three proterozoic orogenic episodes and an intervening exhumation event in the black canyon of the gunnison region colorado abstract u pb zircon titanite geochronology in situ monazite geochronology and 40ar 39ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of proterozoic rocks exposed in the black canyon gunnison colorado these new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses 1 yavapai orogeny 1741 1689 ma 2 exhumation marked by an angular unconformity beneath post yavapai pre mazatzal quartzites 3 mazatzal orogeny postquartzite deposition and 4 1434 1403 ma intracratonic tectonism supracrustal rocks of the black canyon succession were deposited or crystallized at or prior to documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wn

laboratory approach to the study of elastic anisotropy on rock samples the experimental approach hardware and software to the study of the elastic anisotropy of rocks on spherical samples under hydrostatic pressure up to 400 mpa is discussed a substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media the innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude several options and results obtained with the innovated laboratory equipment are presented

ceratopsia increase history and trends1 the taxonomic history of the ceratopsia began in 1876 with the description of monoclonius crassus cope followed in 1889 by triceratops horridus marsh after a peak of discovery and description in the 1910s and 1920s resulting from the canadian dinosaur rush in the province of alberta and the central asiatic expeditions to mongolia of the american museum of natural history the study of ceratopsians declined to a low level until the 1990s when discoveries in china montana utah alberta and elsewhere abetted by increased biostratigraphic and phylogenetic precision led to an unprecedented resurgence of activity even richard c fox along with colleagues from peking university joined in the activity by naming psittacosaurus lujiatunensis to place the activity in historical perspective half of all known ceratopsians have been described since 2003 despite important finds of basal ceratopsians in china mongolia and korea north america continues to dominate ceratopsian especially ceratopsid diver

measurements of elastic and electrical properties of an unconventional organic shale under differential loading abstractwe have developed an experimental approach to simultaneously measure the stress dependence of ultrasonic wave velocities at 1 mhz and therefore the components of the undrained elastic stiffness tensor as well as the components of the complex conductivity tensor in the frequency range from 100 mhz to 10 hz we performed the experiments on a cylindrical core sample from the haynesville formation porosity of approximately 0 08 bound water excluded and clay content mostly illite approximately 30 40 wt we performed experiments under controlled confining and pore fluid pressures achieving differential pressure states representative of autochthonous reservoir conditions directional measurements were made using independent acquisition arrays piezoelectric crystals and nonpolarizing electrodes distributed azimuthally on the core sample external surface the bedding plane being along the axis of the cylindrical core sample ultrasonic waveforms were recorded on a high resolution oscilloscope

new information on the rare horned dinosaur arrhinoceratops brachyops ornithischia ceratopsidae from the upper cretaceous of alberta canada arrhinoceratops brachyops is a poorly understood chasmosaurine ceratopsid from the upper cretaceous horseshoe canyon formation of alberta previously described on the basis of only a single skull here we report on a second specimen attributable to this species including a relatively complete skull syncervical and partial left forelimb this second specimen clarifies aspects of morphology not visible in the holotype and also elucidates variation in a brachyops the species is distinguished by a square shaped triangular process of the premaxilla a steeply inclined triturating surface of the predentary and a triangular nasal horncore in horizontal section the dentary is also distinctive in bearing a bony lateral ridge similar to that of anchiceratops ornatus but more strongly developed phylogenetic analysis cannot resolve the relationships of arrhinoceratops beyond the level of chasmosaurinae owing to both missing data and conflicting characters however we do find some support for a deep split

static and dynamic pressure sensitivity anisotropy of a calcareous shale optimizing the productivity of nonconventional low permeability shale reservoirs requires detailed knowledge of the mechanical properties of such materials these rocks elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional duvernay reservoir of alberta canada the complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 mpa wave speed anisotropies of up to 35 are observed at even the highest confining pressures furthermore the stress sensitivity of the wave speeds and hence moduli is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure whereas those along the bedding plane show unexpectedly nearly no pressure dependence these observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images these results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions for the concentration of stress within such formations and for estimation of static engineering moduli from sonic log wave speeds

estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis summary this paper reports a new approach for the estimation of thomsen anisotropy parameters and symmetry axis orientation from ultrasonic p wave traveltime measurements on transversely isotropic shale samples of arbitrary geometry this approach can be used for core samples cut in any direction with respect to the bedding plane because no a priori assumption regarding the symmetry axis orientation is made this orientation is rather part of the solution of the inverse problem together with the anisotropy parameters themselves very fast simulated reannealing is used to search for the best possible estimate of the model parameters the methodology is applied to spherical and cylindrical anisotropic shale samples

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

estimation of stress dependent anisotropy from p wave measurements on a spherical sample our aim is to understand the stress dependent seismic anisotropy of the overburden shale in an oil field in the north west shelf of western australia we analyze data from measurements of ultrasonic p wave velocities in 132 directions for confining pressures of 0 1 400 mpa on a spherical shale sample first we find the orientation of the symmetry axis assuming that the sample is transversely isotropic and then transform the ray velocities to the symmetry axis coordinates we use two parameterizations of the phase velocity one in terms of the thomsen anisotropy parameters a b e d as the main approach and the other in terms of a b g d we invert the ray velocities to estimate the anisotropy parameters a e d and g using a very fast simulated reannealing algorithm both approaches result in the same estimation for the anisotropy parameters but with different uncertainties the main approach is robust but produces higher uncertainties in particular for g whereas the alternative approach is unstable but gives lower uncertainties these approaches are used to find the anisotropy parameters for the different confining pressures the dependency of p wave velocity a on pressure has exponential and linear components which can be contributed to the compliant and stiff porosities the exponential dependence at lower pressures up to 100 mpa corresponds to the closure of compliant pores and microcracks whereas the linear dependence at higher pressures corresponds to contraction of the stiff pores the anisotropy parameters e and d are quite large at lower pressures but decrease exponentially with pressure for lower pressures up to 10 mpa d always is larger than e this trend is reversed for higher pressures despite the hydrostatic pressure the symmetry axis orientation changes noticeably in particular at lower pressures

effects of heterogeneities and anisotropy on sonic and ultrasonic attenuation in rocks we compare the attenuation obtained by the resonant bar technique in the sonic frequency range 3 10 khz with that obtained by the pulse transmission technique in the ultrasonic frequency range 500 khz on a set of 30 rocks including sandstones and limestones the sonic and ultrasonic measurements were performed under high effective pressure on adjacent water saturated samples from each rock block compressional ultrasonic attenuation was typically larger than extensional sonic attenuation particularly in limestones this is attributed to the presence of density heterogeneities that can be seen on x ray scanner imagery heterogeneities at the scale of the ultrasonic wavelength produce diffraction of the waves and as a consequence high attenuation values at ultrasonic frequencies large apparent shear attenuation values compared to compressional attenuation values are explained by shear wave splitting

redescription of ualvp 40 an unusual specimen of chasmosaurus lambe 1914 ceratopsidae chasmosaurinae bearing long postorbital horns and its implications for ontogeny and alpha taxonomy of the genus ualvp 40 an articulated and reasonably complete skull of a small chasmosaurine dinosaur collected in 1920 by george f sternberg from the lower unit of the dinosaur park formation dinosaur provin

a robust experimental determination of thomsen s δ parameter abstracta novel inversion method for the laboratory determination of thomsen s anisotropy parameter on cylindrical rock specimens from ultrasonic data has been recently reported in the literature we further assessed this method through a direct comparison of the results of the traditional method involving a single off axis p wave velocity measurement at 45 and the new method involving 65 p wave velocity measurements at several angles to the symmetry axis we prepared and characterized two vertical shale specimens from the same preserved vertical core to assess their similarity in terms of structure mineralogy porosity and density the shale was assumed to be transversely isotropic in view of the observed horizontal bedding we subjected both specimens to the same brine saturation and effective stress state using the two methods we obtained similar results for thomsen s vertical p wave and e p wave anisotropy parameters however a significant discrepancy was observed for thomsen s p

petrogenesis of the highly potassic 1 42 ga barrel spring pluton southeastern california with implications for mid proterozoic magma genesis in the southwestern usa syenites from the barrel spring pluton were emplaced in the early proterozoic mojave crustal provine of southeastern california at 1 42 ga all rocks even the most mafic are highly enriched in incompatible elements e g k2o 4 12 wt rb 170 370 ppm th 12 120 ppm la 350 1500xchondrite la ybn 35 100 elemental compositions require an incompatible element rich but mafic or ultramafic source trace element models establish two plausible sources for barrel spring magmas 1 lree enriched garnet websterite with accessory apatite rutile enriched lithospheric mantle and 2 garnet amphibolite or garnet hornblende granulite with enriched alkali basalt composition also with accessory apatite rutile mafic lower crust nd and pb isotopic ratios do not distinguish a crust vs mantle source but eliminate local mojave province crust as the principal one and indicate that generation of the enriched source occurred several hundred million years before emplacement of the barrel spring pluton 1 40 1 44 ga potassic granites are common in southeastern california suggesting a genetic link between the barrel spring pluton and the granites however although the same thermal regime was probably responsible for producing both the granitic and syentic magmas elemental and isotopic compositions preclude a close relationship isotopic similarity of the barrel spring pluton to 1 40 1 44 ga granites emplaced in the central arizona crustal province to the east may imply that a common component was present in the lithosphere of these generally distinct regions

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

syncontractional crustal anatexis and deformation during emplacement of 1435 ma plutons western needle mountains colorado mesoproterozoic deformation and biomodal magmatism in southwest colorado offer important insight into the nature and tectonic regime of 1 4 ga magmatism in the western united states we document syncontractional emplacement of coeval gabbroic and granitic plutons in the middle crust at 1435 ma in the western needle mountains this is incompatible with extension dominated anorogenic models proposed for the generation of 1 4 ga plutonic rocks in the southwest but lends further support for synkinematic intracontinental magmatism in response to regional tectonic strains created by transpressive or compressive plate margin interactions between 1500 1300 ma intrustion of the 1435 ma electra lake gabbro and eolus granite into paleoproterozoic rocks caused local crustal anatexis and extensive thermal metamorphism in the needle mountains deformation of paleoproterozoic country rocks at 1435 ma is widespread but is concentrated in pluton aureoles where thermally softened crust accommodated the strain we int

geomechanical and ultrasonic characterization of a norwegian sea shale anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation including depth conversion and fluid identification in addition mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well preserved samples multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the norwegian sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation in addition standard rock physical properties were characterized as well as composition the shale microfabric is seen to be strongly laminated with alternating thick clay rich laminae and thin silt rich laminae occasional microfractures are also noted parallel to these laminations the shale has low friction coefficient and cohesive strength and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric the orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased s wave anisotropy was significantly affected by the increasing stress anisotropy stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale

elastic anisotropy modeling of kimmeridge shale 1 anisotropy of elastic properties in clay rich sedimentary rocks has been of long standing interest these rocks are cap rocks of oil and gas reservoirs as well as seals for carbon sequestration elasticity of shales has been approached by direct velocity measurements and by models based on microstructures here we are revisiting the classical kimmeridge shale studied by hornby 1998 by first quantifying microstructural features such as phase volume fractions grain shapes and grain orientations and pore distributions with advanced analytical methods and then using this information in different models to explain bulk elastic properties it is shown that by application of a self consistent algorithm based on eshelby s 1957 model of inclusions in a homogeneous medium it is possible to explain most experimental elastic constants though some discrepancies remain which may be due to the interpretation of experimental data using a differential effective medium approach an almost perfect agreement with experimental stiffness coefficients can be obtained though the physical basis of this method may be questionable the influence of single crystal elastic properties grain shapes preferred orientation and volume and shapes of pores on elastic properties of shale is explored

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

comparison between permeability anisotropy and elasticity anisotropy of reservoir rocks we developed new experimental and theoretical tools for the measurement and the characterization of arbitrary elasticity tensors and permeability tensors in rocks they include an experimental technique for the 3 d visualization of hydraulic invasion fronts in rock samples by monitoring the injection of salt solutions by x ray tomography and a technique for inverting the complete set of the six coefficients of the permeability tensor from invasion front images in addition a technique for measuring the complete set of the 21 elastic coefficients a technique allowing the identification and the orientation in the 3 d space of the symmetry elements planes axes and a technique for approximating the considered elastic tensor by a tensor of simpler symmetry with the quantification of the error induced by such an approximation have been developed we apply these tools to various types of reservoir rocks and observed quite contrasted behaviors in some rocks the elastic anisotropy and the hydraulic anisotr

stress induced anisotropy in brine saturated shale summary this paper reports the intrinsic and crack induced anisotropic properties of a set of preserved brine saturated shale samples and their response to external stresses we used undrained multistage triaxial tests to evaluate how the ultrasonic wave velocities and their anisotropy changed with increasing isotropic and differential stress conditions in addition the impact of stress orientation with respect to fabric orientation was evaluated an array of ultrasonic transducers allowed to measure five independent wave velocities which were used to calculate the elastic properties of the shale results indicate that in this shale p and s wave velocities vary with stress in a different manner dependent on the maximum principal stress orientation with respect to the fabric where the maximum stress is normal to bedding vpv and vs1 increase monotonically with increasing effective stress however vph and vsh decrease during individual loading stages but increase from stage to stage as confining pressure increases the reverse occurs when the microfabric is parallel to the maximum principal stress where the maximum stress is bedding normal velocity anisotropy decreases as differential stress increases when maximum stress is fabric parallel anisotropy increases elastic anisotropy is related to the initial composition and the spatial distribution of the different minerals fabric in the sediment and the presence of microfractures while changes in elastic anisotropy result from the applied stresses their orientation with respect to the rock fabric and the degree of stress anisotropy

thomsen s parameters from p wave measurements in a spherical sample the aim of this paper is to understand the seismic anisotropy of the overburden shale in an oilfield in the north west shelf of western australia to this end we first find the orientation of the symmetry axis of a spherical shale sample from measurements of ultrasonic p wave velocities in 132 directions at the reservoir pressure after transforming the data to the symmetry axis coordinates we find thomsen s anisotropy parameters and using these measurements and measurements of the shear wave velocity along the symmetry axis from a well log to find these anisotropy parameters we use a very fast simulated re annealing algorithm with an objective function that contains only the measured ray velocities their numerical derivatives and the unknown elasticity parameters the results show strong elliptical anisotropy in the overburden shale this approach produces smaller uncertainty of thomsen parameter than more direct approaches

full wavefield modeling and reverse time migration of laser ultrasound data a feasibility study abstractlaser ultrasound lu data acquired on cylindrical core samples effectively probe the physical properties of geologic materials although most lu analyses focus on estimating and inverting traveltimes of direct arrivals it is important to recognize that lu data sets can have rich wavefield coda and can now be acquired with a sufficient spatial density to enable the application of exploration seismic full wavefield techniques such as reverse time migration rtm and potentially full waveform inversion fwi we have developed a feasibility study that examines the applicability of 2d acoustic forward modeling and 2d rtm analyses on laboratory lu data acquired on cylindrical polymer samples forward modeled waveforms from our numerical tests matched the kinematics of the lu body waves measured through homogeneous samples as well as the scattered wavefield generated by fractures induced in an otherwise homogeneous medium the scattered wavefield is then used in an rtm scheme to directly image mill

a new species of chasmosaurus dinosauria ceratopsia from the dinosaur park formation of southern alberta chasmosaurus irvinensis sp nov is distinguished from other species of this genus by the possession of a broad snout absence of a brow horn the position of which is occupied by a pit or rugosities suggestive of bone resorption broadly rounded and open jugal notch subrectangular squamosal straight posterior parietal bar bearing 10 epoccipitals eight of which are flattened strongly curved anterodorsally and nearly indistinguishably coossified to their neighbours and small transversely oriented parietal fenestrae restricted to the posterior portion of the frill this species restricted to the upper part of the dinosaur park formation is significantly younger than the other recognized canadian chasmosaurus species c belli and c russelli phylogenetic analysis shows that c irvinensis is most closely related to the other canadian chasmosaurus species and more distantly related to chasmosaurus mariscalensis from texas

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

a comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales implication for geomechanical investigations abstractwe obtained the complete set of dynamic elastic stiffnesses for a suite of shales representative of unconventional reservoirs from simultaneously measured p and s wave speeds on single prisms specially machined from cores static linear compressibilities were concurrently obtained using strain gauges attached to the prism regardless of being from static or dynamic measurements the pressure sensitivity varies strongly with the direction of measurement furthermore the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100 compliant cracklike porosity seen in scanning electron microscope images controls the elastic properties measured perpendicular to the rock s bedding plane and results in highly nonlinear pressure sensitivity in contrast those properties measured parallel to the bedding are nearly insensitive to stress this anisotropy to the pressure dependency of the stra

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

quimby iowa scientific drill hole definition of precambrian crustal features in northwestern iowa geophysical data and sparse subsurface samples suggest that the spirit lake trend slt in the aeromagnetic fabric of northwest iowa is the southern boundary of the archean superior craton several small diameter positive aeromagnetic anomalies south of the slt have been interpreted as middle proterozoic anorogenic magnetite bearing granites that intruded juvenile early proterozoic crust a scientific drill hole 609 m deep was drilled into a 1200 gamma aeromagnetic anomaly near quimby iowa to test these interpretations precambrian basement was reached at a depth of 510 m and 99 m of undeformed megacrystic magnetite bearing granite core was collected petrographic and chemical data are consistent with derivation of the granite magma by melting of preexisting tonalitic continental crust a u pb zircon age of 1433 4 ma shows that this granite is part of the older anorogenic granite rhyolite suite of the united states sm nd data yield a depleted mantle separation age of 1860 ma which confirms that the source for the pluton magma was early proterozoic crust all data are consistent with the hypothesis that the aeromagnetic anomalies are caused by middle proterozoic anorogenic plutons and with interpretation of the slt as an archean early proterozoic crustal boundary