penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

aeolian sediments evolution controlled by fluvial processes climate change and human activities since lgm in the qaidam basin qinghai tibetan plateau abstract aeolian sediments are widely distributed in the eastern qaidam basin qb the main habitats for human in the hyper arid basin during the holocene especially since 3 ka the evolution of aeolian sediments is an important factor for the environmental change and influence human activities and migration however many questions e g when the aeolian sediments start to accumulate what controls their initiation and how their evolution responds to climate change and human activities still need further studies in this study we present a detailed optically stimulated luminescence osl chronology for both aeolian and underlying fluvial sediments from the tiekui desert in the eastern qb to discuss aeolian and fluvial processes climatic changes desert evolution and human activities dating results show that 1 underlying fluvial sediments were formed during 23 9 12 1 ka and the erosion caused by the fluvial process may provide an explanation for the absence of aeolian sediments during and before this period 2 aeolian sediments accumulated from ca 9 8 ka to modern times with loess development from 9 8 ka to 1 6 ka and 1 4 0 7 ka and dune sand accumulation at 1 6 1 4 ka and 0 7 0 ka through the comparison with the local and global palaeoclimatic records we suggest that desert evolution in this region was sensitive to climatic changes induced by the asian summer monsoon detailed local historical records of the past 2000 years suggest that desert evolution was also influenced by human activities

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

distinct erosional progressions in the medusae fossae formation mars indicate contrasting environmental conditions abstract the form of erosional remnants of the medusae fossae formation mff on mars provide evidence of their development progression and implicate two spatially distinct environments in the equatorial regions of mars ubiquitous yardangs are clearly the product of strong unidirectional winds acting over time on variably indurated deposits yardang orientation is used as a proxy to map regional and local wind direction at meso scale resolution in other more limited areas not subjected to strong unidirectional winds randomly oriented kilometer scale mesas and buttes are found to be remnants of progressive cliff recession through mass wasting as support is lost from within the mff lithology at its margins the differing processes that dominate the formation of the distinctive landforms have implications for meso scale variations in climate that remain unresolved by current modeling efforts additionally the variability of erosional forms within the deposit emphasizes the overall complexity of this extensive formation

aeolian erosional lineations in the libyan desert dakhla region egypt abstract this paper presents results of a study of aeolian erosion at the landscape scale there have been few such studies in desert geomorphology compared to those focused on individual landforms and on rock surface sculpture the present study area lies in the southern part of the libyan desert in south central egypt between 25 and 27 n 29 and 30 e bedrock comprises paleogene limestone of various lithologies climate is hyperarid the following topics are treated i correspondences between rock outcrop belts and belts of terrain lineated by aeolian erosion and unlineated terrain ii the effect of lithology on aeolian lineation which works through the presence or absence of chert in the limestones lineation is produced by aeolian erosion in chert free poor rocks whereas erosion of chert rich rocks produces a desert pavement that armors the surface suppressing erosion iii the effect of large valleys eroded upwind of lineated terrain which deflect winds and trap sand ending erosion so that downwind lineations are reduced and finally erased by weathering iv sample lineated landscapes in the area show stages of evolution arranged in the time domain into a proposed cycle of aeolian erosion the cycle progresses from initial smooth plain to grooves separating long blade shaped ridges to segmentation of ridges into shorter blades along diagonal joints to streamlining of shorter blades and size reduction to final planation in any one wind parallel swath of lineated terrain stages in the cycle progress downwind in the space domain so that upwind landscapes are more advanced in the cycle v the structure of air flow responsible for lineation is still uncertain but initial grooving may respond to stable longitudinal horseshoe vortices or self organized regularity of erosion by random vortices subsequently the erosion pattern is fixed by evolving relief vi large smooth basins within the lineated terrain were carved by aeolian erosion before oxygen isotope stage ois 5 70 130 ka as were similar basins along the dakhla piedmont below the scarp little geomorphic change has occurred since so in this field of aeolian erosional lineations aels the aeolian erosion cycle may have occupied 10 times as long since continental scale aridity set in at ca 2 4 ma there have been only two cycles in this area a completed cycle earlier than the current incomplete one is indicated by rare small yardangs riding piggyback on larger ones

ice age winds an aquaplanet model abstract factors controlling the position and strength of the surface winds during the last glacial maximum lgm are examined using a global multilevel moist atmospheric model the idealized aquaplanet model is bounded below by a prescribed axisymmetric temperature distribution that corresponds to an ocean covered surface various forms of this distribution are used to examine the influence of changes in the surface cooling and baroclinicity rates the model omits seasonal variations increasing the cooling lowers the tropopause and greatly reduces the moist convection in the tropics thereby causing a weakening and equatorward contraction of the hadley cell such a cooling also weakens the surface westerlies and shifts the peak westerly stress equatorward an extra surface baroclinicity in midlatitudes implicitly associated with an increase in the polar sea ice also shifts the peak westerly stress equatorward but strengthens the surface westerlies thus calculations with combined surface cooling an

wind as the primary driver of erosion in the qaidam basin china deserts are a major source of loess and may undergo substantial wind erosion as evidenced by yardang fields deflation pans and wind scoured bedrock landscapes however there are few quantitative estimates of bedrock removal by wind abrasion and deflation here we report wind erosion rates in the western qaidam basin in central china based on measurements of cosmogenic 10 be in exhumed miocene sedimentary bedrock sedimentary bedrock erosion rates range from 0 05 to 0 4 mm yr although the majority of measurements cluster at 0 12570 05 mm yr these results combined with previous work indicate that strong winds hyper aridity exposure of friable neogene strata and ongoing rock deformation and uplift in the western qaidam basin have created an environment where wind instead of water is the dominant agent of erosion and sediment transport its geographic location upwind combined with volumetric estimates suggest that the qaidam basin is a major source up to 50 of dust to the chinese loess plateau to the east the cosmogenically derived wind erosion rates are within the range of erosion rates determined from glacial and fluvial dominated landscapes worldwide exemplifying the effectiveness of wind to erode and transport significant quantities of bedrock

links between topography wind deflation lakes and dust the case of the bodele depression chad the bodele depression chad is the planet s largest single source of dust deflation from the bodele could be seen as a simple coincidence of two key prerequisites strong surface winds and a large source of suitable sediment but here we hypothesise that long term links between topography winds deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land atmosphere processes with topography acting as the overall controlling agent we use a variety of observational and numerical techniques including a regional climate model to show that 1 contemporary deflation from the bodele is delineated by topography and a surface wind stress maximum 2 the tibesti and ennedi mountains play a key role in the generation of the erosive winds in the form of the bodele low level jet llj 3 enhanced deflation from a stronger bodele llj during drier phases for example the last glacial maximum was probably sufficient to create the shallow lake in which diatoms lived during wetter phases such as the holocene pluvial winds may therefore have helped to create the depression in which erodible diatom material accumulated instead of a simple coincidence of nature dust from the world s largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world s largest dust source similar processes plausibly operate in other dust hotspots in topographic depressions

yardangs on earth and implications to mars a review abstract yardangs as typical aeolian landforms are extensively identified in arid hyper arid areas on earth and other terrestrial bodies in this review based on analyses of morphology distribution age climate and geologic condition of yardangs worldwide we 1 assess the impacts of various controlling factors on yardang development to generalize a model based on morphology 2 illustrate the climate driven mechanism for yardangs 3 propose a geomorphological evolutionary model of yardang fields and 4 discuss potential implications of the above two models of yardang evolution on earth to mars it is demonstrated that both deflation and abrasion work on yardang development and it is the lithology to determine which one will be more effective in addition the wind action dominates the general aerodynamic form of yardangs while non aeolian factors account for the diversity in yardang morphology thus a model including four stages and initiating mechanisms is generalized for yardang processes from initiation to demise the synthetic analyses of meteorological data chronology and paleoclimatic proxies show that yardang development is mostly controlled by westerlies and would be accelerated during glacial periods and interrupted by lake formation during interglacial periods due to dry humid fluctuations and changes in atmospheric circulation driven by variations in solar radiation at orbital scales this leads to the zonal distributions of yardangs near 30 in both hemispheres depressions would be created or enlarged in yardang fields during glacial period along with activities of dust release and transport leading to aeolian deposition e g loess downwind the depressions then could be turned into lakes during wet phase of interglacial period and evolved into new yardangs in the following glacial period due to wind erosion this climate controlled geomorphological process under glacial interglacial cycles suggests that high accumulation rate in sediments from enclosed inland basins e g the qaidam basin doesn t mean high resolution climatic record due to the hiatus by wind erosion indicating the significance of robust chronology establishment before any climatic correlation under the rules of earth based yardang evolution it is potential to identify the specific level of development and explore the geomorphological processes as well as the climatic background for yardangs on mars

ice core evidence for a very tight link between north atlantic and east asian glacial climate 1 corresponding millennial scale climate changes have been reported from the north atlantic region and from east asia for the last glacial period on independent timescales only to assess their degree of synchrony we suggest interpreting greenland ice core dust parameters as proxies for the east asian monsoon systems this allows comparing north atlantic and east asian climate on the same timescale in high resolution ice core data without relative dating uncertainties we find that during dansgaard oeschger events north atlantic region temperature and east asian storminess were tightly coupled and changed synchronously within 5 10 years with no systematic lead or lag thus providing instantaneous climatic feedback the tight link between north atlantic and east asian glacial climate could have amplified changes in the northern polar cell to larger scales we further find evidence for an early onset of a younger dryas like event in continental asia which gives

application of self organizing map and srtm data to characterize yardangs in the lut desert iran abstract yardangs an exclusive landform due to intensive wind erosion cover a large area in the hyper arid lut desert of iran this paper presents a new approach using self organizing map som as unsupervised algorithm of artificial neural networks for analysis and characterization of yardangs nowadays the shuttle radar topography mission srtm with 3 arc sec data approximately 90 m resolution and nearly world wide coverage provides uniform good quality data the srtm 3 arc sec data were re projected to a 90 m utm grid bivariate quadratic surfaces with moving window size of 5 5 were fitted to this dem the first derivative slope steepness and the second derivatives minimum maximum curvature and cross sectional curvatures were calculated as geomorphometric parameters used as input to the soms 42 soms with different learning parameter settings e g initial and final radius number of iterations and the effect of random initial weights on average quantization error were investigated a som with a low average quantization error 0 1040 was used for further analysis feature space analysis morphometric signatures three dimensional inspection auxiliary data like landsat etm and high resolution satellite imagery from quickbird facilitated the assignment of semantic meaning to the output classes in terms of geomorphometric features results are provided in a geographic information system as thematic maps of landform entities based on form and slope e g yardangs ridge corridors valley or planar areas the results showed that all yardangs and corridors were clearly recognized and classified by this method when their width was larger than the dem resolution but became unrecognizable if their width is much smaller than the grid resolution the identified yardangs and corridors are aligned nnw sse parallel to the prevailing direction of the strong local 120 days wind and cover about 31 and 42 of the study area respectively the results demonstrate that som is a very efficient tool for analyzing aeolian landforms in hyper arid environments that provides very useful information for terrain feature analysis in remote regions

geomorphology and quaternary geology of the dakhla oasis region egypt abstract dakhla oasis 25 5 n 29 e occupies a structurally localized depression at 90 140 m above sea level 1200 km 2 in area below a 300 m escarpment bordering the libyan plateau western desert of egypt semi arid intervals of the quaternary period generated eight sedimentary formations separated by erosion during hyper arid intervals sediments comprise three generations of colluvial fluvial fanglomerates two generations of tabular spring laid clastic and chemical sediments two generations of mound springs and basinal sediments of fluvio lacustrine evaporitic pluvio aeolian and aeolian origins discussion of these sediments is organized according to geomorphic region from north to south plateau scarp and piedmont lowland and cuesta plain chronological evidence is restricted to many radiocarbon dates of holocene cultural material associated with playa sediments 9 4 5 ka a th u isochron age of 62 0 7 6 ka for basinal evaporites and two th u ages of 176 and 170 ka for a boulder of derived travertine the regional quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces it is broadly similar to sequences earlier reconstructed in the topographically similar kharga oasis region 150 km to the east and kurkur oasis 400 km to the south southeast speculations on chronology and driving mechanism are offered in conclusion

osl chronology and palaeoclimatic implications of aeolian sediments in the eastern qaidam basin of the northeastern qinghai tibetan plateau abstract aeolian sediments are widely distributed in the hyper arid qaidam basin and are good palaeoclimatic records due to limited age control aeolian processes and their relevance to palaeoclimatic change are poorly understood in this study we present 28 optically stimulated luminescence osl ages for both loess 14 samples and aeolian sand 14 samples from 8 profiles in eastern qaidam basin eqb in order to provide a detailed chronology for understanding the timing of aeolian processes and associated environmental conditions we reconstructed the history of aeolian activity in the eqb since deglaciation by combining osl chronologies lithologic stratigraphy and grain size analysis the results indicate that 1 aeolian sand underlying the loess accumulated at ca 12 4 11 5 ka and 10 8 ka but not during the last glacial maximum 2 loess accumulation started at 10 ka and lasted to 0 45 ka at least while most of the loess was deposited during 8 4 5 ka 3 palaeoclimates in the eqb are inferred to be arid during 12 4 11 5 ka relatively humid during 10 8 ka humid during 8 4 5 ka and relatively arid during 4 5 0 45 ka and 4 evolution of aeolian sediments were mainly controlled by effective moisture and also affected by local topography

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

holocene climate change inferred from stratigraphy and osl chronology of aeolian sediments in the qaidam basin northeastern qinghai tibetan plateau abstract paleoclimatic reconstruction based on aeolian sediments in the eastern qaidam basin qb has been hindered by the limited chronological data here we present 61 optically stimulated luminescence osl ages on the basis of these osl ages and the lithologic stratigraphy we propose the effective moisture index emi for aeolian sediments to reconstruct the effective moisture change based on the emi from twelve sections the effective moisture change moisture sources and relevant mechanisms for paleoclimatic change in the eastern qb are discussed the results indicate that 1 aeolian deposition started at least before 12 4 0 7 ka during the deglaciation the paleosols developed at the early and mid holocene and aeolian sand and loess accumulated at mid and late holocene 2 effective moisture history was hyper arid at 12 8 11 6 ka humid and variable at 11 6 8 3 ka moderately humid and stable at 8 3 3 5 ka and increasingly arid at 3 5 0 ka 3 the effective moisture change was mainly controlled by the asian summer monsoon asm which mainly followed the change of northern hemispheric summer insolation and the westerlies strengthened and increased the aridity in the qb when the asm shrank

holocene yardangs in volcanic terrains in the southern andes argentina yardangs of different sizes were developed in the payun matru volcanic field a semiarid area east of the southern andes mountains yardangs from volcanic terrains have not been described previously from earth although studies from mars interpreted linear ridges found by mariner and viking images as yardangs the payun matru volcanic field is an extensive plateau at 2000 m a s l covered by basaltic lava and ignimbrite flows strong westerly winds affect the extensive plateau micro and mesoyardangs are formed on the ignimbrite rock blanket and macroforms or megayardangs several kilometres in length are developed in the basaltic lava flows as long parallel troughs they all have a distinctive 320 azimuth which is the prevailing wind direction no yardang features are noted in the more recent lava flows younger than 1000 years indicating that their formation needed a longer time or they developed in earlier periods with stronger winds the yardang development is explained by the strong unidirectional winds the poor vegetational cover due to the aridity of the region the available quartz sand and volcanic ash particles as abrasive agents and the volcanic lithology texture and flow structure copyright 2001 john wiley sons ltd

radar scattering of linear dunes and mega yardangs application to titan the ku band 13 8 ghz 2 2 cm radar instrument onboard the cassini huygens spacecraft has revealed the richness of the surface of titan as numerous seas lakes rivers cryo volcanic flows and vast dune fields have been discovered linear dunes are a major geomorphological feature present on titan covering up to 17 of its surface mainly in equatorial regions however the resolution of the radar instrument is not good enough to allow a detailed study of the morphology of these features in addition other linear wind related landforms such as mega yardangs linear wind abraded ridges formed in cohesive rocks are likely to present a comparable radar signature that could be confused with the one of dunes we conducted a comparative study of the radar radiometry of both linear dunes and mega yardangs based on representative terrestrial analogues the linear dunes located in the great sand sea in western egypt and in the namib desert in namibia and the mega yardangs observed in the lut desert in eastern iran and in the borkou desert in northern chad we analysed the radar scattering of both terrestrial linear dunes and mega yardangs using high resolution radar images acquired by the x band 9 6 ghz 3 1 cm sensor of the terrasar x satellite variations seen in the radar response of dunes are the result of a contrast between the dune and interdune scattering while for mega yardangs these variations are the result of a contrast between ridges and erosion valleys we tested a simple surface scattering model with parameters derived from the local topography and surface roughness estimates to accurately reproduce the radar signal variations for both landforms it appears that we can discriminate between two types of dunes bare interdunes as in egypt and sand covered interdunes as in namibia and between two types of mega yardangs young yardangs as in iran and older ones as in chad we applied our understanding of the radar scattering to the analysis of cassini radar t8 acquisitions over the belet sand sea on titan and show that the linear dunes encountered there are likely to be of both egyptian and namibian type we also show that the radar bright linear features observed in cassini radar t64 and t83 acquisitions are very likely to be mega yardangs possible remnants of ancient lake basins at mid latitude formed when titan s climate was different

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

holocene record of eolian activity from genggahai lake northeastern qinghai tibetan plateau china the history of dust emission and eolian activity in dust source areas remains unclear due to the scarcity of geological archives grain size data from genggahai lake on the northeastern qinghai tibetan plateau show that sand sized particles in the lake sediments were transported primarily by strong winds to the lake and therefore can be used as a proxy for eolian activity eolian activity was weak from 10 3 to 6 3 ka which may be a response to increased vegetation cover due to the strengthened asian summer monsoon in contrast eolian activity occurred episodically when the summer monsoon weakened the abrupt intense sand deposition events are likely to have resulted from strong wind regimes in turn linked to cooling events in the north atlantic our results suggest that changes in atmospheric circulation patterns may have strongly affected the moisture balance and wind strength in the dust source area and hence dust emissions

palaeo yardangs wind scoured desert landforms at the permo triassic unconformity in canyonlands national park south east utah at least 29 partly exhumed aligned sandstone ridges trending generally n20 w occur at the upper unconformable surface of the lower permian leonardian white rim sandstone the ridges are at least 1 5 km long 250 m wide and have up to 14 m of vertical relief mean of 9 m a thin lag of coarse sandstone that contains wind ripple laminae and granule ripples directly overlies the ridges angular blocks of sandstone within the lag and sand filled fissures immediately below the lag within the ridges attest to early cementation of the ridge forming material se dipping aeolian cross strata within the white rim sandstone and within the lag closely parallel the ridge trend the ridges are interpreted as wind sculpted desert landforms yardangs that developed on the lithified upper surface of the white rim sandstone during an extended period of hyperaridity towards the end of the permian

geomorphological investigations and luminescence dating in the southern part of the khangay and the valley of the gobi lakes central mongolia geomorphological investigations in the catchment area of the baydragiyn river along the southern slope of the khangay and in the valley of the gobi lakes in western mongolia provide evidence for late quaternary glaciations and lake level changes thermoluminescence tl and infrared optically stimulated luminescence irsl dating of aeolian and colluvial sediments from the central khangay place the sediments that overlie fluvial and glaciofluvial terraces in the holocene an age of 21 ka is determined for a sand deposit overlying the terrace that is related to the last glacial ice margin lacustrine sediments from higher beach lines in the valley of the gobi lakes provide evidence for a slightly more humid period around 1 5 ka and a larger extent of the lakes in the early holocene at about 8 5 ka as also reported from other parts of central asia remnants of lacustrine sediments buried by alluvial gravel and indicating a huge palaeolake in the basin of the orog nuur however date to the early stage of the last glaciation around 70 ka copyright 2001 john wiley sons ltd

deflation in the dustiest place on earth the bodele depression chad the bodele depression in chad is the largest single source of dust on earth because of a combination of strong near surface winds and a large reservoir of readily eroded and easily entrained low density sediment during the holocene and late pleistocene the bodele depression was host to a great lake palaeolake megachad that is now completely desiccated leaving the lake bed sediments exposed to deflation deflation in the bodele depression is revealed in erosional remnants of lake bed deposits exposed as yardangs on the lake floor erosional remnants indicate that locally up to 4 m of sediment has been removed by deflation optically stimulated luminescence dating shows that this occurred in less than 2400 years giving a rate of deflation of at least 1 6 mm yr 1 a range of other geomorphological features indicate that in some areas rates of deflation may be greater than or equal to 10 mm yr 1 deflation appears to be greatest in an arc around the northeastern margins of the lake basin where the diatomite deposits have been removed and revealed an underlying network of distributary channels preserved as gravel capped ridges the ridges which are part of an inverted topography are interpreted as deltaic distributary channels from an inland delta similar to the okavango delta examples of barchan dunes exist that were flooded by the palaeolake and which have now been exhumed from beneath layers of diatomite the distribution of extensive deflation around the northeasterly upwind end of the bodele depression probably results from a combination of large wind velocities an upwind source of abrasive sand and thinner diatomite deposits around the lake margin satellite image analysis shows that outcropping diatomite covers 24 049 km2 of the bodele depression furthermore the area from which diatomite has been removed by deflation is around 14 000 km2 combining this information with the ages and rates of deflation mentioned above indicates that some 61 000 km3 of diatomite has been eroded from the bodele depression during the past 1000 years

evolution of the yardangs at rogers lake california yardangs are streamlined wind eroded hills common to most deserts yardangs at rogers lake mojave desert california have streamlined forms characteristic of objects eroded by moving fluids a teardrop shape that approaches an ideal 1 4 width to length ratio in wind tunnel simulations miniature forms of various shapes changed sequentially by 1 erosion of the windward corners 2 erosion of the windward slope 3 erosion of the leeward corners and flanks and 4 erosion of the leeward slope prominent mechanisms in yardang evolution apparently are abrasion at the windward end and deflation and reverse air flow near the middle and at the downstream end width to length ratios of yardangs are grossly similar to those of some fluvial and glacial streamlined landforms the low kinetic energy of wind relative to ice and water the erosional resistance to wind of most rocks the rarity of long term unidirectional winds and the presence of running water topographic roughness and vegetation all limit the abundance of yardangs

origin and characteristics of yardangs in the um al rimam depressions n kuwait article i nfo although arabia hosts one of the largest deserts in the world studies regarding aeolian erosional features in general and yardangs in particular are rare the principal aim of this study is to delineate and investigate the various forms of yardangs in the um al rimam depressions in the northern part of kuwait the study area consists of two main depressions connected by neck area made up of continental sediments both depressions are surrounded by a dissected escarpment and their floors host muddy playas on lithological bases three main types of yardang have been identified 7 yardangs are sculptured in sandstones of lower fars formation lower to middle miocene 23 are carved in calcretic rocks of ghar formation oligocene to lower miocene and 11 yardangs are developed in quaternary sediments their mean orientation nw 297 coincides with the prevailing direction of the strong local northwesterly wind called the shamal the average length width ratio is 1 5 1 the wide geographic distribution of yardangs around the margins of the northern depression is due to sand blasting this is explained by the annual sand accumulation measured in the study area where the northern depression shows 143 times higher accumulation than the southern depression the neck area and the platform above the depressions also the field measurements for annual erosional rates show that the sides of the yardangs are more affected by erosion compared to their middle parts remarkably slight mineralogical variations were detected within the surface sediments of um al rimam depressions and the quaternary muddy yardangs which indicate a common origin the age of yardangs is unknown but annual erosional rates on a small quaternary muddy yardang suggest that they range in age between 44 and 1500 years depending on yardang size it is believed as indicated from field observation and interpretation of aerial photos that the majority of yardangs are pre existing bedrock forms these forms were developed by paleo surface hydrological processes which were modified by wind action in latter phase

delayed build up of arctic ice sheets during 400 000 year minima in insolation variability an east asian winter monsoon proxy record using grain size variations in chinese loess over the past 900 000 years shows that for up to 20 000 years after the interglacials at 400 000 year intervals the weak monsoon winds maintain a mild non glacial climate at high northern latitudes qingzhen hao and colleagues present a record of grain size variations in the chinese loess plateau a proxy of variations in the strength of the east asian winter monsoon and show that relatively high insolation at 400 000 year intervals held off the inception of the subsequent ice age for about 20 000 years relative to other glacial inceptions mechanistically the extension of warm conditions was probably linked to a weak siberian high pressure system associated with a delayed build up of northern ice and snow the authors speculate that these observations imply that arctic climate may remain in non glacial mode for more than 40 000 years even in the absence of anthropogenic greenhouse gases knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial1 may help to inform our understanding of future climate change unfortunately long term continuous records of ice sheet variability in the northern hemisphere only are scarce because records of benthic 18o content represent an integrated signal of changes in ice volume in both polar regions2 however variations in northern hemisphere ice sheets influence the siberian high3 an atmospheric pressure system so variations in the east asian winter monsoon eawm as recorded in the aeolian dust deposits on the chinese loess plateau can serve as a useful proxy of arctic climate variability before the ice core record begins here we present an eawm proxy record using grain size variations in two parallel loess sections representative of sequences across the whole of the chinese loess plateau over the past 900 000 years the results show that during periods of low eccentricity and precessional variability at approximately 400 000 year intervals the grain size inferred intensity of the eawm remains weak for up to 20 000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis in contrast there is a rapid increase in the eawm after the end of most other interglacials we conclude that for both the 400 000 year interglacials the weak eawm winds maintain a mild non glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records during these times the less severe summer insolation minima at 65 n ref 4 would have suppressed ice and snow accumulation leading to a weak siberian high and consequently weak eawm winds

morphological and morphostructural features of kuwait abstract morphostructural analysis and interpretation of the geomorphic features of the surface of kuwait are essentially dependant on the recognition of the structural configuration of the top of the upper eocene dammam formation and its influence on the overlying sediments of the kuwait group the top surface of the dammam formation has an undulatory form representing a series of n s to nnw sse trending domal and flexural structures this surface has regulated to a variable extent the depositional regime and thickness of the overlying kuwait group structures of the dammam formation have directly left an impression on the surface as morphostructural forms and also indirectly controlled the geomorphic forms of the overlying sediments fifteen geomorphic zones characterized by distinct physiographic patterns slope gradients and dependant features are presented on a map data based on the recognition of drainage patterns and slope characteristics were incorporated significant deflection in topographic contours was also identified and geomorphic discontinuities and anomalies were delineated further treatment of the geomorphic zonation data with input from existing geological structural and tectonic data has resulted in the construction of the first morphostructural map of kuwait

