tectonic evolution of the chos malal fold and thrust belt neuquen basin argentina from u th he and fission track thermochronometry

dietary reconstruction of miocene gomphotherium mammalia proboscidea from the great plains region usa based on the carbon isotope composition of tusk and molar enamel abstract the miocene of the great plains of north america has long been recognized as an interval of major ecological reorganization to reconstruct the dietary response of the proboscidean gomphotherium to miocene ecosystem change in the great plains we analyzed the carbon isotope composition of 185 serial samples of tusk enamel from 17 individuals and bulk samples of posterior molars from 15 individuals of gomphotherium from localities in the great plains ranging in age from the early barstovian land mammal age ca 15 ma to the early hemphillian land mammal age ca 8 ma sets of samples from each tusk were designed to encompass about 1 year of tusk growth based on cheek tooth morphology gomphotherium is thought to be a browser with a diet primarily of dicots the mean 13 c of all samples is 9 8 1 2 indicating that the diet of gomphotherium was dominated by c 3 biomass if gomphotherium habitually foraged on water stressed plants in arid habitats which would have 13 c values higher than the average composition for c 3 and c 4 plants then all but one individual in this study consumed less than 50 c 4 biomass the maximum percentage of c 4 in the diet would be much lower if food plants had average 13 c values or if gomphotherium foraged in closed canopy habitats differences in 13 c values between specimens from the southwestern us and the great plains as well as between some coeval specimens from nebraska suggest geographic differences in either diet or typical foraging habitat the data do not indicate a trend toward inclusion of more c 4 vegetation in the diet of gomphotherium during the miocene and none of the serially sampled tusks exhibit seasonally varying 13 c profiles for most of its history in north america gomphotherium was a c 3 browser or a mixed feeder with a preference for browse our results indicate that areas of wooded habitat sufficient to support herds of large bodied herbivores remained available in the great plains through the late miocene

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

the effects of slope length and slope gradient on the size distributions of loess slides field observations and simulations abstract in this study we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides to carry out this study we employ data on 275 loess slides within zhidan county central loess plateau china these data were collected in the field and supplemented by the interpretation of remote sensing images both the field observations and slope stability analysis show that loess slide size increases with the slope length slide sizes is significantly correlated with slope length showing a power law relationship in both cases however the simulation results show that slope gradient is not associated with loess slide size the main part of the link between slope gradient and slide size seen in the observations is only apparent as indicated by the strong connection between slope gradient and length statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations in addition the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation this analysis shows that slope length controls the rollover of the frequency size distribution of loess slides the scaling exponent increases with slope length

the last dicynodont re assessing the taxonomic and temporal relationships of a contentious australian fossil abstract dicynodonts a lineage of non mammalian therapsids who s derived taxa evolved edentulous beaked jaws sporting a pair of caniniform tusks dominated the herbivorous terrestrial vertebrate fauna for much of the permian and triassic periods long assumed to have met their demise during the end triassic extinction event the discovery of a fragmentary possible dicynodont in cretaceous rocks in queensland australia potentially extended the longevity of the lineage by nearly 100 million years this study reassesses the geological anatomical and historical aspects of this specimen through museum archival research detrital zircon geochronology trace element analysis and x ray synchrotron microtomography and present new knowledge regarding its temporal geographical and biological origins supporting a late cenozoic pliocene pleistocene mammalian megafaunal affinity for the specimen resulting in a lack of evidence for post triassic survival of dicynodonts

influence of grading on the mechanical behaviour of stava tailings tailings dams can be fragile structures and too often they are subject to liquefaction the material they are composed of is rather peculiar having a man made origin and their behaviour is still not very well understood the soil from the stava tailings dams structures that were subject to liquefaction in 1985 causing extensive destruction was investigated in this study as an example of tailings two main aspects of their behaviour have been examined the influence of the percentage of silt and sand that compose the soil on its mechanical behaviour and the susceptibility to liquefaction analysing the behaviour within a critical state framework in this paper it is shown that as the quantity of silt increases the slope and intercept of the normal compression line and critical state line at higher pressures decrease until an inversion of behaviour is observed while at lower stress levels the critical state line changes its position but not its slope this means that the effect of adding silt on the

plastic and viscous shear displacements of a deep and very slow landslide in stiff clay formation deep and superficial displacements have been measured since 2005 in a slow active landslide that has occurred in a stiff clay formation of the italian southern apennines recently new inclinometer casings have been installed to achieve further information on the displacement field in this paper standard inclinometer profiles and fixed in place probe data are analysed over time new data confirm previous hypotheses on geometry and kinematics and add more information on the viscous component of displacements the mechanism of movement in most of the track essentially corresponds to sliding localized on a shear surface consistently with stress and strength distribution however locally internal viscous deformations also occur especially in the weathered and softened zones of the landslide and contribute to the soil discharge continuity viscous displacements can be interpreted by a simplified rheological model based on the bingham equation the residual shear strength has been considered as the creep threshold value and the dynamic viscosity has been considered dependent on the stress level on the basis of long term direct shear tests under controlled shear stresses which were carried out in laboratory

neogene mammalian faunal change in southern asia correlations with climatic tectonic and eustatic events the fluvial neogene siwalik formations of northern pakistan span long time intervals with only minor hiatuses and being highly fossiliferous are uniquely suited for studies of change in mammalian faunas magnetostratigraphic correlations of a critical stratigraphic section give dates for 45 middle and late miocene biostratigraphic events these mark either first appearances or extinctions in the mammal fauna and show that in the siwaliks there were major fauna turnovers at between 20 and 16 ma and at 9 5 and 7 4 ma two minor faunal events are dated at 13 2 and about 12 ma many species making their first appearance were immigrants from europe or africa and indicate when connections to those regions existed immigration and extinction were the dominant modes of faunal change in situ evolution was much less important the siwalik biostratigraphic record correlates closely to climatic oceanographic and tectonic events which probably controlled immigration into southern asia abiotic events were therefore important factors affecting evolution of the mammal communities

a fluidized landslide occurred in the loess plateau a study on loess landslide in south jingyang tableland abstract the south jingyang tableland is located on the southern loess plateau of china ever since the introduction of the water division project in the 1970s more than 40 loess landslides have occurred in this tableland terrace slope topography here on the morning of march 8 2016 a loess landslide induced by irrigation occurred in jiangliu village on the south jingyang tableland and around 20 000 m 3 of loess rapidly slid along a 65 m high slope for 260 m the moisture content of the slip mass displayed a dramatic change along the slip direction the water saturation degree in the landslide depression was relatively high and the leading edge was in a flow state there were some local natural sub areas but the overall area showed a characteristic fluidized a field investigation indicated that while macropores developed in the loess and deep joints provided a preferential passage for the infiltration of irrigation water which became a major water source for the slip mass the softening of the toe part of the slope caused by irrigation became the major factor resulting in the instability of the slip mass undrained triaxial shear tests on loess in natural water content and fully saturated state show that the enhanced saturation degree not only lowered the soil mass strength but also increased pore water pressure resulting in the zoning status of the jiangliu landslide the angle of reach formed during this landslide was approximately 14 which demonstrated motion characteristics of long runout further considering the standing water at the slope foot and unique properties of slip soils after the landslide occurred it is speculated that the motion mechanism of this high speed and long runout landslide was associated with loess liquefaction that led to sharp decrease in shear strength of the displaced landslide materials during the shear process

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

interaction between landsliding materials and the underlying erodible bed in a loess flowslide abstract loess landslides exhibit strong interactions with the terrace sediments of the jing river on the south jingyang platform jingyang xi an china analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface accompanied by other terrace sediments of carrying this led to the formation of a thrust nappe structure over a long distance we performed ring shear tests to examine the shear behavior of this sand layer with the finding that saturated sand was highly susceptible to liquefaction induced failure the groundwater level of the study area is high resulting in near saturation of the sand layer therefore topographic interferences contributed additional variables and increased interaction complexities simulations indicated that the liquefied sand layer was compressed and forced due to the absence of constraints the sand layer near the bottom of the slope was sheared out over a relatively short distance on the other hand particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground finally an initiation movement model of loess flowslides is proposed it describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands the landslide experienced four stages as they moved scraping collisions floating scrapes folded thrusts and nappe accumulation

geomorphic evidence for plio quaternary compression in the andean foothills of the southern neuquen basin argentina the southern central andes foothills are made of imbricate thick and thin skinned fold and thrust belts they were formed during cretaceous and miocene compressive periods by successive eastward propagation episodes of the orogenic front we analyze remnant terraces and alluvial deposits of the neuqun river and its tributaries to study the plio quaternary tectonic regime in the southern neuqun basin topographic profiles of remnant terraces show a crustal scale tens of kilometers anomaly above the chihuido south anticline this anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline another anomaly in the terrace profiles correlated with a knickpoint in the current neuqun river is observed farther east near aelo we interpret these anomalies to be the consequence of a plio quaternary uplift of the chihuidos and aelo anticlines folding and surface faulting of plio quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the miocene orogenic front and of the predominantly thin skinned agrio fold and thrust belt from these data we infer that the southern neuqun basin is still shortening under a compressive stress regime and that the andean orogenic front is migrating farther to the east extensional features in the study area correspond mainly to thin skinned gravitational gliding resulting from crustal uplift thus we argue that the tectonic compressive regime is preserved in the southern neuqun basin throughout the plio quaternary though the slab may have steepened during this period

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

analysis of a retrogressive landslide in glaciolacustrine varved clay abstract the largest landslides in estonia are associated with glaciolacustrine varved clays one of the recent slope failures audru landslide was chosen for detailed investigation landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events the first stage of audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body the influence of the various modeling parameters on the overall slope stability was also investigated

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

microstructures in landslides in northwest china implications for creeping displacements abstract microstructures mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the gansu province china were examined with optical microscopy transmission electron microscopy tem x ray diffraction xrd and synchrotron x ray diffraction measurements common sheet silicates are chlorite illite muscovite kaolinite pyrophyllite and dickite other minerals are quartz calcite dolomite and albite in one sample graphite and amorphous carbon were detected by tem edx analyses and tem high angle annular dark field images the occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the suoertou and xieliupo landslides is particularly significant for reducing the frictional strength of the landslides it is proposed that the landslides underwent comparable deformation processes as fault zones the low friction coefficients provide strong evidence that slow moving landsliding is controlled by the presence of weak minerals in addition tem observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion for calcite and quartz grain size reduction was attributed to both pressure solution and cataclasis therefore besides landslide composition the occurrence of ultrafine grained slip zone material may also contribute to weakening processes of landslides tem images of slip zone samples show both locally aligned clay particles as well as kinked and folded sheet silicates which are widely disseminated in the whole matrix small newly formed clay particles have random orientations based on synchrotron x ray diffraction measurements the degree of preferred orientation of constituent sheet silicates in local shear zones of the suoertou and duang he ba landslide is strong this work is the first reported observation of well oriented clay fabrics in landslides

southern patagonian plateau basalts and deformation backarc testimony of ridge collisions abstract the distribution and volume of tertiary patagonian plateau basalts and the evolution of the patagonian fold and thrust belt between 46 and 49 s appear to be closely tied with ridge trench interactions along the continental margin to the west eocene plateau basalts south of 43 s are associated with a gap in the eocene arc and can be related to a proposed collision of the aluk farallon ridge against the trench at this time eruptions of late miocene to recent plateau basalts between 46 and 49 s can be related to time transgressive slab windows in the underlying mantle generated by the collision of segments of the chile ridge at 10 14 ma and 6 ma the principal deformation in the patagonian fold and thrust belt predates the eruption of the basalts and also appears to be related with late miocene ridge collision comparison of plateau basalts related to the collision of the three distinct ridge segments suggests that the volume of basalt erupted increases with the length of the collided ridge segment almost all eocene to recent plateau basalts between 46 and 49 s have oib like ocean island basalt trace element signatures showing that the mantle source region changed little with time plateau basalts with more arc like signatures appear to be contaminated by continental crust relative melting percentages inferred from the trace element chemistry of the plateau basalts correlate with volumes of erupted basalt implying spatial and temporal changes in temperatures in the mantle source that can be correlated with slab windows

analysis of rainstorm induced slide debris flows on natural terrain of lantau island hong kong abstract lantau island the largest outlying island of the territory of hong kong experienced a severe rainstorm on 4 5 november 1993 which induced 800 slope failures on natural terrain there detailed field investigations were carried out to study the failure modes in relation with various influencing factors it was found that the occurrence of slide debris flows has a close relationship with bedrock geology slope gradient vegetation cover and micro landform the failure modes of slide debris flows may be classified into translational slides and rotational slides and the former are predominant analysis of the hydrological response of colluvial slopes during the rainstorm indicated that the majority of the failures were caused by the development of a perched water table in the thin surface layer of colluvium of volcanic origin due to infiltration during the heavy rain undisturbed soil samples from south lantau have been subjected to anisotropically consolidated undrained compression tests at comparatively low stress levels constant deviatoric stress path tests cqd simulating the stress path in the field at in situ stress levels have been performed to investigate soil behavior the cqd test results indicate that the material of slopes at undisturbed state is brought to dilation because of the increase in pore water pressure caused by infiltration of rain water for a translational slide the displacement resulting from dilation may destroy cohesion along the failure surface and locally within the interior of the slide the surplus water during the intense rainstorm was able to equilibrate the reduction in pore pressure caused by dilation and the dilation and displacement may be further increased the strain softening after significant strains triggered debris flow mobilization however for a rotational slide the increase in pore water pressure caused by surplus water infiltration during the intense rainstorm could not equilibrate the reduction in pore pressure caused by dilation much or even all of the sliding block could not mobilize into a debris flow

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

formation mechanism analysis of irrigation induced retrogressive loess landslides abstract the loess plateau covers about 6 6 of the total land area of china landslides are serious concerns in loess plateau of china and the south jingyang tableland on the loess plateau of china has received significant attention because of frequent occurrence of gradual retrogressive loess landslides grll there however the characteristics and mechanism of grll are largely unknown in this study three typical landslide groups namely miaodian zaitou landslide group jiangliu landslide group and dabuzi landslide group are chosen as examples to analyze the characteristics of grll by performing a field survey and undrained triaxial shear tests loess fissures are found to play a key role in controlling the evolution of landslides on the one hand the mechanical properties of loess surrounding fissures rapidly weaken due to water infiltration into loess fissures on the other hand the self weight of the overlying loess increases since water infiltrates into fissures the undrained triaxial shear tests results indicate that loess specimen shows either strain hardening or strain softening behavior depending on its initial moisture content furthermore reduction in the shear strength of loess samples is observed as moisture content increases three factors associated with the characteristics and mechanism of grll group including strata lithology slope shape irrigation and rainfall are discussed finally the formation mechanism and evolution of grll are summarized into three stages namely a creep tensional stage a localized liquefaction stage and a sliding stage this study provides important insights on gradual retrogressive characteristics of loess landslides and facilitates appropriate safeguards to reduce the risk of such landslide hazards

growth increments in gomphotherium tusks and implications for late miocene climate change in north america abstract changes in mammalian faunas in north america during the late miocene are thought to have been caused by the replacement of woodland habitats with grassland or steppe the proposed cause of this habitat shift is the transition from the relatively low seasonality early miocene climate to a more highly seasonal climate regime by the end of the miocene tusks which are highly modified incisor teeth of late miocene gomphotherium mammalia proboscidea were sectioned to document the nature of tusk growth in this genus and to test for patterns of seasonal growth both the dentin and enamel of gomphotherium tusks preserve incremental growth lines dentin has increments on three scales inferred to represent annual first order weekly second order and daily third order periodicities luminance and second order increment thickness profiles were measured on transverse thin sections of tusk dentin viewed at low magnification and the data were examined with bivariate plots and autocorrelation autocorrelograms of luminance data support the consistent identification and measurement of second order increments within and among the tusks sampled profiles of second order increment thickness in three tusks from the barstovian north america land mammal age nalma show no indication of seasonal patterns of growth one tusk from the late clarendonian and one from the early hemphillian nalma have patterns of growth consistent with an increase in seasonality during the late miocene an interpretation supported by autocorrelation of the increment thickness data from these tusks the growth patterns are consistent with the hypothesized changes in north american climate during the late miocene and are suggestive of an increase in aridity and development of a wet season tests of this hypothesis are suggested

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

three dimensional structural model of the rhourde el baguel field algeria the rhourde el baguel field located in the ghadames basin is one of the largest oil fields in algeria it produces oil from fractured cambrian sandstones at subsea depths of 2300 3070 m the structure is reinterpreted as a compressive fold related to two reverse faults which cut and deform a preexisting normal fault the structure formed during three main episodes of deformation 1 triassic to liassic extension resulting in normal faults having significant throw 2 middle jurassic flowage of liassic salt resulting in low amplitude structures in this unit and 3 austrian early cretaceous compression resulting in a basement involved fault propagation fold the revised structural model explains the complex fault patterns and anomalous thickness variations of units observed in a number of deep wells on the west flank of the structure the model has been used to sidetrack some existing deep wells into locations within the field and to optimize the location of new wells in the field

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

oxygen isotope variation in the tusks of extinct proboscideans a measure of season of death and seasonality centimetre scale laminae in tusk and molar dentine of late pleistocene mastodonts and mammoths have been interpreted as annual growth bands produced in part by seasonal variation in growth rate to test this interpretation we measured the oxygen isotope composition 18 o of the co 3 fraction of dentinal hydroxyapatite from samples covering consecutive inferred years of growth in tusks in mammals changes in the 18 o value of dental tissues within individuals predominantly reflect variation in the 18 o value of body fluids which is controlled mainly by the isotopic composition of ingested water in northern hemisphere continental regions winter precipitation has substantially lower 18 o values than does precipitation in other seasons if ingested water tracks focal precipitation then seasonal variations in dentinal isotope composition should result the lowest 18 o values representing winter growth we demonstrate that there are substantial variations in the oxygen isotope composition of proboscidean dentinal apatite and that isotopic identifications of winter i e low 18 o values coincide with those based on growth rate i e slow growth zones finally the potential of oxygen isotope analyses of terrestrial mammals for assessing the seasonality of paleoclimates is considered

late miocene climate and life on land in oregon within a context of neogene global change abstract clarendonian 12 ma fossil soils plants molluscs fish and mammals of eastern oregon allow reconstruction of late miocene paleogeography paleoclimate and paleoecology on land between the global thermal maximum of the middle miocene 16 ma and global cooling and drying of the late miocene 7 ma six different pedotypes of paleosols recognized near unity and juntura allow reinterpretation of local mammalian paleoecology fossil beavers dominated gleyed entisols of riparian forest abundant camels and common hipparionine horses dominated alfisols of wooded grassland and grassy woodland diatomites overlying mammal bearing beds have bullhead catfish ictalurus ameiurus vespertinus as well as fossil leaves dominated by live oak quercus pollardiana fossil plants and soils of unity and juntura are most like those of grassy live oak woodland and savanna on the western slopes of the sierra nevada in northern california today fossil plants and soils indicate mean annual temperature of 12 9 7 7 17 7 c and mean annual precipitation of 879 604 1098 mm miocene paleoclimatic changes in eastern oregon show no relationship to changes in oxygen isotopic composition of marine foraminifera usually taken as an index of global paleoclimatic change mismatch between land and sea paleoclimatic records is most likely an artefact of global ice volume perturbation of oxygen isotopic values instead miocene paleoclimatic change in eastern oregon parallels changes in carbon isotopic composition of marine foraminifera presumably through fluctuations in greenhouse gases

latest miocene to earliest pliocene sedimentation and climate record derived from paleosinkhole fill deposits gray fossil site northeastern tennessee u s a abstract lacustrine sediments deposited within a paleosinkhole at the gray fossil site gfs in northeastern tennessee usa provide a latest miocene and earliest pliocene 4 5 7 ma record of sedimentation and paleoclimate the basal graded facies consists of mm to cm thick normally graded layers of primarily locally derived terrigenous silts and fine sands with low organic content which record storm flow influxes into a 40 m deep paleosinkhole lake the graded facies is overlain by the laminated facies which is characterized by mm thick non graded a b couplets of abundant macerated terrestrial organic matter and fine to coarse quartz sand a alternating with quartz and carbonate silt b isotopic evidence for establishment of either c4 dominated or mixed c3 c4 terrestrial ecosystems is not evident at this site 13 c values of bulk organic matter from the basal graded facies range from 24 to 26 pdb and decrease upsection to 28 to 30 in the organic rich laminated facies isotope values covary with changes in both total organic content toc 0 25 1 wt in graded facies 2 12 wt in laminated facies and in carbon nitrogen ratio c n 1 2 in graded facies 20 50 in laminated facies these upsection changes in sedimentary facies and organic geochemistry within the gfs are attributed to either 1 a climate shift characterized by increased precipitation and concomitant increased vegetation within the paleosinkhole watershed over time or 2 progressive shallowing and eutrophication of the paleosinkhole lake coupled with organic diagenesis within either the watershed or the paleosinkhole sediments in which there was isotopic discrimination associated with organic matter decomposition subaerial exposure of the paleosinkhole lake is recorded by paleosol development

stress strain behaviour of a loosely compacted volcanic derived soil and its significance to rainfall induced fill slope failures the stress strain behaviour of a soil is crucial to the recognition of the mechanism of slope failure triaxial tests composed of isotropically consolidated drained icd and undrained compression icu tests and anisotropically consolidated constant deviatoric stress path cqd tests were carried out with the aim of investigating the stress strain behaviour of loosely compacted volcanic derived soils the fact that the critical states are the same for icu icd and cqd tests may show that the critical state is independent of the above three stress paths the critical state line as defined in critical state soil mechanics is obtained from the e log p and q p plots based on the results of the above tests the initial state of the consolidated specimens at initiation of failure may be classified as dilative or contractive in the light of the locations of the soil state relative to the critical state line for contractional soils the increased pore water pressure generated by rainfall infiltration leads to a contractive failure in a drained manner giving rise to high excess pore water pressure the excess pore water pressure caused by contraction cannot be dissipated instantly resulting in a decrease in the shear resistance of the soil the failure process is rapid the failed soil mass is prone to flow after failure under the action of gravity due to its high moisture content and inflow of surface runoff and rainwater for dilational soils the increased pore water pressure resulting from infiltration leads to dilation which reduces pore water pressure and thus increases the shear resistance of the soil however continued rainfall infiltration may be able to equilibrate the reduction in pore water pressure caused by dilation and therefore the dilation or displacement can continue in hong kong volcanic derived soil is characterized by high permeability both the high permeability of volcanic derived soil and a shallow failure surface make it possible for the reduction in pore pressure to equilibrate relatively quickly therefore the failure is also rapid at least for poorly compacted fill slopes c 1999 elsevier science b v all rights reserved

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

travel distance angle for rapid landslides in constructed and natural soil slopes rapid landslides in constructed and natural soil slopes have the potential to cause loss of life destruction of property and damage to the natural environment because the velocity of the slide

the mechanism of high speed motion and damming of the tangjiashan landslide abstract understanding the mechanisms of landslide failure and resulting damming processes is crucial for constraining the hazard chain associated with landslide damming events on may 12 2008 the wenchuan earthquake caused a large number of secondary hazardous events such as landslides and collapses most of which occurred in high mountain gorges in these areas the sliding distance of landsides is often very short and the landslides are often characterized by high speed short distance and damming using the tangjiashan landslide damming events induced by the wenchuan earthquake as a model this paper reconstructs the three dimensional failure and associated damming caused by the landslide based on a detailed geological investigation of the landslide area and using the dynamic finite element technique the study proposes a four stage model for the failure and damming process of the tangjiashan landslide earthquake induction and progressive destruction of the slide body destruction and high speed sliding of the slide body slide body impact disintegration and river blockage for the formation of a damming body and vibration compression the average speed of the tangjiashan landslide reached a maximum value of 22 m s about 30 s after the earthquake and the landslide reached stability about 60 s later

the mechanics of a saturated silty loess and implications for landslides the results from an intensive experimental investigation on a loess that was retrieved from a typical silty loess zone in the north western chinese loess plateau are presented and interpreted triaxial and oedometer tests were performed on intact and reconstituted samples in a saturated condition the soil behavior was found to be strongly affected by structure the compression paths of the intact samples crossed the intrinsic compression line of the reconstituted soil and reached well defined gross yield points after which the compression paths converged towards the intrinsic compression lines two critical state lines were defined for the intact and reconstituted soils in the volumetric plane as a result of a robust element of natural structure comparisons were made with a structured clayey loess retrieved from the south eastern loess plateau it was found that the effects of structure on the behavior of the two loess soils are similar though they are very different in natural properties this indicates that their natural structures might have experienced similar forming processes perhaps related to their common origin catastrophic flowslides commonly occur in the study area and the patterns of behavior observed in the laboratory tests may create some new insights into mechanisms of landslide initiation and subsequent movement as discussed in the study

a relationship describing the shear strength of unsaturated soils a relationship describing the shear strength profile of a desiccating soil deposit is essential for the purpose of analysis especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation dependent shear strength value the matric suction profile of a desiccating soil deposit is nonlinear up to the air entry value an increase in matric suction is associated with a linear increase in shear strength beyond air entry as the soil starts to desaturate a nonlinear increase in shear strength occurs the soil water characteristic curve is stress dependent as is the shear strength gain as matric suction increases in this paper a three dimensional nonlinear regression analysis showed that a power additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction the proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength

laboratory study on soil behavior in loess slope subjected to infiltration abstract in recent years heifangtai plateau in gansu province china has received significant attention as a loess region in which landslides frequently occur this study aims to examine the soil behavior and failure mechanism s of loess slopes subjected to water infiltration high quality samples were retrieved behind the failure plane of a landslide in heifangtai three sets of stress path tests were conducted to mimic the process of loess slope failures these tests include undrained compression on anisotropically consolidated saturated samples drained shear by decreasing mean effective stress at constant axial load on saturated samples and wetting by decreasing matric suction at constant axial load on unsaturated samples loess behavior was evaluated in terms of shear strength deformation upon shearing critical state state parameter and soil water characteristic curve three major observations were drawn from the test results first the anisotropically consolidated saturated loess exhibits a noticeable strain softening behavior upon undrained compression the peak shear strength is mobilized at less than 1 axial strain the ultimate shear strength is only 20 30 of the peak value second when subjected to shear by decreasing mean effective stress at constant axial load the saturated loess exhibits sudden failure when the confining stress is low at higher stresses the soil exhibits progressive failure third unsaturated loess deforms progressively when subjected to a reduction in matric suction i e wetting at constant axial load the failure mechanisms of the loess slopes are discussed based on the experimental findings

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

a new model for large landslides in sensitive clay using a fracture mechanics approach a new model is proposed for the development of large landslides in sensitive clay and supported by concepts from fracture mechanics a key assumption in this new model is that the complete failure surface develops before the onset of significant movement thus predetermining the final extent of failure the appearance of retrogression is actually the rear ward advancing disruption of a monolithic slide mass over a growing zone of liquefied clay it is seen that the likelihood of propagation of failure and the resulting occurrence of a large landslide depend primarily on the brittleness of the sensitive clay the potential length of shear band propagation is limited by slope geometry and increases for higher riverbanks and for flatter slopes above the riverbank the model explains why large landslides in sensitive clay often terminate just adjacent to a reverse break in slope such as an older landslide crater or a stream gully the model also indicates that large landslides in sensitive clay could be expected to occur suddenly after a large single perturbation such as an earthquake or after a seemingly innocuous small trigger following the accumulation of a large number of annual load cycles as observed fre quently in nature

formation and development of the structure of collapsing loess in china abstract gao g 1988 formation and development of the structure of collapsing loess in china eng geol 25 235 245 it is well known that in china the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility gradually decreasing from the northwest to the southeast these differences are consistent with variations in climatic conditions this indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment based on the microstructure analyses it can be assumed that the formation and development of the structure of collapsing loess in china has undergone five stages the loessization stage the formation stage the development stage the degeneration stage and the clayization stage the five stages of loess regularly exist in different regions of the loess plateau this also shows that under the modern climatic condition the collapsing loess in the northwest of the loess plateau in china is still developing however the feature of collapsing loess is gradually disappearing in the southeast of the loess plateau

occurrence of landsliding on slopes where flowsliding had previously occurred an investigation in a loess platform north west china abstract loess slides in south jingyang platform shaanxi province usually occur on slopes where loess flowslides had previously occurred numerical modeling shows that flowslide occurrence causes conditions that increase shear stress and water content in the subsequent slopes both of these factors move the soil stress states towards its theoretical failure line under these conditions only small increases in water content can cause soil collapse this leads to the backscarps of former flowslides being much more prone to landsliding wetting test results show that the loess can collapse suddenly as the water content gradually increases therefore the wetting process induced by continued irrigation may result in the subsequent slides during constant water content tests of the loess material soil shear strength increases with the development of specimen deformation therefore slide mobilization which may be a relatively slow process is dependent on whether the wetting conditions exist finally a slope evolution model for loess platforms is proposed in this study

influence of topography and volume on mobility of loess slides within different slip surfaces mobility of loess slides has been evaluated using an empirical approach based on a detailed field investigation and remote sensing image interpretation for all the loess slides the affected area increases with increasing loess slides volume from the statistical analysis it is seen that the travel distance has an increasing trend while the coefficient of friction has a decreasing trend with the increase in landslide volume landslide volume determine its travel distance and coefficient of friction that can be shown with a regression equation having simple power law form which indicates that the mobility of loess slides increases with increasing volumes by analogy the greater the energy of the sliding loess mass the stronger is the mobility of loess slide a plot of the travel distance of loess slide versus fall height shows a significant positive power law correlation indicating the increase in mobility of loess slide with fall height the negative power law correlation observed between the travel distance and slope inclination implies that the mobility decreases with the increase of slope inclination three datasets of loess slides characterized by different slip surfaces were distinguished the red clay contact landslides have the strong mobility than landslides in loess and bedrock contact

abrupt landscape change post 6 ma on the central great plains usa the principal control on landscape evolution in the central great plains of the united states over the past 10 m y is a contentious subject new sedimentary data collected from late miocene ogallala group and pliocene broadwater formation of the nebraskan great plains demonstrates a twofold increase in the median grain size from 20 mm to 40 mm exported from the rocky mountains across the miocene pliocene boundary paleoslope reconstructions derived from these data support the tilting of the miocene ogallala group after 6 ma but demonstrate that the transport slope of the lower part of the unconformably overlying pliocene succession is identical to the present day slope these data allow us to constrain the timing of differential uplift in the great plains to between 6 and 3 7 m y the wavelength and short duration of this tilting are best explained by the initiation of localized dynamic topography our results also suggest a threefold to fourfold increase in specific stream power at this time meaning that pliocene rivers draining the central rockies were considerably more competent than their miocene predecessors incision during this period was not continuous a significant episode of aggradation from 3 7 to 2 5 ma is best explained by high rates of sediment supply relating to the warm wet mid pliocene climate optimum the modern pattern of incision on the great plains occurred from 2 5 ma and not from the end of the miocene as is sometimes supposed reflecting the onset of major northern hemisphere glaciation

tooth enamel biomineralization in extant horses implications for isotopic microsampling abstract isotopic analyses of tooth enamel from fossil equids are increasingly being used to reconstruct paleoclimatic and paleoenvironmental conditions however the accuracy of these reconstructions is currently limited partly because the precise timing and spatial patterns of enamel mineralization in equids have not been documented we used radiographic analyses of mandibles collected from modern juvenile and adult domestic horses equus caballus to document the timing of enamel mineralization in equid cheek teeth premolars and molars optical and radiographic analyses of thin sections of mature and developing teeth were used to document the spatial pattern of enamel mineralization in each tooth we found that the enamel layers in equine cheek teeth took longer to mineralize than had been previously assumed largely because the enamel continued to mineralize for approximately 6 to 12 months after each tooth had begun to erupt total enamel mineralization times for individual teeth ranged from 1 5 to 2 8 years examination of thin sections revealed that retzius striae extend outward from the enamel dentin junction at an angle of 5 to 10 and run near parallel to the nonocclusal surface of the tooth daily cross striations average 5 m in width suggesting that during the initial phase of enamel mineralization matrix formation new material is added at a rate of 5 m day radiographic analyses demonstrate that the secondary mineralization front enamel maturation front is orientated approximately parallel to the retzius striae but complete maturation i e full mineralization lags behind matrix formation by several weeks to months

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

influence of lixiviation by irrigation water on residual shear strength of weathered red mudstone in northwest china implication for its role in landslides reactivation abstract irrigation in loess tableland areas of northwest china has induced a large number of landslides around their edges of which loess red mudstone landslide is one of the most frequent types salt sinters commonly observed at the toes of these landslides where the weathered red mudstone wrm outcrops have raised the possibility that removal of soluble salts in the wrm by irrigation water could be crucial in the reduction of its shear strength and thus in the occurrence of these landslides in order to investigate the effects of lixiviation by irrigation water on residual shear strength of the wrm samples of the wrm close to two landslides in lanzhou city one of the largest cities in northwest china were tested after being treated under different conditions these included 1 saturation with the yellow river water the only source of irrigation 2 saturation with groundwater and 3 saturation and leaching with deionized water based on the results of these tests specific mechanisms of residual shear strength reduction of the wrm due to lixiviation by irrigation water were discussed in terms of physico chemical interactions between the wrm and water it was found that lixiviation reduced residual shear strength and residual friction angle r of the wrm by up to 65 and 62 respectively after being leached 6 times this coincided with a dramatic dissolution and leaching of soluble salts from the wrm particle size distribution showed that the more the wrm was leached the more the clay fraction and the lesser coarser fractions this suggested that reduction in residual shear strength of the wrm could be attributed to mainly disaggregation of particles coarser than clay and to a lesser degree to weakening of interparticle forces among individual clays it was further postulated that variation in clay mineralogy may influence performance of particle disaggregation

effect of irrigation induced densification on the post failure behavior of loess flowslides occurring on the heifangtai area gansu china abstract irrigation resulted in serious ground settlement on the heifangtai terrace in china and also repeatedly triggered a lot of loess flowslides on the margin of the terrace to study the possible effect of resultant loess densification accompanying the ground settlement on the sliding behavior of these landslides we took loess samples from the source area of a landslide in the heifangtai terrace and performed a series of undrained ring shear tests to examine the undrained shear behaviors of these samples at differing initial void ratios results showed that all these tested samples exhibited purely contractive behavior throughout the entire undrained shearing process the loose samples suffered collapse failure behavior while those relatively denser samples experienced gradual increase in pore water pressure after the shear failure occurred the peak and steady state shear strengths increased as void ratio decreased however the brittleness index decreased with reduction of void ratio until a certain value after that it increased with further reduction of void ratio therefore we concluded that irrigation induced densification may have affected the occurrence and mobility of landslides occurring on the terrace margin of the heifangtai area

environmental seasonality and incremental growth rates of beaver castor canadensis incisors implications for palaeobiology abstract periradicular bands are incremental structures seen on the external dentin surfaces of rodent incisors they correspond to circadian developmental rhythms in dentin growth and provide a record of the growth rate of the incisor along its longitudinal axis in the present study we investigate the relationship between daily environmental temperatures and longitudinal growth rates of incisors in 40 recent beavers castor canadensis we also look for trends in growth rates that reflect precipitation or photoperiod the goal is to explore the potential of using longitudinal growth data as indicators of seasonality in past environments the sample consists of upper and lower incisors of fall harvested beavers and upper incisors of winter harvested beavers with known dates of death all distances between sequential periradicular bands were measured using a dissecting microscope fitted with an ocular micrometer all increments for each individual were matched to corresponding dates of formation records of daily temperatures precipitation and photoperiod corresponding to the locality and period of growth represented by the teeth were obtained from the national weather service time series for both dental increments and temperature were smoothed using nonparametric regression to partition primary seasonal or long term and secondary daily or short term signals upper and lower incisors differ in their primary signals in that uppers exhibit a marked decline in growth rate during the late summer and early fall leveling off in the late fall this trend roughly parallels seasonal decreases in temperature precipitation and photoperiod although the decline in growth rate begins while the weather is still warm in late summer in contrast lower incisors show only a very weak seasonal trend in growth rate analysis of residuals from the trend lines reveals only a weak association between daily growth rate and both daily temperature changes and precipitation the results suggest that longitudinal growth rates in upper incisors may be used to estimate season of death in fossil rodents

undrained shear behavior of loess saturated with different concentrations of sodium chloride solution abstract a series of ring shear tests was conducted on saturated loess to investigate the effects of nacl concentration in pore water and desalinization on the shear behavior under undrained conditions the loess samples were taken from the ground surface of a frequently active landslide in china were saturated by de aired distilled water with different concentrations of nacl and then were sheared undrained after that the samples were retrieved remolded re set into the shear box and re saturated by passing through de aired distilled water such that the samples were desalinized and then were sheared undrained again through comparing the undrained shear behavior the effects of nacl in the pore water and desalinization on the undrained shear behavior of loess were examined the results showed that the variation of nacl concentration in pore water can strongly affect the shear behavior of saturated loess both the peak shear strength and steady state strength increased with increase of nacl concentration until a certain value after which they decreased with further increase of nacl concentration meanwhile the peak shear strength and steady state strength of the desalinized samples recovered to those of the original sample hence the effects of salinization are reversible these findings may be of practical importance to better understand the repeated occurrence of some irrigation induced loess landslides in china

substrate controlled ichnofacies along a marine sequence boundary the intra valanginian discontinuity in central neuquen basin argentina abstract the intra valanginian discontinuity in the neuquen basin argentina marks a dramatic sea level fall within lower cretaceous strata and can be mapped for tens of kilometers both along depositional strike and dip in the proximal region of the lowstand configuration the subaerial segment of the sequence boundary is demarcated by alluvial conglomerates basal mulichinco formation onto deep marine black shales vaca muerta formation in the distal marine realm the time equivalent marine sequence boundary separates black shales and marls beneath from shallow marine carbonate deposits above this paper documents and discusses substrate controlled trace fossils demarcating the marine sequence boundary across more than 30 km in a proximal distal transect in order to shed light onto processes affecting the sea floor during the generation biogenic modification and preservation of this regionally extensive omission surface the downdip expression of the marine sequence boundary is well exposed across a 20 km long strike oriented outcrop everywhere in this region the discontinuity is demarcated by robust thalassinoides with well defined walls and circular cross sections suggesting that the marly substrate was relatively firm during excavation the burrow system is filled with bioclasts of echinoids and bivalves not present in underlying strata up to pebble size intraclasts that were eroded from the underlying succession and authigenic minerals glauconite phosphates this trace fossil suite illustrates the glossifungites ichnofacies the updip expression of the marine sequence boundary in the study area was recorded in a cored well located about 20 km from the outcrops as in the distal region a first generation of passively filled thalassinoides excavated into a firm marly substrate is attributed to the glossifungites ichnofacies however this suite is cross cut at the top by gastrochaenolites and other unidentified borings bored intraclasts also occur above the omission surface this trace fossil suite represents the trypanites ichnofacies the intra valanginian discontinuity records a complex history after the onset of the dramatic sea level fall extensive erosion and exhumation of previous sediments as well as early cementation combined to produce different types of substrates during the generation of the omission surface firmgrounds and hardgrounds colonization of firm substrates probably started firstly in proximal regions when relative sea level was still falling during early transgression firmgrounds were occupied in distal regions and borers colonized the hardgrounds developed in proximal regions thus the surface demarcates a composite surface involving a sequence boundary plus a transgressive surface draped in turn by a mixing of sediments suggesting siliciclastic starvation the generation and preservation of the features associated with the intra valanginian discontinuity are thought to result from the combination of a ramp type pre existing morphology coupled with a high amplitude sea level fall and a relatively deep marine setting prior to the formation of the omission surface

three dimensional structural modeling and its application for development of the el porton field argentina the el portn field located in the neuqun basin belongs to one of the largest oil and gas trends of argentina fields in the area produce oil from middle cretaceous fluvial and eolian porous sandstones at about 600 m 1968 ft below sea level the field structure is described as a triangle zone located in front of the neuqun fold and thrust belt that was formed during the andean orogeny by a combination of tight detachment folds and fault propagation folding the structure has a basal detachment through the contact between the evaporites of the auquilco formation and the shales of the vaca muerta formation the upper detachment corresponds to the salt layers of the huitrn formation the structure was reactivated by basement fault inversion that produced tightening of the preexisting geometry and backthrusts that increased the structural complexity a three dimensional 3 d structural model has been constructed using 3 d seismic data and well information to plan new horizontal wells in steeply dipping to overturned limbs through 50 60 m 164 196 ft of productive reservoir avoiding pilot and sidetrack wells the results of the modeling have made the company consider as a priority the 3 d structural model building procedure for the development of fields located in fold and thrust belts

laboratory characterization of rainfall induced loess slope failure loess slopes are widely distributed throughout the northwestern region of china and are prone to slope failure in response to heavy rainfall we undertook three groups of flume experiments in the laboratory to study loess slope dynamics under artificial rainfall conditions additionally a laser scanner was used to observe loess landslide deformation characteristics and failure development a numerical analysis of unsaturated seepage in loess slopes because of rainfall infiltration was performed moisture content pore water pressure and slope deformation were monitored to quantify the relationship between rainfall infiltration and loess slope stability movement of the wetting front near the slope surface was triggered by rainfall and related to rainfall intensity and duration which is consistent with the numerical solution rainfall infiltration increased pore water pressure producing gravity driven landslides we observed that landslide development began with local failure in the toe slope that gradually retreated toward the crown forming a multi sliding displacement and eventually resulting in total slope failure

pore pressure generation and fluidization in a loess landslide triggered by the 1920 haiyuan earthquake china a case study abstract during the 1920 haiyuan earthquake numerous catastrophic landslides were triggered in the loess area in northwest china we investigated in detail a large example of these landslides referred to as dangjiacha landslide in this paper this landslide originated from a slope of about 20 and the displaced soil mass traveled about 3200 m damming a valley we performed a field survey and found that standing water existed in the landslide area and the loess had high porosity we infer that it was the liquefaction of the water saturated loess layer rather than the suspension of silt in the pore air in the loess that caused the great mobility of this landslide to test this inference we performed undrained triaxial compression and ring shear tests on loess samples to examine the shear behavior of loess saturated by either air or water the test results showed that the water saturated loess soil was highly susceptible to flow liquefaction failure fast shear tests on naturally air dried loess samples revealed that the generated pore air pressure was small under the undrained condition and no significant reduction in the shear resistance was observed implying that air entrapped in the loess was unlikely to be the main contributor to the high mobility of this large scale landslide