impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

holsteinian interglacial marine isotope stage 11 abstract the problem of correllating the holsteinian interglacial with the marine isotope stage mis is still disputed generally a view persists that this interglacial should be linked with mis 11 although this approach has many adversaries palynologic and geochemical data from well preserved fossil lake deposits from the holsteinian interglacial in eastern poland have enabled their correlation with mis 11

aminostratigraphic evaluation of conflicting age estimates for the young loess of hungary abstract as part of a regional investigation of the aminostratigraphy of central european loess deposits we have sampled and analyzed the amino acid composition of fossil gastropod shells from stratotype loess profiles at mende basaharc and paks plus the profile at sutto in an effort to correlate independently loess paleosol formations of the young loess of hungary with loess units elsewhere in the region the measured extent of isoleucine epimerization in fossil gastropod shells preserved in loess sediments was used to evaluate the relative ages of stratigraphic units and correlate between discontinuous exposures based on amino acid epimerization ratios we propose a new chronology for the standard young loess profile of hungary amino acid geochronological data suggest that paleosol complexes mf bd1 2 and ba formed during interglaciations rather than interstades correlations are suggested with pk 2 3 last interglaciation pk 4 penultimate interglaciation and pk 5 respectively from previously described czech and slovak localities

searching for distal ejecta on the craton the sedimentary effects of meteorite impact abstractdistal ejecta from meteorite impacts are rare and hard to spot in the field because of their thinness 5 mm diameter sediments and produce high flow regime bedforms megaripples dunes upper plane beds and possi

ejecta from impact craters an important feature of impacts into solar system bodies is the fate of crater ejecta the near surface material launched during the highly dynamic crater formation process laboratory measurements of impact crater ejecta from 18 studies are summarized the data are examined and used to assess our understanding of how the ejecta velocity and mass distributions depend on the conditions of an impact event the effects of impact speed on the ejecta are reasonably well understood but the dependences on target properties such as strength and porosity are only poorly constrained a point source scaling model for the ejecta mass and velocity distributions is developed and fit to the data for several classes of materials distinguished by porosity

dispersions and attenuations in a fully saturated sandstone experimental evidence for fluid flows at different scales dispersion and attenuation of elastic waves have been observed in crustal rocks existing theories and experimental measurements evidenced the existence of different energy loss mechanisms in rocks fully saturated by a newtonian fluid one major candidate is fluid flow at different scales separating three regimes the drained undrained and unrelaxed regimes here two elastic transitions between these three regimes are investigated both the cause and the consequence of the drained undrained transition are evidenced because the second transition measured occurs at higher frequency where no global fluid flow occurs it in turn is associated to the undrained unrelaxed transition or squirt flow for both transitions the amount of open microcracks seems to be the major contributor to the magnitudes of attenuation

early stage ejecta velocity distribution for vertical hypervelocity impacts into sand the ejecta dynamics during main stage excavation flow in a cratering event have previously been well characterized particularly for vertical impacts in this experimental study we present new results addressing the early time low angle high speed component of the ejecta velocity distribution as a function of time for hypervelocity vertical impacts into sand although this regime represents a very small portion of total ejected mass in laboratory experiments it comprises a greater percentage of growth for larger craters

impact crater formation in icy layered terrains on mars we present numerical simulations of crater formation under martian conditions with a single near surface icy layer to investigate changes in crater morphology between glacial and interglacial periods the ice fraction thickness and depth to the icy layer are varied to understand the systematic effects on observable crater features to accurately model impact cratering into ice a new equation of state table and strength model parameters for h2o are fitted to laboratory data the presence of an icy layer significantly modifies the cratering mechanics observable features demonstrated by the modeling include variations in crater morphometry depth and rim height and icy infill of the crater floor during the late stages of crater formation in addition an icy layer modifies the velocities angles and volumes of ejecta leading to deviations of ejecta blanket thickness from the predicted power law the dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials our simulations suggest that many of the unusual features of martian craters may be explained by the presence of icy layers including shallow craters with well preserved ejecta blankets icy flow related features some layered ejecta structures and crater lakes therefore the cratering record implies that near surface icy layers are widespread on mars

geochronology of middle and upper pleistocene loess sections in hungary abstract the application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied classical hungarian loess paleosol sequences from basaharc mende and paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial glacial cycle based on this combined luminescence dating study a new chronology is proposed for the young loess in hungary luminescence dating suggests that the loess below the mf2 horizon formed during the penultimate glaciation the mf1 horizon probably formed during an interstade within oxygen isotope stage 3 for the youngest loess overlying mf1 a very high accumulation rate was determined large time gaps occur above mf2 and mf1 indicating that most of the record of the last glaciation is missing in the standard sections at basaharc mende and paks either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil forming periods high resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in hungary although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites

scaling and reproducibility of craters produced at the experimental projectile impact chamber epic centro de astrobiologia spain the experimental projectile impact chamber epic is a specially designed facility for the study of processes related to wet target e g marine impacts it consists of a 7 m wide funnel shaped test bed and a 20 5 mm caliber compressed n2 gas gun the target can be unconsolidated or liquid the gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal to test the functionality and quality of obtained results by epic impacts were performed into dry beach sand targets with two different projectile materials ceramic al2o3 max velocity 290 m s 1 and delrin max velocity 410 m s 1 23 shots used a quarter space setting 19 normal 4 at 53 from horizontal and 14 were in a half space setting 13 normal 1 at 53 the experiments were compared with numerical simulations using the isale code differences were seen between the nondisruptive al2o3 ceramic and the disruptive delrin polymer projectiles in transient crater development all final crater dimensions when plotted in scaled form agree reasonably well with the results of other studies of impacts into granular materials we also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results as well as demonstrated that the epic quarter space experiments are a reasonable approximation for half space experiments altogether the combined evaluation of experiments and numerical simulations support the usefulness of the epic in impact cratering studies