yardang evolution from maturity to demise yardangs are enigmatic wind parallel ridges sculpted by aeolian processes that are found extensively in arid environments on earth and mars no general theory exists to explain the long term evolution of yardangs curtailing modeling of landscape evolution and dynamics of suspended sediment release we present a hypothesis of yardang evolution using relative rates of sediment flux interyardang corridor downcutting yardang denudation substrate erodibility and substrate clast content to develop and sustain yardangs corridor downcutting must exceed yardang vertical denudation and deflation however erosion of substrate yields considerable quantities of sediment that shelters corridors slowing downcutting we model the evolution of yardangs through various combinations of rates and substrate compositions demonstrating the life span suspended sediment release and resulting landscape evolution we find that yardangs have a distinct and predictable evolution with inevitable demise and unexpectedly dynamic and autogenic erosion rates driven by subtle differences in substrate clast composition

danghe area western gansu china biostratigraphy and implications for depositional history and tectonics of northern tibetan plateau the danghe area in western gansu province is at the focal point of interaction of the northeastern end of the left lateral altyn tagh fault and growing ramp thrusts of the danghe nanshan mountains along the northern rim of the qinghai tibetan plateau with a thick sequence of tertiary sediments and associated fossil records the danghe area is one of few places on the tibetan plateau that can offer integrated studies of its tectonic history depositional environment and biological records including vertebrate and plant fossils past studies however have not been able to capitalize on the paleontological data or were often misguided by an outdated notion of regional chronology incorrect age estimates in these studies often have profound effects on tectonic interpretations we present new stratigraphic and paleontologic evidence from the danghe area and demonstrate a new chronologic scheme that indicates a much younger age for the majority of the sediments we recognize three packages of sediments in the danghe area 1 oligocene paoniuquan new name formation basal predominantly fine grained dark purple mudstones and siltstones that include the classic yindirte fauna which forms the basis of the tabenbulukian mammal age 2 early miocene to early late miocene tiejianggou new name formation that contains a new platybelodont proboscidean in a coarsening upward sequence terminating in a massive conglomerate and 3 an unnamed late neogene formation that contains another coarsening upward sequence in light of our new stratigraphic framework we reinterpret a previously published magnetic column for the middle sequence in xishuigou as representing chrons c6n through c4ar corresponding to a span of about 20 9 3 ma much younger than has been realized so far this new chronological framework suggests a depositional history of the danghe nanshan that spans at least the early oligocene through late miocene to possibly pliocene early depositions during the oligocene through middle miocene are dominated by fine grained sediments indicating a distant source of sedimentation paleontological data suggest a relatively dry environment as is typical of northern china today by late miocene around 9 12 ma the danghe area began to receive coarse sediments and was much closer to the mountain front the new stratigraphic framework indicates an earlier onset of sedimentation than has generally been assumed but also suggests the presence of sediments much younger than many have realized c 2003 elsevier science b v all rights reserved

step wise growth of biotite porphyroblasts in pelitic schists of the western lys caillaouas massif pyrenees abstract detailed optical and electron microscope sem and tem examination of biotite blasts from pelitic schists of the western lys caillaouas massif in the pyrenees reveals a variety of microstructures suggesting growth of the blasts before and after a thermal peak during the d2 deformation in the early stages of growth the biotites had 001 at high angles to s1 and they appear to have existed as thin 001 parallel plates in many cases blastesis is suggested to have involved growth of the biotites into their own continuously dilating pressure shadows inclusions with dentate grain boundaries banded structures and radiator fin intergrowths suggest a mechanism analogous to the ramsay crack seal model for vein formation but here involving step wise dilation of a pressure shadow cavity into which the adjacent blast itself was growing