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

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

discussion of the relationship between dustfall grain size and the desert border taking the southern border of the tengger desert and the southern dust deposit area as an example abstract in northern china high spatial and temporal instability exists in the southern desert border since the region is very sensitive to the changes of global climate and the migration of the southern desert border threatens the survival of surrounding inhabitants it is very important to strengthen the research about the migration of the southern desert border of northern china the dust in the downwind of the desert contains relevant information of the desert evolutionary history in order to investigate the relationship between dustfall grain size and the southern border of northern china desert we collected 56 eolian surface soil samples from the south of the tengger desert selected two near north south transects from these samples and used the grain size class standard deviation method we finally obtained three sensitive grain size components ranking by degree of sensitivity from high to low 61 8 185 4 m 18 2 61 8 m and 2 3 18 2 m the values of the three sensitive grain size components from the 56 eolian surface soil samples and the three commonly used grain size indicators which are the median grain size 20 m and 63 m particle content have been converted to the grain size contour figures in the six grain size contour figures the contour of the 61 8 185 4 m particle content component has the highest degree of similarity with the southern border of the tengger desert followed by the 63 m particle content component and then the components of the median grain size 18 2 61 8 m particle content 20 m and 2 3 18 2 m particle content in turn relative to the 20 m and 63 m particle content indicators the indicator of 61 8 185 4 m particle content is not only the most sensitive one in theory but also has the highest degree of similarity between its contour and the southern desert border in practical terms moreover this indicator is further defined as the upper limit of coarse grain size since the coarse grains in the eolian deposits are mainly from the near source desert the component of 61 8 185 4 m particle content within the loess to the south of the tengger desert could be regarded as the indicator of the migration of the southern desert border which could be used to quantitatively reconstruct the desert palaeo border in the future

holocene climatic changes revealed by aeolian deposits from the qinghai lake area northeastern qinghai tibetan plateau and possible forcing mechanisms previous palaeoclimatic studies in the northeastern qinghai tibetan plateau netp during the holocene mainly using lake sediments have deepened our understanding of the climatic system in this remote region the timing and forcing mechanisms of climatic change in this region are still controversial however aeolian sand and silt deposits which are widely distributed in the netp can be readily dated by optically stimulated luminescence osl techniques and reveal the sensitive response of the landscape to climatic change in this study aeolian sand and loess at six sites around qinghai lake were studied to reconstruct millennial scale climatic changes during the holocene multiproxy data along with 24 osl age determinations show that low effective moisture and aeolian activity occurred at c 13 ka 10 9 1 ka and 8 9 7 8 ka periods of greater effective moisture may have occurred at 11 ka and 9 ka and there is evidence for a previously undocumented wet climate at 4 3 ka these results show that mi

dust supply from river floodplains the case of the lower huang he yellow river recorded in a loess palaeosol sequence from the mangshan plateau the mangshan plateau is located on the south bank of the huang he yellow river just west of the city of zhengzhou well outside the loess plateau in central china mixing models of the grain size data indicate that the loess deposits are mixtures of three loess components comparison of the mixing model with existing models established for a series of loess palaeosol sequences from the loess plateau indicates that the mangshan loess has been supplied from a proximal dust source the huang he floodplain during major dust outbreaks the high accumulation rates the composition of the loess components and especially the high proportions of a sandy loess component support this owing to the exceptionally high accumulation rates the mangshan grain size magnetic susceptibility and carbonate records provide a high resolution archive of environmental and climate change copyright 2008 john wiley sons ltd

holocene climate variations from zhuyeze terminal lake records in east asian monsoon margin in arid northern china zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved

changes in sand content of loess deposits along a north south transect of the chinese loess plateau and the implications for desert variations geological records have shown that the deserts east of the helan mountains in northern china were covered by grass during the holocene optimum whereas during marine oxygen isotope stages 2 and 4 distribution of the deserts was almost the same as at present the wide advance retreat cycles of the deserts may have exerted an important control on grain size changes in the loess of the loess plateau by altering the distance between the source and the accumulation zone of the loess this challenges the widely accepted model that winter monsoon winds were the sole factor responsible for spatial and temporal changes in loess texture to observe spatial changes in sedimentological characteristics of loess during the last glacial interglacial cycle the texture of loess was measured along a north south transect of the loess plateau this transect consists of nine loess sections starting at yulin in the transitional region between the loess plateau and the mu us desert and ending at weinan in the southernmost part of the loess plateau southward changes in sand 63 m content along the transect suggest that variations in desert extent have indeed played a significant role in loess grain size distributions particularly in the northern part of the loess plateau it is proposed that sand content 63 m of loess in the loess desert transitional zone may be used as a proxy indicator for proximity to the desert margin

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

calibration of modelled mixing patterns in loess grain size distributions an example from the north eastern margin of the tibetan plateau china genetically meaningful decomposition unmixing of sediment grain size distributions is accomplished with the end member modelling algorithm unmixing of the loess grain size distributions of a late quaternary loess palaeosol succession from the north eastern tibetan plateau indicates that the loess is a mixture of three end members representing very fine sandy coarse silty and medium silty loess the unmixing approach potentially enables the unravelling of sediment fluxes from multiple dust sources opening the way to significant advances in palaeoclimatic reconstructions from loess grain size distribution data however as laser diffraction size analysis is a volume based technique the proportional contributions of the modelled end members might deviate significantly from weight proportions hence calibration of the end member volume proportions to weight proportions must be established before one can calculate the source specific dust fluxes this paper reports the findings of a sediment mixing experiment which enables calibration of the modelled mixing patterns established for the tibetan loess palaeosol succession 2005 international association of sedimentologists

rivers and loess the significance of long river transportation in the complex event sequence approach to loess deposit formation abstract rivers are essential for loess deposit formation river systems which relate directly to loess deposit formation include the danube and the rhine the mississippi and the missouri the thames and the medway the indus ganges and brahmaputra the dnepr don and volga the clutha mataura and rakaia new zealand rivers the yellow river rivers in south america siberian rivers flowing north the odra and the wisla between the mountains and the ice the syr darya and amu darya into the desert the contention is that rivers are not just important in major loess deposit formation they are mandatory necessary imperative obligatory essential indispensable requisite for a complete and satisfactory study of a loess deposit we need to know how the material is produced how it is transported and distributed across the landscape how intermediate deposits are formed how transportation provides the defining properties i e open structure collapsibility draping across the landscape and what may happen post deposition e g chernozemisation fragipan formation increased collapsibility etc if rivers are essential then it would appear that the british loess is probably alpine material delivered by the proto rhine and the polish loess is not derived from the ice sheet to the north but from the mountains to the south the lack of loess in canada is explained by the absence of suitable rivers the loess in russia and neighbouring countries can be classified as jefferson et al jefferson i f evstatiev d karastenev d mavlyanova n g smalley i j 2003b the engineering geology of loess and loess like deposits a commentary on the russian literature engineering geology 68 333 351 suggested on the basis of associated rivers a new deposit of glacial loess is recognised associated with the dnepr don and volga rivers the uswr loess the smalley leach smalley i j leach j a 1978 the origin and distribution of the loess in the danube basin and associated regions of east central europe a review sedimentary geology 21 1 26 available from www geo edu ro sgr mod downloads pdf smalley sedgeo 1978 pdf vision of the loess in the danube basin and east central europe is probably misconceived they assigned a great significance to glacial action and put loess in a northern band it appears that this proposed glacial influence is minimal and that the danube loess is essentially mountain loess derived from the alps the carpathians the sudeten mountains and other high regions the danube system is a classic example of a river controlling loess distribution

grain size of fine grained windblown sediment a powerful proxy for process identification abstract dust transport by the wind is not a uniform process but may occur in different modes according to source area conditions and transport height and distance subsequently these differences are expressed in terms of grain size and fluxes of the aeolian deposits transport distances may vary from several tens of meters to thousands of kilometers while the height accordingly may vary from meters to more than thousand meters a relation with grain size distributions may be established on the base of type occurrences of different loess facies three main loess populations and several subpopulations of primary windblown origin may be defined according to their grain size dominated by fine sand to very coarse silt silt and very fine silt to clay respectively each of them reflects a specific aeolian process and transport conditions it follows that the grain size distribution of a loess deposit is an excellent proxy for the reconstruction of aeolian processes and wind circulation patterns apart from primary pure wind deposition loess may also be affected by secondary post depositional processes examples are settling of loess particles in a lacustrine setting and reworking by rivers or surface runoff although the primary loess characteristics are maintained reworking processes leave also their imprint in the grain size distribution as a useful tool for secondary process identification

younger dryas event recorded by the mirabilite deposition in huahai lake hexi corridor nw china abstract deposits from the huahai ancient lake in the hexi corridor were dated using conventional and ams 14c a 2500a carbon storage effect was defined at 9 25 m depth according to the 14c age difference between a plant macrofragment and detrital organic matter from the same layer the chronology of this strata indicated that the mirabilite layer at the depth of 8 05 m 9 15 m had formed during the younger dryas yd event the formation of the mirabilite layer indicated that the mean annual temperature in the hexi corridor dropped by 11 c during the yd event compared with today the lowest cold event occurred early in the yd which is consistent with what has been revealed by other high resolution records such as those of arctic ice cores and stalagmites in mid latitude regions

late quaternary aeolian sedimentation in central and south eastern tibet abstract the geomorphology and the cover sediments in the central and south eastern part of the tibetan plateau provide information about climatic change luminescence dating of aeolian and colluvial silts on top of different moraine sequences provides the first indications for the timing of these sediments during the late quaternary and holocene although there is a widespread cover of aeolian mantles in tibet only a few papers have focussed on them up to now samples from silt layers on top of pleistocene moraines or solifluction debris from central and southern tibet at elevations above 4000 m asl provide early holocene ages in most sections the aeolian silt on top of the bomi moraine in southeastern tibet situated at an elevation of about 3000 m asl provides an age of 25 ka according to geomorphological investigations the bomi moraine dates from the last ice age which can be confirmed by the luminescence data moreover one sample from a silt layer in between gravel layers xainxa is also pleistocene in age according to its sedimentary and geomorphological situation in the tibetan plateau pleistocene loess mainly occurs below 4000 m asl the holocene material a more sandy silt lying above 4000 m asl however aeolian material capping the moraines provides only minimum ages for the terminal moraines the time interval between glacier retreat and the accumulation of aeolian sediments may be several thousand years the most important fact is the trapping of dust in general lakes and a denser vegetation cover are or were the main traps for the typical loess found in the mountain areas of the tibetan plateau

deposits and soils of the past 130 000 years at the desert loess transition in northern china the desert loess transitional zone in north central china has long been thought sensitive to quaternary climatic change however reconstruction of quaternary climates in this area has been hindered by incompleteness of geological sections here we report the analytical results of two recently found sand loess soil sections both sections have thick eolian deposits from the last interglacial glacial cycle and can be correlated with one another field observations thermoluminescence dating and other laboratory analyses show that the last interglacial period produced three paleosols and two intercalated loess layers loess from the last glacial period is interbedded with three sand horizons that represent desert extension the expansion and contraction of desert in northern china may have been forced by the east asia monsoon

loess mantle spatial variability and soil horizonation southern wisconsin usa abstract loess is an important quaternary sediment that records evidence of landscape instability in sediment source areas and landscape stability in accumulation areas in wisconsin usa loess mantles glaciogenic deposits dating to the last glaciation but the landscape distribution and effects of the loess mantle on soil formation have received very little attention this study investigates the influence of glacial landforms on the spatial pattern of loess thickness and how the presence or absence of a loess mantle overlying glaciogenic sediments has influenced soil profile morphology namely thickness and nature of horizonation loess thickness follows systematic trends along hillslopes with slope percentage explaining most loess thickness variation between summit and backslope positions in the presence of a loess mantle solum and bt horizon thickness is proportional to the thickness of the loess mantle in well drained profiles in the absence of a loess mantle landscape and sediment characteristics that control permeability and water throughflow appear to be the most important determinants of profile characteristics the loess mantle modulates soil formation above the lithologic discontinuity with sandy calcareous glacial sediments by controlling soil water behavior and having physical and chemical characteristics conducive to transformation to soil genetic horizons

pathways of dust input to the chinese loess plateau during the last glacial and interglacial periods abstract it has been established that loess deposited on the chinese loess plateau was derived from arid and semi arid regions in north and northwest china but the specific pathways of dust transport are still not proved in this study 32 loess palaeosol profiles of the last glacial and interglacial periods were measured for magnetic susceptibility in order to investigate the dust transport pathways of dust input to the loess plateau the magnetic susceptibility variations of the loess palaeosol deposits within the last glacial cycle can be correlated with marine oxygen isotope variations to estimate the ages of boundaries of the loess units and intercalated palaeosols the sedimentation rate of each depositional unit can be obtained by dividing the thickness by the time that it represents because sedimentation rates decrease downwind from the dust source the spatial distribution of dust sedimentation rates shows that northwest and west winds were the two most important agents for transport of dust to the loess plateau during the last glacial cycle the north and northeast winds played an almost negligible role in addition topography and dust from local sources strongly affected the dust accumulation rates at some measured sites

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

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

some exact solutions to the nonlinear shallow water wave equations these exact solutions correspond to time dependent motions in parabolic basins a characteristic feature is that the shoreline is not fixed it is free to move and must be determined as part of the solution in general the motion is oscillatory and has the appropriate small amplitude limit for the case in which the parabolic basin reduces to a flat plane there is a solution for a flood wave these solutions provide a valuable test for numerical models of inundating storm tides

loess sedimentation in tibet provenance processes and link with quaternary glaciations abstract well preserved loess deposits are found on the foothills of mountains along the middle reaches of the yarlung zangbo river in southern tibet optically stimulated luminescence osl dating is used to determine loess ages by applying the single aliquot regeneration technique geochemical mineralogical and granulometric measurements were carried out to allow a comparison between loess from tibet and the chinese loess plateau our results demonstrate that i the loess deposits have a basal age of 13 11 ka suggesting they accumulated after the last deglaciation ii loess in southern tibet has a glacial origin resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near surface winds and iii the present loess in the interior of tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt the lack of full glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial such processes would have been repeated during each glacial interglacial cycle of the quaternary

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

suspended sediment transport under seiches in circular and elliptical basins abstract enclosed bodies of water such as lakes or harbours often experience large scale oscillatory motions seiching as a simple model of such flow we investigate exact solutions to the shallow water equations which represent oscillatory flow in an elliptical basin with parabolic cross section specifically we consider two fundamental modes of oscillation in one of which the flow is parallel to the axis of the ellipse while in the other it is radial we obtain periodic analytical solutions for sediment transport including erosion deposition and advection under either mode of oscillation and present a method for obtaining such solutions for a more general class of flow fields and sediment transport models our solutions provide estimates of the morphodynamical importance of seiching motions and also reveal a characteristic pattern of net erosion and deposition associated with each mode in particular we find that a net flux of suspended sediment can be transported from the deeper to the shallower regions of the basin these transport patterns which are driven essentially by settling lag are highly robust to the formulation of the sediment transport relation and appear not to be substantially affected by the omission of frictional terms in the hydrodynamics they should thus provide considerable insight into sediment transport in less idealised systems

regional grain size variations in aeolian sediments along the transition between tibetan highlands and north western chinese deserts the influence of geomorphological settings on aeolian transport pathways sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains qilian shan and their arid forelands hexi corridor in north western china six main sediment types were classified medium scale 103 m geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability a tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident aeolian sediments e g loess and dune sands are widespread they are used to identify aeolian transport pathways the mu fs ratio 5 11 m 48 70 m among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions the first fraction is attributed to long distance transport in high suspension clouds whereas the latter represents local transport in saltation mode the ratio shows strong correlation with elevation r2 0 77 thus it indicates a relatively higher far traveled dust supply in mountainous areas 3000 m above sea level a s l compared to the foreland the contribution of westerlies to high mountain loess deposits is considered likely hereby the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent the contribution from distant dust sources is ubiquitous in the study area however the far distance contribution may be reduced by the availability of fine sand provided in low topography settings plain foreland areas support fine sand deflation from supplying river beds allowing the formation of sandy loess in foreland areas and intramontane basins in contrast high mountain topography inhibits strong sand deflation into loess deposits eastern parts of the hexi corridor show higher aeolian sand occurrence in contrast the western parts are dominated by gravel gobi surfaces this is attributed to higher sand supply in eastern parts provided by the badain jaran desert and fluvial storages as sand sources copyright 2014 john wiley sons ltd

dune mobility and aridity at the desert margin of northern china at a time of peak monsoon strength wind blown sands were mobile at many sites along the desert margin in northern china during the early holocene 11 5 8 ka ago based on extensive new numerical dating this mobility implies low effective moisture at the desert margin in contrast to growing evidence for greater than modern monsoon precipitation at the same time in central and southern china dry conditions in the early holocene at the desert margin can be explained through a dynamic link between enhanced diabatic heating in the core region of the strengthened monsoon and increased subsidence in drylands to the north combined with high evapotranspiration rates due to high summer temperatures after 8 ka ago as the monsoon weakened and lower temperatures reduced evapotranspiration eolian sands were stabilized by vegetation aridity and dune mobility at the desert margin and a strengthened monsoon can both be explained as responses to high summer insolation in the early holocene

seven million years of wind and precipitation variability on the chinese loess plateau abstract recent studies of the eolian deposits in northern china have extended the east asian monsoon history back to the early miocene however the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the pleistocene epoch remain poorly constrained mainly due to uncertainties in the interpretation of proxy indices generated from the mio pliocene red clay sequences here we reconstruct east asian monsoon oscillations over the past 7 ma using magnetic susceptibility and carbonate content as summer monsoon precipitation proxies and quartz grain size as a winter monsoon wind intensity index our results suggest that precipitation and wind intensity exhibited significant orbital scale variations prior to 4 2 ma followed by slightly damped variability between 4 2 and 2 75 ma subsequently east asian monsoon circulation experienced two large shifts at about 2 75 and 1 25 ma characterized by stepwise strengthening of glacial wind and interglacial precipitation a remarkable change in east asian monsoon seasonality occurred around 3 15 2 75 ma prior to 3 15 ma strong winds were positively correlated with high effective precipitation whereas after 2 75 ma strong winds were negatively correlated with heavy precipitation this shift was probably induced by a change from an insolation forced system to one strongly influenced by the combined effects of the phased uplift of the himalaya tibetan plateau and the simultaneous development of the northern hemisphere ice sheets

environmental variability within the chinese desert loess transition zone over the last 20000 years the desert loess transition zone in northern china is sensitive to climate variability which is con trolled mainly by the relative strengths of the east asian summer and winter monsoons sandy loess layers found in the loess plateau and palaeosol sequences found in the sandy desert demonstrate latitudinal shifts of the southern desert margin over the last 20000 years stratigraphic investigations together with radiocarbon and some thermoluminescence dating show that during the last glacial maximum the desert margin was at its most southerly position 38 n during the early holocene it moved northward about three degrees in latitude 41 n at present the desert margin is again close to its most southerly position 38 219 n yet the northern boundary position of modern summer monsoon activity is placed at 41 459 n which is close to the estimated holocene optimum desert margin 41 n this situation cannot be explained from natural climate models hence an external driving mechanism needs to be considered and the most obvious one is that caused by human activity on the natural environment over the last 3000 years historical evidence tends to reinforce this consideration

hydrological changes and holocene climate variations in nw china inferred from lake sediments of juyanze palaeolake by factor analyses abstract the eastern juyanze palaeolake in hyperarid north western china 41 75 42 n 101 5 102 e provides evidence of a complex hydrological pattern during the holocene multivariate statistics based on lithological geochemical and mineral data from the reference site g36 in the centre of the lake were performed to reconstruct the interrelation between lake hydrology and climate variability of the last 11 000 yr principal component analyses pca analyses enabled us to extract the three system variables runoff lake level water budget and salinity as the major factors which have influenced the lake history during a highly variable holocene climate we can also demonstrate that the independent variable total organic carbon toc is not only a function of bio productivity in lakes under warm wet climate conditions but more frequently related to surface runoff processes which can result in over estimation of pollen types used for climate reconstructions a combined consideration of all system variables with lithological parameters catchment characteristics and the local groundwater situation show that lake formation and its persistence strongly depended on local rainfall runoff and the status of the underlying aquifer our results indicate remarkable differences between the early holocene and mid to late holocene lake formation owing to changes in the aquifer system beneath the lake at about 10 700 cal bp freshwater lake formation starts with extreme runoff events under a wet climate repeated dry climate spells of reduced runoff the overall climate during the early holocene points to wet conditions with frequent phases of very high runoff and highest lake levels until about 8900 cal bp extremely low runoff occurred between 8900 and 8100 cal bp indicating already dry climate conditions some hundred years prior to the worldwide recorded responses of the 8 2 ka cold dry event a second period of major dry climate conditions with generally low but fluctuating runoff unstable water budget and deposition of aeolian sand lasted for about 2100 yr between 7500 and 5400 cal bp these climate conditions corroborate previous assumptions of a mid holocene dry period in arid north western china increased runoff after 5400 cal bp under wet climate conditions led to a complete refill of the aquifer at about 5000 cal bp and favoured the development of a saline lake for about 3500 yr in terms of hydrology the time between 5400 and 4000 cal bp appears to be the climate optimum compared with the early holocene wet climate the mid to late holocene local rainfall was less pronounced and displays a general decreasing trend towards complete desiccation of the lake our results indicate an extremely variable moisture availability in arid regions of north western china during the entire holocene owing to the interplay of the east asian summer monsoon with the westerly waves at the boundary of the summer monsoon limit variations from dry to wet climate conditions seem to have been more pronounced than in other monsoon regions of china

variability of east asian winter monsoon in quaternary climatic extremes in north china in order to examine high frequency variations of east asian winter monsoon in quaternary climatic extremes two typical loess paleosol sequences in the chinese loess plateau were investigated sandy layers in the loess deposits the upper sand and lower sand layers l9 and l15 respectively which represent a high resolution record of paleomonsoon changes have been sampled at intervals of 5 6 cm from sections at luochuan and xifeng the grain size and magnetic susceptibility was measured for all samples the grain size results a proxy of winter monsoon strength indicate that the winter monsoon strength fluctuated on a millennial timescale during cold climatic extremes with climatic events of a few hundred to a few thousand years however the winter monsoon was relatively stable during warm periods the magnetic susceptibility signal a proxy of summer monsoon intensity is practically constant over the same period this is tentatively explained by the assumption that the summer monsoon intensity was too low to be recorded in the magnetic susceptibility signal the intensified winter monsoon events show periodicities in a range of 1000 to 2770 yr with a dominant cycle of approximately 1450 yr the detection of this oscillation in older glacial stages strongly suggests that it may be a pervasive cycle of the cold climatic phases of the quaternary millennial scale variations of the winter monsoon may be caused by instability of the westerly jet which is determined by temperature differences between the polar and the equatorial regions

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

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

low slip rates and long term preservation of geomorphic features in central asia in order to understand the dynamics of the india asia collision zone it is important to know the strain distribution in central asia whose determination relies on the slip rates for active faults1 2 3 4 5 many previous slip rate estimates of faults in central asia were based on the assumption that offset landforms are younger than the last glacial maximum 20 kyr ago 6 7 8 9 10 11 in contrast here we present surface exposure ages of 40 to 170 kyr obtained using cosmogenic nuclide dating for a series of terraces near a thrust at the northern margin of the tibetan plateau combined with the tectonic offset the ages imply a long term slip rate of only about 0 35 mm yr 1 for the active thrust an order of magnitude lower than rates obtained from the assumption that the terraces formed after the last glacial maximum our data demonstrate that the preservation potential of geomorphic features in central asia is higher than commonly assumed

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

measurements of dust deposition in gansu province china 1986 2000 abstract dust samples collected monthly for 15 years from 50 urban sites in 10 cities in gansu province china provide information on modern rates of dust deposition in the desert and gobi areas and in the loess plateau dust deposition is highest during spring months and lowest during autumn months in both the desert and gobi areas and the loess plateau there is a significant positive correlation between dust deposition and dust event and an inverse correlation between dust deposition and precipitation the 15 year mean maximums in the desert and gobi areas and the loess plateau are 498 64 and 327 02 t km 2 year 1 respectively and the mean minimums are 290 22 and 180 86 t km 2 year 1 respectively drought may have a widespread major influence on the modern rates of the dust deposition

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

on fine sediment transport by long waves in the swash zone of a plane beach we calculate suspended sediment transport erosion and deposition under reflected long waves on a plane beach our method employs the shallow water equations and is based on the calculation of the concentration field in lagrangian coordinates this allows results to be obtained readily throughout the whole domain including the often troublesome shoreline region these results suggest that the tendency of wave dominated muddy shores to export sediment and erode over long time scales is not due to wave forcing at infragravity frequencies since the sediment transport under such waves is localized close to the shoreline and is principally directed shorewards they also provide easily reproduced test cases against which to validate the numerical methods used in more detailed studies of coastal sediment transport and morphodynamics

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

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

china materials for a loess landscape abstract for various reasons it was thought that material for the great chinese loess deposits originated in the deserts of the north and the idea of a desert origin was widely accepted but butler in australia in 1956 cast doubt on the actual existence of desert loess and this led to considerable discussion one facet of the argument advocated by smalley and vita finzi 1968 proposed that there were no desert specific mechanisms which could produce the large amounts of loess material observed applying this idea to the chinese loess was particularly appropriate because of the huge extent and thickness of the deposits how was this vast amount of loess material produced smalley and krinsley 1978 proposed a sequence of events that could lead to the formation of the chinese loess this required that the loess be a mountain loess eventually defined by smalley and derbyshire 1990 the material was made in the mountains to the west and the yellow river had a role to play in bringing it to the loess deposit region and that loess material in desert regions was in a state of transit the 1978 model has been proved to be true by a whole sequence of ingenious and intricate experiments in particular the analysis of zircons has produced data allowing particle sources to be identified the zircon particle proves to be a key component of the loess landscape but the mode particle remains the silt sized quartz particle the problem running in parallel with the how did the material form question is the puzzle of why loess material has such a restricted size range what controls operate on the formation of loess material in the quartz particles it appears that a combination and interaction of two events produce a size control the high low quartz transformation introduces tensile stresses the eutectic sizing of the quartz particles in the original granite also constrains the level of stress development the stress levels produced cause a particle size product of around coarse silt size

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

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

topographic and climatic influences on accelerated loess accumulation since the last glacial maximum in the palouse pacific northwest usa abstract topographic and climatic influences have controlled thick loess accumulation at the southern margin of the palouse loess in northern oregon juniper and cold springs canyons located on the upwind flank of the horse heaven hills are oriented perpendicular to prevailing southwesterly winds these canyons are topographic traps that separate eolian sand on the upwind side from thick accumulations nearly 8 m of latest pleistocene to holocene l1 loess on the downwind side silt and sand rich glacial outburst flood sediment in the umatilla basin is the source of eolian sand and loess for the region sediment from this basin also contributes to loess accumulations across much of the columbia plateau to the northeast downwind of cold springs canyon mt st helens set s and glacier peak tephras bracket 4 m of loess demonstrating that approximately 2500 g m 2 yr 1 of loess accumulated between about 15 400 13 100 cal yr b p mass accumulation rates decreased to approximately 250 g m 2 yr 1 from 13 100 cal yr b p to the present tephrochronology suggests that the bulk of near source palouse loess accumulated in one punctuated interval in the latest pleistocene characterized by a dry and windy climate

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

the processes and mechanisms of severe sandstorm development in the eastern hexi corridor china during the last glacial period abstract dust transported by sandstorms has been an important feedback in climate change in the past and its environmental effects are predicted to have a great impact on future global climatic change investigating the grain size classes and the standard deviations of the modern sandstorm samples and the samples in the shagou section situated in the eastern hexi corridor lead us to suggest that the sand fraction within the range of 275 4 550 m in this section can be used as a sensitive indicator of severe sandstorms we selected the size range in the l1 stratum of the shagou loess section as indicative of temporal changes in sandstorm intensity in the eastern hexi corridor and found that during the last glacial period severe sandstorms in the eastern hexi corridor occurred with high frequency during these periods i 70 54 ka b p ii 51 48 ka b p iii 45 42 ka b p iv 38 33 ka b p v 31 28 ka b p and vi 26 12 ka b p in general the frequency and intensity of dust storms in the early mis 4 and late mis 2 periods were both high but they were reduced in the middle period mis 3 the primary factors controlling severe sandstorms are hydrology and wind power followed by the expansion of the source extent reduced precipitation caused the source region of sandstorms to expand in addition wind speeds also increased at this time these factors may have directly contributed to the abundance of severe sandstorms based on the grain size from a loess section the shagou section in the eastern hexi corridor we propose an evolutionary sequence of the severe sandstorms during the last glacial period this sequence is consistent with the dust records in the arctic the antarctic and low latitude the central equatorial pacific areas thus globally synchronous periods of high dust activity occurred in the last glacial period the strong winds proposed here provide a potential explanation for the global consistency of dust flux changes during the last glacial period

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

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

stratigraphy and palaeoenvironmental implications of pleistocene and holocene aeolian sediments in the lhasa area southern tibet china abstract along the middle and lower reaches of the kyichu river and its tributaries lhasa area southern tibet a multidisciplinary study was carried out in order to investigate the areal distribution sedimentological properties ages and palaeoenvironmental implications of aeolian deposits including intercalated palaeosols this research was initiated to investigate to what extent southern tibet is influenced by past human activity as even recent evaluations perceive the present treeless desertic environment as natural fifteen profiles were recorded at an altitude of 3540 4580 m a s l with subsequent sedimentological geochronological osl ams 14 c and palaeobotanical charcoal analyses sediment properties of both loesses and aeolian sands reveal an origin from aeolian sorting of nearby fluvial deposits the calculated ages are the oldest obtained thus far on aeolian sediments from southern and interior tibet revealing natural aeolian sedimentation before and around the last glacial maximum c 20 ka however a distinct portion of late holocene sandy aeolian sediments also occurs both the evidence for the aeolian dynamics widespread pleistocene loess and aeolian sand deposition local late holocene aeolian sand deposition modern reactivation of widespread pleistocene aeolian sands and the palaeobotanical findings late holocene vegetation change from a tree bearing to a widely treeless landscape provide evidence that the lhasa area was strongly influenced by human activity since at least the late neolithic c 4200 cal yrs bp thus the present day desertic environment might not primarily be a result of the semiarid climate or the high altitude conditions but rather of activities of the humans and their collateral effects however once established this semi natural ecosystem persisted controlled by strong grazing firewood extraction erosion and harsh edaphic conditions preventing the recovery of trees

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

on the interpretation of chinese loess as a paleoclimate indicator the records of wind blown dust i e loess in china are some of the most important terrestrial records of past climate changes stretching back over the last 10 ma in the paleoclimate literature intervals of increased dust generation have been almost always interpreted as being associated with more intense or prolonged wintertime conditions here it is shown that in accordance with modern observations dust outbreaks in asia are predominantly springtime phenomena during spring frequent cyclogenesis in the lee of the mongolian altai and the passage of strong cold fronts produce the intense windstorms that loft and entrain dust into the air the meteorology governing such outbreaks is likely robust in past climates contrary to the common paleoclimate presumption it is actually the breakdown of the siberian high that permits the dust producing windstorms to occur the importance of cold fronts in generating such windstorms suggests that cooling of high latitude climate during the miocene or during glacial intervals might play a significant role in the signal recorded in the loess deposits the unique springtime factors that generate dust storms are an example of why the common partitioning of asian climate into a winter and summer monsoon is oversimplified and can be misleading

the plio quaternary uplift of the apennine chain new data from the analysis of topography and river valleys in central italy abstract this study aims at the reconstruction of magnitude and timing of surface uplift affecting a wide sector of the central apennines italy by means of morphometric and morphostructural analyses in the chain interiors where stratigraphic and geomorphological markers of past sea level positions are lacking the study is based on analysis of erosional landforms and river valleys a large scale topographic analysis by processing 90 m and 230 m dems is performed the spatial distribution of several morphometric parameters together with characteristic wavelengths of relief allowed the differentiation of three main regions affected by different cumulative surface uplift and tectonic erosional fragmentation a peri tyrrhenian belt an axial belt and a peri adriatic belt particular attention is devoted to fluvial landforms with analysis of longitudinal profiles and geometric pattern of the main drainage lines and their relations with the major structures major differences occur between the tyrrhenian and adriatic valley systems the tyrrhenian drainage mainly consists of longitudinal valleys displaying overall concave up longitudinal profiles the adriatic drainage is mainly constituted by transverse streams and shows less regular longitudinal profiles topographic features and the river valley architecture seem related to different styles and amounts of uplift in the three belts within the study area a coast to coast transect gaeta vasto transect gvt has been investigated in detail focusing the analysis on its axial sector around the apennines main divide main divide area mda a possible scheme of quaternary surface uplift along the gvt is proposed in the mda the main stages of landscape evolution and drainage organization can be reconstructed by means of the analysis of paleosurfaces coupled with study of the relict and present day drainage networks this allowed the recognition of a major phase of surface uplift exceeding 1500 m in the meta mainarde massif that occurred in response to thrusting during the pliocene for quaternary surface uplift a minimum value of 400 m can be estimated this study suggests that during the quaternary the peri tyrrhenian belt suffered a subdued uplift acting over small wavelengths 10 15 km while the axial and peri adriatic belts were subject to a larger and long wavelength 90 km surface uplift with maximum values about 700 m shifted to the ne of the axial belt and tapering to zero towards the adriatic coast the reconstructed pattern of uplift is coherent with the topographic properties of the three belts and with the observed drainage features

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

size dependent geochemical signatures of holocene loess deposits from the hexi corridor china well dated holocene loess sequences from uplifted river terraces at the northern margin of the tibetan plateau are characterised by their chemical grain size sr isotope and their oxygen and carbon isotope composition of the carbonate fractions prevailing wind directions suggest the source areas of the loess to be largely restricted to dry lands in northwest china and the deserts north to the hexi corridor e g badain jaran and tengger desert which receive fluvial input by rivers draining the qilian shan the dry lands of northwest china are one of the most important dust source areas globally local and conditions make the investigated loess sequences insensitive to element leaching the loess is characterised by a relatively narrow variation of sr 87 sr 86 0 7139 0 7164 the sr 87 sr 86 ratios of surface and carbonate bound sr are similar 0 7114 and 0 7111 and lower than those of silicate bound sr 63 2 mu m fractions similar to 0 7196 2 mu m fractions similar to 0 7247 since the clay fractions have higher caco3 contents than the silt fractions the isotopic contrast between the silicate debris of clay and silt size is camouflaged in the bulk compositions of these grain size fractions oxygen isotope and chemical compositions of clay and silt sized carbonate particles differ significantly silt sized loess carbonates formed authigenically and they are largely present as coatings of silicate grains whereas clay sized carbonate particles are of remote provenance and precipitated under evaporative conditions in line with further implications from the multi proxy study upward trends in the composition of the pedogenic carbonate document climate change to drier conditions after the mid holocene c 2009 elsevier ltd all rights reserved

interaction of geomorphological processes on the north eastern tibetan plateau during the holocene an example from a sub catchment of lake donggi cona abstract geomorphological landforms on a large alluvial fan and neighboring areas on the eastern side of the donggi cona show a complex spatial pattern sediment availability is an important factor in the formation of these archives and is partly associated with lake level fluctuation different sedimentary archives therefore show a similar geomorphological signal while in some cases similar archives are related to different forcing the chronology of the processes is based on 22 optical stimulated luminescence osl ages obtained from coarse grained quartz or potassium feldspar the base of the alluvial fan formed during the late pleistocene but deposition of cover sediments on the fan only started at around 7 ka ago silty sediments form a thin cover on the uppermost terraces and have been available only during short timespans most of the sediments are sandy deposits which form an internal sediment cycle on the fan they developed throughout the holocene sandy deposits on the footslopes of the neighboring hills have been preserved since the pleistocene holocene transition thicker eolian deposits accumulated during the late holocene these sediments were washed into the donggi cona and formed sandy lake sediments which were susceptible to remobilization during lower lake levels in combination with drier climatic conditions during the late holocene these sediments formed small dunes on the fan sediments on the alluvial fan are highly active for which erosion and deposition vary in space and time the interaction of fluvial and eolian processes is an important part of this dynamic high mountain system

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

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

swash overtopping a truncated plane beach swash on a plane beach is modelled by using a solution of the shallow water equations due to shen meyer 1963 the equations are used in a form appropriate for a plane at a finite angle to the horizontal the beach is cut off at a level below that of the maximum run up and the water is taken to fall freely over the end of the beach an explicit solution is found which permits evaluation of the overtopping flow and total volume for one swash event