experiencing new perspectives in the application of reflectance spectroscopy in loess research abstract diffuse reflectance spectroscopy drs parameters such as the redness index and hematite goethite ratios are popular in the study of loess paleosol sequences the suggested parameters however have their limitations only some parts of the whole reflectance spectrum are being used and the spectra of some important components may be excluded from the analysis a mathematical statistical method hierarchical cluster analysis was applied to the loess paleosol succession at mala nad hronom slovak republic in order to characterize the entire reflectance spectrum and to classify sediment groups the sedimentary units were classified into seven different cluster groups such as sediments weak and well developed paleosols the distribution of the spectral features in the reflectance spectra was located by using the key wavelength provided by the wilk s lambda analysis the key minerals which play an important role in the classification were determined by characteristic extrema in the second derivative of reflectance spectra of the seven reference minerals hematite goethite muscovite illite montmorillonite kaolinite and calcite mineral groups influence certain wavelengths within the measured range therefore curve sections modified by individual minerals only in a few cases the mentioned mineral groups refer to characteristics of the formation environment and to climate change during the pleistocene

phosphogenesis in the immediate aftermath of the great oxidation event evidence from the turee creek group western australia abstract phosphatic peloids and pebble sized microbially bound sediment clasts have been identified within dolomitic sediment that separates centimetric columnar stromatolites in a 20 150 cm thick horizon from the 2 4 2 2 ga turee creek group in western australia petrographic examination of the phosphatic clasts reveals complex internal textures that are defined by different mixtures of fine grained apatite medium grained dolomite irregular domains of partly euhedral micro quartz and carbonaceous matter phosphatic sand sized peloids observed within microbially bound sediment clasts are similar in size texture and composition to the individual peloids in the intercolumn sediment both occurrences have finely dispersed kerogen throughout and zoned cores that are packed with both microscopic apatite granules and larger euhedral quartz crystals the percentage of apatite vs quartz vs kerogen varies between studied peloids similar sized white peloids in the intercolumn sediment and in the microbially bound sediment clasts contain illite and are lined internally by euhedral apatite crystals 20 100 m in size some peloids are kerogenous in one domain and illite bearing in another the phosphatic microbially bound sediment clasts and peloids are interpreted to represent fragments of a peritidal phosphorite redeposited in an offshore setting during high energy events peloids formed within the microbially bound sediment and were subsequently eroded out and redeposited in the intercolumn sediment white peloids are interpreted to represent peloids affected by surficial weathering during temporary exposure when the fine grained kerogenous interior was replaced by clays these weathered peloids were then re sedimented and captured both within microbially bound sediment and in the intercolumn sediment euhedral apatite crystals that line the insides of illite bearing white peloids were dated to 2104 70 ma and 2041 33 ma using u pb and th pb dating methods respectively this age is interpreted to represent the time of metamorphic fluid circulation during a period of known regional metamorphism and provides a minimum age of the reef complex

evidence for the carnian pluvial episode in gondwana new multiproxy climate records and their bearing on early dinosaur diversification abstract the triassic hothouse world experienced dynamic changes in climate and ecosystems that set the earth s climate and biotic states for much of the mesozoic era a critical time interval was the carnian stage 237 227 ma which not only saw the first appearance of dinosaurs in the fossil record but witnessed a large igneous province eruption wrangellia lip and a sudden climate shift the carnian pluvial episode cpe compelling hypotheses suggest that the wrangellia eruptions caused the cpe which in turn set the stage for the origin and initial diversification of dinosaurs unfortunately testing these hypotheses is difficult because most relevant carnian sedimentary archives possess few if any absolute age constraints and there are little detailed paleoclimatic data for the cpe outside of the tethys region there is little existing evidence for the cpe in gondwana even though this region contains by far the best fossil record of early dinosaurs and their close relatives we present new high resolution geochronologic and paleoclimatic data from carnian aged strata in the ischigualasto villa union basin of northwest argentina which also preserves fossils of the earliest known dinosaurs new ca tims u pb zircon age of 234 47 0 44 ma from the lower los rastros formation demonstrates that most of the overlying lacustrine strata within this basin was deposited during or after the cpe including large dinosauriform footprints multiproxy paleoenvironmental data sedimentology clay mineralogy c and o stable isotopes and fossils from the same strata are the first detailed paleoclimate data for the cpe in gondwana and provide evidence that the cpe interval in western gondwana was indeed warmer and more humid than before or after these data are consistent with the interpretation of the cpe as a global event but direct linkages in gondwana and the tethys with the origin and initial diversification of dinosaurs are less clear

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

palaeclimatic significance of the xiantai fluvio lacustrine sequence in the nihewan basin north china based on rock magnetic properties and clay mineralogy summary here we report an increased cooling coupled with an intensified aridification for the xiantai fluvio lacustrine sequence of pleistocene age 1 9 0 1 ma in the nihewan basin north china known for the occurrence of several hominin sites the cooling is related to an up section decrease in propensity to chemical weathering as inferred from an increase in lowfield susceptibility after cycling to 700 c close to 700 c reacting chlorite is providing the iron source for newly formed very fine grained ferrimagnetic minerals which enhances the susceptibility signal the reactivity of chlorite after annealing at temperatures above 600 c is documented with x ray diffraction and the up section decrease in propensity to chemical weathering is confirmed by the up section declining illite chlorite ratios and increasing chlorite and illite contents based on x ray diffraction analysis on selected samples

