional climate instability evidence from the western north atlantic high resolution 3 k y d 18 o records from middle eocene mixed layer dwelling planktonic foraminifera from the western north atlantic show pronounced 1 variability the magnitude of change is greater than that seen in open ocean pleistocene records but could not have been caused by ice volume and or sea level fluctuations instead the oxygen isotope shifts resulted primarily from large oscillations in sea surface temperatures and indicate that the regional paleoceanography of the middle eocene western north atlantic was not consistently warm or stable the large shifts in sea surface temperatures could reflect variations in the position of the gulf stream relative to blake nose or variations in upwelling intensity

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations

integrated biomagnetostratigraphy of the alano section ne italy a proposal for defining the middle late eocene boundary the alano section has been presented at the international subcommission on paleogene stratigraphy isps as a potential candidate for defi ning the global boundary stratotype section and point gssp of the late eocene priabonian stage the section is located in the venetian southern alps of the veneto region ne italy which is the type area of the priabonian being exposed along the banks of the calcino torrent near the village of alano di piave it consists of 120 130 m of bathyal gray marls interrupted in the lower part by an 8 m thick package of laminated dark to black marlstones intercalated in the section there are eight prominent marker beds six of which are crystal tuff layers whereas the other two are bioclastic rudites these distinctive layers are useful for regional correlation and for an easy recognition of the various intervals of the section the section is easily accessible crops out continuously is unaffected by any structural deformation is rich in calcareous plankton and contains an expanded record of the critical interval for defi ning the gssp of the priabonian in order to further check the stratigraphic completeness of the section and constrain in time the critical interval for defi ning the priabonian stage we performed a high resolution study of integrated calcareous plankton biostratigraphy and a detailed magnetostratigraphic analysis here we present the results of these studies to open a discussion on the criteria for driving the golden spike that should define the middle eocene late eocene boundary

middle eocene late oligocene climate variability calcareous nannofossil response at kerguelen plateau site 748 a major deterioration in global climate occurred through the eocene oligocene time interval characterized by long term cooling in both terrestrial and marine environments during this long term cooling trend however recent studies have documented several short lived warming and cooling phases in order to further investigate high latitude climate during these events we developed a high resolution calcareous nannofossil record from odp site 748 hole b for the interval spanning the late middle eocene to the late oligocene 42 to 26 ma the primary goals of this study were to construct a detailed biostratigraphic record and to use nannofossil assemblage variations to interpret short term changes in surface water temperature and nutrient conditions the principal nannofossil assemblage variations are identified using a temperate warm water taxa index twwt from which three warming and five cooling events are identified within the middle eocene to the earliest oligocene interval among these climatic trends the cooling event at 39 ma cooling event b is recorded here for the first time variations in fine fraction 18o values at site 748 are associated with changes in the twwt index supporting the idea that significant short term variability in surface water conditions occurred in the kerguelen plateau area during the middle and late eocene furthermore odp site 748 calcareous nannofossil paleoecology confirms the utility of these microfossils for biostratigraphic paleoclimatic and paleoceanographic reconstructions at southern ocean sites during the paleogene

evolution of deep sea sediments across the paleocene eocene and eocene oligocene boundaries abstract the composition and distribution of deep sea sediments is the result of a multitude of climatic biotic and oceanic conditions relating to biogeochemical cycles and environmental change here we utilize the extensive sediment archives of the international ocean discovery program iodp and its predecessors to construct maps of deep sea sediment type across two critical but contrasting boundaries in the paleogene one characterised by an interval of extreme warmth paleocene eocene and the other by global cooling eocene oligocene ocean sediment distribution shows significant divergence both between the latest paleocene and paleocene eocene thermal maximum petm across the eocene oligocene transition eot and in comparison to modern sediment distributions carbonate sedimentation in the latest paleocene extends to high southern latitudes disappearance of carbonate sediments at the petm is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon cycle perturbation biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early paleogene ocean in the southern ocean we attribute the low in biosiliceous burial to the warm deep water temperatures which would have impacted biogenic silica preservation in the late eocene our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial pacific enhanced biosiliceous deposits in the late eocene equatorial pacific and south atlantic are due to increased productivity and the spin up of the oceans our compilation documents the enhanced global carbonate sedimentation in the early oligocene confirming that the drop in the carbonate compensation depth was global

quantifying uncertainties in multi scale studies of fractured reservoir analogues implemented statistical analysis of scan line data from carbonate rocks in this study we performed a fracture analysis on a cretaceous bedded carbonate succession well exposed in the sorrento peninsula the studied succession includes stratigraphic units that are very similar to the productive units of the buried apulian platform reservoir rocks in southern italy we analyzed eight carbonate beds including both limestones and dolomites the basic technique used in this study consisted of measuring fractures along bedding parallel scan lines for one limestone bed a microscale scan line about 15 cm long was also analyzed using a digital microcamera provided the cumulative distribution of fracture apertures is well described by a power law our analysis shows how the uncertainty in the estimate of fracture aperture cumulative frequencies grows for large aperture values this feature results in a large uncertainty in the estimate of the slope of the least squares line in a bi logarithmic diagram approximating the data distribution which is the exponent of the power law as the latter represents a fundamental parameter characterizing a fracture set and fracture distribution over different scales reducing the uncertainty in the estimate of the slope of the curve represents an important objective of quantitative fracture analysis this is obtained in this study by the application of multi scale analysis and by integrating micro scan line data with classic outcrop based scan line analysis the quantification of uncertainties in the cumulative distribution estimates of fracture apertures is performed by analyzing in detail the spacing distribution and consequently fracture density distribution for each aperture value our results suggests that a meaningful statistical analysis of fracture attributes such as aperture or opening displacement may be effectively carried out by using properly determined confidence intervals and by the integration of outcrop based and micro scan line data sets

strontium isotope stratigraphy in the upper cenomanian shallow water carbonates of the southern apennines short term perturbations of marine 87sr 86sr during the oceanic anoxic event 2 abstract strontium isotope stratigraphy of shallow water carbonates from the southern apennines italy indicates that the late cenomanian early turonian evolution of marine 87sr 86sr is not accurately depicted by the marine reference curve using the low mg biotic calcite of well preserved rudist shells as a study material and carbon isotope stratigraphy for correlation to the standard ammonite biozonal scheme of northern europe new 87sr 86sr values are proposed for four different stratigraphic levels the middle and uppermost part of the guerangeri zone the lower and upper part of the geslinianum zone the southern apennines data suggest that a sharp positive shift at the onset of oceanic anoxic event 2 precedes the well known sr isotope negative shift the positive shift is interpreted in terms of enhanced rates of chemical weathering driven by global warming forced by volcanogenic co2 outgassing a stratified ocean is invoked to reconcile the high gradient and the short lag time of the perturbation with estimates of present day total mass and residence time of strontium in the ocean the sharp switch to the negative shift is related to the collapse of water column density gradient driven by thermal instability during a late cenomanian cool event more active ocean circulation suddenly delivered to surface waters the signal of increased submarine volcanism that had accumulated in deep waters

early dolomitization in the lower cretaceous shallow water carbonates of southern apennines italy clues about palaeoclimatic fluctuations in western tethys abstract a multidisciplinary study of the dolomitized bodies present in the lower cretaceous platform carbonates of mt faito southern apennines italy was carried out in order to explore the connection between early dolomite formation and fluctuating climate conditions the berriasian aptian investigated succession is 466 m thick and mainly consists of shallow water lagoonal limestones with frequent dolomite caps the dolomitization intensity varies along the succession and reaches its peak in the upper hauterivian lower barremian interval where it is present a completely dolomitized interval about 100 m thick field relations petrography mineralogy and geochemistry of the analyzed dolomite bodies allowed identifying two populations of early dolomites a fine medium crystalline fmdol and a coarse crystalline dolomite cdol both interpreted as the product of mesohaline water reflux according to our interpretation fmdol precipitated from concentrated brines in the very early stage of the reflux process producing typical sedimentary features as dolomite caps in the successive step of the process the basin ward latent reflux precipitated cdol from less concentrated brines a peculiar feature of the studied succession is the great consistency between stratigraphic distribution of dolomite bodies and their geochemical signature the completely dolomitized hauterivian barremian interval in fact is characterized by geochemical values suggesting an origin from distinctly saltier brines considering that the observed near surface dolomitization process is controlled by physical and chemical parameters reflecting the paleoenvironmental and paleoclimatic conditions during dolomite formation we propose that the stratigraphically controlled dolomitization intensity reflects periodic fluctuations in the salinity of dolomitizing fluid in turn controlled by long term climate oscillations the present work highlights that the stratigraphic distribution of early diagenetic dolomite may be used as proxy to define the climatic fluctuations that have influenced the sedimentary dynamics in the early cretaceous moreover considering that a comparable early dolomite distribution is present also in the dinaric platform we suggest that a regional scale climate control acted on early dolomite formation and distribution refining the knowledge of such a key control may have a significative impact on hydrocarbon reservoir characterization and exploration in the periadriatic area

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

can humans force a return to a cretaceous climate abstract the modern pole to equator sea level temperature difference is about 50 c that of the mid cretaceous ranged from 30 c to as little as 24 c implying a much more equable climate this may have been caused by 1 reduction of the ice forced albedo of the polar regions 2 more efficient meridional energy transport by the atmosphere and ocean and 3 increased atmospheric greenhouse gas concentrations earth s icy polar regions stabilize its present inequable climate through the ice albedo feedback effect the polar ice results in permanent atmospheric highs that stabilize earth s wind systems in turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low and high latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses increased ocean heat transport can assist in making a more equable climate but unrealistic volume transports would be required to warm the polar regions to cretaceous levels the major factor forcing the equable climate of the cretaceous is now thought to be increased greenhouse gas concentrations dominated by co2 the modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing this compares with 1 ppmv per century during the last deglaciation at current rates of fossil fuel burning atmospheric co2 levels will reach cretaceous levels of 2 times the pre industrial level about 2070 and 8 times the pre industrial level shortly after 2300 it is likely that cretaceous atmospheric co2 concentrations will last for many thousands to tens of thousands of years in addition to increased atmospheric greenhouse gas concentrations a return to climatic conditions resembling those of the cretaceous would require ice free poles and large changes in atmospheric and oceanic circulation arctic sea ice is melting much more rapidly than had been expected and the arctic ocean will soon be free of sea ice in summer the greenland ice sheet is melting more rapidly than expected because of greenhouse warming surface meltwater forms lakes and then flows down through crevasses and holes in the ice to lubricate the base allowing ice steams to flow much more rapidly the lifetime of the greenland ice sheet may be only a few hundred years the west antarctic ice sheet is inherently unstable being grounded on rock well below sea level the ice shelves blocking ice streams off west antarctica have begun to melt from beneath and break up as the southern ocean warms the east antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate i conclude that a return to climatic conditions resembling those of the mid cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop co2 emissions to the atmosphere and remove some of the excess co2 already introduced

new biostratigraphic magnetostratigraphic and isotopic insights into the middle eocene climatic optimum in low latitudes the middle eocene climatic optimum meco was a warming event that interrupted the long term eocene cooling trend while this event is well documented at high southern and mid latitudes it is poorly known from low latitudes and its timing and duration are not well constrained because of problems of hiati microfossil preservation and weak magnetic polarity in key sedimentary sections here we report the results of a study designed to improve the bio magneto and chemostratigraphy of the meco interval using high resolution records from two low latitude sections in the atlantic ocean ocean drilling program odp sites 1051 and 1260 we present the first detailed benthic foraminiferal stable isotope records of the meco from the low latitudes as well as the biostratigraphic counts of orbulinoides beckmanni and new magnetostratigraphic results our data demonstrate a 750 kyr long duration for the meco characterized by increasing 13c and decreasing 18o with minimum 18o values lasting 40 kyr at 40 1 ma coincident with a short lived negative 13c excursion thereafter 18o and 13c values recover rapidly the shift to minimum 18o values at 40 1 ma is coincident with a marked increase in the abundance of the planktonic foraminifera o beckmanni consistent with its inferred warm water preference o beckmanni is an important eocene biostratigraphic marker defining planktonic foraminiferal zone e12 with its lowest and highest occurrences lo and hos our new records reveal that the lo of o beckmanni is distinctly diachronous appearing 500 kyr earlier in the equatorial atlantic than in the subtropics 40 5 versus 41 0 ma we also show that at both sites the ho of o beckmanni at 39 5 ma is younger than the published calibrations increasing the duration of zone e12 by at least 400 kyr in accordance with the tropical origins of o beckmanni this range expansion to higher latitudes may have occurred in response to sea surface warming during the meco and subsequently disappeared with cooling of surface waters

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

evidence and causes of the main extinction events in the paleogene based on extinction and survival patterns of foraminifera abstract we review the four main extinction events in the paleogene from the cretaceous paleogene boundary to the eocene oligocene boundary integrating the results obtained from a study of foraminiferal assemblages with other paleontological and geological data different survival strategies followed by the species are described and the duration of the phases of extinction survival and recovery is estimated the models and patterns of extinction of the foraminifera are highlighted we present a range of evidence and paleo environmental factors and analyze the possible causes of extinction a new terminology for mass extinction events is proposed sudden mass extinction would have happened virtually instantaneously and the process would have taken a few years or decades cretaceous paleogene boundary rapid mass extinction is defined as that which occurred in relatively short events around 100 kyr paleocene eocene and eocene oligocene boundaries slow mass extinctions are suggested to have lasted around 1 myr bartonian priabonian transition and may even have lasted for several million years

deep velocity structure of rifted continental crust u s mid atlantic margin from wide angle reflection refraction data we present new ocean bottom wide angle seismic data collected during the 1990 edge mid atlantic multichannel seismic experiment which provide a measurement of the deep velocity structure of rifted appalachian continental crust beneath the u s east coast continental margin reflections from the entire crust and moho are visible from offsets of zero to 100 km one dimensional inverse traveltime modeling reveals a 34 km thick crust consisting of four layers beneath the post rift sediments with velocities of 5 9 6 3 6 4 and 6 85 km s this velocity structure is indistinguishable from that found beneath several appalachian terranes in the northern appalachians of new england the average velocity of 6 85 km s in the lower crust limits the landward extent of the high velocity 7 2 7 4 km s lower crust found farther seaward and supports the interpretation of that layer as the result of rift related magmatic underplating rather than as thinned pre existing lower continental crust

radiolaria and pollen records from 0 to 50 ka at odp site 1233 continental and marine climate records from the southeast pacific abstract site 1233 drilled during leg 202 of the ocean drilling program provides a detailed record of marine and continental climate change in the southeast pacific and south american continent splits from over 500 samples taken at 20 cm intervals for quantitative analysis of radiolarian and pollen populations yield a temporal resolution of 200 400 years in each sample 39 pollen taxa and 40 radiolarian species and genera were evaluated age control is provided by 25 ams 14c dates lamy f kaiser j ninnemann u hebbeln d arz h w stoner j 2004 science 304 1959 1962 multivariate statistical analyses of these data allow us to conclude the following 1 during the past 50 ka the region of the central chile coast is not directly influenced by polar water from the antarctic region 2 changes in ocean conditions off central chile during this time interval primarily reflect north south shifts in the position of the south pacific transition zone 3 changes in chilean vegetation reflect comparable latitudinal shifts in precipitation and the position of the southern westerlies 4 the first canonical variate of radiolarian and pollen records extracted from site 1233 are remarkably similar to each other as well as to temperature records from the antarctic which suggests that marine and continental climate variability in the region is tightly coupled at periods longer than 3000 years 5 the phase coupling of these climate records which lead variations of continental erosion based on iron abundance at the same site are consistent with a hypothesis that erosion is linked to relatively long i e few thousand years response times of the patagonian ice sheet and thus is not a direct indicator of regional climate

astronomical forcing in late eocene marine sediments we use an x ray fluorescence xrf core scanner to obtain records of elemental concentrations in sediment cores from ocean drilling program odp leg 171b site 1052 blake nose atlantic margin of northern florida this record spans the middle to late eocene as indicated by bio and magnetostratigraphy and displays cyclicity that can be attributed to the orbital forcing of a combination of climate ocean circulation or productivity we use the xrf counts of iron and calcium as a proxy of the relative contribution from calcium carbonate and terrestrial material to construct a new composite depth record this new composite depth record provides the basis to extend the astronomically calibrated geological time scale into the middle eocene and results in revised estimates for the age and duration of magnetochrons c16 through c18 in addition we find an apparent change in the dominance of orbitally driven changes in obliquity and climatic precession at around 36 7 ma on our new time scale long term amplitude modulation patterns of eccentricity and obliquity in the data do not seem to match the current astronomical model any more suggesting the possibility of new constraints on astronomical calculations

long and short term hydroclimatic variabilities in the aptian tethys clues from the orbital chronostratigraphy of evaporite rich beds in the apennine carbonate platform mt faito southern italy abstract the stratigraphic signature of the global late aptian cooling episode and sea level lowstand has been investigated in the mt faito section of the apennine carbonate platform apcp of southern italy several meter scale fine grained limestone intervals with abundant quartz pseudomorphs after anhydrite and minor calcite pseudomorphs after gypsum are present in the middle upper gargasian straddling the marly orbitolina level a regional key marker correlative with part of the fallot oceanic anoxic event the evaporite rich intervals were deposited in a mudflat saltern setting and together with frequent transgressive shallow marine interlayers alternate quite regularly with lacustrine paralic or very shallow marine deposits suggestive of overall wetter conditions three to five couplets of cyclic arid wet phases are thus identified their timing and duration determined by an original cyclostratigraphically constrained age model tuned with the astrochronology from deep water tethyan reference sections suggest fluctuating hydroclimatic conditions arid semiarid vs wet phases over time scales as brief as 100 and 400 ky they are considered to reflect astronomically induced latitudinal migrations of intertropical climate belts a secular climate shift from arid to humid conditions supra regionally correlatable across the upper gargasian of the tethyan realm is dated at 118 1 my it corresponds to the onset of persistent lacustrine deposits on the partially emerged apcp and of abundant river borne supply of siliciclastics along the opposing tethyan margin the observed climate fluctuations occurred during a major apcp subaerial exposure which lasted for 4 4 my precise supra regional correlations suggest that the platform exposure was glacioeustatic in origin and coeval with a long lived late aptian cooling episode which interrupted the mid cretaceous greenhouse biostratigraphic and astrochronological tuning from the apcp indicates that the glacioeustatic lowstand terminated in the earliest albian just above the o reicheli key marker

radiolarian faunal turnover and paleoceanographic change around eocene oligocene boundary in the central equatorial pacific odp leg 199 holes 1218a 1219a and 1220a continuous eocene through oligocene sedimentary sedimentary sections were obtained at holes 1218a 1219a and 1220a drilled during leg 199 of the ocean drilling program in the central equatorial pacific quantitative analysis of radiolarian assemblages between the upper eocene through lower oligocene sedimentary successions revealed that major faunal changes of radiolarians occurred in the late eocene 35 5 35 7 ma subchron c16n1 around the eocene oligocene boundary 33 7 33 8 ma upper subchron c13r and in the early oligocene 30 9 31 3 ma uppermost subchron c12r the faunal change in the late eocene is characterized by a stepwise decrease of tropical eocene species and an increase in cosmopolitan probably cool water tolerant radiolarians however without a significant change in species diversity and radiolarian accumulation rates the stratigraphic level of this late eocene turnover came after the late eocene impact event and may have been more related to global cooling and associated oceanographic changes than to asteroid impact the turnover around the eocene oligocene boundary corresponding to the oi 1 event is the most critical during the eocene oligocene transition many biotic events such as a sudden drop of species diversity an increase in the cosmopolitan radiolarian group a large number of species turnovers and a drop in radiolarian accumulation rates occurred at or just above this level together these indicators suggest a major restructuring of radiolarian assemblages from the high diversity eocene fauna to a low diversity oligocene one the third turnover event within early oligocene is represented by a replacement of dominant species with a sudden decrease in radiolarian accumulation rates however this oligocene turnover is not consistent with other major 18o isotope events such as oi 1b and oi 2

the ellsworth terrane coastal maine geochronology geochemistry and nd pb isotopic composition implications for the rifting of ganderia the ellsworth terrane is one of a number of fault bounded blocks that occur along the eastern margin of ganderia the westernmost of the peri gondwanan domains in the northern appalachians that were accreted to laurentia in the paleozoic geologic relations detrital zircon ages and basalt geochemistry suggest that the ellsworth terrane is part of ganderia and not an exotic terrane in the penobscot bay area of coastal maine the ellsworth terrane is dominantly composed of bimodal basalt rhyolite volcanic sequences of the ellsworth schist and unconformably overlying castine volcanics we use new u pb zircon geochronology geochemistry and nd and pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the ellsworth terrane and its relationship with ganderia u pb zircon geochronology for rhyolites indicates that both the ellsworth schist 508 6 0 8 ma and overlying castine volcanics 503 5 2 5 ma are middle cambrian in age two tholeiitic basalt types are recognized type tb 1 basalt present as pillowed and massive lava fl ows and as sills in both units has depleted la and ce la nd n 0 53 0 87 values fl at heavy rare earth element ree values and no positive th or negative ta anomalies on primitive mantle normalized diagrams in contrast type tb 2 basalt present only in the castine volcanics has slightly enriched lree la yb n 1 42 2 92 values and no th or ta anomalies both basalt types have strongly positive e nd 500 values tb 1 7 9 8 6 tb 2 5 6 7 0 and relatively enriched pb isotopic compositions 206

monitoring the variations of the socotra upwelling system during the last 250 kyr a biogenic and geochemical approach abstract a combination of changes in the species composition of the radiolarian populations and in the sediment chemical composition content and mass accumulation rates of carbonate organic carbon and selected major and trace elements with special attention paid to ba is used to reconstruct the variations in upwelling activity over the last 250 kyr in the socotra gyre area somali socotra upwelling system nw indian ocean in the socotra gyre core md 962073 at 10 n the variations in upwelling intensity are reconstructed by the upwelling radiolarian index uri while the thermocline surface radiolarian index tsri testifies to productivity variations during non upwelling intervals despite an origin related both to marine and terrigenous inputs the geochemical records of organic carbon silica and trace elements ba p cu and zn normalized to al are controlled by the variations in surface paleoproductivity the data indicate a continuous increase in upwelling intensity during the last 250 kyr with a maximum activity within the mis 3 while high productivity periods in between the upwelling seasons occurred both during glacial and interglacial intervals a comparison of our data with published observations from another gyre of the somalian upwelling area located at 5 n in the somali gyre area shows differences regarding periods of upwelling activity and their geochemical imprint three hypotheses are proposed to explain these differences 1 changes in the planktonic community resulting in more silica rich deposits in the socotra gyre and more carbonate rich deposits in the somali gyre that are controlled by differences in the source water of the upwelling 2 a more important terrigenous input in the southern gyre and 3 a different location of the sites relative to the geographic distribution of the upwelling gyres and hydrologic fronts

radiolarian stratigraphy near the eocene oligocene boundary three sites from the equatorial pacific odp 1218 iodp u1333 and u1334 are judged to have a complete stratigraphic sequence across the eocene oligocene boundary the sections of all three sites from 40 ma to 30 ma have been sampled and the samples merged into a single composite section with an average sample spacing 20 kyr a total of 76 radiolarian species species groups and specific variant forms provide a detailed radiolarian stratigraphy across this climatically important boundary altogether 47 eocene radiolarian species had their last appearance between 40 ma and the end of the final step of the eocene oligocene climate transition many of them in discreet episodes of extinction that grew in magnitude as the transition was approached first appearance datums appear to cluster at the base of the cool down from the middle eocene climate optimum and near the base of the oligocene following a maximum in radiolarian last appearances and coincident with relatively abundant diatoms there appears to be little relationship between paleoproductivity as measured by barite accumulation rates and both first and last appearances of radiolarians diatoms are not common in the eocene and their blossoming in the oligocene is preceded by the major episodes of radiolarian extinctions in the oligocene radiolarian extinctions appear to be associated with low to moderate diatom abundance whereas species first appearances seem to be associated with moderate to high diatom abundance neither paleoproductivity nor a competition for the dissolved silica a resource necessary for diatom frustule and radiolarian test construction appears to control the episodic extinction of radiolarians in the eocene or the more dispersed loss of species in the oligocene

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

atlantic eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography reconstruction of atlantic ocean vertical and meridional water characteristics is based on combined synoptic fossil census data stable isotope records and measurements of individual planktonic foraminiferal species correlations between planktonic foraminiferal indices and specific water types and or chemical conditions are used to trace seven stages in the history of atlantic circulation during eocene climatic changes 1 warm equable probably saline productive ocean of the early eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water 2 early middle eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters 3 maximal partitioning of water types faunas and bioprovinces in middle eocene zone p11 accompanying maximum planktonic foraminiferal diversity accelerated near surface and deepwater cooling and intensified upwelling 4 latest middle eocene zone p14 maximal planktonic foraminiferal evolutionary overturn during accelerated cooling deep and surface water ventilation and transformation of tropical surface water habitat with the expansion of temperate water types and faunas this accompanied the reduction of meridional heat transport in boundary currents 5 late eocene bottom water and middle latitude cooling broadening of meridional temperature gradients and expanded oxygen minimum but faunal homogenization following the decreased import of mediterranean water ourflow 6 weakening and or shoaling of the nutricline an oxygen minimum and the thermocline preceding a diminution of primary productivity at the eocene oligocene boundary and 7 earliest oligocene low productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small sized individuals the increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic forcing mechanism in the latest middle and late eocene

a holocene paleotemperature record based on radiolaria from the northern okinawa trough east china sea using a radiolarian based transfer function mean annual sea surface temperature sst and seasonal temperature range are reconstructed through the last 10 500yrs in the northern okinawa trough down core sst estimates reveal that throughout the holocene the changes of mean annual sst display a three step trend i an early holocene continuous warming between 10 500 and 8500yr bp which ends up with a abrupt cooling at about 8200yr bp ii a relatively stable middle holocene with high sst that lasted until 3200yr bp and iii a late holocene distinct sst decline between 3200 and 500yr bp this pattern is in agreement with the ice core and terrestrial paleoclimatic records in the chinese continent and other regions of the world five cooling events with abrupt mean annual sst drops which occur at similar to 300 600 1400 3100 4600 5100 and 8200yr bp are recognized during the last 10 500yrs comparison of our results with records of gisp2 ice core and marine sediment in north atlantic region suggests these cooling events are strongly coupled which implies a possible significant climatic correlation between high and low latitude areas c 2007 elsevier ltd and inqua all rights reserved

evolution of eastern pacific warm pool and upwelling processes since the middle miocene based on analysis of radiolarian assemblages response to indonesian and central american seaways a quantitative racholarian study at ocean drilling program site 1241 in the eastern tropical pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle miocene today this site is located just under the eastern pacific warm pool epwp based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes it is suggested that three notable changes occurred at 10 6 9 8 and 4 2 ma in the region four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following 1 stratified seawater 12 0 to 10 6 ma 2 a shallowing of the thermocline and an increasing of upwelling 10 6 to 9 8 ma 3 significant inflow of warm water to the eastern tropical pacific caused by an intensified northern equatorial countercurrent necc resulting in the formation of epwp 9 8 to 4 2 ma and 4 the reduction of the epwp and the necc and an increase in upwelling 4 2 to 0 ma the timing of these paleoceanographic events indicated the strong relations with the opening and closing of the indonesian and central american panama seaways the reduction of the epwp this study and the deepening of the thermocline in western pacific at about 4 2 ma cannariato and ravelo 1997 chaisson and ravelo 2000 indicated a change from a state resembling el nino in the late miocene and the early pliocene time to a state resembling la nina by the late pliocene c 2009 elsevier b v all rights reserved

avalon terrane in eastern coastal maine seismic refraction wide angle reflection data a 145 km long seismic refraction line recorded parallel to the eastern coastline of maine within the avalon terrane provides information about the crustal velocity structure within the avalon block and its relation to other appalachian terranes a crustal velocity model for the upper 8 km determined by using two dimensional ray tracing accounts for all first arrivals on the traveltime curves for each of the shots recorded and shows that except for a thin surficial layer of velocity 5 0 5 3 km s upper crustal granites and country rocks have velocities in the range 6 0 6 3 km s and gabbros have a 6 5 km s velocity to determine the lower crustal structure deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing major reflective boundaries at approximately 3 4 7 and 10 11 s two way traveltime are easily distinguished and are similar to those observed in a near vertical seismic reflection survey crossing the refraction profile at its southwestern end the deepest reflections correspond to the crust mantle boundary at a depth of 34 35 km

tectono stratigraphic and kinematic evolution of the southern apennines calabria peloritani terrane system italy abstract temporal controls such as sedimentation ages in foredeep and wedge top basins combined with information about stratigraphic and metamorphic evolution ages and characterization of magmatic rocks deep structures burial and exhumation histories allowed us to obtain kinematic estimations of the southern apennines calabria peloritani terrane system evolution from the late oligocene to recent calculated thrust front velocities suggest to subdivide the orogenic evolution in main five kinematic stages characterized by different velocity trends nine kinematic complexes from a to i i e sets of tectonic units deformed in the same time range are determined according to foredeep ages these complexes bounded by main regional thrust faults encompass one or more tectonic sub units and successions of different paleoenvironment domains paleogeographic evolution model indicates according to available paleomagnetic data a counterclockwise rotation with a mean angle of 60 for the apennine platform carbonates whereas a mean angle of 20 for the eastern sector of the apennine platform and western side of apulian platform shortening estimations for the apennine successions show values ranging between 55 and 88 and a linear best fit indicating an increase from 60 nw sector to ca 90 se sector such high values are consistent with a deformation dominated by a thin skinned tectonics on the contrary the low value of 28 calculated for mt alpi suggests an exhumation ruled by high angle deep seated structures characterized by limited displacements tectonic vergences referred to middle late miocene late miocene and pliocene middle pleistocene when restored indicate an average eastward tectonic transport finally tectonic evolution is summarized in eleven schematic cross sections and corresponding paleogeographic maps

radiolarian and sedimentologic paleoproductivity proxies in late pleistocene sediments of the benguela upwelling system odp site 1084 the changing composition of radiolarian faunas from late neogene deep sea sediments has been used in recent years as a proxy for changes in marine paleoproductivity we examine radiolarian faunas organic carbon content toc opal and coarse fraction components over the last 270 000 years in sediments from odp hole 1084a drilled in a high productivity upwelling region within the benguela upwelling system off the west coast of africa age control is provided by stable oxygen isotope measurements of benthic foraminifera prior research has established that late pleistocene glacial intervals in this upwelling system generally had higher productivity than interglacials the radiolarian wade water depth ecology paleoproductivity index correlates well with toc and opal in these samples and all three parameters change in synchrony with the benthic isotope curve over all but the mis 5e 6 time interval wade inferred productivity is significantly higher in glacials than interglacials we conclude that the wade index is a useful proxy for paleoproductivity at this location as are also opal and organic carbon accumulation rates carbonate and carbonate based indices such as the accumulation rate of benthic foraminifera bfar by contrast do not correlate well either to productivity indices or to the glacial interglacial cycle and are interpreted to primarily reflect carbonate dissolution

early and middle eocene radiolarian assemblages in the eastern equatorial pacific ocean iodp leg 320 site u1331 faunal changes and implications for paleoceanography abstract quantitative faunal analyses of radiolarians were used to reconstruct paleoceanographic conditions spanning the interval from zones rp8 early eocene to rp16 middle eocene in pelagic sequences recovered at integrated ocean drilling program iodp site u1331 in the eastern equatorial pacific ocean on the basis of relative abundance data from the low to high latitudes reported in the previous literature paleoceanographic indices were identified 1 species indicative of warmer conditions include stylosphaera coronata coronata phormocyrtis embolum dendrospyris didiceros phormocyrtis cf proxima and thyrsocyrtis triacantha 2 species indicative of cooler conditions include the lophocyrtis aspera group the lithocyclia ocellus group hexacontium sp a hexacontium sp b thecosphaerella glebulenta and lithelius sp a two warming and at least six cooling events in the early to middle eocene were identified from radiolarian assemblage variations the paleoclimatic trends can be summarized as follows warming in c23n 2n to c21r 51 5 49 0 ma and c18n 40 2 39 0 ma cooling in c21r 48 5 47 8 ma lower c20r 46 2 45 2 ma top c20r to c20n 44 0 43 0 ma top c20n to c19r 43 0 41 7 ma c19n to c18r 41 7 40 2 ma and c18n 1n 39 0 38 5 ma these cooling events corresponded to the eli and bli events which were identified in benthic foraminiferal 18 o of the southern ocean in general radiolarian and opal mass accumulation rates mars in the eastern equatorial pacific had higher values in cooling conditions during the middle eocene the changes in biological productivity in the eastern equatorial pacific were associated with cooling of tropical surface water the change in relative abundance of radiolarians and caco 3 content at site u1331 indicated that middle eocene carbonate events carbonate accumulation events caes lyle et al 2005 coincided with the cooling events of tropical surface water at least cae 2 and cae 3 were associated with high biological productivity as well as cooling

radiolarian magnetobiochronology and faunal turnover across the middle late eocene boundary at ocean drilling program site 1052 in the western north atlantic ocean quantitative radiolarian assemblage analysis has been conducted on middle and upper eocene sediments zones rp16 to rp18 from ocean drilling program site 1052 in order to establish the radiolarian magnetobiochronology and determine the nature of the faunal turnover across the middle late eocene boundary in the western north atlantic ocean we recognize and calibrate forty five radiolarian bioevents to the magneto and cyclo stratigraphy from site 1052 to enhance the biochronologic resolution for the middle and late eocene our data is compared to sites in the equatorial pacific leg 199 to access the diachrony of biostratigraphic events eleven bioevents are good biostratigraphic markers for tropical subtropical locations south of 30 n the primary markers lowest occurrences of cryptocarpium azyx and calocyclas bandyca which are tropical zonal boundary markers for zones rp17 and rp18 provide robust biohorizons for correlation and age determination from the low to middle latitudes and between the atlantic and pacific oceans some other radiolarian bioevents are highly diachronous 1 million years between oceanic basins a significant faunal turnover of radiolarians is recognized within chron c17n 3n 37 7 ma where 13 radiolarian species disappear rapidly in less than 100 kyr and 4 new species originate the radiolarian faunal turnover coincides with a major extinction in planktonic foraminifera we name the turnover phase the middle late eocene turnover mlet assemblage analysis reveals the mlet to be associated with a decrease in low mid latitude taxa and increase in cosmopolitan taxa and radiolarian accumulation rates the mlet might be related to increased biological productivity rather than to surface water cooling

equatorial pacific productivity changes near the eocene oligocene boundary there is general agreement that productivity in high latitudes increased in the late eocene and remained high in the early oligocene evidence for both increased and decreased productivity across the eocene oligocene transition eot in the tropics has been presented usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the eot itself a complete record of the eocene oligocene transition was obtained at three drill sites in the eastern equatorial pacific ocean odp site 1218 and iodp sites u1333 and u1334 four paleoproductivity proxies that have been examined at these sites together with carbon and oxygen isotope measurements on early oligocene planktonic foraminifera give evidence of ecologic and oceanographic change across this climatically important boundary export productivity dropped sharply in the basal oligocene 33 7 ma and only recovered several hundred thousand years later however overall paleoproductivity in the early oligocene never reached the average levels found in the late eocene and in more modern times changes in the isotopic gradients between deep and shallow living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early oligocene that on average affected accumulation rates of barite benthic foraminifera and opal as well as diatom abundance near 33 5 ma an interval with abundant large diatoms beginning at 33 3 ma suggests an intermediate thermocline depth which was followed by further shoaling a dominance of smaller diatoms and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

early paleogene biosiliceous sedimentation in the atlantic ocean testing the inorganic origin hypothesis for paleocene and eocene chert and porcellanite abstract the widespread occurrence of lower eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling and both biotic and abiotic forcings have been proposed to explain it we present a reconstruction of indurated siliceous sediment iss and preserved biosiliceous sediment pbs occurrences in the atlantic ocean through the paleocene and eocene 66 through 34 ma iss and pbs distributions reveal dissimilar temporal trends with the peak of iss occurrences coinciding with the early eocene climatic optimum in line with previous studies pbs occurrences show a generally increasing trend culminating between 44 and 43 ma the common co occurrence of iss and pbs and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread paleogene iss and argues against an inorganic mode of early cenozoic chert and porcellanite precipitation weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification 1 silicification due to prolonged exposure of biogenic opal rich sediments to corrosive bottom waters and 2 silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal rich deposits the confinement of iss and pbs to proximal sites along continental margins points to the reliance of siliceous sedimentation through the paleocene and eocene on terrestrial supply of dissolved silicon consistent with this quantitative siliceous microfossil assemblage records from the blake nose in the nw atlantic indicate that the nutrient rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early paleogene the inorganic sio2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early paleogene iss we favor the biogenic iss precursor scenario and reconcile it with the low productivity early cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western north atlantic ocean from the north american margin through the paleocene and eocene dissolution of this surplus silica was facilitated by an early southwestward flow of young sio2 depleted waters from the north atlantic all these factors contributed to iss and pbs focusing in the western north atlantic through the early paleogene

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

the crustal structure in central maine from coherency processed refraction data in 1984 the u s geological surcvey and the canadian department of energy mines and resources conducted an extensive seismic refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surface velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surf ace velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from the ne to the sw end of the profile surface rocks at the sw end of the profile have a metamorphic depth of burial of at least 15 km indicating that the crust below the central maine synclinorium may have been thickened to at least 55 km during paleozoic collisions

eustatic control on early dolomitization of cyclic peritidal carbonates evidence from the early ordovician upper knox group appalachians the early ordovician upper knox group is characterized by stacked meter scale peritidal cycles that repeat at high frequencies 10 4 to 10 5 yr stacking patterns stratigraphic trends in lithofacies and cycle thickness of meter scale cycles define five depositional sequences that in conjunction with fischer plots delineate five long term relative sea level fluctuations during upper knox deposition intrabasinal and interbasinal correlation of upper knox fischer plots suggests that the third order sea level events were eustatic meter scale peritidal cycles likely formed in response to high frequency fourth and fifth order eustatic sea level fluctuations superimposed on these third order sea level events upper knox cyclic carbonates are extensively dolomitized as much as 85 of all dolomite is stratiform and consists of early dolomite exhibiting minor to extensive modification by burial dolomite synsedimentary dolomitization likely occurred in modified sea water during tidal flat progradation governed by high frequency sea level events this is suggested by the common association of dolomite with mud cracked laminites and silicified evaporite nodules the systematic decrease in dolomite abundance below laminite cycle caps and the presence of dolomite clasts in regoliths veneering high frequency cycle tops or in transgressive limestones of the overlying cycle dolomite distribution within depositional sequences shows a strong relationship to third and fourth order eustatic sea level events indicating that long term eustasy also strongly controlled early dolomitization of upper knox carbonates mass balance calculations show that the proposed sabkha model of dolomitization in concert with composite eustasy could generate stratiform dolomite of considerable vertical and lateral extent in peritidal cyclic carbonates this reflects the duration of progradation and supratidal exposure 10 4 to 10 5 yr available for dolomitization to proceed and the broad zone of active dolomitization that would develop during continued progradation throughout each cycle period

tethyan mediterranean organic carbon rich sediments from mesozoic black shales to sapropels the jurassic to holocene record of black shale deposition in the tethys mediterranean region is unrivalled by that of any other ocean basin either in land sections or drill cores the term black shale is used here broadly for sediments with elevated organic carbon concentrations 1 including the pliocene to recent sapropels most of the black shales are devoid of benthonic organisms are laminated and were deposited in distinct rhythms during periods when the deep waters of the ocean basins were anoxic or dysoxic the tethyan black shale records have become essential in studies of the transfer of organic carbon into the sediment record and for astronomical tuning and geological time scales these records have been central in understanding climate control on ocean dynamics and biogeochemical cycles the mesozoic black shales were deposited within well defined time envelopes of around 0 5 to 1 myr these black shales which were confined to certain chronostratigraphic intervals in the jurassic and cretaceous were recognized as expressions of global oceanic anoxic events in the mid 1970s and subsequently named after prominent researchers bonarelli selli goguel the black shale episodes were dated by biostratigraphic methods and by high resolution chemostratigraphy and cyclostratigraphy mesozoic black shales are now interpreted as the oceanographic expression of major perturbations of the global carbon cycle and climate research into younger pliocene to pleistocene sedimentary cycles including black shales termed sapropels exposed in land sections or found in pelagic and hemipelagic marine sediment cores of late quaternary age started in the 1950s main threads pursued from this end of the record were the climatic control of oceanic processes that permitted the development of highly detailed and precise time scales tuned to the astronomical clock of insolation changes palaeoclimate evolution of the circum mediterranean area and biogeochemical dynamics in anoxic basins after 50 years of intensive research the tethyan and mediterranean black shales remain subjects of fascination in earth science tracing the origins and building upon recent progress the current hypotheses on their formation are reviewed here it is a panorama of complex interplays between global and regional tectonics climate dynamics during both ice house and greenhouse states of global and regional climate oceanographic responses to these climate changes and biogeochemical adaptations that were all needed to shape an extraordinary archive of global change in the absence of human activity

the valanginian δ13c excursion may not be an expression of a global oceanic anoxic event abstract marine and terrestrial sediments of the valanginian age display a distinct positive 13 c excursion which has recently been interpreted as the expression of an oceanic anoxic episode oae of global importance here we evaluate the extent of anaerobic conditions in marine bottom waters and explore the mechanisms involved in changing carbon storage on a global scale during this time interval we asses redox sensitive trace element distributions rste uranium vanadium cobalt arsenic and molybdenum and the quality and quantity of preserved organic matter om in representative sections along a shelf basin transect in the western tethys in the polish basin and on shatsky rise om rich layers corresponding in time to the 13 c shift are generally rare in the tethyan sections and if present the layers are not thicker than several centimetres and total organic carbon toc contents do not surpass 1 68 wt palynological observations and geochemical properties of the preserved om suggest a mixed marine and terrestrial origin and deposition in an oxic environment in the polish basin om rich layers show evidence for an important continental component rste exhibit no major enrichments during the 13 c excursion in all studied tethyan sections rste enrichments are however observed in the pre 13 c excursion om rich barrande levels of the vocontian trough in addition all tethyan sections record higher mn contents during the 13 c shift indicating rather well oxygenated bottom waters in the western tethys and the presence of anoxic basins elsewhere such as the restricted basins of the north atlantic and weddell sea we propose that the valanginian 13 c shift is the consequence of a combination of increased om storage in marginal seas and on continents as a sink of 12 c enriched organic carbon coupled with the demise of shallow water carbonate platforms diminishing the storage capacity of 13 c enriched carbonate carbon as such the valanginian provides a more faithful natural analogue to present day environmental change than most other mesozoic oaes which are characterized by the development of ocean wide dysaerobic to anaerobic conditions

fate of reflux brines in carbonate platforms active reflux may occur during periods of platform top brine generation but the role and fate of these brines after reflux events are uncertain we have used a numerical flow model to investigate and quantify the response of reflux brines to changes in platform top salinity simulations suggest that reflux brines originally concentrated to gypsum saturation 150 have a relatively long platform residence time on the order of 100 times the duration of the reflux event when brine generating conditions cease brines will continue to sink through the platform entraining seawater a variant of reflux circulation we term latent reflux mesosaline brines intercepted by drilling of carbonate margins by the ocean drilling program may have originated from pleistocene reflux event s on the adjacent platform top and be currently moving by latent reflux latent reflux circulation could deliver a significant quantity of dissolved reactants to platform carbonates including mg for dolomitization

pelagic productivity changes in the equatorial area of the northwest indian ocean during the last 400 000 years abstract major and selected trace element al fe mg k ba p mn v cu ni and ti records were analyzed in two cores recovered from the northwestern indian ocean core md 90940 on the madingley rise and core md 85668 in the somali basin in order to monitor the sedimentary response to pelagic productivity in this area during the last 400 000 years geochemical proxies such as bulk mass accumulation rate mar al normalized major and trace element contents major and trace element mars were compared to biologic markers of palaeoproductivity a new radiolarian index rad ratio and the variations of foraminiferal and radiolarian assemblages special attention being paid to the barium record a sequential leaching procedure determined the main ba carrier fraction in the sediment and thus the amount of biogenic barium the blue ocean sedimentation on the madingley rise core md 90940 is characterized by a low mar and an insignificant terrigenous input the bulk mar variations are directly related to the variations of the rad ratio reflecting a direct link between surface productivity and pelagic sedimentation at this site in this sediment barium is mainly found as barite and can be considered as a palaeoproductivity proxy in the somali basin core md 85668 the terrigenous inputs are relatively higher but the bulk mar variations are still related to the variations of surface productivity no barite was found and barium is mainly linked to the terrigenous input a comparison of the two pelagic sites of the madingley rise and the somali basin points out the differences between the barium records at both sites despite the location of both cores in the pelagic domain the geochemical record and especially the barium one is different from one core to the other the comparison of the variations of the bulk mar which reflects the variations of the surface productivity presents significant discrepancies between both sites in the blue ocean core md 90940 the productivity peak values are mainly recorded during glacial intervals but their maximum values are observed during interglacial isotope stage 9 in the somali basin core md 85668 high bulk mar periods occurred during glacial isotope stages the interglacial episode of high productivity recorded on the madingley rise the absence of significant variations of productivity at the 8 7 transition in the somali basin as well as the absence of a time lag between both records indicate that the surface productivity is in this area controlled more by the local variations of the palaeoceanographic patterns than the global climatic changes e g the glacial interglacial alternations

biostratigraphic implications of mid latitude palaeocene eocene radiolarian faunas from hole 1051a odp leg 171b blake nose western north atlantic

orbitally forced climate change in late mid eocene time at blake nose leg 171b evidence from stable isotopes in foraminifera previous stable oxygen isotopic data from surface dwelling foraminifera indicate that eocene tropical sea surface temperatures ssts were significantly lower than at present here we show that stable isotopic analyses 180 13c of the late mid eocene mixed layer dweller morozovella spinulosa are consistent with in mid eocene mid latitudes ssts close to or slightly lower than modern temperatures at blake nose western north atlantic in contrast isotopic analyses of the benthic foraminiter nuttalides truempyi reveal a gradual fall in mean bottom water temperatures from 8 to 7 c over c 500 ka years these deep intermediate water temperatures are significantly higher than modern ones and are similar to intermediate and bottom water temperatures recorded from earlier in palaeogene and late cretaceous time large shifts arc seen in the 18o and 13c values of the planktonic foraminifers of up to 1 and 2 6 respectively that probably reflect temperature and nutrient fluctuations controlled by regional changes in upwelling intensity and runoff the surface to benthos 18o gradient decreases from 3 pdb to a minimum of c 0 5 pdb over 400 ka which could relate to the intensity of upwelling spectral analysis reveals precessional forcing in the foraminiferal 18o records which shows the direct influence of low latitude insolation on surface water stratification monsoonal wind systems may have forced the upwelling cycles and or freshwater input the benthic foraminifer 18o record also contains the obliquity cycle in addition to the precessional cycles indicating the inheritance of mid and high latitude forcing to subtropical deep waters

radiolarian evidence for the stratigraphy and palaeo oceanography of the deep water passive margin of the indian plate karamba formation indus suture zone ladakh himalaya abstract new radiolarian biostratigraphical information sheds light on the mesozoic sedimentary tectonic and palaeoceanographic evolution of a south tethyan margin in northern india radiolarian cherts studied here form part of deformed deep water successions within the indus suture zone ladakh himalaya these are defined as the karamba formation and interpreted as the stratigraphically higher and palaeogeographically more distal parts of a passive margin lamayuru group this formation includes radiolarites pelagic carbonates redeposited limestones ferruginous shales sandstones and abundant mafic extrusive rocks radiolarian assemblages of early and late middle jurassic mid cretaceous mid albian to cenomanian and late cretaceous santonian age were obtained from four measured sequences results indicate i long intact jurassic cretaceous successions rather than disrupted melange are present in the karamba formation ii extensive basic volcanism took place during the middle jurassic and can be correlated with an extensional phase affecting the nw indian continental margin iii non calcareous radiolarian rich sediments accumulated during the middle jurassic reflecting the influence either of a broad jurassic equatorial upwelling zone or a more localised coastal upwelling system after drowning of the zanskar clastic shelf in the late albian sedimentation on the distal shelf and upper slope was restricted by bottom current activity late albian cenomanian radiolarites of the karamba formation are contemporaneous with stratigraphie gaps and glauconite phosphorite deposition on the zanskar shelf a well developed eastward boundary current off the northern margin of india may have persisted until near the end of the late cretaceous during the late albian cenomanian current activity and coastal upwelling were probably strong and radiolarian rich sediments accumulated on the distal margin beneath the ccd pelagic limestones accumulated during the turanian over the entire margin possibly related to eustatic sea level rise and consequent reduction in bottom current activity intense oceanic circulation apparently was renewed during the coniacian santonian as indicated by sedimentary hiatuses in the zanskar shelf succession and accumulation of carbonate free radiolarian ooze in the karamba formation

environmental change in the subtropics during the late middle eocene greenhouse and global implications 1 oxygen isotope records from odp site 1052 blake nose subtropical north atlantic ocean indicate significant short term high amplitude variability up to 1 4 in about 2500 to 4000 years during the late middle eocene 37 9 37 5 ma these variations reflect a combination of changes in sea surface temperature and the oxygen isotope composition of the regional seawater in order to independently evaluate the magnitude of sst changes at blake nose and better understand the nature of environmental change during the late middle eocene we present planktonic foraminiferal mg ca data combined with 18o data from the same samples the calculated mg ca paleotemperatures indicate a decrease in ssts over the study interval from 33 to 28 c at the same time that previously published foraminiferal 18ocalcite values from the same samples also decrease thus the 18ocalcite values must reflect a significant component of seawater 18o change in order to reconcile the opposite paleotemperature trends reflected by both proxies calculated 18oseawater values decreased from 3 at 37 83 ma to 2 at 37 6 ma the combined trends of the sst and 18oseawater cannot be explained by an increase of continental ice over this time interval instead the data favor an overall weakening of the hydrological cycle as global climate transitioned from the greenhouse to icehouse

tex86 and stable δ18o paleothermometry of early cretaceous sediments implications for belemnite ecology and paleotemperature proxy application abstract recent studies have cast doubt on the unadjusted usage of jurassic and cretaceous 18 o paleotemperature data derived from belemnites since the latter data often reflect cooler paleotemperature estimates than would be expected in this study we address this problem by analysing rocks of barremian to early aptian age from two outcrops in northern germany using tex 86 paleothermometry along with 142 belemnite guards studied for their stable isotope 13 c 18 o and trace element composition magnesium strontium iron and manganese both tex 86 and 18 o bel indicate very warm water temperatures for a distinctive black shale sequence of late early barremian age hauptblatterton with temperatures of up to 29 c and 23 c respectively we observe a constant offset of tex 86 temperatures versus the 4 to 5 c cooler 18 o belemnite signal for this interval the late barremian sequence shows an increase of the 18 o bel values from 1 to 0 reflecting temperatures around 16 to 12 c while the contemporaneous tex 86 temperatures vary between 26 and 32 c the common occurrence of belemnites in the anoxic sediments of the early barremian implies however clearly a nektonic way of life similar to that of recent teuthids rather than a nektobenthic one like sepia this in turn suggests that the belemnites investigated here genera praeoxyteuthis aulacoteuthis oxyteuthis and neohibolites were active swimmers which inhabited a deeper habitat below the thermocline in an epicontinental sea of perhaps 100 to 250 m water depth the offset of the tex 86 and 18 o bel data is therefore interpreted to reflect temperature signals from two different depth habitats i e the tex 86 is selectively derived from warm sea surface waters and the belemnites likely occupied deeper and cooler waters with relative increasing salinities in the late barremian this study stresses the importance that the taxonomy paleobiology and ecology of the belemnite taxa genera species used for paleotemperature reconstructions must be considered before the 18 o bel signal can be further interpreted the variation of the 18 o signature gained from one belemnite population of 22 specimens by 1 1 suggests that the 18 o data of individual belemnites should be used with caution for reconstructing long termed paleotemperature trends

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

tomographic inversion for the seismic velocity structure beneath northern new england using seismic refraction data the seismic velocity structure of the crust and the upper mantle beneath northern new england was investigated from the travel time data of the 1984 maine seismic refraction profile and the 1988 ontario new york new england seismic refraction profile seismic refraction experiments by using tomographic inversion techniques strong lateral seismic velocity variations were found in the upper 15 km of the crust and these variations are correlated with regional geologic and tectonic structures the grenville basement in the adirondack mountains of eastern new york is characterized by an unusually high p wave velocity of 6 7 km s in the upper 15 km of the crust this high velocity basement extends eastward below western vermont to a depth between 15 and 20 km from the surface more typical upper crustal p wave velocities of 5 6 to 6 4 km s were generally found in central and southern maine and in new hampshire and the anisotropic upper crustal zone west of penobscot bay in maine was imaged by locally slower velocities the correlation of the inversion velocity structure with the tectonic features of northern new england shows that the appalachian mountains in northern new england may extend tectonically to at least 20 km deep in the crust the velocity distribution at 20 km depth shows three northeast elongate juxtaposed belts which correspond to the connecticut valley gaspe synclinorium the bronson hill anticlinorium and the kearsarge central maine synclinorium respectively the connecticut valley gaspe and kearsarge central maine synclinoria have relatively high velocities from 6 94 to 7 12 km s while the bronson hill anticlinorium has relatively low velocities from 6 52 to 6 75 km s in the lower crust another low velocity area of 6 52 km s at 20 km depth is imaged beneath the white mountain batholith in central new hampshire and may be a lower crustal expression of this batholith upper mantle velocity structures were obtained for the grenville basement the appalachians in northern new england and the avalon terrane in southeastern maine from the long range seismic refraction data generally the older grenville lithosphere about 1100 ma in quebec has higher velocity in the upper mantle than does the younger avalon terrane no older than 650 ma in the southeastern part of northern new england the data suggest that the velocity of the upper mantle beneath the old north american craton increases stepwise with observable velocity discontinuities in depth while that beneath the avalon terrane does not increase through the first 40 km of the upper mantle the data analysis also shows that the upper mantle suture between the grenville basement and the avalon terrane occurs in a narrow belt beneath the appalachian mountains of central maine and new hampshire the did of the moho discontinuity beneath northern new england is modeled as nearly flat as 0 7 in the n57 w direction and as steep as 1 2 beneath the grenville basement

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

paleoceanography and the diachrony of radiolarian events in the eastern equatorial pacific the development of an orbitally tuned time scale for the odp leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework with this framework we are better able to define which of the first and last appearances of species appear to be synchronous in addition the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped these maps not only provide information on the process of evolution migration and extinction they can also be related to water mass distributions and near surface circulation of the ocean of 39 radiolarian events studied at 11 sites in the eastern equatorial pacific 28 were found to have a minimum range in their estimated age that exceeded 0 15 m y the temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 ma these changes in the locations of high gradient regions suggest that the south equatorial current sec was north of its present position prior to approximately 7 ma there was a southward shift in the northern boundary of this current between approximately 6 and 7 ma and the development of a relatively strong gradient between the northeastern and northwestern sites between approximately 3 7 and 3 4 ma there was a very slight northward shift in the northern boundary of the sec and the steep gradients between the northeastern and northwestern sites may have disappeared this change is thought to be associated with the closing of the isthmus of panama the temporal spatial patterns of diachronous events younger than 3 4 ma are consistent with patterns of circulation in the modern ocean

cyclostratigraphy of a carbonate platform as a tool for high precision correlation abstract mesozoic carbonate platforms of southern italy are thick 3000 m and well stratified bodies uplifted by the late tertiary quaternary deformation of the northern gondwanian continental margin they formed mostly in the shallow ramp open to restricted lagoon and peritidal supratidal settings and show a prevailingly cyclic organization consisting of m scale shallowing upward units we think that this cyclicity is demonstrably controlled by the earth s orbital perturbations individual cycle duration hierarchical organization numerical analysis of their sedimentological and petrophysical features the genetic mechanisms of the cyclicity have a climatic dictator allocyclicity that is coupled with eustatic oscillations evidenced by features related to subaerial exposure ranging from microkarst to more mature karst and paleosoils exposure features are widespread at the top of the cycles even when these units are formed by only subtidal deposits suggesting eustatic control this paper presents a study of three sections of the aptian in the campania region of southern italy here a total of 250 m has been studied at a cm scale sections include serra sbregavitelli central matese mountains 160 m upper aptian lower albian monte faito sorrento peninsula 55 m upper aptian lower albian and monte tobenna picentini mountains 35 m upper aptian the latter two outcropping 100 km sse of the former the three sections have a hierarchical organization composed of elementary cycles in turn grouped in bundles and superbundles that have been related respectively to the earth s short and long orbital eccentricity oscillation while the elementary cycles mostly appear to correspond to the precession or to a combination of precession and obliquity periodicities in these successions the stratal pattern shows a dominant aggradational configuration the thickness of the cycles and their groups appears environmentally controlled the thicker cycles being those formed in more open marine settings and vice versa if analysed in terms of sequence stratigraphy we may recognize in the superbundles a transgressive and a highstand system tract that together with maximum flooding surfaces and sequence boundaries was used to develop chronostratigraphic diagrams and to identify cycle omissions at the bundle and superbundle level the number and amplitude of omissions in the successions appear proportional to the environmental conditions the more restricted the water circulation in their original depositional sites the more prone they were to cycle omissions the sections of monte tobenna and monte faito were punctuated by omissions one of them at the superbundle level while in serra sbregavitelli we recognize a smaller number of gaps not reaching the superbundle level lower frequency oscillations 800 2000 k y are also evident and suggest a long term eustatic oscillation of the same periodicity during the lower cretaceous based on the hierarchical organization of the cyclic successions analysed and taking into account the recognized omissions we have correlated the serra sbregavitelli section sss with the two distant sections of monte tobenna corresponding to the lower sss and of monte faito corresponding to the upper sss using appropriate biostratigraphic markers a correlation appears possible at the scale of bundles of cycles 100 k y and sometimes also at the elementary cycle level 50 k y

paleoclimatic analyses of middle eocene through oligocene planktic foraminiferal faunas quantitative faunal analyses and oxygen isotope ranking of individual planktic foraminiferal species from deep sea sequences of three oceans are used to make paleoceanographic and paleoclimatic inferences species grouped into surface intermediate and deep water categories based on 18o values provide evidence of major changes in water mass stratification and individual species abundances indicate low frequency cool warm oscillations these data suggest that relatively stable climatic phases with minor cool warm oscillations of 0 5 m y frequency are separated by rapid cooling events during middle eocene to early oligocene time five major climatic phases are evident in the water mass stratification between middle eocene through oligocene time phase changes occur at p14 p15 p15 p16 p20 p21 and p21 p22 zone boundaries and are marked by major faunal turnovers rapid cooling in the isotope record hiatuses and changes in the eustatic sea level a general cooling trend between middle eocene to early late oligocene is indicated by the successive replacement of warm middle eocene surface water species by cooler late eocene intermediate water species and still cooler oligocene intermediate and deep water species increased water mass stratification in the latest eocene p17 indicated by the coexistence of surface intermediate and deep dwelling species groups suggest that increased thermal gradients developed between the equator and poles nearly coincident with the development of the psychrosphere this pattern may be related to significant ice accumulation between late eocene and early late oligocene time