a high resolution micromorphological record of changing landscapes and climates on the western loess plateau of china during oxygen isotope stage 5 abstract the micromorphological characteristics of a continuous set of block samples from 24 38 m depth in a well section on jiuzhoutai mountain lanzhou china are described the shape of the magnetic susceptibility curve together with previously published radiocarbon luminescence and geomagnetic dates indicates that this sample set encompasses the whole of the last interglacial s1 palaeosol complex and extends into the overlying and underlying loess l1 and l2 units seven pedosedimentary units are recognised on the basis of trends in the bulk properties and the key micromorphological indicators excrements textural concentrations shell fragments and calcite and gypsum features high rates of loess deposition with significant cryogenic activity gypsum precipitation and only weak bioturbation characterised oxygen isotope stage ois 6 and ois 4 at lanzhou depositional rates were moderately high in ois 5d and 5b with slightly higher bioturbation and no significant cryogenesis or gypsum precipitation ois 5e 5c and 5a were marked by low rates of accretion more extensive bioturbation and limited leaching this reconstruction reflects the pedosedimentary responses to fluctuating dominances of monsoonal controls during this period of global climatic change comparison of earlier micromorphological results from sites to west and east of lanzhou along a dry to humid climatic gradient indicate a clear regional pattern with reduced loess accumulation rates and enhanced bioturbation and leaching in the humid east tianshui and xian clay translocation occurred only in ois 5e at xian the warmest and most humid site on the transect

diatom stable isotopes sea ice presence and sea surface temperature records of the past 640 ka in the atlantic sector of the southern ocean 1 high resolution 13c and 15n records of diatom bound organic matter 13cd 15nd from odp site 1094 south of the polar front are combined with reconstructions of summer sea surface temperature and winter sea ice to establish changes in surface water characteristics associated with the main climatic events of the past 640 ka the six glacial interglacial 13cd cycles show excellent agreement with specmap 18o and vostok co2 content suggesting that global physical processes rather than local biological factors were the main influences on 13cd by contrast there is weak correspondence between the vostok dust record and the 13cd and 15nd records the data do not support the hypothesis that glacial iron fertilization of the southern ocean was the main factor lowering atmospheric co2 if dust accumulation represents iron input the records indicate that sea ice cover water column stratification and iron addition from deep water mixing are more likely to explain our observations

micromorphological variation of the s 1 paleosol across northwest china abstract a micrornorphological approach based upon sets of closely spaced thin sections taken from three sites located along a climatic and depositional gradient has been utilised to reconstruct the sequence of pedogenic and sedimentary events leading to the development of the s1 paleosol in northwest china two main pedosedimentary stages related to regional changes in monsoonal controls are evident at each site although the resolution processes and resultant features vary in a manner reflecting differences in climate and rates of loess deposition around xining in the west where loess accumulation rates were high and pedogenic processes were restricted to shallow leaching and limited bioturbation by the low rainfall s 1 comprises two discrete weakly developed paleosol units separated by a less pedogenically altered layer of loess in contrast at sites farther away from the loess source area in the more humid southeast s 1 is a thinner welded and more pedogenically developed unit dominated by the effects of extensive leaching bioturbation and sometimes even clay translocation processes

loess paleosol stratigraphy of dukso area namyangju city korea south abstract as korea lies between china with a drier climate and the wetter japanese islands the korean loess paleosol stratigraphy constitutes an important record of variations in the east asian monsoon climate the loess paleosol sequence consists of three loess layers l1ll1 l1ll2 and l2 and three paleosols l1ss1 s1 and s2 in the study area l1ll1 accumulated near the surface and is only about 5 cm in outcrop because it was removed for farming l1ss1 is about 103 cm thick soil crack structures developed in the upper part of l1ss1 were formed by shrinkage or as seasonally frozen ground soil wedges during the early cold dry stage of glacial period l2 is 48 cm thick with osl ages of 167 000 and 186 000 yr magnetic susceptibilities of paleosols were higher than the loess layers fine quartz grains in the loess layers are characterized by rounded shape and pitted surfaces based on the presence of the at tephra osl ages soil color soil crack structure magnetic susceptibility and median diameter the loess paleosol sequence of the dukso section can be correlated with the chinese loess paleosol sequence between mis 2 and 7

