applying end member modeling to extricate the sedimentary environment of yardang strata in the dunhuang yardang national geopark northwestern china abstract formative mechanisms and sedimentary environments of yardang landform distribution in arid and semiarid regions of northwestern china remain poorly understood due to their unique formation and enigmatic causation considerable controversy remains as to whether yardang deposits evolve from aeolian or aqueous forces and no reliable quantitative method has yet been made available to resolve this issue this study conducted a comparative analysis between yardang strata and modern surface sediments to characterize the sedimentary environment using end member modeling analysis emma results show that yardang and surface sediment end members corresponded well and that the yardang depositional environment can be classified into three typical types aeolian 200 550 m mode value range alluvial 150 300 m and 8 20 m and lacustrine subclassified into shoreline 80 110 m lake center 3 15 m and transitional the transition between the littoral and limnetic zones 15 60 m based on this method we determined that lacustrine aeolian and alluvial concentrations were 63 92 20 80 and 15 28 ya profile respectively and 53 68 28 30 and 18 02 yb profile respectively additionally a significant difference was found between the sedimentary processes of the two profiles where ya had more lacustrine sediments and yb had more aeolian sediments likely resulting from paleotopography generally yardang derives from alternating lacustrine aeolian and alluvial sedimentary deposits although lacustrine sediments predominated aeolian sediments also accounted for a considerable overall proportion this study provides new insight into the formation and development of yardang landforms as well as evidence for the reconstruction of paleo geomorphologic patterns

provenance and transport process for interdune sands in the kumtagh sand sea northwest china abstract interdune areas are an important part of dune systems as they affect dune evolution and sand sea development however there has been little work on the provenance of interdune sediments our lack of knowledge of these sediments prevents a more complete understanding of sand sea formation and evolution in the present study we focused on the provenance of interdune sediments in the kumtagh sand sea based on their granular mineral and geochemical characteristics then further identified the spatial scope of the contribution of these sources to the interdune sediments and the associated transport mechanisms although sediment supply analysis suggested that the interdune sand may derive from the altyn tagh mountains beishan mountains and sanlongsha dune field the provenance signature based on the k rb and k ba ratios revealed that the ultimate sources were the altyn tagh mountains in the south and the beishan mountains in the north by plotting the identified provenance results on a map of the sand sea we found that the spatial scopes of contributions from these sources were separated at around 40 n however the existence of a fluvial load em1 and of reworked coarse particles em3 in the northern sand sea demonstrated that the interdune sands in this region were partly derived from the altyn tagh mountains in the south consequently by combining our results with the transport agents condition we concluded that the altyn tagh mountains supplied sediments to interdune areas by fluvial transport throughout the sand sea but that sediment in the northern sand sea was subsequently reworked and mixed with windblown sand originated from the beishan mountains

gravel bodies in the kumtagh desert and their geomorphological implications although developed in predominantly arid environments desert geomorphology sometimes bears information about past environmental change china s kumtagh desert has only recently been studied by researchers these investigations revealed the existence of several unique features compared with other chinese deserts including gravel bodies distributed in the northern part of the desert this paper summarizes the results of previous research in the region as well as information obtained from remote sensing and field investigations then discusses the geological background underlying quaternary geomorphology and the types development stages and geomorphological implications of the desert s gravel bodies four main types of gravel bodies and four developmental stages were identified it is suggested that the great elevation difference between the altyn tagh mountains and the kumtagh desert caused by uplift of the qinghai tibetan plateau constitutes the overall background for the development of gravel bodies but subsequent climatic events were the direct causes of their evolution the gravel bodies resulted from alluvial deposits on loose fine sediments mainly of aeolian origin that were subsequently subjected to wind erosion erosion cycles then progressively scattered these gravels to form gravel sheets the gravel bodies have three main geomorphological implications they record anomalous ancient climate events after the dune field formed and have little influence on the development of nearby seif dunes in the northeast demonstrate that the altyn tagh mountains are the main sediment source for the kumtagh desert and suggest that the evolution of the environment and geomorphology of the kumtagh desert have been influenced by neotectonic movements

evaluation of simple geochemical indicators of aeolian sand provenance late quaternary dune fields of north america revisited abstract dune fields of quaternary age occupy large areas of the world s arid and semiarid regions despite this there has been surprisingly little work done on understanding dune sediment provenance in part because many techniques are time consuming prone to operator error experimental highly specialized expensive or require sophisticated instrumentation provenance of dune sand using k rb and k ba values in k feldspar in aeolian sands of the arid and semiarid regions of north america is tested here results indicate that k rb and k ba can distinguish different river sands that are sediment sources for dunes and dune fields themselves have distinctive k rb and k ba compositions over the basin and range and great plains regions of north america the hypothesized sediment sources of dune fields are reviewed and assessed using k rb and k ba values in dune sands and in hypothesized source sediments in some cases the origins of dunes assessed in this manner are consistent with previous studies and in others dune fields are found to have a more complex origin than previously thought use of k rb and k ba for provenance studies is a robust method that is inexpensive rapid and highly reproducible it exploits one of the most common minerals found in dune sand k feldspar the method avoids the problem of using simple concentrations of key elements that may be subject to interpretative bias due to changes in mineralogical maturity of quaternary dune fields that occur over time

velocity variabilities and other physical properties of marine sediments measured by crosswell acoustic tomography high resolution images of the compressional wave velocity structure within various bottom sediments have been determined from high frequency crosswell acoustic tomography the three dimensional wave number spectra of the velocity variabilities were determined for each measured velocity image the sediment velocity variability spectra are anisotropic in general the variability frequency in the vertical direction is much higher than in the horizontal direction the aspect ratio of the two is found to be approximately 5 0 in addition the major and minor axes of the anisotropy are often tilted from the vertical and the horizontal direction respectively the angle of tilt called dip is found to be as much as 33 deg the measured velocity power spectra approximate a power law the spectral strength depends on the sediment type and the location based on the rock mechanics transformation procedure by yamamoto et al geophysics 59 1530 1541 1994 the sediment porosity density permeability and shear st

raked linear dunes in the kumtagh desert china abstract linear dunes are extensive in sand seas and dune fields around the world but they take a range of forms due to the complex factors that control their development raked linear dunes composed of primary ridges and subsidiary ridges that lie almost perpendicular to the primary ridges were recently identified in the northern part of china s kumtagh desert the primary ridges are typical linear dunes but the subsidiary ridges display vestiges of barchan dunes the subsidiary ridges are sufficiently short that they do not greatly affect the general appearance of the linear dunes however the raked linear dunes in the kumtagh desert have several unique characteristics that distinguish them from typical linear dunes these dunes develop in an environment that is deficient in available sediment and under a wind regime typical of linear dunes an environment with a high wind energy and a directional variability index rdp dp around 0 5 the raked linear dunes appear to have evolved from barchans following a modified form of tsoar s 1984 model barchans formed under a northern wind regime were modified by an eastern wind regime oriented at an oblique angle to the barchans the strengths of the two wind regimes are similar under these conditions the barchans became reoriented with the limbs farthest from the eastern winds extending to form subsidiary ridges and the limbs closest to the eastern winds forming the primary ridges which appear to form mainly from dune collisions

interdune deposits of the namib sand sea abstract the namib sand sea of southwestern africa is dominated by large north south trending linear dunes interdune areas however comprise about 50 of the area of the sand sea and may consist of exposures of the pre dune surface or sediments deposited between the dunes four major types of interdune deposits are identified and described 1 1 coarse poorly sorted aeolian sands 2 2 localized calcareous lacustrine deposits 3 3 silty deposits of ephemeral rivers that have flooded into the sand sea margins 4 4 sabkhas and salt marshes near the coast the preservation potential of these sediments is poor except where they are buried and protected by dunes or stabilised by high groundwater levels in coastal areas

paroxysmal summit activity at mt etna italy monitored through continuous soil radon measurements 1 soil radon emissions have been proved as a useful tool for predicting earthquakes and volcanic eruptions and furthermore aided in determining the location of active faults continuous radon monitoring was carried out near southeast crater of mt etna in september november 1998 during a period of frequent eruptive episodes at that crater radon anomalies were detected when eruptive episodes and the accompanying volcanic tremor became increasingly intense no anomalies in radon activity were observed during the first five and weaker eruptive episodes whereas significant spikes in radon activity preceded the latter five episodes by 46 hours this probably reflects increased gas leakage through fractures intersecting the shallow plumbing system as gas pressure in the southeast crater conduit became higher with time radon monitoring thus might serve to better understand eruptive mechanisms and possible precursors making further studies in this field a promising perspective

porosity permeability shear strength crosswell tomography below an iron foundry crosswell tomography of a sedimentary foundation at an iron foundry was affected by very high background noise nevertheless high resolution velocity images were obtained between wells separated by long distances 120 to 250 m a piezoelectric source in a water filled well used long sequences 4095 cycles of pseudorandom binary codes at high carrier frequencies 1 to 10 khz a 24 channel hydrophone array in another well received the signal beamforming of common source data selected the directions and arrival times of multiple raypaths and tube waves and further enhanced the signal to noise ratio inversion of first arrival times by damped least squares imaged the compressional wave velocities assuming the normal consolidation condition the porosity and shear strength images are predicted from the compressional wave velocity image the direct measurements of porosity and shear strength conducted on the cores and boreholes were used to verify the tomographic predictions the slight differences in the

characteristics of near surface wind regimes in the taklimakan desert china abstract using wind data from 17 meteorological stations distributed throughout the taklimakan desert we described the characteristics of the desert s wind regimes and analyzed the spatial and temporal variations in wind direction and sand drift intensity the near surface wind regimes were closely related to general atmospheric circulation patterns and the surrounding topography there are two prevailing wind directions in the desert in general the eastern part of the desert is mainly affected by ne winds and the western part is affected by nw winds in the area towards the center of the desert but not around its edges the monthly mean wind velocity is strongly correlated with the monthly mean temperature with the exception of ruoqiang on the eastern edge of the desert the drift potential dp is less than 200 vu and the desert thus belongs to a low energy environment based on fryberger s classification in addition most parts of the desert have an rdp resultant dp dp value greater than 0 4 suggesting that the wind regimes have mainly unimodal or bimodal characteristics in contrast with the sand drift intensity which was highest in the north and east parts of the desert the highest frequency of sand dust storms occurred at the southwestern margin of the desert this results primarily from the differences of dust content on ground surfaces and land use types

geochemical and mineralogical variations as indicators of provenance changes in late quaternary deposits of se po plain combined geochemical and mineralogical characterisation of mudstone prone successions can provide suitable indicators of sediment provenance a case study from the late quaternary depositional sequence of southeastern po plain shows that major changes in geochemical and mineralogical composition can be ascribed to changes in sediment dispersal patterns occurring during the last 30 ka in response to fluctuating sea level the po river with a mixed contribution from the alpine and apenninic chains and its southern tributaries flowing from the apennines acted as the major feeders for the study area during the late quaternary chromium and nickel among trace elements and serpentine and dolomite among minerals appear as the major provenance indicators for the study succession allowing distinction of an apenninic chromium and serpentine poor province from a mixed alpine apenninic po related chromium and serpentine rich province the relatively low cr al2o3 and serpentine silicate ratios recorded in sediments of late pleistocene age 30 ka bp which accumulated at the last glacial maximum suggest that during lowstand times and early stages of transgression the southeastern po plain was beyond the po river influence being fed uniquely by rivers of apenninic provenance increasing cr al2o3 and serpentine silicate ratios recorded within back barrier transgressive deposits 8 10 ka bp in the comacchio and ravenna sectors reflect a major change in sediment supply taking place during the holocene when partially barred environments largely connected with the open sea became established in the study area and po derived detritus was delivered to estuaries and lagoons by littoral drift maximum chromium and serpentine values are recorded at peak transgression and during the following sea level highstand 6 ka bp present when sediment supply exceeded the rate at which new accommodation space was created leading to extensive po delta progradation the drop in cr al2o3 and serpentine silicate ratios recorded in some cores at top of the holocene succession reflects the local reestablishment behind the prograding po delta complexes of an alluvial plain drained by rivers of apenninic provenance as a result of distributary channel switching and delta lobe abandonment geochemical and mineralogical analyses show negligible compositional variations between pleistocene and holocene deposits landward of the line of maximum marine incursion especially close to the basin margin in these instances sample composition throughout the entire stratigraphic succession clearly suggests an ongoing supply from the adjacent apenninic chain comparison with sand compositional analyses from major sand bodies of the same stratigraphic succession highlights the complementary but fundamental role of geochemical and mineralogical characterisation of clays for provenance research

the provenance of taklamakan desert sand sand migration in the vast taklamakan desert within the tarim basin xinjiang uyghur autonomous region pr china is governed by two competing transport agents wind and water which work in diametrically opposed directions net aeolian transport is from northeast to south while fluvial transport occurs from the south to the north and then west to east at the northern rim due to a gradual northward slope of the underlying topography we here present the first comprehensive provenance study of taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea and to consider the potential of the tarim basin as a contributing source to the chinese loess plateau clp our dataset comprises 39 aeolian and fluvial samples which were characterised by detrital zircon u pb geochronology heavy mineral and bulk petrography analyses although the inter sample differences of all three datasets are subtle a multivariate statistical analysis using multidimensional scaling mds clearly shows that tarim desert sand is most similar in composition to rivers draining the kunlun shan south and the pamirs west and is distinctly different from sediment sources in the tian shan north a small set of samples from the junggar basin north of the tian shan yields different detrital compositions and age spectra than anywhere in the tarim basin indicating that aeolian sediment exchange between the two basins is minimal although river transport dominates delivery of sand into the tarim basin wind remobilises and reworks the sediment in the central sand sea characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the tarim river and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea smaller ephemeral rivers from the kunlun shan end in the desert and discharge their sediment there both river run off and wind intensity are strongly seasonal their respective transport strength and opposing directions maintain the taklamakan in its position and topography

geochemical mineralogical and sedimentological studies on the taklimakan desert sands major element composition mineral composition and grain size distribution have been studied for quaternary aeolian sediments from the taklimakan desert north western china together with the variation of chemical and mineralogical compositions of different grain size fractions aeolian sediments from the taklimakan desert have higher ratios of feldspar quartz and calcite quartz finer grain size poorer roundness of quartz and feldspar grains and lower abundances of frosted quartz than found in aeolian sediments from other deserts such as the saudi arabian desert in spite of these immature mineralogical and sedimentological features the aeolian sediments from the taklimakan desert show low regional variations in major element and mineral compositions and are homogenized these observations confirm that two processes glacial activity within surrounding mountains and aeolian activity at the tarim basin are important in the homogenization of the taklimakan desert sands taklimakan desert sediments are constantly and effectively supplied from basement rocks in the surrounding mountains by glacial erosion the supplied sediments are further homogenized by aeolian activity in the desert and are partly blown away serving as the source of chinese aeolian loess compositional differences are observed between loess mainly 10 40 m particles and the 45 m fraction of the taklimakan desert sediments as well as between loess and whole rock of the taklimakan desert sediments these observations provide constraints for precise modelling of loess formation and for assessment of the chemical composition of the upper continental crust based on the chemical composition of aeolian loess

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

anomalous non isotropic temporal variation of gamma radiation from radon progeny within air in confined conditions summary new experimental results add information on the space time variation pattern of nuclear radiation from radon in air at confined conditions using five gamma sensors placed around a canister containing radon in gas demonstrated temporal variation consisting of a long term variation which may be related to an annual variation multiday md signals and periodic daily radon dr signals separate processes drive the md and dr signals both md and dr signals exhibit inverse temporal variation patterns in the east west and north south directions the md and dr signal patterns along the vertical axis are associated with the north south directed radiation pattern suggesting that the up down axis of the system is actually inclined relative to the vertical axis of the canister i e related to the latitude of the experiment the relations of the time space variations including the apparent tilt relative to a principal geographic direction imply a connection to global orientation these results are in line with the proposition of an influence of a component of solar irradiation on variation patterns of nuclear radiation from radon

geomorphology of star dunes in the southern kumtagh desert china control factors and formation star dunes have received less study than other major dune types though they are widely recognized to represent a major dune type that develops under a multi directional wind regime several types that include simple compound and complex star dunes are identified in the south of china s kumtagh desert it is suggested that the formation and development of these star dunes is controlled by wind regime the underlying and surrounding topography and sediment availability a complex wind regime and rich sediment availability are generally required for the development of star dunes especially wind regime appears to be the most important control factor the wind regime under which star dunes arise is characterized by the drift potential amount of variability in drift direction and the direction distribution mode of the drift potential it is strongly suggested that a rectangular bimodal wind direction distribution mode has unique significance in star dune formation under this mode star dunes can develop in areas with a directional variability index typical of linear dunes or even barchan dunes a development model is proposed for star dunes based on the following evolution barchan dunes transverse ridges dune networks simple star dunes compound star dunes star dunes atop complex linear dunes

eustatic and climatic controls on the development of the wahiba sand sea sultanate of oman aeolian sand sea accumulations can serve as valuable archives of climate change in continental environments the wahiba sand sea is situated at the northern margin of the area presently affected by indian summer monsoon circulation and it records environmental changes associated with this major climatic boundary over the last 160 000 years the internal stratigraphy and evolution of the sand sea is investigated using a combination of outcrop borehole seismic and luminescence data proximity to the indian ocean means that the sand sea succession shows the influence of sea level changes on the sedimentary architecture and composition of the dune deposits during the last two glacial periods low global sea level was associated with a high input of bioclastic grains reflecting the significance of subaerially exposed shelf areas as one of the main sources of aeolian sediment the onset of aeolian sediment transport and deposition was related to the breakdown of stabilizing vegetation during arid periods that equate with sea level lowstands the preservation of aeolian sediments by the formation of supersurfaces and associated palaeosoils took place during times of increased wetness and elevated groundwater tables this interplay of constructive and destructive periods greatly influenced the sedimentary architecture oscillations of wet and dry periods between 160 000 and 130 000 years and 120 000 105 000 years ago are attributed to the evolution of a wet aeolian system younger periods of aeolian deposition around and after the last glacial maximum were characterized by dry aeolian conditions no soil horizons developed during these times