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

application of nondestructive testing methods to study the damage zone underneath impact craters of memin laboratory experiments within the framework of the multidisciplinary experimental and modeling impact research network memin research group the damage zones underneath two experimentally produced impact craters in sandstone targets were investigated using several nondestructive testing ndt methods the 20 20 20 cm sandstones were impacted by steel projectiles with a radius of 1 25 mm at approximately 5 km s 1 resulting in craters with approximately 6 cm diameter and approximately 1 cm depth ultrasound us tomography and vibrational analysis were applied before and after the impact experiments to characterize the damage zone and micro computer tomography l ct measurements were performed to visualize subsurface fractures the newly obtained experimental data can help to quantify the extent of the damage zone which extends to about 8 cm depth in the target the impacted sandstone shows a local p wave reduction of 18 below the crater floor and a general reduction in elastic moduli by between approximately 9 and approximately 18 depending on the type of elastic modulus the results contribute to a better empirical and theoretical understanding of hypervelocity events and simulations of cratering processes

climatic variability of marine isotope stage 7 direct land sea ice correlation from a multiproxy analysis of a north western iberian margin deep sea core abstract the direct land sea ice correlation performed in the north western iberian margin core md01 2447 shows that marine isotope stage 7 mis 7 is marked by an alternation of five warm and cold periods this climatic variability is in general synchronously detected in marine and terrestrial realms by our record termination iii is marked by three cold episodes the last one interrupts the forest development in north western iberia related to the deglacial climatic amelioration it begins in the middle of termination iii but the maximal cold conditions occur at the beginning of low ice volume conditions mis 7 is characterised by three periods of very low ice volume associated with marine and continental high temperatures in and off north western iberia the correlation of our record with odp site 980 shows that the climatic variability detected in the north western iberian region has also an imprint in northern north atlantic it also highlights that most of the cold periods are associated with iceberg discharges in the north atlantic the comparison of the north western iberian margin sequence with the long european pollen records has allowed refining the correlation of the marine and continental stratigraphy for mis 7

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

fluids and frequency dependent seismic velocity of rocks summary compressional and shear velocities of rocks are dependent on frequency and this dispersion may be significant even within the seismic band the amount and position of dispersion will be largely a function of fluid properties distribution and motion in the pores velocities are thus directly coupled to rock permeability and pore compliance propagation often will be in the high frequency regime even at a few tens of hertz static or low frequency models such as gasmann will fail under such conditions in addition biot theory will not correctly model wave propagation in many cases

hypervelocity impacts on dry and wet sandstone observations of ejecta dynamics and crater growth this study deals with the investigation of highly dynamic processes associated with hypervelocity impacts on porous sandstone for the impact experiments two light gas accelerators with different calibers were used capable of accelerating steel projectiles with diameters ranging from 2 5 to 12 mm to several kilometers per second the projectiles impacted on dry and water saturated seeberger sandstone targets the study includes investigations of the influence of pore water on the shape of the ejecta cloud as well as transient crater growth the results show a significant influence of pore water on ejecta behavior steeper ejecta cone angles are observed if the impacts are conducted on wet sandstones the transient crater grows at a faster rate and reaches a larger diameter if the target is water saturated in our experiments target porosity leads to smaller crater sizes compared with nonporous targets water within the pore space reduces porosity and counteracts this process power law fits were applied to the crater growth curves the results show an increase in the scaling exponent with increasing pore space saturation

experimental ejection angles for oblique impacts implications for the subsurface flow field a simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times a specific example of such an analytical solution is maxwells z model which is based on a point source assumption here the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the nasa ames vertical gun range data from experiments reveal that impacts at angles as high as 45 to the targets surface generate subsurface flow fields that are significantly different from those created by vertical impacts the initial momentum of the projectile induces a subsurface momentum driven flow field that evolves in three dimensions of space and in time to an excavation flow field during both vertical and oblique impacts a single stationary pointsource model specifically maxwells z model however is found inadequate to explain this detailed evolution of the subsurface flow field during oblique impacts because 45 is the most likely impact angle on planetary surfaces a new analytical model based on a migrating point source could prove quite useful such a model must address the effects of the subsurface flow field evolution on crater excavation ejecta deposition and transient crater morphometry

towards a revised chronostratigraphy of loess in austria with respect to key sections in the czech republic and in hungary abstract the stratigraphic ages of some well known and characteristic paleosols in austrian and hungarian loess sections have been questioned by several workers since the mid 1970s in particular a generally accepted correlation of austrian and hungarian loess stratigraphies with the well established czech loess stratigraphy has not been put forward this paper presents 41 new thermoluminescence tl dates and the first results from amino acid chronology of key sections in these areas the results are in agreement and suggest a new interregional correlation of loess paleosol sequences for loess older than the last interglacial quartz and feldspar inclusions yield more reliable tl ages than the polymineralic fine grain fraction

an overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability fluid properties and saturation however in order to use attenuation as an attribute to extract information on rock fluid properties from seismic data experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies an appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method but technical challenges kept this technique from being widely used there is a need for the standardization of devices employing this method and a comparison of existing setups is a step towards it here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency dependent attenuation in fluid saturated and or dry reservoir rocks under small strains 10 8 10 5 we list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one we also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far

historical developments and recent advances in amino acid geochronology applied to loess research examples from north america europe and china abstract amino acid geochronology provides important chronostratigraphic insight in the regional correlation and paleoclimatic evaluation of loess paleosol sequences in the midwestern us throughout western central and eastern europe and in china in general loess of the last four glacial cycles corresponding to marine oxygen isotope stages ois 2 4 6 8 and 10 respectively can be distinguished on the basis of alloisoleucine isoleucine a i ratios measured in fossil gastropod shells preserved in the loess the racemization reaction is much slower in older samples resulting in decreased temporal resolution in the midwestern us and europe it is not possible to confidently subdivide the last glacial cycle on the basis of aminostratigraphic data however in china where effective temperatures were higher during the late pleistocene loess above and below l1ss1 the ois 3 interstadial paleosol can be distinguished using amino acid racemization data with improvements in analytical methods multiple amino acid d l enantiomers are now being measured using reverse phase liquid chromatography aspartic acid racemizes at a higher rate than the traditionally measured alloisoleucine isoleucine diastereomers and can be measured more rapidly this development offers hope for better temporal resolution and enhanced stratigraphic subdivision of loess units than has been achieved previously

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

frequency and fluid effects on elastic properties of basalt experimental investigations 1 in order to investigate the effects of fluid and frequency on the elastic properties we performed hydrostatic experiments on an icelandic basalt specimen under both dry and saturated conditions this basalt is characterized by a bimodal porosity i e cracks and equant pores the elastic properties bulk moduli in our case were investigated under high pressure through two experimental methods 1 a classical one using ultrasonic p and s waves velocities frequency 106 hz 2 and a new one using oscillation tests frequency 10 2 hz in dry condition experimental data show no significant difference between high hf and low lf frequency bulk moduli however in saturated conditions two effects are highlighted a physico chemical effect emphasized by a difference between drained and dry moduli and a squirt flow effect evidenced by a difference between hf and lf undrained moduli

dispersion of elastic moduli in a porous cracked rock theoretical predictions for squirt flow abstract crustal rocks contain variable amount of both cracks and equant pores depending on tectonic and thermal stresses but also on their geological origin crack damage and porosity change result in effects on elastic waves velocities when rocks are fluid saturated dispersion of the p and s waves should be taken into account this paper deals with frequency dispersion of elastic moduli in a fluid saturated porous and cracked rock with the assumption that squirt flow is the dominant process we develop a theoretical approach to calculate both high hf and low lf frequency bulk and shear moduli the hf moduli are derived from a new effective medium model called cpem with an isotropic distribution of pores or cracks with idealized geometry respectively spheres and ellipsoids lf moduli are obtained by taking hf dry moduli from the cpem and substituting into gassmann s equations in the case of a porosity only supported by equant pores the calculated dispersion in elastic moduli is equal to zero in the case of a crack porosity no bulk dispersion is predicted but a shear dispersion appears finally in the general case of a mixed porosity pores and cracks dispersion in bulk and in shear is predicted our results show that the maximum dispersion is predicted for a mixture of pores and spheroidal cracks with a very small aspect ratio 10 3 our theoretical predictions are compared to experimental data obtained during hydrostatic experiment performed on a basaltic rock and a good agreement is observed we also used our theoretical model to predict elastic waves velocities and vp vs ratio dispersion we show that the p waves dispersion can reach almost 20 and the vp vs dispersion a maximum value of 9 for a crack porosity of about 1 since laboratory data are ultrasonic measurements and field data are obtained at much lower frequencies these results are useful for geophysicists to interpret seismic data in terms of fluid and rock interactions

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

an attempt at correlation between the velay pollen sequence and the middle pleistocene stratigraphy from central europe abstract long continuous lacustrine sequences constitute on the continent a precious tool for coupling the long term continental environmental changes with deep sea and ice core records using the count from the top method moreover they can contribute to long distance correlation on the continent itself and thus help to classify discontinuous sedimentary records palynostratigraphical correlation is proposed here between the velay long sequence and the late middle pleistocene series from central europe with special attention to temperate episodes the similarities between the praclaux and the holsteinian interglacial suggest that they are both contemporaneous with marine isotopic stage mis 11 even if absolute dates are still divergent the evidence of two major warm periods with an interglacial type of vegetation between the holsteinian and the eemian is confirmed by the velay record

shear modulus and internal friction of calcite rocks at seismic frequencies pressure frequency and grain size dependence abstract the shear modulus g and associated internal friction q 1 have been measured at seismic frequencies for a suite of four essentially monomineralic calcite rocks with grain sizes ranging from 4 to 1000 m the measurements are based on a previously described technique for the observation of forced torsional oscillations of a series combination of a rock cylinder and a steel standard under high confining pressure at room temperature the behaviour of each rock has been studied as a function of strain amplitude 10 8 10 6 maximum at surface pressure 0 300 mpa and oscillation period 1 300 s no evidence is found of any departure from linearity in the range of strain amplitudes studied corrections which are significant only at the shortest periods 1 3 s have been applied to the raw data to account for the influence of torques exerted on the specimen assembly by the gas pressure medium up to about 100 mpa increase in pressure results in a marked increase in g and decrease in q 1 attributable to the closure of crack porosity except in the fine grained solnhofen limestone in which both g and q 1 are insensitive to change in pressure indicative of the virtual absence of crack porosity at higher pressures g is much less pressure sensitive and q 1 is essentially pressure independent with values less than 0 001 in all four rocks since the rock specimens were jacketted under conditions of normal humidity these relatively low values of q 1 indicate a diminished role for adsorbed water in the anelasticity of rocks at high effective pressures within the pressure independent regime q 1 is essentially independent of frequency for periods of 3 100 s and increases by only 30 as the grain size decreases from 1000 to 4 m thus within this regime it is concluded that the observed value of q 1 results to a large degree from an intracrystalline mechanism with a broad range of relaxation times the possibility of significant dislocation damping will be discussed

seismic wave attenuation and modulus dispersion in sandstones abstractwe have conducted laboratory experiments over the 1 200 hz band to examine the effects of viscosity and permeability on modulus dispersion and attenuation in sandstones and also to examine the effects of partial gas or oil saturation on velocities and attenuations our results have indicated that bulk modulus values with low viscosity fluids are close to the values predicted using gassmann s first equation but with increasing frequency and viscosity the bulk and shear moduli progressively deviate from the values predicted by gassmann s equations the shear moduli increase up to 1 gpa or approximately 10 with high viscosity fluids the p and s wave attenuations qp 1 and qs 1 and modulus dispersion with different fluids are indicative of stress relaxations that to the first order are scaling with frequency times viscosity by fitting cole cole distributions to the scaled modulus and attenuation data we have found that there are similar p wave shear and bulk relaxations and attenuation pe

the extra large light gas gun of the fraunhofer emi applications for impact cratering research abstract the extra large light gas gun xllgg at the fraunhofer ernst mach institut emi efringen kirchen germany is a two stage light gas gun that can accelerate projectile masses of up to 100 g up to velocities of 6 km s 1 the accelerator s set up allows various combinations of pump and launch tubes for applications in different fields of hypervelocity impact research in the framework of the memin multidisciplinary experimental and modeling impact research network program the xllgg is used for mesoscale cratering experiments with projectiles made of steel and of iron meteorites and targets consisting of sandstone and other rocks the craters produced with this equipment reach a diameter of up to 40 cm a size unique in laboratory cratering research with the implementation of neural networks the acceleration process is being optimized currently yielding peak velocities of 7 8 km s 1 for a 100 g projectile here we summarize technical aspects of the xllgg

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

crater ejecta scaling laws fundamental forms based on dimensional analysis a model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events general relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation the so called gravity and strength regimes in the gravity regime ejecta velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity this relation implies geometric similarity of ejecta blankets that is the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii in the strength regime ejecta velocities are independent of crater size consequently ejecta blankets are not geometrically similar in this regime for points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws the exponents in these power laws are functions of an exponent that appears in crater radius scaling relations thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta predicted ejection velocities and ejecta blanket profiles based on measured values of are compared to existing measurements of velocities and debris profiles

re interpretation of the meikirch pollen record swiss alpine foreland and implications for middle pleistocene chronostratigraphy the meikirch drilling site in the swiss midlands north of bern is re interpreted using a combination of sedimentological logging pollen analyses and luminescence dating the sedimentary sequence comprises about 70 m of lacustrine deposits overlain by about 39 m of coarse glacial outwash interpreted to represent at least two independent ice advances pollen analyses of the apparently complete limnic sequence reveal a basal late glacial period followed by three warm phases that are interrupted by two stadial periods meikirch complex the warm periods were previously correlated with the holsteinian and eemian interglacials according to luminescence dating and with consideration of evidence for middle pleistocene climate patterns at other central european sites a correlation of the meikirch complex with marine isotope stage mis 7 is now proposed if this correlation is correct it implies the presence of three intervals with interglacial character during mis 7 however the late middle pleistocene vegetational features of the meikirch complex show significant differences when compared with the pollen record from the velay region central france possible explanations for this discrepancy are distinct middle pleistocene patterns of atmospheric circulation over central europe and a different distribution of vegetation refugia compared to the eemian interglacial and the holocene copyright 2005 john wiley sons ltd

numerical 230th u dating and a palynological review of the holsteinian hoxnian interglacial abstract earth scientists increasingly consider the holsteinian interglacial and mis 11 as synonyms despite the limited number of numerical dates and ambiguous stratigraphic and palynological correlation with the numerical marine isotope timescale hence we present new tims 230th u dates from two fen peat layers of the holsteinian reference site at bossel in northern germany and re evaluate published numerical data from two sites with hoxnian deposits in england a new method for the calculation of methodically controlled minimum 230th u ages mcma was developed the synopsis of the 230th u dates allows a correlation of both the holsteinian and hoxnian interglacials to mis 9 this correlation is supported by supplementary 230th u dates of fen peat from several pre eemian but non holsteinian sites in germany there is palynological evidence for a reliable correlation between precisely investigated and numerically dated holsteinian deposits in poland germany england sw ireland and france an apparently contradictory palynological correlation from the french central massif is discussed

alpine evidence for atmospheric circulation patterns in europe during the last glacial maximum the configuration of alpine accumulation areas during the last glacial maximum lgm has been reconstructed using glacial geological mapping the results indicate that the lgm ice surface consisted of at least three major ice domes all located south of the principal weather divide of the alps this implies that the buildup of the main alpine ice cover during oxygen isotope stage ois 2 was related to precipitation by dominant southerly atmospheric circulation in contrast to today s prevalent westerly airflow such a reorganization of the atmospheric circulation is consistent with a southward displacement of the oceanic polar front in the north atlantic and of the associated storm track to the south of the alps these results combined with additional paleoclimate records from western and southern europe allow an interpretation of the asynchronous evolution of the different european ice caps during the last glaciation 18o stages ois 4 and 3 were characterized by location of the polar front north of 46 n gulf of biscay this affected prevailing westerly circulation and thus ice buildup in western scandinavia the pyrenees vosges and northern alps at the lgm however the polar front lay at 44 n causing dominating southerly circulation and reduced precipitation in central and northern europe

a new seismic wave attenuation module to experimentally measure low frequency attenuation in extensional mode abstract a seismic wave attenuation module is developed to experimentally measure the attenuation in extensional mode qe 1 and the young s modulus of copper jacketed 60 mm long and 25 4 mm in diameter samples in a gas medium paterson rig the new module is suitable for natural rock samples and was tested under confining pressure up to 50 mpa and room temperature the module is designed to operate at a strain 10 6 for which rocks behave linearly to calculate attenuation both the applied force and the bulk shortening of the sample are measured employing linear variable differential transformers this technique allows measuring samples with a high degree of heterogeneity attenuation at low seismic frequencies 10 2 102 hz is obtained for rocks at dry and various saturation conditions we present a series of measurements on berea sandstone in a room dry condition and saturated with different fluids water and glycerine solutions with viscosities of 10 cp and 22 cp respectively at a confining pressure of 10 mpa and with a pore pressure of 1 mpa the accuracy of the attenuation data expressed as a phase shift is 0 0019 rad

loess chronology of the last interglacial glacial cycle in bohemia and moravia czech republic abstract combined infrared and green light stimulated luminescence and thermoluminescence dating applied to the extensively studied bohemian and moravian loess palaeosol sequences from sedlec suchdol kutna hora dolni v stonice lechovice mod ice bulhary and cerven kopec provides a reliable chronological framework for the last interglacial glacial cycle based on this luminescence dating study a new chronology is proposed for the last interglacial glacial loess palaeosol sequences from the czech republic irsl and tl dating suggests that the bt horizon of a truncated brown forest soil lower pk iii formed during the last interglacial equivalent to oxygen isotope substage 5e the upper chernozem of pkii belongs to oxygen isotope stage 3 if the combined irsl and tl age estimates are taken into account although from geological estimates an age range within oi substage 5a is most likely the upper weichselian loess accumulated at a very high rate owing to the high accumulation rate there is no time difference in sedimentation ages between the tundra gley palaeosols above pk i which include the upper weichselian sediments in central europe

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

ejection behavior characteristics in experimental cratering in sandstone targets within the frame of the memin research unit multidisciplinary experimental and numerical impact research network impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass velocity and target water saturation on the cratering and ejection processes the projectiles were accelerated with two stage light gas guns ernst mach institute onto fine grained targets seeberger sandstone with about 23 porosity collection of the ejecta on custom designed catchers allowed determination of particle shape size distribution ejection angle and microstructures mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high speed videos the increase in projectile mass from 0 067 to 7 1 g correlates with an increase in the total ejected mass ejecta angles however are similar in range for all experiments the increase in projectile velocity from 2 5 to 5 1 km s 1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency and a widening of the ejecta cone a higher degree of water saturation of the target yields an increase in total ejecta mass up to 400 with respect to dry targets higher ejecta velocity and a steeper cone these data in turn suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution

theoretical derivation of a brie like fluid mixing law prediction of the velocity of acoustic waves in partially saturated rocks is very important in geophysical applications the need to accurately predict acoustic velocities has resulted in a widespread popularity of brie s effective fluid mixing law this empirical model together with gassmann s formula are used routinely in fluid substitution problems in petroleum geophysics and seismic monitoring of carbon capture and storage most attempts to justify brie s model have been focused on interpretation in terms of patchy saturation models and attaching meaning to the brie parameter in terms of the patch size in this paper using a microstructural description of the rock and a parameter relating to capillary pressure we calculate an effective fluid modulus that is very similar to brie s law the fluid mixing law we propose is independent of frequency and has a solid theoretical foundation this proposed law produces analytically harmonic and arithmetic averaging at the endpoints our results indicate that brie like behaviour may not necessarily be related to frequency and patch size dependent phenomena

a laboratory study of low frequency wave dispersion and attenuation in water saturated sandstones abstract laboratory measurements of elastic and anelastic parameters of dry and water saturated sandstones with low 0 7 and 1 1 md and high 425 md permeability have been conducted at seismic frequencies 0 1 to 120 hz the experiments were performed with a laboratory apparatus that measures the stress strain relationship in the linear regime the extensional attenuation in water saturated low permeability sandstones exhibits prominent peaks in the seismic band accompanied by considerable dispersion variations in attenuation and dispersion in the high permeability sandstone are below the measurement error as is the moduli dispersion in all the sandstones in dry condition the experiments demonstrate that for low permeability rocks seismic frequencies do not necessarily correspond to the low frequency limit relaxed pore fluid pressures of acoustic wave dispersion

upper pleistocene loess stratigraphy in southern germany abstract the detailed loess paleosol sequences of southern germany provide a highly sensitive record of the regional climate and environmental changes of the upper pleistocene combined infrared stimulated luminescence irsl and thermoluminescence tl dating was carried out on loess and loess derivatives at upper pleistocene type sections from the mainz basin the middle neckar valley and the alpine foreland with the aim of setting up a reliable chronological framework for the past 130 000 years the irsl and tl age estimates are in agreement with the geological estimates up to 70 000 years however the chronostratigraphic position of the first truncated brown forest soil in the sections at bockingen bonnigheim and bobingen considered to be the eemian soil or equivalent to oxygen isotope oi substage 5e remains uncertain the methodological results indicate that irsl dating is the more advantageous technique for the upper and middle weichselian periglacial deposits as demonstrated for the loess paleosol sequence in mainz weisenau

seismic attenuation in partially saturated berea sandstone submitted to a range of confining pressures using the forced oscillation method we measure the extensional mode attenuation and young s modulus of a berea sandstone sample at seismic frequencies 0 5 50 hz for varying levels of water saturation 0 100 and confining pressures 2 25 mpa attenuation is negligible for dry conditions and saturation levels 80 for saturation levels between 91 and 100 attenuation is significant and frequency dependent in the form of distinct bell shaped curves having their maxima between 1 and 20 hz increasing saturation causes an increase of the overall attenuation magnitude and a shift of its peak to lower frequencies on the other hand increasing the confining pressure causes a reduction in the attenuation magnitude and a shift of its peak to higher frequencies for saturation levels above 98 the fluid pressure increases with increasing confining pressure when the fluid pressure is high enough to ensure full water saturation of the sample attenuation becomes negligible a second series of comparable experiments reproduces these results satisfactorily based on a qualitative analysis of the data the frequency dependent attenuation meets the theoretical predictions of mesoscopic wave induced fluid flow wiff in response to a heterogeneous water distribution in the pore space so called patchy saturation these results show that mesoscopic wiff can be an important source of seismic attenuation at reservoir conditions

a new laboratory apparatus for the measurement of seismic dispersion under deviatoric stress conditions abstract a better understanding of seismic dispersion and attenuation of acoustic waves in rocks is important for quantitative interpretation of seismic data as well as for relating seismic data sonic log data and ultrasonic laboratory data in the present work a new laboratory setup is described allowing for combined measurements of quasistatic deformations of rocks under triaxial stress ultrasonic velocities and dynamic elastic stiffness young s modulus and poisson s ratio at seismic frequencies the setup has been used mainly for the study of shales for such rocks it is crucial that the saturation of the samples is preserved which requires fast sample mounting the design of our setup together with a technique that was developed for rapid mounting of strain gauges onto the sample and subsequent sealing of the sample allows for sample preservation which is of particular importance for shales the performance of the new experimental setup and sample mounting procedure is demonstrated with test materials aluminium and polyetheretherketone and two different shale types mancos shale and pierre shale furthermore experimental results are presented that demonstrate the capability of measuring the impact of saturation stress and stress path on seismic dispersion for the tests with mancos shale and pierre shale large dispersion up to 50 in young s modulus normal to bedding was observed increased water saturation of mancos shale results in strong softening of the rock at seismic frequencies whereas hardening is observed at ultrasonic frequencies due to an increase in dispersion counteracting the rock softening the poisson s ratio of mancos shale strongly increases with the level of saturation but appears to be nearly frequency independent we have found that the different types of shale exhibit different stress sensitivities during hydrostatic loading and that the stress sensitivity is different at seismic and ultrasonic frequencies

a long pollen record from lac du bouchet massif central france for the period ca 325 to 100 ka bp ois 9c to ois 5e abstract pollen analysis was carried out on sediments older than the wurm pleniglacial ois 4 in two new sequences h and i derived from the centre of lac du bouchet massif central the inferred vegetation history enables for the first time in france five temperate episodes to be defined which pre date the last interglacial these temperate episodes alternate with episodes during which the changes in vegetation are indicative of glacial climates comparison of these climatic episodes with the oceanic isotope record shows that the pollen record of sequences h and i from lac du bouchet spans the time interval from ois 9c ussel interstadial to ois 5e ribains eemian interglacial in the organic sediments from the amargiers interstadial ois 9a a trachytic layer ar ar dated to ca 275 ka enables a correlation to be established with the upper part of a sequence derived from the nearby praclaux crater the lower part of this sequence being of holsteinian age ois 11c the cross dating of the pollen sequences from lac du bouchet cores h i and d and from praclaux provides a complete record from the massif central southern france of successive glacial and interglacial episodes that span the last ca 400 ka that is the interval from the holsteinian to the holocene

vegetation and climate in the early and pleni weichselian in northern central europe analysis of numerous pollen diagrams from north and central germany and from the adjacent lowlands of the netherlands denmark poland and belarus have facilitated a regional comparison of the vegetation and climatic evolution from the beginning of the early weichselian glaciation to the weichselian pleniglacial data from geological studies and analysis of fossil beetles and plant macroremains have been used to supplement the palaeoclimatic reconstruction up to the end of the oerel interstadial the palaeoclimate was characterised by increasing continentality the winter temperatures in particular tended to fall continuously during the stadials and the interstadials of the early weichselian and early pleniglacial in the brorup and odderade interstadials summer temperatures where sufficiently high to enable boreal forests to grow whereas in the oerel interstadial summer temperatures were such that tree growth was inhibited it is probable that falling sea level and the consequent extension northwards of the north sea coast were the main causes of increasing continentality in the latter part of the pleniglacial peat accumulation frequently took place and humic silts were deposited under lacustrine conditions correlation between various sites is extraordinarily difficult pollen diagrams from the so called interstadials of the glinde moershoofd complex hengelo and denekamp are similar to those of the known early weichselian stadials it is proposed therefore that these interstadials should be called intervals and that the term interstadial be reserved for climatic variations that result in distinctive pollen assemblages and which in turn reflect distinctive vegetation dynamics interstadials should be capable of being characterised on a biostratigraphical basis and it should be possible to establish correlations over considerable distances according to this definition the first three warm oscillations of the weichselian glaciation in the central european lowlands are the brorup odderade and oerel interstadials all other pleniglacial peat layers should be assigned the rank of interval copyright 2001 john wiley sons ltd

palynostratigraphy of the last interglacial glacial cycle in germany abstract the last interglacial glacial cycle comprises the eemian and the weichselian in the area of the scandinavian glaciation respectively the riss wurm and the wurm in southern germany drastic changes of the vegetation have occurred several times during this period in europe the best known in germany is the development of the forests of the last interglacial stage and of the two succeeding early glacial interstadial phases the brorup and the odderade above the odderade sediments of two more middle weichselian interstadials the oerel and the glinde with a shrub tundra vegetation have been found at one site in northern germany in southern germany the palynological record ends somewhat earlier i e with the equivalent of the oerel interstadial which here in the south had a forest vegetation numerous single occurrences of interstadial sediments of different age and vegetation have been studied but unfortunately their stratigraphic position is most frequently unclear therefore a general survey can only rely on few but long sequences their comparison shows that vegetational gradients of different steepness existed at different times which mirror the changing climatic gradients of this period the main points of the vegetational zonation as far as it is known from germany for the cycle are summarized

an introduction to the middle and upper pleistocene loess paleosol sequence at ruma brickyard vojvodina serbia abstract six loess units and five paleosols are preserved in the 20 m thick exposure of middle and late pleistocene sediments at ruma brickyard vojvodina serbia amino acid geochronology provides stratigraphic correlations between loess paleosol units sl l1 s1 sl l2 s2 sl l3 s3 and sl l4 at ruma with loess of glacial cycles b c and d and e respectively at other central and southeastern european localities the profile represents one of the best potential sections in the region for reconstructing detailed paleoclimates and paleoenvironments of the last ca 350 000 yr initial sedimentological magnetic and malacological evidence indicate many episodes of drier conditions in the region than in other parts of central and southeastern europe during the later part of the middle and late pleistocene

variation of unjacketed pore compressibility using gassmann s equation and an overdetermined set of volumetric poroelastic measurements gassmann s original equation provides a means to relate bulk elastic parameters of a porous material with the compressibility of the pore fluid the original analysis assumed microhomogeneity and isotropy which assumed that pore compressibility was equal to grain compressibility although subsequent theoretical arguments have shown that gassmann s original assumption is violated for most rocks and that pore compressibility need not equal grain compressibility few experimental studies have compared the two compressibilities the assumption that pore compressibility equals grain compressibility is still commonly made we measured hydrostatic poroelastic constants of berea sandstone and indiana limestone under drained undrained and unjacketed conditions over a range of confining and pore pressures to test the assumption that pore compressibility equals grain compressibility these two rocks were chosen because they havesimilar values of porosity but different elastic behaviors berea sandstone is nonline

effect of fluids and frequencies on poisson s ratio of sandstone samples abstractpoisson s ratio is an important parameter when interpreting measured geophysical and seismic data for an isotropic medium it directly relates to the ratio of p and s wave velocities we have measured as a function of pressure and frequency in fluid saturated sandstones the method of measuring was first tested as a function of pressure and frequency using standard samples the phase shift between radial and axial strains was also measured for all standard samples such as the linear viscoelastic plexiglas the data indicated that tan correlated with and related to a dissipation on then and tan were measured as a function of pressure and frequency for two dry and fluid saturated fontainebleau sandstone samples under dry conditions no frequency dependence and very small pressure dependence were observed unusual behaviors were observed under fluid saturated conditions in particular of one sample indicated a frequency dependent bell shaped dispersion under water and gl

laboratory based seismic attenuation in fontainebleau sandstone evidence of squirt flow at seismic frequencies 1 100 hz we studied attenuation in the laboratory using the forced oscillation method we adopted the longitudinal mode of oscillation which yields the young s modulus and the corresponding attenuation here defined as the inverse quality factor a fontainebleau sandstone with a porosity of 8 and a permeability of 12 md was saturated with different fluids and investigated at the confining pressures of 5 10 and 15 mpa at all the measured confining pressures while attenuation was zero for the dry sample for partial and full water saturation it gradually increased from nearly zero to 0 02 with increasing frequency the sample was then fully saturated with glycerin water mixtures of varying viscosities up to that of glycerin 8 92 485 and 1414 cp at the confining pressure of 5 mpa a bell shaped attenuation curve peaking at 6 hz with a magnitude of 0 11 was observed when the sample was fully saturated with glycerin 1414 cp a decrease in viscosity of the saturating fluid shifted the attenuation curve to higher frequencies and an increase in confining pressure caused a decrease in the overall magnitude of attenuation the data obtained for glycerin were compared to a simple squirt flow model with sufficient agreement implying that squirt flow is the dominant mechanism responsible for the observed attenuation

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

high precision constraints on timing of alpine warm periods during the middle to late pleistocene using speleothem growth periods a long standing problem in the reconstruction of warm climate periods during the late quaternary is the difficulty of determining absolute ages for undisturbed terrestrial climate archives speleothems offer an important source of information about the timing and duration of middle and late pleistocene warm phases a flowstone from the high elevation spannagel cave zillertal alps austria provides a new absolutely dated climate record which includes the most prominent warm phases between 260 and 50 ka before present new data from the penultimate interglacial improve our knowledge about the timing and progression of warm periods in the alps corresponding to marine isotope stages 7 and 8 speleothem growth phases were identified from 261 to 249 from 236 to 229 and from 200 to 192 ka an early onset of the last interglacial is corroborated by a growth phase commencing at 136 7f2 8 ka and the youngest section of the flowstone provides further evidence for an alpine climate during time intervals corresponding to marine isotope stages 5a and 3 sufficiently warm to allow speleothems to grow the high resolution stable isotope profile taken along the growth axis of the flowstone provides information about the hydrological conditions during the growth phases d 2005 elsevier b v all rights reserved

crater morphology in sandstone targets the memin impact parameter study hypervelocity 2 5 7 8 km s 1 impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass target pore space saturation target projectile density contrast and target layer orientation on crater size and shape crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation craters in water saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone morphometric analyses of the resultant craters 5 40 cm in diameter reveal features that are characteristic of all of our experimental craters regardless of impact conditions i a large central depression within a fragile light colored central part and ii an outer spallation zone with areas of incipient spallation two different mechanical processes grain fragmentation and intergranular tensile fracturing are recorded within these crater morphologies zone i approximates the shape of the transient crater formed by material compression displacement comminution and excavation flow whereas ii is the result of intergranular tensile fracturing and spallation the transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models the dimensions of this transient and of the final crater show the same trends both increase in volume with increasing impact energy and with increasing water saturation of the target pore space the relative size of the transient crater in percent of the final crater volume decreases with increasing projectile mass and velocity signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased

european middle pleistocene loess chronostratigraphy some considerations based on evidence from the wels site austria a combination of site logging luminescence dating and comparison with different long and continuous records of past environmental conditions is used to elaborate an age model for the wels loess palaeosol site austria according to this model marine isotope stage mis 7 is reflected in the development of three red forest soils luvisols at this particular site this is contrary to previous assumptions that suggested the development of such soils in the region at 100 ka cyclicity if these results are correct this may question some previous conclusions regarding the general loess stratigraphy in many parts of europe

shock wave profile study of tuff from the nevada test site shock wave equation of state and release behavior of tuff from the nevada test site were measured in the range 8 to 107 gpa by recording shock wave profiles produced by impact of projectiles accelerated by a two stage light gas gun shock wave profiles were measured with a fast optical interferometer hugoniot sound speed and effective gruneisen parameter data were determined from the profiles the specimen geometry allows direct observation of the shape of the leading edge of the shock in which complex compressive dynamics caused by pore crushing or phase transitions can manifest themselves the tuff specimens were tested in both a water saturated and semidry state hydration of the rock increases both the shock and sound speeds for a given compression the us up relation for our water saturated tuff is slightly nonlinear and can be approximated as us 2 00 1 42 up for 0 up 6 km s and us 2 29 1 29up for 0 up 3 km s for semidry tuff at pressures less than 18 gpa us 1 70 1 28up

vegetation and climate during warmer intervals in the late pleistocene of western and central europe abstract many warmer intervals occurred during the last interglacial glacial cycle 130 10 ka in europe the vegetational record shows several types of such intervals among which the forest periods of the eemian interglacial and the amersfoort brorup interstadials of the early weichselian are of special interest a series of map reconstructions is used to present some of the relevant vegetational and paleoclimatic characterizations they represent two types of temperate intervals occurring in the late pleistocene in europe one with a rather uniform distribution of vegetation types a warmer oceanic climate and a high sea level the other type shows strong vegetation gradients both north south and east west a more continental climate and a relatively low sea level inland ice probably persisted in the far north during this last type of interval it is suggested that these two types of interglacial occurred throughout the pleistocene

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

non intrusive measurements of crater growth abstract an experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point unlike previous so called quarter space experiments where projectiles were launched along a transparent plexiglas sheet so that growth of half a crater could be viewed the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process this technique indicates that for low velocity impacts 300 m s into 220 m glass beads that are without cohesion and where the projectile is not disrupted craters initially grow somewhat proportionally but that later their depths remain essentially constant while their diameters continue to expand in addition these experiments indicate that as the impact velocity increases the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases these last two observations are probably due to the large time of penetration of the projectile which becomes a significant fraction of the time of crater formation this is contrary to the expectations for the scaling rules which assumes a point source very high curtain angles 45 are also seen and could be due to the low friction angle of the target significant crater modification which is rarely seen in quarter space experiments is also observed and appears to be controlled by the dynamic angle of repose of the target these latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta mass distributions and large scale crater modification processes on the planets