modelling controls on aeolian dune field pattern evolution a second generation source to sink cellular automaton based model presented here captures and quantifies many of the factors controlling the evolution of aeolian dune field patterns by varying only a small number of parameters the role of sediment supply sediment availability and transport capacity together defined as sediment state in the development and evolution of an aeolian dune field pattern over long time scales is quantified from model simulations seven dune field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of dune interactions the sediment availability of the system and ultimately the development of dune field patterns this model allows predictions to be made about the range of sediment supply and wind strengths required to produce the dune field patterns seen in the real world a new clustered dune field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed dunes bedforms are hypothesized to cluster together simultaneously forming two spatial scales of bedforms without first developing a large basal dune with small superimposed dunes manipulation of boundary conditions produces evolving dune fields with different spatial configurations of sediment supply trends of spacing and crest length increase with decreasing variability as the dune field matures this simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian dune field patterns

aeolian sand sea development along the mid cretaceous western tethyan margin spain erg sedimentology and palaeoclimate implications the existence of a mid cretaceous erg system along the western tethyan margin iberian basin spain was recently demonstrated based on the occurrence of wind blown desert sands in coeval shallow marine deposits here the first direct evidence of this mid cretaceous erg in europe is presented and the palaeoclimate and palaeoceanographic implications are discussed the aeolian sand sea extended over an area of 4600 km2 compound crescentic dunes linear draa and complex aeolian dunes sand sheets wet dry and evaporitic interdunes sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub tropical arid belt along the western tethyan margin sub critically climbing translatent strata grain flow and grain fall deposits pin stripe lamination lee side dune wind ripples soft sediment deformations vertebrate tracks biogenic traces tubes and wood fragments are some of the small scale structures and components observed in the aeolian dune sandstones at the boundary between the aeolian sand sea and the marine realm intertonguing of aeolian deposits and marine facies occurs massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events the cyclic occurrence of soft sediment deformation is ascribed to intermittent marine flooding of aeolian dunes and associated rise in the water table the aeolian erg system developed in an active extensional tectonic setting that favoured its preservation because of the close proximity of the marine realm the water table was high and contributed to the preservation of the aeolian facies a sand drift surface marks the onset of aeolian dune construction and accumulation whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period a prominent aeolian super surface forms an angular unconformity that divides the aeolian succession into two erg sequences this super surface formed in response to a major tectonic reactivation in the basin and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas the location of the mid cretaceous palaeoerg fits well to both the global distribution of other known cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea level lowstand during early mid cretaceous times the occurrence of a sub tropical coastal erg in the mid cretaceous of spain correlates with the exposure of carbonate platforms on the arabian platform during much of the late aptian to middle albian and is related to this eustatic sea level lowstand

how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

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

geological geophysical and thermal characteristics of the salton sea geothermal field california abstract the salton sea geothermal field is the largest water dominated geothermal field in the salton trough in southern california within the trough local zones of extension among active right stepping right lateral strike slip faults allow mantle derived magmas to intrude the sedimentary sequence the intrusions serve as heat sources to drive hydrothermal systems we can characterize the field in detail because we have an extensive geological and geophysical data base the sediments are relatively undeformed and can be divided into three categories as a function of depth 1 low permeability cap rock 2 upper reservoir rocks consisting of sandstones siltstones and shales that were subject to minor alterations and 3 lower reservoir rocks that were extensively altered because of the alteration inter granular porosity and permeability are reduced with depth field permeability is enhanced by renewable fractures i e fractures that can be reactivated by faulting or natural hydraulic fracturing subsequent to being sealed by mineral deposition in the central portion of the field temperature gradients are high near the surface and lower below 700 m surface gradients in this elliptically shaped region are fairly constant and define a thermal cap which does not necessarily correspond to the lithologic cap at the margin of the field a narrow transition region with a low near surface gradient and an increasing gradient at greater depths separates the high temperature resource from areas of normal regional gradient geophysical and geochemical evidence suggest that vertical convective motion in the reservoir beneath the thermal cap is confined to small units and small scale convection is superimposed on large scale lateral flow of pore fluid interpretation of magnetic resistivity and gravity anomalies help to establish the relationship between the inferred heat source the hydrothermal system and the observed alteration patterns a simple hydrothermal model is supported by interpreting the combined geological geophysical and thermal data in the model heat is transferred from an area of intrusion by lateral spreading of hot water in a reservoir beneath an impermeable cap rock

mapping and characterization of small scale aeolian structures on mars an example from the msl landing site in gale crater abstract a new set of methodologies which allow a simple and fast mapping and characterization of small scale aeolian structures on mars is introduced in this work we follow an object based approach in which the bedform crestlines are automatically mapped and characterized from the methodology validation we conclude that the quality of the obtained results is comparable with human produced photointerpretations we show that the accuracy associated with the measurement of mean trends from the automatically mapped patterns is less than 10 through the analysis of two areas located near the msl landing site in gale crater we explore some of the possibilities that the automatic mapping technique enables namely for multitemporal surveys and ripple pattern analysis we demonstrate how the mapped ripple patterns can be used to assess local wind orientations and we analyze some examples that illustrate the diversity of wavelength spatial distributions that can be found on mars we try to relate these pattern wavelength variations with the possible local influence of granulometry and wind shear velocity

paleoclimatic implications of holocene plant remains from the sierra bacha sonora mexico abstract a total of 93 plant taxa were identified from 11 packrat neotoma sp midden samples from the sierra bacha on the coast of the gulf of california near puerto libertad sonora mexico nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr b p sonoran desertscrub was present on rocky slopes throughout the holocene early holocene assemblages dominated by fouquieria columnaris boojum tree reflect vegetation and climate more like modern baja california with greater winter rainfall and cooler summers middle holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold water upwelling locally inhibits summer precipitation the results are similar to all previous midden reconstructions of early and middle holocene climates in the sonoran desert but contradict general atmospheric circulation model simulations

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

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

regional aeolian dynamics and sand mixing in the gran desierto evidence from landsat thematic mapper images spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea the gran desierto of sonora mexico mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes the results were used to interpret the quaternary geologic history of the tectonically active region at the mouth of the colorado river landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain a spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper a simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low albedo accessory grains occurring on dormant aeolian surfaces a technique for discriminating between low albedo materials and macroscopic shade is implemented by combining thermal images with the results of the spectral mixing model the image analysis revealed important compositional variations over large areas that were not readily apparent in the field

holocene vegetation and climate in the puerto blanco mountains southwestern arizona abstract plant macrofossils from 21 pack rat neotoma sp middens at 535 605 m from the puerto blanco mountains southwestern arizona provide and excellent history of vegetation and climate for the last 14 120 yr b p in the sonoran desert a late wisconsin juniper joshua tree woodland gave way to a transitional early holocene desertscrub with sparse juniperus californica california juniper by 10 540 yr b p important sonoran desert plants including carnegiea gigantea saguaro and encelia farinosa brittle bush were dominants riparian trees such as acacia greggii catclaw acacia prosopis velutina velvet mesquite and cerdicium floridum blue palo verde grew on dry south facing slopes in a middle holocene sonoran desertscrub in a warm wet summer climate with frequent winter freezes modern subtropical sonoran desertscrub formed about 4000 yr b p as summer rainfall and winter freezes declined cercidium microphyllum foothills palo verde sapium biloculare mexican jumping bean olneya tesota ironwood and stenocereus thurberi organ pipe cactus became dominant as riparian trees retreated to wash habitats the inferences of a latest wisconsin early holocene summer monsoonal maximum by j e kutzbach 1983 modeling of holocene climates in late quaternary environments of the united states vol 2 the holocene h e wright ed pp 271 277 univ of minnesota press minneapolis are not supported for the southwest apparently the persistence of late wisconsin circulation patterns offset any increases in insolation

spatial analysis of sand dunes with a new global topographic dataset new approaches and opportunities on june 29 2009 version 1 of the aster gdem advanced spaceborne thermal emission and reflection radiometer global digital elevation model was made available at no cost or restrictions to users worldwide via electronic download the aster gdem provides expanded spatial coverage and better resolution than other global digital elevation models dems in this paper we demonstrate how the aster gdem provides new opportunities for investigating large aeolian sand dunes in three dimensions two dune specific spatial analysis methods are presented to illustrate potential applications of these data for discriminating dune generations and quantifying spatial variations of sediment supply moreover we review how existing and emerging fields of dune pattern analysis and simulation modeling will be able to make significant advances through application of these data potentially leading to future progress in studies of dune morphodynamics environmental controls and paleoenvironmental reconstructions copyright 2010 john wiley sons ltd

paleomagnetism of large igneous provinces case study from west greenland north atlantic igneous province abstract we present new paleomagnetic and multi model stereo photogrammetry data from lava sequences in the west greenland part of the north atlantic igneous province naip the joint analyses of paleomagnetic and photogrammetric data yield a well defined paleomagnetic pole located at lat 73 6 n long 160 5 e n 44 95 6 2 k 13 1 age 61 55 ma which is statistically indistinguishable from a pole recently obtained for the eurasian part of the naip on faroe islands riisager et al earth planet sci lett 201 2002 261 276 combining the two datasets we obtain a joint naip paleomagnetic pole in greenland coordinates lat 71 1 n long 161 1 e n 87 95 4 3 k 13 6 age 61 54 ma the results presented here represent the first study in which photogrammetry profiles were photographed at the exact same locations where paleomagnetic fieldwork was carried out and a direct flow to flow comparison of the two datasets is possible photogrammetry is shown to be particularly useful because of i highly precise dip strike measurements and ii detailed field observations that can be made in the laboratory highly precise determination of the structural attitude of well exposed kanisut mb lava sequences demonstrates that their apparently reliable in field dip strike measurements typically are up to 6 wrong erroneous dip strike readings are particularly problematic as they offset paleomagnetic poles without affecting their confidence limits perhaps more important for large igneous provinces is the recognition of a variable temporal relationship between consecutive lava flows we demonstrate how correct interpretation of paleosecular variation facilitated by the detailed photogrammetry analysis is crucial for the rapidly emplaced vaigat formation lavas inaccurate tectonic correction non averaged paleosecular variation and unrecognized excursional directions may perhaps explain why coeval paleomagnetic poles from large igneous provinces are often discordant the difference between the joint naip paleomagnetitc pole and apparent polar wander path poles suggests that they may be less reliable than suggested by their confidence limits

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

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

soil carbonate genesis in the pinacate volcanic field northwestern sonora mexico uranium series methods were used to date and evaluate pedogenic caco3 genesis in the pinacate volcanic field northwestern sonora mexico soils are developed in eolian deposits on lava flows 230th234u dates of pedogenic carbonate are mininum soil ages because of 1 the time needed to yield clasts from flows and to accrete enough carbonate to sample 2 subsequent additions of uranium and 3 continued solution and reprecipitation of carbonate rinds k ar dates of basalt flows are maximum soil ages maximum and minimum rates of caco3 accumulation are calculated from the th u dates and k ar dates respectively the mean maximum rate is 0 13 g caco3 cm2 1000 yr and the mean minimum rate is 0 05 g caco3 cm2 1000 yr least squares regressions of pedogenic carbonate and clay content and of th u ages against k ar ages suggest additions to soils from atmospheric sources throughout the late quaternary morphology of pedogenic carbonate and laboratory data for soluble salts indicate that the climate of the pinacate has not changed significantly during the past 150 000 yr soil variability is influenced by proximity of the eolian source near the periphery of the pinacate carbonate and clay are evenly distributed throughout soil profiles within the volcanic field carbonate and clay are concentrated in soil horizons suggesting that additions from atmospheric sources are slow enough to allow translocation

parabolic megadunes in a subtropical quaternary inland dune field southwestern pampas argentina abstract the utracan paleo dune field la pampa province argentina southern south america was examined by remote sensing morphometric analyses and field surveys as a case study of complex megadunes of inland deserts the paleo dune field is within the utracan argentino valley one of the transverse valleys of la pampa province excavated into a regional structural plain similar paleo dune fields occur within these valleys utracan dunes are mostly stabilized by grasses deeply disturbed by cattle grazing and agriculture the paleo dune field is formed by complex parabolic megadunes with superimposed dunes parabolic megadunes present lengths of trailing arms of 3 3 12 9 km widths between them of 2 2 9 km and heights of 7 38 m the position of the dune noses at the northeastern tip of the bedform and measured sw ne orientation of arms indicate a mean transport direction to azimuth 68 2 above the parabolic arms and isolated in the paleo dune field there are compound blowout dunes clusters of several blowouts forming a larger bedform they show the depositional lobes to the ne with a measured mean transport direction to azimuth 58 1 the sw ne longitudinal length varies between 324 and 1302 m and the nw se transverse length between 114 and 622 m other parabolic arms show low

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

variations in titan s dune orientations as a result of orbital forcing abstract wind blown dunes are a record of the climatic history in titan s equatorial region through modeling of the climatic conditions associated with titan s historical orbital configurations arising from apsidal precessions of saturn s orbit we present evidence that the orientations of the dunes are influenced by orbital forcing analysis of 3 titan general circulation models gcms in conjunction with a sediment transport model provides the first direct intercomparison of results from different titan gcms we report variability in the dune orientations predicted for different orbital epochs of up to 70 although the response of the gcms to orbital forcing varies the orbital influence on the dune orientations is found to be significant across all models furthermore there is near agreement among the two models run with surface topography with 3 out of the 5 dune fields matching observation for the most recent orbital cycle through comparison with observations by cassini we find situations in which the observed dune orientations are in best agreement with those modeled for previous orbital configurations or combinations thereof representing a larger portion of the cycle we conclude that orbital forcing could be an important factor in governing the present day dune orientations observed on titan and should be considered when modeling dune evolution

haynesville and bossier mudrocks a facies and sequence stratigraphic investigation east texas and louisiana usa abstract upper jurassic haynesville and bossier shale gas plays of the northwestern gulf of mexico gom basin produce from organic rich marine transgressive to highstand mudrocks within mixed carbonate clastic depositional systems modern wireline log suites from 200 deep wells were used for detailed correlations and 10 cores throughout the upper kimmeridgian to lower tithonian basin were incorporated into detailed facies stratigraphic and lithologic analyses the haynesville shale lies within a 2nd order transgressive systems tract tst that encompasses back stepping ramp carbonates proximal and marine shales distal below a maximum flooding surface mfs this shale onlaps retrogradational carbonates and basement highs and is capped by the 2nd order mfs bossier shales and local sandstones prograde basinward above the haynesville shale and downlap the 2nd order mfs they grade upward and updip into the thick highstand systems tract hst fluvio deltaic sandstones of the cotton valley group distally organic rich facies developed in restricted bossier environments creating another productive gas shale opportunity several preexisting basement highs in the south and carbonate platforms in the northwest and west restrict and partition the basin thus influencing deposition of highly organic versus nonorganic and siliciclastic dominated versus carbonate dominated lithologies haynesville and bossier shales each compose three upward coarsening cycles that probably represent 3rd order sequences within the larger 2nd order tst and early hst respectively most of the three bossier 3rd order cycles are dominated by varying amounts of siliciclastics deposition of the haynesville mudrocks occurred below storm wave base under mostly dysoxic conditionsm allowing settlement of benthic bivalve communities and bioturbating organisms and oscillating periodically to more anoxic conditions on the seafloor however most of the sparse faunae found in these mudrocks are of planktonic origin bossier mudrocks exhibited more oxygenated and clastic rich lithologies related to progradation of the clastic shoreline and sea level highstand knowledge of lithologic stratigraphic geochemical and faunal variations across mudrock basins needs to be detailed so that shale gas basins might be successfully explored

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

rates of late cenozoic tectonism in the vallecito fish creek basin western imperial valley california the kinetics of continental rifting are recorded in the late neogene sediments of the western imperial valley california the gulf of california opened in its present form about 4 m y ago capturing the colorado river some 5 km of deltaic and fluvial sediments accumulated in the vallecito fish creek area during the interval 4 3 0 9 m y ago initial sedimentation rates were 5 5 mm yr 1 which diminished in an exponential fashion to 0 5 mm yr 1 when isostatic adjustments are accounted for this implies tectonic subsidence rates of 1 5 mm yr 1 decreasing systematically to 0 1 mm yr 1 after 0 9 m y ago right lateral shearing along the elsinore fault zone cut across the basin causing it to be tilted and uplifted at a mean rate of 5 9 mm yr 1 the basin was concurrently rotated as a unit 35 clockwise the dissected pediments and badlands that now characterize the area were formed and eroded in the past 0 9 m y

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

sticky dunes in a wet desert formation stabilisation and modification of the australian desert dunefields independent dating evidence and dune morphology indicate great stability of the australian dunefields most dunefields have seen only minor superficial modification since they were formed up to 1 million years ago despite quite large changes in climate conditions this stability may be partly due to the relatively dense vegetation cover on australian dunes under the marginally arid climate but new studies supported by many older observations suggest that sticky dunes where sand grains are bonded or cemented may form under a broader range of wind climates than widely thought and have greater resistance to reworking new mapping of the australian continental dunefields from satellite imagery shows a previously unrecognised diversity of dune morphologies dune orientation continuity connectedness crest planform crest sharpness spacing and setting all show patterns of variation over the continent these are consistent with the overall low sand supply and variable wind climate that contribute to the dominance of longitudinal dunes but also with only superficial modification of the dunes after their initial formation the longevity of the dunes is likely also partly due to the stabilisation of dune sand by pedogenesis the bonding of sand by pedogenic calcium carbonate gypsum silica and translocated clays the extremely low mobility of the sand dunes has led to preservation of dunes of great age with stacked accretionary units and multiple palaeosols

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

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

paleocurrent evidence for lateral displacement of the pliocene colorado river delta by the san andreas fault system southeastern california more than 600 paleocurrent measurements from fluvial paleochannels of the early colorado river delta plain preserved in the palm spring formation in the fish creek vallecito fcv section of southern california indicate that the fcv section was on the gulf of california southeastern flank of the delta plain as recently as 2 8 ma these measurements imply 130 km of tectonic translation to the northwest since 2 8 ma which can be accounted for by the displacement histories of baja california and component faults of the san andreas system stratigraphic data from the fcv section and other neogene localities when plotted on a palinspastic base indicate 1 marine transgression of a narrow gulf of california rift basin and bouse embayment site of modern lower colorado river by 5 5 ma and 2 uplift of the bouse embayment initiation of the lower colorado river and southward progradation of the delta to essentially its present position by 4 ma

holocene development of multiple dune generations in the northeast rub al khali united arab emirates it has been hypothesised that in sand seas where multiple dune generations occur each generation represents a distinct terrestrial response to contrasting palaeoatmospheric circulation conditions lancaster n kocurek g singhvi a pandey v deynoux m ghienne j f et al 2002 late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania geology 30 991 994 however reconstructing dunefield accumulation and preservation chronologies has often utilised a limited suite of samples because of the difficulties realised in accessing unconsolidated aeolian sands which has limited the capacity to test this hypothesis in the eastern united arab emirates artificial excavation for quarrying and construction have generated a unique opportunity to examine and sample the internal structures of dune systems and to generate data to test the hypothesis of dune generational development this paper presents new data and chronologies from a multigenerational analysis of dune

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

decadal scale evolution of a small dune field keeler dunes california 1944 2010 abstract aerial photographs and satellite images have been used to document the evolution of a small 2 dunefield over the past 60 70 years over this period the dunefield has undergone significant changes including development of well defined linear and crescentic dunes from an initial small area of partially vegetated dunes resulting in an increase in the area of the dunes by a factor of 3 since 1944 the dune field continues to expand toward the southeast but its upwind margins are now experiencing significant erosion because the sand supply is now cut off by dust control measures in the source area and transport pathway this study provides some information on the timescales of dune development in a high energy aeolian environment which formerly experienced an abundant supply of sand with rapid development of crescentic dunes over a period of 20 years the complexity of dunefield development is also highlighted even on decadal timescales and the important role of episodic sediment supply in forming new generations of dunes periods of rapid dunefield change involving lagged input of additional sand from external sources appear to be linked to episodes of high flows in the owens river which is the main sediment source for the keeler dunes

object based dune analysis automated dune mapping and pattern characterization for ganges chasma and gale crater mars abstract a method that enables the automated mapping and characterization of dune fields on mars is described using ctx image mosaics the introduced object based dune analysis obda technique produces an objective and reproducible mapping of dune morphologies over extensive areas the data set thus obtained integrates a large variety of data allowing a simple cross analysis of dune patterns spectral and morphometric information and mesoscale wind models two dune fields located in gale crater and ganges chasma were used to test and validate the methodology the segmentation of dune related morphologies is highly efficient reaching overall accuracies of 95 in addition we show that the automated segmentation of slipface traces is also possible with expected accuracies of 85 90 a qualitative and quantitative comparison of the final outputs with photointerpretations is performed and the precision of the directional characterization of the dune patterns is evaluated we demonstrate a good agreement between the obda outputs and the photointerpreted dune morphologies with local trend deviations below 45 for 80 95 of the mapped areas because the developed algorithm is tuned for the recognition of linear features from the imagery the slipfaces of small barchans can be preferentially overlooked owing to their small extent at the spatial resolution of the ctx mosaics dune types composed of longer linear morphologies are much better represented including correct mapping of secondary structures having proved the effectiveness and accuracy of the mapping procedure we discuss its future applications for the improvement of dune catalogs on mars

sand dune movement in the victoria valley antarctica we use vertical aerial photographs and lidar topographic survey data to estimate dune migration rates in the victoria valley dunefield antarctica between 1961 and 2001 results confirm that the dunes migrated an average of 1 5 m year these values are consistent with other estimates of dune migration from cold climate deserts and are significantly lower than estimates from warm deserts dune migration rates are retarded by the presence of entrained ice soil moisture and a reversing wind regime dune absorption merging and limb extension are apparent from the time series images and account for significant changes in dune form and the field scale dune pattern dune field pattern analysis shows an overall increase in dune field organization with an increase in mean dune spacing and a reduction in total crest length and defect density these data suggest that dunes in other cold desert environments on earth mars or titan that may also have inter bedded frozen laminae still have the potential to migrate and organize albeit at lower rates than dunes in warm deserts

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

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

dune field pattern formation and recent transporting winds in the olympia undae dune field north polar region of mars high resolution imaging science experiment hirise imagery of the central olympia undae dune field in the north polar region of mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines with apparent slipfaces on the primary crests ubiquitous wind ripples areas of coarse grained wind ripples and deflated interdune areas geomorphic evidence and dune field pattern analysis of dune crest length spacing defect density and orientation indicates that the pattern is complex representing two constructional generations of dunes the oldest and best organized generation forms the primary crestlines and is transverse to circumpolar easterly winds gross bed form normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and ne winds and is reworking the older pattern mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the ne the younger pattern appears to represent an influx of sediment to the dune field associated with the development of the olympia cavi reentrant with ne katabatic winds channeling through the reentrant a model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography

the dynamics of star dunes an example from the gran desierto mexico observations of patterns of erosion and deposition and surface wind velocity and direction on a 40 m high star dune in the gran desierto sand sea indicate that interactions between dune form and airflow as winds change direction seasonally play a major role in the formation of this dune type such interactions lead to deposition of sand in the central parts of the dune giving rise to its pyramidal shape as well as to some extension of the linear arms the major arms of the dune studied are oriented ne sw or transverse to summer sse and winter nnw winds an avalanche face up to 10 m high develops during the course of each season flow separation at the main crestline gives rise to a wide zone of lee side secondary flow which moves sand along the base of the avalanche face towards the central part of the dune where it is deposited as wind ripples migrate into zones of locally reduced flow velocity reattachment of the separated flow occurs on the lower part of the n or s arms parallel to the flow spring westerly winds move sand obliquely up the s and n arms of the dune and outwards on the e arm large scale flow separation and diversion are replaced by the development of strong helical eddies in the immediate lee of the main crestline which move sand along avalanche faces and into zones of lower flow velocity at the end of dune arms formation of star dunes in the gran desierto follows a sequence in which crescentic dunes migrating into areas of opposed winds first develop a reversing crestal ridge convergent leeside secondary flows are developed which result in the formation of linear elements parallel to each major wind direction and the concentration of sand in the central part of the dune examples of star dunes at different stages of their development can be documented

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

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

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

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

white sands dune field new mexico age dune dynamics and recent accumulations abstract the white sands dune field situated within the tularosa basin in southern new mexico is thought to have been largely derived by a stepwise progressive deflation of pleistocene lake otero strata with the onset of regional aridity optically stimulated luminescence osl dating of samples from a core that penetrated the gypsum accumulation of the dune field confirm a time of origin at 7000 yr dune sediment is characterized as lagged influx from previously stored lake otero sediment and contemporaneous influx derived from subsequent playas sediment became available for aeolian transport and dune field construction because of a falling water table driven by the regional aridity the current dune field is primarily a wet aeolian system in which the behavior of the accumulation surface over time is a function of the water table although surface cementation by gypsum also imparts aspects of a stabilizing system dune crests are oriented borderline transverse to the annual transport resultant and a monitored dune and its cross strata show that transverse winds from the sw during the late winter and spring account for most of the crest normal migration but a significant along crest component of migration of dune sinuosity occurs with fall and winter winds from the nw and n that strike the crests obliquely trenches across three interdune areas show dune sets and interdune strata climbing at about 0 1 depth of interdune scour increases with interdune streamwise length which acts to enhance the probability of dune cross strata deflation during arid years but also increases the probability of interdune accumulation because the water table shows a net rise over time within the trenches dune sets show a bundling of foresets between reactivation surfaces interpreted as annual cycles that reveal lee face reworking by the oblique nw and n winds and slipface progradation fostered by transverse winds from the sw a progression from grainflow dominated to wind ripple dominated cross strata within a single set revealed in the longest trench is consistent with along crest migration of dune sinuosity interdune laminations show light dark couplets interpreted as annual varves reflecting dry wet portions of the year the number of laminations preserved in vertical sections across an interdune area shows that the record is incomplete and endorses the interpretation of periods of interdune deflation a calculation of the current accumulation rate as based upon the climbing strata within the trenches is significantly greater than the long term accumulation rate determined by osl dates taken from the core in addition to compaction and possible dissolution of gypsum as partial explanations the long term accumulation rate may reflect significant variation in the accumulation rate over time short term deflation of accumulations on a regular basis and or the presence of unconformities within the gypsum body

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

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

basal flow characteristics of a linear medium sliding frictionless over small bedrock undulations the basal deformation of a gravity driven linear creeping flow sliding frictionless over slowly varying bed undulations in two dimensions is analysed analytically using results from second order perturbation theory one of the key results is that close to sinusoidal bedrock undulations up to two different spatial regions of local extrusion flow may arise the offset and onset of extrusion flow is controlled primarily by the amplitude to wavelength ratio above the crest of a sinusoidal bed line a local maximum of the surface parallel velocity develops for e ak 0 138 where a is the amplitude and k is the wave number as e increases from zer to this critical value the vertical position of the velocity maximum moves from kz 1 to kz 1 98 where z is the vertical distance above the mean bed line within and above the trough of a sinusoid a region of local minimum of the surface parallel velocity component develops which shifts from kz 1 towards the bed line as e increases front zero to 1 2 below this velocity minimum and for some distance above the velocity maximum the surface parallel velocity increases with depth this type of extrusion flow will cause a reversal of borehole inclination profiles close to the bedrock

analyzing dune dynamics at the dune field scale based on multi temporal analysis of landsat tm images abstract studying dune dynamics at the dune field scale requires intensive fieldwork and a relatively huge dataset however this is not always possible with the high cost and the limited availability of data here we present a technique based on the analysis of multi temporal landsat tm images for studying the dynamics of different dune morphologies from five dune field sites around the world a pair of landsat tm images for each site has been used after performing several steps of image pre processing and enhancement i e image co registration radiometric calibration and histogram equalization rgb clustering is a commonly used algorithm for data compression and iso clustering in this study we implemented this technique as an unconventional change detection algorithm with 32 clustering partitions per band a bi temporal layerstack of the near infrared bands was the input for the rgb clustering process rgb clustering produced thematic maps that gave an immediate insight into the dune dynamics at the dune field scale given the availability of landsat images the technique gave the best results with dunes developed under uni directional wind pattern in addition it was also easier to detect migration of simple dunes than in compound or complex dunes these maps can be used as a bi temporal digital atlas of large dune systems and help in defining areas for detailed field measurements on dune dynamics and migration moreover it can be implemented in analyzing aeolian systems where field measurements are practically impossible i e large and extra terrestrial aeolian systems

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

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

morphodynamics boundary conditions and pattern evolution within a vegetated linear dunefield abstract the controls on the evolution of linear dunefields are poorly understood despite the potential for reactivation of dunefields which are currently stabilized by vegetation under the influence of 21st century climate change the relative roles of local influences i e boundary conditions and morphodynamic influences i e emergent properties remain unclear chronostratigraphic and sedimentological analyses were conducted on two pairs of linear dunes exhibiting different spatial patterning in the strzelecki desert of central australia it was hypothesized that morphodynamic influences via pattern coarsening would mean that dunes from the simpler pattern defined in terms of the frequency of defects i e junctions and terminations would be more mature older landforms optically stimulated luminescence osl dating of full depth regularly sampled profiles was used to establish accumulation histories for the four dunes and supported by sedimentological analysis to investigate possible compositional differences and similarities between the dunes whilst three of the dunes the two more simply patterned dunes and one of the more complex dunes have accumulation histories beginning between 100 ka and 150 ka and document sporadic net accumulation throughout the last interglacial glacial cycle to the late holocene one of the dunes with relatively complex patterning reveals that the majority of the dune accumulation 7 m at that site occurred during a relatively short window at 50 ka there is no clear sedimentological reason for the different behaviour of the younger dune the data suggest that small scale and essentially stochastic nature of the aeolian depositional erosional system can overprint any large scale morphodynamic controls the concept of dating landscape change by pattern analysis is thus not supported by this study and would require very careful interpretation of the scales being considered this further suggests caution when interpreting dune chronostratigraphies palaeoenvironmentally as different dunes are able to respond very differently to the same external stimulus e g climate in the case studied here a mechanism is proposed to account for the rapid accumulation of the anomalous dune by avulsion of the local aeolian accumulation from one dune ridge to another

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

relations between dune generations in the gran desierto of mexico multiple generations or genetic units of dunes characterized by different morphologies sand grain size and sorting and degree of post depositional alteration of sediments occur in the gran desierto sand sea of mexico dune generations are separated by super bounding surfaces episodic accumulation of dunes is a result of a complex response of different sediment sources to regional climatic and eustatic changes based on examples from three parts of the sand sea relations between different generations of dunes suggest that there are two end member modes of sand sea accumulation 1 stacking or superposition of dune generations and 2 accumulating mosaics of dunes of different morphological units the mode of accumulation is determined by sand supply and accumulation rate stacking occurs where sand supply is high and or the sand sea area is restricted by topography accumulation of mosaics is the preferred mode of accumulation where sand supply is low

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

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

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 dune field pattern boundary conditions aeolian dune field patterns reflect the complex external environment within which the pattern evolves these external environmental controls are the boundary conditions on aeolian dune field pattern formation the influences of boundary conditions such as wind regime and sediment supply are well known however boundary conditions represent a relatively unexplored area of dune field pattern formation source area geometry and areal limits are two newly recognized boundary conditions measurements of crest spacing and crest length from satellite images of dune field patterns with point and line source area geometries show an increase in spacing and crest length over distance whereas spacing and crest length in plane sourced patterns emerge equally across the dune field the impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area and that dune fields that are five times longer in the direction of dune migration than in the crest parallel direction can achieve the greatest spacing within a given area empirical measurements of spacing defect density and dune field area from ten different dune fields ranging over four orders of magnitude in size show that spacing increases and defect density decreases as dune field area increases because the formation of all dune fields involves a wind regime and sediment supply there must be interplay of boundary conditions within the same dune field at different stages of pattern development one boundary condition may dominate over others and with changing climatic eustatic or tectonic parameters boundary conditions may change to modify an existing pattern recognizing boundary condition controls on aeolian dune field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change