identifying the effects of parameter uncertainty on the reliability of modeling the stability of overhanging multi layered river banks abstract composite river banks consist of a basal layer of non cohesive material overlain by a cohesive layer of fine grained material in such banks fluvial erosion of the lower non cohesive layer typically occurs at a much higher rate than erosion of the upper part of the bank consequently such banks normally develop a cantilevered bank profile with bank retreat of the upper part of the bank taking place predominantly by the failure of these cantilevers to predict the undesirable impacts of this type of bank retreat a number of bank stability models have been presented in the literature these models typically express bank stability by defining a factor of safety as the ratio of resisting and driving forces acting on the incipient failure block these forces are affected by a range of controlling factors that include such aspects as the overhanging block geometry and the geotechnical properties of the bank materials in this paper we introduce a new bank stability relation for shear type cantilever failures that considers the hydrological status of cantilevered riverbanks while beam type failures are analyzed using a previously proposed relation we employ these stability models to evaluate the effects of parameter uncertainty on the reliability of riverbank stability modeling of overhanging banks this is achieved by employing a simple model of overhanging failure with respect to shear and beam failure mechanisms in a series of sensitivity tests and monte carlo analyses to identify for each model parameter the range of values that induce significant changes in the simulated factor of safety the results show that care is required in parameterising i the geometrical shape of the overhanging block and ii the bank material cohesion and unit weight as predictions of bank stability are sensitive to variations of these factors

late cenozoic sedimentation of nihewan basin central north china and its tectonic significance abstract late cenozoic sediments of the nihewan basin in the northeastern part of the shanxi graben north china craton include buried late neogene rocks and exposures of the pliocene yuxian formation the pleistocene nihewan formation and xiaodukou formation with the age at least from 3 6 to 0 11 ma the sedimentary succession records the tectonic processes of the graben in the eastern nihewan basin on the basis of sedimentary facies and provenance analysis we have identified three main evolution stages during the late cenozoic the first stage was rapid expansion of the basin in the neogene which is thought to have commenced at least from 3 6 ma and lasted until 2 6 ma this stage is characterized by lacustrine facies dark colored mud and silt in depocenter of the basin with a potential source area from the northeast of the basin the following stage was a period of contraction at 2 6 1 8 ma characterized by deltaic deposits in depocenter of the basin and braided fluvial deposits in northeast margin of the basin and the deposition of cross bedded sands that were derived from erosion of archean proterozoic paleozoic and jurassic rocks from the north northwest and south of the basin the last stage was one era of gradually extinction of the basin from 1 8 to 0 11 ma followed by dried up of the basin and replaced by loess sediments were deposited in deltaic in depocenter of the basin and alluvial fan in northeast margin of the basin these coarse grained sands and pebbles were derived mainly from north and north northeast of the basin and generally from archean proterozoic and paleozoic rocks these three stages and the conversion ages 2 6 1 80 and 0 11 ma are largely consistent with three episodes of tibetan plateau rapid uplift therefore we infer that the evolution of the nihewan basin was predominantly influenced by the far field effect of the progressive uplift and northeastward expansion of the tibetan plateau

characteristics of surface soil creep on a forest slope in japan abstract soil creep was monitored for 6 years using the strain probe method and compared to soil moisture conditions in order to reveal details of the soil creep mechanism on a forest slope in a weathered granite area of central japan the results revealed a relationship between soil creep and soil moisture changes bending strain of the topsoil was induced downslope by soil drying and was reversed by soil wetting however an amount of bending strain remained which accumulated annually to form net soil creep on the upper slope when rainfall exceeded a certain threshold miniature sliding sometimes occurred caused by soil destruction in areas where shear deformation became concentrated on the middle slope topsoil deformation was more complex in order to monitor the soil creep phenomenon related to the concentration of shear deformation in a narrow zone improvement of the strain probe method is needed

macroscopic turbulence models and their application in turbulent vegetated flows turbulent flow in porous media terrestrial and aquatic canopies and urbanlike roughness is usually investigated using the macroscopic approach which is based on the volume average theory vat two different methodologies have been developed in the past leading to different equations for both the mean and the turbulence quantities time averaging the volume averaged equations and volume averaging the time averaged equations in this study four models of the volume averaging methodology are applied for modeling the flow in open channels with submerged vegetation the vegetation is considered rigid simulated as cylindrical roughness in a staggered or nonstaggered arrangement three of the models are of the k e type and one is of the reynolds stress type the latter has been applied using a modified e equation to account for the extra dissipation attributable to vegetation numerical results for both mean and turbulence flow characteristics are compared against available experimental measurements for dense canopies under shallow and deep flow conditions in addition relevant characteristics displacement thickness canopy shear layer parameter mixing length penetration length scale and etc are calculated for both computed and experimental data for assessing the performance of the models

velocity distribution characteristics in meandering compound channels with one sided vegetated floodplains abstract to discuss the effects of asymmetrically vegetated floodplains on the velocity distribution characteristics and discharge capacity of a meandering main channel in this paper continuous river bend models with smooth floodplains and one sided vegetated floodplains were designed in a generalized way three dimensional instantaneous velocity data were obtained with an acoustic doppler velocimeter adv and the velocity distribution characteristics and discharge capacities of the generalized models were compared compared with the smooth floodplain conditions the one sided vegetated floodplain conditions are associated with lower cross sectional average velocities lower ratios of main channel discharge to total discharge near the bending apexes with minimal extension of vegetated floodplain but higher ratios near the bending apex with maximal extension of vegetated floodplain the deflection degrees of depth averaged velocities in the meandering main channel are related to the cross sectional position relative depth and floodplain vegetation the depth averaged velocities near the bending apexes are inclined towards the main channel concave sides those in the upstream crossover area are generally inclined towards the vegetated side and those in the downstream crossover area are obviously inclined towards the smooth side for a given relative depth the deflection degrees near the bending apexes are smaller than those in the crossover areas the deflection degrees near the bending apexes with minimal extension of vegetated floodplain are smaller than those under smooth floodplain conditions but the deflection degrees near the bending apex with maximal extension of vegetated floodplain are obviously larger than the corresponding values under smooth floodplain conditions near the bending apexes the longitudinal depth averaged velocities are higher close to the main channel convex side and lower adjacent to the concave side when the relative depth is small one sided vegetated floodplain conditions feature larger transverse gradients of the cross sectional longitudinal depth averaged velocities near the bending apexes with minimal extension of vegetated floodplain when the relative depth is large the transverse gradients near the bending apexes with minimal extension of vegetated floodplain are all much smaller than the corresponding values of the smooth floodplain conditions however near the bending apex with maximal extension of vegetated floodplain there are no significant differences concerning the transverse gradients of the cross sectional longitudinal depth averaged velocities under the both floodplain conditions one sided vegetated floodplain conditions significantly influence the longitudinal velocity distributions in the meandering main channel for a given relative depth the longitudinal velocities at the cross sectional positions under one sided vegetated floodplain conditions are lower than those under smooth floodplain conditions to varying extents

