structural characterization of natural loess and remolded loess under triaxial tests this paper characterizes the microstructural evolution of saturated natural loess from a site in jingyang china during triaxial test along two stress paths for comparison the same soil in remolded state is also characterized mercury intrusion porosimetry mip scanning electron microscopy sem and environmental scanning electron microscopy esem were used for the microstructure investigation results show that the microstructure of natural loess is similar to that of remolded loess before the consolidated undrained cu triaxial tests including conventional triaxial compression ctc test and reduced triaxial compression rtc test on the contrary their microstructures are different after the tests deeper examination shows that loading led to a significant change of inter aggregate pores without modifying the intra aggregate pores in addition the volume of inter aggregate pores after the rtc test is greater than that after the ctc test under the same consolidation stress the microstructure features of natural and remolded loess after the tests are further used to analyze the macro mechanical behavior for better understanding the relationship between them the results show that it is the cementation bonds of which breakage is influenced by stress path and confining pressure that play important roles in the strength and deformation behavior

characterization of the mechanisms underlying loess collapsibility for land creation project in shaanxi province china a study from a micro perspective abstract using the major land creation project to bulldoze mountains to build cities implemented in the city of yan an as an example the collapse potential microscopic observations quantitative analyses and qualitative characterization of the microstructures of loess sampled from yan an were investigated to probe the fundamental mechanisms of loess collapsibility at the micro scale the results show that loess in yan an exhibits a severe degree of collapse potential as indicated by its maximum collapse index of 8 10 at a vertical stress value of 600 kpa from a compositional and microstructural perspective a large proportion of loosely arranged skeletal particles are widely separated by variants of clay fabric forming a metastable structure with a high pore area ratio of 32 67 and demonstrating an unstable contact between particles in natural loess these intrinsic microstructural features with a high degree of collapse potential act synergistically to augment collapse when loess is saturated under a certain load the initially high stiffness provided by the delicate clay fabric can be destroyed by its softening dispersion or disruption unsupported skeletal particles are then rearranged significantly into a more stable structure at the same time pores larger than 60 m create favorable spatial conditions for wetting deformation thereby spurring an abrupt reduction in pore size and area particles reorganize into a closely packed structure more interlocking pores of

transition from symmetry to asymmetry during continental rifting an example from the bight basin terre adelie australian and antarctic conjugate margins the rifting history of the magma poor conjugate margins of australia and antarctica is still a controversial issue in this article we present a model for lithosphere scale rifting and deformation history from initial jurassic rifting to late cretaceous breakup for the conjugate bight basin terre adelie section of the margin based on the interpretation of two regional conjugate seismic profiles of the margins and the construction of a lithosphere scale balanced cross section sequentially restored through time the model scenario highlights the symmetric pattern of initial stretching resulting from pure shear at lithospheric scale accompanied by the development of four conjugate detachments and crustal half graben systems this system progressively evolves to completely asymmetric shearing along a single south dipping detachment at the scale of the lithosphere antarctica plays the role of the upper plate and australia the lower plate the detachment accounts for the exhumation of the mantle part of the australian lithosphere and the isolation of a crustal klippe separated from the margin by a serpentinized peridotite ridge the total elongation amount of the australian antarctic conjugate system reaches 473km 178 elongation was partitioned through time 189 and 284km during symmetric and asymmetric stages respectively during the symmetric stage both margins underwent approximately the same degree of crustal stretching 105km 75 and 84km 67 for australia and antarctica respectively again both margins accommodated relatively the same elongation during the asymmetric stage the antarctic upper plate records an elongation amount of 284km 88 as crustal mantle stretching above the inferred low angle south dipping detachment zone whereas the australian lower plate underwent 270km 206 of elongation through mantle exhumation although the restoration process does not allow reconstruction of the precise geometry before deformation we propose that the jurassic early geometric evolution of the margins may have been controlled by the inherited structure or rheological heterogeneities of the continental crust its later evolution is thought to relate to the mechanical evolution of the crustal and mantle material during exhumation with a strong increase in localization of shear in the lower crust and mantle part of the australian margin the geometry of the rifted margins is comparable to other magma poor rifted margin such as the newfoundland iberia margins or the exhumed alpine tethys margin exposed in the central alps 2012 blackwell publishing ltd

nitrate perchlorate and iodate co occur in coastal and inland deserts on earth abstract deserts accumulate soluble salts from atmospheric deposition that impact human health are a source of nutrients for organisms and provide insight into how landscapes evolved on earth and mars we quantified perchlorate nitrate and iodate abundances and co occurrence in terrestrial deserts to identify fundamental controls on soluble salt deposition and post depositional cycling soils and nitrate deposits were examined in death valley usa atacama desert chile kumtag desert china and along an environmental gradient in the transantarctic mountains antarctica concentrations of soluble salts were highest in the transantarctic mountains and atacama desert where stable hyper arid landscapes accumulate atmospheric salts over million year time scales average nitrate concentrations of 61 3 g kg 1 in the transantarctic mountains and 53 0 g kg 1 in the atacama desert were significantly greater than respective averages of 8 60 g kg 1 and 5 14 g kg 1 in kumtag desert and death valley perchlorate and iodate concentrations in the atacama desert averaged 206 mg kg 1 and 344 mg kg 1 respectively which were two to three orders of magnitude greater than in antarctica and other sites our findings suggest that local processes in the atacama desert result either in higher rates of perchlorate and iodate deposition or a greater preservation of these salts relative to nitrate when compared to antarctic landscapes lower salt concentrations in the death valley and kumtag desert deposits likely result from relatively wet present day and paleoclimatic conditions a more active geologic history and a greater likelihood that biocycling disrupted long term salt accumulation associations of perchlorate and nitrate were significantly higher than iodate nitrate and iodate perchlorate correlations in the four deserts perchlorate nitrate relationships ranged from insignificant to highly significant with stronger correlations in the atacama desert and kumtag desert compared to the transantarctic mountains and death valley weaker geochemical associations with iodate were attributed to differences in local deposition rates or post depositional cycling interestingly relationships among perchlorate nitrate and iodate were generally stronger when examined by site within each desert compared to analyzing the soils for each desert as a whole suggesting more localized controls on soluble salt preservation we conclude that soluble salts vary in concentration and type across earth s deserts as a result of present day environment paleoclimate conditions biocycling and geologic age

nature of the continent ocean transition on the non volcanic rifted margin of the central great australian bight a region of 50 120km width defines the continent ocean transition cot in the central great australian bight it is characterized by a thin apron of post break up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the cot and basement ridge modelled gravity and magnetic data and features interpreted from seismic data are consistent with aspects of extensional and break up models proposed for the west iberia margin many of the features and relationships observed beneath the outer margin of the central great australian bight can be explained by extension within a lithosphere scale pure shear environment involving four layers brittle upper crust and upper mantle and ductile lower crust and lower lithospheric mantle the cot is interpreted to be underlain by extended continental lithosphere thus the continentocean boundary is unequivocally defined between oceanic crust and the cot and appears to be associated with sea floor spreading magnetic anomaly 33 indicating that break up and sea floor spreading did not commence until c 83 ma early carnpanian time later than the currently accepted 95ma age the major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting the magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly but one that does not relate to break up and sea floor spreading

new aeromagnetic data from the western enderby basin and consequences for antarctic india break up 1 in order to enhance our understanding of the continental break up between east india and antarctica a japanese german aerogeophysical survey was conducted off eastern dronning maud land and western enderby land antarctica the systematic survey with a line spacing of 20 km provides strong constraints on the timing of the initial break up of india antarctica compared to the conjugate margin south of sri lanka while the continent ocean transition is very well marked by pronounced positive and negative magnetic anomalies no hints on the existence of magnetic spreading anomalies north of this zone has been found in the new data set thus in contrast to most recently published models the data only support kinematic models which include a final break up of sri lanka india from our investigated area some 90 118 ma within the cretaceous normal superchron

response to comment on major australian antarctic plate reorganization at hawaiian emperor bend time accurately locating boundaries between continental and oceanic crust is topical in view of locating offshore boundaries relevant to margin formation models plate kinematics and frontier resource exploration although we disagree with tikku and direen s interpretations the associated controversies reflect an absence of agreed upon geophysical criteria for distinguishing stretched continental from oceanic crust and a lack of samples from nonvolcanic margins

tectonic significance of the lambert graben east antarctica reconstructing the gondwanan rift antarctica s lambert graben australia s north west shelf and the eastern indian peninsula all host thick fault bounded permian triassic successions these terranes were adjacent to each other in gondwana the lambert graben intersects the modern coastline strikes oblique to shelf architecture and has a geophysical signature that can be traced 1000 km inland vitrinite reflectance data from the graben margins record permian triassic infill australia s north west shelf is the relict of an intracontinental carboniferous permian rift that was infilled during the permian triassic then driven to oceanic completion during jurassic cretaceous gondwana breakup this rift was compartmentalized over length scales of 650 km corresponding to accommodation zones margin normal geophysical lineaments and long lived crustal weaknesses in eastern india similar compartmentalization is marked by extensive coal bearing graben systems gondwana reconstructions indicate that the lambert graben corresponds to the orientation and length scale of carboniferous permian rift compartmentalization the lambert graben represents an accommodation zone of a wide intracontinental rift that extended from australia s north west shelf between india and antarctica to southern africa this rift collected gondwana s thick permian triassic sedimentary blanket and rich alluvial coal deposits

evolution of the eastern indian ocean since the late cretaceous constraints from geosat altimetry we propose a new model for the tectonic evolution of the eastern indian ocean from the late cretaceous to the present two types of data are used to improve previously published reconstructions first recent reinterpretations of seafloor magnetic anomalies between australia and antarctica and in the wharton basin provide new constraints on spreading rates and the timing of major reorganizations second vertical deflection profiles i e horizontal gravity anomaly derived from 22 repeat cycles of geosat altimeter data reveal the tectonic fabric associated with fracture zones these new geosat data provide tight constraints on paleospreading directions for example three prominent fracture zones can be traced from south of tasmania to the george v basin antarctica providing an important constraint on the relative motions of australia and antarctica through the late eocene in addition the geosat profiles are used to locate the conjugate continental margins and continent ocean boundaries of australia and antarctica as well as the conjugate rifted margins of kerguelen plateau and broken ridge based on a compilation of magnetic anomaly data from the crozet basin the central indian basin the wharton basin and the australian antarctic basin ten plate tectonic reconstructions are proposed reconstructions at chrons 5 11 ma 6 21 ma 13 36 ma and 18 43 ma confirm that the southeast indian ridge behaved as a single plate boundary since chron 18 the constraints from the geosat data provide an improvement in the fit of the kerguelen plateau and broken ridge at chron 20 46 ma to avoid overlaps between broken ridge and the kerguelen plateau prior to their breakup our model includes relative motions between the northern and southern provinces of the kerguelen plateau finally we examine the implications of our model for the relative motions of india australia and antarctica on the tectonic evolution of the kerguelen plateau and broken ridge and the adjacent labuan basin and diamantina zone as well as the emplacement of the ninetyeast ridge and the kerguelen plateau over a fixed hot spot

on the fit of broken ridge and kerguelen plateau abstract we present revised finite rotation parameters for australia and east antarctica in the early tertiary incorporating new magnetic data off of wilkes land antarctica reconstructions based on these and recently published rotation parameters document a relatively stationary position of broken ridge abutted against central kerguelen plateau between chron 34 83 ma and chron 20 43 ma prior to the commencement of seafloor spreading between the two late cretaceous features these reconstructions are significant as they are the first which are consistent with geological and geophysical constraints in not producing an overlap of broken ridge and kerguelen plateau between chron 34 and chron 24 53 ma and not requiring significant extension or strike slip motion within kerguelen plateau we also find that the finite rotations for chrons 20 to 34 outline the area of rough topography inferred from the satellite derived free air gravity for the diamantina zone and labuan basin a consequence of these rotations is that there is considerable overlap of continental crust in the region of tasmania the south tasman rise and east antarctica in the late cretaceous solutions to this problem may imply either post santonian 79 ma extension or transform motion in the bass strait or late cretaceous or cenozoic extension in wilkes land the reconstructions also agree with prior estimates of roughly 150 km of motion between east and west antarctica since chron 20

non darcian flow in loess at low hydraulic gradient abstract determining the mechanism of water flow in loess involves many problems that are vital to science and engineering water flow through loess has usually been assumed to follow darcy s law but this has not been properly validated the main objective of this study is to validate the applicability of darcy s law for loess for this purpose we conducted constant head permeability experiments and mercury injection porosimetry mip on loess specimens of different dry densities the results indicate that darcy s law is not suitable for describing water seepage in loess at low hydraulic gradient since there is a threshold hydraulic gradient i0 below which no flow is observed and a critical hydraulic gradient icr below which the relationship between the hydraulic gradient i and seepage velocity v is non linear the mip results show that variation in hydraulic conductivity is closely related to the pore size distribution psd in loess specimens i0 is positively correlated with the content of pores with diameters in the range of 0 01 1 m and negatively correlated with the content of pores with diameters larger than 3 m the existence of bound water on loess is the main reason that its permeability deviates from darcy s law the mechanism of water movement in loess can be fully understood by considering the effect of bound water

australia s southern margin a product of oblique extension abstract recently developed detachment models of continental margin formation interpret the southern margin of australia to have formed when the lower plate australian margin was pulled out from beneath the upper plate antarctic margin data now available and summarised in this paper point very strongly to a generally nw se direction of initial continental extension for the southern margin in contrast to the widely held picture of simple n s rifting the evidence for this extension direction comes from the analysis of deep seismic data acquired by the bureau of mineral resources in 1986 in the central great australian bight gab the gravity field of the gab seismic and magnetic basement structures in the eyre sub basin polda trough ceduna depocentre and duntroon basin and from the analysis of the magnetic seafloor spreading anomalies produced during the slow first phase of drifting between australia and antarctica further it is now believed that the formation of the southern margin of australia can be described in terms of three phases of continental extension el to e3 and two phases of drifting d1 and d2 in summary these phases were as follows 1 e1 approximately 300 km of late jurassic or older to early cretaceous nw se oriented extension in the gab with strike slip motion in the nascent otway basin and along the tasmanian margin 2 e2 120 km of early cretaceous nne ssw oriented extension which formed the basins of southeastern australia otway bass gippsland and which probably produced a structural overprinting in the gab basin 3 e3 d1 minor continental extension and the first 500 km of slow drift between australia and antarctica on an azimuth of 165 wrenching on the tasmanian margin 4 d2 2600 km of fast drifting between australia and antarctica on a n s azimuth

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

dominant symmetry of a conjugate southern australian and east antarctic magma poor rifted margin segment synthesis and modeling of published deep seismic and potential field data from the conjugate magma poor rifted margins of the great australian bight southern australia and central wilkes land east antarctica show that there is pronounced symmetry of structures in a 300 km wide zone straddling the axis of final breakup this symmetry is observed consistently for a distance of some hundreds of kilometers along strike from inboard to outboard both margins comprise a narrow zone of attenuation of the crystalline continental crust an approximately 4 km high basement ridge interpreted as unroofed peridotites at the location of maximum thinning of the continental crust and a 60 70 km wide continent ocean transition zone that contains a sedimentary basin that may be underlain by altered mantle and fragments of crystalline continental crust the marked breakup symmetry described here is in contrast to the asymmetry of the iberia newfoundland margin and is consistent with the operation of a symmetrical extensional detachment system deforming the whole crust in the center of the rift as envisaged by some numerical models for the continental rifting process

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

a review of shear and tensile strengths of the malan loess in china abstract loess deposits cover about 640 000 km 2 of china equivalent to about 6 7 of the total area of the country the loess plateau alone covers approximately 317 000 km 2 making it the largest bulk accumulation of loess on the earth land instability hazards in the loess plateau are frequent and varied among which the cracking sliding beng hua in chinese failure is a typical mode cracking sliding failures commonly occur in the malan loess at volumes of the order of 100 m 3 and cause more than 100 deaths per year as the tension in the upper part of the failure plane and shearing sliding along the lower part mobilize cracking sliding failures this failure mode demands an investigation into the tensile and shear strengths this paper presents a review of these properties based on a large collection of literature both tensile and shear strengths of the malan loess decrease with water content and increase with dry density resulting in close multi regression correlations large differences between undisturbed and disturbed tensile strengths of the loess indicate the significance of its structure shear strength of the loess is direction dependent indicating strong anisotropy of the loess structure test method sample size and loading rate all influence the measured tensile strength

loess geohazards research in china advances and challenges for mega engineering projects 2019 loess is a meta stable cemented assemblage of mainly silt and clay sized particles of low plasticity when dry it behaves like a brittle material but when wetted up the fabric rapidly collapses unique geomorphological features include extensive surface erosion soil piping loess karst catastrophic landslides and widespread collapse hydro consolidation the chinese loess plateau is a more or less continuous drape of thick loess covering some 440 000 km2 it is one of china s regions that is most prone to geohazards this paper reviews advances in the research related to loess geohazards drawing particular attention to the need to apply research findings to recent very large mega construction projects in loess terrain such as the mountain excavation and city construction in yan an levelling 78 km2 for urban expansion the lanzhou new district creating 246 km2 of new level ground for construction and large engineered interventions in the landscape for gully control and land reclamation such as those in shaanxi and gansu generating agricultural land covering an area of some 8000 km2 these projects are in response to increasing pressures to facilitate expansion of urban centres their interconnecting infrastructures and their agricultural support systems it is argued that where proper application of scientific knowledge for engineering control e g densification drainage of these new landscapes is absent these projects could generate a substantial and costly geohazard legacy for future generations

correlations between tasmania and the tasman transantarctic orogen evidence for easterly derivation of tasmania relative to mainland australia reconstructions of southern gondwana place tasmania at the triple junction of paleozoic australia antarctica and new zealand tasmania however differs in pre jurassic stratigraphy and structural style from the southeastern australian mainland and northeast victoria land antarctica most notably 1 precambrian basement is exposed in tasmania but not in the lachlan fold belt of the australian mainland precambrian basement in northeast victoria land and the adelaide kanmantoo fold belt of southeast australia differ in stratigraphy and metamorphic history from that in tasmania and 2 western tasmania is dominated by west verging cambrian and devonian thrusts whereas the lachlan fold belt is dominated by east verging devonian thrusts the adelaide kanmantoo fold belt is dominated by westverging ordovician thrusts and northeast victoria land is dominated by east verging ordovician thrusts an explanation for the misfit between tasmania and the other regions is that ancestral tasmania 1 was positioned east of mainland australia with possible precambrian links to north america sweat hypothesis and 2 was progressively emplaced by a combination of west directed cambrian and devonian thrusting cretaceous crustal stretching to form the gippsland and bass basins and finally tertiary wrenching south of the gambier gabo line

a reassessment of paleogeographic reconstructions of eastern gondwana bringing geology back into the equation abstract in recent years several tectonic reconstructions have been presented for australia antarctica break up with each putting the australian plate in a different location with respect to antarctica these differences reflect the different datasets and techniques employed to create a particular reconstruction here we show that some of the more recent reconstructions proposed for australia antarctica break up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins we also show how these incorrect reconstructions influence the fit of the indian plate against antarctica if its movement is tied to the australian plate such errors can have a major influence on the tectonic models of other parts of the world in this case we show how the position of the australia plate can predetermine the extent of greater india which is rightly or wrongly used by many as a constraint in determining the timing of india asia or india island arc collisions during the closure of tethys we also discuss the timing of australia antarctica break up and which linear magnetic features are a product of symmetric sea floor spreading versus those linear magnetic features that result from rifting of a margin the 46 ma to 84 ma rotational poles previously proposed for australia antarctica break up and confined to transitional crust and the continent ocean transition zone more likely formed during earlier stages of rifting rather than during symmetric sea floor spreading of oceanic crust so rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction a new reconstruction of the australia antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

crustal structure based on gravity magnetic modelling constrained from seismic studies under lambert rift antarctica and godavari and mahanadi rifts india and their interrelationship modelling of gravity and magnetic anomalies along selected profiles across the lambert glacier antarctica constrained from the results of deep seismic sounding dss along a profile provide i 6 7 km thick sediments of low density 2 35 g cm3 which represent permian triassic sediments as they are exposed along the margins of this basin ii high density 2 75 g cm3 and high susceptibility rocks with a stable natural magnetization of 0 025 0 035 gauss as the basement iii a high density body 2 80 g cm3 along the western shoulder which may represent mid crustal granulite and charnockite rocks exposed in the prince charles mountains iv a thin crust of 25 km with a high density 3 05 g cm3 and high velocity underplated lower crust these signatures suggest that the lambert rift and the amery ice shelf represent an active continental rift valley with signatures of magmatism the adjoining prydz bay basin along the east coast of antarctica is also characterized by 5 6 km thick permian triassic cretaceous sediments with seaward dipping reflectors of basic volcanic rocks the godavari and the mahanadi gondwana rift valleys of almost same period and length 500 600 km across the east coast of india are also characterized by permian triassic cretaceous sediments of almost same density and thickness the mahanadi basin depicts a thin crust 33 34 km with a high density 3 00 g cm3 underplated lower crust similar to the lambert rift and a low density 2 65 g cm3 layer in the upper crust it indicates substantial rift magmatism in the coastal part of the mahanadi basin and adjoining continental shelf which forms a part of the early cretaceous volcanic province of east india as the east coast of india and antarctica were juxtaposed together at the time of evolution of these rift valleys the above similarities between them might be due to their common heritage the signatures of magmatism in the lambert rift of antarctica and the mahanadi basin of india indicate that the thermal source at the time of their evolution was located under the eastern part of east antarctica which might be responsible for its uplift supplying sediments of same provenance and fossil record in these basins

water retention and volumetric characteristics of intact and re compacted loess a laboratory testing program was conducted to investigate the effects of microstructure on the water retention curve wrc and wetting drying induced volume change in loess the axis translation an

fossil seaward dipping reflector sequences preserved in southeastern australia a 600 ma volcanic passive margin in eastern gondwanaland evidence for a c 600 ma rifted passive margin in eastern australia exists in the form of multiple belts of mafic volcanic rocks preserved along the western margin of the tasman fold belt system and giving rise to elongate magnetic anomalies outcrop drillhole and geophysical evidence points to piles of lavas volcaniclastic and intrusive rocks up to 6 km thick extending for strike lengths of hundreds of kilometres in individual segments the distinctive unifying characteristics of these piles are apparent common formation ages 600 580 ma presence of early more landward transitional alkaline basalts and more seaward abundant rift tholeiites with high temperature picrites and olivine rich basalts at most localities despite later structural reorganization these belts have close geochemical geometric and lithological affinities with mesozoic seaward dipping reflector sequences along the north atlantic and northwestern australian volcanic passive margins and strongly imply the formation of a volcanic passive margin in eastern gondwanaland at the close of the neoproterozoic recognition of this event has implications for the position of an implied earlier rifted margin related to the break up of rodinia around 780 ma a rifting event at 600 ma in eastern gondwanaland helps explain both the lack of evidence for volcanism from rodinia break up and a widespread 600 ma population of inherited zircons within rocks of the lachlan orogen which developed outboard of the passive margin in earliest palaeozoic time

on the relationship between water flux and hydraulic gradient for unsaturated and saturated clay summary experimental results indicate that the traditional form of darcy s law is not adequate for describing water flow processes in clay media because the observed relationship between water flux and hydraulic gradient can be highly non linear to capture this non darcian flow behavior we propose a new relationship between water flux and hydraulic gradient by generalizing the currently existing relationships the new relationship is shown to be consistent with experimental observations for both saturated and unsaturated conditions in this paper we also develop an empirical relationship between permeability and threshold hydraulic gradient an important measure of non darcian behavior the latter relationship is practically useful because it can reduce the number of parameters whose values need to be determined from experiment data in order to model non darcian behavior how to incorporate the impacts of temperature and electrolyte concentrations into the proposed relationships needs further research

interactions between continental breakup dynamics and large scale delta system evolution insights from the cretaceous ceduna delta system bight basin southern australian margin 1 the interpretation of two regional seismic reflection profiles and the construction of a balanced cross section through the southern australian margin bight basin are designed to analyze the influence of the australia antarctica continental breakup process on the kinematic evolution of the cretaceous ceduna delta system the data show that the structural architecture of this delta system consists of two stacked delta systems the lower white pointer delta system late albian santonian is an unstable tectonic wedge regionally detached seaward above late albian ductile shales sequential restoration suggests that the overall gravitational sliding behavior of the white pointer delta wedge 45 km of seaward extension i e 27 is partially balanced by the tectonic denudation of the subcontinental mantle we are able to estimate the horizontal stretching rate of the mantle exhumation between 2 and 5 km ma 1 the associated uplift of the distal part of the margin and associated flexural subsidence in the proximal part of the basin are partially responsible for the decrease of the gravitational sliding of the white pointer delta system lithospheric failure occurs at 84 ma through the rapid exhumation of the mantle the upper hammerhead delta system late santonian maastrichtian forms a stable tectonic wedge developed during initial slow seafloor spreading and sag basin evolution of the australian side margin lateral variation of basin slope related to the geometry of the underlying white pointer delta wedge is associated with distal raft tectonic structures sustained by high sedimentation rates finally we propose a conceptual low angle detachment fault model for the evolution of the australian antarctic conjugate margins in which the antarctic margin corresponds to the upper plate and the australian margin to the lower plate

development and evolution of loess vertical joints on the chinese loess plateau at different spatiotemporal scales abstract the vertical joints of aeolian loess are ubiquitous on the chinese loess plateau clp the distribution variability of which mainly depends on the differences in structural characteristics of loess water drivers e g rainfall or irrigation loess strata e g sedimentary depth and microtopography this study conducted extensive field investigation and experiments to enhance the understanding of morphologies cross scale transformation mechanism and structural bases of loess vertical joints lvjs moreover the development and evolution processes of lvjs were refined by considering loess sedimentary dynamics results show that 1 lvjs are the product of diagenesis in loess strata during loess historical sedimentary process 2 the pore concentration zones and vertical tubular channels in loess are the structural bases of forming original vertical joints ovjs at the micro mesoscale which is supported by the results from the three dimensional computing tomography ct scanning and scanning electron microscopy sem tests and 3 the morphologies of lvjs vary with the microtopography at different spatiotemporal scales and is characterized by the cross scale transformation mechanism i e that they could transform up i e an expansion behavior or down i e a degradation behavior at the micro meso and sub macro scales under the influences of dry wet cycles loess pile thickening and exogenic forces besides we also propose the development and evolution mechanism of ovjs in loess from the viewpoint of unsaturated loess which would help understand the loess anisotropic genesis structural evolution preferential flow and the occurrence of geohazards such as landslides and soil erosion

brittle faulting in the prince charles mountains east antarctica cretaceous transtensional tectonics related to the break up of gondwana abstract the lambert glacier amery ice shelf occupies a narrow nne ssw orientated fault bound depression referred to as the lambert graben deep faults associated with this structure are recognised geophysically and are interpreted to extend at least 700 km inland from the antarctic coast kinematic and palaeostress data from quartz and calcite bearing faults inferred to represent the surface expression of these deeper structures suggest that a single faulting event occurred in response to nw se directed extension oblique to the axis of the graben the bulk of the movement along these faults was dextral strike slip accommodating components of both normal and reverse offset in the northern prince charles mountains these faults disrupt the permo triassic amery group and juxtapose it against proterozoic basement equivalent strike slip faults in the southern prince charles mountains produce dextrally offset tectonic boundaries and metamorphic isogrades across the lambert glacier the similarity in orientation between the palaeostress field calculated for these faults and the cretaceous divergence vector between india and antarctica strongly supports the inference that faulting was of cretaceous age and related to the break up of gondwana

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

full fit palinspastic reconstruction of the conjugate australian antarctic margins 1 despite decades of study the prerift configuration and early rifting history between australia and antarctica is not well established the plate boundary system during the cretaceous includes the evolving kerguelen broken ridge large igneous province in the west as well as the conjugate passive and transform margin segments of the australian and antarctic continents previous rigid plate reconstruction models have highlighted the difficulty in satisfying all the available observations within a single coherent reconstruction history we investigate a range of scenarios for the early rifting history of these plates by developing a deforming plate model for this conjugate margin pair potential field data are used to define the boundaries of stretched continental crust on a regional scale integrating crustal thickness along tectonic flow lines provides an estimate of the prerift location of the continental plate boundary we then use the prerift plate boundary positions along with additional constraints from geological structures and large igneous provinces within the same australian and antarctic plate system to compute full fit poles of rotation for australia relative to antarctica our preferred model implies that the leeuwin and vincennes fracture zones are conjugate features within gondwana but that the direction of initial opening between australia and antarctica does not follow the orientation of these features rather the geometry of these features is likely related to the earlier rifting of india away from australia antarctica previous full fit reconstructions based on qualitative estimates of continental margin overlaps generally yield a tighter fit than our preferred reconstruction based on palinspastic margin restoration

spatial variation of saturated hydraulic conductivity of a loess slope in the south jingyang plateau china abstract water infiltration in loess soils is an important trigger causing landslides in which the hydraulic conductivity of the loess plays an important role by analyzing a soil trench and soil samples from the south jingyang plateau northwest china a loess slope was investigated a horizontal adit in a lishi loess layer was also analyzed using variable head permeability tests the saturated horizontal hydraulic conductivity k h and saturated vertical hydraulic conductivity k v of the loess samples were measured results showed that the majority of the k h values are larger than the k v values indicating that the loess exhibits permeability anisotropy lilliefors test was used to determine the normality of the k h and k v results test results indicate that k h and k v measurements of the loess samples collected in the trench and adit all show log normal distribution while a number of the k h and k v values also reflect a normal distribution geo statistical analysis shows that the spherical model and the gaussian model provide the best fit variograms of k h and k v values along the trench analysis along the adit indicated the opposite results the variogram range values suggest that the spatial correlation of loess k v is greater in the vertical direction in a horizontal plane while the spatial correlation of k h in the adit is greater than that in the vertical direction loess structure rather than randomness decides the spatial variation of k h and k v measurements except for k h variation along the adit which depends on both structural factor and randomness k h and k v values of loess tend to decrease with depth results which can be described by an exponential decay model

comment on major australian antarctic plate reorganization at hawaiian emperor bend time whittaker et al reports 5 october 2007 p 83 presented reconstructions for australia and antarctica showing a change in relative plate motion 53 million years ago coincident with an inferred major global plate reorganization this comment addresses problematic areas in their assumptions and the geological consequences of their reconstructions

distribution and characteristics of landslide in loess plateau a case study in shaanxi province abstract every year about one third of the geohazards in china occur in the loess plateau causing human loss damaging gas and oil pipelines destroying highways railways and degrading farmland field investigation and monitoring in situ tests and laboratory experiments were performed to improve our understanding of the factors effecting the distribution characteristics and causes of loess landslides first we find that 79 of the landslides are shallower than10m 85 have a volume of less than 100 000 m3 second landslides on the loess plateau occur primarily on concave slope profiles that have slope angles of 20 35 and that face south east third the equivalent coefficient of friction of loess landslides is very low resulting in long run out with a low angle sliding surface loess landslides generally transform into mud flows resulting in an increase in volume in transit and forming a geohazard chain antecedent rainfall plays an important role in triggering loess landslides finally clusters of landslides in the loess plateau occur because the loess easily disintegrates under high pressure due to its loose and highly porous structure there is a sharp decrease in cohesive strength with increase in deformation and water content and thus landslides tend to undergo static liquefaction during sliding

optimization of compaction zoning in loess embankments extensive centrifuge model tests were carried out to investigate optimum compaction density zones within loess embankments 30 and 63 8 m high in these tests water infiltration into the slopes and upstream storm water ponds were modelled to simulate the most unfavourable working conditions displacement contours in the cross sections were measured and crest settlements were monitored during the tests finally the optimum compaction zoning was analysed based on the comprehensive evaluation of the total crest settlement the postconstruction settlement and the slope stability of the embankments it was indicated that a properly designed high loess embankment could perform satisfactorily with the lower part compacted looser than the conventional code requirements in terms of total crest settlement and embankment cracking the degree of compaction k of loess fills should not be less than 0 85 for 30 m high embankments and not less than 0 90 for 63 8 m high embankments in terms of the postconstruction settlement 0 2 0 3 m and construction feasibility it is expedient to compact the lower one third to k 0 85 and the top two thirds to k 0 90 for 63 8 m high embankments for 30 m high embankments the bottom zone with k 0 85 can make up two thirds of the height