monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

the dole effect over the last two glacial interglacial cycles detailed measurements of 18 o of atmospheric oxygen performed on air trapped in the vostok ice cores antarctica are used to extend the record of the dole effect over two climatic cycles back to 240 kyr b p except for glacial terminations i and ii and for an unexpected minimum occurring around 175 kyr the dole effect shows small variations adole within 0 5 these small variations however show a well marked 23 kyr precessional periodicity thus confirming the results obtained by bender et al 1994a for the first climatic cycle to explain the minimum value reached around 175 kyr we invoke the possibility of a peak in the oceanic productivity linked to climatic events induced at low latitudes under glacial conditions

the formation of loess deposits in the tashkent region and parts of central asia and problems with irrigation hydrocollapse and soil erosion abstract there are large problems of irrigation hydrocollapse and soil erosion associated with the loess deposits of central asia to get to grips with these we need a clear view of the nature and formation of the loess and in this region there are still disputes and disagreements and controversies important events in the loess deposit formation process can be identified and studied and relative significances assigned there are large loess deposits in the vicinity of tashkent in the north east of uzbekistan these were mapped and studied for many years by g a mavlyanov and associates they used a terminology which appears to be based on pavlov s nineteenth century usage and developed a polygenetic formation theory for loess deposits this was a formation theory very much associated with central asia and essentially favouring a proluvial mechanism a speculative look at the deposits near tashkent allows alternative terminologies and formation mechanisms to be considered in particular the widespread soviet antipathy to aeolian deposition can be examined the deposits associated with the chirchik river upstream of tashkent might be affected by the pavlov mechanisms but could be topped by aeolian deposits the collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water in particular in central asia hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground dust clouds in eastern uzbekistan are largely loess related but in the west dust material is raised from the drying aral sea bed this is often clay mineral agglomerate material and can carry dangerous pollutants

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

pronounced changes in atmospheric circulation and dust source area during the mid pleistocene as indicated by the caotan loess soil sequence in north china the quaternary loess soil sequence in north china is of significant value for tracing variations in atmospheric circulation in this study we measured the anisotropy of magnetic susceptibility ams of the caotan ct loess soil sequence from the northeastern margin of the tibetan plateau tp and analyzed the surface textural features of quartz grains of representative samples the ams results indicate a primary sedimentary magnetic fabric without significant disturbance by pedogenesis the dec kmax values indicate a significant shift of the dominant surface wind direction from nearly n s to w e since 300 ka while the surface textural features of the quartz grains indicate an increase in the contribution from fluvioglacial sediments derived from the tp at the same time as there is no evidence of significant climatic changes around 300 ka we attribute the coeval changes of atmospheric circulation and dust source area to the uplift of the tp during the mid pleistocene and the resulting climatic cooling cooling of the tp may have led not only to the enhancement of the plateau monsoon but also to the significant accumulation of plateau glaciers which would have resulted in accelerated physical erosion of the underlying rocks thus increasing the quantity of fine grained fluvioglacial sediments to be transported to the study site

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

quaternary surface processes indicated by the magnetic fabric of undisturbed reworked and fine layered loess in hungary abstract statistical analytical methods were applied to classify the magnetic fabric of samples from different hungarian loess profiles a previous study of the anisotropy of magnetic susceptibility ams of hungarian loess suggested that typical wind blown or undisturbed and redeposited loess were well differentiated by known statistical methods the analyses of new samples require a review of previous results and the terms like typical wind blown reworked and redeposited loess the type of magnetic fabric of fine layered loess is classified by a new mathematical method in ams study of loess hierarchical cluster analysis the following quaternary surface processes were revealed by characteristics of the magnetic fabric of hungarian loess the primary magnetic fabric preserves the possible transport or accumulation direction of dust direction of maximum susceptibility ne sw axis and the structure of the fabric was affected by compaction in the case of loess the deviation of the inclination from vertical indicates the accumulation of dust on a sloping surface the secondary magnetic fabric fabric of the material after reworking or redeposition of loess shows the magnetic fabric characteristics of reworked or redeposited material scattered values of the principal susceptibilities indicate the effect of bioturbation redeposition fine layered loess samples is indicated by the alignment of the direction of maximum and intermediate susceptibilities on a stereographic plot and the degree of alignment possibly indicates the energy of the surface process lower or higher degree of energy connected to different kind of surface process can produce different kind of magnetic fabric the magnetic mineralogy of the pilot samples is determined by isothermal remanent magnetisation irm measurements no differences between loess samples with different sedimentary structure could be shown the dominant phase in the magnetic fabric that determined the magnetic character of samples was magnetite maghemite

atmospheric methane during the last four glacial interglacial cycles rapid changes and their link with antarctic temperature 1 atmospheric methane ch4 recorded in antarctic ice cores represents the closest ice proxy available for greenland temperature changes beyond times when greenland climate records are available the record over four climatic cycles from the vostok ice core offers the opportunity to study the phase relationship between greenland and antarctic climate changes through detailed ch4 profiles combining american and french analytical efforts we have improved the time resolution of the existing ch4 record from petit et al 1999 spectral analyses reveal high and low frequency variability including a strong precessional component the phase relationship between ch4 and the antarctic temperature proxy d shows a systematic lag of ch4 versus temperature by 1100 200 years on long timescales 50 400 kyr and a more complex behavior over shorter timescales i e 25 kyr suggesting that dansgaard oeschger type of climatic variability and associated interhemispheric linkage are robust features of late quaternary climate

deposit scale structural controls on orogenic gold deposits an integrated physical process based hypothesis and practical targeting implications the application of deposit scale structural targeting to orogenic gold deposits is primarily concerned with locating volumes of higher grade mineralisation ore shoots within a broader host structural system although empirical correlations between structural heterogeneities and ore shoots have long been noted and certain key physical processes elucidated no integrated system based synthesis has been previously published however linking the existing understanding with important recent advances in understanding of the dynamic physical processes of emplacement of hydrothermal ore systems now provides the opportunity to develop such a synthesis the most important of these new concepts includes the idea that deposits form in vertically extensive conduit systems linking source to sink and the related concept of the phenomena of injection driven swarm behaviour integration of all of these elements leads to the proposal of a coherent physical process based model for the structural emplacement of orogenic gold systems and the local formation of gold enriched volumes this model considers that an orogenic gold deposit must be viewed from the perspective of three different geometric elements each with a particular meaning in terms of physical process and which typically relate to different scales these elements include a the integrated swarm volume isv which is the rock volume which bounds the limits of the mineralisation hosting structural system and is effectively the geological entity that defines a deposit b fluid pathways which are 3d pathways through the isv where dynamic ore fluid emplacement has been repeatedly strongly focused and c ore shoots which are localised volumes of high grade gold deposition that are interpreted to represent volumes of anomalous dilation or second order valve sites within host fluid pathways consideration of this new framework suggests significant potential to improve the effectiveness of structural targeting at the deposit scale in particular ore shoots are only expected within fluid pathways and equivalent dilatant zones outside such pathways are predicted to be barren a key theme is that the rheological architecture of the host rock mass is the most important predictive input to targeting both at the scale of emplacement of the ore hosting conduit system and the scale of localised ore shoots

