thermo tectonic history of the tethyan himalayas deduced from the palaeomagnetic record of metacarbonates from shiar khola central nepal abstract palaeomagnetic measurements were carried out on low grade metamorphic carbonates of mesozoic age from the shiar area 85 1 e 28 6 n of the tethyan himalaya th in north central nepal two characteristic remanence components carried by pyrrhotite chrm 1 and magnetite chrm 2 could be identified by their unblocking temperature spectra of 270 340 and 430 580 c respectively fold tests are not significant due to the uniform bedding of all sites however according to results from other areas of the th the pyrrhotite component has been probably acquired as a secondary p trm during exhumation and cooling thus the age of remanence acquisition can be related to the last cooling event 25 17 ma in the surrounding areas the inclination of the magnetite component matches the value expected from the indian apwp this may the primary origin of the chrm 2 pyrrhotite site mean directions show a small circle distribution with a best fit parallel to the n s direction backtilting to the expected inclination i exp by intersection of the remanence small circle with the small circle of constant i exp yields a clockwise block rotation of 30 35 with respect to the indian plate characteristics of the pyrrhotite component small circle distribution of site means secondary origin p trm with unblocking temperatures below about 300 c allow the interpretation of the chronologic order of the thermo tectonic history i an earlier main folding phase at elevated temperatures ii a later event of cooling through about 300 c coinciding with the acquisition of chrm 1 iii clockwise block rotations with respect to the indian plate and iv long wave folding as the youngest tectonic event

continuum discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales abstract the stability of circular excavations in clay shales is a key issue in the drilling and tunnelling industries as well as in the field of deep geological waste storage a large body of experimental evidence indicates that the damaged zone around these cavities is influenced by strong mechanical anisotropy induced by the layered material structure the vast majority of numerical models adopted to date to analyse the stability of openings in layered rocks have been based on continuum mechanics principles using classic shear failure theory for elasto plastic materials however a number of experimental observations demonstrate that clay shales may fail in a brittle manner under low confinement conditions such as those characterizing the near field of the excavation therefore an alternative numerical approach based on non linear fracture mechanics principles and the discrete element method is adopted to gain new insight into the failure process of this class of geomaterials in order to account for the influence of clay shale microstructure on its mechanical behaviour a newly developed approach to capture the anisotropy of strength is proposed with this numerical approach the cohesive strength parameters of the fracture model are assumed to be a function of the relative orientation between the element bonds and the layering orientation the effectiveness of the numerical technique is quantitatively demonstrated by simulating standard rock mechanics tests on an indurated claystone namely opalinus clay emergent strength and deformation properties together with the simulated fracture mechanisms are shown to be in good agreement with experimental observations the modelling technique is then applied to the simulation of the excavation damaged zone edz around a circular tunnel in horizontally bedded opalinus clay the simulated fracturing process is mainly discussed in the context of the damage mechanisms observed at the mont terri url furthermore the influence of in situ stress on resulting edz geometry is analysed together with possible implications for ground support and tunnel constructability modelling results highlight the importance of shear strength mobilization along bedding planes in controlling the edz formation process in particular slippage of bedding planes is shown to cause rock mass deconfinement which in turn promotes brittle failure processes in the form of spalling the numerical technique is currently limited to two dimensional analyses without any thermo hydro mechanical coupling

constant holocene southern ocean 14c reservoir ages and ice shelf flow rates article i nfo southern ocean radiocarbon reservoir ages i e non zero radiocarbon ages in seawater are the highest in the world s surface ocean constraining these reservoir ages at present and in the past is important not only because unknown reservoir ages limit the interpretation of antarctic radiocarbon chronologies but also because reservoir ages provide information about ocean circulation as a recorder of past circulation and as an end member for major deep water masses in today s ocean in this study we use paired u th and 14 c ages of an unusual set of solitary coral samples trapped by fringing ice shelves in the ross sea to provide the first detailed study of holocene reservoir ages for the southern ocean our results indicate a relatively constant marine radiocarbon reservoir age of 1144 120 years for the past 6000 years these results are consistent with extrapolation of the relationship between 14 c and alkalinity seen elsewhere supporting the use of this empirical relationship in high latitudes the results also suggest constant deep ocean circulation and air sea exchange during the holocene and provide a good target for tuning ocean models of modern circulation combining the new ages for corals with their distance from the modern day ice shelf grounding line provides some of the first long term records of ice shelf velocities for any region and indicates constant flow of the mcmurdo ice shelf during the holocene at a rate similar to that observed today

experimental study on the formation of faults from en echelon fractures in carrara marble abstract en echelon fractures have been commonly observed in a fault zone to better understand how en echelon fractures interact to produce a fault rock specimens containing multiple artificial flaws en echelon flaws under uniaxial compression are examined in the present study the fracture process zone white patch linking behaviors of flaws structures in fault tips and correlations between stress and flaw configuration are investigated in detail by the usage of an optical microscope and an image recording system the results suggest that two typical white patches characterized by different appearance in both unaided and microscopic observations would develop in carrara marble prior to the occurrence of visible cracks the linking behaviors are controlled by the regime of configurations where only tensile cracks occur in the extensional regimes and different types of shear cracks are involved in the contractional regimes although the linking coalescence behaviors between en echelon flaws are observed to be similar to those of two flaws in previous studies special linking phenomena are particularly observed in specimens of 15 and 30 where is the flaw array angle the influence of en echelon flaw geometries is also reflected by the structures in fault tip and the development of tensile wing cracks stress analysis shows that the configurations of en echelon flaws dictate the coalescence stress with the increase of flaw inclination angle the coalescence stress increases in the contractional regime but decreases in the extensional regime finally by comparing the coalescence stress and the corresponding linking behaviors of each en echelon flaw configuration a correlation between the coalescence stress and the linking crack types is proposed linking patterns of fault segments obtained from both experiments and field investigations are discussed towards the end of the paper

coupling of late orogenic tectonics and secondary pyrrhotite remanences towards a separation of different rotation processes and quantification of rotational underthrusting in the western himalaya northern india abstract the total amount of crustal shortening within the indian plate includes straight forward and rotational shortening the complex tectonic history of the western himalaya impedes a direct observation of rotational shortening between india and its northern margin a combination of palaeomagnetic results and tectonic structures along a 300 km nw se section from nw zanskar 33 9 n 76 5 e to malari 30 0 n 79 6 e in northern india enable a separation of rotations on different scales correction of the observed rotations and quantification of uniform rotational shortening new palaeomagnetic results from metacarbonates of the tethyan himalaya in sarchu losar and spiti and earlier studies from nw zanskar and malari reveal a characteristic remanent magnetisation carried by pyrrhotite unblocking spectrum 250 330 c negative fold tests 99 level indicated remanence acquisition after the main folding of the himalaya the formation of pyrrhotite during thermal events t 200 c suggests a remanence acquisition related to exhumation and cooling temperatures of about 200 300 c indicate a thermochemical remanence acquisition with an eohimalayan age dated in two areas by 40k 39ar techniques on illites the resulting rotation angles in respect to stable india show an anomalous counterclockwise rotation in nw zanskar and a trend of decreasing clockwise rotations to the se these variations may be attributed to meso scale 100 km tectonic features and oroclinal bending for the first time block rotations with respect to stable india are separated into local meso scale and regional significant ones after elimination of local and meso scale effects using structural analysis of late orogenic features modelled rotations due to oroclinal bending were subtracted regionally significant rotations of 0 20 clockwise are interpreted to be caused only by uniform rotational underthrusting

cryogenic brines as diagenetic fluids reconstructing the diagenetic history of the victoria land basin using clumped isotopes abstract the isotopic analyses 13c 18o and 47 of carbonate phases recovered from a core in mcmurdo sound by antarctic geologic drilling andrill 2a indicate that the majority of secondary carbonate mineral formation occurred at cooler temperatures than the modern burial temperature and in the presence of fluids with 18owater values ranging between 11 and 6 vsmow these fluids are interpreted as being derived from a cryogenic brine formed during the freezing of seawater the 47 values were converted to temperature using an in house calibration presented in this paper measurements of the 47 values in the cements indicate increasingly warmer crystallization temperatures with depth and while roughly parallel to the observed geothermal gradient consistently translate to temperatures that are cooler than the current burial temperature the difference in temperature suggests that cements formed when they were 260 100 m shallower than at the present day this depth range corresponds to a period of minimal sediment accumulation from 3 to 11 myr it is therefore interpreted that the majority of cements formed during this time this behavior is also predicted by time integrated modeling of cementation at this site if this cementation had occurred in the presence of these fluids then the cryogenic brines have been a longstanding feature in the victoria land basin brines such as those found at this site have been described in numerous modern high latitude settings and analogous fluids could have played a role in the diagenetic history of other ice proximal sediments and basins during glacial intervals throughout geologic history the agreement between the calculated 18owater value and the measured values in the pore fluids shows how the 47 proxy can be used to identify the origin of negative 18o values in carbonate rocks and that extremely negative values do not necessarily need to be a result of the influence of meteoric fluids or reaction at high temperature

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

digital image based numerical modeling method for prediction of inhomogeneous rock failure abstract this paper presents a two dimensional digital image based numerical modeling method for prediction of inhomogeneous rock failure behavior under loadings actual inhomogeneities of granitic rocks are extracted from color images of the granite cross sections they are represented as the internal spatial distribution of three main granite minerals quartz feldspar and biotite the actual mineral spatial distribution on granite cross section is then incorporated into conventional numerical software packages to examine the rock failures under loading some digital image processing algorithms are presented to isolate and identify the main internal minerals and their distribution from color digital images a simple method is proposed to transform the actual image data into vector data for generation of finite meshes or grids the vector data are used directly as uniform square element meshes or grids that can be inputted into the existing software packages the finite difference software package flac is used as an example for the present investigation the conventional mohr coulomb and tensile stress failure criteria are used to examine the failure behavior of a circular granite cross section under the conventional brazilian indirect tensile test loading conditions the numerical results indicate that the vertical tensile crack initiates in a biotite located near the geometrical center of the granite cross section and the actual spatial distribution of the three minerals plays an important role in modifying the propagation pattern of the tensile crack from its theoretical position at the central vertical diameter of a homogeneous circular cross section the numerically predicted failure load and tensile strength values for inhomogeneous granite are much lower than the expected values

uranium in aragonitic marine bivalve shells abstract uranium concentrations in foraminiferal and coral skeletons track oceanic co 3 2 and can be useful as a proxy of ocean acidification but this ph proxy is yet to be investigated in bivalves two saxidomus giganteus shells from the industrialized puget sound wa usa and one from the more pristine kodiak island ak usa were sampled through ontogeny for u ca using laser ablation inductively coupled mass spectrometry all three shells show a similar pattern of seasonal u ca cycles during the first six years of life followed by a sharp decrease to below the detection limit for the remainder of the clams life 10 20 years consistent with a biological or ontogenic forcing vital effect however analyses along a growth line carbonate formed at the same time show a decrease in u ca from the outside of the shell toward the inside consistent with diagenesis clearly u ca is not under environmental control in these aragonite shells but the cause of the variability is not currently clear

reconstructing holocene conditions under the mcmurdo ice shelf using antarctic barnacle shells this study evaluates the potential of barnacles for paleoceanographic reconstruction and in particular of the antarctic species bathylasma corolliforme to reconstruct past conditions under ice shelves like other barnacle species this antarctic barnacle secretes a robust low mg calcite shell with distinct growth increments on the external surface indicating growth over a number of years 30 50 in samples studied here the bathylasma samples used in this study grew in the ross sea and became entrained at the grounding line of a coastal ice shelf in mcmurdo sound offering potential as an archive of changing conditions in this difficult to access environment under the mcmurdo ice shelf nine barnacle shells were subsampled at high resolution 60 m for 18o and 13c analysis these samples were dated with 14c and u th techniques although the later did not yield useful age information due to open system behaviour of barnacle calcite measured 18o values indicate that bathylasma calcifies close to equilibrium with ambient seawater one older sample 200 ka has similar 18o and 13c values as the eight holocene samples suggesting that barnacle calcite is not prone to significant diagenesis in this setting apparent isotope equilibrium and lack of diagenesis make barnacles a promising archive for reconstruction of past ocean conditions cycles of 18o observed within each sample sometimes correlate with the external growth ridges but not always and have amplitudes of typically 0 6 this magnitude of variation suggests shell growth during a significant portion of the year although it remains unclear whether growth continues throughout the year however the prominent growth bands suggest at least a signficant seasonal slowing in growth rate variations in barnacle 18o within each plate and between plates are too large to be caused by temperature and instead reflect changes in 18o of the seawater allowing some assessment of seawater salinity under the ice shelf salinities are lowered by addition of meltwaters but the barnacle 18o data suggest values do not go below 33 these data indicate that bathylasma has potential as an archive of paleoclimate information for shallow intermediate water depths and in particular for difficult to reach environments such as below ice shelves of antarctica

flow controlled inverted metamorphism in shear zones abstract numerous processes and models have been developed in order to explain inverted metamorphism in shear zones this article demonstrates by means of continuum mechanics that the orientation of a sample profile across a shear zone before and after deformation can be used to quantify the conditions under which inverted metamorphism is likely to have developed a thrusting shear zone deforming under ideal simple shear will develop an inverted metamorphic zonation if the angle between the thrust and isotherms is greater than 5 10 even at only moderate strains if the flow is general shear this angle is considerably larger i e 60 for a kinematic vorticity number of w k 0 5 additionally the stretch of the sample profile across the shear zone which is not influenced by the flow type bears important implications for the interpretation of petrological geochronological and structural data although this kinematic model is clearly an end member model neglecting dissipative processes it can easily account for the structural and petrological data of the inverted metamorphism observed throughout the higher himalayan crystalline wedge in the sutlej valley india

experimental investigation on fracture coalescence behavior of red sandstone containing two unparallel fissures under uniaxial compression natural rock usually contains a lot of flaws such as fissures joints weak surfaces and faults which have a significant effect on the strength deformability and crack coalescence behaviors of rock material 1 5 in order to improve the understanding of fracture mechanism of rock engineering containing intermittent structures a lot of experimental studies have been performed for all kinds of rock materials or rock like materials containing two fissures 6 10 wong and chau 6 investigated the crack propagation and coalescence on rock like materials containing two inclined open or closed fissures which obtained three main modes of crack coalescence in two fissured specimens under uniaxial compression feng et al 7 carried out a number of experimental studies to explore the mechanism of multi crack interaction in limestone specimens the size of the specimen was 15 30 3 mm with two fissures of different geometries under the coupled uniaxial compressive stress and chemical solutions with different ionic concentrations and ph values yang et al 8 made uniaxial compression tests for cylindrical marble specimens with different pre existing fissures which analyzed the effect of fissure geometry on strength and deformation failure behaviors of brittle marble material wong and einstein 9 summarized the effects of the flaw angle ligament angle and length on the cracking processes and coalescence patterns of carrara marble specimens containing two open fissures and used a high speed camera to observe the specimens at a macroscopic scale yang 10 performed an experimental study on the influence of coplanar fissure angle on the strength deformation

environmental controls on the stable isotopic composition of mercenaria mercenaria potential application to paleoenvironmental studies 1 we have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of north america seasonal profiles of 18o and 13c obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity we show that m mercenaria 18o profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell 18o values growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10 c implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations although further measurements of water 18o and a better understanding of seasonal variations of the water 18o salinity relationships are necessary mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium whereas the amplitude of the seasonal profiles of 18o reflects variations in water temperature the annual average 18o decreases with latitude reflecting the trend of rainfall and riverwater 18o with latitude over the northern american continent

an open system model for u series age determinations of fossil corals the source of excess 234u in fossil corals and its relationship to u series age determinations has been an outstanding problem in geochronology for more than 20 years with increasing numbers of u series isotope measurements in corals and significant improvements in analytical precision through mass spectrometry it is increasingly apparent that a substantial fraction of observed isotope ratios cannot be reasonably explained by closed system decay moreover observations of a positive correlation between 234u 238u and 230th 238u ratios in corals from the same terrace are difficult to explain however the decay of dissolved uranium and recoil mobilization of uranium daughters produce particle reactive 234th and 230th and the coupled addition of these th isotopes could simultaneously increase coral 234u 238u and 230th 238u here we present a quantitative model based on decay dependent redistribution of 234th and 230th permitting calculation of open system coral ages these equations provide a general solution to the recoil redistribution problem applicable to any alpha decay series while measured isotope ratios of corals from the three youngest stratigraphically defined barbados terraces are inconsistent with closed system decay they fall in broadly linear arrays agreeing with model predictions isotopic arrays of older barbados corals and corals from terraces around the world are also consistent with model predictions suggesting the open system model is generally applicable corals with extreme isotopic compositions that are impossible to produce by closed system decay are consistent with the limited range of isotopic compositions predicted by the model at ages older than 600 ka for corals from a single terrace 234th and 230th redistribution appears to be a source of systematic conventional age error even for corals with slightly elevated 234u however open system ages are consistent even for corals with extremely elevated 234u for the youngest three barbados terraces mean open system terrace ages are consistent with mean conventional terrace ages calculated from pristine samples if the most accurate conventional ages are from corals with an initial 234u 238u identical to modern seawater then the open system model will improve the accuracy of coral u series age determinations and dramatically increase the number of reliable ages

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

a recount of ross sea waters abstract oceanographic observations within the ross sea have grown dramatically in recent years both in number and quality this has prompted a parallel recount of the circulation and structure of all water masses in the southwestern continental margins of the pacific ocean a high resolution set of horizontal property distributions was combined into a new climatology which in turn is the basis of a fine volumetric s census of all ross sea water masses inshore of the shelf break 700 m isobath the ross sea volume 25 10 4 km 3 partitioning into layers of neutral density n is 25 in the top layer n 3 of antarctic surface water aasw 22 in the middle layer 28 00 kg m 3 n 3 of oceanic thermocline water 12 and modified circumpolar deep water mcdw 10 and 53 in the bottom layer n 28 27 kg m 3 of shelf water sw 1 85 c 22 precursor of the antarctic bottom water aabw offshore aasw flows westward along the outer shelf and southward along the eastern coast past cape colbeck oceanic thermocline waters 28 00 kg m 3 n 3 cross the shelf break west of 170 w and follow southward paths along banks shoaling progressively to near the sea surface of the central and western inner shelves winter buoyancy loss converts aasw and oceanic thermocline water into denser types of mcdw and sw which move cyclonically toward the sills of major troughs the census shows a continuous mode of relatively dense mcdw 28 10 kg m 3 n 3 directly linked to the circumpolar deep water cdw offshore effectively ventilating and freshening the deep ocean at levels below the salinity maximum and above aabw mcdw outflows from the ross sea shelf are traced to the antarctic circumpolar current near 155 e into the australian antarctic basin along the northern flank of the southwest pacific ridge and to near 135 w past the eastern end of the ross gyre two sources of salty sw are inferred near the coastal polynyas in the terra nova bay and western ross ice shelf areas the latter contributes to a major outflow of ice sw that reaches the shelf break along 180 vertical mixing of mcdw and sw produce msw over the shelf continuing over the sills as new aabw export of low salinity aabw s

correlation between petrographic characteristics and failure duration in clastic rocks being the inherent attributes of rock the petrographic characteristics such as mineral composition and microstructure are the constructive parameters which influence its bursting potential in the laboratory rock specimens with different petrographic characteristics are tested to study their rock strength and failure duration and correspondingly composition and microstructure of each rock specimen are analyzed in thin sections to determine the mineral composition content grain size cement and contact modes between grains the results show that the petrographic characteristics of clastic rock have an intrinsic influence on its strength and failure duration with the increase of the rock detritus content or quartz the uniaxial compressive strength increases according to a logarithmic expression and the failure duration decreases according to a negative logarithmic expression with increasing average size of detritus grains in rock the stiffness and brittleness of rock strengthens the uniaxial compressive strength of rock has a logarithmic variation with its average size of detritus grains and the failure duration decreases with its increasing average size of detritus grains according to a negative logarithmic expression

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

geochemistry of a dry steam geothermal zone formed during rapid uplift of nanga parbat northern pakistan abstract natural dry steam zones vapour only are relatively rare most geothermal systems contain both liquid and vapour and typically follow a boiling point depth bpd relationship the nanga parbat uplift driven conductive thermal anomaly results in a geothermal system which follows a bpd relationship at shallow levels but below about 3 km fluid inclusions show that the hydrothermal fluid is dry steam with fluid densities from 0 36 to as low as 0 07 g cm 3 this dry steam zone may persist down to the brittle ductile transition the dry steam has salinities up to 5 wt dissolved salts and up to 22 mole dissolved co 2 the dry steam originated as meteoric water high on the slopes of nanga parbat with 18 o as low as 16 oxygen isotopic exchange with the host rock was facilitated by high temperatures 340 to 450 c and low fluid densities so that the fluid meteoric isotopic signature was completely obliterated hence quartz veins formed by the migrating dry steam have 18 o between 9 and 15 a range which is indistinguishable from quartz in the host rocks quartz vein precipitation from dry steam requires 3 to 5 orders of magnitude greater volume of fluid than typical hydrothermal fluids the dry steam zone at nanga parbat has formed due to near isothermal depressurization of very hot fluid during rapid tectonic uplift at rates 3 6 mm year

the temperature and salinity fine structure of the ocean under the ross ice shelf a series of temperature and salinity profiles was made in the ocean under the ross ice shelf at 82 22 5 s 168 37 5 w where the ice was 420 and the underlying seawater 240 m thick the water structure consisted of a fairly well mixed low salinity layer at the in situ freezing point of the ice water interface about 30 m thick a transition layer characterized by intrusions about 85 m thick a strongly stratified layer with increasing temperature and salinity about 50 m thick another transition layer characterized by intrusions about 45 m thick and an isohaline bottom layer with a nearly abiabatic temperature gradient about 30 m thick the temperature fluctuations in the two transition layers can be attributed mainly to intrusive activity even though internal wave activity was highest in these regions in the central stable layer internal waves probably contribute to the temperature fluctuations equally with intrusions the internal wave dropped displacement spectrum seems to be very similar to those found in the open ocean some profiles showed intrusions in the top transition layer colder than the top boundary layer and some showed intrusions in the bottom transition layer warmer than the bottom boundary layer indicating that horizontal shear must be present internal waves of near inertial frequency excited by the semidiurnal tides combined with shear induced instabilities seem to be the likely causes of the observed fine structure

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

bonded particle discrete element modeling of mechanical behavior of transversely isotropic rock abstract this paper presents bonded particle discrete element modeling with embedded smooth joints for simulating the mechanical behavior of transversely isotropic rock with systematic verifications and extensions to laboratory and upscaled problems verification was conducted against the analytical solutions in terms of anisotropic elastic and strength behavior the developed model was compared with laboratory observations of three rock types gneiss shale and schist leading to good agreements bonded particle dem modeling successfully captured the failure patterns observed in anisotropic rock in which weak planes play a significant role the model was upscaled to large scale foundation problems subjected to surface line load the study achieved reasonable agreements both for isotropic and anisotropic solutions the results demonstrate that the bonded particle dem with embedded smooth joints can model the equivalent anisotropic medium and it has potential to be applied to problems of larger engineering problems in which anisotropy is important

measurement of rock fracture toughness under modes i and ii and mixed mode conditions by using disc type specimens rock fracture mechanics has been widely applied to blasting hydraulic fracturing mechanical fragmentation rock slope analysis geophysics earthquake mechanics hot dry rock geothermal energy extraction and many other practical problems but a standard method to accurately determine fracture toughness of rocks one of the most important parameters in fracture mechanics as an intrinsic property of rock has not been yet well established to obtain rock fracture toughness disc type specimens were used in this study rock fracture toughness under mixed mode conditions was measured by using the straight through crack assumption stca applied to the cracked chevron notched brazilian disc ccnbd specimen and the semicircular bend scb specimen size effects in terms of specimen thickness diameter and notch length on fracture toughness were investigated from the mixed mode test results fracture envelopes were obtained by applying various regression curves the mixed mode test results were also compared with the three well known mixed mode failure criteria

micromechanical modeling of cracking and failure in brittle rocks dynamic micromechanical models are used to analyze crack nucleation and propagation in brittle rock models of rock are created by bonding together thousands of individual particles at points of contact the feasibility of using these bonded particle models to reproduce rock mechanical behavior is explored by comparing model behavior to results from actual laboratory tests on different rock types the behavior of two granite models are examined in detail to study cracking and failure patterns that occur during compressional loading because discontinuum models are being used the rock models are free to crack and break apart under stress such that the micromechanics of cracking can be examined stress waves are allowed to propagate outward from each crack and it is shown that these dynamic waves significantly affect the rock behavior as the peak stress in the modeled rock is approached and many of the bonds are close to breaking a passing wave from a nearby crack is sufficient to break more bonds this causes clusters of cracks to be created and then eventual macroscopic shear failure occurs as these clusters connect to bisect the sample the failure patterns observed in the granite models are similar to those observed in actual laboratory tests

u th dating of marine isotope stage 7 in bahamas slope sediments in order to understand the driving forces for pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing in contrast to the last interglacial marine isotope stage mis 5 the timing of the penultimate interglacial mis 7 is poorly constrained this study constrains its timing and structure by precise u th dating of high resolution n 18 o records from aragonite rich bahamian slope sediments of odp leg 166 sites 1008 and 1009 the major glacial interglacial cycles in n 18 o are distinct within these cores and some mis 7 substages can be identified these sediments are well suited for u th dating because they have uranium concentrations of up to 12 ppm and very low initial 230 th contributions with most samples showing 230 th 232 th activity ratio of s 75 u and th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry with the latter providing dramatically better precision twenty nine of the 41 samples measured have a n 234 u value close to modern seawater suggesting that they have experienced little diagenesis ages from 27 of the 41 samples were deemed reliable on the basis of both their u and their th isotope ratios ages generally increase with depth although we see a repeated section of stratigraphy in one core extrapolation of constant sedimentation rate through each substage suggests that the peak of mis 7e lasted from v237 to 228 ka and that 7c began at 215 ka this timing is consistent with existing low precision radiometric dates from speleothem deposits the beginning of both these substages appears to be slightly later than in orbitally tuned timescales the end of mis 7 is complex but also appears to be somewhat later than is suggested by orbitally tuned timescales although this event is not particularly well defined in these cores fl 2002 elsevier science b v all rights reserved

the himalaya bengal fan denudation accumulation system during the past 20 ma mass balances for both denudation in the himalayas and sediment accumulation in the subhimalayan basins including the bengal deep sea fan but excluding the indus fan yield 7 1 106 km3 and 7 4 106 km3 s 20 rock of 2 75 g cm3 density respectively for the past 20 million years coarsening and increased sediment accumulation rates in the foreland basin and in the bengal foredeep indicate accentuated tectonic activity and unroofing in the himalayas since that time the sediment volume includes 1 106 km3 of neogene bengal fan sediment that was lost via the nicobar fan to the sunda accretionary wedge in addition the indian peninsular rivers contributed about c 0 6 106 km3 of solid load to the basins average denudation during the past 20 m y as derived from geothermobarometric data and restored cross sections occurred most rapidly along the high himalayan crystalline chain vertical unroofing c 1000 m m y northward lateral retreat of southern himalayan slope exposed to monsoonal rain

reliability of multitaxon multiproxy reconstructions of environmental conditions from accretionary biogenic skeletons abstract evaluation and quantification of climate change require data on subseasonal to daily environmental extremes from those periods before instrumental records were available this study employs a high resolution multitaxon multiproxy approach and analyzes how faithfully accretionary biogenic skeletons record environmental extremes six specimens of two bivalve mollusks chione fluctifraga mytella guyanensi and one barnacle species chthamalus fissus from a single habitat northern gulf of california mexico were collected contemporaneous shell portions from these specimens were analyzed for shell growth rates sclerochronology and stable isotopes 18o 13c and were compared to instrumental records the results of these analyses included some significant observations first shell 18o values overestimate winter temperatures and underestimate summer temperatures second the actual diurnal temperature range is not recorded in the biogenic skeletons third skeletal growth is biased toward a

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf antarctica this paper presents observations and measurements of debris characteristics and ice shelf dynamics in the ablation region of the mcmurdo ice shelf in the ross sea sector of antarctica ice shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions ground penetrating radar investigations and through ablation velocity and ice thickness measurements field data show that in the study area the ice shelf moves relatively slowly 1 5 18 3 m a 1 has high ablation rates 43 441 mm during 2003 04 summer and is thin 6 22 m the majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice sheet ice shelf system at the last glacial maximum this debris is concentrated on the ice shelf surface and is continually redistributed by surface ablation creating an ice cored landscape of large debris rich mounds ice shelf flow forming medial moraines and meltwater streams locally reworking material and redistributing it across the ice shelf surface a conceptual model for supraglacial debris transport by contemporary antarctic ice shelves is presented which emphasizes these links between debris supply surface ablation and ice shelf motion low velocity ice shelves such as the mcmurdo ice shelf can maintain and sequester a debris load for thousands of years providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

multi scale approach for modeling the transversely isotropic elastic properties of shale considering multi inclusions and interfacial transition zone multiscale approach based explicit analytic predictions are obtained for the transversely isotropic properties of shale rock considering the multi inclusion and interfacial transition zone itz effects representative volume elements rves are utilized to describe the material s hierarchical microstructures from the nanoscale to the macroscale a new multilevel micromechanical homogenization scheme is presented to quantitatively estimate the material s transversely isotropic properties with the multi inclusion and itz effects the itz is characterized by the interphase material whose effects are calculated by modifying the generalized self consistent model furthermore the explicit form solutions for the transversely isotropic properties are obtained by utilizing the hill polarization tensor without numerical integration and the standard tensorial basis with the analytic inversions of fourth rank tensors to verify the proposed multiscale framework predictions obtained via the proposed model are compared with experimental data and results estimated by the previous work which show that the proposed multi scaling approaches are capable of predicting the macroscopic behaviors of shale rocks with the multi inclusion and itz effects finally the influences of itz and inclusion properties on the material s macroscopic properties are discussed based on the proposed multiscale framework

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

low cost colorimetry for assessment of fire damage in rock abstract tunnels and caverns excavated for the purpose of mining tend to be designed for short term use and would usually be unlined fire hazard within a mining cavern or tunnel poses concerns on the structural integrity of the surrounding rock hence a fast non destructive method for assessing the strength of a rock mass after a fire would be useful in deciding whether to salvage a mining operation or to abandon it colorimetry as a technique to estimate the heating temperature of concrete has proven useful however the use of colorimetry imposes a need to balance ease of use such as low cost digital cameras and computer scanners with accuracy achievable with expensive spectrometers and spectrophotometers this technical note shall investigate the use of a digital single lens reflex dslr camera and matlab as a means of performing non destructive testing on rocks exposed to temperatures of between 200 c to 500 c to estimate the degradation of the rocks tensile strength the cie l a b color space is used the effects of soot and smoke on the rocks are also simulated using high temperature grease to mimic real world conditions the brazilian tensile strength and p wave velocity are two other properties investigated in this technical note the results suggest that the a and b color values have an almost linear relationship with the heating temperature of the rock whereas the tensile strength of the rock has a quadratic relationship additional tests indicate the robustness of the colorimetry process as the simulated smoke and soot damage did not significantly affect the relationship between heating temperature a and b color values provided the surface of the rock was cleaned after the fire event the mechanism of the strength degradation may be attributed to generation of microcracks due to thermal loading while the color change is attributed to either chemical changes within the rock or scattering of light due to the generated microcracks a key finding of this study is that the colorimetry process outlined is not only relatively cheap to use as compared to expensive spectrometers and spectrophotometers but also fast as the photo taking process can be completed within 10 min this makes it easier for multiple teams to be deployed after a fire incident in an underground rock tunnel or cavern minimising the amount of time that workers need to spend in potentially hazardous environment