climate variations since the last interglacial recorded in czech loess 1 magnetic susceptibility organic matter content and grain size were measured on a loess palaeosol sequence deposited since the last interglacial at the dolni vestonice section in the czech republic high values in magnetic susceptibility and organic matter content in palaeosols pk0 pk2 and pk3 indicate that they were strongly influenced by long term pedogenesis and high vegetation density linked to interglacials or interstadials grain size variations record a series of cold wind strengthened events during the last glacial which we interpret as a record of the distinctive younger dryas episode and millennial scale climate oscillations that correlate with the grip ice core 18o record and north atlantic heinrich events these climate events as indicated by grain size peaks combined with previous climate records at french massif central and lago grande di monticchio in italy suggest that the climate over these areas might have undergone synchronous oscillations with the shifts in sea surface temperatures of the north atlantic and air temperature changes above greenland

the effects of soluble salts on the threshold shear velocity of fine sand wind tunnel tests were carried out to investigate the effects of two soluble salts nacl and kci on the threshold shear velocity of a well sorted fine sand a sensitive laser monitoring system was used to detect initial grain motion during the tests results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement like bonds formed between grains that tend to hold individual particles in place however with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity this is indicated by increased scatter of data on the threshold shear velocity surface salt concentration plots for both nacl and kcl although data scatter is evident significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case

high resolution record of the environmental response to climatic variations during the last interglacial glacial cycle in central europe the loess palaeosol sequence of dolni věstonice czech republic abstract high resolution multidisciplinary investigation of key european loess palaeosols profiles have demonstrated that loess sequences result from rapid and cyclic aeolian sedimentation which is reflected in variations of loess grain size indexes and correlated with greenland ice core dust records this correlation suggests a global connection between north atlantic and west european air masses herein we present a revised stratigraphy and a continuous high resolution record of grain size magnetic susceptibility and organic carbon 13c of the famous of dolni vestonice dv loess sequence in the moravian region of the czech republic a new set of quartz osl ages provides a reliable and accurate chronology of the sequence s main pedosedimentary events the grain size record shows strongly contrasting variations with numerous abrupt coarse grained events especially in the upper part of the sequence between ca 20 30 ka this time period is also characterised by a progressive coarsening of the loess deposits as already observed in other western european sequences the base of the dv sequence exhibits an exceptionally well preserved soil complex composed of three chernozem soil horizons and 5 aeolian silt layers marker silts this complex is at present the most complete record of environmental variations and dust deposition in the european loess belt for the weichselian early glacial period spanning about 110 to 70 ka allowing correlations with various global palaeoclimatic records osl ages combined with sedimentological and palaeopedological observations lead to the conclusion that this soil complex recorded all of the main climatic events expressed in the north grip record from greenland interstadials gis 25 to 19

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

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

loess record of the aerodynamic environment in the east asia monsoon area since 60 000 years before present 1 the multimodal distribution of grains in loess and dust storm deposits has been widely reported in recent years our analysis demonstrates that the interaction of wind atmospheric turbulence and dust grain gravity along the dust transportation path results in a multimodal grain size distribution for suspended dust changes in the median sizes of the coarse and medium modes are related to variation in aerodynamic forcing lift force related to vertical wind and turbulence during dust entrainment in the source area and turbulence intensity in the depositional area on the basis of the numeric characteristics of the three modes of suspended particles a tentative model has been constructed which is used to study fluctuations of paleoaerodynamic environments from a time series of paleoatmospheric environmental changes of the loess plateau for the past 60 000 years we find that there are three patterns of aerodynamic environments in the dust source area stronger strong weak and 13 strong turbulence events since 60 000 years b p climatic variability in the dust depositional area is stronger than in the source area during the last glacial period the aerodynamic environment changed synchronously in the dust source and depositional areas over the entire trend however after 8000 years b p the aerodynamic force is strong in the dust source area while the turbulence intensity is weak in the dust depositional area differing from that of the last glacial period the strong turbulence periods correspond to the cooling events such as the heinrich events and the younger dryas cold event and may not be related to factors forcing the alternation between glacial and interglacial periods since 60 000 years b p the three patterns of aerodynamic environments are mainly controlled by the environmental changes in the dust source area and may be related to fluctuations of the winter monsoon in each pattern fluctuations of the turbulence intensity in the dust depositional area and the distance from dust source to dust depositional area are the major changes of the environment the summer monsoon recorded by magnetic susceptibility may vary prior to the winter monsoon since 50 000 years b p changes in the intensity of the summer monsoon may force changes in the advance retreat cycles of dust source areas in each winter monsoon pattern

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

laboratory investigation into off fault seismic activity abstract the off fault pattern of weak seismic activity which was observed in the laboratory around fault pairs with already generated tensile cracks led to the comparison with similar patterns observed in nature in some seismoactive regions on the basis of the results of the laboratory model experiments the off fault seismic activity can be attributed to fault segments oriented obliquely or roughly perpendicular to the main fault system these fault segments may have originated as tensile fractures during one of the foregoing strong earthquakes to study the off fault foreshock and aftershock occurrences a method of laboratory seismology physical modeling was employed the use of this method is based on the assumption that the obtained information on the seismic regime of fault models is relevant to the seismic manifestation of faults in the earth the results of laboratory experiments can thus be used to analyze the pattern of seismic energy release in selected seismoactive fault regions

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

an experimental study on the susceptibility of crusted surfaces to wind erosion a comparison of the strength properties of biotic and salt crusts abstract penetrometry has been employed in a number of studies investigating the strength of crusted sediments as related to their stability to particle impact in aeolian systems despite the early success of this procedure questions remain concerning the effect of the angle of penetration the role of fatigue and the relative importance of the ultimate strength as compared to the elasticity of the crust this paper reports on a series of penetrometer and wind tunnel experiments that consider these effects in the context of both salt and biotic crusts the results demonstrate that the angle of penetration is not important but the density of penetrations is the decreased strength observed with high densities of penetration repeated loading and continual impact in wind tunnel experiments provides further confirmation that sedimentary crusts progressively become weaker during mass transport events the elasticity of the surface appears to be at least as important to consider as the ultimate strength although much stronger the salt crusts were found to break down and erode sooner than biotic crusts in wind tunnel studies the notable elasticity of biotic crusts appears to afford them some protection against abrasion

a new model of wind erosion in the presence of vegetation 1 vegetation is known to impact strongly the erosion of soil by the wind lateral cover is the primary parameter used to represent the amount of vegetation in aeolian research and in particular shear stress partitioning research although lateral cover provides a simple means for representing how much vegetation is in an area it is not capable of characterizing how vegetation is distributed a new nonequilibrium model for the representation of nonerodible roughness elements is presented that uses the size distribution of erodible gaps between plants to characterize the ratio of the maximum shear stress to the average shear stress at the surface the model shows very good agreement with measured shear stress ratios from the laboratory and field experiments the model also satisfactorily explains relatively high horizontal aeolian sediment flux at high lateral cover the relationship between this model and another shear stress partitioning model is explored and the new model is found to be superior to the existing model because it 1 utilizes parameters with physical meaning that are measurable in the field or laboratory 2 explains observations of horizontal flux at high cover 3 overcomes difficulties inherent in the use of lateral cover to characterize vegetation on the surface 4 is scale explicit and 5 can be used at multiple scales from an individual unvegetated gap to an entire landscape

fault interaction and seismicity laboratory investigation and its seismotectonic interpretation systems of two parallel linear faults of the same length with the angle of inclination 45 were investigated under uniaxial linearly increasing load perspex plates were used as models for each treated fault configuration the morphology of tensile cracks and the sequence of seismoacoustic events of shear and tensile origin were studied

