rock magnetism iron oxide mineralogy and geochemistry of quaternary red earth in central china and their paleopedogenic implication abstract this paper presents a detailed investigation on the rock magnetism iron oxide mineralogy and geochemistry of a quaternary red earth qre in central china the magnetic profile of qre showed a characteristic vertical variation pattern the uniform red clay urc section 0 2 2 m of the profile had a higher magnetic susceptibility while vermiculated red clay vrc section 2 6 m had a very low 8 m 3 kg 1 rock magnetism and differential xrd analysis revealed that magnetite maghemite and hematite were the main magnetic carriers in the urc section the major elements fe 2 o 3 and al 2 o 3 of qre increased with depth while the sio 2 content decreased with depth indicating a leaching of the mobile elements and an enrichment of the immobile elements in comparison with the urc the vrc has a greater depletion in the content of na mg k and mg indicating a stronger weathering intensity the dithionite citrate bicarbonate dcb extracted iron fed the ratio of fed to total iron oxide fe fet and the weathering indices of qre confirmed that the vrc had experienced a stronger pedogenesis than the urc strong pedogenesis in the vrc resulted in a transformation of the highly magnetic maghemite to the weakly magnetic hematite which was responsible for the weak magnetism and hard magnetic behavior of the vrc our studies suggest that the vrc had experienced a hot climate with a dry season following one that was warm and moister magnetic reduction of the vrc section resulting from the transformation of highly magnetic maghemite to weakly magnetic hematite appeared to be an important paleopedogenic process in the qre we concluded that the magnetic parameters hard isothermal remanent magnetization hirm and sirm of qre can be used for the analysis of paleopedogenic processes

distribution provenance and onset of the xiashu loess in southeast china with paleoclimatic implications abstract loess deposits are important archives of past climate change in subtropical china where long term terrestrial records are scarce however only a few long term records with reliable dating were reported in jiangsu province where loess deposits in southeastern china were first discovered and designated as the xiashu loess moreover the provenance of the xiashu loess is still controversial this study presents the magnetostratigraphy and detrital zircon u pb age results of loess deposits at zhoujiashan in nanjing jiangsu province to date this section with basal age of approximately 0 88 ma may be the oldest loess deposits discovered in southeastern china based on the detrital zircon u pb ages of the zhoujiashan section together with published results of geochemistry geomorphology sedimentology and meteorology we propose that the xiashu loess has two mixed sources local materials derived from the yangtze river basin including exposed river lake beds floodplains and mountains served as a major contributor the distal eolian dust that originated from the arid areas of north china including deserts piedmont alluvial fans and drylands played a minor role in the formation process of the xiashu loess the nearly synchronous onset age approximately 0 88 0 85 ma of the xiashu loess was attributed to a regional environmental event during the middle pleistocene transition

the high level marine shell bearing deposits of clava inverness shire and their origin as glacial rafts abstract the enigmatic high level till covered cold water marine shell bearing deposits at clava inverness shire are described systematically in the light of new observations made at sites documented in the literature the marine deposits named here as the clava shelly formation include three members the unfossiliferous clava sand the underlying clava shelly clay and a shelly diamicton known as the clava shelly till the first two members form a conformable coarsening upwards sequence containing a shallow water high boreal to low arctic fauna and flora the clava shelly till is essentially glacially re sedimented glaciomarine clay containing a sparse fauna but its stratigraphic relationship and age are not absolutely clear the shelly clay is ascribed to a mid devensian interstadial episode on the basis of amino acid dating it is concluded that the clava shelly clay and several discrete masses of clava sand and shelly till are glacially transported allochthons derived from the great glen the rafts were probably detached as a result of high pore water pressure building up in laterally restricted aquifers beneath a confined glacier that flowed north eastwards across the loch ness basin this glacier was deflected eastwards and upwards towards clava by ice flowing from the northern highlands along the beauly firth during the build up of the last scottish ice sheet the rafts were stacked at the ice margin when the glacier entered the nairn valley before being overriden by the expanding ice sheet

kaolinite smectite mixed layer clays in the jiujiang red soils and their climate significance abstract clay mineralogy of the jiujiang soils classified as red earth on summit and slope were investigated using x ray diffraction xrd cation exchange capacity cec determination and high resolution transmission electron microscopy hrtem the xrd results show that the soils included kaolinite illite vermiculite and mixed layer i s and k s as clay minerals in xrd patterns of clay separates the low angle shoulder on the kaolinite 001 peak shifted to 8 a on glycolation indicating the presence of mixed layer k s clays in the soils kaolinite content in the interstratified kaolinite smectites was estimated to be 95 for samples of the middle to lower soil profile and 60 for that of the upper portion respectively a broad reflection for 10 14 a disappeared and an 18 7 a peak occurred in the xrd patterns after formamide treatment the 10 a peak became much more intense on heating to 400 c indicating that the 10 14 a peak was expandable and easily contractible and thus originated from mixed layer illite smectite i s clays after heating to 550 c the 7 a peak disappeared while the 10 a peak became more intense and showed a low angle tail indicating the interstratified smectite component was hydroxy interlayered the higher cec values of the jiujiang clay separates 22 2 27 3 cmol kg also pointed to the occurrence of smectite in the soils hrtem analysis showed different lattice fringes for clay particles in the samples a great majority of layer spacings were in the range 10 20 a with a minority of 7 and 25 a particles with 7 a fringes showed a lateral transition of two 7 a kaolinite layers merging into one 12 a smectite layer this can be interpreted as the partial intercalation of one smectite layer in kaolinite there was no long range order in the stacking sequence of k s layers and the interstratification was of a random nature in the uniform soil horizon of the upper profile there was more vermiculite and illite but less i s and k s while in the net like soil horizon of the middle lower profile there was more kaolinite i s and k s with only a trace of vermiculite the occurrence of k s clays confirmed that the jiujiang red earth was derived from syndepositional pedogenesis and the climates changed from warm and seasonally dry to warm and more humid conditions during the soil forming period

chemical weathering of the loess deposits in the lower changjiang valley china and paleoclimatic implications abstract loess deposits xiashu loess are widely distributed in the lower changjiang valley east china and are considered to be of eolian origin with a similar provenance to the well documented loess of north central china the xiashu loess is characterized by strong dissolution of carbonate and considerable weathering of some silicate minerals especially plagioclase chemical mobility of ca sr na mg was observed in the xiashu loess sediments whilst most transition metals are relatively enriched chemical index of variation cia and element ratios of k na and k ca record several paleoclimate events in the lower changjiang valley during the mid late quaternary corresponding with isotopic records in deep sea sediments east china might be governed by stronger summer monsoons than north central china during interglacial periods of the mid late quaternary which may somewhat obscure the record of winter monsoons during glacial periods

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

color variations of the quaternary red clay in southern china and its paleoclimatic implications abstract the red clay and red weathering crust are widely distributed in southern china to study the possible relationship between soil color and paleoclimatic environment three color parameters lightness l redness a and yellowness b of twelve quaternary red clay qrc profiles in southern china were measured using a colorimeter colors of the qrc profiles vary vertically a and b generally increase downward and l decreases downwards colors of the qrc also show spatial variation a and b generally increase towards the equator whereas l increases away from it both a and b are positively significantly correlated with clay

effectiveness of sediment control structures relative to spatial patterns of upland soil loss in an arid watershed wyoming rainfall simulation experiments have been used to identify the variables that control rates of gross soil erosion in upland areas of the fifteenmile creek drainage in wyoming rates of gross soil erosion were found to be most closely related to slope gradient vegetation density and soil texture these variables were mapped for the drainage and digitized files of these maps were combined in a geographic information system to depict the spatial pattern of soil mobilization gross soil erosion in badland areas was found to be extreme when compared to the remainder of the drainage neither structural nor non structural sediment control strategies are well suited to these badland areas engineering structures to control sediment export had been constructed in poorly chosen locations at extreme and unnecessary expense to taxpayers

magnetic properties and geochemistry of the xiashu loess in the present subtropical area of china and their implications for pedogenic intensity variations in the magnetic susceptibility of chinese loess have been used to indicate pedogenic intensity and therefore past climate across the chinese loess plateau clp however the relationship between climate and magnetic properties has not been fully resolved and therefore a study of loess sections distributed over a wider climatic region is timely in this study we have investigated a 22 1 m loess section named the xiashu loess at dagang china by integrating both rock magnetic and geochemical proxies this loess profile is situated in a modern subtropical climate region with annual mean precipitation and temperature of 1100 mm and 15 4 c respectively and therefore has experienced a stronger weathering intensity due to its lower latitude higher temperature and rainfall geochemical and magnetic evidence indicate the same source area for the xiashu loess as for loess in northern china the magnetic mineral assemblage of the xiashu loess is dominated by a higher concentration of superparamagnetic sp single domain sd magnetite maghemite grains in strongly weathered paleosols than in the loess layers consistent with the production of fine grained ferrimagnetic minerals during pedogenic processes nevertheless compared to loess in the clp the xiashu loess shows 1 reduced contrasts in magnetic susceptibility hard isothermal remanent magnetization hirm and remanence of coercivity bcr between loess and paleosols units which indicates that the loess units have undergone stronger pedogenic alterations 2 lower peak values of hirm and in paleosols in addition the ratios sirm arm sirm where sirm and arm are saturation isothermal remanent magnetization and the susceptibility of anhysteretic remanent magnetization respectively and bcr are found to be significantly correlated with the quotient cao na2o mgo tio2 a geochemical indicator of pedogenic intensity overall it seems that pedogenic processes in the xiashu loess lead to a relative increase in fine grained ferrimagnetic sp sd grains but depletion of anti ferromagnetic minerals magnetic and geochemical proxies indicate strengthened east asia summer monsoon during marine isotope stages 13 11 and 5 which is in good agreement with the records from the clp and the south china sea 2007 elsevier b v all rights reserved

magnetic susceptibility of the quaternary red clay in subtropical china and its paleoenvironmental implications abstract magnetic susceptibility lf and other magnetic parameters of 11 typical profiles of quaternary red clay qrc in subtropical china were measured lf curves of the qrc profiles show similar vertical variations lf of the uppermost yellow brown earth ybe and uniform red clay urc of the profiles is high mostly ranging from 50 to 150 10 8 m 3 kg 1 that of the reticulate red clay rrc sharply decreases downwards especially in the lower rrc lrrc with dense reticulate pattern lf is often less than 10 10 8 m 3 kg 1 grain size characteristics and geochemical properties of the qrc suggest that the sharp decrease of lf in the rrc is not related to sudden change of parent materials but to the formation of the reticulate pattern further study indicates that pedogenic fine ferrimagnetic minerals fm superparamagnetic particles sp and or stable single domain ssd are the main magnetic carriers of the qrc the ybe and urc with higher lf show low coercivity and magnetic soft behavior the rrc especially the lrrc with weak magnetism shows high coercivity and magnetic hard behavior the temperature dependent susceptibility tds of the qrc suggests that the dominant type of fm in the ybe and urc is pedogenic maghemite the rrc especially the lrrc however contains little maghemite but a trace amount of lithogenic multi domain md magnetite inherited from the parent rock during post depositional hydromorphic processes pedogenic maghemite was more easily dissolved than hematite which caused the sharp decrease of lf in the rrc as lf of the qrc was mainly controlled by the intensity of hydromorphic processes rather than the weathering degree lf of the qrc in subtropical china cannot accurately indicate the paleoclimate during the quaternary period when the red clay was initially formed

climate influenced cave deposition and human occupation during the pleistocene in zhiren cave southwest china abstract a large number of hominin fossil bearing caves in south china have yielded evidence for the occupation of early modern humans during the middle to late pleistocene however the geology of these caves and the paleoenvironmental context of human occupation remain poorly documented and understood in this study we obtained new ages yielded by mc icpms uranium series dating of speleothems from zhiren cave guangxi where a partial early modern human mandible and 2 m have been recovered the ages demonstrate that cave infilling of zhiren cave began at 1 ma much earlier than the date previously suggested our dating results also suggest that fossils of anatomically modern human were deposited in zhiren cave during marine isotope stage mis 6 between 190 and 130 ka representing the oldest known anatomically modern human remains in east asia the cave s sedimentary processes and the paleoenvironmental changes were reconstructed based on detailed analyses of lithostratigraphy grain size pollen assemblages and the chemical weathering intensity of the sediments inside zhiren cave the results show that major climatic changes in the middle pleistocene led to the accelerated incision of local streams and the erosion of cave sediments by controlling the regional hydrological response during the early to middle pleistocene after 300 ka increased climatic contrasts between glacial and interglacial periods dominated the accumulation of sediments and the occupation of mammals and early modern humans in zhiren cave gradually desiccating climatic conditions and reduced forest cover during the penultimate glacial period mis 6 may have define a temporal window for the human occupation of zhiren cave providing ideal environmental conditions however floodwater incursion and or dense vegetation cover corresponding to a much warmer and wetter climate in the subsequent last interglacial mis 5 may have discouraged humans from further occupying zhiren cave

late pleistocene loess like deposits in the coastal area of south china abstract a layer of yellow silt with thickness from tens of centimeters to a few meters is widely distributed on low hills and terraces in the coastal area of south china the yellow silt has different sedimentological characteristics from other common types of quaternary sediments and the bedrock weathering material in the area five representative sections were studied using scanning electron microscopy grain size analysis diffuse reflection spectroscopy geochemical analysis and optically stimulated luminescence osl dating to reveal the sedimentary characteristics deposition environment origin and age of the yellow silt subrounded subangular quartz grains showed typical aeolian impact pits such as dish like and crescent pits and chemical precipitation and corrosion on grain surfaces the grain size composition grain size parameters and unimodal frequency distribution curves of the yellow silt were similar in all sections examined and consistent with those of north and central china loess the iron mineral content of the yellow silt was dominated by hematite indicating a similar sedimentary environment to that of typical chinese loess the major oxide composition of the yellow silt with respect to normalized upper continental crust ucc distribution patterns was close to that of the ucc and similar to north china loess and other aeolian deposits in china however the data suggested that the yellow silt in the coastal area of south china had suffered strong weathering after deposition the osl ages of the yellow silt indicated a deposition age of late pleistocene the results of the various analytical methods all showed an origin correlation and regular transition of loess deposits from northwest to southeast china hence it was concluded that the yellow silt widely distributed in the coastal area of south china is a loess like deposit formed during the late pleistocene it probably mostly originated from northwest inland china and constitutes the south extension of other loess in china

aeolian origin of the red earth in southeast china a clay like deposit known as red earth is widely distributed over the terraces and high lands of the yangtze river valley in southeast china its typical pedo stratigraphical features have attracted the interest of pedologists and geologists for many years although its origin is still debated here we report an analyses of the grain size distributions rare earth element bee patterns and upper continental crust ucc normalised major elemental composition of the red earth and compare them with those of the loess and other aeolian deposits in northern china the results show that the red earth in southeast china has two or three end member grain size distributions similar to the sedimentary characteristics and geochemical composition of aeolian deposits found in northern china together with other evidence from field observations these results suggest that the red earth is probably of acolian origin on the basis of these data we suggest that thick aeolian dusts were also deposited in the wet subtropics and that the effect of the winter monsoonal winds upon the dust transport in eastern china was more important than previously believed copyright c 2002 john wiley sons ltd

environmental changes based on multi proxy analysis of core sediments in lake aktas turkey preliminary results abstract a sediment core covering the last millennium from lake aktas a shallow alkaline soda lake in the northeast anatolian highland of turkey was studied for pollen and physical and chemical proxies to reconstruct past climate change the sediments were dated by ams radiocarbon dating of bulk organic carbon among arboreal pollen ap from around 930 years ago dominant trees were pinus sylvestris picea orientalis abies betula fagus and quercus ap exceeded nap non arboreal pollen in this time whereas the opposite is the case in a pollen trap in the same region collecting the pollen for one year in 2015 2016 the comparison of modern and fossil pollen influx indicates that in that period trees were more widely distributed around the lake than today where steppe vegetation now prevails inferred causes for the disappearance of trees are anthropogenic impacts and climatic change towards more continental conditions the results also identify the onset of the little ice age in the ne anatolian highland of turkey

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

evidence for an aeolian origin of the holocene lateritic surface cover of gabon central africa abstract field granulometric and geochemical data are reported for a set of twenty one samples collected at six sites spread over gabon in the extensive lateritic clayey to sandy layer cover horizon which constitutes the upper part of the profiles of surficial formations granulometric analyses show that this material of homogeneous aspect is a mixture of two fractions a clay fraction and a medium to coarse grained sandy fraction relative proportions of these two constituents show strong variations from one site to another but are almost constant from the bottom to the top of a given profile the coarse grained fraction includes lithic elements of local provenance irrespective of their underlying basement the samples display many common geochemical features including a lack of ca na and mg their major element compositions may be accounted by the combination of a discrete number of mineralogical phases namely quartz kaolinite gibbsite fe oxides hydroxides and subordinate k minerals micas the normative contents of aluminous and ferrous phases regularly increase with the weight percent of clays conversely the quartz regularly decreases this inverse relationship is consistent with mixing between an al and fe bearing clay fraction and a coarse grained fraction dominated by quartz correlations between most immobile trace elements and the weight percent of clays indicate a control of those elements by al and fe bearing phases the main exception is for zr and hf as those elements are probably associated with zircons in the coarse fraction because of the control of the trace element distribution by secondary phases the geochemical signatures of all samples are clearly distinct from those of the upper continental crust and any basement rocks thus the trace element characteristics of the cover horizon carry no sign of any source material being the sole consequence of mineralogical sorting prior to deposit from field granulometric and geochemical data an aeolian origin appears as the most probable for the cover horizon geochronological constraints including archaeological data and 14 c dating indicate that this aeolian event took place during the holocene and probably occurred in less than 3000 y additional works will be necessary to assess the global context which made possible this very fast and extended event over large areas of central africa

a quantitative reconstruction of a loess paleosol sequence focused on paleosol genesis an example from a section at chaoyang china abstract a typical loess paleosol sequence at chaoyang in china deposited continuously since 423 ka bp was examined to quantitatively reconstruct a loess paleosol sequence first particle size distribution was evaluated based on clay free fractions where the sum of sand silt 100 and fine earth fractions and used to characterize the parent material uniformity as well as field morphology geochemical features and micro morphology characteristics second mass balance mb and soil reconstruction sr approaches were employed to examine the linkage between pedogenesis and loess deposition the results indicated a uniform loess deposit below 228 cm depth and the presence of four reddish stratigraphic layers interbedded with four yellowish stratigraphic layers all derived mostly from silt eolian deposits the main soil pedogenic processes following silt deposition were clay eluviation illuviation silification and ferrallitization the strongest pedogenesis occurred for the s3 deposit layer during 225 243 ka bp and was associated with the greatest mass loss of non clay 7 6 na2o 42 cao 21 mgo 28 sio2 10 and at the same time with the greatest gains in clay 42 fe2o3 8 and al2o3 4 together with mass loss changes mc of 620 g 100 cm2 the greatest mass gain changes 234 g 100 cm2 occurred in the l4 deposit layer during 243 311 ka bp and were associated with gains in na2o 18 and p2o5 4 5 indicating the fastest deposition rate during the long period of sedimentation 423 ka bp loess deposition was predominant during dry cold periods whereas paleosol formation from pedogenic processes was predominant during wet warm periods thus the formation of paleosols and loess deposition were dependent on the relative rate of pedogenesis and deposition as controlled by climate change under an east asian summer monsoon eas paleosol formation dominated whereas loess deposition dominated under an east asian winter monsoon eaw quantification of the degree of loess development paleosols or loess deposits aids reconstructing soil genesis and understanding the loess paleosol formation sequence and its linkage to climate change

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

regional distribution of the quaternary red clay with aeolian dust characteristics in subtropical china and its paleoclimatic implications abstract grain size and geochemical characteristics of 18 quaternary red clay qrc profiles mainly located in the lower and middle reaches of the yangtze river in subtropical china were studied the results showed that all the qrc profiles can be classified into three types type a mainly distributed between 29 n and 31 n share the similar characteristics with the xiashu loess with the uniformity of grain size and elemental compositions and the enrichment of the basic dust fraction 10 m 63 m which may originate from aeolian dust deposits and is hence called a loess like qrc type b mainly distributed between 25 n and 28 n shows alluvial features with many coarse grains and large scale vertical variation of grain size and chemical compositions type ab distributed between type a and type b approximately 28 n 29 n shows double unit structure the upper part is similar to type a the lower however shows alluvial features like type b the loess like qrc is mainly distributed along the yangtze river but gradually declines southwards and is rarely seen south of 28 n the existence of the loess like qrc is strong evidence for the occurrence of heavy dustfalls in the modern red soil areas in subtropical china during the quaternary glacial periods the region distributed with the loess like qrc is at least 3 latitude south of the xiashu loess implying that the loess red clay boundary in the yangtze valley had once oscillated with the alternations between glacial and interglacial climates during the quaternary period the loess like qrc actually includes both glacial and interglacial paleoclimatic information we suggest that the yellow brown earth ybe in the upper qrc was formed during the last glacial period the underlying red clay with the aeolian dust characteristics but being strongly weathered was initially deposited during the second last glacial or earlier glacial stages but heavily weathered and rubefied in the subsequent interglacial events no multi cyclical paleoclimatic records were found in the qrc profiles due to the overlapped information but the weathering degree of the profiles clearly show a trend of decreasing upwards which suggests that the climate in the yangtze valley has become colder and drier since the late quaternary period

extraordinary flood events and the response to monsoonal climatic change during the last 3000 years along the middle yangtze river valley china abstract well dated long term flood data series is very important in studying of hydrological response to past climatic change along the mainstream of the yangtze river five palaeoflood events recorded by slackwater deposits were identified by the sedimentological criteria and analytical results a detailed chronological framework of palaeoflood events during the late holocene was established by optically stimulated luminescence dating in combination with anthropogenic remains and with pedo stratigraphic correlations with well dated holocene loess soil profiles within the middle yangtze river basin the five palaeoflood events were dated to 2 43 0 18 ka 1 82 0 17 ka 0 94 0 07 ka 0 72 0 06 ka and 0 59 0 05 ka respectively these results are consistent with geological records at other palaeoflood sites and historical flood records along the middle yangtze river valley a regional synthesis of the palaeoflood chronology over the last 3000 years was compiled along the middle yangtze river extraordinary flood events generally seem to be correlated with late holocene climatic variability i e neoglacial cooling roman warm period dark ages cold period medieval climate anomaly and little ice age the high resolution climatic proxies from stalagmites of the dongge cave and heshang cave ice cores of the grip the total solar irradiance variations and sunspot number and enso activities suggest that these hydroclimatic events are possibly related to the weaker asia summer monsoon and the cooling climatic events as well as the stronger enso activities during the late holocene in the yangtze river valley these results provide insights into the response of hydroclimatic system to global change in the large rivers of asia

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

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