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

a drying upward aeolian system of the bohdasin formation early triassic sudetes of ne czech republic record of seasonality and long term palaeoclimate change abstract the record of aeolian processes was studied in early triassic sandstones of the upper part of the bohdasin formation ne bohemia an isolated erosional relict of a triassic fluvial aeolian succession in the sudetes block of the bohemian massif central europe the aeolian system exposed in the dev t k i quarry near cerven kostelec provides a significant addition to the generally poorly preserved record of early triassic palaeoclimate and palaeowind regime in central europe two mutually interbedded facies occur in the aeolian succession 1 dune facies comprising cross strata that show interdune reactivation and superimposition bounding surfaces and 2 interdune facies formed by horizontally stratified commonly mud draped sandstones which display a number of indicators of damp to wet conditions and fluctuations in water table the succession of the dev t k i sandstones is interpreted as a record of migration and climb of dunes with intervening interdune flats which replaced an underlying fluvial system it is likely that a coeval fluvial system existed near the dev t k i dune field providing available sand in dry periods and flooding in wet periods dominant palaeowind directions are southwestward and northward in present day coordinates repeated reversals of palaeowind direction interpreted as seasonal are recorded in changes in the internal structure of the cross strata reworking and reactivation in the dune migration direction at least some episodes of dune reworking occurred simultaneously with episodes of water table rise a drying upward trend in the aeolian succession is interpreted from evidence for increased availability of sand through time the upward transition from a braided fluvial to a wet drying upward aeolian system within the bohdasin formation represents a shift toward maximum aridity of the palaeoenvironment which marks also the peak arid conditions in the long term palaeoclimatic evolution of the carboniferous triassic succession of the sudetes region and correlates with the establishment of aeolian settings in other regions of central europe during the early triassic the record of changing palaeowind directions documented in several cases to have been coupled with episodes of rapid rise in water table is taken as evidence for pronounced climatic seasonality and brings additional support to the models predicting strong monsoonal circulation during the early triassic affecting particularly the eastern subequatorial coast of pangaea and adjoining regions

the variability of nonmigrating tides detected from timed saber observations this paper deals with the variability of the nonmigrating tides detected from the observation of the saber instrument on board the timed satellite during the 11 year solar period from 2002 to 2012 the longitudinal wave number spectra with 1 day resolution were first estimated from the temperature data measured at the mlt altitudes 70 110 km and at the lower midlatitudes and low latitudes between 45 then we used the wave number 4 component to obtain the nonmigrating tides in which the dominant component de3 was further analyzed in detail we found that the properties of the spatial distribution and large time scale variation of the de3 component are similar to those of the previous works which used the interpolated data with 2 month resolution these properties are that the de3 component occurs mainly at the low latitudes within 30 and at the altitudes from 90 to 110 km the tidal amplitude is larger during boreal summer and early autumn smaller in spring and almost tends to disappear in winter the component is slightly stronger during the eastward wind qbo phase than the westward phase practically the higher resolution data were used to reveal the day to day variability of the de3 component it is found that 1 the variability occurs mainly at the altitudes from 100 to 110 km with a peak at 106 km 2 it is strong at the low latitudes and peaks around the equator as well slightly stronger in the southern hemisphere than in northern one 3 it is considerably larger around solstitial months than equinoctial months and 4 it would not experience an obvious interannual variation the day to day variability of the de3 component may be explained by the variance of the absolute amplitudes and the contribution of the wave phases and the later seems to play more important role

high resolution stratigraphy and depositional model of wind and water laid deposits in the ordovician guaritas rift southernmost brazil abstract the upper portion of the pedra pintada alloformation includes about 100 m of mostly eolian deposits this paper emphasizes the vertical succession and lateral association of sedimentary facies based on analysis of outcrop data and aerial photographs as well as the hierarchy and origin of bounding surfaces it aims to propose a high resolution stratigraphic and depositional model that may be useful to exploitation of eolian reservoirs the succession has been preserved due to basin subsidence and is described in terms of four facies associations that constitute three dominantly eolian units these units are sharply bounded by major flooding surfaces super surfaces that in turn are overlain by 1 to 2 m thick dominantly water laid facies lacustrine fluvial deltaic and eolian both their internal organization and boundaries were controlled by changes in the base level rise rate the basal eolian unit is composed of crescentic eolian dunes and damp interdune deposits ascribed to a wet eolian system on the other hand eolian units ii and iii also characterized by crescentic eolian dunes simple and compound deposits were related to dry eolian systems since they comprise dry eventually wet interdune facies eolian unit iii is truncated by basinwide unconformity which is then overlain by the ephemeral fluvial deposits varzinha alloformation this second type of super surface is related to climate induced wind erosion deflation down to the water table level regional stokes surface followed by fluvial incision linked to tectonic activity

sedimentology diagenesis and reservoir characterization of the permian white rim sandstone southern utah implications for carbon capture and sequestration potential rising co2 emissions have caused scientists and policy makers to explore potential solutions to reduce atmospheric co2 levels including carbon capture and sequestration this project funded through the department of energy carbonsafe initiative aims to characterize the potential storage capacity and preferential fluid flow pathways through the permian white rim sandstone on and near the san rafael swell utah to assess the formation s viability as a possible co2 sequestration reservoir a diverse suite of sedimentological observations and diagenetic analyses was used to assess the white rim sandstone s reservoir potential including detailed outcrop observations facies descriptions and ichnology measured stratigraphic sections with associated correlations permeability measurements thin section petrography and visible and near infrared spectroscopy stratigraphically the white rim sandstone has two major units separated by a marine transgressive surface the lower eolian unit is characterized by decimeter to meter scale trough cross bedded grain flow and wind ripple facies the upper reworked shallow marine unit has a consistent set of facies at all three field sites 1 soft sediment deformation facies e g contorted bedding or clastic pipes 2 symmetric ripple laminations 3 bioturbated dominantly horizontal and 4 bioturbated dominantly vertical this set of four facies represents the transgression of the permian kaibab sea over the permian white rim coastal dune field the outcrop samples and subsurface core samples 1561 2243 m deep and 33 50 km away from the outcrop localities experienced different diagenetic fluid flow histories that drastically impacted the reservoir properties outcrop samples have initial quartz overgrowth cements followed by rim forming calcite cements iron oxide cements and occasional oil staining in contrast the core samples show significant compaction followed by quartz overgrowth cementation and a later stage of patchy large pore filling calcite cement that eliminated the porosity and permeability of the potential reservoir 0 1 md outcrop permeability values tend to reflect textural differences in facies particularly the presence and spacing of internal laminations and bounding surfaces facies with fewer internal laminations such as the grain flow facies have higher permeability values than facies with closely spaced internal laminae such as the wind ripple facies disruption of original bedding e g soft sediment deformation or bioturbation alters original depositional textures and creates preferential flow pathways with the potential to increase permeability overall if the diagenesis and resulting low permeability values of the core samples are representative of the white rim sandstone at depth then the white rim sandstone would not make a high quality storage reservoir despite initial promising outcrop results

ductile rebound of an orogenic root case study and numerical model of gravity tectonics in the western gneiss complex caledonides southern norway the main caledonian deformation in the western gneiss complex southern norway has been interpreted as resulting from the gravity driven ductile rebound of the orogenic root detailed field data from the sognefjord profile a 60 km long continuously exposed shore section through the complex are compared with the results of a numerical scale model of root rebound dimensioned according to reconstructions of the overall tectonic evolution the strain pattern in the model can be closely tied to the previously recognized structural regimes from east to west r1 little deformed precambrian basement stiff orogenic lid basal part of upper crust r2 heterogeneously sheared basement simple shear domain at upper crust lower crust boundary r3 completely overprinted basement with eclogitic remnants pure shear regime in the lower crust of the rebounded root subsequent to root rebound the profile remained practically unaffected by later tectonic events except for tilting uplift erosion providing a unique example of deep seated gravity tectonics

controls on marine erg margin cycle variability aeolian marine interaction in the mid cretaceous iberian desert system spain the interaction between aeolian dunes of the iberian erg and tethys waters during the mid cretaceous led to a variety of sedimentary facies associations such as subtidal deposits aeolian dunes playa lakes coastal lakes with tidal creeks and marshes and lagoonal embayments with tide influenced delta deposits facies associations are organized in several stacked cycles every cycle is defined by a sand drift surface separating playa lake deposits below from aeolian dune deposits above followed by a transgressive surface separating aeolian deposits below from shallow marine deposits above the latter are covered by playa lake deposits and finally topped by the next sand drift surface similar marine erg margin cycles have been explained previously in terms of high order relative sea level variations normally controlled by glacioeustasy the studied erg margin developed during the mid cretaceous which is considered to be the archetypal example of a polar ice free greenhouse period this manuscript presents an alternative explanation for the cycles as caused by climate induced variations in the aeolian sediment supply in this scenario orbitally induced latitudinal shifts of the boundary between climate belts led to alternating periods of increased and decreased precipitation in the highland catchments of the back erg system variscan iberian massif when climate belts shifted to lower latitudes back erg highlands were under the influence of the northern warm humid belt while arid conditions prevailed in the lowland central erg increased precipitation in the highlands and the consequent recharge of ground water led to a rise of the phreatic level in the erg system that diminished wind erosion and windblown sediment input to the fore erg so that the desert margin contracted with ongoing basin subsidence this favoured the transgression the increased desert ground water flux favoured permanent coastal lakes in the fore erg margin and the local development of vegetation in places where such lakes lagoons were connected to the sea tidal channels were active as seen nowadays along the desert coast of qatar persian gulf when climate belts moved to higher latitudes the catchment areas in the back erg iberian massif were under the influence of the northern hot arid belt and a decrease of precipitation led to a drop of the phreatic level allowing deflation of dunes and exposed wadi channel floors and the formation of desert pavements and deflation lags in the back erg area this favoured the import of large volumes of windblown sand and dust forcing progradation of the erg and consequently a retreat of the coastline the sand fraction accumulated in climbing aeolian dunes and dust was trapped in extensive playa lake systems another long term allocyclic control is formed by active extensional tectonics that enhanced the creation of accommodation space especially in the first cycle a high ground water table sustained by subsurface water supply from the variscan iberian massif generated coastal fresh brackish lakes in which tide influenced meandering channels and salt marshes developed erg margin cycles thin upward in response to a decrease of the rate of basin subsidence suggesting that transgressions led to deep erosion of the underlying aeolian dune sands

an example of liquefaction induced interdune sedimentation from the early jurassic navajo sandstone usa abstract extensive outcrops of navajo sandstone in the southwestern united states expose eolian dune deposits that are subdivided in a complex array of foresets and bounding surfaces in the glen canyon region and other places this architecture is frequently disrupted by large scale soft sediment deformation features these features have been attributed to episodic liquefaction events that affected saturated sand below the level of the interdune surface though erosional truncation of deformation features indicates that liquefaction often occurred in the uppermost levels of navajo dune deposits very few paleotopographic disruptions due to subsurface deformation have been documented navajo sandstone outcrops in west canyon utah provide unusually comprehensive exposure of architectural details linking large scale deformation features and associated interdune deposits enabling a well constrained appraisal of their genesis at this location a 23 m succession of sandstone mudstone carbonate and chert deposits overlies a zone of deformation that extends laterally for hundreds of meters this horizontally stratified lens occupies an abrupt synform along a bounding surface between successive crossbeds that otherwise appears as a featureless sub horizontal plane large scale foresets below this bounding surface oversteepen at the margins of the synform and grade downdip into contorted stratification and structureless expanses the authors propose that liquefaction in the jurassic erg caused localized subsidence of a minor portion of a dry interdune surface to a position several meters below the contemporary water table a succession of hyperpycnal sand flows lacustrine evaporites and eolian sheet and dune deposits filled this depression prior to the advance of large dunes across the site the process response dynamics evident in this outcrop suggest that deformation may have exercised significant non systematic control over depositional architectures in areas of the erg prone to liquefaction similar dynamics are unknown from modern desert environments and their intrinsic scale defies laboratory simulation therefore close investigation of these ancient features is essential for exploring the full range of depositional controls that may be encountered in other ancient eolianites on earth and in eolian accumulations on other planets

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

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

eolian deposits of the northern margin of the south china jianghan basin reconstruction of the late cretaceous east asian landscape in central china abstract the late cretaceous honghuatao formation includes a succession of thick clastic sedimentary sequences which are widely exposed in northwestern jianghan basin central china here detailed sedimentological and facies architectural analyses are performed allowing to re interpret and identify the controversy for sedimentary environment and to investigate the paleoclimatic condition the honghuatao stratigraphic sequence includes eolian dunes and dry interdunes deposits with fluvial channel deposits at the bottom and top the vertical change between fluvial and eolian systems indicates alternating wet and dry climate at the same time the provenance analysis combined with the paleocurrents from the w nw and ne indicates that huangling dome south qinling belt and dabie orogen supply the main detrital source for the honghuatao formation the late cretaceous first rifting subsidence in the jianghan basin provided accommodation space for the preservation of the aeolian accumulation moreover the existence of the mountain belts around the basin that is the orographic effect precluded the winds from transporting humidity to the interior of the jianghan basin generating the desert system this study shows that the formation of eolian deposits in the honghuatao formation and coeval strata in numerous adjacent basins was a sedimentary response to the prevailing desert climate in the mid to low latitude areas of the northern hemisphere during the late cretaceous which was predominately controlled by the subtropical high pressure system on a planetary scale

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

overview of the meso to neoproterozoic evolution of the vindhyan basin central india abstract despite its origin in a stable intracratonic basin the vindhyan supergroup central india embodies tectonic driven depositional cycles of various orders a marked change in sedimentation pattern was coupled with a transient plate margin compression in the otherwise extensional regime an unconformity laterally correlatable with a conformity that divides the supergroup in two sequences arose in consequence maximum flooding surfaces mfs within the sequences can generally be correlated with intrabasinal volcanism that drastically diminished through the initial rift to later sag stage of basin evolution concomitantly with the change in tectonic milieu paleoseismic deformation structures and related deposits also became drastically reduced in scale nevertheless metre and decametre scale depositional cycles correlate well with the subtle record of paleoseismicity intermittent tilting of the depositional substratum is demonstrable in systematic bed dip changes in metre scale fining upward depositional cycles in the rift stage in the sag stage it is reflected merely in consistent deflection of paleocurrent directions at the top of the decametre scale parasequence sets towards the top of the supergroup progressive thickening and decreasing frequency of parasequences indicates a declining rate of basin subsidence progradation despite punctuation thus resulted in basin filling

inconsistencies between pangean reconstructions and basic climate controls the supercontinent pangea dominated our planet from the permian into the jurassic paleomagnetic reconstructions have been used to estimate the latitudinal position of pangea during this 100 million year period atmospheric circulation recorded by eolian sandstones in the southwestern united states shows a broad sweep of northeasterly winds over their northernmost extent curving to become northwesterly in the south this evidence is consistent with paleomagnetic reconstructions of the region straddling the equator in the early permian but is at odds with its northward movement to about 20 n by the early jurassic at least one of the following scenarios must be true the latitude based on paleomagnetism is incorrect the interpretation of how winds shaped the dunes is mistaken the basic climate controls in the jurassic were different from those of today or the paleogeographic reconstructions available are insufficient to adequately reproduce the wind fields responsible for dune formation

marine to fluvial transition proterozoic upper rewa sandstone maihar india abstract the proterozoic upper rewa sandstone in central india is generally interpreted as entirely marine a detailed study in maihar madhya pradesh however reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints facies associations differ in stratal geometry and arrangement palaeocurrent direction and pattern as well as in grain size and sorting the fine grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross stratification and their packages as well as local evidence of current reversals subordinate beach deposits are also present the major palaeocurrent direction is highly consistent and westward the coarse grained often granule rich sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear these braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence the palaeocurrent pattern is unimodal and northwestward but its dispersion covers 180 the rocks are poorly sorted and at places incorporate sand clasts although they are virtually mud free and mineralogically mature as in two other associations the medium to fine grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry they incorporate representatives from the previous two associations as well as translatent strata interdune erg deposits and possibly aeolian cross strata consequently the palaeocurrent pattern is polymodal with a spread over 270 an overall coarsening up trend in the fluvial part and thinning up trend in the tidal part imply progradation in spite of evidence of basin subsidence a high rate of sediment discharge from a perennial river system in a humid climate is suggested

sedimentary structure of large sand dunes examples from dumont and eureka dunes california the current research presents ground penetrating radar images up to 30 m in depth of two large desert dunes in california usa a barchanoid ridge in the dumont field and a linear dune in the eureka expanse the radar images show a complicated structure of internal layering with ascending cross strata cross bedding and bounding surfaces cutting through layers additional research using seismic refraction surveys and sand sampling refine the image of the subsurface 5 m structure the sedimentary structure of the dune shows a strong internal layering with a cemented structure that may immobilize and influence migration of dune expanses the subsurface features of the sand dune fields in the mojave desert provide evidence of dune building wind regime and precipitation history

stratigraphic architectures spotted in southern melas chasma valles marineris mars comment comment dromart et al 2007 1 describe a spectacular stratigraphic complex within southern melas chasma vallis marineris mars following a rigorous stratigraphic description of the complex they proceed to interpret the responsible depositional processes as analogous to subaqueous channel levee

morphology internal structure and mechanics of small longitudinal seif dunes in an aeolian horizon of the proterozoic dhandraul quartzite india the excellently preserved metre scale linear bedforms in an aeolian horizon of the proterozoic dhandraul quartzite india show oppositely dipping strata arranged in a zigzag pattern the strata are dominantly of translatent type deposited by along crest migrating ripples preserved on the flanks of dunes the bedforms thus may be interpreted in a morphodynamic sense as longitudinal seif dunes in order to determine the regional palaeoflow pattern the migration directions of ripples preserved at the top of sheet sandstones that are associated with the dune cross strata and internally show subhorizontal translatent strata were measured a directionally varying flow with a mean direction nearly parallel to the mean axial trend of the dunes is indicated the kinematics of the dunes were thus largely the result of alternate operation of two oblique flow components each of which was deflected at a dune crest into an along crest flow on the downwind flank of the dune the deflected flow formed along crest migrating ripples which in turn deposited climbing ripple strata alternate deposition on the two opposite flanks resulted in near vertical accretion of the dunes as is indicated by the zigzag pattern of stratal arrangement

initiation of 2 45 2 1 ga intracratonic basin sedimentation of the hurwitz group keewatin hinterland northwest territories canada continental to shallow marine rocks of the hurwitz group exposed as outliers across the hearne province in northern canada were deposited between 2 45 and 2 11 ga on a 3 3 2 6 ga granite greenstone basement initiation of the hurwitz basin was characterized by low relief and rates of subsidence that never progressed beyond the intensity of regional sagging during stage 1 polymictic conglomerate lower noomut formation was deposited in palaeovalleys cut into archaean basement and subarkose to quartz arenite quartz pebble conglomerate upper noomut formation was deposited on a low relief sand plain abundant first cycle quartz rich sandstones are attributed to intense humid climate weathering in low relief source areas and at sites of temporary storage as well as to repeated fluvial and eolian reworking interbedding of pyritic palaeoplacers and continental redbeds denotes fluctuating levels of atmospheric oxygen disappearance of pyritic palaeoplacers upsection signifies ultimate changeover to an atmosphere with sustained free oxygen stage 2 padlei formation was marked by a climatic shift toward cold glacial conditions as indicated by dropstones greywacke till pellets and possible ikaite pseudomorphs in lacustrine rhythmites stage 3 kinga formation represents a return to wet warm conditions with fluvial eolian deposition of subarkose and quartz arenite on a low relief sand plain maguse member and deposition of supermature quartz arenite in a vast 100 000 km2 minimum shallow water lake or series of lakes whiterock member local chert beds at the top of the kinga formation hawk hill member formed by spring discharge due to regional gravity driven convective groundwater flow an intracratonic setting is implied by 1 a symmetric basin centred fill 2 absence of features indicating a shelf slope break 3 absence of rift rocks 4 a prolonged slow subsidence history 5 likely correlation with other continental to shallow marine deposits scattered across the keewatin hinterland and 6 positioning 1000 2000 km away from closest coeval passive margin sequences we speculate that hurwitz basin formed due to lithospheric stretching related to a large scale mantle upwelling during the protracted breakup of an earliest palaeoproterozoic supercontinent kenorland

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

reconstruction of three dimensional eolian dune architecture from one dimensional core data through adoption of analog data from outcrop data derived from core and well logs are essentially one dimensional and determining eolian system type and likely dimensions and orientation of architectural elements present in subsurface eolian reservoir successions is typically not possible from direct observation alone this is problematic because accurate predictions of the three dimensional distribution of interdune and dune plinth elements that commonly form relatively low permeability baffles to flow of net gross and of the likely distribution of elements with common porosity permeability properties at a variety of scales in eolian reservoirs is crucial for effective reservoir characterization direct measurement of a variety of parameters relating to aspects of the architecture of eolian elements preserved as ancient outcropping successions has enabled the establishment of a series of empirical relationships with which to make first order predictions of a range of architectural parameters from subsurface successions that are not observable directly in core in many preserved eolian dune successions the distribution of primary lithofacies types tends to occur in a predictable manner for different types of dune sets whereby the pattern of distribution of grain flow wind ripple and grain fall strata can be related to set architecture which itself can be related back to original bedform type detailed characterization of individual eolian dune sets and relationships between neighboring dune and interdune elements has been undertaken through outcrop studies of the permian cedar mesa sandstone and the jurassic navajo sandstone in southern utah the style of transition between lithofacies types seen vertically in preserved sets and therefore measurable in analogous core intervals enables predictions to be made regarding the relationship between preserved set thickness individual grain flow thickness original bedform dimensional properties e g wavelength and height the likely proportion of the original bedform that is preserved to form a set the angle of climb of the system and the likely along crest variability of facies distributions in sets generated by the migration of sinuous crested bedforms a series of graphical models depict common facies arrangements in bedsets for a suite of dune types and these demonstrate inherent facies variability

sulfate rich eolian and wet interdune deposits erebus crater meridiani planum mars this study investigates three bedrock exposures at erebus crater an 300 m diameter crater approximately 4 km south of endurance crater on mars these outcrops called olympia payson and yavapai provide additional evidence in support of the dune interdune model proposed for the formation of the deposits at the opportunity landing site in meridiani planum there is evidence for greater involvement of liquid water in the olympia outcrop exposures than was observed in eagle or endurance craters the olympia outcrop likely formed in a wet interdune and sand sheet environment the facies observed within the payson outcrop which is likely stratigraphically above the olympia outcrop indicate that it was deposited in a damp wet interdune sand sheet and eolian dune environment the yavapai outcrop which likely stratigraphically overlies the payson outcrop indicates that it was deposited in primarily a sand sheet environment and also potentially in an eolian dune environment these three outcrop exposures may indicate an overall drying upward trend spanning the stratigraphic section from its base at the olympia outcrop to its top at the yavapai outcrop this contrasts with the wetting upward trend seen in endurance and eagle craters thus the series of outcrops seen at meridiani by opportunity may constitute a full climatic cycle evolving from dry to wet to dry conditions

stratigraphic architecture of alluvial aeolian systems developed on active karst terrains an early pleistocene example from the ebro basin ne spain abstract during the early pleistocene fluvial alluvial and aeolian depositional systems interacted in the central ebro basin spain constructing wide alluvial plains over a neogene evaporite substratum fluvial sediments mainly longitudinal gravel bars and channels are interdigitated with gravel mass flow and distal mudflat deposits aeolian sedimentation is registered as aeolian dunes and sand sheets episodes of fluvial deposition alternated with periods of alluvial fan progradation and aeolian deposition these changes are related to climate driven water availability stratigraphic units and deformation structures show synsedimentary karstification of the evaporite substratum that although karst was not restricted to any particular climate scenario was probably favoured during periods of high water availability karstification conditioned the development of local sedimentary depocentres which in turn influenced the distribution of sedimentary subenvironments as well as the accumulation and preservation of aeolian dunes and lacustrine palustrine deposits stratigraphic architecture shows that thickening of the series due to karst subsidence did not occur homogeneously but was controlled by diachronous subsidence resulting in numerous angular unconformities in subsiding karst areas transport capacity was reduced and sediment preservation increased

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

cyclic cross bedding in the eolian dunes of the sergi formation upper jurassic reconcavo basin inferences about the wind regime abstract the upper jurassic sergi formation displays eolian cyclic cross bedding composed of a regular intercalation of grain flow and wind ripple packages forming 1 3 m thick cycles each cycle is bound by erosive downwind surfaces and it comprises a sequence of lower angle wind ripple laminae followed by steeper grain flow strata that built out upon the wind ripple wedges in the migration direction the cross strata mean vectors dip consistently towards sw these cycles are related to seasonal changes in wind direction the cyclic stratification pattern suggests an alternation of northeasterly transverse winds responsible for slipface evolution and dune migration followed by reverse transversal or oblique winds overall southerly winds these winds caused dune degradation and reworking and led to the formation of reactivation surfaces and the related deposition of wind ripple wedges the wind pattern inferred from the eolian cyclic cross bedding is consistent with the quantitative atmospheric circulation model that indicates that a monsoonal wind regime operated in the low latitudes of gondwana during the late jurassic

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

giant calcite concretions in aeolian dune sandstones sedimentological and architectural controls on diagenetic heterogeneity mid cretaceous iberian desert system spain aeolian dune sandstones of the iberian erg system cretaceous spain host giant calcite concretions that constitute heterogeneities of diagenetic origin within a potential aeolian reservoir the giant calcite concretions developed in large scale aeolian dune foresets at the transition between aeolian dune toeset and damp interdune elements and in medium scale superimposed aeolian dune sets the chemical composition of the giant concretions is very homogeneous they formed during early burial by lowmg calcite precipitation frommeteoric pore waters carbonate componentswith yellow orange luminescence form the nuclei of the poikilotopic calcite cement these cements postdate earlier diagenetic features characterized by earlymechanical compaction fe oxide cements and clay rims around windblown quartz grains resulting from the redistribution of aeolian dust over the grain surfaces the intergranular volume igv in friable aeolian sandstone ranges from 7 3 to 15 3 whereas in cemented aeolian sandstone it is 18 6 to 25 3 the giant calcite concretions developed during early diagenesis under the influence of meteoric waters associated with the groundwater flow of the desert basin although local e g activity of fluid flow through extensional faults and or other regional controls e g variations of the phreatic level associated with a variable water influx to the erg system and varying sea level could have favoured the local development of giant calcite concretions the spatial distribution pattern of carbonate grains and the main bounding surfaces determined the spatial distribution of the concretions in particular the geometry of the giant calcite concretions is closely associated with main bounding aeolian surfaces thus interdune superimposition and reactivation surfaces exerted a control on the concretion geometries ranging fromflat and tabular ones e g bounded by interdunes towedge shaped concretions at the dune foresets e g bounded by superimposition and reactivation surfaces determining the spatial distribution of the heterogeneities of diagenetic origin in the aeolian reservoir

styles of interaction between aeolian fluvial and shallow marine environments in the pennsylvanian to permian lower cutler beds south east utah usa the pennsylvanian to permian lower cutler beds comprise a 200 m thick mixed continental and shallow marine succession that forms part of the paradox foreland basin fill exposed in and around the canyonlands region of south east utah aeolian facies comprise i sets and compound cosets of trough cross bedded dune sandstone dominated by grain flow and translatent wind ripple strata ii interdune strata characterized by sandstone siltstone and mudstone interbeds with wind ripple wavy and horizontal planar laminated strata resulting from accumulation on a range of dry damp or wet substrate types in the flats and hollows between migrating dunes and iii extensive near flat lying wind rippled sandsheet strata fluvial facies comprise channel fill sandstones lag conglomerates and finer grained overbank sheet flood deposits shallow marine facies comprise carbonate ramp limestones tidal sand ridges and bioturbated marine mudstones during episodes of sand sea construction and accumulation compound transverse dunes migrated primarily to the south and south east whereas south westerly flowing fluvial systems periodically punctuated the dune fields from the north east several vertically stacked aeolian sequences are each truncated at their top by regionally extensive surfaces that are associated with abundant calcified rhizoliths and bleaching of the underlying beds these surfaces record the periodic shutdown and deflation of the dune fields to the level of the palaeo water table during episodes of aeolian quiescence fluvial systems became more widespread forming unconfined braid plains that fed sediment to a coastline that lay to the south west and which ran approximately north west to south east for at least 200 km shallow marine systems repeatedly transgressed across the broad low relief coastal plain on at least 10 separate occasions resulting in the systematic preservation of units of marine limestone and calcarenite between units of non marine aeolian and fluvial strata to form a series of depositional cycles the top of the lower cutler beds is defined by a prominent and laterally extensive marine limestone that represents the last major north eastward directed marine transgression into the basin prior to the onset of exclusively non marine sedimentation of the overlying cedar mesa sandstone styles of interaction between aeolian fluvial and marine facies associations occur on two distinct scales and represent the preserved expression of both small scale autocyclic behaviour of competing coeval depositional systems and larger scale allocyclic changes that record system response to longer term interdependent variations in climatic and eustatic controlling mechanisms the architectural relationships and system interactions observed in the lower cutler beds demonstrate that the succession was generated by several cyclical changes in both climate and relative sea level and that these two external controls probably underwent cyclical change in harmony with each other in the paradox basin during late pennsylvanian and permian times this observation supports the hypothesis that both climate and eustasy were interdependent at this time and were probably responding to a glacio eustatic driving mechanism

high resolution stratigraphic architecture and lithological heterogeneity within marginal aeolian reservoir analogues marginal aeolian successions contain different lithological units with variable geometries dimensions and spatial distributions such variations may result in considerable heterogeneity within hydrocarbon reservoirs developed in successions of this type which poses a high risk to their efficient development here such heterogeneity is described and characterized at inter well 1 km scales using two well exposed outcrop analogues of end member marginal aeolian deposits from the permian cedar mesa sandstone and jurassic page sandstone of south central utah usa the sedimentology and stratigraphic architecture of the cedar mesa sandstone was studied in a 1 2 km2 area in the indian creek region of southern utah where the interval consists of interbedded fluvial and aeolian deposits representative of a fluvial dominated erg margin the page sandstone was studied in a 4 3 km2 area near escalante close to the utah arizona border where it consists of interbedded sabkha and aeolian deposits representative of a transitional marine erg margin the three dimensional stratigraphic architectures of both reservoir analogues have been characterized in order to establish the dimensions geometries and connectivity of high permeability aeolian sandstones facies architecture of the aeolian sabkha deposits is characterized by laterally continuous aeolian sandstone layers of relatively uniform thickness that alternate with layers of heterolithic sabkha deposits aeolian sandstones are thus likely to form vertically unconnected but laterally widespread flow units in analogous reservoirs facies architecture in the aeolian fluvial deposits is more complex because it contains alternating intervals of aeolian sandstone and fluvial heterolithic strata both of which may be laterally discontinuous at the studied length scales aeolian sandstones encased by fluvial heterolithic strata may form small isolated flow units in analogous reservoirs although the limited continuity of fluvial heterolithic strata results in vertical connectivity between successive aeolian sandstones in other locations these architectural templates may be used to condition zonation schemes in models of marginal aeolian reservoirs

late jurassic fluvial eolian deposits from the tianchihe formation ningwu jingle basin shanxi province china abstract eolian systems were widespread in china in the cretaceous however the reports of pre cretaceous eolian and its related systems are scarce which prohibits studying the construction accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors in this paper we report on fluvial eolian successions from the late jurassic tianchihe formation in the ningwu jingle basin these successions represent the oldest reported inland fluvial eolian systems in china fourteen lithofacies types are recognized in the tianchihe formation and have been grouped into six facies associations including meandering fluvial channel levee and overbank in the lower part and eolian sandsheet eolian dune ephemeral fluvial channel and floodplain in the upper part the fluvial system comprises a series of wetting upward cycles which indicate humid climate culminating in high precipitation and shallow water table level eolian dune deposits composed of grainflow grainfall wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface suggesting compound dunes or draas eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination the association of eolian dune and eolian sandsheet is development of a dry eolian system twelve drying upward cycles mainly composed of eolian sandsheet eolian dune successions and four wetting upward cycles consisting of eolian sandsheet dune ephemeral fluvial channel floodplain successions occur in the eolian system these repeated cycles likely reflect an evolving erg system directly controlled by sediment supply sediment availability and relative water table the vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions which may be related with the uplift of the east china plateau in the late jurassic

3 2ga eolian deposits from the moodies group barberton greenstone belt south africa implications for the origin of first cycle quartz sandstones abstract the 3 2 ga moodies group in barberton greenstone belt south africa contains the oldest recognized evidence for eolian processes on earth these eolian facies indicate that significant wind regimes existed in the archean atmosphere eolian deposits are developed in the lower moodies group in the central part of the belt and consist of stacked inversely graded strata ranging in thickness from 2 to 10 mm individual strata consist of fine to medium grained quartz sandstone at the base that passes vertically into very coarse to coarse grained quartz sandstone strata make up cross bed sets up to 3 5 m thick sets of wind ripple strata are either tabular tangential or in the form of broad troughs this type of inversely graded stratification is the product of wind ripple migration the coarse grain size of the sediment combined with the low angle of inclination of the strata is best interpreted as the product of sand sheet or dune plinth preservation based on the geometry of eolian set boundaries dunes were probably simple barchan form the tens of meters thick eolian deposits are underlain by braided stream deposits composed of subfeldspathic pebbly sandstones the vertical change from braided stream subfeldspathic sandstones to eolian quartz arenites highlights the underappreciated capacity of eolian processes to generate first cycle quartz sandstones on landscapes pre dating the advent of land vegetation

interacting tectonic faulting karst subsidence diapirism and continental sedimentation in pleistocene deposits of the central ebro basin spain during early as proposed by the international commission on stratigraphy pleistocene times interacting fluvial and aeolian processes constructed wide alluvial plains over an evaporite dominated miocene substratum in the central ebro basin an exceptional site where these deposits show faults folds diapirs karst structures and unconformities has been studied in detail analysis of particular structures demonstrates the interaction by that time of tectonic faulting diapirism karstification and sedimentation in an area where deformation was traditionally linked to the presence of underlying evaporites without proposing any precise mechanism multiple approaches sedimentology structural geology and geophysics have been used in order to discriminate the origin of each type of structure as well as to understand the interaction between different processes numerous normal faults and fractures of variable size are consistent with the regional stress field pleistocene deposits are pierced by diapirs of miocene evaporites and disrupted by karst structures with different geometries tubular funnel and vault both partially controlled by tectonics the example described is proposed as an analogue model that could successfully illustrate evolution patterns of basins of potential interest for petroleum geology where similar processes have actuated resulting in complex stratigraphical architectures

facies distribution as a response to early rift tectonic activity in the sergipe alagoas basin northeastern brazil abstract accommodation rates in rift basins are mainly controlled by tectonics however during early rift stages normal fault activity is dispersed and incipient which makes it difficult to recognize the effects of early crustal extension the sedimentary stacking pattern of rift related depositional environments can be decisive to address this question this paper aimed to evaluate the stratigraphic record of the tithonian berriasian serraria formation sergipe alagoas basin brazil which was deposited in the afro brazilian depression as a result of the early extension of west gondwana in total 14 lithofacies were described interpreted and arranged into 7 facies associations at the base of the formation bars and sand sheets were deposited by low discharge braided channels which were deposited on top of lacustrine mudstones of the bananeiras formation there is a change in stratigraphic architecture in the middle of the section where fluvial channels become deeper due to increasing discharge promoting an increase in grain size of the transported bedload and greater rates of coarse sand and gravel bar stacking rare crevasse channels and restricted aeolian dune fields occur adjacent to braided channel belts upwards the serraria formation becomes dominated by delta front and delta plain deposits the fluvial and aeolian facies associations represent a progressive decrease in accommodation while the upper fluvio deltaic interval means an increase in accommodation pointing to the early rift stage climax the fluvial caioba sandstone on top of the serraria formation indicates reestablishment of fluvial drainage either due to decreasing tectonism or due to low accommodation at the time of deposition thus the sedimentary stacking pattern of serraria formation represents higher frequency cycles within an early rift tectonic system tract

evidence for climate shifts in the 2 0ga upper makgabeng formation erg south africa abstract eolian ergs and associated environs are sensitive to short and long term climatic changes in one of the oldest erg deposits the 2 0 ga makgabeng formation vertical changes in facies associations reflect one of the earliest records of short term climatic shifts in a continental setting the makgabeng formation is separated into lower and upper erg deposits by a playa or saline pan deposit the lower erg deposit consists of dune sets with thin lenses of dry and deflationary interdune strata that transition vertically to thicker damp to wet interdune strata a laterally persistent playa deposit in the middle of the section consists of mudstone with deep and shallow penetrating mud cracks and subordinate siltstone and sandstone interbeds above this lower mudstone interval the playa strata are sandy overlying the playa deposit the upper erg deposit consists of thick eolian sets with thin lenses of dry interdune deposits grain size change near the top of the upper erg deposit corresponds with the appearance of fluvial sheet flood eolian cross beds sculpted by mass flows and thin playa deposits vertical stacking of facies associations demonstrates temporal shifts in precipitation and fluctuating water tables fluvial and playa deposits record high water tables whereas low water tables are reflected in the core erg the transition from a lower to higher water table is recorded by wet interdune interspersed within the dune strata toward the top of this interval rapid climatic amelioration occurred near the termination of the makgabeng erg resulting in impingement of ephemeral river systems development of playas and generation of massive sand flows this 2 0 ga erg demonstrates the impact of climate change on erg development resulting from shifts in monsoonal impingement through time

a marine to fluvial transition in the paleoproterozoic koolbye formation turee creek group western australia abstract although no unambiguous biogenic criteria exist to discriminate precambrian shallow marine successions from fluvial deposits physical sedimentological evidence including an association of primary sedimentary structures and textures stratigraphic position and comparison with phanerozoic and modern examples has been found useful in identifying these deposit types our high resolution sedimentary facies analysis coupled with new mapping clearly indicates shallow marine to beach aeolian to fluvial sedimentation in the paleoproterozoic koolbye formation of the turee creek group western australia a falling stage systems tract within the koolbye formation has been documented our sedimentary facies analysis in combination with sedimentological analysis of the underlying kungarra formation indicates development of at least three falling stage systems tracts within the turee creek group across the rise of atmospheric oxygen the great oxidation event

pleistocene alluvial and aeolian deposits with tephra on the island of lopud eastern mid adriatic croatia provenance wind regime and climate controls abstract pleistocene alluvial and aeolian sediments occur as small patches in many places in the area of the eastern adriatic coast and on the islands on the southeasternmost mid adriatic island of lopud they were studied along two lateral sections in sunj bay where a lense of reworked tephra is intercalated within the alluvial deposits the interpretation of the depositional mechanism the sand source the wind regime and the volcanic activity was based on facies analysis sedimentological characteristics and mineralogical and geochemical composition alluvial deposits represent recycled aeolian sand accumulated in a small scale alluvial plain during a relatively long lasting humid phase while overlying aeolian sands were deposited under the influence of the sea ward blowing nnw wind during more arid and windy periods sporadically occurring breccia lenses composed of limestone fragments from the cretaceous basement strata are the result of occasional high sediment concentration flows and deposition in shallow stream channels alluvial sand is composed of siliciclastic detritus derived from different metamorphic magmatic and older sedimentary rocks of the inner dinarides while the aeolian sand represents a mixture of siliciclastic detritus of the same provenance and carbonate clastic detritus sourced from the karst dinarides the lack of carbonate detritus in the alluvial deposits is probably a consequence of dissolution due to the humid climate the tephra lense represents pyroclastic material that was reworked by water and pedogenically altered the tephra belongs to the high k calc alcaline and shoshonite series with a trachyte trachydacite composition indicating an origin from the campanian province in southern italy as the most probable source area the similar composition of clastic material on lopud to the composition of aeolian and alluvial deposits on the neighbouring eastern mid adriatic localities islands of mljet korcula and lastovo and peljesac peninsula suggests their common source while the tephra lense documents pleistocene volcanic activity and suggests the influence of a southern wind during the humid phase

karst subsidence as a control on the accumulation and preservation of aeolian deposits a pleistocene example from a proglacial outwash setting ebro basin spain meltwater flows emanating from the pyrenees during the pleistocene constructed a braided outwash plain in the ebro basin and led to the karstification of the neogene gypsum bedrock synsedimentary evaporite dissolution locally increased subsidence rates and generated dolines and collapses that enabled the accumulation and preservation of outwash gravels and associated windblown deposits that were protected from erosion by later meltwater flows in these localized depocentres maximum rates of wind deceleration resulted from airflow expansion enabling the accumulation of cross stratified sets of aeolian strata climbing at steep angles and thereby preserving up to 5 m thick sets the outwash plain was characterized by longitudinal and transverse fluvial gravel bars channels and windblown facies organized into aeolian sand sheets transverse and complex aeolian dunes and loess accumulations flat lying aeolian deposits merge laterally to partly deformed aeolian deposits encased in dolines and collapses synsedimentary evaporite dissolution caused gravels and aeolian sand deposits to subside such that formerly near horizontal strata became inclined and generated multiple internal angular unconformities during episodes when the wind was undersaturated with respect to its potential sand transporting capacity deflation occurred over the outwash plain and coarse grained lags with ventifacts developed subsequent high energy flows episodically reached the aeolian dune field leading to dune destruction and the generation of hyperconcentrated flow deposits composed in part of reworked aeolian sands lacustrine deposits in the distal part of the outwash plain preserve rhythmically laminated lutites and associated gilbert type gravel deltas which developed when fluvial streams reached proglacial lakes this study documents the first evidence of an extensive pleistocene proglacial aeolian dune field located in the ebro basin 41 50 n south of what has hitherto been considered to be the southern boundary of pleistocene aeolian deposits in europe a non conventional mechanism evaporite karst related subsidence for the preservation of aeolian sands in the stratigraphic record is proposed

eolian aqueous interactions in the development of a proterozoic sand sheet shikaoda formation hosangabad india abstract a 40 m thick eolian sand sheet deposit characterizes the upper part of the proterozoic shikaoda formation near hosangabad it sharply overlies shoreface deposits and comprises wind ripple strata 50 adhesion strata 17 and subaqueous strata 33 each stratification type defines stratal packages tens of centimeters thick and few meters wide that are superposed upon one another in a nearly random fashion the eolian facies is inferred to have been deposited in a low gradient sandy supratidal setting the subaqueous deposits of the sand sheet also reflect a tide affected westward opening coastal setting with an approximately north south shoreline abundance of aqueous and adhesion strata coupled with the absence of granule rich coarse grained layers corrugated erosion surfaces and evaporites are the typical features of the shikaoda eolian sand sheet these features indicate that in spite of abundant sand supply from the coastal sources and a net aggradational setting repeated flooding and high surface moisture were the principal factors that inhibited dune building processes and favored the growth of a flat bedded eolian sand sheet in the shikaoda sandstone numerous subhorizontal nearly flat bounding surfaces split the sand sheet succession into tabular sediment bodies 50 100 cm thick each of the bounding surfaces can be traced for a few tens of meters and can be correlated to an event of aqueous flooding vertical stacking of tabular sandstone bodies implies that long term sediment aggradation rate in the low lying supratidal region kept pace with that of basin subsidence the sedimentological features of the shikaoda sand sheet facies when compared with known modern and ancient sand sheet deposits suggest that the shikaoda sand sheet developed independent of an erg in a comparatively wet climatic setting the sub humid coastal eolian sedimentary system of padre island texas is probably the closest modern analogue of the shikaoda sand sheet facies

arid climate 2 5 ma in the plio pleistocene valdarno basin northern apennines italy abstract distinctive eolian dominated sandy deposits 35 m thick exposed along the sw margin of the plio pleistocene valdarno basin in the northern apennines italy reflect an unusually arid period in the region paleomagnetic investigation and 40 ar 39 ar dating of a tephra layer 10 m above the eolian sand suggest that the sand was deposited between about 2 7 and 2 4 ma this age is coeval with the global climatic deterioration that occurred at the middle upper pliocene transition eolian sediments are represented by cross bedded sand rippled sand and horizontal bedded sand the alluvial deposits associated with the eolian sediment consist of sheet like beds of coarse sand and erosively based pebbly sand bodies eolian sand together with fluvial sandy deposits was formed in the medial distal portion of an alluvial system and represents the rena bianca sand unit the eolian and alluvial deposits are arranged into sedimentary cycles 2 6 m thick displaying a wetting drying wetting upward trend recording second order climatic oscillations of ca 40 ka each cycle is enclosed between major bounding surfaces defined by iron mineral encrustations these bounding surfaces represent periods of reduced eolian sand accumulation caused by a rising water table during the 2 5 ma global cooling the valdarno basin experienced a period of arid conditions owing to the influence of cold and dry easterly and northeasterly winds in contrast during the pleistocene the uplift of the pratomagno ridge protected the valdarno basin from easterly and northeasterly winds giving rise to relatively warm and wet conditions and mitigating the regional and global climatic changes

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

facies architecture and stratigraphic evolution of aeolian dune and interdune deposits permian caldeirao member santa brigida formation brazil abstract the permian caldeirao member santa brigida formation located in the tucano central basin northeast region of brazil is characterized by a sandstone succession of aeolian origin that comprises the preserved deposits of dunes and interdunes grainflow and translatent wind ripple strata and frequent presence of reactivation surface compose the cross bedding of crescent aeolian dune deposits the aeolian cross strata show a mean dip toward the ene in places interlayered with dune cross beds occur interdune units composed of facies indicative of dry damp and wet condition of the substrate suggesting spatial and or temporal variations in the moisture content of the interdune accumulation surface the presence of nnw current ripple cross lamination in wet interdune areas indicates streamflows confined to interdune corridors and oriented perpendicular to aeolian transport direction lenses of damp and wet interdune strata exhibit mainly interdigitated and transitional relationships with the toe sets of overlying aeolian dune units in sections parallel to aeolian transport indicating that dune migration was contemporaneous with accumulation in adjacent interdunes lateral variations in the preserved thickness of the interdune units and the associated rare occurrence of abrupt and erosive contacts between interdune and overlying dune sets suggest temporal variations in the angle of dune and interdune climb that may be related to high frequency changes in water table position four stratigraphic intervals in the caldeirao member can be identified two intervals showing cross bedding of aeolian dunes without wet interdune areas and two intervals exhibiting aeolian dunes separated by wet interdune areas marking the transition between dry aeolian systems intervals i and iii and wet aeolian systems intervals ii and iv the temporal alternations between dry and wet aeolian systems reflect changes in the availability of dry sand and or the rate in the water table rise possibly controlled by orbitally driven climatic fluctuations

new constraints on equatorial temperatures during a late neoproterozoic snowball earth glaciation intense glaciation during the end of cryogenian time 635 million years ago marks the coldest climate state in earth history a time when glacial deposits accumulated at low tropical paleolatitudes the leading idea to explain these deposits the snowball earth hypothesis predicts globally frozen surface conditions and subfreezing temperatures with global climate models placing surface temperatures in the tropics between 20 c and 60 c however precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined here we make new geologic observations of tropical periglacial aeolian and fluvial sedimentary structures formed during the end cryogenian marinoan glaciation in south australia these observations allow us to constrain ancient surface temperatures we find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith the wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2 4 m below the ground surface these observations paired with a model of ground temperature forced by solar insolation constrain the local mean annual surface temperature to within a few degrees of freezing this temperature constraint matches well with our observations of fluvial deposits which require temperatures sufficiently warm for surface runoff although this estimate coincides with one of the coldest near sea level tropical temperatures in earth history if these structures represent peak marinaon glacial conditions they do not support the persistent deep freeze of the snowball earth hypothesis rather surface temperatures near 0 c allow for regions of seasonal surface melting atmosphere ocean coupling and possible tropical refugia for early metazoans if instead these structures formed during glacial onset or deglaciation then they have implications for the timescale and character for the transition into or out of a snowball state

dune deformation in a multi directional wind regime white sands dune field new mexico as with most dune fields the white sands dune field in new mexico forms in a wind regime that is not unimodal in this study crescentic dune shape change deformation with migration at white sands was explored in a time series of five lidar derived digital elevation models dems and compared to a record of wind direction and speed during the same period for the study period of june 2007 to june 2010 244 sand transporting wind events occurred and define a dominant wind mode from the sw and lesser modes from the nnw and sse based upon difference maps and tracing of dune brinklines overall dune behavior consists of crest normal migration to the ne but also along crest migration of dune sinuosity and stoss superimposed dunes to the se the sw winds are transverse to dune orientations and cause most forward migration the nnw winds cause along crest migration of dune sinuosity and stoss bedforms as well as se migration of ne trending dune terminations the sse winds cause ephemeral dune deformation especially crestal slipface reversals the dunes deform with migration because of differences in dune segment size and differences in the lee face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation each wind event deforms dune shape this new shape then serves as the boundary condition for the next wind event shared incidence angle control on dune deformation and lee face stratification types allows for an idealized model for white sands dunes copyright 2015 john wiley sons ltd

mesoproterozoic erg and sand sheet system architecture and controlling factors galho do miguel formation se brazil abstract aeolian systems of the precambrian time were established in different palaeoclimatic and palaeogeographic conditions than the present different morphologies of dunes draas as linear oblique and star forms are widespread in the recent aeolian systems however the ancient aeolian deposits are rarely interpreted as these types of bedforms and usually referred to as transverse dunes the nature and complexity of bedform morphology in precambrian aeolian systems as well as the factors that allow the construction accumulation and preservation of these environments are still not well defined extensive exposures of galho do miguel formation in southeastern brazil represent a mesoproterozoic erg succession and exhibit a distinct facies architecture which contributed to the understanding of these deposits three architectural elements were identified i tangential cross stratified sandstone with superimposed trough cross bedded sandstone ii planar laminated sandstone and iii extensive flat bedded sandstone dominated by wrinkly laminae these elements are organized into three succession groups representative of simple transverse dune oblique compound draa and sand sheet systems the simple to compound dune draa system corresponds to the most central parts of the erg associated with a higher sediment availability and lower water table level conversely the sand sheet system occurs under low sediment availability and higher water table level in the marginal portions of the erg precambrian climatic oscillations may have changed the aeolian system morphology allowing the alternation of simple and complex aeolian dunes resulting in high frequency changes in sand sheet system and the remobilization of previously accumulated sediments over large geographic areas

development and steady states of transverse dunes a numerical analysis of dune pattern coarsening and giant dunes we investigate the development and steady states of transverse dunes for ranges of flow depths and velocities using a cellular automaton dune model subsequent to the initial bed instability dune pattern coarsening is driven by bed form interactions collisions lead to two types of coalescence associated with upstream or downstream dominant dunes in addition a single collision ejection mechanism enhances the exchange of mass between two adjacent bed forms throughpassing dunes the power law increases in wavelength and amplitude exhibit the same exponents which are independent of flow properties contrary to the wavelength dune height is limited not only by flow depth but also by the strength of the flow superimposed bed forms may propagate and continuously destabilize the largest dunes we identify three classes of steady state transverse dune fields according to the periodicity in crest to crest spacing and the mechanism of size limitation in all cases the steady state is reached and maintained through the dynamic equilibrium between flow strength and dune aspect ratio in the limit of low flow strength where it becomes the primary factor of size limitation the bed shear stress in the dune trough regions is close to its critical value for motion inception comparisons with natural dune fields suggest that many of them may have reached a steady state finally we infer that the sedimentary patterns in the model may be used to bring new constraints on the development of modern and ancient dune fields