weakening and strengthening of the indian monsoon during heinrich events and dansgaard oeschger oscillations the dansgaard oeschger oscillations and heinrich events described in north atlantic sediments and greenland ice are expressed in the climate of the tropics for example as documented in arabian sea sediments given the strength of this teleconnection we seek to reconstruct its range of environmental impacts we present geochemical and sedimentological data from core so130 289kl from the indus submarine slope spanning the last similar to 80 kyr elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the indus river in contrast stadials are characterized by an increased contribution of aeolian dust from the arabian peninsula decadal scale shifts at climate transitions such as onsets of interstadials were coeval with changes in productivity related proxies heinrich events stand out as especially dry and dusty events indicating a dramatically weakened indian summer monsoon potentially increased winter monsoon circulation and increased aridity on the arabian peninsula this finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events our results strengthen the evidence that circum north atlantic temperature variations translate to hydrological shifts in the tropics with major impacts on regional environmental conditions such as rainfall river discharge aeolian dust transport and ocean margin anoxia key points intensity of indian monsoon is traced with geochemical and grain size analyses of sediments fluvial versus aeolian sediment input to arabian sea mimics do oscillations during heinrich events the indian monsoon weakened distinctly

scaling and parametrization of clear sky solar radiation over complex topography 1 solar radiation at the land surface is influenced by slope aspect shadows and obstruction of the sky all of which vary over a wide range of length scales in regions of complex topography with important consequences for the surface energy balance atmospheric models however generally assume the surface to be flat on subgrid scales for four areas in north america ranging in latitude from 39 n to 69 n and in topography from rolling to mountainous we simulate spatial patterns of clear sky incoming solar radiation it is found that distributions of slope components and variations in shaded area with solar elevation can be approximated by simple functions that scale to each of the areas studied from these results parametrizations are developed for averages standard deviations and distributions of direct beam and diffuse solar radiation results from these parametrizations and from a modified form of a simpler parametrization presented previously compare well with statistics from the spatial simulations the only topographic input required by the parametrizations is the standard deviation of slope components this parameter is again found to have simple scaling relationships with the resolution and extent of the underlying elevation grid and with the standard deviation of elevation

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

unroofing of active metamorphic core complexes in the d entrecasteaux islands papua new guinea metamorphic core complexes in the d9entrecasteaux islands are forming as a result of active extension at the western end of the woodlark basin spreading center high grade metamorphic rocks exist in the cores of gneissic domes including eclogites formed at minimum depths of 45 75 km i e 13 21 kbar high temperatures were maintained during uplift of basement rocks from 13 21 kbar t 730 900 c through 7 11 kbar t 570 730 c to 5 6 kbar t 730 c subsequent rapid cooling 100 c m y of the basement occurred between 1 and 2 ma on the basis of 40 ar 39 ar geochronology the core zone rocks were transected by kilometre scale amphibolite facies ductile shear zones active at depths of 25 35 km extensive intrusion of granodiorite plutons occurred and the age of granodiorite intrusions constrains late stage shear zone activity to 2 ma and younger unroofing was accomplished by faults and shear zones bounding the gneiss domes juxtaposing them against ultramafic rocks and sedimentary deposits surface uplift continues today and has led to topographic elevations of up to 2 5 km

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

mudflat distal fan and shallow lake sedimentation upper vallesian turolian in the tianshui basin central china evidence against the late miocene eolian loess the tianshui basin in central china contains a thick sedimentary sequence 1400 m of continental deposits aragonian to villafranchian miocene pliocene in age intense himalayan movements around the paleogene miocene boundary triggered the uplift of mountain ranges around the tianshui basin providing the deposition site for continental sediments the sedimentary infill of the basin consists of four stratigraphic units i to iv this paper focuses on unit ii most of the accommodation space was occupied by unit i so during the sedimentation of unit ii the morphology of the basin was relatively flat promoting the development of wide distal fan mudflat areas and wide shallow lakes deposits include red mudstones pedogenic and groundwater calcretes reworked calcrete deposits sheet floods fluvial channels rippled sandstones siltstones ooidal peloidal packstones palustrine limestones bioturbated marls and intraclastic limestones marls the characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments within the distal fan mudflat the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays at the lake margins the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings the origin of some of the deposits of the basin s qa i section is under discussion and their consideration as eolian has been recently proposed however we believe this possibility is precluded by the characteristics of the deposits our proposal has important implications for revising the interpretation of miocene paleoclimatic conditions in central asia

dust supply from river floodplains the case of the lower huang he yellow river recorded in a loess palaeosol sequence from the mangshan plateau the mangshan plateau is located on the south bank of the huang he yellow river just west of the city of zhengzhou well outside the loess plateau in central china mixing models of the grain size data indicate that the loess deposits are mixtures of three loess components comparison of the mixing model with existing models established for a series of loess palaeosol sequences from the loess plateau indicates that the mangshan loess has been supplied from a proximal dust source the huang he floodplain during major dust outbreaks the high accumulation rates the composition of the loess components and especially the high proportions of a sandy loess component support this owing to the exceptionally high accumulation rates the mangshan grain size magnetic susceptibility and carbonate records provide a high resolution archive of environmental and climate change copyright 2008 john wiley sons ltd

topographic distribution of clear sky radiation over the konza prairie kansas this research analyzes the topographic distribution of clear sky incoming solar radiation over the tallgrass konza prairie site of fife the first islscp international satellite land surface climatology program field experiment using a two stream atmospheric radiation model and digital elevation grids of 25 50 and 100 m grid spacing clear sky radiation is simulated throughout the day for three dates december 15 march 15 and june 15 geostatistical analysis is used to characterize the spatial and temporal variability in modeled radiation at each grid spacing the variance and spatial autocorrelation of simulated incoming radiation depend on sun angle and elevation grid spacing the behavior of the variance as a function of sun angle optical depth and mean terrain slope can be explained by considering direct radiation variability on a simplified terrain model of uniform albedo where slopes are equal and azimuths are distributed uniformly in all directions for this constant slope model it can be shown analytically that the solar zenith angle at which variance is maximized is a function of optical depth only and is independent of elevation slope and aspect results from the two stream simulations support this conclusion and suggest its applicability to real terrain

exhumation and doming of the thasos metamorphic core complex s rhodope greece structural and geochronological constraints abstract the thasos island metamorphic core complex s rhodope n aegean sea was generated between 26 and 13 ma progressive extensional tectonics was associated with upwarping of the deeper parts of this core complex to a narrow gneiss dome and with formation of a steep topographic high we present a combined structural microstructural and geochronological study that constrains the deformation time path of progressive extension and exhumation thasos island consists of three superimposed more or less flat lying metamorphic units with downward decreasing geochronologic ages which are separated by two systems of low angle normal detachment surfaces trending nw se the upper unit stayed in supracrustal level since 50 ma representing the upper plate during an early phase of extension not later than 26 23 ma upper levels of the core complex intermediate unit underwent pervasive mylonitization with top to the sw shear from about 21 ma onward the intermediate unit was rigid and top to the sw slip continued at least until 13 8 ma on the discrete detachment surface that separates the core complex from the upper plate yet in the 21 15 ma period deeper levels lower unit still deformed plastically and deformation successively concentrated in zones of high strain and in discrete detachment surfaces that caused decoupling of the lower from the intermediate unit these indicate downdip movements in opposite sense associated with doming of the lower unit at that stage simultaneously the intermediate unit was fragmented on high angle normal faults that sole into the dome bounding detachment surface and roof into the core complex bounding detachment surface these faults confine tilt blocks that are arranged around the lower unit gneiss dome doming of the core complex occurred simultaneously with subsidence of basins located on the upper plate

grain size of fine grained windblown sediment a powerful proxy for process identification abstract dust transport by the wind is not a uniform process but may occur in different modes according to source area conditions and transport height and distance subsequently these differences are expressed in terms of grain size and fluxes of the aeolian deposits transport distances may vary from several tens of meters to thousands of kilometers while the height accordingly may vary from meters to more than thousand meters a relation with grain size distributions may be established on the base of type occurrences of different loess facies three main loess populations and several subpopulations of primary windblown origin may be defined according to their grain size dominated by fine sand to very coarse silt silt and very fine silt to clay respectively each of them reflects a specific aeolian process and transport conditions it follows that the grain size distribution of a loess deposit is an excellent proxy for the reconstruction of aeolian processes and wind circulation patterns apart from primary pure wind deposition loess may also be affected by secondary post depositional processes examples are settling of loess particles in a lacustrine setting and reworking by rivers or surface runoff although the primary loess characteristics are maintained reworking processes leave also their imprint in the grain size distribution as a useful tool for secondary process identification

identifying eolian dust in the geological record abstract recognition of terrestrial dust in geological records is essential for reconstructing paleoenvironments and quantifying dust fluxes in the past however in contrast to eolian sands silt sized dust is difficult to recognize in pre quaternary records due to a lack of macroscopic features indicating eolian transport and mixing with alluvial sediments windblown dust deposits are commonly identified by comparing their sedimentological and petrological features with quaternary examples of dust known as loess here we review the characteristics of terrestrial dust deposits and conclude that most of these features are not exclusively windblown and may be formed by alluvial deposits as well we therefore synthesize a set of criteria which enable a reliable identification and quantification of dust while acknowledging potential contributions of alluvial components these methods include quartz grain surface morphology analysis to distinguish eolian and alluvial transport modes provenance studies to identify local and extrabasinal sources grain size shape end member modelling to quantify the various sedimentary contributions to the record and a basin scale stratigraphic approach to derive regional patterns and avoid interpretation of local phenomena we reassess the eocene to pliocene records of the chinese loess plateau and conclude that these strata represent both alluvial and eolian sediments deposited in extensive mudflat systems quaternary loess by contrast is almost exclusively composed of windblown dust the early pleistocene shift from mudflat to loess deposits is associated with a significant increase in accumulation rates likely due to increased dust production upwind overwhelming and blanketing the local mudflat systems in central china

contrasting dust supply patterns across the north western chinese loess plateau during the last glacial interglacial cycle loess grain size distributions of four loess paleosol sequences located on a west to east transect from the north eastern tibetan plateau tp to the north western chinese loess plateau clp are unmixed with the end member modelling algorithm emma the unmixing results indicate that the loess is a mixture of three components representing very fine sandy coarse silty and medium silty loess the proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last glacial interglacial cycle two contrasting dust supply patterns were active over the north eastern tp and the north western clp a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess the variable input of the two coarse dust components is the main cause for the variation in grain size patterns and mass accumulation rates between the studied sites alluvial fans and river floodplains in the intra mountainous basins of the tibetan plateau and the deserts of northern china and inner mongolia are the main dust source areas for loess deposits of the north eastern tp and the clp respectively the sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition in general high dust fluxes are recorded during the last glacial period marine isotope stages mis 2 4 and low dust fluxes during the last interglacial mis 5 the loess sections in the two regions tp clp show contrasting dust flux patterns during mis 3 the records from the clp show a relatively low dust input in this period most likely related to increased humidity in the northern dust sources deserts where an increased vegetation cover minimized dust deflation in contrast to this the tibetan plateau records appear to show increased and highly variable dust fluxes for mis 3 alternating periods of increased humidity and aridity on the tibetan plateau during mis 3 have resulted in an overall increase in fluvial alluvial activity hence the enhanced availability of exposed fine grained fluvial alluvial sediments on the tibetan plateau facilitated dust entrainment which resulted in an increased dust supply towards the tibetan plateau sites during this period

effect of digital elevation model resolution on the simulation of the snow cover evolution in the high atlas the snow melt from the high atlas represents a crucial water resource for crop irrigation in the semiarid regions of morocco recent studies have used assimilation of snow cover area data from high resolution optical sensors to compute the snow water equivalent and snow melt in other mountain regions these techniques however require large model ensembles and therefore it is a challenge to determine the adequate model resolution that yields accurate results with reasonable computation time here we study the sensitivity of an energy balance model to the resolution of the model grid for a pilot catchment in the high atlas we used a time series of 8 m resolution snow cover area maps with an average revisit time of 7 5 days to evaluate the model results the digital elevation model was generated from pleiades stereo images and resampled from 8 to 30 90 250 500 and 1 000 m the results indicate that the model performs well from 8 to 250 m but the agreement with observations drops at 500 m this is because significant features of the topography were too smoothed out to properly characterize the spatial variability of meteorological forcing including solar radiation we conclude that a resolution of 250 m might be sufficient in this area this result is consistent with the shape of the semivariogram of the topographic slope suggesting that this semivariogram analysis could be used to transpose our conclusion to other study regions

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

deformation in the diffuse india capricorn somalia triple junction from a multibeam and magnetic survey of the northern central indian ridge 3 s 10 s 1 we use new multibeam and magnetic observations from 3 s 10 s along the central indian ridge to describe morphotectonic features and spreading fabrics within the study area and quantify deformation across the diffuse india capricorn somalia triple junction a megamullion adjacent to the vityaz transform fault is the first reported for the northern central indian ridge the principal transform displacement zone ptdz of the vema transform fault consists of several closely spaced faults that can be traced for more than 150 km serpentinite or volcanic intrusions that are offset by the vema pdtz have inferred ages of 30 000 45 000 years testifying to the youth of active features on the valley floor abyssal hill orientations throughout the study area have remained constant since at least 4 ma implying little or no change in the opening direction during this period abyssal hills from opposite sides of the ridge have the same orientations within our 1 3 errors implying that slip along reactivated fracture zones in the diffuse triple junction neither significantly rotates nor shears the intervening seafloor transform fault azimuths in the survey area agree with the nuvel 1 africa australia slip direction but are 5 9 clockwise from the africa india direction in contrast seafloor spreading rates in the study area agree better with the nuvel 1 africa india predictions these seemingly conflicting observations are reconciled by a model in which seafloor within the diffuse triple junction rotates about the india capricorn pole at angular rotation rates that increase monotonically from zero to the full rotation rate across the deforming zone

pathways of dust input to the chinese loess plateau during the last glacial and interglacial periods abstract it has been established that loess deposited on the chinese loess plateau was derived from arid and semi arid regions in north and northwest china but the specific pathways of dust transport are still not proved in this study 32 loess palaeosol profiles of the last glacial and interglacial periods were measured for magnetic susceptibility in order to investigate the dust transport pathways of dust input to the loess plateau the magnetic susceptibility variations of the loess palaeosol deposits within the last glacial cycle can be correlated with marine oxygen isotope variations to estimate the ages of boundaries of the loess units and intercalated palaeosols the sedimentation rate of each depositional unit can be obtained by dividing the thickness by the time that it represents because sedimentation rates decrease downwind from the dust source the spatial distribution of dust sedimentation rates shows that northwest and west winds were the two most important agents for transport of dust to the loess plateau during the last glacial cycle the north and northeast winds played an almost negligible role in addition topography and dust from local sources strongly affected the dust accumulation rates at some measured sites

