dynamic response of a thawing soil around the tunnel under the vibration load of subway a certain thickness of thawing soil remains after the construction of subway tunnel by the artificial freezing method in soft soil area the physical and mechanical properties of soil change a lot after freezing and thawing therefore the dynamic response of thawing soil is different from that of undisturbed soil under the same vibration loads of subway the numerical simulations of thawing soil and undisturbed soil were conducted in this paper the variations of the acceleration and the displacement of the surface and some special points were analyzed the propagation characteristics of wave in the soil and the differences between thawing soil and undisturbed soil were obtained

case study of slope deterioration characteristics simbal landslide salt range pakistan for a slope structure various deterioration phenomena progress in the slope over time and failure may occur which decreases the durability life and service life the approach to slope stability due to deterioration is a different concept from the existing limit equilibrium analysis which is limited to the physical characteristics and geometrical structure of the ground and groundwater in this study with a comparative review of various literatures related to the slope failure characteristics due to deterioration the optimal formulas for shear strength reduction such as the exponential function logarithmic function and inverse hyperbolic function are found to be the best fits for the variations in strength reduction in addition a case study was performed for the simbal landslide salt range pakistan where the slope failure of some carbonate rock formations vulnerable to deterioration occurred as a result it was confirmed that landslide occurred because of the reduction in shear strength by deterioration since the safety factor was approx 1 0 when the slope failure occurred finally as a quantitative approach to evaluate the slope stability due to deterioration a methodology to evaluate the slope stability using the limit equilibrium analysis of the slope with optimal strength reduction curves was proposed

palaeclimatic significance of the xiantai fluvio lacustrine sequence in the nihewan basin north china based on rock magnetic properties and clay mineralogy summary here we report an increased cooling coupled with an intensified aridification for the xiantai fluvio lacustrine sequence of pleistocene age 1 9 0 1 ma in the nihewan basin north china known for the occurrence of several hominin sites the cooling is related to an up section decrease in propensity to chemical weathering as inferred from an increase in lowfield susceptibility after cycling to 700 c close to 700 c reacting chlorite is providing the iron source for newly formed very fine grained ferrimagnetic minerals which enhances the susceptibility signal the reactivity of chlorite after annealing at temperatures above 600 c is documented with x ray diffraction and the up section decrease in propensity to chemical weathering is confirmed by the up section declining illite chlorite ratios and increasing chlorite and illite contents based on x ray diffraction analysis on selected samples

reconstruction of palaeosalinity using carbon isotopes and benthic associations a comparison carbon and oxygen isotopes were determined on 40 recrystallized shells of late jurassic bivalves from the lusitanian basin of portugal in contrast with the oxygen isotopes which exhibited considerable diagenetic distortion the carbon isotopes are thought to preserve a record of the salinity of the jurassic marginal marine seas in which these bivalves lived the reconstructed palaeosalinities range from 35 o euhaline to 5 oligohaline comparing these values with the palaeosalinity reconstructed from a palaeoecological analysis of 17 stratigraphic levels within the basin the independently derived values agree in most cases strongly differing values are explained as being due to biotic factors and to diagenetic distortion of the isotopic signal they are less likely to be due to smallscale time averaging or insufficient microstratigraphic sampling on the whole the carbon isotope analyses are thought to produce reasonable palaeosalinity values although data from infaunal originally aragonitic bivalves appear to be less reliable than those from epifaunal bivalves with a predominantly or exclusively calcitic shell as diagenetic alteration of the carbon isotope signal is however unpredictable and biotic effects on the isotopic composition are insufficiently known palaeosalinity reconstructions based on stable isotope data should be supported by palaeoecological data

an investigation of the magnetic carriers and demagnetization characteristics of the gulang loess section northwestern chinese loess plateau we report the results of a rock magnetic and paleomagnetic investigation of unit l9 of the gulang gl loess section in the northwestern chinese loess plateau clp we demonstrate that the dominant magnetic remanence carriers are coarse grained pseudo single domain multidomain magnetite particles and hematite the application of either thermal thd or alternating field demagnetization afd yielded several normal polarity intervals interbedded with intervals of reversed polarity but which cannot be correlated with standard geomagnetic polarity time scales a greater number of normal polarity intervals however were evident after thd than after afd we propose that the normal polarities are either the result of overprinting of a viscous remanent magnetization vrm carried by coarse magnetite particles on the original depositional remanent magnetization drm or that they represent genuine geomagnetic excursions such as the kamikatsura and santa rosa excursions which are difficult to identify in addition we propose that in the case of the gl loess section the effect of thermal demagnetization tails of a vrm is a possible reason why thd treatment yielded a greater number of normal polarity intervals than does afd however reversed polarities obtained by either thd or afd may be credible for sedimentary intervals with a relatively high content of hematite particles which preserve the primary drm although numerous studies have proposed that thd provides more reliable paleomagnetic directions for loess sediments from the clp our results suggest that careful attention needs to be paid to the type of demagnetization method chosen especially in the case of coarse grained loess deposits

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

geochemical and paleoenvironmental variations across the cretaceous tertiary boundary at braggs alabama abstract the cretaceous tertiary k t boundary in southern alabama occurs in a sequence of interbedded shallow marine limestones and marls deposited during a late maastrichtian regression and subsequent danian transgression the presence of a diverse assemblage of cretaceous and paleocene benthic micro and macrofossils has allowed detailed examination of paleoenvironmental changes in this shallow marine setting at the time of the k t boundary extinctions although extensive diagenesis has resulted in the recrystallization and cementation of whole rock carbonate a few molluscan macrofossils have retained their original calcitic structure the oxygen isotopic record of these macrofossils shows a gradual cooling of 2 3 c over a 3 m y period which began in the late maastrichtian and continued into the danian the characteristic depletion in 13 c across the k t boundary displayed by planktonic microfossils from pelagic sequences is not recorded at braggs major changes in whole rock trace and minor element chemistry reflect the decrease in terrigenous mineral fluxes to this location brought about by the rapid early paleocene transgression

