new absolute time scale for the quaternary climate in the chinese loess region by grain size analysis continuous loess sequences in china provide not only information for paleoclimatic reconstructions but also permit the establishment of a reliable absolute time scale for the quaternary an empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short well dated reference section step 1 this relationship is extrapolated to the complete quaternary section step 2 after derivation of the sedimentation rate by measuring the grain size in all the layers of the sequence the duration of deposition of each layer is obtained by dividing thickness by sedimentation rate and subsequently the age of each point in the sequence is calculated by adding together all the duration values of the overlying layers the chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

chronology and paleoenvironmental records of a drill core in the central tengger desert of china abstract the desertification history of inland asia provides most direct evidence for asian drying history but the formation ages of the most asian deserts are not clear due to the lack of outcrops the tengger desert one of the main proximal deserts of the chinese loess plateau clp is of special paleoclimatic significances for its dust emission and environmental affection here we report lithofacies paleomagnetic ages and paleoenvironmental proxy indexes of the first drill core wedp01 from the central tengger desert paleomagnetism measurements reveal that the core spans from 3 55 ma to present consistent with the electron spin resonance esr dating results the strata of the central desert consist of alluvial fluvial deposits lacustrine fluvial deposits mixed with dust and eolian sand from bottom to top sedimentary analysis reveals that continuous eolian sand started by 0 9 ma marking the initial formation of the tengger desert and the domination of eolian sand in the strata with similar characters of the modern desert appeared by 0 68 ma indicating expansion of the tengger desert the proximal deserts formation and simultaneous increase of dust accumulation in the clp and the north pacific ocean in mid pleistocene demonstrate the role of proximal deserts for the dust loading of northern china and even northern hemisphere our analysis suggests the uplift of tibetan plateau in the mid pleistocene probably played the main role for this drying event and desert formation while global cooling may strength the arid environment of the proximal deserts

loess record of the aerodynamic environment in the east asia monsoon area since 60 000 years before present 1 the multimodal distribution of grains in loess and dust storm deposits has been widely reported in recent years our analysis demonstrates that the interaction of wind atmospheric turbulence and dust grain gravity along the dust transportation path results in a multimodal grain size distribution for suspended dust changes in the median sizes of the coarse and medium modes are related to variation in aerodynamic forcing lift force related to vertical wind and turbulence during dust entrainment in the source area and turbulence intensity in the depositional area on the basis of the numeric characteristics of the three modes of suspended particles a tentative model has been constructed which is used to study fluctuations of paleoaerodynamic environments from a time series of paleoatmospheric environmental changes of the loess plateau for the past 60 000 years we find that there are three patterns of aerodynamic environments in the dust source area stronger strong weak and 13 strong turbulence events since 60 000 years b p climatic variability in the dust depositional area is stronger than in the source area during the last glacial period the aerodynamic environment changed synchronously in the dust source and depositional areas over the entire trend however after 8000 years b p the aerodynamic force is strong in the dust source area while the turbulence intensity is weak in the dust depositional area differing from that of the last glacial period the strong turbulence periods correspond to the cooling events such as the heinrich events and the younger dryas cold event and may not be related to factors forcing the alternation between glacial and interglacial periods since 60 000 years b p the three patterns of aerodynamic environments are mainly controlled by the environmental changes in the dust source area and may be related to fluctuations of the winter monsoon in each pattern fluctuations of the turbulence intensity in the dust depositional area and the distance from dust source to dust depositional area are the major changes of the environment the summer monsoon recorded by magnetic susceptibility may vary prior to the winter monsoon since 50 000 years b p changes in the intensity of the summer monsoon may force changes in the advance retreat cycles of dust source areas in each winter monsoon pattern

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

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

pronounced changes in paleo wind direction and dust sources during mis3b recorded in the tacheng loess northwest china abstract central asia loess deposits can yield detailed records of aridification across the asian interior as well as the atmospheric circulation in this study we presented grain size heavy mineral assemblage rock magnetism and anisotropy of magnetic susceptibility of a loess section in the tacheng basin in xinjiang region nw china the results of anisotropy of magnetic susceptibility indicated that a near surface se wind prevailed in the tacheng area since marine isotope stage mis 3 while a near surface sw prevailing wind developed during mis3b we inferred that the change of wind direction was due to glacial advance during mis3b combining the result of anisotropy of magnetic susceptibility with grain size heavy mineral assemblage data and previously published low field mass susceptibility revealed that dust transported by the near surface sw wind had a greater ability to enhance magnetic susceptibility and higher amphibole epidote ratio additionally a strong siberian high during heinrich event h 5 at ca 48 ka blocked the advection of moisture into the region via mid latitude westerlies causing glacial recession and the weakening of the prevailing sw wind our study has implications for identifying changes in paleo wind direction and dust source which can aid understanding of the influence of westerlies and the siberian high on dust accumulation as well as their interactions

adaptation of a triaxial cell for ultrasonic p wave attenuation velocity and acoustic emission measurements adaptation of a triaxial cell for ultrasonic p wave attenuation velocity and acoustic emission measurements j a donald s d butt s iakovlev department of mining and metallurgical engineering dalhousie university 1360 barrington street sexton campus p o box 1000 halifax nova scotia canada b3j 3x4 department of engineering mathematics dalhousie university 1360 barrington street sexton campus p o box 1000 halifax nova scotia canada b3j 3x4

magnetostratigraphic age and monsoonal evolution recorded by the thickest quaternary loess deposit of the lanzhou region western chinese loess plateau abstract the loess paleosol sequences of the chinese loess plateau clp are major paleoclimatic archives which document the evolution of the east asian monsoon eam and changes in the northern hemisphere ice sheets during the quaternary glacial interglacial cycles however the mechanisms regulating the trend of eam variations on a tectonic scale are unclear the loess deposits of the western clp which have a close relationship with tectonics and climate are much better suited to exploring these mechanisms than those of the central clp however studies of long term eam evolution from the western clp have been hindered by the lack of long accurately dated sequences with high sediment accumulation rates here we address this problem via high resolution magnetostratigraphic magnetic susceptibility and grain size analyses of a 416 2 m long drill core located at xijin village near lanzhou paleomagnetic dating indicates that the basal age of the xijin loess is 2 2 ma the and grain size records reveal that the east asian summer monsoon easm and east asian winter monsoon eawm strengthened synchronously at 1 24 ma subsequently during interglacial periods the easm began to penetrate and then dominate in the lanzhou region this was followed by two stepwise uptrends commencing at 0 87 and 0 62 ma which resulted in an increasingly moist interglacial climate in the region we suggest that the uplift of the tibetan plateau was largely responsible for these three stepwise enhancements of the easm overall however the long term trend of strengthening in eawm in the area may have been primarily caused by long term global cooling from the late pliocene onwards

grain size distribution of pedogenic magnetic particles in chinese loess paleosols 1 variations in magnetic parameters of the long chinese loess paleosol sequences reflect paleoclimatic fluctuations however there remain ambiguities whether the magnetic proxies are controlled by the concentration or by the distribution of magnetic grain sizes we systematically investigated the frequency dependence of low field magnetic susceptibility fd and the decay rate dr dependence of anhysteretic remanence magnetization arm susceptibility arm dr for a set of representative loess paleosol samples from the yuanbao section western chinese loess plateau after removing the effect of aeolian coarse grained magnetites both fd and arm dr are nearly independent of the degree of pedogenesis indicating a presence of fine grained magnetic particles ranging from superparamagnetic to single domain with an almost constant grain size distribution therefore the magnetic enhancement of magnetic susceptibility or arm is caused dominantly by changes in the concentration of these fine grained pedogenic grains

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

grain size characterization of reworked fine grained aeolian deposits abstract after a previous review of the grain size characteristics of in situ primary fine grained aeolian deposits reworked secondary aeolian deposits as modified in lacustrine environments and by alluvial and pedogenic processes are discussed in this paper as a reference the grain size characteristics of primary loess deposits are shortly described commonly pedogenesis and weathering of primary loess may lead to clay neoformation and thus to an enrichment in grain diameters of 4 8 m a size which is comparable to the fine background loess remarkably the modal grain size values of primary loess are preserved after re deposition in lakes and floodplains but secondary lacustrine settings show a very characteristic admixture with a clayey population of 1 2 5 m diameter due to the process of settling in standing water similarly alluvial settings show often an addition with coarse grained sediment supplied by previously eroded sediment however floodplain settings show also often the presence of pools and other depressions which behave similarly to lacustrine environments as a result alluvial secondary loess sediments are characterized by the poorest grain size sorting when compared with the other secondary loess and primary loess despite the characteristic texture of each of these deposits grain size characteristics of the described individual sediment categories are not always fully diagnostic and thus grain size analysis should be complemented by other information as sedimentary structures and fauna or flora to reliably reconstruct the sedimentary processes and environments

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

the effect of pore pressure depletion and injection cycles on ultrasonic velocity and quality factor in a quartz sandstone passing seismic waves generate transient pore pressure changes that influence the velocity and attenuation characteristics of porous rocks compressional ultrasonic wave velocities vp and quality factors qp in a quartz sandstone were measured under cycled pore pressure and uniaxial strain conditions during a laboratory simulated injection and depletion process the objectives were to study the influence of cyclical loading on the acoustic characteristics of a reservoir sandstone and to evaluate the potential to estimate pore fluid pressure from acoustic measurements the values of vp and qp were confirmed to increase with effective stress increase but it was also observed that vp and qp increased with increasing pore pressure at constant effective stress the effective stress coefficient n was found to be less thanone and dependent on the pore pressure confining stress and load at low pore pressures n approached one and reduced nonlinearly at high pore pressures the change in vp and qp with respect

grain size and accumulation rate records from late cenozoic aeolian sequences in northern china implications for variations in the east asian winter monsoon and westerly atmospheric circulation we attempt to reconstruct the history of westerly and monsoonal circulations in northern china using variations in sediment grain size and accumulation rate at four loess sections in the central chinese loess plateau the initiation of aeolian accumulation at about 7 6 ma in the main part of the chinese loess plateau probably marked the onset of the monsoonal circulation both the monsoonal and westerly circulations weakened from 7 6 to 5 2 ma subsequently the monsoonal circulation strengthened progressively from 5 2 ma to the present in addition the westerly circulation strengthened from 5 2 to 0 6 ma but then weakened thereafter and especially during the last 0 6 ma comparison of our aeolian records and the deep sea sediment record suggests that the strengthening trends of the monsoonal and westerly circulations were associated with the progressive development of global ice sheets during the late cenozoic abrupt changes of both the monsoon and westerly circulations occurred at 7 6 3 4 and 1 2 0 9 ma together with a weakening trend of the westerly circulation in the last 0 6 ma and are interpreted as the consequence of the episodic uplift of the tibetan plateau spatial differences in the grain size characteristics amongst the four sections suggest that the circulation intensity and variability decreased from west to east across the loess plateau due to the topographic effect of the tibetan plateau in addition some spatial differences may have been the result of local topographic effects c 2008 elsevier b v all rights reserved

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

grain size of lake qinghai sediments implications for riverine input and holocene monsoon variability abstract grain size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment various grain size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake here we present the grain size results of a 5 m core retrieved from lake qinghai northeastern tibetan plateau in order to address the links between holocene depositional process and climatic change our results indicate that two parameters skewness and grain size ratio of 8 50 2 8 m are sensitive to hydrodynamic changes in lake qinghai which are further linked to the strength of the asian summer monsoon variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late holocene superimposed by persistent centennial variability with dominant periods at 0 35 0 23 and 0 12 kyr comparison of grain size variations with solar activities and north atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability

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

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

magnetostratigraphy and palaeoclimatic significance of late tertiary aeolian sequences in the chinese loess plateau summary the aeolian red clay sequence in the central part of the chinese loess plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records from the results we deduce that aeolian dust accumulation and the related east asia palaeomonsoon system began at least 7 6 myr ago and that the tibetan plateau had reached a significant elevation by that time the late tertiary palaeoclimatic history of the red clay as reflected by magnetic susceptibility is reconstructed for the time period 7 6 2 5 ma increases in aeolian dust accumulation for the last 7 6 myr appear to have a close relation with the uplift processes of the tibetan plateau the remarkable increase of aeolian dust accumulation beginning at 3 2 ma appears to reflect the influence of an increasing global ice volume on the east asian monsoon and aeolian dust accumulation

geochemical and magnetic characteristics of aeolian transported materials under different near surface wind fields an experimental study by combining field investigations field sampling wind tunnel experiments and laboratory measurements the relationships between near surface winds and the geochemical and magnetic characteristics of windtransported materials were statistically analyzed our study was conducted using bulk surface samples from a major potential dust source area in central asia the ala shan plateau under near surface wind velocities ranging from 8 to 22 m s the coefficients of variation ranged between 1 6 and 14 9 for chi if 1 4 and 11 0 for chi arm and 0 7 and 123 for sirm of the transported materials for the 26 elements and oxides investigated the coefficients of variation of ti cr as zr ce pb and cu in the samples were greater than 10 no consistent patterns were found between magnetic characteristics and elemental and iron oxide concentrations as a function of variations in near surface wind velocities in potential dust source areas under near surface wind velocities there are variations in the relationships between magnetic and geochemical characteristics in the fine fractions of transported materials with different particle sizes given the wide variation in magnetic and geochemical characteristics of aeolian transported materials under different near surface winds their use as proxies for past climate reconstruction must be carefully appraised c 2015 elsevier b v all rights reserved

optical dating of holocene paleosol development and climate changes in the yili basin arid central asia optically stimulated luminescence osl dating was conducted on the k feldspar and quartz fractions of a holocene loess paleosol sequence in the yili basin in the core area of arid central asia a

in situ remagnetization experiments of loess on the chinese loess plateau evidence for localized post depositional remanent magnetization 1 inconsistent stratigraphic positions of reversal boundaries and spurious paleomagnetic variations associated with polarity reversals recorded by loess paleosols on the chinese loess plateau clp have in general been attributed to inferred delayed acquisition of magnetization and high frequency variations of the geomagnetic field respectively these conclusions are partly based on an incomplete knowledge of the magnetization acquisition process of loess recent laboratory experiments which demonstrate that dry deposited loess acquires a stable remanent magnetization after its first wetting precipitation resulted in significant inclination errors that are not generally encountered in chinese loess laboratory experiments only remotely mimic natural conditions and we have therefore performed in situ experiments at two sites on the clp separated by some 650 km to elucidate whether variations in natural conditions can impose secondary remanent magnetization components in loess l1 the experiments were performed by relocating blocks volume 5 10 3 m3 of last interglacial loess after being turned upside down inside loess exposures inverted blocks were retrieved and analyzed after 8 and 17 months respectively thermal demagnetization reveals that partial remagnetization has occurred within different parts of the loess blocks this secondary magnetization which is characterized by blocking temperatures that overlap with those of the primary component to above 450 c cannot be attributed to a viscous remanent magnetization and is therefore proposed to represent local and partial realignment of magnetic grains we tentatively propose that physical unlocking and realignment of magnetic grains may be assisted by pressure release caused by differential thermal expansion of the different mineral grains in loess localized remagnetization may account for a number of reported spurious paleomagnetic results from clp

pedosedimentary reconstruction of a thick loess paleosol sequence near lanzhou in north central china abstract a 38 m well section near lanzhou at the semiarid western margin of the loess plateau china contained a continuous high resolution loess paleosol sequence spanning the last 130 000 yr depth functions of micromorphological features magnetic susceptibility calcium carbonate organic carbon and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol complexes s1 sm and s0 each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces three periods of reduced dust inputs and enhanced pedogenic activity notably bioturbation and weak leaching can be identified from within the s1 pedocomplex these soil forming intervals were separated by phases of varying land surface instability characterized by arid dust deposition semiarid accretionary pedogenesis water reworking and crust formation or even freeze thaw modification the sm pedocomplex represents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces the s0 pedocomplex is clearly more pedogenically developed although erosion reworking and mixing by water have partly homogenized the property depth functions

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

late quaternary aeolian dust input variability on the chinese loess plateau inferences from unmixing of loess grain size records abstract the grain size distributions gsds of loess paleosol sequences may provide valuable information on provenance transport and paleoclimate variability and consequently a wide range of methods to extract genetic information from loess gsds has been proposed here it is shown that a genetically meaningful decomposition of a series of late quaternary loess grain size records extending across the chinese loess plateau can be accomplished with the end member modelling algorithm emma the unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the loess plateau during the last glacial interglacial cycle i a background sedimentation pattern that was dominant during interglacial periods especially over the central and southern parts of the loess plateau is reflected by the constant flux of the fine grained loess component ii an episodic highly variable dust input pattern that was dominant during glacial periods throughout the loess plateau and noticeable during interglacial periods mainly over the northern loess plateau and almost disappearing over the southern loess plateau is reflected in the admixture of two coarse grained loess components a genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their gsd and flux rates

mineralogical and clay mineralogical aspects of loess research abstract mineralogical and clay mineralogical investigations under certain circumstances allow conclusions regarding the rate and kind of pedogenetic weathering especially clay mineral formation together with soil physical and chemical and mainly micromorphological investigations paleoclimatic conclusions can be drawn in central european holocene and pleistocene loess soils as well as in relict loess soils in the central and northern part of the great plains of the u s a smectite is the dominant pedogenetically formed mineral in the fine clay fraction

magnetic mineralogy of chinese loess and its significance summary the topmost 16 metres of the loess section at xifeng central chinese loess plateau which cover the last 128000 years consist of two palaeosol beds interlayered by a loess horizon hysteresis parameters frequency dependent field and temperaturedependent susceptibility show very similar and stable magnetic mineral constituents in both loess and palaeosol samples the concentration and grain size of magnetite maghaemite and haematite control the magnetic properties of chinese loess susceptibility and loess thickness are closely related to geographic position and present climate across the loess plateau the loess and palaeosol magnetic properties are largely controlled by the fine grained magnetite formed in various quantities and grain sizes under the influence of pedogenesis during variable palaeoclimatic conditions therefore regional and global palaeoclimatic development during the last 2 5 myr can be reconstructed from susceptibility records in the loess plateau

intensified pedogenesis caused the increase in the fine particle content of late cenozoic fluvial and lacustrine deposits in the ne tibetan plateau abstract the grain size composition of fluvial lacustrine deposits in terrestrial basins is commonly used to reconstruct temporal variations in sedimentary processes tectonic activities and paleoclimatic conditions however previous studies have generally ignored possible grain size alteration induced by post depositional weathering and pedogenesis which undermines the use of grain size analysis for reconstructing depositional environments and paleoclimatic changes in the present study the grain size distributions of late cenozoic fluvial lacustrine deposits in the xining basin xnb in the ne tibetan plateau tp were analyzed the results demonstrate that the contents of the ultrafine

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

correlation of the magnetic susceptibility stratigraphy of chinese loess and the marine oxygen isotope record chronological and palaeoclimatic implications abstract the thick deposits of wind blown silt of the loess plateau in central china constitute arguably the most important terrestrial record of the late pliocene and pleistocene climate magnetic susceptibility stratigraphy has proven extremely useful for quantifying the palaeoclimatic record of chinese loess with intervals of high magnetic susceptibility corresponding to warm humid interglacials and intervals of low susceptibility to cooler drier glacials several workers have noted that the magnetic susceptibility stratigraphy strongly resembles the marine oxygen isotope record for which a high resolution chronology is available from tuning to the frequencies of earth orbital parameters attempts have been made to correlate the two records statistically and we use this approach to generate a new magnetic susceptibility time series for the central chinese loess plateau our results suggest that the two records are sufficiently similar over the interval ca 0 1 5 my bp for this approach to yield a useful age model for loess accumulation spectral analysis of the resulting magnetic susceptibility time series clearly shows that the growth of 100 ky variance which occurs in the marine oxygen isotope record after about 1 my bp also occurs synchronously in the magnetic susceptibility record reinforcing recent suggestions of a strong linkage between the high latitude northern hemisphere and the asian climate we also show that a significant improvement in the strength of the loess magnetic susceptibility marine oxygen isotope correlation occurs after about 1 5 my bp which corresponds to a significant increase in the rate of sediment accumulation across the loess plateau

precursory monitoring of impending rockbursts in kolar gold mines from microseismic emissions at deeper levels microseismic emissions generated by deformation and cracking of the rock around an opening inside a mine as the rock tends to achieve equilibrium in a new geometry under changing stress conditions have been found to provide useful clues to an impending major rockburst in the mine since the spatio temporal patterns of occurrence of such microseismic emissions are known to be intimately related to stress changes within the rock mass the typical characteristics of these emission patterns are shown to be of diagnostic value in sensing in advance major rockburst events that invariably follow such emissions among several parameters investigated the three reliable short term precursors are found to be the rate of change of microseismic event count strain energy release and predominant signal frequency the extent of predictive utility of these parameters is illustrated by extracting them from the microseismic emission data of major rockbursts in the champion reef mine of the kolar gold fields kgf in southern india of which two representative examples out of several similar ones studied are discussed here

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

paleomagnetic chronology and paleoenvironmental records from drill cores from the hetao basin and their implications for the formation of the hobq desert and the yellow river abstract reconstructing the cenozoic environmental history of hetao basin in the northern part of the ordos plateau in north china is important not only for revealing the evolution of the yellow river but also for understanding the formation of the hobq desert here we present the stratigraphic framework of drill core dr01 with length of 2503 18 m and the results of magnetostratigraphic and esr dating and multi proxy analyses of drill core wedp05 with length of 274 60 m from the hetao basin the magnetostratigraphic and esr results indicate that core wedp05 spans the last 1 68 ma stratigraphic sequence of core dr01 indicates that the hetao area was uplifted and eroded during the early cenozoic before subsiding to form a sedimentary basin subsequently the basin was a fluvio lacustrine environment during the pliocene and then experienced alternating desert and fluvio lacustrine conditions during the quaternary sedimentary facies and multi environmental proxy analyses of core wedp05 indicate that the basin was occupied by a fluvio lacustrine system during the following intervals 1 47 1 30 ma 1 17 1 07 ma 0 68 0 60 ma and from 0 47 ma to the last interglacial and that a desert environment developed during the lake regression phases of 1 30 1 17 ma 1 07 0 68 ma and 0 60 0 47 ma the presence of aeolian sand at the base of core wedp05 suggests that the origin of the hobq desert can be traced back to the early pleistocene and resulted from the erosion and transportation of exposed fluvio lacustrine sediments by near surface winds associated with the asian winter monsoon a large river channel in the hetao basin may have existed as early as the pliocene which was occupied by the yellow river when its upper reaches formed by at least 1 6 ma subsequently at least since 1 2 ma the yellow river formed its drainage system around the hetao basin and controlled the paleoenvironment evolution of the basin

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

syntaxial overgrowths on dolomite crystals in the bluff formation grand cayman british west indies abstract complex syntaxial overgrowths are common on many dolomite crystals that line the walls of cavities in dolostones of the bluff formation exposed along the coastline of grand cayman scanning electron microscopy shows that the siting and development of the overgrowths which are initiated on seed crystals less than 0 1 m long are predetermined by the crystallographic structure of the host crystal based on their three dimensional form the overgrowths are divided into 1 aggregate trigonal prisms 2 needle wall and sheet overgrowths and 3 needle crystals the aggregate trigonal prisms with sides up to 12 m long are formed of four orders of crystals the first order crystals less than 1 m long are vertically stacked to form 2nd order crystals that are commonly capped by multifacetted crystals the 2nd order crystals each maintaining their identity are arranged in a triangular outline thereby forming a 3rd order trigonal prism filling the spaces in the 3rd order crystals creates a solid 4th order crystal needle overgrowths are formed of vertically stacked subcrystals rounded hexagons 0 5 to 1 0 m long and 0 1 m thick lateral merger produces wall overgrowths which in turn merge to form solid sheet overgrowths such overgrowths usually 4 to 5 m thick can occur on all faces of the host dolomite crystal needle crystals are non aggregate elongate up to 10 m long crystals that have a round cross section all the overgrowths occur in near surface cavities that are subjected to daytime temperatures of 27 to 30 c and periodic influxes of rainwater and seawater rapid evaporation of the water leaks films of water on the cavity walls from which the syntaxial overgrowths precipitate

grain size distribution of pleistocene loess deposits in northern iran and its palaeoclimatic implications abstract the loess deposits in northern iran are located in a key region connected to the european and central asian loess belts however the lack of previous detailed sedimentological and palaeoclimatic studies of the pleistocene loess in the region limits our understanding of the nature of ancient aeolian processes and loess history in the mid latitudes of euro asia as a whole here we present the results of grain size analyses of the pleistocene loess from the so called iranian loess plateau ilp in northern iran our results reveal that the grain size distribution of the deposits is characterized by trimodal and bimodal distributions comprising a dominant well sorted coarse dust component ca 7 75 m a small poorly sorted fine dust component ca 2 7 m and a minor pedogenic clay component

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

micromorphology of loess paleosol sequences a record of paleoenvironmental change abstract the record of paleoenvironmental change retained within thin sections from loess paleosol sequences is discussed with reference to case studies from western europe china and northwestern usa the paleoenvironmental significance of individual micromorphological features such as calcitic concentrations clay coatings and cryogenic structures are first evaluated and the value of recognising and interpreting microstratigraphic relationships of features in terms of paleoenvironmental change is illustrated recent developments have seen a greater emphasis on using micromorphology within a pedosedimentary approach whereby both pedogenic and sedimentary processes are taken into account when interpreting loess paleosol sequences this has led not only to the acquisition of important information on conditions during phases of enhanced loess accretion and periods of climatic transition but also to an increased awareness of spatial changes in processes and environmental controls during particular time periods micromorphologically based reconstructions have enabled the isolation of key stages of pedosedimentary development although absolute dating of stages is often limited by lack of age controls a novel approach aimed at addressing this limitation afforded by presence of datable tephra in microstratigraphic association with key micromorphological features is discussed

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

variations in the westerlies in central asia since 16 ka recorded by a loess section from the tien shan mountains abstract central asia comprises a vast area of arid terrain which has an important impact on the global climate system although still debated the pattern of climatic variations in central asia is regionally distinctive and does not appear to be strongly related to changes in insolation to understand the climatic evolution of central asia as well as its forcing mechanisms it is necessary to characterize variations in the westerlies which have had a major influence on climate change in the region past variations in the westerlies are commonly reconstructed from records of the composition grain size and mass accumulation rate mar of loess and the eolian component of lacustrine sediments which are commonly mixed by the signal of surface atmospheric circulation here we present the results of grain size analysis of a section of last glacial and holocene loess deposits in the tien shan mountains the results indicate that the strength of the westerlies was weakest during the last deglacial and early holocene 16 6 ka strongest during the mid holocene 6 3 1 ka and moderate during the late holocene 3 1 0 ka by comparison with an independent record of humidity we propose that the westerlies were an important driver of moisture variations in central asia with strong westerlies circulation resulting in high precipitation and vice versa during the past 16 kyr

cenozoic paleo environmental evolution of the pamir tien shan convergence zone abstract the retreat of the tethys sea and the uplift of the tibetan plateau play the critical roles in driving asian climatic changes during the cenozoic in the pamir tien shan convergence zone over 3000 m of cenozoic successions consisting of marine deposits in the lower continental clay and fine sand in the middle and molasse in the upper part record the evolution of the tethys sea the asian aridification and the deformation of the pamir in this work the existing biostratigraphic subdivisions and new electronic spinning resonance dating results were used to assign ages to formations within the ulugqat section sedimentary facies analysis and multi proxy indices were used to reconstruct the paleo environmental evolution the results show 1 the pamir tien shan convergence zone has undergone progressive environmental changes from shallow marine before 34 ma to arid land at 23 ma and finally to inter mountain basin by 5 3 ma 2 the overall increase in mean size of grains decrease in redness in magnetic susceptibility and in proportion of the ultrafine component of the sediments studied revealed a long term strengthening in potential energy to transporting medium cooling and enhanced continental aridity respectively 3 the easternmost edge of the tethys sea prevailed in the western tarim basin from late cretaceous to early cenozoic and finally retreated from this region around the eocene oligocene transition which in turn strengthened the asian aridification 4 accumulation of molasse with an upper age of 1 ma suggests that the deformation front of the pamir migrated to this area at or before that time

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

clay illuviation in red mediterranean soils abstract theories regarding pedogenesis in red mediterranean soils have undergone several stages of development the concept of clay illuviation in these soils was not a part of early theories and it is not yet unanimously accepted as a leading soil forming process a methodology is presented for studying the illuviation of clay in these soils emphasizing typology of textural features and fabrics the problem of age determination is also addressed through the use of radiometric dates and correlation with archaeological artifacts clay illuviation in red mediterranean soils under present day environmental conditions suggests that it occurs presently only on humid and sub humid margins of the mediterranean basin elsewhere illuvila clay accumulations are inherited from interglacial periods red mediterranean soils during glacial periods were eroded coluviated aggraded with aeolian dust calcitic fraction of which was redistributed in form of calcitic features and eventually were affected by water logging an example of water logging of red mediterranean soils mamora morocco which took place during the last glacial cycle consists of yellow illuvial clays accompanied by a yellowing of the ground mass during earlier cycles water logging resulted in whitish grey stains in which hydromorphic textural features were deposited

grain size partitioning in loess paleosol sequence on the west coast of south korea using the weibull function abstract this study aims to partition the grain size of the loess paleosol sequence on the west coast of south korea and investigates the limitations and applicability with the partitioning method through the help of a laser diffraction grain size analyzer two to four components depending on the samples and theories employed to convert the laser diffraction data to grain size data are identified through the partitioning process however the identification of one component is thought to be contingent upon the theories employed rather than natural processes the partitioning results reveal that the sequence consists mostly of fine and coarse components transported by the same mechanisms as in the chinese loess plateau and shares common source areas with the chinese loess plateau the sequence also contains a small quantity of material from the local sources and this component is expected to provide crucial information about paleoclimatic variations in korea this study suggests that considerations of the theories are essential in modeling processes of grain size because the theories greatly influence the results of grain size analysis and the number of components and that conversions using the fraunhofer approximation seem to provide more reliable results than those using the mie theory

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

quaternary paleoenvironmental evolution of the tengger desert and its implications for the provenance of the loess of the chinese loess plateau abstract the dust sources of the loess deposits of the chinese loess plateau clp are suggested to be the gobi deserts in north china and the tibetan plateau in southwest china the tengger desert td a major desert situated to the northeast of the tibetan plateau and to the northwest of the clp on the western margin of the present day asian summer monsoon domain is an ideal area for assessing which of these potential dust source areas may be dominant a 104 m long drill core bj14 was obtained from the northwestern td the magnetostratigraphy constrained by electron spin resonance dating in the upper part of the core includes the brunhes matuyama and beginning of the gauss polarity chrons with their boundaries at the depths of 44 57 m and 94 31 m respectively sedimentary facies analysis based on lithological grain size magnetic susceptibility and micropaleontological evidences indicates that the core is primarily composed of lacustrine deposits combined with the results of previous studies in the eastern td and the adjacent regions the sedimentary sequence of core bj14 indicates that lakes occupied the northern and eastern td during most of the early pleistocene and that the onset of a desert environment occurred at 0 9 ma our results suggest that the td may have contributed only a limited amount of dust to the clp during the early pleistocene

a study of the application of vsp to exploration ahead of a tunnel the vertical seismic profiling technique vsp was applied to the exploration ahead of a railway tunnel near ingolstadt germany before processing the field data the potential of vsp under the geometrical constraints of a tunnel is demonstrated with synthetic data the field test comprised two receiver sections with four receivers each in radially drilled boreholes the seismic waves were generated by blasting at the tunnel face despite the unfavourable geology very inhomogeneously weathered rock with no large scale discontinuities the most prominent geological feature a transition to better rock quality could be identified 40 m ahead of the tunnel face as an item for further improvement we discuss the ambiguous determination of the static corrections and the velocity field

particle size contributions to bulk magnetic susceptibility in chinese loess and paleosol abstract the magnetic enhancement of paleosol is observed in the chinese loess the origin of this magnetic enhancement is still very uncertain it is however a key problem in correctly understanding the paleoclimatic significance of changes of magnetic susceptibility and in transferring the magnetic signals to paleoclimatic parameters two main models have been proposed to explain the mechanism of magnetic enhancement in paleosols a depositional model and a pedogenic model together with composition and concentration grain size distribution of magnetic minerals also plays an important role to the magnetic enhancement of paleosols systematic susceptibility measurements were carried out on the samples of the upper part s0 to top of l2 of three loess sections from jixian xifeng and xining along an east west transect in the loess plateau china the samples with the highest value of magnetic susceptibility in s1 and the lowest value in l2 of each section were selected as the representatives these representatives were separated into different grain size fractions based on stokes law for coarse grains and by centrifuge for fine grains measurements of magnetic susceptibility and mass have been carried out on these fractions results show that for the loesses magnetic susceptibility changes little in the fractions with different grain size and for the paleosols it increases with decreasing grain size the magnitude of changes is bigger in the east jixian and xifeng than that in the west xining the fraction with the finest particle size in paleosols does not show very high magnetic susceptibility values a new approach is used to estimate the contribution of each fraction to total magnetic susceptibility the contribution comes mainly from coarse grains 10 m for loess samples it reaches about 90 the main contribution comes however from the particles with medium size 10 0 2 m the very fine grained particle

rock magnetic and grain size evidence for intensified asian atmospheric circulation since 800 000 years b p related to tibetan uplift abstract paleomagnetic rock magnetic and grain size studies of a thick loess sequence in the west qin ling mountain range show that loess deposition there began about 800 ka the data reveal a progressively increasing coarse grain size fraction upwards into the holocene the averages of these coarse size fractions are higher than in the central loess plateau which was apparently farther from the source area and slightly lower than those of the western loess plateau and the eastern tibetan plateau which were therefore closer to the source area the coarsening and source area location suggest 1 that asian air circulation may have changed and intensified at about 800 ka resulting in dust deposition in west qin ling 2 that dust carrying winds were driven not only by the asian winter monsoon but included also the westerlies and a winter monsoon caused by the tibetan plateau high and 3 that intensification of all these air circulation systems continues to the present increased elevation of the tibetan plateau so that it reached into the cryosphere by about 800 ka and a subsequent persistent uplift of the plateau may have been the mechanisms to trigger a change and intensify the air circulation system moreover this circulation shift and intensification simultaneous with a shift in milankovitch periodicity may have contributed to large global climate changes such as the 15 increase in global ice volume at ca 800 ka

pedogenic components of xijin loess from the western chinese loess plateau with implications for the quaternary climate change abstract chinese loess deposits preserve abundant information on the aridification of the asian interior and asian monsoon evolution during the quaternary although substantial progress has been made in deciphering the paleoclimatic record of the thick loess deposits in the western chinese loess plateau clp the environmental significance of variations in the magnetic susceptibility and the ultrafine 40 m fractions of the 416 m long xijin loess core from the lanzhou basin northeastern tibetan plateau our results indicate that the 40 m fraction and marine oxygen isotope record consequently we conclude that the pedogenic component is a more accurate and sensitive indicator of weathering and soil formation than the record and it is well suited to reconstructing high resolution quaternary climatic change in the western clp furthermore the proportion of the pedogenic component increased systematically over the past 2 2 million years which may have been primarily caused by long term global cooling since the early pleistocene together with the episodic uplift of the tibetan plateau

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

the ultrafine component in chinese loess and its variation over the past 7 6 ma implications for the history of pedogenesis grain size data from different climatic zones across the chinese loess plateau show that the loess generally contains an ultrafine component which has a consistent modal grain size of ca 0 center dot 37 mu m and a variable proportion of 4 to 10 the variation of the ultrafine component through a loess section is characterized by a high proportion and fine grain size in palaeosols and by a low proportion and coarse grain size in loess layers its proportional content in a stratum roughly increases from north west to south east across the loess plateau quantitative x ray diffraction analysis indicates that the ultrafine component is composed mainly of clay minerals ca 70 which are mostly illite ca 80 and with significant amounts of kaolinite ca 8 and chlorite ca 2 the temporal and spatial variations of the ultrafine component and the degree of illite crystallinity suggest that this component in aeolian sediments is linked closely to the process of pedogenesis weakly altered loess on the north western margin of the loess plateau contains considerable amounts of detrital clay minerals derived from the aeolian source areas results from a loess section with a basal age of 7 center dot 6 ma in the central loess plateau show that the ultrafine component increased from 7 center dot 6 to 5 ma and progressively decreased thereafter this trend was punctuated by two abrupt changes at 2 center dot 6 and 0 center dot 6 ma these variations reflect to a considerable extent the history of pedogenesis during the late cenozoic

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess