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

quantification of the pore structures of malan loess and the effects on loess permeability and environmental significance shaanxi province china an experimental study the pore microstructures of loess control the porosity and permeability of the loess affecting the patterns of groundwater flow and the transport of contaminants in the present study the pore microstructure of malan loess was investigated quantitatively in samples from five different loess layers specimens were examined via sem and pore microstructure parameters were determined using the digital image analysis method pore structures including pore area ratio par pore size distribution pore shape and pore morphology the effects of the pore structure on loess permeability and the environmental significance of these factors are discussed in this paper the results indicate that the samples of five loess layers in this study are considered to be porous soil according to both the par and porosity values the number of micropores small pores mesopores and macropores decreased significantly the differences in number were mainly due to the significant reduction in the number of round pores indicating that round pores tend to be small in terms of area micropores small pores mesopores and macropores were dominated by elongated and irregular pores the macro and mesopore structural characteristics of loess determined the transfer characteristics of groundwater and pollutants in the loess additionally the 62 area reduction in the area of elongated or irregular macro and mesopores and the decreasing connectivity from top to bottom layers caused by the deformation and destruction of the pores due to the overlying soil reduced the permeability and the water pollutant migration rate with depth

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

particle packing from an earth science viewpoint abstract particle packings are relevant to many aspects of the earth sciences and there is a long history of the study of packings from an earth science viewpoint packings have also been studied in connection with other subjects and disciplines allen 1982 produced a major review which provides a solid base for earth science related studies this review complements allen s work and in particular focuses on advances in the study of random packings over the last ten years transitions from packing to packing may be as important as the packings themselves and possibly easier to model this paper places emphasis on certain neglected works in particular morrow and graves 1969 and the packing transition envelope kahn 1956 and the measurement of packing parameters griffiths 1962 on packings in one dimension and getis and boots 1978 on packings in two dimensions certain packing problems are relevant to current areas of study including structure collapse in loess hydroconsolidation flowslides in very sensitive soils wind erosion jewel quality in opals and the structure and functions of sand dunes the region where interparticle forces become active particles

influence of structure on the behavior of a saturated clayey loess an intensive experimental investigation by means of triaxial and oedometer tests was performed on a clayey loess that was retrieved from two depths at a location on the southern chinese loess plate

microstructural constraints on geotechnical properties of malan loess a case study from zhaojiaan landslide in shaanxi province china abstract the microstructure of malan loess a late pleistocene loess deposit in china dominates its macroscopic geotechnical properties when subject to inundating or humidifying conditions the distinct metastable structure of the malan loess is sensitive to collapse thus its geotechnical properties undergo change the results of triaxial and uni axial compression tests under the humidifying conditions on undisturbed loess samples demonstrate that its geotechnical properties of the top loess were dominated by metastable structure while the basal loess were more influenced by inter particles cementation bond based on analyses from scanning electron microscopy images change of the loess pore structure can be primarily attributed to the ratio of metastable pores 5 m accordingly an end member model is proposed to illustrate how varying in the size and distributions of very large pores 200 m large pores 50 200 m medium pores 5 50 m and small pores

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

modelling gravel barrier profile response to combined waves and tides using xbeach laboratory and field results abstract xbeach a process based numerical model capable of computing nearshore circulation and morphodynamics including overwash and breaching has been used in 1d mode to simulate erosion occurring on a gravel barrier beach d50 11 mm subjected to wave and tidal forcing during selected tests undertaken during the bardex experiments the model demonstrated good quantitative skill brier skill score bss typically 0 65 with respect to beach face erosion offshore accretion and morphological impacts of washover xbeach was also used to model storm impacts on a steep average tan 0 12 4 5 km long and 100 m 140 m wide macrotidal gravel barrier d50 2 mm to 10 mm located in sw england although the development of a storm berm was not reproduced well erosion was predicted with sufficient skill bss 0 60 to meet practical engineering requirements concerned with predicting storm impacts and threshold wave and water level conditions for gravel barrier overwashing

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

effects of soil structure on soil behaviour illustrated with loess glacially loaded clay and simulated flaser bedding examples soil structure is considered to be a systematic homogeneously repetitive heterogeneity of properties and conditions of soil for upscaling and homogenisation of properties and conditions it is necessary to understand the ways in which soil structures occur and to obtain understanding of the ways in which it influences soil behaviour using three case studies different aspects of the effects of soil structure in soil mechanics are discussed the very loose grain scale packing of loess deposits held together by weak structural bonds between particles results in dramatic propagating failure when the strength of the bonds is exceeded by deformations as illustrated in the first case nonhorizontal stresses induced in the subsurface below moving continental ice sheets result in rotated stress fields within the affected soil the rotated stress field is stored in the structure of the soil as is shown in the second case and influences present day properties and behaviour of these clays it is shown in the third case that there is a large difference in the behaviour of clayey sand depending on whether the clay occurs in the form of the common clay flasers or whether the clay is homogeneously dispersed in the sand the deformation and stress propagation in the case of sand with clay flasers results in local failures and shear planes due to the large contrast in the properties of the materials making up the sedimentary structure the result is that many of the properties of sand with flasers are rather more like the clay of the flasers than the sand incorporation in the engineering practice of effects of common types of soil structure is made possible with the widespread availability of techniques such as numerical modelling these techniques enable the development of appropriate tools for practical application

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

influence of subsurface flow by lidar dems and physical soil strength considering a simple hydrologic concept for shallow landslide instability mapping abstract high resolution dems and physical soil strength among other factors have significant effects on the shallow landslide instability mapping subsurface flow in soil mantle normally is assumed by slope parallel flow based on resolution of dems and measuring soil strength which is affected by subsurface flow within the soil mantle is difficult in both the field and the laboratory thus the aims of this study are to investigate the effect of subsurface flow by high resolution lidar dems and the effect of physical soil strength attributes on shallow landslide instability mapping respectively in this study two dems with 1 m and 5 m resolutions were used and physical soil strength was calibrated using a simple subsurface hydrological concept with lidar and field survey data in order to quantify the influence of soil strength on shallow landslide instability mapping to this end various field surveys were performed at woomyeon mountain seoul republic of korea where shallow landslides occurred in 2012 the physical shallow landslide stability shalstab model were applied the modified success rate msr method were applied to assess the predicted results in the first series of simulations using the two dems and experimentally derived soil strength values relatively low msr values of 0 42 0 468 for the 1 m dem and 0 42 0 47 for the 5 m dem were recorded in the second series of simulations using soil strength calibrated using a simple theoretical approach the msr for the 1 m dem was 0 78 0 823 and the msr for the 5 m dem was 0 723 0 80 these results indicated that soil strength had a more important role in shallow landslide instability mapping than assuming subsurface flow by topographic resolution therefore it may be useful to apply field collected soil strength data using hydrological concepts to improve the accuracy of predictive models based on high resolution surface data

a review and assessment of longshore sediment transport equations for coarse grained beaches previous assessments of analytical longshore sediment transport formulae have been heavily biased towards sand sized sediment all have noted the shortage of high quality field data from coarse grained beaches against which to test predictions of longshore transport rates in this paper 12 existing formulae were identified as being potentially applicable for coarse grained sediments and predictions from these formulae are compared using a measured annual transport rate from a shingle beach and a concurrent hindcast wave climate two new empirical equations are also derived one from a numerical model calibrated against the same data set the other derived from field experiments on coarse grained beaches energetics based equations are found to give reasonable predictions of the shingle transport despite being derived for sand beaches in contrast those dimensional analysis type equations which had been validated using laboratory data grossly over predicted the measured transport rates the most accurate predictions were from formulae previously validated at sites similar to that used for this comparison and therefore require further testing against field data from dissimilar sites

the loess of north central china geotechnical properties and their relation to slope stability abstract loess is an aeolian deposit consisting of predominantly silt sized quartz particles and containing variable amounts of clay sized minerals loess is generally classified as a water softening material because upon wetting the loess fabric rapidly weakens or collapses the strain hardening of malan loess and the brittle failure of lishi and wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state from tests carried out on samples with varying moisture contents using a modified bromhead ring shear apparatus it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content when the moisture content reaches a material specific threshold the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value the frequent failure of loess slopes in the western part of the chinese loess plateau is closely related to progressive weathering along zones in these slopes which causes a dramatic decrease in strength from the peak strength condition progressive weathering is common in the loess slopes in the western part of the chinese loess plateau during the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts destruction of cementation bonds and redistribution of particles localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane therefore the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed and unweathered central parts of the slopes it is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes many of which are steepand lie directly above domestic and industrial urban areas

internal architecture and evolution of bioclastic beach ridges in a megatidal chenier plain field data and wave flume experiment beach ridges in macrotidal environments experience strong multi annual to multi decennial fluctuations of tidal inundation the duration of tide flooding directly controls the duration of sediment reworking by waves and thus the ridge dynamics flume modelling was used to investigate the impact of low frequency tidal cycles on beach ridge evolution and internal architecture the experiment was performed using natural bioclastic sediment constant wave parameters and low frequency variations of the mean water level the morphological response of the beach ridge to water level fluctuations and the preservation of sedimentary structures were monitored by using side view and plan view photographs results were compared with the internal architecture of modern bioclastic beach ridges in a macrotidal chenier plain mont st michel bay france surveyed with ground penetrating radar the experimentally obtained morphologies and internal structures matched those observed in the field and the three ridge development stages identified in ground penetrating radar profiles early transgressive late transgressive and progradational were modelled successfully flume experiments indicate that flat bioclastic shapes play a key role in sediment sorting in the breaker zone and in sediment layering in the beach and washover fans water level controls washover geometry beach ridge evolution and internal structure low water levels allow beach ridge stabilization and sediment accumulation lower on tidal flats during subsequent water level rise accumulated sediment becomes available for deposition of new washover units and for bayward extension of the beach ridges in the field low frequency water level fluctuations are related to the 4 4 year and 18 6 year tidal cycles experimental results suggest that these cycles may represent the underlying factor in the evolution of the macrotidal chenier coast at the multi decadal to centennial time scale

rock magnetic properties and relative paleointensity stack for the last 300 ka based on a stratigraphic network from the subtropical and subantarctic south atlantic abstract we present a detailed study of natural remanence and rock magnetic properties of eight sediment cores from a south north profile across the subtropical front stf in the south atlantic which previously have been combined into a stratigraphic network based on these measurements we construct a first relative paleointensity rpi stack for the central south atlantic sas 300 covering the last 300 ka the degree of down core homogeneity of magnetic mineral concentration as well as magnetic mineral content and grain sizes vary between all cores and are quantified by high resolution rock magnetic measurements in the cores north of and close to the stf the magnetic remanence is mainly carried by magnetite the cores in the south also contain a high coercive mineral fraction based on a linear model of the sediment matrix we propose to apply principal component analysis pca of natural remanent magnetization nrm anhysteretic and isothermal remanent magnetization arm and irm to determine a homogeneity interval where remanences are only affected by a single environmental signal this reduces lithologic and climatic influence upon the relative paleointensity record for our data set pca indicates that all remanences in the 30 mt to 80 mt demagnetization interval are dominated by a single environmental influence single core rpi estimates are then obtained by normalizing the nrm fraction in this homogeneity interval with respect to either irm arm in the same interval or by by direct averaging we obtain the stack sas 300 which is compared to other paleointensity series such as sint 800 or the rpi records from odp sites 1089 subantarctic south atlantic and 983 gardar drift the detailed documentation of environmental influences combined with the presentation of seven different recordings of the same geomagnetic signal allows to connect southern and northern hemisphere rpi data also with respect to possible common environmental distortions

a new astronomical timescale for the loess deposits of northern china here we present a refined timescale for the entire sequence of quaternary chinese loess which relies upon the correlation of detailed monsoon records to the astronomical solution of laskar 1990 and the oceanic odp677 18o record of shackleton et al 1990 the chronological scheme considers in detail the relative structures of the palaeoclimatic and palaeomagnetic records to produce an accurate timescale that is consistent with the current understanding of loess depositional and post depositional processes analysis of this chronological framework demonstrates downward displacement of the palaeomagnetic horizons with respect to the climatic record

morpho sedimentary dynamics of a micro tidal mixed sand and gravel beach playa granada southern spain abstract this paper addresses the changes in the morphology and sedimentology of a micro tidal mixed sand and gravel beach playa granada southern spain forced by wave and water level variations and human intervention through nourishment monthly and storm event driven beach surveys consisting of topographical measurements and sediment sampling in two selected areas were carried out over a one year period three prevailing sediment fractions sand fine gravel and coarse gravel and two end member morphological states of the upper beach profile convex with multiple berms and concave with a single storm berm were identified between them several transitional profiles were formed characterized by developing berms that progressively overlapped generating sediment variability both across the beach profile and with depth the results indicate that the total run up including water level reached during an event represents a more accurate threshold for differentiating between erosional and depositional conditions than wave height they also suggest that mixed sand and gravel beaches recover faster from storm erosion than sandy beaches the long term benefit of the artificial nourishment that took place at the end of the survey period was very limited and this is attributed to the too fine sediment used for the nourishment and its placement too high on the beach clearly nourishment interventions must take into account the natural sediment distribution and the profile shape to avoid rapid losses of the nourished sediment

geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison abstract derbyshire e and mellors t w 1988 geological and geotechnical characteristics of some loess and loessic soils from china and britain a comparison eng geol 25 135 175 loess and loessic deposits cover some 630 000 km 2 of the surface of mainland china the loess plateau of shanxi shaanxi gansu and ningxia being the type region of this formation loess thickness generally exceeds 100 m over large areas of the loess plateau the maximum recorded thickness being 335 m in eastern gansu province near the city of lanzhou in britain loess and loessic deposits form part of a group of materials collectively known as brickearth they occur predominantly as sporadic accumulations in the southeast of england and rarely attain a thickness of more than four metres despite their geographical separation the deposits from china and britain have a remarkable similarity in some of their physical and geotechnical characteristics samples from both locations have been examined and tested in the laboratory and the results are presented the scope of the testing programme involved mineralogical analyses soil microfabric studies using a scanning electron microscope index testing including plasticity grading and density measurements and the investigation of the compressibility characteristics of the soils with particular reference to their susceptibility to collapse a soil structure model based on scanning electron microscope studies is presented and discussed in relation to the perceived mode of formation of the soils and their postdepositional history

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

norwegian fjord sediments reveal nao related winter temperature and precipitation changes of the past 2800 years abstract the north atlantic oscillation nao is the leading mode of atmospheric circulation variability in the north atlantic region associated shifts of storm tracks precipitation and temperature patterns affect energy supply and demand fisheries and agricultural as well as marine and terrestrial ecological dynamics long term nao records are crucial to better understand its response to climate forcing factors and assess predictability and shifts associated with ongoing climate change a recent study of instrumental time series revealed nao as main factor for a strong relation between winter temperature precipitation and river discharge in central norway over the past 50 years here we compare geochemical measurements with instrumental data and show that primary productivity recorded in central norwegian fjord sediments is sensitive to nao variability this observation is used to calibrate paleoproductivity changes to a 500 year reconstruction of winter nao luterbacher et al 2001 conditioned on a stationary relation between our climate proxy and the nao we establish a first high resolution nao proxy record nao tfj from marine sediments covering the past 2800 years the nao tfj shows distinct co variability with climate changes over greenland solar activity and northern hemisphere glacier dynamics as well as climatically associated paleo demographic trends the here presented climate record shows that fjord sediments provide crucial information for an improved understanding of the linkages between atmospheric circulation solar and oceanic forcing factors

a 580 kyr paleomagnetic record from the sub antarctic south atlantic ocean drilling program site 1089 1 we report geomagnetic directional paleosecular variation relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth mcd at south atlantic ocean drilling program odp site 1089 40 56 2 s 9 53 64 e 4620 m water depth the age model is provided by high resolution oxygen isotope stratigraphy augmented by radiocarbon dates from the upper 8 mcd of nearby piston core rc11 83 mean sedimentation rates at site 1089 are in the range of 15 to 20 cm kyr two intervals during the brunhes chron at 29 6 mcd 190 ka and at 48 mcd 335 ka have component magnetization directions with positive reverse polarity inclination however the excursional directions are heavily overprinted by the postexcursional field magnetite is the dominant carrier of magnetic remanence and occurs in the pseudosingle domain psd grain size an additional higher coercivity magnetic carrier characterized by low unblocking temperatures 350 c is assumed to be authigenic pyrrhotite a decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate indicating diagenetic reduction of magnetite despite down core changes in magnetic mineralogy normalized intensity records from site 1089 are comparable with high resolution paleointensity records from the north atlantic e g odp sites 983 and 984 sediment properties and sedimentation patterns within the cape site 1089 and iceland sites 983 and 984 basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation variations in normalized intensity from site 1089 therefore appear to reflect changes in global scale geomagnetic field intensity

correcting relative paleointensity records for variations in sediment composition results from a south atlantic stratigraphic network abstract marine sediments record direction and intensity of the earth s magnetic field by the alignment of magnetic particles during deposition for determining relative paleointensity rpi from sediment records it is commonly assumed that their natural remanent magnetization nrm is proportional to the earth s magnetic field during deposition and also proportional to the concentration of remanence carriers in the sediment layer however little is known how varying sediment composition and environmental conditions during deposition influence the nrm here we try to identify and quantify such sedimentary influences for eight sediment series from the subtropical and subantarctic south atlantic the cores were recovered in a constraint area crossing the subtropical front stf they have widely different sediment lithologies which can be divided into three lithologic groups due to their mutual proximity they have experienced approximately the same magnetic field history and differences in their rpi signals must be caused by their varying sediment composition and recording properties based on high resolution rock magnetic and compositional data from two previous studies it is possible to quantitatively test and compare the influences of different sediment properties upon the nrm it is found that magnetic grain size as measured by the magnetic parameter arm irm is most influential among the parameters tested weak to moderate reductive diagenesis as measured by the parameter fe turns out to have minor impact by comparing the sensitivity of different normalization procedures for rpi determination it is found that induced remanent magnetization irm is most robust based on an extended linear rpi theory we can calculate a corrected rpi stack for the investigated cores this correction improves the correlation with independent global paleointensity stacks in comparison to our previous uncorrected rpi stack hofmann d fabian k 2007 rock magnetic properties and relative paleointensity stack for the last 300 ka based on a stratigraphic network from the subtropical and subantarctic south atlantic earth planet sci lett 260 297 312 the ratio between corrected and uncorrected rpi stacks reveals a hidden global climate signal which indicates that climatic variations in sediment composition are inevitably present in non ideal sediment sequences

centrifuge model testing of a loess landslide induced by rising groundwater in northwest china abstract considerable artificial irrigation in the heifangtai area has caused the continued rise of groundwater levels which has resulted in several large scale landslides in the loess platform area considering the no 13 landslide of jiaojia in the heifangtai area as a geological archetype a series of centrifuge tests was conducted to study the deformation and failure characteristics of the slope due to the continuous rise in the groundwater level meanwhile the pore water pressure earth pressure deformation and evolution characteristics of the slope were monitored and recorded in real time furthermore isotropically consolidated undrained triaxial testing icu was conducted to investigate the static liquefaction of loess specimens which was related to the slope instability the centrifuge test results showed that a series of parallel and steep tension cracks at the top of the slope were present before the landslide which was caused by the rising groundwater the icu experimental results showed that as the pore water pressure increased strong strain softening and static liquefaction of saturated loess soils were found which was related to the sudden destruction of the slope

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

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

metal enrichment and magnetic properties of core sediments from the eastern yellow sea east asia implications for paleo depositional change during the late pleistocene holocene transition abstract to investigate the paleo depositional environments sediment cores yj1 and yj2 from a tidal flat of the eastern yellow sea were analyzed for the vertical variations of metal concentrations particle size clay mineralogy magnetic properties and total organic carbon content toc fe and mn concentrations determined by both partial and total acid extraction increased at 15 m depth in yj1 and 10 m in yj2 the layer directly below these fe rich brownish horizons showed dramatic decreases in clay mineral content and trace metals zn pb cu cr co ni and as but increases in sand fraction magnetic susceptibility and toc all results were inverse in the upper metal rich layer these dramatic changes in multi parameters are likely due to an environmental change during the late pleistocene holocene transition the rapid environmental change sand rich and oxic clay rich and anoxic resulted in aqueous dissolution of redox sensitive metals e g fe and mn from the lower sandy layer materials the dissolved metals diffused upward and concomitantly were immobilized within the upper clay rich layer the reprecipitated fe or mn hydro oxides then scavenged trace metals by coprecipitation and or adsorption this study suggests that metal distribution patterns can provide new insights into the paleo depositional processes during the pleistocene holocene period

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

does lithology influence relative paleointensity records a statistical analysis on south atlantic pelagic sediments abstract the relative paleointensity rpi method assumes that the intensity of post depositional remanent magnetization pdrm depends exclusively on the magnetic field strength and the concentration of the magnetic carriers sedimentary remanence is regarded as an equilibrium state between aligning geomagnetic and randomizing interparticle forces just how strong these mechanical and electrostatic forces are depends on many petrophysical factors related to mineralogy particle size and shape of the matrix constituents we therefore test the hypothesis that variations in sediment lithology modulate rpi records for 90 selected late quaternary sediment samples from the subtropical and subantarctic south atlantic ocean a combined paleomagnetic and sedimentological dataset was established misleading alterations of the magnetic mineral fraction were detected by a routine fe test funk j von dobeneck t reitz a 2004 integrated rock magnetic and geochemical quantification of redoxomorphic iron mineral diagenesis in late quaternary sediments from the equatorial atlantic in wefer g mulitza s ratmeyer v eds the south atlantic in the late quaternary reconstruction of material budgets and current systems springer verlag berlin heidelberg new york tokyo pp 239 262 samples with any indication of suboxic magnetite dissolution were excluded from the dataset the parameters under study include carbonate opal and terrigenous content grain size distribution and clay mineral composition their bi and multivariate correlations with the rpi signal were statistically investigated using standard techniques and criteria while several of the parameters did not yield significant results clay grain size and chlorite correlate weakly and opal illite and kaolinite correlate moderately to the nrm arm signal used here as a rpi measure the most influential single sedimentological factor is the kaolinite illite ratio with a pearson s coefficient of 0 51 and 99 9 significance a three member regression model suggests that matrix effects can make up over 50 of the observed rpi dynamics

on the age of the laschamp geomagnetic excursion abstract the laschamp geomagnetic excursion is a critical tie point found directly in deep sea sediment cores and revealed in polar ice as an abrupt change in the rate of cosmogenic nuclide flux despite the importance of this excursion to quantifying paleoclimate proxy records archived in sediment and ice and to providing an independent calibration of the radiocarbon calendar its timing remains poorly known previous k ar 40 ar 39 ar and u th isochron determinations from lava flows at the type locality in the massif central france vary widely are imprecise and suggest a mean age of about 46 2 2 5 ka 2 results of 6 new unspiked k ar and 13 40 ar 39 ar incremental heating experiments on subsamples from three sites on the laschamp and olby flows are concordant and give a weighted mean age of 40 4 1 1 ka 2 uncertainty including analytical sources only that is 10 younger than the previous estimates considering that the 40 k 40 ar decay constant is not known to a precision better than 2 4 the most probable radioisotopic age for the laschamp excursion is 40 4 2 0 ka 2 analytical plus decay constant uncertainties this new age for the laschamp excursion agrees precisely with that deduced from the napis 75 deep sea sediment paleointensity stack when calibrated against the gisp2 ice core chronology using the o isotopes in ice and the magnetic properties of the marine cores

the south atlantic current in this paper we use the historical hydrographic data base for the south atlantic ocean to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the sub tropical front stf and ii the southern current band of the gyre which is called the south atlantic current sac the stf begins in the west in the brazil falkland malvinas confluence zone but at locations at and west of 45 w this front is often coincident with the brazil current front east of 45 w the stf appears to be a distinct feature to at least the region south of africa whereupon it continues into the indian ocean the associated current band of increased zonal speed is the sac which except for one instance is found at or north of the surface stf until indian ocean water from the agulhas retroflection is reached a reversal of baroclinicity in the stf is observed south of a highly saline agulhas ring causing the sac to separate from the stf and turn north into the benguela current zonal flow south of the stf is generally weak and serves to separate the south atlantic and circumpolar currents in the argentine basin the sac has a typical volume transport of 30 sv 1 sv 106m3s 1 in the upper 1000 m relative to a deep potential density surface 4 45 87 kg m 3 and can be as high as 37 sv it is thus comparable to or stronger than the brazil current in the cape basin the transport of the sac is reduced to about 15 sy before it turns north to feed the benguela current in late 1983 this flow was joined by about 8 sv of water from the agulhas current

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

stress deformation properties of macroporous loess soils abstract milovic d 1988 stress deformation properties of macroporous loess soils eng geol 25 283 302 herein are presented the results of laboratory and field tests which were carried out on loess in yugoslavia experience gained during recent decades show that the loess soil in some cases undergoes structural collapse and subsidence due to inundation in order to find the explanation of such behaviour numerous laboratory and field load tests on loess soil have been performed using the obtained results several correlations have been established on the basis of the unconfined test results a correlation between the initial dry density initial water content and unconfined compression strength has been established a relatively large number of the consolidation subsidence tests about 550 carried out on undisturbed loess samples made possible the determination of the degree of subsidence and the corresponding values of the dimensionless coefficients of subsidence these coefficients have been determined for several values of the initial dry density for various degrees of saturation and for several stress levels upon wetting using these coefficients the values of the additional settlement caused by flooding of loess under the foundation can easily be calculated it is of particular interest to note that in general water penetrates under one part of the building producing differential settlements which are in most cases very dangerous by the comparative laboratory investigation of the undisturbed loess samples obtained by thin walled sampler and samples obtained from pits it has been shown that the mechanical disturbance is an extremely important factor which governs the shear and deformation parameters of loess soils the laboratory test results obtained on undisturbed loess samples cut from blocks in the vertical and horizontal direction have shown that this soil exhibits anisotropic properties for this reason a stress deformation problem in an anisotropic medium has been treated by the finite element method static penetration tests and field load tests in loess soils with natural water content and also after saturation have been performed and are described the results of the observed settlements for two statically identical multi storey buildings are also presented using the coefficients of subsidence for the undisturbed samples cut from blocks very good agreement between the calculated and the observed settlements has been obtained

diagnostic investigation of impulsive pressures induced by plunging breakers impinging on gravel beaches abstract this paper presents an integrated investigation of physical processes generating impulsive pressures under the action of plunging breakers impinging on gravel beaches this work is an extension of a recent investigation which suggested that wave impacts from plunging breakers acting on gravel beaches may be a key mechanism to enhance sediment mobilisation in particular comparisons of full scale laboratory measurements against model results from a well validated phase depth resolving numerical model based on the reynolds averaged navier stokes rans equations are presented this represents the first attempt at comparison with such a tool against observed hydrodynamics on steep slope 1 8 gravel beaches at prototype scale in order to understand how impulsive pressures are generated under plunging waves the numerical model is used to carry out a detailed investigation to examine the role of each of the acceleration terms in the momentum balance consistent with prior studies numerical results show that under plunging breakers the local acceleration u t alone cannot be used as a proxy for pressure gradients however the contribution of the third term w u z of total acceleration is recognized for the first time and indicates that this term has an important role in both the induced pressure gradient and sediment mobilisation as induced by this particular type of breaking furthermore results suggest that a parameterisation of the pressure gradient in terms of u t u u x may not suffice when dealing with plunging breakers and hence there is a lack of a suitable parameterisation of this process in the present literature thus for different types of breaking it may be necessary to consider a different characterisation of the pressure gradient toward the parameterisation of sediment transport inside the surf zone

extreme wave deposits on the pacific coast of mexico tsunamis or storms a multi proxy approach abstract historical and instrumental data show that the pacific coast of mexico has been exposed to destructive tsunamis over at least the past 500 years this coast is also affected by hurricanes generated in the eastern pacific the great 1985 mexico earthquake and its aftershock generated tsunamis that affected the ixtapa zihuatanejo and michoacan coast the purpose of our study was two fold a to determine whether storm and tsunami deposits could be distinguished and b whether tsunami deposits from historical events are preserved in the tropical environments of the ixtapa zihuatanejo coast two anomalous sand units in the ixtapa estuary are interpreted to be the result of high energy marine inundation events that occurred in the last century several lines of evidence using a multi proxy approach historical studies interviews with local witnesses geomorphological and geological surveys coring and trenching laboratory analyses including grain size micropaleontology geochemistry magnetic susceptibility and radiometric dating and numerical modeling indicate the occurrence of two tsunamis that we link to local events the 21st september 1985 mexico and possibly the 14th march 1979 petatlan earthquakes we thereby provide the first onshore geological evidence of historical tsunamis on the pacific coast of mexico

changes in tensile strength and microstructure of loess due to vibration abstract loess soils typically have an open and metastable structure humidification and vibration can modify their microstructure and thus influence their mechanical behavior in the present study to investigate the influence of train vibration on the tensile strength behavior of loess the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph in addition the microstructures of vibrated and non vibrated loess specimens before and after the tensile tests were characterized changes in the loess microstructure due to vibration and that in the tensile test were analyzed the results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function the axial displacement at failure varies at the same manner as tensile strength with respect to water content in comparison to intact loess occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens while aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests this indicates that vibration reduces the tension resistance and ductility of loess soil structure which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates in the tensile test the soil structure goes through two distinct phases of change i e stretching phase and cracking phase in the stretching phase the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly in the cracking phase weak cementations fail to resist tensile deformation and suffer from breakage once a through crack is developed the specimen breaks in two leading to a catastrophic drop of tensile stress

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

swash overtopping and sediment overwash on a truncated beach new experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach approximating the conditions at the crest of a beach berm or inter tidal ridge runnel the experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model both of which are restricted to individual swash events the analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f w 0 024 this is in good agreement with a broad range of published field and laboratory data however the influence of long waves and irregular wave run up on the overtopping and overwash remains to be assessed the good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone which has application in predicting the growth and height of beach berms c 2005 elsevier b v all rights reserved

modelling gravel beach dynamics with xbeach abstract numerical cross shore profile evolution models have been good at predicting beach erosion during storm conditions but have difficulty in predicting the accretion of the beach during calm periods this paper describes the progress made in modifying and applying the public domain xbeach code to the prediction and explanation of the observed behaviour of coarse grained beaches in the laboratory and the field under accretive conditions the paper outlines in details the changes made to the original code version 12 including the introduction of a new morphological module based upon soulsby s sediment transport equation for waves and currents and the incorporation of packwood s infiltration approach in the unsaturated area of the swash region the competence of this modified model during calm conditions for describing the steepening of the profile and the growth of the beach berm is demonstrated preliminary results on the behaviour of the beach subject to both waves and tides are presented good agreement is found between the model simulations and large scale laboratory measurements as well as field observations from a composite beach in the uk the reasons for the model s capabilities are discussed

the water retention properties of a natural unsaturated loess from northern france the water retention properties of a natural loess from northern france were investigated on intact block samples that were excavated along a high speed train line tgv that experienced stability problems during heavy rain episodes suction measurements were made by using the filter paper method and an in house constructed high capacity tensiometer hct so as to determine the water retention curve of the loess the results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values reasonably compatible with the hct measurements the water retention curve obtained exhibited a peculiar form with no hysteresis observed around the natural water content 14 4 and two hysteresis loops on both the wet and dry sides of the curve it is hypothesised that this zone with no hysteresis corresponds to the natural variations of the water content under seasonal changes providing a range of natural suction between 20 and 80 kpa and it is suggested that th

microstructure and soil water retention behavior of compacted and intact silt loess abstract there are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the loess plateau of china which significantly changes the hydrological and geological equilibrium state of the site the formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers most disasters occurring in the loess area are related to water the soil water retention curve swrc is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil in this study the swrcs and microstructure of intact and compacted specimens from lanzhou and yan an two typical cities that have new land creation projects are investigated the swrc is obtained using the filter paper method the mercury intrusion porosimetry mip and scanning electron microscope sem techniques are used to explore the microstructure the results highlight that the intact loess has a higher air occlusion value aov and a similar slope of swrc in the transition zone compared with the remolded specimens that compacted at the natural water content the normalized swrc i e degree of saturation versus suction avo of the intact specimen is approximately the same as the remolded specimens compacted as the natural water content the difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the swrc

monitoring near shore shingle transport under waves using a passive acoustic technique passive acoustic techniques have been used to measure shingle gravel sediment transport in very shallow water near the wave breaking zone on a beach the experiments were conducted at 1 1 scale in the large wave flume grose wellen kanal gwk at hannover germany the frequency spectrum induced by shingle mobilized under breaking waves can be distinguished from other ambient noise and is found to be independent of water depth and wave conditions the inverse relationship between centroid frequency and representative grain size is shown to remain valid in shallow water wave conditions individual phases of onshore and offshore transport can be identified analysis of the acoustic frequency spectrum provides insight into the mechanics of phase resolved shingle transport

effects of soil structure on the shear behaviour of an unsaturated loess at different suctions and temperatures previous studies of shear behaviour at different suctions and temperatures focused mainly on recompacted soils limited attention has been paid to intact soil in this paper the shear behaviour of

reconstruction of paleoceanography off nw africa during the last 40 000 years influence of local and regional factors on sediment accumulation abstract a set of 43 sediment cores from around the canary islands is used to characterise this region which intersects meridional climatic regimes and zonal productivity gradients in a high spatial resolution using rapid and nondestructive core logging techniques we carried out fe intensity and magnetic susceptibility ms measurements and created a stack on the basis of five stratigraphic reference cores for which a stratigraphic age model was available from 18 o and 14 c analyses on planktonic foraminifera by correlation of the stack with the fe and ms records of the other cores we were able to develop age depth models at all investigated sites of the region we present the bulk sediment accumulation rates ar of the canary islands region as an indicator of shifts in the upwelling influenced areas for the holocene 0 12 ky the deglaciation 12 18 ky and the last glacial 18 40 ky general observations are an enhanced productivity during glacial times with highest values during the deglaciation the main differences between the analysed time intervals we interpret as result of the sea level effects changes in the extent of high productivity areas and current intensity

high resolution reconstruction of southwest atlantic sea ice and its role in the carbon cycle during marine isotope stages 3 and 2 1 recent modeling suggests that changes in southern ocean sea ice extent potentially regulated the exchange of co2release between the ocean and atmosphere during glacials unfortunately a lack of high resolution sea ice records from the southern ocean has prevented detailed testing of these model based hypotheses with field data here we present high resolution records of southern ocean sea ice for the period 35 15 cal ka bp derived from diatom assemblages measured in three glacial sediment cores forming an 8 transect across the scotia sea southwest atlantic chronological control was achieved through a novel combination of diatom abundance stratigraphy relative geomagnetic paleointensity data and down core magnetic susceptibility and ice core dust correlation results showed that the winter sea ice edge reached its maximum northward extent of 53 s at least 3 north of its modern limit between 25 and 23 5 cal ka bp predating the last glacial maximum lgm maximum northward expansion of the summer sea ice edge also pre dated the lgm advancing to at least 61 s and possibly as far north as 55 s between 31 and 23 5 cal ka bp a 12 advance from its modern position a clear shift in the seasonal sea ice zone is evident following summer sea ice edge retreat at 23 5 cal ka bp potentially related to austral insolation forcing this resulted in an expanded seasonal sea ice zone between 22 5 cal ka bp and deglaciation our field data confirm that southern ocean sea ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre formed nutrients our data indicates that southern ocean sea ice was most effective as a physical barrier between 31 and 23 5 cal ka bp and as a mechanism capable of reducing vertical mixing between 22 5 cal ka bp and deglaciation however poor correlations with atmospheric co2 variability recorded in ice cores particularly the lack of a co2response during a rapid sea ice meltback event recorded at our study sites at the same time as antarctic isotopic maximum 2 suggest that southern ocean sea ice in the scotia sea did not play a controlling role in atmospheric co2 variation during the glacial

limitations on stratigraphic analyses due to incomplete age control and their relevance to sedimentary paleomagnetism abstract a major limitation in the analysis of physical quantities measured from a stratigraphic core is incomplete knowledge of the depth to age relationship for the core records derived from diverse locations are often compared or combined to construct records that represent a global signal time series analysis of individual or combined records is commonly employed to seek quasi periodic components or characterize the timescales of relevant physical processes assumptions that are frequently made in the approximation of depth to age relationships can have a dramatic and harmful effect on the spectral content of records from stratigraphic cores a common procedure for estimating ages in a set of samples from a stratigraphic core is to assign based on complementary data the ages at a number of depths tie points and then assume a uniform accumulation rate between the tie points imprecisely dated or misidentified tie points and naturally varying accumulation rates give rise to discrepancies between the inferred and the actual ages of a sample we develop a statistical model for age uncertainties in stratigraphic cores that treats the true but in practice unknown ages of core samples as random variables for inaccuracies in the ages of tie points we draw the error from a zero mean normal distribution for a variable accumulation rate we require the actual ages of a sequence of samples to be monotonically increasing and the age errors to have the form of a brownian bridge that is the errors are zero at the tie points the actual ages are modeled by integrating a piecewise constant randomly varying accumulation rate in each case our analysis yields closed form expressions for the expected value and variance of resulting errors in age at any depth in the core by monte carlo simulation with plausible parameters we find that age errors across a paleomagnetic record due to misdated tie points are likely of the same order as the tie point discrepancies those due to accumulation rate variations can be as large as 30 kyr but are probably less than 10 kyr we provide a method by which error estimates like these can be made for similar stratigraphic dating problems and apply our statistical model to an idealized marine sedimentary paleomagnetic record both types of errors severely degrade the spectral content of the inferred record we quantify these effects using realistic tie point ages their uncertainties and depositional parameters

magnetic signature of the 22 june 1932 tsunami deposits jalisco mexican pacific coast recent studies have demonstrated that rock magnetic analysis may provide additional information to distinguish and characterize extreme marine inundation events such as tsunamis rock magnetic proxies reinforce and improve the environmental evidences supplied by other methods adding some decisive clues for the interpretation of the origin and genesis of the sedimentary deposits here we report rock magnetic xrd and sem microscopy results obtained in the palo verde estuary colima pacific coast mexico in order to enhance the tools for identification and reconstruction of two tsunami induced deposits the sedimentary sequence includes two sand units a tsunami deposit pv1 associated with the 22 june 1932 tsunami and a deeper sandy layer pv2 related to a possible palaeotsunami that occurred around 1300 ce both sandy units are topped by finer grained units magnetic properties exhibit a significant correlation with the stratigraphy high susceptibility and high saturation isothermal remanence sirm values typical of high concentrations of titano magnetite are a distinctive feature of the most recent sandy tsunamigenic unit pv1 and the overlaying soil the lower sandy tsunamigenic unit pv2 shows significantly lower and sirm values indicating lower concentration of titano magnetite in this unit and the overlaying clayey silt unit the latter also shows a higher coercivity component associated to titano hematite magnetic grain size differences are also observed between pv1 and pv2 suggesting differences in hydraulic conditions at the time of deposition the bulk mineralogical composition and sediment texture of these units also supports the hypothesis of different provenances for each tsunamigenic unit as inferred from magnetic properties

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

oceanographic control of biogenic opal and diatoms in surface sediments of the southwestern atlantic based on 66 surface sediment samples collected in the sw atlantic ocean between 27 and 50 s this study presents an overview of the spatial distribution of biogenic opal and diatom concentrations and diatom assemblages biogenic opal has highest values in the deepest pelagic stations and decreases toward the slope diatoms closely follow the spatial trend of opal diatom assemblages reflect the present day dominant hydrographical features antarctic diatoms are the main contributors to the preserved diatom community in core top sediments with coastal planktonic and tropical subtropical diatoms as secondary components dominance of antarctic diatoms between 35 and 50 s in the pelagic realm mirrors the northward displacement of antarctic source water masses characterized by high nutrient content and low salinity northward of ca 35 s the highest contribution of tropical subtropical pelagic diatoms typical for nutrient poor and high salinity waters matches the main southward path of the brazil current mixing of antarctic and tropical waters down up to 45 s is clearly illustrated by the diatom assemblage concentrations of biogenic opal and diatoms rather reflect the path of predominant water masses but are less correlated with surface water productivity in the sw atlantic

the structure degradation of a silty loess induced by long term water seepage abstract loess is a typical silt sized aeolian soil that is widely deposited and possesses a fragile soil structure susceptible to collapse upon wetting the instability of shallow loess slopes is well documented but deeper failures triggered by rainfall and irrigation can also occur in the case of long term seepage clay particles and salts have been observed to leach out of the loess slopes this paper presents a systematic laboratory study of the effects of water conditions on the mechanical behaviour of silty loess with isotropic compression and bender element tests carried out on natural and reconstituted loess recovered at 10 m depth from a site in china the results show that saturation causes reduction in both the compression yield stress and small strain stiffness of the soil and that after being exposed to seepage they decrease further the possible mechanism of structure degradation is investigated by means of microscopic and chemical analyses and it is found that seepage will cause the pore ions concentration to reduce with a loss of clay mineral bonding strength resulting in the detachment of silt particles from aggregates this work highlights the importance of monitoring the water outflow in the field at the loess slope edge since it may causes large deformation in the long term

a high resolution sub aerial and sub aqueous laser based laboratory beach profile measurement system abstract this note presents a new method for high resolution beach profiling in small and medium scale laboratory wave flumes the combined use of laser distance sensors for elevation z measurements and a barcode reader for cross shore x coordinates provides a non contact rapid and accurate method to measure beach profiles through the water surface the system reduces errors from wheeled or contact sensors and eliminates the need to drain the wave tank to perform measurements the need for a bed follower or motorised traverse and encoder is also eliminated the system resolves the beach profile both below and above the waterline with x and z coordinates provided with 1 mm resolution and repeatability of 1 mm so also resolving wave ripples to a high level of detail the method is demonstrated with an array of 8 sensors spaced across a 1 m wide tank which enables accurate calculation of the cross shore distribution of the total sediment transport at short intervals using multiple beach profiles to account for minor cross tank variation in the bed elevation

loess geology and surface processes an introductory note abstract loess is a type of quaternary sediments of the wind origin in arid and semi arid regions this type of sediment is widely and thickly distributed in china forming the loess plateau which is the largest bulk accumulation of loess on the earth the loess plateau of china has received great attention from scientific communities including geologists geophysicists and engineers worldwide accordingly a wealth of investigations has been undertaken on various problems arising in this area however some scientific questions remain relevant and unresolved these questions mainly present in the areas of evolution and surface processes of loess landform depositional environments of loess sediments impacts due to neotectonics and fault activities in loess areas and natural and man made geohazards in recent years extensive innovative studies have been carried out to further understand the above mentioned topics substantial new data theories and insights have become available this special issue provides a timely overview on the recent case histories theoretical advances laboratory and field testing and state of art methods in the theme of loess geology and surface processes the papers gathered in this special issue are introduced in this article

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

determination of the shear strength parameters of an unsaturated soil using the direct shear test multistage direct shear tests have been performed on saturated and unsaturated specimens of a compacted glacial till a conventional direct shear apparatus was modified in order to use the axis tra

vertical structure of pore pressure under surface gravity waves on a steep megatidal mixed sand gravel cobble beach the vertical structure of surface gravity wave induced pore pressure is investigated within the intertidal zone of a natural steeply sloping megatidal mixed sand gravel cobble beach results from a coherent vertical array of buried pore pressure sensors are presented in terms of signal phase lag and attenuation as functions of oscillatory forcing frequency and burial depth comparison of the observations with the predictions of a theoretical poro elastic bed response model indicates that the large observed phase lags and attenuation are attributable to interstitial trapped air in addition to the dependence on entrapped air volume the pore pressure phase and attenuation are shown to be sensitive to the hydraulic conductivity of the sediment to the changing mean water depth during the tidal cycle and to the redistribution rearrangement of beach face material by energetic wave action during storm events the latter result indicates that the effects on pore pressure of sediment column disturbance during instrument burial can persist for days to weeks depending upon wave forcing conditions taken together these results raise serious questions as to the practicality of using pore pressure measurements to estimate the kinematic properties of surface gravity waves on steep mixed sand gravel beaches

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

a numerical empirical approach for evaluating morphodynamic processes on gravel and mixed sand gravel beaches abstract pedrozo acuna et al pedrozo acuna a simmonds d j otta a k and chadwick a j 2006 on the cross shore profile change of gravel beaches coastal engineering 53 4 335 347 presented a numerical empirical investigation of the processes that control sediment transport in the swash zone on steep gravel beaches this was based on a sensitivity analysis of a sediment transport profile model driven by a highly non linear boussinesq model lynett p j wu t r and liu l f p 2002 modelling wave run up with depth integrated equations coastal engineering 46 89 107 which was compared to near full scale measurements performed in the gwk flume in hanover in this paper we have extended our analysis to compare these earlier results with those relating to a mixed sediment gravel and sand beach the parametric sensitivity analysis also incorporates a discussion of the effects of acceleration about which there is much debate the sensitivity analysis suggests that fluid acceleration can contribute to the onshore movement of sediment that causes steepening of initially flat beach faces composed of coarse sediment however acceleration alone cannot be the cause of the observed berm growth during the gwk tests instead a complex balance of processes is responsible for the profile evolution of coarse grained beaches with no single dominant process

the role of combined laser scanning and video techniques in monitoring wave by wave swash zone processes abstract simulating swash zone morphodynamics remains one of the major weaknesses of beach evolution models one of the reasons is the limited availability of data on morphological changes at the temporal scales of individual swash events this paper sets out to present a new hybrid system consisting of 2d 3d laser scanners and several video cameras which was designed to monitor swash zone topographic change on a wave by wave basis a methodology is proposed consisting of sensor calibration and several data processing steps allowing a fusion of different sensors such an approach can improve the performance of several field laboratory optical technique applications for nearshore hydro and morpho dynamic measurements digital elevation models from a 3d scanner were used in the extrinsic camera calibration procedure and reduced the geo rectification errors from 0 035 m dz 10 cm the sediment transport direction and intensity of the monitored swash events was relatively balanced and sediment transport rates ranged between 3 5 kg m 1 s 1 q t 3 5 kg m 1 s 1 extreme transport swash events became rarer as the morphology was reaching equilibrium

experimental study on the effect of water gushing on loess metro tunnel in the construction of metro tunnels water gushing accidents caused by the rupture of underground pipeline often occur and in loess area the collapsibility of loess makes this problem more complex and difficult to investigate the damage of metro tunnel caused by collapsible loess under the action of local dynamic water gushing water a model experiment was conducted based on the pipeline water gushing accident happened in the construction of metro tunnel located in loess area through the study of similar materials of loess and tunnel lining the test materials and apparatus were prepared according to similarity criterion by simulating water gushing environment in the loess stratum this paper analyzed mechanical characteristics of tunnel water pressure of surrounding rock contact pressure and internal force of tunnel lining and deformation of surrounding rock and tunnel furthermore combining with the process of local collapse of loess in the model experiment it is concluded that the formation of water transport channel is the main reason for the difference of tunnel structural response when water gushing occurs at different locations finally a three dimensional spatial model of water transport channel in loess stratum under the environment of local water gushing was established to study the rule of water transport

large scale experiments on gravel and mixed beaches experimental procedure data documentation and initial results abstract this paper provides information on the experimental set up data collection methods and results to date for the project large scale modelling of coarse grained beaches undertaken at the large wave channel gwk of fzk in hannover by an international group of researchers in spring 2002 the main objective of the experiments was to provide full scale measurements of cross shore processes on gravel and mixed beaches for the verification and further development of cross shore numerical models of gravel and mixed sediment beaches identical random and regular wave tests were undertaken for a gravel beach and a mixed sand gravel beach set up in the flume measurements included profile development water surface elevation along the flume internal pressures in the swash zone piezometric head levels within the beach run up flow velocities in the surf zone and sediment size distributions the purpose of the paper is to present to the scientific community the experimental procedure a summary of the data collected some initial results as well as a brief outline of the on going research being carried out with the data by different research groups the experimental data is available to all the scientific community following submission of a statement of objectives specification of data requirements and an agreement to abide with the gwk and eu protocols

high frequency in situ field measurements of morphological response on a fine gravel beach during energetic wave conditions this paper presents novel data collected over four weeks at loe bar a fine gravel barrier d50 3 5 mm exposed to energetic wave conditions hs10 2 4 m combined remote and in situ measurements were used to identify 3d morphological response profile change and runup behaviour during successive energetic periods hs 2 5 m small intertidal beach volume losses occurred under high steepness waves h0 l0 0 01 but in general the overall beach volume was remarkably stable in fact the greatest morphological response was evident not in cross shore sediment exchanges but due to the alongshore redistribution related to the three dimensional beach cusp system specifically during energetic wave conditions the cusp morphology underwent horn growth and embayment deepening leading to increased cusp definition an additional explanation for the stability of the cross shore beach profile is related to the development of the beach step during energetic conditions and long period waves significant deposition c 1 m occurred at the top of the beach step above the still water line the enhanced step provided a focal point for wave breaking considerably curtailing the swash motion and reducing the runup limit thereby providing protection to the upper beach this study provides much needed insight into complex morphological response and runup characteristics on gravel beaches fundamental for improved model development and leading towards better predictive tools

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

on the cross shore profile change of gravel beaches abstract this paper investigates cross shore profile changes of gravel beaches with particular regard to discussing the tendency for onshore transport and profile steepening in the swash zone the discussion includes observed morphological changes on a gravel beach from experimental investigations at the large wave flume gwk in hanover germany during the tests all the profile changes occurred in the swash zone resulting in erosion below the still water line swl and formation of a berm above the swl we investigate the profile evolution evaluating the transport rates from a bed load sediment transport formulation coupled with velocities calculated from a set of boussinesq equations that have been validated for its use in the surf and swash zones lynett p j wu t r and liu l f p 2002 modelling wave runup with depth integrated equations coastal engineering 46 89 107 otta a k and pedrozo acuna a 2004 swash boundary and cross shore variation of horizontal velocity on a slope in j m smith editor proceedings 29th international conference on coastal engineering world scientific lisbon portugal pp 1616 1628 we discuss the influence of bottom friction on the predicted profiles using reported friction factors from experimental studies it is shown that the use of a different friction factor within a realistic range in each phase of the swash uprush and backwash improves prediction of the beach profiles although quantitative agreement between the measured and computed profile evolutions is not satisfactory furthermore if the friction factor and the transport efficiency c of the sediment transport formulation are kept the same in the uprush and backwash accurate representation of profile evolution is not possible indeed the features of the predicted profiles are reversed however when the c parameter is set larger during the uprush than during the backwash the predicted profiles are closer to the observations differences between the predicted profiles from setting non identical c values and friction factors for the swash phase are believed to be linked to both the infiltration effects on the flow above the beachface and the more accelerated flow in the uprush

coupling cross shore and longshore sediment transport to model storm response along a mixed sand gravel coast under varying wave directions abstract this paper investigates the profile response of a mixed sand gravel deltaic beach playa granada southern spain forced by storm waves from varying directions beach morphology was monitored over a 36 day period with variable wave conditions and profile response was compared to model predictions using the xbeach g model and a longshore sediment transport lst formulation xbeach g was applied over 2 day periods of low energy south westerly sw storm and south easterly se storm conditions and was coupled to lst using a parametric approach which distributes the lst across the swash surf and nearshore zones a calibrated wave propagation model delft3d was used to obtain the inshore conditions required to drive the xbeach g model and the lst formulation the storm response is clearly influenced by the free board difference between the height of the berm and the total run up and is also strongly dependent on storm wave direction with the sw storm eroding the surveyed area while the se storm induced beach accretion model results indicate that xbeach g on its own is capable of adequately reproducing the response of the beach under sw storm conditions b s s 0 95 but not under se storms due to the higher lst gradients at the study location the combination of xbeach g and lst fits the measured profiles reasonably well under both sw b s s 0 96 and se b s s 0 88 storms inspiring confidence in the coupled model to predict the storm response under varying wave conditions the combined xbeach g lst model was applied to the entire 6 8 km deltaic coastline to investigate the impact of extreme sw and se storm events and the model results reiterate the importance of cross shore and longshore sediment transport in driving coastal storm response at this location the approach proposed in this work can be extended to other worldwide coasts highly influenced by both cross shore and longshore sediment transport such as beaches with different coastline orientations and or forced by varying wave directions

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

a stratigraphic network across the subtropical front in the central south atlantic multi parameter correlation of magnetic susceptibility density x ray fluorescence and δ18o records abstract computer aided multi parameter signal correlation is used to develop a common high precision age model for eight gravity cores from the subtropical and subantarctic south atlantic since correlations between all pairs of multi parameter sequences are used and correlation errors between core pairs a b and b c are controlled by comparison with a c the resulting age model is called a stratigraphic network precise inter core correlation is achieved using high resolution records of magnetic susceptibility wet bulk density and x ray fluorescence scans of elemental composition additional 18o records are available for two cores the data indicate nearly undisturbed sediment series and the absence of significant hiatuses or turbidites after establishing a high precision common depth scale by synchronously correlating four densely measured parameters fe ca the final age model is obtained by simultaneously fitting the aligned 18o and records of the stratigraphic network to orbitally tuned oxygen isotope j imbrie j d hays d g martinson a mcintyre a c mix j j morley n g pisias w l prell n j shackleton the orbital theory of pleistocene climate support from a revised chronology of the marine 18o record in a berger j imbrie j hays g kukla b saltzman eds milankovitch and climate understanding the response to orbital forcing reidel publishing dordrecht 1984 pp 269 305 d martinson n pisias j hays j imbrie t c moore jr n shackleton age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy quat res 27 1987 1 29 or susceptibility stacks t von dobeneck f schmieder using rock magnetic proxy records for orbital tuning and extended time series analyses into the super and sub milankovitch bands in g fischer g wefer eds use of proxies in paleoceanography examples from the south atlantic springer verlag berlin 1999 pp 601 633 besides the detection and elimination of errors in single records the stratigraphic network approach allows to check the intrinsic consistency of the final result by comparing it to the outcome of more restricted alignment procedures the final south atlantic stratigraphic network covers the last 400 kyr south and the last 1200 kyr north of the subtropical front stf and provides a highly precise age model across the stf representing extremely different sedimentary regimes this allows to detect temporal shifts of the stf by mapping mn fe it turns out that the apparent stf movements by about 200 km are not directly related to marine oxygen isotope stages

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

wave impact characteristics of plunging breakers acting on gravel beaches abstract this paper presents observations of pressure impulses from wave impacts of breaking waves on steep coarse grained beaches it builds upon recent investigations on gravel beaches which suggest the wave impact of a plunging breaker is an important process that shapes the morphology of these beaches and that is not taken into account under many modelling frameworks pedrozo acuna a simmonds d j chadwick a j and silva r 2007 a numerical empirical approach for evaluating morphodynamic processes on mixed and gravel beaches mar geol 241 1 2 1 18 full scale laboratory measurements of induced pressures by plunging breakers acting on gravel beaches are reported showing that these are more significant than those reported for sandy beaches under the forcing of similar wave conditions additionally four different types of pressure curves are identified and classified in terms of the type of forcing behind its generation it is shown that measured impact pressures within the gravel beach are a consequence of plunging breakers propagating over the beach profile with maximum pressure values being up to 4 5 times the quasi hydrostatic induced pressure for a given wave height it is demonstrated that the largest measured impacts are not only related to larger values of wave height and vertical displacement of the free surface but also to the wave steepness of the incident wave results suggest that between two plunging breakers of the same height the steeper will produce a stronger wave impact the plunging of breakers onto a gravel beachface and the ensuing pressure gradients are suggested as a key mechanism for understanding sediment transport and the resulting morphology of gravel beaches

a review of the geotechnical characteristics of loess and loess derived soils from canterbury south island new zealand abstract loess and loess derived soils cover much of canterbury from the foothills of the southern alps to the pacific coast these deposits are of variable thickness from a few metres up to 40 m at the base of slopes on banks peninsula in many areas the primary air fall loess has been reworked by slope processes to form a loess colluvium although primarily silty these soils contain up to 45 clay giving rise to low plasticity clay behaviour these deposits are relatively dense with dry densities of 1 6 t m3 and 1 8 t m3 hence they do not display collapse behaviour common to other loess deposits around the world loess and loess derived soils across canterbury have high dry strength but weaken rapidly with small increases in moisture content in the wetter parts of the region on banks peninsula in particular periodic wetting leads to a variety of slope failures related to internal erosion tunnel gullying and rapid loss of shear strength debris flows soil slides and rotational failure elsewhere in the drier parts of south canterbury loess deposits commonly form vertical exposures and evidence of slope instability is comparatively rare the current understanding of the geotechnical characteristics of these deposits is based on a limited number of studies with restricted geographic extent thus a full understanding of regional and stratigraphic variability is yet to be established macroscale heterogeneities including fissuring development of fragipan cemented horizons and stratification indicates that as well as the general behaviour presented in this paper there may also be significant local variation in addition the effects of soil microstructure including bonding and particle shape and orientation on overall soil behaviour are recognised but have yet to be investigated in detail

relative variations in geomagnetic intensity from sedimentary records the past 200 000 years abstract eighteen records of relative paleointensity from marine sediments have been compiled in order to retrace the global changes in geomagnetic intensity during the past 200 kyr before dealing with any other source of noise we focused on problems inherent to the depth versus time correlations the accuracy and resolution of dating mostly deduced from isotopic stratigraphy were identified as significant factors of distortion we found also that different time scales have been used by authors after readjustment with respect to the same time scale the records were stacked together and the statistical significance of the results tested by a bootstrap technique seventeen records shown to be coherent were combined into a synthetic curve defined as sint 200 other stacks combining various subsets of data were found to be identical to sint 200 except for changes in dispersion in fact the dispersion around sint 200 could be reduced further by improving the correlations without violating the stratigraphy a procedure which at least for some records emphasizes the need for more detailed depth time correlations another characteristic emerging from the results is that paleointensity features as short as 10 kyr are observed between 120 200 ka and can thus in principle be resolved however subsequent refinement is still necessary for this period which is documented by fewer records than the following 120 kyr finally we compared sint 200 with the records from the labrador sea and the lac du bouchet ldb both of which rely mostly on 14c chronology the two records show satisfactory agreement with sint 200 when transferred with respect to the age model established by correlating their 18o labrador and susceptibility features ldb with the 18o reference record the offset of 7 kyr at 40 ka measured in both cases between the 14c and 18o ages is higher than the value deduced from a recent model of a geomagnetic field control of 14c production 1 but is not inconsistent with recent u th dates

experimental evaluation of mechanical behavior of unsaturated silty sand under constant water content condition abstract there are very few experimental data on the mechanical behavior of unsaturated soils particularly in constant water content condition because of the technical difficulties and time consuming nature of measuring suction and deformation this paper presents the results of a series of constant water constant triaxial tests on the specimens of an unsaturated silty sand constant water content tests correspond to a field condition where the rate of loading is much quicker than the rate at which the pore water is able to drain out of the unsaturated soil the axis translation technique and a double walled triaxial cell have been used to measure the soil matric suction and variation of pore air volume respectively test specimens were prepared at two different compaction conditions prior to testing to achieve different initial density it is found that the mechanical behavior of the soil mainly depends on the initial density the mean net stress and the initial matric suction also the volume and pore water pressure changes are significantly different in specimens with different initial condition the results of tests indicated that the shearing strength of silty sand increases non linearly with matric suction

experimental study on the shear behavior of loess and paleosol based on ring shear tests abstract landslide hazards frequently occur in the chinese loess plateau every year causing devastating casualties damage to engineering structures and reduction in land resources this work presents an experimental investigation of four samples retrieved from jingyang in the southeast of the chinese loess plateau using ring shear tests and microscopic observation in an attempt to explore the shear behavior of loess and paleosol under the larger deformations that are involved in landslide hazards the results of ring shear tests reveal that the loess and paleosol samples exhibited different strength characteristics the residual strength envelopes could be assumed to be a straight line and the overconsolidated state had negligible influence on the residual shear strength after the shear experiment shear bands were studied from both macroscopic and microscopic perspectives macroscopic observation and mechanical analysis indicate that all samples developed a main horizontal failure plane related to the maximum shear stress while loess samples also developed en echelon failure planes tilting from the horizontal at angles of 14 18 which are interpreted as coulomb slip planes scanning electron microscopy reveals that the particles inside shear bands tend to be re oriented particle crushing occurred in the shear process which was also verified by particle size distribution analysis

a first order correction to minimize environmental influence in sedimentary records of relative paleointensity of the geomagnetic field we propose a simple method to minimize the residual environmental influence which may exist in paleointensity records obtained from sediments it consists of adding or subtracting a fraction of the normalizer arm or irm to the normalized intensity record so that the corrected record exhibits fluctuations uncorrelated with those of the normalizer this method was tested with paleointensity records obtained from two cores taken at midlatitude in the south indian ocean cores eastward of the kerguelen plateau for each core correction increases the correlation between the three normalized intensity records nrm nrm arm and nrm irm it also reduces the coherence between paleointensity records and bulk magnetic parameters used as normalizers although it has to be used with caution this correction may improve paleointensity records by reducing nongeomagnetic influence it can also be used to detect intervals where paleointensity may be unreliable i e intervals where large differences between uncorrected and corrected records are observed before and after correction

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