paleoclimatic significance of magnetic properties on the red clay underlying the loess and paleosols in china abstract the red clay unit of northern china is a widespread miocene pliocene 7 2 2 5 ma aeolian deposit that underlies much of the quaternary loess paleosol sequence in the central loess plateau it comprises a sequence of highly developed soils and interbedded layers of less weathered loess like material here referred to as reddish loess in common with the loess paleosol alternations of the overlying quaternary deposits the soil reddish loess alternations are interpreted to represent climatic fluctuations in this case between warm humid and relatively dry cool conditions however while magnetic susceptibility variations in the quaternary deposits provide a good proxy for pedogenic intensity in the red clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis in an attempt to resolve this issue we have investigated a red clay section and overlying loess paleosol sequence at xifeng and have supplemented these data with samples from the red clay at lingtai our study indicates that the red clay and loess paleosol sequence have a common magnetic mineralogy comprising magnetite maghemite and hematite and possibly goethite and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic sp component this implies that susceptibility enhancement in the red clay is strongly related to the magnitude of the sp content a component that is widely recognised as having a pedogenic origin in quaternary deposits further support for a correlation between pedogenesis and magnetic susceptibility in the red clay is provided by a good correlation between magnetic susceptibility and the rb sr ratio an independent weathering index however differences in the magnetic mineralogy of the two units are also evident the minimum magnetic susceptibility of the red clay is less than half the value of the overlying quaternary deposits at locations such as xifeng and lingtai while the maximum sp content is relatively larger than for the quaternary deposits while we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units climate may also be a contributory factor in explaining these differences precipitation is a major control on magnetic enhancement in paleosols maher and thompson 1995 quat res 44 383 391 liu et al 1995 palaeogeogr palaeoclimatol palaeoecol 113 243 248 but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive central loess plateau china magnetic enhancement negative alaska siberia magnetic destruction or uncertain pakistan argentina new zealand cycles of enhancement and destruction while our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the red clay they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary but independent techniques more work is required to deconvolve the climatic record of the red clay but the reward may be the extension of the record of paleomonsoon evolution back into the pliocene and late miocene

holocene climatic evolution at the chinese loess plateau testing sensitivity to the global warming cooling events abstract a high resolution petromagnetic analysis demonstrates that pedogenic alterations in holocene loess sand sequences from the regions of the guanzhong basin and the mu us desert on the chinese loess plateau clp were affected by climatic variations in temperature and precipitation three warm humid intervals 8 4 3 7 2 4 1 2 and 0 81 0 48 ka associated with soil formation and relatively high values of petromagnetic parameters occurred during the holocene a substantial paleosol development from 8 4 to 3 7 ka and higher petromagnetic parameter values indicate a generally strong warm humid phase in the mid holocene which can be attributed to the holocene climatic optimum our study demonstrates that the holocene climate in the eastern part of the clp is sensitive to warming and cooling events linked to global changes in temperature and precipitation a complete holocene climate record is constructed correlating well with the other regional climate records along the south to north profile on eastern clp and suggesting that similar climatic changes occurred in eastern monsoonal china during the holocene results are supported by other climate records in different regions of the world and imply that the holocene climatic optimum in the northern hemisphere probably took place at the same time

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

iron oxide characteristics of the chinese loess red clay sequences and their implications for the evolution of the east asian summer monsoon since the late oligocene abstract the most significant climatic change in east asia involved the formation and evolution of the coupled monsoon arid environmental system during the cenozoic which was dynamically linked to global cooling and the growth of the qinghai tibet plateau however our understanding of monsoon evolution since the late oligocene remains controversial due to differences in the interpretation of various environmental proxies from loess archives in this study the composition and relative abundance of pedogenic iron oxides of two eolian sequences from the lingtai section and the zhuanglang drill core were investigated using rock magnetic optical spectroscopy and geochemical analyses the results indicate that while the composition of iron oxides in the mio pliocene red clay and quaternary loess paleosol sequences is similar the concentrations of magnetite maghemite hematite and goethite are quite different between loess paleosol and red clay the combination of magnetic proxies magnetic susceptibility fed fet and color a values reveals that precipitation and temperature played varying roles in driving pedogenesis and chemical weathering since the late oligocene during the late oligocene to early miocene the occurrence of relatively strong pedogenesis and chemical weathering was likely the result of high temperatures rather than high precipitation the east asian summer monsoon intensified during the middle miocene climate optimum 16 5 14 5 ma in response to global climatic warming subsequently during the middle to late miocene the monsoon intensity gradually weakened due to global cooling after 8 ma the summer monsoon strengthened substantially and reached a maximum during 4 5 2 6 ma possibly as a result of the uplift of the northeastern margin of the qinghai tibetan plateau during the late miocene the monsoon intensity then commenced a decreasing trend in the early pleistocene but then strengthened again after 1 0 ma

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

quantification of the contribution of pedogenic magnetic minerals to magnetic susceptibility of loess and paleosols on chinese loess plateau paleoclimatic implications 1 this study investigates the grain size dependent properties of magnetic minerals in chinese loess samples with an aim to better understand the contribution of pedogenesis to magnetic susceptibility enhancement of the paleosols samples of loess and paleosol were divided into two fractions magnetic extracts and residues by extraction in a weak magnetic field both the raw samples of loess and paleosol i e before magnetic extraction and the samples of residues after magnetic extraction were then separated into five grain size fractions by gravitational settling and centrifugation low field magnetic susceptibility ms and the frequency dependent ms of these samples were measured and samples treated with citrate bicarbonate dithionite cbd to remove the iron oxides were also analyzed for loess samples coarse grains 2 m contribute more than 50 of the magnetic signal the 0 3 m fraction considered to be of pedogenic origin contributes 22 before magnetic extraction or 36 after magnetic extraction of the magnetic signal in loess a different pattern is found in the paleosol samples for these samples the 0 3 m fraction contributes 60 before magnetic extraction or 71 after extraction to the bulk ms in addition 91 of the magnetic signal in paleosol s5 is cbd extractable the cbd technique is able to extract pedogenic superfine grained magnetic particles and coarse dust magnetic particles these results confirm that pedogenesis leads to enhanced ms and helps to quantify the multiple origins of the bulk magnetic material that defines loess and paleosol ms this approach provides a reliable estimate of the contribution of pedogenic magnetic materials to ms our study indicates that multiple methods should be employed in analyzing paleoclimatic changes recorded by ms in the chinese loess paleosol sequences

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

signature of magnetic enhancement in a loessic soil in nebraska united states of america our study of a loessic soil profile from east central nebraska shows that the a horizons of the modern soil are characterized by higher concentrations of fine grained b0 1 am magnetic minerals this pedogenic magnetic component leads to higher values of concentration dependent parameters such as magnetic susceptibility v isothermal remanent magnetization irm and anhysteretic remanent magnetization arm combined with increases in frequency dependent susceptibility vfd and arm irm ratios hysteresis properties are relatively insensitive towards the presence of this pedogenic magnetic component the magnetic properties of the soil profile are dominated by ferrimagnetic magnetite or maghemite analyses of bsoftq irm sirm and bhardq irm hirm however do show that approximately 80 90 of the remanence carrying magnetic component exists in the form of hematite or goethite and that the magnetically enhanced horizons are enriched in both ferri and antiferromagnetic minerals the pedogenic magnetic component is most likely caused by the conversion of paramagnetic iron bearing minerals to ferriand antiferromagnetic minerals soil compaction lessivage or decalcification cannot explain the observed magnetic soil properties magnetic analyses of loess paleosol sequences from the midwestern united states may yield valuable information about regional variability of paleoclimate based on the fine grained nature of the pedogenic magnetic component we expect grain size dependent proxies arm arm irm vfd to yield better paleoclimatic information than low field magnetic susceptibility used in previous analyses d 2004 elsevier b v all rights reserved

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

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

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

clumped isotope paleotemperatures from mis 5 soil carbonates in southern hungary abstract quantitative paleotemperature reconstructions for the continents including east central europe over marine isotope stage 5 mis 5 and specifically the last interglacial lig mis 5e are scarce and mostly based on pollen assemblages here we provide soil and air temperature reconstructions for the summer season of mis 5e 5c using carbonate clumped isotope thermometry applied to soil carbonate concretions in the dunaszekcs loess paleosol record southern hungary the sediments making up the s1 pedocomplex investigated represent the mis 5 as demonstrated by bracketing k feldspar post ir irsl225 290 ages of 63 to 164 ka both the absolute ages and pedogenic susceptibility p curve indicate that all the subtages of mis 5 were found to be recorded in the sequence and soil carbonates found 1 m depth below the paleosurface of the s1 soil provide pristine undisturbed isotopic signals the soil carbonate concretions likely formed during mis 5e at a relatively shallow 20 50 cm depth but a later formation during mis 5c at 50 cm depth is also plausible clumped isotope based soil temperatures st 47sc ranged from 16 to 20 c and reconstructed summer season air temperatures sats for the lig are consistently lower than the modern values at the site by 1 5 c matching surprisingly well the soil bacteria membrane lipid based mis 5e air temperature estimates from a nearby serbian site at the same time the reconstructed sat values do not match the 2 4 c positive warm season anomalies modeled for east central europe between lig and present day in paleoclimate simulations st uncertainties of 1 6 c infiltration driven cooling of soil temperatures and the possibility of mis 5c formation of the investigated carbonates may account for this proxy model data discrepancy oxygen isotope compositions of summer season paleo rainwaters for mis 5e 5c as reconstructed using the st 47sc and 18osc data of soil carbonates were found in a range of 6 7 and 6 4 matching the modern mean summer season value of 6 2 0 94 within error

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

the different climatic response of pedogenic hematite and ferrimagnetic minerals evidence from particle sized modern soils over the chinese loess plateau abstract in recent years increasing interest in loess studies has focused on qualitative and quantitative paleoclimatic reconstruction using the imperfect antiferromagnetic mineral hematite however the linkage between the hematite formation and climatic variables remains controversial here we present the results of a comprehensive investigation of the magnetic properties and statistical analysis of a suite of clay and silt fractions of modern soil samples from 179 sites across the chinese loess plateau clp and adjacent regions our objective was to clarify the relationships between modern climatic variables and pedogenic hematite as well as pedogenic ferrimagnetic minerals first order reversal curve measurements were also conducted on representative particle sized subsamples from a n s transect to understand the differences in magnetic mineralogy between the two fractions our results show that pipette extraction separates the fine grained superparamagnetic sp and most of the single domain sd magnetic grains into the clay fraction and that the remaining silt fraction displays the magnetic properties of coarse pseudo single domain psd or a mixture of multidomain md psd and a few sd particles only the pedogenic clay fraction shows a strong correlation with climatic variables the application of redundancy analysis helps to distinguish the climate variables controlling the formation of ferrimagnetic minerals and hematite during pedogenesis on the clp pedogenic ferrimagnetic minerals are sensitive to mean annual precipitation while pedogenic hematite formation is preferentially dependent on mean annual temperature the confirmation of the temperature dependent nature of hematite on the clp provides a new possibility for quantitatively reconstructing the paleotemperature history of chinese loess paleosol sequences

magnetic enhancement and palaeoclimate study of a loess palaeosol couplet across the loess plateau of china summary the origin of the milankovitch palaeoclimatic signal so dramatically recorded in the chinese loess remains uncertain at least five hypotheses have been put forward to explain the well documented enhancement of magnetic susceptibility in palaeosols which formed when conditions were warmer and wetter we report here a magnetic study of a prominent loess soil couplet l4 s3 at three widely separated sites where present day mean annual rainfall and temperature range from 350mm to 700mm and from 6 c to 13 c the properties determined are laboratory remanences isothermal irm anhysteretic arm viscous vrm including viscous decay room temperature susceptibility and thermomagnetic behaviour at fields beyond 100 mt the irm spectra are all essentially identical both in shape and in absolute magnitude suggesting a uniform magnetic component widespread across the plateau subtracting the signal of this component isolates a second component the amount of which varies by an order of magnitude between sites the magnetic properties of this latter material are remarkably similar to those reported for bacterial magnetite in geological sediments and modern soils viscous decay of vrm takes place in two distinct stages one of which falls to zero in 10min we attribute magnetic enhancement which is the source of the palaeoclimatic signal to in situ pedogenetic formation of magnetite which we characterize in our interpretation as two separate forms of bacterial magnetofossils the most magnetic sample requires a mass fraction of about half of one per cent of this biogenic material

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

the role of north brazil current transport in the paleoclimate of the brazilian nordeste margin and paleoceanography of the western tropical atlantic during the late quaternary abstract reconstructions of surface paleoceanographic conditions of the western equatorial atlantic and past climates of the adjacent northeast brazilian the nordeste continental margin were undertaken by analyzing sediments from a piston core and associated gravity and box cores recovered from 3107 meter water depth at 0 20 n on the equatorial brazilian continental slope the record is dated by radiocarbon analysis and oxygen isotopic stratigraphy of planktonic foraminifers and spans from near modern to approximately 110 ka high resolution xrf analysis provides insight into the paleoclimate history of the nordeste during the last glacial interval several large amplitude and abrupt peaks are observed in the time series of ti ca and are usually accompanied by peaks of fe k together these record periods of increased precipitation and intense weathering on the adjacent continent and increased terrestrial sediment discharge from nordeste rivers into the atlantic within the limits of dating accuracy most ti ca peaks correlate with heinrich events in the north atlantic this record thus corroborates and extends back in time the previous record of arz et al 1998 determined on sediment cores from farther southeast along the nordeste margin stable oxygen isotopic analysis and mg ca paleothermometry on the near surface dwelling planktonic foraminiferal species globierinoides ruber find that mean sea surface temperature sst during glacial time 20 55 ka n 97 was 23 89 0 79 c and the mean sst during the late holocene 0 5 ka n 14 was 26 89 0 33 c ssts were 0 5 2 c higher and inferred sea surface salinities were lower during most of the periods of elevated ti ca thus as observed in previous studies the western equatorial atlantic was warm at least locally and the adjacent southern tropical continent was wet at the same time that the high latitude north atlantic was cold using the syntrace ccsm3 fully coupled climate model with transient forcing for the period 22 ka to present we find that decreased transport of the north brazil current co occurs with reduced atlantic meridional overturning circulation and colder than normal ssts in the north atlantic region these simulated conditions are invariably associated with significantly increased precipitation in the nordeste region

middle pleistocene magnetostratigraphy and susceptibility stratigraphy data from a carbonate aeolian system mallorca western mediterranean abstract this study shows that successions of pleistocene carbonate aeolian deposits can be placed successfully in a geochronologic framework using magnetostratigraphic and susceptibility stratigraphic analysis supplemented by luminescence dating studies of wave cut platforms and biostratigraphic evidence the investigated aeolian system covers a significant part of southernmost mallorca and is exposed in impressive coastal cliff sections at the study site at els bancals the aeolian system has a maximum thickness of 16 m and is composed of alternating dark red colluvial deposits and greyish red aeolian dune and sand sheet deposits forming seven cyclostratigraphic units each cyclostratigraphic unit represents landscape stabilisation colluviation and soil formation followed by dunefield development when marine carbonate sand was transported far inland by westerly or north westerly winds the aeolian system is located on top of a wave cut marine platform 12 14 m a s l this platform probably formed during a sea level highstand in marine isotope stage mis 11 427 364 ka and renewed marine activity probably later in mis 11 is indicated by the formation of beach deposits two sections at els bancals were sampled for a paleomagnetic study additional samples were taken to detect variations in magnetic susceptibility ms the characteristic remanent magnetisation has been recovered for the most part of the succession in spite of diagenetic overprinting there is evidence for two probably three reversal polarity excursions possible connected to the levantine cr1 and cr0 biwa iii episodes if this correlation is correct the sampled succession represents a time interval in the middle pleistocene between ca 410 and ca 260 ka this age estimate is supported by the ms study and by luminescence dates of 333 70 ka aeolianite from lower part of the succession and 275 23 ka aeolianite from the top of the succession the nature of the succession suggests deposition during alternating warm and moist colluvial deposition soil formation and cold dry and windy conditions dunefield formation the susceptibility signal can be correlated with the insolation signal at 65 n suggesting that environmental variation on mallorca was linked to orbitally forced climate change and it seems that aeolian activity and dunefield formation were linked to glacial or stadial periods

rock magnetism and pedogenetic processes in luvisol profiles examples from central russia and central mexico abstract despite a vast literature concerning magnetic properties of loess sequences we still do not fully understand how magnetic components and properties are related to particular soil forming processes that can vary with each type of genetic horizon in order to establish the role of lithogenic factors in the link between magnetic properties and soil forming processes we carried out a study of two complete profiles of buried interglacial luvisols one formed in loess in russia alexandrovsky quarry and the other in volcaniclastics in mexico barranca tlalpan in both profiles soil genetic horizons have contrasting differences of their magnetic properties in the alexandrovsky profile the magnetic susceptibility is enhanced in the paleosol compared to parent material in the barranca tlalpan sequence enhancement is absent in the soil profile increase of fine grained magnetic components in the soil is attributed to neoformed minerals however this process cannot compensate for the loss of lithogenic magnetic minerals in any of the genetic horizons and the resulting trend is depletion in the whole soil profile the pedogenic environment of eluvial horizons in both luvisols is destructive to all magnetic components both primary and secondary higher concentrations of antiferromagnetic components hematite and goethite found in e horizons are related to redoximorphic processes

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

stratigraphy sedimentology and geochemistry of the upper mississippian pride shale in the appalachian basin tide dominated or tide influenced coastal marine deposits form some of the most complicated and largest hydrocarbon fields in the world wood 2004 and references cited therein good outcrop analogs can provide significant insight to geologists for recognizing tidal influence in core and interpreting petrophysical log data thus reducing uncertainty and risk when developing depositional models and planning for field development despite the observation that 8 of the 12 largest deltas in the modern world are either tide dominated or strongly tidally influenced middleton 1991 many geologists fail to recognize tidal influence in the rock record perhaps in part because of the influence of preexisting paradigms this seems to be particularly so for many geologists prospecting for hydrocarbons within pennsylvanian sediments in the arkoma and anadarko basin of the southcentral united states although good ancient analogs of tide dominated deltas exist see summary table in feldman et al 2014 many of these studies inferred tidal influence from the intercalation of sandstone and mudstone an abundance of fluidized mud deposits a dominance of structures formed from currents and the shoreline perpendicular orientation of elongate sandstone bodies few studies have identified sedimentary structures in delta front and prodelta settings that can be directly related to semidiurnal semimonthly and longer term tidal deposition this may reflect background interference from storms or variable fluvial discharge that disrupted tidal deposition and thus obscures evidence of fortnightly or longer tidal signals or it may reflect

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

magnetic properties of loess deposits on the northeastern qinghai tibetan plateau palaeoclimatic implications for the late pleistocene summary the loess palaeosol deposit on the northeastern qinghai tibetan plateau is sensitive to environmental changes thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes detailed rock magnetic investigations and grain size determination were carried out on a 35 m thick loess palaeosol sequence at dongchuan the northeastern qinghai tibetan plateau the principal ferrimagnetic minerals in both the loess and palaeosol units are large pseudo single domain magnetite maghemite palaeosol units are generally enriched in ultrafine grained magnetite maghemite of pedogenic origin variations of low field magnetic susceptibility and frequency dependent susceptibility in the loess and palaeosols can mainly be attributed to changes in the concentration of these minerals higher values of frequency dependent susceptibility occur in the palaeosol horizons except for the weakly developed palaeosol suggesting that higher concentrations of ultrafine magnetite maghemite particles occur in palaeosol units due to in situ pedogenesis the frequency dependent susceptibility of the loess units is very low and uniform indicating absence of the super paramagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility generally magnetic susceptibility combined with the frequency dependent susceptibility of the loess palaeosol sequences reflect the glacialinterglacial changes thus can be employed as a proxy measure of palaeoclimate in this region however the low field magnetic susceptibility record does not consistently correlate to the variations in stratigraphy of the dongchuan loess palaeosol sequence it is thus suggested that multiparameter rock magnetic investigations combined with non magnetic measurements such as grain size analysis represent a more powerful approach for palaeoclimatic research into the complex loess palaeosol record in the qinghai tibetan plateau

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

analysis of lithic technology of lower pleistocene sites and environmental information in the nihewan basin north china the nihewan basin is an important area for studying the evolution of early hominids in china among 15 recently discovered and reported lower pleistocene sites in the basin eight majuangou xiaochangliang dachangliang banshan donggutuo feiliang huojiadi xujiapo have been specifically analyzed by the authors this paper is a synthesis of results of analysis of lithic technology and palaeoenvironmental information of these sites three distinct arrangements of techniques are identified from the eight sites which represent the different lithic techniques cognitive capability and cultural contents the dgt core from donggutuo indicates that the cognitive capability and the culture deepness of early hominids in china surpassed expectations re evaluation is required of early human technology and behavioral mode in china

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

paleoclimate and weathering of the tokaj hungary loess paleosol sequence abstract the tokaj loess paleosol sequence northeast hungary is a well studied site in southeast europe where detailed paleoenvironmental reconstructions of the quaternary have been carried out in this study the geochemical composition of samples from the upper part of the sequence 45 21 ka was analyzed and a variety of commonly used weathering indices and element ratios were applied to estimate weathering intensity a common semi quantitative proxy of paleoclimatic conditions further similarities and differences between these weathering indices and their sensitivity to changes in paleoclimatic conditions were assessed results indicate that all of them accurately track changes in weathering intensity and are with minor exceptions very similar to each other based on different transfer functions for major and trace element concentrations xrf mass specific magnetic susceptibility and stable carbon isotopic 13c data mean annual paleotemperature and mean annual paleoprecipitation for the time intervals of paleosol formation 45 27 ka and dust deposition 27 21 ka were calculated results differ depending on the respective transfer function and method but agree with x 13c based or slightly overestimate xrf based previously published paleoclimate data of the region xrf and 13c based results converge to a mean annual temperature mat range of 8 5 10 c paleosol and 8 9 c loess and a mean annual precipitation map range of 700 900 mm a 1 paleosol and 550 700 mm a 1 loess based results are most consistent with literature data and yield mats of 8 4 c paleosol and 6 6 c loess and maps of 300 500 mm a 1 paleosol and 220 mm a 1 loess

rainfall dependent transformations of iron oxides in a tropical saprolite transect of hainan island south china spectral and magnetic measurements 1 the iron oxide content of soils and sediments controlled by weathering and pedogenesis is generally considered a reasonable indicator of climate previous studies in temperate zones have established a positive correlation in aerobic soils between ferrimagnets and low to moderate rainfall the correlation seems to be reversed under extreme climates with high rainfall here we present a transect of saprolitic soils from hainan island south china with high rainfall 1440 2020 mm yr little temperature variation 23 24 c and extreme weathering along this transect we observed that both hematite concentration and magnetic susceptibility decrease with increasing rainfall whereas goethite concentration displays a large increase however there is no systematic trend in the total amount of iron oxides related to chemical weathering intensity along the transect goethite is the favored mineral phase of iron oxide with increasing rainfall and accumulates at the expense of hematite and maghemite through the dominance of rainfall driven processes these pedogenic processes coincide with the fundamentals of previous nonmonotonic models of hematite magnetic susceptibility and rainfall control of an inflection point this study also verifies a common genetic relationship between hematite and pedogenic ferrimagnets across a wide climate range a conceptual model considering both rainfall and temperature is proposed to help interpret the mechanism of ferrimagnet formation and changes in the rainfall inflection point

magnetic mineralogy of chinese loess and its significance summary the topmost 16 metres of the loess section at xifeng central chinese loess plateau which cover the last 128000 years consist of two palaeosol beds interlayered by a loess horizon hysteresis parameters frequency dependent field and temperaturedependent susceptibility show very similar and stable magnetic mineral constituents in both loess and palaeosol samples the concentration and grain size of magnetite maghaemite and haematite control the magnetic properties of chinese loess susceptibility and loess thickness are closely related to geographic position and present climate across the loess plateau the loess and palaeosol magnetic properties are largely controlled by the fine grained magnetite formed in various quantities and grain sizes under the influence of pedogenesis during variable palaeoclimatic conditions therefore regional and global palaeoclimatic development during the last 2 5 myr can be reconstructed from susceptibility records in the loess plateau

a 15 400 year record of environmental magnetic variations in sub alpine lake sediments from the western nanling mountains in south china implications for palaeoenvironmental changes abstract a detailed environmental magnetic investigation has been performed on a sub alpine sedimentary succession deposited over the past 15 400 years in daping swamp in the western nanling mountains of south china magnetic parameters reveal that fine grains of pseudo single domain psd magnetite or titanomagnetite are the dominant magnetic minerals in the lake sediments and surface soils collected from the catchment which suggests that magnetic minerals in lake sediments mainly originated from surface soil erosion of the catchment variation of surface runoff caused by rainfall is interpreted as the main process for transportation of weathered soils into the lake in the last deglacial period lgp 15 400 11 500 cal a bp the influx of magnetic minerals of detrital material may have been significantly affected by the severe dry and cold conditions of the last glacial maximum stabilised conditions of the catchment associated with increased vegetation coverage e g 8000 4500 and 2500 1000 cal a bp limited the input of magnetic minerals intensive soil erosion caused by increased human activity may have given rise to abnormal increases in multiple magnetic parameters after 1000 cal a bp because changes in runoff and vegetation coverage are closely related to asian summer monsoon asm intensity the sedimentary magnetism of daping swamp provides another source of information to investigate the evolution of the asm

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

time dependence of magnetic susceptibility of soil chronosequences on the california coast abstract as the age of the soils in a chronosequence on the california coast increases the difference between the magnetic susceptibility of eluvial and illuvial horizons increases and the residual susceptibility after extraction with citrate bicarbonate dithionite cbd decreases enhanced susceptibility results from the conversion of nonferrimagnetic minerals to secondary ferrimagnetic forms most likely maghemite and the preferential accumulation of inherited and pedogenic magnetic minerals little enhancement occurs for pedons younger than 40 000 yr by 124 000 yr most of the magnetic susceptibility can be attributed to forms soluble in cbd magnetic susceptibility appears to vary systematically over time for three chronosequences from areas with mean annual precipitation ranging from 650 to 1500 mm yr 1 magnetic susceptibility enhancement may be a useful parameter for estimating soil age in certain climates

late pleistocene holocene uplift driven terrace formation and climate tectonic interplay from a seismically active intraplate setting an example from kachchh western india abstract fluvial terrace formation is often regulated by external forcings like climate tectonic and eustatic changes these terraces particularly in a dryland environment preserves the discrete signatures of these external forcings thus enabling us to reconstruct the fluvial response to the late quaternary palaeoenvironmental changes and factors governing them the present study focuses on reconstructing the aggradation incision phases in the lotia river which is located in the eastern segment of the northern hill range nhr of the kachchh peninsula the lotia river drains through mesozoic rocks before cutting across the kachchh mainland fault kmf and finally debouch in the banni plains reconstruction based on tectonic geomorphology sedimentology sediment geochemistry mineral magnetic and osl chronology suggests the fluvial response to monsoon variability archived during the last 15 ka the time frame was also marked by incision enhanced by uplift along the kmf which led to strath terrace formation the accommodation space thus created was filled by an aggradational event between 14 8 ka and 10 6 ka sedimentological and geochemical parameters have also suggested that the time period between 12 5 ka and 11 5 ka showed a decline in the monsoon strength which coincides with younger dryas it has been observed that the sediments spanning between 10 6 ka and 7 8 ka are absent from the archive which is most likely the manifestation of the early holocene optimum that led to severe erosional processes the period between 7 8 ka and 3 3 ka is marked as another aggradational phase with fluctuating climatic conditions at 3 3 ka the region has experienced an incision of 4 m which led to the formation of holocene terrace t 1 most likely due to tectonic uplift during the last 3 3 ka another pulsative uplift has occurred which led to the formation of unpaired holocene terrace t 2 along with tilting of the lotia basin based on the osl chronology of bedrock strath terrace we reported a minimum uplift rate of 1 04 mm a for the eastern kmf during the late pleistocene holocene period hinting seismically active nature of the kmf during this period the terrace formation in the eastern northern hill range is mostly regulated by tectonic uplifts along the kmf

magnetic properties and magnetic fabrics of pleistocene loess palaeosol deposits along west central siberian transect and their palaeoclimatic implications

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

pollen evidence of changing holocene monsoon climate in sichuan province china pollen evidence from lake shayema mianning county was obtained to examine postglacial vegetation and climatic change in southwestern sichuan china the sclerophyllous character of the region s warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the asian monsoons the pollen record displays several changes in the vegetation over the last 11 000 yr from 11 000 to 9100 yr b p cold tolerant species such as abies betula and deciduous oaks dominated the vegetation between 9100 and 7800 yr b p the abundance of deciduous oaks decreased and evergreen oaks increased as did tsuga and mesic deciduous species this change suggests a warming climate with increased precipitation from 7800 to 4000 yr b p sclerophyllous species increased at the expense of mesic deciduous species an indication that precipitation was becoming more seasonal except for increased disturbance starting ca 1000 yr b p the predominance of sclerophyllous vegetation continued until today the pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid holocene

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

northwestward decline of magnetic susceptibility for the red clay deposit in the chinese loess plateau 1 the loess paleosol red clay sequence in the chinese loess plateau has attracted attention for its potential in recording late cenozoic climatic changes over northern china although the details of the climatic implications of the proxies for example magnetic susceptibility and the reconstructed summer monsoon changes remain unclear here we report on a new section from baishui in gansu province and compare it with the lingtai and jingchuan sections by correlating the magnetic susceptibility from these sections we show that there is a clear systematic decrease of the magnetic susceptibility in the red clay deposits from the southeast lingtai section to the northwest baishui section this result suggests that the climatic parameters probably precipitation had a decreasing northwestward gradient during the red clay deposition this climatic pattern is similar to the present condition implying that the influence of the east asian summer monsoon on the chinese loess plateau has persisted from at least 6 ma

investigating soil magnetic properties with pedogenic variation along a precipitation gradient in loess derived soils of the golestan province northern iran abstract in the golestan province in northern iran extensive loess deposits and widespread loess derived soils crop out while a strong precipitation gradient 200 700 mm per year from north to south is characteristic temperature differences are negligible 17 18 c per year recently many studies on loess derived palaeosols and modern soils from this region were published however in these publications only limited information on the magnetic properties of loess and loess derived soils is given nor the potential of these properties to be applied as proxies for palaeoclimate reconstruction in order to study soil magnetic properties along the precipitation gradient in the golestan province six pedons of modern soils were selected the physicochemical properties the clay mineralogy and magnetic parameters of soil samples were analysed susceptibility measurements 20 2 130 77 10 8 m3kg 1 arm susceptibility values 0 00489 0 068 m3kg 1 irm values 0 0027 0 0105 am2kg 1 and hysteresis measurements provide significant evidences for an increase of the content of fine grained ferromagnetic minerals with increasing mean annual precipitation simultaneously the amount of sp sized particles increase magnetite maghemite and hematite are the major magnetic minerals in the studied samples whereby magnetite seems to be dominant in the soils of the loess plateau of northern iran by presenting data from this region of the northern iran for the first time another example is provided for the application of magnetic properties as proxies for the reconstruction of the paleoclimate the results are compared to data of the chinese loess plateau the russian steppe and loessic soils from the midwestern united state with similar relations of pedogenic susceptibility and map

moisture evolution in central asia since 26 ka insights from a kyrgyz loess section western tian shan abstract central asia ca is located in the hinterland of the eurasian continent and faces an extreme risk of continued aridification under the current global warming trend to predict future climate change in ca paleoclimate studies provide essential references however the mechanisms underlying climate changes in ca remain relatively poorly known here we investigate moisture variations in ca as recorded in a 6 m loess section in the western tian shan kyrgyzstan which has accumulated since 26 ka based on the radiometric ams 14c dating we reconstructed the evolution of the wind regime and moisture conditions in the western tian shan with a modified grain size index gsim and a new l proxy l while the frequency dependent magnetic susceptibility fd redness a and yellowness b did not provide reliable paleoclimatic indicators due to weak pedogenesis and other controlling factors the gsim records demonstrated a precipitation maximum in summer before 15 ka shifting to a maximum in spring after 15 ka probably associated with large scale modulation of the latitudinal climatic zones and atmospheric circulation in response to retreat of the northern hemisphere ice sheets based on the l records we place emphases on the important role of temperature modulated evaporation in moisture evolution across ca however this has only influenced moisture evolution in spring and summer with little effect on winter moisture conditions moreover the l records may also indicate that atmospheric humidity can partly affect the long term effective moisture variations

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

bed sediment sources and mixing in the glacierized upper fraser river watershed east central british columbia the geochemical mineralogical and lithological composition of modern stream bed material is examined in order to characterize sources and evaluate downstream mixing of sediments in the upper fraser river drainage basin british columbia the 63 m fraction is emphasized for its relative mobility and ease of analysis using instrumental neutron activation overall the composition of the stream sediments closely re ects bedrock distribution samples dominated by limestone and dolostone calcite and dolomite and related elements ca mg sr etc correspond to lower and middle cambrian carbonate bedrock largely con ned to the moose river sub basin clastic and non quartzite metamorphic lithologies primary and secondary aluminosilicate minerals and related elements al cs rb etc are largely derived from miette group bedrock and associated with the uppermost fraser river sub basin except in the case of the moose river fraser river junction the determination of proportional tributary contributions is complicated by variable or delayed mixing localized oodplain or valley side sources and limited contrast between source areas at present the moose river sub basin contributes a greater proportion of the total and ne grained sediment loads of the combined fraser river than would be expected from drainage basin area alone the imbalance is related to greater relief precipitation and runoff in the moose river sub basin however the spatial association of carbonate rich stream sediments ice cover and carbonate bedrock exposure indicates that glaciers play a particularly important roll in generating ne grained uvial sediment since differences in glacier cover and glacier potential in the two major sub basins are likely to be persistent and since relative sediment yields from the sub basins can be determined from sediment composition a potential indicator of glacier variation and climate change during the holocene is therein available copyright 2004 john wiley sons ltd

sediment magnetic signature of climate in modern loessic soils from the great plains our magnetic analysis of 40 modern loessic soil profiles from the midwestern united states shows that the upper soil horizons of all sites are characterized by an increase in the concentration of fine grained do0 1mm ferrimagnetic minerals magnetite and or maghemite our sites were selected from stable upland positions along a precipitation gradient extending from sw nebraska mean ann precip o500 mm yr to central missouri mean ann precip 41000 mm yr changes in magnetic remanence parameters irm arm and magnetic susceptibility w between soil and parent material vary systematically along the transect and are likely to reflect changes in source area and transport distance magnetic enhancement is calculated for several magnetic parameters by taking the ratio menhanced mparent material where m stands for either arm irm or w our analyses show that magnetic enhancement of modern soils based on irm and w correlates with changes in mean annual precipitation the best correlation however is observed when arm is used as a proxy of magnetic enhancement which might reflect the bias of arm towards small single domain grains of likely pedogenic origin our study shows that magnetic soil properties in combination with non magnetic proxies such as solum depth b horizon color depth to carbonates or other weathering indices have the potential to yield reliable reconstructions of paleoclimate in parts of the great plains where well preserved loessic paleosols exist

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

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

iron mineralogical proxies and quaternary climate change in se european loess paleosol sequences abstract the loess paleosol sequences batajnica stari slankamen serbia and mircea voda romania represent key archives for the climate and landscape development of the middle and lower danube basin during the last 700 000 years for deciphering the quaternary climate evolution in these regions the batajnica stari slankamen and mircea voda sites are for the first time studied by a multi proxy approach based on iron mineralogical parameters changes in the iron mineralogical composition are identified and characterized by rock magnetic investigations diffuse reflectance spectroscopy drs and munsell color based proxies the results show that environmental conditions during mid and early middle pleistocene interglacials were more favorable for hematite formation suggesting a more oxidizing pedoclimate as in the more recent interglacials this is also reflected in a gradual increase of the anhysteretic remanent magnetization vs saturation isothermal remanent magnetization arm sirm ratio in the studied profiles changes in this ratio can be linked to a preferential hematitization of coarse grained ferrimagnetica and relates to warmer climate conditions and a more extended estival dry period at the same time rock magnetic parameters indicate a preferential destruction of fine grained magnetic particles in older paleosols resulting from seasonal excess moisture a progressive cooling and decrease of rainfall during the middle and late pleistocene is evidenced not only for interglacial pedocomplexes but also for glacial loess layers this finding is in line with previously published proxy records of silicate weathering and clay formation at these sites and similar trends reported from other sites in the european steppe belt relating iron mineralogical proxies to paleopedological characteristics and proxies of silicate weathering additionally a change in the seasonal pattern of the interglacial temperature and precipitation regime from a mediterranean type to a steppe type climate is revealed highlighting the potential of such a multi proxy approach possible triggers for this paleoenvironmental evolution are discussed as well finally highlighting a quaternary uplift hypothesis which best could explain the inferred trend of cooling aridification and increasing continentality accordingly changes in atmospheric circulation and rain shadow effects induced by small scale uplift of european mountain belts alps carpathians dinaric alps would provide a driving mechanism for the westward extension of the eurasian steppe belt into central and se europe during the quaternary

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

magnetic and geochemical characterization of andosols developed on basalts in the massif central france identification of andosols is primarily based upon the content of their colloidal constituents clay and metal humus complexes and on the determining of andic properties this needs time and cost consuming geochemical analyses our primary aim of this study is to describe the magnetic and geochemical properties of soils rich in iron oxides derived from strongly magnetic volcanic basement in this case andosols secondary aim is to explore links between magnetic and chemical parameters of andic soils with respect to genesis factors parent material age precipitation and thickness of the soil profile six pedons of andic properties developed on basaltic lavas were analyzed down to parent rock by a set of magnetic and geochemical methods magnetic data of soil and rock samples reflect the type concentration and particle size distribution of ferrimagnetic minerals geochemical data include soil reaction ph in h2o cation exchange capacity organic carbon and different forms of extractable iron and aluminum content our results suggest the following 1 magnetic measurements of low field mass specific magnetic susceptibility can be a reliable indicator for estimating andic properties and in combination with thermomagnetic curves may be suitable for discriminating between alu andic and sil andic subtypes 2 in the studied andosols strong relationships were found between a magnetic grain size parameters precipitation and exchangeable bases b concentration of ferrimagnetic particles and degree of crystallization of free iron and c parameters reflecting changes in magneto mineralogy and soil genesis parent material age soil depth

separation of pedogenic and lithogenic components of magnetic susceptibility in the chinese loess palaeosol sequence as determined by the cbd procedure and a mixing analysis summary magnetic susceptibility variations in the chinese loess palaeosol sequences have been used extensively for palaeoclimatic interpretations the magnetic signal of these sequences must be divided into lithogenic and pedogenic components because the palaeoclimatic record is primarily reflected in the pedogenic component in this paper we compare two methods for separating the pedogenic and lithogenic components of the magnetic susceptibility signal the citrate bicarbonate dithionite cbd extraction procedure and a mixing analysis both methods yield good estimates of the pedogenic component especially for the palaeosols the cbd procedure underestimates the lithogenic component and overestimates the pedogenic component the magnitude of this eect is moderately high in loess layers but almost negligible in palaeosols the mixing model overestimates the lithogenic component and underestimates the pedogenic component both methods can be adjusted to yield better estimates of both components the lithogenic susceptibility as determined by either method suggests that palaeoclimatic interpretations based only on total susceptibility will be in error and that a single estimate of the average lithogenic susceptibility is not an accurate basis for adjusting the total susceptibility a long term decline in lithogenic susceptibility with depth in the section suggests more intense or prolonged periods of weathering associated with the formation of the older palaeosols the cbd procedure provides the most comprehensive information on the magnitude of the components and magnetic mineralogy of loess and palaeosols however the mixing analysis provides a sensitive rapid and easily applied alternative to the cbd procedure a combination of the two approaches provides the most powerful and perhaps the most accurate way of separating the magnetic susceptibility components