unmixed loess grain size populations along the northern qilian shan china relationships between geomorphologic sedimentologic and climatic controls abstract grain size analysis provides a useful tool in reconstructing aeolian transport processes and allows deductions about environmental evolution however the sedimentological mechanisms driving the investigated imprint are often underrepresented in the interpretation of loess sections and may therefore lead to erroneous conclusions we present a study from the north eastern margin of the tibetan plateau qilian shan hexi corridor in which 11 mainly holocene loess sections up to 2 20 m depth and a set of surface samples were analysed for their grain size distribution a three end member mixing model yields grain size populations with modes of 63 m 33 m and 9 m respectively representing the major contributing transport processes from different sources these processes were identified in short term suspension and saltation from fluvial storages low level suspension driven by dust storms and high level suspension from distant sources sedimentology supply availability site specific geomorphology distance to potential sources and climate conditions such as effective moisture controlling dust trapping vegetation covers set up a complex system loess deposition and preservation depend on these steering factors large sediment supply from the last glacial cycle became available for deflation during early holocene moisture optimum this phase is represented by a high contribution of the coarsest grain size population in the late glacial early holocene loess record when climate amelioration allowed the establishment of a dust trapping vegetation cover comparable to mis 3 conditions the mid holocene loess deposits formed under more stable landscape conditions represented by much lower contributions from local sources accordingly relative contribution of far travelled dust was at its climax during the mid holocene the late holocene exhibits a relative increase in dust storm contribution which is in accordance to increasingly drier climatic conditions hence this study suggests a thorough consideration of the different system components when interpreting grain size records obtained from loess deposits

the transition between orogenic and anorogenic magmatism in the western mediterranean area the middle miocene volcanic rocks of isola del toro sw sardinia italy the isola del toro is a small island 1k m 2 about 5 nautical miles sw of sardinia entirely made up of mildly alkaline sodic evolved rocks benmoreites and trachytes related to each other by fractionation processes 40 ar 39 ar dating of an anorthoclase mineral separate from a trachyte gave an age of 11 83 0 10 ma this age estimate falls within an interval previously considered a magmatic in sardinia the results of this study shift the beginning of the middle miocene quaternary anorogenic volcanism of sardinia back to the late serravalian the transition between orogenic and anorogenic activity in sardinia is markedly different from that recorded in the rest of the circum mediterranean area where this transition is much more gradual both in time and in terms of magma composition on the other hand the transition between orogenic and anorogenic magmatism in sardinia is rather sharp and lacks hybrid compositions the isola del toro volcanic rocks represent the first anorogenic products produced during the opening of the western mediterranean sea

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

spatial and temporal analysis of a seismic series using a new version of the three point method application to the 1989 antequera spain earthquakes abstract the three point method tpm has been successfully applied to several seismic series and has provided information about the spatial characteristics azimuth and dip of the fault planes activated in the rupture process a new development of the tpm to determine temporal characteristics is presented to obtain the evolution of the fracturing process of an active fault system for the analysis of the 158 microearthquakes and earthquakes that took place in the seismic series of antequera in june 1989 the choice of a threshold magnitude m u 2 5 has permitted the events related to the most relevant fractures to be distinguished secondly only the events between two concentric spheres here named spatial crown with respect to a given earthquake have been used in order to avoid taking into account earthquakes that are too close to each other together with the very distant events that have little relation to the event analysed the spatial crown has permitted some clear results in the antequera series where we have found that the fracturing process began fundamentally with n 80 e planes and evolved to n 65 w planes finally an error analysis enables an estimation of the uncertainty in the results to be obtained from the errors in the data

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

klyuchevskoy volcano kamchatka russia the role of high flux recharged tapped and fractionated magma chamber s in the genesis of high al2o3 from high mgo basalt

towards identifying the origin of metamorphic components in austrian loess insights from detrital rutile chemistry thermometry and u pb geochronology abstract trace element cr nb zr geochemistry and u pb geochronology of detrital rutile grains provide constraints on the nature of potential metamorphic sources of loess in austria cr and nb compositions reveal rutile sources with a predominance of metapelitic lithologies for all three loess samples by contrast zr in rutile geothermometry indicates that formation temperatures for loess rutiles around krems at the bohemian massif bm proved to be ca 100 125 c higher t median 717 and 737 c for two samples from stratzing and krems than those at wels close to the eastern alps ea t median 612 c implying that rutiles in loess at wels were derived from alpine lower amphibolite grade rocks while those in loess around krems from rocks formed under upper amphibolite to granulite grade conditions metamorphic temperatures recorded in rutiles from loess at the bm closely match the two reaction thermobarometry estimates of the last high t overprint 7 11 kbar and 700 800 c of rocks making up the varied series and gfohl units around krems this event dated at 340 to 350 ma is believed to be captured by the detrital rutile u pb data as well e g 349 21 and 352 32 ma all these data demonstrate the significance of proximal bm sources varied series and gfohl unit drained by the danube in loess formation around krems fluvial transport is believed to have played a substantial role in entraining and accumulating rutiles for subsequent aeolian deflation for loess near wels while the ultimate sources of these grains are likely to be in the eastern alps the recycling of these rutiles from the flysch zone of the ea cannot be ruled out despite the uncertainties of cr nb based source discriminations in some cases and the potential decoupling of zr and u pb systematics recognized in rutiles this study demonstrates that rutiles may provide unique details on the nature and metamorphic history of their parent rocks if used with caution and by knowing its limitations under certain conditions it is anticipated that beyond zircon rutile geochemistry will become a powerful provenance tracer in loess studies too this seems to be particularly important to gain a better understanding on the erosion and rutile fertility of different metamorphic terrains and their contributions to loess material issues that have not been adequately addressed thus far

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

making the material the formation of silt sized primary mineral particles for loess deposits abstract in 1911 e e free wrote it may be well to point out that there are really two problems of the loess a problem of the origin of material and a problem of deposition the problem of the origin of material has been relatively neglected in comparison to problems of deposition of the formation of deposits and latterly in comparison to studies of loess stratigraphy if we are to understand the true nature of loess this fascinating material we need to be aware of all the significant events in the processing of the particles which form a deposit a large amount of silt sized primary mineral material has to be produced to make a loess deposit loess is a quaternary phenomenon and we see the entire process being completed in quaternary times some powerful quaternary forces are able to produce very large amounts of granular material glacial grinding vigorously supported by smalley 1966a provides an obvious source for some loess material but the vast deposits of north china and central asia have no obvious glacial connection however they are adjacent to high asia a region of vast tectonic activity and an enormous release of terrestrial energy in the last several million years high asia is a large producer of loess silt much of which finds its way south to make the ganges delta but large amounts are moved north and east to make huge loess deposits africa presents a problem recent work e g coude gaussen 1987 suggests that there is a region of peri saharan loess but earlier observations e g penck indicate quite clearly that the sahara region is free of loess rathjens 1928 in his study of tripolitania indicated the presence of loess like deposits and described their nature but he did point out that 90 of the granular material was greater than 100 pm in diameter which would remove it from a strict loess definition on the soil taxonomy map of africa there is a belt of soil d3 which could include considerable loess deposits it stretches from the matmata loess in tunisia across northern libya to the western part of the egyptian coastal region if d3 contains loess this points to a genuine desert loess particle producing mechanism operating in the sahara

