oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

pleistocene chemical weathering history of asian arid and semi arid regions recorded in loess deposits of china and tajikistan quaternary loess soil sequences in china and tajikistan are valuable archives of the chemical weathering history for arid and semiarid regions of asia the development of new proxies independent of grain size are vital to reconstruct the long term chemical weathering history of eolian deposits in this study we analyze major elemental and rb sr and ba concentrations of decarbonated residue from representative loess and soil units along a north south transect on the chinese loess plateau and compare these concentrations among different grain size fractions results show that most of the elemental abundances and ratios vary considerably among different grain size fractions for both loess and paleosols indicating transport driven compositional differentiation of minerals during subaerial transport however cao na2o mgo tio2 ratios show little variation among different size fractions for the loess soil transect loess soil sequences at lingtai northern china and chashmanigar southern tajikistan for the past 1 50 1 77 ma show lower cao na2o mgo tio2 ratios in soil units than in adjacent loess horizons in good agreement with greater weathering intensity in soils than in loess units the cao na2o mgo tio2 ratio of the decarbonated residue is therefore a reliable proxy for chemical weathering of loess deposits that is independent of grain size the cao na2o mgo tio2 ratios of the lingtai and chashmanigar sections display a relatively regular oscillation within a narrow range in the early pleistocene and a rapid increase in average values and in variance from 0 85 0 6 ma to the present indicating lowered chemical weathering intensity in both the dust source regions and the depositional areas this event may be causally related to the expansion of northern hemisphere ice and or the regional tectonic uplift of high mountains in asia since the mid pleistocene

mountains and arid climates of middle latitudes simulations from a global climate model with and without orography have been used to investigate the role of mountains in maintaining extensive arid climates in middle latitudes of the northern hemisphere dry climates similar to those observed were simulated over central asia and western interior north america in the experiment with mountains whereas relatively moist climates were simulated in these areas in the absence of orography the experiments suggest that these interior regions are dry because general subsidence and relatively infrequent storm development occur upstream of orographically induced stationary wave troughs downstream of these troughs precipitation bearing storms develop frequently in association with strong jet streams in contrast both atmospheric circulation and precipitation were more zonally symmetric in the experiment without mountains in addition orography reduces the moisture transport into the continental interiors from nearby oceanic sources the relative soil wetness of these regions in the experiment without mountains is consistent with paleoclimatic evidence of less aridity during the late tertiary before substantial uplift of the rocky mountains and tibetan plateau is believed to have occurred

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

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

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

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

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

comparison of particle size characteristics of the tertiary red clay and pleistocene loess in the chinese loess plateau implications for origin and sources of the red clay the origin of the tertiary red clay underlying the pleistocene loess in the chinese loess plateau remains controversial although several lines of evidence have suggested a wind blown origin this study examines the particle size parameters of the late miocene and pliocene red clay by comparing it with those of the late pleistocene loess the particle size distribution of a total of 15 339 loess and 6394 red clay samples taken from 12 loess sections along a north south transect and two red clay sequences at lingtai and jingchuan was systematically analysed the median grain size skewness and kurtosis of the late pleistocene loess all show a systematic southward change and are principally influenced by distance from source region the spatial and temporal differentiation of dust deposits is expressed in a skewness kurtosis median grain size ternary diagram from which the distance to the source region can be inferred the particle size characteristics of the tertiary red clay sediments are very similar to those of the palaeosols within the late pleistocene loess deposits suggesting an aeolian origin for the red clay based on the comparison of red clay and loess in the ternary diagrams it is inferred that the source sink distance was greater in the neogene than in the last and penultimate interglacials and that the dust source region in north western china underwent a progressive expansion during the period from at least 7ae0 ma to the present

on the reliability and comparability of laser diffraction grain size measurements of paleosols in loess records abstract laser diffraction grain size data and size distributions of paleosols are widely used in paleoenvironmental reconstructions as physicochemical alteration related proxies of past changes of the sedimentary environment different laser diffraction devices optical theories and optical settings are being applied nowadays and ignorance of several uncertainty factors and drawbacks of this indirect grain size characterization approach has led to poorly comparable and reproducible granulometric datasets here we present a detailed comparison of grain size results acquired by three state of the art widely used laser diffraction devices fritsch analysette 22 microtec plus horiba partica la 950 v2 and malvern mastersizer 3000 grain size distributions were calculated using both the fraunhofer and mie scattering theories and a wide variety of optical settings 68 different complex refractive indices 1 45 1 6 0 01i 1i for 10 samples from loess paleosol sequences of the carpathian basin our findings demonstrate that optical settings have significant effects on grain size distributions especially for the finest fractions clay and fine silt populations interestingly the selection of laser diffraction devices was an even more deterministic factor in grain size characterization as revealed by network analyses clustering of bulk and size fractionated grain size records was primarily determined by the device used and also by the applied optical settings at the same time the real physical differences of samples were found to be deterministic exclusively for the sand sized fraction as such these findings emphasize the importance of the accurate description of applied methodological details in research papers as comparability and reproducibility of granulometric datasets cannot be ensured with a lack of information about instrumental conditions and settings

weathering histories of chinese loess deposits based on uranium and thorium series nuclides and cosmogenic 10be the long continuous deposition of dust in the chinese loess plateau liu et al 1985 kukla and an 1989 ding et al 1991a offers an unique opportunity to study the nature of soil weathering in a wide range of climatic conditions in this paper we report on measurements of concentrations of u and th series nuclides and of major cations in 150 loess and paleosol samples from five sites going back 2 5 ma using the results for 10be concentrations in these soils gu et al 1996 we determined the absolute amounts of water added to several soil units and obtained 1 first order leaching constants for u and several cations and 2 the compositions of the soils contributing to the dust source regions and of the dust at deposition further based on analyses of 230th in soils deposited in the past ca 140 ka we determined when the soils weathered in the source regions we conclude that most of the weathering in the dust source regions may have occurred during the interglacials

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

mineralogical and geochemical trends across the loess plateau north china abstract the mineralogy and major element geochemistry of malan loess the uppermost loess layer were studied along two transects from the baiyu mountains in the north to the wei river lowlands 350 km to the south the mineralogy of the coarse silt fine silt and clay fractions is generally uniform across the loess plateau however in the coarse silt fraction there is a decrease in the weight percentage of heavy minerals and in the hornblende epidote ratio southwards also in the clay fraction mica contents increase slightly southwards and smectite increases northwards along one transect the major element geochemistry of malan loess shows several clear trends silicon sodium and magnesium generally decrease from north to south while aluminium iron potassium titanium and manganese generally increase the observed mineralogical and chemical patterns appear to be mainly related to the changing particle size from sandy loess in the north to clayey loess in the south slightly higher potassium and phosphorus contents in the clayey loess suggest that this loess has a greater natural fertility overall the results confirm particle size evidence that malan loess was derived from a desert source area to the north and northwest of the loess plateau

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

the loess record in southern tajikistan and correlation with chinese loess in the present study the chashmanigar loess soil sequence in southern tajikistan is studied this loess section has a paleomagnetic basal age of about 1 77 myr magnetic susceptibility color reflectance and grain size were systematically measured for closely spaced samples from the section paleosols consistently have a finer grain size distribution higher magnetic susceptibility redder color reflectance and lower dust sedimentation rate than loess horizons suggesting a colder drier and dustier environment during glacial periods than in interglacial periods the grain size record was tuned to variations in obliquity and precession of the earth s orbit the resulting magnetic susceptibility grain size and color reflectance time series all show well expressed astronomical periodicities during the pleistocene the mid pleistocene climate transition characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1 0 0 8 myr is clearly documented in these proxy records comparison of the chashmanigar loess record with the lingtai loess section in china and the odp site 677 n 18 o record shows that during the entire pleistocene the climate cycles recorded by the central asian loess can be well correlated to the chinese loess and deep sea oxygen isotope records it is suggested that alternations of loess and soil horizons both in central asia and china could be basically forced by global ice volume variations although different wind systems have controlled the pleistocene loess transport and sedimentation in the two areas 2002 elsevier science b v all rights reserved

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

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

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

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

an introductory overview to the concept of displaced terranes on land much of the pacific margin is composed of allochthonous terranes which are of continental and noncontinental origins in the oceans numerous oceanic rises some of which are submerged continental fragments are presently embedded in the oceanic plates these oceanic rises are probably future accreted terranes they thus represent one stage in the development of allochthonous terranes found in orogenic zones minerals found in these terranes were formed at locations that in the past could have been thousands of kilometres away this is because some oceanic terranes were split into several parts that moved with their respective plates in different directions also faulting at the continental margins caused large scale concurrent and post accretionary horizontal translations of hundreds of kilometres of the allochthonous terranes studying the allochthonous terranes may provide important information about the paleozoic and early mesozoic history of the pacific ocean because most of the oceanic crus

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

loess stratigraphy of central asia palaeoclimatic and palaeoenvironmental aspects abstract the loess palaeosol succession of central asia is comparable with that of the loess plateau in north china palaeomagnetic investigations and palaeontological studies in south tadjikistan suggest a date of 2 2 5 ma for the oldest loess indicating that dust storms became frequent in the region since 2 2 5 ma bp under the prevalently arid and semi arid environments of central asia aeolian processes had a gradually increasing influence on subaerial sedimentation during the pleistocene however atmospheric aeolian processes in central asia have mainly developed in accordance with pleistocene climatic cyclicity without extremely high intensification during the late pleistocene as implied by the previous tl dating results the identification of loess and palaeosol horizons with respective glaciations and interglacials is sometimes disputable nevertheless the available data in spite of limited evidence characterise well developed palaeosols of the middle and late pleistocene as warm and wet intervals associated with interglacials palynological studies of loess sections show that loess and palaeosol horizons have palynological spectra that are sometimes difficult to interpret interregional loess palaeosol correlation with glacial interglacial events as well as with oxygen isotope records should be supplied by multidisciplinary investigations

tephra deposits associated with a large lava dome collapse soufriere hills volcano montserrat 12 15 july 2003 abstract the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat was the largest event of its kind during the eruption thus far 1995 2005 involving the removal of 210 million m 3 of the lava dome complex over 18 h less than 2 of the total volume of material involved in the dome collapse was deposited on land a pyroclastic density current deposit alongshore and inland from the tar river fan was generated from a single blast originating at the shoreline the blast was caused by the interaction of pyroclastic flows with seawater we propose that at the peak of the lava dome collapse a sharp increase in the volume flux of pyroclastic flows caused substantial displacement of seawater from the shoreline followed by inrush of seawater when the flux decreased a few minutes later the tsunami allowed penetration of seawater into the main body of the pyroclastic flow at the shoreline which led to explosive fragmentation of pyroclastic blocks tephra fall deposits accumulated at a high rate on montserrat causing extensive damage to vegetation and buildings their stratigraphy recorded fallout from high co pyroclastic flow clouds from a vulcanian explosion cloud at the peak in collapse rate caused by the fragmentation of degassed lava dome and from four vulcanian explosion clouds after the dome collapse caused by fragmentation of bubbly magma in the conduit the total tephra fall volume is estimated at 10 20 million m 3

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

stratigraphic evidence for the uplift of the tibetan plateau between 1 1 and 0 9 myr ago uplift of the tibetan plateau is manifest not only in widespread denudation but also by an increased deposition rate of sediment near or far from the exhumed regions our results indicate that the mass accumulation rate mar of eolian dust increased between 1 1 and 0 9 myr ago we associate this increase in mar and median grain size with uplift of the tibetan plateau and its adjacent regions during this period this middle pleistocene uplift can also be evidenced by the age of volcanism in the marginal region the existence of thick conglomerate deposits surrounding the uplifted plateau and the increased sedimentation rate of lacustrine deposits in the qaidam basin northeastern tibetan plateau between 1 1 and 0 9 myr ago the correlation between the loess and marine records indicates that after 0 9 myr ago these two records correlate well this good correlation probably suggest that the middle pleistocene upheaval event not only brought the plateau into the cryosphere but also enhanced the coupling of regional scale chinese loess transportation and deposition to the global ice volume variations through its effects on glacial grinding rock denudation and east asian monsoonal circulation

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene