tidal dissipation in the early eocene and implications for ocean mixing 1 the tidally driven vertical diffusivity in the abyssal ocean during the early eocene 55 ma is investigated using an established tidal model a weak tide is predicted in the eocene ocean except in the pacific consequently the integrated global tidal dissipation rate is a mere 1 44tw of which 40 dissipate in the pacific however due to a stronger abyssal vertical stratification the predicted eocene vertical diffusivities are consistently larger than at present the results support the hypothesis that altered tidal dissipation may play a role in explaining the maintenance of past climate regimes especially the anomalously warm temperatures in the southwest pacific in the eocene and the low dissipation rates may be important for lunar evolution history

breaking the glass ceiling for high resolution nd isotope records in early cenozoic paleoceanography abstract we report an optimized method for extracting neodymium nd from fossil fish teeth with a single stage column 125 l stem volume ln resin eichrom industries darien illinois for isotopic analysis by multi collector inductively coupled mass spectrometry mc icmps three reference materials basalt bcr 2 bhvo 2 phosphate fossil bone composite and splits of fossil fish teeth samples previously processed with existing two stage column methods were processed using the single stage column method 143 nd 144 nd values of reference materials agree within error with published values and the values for fish teeth correspond with sample splits processed with two stage columns precision to 0 23 e nd was achieved for 30 ng nd samples of reference materials and nd isotope measurements of fossil fish tooth sample replicates as small as 7 ng nd were reproducible within long term instrumental uncertainty we demonstrate the utility of the new method with the first high resolution nd isotope record spanning the 40 0 ma middle eocene climatic optimum which shows an excursion of 0 65 e nd during the peak warming at the study site ocean drilling program leg 119 site 738 30 kyr sample spacing from 40 3 to 39 6 ma ln resin is already used in standard methods for separating nd and nd isotopes are routinely measured by mc icpms with high efficiency inlet systems our innovation is a single small volume ln resin column for nd separation the streamlined approach results in a 10 increase in sample throughput

integrated hyperspectral remote sensing geochemical and isotopic studies for understanding hydrocarbon induced rock alterations abstract the main objective of this work was to determine if there are characteristic mineral assemblages and chemical changes in areas affected by hydrocarbon microseepages for this purpose remote sensing was utilized for mapping surficial rock alterations and geochemical tools were used to understand the alteration processes the key area chosen for this type of work were altered and unaltered wingate sandstone outcrops in lisbon valley utah the spectral angle mapper method was applied on hymap hyperspectral data to classify the extent of altered and unaltered outcrops as well as to map the changes in mineral content within the outcrops the spectral feature fitting method was used to identify lithological changes in the area reflectance spectroscopy thin section studies major minor and trace element analyses and stable carbon and oxygen studies on both bleached altered and unbleached unaltered samples were successfully used to delineate areas of similar rock composition and relate changes due to hydrocarbons leaking from underlying petroleum reservoirs unbleached wingate sandstone samples had higher hematite and feldspar content than bleached wingate samples which were characterized by larger amounts of clay calcite and pyrite some bleached samples also had higher concentrations of elements u mo characteristic of hydrocarbon related reducing environments and were depleted in 13c when compared to the unbleached samples based on these results the following model of chemical reactions is suggested for diagnostic changes within wingate sandstone hydrocarbon induced reducing environment caused the transformation of sulfate ion obtained from groundwater or from oxidation of h2s to sulfide ion resulting in the reduction of hematite to pyrite the released hydrogen ion from this reaction reacted with available feldspars in the rock leading to precipitation of kaolinite these conditions favor the reaction between bicarbonate ion and ca2 ions that can be obtained from the groundwater leading to precipitation of calcite in pore spaces left open after the reduction and removal of hematite

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

metalliferous sediments and the scavenging residence time of nd near hydrothermal vents the isotopic composition of nd is uniform in metalliferous sediments formed at distances varying from 1000 km to within 10 km of the east pacific rise epr palaeoridge these data indicate that hydrothermal vent fluids despite having concentrations more than 500 times greater have no effect on the nd isotopic composition of seawater this implicates efficient scavenging of hydrothermal nd by particulates resulting in extremely short residence times 1 year close to the hydrothermal vents therefore nd isotopic studies of ancient seawater precipitates particularly metalliferous sediments cannot be used to delimit the magnitude of past hydrothermal circulation without independent constraints on local scavenging rates or residence times relative to those of modern oceans

paleogene deepwater mass composition of the tropical pacific and implications for thermohaline circulation in a greenhouse world 1 the pacific ocean likely exerted the greatest marine influence on climate during the greenhouse interval of the paleogene the first step toward assessing the role of pacific deepwater circulation in global heat transport is a comprehensive reconstruction of deepwater mass composition and circulation patterns we present new deepwater mass nd isotope data from odp leg 199 sites 1215 1217 1219 and 1221 to augment the existing coverage provided by ferromanganese crust and fossil fish debris data the new data corroborate the notion that the pacific ocean operated in a bimodal pattern with deepwater sources in both the southern ocean and north pacific for much of the early to middle paleogene in addition the data indicate that there was little to no influence of atlantic waters on the deepwater composition of the tropical pacific the available deepwater nd isotope data provide refined constraints on the geographic and depth range of influence of both a southern ocean and north pacific deepwater mass from 65 to 45 ma the deep tropical pacific was the mixing location of deep waters sourced from the southern ocean and the north pacific the southern ocean deepwater mass extended from 1800 m to abyssal depths until 53 6 ma it circulated northward in the western pacific at least as far as the paleolocation of fe mn crust cld01 5 n paleolatitude and in the eastern portion of the pacific as far as site 1215 10 n paleolatitude a north pacific deepwater mass extended from at least 2400 m to 2900 m water depth from 65 to 54 ma south to shatsky rise paleolatitude 10 15 n and possibly as far as site 1215 700 km to the south of shatsky rise sites 1209 and 1211

association between magnetic susceptibilities and hydrocarbon deposits in the barinas apure basin venezuela we have measured the magnetic susceptibility of 5425 drill cuttings coming from 20 oil wells distributed in eight fields of the petroliferous barinas apure basin barinas venezuela seeking evidence of magnetic anomalies associated with the presence of hydrocarbon deposits the rock samples are located between the near earth s surface and the basement s top approximately 4000 m in the magnetic susceptibility profiles we observed high magnetic susceptibilities at the top of the sedimentary units corresponding to reservoir and source rocks of oil producing wells whereas in the case of nonproducing wells we observed low magnetic susceptibilities a basic statistical analysis of the magnetic susceptibility measurements shows a significant difference between the mean values across producing and nonproducing wells at the correspondent oilrelated formations with a ratio of 4 1 of producing to nonproducing wells in the producing wells we have found a relation between the magnitudes of the magnetic susceptibility and the age of the formation the larger the magnetic susceptibility the younger the geological stratum the age and depth of the formations where the cuts were obtained exclude the presence of cultural human origin contamination of the samples suggesting the evidence of authigenic origin of the magnetic minerals due to the reductive effect of hydrocarbons in rocks

hydraulic fracture diagnostics from krauklis wave resonance and tube wave reflections abstractfluid filled fractures support guided waves known as krauklis waves the resonance of krauklis waves within fractures occurs at specific frequencies these frequencies and the associated attenuation of the resonant modes can be used to constrain the fracture geometry we use numerical simulations of wave propagation along fluid filled fractures to quantify fracture resonance the simulations involve solution of an approximation to the compressible navier stokes equation for the viscous fluid in the fracture coupled to the elastic wave equation in the surrounding solid variable fracture aperture narrow viscous boundary layers near the fracture walls and additional attenuation from seismic radiation are accounted for in the simulations we then determine how tube waves within a wellbore can be used to excite krauklis waves within fractures that are hydraulically connected to the wellbore the simulations provide the frequency dependent hydraulic impedance of the fracture which can then be used

role of fluid mixing and fault related sulfide in the origin of the ray point uranium district south texas the lamprecht and felder deposits are two of many roll type uranium deposits hosted by the miocene oakville sandstone in the ray point south texas uranium district the deposits in this district are aligned parallel to or are intersected by the oakville fault which suggests control by the faults on their origin and or preservation the lamprecht and felder deposits show fundamentally similar patterns of geochemical zonation and of distribution of authigenic iron disulfide fes sub 2 minerals distribution of u mo and se are typical of roll type deposits that result from invasion of geochemically reduced rock by oxygenated uranium bearing solutions sulfur content of these deposits is high as much as 9 with almost all sulfur occurring as fes sub 2 minerals organic carbon is virtually absent four distinct stages of fes sub 2 mineral formation are recognized 1 a generation of isotopically light delta sup 34 s 0 o and 4 a yet later generation of marcasite with isotopically light sulfur close to the values of stages 1 and 2 the alteredmore tongue in these deposits is anomalous in that it contains fes sub 2 minerals in contrast to other texas and wyoming roll type deposits which typically have an oxidized ferric iron bearing altered tongue the dominant fes sub 2 mineral in the altered tongue is isotopically heavy pyrite stage 3 with subordinate amounts of late marcasite stage 4 less

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

effects of in situ permeability on the propagation of stoneley tube waves in a borehole we investigated the theoretical relationship between propagation characteristics of stoneley tube waves in a borehole and in situ permeability by using a modified formulation of a borehole model with a formation that behaves as a biot porous medium we found that stoneley wave attenuation and phase velocity dispersion increased with increasing permeability and porosity and decreased with increasing frequency in rocks with low to medium permeabilities less than 100 md variations in formation velocity and attentuation were major contributors to variations in stoneley wave properties at normal logging frequencies however in high permeability rocks greater than 100 md coupling between the borehole and pore fluids associated with in situ permeability was more important than lithological changes in controlling stoneley wave properties pore fluid viscosity had an effect on stoneley wave propagation equal but opposite to permeability and hence must he taken into account we compared our theoretical

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

the isotopic composition of neodymium in the north pacific abstract we have determined the isotopic composition of neodymium in two water column profiles in the western north pacific and in bottom waters from three other locations in the north pacific the vertical profiles reveal that the water column is stratified with respect to isotopic composition mid depths associated with pacific deep water are uniform having nd 0 3 shallow waters are variable but deep waters are less radiogenic having md 0 4 4 to 5 in the western basin the more negative bottom waters in the western north pacific provide evidence for the advective transport of rare earth elements from antarctic sources to this region bottom waters in the eastern north pacific are more radiogenic nd 0 3 3 to 3 8 indicating very little transport of ree from antarctic sources to this basin overall the isotopic composition of nd in pacific bottom waters appears to be conservative when compared to the silica distribution in spite of evidence for nd removal the findings are generally compatible with other parameters such as temperature salinity and nutrient distributions the presence of nd isotopic signatures associated with antarctic sources in these waters provides evidence for a small component of rare earth elements of north atlantic origin in the bottom waters of the north pacific this is the first tracer evidence to corroborate the suggestion of reid and lynn 1971 that some of the temperature and salinity properties of the deep waters of the north pacific originated in the norwegian and greenland seas

effects of the oligocene climatic events on the foraminiferal record from fuente caldera section spain western tethys abstract an expanded succession of upper priabonian upper eocene to chattian upper oligocene hemipelagic marls interbedded with turbiditic sandstone layers is present in the spanish fuente caldera section subbetic zone western tethys we analyzed foraminifera from this section quantitatively with emphasis on biostratigraphy and paleoecology benthic foraminifera indicate an upper to possibly upper middle bathyal depth of deposition for most of the studied section with paleobathymetric analysis made difficult because of the common presence of shallow water taxa some reworked by turbidites and others epiphytic taxa which may have been transported by turbidites or by floating plant material we identified three major biotic and paleoenvironmental events 1 the major planktonic foraminiferal turnover across the eocene oligocene boundary which includes several first and last occurrences as well as a decrease in the percentage of surface water dwellers possibly linked to global cooling 2 a dramatic sea level drop indicated by the presence of a 37 m thick sequence of calcarenites lower half of planktonic foraminiferal zone o2 31 5 ma with abundant trace fossils and allochthonous foraminifera this sea level fall which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin apparently post dated the major glacial expansion on the antarctic continent oi1 33 7 ma and predated the later major expansion oi2 through oi2b 27 30 5 ma thus may have been tectonically controlled 3 a warming event starting in the chattian lowermost part of zone o6 27 1 ma which could be correlated to the globally recognised late oligocene warming event but apparently started somewhat earlier 27 1 ma as compared to 26 5 ma

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

characterization and imaging of a hydrothermally active near vertical fault zone in crystalline rocks based on hydrophone vsp data abstract a shallow hydrothermally active fault zone embedded in fractured crystalline rocks of the central swiss alps has been drilled and geophysically explored in view of its potential analogies to planned petrothermal reservoirs in the alpine foreland vertical seismic profiling vsp experiments have been performed using a 24 channel borehole hydrophone array with a sensor spacing of 1 m in order to image the fault core and to detect hydraulically open fractures the dense sensor spacing allows for an accurate sampling of the wavefields this in turn enables their separation through standard seismic processing methodologies thus allowing for the generation of seismic body wave vsp profiles and a tube wave corridor stack which maps brittle deformation in the surrounding rock mass multiple offset hydrophone vsp data were acquired with a crooked line survey geometry and processed with 3d methods hereby a laterally changing velocity cube representative of the vertical structural variations associated with the fault zone is generated and utilized for kirchhoff pre stack depth migration psdm imaging the resulting seismic image delineates various vertical structures notably the target fault zone the interpretation of the vsp data is complemented by and corroborated through a suite of geophysical borehole logs which characterize the fine scale petrophysical variations in response to brittle deformation in the fault core and the surrounding damage zones this study exemplifies typical targets of hardrock seismic exploration where the structures are frequently near vertical discontinuous and where acoustic impedance contrasts are commonly associated with deformation as such it illustrates the benefits of using borehole seismic methods in such environments and the use of borehole hydrophone arrays for targeting fractures and shear zones