multiple rind structure in pillow lava as an indicator of shallow water multiple rind structure is common among shallow water pillows with diameters larger than about 1 m in oamaru new zealand on the columbia plateau usa and elsewhere a rind consists of sideromelane tachylyte and tachylytic basalt a multiple rind is a concentric set of repeated rinds in various forms e g a portion of a broken rind thrust under another part a series of short and detached subparallel rinds or a pouch shaped depression transitions and combinations of these three forms are common multiple rind structure develops at any part of the pillow perimeter but does not cover the pillow completely it is always accompanied by a rupture in the outermost rind up to 13 rinds have been observed but two to four rinds are most common the multiple rind structure is formed by implosion resulting from condensation of exsolved h2o when h2o condenses a pressure difference between the interior and exterior of a pillow is created above a certain threshold pressure difference the outer skin of a pillow is torn at weak points such as radial joints and thrusts under the neighboring skin buckles to form a pouch shaped depression or produces some variation of these one set of multiple rinds is thus formed further exsolution and condensation of h2o in solidifying pillows may cause development of additional rinds h2o exsolution and condensation and subsequent implosion are limited to low pressure environments so that multiple rind structure is characteristic of shallow water pillow lava

transport direction of peoria loess in nebraska and implications for loess sources on the central great plains abstract in the midwestern united states large rivers draining the laurentide ice sheet lis were the most important sources of peoria loess deposited during the last glaciation loess deposition near those rivers may have responded primarily to ice sheet dynamics rather than direct effects of climatic change in contrast it has been proposed that thick peoria loess on the central great plains was derived mainly from unglaciated landscapes northwest of the main loess deposits in this study transport directions inferred from more than 600 measurements of peoria loess thickness in nebraska are used to test the hypothesis that much of the peoria loess on the great plains is nonglaciogenic a strong northwest to southeast thickness trend indicates that most peoria loess in nebraska was transported from one or more unglaciated northwestern source areas rather than from glacially influenced river floodplains the missouri river draining the lis the platte river draining alpine glaciers and the elkhorn river unglaciated basin were secondary sources their contribution is not detectable beyond a distance of 40 60 km peoria loess deposition on the central great plains was largely a direct response to climatic change in the unglaciated source region

miocene shoshonite volcanism in sardinia implications for magma sources and geodynamic evolution of the central western mediterranean in this paper we document the existence of a miocene shoshonite sho volcanism in northern sardinia anglona this occurrence completes the spectrum of orogenic magmas related to the subduction process which developed from the eocene along the palaeo european continental margin in concert with the opening of the ligurian balearic back arc basin and southeastward drift rotation of the sardinia corsica continental block k ar ages show that the oldest volcanics of the area are calcalkaline ca basalts and andesites 21 ma overlain by 19 7 18 4 ma old more potassic products such as high potassium calcalkaline hk ca and sho lavas ca hk ca and sho suites include basalts and differentiated lavas of andesite and latite composition respectively that according to the pele software modelling represent 40 45 residual liquid fraction after shallow fractional crystallization application of the arc magma simulator software suggests that the generation of primary melts of the distinct suites may occur at similar degrees of partial melting 5 8 and melting pressures 2 2 2 gpa 60 70 km depth in the mantle wedge by contrast the potassic character of parental melts of ca hk ca and sho suites is controlled by 1 the amount of subducted continental components possibly terrigenous sediments and 2 the pressure depth at which these metasomatic agents are released from the slab results suggest that the slab depth beneath the volcanic district increased from 80 100 to 100 120 km for ca and sho magmas respectively accordingly the evolution from ca to sho magmatism in the same plumbing system could be related to slab deepening and increase of the subduction angle of 5 10 in the time span of 2 3 ma this tectono magmatic scenario conforms to the major anticlockwise rotation 30 event of the sardinia block between 20 5 and 18 ma this geodynamic evolution preludes the development of the volcanism in the apennine tyrrhenian domains where the final collisional post collisional stages of subduction were characterized by accentuated slab retreat and roll back inter arc extension and eruption of highly potassic magmas in the frontal arc roman and aeolian provinces

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

sedimentation and diagenesis of chinese loess implications for the preservation of continuous high resolution climate records chinese loess has been extensively utilized to produce continuous and high resolution climate records of the late cenozoic such work assumes uninterrupted loess deposition and limited diagenesis here closely spaced optically stimulated luminescence osl dates are used to characterize the holocene and late pleistocene sedimentation histories of three sites across a nw se transect of the chinese loess plateau the results suggest that sedimentation is episodic at subglacial interglacial time scales with rates rapidly varying within units and between sites unconformities noneolian deposition and mixing of sediments also appear to be common existing understanding of loess deposition therefore requires reexamination while previous reconstructions of rapid climate change not dated using absolute methods should be regarded with caution loess deposits may still yield detailed climate records from specific high sedimentation rate strata and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating the rapid changes in sedimentation presented here indicate the east asian monsoon has the capacity to vary on millennial scales

the global surface energy system and the geological role of wind stress abstract deserts and the loess plateau in north china constitute an environmental coupling system which has undergone periodic changes in the quaternary period attributable mainly to the variations of the global surface energy system thirty seven loess paleosol formations of the last 2 5 ma have been identified in the loess plateau representing thirty seven cycles of climate from cold to warm and of wind intensity from strong to weak in historical literature more loess falling events in relatively cold dry periods have been recorded than in comparatively warm humid periods loess is being currently deposited analyses on three contemporary dust storm events show that the scope mass fluxes and manners of loess deposition are controlled by different atmospheric circulation systems

impacts of post depositional processes on rapid monsoon signals recorded by the last glacial loess deposits of northern china abstract rapid east asian monsoon oscillations recorded by chinese loess are thought to be dynamically linked to north atlantic climate however few efforts have been made to assess the effects of post depositional processes e g surface mixing and pedogenesis on loess paleoclimatic records here a detailed optically stimulated luminescence dating of a thick loess sequence from the western loess plateau is presented offering a reliable chronology for last glacial deposits magnetic susceptibility and mean grain size records from three loess paleosol sequences along a northwest southeast transect are investigated to evaluate impacts of post depositional processes on these loess based proxy records our results indicate that 1 loess sequences developed within the flat tableland of the central and western loess plateau are nearly continuous during the last glaciation and 2 post depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions in the central loess plateau rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity in the northwestern loess plateau however due to high sedimentation rate and relatively weak pedogenesis high resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the greenland ice core and hulu cave stalagmite

break away of south china from gondwana insights from the silurian high nb basalts and associated magmatic rocks in the diancangshan ailaoshan fold belt sw china abstract the diancangshan ailaoshan fold belt yunnan sw china represents the remnants of the once vast ailaoshan ocean a branch or back arc basin of the eastern paleotethys however when and how this ocean back arc basin opened and rifted south china away from gondwana are still unresolved in this study ordovician silurian high nb basalts hnbs 420 ma mg rich andesite 435 ma high mg basalt 446 ma and i type granite 423 ma were newly identified in the diancangshan ailaoshan fold belt the hnbs are alkaline with high tio2 1 8 1 9 wt and nb 16 9 23 1 ppm contents high nb u 36 8 39 1 and nb th pm 1 17 1 21 ratios positive nb ta anomalies primitive mantle normalized and positive end t values 3 2 the hnbs were likely derived from an oib arc mixed mantle source in the garnet stability field the mg rich andesites are medium k calc alkaline andesite with negative end t values 10 1 and negative nb ta anomalies the magma was likely derived from a mixture of depleted mantle peridotites and subducted sediments under low pressure and high h2o conditions the high mg basalts are high k calc alkaline and characterized by high mgo contents 9 3 9 4 wt mg 70 high cr 369 379 ppm and low al2o3 13 6 13 9 wt contents they were likely derived from an enriched mantle source metasomatized by marine sediment derived fluids the i type granites show medium sio2 content 63 6 wt low a cnk ratio 0 9 and negative end t value 9 8 and may have formed by the partial melting of meta basalts these hnb mg rich andesite high mg basalt and i type granite were likely formed in an intracontinental back arc rift setting integrated with our published detrital zircon u pb age and lu hf isotope evidence we propose that south china may have commenced its break up from gondwana in response to the late ordovician silurian 446 420 ma proto tethyan subduction which opened a back arc basin along the ailaoshan fold belt

