chirp 2 7 khz echo characters of the south korea plateau east sea styles of mass movement and sediment gravity flow abstract the south korea plateau is a complex of ridges seamount chains troughs and a basin detailed analysis of 12 019 line km chirp 2 7 khz subbottom profiles from the south korea plateau and the eastern continental slope of korea reveals a distinctive zonal distribution of echo types depending systematically on seafloor morphology pelagites hemipelagites type i 2 and basement highs type iii 1 prevail on the ridge summits seamount chains and the upper to middle part of the eastern continental slope of korea and are commonly bounded downslope by creeps type iii 3 and slides slumps type iv 1 that occur extensively over the entire slope areas of the ridges seamount chains and eastern continental slope the mass movement deposits change downslope to debrites and turbidites types ii iii 2 iv 2 and iv 3 in the troughs and onnuri basin suggesting successive downslope evolution from slide and slump to debris flow and turbidity current the voluminous creeps slides and slumps over the entire slope areas of the plateau and eastern continental slope deeper than 300 m in water depth were most likely generated by frequent seismic shakings

mass transport processes on amazon cone western equatorial atlantic three large mass transport deposits occur on the upper to middle amazon cone these slump debris flow complexes have been mapped from 3 5 khz echograms and cover approximately 75 000 sq km or about 10 of the cone the debris flows traveled down slopes with gradients as low as 1 90 to 1 165 0 3 to 0 6 for distances up to 300 km these deposits average 10 to 50 m in thickness and the total amount of sediments displaced may exceed 3 800 cu km the upslope parts of these complexes generally consist of hummocky slump or slide deposits which are commonly bounded by scarps of varying relief downslope from this zone of removal the deposits consist of thin the occurrence of such widespread mass movements on the amazon cone indicates that mass transport is probably an important sedimentation process on deep sea fans however most studies and models of modern deep sea fans have minimized or ignored the potential importance of mass transport processes in fan development we suggest that in the future both ancient and modern deep sea fans be more closely examined for mass transport deposits so that the importance of this process to overall fan development can be more accurately assessed

one dimensional compression and consolidation of shales abstract this paper presents a comprehensive methodology for analysing the compression and consolidation behaviour of shales an apparatus was designed to perform oedometric high pressure tests by applying a maximum vertical total stress of 100 mpa and simultaneously controlling the pore water pressure of the specimen an analytical method was formulated to analyse the shale consolidation behaviour which allows information to be gathered on the coefficient of consolidation stiffness poroelastic properties secondary compression and permeability of the tested material as a function of the applied stress conditions results obtained on opalinus clay shale using the developed methodology are presented and discussed

physical properties of shocked and thermally altered nontronite implications for the martian surface both shock recovery and thermal annealing experiments have been carried out on riverside nontronite an iron rich smectite clay that closely matches the composition but neither the color nor magnetic properties of the martian fines nontronite was recovered from peak shock pressures between 7 and 32 gpa with calculated peak mean bulk temperatures ranging from 125 to 1100 c other nontronite samples were heated in air for one hour at temperatures ranging from 400 to 1000 c at 100 c increments both shocked and heat treated samples were analyzed by magnetic measurements x ray diffraction and mossbauer spectroscopy nontronite powders shock loaded to peak calculated temperatures of 650 c to 750 c show a dramatic increase in ferromagnetic saturation magnetization ms a similar increase in magnetization in the same temperature range is observed in isothermally annealed powders at atmospheric pressure the x ray diffraction and mossbauer studies show however that for samples that experienced temperatures of 600 c or more the shocked material has little structural similarity to the isothermally annealed nontronite this suggests that the ferromagnetic properties may be due to a minor phase there is evidence from mossbauer spectra for metallic iron in the shocked samples and for superparamagnetic fe2o3 in the annealed samples in addition to magnetic and structural changes the shock and heating experiments altered the color of the nontronite from olive yellow toward reddish brown yielding material that matches the observed properties of the martian fines much more closely than the starting material does if nontronite is the major component of the martian fines as some workers suggest some mechanism for altering its properties is necessary the most likely being repeated impacts onto the surface of mars

experimental analysis of the water retention behaviour of shales shales are among the most commonly considered geomaterials in current energy related geomechanical investigations as they are involved in engineering applications such as the extraction of natural gas co2 sequestration and nuclear waste storage a deep understanding of their behaviour with regard to variations in the degree of saturation is of significance for such applications with the aim to establish a sound protocol for shale retention behaviour analysis this paper presents an experimental methodology that takes into account the specificities of shales such as small pore size dimensions and the large variations in water potential to be applied to induce significant changes in the degree of saturation the technique involves the direct control of the shale water content and the subsequent measurement of the suction at equilibrium by a psychrometer a fluid displacement technique with a non polar liquid is also used to assess the volume changes of the shale and to compute the degree of saturation selected test results are presented for various shale samples that have been cored at different depths the results indicate that important features of the retention behaviour of geomaterials are fundamental aspects to be considered when analysing the retention behaviour of shales such as the existence of main wetting and drying paths the hysteresis domain and the dependency of the air entry value on the void ratio 2014 elsevier ltd all rights reserved

water saturation relations and their diffusion limited equilibration in gas shale implications for gas flow in unconventional reservoirs author s tokunaga tk shen w wan j kim y cihan a zhang y finsterle s abstract 2017 american geophysical union all rights reserved large volumes of water are used for hydraulic fracturing of low permeability shale reservoirs to stimulate gas production with most of the water remaining unrecovered and distributed in a poorly understood manner within stimulated regions because water partitioning into shale pores controls gas release we measured the water saturation dependence on relative humidity rh and capillary pressure pc for imbibition adsorption as well as drainage desorption on samples of woodford shale experiments and modeling of water vapor adsorption into shale laminae at rh 0 31 demonstrated that long times are needed to characterize equilibrium in larger 5 mm thick pieces of shales and yielded effective diffusion coefficients from 9 10 9 to 3 10 8 m2 s 1 similar in magnitude to the literature values for typical low porosity and low permeability rocks most of the experiments conducted at 50 c on crushed shale grains in order to facilitate rapid equilibration showed significant saturation hysteresis and that very large pc 1 mpa are required to drain the shales these results quantify the severity of the water blocking problem and suggest that gas production from unconventional reservoirs is largely associated with stimulated regions that have had little or no exposure to injected water gravity drainage of water from fractures residing above horizontal wells reconciles gas production in the presence of largely unrecovered injected water and is discussed in the broader context of unsaturated flow in fractures

experimental investigation into the effects of meteoritic impacts on the spectral properties of phyllosilicates on mars 1 phyllosilicates have been identified in some of the most highly cratered noachian terrains on mars to study the effects of such impacts on the properties of phyllosilicates we experimentally shocked six phyllosilicate minerals relevant to the martian surface montmorillonite nontronite kaolinite prehnite chlorite and serpentine the shock treated samples were analyzed with x ray diffraction xrd near and mid infrared nir and mir spectroscopy raman spectroscopy cathodoluminescence cl and the shock pressures and temperatures in some were modeled using autodyn modeling software xrd data show that the structure of each mineral except prehnite underwent partial structural deformation or amorphization we also found that while the nir spectra of shocked samples were very similar to that of the original sample the mir spectra changed significantly this may explain some of the discrepancies between crism omega data nir and tes themis mir observations of phyllosilicates on mars quartz was identified as a secondary phase in the xrd of shocked chlorite

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

fundamentals of desiccation cracking of fine grained soils experimental characterisation and mechanisms identification this paper presents the results of a comprehensive experimental study of the desiccation of fine grained soils air drying of initially saturated soil slabs in controlled conditions is investigated by performing three kinds of tests free desiccation tests constrained desiccation tests prevented shrinkage and crack pattern tests strains suction water con tent and crack geometry are investigated results reveal that unconstrained drying exhibits two stages a domain with large mostly irrecoverable deformations and degree of saturation close to 100 followed by a domain with lower defor mations at a decreasing degree of saturation homogeneous soil macroscopic cracking is possible only in the presence of boundary constraints and or moisture gradients inducing the build up of tensile stresses results also show that for the initially saturated remoulded soils tested here in the whole sample and near a crack initiation point the degree of satura tion remains very close to 100 until cracking while cracking onset the air entry suction and the shrinkage limit are close to each other cavitation nuclei and the formation of an irregular drying front at cracking initiation are commented upon in light of this observation finally results suggest that the crack pattern geometry is the result of energy redistribu tion a quantification of the process is proposed resume cet article presente les resultats d une etude experimentale complete de la dessiccation de sols fins le sechage de sols initialement satures est etudiedans des conditions controlees et atemperature ambiante trois types d essais ont eteeffectues essais de dessiccation libre essais de dessiccation avec contraintes le retrait est empechedans une direc tion et essais de plans de fissures les deformations la succion la teneur en eau et la geometrie des fissures ont eteinves tiguees les resultats demontrent que le sechage sans contrainte presente deux etapes un domaine durant lequel les deformations sont grandes et irreversibles et le degrede saturation reste pres de 100 suivi d un domaine durant lequel les deformations sont plus faibles et le degrede saturation diminue pour un sol homogene des fissures macroscopiques apparaissent seulement lorsqu il y a des contraintes aux frontieres et ou des gradients d humidite ce qui induit des contraintes en tension les resultats montrent aussi que pour les silts et argiles remanies initialement satures utilises dans cette etude le degrede saturation reste tres pres de 100 jusqu ala fissuration de plus la fissuration l entree d air et la limite de retrait sont proches les unes des autres suite a ces observations l existence de germes de cavitation et la forma tion d un front de sechage irregulier lors de l initiation des fissures sont discutees finalement les resultats suggerent que la geometrie des fissures resulte d une redistribution de l energie a travers le corps une quantification du processus est proposee mots cles dessiccation initiation de fissure succion succion a l entree d air geometrie des fissures

shale claystone response to air and liquid exposure and implications for handling sampling and testing abstract this paper documents the results of scientific studies to quantify the impact on shales and claystones of exposure to air and to different liquids these studies show that the water content of such rocks is controlled by the relative humidity of the surrounding air most shales claystones will lose water shrink and desaturate if exposed to air unless the relative humidity is sufficiently high usually 80 96 causing desiccation damage while exposure to brine will prevent desiccation it results in water uptake and swelling and a different type of alteration and damage confining stress will limit this swelling well preserved shales are generally fully saturated under zero stress conditions but they have a negative pore water pressure hydrocarbon will not normally enter a fully saturated shale based on these findings it is recommended that shale water content should not be altered unless it is done so under controlled conditions to accomplish this one must minimize exposure to air and avoid contact with water or brine unless the shale is under stress specific guidelines are provided for core handling and preservation sampling and testing gas shales are both similar to and different than claystone shales and this alters slightly the findings and guidelines

semidiurnal internal tide incoherence in the equatorial pacific the jets in the equatorial pacific ocean of a realistically forced global circulation model with a horizontal resolution of 1 12 5 cause a strong loss of phase coherence in semidiurnal internal tides that propagate equatorward from the french polynesian islands and hawaii this loss of coherence is quantified with a baroclinic energy analysis in which the semidiurnal band terms are separated into coherent incoherent and cross terms for time scales longer than a year the coherent energy flux approaches zero values at the equator while the total flux is 500 w m the time variability of the incoherent energy flux is compared with the internal tide travel time variability which is based on along beam integrated phase speeds computed with the taylor goldstein equation the variability of monthly mean taylor goldstein phase speeds agrees well with the phase speed variability inferred from steric sea surface height phases extracted with a plane wave fit technique on monthly time scales the loss of phase coherence in the equatorward beams from the french polynesian islands is attributed to the time variability in the vertically sheared background flow associated with the jets and tropical instability waves on an annual time scale the effect of stratification variability is of equal or greater importance than the shear variability is to the loss of coherence in the model simulations low frequency equatorial jets do not noticeably enhance the dissipation of the internal tide but merely decohere and scatter it

structural and spectroscopic changes to natural nontronite induced by experimental impacts between 10 and 40 gpa many phyllosilicate deposits remotely detected on mars occur within bombarded terrains shock metamorphism from meteor impacts alters mineral structures producing changed mineral spectra thus impacts have likely affected the spectra of remotely sensed martian phyllosilicates we present spectral analysis results for a natural nontronite sample before and after laboratory generated impacts over five peak pressures between 10 and 40 gpa we conducted a suite of spectroscopic analyses to characterize the sample s impact induced structural and spectral changes nontronite becomes increasingly disordered with increasing peak impact pressure every infrared spectroscopic technique used showed evidence of structural changes at shock pressures above 25 gpa reflectance spectroscopy in the visible near infrared region is primarily sensitive to the vibrations of metal oh and interlayer h2o groups in the nontronite octahedral sheet midinfrared mir spectroscopic techniques are sensitive to the vibrations of silicon and oxygen in the nontronite tetrahedral sheet because the tetrahedral and octahedral sheets of nontronite deform differently impact driven structural deformation may contribute to differences in phyllosilicate detection between remote sensing techniques sensitive to different parts of the nontronite structure observed spectroscopic changes also indicated that the sample s octahedral and tetrahedral sheets were structurally deformed but not completely dehydroxylated this finding is an important distinction from previous studies of thermally altered phyllosilicates in which dehydroxylation follows dehydration in a stepwise progression preceding structural deformation impact alteration may thus complicate mineral specific identifications based on the location of oh group bands in remotely detected spectra this is a key implication for martian remote sensing arising from our results

the influence of soil structure and stress history on the soil water characteristics of a compacted till the soil water characteristic defines the relationship between the soil suction and gravimetric water content w or the volumetric water content or the degree of saturation s theoretical and

late quaternary depositional systems and sea level change santa monica and san pedro basins california continental borderland a suite of seismic reflection data that provides different degrees of resolution and penetration was used to map the depositional systems that have developed in santa monica and san pedro basins during the late quaternary submarine fan growth particularly at the mouths of hueneme and redondo canyons has been the dominant mode of basin filling mass movement processes ranging from creep to large scale catastrophic slumping have been important locally in general large scale fan growth fits normark s model in which the suprafan is the primary locus of coarse sediment deposition smaller scale morphologic and depositional patterns on the hueneme and redondo fans e g distributary channels and coarse sediment concentrations basinward of the inner suprafan suggest that a significant amount of coarse sediment presently bypasses the suprafans however long distance coarse sediment transport was particularly pronounced during late wisconsinan lowstand of sea level and resulted in progradation of lower mid fan and lower fan deposits as sea level rose rapidly between 18 000 y b p and 10 000 y b p shelves trapped much of the sediment supply consequently rates of basin sedimentation decreased markedly and the area of fan developmen was restricted as the rate of shelf sedimentation decreased concomitantly with a decrease in the rate of sea level rise 10 000 y b p sediment transport to the basins was renewed and modern depositional patterns were established fan development also has been influenced by large scale mass movement extensive mid fan overbank flow and the consequent development of sediment waves deflection of turbidity currents by bathymetric obstacles and local tectonism correlations between sand layer characteristics and high resolution echo types for fan and basin plain deposits show trends similar to some of those observed in deep sea depositional environments however because santa monica and san pedro basins are small enclosed tectonically active basins that receive sediment from relatively large drainage areas proximal to distal changes in sand layer thickness abundance and frequency are less pronounced than those observed in deep sea environments

shock metamorphism of clay minerals on mars by meteor impact a large fraction of clay minerals detected on mars by infrared remote sensing represent materials exhumed from the subsurface by meteor impact begging the question of whether the infrared features used to detect the clays are affected by shock associated with the impacts we used x ray diffraction and infrared and mossbauer spectroscopy to evaluate the mineralogy of five clay minerals after experimentally shocking them to six shock pressures from 10 40 gpa the shocked clays exhibit three main relevant shock effects 1 an overall decrease in infrared spectral contrast in the impact fragmented materials 2 oxidation of fe in ferrous clays and 3 loss of some spectral structure in relatively well ordered clays such as kaolinite other than the widespread oxidation of ferrous clays shock metamorphism likely has little effect on the accurate interpretation of clay mineralogy on mars from remote sensing data however we are able to identify rare cases of extreme shock in some martian clay deposits

the early neogene continental rise off the eastern united states abstract single and multichannel seismic data were used to investigate depositional components comprising the late oligocene middle miocene constructional phase of the united states atlantic continental rise in the georges bank blake plateau region the seismic sequence studied was bounded by the eocene oligocene age horizon a u unconformity at the base and a newly defined late middle miocene age horizon g at the top late oligocene middle miocene accretion onlapping the paleocontinental slope and downlapping onto horizon a u basinward was derived primarily from erosion of the uplifted central appalachian mountains this accretion up to 3 2 km thick was characterized by seven depocenters the lower paleocontinental slope upper rise depocenters situated off southern new england and the delmarva peninsula were interpreted as deep sea fan complexes or a broadly overlapping series of sedimentary blankets a whereas the closely associated oceanographer and wilmington depocenters were inferred to be levee complexes immediately north of the developing blake bahama outer ridge two n ne oriented sediment ridges that were probably built by gulf stream flow during an early miocene sea level lowstand were observed on the lower continental rise the proto hatteras and mytilus outer ridges from 0 4 to 0 8 km thick were probably formed from the wilmington and oceanographer levee complexes in early middle miocene time through the interaction of the growing levee complex with the sw moving abyssal current late middle miocene 12 11 5 ma bottom current erosion created the horizon g unconformity and brought to an end this initial stage of continental rise construction nevertheless the basic morphological framework that controlled late neogene and quaternary continental rise evolution was now in place

nature and classification of waterlain glaciogenic sediments exemplified by pleistocene late paleozoic and late precambrian deposits this study of waterlain glaciogenic sediments is designed to present both a review and new information on glaciogenic subaquatic deposits of differing age in a number of localities in north and south america and south africa the late paleozoic glaciogenic deposits of the parana basin in brazil and the karoo basin of south africa are singled out for special attention as they show a reasonably complete lateral sequence of terrestrial to off shore glaciogenic sedimentation although the environment of subaquatic glaciogenic sedimentation varies from one area to the next certain common elements are found which can be used to develop a generalized model for both glaciomarine and glaciolacustrine sedimentation for descriptive purposes the model is divided into two broad categories a shelf facies and a basinal facies the shelf facies is marked by massive diamicton ite which may be 200 m or more in thickness and which is frequently overlain by a complex of clastic sediments consisting primarily of gravity and fluid flows the basinal facies is marked by products of subaquatic slumps and more distal turbidites and glaciomarine sediments new terminology is introduced the massive diamicton ite which is diagnostic of the shelf facies probably represents deposition from the base of active ice in a subaquatic environment and is termed undermelt diamicton ite the gravity and fluid flows which are usually found overlying undermelt diamicton ite and in the basinal facies are subdivided into six categories glaciogenic subaquatic outwash glaciogenic suspension flow glaciogenic chaotic debris flow glaciogenic subaquatic debris flow glaciogenic slurry flow and glaciogenic turbidity flow the relative abundance of undermelt diamicton ite and the various types of gravity and fluid flows can be used to define inner shelf outer shelf inner basin and outer basin facies of glaciomarine sedimentation

astronomical pacing of late cretaceous third and second order sea level sequences in the foz do amazonas basin abstract because of their relatively reduced tectonic influence post rift sedimentary successions have a propensity to preserve climatically driven cyclicity over long durations here we present an integrated cyclostratigraphic and sequence stratigraphic study of the post rift limoeiro sedimentary formation fm of the foz do amazonas basin offshore brazil which spans the entire late cretaceous epoch almost 35 myr long the principal goal of the present study is to decipher very long multi myr sedimentary cyclicities and their potential origin s in order to delineate the main controlling factors of post rift sediment sequences and packages we used gamma ray gr well log data for cyclostratigarphy and seismic data for sequence stratigraphy time series analysis of gr data shows a rich series of milankovitch frequency bands in particular long period cyclicities 405 kyr 2 4 myr 4 7 myr and 9 5 myr are detected with high fidelity seismic and sequence stratigraphic interpretation shows a striking sea level sl depositional sequence order matching the 4 7 myr orbital cyclicity inferred from cyclostratigraphy longer sl sequences interpreted in previous studies from the limoeiro fm closely match the 9 5 myr gr related orbital cycles thus we infer that the post rift limoeiro fm was deposited continuously under astronomical forcing over the late cretaceous epoch resulting in an extraordinary record of direct base and sea level responses to milankovitch climatic forcing including longer multi myr periodicities the 4 7 myr orbital component is recorded for the first time in sl sedimentary proxies thus allowing here to update sl hierarchical orders we suggest that third order and second order and suborders sl sequences were most likely paced by long period astronomical cycles 2 4 myr eccentricity and 4 7 and 9 5 myr orbital cycles respectively

microbially mediated iron redox cycling of subsurface sediments from hanford site washington state usa abstract iron bearing clay minerals are predominant in soils and sediments and they undergo oxidation reduction cycles as a result of natural processes such as wetting drying cycles and plant root respiration however the kinetics and mechanisms of multiple redox cycles of iron in clay rich sediments and consequences of such cycling on sediment properties are poorly understood the objective of this study was to understand how multiple redox cycles of fe in clay rich sediment affect the rate and extent of fe bioreduction and the physicochemical properties of the sediment a natural sediment sample containing fe bearing montmorillonite from hanford washington usa was size fractionated 2 0 to 0 5 m hanford c and 0 5 to 0 02 m hanford f and redox cycled for four times bioreduction was achieved utilizing geobacter sulfurreducens and re oxidization was performed with sparged air time course change of total fe ii was monitored to measure the rate and extent of fe iii bioreduction redox cycled sediments were characterized to determine the physicochemical changes both the initial rate and extent of bioreduction fluctuated across the four redox cycles but they ultimately decreased from 5 3 mol g 1 h 1 and 22 9 to nearly zero by the fourth cycle these fluctuation patterns were likely due to a combined effect of reductive dissolution of small poorly crystalline clay particles by 3 5 and clay mineral structural changes as evidenced by redox induced changes of aqueous chemistry surface area cation exchange capacity mineralogy and mossbauer parameters once these small poorly crystalline clay particles were dissolved structural fe in residual larger and more crystalline clay particles was largely reversible across additional redox cycles as revealed by mossbauer spectroscopy through the first three cycles

hydrothermal nontronite formation at eolo seamount aeolian volcanic arc tyrrhenian sea abstract a sediment core containing a yellowish green clay bed was recovered from an area of extensive hydrothermal deposition at the se slope of the eolo seamount tyrrhenian sea the clay bed is composed of pure nontronite described for the first time in the tyrrhenian sea which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits the high al content suggests precipitation from al containing hydrothermal solutions the ree distribution of the eolo nontronite has a v shape pattern the heavy ree enrichment is in part due to their preferential partitioning in the nontronite structure this enrichment was possibly further enhanced by the hree preferential sorption on bacterial cell walls the light ree enrichment is the result of scavenging uptake by one of the nontronite precursors i e poorly ordered fe oxyhydroxides from the hydrothermal fluids oxygen isotopic composition of the nontronite yields a formation temperature of 30 c consistent with a low temperature hydrothermal origin the relatively radiogenic nd isotopic signature of the nontronite compared to the present day mediterranean seawater indicates that approximately half of nd and presumably the rest of the lree are derived from local volcanic sources on the other hand 87 sr 86 sr is dominated by present day seawater sr scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube like filaments which are indicative of bacteria assisted precipitation bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly ordered hydrothermal fe oxyhydroxides and silica precipitated upon aging the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite finally the well balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero thus the ubiquitous nontronite precipitation along the active plate boundaries and around the hot spots has no significant impact on oceanic trace element chemistry

ultrasonic imaging of the onset and growth of fractures within partially saturated whitby mudstone using coda wave decorrelation inversion using active ultrasonic source survey data coda wave decorrelation cwd time lapse imaging during the triaxial compression of whitby mudstone cores provides a 3 d description of the evolution and

seismic structure gravity anomalies and flexure of the amazon continental margin ne brazil 1 seismic and gravity data have been used to determine the structure of the sediments crust and upper mantle that underlie the amazon continental margin offshore ne brazil seismic reflection profile data reveal a major unconformity at 7 s two way travel time twtt which we interpret as marking the onset of the transcontinental amazon river and the formation of the amazon deep sea fan system in the late miocene seismic refraction data show mean sediment velocities that decrease by 1 5 km s 1 in a seaward direction we attribute this decrease to facies changes associated with sediment progradation and the development of topset foreset and bottomset beds seismic refraction data show that the sediments are underlain by oceanic crust that has a similar velocity structure compared to elsewhere in the atlantic ocean but is unusually thin 4 2 km we attribute the thin crust to either slow seafloor spreading or a limited magma supply during the initial rifting of south america and africa in the early cretaceous the seismic data have been used to construct a new sediment thickness grid that together with gravity anomaly data suggests the amazon fan loaded lithosphere with an unusually high flexural strength while a high strength lithosphere explains the overall depth of the seismic moho there are discrepancies of up to 2 km beneath the upper fan where the modeled flexed moho is shallower than the seismic moho and beneath the middle fan where it is deeper gravity and seismic modeling suggest these discrepancies are caused by lateral changes in subcrustal density such that the mantle underlying the upper fan is denser than it is beneath the middle fan we attribute these lateral density differences to proximity to the ceara rise which is believed to have formed during the late cretaceous in a mid ocean ridge setting fan loading of a relatively strong dense and hence cold lithosphere predicts stress orientations that are consistent with borehole breakout data and the location and height of the gurupe arch onshore despite its proximity to leaky transform faults the margin that underlies the amazon fan appears to be of nonvolcanic origin the main differences with other nonvolcanic margins such as west iberia and newfoundland are a greater sediment accumulation a narrower zone of transitional crust and a lack of any evidence for extreme extension and mantle serpentinization

two scale gravitational collapse in the amazon fan a coupled system of gravity tectonics and mass transport processes abstract gravity tectonics affects the entire marine sedimentary sequence of the foz do amazonas basin including the topmost amazon fan during the various stages of the margin9s evolution the sedimentary loading and bathymetric slope induced the formation of a linked extensional compressional system in which gravitational fold and thrust belts form significant structural features on the continental slope seismic analysis carried out in this study shows that sea floor relief created along these thrust belts can trigger recurrent mass transport deposits in the upper middle amazon fan suggesting a long lasting linkage between gravity tectonics and mass transport processes throughout the sedimentary evolution of the amazon fan supplementary material uninterpreted seismic sections are available at http www geolsoc org uk sup18393

an insight into the water retention properties of compacted clayey soils experimental data from different testing methodologies on different compacted clayey soils with dominant bimodal pore size distribution are presented and analysed to provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths fabric changes are analysed both from the porous network viewpoint by means of careful mercury intrusion porosimetry investigation and from the soil skeleton viewpoint by quantifying swelling and shrinkage of the aggregates in an environmental scanning electron microscopy study the consequences of the aggregated fabric evolution on the water retention properties of compacted soils are analysed and discussed a new model for water retention domain is proposed which introduces a dependence of the intra aggregate pore volume on water content the model succeeds in tracking correctly the evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths the proposed approach brings to l

amazon cone isotopic stratigraphy evidence for the source of the tropical freshwater spike abstract the isotopic stratigraphy of piston cores from the upper fan of the amazon cone reveals a negative planktic foraminiferal 18o deviation from the global oxygen isotope signal that extends back into the last deglacial period the benthic foraminiferal 18o signal agrees with the global oxygen isotope signal and supports the lithological interpretation that the glacial interglacial boundary occurs at the iron rich crust on the amazon cone the negative planktic foraminifera 18o deviation from the global 18o signal is interpreted as evidence of increased deglacial amazon freshwater discharge to the equatorial atlantic ocean 14c dates suggest that the amazon tropical freshwater discharge initiated at 13 5 ky b p peaked at 9 6 ky b p and terminated at approximately 6 ky b p the timing of the tropical meltwater spike showers and margolis 1985 which peaked in the southern venezuelan basin at 9 6 ky b p can be linked to the flooding of the amazon shelf and the reinitiation of the brazilian coastal current this change in equatorial circulation and advection of amazon river freshwater to the north atlantic via the caribbean surface current the gulf of mexico loop current the western atlantic gulf stream and the north atlantic drift may be the cause for the rapid termination of the younger dryas cool period

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

on the hydro mechanical behaviour of remoulded and natural opalinus clay shale the geo energy sector makes use of advanced technologies such as shale gas extraction co2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations due to the great depths involved in these applications and the difficulties in retrieving intact samples remoulded shale specimens are often adopted for hydro mechanical testing remoulded and intact shales may substantially differ in their hydro mechanical behaviour due to the particular structure of the natural material which is the result of diagenesis and burial history this paper presents an experimental campaign aimed at i characterizing the role of diagenesis and depth for opalinus clay shale and their impact on the hydro mechanical behaviour of the material and ii understanding how representative the behaviour of the remoulded material is with respect to that of the natural shale in this paper the hydro mechanical behaviour of remoulded and intact specimens from the opalinus clay shale formation is investigated by means of a comprehensive oedometric testing campaign the effects of depth and diagenesis on the material behaviour are analysed by testing intact specimens that come from two different sites and depths of the considered shale formation the results highlight a considerably greater stiffness for the natural opalinus clay with respect to the remoulded specimens when the same vertical effective stress is considered together with a significantly lower porosity for the former which is shown to be the result of diagenetic processes rather than solely mechanical compaction a lower swelling sensitivity is also manifested by the natural material with respect to the remoulded specimens as a result of the formation of bonding on the other hand the diagenetic processes do not seem to have a strong impact on the permeability of the material finally creep effects are reduced when diagenesis occurs while they become more relevant when the material is disturbed or remoulded the obtained results provide significant insight into the roles of depth diagenesis and structural disturbance on the hydro mechanical behaviour of the opalinus clay shale

magnetic changes accompanying the thermal decomposition of nontronite in air and its relevance to martian mineralogy thermal treatment of nontronite in air for long periods at 700 c or short periods at 900 c results in destruction of the nontronite structure a distinct reddening in color and a spectacular increase in magnetic susceptibility and saturation magnetization up to 4 4 am2 kg magnetic property measurements and calculations suggest that the magnetism is due to the presence of ultrafine particles of or fe2o3 the precise identity has not yet been resolved the highly magnetic thermally treated nontronite is amorphous to x rays consistent with an ultrafine grain size prolonged heating results in the growth of fe2o3 as suggested by x ray ir and magnetic measurements reflectivity spectra of a sample heated for 1 hour at 900 c indicates in addition to fe2o3 the presence of an opaque magnetite like phase given the composition of the starting material and the experimental conditions the presence of fe3o4 is unlikely the cause of this opacity is as yet unknown thermally treated nontronite has chemical color and magnetic properties akin to those found by viking on mars these results favor an origin for the fine grained martian surface material by repeated impacts into an fe rich smectite charged regolith weldon et al 1980