automated upscaling of river networks for macroscale hydrological modeling 1 we developed a hierarchical dominant river tracing drt algorithm for automated extraction and spatial upscaling of basin flow directions and river networks using fine scale hydrography inputs e g flow direction river networks and flow accumulation in contrast with previous upscaling methods the drt algorithm utilizes information on global and local drainage patterns from baseline fine scale hydrography to determine upscaled flow directions and other critical variables including upscaled basin area basin shape and river lengths the drt algorithm preserves the original baseline hierarchical drainage structure by tracing each entire flow path from headwater to river mouth at fine scale while prioritizing successively higher order basins and rivers for tracing we applied the algorithm to produce a series of global hydrography data sets from 1 16 to 2 spatial scales in two geographic projections wgs84 and lambert azimuthal equal area the drt results were evaluated against other alternative upscaling methods and hydrography data sets for continental u s and global domains these results show favorable drt upscaling performance in preserving baseline fine scale river network information including 1 improved automated extraction of flow directions and river networks at any spatial scale without the need for manual correction 2 consistency of river network basin shape basin area river length and basin internal drainage structure between upscaled and baseline fine scale hydrography and 3 performance largely independent of spatial scale geographic region and projection the results of this study include an initial set of drt upscaled global hydrography maps derived from hydro1k baseline fine scale hydrography inputs these digital data are available online for public access at ftp ftp ntsg umt edu pub data drt

timing of the nihewan formation and faunas abstract magnetostratigraphic dating of the fluvio lacustrine sequence in the nihewan basin north china has permitted the precise timing of the basin infilling and associated nihewan mammalian faunas the combined evidence of new paleomagnetic findings from the hongya and huabaogou sections of the eastern nihewan basin and previously published magnetochronological data suggests that the nihewan formation records the tectono sedimentary processes of the plio pleistocene nihewan basin and that the nihewan faunas can be placed between the matuyama brunhes geomagnetic reversal and the onset of the olduvai subchron 0 78 1 95 ma the onset and termination of the basin deposition occurred just prior to the gauss matuyama geomagnetic reversal and during the period from the last interglaciation to the late last glaciation respectively suggesting that the nihewan formation is of late pliocene to late pleistocene age the nihewan faunas comprising a series of mammalian faunas such as maliang donggutuo xiaochangliang banshan majuangou huabaogou xiashagou danangou and dongyaozitou are suggested to span a time range of about 0 8 2 0 ma the combination of our new and previously published magnetostratigraphy has significantly refined the chronology of the terrestrial nihewan formation and faunas

stepwise expansion of desert environment across northern china in the past 3 5 ma and implications for monsoon evolution abstract a systematic study of the last glacial cycle along three transects across the chinese loess plateau shows that sand sized particle content within loess decreases rapidly from north to south and that markedly high sand particle contents in loess horizons occur only in the northern part of the plateau this suggests that variation in the sand sized particle fraction within loess near the desert margin is closely linked to migration of the southern desert border in northern china where sand grains move mainly in saltation or modified saltation mode near the ground surface as desert margin shift is essentially controlled by the amount of monsoon precipitation the sand sized particle content within loess near desert margin is regarded as a new and readily applied proxy for variations in the strength of the east asian summer monsoon a continuous record of sand content in loess along the loess desert transitional zone shows that the mu us desert migrated southward at 2 6 1 2 0 7 and 0 2 ma suggesting a stepwise weakening of the east asian summer monsoon during the past 3 5 ma this evolutionary pattern is significantly different from that previously inferred from loess magnetic susceptibility records a widely used monsoon proxy our results further suggest that changes in global ice volume may have been an essential factor in controlling plio pleistocene monsoon evolution and that the anticipated future melting of polar ice cover may lead to a northward migration of the monsoon rainfall belt in northern china

multiple expansions of c4 plant biomass in east asia since 7 ma coupled with strengthened monsoon circulation the expansion of plants using the c4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the cenozoic era a significant late miocene expansion is well documented however the existence and cause of subsequent expansions are still not clear owing in part to the lack of long continuous climate vegetation records here we present two high resolution carbon isotope time series covering the past 7 m y derived from eolian deposits on the chinese loess plateau the data indicate three intervals of significant c4 plant expansions within the semiarid monsoonal region of east asia ca 2 9 2 7 ma 1 3 0 9 ma and 0 6 ma present these expansions covary with strengthened east asian summer monsoon circulation we conclude that in east asia large scale late miocene c4 c3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation

evidence for a geomagnetic excursion recorded in the sediments of lac st front france a link with the laschamp excursion anomalous paleomagnetic directions accompanied by low intensities of natural remanent magnetization are recorded at 17 m depth in the sediments cored from lac st front massif central france the rock magnetic properties and the parameters characterizing anisotropy of susceptibility of samples taken from the sediment horizons carrying these anomalous directions spanning some 30 40 cm are identical to those of samples taken from the other stratigraphic intervals carrying a record of normal geomagnetic secular variation therefore the sequence of anomalous directions is interpreted as a geomagnetic excursion furthermore it is concluded that this excursion occurred at a time when the paleointensity field was low the excursion is dated at about 33 14c 37 ka b p by correlating the susceptibility and paleomagnetic logs from lac st front with the corresponding logs from the nearby lac du bouchet sedimentary sequence the excursional directions in lac st front can be averaged out with a triangular window of 20 cm these smoothed excursional directions resemble the directional variations observed in the corresponding lac du bouchet interval this finding indicates that the absence of this excursion in lac du bouchet may be due to a larger smoothing of the geomagnetic signal

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

early to late pleistocene human settlements and the evolution of lithic technology in the nihewan basin north china a macroscopic perspective the paleolithic of the nihewan basin is characterized by large numbers of sites a long term scale definite strata and rich cultural remains recently obtained evidence of human activities and dates indicate that the early to late pleistocene paleolithic sites in the nihewan basin form a concentrated time and cultural sequence lithic technology developed according to a continuous evolution model the development of the small tool industry is generalized as the donggutuo zhiyu also called shiyu series and the origin of microlithic technology could be traced back to the early pleistocene which supports the theory of local origin the complexity of lithic technology development is also discussed

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

effect of particle concentration on sediment and turbulent diffusion coefficients in open channel turbulent flow to achieve a complete knowledge about the effect of particle concentration on sediment and turbulent diffusion coefficients in open channel turbulent flow is a long standing problem for the community of researchers the effect of particle concentration is investigated on the sediment and turbulent diffusion coefficients through the inverse of turbulent schmidt number or which is defined by the ratio of sediment diffusion coefficient to turbulent diffusion coefficient it is observed that with increasing particle concentration the sediment diffusion coefficient decreases more in comparison with the turbulent diffusion coefficient for both dilute and non dilute sediment laden flows the physical characteristics of observed are expressed mathematically in terms of normalized settling velocity reference level and reference concentration the applicability of the mathematical formulae is confirmed by the agreement analysis between experimental data and particle concentration profile computed from the rouse equations modified through the newly proposed expression of apart from the better agreement between dilute particle concentration data and the developed rouse equation the striking observation is that the modified rouse equation shows reasonable computational accuracy for non dilute particle concentration data also minimum error is obtained from the present model when it is compared with the models proposed by the previous researchers

the mid pleistocene transition in the tropical pacific a sea surface temperature sst record based on planktonic foraminiferal magnesium calcium ratios from a site in the western equatorial pacific warm pool reveals that glacial interglacial oscillations in sst shifted from a period of 41 000 to 100 000 years at the mid pleistocene transition 950 000 years before the present sst changes at both periodicities were synchronous with eastern pacific cold tongue ssts but preceded changes in continental ice volume the timing and nature of tropical pacific sst changes over the mid pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time

magnetostratigraphic dating of the donggutuo and maliang paleolithic sites in the nihewan basin north china a detailed magnetostratigraphic investigation coupled with rock magnetic studies was carried out on a lacustrine sequence in the eastern nihewan basin northern china which contains the donggutuo and maliang paleolithic sites magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations magnetostratigraphic results show that the lacustrine sequence recorded the late matuyama and brunhes chrons furthermore the maliang artifact layer occurs just below the brunhes matuyama boundary and the donggutuo artifact layer is just below the jaramillo onset therefore the age of the maliang and donggutuo artifact layers can be definitely estimated to be about 0 78 myr and 1 1 myr respectively these two paleomagnetic ages coupled with previously obtained paleomagnetic data of the majuangou xiaochangliang banshan lantian and xihoudu paleolithic sites suggest an expansion and lengthy flourishing of human groups from northern to north central china during the entire early pleistocene

the nihewan basin of north china in the early pleistocene continuous and flourishing or discontinuous infrequent and ephemeral occupation the prevailing interpretation of the evidence for early pleistocene hominin occupation of the nihewan basin north china is that it indicates continuous settlement by hominins that were able to adapt to a wide variety of environmental conditions ranging from full interglacial to full glacial it has further been suggested that they were able to do so by the routine hunting of large mammals this paper argues that there is no evidence that hominins inhabited the nihewan basin year round or under cold conditions and no evidence that they hunted instead it is suggested that hominins are likely to have visited nihewan during the summer months and probably avoided it when conditions were significantly colder than today this scenario is consistent with what is known of the climatic sensitivity of the earliest hominin occupation of other regions in eurasia at comparable latitudes such as the chinese loess plateau tajikistan the caucasus and spain and in similar strongly seasonal environments with sub freezing winters such as britain overall hominin settlement in the nihewan basin was likely discontinuous infrequent and ephemeral

magnetostratigraphic dating of the danangou and dongyaozitou mammalian faunas in the nihewan basin north china abstract the fluvio lacustrine sequences in the nihewan basin of north china are rich sources of mammalian faunas and paleolithic sites thus providing unique insights into our understanding of land mammal biochronology and early human settlements in east asia among the nihewan fauna sensu lato the danangou dng and dongyaozitou dz faunas are two of the important pleistocene and pliocene mammalian faunas in the nihewan basin except for a biostratigraphy precise age control on the dng and dz faunas remains unavailable here we report high resolution magnetostratigraphy results that stringently constrain their ages the results show that the dng sequence recorded the brunhes normal chron the matuyama reverse chron and the late gauss normal chron yielding the fossil rich layers of dng fauna with an age of ca 1 95 ma to 1 78 ma during the olduvai normal subchron the dz sequence was located at the late gauss normal chron yielding an age of ca 3 04 2 58 ma before the termination of the kaena reverse subchron

magnetostratigraphic evidence of a mid pliocene onset of the nihewan formation implications for early fauna and hominid occupation in the nihewan basin north china the fluvio lacustrine sediments in the nihewan basin of north china known as the nihewan formation are well known for an abundance of early pleistocene mammalian fossils known as the nihewan fauna sensu lato and paleolithic sites the age at which the sedimentation started is thus crucial for our understanding of early fauna and hominid occupation and infilling history of the basin but it is poorly constrained to date here we report on a detailed paleomagnetic investigation of the yangshuizhan section that crops out in the northeastern nihewan basin supplemented by rock magnetic analyses into the carriers of the natural remanent magnetization magnetite and hematite are shown to be the main carriers of the characteristic remanent magnetization magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the onset of the nihewan formation in this section occurs at w3 7 ma just below the gilbertegauss boundary and ca 1 myr earlier than previously established evidence this pushes the lower limit of the nihewan formation back in time from very late pliocene 2 8 ma to at least the mid pliocene combining the previously established magnetostratigraphic data with the present study we arrive at a better understanding of the chronological framework and spatio temporal history of the deposition of the terrestrial nihewan formation furthermore it provides new perspectives of early fauna and hominid occupation in the nihewan basin

magnetostratigraphic dating of the xiashagou fauna and implication for sequencing the mammalian faunas in the nihewan basin north china the nihewan basin sedimentary sequences in northern china are rich in mammalian fossil and paleolithic sites thus providing insights into our understanding of quaternary land mammal biochronology and early human settlements in east asia here we present high resolution magnetostratigraphic results that place stringent age controls on the xiashagou xsg fauna that is the well known nihewan fauna sensu stricto in the nihewan basin northern china results show that the xsg sequence recorded the brunhes normal chron the matuyama reverse chron and the late gauss normal chron the xsg fauna resides in the matuyama reverse chron between the pre reunion matuyama chron and the post olduvai matuyama chron yielding an estimated age of ca 2 2 1 7 ma the pliocene pleistocene boundary gauss matuyama boundary is located in the lower part of the xsg section the combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern nihewan basin can be placed between the gauss matuyama geomagnetic reversal and the matuyama brunhes geomagnetic reversal 2 58 0 78 ma leading to a time range of ca 2 6 0 8 ma for the nihewan mammalian faunas

magnetostratigraphic dating of the huojiadi paleolithic site in the nihewan basin north china the fluvio lacustrine sequences in the nihewan basin northern china provide important terrestrial archives of paleoclimate and paleoenvironment as well as an important source of paleolithic settlements and therefore early human occupation in the eastern old world magnetostratigraphic dating of the sequences has permitted the precise timing of the basin infilling and associated paleolithic and mammalian fauna sites here we report new magnetostratigraphic results that place stringent age controls on the huojiadi paleolithic site in this basin partially oxidized magnetite and hematite were identified as the major carriers for the characteristic remanent magnetizations magnetostratigraphic results show that the huojiadi sequence recorded the very late matuyama reverse chron and the jaramillo normal subchron the stone artifact layer resides in the jaramillo normal subchron yielding an estimated age of around 1 0 ma for the huojiadi paleolithic site furthermore by combining our magnetostratigraphy and previously published magnetochronology data a magnetochronological sequence of the early pleistocene paleolithic sites in the nihewan basin has been established the chronological sequence implies that early humans may have persistently colonized the high latitude temperate areas in the eastern old world such as the nihewan basin during the early pleistocene

new magnetostratigraphic dates of lantian homo erectus skeletal remains of homo erectus found in pleistocene loess at two sites near lantian in central china are of greatly different geologic age the cranium found in the fossil bearing strata at gongwangling is about 1 15 myr old whereas the remains found at the chenjiawo locality in middle pleistocene loess are about 0 65 myr old the dating is based on new paleomagnetic polarity determinations and on the lithostratigraphic position of the fossils in the loess paleosol sequence our results confirm that both localities are older than the first occupation of zhoukoudian new dates palaeoenvironmental settings and morphological features of the hominids from lantian localities have significant bearing on the understanding of adaptive radiations of the middle and late hominids in asia

vegetation succession and climate change during the early pleistocene 2 2 1 8 ma in the nihewan basin northern china abstract the nihewan formation northern china is ideal for studying environmental changes during the early pleistocene in conjunction with palaeomagnetic measurements pollen and grain size analyses were conducted on 120 samples from a 24 m long section 2 2 1 8 ma of core nha from the nihewan basin in order to reconstruct past vegetation and climatic changes the pollen assemblages were dominated by pinus indicating that the vegetation was primarily pine forest and that the climate was relatively warm and wet from 2 15 1 92 ma deciduous broad leaved tree pollen significantly increased to 10 of the total showing that more broad leaved trees grew in the study area during the warmest and wettest period in the study section from 1 92 1 78 ma coeval with the olduvai event pinus and broad leaved tree pollen types decreased the percentages of picea 20 artemisia and chenopodiaceae increased indicating that spruce forests expanded the openness of the forested areas increased and the climate became cold and dry the vegetation changes reconstructed during the olduvai period indicates that the climate in the nihewan basin was cold and dry relating to global cooling facilitated by the uplift of the tibetan plateau and the strengthening of the winter monsoon

paleoenvironmental conditions at madigou mdg a newly discovered early paleolithic site in the nihewan basin north china abstract paleoenvironmental reconstructions provide the context for human evolution and behavior however it is difficult to resolve relative proportions of specific habitats at a given place and time how these may have changed over time and the explicit nature of particular habitats for human adaptation this paper examines the paleoenvironmental context of early pleistocene archaeological occurrences at madigou hebei province north china but with particular emphasis on the setting for early stone tool makers madigou mdg is one of several early pleistocene paleolithic sites in the east part of the nihewan basin north china sedimentological features of the excavated section indicate that the site was formed near the margin of a lake paleomagnetic results suggest that hominins occupied the site ca 1 2 ma based on well constructed pollen sediment grain size magnetic susceptibility isotopic 13 c and 18 o and iron oxide analysis of the section excavated in 2011 and 2012 five stages of environmental change in the nihewan beds are identified in the earliest phase the environment and climate changed from 1 cool and semi humid with open grassland to 2 cold and dry with open sparse steppe usually temperate herbaceous not just grass and then 3 warm and humid climate with lightly wooded grassland followed by 4 cold and dry climate with sparse steppe and finally 5 temperate and semi humid with open grassland this evidence suggests that hominins occupied the site from stages 2 4 in an open habitat varying from lightly wooded grassland to an ecosystem dominated by sparse steppe

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

sedimentary record of two geomagnetic excursions within the last 15 000 years in beijing china a fresh water sedimentary sequence from haidian in the beijing basin has been sampled in three parallel trenches up to 300 m apart for paleomagnetic study age control is provided by nine radiocarbon dates indicating an average accumulation rate of 45 cm ka a total of 683 specimens were measured for paleomagnetic directions two short excursions of field direction are recorded at closely comparable depths in all three cores occurring between 5 060 and 4 860 90a b p and 14 230 and 13 690 130 a b p interpolated ages the paleomagnetic records for the individual trenches were adjusted to a common depth scale using stratigraphic markers and then merged the record correlates quite well with a paleomagnetic record in beijing basin sediments 55 km to the southwest changgou section with regard to both the large excursions and also some of the smaller variations in direction the excursions appear to reflect real geomagnetic phenomena not artifacts of recording but the spatial extent regional or global of the anomalous geomagnetic signals is not known

suspended load transport of sediment mixtures careful experiments were conducted on alluvial beds of four sediment mixtures having different arithmetic mean diameters and standard deviations the suspended load transport rates of individual fractions were measured and compared with both einstein s and holtroff s methods of calculation of suspended load for individual fractions these methods were found to be unsatisfactory in the present range of sediment parameters a relationship is found to exist between the dimensionless shear stress and the suspended transport rate for uniform sediment to make this relation applicable to nonuniform sediments a corrective multiplying factor for shear stress is introduced the dimensionless parameters which govern this correction factor are identified and a relation for the same obtained in this manner the relation can be applied to individual size portions of a sediment mixture

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

magnetic signature of environmental change reflected by pleistocene lacustrine sediments from the nihewan basin north china abstract a mineral magnetic study has been conducted on pleistocene lacustrine sediments from the xujiayao paleolithic site within the nihewan basin north china the magnetic signal is characterized by a dominance of high coercivity hematite minerals that is modulated by low coercivity magnetite maghemite assemblages during interglacials a high amplitude record of the composition dependent magnetic s 0 3 t parameter varies in accord with composite marine oxygen isotope records suggesting climate modulation of magnetic composition the xujiayao site is situated at the northern outskirts of the chinese loess plateau clp and has neither received significant eolian input nor been exposed to pedogenic processes comparable to those acting on clp mineral magnetic analyses suggest that variations in both magnetite and hematite are primarily controlled by detrital fluxes rather than by authigenic production of magnetic minerals here we propose that the fluctuations of magnetic signals at xujiayao are not derived from varying compositions of eolian flux with glacial interglacial periods or minute eolian influx during interglacials but is likely dominated by runoff related processes by which some weathered pedogenized loess and soils with stronger magnetic signals have been eroded and transported to the catchment during interglacials resulting in magnetic enhancement the inferred continuous deposition from the brunhes matuyama boundary to the paleosol s 1 ca 129 ka gives the age of ca 500 ka for the sediments carrying the xujiayao paleolithic site suggesting an allogenic origin of the paleolithic artifacts and mammalian bones dated by u th method to ca 100 ka

magnetochronology of the feiliang paleolithic site in the nihewan basin and implications for early human adaptability to high northern latitudes in east asia 1 we present a new magnetostratigraphic dating of the feiliang paleolithic site in the nihewan basin northern china partially oxidized magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations of the fluvio lacustrine sediments paleomagnetic results suggest that the sequence recorded the very early brunhes chron and the upper matuyama chron including the jaramillo subchron the feiliang artifact layer was determined to be within the pre jaramillo matuyama chron with an estimated age of ca 1 2 ma our finding coupled with previously published magnetochronology strongly indicates a prominent early human flourishing in the high northern latitudes of east asia during or just prior to the mid pleistocene climate transition

dating transitionally magnetized lavas of the late matuyama chron toward a new 40ar 39ar timescale of reversals and events the k ar based geomagnetic polarity timescale was constructed using data from lavas and tuffs that bracketed but rarely dated the transitions between polarity intervals subsequent 40ar 39ar dating indicated that the ages of some polarity transitions had been underestimated by about 6 although the accepted ages of the polarity chron boundaries have increased their precise temporal definition remained uncertain we have taken a different approach and used incremental heating techniques to obtain 18 new 40ar 39ar ages from basaltic lavas within flow sequences at punaruu valley tahiti and haleakala volcano hawaii these lavas record transitional paleomagnetic directions corresponding to four mid pleistocene polarity reversals or events three lavas from punaruu valley previously thought to record the cobb mountain normal polarity subchron cmns gave a mean age of 1 105 0 005 ma indicating that they were erupted about 76 kyr after the cmns this period of transitional field behavior is designated the punaruu event in addition seven new 40ar 39ar ages from the punaruu valley indicate that the jaramillo normal polarity subchron jns lasted about 67 kyr starting at 1 053 0 006 ma and ending 0 986 0 005 ma this agrees with astronomical estimates but conflicts with jns ages proposed by spell and mcdougall 1992 and izett and obradovich 1994 on the basis of 40ar 39ar dating of rhyolite domes in the valles caldera indistinguishable 40ar 39ar ages of seven lavas including one from punaruu valley and six from haleakala that record broadly similar intermediate paleodirections suggest that the kamikatsura event occurred at 0 886 0 003 ma moreover these data indicate that the kamikatsura event occurred 20 40 kyr after another geomagnetic event most probably taking place at 0 92 ma we designate this earlier field behavior the santa rosa event adopting its name from that of a transitionally magnetized rhyolite dome which happened to figure prominently in the original definition of the end of the jns in the 1968 study of doell et al 1968 the discovery of these new short lived polarity events during the matuyama reversed chron suggests that the 400 kyr period between 1 18 and 0 78 ma experienced no less than 7 and perhaps more than 11 attempts by the geodynamo to reverse this newly determined higher frequency of geomagnetic activity illustrates vividly the importance of obtaining precise age control directly from transitionally magnetized rocks

high resolution magnetostratigraphy and deposition cycles in the nihewan basin north china and their significance for stone artifact dating abstract three lacustrine sections in the nihewan basin xiaodukou donggutuo and xiaochangliang 40 1 40 4 n 114 6 114 7 e were closely sampled for magnetostratigraphic and deposition cycle analysis rock magnetic investigations show that the characteristic remanent magnetization of the sediments is mainly carried by magnetite and hematite the xiaodukou sequence is one of the most complete sections in the basin and has recorded substantial parts of the brunhes and matuyama chrons back to the termination of the olduvai subchron several subchrons within the matuyama period have been documented such as the jaramillo the cobb mt and others the matuyama brunhes boundary the jaramillo as well as the cobb mountain events were observed also at donggutuo on the basis of grain size and susceptibility data and of field investigations the sections are divided into two longer lasting lacustrine episodes with a fluvio lacustrine deposit in between they are structured by 15 high frequency deposition sub cycles in each cycle the grain size fines upwards while magnetic susceptibility decreases this behavior is due to cyclic water level change of the ancient lake nihewan at xiaodukou the variations of the 0 2 to 7 5 m grain size fraction can be correlated with the marine oxygen isotope stages ois 64 ois 11 the grey green clayey to silty paleolithic stone artifact layers at xiaochangliang and donggutuo are located at depths of 55 4 m and 43 38 7 m respectively they were buried when the lake level was rising the artifact layers have been deposited around the cobb mountain event during the sedimentary sub cycle 6 of the older lacustrine phase corresponding to ois 35 36 thus in contrast to the results of other studies the estimated age of the xiaochangliang stone artifact layer does not exceed 1 26 ma while the donggutuo stone artifact layers date back to 1 21 1 15 ma this age determination brings the nihewan hominids in close relation to the findings of homo erectus at lantian on the chinese loess plateau

summer monsoon variations over the last 1 2 ma from the weathering of loess soil sequences in china the loess soil sequence in northern china contains a near continuous record of quaternary paleoclimate magnetic susceptibility and grain size have so far been the only proxies available to address the long term changes of the east asian paleomonsoon extending back to more than one million years in this study the ratio of cbd citrate bicarbonate dithionite extractable free fe2o3 fed a measure of iron liberated by chemical weathering versus the total fe2o3 available fet was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1 2 ma variations of this index are highly consistent with other pedological indicators but in addition provide a quantitative measurement of the degree of pedogenesis in the loess plateau since chemical weathering in the region mainly depends upon summer precipitation and temperature weathering intensity primarily reflects changes in the east asian summer monsoon the new proxy has been used to document a series of summer monsoon changes of global significance which are not necessarily recorded by magnetic susceptibility

estimation of the bed shear stress in vegetated and bare channels with smooth beds the shear stress at the bed of a channel influences important benthic processes such as sediment transport several methods exist to estimate the bed shear stress in bare channels without vegetation but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production this study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds the model which is supported by measurements indicates that for both bare and vegetated channels with smooth beds within a viscous sublayer at the bed the viscous stress decreases linearly with increasing distance from the bed resulting in a parabolic velocity profile at the bed for bare channels the model describes the velocity profile in the overlap region of the law of the wall for emergent canopies of sufficient density frontal area per unit canopy volume a 4 3 m 1 the thickness of the linear stress layer is set by the stem diameter leading to a simple estimate for bed shear stress

magnetostratigraphic dating of early humans in china abstract china is a key area for research into human occupation in the old world after the initial expansion of early humans out of africa reliable age determinations are pivotal for assessing the patterns of human evolution and dispersal in this region this paper reviews magnetostratigraphic studies of some early pleistocene strata bearing hominin remains and or artifact stone tools from northern to southern china the quality and reliability of the paleomagnetic dates are also evaluated new magnetostratigraphic results for the xihoudu paleolithic site in north central china are also presented among the few hominin or paleolithic sites in china from the early pleistocene five have been well investigated three of these are in northern china at xiaochangliang donggutuo and gongwangling the remaining two in southern china at longgupo and yuanmou considerable progress has been made during the past three decades towards paleomagnetically dating these sites indeed the age estimates at xiaochangliang and gongwangling have been widely accepted magnetostratigraphic consensus about the age of the donggutuo site has also been reached however the age determination for the two sites in southern china is still contested the integration of rock magnetic stratigraphy with magnetic polarity stratigraphy has resulted in a determined age of 1 36 ma for a stone tool containing layer of lacustrine sediments at the xiaochangliang site in the nihewan basin lithostratigraphic constraints have significantly contributed to determining the age of lantian homo erectus at gongwangling which occurred in a loess paleosol sequence of the southern loess plateau its age paleomagnetically derived is about 1 15 ma these two paleomagnetic ages suggest an expansion and flourishing of human groups from northern to north central china during the early pleistocene this suggestion has been reinforced by our new magnetostratigraphic age estimate of about 1 27 ma for the xihoudu site as will be presented in this paper however more work is needed for the age determinations of the hominin bearing strata at the longgupo and yuanmou sites in southern china finally we stress that it is necessary to combine biostratigraphy lithostratigraphy and rock magnetic stratigraphy with the traditional magnetic polarity stratigraphy in order to obtain reliable age determinations for strata bearing hominin remains or stone artifacts

40ar 39ar dating links albuquerque volcanoes to the pringle falls excursion and the geomagnetic instability time scale abstract incremental heating of basaltic lava groundmass from the albuquerque volcanoes new mexico and plagioclase from ash d at pringle falls oregon yield 40ar 39ar isochron ages of 218 14 and 211 13 ka respectively sediments in which ash d was deposited and the eight lava flows of the albuquerque volcanoes display excursional paleomagnetic data with virtual geomagnetic poles vgps in the southern hemisphere and together with the statistically indistinguishable 40ar 39ar dates establish that both sites record the pringle falls excursion this excursion is also recorded by the 227 8 ka mamaku ignimbrite new zealand and by high deposition rate sediments at odp site 919 in the north atlantic ocean that are dated astrochronologically at 209 207 ka we propose that the names albuquerque and jamaica excursion be abandoned and that a radioisotopic age of 211 13 ka be adopted for the pringle falls excursion which is one of five globally expressed well documented excursions in marine sediment cores or dated by 40ar 39ar methods that took place from 220 to 30 ka together with at least five other well dated excursions between 730 and 520 ka some ten excursions define the geomagnetic instability time scale gits for the bruhnes chron eight of these excursions have been dated using 40ar 39ar methods if the temporal clustering of excursions in the gits is not a sampling artefact this suggests that the geodynamo is not intrinsically unstable but rather that instability in the flow pattern of the outer core fluid flow causes the main dipole field to be considerably weakened such that it becomes unstable with a 200 to 300 ka recurrence interval excursions are an important part of dynamo behavior over geologic time scales that in addition to reversals of the main dipole field need to be fully considered when assessing whether theoretical and numerical simulations of the dynamo produce earth like results

model for calculating bed load transport of sediment a bed load transport model based on the mechanics of sediment moving by saltation yields predicted values of bed load flux as a function of boundary shear stress grain diameter and density the parameters required to calculate bed load transport particle velocity bed load sediment concentration and the height of the bed load layer can all be determined from our model which computes sequences of trajectories of individual saltating grains as well as the concentration of moving grains that the flow can support the latter is related to the momentum the accelerating grains extract from the flow predicted curves of bed load transport vs boundary shear stress agree well with transport data collected by gilbert meyer peter iet al n and the waterways experimental station measured shear stress was corrected for pressure drag when bed forms were present comparison of predicted bed load transport with common bed load equations reveals considerable similarity among the relationships the best agreement with the data is produced by relationships in which the transport rate vanishes as the shear stress approaches the critical shields number as in our model and yalin s equation

estimating the distribution of suspended sediment concentration in submerged vegetation flow based on gravitational theory abstract vegetation plays a significant role in river ecosystem which has a great influence on hydraulic structures and sediment transport understanding the vertical distribution of suspended sediment concentration ssc in canopy flow is helpful to study the process of riverbed erosion and deposition in vegetated channels aiming at the sediment laden flow in open channel covered with submerged vegetation this study divides the water depth into two layers along the vertical direction with the vegetation height as the boundary and then proposes a new ssc distribution model based on gravitational theory to estimate the vertical distribution of relative ssc in the free water layer and vegetation layer respectively in the meanwhile a new formula is also proposed to evaluate the reynolds shear stress below the submerged vegetation height which has been successfully applied in the derivation of the new ssc distribution model the validation results of the simplified velocity model the new reynolds shear stress formula and the new ssc model compare well with the collected experimental data series on top of that it is found that the uniformity of ssc distribution profile progressively decreases with the increasing sediment particles diameters besides according to the validation results and discussion it is believed that the controversy point about gravitational theory would not have obvious influence on the estimation of ssc distribution so that the gravitational theory can be adopted to investigate suspended sediment transport in vegetation flow that would be benefit for river ecological restoration and better management

magnetostratigraphic age of the xiantai paleolithic site in the nihewan basin and implications for early human colonization of northeast asia timing of the early habitation and stone technologies in the nihewan basin north china has provided insights into our understanding of early human adaptability to high northern latitudes in east asia here we contribute to this topic with detailed magnetostratigraphic investigation coupled with mineral magnetic measurements and palynological analyses on a lacustrine sequence in this basin which contains the xiantai paleolithic site magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations magnetostratigraphic results show that the xiantai lacustrine sequence recorded the brunhes chron the jaramillo and the olduvai subchrons and successive reverse polarity portions of the intervening matuyama chron stratigraphic correlation in terms of lithology magnetic susceptibility and magnetic polarity sequences between the xiantai and xiaochangliang sections indicates that the xiantai artefact layer is readily contemporary with the xiaochangliang artefact layer which has been previously estimated to be about 1 36 ma r x zhu k a hoffman r potts c l deng y x pan b guo c d shi z t guo b y yuan y m hou w w huang earliest presence of humans in northeast asia nature 413 2001 413 417 early humans of the xiantai paleolithic site lived in a steppe paleoenvironment indicated from fossil pollens furthermore the combined evidence of our magnetostratigraphy and previously published magnetochronology and paleoclimate data documents that early humans of north china were able to adjust to an increasing variability of paleoclimates and paleoenvironments over the early pleistocene