binary sources of loess on the chinese loess plateau revealed by u pb ages of zircon the age distribution of detrital zircon has been used to trace sediment sources existing datasets show great similarity of zircon ages between the loess on the chinese loess plateau clp and the sediments from the north tibetan plateau ntp implying that eolian dust is delivered from the ntp to the clp by westerly winds or via the yellow river however ntp dust can also be transported by northwesterly winds from the alxa arid lands aals where materials are received from both the ntp and the gobi altay mountains gams here we report u pb zircon ages for aals sands and ntp and clp loess the results show that the zircons in the aals are mixed from ntp and gams zircons ntp loess is mainly derived from local sources mixing of materials from the ntp and gams defines the zircon ages of the loess on the clp better than the pure ntp source no temporal and spatial heterogeneities of zircon ages have been observed for the loess on the clp which suggests that the well mixed materials in the aals likely have an eolian source

the late miocene and pliocene climate in east asia as recorded by grain size and magnetic susceptibility of the red clay deposits chinese loess plateau abstract grain size characteristics of the aeolian red clay sediment series in china demonstrate the existence of warm cool alternations during the late miocene and pliocene from the dissimilarity between the temporal patterns of grain size and magnetic susceptibility it is inferred that the finest grain size fraction in the red clay clay and very fine silt is transported by the wind as is the case of the coarser silty component relatively cool climatic conditions are indicated by increased loess supply represented by the silty component from the nw caused by a stronger winter monsoon as in the overlying quaternary system it is striking that at the same time the amounts of clay also increased probably due to transportation by intensified westerly circulation relatively warm periods are characterized by opposite grain size properties these warm cool alternations on the asian continent dated by palaeomagnetic analyses correlate well with already established changes in sea level and ice sheet volumes up to 6 ma in addition time series analysis of the grain size signal points to an orbitally forced climatic cyclicity precession eccentricity and weak obliquity

comparison of particle size characteristics of the tertiary red clay and pleistocene loess in the chinese loess plateau implications for origin and sources of the red clay the origin of the tertiary red clay underlying the pleistocene loess in the chinese loess plateau remains controversial although several lines of evidence have suggested a wind blown origin this study examines the particle size parameters of the late miocene and pliocene red clay by comparing it with those of the late pleistocene loess the particle size distribution of a total of 15 339 loess and 6394 red clay samples taken from 12 loess sections along a north south transect and two red clay sequences at lingtai and jingchuan was systematically analysed the median grain size skewness and kurtosis of the late pleistocene loess all show a systematic southward change and are principally influenced by distance from source region the spatial and temporal differentiation of dust deposits is expressed in a skewness kurtosis median grain size ternary diagram from which the distance to the source region can be inferred the particle size characteristics of the tertiary red clay sediments are very similar to those of the palaeosols within the late pleistocene loess deposits suggesting an aeolian origin for the red clay based on the comparison of red clay and loess in the ternary diagrams it is inferred that the source sink distance was greater in the neogene than in the last and penultimate interglacials and that the dust source region in north western china underwent a progressive expansion during the period from at least 7ae0 ma to the present

spatial pattern of grain size in the late pliocene red clay deposits north china indicates transport by low level northerly winds abstract the confirmation of an eolian origin of the tertiary red clay from north china would make it a valuable terrestrial paleoclimatic record however it is still controversial as to which wind primarily transported the dust forming the red clay onto the loess plateau careful consideration of this question is a prerequisite for better understanding the history of atmospheric circulation in central and east asia during the miocene and pliocene epochs in this paper the grain size distributions of bulk samples and chemically isolated quartz grains of the late tertiary red clay were investigated to explore the potential transportation mechanisms of the dust as well as the atmospheric circulation at the time of deposition the samples were taken from six localities spanning across 550 km on the loess plateau the results show that the mean grain size of both bulk and quartz samples decreases southward as does the coarse fraction content 42 m these data not only give new evidence for the eolian origin of the red clay but also indicate that the red clay was probably transported mainly by northerly low level winds or the winds at least had a strong northerly component therefore the spatial distribution of grain size of the red clay is comparable to that of the overlying quaternary eolian loess which demonstrates a remarkable northwest southeast decrease in grain size sedimentation rate and thickness during the last glacial coinciding with the dominant wind direction of the northwesterly east asian winter monsoon however the grain size of the red clay is generally finer than the corresponding loess this indicates that the red clay may have been transported by a weaker winter monsoon associated with stronger pedogenic modification and or the dust source area was not extensive compared to that during the quaternary moreover the high content of grains coarser than 19 m transported mainly by energetic low level winds over short distances suggests that the dusts were not transported by upper level westerly

heterogeneity in homogeneous brabantian loess during the late pleniglacial abstract the brabantian loess is often seen as a homogeneous sediment package deposited under cold and dry climatic conditions haesaerts et al 1981 however in 1981 two small tundra gleysols were discovered in the brabantian loess haesaerts et al 1981 to unravel other possible changes in the sedimentary system during deposition a more detailed look at the homogeneous brabantian loess is carried out the loess transporting process is reconstructed based on the combination of both grain size and grain shape parameters these parameters are defined with automated dynamic image analysis and statistically compared with the two dimensional kolmogorov smirnov test as suggested by vandenberghe et al 1998 our gleysols are generally correlated to a period of reduced grain size most likely the more subtle the gleysols the weaker the link between their formation and grain size reduction mazzullo et al 1992 already stated that aeolian transport was very selective regarding grain size and sorting capacities our research points toward an extremely selective aeolian transport regarding the shape of the grains therefore combining both particle size and particle shape can be very useful when reconstructing aeolian transport processes this combination can also discriminate samples with a different transport and sedimentation history

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

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

silt 2 62 μm 9 4φ the particles in finer grained detrital sediments are usually composed of quartz they fall into two size grades sand 2 mm 62 m and silt 62 m 2 m these size gradings conceal important geological processes since there are geological controls on both the quartz sand and silt populations sand nature is largely controlled by geochemical reactions for example in cooling granite from which it is eventually released by weathering action the quartz is among the last part of the rock system to solidify and the eutectic like reaction which occurs ensures that the quartz exists as small crystalline units each suffering considerable cooling and recrystallisation stresses silt is broken quartz and has traditionally been considered to lack a specific geological control the situation is confused by the large range of materials that fall into the size category but there do seem to be distinguishable modes and possibly comminution limits within the 60 m span the controls operating in this size range are probably the critical concentration of moss defects in the quartz particles moss postulated the formation of specific crystal defects in the quartz formed in granites these affect sand formation and it is possible that they also control the mode size of silt particles within the silt range there may be several usefully definable populations as moss proposed for sand the quaternary appears to be a silt rich period due to tectonic and glacial activity but silt production is apparent throughout the sedimentary record very long term silt producing processes are required to produce silt in nature on a large scale very energetic processes are required many processes that are believed to generate silt particles have been listed however large scale production is essentially due to glacial grinding or to intense weathering processes in high cold tectonically active mountain regions the region of high asia of crustal overlap is a major generator of silt particles these form the productive alluvial soils of north india most of the nation of bangladesh the loess deposits along the syr darya and amu darya rivers in central asia and the great loess deposits of north china some claims have been made for silt production in hot deserts large amounts of very fine aerosolic dust are produced but in terms of loess sized particles this is a small scale process and leads to modest disputed deposits the loess deposits around the sahara usually have smaller mode sizes e g nigeria or larger mode sizes e g libya tunisia than the true chinese mode at 25 m this paper aims to introduce the distinguishing properties of sand and silt discuss in detail the possible processes of silt formation in relation to the evidence of what is produced describe the major silt populations and conclude on the most likely formation process es in particular three silt ranges are discussed in relation to the r size diagram c 2 5 m d1 20 30 m and d2 60 m these can represent canadian quickclay qq chinese loess and the ideal loughborough loess ll and north african loess nal it is intended that this paper will put into context the diverse work in the area and in so doing shed light on what is an often overlooked subject

the evaluation of macroscopic and microscopic textures of sand grains using elliptic fourier and principal component analysis implications for the discrimination of sedimentary environments a method that integrates elliptic fourier and principal component analysis is a new development in the analysis of the shapes of sand grains however conventional elliptic fourier and principal component analysis based on the variance covariance matrix of the elliptic fourier results can determine only the form of sand grains and fails to quantify fine scale boundary smoothness of grains in this study sand grains from glacial fluvial foreshore and aeolian environments were analysed using both elliptic fourier and principal component analysis and an extension of elliptic fourier and principal component analysis based on the correlation matrix to extract information on grain form macroscopic and grain boundary smoothness microscopic separately conventional elliptic fourier and principal component analysis based on the variance covariance matrix produces macroscopic particle shape descriptors such as the elongation index and bump indices these indices indicate that sand grains exposed to subaqueous transportation fluvial and foreshore have forms that are more elongated than those exposed to subaerial transportation aeolian dunes however elliptic fourier and principal component analysis based on the correlation matrix is in addition able to extract microscopic particle features which can be interpreted in terms of a boundary smoothness index the boundary smoothness index indicates that the surfaces of glacial grains are the most rugged whereas the surfaces of aeolian grains are the smoothest on bivariate plots of the boundary smoothness and elongation indices samples from fluvial foreshore aeolian and glacial environments cluster in discrete regions in addition the analysis reveals that glacial grains are exposed to different morphological maturation pathways than those from fluvial foreshore and aeolian environments

the effects of wind transport on the shapes of quartz silt grains abstract wind blown terrigenous silt is a common component in marine sediment but it is often difficult to distinguish from fluvial silt a field experiment was conducted in the loess plateau of china to determine the effect of eolian transport on the shapes of detrital quartz silt grains and to define grain shape criteria for the recognition of eolian silt the results show that eolian transport results in a rapid downwind increase in the roundness of quartz silt grains and that this increase in roundness is apparently due to preferential transport or shape sorting of more rounded grains this capacity for shape sorting distinguishes eolian from fluvial transport which has no great effect upon the shapes of quartz silt grains and provides a petrographic criteria for the distinction of t e eolian and fluvial silt components in marine sediments

provenance of northwestern patagonian river sediments 44 48 s a critical evaluation of mineralogical geochemical and isotopic tracers abstract the ability to trace and quantify sediment provenance in northwestern patagonia is increasingly needed to properly understand modern sediment erosion and transport processes in this rapidly changing environment and to accurately interpret sediment records from adjacent basins in terms of climate and environmental change nonetheless no study so far has systematically evaluated the effectiveness of different tracers to reconstruct sediment provenance in this region to fill this gap we assess the effectiveness of commonly used provenance indicators including bulk mineralogy major and rare earth element ree geochemistry and sr and nd isotopes to reconstruct sediment provenance in northwestern patagonia first the ability of these tracers to discriminate between the main sources of sediment in the region is investigated mostly using data compiled from the literature then the potential of these tracers for provenance reconstruction is assessed by comparing the composition of sediments from six major chilean rivers between 44 and 48 s to lithological proportions in their respective watersheds the results suggest that mineralogy major element geochemistry and ree geochemistry can be used as qualitative tracers of sediment provenance however the compositional overlap between the sources and the relatively large variability within them prevent quantitative reconstructions by comparison 87sr 86sr and end allow to clearly differentiate between the sources most likely due to significant age differences between the main lithologies and to estimate the relative contribution of each source end member mixing results based on sr and nd isotopes show that the relative source contributions are in general agreement with the lithological proportions in the river watersheds differences between estimated contributions and lithological proportions in the watersheds are interpreted as the result of the high regional precipitation gradient and unequal glacier distribution which lead to variable erosion rates across the study area our results demonstrate the suitability of 87sr 86sr and end for quantitative provenance reconstruction in northwestern patagonia they constitute a strong basis for the interpretation of sediment archives from the patagonian fjords and from the eastern south pacific and they should be particularly useful to quantitatively investigate modern and past earth surface processes

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

aeolian dust supply from the yellow river floodplain to the pleistocene loess deposits of the mangshan plateau central china evidence from zircon u pb age spectra the thick loess palaeosol sequences in the mangshan loess plateau mlp central china along the south bank of the lower reach of the yellow river provide high resolution records of quaternary climate change in addition substantial increases in grain size and accumulation rate have been inferred in the upper part of the loess sequence above palaeosol layer s2 this study investigates the sources of the long term dust supply to the mlp and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since s2 240 ka by using end member modelling of the loess grain size dataset and single grain zircon u pb dating our results indicate that the lower yellow river floodplain directly north of the mlp served as a major dust supply for the plateau at least since the deposition of loess unit l9 and indirectly suggest that the integration of the yellow river and the disappearance of the sanmen palaeolake took place before l9 900 ka the sudden change in sedimentology of the mangshan sequence above palaeosol unit s2 may result from an increased fluvial sediment flux being transported to the lower reaches of the yellow river because of tectonic movements initiated in the weihe basin around 240 ka furthermore sediment coarsening can be explained by the gradual southward migration of the lower yellow river floodplain towards the mlp since the deposition of palaeosol s2 the migration is evidenced by the formation of an impressive scarp and is likely caused by tectonic tilting of the floodplain area 2018 elsevier ltd

a 550 ka record of aeolian activity near north west cape australia inferences from grain size distributions and bulk chemistry of se indian ocean deep sea sediments abstract the terrigenous fraction of sediments from a deep sea sediment core recovered from the northwestern western australian continental slope offshore north west cape se indian ocean reveals a history of western australian climate throughout the last 550 ka end member modelling of a data set of grain size distributions n 438 of the terrigenous sediment fraction allows to interpret the record in terms of aeolian and fluvial sediment deposition both related to palaeo environmental conditions in the north west cape area the data set can be best described by two aeolian end members and one fluvial one changes in the ratio of the two aeolian end members over the fluvial one are interpreted as aridity variations in northwestern western australia these grain size data are compared with bulk geochemical data obtained by xrf scans of the core log ratios of the elements zr fe and ti ca which indicate a terrigenous origin corroborate the grain size data we postulate that the mid to late quaternary near north west cape climate was relatively arid during the glacial and relatively humid during the interglacial stages owing to meridional shifts in the atmospheric circulation system opposite to published palaeo environmental records from the same latitude 20 s offshore chile and offshore namibia the australian aridity record does not show the typical southern hemisphere climate variability of humid glacials and dry interglacials which we interpret to be the result of the relatively large land mass of the australian continent which emphasises a strong monsoonal climatic system

spatial and glacial interglacial variations in provenance of the chinese loess plateau the chinese loess plateau clp covers an extensive area over 440 000 km2 and provides an unprecedented terrestrial record of neogene climate however it is still unclear whether the provenance of these loess deposits is uniform or contains spatial and temporal differences here this is addressed by comparing detrital zircon age spectra of typical loess and paleosol samples from three distant sites located at the western middle and southeastern parts of the clp our results reveal that the zircon age spectra not only change between loess and paleosol layers but also vary from the western to the eastern clp at least during the last glacial cycle the discrepancies of the zircon age spectra among different sites suggest that the loess provenance of clp is heterogeneous and spatially variable although it has been suggested that the mineralogical elemental and isotopic compositions of loess deposits on clp are highly homogenous spatially and in glacial interglacial cycles

aeolian silt transport processes as fingerprinted by dynamic image analysis of the grain size and shape characteristics of chinese loess and red clay deposits abstract this study applied dynamic image analysis dia sympatec qicpic to characterize the grain size and shape of chinese aeolian sediments in order to fingerprint their transportation processes this is the first time this technique has been applied to late neogene and quaternary silt particles 2 63 m from the chinese loess plateau clp we selected four well studied quaternary loess palaeosol sequences along a north south transect across the clp and compared their grain size distribution obtained by dia with that yielded by laser diffraction particle size analysis ld fritsch analysette 22 and sympatec helos kr this comparison demonstrated that dia is successfully able to differentiate loess units from palaeosols and to characterize clearly spatiotemporal variations in the grain size records of loess palaeosol sequences formed during the last two glacial and interglacial periods this is consistent with grain size results obtained using ld dia is also able to characterize spatial variations in the more fine grained aeolian red clay deposits underlying the quaternary loess and allows the quantification of the fluvial contribution to red clay sequences dia of the characteristics of grain shapes in loess palaeosol sequences and red clay deposits revealed a systematic pattern whereby the aspect ratio decreased with increasing grain size indicating that systematic shape sorting occurred during the aeolian transportation of these dust particles it could be inferred from our study that particles in a certain grain size range correspond to a specific aspect ratio range and may in turn be aerodynamically distinguishable from each other and further correlated with the wind velocity strength also evident from analysis of our dia data was a subtle but systematic downwind decrease in the aspect ratio of the particles in the loess units this observation suggests that elongated and or flat particles with a low aspect ratio were transported further downwind than more symmetrically shaped particles with a high aspect ratio this study indicates that dia of grain size and shape characteristics can be an additional powerful tool for identifying grain size and shape sorting trends determining the dominant mode of transport and reconstructing transport pathways of silt sized aeolian sediments

fluvial or aeolian unravelling the origin of the silty clayey sediment cover of terraces in the hanzhong basin qinling mountains central china this study is focused on a silty clayey sedimentary sequence on a terrace in the intramontane hanzhong basin located in the qinling mountains qlm central china traditionally the qlm are considered to have blocked dust transport from northwest to southeast china however in recent years geo archaeological studies have documented loess palaeosol sequences at numerous locations in and surrounding the qlm in the loess deposits overlying the terraces of the hanjiang river in the hanzhong ankang and yunxian basins abundant artefacts flakes stone tools e g scrapers and choppers and cores are commonly found the loess deposits have been deposited with lower sedimentation rates and they are finer grained and more intensely weathered compared to the loess deposits on the central loess plateau clp the loess deposits overly coarse sandy and gravely fluvial deposits terraces silty fluvial deposits are situated in between them discrimination between these two types of deposits could prove difficult because both deposits are fine grained silt and clay and can have similar grain size distribution characteristics this is however crucial for palaeo environmental interpretations during hominin occupation understanding fluvial morphodynamics and for pedostratigraphic correlation with the typical loess palaeosol sequences on the clp the aim of this research is to determine and characterize the transition of the fluvial to aeolian depositional environment in a fine grained sequence based on field observations organic matter and carbonate content grain size and shape analyses mineral content mica s and end member modelling of the grain size dataset in addition terrestrial cosmogenic nuclides tcn burial dating is used to determine the age of the basal coarse grained fluvial deposits the determined age 0 6 0 14 ma allows for a chronological correlation of the deposits to the loess palaeosol sequence on the clp independent from the pedostratigraphic correlation this age also gives insight in terrace abandonment and the fluvial morphodynamics of the hanjiang river the result indicates a clear distinction between sediments deposited in a fluvial environment and those formed in an aeolian depositional environment however the aeolian loess deposits show some atypical characteristics for example the end member model results show a coarsening in the five palaeosol layers this is in contrast with the fine grained nature of palaeosols on the clp the coarsening observed in the studied palaeosol layers is interpreted as the result of local surface runoff processes eroding fine sediment and or depositing relatively coarse material during interglacial periods because of the known depth of the fluvial aeolian transition and the absolute age of the tcn burial dated terrace deposits pedostratigraphic correlation of the palaeosol layers with the central loess plateau is possible the oldest palaeosol is correlated with s5 0 625 0 503 ma the transition from a fluvial to aeolian environment takes place in l6 between 0 625 and 0 693 ma this is consistent with the tcn age of 0 6 0 14 ma this age also marks the abandonment of the terrace caused by incision of the hanjiang river which is possibly related to an uplift phase of the qlm 2020 elsevier b v

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

sedimentation of the late miocene bahe formation and its implications for stable environments adjacent to qinling mountains in shaanxi china abstract an important key site along the bahe river in the lantian area shaanxi province northern china exposes a conformable sedimentary sequence that records the transition from early late miocene fluvial sediments into late miocene and pliocene aeolian red clay and finally into pleistocene loess although the red clay and pleistocene loess in northern china have been intensively studied over the years the bahe formation beneath the red clay in the lantian area has been less well studied here we present the preliminary results of a detailed lithostratigraphical investigation of the bahe formation on the northern slopes of the bailuyuan plateau and discuss the style of sedimentation during its deposition the bahe formation in the lantian area is composed of fluvial and lacustrine deposits laid down in the weihe graben during the late miocene six main facies assemblages have been distinguished 1 massive or crudely bedded conglomerates 2 cross stratified conglomerate and sandstone deposits 3 minor sandstone deposits 4 fine grained deposits 5 gritty mudstone and sandstone deposits and 6 marl deposits these assemblages represent the deposits of active channels crevasse splays sheet floods and floodplains with paleosols and lakes thick and laterally pervasive units of fine grained sediments formed as suspension fall out on the floodplain indicating low energy conditions and a relatively gentle surface gradient in the area are by far the most common sedimentary component channel related sandstones and conglomerates indicate that the rivers had a low sinuosity and were braided to anastomosing types the bahe fluvial system operated for several million years in a tectonically inactive setting in a vegetated area under a relatively arid climate this environmental interpretation is consistent with that derived from the interpretation of the vertebrate fossil fauna recovered from the sediments

magnetostratigraphy of a late miocene pliocene loess soil sequence in the western loess plateau in china 1 eolian deposits of pliocene age have never been reported from the western loess plateau in china here a 73 7 m eolian sequence is dated using magnetostratigraphic method and micromammalian fossils the polarity zonation correlates with the geomagnetic polarity timescale gpts from chron 3br 1r to chron 2an 3n indicating an age from 7 10 to 3 52 ma bp the sequence is characterized by clear expression of eighty four pairs of loess and soil layers while individual soils are basically indefinable for the eolian deposits of the same age in the eastern loess plateau suggesting that the later has experienced other geological processes this sequence extends the upper limit of the previously reported miocene loess soil sequences at qinan into the pliocene about 3 52 ma bp

late quaternary aeolian dust input variability on the chinese loess plateau inferences from unmixing of loess grain size records abstract the grain size distributions gsds of loess paleosol sequences may provide valuable information on provenance transport and paleoclimate variability and consequently a wide range of methods to extract genetic information from loess gsds has been proposed here it is shown that a genetically meaningful decomposition of a series of late quaternary loess grain size records extending across the chinese loess plateau can be accomplished with the end member modelling algorithm emma the unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the loess plateau during the last glacial interglacial cycle i a background sedimentation pattern that was dominant during interglacial periods especially over the central and southern parts of the loess plateau is reflected by the constant flux of the fine grained loess component ii an episodic highly variable dust input pattern that was dominant during glacial periods throughout the loess plateau and noticeable during interglacial periods mainly over the northern loess plateau and almost disappearing over the southern loess plateau is reflected in the admixture of two coarse grained loess components a genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their gsd and flux rates

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

structural evolution of the dayman dome metamorphic core complex eastern papua new guinea a shallow dipping ductile mylonitic shear zone and concordant brittle detachment fault mai iu fault together make up the dominant geological structure that controls the orientation of dip slopes on the fl anks of mount dayman eastern papuan peninsula papua new guinea the dip slopes dip in all directions from the peak of mount dayman and form a domed landform that is much less dissected by streams compared to the adjacent mount suckling domed landform the orientation of megacorrugations on the domed surface of mount dayman footwall is consistent with nne directed transport of the hangingwall block which is composed of low grade undifferentiated volcanic and sedimentary rocks and minor ultramafi c rocks though previously documented as a thrust surface the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation s1 and mineral elongation lineation l1 the fi eld relationships are consistent with the domed landform comprising the core of a metamorphic core complex observations of dominantly nne trending regional lineaments in aerial photography and shuttle radar topography mission srtm data correlate with detailed fi eld analysis of mineral elongation lineations l1 in the main metamorphic core complex bounding shear zone field relationships show a crosscutting sequence of structures that includes 1 ductile s2 folia with ese plunging blue sodic calcic amphibole mineral elongation lineations 2 narrow steeply dipping ductile d2 shear zones and 3 semibrittle to brittle fault zones s c fabrics asymmetric strain shadows around porphyroclasts and fault drag indicate a top down to the nne sense of shear for most structures kinematic vorticity analysis of the highest grade ductile deformation indicates a kinematic vorticity number wk between 0 34 and 0 56 suggesting general shear for the early stage of deformation d1 the nne directed lineaments and l1 mineral elongation lineations are consistent with the australia woodlark eulerian pole for periods between the early pliocene 3 6 ma and pleistocene 0 52 ma this observation is consistent with ca 3 3 ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3 3 ma on mount suckling a se dipping sedimentary sequence gwoira conglomerate characterizes part of the hanging wall of the metamorphic core complex petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source the unit is in fault contact with the metabasite footwall across prehnite bearing d3 brittle fault zones

variations in the provenance of the late neogene red clay deposits in northern china abstract the voluminous loess red clay deposits in northern china forming part of the chinese loess plateau clp are valuable terrestrial archives of climatic evolution for the late cenozoic era fundamental in reconstructing the late miocene and pliocene wind patterns and aridification history is a detailed knowledge of the provenance of these deposits this paper provides end member modelling of bulk grain size distributions and u pb dating of detrital zircons for three distant red clay sequences in the northeastern baode southern lantian and western dongwan clp data show that these different sections each display a distinctive compositional structure indicating variable depositional processes but they also share two significant zircon age populations of 200 300 ma and 400 500 ma while the permian triassic 200 300 ma group accounts for a larger proportion of zircons ages in the northeastern ne clp the ordovician silurian 400 500 ma component is dominant in the southern and western clp it is suggested that the red clay in the southern and western clp was mainly derived from the northern tibetan plateau ntp and the taklimakan desert by low level westerly winds samples of the ne clp show an increased signature of sediments transported by near surface northwesterly winds from the broad area of the central asian orogen belt caob this spatial transport and deposition pattern is supported by the results from the backtrace trajectory modelling of the dominant dust transport pathways in the clp it is noted that the red clay sample of around 3 6 ma obtained from the ne clp shows increased detrital contributions from its west possibly indicating an intensified westerly wind strength and or aridity of the ntp and taklimakan desert due to the uplift of the tibetan plateau and tianshan mountains in the pliocene the onset of enhanced drainage of the yellow river caused by the increased denudation of the netp since 3 6 ma could also have contributed to this

a tale of two eras pliocene pleistocene unroofing of cenozoic and late archean zircons from active metamorphic core complexes solomon sea papua new guinea u pb ion microprobe analyses of zircons from gneisses and granodiorites exposed in the d9entrecasteaux islands and from conglomerate sections of the goodenough no 1 well in the adjacent trobriand basin provide constraints on the age of magmatism peak metamorphism and nature of rocks unroofed during initial stages of metamorphic core complex formation in the solomon sea the youngest populations of zircons from felsic gneisses and granodiorites indicate late pliocene 206 pb 238 u ages no inherited zircons were identified in the granodiorites and the 206 pb 238 u ages 1 65 0 18 ma 1 98 0 08 ma 2 are interpreted as crystallization ages these synkinematically emplaced granodiorites intruded into actively extending continental crust are some of the youngest known granitoids currently exposed at the earth9 surface zircon ages from felsic gneisses 2 63 0 16 ma 2 72 0 28 ma 2 are interpreted to date zircon growth subsequent to eclogite facies metamorphism felsic gneiss samples also contained zircon xenocrysts from cretaceous miocene protoliths in striking contrast zircons from igneous and metamorphic clasts from the goodenough no 1 well indicate a single population with a 207 pb 206 pb age of 2781 9 ma 2 we speculate that they are derived from basement rocks unroofed during initial stages of development of the d entrecasteaux metamorphic core complexes these results provide the first direct evidence for the existence of archean protoliths in the basement rocks of southeastern papua new guinea

gps and seismological constraints on active tectonics and arc continent collision in papua new guinea implications for mechanics of microplate rotations in a plate boundary zone 1 the island of new guinea is located within the deforming zone between the pacific and australian plates that converge obliquely at 110 mm yr new guinea has been fragmented into a complex array of microplates some of which rotate rapidly about nearby vertical axes we present velocities from a network of 38 global positioning system gps sites spanning much of the nation of papua new guinea png the gps derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in png we simultaneously invert gps velocities earthquake slip vectors on faults and transform orientations in the woodlark basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region the data are best explained by six distinct tectonic blocks the australian pacific south bismarck north bismarck and woodlark plates and a previously unrecognized new guinea highlands block significant portions of the ramu markham fault appear to be locked which has implications for seismic hazard determination in the markham valley region we also propose that rapid clockwise rotation of the south bismarck plate is controlled by edge forces initiated by the collision between the finisterre arc and the new guinea highlands

an evaluation of shape indices as palaeoenvironmental indicators using quartzite and metavolcanic clasts in upper cretaceous to palaeogene beach river and submarine fan conglomerates the feasibility of using quantitative shape measurements to discriminate between clast populations from different depositional settings was evaluated using samples from 11 fluvial six submarine fan and four beach conglomerates from south west california these origins had been established previously by facies analysis quartzite and metavolcanic clasts were characterized by the following indices modified wentworth roundness rw maximum projection sphericity p oblate prolate index opi and long l intermediate i and short s axial ratios these indices were compared with those documented previously for modern gravels the results show that certain indices are useful palaeoenvironmental indicators despite inherited differences in shape due to texture provided that multiple sites are sampled and a statistical approach is used statistically the most effective shape indices are p and s l which give good results with the zingg classification i l vs s i better results are also obtained using quartzite clasts the opi is useful for discriminating between beach and river conglomerates which consist largely of oblate and prolate clasts respectively the relative abundance of blade shaped clasts is a useful index of sediment maturity being greatest for river clast samples and smallest for submarine fan clast samples the latter are dominated by spherical particles no correlation between palaeoenvironment and rw is observed hence the abundance of disc shaped clasts in the beach conglomerates studied is attributed to selective transport in suspension and sediment by passing during fluvial transport prior to deposition in the surf zone selective transport of rollers spheres and rods by traction in a shallow marine setting prior to redeposition by mass transport may be responsible for the dominance of spherical particles in submarine fan conglomerates

an energy balance model of lake ice evolution a physically based mathematical model of the coupled lake lake ice snow and atmosphere system is developed for studying terrestrial atmospheric interactions in high elevation and high latitude regions the ability to model lake ice freeze up break up total ice thickness and ice type offers the potential to describe the effects of climate change in these regions model output is validated against lake ice observations made during the winter of 1992 93 in glacier national park montana u s a the model is driven with observed daily atmospheric forcing of precipitation wind speed and air temperature in addition to simulating complete energy balance components over the annual cycle model output includes ice freeze up and break up dates and the end of season clear ice snow ice and total ice depths for two nearby lakes in glacier national park each in a different topographic setting modeled ice features are found to agree closely with the lake ice observations model simulations illustrate the key role that the wind component of the local climatic regime plays on the growth and decay of lake ice the wind speed affects both the surface temperature and the accumulation of snow on the lake ice surface higher snow accumulations on the lake ice depress the ice surface below the water line causing the snow to become saturated and leading to the formation of snow ice deposits in regions having higher wind speeds significantly less snow accumulates on the lake ice surface thus limiting snow ice formation the ice produced by these two different mechanisms has distinctly different optical and radiative properties and affects the monitoring of frozen lakes using remote sensing techniques

experimental insights into laser diffraction particle sizing of fine grained sediments for use in palaeoceanography grain size measurements of fine grained sediments based on laser diffraction may contain spurious information due to the over estimation of the size and proportion of platy particles consequently some regard the use of laser diffraction particle sizing in palaeoceanography inappropriate here it is shown experimentally that such concerns are not warranted laser diffraction particle sizing is known to be fast precise and allows for detailed particle sizing over a broad size range it is therefore potentially a very powerful technique if the complications associated with it can be overcome as most sediments are mixtures of different components transported by different mechanisms inferences of past environmental parameters require decomposition of the grain size record in question useful decomposition can only be performed if changes in the contribution of the components are registered predictably by the measuring device this study reports on mixing experiments which show that the fritsch a22 laser diffraction particle sizer does indeed register small changes in the contribution of the mixing components in a predictable way mixing proportions estimated from the measurements do however differ from the initial mixing proportions but these can be converted with only small errors application of the conversion equations to a north atlantic grain size record that showed consistent slowdown of deep ocean circulation in response to millennial scale ice rafting events during the last glacial does not quantitatively affect the original inferences laser diffraction particle sizing of fine grained sediments therefore yields reproducible and useful data for palaeoceanographic reconstructions

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

correcting for the influence of ice rafted detritus on grain size based paleocurrent speed estimates the grain size of deep sea sediments provides an apparently simple proxy for current speed however grain size based proxies may be ambiguous when the size distribution reflects a combination of processes with current sorting only one of them in particular such sediment mixing hinders reconstruction of deep circulation changes associated with ice rafting events in the glacial north atlantic because variable ice rafted detritus ird input may falsely suggest current speed changes inverse modelling has been suggested as a way to overcome this problem however this approach requires high precision size measurements that register small changes in the size distribution here we show that such data can be obtained using electro sensing and laser diffraction techniques despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction down core size patterns obtained from a sediment core from the north atlantic are similar for both techniques reinforcing the conclusion that both techniques yield comparable results however ird input leads to a coarsening that spuriously suggests faster current speed we show that this ird influence can be accounted for using inverse modelling as long as wide size spectra are taken into account this yields current speed variations that are in agreement with other proxies our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments

continental rifting and metamorphic core complex formation ahead of the woodlark spreading ridge d entrecasteaux islands papua new guinea 1 we evaluate the role of a metamorphic core complex mcc on normanby island in the woodlark rift located 1 km thickness of blueschist derived mylonites formed in a midcrustal shear zone during the pliocene at 400 500 c this top to the north zone appears to have reactivated the gently dipping base of the papuan ophiolite papuan ultramafic body pub and its continued activity appears to control the north dipping asymmetry of active half grabens to the north of the mcc and rapid subsidence of the woodlark rise mylonites in the mcc s lower plate have been exhumed along a detachment as a result of 50 km of slip at rates of 12 mm yr the inactive back tilted detachment preserves fault surface megamullions and mylonitic lineations parallel to the plio pleistocene plate motion a second se vergent detachment has been established on the opposite flank of this rolling hinge style mcc probably since 0 8 at depth and provide a sufficient mechanism for activating low angle normal faults in the rift mcc inception was not localized to the tip of the woodlark mor instead extreme crustal thinning near the mcc preconditioned later continental breakup the lower crust appears to be weak thickening beneath unloaded footwalls to uplift mccs above sea level and flowing laterally to even out regional crustal thickness contrasts on a 1 6 m y timescale deep seated transforms separate rheologically distinct domains in which extension has been localized along the weak pub to cause mcc formation vs those in which slip is distributed across an imbricate zone of more uniform strength normal faults the trobriand fault connects in the eastern woodlark rift to the owen stanley fault in the papuan ranges which is probably moving at nearly the full plate velocity

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

a model for linking grain size component to lake level status of a modern clastic lake abstract grain size distributions of fluvial eolian and marine sediments were explicated decades ago for lake sediments however there is still great uncertainty in explaining the genesis of grain size components due to the inherent complexity of their polymodal distributions in this study the grain size components of the surface sediments of daihai lake inner mongolia were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated the data indicate that the modern clastic sediments of daihai lake contain five distinct unimodal grain size distributions representing five grain size components each of the components retains its identity including modal size manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake these components are specified from fine to coarse modes as long term suspension clay offshore suspension fine silt and medium to coarse silt and nearshore suspension fine sand and saltation medium sand the percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past the model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core the coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain size component lake level status model for lake s paleohydrological reconstruction

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

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

aeolian origin and palaeoclimatic implications of the red clay north china as evidenced by grain size distribution the red clay is an important deposit underlying the quaternary loess palaeosol sequence in the chinese loess plateau being regarded as an excellent record of palaeoclimate changes in the late tertiary several properties of the red clay have been measured previously in order to derive climatic information however the sedimentary processes involved and the origin of the materials remain controversial here we present results of grain size analyses of the red clay from four representative sites in the chinese loess plateau in particular their grain size distribution is compared with that of typical quaternary aeolian loess palaeosol as well as lacustrine and fluvial sediments it appears from the sedimentological evidence that the major part of the red clay is of aeolian origin it is rather similar in some of its properties to the quaternary loessic palaeosols the dust forming the red clay was transported by a wind system that was weaker than that involved in the accretion of the quaternary loess furthermore the red clay sediment has been modified by post depositional weathering copyright 2001 john wiley sons ltd

particle size distribution analysis of sand sized particles by laser diffraction an experimental investigation of instrument sensitivity and the effects of particle shape laser diffraction is now widely used for particle size distribution analysis of sediments and soils the technique can be very precise and offers advantages of speed and cost over many other methods when used to analyse mixtures of sand silt and clay this study presents the results of an experimental investigation that examined the sensitivity of the beckman coulter ls230 instrument to mixtures of different grain populations and differences in particle shape the instrument was found to have high sensitivity to coarse particles in a finer matrix detection threshold 1 2 but much lower sensitivity to finer particles in a coarser mixture detection threshold 12 17 experiments using near spherical ballotini showed that laser analysis provides very similar values to dry sieving for the mean median and mode but for a range of natural sand samples values for the mean median and mode were offset by 8 21 with an average of ca 15 compared with sieving analysis using a beckman coulter rapidvue instrument which provides both size and shape information provided support for the hypothesis that the differences between laser analysis and sieving are partly attributable to the effects of particle shape however an additional factor is the way in which the laser software interprets the optical diffraction data the software predicts a high degree of log normality in the size distribution such that highly skewed truncated or bimodal samples are poorly represented experiments using sieved fractions of ballotini indicated that even with near perfectly spherical particles the particle size distribution predicted by the laser software includes a relatively large percentage of particles outside the sieve class limits

granulometric characterization of paleosols in loess series by automated static image analysis abstract an automated image analysis method is proposed here to study the size and shape of siliciclastic sedimentary particles of paleosols of central european loess sequences several direct and indirect measurement techniques are available for grain size measurements of sedimentary mineral particles indirect techniques involve the use of some kind of physical laws however all requirements for calculations are in many cases not known even so the direct manual microscopic observation and measurement of large representative number of grains is time consuming and sometimes rather subjective therefore automated image analyses techniques provide a new and perspective way to analyse grain size and shape sedimentary particles here we test these indirect laser diffraction and direct automated static image analysis techniques and provide new granulometric size and shape data of paleosols our results demonstrate that grain size data of the mineral dust samples are strongly dependent on shape parameters of particles and shape heterogeneity was different between different size classes due to the irregular grain shape parameters uncertainties have arisen also for determination of grain sizes in this paper we present a possible correction procedure to reduce the differences among the results of the laser diffraction and image analysis methods by applying new correction factors results of the two approaches could become closer but the unknown thickness of particles remains a problem to solve the other presented correction procedure to assess the uncertain 3rd dimension of particles by their intensity size relationships makes us able to reduce further the deviations of the two sizing methods

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

a new magnetostratigraphic framework for late neogene hipparion red clay in the eastern loess plateau of china abstract mammalian fossils especially the hipparion fauna found in the red clay of the loess plateau are of immense value for reconstructing late neogene paleoecology and paleoclimatology in northern china the lack of a precise chronological framework for these fossil sites has impeded our understanding of the evolution of the chinese mammalian fauna their correlation with european mammalian units and the retrieval of paleoclimatic information in this study a field survey of regional stratigraphy in the baode area of shanxi was carried out and three profiles tanyugou yangjiagou i and yangjiagou ii of late neogene deposits were selected for detailed investigation a new chronological framework of the late neogene sequences in the baode area is established by means of paleomagnetism our results show that the red clay accumulation in the baode area began at least 7 23 ma ago deposition continued to the superposed jingle formation the most continuous and complete exposure of the jingle formation known to date was identified and dated to 2 72 5 34 ma a lithological distinction between the jingle formation and the underlying baode formation forms a clear boundary in the red clay that is not coincident with the miocene pliocene boundary documented elsewhere three rich fossil layers are found in the yangjiagou ii profile and dated to 6 43 6 54 ma 6 83 6 86 ma and 7 15 7 18 ma respectively with the application of three different demagnetization techniques the matuyama gauss geomagnetic reversal boundary was identified in a transitional unit between loess and typical red clay deposits a lock in depth of as large as 6 8 m corresponding to ca 65 ka was inferred but remains unexplained

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

grain shape analysis a new method for determining representative particle shapes for populations of natural grains abstract the size sorting and shape sorting of gravel bedload by running water often is investigated using identifiable tracer grains that represent the grains within the riverbed a new robust and reproducible method is described for the objective selection of three dimensional shapes that are representative of the variety of shape within any whole sample widespread adoption of the method would ensure comparability between the shape sorting results of different experiments the approach identifies average and extreme grain shapes from natural gravel samples importantly tracer dimensions are derived that form shapes with equal volume thus ensuring that the shape of the tracers is the only transport variable the method is tested on seven gravel samples from a range of fluvial beach and scree slope environments as well as different sieve sizes initially measurements of the short s intermediate i and long l orthogonal axes of clasts are made from selected sieve intervals that represent the spread in the size distribution of the natural gravel shapes are identified to be within the realms of the observed shapes of the sampled population four extreme shapes are identified a blade a rod a spheroid and a discoid as well as a median form the starting points of the analysis are the zingg ratios s i and i l however these quantities require polar coordinate transformation to be useful in shape selection the polar coordinate quantities form a joint probability density function that is the product of the marginal distributions of the new shape indices and the axes of the shape diagram utilizing and combining extreme percentiles of these latter distributions identifies the required shapes a reverse transformation returns these selected quantities back into zingg indices finally using the intermediate axial dimensions and the volume ratio the final tracer dimensions are found

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

coeval extensional shearing and lateral underflow during late cretaceous core complex development in the nigde massif central anatolia turkey 1 the nigde massif at the southern tip of the central anatolian crystalline complex consists of two structural units foliations in the lower unit define a dome cored by migmatites the contact between the two units bears all the elements of a ductile to brittle extensional detachment hence the nigde massif represents an extensional metamorphic core complex top to ne ene shearing at higher levels of the lower unit relates to displacement along the detachment deeper levels of the lower unit display high temperature top to ssw ductile shearing the two shearing deformations show a difference in the mean trend of stretching lineations of up to 58 new 40ar 39ar ages combined with previously published data enable us to infer that the two shears were contemporaneous in our favored interpretation oblique shearing in the core of the dome reflects lateral underflow i e horizontal flowing of the lower crust in a direction highly oblique to the direction of extension as a result of the interaction between lateral underflow and downdip shearing along the overlying detachment distinct structural domains are expected to exist within the migmatitic part of the core complex with observed counterparts in the nigde dome lateral underflow may reflect inward flow on the scale of the core complex regional scale channel flow is an alternative that would better account for the record of non coaxial deformation in the core of the dome more generally we suspect that the development of lateral underflow in a metamorphic core complex more likely reflects regional channel flow rather than local inward flow

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