transport and mixing of eolian sand from local sources resulting in variations in grain size in a gypsum dune field white sands new mexico usa abstract the white sands dune field new mexico usa provides a unique opportunity to study sources and eolian transport of sand end member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types textural differences between sources allow local transport paths to be deduced in total 1214 surface samples from 10 dunes and 2 downwind oriented transects were collected neither elevation on the dune lee or stoss location nor distance downwind correlated with mean grain size coarsest 10 d90 or sorting instead grain size distributions are controlled by mixing of locally sourced sand populations adjacent dunes can have different mean grain sizes resulting from different local source populations local within dune and between dune variability resulting from different sand sources dominates any larger scale trends across and within dunes four sand populations are identified based on microscopically observable differences in grain size shape and angularity each correlates with high loading of a different statistical factor derived from end member mixing analysis end member 1 em1 correlates with well sorted populations of finer grained equant rounded sands em2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes em3 is associated with samples of moderately to poorly sorted fine grained sand containing fine sand sized gypsum needles collected from areas of vegetated interdunes and em4 is associated with moderately well sorted coarse and very coarse grained sands collected from granule ripples these results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field rather than by dune scale or erg scale transport and sorting

the geomorphological significance of airflow patterns in transverse dune interdunes abstract the interdunes between aeolian dunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves this neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole especially with regard to dune spacing this paper considers the mean airflow within four relatively simple transverse dune interdunes the study locations were chosen in order to sample interdunes with different size and surface characteristics the dynamics of which were investigated for when incident flow was normal to the upwind crest the findings confirm existing models of flow reattachment length and recovery for aeolian dune lee side flow and show a consistent pattern of increasing near surface velocity downwind of reattachment that supports a mechanism for interdunes as sand free features flow dynamics are characterised for the different types of interdune observed where two groups are recognised the flow patterns in relatively short interdunes where dunes are closely spaced with a sandy surface were accordant with those of the flow response model in extended interdunes where bounding dunes were spaced with a length well over that for flow separation evidence at the downwind edge of the interdunes suggested that flow reacted to the subsequent dune for the case of these extended interdunes a new descriptive model is presented to characterise their dynamics in this model the variation in near surface flow allowed process zones to be identified through the interdune the geomorphological significance of the processes dominating each zone is discussed and comparisons are made between the flow response case and the new interdune model from this study in a discussion on the controls of spacing between dunes where reattachment length exerts a fundamental control the role of sediment availability is also highlighted as a significant factor the presence of a sandy bed can in some circumstances determine whether dune development and therefore spacing is controlled primarily by elements of flow response

measuring and defining bimodal sediments problems and implications gravel bed rivers close to the transition to a sand bed often have bimodal grain size distributions these can be quantified in several ways giving wide differences in derived statistics and calculations problems associated with measuring summarizing and defining bimodality are examined using evidence from flume experiments and a simple numerical simulation of sand deposition no single index of bimodality serves all purposes alternatives are suggested measured near bed hydraulic properties relate more closely to grain size statistics calculated by area than by volume this has implications for the abrupt downstream transition often found from gravel to sand bed

a model data comparison for low frequency bottom backscatter this article describes a model for bottom backscattering strength applicable over the frequency range 100 1000 hz the model includes backscatter due to both a rough water sediment interface and internal sediment inhomogeneities i e sediment volume scattering within an upward refracting sediment the net result is predictions for bottom backscattering strength that depend on the following frequency sound speed of the water near the water sediment interface density ratio sound absorption within the sediment near surface sound speed gradient within the sediment two interfacial roughness parameters and a parameter proportional to the scattering cross section of a unit volume of sediment the sediment sound speed profile is specified in terms of near surface values for the sound speed ratio and gradient salient features of the modeled backscatter strength include marked departures from lambert s law for sediments with sound speed ratios greater than 1 1 5 db oscillations as a function of grazing an

geomorphology and origin of yardangs in the kumtagh desert northwest china yardangs are typical wind eroded landforms that are found in most of the world s major deserts this paper describes the morphology of yardangs in the kumtagh desert analyzes their control factors and discusses their development processes age and rates of formation yardangs in the kumtagh desert lack the ideal streamlined morphology and the length to width ratio close to 4 1 that have been previously described as being due to their unique controlling factors which include a combination of stratigraphic structures wind erosion and fluvial erosion fluvial erosion plays a particularly important role in the development of the yardangs though wind continuously sculpts their morphology the development of yardangs can be divided into four stages an embryonic stage adolescence maturation and recession most yardangs in the kumtagh desert are in the mature to receding stages we determined an approximate age for the yardangs based on the erosion rates estimated by several researchers on this basis the yardangs in the kumtagh desert appear to have formed during the holocene

the influence of source rock type chemical weathering and sorting on the geochemistry of clastic sediments from the quetico metasedimentary belt superior province canada abstract the geochemistry of clastic sediments is controlled by at least four factors source rock composition weathering of the source rocks sorting of the weathered detritus and post depositional alteration during diagenesis and metamorphism in order to evaluate the relative importance of these factors major trace and rare earth element contents were determined for distal and proximal clastic turbidites from the archaean quetico metasedimentary belt the degree of metamorphism of the samples ranges from middle greenschist to upper amphibolite facies simple mixing of archaean mafic and acidic rocks of similar composition to those found in the adjacent granite greenstone terrains will account for the tio2 feot mgo cr sc y and hree contents of the clastic turbidites the metasediments are enriched in lree relative to the mafic acidic rock mixing line indicating that the acidic source was enriched in the lree compared to archaean terrains from other parts of the world some quetico turbidites have an additional fe rich source component possibly a chemical sediment incorporated at the time of turbidite slumping cao na2o k2o rb and sr form trends on bivariant plots that are oblique to the mafic acidic rock mixing line and hence cannot be accounted for by simple mixing of the source rocks chemical weathering of feldspars prior to deposition can account for cao na2o k2o rb and sr trends since cao na2o and sr are lost to the weathering solutions and k2o and rb are retained on the product clays the higher na 2 o cao k 2 o na 2 o rb k 2 o and sr cao ratios but lower cao content of the distal samples suggest that they were derived from a bulk sediment that had experienced a greater degree of chemical weathering than the proximal sediments sorting is the factor that most strongly influences the composition of individual samples within the proximal sample group the coarse grained metagraywackes with their higher quartz feldspar and heavy mineral contents are enriched in sio2 cao na2o sr lree zr and hf relative to the fine grained clay rich metapelites metapelites are enriched in tio2 al2o3 feot mgo k2o cr zn sc y hree cs and rb as a result of their higher clay contents thus the use of clastic sediment compositions in determining average crustal compositions e g for the ree can only give satisfactory results when all grain size fractions are sampled in their correct relative proportions the chemical differences observed between the high and low grade samples can be accounted for by source rock type chemical weathering of the source rocks or sorting post depositional element mobility does not appear to be an important factor in determining the composition of the quetico metasediments

biot model of sound propagation in water saturated sand elastic theory of wave propagation and the measured speed of sound in sandy ocean sediments indicate that such sediments are impenetrable to high frequency sound at shallow grazing angles the speed of sound in water saturated unconsolidated sand is in the region of 1700 m s which under the elastic theory of wave propagation gives it a critical grazing angle in the region of 28 at shallower grazing angles refraction is not permitted and total internal reflection is predicted recent experimental measurements contradict this view biot s theory of acoustic propagation in porous sediments is the most likely explanation biot s theory of acoustic propagation as it applies to water saturated sand is reviewed the speed of the slow wave is found to be higher than previously predicted new input parameter values are deduced

geochemistry and mineralogy of late quaternary loess in the upper mississippi river valley usa provenance and correlation with laurentide ice sheet history abstract the midcontinent of north america contains some of the thickest and most extensive last glacial loess deposits in the world known as peoria loess peoria loess of the upper mississippi river valley region is thought to have had temporally varying glaciogenic sources resulting from inputs of sediment to the mississippi river from different lobes of the laurentide ice sheet here we explore a new method of determining loess provenance using k rb and k ba values in k feldspars and micas in loess from a number of different regions in north america results indicate that k rb and k ba values can distinguish loess originating from diverse geologic terrains in north america further different loess bodies that are known to have had the same source sediments using other criteria have similar k rb and k ba values we also studied three thick loess sections in the upper mississippi river valley region at each site the primary composition of the loess changed over the course of the last glacial period and k rb and k ba values parallel changes in carbonate mineral content and clay mineralogy we thus confirm conclusions of earlier investigators that loess composition changed as a result of the shifting dominance of different lobes of the laurentide ice sheet and the changing course of the mississippi river we conclude that k rb and k ba values are effective robust and rapid indicators of loess provenance that can be applied to many regions of the world

a stratigraphic model to account for complexity in aeolian dune and interdune successions wet aeolian systems in which the water table or its capillary fringe are in contact with the accumulation surface such that moisture influences sedimentation are well known from modern aeolian systems and several ancient preserved successions are recognized from outcrop one common mechanism by which accumulation of wet aeolian system deposits occurs is via a progressive rise in the relative water table level that is coincident with ongoing dune and interdune migration the angle of dune climb being determined by the ratio between the rate of relative water table rise and the rate of downwind migration of the bedforms accumulations of wet aeolian system deposits tend to be characterized by units of climbing dune strata separated by units of damp or wet interdune strata for simple geometric configurations where the size of the dune and interdune units the rate of bedform migration and the rate of aggradation all remain constant over space and time the resulting accumulation has a simple architecture characterized by sets of uniform thickness inclined at a constant angle however the dynamic nature of most aeolian dune systems means that such simple configurations are unlikely in nature the complexity inherent in these systems is accounted for here by a numerical model in which key controlling parameters including dune and interdune wavelength and spacing migration rate and aggradation rate are allowed to vary systematically both spatially from a dune field centre to its margin and temporally in response to changes in sediment availability or water table level the range of synthetic stratigraphic architectures generated by the model accounts for all the best known examples of aeolian dune and interdune stratigraphic configurations documented from the stratigraphic record modelling results have enabled the erection of a scheme for the classification of dune system type whereby the many elaborate stratal architectures known to exist in nature can effectively be accounted for by only four parameters that are allowed to vary over space and time dune and interdune wavelength and spacing rate of bedform migration and rate of accumulation results have applied implications including the modelling of reservoir heterogeneity and the prediction of fluid flow pathways of hydrocarbons water co2 and contaminants in subsurface reservoirs and aquifers in which low permeability interdune units might act as baffles or barriers

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

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

statistically significant relation between radon flux and weak earthquakes in the dead sea rift valley detailed monitoring of radon rn flux in gravel was carried out for a period of eight years near the active dead sea rift fault the temporal relationship between hundreds of weak earthquakes 4 6 ml 0 and rn flux signals was tested for time intervals related to the start time of 110 rn flux signals earthquakes located within three pull apart grabens of the dead sea rift valley were found to occur preferentially within the time interval of the first 3 days after the start time of 110 rn anomalies and the excess of earthquakes 82 relative to the expected value is highly significant p 003 however a similar relationship is not found in the two weeks preceding or following the start time of the rn anomalies for earthquakes occurring within the dead sea rift in structurally higher segments or out of the dead sea rift

high resolution radon monitoring and hydrodynamics at mount vesuvius a yearlong high resolution radon survey has been carried on at mount vesuvius starting in may 1998 radon activities were acquired by exposing charcoal canisters and track etch detectors sampling stations were deployed along two major summit faults and around the caldera bottom volcanically related earthquakes with md 2 5 may be discriminated from regional seismic events since their cumulative radon anomalies are recorded from stations located along all the above structural features on the contrary radon anomalies correlated to regional earthquakes with md 4 are essentially recorded by the sampling sites located along the two summit faults whose roots extend deeper into the tertiary basement rocks that underlay the volcano radon migration to the surface is ruled by convection within a porous medium of relatively low porosity 10 5 suggesting that fluid motion is strongly localised along fractures it is suggested that fluid pressure build up followed by fluid release and migration during incipient fracturing of the porous medium precede the onset of volcanically induced earthquakes

geochemical evidence of the chinese loess provenance during the late pleistocene abstract the provenance of chinese loess plateau sediments is an often posed question that has not been satisfactorily resolved elemental geochemistry characteristics of the deposition may provide important evidence in this regard to this end geochemical analyses were undertaken on densely sampled strata from four loess sections one of which is located in northwestern china at the desert margin and the other three on the loess plateau as well as sediments from the badain jaran desert it was found that loess deposition on the chinese loess plateau and the northern foot of the qilian mountains had strong geochemical similarity during the last glacial cycle but had remarkable differences with the badain jaran desert samples it is inferred that the desert was not the most important direct provider of dust material to the loess plateau rather one of the main source areas appears to have been the vast silt rich piedmont alluvial fan distributed at the northern foot of the qilian mountains

new geochemical evidence for the origin of north america s largest dune field the nebraska sand hills central great plains usa abstract the nebraska sand hills region is the largest dune field in north america and has diverse aeolian landforms it has been active during both the late pleistocene and late holocene despite decades of study the source of sediment for this large sand sea is still controversial here we report new trace element compositions of aeolian sand that are compared to four hypothesized sediment sources tertiary rocks of the arikaree group and ogallala group unconsolidated sands of pliocene age and platte river system sands all four potential sources have a mineralogy that is similar to the nebraska sand hills k rb k ba sc th la eu eu lan ybn as sb and fe sc values show however that pliocene sediments and sands from the platte river system are not likely sources the arikaree group could be a minor contributor but sands from the ogallala group appear to have the best compositional fit to the nebraska sand hills although past studies have proposed the ogallala group as an important sand source the hypothesis has been questioned because the unit is well cemented by calcrete in its upper part however examination of the landscape upwind of the nebraska sand hills shows that the ogallala group where it occurs at the land surface is highly dissected in much of this region which makes sand sized particles available for aeolian entrainment whenever drought conditions diminish a protective vegetation cover

a model for high frequency acoustic backscatter from gas bubbles in sandy sediments at shallow grazing angles a model for acoustic backscatter from trapped bubbles in sandy sediments was developed the model combines a biot acoustic penetration model with a resonance scattering mechanism from trapped bubbles the bubble size distribution is assumed to mirror the size distribution of the fluid pores that exist between sand grains an estimate of the pore size distribution is constructed from the grain size distribution based on the known pore structure between dense random packings of hard spheres the principle of acoustic reciprocity is employed to compute backscattered acoustic pressure in terms of the incident pressure and the scattering cross section of a bubble distribution the model is applied to data from experiments recently taken at sea it is concluded that trapped gas is often a likely cause of observed backscatter from sandy sediments very small amounts of gas appear to be sufficient to produce significant backscatter

research progress in china s lop nur abstract china s lop nur is one of the world s largest playas and is located in the driest part of central asia scientific explorations by chinese and foreign researchers have been continuously conducted there since the mid to late 1800 s and much progress has been made but many issues remain hotly debated particularly intense debate focuses on the formation environmental evolution drying date of the lop nur lake and cause of the helical salt crusts recently revealed by remote sensing images in this paper we review the status of this research to provide insights that can inform studies in other arid zones that resemble the lop nur the lop nur depression is a secondary unit of the tarim block controlled by faults and fractures formed by the himalayan orogeny but various competing explanations have been proposed for how these geological structures gave rise to the depression the depression s formation date also remains unclear several boreholes have been created to reconstruct the environmental evolution at different time scales since the quaternary and deposition rates of lake sediments especially since the late pleistocene have averaged less than 1 mm annually the drying date of the lop nur lake is also debated the helical salt crust structures appear to have formed as the lake shrank but how and when they formed is unclear huge potash reserves have been found and large scale potash fertilizer production has begun but the origin of these deposits is debated understanding the factors causing environmental evolution in this region is a central issue that will help us to clarify these and other debated issues

geochemical composition and provenance of aeolian sands in the ordos deserts northern china abstract identifying the provenance of aeolian sediments in deserts is of great importance for understanding the earth surface processes in this context we conducted detailed fieldwork in the ordos deserts maowusu and kubuqi in the middle portion of the desert belt in northern china and measured the major trace and rare earth elements ree of aeolian sands and their potential source rocks and sediments our results show that aeolian sands in the eastern northeastern and western southwestern maowusu mu us sandy land exhibit different degrees of mineralogical maturity and eu eu values thus we interpret that these aeolian sands have different provenances though in the same sandy land our data suggest that the local lacustrine sediments and sandstones are the main sources of aeolian sands in the eastern province of the maowusu sandy land while aeolian sands in the western maowusu sandy land and the kubuqi desert have the same external sources the comparison of geochemical compositions of sediments in the ordos deserts with their potential sources in adjacent regions indicates that there is no genetic linkage between the helan mountains the yinshan mountains and the ordos deserts although they are not far apart the qilian orogenic belt in the northeastern margin of the tibetan plateau is however the most likely original provenance for the western maowusu mu us sandy land and the kubuqi hobq desert but with fluvial sediments in the ningxia inner mongolian section of the yellow river as the immediate source in one side our results demonstrate that dune fields that are close to each other can have significantly different source sediments on the other hand our work suggests that some dune fields and landforms that are far apart from one another e g the badain jaran desert in western inner mongolia the ordos deserts and the fluvial sediments in ningxia inner mongolian section of the yellow river can share the same ultimate sources

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

the simpson strzelecki and tirari deserts development and sand provenance abstract sands of the simpson strzelecki and tirari deserts central australia can be divided into two main groups on the basis of their physical and chemical characteristics colour grainsize heavy minerals quartz oxygen isotope composition zircon u pb ages the first group encompasses the strzelecki tirari and southeastern simpson deserts while the second occupies the northern and the western simpson desert the boundary between the two groups corresponds approximately to the northern most extent of the kallakoopah lakes several lines of evidence suggest derivation of the sands mainly from local bedrock with very little subsequent aeolian transport ultimate protosources for the sands in order of importance are for the southeastern simpson tirari and strzelecki deserts the tasman orogenic system new england and lachlan fold belts georgetown inlier musgrave and arunta blocks gawler and curnamona cratons and for the north and western simpson desert arunta musgrave and mount isa blocks and tennant creek inlier sediment from the tasman orogenic system includes an additional exotic component from palaeozoic sediments probably derived mainly from antarctica sediment transport from these protosources across the several hundred kilometres to the surficial sedimentary basins was dominantly by fluvial not aeolian means quaternary aeolian transport or reworking has been minimal serving only to form the dunes by vertical corrasion of underlying sedimentary rocks or residual products of local basement weathering the deserts have received some recent localised sediment input from modern fluvial systems

low grazing angle bistatic sea floor scattering on the florida atlantic coastal shelf observations of bistatic scattering at moderate frequencies 3750 hz 7500 hz and 15 000 hz and low grazing angles 2 20 are presented with a geoacoustical description of the site given a source receiver separation of 80 7 m bistatic scattering strengths in the sandy sediments at the measurement site range from 70 to 15 db the observed bistatic scattering at low grazing angles depends primarily on the incident bearing angle bistatic scattering values are highest along the transect between the source and receiver maximum scattering strengths 20 to 15 db appear 30 m from the receiver regions of high scattering 30 db strength are centered along the direct path between the source and receiver the contribution of volume scattering to the observed scattering pattern is not very clear however given the sandy sediments found at the site roughness scattering is expected to be a major contributor to the observed bistatic scattering patterns

a clear case of radon anomaly associated with a micro earthquake event in a stable continental region 1 though many worldwide attempts to establish radon anomalies in soil and groundwater as precursors for major earthquakes are made yet practically no such work has been reported for micro earthquakes in a stable continental region scr from the continuous radon measurements for five months at a depth of 1 m in fractured granitic area we report for the first time that enhanced radon concentration preceded seventeen hours the occurrence of micro earthquake the peak radon level twice the normal concentration was reached thirteen hours before the occurrence of the event and decayed exponentially during the next 5 days to come to normal level this radon precursor pertains to a dry period unaffected by meteorological factors thus exemplifies clearly its association with micro earthquake

radon signals in the gavnunim intrusion makhtesh ramon israel summary high time resolution monitoring of radon using alpha detectors is carried out in a massive and jointed syenite located in arid southern israel monitoring at a resolution of 15 min is conducted in two boreholes at depths of 1 2 and 85 90 m resulting in more then 10 yr long time series systematic temporal variation patterns manifesting large relative signals are composed primarily of annual ar multiday md daily dr and subdaily sdr radon signals prominent periodic diurnal variation underlies the dr and probably also the sdr signals diurnal s1 24 hr and semidiurnal s2 12 hr constituents characterize the dr signal at 1 2 m while diurnal constituents typical for gravity related periodicities m2 o1 are absent the amplitudes of the s1 and s2 constituents calculated for consecutive 512 hr long time intervals exhibit a similar covarying annual pattern the periodic dr signal is absent at 85 m depth the peak time of sdr signals occurring at this depth in some days exhibits a 24 and 12 hr periodicity time offsets of hours are observed between time series of the measured signal from the two levels the lag investigated for the decomposed md signal using consecutive 20 d long time intervals shows that the signal at depth systematically lags by around 9 hr the signal at the shallow level discrepancy of the patterns of the temporal variation in the time domain and also in the frequency and time frequency domains of the diurnal periodic components indicates that atmospheric influence on the radon signal is insignificant even at a depth of 1 2 m combining this conclusion with the compound interrelations occurring among the different radon signals suggests that other geophysical processes are driving the radon variation in the subsurface geogas it is suggested that the significant s1 and s2 signatures and their modulations are imposed on the radon system by means of a direct link with solar radiation tide

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

pilot experiment for the acquisition of marine sediment properties via small scale tomography system a 3 d high resolution crosswell acoustic tomography system was designed and tested in a shallow water environment this system makes use of a damped least squared inversion technique and is used to construct compressional wave velocity images from measured travel time data use of singular value decomposition allowed checks of the linear inversion confirming the validity of the modeled environment it is shown that when the ratio of width to depth of the cross section is about unity or smaller and the domain has not been overparametrized the inverted image model has sufficiently good figures of merit in resolution and variance to visualize small variations in the magnitude compressional velocity field

aeolian fluvial interaction evidence for late quaternary channel change and wind rift linear dune formation in the northwestern simpson desert australia in central australia the most easterly extent of the macdonnell ranges border the simpson desert dunefield where widely spaced strike ridges intercept and isolate pockets of broad crested linear dunes that reflect regional changes in late quaternary climate flow regime and channel avulsion an energetic todd river reworked the eastern part of camel flat basin from 75 65 ka until the last glacial maximum lgm when it shifted eastwards but with some flows persisting through the basin until about 10 ka resulting desert surfaces of different age facilitate temporal comparisons of linear dune formation fine grained red dunes 75 65 ka in age occur on the western floor of the basin and are ramped against the foot slopes of the range after the lgm and especially during the holocene the river s departure enabled small pale coloured closely spaced coarser textured linear dunes to form on the abandoned floodplain in the eastern basin their orientation 20 farther west than the larger and older red dunes this realignment indicates that the australian wind whorl shifted southwards some 160 km or 1 5 after the lgm linear dunes in the northwestern simpson desert were formed by wind rifting involving vertical accretion of sand from a proximal source not by long distance sand transport with linear extension the blocking ranges have caused negligible downwind sediment accumulation over the past 75 ka

a complex origin for the kelso dunes mojave national preserve california usa a case study using a simple geochemical method with global applications abstract the kelso dune field in southern california is intriguing because although it is of limited areal extent 100 km2 it has a wide variety of dune forms and contains many active dunes 40 km2 which is unusual in the mojave desert studies over the past eight decades have concluded that the dunes are derived primarily from a single source mojave river alluvium under a dominant westerly to northwesterly wind regime the majority of these studies did not however present data to support the mojave river as the only source we conducted mineralogical and geochemical studies of most of the 14 geomorphically defined dune groups of the kelso dune field as well as potential sand sources alluvial sediments from the surrounding mountain ranges results indicate that sands in the nine western dune groups have k rb and k ba primarily from k feldspar compositions that are indistinguishable from mojave river alluvium westerly northwesterly winds and budweiser wash alluvium southwesterly winds permitting an interpretation of two sources in contrast sands from the five eastern dune groups have k rb and k ba values that indicate significant inputs from alluvial fan deposits of the providence mountains this requires either rare winds from the east or southeast or more likely aeolian reworking of distal providence mountain fan sediments by winds from the west at a rate greater than input from the mojave river or other western sources the results indicate that even a small dune field can have a complex origin either from seasonally varying winds or complex alluvial fan dune interaction application of k rb and k ba in k feldspar as a provenance indicator could be used in many of the world s ergs or sand seas where dune origins are still not well understood or are controversial four examples are given from africa and the middle east where such an approach could yield useful new information about dune sand provenance

long term measurements of aeolian transport directional variations over a zibar surface in the northern kumtagh sand sea abstract zibars are aeolian bedforms created by armoring of the surface by coarse grains the existence and movement of these grains strongly influence zibar morphodynamics although aeolian sediment transport has been investigated for arid surface processes with a range of grain sizes the measurement durations were short making it difficult to establish the relationship between microscopic aeolian transport processes and macroscopic geomorphological processes in the present study we conducted field observations of aeolian sediment transport above a zibar in northern china s kumtagh sand sea with a segmented sand trap during six measurement periods throughout 2014 the sampler collected 314 76 kg of sediments within 1 m above the ground the directional variation indicated that about 52 5 of the sediments came from the north northeast and northwest the southeast provided the least sediments the strongest aeolian transport occurred between august and october the weakest was in winter the aeolian sediment flux decreased with height and 54 of particles were transported within 0 1 m above the ground the transport profiles fit an exponential decay function the flux s directional variation resulted from the combined effects of sediment availability and wind regime so the calculated net transport differed from the drift potential the seasonal and directional variations of aeolian transport significantly affect the morphodynamic process of zibars the trend and the internal sedimentary structure of zibars were closely related to the aeolian transport process

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

acoustic scattering from the seafloor modeling and data comparison an existing model of seafloor backscattering d r jackson d p winebrenner and a ishimaru j acoust soc am 79 1410 1422 1986 was implemented with the additions of volume scattering from a random inhomogeneous continuum and scattering from subbottom interfaces results of computer simulations with the extended model were compared with values of scattering strength obtained from processed gloria data from the monterey fan off the coast of california regions of well delineated high and low backscatter are seen in the gloria imagery the geoacoustic input parameters for the simulation runs were either taken directly from or estimated from core data obtained by ground truth sampling in the image area from the model simulation results it appears that the main factor causing the observed dichotomous character of the strength of returns in the fingers area is the presence or absence of a topmost inhomogeneous silt clay layer with a thickness of around 1 1 5 m in the high backscatter areas inh

radon daily signals in the elat granite southern arava israel 1 high time resolution monitoring of radon 222rn in three boreholes 4 10 and 53 m deep along a 0 6 km transect is carried out in massive granite in southern israel three components of variation occur in the measured signal ms seasonal radon sr periodic multiday md and daily radon dr periodic temporal variation of the components suggests an association between the overall level of the long term variation and the amplitude of the daily variation the daily mean level of radon and the daily standard deviation vary periodically throughout the year time offsets occur among time series of the ms and were investigated also for the md and dr components using consecutive 20 day intervals spanning 900 days the resulting time series show that systematic time offsets occur whereby the radon signal always occurs first at the easternmost site the md shows a gradually varying lag of 0 12 h and the dr a stable 1 3 h lag spectral analysis shows that diurnal 24 h and semidiurnal 12 h periodic components characterize the dr the amplitudes of these components exhibit regular temporal variation having a seasonal pattern the ratios of co occurring amplitudes of these components define a linear pattern indicating a fundamental statistical property in the frequency domain of the radon time series the results indicate that unrecognized dynamic processes are driving the radon signal in the subsurface regime of the pluton suggesting new prospects for radon behavior in the frame of interacting geodynamic tectonic and earth sun system related processes

the formation of the namib sand sea inferred from the spatial pattern of magnetic rock fragments the formation of the namib sand sea inferred from the spatial pattern of magnetic rock fragments

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

high spatial resolution radon measurements reveal hidden active faults on mt etna radon emissions are frequently monitored in volcanically and tectonically active areas in order to reveal changes in soil degassing as radon acts a tracer for the more abundant co2 degassing commonly observed in such areas between july 2002 and may 2003 a series of discrete measurements of radon concentrations in soil were made with high spatial resolution similar to5 100 m in the santa venerina area on mt etna these measurements revealed well defined linear anomalies that we interpret as being caused by active faults whose higher porosity than surrounding soils allows an increased co2 flux carrying radon from beneath these faults were not visible at the surface and were therefore revealed at high spatial resolution by our radon survey our hypothesis that the positive anomalies are attributable to active faults was strengthened by the observation of concentrated damage along this geometry during the earthquakes that struck this area in late october 2003