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

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

does timing or location matter the influence of site variability and short term variations in precipitation on magnetic enhancement in loessic soils abstract the magnetic properties of soils are often used to quantify soil development and reconstruct past climates in regions where other recorders of paleoclimate are unavailable soil based paleoclimate reconstructions rely on transfer functions that link soil magnetic properties to the climatic conditions during pedogenesis recently the reliability of these transfer functions has been discussed but the variability of soil magnetic properties at a given site is poorly known this study analyzes multiple cores of a loessic soil that have been collected at one locality over the timespan of five years an extensive magnetic characterization of these cores shows that the soil magnetic signal and any climate proxies derived from magnetic data are reproducible between cores from one site and do not depend on short term annual or seasonal fluctuations in precipitation therefore the observed scatter in existing soil climate transfer functions is likely due to variation in microclimates soil drainage and pedogenesis processes rather than sampling existing sites multiple times existing transfer functions are best improved by careful site selection that controls non climate related soil forming factors as well as possible

stratigraphy and spatial and temporal paleoclimatic trends in southeastern eastern european loess paleosol sequences abstract the loess paleosol sections batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine are presently located in areas of different types of steppe and are highly sensitive for recording climatic changes a stratigraphy for these three southeastern eastern european sections is presented based on pedostratigraphy and correlation of recently obtained susceptibility records with susceptibility data of other sections of the area koriten mostistea vyazivok of the chinese loess plateau and with the benthic 18o record of odp 677 six pedocomplexes were studied at the serbian and romanian sections and five at the ukrainian section the oldest are related to marine isotope stage mis 17 batajnica stari slankamen and mircea voda and mis 13 15 stary kaydaky some points concerning the existing loess chronostratigraphies of bulgaria ukraine and china are discussed comparative study of the profiles allows the tracing of paleoclimatic and paleoenvironmental changes in southeastern eastern europe in time and space reconstruction of paleoprecipitation based on susceptibility rainfall relationships and calculations of sedimentation rates are evaluated

magnetic geochemical and pedological characterisation of soil profiles from different environments and geological backgrounds near coimbra portugal abstract this study presents an application of environmental magnetism techniques for the characterisation of the soils near coimbra central portugal magnetic measurements scanning electron microscopy and geochemical studies were carried out on samples collected in 6 soil profiles in order to find possible relationships and to interpret environmental implications magnetic susceptibility saturation isothermal remanent magnetisation and isothermal remanent magnetisation at the backfield of 100 mt and 300 mt were measured hardirm sirm and s ratios were also calculated polluted soils showed higher values of magnetic parameters in the superficial soil horizons closer to the roads plants and urban areas the lowest values were observed in the deeper horizons of the soil and in the areas least disturbed by human activity the magnetic results also suggested that the magnetic signal of these soils is mainly influenced by ferrimagnetic magnetite like minerals and with only a minor contribution from antiferromagnetic carriers such as hematite minerals in unpolluted soils lithogenic contribution is reflected by the enhancement of magnetic susceptibility near parental rock material scanning electron microscope images of the topsoil samples revealed the presence of magnetic spherules typical of vehicular exhaust and combustion processes this evidence suggests that the atmospheric deposition of fly ash is the main reason for the enhancement of the magnetic signal in the topsoil chemical analyses showed that the concentration of various heavy metals was higher than the mean background values for portuguese soils and higher in superficial soils heavy metals showed significant positive correlation with magnetic properties the conclusions highlight the importance of using environmental magnetism methods and techniques in the evaluation process of soil evolution and pollution history throughout time

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

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

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

climatic interpretation of a 1 9 ma environmental magnetic record of loess deposition and soil formation in the central eastern pampas of buenos aires argentina abstract much of what we know about quaternary climate has been learned from sedimentary records from the world s oceans with the exception of the extensive studies of the chinese loess paleosol sequence and more recent studies of long lake records there are few long terrestrial climate records particularly from the southern hemisphere the loess record of argentina provides an important opportunity to further our understanding of climate change from a terrestrial environment but its complexity and discontinuity have led to difficulty in formulating a climatological model of depositional and pedogenic processes in this study we present one of the longest and most continuous loess loessoid records from the central eastern pampas of argentina our age model is based on optically stimulated luminescent dates and a paleomagnetic reversal stratigraphy and indicates a basal age around 1 9 ma within the age model uncertainties we characterize the environmental magnetic properties associated with loess deposition and soil formation with respect to wind patterns moisture availability and temperature major changes in magnetic grain size are linked to a differential northward shift of the subtropical high pressure cell during glacial periods we suggest that coarser finer magnetic grains correspond to weaker stronger glacial periods when the high pressure cell is located in a more southerly northerly position and the source region is more proximal distal to our study area an abrupt increase in the ultrafine grained magnetic material around 0 9 ma is related to an increase in moisture transport from the south atlantic driven by an increase in summer sea surface temperatures at the mid pleistocene transition 1 ma in addition to these grain size variations there is a relative decrease in the amount of goethite compared to hematite beginning around 0 5 ma which has been related to the temperature increase observed after the mid brunhes event 450 ka in the epica ice core temperature record a more detailed comparison to insolation indicates that for portions of the record ferrimagnetic minerals are depleted during periods of low insolation this result suggests that argentine loess deposition and soil formation follows a model more similar to the alaskan loess sequences than the chinese loess sequences although further work is needed to validate the models and mechanisms proposed in this study our record indicates that the mineral magnetic properties of the loess and paleosol deposits record major changes in deposition and soil formation and provide insight into possible mechanisms relating to global and or hemispheric climate change

mineral magnetic properties of an alluvial paleosol sequence in the maya lowlands late pleistocene holocene paleoclimatic implications abstract in the maya lowlands region along the usumacinta river late pleistocene holocene profiles exhibit sedimentary characteristics and soil formation processes as a result of environmental conditions and human environmental interactions here we report a comprehensive environmental magnetic investigation on paleosols and sediments at the tierra blanca archaeological site which shows clear evidences of human occupation the pedogenetical magnetic properties were characterized by rock magnetism studies to determine the composition concentration and domain size distribution of magnetic minerals the late pleistocene paleosols were formed under the influence of a humid climate as shown by the presence of recent fine hematite formation directly related to reduction oxidation processes during gleysol development the transition from early to middle holocene was obtained from a paleovertisol dated as 2 34 2 3 ka which showed a marked heterogeneity in its magnetic parameters due to continuous argilloturbation processes the environmental conditions retrieved indicate the presence of a drought period around 5 5 ka the upper two paleosols were less developed and seems to be strongly affected by human activities during the maya classic period dated between 1 14 and 0 97 ka these soils were formed under more humid conditions and yielded a magnetic mineralogy hematite magnetite maghemite due to incipient weathering and anthropic disturbance

environmental magnetic study of a xeralf chronosequence in northwestern spain indications for pedogenesis article i nfo magnetic enhancement of a and b horizons during soil development is a common phenomenon to better understand the exact mechanism for the magnetic enhancement especially the mineral transformation pathways systematic rock magnetic studies were conducted on a xeralf chronosequence in northwestern spain a positive correlation was found between the average grain size and the concentration of pedogenic maghemite particles with the exception of some a horizons in which multiple factors seem to influence the nature and concentration of neoformed ferrimagnets it is argued that the interaction between the positively charged iron oxides and the anionic ligands present in the solution of these acidic soils plays an important role in this respect the time trends of the average grain size of pedogenic ferrimagnets and the strong correlation between the concentrations of hematite and maghemite in the magnetically enhanced horizons a and b are consistent with the hypothesis of a gradual formation of maghemite later converted into hematite via a precursor most likely ferrihydrite therefore this study provides strong evidence for the dynamic evolution of magnetic minerals upon pedogenesis

holocene colluviation and its implications for tracing human induced soil erosion and redeposition on the piedmont loess lands of the qinling mountains northern china abstract colluvial components incorporated in loess soil sequences have preserved evidence of soil erosion and redeposition in the middle reaches of the yellow river drainage basin holocene loess soil sequences on the gentle sloped lands were studied by measuring magnetic susceptibility particle size distribution caco3 and extraction and identification of the non dust materials the analytical results indicate that in the early holocene soil erosion and redeposition by overland flow occurred even on the loess lands with small ground gradient in response to climatic amelioration linked to global climatic change no obvious soil erosion and redeposition events were found to correspond with the climatic fluctuations recorded in the loess soil sequence during the holocene climatic optimum the primary neolithic farming did not cause apparent erosion and redeposition because the loess landscape was mantled by well developed ustic luvisols and probably by forest vegetation both provided adequate resistance to sheet erosion by overland flow enhanced soil erosion and redeposition are traceable back to ca 4000 a b p it is attributed to intensified land use of arable farming and human settlement from the early bronze age onward a major event of sheet erosion and redeposition by overland flow occurred in the loess landscape during 4000 3600 a b p in the xia dynasty soil degradation and reduced resistance caused by climatic aridity and intensified dust accumulation may have played a secondary role in promoting soil erosion since 3100 a b p these results provide new insights into the history of soil erosion in the semi arid and semi humid loess regions and into the evaluation of human induced accelerated soil erosion against the background of the holocene natural erosion forced by monsoonal climatic fluctuation

loess like and palaeosol sediments from lanzarote canary islands spain indicators of palaeoenvironmental change during the late quaternary abstract on lanzarote canary islands quaternary saharan dust and weathered local volcanic material were trapped in miocence to pliocene valleys dammed by younger volcanic edifices these sediments show sequences of alternating reddish clayey and loess like yellowish silty material in order to investigate if reddish clayey layers contain material derived from local pedogenesis and if so which pedogenetic processes were active we performed sedimentological micromorphological and environmental magnetic analyses the analyses demonstrate that these layers contain material derived from local soils these soils were characterised by clay formation rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture thus they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of lanzarote the distribution of soil material in the profiles shows that cold periods of the late quaternary were characterised by more humid conditions than today using palaeontological remains and a comparison with recent soils on tenerife we can roughly estimate maximal palaeoprecipitation values during more humid periods

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 is linked to and precedes hematite formation in aerobic soil 1 soil formation usually increases magnetic susceptibility most often by increasing the concentrations of magnetite and maghemite which are two ferrimagnetic iron oxides here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite which is later transformed into hematite the iron oxide that gives red color to soil we show that the maghemite hematite ratio is influenced by the particular environment and the degree of soil development so it constitutes an effective tool for paleoenvironmental and planetary studies

characteristics and genesis of maghemite in chinese loess and paleosols mechanism for magnetic susceptibility enhancement in paleosols abstract morphological characteristics and microstructures of magnetic minerals extracted from chinese loess and paleosols were investigated using powder x ray diffraction xrd and high resolution transmission electron microscopy hrtem our results indicate that maghemite in loess paleosol sequences was transformed from magnetite through oxidation of magnetite maghemite transformed from eolian magnetite during chemical weathering has low angle grain boundaries among maghemite nano crystals some nano crystalline maghemites with nanoporous texture resulted from microbe induced precipitation of magnetite or transformation of poorly crystalline ferric fe oxy hydroxides in presence of fe reducing bacteria aggregates of euhedral maghemite nano crystals were transformed from magnetite magnetosomes both microbe induced nanoporous magnetite and microbe produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols it is proposed that the formation of nano crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility although the total amount weight percent of magnetic minerals in both paleosol and loess units is similar our results also show that nano crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi arid soil environments instead of hematite although hematite is a thermodynamically stable phase this result also indicates that a decrease in crystal size will increase stability of maghemite it is also inferred that surface energy of maghemite is lower than that of hematite

how long does iron oxide dissolution and transformation require under water logged conditions a perspective from agricultural activity abstract previous studies have revealed that magnetic enhancement caused by the pedogenic process often occurs in aerobic soils experiencing low to moderate rainfall while magnetic reduction caused by iron oxide dissolution often occurs in anaerobic soils experiencing high rainfall to explore the time required for iron oxide dissolution when the soil conditions transform from aerobic to anaerobic a typical weathering crust profile was selected the results show the complete process of magnetic enhancement and reduction and that the former occurred in aerobic soil due to the newborn magnetic minerals during the pedogenic process while the latter occurred under water logged conditions caused by rice cultivation with a history of approximately 200 years therefore it can be inferred that the time required for the significant dissolution of iron oxides is probably shorter than 200 years which is longer than that determined by indoor experiments but much shorter than the theoretical weathering model

spatial and altitudinal variations in the magnetic properties of eolian deposits in the northern tibetan plateau and its adjacent regions implications for delineating the climatic boundary abstract delineating the climatic boundary i e of precipitation and temperature in the northern tibetan plateau and along its margins is important for understanding the dynamics of global atmospheric circulation and the processes of dust production in central asia to date however meteorological data are scarce for this vast region which limits our understanding of regional climatic patterns and past climatic changes in eurasia in the present study we use a synthesis of both new and published rock magnetic data from the late pliocene the last glacial interglacial cycle and modern eolian sediments to identify the climatic boundary in the northern tibetan plateau and its adjacent areas the results demonstrate that eolian deposits under different environmental scenarios exhibit a clear contrast in the type and grain size distribution of magnetic minerals with the transition from humid to arid climatic regimes a gradual shift from magnetic minerals of predominantly pedogenic origin to predominantly detrital origin can be observed in the surface soils the spatial and altitudinal variations in the magnetic properties of surface soils reveal a distinct boundary of pedogenic intensity in the eastern qilian mountains the western pamir plateau and the northern tianshan mountains the inferred variations in pedogenic intensity combined with analysis of the available meteorological data demonstrate that the pedogenic boundary represents a critical climatic boundary between sub humid to semi arid and arid regions in the northern tibetan plateau and the adjacent regions stronger pedogenesis occurs in surface soils at higher altitudes on the windward side of the major mountains of the northern tibetan plateau supporting the conclusion that precipitation rather than temperature exerts the dominant effect on the magnetic enhancement of surface soils in addition a comparison of several late pliocene pleistocene and last glacial interglacial loess red clay sequences suggests that the modern spatial pattern of the climatic gradients in the northeastern tibetan plateau and the adjacent regions has been maintained since at least the late pliocene or early pleistocene moreover the results demonstrate that during the warm and humid interglacial periods a steepened rainfall gradient occurred in the northern tibetan plateau and its adjacent regions in the future detailed rock magnetic investigations of eolian deposits or surface soils could provide new insights into the dynamics of atmospheric circulation and the natural boundary conditions for paleoclimate modeling in the northern tibetan plateau

the middle palaeolithic site of birzgane tebessa algeria rock magnetic property characterisation and past rainfall reconstruction abstract a new middle palaeolithic site was discovered at birzgane south of the city of tebessa in eastern algeria the archaeological study revealed richness in archaeological artefacts belonging probably to the aterian culture but an absence of pedunculates the aterian archaeological layer was assigned to the end of the middle pleistocene by uranium thorium dating the environmental conditions at the time were assessed by means of magnetic proxy data such as hysteresis parameters magnetic susceptibility and remanent magnetisation the magnetic fraction of the alluvial sediment contains mainly oxidised magnetite and smaller amounts of haematite and goethite indicated by thermal demagnetisation curves of isothermal remanent magnetisation magnetic properties such as enhanced susceptibility anhysteretic remanent magnetisation and frequency dependent susceptibility indicate that the upper part of the section was subjected to pedogenesis after deposition a conceptual magnetic enhancement model was applied to reconstruct past rainfall quantities in the upper part taking into account present day temperatures and rainfall water saturation soil moisture and magnetic susceptibility a precipitation quantity of 560 40 mm was estimated for the transition period from mis 5 to 4 corresponding to the saharan pluvial an extended humid climate period in northern africa between 100 000 and 70 000 years before present

mineral magnetic properties of surface soils and sands across four north african transects and links to climatic gradients 1 in light of their earlier success in characterizing and differentiating soils sediments and atmospheric particulates magnetic measurements were carried out on samples of north african surface soils and sands the main aims were to document spatial variations in magnetic properties explore their possible links to climatic gradients and their likely basis and thereby help to differentiate potential sources for sahara sahel derived dusts samples were collected along four broadly north to south orientated transects located in egypt niger mali and benin and southern togo these transects cover major climatic gradients ranging from hyper arid to tropical across the rainfall range spanned by the niger and mali transects 800 mm yr there are significant north to south gradients in magnetic mineral concentrations this is seen most clearly in the concentrations of the finest ferrimagnetic minerals magnetite maghemite which are strongly represented in the clay fraction concentrations of the imperfect antiferromagnetic minerals predominantly haematite also increase with increasing rainfall by analogy with studies spanning a similar rainfall gradient in areas of more uniform lithology we suggest that the most likely cause for these trends is increased chemical weathering linked to the progressively wetter climate across the sahara sahel transition within the set of samples from egypt rainfall 100 to 5 mm yr there is a marked gradient in the coercivity of remanence in the antiferromagnetic minerals present with coercivity increasing southwards paralleling the trend toward increasing aridity given the strong spatial discrimination demonstrated especially in the niger and mali transects these potentially climate linked gradients hold out the promise of discriminating between dust source regions

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

variation of soil magnetism across the russian steppe its significance for use of soil magnetism as a palaeorainfall proxy abstract modern soils across the chinese loess plateau exhibit strong but disputed correlation between their pedogenic magnetic content and annual rainfall a soil magnetism rainfall transfer function could provide a quantitative proxy of quaternary rainfall for this region however some argue that magnetic dilution through spatially varying fluxes of weakly magnetic dust controls the soil magnetic properties here we test the soil magnetism rainfall couple by examining 22 russian steppe soils free of present dust accumulation across a climatic transect from the semi arid caspian region to the more humid caucasus the soils display systematic increases in topsoil ferrimagnetic concentrations with the exception of climate and its co variant vegetation soil forming factors are essentially constant across this stable area hence the soil magnetic variations dominantly reflect climate and from statistical analysis principally rainfall further the russian steppe magnetic rainfall relationship matches that observed for the chinese loess plateau these independent data thus substantiate the soil magnetism rainfall climofunction and by inference eliminate dust dilution as a significant magnetic factor

quantitative estimates of palaeoprecipitation at xifeng in the loess plateau of china abstract using10be recent studies heller et al 1993 beer et al 1993 have tried to reconstruct palaeoclimatic records by separating the secondary pedogenic and primary aeolian detrital contributions to the magnetic susceptibility of chinese loess here we use a technique which monitors the temperature dependence of magnetic remanence to estimate the magnetisation and relative contribution of the superparamagnetic sp single domain sd and multidomain md ferrimagnetic components in the xifeng loess section on the assumption that the sp ferrimagnetic component is dominantly of pedogenic origin the magnetisation of this component has also been determined for samples taken from the topmost palaeosol s0 at six sites over the loess plateau and directly correlated with present day precipitation at these sites this correlation is then used to estimate quantitatively palaeoprecipitation for the topmost 16 m of the xifeng section which covers about the last 140 000 years the data indicate a considerably reduced precipitation during the glacial loess forming periods and a significantly higher level of precipitation than today during the last interglacial period

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

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

particle size and energetics of gouge from earthquake rupture zones surprisingly considering the forces that we see at the surface not all the energy involved in an earthquake is transformed into ground motion much of it is consumed by frictional heating and rock pulverization an analysis of pulverized rock or gouge collected from the san andreas fault in california and from a rupture zone at 2 km depth in a south african gold mine contradicts the commonly held view that gouge surface energy is a negligible component of earthquake energy balance the analysis reveals unexpected diminutive particles in gouge samples indicating that pulverization not frictional heating is the major consumer of earthquake energy at depth this might explain the heat flow anomaly seen in the san andreas fault system and perhaps some other long standing puzzles in earthquake energetics grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales1 2 3 4 and most slip along mature faults is observed to have been localized within gouge zones5 6 this fine grain gouge is thought to control earthquake instability3 6 7 8 and thus understanding its properties is central to an understanding of the earthquake process7 9 here we show that gouge from the san andreas fault california with 160 km slip and the rupture zone of a recent earthquake in a south african mine with only 0 4 m slip display similar characteristics in that ultrafine grains approach the nanometre scale gouge surface areas approach 80 m2 g 1 and grain size distribution is non fractal these observations challenge the common perception that gouge texture is fractal10 11 and that gouge surface energy is a negligible contributor to the earthquake energy budget3 9 12 we propose that the observed fine grain gouge is not related to quasi static cumulative slip but is instead formed by dynamic rock pulverization during the propagation of a single earthquake

magnetic susceptibility of early paleozoic and precambrian paleosols abstract paleosols formed by weathering and plant colonization during breaks in eolian deposition of quaternary loesses are marked by enhanced magnetic susceptibility these paleosols can be recognized in the field from their soil structure and soil horizons but the most obvious and diagnostic feature of paleosols are root traces for paleosols of early paleozoic and precambrian age pre dating the evolution of rooted land plants root traces cannot be used as a diagnostic field criterion for recognizing paleosols surficial enhancement of magnetic susceptibility can be useful confirmation that some precambrian and early paleozoic rocks were paleosols unfortunately magnetic susceptibility enhancement of some paleosol profiles is compromised by burial gleization which reduces overall susceptibility values but especially susceptibility at the surface of the profile and produces a marked covariance of magnetic susceptibility with total iron content groundwater and surface water gleization during soil formation also depletes susceptibility over a wide range of iron content to give relatively flat depth functions of susceptibility in contrast well drained soils and paleosols have pronounced surficial susceptibility enhancement over a narrow range of iron content magnetic susceptibility peaks are useful supporting evidence for paleosols entirely red and oxidized but not for paleosols with common green gray reduction spots abundant organic matter iron manganese nodules or other evidence of gleization all known paleozoic and precambrian paleosols have susceptibility an order of magnitude less than in comparable quaternary paleosols and soils so that quaternary magnetic susceptibility climofunctions and chronofunctions cannot yet be applied to paleozoic and precambrian paleosols although their susceptibility values are comparable with those of modern gleyed soils paleozoic and precambrian paleosols maintain a depth function of surficial enhancement of susceptibility as well as red color deeply penetrating cracks and other features of well drained soils burial recrystallization of fine grained magnetite and maghemite may have compromised the magnitude of their susceptibility peaks alternatively they may not have been as biologically active in susceptibility enhancing microbes as modern soils

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau by balsamreply to letter to the editor on dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau by balsam

climatic thresholds for pedogenic iron oxides under aerobic conditions processes and their significance in paleoclimate reconstruction abstract iron oxides are widely distributed across the surface of the earth as a result of the aerobic weathering of primary fe bearing minerals pedogenic iron oxides which consist mainly of hematite hm goethite gt maghemite mgh are often concentrated synchronously in aerobic soils under low to moderate rainfall regimes magnetic susceptibility and redness which respectively reflect the content of mgh and hm in soils are considered reasonable pedogenic and climatic indicators in soil taxonomy and paleorainfall reconstruction however under high rainfall regimes the grain growth of mgh and transformation to hm combined with the prior formation of gt under conditions of high relative humidity rh can result in magnetic reduction and dramatic yellowing of soils and sediments which explains the existence of rainfall thresholds for mgh and hm at a large scale even before the pedogenic environment turns anaerobic in order to capture the rainfall thresholds for mgh and hm occurring under aerobic conditions we explored a tropical transect across a granitic region where the soil color turned from red to yellow under a wide rainfall range of 900 2200 mm yr and a corresponding mean annual rh range of 77 85 we observed a lower rainfall threshold of 1500 mm yr and a corresponding rh 80 for mgh and hm along this transect as well as a higher rainfall threshold of 1700 mm yr and a corresponding rh of 81 for gt and total pedogenic iron oxides citrate bicarbonate dithionite extractable fe fe d cross referencing with comparable studies in temperate and subtropical regions we noted that the rainfall or rh thresholds for fe d and hm or mgh likewise increase with temperature moreover the different thresholds for total and individual iron oxide phase indicates that a negative correlation between chemical weathering intensity and redness or in sediment sequences can occur under the prevalent climate regime just between their thresholds finally we developed an integrated model to interpret the sequential formation of rainfall thresholds for different pedogenic iron oxides in soils and sediments with conditions from aerobic to anaerobic

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

iron oxide characteristics of mid miocene red clay deposits on the western chinese loess plateau and their paleoclimatic implications abstract the middle miocene climate optimum mmco 14 3 16 3 ma was a warm climatic interval that may provide an analog for future climates in the context of ongoing global warming in continental regions however reconstruction of the mmco remains controversial due to the lack of robust proxies from continuous sedimentary sequences in this study we investigated the composition and relative abundance of pedogenic iron oxides in the zhuanglang red clay deposits from the western chinese loess plateau using rock magnetic color reflectance and geochemical analyses our aim was to assess the climatic sensitivity of iron oxides in order to produce robust proxies for reconstructing regional temperature and moisture relationships during the mmco our results indicate that the mmco in the study region was characterized by high effective precipitation relatively high temperature and strong pedogenesis suggesting a strong east asian summer monsoon easm the strengthening of the easm intensity during the mmco is consistent with records of enhanced terrigenous chemical weathering in the south china sea and the occurrence of a relatively warm and humid climate on a global scale implying the strong coupling between asian monsoon evolution and global climate change during the middle miocene in addition the magnetic susceptibility record of the zhuanglang red clay demonstrates that eccentricity played the dominant role in controlling the easm during the mmco

magnetic susceptibility and geochemical characterization of an upper mississippian cyclothemic section polotnyanyi zavod moscow basin russia

rock magnetic properties of a soil developed on an alluvial deposit at buttermilk creek texas usa 1 the evolution of magnetization within a floodplain soil begins with initial deposition of magnetic particles during sedimentation and continues via subsequent alteration and growth of iron bearing compounds by pedogenic and biologic processes measurements of soil magnetic properties capture information about the developmental history of the soil and are a convenient method by which to investigate environmental change and pedogenesis using a range of magnetic measurements a comprehensive scenario for soil development was constructed for floodplain sediments at the debra l friedkin site an important archeological site near buttermilk creek texas floodplain deposits have traditionally been avoided for soil magnetism studies because it is thought that the episodic input of sediment would form soils characterized by discrete sedimentary units rather than a continuous record of pedogenesis we demonstrate that alluvial deposits can sometimes carry a straightforwardly interpretable magnetic signal similar to those typically seen in loess deposits smooth variation of rock magnetic parameters as a function of depth also leads us to conclude that the soil at this site is largely undisturbed and that the age of lithic artifacts found within the soil may be interpreted within stratigraphic context

palaeoclimatic indicators in soils buried under archaeological monuments in the eurasian steppe a review the russian experience of the local reconstruction of the eurasian steppe climate during the last 5000 years based on geoarchaeological approaches is reviewed examples of traditional palaeoclimatic reconstructions in russia based on organic matter highly soluble salts and gypsum content and location of salts and gypsum horizons in the profile of buried soils are given pedogenic carbonate as a palaeoclimatic indicator is considered the possibilities of the quantitative reconstruction of the palaeoprecipitation based on magnetic properties of buried soils are observed the innovative approach of palaeoclimatic reconstruction based on soil microbiology methods is reviewed the problem of temporary transformation of palaeoclimatic indicators in buried soils is shown a methodology for the interpretation of palaeoclimatic indicators of buried soils for a local palaeoclimatic reconstruction is given

inter profile correlation of the chinese loess paleosol sequences during marine oxygen isotope stage 5 and indications of pedogenesis abstract low field magnetic susceptibility has been widely used to determine the pedostratigraphy of the chinese loess paleosol sequences however uncertainties remain in correlating between the loess magnetic susceptibility and the marine oxygen isotope records because susceptibility variations are affected by both global and local paleoclimatic changes to provide a more sound paleoclimatic interpretation of magnetic susceptibility variations age models across marine oxygen isotope stage mis 5 for the jiuzhoutai jzt and yuanbao yb sections western chinese loess plateau were constructed through an integrated approach by linking the major pedostratigraphic boundaries of the loess profiles to the specmap oxygen isotope curve and by correlating relative magnetic paleointensity records with both the sint800 global paleointensity stack from marine sediments and 36cl records from the grip ice core results indicate good correlation of sirm60 mt a residual remanence of saturation isothermal remanent magnetization after a 60 mt alternating field demagnetization variations between these two sites which agree well with fluctuations in subtropical atlantic sea surface temperatures all cooling events recorded by ice core and atlantic marine sediments within mis5 have counterparts in sirm60 mt sirm60 mt is partially controlled by the degree of low temperature oxidation which is strongly temperature dependent however strong pedogenesis can decrease sirm60 mt due to further oxidation of partially oxidized magnetites above some critical points therefore we propose that sirm60 mt is best suited to record paleotemperature changes in loess profiles from the western chinese loess plateau where pedogenesis is the weakest furthermore by inter profile correlation between the yb and jzt sections we note that the seemingly uniform sub paleosol unit with a broad susceptibility peak previously assigned to mis5c between 34 4 and 37 4 m in the yb profile actually consists of two independent units lower part of s1l1 mis5b and s1s2 mis5c this indicates that susceptibility values can be strongly affected by local factors e g mainly precipitation therefore beside the simplistic traditional paleoclimatic interpretation of variations in loess susceptibility involving only cold dry and warm humid scenarios cold humid and warm dry scenarios should also be considered

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

late holocene climate reconstructions for the russian steppe based on mineralogical and magnetic properties of buried palaeosols abstract insights into past climate changes and corresponding evolution of soils and the environment can be gained by multidisciplinary studies of palaeosols here we focus on palaeosols buried beneath archaeological monuments specifically funerary mounds kurgans in the russian steppe the kurgans were constructed and each of the palaeosols buried over a range of different timesteps from the mid holocene to 600 years before present yr bp integrated magnetic mineralogical and pedological data were used to obtain estimates of past climate especially precipitation changes through both time and space a soil magnetism based climofunction derived previously from modern steppe soils and modern climate was applied to each set of palaeosols to obtain quantitative reconstructions of annual precipitation for the time at which the soils were buried independent soil property data clay mineralogy salt content iron mineralogy from mossbauer analysis and optical and electron microscopy were also obtained in order to test and substantiate the magnetic inferences the data obtained indicate that the climate of the lower volga steppe area has varied from the mid holocene onwards precipitation minima occurred at 5000 3800 and 1600 yr bp with intervals of enhanced precipitation at 1900 yr bp and 600 yr bp these rainfall variations appear to occur synchronously with changes in middle eastern precipitation and lake levels suggesting they are controlled by index changes in the north atlantic oscillation

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

investigating the penultimate and last glacial cycles of the suttő loess section hungary using luminescence dating high resolution grain size and magnetic susceptibility data the loess paleosol record at sutt provides an excellent high resolution archive of climate and environmental changes loess deposits with a thickness of 20 m cover the travertine at sutt in the northern part of hungary next to the right bank of the danube river the loess sequence is intercalated with two greyish stratified horizons three brownish steppe like soils and a pedocomplex including a reddish brown paleosol covered by a chernozem like paleosol detailed infrared stimulated luminescence irsl dating was carried out revealing more or less continuous sedimentation from marine isotope stage mis 6 mis 2 sedimentological and paleomagnetic investigations have been performed to provide a high resolution study of the sutt loess paleosol sequence in order to reconstruct the paleoclimate and environmental changes during the penultimate and last glacial cycles grain size and magnetic susceptibility ms records of the sutt profile basically show similar patterns to those of other european loess sections however small differences are traced at sutt including more intensive deposition of coarser grained materials during mis 6 4 the loess record at sutt has a transitional position within the european loess belt as its sediment was deposited under an intermediate climate between the loess successions from the southern carpathian basin which accumulated under drier climate and the loess sequences from western europe which developed under wetter climate during the middle and late pleniglacial

the state of microbial communities in buried paleosols in relation to prevailing climates in steppes of the lower volga region abstract the microbial communities of paleosols buried beneath kurgans archeological site salomatino volgogradskaya oblast russia dated to the srubnaya ca 1500 bc the late sarmatian ca ad 150 250 cultures and the golden horde time ca ad 1300 1400 and modern surface soils kastanozems and solonetzes were studied in the paleosols the amounts of viable microbial biomass constituted 40 65 aeh ae or ea horizon 27 76 bt or btn horizon and 47 287 bk horizon of the amounts in modern surface soil and reached 5 8 of total corg remained the abundances of viable microbial cells calculated from the phospholipid content in the modern surface and buried soils were similar 2 5 1010 and 1 6 2 5 x 1010 respectively the abundances of microorganisms capable of growth on selected media were 4 orders less than total numbers of viable microbial cells the regularities of the profile distribution of viable microbial biomass ecological trophic structure of microbial communities and the oligotrophy indexes in sub kurgan paleosols and their modern surface analogs were indicative for tracing the dynamics of climate humidity in the region studied the climatic conditions at the time of the srubnaya culture were more arid compared to the current time although generally this period may be considered humid the climate within the late sarmatian time was changeable arid conditions alternated with more humid ones and these periods lasted for several decades the late period of the golden horde time was characterized by more arid conditions compared to the previous humid period and the current time the microbiological data in general correspond to morphological and physicochemical properties of paleosols and in some cases might provide more detail evidence about the climate fluctuations and climatic phases of shorter duration

charcoal records of fire history in the holocene loess soil sequences over the southern loess plateau of china abstract charcoal preserved in accretionary loess soil profiles within the southern part of the loess plateau has recorded fire history and landscape evolution connected with climatic variations and human activities local wildfires occurred frequently during the late last glacial period and the early holocene before 8500 years bp when steppe vegetation expanded from the inner mongolian plateau southerly over the loess plateau during the holocene climatic optimum between 8500 years bp and 3100 years bp natural wildfires were largely reduced pedogenesis of the luvisols and isohumisols was intensified because of the increased monsoonal precipitation and soil moisture localized fires in connection with human activities occurred in different patterns at the study sites fire seems to have been applied to vegetation clearance for land reclamation for millet cultivation at many places during the neolithic and early bronze age levels of biomass burning were very high during the late holocene when the climate became drier and historical land use became more intensive at some sites the intensity of human disturbance by fire and cultivation increased continuously during the last 3100 years at the other sites local fires occurred most frequently between 3100 years bp and 1500 years bp during the major period of land reclamation for cereal cultivation human burning of the landscape has been reduced since then

rock magnetic characterization of pedogenesis under high energy depositional conditions a case study from the mio pliocene siwalik fluvial sequence near dehra dun nw himalaya india abstract systematic rock magnetic studies accompanied by field investigations are presented for 51 pedogenic horizons from magnetostratigraphically constrained middle upper siwalik fluvial sequence 9 4 ma near dehra dun in the himalayan foreland basin hfb detailed sedimentologic studies infer predominantly proximal to distal alluvial fan setting with considerably high rate of sedimentation 55 cm ka paleosol profiles in the mohand rao mr section are commonly truncated by channel activity these paleosols display few rootlets diffused color contrast amongst variegated pedogenic horizons rare concretions intense gleying at places and frequent incursions by sand silt layers the mean mass specific magnetic susceptibility lf for pedogenic horizons is 0 95 10 8 m3 kg max 1 4 10 8 m3 kg min 0 5 10 8 m3 kg and the associated non pedogenic layers is 0 82 10 8 m3 kg max 1 2 10 8 m3 kg min 0 4 10 8 m3 kg the low frequency dependence of the susceptibility fd mean 2 and high coercivities bocr mean 425 mt of the pedogenic layers infer the absence of finer pedogenic superparamagnetic sp fraction that might have depleted during post depositional burial processes acquisition of isothermal remanent magnetization irm shows under saturation and gentle upward trend even at high applied fields 4000 mt advocating the predominance of hematite and goethite sympathetic variation in the total organic and inorganic carbon content with iron oxides stable under warm humid oxidative arid and cold restricted conditions confirm the sensitivity of the rock magnetic parameters to ambient climatic condition relative variations in goethite hematite and ferrimagnetic contents have been derived from ratios mainly based upon selective irm saturations and their coercivities these studies are validated by sandstone petrography and clay mineralogy for the same section however the variation in rock magnetic parameters shows a better amplification and allows relative quantification of the ambient climatic conditions the assemblage of iron oxides using the rock magnetic ratios of the pedogenic layers in these high energy conditions broadly infer the prevalence of semi humid to semi arid climate entirely during the late miocene to early pliocene period in the hfb with an increased seasonality during early pliocene the present approach envisages a great scope for quantitative database under the given setup of high energy conditions that are common in the mio pliocene hfb

pedo chemical climate proxies in late pleistocene serbian ukranian loess sequences abstract the last glacial interglacial loess paleosol sequences of serbia and ukraine provide a good climate reconstruction potential for this part of europe four loess sections distributed over an area with present day moist to semi arid climates were studied in addition to traditional paleoclimate proxies such as grain size distribution as proxy for wind strength and source aridity and magnetic susceptibility as proxy for precipitation and temperature pedo chemical elemental ratios obtained by selective sediment leaching procedures function as sensitive recorders of variations in weathering intensity due to changes in precipitation and temperature especially the earth alkaline element ratios of ba sr and sr ca are subject to strong variations as a result of carbonate dissolution precipitation and variable cation exchange capacity on clay minerals along the elemental sequence of ca sr ba as shown by the close similarity to the magnetic susceptibility records in the different loess sections these ratios reflect the effects of weathering intensity as a result of precipitation changes the fact that ba sr unequivocally shows higher values in both soils and paleosols in the four studied sections over the present day climate gradient singles this elemental ratio out as an interesting paleoclimate proxy

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

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

a preliminary magnetic study of soil samples from west central minnesota abstract various rock magnetic techniques were applied to characterize magnetically the samples of a soil profile taken from west central minnesota there is a marked change in magnetic properties as a function of depth in the core x ray analysis and curie temperature measurements carried out on the magnetic fractions indicate that magnetite is the dominant iron oxide in both the top soil and the subsoil the intensity of anhysteretic remanent magnetization arm decreases sharply as the depth increases in contrast the stability of arm was found to be higher for the subsoil the surface soil sample was capable of acquiring a significant amount of viscous remanent magnetization vrm the vrm acquisition coefficient s a of the subsoil s a 3 18 10 6 emu g 1 3 18 10 6 a m 2 kg 1 was about ten times weaker than that of the top soil sample s a 3 868 10 7emu g 1 3 868 10 7 a m 2 kg 1 the magnetic domain state indicator the ratio of coercivity of remanence to coercive force h cr h c was 1 5 and 3 85 for the top soil and subsoil respectively it appears that the observed variations in magnetic properties down the present soil core is due only to a difference in grain size we conclude that the magnetic grains in surface soil samples were more single domain sd like whereas the magnetite grains in the subsoil samples were more likely in pseudo single domain psd or small multidomain md range the observed lower stability for the surface soil samples is attributed to the presence of superparamagnetic grains whose presence was confirmed by transmission electron micrographs

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

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

holocene variability of the east asian summer monsoon from chinese cave records a re assessment oxygen isotope records from stalagmites in caves in southern china interpreted as proxy rainfall records reflecting the intensity of the east asian summer monsoon indicate gradual monsoon weakening for the last 9000 years as also documented for the indian monsoon coupled with high precision dating the speleothem proxy records have been used to test monsoon links with orbital forcing solar changes iceberg discharges in the north atlantic ocean currents and atmospheric methane however these benchmark cave records do not match other published dated e asian proxy rainfall record specifically here independently calibrated rainfall records from loess palaeosol magnetic properties and cave oxygen isotope intercomparisons which show variable e asian monsoon intensity through the entire holocene the strong correlation of the cave records with the extraregional indian monsoon record yet their mismatch with these other dated chinese rainfall records might be reconciled if the speleothem isotope variations reflect not changes in holocene rainfall amount but in rainfall source declining holocene influence of isotopically lighter indian monsoon sourced moisture over china would have resulted in increasing proportions of isotopically heavier rainfall sourced from the more oceanic e asian monsoon individual speleothems may thus regionally record holocene changes in indian monsoon intensity and isotopic influence conversely the other chinese proxy records described here reflect changes in rainfall amount and thus in e asian summer monsoon intensity for the holocene the e asian and the indian monsoon responses to orbital forcing are likely to have differed specifically due to e asian internal feedbacks and the seasonal contrasts between the two monsoon systems

weathering characteristics of interflow volcanic boles from mandla lobe eastern deccan volcanic province abstract the deccan volcanism straddling the cretaceous paleogene boundary resulted into one of the most extensive continental flood basalts in the western and central peninsular india the interflow sedimentary units boles often cited as paleosols are the rare archives of paleoenvironmental conditions existed during successive lava flows a debate on the origin of boles as true paleosols exists therefore in order to trace out regional extent of such conditions pedogenic non pedogenic in the context of their paleoenvironmental significance during the deccan volcanism we studied here mineral magnetic characteristics of 36 color differentiated bole beds from the mandla lobe in the eastern deccan volcanic province edvp classified into four types gray yellow brown and red based on their munsell notations the gray yellow and brown boles show dominantly ferrimagnetic composition chiefly magnetite and titanomagnetite while red boles characterize mixed ferri and antiferromagnetic mainly hematite mineralogy the granulometric domain parameters suggest larger single domain sd and the multidomain md ferrimagnets in the majority of cases whereas superparamagnetic sp particles with frequency dependent susceptibility fd 2 6 to 20 3 10 8 m 3 kg 1 are limited to the few red and brown boles only the significant presence of primary parent magnetic minerals i e coarse sd md titanomagnetite and magnetite in the majority of boles depict incipient to moderate weathering owing to limited time intervals during successive eruptions the combination of hematite and sp particles present only in the few red and brown boles depicts baking effect rather than pedogenesis the comparison of magnetic properties of boles from edvp and western deccan volcanic province wdvp shows significant differences in the concentration of sp ferrimagnetic particles and hematite attributed to variable weathering intensity duration and heating related alterations from the upper flows both edvp and wdvp boles indicate similar first order paleoenvironmental conditions without any major pedogenesis that can be regionally correlated

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

controlling factors for the spatial variability of soil magnetic susceptibility across england and wales abstract we review the nature and importance of soil factors implicated in the formation of secondary ferrimagnetic minerals in soils and palaeosols worldwide the findings are examined with respect to temperate regions through a comprehensive analysis of over 5000 samples of surface soil from england and wales taken from a 5 5 km grid over 30 soil and environmental attributes are considered for each sample as proxies for soil forming factors measurements of low field magnetic susceptibility mass specific and frequency dependent susceptibility mass specific and percentage on each sample provide estimates of the concentration and grain size of ferrimagnetic minerals maps of soil magnetism across england and wales show non random distributions and clusters one subset of data is clearly linked to contamination from atmospheric pollution and excluded from subsequent analyses the concentration of ferrimagnetic minerals in the non polluted set is broadly proportional to the concentration of minerals falling into the viscous superparamagnetic domain size range 15 25 nm this set shows clusters of high magnetic concentrations particularly over specific parent materials such as schists and slates mudstones and limestones bivariate analyses and linear multiple regression models show that the main controlling factors are parent material and drainage the latter represented by soil drainage classes and particle size together these two factors account for 30 of the magnetic variability in the complete dataset a second group of factors including climate mean annual rainfall relief slope and altitude and organisms land use organic carbon and ph have subordinate control climate as represented by mean annual temperature and also pedogenic time are deemed not relevant at these spatio temporal scales the findings are consistent with a largely abiotic system where the role of iron reducing bacteria appears minor at coarse spatial and temporal scales secondary ferrimagnetic mineral formation is controlled by the weathering capacity to supply fe to the surface soil at finer scales soluble fe precipitates as ferrihydrite before transformation in response to periodically anaerobic conditions into other minerals including nanoscale magnetite

wildfire history and climatic change in the semi arid loess tableland in the middle reaches of the yellow river of china during the holocene evidence from charcoal records high resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess paleosol profiles on the semi arid loess tableland landsca

quantitative relationships between magnetic enhancement of modern soils and climatic variables over the chinese loess plateau environmental magnetism has been widely employed to reconstruct past climate changes on the chinese loess plateau clp and several climofunctions based on the magnetic properties of loess have been developed however systematic investigation of the quantitative relationship between topsoil magnetic enhancement and modern climate remains uncommon in this study we obtained surface soil samples from 257 sites over the clp and adjacent regions from this set we used 180 samples from sites unaffected by potential contamination to investigate the relationship between the commonly measured magnetic properties of magnetic susceptibility and magnetic remanence and modern climatic variables the spatial distribution of the results demonstrates a strong nw se gradient of the magnetic enhancement of surface soils the results of more detailed magnetic parameters indicate that pedogenic viscous superparamagnetic and stable single domain particles are mainly responsible for the magnetic enhancement of the soils in the studied region and that the magnetic grain size distribution of the ferrimagnetic components of pedogenic origin remains almost constant independent of pedogenic intensity the uniform mechanism of magnetic enhancement mainly linked with the concentration of the pedogenic components rather than with variations in magnetic grain size decreases the level of ambiguity in climate reconstructions based on magnetic measurements of chinese loess statistical analyses including correlation principal component analysis pca and multiple regression analysis suggest that annual rainfall rather than temperature exerts the dominant effect on soil magnetic enhancement finally we used the results to develop several transfer functions to reconstruct mean annual precipitation map transfer functions based on frequency dependent susceptibility fd and anhysteretic remanent magnetization arm provide the most reliable estimates of map this study significantly improves the understanding of the relationship between soil magnetic properties and climate

quantifying paleoprecipitation of the luochuan and sanmenxia loess on the chinese loess plateau abstract paleoprecipitation is one of the most important paleoclimatic factors for monsoon studies magnetic properties of the chinese loess paleosol sequences have been demonstrated to be controlled strongly by the mean annual precipitation map in this study temporal variations of maps were systematically investigated for the luochuan lc and sanmenxia smx sequences from the loess unit l1 10 ka to the paleosol unit s5 620 kyr by applying the new climofunction map 8 06 fd hirm 254 where fd and hirm are frequency dependent magnetic susceptibility and hard isothermal remanent magnetization respectively for both the lc and smx sequences our climofunction indicates paleosols have higher maps than loess units and the maximum map value occurs in s5 indicating that the east asian summer monsoon was the strongest during the formation of s5 in agreement with previous studies overall maps of smx are higher than those of lc as smx is in the southeast of lc and receives more precipitation the positive correlation between the reconstructed maps and fd and arm suggests that precipitation is a key factor controlling degree of pedogenesis maps of paleosols from smx display a negative correlation with synchronous insolation maxima and a positive correlation with corresponding insolation minima however at lc maps have a less significant relationship with insolation this may be because the summer monsoon signals are relatively weak in lc and covered by local climate and environmental alterations in interglacials the summer monsoon associated with precipitation is controlled by the corresponding insolation maxima and minima in addition the map gradient between lc and smx is also modulated by the insolation amplitude

the evolution of mediterranean wetlands in the first millennium ad the case of les arenes floodplain tortosa ne spain abstract mediterranean wetlands are characterised by two factors 1 a remarkable seasonal fluctuation in the water table and 2 a long history of anthropisation being exceptional archives for palaeoenvironmental and archaeological research humid areas have been thoroughly studied to assess the interplay between people and the environment during the holocene we present here the study of a sedimentary sequence from a mediterranean wetland the les arenes floodplain tortosa ne spain fully dry to date les arenes is documented as a partially drained floodplain in the 12th century records with the aim of assessing the climatic and anthropic contribution to its desiccation we report here the results of bulk sediment analyses environmental magnetism soil micromorphology and ams dating of this sedimentary sequence plus a review of the available historical records the outcome is a clearer understanding of the evolution of this mediterranean floodplain during the 1st millennium ad which implications may be extrapolated to other floodplain wetlands in the iberian peninsula and the mediterranean wet conditions and a low to medium energy depositional environment are attested in les arenes between the 1st and 7th centuries coinciding with the iberian roman humid period irhp and the dark age humid period dahp drier conditions between the 7th and 10th centuries concur with enhanced fluvial dynamics the medieval climate anomaly mca and the first arrival of arabic berber populations in the iberian peninsula al andalus starting in ad 711 results suggest that although the shift from wet to dry conditions in les arenes complies with major climatic trends the construction of the first drainage canals by arab berber groups likely contributed to the enhancement of on going climate related environmental processes

validation of wiggle matching using a multi proxy approach and its palaeoclimatic significance research into global millennial scale climate oscillations during the last glacial requires wiggle matching one method for adequate wiggle matching is based on the dating of the climate proxy records luminescence dating methods are needed for estimates of last glacial ages in terrestrial records however such dating methods are not accurate enough for millennial scale wiggle matching it is shown that a multi proxy comparison of two sections that are situated close to each other may considerably improve the accuracy of wiggle matching the method is tested by an application on two loess sections of last glacial age in vojvodina serbia the climate proxies include magnetic susceptibility leachate ba sr and grain size firstly single proxy wiggle matches between both sections are analysed successively with the same and with different proxies secondly a multi proxy wiggle match based on all three proxies of the two sections is presented and compared to the single proxy tests in such a procedure it becomes clear which wiggles are mainly determined by local conditions and which have a more extended significance it is concluded that a multi proxy approach results in the best and the most unique wiggle matches copyright 2009 john wiley sons ltd