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

isotopic composition of neodymium in waters from the drake passage the isotopic composition of neodymium has been determined in seawaters from the drake passage the antarctic circumpolar current which controls interocean mixing flows through this passage the parameter e nd 0 which is a function of the ratio of neodymium 143 to neodymium 144 is found to be uniform with depth at two stations with a value which is intermediate between the values for the atlantic and the pacific and indicates that the antarctic circumpolar current consists of about 70 percent atlantic water cold bottom water from a site in the south central pacific has the neodymium isotopic signature of the waters in the drake passage by using a box model to describe the exchange of water between the southern ocean and the ocean basins to the north together with the isotopic results an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the pacific and the southern ocean concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth these results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo oceanographic studies

observed relation of soil magnetic susceptibility and soil gas hydrocarbon analyses to subsurface hydrocarbon accumulations magnetic susceptibility ms studies on soils over 19 oil and gas fields showed anomalously large amounts of diagenetic magnetic minerals in shallow depth samples in about 89 of the cases tested soil ms anomalies were compared with soil gas hydrocarbon ghc anomalies over 12 oil and gas fields including several stratigraphic traps and one gas storage reservoir samples were collected along the same profiles six examples are presented with detailed data listings our goal is to test the utility of soil magnetic susceptibility and soil gas hydrocarbons as petroleum prospecting methods we emphasize statistical evaluation of anomalies and their empirical correlation with producing areas and leads identified by other geochemical geological or geophysical data for direct comparison of anomaly strengths data are expressed statistically in terms of the appropriate background mean and standard deviation soil ms and soil ghc data complement each other providing better guidance to productive areas than either data set alone when used in an integrated exploration program their combined positive evidence of hydrocarbon presence under prospects could result in fewer dry holes than when drilling with structural information only

squirt flow influence on sonic log parameters s u m m a r y most sedimentary rocks contain movable fluid in the pores hydrodynamic effects due to waveinduced oscillatory fluid flow can lead to significant changes of velocities and attenuations of elastic waves in these rocks in this paper we consider the influence of a squirt flow local flow between the pores of different compressibility on the sonic log response the calculations are performed using a unified model describing the joint influence of squirt flow and biot s global flow the results show that the influence of the squirt flow increases with increase of a signal frequency this influence is relatively small in the case of the stoneley wave but it is significant in the case of p and s waves

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

late paleocene middle eocene benthic foraminifera on a pacific seamount allison guyot odp site 865 greenhouse climate and superimposed hyperthermal events we investigated the response of late paleocene middle eocene 60 37 5 ma benthic foraminiferal assemblages to long term climate change and hyperthermal events including the paleocene eocene thermal maximum petm at ocean drilling program odp site 865 on allison guyot a seamount in the mid pacific mountains seamounts are isolated deep sea environments where enhanced current systems interrupt bentho pelagic coupling and fossil assemblages from such settings have been little evaluated assemblages at site 865 are diverse and dominated by cylindrical calcareous taxa with complex apertures an extinct group which probably lived infaunally dominance of an infaunal morphogroup is unexpected in a highly oligotrophic setting but these forms may have been shallow infaunal suspension feeders which were ecologically successful on the current swept seamount the magnitude of the petm extinction at site 865 was similar to other sites globally but lower diversity postextinction faunas at this location were affected by ocean acidification as well as changes in current regime which might have led to increased nutrient supply through trophic focusing a minor hyperthermal saw less severe effects of changes in current regime with no evidence for carbonate dissolution although the relative abundance of infaunal benthic foraminifera has been used as a proxy for surface productivity through bentho pelagic coupling we argue that this proxy can be used only in the absence of changes in carbonate saturation and current driven biophysical linking

nd isotopic structure of the pacific ocean 70 30 ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world the oceanic meridional overturning circulation moc is a crucial component of the climate system impacting heat and nutrient transport and global carbon cycling past greenhouse climate intervals present a paradox because their weak equator to pole temperature gradients imply a weaker moc yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients to investigate the mode of moc that operated during the early cenozoic we compare new nd isotope data with nd tracer enabled numerical ocean circulation and coupled climate model simulations assimilation of new nd isotope data from south pacific deep sea drilling project and ocean drilling program sites 323 463 596 865 and 869 with previously published data confirm the hypothesized moc characterized by vigorous sinking in the south and north pacific 70 to 30 ma compilation of all pacific nd isotope data indicates vigorous distinct and separate overturning circulations in each basin until 40 ma simulations consistently reproduce south pacific and north pacific deep convection over a broad range of conditions but cases using strong deep ocean vertical mixing produced the best data model match strong mixing potentially resulting from enhanced abyssal tidal dissipation greater interaction of wind driven internal wave activity with submarine plateaus or higher than modern values of the geothermal heat flux enable models to achieve enhanced moc circulation rates with resulting nd isotope distributions consistent with the proxy data the consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

a dynamic model for fluid flow in open borehole fractures the attenuation of stoneley waves by an open borehole fracture is closely related to fluid flow in the fracture we consider the dynamic response of a viscous fluid in a borehole fracture to the oscillating pressure excitation of stoneley waves at the fracture opening a dynamic model has been developed to describe the fluid motion in the fracture this model relates both viscous shear effects at the fracture surface and the acoustic wave propagation in the fracture fluid the dynamic conductivity is derived to characterize the fluid conduction through the fracture this model is applied to study stoneley wave attenuation across a horizontal and along a vertical borehole fracture in the horizontal fracture case the theory is found to agree with laboratory fracture modeling data after minimizing scattering effects due to the fracture in the vertical fracture case where the scattering effects are minimal the theory is in excellent agreement with the laboratory data

propagation of tube waves generated by an external source in layered permeable rocks summary tube wave characteristics generated in a fluid filled borehole may be used to determine enclosing media parameters and in particular to localize petroliferous strata if any and estimate their permeabilities as a rule tube waves are generated by an external seismic source of explosive type located some distance away from a borehole embedded in a layered medium the modelling of tube wave excitation and propagation is a complicated problem whose solution is necessary for solving the inverse problem in the present study an efficient numerical algorithm is presented to compute the tube waves propagation caused by external explosive perturbations in a fluid filled borehole located in a layered enclosing medium fluid flow between the borehole interior and the enclosing saturated porous rocks can easily be taken into account within the framework of the algorithm the solution is obtained by sommerfeldintegral representation of external field potentials on the borehole axis and subsequent analytical integration of the external field along the borehole intervals of homogeneity the resultant tridiagonal amplitude matrix is solved numerically the method was tested in detail numerical results for simple medium configurations surrounding a fluid filled borehole have been obtained the modelling of tube waves caused by the incident p reflected pp ps and the rayleigh wave in a fluid filled borehole of finite length located in an elastic half space adequately describes the main features of tube wave propagation tube wave modelling that includes the presence of a layer with hydraulic conductivity shows a high efficiency of tube wave generation at the layer boundaries and significant amplitude attenuation inside it it follows from the results of testing that the algorithm developed can be used for adequate modelling of vsp data

theoretical analysis of long offset time lapse frequency domain controlled source electromagnetic signals using the method of moments application to the monitoring of a land oil reservoir 1 we present a sensitivity study applied to water front monitoring of an onshore oil reservoir using a remote controlled source electromagnetic method csem with electric dipoles and a borehole to surface configuration we have developed an optimized and parallelized code based on the method of moments in order to study the influence of several static or time varying background uncertainties on the time lapse csem signal also called 4 d csem analysis of the relative and absolute variations in phase or quadrature of the time lapse signal induced by the fluid substitution process inside the reservoir has shown that the vertical electric dipole allows the shape of the water front to be monitored while remaining less sensitive compared to a horizontal electric source dipole to the total volume of substituted fluid we have examined the influence of missed anomalies 1 d 3 d with more or less conductive properties near to the ground surface or the reservoir and with or without time varying properties in most cases the 4 d signal behaves like a reliable filter canceling almost all response anomalies however it can also lead to strong local perturbations of the time lapse signal we have also shown that in the presence of steel cased boreholes at the source location or with outlying steel cased boreholes the recording of exploitable data does not present insurmountable difficulties at low frequencies 1 hz and for a dense array of surface receivers these positive results with csem monitoring suggest that minimal coarse time 3 d explorations should be used to ensure reliable interpretation of the monitored data

evolution of the sedimentary system beneath the deep pacific inflow off eastern new zealand results from ocean drilling program sites 1121 1124 show the eastern new zealand oceanic sedimentary system enzoss evolved in response to 1 the inception of the circum antarctic circulation 2 orbital and non orbital regulation of the global thermohaline flow and 3 development of the new zealand plate boundary enzoss began in the early oligocene following opening of the tasmanian gateway and inception of the ancestral antarctic circumpolar current acc and sw pacific deep western boundary current dwbc widespread erosion marked by the marshall paraconformity was followed by extensive drift formation in the late oligocene early miocene alternating nannofossil chalk and nannofossil rich mud deposited in response to 41 kyr orbital regulation of the abyssal circulation with the mudstones representing times of increased inflow of corrosive southern source waters drift deposition at the deepest sites was interrupted by bouts of erosion coincident with mi1 5 isotopic events signifying expansions of the east antarctic ice sheet and enhanced bottom water formation by late miocene times the basic enzoss was established south of bounty trough the energetic acc instigated an erosional low depositional regime to the north where the dwbc prevailed orbitally regulated drift deposition continued increased convergence at the new zealand plate boundary enhanced the terrigenous supply but little of this sediment reached the deep enzoss as the three main sediment conduits solander bounty and hikurangi channels had not fully developed the plio pleistocene heralded a change from a carbonate to terrigenous dominant supply caused by interception of the dwbc by the three channels 1 6 ma for bounty and hikurangi time of solander interception unknown the solander and bounty fans and hikurangi fan drift systems formed and drifts downstream of those systems received terrigenous detritus supply increased with accelerating uplift along the plate boundary but delivery to the dwbc was regulated by eustatic fluctuations of sea level times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased bounty solander or reduced hikurangi in highstands in glacial times sediment was entrained by a dwbc invigorated by an increased input of antarctic bottom water the acc also accelerated under strengthened glacial winds thus glacials were times of optimum sediment supply to enzoss depocentres where depositional rates were 2 3 times more than interglacial rates

post eocene intensification of deep water circulation in the central south pacific micropalaeontological clues from dredged sites along the eastern manihiki plateau margin reconstruction of early cenozoic deep water circulation is one of the keys to modelling earth s greenhouse to icehouse surface evolution but it has long been hampered by the paucity of information from the central south pacific to help overcome this knowledge gap we present new micropalaeontological data from dredged carbonates r v sonne expedition so193 at several eastern volcanic salients of the manihiki plateau interestingly despite appreciable longitudinal separations among the dredged sites ages indicated by the foraminiferal assemblages are consistently around the middle eocene including mixed turonian late cretaceous eocene at a single site suggesting widespread post eocene cessation of the pelagic sedimentation by integrating with independent seismic and chronostratigraphic data deep sea drilling project leg 33 for large scale erosion of top eocene oligocene sedimentary units on the eastern manihiki plateau our results can be viewed as novel physical evidence for the intensification of central south pacific deep water circulation since the eocene oligocene climatic transition

extinction dissolution and possible ocean acidification prior to the cretaceous paleogene k pg boundary in the tropical pacific abstract biotic perturbations and changes in ocean circulation during the maastrichtian stage of the latest cretaceous raise questions about whether the biosphere was preconditioned for the end cretaceous mass extinction of calcareous plankton a brief acme of inoceramid clams at 71 ma on shatsky rise in the tropical north pacific was followed by their extinction during the mid maastrichtian event at 70 1 ma associated with an abrupt warming of deep waters this was later followed by an interval of intense dissolution beginning 67 8 ma at odp site 1209 2387 m the late maastrichtian dissolution interval was initially gradual and is characterized by a low planktic benthic p b ratio highly fragmented planktic foraminifera mostly an absence of larger taxa low abundances of smaller taxa extremely low planktic foraminiferal numbers and low planktic foraminiferal and nannofossil species richness a partial recovery in carbonate preservation and calcareous plankton simple diversity began 250 kyr prior to the k pg boundary associated with the incursion of a younger more enriched 13c deep water mass although total abundances of planktic foraminifera in the sediment remained a tiny fraction of their earlier maastrichtian values a second brief dissolution event occurred 200 kyr before the boundary evidenced by renewed increase in planktic fragmentation but without a decrease in p b ratio our data show that changing deep water masses coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the first 1 6 myr dissolution interval while deccan traps volcanism may have caused surface ocean acidification 200 kyr prior to the k pg mass extinction event

investigation of permeable fracture zones by tube wave analysis summary in vertical seismic profiling tube waves are generally classified as noise they have however useful applications tube waves can be generated by compressional waves at fluid filled cracks crossing the wall of the borehole in this case the permeability of the fracture zone can be estimated from the amplitude ratio of the incident p wave and the generated tube wave in the present study an improved model for tube wave amplitude interpretation is presented while former models assumed isolated cracks now the consideration of fracture zones of a certain porosity permeability and width is allowed master curves are used to check the sensitivity of the amplitude ratio of tube and p waves with respect to the formal parameters of computation it is shown moreover that mainly those parts of a fracture contribute to the tube wave generation which are within a radius of about 1 m of the borehole the problem of localization and characterization of fracture zones by tube waves was investigated with several complementary field experiments in shallow boreholes in crystalline rocks as vertical seismic profiling vsp with three component borehole geophones and hydrophones televiewer measurements well tests and temperature measurements it turned out that fracture zones were met at all depths where tube waves were generated however not all of them were found to be hydraulically activated during well tests and temperature measurements this means that fractures detected by tube wave vsp are not necessarily of hydrological importance transmissivity values based on tube wave analysis are therefore an upper limit for the well under consideration on the other hand the transmissivity values derived from the well tests agreed quite well with those of the tube wave analysis if only the open fracture zones were considered a fact which seems to confirm our theoretical model

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

the vibroseis system a high frequency tool exploration methods are extended to their limits as we continue the search for energy resources successful application of high frequency seismic method requires evaluating each element in the seismic acquisition system and ensuring that each part of the system contributes to the success of the method this extends from seismic signal generation through data processing where good equipment performance and correct parameter selections are required the vibroseis system depends upon the ability of vibrators to generate synchronous repeatable sweeps over the frequency range of interest to support our high frequency seismic efforts conoco inc has developed and built a new high frequency vibrator this paper includes some of the consideration used in building the vibrator along with typical baseplate responses showing excellent drive levels to the design goal of 200 hz with an excellent source available correct application is essential to assure retention of high frequency data recording offsets ar

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

the geochemistry of rare earth elements in the amazon river estuary abstract the estuarine geochemistry of rare earth elements rees was studied using samples collected in the amazon river estuary from the amasseds amazon shelf sediment study cruise of august 1989 extensive removal of dissolved 0 22 m filtered trivalent rees from river water occurs in the low 0 6 salinity region removal by the salt induced coagulation of river colloids leads to fractionation among the ree iii series the order of removal is light rees middle rees heavy rees there also is the enhanced removal of ce relative to trivalent la and nd in the low salinity 0 6 zone and in the zone of high biological activity this is the first field observation of strong ce removal associated with coagulation of river colloids and biological productivity the argument is made that the decrease in the ce anomaly across a biological front is caused by biologically mediated oxidation of ce iii to ce iv coagulation of river colloids and biologically mediated oxidation of ce iii lead to fractionation of ree iii and redox modification of ce these processes result in the ree composition becoming fractionated relative to the amazon river water and crust and more evolved toward the ree composition of the oceans this study implies that reactions in estuaries play significant yet poorly understood roles in controlling the ree composition and ce anomaly of the oceans

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

useful characteristics of shallow and deep marine csem responses inferred from 3d finite difference modeling hydrocarbon reservoirs can be mapped if sufficient resistivity contrastsexistbetweenthemandtheirconfininglayers butpractical problems remain in target discrimination in deep and shallowwaters especiallyinthepresenceofheterogeneousoverburden wehavedevelopedanefficient3dstaggered gridfinite difference controlled source electromagnetic csem modeling code that enables study of the physics underlying some practical problems we undertook a comparative analysis of reservoir detection in 2000 m and 300 m deep waters using the simulated electric and magnetic field responses of a simple 3d reservoir we examined the effect of two types of near surface heterogeneitymimickingdisconnectedgascloudsand orpatchygeochemicalalterationhalosonthe3dreservoirresponse wefoundthat small scale shallowheterogeneitiescausedistortionsthatarealmost independent of the source frequency these persist at all source receiver offsets in the electric amplitude response in deep and shallow waters and phase response in shallow water they decrease in magnitude with increasing offset in deepwater phase response large scale near surface heterogeneities distort the horizontal electric field response more significantly than the small scale ones but the near surface response gets smaller in amplitude as the offset increases the distortions in shallow water are much smaller in magnitude than those for the deepwater case so that the reservoir signatures still are visible on the responseprofiles thismightbeconsideredasapositivefeaturefor shallow water inline electric field exploration the magnetic field responses for the orthogonal direction provide diagnostic target signatures that are similar to the inline electric field responsesindeepwaterbutthataredifferentinshallowwater the magnetic responses are affected by the airwave in a different manner from the electric field suggesting that combined 3d electric and magnetic field analysis might be vital for handling theairwaveproblem

cased borehole effects on downhole seismic measurements both approximate and exact formulations for the interaction of an incident elastic wave with a cased borehole are presented in the approximate method simple and explicit formulae are derived for the pressure in fluid at low frequencies in the exact method elastic potentials in each annulus are presented as a superposition of fundamental solutions to the helmholtz equations continuity of displacements and stresses across layer boundaries are used to determine unknown coefficients a global matrix algorithm is employed to compute simultaneously these coefficients in individual layers calculations show that in cased boreholes the borehole effects on downhole seismic measurements are more significant than in open boreholes a strong resonance occurs in the fluid for sv wave incidence from a soft formation this resonance is prominent even at very high frequencies because the tube wave velocity is raised well above the formation shear velocity by the steel pipe at a particular angle of incidence of a plane p wave the pressure in the fluid is near zero at low frequencies the cased borehole screening phenomenon for hard formations and frequencies above 1 khz the cased borehole influence on a downhole geophone measurement is significant especially at grazing incidence for soft formations both the pressuremore in the fluid and the solid displacement on the borehole wall show strong dependence on frequency and angle of incidence even at low frequencies less

late early oligocene deep sea benthic foraminifera and their faunal response to paleoceanographic changes in the eastern equatorial pacific abstract we documented new data on the late early oligocene benthic foraminifera and sediment geochemistry in the eastern equatorial pacific ocean eep from integrated ocean drilling program exp 320 site u1334 paleo water depth 3650 to 3850 m with some published data on those from ocean drilling program leg 199 sites 1218 3850 to 4000 m and 1219 4270 to 4370 m in order to understand the response of abyssal benthic foraminifera to paleoceanographic conditions during the interval 32 28 ma the relative abundances of nuttallides umbonifer were distinctly different between sites 1218 and 1219 during 31 0 to 29 9 ma although other major taxa e g globocassidulina subglobosa cibicidoides spp and oridorsalis umbonatus showed no marked changes the characteristics e g shannon wiener h of the benthic foraminiferal fauna are affected by the abundance of a few dominant species rather than by the change in the number of species in the eep based on multi dimensional scaling mds two mds axes were recognized mds axis 1 characteristic taxa n umbonifer and cibicidoides sp a and mds axis 2 characteristic taxa g subglobosa and bolivina huneri the tendency of both mds axes 1 and 2 showed a distinct depth gradient among the three sites after 28 6 ma whereas the tendency was different from 31 0 to 28 6 ma especially at site 1218 increased abundance of n umbonifer in the eep after 29 ma was similar to that in the atlantic ocean after the expanded distribution of this species to shallower depths was finished the faunal change at 28 6 ma might be related to the change of deep water circulation possibly with the influences of the southern component water scw and or northern component water in the south atlantic ocean in contrast the faunal change at 31 0 ma might be related to the formation of the scw and or meridional overturning circulation in the southern ocean in particular mds axis 1 exhibited the opposite tendency between sites 1218 and 1219 around the oi 2 event whereas the depth gradient was clearly observed among the sites around the oi 2 event the opposite tendency of mds axis 1 around the oi 2 event might be explained by the varying influences of the scw on different depths of the eep especially in terms of carbonate undersaturation the influence of the scw on benthic foraminifera in the eep was different among the depths of the three sites in the oi 2 event however the depth gradient of the scw influence was gradually intensified in the oi 2 event and the 28 6 28 0 ma interval

ocean and atmosphere feedbacks affecting amoc hysteresis in a gcm theories suggest that the atlantic meridional overturning circulation amoc can exhibit a hysteresis where for a given input of fresh water into the north atlantic there are two possible states one with a strong overturning in the north atlantic on and the other with a reverse atlantic cell off a previous study showed hysteresis of the amoc for the first time in a coupled general circulation model hawkins et al in geophys res lett doi 10 1029 2011gl047208 2011 in this study we show that the hysteresis found by hawkins et al 2011 is sensitive to the method with which the fresh water input is compensated if this compensation is applied throughout the volume of the global ocean rather than at the surface the region of hysteresis is narrower and the off states are very different when the compensation is applied at the surface a strong pacific overturning cell and a strong atlantic reverse cell develops when the compensation is applied throughout the volume there is little change in the pacific and only a weak atlantic reverse cell develops we investigate the mechanisms behind the transitions between the on and off states in the two experiments and find that the difference in hysteresis is due to the different off states we find that the development of the pacific overturning cell results in greater atmospheric moisture transport into the north atlantic and also is likely responsible for a stronger atlantic reverse cell these both act to stabilize the off state of the atlantic overturning

biogenetic control of gases in marine sediments of santa barbara basin california abstract the primary controls on the quantity of methane found in sediments are the rates of production and the rates of diffusion in santa barbara basin sediments the diffusion rate of methane is found to be very slow compared to the rate of bacterial production the production rate correlates with the amount of organic matter in the sediment thus the quantity of methane at any depth in the sediment is a function of the amount of marine organic matter initially trapped in the sediment sediment cores show the concentration of so4 decreasing from 27 6 mm at the surface to zero below 2 m the methane concentration is 3 decreases from 1 5 10 4 mmol cu cm year at the surface to less than 10 7 mmol cu cm year at 9 m the production rate of hco3 fluctuates in direct correlation with organic carbon content methane production decreases in a similar manner the dgr13c distribution of biogenic methane variesfrom 92 8 to 23 6 ppt heavy biogenic methane occurs in the upper sulfate reducing zone and may result from the preferential anaerobic oxidation of light methane by sulfate reducin bacteria the diffusive flux of methane into the sulfate reducing zone is between 8 6 10 5 mmol sq end page 919 cm year and 1 75 10 7 mmol sq cm year the diffusion coefficient in this zone is in the range of 2 8 10 7 to 4 2 10 7 sq cm sec below 4 m the diffusion coefficient was less than 5 4 10 8 sq cm sec end of article last page 920

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

benefits of the induced polarization geoelectric method to hydrocarbon exploration delineation of hydrocarbon prospective areas is an important issue in petroleum exploration the geoelectric method helps to identify attractive areas and reduces the overall drilling risk for this purpose induced polarization ip effects are mapped caused by the presence of epigenetic pyrite microcrystals in sedimentary rocks these crystals occur in a shallow halo shaped mineralogical alteration zone often overlying a deeper seated hydrocarbon accumulation local enrichment in pyrite results from reducing geochemical conditions below an impermeable layer the imperfect top seal of the accumulation permits minor amounts of hydrocarbons to escape and migrate through the overlying rocks to shallower levels during migration hydro carbons encounter an impermeable barrier forming an altera tion zone induced polarization logging and coring in wells confirm this working model geoelectric surveying visual izes anomalies in electric potential difference measured be tween receiver electrodes the differen

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

antarctic climate southern ocean circulation patterns and deep water formation during the eocene we assess early to middle eocene seawater neodymium nd isotope records from seven southern ocean deep sea drill sites to evaluate the role of southern ocean circulation in long term cenozoic climate change our study sites are strategically located on either side of the tasman gateway and are positioned at a range of shallow 500 m to intermediate deep 1000 2500 m paleowater depths unradiogenic seawater nd isotopic compositions reconstructed from fish teeth at intermediate deep indian ocean pelagic sites ocean drilling program odp sites 738 and 757 and deep sea drilling project dsdp site 264 indicate a dominant southern ocean sourced contribution to regional deep waters end t 9 3 1 5 iodp site u1356 off the coast of adelie land a locus of modern day antarctic bottom water production is identified as a site of persistent deep water formation from the early eocene to the oligocene east of the tasman gateway an additional local source of intermediate deep water formation is inferred at odp site 277 in the sw pacific ocean end t 8 7 1 5 antarctic proximal shelf sites odp site 1171 and site u1356 reveal a pronounced erosional event between 49 and 48 ma manifested by 2 end unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites this erosional event coincides with the termination of peak global warmth following the early eocene climatic optimum and is associated with documented cooling across the study region and increased export of antarctic deep waters highlighting the complexity and importance of southern ocean circulation in the greenhouse climate of the eocene

enrichment of dissolved silica in the deep equatorial pacific during the eocene oligocene silicon isotope ratios expressed as 30si in marine microfossils can provide insights into silica cycling over geologic time here we used 30si of sponge spicules and radiolarian tests from the paleogene equatorial transect ocean drilling program leg 199 spanning the eocene and oligocene 50 23 ma to reconstruct dissolved silica dsi concentrations in deep waters and to examine upper ocean 30si the 30si values range from 3 16 to 0 18 and from 0 07 to 1 42 for the sponge and radiolarian records respectively both records show a transition toward lower 30si values around 37 ma the shift in radiolarian 30si is interpreted as a consequence of changes in the 30si of source dsi to the region the decrease in sponge 30si is interpreted as a transition from low dsi concentrations to higher dsi concentrations most likely related to the shift toward a solely southern ocean source of deep water in the pacific during the paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes sponge 30si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past

remote sensing and geochemistry for detecting hydrocarbon microseepages this work tests the hypothesis that chemical and mineralogical alterations in rocks and soils are related to hydrocarbon microseepages above some of the major oil fields in this study we used hyperion hyperspectral imaging sensors to map alterations that appear to be associated with hydrocarbon microseepages in the patrick draw area of wyoming our mineralogical geochemical and carbon isotope data support the presence of hydrocarbon microseepages satellite imagery training classifications defined by areas of hydrocarbon microseepage have resulted in the successful identification of the areal extent of an anomalous area geochemical characteristics of samples that define this anomalous area were then compared to the remaining non anomalous samples using x ray diffraction xrd reflectance spectroscopy and carbon isotope techniques xrd analyses demonstrated the increased presence of feldspars in non anomalous samples compared to anomalous samples spectroscopy results demonstrated higher proportions of clays within the anomalous samples compared to non anomalous samples the 13 c values range from 2 88 to as low as 45 32 indicating hydrocarbon sources these methods may provide a foundation upon which further hydrocarbon exploration techniques can develop

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

the evolution of late cretaceous deep ocean circulation in the atlantic basins neodymium isotope evidence from south atlantic drill sites for tectonic controls 1 the south atlantic basins during the late cretaceous were characterized by overall expansion and the opening of deep water connections eventually permitting deep ocean circulation with the indian and north atlantic basins however the evolving pattern of deep ocean circulation through the late cretaceous particularly the timing of the connection between various basins is not well constrained here we present new neodymium isotope data from five sites in the south atlantic to reconstruct water mass chemistry and circulation patterns the new data combined with previously published data indicate deep water formation occurred in the high latitude south atlantic throughout the late cretaceous tectonic boundaries restricted the circulation of southern component water until the opening of the equatorial atlantic gateway and the subsidence of rio grande rise between 79 and 75 ma subsidence of these features permitted the northward flow of southern component water which then ventilated the deep north atlantic nd isotope data indicate that the south atlantic water column during the cenomanian to santonian was vertically stratified between intermediate and deep waters with increased mixing evident during the campanian and maastrichtian

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

determination of in situ attenuation from full waveform acoustic logs method for the determination of in situ p and s wave attenuation from full waveform acoustic logs are developed for p waves the peak amplitude ratios of the refracted p waves from two different receivers can be used with geometrical spreading taken into account for s waves owing to the contamination by the guided waves its attenuation cannot be determined directly instead s wave attenuation is determined from the attenuation of the guided waves using the partition coefficients normalized partial derivatives of the phase velocity with respect to the body wave velocities analytical forms of these partition coefficients are presented here along with examples for a number of different rock formations granite limestone sandstone and soft sediments the results show that in high velocity rocks the fluid attenuation controls the guided wave attenuation except near the cut off frequency of the pseudo rayleigh wave for low velocity rock formations especially in the case where the s wave velocity is lower than the fluid velocity the s wave attenuation is the main contributor to the guided wave attenuation synthetic microseisgmogram calculated with the measured body wave attenuation agrees well with the actual microseismograms

new evidence for the hawaiian hotspot plume motion since the eocene abstract a thick mound of fossiliferous sediments reflecting high biogenic productivity at the equator can be used to determine latitudinal motion of the pacific lithospheric plate plate motion estimates based on the latitudinal movement of equatorial facies are independent of paleomagnetic data and hotspot tracks and thus permit further testing of kinematic models we have determined the northward motion of the pacific plate for the last 53 myr based on the position of the paleoequator as shown by equatorial sediment facies between 26 and 69 dsdp and odp sites sample the past 53 myr in the tropical pacific based on the mapped patterns of accumulation rates in these sites we were able not only to determine the position of the paleoequator but also to estimate the equatorial great circle and hence the relative position of the spin axis since the early eocene the northward motion of the pacific plate inferred from the change in latitude of dated hawaiian chain seamounts relative to the hawaiian hotspot is consistently higher than that deduced from the analyses of equatorial sediment facies such a difference results from a latitudinal shift of the hawaiian hotspot during the last 53 myr all together our observations and recent paleomagnetic results from the detroit nintoku and koko seamounts j a tarduno r a duncan d w scholl r d cottrell b steinberger t thordarson b c kerr c r neal f a frey m torii m c carvallo the emperor seamounts southward motion of the hawaiian hotspot plume in earth s mantle science 301 2003 1064 1069 1 are consistent with a progressive southward motion of the hawaiian mantle plume since the late cretaceous our results suggest that the hawaiian hotspot moved at 32 mm yr to the se during the past 43 million years and that the pacific plate moved 12 northward since 53 ma at an average rate of 25 mm yr

biogenic and nonbiogenic ore forming processes in the south texas uranium district evidence from the panna maria deposit geochemical and petrographic studies of core samples from the panna maria uranium deposit a roll type orebody in the eocene jackson group in karnes county texas yield important information on the origin of the deposit organic carbon content averages about 0 42 weight percent in reduced rock and correlates postively with sulfur content pyrite is the dominant iron disulfide fes 2 mineral in most of the ore zone and throughout a surrounding zone of reduced barren ground and it is commonly associated with organic debris marcasite is sparse except in ore adjacent to the altered tongue in one core and locally in mineralized lignite sulfur isotopic compositions delta 34 s of fes 2 minerals range broadly from 1 to 34 per mil the lightest delta 34 s values less than 20 per mil were measured in samples from mineralized lignite and from the nose of the ore roll petrographic and geochemical characteristics of the panna maria deposit contrast greatly with those of three other south texas roll type uranium deposits the benavides felder and lamprecht deposits which are devoid of organic carbon and which contain more sulfide than does the panna maria these three deposits are characterized by abundant isotopically light ore stage marcasite and by isotopically heavy preore in the benavides or postore in the felder and lamprecht pyrite we have concluded previously that sulfide bearing fault leaked solutions from underlying hydrocarbon accumulations were important in the formation of the benavides felder and lamprecht deposits although the panna maria deposit shows an apparent alignment along a fault zone and although underlying formations in the karnes county area contain sour gas delta 34 s asymp 14 per mil and produce oil the deposit lacks characteristics indicating that its formation or preservation involved extrinsically derived reductants such as fault leaked aqueous sulfide mineralization of the panna maria rather appears to have been controlled by intrinsically derived reductants related either directly or indirectly to the presence of organic matter

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

epigenetic zoning in surface and near surface rocks resulting from seepage induced redox gradients velma oil field oklahoma abstract abstract surface and near surface permian sandstone has been drastically altered over the productive part of the structurally complex velma oil field as a consequence of petroleum microseepage buried permian sandstone along the northwest southeast trending anticline is cemented with abundant pyrite ferroan calcite and ferroan dolomite at the surface along the anticlinal crest iron disulfide is scarce isotopically anomalous carbonate cemented sandstone is overlain by sandstone that is massively impregnated by hematite cement permian sandstone is normally reddish brown throughout southern oklahoma but along the anticlinal flank it has been bleached yellow and white owing to iron loss some units contain abundant solid bitumen the mineralogy in the vertical section over the anticline follows the calculated stability relations for iron sulfide iron carbonate and iron oxide along a gradient from strongly reducing conditions at depth to oxidizing conditions at the surface reducing conditions were provided by seeping hydrocarbons from subsurface reservoirs of this multizone giant field production depths range from 120 to 2 975 m the principal evidence that these alterations are seepage induced is provided by reports of oil seeps in the early literature by zones of solid bitumen cements and by c13 pdb values for carbonate cements that range from 7 8 to 36 7 ppt

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

stoneley wave generation by an incident p wave propagating in the surrounding formation across a horizontal fluid filled fracture abstract this study investigates the generation of the low frequency borehole stoneley wave tube wave by a plane p wave propagating through the surrounding elastic formation which is intersected by a fluid filled fracture a model is constructed taking into account the dynamic fluid coupling between the borehole interior and the fluid filled fracture of infinite extent with parallel walls the basic mechanism of such coupling is due to the contraction of the fracture walls by the incident p wave leading to seismic radiation into the fracture the dynamic fluid flux from the fracture into the borehole interior and vice versa is the source of the low frequency stoneley wave an expression for the monopole pressure source exciting the tube wave is obtained the tube wave equation in the long wave approximation is derived in the presence of a fluid filled fracture of infinite extent amplitudes and waveforms of stoneley waves are analysed in the seismic wavelength range for p wave pulses of various shapes it is shown that the amplitude and waveform of the stoneley wave depends significantly on the two dimensionless parameters of the problem 1 the ratio of the borehole radius to the dominant wavelength of the incident pulse 2 the ratio of the fracture width to the borehole radius it is found that the amplitude of the generated stoneley wave can be of the order of the p wave amplitude in the borehole fluid stoneley waveforms are found to be completely different from those of the incident pulse

iron sulfide minerals at cement oil field oklahoma implications for magnetic detection of oil fields aeromagnetic anomalies at cement oil field anadarko basin oklahoma have been attributed to authigenic magnetite the following characteristics of the magnetite however indicate that it is contamination introduced by drilling 1 occurrence as sharp angular blades and as spheres commonly with metallographic textures typical of industrial alloys and with associated steel and wustite feo 2 presence only in well cuttings and absence from core and quarry samples and 3 lack of association with detrital framework grains or with authigenic carbonate and sulfide minerals ferrimagnetic pyrrhotite occurs in well cuttings cores and quarry samples at cement and is a possible natural source of the magnetic anomalies pyrrhotite which is intergrown with more abundant fes 2 minerals formed as a result of hydrocarbon seepage pyrrhotite is confined to beds above oil and gas reservoirs these beds which lack detrital organic matter contain higher mineral sulfide and lower mineral sulfate sulfur 1 7 and 0 1 wt respectively than do correlative beds off the field 0 2 and 1 1 wt respectively in the field isotopic values of sulfide s show a systematic decrease upward through the permian section from positive values maximum 12 per mil at 610 760 m depth to negative values 1 to 11 per mil between 32 and 230 m 26 to 30 per mil at the surface geochemical results together with time temperature data derived from burial curves limit the major sources of the sulfide in the fe s minerals to two possibilities isotopically heavy sulfide was generated either inorganically at temperatures 90 c in beds beneath permian beds or by bacterial sulfate reduction at temperatures

source of anomalous magnetization in area of hydrocarbon potential petrologic evidence from jurassic preuss sandstone wyoming idaho thrust belt the jurassic preuss sandstone which crops out in the central part of the wyoming idaho thrust belt on trend with a hydrocarbon producing region to the south has been previously identified as the source of anomalous magnetization in the area elsewhere anomalous magnetization in sedimentary rocks near hydrocarbon accumulations has been attributed to hydrocarbon engendered magnetic minerals but magnetization of the preuss is controlled by detrital magnetite evidence of a detrital origin for magnetite includes 1 concentration of magnetite grains along laminations containing other heavy minerals 2 the presence of exsolved ilmenite hematite and spinel in the magnetite grains and 3 titanium contents typical of igneous derived magnetite that detrital magnetite is responsible for the anomalous magnetization in the preuss is further indicated by the systematic eastward decrease in magnetite abundance corresponding to a similar eastward decrease in magnetic susceptibility and remanent magnetization of the unit petrologic and vitrinite reflectance studies indicate a complex low temperature 150 c or 302 f diagenetic history for the preuss nevertheless preservation of detrital magnetite the presence of diagenetically early ferric oxide minerals and the absence of sulfide minerals all indicate that the preuss has not experienced sulfidic reducing conditions common in areas of hydrocarbon seepage the marine carbon isotopic composition of calcite that cements most preuss sandstones dgr13c values ranging from 2 47 to 1 48 pmil is evidence that carbonate diagenesis also was not influenced by hydrocarbons the results of this multidisciplinary study of the preuss underscore the importance of similar studies when evaluating the sources of aeromagnetic anomalies in areas of hydrocarbon potential

elastic wave propagation in a fluid filled borehole and synthetic acoustic logs the propagation and dispersion characteristics of guided waves in a fluid filled borehole are studied using dispersion curves and modeling full wave acoustic logs by synthetic microseismograms the dispersion characteristics of the pseudo rayleigh reflected and stoneley waves in a borehole with and without a tool in the center are compared effects of different tool properties are calculated the effect of a rigid tool is to make the effective borehole radius smaller as an approximation dispersion characteristics of the guided waves in a borehole with a tool can be calculated as a purely fluid filled borehole with a smaller effective radius theoretical waveforms microseismograms of elastic waves propagating in a borehole are calculated using a discrete wavenumber integration with an appropriate choice of parameters our results look similar to the acoustic waveforms recorded in a limestone and a shale formation several factors affect the shape of an acoustic log microseismogram the effective rad

coupled climate impacts of the drake passage and the panama seaway tectonically active gateways between ocean basins have modified ocean circulation over earth history today the atlantic and pacific are directly connected via the drake passage which forms a barrier to the time mean geostrophic transport between the subtropics and antarctica in contrast during the warm early cenozoic era when antarctica was ice free the drake passage was closed instead at that time the separation of north and south america provided a tropical seaway between the atlantic and pacific that remained open until the isthmus of panama formed in the relatively recent geological past ocean circulation models have previously been used to explore the individual impacts of the drake passage and the panama seaway but rarely have the two gateways been considered together and most explorations have used very simple atmospheric models here we use a coupled ocean ice atmosphere model gfdl s cm2mc to simulate the impacts of a closed drake passage both with and without a panama seaway we find that the climate response to a closed drake passage is relatively small when the panama seaway is absent similar to prior studies although the coupling to a dynamical atmosphere does increase the temperature change however with a panama seaway closing drake passage has a much larger effect due to the cessation of deep water formation in the northern hemisphere both gateways alter the transport of salt by ocean circulation with the panama seaway allowing fresh pacific water to be imported to the north atlantic and the drake passage preventing the flow of saline subtropical water to the circum antarctic a flow that is particularly strong when the panama seaway is open thus with a panama seaway and a closed drake passage the southern ocean tends to be relatively salty while the north atlantic tends to be relatively fresh such that the deep ocean is ventilated from the circum antarctic ensuing changes in the ocean heat transport drive a bi polar shift of surface ocean temperatures and the intertropical convergence zone migrates toward the warmer southern hemisphere the response of clouds to changes in surface ocean temperatures amplifies the climate response resulting in temperature changes of up to 9 c over antarctica even in the absence of land ice feedbacks these results emphasize the importance of tectonic gateways to the climate history of the cenozoic and support a role for ocean circulation changes in the glaciation of antarctica

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

evolution of the neodymium isotopic signature of neritic seawater on a northwestern pacific margin new constrains on possible end members for the composition of deep water masses in the late cretaceous ocean the neodymium nd isotope composition of fish remains has beenwidely used to track past changes in oceanic circulation although the number of published nd isotope data for the cretaceous has markedly increased in the last years no consensus has been reached on the structure of the oceanic circulation and its evolution during the late cretaceous yet this period is characterised bymajor geodynamical and climatic changes andmarked by the disappearance of global oceanic anoxic events inwhich changes in oceanic circulation modesmay have played a significant role in this study we present the first record of nd isotopic composition of fish remains from continental margin environments on the northwestern pacific margin yezo group in the hokkaid area northern japan for the late cretaceous period this record interpreted in terms of nd isotopic composition of local neritic seafloor seawater is characterised by relatively radiogenic nd isotope compositions and presents variations of several e units from the turonian to the campanian ranging from 5 5 to 0 5 e units although most values remain in the 1 to 3 range conversely the local detrital fraction remains more constant and around 4 e units on the studied interval this new set of seawater nd data contains some of the most radiogenic values for the cretaceous published yet the more radiogenic seawater nd isotope values compared to that of the sediments points to an input of radiogenic seawater in the studied area by surface currents during the late cretaceous similarly to the modern configuration these radiogenic waters could have been conveyed in the studied area by a southward current comparable to the modern oyashio current bathing the hokkaid area our data are then consistent with the presence in the northern pacific of highly radiogenic seawater and support the northern and northwestern pacific as a possible radiogenic source for the deep parts of the basin as such this work represents a first step toward a better characterisation of the various end members that could have contributed to the nd isotopic signature of the deep water masses filling the cretaceous oceans

detection of open fractures with vertical seismic profiling in vertical seismic profiling surveys tube waves are generated by compressional waves impinging on subsurface fractures or permeable zones the problem of generation of these waves by a nonnormal incident p wave for an inclined borehole intersecting a tilted parallel wall fracture is formulated theoretically the amplitude of tube waves depends on the permeability the length of the fracture and the frequency the relative effects of these parameters are studied individually the problem is also formulated for a thin oblate ellipsoidal penny shaped fracture the results for the two fracture models are compared and contrasted field data from tyngsboro massachusetts are shown for open fractures in granite from tube wave amplitudes normalized to p wave amplitudes calculated permeabilities are of the order of 100 mdarcy

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved

neogene evolution of atlantic thermohaline circulation perspective from walvis ridge southeastern atlantic ocean 1 we present new nd isotope records from walvis ridge ocean drilling program odp sites 1262 1264 southeastern atlantic spanning the past 24 ma to investigate the neogene evolution of atlantic thermohaline circulation the new data indicate that deepwater nd t values from odp site 1262 decrease from 11 0 at 10 6 ma to 12 5 by 7 3 ma this decrease parallels the nd isotope trends contained in fe mn crust records from the northwestern atlantic however the shift at odp site 1262 4755 m water depth occurred up to 6 ma earlier than the corresponding changes in crust records from the atlantic and earlier than any atlantic site shallower than 2700 m paleowater depth recent interpretations of the rapid decrease in fe mn crust nd nd t ssvalues invoke changes in weathering inputs to the labrador sea region rather than a fundamental change in deepwater convection in the labrador sea however the new evidence for significant depth stratification of the nd isotope signal in the southeastern atlantic between 10 6 and 7 3 ma suggests that the onset of deepwater convection in the labrador sea may have played a role in the deepwater decrease in nd isotopic composition climatic conditions during the middle to late miocene likely favored an increase in the importance of glacially induced mechanical weathering while at the same time promoting deep convection in the labrador sea