regional grain size variations in aeolian sediments along the transition between tibetan highlands and north western chinese deserts the influence of geomorphological settings on aeolian transport pathways sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains qilian shan and their arid forelands hexi corridor in north western china six main sediment types were classified medium scale 103 m geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability a tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident aeolian sediments e g loess and dune sands are widespread they are used to identify aeolian transport pathways the mu fs ratio 5 11 m 48 70 m among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions the first fraction is attributed to long distance transport in high suspension clouds whereas the latter represents local transport in saltation mode the ratio shows strong correlation with elevation r2 0 77 thus it indicates a relatively higher far traveled dust supply in mountainous areas 3000 m above sea level a s l compared to the foreland the contribution of westerlies to high mountain loess deposits is considered likely hereby the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent the contribution from distant dust sources is ubiquitous in the study area however the far distance contribution may be reduced by the availability of fine sand provided in low topography settings plain foreland areas support fine sand deflation from supplying river beds allowing the formation of sandy loess in foreland areas and intramontane basins in contrast high mountain topography inhibits strong sand deflation into loess deposits eastern parts of the hexi corridor show higher aeolian sand occurrence in contrast the western parts are dominated by gravel gobi surfaces this is attributed to higher sand supply in eastern parts provided by the badain jaran desert and fluvial storages as sand sources copyright 2014 john wiley sons ltd

a comprehensive numerical model of steady state saltation comsalt 1 the blowing of sand by wind known as saltation ejects dust aerosols into the atmosphere creates sand dunes and erodes geological features we present a comprehensive numerical model of steady state saltation comsalt that in contrast to most previous studies can reproduce a wide range of measurements and can simulate saltation over mixed soils comsalt calculates the motion of saltating particles due to gravity fluid drag particle spin fluid shear and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles furthermore we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results comsalt is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold i e the lowest shear velocity for which saltation is possible and of the aerodynamic roughness length in saltation it also reproduces a range of other saltation processes including profiles of the wind speed and particle mass flux and the size distribution of saltating particles as such comsalt is the first physically based numerical model to reproduce such a wide range of experimental data since we use a minimum of empirical relations comsalt can be easily adapted to study saltation under a variety of physical conditions such as saltation on other planets saltation under water and saltating snow

seven million years of wind and precipitation variability on the chinese loess plateau abstract recent studies of the eolian deposits in northern china have extended the east asian monsoon history back to the early miocene however the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the pleistocene epoch remain poorly constrained mainly due to uncertainties in the interpretation of proxy indices generated from the mio pliocene red clay sequences here we reconstruct east asian monsoon oscillations over the past 7 ma using magnetic susceptibility and carbonate content as summer monsoon precipitation proxies and quartz grain size as a winter monsoon wind intensity index our results suggest that precipitation and wind intensity exhibited significant orbital scale variations prior to 4 2 ma followed by slightly damped variability between 4 2 and 2 75 ma subsequently east asian monsoon circulation experienced two large shifts at about 2 75 and 1 25 ma characterized by stepwise strengthening of glacial wind and interglacial precipitation a remarkable change in east asian monsoon seasonality occurred around 3 15 2 75 ma prior to 3 15 ma strong winds were positively correlated with high effective precipitation whereas after 2 75 ma strong winds were negatively correlated with heavy precipitation this shift was probably induced by a change from an insolation forced system to one strongly influenced by the combined effects of the phased uplift of the himalaya tibetan plateau and the simultaneous development of the northern hemisphere ice sheets

transport direction of wisconsinan loess in southeastern minnesota a study of wisconsinan loess in part of southeastern minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the mississippi river two wisconsinan loess units the peoria loess and roxana silt occur in the study area peoria loess 1 8 m thick fines systematically eastward from an abrupt western border toward the mississippi there are no apparent grain size trends away from other adjacent rivers peoria loess thickness generally decreases eastward but is highly variable probably because of differential erosion potential sources for this unit are pre wisconsinan sediments on the iowan erosion surface immediately west of the border of thick loess and wisconsinan glacial sources tens or hundreds of kilometers to the west the underlying roxana silt up to 1 m thick occurs only near the mississippi and fines away from that river the roxana silt deposit could reflect aggradation of the mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area by contrast transport of the peoria loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive very sparsely vegetated surfaces west of the study area when the peoria loess accumulated

tectonic setting of primitive magmas in volcanic arcs an example from the antarctic peninsula abstract primitive magmas representing mantle partial melts minimally affected by fractionation and assimilation are rare in the magmatic arc environment most examples are either associated with high rates of arc parallel extension or occur along faults and dykes perpendicular to the trend of the arc and related to arc compression in two cases the vanuatu and solomon islands arcs such arc compression is being caused by collision of seamounts in the antarctic peninsula primitive mafic dykes were emplaced perpendicular to the continental arc ar ar and k ar data suggest intrusion of the dykes at c 126 106 ma possibly during mid cretaceous regional compression of the arc the dykes form two compositional groups one group has low la n yb n ratios 0 31 0 49 lower nb yb and higher th nb than n morb age corrected nd values of 7 3 to 7 9 and are interpreted as melts of subduction modified sub arc asthenosphere the other has high la n yb n ratios 3 86 8 92 higher nb yb and th nb than n morb age corrected nd values of 2 8 to 3 4 and are interpreted as melts of sub arc lithosphere the absence of dykes compositionally between these groups suggests that the primitive magmas avoided storage and mixing in magma chambers

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

glacial and interglacial eolian dust dispersal patterns across the chinese loess plateau inferred from decomposed loess grain size records previous studies have indicated that a genetically meaningful decomposition unmixing of loess grain size distributions can be accomplished with the end member modeling algorithm emma the independent decomposition of two series of loess grain size records from the ne tibetan plateau and loess plateau spanning the last glacial interglacial cycle indicates that the two data sets are described by very similar mixing models the average mixing model presented here is regarded as representative for the vast loess region in northern china and allows quantification of the contribution of three loess components to the loess grain size distributions a genetic interpretation and the paleoclimatic significance of the average mixing model have been provided by comparison of the modeled loess components with modern dust samples in terms of their grain size distribution and flux rates and by the distribution patterns of the loess components across the loess plateau reconstructed for the last two glacial interglacial cycles the sandy and silty loess components represent the coarse dust fraction supplied by saltation and short term suspension processes over the proximal part of the loess plateau during major dust outbreaks in spring and early summer the low level winter monsoon northwesterly wind system is the likely transporting agent for these dust events a clayey loess component represents the fine dust component supplied over the entire loess plateau by long term suspension processes during major dust outbreaks and as part of a background supply system the clayey loess component in the glacial loess deposits is dominantly supplied during major dust outbreaks by the northwesterly winter monsoon whereas the clayey loess component in the interglacial paleosols is mainly supplied by non dust storm processes possibly with a significant contribution by the high level subtropical jet stream westerly winds

abrupt millennial climatic changes from nussloch germany upper weichselian eolian records during the last glaciation abstract increasing attention has been focussed on the massive iceberg discharges in the north atlantic heinrich events during the last glaciation and their worldwide terrestrial counterparts however these events are particular episodes among more regular cyclic events named dansgaard oeschger events in ice cores or bond cycles in marine cores here we examine grain size 13c and magnetic susceptibility data from nussloch one of the most complete west european eolian sequence examined so far these indices indicate that during the 31 19 kyr interval using chronology provided by radiocarbon osl and tl dates millennial scale variations occurred affecting both precipitation and vegetation furthermore these are associated with oscillations in the wind strength matching the dust deposition rate in greenland as recorded in the grip ice core our study shows that the abrupt climatic changes the dansgaard oeschger events are also recorded in the west european loess sequences this implies an atmospheric mechanism linking dust deposition over greenland and europe which is probably connected to global climatic events during the last glaciation

glacial and interglacial patterns for asian dust transport abstract particle size distributions and depositional fluxes were investigated for present day asian dust and for the late quaternary loess palaeosol sequences from central china the regional scale transport of asian dust during interglacial stages is mainly attributable to non dust storm processes and is dominated by northwesterly surface winds conversely during glacial stages the impact of dust storms on the accumulation of loess is enhanced these regional effects are in contrast to the global dispersal of dust which is associated with transport by upper level westerly winds and is mainly the result of desert dust storms during both glacial and interglacial conditions temporal differences in the dust transport patterns to the loess plateau suggest that the variability in the coarse particle fraction 20 m during interglacial times is not directly attributable to the strong dust storms and dust fall events that have been linked to a strengthening of east asian winter monsoonal winds this is in contrast to the dust deposition rates which are strongly influenced by the monsoonal circulation

the stabilizing role of bonding agents on the entrainment of sediment by wind well sorted fine sand pretreated with varying concentrations of two soluble salts mgcl2 and cacl2 was tested for threshold shear velocity in a recirculating wind tunnel these tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity however the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different which is similar to the results for monovalent chlorides presented by nickling ecclestone a general relationship between threshold shear velocity and total surface soluble salt content is presented

the full glacial forests of central and southeastern europe the presence of trees in central and southern europe during the last full glaciation has long been a matter of debate a low but persistent presence of fossil tree pollen in central and southern european full glacial paleoecological sequences has been interpreted either as representing long distance pollen transport from southerly refuges or as representing in situ refugial populations here we present macroscopic charcoal results from 31 sequences located throughout hungary that provide unequivocal evidence for the presence of at least seven different tree types between approximately 32 500 and 16 500 14c yr b p this evidence is presented in conjunction with molluscan and pollen analyses to indicate that during the last full glaciation trees grew as far north as hungary probably in microenvironmentally favorable sites these areas provided an important cold stage refugium for the european flora and fauna

spatio temporal seismicity patterns using mutual information application to southern iberian peninsula spain earthquakes abstract a quantitative method to characterize the spatio temporal evolution of the seismic activity of a region for a given time interval is proposed in this paper the epicentral region is divided in equal area parallelograms that we call cells a probability p i is assign to every cell depending on its seismic activity level the evolution of the mutual information based on these probabilities allows us to fit the optimal value for p i s the analysis results show that is possible to monitor the change of seismic activity quantitatively we show that a propagation model based on cross template model ct model give us a criteria whether or not an area whose size is determined by the model mathematically is going to be considered seismically activated in a period of time whose value is also the result of the application of the method our method is applied to the data of southern iberian peninsula seismicity including more than 10 000 earthquakes data available from the andalusian seismic network is used from 1985 to 1995

the climate and landscape of the middle part of the weichselian glaciation in europe the stage 3 project abstract oxygen isotope stage 3 ois 3 was a mild interval between the two cold maxima of the last weichselian glaciation marked by climate changes oscillating on a 100 1000 yr time scale between near interglacial and peak glacial conditions during ois 3 modern humans entered europe and somewhat later their neanderthal predecessors became extinct our understanding of this momentous event depends on an answer to the question did the unstable environmental conditions of the time play a significant role in early human history the stage 3 project is an interdisciplinary study with two main goals 1 to describe with existing data and to simulate the climates and landscapes of typical warm and cold phases between 45 000 and 30 000 yr ago and 2 to compare the results with the spatial and temporal distribution of human beings in this context this paper introduces the stage 3 project and provides background to a set of papers on the climate and landscape aspects of the project that will appear in quaternary research and to studies of their relevance to the early upper paleolithic of europe to appear in journals yet to be determined

a parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment abstract a new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented it is based on the balance of moments acting on particles at the instant of particle motion the model hence includes a term for the aerodynamic forces including the drag force the lift force and the aerodynamic moment force and a term for the interparticle forces the effect of gravitation is incorporated in both terms rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature a constant aerodynamic coefficient was introduced from consideration of the van der waals force between two particles it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared the interparticle force was further extended to include wet bonding forces the latter were considered as the sum of capillary forces and adhesive forces a model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well known model of fisher and the young laplace equation the adhesive force was assumed to be equal to tensile strength and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived by combining the capillary force model and the adhesive force model the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential the latter was loglinearly related to the gravimetric moisture content a relationship that is valid in the low moisture content range that is important in the light of deflation of sediment by wind by introducing a correction to force the relationship to converge to zero moisture content at oven dryness the matric potential moisture content relationship contained only one unknown model parameter viz moisture content at 1 5 mpa working out the model led to a rather simple parameterisation containing only three coefficients two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by iversen and white sedimentology 29 1982 111 the third parameter for the wet sediment part of the model was determined from wind tunnel experiments on prewetted sand and sandy loam aggregates the model was validated using data from wind tunnel experiments on the same but dry sediment and on data obtained from simulations with the model of chepil soil sci soc am proc 20 1956 288 the experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density furthermore it was shown that the surface had to dry to a moisture content of about 75 of the moisture content at 1 5 mpa before deflation became sustained the threshold shear velocities simulated with our model were found to be in good agreement with own observations and with simulations using chepil s model

paleoenvironmental fluctuations as recorded in the loess paleosol sequence of the upper paleolithic site krems wachtberg abstract the loess paleosol sequence of krems wachtberg is famous for its archeological findings above all its gravettian infant burials it represents a complex system of paleoclimatic fluctuations which is nearly complete and thus enables the correlation with global paleoclimatic records this sequence comprises activity phases with dominant eolian and partly erosional processes as well as stable short periods of weak pedogenesis periglacial environment with drier climate conditions and high eolian sedimentation rates characterize the upper part of the sequence and in periods with lower sedimentation rates cryosols and permafrost induced structures are developed although the krems wachtberg site is situated at a slope position intensive erosional phases events can be excluded the basal parts of the sequence show signs of decalcification bioturbation organic inclusions as well as changes in element distribution pedogenic horizons are partly overprinted by permafrost related structures and are disturbed by redepositional processes to a minor degree remarkably the archeological horizon is not affected by permafrost in contrast to the layers below and above the focus of this study is deciphering stratigraphy by a combination of paleopedological sedimentological analyses with rock magnetic analyses on the chronological scale the sequence records a timespan from 35 ka to 20 ka altogether there is evidence of five pedogenic units and one archeological layer which are correlated with the greenland interstadials gi 7 to gi 2 however an equivalent of a mis 3 interstadial soil comparable with the lohne soil or stillfried b soil could not be detected

the early miocene bisciaro volcaniclastic event northern apennines italy a key study for the geodynamic evolution of the central western mediterranean the early miocene bisciaro fm a marly limestone succession cropping out widely in the umbria romagna marche apennines is characterized by a high amount of volcaniclastic content characterizing this unit as a peculiar event of the adria plate margin because of this volcaniclastic event also recognizable in different sectors of the central western mediterranean chains this formation is proposed as a marker for the geodynamic evolution of the area in the bisciaro fm the volcaniclastic supply starts with the raffaello bed earliest aquitanian that marks the base of the formation and ends in the lower portion of the schlier fm late burdigalian langhian p p forty one studied successions allowed the recognition of three main petrofacies 1 pyroclastic deposits volcanic materials more than 90 including the sub petrofacies 1a vitroclastic crystallo vitroclastic tuffs 1b bentonitic deposits and 1c ocraceous and blackish layers 2 resedimented syn eruptive volcanogenic deposits volcanic material 30 90 including the sub petrofacies 2a high density volcanogenic turbidites 2b low density volcanogenic turbidites 2c crystal rich volcanogenic deposits and 2d glauconitic rich volcaniclastites 3 mixing of volcaniclastic sediments with marine deposits volcanic material 5 30 mixed with marine sediments marls calcareous marls and marly limestones coeval volcaniclastic deposits recognizable in different tectonic units of the apennines maghrebian and betic chains show petrofacies and chemical geochemical features related to a similar calc alkaline magmatism the characterization of this event led to the hypothesis of a co genetic relationship between volcanic activity centres primary volcanic systems and depositional basins depositional processes in the early miocene palaeogeographic and palaeotectonic evolution of the central western mediterranean region the results support the proposal of a geodynamic model of this area that considers previously proposed interpretations

aeolian deposition of dust over hills the effect of dust grain size on the deposition pattern wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits experiments were performed on three isolated hills having various size and aspect ratios the longitudinal profile of the median grain diameter was investigated for each hill the longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 m as were wind and dust concentration profiles in the atmosphere upwind of over and downwind of a hill the wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography most apparent is the occurrence of a zone of reduced grain size on the leeside of hills which extends from just upwind of the summit to a distance of several times the height of the hill slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size but the increase in grain size in these zones remains very small although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size systematic trends are observed the most important tendencies are 1 a progressive extension in the downwind direction of a zone of decreased dust deposition on the leeside of a hill the coarser the grains the further downwind the zone of reduced deposition extends 2 a progressive increase in dust deposition immediately upwind of a hill the finer the grains the higher the deposition value upwind of a hill becomes both tendencies are explained by the difference in inertia of the grains which is controlled by grain size copyright 2005 john wiley sons ltd

on the rate of aeolian sand transport a simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning the curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well established peak in fact the theory developed in the paper can explain the peaked shape of this curve three empirically determined coefficients in the formula can be given a physical interpretation the formula is shown to fit transport rates measured in wind tunnel experiments well except for very coarse sand formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory

a seismotectonic analysis of the anza seismic gap san jacinto fault zone southern california small earthquake epicenters near the anza seismic gap define a 20 km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity recent moderate earthquakes on and near the san jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism the locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting from the convergent geometries of the local active discontinuous faults and the oblique orientation of the regional maximum compressive stress strain is not being relieved by aseismic fault creep a swarm of small earthquakes in the crustal block 13 km southwest of the anza gap beneath the cahuilla valley recently released stress in an area which was previously highly active before the 1918 m 6 8 and 1937 m l 6 0 earthquakes the occurrence of these periods of increased seismicity near cahuilla in the years immediately before the nearby closer than 35 km large earthquakes and the recent swarm suggest that the ground beneath cahuilla may be acting as a stress meter signaling the presence of high stresses before large local earthquakes the length of the quiescent fault segment suggests potential for about an m 6 5 earthquake if the entire segment ruptures at once

the effect of surface moisture on the entrainment of dune sand by wind an evaluation of selected models reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not among the several factors that govern the initiation of soil movement by wind surface moisture is one of the most significant some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated wind tunnel experiments were conducted on pre wetted dune sand with moisture contents ranging from 0 00 to 0 04 kg kg 1 sand samples were exposed to different wind speeds for 2 min moisture content was determined gravimetrically before and after each experiment and the saltation of sand particles was recorded electronically with a saltiphone shear velocities were deduced from the wind speed profiles for each moisture content the experiments were repeated at different shear velocities with the threshold shear velocity being determined by least squares analysis of the relationships between particle number rates and shear velocity within the 2 min test runs temporal changes in particle number rates and moisture contents were detected a steep increase in the threshold shear velocity with moisture content was observed when comparing the models large differences between the predicted results became apparent at a moisture content of 0 007 kg kg 1 which is half the moisture content retained to the soil matrix at a water tension or matric potential of 1 5 mpa the increase in wet threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117 to 171 the highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment nevertheless the models of chepil 1956 proc soil sci soc am 20 288 292 and saleh fryrear 1995 soil sci 160 304 309 are the best alternatives available

geodynamic implications of the latest chattian langhian central western peri mediterranean volcano sedimentary event a review abstracthigh amounts of chattian langhian orogenic magmatism have generated volcaniclastic deposits that are interbedded within the penecontemporaneous sedimentary marine successions in several cen

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

laser diffraction analysis of the disintegration of aeolian sedimentary aggregates in water abstract a new method for the analysis of aggregate disintegration in water was tested using aeolian sediment samples the response of aeolian sedimentary aggregates to wetting and mechanical energy has important implications for the immobilization of aeolian sediments by rainfall and their susceptibility to post depositional erosion by water repeated laser diffraction analysis of a single sample circulating in deionized water provides a detailed view of the changes in particle size distribution as aggregates disintegrate this methodology also allows experiments on the effects of water chemistry exchangeable cation chemistry and prewetting results presented here suggest that aggregates of widely varying stabilities can occur in a wide range of particle size classes that is aggregate stability may to some extent be independent of the hierarchy of aggregate sizes emphasized in earlier research the methods described here are broadly applicable to a variety of soils and sediments but experiments are needed to relate the results more specifically to aggregate behavior under field conditions

tectonic stress orientation and the seismic regime of a single fault abstract the seismic regime of tectonic faults was studied by the method of physical modelling this method is based on the assumption that the physical processes in actual seismo active fault zones can be scaled in laboratory conditions the results of our laboratory experiments on plate models proved the great importance of tectonic stress orientation on the seismic regime of tectonic faults changes in the fault inclination led to distinct changes both in the recurrence time intervals between individual seismic events and in the amount of seismic energy released for some fault inclinations the seismic activity of faults vanished altogether only a limited zone in the fault plane was found to participate in the process of seismic energy release the extent of this so called seismo active zone depends not only on the contact conditions but also on the value of the acting load and on the fault inclination this presumption is supported by the fact that for each inclination there exists an upper limit to the seismic energy that can be released in one seismic event

an overview of the role of weathering in the production of quartz silt abstract quartz silt is a widespread detrital sediment with large aeolian loess and alluvial silt deposits forming important components of many contemporary landscapes despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments e g glacial grinding fluvial comminution aeolian abrasion frost weathering salt weathering insolation weathering and deep weathering the glacial aeolian hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a quaternary phenomenon as a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre quaternary environments in particular earth scientists may have considerably underestimated the role of weathering in global silt generation as there are now many references to the existence of a patchy but widespread distribution of pre quaternary weathering profiles across the glacial and periglacial landscapes of the northern hemisphere e g north america british isles north and central europe landscapes within which many of the classical loess deposits are located these observations suggest that weathering profiles may have covered large tracts of the northern hemisphere land surface prior to the quaternary glaciations this in turn may have important implications for quartz silt generation as 1 experimental studies indicate that many weathering processes are capable of generating significant quantities of silt sized debris and 2 particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt sized material or quartz grains that are weakened by weathering derived microfractures thus weathering profiles may represent mines of actual and potential quartz silt available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial fluvial and aeolian erosion

ams 14c and osl irsl dating of the dunaszekcső loess sequence hungary chronology for 20 to 150 ka and implications for establishing reliable age depth models for the last 40 ka abstract as revealed by 18 ams radiocarbon and 24 osl irsl ages the dunaszekcs loess paleosol sequence is an excellent terrestrial record of paleoenvironmental change in the carpathian basin for the last 130 ka with significant soil forming episodes during the eemian interglacial 130 115 ka mis 5e and in some subsequent mis 5 stages and distinct periods of loess accumulations during the mis 4 and mis 2 charcoals from the sequence made it possible to test the accuracy of 14 c ages from mollusc shells this approach revealed that 14 c ages from some gastropods having small shells succinella oblonga vitrea crystallina are statistically indistinguishable from the ages of charcoals while others clausiliidae sp chondrula tridens show age anomalies up to 600 800 years osl and pirir 290 ages are found to be consistently older while post ir osl ages are younger than the 14 c ages from charcoals and molluscs by some thousands of years except for pirir 225 ages that match the radiocarbon ages quite well osl and irsl ages have scatters up to 7 10 thousand years within 40 ka while charcoals and small molluscs yield consistent ages with relatively low variability beyond the observation that some small molluscs seem to yield reliable 14 c ages calibrated 2 age ranges of the radiocarbon data ca 500 800 years for 20 to 30 ka are an order of magnitude narrower than those of the osl irsl methods 1800 4000 years for 25 to 35 ka thus for establishing chronologies within 40 ka which are both accurate and precise enough to address issues like synchroneity of millennial scale paleoenvironmental events across regions e g north atlantic and europe ams radiocarbon dating of shells of specific loess molluscs and charcoals may probably be a powerful chronological tool however additional work is definitely required involving 14 c and osl irsl dates from other loess sequences to further test the performance of these two supposedly robust chronometers

responses of terrestrial ecosystems to dansgaard oeshger cycles and heinrich events a 28 000 year record of environmental changes from se hungary abstract according to the findings of a complex sedimentological geochemical malacological and pollen study implemented on a core sequence of an alkaline lake feher lake interstadials in the se great hungarian plain were characterized by increased boreal woodland cover during marine isotope stage 2 mis 2 29 700 14 500 cal bp these interstadials were dated to 26 420 27 970 23 185 24 880 and 18 810 20 770 cal bp and correlate well with the dansgaard oeschger do interstadials 2 and 3 and the post lgm warm interval seen in the greenland ice core oxygen isotope records intervening cold phases on the other hand were found between 24 880 26 420 and 20 770 23 185 cal bp correlating with heinrich event 2 and the lgm these data overall confirm that millennial scale climate variability during marine isotope stage 2 had profound effect on the terrestrial ecosystems in the continental interior of se europe leading to periodic boreal woodland expansions and contractions and wildfires

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

middle and late pleistocene loess sequences at batajnica vojvodina serbia abstract loess sequences in the vojvodina region northern serbia reveal a continuous record of paleoclimatic variations during the middle and late pleistocene the most detailed stratigraphic information comes from remarkable exposures on the cliffs of the right danube bank from vukovar to belgrade the batajnica loess section has been recognized as one of the most complete middle and late pleistocene records in this region a more than 40 m thick loess paleosol succession represents environmental transition from relative thin loess layers and rubified soils in lower part of profile to thick loess and fossil chernozems characterizing the last three glacial interglacial cycles the proposed stratigraphic model is based on a detailed magnetic susceptibility ms record which is related to the deep sea isotope stratigraphy and on correlation with other eurasian loess records using the distinct ms pattern of selected loess paleosol couplets this new stratigraphic model suggests serious revision of previous chronological interpretations ms as function of depth shows a well known pattern of low values in loess and high values in paleosols indicating strong enhancement of magnetic minerals during soil formation with the exception of the recent soil v s0 which is strongly contaminated by archaeological artifacts the third paleosol v s3 reveals the highest values in ms and a very distinct double peak the rock magnetic signal at batajnica resembles the typical pattern of the enviromagnetic records determined from other eurasian loess sites the paleopedological interpretations rubification index values and rock magnetic record at batajnica yield valuable data for the reconstruction of paleoclimatic fluctuations for the last 5 glacial interglacial cycles at least moreover the record provides an important link between the classical central european loess sites and the central asian and chinese loess provinces

climatic changes in eurasia and africa at the last glacial maximum and mid holocene reconstruction from pollen data using inverse vegetation modelling in order to improve the reliability of climate reconstruction especially the climatologies outside the modern observed climate space an improved inverse vegetation model using a recent version of biome4 has been designed to quantitatively reconstruct past climates based on pollen biome scores from the biome6000 project the method has been validated with surface pollen spectra from eurasia and africa and applied to palaeoclimate reconstruction at 6 cal ka bp calendar years the climate was generally wetter than today in southern europe and northern africa especially in the summer winter temperatures were higher 1 5 c than present in southern scandinavia northeastern europe and southern africa but cooler in southern eurasia and in tropical africa especially in mediterranean regions summer temperatures were generally higher than today in most of eurasia and africa with a significant warming from 3 to 5 c over northwestern and southern europe southern africa and eastern africa in contrast summers were 1 3 c cooler than present in the mediterranean lowlands and in a band from the eastern black sea to siberia at 21 cal ka bp a marked hydrological change can be seen in the tropical zone where annual precipitation was 200 1 000 mm year lower than today in equatorial east africa compared to the present a robust inverse relationship is shown between precipitation change and elevation in africa this relationship indicates that precipitation likely had an important role in controlling equilibrium line altitudes ela changes in the tropics during the lgm period in eurasia hydrological decreases follow a longitudinal gradient from europe to siberia winter temperatures were 10 17 c lower than today in eurasia with a more significant decrease in northern regions in africa winter temperature was 10 15 c lower than present in the south while it was only reduced by 0 3 c in the tropical zone comparison of palaeoclimate reconstructions using lgm and modern co2 concentrations reveals that the effect of co2 on pollen based lgm reconstructions differs by vegetation type reconstructions for pollen sites in steppic vegetation in europe show warmer winter temperatures under lgm co2 concentrations than under modern concentrations and reconstructions for sites in xerophytic woods scrub in tropical high altitude regions of africa are wetter for lgm co2 concentrations than for modern concentrations because our reconstructions account for decreased plant water use efficiency

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

wind transport of sand surfaces crusted with photoautotrophic microorganisms abstract wind tunnel experiments show that while surfaces inoculated with photoautotrophic organisms are stable in winds up to 19 m s 1 only filamentous cyanobacteria especially nostoc commune afford considerable protection against abrasion from windborne particles crusts formed by the polysaccharide secreting alga chlamydomonas acidophila break down easily under impact the entrainment of large low density aggregates possibly contributing to higher transport rates than would otherwise be expected for untreated sediment surface disintegration encompasses a suite of complex scale dependent processes which vary with the structure thickness and strength of the crust independent measurements of crust strength based on flexure testing are in good agreement with wind tunnel evaluation of crust stability the accommodation of a relatively large amount of deformation without rupture is an important property of fibrous photoautotrophic mats perhaps outweighing consideration of their peak strength

seismic regime of a single fault model a special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field the recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin

high mg tertiary basalts in southern sardinia italy abstract high mg basaltic pillow lavas important for an understanding of the petrogenetic evolution of the tertiary volcanism of sardinia have recently been recognized in the lower part of the early burdigalian volcano sedimentary succession of the villanovaforru vf area southern sardinian trough their textures vary from porphyritic to highly phyric types doleritic and the paragenesis is represented by pl ol cpx opx opq these basalts are sub alkaline with a tholeiitic tendency they display high mgo mg number 64 68 high ni and cr contents and their geochemical features are related to subduction related magmas with large ion lithophile element enrichment and negative nb zr and ce spikes in mantle normalized diagrams the mineralogical and geochemical characteristics indicate that the vf basalts crystallized from primitive magmas within an extension dominated tectonic setting the presence of primitive basalts suggests crustal thinning in association with the burdigalian extensional tectonics affecting the sardinian trough

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

phase relations of a high mg basalt from the aleutian island arc implications for primary island arc basalts and high al basalts many volcanic centers in the aleutian islands have erupted lavas that range in composition from high mg basalt mgo 9 wt to more fractionated and voluminous high al basalts and basaltic andesites the petrogenetic relationships between these rock types and the composition of primary magmas has been vigorously debated the phase relations of a typical high mg basalt from the makushin volcanic field on unalaska island provide important constraints on petrogenetic models results of one atmosphere and moderate to high pressure 5 20 kb anhydrous experiments are similar to results obtained from primitive morb at low pressures olivine is the liquidus phase joined by plagioclase and clinopyroxene at progressively lower temperatures clinopyroxene is the second phase to crystallize at pressures greater than 5 kb and replaces olivine on the liquidus at approximately 10 kb above 10 kb the liquidus pyroxene is aluminous augite and orthopyroxene is the second phase to crystallize glasses in equilibrium with olivine and clinopyroxene at intermediate pressure 5 to 10 kb are similar in composition to high al basalt plagioclase is not involved and most likely does not become a liquidus phase until the liquid has evolved significantly although our studies do not confirm the primary nature of high mg basalts they do support a model in which high al basalts are generated by moderate amounts of crystal fractionation from more primitive high mg mg fe lower al2o3 basaltic magmas near the arc crust mantle boundary

dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle

recalibrating aeolian sand transport models a quality controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models those of bagnold kawamura zingg owen hsu and lettau and lettau and to recalibrate the empirical constants in those models shear velocity estimates were obtained using the von karman constant and an apparent von karman parameter models were recalibrated using non linear regression and non linear regression with least squares lines forced through axes origins recalibration using the apparent von karman parameter and forced regression reduced the empirical constants for all models the disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude the recalibrated lettau and lettau model provided the greatest statistical agreement between observed and predicted transport rates with a coefficient of determination of 0 77 evaluation of the results suggests that our estimations of threshold shear velocity may be too slow causing errors in predicted transport rates copyright 2012 john wiley sons ltd

glacial comminution of quartz sand grains and the production of loessic silt a simulation study abstract traditional views have attributed the formation of loess sized quartz silt particles to glacial processes glacial grinding was considered to be the only mechanism capable of producing loessic silt in the quantities necessary for the formation of loess deposits this idea has been strengthened by the apparent close association between present or former glacierised regions and major global loess deposits however some doubts exist as to whether or not glacial grinding is capable of producing sufficient quantities of quartz silt because of the difficulties entailed in the observations and direct measurement of subglacial abrasion and crushing this paper describes and discusses the results of a simulation study designed to examine abrasion and size reduction of quartz grains under grinding conditions analogous to those experienced in a subglacial environment the findings from these experimental runs suggest that although particle breakage and comminution does occur little silt sized material is actually produced the amount of silt produced ranges from approximately 9 of the original sample in one experimental run to less than 1 for the other seven runs it is suggested that the results obtained may show considerably less abrasion and loessic silt production than may be expected to occur within a natural subglacial environment because 1 subglacial grains experience much greater overburden pressures for much longer periods of time 2 the use of sand sized grains may represent a stable component resistant to further size reduction through crushing or abrasion and 3 the use of a monomineralic sample of relatively sound quartz grains although care must be taken when relating results obtained from these experimental runs to silt production within a glacial environment findings from this work do question whether large amounts of quartz silts are produced within subglacial environments the importance of glacial processes in the formation of loess deposits may lie in the reworking of pre existing sediments by ice rather than the actual production of vast quantities of silt this in turn suggests that care should be taken in the interpretation of the provenance of particles comprising loess deposits

influence of soil texture on the binding energies of fine mineral dust particles potentially released by wind erosion abstract models of the two aeolian processes saltation and sandblasting that lead to emission of fine dust particles pm20 by wind erosion in arid and semi arid areas have been combined to form the so called dust production model dpm in this model the size dependent binding energies of pm20 embedded within the wind erodible loose soil aggregates or in the soil surface itself are key input parameters indeed their values condition at the same time the intensity of emissions and their initial size distribution previous comparisons of vertical mass fluxes measured on field with the model predictions suggest that these energies might be relatively independent of soil texture and also probably composition because this would greatly facilitate application of the dpm at regional or global scale the objective of this work is to check experimentally the veracity of this result the strategy that has been designed for this has involved selecting four natural soil samples collected in various source areas of the world and covering a wide range of textures and compositions then these soil samples have been used to perform carefully controlled wind erosion simulations in a wind tunnel during the experiments which were carried out at different wind speeds with each soil the horizontal flux f h of saltating soil aggregates has been monitored at the same time number concentrations c i of pm20 released by the sandblasting process were recorded in the 6 size classes of an optical size analyzer thus the efficiency of the sandblasting process defined as the ratio of c i to f h could be determined for each of these size classes analysis of the results obtained in similar saltation conditions shows that for the four tested soils and within the range of contents in clay and other components favoring aggregation mostly organic matter and carbonates the influence of soil composition and texture on binding energies of the pm20 particles within soil aggregates is at best a second order effect that can be neglected in large scale modeling of wind erosion by the dpm

dust emission and transport in mali west africa vertical dust fluxes were measured in the inland delta region of the niger river mali west africa during april june 1989 and 1990 measurements of dust flux represent for the most part non dust storm conditions or dust haze periods the observed concentration versus height relationships are similar to data presented by other investigators the relationship between wind shear velocity u m s 1 and vertical dust flux f g m 2 s 1 can be described by a relationship in which f is proportional to u 4 however there is considerable scatter within the data set which is attributable to textural controls and surface conditions the vertical dust fluxes measured in mali are compared to dust fluxes measured in texas usa and yukon territories canada the significantly different values for the constant of proportionality a in the f a u 4 relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream dust concentrations measured in mali were found to be uniformly high and in general exceed who health standards for acceptable total suspended particulate loadings as a result background dust may be considered a long term stress on health for the people of this region of mali

surface textural analysis of quartz grains by scanning electron microscopy sem from sample preparation to environmental interpretation abstract surface microtextures on quartz grains provide an insight into the sedimentary history of clastic sediments not only information on the depositional environment is provided but also in some cases successive sedimentary cycles can be recognised sample preparation and sem imaging are the initial and therefore crucial steps in the study of microtextures a sample preparation procedure using 15 hydrochloric acid and 50 g l tetrasodium pyrophosphate solutions removes most of the grain coatings and adhering particles the study of microtextures on 1300 quartz grains from a wide variety of environments was complemented with the reference works and atlases krinsley and doornkamp 1973 le ribault 1977 higgs 1979 mahaney 2002 to construct an interpretation scheme allowing to differentiate between fluvial marine eolian glacial and diagenetic alteration environments based on microtextures in a case study the known littoral setting of two samples was confirmed by using the interpretation scheme for quartz microtextures furthermore successive reworking of the grains in eolian and intertidal environments was recognised by presenting the research of microtextures from starting point to interpretation new researchers may find this review a useful and practical introduction into the technique

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds