avalanche grainflow on a simulated aeolian dune 1 avalanches maintain the slipface of aeolian dunes which alters their airflow characteristics and sediment dynamics and results in the development of grainflow cross bedding we report on a series of experiments in which avalanches were observed on a 1 1 replica of a small 1 2 m brink height transverse dune in the dune simulation wind tunnel under wind velocities of 8 11 m s 1 changes in slipface topography were observed photographically and measured utilizing a 3 d laser scanner with 1 mm2 spatial resolution avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced changes in local slope confirm that the steep pre avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand 32 over all involved portions of the slipface avalanche volumes are measured and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed this independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

interaction between aeolian fluvial and playa environments in the permian upper rotliegend group uk southern north sea the permian upper rotliegend group in offshore uk quadrants 42 43 47 and 48 comprises a sequence of mixed aeolian fluvial playa deposits these deposits are up to 300 m thick and contain a record of the interaction between desert fluvial systems and adjacent aeolian and playa environments the relative dominance of water vs wind transport and deposition in this stratigraphic package was a function of fluctuations in the discharge of ephemeral fluvial systems and changes in water table playa level driven by a combination of climatic change and syndepositional tectonics the rotliegend sedimentary record is punctuated by numerous surfaces recording erosion by wind and water the origin of these surfaces is mostly climatic with periods of increased runoff resulting in fluvial incision especially near active faults during periods of reduced runoff wind erosion of fluvial deposits occurred with fluvially derived sand being reworked into expanding aeolian dune fields wind erosion also occurred as a rising water table isolated dunes from their sediment supply resulting in deflation of dunes down to the water table these surfaces formed in a basin that was subsiding thus even in a background of overall increasing accommodation space climatically driven falls in the water table allowed for periods of erosion the occurrence of significant erosion especially near syndepositional fault zones resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations

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

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

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

large wind ripples on mars a record of atmospheric evolution wind blowing over sand on earth produces decimeter wavelength ripples and hundred meter to kilometer wavelength dunes bedforms of two distinct size modes observations from the mars science laboratory curiosity rover and the mars reconnaissance orbiter reveal that mars hosts a third stable wind driven bedform with meter scale wavelengths these bedforms are spatially uniform in size and typically have asymmetric profiles with angle of repose lee slopes and sinuous crest lines making them unlike terrestrial wind ripples rather these structures resemble fluid drag ripples which on earth include water worked current ripples but on mars instead form by wind because of the higher kinematic viscosity of the low density atmosphere a reevaluation of the wind deposited strata in the burns formation about 3 7 billion years old or younger identifies potential wind drag ripple stratification formed under a thin atmosphere

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

new evidence for the timing of aeolian sand supply to the algodones dunefield and east mesa area southeastern california usa results are presented from a preliminary investigation undertaken to provide insight into the timing and causes of aeolian sand supply and dune dynamics within the east mesa algodones dunefield area of southeastern california samples for radiocarbon and optically stimulated luminescence osl dating were collected from a number of sites along a west east transect extending from the 12 m shoreline of palaeolake cahuilla to the central part of the algodones dunefield the western algodones dunefield is underlain by weathered aeolian sands which yielded an osl age of c 31 ka confirming earlier estimates of the timing of dunefield initiation these deposits are largely buried by unweathered aeolian sediments which gave osl ages of c 3 1 ka and 0 4 ka these ages correspond quite closely with radiocarbon and osl ages obtained from deposits within and immediately overlying the former lake shorelines providing support for the hypothesis that the shorelines acted as an important source of aeolian sediment dates from within the algodones suggest an average long term eastward movement of the dunefield of c 16 6 m ka 1 individual transverse megadunes are indicated to have moved southeastwards at an average rate of 2 5 m a 1 over the last 100 200 yr an order of magnitude higher than previous estimates based on process studies

sedimentology of a proterozoic erg the venkatpur sandstone pranhita godavari valley south india reappraisal of the late proterozoic venkatpur sandstone indicates that the bulk of the sandstone is aeolian in origin aeolian stratification types namely i inverse graded translatent strata ii adhesion laminae iii grainflow strata and iv grainfall strata are present throughout the outcrop belt nine facies have been identified that represent both aeolian and related aqueous environments within a well developed erg cosets of large cross beds at the bellampalli section in the nw of the study area record dune fields in the interior of the sand sea to the se at the godavari river and ramgundam sections a progressive increase in the relative proportion of the flat bedded to cross bedded facies and intercalated non aeolian facies delineates the transition from the dune field to sand sheet environment an alternating sequence of aeolian and marine sediments at laknavaram in the extreme se marks the termination of the sand sea palaeocurrent data suggest that the nw se trend of the sections represents a transect across the sand sea in a direction normal to the resultant primary palaeowind direction abundant horizontally stratified units in the vankatpur sandstone do not always represent the interdune sediments on the basis of the thickness and geometry of the units nature of bounding surfaces and associated facies sequence the facies is variously interpreted to represent interdune inland sabkha sand sheet and coastal sand flat deposits

airflow up the stoss slope of sand dunes limitations of current understanding the windward stoss side of a sand dune acts as a streamlined obstacle in the path of the wind continuity principles necessitate compression of the flow field up the stoss slope of a dune and shear stress must progressively increase as the flow accelerates measurements in transverse flow over thirteen dunes at padre island texas the algodones california and white sands new mexico confirm that velocity profiles on the stoss slope are not log linear and that flow acceleration occurs very close to the surface within an internal boundary layer as a consequence in the overlying flow where measurements have historically been made an overall decrease in shear stress occurs up the slope the actual shape of the velocity profiles and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means

morphometric analysis of slipface processes of an aeolian dune implications for grain flow dynamics grain flows are an integral part of sand dune migration they are a direct response to the local windregime and reflect complex interactions between localized over steepening of a dune slipface andcomplex turbulent airflow on the lee slope grain flows are primarily responsible for delivering sediment to the base of a dune thus driving slipface advancement yet there are few constraints on their morphological and spatial characteristics or the amount of sediment that is redistributed bythese flows using a combination of high resolution terrestrial laser scanning and video recordings four distinct grain flow types are identified based on morphology and area on a dune slipface grainflow morphologies range from small superficial flows to larger flows that affect greater portions of the slipface moving significant amounts of sediment detailed field observations are presented of the dynamics of lee slopes including measurements of the initiation location thickness magnitude and frequency statistics of grain flows as well as volume estimates of redistributed sediment for each grain flow observed high resolution laser scans enable accurate quantification of bulk sediment transfer from individual grain flows and can be used to study grain flows in a variety of environments a categorization of grain flow morphologies is presented that links styles of flows with wind strength and direction turbulent airflow sediment deposition and environment

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

case study of inhomogeneous cloud parameter retrieval from modis data 1 cloud parameter retrieval of inhomogeneous and fractional clouds is performed for a stratocumulus scene observed by modis at a solar zenith angle near 60 the method is based on the use of neural network technique with multispectral and multiscale information it allows to retrieve six cloud parameters i e pixel means and standard deviations of optical thickness and effective radius fractional cloud cover and cloud top temperature retrieved cloud optical thickness and effective radius are compared to those retrieved with a classical method based on the homogeneous cloud assumption subpixel fractional cloud cover and optical thickness inhomogeneity are compared with their estimates obtained from 250m pixel observations this comparison shows a fairly good agreement the cloud top temperature appears also retrieved quite suitably

periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone white canyon southern utah usa the permian cedar mesa sandstone represents the product of at least 12 separate aeolian erg sequences each bounded by regionally extensive deflationary supersurfaces facies analysis of strata in the white canyon area of southern utah indicates that the preserved sequences represent erg centre accumulations of mostly dry though occasionally water table influenced aeolian systems each sequence records a systematic sedimentary evolution enabling phases of aeolian sand sea construction accumulation deflation and destruction to be discerned and related to a series of underlying controls sand sea construction is signalled by a transition from damp sandsheet ephemeral lake and palaeosol deposition through a phase of dry sandsheet deposition to the development of thin chaotically arranged aeolian dune sets the onset of the main phase of sand sea accumulation is reflected by an upward transition to larger scale ordered sets which represent the preserved product of climbing trains of sinuous crested transverse dunes with original downwind wavelengths of 300 400 m regularly spaced reactivation surfaces indicate periodic shifts in wind direction which probably occurred seasonally compound co sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger slipfaceless draa each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio eustatic origin that characterize many permo carboniferous age successions sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level the main sand supply being former shallow marine shelf sediments that lay to the north west sand sea deflation and destruction would have commenced at or shortly after the time of maximum aridity as the available sand supply became exhausted restricted episodes of non aeolian accumulation would have occurred during humid interglacial phases accumulation and preservation being enabled by slow rises in the relative water table subsidence analysis within the paradox basin together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the cedar mesa erg sequences could be the product of 413 000 years so called long eccentricity cycles by contrast annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the cedar mesa succession was reserved for supersurface development

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

windblown desert sands in coeval shallow marine deposits a key for the recognition of coastal ergs in the mid cretaceous iberian basin spain introductionthe action of the wind in ancientsedimentary records is commonlybased on the direct observations ofdune and interdune deposits within ahierarchy of aeolian bounding surfa ces a direct observation of ancientaeolian systems is not always possibleas they are prone to erosion and to theremoval of sand into other uvial andmarine systems although the aeoliandeposits may no longer be present their former existence can be inferredon the basis of grain size characteris tics and aeolian features on grainsurfaces aeolian sediments indeedconstitute an important source formarine deposits kukal and saadal lah 1973 fryberger et al 1983 widespread ne grained very well sorted quartz sandstones characterizeshallow marine facies in the mid cre taceous of the eastern spain iberianbasin the good sorting and round ness of the grains hint at the presenceof a nearby erg system suggestive ofan arid climatic zone along the west ern tethyan margin during the mid cretaceous geological settingthe mesozoic iberian basin along thewestern tethyan margin has one ofthe more complete lower middle cre taceous sedimentary records in eur ope the iberian range is a nw sestriking intraplate fold belt generatedby the tectonic inversion of theiberian basin during the palaeogene fig 1a b salas and casas 1993 capote et al 2002 this basin wasformed by crustal thinning duringthe late permian triassic and latejurassic early cretaceous rift stages salas and casas 1993 arche andlo pez go mez 1996 during thesecond rift stage extensional sub basins were formed as part of thelarger maestrazgo basin i e the east ern sector of the iberian basin fig 1b soria 1997 sands of boththe last synrift unit of these sub basins the escucha formation and of the rst post rift unit of the iberian basin the utrillas formation were depos ited across the estuarine deltaic and uvial environments fig 1c quer ol et al 1992 the sands are domi nantly ne grained show excellentsorting and as they consist almostpurely of quartz they are mineralog ically very mature the escucha and the utrillasformationsthe upper aptian middle albian es cucha formation aguilar et al 1971 sole de porta et al 1994 fig 1c was formed during the last phases ofthe second rift stage that a ected theiberian basin salas and casas 1993 it is a tidally in uenced heterolithicunit dominated by very well sorted ne sand and clay with coal bearingdepositsinitslowerpart andlocallyinthe basal part coarse grained siliciclas tic levels it lies upon the limestonesand marls of the urgonian platform aptian and is covered by sandstonesof the utrillas formation fig 1c pardo 1979 querol 1990 the es cucha formation was interpreted as adeltaic estuarine succession querolet al 1992 with a barrier island sys tem in the northern part of the olietesub basin rodri guez lo pez et al 2005 it was deposited in extensionalsub basins bounded by palaeogeo graphic thresholds produced by listricand block rotation faults the utrillasformation overlies the escucha for mation and is late albian early cen omanian in age and represents uvialdeposits pardo 1979 however theabstract

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

dune migration and slip face advancement in the rabe crater dune field mars 1 eight overlapping images of a dune slip face in rabe crater 35 e 44 s from the mars global surveyor mars orbiter camera show changes interpreted to be multiple grainflow events that would indicate present day sand saltation and dune migration new occurrences of these features appear sporadically throughout late southern summer and early fall and then no further changes occur throughout winter by the following summer the pattern of old streaks had been almost completely covered by new dark streaks assuming that this activity is typical from year to year migration rates are estimated to be on the order of 1 2 cm per martian year produced by south to southeasterly winds that blow mostly during the southern spring and early summer this slow migration rate is consistent with a present day sediment state that is either transport or availability limited

climbing zibars of the algodones abstract zibars are coarse grained low relief slipfaceless eolian bedforms that occur on sand sheets and within interdune corridors of many eolian sand seas zibar surface features consist exclusively of wind ripples and local shadow and shrub coppice dunes associated with vegetation a study of zibars located on the southwestern margin of the algodones dune field california shows that zibars and their associated interzibar areas are migrating features oriented transverse to oblique to the resultant sand transport direction zibars leave deposits formed by deposition on the zibar lee face the zibar shape modifies the near surface airflow to produce a subtle grain size change across the zibar interzibar surface flow expansion not separation leeward of the zibar crest causes the lee face deposits those preserved upon bedform migration to have the finest grain size on the zibar interzibar surface sediment coarser than that deposited on the zibar lee face is transported more slowly and less frequently and thus becomes concentrated on the zibar stoss slope and ultimately becomes interzibar deposits migration of zibars and interzibar areas can produce two characteristic depositional sequences depending upon the angle of climb for low angles of climb a sequence of stacked amalgamated interzibar deposits is preserved zibar deposits are absent amalgamated interzibar deposits consist of low angle usually less than 5 wind ripple laminae of medium to coarse sand given higher angles of climb deposits of both the entire interzibar and zibar lower lee face are preserved low angle interzibar deposits of medium to coarse sand are overlain tangentially by finer grained fine to medium sand wind ripple laminae dipping less than 15 of the zibar lee face lee face wind ripple laminae are sharply truncated and overlain by the succeeding set of interzibar wind ripple deposits this zibar interzibar sequence is distinctive and allows for the detailed interpretation of some ancient sand sheet deposits as left by migrating zibars a possible example of ancient zibar deposits is present in the entrada sandstone jurassic of southwestern colorado

sedimentary record of erg migration the sedimentary record of erg eolian sand sea migration consists of an idealized threefold division of sand sea facies sequences the basal division here termed the fore erg is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment these sand bodies consist of eolian strata deposited by small dune complexes zibars and sand sheets the fore erg represents the downwind leading edge of the erg and records the onset of eolian sedimentation basin subsidence coupled with erg migration places the medial division termed the central erg over the fore erg strata the central erg represented by a thick accumulation of large scale cross stratified sandstone is the product of large draa complexes eolian influence on regional sedimentation patterns is greatest in the central erg and most of the sand transported and deposited in the erg is contained within this region reduction in sand supply and continued erg migration will cover the central erg deposits with a veneer of back erg deposits this upper division of the erg facies sequence resembles closely the fore erg region similar types of eolian strata are present and organized in sand bodies encased in sediments of the upwind flanking depositional environment s back erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration or they may be completely absent because of great susceptibility to postdepositional erosion tectonic climatic and eustatic influences on sand sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence the resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western north america europe southern africa and south america

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

an empirical model of aeolian dune lee face airflow airflow data gathered over dunes ranging from 60 m tall complex crescentic dunes to 2 m tall simplecrescentic dunes were used to develop an empirical model of dune lee face airflow for straight crested dunes the nature of lee face flow varies and was found to be controlled by the interaction of at least three factors dune shape the incidence angle between the primary wind direction and the dune brinkline and atmospheric thermal stability three types of lee face flow separated attached and deflected along slope or attached and undeflected were found to occur separated flows characterized by a zone of low speed 0 3o of crestal speed back eddy flow typically occur leeward of steep sided dunes in transverse flow conditions unstable atmospheric thermal stability also favours flow separation attached flows characterized by higher flow speeds up to 84 of crestal speed that are a cosine function of the incidence angle typically occur leeward of dunes that have a lower average lee slope and are subject to oblique flow conditions depending on the slope of the lee face attached flow may be either deflected along slope lee slopes greater than about 20 or have the same direction as the primary flow lee slopes less than about 20 neutral atmospheric thermal stability also favours flow attachment as each of the three types of lee face flow is defined by a range of wind speeds and directions the nature of lee face flow is intimately tied to the type of aeolian depositional process i e wind ripple or superimposed dune migration grainflow or grainfall that occurs on the lee slope and the resulting pattern of dune deposits therefore the model presented in this paper can be used to enhance the interpretation of palaeowind regime and dune type from aeolian cross strata

modeling heterogeneity in a low permeability gas reservoir using geostatistical techniques hyde field southern north sea hyde field is a small 133 gcf footnote reserves gas field in the united kingdom southern north sea the reservoir the permian rotliegende group contains eolian fluvial and sabkha facies the eolian facies constitute the dominant flow units illite cementation results in low reservoir quality in the eolian facies permeability averages 2 5 md and rarely exceeds 10 md to maximize recovery from this field with its thin gas column and low reservoir quality hyde has been developed with three long reach horizontal wells a reservoir model that could accurately predict future production had to include a full range of heterogeneities from the effects of thin muddy laminations at the core plug scale to the spatial distribution of eolian fluvial and sabkha facies over the entire field at the largest scale by carefully defining the model s layering scheme we incorporated strongly deterministic elements where facies trends were influenced by laterally extensive stratigraphic surfaces the distribution of facies within stratigraphic units was modeled using geostatistical techniques average permeability values were assigned to the poorest quality fluvial and muddy sabkha facies permeability values for the eolian and sandy sabkha facies were determined by upscaling models of their internal permeability structure the resulting distribution of permeabilities across the field present in a 2 2 million cell model was upscaled into a coarser grid suitable for simulating the full field this new model produced a significantly better match to dynamic data than did an earlier simple layer model that was used to take the field to sanction the results of our work suggest that stochastic modeling allowed us to represent a level of heterogeneity that was not captured by the earlier simple layer model by capturing this level of heterogeneity we were able to achieve a significantly better match of model predictions to production data

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

erg deposits in the lower jurassic wingate sandstone northeastern arizona oblique dune sedimentation the lower jurassic erg aeolian sand sea deposits of the wingate sandstone on the colorado plateau are beautifully exposed near many farms arizona these 3 d outcrops allow a detailed study of structures and sequenses in the erg body the erg sequence comprises chiefly oblique dune deposits the dune facies are in most cases characterized by a well developed tripartite upbuilding each dune coset contains unusually thick and intricate bottomsets medial low angle dipping toesets and upper steeply dipping foresets the foresets reveal significant across crest transport of sand and dip within a narrow range of directions towards the ese the bottomset beds are composed of compound cross bedding that documents strong along crest transport towards the ssw whereas the toeset beds reveal upslope downslope and along crest transport of sand the ancient dunes apparently formed in a directionally varying wind flow with prevailing winds early summer from the nw and periodic strong winds late summer from the sw the dunes were oblique not only to seasonal transport directions but also to the resultant annual transport direction and dune migration direction this was caused by the interaction of the dune system with the primary winds which resulted in secondary airflow and significant along crest transport of sand the erg deposits at many farms are separated by a number of super bounding surfaces suggesting several episodes of erg formation and destruction the initial erg system was dominated by transverse dunes but overlying ergs only contained oblique dunes all erg systems were bounded to the sw by wide regions of erg margin environments in which aeolian sand sheet fluvial and lacustrine facies were deposited even though fluvial deposits are absent from the main part of the sequence at the study area the effects of this system are reflected within the erg deposits at many farms

the relationships between sedimentary structures transport directions and dune types in mesozoic aeolian sandstones atacama region chile extensive occurrences of upper jurassic to lower cretaceous aeolian sandstones form part of a thick sequence of terrigenous red beds in northern chile these sediments accumulated in a n s elongated intermontane back arc basin on the landward side of an active volcanic chain this volcanic chain which was produced by subduction beneath the continental margin provided the source of almost all the clastic sediments the aeolian sands formed isolated dune fields covering only part of the depositional basin at any one time cosets of cross bedded sandstone up to 40 m thick represent the deposits of linear draas cross bedded sets which average between 0 5 and 1 m in thickness were produced by the migration of small dunes down and along the gentle lee slopes of the draas the majority of foreset laminations in the cross bedded sets are thin parallel and persistent they are the product of the lateral migration of dunes which developed oblique to the prevailing winds foreset laminations dip at low angles averaging 19 well below the angle of repose of dry sand most of the laminations originated by tractional processes rather than by grainflow avalanching or grainfall this conclusion indicates that the dunes were gently undulating with no slip faces the orientation of the direction of maximum dip of foreset laminations does not provide a reliable indicator of the palaeowind direction although individual sets or cosets commonly show a unidirectional pattern significant variations have been recorded between sets of the same age at nearby locations and vertically between one coset and the next variations in vertical sections were produced by the superimposition of draas with different orientations

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

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

aeolian stratification and facies association in desert sediments arran basin permian scotland abstract permian aeolian sediments on the island of arran are divisible into dune including draa and interdune deposits both types display a distinctive and unusually wide variation in grain size the dominant features of the dune deposits are grainfall lamination sandflow lamination and inverse graded lamination associated with ripple form lamination and normal graded lamination the flat lying aeolian interdune deposits are characterised by granule and sand ripples horizontal lamination in coarse sand and granules plane bed lamination and inverse graded lamination associated structures include ripple form lamination and deflation lags three types of trace fossil associated with completely bioturbated horizons occur in some low angle dune and interdune deposits the aeolian facies interfinger with alluvial fan deposits giving rise to three recognizable facies belts marginal aeolian deposits are associated with fluvial conglomerates and are dominated by interdune deposits and occasionally very thin barchan deposits set height 3 37 cm intermediate aeolian deposits are characterized by interbedded crescentic dune small draa dune set height 5 cm 4 5 m and interdune deposits and rare fluvial and lake sediments basinal aeolian deposits are dominated by draa deposits dune set height 0 2 28 m associated with rare interdune sediments transverse dunes and draas were moved by north eastern palaeowinds towards the foot of the alluvial fans the aeolian sediments were deposited in a fault bounded desert basin

development of spatially diverse and complex dune field patterns gran desierto dune field sonora mexico the pattern of dunes within the gran desierto of sonora mexico is both spatially diverse and complex identification of the pattern components from remote sensing images combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns age bracketing by optically stimulated luminescence osl indicates that the simple patterns represent relatively short lived aeolian constructional events since 25 ka the simple dune patterns consist of i late pleistocene relict linear dunes ii degraded crescentic dunes formed at 12 ka iii early holocene western crescentic dunes iv eastern crescentic dunes emplaced at 7 ka and v star dunes formed during the last 3 ka recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern palaeowind reconstructions based upon the rule of gross bedform normal transport are largely in agreement with regional proxy data the sediment state over time for the gran desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment ancestral colorado river sediment and contemporaneous influx from the lower colorado river valley and coastal influx from the bahia del adair inlet aeolian constructional events are triggered by climatic shifts to greater aridity changes in the wind regime and the development of a sediment supply the rate of geomorphic change within the gran desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests

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

algodones dune field of southeastern california case history of a migrating modern dune field the algodones dune field of southeastern california is one of the largest active dune fields in north america the dune field is migrating in an easterly direction oblique to the resultant sand flow direction s 24 e the migration of the algodones results from an interaction between regional winds and the dune field this interaction generates a localized secondary flow that has caused the dune field to migrate in a direction oblique to the resultant sand flow direction four lines of evidence suggest that the algodones has migrated in an easterly direction 1 a ramp interpreted as the trailing edge of the dune field 35 m thick and 500 m wide composed of aeolian deposits that borders the western edge of the dune field no similar deposits are found on the eastern leading edge margin of the dune field 2 leading edge sand sheet deposits are exposed in interdune areas within the dune field these deposits are west of the modern leading edge sand sheet 3 across the breadth of the dune field sands are consistently coarser and more poorly sorted in the west and finer and better sorted in the east this observation suggests that sand is transported from west to east 4 eastward migration of a large compound complex crescentic dune if the dune field continues to migrate it will deposit a vertical sequence consisting of a basal sand sheet deposit consisting of wind and water ripple laminae small scale aeolian cross strata and ephemeral stream wadi deposits aeolian dune deposits consisting of medium scale aeolian compound cross strata small scale simple sets of aeolian cross strata with highly variable dip directions a sand sheet containing low angle wind ripple cross strata capped by a coarse sand lag super bounding surface

modeling the influence of moho topography on receiver functions a case study from the central hellenic subduction zone 1 pseudospectral 2d modeling of wave propagation provides a fresh look at receiver function data from the hellenic subduction zone it is shown that distinct moho topography which is suggested for this complex subduction environment from various geophysical data sets can provide a conclusive explanation for previously observed inverted moho phases in the forearc as well as for a complex sequence of apparently dipping conversions in the volcanic arc prominent effects of strongly dipping discontinuities include the change of sign in ps phases refracted past the vertical and multiple p reflections that cannot be separated from ps conversions during receiver function processing unambiguous identification of these phenomena can be hampered by poor azimuthal coverage of the data still in regions where discontinuity topography can reasonably be expected its effects should be considered when interpreting receiver functions as results might be spurious otherwise

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation