magnetic parameter variations in the chaona loess paleosol sequences in the central chinese loess plateau and their significance for the middle pleistocene climate transition abstract a high resolution rock magnetic investigation was performed on the chaona quaternary loess paleosol sequences in the central chinese loess plateau based on a newly developed independent unturned time scale and magnetic records we reconstructed the history of the east asia monsoons during the last 3 ma and explored the middle pleistocene climate transition mpt rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity lower magnetic susceptibility ms and that the paleosol layers are characterized by relatively high ms saturation magnetization and remanent saturation magnetization spectrum analyses indicate that there are various periods in addition to orbital periodicities according to the onset and stable appearance of 100 kyr period we consider that the mpt recorded in this section began at 1 26 ma and was completed by 0 53 ma which differs from previous investigations based on orbitally tuned time scales the forcing mechanism for the mpt was more complicated than just the orbital forcing we conclude that the rapid uplift of the tibetan plateau may have played an important role in the shift of periodicities during the middle pleistocene

assessing the utility of visible to shortwave infrared reflectance spectroscopy for analysis of soil weathering intensity and paleoclimate reconstruction abstract visible to shortwave infrared reflectance vswir spectroscopy is a fast and efficient approach for estimation of soil properties in order to test whether soil weathering intensity can be predicted using reflectance spectra in the vswir range 350 2500 nm and to examine the efficacy of this methodology to supplement or substitute for traditional mineralogical and geochemical techniques of paleoclimate reconstruction we investigated a quaternary soil sequence at shengli in the sichuan basin of southwestern china vswir absorption bands can be characterized by geometrical parameters including position p depth d width w asymmetry as and full width at half maximum f our results indicate that spectral features in the visible to near infrared vnir 350 1000 nm range can be interpreted in terms of the presence and or concentration of individual fe oxide phases spectrally detected water is mostly bound in clay minerals and this single dominant water source facilitates interpretation of shortwave infrared swir 1000 2500 nm parameters soil spectral parameters were compared with the fe oxide mineralogy major element composition and clay mineralogy of soil samples obtained from conventional laboratory analyses strong correlations are found between vnir parameters and fe oxide mineralogy with d 900 serving as the best proxy for total ferric iron concentration p 900 and d 700 d 500 exhibit similar variation trends and relationships to the hematite hematite goethite h h g ratio of soil samples confirming their value as monsoonal weathering intensity proxies lower values of p 900 and d 700 d 500 indicate warmer and seasonally drier pedoenvironments reflecting a stronger east asian summer monsoon the utility of some swir parameters for assessment of weathering intensity declines in inhomogeneous soils e g those having vermiform structure thus spectral evaluation of weathering intensity is most effective in soils that are relatively homogeneous for which weathering degree is highly correlated to as 2200 d 2200 d 1900 and as 1400 the utility of these spectral proxies depends mainly on the mineral composition of soils and the application type i e laboratory versus field studies the application of vswir in the field e g imaging spectroscopy or is shows promise for rapid in situ mapping of weathering intensity thus providing a convenient approach to paleoclimate reconstruction in remote and inaccessible regions

clay mineral record in lake baikal sediments the holocene and late glacial transition abstract we analyse the clay mineralogical composition of two 1 m long cores from elevated plateaus in the southern and northern basins of lake baikal our aim is to test the limits of classically used clay proxies for climate reconstructions mineralogical signature is determined by x ray diffraction on oriented aggregates from holocene and late glacial sediments mineralogical results are presented on a palaeomagnetic derived time scale sampling at a centimeter resolution allows for a sub millenial order reconstruction the evolution of clay derived climate proxies smectite illite peak intensity ratio s i is compared between the two locations with respect to other climate reconstructions for the lake baikal area and siberia during the late glacial punctual increases of s i are related to changes of particle source rather than any climate change at both sites the most intense chemical weathering conditions occured during the subboreal lagging the eurasian middle atlantic climate optimum s i follows a gradual but irregular increase through the holocene probably related to slow warming favourable to the development of the siberian soils the different sensitivity to hydrolysing conditions in northern and southern sites can be explained by a combination of local lithological and topographical parameters

magnetostratigraphy of chinese loess paleosol sequences abstract as one of the longest and most continuously deposited terrestrial sedimentary archives in the world chinese loess paleosol sequences record paleoclimatic and paleomagnetic variations at a range of time scales magnetostratigraphic studies provide a first order chronological framework for chinese loess sequences in this review we highlight recent developments in loess magnetostratigraphy including pedostratigraphy based on magnetic susceptibility variations we highlight progress in understanding the mechanisms by which the natural remanent magnetization nrm is acquired and discuss in detail the fidelity of paleomagnetic recording in loess records including the recording of magnetic polarity reversals excursions and relative paleointensity variations finally we discuss future prospects for studies of loess nrm

new constraints on climate forcing and variability in the circum mediterranean region from magnetic and geochemical observations of sapropels s1 s5 and s6 eastern mediterranean sapropels are organic rich layers whose formation was triggered during boreal summer insolation maxima precession minima sapropel formation is associated with increased precipitation and runoff from europe and north africa although the relative influence of high and low latitude climate mechanisms is not fully resolved likewise it remains uncertain how centennial scale interruptions in conditions that give rise to sapropels may reflect atmospheric circulation changes in low latitudes we present magnetic geochemical and diffuse reflectance spectroscopy data from three sapropels that are representative of glacial s6 and interglacial s1 s5 conditions in the eastern mediterranean sea to assess environmental changes associated with sapropel formation the extent of diagenetic magnetite dissolution and authigenic formation of fine grained greigite in these sapropels and their underlying dissolution intervals are linked to enhanced sulphidic conditions during sapropel formation aeolian hematite and goethite are largely unaffected by this reductive dissolution except within the interglacial sapropel s5 and its underlying dissolution interval which formed under relatively stronger sulphidic conditions nevertheless low hematite contents indicate that the three studied sapropels accumulated under reduced aeolian dust inputs in response to an intensified african monsoon which resulted in expansion of savannah landscapes into ne saharan dust source areas small variations in goethite contents across sapropels indicate additional aeolian entrainment of goethite that formed under previous wet phases in the ne sahara or in subtropical savannahs located further south we link short lived dust abundance peaks within sapropels s1 and s6 to centennial scale periods of enhanced bottom water circulation reported previously for these sapropels although these sapropel interruptions are driven by high latitude cooling events our results indicate that such centennial scale episodes of atmospheric reorganization affected not only the eastern mediterranean northern borderlands but also subtropical north africa overall our results point to a dominant low latitude forcing on sapropel formation via boreal summer insolation maxima and intensification of the african monsoon

distinction between the youngest toba tuff and oldest toba tuff from northern sumatra based on the area density of spontaneous fission tracks in their glass shards abstract determination of the area density of spontaneous fission tracks s in glass shards of toba tephra is a reliable way to distinguish between the youngest toba tuff ytt and the oldest toba tuff ott the s values for ytt uncorrected for partial track fading range from 70 to 181 tracks cm2 with a weighted mean of 108 5 tracks cm2 based on 15 samples corrected s values for ytt are in the range of 77 140 tracks cm2 with a weighted mean of 113 8 tracks cm2 within the range of uncorrected s values no significant difference in s exists between ytt samples collected from marine and continental depositional settings the uncorrected s for ott is 1567 114 tracks cm2 so that confusion with ytt is unlikely the s values of the toba tephra at bori morgaon and gandhigram in northwestern india indicate a ytt identity in agreement with geochemical data on their glass shards the presence of multiple glass populations and a glass fission track age determination therefore the view of others that ott is present at these sites and thereby indicates an early pleistocene age for the associated acheulean artifacts is incorrect

enhanced framboidal pyrite formation related to anaerobic oxidation of methane in the sulfate methane transition zone of the northern south china sea abstract many studies have confirmed that size distributions of framboidal pyrite can be an effective indicator of bottom water redox conditions in modern as well as ancient sedimentary environments however one environment in which production of framboidal pyrite has not been sufficiently studied to date is the sulfate methane transition zone smtz in which anaerobic oxidation of methane aom is coupled with microbial sulfate reduction msr to enhance iron sulfide mineral precipitation e g fes2 fes and fe3s4 here we document for the first time size distributions for pyrite framboids from the smtz based on data from two sites in the methane hydrate bearing region of the northern south china sea on the basis of framboid size pyrite concentration and sulfur isotope data we propose new insights into the formation process of authigenic pyrite framboids within the smtz we conclude that 1 enhanced anaerobic oxidation of methane aom not only plays a dominant role in the accumulation of 34s enriched pyrite but also is responsible for formation of highly variable and sometimes exceptionally large pyrite framboids in the smtz 2 most framboids occur in framboid clusters which commonly exhibit rod like shapes secondary overgrowths heavier 34s values and unusual size distributions e g mean size 20 m and standard deviation 3 0 m in the smtz 3 pyrite framboids formed in the smtz which have characteristics different from those formed in the sulfate reduction zone srz do not comment on redox conditions of the overlying water column and 4 framboid occurrences with similar characteristics in ancient marine deposits may be considered indicators of enhanced aom and mark the former position of the smtz in the paleo marine system in addition significant quantities of elemental sulfur were observed in the smtz possibly related to anaerobic oxidation of hydrogen sulfide and fluctuations of the smtz

no short reversals of brunhes age recorded in the toba tuffs north sumatra indonesia paleomagnetic and 40ar 39ar data indicate that two tuffs are present at siguragura north sumatra indonesia a reversely magnetized tuff the earliest eruptive unit of the toba caldera of matuyama age 0 84 ma and a normally magnetized tuff the last eruptive unit of the toba caldera of late brunhes age no reversely magnetized tuffs of late brunhes age are present at this location as suggested by previous investigators

a study of the hydrothermal alteration in paleoproterozoic volcanic centers sao felix do xingu region amazonian craton brazil using short wave infrared spectroscopy abstract hypogene hydrothermal minerals have been identified by short wave infrared spectroscopy in hydrothermally altered rocks from the sobreiro and santa rosa formations which belong to a paleoproterozoic volcano plutonic system in amazonian craton three clay minerals are spectrally recognized montmorillonite kaolinite and illite the integration of these data with those available in the literature including gold occurrences suggests that those rocks are hydrothermal products of both volcanic thermal sources and later crustal intrusions as evidenced by variable styles of propylitic sericitic potassic and intermediate argillic alteration the influence of meteoric fluids is emphasized this low cost exploratory technique which can be applied to hand samples seems to be promising in the separation of hydrothermally altered volcano plutonic centers in regions submitted to severe weathering conditions in addition to aid elaborating models for prospecting mineral deposits

mixed layer illite vermiculite as a paleoclimatic indicator in the pleistocene red soil sediments in jiujiang southern china abstract the mineralogy and chemical composition of the jiujiang red soil sediments were investigated using x ray diffraction xrd x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms mixed layer illite vermiculite i v was confirmed based on the conditions that a broad peak of 1 0 to 1 4 nm appeared in xrd after mg saturation and its d spacing did not change after glycol treatment but collapsed to 1 0 nm after heating owing to the loss of water and hydroxy cations from its interlayer the mixed layer i v contents fluctuate throughout the section but show a decreasing trend upwards suggesting decreased weathering towards the surface of the section the chemical index of alteration cia values and rb sr ratios also exhibit upward decreasing trends jointly revealing the climate shift from warm humid to cool dry from the middle to the late pleistocene although the general climate evolution can be evaluated by cia values and rb sr ratios sub climatic events within the jiujiang red soil sediments cannot be identified the sio2 al2o3 al2o3 fe2o3 and sio2 fe2o3 ratios clearly fluctuate along the section especially within the net like red soil sediments but they do not reveal multiple climate cycles this is because of an inhomogeneous distribution of sio2 al2o3 and fe2o3 in the white veins and the red matrix and also non uniform sampling the variation in the content of mixed layer i v show a strong positive correlation with changes in magnetic susceptibility of loess paleosol sediments and in marine oxygen isotope ratios revealing multiple sub climate cycles on a global scale since the middle pleistocene therefore the mixed layer i v contents not only reveal the whole climate trend documented in the red soil sediments since the middle pleistocene but also disclose the sub climate cycles related to the deposit pedogenesis process

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

direct correlation of the marine oxygen isotope record with the chinese loess plateau iron oxide and magnetic susceptibility records abstract monsoons are a major feature of global atmospheric circulation and derive heat and moisture from the oceans and transports much of that heat and moisture to nearby continents the east asian monsoon derives its heat and moisture from the eastern equatorial pacific and transfers it to southeast asia and the loess plateau of central china in order to examine the phasing of marine and terrestrial climatic events associated with this monsoon we have analyzed a core from the western pacific v21 146 downwind from the loess plateau iron oxides and magnetic susceptibility were analyzed because they have been used as loess plateau paleoclimate proxies comparison of temporal changes in both iron oxide and susceptibility signals in v21 146 to the well known luochuan loess section reveals an excellent correlation both in the timing and direction of the variations comparison of our loess plateau paleoclimatic proxies in v21 146 to previously published oxygen isotope data from this core suggests that through marine isotope stage mis 9 coincident with loess plateau interglacial soil level 3 s3 ocean temperature increases and the onset of monsoonal conditions on the loess plateau were synchronous however for mis 11 12 interglacial glacial s4 l5 changes in the ocean appear to significantly lead those on land and there is a lack of correlation between mis 13 and s5 these out of phase events may be a response to a reorganization of the ocean atmosphere system as indicated by changes in the 13c record it has previously been suggested that changes in eolian flux record eolian transport from the loess plateau but we find little correlation between eolian flux and our loess plateau proxies suggesting that some of the eolian sediments were derived from outside the loess plateau

determining magnetic susceptibility in loess paleosol sections by near infrared reflectance spectroscopy 1 loess deposits are widespread covering about 10 percent of the earth s land surface magnetic susceptibility ms an important parameter in loess deposits is a function of the concentration of magnetic minerals which exhibit diagnostic features in their visible and near infrared nir spectra therefore ms should correlate with spectral reflectance to determine if a relationship exists between ms and reflectance spectra we analyzed nir spectra and ms of over 550 samples from seven loess paleosol sequences on loess plateau of central china nir reflectance data were first converted into eight spectral bands and then a step wise multiple linear regression was applied to a calibration dataset to establish a model to predict ms values test datasets indicate our model is very successful all produced an r2 0 9 by applying this new method for estimating ms to hyperspectral remote sensing data we anticipate mapping soil quality and ms on the loess plateau

stratigraphy paleomagnetism and magnetic fabric of the toba tuffs constraints on the sources and eruptive styles the toba depression in north central sumatra is a complex of several overlapping calderas resulting from three major ignimbrite forming eruptions within the depression the upland masses of samosir and northern uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment hitherto interpreted to be two parts of a single resurgent dome this study has demonstrated that the welded tuffs of samosir and uluan have different magnetic polarities and therefore at least two different ignimbrites are present the samosir uluan massif may consist of parts of two resurgent domes the first ignimbrite eruption occurred at 0 84 ma and produced a very thick 400 m densely welded unit having a reversed polarity anisotropy of magnetic susceptibility ams flow direction and lithic size data indicate that the source lies in the southern part of the toba depression and the thick deposit of uluan is thought to have ponded in a 40 km wide caldera the second ignimbrite is normally magnetized ams flow direction data indicate two separate source vents one to the north in the haranggaol caldera and another to the south the thick deposit at samosir is thought to have ponded in the southern caldera coarse sediments then accumulated over samosir and northern uluan and were capped by lacustrine deposits a renewed episode of resurgence then uplifted samosir island and possibly the northern part of uluan at approximately 0 075 ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the toba depression this ignimbrite is mostly nonwelded and normally magnetized part of the uluan dome was destroyed by collapse of the sibandung caldera and latung graben and concomitant with renewed subsidence of the haranggaol and porsea calderas

pleistocene environmental dynamics recorded in the loess of the middle and lower danube basin abstract the substantial loess deposits of the middle and lower danube basin in southeastern europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent yet are also the least well understood environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions which nevertheless reflect oscillations between relatively warm humid interglacial and cold dry glacial intervals this relative environmental stability may have proven important for hominins migrating into and through the region the loess stratigraphy comprises distinct loess paleosol sequences reflecting glacial interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry these phases are emphasised by variations in vegetation and malacofauna which respond to climatic change the loess deposits demonstrate broadly similar sedimentological characteristics across the basin danubian loess deposits initiated in response to the tectonic formation of the pannonian basin retreat of the large palaeolakes and increased sediment supply from the danube the period from 1 ma 500 ka mis 27 13 was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively in response to relatively humid forested conditions this period represents the opening of the danube corridor and provides the backdrop for initial hominin arrival into europe after 500 ka and particularly after mis 9 loess accumulation rates increased in response to relatively more steppic arid environments mis 9 and 13 15 were the most humid phases of the last 600 ky the mis 5 interglacial period was the warmest and relatively most humid period preceding the holocene and was followed by substantially increased loess accumulation during mis 4 which may be linked to north atlantic circulation the complexity of the mis 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time mis 3 corresponds with the first arrival of anatomically modern humans to europe the last glacial maximum and younger dryas of mis 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the north atlantic although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota as may also have been the case for most of the pleistocene glacial cycles the holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial

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

high resolution hematite goethite records from chinese loess sequences for the last glacial interglacial cycle rapid climatic response of the east asian monsoon to the tropical pacific 1 in order to study the variability of dry versus humid conditions resulting from the east asian monsoon eam we analyzed hematite and goethite from two high resolution chinese loess sections by diffuse reflectance spectroscopy the hematite and goethite concentrations are higher in interglacial paleosols than in glacial loess sediments whereas the hematite goethite hm gt ratios are lower in paleosols than in loess such changes are consistent with higher precipitation and temperature and increased pedogenesis during interglaciation and lower precipitation and temperature and decreased pedogenesis during glaciation the hm gt ratio can be employed as a tool to assess short term variations in humidity and aridity of the eam the hm gt ratios of the last glacial loess displays millennial scale abrupt climate oscillations revealing a pattern of significantly reduced and enhanced summer monsoon moisture our results indicate that the eam responded to tropical pacific climate by millennial scale changes in precipitation during the last glaciation

correlation of the magnetic susceptibility stratigraphy of chinese loess and the marine oxygen isotope record chronological and palaeoclimatic implications abstract the thick deposits of wind blown silt of the loess plateau in central china constitute arguably the most important terrestrial record of the late pliocene and pleistocene climate magnetic susceptibility stratigraphy has proven extremely useful for quantifying the palaeoclimatic record of chinese loess with intervals of high magnetic susceptibility corresponding to warm humid interglacials and intervals of low susceptibility to cooler drier glacials several workers have noted that the magnetic susceptibility stratigraphy strongly resembles the marine oxygen isotope record for which a high resolution chronology is available from tuning to the frequencies of earth orbital parameters attempts have been made to correlate the two records statistically and we use this approach to generate a new magnetic susceptibility time series for the central chinese loess plateau our results suggest that the two records are sufficiently similar over the interval ca 0 1 5 my bp for this approach to yield a useful age model for loess accumulation spectral analysis of the resulting magnetic susceptibility time series clearly shows that the growth of 100 ky variance which occurs in the marine oxygen isotope record after about 1 my bp also occurs synchronously in the magnetic susceptibility record reinforcing recent suggestions of a strong linkage between the high latitude northern hemisphere and the asian climate we also show that a significant improvement in the strength of the loess magnetic susceptibility marine oxygen isotope correlation occurs after about 1 5 my bp which corresponds to a significant increase in the rate of sediment accumulation across the loess plateau

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

microorganism induced weathering of clay minerals in a hydromorphic soil abstract in order to improve the understanding of factors influencing weathering in hydromorphic soils the clay mineral and chemical compositions iron hydr oxides organic compounds and sr and nd isotopic compositions of hydromorphic soils on the banks of the liangzi lake hubei province south china were investigated the b horizon in the lower profile exhibits a distinct net like pattern with abundant short white veins within the red brown matrix their various 87sr 86sr and 143nd 144nd isotopic compositions showed only small variations of 0 7270 0 7235 and 0 51200 0 51204 respectively consistent with the composition of yangtze river sediments indicating that the soils were all derived from alluvium from the catchment the white veins contained notably more sio2 al2o3 tio2 and mobile elements relative to the red brown matrix while they both showed similar values for the chemical index of alteration of 86 7 and 87 1 respectively and displayed similar degrees of weathering the clay minerals in a ae and e horizons of the soil profile were illite kaolinite and mixed layer illite smectite these same three clay minerals comprised the white net like veins in the soil b horizon whereas only illite and kaolinite were observed in the red brown matrix iron hydr oxides in a ae and e horizons of the soil profile were hematite and goethite whereas in the red brown matrix of the b horizon they were hematite goethite and ferrihydrite different organic compounds were observed for the white vein and the red brown matrix in the soil b horizon an 18 2 fatty acid biomarker for fungi in the net like vein but not in the red brown matrix compared with the red brown matrix the white net like vein also clearly contained more mono unsaturated fatty acids which are sometimes associated with bacteria that have the capacity to reduce fe iii thus migration of iron and the formation of the net like veins involved the participation of biota during the hydromorphic pedogenesis process as ferrihydrite is usually formed with the assistance of biota redoximorphic processes will chemically affect phyllosilicates by changing their charge and fe iii in illite may serve as electron acceptor for fe iii reducing microorganisms this leads to an increase in negative charge in the illite structure which could be neutralized by electrostatic displacement of interlayer cations and adsorption of protons thereby promoting transformation of illite to mixed layer illite smectite and dissolution of the pre existing illite mineral our results suggest that microorganisms brought about iron leaching and dominated the alteration of clay minerals by redox processes and different mineral volumes formed in the net like b horizon of the hydromorphic soil were attributed to the microorganism induced weathering process

three dimensional mapping of soil organic matter content using soil type specific depth functions abstract this paper proposes a method for mapping depth functions of soil organic matter som that combines general pedological knowledge with geostatistical modeling a pedometric soil map that represents soil type at any location with a probability distribution formed the starting point for each of the ten soil types depicted on this map a depth function structure was defined that describes the variation of som over depth based on pedological knowledge about soil profile morphology to this end five depth function building blocks were defined referred to as model horizons for each soil type the depth function structure was obtained by stacking a subset of model horizons the parameters of the ten soil type specific depth functions were calibrated with data from soil profile descriptions and spatially interpolated using environmental covariates as predictors the predicted parameters and the soil type specific depth function structures then allowed us to construct the depth function of som for each soil type at each prediction site by combining the soil type specific depth functions with the probability distributions of the soil types a probability distribution of depth functions was obtained at each location in the study area the soil type specific depth functions and their associated probabilities were used to map the som stock for depth intervals 0 30 cm 30 60 cm 60 90 cm and 0 90 cm the mapped som stocks were validated with an independent probability sample r 2 values ranged between 0 09 and 0 75 with 0 46 for the 0 90 cm layer the rsme was largest for the 30 60 cm layer 13 4 kg m 2 this is typically the layer with the largest within soil type and between soil type variation of som and is therefore the most challenging to predict similar to other studies better predictions were found for the top layer than for subsurface layers which illustrates a general challenge of capturing subsurface variation of soil properties by our pedometric models the pedometric approach to three dimensional mapping of som presented in this paper is closely related to the conventional approach that represents depth distribution of soil properties with representative profile descriptions that are associated to the map units of a soil type map a comparison of our pedometric approach with the conventional approach showed that there was little difference in performance however our modeled depth functions might give a more realistic representation of the vertical variation than the discrete stepped functions based on representative soil profile descriptions and thus might provide better predictions of the som content at small depth intervals

china materials for a loess landscape abstract for various reasons it was thought that material for the great chinese loess deposits originated in the deserts of the north and the idea of a desert origin was widely accepted but butler in australia in 1956 cast doubt on the actual existence of desert loess and this led to considerable discussion one facet of the argument advocated by smalley and vita finzi 1968 proposed that there were no desert specific mechanisms which could produce the large amounts of loess material observed applying this idea to the chinese loess was particularly appropriate because of the huge extent and thickness of the deposits how was this vast amount of loess material produced smalley and krinsley 1978 proposed a sequence of events that could lead to the formation of the chinese loess this required that the loess be a mountain loess eventually defined by smalley and derbyshire 1990 the material was made in the mountains to the west and the yellow river had a role to play in bringing it to the loess deposit region and that loess material in desert regions was in a state of transit the 1978 model has been proved to be true by a whole sequence of ingenious and intricate experiments in particular the analysis of zircons has produced data allowing particle sources to be identified the zircon particle proves to be a key component of the loess landscape but the mode particle remains the silt sized quartz particle the problem running in parallel with the how did the material form question is the puzzle of why loess material has such a restricted size range what controls operate on the formation of loess material in the quartz particles it appears that a combination and interaction of two events produce a size control the high low quartz transformation introduces tensile stresses the eutectic sizing of the quartz particles in the original granite also constrains the level of stress development the stress levels produced cause a particle size product of around coarse silt size

determining hematite content from nuv vis nir spectra limits of detection hematite occurs in various geologic settings including igneous metamorphic and sedimentary rocks as well as in soils however it frequently occurs at low concentrations especially in soils where it may be 1 by weight because hematite has the potential to be an indicator of oxidizing and climatic conditions in soils and paleosols it is important to understand its limit of detection in this paper we examine the limits of detection of hematite visually and with diffuse reflectance spectrophotometry drs and x ray diffraction xrd to accomplish this we used a sample set consisting of knowns or calibration samples these known samples consisted of 15 different matrices of varying mineral composition into which hematite in 7 different concentrations ranging from 0 01 to 4 by weight were mixed including the 0 hematite our calibration data set consisted of 120 samples visually hematite can be detected at a concentration of 0 01 by weight in a light matrix and 0 5 in the darkest of our matrices however because of metamerism visual techniques cannot specifically identify hematite we find that for both drs and xrd the limit of detection is also dependent on the matrix for xrd the limit of detection for hematite in bulk samples is about 1 for drs the limit of detection depends on the data reduction technique used the commonly used kubelka munk remission function and its first and second deriva tives can easily identify hematite at the 0 5 level however the first derivative of the percent reflectance curve can detect hematite at 0 01 by weight in a light matrix and 0 05 in a dark matrix we suggest that the first derivative of drs curves is the best currently available method for qualitatively detecting the mineral hematite at low concentrations found in soils sediments and rocks work described in this paper may be applied in several situations our study of visual limits of hematite detection should aid field geologists in assessing hematite content analysis of color wave length bands may also have application in remote sensing by indicating which bands are most sensitive to hematite reported to be an important constituent of the martian surface furthermore this study could help clarify remotely sensed terrestrial albedo changes especially the sahara sahel transition where the sediments change from light quartz dominated to dark hematite dominated our study also points out that with laboratory based spectra the first derivative of the reflectance curve is the most sensitive transform for processing spectral data for hematite thereby allowing concentrations as low as 0 01 to be detected

soil moisture balance and magnetic enhancement in loess paleosol sequences from the tibetan plateau and chinese loess plateau abstract we present a first combined environmental magnetic and geochemical investigation of a loess paleosol sequence

potential of vnir spectroscopy for prediction of clay mineralogy and magnetic properties and its paleoclimatic application to two contrasting quaternary soil deposits abstract the properties of phyllosilicates iron oxides oxyhydroxides and magnetic minerals in soils can respond to changes in pedogenic weathering intensity and past climate numerous paleoclimate reconstructions using soil mineralogy have made use of only one or two of these mineral types generally in order to limit analytical effort or expense thereby foregoing comparisons between different mineralogic proxies quaternary soil deposits in china afford a unique opportunity for assessing the potential of visible and near infrared reflectance vnir spectroscopy for analysis of soil minerals chemical weathering and paleoclimate reconstruction here we investigated two typical quaternary soil types exhibiting different weathering degrees i e a loess paleosol sequence in northern china and a red earth deposit in southern china clay and iron mineralogy from the soils was compared with vnir data using partial least squares regression plsr and continuum removal based multiple linear regression mlrcr approaches vnir spectra show potential for analysis of pedogenic weathering and paleoclimate reconstruction in weakly to highly weathered soils in that spectral behavior is strongly related to both clay mineral composition and magnetic properties both higher concentrations of minerals and their wider variability can improve model predictive ability phyllosilicates and non magnetic fe oxides are predicted more accurately for highly weathered red earth deposits whereas soil magnetic properties are predicted more accurately for loess paleosols the predictors identified by the mlrcr method d2200 d680 and d900 and the ranges constrained by the plsr method 650 700 and 2150 2250 nm deserve more attention in future studies of spectral pedology and chemical weathering we suggest that vnir spectroscopy has the potential to be an alternative and broadly applicable tool for reconstructing paleoclimate using soil mineral properties substituting for a series of common mineralogic analyses this would significantly reduce the workload and expense of experiments and improve the resolution of paleoclimate studies

clay mineralogical constraints on weathering in response to early eocene hyperthermal events in the bighorn basin wyoming western interior usa series of transient greenhouse warming intervals in the early eocene provide an opportunity to study the response of rock weathering and erosion to changes in temperature and precipitation during greenhouse warming chemical weathering is thought to increase the uptake of carbon from the atmosphere while physical weathering and erosion control sediment supply a large ancient greenhouse warming event is the paleocene eocene thermal maximum at 56 ma in many coastal sites an increase in the abundance of kaolinite clay during the paleocene eocene thermal maximum is interpreted as the result of reworking from terrestrial strata due to enhanced runoff caused by increased seasonal precipitation and storminess during a time of decreased vegetation cover in the continental interior of north america paleocene eocene thermal maximum paleosols show more intense pedogenesis and drying which are indicated by deeply weathered and strongly oxidized soil profiles the weathering and oxidation could be related to temperature and precipitation changes but also to increased time available for weathering and increased soil permeability in coarser sediment here we provide evidence for enhanced climate seasonality increased erosion of proximal laterites and intrabasinal floodplain soils and a potential slight increase in chemical weathering during the smaller early eocene hyperthermals eocene thermal maximum 2 including h1 and h2 postdating the paleocene eocene thermal maximum for which no previous clay mineral data were available hyperthermal soil formation at the site of floodplain deposition causes a similar insignificant clay mineralogical change as occurred during the background climates of the early eocene by showing small increases in smectite and decreases in illite smectite and illite remarkably the detrital sediments during the hyperthermals show a similar pedogenic like increase of smectite and decreases of mixed layer illite smectite and illite while the kaolinite and chlorite proportions remained low and unchanged since sedimentation rates and provenance were similar during the events enhanced smectite neoformation during soil formation in more proximal settings and associated reworking is the likely process causing this clay mineralogical change the hundreds to thousands of year time scales at which individual paleosols were formed were probably too short for significant alteration of the rocks by in situ chemical weathering despite changing climates during the two post paleocene eocene thermal maximum greenhouse warming episodes the relatively small signal however raises the question of whether increased chemical weathering can indeed be a strong negative feedback mechanism to enhanced greenhouse gas warming over the time scales at which these processes act

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

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

bathyal records of enhanced silicate erosion and weathering on the exposed luzon shelf during glacial lowstands and their significance for atmospheric co2 sink abstract we present a new high resolution multiproxy data set of mass accumulation rates sr nd isotopes as well as major and trace elements for the siliciclastic sediment fraction from international marine global change study core md06 3052 located on the continental slope of the western philippine sea we integrate our new data with published grain sizes and sea surface temperatures from the same core as well as with equatorial pacific sea level and east asian summer monsoon precipitation in order to constrain at high resolution changes in physical erosion and chemical weathering intensities on luzon and sediment source to sink processes we assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric co2 since 156 kyr bp sr nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on luzon 68 100 with a lesser contribution from asian dust 0 32 different indices indicate that stronger physical erosion and chemical weathering occurred during marine isotope stage mis 6 130 156 kyr bp as well as in the latter stage of mis 3 and mis 2 14 40 kyr bp the large sea level lowstands and associated significant exposure of continental shelf in the western philippine sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf furthermore we notice the relatively good coherence between chemical weathering intensities on luzon and global atmospheric co2 concentrations over these cold intervals we suggest that strengthening of chemical weathering of silicates on luzon and other tropical arcs within 20 of the equator during the quaternary glacial sea level lowstands may significantly contribute to the lowering of atmospheric co2 concentrations during ice ages we estimate that a significant fraction up to 16 i e 8 ppmv of all atmospheric co2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only 1 of the exorheic drainage area worldwide

stratigraphy of the toba tuffs and the evolution of the toba caldera complex sumatra indonesia during the past 1 2 m y a magma chamber of batholithic proportions has developed under the 100 by 30 km toba caldera complex four separate eruptions have occurred from vents within the present collapse structure which formed from eruption of the 2800 km3 youngest toba tuff ytt at 74 ka eruption of the three older toba tuffs alternated from calderas situated in northern and southern portions of the present caldera the northern caldera apparently developed upon a large andesitic stratovolcano the calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the ytt samosir island and the uluan block are two sides of a single resurgent dome that has resurged since eruption of the ytt samosir island is composed of thick ytt caldera fill whereas the uluan block consists mainly of the oldest toba tuff ott in the past 74000 years lava domes have been extruded on samosir island and along the caldera s western ring fracture this part of the ring fracture is the site of the only current activity at toba updoming and fumarolic activity the toba eruptions document the growth of the laterally continuous magma body which eventually erupted the ytt repose periods between the four toba tuffs range between 0 34 and 0 43 m y and give insights into pluton emplacement and magmatic evolution at toba

magnetism of a red soil core derived from basalt northern hainan island china volcanic ash versus pedogenesis red soil volcanic ash versus pedogenesis similar to loess paleosol sequences in northwestern china terrestrial sedimentary sequences red soils in southern china also provide sensitive quaternary records of subtropical tropical paleoclimate and paleoenvironment compared with red clay sequences originated from eolian dust red soils derived from bedrock have received little attention in this study a long core of red soil derived from weathered basalt in northern hainan island china was systematically investigated by using detailed magnetic measurements and rare earth element analyses the results show that an extremely strong magnetic zone with a maximum magnetic susceptibility 10 10 5 m3 kg 1 is interbedded in the middle of the core profile this layer contains a significant amount of superparamagnetic magnetite maghemite particles that primarily originated from volcanic ash with secondary contributions from pedogenesis the former has an average grain size of 19 nm with a normal distribution of volume and the latter has a much wider grain size distribution the presence of volcanic ash within the red soil indicates that these quaternary basalts were not formed by continuous volcanic eruptions moreover the magnetic enhancement patterns differ between the upper and lower zones the upper zone is more magnetically enhanced and experienced higher precipitation and temperature than the lower zone discrimination of superparamagnetic particles originating from pedogenic processes and volcanic ash thus provides a sound theoretical base for accurate interpretation of magnetism in red soils in this region

monsoonal climate evolution in southern china since 1 2 ma new constraints from fe oxide records in red earth sediments from the shengli section chengdu basin abstract southern china has experienced a dominantly monsoonal climate since the early quaternary owing to the influence of asian monsoons from several directions during that period pedogenic fe oxides hematite and goethite are regarded as sensitive indicators of monsoonal paleoclimates to obtain a better understanding of monsoonal climate changes in the subtropical zone of southern china samples from the shengli section chengdu basin were investigated using diffuse reflectance spectroscopy drs high resolution transmission microscopy hrtem x ray diffraction xrd x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms tem results show that both hematite and goethite occur as fine particles with an irregular morphology most hematite grains have low crystallinity and nanoporous structure suggesting that they formed from a ferrihydrite precursor uniformity of trace element and ree distribution patterns eu and ce anomalies and la yb n ratios throughout the section suggests that the shengli deposits were probably well mixed in the source area prior to transport and deposition and that there has been little change in the source areas of primary materials since 1 2 ma the high chemical index of alteration cia of the red earth 79 88 reflects strong chemical weathering processes in southern china besides drs analyses of fe oxides show that most red earth samples at shengli contain more hematite than goethite which is opposite to typical loess paleosol profiles from northern china these results confirm that southern china generally experienced more intense weathering processes than northern china since 1 2 ma large fluctuations in major element oxide concentrations and clay mineral assemblages in the lower part of the section indicate climatic fluctuations between perennially humid and seasonally humid conditions in the mid pleistocene monsoonal climate evolution as proxied by the hematite hematite goethite hm hm gt ratio shows a long term but stepwise cooling and drying pattern in the chengdu basin with major transitions at 1 0 0 45 and 0 1 ma these transitions were probably triggered by episodes of tectonic uplift of the tibetan plateau and global climate change with consequent effects on the asian monsoons the transitions in our paleoclimate proxy records for southern china match well with shifts in the marine oxygen and carbon isotope records since the mid quaternary providing evidence of strong teleconnections between global and regional climates terrestrial weathering and the global carbon cycle

the 73 ka toba super eruption and its impact history of a debate abstract toba volcano in northern sumatra is located at the intersection of two major tectonic lineaments in one of the most seismically active regions in the world and its caldera is considered the largest quaternary caldera on earth the most recent toba explosive eruption at 73 ka was an order of magnitude larger than that of tambora in 1815 and has a volcanic explosivity index of 8 the exceptional magnitude of this super eruption and the widespread distribution of the younger toba tuff ytt in marine cores in the indian ocean the arabian sea and the south china sea have prompted sustained debate as to its global and regional impact on climate ecosystems and prehistoric human populations however despite climate modelling and appeals to a variety of proxy climatic data including geochemistry pollen analysis archaeology and stable isotopes the extent of the impact remains unclear in order to achieve better progress in the future greater care is needed to obtain higher resolution and more precise chronologies from the marine and terrestrial proxy records used to test whether or not the 73 ka toba super eruption had a significant environmental impact records from speleothems and ice cores have much to offer in this regard