the rock physics and geochemistry of carbonates exposed to reactive brines when carbonate rich rocks are brought into contact with an acidic brine their mechanical and acoustic responses depend on many factors including ph porosity permeability effective stress and time these complexities hinder the understanding of processes such as hydrothermal fluid circulation seismicity and deep burial diagenesis the present study addresses how different lithofacies exposed to the same reactive brine undergo varying degrees of transformation and whether it is possible to remotely detect these phenomena in the earth results are presented from fluid injections carried out on a large and varied set of calcareous rocks under hydrostatic stress the output brine was analyzed for dissolved mineral concentrations and the rock porosity permeability axial strain ultrasonic velocity and images from electron microscopy were contrasted before and after injection microbialites were found to be the lithofacies most vulnerable to changes in their transport properties however all samples irreversibly compacted with the greatest strain in the most porous and permeable cores the most extreme structural changes discovered through imaging were the welding of microporous zones grain sliding and the fracturing of various phases observations are consistent with a chemically enhanced weakening of the rock frame that generated compliant pores the associated decrease in velocity of the dry rock can be approximated with linear relations that depend on both porosity and effective stress

understanding of elastic anisotropy of shale under triaxial loading porosity deformation approach abstracttheoretical models for the description of stress dependencies for anisotropic rocks are important for building velocity models and the interpretation of seismic data with respect to stress lithology and pore content especially important is the accurate description of the change of anisotropy due to applied anisotropic stress by means of a quantitative model to aid the interpretation the porosity deformation approach pda originally introduced as the piezosensitivity theory describes stress induced changes of elastic properties without any knowledge about the geometry and orientation of the microcracks we have developed a formulation of the theory for a transverse isotropic rock which was loaded parallel to the bedding plane and we found that it can be described theoretically as an orthorhombic rock we also found out how properties that described the velocity change due to hydrostatic loading can be used to predict elastic anisotropy under additional axial loading the number of free para

gassmann s fluid substitution and shear modulus variability in carbonates at laboratory seismic and ultrasonic frequencies carbonates have become important targets for rock property research in recent years because they represent many of themajoroilandgasreservoirsintheworld someareundergoing enhanced oil recovery most laboratory studies to understand fluid and pressure effects on reservoir rocks have been performed on sandstones but applying relations developed for sandstones to carbonates is problematic at best we measure in the laboratory nine carbonate samples from the same reservoir at seismic 3 3000 hz and ultrasonic 0 8 mhz frequencies samples are measured dry humidified and saturated with liquid butane and brine our carbonate samples showed typical changes in moduli as a function of porosity andfluid saturation however we explore the applicability of gassmann s theory on limestone and dolomite rocks in the context of shear and bulk modulus dispersion andgassmann stheoryassumptions forourcarbonatesetat high differential pressures and seismic frequencies the bulk modulus of rocks with high aspect ratio pores and dolomite mineralogy is predicted by gassmann s relation we also explore in detail some of the assumptions of gassmann s relation especiallyrock framesensitivitytofluidsaturation our carbonate samples show rock shear modulus change from dry to brine saturation conditions and we investigate several rock fluid mechanisms responsible for this change to our knowledge these are the first controlled laboratory experimentsoncarbonatesintheseismicfrequencyrange

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

late oligocene climatic changes evidence from calcareous nannofossils at kerguelen plateau site 748 southern ocean abstract palaeoecological changes in nannofossil assemblages in the southern ocean during oligocene times are examined through high resolution quantitative analyses of samples from ocean drilling program odp site 748 kerguelen plateau we quantitatively characterized the palaeoecological preference of groups of species and compared their general trends with those determined at maud rise odp sites 690 and 689 persico d villa g 2004 eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica palaeoecological and palaeoceanographic implications marine micropaleontology 52 153 179 we then attempt a correlation between the main assemblage variation and sea surface temperature sst changes in the southern ocean at this time relatively stable cool conditions are interpreted to have persisted from earliest to late oligocene times when an increase in abundance of temperate water taxa is recorded both at maud rise and kerguelen plateau before the mi 1 event this reveals a climatic event that probably involved both sites and which is comparable to that indicated by the global oxygen isotope curve miller k g wright j d fairbanks r g 1991 unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion journal of geophysical research 96 6829 6848 zachos j pagani m sloan l thomas e billups k 2001 trends rhythms and aberrations in global climate 65 ma to present science 292 686 693 in the uppermost oligocene at site 689 the temperate water taxa index temperate temperate cool 100 increases from 25 2 ma similarly at site 748 the temperate water taxa index indicates an increase in sst in the late oligocene from about 26 5 ma at the base of chron c8n 2n which is offset by about 1 m y between the two areas the reason for this time difference can probably be found in the location of site 748 with respect to site 689 and in the palaeoceanographic setting taking into account that site 748 lies north of a deep water passage that separates kerguelen plateau from antarctica and north of the present day front of the antarctic circumpolar current the presence of warm water taxa exclusively at site 748 corroborates this hypothesis

changes of shear moduli in carbonate rocks implications for gassmann applicability in laboratory experiments we measured the saturation effects on the acoustic properties in carbonates and the results question some theoretical assumptions in particular these laboratory experiments under dry and wet conditions show that shear moduli do not remain constant during saturation this change in shear modulus puts gassmann s assumption of a constant shear modulus into question and also explains why velocities predicted with the gassmann equation can be lower or higher than measured velocities

refining ancient carbon dioxide estimates significance of coccolithophore cell size for alkenone based pco2 records 1 long term alkenone based pco2 records are widely applied in paleoclimate evaluations these pco2 estimates are based on records of the carbon isotope fractionation that occurs during marine haptophyte photosynthesis p37 2 in addition to the concentration of aqueous co2 co2 aq the magnitude of p37 2 is also influenced by algal growth rates and cell geometry to date the influence of haptophyte cell geometry on the expression of ancient p37 2 values has received little attention this study evaluates changes in cell geometry of ancient alkenone producing algae at deep see drilling project site 516 in the southwest atlantic ocean by analyzing individual coccolith dimensions which are proportional to algal cell volume and surface area we show that during part of the early miocene mean cell sizes of alkenone producing algae were smaller relative to modern emiliania huxleyi cell size variations coincide with significant changes in p37 2 with a distinct 6 decrease in p37 2 at 20 3 ma associated with a 27 increase in haptophyte cell sizes these changes in cell size impact p37 2 based interpretations of growth rate variation and co2 aq estimates for this southwest atlantic site after correcting for cell geometry co2 aq estimates at site 516 are consistent with those reported from other oligotrophic sites during this time resulting in overall low atmospheric pco2 estimates 350 ppmv for the early miocene

acoustic measures of partial gas saturation in tight sandstones the acoustic properties of tight sandstones are very sensitive to partial gas water saturation measurements at 5 khz show that compressional velocity drops sharply with undersaturation extensional and shear losses at 5 khz are large in both fully and partially saturated sands the shear loss qs 1 declines linearly with increasing gas content the extensional loss qe 1 peaks at 0 80 water saturation q 1 is frequency dependent the attenuation is well explained by hydrodynamic relaxation in the grain contacts the measurements indicate velocity dispersions consistent with this mechanism ultrasonic velocities at 500 khz are roughly 10 25 higher than acoustic velocities at 5 khz the ultrasonic velocities exhibit a weak dependence on saturation frame moduli are unrelaxed at these frequencies

estimating the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks seismic methods are widely used for the geotechnical investigations in volcanic areas or for the determination of the engineering properties of pyroclastic rocks in laboratory therefore developing a relation between the wet and dry rock p wave velocities will be helpful for engineers when evaluating the formation characteristics of pyroclastic rocks to investigate the predictability of the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks p wave velocity measurements were conducted on 27 different pyroclastic rocks in addition dry rock s wave velocity measurements were conducted the test results were modeled using gassmann s and wood s theories and it was seen that estimates for saturated p wave velocity from the theories fit well measured data for samples having values of less and greater than 20 practical equations were derived for reliably estimating wet rock p wave velocity as function of dry rock p wave velocity

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

on the intermediate and deep water flows in the south atlantic ocean a multiparameter analysis is applied on zonal and meridional hydrographic sections obtained for the south atlantic ventilation experiment save to determine the spreading and mixing of water masses in the south atlantic ocean focusing our interest on the large scale flow of intermediate and deep waters the method utilizes all information from the hydrographic data set including temperature salinity dissolved oxygen and nutrient fields mixing proportions are quantified and plotted along the eight sections considered results show no evidence of a primary route of antarctic intermediate water along the western boundary of the south atlantic in the eastern basin the eastward extension of the upper north atlantic deep water nadw in the guinea basin following the cyclonic subequatorial gyre is confirmed in the angola basin a weak but thick nadw core layer is observed in conjunction with very little presence of lower circumpolar deep water lcdw high lcdw concentrations in cape basin are indicative of the communication of this basin to cold water sources in the south the method is sensitive enough to detect for instance the presence of the congo river plume in the angola basin or the influence of the weddell sea deep water in the vicinity of the romanche and chain fracture zones in the equatorial region in conjunction with the multiparameter analyses along save sections an analysis of components of the residual vector r indicates a middepth minimum in the rn p utilization ratio both a suitable explanation for the minimum and the potential consequences for the multiparameter analyses of south atlantic water mass circulation are still to be found

investigation of elastic weakening in limestone and sandstone samples from moisture adsorption summary elastic and mechanical weakening from water saturation are widely known to occur in sedimentary rocks and particularly in carbonate rocks to improve our understanding of the physics underlying this phenomenon ultrasonic f 0 5 mhz elastic properties are measured on a large suite of clean limestones and sandstones at very low saturations from relative humidity rh variations at ambient conditions measurements clearly highlight an elastic weakening i e decrease in elastic wave velocity from moisture adsorption p and s wave velocities are similarly affected by adsorption but in a different way for limestones and sandstone samples while the elastic properties of limestone samples show almost no rh dependence a large weakening is observed for samples of fontainebleau sandstone that increases with the samples porosity the main elastic weakening effect is likely to result from adsorption of fluid at grain contacts it thus affects particularly granular rocks such as sandstones while well cemented limestones are not affected the granular model from murphy et al accounting for surface energy effects proves to be appropriate applying this model it is shown that i p and s wave velocities have the same dependence on surface energy which is consistent with the measurements and ii surface energy values obtained from the ultrasonic data using this model correlate with rh and are consistent with the expected value for quartz crystals at vapour pressure yet porosity which relates to degree of cementation in the particular case of fontainebleau sandstone appears to be an additional parameter a modified model is thus derived using the cementation model from digby accounting for a bonding radius at grain contact it proves to apply well to the measured data the fundamental difference between limestones and sandstones dependence to rh appears to be related to a microstructural difference saturation variations from rh increase depend on specific surface area which is particularly low in fontainebleau sandstones and large in microporous limestones however elastic weakening from rh is more important in sandstones owing to their granular microstructure

new magnetobiostratigraphic chronology and paleoceanographic changes across the oligocene miocene boundary at dsdp site 516 rio grande rise sw atlantic new magnetobiostratigraphic data for the late oligocene through early miocene at deep sea drilling project dsdp hole 516f provide a significantly revised age model which permits reevaluation of developments that led to the mi 1 glacial event at the oligocene miocene boundary our new high resolution paleomagnetic study which is supported by quantitative calcareous nannofossil and planktonic foraminiferal analyses significantly refines previous age models for oligocene miocene sediments from dsdp hole 516f with ages that are systematically younger than those previously determined in some parts of the oligocene the discrepancy with previous studies exceeds 450 kyr based on this new age model we infer a progressive increase in sedimentation rate and paleoproductivity between circa 23 9 ma and circa 22 9 ma with the highest rate coinciding with the mi 1 glacial event at the oligocene miocene boundary this productivity increase would have resulted in higher rates of carbon burial and in turn a drawdown of atmospheric co2 immediately afterward an abrupt decrease in sedimentation rate and paleoproductivity suggests that the mi 1 deglaciation was associated with decreased carbon input into the ocean elevated sedimentation rates are also documented at 24 5 ma coincident with the oi2d glacioeustatic event the presence of volcanic material within the sediments during these glacial events is interpreted to have resulted from redeposition of sediment scoured from nearby sites on the rio grande rise due to transient variations in bottom water flow patterns

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

a potential barrier to deep antarctic circumpolar flow until the late miocene the central scotia sea located between the south american and antarctic plates is an integral part of the marine conduit that permits eastward deep water flow from the pacific ocean to the atlantic ocean the geologic history of the central scotia sea is therefore critical for a full understanding of the initiation and subsequent evolution of the complete deep antarctic circumpolar current widely believed to have been a key factor in the history of antarctic glaciation here we present new evidence on the nature and age of the central scotia sea floor multibeam surveys and the first dredged samples indicate that a now submerged remnant volcanic arc may have formed a barrier to deep eastward oceanic circulation until after the mid miocene climatic optimum inception and development of a full deep antarctic circumpolar current may therefore have been important not in the drop in global temperatures at the eocene oligocene boundary as long surmised but in the subsequent late miocene global cooling and intensification of antarctic glaciation

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

alkenone producers during late oligocene early miocene revisited this study investigates ancient alkenone producers among the late oligocene early miocene coccolithophores recorded at deep sea drilling project dsdp site 516 contrary to common assumptions reticulofenestra was not the most important alkenone producer throughout the studied time interval the comparison between coccolith species specific absolute abundances and alkenone contents in the same sedimentary samples shows that cyclicargolithus abundances explain 40 of the total variance of alkenone concentration and that the species cyclicargolithus floridanus was a major alkenone producer although other related taxa may have also contributed to the alkenone production at dsdp site 516 the distribution of the different alkenone isomers mec37 2 etc38 2 and mec38 2 remained unchanged across distinct changes in species composition suggesting similar diunsaturated alkenone compositions within the noelaerhabdaceae family during the late oligocene early miocene however the overall larger cell size of cyclicargolithus may have implications for the alkenone based reconstruction of past partial pressure of co2 our results underscore the importance of a careful evaluation of the most likely alkenone producers for periods 1 85 ma predating the first occurrence of contemporary alkenone producers i e emiliania huxleyi and gephyrocapsa oceanica

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

quantifying ultrafine pedogenic magnetic particles in chinese loess by monitoring viscous decay of superparamagnetism we propose a new approach for quantifying pedogenically produced ultrafine nanometer scale magnetic particles in chinese loess we have recorded the viscous decay t 100 s of imposed isothermal remanent magnetization irm assumed to be selectively carried by superparamagnetic particles jv application of viscosity measurements relaxometry to loess paleosol sequences from the se extremity of the chinese loess plateau reveals that jv aptly reflects contributions of viscous superparamagnetic sp particles to the total remanence carried by an assemblage of magnetic particles time decay of jv can be determined with a higher resolution than the conventionally used frequency dependent susceptibility fd for characterizing the relative abundance of sp particles the nearly logarithmic time decay of irm implies a rather broad grain size distribution of pedogenic particles in chinese loess that may range from a lower size limit of 10 nm to an upper limit of 40 nm with a prevalent grain size maximum of 21 25 nm numerical calculations of the time dependence of irm decay demonstrate that the actual contribution of fine grained pedogenic magnetite maghemite to the total remanence is at least twice as large as that estimated by both fd and our proposed jv parameter we therefore propose that determination of superparamagnetic contributions by the time dependence of irm viscosity is a useful technique for tracking pedogenic processes and hence paleoclimatic conditions of chinese loess

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

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

interrelations of the petrophysical sedimentological and microstructural properties of the oolithe blanche formation bathonian saline aquifer of the paris basin abstract the paris basin seems a suitable location for co2 capture and storage given both the amount of co2 produced and the availability of depleted fields and deep saline aquifers this study investigates the petrophysical properties in relation to the sedimentary and diagenetic environment of the oolithe blanche formation middle jurassic a deep saline aquifer considered a potential candidate for co2 storage because of the scarcity of core data in the paris basin our investigation was based on the study of field analogues in the south east part of the paris basin the oolithe blanche formation bathonian is 70 80 m thick eighteen oriented blocks were collected from three outcrops selected for the different sedimentological facies identified in the formation their petrophysical properties were measured porosity pore size distribution derived from mercury injection tests permeability and capillary imbibition parameters the sedimentary and diagenetic facies were defined by using optical microscopy coupled with image analysis on thin sections and sem the oolithe blanche formation is composed of oolitic and bioclastic limestones deposited in a shallow marine setting three main sedimentological facies were defined the oolitic shoal facies the tide dominated facies and the prograding oolitic facies they exhibit subtle variations in composition and in the distribution of carbonate textures porosity measured using the water saturation triple weight method ranges from 6 to 34 permeability values are low between 0 1 md and 9 md the data from mercury intrusion porosimetry show that the distribution of the pore throat diameter is either unimodal microporosity only or bimodal macro and microporosity microporosity is intraparticle intraooid and macroporosity is interparticle and is related to dolo dedolomitization variations of petrophysical parameters can be explained by the microstructure now these latter results calibrated by studying field analogues must be extended to borehole data and core data to optimize our knowledge of the deep saline aquifer of the oolithe blanche formation without such investigations it will be impossible to estimate the suitability of this deep saline aquifer for co2 storage

laboratory measurements of porosity permeability resistivity and velocity on fontainebleau sandstones the relations among the resistivity elastic wave velocity porosity and permeability in fontainebleau sandstone samples from the ile de france region around paris france were experimentally revisited these samples followed a permeability porosity relation given by kozeny carman s equation for the resistivity measurements the samples were partially saturated with brine archie s equation was used to estimate resistivity at 100 water saturation assuming a saturation exponent n 2 using self consistent sc approximations modeling with grain aspect ratio 1 and pore aspect ratio between 0 02 and 0 10 the experimental data fall into this theoretical range the sc curve with the pore aspect ratio 0 05 appears to be close to the values measured in the entire porosity range the elastic wave velocity was measured on these dry samples for confining pressure between 0 and 40 mpa aloading and unloading cycle was used and did not produce any significant hysteresis in the velocity pressure behavior for the velocity data using the sc model with a grain aspect ratio 1 and pore aspect ratios 0 2 0 1 and 0 05 fit the data at 40 mpa pore aspect ratios ranging between 0 1 0 05 and 0 02 were a better fit for the data at 0 mpa both velocity and resistivity in clean sandstones can be modeled using the sc approximation in addition a linear fit was found between the p wave velocity and the decimal logarithm of the normalized resistivity with deviations that correlate with differences in permeability combining the stiff sand model and archie for cementation exponents between 1 6 and 2 1 resistivity was modeled as a function of p wave velocity for these clean sandstones

elastic wave velocities during evaporative drying laboratory measurements of drying rates and elastic wave velocities are made on limestone dolomite and sandstone samples during evaporative drying the drying rate data are very similar in form there is a constant rate period at higher saturations and a falling rate period below saturation levels of approximately 0 2 the falling rate period marks the transition in the sample from hydraulically connected to disconnected water there is a strong link between elastic wave velocities and the drying process because different pore geometries drain at different stages in drying the drainage of these different geometries results in specific changes in the moduli and velocities simple models of the pore geometries and the drying process are used to model the velocity data the velocity saturation relationship for each of the three samples is very different in form because of differences in pore space microgeometry of particular interest is the velocity response during the falling rate period of drying in the limestone and the sandstone there is a significant decrease in bulk and shear moduli and elastic wave velocities because of the drainage of crack like pores and grain contacts in contrast the absence of these pore geometries in the dolomite results in essentially no changes in the moduli at low saturations an understanding of the drying process and resulting pore scale fluid distribution provides useful insights into the observed form of the velocity saturation relationship

revised correlations of early and middle miocene calcareous nannofossil events and magnetostratigraphy from dsdp site 563 north atlantic ocean abstract deep sea drilling project site 563 located on the west flank of the northern mid atlantic ridge recovered a long miocene section from which magnetostratigraphic and isotopic stratigraphy are available quantitative analyses of calcareous nannofossil assemblages have been performed in the lower and middle miocene sediments from site 563 the abundance patterns of the identified species allow us to determine several bioevents for this time interval the recognized biohorizons related to the available magnetostratigraphy provide new data on the biostratigraphic value of many species and on the synchroneity of the events over a wide geographic area relations with the oxygen isotope stratigraphy are also reported sphenolith distribution is examined in particular detail due to their biostratigraphic importance in the early miocene in particular the recently described species sphenolithus procerus sphenolithus tintinnabulum and sphenolithus multispinatus can be useful to subdivide the lower miocene zones nn2 and nn3 a large variety of reticulofenestra pseudoumbilicus has been identified within zones nn6 and nn7

ultrasonic monitoring of spontaneous imbibition experiments acoustic signature of fluid migration capillary rise experiments spontaneous imbibition tests were conducted in the laboratory with ultrasonic and x ray monitoring on the sherwood sandstone and the majella grainstone the aim was to provide a direct comparison between the variation in seismic attributes amplitude velocity spectral content and energy and the actual fluid distribution in the rock two pairs of ultrasonic p wave sensors located at different heights on a cylindrical rock specimen recorded every 5 s the waveforms when capillary forces make water rise up into the rock from the bottom in contact with a water tank simultaneously computerized tomography scan images of a vertical cross section were also recorded two important results were found i the amplitude of the first p wave arrival is impacted by the upward moving fluid front before the p wave velocity is while the fluid front has not yet reached the sensors level in contrast the p wave velocity decreases when the fluid front reaches the fresnel clearance zone the spectral analysis of the waveforms shows that the peak frequency amplitude is continuously decreasing without noticeable frequency shift ii a methodology based on the calculation of the analytical signal and instantaneous phase was designed to decompose each waveform into discrete wavelets associated with direct or reflected waves the energy carried by the wavelets is very sensitive to the fluid substitution process the coda wavelets related to reflections on the bottom end face of the specimen are impacted as soon as imbibition starts and can be used as a precursor for the arriving fluid

fluid systems above basement shear zones during inversion of pre orogenic sedimentary basins external crystalline massifs western alps abstract in the inner part of the external alps inherited liassic basins were buried and inverted during the oligo miocene collisional phase of the alpine orogeny in northern oisans during crustal shortening the basement was locally sheared while the cover was disharmonically folded above the main basement shear zones that did not propagate into the cover in this contribution we analyze the witnesses of paleo fluid circulations associated with these crustal deformations focusing particularly on bourg d oisans and mizoen basins external western alps on the basis of structural and microstructural observations coupled to geochemical analyses cathodoluminescence o and c stable isotopes trace elements of vein versus host rock minerals we show that in the cover fluids mainly circulated over short distances closed system however trace element data also show that percolation of small amounts of basement derived fluids occurred over several tens of meters in cover rocks right above basement shear zones indeed the three successive vein sets recognized in the field display enrichments in basement derived ni co and cr which indicate that fluid transfer from the basement was efficient since the beginning of basin inversion therefore confirming the synchronous deformation of cover and basement fluid temperatures and pressures are estimated microthermometry coupled to 18o of vein minerals to about 250 400 c and 2 5 kbar for veins that most likely formed at or close to metamorphic peak conditions these results coupled to literature data are finally integrated into a model of fluid circulation evolution through progressive deformation of the whole external western alps

new method for measuring compressibility and poroelasticity coefficients in porous and permeable rocks over the last decades a large understanding has been gained on the elastic properties of rocks rocks are however porous materials which properties depend on both response of the bulk material and of the pores because in that case both the applied external pressure and the fluid pressure play a role different poroelasticity coefficients exist while theoretical relations exist measuring precisely those different coefficients remains an experimental challenge accounting for the different experimental complexities a new methodology is designed that allows attaining accurately a large set of compressibility and poroelasticity coefficients in porous and permeable rocks this new method relies on the use of forced confining or pore fluid pressure oscillations in total seven independent coefficients have been measured using three different boundary conditions because the usual theories predict only four independent coefficients this overdetermined set of data can be checked against existing thermodynamic relations measurements have been performed on a bentheim sandstone under water and glycerine saturated conditions for different values of confining and pore fluid pressure consistently with the poroelasticity theory the effect of the fluid bulk modulus is observed under undrained conditions but not under drained ones using thermodynamic relations i the unjacketed quartz and skeleton zimmerman s relation bulk moduli fit ii the drained and undrained properties fit and iii it is directly inferred from the measurements that the pore skeleton compressibility c phi is expected to be constant with pressure and to be exceedingly near the bulk skeleton c s and mineral c m compressibility coefficients plain language summary poroelastic properties of rocks are a major information for a large variety of applications linked to rupture processes in saturated media theories exist to link the properties to measurable parameters yet only little measurements exist to confront those theories this article aims at providing a method for accurately measuring those properties moreover for one particular rock a large amount of compressibility and poroelastic coefficients is measured and used to confront those theories

modelling the drained undrained transition effect of the measuring method and the boundary conditions abstract the dependence of fluid saturated rocks elastic properties to the measuring frequency is related to fluid flow phenomena at different scales in the frequency range of 10 3 106 hz for fully saturated rocks two phenomena have been experimentally documented i the drained undrained transition i e global flow and ii the relaxed unrelaxed transition i e local flow when investigating experimentally those effects or comparing different measurements in rocks one needs to account for both the boundary conditions involved and the method of measurement used a one dimensional poroelastic model is presented which aims at calculating the expected poroelastic response during an experiment the model is used to test different sets of boundary conditions as well as the role of the measuring setup i e local strain gauges or global linear variable differential transformer strain measurement four properties are predicted and compared with the measurements i e bulk modulus bulk attenuation pseudo skempton coefficient and pore pressure phase shift for the drained undrained transition because fluid pressure may not be homogeneous in the sample local and global measurements are predicted to differ furthermore the existence of a dead volume at both sample s ends is shown to be important due to the existence of the dead volume an interplay between sample s and dead volumes storage capacity determines both the magnitudes and the frequency dependence of the dispersion attenuation measurements the predicted behaviours are shown to be consistent with the measurements recently reported on very compressible and porous sandstone samples

enhanced deformation of limestone and sandstone in the presence of high fluids 1 geological repositories subject to the injection of large amounts of anthropogenic carbon dioxide will undergo chemical and mechanical instabilities for which there are currently little experimental data this study reports on experiments where low and high 8 mpa aqueous fluids were injected into natural rock samples the experiments were performed in flow through triaxial cells where the vertical and confining stresses temperature and pressure and composition of the fluid were separately controlled and monitored the axial vertical strains of two limestones and one sandstone were continuously measured during separate experiments for several months with a strain rate resolution of 10 11 s 1 fluids exiting the triaxial cells were continuously collected and their compositions analyzed the high fluids induced an increase in strain rates of the limestones by up to a factor of 5 compared to the low fluids injection of high fluids into the sandstone resulted in deformation rates one order of magnitude smaller than the limestones the creep accelerating effect of high fluids with respect to the limestones was mainly due to the acidification of the injected fluids resulting in a significant increase in solubility and reaction kinetics of calcite compared to the limestones the much weaker response of the sandstone was due to the much lower solubility and reactivity of quartz in high fluids in general all samples showed a positive correlation between fluid flow rate and strain rate x ray tomography results revealed significant increases in porosity at the inlet portion of each core the porosity increases were dependent on the original lithological structure and composition the overall deformation of the samples is interpreted in terms of simultaneous dissolution reactions in pore spaces and intergranular pressure solution creep