early proterozoic aucou mineralization in the kuusamo district northeastern finland abstract the kuusamo volcano sedimentary belt is part of an early proterozoic rift system in the fennoscandian shield extending from the norwegian sea to lake onega the rocks range in age from 2 5 to 2 0 ga sulphide deposits are confined to the two lowermost sedimentary units the sericite quartzite and siltstone formations these are intruded by albite diabase and syenite dikes and sills the mineralization is associated with pervasive hydrothermal alteration spilitization and albitization predate mineralization and appear to be premetamorphic the later fe mg silicate and k silicate alteration is associated with mineralization in ductile shear zones whereas carbonatization and silicification dominate in brittle zones ore deposits and occurrences can be divided into three groups uranium deposits co au u bearing sulphide deposits and fe sulphide deposits uranium deposits are of the sulphide poor stratiform sandstone type often associated with an albitization front the u deposits are also related to albite diabase dikes and alkaline granitic intrusions the co au u deposits can be subdivided into two end members replacement ores in a ductile deformation zone and breccia ores in a brittle deformation zone at juomasuo the sulphide mineralization is located in a fe mg silicate and k silicate alteration zone within a ductile shear zone surrounded by a wide albitized zone the ore reserves are 1 mt grading 5 6 g t au and 0 2 co other enriched elements are cu u w mo se te and bi the konttiaho deposit represents a breccia ore in a brittle deformation zone where the co au u mineralization is associated with carbonate and quartz within albitized country rocks typical ore minerals in both types are pyrite pyrrhotite cobaltite co pentlandite chalcopyrite uraninite molybdenite scheelite gold and tellurides the fe sulphide deposits are similar to the co au u deposits but lack precious metals sulphide mineralization is epigenetic post peak metamorphic and related to the svecokarelian orogeny at 1 8 1 9 ga the mineralization is controlled by stratigraphy antiform structures and shear zones in the central part of the volcano sedimentary belt the broad elemental spectrum suggests a complex origin and probably a deep seated source for the metals

late quaternary glacial history of the karlik range easternmost tian shan derived from 10be surface exposure and optically stimulated luminescence datings abstract the karlik range located in the easternmost part of the tian shan is a key area in reconstructing paleoclimate in central asia but few studies have been conducted to constrain the timing and extent of quaternary glaciations in its highlands we investigated the late quaternary glacial history in the turgan valley on the northern slopes of the karlik range using cosmogenic 10be surface exposure and optically stimulated luminescence osl dating techniques four major glacial events were dated to 0 79 0 59 ka little ice age lia 15 8 1 6 ka lateglacial 37 4 4 0 44 2 4 3 ka marine oxygen isotope stage mis 3 and 60 2 3 3 79 3 5 2 ka mis 4 or older with a pattern of continuously restricted glaciations after mis 4 this glacial chronology is consistent with the studies from other parts of the tian shan the overall pattern of glaciations across the tian shan suggests that change in precipitation brought by the westerlies was the primary factor influencing the timing and extent of glacial advances during the last glaciation however lower temperature of the karlik range affected by the siberian high may counteract the effect of lower precipitation to drive a relatively extensive glacial advance in the easternmost tian shan

pronounced changes in paleo wind direction and dust sources during mis3b recorded in the tacheng loess northwest china abstract central asia loess deposits can yield detailed records of aridification across the asian interior as well as the atmospheric circulation in this study we presented grain size heavy mineral assemblage rock magnetism and anisotropy of magnetic susceptibility of a loess section in the tacheng basin in xinjiang region nw china the results of anisotropy of magnetic susceptibility indicated that a near surface se wind prevailed in the tacheng area since marine isotope stage mis 3 while a near surface sw prevailing wind developed during mis3b we inferred that the change of wind direction was due to glacial advance during mis3b combining the result of anisotropy of magnetic susceptibility with grain size heavy mineral assemblage data and previously published low field mass susceptibility revealed that dust transported by the near surface sw wind had a greater ability to enhance magnetic susceptibility and higher amphibole epidote ratio additionally a strong siberian high during heinrich event h 5 at ca 48 ka blocked the advection of moisture into the region via mid latitude westerlies causing glacial recession and the weakening of the prevailing sw wind our study has implications for identifying changes in paleo wind direction and dust source which can aid understanding of the influence of westerlies and the siberian high on dust accumulation as well as their interactions

aeolian dust dynamics in central asia during the pleistocene driven by the long term migration seasonality and permanency of the asiatic polar front loess paleosol sequences preserve detailed archives of climate change reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere the detailed investigation of particle size distributions psds of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics the central asian loess belt offers the potential to reconstruct pleistocene atmospheric circulation patterns along an adjacent west east transect within interior eurasia through granulometric studies in this study we present the aeolian dust record of the loess sequence at remisowka se kazakhstan which reflects a detailed signal of glacial interglacial climate and atmospheric dynamics in central asia on the basis of radiocarbon and amino acid geochronologic data long term semicontinuous trends in the aeolian dust record of the last glacial cycle are observed and interpreted to reveal their paleoclimate signal in consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central asia it is likely that the observed trends reflect the long term migration seasonal duration and permanency of the polar front during the late pleistocene previously published models which focused on the reciprocal glacial interglacial influence of the zonal westerlies and the asiatic high on the aeolian dust transport in central asia were overly simplified and should be modified to include the major influence of the asiatic polar front as the polar front activity is intimately connected with the development and position of the interhemispherically active high level planetary frontal zone hpfz the presented data give insight to long term aeolian dust dynamics and climate variability of interior eurasia which are linked with interhemispheric climates

glacial geomorphology and glacial history of the muzart river valley tianshan range china abstract the muzart river originates on the southeastern slope of tumur peak the largest center of modern glaciation in the tianshan range glacial landforms and sediments indicate that there are four major quaternary glaciations in this drainage the glacial landforms contain considerable information about the changes of the ancient glaciers dating the landforms allows the temporal and spatial variations of the ancient glaciers in this valley to be understood and provides essential information in reconstructing the paleoenvironment in this region electron spin resonance esr dating of a well exposed section the multiple end moraines of the pochengzi glaciation the third set of moraines and the local outwash and fluvial sediments on the kezibulake glacial plain the fourth set of moraines was carried out using germanium ge centers in the glacial quartz grains which are sensitive to both sunlight and grinding eleven depositional ages have been determined based on the dating results the principle of superposition and the glaciations pattern reported in the adjacent valley the pochengzi end moraines were determined to be deposited during the major glacial intervals that are equivalent in age to marine oxygen isotope stages mis 2 mid mis 3 and mis 4 and the kezibulake glacial deposits were determined to be equivalent in age to mis 6 furthermore the tugaibieliqi end moraine the second set of moraines was deposited during the neoglaciation a cold period between 3 and 4 ka and the 3 4 end moraines located at the terminuses of the modern glacier were deposited during the little ice age the ages of the pochengzi glacial deposits can be subdivided into three clusters they are 13 6 25 3 ka 39 5 40 4 ka and 64 2 71 7 ka respectively the largest local last glacial maximum lgm l occurred during mis 4 rather than the global last glacial maximum lgm g of mis 2 furthermore a glacier that is slightly larger than that of mis 2 developed in this drainage during mid mis 3 the ancient muzart glaciers were compound valley glaciers during the neoglaciation mis 2 and mid mis 3 and piedmont glaciers during mis 4 and mis 6

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

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

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

the chinese loess in xifeng ii a study of anisotropy of magnetic susceptibility of loess from xifeng summary measurements of specimens from the loess profile of xifeng gansu province china all show original magnetic fabric for sediments i e nearly horizontal foliation and the commonly oblate magnitude ellipsoid the degree of anisotropy always shows a strong correlation with the foliation f rather than with the lineation l specimens from wind blown loess redeposited water lain loess and red clay show their own distribution areas respectively in a diagram of l versus f magnetic fabric provides evidence for the suggestion that the red clay like the overlying wind blown loess is aeolian in origin the data points from the red clay all falling within the distribution area of the wind blown loess data points the magnetic fabric measured from present day palaeosols may still represent the features of the parent loess although the orientation of fabric has been slightly weakened through pedogenesis as shown in the present study

grain size dependent geochemical characteristics of middle and upper pleistocene loess sequences from the junggar basin implications for the provenance of chinese eolian deposits abstract thick loess paleosol sequences are widely distributed in the arid inland basins of northwestern china the geochemical composition of these sediments provides important constraints on the provenance of chinese eolian deposits however grain size dependent geochemical characteristics of early middle pleistocene loess deposits from these arid inland basins have not been investigated the paucity of such studies hinders a full understanding of provenance changes of loess deposits from the chinese loess plateau clp in the present study we performed a detailed major trace and rare earth element analysis of multiple grain size fractions of middle pleistocene loess deposits from the dongwan section dw in the junggar basin we found that the major trace and rare earth element concentrations of the dw loess are grain size dependent with higher concentrations in the fine fraction in addition the 75 m from the dw section changed significantly at 0 5 ma which may have arisen from intensified physical erosion or increased wind speeds in the northern tianshan area

