fluvial dispersal potential of guanaco bones lama guanicoe under controlled experimental conditions the influence of age classes to the hydrodynamic behavior hydrodynamic sorting is a taphonomic process able to transport and scatter bones deposited in archaeological and paleontological sites this study presents the results of experimentation performed in an artificial flume with guanaco lama guanicoe bones of different ontogenetic development dry and saturated in water in hydric flows velocities of 15 and 30 cm s the obtained results show that bone global density the age of the individual the dry or wet bone state and the hydric flow velocity influence significantly bone dispersion in this way bones from immature individuals with unfused secondary growth centers and relatively low bulk density have better possibility of being transported than fused bones from adult individuals taking into account the results obtained in this experimentation and the feasibility of discriminating age categories in fossil assemblages two bone groups with differential potential transport are presented in this paper these transport groups constitute a methodological tool to evaluate the role hydric current may had played in the formation of a fossil assemblage

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

influence of aquifer heterogeneity and return flow on pumping test data interpretation abstract analytical solutions of drawdown in unconfined aquifers are widely applied for determining the specific yield s y and the horizontal and the vertical hydraulic conductivity k r and k z respectively in many previous studies estimates of s y and k z were observed to be highly variable and physically unrealistic this has been attributed to the conceptualization of flow above the declining water table and aquifer heterogeneity in the applied models we present the analysis of time drawdown data from a pumping test instrumented with depth differentiated observation piezometers arranged in clusters applying homogeneous anisotropic aquifer models in combination with nonlinear least squares parameter identification techniques the data were analyzed in different groups analysis of data from individual piezometer clusters and simultaneous analysis of the entire data set from all piezometer clusters global analysis from the cluster analyses estimates of s y and k z exhibit large variances and depart from a priori estimates inferred from the hydrostratigraphy parameter estimates from the global analysis do not fall within the parameter bounds minimum and maximum values defined by the cluster analyses while heterogeneity appears to be the important reason for large parameter variances we discuss the influence of rarely considered aquifer return flow on drawdown and the inconsistent results from the cluster and global analyses we corroborate our findings with data on hydraulic gradients slug test data and results from the application of a more realistic numerical flow model

taphonomy of old archaeofaunal collections new site formation and subsistence data for the late paleolithic nile valley abstract archaeofaunal remains play an important role in the studies of late pleistocene human adaptations in africa salvage excavations and surveys along the nile valley in the kom ombo plain upper egypt and opposite wadi halfa northern sudan respectively conducted in the 1960s by yale and the university of colorado produced several late paleolithic ca 22 5 14 5 years bp faunal assemblages which have never been published here i present a comprehensive taphonomic and zooarchaeological analysis of the faunal assemblages with the aim of first understanding their integrity through identifying the depositional post depositional and collection biases and second characterizing the latest pleistocene animal economy in the nile valley the faunal assemblages come from both surveys and controlled excavations and in most cases the collections appeared to have been fully retained the excavated remains were deposited in thin horizons representing small camps associated with diverse lithic assemblages and sometimes hearth features in one case the fauna originates from a large cemetery the 6b36 site opposite wadi halfa taphonomic criteria indicate that the faunas are anthropogenic and attest to consumption of predominantly medium and large ungulates as well as hippopotamus the preservation of the material is variable and was chiefly affected by dispersal processes and the pace of burial the assemblages characteristics and their context suggest non intensified animal exploitation and consequently low site occupation intensity in the nile valley during the latest pleistocene

control of the geometry of precursor brittle structures on the type of ductile shear zone in the adamello tonalites southern alps italy abstract amphibolite facies ductile shear zones developed during the immediate post intrusive cooling history of the adamello tonalites southern alps italy shear zones include i thin a few mm s thick fault like shear zones that accommodate shear strain values up to several 100 s the dominant type ii mylonitic horizons dm s thick in sharp contact with the undeformed wall rock iii continuous shear zones with sigmoidal shaped s or composite s c foliations a transition between the different types occurs along strike over short distances discontinuous shear zones are also localized on pegmatite dykes and quartz veins and both i and ii are discontinuously outlined by quartz layers detailed surface mapping reveals that most fault like shear zones are arranged en echelon mainly forming contractional steps markers crosscut by shear zones allow the displacement to be measured at several positions along shear zones and this reveals very steep displacement gradients close to the shear zone tips differential displacement is mainly accommodated at contractional steps by the development of foliated domains geochemical analyses of major and trace elements show that there is no compositional change along strain gradients the overall features are consistent with nucleation of shear zones on former sets of en echelon joints in many cases intruded by pegmatite dykes or filled with quartz reactivation of joints produced strongly localized shear zones whereas broader foliated zones evolved from the contractional jogs between adjacent stepped joint terminations during progressive shearing these jogs were progressively involved in the accommodation of shear displacement and overall shear zone development

modeling the effect of clay drapes on pumping test response in a cross bedded aquifer using multiple point geostatistics this study investigates whether small scale clay d rapes can cause an anisotropic groundwater pumping test response at a much larger scale the measured drawdown values from a pumping test in the cross bedded brussels sands aquifer belgium reveal an elliptical shaped pumping cone the major axis of the pumping ellipse is parallel with the strike of small scale clay drapes that are observed and measured in several outcrops this stu dy investigates 1 whether this large scale anisotropy can be the result of sm all scale clay drapes and 2 whether application of multiple point geostatistics can improve the analysis of pumping tests this study uses the technique of di rect multiple point geostatistical simulation of edge properties which enables simulating thin irregularly shaped surfaces with a smaller cpu and ram demand than the conventional multiple point statistical methods th e proposed method uses model cell edge properties for indicating the presence of thin irregularly shaped surfaces instead of pixel values model cell edge properties such as edge transmissibility indicating the presence of irregularly shaped surfa ces are simulated using the multiple point geostatistical algorithm snesim the modelling strategy of this study consists of the following steps first a tra ining image displaying clay drape occurence is constructed secondly this small grid cell size training image is converted into an upscaled edge training image whic h is used as input training image to perform snesim simulations the resulting simulations indicate at which cell edges horizontal or vertical clay drapes are present this information is incorporated in a local 3d groundwater model of the pumping test site by locally adapting vertical leakance values and by locally in serting horizontal flow barriers all hydraulic parameters including the clay drapes properties are calibrated using the measured drawdown time series in six observatio n wells results show that the anisotropic pumping cone can be attributed to the p resence of the clay drapes

sampling procedure for small scale heterogeneities crossbedding for reservoir modelling sampling permeability from individual laminae in crossbedded rocks is very well possible by making use of a so called probe permeameter the methodology and calculation of permeabilities from the output of this instrument are fairly well established however what is hardly established is a sampling strategy that guarantees adequate representation of permeability contrast between laminae especially so because finer foreset and bottomset are difficult to sample yet their permeabilities are critical to fluid flow through a crossbed therefore we propose to systematically sample laminae to this end we suggest a sampling strategy that is adapted to the heterogeneity under study namely to the thickness of the finer foreset

late magmatic healed fractures in granitoids and their influence on subsequent solid state deformation abstract late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and or leucocratic veins but have not been previously described such biotite rich trails with lengths of a few centimetres to several tens of centimetres widths of a few millimetres and a variable orientation are ubiquitous in meta granitoids of the neves area tauern window eastern alps italy these pre alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the alpine orogeny allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid state ductile shear zones to be directly assessed numerical models considering power law viscous materials predict that planar arrays of a weaker mineral e g biotite oriented at around 45 to the shortening direction should nucleate and localize viscous deformation however no discernible localization on the natural small scale biotite trails is observed even when they delineate planes that were well oriented for shear reactivation in contrast heterogeneous shear zones nucleated on larger scale 1 10 m long planar compositional or structural boundaries such as joints dykes quartz veins alteration layers surrounding veins and zones of magma mingling outlined by densely packed clusters of basic enclaves irrespective of their orientation relative to the imposed shortening direction clearly some crucial aspect is missing from purely viscous numerical models we propose that this missing aspect is the observed interplay between fracture and flow with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre existing healed magmatic fractures natural granitoids have a truly elasto plasto viscous rheology even at low differential stress as in the neves example and for high grade metamorphic conditions considered as typical of wet ductile middle crust

islands in a stream reconstructing site formation processes in the late middle paleolithic site of ein qashish northern israel abstract information retrieved from open air sites is necessary for a more complete reconstruction of middle paleolithic behaviors which is currently often based mainly on data from caves and rockshelters however open air sites present methodological and analytical challenges that differ from those encountered in cave sites being essentially an integral part of their paleo landscape open air sites are affected by localized as well as landscape scale processes that need to be distinguished from the anthropogenic signatures ein qashish is an open air late middle paleolithic occurrence located in the yizra el valley just east of mt carmel situated on the pleistocene floodplain of the qishon stream the site is found at the interface of the sediments deposited by the qishon stream which drains the yizra el valley and paleo wadi qashish which flowed off mt carmel artifacts and bones are dispersed over a vertical distance of some 90 cm observations in geological trenches located at variable distances from the excavated area indicate that this cluster of finds occurred at a circumscribed locality on the landscape rather than as a part of a continuous distribution on the paleo surface we reverse engineer site formation processes starting with the latest post depositional moving to earlier syn depositional processes and relate them to their most likely causative agents through the examination of a series of explicit models gis techniques were applied in order to parse the variable lines of information which include lithic and faunal taphonomy size distributions and spatial and stratigraphic dispersal of objects fabric analysis and osl results we discuss the implications of the results for distinguishing anthropogenic from non anthropogenic effects and for reconstructing the timeline of depositional events that led to the current distribution of artifacts insights into these questions inform our understanding of human activities at the site suggesting that the excavation samples the margins of an occupation horizon where activities focused on knapping and resource processing rather than task specific behaviors such as hunting

control of the geometric arrangement of material heterogeneities on strain localization at the brittle to ductile transition in experimentally deformed carbonate rocks abstract triaxial high temperature 900 c deformation experiments were conducted at constant strain rate in a paterson type deformation apparatus on cylinders of carrara marble with two right or left stepping non overlapping weak inclusions of solnhofen limestone oriented at 45 to the cylinders longitudinal axes applying different values of confinement 30 50 100 and 300 mpa we induced various amounts of brittle deformation in the marble matrix and investigated the effect of brittle precursors on the initiation and development of heterogeneity induced high temperature shear zones viscosity contrast between the matrix and the inclusions induces local stress concentration at the tips of these latter the initial arrangement of the inclusions results in either an overpressured contractional or underpressured extensional domain in the step over region of the sample at low confinement 30 and 50 mpa abundant brittle deformation is observed but the spatial distribution of microfractures is dependent on the kinematics of the step over region microcracks occur either along the shearing plane between inclusions in extensional bridge samples or broadly distributed outside the step over region contractional bridge samples accordingly ductile deformation localizes along the inclusions plane in the extensional bridge samples as opposed to distributing over large areas of the matrix in the contractional bridge samples if microcracking is suppressed high confinement strain is accommodated by viscous creep and strain progressively de localizes in extensional bridge samples our experiments demonstrate that brittle precursors enhance the degree of localization in the ductile deformation regime but only if the interaction of pre existing heterogeneities induces an extensional mean stress regime in between

taphonomic and paleoecologic investigations of the late cretaceous santonian iharkut vertebrate assemblage bakony mts northwestern hungary abstract the iharkut vertebrate locality an open pit mine in the bakony mountains western hungary has provided a rich and diverse assemblage of late cretaceous santonian continental vertebrates the isolated and associated remains represent 31 different taxa including fish amphibians turtles lizards pterosaurs crocodilians non avian dinosaurs and birds sedimentologic investigations suggest that the iharkut depositional environment was represented by the floodplain of a very low gradient river the 10 50 cm thick bonebed of site sz 6 is the most important fossiliferous layer in the open pit mine and analysis of this site indicates alternating energy conditions during the bone accumulation which resulted in fossils of different states of preservation being deposited together the vertebrate assemblage of site sz 6 includes three main different subsets with widely different taphonomic history the characteristics and the preservation mode high rate of abrasion and the spherical shape of the bone pebbles suggest that this type of the isolated bones was more exposed to abrasion and probably the remains were transported from farther away than the other isolated bones the second group includes 88 of the iharkut collection containing most of the identified isolated bones and teeth and represents polytypic attritional remains transported and deposited by high density flow during ephemeral flood events meanwhile the monospecific ankylosaur skeletal material from iharkut site sz 6 may represent a mass death assemblage because seven skeletons of hungarosaurus were discovered from an area of approximately 400 m 2 and in many cases close to each other in the same layer the iharkut vertebrate assemblage is dominated by bones of aquatic semi aquatic animals while the number of terrestrial animal remains is subordinate the taphonomic analysis of the ankylosaur material from iharkut locality further strengthens the previously suggested hypothesis that some of the ankylosaurs preferred wetland habitats e g areas along fluvial systems while the other two herbivorous dinosaur groups from iharkut ornithopods and ceratopsians were probably living in distal habitats

microstructures and rheology of hydrous synthetic magmatic suspensions deformed in torsion at high pressure the relationship between magma rheology and characteristic magmatic microstructures was investigated by performing high temperature high pressure deformation experiments on hydrous synthetic magmatic suspensions in the range of 0 to 76 solid fraction alumina grains torsion experiments were conducted at 300 mpa confining pressure temperatures ranging from 475 c to 1000 c and shear strain rates ranging from 2 0 10 5 to 2 1 10 3 s 1 up to total strains of 21 3 flow is newtonian for a solid fraction of s 0 0 0 16 with a log dynamic viscosity 10 3 pa s t 500 c a deviation from newtonian behavior is observed for s 0 16 with an increase in apparent viscosity of about 1 order of magnitude between s 0 16 and 0 54 the shape fabric of the solid phase is characterized by a unimodal orientation that is almost stable and nearly parallel to the shear direction both shape fabric and deviation from newtonian behavior originate from the increase in the number of particle clusters in the suspension the apparent viscosity increases by 1 5 orders of magnitude between s 0 54 and 0 65 and extrapolation of the data suggests a very sharp increase in apparent viscosity for s 0 65 at t 550 c and s 0 54 the solid phase forms an almost entirely connected network composed of two alternating orientation domains at t 550 c and s 0 65 intragranular fracturing and tensile fractures result from high local stresses at contact points between neighboring particles the resulting bulk extensional fabric is almost parallel to the shortening direction

autochthonous anisotropy of archaeological materials by the action of water experimental and archaeological reassessment of the orientation patterns at the olduvai sites abstract anisotropic patterns documented indirectly through m leakey s drawings of olduvai archaeological sites have led to questions about the integrity of these sites most experiments on bone transport by water have been carried out using complete elements that do not replicate specimen bone breakage and size as documented in archaeological sites in the present work an experimental framework is provided using experimental proxies of archaeological assemblages results show that autochthonous assemblages affected by hydraulic processes can adopt anisotropy in their fabric archaeological comparisons between drawings and excavated sites at olduvai stress the bias in leakey s drawings of flk zinj and flk north in bed i a large scale open excavation recently carried out at tk bed ii exposes an area comparable in size to leakey s excavations comparing the orientation patterns of this site to those reported by leakey shows how biased the drawing of the site is and how easily this can lead to misinterpretations of isotropy anisotropy with fatal consequences for the understanding of site formation processes

brittle ductile brittle deformation during cooling of tonalite adamello southern italian alps abstract late to post magmatic deformation in slightly diachronous contiguous intrusions of the north western adamello batholith southern alps italy is recorded as from oldest to youngest i joints ii solid state ductile shear zones iii faults associated with epidote k feldspar veins and iv zeolite veins and faults structures ii to iv are localized on the pervasive precursory network of joints i which developed during the earliest stages of pluton cooling high temperature 500 c ductile overprinting of joints produced lineations defined by aligned biotite and hornblende on the joint surfaces and highly localized mylonites the main phase of faulting producing cataclasites and pseudotachylytes occurred at 250 c and was associated with extensive fluid infiltration cataclasites and pseudotachylytes are clustered along different e w striking dextral strike slip fault zones correlated with the activity of the tonale fault a major tectonic structure that bounds the adamello batholith to the north ductile deformation and cataclastic veining episodes occurred at p 0 25 0 3 gpa during rapid cooling of the batholith to the ambient temperatures 250 c that preceded the exhumation of the batholith timing of the sequence of deformation can be constrained by 39 ar 40 ar ages of 30 ma on pseudotachylytes and various existing mineral ages in the whole composite adamello batholith multiple magma pulses were intruded over the time span 42 30 ma and each intrusive body shows the same ductile to brittle structural sequence localized on the early joint sets this deformation sequence of the adamello might be typical of intrusions undergoing cooling at depths close to the brittle ductile transition

spatial and size distributions of garnets grown in a pseudotachylyte generated during a lower crust earthquake abstract in the bergen arc western norway rocks exhumed from the lower crust record earthquakes that formed during the caledonian collision these earthquakes occurred at about 30 50 km depth under granulite or amphibolite facies metamorphic conditions coseismic frictional heating produced pseudotachylytes in this area we describe pseudotachylytes using field data to infer earthquake magnitude m 6 6 low dynamic friction during rupture propagation d

taphonomy of some articulated skeletal remains transport potential in an artificial environment flume experiments demonstrated that disarticulated bones did not display the same behaviour when combined as articulated elements the character of movement and rates of movement were recorded skeletal elements were identified as displaying either a transportable or a non transportable potential some of which were common to all three species that were tested the experiments demonstrated that articulated bones displayed a greater transport potential and that in one species the rate of movement was significantly faster than when disarticulated it is suggested that the taphonomic history of a fluvial transported assemblage could be misinterpreted if the bones were treated as a mixture of individually transported elements

petrologic constraints on imbrication metamorphism and uplift in the sw tauern window eastern alps the pressure temperature time deformation pttd history of two tectonic units in the southwest tauern window austria italy is evaluated from p t paths of metamorphism and uplift geochronologic data and observations on fabric development petrologic data indicate burial of the lower schieferhulle lsh to depths of 35 km and the adjacent upper schieferhulle ush to only 24 28 km the units are now separated by only 2 km of section metamorphism was postkinematic in the lsh and synkinematic in the ush correlation of p t path reversals calculated from zoned garnets in the two units however indicates that juxtaposition of the lsh and ush occurred prior to metamorphism temperature time and depth time diagrams for both units show increasing cooling rates and decreasing uplift rates as the rocks approached the surface both the petrologic data and the depth time profiles for the lsh and ush point to a history of differential uplift in the early stages of decompression textural features indicate that the lsh behaved as an essentially rigid body during uplift whereas the ush experienced extensive ductile shearing the pttd data for the lsh and ush are incorporated into a model for continental collision in the eastern alps initial tectonic uplift of the lsh was accompanied by ductile thinning of the ush and overlying austroalpine units final uplift and erosion affected all of the units en masse

single layer buckle folding in non linear materials i experimental study of fold development from an isolated initial perturbation abstract scale model experiments involving pure shear compression of a single layer embedded in a weaker matrix were carried out to study the influence of a pre existing isolated perturbation in the shape of an otherwise planar layer on the location and shape of folds different grades of paraffin wax were used as analogues for rocks with power law rheology the wax used for the matrix flows in steady state with a stress exponent of about 3 8 the layer has a stress exponent of about 3 and strain softens viscosity ratios considered at yield stress for the layer and matrix of 30 1 and 8 1 were used bell shaped perturbations were introduced into the layer with initial average wavelengths of 8 16 and 32 times layer thickness and corresponding initial limb dips of 12 5 and 3 respectively the fold packet develops at the site of the introduced perturbation and spreads slowly along the layer with increasing shortening the shape of the initial perturbation strongly influences the fold geometry broader initial perturbations develop broader folds undergo more layer parallel shortening and develop a wider zone of contact strain the influence of the introduced perturbation shape is most marked when its average wavelength component is larger than the dominant wavelength i e the wavelength of maximum growth rate the degree of bonding between layer and matrix also influences fold development folds with welded layer matrix boundaries amplify much more slowly with a greater proportion of layer parallel shortening than folds where slip between layer and matrix is promoted

on the petrology of brittle precursors of shear zones an expression of concomitant brittle deformation and fluid rock interactions in the ductile continental crust the inherited localization model for shear zone development suggests that ductile deformation in the middle and lower continental crust is localized on mechanical anisotropies like fractures referred to as shear zone brittle precursors in the neves area western tauern window eastern alps although the structural control of these brittle precursors on ductile strain localization is well established the relative timing of the brittle deformation and associated localized fluid flow with respect to ductile deformation remains in most cases a matter of debate the present petrological study carried out on a brittle precursor of a shear zone affecting the neves metagranodiorite aims to determine whether brittle and ductile deformations are concomitant and therefore relate to the same tectonic event the brittle precursor consists of a 100 500 m wide recrystallized zone with a host mineral controlled stable mineral assemblage composed of plagioclase garnet quartz biotite zoisite white mica pyrite plagioclase and garnet preserve an internal compositional zoning interpreted as the fingerprint of alpine metamorphism and fluid rock interactions concomitant with the brittle deformation phase equilibrium modelling of this garnet bearing brittle precursor shows that metamorphic garnet and plagioclase both nucleated at 0 6 0 05 gpa 500 20 c and then grew along a prograde path to 0 75 0 05 gpa 530 20 c these amphibolite facies conditions are similar to those inferred from ductile shear zones from the same area suggesting that both brittle and ductile deformation were active in the ductile realm above 500 c for a depth range between 17 and 21 km we speculate that the neves area fulfils most of the required conditions to have hosted slow earthquakes during alpine continental collision that is coupled frictional and viscous deformation under high fluid pressure conditions 450 c further investigation of this potential geological record is required to demonstrate that slow earthquakes may not be restricted to subduction zones but are also very likely to occur in modern continental collision settings

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

groundwater flow and solute transport in fractured lacustrine clay near mexico city a network of piezometers was installed in a surficial lacustrine clay aquitard overlying a thin saline water aquifer of volcanoclastic origin at a study site near mexico city in the basin of mexico the aquifer is underlain by additional lacustrine sediments which in turn overlie a thick regional freshwater aquifer the regional aquifer provides approximately 70 of the water supply for 20 million people in the basin of mexico in the study area major ions oxygen 18 and deuterium in the pore water of the surficial aquitard exhibit large variations with depth the nature of these variations suggests that the saline pore water is being displaced downward by infiltrating meteoric water the infiltration has been induced by strong downward hydraulic gradients imposed two to three decades ago when heavy aquifer pumping of the thin saline water aquifer began one dimensional analytical models representing solute transport in both fractured and unfractured porous media were used to simulate the geochemical profiles in the surficial aquitard the fractured porous medium model using a realistic mean hydraulic gradient and fracture spacing 1 5 m and small but significant fracture aperture 30 m provide nearly an exact match to the field data from this we infer that because of vertical fractures there is a much greater potential for downward leakage of water and contaminants through the mexico city clay into underlying aquifers than has been previously thought

autochthony and orientation patterns in olduvai bed i a re examination of the status of post depositional biasing of archaeological assemblages from flk north flkn recent excavations at flk north olduvai gorge tanzania have produced new information on the orientation of archaeological materials at various levels of the site this information includes the uniform distribution of material azimuths which contrasts with previous inferences of highly patterned orientations of materials in the bed i archaeological sites those previous inferences of patterned material orientations are based on mary leakey s 50 year old drawings of artifact and fossil bone distribution but are not verified by our precise measurements of archaeological objects made in situ nor do those previous results agree with the general lack of geological geomorphological and or taphonomic data that would indicate significant post depositional movement of archaeological materials in the sites we argue here that leakey s drawings are incomplete only portions of each assemblage were drawn and inaccurate in their representation of the original locations shapes and orientations of most archaeological specimens this argument is supported by several important mismatches in object representations between a photograph taken of a small portion of the flk 22 zinjanthropus site floor before the removal of the archaeological items and the sketch of the same area drawn by leakey thus we conclude that primary orientation data of excavations i e direct measurements taken from items generated prior to object removal are the only valid indicators of the relative isotropy or anisotropy of these important paleoanthropological assemblages

fluvial transport of bovid long bones fragmented by the feeding activities of hominins and carnivores this study explores the hydraulic transportability of bovid long bone fragments created through hominin and carnivore carcass consumption in order to determine the effect of fluvial transport on the incidences of hominin and carnivore induced bone surface modifications transportability was determined using an oval race track flume and 311 long bone fragments from modern control collections of hominin and carnivore modified bone results show that the fluvial transport of long bone fragments is predicted by animal size class and bone specimen size as measured by maximum cortical thickness maximum length and maximum width all of these variables can be measured on fossil specimens long bone portion midshaft near epiphysis and epiphysis does not affect transport and hydraulic transport does not substantially modify the incidences of tooth percussion and cut marking in transported or lag assemblages in low energy fluvial environments implications of this study are 1 animal size classes and cortical thickness length and width of long bone fragments can be used to identify fluvial winnowing in fossil assemblages 2 analyses concerning the relative timing of hominin and carnivore carcass consumption based on the proportions of long bone fragments bearing tooth percussion or cut marks can be meaningfully applied to fossil assemblages deposited in low energy fluvial environments

bayesian data fusion for water table interpolation incorporating a hydrogeological conceptual model in kriging 1 the creation of a contour map of the water table in an unconfined aquifer based on head measurements is often the first step in any hydrogeological study geostatistical interpolation methods e g kriging may provide exact interpolated groundwater levels at the measurement locations but often fail to represent the hydrogeological flow system a physically based numerical groundwater model with spatially variable parameters and inputs is more adequate in representing a flow system because of the difficulty in parameterization and solving the inverse problem however a considerable difference between calculated and observed heads will often remain in this study the water table interpolation methodology presented by fasbender et al 2008 in which the results of a kriging interpolation are combined with information from a drainage network and a digital elevation model dem using the bayesian data fusion framework is extended to incorporate information from a tuned analytic element groundwater model the resulting interpolation is exact at the measurement locations whereas the shape of the head contours is in accordance with the conceptual information incorporated in the groundwater flow model the bayesian data fusion methodology is applied to a regional unconfined aquifer in central belgium a cross validation procedure shows that the predictive capability of the interpolation at unmeasured locations benefits from the bayesian data fusion of the three data sources kriging dem and groundwater model compared to the individual data sources or any combination of two data sources

the interaction of viscous heating with grain size dependent rheology in the formation of localized slip zones the formation of localized shear zones is important for understanding many local and global processes in geodynamics we have developed a self consistent thermal mechanical model together with a rheology which depends on temperature strain rate and grain size distribution the grain size distribution has contributions from both dynamic recrystallization and grain growth processes and is governed locally by a nonlinear ordinary differential equation a one dimensional model with 104 points is employed to resolve all of the scales involving grain size and temperature we found that grain growth inhibits the development of shear zones and that there is a delicate interplay between viscous heating and grain growth process in determining whether narrow fault zones are developed quickly for realistic parameters of rheology and grain boundary processes for wet olivine the magnitude of the rate of grain growth is crucial to determine whether shear zones are stable or unstable at temperature t 1000 k or shear stress 100 mpa

nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions abstract in the neves area the pre alpine intrusive protolith of the zentralgneise unit tauern window eastern alps is well preserved in a kilometric scale low strain domain without pervasive alpine deformation it is compositionally heterogeneous consisting predominantly of granodiorites with lesser leucocratic granites and different generations of lamprophyres and aplites the intrusive rocks are crosscut by fractures that were locally infiltrated by fluids and surrounded by alteration haloes incipient alpine amphibolite facies ductile deformation is strongly localized on these precursor fractures and on lithological planar heterogeneities resulting in the development of several different types of shear zones fractures without alteration haloes initially accommodate slip entirely on the fracture itself with increasing deformation a foliation is progressively developed in the adjacent host rock eventually producing a single heterogeneous ductile shear zone with the typical sigmoidal foliation pattern strong layers aplite dykes and bleached alteration haloes developed to either side of precursor fractures localize shear on their boundaries to produce characteristic paired shear zones shearing is more evenly distributed within weak layers lamprophyres and quartz veins with a marked discontinuity in shear strain against the adjacent little deformed granodiorite shear zone development was accompanied by the formation of new fractures and quartz rich veins in the host rock which in turn also localized shear magmatic contacts fractures and quartz veins are mostly steeply dipping and effectively span the complete range of strike orientations the kinematics of the overprinting strike slip shear zones was determined by the orientation of the initial discontinuities relative to the local principal compressive stress axis 1 here oriented ca 345 discontinuities of almost all orientations show shear reactivation even in the case of very low resolved shear stress indicating an overall viscous response of the system without a specific yield stress the geometry and kinematics of the shear zone network suggest that the overall deformation in low strain domains was close to coaxial during deformation along the shear zone network compatibility was maintained by fracturing with the development of new quartz veins and by distributed ductile deformation of the host rock especially within contractional domains of the shear network and at shear zone intersections deformation never propagates into the undeformed homogeneous granodiorite as discrete ductile shear zones but is limited by the original extent of the precursor discontinuities shear zone development in intact rock is always preceded by fracturing which localizes subsequent shear reactivation

emplacement related deformation of granitoid magmas southern adamello massif italy the lago della vacca suite in the tertiary adamello massif italian alps is a small 10 km 2 crudely zoned granitoid pluton emplaced at a pressure of 3 5 kbar into folded mesozoic sediments and precursor intrusive rocks field relations and detailed mapping reveal a temporal evolution in the style of emplacement from early passive stoping by the mafic to intermediate composition marginal units to later forceful emplacement of the more silicic core marginal units of the pluton have highly discordant stoped outer contacts against folded triassic carbonates and precursor mafic ultramafic rocks in contrast the core units have steeply inward dipping contacts against these marginal units magmatic foliations defined by the planar alignment of plagioclase amphibole and biotite and by mafic enclaves are well developed in all units they describe steeply inward dipping concentric trajectories that approximately parallel unit contacts and in general increase in intensity toward the pluton margin lineations are rarely present the most intensely foliated rocks occur in the marginal units as anastomosing sinuous bands that wrap around lenses of less intensely foliated granitoid three dimensional strain analysis using mafic enclaves from throughout the pluton indicates that these bands represent zones of very high strain strain ellipsoids are weakly prolate within the core of the pluton becoming increasingly oblate as strain increases toward the pluton margin the short axis z of the strain ellipsoid is uniformly subnormal to the foliation suggestive of radial flattening textures of the marginal rocks which record high strain coupled with amphibole plagioclase thermometry indicate that deformation occurred in the magmatic or submagmatic state 650 780 c and was accompanied by significant migration of interstitial melt the documented transition from passive to forceful emplacement and final geometry of the suite resulted from temporal changes in the rheology of both the magma and adjacent country rocks pulses of low density hydrous magma were initially emplaced by stoping denser country rocks on cooling and solidification these magmas contracted by 15 20 creating an unpressured volume which allowed subsequent magma pulses to be emplaced into the pluton core these pulses distended and flattened their partially molten carapace and those parts of the aureole that had been thermally softened by intrusion of earlier magmas emplacement of the lago della vacca suite was therefore the product of several internal or magma related processes an interaction between stoping radial expansion and volume contraction on solidification of the hydrous magmas the heterogeneous distribution of strain in the marginal units reflects local variations in temperature and most importantly in the distribution of interstitial melt during emplacement

reconstructing taphonomic histories using histological analysis abstract recent years have seen rapid advances in the understanding of diagenetic changes to bone tissues and how these influence the chemistry microstructure and histological appearance of ancient bone it is now possible to recognise many characteristic features of diagenetically modified bone and this has led to the potential use of these parameters in estimating the potential survival of biogenic signals such as dna lipids proteins and stable isotopes these characteristic features also hold the potential for preserving a record of different post mortem environments in individual bones or assemblages of bones from the same site in sites where the burial conditions have changed over archaeological or geological timescales histological analyses can shed light on these different burial environments and permit the reconstruction of taphonomic histories of some bones examination of polished sections of bone using bse sem has been used to identify characteristic features attributed to aerobic soil bacteria cyanobacteria and sulphate reducing bacteria the approach shows promise for providing supplementary evidence when phasing complex sites such as graveyards which developed over several hundred years

testing heterogeneity in faunal assemblages from archaeological sites tumbling and trampling experiments at the early middle pleistocene site of gesher benot ya aqov israel abstract the current paper reports an experimental case study to test the heterogeneity of faunal assemblages from the early middle pleistocene layers v 5 and v 6 of the gesher benot ya aqov acheulian site israel tumbling and trampling experiments were initiated to gain qualitative insight into processes of bone modification and to assess the timing of the biostratonomic chronology as it was assumed that both mechanisms were responsible for the formation of striations documented on the bone surfaces from the site the tumbling experiments mimicked sediment movement in a calm lacustrine shoreline environment whereas the trampling experiments investigate the role of animal hominin activities in dry muddy and wet environments models for the internal operational sequence of an abrasional process due to uni and multidirectional water movement and of a trampling scenario are presented these models are used for the interpretation of the fauna from gesher benot ya aqov

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

three dimensional high resolution fluvio glacial aquifer analog part 2 geostatistical modeling summary the heterogeneity of sedimentary structures at the decimeter scale is crucial to the understanding of groundwater flow and transport in a series of two papers we provide a detailed analysis of a fluvio glacial aquifer analog the herten site the geological data along a series of 2d sections in a quarry the corresponding gpr measurements and their sedimentological interpretation are described in the companion paper in this paper we focus on the three dimensional reconstruction of the heterogeneity the resulting numerical model is provided as an electronic supplementary material for further studies furthermore the geostatistical parameters derived from this analysis and the methodology described in the paper could be used in the future for the simulation of similar deposits where less data would be available to build the 3d model we propose a hierarchical simulation method which integrates various geostatistical techniques first we model the subdivision of the domain into regions corresponding to main sedimentological structures e g a sedimentation event within these volumes we use multiple point statistics to describe the internal heterogeneity what is unusual here is that we do not try to use a complex training image for the multiple point algorithm accounting for all the non stationarity and complexity but instead use a simple conceptual model of heterogeneity ellipsoidal shapes as a training image and constrain the multiple point simulations within the regions by a detailed interpolation of orientation data derived from the 2d sections this method produces realistic geological structures the analysis of the flow and transport properties hydraulic conductivity and tracer breakthrough curves of the resulting model shows that it is closer to the properties estimated directly from the 2d geological observations rather than those estimated from a model of heterogeneity based on probability of transitions and not including the modeling of the large scale structures

high temperature fracturing and ductile deformation during cooling of a pluton the lake edison granodiorite sierra nevada batholith california abstract in the bear creek area of the sierra nevada batholith california the high temperature postmagmatic deformation structures of the lake edison granodiorite include steeply dipping orthogneiss foliations joints and ductile shear zones that nucleated on joints and leucocratic dykes exploitation of segmented joints resulted in sharply bounded thin shear zones and in large slip gradients near the shear zone tips causing the deformation of the host rock at contractional domains the orthogneiss foliation intensifies towards the contact with the younger mono creek granite and locally defines the dextral rosy finch shear zone rfsz a major kilometre wide zone crosscutting the pluton contacts joints predominantly strike at n70 90 e over most of the lake edison pluton and are exploited as sinistral shear zones both within and outside the rfsz in a narrow 250 m thick zone at the contact with the younger mono creek granite within the rfsz the lake edison granodiorite includes different sets of dextral and sinistral shear zones joints the latter corresponding to the set that dominates over the rest of the lake edison pluton these shear zones joints potentially fit with a composite y r r shear fracture pattern associated with the rfsz or with a pattern consisting of y r shear fractures and rotated t mode i extensional fractures the mineral assemblage of shear zones and the microstructure and texture of quartz mylonites indicate that ductile deformation occurred above 500 c joints and ductile shearing alternated and developed coevally the existing kinematic models do not fully capture the structural complexity of the area or the spatial distribution of the deformation and magmatic structures future models should account more completely for the character of ductile and brittle deformation as these plutons were emplaced and cooled

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

steppe mammoth mammuthus trogontherii remains in their geological and cultural context from belchatow poland a consideration of human exploitation in the middle pleistocene abstract in 1981 and 1991 mammoth remains and associated fauna were found in central poland at the belchatow opencast mine in sandy gravel deposits most of them lay at approximately 160 175 m above mean sea level a s l located in the lower and upper members of the alluvial chojny formation this formation belongs to the middle pleistocene and can be connected with the mazovian mis 11 holsteinian or zbojnian mis 9 reinsdorf interglacial the belchatow mammoth assemblage described here consists of cranial and postcranial elements analysis of their morphological characteristics and osteometrics are used to demonstrate that at least two molars and one tusk belong to mammuthus trogontherii and that the tusk belonged to a male on the basis of the minimum number of elements of the most common element left incisors the mammoth remains represent at least two individuals based upon the different ages of death for the various elements it appears that they represent several individuals the bulk of the mammoth remains were recovered from the oldest depositional cycle in the lower member of chojny formation and are therefore coincident with a shrub tundra environment and cool temperate conditions they were deposited in sediments formed by a meandering river with a fairly low power of flow and were buried soon after transport over a short distance this conclusion is also supported by the palaeobotanical data an additional element a costa was recovered from the upper member of the chojny formation which is associated with the cooling conditions the enveloping deposit appears to be the result of a series of more rapid discharge events by a braided river this element is distinguished from those elements recovered from the lower member due to the presence of a series of unusual striations sem analysis suggests that some of the striations were probably made by chipped stone tools used in a slicing action as if the result of the filleting of flesh from the rib area the time frame for the depositional context of the costa suggests that the striations may have been made by one of several possible human taxa that occurred in central europe during this period including homo heidelbergensis given the dearth of human skeletal remains from this region and time period this represents the earliest and only example of middle pleistocene human butchering activity in poland the remains discussed in this paper are presented in light of their depositional and cultural contexts which not only increases our knowledge of the occurrence of m trogontherii in poland but also provides increased evidence for lower palaeolithic human activity in central europe during an early interglacial

holocene large mammal mass death assemblage from south africa abstract a fossilised large mammal bonebed was discovered eroding out of a gully in the free state of south africa the bonebed is 1 5 m below the modern land surface and extends over an area 35 13 m surface scatters of stone tools occur in a 1 km radius of the site and a large fire place associated with spirally fractured burnt bone is preserved to one side the purpose of this research was to excavate and taphonomically analyse the faunal sample to elicit the cause of death and radiocarbon date it to establish when it happened the bonebed is represented by black wildebeest including juvenile and adult individuals faunal remains are randomly oriented and many are complete weathering stage 1 on most of the bones together with the articulation pattern suggest that the carcasses were exposed for more than a year and less than three before being buried by hillslope sediment two thirds of those fractured record a spiral breakage pattern there are a few trample marks on bones and evidence of some termite activity no stone tools were found in the section of bonebed we excavated and there is no evidence of manmade or carnivore damage on the fauna calcrete nodules in the underlying deposits and phytoliths representative of desertification throughout the sedimentary sequence suggest that the animals died under drought conditions between 3840 40 and 3500 40 cal bp and that human activity at the site was marginal

the viscous brittle transition of crystal bearing silicic melt direct observation of magma rupture and healing magmas may fl ow or break depending on their deformation rate the transition between such viscous and brittle behavior controls the style of volcanic eruptions while the brittle failure of silicate melts is reasonably well characterized the effect of crystals on the viscous brittle transition has not yet been constrained here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures 600 900 c strain rates 10 4 10 1 s 1 and confi ning pressures 200 300 mpa relevant for volcanic systems we present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction furthermore the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present the fractures formed during brittle failure of crystal bearing magma originate in the melt phase which enables gas to escape and hence to reduce gas overpressure these degassing pathways heal on relatively short time scales owing to the high confi ning pressure at depth highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing

identifying discrete geologic structures that produce anomalous hydraulic response an inverse modeling approach 1 subsurface hydraulic response is controlled by discrete geologic structures in a variety of aquifer settings in this work we analyze data from the well studied alluvial fan system that underlies the lawrence livermore national laboratory there subsurface flow and transport behavior is strongly influenced by discrete channel deposits which are embedded within less permeable floodplain deposits we model the distribution of these deposits using a multiple point geostatistical approach that enables simulation of geologically plausible connected permeable bodies consistent with a training image by coupling the geostatistical model with a dynamic flow model in a simulation inversion framework we identify specific channel structures that are consistent with transient aquifer test data at six observation wells we perform shortest path analysis to characterize the geometry of the simulated channels and to locate critical high permeability conduits that control the system s response to pumping in one area all successful inverse solutions identify the same set of stacked channel deposits a geologic feature that provides an explanation for anomalous response behavior observed during the aquifer test

gombore ii melka kunture ethiopia a new approach to formation processes and spatial patterns of an early pleistocene acheulean site abstract to assess the integrity of pleistocene archaeological sites is crucial in the analysis of human behaviour most of the early palaeolithic sites are in active fluvial environments where it is necessary to understand the degree of sedimentary disturbance the analysis of the formation processes through geoarchaeological and geostatistical techniques offers new tools to evaluate if the archaeological assemblage is in autochthonous or allochthonous position gombore ii 850 ka within the archaeological and paleontological complex of melka kunture ethiopia extends over estimated 1000 m2 and yielded a large number of acheulean artefacts fossil mammal bones and two fossil hominin remains the geomorphological setting and deposition patterns of high energy sedimentation in a fluvial channelized environment are similar to those of many other early palaeolithic african sites this is traditionally described as producing a disturbed record with the fortuitous association of faunal remains and lithic industry driven by fluvial processes to assess this hypothesis we analyse here the formation processes and the spatial patterning of the remains we apply geoarchaeological orientation and fabric and spatial tests density grouping k means to the mapped archaeological surfaces and to a present day fluvial surface we observe substantial differences in geoarchaeological features and spatial patterning between the archaeological record lithic materials and faunal remains and the natural clasts of both the archaeological deposit and the bed of the present day river this suggests different depositional processes or temporal events we conclude that the remains produced by the hominins did not haphazardly accumulate after extensive erosion and re sedimentation they rather preserve a reasonable degree of taphonomic and spatial integrity and are possibly representative of different activities

one bone two bones wet bones dry bones transport potentials under experimental conditions flume experiments demonstrated that bones had varying hydraulic transport potentials depending on whether the bones were wet or dry articulated or disarticulated when placed into a water flow dry and articulated bones demonstrated the greatest transport potential while wet and disarticulated bones demonstrated the least the velocity at which bones were transported was plotted against a range of attributes such as the shape weight volume and density of the bones with varying degrees of success although several attributes did prove to be significant as indicators of bone transport potential no single attribute emerged as more useful than another

thermal mechanical effects of low temperature plasticity the peierls mechanism on the deformation of a viscoelastic shear zone we studied for the first time the effects of low temperature plasticity on the formation of shear zones a thermal mechanical model has been developed for describing the shear deformation of maxwell viscoelastic material with a rheology close to dry olivine we employed a one dimensional model with a half width of l deforming under a constant velocity u at the boundary and the spatially averaged strain rate u l was set to o 10 14 s 1 in addition to diffusion and power law creep we included deformation by low temperature plasticity called the peierls mechanism which is significant at low temperatures and has a strong exponential dependence on the stress when a sufficient magnitude of heat is generated by the rapid conversion from elastically stored energy into viscous dissipation thermal instability takes place and the deformation localizes in a narrow region by comparing the condition for thermal instability we found that the low temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate the peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power law creep the enhanced deformation by low temperature plasticity produces lower amount of dissipative heating and thus stabilizes the shear zone comparing the stability between constant strain rate and constant stress boundary conditions we found that the peierls mechanism exerts an opposite destabilizing effect in the case of constant stress for dry olivine rheology and realistic magnitude of the strain rate the effect of low temperature plasticity is significant for temperatures between around 800 k and 1000 k this finding suggests that the low temperature plasticity may be crucial in determining the thermal mechanical stability in the shallow portion of slabs

finite element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting the development of shear zones initiating on random weaker initial perturbations is modelled numerically for low deborah number viscoelastic materials considering the influence of effective viscosity contrast power law rheology strain softening and different imposed bulk deformation geometries ranging from pure to simple shear conjugate shear zones initiate at 90 to one another and rotate with increasing bulk deformation the basic pattern not being markedly influenced by the vorticity of imposed deformation the rate of propagation of individual conjugate shear zones is little affected by increased effective viscosity contrast between matrix and inclusion but is promoted by power law rheology however the most marked effect is observed for strain softening behaviour where rapid propagation produces straighter and narrower shear zones the localisation of strain is reflected in a correspondingly heterogeneous stress distribution in particular mean stress or pressure is higher in the extending near planar weaker zones of localised shear melting of gneissic or pelitic compositions is pressure dependent with free water present increased pressure promotes melting whereas the opposite is true for water absent melting for water present conditions a positive feedback could develop between localised shearing increased pressure and partial melting this is potentially more effective in concentrating melt in shear zones than shear heating where melt related softening has a negative feedback effect

taphonomy of debris flow hosted dinosaur bonebeds at dalton wells utah lower cretaceous cedar mountain formation usa abstract a taphonomic study of the lower cretaceous dalton wells dw dinosaur bonebeds near moab utah provides insight into the origins preservational biases and paleobiological significance of one of the richest and most diverse early cretaceous dinosaur sites known the bonebeds occur in a stacked succession of debris flows at the base of the yellow cat member of the cedar mountain formation which was deposited in a seasonally dry alluvial lacustrine setting although only 5 of the locality has been collected more than 4200 bones were recovered representing an assemblage overwhelmingly dominated by dinosaurs with a minimum of 67 individuals that represent at least eight genera the assemblage also includes eight elements from four non dinosaurian reptiles the dinosaur fauna is sauropod dominated mni minimum number of individuals 41 a basal macronarian mni 15 venenosaurus mni 3 a camarasaurid mni 2 and a large number mni 21 of generically unassigned sauropod elements other dinosaurs include the theropods utahraptor mni 9 nedcolbertia mni 2 a possible ornithomimid mni 2 plus a large iguanodontid mni 4 and the ankylosaurid gastonia mni 9 patterns of skeletal articulation and clustering ontogenetic representation and bone surface modification indicate that the assemblage accumulated and was exposed for more than a year as the result one or more multiple mass mortality events likely droughts that culled large numbers of subadults from the biocoenose carcasses and disarticulated elements were reworked then later transported a short distance and buried by a succession of debris flows skeletal representation data patterns of sorting breakage burrows abrasion and scratch marks provide evidence for sorting trampling and scavenging prior to debris flow reworking pre debris flow sorting is attributed to earlier hydraulic winnowing of easily transported elements the intensity and thoroughness of breakage involving 97 of the elements suggest highly focused high load impacts compatible with trampling by sauropods and iguanodontids lightly abraded and vertically displaced elements indicate episodes of trampling in soft mud trampling occurred before and after debris flow transport theropod tooth marks are uncommon but bone scavenging by osteophagous insects was common and severe resulting in substantial damage to articular surfaces comparisons of dw and other debris flow hosted bonebeds indicate that there are few consistent patterns among fossil assemblage and bone modification data however there are numerous similarities in the geological and spatial taphonomy datasets from these sites resulting from the similar physico hydraulic conditions under which elements were transported reworked and buried geologically and taphonomically dalton wells is similar to the blagoveshchensk monodominant hadrosaur bonebed in the udurchukan formation of eastern russia which also is interpreted as a debris flow hyperconcentrated flow deposit dalton wells also shares geologic and taphonomic characteristics with four bonebeds southeast of the town of green river utah and all occur at the base of the yellow cat member the uniform stratigraphic occurrences of the dalton wells blagoveshchensk and the green river sites resting on an unconformity and their shared sedimentologic and taphonomic features indicate that these sites originated in response to similar tectonic depositional and biostratinomic factors

the brittle ductile transition in high level granitic magmas material constraints granitic magmas residing at high levels in the continental crust of deformation the characterization of this transition and may be subjected to stress transients on a wide range of time scales the quantification of the conditions necessary to achieve the origins of the stress transients may be internal deriving from it are not well understood for magmas fluid saturated the volume evolution of the magmatic system or external such as granitic magmas residing at high levels in the earth s crust the rapid release of stresses during tectonic and volcanically derived can potentially experience the transition from viscous to earthquakes the strain response of the granitic magma is critically brittle deformation under a variety of sources of transient dependent upon its viscosity and the magnitude and time scale of stress related to their internal chemical and physical the application or release of the stress the response of the magma evolution and the external circumstances of their emmay be either ductile or brittle prediction of the expected response placement and or eruption dingwell 1995 of the magma requires an accurate and reliable method for determining significant experimental progress towards quanthe location in temperature and time scale of the transition of the tification of the conditions necessary for the transition response of the melt from ductile to brittle by analogy to the glass and prediction of the material response of the magma transition determined by frequency domain relaxation studies the to it has been achieved in the past few years chiefly in application of the maxwell criterion which treats the magma as a the field of experimental deformation of magma here viscoelastic medium in the linear stress strain regime provides such the quantification of the properties of magma which a method application of this method requires accurate viscosity and are chiefly responsible for controlling the mechanical elastic modulus data for the magma the consequence of intersecting response of high level granitic systems is reviewed the glass transition in a system where the total strains are significant high level granitic magma is likely to be subject to is brittle failure of the melt phase here the material constraints transient stresses stemming from a variety of internal and on the brittle ductile transition of granitic magma are reviewed external stresses those stresses may contain volume and or shear components the internal stresses include those stemming from volume changes associated with boiling and crystallization phenomena as well as ascent of the magma as a whole the external stresses include

small scale ductile shear zones neither extending nor thickening nor narrowing abstract the length thickness and strain gradients of small scale 10 3 10 1 m thick ductile shear zones are pre determined by the presence of surface precursors e g fractures or compositional layers and associated fluid rock interaction fractures with their surrounding host rock damage zone and concurrent tectonic under pressure during dilation provide efficient fluid pathways and networks with diffusive fluid rock interaction at their margins the fluid induced gradational to zoned compositional haloes that symmetrically surround a fracture control the strain gradients of developing shear zones and result in a diversity of geometric types including single homogeneous to heterogeneous shear zones and paired shear zones as a consequence geochemical differences between shear zone and host rock may reflect fluid rock interaction during the precursor brittle history rather than during slip especially considering that shear zones with even a small component of stretch may be over pressured and therefore unable to drain fluids from the surrounding rocks support from field observation for this interpretation is given by 1 the lack of correlation between shear zone thickness and accumulated displacement and 2 the similar thickness of shear zones and locally unexploited alteration haloes surrounding fracture precursors most small scale shear zones in massive rocks granitoids are initially neither thickening nor narrowing with increasing strain this concept may also apply to more foliated rocks but does not necessarily hold for larger scale shear zones

quantitative outcrop data for flow simulation abstract an architectural analysis documents variations in bedding geometry and rock properties within a tide influenced deltaic sandstone exposed in the cretaceous frontier formation of central wyoming usa digital maps of bedding lithofacies and diagenetic cements as well as vertical logs of grain size lithofacies and permeability describe rock properties that potentially influence fluid flow behavior these records are used to construct simulation models that assess the relative importance of different types of geologic variability on prediction of subsurface fluid flow two 25 meter thick tide influenced deltaic sandstone bodies coarsen upward and contain inclined beds that reflect episodic delta front progradation decimeters to meters thick beds within bodies alternate between cross stratified sandstones formed during rapid flows and shales deposited during more quiescent conditions down depositional dip bed draping shales are more continuous and lithofacies within sandstone beds become finer grained and increasingly heterolithic as sandstone beds fine down dip mean permeability values decrease and coefficients of variation increase permeability values change from nearly normal distributions to highly right skewed and permeability values become more strongly spatially correlated nodular cements also affect permeability all of these variations were modeled using stratigraphic cornerpoint grids that preserve stratal geometry and gridblocks with properties assigned using a combination of rock property maps and statistical models based on rock property logs simulations predict effects on fluid flow of geologic heterogeneity at different scales the influences of process variables and the effects of different methods of grid construction and rock property assignment flow simulations of water flooding through a 22 m thick by 360 m long segment of a deltaic sandstone oil reservoir predict that 1 rapid flow through coarser grained deposits at the top of the sandstone body tends to draw water upward 2 thin shales draping sandstone beds shunt downdip directed flow downward and updip directed flow upward 3 cement nodules cause more tortuous flow patterns but have little effect on recovery efficiency 4 methods of predicting intrafacies correlation of permeability have little effect on flow behavior at this scale a simulation model constructed using a high resolution cartesian grid did not resolve the effects of inclined shales demonstrating the usefulness of stratigraphic cornerpoint grids for modeling flow through complex geologic deposits flow simulations of tracer flow through a meter thick cross stratified bed within the deltaic sandstone body showed that at this scale shale drapes and models of the intrafacies distribution of permeability have statistically significant effects

akhalkalaki the taphonomy of an early pleistocene locality in the republic of georgia as part of our investigations into the potential of the republic of georgia for providing information on early hominin occupation of eurasia we report here on akhalkalaki a large late early pleistocene locality located along the lower slopes of a miocene andesitic cone originally excavated in the 1950s as a palaeontological site it was re opened in the 1990s and stone tools were found associated with the fauna suggesting that it is also an archaeological occurrence excavations in the 1950s and 1990s uncovered thousands of bones of an early galerian fauna including the remains of new species of hippopotamus equus and canis vekua 1962 1987 and dominated by the remains of equus

biotic and abiotic processes affecting the formation of bk level 4c bed ii olduvai gorge and their bearing on hominin behavior at the site abstract excavations at bk have provided insights into the behavior of early hominins through the study of several archaeological levels the present study shows the results for a new archaeological sub level bk4c the main goal is to contribute to the knowledge of the different taphonomic processes that shaped bk4c and to better understand the role played by hominins in its formation due to the presence of a fluvial depositional context and a slight channel in bk4c a spatial analysis has been applied in order to determine the impact caused by water flows we conclude that water played a role in the rearrangement of the assemblage however the spatial properties of the assemblage indicate a limited impact of post depositional disturbance processes supporting the autochthonous nature of the site the taphonomic study of this sub level indicates that hominins had a primary role in the accumulation bulk defleshing and demarrowing of carcasses bk4 assemblages bk4b and bk4c indicate a repeated occupation of the site for short time periods this is interpreted by the overall fast sedimentation recorded in the fluvial system and the paucity of highly weathered bones showing extensive periods of sub aerial exposure in between sedimentary episodes the site functionality is potentially different from that inferred for earlier oldowan periods where sites were smaller and showed less marked spatial clustering of lithics and stone tools caused by hominin behavior

a tale of two viscosities abstract we describe a series of 12 large strain two dimensional simple shear numerical experiments on two phase linear and non linear viscous materials the modal percentage of the two phases their relative viscosities and the stress exponent of the dependence of viscosity on stress were systematically varied allowing us to observe the effects of these parameters on the flow behaviour of the system all experiments exhibited localisation but the extent and type of localisation varied considerably and the range of parameters allows both classical sc as well as sc structures to form the inter granular finite strain geometries also varied systematically although there is a tradeoff between non linearity of viscosity and the viscosity contrast that results in similar geometries for quite different mechanical behaviour the finite rotation of the harder phases was similar within any one experiment originally parallel passive marker lines thus remain sub parallel after deformation and rotation which may be mistaken for non rotation the internal deformability and interaction between grains allows meta stable grain elongation orientations to form without any additional consideration of external slip surfaces the slight variability of initial grain geometry and subsequent grain interactions leads to a wide variability in final grain shapes for the same initial viscosities

three dimensional interference test interpretation in a fractured aquifer using the pilot point inverse method a geostatistical conditional simulation routine that employs both parametric and nonparametric geostatistics is coupled to the pilot point inverse method to simulate the spatial distribution of conductivities in a dolomitic aquifer which is fractured in some areas and unfractured in others an inversion is then conducted to obtain the conductivities within the fractured and nonfractured parts of the aquifer to match interference data from a series of three dimensional pumping tests for an ensemble of 100 conditional simulations the calibrated and predicted drawdowns match the observed drawdowns well a comparison to the transmissivity interpreted from a single well pumping test compared very well to the geometric mean transmissivity calculated from the calibrated realizations in this study the results from this study indicate that conditioning the conductivity fields to the geologic facies data in this case fractured unfractured categorical data as well as to ample transient hydraulic data can lead to robust groundwater flow models which can adequately predict the response to other hydraulic interference tests

evidence for late carboniferous subduction type magmatism in mafic ultramafic cumulates of the sw tauern window eastern alps hectometric bodies of fresh mafic ultramafic cumulates have been discovered within the central gneiss of the zillertal massif sw tauern window eastern alps italy the cumulates intruded by the central gneiss granitoids are amphibole bearing harzburgites and norites made of cumulitic olivine fo73 80 spinels sulphides and plagioclase an79 87 included in orthopyroxene en76 83 and ti pargasite mg 0 73 0 81 major and trace element geochemistry indicates that these rocks represent olivine spinel plagioclase cumulates in which interstitial melt crystallized as orthopyroxene ti pargasite the parental melt has trace element patterns typical of subduction zone magmas the crystallization sequence mineral compositions and modes indicate that cumulates formed from a h2o rich basaltic andesite which intruded at low pressure 2 kbar and temperatures of 1 050 1 100 c shrimp u pb dating of zircons from ultramafic cumulates and adjacent metagranodiorite yielded ages of 309 5 and 295 3 ma respectively in agreement with field relationships these results show that the mafic ultramafic cumulates represent a co genetic early product of the late carboniferous plutonic activity in the western tauern window which started in the westphalian earlier than previously thought our data on the most primitive rocks in the zillertal massif permit for the first time insight into the parental magma and thus into the origin of this late carboniferous calc alkaline magmatism which was most likely related to slab break off during the late variscan convergence

magma tectonic interaction and the eruption of silicic batholiths abstract due to its unfavorable rheology magma with crystallinity exceeding about 50 vol and effective viscosity 106 pa s is generally perceived to stall in the earth s crust rather than to erupt there is however irrefutable evidence for colossal eruption of batholithic magma bodies and here we analyze four examples from spain mexico usa and the central andes these silicic caldera forming eruptions generated deposits characterized by i ignimbrites containing crystal rich pumice ii co ignimbritic lag breccias and iii the absence of initial fall out the field evidence is inconsistent with most caldera forming deposits which are underlain by initial fall out indicating deposition from a sustained eruption column before the actual collapse sequence in contrast the documented examples suggest early deep level fragmentation at the onset of eruption and repeated column collapse generating eruption volumes on the order of hundreds of cubic kilometers almost exclusively in the form of ignimbrites these examples challenge our understanding of magma eruptability and eruption initiation processes in this paper we present an analysis of eruption promoters from geologic theoretical and experimental considerations assessing relevant dynamics and timescales for failure of crystal melt mush we propose a framework to explain eruption of batholithic magma bodies that primarily involves an external trigger by near field seismicity and crustal failure strain rate analysis for dynamic and static stressing chamber roof collapse and rapid decompression indicates that large solid like silicic reservoirs may undergo catastrophic failure leading to deep level fragmentation of batholithic magma at approximately 2 orders of magnitude lower strain rates than those characteristic for failure of crystal poor magmas or pure melt eruption triggers can thus include either amplified pressure transients in the liquid phase during seismic shaking of a crystal melt mush decompression by block subsidence or a combination of both we find that the window of opportunity for the eruption of large silicic bodies may thus extent to crystallinities beyond 50 vol for strain rates on the order of 10 3 to 10 4 s 1

relating small scale sedimentary structures and permeability in a cross bedded aquifer summary the objective of this study is to investigate the relation between small scale sedimentary structures and permeability in the brussels sands formation an early middle eocene shallow marine sand deposit in central belgium that constitutes a major groundwater source in the region a field campaign was carried out consisting of field observations of the sedimentary structures and in situ measurements of air permeability the sedimentary structures were interpreted sketched digitally photographed and measured in a representative outcrop additionally a total of 2750 cm scale air permeability measurements were carried out in situ analysis of the spatial distribution of sedimentary structures and permeability shows that clay rich sedimentary features such as bottomsets and distinct mud drapes exhibit a different statistical and geostatistical permeability distribution compared to the other lithofacies in the cross bedded sands spatial analysis of the air permeability data shows that permeability anisotropy in the cross bedded lithofacies is dominated by the foreset lamination orientation these results show that small scale sedimentary heterogeneity strongly influences the local spatial distribution of the hydraulic properties and results in permeability heterogeneity and stratification that would produce anisotropy in upscaled permeability values

stochastic analysis of the effect of heterogeneity and fractures on radionuclide transport in a low permeability clay layer deep low permeability clay layers are considered as safe environments for disposal of high level radioactive waste in belgium the boom clay is a candidate host rock for deep geological disposal in this study we analyze the effects of fractures and spatially variable hydraulic conductivity on radionuclide migration through the clay fracture geometry and properties are simulated with monte carlo simulation the heterogeneity of hydraulic conductivity is simulated by direct sequential co simulation using measurements of hydraulic conductivity and four types of secondary variables the hydraulic conductivity and fracture simulations are used as input for a transport model radionuclide fluxes computed with this heterogeneous model are compared with fluxes obtained with a homogeneous model the output fluxes of the heterogeneous model differ at most 8 from the homogeneous model the main safety function of the boom clay is thus not affected by the fractures and the spatial variability of hydraulic conductivity

the control of precursor brittle fracture and fluid rock interaction on the development of single and paired ductile shear zones abstract ductile shear zones can occur as relatively isolated single structures as arrays or as characteristic paired zones in continuous glaciated exposures of metagranodiorites from the tauern window eastern alps the control of initial dilatant brittle fracture and associated fluid rock interaction on the geometry of subsequent ductile shear zones can be unequivocally established shearing occurred under amphibolite facies conditions fractures in weakly deformed metagranodiorites are often less than 1 mm thick but extend for tens of metres many are healed joints without shear offset others show minor mm cm discrete dextral offset such brittle faults commonly display a low angle en echelon arrangement with displacement transferred between discrete fracture segments by ductile compressive bridges the geometry of more strongly reactivated zones depends on the degree and heterogeneity of fluid rock interaction which is related to fluid infiltration and veining along the primary fractures with little fluid rock interaction reactivation produces single heterogeneous ductile shear zones centred on and immediately flanking the pre existing fracture with increased fluid rock interaction a bleached halo is developed symmetrically to either side of a central epidote quartz garnet calcite vein ductile shear zones commonly flank this bleached zone to develop a characteristic paired pattern strain is partitioned localizing in the central fracture vein and the flanking shear zones paired zones may anastomose in accordance with changes in the width of the central bleached zone but are always symmetrically spaced with regard to the central fracture vein with increasing deformation the ductile shear zones broaden into the adjacent metagranodiorite but not into the bleached zone which remains preserved as a low strain region paired shear zones can also develop to either side of aplite dykes examples of characteristic paired shear zones usually with a clear central vein are found in many areas ranging from greenschist to eclogite facies suggesting that the mechanism of their formation is quite general

how ductile are ductile shear zones three premises of ductile deformation in the middle and lower crust are widely accepted 1 rocks flow with power law viscous rheology 2 localization in ductile shear zones involves strain softening and 3 fluid flows into and is channelized within ductile shear zones ductile viscous shear zones should therefore initially develop along planes of maximum shear stress strain soften and rotate as material planes into the field of progressive extension however the mean stress or pressure within a weak elongate viscous band being stretched is higher than the surrounding matrix and this is difficult to reconcile with premise 3 in contrast mohr coulomb brittle faults always have lower pressure within the fault zone flow of fluid and melt into high temperature shear zones therefore implies that ductile shear zones are not perfectly viscous but have a pressure dependent viscoplastic rheology the continued pressure dependence may reflect significant microcracking on the grain scale even when localized deformation does not produce larger scale discrete fractures

melt bearing shear zones analogue experiments and comparison with examples from southern madagascar abstract analogue model experiments were conducted to investigate the influence of irregularly distributed weak sites in localising strain as an aid to understanding shear zone development in partially molten rocks the very weak inclusions consisted of vaseline in a homogeneous matrix of paraffin wax which has a power law viscous rheology boundary conditions were those of pure shear at constant natural strain rate and confining stress 3 the inclusions were initially perfect cylinders with axes parallel to the intermediate bulk strain axis y conjugate shear zones nucleate on the inclusions and link up to form an anastomosing pattern of high strain zones of concentrated shear surrounding much more weakly deformed pods of near coaxial strain the zones initiate at angles near 45 to the bulk shortening axis z but stretch and rotate towards the x axis with increasing bulk strain all inclusions nucleate shear zones so that with increasing development of the anastomosing pattern weak material occurs only within the high strain zones the restriction of migmatite leucosomes to shear zones in natural examples could also reflect a corresponding control of melt on the sites of shear zone nucleation rather than implying accumulation from the surrounding wall rock the model geometry is very similar to that observed in small scale shear zones in migmatites of southern madagascar elongate zones rich in weak inclusions originally either perpendicular or at 45 to the z axis were also modelled for direct comparison with the regional scale geometry of the pan african high grade shear zones on madagascar

submagmatic microfractures in granites microstructures in hercynian granite plutons of the pyrenees indicate fracturing of plagioclase crystals in the presence of melt this is represented mainly by quartz and or feldspar that fills fractures electron microprobe analyses demonstrate that in compositional agreement with the rims of the zoned plagioclase the feldspar infillings are more sodic with decreasing melt fraction fracturing resulted from concentration of stress at contacts between grains while the granite was submagmatic i e when the melt was below the critical fraction for magmatic flow material compositionally far from eutectic is petrologically the best candictate to develop submagmatic fractures because during cooling the volume fraction of melt remains low for a large temperature range a strong tendency for microfractures to be oblique to flow foliation may constitute a new criterion for shear sense in magmas

why calcite can be stronger than quartz 1 in the neves area eastern alps calcite forms asymmetric centimeter scale single crystal porphyroclasts in quartz mylonites developed during hydrous amphibolite facies metamorphism at 550 c under these conditions coarse calcite was clearly stronger than the surrounding polycrystalline dynamically recrystallized quartz matrix experimental results indicate that coarse calcite is less strain rate sensitive than wet quartzite consistent with an inversion in strength on extrapolation to natural strain rates for this to occur wet quartzite must be weak flowing at differential stress of 10 mpa the lack of high temperature twins showing bulging or recrystallization in calcite clasts is consistent with such low stresses during shear zone development under near peak metamorphic conditions the maximum effective viscosity ratio of coarse calcite to quartzite for these conditions is probably not large 10 however numerical modeling shows that ratios of around 2 are sufficient to maintain near rigid calcite clast behavior for power law rheology with stress exponents appropriate to quartz n 3 4 and coarse calcite n 6 the inversion in relative strength reflects the difference in influence of water on the crystal plastic flow of calcite and quartz water has a dramatic effect for quartz but little or no effect for calcite quartz rich rocks under hydrous amphibolite facies conditions in the middle to lower crust are therefore relatively weak in fact weaker than coarse calcite and flow at much lower stresses than dry quartz rich rocks at similar crustal levels

alpine metamorphism and veining in the zentralgneis complex of the sw tauern window a model of fluid rock interactions based on fluid inclusions abstract the granitic to tonalitic gneisses of the zentralgneis complex in the sw tauern window contain numerous discordant quartz biotite plagioclase veins occurring either as isolated or in parallel sets with a preferential orientation perpendicular to the main foliation of host rocks veins show a zonal distribution of minerals with plagioclase and biotite at the walls and quartz in the centre quartz contains abundant fluid inclusions fi mostly occurring along secondary planes all primary and most secondary inclusions three phase h2o co2 inclusions formed from a dominant fluid type of aqueous carbonic composition fi have been characterized by microthermometry laser raman and laser ablation optical emission spectroscopies which have confirmed their similarity also with respect to composition and density fluids display a somewhat unusual composition especially a wide range of rather high salinities 3 7 mol deduced from the final melting temperature of clathrate which covers a wide range from 4 2 to 4 0 c the volatile phase is dominated by co2 3 12 mol with small amounts of n2 the final homogenization temperature of these inclusions is generally 300 c but independently constrained trapping temperatures of 550 600 c yield to pressure estimates of 3 5 7 5 kbar highest pressures are in agreement with the p t conditions reached during the tauern metamorphism peak veining was triggered by hydrofracturing induced by pl bt producing devolatilization and probably decarbonation reactions in the adjacent gneisses and quartz precipitated in response to the significant pressure and or salinity fluctuations shown by fi during each microfracturing healing stage

seismicity preceding volcanic eruptions new experimental insights a variety of seismic signals representing different physical mechanisms precedes volcanic eruptions the most meaningful signals are high and low frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice we provide experimental support for this association by reproducing magma migration while recording seismic signals opening fractures emit high frequency acoustic events while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation

numerical analysis of solute migration through fractured clayey deposits into underlying aquifers this study examines the degree to which vertically fractured clayey aquitards protect an underlying aquifer from near surface sources of contamination evidence from field studies indicates that many clayey aquitards previously assumed to be unfractured at depth have vertical fractures that actively transmit groundwater calculated groundwater velocities within these fractures can exceed several meters per day for apertures in the range of those reported to occur in clays if this is the case significant quantities of dissolved contaminants originating in near surface zones may move rapidly downward through the fracture network into underlying aquifers a two dimensional laplace transform galerkin finite element model sudicky and mclaren this issue was used to assess the importance of idealized planar vertical fractures on flow and solute transport through a 15 m thick aquitard and subsequent plume evolution within an underlying aquifer in which groundwater flows horizontally sensitivity analyses indicate that solute transport through the aquitard is strongly affected by downward flow in widely spaced deep fractures with apertures as small as 10 m and that a plume of large lateral extent and significant concentration forms within the underlying aquifer in a few tens of years for apertures of the order of 20 m or much sooner if the apertures are 50 m this finding suggests that small hydraulically active fractures that are very difficult to detect or identify within an otherwise protective clayey barrier may cause rapid and large scale contamination of groundwater beneath the barrier

generation of intermediate depth earthquakes by self localizing thermal runaway the conditions leading to rock failure during intermediate depth earthquakes in subduction zones are not clear particularly in the absence of free fluid field observations and numerical simulations indicate that thermal weakening due to high temperature shear instabilities may trigger earthquakes under such circumstances intermediate depth 50 300 km earthquakes commonly occur along convergent plate margins but their causes remain unclear in the absence of pore fluid pressures that are sufficiently high to counter the confining pressure in such settings brittle failure is unlikely in such conditions the rocks could fail by the mechanism of progressively self localizing thermal runaway1 whereby ductile deformation in shear zones leads to heating thermal softening and weakening of rock1 2 3 here we test this hypothesis by focusing on fault veins of glassy rock pseudotachylyte formed by fast melting during a seismic event as well as associated ductile shear zones that occur in a precambrian terrane in norway our field observations suggest that the pseudotachylytes as well as shear zones have a single event deformation history and we also document mineralogical evidence for interaction of the rocks with external fluids using fully coupled thermal and viscoelastic models we demonstrate that the simultaneous occurrence of brittle and ductile deformation patterns observed in the field can be explained by self localizing thermal runaway at differential stresses lower than those required for brittle failure our results suggest that by perturbing rock properties weakening by hydration also plays a key role in shear zone formation and seismic failure however thermal runaway enables the rocks to fail in the absence of a free fluid phase

hydrogeological modeling of radionuclide transport in low permeability media a comparison between boom clay and ypresian clay deep low permeability clay layers are considered as suitable environments for disposal of high level radioactive waste in belgium the boom clay is the reference host formation and the ypresian clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste in this study two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations transport parameter heterogeneity is incorporated in the models using geostatistical co simulations of hydraulic conductivity diffusion coefficient and diffusion accessible porosity the calculated radionuclide fluxes in the two clay formations are compared the results show that in the ypresian clay larger differences between the fluxes through the lower and the upper clay boundary occur larger total output radionuclide amounts are calculated and a larger effect of parameter heterogeneity on the calculated fluxes is observed compared to the boom clay

three dimensional high resolution fluvio glacial aquifer analog part 1 field study summary describing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation however hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved aquifer analogs serve as surrogates to construct models of equivalent heterogeneity and thus imitate those features relevant for flow or transport processes gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil this paper describes an approach to also inspect the third dimension by mapping during the ongoing excavation it is possible to obtain a three dimensional representation of the subsurface within a short period of time a detailed description of a case study is presented and the findings from sedimentological hydrogeological and geophysical analyses are compared the gravel pit is located near the town of herten in southwest germany where relatively young unconsolidated fluvio glacial and fluvial sediments in the rhine basin are mined the excavated gravel body is built up by architectural elements typical for braided river deposits the study generated a high resolution data set of lithofacies hydrofacies and ground penetrating radar gpr profiles it represents the basis for a full three dimensional geostatistical reconstruction presented in the second part comunian et al 2011

deformation at the frictional viscous transition evidence for cycles of fluid assisted embrittlement and ductile deformation in the granitoid crust abstract mid crustal deformation is classically characterized by the transition from ductile to brittle deformation defining the frictional to viscous transition fvt here we investigate an exhumed continental mid crustal basement section in order to envisage the relationship between ductile and brittle deformation at the fvt our detailed study from km to micro scale shows that under greenschist metamorphic conditions deformation is accommodated by a dense network of highly localized ductile shear zones in the investigated case it is not quartz which defines the overall ductile deformation behavior but the viscous granular deformation in shear zones with an ultrafine grained polymineralic matrix consisting of quartz feldspar sheet silicates and epidote during viscous granular flow mass transfer processes under the presence of fluids promote a chemo mechanical mixing resulting in grain size reduction and reaction softening coeval with this ductile deformation fluid assisted embrittlement occurs as indicated by biotite coated fractures cataclasites and injection of non cohesive polymineralic gouge material into secondary fractures inside the host rock the embrittlement during predominant ductile deformation occurs in cycles i e prolonged periods of slow viscous granular flow are interrupted by rapid brittle deformation we interpret this fluid assisted cyclic embrittlement evidenced by injection of the fluidized material into off fault fractures as an alternative equivalent to pseudotachylites and as a microstructural indicator for paleo seismic activity with exhumation and associated cooling localized deformation persists in the ultrafine grained polymineralic shear zones but progressively transitions to cataclastic flow and finally to pressure dependent frictional flow always showing cycles of slow interseismic flow and fast seismic injection events overall in the granitic crust of the aar massif brittle and ductile deformation coexist up to deformation temperatures of minimum 450 c indicating that the fvt has to be placed in a rather wide range from 8 km up to 18 20 km in the granitoid crust

the timing and cause of megafauna mass deaths at lancefield swamp south eastern australia abstract lancefield swamp south eastern australia was one of the earliest sites to provoke interest in pleistocene faunal extinctions in sahul pleistocene australia new guinea the systematic investigation of the deposit in the early 1970s identified megafaunal remains dominated by the 100 200 kg kangaroo macropus giganteus titan associated radiocarbon ages indicated that the species was extant until c 30 000 bp suggesting significant overlap with human settlement of sahul this evidence was inconsistent with contemporary models of rapid human driven extinctions instead researchers inferred ecological tethering of fauna at lancefield swamp due to intense drought precipitated localised mass deaths consistent with late pleistocene climatic variability later investigations in another part of the swamp the mayne site remote to the initial investigations concluded that mass flow disturbed this area and electron spin resonance esr analyses on megafauna teeth returned wide ranging ages to clarify site formation processes and dating of lancefield swamp we excavated new test pits next to previous trenches in the classic and mayne sites we compared absolute chronologies for sediments and teeth sedimentology palaeo topography taphonomy and macropod age at death across the swamp luminescence dating of sediments and esr analysis of teeth returned ages between c 80 000 and 45 000 years ago we found no archaeological remains in the bone beds and evidence of carnivore activity and fluvial action in the form of reactivated spring flow the latter disturbed limited parts of the site and substantial areas of the bone beds remained intact the faunal assemblage is dominated by megafaunal adult macropus consistent with mass die offs due to severe drought such droughts appear to have recurred over millennia during the climatic variability of marine isotope stages 4 and 3 these events began tens of millennia before the first appearance of aboriginal people in sahul and only the very youngest fossil deposits could be coeval with the earliest human arrivals therefore anthropogenic causes cannot be implicated in most if not all of mass deaths at the site climatic and environmental changes were the main factors in site formation and megafauna deaths at lancefield swamp

effects of temperature dependent thermal diffusivity on shear instability in a viscoelastic zone implications for faster ductile faulting and earthquakes in the spinel stability field the introduction of a new model of thermal diffusivity has motivated us to reinvestigate a one dimensional viscoelastic shear zone model with realistic rheology temperature dependent thermal diffusivity t and viscous dissipation although thermal diffusivity in the shear zone is spatially heterogeneous with t and viscous heating the spatial distribution of t does not affect shear zone evolution for the mesh resolution used in the model as temperatures increase above room temperature thermal diffusivity decreases the lower thermal diffusivity causes a slight spatial thinning of the shear zone and an acceleration of the onset of instability relative to cases using a room temperature value of thermal diffusivity increasing the nonlinearity of t enhances shear zone thinning and speed up of instability the amount of enhancement depends on temperature mineralogy and the rate of shear heating the rheology of spinel creates a more unstable situation for the shear zone than that of olivine but the boundary separating instability and stability is sensitive to changes in material properties a decrease in the grain size does not influence the timescale of instability unless grain size reduction causes diffusion creep to be the dominant deformation mechanism viscoelastic thermal mechanical instabilities occur on timescales ranging from a few hundred to several thousand years in most slabs no instability is found to occur in spinel regions at temperatures above 1200 k likewise shear instability in olivine at upper mantle depths will not occur at temperatures greater than 1100 k