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

grain size analysis of upper pliocene red clay deposits from linxia basin implications for asian monsoon evolution on the ne margin of the tibetan plateau abstract little is known about the evolution of the east asian winter monsoon eawm on the ne margin of the tibetan plateau tp during the late pliocene early pleistocene due to the poor exposure of pre quaternary eolian deposits and ambiguities in the interpretation of paleoclimatic proxies in this study we performed detailed grain size analyses of eolian sequences spanning 3 7 2 4 ma from two new boreholes in linxia basin in the ne tp we compared our results with contemporaneous loess red clay sequences across the chinese loess plateau clp and identified a substantial decrease in the thickness and grain size of upper pliocene lower pleistocene loess and red clay sediments from the western to central parts of the clp this observation supports the view that the grain size of upper pliocene eolian sequences from linxia basin can be used to reconstruct the evolution of the eawm in addition it demonstrates that the modern spatial pattern of the eawm regime in the western clp has been maintained since at least the late pliocene records of both median grain size md and sand content from the boreholes exhibit an overall upward increasing trend during the interval from 3 7 2 4 ma indicating a long term stepwise intensification of the eawm and aridity on the ne margin of the tp in addition a dramatic coarsening of the grain size in loess unit l34 documents a large climatic shift at 2 75 ma which may be closely linked with the major intensification of northern hemisphere glaciation during the late pliocene

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

correlation and interpretation of paleosols and loess across european russia and asia over the last interglacial glacial cycle abstract loess paleosol sequences of the last interglacial glacial cycle are correlated from european russia to central siberia and the chinese loess plateau during cold periods represented by marine oxygen isotope stages ois 2 and 4 loess deposition dominated in the russian plain and the loess plateau in central siberia loess deposition took place also but five to seven thin weakly developed paleosols are identified in both stages ois 3 in the chinese loess plateau near yangchang consists of a loess bed that is flanked by two weakly developed paleosols at kurtak siberia ois 3 is represented by two distinct stacked paleosols with no loess bed separating the paleosols in the russian plain ois 3 consists of a single possibly welded paleosol representing upper and lower stage 3 climates brunisols and chernozems dominate the profiles in china and siberia whereas regosols luvisols and chernozems are evident in the northern and southern russian plain respectively ois 5 is represented in china and the russian plain by pedo complexes in a series of welded soils whereas in contrast the kurtak site consists of six paleosols with interbedded loess the paleosols consist largely of brunisols and chernozems although the three areas examined have different climates geographical settings and loess source areas they all had similar climate changes during the last interglacial glacial cycle

influence of structure on the behavior of a saturated clayey loess an intensive experimental investigation by means of triaxial and oedometer tests was performed on a clayey loess that was retrieved from two depths at a location on the southern chinese loess plate

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

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

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

mt and reflection an essential combination summary at many localities in the world there have been coincident comprehensive electromagnetic em studies and seismic reflection profiles conducted unfortunately over many more regions the seismic reflection images are interpreted without the constraints afforded by electrical conductivity information this paper is an attempt to convince the reader that a collocated magnetotelluric mt study should in almost every case be made wherever a seismic reflection survey is undertaken examples are shown from six studies in which the em results aided the geological tectonic interpretations of the seismic sections also difficulties with the mt technique are discussed and the interpretations of conducting zones within the lower crust are examined finally a generalised model is proposed for the continental crust that may account for both the reflectivity and conductivity of the zone at the top of the lower crust

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

end member modeling of the grain size record of loess in the mu us desert and implications for dust sources abstract the arid and semiarid northern region of china is the most important loess region in the world in this region loess records from the chinese loess plateau clp have been studied extensively but they are often underrepresented in sedimentological palaeoenvironmental studies dealing with sites in the mu us desert thus the dust sources and sedimentary characteristics of loess in the mu us desert are poorly understood to address this 9 loess sections and 44 modern surface samples with different sediment types in the mu us desert are analyzed to determine their grain size distributions the grain size dataset is subdivided into three end members ems using em modeling and the em modeling results of loess and surface sediments are compared through the above work we obtain the following information 1 the modes of em1 em2 and em3 are 16 m 70 m and 234 m respectively thus representing different transport processes from different dust sources among them em1 represents long term suspension from distant sources em2 represents short term suspension and saltation driven by dust storms from local sources and em3 represents saltation with shorter transport distance than em2 2 from northwest to southeast the content of loess in em1 em2 and em3 shows a gradual decreasing trend a gradual increasing trend and a gradual increasing or irregular trend respectively this spatial distribution indicates that although the winter monsoon is the main driving force for loess materials it is not the main controlling factor of the loess grain size the loess grain size of the mu us desert is greatly affected by the dust sources 3 the dust sources of loess in the mu us desert are complex in addition to the common dust sources with the clp loess there are also the contributions of local loose sediments such as alluvial lacustrine sediments floodplain sediments and dune sands from the mu us desert

changes in fire regimes on the chinese loess plateau since the last glacial maximum and implications for linkages to paleoclimate and past human activity abstract a high resolution black carbon bc record from 27 5 kyr bp to present was reconstructed using a chemical oxidation method on loess and paleosol samples from the lijiayuan section of the chinese loess plateau the black carbon mass sedimentation rates bcmsr and carbon isotopic record reveal a paleofire history and its relationship with climate and vegetation changes at the study site the bcmsr record was decomposed into two components background bcmsr and the bcmsr peaks the background bcmsr represents regional fires and shows high fire activities occurred contemporaneous with the younger dryas older dryas heinrich events and greenland stadials as registered in the loess grain size record this suggests a rapid response of regional fires on the loess plateau to abrupt climate changes spectral analysis of background bcmsr showed two meaningful periodicities of 1620 and 1040 years close to the cyclicity of the east asian monsoon as recorded in the stalagmite 18o record in central china this indicates a tight control of millennial scale wet dry changes in the monsoonal climate on regional fires on the loess plateau by contrast the bcmsr peaks are considered to reflect local fire episodes the occurrences of local fires were more frequent during the last glacial period with a maximum frequency of 6 episodes 1000 years during the last glacial maximum lgm 22 3 to 14 6 kyr bp when the climate was drier and more continuous grassy fuels existed on the landscape during the last glacial interglacial transition lgit period 14 6 to 11 0 kyr bp fire frequency was largely reduced due to an increase in precipitation and more woody vegetation if the lgit period is taken as an analog for the projected near future then future global warming alone may not produce large wildfires in northwestern china wildfires remained infrequent during the early to middle holocene biomass burning increased after 4 0 kyr bp when the climate became drier and land use was more intensive bc carbon isotope ratios may well reflect changes in the vegetation being burnt i e grasses versus trees yielding results consistent with the associated pollen data in the region

advance retreat history of the east asian summer monsoon rainfall belt over northern china during the last two glacial interglacial cycles abstract in northern china the history of desert migration provides a good measure of the east asian summer monsoon variations since the desert margin environment is very sensitive to changes in summer monsoon rainfall desert margin migration can be well documented in the downwind loess deposits since the grain size of chinese loess is principally controlled by source to sink distance and hence the loess grain size is an effective proxy for reconstructing the history of the east asian summer monsoon in order to investigate the pattern and migration of the summer monsoon rainfall belt over northern china during the past two glacial interglacial cycles contour maps of loess grain size were constructed for mis 2 3 4 5 6 and 7 all the grain size isolines show a near north south gradient for both glacials and interglacials indicating a dominant dust source region in north and an approximately north south dust transport pathway for dust deposits in the main body of the loess plateau at least for the past two glacial interglacial cycles the reconstructed southeast desert margin for mis 2 3 4 5 6 and 7 roughly parallels the present isohyets implying that the pattern of the east asian summer monsoon rainfall belt during the past two glacial interglacial cycles is similar to the present i e a northeast southwest trend for the isohyets of the summer monsoon despite the glacial interglacial cycles using the grain size isolines of mis 2 as a reference we derive a northerly desert retreat of 160 km 19 km 225 km and 223 km for mis 3 4 5 and 7 respectively and a southerly desert advance of 29 km for mis 6 that could be preliminarily regarded as the relative migration distance for the east asian summer monsoon rainfall belt in addition the inferred climate conditions in mis 3 are cool and humid in northern china while the driest and coldest interval of the last two glacial periods occurs in mis 6

grain size of loess palaeosol and red clay deposits on the chinese loess plateau significance for understanding pedogenic alteration and palaeomonsoon evolution abstract to assess pedogenic modification to grain size distributions of loess palaeosol and red clay deposits on the chinese loess plateau and to understand long term evolution of the east asian palaeomonsoon since the late miocene we investigate a continuous loess palaeosol red clay sequence at lingtai south chinese loess plateau and another parallel red clay sequence at zhaojiachuan central chinese loess plateau by analyzing the grain size distributions of bulk samples and chemically isolated quartz samples the relative intensity of pedogenic alteration of the loess palaeosol and red clay deposits can be quantified comparisons of the grain size distributions and contents of different grain size fractions between the bulk and the quartz samples suggest that pedogenic alteration is apparently stronger in the red clay sequence than in the overlying loess palaeosol deposits furthermore grain size parameters derived from the bulk and the quartz samples such as mean grain size coarse fraction content and u ratio exhibit similar variations in the loess palaeosol sequence quaternary 0 2 6 ma whereas these grain size parameters of quartz samples show different variability from those of bulk samples in the red clay sequence late miocene to pliocene 2 6 7 ma grain size of quartz from the loess palaeosol and red clay deposits exhibits distinct and persistent oscillations from the late miocene to the pleistocene implying that significant fluctuations of the palaeomonsoon climate in east asia might have occurred at least since late miocene time

rare earth elements of aeolian deposits in northern china and their implications for determining the provenance of dust storms in beijing this paper contributes to a better understanding of the source of dust storms in northern china and the relationship between these sources and other aeolian sediments in this region sediment samples in potential source areas were collected from the hunshandake sandy land heaven desert the loess deposits of the bashang area the mountainous basins and valleys north of beijing and from the badain jaran desert and hulunbaier sandy land fig 1 dust samples were collected in beijing during two dust storms in march 2002 and april 2006 the laboratory methods used in this study included measurements of abundance of trace elements in particular the rare earth elements rees mineral assemblages and grain size the ree contents eu and ce anomalies show clear differences between various deposits provenance is considered to be the key factor influencing ree patterns in the study areas the ree abundances and patterns indicate that the aeolian sand north of beijing such as in the heaven desert is mainly of local origin rather than from desert encroachment from the north the mineral grains carried in dust storms however are highly mixed and may come partly from local sources but mainly from distant desert regions in western china

long term weakening of the east asian summer and winter monsoons during the mid to late holocene recorded by aeolian deposits at the eastern edge of the mu us desert abstract the east asian summer monsoon easm and east asian winter monsoon eawm are major drivers of environmental conditions in east asia however due to the lack of high resolution eawm records the phase relationship between the easm and eawm during the holocene epoch is still debated here we use magnetic and grain size measurements from a sequence of aeolian sediments from the eastern edge of the mu us desert to track the history of the easm and eawm from 7 5 to 2 5 ka the results show that both the easm and eawm exhibit a similar long term weakening trend during this interval in view of the stable glacial boundary conditions and the significantly decreased rates of atmospheric co 2 rise since the mid holocene we suggest that orbitally induced insolation was the major cause of the weakening of both the easm and eawm decreasing summer insolation and increasing winter insolation reduced the thermal contrast between the ocean and the asian continent in both summer and winter time resulting in the weakening of both monsoon systems during the mid to late holocene

environmental status of the jilantai basin north china on the northwestern margin of the modern asian summer monsoon domain during marine isotope stage 3 abstract two drill cores were obtained from the jilantai sub depression jlt d and the neighboring dengkou sub uplift dk u within a huge former lake basin in northern china from an analysis of the lithology and pollen assemblages combined with radiocarbon dating of extracted pollen and osl dating of extracted quartz we concluded the following jlt d was continuously occupied by lakes since 85 ka however dk u the neighboring sub uplift was covered by lakes during 80 74 ka 50 44 ka 32 5 27 5 ka and

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

comparison of particle size characteristics of the tertiary red clay and pleistocene loess in the chinese loess plateau implications for origin and sources of the red clay the origin of the tertiary red clay underlying the pleistocene loess in the chinese loess plateau remains controversial although several lines of evidence have suggested a wind blown origin this study examines the particle size parameters of the late miocene and pliocene red clay by comparing it with those of the late pleistocene loess the particle size distribution of a total of 15 339 loess and 6394 red clay samples taken from 12 loess sections along a north south transect and two red clay sequences at lingtai and jingchuan was systematically analysed the median grain size skewness and kurtosis of the late pleistocene loess all show a systematic southward change and are principally influenced by distance from source region the spatial and temporal differentiation of dust deposits is expressed in a skewness kurtosis median grain size ternary diagram from which the distance to the source region can be inferred the particle size characteristics of the tertiary red clay sediments are very similar to those of the palaeosols within the late pleistocene loess deposits suggesting an aeolian origin for the red clay based on the comparison of red clay and loess in the ternary diagrams it is inferred that the source sink distance was greater in the neogene than in the last and penultimate interglacials and that the dust source region in north western china underwent a progressive expansion during the period from at least 7ae0 ma to the present

east asian monsoon variability over the last seven glacial cycles recorded by a loess sequence from the northwestern chinese loess plateau a 180 m thick loess paleosol sequence from the northwestern chinese loess plateau was investigated to construct a high resolution record of the east asian monsoon variability over the last seven glacial interglacial cycles the low field magnetic susceptibility mass specific and the mean grain size are used as proxies for changes in the intensity of the east asian summer and winter monsoon respectively because of the weaker pedogenesis at the northwestern chinese loess plateau compared to the central chinese loess plateau our and mean grain size records show a muted glacial interglacial contrast for the asian summer monsoon but an enhanced contrast for the asian winter monsoon although better resolved most orbital scale east asian monsoon variations captured by our and grain size records are similar to those reported from the central chinese loess plateau nevertheless variations in exhibit clear precessional cycles in three paleosol layers i e s1 s2 and s3 corresponding with solar insolation maxima furthermore unlike records at the central chinese loess plateau where is dramatically enhanced at paleosol s5ss1 corresponding to marine isotope stage 13 our new record shows a major enhancement at paleosol s4 corresponding to marine isotope stage 11 which indicates geographic differences in the timing of local monsoon precipitation in the two regions

new perspectives on the li isotopic composition of the upper continental crust and its weathering signature abstract lithium isotopes are increasingly used to trace both present day and past weathering processes at the surface of the earth and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust ucc yet the previous estimate of average 7li of the ucc has a rather large uncertainty hindering the use of li isotopes for this purpose new 7li for desert and periglacial loess deposits windblown dust from several parts of the world europe argentina china and tajikistan demonstrate that the former are more homogeneous than the latter and may therefore serve as excellent proxies of the average composition of large tracts of the ucc the li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered fine grained end member dominated by phyllosilicates and having low 7li and an unweathered coarse grained end member that is a mixture of quartz and plagioclase having higher 7li we use correlations between insoluble elements ree nd hf and fe2o3 sio2 li concentrations henceforth referred as li and 7li to estimate a new more precise average li isotopic composition and concentration for the ucc li 30 5 3 6 2 ppm and li 7 0 6 0 6 2 the 7li for desert loess deposits is anti correlated with the chemical index of alteration cia using this relationship along with our average 7li we infer that 1 the present day cia of the average ucc is 61 2 4 2 higher than the common reference value of 53 and 2 the average proportion of chemically weathered components is as high as 37 10 17 2 at the surface of the earth

periodicities of palaeoclimatic variations recorded by loess paleosol sequences in china abstract palaeoclimatic periodicity recorded by chinese loess paleosol sequence has been investigated for a number of years however conclusions from previous investigations are still controversial and interpretation of cycle evolution is quite equivocal in this study two typical loess paleosol sequences 148 and 191 m in thickness respectively in the central chinese loess plateau are sampled 3872 samples total and measured for grain size distribution and magnetic susceptibility in order to reconstruct the palaeoclimatic changes over the past three million years on the basis of a new sensitive proxy indicator of palaeoclimate and a newly developed independent time scale not orbitally tuned two time series of asian dust storm variations which are highly related to the palaeoclimate system changes are obtained wavelet and spectrum analyses indicate that there are approximately 400 200 100 66 57 41 31 27 and 22 kyr cycles in these typical loess paleosol records some orbital driven cycles are weak and are not well presented in the new time series while some non orbital cycles are found since the eccentricity frequencies of the solar irradiance of approximately 400 and 100 kyr are preserved in these palaeoclimatic sequences the lack of relatively short time orbital cycles of 41 kyr obliquity and 22 kyr precession cycles in part of the two time series may be explained by the relatively low time resolution of the loess paleosol deposits through an astronomical estimate the obliquity and precession cycles should leave stronger footprints on records of palaeoclimatic variations at the middle latitudes of the northern hemisphere the presence of non orbital cycles may be explained by unstable dust deposition processes and pedogenic processes in the paleosol units which could misrepresent or obliterate the imprint of the solar irradiance frequency this conclusion may indicate that one should be cautious when investigating specific palaeoclimatic changes e g at sub orbital time scales recorded in loess deposits especially in the paleosol units

evolution of eureka flat a dust producing engine of the palouse loess usa sedimentologic stratigraphic and pedologic evidence demonstrates that eureka flat ef a narrow 80 km long deflation plain in south central washington usa is the source for the thick and widespread loess of the palouse region located in the southern columbia plateau ef has been a depocenter for abundant clay to sand sized sediment derived from repeated glacial outburst floods that swept through the area during the pleistocene prevailing sw winds that were funneled across ef remobilized flood sediment into sand dunes sand sheets and loess an eolian sand sheet buried beneath 1 8 m of loess at the downwind end of ef attests to bioclimatically driven changes in the style of eolian deposition the depositional transition from sand sheet to loess is characterized by a change from wind rippled strata to structureless bimodal sand and silt with insect burrows and rhizoliths to unimodal sandy loess soil moisture and density of dust trapping vegetation control where sand dunes and loess accumulate up to 4 5 m of post lgm loess mantles the landscape adjacent to and downwind from ef some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the touchet river and its tributary valleys the removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps patterns of loess accumulation across the columbia plateau are identified on isopach maps of major pre and post lgm loess units and show that ef has been the major engine for the production of atmospheric dust and loess during both times

holocene erosion triggered by climate change in the central loess plateau of china abstract understanding changes in holocene erosion is essential for predicting soil erosion in the future however the quantitative response of natural erosion to holocene climate change is limited for the loess plateau of china in this study two soil profiles were investigated on the luochuan and yanchang sites in the central loess plateau of china and four climate indicators i e magnetic susceptibility calcium carbonate content total organic carbon content and clay content

quartz osl dating of late quaternary chinese and serbian loess a cross eurasian comparison of dust mass accumulation rates abstract reconstructing dust mass accumulation rate mar from loess deposits is critical to understanding past atmospheric mineral dust activity and requires accurate independent age models from loess deposits across europe and asia previous correlations of loess in europe and china have tended to focus on multi millennial timescales with no detailed examination of dust mar at the two ends of the eurasian loess belt on shorter sub orbital scales here we present a detailed quartz optically stimulated luminescence osl chronology from the serbian titel loess plateau veliki surduk loess core and the chinese loess plateau lingtai section the luminescence ages pass internal tests and show consistent increases in age with depth with no obvious major hiatuses however as reported before it seems the quartz osl technique is only capable of accurate age determination up to accrued doses of ca 150 gy ca 30 40 ka due to approaching field saturation of the quartz osl signal two age depth models were used to reconstruct dust mars where one utilises osl data solely and the other additionally makes assumptions about sedimentation rates although short term fluctuations in mar are model dependent general mar patterns between the two sites are very similar with peak mar occurring rather late in the last glacial ca 13 25 ka this suggests that at least broad scale trends in dust activity within the last glacial period may be similar at a continental scale

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

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

loess and the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database abstract mineral dust is an important constituent of the solid load in earth s atmosphere the total atmospheric aerosol loading being both a function of and a factor affecting climatic change human actions have progressively enhanced atmospheric dust loading especially in the past century so that both natural and human induced effects of atmospheric dust on climatic change require more detailed research records of changing climate are preserved in cores from the ocean floors glaciers and ice sheets as well as in terrestrial sedimentary sections quantitative data on the present day distribution of atmospheric dust are sparse but simulation of dust transport and deposition has been modelled with some success the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database was designed to serve as a global validation data set for use with earth system models of the palaeo dust cycle loess a wind borne silt deposited on the continents particularly in the past 2 6 myr is an important potential source of information on past atmospheric dust accumulation a recent initiative sought to improve the terrestrial data coverage within the existing dirtmap database by involving representatives from key loess regions in coordinating the data synthesis process so as to facilitate interaction between the dust modelling and the data collection communities the results are presented in this issue in order to compare past minerogenic dust records loess with those in ice and ocean cores mass accumulation rates mars have been calculated as fluxes in g m2 yr the loess regions covered include north and south america europe siberia eastern asia and australasia it is acknowledged that provision of age models for the calculation of realistic mar values depends upon a number of conditions most notably sound chronostratigraphy and realistic values of loess dry bulk densities the mar data sets presented here show some notable variation both within and between the studied regions regional mar coverage also varies reflecting differences in the availability of key data on loess from one world region to another loess facies vary according to specific site and source conditions as well as in response to post depositional re working of primary wind lain loess by surface geomorphic processes mean particle size consistently declines downwind and terrace valley and upland sites generally yield the highest mar values characteristics noted in all regions discussed here the loess accumulations in two major world regions central and eastern asia and the great plains region of north america differ in some important respects from loess elsewhere in that they lie peripheral to deserts and are remote from the former sites of major quaternary ice sheets it is concluded that the mars for terrestrial sites obtained from loess are consistently higher than those obtained from ocean and ice cores so that future climatic models designed to study the role of global atmospheric dust will have to take full account of the present and past dust records over the continents

tectonic and climatic controls on provenance changes of fine grained dust on the chinese loess plateau since the late oligocene abstract provenance variations of late cenozoic aeolian deposits on the chinese loess plateau clp were closely associated with regional tectonic activity and climatic change previous studies however have not reached a consensus regarding the nature and origin of past variations in source this study presents the results of oxygen isotope 18 o analyses of fine grained quartz 18 o variations exhibit distinct trends and patterns of variation over six time intervals i e 25 20 20 12 12 7 7 2 6 2 6 1 2 and 1 2 0 ma in comparison with quartz 18 o results from east asian dust sources and previous provenance studies of the same aeolian sequences we identify three significant composition changes of the dust source system at around 20 12 and 2 6 ma the dust source system was also rather unstable at 25 20 12 7 and 1 2 0 ma while three stable stages occurred at 20 12 7 2 6 and 2 6 1 2 ma the correlation between the provenance changes and paleoclimatic and tectonic evidence suggests that both tectonic and climatic factors were important in driving the observed stepwise provenance changes however the changes were mainly constrained by tibetan plateau uplift prior to the quaternary and by global climate change thereafter

the influence of dry lakebeds degraded sandy grasslands and abandoned farmland in the arid inlands of northern china on the grain size distribution of east asian aeolian dust dry lakes degraded sandy grasslands abandoned farmland and mobile dunes which are widely distributed throughout the arid areas of northern china have been investigated in this work gain size distribution of the surface sediments of manas lake in junggar basin juyan lake in the alxa plateau zhuye lake in minqin basin and most deserts such as mu us desert otindag desert horqin desert and hulun buir desert in china have been analyzed the results show clay with particle sized 60 and 50 of the total mass since the tiny particles on the surface of abandoned farmland are blown away easily and rapidly the content of clay particles in minqin basin is 63 m and few particles 10 m consequently although sand dust storms originate primarily in the western deserts the gobi areas of the alxa plateau the north and east of hexi corridor and in central mongolia the widely distributed dry lakebeds sandy grasslands and abandoned farmland adjacent to the deserts also contribute to aeolian dusts hence the material sources for sand dust storm in east asia include inland deserts but also dry lakes sandy grasslands and abandoned farmland which are widely distributed throughout the arid inlands of northern china

hydrologic and geologic factors that influenced spatial variations in loess deposition in china during the last interglacial glacial cycle results from proxy climate and gcm analyses abstract results from climate proxy and general circulation model gcm analyses suggest that variations in soil moisture and desert expansion are key hydrologic and geologic factors respectively influencing temporal and spatial variations in loess texture and distribution in the loess plateau of china during the last glacial period a reduction in soil moisture led to dune destabilization and a southward expansion of the desert the source of loess toward the loess plateau changes in soil moisture in east asia may have been influenced by the size and extent of the fennoscandian ice sheet and the atmospheric circulation pattern that it induced downstream these results suggest that both regional factors i e changes in soil moisture and the position of the desert margin and hemispherical factors i e changes in the size and extent of the eurasian ice sheets have influenced loess deposition on the loess plateau of china

regional lithofacies and pedofacies variations along a north to south climatic gradient during the last glacial period in the central loess plateau china abstract five lateral sand loess palaeosol continua occur within the last glacial sediments of the central loess plateau of china along a 500 km north to south climatic gradient the continua shift southward or northward in concert with desert expansion or contraction respectively lateral lithofacies desert sand to loess variations are evident at the north end of the gradient and follow walther s law of the correlation of facies lateral pedofacies loess to palaeosol variations are present near the south end of the gradient where the climate was warmer and wetter the lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds in contrast alternating loess and palaeosols occur within the same stratigraphic interval in the southern loess plateau where dust accretion rates were lower however in high resolution studies of climate change vertical profiles of alternating loess and palaeosols especially weak palaeosols may not reflect regional or global climate change alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions thus some of the high resolution loess palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change

strontium isotope compositions of river waters as records of lithology dependent mass transfers the garonne river and its tributaries sw france the relation of lithology in the drainage basin to the dissolved load of the garonne river and its main tributaries in southwestern france was evaluated by determining 87sr 86sr ratios and concentrations of major and trace elements during a 2 year long survey in the upper drainage basin the garonne river waters were isotopically varied at two observation points 0 71131 0 00030 2 for 84 18 ppb 2 and 0 71272 0 00044 for 86 10 ppb respectively in the lower drainage basin the garonne river waters were isotopically identical at three observation points at 0 71020 0 00024 for 125 22 ppb by contrast the tributaries lot truyere aveyron arriege gers and salat are widely varied in their 87sr 86sr ratios and sr concentrations from 0 70836 0 00049 to 0 71058 0 00057 and from 18 8 to 280 116 ppb the sr isotope ratios and concentrations suggest a dominant supply of two reservoirs of sr one of which is with low 87sr 86sr ratios and high sr contents that is typically characteristic of carbonate rocks and the other with high 87sr 86sr ratios and low sr concentrations that is characteristic of felsic rocks locally as in the lot waters draining the massif central and within the pyrenees mountains a third source of sr from mafic rocks may be involved mass balance calculations based on the mean 87sr 86sr ratios and contents of the dissolved sr and on the mean discharges integrating the 2 year survey suggest that contribution of the silicate reservoir amounts 3 8 of the total dissolved sr flux mass balance calculations also suggest that variation in the supply of sr from either of the two major reservoirs does not exceed the analytical uncertainty at about 5 the 87sr 86sr ratios of hcl and nh4cl leachates of suspended loads of the garonne river are different from that of the associated dissolved sr this leaching related supplementary sr represents less than 10 of the total amount of sr transported by the garonne waters the sr isotope characteristics of the leachates are probably records of an intermediate pedogenic episode in the weathering erosion process occurring in the garonne drainage basin

linking coarse silt production in asian sand deserts and quaternary accretion of the chinese loess plateau the chinese loess plateau clp is a large spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the east asian monsoon many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions although spatial and temporal variations in the grain sizes of clp sediments are fundamental to this effort controversy over the origin of the dominant coarse quartz silt has limited interpretations reexamination of the spatial pattern of grain size distribution across the clp and a field scale experiment conducted in the gobi desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal mu us tengger and badain jaran sandy deserts our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in central asia and identify this process as the most consistent with the well recognized systematic northwest southeast depositional pattern of the clp we suggest that only abraded coarse quartz grains transported short distances by long term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau these results decouple the production and transport of coarse silt and finer silt and clay particles which have a more distant and wider provenance changing the constraints on previous paleoclimatic reconstructions

climatic implications of loess deposits from the beijing region variations in magnetostratigraphy pedostratigraphy grain size and magnetic suscep tibility of the loess deposits near beijing have been studied at two sections the sections are about 400 km east of the main loess deposits in china have a maximum thickness of 100 m and extend back to 1 1 ma the sequence consists of 14 loess palaeosol couplets s0 s14 which correlate well with sequences in the loess plateau susceptibility records from the sites near beijing are comparable to the xifeng luochuan and baoji sections located in the middle part of the loess plateau however the down core variations in the grain size in the upper lishi formation exhibit some differences the median grain size increases by about 25 30 m from l4 to l2 with the sandy grains 63 m increasing from 10 20 wt to 40 50 wt this implies that the depositional environment of the dust sources in the beijing loess section is different in some aspects from the loess plateau the beijing loess may have had a different dust source than the loess plateau copyright 2001 john wiley sons ltd journal of quaternary science

influence of tectonic uplift of the qinling mountains on the paleoclimatic environment of surrounding areas insights from loess paleosol sequences weihe basin central china abstract the southern edge of the chinese loess plateau affected by the stepwise uplift of the qinling mountains is a transitional climatic area between the different climatic environments and sedimentary characteristics to the north and south sides of the qinling mountains the study of different quaternary loess deposits in this region is conducive to improving our understanding of the micro scale climatic effects of tectonic developments here we use a series of experimental methods on a well preserved loess paleosol sequence in the south jingyang plateau to obtain proxy data including grain size magnetic susceptibility loss on ignition and geochemical elemental changes in grain size magnetic susceptibility and loss on ignition indicate that the east asian monsoon has undergone significant changes due to the continued global cooling and mid pleistocene climate transition during the deposition process of xsd loess i e the intensities of the winter and summer monsoons were simultaneously enhanced elemental correlations and factor analysis indicate the sedimentary environment and provenance of the deposits while elemental enrichment and element ratios including si ti al ti rb sr and zr rb are consistent with changes in the intensity of pedogenic and of the east asian monsoon as reflected by climate proxies illustrating that xrf core scanning analysis technology has great potential in the field of quaternary environmental changes of loess furthermore the stepwise uplift of the qinling mountains which has blocked the winter and summer monsoons to a certain extent has had a significant impact on the relative degree of loess accumulation and pedogenic in the northern piedmont southern piedmont and intermontane basin of the qinling mountains and also appears to have promoted settlement by early humans hence the study of paleoclimate in areas of active tectonic movement has the potential to promote our understanding of micro scale climate change in this region in the future

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

a 94 10 ka pollen record of vegetation change in qaidam basin northeastern tibetan plateau drill core isl1a was obtained from the qarhan salt lake in central eastern qaidam basin northeastern tibetan plateau ne tp fossil pollen and the lithology of the core sediment were analyzed in conjunction with ams c 14 and th 230 dating the results indicated that artemisia and chenopodiaceae dominated the steppe desert steppe vegetation developed around the lake between 94 and 51 2 ka corresponding with the organic rich silty clay deposited in the core sediments pediastrum continuously appeared in the core sediments between 94 and 51 2 ka indicating freshwater to oligohaline conditions of the paleo qarhan lake during the late marine isotope stage mis 5 mis 4 and early mis 3 during the 51 2 to 32 5 ka period ephedra dominated shrub desert vegetation expanded in the basin while pediastrum disappeared in the core sediments the core sediments consisted of interbedded layers of halite silt and clay rich halite between 51 2 and 32 5 ka signifying a shift toward drier hydrologic conditions thus the paleo qarhan lake experienced periods of desiccation and shallow water levels artemisia and chenopodiaceae dominated steppe desert steppe vegetation appeared again from 32 5 to 253 ka with clay rich sediments in the core thereby suggesting an increase of runoff from the lake under relatively wetter climatic conditions since 253 ka however pollen concentrations declined corresponding with the amount of halite deposited in the core sediment and suggesting a cold dry climatic condition during mis2 our findings have important implications for understanding complex regional vegetation and climatic responses to large scale forcings in the qaidam basin c 2015 elsevier b v all rights reserved

from dust to dust quaternary wind erosion of the mu us desert and loess plateau china the ordos basin of china encompasses the mu us desert in the northwest and the chinese loess plateau to the south and east the boundary between the mostly internally drained mu us desert and fluvially incised loess plateau is an erosional escarpment up to 400 m in relief composed of quaternary loess linear ridges with lengths of 10 2 10 3 m are formed in cretaceous quaternary strata throughout the basin ridge orientations are generally parallel to near surface wind vectors in the ordos basin during modern winter and spring dust storms our observations suggest that the loess plateau previously extended farther to the north and west of its modern windward escarpment margin and has been partially reworked by eolian processes the linear topography mu us desert internal drainage and escarpment retreat are all attributed to wind erosion the aerial extent of which expanded southeastward in china in response to quaternary amplification of northern hemisphere glaciation

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

palaeoenvironment of mid to late holocene loess deposit of the southern margin of the tarim basin nw china holocene environmental history in the tarim basin and the taklimakan desert is known mainly from isolated eolian and lacustrine deposits and remain puzzling here we present an adequately preserved loess section covering the past 5000 years at a highland 2 850 m a s l on the northern slope of kunlun mountains pollen preserved in the section reveal a drying trend with significant moisture fluctuations around 3000 2600 cal yr bp and 1800 cal yr bp at the study site comparing the pollen grain size from the same section provides a different scene occurred in the tarim basin and the taklimakan desert comparison of grain size to a c ration of pollen suggests that active sand southward shifting in south margin of the desert is coincident with increasing moisture condition at the section locality implying a casual link this moisture pattern occurred at the upper and lower elevation of the slope is best explained by the vertical variation of local precipitation along the slope

reconstructing early permian tropical climates from chemical weathering indices this study was financially supported by the national natural science foundation of china grants 41302083 41572078 the national basic research program of china grant 2011cb808800 and the fundamental research funds for the central universities grant cugl140402 china university of geosciences wuhan p a cawood acknowledges support from nerc grant ne j021822 1

evaluating the paleoclimatic significance of clay mineral records from a late pleistocene loess paleosol section of the ili basin central asia in this study we present clay mineral records from a late pleistocene loess paleosol sequence in the ili basin central asia and assess their significance for paleoclimatic reconstruction the results show that the clay minerals are mainly illite average 60 and chlorite 28 with minor kaolinite 9 and smectite 3 illite was of detrital origin with no obvious modification to its crystal structure increases in illite content in the loess are ascribed to wind intensity rather than pedogenesis high proportions of illite in the clay fraction and of muscovite in the bulk samples of the paleosol units may lead to an overestimation of the weathering intensity kaolinite was likely inherited from the sedimentary rocks while chlorite might have been inherited from both sedimentary and metamorphic rocks the paleoclimatic signals of kaolinite and chlorite were unclear due to reworking by both fluvial and eolian systems smectite was more likely formed by the transformation of biotite and illite and its variation in the loess sequence was also controlled by wind intensity this was largely due to aggregation and is unlikely to reflect moisture changes although the interpretation of paleoclimate evolution may contain some uncertainties clay mineralogy does provide the possibility of tracing dust provenance

climatic conditions recorded by terrestrial mollusc assemblages in the chinese loess plateau during marine oxygen isotope stages 12 10 abstract past analogs for our present interglacial have been sought for better understanding of our present and future climate marine isotope stage 11 mis 11 has long been considered to be a good candidate and has gained increasing attention in recent studies of marine and terrestrial records in the chinese loess paleosol sequences s4 soil interpreted as equivalent to mis 11 yields a very precise terrestrial paleoclimate record of environmental changes that prevailed during this period in this study two high resolution terrestrial mollusc records from the loess plateau have been analyzed to characterize climate variability during the periods of mis 12 10 the changes in environment and climate indicated by the variations in abundance of land mollusc species are thus documented our mollusc results show that the l5 loess equivalent of mis 12 developed under relatively cold and dry conditions climate during this period was not as severe as indicated in the marine isotopic records an episode of warmer and more humid condition occurred at the middle stage of the mis 12 reflecting a summer monsoon strengthened during the glacial interval a similar scenario has been observed in the middle part of mis 10 in addition our mollusc records provide insight into the climate conditions over the loess plateau during mis 11 a general warm humid climate dominated during the formation of s4 soil but at least four fluctuations occurred at xifeng region reflecting unstable climate conditions and regional climate differences within the loess plateau during this period our study shows that the early part of s4 spanning over 30 ka was very warm and humid while the late part was characterized by mild cool conditions comparison of mollusc species compositions of both mis 11 and holocene intervals reveals different climate conditions the early part of mis 11 was warmer and more humid than the holocene optimum period while the late part of mis 11 was similar or cooler our study indicates that the extent of warming during the holocene in the loess plateau might be significantly less than the conditions that prevailed during the mis 11 interglacial period

pleistocene paleoenvironmental changes in the high mountain ranges of central china and adjacent regions abstract during several joint chinese german expeditions the quaternary landscape and paleoclimatic evolution of the mountain ranges and grabens surrounding the loess plateau of central china was studied the results are compared with proxy data from the interior loess plateau to help reconstruct atmospheric circulation during late pleistocene times middle to late pleistocene alluvial terraces and fans capped with loess units and paleosols show that aggradational episodes correlate with periods of glaciation and increased loess accumulation in turn degradation correlates with interglacials or interstadials and increased soil formation this implies that climate is the primary control on quaternary paleohydrology and alluvial sedimentation and erosion the high mountains which barely reached the last glacial ela were only glaciated during the most favourable climatic period of glaciation the glaciation the glacial and alluvial forms point to a cool early to maximum glacial period with increased precipitation and to a maximum to final period with cold dry conditions during the last glaciation the maximum advance of the small glaciers took place towards the end of a relatively humid and cold period between ca 32 and 23 ka the following dry cold stage between ca 23 and 13 ka was rather unfavourable for glacial advance proxy data from the loess plateau supports the view that glaciations were more or less dominated by cold dry winter monsoon climate whereas during the interglacial interstadials a warmer and more humid climate prevailed implying a strengthening of the summer monsoon influence the results prove variations of the monsoon that in turn modulates paleohydrology periglacial dynamics glacier advances dust flux and soil formation

grain size magnetic susceptibility and geochemical characteristics of the loess in the chaohu lake basin implications for the origin palaeoclimatic change and provenance abstract rare studies on the aeolian deposit located in north bank of the yantgze river are documented recently it is found in the field investigations and in bore sections that the loess in the chaohu lake basin has the largest thickness of over 40 m in this study the probability cumulative curves frequency distribution the grain size distributions and the discriminant function of the grain size suggest that the loess in the chaohu lake basin is of eolian origin the magnetic susceptibility curves of the loess in the basin coincide perfectly with those of the loess in the northern china and the marine isotope stages mis and show that paleoclimatic cycles and sub cycles were documented since l3 during middle late pleistocene in the basin the ms curve of paleosol s1 paleosol s2 and loess l3 in the basin coincide perfectly with mis5 mis 7 and mis 8 respectively the good correspondence indicates that the loess in the basin has given a sensitive response to the globe paleoclimatic change since l3 on the other hand the climate changes in some stages recorded by the loess has regional characteristics obviously which might be the result of the dual effect of globe climate changes and east asia monsoon climate changes the result of geochemical characteristics suggests that the loess in the basin has undergone moderate to strong chemical weathering most elements are mobilized during chemical weathering na and ca of the loess are markedly lost and the removal of k is also evident and chemical weathering doesn t evidently turn into the si removal stage the chemical weathering of the loess is more intensive than that of the loess deposits in northwestern china and the upper reaches of the yantgze river the intensive chemical weathering has been documented by the loess might be related to strong monsoon climate in chaohu lake basin the provenance of the loess also differs from that in northern china and is discussed firstly with the lithofacies palaeogeography the well developed alluvial lacustrine deposits in the huaihe floodplain seem to be the major source materials of the loess

terminations and their correlation with solar insolation in the northern hemisphere a record from a loess section in northwest china a high resolution loess section in northwest china is analyzed for the major climate terminations and their correlation with solar insolation over the past 0 8 ma based on age controls and a grain size age model proposed by porter and an porter s c an z s 1995 correlation between climate events in the north atlantic and china during the last glaciation nature 375 305 308 a timescale for the shagou loess section is constructed which is independent of orbital tuned results the timescale is similar to other loess sections and the mid point ages of the boundary between a paleosol and its underlying loess layer are very close to that of terminations recorded in the marine record shagou section records indicate that grain size changed sharply during the termination process terminations occurred at the time of the maximum or increase of july radiation in the northern hemisphere at high latitudes suggesting that insolation might be a factor affecting terminations in the chinese loess this result supports the milankovitch hypothesis however variations in the amplitude of the insolation and grain size records are not proportionally matched so that the mechanism remains unsolved

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

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

damped fluctuations in chinese loess grain size 1 the sediment record of the loess paleosol sequence in the chinese loess plateau reveals a strong relationship between grain size fluctuations and glacial interglacial cycles documented by marine oxygen isotope variations however on tectonic time scales differences between the loess paleosol grain size record and the marine oxygen isotope record can be identified analytical results from the baishui jingchuan and lingtai sections show that the grain size of eolian loess superimposed on a coarsening trend has two abrupt shifts at about 2 55 and 1 25 ma which are followed by significantly damped fluctuations in grain size this is different from the global oxygen isotope record which demonstrates higher amplitude variations since the late pliocene early pleistocene and lacks analogs of the abrupt shifts we propose that the progressive uplift of the tibetan plateau may have forced the regional environmental system across two thresholds at the late pliocene early pleistocene and the middle pleistocene respectively inducing two pulses of climatic and environmental changes over north western china which are superimposed on the global cooling trend and orbital climate changes

the dry holocene megathermal in inner mongolia the paleoclimate since 14 kyr bp 14c age was reconstructed based on a 16 22 m long sediment core collected from lake yanhaizi a saline lake located near the northern limit of the east asian summer monsoon in inner mongolia coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated these sediments have low organic carbon contents but high maturity indices indicating that they were deposited in an arid environment by contrast based on high organic contents and low maturity indices fine sediments were deposited during periods of high lake stand in a humid environment it was in general dry between 8 0 and 4 3 kyr bp the above dry and wet phases are consistent with those recovered from the arid semiarid transition zone elsewhere but are unlike the widely perceived humid holocene megathermal reported in east china and the newly reconstructed record in the alpine retreat lake in taiwan the discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon on the other hand much enhanced evaporation over higher monsoon precipitation at lake yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon this also accounts for the fact the high temperature holocene megathermal as revealed in the okinawa trough and the northern south china sea is correlated to the dry phases at lake yanhaizi conversely the 4 2 kyr bp coldest period in the holocene corresponds to a wet phase at lake yanhaizi

paleoenvironmental changes recorded in a luminescence dated loess paleosol sequence from the tianshan mountains arid central asia since the penultimate glaciation abstract mid latitude arid central asia aca is one of the driest regions in the world and is a key source area of global atmospheric dust loess records of paleoclimatic changes in aca are complex and interpretations are problematic due primarily to the lack of robust chronologies quartz osl and k feldspar pirir dating methods were employed to date 8 quartz and 30 k feldspar samples from a 30 m loess sequence byh10 section on the northern slope of the tianshan mountains central aca northwest china the reliability of quartz and k feldspar ages was monitored by internal checks of luminescence characteristics and by comparison of the quartz and k feldspar ages the section lithology proxy indexes of grain size and magnetic susceptibility and the high resolution osl chronology together indicate 1 quartz osl dating can be used to date aca loess samples less than 40 ka while k feldspar pirir dating is reliable for loess samples at least as old as 150 ka from aca 2 aeolian loess began to be deposited on the northern slope of tianshan mountains beginning at least 145 ka ago and was deposited primarily during the penultimate and last glaciation periods 3 rapid loess deposition occurred during mis 6 mis 4 to early mid mis 3 and mis 2 but little or no loess deposition occurred during mis 5 mis 3a and mis 1 4 this loess depositional sequence is comparable to previously published stalagmite growth records in the region on glacial interglacial cycles rapid dust deposition and lack of stalagmite growth during glacials and lack of loess deposition and stalagmite growth during interglacials indicate a climatic pattern of wet warm interglacial and dry cold glacial climatic regimes on orbital cycles in aca 5 variation in the loess deposition rates in aca was much larger than in the central loess plateau during the last glaciation 6 depositional hiatuses of 50 kyr occur in aca loess sequences and high resolution chronologies are needed when reconstructing past climatic changes

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the 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

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

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

oxygen isotope signatures of quartz from major asian dust sources implications for changes in the provenance of chinese loess abstract we present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions 18 o values of both the fine and coarse fractions from the various sources are overlapped to varying degrees thus making it difficult to differentiate them nevertheless the quartz 18 o values of both fractions exhibit an increasing trend from the mongolian gobi to the northern chinese deserts and then to the taklimakan desert this implies that the geological settings of the source areas are different which in turn results in differing contributions of high temperature igneous rocks the combination of quartz 18 o results with other quartz based provenance tracers can clearly differentiate the three major source areas i e the taklimakan desert the mongolian gobi and the northern chinese deserts in addition comparison of our results with previous 18 o measurements of fine grained quartz from the luochuan loess sequence suggests the likely glacial interglacial fluctuations in dust provenance finally we suggest that the combination of quartz 18 o signatures and other dust provenance tracers can potentially improve the recognition of long term fluctuations in the provenance of chinese loess red clay deposits

thermoluminescence chronology of sand profiles in the mu us desert china abstract thermoluminescence tl is used to calculate the ages of two sand loess profiles in the marginal zone of the mu us desert china alternating units of dune sand and loess with palaeosols in the two profiles imply episodes of dune formation separated by periods of loess accumulation and pedogenesis our results indicate that there are three layers of dune sand intercalated in sediments of the last full glacial cycle suggesting the occurrence of three arid episodes during this time the first arid episode within this period occurred between

historical desertification of the mu us desert northern china a multidisciplinary study abstract the problem of historical desertification of the mu us desert northern china has been paid considerable attention during the past several decades through the analysis of stratigraphic evidence historical records and archaeological discoveries this paper studied the problem using a multidisciplinary approach the results show that two phases of serious desertification occurred during the last two millennia one is during the mid to late tang dynasty about a d 800 and the other during the late ming dynasty about a d 1500 1600 further investigation of the cause of each phase of desertification demonstrates that the former phase of desertification is closely related to abrupt climate change occurring in the mid eighth century but the latter which started during the ming dynasty and stopped at late 1980s is not consistent with climatic causation therefore we suggest that human activities contributed to the development of the latter phase of desertification

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

distribution and composition of loess sediments in the ili basin central asia loess deposits in central asia provide an important record of regional climate and environmental change however in contrast to the intensively investigated loess deposits on the chinese loess plateau clp loess sediments in the ili basin of eastern central asia are poorly understood based on field investigation and existing literature this paper presents a preliminary study of the distribution strata and composition of the ili loess the distribution of the ili loess is clearly controlled by topographic and geomorphic conditions mainly in the river terraces low uplands and slopes of the tianshan mountains the thickness of the loess varies from several meters to over two hundred meters to characterize the ili loess composition the authors analyzed its grain size geochemistry x ray diffraction pattern and heavy mineral assemblage grain size analyses reveal that the ili loess consists predominantly of silt 4 63 mu m with a minor proportion of sand which is coarser than the loess of the clp and suggests a nearby provenance the bulk mineral components of the ili loess are dominated by quartz and feldspar with minor amounts of calcite chlorite mica dolomite and hornblende more than 20 types of heavy minerals were observed with major components of amphibole magnetite and epidote the major elements of the ili loess are characterized by high abundance of sio2 al2o3 and cao and minor amounts of fe2o3 mgo na2o and k2o compared to the clp loess the ili loess is relatively rich in na2o and displays higher na2o al2o3 ratios suggesting weak weathering the distribution patterns of rees indicate that both the ili loess and clp loess are of typical upper crustal composition with enrichment in lree negative eu anomalies and depletion of hree both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the ili basin may have contributed only a little to the loess sediments c 2014 elsevier ltd and inqua all rights reserved

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

changes in sand fractions of binggou section and the expansion and contraction of the tengger desert during 50 30 ka signs of the evolutionary process are well preserved in the aeolian deposits of desert margins and enable reconstruction of desert expansion and contraction the sand content percentage 63 m of loess in the loess desert transitional zone was used as a proxy indicator for determining the proximity of the desert margin according to the dominant wind direction generally nw se in the northwest chinese loess plateau a transect was projected to observe spatial changes in sedimentological characteristics of aeolian deposits during the last glacial period the transect consists of 12 loess sections starting at shapotou in the transitional region between the loess plateau and the tengger desert and ending at tianshui which is located at the north foot of the western qinling mountains in the southernmost part of the loess plateau it shows the properties of temporal and spatial distribution of the malan loess with reduced sand content from northwest to southeast a linear correlation model of sand content and distance was obtained which was similar to the east of the chinese loess plateau according to this model and on the basis of optically stimulated luminescence osl dating from binggou section a detailed and quantificational expansion and contraction for the tengger desert was established copyright 2006 john wiley sons ltd

loess record of climatic changes during mis 12 10 in the jingyuan section northwestern chinese loess plateau abstract marine isotope stage 11 mis 11 has been considered as a potential analog for the present interglacial based on orbital scale solar insolation variations therefore increasing attention has been paid to mis 11 and the contiguous stages in recent studies of marine and terrestrial records as they may provide clues for predictions of future climate change in the chinese loess palaeosol sequences s4 soil interpreted as corresponding to mis 11 yields a precise terrestrial palaeoclimate record for this period in this study a loess palaeosol sequence l4 l5 from the jingyuan section on the northwestern margin of the chinese loess plateau clp was investigated to reconstruct the climatic variability during the periods mis 12 10 using proxies of grain size magnetic susceptibility total organic carbon and soil color index the results suggest that the l4 l5 sequence in the jingyuan section is much thicker 40 m than those in the central loess plateau areas 12 m the l5 loess equivalent to mis 12 developed under relatively cold and dry conditions climate evolution during this period was not as severe as that indicated in the marine isotopic records an episode of warmer and more humid conditions occurred during the middle stages of mis 12 reflecting a strengthened summer monsoon during the glacial period a similar scenario has been observed in the middle part of mis 10 high resolution multi proxy records for mis 11 suggest that a general warm humid climate was dominant during the formation of s4 soil however at least four fluctuations occurred reflecting unstable climate conditions and regional climate differences within the northwestern margin of the clp during this period the study also shows that the early part of s4 spanning over 30 ky was very warm and humid while the later part was characterized by mild cool conditions

using pca to characterize and differentiate loess deposits in wisconsin and upper michigan usa abstract data on loess thickness as well as a variety of particle size fractions were determined for 875 samples taken from several loess sheets across wisconsin and upper michigan because the particle size characteristics of these samples varied widely within and between the loess sheets we used principal components analysis pca as a way of isolating the major textural components or signals that exist across the various loess sheets the purpose of this research was to examine and interpret these principal components or particle size signatures common to the different loesses in order to better understand the loess sheets character formation mechanisms and likely sources our initial assumption that many of these loesses varied markedly from the classical silty loess was supported by the particle size data and the pca although component 1 was interpreted as thick silty loess dominated by medium silts component 2 was mainly composed of very fine sand and coarse silt and is better viewed as coarse loess components 3 and 4 were less texturally homogeneous and may reflect mixing between the loess and the underlying sediment especially where the loess is

climatic signals in the chinese loess record for the last glacial the influence of northern high latitudes and the tropical pacific the high resolution shagou loess section near the northwest limit of the east asian summer monsoon northwest china was analyzed the timescale of this section was set up based on a grain size age model and age controls the record of the shagou section shows that the millennial scale oscillations are superimposed on an orbital scale trend which can be correlated with the variations found in greenland and the sulu sea differences in the corresponding dansgaard oeschger cycles between the records in greenland and the chinese loess sections including the orbital scale trend the timing and the amplitude suggest that the climatic signals in chinese loess might not be singularly regulated by the north atlantic the differences in trend and amplitude can be reasonably explained when compared with the sulu sea record this suggests that the western tropical pacific also exerted an important influence on climatic signals found in the chinese loess record possibly countering the impact of high latitude factors during the last glacial

a coupled environmental system formed at about 2 5 ma in east asia abstract the somewhat abrupt commencement of loess deposition on a large scale in north central china is palaeomagnetically measured at about 2 5 ma the formation of the dynamical conditions responsible for windblown loess processes implies a reorganization of the atmospheric circulation over eastern asia it is speculated that at that time the accelerated uplift of the tibetan plateau had reached a threshold height giving rise to the intensification and northward shift of the siberian high and deepening of the cyclone in the lee of the tibetan plateau the uplift of tibet and the resulting reorganization of atmospheric circulation at about 2 5 ma would initiate a coupled environmental system tibetan plateau inland desert loess plateau in eastern asia that could be a key system in understanding the onset of glaciation in northern hemisphere and climatic change in the quaternary the climatic shift from near continuous warm condition before 2 5 ma to frequent and chaotic fluctuations after is speculated to be triggered to a significant extent by the uplift of the tibetan plateau an orography cold surge albedo temperature feedback mechanism is developed in explaining the harsher climate over east asia during glacial time and is thought to be one of the major contributors in promoting glacial development on the globe

a critical reevaluation of palaeoclimate proxy records from loess in the carpathian basin abstract in the carpathian basin loess is the most important archive of quaternary palaeoclimate evolution but only in the past two decades systematic and high resolution investigations were conducted those studies remarkably improved our knowledge of the regional past environmental change palaeoclimate inferences based on the magnetic susceptibility and grain size distribution as the most commonly used palaeoenvironmental proxies for the carpathian basin loess indicate colder and drier climatic conditions during glacials when compared to interglacials with an increasing number of studies using novel proxies in loess research such a traditional understanding of dry and cold glacials and humid and warm interglacials in the carpathian basin has been questioned as an illustrative example mollusc based climate reconstructions suggest generally warm and very dry summer conditions with mean july temperatures up to 21 c for the southern carpathian basin during the last glacial results based on stable carbon isotopes strongly oppose such high summer temperatures but studies based on n alkanes are in general agreement with the mollusc data when it comes to the vegetation reconstruction indicating mostly steppic conditions however n alkanes studies contradict warm and dry glacial conditions as indicated by mollusc based reconstructions pointing instead to cold and relatively humid glacials in addition there is an ongoing debate whether or not millennial scale climatic oscillations can be observed in the carpathian basin loess as well as whether this area was an important northern hemisphere dust source or rather a sink of far distance dust transport consequently the current state of the art of the palaeoclimate reconstructions from loess in the carpathian basin is rather inconsistent in order to make sense of the existing palaeoclimate data from the carpathian basin loess we have reevaluated and reinterpreted the available data we discuss and propose a coherent interpretation of rock magnetic grain size malacological stable carbon and nitrogen isotope n alkane and bacterial membrane lipid data for the last glacial cycle loess archives from the carpathian basin we show that glacial conditions in the carpathian basin led to a notable increasing north south gradient in temperature and an even stronger expressed decreasing trend in humidity and that most of the biomarker proxy data conducted in loess for the very dry southern part of the carpathian basin show a strong bias towards arid conditions in particular palaeotemperature reconstructions seem to be misleading glacial conditions were drier and colder than previously proposed summer temperatures likely under 15 c during glacials but notably warmer than in other parts of western central and eastern europe the vegetation consisted mostly of steppic environments during both glacials and interglacials we indicate that the carpathian basin has a potential to be a major dust source of the northern hemisphere during glacials although it was at the same time exposed to the deposition of fine far distance travelled dust moreover the main issues in the regional and continental correlation of loess are highlighted as well as the sensitivity of the carpathian basin loess to the millennial scale climate variability recorded in other northern hemisphere records finally we suggest that the onset of loess formation in the investigated area occurred during the middle pleistocene transition and it was probably related to intensive silt production related to glacier dynamics in the alpine ice cap

patterns of local and regional grain size distribution and their application to holocene climate reconstruction in semi arid inner mongolia china abstract the semi arid temperate steppe in northern central china is one of the main areas influenced by frequent dust and sand storms and is at the same time a primary source of dust from deteriorated grasslands thus the sediment grain size distribution of inland lakes in this region can be a particularly useful indicator of palaeoenvrionmental change the local pattern of grain size suggests that aeolian activity is the most important agent for sedimentation in the lake center in this region as strong northwesterly winds prevail for most of the year and the surface runoff is very weak meanwhile the regional pattern of topsoil grain size and its close association with mean annual precipitation map allows the establishment of a statistical model for palaeo moisture reconstruction from sediment grain size in this study we reconstructed a humidity time series based on the sediment grain size sequence from anguli nuur lake on the southern inner mongolian plateau in china and found that it coincides very closely with the c n ratio carbon to nitrogen ratio and other humidity indices revealed in previous studies of this temperate steppe region and from the 18 o values of stalagmite calcite in southern monsoon dominated china this close relationship suggests that climate change in the semi arid areas of asia is strongly influenced by the pacific summer monsoon and that it is reasonable to use sediment grain size as an indicator of humidity variability in the semi arid steppe region the reconstructed humidity increased during the early holocene and generally humid conditions lasted from about 10 400 until 7000 yr bp the period from around 7000 to 5200 yr bp was a transition phase from humid to semi arid conditions and the monsoon intensity of that time may have been at the threshold for a semi arid vegetation ecosystem finally since approximately 5200 yr bp to present the climate has become more arid with corresponding vegetation deterioration and strong aeolian activity

the last interglacial in the chinese loess plateau a petromagnetic investigation of samples from a north south transect abstract magnetic properties are reported for samples from the last interglacial palaeosol s1 oxygen isotope stage 5 and its underlying loess l2 at three sites representing the north wupu middle yichuan and south pucheng portions of a 560 km transect across the chinese loess plateau clp the main objective was to test the magnetic model put forward by evans and heller 1994 geophysical journal international 117 257 264 as a result of their work on the s3 l4 couplet and to check to what extent it may vary in time and space their model argues for two magnetic components an original aeolian input containing a mixture of hematite magnetite and maghemite superimposed upon which is a pedogenic component consisting of ultrafine magnetite particles we find that the model is readily applicable but that a difficulty arises at the southern end of the transect where it appears that wetter and warmer climatic conditions arrest or even reverse the magnetic enhancement typical of most soils across the clp a secondary aim was to assess the use of magnetic susceptibility to quantitatively estimate palaeo precipitation the methods of maher et al 1994 earth and planetary science letters 125 461 471 and han et al 1996 studia geophysica et geodaetica 40 262 275 do not agree and once again the southerly wetter warmer gradient leads to particular difficulties

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