valles marineris dune sediment provenance and pathways abstract although low albedo sand is a prevalent component of the martian surface sources and pathways of the sands are uncertain as one of the principal present day martian sediment sinks the valles marineris vm rift system hosts a diversity of dune field populations associated with a variety of landforms that serve as potential sediment sources including spur and gully walls interior layered deposits ilds and landslides here we test the hypothesis that vm dune fields are largely derived from a variety of local and regional intra rift sediment sources results show several dune fields are superposed on ancient wall massifs and ilds that are topographically isolated from extra rift sand sources spectral analysis of dune sand reveals compositional heterogeneity at the basinal dune field and dune scales arguing for discrete relatively unmixed sediment sources in coprates and melas chasmata mapping is consistent with the principle sand source for dunes being noachian aged upper and lower wall materials composed of primary igneous minerals and glasses some of which show evidence for alteration in contrast dune fields in capri juventae and ganges chasmata show evidence for partial sediment derivation from adjacent early hesperian aged hydrated sulfate bearing ild units this finding indicates that these ilds act as secondary sand sources dunes containing soft secondary minerals e g monohydrated sulfate are unlikely to have been derived from distant sources due to the physical weathering of sand grains during transport isolated extra rift dune fields sand sheets and sand patches are located on the plateaus surrounding vm and the adjoining areas but do not form interconnected networks of sand pathways into the rift if past wind regimes with respect to directionality and seasonality were consistent with more recent regimes inferred from morphological analysis i e dune slip faces wind streaks and were sufficient in strength and duration small dune populations within aurorae chaos and north of eastern vm might have resulted from extended sand pathways into vm however we favor local and regional derivation of dune sand from a variety of intra rift lithologic sources for most cases dune sand sources and the mechanism by which the sand is liberated are discussed in the context of findings described herein but are broadly applicable to analysis of sediment production elsewhere on mars

infra red stimulated luminescence dating of sands from the cronese basins mojave desert abstract potassium rich feldspars separated from aeolian sands from the east and west cronese basin have been dated by infra red stimulated luminescence sands from shoreline reworked aeolian dune ridges in the west cronese basin suggest that late holocene playa lakes have existed in the basin within the last 2000 years four dates from these ridges suggest that a phase of aeolian deposition and stabilisation occurred 150 250 years ago a date of 250 75 years on a yardang formed from horizontally bedded sand however implies that at least a metre of erosion in the west cronese basin has occurred since that time in response to a dominant southwesterly wind late pleistocene dates ranging from 18 850 to 23 350 years were obtained from an aeolian unit in the east cronese basin giving limiting ages on wavecut shorelines formed in the deposit this aeolian sand appears to have been deposited and stabilised at a similar time to part of the nearby cat dune sand ramp

record of middle pleistocene climate change from buck lake cascade range southern oregon evidence from sediment magnetism trace element geochemistry and pollen comparison of systematic variations in sediment magnetic properties to changes in pollen assemblages in middle pleistocene lake sediments from buck lake indicates that the magnetic properties are sensitive to changes in climate buck lake is located in southern oregon just east of the crest of the cascade range lacustrine sediments from 5 2 to 19 4 m in depth in core contain tephra layers with ages of 300 400 ka at 9 5 m and 400 470 ka at 19 9 m in these sediments magnetic properties reflect the absolute amount and relative abundances of detrital fe oxide minerals titanomagnetite and hematite the lacustrine section is divided into four zones on the basis of magnetic properties two zones 19 4 17 4 m and 14 5 10 3 m of high magnetic susceptibility contain abundant fe oxides and correspond closely to pollen zones that are indicative of cold dry environments two low susceptibility zones 17 4 14 5 m and 10 3 5 3 m contain lesser amounts of fe oxides and largely coincide with zones of warm climate pollen transitions from cold to warm climate based on pollen are preceded by sharp changes in magnetic properties this relation suggests that land surface processes responded to these climate changes more rapidly than did changes in vegetation as indicated by pollen frequencies magnetic properties have been affected by three factors 1 dissolution of fe oxides 2 variation in heavy mineral content and 3 variation in abundance of fresh volcanic rock fragments trace element geochemistry employing fe and the immobile elements ti and zr is utilized to detect postdepositional dissolution of magnetic minerals that has affected the magnitude of magnetic properties with little effect on the pattern of magnetic property variation comparison of ti and zr values proxies for heavy mineral content to magnetic properties demonstrates that part of the variation in the amount of magnetite and nearly all of the variation in the amount of hematite are due to changes in heavy mineral content variation in the quantity of fresh volcanic rock fragments is the other source of change in magnetite content magnetic property variations probably arise primarily from changes in peak runoff at low to moderate flows magnetic properties reflect only the quantities of heavy minerals derived from soil and highly weathered rock in the catchment at high flows however fresh volcanic rock fragments may be produced by breaking of pebbles and cobbles and such fragments greatly increase the magnetite content of the resulting sediment climatically controlled factors that would affect peak runoff levels include the accumulation and subsequent melting of winter snow pack the seasonality of precipitation and the degree of vegetation cover of the land surface our results do not distinguish among the possible contributions of these disparate factors

mapping the interactions between rivers and sand dunes implications for fluvial and aeolian geomorphology article i nfo the interaction between fluvial and aeolian processes can significantly change earth surface morphology when riversandsanddunes meet theinteractionofsedimenttransportbetweenthetwosystemscanleadtochangein eitherorboth systems however these two systemsare usuallystudied independently which leavesmanyques tions unresolved in terms of how they interact this paper carries out a global inventory using satellite imagery to identify 230 sites where there are significant fluvial aeolian interactions at each location key attributes such as wind river direction net sand transport direction fluvial aeolian meeting angle dune type and river channel pattern were identifiedand relationshipsbetween each factorwere analysed from thesedata six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems results from this classification confirm that only certain types of interaction were significant the meeting angle and dunetype themeeting angle and interaction type and finally thechannel pattern andinteraction type however the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images

radiometric normalization and image mosaic generation of aster thermal infrared data an application to extensive sand sheets and dune fields abstract data from the advanced spaceborne thermal emission and reflection radiometer aster have a significant advantage over previous datasets because of the combination of high spatial resolution 15 90 m and enhanced multispectral capabilities particularly in the thermal infrared tir atmospheric window 8 12 m of the earth where common silicate minerals are more easily identified however the 60 km swath width of aster can limit the effectiveness of accurately tracing large scale features such as eolian sediment transport pathways over long distances the primary goal of this paper is to describe a method for generating a seamless and radiometrically accurate aster tir mosaic of atmospherically corrected radiance and from that extract surface emissivity for arid lands specifically sand seas the gran desierto in northern sonora mexico was used as a test location for the radiometric normalization technique because of past remote sensing studies of the region its compositional diversity and its size a linear approach was taken to transform adjacent image swaths into a direct linear relationship between image acquisition dates pseudo invariant features pifs were selected using a threshold of correlation between radiance values and change pixels were excluded from the linear regression used to determine correction factors the degree of spectral correlation between overlapping pixels is directly related to the amount of surface change over time therefore the gain and offsets between scenes were based only on regions of high spectral correlation the result was a series of radiometrically normalized radiance at surface images that were combined with a minimum of image edge seams present these edges were subsequently blended to create the final mosaic the advantages of this approach for tir radiance as opposed to emissivity data include the ability to 1 analyze data acquired on different dates with potentially very different surface temperatures as one seamless compositional dataset 2 perform decorrelation stretches dcs on the entire dataset in order to identify and discriminate compositional units and 3 separate brightness temperature from surface emissivity for quantitative compositional analysis of the surface reducing seam line error in the emissivity mosaic the approach presented here is valid for any aster related study of large geographic regions where numerous images spanning different temporal and atmospheric conditions are encountered

evidence of cyclic dust deposition in the us great plains during the last deglaciation from the high resolution analysis of the peoria loess in the eustis sequence nebraska usa the peoria loess unit is a well defined stratigraphical unit in the upper pleistocene of the north american quaternary deposited between 30 25 ka and about 12 ka ago it has been indicated that this unit shows the highest known worldwide depositional rate for eolian deposits as its thickness varies near the source area between 19 m and 46 m extreme values that are not even recorded in the chinese sequences the results of our present investigation indicate that this particular unit is not homogenous its shows different subunits where lithological variation can be observed through the occurrence of embryonic gley horizons alternating with laminated loess furthermore the grain size analysis shows cycles corresponding to variations in the eolian dynamics responsible for dust transportation and deposition a grain size index interpreted as characterizing the eolian dynamics higher values corresponding to stronger wind conditions shows higher values than those observed in europe a comparison of this index is proposed with the greenland dust and 18 o records it shows that the main climatic history as corresponding to events occurring mainly in north atlantic domain is recorded in the peoria loess deposits however the variation in the magnitude of the eolian events indicates differences from the european loess sequences the strong north atlantic coolings expressed by heinrich events as recorded in europe by coarser deposits are not differentiated in the studied sequence hence they follow more closely observations obtained off california for the north east pacific domain 2007 elsevier b v all rights reserved

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

infrared stimulated luminescence irsl dating of late holocene aeolian sands in the mojave desert california usa a new method of dating potassium feldspar grains from aeolian sands is demonstrated a luminescence signal is measured whilst the grains are stimulated in the near infrared at 880 nm a surface sand sample gave an age of 40 15 years showing that this method is able to provide ages for very young samples since the measurement of an infrared stimulated luminescence irsl signal can take place with a short infrared exposure the irsl signal of the grains is not depleted thus growth curves can be obtained for 5 mg sample aliquots this procedure was exploited in this paper dates were obtained for 10 samples from the kelso dune field as a demonstration of the applicability of the method in a desert environment where there is no material suitable for radiocarbon dating although the number of dates are limited sand from an area at the eastern end of the dune field with crescentic dunes showing a different wind direction from that of today had an age of 4115 335 years similar to the 3960 385 years fo

soil geomorphology and wet cycles in the holocene record of north central mexico abstract the distinction between the impact of climatic periodicities or land use practices on soil erosion is an important issue for pre hispanic and colonial mexico that question can best be addressed by first documenting the dynamics of changing wet cycles during the holocene in the central mexican region between the northern limits of pre hispanic agriculture and its southern margins in northwestern chihuahua consequently the laguna project targeted a 125 000 km 2 sector of north central mexico 250 km from north to south and 500 km from east to west from saltillo to durango some 40 sedimentary profiles with multiple cumulic soils were studied in the field and laboratory supported by 163 conventional 14 c and ams dates on charcoal and soil humates we distinguish 1 wet floodplains with humic paleosols redox phenomena reflecting high water tables channel ponding sequences and interbedded tufas that imply aquifer recharge sustained base flow and mainly low energy conditions and 2 high energy pulses of discharge that mobilized cobble gravels or forced channel entrenchment gullying and were tied to episodic excessive rains that promoted valley and slope instability in between such wet cycles and recurrent disequilibrium events climate was similar to today probably less humid with limited geomorphologic change or slow soil formation wet cycles were rare at the end of the pleistocene but prominent during the holocene disequilibrium proxies became common and dramatic after 2500 bp the drainages from the eastern and western sierra madres responded in phase but varied in detail around ad 1050 1200 natural erosion led to loss of soil organic carbon as alternating severe droughts and heavy rains destroyed the ground cover and led to ecological aridification well before arrival of spanish miners and settlers the evidence that human activity triggered pre hispanic or colonial erosion in central mexico should therefore be re evaluated global comparisons and interpretations are discussed but with caution since no single theory can explain the whole of the record the soil geomorphology geoarchive of north central mexico primarily is an environmental history of alternating wet cycles rather than of sustained wet or dry climates the critical differences between soaking and excessive rains with their respective impacts may be due to switching between winter and summer storm categories

holocene dune formation at ash meadows national wildlife area nevada usa abstract small isolated dune fields in the northern mojave desert are important centers of biodiversity and archaeological occupation sites currently dunes at ash meadows nevada are stabilized by vegetation and are experiencing erosion of their upwind margins indicating a negative sediment budget new osl ages from dunes at ash meadows indicate continuous eolian accumulation from 1 5 to 0 8 ka with further accumulation around 0 2 ka prior studies e g mehringer and warren 1976 indicate periods of dune accumulation prior to 3 3 ka 1 9 1 ka and after 0 9 ka these periods of eolian accumulation are largely synchronous with those identified elsewhere in the mojave desert the composition of the ash meadows dunes indicates their derivation from regional fluvial sources most likely during periods when axial washes were active as a result of enhanced winter precipitation

long period events and tremor at popocatepetl volcano 1994 2000 and their broadband characteristics following an initial phreatic eruption on 21 december 1994 activity at popocatepetl has been dominated by fumarolic emissions interspersed with more energetic emissions of ashes and gases a phase of repetitive dome building and dome destroying episodes began in march 1996 and is still ongoing at present we describe the long period lp seismicity accompanying eruptive activity at popocatepetl from december 1994 through may 2000 using data from a three component broadband seismometer located 5 km from the summit crater the broadband records display a variety of signals with periods ranging in the band 0 04 90 s long period events and tremor with typical dominant periods in the range 0 3 2 0 s are the most characteristic signals observed at popocatepetl these signals appear to reflect volumetric sources driven by pressure fluctuations associated with the unsteady transport of gases beneath the crater very long period vlp signals are also observed in association with lp events and tremor the vlp signals which accompany lp events display ricker like wavelets with periods near 36 s whereas vlp signals associated with tremor waveforms typically show sustained oscillations at periods ranging up to 90 s the spectra and particle motion patterns remain similar from event to event for the majority of lp and tremor signals analyzed during the time span of this study suggesting a repeated non destructive activation of a common source hypocenters determined by phase pick analyses of selected lp events recorded by the seven station permanent popocatepetl short period network suggest that the majority of these events are confined to a source region in the top 1 5 km below the crater floor the repetitive occurrences of vlp signals with closely matched waveform characteristics are consistent with a non destructive reactivation of at least two sources one source appears to coincide with the main source region of lp seismicity whereas the second is a deeper source whose activity appears to be intimately linked with episodes of monochromatic tremor

luminescence dating of sand ramps in the eastern mojave desert abstract until recently the timing of the movement of sand and accumulation of sand by aeolian processes in the eastern mojave desert has remained the subject of speculation the results of a luminescence dating program involving 78 samples of material from nine sand ramp complexes have enabled recognition of regional and local patterns of sand accumulation in the eastern mojave the study area extends from lake manix in the west to the colorado river in the east the periods of accumulation have been identified on the basis of quartz tl dating and potassium feldspar tl and irsl dating at a regional scale two major depositional phases can be identified 1 late pleistocene 20 30 ka with sequences at hank s mountain balch dale lake and the big marias and 2 late pleistocene early holocene 15 7 ka with sequences at cat dune dale lake iron mountain big marias above palaeosol and at the western end of the study area at soldier mountain 20 7 ka late holocene sequences appear to be much more localized and are confined to the west cronese old dad mountain and balch sand ramps the earliest phases of sand accumulation on the ramps studied immediately predate the formation of pluvial lake mojave ca 24 5 ka the later main phases of accumulation coincide with the existence of lake mojave and the end of accumulation on the majority of the sand ramps immediately post dates the final end of intermittent lake mojave iii 9 7 ka the continuity of sand supply to potential deflation areas is seen as a critical condition for accumulation of material on the sand ramps during the late quaternary in the eastern mojave

late holocene eolian activity in the mineralogically mature nebraska sand hills abstract the age of sand dunes in the nebraska sand hills has been controversial with some investigators suggesting a full glacial age and others suggesting that they were last active in the late holocene new accelerator mass spectrometry radiocarbon ages of unaltered bison bones and organic rich sediments suggest that eolian sand deposition occurred at least twice in the past 300014c yr b p in three widely separated localities and as many as three times in the past 80014c yr at three other localities these late holocene episodes of eolian activity are probably the result of droughts more intense than the 1930s dust bowl period based on independent great plains climate records from lake sediments and tree rings however new geochemical data indicate that the nebraska sand hills are mineralogically mature eolian sands in nebraska have lower k feldspar and k2o rb and ba contents than most possible source sediments and lower k feldspar contents than dunes of similar age in colorado the most likely explanation for mineralogical maturity is reduction of sand sized k feldspar to silt sized particles via ballistic impacts due to strong winds over many cycles of eolian activity therefore dunes of the nebraska sand hills must have had a long history probably extending over more than one glacial interglacial cycle and the potential for reactivation is high with or without a future greenhouse warming

eolian landscape evolution and soil formation in the chaco dune field southern colorado plateau new mexico abstract eolian deposits of the chaco dune field cover a broad expanse of the southeastern colorado plateau in new mexico and comprise a large part of the late quaternary sedimentary record in this region the primary eolian landforms include sand sheets parabolic and modified parabolic dunes barchan barchanoid dune complexes and ridge dunes many of the eolian landforms in the chaco dune field have remained stable over a sufficiently long time to permit soil development weakly to moderately developed calcic soils which formed in eolian deposits of mid holocene and latest pleistocene age possess clay enriched weak argillic b horizons these soils have been buried progressively by younger eolian sediments forming regionally correlative bounding surfaces over the chaco dune field and recording relict latest pleistocene and middle holocene eolian landscapes soil geomorphic relations and radiocarbon dated material within the eolian deposits have been useful in 1 delineating three regionally correlative soil stratigraphic units and their associated landforms and 2 studying the types and rates of landscape evolution and climatic changes within this portion of the colorado plateau the most significant period of eolian landform construction is inferred to have occurred during the latest pleistocene glacial to interglacial climatic change forming widespread sand sheets and modified parabolic dunes eolian deposition during the middle and late holocene were dramatically influenced by the presence of previously developed latest pleistocene to early holocene buried soils which may have enhanced sand sheet and parabolic dune development due to the binding effect of the soils middle holocene eolian deposition may be related primarily to neoglacial climatic changes which enhanced ground surface moisture and promoted sand sheet and parabolic dune formation the youngest period of wolian deposition occurred after 1 5 ka and resulted in the formation of the most diverse suite of eolian landforms and deposition of volumetrically more eolian sediments than the mid holocene event in contrast to earlier interpretations the classic mid holocene or altithermal event apparently did not play a major role in the formation of eolian landscapes in the chaco dune field

sand supply to the algodones dunefield south eastern california usa in an effort to gain a better understanding of the relationship between climate sand supply and aeolian sand deposition an investigation was undertaken in the algodones dunefield of south eastern california to determine 1 the source of the sand and 2 the mode of sand supply to the algodones dunefield textural geochemical and mineralogical analyses show that the dune sands were mainly derived from colorado river sands during episodes when the colorado river drained west to the salton basin instead of south to the gulf of california a model is presented which relates episodic aeolian deposition in the algodones dunefield to the growth of the resulting lake under a persistent intense north westerly wind regime and to subsequent desiccation of the lake following diversion of the colorado river to the gulf of california late holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south western united states these conditions are likely to have been the cause of intensified north westerly winds which coincided with high stands of lake cahuilla although diversion of the colorado river to the salton basin occurred at least three times during the late holocene it is evident that the river did not change its course in response to the majority of the floods it appears that the critical control on diversion of the river was the difference in gradient between courses leading to the salton basin and gulf of california which in turn was influenced by fluvial deposition and tectonic activity flooding was able to cause diversion of the colorado river to the salton basin only when the difference in gradient between the two courses was relatively small

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

dune dammed paleovalleys of the nebraska sand hills intrinsic versus climatic controls on the accumulation of lake and marsh sediments although running water is the dominant geomorphic agent on earth eolian processes can gain ascendancy in regions where the climate is arid vegetation is sparse and abundant sand is available for transport with climate change the boundaries between fluvial dominated and eolian dominated areas may shift although there have been few reports in the north american literature of river systems blocked by dune sand our work in the nebraska sand hills provides evidence of multiple episodes of such blockage events during prolonged arid intervals in latest pleistocene and middle holocene time eolian dune sand blocked two large valley systems in western nebraska these blockages raised the water table of the high plains aquifer as much as 25 m over an area of 7000 km2 and created over one thousand lakes wetlands far removed from the discharge points of the buried paleovalley system are strongly alkaline exceeding 250 000 mg l total dissolved solids tds relatively fresh 280 mg l tds flow through lakes are present at the distal end of the system where the gradient of the water table is steep and the cross section of the buried valley is large anomalously thick marsh and lake sediments accumulated in deep paleovalleys upstream of dune dams near the southern margin of the sand hills our cores and radiocarbon dates from blue and crescent lakes reveal their histories to be quite distinct from adjacent swan lake these differences are best explained by multiple blockage events our work explains why lakes are most abundant in the driest part of the sand hills it also provides another line of evidence for major dune activity in the sand hills region during holocene time and shows that factors other than regional climate specifically location height and hydraulic conductivity of dune dams can control the rise and fall of the ground water table and the chemistry of lakes

eolian dynamics and sediment mixing in the gran desierto mexico determined from thermal infrared spectroscopy and remote sensing data the gran desierto dune field is only partially composed of quartz rich sands from the ancestral colorado river local sources have been previously underestimated as a major source of sand because previous remote sensing studies were limited in their capability to detect silicate minerals compositions of sands were evaluated in this study using a combination of laboratory thermal emission spectroscopy and thermal remote sensing data acquired from the advanced spaceborne thermal emission and reflection radiometer aster instrument the spatial interpolation of sample compositions allowed visualization of the sand transport pathways from feldspar rich local sources by revealing gradients of composition between the dune field and surrounding local sources the laboratory data were comparable to the remote sensing retrievals of quartz and feldspar abundance the mineralogical maturity of the desierto dunes could be determined by the quartz feldspar ratio therefore providing a context for understanding the provenance of the gran desierto in relation to other mojave and sonoran dune fields the composition of a previously undescribed group of dunes east of the pinacate the sonoyta dunes was measured as higher in potassium feldspar relative to the rest of the dune field the composition of sonoyta dunes is characteristic of other mojave dune fields which are more isolated near local feldspar rich sources south of the pinacate quartz rich sand from the west admixes with feldspar rich sand from the sonoyta dunes to the east the northern margin of the gran desierto is similarly enriched in feldspar from alluvial fans and the coastal sand is influenced by carbonate sand that does not appear to survive transport to the inland dunes

infra red stimulated luminescence ages from aeolian sand and alluvial fan deposits from the eastern mojave desert california abstract infra red stimulated luminescence irsl from coarse grained 180 212 m potassium rich feldspars has been used to date deposits associated with the western piedmont of the providence mountains in the eastern mojave desert these deposits consist of alluvial fans aeolian sand which exists in the form of lenses within the fan matrices and sand from the kelso dune field which abuts the distal end of the fan sequence deposition and subsequent stabilisation of these sand units appears to have occurred in both aird and intermittent climates associated with pluvial phases during the holocene and late pleistocene ages of 6600 870 and 7840 1790 years were obtained from dune sand bracketing the mazama ash at skull creek dunes oregon giving an independent age control on the single aliquot irsl method which was used on the mojave samples

geochemical evidence for an eolian sand dam across the north and south platte rivers in nebraska abstract geochemical and geomorphic data from dune fields in southwestern nebraska provide new evidence that the nebraska sand hills once migrated across the north and south platte rivers and dammed the largest tributary system to the missouri river the lincoln county and imperial dune fields which lie downwind of the south platte river have compositions intermediate between the nebraska sand hills quartz rich and northeastern colorado dunes k feldspar rich the most likely explanation for the intermediate composition is that the lincoln county and imperial dunes are derived in part from the nebraska sand hills and in part from the south platte river the only mechanism by which the nebraska sand hills could have migrated this far south is by complete infilling of what were probably perennially dry north platte and south platte river valleys such a series of events would have required an extended drought both for activation of eolian sand and decreased discharges in the platte river system a nearby major tributary of the north platte river is postulated to have been blocked by eolian sand about 12 000 14c yr b p we propose that an eolian sand dam across the plattes was constructed at about this same time

bottom friction and wind drag for wave models abstract waves propagating in shallow water dissipate energy in a thin turbulent boundary layer near the bottom this friction can be estimated with a simple quadratic friction law scaled with an empirical coefficient two values of this coefficient have been recommended by previous studies for sandy bottoms a high value for waves in a storm and a low value for swell we show here that in contrast to current practise the lower value should be used for both applications the reason is that the high value dating from the early 1980s was inferred from observations in a severe storm using a relatively high wind drag our review of a large number of more recent observations gives a new wind drag parameterization with lower values with this new parameterization we infer from the same storm the lower value of the bottom friction coefficient using this lower value also improves the estimates of wave growth in shallow water and of low frequency wave decay in a tidal inlet independent of the wind drag

sedimentological modal analysis and geochemical studies of desert and coastal dunes altar desert nw mexico sedimentological compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the altar desert sonora mexico grain size distributions of the desert dune sands are influenced by the colorado river delta sediment supply and wind selectiveness the desert dune sands are derived mainly from the quartz rich colorado river delta sediments and sedimentary lithics the dune height does not exert a control over the grain size distributions of the desert dune sands the quartz enrichment of the desert dune sands may be due to wind sorting which concentrates more quartz grains and to the aeolian activity which has depleted the feldspar grains through subaerial collisions the desert dune sands suffer from little chemical weathering and they are chemically homogeneous with chemical alteration indices similar to those found in other deserts of the world the desert sands have been more influenced by sedimentary and granitic sources this is supported by the fact that ba and sr concentration values of the desert sands are within the range of the ba and sr concentration values of the colorado river quartz rich sediments the sr values are also linked to the presence of ca bearing minerals the zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes the golfo de santa clara and puerto penasco coastal dune sands are influenced by long shore drift tidal and aeolian processes coarse grains are found on the flanks whereas fine grains are on the crest of the dunes high tidal regimens long shore drift and supply from colorado delta river sediments produce quartz rich sands on the beach that are subsequently transported into the coastal dunes outcrops of quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands the chemical index of alteration cia values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous the trace element values for the coastal dune sands are similar to those found for the desert dune sands however an increase in sr content in the coastal dune sands may be due to more caco3 of biogenic origin as compared to the desert dune sands correlations between the studied parameters show that the dune sands are controlled by sedimentary sources e g colorado river delta sediments since heavy minerals are present in low percentages in the dune sands probably due to little heavy mineral content from the source sediment grain sizes in the dune sands are coarser than those in which heavy minerals are found and or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune a cluster analysis shows that the el pinacate group is significantly different from the rest of the dune sands in terms of the grain size parameters due to longer transport of the sands and the long distance from the source sediment whereas the puerto penasco coastal dune sands are different from the rest of the groups in terms of their geochemistry probably caused by their high caco3 content and slight decrease in the cia value copyright 2006 john wiley sons ltd

eolian sand transport pathways in the southwestern united states importance of the colorado river and local sources geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions along such pathways sediment transport by wind can surmount topographic obstacles and cross major drainages recent studies have suggested that three distinct eolian sand transport pathways exist or once existed in the mojave and sonoran desert regions of the southwestern united states one hypothesized pathway is eolian sand transport from the eastern mojave desert of california into western arizona near parker and would require sand movement across what must have been at least a seasonally dry colorado river valley we tested this hypothesis by mineralogical geochemical and magnetic analyses of eolian sands on both sides of the colorado river as well as sediment from the river itself results indicate that dunes on opposite sides of the colorado river are mineralogically distinct eastern california dunes are feldspar rich whereas western arizona dunes are quartz rich derived from quartz rich colorado river sediments because of historic vegetation changes little new sediment from the colorado river is presently available to supply the parker dunes based on this study and previous work the colorado river is now known to be the source of sand for at least three of the major dune fields of the sonoran desert of western arizona and northern mexico on the other hand locally derived alluvium appears to be a more important source of dune fields in the mojave desert of california although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields few empirical data actually exist to support this theory the results presented here demonstrate that a major river system in the southwestern united states is a barrier to the migration of some dune fields but essential to the origin of others published by elsevier science ltd

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

effects of sand supply on the morphodynamics and stratigraphy of active parabolic dunes bigstick sand hills southwestern saskatchewangeological survey of canada contribution 20060654 sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings in this study aerial photographs ground penetrating radar gpr and stratigraphic analysis d

a preliminary study of the dynamics of a modern draa algodones southeastern california usa a transverse crescentic draa in the algodones dune field california was monitored for a year using surface process mapping aerial photography and supplemental wind measurement the draa is oriented by the long term resultant wind whereas its superimposed features are in equilibrium with the bedform modified secondary airflow surface airflow and the movement of superimposed bedforms is typically oblique or parallel to the draa brinkline particularly on the lee slope comparison of measurements of draa movement and sand deposition on the lee slope with expected rates calculated from wind data and draa size confirm that there is a significant component of sand flow parallel to the draa brinkline the internal structure being generated at the base of the draa lee slope is inferred from the surface processes active there within the space of a kilometer two types of compound cross strata separated by an area of simple cross strata are being produced this has significant implications for interpretations of ancient aeolian strata variations in internal structure types found in lateral sequence may be generated by one complex bedform and these cross strata may be simple or compound second order bounding surface orientations indicate resultant primary palaeowind directions compound cross strata dip directions indicate secondary flow conditions the existence of cross strata dip directions oblique or perpendicular to the second order surface indicates longitudinal secondary flow on the lee face but not necessarily a longitudinal or oblique draa without further detailed knowledge about various draa configurations and behaviour stratification attributed to draas can be used only to interpret activity on the lower draa lee face

luminescence dating of late quaternary aeolian deposits at dale lake and cronese mountains mojave desert california abstract relict aeolian deposits and landforms that can provide important information on the timing geographical extent and intensity of periods of aeolian sand accumulation are widespread in the mojave desert california the pleistocene part of the record is mostly undated the stratigraphy and sedimentology of sites near dale lake dale lake sand ramp and the cronese mountains cat dune were studied and luminescence dating techniques used to try to establish a chronological framework for the deposits the dating of these sites proved difficult with major disparities between the results of quartz and feldspar thermoluminescence tl dating particularly where the sediments comprised a mixture of aeolian and colluvial meterial however initial results based on quartz tl and feldspar infra red stimulated luminescence dating indicate the existence of two main periods of late pleistocene aeolian deposition between 35 to 25 ka and 15 to 10 ka

development of the gran desierto sand sea northwestern mexico three major eolian sand populations can be recognized in the gran desierto sand sea of northwestern mexico by using spectral data from the landsat thematic mapper in conjunction with textural and mineralogical studies of surface sands each sand population has distinct textural mineralogic and spectral properties that can be related to sand dune morphology and position with reference to source areas and transport paths of the sands the oldest eolian sediment in the sand sea was derived from the early to middle pleistocene colorado river that flowed through the area of the western gran desierto subsequent inputs of eolian sands came from the area of the present colorado river valley and the coast south of the sand sea the spatial and temporal pattern of eolian deposition in the region has been controlled by quaternary tectonic and climatic changes resulting in the episodic input and deposition of sand

atmospheric mineral dust in dryland ecosystems applications of environmental magnetism irm mean of 67 samples 6 72 10 3 am 2 kg 1 is more than two orders of magnitude greater than that for underlying paleozoic and mesozoic sedimentary rocks this contrast is mainly caused by the presence of silt size titanium bearing magnetite particles in the surficial deposits and their absence in bedrock because of their size composition and isolated location the magnetite particles represent a component of atmospheric dust likely deposited over the past few centuries the positive correlation of sediment irm values with amounts of potential plant nutrients reveals the importance of atmospheric dust to soil fertility over much of the american southwest subsequent disturbance of landscapes by domestic livestock grazing as an example commonly results in wind erosion which then depletes exposed surfaces of original aeolian magnetite and associated fine grained sediment declines in soil fertility and water holding capacity in these settings can be estimated in some field settings via decreases in magnetic susceptibility relative to nearby undisturbed areas along gentle hillslope gradients of the colorado plateau field measures for aeolian magnetite demonstrate that the redistribution of deposited atmospheric dust influences landscape level patterns in the distribution of invasive exotic plant species our results indicate that environmental magnetism has high potential for assessing the development and degradation of dry landscapes elsewhere

dunes of the gran desierto sand sea sonora mexico the gran desierto sand sea contains dunes of crescentic and star form in simple compound and complex varieties the dunes have developed in bimodal to complex wind regimes of intermediate energy transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds although wind regimes appear to be the major control of dune morphology in this sand sea there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile

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

lacustrine sediments at narabeb in the central namib desert namibia abstract deep within the hyper arid namib desert at narabeb which is today isolated by 100 m high linear dunes is a 36 m section of lacustrine mudstones and interbedded sands the slightly calcareous and laminated sands of this sequence are composed mainly of rounded to subrounded lightly stained quartz that is similar to the sands of the underlying tertiary tsondab sandstone formation and the surrounding dunes of the namib sand sea the six calcareous mudstone units in this sequence are variably laminated and sandy contain halite filled fractures and have been radiocarbon dated at 20 000 26 000 yr b p the interrelationship of sediments at this site with middle to early stone age implements suggests an age of more than 20 000 years whereas 234u 230th dating of the basal mudstone gave an age of 210 000 260 000 yr b p the calcareous mudstones were deposited in a lake at the former end point of the tsondab river which was prevented from reaching the atlantic ocean by n s trending linear dunes of the namib sand sea the interbedded sands were deposited during low water or dry stages of the lake sometime before 14 000 yr b p the terminus of the tsondab river shifted eastward from narabeb in response to the northward encroachment of linear dunes and the present end point was eventually established at tsondab vlei 38 km to the east lacustrine deposition at narabeb just as at tsondab vlei today probably occurred mainly in response to precipitation in the headwaters of the tsondab river although no major climatic change is necessary to explain the sequence at narabeb the clustering of radiocarbon dates on carbonate from the namib desert in the periods 20 000 35 000 yr b p and 10 000 14 000 yr b p suggests an increase in precipitation during those times

holocene eolian activity in the minot dune field north dakota stabilized eolian sand is common over much of the great plains region of the united states and canada including a subhumid area of 1500 km2 near minot north dakota eolian landforms consist of sand sheets and northwest trending parabolic dunes dunes and sand sheets in the minot field are presently stabilized by a cover of prairie grasses or oak woodland stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late holocene pedologic data suggest that all of the dune field has experienced late holocene dune activity though not all parts of the dune field may have been active simultaneously similar immobile element ti zr la ce concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments however glaciolacustrine and glaciofluvial source sediments have high ca concentrations from carbonate minerals whereas dune sands are depleted in ca

the history and nature of wind erosion in deserts recently the importance of wind erosion has been reevaluated many low angle surfaces developed on susceptible materials possess closed depressions pans and these often have a distinctive morphology and lunette dunes on their lee sides it has also become apparent that in drylands there are extensive areas of stone pavements some of which have been molded by deflation however it is now recognized that other horizontal sorting processes have played a role especially movement of fines by overland flow vertical sorting associated with wetting and drying salt heave bioturbation frost action and dust accretion have also played a role in hyperarid areas especially with unidirectional winds bedrock outcrops and old lake beds have been molded to give aerodynamic forms called yardangs the study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation especially in hyperarid areas with centripetal drainage deflation hot spots such as the bo

pilot study on provenance and depositional controls on clay mineral coatings in active fluvio eolian systems western usa abstract understanding the distribution of grain coating minerals in sandstones may be crucial in evaluating the reservoir quality of deeply buried lithologies since they can inhibit syntaxial overgrowth cementation and thus preserve intergranular pore space in unconsolidated sediments the presence of clay mineral grain coatings and their coverage are often related to the depositional subenvironment grain size sorting and skewness these properties are interpreted to reflect the amount of clay minerals present to form coatings and relate to sediment transport and reworking samples from three active fluvio eolian depositional systems in the usa mesquite flat sand dunes near stovepipe wells ca algodones dunes near brawley ca and coral pink sand dunes near kanab ut were studied using petrography transmitted light and sem and xrd analyses to test and apply the available correlations to fluvio eolian sediment samples the frequently used correlations to the depositional subenvironment grain size sorting and skewness only show poor fits r2

late quaternary arid humid cycles in the mojave desert and western great basin of north america abstract this paper discusses the late quaternary environmental changes that occurred in the drylands of western north america with particular emphasis on the aeolian lacustrine record from the mojave desert the basin and range province which includes the great basin and the mojave sonoran and chihuahuan deserts the primary physiographic region within the north american arid zone is characterized by a wide variety of landforms within a predominantly endoreic block faulted tectonic setting in these closed drainage basins lacustrine and aeolian geomorphic features and sediments have provided some of the best records for deciphering environmental changes about 100 of the basins contained lakes during the last glacial maximum lgm at larger temporal scales milankovitch dansgaard oeschger cycles lake levels seem to be well correlated with large scale atmospheric circulation controls such as the higher lake stands associated with wetter than present conditions in the southwestern drylands during the lgm on the other hand aeolian deposition was highly episodic during late quaternary time and is believed to be largely controlled by variations in sediment supply and production storage and transport capacity

osl age and stratigraphy of the strauss sand sheet in new mexico usa abstract the strauss sand sheet occurs in south central new mexico usa and northern chihuahua mexico covering an area of about 4740 km2 its chronology is determined by 19 osl ages the sand sheet formed primarily during three phases of eolian deflation and deposition each phase with a separate sand source and under different climatic and environmental circumstances the first phase of eolian sedimentation occurred 45 to 15 ka with the deposition of unit 1 the sand source for the first phase was beach related features along the eastern shoreline of pluvial lake palomas in mexico the glacial age climate was cool wet and windy because of the southern path of the jet stream at that time after 15 ka with the onset of warmer conditions of the bolling allerod the shutting down of the palomas sand source and wet conditions of the younger dryas the sand sheet stabilized with weak soil development in unit 1 by 11 ka the climate shifted to holocene drying conditions and the second phase of sand accumulation began forming unit 2 the sand source was the local deflation of the previously deposited unit 1 sand the sand sheet stabilized again by 1 9 ka with slightly wetter late holocene climate a weak soil formed in unit 2 sand about a d 1500 and extending to about a d 1850 or later an a horizon formed on the sand sheet probably in response to a desert grassland vegetation during the period of wet climate of the little ice age in an anthropogenic third phase of eolian activity after a d 1850 the vegetation was likely disturbed by overgrazing and the unit 2 and a horizon unit 3 sands were deflated resulting in the deposition of a thin layer of massive eolian sand unit 4 across the sand sheet by about a d 1900 mesquite shrubs had increased in abundance and deflated sand largely from unit 2 began to accumulate around the shrubs forming coppice dunes unit 5 mesquite coppice dunes continued to increase in number and volume during the twentieth century and at present dominate most of the sand sheet this third phase of eolian deflation deposition is ongoing today

geochemical indicators of separate sources for eolian sands in the eastern mojave desert california and western arizona low stabilized sand dunes cover much of the cactus and la posa plains in western arizona near the town of parker the provenance of the dunes is not well defined and it had been hypothesized that they were possibly related to extensive eolian sand deposits in the eastern mojave desert of california on the other side of the colorado river major oxide analyses of bulk sand samples collected from southeastern california and western arizona show clear chemical differences the mojave sands all have sio 2 10 wt and na 2 o k 2 o 5 wt whereas the colorado river and arizona sands have sio 2 81 wt al 2 o 3 6 wt and na 2 o k 2 o 4 wt these results show that the stabilized dunes near parker are chemically indistinguishable from colorado river sands the chemical differences between the southeastern california sands and the western arizona sands are supported by x ray diffraction results that indicate these two sand populations have significant differences in the relative abundance of quartz and feldspar our data also indicate a near source origin for the mojave sands whereas the colorado river and arizona sands have undergone more prolonged chemical weathering the major oxide results are consistent with published trace element studies by others that clearly distinguished between mature and immature sands in california and colorado the quartz feldspar ratio may be amenable to measurement by some advanced remote sensing instruments

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

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

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

geochemistry of sediments from quaternary sand ramps in the southeastern mojave desert california abstract trace element analyses of sediment from sand ramps in the bristol trough and clark s pass aeolian corridors of the mojave desert california were conducted to determine their depositional history and relation to sources of sediment within sand transport corridors sand ramps are topographically controlled depositional systems consisting of amalgamated accumulations of aeolian fluvial and talus deposits these landforms contain a variety of deposits formed in different environments and are therefore a valuable source of paleoenvironmental information sediments were studied from three sand ramps the iron mountain big maria and dale lake sand ramps and from two sand sheets rice valley and cactus plain cactus plain is located on the eastern side of the colorado river in arizona but previous researchers have suggested that it is related to the corridors of the western california side geochemical data from units within individual sand ramps indicate that sources for each sand ramp changed through time probably as sediment availability from different local fluvial playa systems changed in response to climate fluctuations analyses also indicate that each sand ramp is composed of sediment from discrete local sources sand deposits in the bristol trough are not integrated and thus the corridor does not act as a coherent sand transport pathway comparisons of sand from cactus plain and sediment from the bristol trough and clark s pass corridors indicates that the cactus plain sand on the east side of the colorado river was not derived from sources on the west side of the river

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

geomorphology and sediments of sand ramps in the mojave desert abstract sand ramps are amalgamated accumulations of aeolian fluvial and talus deposits they have developed as a result of the interactions of wind blown sand and desert piedmont processes adjacent to mountain ranges in the mojave desert and occur next to regional and local sand transport corridors sand ramps are dominated by aeolian sand that was deposited as sand sheets against the mountain front but also include significant fluvial units periods of geomorphic stability are represented by paleosols and talus accumulations the sand ramps provide a record of the response of aeolian processes to climatic change in the mojave desert most are now relict features and accumulated in periods of higher sediment supply from fluctuating and or desiccating paleolakes during the late pleistocene and early holocene

origin of late quaternary dune fields on the southern high plains of texas and new mexico mostly stabilized late holocene eolian sands on the southern high plains of the united states were studied to determine their origins and to assess whether present dune stability depends more strongly on sediment supply sediment availability or transport limitations geomorphic sedimentological and geochemical trends indicate that late holocene dunes formed under westerly paleowinds broadly similar to those of today mineralogical and geochemical data indicate that the most likely source for the sands is not the pecos river valley but the pleistocene blackwater draw formation an older extensive eolian deposit in the region these observations suggest that new sand is supplied whenever vegetation cover is diminished to the extent that the blackwater draw formation can be eroded in agreement with modern observations of wind erosion in the region we conclude therefore that southern high plains dunes are stabilized primarily due to a vegetation cover the dunes are thus sediment availability limited this conclusion is consistent with the observation that in the warmest driest part of the region where vegetation cover is minimal dunes are currently active over a large area geochemical data indicate that southern high plains dunes are the most mineralogically mature quartz rich sands yet studied in the great plains which suggests a long history of eolian activity either in the dune fields or during deposition of the blackwater draw formation

geochemical and mineralogical evidence from eolian sediments for northwesterly mid holocene paleowinds central kansas usa a prominent 4500 km2 dune eld in the great plains is the great bend sand prairie of south central kansas dunes here overlie late quaternary alluvium and were reactivated extensively in the late holocene geomorphic and soil evidence suggests that the most likely eolian sand source is the arkansas river valley to the northwest nevertheless orientations of stabilized dunes indicate that the most recent dune forming winds came from the south or southwest in agreement with modern wind data mineralogy and trace element concentrations in eolian sands of the great bend sand prairie are similar to those of the arkansas river which permits the arkansas river as a sediment source ca and sr abundances which re ect small amounts of carbonate minerals are higher in arkansas river sand compared to eolian sands and show a systematic depletion away from the arkansas river to the southeast these trends are likely due to carbonate mineral depletion downwind from abrasion and size reduction thus paleowinds probably were northwesterly during initial deposition northwesterly winds occur today when dry paci c derived air is dominant we hypothesize that the residence time of this air mass was much greater while dunes initially formed possibly during a warmer and drier mid holocene period 2000 elsevier science ltd and inqua all rights reserved