temperature dependence of magnetic susceptibility in an argon environment implications for pedogenesis of chinese loess palaeosols summary temperature dependence of magnetic susceptibility t has been widely used to determine changes in mineralogy of natural samples during heat treatment we carried out integrated rock magnetic experiments to interpret the t curves of the chinese loess palaeosols in argon we used both raw materials and heated samples in addition we also investigated the magnetic properties of magnetic extracts and residues to quantify contributions from each fraction to the bulk magnetic properties for the heating curves the susceptibility loss 30 per cent between 300 400 c is caused by the inversion from pedogenic fine grained maghemite to haematite suggesting that the susceptibility loss can be used as a new concentration index of the pedogenic fine grained superparamagnetic sp particles in the chinese loess palaeosols unlike the warming curves the cooling curves are dominated by newly formed fine grained magnetites with a dominant size of 35 nm the onset for the new production of these fine grained magnetic particles occurs at 400 c it is interesting that the room temperature magnetic susceptibility ph of the samples heated after a 700 c run is independent of the degree of pedogenesis and saturates at approximately 33 35 10 7 m3 kg 1 indicating that the susceptibility enhancement is controlled only by the reduction of fe bearing aeolian minerals during heating it appears that the 700 c thermal treatment in argon could be in some sense an analogue to the pedogenic processes thus we predict that 33 35 10 7 m3 kg 1 is the maximum susceptibility that pedogenesis can generate for the last interglacial palaeosol unit s1 in practice ph would be useful to quantify the aeolian inputs to the chinese loess plateau

a revised paleomagnetic age of the nihewan group at the xujiayao palaeolithic site china abstract the age of the nihewan group lacustrine sediments shanxi province china has been a matter of dispute for decades the sediments were initially assigned a lower pleistocene age which was subsequently extended to late pleistocene based on palaeolithic evidence and mammal fossils a short zone of reversed paleomagnetic polarity was proposed to represent the blake geomagnetic excursion 0 117 myr in accord with a late pleistocene age liu c su p jin z 1992 discovery of blake episode in the xujiayao paleolithic site shanxi china scientia geologica sinica 1 87 95 we report on a high resolution palaeomagnetic investigation of two stratigraphic sections at xujiayao based on progressive thermal demagnetisation experiments alterations of magnetic minerals occur during heating susceptibility crisis but experiments indicate no significant effects on remanence properties the uppermost ca 15 m carries a normal polarity magnetisation overlying a reversed polarity zone extending to the base of the sampled sections the reversed polarity zone is too extensive 6 12 m to represent a geomagnetic excursion and is proposed to represent the matuyama chron the nihewan group at xujiayao palaeolithic must hence be older than late pleistocene in general accord with palaeomagnetic results of nihewan type sections at dadaopo some 50 km ne from xujiayao

mineral magnetic variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling a high resolution mineral magnetic investigation has been carried out on the jingbian loess paleosol sequence at the northern extremity of the chinese loess plateau results show that the magnetic assemblage is dominated by large pseudo single domain and multidomain like magnetite with associated maghemite and hematite variations in the ratios of sirm100mt sirm sirm100mt sirm30mt and sirm100mt sirm60mt sirm is the saturation isothermal remanent magnetization sirmnmt represents the residual sirm after an n mt alternating field demagnetization have been used to document regional paleoclimate change in the asian interior by correlating the mineral magnetic record with the composite 18o record in deep sea sediments the long term up section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema respectively which reveals a long term decreasing trend in chemical weathering intensity in both glacial stage source region the gobi and deserts in northwestern china and interglacial stage depositional area the loess plateau region we further relate this long timescale variation to long term increasing aridification and cooling during both glacial extrema in the dust source region and interglacial extrema in the depositional area over the quaternary period changes in those ratios are most likely due to quaternary aridification and cooling driven by ongoing global cooling expansion of the arctic ice sheet and progressive uplift of the himalayan tibetan complex during this period

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

vertical sediment distribution so far various calculation models for the vertical distribution of suspended sediment concentration have been produced by several investigators from different theories the limitations of all these models imply that it is possible to find a more reasonable model for which each previous model can be included as special case the formulation of a reasonable general model is the purpose of this paper

identifying the effects of parameter uncertainty on the reliability of riverbank stability modelling bank retreat is a key process in fluvial dynamics affecting a wide range of physical ecological and socioeconomic issues in the fluvial environment to predict the undesirable effects of bank retreat and to inform effective measures to prevent it a wide range of bank stability models have been presented in the literature these models typically express bank stability by defining a factor of safety as the ratio of driving and resisting forces acting on the incipient failure block these forces are affected by a range of controlling factors that include such aspects as the bank profile bank height and angle the geotechnical properties of the bank materials as well as the hydrological status of the riverbanks in this paper we evaluate the extent to which uncertainties in the parameterization of these controlling factors feed through to influence the reliability of the resulting bank stability estimate this is achieved by employing a simple model of riverbank stability with respect to planar failure which is the most common type of bank stability model in a series of sensitivity tests and monte carlo analyses to identify for each model parameter the range of values that induce significant changes in the simulated factor of safety these identified parameter value ranges are compared to empirically derived parameter uncertainties to determine whether they are likely to confound the reliability of the resulting bank stability calculations our results show that parameter uncertainties are typically high enough that the likelihood of generating unreliable predictions is typically very high 80 for predictions requiring a precision of 15 because parameter uncertainties are derived primarily from the natural variability of the parameters rather than measurement errors much more careful attention should be paid to field sampling strategies such that the parameter uncertainties and consequent prediction unreliabilities can be quantified more robustly

magnetostratigraphic dating of the linyi fauna and implications for sequencing the mammalian faunas on the chinese loess plateau the chinese loess plateau clp in north china is an important terrestrial archive that witnessed the environmental changes and mammal and early human evolution in asia over the past 2 6 ma establishing precise ages for the pleistocene faunas on the clp is critical for better understanding of these environmental biological and archaeological issues here we report a new magnetostratigraphic record that places age constraints on the linyi fauna on the southeastern clp our investigated 170 m thick linyi section mainly consists of two portions 1 an overlying eolian quaternary loess paleosol sequence and 2 underlying fluvial lacustrine sand and silty clay paleomagnetic results suggest that the composite section records the brunhes chron jaramillo and olduvai subchrons and successive reverse polarity portions of the intervening matuyama chron the linyi fauna is located between jaramillo and olduvai subchrons in the fluvial lacustrine interval with an estimated age of 1 5 1 6 ma combining previously dated faunas we establish a pleistocene magnetochronology spanning from 2 54 to 0 65 ma for the faunas on the clp

magnetostratigraphic and archaeological records at the early pleistocene site complex of madigou nihewan basin implications for human adaptations in north china abstract the nihewan basin in north china contains the densest concentration of early pleistocene paleolithic sites outside africa this paper introduces a new archaeological site complex at madigou mdg that was systematically excavated from 2011 to 2014 in the northeastern part of the nihewan basin the site contains fossils and well preserved stone artefacts in fluvio lacustrine sediments our magnetostratigraphic results situate the mdg sedimentary sequence in the early brunhes normal chron and the late matuyama reverse chron including the jaramillo normal subchron the mdg artifact layers are positioned within the pre jaramillo matuyama chron with an estimated age of ca 1 2 ma close to the onset of mid pleistocene climate transition the mdg core and flake technology includes bipolar flaking of siliceous dolomite cobbles and freehand flaking of chert and brecciated chert block fragments mammalian fauna and pollen compositions indicate that the mdg hominins lived in an open habitat varying from lightly wooded grassland to an ecosystem dominated by sparse steppe near the shore of the nihewan paleolake our combined results in the fields of archaeology paleontology palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of mid pleistocene climate transition

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

magnetic mineral dissolution in pleistocene fluvio lacustrine sediments nihewan basin north china abstract the nihewan fluvio lacustrine sequence north china has recorded late pliocene pleistocene climatic and environmental changes and contains valuable information on early human evolution in high latitude east asia we carried out a combined mineral magnetic and geochemical investigation on a sequence from the xiantai section eastern nihewan basin results suggest that large amplitude magnetic property variations between so called high magnetic and low magnetic units mainly result from preservation dissolution cycles of detrital magnetic minerals in alternating oxic and anoxic depositional environments in our preservation dissolution model the high and low magnetic units represent glacial and interglacial deposits respectively this contributes to a better understanding of the link between magnetic properties and climate in the xiantai fluvio lacustrine sequence based upon this relationship early humans may have occupied the xiantai and xiaochangliang sites during an interglacial period during both interglacial and glacial periods at the donggutuo site and during a glacial period at the maliang site our work provides a paleoenvironmental context for early human adaptation and occupation in mainland east asia during the early pleistocene

high resolution record of geomagnetic excursions in the matuyama chron constrains the ages of the feiliang and lanpo paleolithic sites in the nihewan basin north china the nihewan basin 40 degrees n in north china is a rich source of early pleistocene paleolithic sites and thus a key area for studying early human evolution in high latitude from an early human perspective east asia here a high resolution magnetostratigraphic investigation is carried out on a fluvio lacustrine section in the northeastern nihewan basin which contains the feiliang and lanpo paleolithic sites paleomagnetic results suggest that this section records the lower portion of the brunhes polarity chron and the upper matuyama polarity chron furthermore the jaramillo polarity subchron and seven of the nine validated geomagnetic excursions within the matuyama polarity chron are identified including the kamikatsura santa rosa intra jaramillo cobb mountain bjorn gardar and gilsa excursions the feiliang artifact layer is located just at the bottom of the cobb mountain excursion thus its age is estimated to be similar to 1 2ma the lanpo artifact layer appears to be coeval with the gilsa excursion yielding an estimated age of similar to 1 6 ma this study provides new evidence for the presence of early humans in north china before 1 5 ma and documents the powerful role of geomagnetic excursions they provide valuable age control points for ongoing efforts to date the early paleolithic sites

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

late pliocene and early pleistocene vegetation and climate change revealed by a pollen record from nihewan basin north china abstract the nihewan formation is an important early quaternary sedimentary formation in north china we conducted pollen analyses of 183 samples and 1611 modern surface samples to characterize the processes of vegetation succession and climate change during the pliocene pleistocene transition 2 89 2 34 ma in the nihewan basin the results show that pollen assemblages are dominated by arboreal pollen indicating that the vegetation in the study area was forest dominated and that the climate was more humid than today however the temperature varied substantially the most substantial vegetation and climate changes occurred at 2 8 ma when the pollen representation of warm and humid tolerant taxa such as evergreen quercus and carya disappeared and also broadleaved deciduous types such as ulmus deciduous quercus and betula decreased obviously on the contrary the pollen representation of cold and drought tolerant taxa increased substantially e g picea from generally less than 20 to more than 30 and chenopodiaceae from generally less than 10 to more than 20 the quantitative reconstructed results indicating that tann decreased by about 2 3 c and pann decreased by 150 mm compared to before 2 8 ma with a maximum decrease of 9 c for tann and 450 mm for pann another important vegetation and climate changes occurred at 2 6 ma which was the coldest and driest of the studied interval when the vegetation was substantially simplified with spruce generally above 80 as the dominated types

high resolution magnetic stratigraphy of fluvio lacustrine succession in the nihewan basin china abstract a detailed paleomagnetic and rock magnetic investigation of nihewan fluvio lacustrine deposits at tai ergou 40 o 12 52 n 114 o 38 22 e hebei province of north china has been carried out the results show that the magnetic mineralogy is dominated by magnetite and high coercivity hematite maghemite occurs mainly in the grayish yellow yellowish brown silt layers and fine grained yellow sand beds either as a detrital component or as the result of low temperature oxidation of magnetite distinct variations in magnetic susceptibility are always associated with changes in lithology i e color and grain size of the sediments reflecting the frequent lowering ascendance of the water table level and change of sedimentation environment based on paleomagnetic results of thermal and af demagnetization experiments we present an unambiguous polarity stratigraphy for the exposed lacustrine fluvial sediments at tai ergou consisting of three normal magnetozones including the brunhes chron the jaramillo and olduvai subchrons and two reversed zones belonging to the matuyama chron this suggests that the nihewan basin carries a long continuous stratigraphic record albeit varying in sedimentation facies and sedimentation rates consequently we concluded that the nihewan lacustrine sediments at tai ergou commenced depositing at the onset of the olduvai subchron and the tai ergou section can be used as a dating tool for biochronological and high resolution magnetostratigraphic purposes

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression