saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

grain size control on sr nd isotope provenance studies and impact on paleoclimate reconstructions an example from deep sea sediments offshore nw africa five sediment cores from offshore nw africa were analyzed for strontium and neodymium isotope ratios to reconstruct temporal variations in continental weathering regimes sediments were taken from three time slices with well known and distinctive environmental conditions present day dry and warm similar to 6 ka wet and warm and similar to 12 ka dry and cold terrigenous sediment samples were split into two size fractions to distinguish between the two dominant transport mechanisms offshore nw africa fluvial 0 10 mu m and aeolian 10 40 mu m sr isotope data record evidence of marked grain size control with higher isotopic ratios in the fine fraction in contrast epsilon nd values are largely unaffected by grain size minor variability in nd isotope data at each sampling site indicates near constant sources of terrigenous matter over the last similar to 12 ka variations in sr isotope ratios are interpreted to reflect major changes in the evaporation precipitation balance we suggest that the sr nd isotope data record a latitudinal shift of the northern limit of the african rainbelt and associated wind systems causing changes in the humidity and rate of chemical weathering over nw africa while hyperarid conditions prevailed similar to 12 ka more humid conditions and intensified monsoonal rainfall at similar to 6 ka resulted in greater breakdown of easily weathered k bearing phases and increased sr 87 sr 86 in the detritus in late holocene times the monsoonal circulation diminished resulting in a return to arid conditions our results clearly show that it is of vital importance in paleoenvironmental studies to carry out isotopic analyses on individual sediment fractions that were carried to the studied deposition site by distinct sediment transport mechanisms if isotopic analyses are carried out on bulk sediments the observed variability in isotopic values most likely represents changes in the particle size and mixing proportions of the sediment subpopulations

progressive failure of aznalcollar dam using the material point method the material point method which combines features of finite element and particle discretisation methods has been extended to solve coupled flow deformation problems in granular media the method is applied to simulate the construction and failure of the aznalcollar dam the brittle foundation clay is characterised by means of a strain softening mohr coulomb elasto plastic model the rupture process of the foundation is associated with a progressive failure mechanism the model predicts the development of a localised shearing band that initiates at the toe of the dam at some intermediate stage of construction and propagates downstream and upstream the shape and position of the failure surface reproduce actual field observations

a new jurassic recent apparent polar wander path for south america and a review of central andean tectonic models abstract the jurassic to recent palaeomagnetic data from the stable cratonic areas of south america and africa are reviewed and evaluated from the combined data set seven mean reference pole positions are calculated for the early middle and late jurassic early and late cretaceous palaeogene and neogene most of these new palaeopoles are well defined and indicate a complex course of apparent polar wander for the south american plate comparison of the palaeomagnetic data from the andean margin with the reference poles indicates vertical axis rotations defining a broad pattern of anticlockwise rotations north of the arica deflection at approximately 19 s and clockwise rotations to the south further analysis indicates however that the distribution and magnitude of rotations is more complicated than this broad division tectonic models proposed to explain the pattern of rotations and the possible origins of the arica deflection are discussed it is suggested that the rotations probably result from localised in situ rotations controlled by strike slip fault systems or thrust sheets rather than large scale rotation mechanisms the broad rotation pattern may result from the influence of pre existing structures in the margin or variations in the flexural rigidity of the brazilian shield behind the deformation zone

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

model for predicting the variation of shear stress in unsaturated soils during strain softening several of the geotechnical structures constructed with unsaturated soils undergo a large deformation prior to reaching failure conditions e g progressive failure of a soil slope during this pr

bulk composition of northern african dust and its source sediments a compilation abstract this paper presents a review of bulk compositional data of northern african dust and its potential source sediments and includes elemental isotope and mineralogical data northern african dust represents about one half of the total global atmospheric mineral dust burden and its uplift transport and deposition have strong impacts on climate and various terrestrial and marine ecosystems the chemical data set shows that an average northern african dust exhibits comparable si fe and mn contents with respect to the average composition of the upper continental crust is slightly depleted in the alkali metals k and na and enriched in ti and p however the complete data set yields clear evidence that northern african dust and its source sediments are compositionally heterogeneous on a regional scale and that this heterogeneity can be used to differentiate between major potential source areas on the basis of so called source markers an evaluation of these compositional fingerprints shows that the following parameters and especially their combination are effective in the discrimination of the most active source areas in northern africa ratio of ca mg fe wt calcite or carbonate content palygorskite occurrence and abundance illite kaolinite ratio nd 0 value and 87sr 86sr ratio for example the data set corroborates previous ideas which assign carbonate illite and palygorskite rich mineral dusts to north west ern source regions because most of the above listed source markers do not change substantially during transport even far traveled dusts may be assigned to specific potential source areas in northern africa some limitations of the presented data set are also discussed our compilation reveals some substantial gaps in the knowledge of the composition of source sediments and mineral dusts from important potential source areas that should be filled in the future the here compiled data set can be used as a reference frame when incorporating the composition of source sediments e g mineralogy into global or regional dust transport models and can be compared with source analysis by remote sensing or back trajectory analysis however source apportionment studies supported by our data set will not only be useful for actual dust samples but will also be helpful for the understanding of paleo wind directions and hence paleo climatological conditions through the investigation of quaternary eolian sediments deposited in and around northern africa

variable hfsrnd radiogenic isotopic compositions in a saharan dust storm over the atlantic implications for dust flux to oceans ice sheets and the terrestrial biosphere isotopic characterization of aerosol mineral particles atmospheric dust of varying sizes is essential in classifying source areas and for determining the source of dust deposited over oceans and icesheets however the effect of atmospheric transport on radiogenic isotopic compositions is not well constrained making provenance interpretation difficult in order to investigate the isotopic variability of 176hf 177hf 87sr 86sr and 143nd 144nd we analyzed eight airborne dust samples in two size fractions collected along a cross atlantic transect through a dust storm originating in the sahara in late 2002 past measurements of 176hf 177hf 87sr 86sr and 143nd 144nd of dust have focused primarily on coarse sized particles 30 m whereas far field deposition is primarily finer particles 2 m strontium or neodymium isotopic sorting based on distance is not evident in our dataset however the combined isotopic ratios of the dust collected suggest a saharan origin hafnium isotopic compositions show an east to west trend towards more radiogenic compositions across the atlantic suggesting grain and mineral sorting during dust transport along the 4000 km transect transport models with variable dust particle diameter and wind speed demonstrate the preferential depletion of the high density mineral zircon during transport of dust from the source area the transport model combined with a simple two component mixing model show that the hf isotopic composition changes can be explained by the loss of the mineral zircon during transport modeling of this zircon effect with distance from the dust source in the hf isotopic composition of marine terrestrial and glacial dust deposits may reveal additional information concerning dust transport and sources in the geologic past

a statistics based discrete element modeling method coupled with the strength reduction method for the stability analysis of jointed rock slopes abstract the stability of jointed rock slopes can be effectively analyzed using the discrete element method dem however the criteria for terminating the dem iterative calculation process and determining the factor of safety fos are not well defined in this paper a displacement statistics based discrete element modeling method dsdm is proposed to analyze the stability of jointed rock slopes by coupling with the shear strength reduction method srm in the presented dsdm two important criteria are defined 1 a statistics based criterion for terminating the iterative calculation process of the dem modeling in the stability analysis of jointed rock slopes and 2 a statistics based criterion for determining the fos of a jointed rock slope when coupling dem and srm the novelty of the proposed dsdm is that statistical information of the global displacements around the potential slip surface of the jointed slope rather than the local displacements of several characteristic points are utilized to define the criteria for terminating the dem iterative calculation process and determining the fos to verify the effectiveness of the proposed dsdm the fos of a simplified jointed rock slope is first calculated using the proposed dsdm and then compared with the fos obtained using the finite difference method fdm moreover the proposed dsdm is applied to analyze the stability of a real high steep bedding rock slope the numerical simulation results for the real rock slope are consistent with the in situ observations the proposed dsdm is thus capable of effectively analyzing the stability of jointed slopes with potential slip surfaces

probabilistic analysis of post failure behavior of soil slopes using random smoothed particle hydrodynamics abstract slope failure or landslide is a common and severe geo hazard which may cause significant casualties and economic losses casualties and economic losses caused by soil slope failure are often determined by volume of sliding soil mass and influence zone during post failure process it is therefore of great importance to study both slope failure probability and post failure behavior estimation of failure probability has attracted much research attention but assessment of post failure behavior especially the influence zone is relatively rare this probably dues to the difficulty in simulating the whole process of slope failure e g initiation of the slope failure transportation and final deposition of the sliding mass for example the factor of safety and critical slip surface obtained from the commonly used limit equilibrium method only correspond to initiation of the slope failure while finite element difference methods may suffer from grid distortion problems when simulating large soil deformation that occurs during slope failure to properly assess the post failure behavior of soil slopes this paper proposed a monte carlo simulation mcs based method called random smoothed particle hydrodynamics rsph in which random field theory is used together with a particle based mesh free numerical method called smoothed particle hydrodynamics sph the proposed approach is able to simulate the whole process of soil slope failure and provide reasonable estimations of failure probability influence zone and volume of sliding mass during post failure process

pliocene near trench magmatism in southern chile a possible manifestation of ridge collision eight shallow level intrusions and an ophiolite complex have recently been discovered in a remote region along the pacific coast of southern chile known as the taitao peninsula the magmatic rocks are found only 10 to 15 km from the buried extension of the peru chile trench the ophiolite body includes serpentinized ultramaflc rocks gabbro dikes and an interbedded sequence of volcanic and marine sedimentary rocks more regionally distributed granodiorite plutons and porphyritic stocks and sills intrude pre late jurassic basement as well as tertiary marine sequences of the south american forearc k ar ages of 3 5 to 4 0 ma of the ophiolite and other intrusions suggest that these rocks represent a short lived pulse of pliocene magmatism directly seaward of the taitao peninsula a segment of the chile rise bounded by the tres monies and taitao fracture zones collided with the chilean forearc and was subducted about 2 5 to 4 0 ma because of this good spatial and temporal correlation the magmatic activity of the taitao peninsula is likely to be a direct result of ridge subduction

rainfall induced slope collapse with coupled material point method abstract rainfall induced slope failures are a major category of slope failure with incidents likely to increase with the predicted escalation of extreme rainfall events traditional numerical methods such as the finite element method are often restricted in their applicability to small deformation analyses therefore incomplete descriptions of the failure mechanism and failure consequence may be obtained due to the evolving deformations and progressive failure being ignored a one point two phase material point method mpm formulation is proposed to consider the influence of rainfall on slope failure due to the characteristics of mpm in capturing the large deformations the complete failure process from initiation to failure of a slope subjected to rainfall infiltration is presented the soil behaviour is described by a mohr coulomb strain softening model based on bishop s effective stress the two phase analysis shows that the rainfall affected slope is initially stable until the soil shear strength reduces due to the reduction of suction in the slope starting from the surface leading to a superficial failure mode which in turn leads to a complete slope failure friction angle and residual cohesion are shown to play important roles in the development of the slope failure

late cenozoic tectonics of the southern chile trench marine geophysical data from off shore of southern chile are used to define the interaction between the chile ridge and chile trench during late cenozoic time we identify three distinct ridge trench collision events between 14 and 10 ma a 700 km long nearly continuous section of the chile ridge was sub ducted between 55 s and 48 s shorter sections of the ridge offset by large transform faults were subducted at 6 and 3 ma between 48 s and 47 s at the present day triple junction the subduction of the ridge has a strong influence on the chile trench in this region the landward trench slope has undergone a recent episode of subduction driven tectonic erosion the trench slope is narrower and steeper than along other sectors of the margin and the trench axis has migrated shoreward evidence exists for late neogene and quaternary uplift and plutonism on the adjacent continental margin south of 48 s where collision took place between 10 and 14 ma the effects of collision are much less pronounced in particular the landward trench slope does not appear to have been subjected to extensive tectonic erosion we conclude that the configuration of the spreading centers and transform faults on the chile rise is the chief factor controlling ridge trench tectonic interaction tectonic erosion of the landward trench slope and tectonic activity in the adjacent continental margin are much greater when short sections of ridge offset by large transform faults are subducted a major sub marine channel leads along the trench axis south ward from the triple junction this channel cuts across the outer trench rise and carries sediment westward to the mornington abyssal plain the paleogene tectonic history of the southern chile trench includes a southward migrating ridge trench collision involving the farallon aluk spreading center in eocene time

seasonal radiogenic isotopic variability of the african dust outflow to the tropical atlantic ocean and across to the caribbean abstract in order to assess the impact of mineral dust on climate and biogeochemistry it is paramount to identify the sources of dust emission in this regard radiogenic isotopes have recently been used successfully for tracing north african dust provenance and its transport across the tropical atlantic to the caribbean here we present two time series of radiogenic isotopes pb sr and nd in dusts collected at the cape verde islands and barbados in order to determine the origin of the dust and examine the seasonality of westerly dust outflow from northern africa aerosol samples were collected daily during two campaigns february 2012 winter and june july 2013 summer at the cape verde atmospheric observatory cvao on the island of sao vicente 16 9 n 24 9 w a one year long time series of aerosols from barbados 13 16 n 59 43 w a receptor region in the caribbean was sampled at a lower monthly resolution our results resolve a seasonal isotopic signal at cape verde shown by daily variations with a larger radiogenic isotope variability in winter compared to that in summer this summer signature is also observed over barbados indicating similar dust provenance at both locations despite different sampling years this constrains the isotope fingerprint of saharan air layer sal dust that is well mixed during its transport this result provides unequivocal evidence for a permanent albeit of variable strength long range transport of african dust to the caribbean and is in full agreement with atmospheric models of north african dust emission and transport across the tropical atlantic in the sal the seasonal isotopic variability is related to changes in the dust source areas mainly the sahara and sahel regions that are active all year round albeit with variable contributions in summer versus the winter months our results provide little support for much dust contributed from the bodele depression in chad the dustiest place on earth reaching cape verde and barbados during the summer while contributions during the winter months are likely patchy and minor at most importantly a short term isotopic excursion is resolved in the cape verde winter record during a dust outbreak on 06 08 february 2012 this features a highly radiogenic pb and sr and unradiogenic nd signature marking a clear shift in dust provenance relative to that of normal days as the dust storm waned continuous gradual changes are observed reflecting mixing and progressive dilution with dust typical of normal days these inferences from radiogenic isotope tracers are corroborated by both satellite images calipso and modis and back trajectory analyses the radiogenic isotope fingerprinting of these presently active north african dust sources and especially the saharan air layer will prove invaluable in studies of past dust emission from northern africa where imagery and back trajectory analysis are unavailable

geochemical fingerprinting of trans atlantic african dust based on radiogenic sr nd hf isotopes and rare earth element anomalies mineral dust is an important component of earth s climate system and biogeochemical cycles on a global scale in order to understand the relationship between climate processes in the source areas and the properties of aerosols at distant receptor sites we must be able to identify the source provenance of dust here we present a multiproxy study that characterizes the temporal variability in the geochemical composition of long range african dust lrad collected between 2003 and 2011 in the trade winds on the caribbean island of barbados we find systematic differences between sr nd hf isotopic composition and rare earth element anomalies of individual dust events and evidence of seasonal shifts in dust source activity and transport these results indicate that coherent geochemical source signatures of lrad can be preserved even after transport across thousands of kilometers we investigated the possibility of identifying the potential source areas through comparisons with literature data however these data are almost entirely based on measurements of soil and sediment samples this could lead to biases because of soil aerosol particle size and composition differences nonetheless our data suggest that many samples are linked to sources in mali and sub saharan regions radiogenic nd hf composition of aerosols can potentially be a useful proxy to study the proximity of mineral dust sources to depositional sites in order to establish firmer links between lrad and dust source areas however we require much more data on the geochemical composition of aerosols from potential source areas in north africa

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

the 7 13 march 2006 major saharan outbreak multiproxy characterization of mineral dust deposited on the west african margin mineral dust deposits were collected at mbour senegal throughout the spring of 2006 and especially during the well documented march 7 13 large saharan dust outbreak during this 7 day period significant changes in mass flux grain size clay mineralogy and sr and nd isotopic compositions were recorded indicating distinct provenances for the dust transported and deposited during and outside the event all these terrigenous proxies as well as freshwater diatom taxa also showed significant temporal variations during the outbreak implying contributions from at least two different provenance regions tri dimensional back trajectories and satellite imaging enabled us to link those distinct signatures to regions increasingly to the southeast within a large area covering mauritania mali and southern algeria identified by the total ozone mapping spectrometer toms as the main source of the prominent winter spring plume over the tropical atlantic the multiproxy characterization of the march 7 13 dust fall therefore enables us to typify the terrigenous signature of two different regions supplying dust off west africa and provide valuable clues for the interpretation of northeastern tropical atlantic ocean dust sedimentary records in terms of changes in provenance regions and transport systems additionally because dust deposition data are scarce flux and grain size data obtained in this study among other parameters such as clay assemblages provide important constraints for atmospheric transport models and dust deposition budget estimates in this area

impacts of the chi chi earthquake on subsequent rainfall induced landslides in central taiwan abstract the influence of the chi chi earthquake on subsequent rainfall induced landslides was evaluated by comparing the occurrence of landslides in the choushui river watershed through eight spot images that covered the period from 1996 to 2001 the chi chi earthquake not only triggered serious coseismic landslides itself but also extensively disturbed surface strata around the epicentral area after surface strata have been highly disturbed heavy rainfalls in 2000 and 2001 have triggered more landslides than the earthquake itself compared with the data obtained from images before the earthquake it is obvious that the density of rainfall induced landslides increased significantly after the earthquake and the places where landslides occurred changed as well although typhoon herb in 1996 brought more precipitation than typhoon toraji in 2001 only 9 77 km 2 landslides were induced by herb while 48 8 km 2 landslides almost five times larger than those caused by herb were triggered by toraji besides landslides induced by herb were mainly distributed in mid slope areas with slopes of 20 30 after the chi chi earthquake the rainfall induced landslides occurred mainly in places with slopes between 40 and 50

simulating retrogressive slope failure using two different smoothed particle finite element methods a comparative study abstract various smoothed particle finite element methods spfems have been developed to simulate large deformation problems but their efficiency and accuracy in simulating progressive landslides in sensitive clays have remained unclear in this study a series of numerical analyses are carried out to investigate the development of retrogressive landslides by two spfems an edge based strain smoothing pfem espfem and a node based strain smoothing pfem nspfem in view of their outstanding performance in large deformation analysis a strain softening mohr coulomb mc model is adopted to simulate the behaviour of sensitive clays during landslide assuming a poisson s ratio of 0 49 to ensure undrained conditions the influence of mesh density on the development of retrogressive failure is evaluated for two spfems numerical analyses of three mesh sizes 0 2 m 0 15 m and 0 12 m are carried out sequentially with all results demonstrating that 1 the spread retrogressive landslides with horsts and grabens can be achieved by both spfems with the adopted soil model 2 run out and retrogression distances decrease as mesh density increases for both methods 3 retrogressive collapse occurs earlier for espfem but is delayed for nspfem with increased mesh density 4 nspfem allows faster calculations and reduces mesh dependency problems when compared with espfem and 5 the increase of shape factor can accelerate retrogressive evolution of landslides finally a real landslide in sensitive clay at sainte monique quebec is simulated to demonstrate espfem s computational efficiency and accuracy

a three year time series of mineral dust deposits on the west african margin sedimentological and geochemical signatures and implications for interpretation of marine paleo dust records keywords saharan dust deposition flux grain size clay mineralogy sr and nd isotopes amma program a b s t r a c t mineral dust deposits in the northeastern tropical atlantic ocean netao are an important contribution for reconstructing paleoenvironments and paleoclimates of west africa however the interpretation of the changes in the sedimentological and geochemical characteristics of the dust deposits recorded in the marine sediments from the netao remains incomplete in order to improve our understanding of dust proxies in particular its mineralogical and geochemical provenance tracers present day dust deposition has been monitored at mbour 80 km south of dakar on the senegalese margin here we report a multi proxy investigation of a unique three year continuous time series of mineral dust deposits collected at a weekly or better temporal resolution over the march 2006 march 2009 period mass deposition flux and mean modal grain size display marked but reverse seasonal features with higher flux during the winter spring seasons and coarser grain size mode in summer when flux is minimal reflecting contrasting transport patterns throughout the year similarly clay mineralogy the illite kaolinite ratio in particular shows seasonal fluctuations manifesting the latitudinal displacement of the contributing domains of provenance in response to the seasonal migration of the itcz position and the associated wind systems our three year record also reveals the occurrence of major deposition events superimposed on the seasonal pattern generally during the winter spring dry seasons and most frequently during the month of march our study shows that these major events which contribute a large fraction of the total annual deposition flux all originate from the western sahara sahel a major area of emission in the region beside the bodele depression stretching from the mauritanian and western saharan coasts to the hoggar mountains combined with air mass tri dimensional back trajectories and satellite images the mineralogical and sr nd isotopic compositions of these large dust events enable us to identify several mineralogically and geochemically distinct provenance sectors within this vast western area unlike the background dust deposits the 87 sr 86 sr and the e nd isotopic signatures of the major dry events closely match that of the netao late holocene sediments supporting the hypothesis that these events account for most of the aeolian terrigenous supply reaching the ocean floor although this database needs to be expanded our results already provide useful constraints for the interpretation of the dust proxies variations in marine sedimentary archives off mauritania senegal in terms of changes in wind regimes and aridity over west africa

new geochemical constraints for the origin of ridge subduction related plutonic and volcanic suites from the chile triple junction taitao peninsula and site 862 leg odp141 on the taitao ridge abstract several features of neogene and quaternary magmatism in the region south of the present day chile triple junction ctj at 46 12 s are directly related to the migration of the triple junction due to the obliquity of the ridge orientation with respect to the subduction front the triple junction migrated from south to north during the last 14 ma the taitao peninsula the westernmost promontory of the chile coast and the taitao ridge a submarine promontory north of the taitao peninsula provide the most complete collection of ridge subduction related magmatic products in the region the emplacement of near trench volcanics the intrusion of a variety of plutonic rocks and the related hydrothermal activity at these two sites have been interpreted as resulting from magma interactions between subducted ridge segments of the chile spreading centre and the continental crust we present new field observations and geochemical data that help to better constrain the problem of the sources and evolution of the taitao magmas the new geochemical data were obtained on samples collected from the taitao peninsula during a field expedition in 1995 and from samples of the taitao ridge during leg odp141 site 862 which have been re sampled in 1996 by one of us selected major and trace element compositions of 20 volcanic rocks from the taitao ridge are discussed together with 53 analyses from different rock types from the taitao peninsula including 24 unpublished analyses nd and sr isotopic compositions were obtained from 5 whole rocks and separated minerals of the taitao peninsula together with the oxygen isotope composition of four separated clinopyroxenes six main magmatic types are identified 1 n type morb 2 e type morb 3 lree depleted morb showing some trace element features typical of arc basalts 4 moderately nb depleted e morb 5 calc alkaline andesites dacites and rhyolites and 6 andesites and dacites with adakitic signature chemical similarities exist between some forearc magmas of the taitao ridge and the taitao peninsula and magmas emplaced at the chile active spreading ridge one important result based on isotope data is that the lavas emplaced over the continental crust taitao peninsula did not originate from melting of continental crust nor from extensive assimilation of such a crust by mantle derived magmas the likely source of these basalts could be the hot convective oceanic mantle of the southern chile spreading ridge buried at moderate depth 10 30 km

magmatic tectonic effects of high thermal regime at the site of active ridge subduction the chile triple junction model abstract high thermal gradients are expected to be found at sites of subduction of very young oceanic lithosphere and more particularly at ridge trench trench rtt triple junctions where active oceanic spreading ridges enter a subduction zone active tectonics associated with the emplacement of two main types of volcanic products 1 morb type magmas and 2 calc alkaline acidic magmas in the forearc also characterize these plate junction domains in this context morb type magmas are generally thought to derive from the buried active spreading center subducted at shallow depths whereas the origin of calc alkaline acidic magmas is more problematic one of the best constrained examples of ridge trench interaction is the chile triple junction ctj located southwest of the south american plate at 46 12 s where the active chile spreading center enters the subduction zone in this area there is a clear correlation between the emplacement of magmatic products and the migration of the triple junction along the active margin the ctj lava population is bimodal with mafic to intermediate lavas 48 56 sio 2 and acidic lavas ranging from dacites to rhyolites 66 73 sio 2 previous models have shown that partial melting of oceanic crust plus 10 20 of sediments leaving an amphibole and plagioclase rich residue is the only process that may account for the genesis of acidic magmas due to special plate geometry in the ctj area a given section of the margin may be successively affected by the passage of several ridge segments we emphasize that repeated passages will lead to the development of very high thermal gradients allowing melting of rocks of oceanic origin at temperatures of 800 900 c and low pressures corresponding to depths of 10 20 km depth only in addition the structure of the ctj forearc domain is dominated by horizontal displacements and tilting of crustal blocks along a network of strike slip faults the occurrence of such a deformed domain implies that an important tectonic coupling may exist between the upper and the lower plates leading to the partitioning of the continental lithosphere and to the tectonic underplating of very young oceanic lithosphere below the continental wedge we assume that in the case of the ctj the uncommon situation of three successive ridge segments entering the trench at 2 3 ma intervals only resulted in a strong and finally long lived thermal anomaly this anomaly caused remelting of underplated portions of very young still hot oceanic lithosphere only particular geometrical rtt configurations are able to produce such features these include linear continental margin short ridge segments slightly oblique to the trench and short transform faults finally the ctj example shows that a possible scenario for the origin of calc alkaline acidic rocks in the near trench region involves coeval tectonic coupling and repeated passage of thermal anomalies due to successive subduction of short ridge segments therefore the local abundance of calc alkaline acidic rocks associated with morb type lavas in ancient series could be the tracer of plate tectonic configurations involving the subduction of short ridge segments in a relatively short duration

eolian transported freshwater diatoms and phytoliths across the equatorial atlantic record temporal changes in saharan dust transport patterns the deposition of freshwater diatoms fd and phytotliths p was determined from sediment traps for a wide region 20 n 7 s in the tropical and equatorial atlantic along a n s transect in the eastern equatorial atlantic around 10 w and in the western equatorial atlantic around 25 w these siliceous organisms are derived from the sahara and sahel regions of africa and eolian transport with direct settling over the open ocean is assumed to be the transport agent depositional rates of fd and p revealed strong coupling with seasonal changes in saharan dust transport that are associated with seasonal precipitation patterns major wind systems and the geographical extension of the dust plume across the atlantic mean daily fluxes were highest south of cape verde fd 9 104 valves m 2 d 1 p 2 104 bodies m 2 d 1 moderately high off cape blanc and in the guinea basin north of the equator of the order of 3 104 valves m 2 d 1 for fd and 0 7 104 bodies m 2 d 1 for p and consistently low south of the equator and in the western equatorial atlantic in traps north of the equator seasonal changes were marked aulacoseira granulata and a islandica were the most abundant fd in the traps regardless of trap location and season however the number of fd species was higher in the cape blanc and cape verde areas the morphological diversity shape and size of the p assemblage decreased with increasing distance from the african continent patterns of fd and p accumulation rates in surface sediments coincided with those in the traps robust freshwater diatom and phytolith records associated with seasonal eolian transport from saharan and sahelian regions into the atlantic furnish clues that can help in our present understanding of the processes linking transport between land atmosphere and ocean

anisotropy of magnetic susceptibility in a palaeozoic flysch basin the windermere supergroup northern england abstract the windermere basin of northern england was initiated in late ordovician times and developed into a foreland basin by collision of the laurentian and eastern avalonian plates during silurian times it was largely filled by axial turbidite input in mid to late silurian times rock magnetic studies suggest that paramagnetic minerals probably mostly chlorite dominate the magnetic susceptibility studies of anisotropy of susceptibility ams identify a bedding related fabric which has survived later acadian deformation in all but the oldest u ordovician units the magnitude of the fabric becomes amplified in the higher more argillaceous parts of individual beds but the direction of maximum susceptibility k1 remains aligned with palaeoflow direction throughout the massive and parallel laminated divisions ams is best defined in those units with well developed planar and cross bedding the mechanism responsible for rippling the upper parts of the beds involves rolling of detrital grains along the bed during traction and alignment of the long axis the grain s rotation axis normal to the current consequently the intermediate axis of ams k2 is in the direction of the secondary current responsible for rippling some beds which are rippled throughout show the same feature hemipelagic facies comprising laminated silty mudstones have highly uniform fabrics to which detrital hematite is an important contributor the k1 directions in the bedding planes show cyclic swings in declination which may be related to some long period perhaps orbitally forced secular oceanographic variation since these sediments were deposited in optimum conditions for preserving grain alignment with the geomagnetic field ams and amr anisotropy of magnetic remanence study of such facies may provide methods for recovering secular variation in the remote geological past and for estimating rates of deposition

geochemical and isotopic characterization of the bodele depression dust source and implications for transatlantic dust transport to the amazon basin the bodele depression chad in the central sahara sahel region of northern africa is the most important source of mineral dust to the atmosphere globally the bodele depression is purportedly the largest source of saharan dust reaching the amazon basin by transatlantic transport here we have undertaken a comprehensive study of surface sediments from the bodele depression and dust deposits chad niger in order to characterize geochemically and isotopically sr nd and pb isotopes this dust source and evaluate its importance in present and past african dust records we similarly analyzed sedimentary deposits from the amazonian lowlands in order to assess postulated accumulation of african mineral dust in the amazon basin as well as its possible impact in fertilizing the amazon rainforest our results identify distinct sources of different ages and provenance in the bodele depression versus the amazon basin effectively ruling out an origin for the amazonian deposits such as the belterra clay layer by long term deposition of bodele depression material similarly no evidence for contributions from other potential source areas is provided by existing isotope data sr nd on saharan dusts instead the composition of these amazonian deposits is entirely consistent with derivation from in situ weathering and erosion of the precambrian amazonian craton with little if any andean contribution in the amazon basin the mass accumulation rate of eolian dust is only around one third of the vertical erosion rate in shield areas suggesting that saharan dust is consumed by tropical weathering contributing nutrients and stimulating plant growth but never accumulates as such in the amazon basin the chemical and isotope compositions found in the bodele depression are varied at the local scale and have contrasting signatures in the silica rich dry lake bed sediments and in the calcium rich mixed diatomites and surrounding sand material this unexpected finding implies that the bodele depression material is not pre mixed at the source to provide a homogeneous source of dust rather different isotope signatures can be emitted depending on subtle vagaries of dust producing events our characterization of the bodele depression components indicate that the bodele calcium rich component identified here is most likely released via eolian processes of sand grain saltation and abrasion and may be significant in the overall global budget of dusts carried out by the harmattan low level jet during the winter

post failure analysis of the maierato landslide using the material point method abstract the 15 february 2010 maierato landslide has become the symbol of the hydrogeological instability of the calabria region southern italy it occurred after a long period of rain in an area prone to landslides some videos filmed during the event documented the high velocity and the flow like character of this landslide after the slope failure several studies focused on the pre failure and failure stages of the maierato landslide in order to interpret its failure mechanism and to establish the main factors of triggering however none of these studies analysed the post failure stage of this landslide in the present study the material point method mpm is used to simulate the run out process of the maierato landslide and provide a possible explanation of this process different scenarios are considered and for each of them the simulated post failure configuration of the displaced material is compared to that detected after the event numerical results match fairly well the observed ones when a severe reduction in the shear strength of the involved soil is accounted for in the analysis this strength reduction is attributed herein to the high excess pore water pressures generated by the large distortions of the moving soil mass moreover the back calculated post failure strength is consistent with that found in several case histories of slope failures involving liquefied materials

the material point method for unsaturated soils the paper describes a three phase single point material point method formulation of coupled flow water and air for hydro mechanical analysis of geotechnical problems involving unsaturated soils the governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics an eulerian computational mesh and a lagrangian analysis of material points general mathematical expressions for the terms of the set of governing equations are given a suction dependent elastoplastic mohr coulomb model expressed in terms of net stress and suction variables is implemented the instability of a slope subjected to rain infiltration inspired from a real case is solved and discussed the model shows the development of the initial failure surface in a region of deviatoric strain localisation the evolution of stress and suction states in some characteristic locations the progressive large strain deformation of the slope and the dynamics of the motion characterised by the hi

climate forcing of the pb isotope record of terrigenous input into the equatorial atlantic abstract pb isotopic compositions of bulk sediment cores from the tropical atlantic are used here to infer variations in the provenance of terrigenous input to the tropical atlantic during pleistocene climate cycles the 200 ka high precision 2 100 ppm pb isotope records of the ceara rise western atlantic and sierra leone rise eastern atlantic cores show a clear glacial interglacial cyclicity reflected by alternating unradiogenic pb and radiogenic pb in both cores the glacial interglacial pb isotopic contrast is also observed in pb pb space and can be explained in terms of binary mixing variations along the mixing lines reflecting changes in the relative proportions of the glacial unradiogenic and interglacial radiogenic pb source s the pleistocene pb isotopic variability of the terrigenous input to the ceara rise can be linked to changes in the weathering styles in the amazon basin and as a result in the amazon river discharge these changes are reflected by a greater contribution from the highlands andes pb source during glacial times and strengthening of the lowlands shield pb source during interglacials on the other hand pb isotopic variations in the sierra leone rise core indicate increased pb inputs from the saharan dust plume during glacial times in agreement with the wind patterns over africa furthermore this result bears some implications on the cause of the enhanced glacial terrigenous fluxes to the tropical atlantic which we infer to be due to increase in winter wind transport rather than glacial hyperaridity the cyclicity of the ceara rise and sierra leone rise pb isotopic records together with changes in the proportions of mixing sources throughout the last 200 ka monitor changes in the hydrological cycle over south america and the wind systems over africa respectively both of which are linked to the seasonal latitudinal migration of the intertropical convergence zone the correlation found between pb isotope cycles and other paleoclimate proxies suggests that pb isotopes may be responding to variations in earth s orbital parameters

paleomagnetism of mesozoic rocks from the central andes of southern peru importance of rotations in the development of the bolivian orocline a paleomagnetic study has been undertaken in jurassic volcanics and cretaceous intrusions from coastal southern peru a secondary magnetization in the jurassic volcanics was identified at 21 sites from three main localities along the southern coast of peru mean virtual geomagnetic pole 59 5 n 190 1 e k 111 95 3 0 this secondary magnetization was acquired during a tectonomagmatic event that may be related to the emplacement of the peruvian coastal batholith and or to the first andean phase of compressional deformation in late cretaceous if we assume that the remagnetization is of late cretaceous age a regional counterclockwise rotation of about 20 is recorded by the forearc of southern peru from 16 s to 18 s primary remanent magnetizations recorded by the volcanics and the batholith reveal a more complex tectonic history of block rotations counterclockwise rotations of 50 to 80 are documented near the localities of chala eight sites ocona two sites and arequipa four sites preliminary results based on three sites of late permian to early triassic sediments from northern bolivia also show a large counterclockwise rotation the observed differences between the primary and the secondary magnetization indicate that large block rotations occurred prior to the acquisition of the secondary magnetization perhaps this first episode of deformation partially structured the andean chain in the central andes and induced an incipient orocline during the cenozoic a differential shortening along the chain gave the present day shape of the bolivian deflection and resulted in a counterclockwise rotation of the forearc system by about 20 as indicated by the remagnetization

development of an sph based method to simulate the progressive failure of cohesive soil slope the landslide of cohesive soil slope is generally characterized by deformation and failure behaviors involving strain softening and strain dependent dilation however numerical simulation of these complex behaviors remains a challenge since no available soil constitutive model can incorporate all these features to resolve this problem a smoothed particle hydrodynamics sph based approach is developed to simulate the landslide of cohesive soil slope the cohesive soil slope is modeled as elasto plastic material with drucker prager yield criterion and the corresponding softening effect is introduced into drucker prager criterion by treating cohesion as a scalar function of accumulative plastic strain rate to reduce excessive volume expansion strain dependent dilation is fulfilled in a straightforward manner by assuming the dilation angle as a function of volumetric and axial plastic strain increment numerical collapse test of cohesive soil pile on a flat plane is conducted to validate the proposed sph based approach the further deformation triggered by softening effect is obtained the obtained results are compared with those of existing sph based method and fem simulation finally the proposed sph based approach is applied to simulate the landslide of an actual cohesive soil slope the simulation results including deposit run out distance slip surface and final outline are compared with the field data and classical fem simulation

paleocurrent patterns of the sedimentary sequence of the taitao ophiolite constrained by anisotropy of magnetic susceptibility and paleomagnetic analyses abstract determination of paleocurrent directions is a robust approach to establish the mechanism of sediment transport and of deposition however in tectonically controlled or affected basins where rotations are suspected it is of critical importance to correct previously calculated paleocurrent directions to establish the original pre tectonic transport and deposition patterns in order to illustrate this we determined the orientations of the anisotropy of magnetic susceptibility ams fabrics from 14 sites distributed along the sedimentary deposits interbedded within the late miocene main volcanic unit mvu of the taitao ophiolite southern chile data were used to estimate characteristics directions and relative velocities of the sediment transporting paleocurrents and orientations of the depositional slope sedimentary deposits consist of a rhythmic sequence of conglomerate base sandstone and mudstone top beds that present a systematic decrease in grain size up sequence as a whole and within individual beds sedimentary deposits of the mvu as well as overlaying effusive volcanic products are disrupted by small and discrete dextral normal brittle faults the distribution of fault planes and their kinematic characteristics suggest the development of a dextral negative flower like fault zone in the area previously reported nw ward paleocurrent directions obtained from the orientations of sedimentary structures roughly agree with our calculations based on the orientations of ams fabrics calculated paleocurrent directions are sub parallel to the nw se trend of estero cono channel the main lineament in the area the spatial distribution of ams axes between and within sites suggest that coarse grain deposits were transported by relatively high velocity flows whereas fine grained deposits were by low to nearly null velocity flows previously reported paleomagnetic analyses indicate that counterclockwise rotations affected the whole taitao ophiolite including the mvu by applying the necessary corrections we obtained paleocurrent directions yielding mostly nnw ward directions restoration of the orientations of beddings indicates that the depositional surface dipped steeply at its easternmost edge and shallowly at the westernmost end we propose here that sediments were transported by turbidite flows generated by slope instabilities in the innermost part of the estero cono these turbidites followed the estero cono lineament while they filled the channel and transported sedimentary material eroded from the upper portions of the ophiolite and nearby units towards the pacific ocean sediments were deposited on a nw to w facing slope and sorted in decreasing grain size along the channel the instability of the slope was most probably triggered by the activity of a transtensional fault zone developed along the mid axis of the estero cono channel

a new high resolution central and western saharan summertime dust source map from automated satellite dust plume tracking 1 in this paper we outline a new objective dust source detection method for the central and western sahara cws based on the automated tracking of individual dust plumes in data from the spinning enhanced visible and infrared imager available every 15 mins at 0 03 spatial resolution the method is used to map the origin of summertime dust storms in the cws for june august 2004 2010 it reveals the sources of these events in unprecedented detail allowing for the identification of specific highly active source areas the study of collocated surface features reveals that many of the dominant sources are likely associated with paleolakes and outwash plains many in close proximity to the saharan mountains extensive nonsource areas are associated with low albedo and elevated terrain pointing to the mountainous regions of the sahara additionally sand seas are not identified as important source areas but their margins sometimes are the automated tracking method also facilitates analysis of the transport direction of dust plumes from key source regions and the inference of emission mechanisms it is found that there are two broad domains within the cws one in southwest algeria and northwest mali characterized primarily by transport toward the southwest and very likely dominated by low level jets embedded in the northeasterly harmattan winds and a second in southern algeria northwest niger and northeast mali where there is no preferred transport direction and a strong potential association between dust events and deep convection pointing toward cold pool outflows as the likely deflation mechanism