magnetic characteristics of loess paleosol sequences in tacheng northwestern china and their paleoenvironmental implications abstract systematic rock magnetic data including magnetic mineralogy and magnetic concentration magnetic susceptibility laboratory induced magnetic remanences are presented from the loess paleosol sequences in tacheng northwestern china to explore the specific paleoenvironmental significance of magnetic characteristics in the xinjiang loess results show that ferrimagnetic minerals such as magnetite and maghemite dominate the magnetic properties in the tacheng tc section similar to the magnetic mineralogy of loess deposits in the chinese loess plateau clp the magnetic particles in the tc section are characterized by multi domain md and pseudo single domain psd behavior representing the detrital primary mineral phase the absolute contents of pedogenic ultrafine superpara sp ferrimagnetic particles are very low in the tc section indicating that pedogenesis has a limited contribution this is quite different from the magnetic enhancement of loess deposits in the clp variation of magnetic susceptibility and median grain sizes could be interpreted by the predominance of paleowind intensity as well as provenance variation a similar pattern was also found in other places in xinjiang such as talede section in yili basin and bole section in the western tianshan our results suggest that variation of detrital inputs might have played a pivotal role in the enhancement of magnetic susceptibility while pedogenesis was probably responsible for the increase of finer single domain sd particles in paleosol units the arm sirm ratio could serve as an indicator for reflecting the degree of pedogenesis in xinjiang loess

the agh band loess palaeosol sequence a terrestrial archive for climatic shifts during the last and penultimate glacial interglacial cycles in a semiarid region in northern iran abstract the northern iranian loess profiles host important information on quaternary climate and palaeoenvironmental changes in the region they build an important link between the eurasian loess belt and european and central asian archives due to a climatic gradient with decreasing precipitation from the west to the east and from the south to the north loess palaeosol sequences formed synchronously under different climatic conditions can be studied over short distance in the iranian caspian lowland the agh band profile is located in the so called iranian loess plateau a semi arid region with 200 350 mm annual precipitation the loess deposits at agh band reach a thickness of 60 m an about 50 m thick step profile was prepared and the litho pedostratigraphy was investigated samples for laser diffractometry grain size measurements were taken every 2 cm the magnetic susceptibility was measured in 4 cm intervals and the caco3 content in 8 cm intervals to establish a chronological framework a pirir290 luminescence dating approach was applied to the 4 11 m polymineral fraction the results show that the agh band profile yields a climate archive reaching from mis 7 to mis 2 several chronological hiatuses of some 10 ka show that periods of intense loess accumulation were interrupted by phases of only minor loess sedimentation and or erosion the agh band profile is subdivided by several shifts in grain size distribution the coarsening and fining up trends correlate with increasing and decreasing wind velocity respectively in the central part of the agh band loess sequence a weakly developed palaeosol is preserved which was developed at around 80 ka furthermore the loess deposits formed from about 100 ka to 60 ka ago show banded structures a pedocomplex including two well developed palaeosols consisting of bw y horizons and a cb horizon as well as intercalated loess can be found in the lower part of the sequence also evidenced by the increased values of magnetic susceptibility the corresponding luminescence age estimates indicate that the palaeosols represent a period of increased humidity and landscape stability during late mis 7 and mis 6 hence in the agh band loess various changes in the palaeo sedimentary system triggered by changes in climate can be observed this yields important information on the sensitive response of sedimentary systems and landscapes within semi arid regions to shifts in moisture and possibly temperature

characteristics of pleistocene climate cycles identified in cerna valley loess paleosol section vertesacsa hungary abstract a climate cycle model was calculated using different methods e g paleomagnetic sedimentological and heavy mineral studies on the loess sequence containing four paleosol and five loess layers in cerna valley the model is based on the development of the sediment sequence created by the influence of the climatic geological and geomorphological phenomena and contains the following cycles the homogeneous non laminated loess was developed during the semiarid 350 400 mm y and cold periods in the pleistocene the magnetic fabric was built up by multidomain ferromagnetic minerals and reflects the direction of dust deposition or and the paleoslope the accumulation period of dust was followed by a more humid 650 mm y pedogenic period indicated by the enrichment of superparamagnetic minerals and by the disturbed or inverse magnetic fabric developed during pedogenesis by different processes e g leaching bioturbation the third period following the pedogenic period is a humid erosional phase indicated by the fine layered reworked loess the magnetic fabric built up by multidomain ferro and superparamagnetic minerals was characterized by better aligned directions of principal susceptibilities than in the wind blown material sheet wash and other water logged surface processes appeared in the fabric of these layers this process is possibly connected to non periodic sudden events with high precipitation and absence of the vegetation the next cycle started with the following dust accumulation period

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

magnetic fabric of loess and its significance in pleistocene environment reconstructions abstract a summary of approximately three decades and greater than thirty loess magnetic fabric studies is presented here the revised studies cover various loess regions from the chinese loess plateau across the european loess belt to alaska although there is still an ongoing argument about the feasibility of the magnetic fabric of loess in paleowind reconstructions the determination of prevailing wind direction during various periods of the pleistocene is the main goal of magnetic anisotropy analysis of the revised loess successions the magnetic fabric analysis of loess from chinese loess plateau provided significant information about the characteristics of paleomonsoon in east asia and the results from other loess regions such as alaska the european loess belt and siberia are also promising as it is shown in this review the synthesis of the paleowind direction results from the studied profiles may already provide a significant foundation for future climate models by the reconstruction of key climate centres and main continental level wind tracks besides the reconstruction of prevailing paleowind directions there are numerous loess magnetic fabric studies using magnetic anisotropy parameters in the reconstruction of the characteristics of long term climate trends climate transitions and glacial interglacial cycles there are some lesser known aspects contributing to magnetic fabric of loess such as the influence of various types of magnetic contributors on the overall fabric i e the study of sub fabrics and their role in environment reconstruction besides the identification of aeolian magnetic fabric not so many studies focus on the magnetic anisotropy characteristics of materials possibly developed by water lain sedimentation pedogenesis mass movements and permafrost activity novel results from hungarian loess especially from paks connected to some of the latter topics are also presented such topics includes the analysis of the nanofabric in paleosols developed by pedogenesis the comparison of magnetic fabric formed during high energy transportation by aeolian or aquatic agents and the periodicity analysis of magnetic parameters during the early middle pleistocene new research lines introduced in this review may inspire new researches and provide new perspectives for the next generation of magnetic anisotropy studies of loess successions

evaluating the timing of former glacier expansions in the tian shan a key step towards robust spatial correlations the timing of past glaciation across the tian shan provides a proxy for past climate change in this critical area correlating glacial stages across the region is difficult but cosmogenic exposure

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

a new paleoprecipitation proxy based on soil magnetic properties implications for expanding paleoclimate reconstructions description of precipitation patterns and changes in the hydrological cycle during periods of past global change is crucial for providing an understanding of terrestrial climate systems and for predicting impacts of future climate change such as shifting water availability while a number of proxies and climofunctions exist for reconstructing paleoprecipitation using paleosols all of the available tools for reconstructing paleoprecipitation are either limited to certain precipitation ranges effective only for low precipitation regimes e g depth to bk chemical index of alteration cia k or are relevant only to a limited range of paleosols single pedotype relationships e g calcium magnesium index calmag here we measure the acquisition of isothermal remanent magnetization in b horizons of modern soils to quantify the ratio of pedogenic magnetic minerals goethite and hematite and we use the relationship between these soil magnetic properties and measured climatic variables at each soil site to derive a new quantitative proxy for precipitation by compiling both literature derived and measured goethite hematite g h ratios and mean annual precipitation estimates for a global suite of modern soils n 70 we describe a strong linear relationship r 2 0 96 between the g h ratios of soil b horizons and mean annual precipitation that can be used to estimate paleoprecipitation values for a wide range of climatic regimes 100 3300 mm yr 1 and soil types inceptisols alfisols ultisols oxisols mollisols aridisols spodosols we tested the new climofunction using paleosols from the early eocene of wyoming which show that estimates based on g h ratios compare favorably to and expand upon previously published estimates based on paleosol data

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

size differentiated ree characteristics and environmental significance of aeolian sediments in the ili basin of xinjiang nw china abstract aeolian loess in the ili basin is an important geological archive for studying the changes in paleoclimate and sources of dust particles size differentiated rare earth elements ree may help to distinguish potential dust sources this study investigates the size differentiated ree characteristics from three sites including the zhaosu loess and the kekdala desert sediments from the ili basin and the chaona loess from the chinese loess plateau clp our results show that the patterns of variation of the ree characteristics in different size fractions can act as improved source tracers for aeolian sediments moreover the ree characteristics of the

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

quaternary glacial chronology of the ateaoyinake river valley tianshan mountains china abstract the ateaoyinake river originates on the southern slope of the tumur peak the largest center of modern glaciation in the central tianshan mountains in china six sets of moraines and associated glacial sediments are well preserved in the ateaoyinake river drainage recording a complex history of quaternary glacial cycles and landscape evolution dating the landforms allow the temporal and spatial shifts of past cryosphere and climate to be determined dating of the tills and outwashes was undertaken with electron spin resonance esr and optically stimulated luminescence osl two osl ages date outwash and till to 7 3 0 8 ka and 12 3 1 2 ka respectively the esr ages date six sets of moraines to 3 4 ka 14 27 ka 40 54 ka 55 62 ka 134 4 12 6 ka and 219 7 20 5 ka 440 6 41 7 ka if these are correct ages of deposition they suggest that glaciers advanced during the neoglacial and during marine oxygen isotope stages mis 2 3b 4 6 and 12 the mis 3b moraine was created by a glacier nearly as large as or possibly larger than those of the global last glacial maximum of mis 2 the oldest till belongs to the qingshantou glacial stage its single age is consistent with two published esr ages 459 7 46 and 471 1 ka from the gaowangfeng till near the headwaters of the urumqi river in the eastern tianshan mountains these dates suggest that the central and the eastern segments of the tianshan mountains were high enough to be glaciated by mis 12 the geochronology of the glacial landforms in this valley is the first step towards understanding glacial and landscape evolution in this region furthermore this geochronology and previously published geochronology near the headwaters of the urumqi river provide a temporal framework for examining the rates of landscape evolution in the glaciated regions of the tianshan mountains

the upwelling area off northwest africa a description of phenomena related to coastal upwelling abstract this paper presents a brief review of the oceanography along the upwelling coast of northwest africa the description contains information on seasonal variations of large scale winds ocean circulation and some gross of features of the hydrography characteristic meso scale patterns of currents during the upwelling season between 16 n and 26 n air and water temperature differences during upwelling season diurnal and semi diurnal variations of temperature atmospheric pressure wind and current regional peculiarities canyons and the banc d arguin

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

heavy mineral assemblages and sedimentation rates of eastern central asian loess paleoenvironmental implications abstract central asian loess deposits record the evolution of aridification across the asian interior however paleoclimatic proxies are strongly influenced by the variation of the dust source and accumulation process in order to decipher the paleoenvironmental changes a sensitive paleoclimatic proxy with clear source and accumulation process will be needed in this study heavy mineral assemblages and sedimentation rates were investigated in a 30 kyr loess section in the ili basin xinjiang northwestern china during marine isotope stage mis 2 trends in dust sedimentation rate were similar to those of the chinese loess plateau clp in anti phase with northern hemisphere summer insolation nhsi at 65 n amphibole epidote ratios contents and mean grain size were low during cold phases such as the late last glacial maximum lgm and heinrich event h 1 their ratios were higher during adjacent warm periods this was attributed to aeolian sorting during transportation namely greater sorting between amphibole and epidote occurred in warmer phases and weaker sorting occurred in colder phases the amphibole epidote ratio could serve as a proxy for wind intensity and thus the siberian high sh intensity amphibole epidote ratio was a more appropriate proxy to record wind intensity than dust sedimentation rate which was also influenced by sediment availability a higher amphibole epidote ratio corresponded to a more negative east asian stalagmite 18o indicating an anti phase relationship between the sh and east asian summer monsoon easm during the mis 2

relation between low latitude insolation and δ18o change of atmospheric oxygen for the last 200 kyrs as revealed by mediterranean sapropels the isotopic ratio of atmospheric o2 18oatm deduced from ice cores displays large fluctuations during climatic cycles these are caused principally by changes in the oxygen isotopic ratio of sea water 18osw and changes in the biosphere and in the hydrological cycle as both 18oatm and 18osw coincide closely over the last 135 kyr bp it is generally believed that 18oatm is driven mainly by 18osw here we focus on the major discrepancy which arises between those two signals during the prior isotopic glacial stage 6 around 175 kyr bp discrepancy which calls into question the role of changes in 18osw as the driving mechanism for 18oatm we present arguments based on the occurrence and pollen content of mediterranean sapropels for another source of the 18oatm change insolation at low latitudes via hydrosphere biosphere activity

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

a synthetic pollen record of the eastern mediterranean sapropels of the last 1 ma implications for the time scale and formation of sapropels abstract the quaternary climate of southern europe south italy and greece is investigated by pollen analysis of the sapropels which were deposited in the deep eastern mediterranean sea during the last 1 million year ma the time scale of core kc01b in the ionian sea has been established by tuning its oxygen isotopic record to the ice volume model of imbrie and imbrie 1980 for the last 250 000 year 250 ka the previous pollen studies and astronomical tuning have been confirmed sapropels were deposited under a large range of mediterranean climates fully interglacial fully glacial and intermediary as revealed mainly by the balance between the respective pollen abundances of oak quercus and sage brush artemisia the high value of the oak reveals the warm and wet climate of an interglacial and the high value of the sage brush the dry and cold climate of a glacial whereas the mediterranean climate is directly related to the variation of the high latitude ice sheets the deposition of sapropels is not so in contrast with the wide climatic range sapropels were deposited only when summer insolation in the low latitudes reached its highest peaks however between 250 ka and 1 ma that stable pattern is not yet established only six sapropels are observed many expected ones do not appear even as ghosts signalled by peaks of barium abundance that remain after the post deposition oxidation of organic matter the pattern of sapropel formation in stable and direct relationship to highest insolation does not seem to apply for five of those sapropels neither climate extremes are observed they mainly formed during intermediary types of mediterranean climate in contrast one sapropel and one ghost relates to a relatively low peak of insolation and its climate is of a unique composite type not seen later this might suggest an unsuspected more complex pattern linking the formation of mediterranean sapropels to the astronomical configuration

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

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

palaeowind directions and sources of detrital material archived in the roxolany loess section southern ukraine abstract measurements of the anisotropy of whole rock magnetic susceptibility ams and u pb ages of detrital zircons have been combined to define the palaeowind directions and sources of wind blown dust in the loess palaeosol key section at roxolany southern ukraine zircon dating has also been used to determine the age and provenance of the interbedded roxolany tephra the distribution of ams axes in the loess indicates that the prevailing wind during its accumulation blew from the north west the same as the mean present day summer wind direction measured in the nerby city of odessa the u pb isotopic ages of the detrital zircons mostly range between 0 25 and 2 ga with clusters at 0 28 0 32 0 45 0 58 1 0 and 1 5 ga single neoarchean grains ca 2 7 ga were also found these ages indicate that material from carpathian and podolian sources formed the roxolany loess this material initially was transported by the dniester river then was wind blown form the dniester liman and the lower dniester valley located nw of roxolany most of the pyroclastic zircons from the roxolany tephra gave ages of 470 840 ka with a peak between 500 and 750 ka this age range is consistent with their being derived from the ciomadul volcano in romania

asian monsoon variation over the late neogene early quaternary recorded by anisotropy of magnetic susceptibility ams from chinese loess this paper discusses the anisotropy of magnetic susceptibility ams records during late neogene to early quaternary from the lantian loess section near the southern margin of the chinese loess plateau the ams results for this site are shown to reflect variations in the direction of the paleomonsoon the lantian loess sediments are largely aeolian in origin but also include a thin layer that exhibits secondary aqueous depositional features the major ellipsoid axis ams orientations in the loess samples indicate a pervasive northwest southeast directional component since the late neogene since that time the w e component gradually overtakes the n s component which may explain the trend toward increased aridity during that time finally a local heavy rainfall event seemingly occurred in the lantian region about 2 6 ma which may have been responsible for the aqueous redeposition of sediments observed in l33 layer in this study

climatic conditions during marine oxygen isotope stage 6 in the eastern mediterranean region from the isotopic composition of speleothems of soreq cave israel at several times during marine oxygen isotope stage 6 the eastern mediterranean region was influenced by two extreme climatic systems the large ice sheet over northern europe and the wet tropics associated with african monsoons during this interval two major climatic events occurred in the region the sapropel s6 layer formed ca 176 ka in the eastern mediterranean basin owing to the increase in the african monsoon and another event although not large enough to form sapropel occurred ca 151 ka the isotopic composition of soreq cave speleothems seems to record these events as very low 18 o 13 c values dated as ca 178 and 152 ka the very low 18 o 13 c values of 6 and 11 to 12 respectively are typical of interglacial intervals but here they were recorded during a glacial interval such low peaks indicate that in this part of the eastern mediterranean region i e israel the rainfall amount increased dramatically moreover the isotopic record of the speleothems also shows that during the entire stage 6 although the climate was as cold as much of the last glacial the conditions were never as dry

application of anisotropy of magnetic susceptibility ams for the determination of paleo wind directions and paleo environment during the accumulation period of bag tephra hungary abstract this study provides the first application of anisotropy of magnetic susceptibility ams measurements for the study of pleistocene wind directions and the environment during the deposition of dust and lithifaction of loess in the carpathian basin a total of 67 samples were taken from seven loess paleosol outcrops to test this method on loess paleosol sequences the samples were collected from the loess overlying the bag tephra a characteristic marker horizon of the middle pleistocene age in the hungarian loess sequences statistical analysis of ams is a good tool to distinguish between redeposited and the undisturbed loess the first measurements indicated a n ne s sw direction dust transport in two outcrops when the principal susceptibilities were placed into a stereographic projection the effect of local slope proved to be important in determining the magnetic fabric the ams results were completed by isothermal remanent magnetization irm measurements to determine the main magnetic mineral components of the samples the dominant magnetic mineral which determines the ams character of the sample was magnetite or maghemite

grain size distribution of pleistocene loess deposits in northern iran and its palaeoclimatic implications abstract the loess deposits in northern iran are located in a key region connected to the european and central asian loess belts however the lack of previous detailed sedimentological and palaeoclimatic studies of the pleistocene loess in the region limits our understanding of the nature of ancient aeolian processes and loess history in the mid latitudes of euro asia as a whole here we present the results of grain size analyses of the pleistocene loess from the so called iranian loess plateau ilp in northern iran our results reveal that the grain size distribution of the deposits is characterized by trimodal and bimodal distributions comprising a dominant well sorted coarse dust component ca 7 75 m a small poorly sorted fine dust component ca 2 7 m and a minor pedogenic clay component

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

phase lag between intertropical convergence zone migration and subtropical monsoon onset over the northwestern indian ocean during marine isotopic substage 6 5 mis 6 5 high resolution faunal and isotopic analyses of foraminifera were performed on core md96 2073 10 94 n 52 62 e 3142 m depth located close to socotra island in the upwelling area of the somali basin nw indian ocean this work focuses on marine isotopic stage 6 5 in order to reconstruct paleo upwelling changes and their links with the arabian sea summer monsoon and the migration of the intertropical convergence zone itcz correspondence and cluster analyses of planktonic foraminiferal abundances partly controlled by temperature and water mass productivity together with an upwelling intensification index show the occurrence of a strong upwelling between 176 and 165 ka this upwelling intensification responds to a northward migration of the itcz an isotopic depletion in the planktonic foraminifera 18o records occurring between 180 and 167 ka is interpreted as proof of a large salinity decrease in the surface waters probably linked to a strong input of fresh rainfall waters induced by an intense monsoon activity the lag between the onset of upwelling intensification and the strong monsoonal impact over the same area suggests a decoupling between both phenomena the migration of the itcz is influenced by obliquity and precessional forcing while the arabian sea summer monsoon precipitation depends only on precessional forcing

structural controls and evolution of gold silver and ree bearing copper cobalt ore deposits blackbird district east central idaho epigenetic origins the cu co au ag ni ree ore deposits of the blackbird district east central idaho have previously been classified as besshi type vms sedex and iocg deposits within an intact stratigraphic section new studies indicate that across the district mineralization was introduced into the country rocks as a series of structurally controlled vein and alteration systems quartz rich and biotite rich veins and alteration zones and minor albite and siderite veinlets maintain consistent order and sulfide mineral associations across the district both early and late quartz veins contain chalcopyrite and pyrite whereas intermediate stage tourmaline biotite veins host the cobaltite barren early and late albite and late carbonate generally siderite form veins or are included in the quartz veins ree minerals principally monazite allanite and xenotime are associated with both tourmaline biotite and late quartz veins the veins are in mineralized intervals along axial planar cleavage intrafolial foliation and shears mineralized intervals are hosted by a variety of metasedimentary rocks including three phyllitic units of mesoproterozoic age and two schistose units all of these units are s tectonites in the footwall of a regional thrust fault specifically the district lies within an oblique thrust ramp containing a series of structural horses three domains in a duplex system the deposits span the three domains and are hosted by metamorphic rocks that range from lower amphibolite facies in the structurally upper domain to lower middle greenschist facies in the lower domain an inverted metamorphic sequence early quartz and biotite veins were introduced during progressive folding and prolonged peak metamorphic conditions and they underwent late tectonic retrograde recrystallization and metamorphic mineral growth to the same extent as the country rocks in each domain where little subsequent deformation occurred early veins are discordant to bedding but where folding was polyphase and fabrics are penetrative mineralized zones are concordant with metamorphic compositional layering late quartz veins in the zones are associated with retrograde minerals and textures and are only locally deformed 40 ar 39 ar dating of unoriented muscovite from the selvage of a late quartz vein yields a late cretaceous age of about 83 ma the time of retrograde metamorphism associated with introduction of late quartz veins textural data at all scales indicate that the host sites for veins and the tectonic evolution of both host rocks and mineral deposits were kinematically linked to late cretaceous regional thrust faulting heat fluids and conduits for generation and circulation of fluids were part of the regional crustal thickening the faulting also juxtaposed metaevaporite layers in the mesoproterozoic yellowjacket formation over blackbird district host rocks we conclude that this facilitated chemical exchange between juxtaposed units resulting in leaching of critical elements cl k b na from metaevaporites to produce brines scavenging of metals co cu etc from rocks in the region and finally concentrating metals in the lower plate ramp structures although the ultimate source of the metals remains undetermined the present cu co au ag ni ree blackbird ore deposits formed during late cretaceous compressional deformation

cryptic post depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility abstract our anisotropy of magnetic susceptibility ams investigation of the gold hill steps ghs2 and halfway house hh3 loess and paleosol profiles in central alaska confirms that post depositional reworking of loess at gold hill steps has taken place and of greater importance identifies the reworked depth intervals in ghs2 the majority of the loess below 7 80 m depth has been reworked the loess at the halfway house site is as stated in the literature a predominantly undisturbed aeolian deposit however we have identified two intervals that have been reworked in hh3 we infer from the depth variation of the ams orientation distribution at ghs2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations permafrost loess behaved 1 as impermeable layers focusing and channeling flow most likely that of groundwater and 2 as rigid bodies undergoing rotations and lateral translations a modern analogue of focused flow by an impermeable layer is identified at hh3

climatic and atmospheric circulation pattern variability from ice core isotope geochemistry records altai tien shan and tibet several firn ice cores were recovered from the siberian altai belukha plateau central tien shan inilchek glacier and the tibetan plateau zuoqiupu glacier bomi from 1998 to 2003 the comparison analyses of stable isotope geochemistry records obtained from these firn ice cores identified the physical links controlling the climate related signals at the seasonal scale variability the core data related to physical stratigraphy meteorology and synoptic atmospheric dynamics were the basis for calibration validation and clustering of the relationships between the firn ice core isotope geochemistry and snow accumulation air temperature and precipitation origin the mean annual accumulation in water equivalent was 106 g cm 2 a 1 at inilchek glacier 69 g cm 2 a 1 at belukha and 196 gc m 2 a 1 at zuoqiupu the slopes in regression lines between the d 18 o ice core records and air temperature were found to be positive for the tien shan and altai glaciers and negative for southeastern tibet where heavy amounts of isotopically depleted precipitation occur during summer monsoons the technique of coupling synoptic climatology and meteorological data with d 18 o and d excess in firn core records was developed to determine climate related signals and to identify the origin of moisture in altai two thirds of accumulation from 1984 to 2001 was formed from oceanic precipitation and the rest of the precipitation was recycled over aral caspian sources in the tien shan 87 of snow accumulation forms by precipitation originating from the aral caspian closed basin the eastern mediterranean and black seas and 13 from the north atlantic

late quaternary glaciation in the kyrgyz tien shan the tien shan of kyrgyzstan contains multiple moraines and drift from late quaternary glaciations the spatial temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture the dominant modern climatic signatures in northern central asia include orographic thunderstorms in summer cold and dry siberian high pressure cells in winter and westerly cyclonic storms from the north atlantic and eastern mediterranean in spring and fall changes in any of these systems during the late quaternary would have varied precipitation delivery to and glacier growth in the kyrgyz tien shan geomorphic mapping and reconnaissance level 10be cosmic ray exposure dating of moraine sequences in six drainages indicate that there were multiple maximum advances of similar extents and equilibrium line depressions across the range glaciers in the north and east of the kyrgyz tien shan last advanced to their maximum positions during marine oxygen isotope stage mis 5 and again during mis 4 while in the south and west of the range advance occurred during mis 3 in contrast to maritime europe and north america there is no evidence of a major glacial advance during mis 2 glacier advances during mis 2 and since were restricted to the vicinity of modern glaciers allowing the older glacial record to be preserved well

millennial scale oscillations of the westerly jet path during the last glacial period abstract it has been established that east asian summer monsoon intensity varies with dansgaard oeschger cycles suggesting a connection between the climates of east asia and the north atlantic on a millennial timescale however the dynamics of such a connection are still unsolved here we demonstrate that temporal changes in the provenance of aeolian dust in japan sea sediments which we interpret to reflect changes in the westerly jet path over east asia exhibit variations in harmony with dansgaard oeschger cycles the dominance of dust with a mongolian gobi provenance during stadials suggests a westerly jet axis located to the south of the himalaya tibetan plateau throughout most of the year whereas the co dominance of dust from both the taklimakan desert and the mongolian gobi during interstadials suggests that the westerly jet axis jumped to the north of the tibetan plateau at latest in summer as the shift of the westerly jet axis to the north of the tibetan plateau is closely related to the onset of the east asian summer monsoon changes of the westerly jet path apparently critically affect the teleconnection between the climates of asia and north atlantic on a millennial timescale

loess stratigraphy of central asia palaeoclimatic and palaeoenvironmental aspects abstract the loess palaeosol succession of central asia is comparable with that of the loess plateau in north china palaeomagnetic investigations and palaeontological studies in south tadjikistan suggest a date of 2 2 5 ma for the oldest loess indicating that dust storms became frequent in the region since 2 2 5 ma bp under the prevalently arid and semi arid environments of central asia aeolian processes had a gradually increasing influence on subaerial sedimentation during the pleistocene however atmospheric aeolian processes in central asia have mainly developed in accordance with pleistocene climatic cyclicity without extremely high intensification during the late pleistocene as implied by the previous tl dating results the identification of loess and palaeosol horizons with respective glaciations and interglacials is sometimes disputable nevertheless the available data in spite of limited evidence characterise well developed palaeosols of the middle and late pleistocene as warm and wet intervals associated with interglacials palynological studies of loess sections show that loess and palaeosol horizons have palynological spectra that are sometimes difficult to interpret interregional loess palaeosol correlation with glacial interglacial events as well as with oxygen isotope records should be supplied by multidisciplinary investigations

timing and extent of quaternary glaciations in the tianger range eastern tian shan china investigated using 10be surface exposure dating abstract reconstructing glacial chronologies with consistent methods is critical for efforts to examine the timing and pattern of past climate change cosmogenic 10be surface exposure dating has been widely used to constrain the timing of glacial events on the tibetan plateau and in central asia however few such studies have been conducted in the chinese tian shan and available 10be ages from this region have only provided evidence for glacial events during the global last glacial maximum glgm and lateglacial here we present 45 10be surface exposure ages from glacial landforms in the ala and daxi valleys two formerly glaciated valleys draining the tianger range eastern tian shan combined with previously published 10be surface exposure ages from the daxi valley in the source area of the urumqi river the new ages record five major glacial events during marine oxygen isotope stages mis 6 or older 4 3 2 and 1 during the little ice age lia landforms from glacial events since mis 2 are found on the northern slope of the tianger range daxi valley whereas evidence for the older glacial events is only preserved on its southern slope ala valley this disparity may be caused by different preservation and micro climatic conditions on the northern and southern slopes of this mountain range due to differences in gradient and aspect the lia glacial advances are apparently the only holocene glacial event recorded in this area earlier holocene glacial events were probably so restricted in extent that they were destroyed by subsequent lia advances

color characteristics of chinese loess and its paleoclimatic significance during the last glacial interglacial cycle abstract the soil color is widely used in paleoclimate and paleoenvironment reconstructions in the chinese loess plateau to better understand the color spatial changes during the glacial interglacial cycle the soil color lightness l characteristic spectra magnetic susceptibilities and mean grain sizes of three loess paleosol sequences were compared results showed that high l and low hematite to goethite ratios hm gt appeared in loess units and low l and high hm gt ratios accompanied paleosol layers indicating glacial interglacial hydrothermal oscillation l in the yulin section was higher than in the chaona and lihuacun sections indicating that different precipitations have great effect on l furthermore hm gt magnetic susceptibility lf and mean grain size are correlated closely with l l and hm gt not only document climatic variations in the glacial interglacial cycle vis a vis loess paleosol sequences but also can identify heinrich cold events and millennial scale dansgaard oeschger d o warm events it suggests that soil color responds sensitively to global climate change driven by ice volumes l and hm gt curves exhibit higher frequencies and larger amplitudes than magnetic susceptibility lf curves indicating that l and hm gt can be regarded as sensitive and reliable proxies for characterizing high resolution climate change during the last glacial interglacial cycle

loess soil sequence at toshan northern iran insights into late pleistocene climate change abstract the knowledge of palaeoclimate in iran is still limited however insight into the timing and the dynamics of quaternary climate change in iran might offer valuable information to improve the global palaeoclimate record the loess soil sequence of toshan provides the first high resolution record of late pleistocene climate dynamics in iran and complements the hitherto known sections at neka now deh and agh band to establish a pedostratigraphic record of the north eastern caspian lowland our spectroscopic and grain size analysis are combined to propose i a pedostratigraphical scheme for the sequence at toshan ii describe and estimate the degree of soil development of selected stratigraphical units iii infer palaeoclimatic information and provide iv a correlation with previous loess palaeosol records of n iran as based on pedostratigraphic assumptions the section at toshan hosts a strongly developed reddish brown argillic palaeosol bt as well as eight moderately to weakly developed brownish palaeosol horizons lacking clay illuviation features bw bwk these remnants of fossil soils are separated by finely textured loess and horizons that host characteristics of both loess and mineral subsoils cb cbk giving evidence for syngenetic soil formation the stratigraphical succession of palaeosols loess and syngenetically altered sediments covering the last ca 130 ka gives evidence for recurrent climate changes as well as fluctuations between dominance of soil formation or dust accumulation in relation to changes in moisture regime the formation of bt and bw bwk horizons is related to relatively humid and warm conditions likely corresponding with interglacial and interstadial climate

paleoenvironmental significance of the magnetic fabrics in chinese loess paleosols since the last interglacial 130 ka abstract we compare new anisotropy of magnetic susceptibility ams data with previously determined paleoclimatically sensitive parameters for a loess profile at lingtai central loess plateau china to unravel factors that control loess ams magnetic lineations are clustered along ne sw and nw se orientations during cold and warm periods respectively which probably corresponded to paleowind directions of both winter and summer monsoons anomalously steep magnetic foliations coincidentally occur at the paleoclimatic stage boundaries indicating sediment disturbance lineation strength appears to be sensitive to millennial scale rapid paleoclimatic fluctuations generally the winter monsoon produces a lower degree of lineation than the summer monsoon furthermore by studying lineation subsets for the cold and warm periods we find that the cold interval lineation strengths co vary with grain size over the last 70 ka during the last interglacial about 74 128 ka the lineation and declination of the susceptibility maximum dec k max are sensitive to rapid fluctuations in winter and summer monsoons long term trends of magnetic foliation and anisotropy degree replicate grain size variations with superimposed short term peaks related to post depositional compaction as suggested by density the ams shape parameter t indicates oblate fabrics these new findings will not only improve our understandings of loess ams but also expand the possibilities of paleoclimatic studies in the chinese loess

new insights into the palaeoclimatic interpretation of the temperature dependence of the magnetic susceptibility and magnetization of mid late pleistocene loess palaeosols in central asia and the chinese loess plateau the temperature dependence of magnetic susceptibility chi t curves and magnetization m t curves has been used as a routine rock magnetic tool to characterize the magnetic mineralogy and magnetic granulometry of chinese loess palaeosols however palaeoclimatic interpretation of these thermomagnetic analyses remains controversial in the present study total organic carbon toc thermomagnetic and low temperature magnetic experiments on mid late pleistocene loess palaeosols in central asia and the chinese loess plateau clp have been conducted we found that the m t cooling curves at room temperature were mostly lower than the corresponding heating curves whereas for the chi t analyses the cooling curves at room temperature were always much higher than the heating curves low temperature magnetic measurements demonstrated that a large amount of superparamagnetic ferrimagnetic particles were produced during the thermal treatment and resulted in the aforementioned differences this finding further indicated that the use of the m t curves to estimate the relative content of maghemite in the loess palaeosols from the clp was problematic in addition a positive correlation exists between the toc and the frequency dependent susceptibility chi fd in the clp suggesting that stronger pedogenesis would result in the simultaneous increase in the content of both maghemite and organic matter consequently the parameters delta chi 1 representing the relative content of pedogenic maghemite delta chi 2 inverted left perpendicular chi ph chi inverted right perpendicular delta chi 1 and chi ph related to the organic matter concentration which can be calculated from the chi t analyses can potentially be used as new indicators of pedogenesis and palaeoclimate in central asia and the clp

cobalt enrichment at the juomasuo and hangaslampi polymetallic deposits kuusamo schist belt finland a role for an orogenic gold fluid the juomasuo co au and hangaslampi au co deposits are located in the kuusamo schist belt part of the 1 9 1 8 ga svecokarelian orogenic belt central finland the deposits are hosted by metasedimentary and mafic rocks and structurally controlled by the f2 kayla konttiaho antiform hydrothermal alteration is spatially zoned from early albite through biotite and then chlorite and late muscovite alteration pipe like chlorite quartz pyrrhotite bodies plunge parallel to the f2 fold axis and are cut by tabular quartz muscovite pyrite gold lodes in the s2 axial plane orientation the chlorite alteration zone contains 10 40 vol pyrrhotite containing approximately 0 25 wt co but whole rock co grades are enhanced by the late stage and heterogeneous enrichment of minor pyrite up to 3 co and introduction of cobaltian pyrite and cobalt pentlandite cobaltite formed where muscovite replaces chlorite within metres of the gold lodes cobaltite and co enriched pyrite formed because co and s were mobilized from pyrrhotite in relatively s poor gold lodes by an as rich gold ore fluid during late d2 potassium cobalt sulfur and arsenic were transported into the mainly chlorite rich wallrocks via veinlets and fractures by the now depleted gold ore fluid approximately 5 vol pyrite in the gold lodes displays extremely variable cobalt contents which is interpreted to reflect mobility of co during formation of the gold lodes the origin of the gold ore fluid is enigmatic but is most plausibly an orogenic gold fluid despite the paucity of carbonate minerals in the gold lodes

grain size partitioning in loess paleosol sequence on the west coast of south korea using the weibull function abstract this study aims to partition the grain size of the loess paleosol sequence on the west coast of south korea and investigates the limitations and applicability with the partitioning method through the help of a laser diffraction grain size analyzer two to four components depending on the samples and theories employed to convert the laser diffraction data to grain size data are identified through the partitioning process however the identification of one component is thought to be contingent upon the theories employed rather than natural processes the partitioning results reveal that the sequence consists mostly of fine and coarse components transported by the same mechanisms as in the chinese loess plateau and shares common source areas with the chinese loess plateau the sequence also contains a small quantity of material from the local sources and this component is expected to provide crucial information about paleoclimatic variations in korea this study suggests that considerations of the theories are essential in modeling processes of grain size because the theories greatly influence the results of grain size analysis and the number of components and that conversions using the fraunhofer approximation seem to provide more reliable results than those using the mie theory

magnetic study of late pleistocene loess palaeosol sections from siberia palaeoenvironmental implications summary rock magnetic properties including anisotropy of magnetic susceptibility were investigated in detail for two loess palaeosol sections in south western siberia bachat and kurtak the results obtained agree with the alaskan type of susceptibility variations for the kurtak section showing maximum susceptibility values in loess horizons and minima in palaeosols for the bachat section the palaeoenvironmental record expressed through susceptibility is not clear in spite of the geographical proximity of the two sections instead frequency dependent magnetic susceptibility fd discriminates well between loess and palaeosol units showing maxima in pedocomplexes and minima in loess units this suggests certain pedogenic formation of fine ferrimagnetic grains in soils studies of anisotropy of magnetic susceptibility ams reveal a well defined sedimentary magnetic fabric for both sections different origins of loess deposition pure aeolian at bachat and aeolian affected by secondary processes at kurtak are reflected in the ams patterns the two sections also show different high temperature behaviour of magnetic susceptibility while for the bachat section only one type of thermomagnetic curve was found the kurtak section shows different behaviour for loess and palaeosol units magnetic properties of samples from the two sections are discussed in terms of palaeoclimatic and depositional conditions

loess accumulation in the tian shan piedmont implications for palaeoenvironmental change in arid central asia whilst correlations have been made between the loess of europe and china deposits in central asia have remained largely overlooked by scientific investigation the nature of the relationship between loess accumulation and palaeoclimate at the core of the eurasian loess belt is particularly poorly understood here we reconstruct palaeoenvironmental change in central asia over the last 40 ky based on data from the remizovka loess profile in the northern foothills of the tian shan in southern kazakhstan our interpretations are based on synthesis of chronostratigraphic colour and magnetic susceptibility data supported by chronostratigraphies from two additional sites nearby maibulak and valikhanova all three sites record substantially increased loess accumulation during late mis 3 into the global last glacial maximum glgm at remizovka increased loess flux occurred in two pulses at c 38 25 ka and 22 18 ka with the intervening period involving incipient pedogenesis at maibulak two loess pulses at c 40 30 ka and c 28 22 ka are separated by a weakly developed paleosol which may date to the same time as pedogenesis at remizovka there is additional possible periglacial influence at maibulak from c 40 33 5 ka at valikhanova there is some age overlap between paleosol and loess samples but overall loess accumulation appears to have increased at c 42 35 ka c 30 ka and the glgm with pedogenesis occurring 40 ka and c 32 ka at all three sites holocene loess accumulation is minimal this period is characterised by pedogenesis the chronostratigraphic variability between our sites highlights a need to interrogate climate driven models for loess formation in piedmont environments we interpret our data in the context of regional palaeoenvironmental archives to indicate that loess accumulation increased coeval with mis 3 glacial advance in the tian shan which was facilitated by northward expansion of the asian monsoon and associated increase in precipitation we hypothesise that increased ice volume impeded teleconnections with the temperate zone westerlies to the north these were compressed against the piedmont resulting in increased wind strength and facilitating increased loess flux peak loess accumulation during the glgm occurred under colder drier climatic conditions with reduced but sustained glacial ice volume and persistent influence of the westerlies in the arid central asian piedmont loess belt in the absence of more widespread reliably dated palaeoenvironmental records from the region our data become of critical importance for understanding past environmental conditions in central asia relative to elsewhere in eurasia and globally

an abrupt shift in dust source on the chinese loess plateau revealed through high sampling resolution osl dating abstract the source of dust that forms the extensive deposits of loess exposed on the chinese loess plateau is highly debated in particular it is not clear whether sources can change abruptly within individual loess units or whether local influences on source can override the influence of far travelled components high vertical sampling resolution 10 40 cm optically stimulated luminescence osl dating of sediments on the loess plateau in china has been successful in providing detailed independent age models for loess accumulation here osl behaviour is used to infer a shift in loess sediment source during the last glacial period osl dating procedures have often utilised the widely applied single aliquot regeneration sar protocol on quartz grains detailed sar osl dating of the last 45 ka of sedimentation at beiguoyuan section on the north of the loess plateau demonstrates anomalous and statistically significant age increases and scatter in age estimates in samples from a c 2 5 m unit at about 20 ka compared to samples above and below many of these samples also fail internal dose recovery tests and show anomalous luminescence signal properties deconvolution of osl decay curves into first order components reveals that many of the age overestimating samples have a significant ultrafast component this behaviour is restricted to the 2 5 m segment and is only likely to be uncovered using high sampling resolution luminescence analysis combined with heavy mineral grain size and geochemical evidence this suggests that the source of material in this unit abruptly shifted at the last glacial maximum potentially to a local source rather than well mixed and recycled multiple distant sources as appears to be the case at other times at the site and other studied sections on the loess plateau the environmental causes of this source shift may be tied to abrupt climate change during the last glacial maximum and demonstrate the highly dynamic nature of the locations of dust generation during the last glacial period the change in source also adds complexity to standard climate proxy analyses of loess using sediment properties

micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system 1 chondrules in chondritic meteorites record the earliest stages of formation of the solar system potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions using first order reversal curves forcs we map the coercivity distributions and interactions of 32 chondrules from the allende karoonda and bjurbole meteorites distinctly different distributions and interactions exist for the three meteorites the coercivity distributions are lognormal shaped with bjurbole distributions being bimodal or trimodal the highest coercivity mode in the bjurbole chondrules is derived from tetrataenite which interacts strongly with the lower coercivity grains in a manner unlike that seen in terrestrial rocks such strong interactions have the potential to bias paleointensity estimates moreover because a significant portion of the coercivity distributions for most of the chondrules is 10 mt low coercivity magnetic overprints are common therefore paleointensities based on the rem method which rely on ratios of the natural remanent magnetization nrm to the saturation isothermal remanent magnetization irm without magnetic cleaning will probably be biased the paleointensity bias is found to be about an order of magnitude for most chondrules with low coercivity overprints paleointensity estimates based on a method we call remc which uses nrm irm ratios after magnetic cleaning avoid this overprinting bias allende chondrules which are the most pristine and possibly record the paleofield of the early solar system have a mean remc paleointensity of 10 4 mt karoonda and bjurbole chondrules which have experienced some thermal alteration have remc paleointensities of 4 6 and 3 2 mt respectively

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

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

glacial anticyclone recorded in palouse loess of northwestern united states climate simulations for the last glacial maximum using general circulation models typically show a glacial anticyclone that produced an easterly wind anomaly south of the north american ice sheets evidence of this phenomenon has not been found in eolian sedimentary deposits that record surface wind patterns luminescence ages of loess and accompanying paleoecologic records from opal phytoliths and paleosol units across the columbia plateau washington state united states document a decrease up to fivefold in regional dust production and accumulation from 35 ka to 15 ka this interval corresponds to simulations indicating that a glacial anticyclone weakened prevailing south southwesterly winds that have shaped the eolian landscape of the columbia plateau since at least 75 ka at the same time that the glacial anticyclone suppressed dust production and accumulation enhanced cold and dry conditions resulted in soil formation dominated by intense bioturbation in periglacial steppe accompanied by shallow calcium carbonate precipitation this is the first evidence from eolian deposits in north america verifying that the glacial anticyclone altered surface wind patterns and affected eolian systems during the last glacial maximum

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

african monsoon enhancement during the penultimate glacial period mis 6 5 170 ka and its atmospheric impact 1 a reconstruction of northwest african summer monsoon strength during the cold marine isotopic stage mis 6 indicates a link to the seasonal migration of the intertropical convergence zone itcz high resolution studies of eolian dust supply and sea surface temperature recorded in marine core md03 2705 on the mauritanian margin provide a better understanding about the penultimate glacial history of northwestern african aridity humidity and upwelling coastal activity today site md03 2705 experiences increased upwelling and dust flux during the winter months when the itcz is in a southerly position analyses of foraminifera isotopic composition suggest that during mis 6 5 180 168 ka the average position of the itcz migrated north marked by an increase in the strength of the summer monsoon which decreased eolian dust transport and the coastal upwelling activity the northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal high resolution analysis of stable isotopes 18o and 13c and microscale resolution geochemical ti al and quartz grain counts determinations reveal that the transition between monsoonal humid mis 6 5 and dry mis 6 4 conditions has occurred in less than 1 3 ka such rapid changes suggest a nonlinear link between the african monsoonal rainfall system and environmental changes over the continent this study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of african summer monsoon and demonstrates that during the penultimate glacial period changes in tropical dynamics had regional and global impacts

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

paleomonsoon route reconstruction along a w e transect in the chinese loess plateau using the anisotropy of magnetic susceptibility summer monsoon model abstract the anisotropy of magnetic susceptibility ams was investigated in three chinese loess plateau sedimentary sections along a w e transect 400 km the loess paleosol sequences in our study represent the most recent 130 kyr interval the measured ams was compared to expected theoretically derived magnetic fabrics occurring in strong and weak current airflow conditions the major and minor ams ellipsoid axis orientations were used to evaluate the paleowind direction along the transect previously published models assumed that cold and dry winter monsoons bringing dust from northwestern desert areas were responsible for the magnetic fabric formation of loess sequences in our new interpretation the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the chinese loess plateau although the material was brought to the area by the winter monsoon the ams was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged settled and fixed we reconstruct the summer paleomonsoon routes for the last 130 kyr these winds prevail from se to nw but appear to be affected by regional topographic factors in the western section the corridor between the north and south liupan mountains disturbed the summer monsoon route shifting it from se to see