anomalous sulfur poor platinum group element mineralization in komatiitic cumulates mount clifford western australia an unusual occurrence of sulfur poor platinum group element pge mineralization has been discovered at mount clifford in the agnew wiluna belt western australia within the lower part of a 1 000 m thick komatiitic dunite body the host body consists primarily of strongly serpentinized olivine adcumulates with accessory chromite high precision whole rock icp ms data show that the pge mineralization extends over tens of meters whereas the lateral extent is unknown palladium and pt abundances are closely associated with base metal sulfides but show offset distribution patterns with maximum concentrations associated with the relatively sulfide poor base of a disseminated sulfide bearing layer whole rock concentrations range up to 4 100 ppb pd and 920 ppb pt iridium rh and ru follow the trends in pd and pt but are strongly depleted ir 0 4 ppb ru 0 5 ppb rh 0 1 ppb platinum group minerals pgm were located in essentially sulfide free serpentine 2 m below the peak in sulfide abundance and can be categorized into three groups pd antimonides pt dominated pgm and pt bearing ni antimonides the pge mineralization zone is underlain by an interval of strong ni depletion within olivine mesocumulates that is characterized by an unusual negative correlation between ni and the mg number of the rock this relationship is interpreted to be the result of an equilibration of olivine of variable forsterite content with a relatively large mass of magmatic sulfide however there is no direct evidence of this sulfide mass anywhere in the entire mount clifford dunite body the ni depletion is accompanied by strong depletion in ipge ir ru and rh the association of the pge zone with a reversal in the mg fe ratio of the host cumulates and a distinctive offset relationship of multiple pt pd and cu s peaks is suggestive of a primary magmatic origin however this is inconsistent with current models for offset reef pge concentrations which involve the onset of sulfide liquid saturation from a previously sulfur undersaturated pge undepleted magma the association of enriched pt and pd with highly depleted ni and ipge in immediately underlying cumulates conflicts with this model we suggest a combination of processes early sulfide segregation at low r values producing ni and ipge depleted olivine partial redissolution and removal of most of this sulfide component during a major replenishment event and subsequent overprint by a migrating pt pd cu rich fluid

influences of pore pressure on short term and creep mechanical behavior of red sandstone abstract short term and creep tests for saturated red sandstone under different pore pressures were carried out by a rock servo controlled triaxial equipment based on the experimental results the influences of confining pressure and pore pressure on short term mechanical behavior of red sandstone are firstly analyzed the results show that the peak strength of dry red sandstone increases with the confining pressure which can be better expressed by the nonlinear hoek brown criterion than the linear mohr coulomb criterion but with the increase of pore pressure the peak strength and elastic modulus of saturated red sandstone all decrease step by step the short term failure mode of red sandstone is dependent of the confining pressure but independent of the pore pressure and then the influence of pore pressure and axial deviatoric stress on the creep mechanical behavior of saturated red sandstone is analyzed quantitatively creep contribution to rock deformation increases with the pore pressure and the specimens show significant time dependent effect at higher deviatoric stresses however the steady state creep rate of saturated red sandstone increases nonlinearly but the viscosity coefficient decreases gradually with increasing axial deviatoric stress and pore pressure an exponential function is suggested to characterize the relationship between the creep parameters including creep strain steady state creep rate and viscosity coefficient and the axial deviatoric stress and pore pressure the calculated curves using the proposed function are compared with the experimental results which is in a good agreement with the experimental data in the end the mechanism that the pore pressure and deviatoric stress affect the creep deformation of saturated red sandstone is discussed in detail the presented experimental results on short term and creep mechanical behavior of red sandstone under different pore pressures are very significant for evaluating the long term stability and safety of deep underground rock mass engineering

single crystal 40ar 39ar dating of the olorgesailie formation southern kenya rift single crystal laser fusion sup 40 ar sup 39 ar analyses and several conventional bulk fusion sup 40 k sup 40 ar dates have been used to determine the age of volcaniclastic strata within the olorgesailie formation and of associated volcanic and sedimentary units of the southern kenya rift in the principal exposures along the southern edge of the legemunge plain the formation spans the interval from approximately 500 to 1 000 ka deposition continued to the east along the ol keju nyiro river where a tuff near the top of the formation has been dated at 215 ka in these exposures the formation is unconformably overlain by sediments dated at 49 ka a possible source for the olorgesailie tephra the ol doinyo nyokie volcanic complex contains as ash flow dated at approximately 1 ma extending the known age range of this complex to encompass that of virtually the entire olorgesailie formation in the legemunge plain these geologic examples illustrate the importance of the single crystal sup 40 ar sup 39 ar dating technique whereby contaminant altered or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits the authors have presented a computer modeling procedure based on an inverse isochron analysis thatmore promotes a more objective approach to trimming sup 40 ar sup 39 ar isotope data sets of this type less

influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from mt etna volcano subjected to elevated pressure abstract we report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from etna italy results were obtained for dry and saturated samples deformed under triaxial compression during each test the effective pressure was first increased up to 190 mpa to investigate the effect of pre existing crack closure on seismic properties then the effective pressure was unloaded down to 20 mpa a pressure which mirrors the stress field acting under a lava pile of approximately 1 5 2 km thick and deviatoric stress was increased until failure of the specimens using an effective medium model the measured elastic wave velocities were inverted in terms of two crack densities i the crack density of the pre existing thermal cracks and v the crack density of the stress induced cracks in addition a link was established between elastic properties elastic wave velocities vp and vs and permeability using a statistical permeability model our results show that the velocities increase with increasing hydrostatic pressure up to 190 mpa due to the closure of the pre existing thermal cracks this is interpreted by a decrease of the crack density i from 1 to 0 2 the effect of pre existing cracks closure is also highlighted by the permeability evolution which decreases of more than two orders of magnitude under deviatoric loading the velocities signature is interpreted in the first stage of the loading by the closure of the pre existing thermal cracks however with increasing deviatoric loading newly formed vertical cracks nucleate and propagate this is clearly seen from the velocity signature and its interpretation in term of crack density from the location of the acoustic emission sources and from microstructural observations this competition between pre existing cracks closure and propagation of vertical cracks is also seen from the permeability evolution and our study shows that mechanically induced cracks has lesser influence on permeability change than pre existing thermal cracks

localization of deformation in fluid saturated sandstone abstract a laboratory study of inelastic deformation and localization was conducted to evaluate microseismicity and fracture in fluid saturated rock plane strain compression experiments were performed on oil and water saturated berea sandstone under dry drained undrained and quasi unjacketed conditions parameters associated with the elastic and inelastic material response were accurately measured and used in a constitutive model to predict localization of deformation under the drained and undrained conditions acoustic emission ae activity was recorded and the onset of inelastic response in fluid saturated rock similar to dry rock coincided with an increase in ae rate fracture initiation and propagation were successfully monitored by ae locations clustering of ae events and the start of inhomogeneous deformation inferred from displacement measurements are shown to be well correlated with the model prediction of the onset of localized deformation under various rock fluid interaction conditions

stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid miocene climatic optimum in idaho u s a abstract the effects of global climate change are manifested at the regional level consequently evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional scale climate data here we test whether climate change influenced faunal and floral patterns leading up to and during the mid miocene climatic optimum mmco based on datasets collected in the railroad canyon section rcs central eastern idaho u s a specifically we use isotope compositions of herbivore tooth enamel to investigate how mean annual precipitation map mean annual temperature mat cold month mean temperature cmmt and temperature seasonality varied through the rcs and how this local record compares to global climate reconstructions isotope compositions of teeth from the fossil equid merychippus and rhinocerotid diceratherium were compared across five time bins from c 23 to c 15 ma bulk 18o values of both taxa indicate that meteoric water compositions were unchanged through the study interval consistently c 15 6 but were c 1 9 higher than current regional meteoric water this difference points to warmer climates in central eastern idaho during the miocene post middle miocene topographic uplift in western north america and or shifts to air mass trajectories serial sampling of enamel shows seasonal fluctuations in water compositions and temperature bulk 13c values indicate an average map of 190 range 10 510 mm yr 1 with no significant change through the study interval comparable to today s map 236 mm yr 1 the reconstructed semi arid seasonal warm climate for the rcs agrees with phytolith assemblage data from the same strata indicating dominantly open grassy habitats however it is inconsistent with previously held ideas of warm wet mid miocene climates in the northern rocky mountains nrm based on paleosol analyses our inferred stable climate conditions for the mmco of the nrm contrast with coeval records from europe and asia indicating sustained or enhanced warm and wet climates these differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

paleomagnetism of miocene east african rift sediments and the calibration of the geomagnetic reversal time scale paleomagnetic stratigraphy and k ar age determinations are reported for the type section of the middle miocene ngorora formation found in the kenya rift valley the magnetostratigraphy is well correlated to the geomagnetic reversal time scale grts and spans from the lower part of chron c5 9 to chron c5ab r 14 k ar dates were determined for euhedral sanidines handpicked from seven tuff horizons within the ngorora formation and the underlying turn phonolite flow these dates can therefore be tied directly to the grts the eight dates fall into three discrete groups averaging 12 5 0 22 ma mean and standard deviation of results from four tuffs 11 6 0 06 ma mean and standard deviation from three tuffs and 10 16 0 38 average of three analyses from one tuff we interpret the age groups as resulting from three successive eruptive episodes the stratigraphic positions of which are well constrained in spite of episodic supply at the eruptive source sediment accumulation is continuous at the resolution of the grts this suggests that accumulation is controlled by basin subsidence rather than sediment supply sanidine dates support an age for the older boundary of marine magnetic anomaly 5 of about 10 ma as opposed to 11 12 ma suggested by the most recent results from icelandic basaltic lava flows

platinum group minerals in the limoeiro ni cu pge sulfide deposit brazil the effect of magmatic and upper amphibolite to granulite metamorphic processes on pgm formation the limoeiro ni cu platinum group elements pge deposit is a recent discovery associated with an igneous tubular conduit system in northeastern brazil representative ores from the deposit have been used for platinum group minerals pgm identification and for pge in base metal sulfides bms quantification ninety eighty percent of the pgm in the massive sulfide ores is homogeneous pt ni bi bearing merenskyite pdte2 enclosed primarily by pyrrhotite suggesting that it is formed by exsolution from monosulfide solid solution mss merenskyite gradually but systematically becomes poorer in pt and ni with increasing fractionation which is interpreted to reflect a transition to a more evolved sulfide liquid that segregated in the eastern parts of the intrusion in massive sulfide ores merenskyite forms unusually large up to 5000 m2 euhedral grains commonly in contact with spherical silicate inclusions bms hosts 12 16 of the pd with the remainder hosted by pgm which is interpreted to indicate that merenskyite recrystallized from a pge bearing bismuthotelluride metamorphic melt formed during high grade metamorphism sperrylite ptas2 is the second most abundant pgm 18 of pgm in disseminated ore and in contrast to merenskyite occurs mainly as very small median of 25 m2 inclusions in high temperature silicates and oxides interpreted to have crystallized at high temperatures directly from sulfide blebs that formed and were transported within the limoeiro magma conduit

dehydration induced damage and deformation in gypsum and implications for subduction zone processes 1 experimental heating tests were performed on volterra gypsum to study the micromechanical consequences of the dehydration reaction the experimental conditions were drained at 5 mpa fluid pressure and confining pressures ranging from 15 to 55 mpa one test was performed with a constantly applied differential stress of 30 mpa the reaction is marked by 1 a porosity increase and homogeneous compaction 2 a swarm of acoustic emissions 3 a large decrease in p and s wave velocities and 4 a decrease in vp vs ratio wave velocity data are interpreted in terms of crack density and pore aspect ratio which modeling pores as spheroids is estimated at around 0 05 crack like spheroid complementary tests performed in an environmental scanning electron microscope indicate that cracks first form inside the gypsum grains and are oriented preferentially along the crystal structure of gypsum most of the visible porosity appears at later stages when grains shrink and grain boundaries open extrapolation of our data to serpentinites in subduction zones suggest that the signature of dehydrating rocks in seismic tomography could be a low apparent poisson s ratio although this interpretation may be masked by anisotropy development due to preexisting crystal preferred orientation and or deformation induced cracking the large compaction and the absence of strain localization in the deformation test suggests that dehydrating rocks maybe seen as soft inclusions and could thus induce ruptures in the surrounding nonreacting rocks

test of climate leaf physiognomy regression models their application to two miocene floras from kenya and 40ar 39ar dating of the late miocene kapturo site abstract to test multiple regression models developed to predict seven variables of climate from leaf margin and size characters leaf character data were collected from modern woodland and rainforest plant communities in uganda these localities were chosen for their structural similarity to two fossil sites for which climate values were desired the test indicated that for these communities the model accurately predicts mean annual temperature however the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities reasons for the models inaccuracies may include no african analog in the non african database on which the model is based too much intraspecific variability in leaf size an important character in precipitation models and relationships between leaf form and climate that may not be well defined by multiple regression mean annual temperatures were reconstructed for two miocene paleobotanical localities from the tugen hills of the eastern rift valley kenya using leaf form data primarily margin characters the results indicate that mean annual temperatures at kabarsero 12 6 ma and kapturo 6 7 7 2 ma were essentially equivalent to temperatures at those localities today and differed little from one another the kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the kabarsero paleofloral assemblage a wet forest with west african floral affinities laser fusion 40 ar 39 ar dating of volcanic materials at kapturo provides the first control of this paleoflora bracketed by a 7 2 ma trachyte at the base of the sedimentary sequence and an age of 6 7 ma on a reworked tuff overlying the fossiliferous horizon the chronologic data places the paleofloral assemblage in stratigraphic context relative to other tugen hills units containing paleofloras and abundant vertebrate remains including hominoids

reconstruction of a fossil forest reveals details of the palaeoecology palaeoenvironments and climatic conditions in the late oligocene of south america abstract this research focuses on the three dimensional reconstruction of an in situ forest based on fossil wood assemblages recovered in the rancahue formation upper oligocene neuquen argentina atherospermataceae lauraceae nothofagaceae eucryphiaceae cunoniaceae and myrtaceae specimens are described the mapping of a forest floor section and in situ tree diameters enabled the estimation of the following palaeoecological quantitative data tree density dominance basal area biomass diametric classes canopy height and age classes palaeoclimatical data was determined on the basis of physiognomic anatomical features using multivariate anatomical analyses these results were compared with other proxies including carlquist s index coexistence approach ca nearest living relatives nlrs and growth rings analyses the structural data from the alumine forest inferred from these analyses includes tree density of 463 701 trees ha mean height of 15 22 m dominance of the genus nothofagoxylon 89 66 m2 ha total basal area of 158 20 m2 ha biomass between 43 and 712 tn ha and mean age of 223 years specimens between 31 and 700 years old these results are comparable to those of mature low to middle altitude extant forests dominated by nothofagus and developed under humid temperate conditions based on the nlrs method the alumine forest has a floristic composition similar to the present day valdivian forest the persistence of nothofagus as the dominant element in temperate rainforests correlates with regimes where large scale disturbances such as volcanism and earthquakes are prevalent the fossil taxa are closely related to the extant laurelia persea eucryphia nothofagus weinmannia myrceugenia and luma the forest shows intermixed deciduous and evergreen elements and taxa with shade intolerance and intermediate shade tolerance also the majority of these taxa need soils with available water the integrated analysis of multiple sets of proxy data suggests that the late oligocene forest grew under temperate and humid climate while the eco anatomical features and sedimentary data provide information about the environmental stress conditions of its development and the violent causes of burial

platinum group minerals from the kambalda nickel deposits western australia the relative abundance compositional variability and geologic occurrence of platinum group minerals have been determined by a study of samples from a number of geologic environments in the kambalda nickel deposits these results have been integrated with findings from a previous study by hudson and donaldson 1984 of platinum group minerals in amalgamation residues from the gold recovery circuit of the kambalda nickel mill to give an overall picture of the nature and distribution of platinum group minerals at kambalda the major platinum minerals are sperrylite and moncheite and the major palladium minerals are sudburyite merenskyite stibiopalladinite palladoarsenide michenerite and testibiopalladite palladium also occurs in solid solution in palladian melonite irarsite is the only iridium mineral recognized and no discrete phases have been observed for the other platinum group elements sperrylite occurs within massive pyrrhotite pentlandite ores and is particularly abundant in ores that are rich in chalcopyrite a high proportion of the pt in the kambalda nickel deposits is believed to occur as sperrylite but not all sperrylite is sufficiently coarse in grain size to enable gravity concentration nevertheless sperrylite is the dominant platinum group mineral recovered in gravity concentrates discrete palladium minerals are most abundant in stringers of sulfide in the footwall to the ore in crosscutting sulfide veins or in reaction zones associated with hydrothermal veins and porphyries within the massive and matrix ores coarse discrete palladium minerals are rare and it is concluded that palladium occurs in solid solution or as finely dispersed submicroscopic grains in sulfide minerals predominantly pentlandite the occurrence within the ore zones of pt as sperrylite and pd dispersed in pentlandite is believed to reflect a primary magmatic distribution however the presence of sudburyite moncheite merenskyite michenerite testibiopalladite and palladian melonite in stringers and reaction zones indicates that their formation may be related to postmagmatic processes in particular metamorphic segregation of sulfides and the interaction of ore sulfides with younger hydrothermal fluids

evidence of neogene wildfires in central chile charcoal records from the navidad formation abstract mediterranean type climate mtc ecosystems are characterized by recurrent wildfires although the majority of wildfires are human ignited non anthropogenic i e natural wildfires are common in all mtc regions except central chile the low frequency of natural wildfires in this chilean region is explained by the scarcity of non anthropogenic ignition sources basically thunderstorm induced lightning and volcanic activity however from a geological perspective the current relative absence of non anthropogenic wildfires in central chile is a recent phenomenon in the transition from the early to middle miocene the climate in the region was likely warm and seasonally dry such climate conditions would allow the growth of fuel during the spring becoming flammable during the dry season this fire prone landscape would likely have been ignited by the high volcanic activity that concomitantly occurred with the orogeny of the andes to evaluate this hypothesis we sampled rocks from the three locations at the navidad formation considering the fossil plant evidence deposited during this warm and seasonally dry period we found a high concentration of charcoal in playa navidad coinciding with the global warming event reported between 17 and 15 ma the predominance of microscopic charcoal particles between 125 and 250 m only allows us to infer the occurrence of neogene fires at a regional scale the fused cell walls preserved in the charcoal anatomy likely suggest that such fire events were highly severe the presence of pumice associated with the high charcoal concentrations supports the hypothesis of volcanic ignition sources very little charcoal was found in punta perro late oligocene early miocene or in cerro los pololos late middle miocene where fire may have been limited by fuel humidity and ignition sources respectively although changes in the depositional environment would also help explain differences in the fire record throughout the navidad formation in conclusion our results provide the first quantitative neogene charcoal record for south america the evidence of fire occurrence in central chile during the neogene will contribute to understanding the evolution of the mediterranean type flora

melonite group minerals and other tellurides from three cu ni pge prospects eastern desert egypt abstract melonite group minerals and other tellurides are described from three cu ni pge prospects in the eastern desert of egypt gabbro akarem genina gharbia and abu swayel the prospects are hosted in late precambrian mafic ultramafic rocks and have different geologic histories the gabbro akarem prospect is hosted in dunite pipes where net textured and massive sulfides are associated with spinel and cr magnetite michenerite merenskyite pd bi melonite and hessite occur mainly as inclusions in sulfides typical magmatic textures indicate a limited role of late and post magmatic hydrothermal processes at genina gharbia ore forms either disseminations in peridotite or massive patches in hornblende gabbro in the vicinity of metasedimentary rocks actinolitic hornblende epidote chlorite and quartz are common secondary silicates sulfide textures and host rock petrography suggest a prolonged late magmatic hydrothermal event michenerite merenskyite pd bi melonite altaite hessite tsumoite sylvanite and native te are mainly present in secondary silicates the abu swayel prospect occurs in conformable lens like mafic ultramafic rocks in metasedimentary rocks and along syn metamorphic shear zone the sulfide ore and host rocks are metamorphosed amphibolite facies 550 to 650 c 4 to 5 kbar and syn metamorphically sheared melonite group minerals are represented by merenskyite and pd bi melonite other tellurides comprise hessite altaite and joseite b melonite group minerals and tellurides occur as inclusions in mobilized sulfides and along cracks in metamorphic garnet and plagioclase the different geological history of the three prospects permits an examination of the role played by magmatic late magmatic and metamorphic processes on the mineralogy of melonite group minerals and diversity of tellurides the contents of pge and te in the ore and temperature of crystallization control the mineralogy and compositional trends of the melonite group minerals crystallization of the melonite group minerals over a wide range of temperatures in a te rich environment enhances the elemental substitutions merenskyite dominates the mineralogy of the group at low te activity while pd bi melonite is the common phase at high te activity

stable isotopes in large herbivore tooth enamel capture a mid miocene precipitation spike in the interior pacific northwest abstract stable carbon and oxygen isotopes of fossil ungulate tooth enamel were used to investigate the paleoclimate of the pacific northwest from the mid oligocene through pleistocene particularly targeting the mid miocene climatic optimum mmco we specifically test whether precipitation as inferred from tooth enamel 13c values relative to the 13c values of atmospheric co2 13c increased with increasing partial pressure of atmospheric co2 pco2 analysis emphasized water dependent equids rhinos and proboscideans but several artiodactyls and castor were also analyzed as available values of 13c 19 5 in the lower john day 27 and 18 ma and mascall 15 16 ma localities imply relatively high mean annual precipitation map ca 550 800 mm yr values of 13c

fluid induced rupture experiment on fontainebleau sandstone premonitory activity rupture propagation and aftershocks 1 a 14 porosity fontainebleau sandstone sample diameter 40 mm length 88 mm was loaded tri axially under 100 mpa confining pressure and 240 mpa differential stress in drained conditions and under constant load pore pressure water was raised until failure was triggered during the experiment elastic wave velocities and permeability were monitored while more than 3000 acoustic emissions ae were located prior and after failure ae locations show that macroscopic fracture propagated from a large nucleation patch at speeds comprised between 0 1 and 4 m s number of ae hits per second followed omori s law with exponents of 0 92 and 1 18 pre and post failure respectively no quiescence was observed post failure except where rupture initially nucleated from fast depressurization of the pore space induced secondary aftershocks located within the fracture plane possibly indicating a heterogeneous fault geometry after rupture of lower permeability that compacted during the release of pore pressure

a paleocene lowland macroflora from patagonia reveals significantly greater richness than north american analogs few south american macrofloras of paleocene age are known and this limits our knowledge of diversity and composition between the end cretaceous event and the eocene appearance of high floral diversity we report new unbiased collections of 2516 compression specimens from the paleocene salamanca formation ca 61 7 ma from two localities in the palacio de los loros exposures in southern chubut patagonia argentina our samples reveal considerably greater richness than was previously known from the paleocene of patagonia including 36 species of angiosperm leaves as well as angiosperm fruits flowers and seeds ferns and conifer leaves cones and seeds the floras which are from siltstone and sandstone channel fills deposited on low relief floodplain landscapes in a humid warm temperate climate are climatically and paleoenvironmentally comparable to many quantitatively collected paleocene floras from the western interior of north america adjusted for sample size there are 50 more species at each palacio de los loros quarry than in any comparable u s paleocene sample these results indicate more vibrant terrestrial ecosystems in patagonian than in north american floodplain environments 4 m y after the end cretaceous extinction and they push back the time line 10 m y for the evolution of high floral diversity in south america the cause of the dis parity is unknown but could involve reduced impact effects because of greater distance from the chicxulub site higher latest cretaceous diversity or faster recovery or immigration rates

compressive failure of mudstone samples containing quartz veins using rapid ae monitoring the role of asperities this paper presents the results of an ongoing experimental investigation of compressive failure of homogeneous and heterogeneous rocks we used a rapid data acquisition system to monitor the spatio temporal distribution of acoustic emission ae during fault nucleation under conditions of either constant rate loading or static loading in order to examine the effect of asperities on faulting we conducted a series of experiments on mudstone with quartz veins the bedding planes of the mudstone were oriented at an angle of 30 with the maximum compressive stress and were expected as the fracture plane the quartz veins are much stronger than the bedding plane of mudstone and thus the samples model faults having strong asperities experimental results show that 1 ae activity initiated close to the peak stress and almost all ae hypocenters appeared at the intersections of the veins and the fault planes suggesting that the vein asperities control faulting 2 the b value changed with time and shows multiple large and short term fluctuations 3 the change of the b value correlated closely with the spatio temporal hierarchy of the fracture process and 4 fault segments along the bedding plane show behavior of slip having large compressive deformation before the peak stress while the vein asperities show large precursor dilatancy prior to dynamic rupture these experimental results are helpful for the understanding of seismic precursor phenomena associated with strain localization dilatancy change in level of ground water as well as the b value

the end triassic mass extinction record of williston lake british columbia abstract triassic jurassic boundary sections on the shore of lake williston british columbia record a spectrum of depositional environments from the western canadian continental margin a primarily deep water anoxic record of deposition indicated by v v ni v cr th u indices and pyrite framboid and facies data is seen throughout the late triassic early jurassic norian hettangian interval in a section at black bear ridge abundant monotis bivalve populations in norian strata are interpreted to have lived on the seabed during transient oxygenation events that punctuated the background anoxic conditions monotis went extinct around the norian rhaetian boundary and the deep water assemblages are subsequently dominated by thin shelled pectinids an intra rhaetian sea level fall generated a major hiatus in the proximal black bear ridge section whilst distinctive lowstand strata were developed in the more distal and more complete ne parle pas point and pardonet creek sections these consist of shallow water phosphatic ooid sand facies that contain diverse bivalves the majority of the infaunal bivalves but not the epifaunal ones disappeared at the acme of the regression this is the end triassic mass extinction event and it occurred shortly before a terminal triassic flooding event this transgressive event is associated with a rapid negative shift of 13corg values interpreted to be the initial isotope excursion of hesselbo et al hesselbo s p robinson s a surlyk f piasecki s 2002 terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism geology 30 251 254 the rhaetian record of williston lake thus records an extinction of shallow water infaunal bivalves during a lowstand prior to the development of a transgressive record that is associated with a major negative c isotope

a methodology for targeting palaeo proxy data acquisition a case study for the terrestrial late miocene when planning the acquisition of new palaeo proxy data for reconstructing past climates many factors influence the decision of where the proxies are to be collected one such influence is the likelihood of recording a significant climate change relative to the modern another consideration which is less often considered is the desire to target regions in which there is significant uncertainty in numerical model predictions of past climate change new proxy data in these regions enables a more rigorous test of model simulations and results in better constraints on the various boundary conditions used to force the models in this paper we present a methodology for targeting new palaeo proxy data based on model simulations we use the terrestrial late miocene 11 6 to 5 3 ma as a case study the late miocene climate provides insights into future climate behavior as it is believed to have been considerably warmer than the modern we carry out a suite of late miocene atmosphere only general circulation model simulations which we initially evaluate relative to an example dataset of terrestrial temperature and precipitation in terms of targeting future data acquisition we locate those regions in the model which exhibit the largest change in temperature and or precipitation relative to the pre industrial we also locate those regions which display the largest variability between the model simulations because new data in these regions are most likely to provide a strict test of the reliability of the model results among other regions the amazon basin the chad basin central canada and northern india are identified as potentially useful areas to collect data

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

the influence of environmental conditions on weathering of porous rocks by gypsum a non destructive study using acoustic emissions gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones to quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles during drying two different temperatures 50 and 25 c and relative humidity low 25 at 50 c and 65 at 25 c and high 99 have been applied the acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions and also higher when drying at 50 c than at room temperature microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature gypsum crystallizes not on the sample surface like in the other samples but deeper in the inner part of the sample in good agreement with previously published data we show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory

failure mode and spatial distribution of damage in rothbach sandstone in the brittle ductile transition to elucidate the spatial complexity of damage and evolution of localized failure in the transitional regime from brittle faulting to cataclastic ductile flow in a porous sandstone we performed a series of triaxial compression experiments on rothbach sandstone 20 porosity quantitative microstructural analysis and x ray computed tomography ct imaging were conducted on deformed samples localized failure was observed in samples at effective pressures ranging from 5 mpa to 130 mpa in the brittle faulting regime dilating shear bands were observed the ct images and stereological measurements reveal the geometric complexity and spatial heterogeneity of damage in the failed samples in the transitional regime at effective pressures between 45 mpa and 130 mpa compacting shear bands at high angles and compaction bands perpendicular to the maximum compression direction were observed the laboratory results suggest that these complex localized features can be pervasive in sandstone formations not just limited to the very porous aeolian sandstone in which they were first documented the microstructural observations are in qualitative agreement with theoretical predictions of bifurcation analyses except for the occurrence of compaction bands in the sample deformed at effective pressure of 130 mpa the bifurcation analysis with the constitutive model used in this paper is nonadequate to predict compaction band formation may be due to the neglect of bedding anisotropy of the rock and multiple yield mechanisms in the constitutive model

modeling porous rock fracturing induced by fluid injection abstract in this paper we describe and implement a theoretical model that captures the physical processes occurring during hydraulic fracturing of saturated and unsaturated porous rock the model is based on a poro elastic plastic rheology with a mohr coulomb yield function and unassociated flow rule and includes frictional hardening cohesion weakening damage and mobilized dilatancy effects in addition fluid injection is described using the richard s approximation we numerically implement the model using a finite difference scheme on a staggered grid and compare the model results with laboratory experiments published in stanchits et al 2011 16 from various experiments performed by stanchits et al we use three different laboratory configurations for comparing our model results and observations a triaxial compression of a drained rock sample b low pressure fluid injection into a drained critically stressed rock and c high pressure fluid injection into a saturated rock sample we find good agreement between model and observations for all cases indicating a proper formulation and implementation of the dominant physical mechanisms acting the model reproduces experimental observations of macroscopic fracture fluid front localization and the stress strain response curves matching observations from laboratory scale experiments establishes a benchmark and a calibrated model for numerically simulating experiments performed at the larger field scale

did south american mixed paleofloras evolve under thermal equability or in the absence of an effective andean barrier during the cenozoic abstract two hypotheses have attempted to explain the development of mixed paleofloras during the cenozoic in south america one of them postulates changes in the climatic tolerances of its component taxa and the other calls for the establishment of atmospheric thermal stability equable climate at the time these floras came into existence we set out to test these hypotheses using leaf physiognomical analyses for eight mixed fossil floras of the cenozoic of chile and argentina in addition to physiognomic analyses of the complete dicotyledonous flora as known from each site we also evaluated the physiognomic significance of fossil nothofagus leaves in relation to current chilean species of the genus our results suggest that fossil nothofagus leaves have a broader climatic envelope relative to the extant species this divergence could be accounted by differences in their respective climatic tolerances we postulate that the mixed paleoflora evolved in a subtropical climate that extended as far south as 40 s with relatively warm temperatures and high annual rainfall with little seasonal variation this climatic scenario is possible only with a much reduced andean massif which would have permitted the spillover of moisture of easterly origin to the pacific andean slopes

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

record of environmental changes in the triassic jurassic boundary interval in the zliechov basin western carpathians abstract the fatra and kopieniec formations in the zliechov basin comprise a record of several environmental crises that may have contributed to the global triassic jurassic t j boundary events the diversity of the benthic fauna decreases at the base of the transition beds the uppermost member of the fatra formation this assemblage comprises many species that do not appear in younger strata in cycle 13 of the fatra formation stable isotope excursions correspond to significant lithological changes in the sequence the negative 13 c excursion is correlated with a positive 18 o peak and the beds containing the excursion are overlain by a thin layer with unusual lithological and mineral composition this layer is composed of small calcitized microspheres showing complex alteration during diagenesis the origin of this layer traceable over tens of kilometres is problematic impact ejecta volcanic glass or altered aragonitic particles an increase in terrigenous sediment recorded by sandy beds in the uppermost part of the fatra formation indicates increased run off a sharp lithological boundary between the fatra and the kopieniec formations marks a sudden termination of carbonate sedimentation followed by deposition of the boundary clay the negative 13 c anomaly recognized in this succession may correspond to the isotopic signature at the t j boundary which has been described from many sections in the world

the distribution of pge and the role of arsenic as a collector of pge in the spotted quoll nickel ore deposit in the forrestania greenstone belt western australia the spotted quoll pge bearing ni deposit in the forrestania greenstone belt in the archean yilgarn block in western australia is a komatiite associated massive sulfide orebody tectonically displaced from its original host the brecciated ore contains clasts of quartz and garnet schist and is located along a shear zone overlain by banded iron formation bif and underlain by bif and quartz biotite metasediments the deformation of the ore has destroyed its magmatic textures and it has been sheared and recrystallized at amphibolite facies then the deformed ore has been subjected to a hydrothermal event that concentrated the pge with au and as often at the edge of the ni ore the pge are distributed between pgm and in solid solution in ni sulfarsenides and pd also occurs in pentlandite the pgm include sudburyite pdsb sperrylite ptas2 and irarsite irass all six pge and minor au are hosted in gersdorffite niass two generations of gersdorffite have been recognized a higher temperature magmatic euhedral co rich gersdorffite encloses ir pt and rh bearing pgm surrounded by halos of rh ir and os rich gersdorffite a lower temperature ni rich gersdorffite forms anhedral grains and rims on grains of nickeline nias in this low temperature gersdorffite pge are concentrated toward the mineral edges sudburyite and gold occur associated predominantly with nickeline the pge and gold are now predominantly associated with sulfarsenides that are the controlling factor for their distribution

taphonomy of a middle miocene autochthonous forest assemblage ngorora formation central kenya abstract a 12 6 million year old forest assemblage of leaves twigs and rare fruit is preserved in the ngorora formation of central kenya the assemblage is autochtonous preserved in airfall tuff and represents well the diversity heterogeneity and richness of the original forest the herbaceous component not usually preserved in paleobotanical assemblages is present nearest neighbor analysis and mapping of the vertical distribution of plant organs indicates that leaves and twigs are preserved near the parent plant and that there is no apparent size weight or species bias in deposition of these remains leaves occur isolated in clusters or attached to branches and fell directly to the ground as a result of ashfall most falling very soon after ashfall commenced the absence of upright trunks and large stems is probably due to post depositional weathering which may also be responsible for the absence of a leaf litter layer however leaf litter may have been absent at the time of ash deposition

role of seepage forces on seismicity triggering 1 borehole fluid injection is commonly used for geological sequestration of carbon dioxide underground storage of natural gas waste injections and during stimulations and development of geothermal and hydrocarbon reservoirs typically the injection process induces significant seismicity with some earthquakes as large as magnitude four induced seismicity has also been observed around producing hydrocarbon boreholes recently it has been argued that some induced seismicity data can be explained by a highly nonlinear fluid diffusion mechanism or by the propagation of fluid pressure pulses the nature of the nonlinearity and the mechanisms by which a pressure pulse can trigger seismicity are still uncertain in this paper i show that the same spatiotemporal variation of seismicity can be explained and predicted by linear diffusion coupled to deformation of a linear poroelastic medium by calculating the propagation of coulomb yielding stress cys perturbation with time it is demonstrated that seismicity can be triggered by this perturbation the change of cys along the diffusion front is caused by seepage forces which are body forces generated by fluid pressure gradients and can explain induced seismicity during borehole fluid injection and extraction using published experimental data i demonstrate how the spatiotemporal distribution of fluid induced seismic events can be used for reservoir modeling and characterization

palaeobotanical evidence for a marked temperature increase following the cretaceous tertiary boundary correspondence analysis of dicot leaf physiognomy of modern vegetational samples from a wide range of environments indicates that 70 of physiognomic variation corresponds to water or temperature factors or both despite wide variation in single physiognomic characters overall trends can be used to distinguish between samples from different climates some climate parameters are well correlated with changes in physiognomy so that climate characteristics can be inferred from physiognomic analyses here i apply this climate leaf analysis multivariate program clamp to leaf assemblages from the cretaceous tertiary boundary the results indicate a fourfold increase in precipitation at the boundary and an increase in mean annual temperature of 10 c these levels persisted for 0 5 1 0 myr after which prea cipitation decreased to about three times the values for the latest cretaceous and the mean annual temperature decreased to 5 6 c above latest cretaceous values

acoustic emissions monitoring during inelastic deformation of porous sandstone comparison of three modes of deformation in some reservoirs large deformations can occur during oil or gas production because of the effective stress change for very porous rocks these production operations can be sufficient to cause inelastic deformation and irreversible damage rock formations can undergo deformation by different mechanisms including dilatancy or pore collapse in the laboratory it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive indeed when subjected to an overall compressive loading a porous rock may fail by shear localization compaction localization or by cataclastic compaction acoustic emission ae records provide important information to understand the failure mode of rocks the spatial evolution of damage as well as the source mechanisms can be followed using this technique in this paper we present three different laboratory axisymmetric compression experiments performed on bleurswiller sandstone which enable us to compare the acoustic emission signature of these three modes of deformation our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures in terms of ae sources characteristics and evolution of ae number in comparison to the acoustic signature from shear localization this implies similar micromechanisms involved during compaction bands formation and cataclastic compaction

mechanical behaviour and failure modes in the whakaari white island volcano hydrothermal system new zealand abstract volcanic hydrothermal systems host a prodigious variety of physico chemical conditions the physico chemical state and mechanical behaviour of rocks within is correspondingly complex and often characterised by vast heterogeneity here we present uniaxial and triaxial compression experiments designed to investigate the breadth of mechanical behaviour and failure modes dilatant or compactant for hydrothermally altered lava and ash tuff deposits from whakaari white island volcano in new zealand a volcano with a well documented and very active hydrothermal system our deformation experiments show that the failure mode of low porosity lava remains dilatant over a range of depths up to pressures corresponding to depths of about 2 km upon failure shear fractures the result of the coalescence of dilatational microcracks are universally present the high porosity ash tuffs switch however from a dilatant to a compactant failure mode driven by progressive distributed pore collapse at relatively low pressure corresponding to a depth of about 250 m we capture the salient features of the dynamic conditions e g differential stress effective pressure in a schematic cross section for the whakaari hydrothermal system and map for the different lithologies areas susceptible to either dilatant vs compactive modes of failure the failure mode will impact for example the evolution of rock physical properties e g porosity permeability and elastic wave velocity and the nature of the seismicity accompanying periods of unrest we outline accordingly the potential implications for the interpretation of seismic signals outgassing ground deformation and the volcanic structural stability for whakaari and similar hydrothermally active volcanoes worldwide

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

acoustic emission and velocities associated with the formation of compaction bands in sandstone received 31 may 2005 revised 2 may 2006 accepted 22 june 2006 published 7 october 2006 1 a series of laboratory experiments has been conducted in which three dimensional 3 d locations of acoustic emissions ae were recorded and used to analyze the development of compaction bands in bleurswiller sandstone which has a porosity of 25 results were obtained for saturated samples deformed under triaxial compression at three different confining pressures 60 80 and 100 mpa a pore pressure of 10 mpa and room temperature we recorded acoustic emissions compressional and shear wave velocities and porosity reduction under hydrostatic condition and under triaxial loading conditions at a constant axial strain rate our results show that seismic velocities and their amplitude increased during hydrostatic pressure build up and during initial axial loading during shear enhanced compaction axial and radial velocities decreased progressively indicating an increase of stress induced damage in the rock in experiments performed at confining pressures of 80 and 100 mpa during triaxial loading acoustic emissions were localized in clusters during progressive loading ae clusters grow horizontally perpendicular to the maximum principal stress direction indicating formation of compaction bands throughout the specimens microstructural analysis of deformed specimens confirmed a spatial correspondence of ae clusters and compaction bands for the experiment performed at a confining pressure of 60 mpa ae locations and microstructural observations show symmetric compaction bands inclined to the cylinder axis of the specimen in agreement with predictions from recent theoretical models

mean annual temperature estimation based on leaf morphology a test from tropical south america abstract are models that predict mean annual temperature mat from leaf morphology applicable globally fifteen models that predict mat from leaf morphology were tested on thirty floral samples from tropical south america to determine the degree to which models based on published data that are primarily from other regions are applicable to floras from tropical south america the models included are based on regional data from north america south america and asia of the fifteen models tested five are simple linear regressions six are multiple linear regressions two are canonical correspondence analyses and two are correspondence analyses followed by nearest neighbor analyses for the seven modern floras with mat 21 c every model overestimates mat for the 23 modern floras with mat 21 c all models produce variable results without a systematic error the range of average model errors is 2 7 7 3 c while the absolute extremes of error are 0 and 15 1 c average 95 predictive confidence intervals range from 1 6 to 6 9 c predicted mat falls within the published standard error of the model for 0 67 of the south american test floras evaluating the seven sites with mat 21 c separately from the 23 sites with mat 21 c shows that no equation accurately estimates mat of the majority of low temperature sites but that four equations accurately estimate 50 of high temperature sites the results suggest that at least for sites of unknown or high elevation mean annual temperature of fossil floras from tropical south america may be better predicted from models based on the leaf morphology of tropical south american floras

what is an equable climate abstract the ideal theoretical equable climate has a mean annual temperature of 14 c and a mean annual range of 0 c since 14 c is and has been the average mean temperature of the earth s surface any departure from 14 c and 0 c results in a climate of lower temperateness or equability therefore reference to an equable paleoclimate is meaningless unless quantified by a centrum from which equability is measured climates of low seasonality are not necessarily equable because such conditions occur from the inner wet tropics into glacial border environments freezing often occurs in climates of moderate to high equability equable climates may support taxa from different vegetation zones a relation also evident in the paleobotanical record

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

initiation and propagation of mixed mode fractures in granite and sandstone abstract we investigate mixed mode fracture initiation and propagation in experimentally deformed granite and sandstone we performed a series of asymmetric loading tests to induce fractures in cylindrical specimens at confining pressures up to 20 mpa loading was controlled using acoustic emission ae feedback control which allows studying quasi static fracture propagation for several hours location of acoustic emissions reveals distinct differences in spatial temporal fracture evolution between granite and sandstone samples before reaching peak stress in experiments performed on granite axial fractures initiate first at the edge of the indenter and then propagate through the entire sample secondary inclined fractures develop during softening of the sample in sandstone inclined shear fractures nucleate at peak stress and propagate through the specimen ae source type analysis shows complex fracturing in both materials with pore collapse contributing significantly to fracture growth in sandstone samples we compare the experimental results with numerical models to analyze stress distribution and energy release rate per unit crack surface area in the samples at different stages during fracture growth we thereby show that for both rock types the energy release rate increases approximately linearly during fracture propagation the study illuminates how different material properties modify fracture initiation direction under similar loading conditions

deriving temperature estimates from southern hemisphere leaves abstract the percentage of woody dicots with entire margined leaves in a flora is known to be positively correlated with mean annual temperature leaf margin analysis lma but this relationship is not globally uniform in particular the floras of australia and new zealand have been regarded as displaying a different physiognomic relationship to climate than floras seen in the northern hemisphere this difference is more marked in new zealand where the lma relationship appears entirely absent here we amass data for both northern and southern hemispheres using standard protocols and show that regional variations in the leaf margin mean annual temperature relationship are real but become less significant when other characters are included even new zealand falls into line and most of the mean annual temperature signal in new zealand floras is encoded in non margin features we introduce a new clamp climate leaf analysis multivariate program calibration dataset for the southern hemisphere comprising leaf physiognomic data from argentina bolivia south africa australia new zealand and other pacific islands that offers comparable precision for climate prediction to similar datasets derived from the northern hemisphere

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

a new method to estimate location and slip of simulated rock failure events abstract at the laboratory scale identifying and locating acoustic emissions aes is a common method for short term prediction of failure in geomaterials above average ae typically precedes the failure process and is easily measured at larger scales increase in micro seismic activity sometimes precedes large earthquakes e g tohoku l aquilla oceanic transforms and can be used to assess seismic risk the goal of this work is to develop a methodology and numerical algorithms for extracting a measurable quantity analogous to ae arising from the solution of equations governing rock deformation since there is no physical property to quantify ae derivable from the governing equations an appropriate rock mechanical analog needs to be found in this work we identify a general behavior of the ae generation process preceding rock failure this behavior includes arbitrary localization of low magnitude events during pre failure stage followed by increase in number and amplitude and finally localization around the incipient failure plane during macroscopic failure we propose deviatoric strain rate as the numerical analog that mimics this behavior and develop two different algorithms designed to detect rapid increases in deviatoric strain using moving averages the numerical model solves a fully poro elasto plastic continuum model and is coupled to a two phase flow model we test our model by comparing simulation results with experimental data of drained compression and of fluid injection experiments we find for both cases that occurrence and amplitude of our ae analog mimic the observed general behavior of the ae generation process our technique can be extended to modeling at the field scale possibly providing a mechanistic basis for seismic hazard assessment from seismicity that occasionally precedes large earthquakes

tectonic events reflected by palaeocurrents zircon geochronology and palaeobotany in the sierra baguales of chilean patagonia abstract the sierra baguales situated north of the torres del paine national park in the magallanes region of southern chile shows a well exposed stratigraphic sequence ranging from the late cretaceous to late pliocene which presents a unique opportunity to study the evolution of sedimentological styles and trends palaeoclimate changes and tectonic events during this period the depositional environment changed from a continental slope and shelf during the cenomanian campanian tres pasos formation to deltaic between the campanian maastrichtian dorotea formation and estuarine in the lutetian bartonian man aike formation during the rupelian a continental environment with meandering rivers and overbank marshes was established rio leona formation this area was flooded in the early burdigalian estancia 25 de mayo formation during the patagonian transgression but emerged again during the late burdigalian santa cruz formation measured palaeocurrent directions in this mesozoic cenozoic succession indicate source areas situated between the northeast and east southeast during the late cretaceous east southeast during the middle eocene and southwest during the early oligocene to early miocene this is confirmed by detrital zircon age populations in the different units which can be linked to probable sources of similar ages in these areas the east southeastern provenance is here identified as the antarctic peninsula or its northeastern extension which is postulated to have been attached to fuegian patagonia during the eocene the southwestern and western sources were exhumed during gradual uplift of the southern patagonian andes coinciding with a change from marine to continental conditions in the magallanes austral basin as well as a decrease in mean annual temperature and precipitation indicated by fossil leaves in the rio leona formation the rain shadow to the east of the andes thus started to develop here during the late eocene early oligocene 34 ma long before the quechua phase of andean tectonics 19 18 ma that is generally invoked for its evolution at lower latitudes

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

an oligocene microthermal forest dominated by nothofagus in sierra baguales chilean patagonia response to global cooling and tectonic events abstract a large fossil leaf assemblage 3700 specimens is reported from the oligocene rio leona formation in the sierra baguales of chilean patagonia the association comprises 29 species but is dominated by nothofagus genera which constitutes 65 of specimens the collection can be classified as a mixed palaeoflora of the austral antarctic association stratigraphic analysis of the assemblage indicates a decrease in species diversity and richness over time which was accompanied by species turnover quantitative studies of foliar morphology clamp leaf margin analysis indicates cool to cold and dry climatic conditions with a mean annual temperature of 9 2 c a relatively high seasonality in temperature and precipitation and a mean annual precipitation of 931 mm nothofagus only became dominant in southeastern patagonia during the rupelian coinciding with a marked global cooling period linked to the initiation of glaciation in antarctica about 34 ma the decrease in precipitation following this event is attributed to the development of a rain shadow to the east of the rising southern patagonian andes which must have been of the order of 1000 m or more for topographic climate forcing to take effect this contrasts with the rain shadow development east of the andes at lower latitudes which was mainly manifested after the middle miocene

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

fracture process zone in granite in uniaxial compression tests performed on aue granite cores diameter 50 mm length 100 mm a steel loading plate was used to induce the formation of a discrete shear fracture a zone of distributed microcracks surrounds the tip of the propagating fracture this process zone is imaged by locating acoustic emission events using 12 piezoceramic sensors attached to the samples propagation velocity of the process zone is varied by using the rate of acoustic emissions to control the applied axial force the resulting velocities range from 2 mm s in displacement controlled tests to 2 m s in tests controlled by acoustic emission rate wave velocities and amplitudes are monitored during fault formation p waves transmitted through the approaching process zone show a drop in amplitude of 26 db and ultrasonic velocities are reduced by 10 the width of the process zone is 9 times the grain diameter inferred from acoustic data but is only 2 times the grain size from optical crack inspection the process zone of fast propagating fractures is wider than for slow ones the density of microcracks and acoustic emissions increases approaching the main fracture shear displacement scales linearly with fracture length fault plane solutions from acoustic events show similar orientation of nodal planes on both sides of the shear fracture the ratio of the process zone width to the fault length in aue granite ranges from 0 01 to 0 1 inferred from crack data and acoustic emissions respectively the fracture surface energy is estimated from microstructure analysis to be 2 j a lower bound estimate for the energy dissipated by acoustic events is 0 1 j

a review of tertiary climate changes in southern south america and the antarctic peninsula part 2 continental conditions abstract climate changes in southern south america and the antarctic peninsula during the tertiary show a strong correlation with ocean warming and cooling events which are in turn related to tectonic processes during periods of accelerated sea floor spreading and mid ocean ridge activity sea levels rose so that parts of the continents were flooded and forests were destroyed however this was balanced by the large scale release of co2 during volcanic outgassing and carbonate precipitation on the continental shelves which caused rising air temperatures and the poleward expansion of sub tropical and temperate forests cooling episodes generally caused an increase in the north south thermal gradient because of an equatorward shift in climate belts so that the westerly winds intensified and brought higher rainfall to the lower latitudes an increase in wind blown dust caused temperatures to drop further by reflecting sunlight back into space the rising andes range had a marked influence on climate patterns up to the middle miocene it was still low enough to allow summer rainfall to reach central and north central chile but after about 14 ma it rose rapidly and effectively blocked the spill over of moisture from the atlantic ocean and amazon basin at this time the cold humboldt current was also established which together with the andes helped to create the arid diagonal of southern south america stretching from the atacama desert to the dry steppes of patagonia this caused the withdrawal of subtropical forests to south central chile and the expansion of sclerophytic vegetation to central chile however at the same time it intercepted more rain from the northeast causing the effect of the south american monsoon to intensify in northwestern argentina and southern bolivia where forest communities presently occur in patagonia glaciation started as early as 10 5 ma but by 7 ma had become a prominent feature of the landscape and continued apparently uninterruptedly into the pleistocene the antarctic peninsula saw its first mountain glaciation between 45 and 41 ma with major ice sheet expansion commencing at about 34 ma isolated stands of nothofagus forests were still present in low lying areas suggesting that the glaciers were initially wet based but dry based glaciers were established at around 8 ma although temperatures rose briefly during the messinian pliocene transition causing sub antarctic flora to retreat to higher elevations of the transantarctic mountains the present cold polar conditions were finally established by about 3 ma

estimation of rainfall variables from leaf characters in tropical africa abstract regression models are defined for leaf physiognomic and climate variables from 30 modern equatorial african plant communities herbarium specimens provide physiognomic data for published species lists for the 30 sites climate data are from a variety of published sources by limiting the sampled region to equatorial africa where annual amount and seasonality of rainfall are critical determinants of vegetation leaf physiognomy is found to be related linearly to moisture variables principal components analysis demonstrates that the pattern of variation among leaf variables is primarily a function of mean annual and wet months total of all months with 50 mm rainfall multiple regression models are derived for mean annual rainfall wet months rainfall and the number of dry months accuracy of each model is tested by comparing the adjusted predicted values the value for a case when it is not included in calculation of the regression line to the actual climate values at the 30 sites leaf size is the strongest correlate of moisture the mesophyll size class has the most significant positive relationship with annual and wet months rainfall entire margined species increase with wet months rainfall and temperature acuminate tip and length width ratio are also positively related to mean annual and wet months rainfall rounded base emarginate tip and acute tip are inversely related to rainfall variables regression models derived from modern plants and climate can be used to reconstruct seasonal and annual rainfall from cenozoic african leaf fossils

dynamic in situ three dimensional imaging and digital volume correlation analysis to quantify strain localization and fracture coalescence in sandstone advances in triaxial compression deformation apparatus design dynamic x ray microtomography imaging data analysis techniques and digital volume correlation analysis provide unparalleled access to the in situ four dimensional distribution of developing strain within rocks to demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution deformation and failure of porous rocks we deformed 3 cm scale cylindrical specimens of low porosity fontainebleau sandstone in an x ray transparent triaxial compression apparatus and repeatedly recorded three dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred experiments were performed at room temperature with confining pressure in the range of 10 20 mpa distinct grayscale subsets indicative of density enabled segmentation of the three dimensional tomograms into intact rock matrix pore space and fractures digital volume correlation analysis of pairs of tomograms provided time series of three dimensional incremental strain tensor fields throughout the experiments after the yield stress was reached the samples deformed first by dilatant opening and propagation of microfractures and then by shear sliding via grain rotation and strain localization along faults for two samples damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure for the third sample a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures the results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of 1 the proportion of shear versus dilatant strain in the sample 2 the amount of dilatancy due to microfracture opening versus pore opening when a fault develops and 3 the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached our study demonstrates how the combination of high resolution in situ dynamic x ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust

changes in geophysical properties caused by fluid injection into porous rocks analytical models author s pride sr berryman jg commer m nakagawa s newman ga vasco dw abstract 2016 european association of geoscientists a engineers analytical models are provided that describe how the elastic compliance electrical conductivity and fluid flow permeability of rocks depend on stress and fluid pressure in order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites the models require a population of cracks to be present in a possibly porous host phase the central objective is to obtain a consistent mean field analytical model that shows how each modeled rock property depends on the nature of the crack population the crack populations are described by a crack density a probability distribution for the crack apertures and radii and the averaged orientation of the cracks the possibly anisotropic nature of the elasticity conductivity and permeability tensors is allowed for however only the isotropic limit is used when comparing to laboratory data for the transport properties of conductivity and permeability the percolation effect of the crack population linking up to form a connected path across a sample is modeled however this effect is important only in crystalline rock where the host phase has very small conductivity and permeability in general the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable

use of s wave anisotropy to quantify the onset of stress induced microfracturing abstractmicrofracturing and induced elastic anisotropy impart changes on body wave velocities with implications to seismic and wellbore testing methods and interpretation we have conducted simultaneous triaxial stress tests and ultrasonic wave propagation monitoring to quantify s wave anisotropy and microfracture development in berea sandstone and silurian dolomite the onset of stress induced microfracturing is detected at the beginning of appreciable s wave anisotropy called the s wave crossover swx the swx and subsequent increases in s wave anisotropy evidence microstructural damage development well before quasistatic indicators such as the volumetric strain point of positive dilatancy ppd and yield failure in all samples x ray microtomography confirmed fracture development and allowed for geometric assessment of fracture orientation stresses at the swx and ppd are compared with peak axial stress to understand linkages between damage and ultimate rock strength in berea sandstone the swx occ

circulation path of thermal waters within the laga foredeep basin inferred from chemical and isotopic δ18o δd 3h 87sr 86sr data abstract the geochemistry of thermal spring waters in the acquasanta terme area located on the adriatic side of central italy has been investigated in order to characterize the geothermal feeding system the springs discharge more than 100 l s at temperature ranging between 20 and 30 c they occur in a tectonic window of mesozoic limestones in the central sector of the acquasanta anticline within the laga foredeep basin chemical and isotopic compositions of thermal and cold fluids were investigated most of them monitored for one year in order to understand the thermal fluid circulation paths the chemistry of the major elements defines the existence of na cl and ca cl so42 hot discharging waters and permits the characterization of the thermal end member hosted in carbonate dominated reservoir burano anhydrites fm calcare massiccio fm this deep fluid is well represented by the sample t1 and shows high temperature and electrical conductivity ec very stable over time and not affected by mixing phenomena this is also confirmed by tritium results 0 t u close to the surface at different depth such water undergoes mixing or dilution processes with hco3 rich freshwaters driven by the complex structural setting of the area and by diffuse karst caves this is identified as the main reason for observed compositional variations of sampled springs and three areas affected by different mixing phenomena have been defined at the surface the concentrations of so42 and h2s suggest redox processes affecting sulfur after interaction with evaporitic formations identified with the burano anhydrites at the base of the umbria marche sedimentary sequence 3500 m deep contribution from this reservoir is also supported by characteristic sr isotope signature 18o and d values indicate a meteoric origin of the thermal waters and allow estimation of an average infiltration altitude ranging between 1500 and 1700 m a s l this datum supported by structural data suggests the laga mountains as the recharge area of the system reservoir temperature inferred by so42 hco3 f ca mg and so42 f geothermometers is about 80 c consistent with the geothermal gradient of the foredeep basin and deserving further investigations for potential economic implications about this low enthalpy geothermal area

acoustic emission microstructure and damage model of dry and wet sandstone stressed to failure twenty three uniaxial compression tests were performed on dry and wet flechtingen sandstone from germany compressive strength of wet core is 60 of the strength of dry core before fracture the transverse p wave speed drops by 13 and the pulse amplitude by 22 for wet and 37 for dry cores accumulated strain energy doubles for dry core acoustic emissions ae are detected with 10 sensors for 19 cores ae activity starts at 84 of the fracture strength of wet cores 55 mpa and at 91 of the strength of dry cores 87 mpa the ratio of located to recorded ae is 0 37 for dry and 0 13 for fully wet cores ae hypocenter patterns document the development of two opposite fracture cones the negative slope of cumulative ae amplitude frequency distribution drops by 50 before failure in dry cores the slope of the wet core drops and recovers energy discrimination of ae detected by a broadband sensor resolves different stages of damage and captures the onset of the dilatant throughgoing macrofracture using the analogy to visible light microfracturing events are separated into high energy short pulses blue ae and low energy pulses with long duration times red ae blue ae are explained by intragranular grain breakage red ae by multiple stick slip on crack planes or grain boundaries deformed cores show highly fractured calcite cement and mostly intact quartz grains the stochastic damage model for brittle composites developed highlights that microfracturing of the sandstone is controlled by the amount and distribution of the weak mineral calcite

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

climate impact of high northern vegetation late miocene and present the late miocene belongs to the late phase of the cenozoic climate at that time was still warmer and more humid as compared to today especially in the high latitudes corresponding to the climate situation palaeobotanical evidences support that vegetation in the high northern latitudes changed significantly from the late miocene until today to quantify the climate impact of this vegetation change we analyse how vegetation in the high northern latitudes contribute to climate evolution for that we perform climate modelling sensitivity experiments for the present and for the late miocene tortonian 11 7 ma for our present day sensitivity experiment we introduce the tortonian vegetation in the high northern latitudes for our tortonian sensitivity experiment we introduce the modern vegetation on the same grid cells in the tortonian and in the present the modern vegetation leads to a strong cooling of the northern extratropics up to 4 c nevertheless the meridional heat transports remain nearly unchanged in both cases in general the vegetation impact on climate is similar in the tortonian and in the present however some exceptions occur due to the tethys ocean in the tortonian temperatures decline only weakly in eastern europe and western asia in the tortonian climate temperatures on the sahara realm rise up to 1 5 c while the temperatures do not change remarkably in the present day climate this different behaviour is caused by a stronger and more sensitive hydrological cycle on the sahara region during the tortonian

role of drainage conditions in deformation and fracture of porous rocks under triaxial compression in the laboratory 1 in order to investigate the role of drainage conditions in deformation and fracture behaviors of porous rocks the authors carried out a series of rock fracture tests under triaxial compression in the laboratory the detailed space time distribution of acoustic emission due to microcracking was used to examine pre failure damage and failure behavior in berea sandstone which has a porosity of 20 and a permeability of 100 md the pore pressures or flow rates at the ends of the test sample were precisely controlled to simulate different drainage conditions experimental results indicate that drainage conditions play a governing role in deformation and fracture the well established dilatancy hardening effect can be greatly suppressed by dilatancy driven fluid flowing under good drainage conditions fast diffusion of pore pressure leads to a significant reduction in rock strength and stabilization of the dynamic rupture process furthermore good drainage conditions have the potential to enlarge the nucleation dimension and duration thereby improving the predictability of the final catastrophic failure in addition compaction bands which were observed in porous rocks under higher confining pressure were also observed at low confining pressure corresponding to a depth of 1 km in undrained tests these results are particularly important for research fields in which fluid migration or pore pressure diffusion is expected to play a role such as hydrocarbon reservoirs enhanced geothermal systems geological storage of co2

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ

major neogene events of the southeastern pacific the chilean and peruvian record abstract according to the biochronostratigraphic model proposed the neogene marine deposits in chile and peru represent two independent transgressive sequences alloformations separated by a major regional hiatus the earlier sequence nseps i would stretch from the top of the early miocene up to the base of the late miocene ca 19 10 m y b p the upper sequence nseps ii would correspond in turn to the late pliocene ca 3 5 1 6 m y b p the regional hiatus separating both sequences would encompass the late miocene and the early pliocene ca 10 3 5 m y b p the planktonic foraminiferal events described suggest an age of terminal early miocene middle miocene and late pliocene respectively the paleoclimatic events recorded are three a warming event lasting from the terminal early miocene to the end of the middle miocene mmwe 18 11 5 m y b p a cooling event of the middle late pliocene lpce 2 5 0 2 m y b p and warming event spanning most of the late pliocene lpwe 3 5 2 2 m y b p restricted to the surface and intermediate sea waters of the middle and low latitudes the last paleoclimatic event not recorded as such so far is both synchronous and mutually exclusive in latitudinal terms with the second one three tectonic regional events are analyzed the quechuan 1 phase 19 1 5 m y b p the quechuan 2 phase 10 1 m y b p and the geographic rhodanian phase 3 5 0 5 m y b p in the studied area there is no late miocene marine sedimentary record to confirm the terminal tortonian or quechuan 3 tectonic phase ca 7 m y b p admitted to occur in the volcanoclastic continental sequences of northern chile and southern peru