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

tectonic versus climatic control on the evolution of a loess paleosol sequence at beremend hungary an integrated approach based on paleoecological clay mineralogical and geochemical data the role of two major factors climate and tectonism in controlling loess paleosol evolution has been evaluated in the present study based on a multi proxy dataset comprising mollusc bulk and clay mineralogical and geochemical data a recent trend has been to use chemical indices such as the chemical index of alteration cia for paleoclimate reconstructions in loess paleosol sequences spanning several hundreds of thousands of years but without any tectonic interpretation possible effects of geodynamic factors on physical erosion chemical weathering and consequently weathering proxies are discussed clearly the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate intensifying tectonic uplift gives rise to enhanced physical erosion leading to increased supply of fresh mineral surfaces having less time to react with weathering agents in theory this process may point towards decreasing chemical weathering in a sequence without any real changes of climate in the studied loess paleosol sequence at beremend hungary a trend of decreasing chemical weathering has been observed which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non linear amplification the findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands or millions of years this is because tectonic effects may impose on the cia signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts

east asian summer monsoon intensity inferred from iron oxide mineralogy in the xiashu loess in southern china abstract the xiashu loess in comparison to the well studied loess sequences in the chinese loess plateau clp provides a good opportunity for studying east asian monsoon variations from a southern china perspective here we present a study of the iron oxide mineralogy of the xiashu loess using integrated geochemical and diffuse reflectance spectroscopy drs measurements as well as magnetic data our results show that the free iron oxide fe d to total iron fe t ratio fe d fe t hematite hm to goethite gt ratio hm gt and saturation isothermal remanent magnetization sirm to magnetic susceptibility ratio sirm all indicate particularly strong summer monsoons during the formation of paleosols ps5 and ps4 equivalent to marine isotope stage 13 and 11 respectively however magnetic susceptibility and fe d fe t are not consistently reliable indicators of summer monsoon intensity for the whole section our results indicate that a multi proxy approach can give a more reliable summer monsoon intensity reconstruction the summer monsoon shows a cooling trend and a declining of precipitation from 0 5 to 0 3 ma after which it becomes warmer and wetter towards the top of paleosol ps1 equivalent to mis 5 however ps1 was formed under a relatively cooler temperature and wetter soil conditions in comparison to ps5 and ps4 such supra orbital variations in the east asian summer monsoon superimposed on the effects of glacial interglacial cycles in southern china are also reflected in the 0 4 0 5 ma cycle of marine carbon isotopes in the global ocean possibly indicating a strong link between terrestrial weathering and the global carbon cycle

clay mineralogy of the upper miocene pliocene red clay from the central chinese loess plateau and its paleoclimate implications abstract study of clay mineral is one of effective methods for reconstruction of the paleoclimate and paleoenvironment here we represent clay mineral records from an upper miocene pliocene red clay succession in the central chinese loess plateau clp on the basis of the existing age model we employ x ray diffraction and scanning electron microscopy to carry out clay mineral analyses the results indicated that illite was the dominant clay mineral and the contents of smectite chlorite and kaolinite were minor from the analysis of contents of clay minerals illite crystallinity illite 5 a 10 a smectite illite chlorite ratio magnetic susceptibility summer monsoon intensity and deep sea 18o values the paleoclimatic evolution between 7 5 and 2 6 ma can be divided into three intervals interval i from 7 5 to 6 9 ma it was cool and dry interval ii from 6 9 to 4 1 ma was cool warm oscillations interval iii from 4 1 to 2 6 ma was significantly warm and humid stage of the seasonal climate conditions the proxy records display a large amplitude transition in the later interval iii from 2 8 to 2 6 ma which implied an abrupt climate and environment variability through comparison the local and global paleoclimatic records we found that clay minerals reflect regional paleoclimatic change superimposing global climatic records during the late miocene pliocene period we conclude that the regional tectonic activity and global cooling had affected east asia monsoon which was characterized by the different temperature and precipitation in the central clp

a mid late quaternary loess paleosol record in simmons farm in southern illinois usa abstract in unglaciated areas of the mississippi valley region the typical full loess paleosol succession contains the modern soil developed in peoria silt weakly developed farmdale geosol developed in roxana silt sangamon geosol developed in loveland silt and yarmouth geosol developed in crowley s ridge silt although a fifth loess called the marianna silt is reported at one area the paleosol that separates the crowley ridge and marianna silts is not well defined previous thermoluminescence tl and optical stimulated luminescence osl age chronology has suggested multiple phases of sangamon geosol developed in loveland silt but clear morphological evidence of polygenetic sangamon geosol profiles have not been found recently a thick loess paleosol sequence has been studied in the middle mississippi valley in unglaciated southern illinois usa soil morphology and analytical results revealed five loesses and associated paleosol units two sangamon bt horizons were found separated by a thick actk horizon interpreted to indicate two phases of sangamon geosol development this well preserved loess paleosol succession provides one of the most complete mid late quaternary loess records in the middle mississippi valley to date and is important for studying the stratigraphic framework and paleoclimate and environment changes

preliminary magnetostratigraphy of the red clay underlying the loess sequence at baoji china magnetic remanence and bulk susceptibility measurements are reported from 93 samples spanning the uppermost 27m of the red clay underlying the loess sequence at baoji shaanxi province china if a new previously undetected short about 20ka excursion or reversed interval near 3 3ma be accepted then a reasonable fit to the standard time scale emerges a linear accumulation rate of 1 5cm ka is implied and the correlation coefficient is 0 992 no significant hiatus occurs between the red clay and the overlying loess so the 27m investigated reach back to about 4 3ma fourier analysis of the bulk susceptibility data yields a strong peak near 400ka in agreement with astronomical calculations of the orbital parameters responsible for climatic forcing

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

clay minerals and their paleoenvironmental interpretation in the baoji loess section southern loess plateau china abstract clay minerals from the loess paleosol section at baoji in north central china were studied by x ray diffraction major components calculated by comparing major peak heights were estimated as follows illite 55 75 kaolinite 10 25 mixed layer chlorite vermiculite 10 20 chlorite

the observed impacts of the two types of el nino on the north equatorial countercurrent in the pacific ocean this study investigates the interannual variations in the north equatorial counter current necc associated with the eastern pacific and the central pacific types of el nino using observational analysis and ocean simulations we show that the wind stress anomalies during the two el nino types are of comparable amplitude but have different spatial structures which results in significant and distinct variations in the necc the necc shifts southward and intensifies during the developing phase of el nino but the variations are confined in the central eastern pacific for the eastern pacific type and the western central pacific for the central pacific type these differences can be attributed to modulations in equatorial kelvin wave and tropical rossby wave propagation as well as ekman pumping plain language summary the north equatorial counter current necc is an eastward flowing surface current that transports a significant amount of water from the warm pool in the western pacific to the east variations in the necc exert profound effects on the tropical pacific climate and need to be better understood this study conducts statistical analyses and ocean model experiments to show that different flavors of el nino can displace the necc location and alter its intensity in distinct ways the cause and the physical mechanisms behind the distinct impacts are identified and verified using specific el nino events of each flavor the findings reported in this study contribute to advance our understanding of el nino diversity and its impacts on the circulation and variability of the pacific ocean

mineralogical and pedogenetic evidence for palaeoenvironmental variations during the holocene on the loess plateau china abstract clay minerals in soils reflect successive stages of mineralogical evolution which depend on the environmental conditions that have prevailed during pedogenesis the objective of this research was to document the mineralogy of the clay fractions

susceptibility time series of the baoji section and the bearings on paleoclimatic periodicities in the last 2 5 ma abstract magnetic susceptibility measurements were conducted at 10 cm intervals in the baoji section a 160 m thick loess deposit in the southern loess plateau an independent time scale was developed under control of paleomagnetic data by assuming that the eolian dust deposition rate during glacial periods is 1 5 times higher than that during interglacial periods the 1600 susceptibility results were then plotted to the time scale which has a basal age of 2 5 ma based on paleomagnetic measurements fourier analysis of the susceptibility time series shows strong spectral peaks centered at about 400 000 100 000 40 000 and 20 000 years coinciding with the milankovitch periods of paleoclimate the dominant climatic periodicity recorded in the loess section appears as a function of the time interval considered the 0 0 8 ma interval is dominated by the period of about 100 000 years the 0 8 1 6 ma interval by 40 000 year cycles and the 1 6 2 5 ma interval also by 100 000 year rhythms

climate changes of the northeastern tibetan plateau since the late glaciation inferred from clay mineralogy of sediments in kuhai lake a high resolution study of clay mineralogy has been carried out on a sediment core recovered from kuhai lake in order to investigate climatic and environmental changes in the northeastern tibetan plateau since the late glacial period clay mineralogy reveals significant changes in sedimentary sources and hydrolysis conditions in the kuhai lake catchment area before 14 9 cal ka bp the predominance of illite and relatively high amount of kaolinite derived mainly from the reworking of sedimentary rocks imply unstable cold arid conditions and significant glacier cover that prevented from weathering of metamorphic and mafic rocks in the high relief of the catchment between 14 9 and 5 4 cal ka bp an increase in smectite and chlorite contents associated with relatively low values of the illite chemistry index indicate that clay minerals derived from the weathering of metamorphic and volcanic rocks in the highlands of the catchment area such modifications were triggered by a melting of glaciers in the lake s catchment during the bolling allerod interstadial followed by an intensification of monsoon precipitations in the early holocene around 10 0 cal ka bp both processes are responsible for significant physical erosion in the highlands together with an efficient transport of smectite and chlorite from areas of high relief to the lake after 5 4 cal ka bp lower smectite and chlorite proportions associated with a predominance of al rich illite and kaolinite indicate a return to relatively dry conditions and a lowering of physical erosion in the drainage basin comparison between clay mineralogy and pollen records indicates that variations in weathering intensity in the kuhai lake catchment area and changes in its surrounding vegetation are synchronous demonstrating the large potential of clay mineralogical analysis to trace climate change of the tibetan plateau

the impact of eastern pacific versus central pacific el ninos on the north equatorial countercurrent in the pacific ocean 1 using a three dimensional ocean reanalysis data product the influence of two types of the el ninos on the north equatorial countercurrent necc across the pacific basin is examined in this study eastern pacific el ninos ep el ninos exert a significant impact on the interannual changes of the necc whereas central pacific el ninos cp el ninos have little influence from the developing to mature phase of the ep el ninos that occursfrequently in the latter half of a calendar year the necc tends to intensify and shift southward while the ep el nino related position changes of the necc is out of phase with its seasonal position changes the ep el nino related intensity variability of the necc is in phase with its seasonal modulation during both types of el ninos the el nino modulated wind stress curl forcing changes the upper ocean thickness modifying the necc intensity and central position the weaker and shorter fluctuations of wind stress curl forcing during the cp el nino events induce irregular and insignificant changes of the necc

the north equatorial countercurrent and heat storage in the western pacific ocean during 1982 83 a sequence of extreme climate anomalies known as an el nino southern oscillation episode was observed in the tropical pacific ocean during 1982 831 2 models suggest that oceanic circulation has an important role in the formation of such anomalies1 3 4 by altering the pattern of sea surface temperature through advection the baroclinic structure of the upper 500 m of the ocean has been monitored routinely in the western pacific since 1979 providing indirect current measurements by the geostrophic method these observations reported here show large changes in the near equatorial currents during 1982 83 which are consistent with currents observed in the central and eastern pacific5 6 in particular the north equatorial countercurrent necc flowed with 25 50 increased strength during the early phase then weakened almost to zero flow the west pacific heat pool cooled by more than 1 c observed changes in circulation were large enough to alter surface heat storage by advection although other potentially important processes may not be negligible

mineral magnetic properties of loess paleosol couplets of the central loess plateau of china over the last 1 2 myr 1 we have conducted a multiparameter investigation of 15 loess paleosol couplets s0 l1 to s14 l15 from the jiaodao section in the central loess plateau of china using environmental magnetic approaches coupled with soil science techniques the magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of pedogenesis high temperature susceptibility curves of paleosols show a generally decreasing trend in reversibility from the base of the lishi formation to the holocene black loam possibly indicating a decrease in weathering intensity this may reflect a long term increase in aridity and or a general long term cooling trend of the interior of the asian continent from 1 2 ma to the present several samples display wasp waisted hysteresis loops these are most pronounced in moderately enhanced paleosols less pronounced in the practically unaltered loess and subdued in the well developed paleosols but wasp waistedness reappears in the most developed paleosols this wasp waistedness sequence suggests that the composition concentration and grain size of magnetic minerals all contribute to the hysteresis behavior of samples from the studied loess paleosol sequence but each factor has a different effect at different stages of pedogenesis

response of silicate weathering to monsoon changes on the chinese loess plateau abstract eolian deposits of loess on the chinese loess plateau are investigated to decipher the influence of sequentially changed monsoon climate on silicate weathering process detailed hydrochloric acid dissolution experiments are applied to establish a sensitive proxy for silicate weathering combined elemental and mineralogical studies show that the minerals which are susceptible to incipient chemical weathering can be totally dissolved in hot hydrochloric acid 80 c 3mol l after 4h while other stable minerals are nearly unaffected thus the hydrochloric acid dissolvable fractions adf of loess and paleosol are more sensitive than bulk samples in the weathering reaction since mg is tend to be leached out from the adf while al is conserved during the incongruent weathering mg al ratio of the adf mg al adf could indicate the weathering intensities of the mg bearing minerals mainly chlorite the mg al adf of the modern soils on the chinese loess plateau is closely correlated to the local precipitation amounts suggests that the intensity of summer monsoon is a key factor in the weathering of mg silicate the silicate weathering intensity of the loess paleosol deposits of past 130kyrs shows strong procession cycle of 23kyrs coupled by glacial interglacial variation the 23krys cycles are coherent to the variations of the intensity of summer monsoon while the 100kyrs glacial interglacial variation may relates to the changes in winter monsoon phased intensification of east asian summer monsoon and thus enhanced silicate weathering and atmosphere co 2 drawdown in response to the uplift of tibetan plateau may be another mechanism relating the late cenozoic tectonics to global cooling

processes of loess lithogenesis during the pleistocene holocene southeast siberia regional studies have been conducted on loess deposits cohesive sands and loess like neoformations in the technogenesis zones in southeast siberia cryogenic processes and distribution of geological formations have been ascribed to influential factors of loess lithogenesis the processes of loess formation are active in the present environment

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

is a middle pleistocene climatic optimum recorded in the loess palaeosol sequences of eurasia abstract an attempted correlation of selected brunhes and uppermost matuyama silt sequences in eurasia and a comparison of the successive pedogenic features raises the question of climatic evolution during the middle pleistocene interglacial stages in the italian piedmont of the alps the strongly developed palaeosols found on the superposed loessic silts show an upward change particularly clear during stages 11 and 9 in the characteristics of their bt horizons this expresses a progressive shift during the brunhes chron from warm and humid to relatively cooler and drier interglacial conditions a simultaneous progressive change in palaeosol features is found in the loess sequences of different climatic regions in western and central europe and in central asia this is in marked contrast to the loess plateau of central china where the best developed palaeosol s5 1 correlates with stage 13 the existence of s5 has recently been referred to penck and bruckner s great interglacial of the alps a classic concept which is however clearly contradicted by the loess palaeosol record in this region apart from the loess plateau which may have experienced some regional irregularities in the strength and extent of the summer monsoon there is no evidence from the loess palaeosol record to support the occurrence of a middle pleistocene climatic optimum in eurasia

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

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

variations of illite chlorite ratio in chinese loess sections during the last glacial and interglacial cycle implications for monsoon reconstruction 1 the variations of the clay minerals illite and chlorite were measured by xrd in the 2 m fraction of four loess sections along a north south transect on the chinese loess plateau clp the ratio of illite to chlorite i c provides a tool to evaluate strong monsoon conditions on the clp i c ratios above 2 5 indicate strong chlorite silicate weathering a process that takes place under a regime which at present in the southern clp has annual precipitation and temperature exceeding 600 mm and 10 c respectively the weathering regime during the last previous interglacial period in the southern clp may have been warmer and had higher rainfall during weathering the chlorite may release iron so that nanometer sized iron oxide minerals may form and the free fe2o3 and magnetic susceptibility are increased in the resulting paleosol if that has occurred in the four sections studied it is only in the southern two

location of natural trace elements in silty soils using particle size fractionation abstract in silty material 80 of the particles range from 2 to 50 m particle size fractionation within this size range allows determination of the main mineral bearers of natural trace elements te in silty soil three silty soils were studied at ch teau thierry in the paris basin at muret in the aquitaine basin and at thann in the alsace plain these soils mainly consist of quartz alkaline feldspars plagioclase micas and chlorite the quantities of which vary with particle size as shown by xrd and chemical analyses of major elements quartz content increases with increasing particle size whereas feldspars micas and chlorites occur mainly in the 2 10 0 2 2 and

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

decadal changes of enso persistence barrier in sst and ocean heat content indices 1958 2001 decadal changes of el nino southern oscillation enso persistence barriers in various indices of sea surface temperature sst and ocean heat content ohc are examined in this study using observations and ocean data assimilation products for the period 1958 2001 it is found that the sst indices in the eastern and central equatorial pacific exhibit very different decadal barrier variability the variability is large for the eastern pacific sst indices nino1 2 and nino3 whose persistence barriers shifted abruptly in 1976 1977 and 1989 1990 in contrast the central pacific sst indices nino3 4 and nino4 experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades the zonal mean ohc index averaged over the equatorial pacific shows decadal barrier changes similar to those in the eastern pacific sst indices and always leads the nino3 sst barrier by about one season it is noticed that the sst persistence barrier appeared first in the eastern pacific before 1976 1977 first in the central pacific between 1976 1977 and 1989 1990 and almost simultaneous in both the eastern and central pacific after 1989 1990 these timings coincide with the westward propagating eastward propagating and standing pattern of enso sst anomalies observed in these three periods these results suggest that enso sst anomalies in the equatorial pacific can be considered to consist of two different processes a central pacific process whose phase transition such as onset and barrier always happen in spring and an eastern pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial pacific

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

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

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

magnetostratigraphy of the baoji loess paleosol section in the north central china loess plateau the baoji section is judged to be the most complete accessible quaternary loess paleosol section in the north central china loess plateau it is located 5 km north of the city of baoji it contains 37 paleosols and was recently named the type pedostratigraphic section the pedostratigraphic units geosols of the baoji section can be correlated throughout the loess plateau by a combination of magnetostratigraphy and character position and association of pedostratigraphic units magnetic properties were determined from 483 samples taken from 159 m of loess that overlies the red clay formation all major reversals that occurred in the last 2 5 ma were recorded the brunhes matuyama boundary occurs at a depth of 58 5 m within loess unit l8 the jaramillo subchron between 72 0 m in loess unit l10 and 76 4 m in paleosol s11 the olduvai subchron between 125 5 m in loess unit l25 and 131 5 m in loess unit l27 and the gauss matuyama boundary at 157 8 m within loess unit l33 just above the contact with the red clay formation this is the only known site where all major magnetic reversals are clearly defined in distinct field identifiable loess soil units in one section the magnetostratigraphy of the baoji section is thus recommended as the type section for the loess plateau

tectonic uplift influenced monsoonal changes promoted hominin occupation of the luonan basin insights from a loess paleosol sequence eastern qinling mountains central china abstract quaternary soil deposits from northern and southern china are distinctly different reflecting variability of the east asian monsoon north and south of the qinling mountains coeval sediments from the transitional climatic zone of central china which are little studied to date have the potential to improve our understanding of quaternary monsoon changes and associated influences on hominin occupation of this region here we investigate in detail a well preserved and continuous quaternary loess paleosol sequence shangbaichuan from the luonan basin using a variety of weathering indices including major and trace element ratios clay mineralogy and fe oxide mineralogy the whole rock samples display similar rare earth element patterns characterized by upper continental crustal ratios la yb n 9 5 and eu eu 0 65 elemental data such as la yb n la th and eu eu ratios show a high degree of homogeneity suggesting that dust in the source region may have been thoroughly mixed and recycled resulting in all samples having a uniform initial composition indices for pedogenic weathering such as na k ba sr rb sr cia ciw cpa pia kaolinite illite kaolinite smectite illite and hematite hematite goethite exhibit similar secular trends and reveal a four stage accumulation history the indices also indicate that the climate was warmer and wetter during the most recent interglacial stage compared with coeval environments of the chinese loess plateau secular changes in weathering intensity can be related to stepwise uplift of the qinling mountains and variation in east asian monsoon intensity both of which played significant roles in controlling climate evolution in the luonan basin furthermore intensified aridity and winter monsoon strength in dust source areas as evidenced by mineralogic and geochemical changes may have been due to the mid pleistocene climate transition based on temporal correlation of warmer and wetter climatic conditions with more frequent hominin occupation we infer that the paleoclimate in the eastern qinling mountains remained mild and favorable during glacial stages of the late quaternary thus promoting early human settlement

paleosol nodules as pleistocene paleoclimatic indicators luochuan p r china abstract loess deposits with their interbedded paleosols in central china record the world wide climatic changes of the past 2 5 ma the carbon and oxygen isotopic compositions of carbonate nodules in a loess profile at luochuan record paleoclimatic and paleoecologic conditions of paleosol formation interglacial periods during the past several 100 000 years it appears that the climatic and ecologic conditions during different periods of paleosol s 1 s 8 formation interglacial periods were very similar at luochuan and are marked by a presence of a mixed c 3 and c 4 type flora or mixed grass and wood and or shrublands

three evolution patterns of central pacific el nino 1 three evolution patterns are identified for the central pacific cp type of el nino based on events that occurred during 1958 2007 1 a symmetric decaying pattern whose sea surface temperature anomalies grow and decay symmetrically with respect to a peak phase 2 a prolonged decaying pattern that decays slowly and is followed by a warm event in the eastern pacific ep and 3 an abrupt decaying pattern that terminates rapidly after the peak and is followed by a cold event in the ep the depth of the equatorial thermocline is found to determine which evolution pattern occurs if the cp el nino occurs in a recharged thermocline state i e deeper than normal depth an ep warming may appear in the decaying phase of the cp event to slow down the decay giving rise to the prolonged decaying pattern if the thermocline is in a discharged state i e shallower than normal depth an ep cooling may occur to abruptly terminate the cp el nino if the thermocline is in a neutral state i e normal depth the cp event may have a symmetric pattern of growth and decay although a few exceptions exist these results indicate that the equatorial thermocline state at the peak phase of a cp el nino event can be a potential predictor of the way the event may decay

mineral magnetic variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling a high resolution mineral magnetic investigation has been carried out on the jingbian loess paleosol sequence at the northern extremity of the chinese loess plateau results show that the magnetic assemblage is dominated by large pseudo single domain and multidomain like magnetite with associated maghemite and hematite variations in the ratios of sirm100mt sirm sirm100mt sirm30mt and sirm100mt sirm60mt sirm is the saturation isothermal remanent magnetization sirmnmt represents the residual sirm after an n mt alternating field demagnetization have been used to document regional paleoclimate change in the asian interior by correlating the mineral magnetic record with the composite 18o record in deep sea sediments the long term up section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema respectively which reveals a long term decreasing trend in chemical weathering intensity in both glacial stage source region the gobi and deserts in northwestern china and interglacial stage depositional area the loess plateau region we further relate this long timescale variation to long term increasing aridification and cooling during both glacial extrema in the dust source region and interglacial extrema in the depositional area over the quaternary period changes in those ratios are most likely due to quaternary aridification and cooling driven by ongoing global cooling expansion of the arctic ice sheet and progressive uplift of the himalayan tibetan complex during this period

climatic implications of the s5 paleosol complex on the southernmost chinese loess plateau the s5 is the most prominent paleosol unit in the chinese loess plateau and is distinguished by its great thickness dark color and well developed clay coatings previous studies led to the proposal that the s5 developed under much warmer and wetter conditions than at present implying a climatic optimum however the s5 is a paleosol complex corresponding in time to a period of weak glacial interglacial oscillations as recorded by marine oxygen isotope stages 15 through 13 to understand the character of this climatic interval two profiles of the paleosol s5 in the guanzhong basin were studied with most of the emphasis being placed on the uppermost and best developed pedon s5 i grain size mineralogical and chemical data indicate that the major pedogenic processes experienced by the s5 i included complete decalcification and mechanical translocation of fine particles chemical alteration of silicate minerals has been weak stable carbon isotope analyses of organic matter showed that c4 plant remains are abundant throughout the profiles these results suggest that grasslands dominated the paleovegetation during s5 i development the prominent development of the s5 paleosol complex may reflect a prolonged period of pedogenesis in contrast to previous reports paleoclimatic conditions perhaps even drier than at present are implied by the data for the s5 profiles the relative strength of the glacial interglacial oscillation in this region related to the east asian monsoon was similar to that indicated for global climate during s5 time

paleoclimates and monsoon variations interpreted from micromorphogenic features of the baoji paleosols china abstract a full climatic interpretation of the loess paleosol sequence in china that covers the last 2 5 ma nearly continuously has been restricted because the soils in the oldest loess unit the wucheng loess spanning about 1 2 2 5 ma are not distinct enough to ensure accurate recognition and subdivision in the field recently the authors investigated the baoji loess paleosol sequence in the southern most part of the loess plateau where 37 paleosols were clearly defined including those of the wucheng loess based on macro and micromorphological observations the major pedogenic processes involved in the formation of the baoji paleosol are believed to be carbonate eluviation and illuviation clay translocation pseudogleization and rubification the diagnostic b horizons of the 37 soils are classified into four types bw or weak bt moderate bt strong bt and very strong bt the holocene soil at baoji contains a moderately developed bt which is interpreted to have formed under steppe forest vegetation most of the soils with bt horizons to the holocene soil are interpreted to be developed under forest and or steppe forest environments primary carbonates in most of the loess beds have been leached with the loess beds acquiring weak to strong granular structures the loess is subdivided into four types massive weakly weathered moderately weathered and strongly weathered they are believed to have mainly accumulated under steppe environments variations of monsoonal rain exhibit frequent and wide oscillations over the last 2 5 ma documented by alternations of loess and paleosol units the oscillatory pattern appears to be a function of the time interval considered

characteristics and formation mechanism of pedogenic hematite in quaternary chinese loess and paleosols abstract hematite is an important iron oxide mineral in loess paleosol sequences in northwest china samples containing hematite and related minerals in the loess and paleosol units from chinese loess plateau were investigated using powder x ray diffraction xrd scanning electron microscopy sem and high resolution transmission microscopy hrtem the results show that there are at least three genetic types of hematite in quaternary loess paleosol sequences of northern china 1 weathering products of fe bearing silicate minerals such as chlorite and biotite that precipitated as aggregates of hematite nano crystals on mineral surfaces 2 oxidation products of eolian magnetite grains with hematite nano crystals closely associated with magnetite 3 coarse silt sized hematite grains present in the fresh loess hematite with a nanoporous texture indicates that dehydration of iron hydroxide ferrihydrite is the main mechanism for the formation of hematite coating during chemical weathering of fe bearing silicates it is proposed that nano phase hematite is primarily responsible for the red color of the paleosol units paleosol layers are also characterized by higher magnetic susceptibility and increased oxidation of eolian magnetite it is proposed that the major contribution to magnetic susceptibility is from the nano phase magnetite that may be related to microbial activity this research demonstrates that the study of mineral characteristics formation mechanisms and the relationship between hematite other iron oxides and fe bearing silicate minerals helps to understand better the geochemical process in loess both before and after dust deposition in addition our study helps to explain the correlation between magnetic susceptibility and paleoclimate in northern china during the quaternary

illite in aridic soils desert dusts and desert loess abstract in some desert loess deposits notably those of central asia illite dominates the clay fraction in others such as in the near east and north africa illite is a minor component the interaction between desert loess deposits and aridic desert soils via desert dusts is used to explain the difference in illite contents vertical profile distribution of illite as well as vertical distributions of soluble and exchangeable potassium are taken to indicate that illite forms pedogenetically in the surface horizon of aridic soils once formed it is stable and accumulates it is postulated that the potassium required for the illitazation process is introduced by aeolian dusts the process is facilitated by wetting and drying cycles dusts originating in deserts where they are presently produced by desert weathering of various rocks are defined as primary or juvenile dusts they have low illite contents such are the dusts that are carried from the eastern sahara and sinai peninsula northeast towards the middle east where they form local loess deposits the central asian dusts on the other hand have been subjected to numerous cycles of deflation and deposition resulting in relatively long residence times in the pedogenic environment of aridic soils this results in the enrichment of these dusts with illite the central asian desert loess deposits that interact with these dusts are consequently enriched with illite similar processes of illite enrichment may have operated in other areas such as australia

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

environmental significance of mineral weathering and pedogenesis of loess on the southernmost loess plateau china soils derived from the loess plateau of china are regionally important and expression of the soil properties along the soil profile may be directly related to climate changes the objective of this research was to analyze the clay mineral transformation of loess from the southernmost loess plateau in relation to the pedogenesis and the regional climate changes the mineralogy of the soil profile at the site was studied by using x ray diffraction the results showed that 2 1 layer type minerals dominated with the illite in the majority throughout the profile the changes of the soil minerals were consistent with the soil genetic horizons and with the variable caco3 content particle size distribution and variations of magnetic susceptibility a relatively high vermiculite content and the presence of hydroxyl interlayered mineral him occurred in the most weathered horizon 50 150 cm corresponding to the buried palaeosol s0 formed during the optimum holocene 8400 3100 b p yr which indicated the acidic conditions with low organic matter in this period during the formation of palaeosol the expected transformation of illite and chlorite into vermiculite through the formation of mixed layers has occurred the distribution of kaolinite was uniform with depth in the palaeosol suggesting inheritance from the original eolian deposition materials generally the depotassication of illite and the degradation of chlorite were the major mineral transformation processes that occurred with soil formation calculation of the total amount of carbonate leaching of the palaeosol suggested that the annual precipitation during the optimum holocene was probably approximately to 880 mm the regional climate during the optimum holocene on the southernmost loess plateau was analogous with the modern climate conditions in the northern subtropical zone the southern slope of qingling mountains for the formation of udic luvisols brown soil however as a result of its specific pedogenic pattern the pedogenic strength of the palaeosol did not reached the level of udic luvisols brown soil the hydroxyl interlayered mineral presence in the 50 150 cm horizon only also illuminated that the palaeosol was buried rapidly by post depositional loess during the abrupt cold dry climate in the late holocene the contradiction between the type clay minerals present and the measured alkaline soil ph values in the palaeosol could be understood by the recalcification caused by the post pedogenic leaching from the overlying loess

mineral composition vs soil forming processes in loess soils a case study from krakow southern poland abstract the mineral composition of soil parent material has a clear impact on soil formation soil properties especially chemical properties and mineral transformation in soil environment despite many studies concerning loess soils detailed quantitative studies on the mineral composition and transformation of clay minerals in loess soils formed during holocene and the influence of the mineral composition of parent material on the properties of loess soils are rare the main aims of the present study were 1 to determine the influence of loess mineral composition on soil genesis and 2 to determine layer silicate transformations and clay mineral formation in loess soils in relation to soil forming processes using qualitative and quantitative x ray diffraction analyses xrd and qxrd the obtained results show that the occurrence of carbonate minerals i e calcite and their influence on chemical properties of soil play a crucial role in the evolution of loess soils in loess that does not contain carbonates dispersion and translocation of clay particles including clay minerals down the profile occur this leads to the formation of luvisols and albeluvisols in carbonate loess clay minerals and soil organic matter form stable humus mineral complexes leading to the accumulation of humus and the formation of chernozems the transformation of mica and or smectite and or vermiculite to hydroxy interlayered minerals hims is the dominant process in the studied loess soils developed in a temperate climate because intense weathering of layer silicates is possible after removal of carbonates from soil profile this indicates that the occurrence of carbonates which maintain soil ph on a level of about 7 or higher is most likely the main factor controlling the rate of weathering of layer silicates in a loess soil environment in carbonate loess the dissolution and leaching of carbonates prevail over the weathering of silicates it is highly likely that the continuous leaching of carbonates assuming that the climate will not change will lead to more intense weathering of layer silicates

the magnetic mechanism of paleosol s5 in the baoji section of the southern chinese loess plateau abstract in the central chinese loess plateau clp the magnetic susceptibility has the highest value in the s5 paleosol unit however at the southern of the clp such as in baoji the magnetic susceptibility value in the s5 paleosol unit is on the lower range of the top 6 paleosols s0 s1 s5 the studies of rock magnetism and geochemistry showed that the baoji s5 experienced a stronger pedogenesis and chemical weathering than the s3 the paleosol s3 was formed under an oxidizing environment where the maghemite and hematite are formed simultaneously maghemite is the main contributor to magnetic enhancement however the concentrations of maghemite in the s5 are lower than in the s3 with the development of pedogenesis the proportion of the maghemite component decreased in the s5 while the concentrations of anti ferromagnetic minerals mainly goethite increased in the field measurable amounts of dark brown iron manganese cutans can be observed on the cranny surface of s5 these indicate that the iron manganese elements in the s5 were assembled and pedogenesis occurred intermittently between wet and dry and strong leaching soil conditions this may have led to fine grained magnetite maghemite and hematite which were gradually converted into weak magnetic goethite therefore resulting in the lower magnetic susceptibility of s5

mechanism of palygorskite formation in the red clay formation on the chinese loess plateau northwest china abstract the morphological characteristics and microstructures of the authigenic palygorskite occurring with smectite and carbonate minerals in the late miocene red clay formation on the chinese loess plateau have been investigated with the powder x ray diffraction xrd scanning electron microscopy sem and high resolution transmission electron microscopy tem the xrd results indicate that the red clay sediments contain quartz feldspar calcite dolomite illite kaolinite chlorite palygorskite and smectite and sem analyses show that palygorskite is a common component delicate palygorskite fibers radiate from the margins of platy smectite suggesting a pedogenic origin during the weathering of pre existing smectite a process that involved intense dissolution of the smectite and an adjustment in its structure moreover palygorskite occurs as coatings pore fillings and pore bridging cements among dolomite rhombs suggesting that the fibrous palygorskite was formed by a direct dolomite precipitation from pore fluids mostly after dolomite crystallization there is evidence to show that these two mechanisms took place synchronously in the red clay formation and that the two processes are related under alkaline conditions with high ph 8 0 fluids rich in magnesium magnesium ions occupy the interlayer positions in the smectite and this results in a misfit between the mg octahedral sheet and the smectite layer thereby allowing interaction between the magnesium ions and smectite layers and a reorganization of the structure to form palygorskite then with this kind of palygorskite as a crystal nucleus more palygorskite grows through a direct chemical deposition process according to previous studies the red clay sediments experienced a steady dry warm climate with periods of high rainfall and evaporation the warm climate would have increased the rate of weathering of minerals and subsequently enhanced the ions content and ph in the soil solutions during dry periods this soil environment is favorable for smectite transformation and palygorskite deposition this study has improved our understanding of the environmental and paleoclimatic changes during the time that palygorskite formed in the arid soils of the chinese loess plateau

the ultrafine component in chinese loess and its variation over the past 7 6 ma implications for the history of pedogenesis grain size data from different climatic zones across the chinese loess plateau show that the loess generally contains an ultrafine component which has a consistent modal grain size of ca 0 center dot 37 mu m and a variable proportion of 4 to 10 the variation of the ultrafine component through a loess section is characterized by a high proportion and fine grain size in palaeosols and by a low proportion and coarse grain size in loess layers its proportional content in a stratum roughly increases from north west to south east across the loess plateau quantitative x ray diffraction analysis indicates that the ultrafine component is composed mainly of clay minerals ca 70 which are mostly illite ca 80 and with significant amounts of kaolinite ca 8 and chlorite ca 2 the temporal and spatial variations of the ultrafine component and the degree of illite crystallinity suggest that this component in aeolian sediments is linked closely to the process of pedogenesis weakly altered loess on the north western margin of the loess plateau contains considerable amounts of detrital clay minerals derived from the aeolian source areas results from a loess section with a basal age of 7 center dot 6 ma in the central loess plateau show that the ultrafine component increased from 7 center dot 6 to 5 ma and progressively decreased thereafter this trend was punctuated by two abrupt changes at 2 center dot 6 and 0 center dot 6 ma these variations reflect to a considerable extent the history of pedogenesis during the late cenozoic

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess