textural characteristics and genesis of the aeolian sediments in the kuwaiti desert several types of aeolian deposits have been recognized in kuwait a smooth sand sheets that resemble desert floor sand b immobile sands that include rugged vegetated sand sheets and wadi fill deposits and c mobile sands that form active sand sheets and sand dunes simple size frequency curves illustrate the genetic relationship between the various aeolian sediment types the four size parameters namely mean size sorting skewness and kurtosis were calculated scatter plot diagrams of sorting versus mean size and sorting versus kurtosis are effective in differentiating smooth sand sheet deposits from dune sands active sand sheet deposits can also be recognized because they are usually located between the two end members smooth sand sheets and dune sands size parameters change with location regardless of their types coarsening and positive skewness usually increase downwind mineralogical and textural characteristics of the aeolian deposits in kuwait revealed that they are mostly derived from the lower mesopotamian muddy flood plain deposits the sand fraction of the al dibdibba gravelly deposits and the disintegrated material from calcretic and gypcretic duricrusts distribution of depositional and deflational areas indicates that the northern desert of kuwait is characterized by a positive sand budget whereas the southern desert has a negative sand budget

holocene coastal dune formation in southern australia a case study abstract the 14 500 km long southern australian coast is exposed to high energy wave and wind regimes which have mobilized shelf derived sediments to produce extensive holocene shoreface deposits the 8000 km of sandy coast are backed by over 2000 km 2 of holocene dunes of varying degrees of stability in places dune deposition above present sea level accompanied the post glacial marine transgression commencing as early as 10 ka b p and has continued episodically to the present day the dunes are widespread in extent but vary in type size and evolution the oldest and often most extensive primary dune fields accompanied the post glacial marine transgression they occurred and in some places continue to form in areas of high wave and wind energy and abundant sand supply many of these systems exhausted their sediment supply by mid holocene and remain as stranded clifftop dunes where sand ramps were eroded or as eroding barriers secondary phases of dune activity occurred on moderate to high energy coasts following an initial period of post stillstand barrier progradation diminished sediment supply resulted in shoreline erosion and secondary dune formation the location size and evolution both of dunes types is largely controlled by the breaker wave regime which in turn influences the rate and volume of sediment supply beach morphodynamics and resulting aerodynamic boundary conditions and foredune erosion a study of dune formation along the 3700 km long south australian coast provides a basis for an overview of dune formation throughout southern australia

reconstructing paleoenvironments and palaeoclimates in drylands what can landform analysis contribute quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets some of which are geomorphological in nature in drylands where organic proxies may be limited the use of landforms is particularly important but challenging the capacity to establish the age of depositional forms particularly through the use of luminescence dating has advanced the use of landforms in dryland palaeo research though interpretation of these geoproxy records can be complex especially at the nexus of palaeoclimate and palaeoenvironmental interpretations of past conditions in this paper the use of aeolian and lacustrine forms in quaternary research is considered focusing on the relationships between dynamics form and climate and on the essential linkage between process research and palaeoenvironmental research it is concluded that landform analysis is a critical part of dryland palaeoenvironmental climate reconstruction contributing a different set of data compared to other data sources in terms of the elements of past conditions that are revealed five principles are identified to improve the use of geoproxy records in quaternary research 1 greater use of geomorphic process studies by quaternary scientists to better inform palaeolandform interpretation 2 further development of the use of chronometric data especially in terms of interpreting large data 3 interpret landform records in location specific contexts not in general terms 4 capitalise of the complexity of spatially extensive landform records which may offer better representations of real quaternary environmental complexity than at a point proxies 5 establish ways of integrating spatially extensive geoproxy records with other palaeoenvironmental records these challenges are major but not insurmountable and should represent goals for geomorphologists chronologists and quaternary scientists alike copyright 2011 john wiley sons ltd

last glacial coastal dunes in eastern australia and implications for landscape stability during the last glacial maximum abstract the last glacial maximum or lgm 25 000 15 000 yr b p has been recognized in australia as a period of increased dryness coolness continentality and windiness compared to earlier and later period enhanced aeolian activity during the lgm occurred in arid and semi arid regions of western central and eastern australia the east coast has been considered to have been better watered and vegetated however at a number of sites from tasmania to north queensland there is evidence for extensive aeolian instability of coastal sand deposits dating by radiocarbon and thermoluminiscence techniques has supported morphologic and stratigraphic evidence of dune formation during the lgm under the influence of westerly offshore winds in the southern sector of the east coast i e south of 31 s latitude and southeast winds to the north it is now apparent that vegetation cover on sandy surfaces was quite patchy during the lgm sand surface instability under conditions of strong west or southeast winds promoted linear and or parabolic dune development this suggests greater concentration of forests in more discrete protected sites along the eastern escarpment than was previously considered by palaeoecologists more widespread drier and cooler climatic conditions operated even in coastal regions on expanded continental shelves at this time stabilization of areas of active dunes became more likely as sea levels rose reduced windiness occurred and precipitation increased as sea surface temperatures began to rise in the holocene

the timing and relation of aeolian sand deposition in central spain to the aeolian sand record of nw europe abstract presented here are tl and osl age determinations on aeolian sediments from four sites around the guadarrama mountains in central spain these show aeolian activity between 8 1 and 13 1 ka the new data when combined with previously published luminescence data shows an inferred phase of aeolian activity in central spain ca 10 13 ka this is compared to a dataset of luminescence ages from the nw european aeolian record which shows a similarly timed peak the abrupt climate changes associated with the younger dryas occurred during this time and are thought to have caused aeolian activity in nw europe the correlation between the two aeolian records presented here is tentatively suggested to indicate that the younger dryas may also be the causal mechanism for intensified aeolian activity in central spain

thermoluminescence dates and palaeoenvironmental information of the late quaternary sand deposits tierra de pinares central spain abstract a large amount of quaternary palaeo environmental evidence lies within the terrestrial aeolian sediments filling the duero basin in central spain previous work has identified a number of stratigraphical units although the absolute age and origin of some of these is equivocal the uppermost unit the focus of this paper is a widely distributed sand which covers most of the tierra de pinares north of segovia detailed investigations of an exposure at burgomillodo reveal over 35 m of laminated and cross bedded sand from which seven thermoluminescence dates were obtained the bedding structures indicate a northwesterly palaeowind direction different from the present dominating westerly winds two phases of sand deposition are identified at the site with evidence of erosion and reactivation phases an upper unit of ca 7 ka during the warm aridity of the atlantic period and a lower unit between 12 5 11 ka coinciding with the cold aridity of the younger dryas event the latter in which at least 25 m of sand were deposited at the site is the dominant phase and is coincident with what has been identified elsewhere in spain from biological data as a period which was both cold and dry the burgomillodos site therefore represents the first sedimentological evidence for this arid phase in the younger dryas in central spain

parabolic dune development modes according to shape at the southern fringes of the hobq desert inner mongolia china since the 1970s parabolic dunes at the southern fringe of the hobq desert inner mongolia china have exhibited many different shapes v shaped u shaped and palmate each with a unique mode of development in the study area parabolic dunes are mainly distributed in regions a b and c with an intermittent river running from the south to the north we used high resolution remote sensing images from 1970 to 2014 and rtk gps measurements to study the development modes of different dune shapes the modes are characterized by the relationship between the intermittent river and dunes formation of the incipient dune patterns the predominant source supply of dunes and the primary formation of different shapes v shaped u shaped and palmate most parabolic dunes in region a are v shaped and closer to the bank of the river the original barchans in this region exhibit disconnected arms behavior with the sand blown out of the riverbed through gullies the nebkhas on the disconnected arms acquire the external sand source through the fertile island effect thereby developing into triangular sand patches and further developing into v shaped parabolic dunes most parabolic dunes in regions b and c are palmate the residual dunes cut by the re channelization of river from transverse dune fields on the west bank are the main sand source of region b the parabolic dunes in region c are the original barchans having then been transformed the stoss slopes of v shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape the dune crest of v shaped parabolic dune is the deposition area which forms the arc shaped sand ridge their two arms are non parallel the lateral airflow of the arms jointly transport sand to the middle part of dunes resulting in a narrower triangle that gradually becomes v shaped palmate parabolic dunes have a steeper stoss slope and height the dune crest of the palmate parabolic dune is the erosion area which forms a long and narrow trough between nebkhas by the funnelling effect this process forces sand towards lee slopes which transform from concave original barchans into convex ultimately resulting in the formation of palmate parabolic dunes

long term persistence of mediterranean pine forests in the duero basin central spain during the holocene the case of pinus pinaster aiton in the southern duero basin of central spain there are vast areas of aeolian sand sheets and dune fields a comprehensive survey of the sand quarries in this area identified a number of palaeosols in sedimentary sequences the identification and ams radiocarbon dating of soil charcoal fragments collected in these palaeosols indicate the persistence of pinus pinaster in this area throughout most of the holocene although potential natural vegetation models have usually considered the pinus pinaster forests in this inland area of artificial origin soil charcoal analysis provides firm evidence of a natural origin our data fit perfectly with the pattern of holocene vegetation development for inland areas of iberia which are characterised by stability of pine forests throughout the holocene finally the growing body of palaeobotanical evidence from iberia macrofossils and pollen is contributing to improve our knowledge of p pinaster ecology showing that this species has been present in most iberian re

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

magnetic enhancement in wildfire affected soil and its potential for sediment source ascription intense rainfall following wildfire can cause substantial soil and sediment redistribution with concern for the increasing magnitude and frequency of wildfire events research needs to focus on hydrogeomorphological impacts of fire particularly downstream fluxes of sediment and nutrients here we investigate variation in magnetic enhancement of soil by fire in burnt eucalypt forest slopes to explore its potential as a post fire sediment tracer low frequency magnetic susceptibility values lf of 10 m material sourced from burnt slopes c 8 0 10 4 10 6 m3 kg 1 are an order of magnitude greater than those of 10 m material derived from long unburnt areas 0 8 10 6 m3 kg 1 susceptibility of anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm values are similarly enhanced signatures are strongly influenced by soil and sediment particle size and storage of previously burnt material in footslope areas whilst observations indicate that signatures based on magnetic enhancement show promise for post fire sediment tracing problems arise with the lack of dimensionality in such data magnetic grain size indicators fd arm sirm and fd arm offer further discrimination of source material but cannot be included in numerical unmixing models owing to non linear additivity this leads to complications in quantitatively ascribing downstream sediment to source areas of contrasting burn severity since sources represent numerical multiples of each other indicating the need to involve additional indicators such as geochemical evidence to allow a more robust discrimination copyright 2005 john wiley sons ltd

investigation of elastic weakening in limestone and sandstone samples from moisture adsorption summary elastic and mechanical weakening from water saturation are widely known to occur in sedimentary rocks and particularly in carbonate rocks to improve our understanding of the physics underlying this phenomenon ultrasonic f 0 5 mhz elastic properties are measured on a large suite of clean limestones and sandstones at very low saturations from relative humidity rh variations at ambient conditions measurements clearly highlight an elastic weakening i e decrease in elastic wave velocity from moisture adsorption p and s wave velocities are similarly affected by adsorption but in a different way for limestones and sandstone samples while the elastic properties of limestone samples show almost no rh dependence a large weakening is observed for samples of fontainebleau sandstone that increases with the samples porosity the main elastic weakening effect is likely to result from adsorption of fluid at grain contacts it thus affects particularly granular rocks such as sandstones while well cemented limestones are not affected the granular model from murphy et al accounting for surface energy effects proves to be appropriate applying this model it is shown that i p and s wave velocities have the same dependence on surface energy which is consistent with the measurements and ii surface energy values obtained from the ultrasonic data using this model correlate with rh and are consistent with the expected value for quartz crystals at vapour pressure yet porosity which relates to degree of cementation in the particular case of fontainebleau sandstone appears to be an additional parameter a modified model is thus derived using the cementation model from digby accounting for a bonding radius at grain contact it proves to apply well to the measured data the fundamental difference between limestones and sandstones dependence to rh appears to be related to a microstructural difference saturation variations from rh increase depend on specific surface area which is particularly low in fontainebleau sandstones and large in microporous limestones however elastic weakening from rh is more important in sandstones owing to their granular microstructure

origin and evolution of playas and blowouts in the semiarid zone of tierra de pinares duero basin spain abstract a large number of blowouts and playas occur in the marginal sectors of the aeolian deposits located in the southern sector of the duero depression tierra de pinares in spain the blowouts are relict landforms that were developed on sand sheets by deflation during dry periods with lower vegetation cover and a deeper water table the studied blowouts form complexes of nw se and nnw sse elongated hollows with accompanying dunes up to 4 km long in the leeward margins some hollows host lakes or swampy areas related to a shallow water table the dunes formed by ne ene winds show steep windward slopes and gentle leeward slopes the studied playas with prevalent nnw sse orientations result from the aeolian excavation of terrace deposits and the underlying marly bedrock it is probable that the formation of these depressions in an initial stage was related to deflation processes affected preferentially nnw sse sandy channels perpendicular to the dominant wind direction the precipitation of salts in the playas generates aggregates of clay particles peloids that are easily removed by the wind once the bottom reached the substratum the deepening of the depressions progressed by the deflation of particles produced by weathering of the argillaceous bedrock

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

a map of pleistocene aeolian deposits in western europe with special emphasis on france he land use and cover area frame statistical survey lucas database on topsoil properties in europe was used to map aeolian deposits the points which satisfy the grain size criteria of coversands loess and transitional facies were extracted from the rasters of predicted soil texture established by kriging of the lucas data by ballabio et al 2016 a comparison with already available maps derived from a conventional eld approach shows a good t in most of the tested areas the new map however suggests a greater extension of loess which seems related to the inclusion of thin loess covers usually omitted by conventional mapping and the presence of previously unmapped areas due to lack of survey or misinterpretation the main source of aeolian particles corresponds to glacio uvial sediments at the margin of the scandinavian and alpine ice sheets coversands and loess form a broad band across northern europe and in the rh one rhine and danube valleys large areas on the outskirts of these deposits also received a signi cant loess contribution which has been reworked in slope deposits conversely southern europe is characterized by much less loess accumulation the atlantic coast has transgressive dune elds that penetrate inland to varying degree

airflow terrain interactions through a mountain gap with an example of eolian activity beneath an atmospheric hydraulic jump the integration of atmospheric soundings from a fully instrumented aircraft with detailed sedimentary and geomorphic analyses of eolian features in the ferris dune field of south central wyoming lends insight into the manner in which topography interacts with airflow to modify eolian activity topographically modified airflow results in zones of airflow deceleration acceleration and enhanced atmospheric turbulence all of which influence the surface morphology and sedimentology extreme lateral confluence of prevailing airflow produces accelerated unidirectional winds these winds correlate with unusually continuous and elongate parabolic dunes that extend into a mountain gap windy gap persistently heightened winds produced at the entrance to windy gap have resulted in a concentration of active sand dunes that lack slipfaces common development of a strongly amplified atmospheric wave analogous to a hydraulic jump in the gap contributes to the formation of a variety of eolian features that mantle the surface of windy gap and the ferris dune field tail heightened unidirectional winds in this zone promote grain size segregation the formation of elongated and aligned sand drifts climbing and falling dunes elongate scour streaks and parabolic dunes that have low angle 20 sup 0 cross stratification deflation of bedrock and loose sediment has been enhanced in the zonemore of maximum turbulence beneath the hydraulic jump less

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 biogeographical role of pinus forest on the northern spanish meseta a new holocene sequence abstract the aim of this paper is to reconstruct the variation in the vegetation during the holocene on the northern meseta through pollen analysis in order to determine the roles played by pinus and quercus in the vegetation dynamics a new pollen sequence camporredondo in the centre of the duero river basin northern meseta spain is presented it covers the period from ca 11 250 to 1630 cal yr bp the camporredondo sequence suggests that a forested landscape existed from the start of the holocene with values of approximately 90 of arboreal pollen mainly derived from pine forests in the surroundings shortly after 8600 cal yr bp pine forests continued to dominate but the landscape became more open while stands of deciduous and evergreen quercus developed around 4500 years ago coinciding with the start of a period of less rainfall the lacustrine areas in these territories began to silt up favouring hydrophytic taxa such as salix or cyperaceae a comparison with other holocene pollen sequences from the central eastern part of the northern meseta confirms the presence of pine forests in the whole region since the early holocene we discuss the variations of the general vegetation pattern in terms of the local or regional conditions at each site throughout the holocene pinus forests dominated at least in the eastern half of the duero river basin the typical holocene substitution of conifers by broadleaf species as recorded in other parts of the iberian peninsula and europe never takes place in the study area the results of the present study suggest that the current view of the potential vegetation in the spanish northern meseta should be reviewed

terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest ohio usa article i nfo article history received 7 may 2010 available online 21 february 2011 optically stimulated luminescence dated sand dunes and pleistocene beach ridges in northwest ohio are used to reconstruct landscape modification more than 5000 yr after deglaciation four of the osl ages 13 3 11 1 ka cluster around the younger dryas cold event five ages 10 8 8 2 ka cluster around the preboreal one young age 0 9 0 7 ka records more recent aeolian activity and one age of 15 1 13 1 ka dates a barrier spit in lake warren in northwest ohio both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the younger dryas however the climate conditions during the preboreal resulting in aeolian activity are not recorded in the available pollen records from this we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler drier episodes of climate and can complement pollen data younger dryas and preboreal aged aeolian activity in northwestern ohio coincides with aeolian records elsewhere in the great lakes region east of the prairie forest ecotone

holocene eolian sediments on the southern border of the duero basin spain origin and development of an eolian system in a temperate zone abstract holocene eolian sediments accumulated in the interior of the iberian peninsula far from typical eolian environments deserts coasts and periglacial arid belts these eolian deposits are interpreted as a wet eolian system with dunes interdune areas and sand sheet areas parabolic dunes predominate indicating a dominant wind direction to the ne interdune areas may be either dry or wet the eolian system is partly relict but also contains sporadically active dunes with visible slipfaces and partial vegetative cover several dunefields exist having larger and more complex dunes at the center and downwind areas dunes originated from dome shaped accumulations in the sand sheet which became simple parabolic dunes and ramps larger compound and complex parabolic dunes and ramps originated by merging and stacking of simple dunes finally transverse dunes originated when the noses of parabolic dunes were stopped by water and the arms continued to move forward the origin and development of the eolian system was related to abundant sand from underlying fluvial terraces deposition in a depression with considerable relief and open to the wind and changes in the water table which controlled eolian accumulation the presence of those eolian deposits in a temperate region suggests that with the appropriate factors eolian sedimentation is relatively independent of climate the potential preservation of these sediments in temperate climates is problematic because they are vulnerable to erosion mainly by water

inland aeolian deposits of the iberian peninsula sand dunes and clay dunes of the duero basin and the manchega plain palaeoclimatic considerations abstract this paper describes the latest research on the geomorphological characteristics formation environment and chronology of the main inland aeolian deposits from the south eastern duero basin db and the manchega plain mp of the iberian peninsula similarities and differences between the aeolian deposits of these two locations are summarised wind deflation from the guadiana and jucar alluvial systems created the aeolian deposits of the mp these deposits are mainly composed of quartz sands however in the san juan alluvial plain mp there is a large extent of clay dunes formed by exposure to prevalent winds of seasonal playa lakes with salt and clay sediments in the db wind remobilisation of the small particles from quaternary terraces and tertiary arkosic sediments left aeolian deposits of quartz feldspar sands textural parameters of the aeolian deposits show large variations depending on the location and the original deposit thus in the db the aeolian sands derived from the deflation of fluvial sediments are better sorted and smaller in grain size than those created by the deflation of arkosic sediments morphologically simple and compound parabolic dunes u v forms hemicyclic lobate and elongate crescentic and linear dunes climbing dunes and blowout dunes have been recognized at both sites barchan and dome dunes are present only in the db while lunette lunette clay dunes are found only in the mp in both locations the large extent of aeolian sand sheets and the predominance of simple and compound parabolic dunes indicates the active role of sparse vegetation cover in the formation of this aeolian system in the db dunes were formed by southwest and west winds while in the mp the aeolian morphologies indicate that the prevalent winds were west and northwest the chronology of the dune deposits is being determined with luminescence tl osl dating and mass spectrometry analysis 14 c ams in this way the aeolian activity and stabilisation stages can be established the latter well marked in the db through soil a horizon development thus the main sand dune formation in the db and the eastern regions of the mp occurred between 13 5 and 7 ka bp during the cold and arid younger dryas episode and the early holocene the clay dunes of the mp accumulated mainly from 29 to 19 ka bp that corresponds with heinrich events he 3 and he 2 and the last glacial maximum however clay dunes were also formed between 13 5 and 7 ka bp in both locations there have been reactivations of some sand deposits in the recent holocene with maximum activity around 5 2 ka bp and 0 5 0 2 ka bp on the other hand three marked stages of stabilisation of the db aeolian system have been established with 14 c ams around 10 2 6 2 and 1 2 ka bp finally the main winds contributing to dune construction were also responsible for the deflation processes with the formation of erosional depressions

thermoluminescence and optically stimulated luminescence dating of spanish dunes abstract the second largest expanse of sand dunes and sand sheets in inland spain is found between the valleys of the rio jucar and the rio guadiana to the south of madrid the dunes in the guadiana valley on the san juan alluvial plain are composed of sands or silty clays the clay dunes are associated with clay saline playas to the south and southwest of the town of alcazar de san juan preserved aeolian landforms indicate a multicyclic origin for the aeolian deposits that overlie upper pleistocene alluvial deposits both the present day and palaeowind directions are dominantly from the west northwest and southwest the results of thermoluminescence and optically stimulated luminescence dating of different samples from these dunes are discussed the dating results exhibit good agreement between the two luminescence methods for most samples the dates obtained span the last glacial interglacial cycle and also indicate late holocene aeolian activity

stabilized dune ridges in northern saskatchewan stabilized dune ridges occurring in northern saskatchewan have previously been identified as variedly as ice crack moraines and longitudinal dunes investigations of their morphological structural and sedimentary attributes reveal that they are indeed of eolian origin but they form a particular group within the parabolic dune association namely the cree lake type dune ridges the ridges occur in association with other types of parabolic dunes and other eolian features such as loess and wind abraded glacial blocks and bedrock outcrops the dunes and the associated eolian features were all formed by southeasterly paleowinds of uniform direction the dune ridges developed from primary parabolic dunes of simple and composite types through the process of dune elongation at the same time exposed rock surfaces were abraded by the wind and loess was deposited downwind from the developing dune fields the southeasterly direction of the paleowinds which is almost directly opposite to the direction of

the quaternary coversands of southwest france detailed stratigraphic analysis and numerical dating osl irsl esr 14c of pleistocene coversands in southwest france enable the construction of a renewed chronostratigraphic framework for sand deposition the chronological data obtained from sandsheet units testify to the development of transgressive dunefields since at least the middle pleistocene mis 10 three main phases of accumulation occurred during the last glacial the oldest one 64 42 ka is associated with wet sandsheet facies histic horizons and zibar type dune fields which reflect deposition in a context strongly influenced by the groundwater table the late pleniglacial 24 14 ka corresponds to the main phase of coversand extension in a drier context silty gley horizons suggest however local interruptions of sand drifting during gs 2 1 lateglacial stabilization of the coversands may not have occurred before gi 1c allerod which was typified by the development of cumulic arenosols these were covered by parabolic dunes during the younger dryas the variations in extent of the emerged continental shelf during the glacial interglacial cycles may explain the uneven geographical distribution of sand deposition through time because of coastline retreat up to 100 km north of 45 n during the lgm lowstand the coversands were unable to reach the northern part of the basin comparison with other european regions highlights stronger affinities of the french record with portugal than with the netherlands and great britain probably because of reduced influence of permafrost

kinetic energy transfer through impact and its role in entrainment by wind of particles from frozen surfaces while extensive aeolian deposits are associated with glaciation little is known of the mechanisms which produced them observation of glaciofluvial sediments in pangnirtung pass n w t indicates that peak deflation occurs in the fall and winter months so that the nature of sediment transport involving frozen surfaces greatly differs from warm environments laboratory experiments indicate that such surfaces are mobilized through abrasion and are most susceptible at low volumetric water content less than 20 and low temperature 20 c stable surfaces have volumetric water contents in excess of 30 and temperatures of 15 c surface stability also increases with decreasing particle size density and possibly transport load collisions with frozen surfaces are relatively elastic with significantly greater kinetic energy transfer to ejected surface grains than observed for loose dry surfaces saltation transport in cold environments could therefore be sustained at lower windspeeds than for dry surfaces provided that some loose particles are available initially but do not accumulate at the surface

lithostratigraphy and geochronology of fills in small playa basins on the southern high plains united states playa basins are small depressions typically 1 5 km 2 on the southern high plains of northwestern texas and eastern new mexico there are about 25 000 playas in the region they lie on the blackwater draw formation pleistocene a widespread eolian deposit and locally on the ogallala formation miocene pliocene understanding the lithostratigraphy and chronostratigraphy of the fill in the basins is important because it should 1 provide clues to the origin and evolution of playas which have been long debated 2 yield a paleoenvironmental record for the region and 3 aid in understanding the history and future of the regional aquifer because playas are the principal source of recharge data from 19 playa basins combined with published data from 4 other basins show that the basin fill is composed of six distinctive facies 1 lacustrine mud 2 lacustrine carbonate 3 lacustrine delta deposits 4 eolian sand and silt 5 eolian loam and 6 accretionary eolian deposits blackwater draw formation mud deposited under ponded conditions is the most common facies and is the surficial deposit on the floors of most playas often producing vertisols the carbonate was precipitated under lacustrine conditions and is another common facies and surface deposit delta deposits are common near the basin margins well sorted layers of eolian sand and silt and poorly sorted eolian loam occur locally above within or below the lacustrine deposits the modern basins in all study areas are locally or completely inset into the blackwater draw formation supporting the interpretation that the basins are at least in part erosional features in larger basins with thicker fills generally coincident with thicker blackwater draw formation the formation interfingers with the lacustrine fill dating is based on radiocarbon ages from the fill in 12 basins and from lunettes adjacent to 5 basins all dated basins were present at the end of the pleistocene and some were present in some form throughout the pleistocene lacustrine mud and other clastic deposits accumulated in the late quaternary and locally much earlier showing that at least some basins contained water throughout the time of human occupation of the region dating of eolian sediments supports other data indicative of aridity and wind deflation in the early and late holocene the lacustrine carbonate is late pleistocene or older and its paleoenvironmental significance is unknown these lithostratigraphic and chronostratigraphic relationships show that some basins have a prolonged history as depressions persisting in more or less the same location as the high plains surface aggraded by eolian addition blackwater draw formation throughout the pleistocene sizes of the basins varied through time as they were encroached upon by the blackwater draw formation enlarged by fluvial lake margin and eolian erosion were filled and reexposed or were buried some basins are newly formed on the high plains surface and have no apparent predecessors the only evidence for subsidence beneath the basins is gently warped fill in the basins on the northern margin of the region known to be affected by salt dissolution in paleozoic bedrock pedogenic carbonates typically are absent from or beneath the basin fill due to focused recharge through the basins playa basins probably have been a ubiquitous component of the high plains landscape through much of the quaternary

surface wind climate during the younger dryas in europe as inferred from aeolian records and model simulations a comparison of well dated and well documented aeolian records from the younger dryas and model simulations executed with an atmospheric general circulation model agcm shows that during this marked cold interval depositional winds in northwestern and central europe came from westerly quadrants two agcm grid cells representing the netherlands and central poland are compared whereas in the netherlands extensive river dunes were formed in poland the younger dryas is considered a phase of remodeling and limited aeolian activity this regional contrast may be explained by differences in the surface wind climate differences in sediment supply by dissimilar river types and differences in the vegetation cover the model simulations show that wind speeds were higher in the netherlands than in central poland due to the proximity of the ocean aeolian landforms indicate that during the younger dryas in the netherlands depositional winds came from the sw to w whereas in central poland w winds dominated model experiments support these observations it is suggested that aeolian processes primarily took place during the winter season

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

conditions favourable for the formation of warm climate aeolian sand sheets aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent sand sheets are ubiquitous to modern warm climate sand seas generally occurring marginal to dune fields although they may exist within the interior of a sand sea or independent of a dune field sand sheet deposits are recognized in ancient aeolian sequences where they may account for significant accumulations of low angle aeolian stratification we suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets a study of six modern sand sheets in north america located at great sand dunes gran desierto dumont algodones padre island and colorado river delta indicates that the factors favourable for sand sheet development are 1 a high water table 2 surface cementation or binding 3 periodic flooding 4 a significant coarse grained sediment population and 5 vegetation these factors are reflected in the nature of stratification and the accessory features of sand sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the triassic dolores and pennsylvanian permian rico formations

isotopic events in the grip ice core a stratotype for the late pleistocene an event stratigraphy for the last termination based on the stratotype of the grip ice core record has been outlined for the north atlantic region it is suggested that such an approach to stratigraphic subdivision may o er a more satisfactory alternative to conventional stratigraphical procedures for those parts of the recent quaternary record that are characterised by rapid and or short term climatic uctuations 1999 elsevier science ltd all rights reserved

last glacial aeolian landforms and deposits in the rhone valley se france spatial distribution and grain size characterization abstract in the rhone valley a north south oriented cenozoic rift in southeast france thick pleistocene loess deposits have been recognized since the beginning of the last century these loess records which are disconnected from the north european loess belt nelb are of significant interest to document the evolution of perimediterranean landscapes and environments during the last glacial to overcome the poor precision of available aeolian distribution maps aeolian deposits were mapped using the topsoil textural database provided by the land use and cover area frame statistical survey project lucas the grain size distribution of aeolian sand and loess was first determined using 116 samples taken from surveyed outcrops then the areas showing a similar grain size composition were extracted from the lucas rasters the resulting map reproduces the conventional maps correctly but suggests a more significant extension of loess in better agreement with the known distribution of outcrops the map shows that the distinctive morphology of the valley dominantly controls the distribution of aeolian deposits the deflation related landforms i e yardangs closed depressions pans and desert pavements are widespread south of narrowings of the rhone valley between latitudes 44 n and 45 n they indicate palaeowinds blowing from the north northwest aeolian sand loessic sand sandy loess and loess deposits successively spread on both sides of the rhone river the loess is characterized by a coarse texture main mode around 60 m strong local thickness 5 m limited extension and abundant bioturbation this preservation results from the persistence of a shrub vegetal cover during the coldest and driest phases of the last glacial that allowed for trapping the saltating and suspended particles close to the alluvial sources

loess and soils in the eastern ebro basin abstract wind blown sandy and silty deposits were formed during the late quaternary in the ne iberian peninsula they are the most significant in the west mediterranean region together with those described in the tagus river basin iberian south subplateau forming small scattered patches across parts of the se ebro depression and sw catalan mediterranean range two major depositional environments are distinguished the first largest outcrop covers the lower ebro reaches on the se border of the ebro depression the prelitoral coastal range and the mora d ebre basin a second outcrop to the north consists of a few patches scattered over a wide amphitheatre surrounding the western tributaries of the segre river from the wind exposed segria platforms to the almenara range in its northernmost part they consist of highly sorted fine sands and silts 1 12 m thick though most typically 3 4 m thick and coarser than typical loess they are highly uniform lack any sedimentary structures and are pale ochre the deposits are calcareous 30 45 caco3 basic to alkaline and with some soluble salts five selected sequences of primary loess namely mas de l alerany tivissa guiamets batea and almenara were studied to ascertain deposit characteristics and soil development all sections show a consistent vertical granulometric variability that may be attributed to wind intensity changes and hinders the recognition of spatial particle size distribution pedogenesis is mostly related to calcium carbonate redistribution which accumulates as nodules large rhizocretions or biogenic calcite secondary gypsum batea and almenara sequences is probably related to primary gypsum blown from the source areas that was redistributed by leaching and precipitation at the bottom of the profiles in a few places mas de l alerany outcrop a fersialitic rubefacted recalcified soil indicates the presence of an older generation of loess while the dominant wnw winds and particle coarseness suggest that the loess originates from nearby alluvial fans and fluvial plains the presence of gypsum and mg anomalies may be evidence of more distant sources of the central ebro depression and ondara corb alluvial fans optical stimulated luminiscence osl ages for the more recent deposits guiamets batea almenara are between 18 and 34 ka while the old mas de l alerany sequence is more than 115 ka these ages indicate loess deposition during the last cold phases of the quaternary and with pedogenesis occuring during warm interglacial periods

origin and morphology of barchan and linear clay dunes in the shuhongtu basin alashan plateau china abstract clay dunes are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed basins in arid and semi arid areas although they are widely distributed aeolian landforms on earth little is known about their development and distribution in asia our field investigations have identified for the first time the occurrence of clay dunes in the alashan plateau north china the clay dunes occur in three isolated lowland areas of the suhongtu sht basin and their morphologies barchans hooked barchans asymmetrical barchans and linear or seif dunes differ substantially from those of the well studied clay dunes in australia africa and north america these differences could be mainly attributed to the asymmetrical bimodal wind regime prolonged drought and sediment physical properties which indicate that dunes of any type can be formed in sand silt or clay based on the known evolution of the sht paleo lake basin and regional climate change we infer that the landscape of modern clay dunes in the desert of the alashan plateau does not predate mis 5 and probably formed during the late holocene analyses of grain size distributions and the contents of trace and rare earth elements combined with geomorphological characteristics indicate that the source sediments of the clay dunes are mainly local cretaceous tertiary and quaternary red fluvial lacustrine mudstone and sediments while the ultimate source is the weathered and denuded products of granitoids of the east altay mountains comparison of the morphology and alignment of the clay dunes with the prevailing wind pattern tends to support tsoar s 1984 model of the transition in dune shape from barchans to seif or linear dunes during 2003 2013 the seif or linear dunes of the sht basin migrated laterally and elongated northeastward at rates of about 2 4 m yr and 16 20 m yr respectively