ba ca in benthic foraminifera thermocline and middepth circulation in the north atlantic during the last glaciation 1 this geochemical investigation utilizes ba ca in the benthic foraminifer cibicides wuellerstorfi from cores taken from the bahama banks and the caribbean sea to reconstruct changes in basal thermocline ventilation 800 1000 m and middepth thermohaline circulation 1000 2000 m in the western north atlantic during the last glacial period focusing on the deglacial transition previous studies show that an increase in ventilation of the north atlantic subtropical gyre during the last glacial maximum lgm caused a 30 60 decrease in labile nutrients within the thermocline layer using foraminiferal ba ca as a proxy of refractory nutrients increased ventilation during the lgm produced a depletion of less than 20 compared to holocene values following glaciation the production of glacial north atlantic intermediate water gnaiw shut down owing to the presence of meltwater in the surface ocean which resulted in a decrease in ventilation as seen by an enrichment of barium in the basal thermocline gnaiw was subsequently replaced by barium rich southern component water in the middepth western north atlantic foraminiferal ba ca data suggest a 38 contribution from southern component water to a depth as shallow as 1475 m and a 14 contribution at 1123 m during deglaciation

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

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

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

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

nd sr isotopic and ree geochemical compositions of late quaternary deposits in the desert loess transition north central china implications for their provenance and past wind systems abstract the nd sr isotopic and ree geochemical compositions of the dishaogouwan profile in the desert loess transition between the ordos desert and the chinese loess plateau were investigated to identify the provenance of the sediments and to reconstruct the regional wind systems of the past the 87 sr 86 sr ratios of 0 7158 0 7175 nd 0 values of 8 9 to 16 8 ree values between 133 g g and 277 g g and roughly flat paas normalized ree patterns which differs from the 75 m fractions in the dishaogouwan profile this is most likely due to mineral sorting and or source features isotopic and geochemical comparisons of the dishaogouwan profile with potential sources show that 1 coarse eolian deposits resulted from wind erosion of the highlands in the adjacent west central ordos and the coarse fluvio lacustrine deposits originated chiefly from water erosion of the underlying eolian deposits in the dishaogouwan profile 2 fine particles of eolian deposits with absolute nd 0 values of 1 originated completely from the highland erosion in west central ordos and the fining of in situ coarse particles but the fine particles of the eolian deposits with absolute nd 0 values of 1 have more complex sources 3 fine fluvio lacustrine deposits were fed from the central loess plateau by water for the chengchuan and middle lower salawusu formations but for the upper salawusu formation they were significantly fed from the east central ordos desert by wind according to the source identification of the dishaogouwan profile the wind systems have been re established over the ordos and surrounding areas in the past 200 ka 1 the northwesterly was the dominant wind for eolian deposits in the dishaogouwan profile and the northeasterly simultaneously affected fine eolian deposits in certain periods the middle part of mis 6 and the lower part of mis 4 2 the summer monsoon was a predominant wind in periods during which most of the fluvio lacustrine deposits developed in the salawusu river valley but was thoroughly displaced by the cold dry northeasterly wind during the transition between mis 5 and 4 this study is helpful for further understanding the evolution of the desert loess transition and the related climate change

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

validation of imaging doppler interferometer winds using meteor radar 1 there has been some debate over the years concerning the accuracy of mesospheric wind observations made using the imaging doppler interferometer idi technique the high potential and increasing use of idi wind data in joint studies with spaced antenna mf and meteor radar systems make it important to quantify the idi results this paper presents a novel comparison of wind measurements between a dynasonde implementation of idi and winds derived from an all sky meteor radar system a widely accepted standard for such measurements both radars were located at the usu bear lake observatory and operated almost continuously for a four month period the winds and tides derived from idi were found to closely match those measured by meteor radar not only during the day but also at night and at all overlapping heights from 80 95 km

grain size control on sr nd isotope provenance studies and impact on paleoclimate reconstructions an example from deep sea sediments offshore nw africa five sediment cores from offshore nw africa were analyzed for strontium and neodymium isotope ratios to reconstruct temporal variations in continental weathering regimes sediments were taken from three time slices with well known and distinctive environmental conditions present day dry and warm similar to 6 ka wet and warm and similar to 12 ka dry and cold terrigenous sediment samples were split into two size fractions to distinguish between the two dominant transport mechanisms offshore nw africa fluvial 0 10 mu m and aeolian 10 40 mu m sr isotope data record evidence of marked grain size control with higher isotopic ratios in the fine fraction in contrast epsilon nd values are largely unaffected by grain size minor variability in nd isotope data at each sampling site indicates near constant sources of terrigenous matter over the last similar to 12 ka variations in sr isotope ratios are interpreted to reflect major changes in the evaporation precipitation balance we suggest that the sr nd isotope data record a latitudinal shift of the northern limit of the african rainbelt and associated wind systems causing changes in the humidity and rate of chemical weathering over nw africa while hyperarid conditions prevailed similar to 12 ka more humid conditions and intensified monsoonal rainfall at similar to 6 ka resulted in greater breakdown of easily weathered k bearing phases and increased sr 87 sr 86 in the detritus in late holocene times the monsoonal circulation diminished resulting in a return to arid conditions our results clearly show that it is of vital importance in paleoenvironmental studies to carry out isotopic analyses on individual sediment fractions that were carried to the studied deposition site by distinct sediment transport mechanisms if isotopic analyses are carried out on bulk sediments the observed variability in isotopic values most likely represents changes in the particle size and mixing proportions of the sediment subpopulations

late neogene loess deposition in southern tarim basin tectonic and palaeoenvironmental implications abstract uplift of the tibetan plateau during the late cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the kunlun and altyn mountains in the southern tarim basin early neogene sediments are characterised by sandstone siltstone and red mudstone representing floodplain to distal alluvial fan environments the early pliocene artux formation consists of medium grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone the late pliocene to early pleistocene xiyu formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits sedimentological investigation together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the xiyu and artux formations point to an aeolian origin suggesting desertic conditions in the tarim basin by the early pliocene the onset of aeolian sedimentation in the southern tarim basin coincided with uplift of the northern tibetan plateau inferred from the lithofacies change from fine grained mudstone and sandstone to coarse clasts tibetan plateau uplift resulted in the shift of sedimentary environments northwards into the southern tarim basin and could well have triggered the onset of full aridity in the taklimakan region as a whole

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

geochemistry and nd isotopic composition of the early paleozoic flysch sequence in the chinese altai central asia evidence for a northward derived mafic source and insight into nd model ages in accretionary orogen abstract although nd isotopic composition of sedimentary rocks is considered as a useful tool to trace the provenance their nd model age tdm is usually misused to discuss the timing of crustal formation in accretionary orogen in the central asian orogenic belt an early paleozoic flysch sequence extensively occurs in the chinese altai and adjacent western mongolian terranes sedimentary rocks in the northwestern chinese altai were collected from the flysch sequence for geochemical and nd isotopic studies although these rocks show different geochemical characteristics e g arenaceous and argillaceous they all have relatively low cia chemical index of alteration values 49 75 indicating a relatively weak weathering source or the absence of compositionally mature alumina rich minerals produced by chemical weathering processes their relatively high icv index of compositional variability values 0 95 1 35 reveal an immature source and indicate that these rocks were probably deposited in an active tectonic setting the sedimentary rocks from the flysch sequence have high mgo sc co and low y nb which suggest significant addition of mafic rocks into the source modeling based on nb cr and zr mgo contents displays nearly 20 to 50 addition of mafic materials in combination with the age and distribution of mafic rocks in the chinese altai and adjacent terranes a northward derived mafic source is recommended for the sedimentary sequence although the sedimentary rocks have nd model ages tdm 1 44 1 57 ga older than devonian granites tdm 1 6 1 1 ga young detrital zircons from the sediments and inherited zircons from the granites 450 500 ma suggest a mixed source consisting of both old crust components and juvenile or less evolved crustal components this reveals that nd model ages tdm of metasedimentary rocks and igneous rocks can hardly provide close constrains on the timing of crustal formation in accretionary orogen with the progresses in adjacent western mongolian terranes a tectonic scenario dominated by subduction accretionary process is suggested to interpret the formation of the early paleozoic flysch sequence in the chinese altai and adjacent terranes

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

sr nd isotopic and ree geochemical constraints on the provenance of fine grained sands in the ordos deserts north central china surface sands and sandstones in the ordos region alluvial sands from the surrounding mountains and fluvial sands in the yellow river are systemically collected for granulometric mineralogical geochemical and isotopic analyses fine grained fractions are small for the ordos desert sands as well as alluvial sands of the surrounding mountains whereas they are abundant for fluvial sands of the yellow river quartz feldspar and muscovite are common minerals but their relative proportions are variable for various sediments ree geochemical compositions are roughly identical but isotopic compositions particularly end 0 values of fine grained sands vary significantly in the ordos deserts based on the integrated sr nd isotopic data the possible source areas are isotopically divided into four regions for fine grained sands in the ordos deserts region a the helan yin mountain ranges region b the ordos sandstone areas region d the tarim basin the alxa plateau the hexi corridor the northern qinghai xizang plateau and the yellow river drainage and region e the jungger basin and the southern mongolia through geochemical and particularly isotopic comparisons in combination with expert meteorological and geographical knowledge fine grained sands in the ordos deserts originated both from weathering of local sandstones and from blowing of fine sediments in region d the input from region d is subordinate to the local source for fine grained sands in the ordos deserts contributions from weathering of local sandstones might be roughly homogeneous from the west to the east of the ordos region as well as the input of fine grained sediments from remote areas such as the tarim basin the qinghai xizang plateau and the alxa plateau geographical nd isotopic variations of fine grained sands in the ordos deserts might be caused by the input from adjacent places such as the yellow river drainage due to the near surface winds

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

geochemical sr nd and zircon u pb hf isotopic studies of late carboniferous magmatism in the west junggar xinjiang implications for ridge subduction abstract voluminous granitic intrusions are distributed in the west junggar nw china and they can be classified as the dioritic rocks charnockite and alkali feldspar granite groups the dioritic rocks sio 2 50 4 63 8 wt are calc alkaline and mg enriched average mgo 4 54 wt mg 0 39 0 64 with high sr y ratios average 21 2 weak negative eu average eu eu 0 80 and pronounced negative nb ta anomalies their sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7035 0 7042 e nd t 4 5 7 9 e hf t 14 1 14 5 show a depleted mantle like signature these features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials the charnockites sio 2 60 0 65 3 wt show transitional geochemical characteristics from calc alkaline to alkaline with weak negative eu average eu eu 0 75 but pronounced negative nb ta anomalies sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7037 0 7039 e nd t 5 2 8 0 e hf t 13 9 14 7 also indicate a depleted source suggesting melts from a hot juvenile lower crust alkali feldspar granites sio 2 70 0 78 4 wt are alkali and fe enriched and have distinct negative eu and nb ta anomalies average eu eu 0 26 low sr y ratios average 2 11 and depleted sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7024 0 7045 e nd t 5 1 8 9 e hf t 13 7 14 2 these characteristics are also comparable with those of rocks derived from juvenile lower crust despite of the differences in petrology geochemistry and possibly different origins zircon ages indicate that these three groups of rocks were coevally emplaced at 305 ma a ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks as the slab window opened upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms partial melting of the subducting slab formed the dioritic rocks partial melting of the hot juvenile lower crust produced charnockite and alkali feldspar granite and partial melting in the mantle wedge generated mafic rocks in the region these results suggest that subduction was ongoing in the late carboniferous and thus support that the accretion and collision in the central asian orogenic belt took place in north xinjiang after 305 ma and possibly in the permian

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

elemental and sr nd pb isotopic geochemistry of late paleozoic volcanic rocks beneath the junggar basin nw china implications for the formation and evolution of the basin basement the basement beneath the junggar basin has been interpreted either as a micro continent of precambrian age or as a fragment of paleozoic oceanic crust elemental and sr nd pb isotopic compositions and zircon pb pb ages of volcanic rocks from drill cores through the paleo weathered crust show that the basement is composed mainly of late paleozoic volcanic rock with minor shale and tuff the volcanic rocks are mostly subalkaline with some minor low k rocks in the western kexia area some alkaline lavas occur in the central luliang uplift and northeastern wulungu depression the lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution except for a few samples from kexia the basalts have low la nb 1 4 typical for oceanic crust derived from asthenospheric melts zircon pb pb ages indicate that the kexia andesite with a volcanic arc affinity formed in the early carboniferous 345 ma whereas the luliang rhyolite and the wucaiwan dacite with syn collisional to within plate affinities formed in the early devonian 395 and 405 ma respectively positive end t values up to 7 4 and low initial 87sr 86sr isotopic ratios of the intermediate silicic rocks suggest that the entire junggar terrain may be underlain by oceanic crust an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the central asia orogenic belt variation in zircon ages for the silicic rocks different ba p ti nb or th anomalies in the mafic rocks and variable nb y and la nb ratios across the basin suggest that the basement is compositionally heterogeneous the heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes

differential weathering and erosion in an inselberg landscape in southern zimbabwe a morphometric study and some notes on factors influencing the long term development of inselbergs abstract a morphometric analysis of inselberg systems in southern zimbabwe indicated that there are two types of inselberg systems that differ in the mode of development inselberg systems characterized by backwearing tend to occur on granitoid rocks that are foliated highly fractured and prone to grusification the inselbergs are mostly of the koppie type and are covered to a great extent with regolith or debris the second type of inselbergs consists of sparsely fractured granitoid rocks and areas underlain by these rocks are characterized by clusters of closely spaced rock domes in the case of these inselbergs backwearing is not indicated they appear to be the result of the exposure of structurally pre designed highly resistant rock compartments the hypothesis that differences in lithology and structure may influence the rate and style of inselberg development was tested by means of a simulation model the simulations are run under the same boundary conditions with differing assumptions concerning role of divergent weathering the results show that both modes of inselberg development may occur alongside one another as long as a critical relief is maintained the modelling provided also indicates that although the inselberg systems must have integrated several sequences of environmental changes during their development these changes were not able to divert the general trend of the process response system away from its steady course lithological and structural factors which are responsible for the differences in the mobility of material on the inselberg sideslopes are thus considered to be the primary source of influence of the different modes of inselberg development it is suggested that the compositional and structural diversity in granitoid rock terrains is what enables inselbergs to pass through different development modes and sequences as rocks of differing resistance become subject to weathering during the development of the landscape

northwestern junggar basin xiemisitai mountains china a geochemical and geochronological approach abstract we report sims u pb zircon elemental and nd sr pb isotopic data for the volcanic rocks and their subvolcanic units from the xiemisitai mountains in the west junggar region xinjiang china aiming to determine their ages source regions and tectonic setting zircon u pb dating results of the volcanic rocks 422 5 1 9 ma 411 2 2 9 ma indicate that the volcanic strata occurred in the xiemisitai mountains at late silurian early devonian time rather than middle devonian as suggested previously they are probably the eastern extension of the early paleozoic cambrian silurian boshchekul chingiz volcanic arc of east kazakhstan in china the xiemisitai volcanic rocks include andesite rhyolite and their pyroclastic equivalents the subvolcanic units are felsite and granite porphyry andesite is moderately lree enriched with a marked negative nb anomaly and th yb enrichment rhyolite felsite and granite porphyry are enriched in lree and th and depleted nb the initial sr isotope values of the xiemisitai volcanic rocks and their subvolcanic units range from 0 702294 to 0 704456 e nd 420 ma from 0 19 to 1 88 with nd model ages ranging from 600 to 803 ma initial pb isotope ratios 206 pb 204 pb are 17 77 17 96 207 pb 204 pb are 15 49 15 54 and 208 pb 204 pb are 37 56 37 80 these features suggest that the xiemisitai volcanic rocks and their subvolcanic units derived from a mantle wedge significant mixed by subducted material emi in a subduction zone they also indicate significant involvement of neoproterozoic primitive crust in the formation of the xiemisitai magmatic arc these rocks are associated with a late silurian early devonian southward subduction of the oceanic lithosphere in the northern west junggar region this gives rise to an ew trending boshchekul chingiz volcanic arc and associated metallogenic belt in the northern west junggar region and adjacent kazakhstan

aeolian microtextures in silica spheres induced in a wind tunnel experiment comparison with aeolian quartz abstract microtextures in quartz attributed to aeolian transport principally bulbous edges and abrasion fatigue have seldom been tested in the laboratory under controlled conditions a wind tunnel experiment was conducted using glass spheres 70 sio 2 as a proxy for quartz with the objective of determining the extent of mechanical damage to silica glass transported in a mixture with quartz beach sand the microspheres were microscopically imaged prior to transport in a wind tunnel subjected at velocities ranging from 4 to 13 m s in sequential runs of 10 min the range in velocity is capable of lifting grains into the air column or saltating quartz grains and silica glass spheres to produce mechanical impact i e abrasion commonly experienced in aeolian transport with increasing velocity silica glass spheres which displayed minor imperfections prior to transport began to show significant grain damage exhibiting increasing depth into the silica glass fabric a result of mechanical contact as well as increasing frequency of craters dislodged plates and abrasion fatigue while pits appear earlier in the experiment 8 m s dislodged plates and abrasion fatigue need a threshold velocity of near 10 m s to become more frequent bulbous edges on the grain surface often considered the hallmark of aeolian transport are not seen in the grain population analyzed possibly because of the initial near perfect sphericity of the silica glass spheres the experiment proved that aeolian transport throughout short distances and during a relatively short period of time is enough to imprint significant abrasion marks in microspheres in fact the microtextures produced were fresh surfaces fractures and abrasion that imprinted areas of different sizes a comparison of microtextural imprints on silica glass spheres relative to coastal dune sands was made to better understand energy thresholds required to achieve grain damage

asian dustfall in the st elias mountains yukon canada in april 2001 a major atmospheric dustfall event occurred in the st elias mountains yukon territory canada field samples were collected and analyzed for particle size mineralogy chemical composition and sr nd and pb isotopes dusts found above 3000 m had their source in the gobi desert region of northern china and inner mongolia and were transported to the yukon following a series of major dust storms that took place in early april dusts found below 3000 m had local yukon or mixed source s the asian dusts had a modal volume diameter of 4 m typical of far traveled mineral aerosols however larger 10 m particles were also found at 5000 m suggesting a very rapid trans pacific transport in the mid troposphere we estimate that the april 2001 event deposited from 5500 to 6335 tons of dust over an area of 21 000 km2 in the southwestern yukon most of which probably fell within a week our findings are consistent with instrumental observations and model simulations of the april 2001 event while the dust cloud was reportedly mixed with volatile pollutants from asia we found no evidence of metal pollution associated with the dustfall in the yukon our findings contribute to clarify the dynamics and the geochemical impact of asian dust long range transport events and to better estimate eolian fluxes of dustborne elements e g fe to the ocean associated with such events they may also assist in identifying past asian dust events in ice cores drilled from the st elias mountains icefields to develop a long term record of their frequency magnitude and source s

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

petrology and geochemistry of shoshonitic plutons from the western kunlun orogenic belt xinjiang northwestern china implications for granitoid geneses abstract a series of granitoids from proterozoic to cenozoic age occurred in the western kunlun orogenic belt xinjiang northwestern china several intrusions such as the west datong middle caledonian age north kuda late caledonian age and kuzigan karibasheng zankan himalayan age plutons have shoshonitic affinity their rock assemblages include quartz monzodiorite quartz monzonite quartz syenite middle caledonian or monzonitic granite granite late caledonian or biotite monzonitic granite diopside granite diopside syenite himalayan generally biotite is iron phlogopite with some eastonite and high mg mg fe t and fe 3 fe 2 ratio amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende with some edenite and higher mg mg fe t and fe 3 fe 2 ratio the rocks show sio 2 contents of 52 77 71 85 and high k 2 o na 2 o mostly 8 average 9 14 k 2 o na 2 o mostly 1 average 1 50 and fe 2 o 3 feo 0 85 1 51 average 1 01 and low tio 2 contents 0 15 1 12 average 0 57 al 2 o 3 contents 13 01 19 20 are high but variable the granitoids are prominently enriched in lile lree and volatiles such as f however the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations suggesting their different geneses the origin of the west datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source the north kuda and himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late orogenic slab break off or lithospheric thinning

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

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

differential weathering of granitic stocks and landscape effects in a mediterranean climate southern iberian massif spain mineralogical and structural features control the weathering processes and landform development of two different crystalline stocks in the iberian massif spain the santa elena and linares stocks the santa elena stock shows irregular saprolite profiles and boulder landforms whereas the linares stock develops broad and plain landscapes with uniform saprolites and less boulder forms the santa elena stock is more closely jointed and fractured than the linares body the main secondary minerals are kaolinite and illite illite smectite interstratification was only observed in deep samples from the linares profile the linares profile is feldspar enriched whereas in santa elena plagioclase is almost absent and clay mineral content especially kaolinite is higher feldspars show dissolution channels developed along cleavage planes filled by clay minerals biotite kaolinite intergrowths have fanned out textures of epitaxial disposition weathered materials are enriched in al and h2o and fe and depleted in ca na mg ti p the santa elena weathered materials are richer in h2o than those from linares and have lower si al ratios mineralogical and geochemical evidence indicate the santa elena materials are more intensely weathered high fracturation and high ca richer plagioclase contents are key factors producing the pervasive santa elena stock weathering fluvial erosion removed the alteration products in incised tectonically controlled streams resulting in boulder accumulation

sr isotopic and elemental characteristics of calcites in the chinese deserts implications for eolian sr transport and seawater sr evolution abstract calcite content sr concentrations and isotopes of calcites in the chinese deserts are systematically studied in this paper calcite contents which are calculated according to acid soluble ca contents in the deserts are generally higher in the sandy deserts than in the sandy lands and decrease roughly from northwest to northeast of china acid soluble sr is well correlated with calcite in the chinese deserts implying acid soluble sr comes mainly from the calcite dissolution sr concentrations in calcites calculated on the basis of calcite contents and acid soluble sr concentrations in the deserts have an inverse relation to calcite contents essentially mirroring the degree of sr substitution for ca in the calcite development desert calcites have regional variations in sr isotopic ratios calcite sr isotopic ratios depend on geological settings and chemical weathering the badain jaran and tengger deserts are probably affected by additional factors such as the remote groundwater cycle or overturning of underlying sand deposits only four deserts taklimakan qaidam badain jaran and tengger appear to be potential sources of eolian deposits in the chinese loess plateau clp isotopic signatures of calcite sr and silicate nd further indicate that the tengger desert was not an important source for eolian deposits in the clp eolian calcite was probably enriched due to wind sorting from the potential sources to the clp and suffered weathering leaching after it accumulated in the clp sr isotopic compositions and ca sr molar ratios of calcites are different between the deserts and the lingtai profile due to the integrated effect of wind sorting and weathering leaching it is essential to calculate accurately the 87sr 86sr ratio and sr concentration of eolian calcite entering the oceans according to geochemical data of the chinese deserts because of the importance of the chinese deserts in the global dust cycle the calculated sr concentration and 87sr 86sr ratio of eolian calcite entering the north pacific ocean are 11 75 mol g and 0 71032 respectively the calculated values in this study are close to the recommended values by jacobson jacobson a d 2004 has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine 87sr 86sr ratios over the past 2 5 million years geochem geophys geosyst 5 12 1 9 q12002 doi 10 1029 2004gc000750 using the same model as that of jacobson 2004 the effect of asia dust on the evolution of seawater sr isotopes is evaluated 87sr 86sr seawater increases by 0 3 10 5 if the lower dust flux of 2 34 108 mol sr yr is used in the model suggesting the little effect of asian dust on the seawater sr record in the quaternary the increase in 87sr 86sr seawater is 1 5 10 5 if the higher value of 1 17 109 mol sr yr is used as observed in the quaternary sr record these results further support the suggestions of jacobson 2004

isotopic tracing sr nd u and hf of continental and marine aerosols in an 18th century section of the dye 3 ice core greenland determining the sources and pathways of atmospheric mineral dust and marine aerosols remains a difficult problem in order to address this problem the radiogenic isotopic composition of the dust and soluble ice components of greenland ice has been determined and used as a source tracer for mineral dust and marine aerosols sr and nd isotopic composition was measured with a yearly to seasonal resolution on both the bulk dust and soluble fractions of a section of the dye 3 1988 ice core from greenland in the age range of 1786 1793 a d hf isotopic composition was also measured for three of the dust samples as a complementary tracer of dust origin the first direct measurement of hf in paleo atmospheric dust measured nd and sr isotopic composition of the dust corrected for carbonate contributions are compared to literature potential source area psa data 6 e units and are decoupled from dust composition indicating that the nd composition of seawater is preserved in the ice the end of the ice suggests variable mixing of aerosols from arctic sea salts with another more radiogenic source during transport

mesoproterozoic grenville age terranes in the kyrgyz north tianshan zircon ages and nd hf isotopic constraints on the origin and evolution of basement blocks in the southern central asian orogen abstract the north tianshan orogenic belt in kyrgyzstan consists predominantly of neoproterozoic to early paleozoic assemblages and tectonically interlayered older precambrian crystalline complexes and formed during early paleozoic accretionary and collisional events one of the oldest continental fragments of late mesoproterozoic grenvillian age occurs within the southern part of the kyrgyz north tianshan using shrimp zircon ages we document two magmatic events at 1 1 and 1 3 ga the younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 ma and is associated with deformation and metamorphism the older event is documented by 1 3 ga felsic volcanism of uncertain tectonic significance and may reflect a rifting episode geochemical signatures as well as nd and hf isotopes of the mesoproterozoic granitoids indicate melting of still older continental crust with model ages of ca 1 2 to 2 4 ga the mesoproterozoic assemblages are intruded by paleozoic diorites and granitoids and nd and hf isotopic systematics suggest that the diorites are derived from melts that are mixtures of the above mesoproterozoic basement and mantle derived material their source is thus distinct from that of the mesoproterozoic rocks emplacement of these plutons into the precambrian rocks occurred between 461 and 441 ma this is much younger than previously assumed and indicates that small plutons and large batholiths in north tianshan were emplaced virtually synchronously in the late ordovician to early silurian the mesoproterozoic rocks in the north tianshan may be remnants of a once larger continental domain whose fragments are preserved in adjacent blocks of the central asian orogenic belt comparison with broadly coeval terranes in the kokchetav area of northern kazakhstan the chinese central tianshan and the tarim craton point to some similarities and suggests that these may represent fragments of a single mesoproterozoic continent characterized by a major orogenic event at 1 1 ga known as the tarimian orogeny

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

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

re os isotope systematics of the taklimakan desert sands moraines and river sediments around the taklimakan desert and of tibetan soils abstract reported here are the first 187os 188os ratios and abundances of os and re for taklimakan desert sands and glacial moraines from the kunlun mountains osmium isotopic data are also reported for river sediments around the taklimakan desert river sediments from the kunlun and tianshan mountains tibetan soils and loesses from the loess plateau as well as sr and nd isotopic data for these samples the taklimakan desert sands from various regions show surprisingly homogeneous os isotopic ratios 187os 188os 1 29 0 08 and abundances os 11 ppt with some variations in re abundances re 130 to 260 ppt and 187re 188os ratios 60 to 140 the 187os 188os ratios for the taklimakan desert sands are close to the average for kunlun moraines river sediments around the taklimakan desert sands and the tibetan soils supporting the idea that the taklimakan desert sands are derived from moraines and river sediments around the desert or from tibetan soils and are homogenized by aeolian activity in the desert furthermore the os isotopic data for the sediments studied here are compared with those 187os 188os 1 04 os 32 ppt re 206 ppt 187re 188os 35 of loesses from the loess plateau reported elsewhere and it is concluded that the re os data for the loess can be used as proxy for the upper continental crust

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

mechanisms of loess sized quartz silt production and their relative effectiveness laboratory simulations the production of loess sized quartz silt is frequently ascribed to glacial grinding mechanisms in this study a series of laboratory simulations was set up the purpose of which was to demonstrate that a range of geomorphic mechanisms are capable of producing silt under laboratory conditions the geomorphic mechanisms investigated were aeolian abrasion fluvial comminution glacial grinding salt weathering and frost weathering the results confirmed that under laboratory conditions all of these mechanisms were capable of producing silt the relative effectiveness of these mechanisms at producing silt under laboratory conditions was then calculated in order to provide a starting point for a consideration of their potential effectiveness within the natural environment these results indicate that fluvial and aeolian activity are highly effective at producing quartz silt over short time periods in a dust storm of four days duration 287 g of silt could potentially be produced from every kilogram of sand entrained while fluvial comminution in a turbulent fluvial environment could potentially produce 900 g of silt from every kilogram of sand entrained within 32 h over longer periods of time the glacial grinding and weathering mechanisms represent more continuous and hence more effective silt producing mechanisms although it is realised that the relative importance of each silt producing mechanism will differ spatially and temporally due to differences in climate relief geology and geomorphic history the findings from this work do have implications for the genesis of loess deposits they demonstrate that glacial and cold weathering processes are not solely responsible for fine particle formation and that efficient silt producing mechanisms can operate within a variety of environments under suitable conditions weathering together with episodic contributions from aeolian and fluvial mechanisms could be responsible for a considerable proportion of global quartz silt production

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

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

nd sr isotope geochemistry of fine grained sands in the basin type deserts west china implications for the source mechanism and atmospheric transport abstract the basin type deserts of west china are among the greatest dust emission areas in the world mineral dust that is emitted from the deserts is transported and deposited in east central china and even in far east regions this study investigates the nd sr isotopic compositions of fine grained surface sands nd 0 10 9 to 15 and 87 sr 86 sr 0 714 to 0 718 while those of the dune sands from the gurbantunggut desert range from e nd 0 4 5 to 6 and 87 sr 86 sr 0 711 to 0 713 the isotopic compositions of the fine grained surface sands are not spatially uniform within each desert and are controlled by the lithological characteristics of the tectonic units in which the deserts are located the isotopic comparison of the dune sands with other sediments indicates that tectonic denudation and fluvial processes are the main mechanisms of fine particle production of the modern desert sands in terms of isotope analyses and forward trajectory results it is further found that the mineral dust is deposited not only in proximal areas such as the hexi corridor the chinese loess plateau and the tibet qinghai plateau but also in distal regions such as japan the pacific ocean and greenland once it is blown out of the taklimakan desert however the transport and sinks of mineral dust vary with the atmospheric currents

precipitation associated with convergence lines precipitation is often organized along coherent lines of low level convergence which at longer time and space scales form well known convergence zones over the world s oceans here an automated objective method is used to identify instantaneous low level convergence lines in reanalysis data and calculate their frequency for the period 1979 2013 identified convergence lines are combined with precipitation observations to assess the extent to which precipitation around the globe is associated with convergence lines in the lower troposphere it is shown that a large percentage of precipitation between 65 and 90 over the tropical oceans is associated with such convergence lines with large regional variations of up to 30 throughout the year especially in the eastern pacific and atlantic oceans over land the annual mean proportion of precipitation associated with convergence lines ranges between 30 and 60 and the lowest proportions less than 15 associated with convergence lines occur on the eastern flank of the subtropical highs overall much greater precipitation is associated with long coherent lines greater than 300 km in length than with shorter fragmented lines less than 300 km and the majority of precipitation associated with shorter lines occurs over land the proportion of precipitation not associated with any convergence line primarily occurs where both precipitation and frequency of convergence lines are low the high temporal and spatial resolution of the climatology constructed also enables an examination of the diurnal cycle in the relationship between convergence lines and precipitation here an example is provided over the tropical maritime continent region

the evolution of dry lands in northern china and in the republic of mongolia since the last glacial maximum abstract the dry lands in china and mongolia include sand seas gravel deserts stable sand dunes desert steppe steppe and scrub woodlands environments distributed in a wide range of geomorphological and tectonic settings from 155 m below sea level to more than 5000 m asl in china the sandy deserts and gravel deserts are located in the arid regions mainly west of the helan mountains 106 e whereas the stable dune regions are distributed in the semi arid areas east of the helan mountains in mongolia deserts cover more than 40 of the country they are mainly distributed in the southern and southwestern part of the country in inter mountain valleys and basins of the altai mountains and in the uvs nuur basin in northwestern mongolia the desert regions enclose mainly gravel desert gobi and comprise some areas with sand fields and dune fields especially in western mongolia relict frost wedges and moraines in the chaidamu and tarim basins of china indicate that the coldest time of the last glaciation occurred at 30 25 ka in these two areas the stratigraphy of the dunes in the badain jaran desert high lake levels in the areas near and within the large deserts in china and in mongolia suggest a much more humid climate in western china and in mongolia during marine isotope stage three however the period after 24 ka to the end of the pleistocene was mostly characterised by increased temperature and reduced precipitation in the chaidamu and tarim basins paleoenvironmental conditions in the eastern part of the chinese desert belt were marked by an extensive widening of dune formation at 21 13 ka reflecting a weaker intensity of east asian summer monsoon during the holocene higher lake levels stratigraphy of dunes and results of palynological isotopical and sedimentological analyses of lacustrine sediments in the western china and mongolia suggest a few wetter periods especially in the earlier part of the holocene the holocene climatic conditions in the eastern part of the chinese deserts have enabled stabilisation of dunes and formation of soils the presently active dunes in this region are a result of desertification due to human influences recent investigations in the dry lands of china and mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates