sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

desert pavement coated surfaces in extreme deserts present the longest lived landforms on earth all exposed rocks on earth s surface experience erosion the fastest rates are documented in rapidly uplifted monsoonal mountain ranges and the slowest occur in extreme cold or warm deserts millennial submeterscale erosion may be approached only in the latter the oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings thus these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape while the surrounding landscape may erode faster and be younger we present erosion rate and exposure age data from the paran plains a typical environment in the near east where vast abandoned alluvial surfaces 10 2 10 4 km 2 are covered by well developed desert pavements these surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m y major factors that reduce erosion converge in these regions extreme hyperaridity tectonic stability fl at and horizontal surfaces i e no relief and effective surface armoring by a clast mosaic of highly resistant lithology the 10 be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern negev israel representing the sahara arabia deserts indicate simple exposure ages of 1 5 1 8 ma or correspond to maximum erosion rates of 0 25 0 3 m m y 1 the 36

total suspended particulate matter emissions at high friction velocities from desert landforms 1 most wind erosion studies that characterize dust emission potential measure particulate matter smaller than 10 mm pm10 for air quality purposes or atmospheric modeling because the pm10 size fraction is only a portion of the total range of fine grained particles potentially emitted from desert landforms we modified the miniature portable in situ wind erosion lab pi swerl by adding a new instrument to measure total suspended particulate matter tsp the modified pi swerl is capable of measuring tsp with diameters 500 mm emitted from highly erodible surfaces at friction velocities up to 1 28 m s 1 undisturbed and artificially disturbed surfaces of six common landforms in the negev desert of israel were studied to evaluate the utility of tsp measurements these landforms include alluvial fans and plains armored by desert pavements loessial soils with silt rich surficial crusts fluvial loess with biological crusts and active sand dunes the landforms differ in character and surface age thereby exhibiting a wide range of surface covers soil properties and soil strengths our results indicate that the magnitude of tsp emission is primarily controlled by geomorphic setting and surface characteristics tsp and pm10 concentrations measured from dust rich loessial soils were significantly correlated and tsp emission was best predicted at all sites using pm10 content and bearing capacity our results demonstrate that further research is needed to determine correction factors for friction velocities related to erodible anisotropic surface roughness elements and that the modified pi swerl is a promising tool to quantify total potential emission flux from desert landforms

new insight into pedogenic processes in extremely arid environments and their paleoclimatic implications the negev desert israel abstract stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern arava valley dead sea rift indicate the existence of a calcic soil developed 50 100 cm beneath the channel surfaces this anomalous calcic soil does not fall within the categories of any standard soil or paleosol definition and thus has been termed fluvial pedogenic unit fpu the fpu occurs at the lower limit of the contemporary scour and fill processes in the aerated zone and it defines the maximum scour and fill during floods the fpu is also found in late pleistocene and holocene terraces termed paleo fpu indicating that the hydrological regime of past floods was similar to the present one the formation of a calcic fpu in this unique environmental setting is associated with the cumulative influence of persistent differences in water availability to various parts of the channel before and during flood events the carbonate accumulation results from low recurrence of flood events relatively limited moisture amounts and almost no involvement of vegetation in its formation the isotopic analyses of calcic crusts in the fpu and in the paleo fpu indicate that arid climatic conditions prevailed during their formation this indicates that the flood regime under arid climatic conditions characterized most of the negev desert during the late pleistocene and the holocene however a clear difference in the 18 o and the 13 c values was detected between the active channels and the terraces this difference suggests a change in the rainwater composition rather than changes of temperature or amounts of rainfall

geochemical isotopic and mineralogical constraints on atmospheric deposition in the hyper arid atacama desert chile abstract modern atmospheric deposition across the atacama was collected by an array of dust traps that stretched from the pacific coast to the andean altiplano and the material was analyzed for its geochemical mass and isotopic composition the coastal trap had the second highest insoluble mineral particle and highest soluble salt deposition rates due to significant inputs from the morro mejillones range and the pacific ocean respectively the andean trap had the highest insoluble mineral particle deposition owing to transport of weathered material but the lowest deposition rate of soluble salts due to its distance from the ocean and anthropogenic sources the removal of oceanic material was effective by the coastal mountains while the westward transport of the andean material was determined to be minimal the atmospheric deposition in the inland traps was mainly from the local entrainment of surface material inland anthropogenic emissions and transport of marine aerosols the nitrate isotopes 15 n and 17 o suggested that no x sources and no 3 chemistry shifted along the west east transect and were greatly impacted by anthropogenic emissions with soil no 3 being a minor source of deposited nitrogen

quaternary scale evolution of sequences of talus flatirons in the hyperarid negev article i nfo talus flatiron sequences are ubiquitous landforms in arid and semiarid regions characterized by horizontal erodible rocks capped by more resistant rocks alternating phases of deposition and erosion lead to the formation of generations of talus flatirons in which ancient ones are located farther from the source cliff the existing conceptual model of this systematic spatial distribution of talus flatirons is related to glacial interglacial climatic cycles and to relatively high rates of cliff retreat three groups of talus flatirons were analyzed in the northeastern hyperarid negev desert the analyses include mapping age determination using optically stimulated luminescence and cosmogenic nuclide exposure dating electrical resistivity tomography and sedimentological and soil analyses all talus flatirons contain gypsic salic soil catena typical to hyperarid climate b80 mm yr 1 no pedogenic indicators of past wetter environments such as buried calcic soil 10 be exposure ages of the talus flatirons suggest that they were deposited during the middle pleistocene 610 ka and 170 ka for the oldest and intermediate aged talus flatiron groups respectively these ages combined with the present location of the talus flatirons relative to the source cliff yield retreat rates of 6 12 and 200 m ma 1 for the bedrock cliff and talus flatiron apex respectively and in opposite directions our results show that a climatic changes at glacial interglacial time scales are not the main controls over the formation of talus flatiron generation and b that significant cliff retreat is not the main cause for the systematic spatial distribution of talus flatiron generations relative to the cliff our results indicate that the process of talus flatiron formation in the negev desert must be associated with the balance between production deposition and removal of clasts under hyperarid conditions with only a minor cliff retreat

the effect of dust deposition on the soils of the land of israel abstract loess and aeolian dust affected soil formation to different degrees in most parts of the land of israel in the arid desert the loess was re eroded from slopes and sedimented as fluvial loess in along the valleys by flood water in areas with slight precipitation loess remains on slopes sedimentation rates are slower and loessial serosems are formed in the mildly arid areas in the northern negev the loess covers most of the landscape and occurs in thick sequences intercalated with several superimposed strongly developed loessial brown soils sedimentary and weathering processes occurred simultaneously and sediment palaeosols profiles up to 12 m thick were formed in areas further away from the desert aeolian deposition decreased as a result loessial brown soils grade into dark brown grumic soils and grumusols aeolian dust input also affected soils of the sand dunes of the coastal plain and in the terra rossa soils of the mountainous region

effect of rock fragment eccentricity on eolian deposition of atmospheric dust abstract the effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel eccentricity was defined as the ratioa b wherea is the longest andb the intermediate axis of the rock fragments the effect of eccentricity on the deposition of dust on the pebbles on the deposition of dust between and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately and this for different values of pebble size pebble flattening cover density and wind speed the more pebbles are elongated the larger dust deposition on them will be this effect is more pronounced as pebbles become larger as they become less flattened and as wind speed increases but no correlation is observed with cover density it also holds that the more pebbles are elongated the less dust settles between and underneath them this effect is more pronounced as pebbles become smaller and cover density becomes larger but there is no relationship with pebble flattening whether or not there is a relationship with wind speed is unclear pebble eccentricity indirectly influences total dust deposition on a pebble field since it determines whether or not and to what extent total dust deposition will be a function of pebble size for circular pebbles total dust deposition is independent of pebble size but once pebbles become elongated total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles it was also demonstrated that the more pebbles are elongated the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation plays a primary role in the deposition of dust on a rock fragment field since it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles highly elongated pebbles oriented parallel to the wind catch much more dust also per unit surface than circular pebbles the surface of which is largely located in a zone of very low deposition dust deposition density on highly elongated pebbles normal to the wind on the contrary is equal to dust deposition on circular pebbles it should be noted that all data in this study refer to initial dust deposition not accumulation since only wind velocities below the dust deflation threshold were tested

spatial soil variability in the cajon pass chronosequence implications for the use of soils as a geochronological tool abstract spatial variation of soil properties on a single geomorphic surface has a significant influence on surface correlations and age determinations made on the basis of soil properties few chronosequence studies have been based on a sufficient number of soils to evaluate the influence of soil variability we described and evaluate 35 soils on four terrace surfaces which constitute part of a previously described well dated soil chronosequence in cajon pass in southern california soils were described on both bar and swale sites removed from the influence of deposition adjacent slopes the influence of eolian silt on the rate of pedogenesis in cajon pass indicates that this sequence of soils cannot be considered a chronosequence in the strict sense of the term furthermore the evidence for a pedogenic threshold in these soils indicates that the soils do not develop monotonically with time and that soil development cannot be defined by a continuous univariant chronofunction the discrete nature of the data from a chronosequence and the complex nature of soil development are better analyzed by multivariate statistical procedures systematic variation in soil properties between soils from bar sites and soils from swale sites is attributed to geomorphic processes which affect either the rate or duration of eolian dust accumulation soils from bar sites were less variable and generally less strongly developed that soils from swale sites from the same surface the degree of variation of soil properties determined for a given landscape position on a surface is sufficient to raise questions concerning the usefulness of chronofunctions for determining the nature of time dependent pedogenic changes and for providing numerical age determinations multivariate statistical methods were used to differentiate among soils developed on three surfaces which differ in age by only 1500 years

the micromorphology of gypsum and halite in reg soils the negev desert israel gypsum and halite are the most common salts in reg soils developed on alluvial parent material under extremely arid conditions in the negev desert israel the aim of this paper is to document the changes in the micromorphology of these salts at different stages of reg soil development on two alluvial fan chronosequences the micromorphological analyses included thin section observations and scanning electron microscope and electron microprobe analyses in this arid soil environment gypsum and halite possess a variety of crystal forms which may change with depth in a single profile and or between profiles of different ages the variety of crystal forms results from changes in the microenvironmental conditions that occur in desert reg soils over time poikilitic lenticular gypsum is found in all reg soils and is distributed throughout the profiles the conditions needed for such crystals to form are high ionic impurities and deposition in a void system where space is not limiting microcrystalline alabastrine gypsum is only found in mature reg soils and is crystallized when the profile has high amounts of fine material and a well developed desert pavement in a well developed reg soil profile indicators such as a well developed desert pavement and high amounts of fine earth limit the leaching depth and cause gypsum deposition from supersaturated soil solutions under high evaporation rates close to the surface prismatic and fibrous gypsum are less common low amounts of prismatic gypsum are found in young and mature soils while fibrous gypsum is found only in mature soils in re cemented shattered gravel the halite crystal form is mainly cubic with low amounts of host material incorporated into the crystal it occurs predominantly in mature reg soil profiles through the crystallization from supersaturated soil solutions at the depth of maximum water penetration although the alabastrine prismatic and fibrous gypsum and cubic halite are deposited in a displacive manner no correlation was found between their occurrence and the distribution of shattered gravel in the soil profile

synoptic conditions of fine particle transport to the last interglacial red sea dead sea from nd sr compositions of sediment cores abstract the sediments deposited at the depocenter of the dead sea comprise high resolution archive of hydrological changes in the lake s watershed and record the desert dust transport to the region this paper reconstructs the dust transport to the region during the termination of glacial marine isotope stage 6 mis 6 135 129 ka and the last interglacial peak period mis5e 129 116 ka we use chemical and nd and sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the dead sea the data is integrated with data achieved from cores drilled at the floor of the red sea thus forming a red sea dead sea transect extending from the desert belt to the mediterranean climate zone the dead sea accumulated flood sediments derived from three regional surface cover types settled desert dust mountain loess soils and loess soils filling valleys in the dead sea watershed termed here valley loess the valley loess shows a distinct 87sr 86sr ratio of 0 7081 1 inherited from dissolved detrital calcites that originate from dried waterbodies in the sahara and are transported with the dust to the entire transect our hydro climate and synoptic conditions reconstruction illustrates the following history during glacial period mis6 mediterranean cyclones governed the transport of saharan dust and rains to the dead sea watershed driving the development of both mountain soils and valley loess then at heinrich event 11 dry western winds blew saharan dust over the entire red sea dead sea transect marking latitudinal expansion of the desert belt later when global sea level rose the dead sea watershed went through extreme aridity the lake retreated depositing salt and accumulating fine detritus of the valley loess during peak interglacial mis 5e enhanced flooding activity flushed the mountain soils and fine detritus from all around the dead sea and red sea marking a significant contraction of the desert belt at the end of mis 5e the effect of the regional precipitation diminished and the dead sea and red sea areas re entered sever arid conditions with extensive salt deposition at the dead sea

revealing sediment sources mixing and transport during erosional crater evolution in the hyperarid negev desert israel abstract to better understand the sedimentary history of the erosional crater of makhtesh hazera in the hyper arid negev desert of southern israel we have measured concentrations of in situ 10 be in alluvial sediments from the active drainage system and from abandoned alluvial terraces and dated them using optically stimulated luminescence osl these sedimentary sequences suggest changes in the drainage system behavior over time and show a periodic pattern in which periods of sediment aggradation alternate with periods of degradation through incision and erosion in alluvial terrace sediments 10 be concentrations were combined with osl ages to gain insight of the temporal framework of sediment deposition and shed light on the process of sediment storage osl and simple 10 be exposure ages of terrace sediments give deposition ages between 340 ka to 50 ka at which time the youngest alluvial terrace was incised deposition was interrupted twice at 300 ka and 160 ka when periods of rapid incision caused the abandonment of the active fluvial surface and the stabilization of a younger and lower fluvial surface in the active drainage system 10 be concentrations suggest several possible quartz sources of which the lower cretaceous sandstone bedrock exposed at the base of the cliff enclosing the makhtesh is the most dominant the results suggest that sediment eroding form these cliffs are conveyed through the active alluvial channels without significant sediment contribution from alluvial terraces or from eroded bedrock exposed within the makhtesh in contrast to our measurements in the active drainage system 10 be concentrations in alluvial terrace sediments record significant storage within the makhtesh we suggest that the geometry of the makhtesh mainly the disproportion between the size of the makhtesh and its narrow outlet leads to significant accumulation of sediment within the makhtesh episodic breaching of the barrier is followed by rapid and short lived incision into the stored sediment the long residence time of sediment within the makhtesh results in high measured 10 be concentrations at the end of each of these short incision episodes when channels are already carved into the alluvial sediment and terraces are formed the channels only convey sediment directly eroded from the bounding cliff of the makhtesh a situation presently observed

runoff generation rill erosion and time scales for hyper arid abandoned alluvial surfaces the negev desert israel abstract sequences of abandoned alluvial surfaces are ubiquitous desert landscapes considered as responding to quaternary timescale climatic fluctuations and tectonic activity the post depositional evolution surficial properties of these alluvial surfaces change with time a surface clast breakdown and development of desert pavement b dust and salts accumulation c reg gravelly desert soil evolution in the present study we focus on the hydrological response and the resulting erosional processes to these changes in surface properties over a sequence of late pleistocene holocene abandoned alluvial surfaces in nahal evrona catchment at the hyperarid southern arava valley north of the towns of eilat israel and aqaba jordan the methods used in the study are a simulated rainfall experiments to determine hydrological characteristics b terrestrial laser scanning tls to determine surface roughness c osl dating for the chronology d surface and soil descriptions and measurements and grain size analyses to determine texture of the uppermost av horizon of the reg soil e gis analysis of the new drainage network developing over the older abandoned alluvial surfaces the results show that with time roughness decreases infiltration decreases to about 8 9 relative to present rates point runoff generation increases 5 fold and as a result rill and gully erosion initiated finally leading to the destruction of the alluvial surface under the current hyper arid climate in the southern negev desert between 30 and 50 ka of surface weathering and soil development are required before significant runoff is generated and 100 ka until effective runoff initiates rill and gully erosion over these abandoned alluvial surfaces this local source runoff and gully erosion essentially destroys the alluvial surfaces in the southern arava valley within a period of 400 500 ka roughness extracted from spaceborne lidar scanning which is inversely related to surface age directly reduces friction and resistance to runoff can provide an estimate for the hydrological characteristics of the surfaces this can support applications such as rainfall runoff models risk assessment etc

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

rock type and dust influx control accretionary soil development on hillslopes in the sandia mountains new mexico usa lower slopes of the sandia mountains are characterized by granitic corestone topography and weathering limited slopes with thin grusy colluvium and weakly developed soils in contrast thick soils with illuvial clay and pedogenic carbonate have developed below aplite outcrops aplite is resistant to chemical decomposition but physically weathers to blocky clasts that enhance surface roughness and erosional resistance of colluvium promoting accumulation of eolian fines thick b horizons on aplite slopes indicate limited erosion and prolonged periods of stability and soil development accretion of eolian material limits runoff and prevents attainment of a steady state balance between soil production and downslope transport

effect of rock fragments on eolian deposition of atmospheric dust abstract the effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel four parameters were studied pebble size pebble flattening cover density and wind speed the effect of these parameters on the deposition of dust on the pebbles on the deposition of dust bewween and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately deposition on the pebbles increased with pebble size pebble flattening and wind speed deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening but there was no consistent relationship with pebble size total dust deposition was not influenced by pebble size pebble flattening and cover density but it increased linearly with wind speed it was also demonstrated that the larger and the flatter the pebbles and the higher cover density the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field as it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles it should be noted that all data in this study refer to dust deposition not accumulation since only wind velocities below the dust deflation threshold were used

desert pavement development and landscape stability on the eastern libyan plateau egypt abstract desert pavement surfaces of the eastern libyan plateau in central egypt represent a stable landscape preserving middle and upper paleolithic artifacts detailed measurements of pavement clasts indicate significant variability in clast size density lithology and orientation between pavements but no spatial relationship among any of these pavement variables over the study area pavement characteristics are unrelated to local geomorphic features including slope gradient and aspect suggesting a desert pavement surface that has developed without significant influence from transporting mechanisms such as overland flow and slope failure meridional vertical cracks in surface clasts implicate thermal stresses due to diurnal solar variation as a mechanical weathering process whereas the presence of a clast free silty layer within all soil profiles indicates that these are accretionary pavement surfaces that have grown upward over time the desert pavement in this region has likely developed in situ through mechanical breakdown of surface clasts and desert pedogenesis indicating long term stability for this region and minimal taphonomic effects on artifacts 2 cm in diameter deposited on this surface over the last ca 100 ka

effect of rock fragment embedding on the aeolian deposition of dust on stone covered surfaces many stone covered surfaces on earth are subject to aeolian deposition of atmospheric dust this study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or inversely become more concentrated on the surface experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles the following parameters were measured dust deposition on the pebbles dust deposition between and underneath pebbles total dust deposition pebbles inter pebble space and the fraction of total deposition of dust caught by the pebbles alone the absolute amount of dust deposition and the dust deposition density dust deposition per unit surface were studied for each parameter the effects exerted by pebble size pebble flattening pebble elongation and wind speed were also investigated dust patterns on and around pebbles were also studied via flow visualization the absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded dust deposition density on pebbles on the other hand increases with embedding the more pebbles become embedded in the soil the more efficient the process of dust deposition on pebbles becomes dust deposition between and underneath pebbles increases with pebble embedding dust deposition density between and underneath pebbles is maximum at 50 per cent embedding showing that in this area dust deposition is most efficient when pebbles are halfway embedded total deposition slightly decreases the more pebbles become embedded but total dust deposition density increases with embedding aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone covered surfaces the more pebbles protrude above the soil the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones flow separation bubbles and shelter areas for the dust all these effects diminish as pebbles become more embedded in the soil however perturbations in dust patterns remain visible until pebbles have disappeared entirely

red sedimentary units as indicators of early pleistocene tectonic activity in the southern negev desert israel abstract alluvial units termed red units accumulated along the western margin of the dead sea rift dsr valley southern negev desert israel in the early pleistocene these sedimentary units consist of coarse to fine grained alluvium of local origin which contain calcic paleosols the sediments of the red units accumulated in stream valleys and newly forming semi closed local tectonic basins during a tectonic phase that deformed the western margin of the dsr as a result of this deformation the pliocene northward flowing regional drainage system of the southern negev disintegrated to the present northeast flowing ephemeral drainage systems of nahal zihor nahal hiyyon and nahal paran all of them draining to the arava valley in the dsr this change was induced by two deformation episodes 1 reactivation of the zihor and the milhan faults two major northeast trending tectonic lines and 2 east and northeast tilting of the entire region during upwarp arching of the central negev the paleosols of the red units are characterized by pedogenic features such as rhizoconcretions and bk horizons the paleosols developed in the alluvial sediments that were deposited and preserved in local small structural basins along the main fault lines and in reversed or abandoned westward flowing pliocene stream valleys formation of paleosols was initiated in the stream valleys when they attained a near horizontal gradient due to gradual eastward directed regional tilting followed by low rates of deposition the sections of the red units in the pliocene valleys were incised due to continuing tilting which completely reversed the primary westward gradient of the valleys and they were incised by new east and northeast flowing streams the red units have paleoclimatic implications since the middle pleistocene the southern negev has been characterized by gypsic and salic soils typical of an extremely arid climate while the calcic soils detected in the red units point to a semi arid climate this indicates a gradual transition from more humid conditions in the early pleistocene to the present extreme aridity therefore the red units reflect a distinct tectonic and climatic regime and can serve as regional morphostratigraphic marker of early pleistocene age in this paper we used this marker to reconstruct the tectonic deformation that established the present configuration of the southern negev terrain

late holocene dust accumulation within the ancient town of marea coastal zone of the south mediterranean sea n egypt abstract the ruins of the marea ancient town are located on the southern shore of maryut lake ancient mareotis 45 km to the southwest of alexandria egypt marea was a very important trade religious and agricultural centre in the 5th 7th century a d the area occupied by a town in the past has diversified relief local hills are built of sandstones constituted by calcified dunes the hills are separated by flat depressions of irregular shape the uppermost layer in the depressions covering loam and sand sediments is made up of structureless aeolian dust of 0 6 1 2 m thickness the following analyses of the sediments were conducted granulometric composition the mineralogical composition of samples the loss on ignition the total organic carbon toc organic matter om and calcium carbonate caco3 clay minerals and geochemistry results of osl dating indicate that the filling of the depressions with silt deposits started probably about 2450 years ago and that it is correlated with dust deposition the rate of the dust accumulation was about 0 49 mm year however diversified humus content in the deposits suggests that it was not a permanent process the accumulation took place during intensive dust storms the sediments in the depressions are fine silt and clay with uni and bi modal particle size distribution likely caused by both the local and the regional origin of the material most dust accumulated within the ancient town of marea originated from the border between sahel and sahara local and even regional sources of material were of lower importance geochemical ratios mg ca fe mn and na k distinguished in the deposits of the depressions show that the beginning of the dust accumulation took place during environmental conditions more humid than the contemporary ones that indicates a slight increase in the humidity of climate dated to ca 10th 12th century a d followed by its significant drying initiated ca 15th 16th century a d in addition results of analysis of trace elements suggest that already in the 5th century bc the town of marea or its closest vicinity may have been the site of development of industrial activity much earlier than the age of the oldest artefacts found within the town

stages and rate of the gravel shattering process by salts in desert reg soils abstract gravel shattering by salts is a common process in gravelly young to mature desert reg soils the shattered gravel is found on the surface and in the b and c horizons down to a maximum depth of 50 cm field studies on the process of salt weathering in deserts are scarce therefore the objectives of this study are to present the stages of development of the gravel shattering process by salts in desert reg soils and to discuss factors influencing the rate of development under natural conditions prevailing in the negev desert the studied reg soils were developed on two alluvial fan chronosequences in the negev desert the fan of nahal ze elim and the fan of nahal shehoret the development of the shattering process can be divided into five stages a e based on chemical physical and micromorphological features of the reg soils stages a d very young yo young reg soils represent the early holocene to the present some 14 000 years salinity values are between 0 27 16 mmho cm and the percentage of the shattered gravel is between 20 and 70 the shattered gravel however still maintains its original shape stage e mature reg soil represents the middle pleistocene to early holocene or 500 000 years salinity values at this stage reach 62 mmho cm although part of the gravel does not keep its original shape and starts to disperse in the profile the percentage of shattered gravel is only 75 80 it was found that the process of salt shattering in reg soils does not depend on concentrations or mineralogy of the salts but on the micro environmental conditions of the soil profile the process requires extreme and rapid variations of temperatures and moisture conditions such as found close to the soil surface to cause salt crystallization in a confined system with time the sealing of the soil surface through the development of desert pavement and a gravel free b horizon results in a change in the soil micro environment this change impedes the process irrespective of the amounts concentrations and types of salt minerals which exist in the profile the fact that in extreme arid regions the gravel shattering process develops primarily close to the reg soil surface suggests that it can be used to identify buried reg soils and to reconstruct climatic and micro environmental conditions of paleosols

hydrologic properties and structure of the mozumi fault central japan 1 analyses of rocks from the active fault survey tunnel afst provides insight into the structure and hydrogeology of the northeast trending mozumi sukenobu fault an active strike slip fault with 125 to 500 m of right lateral slip in central japan interlayered regions of sub vertical permeability zones formed by cataclasis and slip on clay rich foliated zones core samples range from 10 19 m2 to almost 10 13 m2 cfc analyses of waters from the fault zone show that water entering the tunnel is 27 36 years old yielding a bulk fault permeability of 10 14 to 10 15 m2 the data support a fault zone model of a fluid saturated low velocity zone with a sharp velocity contrasting with the protolith pore fluid pressures could build and dissipate in isolated high permeability pods 10 s 100 s m in dimension

the behavior of the electric field within the substorm current wedge we use the goose bay hf radar to investigate the behavior of the electric field within the substorm current wedge for a small substorm 200 nt which occurred on february 15 1992 mid and high latitude magnetometer data helped to locate the radar backscatter with respect to the longitudes and latitudes of the substorm currents as well as describing the time development of the substorm itself velocities in the portion of the field of view of the goose bay hf radar closest to the frederikshab magnetometer in greenland were compared directly with the ionospheric currents inferred from the magnetometer during the early growth phase the plasma flow and current gradually increased in response to the dp2 electric field and are related by an estimated effective height integrated conductivity 1 s the plasma flow and current continued to increase in the same proportion i e was still 1 s as the electrojet intensified in stages during the late growth early expansion phase in this interval there was probably a pseudo breakup which established a longitudinally and latitudinally narrow substorm current wedge the increased plasma flow and current measured at frederikshab are attributed to the superposition of the pseudo breakup current wedge electric field on the preexisting dp2 electric field evidently the enhanced ionospheric conductivity strip usually associated with the current wedge is initially located equatorward of frederikshab since its effect is not apparent at that location during the expansion phase proper a clearly resolved current wedge expanded so that the radar backscatter lay within it the expansion led to an increased current over frederikshab but a slightly suppressed plasma flow related by an increased 4 s the effect of the precipitation induced conductivity strip now apparent it is suggested that near earth current disruption may play a significant role in the onset of this particular substorm which occurred during a nonstorm time interval

quaternary evolution of a hyperarid drainage under climatic fluctuations and rift margin base level fall ne negev israel abstract the long term bedrock incision of streams in the northeastern negev has been dictated since the early pliocene by the subsidence of the dead sea basin however this incision is accompanied by very long intervals of sediment aggradation here we document the quaternary scale fluvial response to changing base level lithology structure and climate along the hyperarid nahal zafit ne negev the oldest 1 2 ma alluvial remnants point to a widespread beveled bedrock pediment at the base of the hazera anticline this pediment like other stream pediment anticline relationships in the region provides the baseline framework into which nahal zafit incises during the early to middle pleistocene this pediment was the base level for all streams emerging out of the anticlines the tectonic subsidence of the regional base level at the rift margin farther downstream has caused incision and upstream migration of bedrock knickpoints triggering the development of a wide incised valley in the mazar syncline adjacent to the hazera anticline since 330 ka fluvial terraces landslides and taluses record intervals of basin wide fluvial deposition under prevailing hyperarid to arid climate despite the general arid climate prolonged fluvial deposition intervals occurred at ca 330 265 230 125 and 110 20 ka rapid and quite short duration bedrock incision occurred in between these much longer intervals of aggradation in addition to the proposed climatic imprint on fluvial aggradation incision cycles and the first order base level control of the rift margin fault the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the quaternary evolution of the ne negev watersheds

the role of rare rainstorms in the formation of calcic soil horizons on alluvial surfaces in extreme deserts abstract soils in similar geomorphic settings in hyperarid deserts 1 should have similar characteristics because a negative moisture balance controls their development however reg soils in the hyperarid southern negev and namib deserts are distinctly different soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics annual rainfall amount can be similar 15 30 mm but storm duration can drastically alter reg soil properties in deserts the cooler fall winter and dry hot summers of the southern negev desert with a predominance brief 1 day rainstorms result in gypsic saline soils without any calcic soil horizon although the namib desert receives only 50 60 of the southern negev annual rainfall its rainstorm duration is commonly 2 4 days this improves leaching of the top soil under even lower annual rainfall amount and results in weeks long grass cover the long term cumulative effect of these rare rain grass relationships produces a calcic gypsic saline soil the development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil moisture regime in deserts and has important implications for the use of key desert soil properties as proxies in paleoclimatology

the role of the nile in initiating a massive dust influx to the negev late in the middle pleistocene the late middle pleistocene initiation of loess accretion in the negev desert israel resulted from a chain of events starting with the exposure of shallow offshore nile delta sands beginning 180 ka during a period of glacially lowered eustatic sea level this exposure allowed the formation of the dunes of the sinai negev erg and the eastward movement of the dunes under the gusty glacial time winds in northern sinai this eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess we postulate that the absence of earlier negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation we based our interpretation on analyses of two long term natural dust traps and the association of coarse quartz silt production with the advancing quartz rich dunes over this carbonate terrain although the nile delta is considered an early to middle pleistocene feature and therefore could have been the source of sand throughout the quaternary it attained the shallow depth range of glacial interglacial sea level changes only during late marine oxygen isotope stage 7 to early stage 6 allowing its wide exposure in quaternary times prior to erg formation negev dust was finer composed of silt and clays derived from distal sources in the sahara and arabian deserts

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

estimating the ages of fault scarps in the arava israel abstract systematic age estimations for the numerous fault scarps that rupture the alluvial fans in the southern arava valley israel are rare or nonexistent here we estimate the morphologic ages of several of these faults by the fault scarp degradation method and show that the ages agree well with ages estimated by the independent earlier soil geomorphic studies the values we use for the coefficient of diffusion for the fault scarp degradation process are calibrated by a few numerical ages these ages were determined by the infrared stimulated luminescence irsl method on one of the fault scarps and are the only numerical ages in the region the morphologic ages are all in a correct stratigraphic order and in agreement with field stratigraphic relationships determined by earlier studies they indicate that the studied fault scarps range in age from the latest pleistocene to very recent times the most recent fault scarps which were analyzed are less than 2000 years old and perhaps much younger they indicate that at least two earthquakes with magnitude 6 5 have affected southern israel and jordan during that period it is emphasized that so far we have studied only a limited number of fault scarps and therefore the number of large earthquakes during the last one to two millennia is a minimum

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

raised channel systems as indicators of palaeohydrologic change a case study from oman abstract the aim of this paper is to determine the extent to which raised channel systems may be used as indicators of long term paleohydrologic change and hence of broader paleoenvironmental changes in arid areas during the cenozoic the paper reviews the paleohydrologic significance of former drainage systems in arid areas and demonstrates the application of paleohydrologic methods to the analysis of the long term evolution of a complex series of exhumed multistorey raised channel systems in interior oman the paper discusses the range of possible autocyclic and allocyclic controls on changes in channel behaviour through time as a means of establishing the paleoenvironmental significance of observed changes in paleochannel pattern morphology sedimentology and stability the paper identifies some of the major allocyclic controls including climatic changes and particularly the seasonality magnitude frequency and distribution of rainfall events during the cenozoic together with the degree of continentality and hence the strength and persistence of arid wind systems base level changes due to eustatic fluctuations and or tectonic activity may also act to control long term patterns of aggradation followed by large scale landscaping lowering however long term fan ageing associated with progressive aggradation and steepening of paleochannel systems may also eventually lead to fanhead trenching independent of any external controls in addition progressive expansion of the drainage network and resulting river capture can lead to marked increases in water and sediment supplies to the fluvial system the paper also emphasizes the difficulties involved both in differentiating the wide range of possible controls on paleohydrologic response and also in developing an accurate and precise chronology for desert paleodrainage systems and in their correlation with non fluvial sedimentological sequences the raised channel systems of interior oman consist of heavily desert varnished chert and or ophiolite rich gravels dating from some time during the plio pleistocene period the paleochannels from sinuous gravel ridges rising the observed changes have resulted from a complex combination of both internally and externally generated environmental changes during the cenozoic progressive extension of the drainage network on to the ophiolite massif of the mountain source area resulted in river capture and a concomitant increase both in paleodischarges and in supplies of ophiolitic sediments to the paleodrainage system the early sinuous channels may have developed under a humid to sub humid climate in which perennial or seasonal flows allowed the distinct meander paleochannels to form ephemeral flows characterized by flash flood regimes were probably associated with the later distributary systems which may reflect semi arid to arid climatic conditions the large scale deflation of the interfluve sediments which resulted in the eventual exhumation of the cemented gravel capped multistorey paleochannel sequence is also likely to have occurred during periods of marked continentality probably during periods of low sea level associated with the quaternary glaciations

indicators of faulting events and periods of quiescence in desert alluvial fans the main objective of the present paper is to present an integrated approach to the study of faulting stages in coarse alluvial deposits the study site is the alluvial fan of nahal shehoret presently under an extremely arid regime the exposure of fault scarps on the fan surfaces enables the identification of several geomorphic indicators employed in analysing and separating faulting events and periods of quiescence a the nature of fault scarp topography b soil catenary development on fault scarps c buried paleosols in alluvial deposits d colluvial bodies e rotated clasts along fault planes these indicators enable us to determine at all sites studied the total amount of displacement to separate faulting events and the amount of their displacement per event and to evaluate scarp stability and the duration of periods of tectonic quiescence

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

late pleistocene aeolian and fluvial interactions in the development of the nizzana dune field negev desert israel the interdunal areas in the nizzana linear sand dune field contain both sandy and silty sediments a series of trenches was excavated across the interdunal corridor exposing stacked sequences of silty and sandy units which are locally restricted to palaeodepressions the silty units contain fining upward sequences and are interpreted as overbank deposits from the nahal nizzana thermoluminescence dating and identification of buried palaeosols indicates that the silt and clay layers were deposited over a period of several thousands of years in the late pleistocene the sands between the silt layers have been fluvially reworked and are not primary aeolian deposits the stacked sequences of fluvial deposits indicate that the palaeodepressions persisted in the landscape for a significant time attesting to long term stability of the interdunal areas it also suggests that the linear dunes themselves have not moved laterally during this time despite climatic changes and devegetation since the end of the late pleistocene the nahal nizzana has downcut and overbank deposition no longer occurs within the interdunal corridors the playa deposits today are positive relief features indicating that topographic inversion has occurred and that the interdunal areas are geomorphically active

late quaternary dune incursions in the southern levant archaeology chronology and palaeoenvironments abstract in this paper the geomorphic history of aeolian sand of western negev and northern sinai is summarized on the bases of archaeological data and rediocarbon dating aeolian sands and sand dunes are associated with epipalaeolithic sites 18 000 10 000 bp and they lie on loess reworked by fluvial transportation that includes upper palaeolithic sites 30 000 20 000 bp the deposition of the aeolian sand therefore slightly predates the last glacial maximum of the late pleistocene isotopic stage 2 the source of the sand has been identified as the nile delta which was exposed to a wider extent than present due to sea level drop the dune incursion from west to east was gradual and time transgressive but relatively rapid and was induced by hyperarid climatic conditions

large floods during late oxygen isotope stage 3 southern negev desert israel abstract slackwater deposits were found in a cave in the nahal netafim catchment 35 km 2 near the head of the gulf of aqaba in the southern negev israel the sedimentological record includes 27 large paleofloods dated by infrared stimulated luminescence to 33 000 29 000 years ago the scatter of the ages and their large uncertainties prevented an assessment of the exact duration of the record and the specific timing of each flood bayesian analysis was used to adjust the dense dating results so that the time interval between the first and last flood deposit preserved in the cave could be estimated minimum peak discharges were reconstructed based on the estimated elevation of the late pleistocene channel bed as indicated by fluvio pedogenic layers found near the cave the average frequency of these large floods 200 600 m 3 s 1 for the period between 33 000 and 29 000 years ago is about 1 flood per 150 years while for the mid late holocene it is only 1 large flood per 1000 years eight floods out of the 27 recorded deviate from the envelope curves of mid late holocene paleofloods and measured floods in the hyperarid negev desert indicating a different hydroloclimatological regime the anomalous large floods are hypothesized to have resulted from an increase in regional rainfall intensity and or duration attributed to increased frequency of the red sea trough low pressure system that affects the region available records indicate that the northern negev and areas farther north in israel controlled by mediterranean pressure systems were wetter 40 20 ka bp at the same time the southern negev probably in response to the red sea trough system also experienced short episodes of more and or larger rainstorms the timing of these episodes in both the northern and the southern negev towards the last glacial maximum points to a potential synchronous strengthening of both the mediterranean and red sea systems currently acting at different seasons these episodes of increased storminess in the area were brief and were not able to alter the general hyperarid conditions in this area

aggradation incision transition in arid environments at the end of the pleistocene an example from the negev highlands southern israel abstract one of the most significant environmental processes that occurred at the transition from the last glacial phase into the present inter glacial phase in arid regions was the shift from aggradation to incision in the drainage systems this is evident by the sharp transition from a fluvial regime depositing fine grained sediment within the wadis to intensive incision which formed gullies and narrow channels that dissected the late pleistocene sediments in order to investigate this transition we studied three small scale basins in the arid region of the negev highlands southern israel although the selected basins drain toward different base levels their geomorphological parameters particle size distribution of alluvial units and their osl ages are similar sediments from the penultimate glacial cycle are found in patches in the bigger catchments fluvial loess was widely deposited since at least 67 ka until after 28 ka covering valleys and slopes between 28 and 24 ka loess was washed from the slopes into the channels exposing the underlying colluvium at 24 ka erosion began with the transport of slope colluvium as gravels into the valleys that eroded the underlying loess sediments incision became dominant at 12 ka and is still ongoing and intensifying dust and reworked loess continued to be deposited during the main incision stages it is proposed that the transition from aggradation to incision was controlled by rates of loess supply and removal until 24 ka dust choked the drainage system and only after reduction in dust supply was erosion and incision possible it began first on the slopes and then in the channels our results show that an increase in precipitation is not a prerequisite for initiation of incision as is often assumed similar processes are described in other arid zones around the world

the evolution of holocene reg gravelly soils in deserts abstract reg soil is an aridisol developed upon a stable alluvial surface composed of sand to coarse gravel the objectives of the present study were 1 to examine the initial evolution of reg soil properties with time 2 to assess and explain the rates of development of different properties 3 to establish the suitability of different soil properties for relative age dating the time dependent soil properties examined were 1 mechanical weathering of surficial rocks and desert pavement evolution 2 chemical and biological weathering of surficial rocks 3 the thickness of soil profiles and soil horizons 4 soil texture in the different horizons 5 salts and gypsum distribution and concentration in different soil horizons 6 degree of mechanical weathering of gravel in c horizons fifteen successive surfaces of the nahal wadi ze elim sequence of alluvial fans were selected for study dead sea region israel under an extremely arid climate the sequence is of holocene age 14 000 years b p to recent the main conclusions are 1 reg soils develop rather fast in several 10 3 years since their initiation however the various soil properties developed at different rates 2 the rates of change of three soil properties decrease with time these are the texture in different horizons change in added airborne and rain washed dust salinity within the soil profile change in added salts and gypsum and the amount of mechanically shattered rocks 3 soil thickness is established rather rapidly young and older holocene soil have practically the same depth surficial weathering rates appear to remain fairly constant with time 4 in coarse gravel the evolution of reg soils is dependent on added fines and salts of airborne origin and the resultant changing hydrologic regime in the soil profile the run off infiltration ratio changes as more fines and salts are added to the soil profile and as desert pavement develops 5 surficial features and fine clay in the soil profile may be used for approximate dating of otherwise undatable holocene alluvial surfaces salts and gypsum content should be cautiously used in a rather general way

environmental changes recorded in the upper pleistocene along the desert boundary southern israel abstract most paleoclimatic studies in the middle east and africa suggest large changes in climate during the last 100 000 years a specific area of interest is the record of environmental changes along the desert boundary this study was conducted in such a boundary in the northern negev israel sedimentological evidence and the 18 o 16 o 13 c 12 c and 14 c content of carbonate nodules formed within the sediments were examined data obtained in two study areas 35 km apart suggest that while soil formation was occurring in the northwest only fluviatile and lake deposition occurred to the southeast the results of this study suggest that during the late pleistocene the boundary was much steeper than in the holocene the period before 35 000 yr b p periodically was wetter than at present with freshwater lakes and soil covered by c 3 plants a change to a more arid condition occurred during the last glacial maximum in europe 18 000 yr b p a second wet period not as wet as the earlier one occurred with the retreat of the glaciers in europe at this time decrease of loess supply and formation of the top soil occurred at both study locations in the southern area this wet period ended with highly evaporated sabkha deposits about 11 000 yr b p the holocene record suggests progressive aridity which was accompanied in the southeast location by covering the area with dunes

soils as a tool for estimating ages of quaternary fault scarps in a hyperarid environment the southern arava valley the dead sea rift israel abstract on the alluvial fan of nahal shehoret in the extremely arid region of the negev desert israel reg soils developed on stable alluvial surfaces in colluvium along terrace risers and in colluvial units on a complex fault scarp were compared the degree of soil profile development provided an age estimate of the surface that was faulted a maximum age estimate of the scarp or terrace riser and an estimate of the maximum recurrence intervals of faulting events irsl dates of the tectonically displaced alluvial surfaces and colluvial units at the same site enabled us to re evaluate the use of reg soils for relative dating the major faulting event started at 34 8 4 3 ka it displaced a late pleistocene surface of the nahal shehoret alluvial fan dated at 56 10 8 ka renewed fluvial activity and deposition of alluvium on the downfaulted block had almost terminated by 13 6 2 3 ka the scarp was formed during the latest pleistocene and was followed by smaller faulting events which had only minor effects on the fault scarp morphology the similarity of age estimates from irsl dating and the degree of soil development in this environment indicates that soils can be used to date surfaces and colluvial units

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

the lake lahontan highstand age surficial characteristics soil development and regional shoreline correlation abstract the lake lahontan basin has been the site of numerous pluvial lakes during the pleistocene we address the question of whether or not the highest remnant shoreline features around the perimeter of the lake were produced during the most recent sehoo highstand 13 ka the penultimate eetza highstand 140 280 ka or both to do so we document surficial characteristics morphologic preservation and soil development on multiple sehoo beach barriers in the jessup embayment to define the range in characteristics displayed by latest pleistocene beach features sehoo barriers generally exhibit original constructional morphology that has been little modified by erosion soils developed on sehoo barriers are generally thin and weakly developed and are strongly influenced by the introduction of eolian fines into the predominately clast supported coarse beach gravels similar observations from 13 other highstand barriers and from seven older than latest pleistocene paleosols located around the basin form the basis for a regional comparison based on similar characteristics including the degree of morphologic preservation and weak soil development we conclude that the widespread and nearly continuous high shoreline around the perimeter of lake lahontan dates from the most recent major lake cycle in all areas except in the walker lake subbasin in the walker lake subbasin isolated early to middle pleistocene lacustrine outcrops and landforms are elevated as much as 70 m above the late pleistocene limit but are differentiated by their degraded form and lack of continuity around the subbasin similar unambiguous landforms were not observed elsewhere and at similar elevations in the northern subbasins of lake lahontan

active sand seas and the formation of desert loess abstract loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains 20 80 m that serve as an important archive of information on quaternary climate change despite the intensive research during the past century on desert loess formation its origin remains poorly understood and is still a fundamental problem in sedimentology the ongoing debate is focused on the first stage of loess formation the production of coarse silt quartz grains although laboratory experiments indicate the potential of dunes with their abundant quartz sand grains as a primary source for generating coarse silt grains this concept has been generally rejected because field based evidence of abrasion from sand grains eolian abrasion is scarce here we have adopted a global view of the sand sea loess association and examine in detail several well known late pleistocene loess regions in different subtropical deserts africa the middle east and arabia this analysis demonstrates that all these loess regions are located downwind of adjacent sand seas together with evidence of mineralogical similarity between the loess and the sand dunes and the contemporaneous deposition of the loess and movement of the dunes these observations suggest that sand seas are an important source for desert loess because there is only limited silt storage in sand dunes we postulate that the silt grains comprising most of the loess are not reworked from the dunes but are generated probably through active eolian abrasion of the sand grains under past climates characterized by intensified winds as a result the role of sand dunes and eolian abrasion in the formation of desert loess may be more important than previously thought

fluid regime in faulting deformation of the waratah fault zone australia as inferred from major and minor element analyses and stable isotopic signatures abstract geochemical studies have been conducted on the waratah fault zone a steep ne sw trending brittle fault zone in the southeastern lachlan fold belt australia strike slip movement along the fault juxtaposed an early devonian turbidite sequence liptrap formation against heavily veined early devonian limestones the fault zone consists of the faulted liptrap formation and faulted limestones and a fault core composed of a fault melange zone and strongly brecciated limestones the fault zone records extensive mineralogical and stable isotope alteration within the deformed turbidites of the liptrap formation and within the limestone sequence for the liptrap formation a volume loss of 28 was calculated for the transition from unaltered sediments to the fault melange zone the volume loss in the limestone gouge is much higher 60 the calculated fluid rock ratios in the limestone sequence are at least an order of magnitude lower than in the fault melange zone stable isotopic and rare earth elemental data document the infiltration of near surface meteoric water during brittle deformation and alteration of the fault zone the interaction of fluids with contrasting lithologies led to different alteration processes affecting fault weakening and or strengthening the cyclic change between large scale fluid infiltration due to brittle failure open system and fault rock cementation closed system may represent a combined conduit barrier system in the limestone sequence within the liptrap formation no cementation took place as the conditions for quartz precipitation were unsuitable hence the fault system remains open in respect to fluids conduit system only additionally the permanent fluid infiltration dissolved silica and altered detrital feldspar resulting in subsequent porosity increase within the fault melange zone our results are consistent with investigations in modern accretionary complexes where major decollements and subsidiary faults have been shown to be important fluid conduits

experimental investigation of silt formation by static breakage processes the effect of temperature moisture and salt on quartz dune sand and granitic regolith weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process these results suggest that crack tip processes are insignificant where mineral grains are not subject to static loading sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains feldspars and mica in the regolith sands were more susceptible to salt action than quartz salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits

field experiments of aeolian dust accumulation on rock fragment substrata the effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long term field experiment in the negev desert of israel four parameters were studied pebble eccentricity pebble size pebble flattening and cover density the effect of these parameters on the accumulation of dust on the pebbles on the accumulation of dust between and underneath the pebbles and on total dust accumulation pebbles interpebble space was measured separately accumulation on the pebbles increased as the pebbles became larger less flattened and more elongated and as cover density increased accumulation between and underneath the pebbles increased as the pebbles became smaller more flattened and more elongated and as cover density increased although the accumulation area available became smaller total dust accumulation increased as the pebbles became smaller more flattened and more elongated and as cover density increased rock fragments act as a dust trap as dust accumulation on pebble covered surfaces is several tens of times larger than dust accumulation on similar but pebble free surfaces however less than 20 of the initially settled dust is protected from further erosion in the negev desert dust erosion by wind is of the order of 10 times larger than dust erosion by water the rate of long term dust accumulation in the negev is of the order of 15 30 g m 2 yr 1 this is considerably lower than the rates proposed elsewhere in the literature which are based upon over optimistic dust retainment percentages

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

desert pavement characteristics on wadi terrace and alluvial fan surfaces wadi al bih u a e and oman abstract in arid mountain areas the dating and correlation of alluvial depositional surfaces is often uncertain especially in regions where the geomorphology is not well known surface modification by the development of soil and desert pavement may allow the correlation of geomorphic surfaces and estimation of at least their relative ages pleistocene wadi terraces and associated alluvial fans occur in wadi al bih u a e and oman for which correlations and age relationships are not known three age related groups of fans and terraces have been identified and mapped on the basis of their morphostratigraphic relationships deposition of the oldest terrace sediments and associated fans followed a long period of sustained incision after miocene uplift of the region the younger two groups of terraces and fans are inset within the older group to identify the gross effects of pavement development comparisons have been made between terrace surface and subsurface particle size distributions the older terraces have finer surface sediments and a greater contrast between finer surface and subsurface sediments than the younger terraces this reflects the degree of pavement development particle size on the fan surfaces is comparable with that on the equivalent terrace surfaces criteria for the classification of pavements were developed based on clast fracturing and angularity size sorting packing and surface texture from which a simple index of pavement development has been derived other properties rock varnish and weathering characteristics were also recorded but these proved to be less discriminatory than pavement characteristics the pavement data have been augmented by observations on soils detailed studies of pavements on terraces 8 sites 12 samples covering the three age groups and fans 5 sites 10 samples covering the three age groups allow differentiation between age groups the three terraces show three different age related pavement types expressed by differences in the pavement development index weakly developed pavements little fracturing sub rounded clasts some modification of the depositional fabric incipient soil development stage i caco3 accumulation occur on the youngest terrace and fan surfaces moderately developed pavements clast fracturing sub angular clasts moderate sorting and packing deeper soil development stage ii caco3 accumulation occur on the middle terrace and fan surfaces well developed pavements complete clast fracturing into small angular fragments mature sorting and packing of the pavement surface deep soil development with strong horizonation stage iii caco3 accumulation occur on the highest terrace and oldest fan surfaces there are minor differences between the youngest pavements on terraces and fans which reflect initial sedimentological differences these differences become less as the pavements develop on the basis of comparative studies the oldest terrace is estimated to date from sometime prior to ca 100 ka bp the second terrace and the most extensive fan surface from the late pleistocene and the youngest terrace and fan phase from the latest pleistocene or early holocene

late quaternary weathering erosion and deposition in nahal yael israel an impact of climatic change on an arid watershed in their seminal paper in 1979 bull and schick proposed a conceptual model for the geomorphic response to pleistocene to holocene climate change based on the hyperarid nahal yael watershed in the southern negev desert in this model the change from semiarid late pleistocene to hyperarid early holocene climates reduced vegetation cover increased the yield of sediment from slopes and accelerated aggradation of terraces and alluvial fans the model is now over 30 yr old and during this time chronologic paleoenvironmental and hydrogeomorphic research has advanced here we reevaluate the model using data acquired in nahal yael over the 30yr since the original model was proposed recent studies indicate that the late pleistocene climate was hyperarid and a transition from semiarid to hyperarid climates did not occur the revised chronology reveals a major 35 20 ka episode of accelerated late pleistocene sediment production on slopes with lower rates probably already at ca 50ka due to increased frequency of wetting drying cycles caused by frequent extreme storms and floods between 35 and 27 ka without lag time these sediments were transported and aggraded in depositional landscape components fluvial terraces and alluvial fans this intensified sediment production and delivery phase is unrelated to the pleistocene holocene transition the depositional landforms were rapidly incised between 20 and 18 ka since and or soon after this last glacial maximum lgm incision most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock using these new data we propose a revision to the bull and schick model in this hyperarid environment our revision suggests that the model should include the frequent storms and floods responsible for a late pleistocene pulse of intense weathering due to numerous cycles of wetting and drying on slopes and coeval sediment transport to fluvial terraces and alluvial fans we also discuss the common use and pitfalls of using the bull and schick conceptual model to explain observations in diverse arid environments usually without sufficient data on basin specific stratigraphic chronologic paleoenvironmental and paleoclimatic information

predicting the thickness and aeolian fraction of soils in upland watersheds of the mojave desert abstract soil thickness and soil texture and their spatial variability at hillslope scales are important inputs for hydrologic models recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles to date however these models have not been tested in arid regions where soils are often thin and highly variable at small scales i e 1 10 m and where the influence of aeolian accretion on soil thickness and soil texture may be significant in addition most of the data available for the fraction of the soil derived from aeolian deposition which can serve as a proxy for soil texture originate from soils developed on stable depositional landforms data for aeolian fractions from upland soils are scarce in this study we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas the model assumes a long term balance between the rates of soil production from bedrock aeolian accretion and soil erosion rates of soil production are quantified in the model using the exponential and humped soil production functions and soil erosion rates are quantified using the nonlinear depth and slope dependent transport functions assuming that only the upper soil horizons a b are capable of transport the rate of aeolian deposition is assumed to be spatially uniform we calibrated the three free parameters of the model at a site in the mojave desert with a granite lithology using a combination of 1 field measured data for soil thickness and 2 estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations we validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence absence of soil and laboratory analysis of the aeolian fraction of soil the study area is characterized by generally thin soils

middle to late pleistocene shift in eolian silts contribution into mediterranean soils at the fringe of the negev loess israel a common spatial feature within loess deposits worldwide is a downwind decrease in thickness and grain size trends that are powerful tools for reconstructing paleowinds and past atmospheric circulation although such trends have been identified there is limited knowledge of similar trends farther downwind from the loess region where eolian influx can influence soil formation and hydrological processes to examine these impacts we studied quaternary sequences in prehistoric sites in jerusalem located only 50 km downwind from the edge of the negev loess all sequences are composed of two units separated by an unconformity the lower unit is of middle pleistocene age it is composed of unimodal clay to silty clay dust deposits with chert clasts and lower middle paleolithic artifacts a non deposition interval characterized the middle to late pleistocene transition when dust accumulation rates were low the upper unit age is late pleistocene to holocene it is composed of bimodal silty clay to silty clay loam quartz k feldspars and plagioclase contents together with the location and amplitude of grain size coarse mode increase up sequence the addition of coarse silts to the upper unit of the sequences was coeval with episodes of loess accretion in the negev these silts were generated most likely by eolian abrasion of sand grains in the upwind dunes similar to the negev the addition of silts resulted in burial of the drainage network and reduced runoff and soil erosion rates we stress the importance of desert loess in determining soil composition and surficial hydrology in wetter areas located in adjacent downwind regions