anhysteretic remanent magnetization of fine magnetic particles 1 various magnetic parameters are in common use for estimating the grain size of magnetic particles among these the ratio of the intensity of anhysteretic remanent magnetization arm to that of isothermal remanent magnetization as well as their alternating field af demagnetization curves are used as an indicator of the domain state of the particles several models have been proposed to describe physically the acquisition of arm in a biased af field jaep 1969 first developed a semiquantitative theory based entirely on the thermal fluctuation analysis developed by neel 1949 1954 1955 significant discrepancies were found between his model and experimental results on magnetite a new general theory of arm based on the work of jaep is presented here with particular regard to the influence of various parameters like grain size coercivity and mineralogy on arm intensity an analytical expression for arm intensity in the special case of very fine particles was derived from this theory and a good agreement with experimental results and data from the literature was found a new estimation of the atomic reorganization time was obtained from arm measurements on a sample of the yucca mountain tuff which has well known mineralogy and grain size distribution the results are in agreement with the value proposed by mcnab et al 1968 for magnetite some authors considered magnetic interactions as the key to understand the arm in fine particles and this is certainly true for strongly interacting samples in this case arm would be useless for the characterization of magnetic grains however many sediments have a very low concentration of well distributed magnetic grains for these samples the explanation of an arm in terms of intrinsic properties of the grains as qualitatively proposed by other authors is more suitable

pedogenic modification of loess significance for palaeoclimatic reconstructions abstract this review considers the role of pedogenic processes in modifying wind blown dust loess concentrating particularly on the ways that resulting properties may be interpreted as indicators of past climatic conditions and changes emphasis is placed on the sequences of palaeosols developed within loess deposits that are frequently regarded as some of the best terrestrial equivalents of marine sediment records of long term global climatic change a palaeosol is generally interpreted in terms of the broad pedogenic processes and environments assumed to be currently responsible for that type of soil forming at the present surface even the very presence of a palaeosol may have palaeoclimatic significance however in that it is often taken to indicate a period of relative land surface stability and warmer and or moister conditions between cold and or arid phases of loess accumulation in reality it may be more useful to consider many loess palaeosol sequences in terms of changing balances between pedogenesis and loess accumulation over geological time in most regions it seems that the balance swings towards pedogenesis during interglacials or interstadials when sediment supply and transport are limited and the climate is warmer and or wetter where accumulation rates are still appreciable during these soil forming intervals however the soils and palaeosols may be accretionary with surface build up keeping pace with pedogenesis welding may also occur where covering sediments are insufficiently thick to isolate an underlying palaeosol from the effects of pedogenesis active at a new land surface further complications occur due to reworking of palaeosols and syndepositional pedogenic alteration of loess units generally such pedocomplexes can only be deciphered if the different pedogenic geomorphic and sedimentary processes are identified and ordered within a pedosedimentary reconstruction a recent trend has been to treat some loess palaeosol sequences as quasi continuous time series particularly when comparing depth functions of climatic proxy properties such as magnetic susceptibility and grain size with marine and ice core isotope curves

discrepancy between mineral residence time and soil age implications for the interpretation of chemical weathering rates virtually all soil chronosequence studies have equated the degree of mineral weather ing with the soil age which is equal to the time since the cessation of erosion or deposition the primary minerals from the parent material however enter the soil as the weathering front propagates downward and are depleted via chemical weathering the residence time of minerals is thus a function of both the rate of conversion of parent material to soil i e soil production and the minerals susceptibility to chemical weathering reactions we fi nd that mineral residence times are signifi cantly shorter than the soil age by mathematically consid ering the interactions among soil production and chemical weathering we demonstrate that traditional estimates of mineral specifi c chemical weathering rates from soil chronosequences may diverge by several orders of magnitude from the actual weathering rates

rock magnetism and geochemistry of two plio pleistocene chinese loess palaeosol sequences implications for quantitative palaeoprecipitation reconstruction abstract stratigraphic and spatial variations in the magnetic properties of chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space recently several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long 2 5 my loess palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau one site duanjiapo is located on the southern humid margin of the plateau and the other site luochuan is located in a drier modern environment some 160 km further north our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at duanjiapo using published approaches would be significantly in error overall our results indicate a complex response of magnetic mineral transformations to climate including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval together with the destruction of magnetic material within some of the palaeosols therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

direct estimates of pedogenic magnetite as a tool to reconstruct past climates from buried soils 1 variations in magnetic properties of buried soils can be used to reconstruct past climatic conditions during paleosol formation most methods however are based on comparisons between the magnetically enriched upper soil horizons and the magnetically unaltered parent material in thin loess paleosol sequences such a comparison can be problematic because all horizons soil and underlying loess may be affected to varying degrees by pedogenesis we propose two direct estimates of pedogenic magnetite based on the analysis of anhysteretic remanent magnetization ratios carm isothermal remanent magnetization and coercivity distributions these estimates are independent of any information regarding the parent material and are possible if pedogenic minerals have similar magnetic properties throughout the study region this condition seems to be met throughout the midwestern united states and a few loessic soils elsewhere the remanence carrying part of pedogenic magnetite is composed of single domain particles with consistent well constrained magnetic properties these particles are extremely well dispersed in the soil matrix as indicated by the absence of noticeable magnetostatic interaction effects our analyses of over 70 modern loessic soil profiles demonstrate that the abundance of pedogenic magnetite correlates well with modern climate and that the method is suited for reconstruction of past climates from paleosols

the ustic isohumisol chernozem distributed over the chinese loess plateau modern soil or palaeosol abstract the ustic isohumisol chernozem widely distributed over the chinese loess plateau is classified as a modern soil by agricultural pedologists and as a palaeosol by geoscientists high resolution investigations into this soil including field observations element analysis optically simulated luminescence dating and measurements of magnetic susceptibility and particle size distribution were carried out over the plateau uplands the results show that the formation of physico chemical properties and development of the soil profiles has kept pace with the land surface growth because of incessant dust accumulation during the holocene the continuously intensified weathering of accumulated dust from 11 500 a b p had resulted in an increased chemical differentiation through time during the early holocene the development of the ustic isohumisol occurred over the uplands between 8500 and 3100 a b p when the chemical differentiation reached its maximum because of increased precipitation and ample soil moisture in response to the mid holocene climatic optimum the soil formation had sustained for ca 5400 years and ceased at 3100 a b p a major pedogenic regression occurred from 3100 a b p because of climatic aridity and intensified dust accumulation over the loess plateau the newly accumulated loess and topsoil has the ustic isohumisol buried at a depth of ca 50 80 cm in general the pedogenic regression has been intensified by incorporation of the reworked components by increased runoff and erosion redeposition large scale land reclamation extended to the uplands at ca 2170 a b p an agricultural landscape of dry farming has formed since ca 1500 a b p thereafter the present topsoil has accumulated and has been affected by the intensified cultivation and addition of barnyard manure in history the solubles are retained in the topsoil because of dry climate and scant soil moisture

relative rates of peoria loess accumulation and pedogenic processes implications for paleoclimatic inference abstract where it is thick enough to extend below the surface soil profile the late wisconsinan peoria loess in the midcontinent of north america has characteristics suggesting relatively little syndepositional pedogenesis in these thicker sections the peoria loess below the surface soil profile commonly displays massive macroscopic structure low organic carbon content and retention of detrital carbonate grains late wisconsinan climatic conditions provide one potential explanation for these observations this paper considers two other non climatic explanations 1 loess accumulation was more rapid than carbonate dissolution or oc accumulation and 2 post depositional diagenesis has removed evidence of syndepositional pedogenesis the approach used is comparison of potential rates for pedogenic processes and loess accumulation even when wide ranges of controlling factors precipitation evapotranspiration and soil carbon dioxide levels are considered loess accumulation was probably too rapid at many sites for carbonate mineral dissolution to keep pace on the other hand data from modern tundra and boreal forest environments suggest that soil oc accumulation could have kept pace with loess deposition in many cases low oc contents observed in the loess today probably reflect post depositional oxidation climatic factors may provide partial or local explanations for the apparent minor extent of syndepositional pedogenesis but loess accumulation rates and diagenesis are key factors as well

determining the climatic boundary between the chinese loess and palaeosol evidence from aeolian coarse grained magnetite summary this paper proposes a new method to distinguish between interglacial deposits and pedogenically overprinted glacial loess based on the concentration variations of coarse grained aeolian magnetically pseudo single domain and multidomain magnetite we apply the method to a sequence from the upper part of the loess unit l2 marine isotope stage mis 6 to the sub loess unit s1l2 mis 5d at the yuanbo yb section in the chinese loess plateau the method is based on the differences in low temperature properties between the coarse grained multidomain and pseudo single domain detrital magnetite and the pedogenic magnetic particles including superparamagnetic sp particles and relatively larger sp maghemite particles the former is characterized by a crystallographic verwey transition around 120 k in contrast the magnetization of the latter continuously decreases in intensity with increasing temperatures the method involves two steps 1 calculating the first derivative of the low temperature thermal demagnetization of the saturated isothermal remanent magnetization acquired at 20 k lt sirm which enhances the behaviour related to the verwey transition and 2 fitting a third order polynomial background to the data between both 50 70 and 150 300 k and then subtracting this background from the total derivative curves the area under the background corrected derivative curves represents the absolute intensity drop associated with the verwey transition j tv this is caused by the aeolian coarse grained magnetite which is very sensitive to the changes in the intensity of the winter monsoon and in turn re

impacts of grain size sorting and chemical weathering on the geochemistry of jingyuan loess in the northwestern chinese loess plateau abstract major and trace elemental compositions of loess samples collected from the jingyuan section in the northwestern chinese loess plateau clp were analyzed to investigate the potential impacts of grain size sorting and chemical weathering on the loess geochemistry and to extract appropriate geochemical indices for better evaluating the east asian monsoon variability based on variations of major and trace elements in different grain size fractions seventeen elements were classified into three types 1 si and na display higher contents with the increased particle sizes 2 al fe mg k mn zn rb cr v are mainly enriched in fine size fractions 3 ti ba zr p ca and sr show irregular variations among different size fractions comparison of al normalized elemental ratios with zr rb and rb sr ratios two commonly employed indicators for grain size sorting and pedogenic weathering indicates that si al zr al ti al variations match well with zr rb and grain size results whilst ca al sr al p al ratios display similar variability as that of rb sr ratio comparison of loess based proxies e g elemental ratios magnetic susceptibility grain size of jingyuan section with speleothem and ice core records confirms that elemental ratios of high resolution loess sequences developed in the northwestern clp can be employed to address fluctuations of the winter monsoon induced grain size sorting and summer monsoon related weathering and pedogenesis at glacial interglacial and millennial timescales

a quantitative model of magnetic enhancement in loessic soils we present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils the model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores the rate at which this occurs depends on the frequency of drying wetting cycles and on the average moisture of the soil both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production which is proportional to a new parameter called magnetite enhancement proxy mep our model is tested by comparing mep calculated for known present day climates with the magnetic enhancement of modern soils the magnetic enhancement factor defined as the ratio between a given magnetic enhancement parameter and mep is expected to be a site independent constant we show that magnetic enhancement differences between soils from the chinese loess plateau and from midwestern u s are explained by our model which yields similar magnetic enhancement factors for the two regions our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate

quantifying grain size distribution of pedogenic magnetic particles in chinese loess and its significance for pedogenesis quaternary glacial interglacial cycles have been imprinted on the chinese loess paleosol sequences through pedogenesis in order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution gsd to date the gsd has not been accurately determined because of the dearth of available means for analyzing extremely fine grained nanometer scale pedogenic magnetic particles using low temperature techniques we systematically investigated the temperature dependency of fd defined as 1hz 10hz where 1hz and 10hz are ac magnetic susceptibility measured at 1 and 10 hz respectively from two characteristic loess profiles one located at the western chinese loess plateau and the other in the central plateau on the basis of neel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures a quantitative gsd for pedogenic particles in chinese loess paleosols was constructed we found that the dominant magnetic grain size lies just above the superparamagnetic single domain threshold 20 25 nm and that the gsd is almost independent of the degree of pedogenesis this observation agrees well with other constraints from previous studies this new gsd model improves our understanding of the pedogenic processes in chinese loess enabling further explicit linkage of environmental magnetism to paleoclimate changes

coral reef island initiation and development under higher than present sea levels coral reef islands are considered to be among the most vulnerable environments to future sea level rise however emerging data suggest that different island types in contrasting locations have formed under different conditions in relation to past sea level uniform assumptions about reef island futures under sea level rise may thus be inappropriate using chronostratigraphic analysis from atoll rim islands sand and gravel based in the southern maldives we show that while island building initiated at different times around the atoll 2 800 and 4 200 calibrated years before present at windward and leeward rim sites respectively higher than present sea levels and associated high energy wave events were actually critical to island initiation findings thus suggest that projected sea level rise and increases in the magnitude of distal high energy wave events could reactivate this process regime which if there is an appropriate sediment supply may facilitate further vertical reef island building

stratigraphies and chronologies of late quaternary loess paleosol sequences in the core area of the central asian arid zone abstract the sporadic distribution of the quaternary loess in central asia makes it hard to establish a regional pedostratigraphy through visual tracing of marker strata the pedostratigraphic correlation presented here is thus completely based on the radiocarbon chronologies of the four studied sections the first noticeable feature is that poorly drained conditions predominated in the period between 48 000 and 30 000 14 c bp during which three entisols developed at 45 000 14 c bp 40 000 14 c bp and 35 000 14 c bp after a period of loess deposition between 30 000 and 18 000 14 c bp under poorly drained conditions an entisol at the westernmost site valikhanov south central kazakhstan developed between 18 000 and 10 000 14 c bp also under poorly drained conditions the time equivalent deposits at romantic and zeketai sections to the east do not exhibit any soil forming characteristics although poorly drained conditions are also imprinted in the time equivalent loess the holocene sequences in the central asian domain consist of an early holocene loess unit deposited between 10 000 and 5 000 14 c bp and a late holocene soil formed during the past 5000 years in comparison the climate was also wet between 48 000 and 20 000 14 c bp during which three mollisols developed under well drained conditions in the chinese loess plateau of the east asian domain the loess deposited between 23 000 and 10 000 14 c bp in the chinese loess plateau has neither observable marks of soil formation nor imprints of poorly drained conditions the holocene sequence in the east asian domain exhibits an out of phase relationship with that in the central asian domain consisting of an early holocene soil formed between 9000 and 4000 14 c bp and a late holocene loess unit deposited during the past 4000 years

age models sediment fluxes and palaeoclimatic reconstructions for the chinese loess and palaeosol sequences palaeomagnetic studies of the chinese loess provided the first firm chronology for these sediments and revealed that their depositional history reaches back over 2 5 ma magnetic susceptibility records can provide an even more detialed chronology through correlation with d18o deep sea stratigraphy the susceptibility fluctuations have been used also either alone or in combination with 10be measurements to reconstruct palaeoclimate however there is still debate as to the origin of the 10be and magnetic minerals in the chinese loess and hence their palaeoclimatic significance here we analyse magnetic data from six sites across the loess plateau and reinterpret the 10be data from luochuan as largely reflecting primary 10be dust loading rather than as a palaeorainfall indicator we discount previous ideas of both constancy of the flux of magnetically susceptible minerals i e susceptibility flux or constancy of the ratio of the flux of 10be and susceptibility we explain the susceptibility of chinese loess in terms of in situ pedogenic ferrimagnetic enhancement the competing effects of reduction and oxidation are taken to control the degree of magnetic enhancement such that magnetic susceptibility is a direct indicator of palaeorainfall our reconstructions yield variations in palaeorainfall of between 28 per cent and 12 per cent in the central loess plateau rather than 100 per cent to 50 per cent as suggested from previous 10be and magnetic susceptibility studies

late quaternary climate change loess sedimentation and soil profile development in the central great plains a pedosedimentary model research on soil genesis often assumes a top down model in which the soil profi le develops downward from a stable land surface this model is inapplicable to upland landscapes affected by frequent dust deposition where soils grow upward as they develop on the central great plains late quaternary loess sections proximal to immediate source areas contain the brady soil a prominent marker separating late pleistocene peoria loess from holocene bignell loess farther from immediate dust source areas the brady soil and bignell loess are not recognizable in the fi eld on loess tablelands in these distal regions surface soils typically contain a prominent clay rich b horizon below a thick silty a horizon assuming top down pedogenesis this could be interpreted as a postglacial soil profi le formed in peoria loess with the b horizon produced by weathering and clay illuviation we propose a strikingly different interpretation in which the upper b horizon at distal sites is the brady soil a horizon that has been transformed by burial organic matter loss and modern subsoil structure formation processes the overlying modern a horizon represents bignell loess properties of the brady soil at proximal sites a distinctive burrowed zone high clay content and tio 2 zro 2 and low volcanic glass content can be traced to the b horizon in distal soils a decrease in smectite abundance above the brady soil at proximal sites is identifi able at the top of the clay rich b horizon in distal soils the spatial variation of clay content in loess and soil horizons is best explained by eolian sedimentation patterns the higher clay content in the brady soil and distal b horizons defi nes a fi ne grained zone that represents a late phase of peoria loess accumulation evidence of chemical weathering is minimal and illuvial clay is rare to absent in the clay rich b horizons illuvial clay does often occur deep in the solum and is related to the depth below the top of the brady soil the depth of occurrence of illuvial clay is not related to modern climate parameters although depth to secondary carbonate appears to be in equilibrium with modern climate upland soils in the central great plains are composite soils their properties are the result of a pedosedimentary history linked to regional climate change that has infl uenced sedimentation and pedogenesis since the late pleistocene

pedogenic factors affecting magnetic susceptibility of the last interglacial palaeosol s1 in the chinese loess plateau the magnetic susceptibility has been used as a quantitative or semi quantitative proxy for reconstructing the summer monsoon intensity in the chinese loess plateau based on extensive studies on climatic or and environmental mechanisms producing the magnetic susceptibility signatures however the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the nalizing and preserving processes of the signatures this paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non magnetic perspectives of soil forming processes we chose nine sections along two transects one across the western part of the chinese loess plateau and another across the eastern part several conclusions can be drawn from our analytical data first clay translocation within the s1 palaeosol pro les as indicated by eld observed clay coatings on ped faces in bt and bk horizons and demonstrated by laboratory analysed clay contents must have moved some of the magnetic minerals downward so that the susceptibility re ects only the post translocation distribution of the magnetic susceptibility producing minerals second the best developed palaeosol s1s3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess l2 and coarse textures tend to lower the susceptibility third carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect to conclude extreme caution must be observed when using magnetic susceptibility signatures to retrieve high resolution records of the last interglacial palaeoclimate in the chinese loess plateau copyright 2004 john wiley sons ltd

hysteresis and thermomagnetic properties of particle sized fractions from loess and palaeosol samples spanning 22 myr of accumulation on the chinese loess plateau summary hysteresis loop measurements and thermomagnetic experiments were carried out to characterize magnetic mineralogy and magnetic grain size in a suite of particle size fractioned samples from the chinese loess plateau representing the main changes in magnetic properties over the last 22 myr we find that 1 the ferrimagnets in the detrital fractions 8 m younger than 14 ma show a magnetite type curie temperature whereas those older than 15 ma have a curie temperature slightly over 600 c owing to low temperature oxidation 2 the dominant ferrimagnets in the clay fractions 2 m are most likely to be maghemite 3 both the hysteresis plots and thermomagnetic experiments reinforce previous indications from low temperature experiments that paramagnetic minerals make a major contribution to the clay fractions in all the samples considered 4 the degree of oxidation indicated by the thermomagnetic curves is highest in the clays and next highest in the oldest coarse fractions 5 day plots provide limited and potentially misleading information on the differences between fine grained pedogenic and coarse grained detrital ferrimagnetic assemblages even when allowance is made for the effects of hematite on the quotients used this study reinforces the view that measurements on bulk samples alone obscure critical distinctions between pedogenic and detrital components

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

genesis of loess like sediments and soils at the foothills of the banat mountains romania examples from the paleolithic sites românesti and cosava abstract the paleolithic sites rom nesti and cosava situated at the foothills of the banat mountains in romania provide an important testament of life of the first european modern humans homo sapiens sapiens during middle pleniglacial even though these sites have been extensively excavated little is known about the site formation of related loess like sediments and soils first luminescence data at the two investigated sections confirm sediments from the penultimate glacial period to the holocene assigning the levels of findings is difficult because the sediments are close to the surface and are overprinted by recent soil development albeluvisols influenced by stagnic features are the typical surface soils in the study area and on comparable morphological positions in the region laboratory analysis has revealed that this soil has a complex genesis from hydrolysis weathering which is connected with the development of a fragic soil horizon overprinting the major find horizons at both sites by using sedimentological and geochemical methods in combination this study aims to reconstruct sedimentary evolution and soil processes at the sites as well as to evaluate the state of preservation and the actual content of the archeological contexts initial results indicate hints for a forest step and higher vegetation during mis 3 at the foothills of the carpathian mountains in the western plain of romania these natural factors offer a local attractiveness of the region which could be the most important reason for the occurrence of first anatomically modern humans our investigations lend a better understanding of the paleoenvironment as well as a first age control of paleolithic levels for the region

diversity and peculiarities of soil formation in eolian landscapes insights from the mineral magnetic records abstract magnetic properties of loess paleosol sequences are widely utilized as sensitive easily obtained and reliable proxy archives of past climate change in continental settings however soil formation in aeolian landscapes may occur under different and changing conditions of dust sedimentation which will affect the growth and development of the pedogenic magnetic component this phenomenon is explored in our study by analyzing depth variations of the following magnetic characteristics frequency dependent magnetic susceptibility anhysteretic magnetic susceptibility and the ratio between anhysteretic susceptibility and isothermal remanent magnetization acquired in a 100 mt back field arm irm 100 mt along three loess paleosol profiles from ne bulgaria a conceptual model for the time evolution of the grain size of the pedogenic magnetic fraction with soil depth is proposed which is build upon the mechanism of soil formation accretional or in stable land surfaces or a combination of the two another magnetic ratio isothermal remanence acquired in a 300 mt back field divided by low field magnetic susceptibility irm 300 mt is utilized as a proxy for the changes in the ratio of silt to clay fractions indicative of changes in dust sedimentation regimes during glacial interglacial transitions according to the proposed conceptual model verified by the magnetic signature of three holocene soils from ne bulgaria discrimination between accretional soils and soils developed without dust additions during soil forming period can be done accretional soils are characterized by parallel changes in grain size sensitive magnetic proxies soils developed at stable landscape conditions show gradation of the depths at which maximum enhancement of various proxies occurs with deepest occurrence of the maximum in fd followed by depth of maximum arm and arm irm 100 mt another implication of the new conceptual model is that the mean coercivity of the pedogenic component of accretional soils will be higher than that of soils developed without eolian input at equal temperature conditions because of the soils thermal gradient and different depths at which pedogenic minerals form in the two settings the results revealed that the holocene soils so has developed under different soil forming conditions than paleosols from the same sites

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

upbuilding pedogenesis under active loess deposition in a super humid temperate climate quantification of deposition rates soil chemistry and pedogenic thresholds abstract although the importance of dust deposition as an integral component of terrestrial biogeochemical cycles is well recognised few studies have directly addressed pedogenic processes associated with dust deposition on the land surface itself and if so mainly as relict features this work addresses this gap by looking at the pedogenic response to an active loess flux gradient in a super humid strong weathering environment on the west coast of new zealand s south island along the gradient seven soil pits were examined for a range of soil physical colour texture bulk density structure roots and chemical properties ph fe o fe d al o soil organic carbon measured to a depth of 50 cm to capture the transitional changes arising from minimal to maximal loess deposition rates maximal deposition rate was estimated to be 28 4 g m 2 y 1 along the gradient towards the highest deposition rate loess free sandy spodosols changed to increasingly more finely textured soils ultimately featuring a two fold increase of silt the pedogenic oxides fe o fe d and al o gradually increased each by 50 and soil organic carbon by 60 these increases were facilitated by continuous accession of loess the loess mixed with organic matter at the surface and became increasingly weathered and leached with the time that it had spent undergoing eluviation subsequently the loess increments were buried within the subsoil as part of an upwardly thickening spodic horizon upbuilding pedogenesis because of the high deposition rates under maximum loess flux spodosol formation became ultimately retarded and an inceptisol formed because loess supply overwhelmed topsoil leaching having also an illuvial subsoil horizon this inceptisol showed the strongest chemical indicators for podzolisation of the gradient soil data from supplementary sites suggested that more developed soils required lower loess fluxes to retard further pedogenic differentiation than younger soils the existence of a loess gradient that is capable of forming distinctive deposits in a super humid environment gives evidence that not only dry arid climates e g during glacials are potentially suitable for the formation of aeolian substrates loess the study indicates enhanced soil organic carbon storage in soils as a result of loess deposition and concomitant pedogenesis

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

magnetic properties of loess grain size fractions from the section at paks hungary abstract the approximately 50 m thick loess palaeosol sequence at paks brickyard hungary was deposited largely during the brunhes normal polarity chron and its magnetic properties resemble those of similar sections in europe central asia and china in order to get information on the grain size dependence of some of the magnetic parameters two loess and two palaeosol samples were separated into a number of grain size fractions the separation method employs consecutive sedimentation and centrifugation steps performed on bulk samples suspended in water and diluted with calgon ten grain size fractions were obtained ranging from 50 m down to 10 nm several magnetic parameters of the different grain size fractions have been measured at room temperature low field susceptibility hysteresis parameters and at low temperature susceptibility and thermoremanent magnetisation they show a strong grain size dependence for the ferromagnetic minerals low temperature measurements allow discrimination of the paramagnetic vs the ferromagnetic signal and give information on the grain size distribution of the very fine ferromagnetic minerals and on the mineral types carrying the magnetic signal strong relationships between weathering processes destruction of paramagnetic minerals and possibly iron hydroxides and enhancement of the ferromagnetic signal are observed

dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle

holocene loess accumulation and soil development at the western edge of the chinese loess plateau implications for magnetic proxies of palaeorainfall a high resolution holocene sequence of loess palaeosols and incipient soils at the western edge of the chinese loess plateau dated usingoptically stimulated luminescence techniques is used to identify the respective influence of dust accumulation rate time and climate on soil magnetic properties dust deposition and soil formation have both been quasi continuous through the holocene at this site the soils are thus accretionary in nature the degree of soil development as indicated both by geochemical and magnetic properties which correlate strongly varied through the holocene compared with the less weathered loess units each palaeosol is enriched in nitrogen and organic carbon depleted of carbonate due to leaching and displays higher values of pedogenic magnetic susceptibility frequency dependent susceptibility remanences and magnetisation magnetic grain size indicators show that the pedogenic ferrimagnets are ultrafine of single domain and superparamagnetic dimensions sediment accumulation rates were lowest from b12 to 2 5 ka providing ample time 100 s of years for weathering and soil formation to proceed yet pedogenesis through this interval was relatively weak conversely soil development was stronger during later intervals when loess accumulation rates were higher and soil forming intervals were correspondingly shorter in terms of jenny s 1941 soil forming equation accumulation rate and thus time sediment source parent material and topography show no systematic variation between the loess and the palaeosols therefore climate seems to be the key soil forming factor which has controlled the geochemical and magnetic properties of these holocene palaeosols r 2002 elsevier science ltd all rights reserved