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

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

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

tectonic versus climatic control on the evolution of a loess paleosol sequence at beremend hungary an integrated approach based on paleoecological clay mineralogical and geochemical data the role of two major factors climate and tectonism in controlling loess paleosol evolution has been evaluated in the present study based on a multi proxy dataset comprising mollusc bulk and clay mineralogical and geochemical data a recent trend has been to use chemical indices such as the chemical index of alteration cia for paleoclimate reconstructions in loess paleosol sequences spanning several hundreds of thousands of years but without any tectonic interpretation possible effects of geodynamic factors on physical erosion chemical weathering and consequently weathering proxies are discussed clearly the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate intensifying tectonic uplift gives rise to enhanced physical erosion leading to increased supply of fresh mineral surfaces having less time to react with weathering agents in theory this process may point towards decreasing chemical weathering in a sequence without any real changes of climate in the studied loess paleosol sequence at beremend hungary a trend of decreasing chemical weathering has been observed which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non linear amplification the findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands or millions of years this is because tectonic effects may impose on the cia signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts

magnetostratigraphy of the suerkuli basin indicates pliocene 3 2 ma activity of the middle altyn tagh fault northern tibetan plateau abstract the left lateral strike slip altyn tagh fault atf forming the northern boundary of the tibetan plateau accommodates parts of the overall convergence between the colliding indian and eurasian plates precise dating of the atf activity is essential for understanding possible mechanisms of tibetan plateau deformation and uplift here we report a magnetostratigraphic study of the suerkuli basin deposits recording depositional changes during the atf activity field investigations reveal a remarkable and widespread change in depositional environment in the suerkuli basin i e a transformation from low energy lacustrine deposits grayish green mud siltstone and brown mud siltstone into high energy alluviul fan deposits poorly sorted gray pebble and cobble conglomerates detailed magnetostratigraphy of the 390 m thick daban section at the southeastern margin of the suerkuli basin 38 43 09 n 90 58 84 e shows that this change in depositional facies occurred at 3 2 ma accompanied by a remarkable increase in sediment accumulation rate we attribute this depositional change to the piocene tectonic activity of the middle atf although the contribution of the pliocene global climate deterioration cannot be excluded

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

mineral magnetic signal of long term climatic variation in pleistocene fluvio lacustrine sediments nihewan basin north china abstract the nihewan basin around 40 n north china is a major focus of investigations into hominid occupation in the eastern asia during the early pleistocene thus the paleoenvironmental evolution in this area is crucial for understanding of early human habitation at high northern latitudes of east asia to retrieve reliable long term paleoenvironmental signals from the nihewan fluvio lacustrine sequences i conduct an environmental magnetic investigation on the pleistocene xiantai fluvio lacustrine sequence at the eastern margin of the nihewan basin results suggest that there exist an up section decreasing trend in magnetic mineral concentration and grain size which is attributed to a long term decrease in abundance of magnetic minerals in the catchments and in transportation of detrital magnetic minerals into the nihewan paleolake i further reveal that these long timescale variations are related to a long term decrease in east asian monsoon precipitation and humidity in the nihewan basin during the pleistocene this paleoclimate inference is consistent with the increasing aridification in asian mainland during the pleistocene an important climate response to increasing global ice volume

clay minerals and their paleoenvironmental interpretation in the baoji loess section southern loess plateau china abstract clay minerals from the loess paleosol section at baoji in north central china were studied by x ray diffraction major components calculated by comparing major peak heights were estimated as follows illite 55 75 kaolinite 10 25 mixed layer chlorite vermiculite 10 20 chlorite

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 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

a comprehensive fluvial geomorphology study of riverbank erosion on the red river in winnipeg manitoba canada summary riverbank erosion on the red river in winnipeg manitoba has raised concerns over the last 20 years and more although several recent studies have shown that fluvial erosion can reduce riverbank stability and promote geotechnical slope failure there are too few that have focused on this phenomenon the present study includes field measurements experimental testing and numerical modelling to quantify fluvial erosion through a 10 km reach of the red river results have shown that seasonal freeze thaw processes can dramatically reduce the critical shear stress and increase erodibility of the riverbanks moreover a simple method has been employed using hydrodynamic numerical models to define the applied shear stresses on the river banks based on the river water level which will be useful for further research and design purposes the temp w numerical model was used to define seasonal frost depth to estimate freeze thaw effects finally all field measurements experimental and numerical models results were used to predict annual fluvial erosion through this reach of the river

mineral magnetic record of the miocene pliocene climate transition on the chinese loess plateau north china pre quaternary terrestrial climate variability is less well understood than that during the quaternary the continuous eolian red clay sequence underlying the well known quaternary loess paleosol sequence on the chinese loess plateau clp provides an opportunity to study pre quaternary terrestrial climate variability in east asia here we present new mineral magnetic records for a recently found red clay succession from shilou area on the eastern clp and demonstrate a marked east asian climate shift across the miocene pliocene boundary mpb pedogenic fine grained magnetite populations ranging from superparamagnetic sp single domain sd up to small pseudo single domain psd sizes i e from

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

magnetite dissolution diachronous greigite formation and secondary magnetizations from pyrite oxidation unravelling complex magnetizations in neogene marine sediments from new zealand detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of neogene marine sediments from the east coast of new zealand is dominated by the authigenic iron sulphide greigite the greigite is present as a mixed population of stable single domain and superparamagnetic grains which is consistent with authigenic growth from solution this growth can result from pyritization reactions soon after deposition which also leads to dissolution of most detrital magnetite however where constrained by field tests our data suggest that remanence acquisition can occur 1 myr after deposition and can vary in timing at the outcrop scale strong viscous overprints result from oxidation of the iron sulphides probably during percolation of oxic ground water this process can sometimes destroy any ancient remanent magnetization this complex magnetic behaviour particularly the presence of late forming magnetizations carried by greigite means that the remanence in new zealand cenozoic sediments and in similar sediments elsewhere cannot be assumed to be primary without confirmation by field tests the reversals test should be employed with caution in such sediments as patchy remagnetizations can lead to false polarity stratigraphies

early pleistocene occurrence of acheulian technology in north china acheulian tools with their associated level of cognizance heralded a major threshold in the evolution of hominin technology culture and behavior thus unraveling occurrence ages of acheulian technology across different regions worldwide constitutes a key aspect of understanding the archeology of early human evolution here we present a magneto cyclochronology for the acheulian assemblage from sanmenxia basin loess plateau north china our results place a sequence of stable normal and reversed paleomagnetic polarities within a regional lithostratigraphic context the acheulian assemblage is dated to be older than the matuyama brunhes boundary at 0 78 ma and is found in strata that are probably equivalent to a weak paleosol subunit within loess layer l9 in the chinese loess paleosol sequence which corresponds to marine isotope stage mis 23 a relatively subdued interglacial period with age range of 0 89 0 92 ma this age of 0 9 ma implies that acheulian stone tools were unambiguously present in north china during the early pleistocene it distinctly enlarges the geographic distribution of acheulian technology and brings its occurrence in north china back into the early pleistocene which is contemporaneous with its first emergence in europe combined with other archeological records the larger area over which acheulian technology existed in east asia during the terminal early pleistocene has important implications for understanding early human occupation of north china

ar ar ages from transitionally magnetized lavas on la palma canary islands and the geomagnetic instability timescale 1 a detailed study of 43 lava flows comprising two stratigraphic sequences exposed along the north and south walls of barranco de los tilos on the island of la palma canary islands reveals a complex temporally segmented record of geodynamo behavior that contains no less than three distinct geomagnetic events the matuyama brunhes m b reversal is recorded in five transitionally magnetized lava flows from the north tn section the isochrons obtained from three of the lower four m b lavas are defined by 14 incremental heating experiments that together with a previous age determination yielded a weighted mean of 798 4 6 2 ka all uncertainties 2s in addition a 780 3 10 3 ka isochron was determined for the overlying transitionally magnetized flow indicating that it was erupted during a distinctly younger portion of the transition near the base of the south ts section one finds a sequence of weakly magnetized flows associated with virtual geomagnetic pole vgp positions in the southwest indian ocean between latitudes 56 s and 65 s suggesting instability of the geomagnetic field beyond that of typical secular variation 40 ar 39 ar isochrons from three of these flows defined by 11 separate incremental heating experiments gave a weighted mean of 822 2 8 7 ka this anomalous field behavior recorded 24 11 kyr prior to the m b reversal may coincide with an event featured in several marine sediment records directly above two normal polarity flows 40 ar 39 ar isochrons of 751 9 18 1 ka and 675 0 15 7 ka are nine transitionally magnetized lavas having magnetization directions associated with low to midlatitude vgps spanning 23 60 n these flows are then capped by a single flow possessing normal polarity based on 12 incremental heating experiments 40 ar 39 ar isochrons of five of these nine lavas along with the uppermost flow gave a weighted mean age of 580 2 7 8 ka for this period of transitional to normal field behavior from these same transitional lavas quidelleur et al 1999 reported three unspiked k ar ages with a weighted mean of 602 24 ka and proposed a new event called the la palma excursion however the 40 ar 39 ar age presented here is three times more precise than the k ar age and is indistinguishable at the 95 confidence level from the 40 ar 39 ar age of a lava from the snake river plain idaho that originally defined the big lost event transitional field behavior of similar age observed in astronomically dated marine cores further establishes that the big lost event recorded at la palma was indeed global in extent rigorous temporal and geomagnetic constraints for several additional periods of geomagnetic field instability during the last several million years will comprise a geomagnetic instability timescale that can be factored confidently into models of the dynamo process index terms 1560 geomagnetism and paleomagnetism time variations secular and long term 1520 geomagnetism and paleomagnetism magnetostratigraphy 1035 geochemistry geochronology 1513 geomagnetism and paleomagnetism geomagnetic excursions keywords argonargon dating lavas excursion paleomagnetism reversal

sedimentary evolution of the foreland basin in the ne tibetan plateau and the growth of the qilian shan since 7 ma we studied the magnetostratigraphy and sedimentary facies of a 550 m long drill core from the jiudong basin in the ne tibetan plateau our aims were to reconstruct the late cenozoic sedimentary evolution of this foreland basin and to determine the spatiotemporal pattern of growth of the qilian shan the magnetostratigraphy indicates that the sedimentary sequence was deposited during ca 7 0 ma from ca 6 7 3 0 ma the sediment accumulation rate increased gradually from similar to 30 mm k y to 120 mm k y which was associated with the gradual evolution of sedimentary facies from a shallow lake delta front to braided rivers the progradation of the depositional system from 7 ma to 3 ma probably reflects the growth of the relief of the qilian shan caused by tectonic uplift the occurrence of a continuous braided river environment from 3 ma to the present suggests that the high relief of the qilian shan developed before 3 ma an abrupt decrease of the sedimentation rate to similar to 46 mm k y during 3 0 1 8 ma and the deposition of coarse grained sediments indicates the uplift of the basin center we interpret this to reflect the propagation of the thrust system of the qilian shan into the basin along a southward dipping decollement from ca 3 ma climatic changes may have influenced the sedimentary sequence by introducing long distancetransported thin coarse sand gravel layers which are sandwiched within the sequence and likely were a response to cooling events or climatic transitions the widespread occurrence of deformation within the basin region in the ne tibetan plateau at ca 3 ma indicates that this date marks the basinward growth of the deformation system

yield states and stress strain relationships in a natural plastic clay reply natural clays are commonly anisotropic due to their mode of deposition and lightly overconsolidated because of a variety of subsequent geological processes they exhibit marked changes in stiffness when they yield yield stresses from individual tests can be generalized into a yield surface for the clay if displacements during loading are taken into account by calculating specific volumes v 1 e throughout the tests this paper describes tests on 76 mm diameter triaxial samples of natural plastic lake agassiz clay from winnipeg the samples were carefully trimmed reconsolidated to approximately their in situ stresses and loaded in stress controlled tests along various stress paths in p q stress space the tests produced well defined yield envelopes in p q p v and q v plots and in corresponding plots where the stresses were normalized with respect to the vertical preconsolidation pressure vc comparison of one dimensional yielding states with results from k0 triaxial tests that were continu

magnetostratigraphic dating of the shixia red sediments and implications for formation of nihewan paleo lake north china abstract the sedimentary sequence in nihewan basin northern china is rich in mammalian fossils and paleolithic sites extensive magnetostratigraphic investigations have been carried out in the nihewan sediments but precise age control on the earliest nihewan red sediments which have a fluvio lacustrine origin in the upper part and an eolian origin in the lower part has remained unavailable the formation process of nihewan paleo lake therefore remains unclear here we contribute to understanding the age of the early nihewan reworked and eolian red clays by presenting detailed magnetostratigraphic and rock magnetic results from the shixia section coupled with geochemical and petrographic analyses magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the shixia sedimentary sequence recorded part of the gilbert chron with the onset of deposition of the nihewan formation occurring prior to the gilbert gauss geomagnetic reversal at 3 6 ma with tectonic development of a graben basin early red clay was deposited first in nihewan basin during the early pliocene before giving way to lacustrine environments in nihewan paleo lake geochemical and petrographic results indicate a wind blown origin for the lower red clay deposits which have been reworked and mixed with conglomerates produced by local tectonic activity to produce the basal nihewan sediments later formation of carbonate nodules has given rise to the sediments that are now exposed in nihewan basin

fourth canadian geotechnical colloquium strength and slope stability in canadian soft clay deposits it is generally admitted that the long term stability of clay slopes should be analysed in terms of effective stresses which necessitates the knowledge of the pore pressure conditions and of the relationship between the shear strength and the effective stresses this paper deals with the determination of shear strength for stability analysis of clay slopes in eastern canada first the various concepts pertinent to slope stability in soft clay are examined and a certain justification of the use of the post peak or large strain strength is demonstrated in a second part 14 case records of natural slopes or permanent excavation slopes are presented and analysed in terms of the post peak strength finally values of post peak strength determined in the laboratory for more than 30 sites are presented and it is attempted to derive correlations by which the shear strength parameters could be readily approximated from other properties such as the apparent preconsolidation pressure or the vane strength

an updated astronomical timescale for the plio pleistocene deposits from south china sea and new insights into asian monsoon evolution abstract here we present an improved astronomical timescale since 5 ma as recorded in the odp site 1143 in the southern south china sea using a recently published asian summer monsoon record hematite to goethite content ratio hm gt and a parallel benthic 18o record correlation of the benthic 18o record to the stack of 57 globally distributed benthic 18o records lr04 stack and the hm gt curve to the 65 n summer insolation curve is a particularly useful approach to obtain refined timescales hence it constitutes the basis for our effort our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the odp site 1143 this updated timescale further enables a detailed study of the orbital variability of low latitude asian summer monsoon throughout the plio pleistocene comparison of the hm gt record with the 18o record from the same core reveals that the oscillations of low latitude asian summer monsoon over orbital scales differed considerably from the glacial interglacial climate cycles the popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low latitude asia in low latitude asia some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages vice versa some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages the well known mid pleistocene transition mpt is only identified in the benthic 18o record but not in the hm gt record from the same core this suggests that the mpt may be a feature of high and middle latitude climates possibly determined by high latitude ice sheet dynamics for low latitude monsoonal climate its orbital scale variations respond more directly to insolation and are little influenced by high latitude processes thus the mpt is likely not recorded in addition the hm gt record suggests that low latitude asian summer monsoon intensity has a long term decreasing trend since 2 8 ma with increased oscillation amplitude this long term variability is presumably linked to the northern hemisphere glaciation since then

analysis of lithic technology of lower pleistocene sites and environmental information in the nihewan basin north china the nihewan basin is an important area for studying the evolution of early hominids in china among 15 recently discovered and reported lower pleistocene sites in the basin eight majuangou xiaochangliang dachangliang banshan donggutuo feiliang huojiadi xujiapo have been specifically analyzed by the authors this paper is a synthesis of results of analysis of lithic technology and palaeoenvironmental information of these sites three distinct arrangements of techniques are identified from the eight sites which represent the different lithic techniques cognitive capability and cultural contents the dgt core from donggutuo indicates that the cognitive capability and the culture deepness of early hominids in china surpassed expectations re evaluation is required of early human technology and behavioral mode in china

a simple model for the interpretation of magnetic records in lacustrine and ocean sediments abstract many sources of magnetic minerals have been implicated as potential influences on the magnetic record of lake and ocean sediments the state of the art of our knowledge of these sources and their properties has been used to define a model which indicates those sedimentary environments where specific magnetic mineral sources may influence the magnetic record authigenically formed magnetic minerals are only likely to be found in estuaries and eutrophic lakes cosmic deposition eolian deposition and magnetic bacteria may be important in low accumulation rate deep ocean sediments whereas catchment derived material is only likely to be the sole source of the magnetic record in high accumulation rate low productivity lakes fly ash is only likely to be a dominant source in very low accumulation rate lake and ocean sediments

a 13 000 year record of environmental magnetic variations in the lake and peat deposits from the chandra valley lahaul implications to holocene monsoonal variability in the nw himalaya abstract an 13 000 year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the chandra valley of the lahaul himalaya is studied to generate the record of environmental magnetic signatures in response to indian summer monsoon ism variability in the nw himalaya the chronology of studied chandra peat trench cpt profile is based on 9 ams 14c calibrated dates cal yr bp the piece wise linear regression analysis of age depth model indicates non linear sedimentation with higher rates from 4142 cal yr bp to the present and lower accumulation during 12 880 4142 cal yr bp the mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat lake sediment sequence i e 1 mixed ferri and antiferromagnetic minerals between 12 880 and 11 019 cal yr bp 2 dominant antiferromagnetic mineralogy from 11 019 to 3172 cal yr bp and 3 significantly increased concentrations of mixed ferri and antiferromagnetic minerals from 3172 cal yr bp to the present with characteristically increased ferrimagnetic concentrations after 2032 cal yr bp the characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from 10 398 to 5770 cal yr bp suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ism intensity during early to mid holocene warm wet climate in the nw himalaya the distinctly increased concentration of antiferromagnetic minerals from 6732 to 5770 cal yr bp indicates mid holocene climate optimum hco in the lahaul himalaya the strengthening and weakening of ism recorded in environmental magnetic signatures during 1260 852 cal yr bp 690 1098 ad and between 852 and 239 cal yr bp 1098 1711 ad corresponds to medieval warm period mwp and little ice age lia events respectively

climate control on the palaeo lake evolution in the southern datong basin north china evidence from 800 ka core records integrated sedimentological and clay mineral analyses of a 300 m depth core reveal the history of the palaeo lake and palaeoclimatic evolution of the southern datong basin over the past 800 ka the sedimentary facies including deep lake shallow lake alternation of lakeside and shallow lake and the river environment are identified based on the general characteristics of the grain size analysis two episodes of warm humid events are responsible for the palaeo lake expansion during the period of 800 480 ka corresponding to the presence of s7 s6 and s5 in the loess plateau a stepwise cooling and drying trend since approximately 480 ka is strongly linked to the gradual shrinkage and extinction of the palaeo lake our results demonstrated that climate change has played an essential role on the palaeo lake expansion shrinkage during the middle pleistocene breaching of shixia gorge by active neotectonic movement since the middle late pleistocene enhanced the shrinkage and extinction of the palaeo lake coupled with a cold dry climate in the last glacial the climatic changes documented by clay minerals and grain size parameters in the datong basin are consistent with the loess paleosol sequences in the loess plateau and fluvio lacustrine sediments in the nihewan basin mainly controlled by the east asian monsoon in response to the regional global change since the mid late pleistocene

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

a 15 400 year record of environmental magnetic variations in sub alpine lake sediments from the western nanling mountains in south china implications for palaeoenvironmental changes abstract a detailed environmental magnetic investigation has been performed on a sub alpine sedimentary succession deposited over the past 15 400 years in daping swamp in the western nanling mountains of south china magnetic parameters reveal that fine grains of pseudo single domain psd magnetite or titanomagnetite are the dominant magnetic minerals in the lake sediments and surface soils collected from the catchment which suggests that magnetic minerals in lake sediments mainly originated from surface soil erosion of the catchment variation of surface runoff caused by rainfall is interpreted as the main process for transportation of weathered soils into the lake in the last deglacial period lgp 15 400 11 500 cal a bp the influx of magnetic minerals of detrital material may have been significantly affected by the severe dry and cold conditions of the last glacial maximum stabilised conditions of the catchment associated with increased vegetation coverage e g 8000 4500 and 2500 1000 cal a bp limited the input of magnetic minerals intensive soil erosion caused by increased human activity may have given rise to abnormal increases in multiple magnetic parameters after 1000 cal a bp because changes in runoff and vegetation coverage are closely related to asian summer monsoon asm intensity the sedimentary magnetism of daping swamp provides another source of information to investigate the evolution of the asm

environmental magnetic record of antarctic palaeoclimate from eocene oligocene glaciomarine sediments victoria land basin summary the onset of continent wide glaciation in antarctica is still poorly understood despite being one of the most important palaeoclimatic events in the cenozoic the eocene oligocene boundary interval has recently been recognized as a critical time for antarctic climatic evolution and it may mark the preglacial glacial transition magnetic susceptibility intensity of natural and artificial remanences hysteresis parameters and magnetic anisotropy of the lower half late eocene early oligocene of the ciros 1 core from mcmurdo sound antarctica reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core pseudo single domain magnetite is the main magnetic mineral throughout the sequence and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the eocene oligocene boundary the detrital magnetite originated from weathering of the ferrar group which comprises basic extrusive and intrusive igneous rocks weathering processes and input of magnetite to the victoria land basin were intense during periods when the antarctic climate was warmer than today but during intervals when the climate was relatively cool chemical weathering of the ferrar group was suppressed and input of detrital magnetite to the victoria land basin decreased our results also indicate that a cold and dry climate was not established in antarctica until the eocene oligocene boundary with major ice sheet growth occurring at the early late oligocene boundary some earlier cold intervals are identified which indicate that climate had begun to deteriorate by the middle late eocene boundary

palaeoclimatic interpretation of stable isotope ratios in molluscan fossils from middle pleistocene marine strata wanganui new zealand abstract fossils molluscan shells from the okehu and kai iwi groups and recent molluscan shells from new zealand coastal waters exhibit considerable intraspecific variation in isotopic composition which is probably related to different infaunal and epifaunal modes of life the epifaunal species chlamys gemmulata proved the most reliable for providing information on changes in temperature or isotopic composition of ocean water during okehuan time analyses of c gemmulata shells indicate a substantial decrease in temperature or increase in size of ice caps at about 0 75 ma probably in the latter part of the gunz glaciation and thereafter minor oscillations with a slight trend towards warming or decreasing ice until about 0 5 ma that is during the cromer interglacial

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

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

variations of illite chlorite ratio in chinese loess sections during the last glacial and interglacial cycle implications for monsoon reconstruction 1 the variations of the clay minerals illite and chlorite were measured by xrd in the 2 m fraction of four loess sections along a north south transect on the chinese loess plateau clp the ratio of illite to chlorite i c provides a tool to evaluate strong monsoon conditions on the clp i c ratios above 2 5 indicate strong chlorite silicate weathering a process that takes place under a regime which at present in the southern clp has annual precipitation and temperature exceeding 600 mm and 10 c respectively the weathering regime during the last previous interglacial period in the southern clp may have been warmer and had higher rainfall during weathering the chlorite may release iron so that nanometer sized iron oxide minerals may form and the free fe2o3 and magnetic susceptibility are increased in the resulting paleosol if that has occurred in the four sections studied it is only in the southern two

iron oxide formation in the active oxidation front above sapropel s1 in the eastern mediterranean sea as derived from low temperature magnetism low temperature magnetic properties of eastern mediterranean sediments from a box core have been investigated this box core contains the present day oxic suboxic boundary that is situated at the top of the relic of the youngest sapropel sl the upper half of sapropel s1 has been oxidized and fe oxides have precipitated in the oxidized sapropel zero field cooling zfc and field cooling fc saturation remanent magnetization m r induced in a field of 2 5 t at 20 k after cooling from 300 k with or without the 2 5 t field was measured during warming to 300 k an m r imparted at room temperature rtsirm was cycled to 20 k as well the difference between zfc and fc curves around the verwey transition as estimated by the parameter f c z f c suggests the presence of magnetosomes in the oxidized part of the sapropel we propose a new parameter d m 1 5 0 3 0 0 k r f c m 1 5 0 1 3 0 0 k r z f c m 3 0 0 k r f c where m 1 5 0 3 0 0 k r z f c represents the average remanence between 150 and 300 k to estimate the difference between zfc and fc curves above the verwey transition this is interpreted as being indicative of the number of defects and the extent of partial maghemitization at the oxic suboxic boundary where fe oxides actively precipitate the magnetite appears to be least maghemitized as inferred from low values for d further upward in the oxidized sapropel in older precipitates the magnetite is slightly more maghemitized just below the sapropel maghemitization is most pronounced in addition the initial slope of zfc and fc curves indicates that small grains or grain coatings that are superparamagnetic at room temperature sp are enriched at the oxic suboxic boundary higher in the oxidized sapropel the relative contribution of sp grains decreases presumably because they age to larger grains

stable carbon and oxygen isotope compositions of mollusc shells from britain and new zealand abstract stable carbon and oxygen isotope analysis of the carbonate shells of two fossil mollusc species from the plio pleistocene of new zealand and two recent species from the west coast of scotland has revealed an unexpectedly high degree of variability for each species and a positive correlation between 13 c and 18 o in each case this phenomenon may be due to kinetic isotope effects which are inherent in fastgrowing shells or areas of shell if this is the case then equilibrium isotope partitioning may not have had time to occur before the completion of calcite precipitation kinetic effects would tend to favour the lighter isotopes of both carbon and oxygen it is therefore the highest 13 c and 18 o values that are most likely to reflect equilibrium with the environment very small carbonate particles often give particularly low 13 c and 18 o values these results have implications for the use of isotopic data in environmental reconstruction based on fast growing shells and may also be applicable to other carbonate precipitating organisms

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

post depositional forcing of magnetic susceptibility variations at kurtak section siberia abstract magnetic susceptibility ms of aeolian deposits on the chinese loess plateau is high in paleosol and low in loess the ms of paleosols is mainly enhanced by ferromagnetic minerals formed during post depositional soil development in central alaska aeolian deposits ms is high in loess and low in paleosol the wind vigor model has been proposed to interpret such ms enhancement for the central alaskan loess this model suggests that the ms variations are determined by pre depositional wind strength the wind vigor model has been introduced to the siberian kurtak section where ms is also high in loess and low in paleosol additionally to the wind vigor model low ms in paleosols could be triggered by post depositional soil development and gleying when the pedogenesis and gleying transforms the ferromagnetic minerals to weak and non magnetic minerals in our study of the most continuous kurtak section in western siberia we found that paleosols have substantially more ferruginous mottles due to water saturated conditions magnetic analysis demonstrates that paleosols contain greater content of hard magnetic minerals compared to the loess temperature analysis of the ms in the ferruginous mottles shows that magnetic susceptibility increases 37 times after heating and cooling half of the ms enhancements are contributed due to the heating in between 600 and 700 c being caused by the decomposition of non magnetic chlorite this suggests that pedogenesis and gleying at the kurtak section produces weak and non magnetic minerals in water saturated anaerobic conditions which deplete the ms in paleosols after deposition of loess

analysis of mudstone deterioration and its effect on tunnel performance abstract tunnelling through tertiary mudstone bedrocks often encounters long term instability in terms of high rock pressure or excessive displacement of tunnel walls these deposits tend to soften due to water absorption upon unloading moisture humidity changes and weathering and deteriorate with time in this paper strength deterioration due to softening of mudstone and its interaction to tunnel performance are briefly discussed then a finite element analysis is presented as an example for illustrating the influence of strength deterioration upon tunnel behaviour also described is stress transfer around tunnel associated with progressive yielding due to softening

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

magnetostratigraphic lithostratigraphic and tephrostratigraphic constraints on lower and middle pleistocene sea level changes wanganui basin new zealand wanganui basin north island new zealand contains a complex sedimentary record of lower and middle pleistocene sea level changes palaeomagnetic results allow identification of the matuyama brunhes transition the jaramillo subchron and the cobb mountain subchron correlations of rhyolitic tuff horizons across the basin are consistent with magnetostratigraphic correlations between sections isothermal plateau fission track itpft ages of 1 05 0 05 ma and 1 63 0 15 ma on two tuffs potaka pumice and pakihikura pumice respectively are consistent with the interpreted magnetostratigraphy and also with the astronomically tuned timescale of odp site 677 magnetostratigraphy and itpft ages allow correlation of sedimentary cycles at wanganui with odd numbered oxygen isotope stages 17 31 in deep sea cores the stratotype section for the new zealand castlecliffian stage is shown to be incomplete relative to other studied sections in the basin below stage 31 the character of the cyclothems changes at wanganui from marine dominated to a greater representation of non marine and estuarine strata this change may be partly related to a change in amplitude and frequency of climatic cycles identified in oxygen isotope records but the primary cause is likely to be increased basinal uplift

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

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

mineral magnetic variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability 1 to retrieve reliable long term paleoclimatic signals from the chinese loess paleosol sequences deposited over the past 2 6 myr multiparameter mineral magnetic investigations have been conducted on the jiaodao section on the chinese central loess plateau first the lithogenic magnetic components and the pedogenic overprinting were chemically separated by the citrate bicarbonate dithionite cbd method the magnetic properties of the least pedogenically altered loess units and post cbd loess paleosols are dominated by coarse grained lithogenic magnetite increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite maghemite long term changes of the pre cbd magnetic properties suggest a long term decrease in summer monsoon intensity and a long term increase in winter monsoon intensity from the late pliocene to the late pleistocene long term variations of the post cbd magnetic properties suggest an increase in both concentration and grain size of coarse grained lithogenic psd md magnetite grains and hence indicate a long term increase in winter monsoon intensity over that period the coercivity decrease of the lithogenic component for the loess unit l15 may be related to the accelerated uplift of the tibetan plateau and its adjacent regions during the period of l15 deposition from paleosol s5 to loess l1 higher values of coercivity of the lithogenic component occur in typical loess and paleosols and lower values are found at the loess paleosol transition these coercivity variations are thought to be related to significant changes in the source region as well as dust deposition in the loess plateau caused by changes in ice snow or vegetational cover these new results lead to a better understanding of the relationships between the effects of tectonic paleoclimatic and paleoenvironmental processes in northwestern china

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

field observations of frost action in intact and weathered champlain sea clay this paper presents the results of a field study on frost action in sensitive saint alban clay both in an intact state never subjected to any freeze thaw cycles and in its weathered state corres

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

form and flow of the academy of sciences ice cap severnaya zemlya russian high arctic 1 the 5 575 km2 academy of sciences ice cap is the largest in the russian arctic a 100 mhz airborne radar digital landsat imagery and satellite synthetic aperture radar sar interferometry are used to investigate its form and flow including the proportion of mass lost through iceberg calving the ice cap was covered by a 10 km spaced grid of radar flight paths and the central portion was covered by a grid at 5 km intervals a total of 1 657 km of radar data digital elevation models dems of ice surface elevation ice thickness and bed elevation data sets were produced cell size 500 m the dems were used in the selection of a deep ice core drill site total ice cap volume is 2 184 km3 5 5 mm sea level equivalent the ice cap has a single dome reaching 749 m maximum ice thickness is 819 m about 200 km or 42 of the ice margin is marine about 50 of the ice cap bed is below sea level the central divide of the ice cap and several major drainage basins in the south and east of the ice cap and of up to 975 km2 are delimited from satellite imagery there is no evidence of past surge activity on the ice cap sar interferometric fringes and phase unwrapped velocities for the whole ice cap indicate slow flow in the interior and much of the margin punctuated by four fast flowing features with lateral shear zones and maximum velocity of 140 m yr 1 these ice streams extend back into the slower moving ice to within 5 10 km of the ice cap crest they have lengths of 17 37 km and widths of 4 8 km mass flux from these ice streams is 0 54 km3 yr 1 tabular icebergs up to 1 7 km long are produced total iceberg flux from the ice cap is 0 65 km3 yr 1 and probably represents 40 of the overall mass loss with the remainder coming from surface melting driving stresses are generally lowest 40 kpa close to the ice cap divides and in several of the ice streams ice stream motion is likely to include a significant basal component and may involve deformable marine sediments

magnetostratigraphic dating of the shanshenmiaozui mammalian fauna in the nihewan basin north china timing of the mammalian faunas in the nihewan basin north china has provided insights into our understanding of quaternary biochronology and biostratigraphy in east asia here we contribute to this topic with detailed magnetostratigraphic investigation coupled with mineral magnetic measurements on a fluvio lacustrine sequence in this basin which contains the shanshenmiaozui mammalian fauna magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations magnetostratigraphic results show that the shanshenmiaozui sedimentary sequence recorded the brunhes chron the jaramillo subchron and the late matuyama chron stratigraphic correlation in terms of lithology magnetic susceptibility and magnetic polarity sequences between the shanshenmiaozui xiaochangliang and dachangliang sections indicates that the shanshenmiaozui mammalian fossil layer is younger than the xiaochangliang and dachangliang artefact layers which have been previously estimated to be about 1 36 ma the age of the shanshenmiaozui mammalian fossil layer at the bottom of the section is estimated to be about 1 2 ma the new magnetostratigraphy of the shanshenmiaozui section provides useful constraints on lithostratigraphic and biostratigraphic correlations in the nihewan basin

effects of freeze thaw and softening on a natural clay at low stresses weathering processes such as softening and freeze thaw cycling affect the properties of clays care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes compacted clay embankments and trench excavations in which significant proportions of the cross section can be affected by climatic weathering samples of plastic lake agassiz clay from winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure they were therefore all overconsolidated with respect to the field preconsolidation pressure the samples were then loaded under drained or undrained conditions along steeply rising stress paths in p q stress space one group of samples was tested immediately to identify the undisturbed behavior a second group was subjected to freeze thaw cycles and a third group allowed to swell freely before testing the freeze thaw cycling produced increased compressibility and pore

development of the east asian monsoon mineralogical and sedimentologic records in the northern south china sea since 20 ma we here reconstruct the past change of the east asian monsoon since 20 ma using samples from ocean drilling program odp site 1146 in the northern south china sea based on a multi proxy approach including a monomineralic quartz isolation procedure identification of clay minerals by x ray diffraction xrd and grain size analysis of isolated terrigenous materials terrigenous supply to odp site 1146 was dominated by changes in the strength of multiple sources and transport processes grain size data modeled by an end member modeling algorithm indicate that eolian dust from the and asian inland and fluvial input have contributed on average 20 and 80 of total terrigenous material to odp site 1146 respectively specifically about 40 53 of the total quartz feldspar and only 6 11 of the total clay is related to eolian supply at the study site detailed analysis of the sedimentary environment and clay minerals combined with previous studies shows that smectite originates mainly from luzon kaolinite from the pearl river and illite and chlorite from the pearl river taiwan and or the yangtze river the proportion and mass accumulation rate mar of the coarsest end member em1 interpreted as eolian dust ratios of illite chlorite smectite quartz feldspar and mean grain size of terrigenous materials at odp site 1146 were adopted as proxies for east asian monsoon evolution the consistent variation of these independent proxies since 20 ma shows three profound shifts in the intensity of east asian winter monsoon relative to summer monsoon as well as aridity of the asian continent occurred at similar to 15 ma similar to 8 ma and the youngest at about 3 ma in comparison the summer monsoon intensified contemporaneously with the winter monsoon at 3 ma the phased uplift of the himalaya tibetan plateau may have played a significant role in strengthening the asian monsoon at similar to 15 ma 8 ma and 3 ma c 2007 elsevier b v all rights reserved

magnetic proxy climate results from the duanjiapo loess section southernmost extremity of the chinese loess plateau we report mineral magnetic results from a 7 5 m loess sequence 150 samples from the southernmost extremity of the chinese loess plateau which includes the last two glacial cycles in this area the loess sediments experienced particularly intense weathering processes the magnetic assemblage is dominated by a mixture of pseudo single domain psd and multidomain md magnetite with associated superparamagnetic sp grains of either magnetite or maghemite in the paleosols and weathered loess horizons all the rock magnetic parameters fluctuate in parallel with marine sediment 18o data over the last 150 kyr thus reflecting changing global paleoclimatic conditions this relationship is also supported by the evidence of milankovitch cycles in the magnetic susceptibility record paleorainfall estimates when compared with other studies from the chinese loess plateau underline the more humid character of this region during the last 130 kyr

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

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

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

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

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

carbon and oxygen stable isotope values in shells of mytilus edulis and modiolus modiolus from holocene raised beaches at the outer coast of the varanger peninsula north norway the amplitudes of isotopic temperatures based on the stable isotope values of the calcite in profiles from shells of mytilus and modiolus from holocene raised beaches earlier dated and in recent modiolus shells were shown to correspond to the observed annual amplitude of the surface water in the area the relation between 13c and 18o values shows that the ocean water has been mixed with fresh water from the rivers at the coast where the molluscs lived the isotopic temperatures were therefore based on this ratio no clear differences in annual temperatures could be demonstrated within the period studied of about 4500 years

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