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

controls on zero order basin morphology zero order basins are common features of soil mantled landscapes defined as unchanneled basins at the head of a drainage network their geometry and volume control how quickly sediment may re accumulate after landslide evacuation and how water and subsequently pore pressure is delivered to hollow axes they also deliver water and sediment to the uppermost portions of the fluvial network despite this role as the moderator between hillslope and fluvial processes little analysis on their morphology has been conducted at the landscape scale we present a method to identify zero order basins in landscapes and subsequently quantify their geometric properties using elliptical fourier analysis we deploy this method across the coweeta hydrologic laboratory usa properties such as length relief width and concavity follow distinct probability distributions which may serve as a basis for testing predictions of future landscape evolution models surprisingly in a landscape with an orographic precipitation gradient and large hillslope to channel relief we observe no correlation between elevation or spatial location and basin geometry however we find that two physiographic units in coweeta have distinct zero order basin morphologies these are the steep thin soiled high elevation nantahala escarpment and the lower gradient lower elevation thick soiled remainder of the basin our results indicate that basin slope and area negatively covary producing the distinct forms observed between the two physiographic units which we suggest arise through competition between spatially variable soil creep and stochastic landsliding

loess is not just the accumulation of dust most regrettably there is much misuse of terminology in connection with the concept of loess and the interpretation of its origin people often speak and write incorrectly about loess accumulation even loess specialists who are aware of the fact that loess as a concept has to satisfy at least 10 criteria loess is not simply dust carried and deposited by wind dust only becomes loess after the passage of a certain amount of time in a given geographical zone i e only through diagenesis in certain ecological environments to state that loess is of aeolian origin is an oversimplification and an incorrect definition because an aeolian origin applies only to the dust from which the loess has been formed we are aware of the fact that airborne dust cannot be transformed into loess in every geographical environment but only under those conditions typical of semi arid grassland or steppe or forested steppe the process primarily occurs where the rate of dust accumulation exceeds sheet wash or weathering soil formation rates if the rate of dust accumulation is less than that of surface erosion or of soil biogenetic processes the dust then develops into soil or through intensive weathering and increased precipitation into loam or clay only part of the aeolian dust transported and deposited in a zone suitable for loess formation remains there permanently and is transformed in situ into loess dust not affected by diagenesis is usually further transported by snowmelt or rainwash and is only transformed into loess after it has been redeposited the loess itself however is easily erodible and its minerals are readily reworked and reaccumulated and given the appropriate conditions it readily undergoes diagenesis again we do not always have sufficient evidence to determine whether a given loess body is of primary or secondary origin traditionally the minerals making up primary loess have been regarded as originating in dust accumulated by aeolian processes secondary loess by contrast is different from typical loess in many ways and it is not unusual to find various loess series in which superimposed dust fractions have been transformed into loess by different processes recently we have observed that the origin of various types of loess is governed by differences in litho ecological conditions rather than by the way in which the mineral material from which the loess is derived dust has been primarily accumulated loessification is therefore determined by environmental conditions

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

provenance of the north pacific sediments and process of source material transport as derived from rb sr isotopic systematics abstract rb sr isotopic systematics of 111 samples of sediments in nine cores from the north pacific of quaternary and pliocene ages have been investigated they provide information on the provenance the process of particle transport and temporal variation in the flux of source material the rb sr isotopic systematics of the core sediments show well correlated pseudo isochrons the pseudo isochrons reflect the mixing of two types of material i e the asian continental material with high 87 rb 86 sr ratios 4 5 6 5 and high 87 sr 86 sr ratios 0 723 0 727 and the volcanic material with low 87 rb 86 sr ratios and low 87 sr 86 sr ratios from island arc volcanics such as the izu ogasawara mariana and the japanese islands and oceanic islands such as the hawaiian islands 0 0 2 0 0 703 0 708 the clearness of the pseudo isochrons implies that the rb sr isotopic composition of the weathering products derived from the asian continental crust is extremely homogenized the fine fraction a few m with a high 87 rb 86 sr ratio 5 0 6 5 is widely transported into the north pacific by the middle latitude westerlies and contributes largely to pelagic sediments the coarser fraction with a lower 87 rb 86 sr ratio

a mineral tracer toward high resolution dust provenance on the chinese loess plateau sem tem and sulfur isotopes of sulfate inclusions in biotite the most important terrestrial archive of the quaternary climate is the chinese loess plateau clp distributed over a vast region peripheral to the deserts of inner asia numerous paleoclimatic studies have examined magnetic chemical and isotopic proxies from deep loess paleosol sections however the highly uniform mineralogy of the clp has made it difficult to track the provenance transportation and deposition of dust particles here we report that the micrometer scale mineralogical heterogeneity of the loess particles has a significant potential in determining high resolution loess provenance scanning and transmission electron microscopy of the chinese loess reveals that biotite particles commonly have microinclusions of ba sr sulfates displacing the micaceous layers along cleavages chemical compositions varied widely from barite to celestine within the same biotite grain the ba rich sulfates precipitated first followed by an overgrowth of sr rich sulfates the frequency of sulfate bearing biotite varied greatly over several loess sections implying a specific source and sedimentation process their abundance on the western clp and sulfur isotopic composition support their derivation from porous sedimentary sequences reacted with hypersaline solutions e g arkosic sandstone probably located west of the clp covering the qilian mountains qaidam basin and surrounding mountains of the tibetan qinghai plateau the sulfate bearing biotite is the first microscopic mineral tracer in the clp provoking further search for other microscopic heterogeneities of the chinese loess and their equivalents in the source regions

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

pedosedimentary development and palaeoenvironmental significance of the s1 palaeosol on the northeastern margin of the qinghai xizang tibetan plateau the s1 pedocomplex correlated to oxygen isotope stage 5 of the ocean cores has been traced west of the loess plateau on to the extreme northeastern margin of the qinghai xizang tibetan plateau in china detailed micromorphological analysis of closely spaced thinsections from the pedocomplex at this site provides the basis for reconstruction of the sequence of pedosedimentary processes and associated palaeoenvironmental changes occurring during this time interval the six pedosedimentary stages identified are interpreted in terms of temporal variations in depositional rates size of particles transported and availability of moisture for pedogenic alteration as determined by changing balances in dominance of winter and summer monsoonal forces two main soil forming intervals are identified the more extensive of the two in terms of resultant pedological features reflects pedogenic alteration at a relatively stable land surface under a semi arid climate during the later part of pedosedimentary stage 2 the other main period corresponds to pedosedimentary stages 4 and 5 when leaching and bioturbation processes were active at aggrading surfaces leading to development of an accretionary unit without clear differentiation of horizons pedosedimentary stages 1 3 and 6 were characterised mainly by rapid rates of coarse loess accumulation with synsedimentary modification restricted to surface slaking and crust formation and minor localised redistribution of calcite

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

rb sr and k ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of sr isotopes abstract biotite is widely used for rb sr and k ar isotopic dating and influences sr isotope geochemistry of hydrological regimes the isotopic system of biotite behaves diversely in response to surface weathering i e the complete preservation of original rb sr and k ar isotopic ages or dramatic reduction in this study we have explored the relation between the behavior of isotopic systems and complex weathering processes of biotites in the weathering profiles distributed on the mesozoic granitoids in south korea in the lower parts of the profiles biotite in the early stages of weathering was transformed into either oxidized biotite or hydrobiotite with a mass release of 87 sr and 40 ar forced by the rapid oxidation of ferrous iron during the transformation to oxidized biotite 87 sr and 40 ar were preferentially released relative to rb and k respectively via solid state diffusion through the biotite lattice resulting in a drastic reduction of original isotopic age the reduction of rb sr age was greater than that of k ar age because k was preferentially released over rb whereas 87 sr and 40 ar were released proportionally to each other however during the transformation of biotite to hydrobiotite i e to regularly interstratified biotite vermiculite 87 sr rb 40 ar and k were completely retained in the alternating biotite interlayer and thus the original isotopic age can be preserved in the upper parts of the profiles where iron oxidation was almost completed 87 sr rb 40 ar and k were gradually and proportionally released with no further significant change in isotopic age during the gradual transformation of the early formed oxidized biotite into hydrobiotite and vermiculite or during their final decomposition to kaolinite the ratios and amounts of isotopes released from weathered biotites are dependent upon the degree of iron oxidation and the pathways of mineralogical transformation regional and local variations in isotopic systems affected by particular weathering processes should be considered when dating biotite or biotite bearing rocks in weathering environments modeling the transfer of sr isotopes to hydrologic regimes and tracking the provenance of sediments

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

deposition and weathering of asian dust in paleolithic sites korea abstract paleolithic stone artifacts in korea typically occur in brown clay silt bcs sequences the origin and depositional environment of these sequences are important for reconstructing the paleoenvironment as well as for establishing chronologies of artifact bearing stratigraphic units we investigated four bcs bearing sections in foothills and river and marine terraces in korea by applying quantitative mineralogical geochemical microtextural and k ar isotopic methods in all four sections the lower units are colluvial and fluvial deposits strongly influenced by diverse local lithology whereas the upper units are characterized by bcs units mineralogical geochemical compositions grain sizes and colors converge into common properties in the upper bcs units in all sections these common properties are consistent with the eastward trends of increasing weathering degree and grain size fining throughout the loess paleosol sections of the chinese loess plateau clp k ar detrital ages of the sections also converge upward into a narrow range similar to the age ranges of the loess and paleosols in the clp the top bcs unit in the jeongok section the thickest section is underlain by an additionally weathered bcs unit with strong red chroma indicating a change from warm to cold climate we did not observe any clear evidence of climatic changes in other thinner sections which may be due to a superposition of cold stage accumulation and warm stage deep weathering the common properties of the bcss in korean sections and their relationship to the clp loess and paleosols indicate widespread deposition of asian dust and subsequent weathering in the late quaternary forming bcs sequences in this respect the bcs sequences investigated here are considered to be the additionally weathered equivalents of the clp loess paleosol sequences having been exposed to the high annual precipitation of the korean peninsula given the wide distribution of bcs sequences at paleolithic sites throughout the peninsula the findings of this study are important for the ongoing debate surrounding the depositional environments of the paleolithic deposits and provide a foundation for the establishment of the chronological framework of the paleolithic artifact bearing layers and lithic assemblages

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

geochemistry of quaternary sediments of the jeongokri archaeological site korea implications for provenance and palaeoenvironments during the late pleistocene the geochemical characteristics of an approximately 6 m long sediment core collected from the jeongokri archaeological site hantan river korea were examined to determine the provenance of the sediments and to reconstruct the palaeoenvironment of the study area during the late pleistocene 200 127 ka the core sediments were subdivided into two parts based on grain size an upper 0 380 cm depth and lower part 380 cm depth the lower part was deposited primarily by fluvial processes during an interglacial period marine isotope stage mis 7 with warm and humid conditions conversely the upper part was mainly deposited by aeolian processes during a cold and dry glacial period mis 6 geochemical characteristics represented by major trace and rare earth element ree compositions and textures of the jeongokri core sediments show distinct differences between the upper and lower parts the mineralogy and major trace and ree compositions indicate that the influence of felsic source rocks e g granite was dominant in the lower sediments which were derived from the hantan river in contrast increased quartz content and the very fine and homogeneous grain size in the upper sediments indicate an aeolian origin ree ratios and distribution patterns and geochemical signatures indicate that these sediments were derived predominantly from chinese loess deposits and partially from local sediments from the korean peninsula the possible source area of the upper sediments is the northern part of the yellow sea basin the yellow sea basin having mixed geochemical signatures between chinese loess and korean derived sediments was exposed because of low sea levels during mis 6 the exposed yellow sea basin was located in the path of winter monsoon winds which may have carried a great deal of airborne sediments from the basin to the jeongokri area copyright 2011 john wiley sons ltd

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

bulk and single particle mineralogy of asian dust and a comparison with its source soils 1 the mineralogical properties of asian dust have been examined in detail and the results have been compared with the chinese source soils using high resolution scanning electron microscopy transmission electron microscopy x ray diffraction and chemical analysis mineralogical classification of asian dust particles showed that the most common single particles were clay aggregates 48 that were often mixed with nanosized calcite followed by particles of quartz 22 plagioclase 11 coarse calcite 6 k feldspar 5 muscovite chlorite kaolinite amphibole gypsum fe and ti oxides which were either partly or entirely attached with clay size mineral grains the clay minerals in asian dust were mostly illite and interstratified illite smectite the average mineral composition of the bulk dust samples by x ray diffraction was quartz 28 plagioclase 11 k feldspar 8 calcite 8 illite 19 interstratified illite smectite 22 chlorite 2 smectite 1 and kaolinite 1 in the silty soils from the source regions the clay minerals and nanosized pedogenic calcite aggregated and covered silt size minerals while the sands were mostly composed of quartz and feldspars and were lined with clay minerals the mineralogy of asian dust was similar to that of the silty soil from the loess plateau but the total phyllosilicate content increased from desert sands 7 silty soil 23 to asian dust 45 fining eastward the optical properties of asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay rich mineral composition the aggregation and attachment of the clay minerals on the coarser minerals and the nanosized calcite

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia