nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

implications of the carbonaceous chondrite mn cr isochron for the formation of early refractory planetesimals and chondrules abstract an excellent 53 mn 53 cr isochron for bulk ci cm co cv cb and ungrouped c3 chondrites seems to suggest that each carbonaceous chondrite group acquired its mn cr ratio 4568 1 myr ago this age is indistinguishable from the age of ca al rich inclusions cais which is considered to be the start of the solar system t 0 however carbonaceous chondrites were not assembled until at least 1 5 5 myr after t 0 to judge by the 207 pb 206 pb and 26 al 26 mg ages of the chondrules within them and by the fact that they were not melted by heat from the decay of 26 al presumably therefore these meteorites inherited their bulk mn cr isochron from precursor materials which experienced mn cr fractionation at t 0 as a possible physical mechanism for how the isochron was established initially and later inherited by the carbonaceous chondrites we propose the rapid formation at t 0 of planetesimals that were variably depleted in moderately volatile elements and hence had variably low mn cr the planetesimals and the undepleted high mn cr primitive dust from which they were made shared the same initial e 53 cr and therefore evolved on an isochron we suggest that later impact disruption of the planetesimals produced dusty debris which became mixed in various proportions with unprocessed high mn cr dust before accreting to the carbonaceous chondrite parent bodies with mixing in a closed system the isochron was unchanged we infer that some debris rich material was converted to chondrules prior to accretion the chondrules could have been formed by flash melting of the mixed dust or could instead have been made directly by the impact splashing of molten planetesimals or by condensation from impact generated vapor plumes

dynamic crystallization of chondrule melts of porphyritic and radial pyroxene composition abstract dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures without preexisting nuclei too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial in the near total absence of nuclei radial textures can form at cooling rates as slow as 5 c hr in this study by varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable analogs to most of the recognized chondrule textures can be produced in a single melt composition olivine inclusions in pyroxene can form readily during an experiment from a starting material which did not initially contain olivine crystals thus care must be taken in the assumption that olivine inclusions in pyroxene represent preexisting crystals

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

crystal morphologies in pillow basalts implications for mid ocean ridge processes abstract we present the results of a detailed petrological study of a sparsely phyric basalt mapco ch98 dr11 dredged along the mid atlantic ridge 30 41 n the sample contains microphenocrysts of olivine that display four different rapid growth morphologies comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample the dendritic morphology swallowtail chain and lattice olivine is directly related to the final quenching during magma seawater interaction in contrast the three other morphologies namely the complex polyhedral crystal the closed hopper and the complex swallowtail morphology result from several cycles of cooling heating corresponding to a maximum degree of undercooling of 20 25 c during crystal growth these thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge the results suggest that the mid atlantic ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation aphyric basalts are emitted during eruptions controlled by the tectonic activity whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas

a short reverse polarity interval within the jaramillo subchron evidence from the jingbian section northern chinese loess plateau 1 a high resolution paleomagnetic and rock magnetic investigation supported by scanning electron microscopy observations x ray diffraction determinations and anisotropy of magnetic susceptibility analyses has been carried out on a loess paleosol sequence from jingbian 37 4 n 108 8 e at the northern extremity of the chinese loess plateau the results indicate that the magnetic assemblage is dominated by pseudo single domain magnetite with associated maghemite and traces of a higher coercivity phase probably hematite the brunhes matuyama and upper jaramillo transitions have been carefully documented and a record of a short reverse polarity interval sri entirely within the jaramillo normal polarity subchron has been obtained the duration of the sri recorded over a stratigraphic interval of 48 cm is 10 1 kyr 29 kyr if the polarity transitions are included these results seem to exclude that rock magnetic variations are adversely affecting the recording process and compel us to reconsider the jaramillo subchron as characterized by a pair of normal polarity intervals interrupted by a short reverse polarity interval

making loess sized quartz silt data from laboratory simulations and implications for sediment transport pathways and the formation of desert loess deposits associated with the sahara abstract results from a series of laboratory simulations designed to investigate quartz silt generation by a number of geomorphic mechanisms are reviewed these findings are then used to discuss potential sediment pathways involved in the formation of desert loess deposits and a pathway is presented to show a proposed sequence of events involved in the formation of the loess deposits associated with the sahara the results indicate that both fluvial and aeolian systems can be very effective at producing quartz silt it is suggested that fluvial systems within hot desert environments may play a central role in both the production and distribution of loessic silt first the highly energetic but periodic fluvial regimes associated with arid and semi arid environments may be responsible for considerable quantities of particle comminution second the intermittent nature of these systems will help maintain geomorphologically active surfaces from which silt sized material can be easily deflated as well as fluvial comminution a range of weathering mechanisms and aeolian abrasion may also be responsible for the generation of silts in desert loess consequently silt sources and mechanisms of silt generation are likely to be much more diverse for desert loess than those associated with glacial loess

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

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

preliminary magnetostratigraphy of a thick eolian red clay loess sequence at lingtai the chinese loess plateau magnetic remanence and bulk susceptibility measurements are reported for a 305 m eolian loess red clay sequence at lingtai the chinese loess plateau polarity zonation defined by about 680 remanence data yields a basal age of about 7 05 ma for the section which represents the oldest wind blown dust deposited continuously in north central china during the late cenozoic the resultant magnetostratigraphic scheme implies a nearly linear accumulation rate about 2 98 cm ka of atmospheric dust on the loess plateau during the period of 7 05 to 2 58 ma comparison of the bulk susceptibility record with the pedogenic characteristics of the red clay observed in the field suggests that magnetic susceptibility in the red clay is not as useful as in the loess soil sequence to indicate summer monsoon variations

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

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

binary sources of loess on the chinese loess plateau revealed by u pb ages of zircon the age distribution of detrital zircon has been used to trace sediment sources existing datasets show great similarity of zircon ages between the loess on the chinese loess plateau clp and the sediments from the north tibetan plateau ntp implying that eolian dust is delivered from the ntp to the clp by westerly winds or via the yellow river however ntp dust can also be transported by northwesterly winds from the alxa arid lands aals where materials are received from both the ntp and the gobi altay mountains gams here we report u pb zircon ages for aals sands and ntp and clp loess the results show that the zircons in the aals are mixed from ntp and gams zircons ntp loess is mainly derived from local sources mixing of materials from the ntp and gams defines the zircon ages of the loess on the clp better than the pure ntp source no temporal and spatial heterogeneities of zircon ages have been observed for the loess on the clp which suggests that the well mixed materials in the aals likely have an eolian source

the provenance of taklamakan desert sand sand migration in the vast taklamakan desert within the tarim basin xinjiang uyghur autonomous region pr china is governed by two competing transport agents wind and water which work in diametrically opposed directions net aeolian transport is from northeast to south while fluvial transport occurs from the south to the north and then west to east at the northern rim due to a gradual northward slope of the underlying topography we here present the first comprehensive provenance study of taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea and to consider the potential of the tarim basin as a contributing source to the chinese loess plateau clp our dataset comprises 39 aeolian and fluvial samples which were characterised by detrital zircon u pb geochronology heavy mineral and bulk petrography analyses although the inter sample differences of all three datasets are subtle a multivariate statistical analysis using multidimensional scaling mds clearly shows that tarim desert sand is most similar in composition to rivers draining the kunlun shan south and the pamirs west and is distinctly different from sediment sources in the tian shan north a small set of samples from the junggar basin north of the tian shan yields different detrital compositions and age spectra than anywhere in the tarim basin indicating that aeolian sediment exchange between the two basins is minimal although river transport dominates delivery of sand into the tarim basin wind remobilises and reworks the sediment in the central sand sea characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the tarim river and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea smaller ephemeral rivers from the kunlun shan end in the desert and discharge their sediment there both river run off and wind intensity are strongly seasonal their respective transport strength and opposing directions maintain the taklamakan in its position and topography

detrital zircon evidence for the ternary sources of the chinese loess plateau abstract the provenance of chinese loess is fundamental for understanding its origin transportation and climatic significance in this paper eight samples were collected for detrital zircon age analysis five from different deserts and three from the jingbian section in the northern chinese loess plateau covering an age range of 2 6 0 03 ma the new results integrated with knowledge of relevant topography and wind patterns demonstrate that the age spectra of the detrital zircons in the loess are different from those of the sands from the tarim junggar and qaidam basins implying that these basins were not the sources of the silts of the loess plateau further analysis suggests that the three sources for the loess are 1 clastic materials eroded from the mountains of the central asian orogenic belt especially the gobi altai and hangay 2 clastic loess sized materials generated by erosion of the qilian mountains in the ne tibetan plateau and 3 minor clastic debris derived from the mountains of the north china craton thus silts of the loess plateau have a complex origin although inland basins long believed to be important sources have only a minor role at most

grain size dependent geochemical characteristics of middle and upper pleistocene loess sequences from the junggar basin implications for the provenance of chinese eolian deposits abstract thick loess paleosol sequences are widely distributed in the arid inland basins of northwestern china the geochemical composition of these sediments provides important constraints on the provenance of chinese eolian deposits however grain size dependent geochemical characteristics of early middle pleistocene loess deposits from these arid inland basins have not been investigated the paucity of such studies hinders a full understanding of provenance changes of loess deposits from the chinese loess plateau clp in the present study we performed a detailed major trace and rare earth element analysis of multiple grain size fractions of middle pleistocene loess deposits from the dongwan section dw in the junggar basin we found that the major trace and rare earth element concentrations of the dw loess are grain size dependent with higher concentrations in the fine fraction in addition the 75 m from the dw section changed significantly at 0 5 ma which may have arisen from intensified physical erosion or increased wind speeds in the northern tianshan area

granoblastic olivine aggregates in magnesian chondrules planetesimal fragments or thermally annealed solar nebula condensates abstract granoblastic olivine aggregates goa have been discovered in some type i magnesian chondrules within carbonaceous chondrites by libourel and krot libourel g krot a n 2007 evidence for the presence of planetesimal material among the precursors of magnesian chondrules of nebular origin earth planet sci lett 254 1 8 who proposed an origin from pre existing planetesimals amoeboid olivine aggregates aoa generally considered as aggregates of solar nebula condensates and found within similar carbonaceous chondrites display similar equilibrium texture though on a finer scale for these reasons we conducted experiments to determine if annealing of olivine required time scales appropriate to planetesimal or nebular heating pressed 88 4 was isothermally heated at temperatures ranging from 1350 1550 c for 1 100 h the 100 h runs yield olivine aggregates with well developed granoblastic texture at all temperatures manifest as a network of randomly oriented and sutured olivine grains with 120 triple junctions individual olivine grains are 4 6 sided and polygonal by 1450 c and equigranular texture is developed at high temperature 1500 1550 c melting of olivine commences at 1450 1500 c and aids in ripening and suturing grain coarsening and grain boundary migration textural equilibrium is clearly met at 1550 c a planetesimal origin cannot be ruled out however the experimental evidence reveals that granoblastic texture can be reproduced in an interval not inconsistent with heating times for nebular objects goa may have experienced higher degrees of thermal processing than the finer grained aoa if the precursors were the same grain coarsening would have to be accompanied by modification to bulk and isotopic compositions however the precursors could have been olivine condensates formed later than aoa annealing may have been a widespread process operating in the primordial solar nebula responsible for thermal processing and formation of goa prior to their incorporation into chondrules

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

source to sink fluctuations of asian aeolian deposits since the late oligocene abstract the source to sink fluctuations of asian aeolian deposits have been investigated over the past two decades using multiple mineralogical and geochemical tracers these source tracers have substantially improved our understanding of the processes of production transport and deposition of asian dust cycling from the asian inland basins to the north pacific ocean however due to differences in the sensitivity and interpretation of these various tracers there is controversy about which regions were the dominant dust sources and whether the dust provenances were stable at tectonic and glacial interglacial timescales here we comprehensively review the source to sink system of asian aeolian deposits on the chinese loess plateau since the late oligocene by assessing the utility of recently employed provenance tracers we conclude that integrating different tracers can effectively distinguish major primary and secondary dust sources the combination of sr nd isotopes quartz esr ci 18o data and zircon age spectra can decipher the source to sink fluctuations of asian aeolian deposits at tectonic and glacial interglacial timescales comparison of these sensitive source tracers with tectonic and climatic evidence indicates that the phased growth of the northern tibetan plateau played a key role in asian dust production and transport during the late oligocene to miocene while the onset and expansion of the northern hemisphere ice sheets had a substantial impact on the source to sink fluctuations since the late pliocene

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

evaluating the timing of former glacier expansions in the tian shan a key step towards robust spatial correlations the timing of past glaciation across the tian shan provides a proxy for past climate change in this critical area correlating glacial stages across the region is difficult but cosmogenic exposure

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

mineralogical evidence for multiple dust sources in an early triassic loessite adw acknowledges with thanks steve hillier of the james hutton institute for guiding her through the procedures of the x ray identification of clay minerals and quantitative mineralogical analysis mjw is appreciative for the sem examination of various rock fragments by evelyne delbos also of the james hutton institute simon kemp nick lancaster and nigel mountney provided insightful review and editorial comments for which we are hugely grateful

textural evolution of polyhedral olivine experiencing rapid cooling rates dynamic crystallization experiments in the cao mgo al2o3 sio2 cmas system have been used to investigate the change in crystal shape when pre existing polyhedral olivine crystals are cooled rapidly 1 639 2 182 c h polyhedral olivines are crystallized initially in a first step using a slow cooling rate 2 c h then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event during this second episode small dendritic olivines also nucleate within the liquid phase observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence polyhedral hopper polyhedral dendritic polyhedral this evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by sunagawa bull miner 104 81 87 1981 morphology of crystals terra scientific publishing company 1987 is proposed

dynamic crystallization of shock melts in allan hills 77005 implications for melt pocket formation in martian meteorites abstract a series of crystallization experiments have been performed on synthetic glasses matching the composition of a melt pocket found in allan hills alh 77005 in order to evaluate the heterogeneous nucleation potential of the melt and the effect of oxygen fugacity on crystallization the starting temperature of the experiments varied from superliquidus liquidus and subliquidus temperatures each run was then cooled at rates of 10 500 and 1000 c h at fmq the results of this study constrain the heating and cooling regime for a microporphyritic melt pocket within the melt pocket strong thermal gradients existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite skeletal olivine in the melt pocket center crystallized from a melt containing few nuclei cooled at a fast rate nearer to the melt pocket margin elongate skeletal shapes progress to hopper and equant euhedral reflecting an increase in nuclei in the melt at the initiation of crystallization and growth at low degrees of supercooling cooling from post shock temperatures took place on the order of minutes an additional series of experiments were conducted for a melt temperature of 1510 c and a cooling rate of 500 c h at the fmq buffer as well as 1 and 2 log units above and below fmq variation in chromite stability in these experiments is reflected in crystal shapes and composition and place constraints on the oxygen fugacity of crystallization of the melt pocket we conclude that the oxygen fugacity of the melt pocket was set by the fe 3 fe 2 ratio imparted by melting of the host rock rather than external factors such as incorporation of co 2 rich martian atmosphere or melting and injection of oxidized surface e g regolith material comparison with previous crystallization experiments on melt pockets in martian basalts indicate that the predominance of dendritic crystal shapes reflects the likelihood that those melt pockets with lower liquidus temperatures will be more completely melted destroying most or all nuclei in the melt in this case crystal growth takes place at high degrees of supercooling yielding dendritic shapes it appears as though the melting process is just as important as cooling rate in determining the final texture of the melt pocket as this process controls elimination or preservation of nuclei at the onset of cooling and crystallization

half precessional cycles recorded in chinese loess response to low latitude insolation forcing during the last interglaciation abstract chinese loess offers favourable conditions for identifying evidence for high resolution climatic changes previous studies have examined orbital scale climatic cycles and the other shorter time scale climatic oscillations similar to the recorded glacial instability in deep sea cores in this study we focus on examining the high resolution palaeoclimatic records in the northwestern loess plateau where the dust accumulation rate is high and the loess soil sequences are highly sensitive to the shifting pattern of the east asian monsoon system our results of magnetic susceptibility and particle size analysis from the northwestern loess plateau reveal well defined half precessional cycles during the last interglaciation culminating at approximately 122 000 111 000 100 000 88 000 and 79 000 yr these variations are a direct response to the low latitude forcing through its modulation on the east asian summer monsoon in this context the east asian summer monsoon has played an important role in conveying climatic signals from tropical pacific to the middle latitude areas

spatial and glacial interglacial variations in provenance of the chinese loess plateau the chinese loess plateau clp covers an extensive area over 440 000 km2 and provides an unprecedented terrestrial record of neogene climate however it is still unclear whether the provenance of these loess deposits is uniform or contains spatial and temporal differences here this is addressed by comparing detrital zircon age spectra of typical loess and paleosol samples from three distant sites located at the western middle and southeastern parts of the clp our results reveal that the zircon age spectra not only change between loess and paleosol layers but also vary from the western to the eastern clp at least during the last glacial cycle the discrepancies of the zircon age spectra among different sites suggest that the loess provenance of clp is heterogeneous and spatially variable although it has been suggested that the mineralogical elemental and isotopic compositions of loess deposits on clp are highly homogenous spatially and in glacial interglacial cycles

stable oxygen and carbon isotope record from a drill core from the hetao basin in the upper reaches of the yellow river in northern china and its implications for paleolake evolution abstract knowledge of the evolution of the paleolakes that developed intermittently within the hetao basin in northern china is important for understanding both the evolution of the upper and middle reaches of the yellow river drainage system and the spatio temporal evolution of regional water vapor transport associated with the east asian summer monsoon however the long term history of these lakes and the driving mechanisms are poorly understood in this study we reconstructed the history of the paleolakes within the hetao basin over the past 1 68 myr based on 18o and 13c records from lacustrine authigenic carbonates in a 274 60 m long drill core from the centre of the hetao basin the absence of covariation of carbonate 18o and 13c during the intervals of 1 47 1 30 ma and 1 17 1 07 ma suggests the existence of a hydrologically open lake system in the hetao basin the relatively low and invariant carbonate 18o values are similar to those of the modern yellow river water suggesting that the paleolakes formed when the lakes and the yellow river were connected the moderately high correlation r 0 61 of carbonate 18o and 13c during 0 68 0 60 ma suggests an intermittently open hydrology of the lake probably with a tendency towards closure within certain intervals the low correlation during 0 47 0 28 ma suggests a hydrologically open lake while the relatively high 18o values suggest a longer residence time of the lake water the high correlation r 0 92 of carbonate 18o and 13c from 0 28 ma to the last interglacial suggests a hydrologically closed lake although the yellow river may have flowed through the hetao basin at that time the interaction of the tectonically controlled relative height of the basin spill point and the climatically driven sediment and water supply of the yellow river was responsible for the long term evolution of the paleolake within the hetao basin strong regional tectonic activity which induced the uplift of the eastern part of the hetao basin and jinshan gorge and raised the relative height of the spill point was the primary cause of the formation of a hydrologically closed lake within the basin

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

temporal variations in pb isotopes and trace element concentrations within chinese eolian deposits during the past 8 ma implications for provenance change article i nfo the pb isotopes and trace element compositions of the silicate fraction of airborne dust from the chinese loess plateau were analyzed to infer provenance change during the past 8 ma the results indicate that the composition of eolian dust changed at 2 6 ma coincident with initiation of the northern hemisphere ice sheet the change in trace element composition at 2 6 ma indicates that a larger component of the eolian dust was derived from felsic rocks after this time pb isotopic evidence demonstrates that the source material of tertiary red clay differs to some extent from that of quaternary eolian deposits although chemical weathering may result in compositional changes in eolian deposits such a scenario is not supported by the present evidence given that glacial grinding and frost weathering processes have been active in the peaks of high mountains during the quaternary eolian dust of this age contains a large proportion of material derived from areas of high topographic relief and relatively little material from low lying cratonic regions such alpine processes played an important role in controlling the distinct changes in pb isotopes and trance element concentrations recorded at around 2 6 ma 2010 published by elsevier b v

role of gas melt interaction during chondrule formation abstract it is generally believed that most chondrules formed in the protoplanetary disk by melting of fine grained solid precursor materials and that during these melting events chondrules behaved as closed systems both chemically and isotopically i e the observed range in chondrule bulk chemistry and modal mineralogy was entirely inherited from solid precursors that experienced melting to varying degrees followed by igneous crystallization accompanied by very limited if any evaporation recondensation our mineralogical and chemical study of magnesium rich porphyritic type i chondrules in primitive ordinary and carbonaceous chondrites revealed that chondrule glasses are not located on the subtraction lines of olivine or low ca pyroxene in appropriate phase diagrams indicating that type i chondrules do not obey closed system crystallization we suggest that gas melt interaction played a major role in evolution of mineralogy bulk chemical and isotopic compositions of type i chondrules chondrules are thus complex objects composed of an inherited solid component and a melt component that equilibrated with nebular gas suggesting that chondrules formed in regions with high ambient gas partial pressures as a result chondrule glasses melts are therefore thermochemical and isotopic sensors of the surrounding nebular gas in the chondrule forming regions of the protoplanetary disk and can be used for evaluating its physico chemical conditions

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

oxygen isotopic constraints on the origin of mg rich olivines from chondritic meteorites chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system the calcium aluminum rich inclusions were condensed from the nebula gas chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk petrographic compositional and isotopic arguments allowed the identification of metal bearing mg rich olivine aggregates among the precursors of magnesian type i chondrules two very different settings can be considered for the formation of these mg rich olivines either a nebular setting corresponding mostly to condensation evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal an ion microprobe survey of mg rich olivines of a set of type i chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the 17o values and the presence of a large range of mass fractionation several within each mode the chemistry and the oxygen isotopic compositions indicate that mg rich olivines are unlikely to be of nebular origin i e solar nebula condensates but are more likely debris of broken differentiated planetesimals each of them being characterized by a given 17o mg rich olivines could have crystallized from magma ocean like environments on partially molten planetesimals undergoing metal silicate differentiation processes considering the very old age of chondrules mg rich olivine grains or aggregates might be considered as millimeter sized fragments from disrupted first generation differentiated planetesimals finally the finding of only a small number of discrete 17o modes for mg rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies

re arrangement of atmospheric circulation at about 2 6 ma over northern china evidence from grain size records of loess palaeosol and red clay sequences abstract recent studies have shown that the red clay sequence underlying the quaternary loess of the chinese loess plateau is wind blown in origin continuous atmospheric dust deposition in the past 7 0 ma has been documented to address the wind system that transported the tertiary red clay two north south transects were studied in the chinese loess plateau one of the transects was designed to study spatial changes in grain size of the last glacial interglacial loess records and the other to observe particle changes of the tertiary red clay underlying the quaternary loess the loess transect consists of nine sections and the red clay transect of four sections analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the late pleistocene which is consistent with the idea that the aeolian materials of the quaternary in the loess plateau are transported by the northerly winter monsoonal winds grain size distribution of the red clay sequences however does not show such a change from north to south along the red clay transect the particle size distribution is almost identical in the four sections suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material it is suggested that the red clay may have been transported by the westerlies from the dust source regions of northwestern china onto the loess plateau a remarkable re arrangement of atmospheric patterns at about 2 6 ma therefore has been recorded by the red clay loess shift it is speculated that this re arrangement of atmospheric patterns may have been caused by the onset of glaciation in the northern hemisphere

oxygen isotopic constraints on the origin of magnesian chondrules and on the gaseous reservoirs in the early solar system abstract we report in situ ion microprobe analyses of the oxygen isotopic composition of the major silicate phases olivine low ca pyroxene silica and mesostasis of 37 magnesian porphyritic type i chondrules from cv vigarano usnm 477 2 vigarano uh5 mokoia and efremovka and cr eet 92042 eet 92147 eet 87770 el djouf 001 mac 87320 and gra 95229 carbonaceous chondrites in spite of significant variations of the modal proportions of major mineral phases in cr and cv chondrules the same isotopic characteristics are observed i olivines are isotopically homogeneous at the level within a chondrule although they may vary significantly from one chondrule to another ii low ca pyroxenes are also isotopically homogeneous but systematically 16o depleted relative to olivines of the same chondrule and iii all chondrule minerals analyzed show 16o enrichments relative to the terrestrial mass fractionation line enrichments that decrease from olivine spinel to low ca pyroxene and to silica and mesostasis the observation that in most of the type i chondrules studied the coexisting olivine and pyroxene crystals and glassy mesostasis have different oxygen isotopic compositions implies that the olivine and pyroxene grains are not co magmatic and that the glassy mesostasis is not the parent liquid of the olivine the 18o and 17o values of pyroxene and olivine appear to be strongly correlated for all the studied cr and cv chondrules according to 18 o pyroxene 0 72 0 16 0 13 18 o olivine 1 21 0 54 0 79 17 o pyroxene 0 81 0 15 0 13 17 o olivine 0 60 1 00 0 95 these correlations are consistent with mass balance of oxygen isotopes calculated in the case of chondrule formation according to the following gas melt mineral reactions mg 2 sio 4 olivine sio 2 melt mg 2 si 2 o 6 pyroxene sio 2 melt sio gas 1 2 o 2 gas these equations imply that 2 3 of the oxygen incorporated by low ca pyroxene during its crystallization in the melt is derived from the dissolution of precursor olivine and 1 3 from the addition of chemical components such as sio from the nebular gas the composition of the nebular gaseous reservoir in which type i cr and cv chondrules formed is determined from the present data set to be 18o gas 3 6 1 and 17o gas 1 8 1 this isotopic composition is in excellent agreement with that of the gaseous reservoir previously inferred from the oxygen isotope systematics of bulk chondrules from various chondrite groups i e cv cr unequilibrated ordinary and eh thus the oxygen isotopic systematic strongly supports the idea that most of the olivines in type i chondrules are relict grains and that gas melt interaction played a major role in the formation of type i chondrules

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

granoblastic olivine aggregates as precursors of type i chondrules an experimental test abstract chondrule formation models involving precursors of granoblastic olivine aggregates goa of either planetesimal or nebular origin have recently been proposed we have therefore conducted chondrule simulation experiments using mixtures of 100 h thermally annealed goa and an en to test the viability of goa as predecessors of porphyritic olivine po chondrules isothermal runs of less than 5 min at 1350 1550 c result in goa disaggregation and fe mg exchange runs of 0 5 4 h show textures superficially similar to granular and po chondrules but with reversely zoned olivine charges isothermally heated at 1550 c for 1 and 4 h before being cooled at 10 and 100 c h undergo olivine crystallization and yield classical po textures although most evidence of origin from goa is erased the cores of normally zoned euhedral crystals are relict as phenocrysts in type i chondrules can be relict such chondrules could have experienced similar peak temperatures to those of type ii chondrules chondrules containing goa with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 c and type i chondrules with subhedral to anhedral olivine plus goa relicts resemble charges heated at the same temperatures but for longer duration type i chondrules with a mass of granular olivine or irregular anhedral olivine grains in the center and much glass nearer the margin on the other hand require limited heating at high temperature 1550 c while type i chondrules with euhedral olivines resemble charges heated at 1550 c for 4 h the majority of type i chondrules in cv chondrites display evidence of derivation from goa many finer grained chondrules in cr and uoc on the other hand could not have been derived from such coarse grained precursors but could have formed from fine grained dustballs as stipulated in the standard paradigm thus both goa and dustballs represent viable chondrule precursors of coarser and finer grained type i po chondrules respectively

isotope geochemistry of quaternary deposits from the arid lands in northern china abstract quaternary deposits of various types lacustrine desert sand river loess and loess like deposits from the southwestern tarim basin north tianshan northeast china and the central loess plateau exhibit an nd 0 range from 5 to 12 8 and a 147 sm 144 nd range from 0 110 to 0 140 their nd depleted mantle model ages are between 1 50 and 1 92 ga with a mean value of 1 7 ga th sc ratios vary over a wide range from 0 1 to 2 comparison of these geochemical signatures with those of the old australian shales and modern pacific ocean dust suggests a continuous input of mantle derived material into the crust over geological time the deposits from the north tianshan show clearly different chemical and isotopic features with significantly higher sm nd high 143 nd 144 nd low 87 sr 86 sr and low la lu and th sc ratios relative to those in the deposits from the other areas this indicates a geological control on the local source which has an overall young age and an enrichment of basic components the ce 0 values of two loess samples from the central loess plateau are 1 8 and 3 9 corresponding to depleted mantle model ages of 2 2 and 3 4 ga like the rb sr system the evolution of the la ce isotopic system in the crust may be to some extent decoupled from the sm nd system due to la ce fractionation by sedimentary processes the loess deposits and the desert sand are not distinguishable in isotopic composition but show somewhat different chemical compositions we conclude that the loess can have originated from desert processes since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation the loess deposits on the central loess plateau chemically and isotopically resemble the desert loess deposits in the southwestern tarim basin but do not resemble those of the north tianshan accordingly the loess on the plateau may have a source region in the tarim basin but clearly not in the north tianshan

origin and evolution of modern loess science 1824 to 1964 abstract loess is the most important aeolian deposit of the quaternary and plays an important role in explorations of the evolution of paleoclimate and paleoenvironment in recent years historians of science have been working on how loess research originated developed and was promoted in europe in the early 19th century the chinese community has a clear history of the loess research from the late 20th century however it remains unclear when and how modern loess studies were communicated between western and eastern academic societies and who contributed to the development and dissemination of modern loess knowledge especially from the western to the eastern societies based on books essays memoirs travel notes published letters and other types of records from geologists such as k leonhard 1779 1862 c lyell 1797 1875 and r pumpelly 1837 1923 the present study clarifies the way and process by which loess research originated from the rhine valley and spread to britain onto the united states and in particular china it was discovered that loess was formally defined in 1824 in the rhine valley in the 1830s l horner 1785 1864 and lyell introduced loess research from the rhine valley to britain at the same time lyell put forward the theory of the fluvial origin of loess and verified his theory by expanding study areas to the united states in 1866 pumpelly the first foreign geologist investigating chinese loess put forward lacustrine formation of loess pumpelly s hypothesis was soon argued against in 1870 by f von richthofen 1833 1905 who thought loess was formed via an aeolian mode based on a wide investigation in the loess plateau of china although the above main hypotheses originated based on investigations of chinese loess they were not disseminated to china and received by chinese scholars in a timely manner and the local loess research in china launched almost 130 years later by the stimulation from work by scholars of the soviet union

condensation of major elements during chondrule formation and its implication to the origin of chondrules abstract two glassy refractory al rich chondrules in semarkona ll3 0 the most primitive unequilibrated ordinary chondrite provide direct evidence for condensation of si and mg on melt droplets during cooling the chondrules are completely rounded rich in ca and al and poor in fe and alkalis they have extraordinarily abundant glass 70 80 vol with a subordinate amount of forsterite as the only crystalline phase that occurs mostly rimming the chondrule edge the groundmass glass is concentrically zoned in terms of si with an outward increase which is overlapped with local heterogeneity of mg and al induced by crystallization of forsterite the outward increase of si mostly compensated by al cannot be formed solely by crystallization of forsterite from a homogeneous melt in a closed system combined with skeletal or dendritic morphology and sector zoning of forsterite it is suggested that si condensed onto totally molten droplets initial melts accompanied by nucleation and rapid growth of forsterite with lowering temperature the initial melts the compositions of which were estimated from the ca contents of the first crystallized forsterite are very similar to type c cai but are notably poorer in mg and si than the bulk chondrules indicating condensation of mg in addition to si with an atomic ratio of mg si 3 2 the condensation after the nucleation of forsterite took place below 1300 c under cooling at 70 c h and amounted to 30 wt of the current chondrule this study suggests a model that a short time and local shock heating event induced melting of type c cai and concomitant evaporation of dusts ferromagnesian chondrules of earlier generation and their fragments to generate mg and si rich gas which condensed onto the melt droplets upon cooling accompanying condensation of type i chondrules

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

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

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

introduction to the special issue of loess and climatic record memory of professor liu tungsheng for his scientific contributions and his centenary birthday abstract this special issue is to memory professor liu tungsheng for his scientific contributions and his centenary birthday liu tungsheng was the former president of the international association for quaternary association inqua and the honorary president of the chinese association for quaternary research chiqua liu s best known contribution to quaternary research is his pioneering and systematic study of the extensive loess deposits of china which has been regarded as the best terrestrial paleoclimatic archive on the earth he won many international awards including the tyler prize for environmental achievement in 2002 and the alexander von humboldt medal in 2007 he was an inspiring leader one of china s and indeed one of the world s most outstanding earth scientists this introduction aims to explore the personal factors behind his great achievements and reviews the papers included in this special issue from his colleagues friends and students

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

localized shock melting in lherzolitic shergottite northwest africa 1950 comparison with allan hills 77005 the lherzolitic martian meteorite northwest africa nwa 1950 consists of two distinct zones 1 low ca pyroxene poikilically enclosing cumulate olivine fo70 75 and chromite and 2 areas interstitial to the oikocrysts comprised of maskelynite low and high ca pyroxene cumulate olivine fo68 71 and chromite shock metamorphic effects most likely associated with ejection from the martian subsurface by large scale impact include mechanical deformation of host rock olivine and pyroxene transformation of plagioclase to maskelynite and localized melting pockets and veins these shock effects indicate that nwa 1950 experienced an equilibration shock pressure of 35 45 gpa large millimeter size melt pockets have crystallized magnesian olivine fo78 87 and chromite embedded in an fe rich al poor basaltic to picro basaltic glass within the melt pockets strong thermal gradients minimum 1 c m existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite dendritic and skeletal olivine crystallized in the melt pocket center has a nucleation density 1 0 x 10 3 crystals mm 2 that is two orders of magnitude lower than olivine euhedra near the melt margin 1 6 x 10 5 crystals mm 2 based on petrography and minor element abundances melt pocket formation occurred by in situ melting of host rock constituents by shock as opposed to melt injected into the lherzolitic target despite a common origin nwa 1950 is shocked to a lesser extent compared to allan hills alh 77005 45 55 gpa assuming ejection in a single shock event by spallation this places nwa 1950 near to alh 77005 but at a shallower depth within the martian subsurface extensive shock melt networks the interconnectivity between melt pockets and the ubiquitous presence of highly vesiculated plagioclase glass in alh 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting

coeval changes in grain size and sedimentation rate of eolian loess the chinese loess plateau to determine the temporal spatial relationship between strength of the winds transporting the chinese loess and aridity conditions of the loess source area six loess sections located respectively in the northern middle and southern loess plateau were studied grain size distributions were analyzed on loess paleosol samples that are closely spaced in the sections time scales were established by tuning each of the grain size records to theoretical changes in the earth s orbital parameters results obtained show that during the last two glacial cycles particle size of the loess co varies with apparent sedimentation rates suggesting that variations in winter monsoon intensity and the aridity of the loess source area are tightly coupled this proximal relationship is in striking contrast with the observation of distal eolian clays in north pacific sediments we propose that this phenomenon may result from the proximity of the loess plateau to the source area and from the significant control of the winter monsoon on the expansion retreat changes of the deserts in the northern and northwestern china

a new high precision u pb date from the oldest known rocks in southern britain a new high precision u pb zircon age of 710 8 1 5 ma for granophyric granitic rock from the stanner hanter complex of the welsh borderland lies just within error of an older rb sr isochron age nd values of 0 3 and 1 2 combined with t dm of 1394 ma and 1468 ma indicate that the magma incorporated an older crustal source component the nd data highlight differences with western avalonia the widely considered late neoproterozoic north american counterpart to southern britain and point toward a closer similarity with other peri gondwanan terranes that incorporate older cratonic source material

a magmatic origin for silica rich glass inclusions hosted in porphyritic magnesian olivines in chondrules an experimental study rare silica rich glass inclusions 69 sio2 82 wt are described within magnesian olivines of porphyritic type ia chondrules these glass inclusion compositions are clearly out of equilibrium with their host mg olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases we performed dynamic crystallisation experiments that demonstrate that these si rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a ci i e solar composition their silica rich compositions are the consequence of the small volumes of inclusions which inhibit the nucleation of secondary crystalline phase ca poor pyroxene but allow olivine to continue to crystallize metastably on the walls of the inclusions we suggest that si rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system exhibiting a ci i e non fractionated composition

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

high frequency pulses of east asian monsoon climate in the last two glaciations link with the north atlantic three loess sections in the loess plateau of china have been studied to characterize the variations of the east asian monsoon climate in the late quaternary period paleo weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity lw in the last glacial and late penultimate glacial loess indicating significantly cooler or and drier conditions most of them are identified at or near the transitional boundaries between loess and soil units suggesting that climatic conditions favorable for lw events tended to occur at or near major climatic boundaries twenty eight radiocarbon and thermoluminescence measurements combined with kukla s magnetic susceptibility age model date these events at 14 21 29 38 52 71 135 and 145 ka bp with 5 10 ka frequency inlaid within the orbitally induced 20 ka periodicity the ages of the first six events in the last glacial period are therefore close to those of the coarse grained heinrich layers in the north atlantic ocean which resulted from massive discharges of icebergs the results indicate that the climate in the area affected by the east asian monsoon has experienced high frequency changes more or less synchronous with the heinrich events these high frequency changes have been reported by porter and an based on the grain size time series from the luochuan loess section our data also reveal that similar events also occurred during the penultimate glaciation the mechanisms linking the heinrich events and the east asian monsoon climate may be similar to that driving the younger dryas event which has been identified in a large number of records in china and in the surrounding oceans

experimental investigation of silt formation by static breakage processes the effect of temperature moisture and salt on quartz dune sand and granitic regolith weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process these results suggest that crack tip processes are insignificant where mineral grains are not subject to static loading sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains feldspars and mica in the regolith sands were more susceptible to salt action than quartz salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits

the loess deposits in northeast china the linkage of loess accumulation and geomorphic climatic features at the easternmost edge of the eurasian loess belt abstract the study of the loess deposits is the key for understanding the linkage between dust accumulation tectonics landform and climate change however little is known about loess accumulation in ne china loess deposits at the easternmost edge of the eurasian loess belt are represented by those in the xinwopu xwp kulungou klg and huangshan hs sections of ne china these loess deposits are much coarser than the loess in the southern chinese loess plateau with a sand 63 m content of 6 39 in the loess deposits and show distinct grain size distribution with a trimodal or bimodal pattern there are markedly different geochemical compositions between the studied loess deposits the xwp loess is characterized by the highest content of cao 9 81 and mgo 2 06 and the highest 87sr 86sr ratios 0 713119 the klg loess is highlighted by the lowest content of the element sc 7 68 ppm v 54 1 ppm cr 36 4 ppm co 6 32 ppm ni 15 6 ppm cu 16 ppm zn 38 8 ppm ga 12 8 ppm and ree 113 ppm the hs loess is of the lowest content of cao 1 15 and the highest content of the element y 84 8 ppm zr 242 ppm nb 18 1 ppm hf 7 2 ppm ta 1 45 ppm th 12 7 ppm and ree 185 ppm the xwp and klg loess samples have similar end 0 values 7 9 moderately higher than those 8 9 of the hs loess the comparison between various geochemical indicators e g low values of sio2 al2o3 zr sc and cia and high icv values shows that these loess deposits have undergone a different and low degree of chemical weathering with a low maturity and recycling history integrated methods including grain size elemental and isotopic composition multidimensional scaling as well as physical geographical elements including the geomorphic and climatic features clearly revealed the onqin daga sandy land the horqin sandy land and the songnen sandy land as main dust provenances of the xwp klg and hs loess respectively

silica bearing chondrules and clasts in ordinary chondrites unusual silica bearing chondrules and clasts have been observed in several unequilibrated ordinary chondrites there appear to be two distinct types i silica low ca pyroxene assemblages and ii silica fayalite intergrowths coexisting with low ca pyroxene only the former types are chondrules the bulk compositions of most of these objects can be expressed in terms of three components mgo feo and sio 2 since ca al and na are essentially trace elements secondary alteration has probably perturbed the fe mg ratios in most objects and produced ca rich pyroxenes in some type ii clasts but the silica low ca pyroxene and fayalite are hard to understand as other than primary phases such silica rich bulk compositions can be understood as an intermediate temperature condensate of a solar gas formed by the loss of refractory solid material by gas solid separation before the complete condensation of silicon alternatively the silicarich bulk compositions could have been formed by extreme reduction of normal chondritic olivine and orthopyroxene however the observed ca al depletion and the lack of ni poor metals are not explained by this model the fayalite bearing clasts can be explained by a relatively complex two stage process involving reduction followed by oxidation partial reduction of olivine in the presence of s produces mg rich pyroxene silica and fefes oxidation of metal and sulfide followed by reaction with silica forms fayalite an alternative is that the fayalite bearing clasts result from the decomposition of ferrosilite but this requires the production of metastable ferrosilite during shock or some other high pressure event the simplest unflawed alternative is that the fayalite bearing clasts result from the mixing of a partially molten silica fayalite liquid with mg rich pyroxene