interdune areas of the back island dune field north padre island texas abstract the small young about 100 yrs back island dune field on north padre island south texas consists of fairly persistant oblique dunes up to 6 m high with well developed interdune areas that grade northwestward to small ephemeral transverse and barchan dunes with interconnected interdune areas thence sheet sand areas the subhumid climate is marked by rain associated with frontal systems and tropical storms winds are seasonally bimodal prevailing southeasterly are punctuated by northerly and northwesterly winds with the passage of frontal systems in winter the entire dune field and individual oblique dunes show a net migration of about 15 m yr 1 to the northwest the dunes however are on a seasonally reversing track changing their slipface direction and migration direction with frontal systems one year of monitoring shows sand transport in the dune interdune system to be complex and cyclic during the wind reversals of winter dunes are very ineffecfive sand traps owing to loss of flow separation and much sand is lost to the interdune areas interdune areas store sand during these wet winter months as a result of the wind reversals and higher moisture content during the summer the interdune areas deflate and the dunes build in size the overall dune field deposit appears to consist of three laterally contiguous zones from southeast to northwest 1 continuous climbing oblique dune and interdune deposits 2 discontinuous lenses of dune sand in overall interdune layers and 3 a chaotic mixture of dune and horizontal deposits of the sheet sand areas one year s mapping and trenching documents that interdune sedimentary structures are extremely variable laterally and vertically reflecting specific microenvironments within the interdune flat wet surface features consist of current and wave ripples channel fill miniature deltas wrinkle marks mini ripples rills algae and sand volcanoes abundant adhesion structures rain impacted ripples brecciated surfaces and microtopography reflect damp surface deposits dry surface features are predominately wind ripples others include small isolated barchan and shadow dunes organic debris lag surfaces deflation scours beetle bioturbation plant root structures associated with shadow dunes and grainfall from the adjacent dunes interdune deposits account for about 40 of the total dune field deposits which seems reasonable compared to some ancient examples by virtue of occupying a relative basin interdune deposits are selectively preserved compared to dune deposits in general interdune sedimentation is enhanced by non eolian depositional mechanisms a high water table early evaporatic cements and a variable wind regime the actual thicknesses of individual dune and interdune deposits are less on padre than ancient examples reflecting the relative scale of the bedforms in many respects sequences of sedimentary structure in padre island interdune deposits are typical of ancient coastal interdune strata but some marked departures occur adhesion structures relatively rare in some ancient examples but abundant within padre interdune deposits seem favored by the small size of dune and interdune area the climate and a variable wind regime penecontemporaneous deformation absent in padre interdune deposits but pronounced in some ancient examples probably reflects dune size and the nature of the deposits wavy laminae in ancient interdune deposits probably result from many causes but seem best represented by modern examples of evaporitic algal bacterial formed structures

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

trace fossils from interdune deposits an example from the lower triassic aeolian tumlin sandstone central poland abstract the tumlin sandstone up to 105 m thick is the deposit of a midcontinent extensive at least 1500 km2 dune field it consists of dune deposits and of subordinate intercalations of interdune deposits the latter are represented by horizontally bedded sandstone accumulated in frequently changing conditions on dry damp and wet surface dry surface deposits predominate subordinate but relatively common are damp surface deposits with characteristic adhesion structures and wet surface deposits represented by very thin mudstone layers and horizons of wave ripples which originated in ephemeral ponds the interdune deposits contain numerous trace fossils whose occurrence is almost entirely connected with wet surface and damp surface deposits the dune deposits are devoid of trace fossils the following forms have been recognized arenicolites isp cruziana problematica diplocraterion isp gordia marina planolites montanus planolites isp palaeophycus tubularis tetrapod footprints radial structures shallow double furrows and various oval depressions in places intensive but shallow bioturbation of sediment is observable the trace fossil assemblage is similar to the scoyenia ichnofacies but lacks scoyenia and ancorichnus the assemblage is more comparable to the mixed arenicolites cruziana ichnofacies sensu bromley and asgaard 1979 the invertebrate burrows show an r selected strategy in sediment colonization around the palaeozoic mesozoic transition the highly diversified ichnofauna compared to that of the permian interdune deposits shows increased colonisation of interdunes by an invertebrate mainly arthropod fauna

eolian dune interdune sand sheet and siliciclastic sabkha sediments of an offshore prograding sand sea dhahran area saudi arabia an offshore prograding sand sea exists along portions of the arabian gulf coastline near dhahran saudi arabia in this region sediments of eolian dune interdune sand sheet and siliciclastic sabkha intercalate with marine deposits this depositional setting is characterized by strong offshore winds which supply abundant sand to the coastline and cause at present time the outbuilding of the dune system this quartz detrital dominant setting contrasts markedly with the carbonate dominant setting resulting from onshore winds in the trucial coast area to the south the broad intercalation of eolian and marine deposits which results creates ideal potential for subregional stratigraphic petroleum traps due to pinch out of porous and permeable dune sands into impermeable m rine mudstones within the eolian system itself are potential reservoir rocks dunes sources organic rich sabkha and interdune deposits and seals zones of early cementation in all deposits early cementation is very common in all facies of the eolian sand sea the early cementation occurs owing to 1 soil formation 2 deposition of pore filling gypsiferous cements from saturated solutions near water table and 3 addition of sand size windblown evaporitic material to sands downwind of sabkhas

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

interdune deposits of the namib sand sea abstract the namib sand sea of southwestern africa is dominated by large north south trending linear dunes interdune areas however comprise about 50 of the area of the sand sea and may consist of exposures of the pre dune surface or sediments deposited between the dunes four major types of interdune deposits are identified and described 1 1 coarse poorly sorted aeolian sands 2 2 localized calcareous lacustrine deposits 3 3 silty deposits of ephemeral rivers that have flooded into the sand sea margins 4 4 sabkhas and salt marshes near the coast the preservation potential of these sediments is poor except where they are buried and protected by dunes or stabilised by high groundwater levels in coastal areas

facies and fluvial architecture of a high energy braided river the upper proterozoic seglodden member varanger peninsula northern norway abstract the seglodden member late proterozoic as studied in two areas of the varanger peninsula northern norway is dominated by sand rich braided river deposits a quantitative summary of described facies emphasises the dominance of structures deposited under high energy conditions and a general absence of fine grained deposits and visible small scale sedimentary structures the sigmoidal and concave up cross stratified planar horizontally stratified and massive sandstone facies represent 80 95 of the total vertical thicknesses of the measured sections architectural elements are defined as sheet sandstone bodies and channel forms and fills and comprise simple bars transitional simple bar dune complexes dune complexes downstream accretion complexes and various types of channel deposits the seglodden fluvial system was operating in a non vegetated setting with well exposed sediment sources probably of a sedimentary origin this situation gave a very erratic discharge system with rapid runoff high denudation rate and very high sediment discharge increased flow within channels was compensated for by a broadening of the channels and it is inferred that the channels were very wide and shallow relative to their depths bounding surfaces of at least six different orders 0th 5th are interpreted within the studied successions with the third order surface as the lowest order surface that bound architectural elements as defined in this study the highest order surface 5th order is probably the result of channel belt switching due to a combination of sedimentary processes and tectonic subsidence of the basin the east and northeasterly palaeocurrent trend in the seglodden area compared to the southeasterly trend in the smellror area indicates that the axis of the depositional system changed significantly in direction basinwards over the 15 20 km distance between the two study areas the controlling mechanisms for this may be autocyclic as well as allocyclic processes although the tectonic influence on sedimentation was probably significant

the formation of shadow dunes abstract an investigation of the modification of airflow by a discrete semi circular roughness element in this case vegetation the resulting flow structure and the formation of pyramidal shaped shadow dunes is presented two erect pioneer sand dune grasses festuca littoralis and ammophila arenaria were used in the experiments which were conducted in both the field and a wind tunnel for a range of wind velocities 4 20 m sec 1 the three dimensional flow structure about the vegetation is dominated by horizontal separation characterized by symmetrically opposed reversing vortices which form within a triangular wake a vertical separation envelope is also formed over the vegetation pyramidal shadow dunes are formed within this flow structure when aeolian sand transport occurs shadow dune height is dependent on element basal width and repose angle of the sand shadow dune length is dependent on element basal width and wind velocity the results are extrapolated to include all semi porous to non porous semicircular discrete roughness elements the role of shadow dune formation in the development of foredunes and related environments is examined

is ambient noise tomography across ocean basins possible 1 based on year long cross correlations of broad band seismic records obtained at sixty six stations within or adjacent to the pacific basin we show that broad band ambient noise is observed to propagate coherently between island stations and between island and continent stations for many station pairs high signal to noise ratio snr fundamental mode rayleigh wave green functions are observed which establishes the physical basis for ambient noise tomography across the pacific similar trends for continental and oceanic stations are observed in the relationship between the ambient noise level at a station and the noise coherence distance the longest distance at which a high snr cross correlation signal is observed for a station because locally generated noise obscures long distance coherent noise situating stations at quiet locations on islands is necessary for the success of ambient noise tomography local noise poses a particular challenge at atoll sites and on the basis of analysis of data from station h2o at ocean bottom sites at periods above 25 sec citation lin f c m h ritzwoller and n m shapiro 2006 is ambient noise tomography across ocean basins possible geophys res lett 33 l14304 doi 10 1029 2006gl026610

wind sedimentation tunnel experiments on the origins of aeolian strata the origins and sedimentary features of grainfall avalanche and ripple produced strata have been studied experimentally in a wind sedimentation tunnel rate of deposition wind velocity and wind duration have been shown to control specific sedimentary features of these types of strata grainfall produced strata were deposited on a horizontal surface and surfaces sloping up to the angle of initial yield for dry sand about 34 thickness of a grainfall produced stratum depended upon rate of deposition and duration of a specific wind event grainfall produced strata were both non graded and graded graded strata were produced by changes in wind velocity which controlled size of sand in transport and flying distances of individual grains distinctive features of grainfall produced strata are a gradual thinning or tapering downwind e g down the simulated slipface and across the simulated interdune b extreme variability of thickness from less than 1 mm wind gusts of a few seconds to 10 cm or more sustained gusts aeolian avalanche produced strata were formed when grainfall produced strata steepened above the angle of initial yield and sheared downslope a rapid transition in sedimentary features from top to bottom of the slipface characterized avalanche produced strata of the slump degeneration type in dry sand derived from grainfall deposition fadeout laminae formed near the top of the simulated slipface and about 1 m farther down the slipface were flame structures and drag folds near the base of the slipface the avalanche truncated and then overrode grainfall produced deposits distinctive features of avalanche produced strata for a 2 5 m long slipface are the deformation structures a thickness of 1 or 2 cm sandflow toes and steep dip 34 each avalanche produced stratum was roughly tabular in cross section parallel to wind direction with gradual pinchout upslope aeolian ripple produced strata were deposited on horizontal surfaces and surfaces sloping to as much as 28 thickness of a ripple produced stratum depended upon rate of deposition morphology of the ripple and rate of ripple migration a maximum thickness of several centimetres was observed for a single ripple produced stratum shape and attitude of ripple foresets was controlled by ripple morphology distinctive features of aeolian ripple produced strata are a presence of ripple foresets b abrupt changes in thickness of a stratum or pinchout over downwind distances of a few centimetres c low average foreset to diastem angle 10 15 d low ripple climb angle 10

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

a playa deposit of pre yellow sands age upper rotliegend weissliegend in the permian of northeast england abstract a complexly interbedded thin succession of sandstone siltstone and mudstone beneath the permian yellow sands formation upper rotliegend weissliegend was cored in a borehole 11 km off the coast of northeast england the cored strata rest unconformably on fissured westphalian b mudstone and mainly comprise low dipping fine to coarse grained grey sandstone with unevenly spaced thinner dark red to grey mudstone beds and laminae most of the sandstone beds are moderately to poorly sorted fine to very fine grained subarkoses with some sublitharenites and are weakly to strongly cemented by dolomite predominant kaolinite and illite sedimentary structures include subhorizontal plane to wavy lamination ripple lamination salt ridges and soft sediment deformation the siltstones and mudstones are more uniform in lithology and primary thickness they contain sandstone filled desiccation cracks mudstone saucers and narrow sandstone dykes traces of possible former evaporite minerals are concentrated in the sandstones by comparison with modem desert depositional environments these strata are interpreted as the deposits of a playa occupying a depression on a stony deflationary desert surface on a rock pediment or peneplain flanking the ancestral pennines the floor of the depression which probably lay in the capillary fringe just above the contemporary water table was periodically flooded so as to form a shallow playa lake comparable successions beneath the yellow sands have not been recorded from surface exposures in northeast england but mudstone beds at this stratigraphical level have been recorded in four other cored offshore boreholes and are presumed to be of similar origin to those described in this study the stratigraphical position of these deposits suggests that they may be of pre yellow sands age and coeval with or younger than the basal permian breccia palynological analysis of mudstone samples from the core reveal the presence of plant material and indeterminate pyrite invested possibly indigenous bisaccate pollen indicative of a vegetated hinterland with deposition occurring within a reducing possibly sulphide rich environment

fluvial aeolian interactions in a proterozoic alluvial plain example from the mancheral quartzite sullavai group pranhita godavari valley india

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

coarse aeolianites sand sheets and zibar interzibar facies from the mesoproterozoic cuddapah basin india abstract the mesoproterozoic arenaceous successions of the egalapenta member cuddapah basin india are regionally developed and cover hundreds of square kilometers in and around the krishna gorge near the northern limit of the basin they are dominated by aeolian sand sheets major facies attributes of the aeolian sandsheets are coarse grained low relief bedforms with packages of wind ripple laminae that constitute the zibar facies and medium to coarse grained sandstones with bundles of wind ripple laminae that represent the interzibar deposits depending on the angle of climb and migration the zibars and interzibars produced two depositional successions which include an amalgamated interzibar facies devoid of zibars and an interbedded zibar interzibar facies in addition other attributes include low angle cross stratification coarse grained high index ripple lamination gently dipping irregular erosional surfaces and normal to inversely graded horizontal lamination fine to medium grained sandstones with high angle cross stratification represent the dune facies which are interstratified with the sandsheets these are associated with calcareous mudstone sandstones forming the sabkha facies and the laminated tabular cross stratified channelised fine to coarse grained sandstones representing the ephemeral fluvial deposits extensive outcrops of the egalapenta member bear strong signatures of aeolian dune interdune facies sand sheets with zibar and interzibar deposits have been considered as marginal erg facies

major bounding surfaces in aeolian sandstones a climatic model large areas of fixed vegetated dunes occur in the sahel and southern margin of the sahara these dunes were active during late pleistocene times and have been stabilized as a result of a change to more humid less windy conditions in the holocene the stabilized surfaces which are in part of erosional origin are of regional extent within aeolian sand sequences such surfaces form the highest order bounding surfaces since regional bounding surfaces of this type occur in all the world s major deserts it is suggested that they should also be present in some ancient aeolian sandstone sequences

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

eolian dune degradation and generation of massive sandstone bodies in the paleoproterozoic makgabeng formation waterberg group south africa abstract massive sandstone bodies in the 1 85 ga makgabeng formation south africa are located within the middle and upper part of the formation and are associated with the oldest reported deposits of barchan and barchanoid ridge dunes bases of massive sandstone bodies are channelized or planar channel based bodies typically overlie low angle or up to 26 inclined wind ripple strata channel margins vary from low angle to vertical rarely massive sandstones at channel margins display vague horizontal stratification and or contain ripped up fragments of wind ripple strata planar based massive sandstone bodies are lenticular and characteristically are interbedded with low angle to horizontal dune toesets these lobate massive sandstone bodies vary from 5 cm to 6 m in thickness and from 3 m to possibly over 50 m in width some of the sandstone bodies onlap dune reactivation surfaces rare dewatering structures parting lineations and adhesion structures occur at tops of the massive sandstone bodies lower boundaries of massive sandstone bodies change from channelized to planar based down the dune foresets massive sandstones were generated by two different mechanisms which are inferred to have been triggered by significant precipitation events the presence of steep margins channeling rip up fragments and dewatering features and a lack of tractional structures indicate that most massive sandstones were deposited from hyperconcentrated flows down the dune lee face flows were initially turbulent analogous to hyperconcentrated flows resulting in scouring of wind ripple strata as hyperconcentrated flows migrated onto the dune plinth rapid deposition produced lobate massive sandstone deposits with planar bases this sedimentation is linked to development of a hydraulic jump at the slipface plinth intersection which increased flow depth and reduced flow velocity some flows maintained their turbulence onto the dune plinth resulting in erosion of the plinth and scouring into the underlying preserved dune deposits massive sandstone bodies linked to reactivation surfaces are more likely a result of partial lee face collapse which generated translational slides

tourmaline in a low grade clastic metasedimentary rock an example of the petrogenetic potential of tourmaline detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions the detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation compositions of the detrital cores vary widely yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke at either the analogous or antilogous pole inner rim compositions proximal to the detrital cores converge despite the substrate tourmaline composition indicating an approach to chemical equilibrium however significant dufferences in al and x site vacancies at the expense of mg na and ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists the presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth this implies that boron was sporadically available during diagenesis and metamorphism based on boron contents of minerals this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and or muscovite as such tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks

aeolian sands in continental red beds of the middle buntsandstein lower triassic at the western margin of the german basin abstract aeolian sands occur widespread in continental red beds of the middle buntsandstein lower triassic at the western margin of the german basin middle europe in the eifel area cross bedded sands were mainly deposited by grainfall on lee slopes of barchanoid type dunes in unimodal wind regime in both low energy and high energy environments occasionally sets are internally truncated by reactivation surfaces crest height of solitary set dunes varies in the range of some meters locally sequences of cosets both of tabular planar and wedge planar type capped by flat or gently windward dipping topset beds represent larger dune complexes of about 10 20 m in height and at least 80 100 m in lateral extent horizontal laminated deposits originated as sand sheets in interdune areas the dune sands were deposited by trade winds of the northern hemisphere in low palaeolatitude predominantly by southeasterly and southwesterly trade winds in summer when the intertropical convergence zone was shifted to the north aeolian sands built up an extensive dune belt in the eifel intersected by braided to anastomosing rivers fluviatile incursions or heavy ephemeral rainfall led to aquatic redeposition of aeolian sediments and origin of shallow lakes in interdune depressions distribution of aeolian and fluviatile sediments in karlstal schichten is different in the southern western and northern eifel middle buntsandstein sequence in the southern eifel reflects an evolution of the fluviatile depositional environment also incorporating the occurrence and distribution of aeolian sands evolution is characterized by increasing spacing and sinuosity of channels weakening supply of coarse detritus from the source areas and decreasing braiding of the river systems aeolian sands occur in the final phase of this evolution which led from local alluvial fans via cobbly and pebbly braided rivers to sandy braided streams and finally to an intertonguing of aeolian dunes and braided to anastomosing rivers matching with the climax of regional diversification of depositional milieu the aeolian sand sea in the eifel covered an area of nearly 2500 km2 at the time of its largest extension the dune belt ended in the northern eifel the alternating sequence passed into an entirely alluvial succession which graded northwards by continuously diminishing grain size into the central playa lacustrine to marine sediment series in northwest germany palaeogeography sedimentology and genesis of the middle buntsandstein at the western margin of the mid european basin and of rotliegendes in northwest germany appear to be partially similar as is revealed by certain characteristics of the palaeogeographical reconstructions concurrence of middle buntsandstein palaeogeographical models for both eifel and the whole german basin most clearly delineates the key position of the eifel for interpretation of the buntsandstein sedimentary environment and the palaeogeography in middle europe

disequilibrium partitioning of oxygen isotopes associated with sector zoning in quartz fractionation of oxygen isotopes during crystal growth is commonly assumed to be an equilibrium process we present evidence here that large variations in delta 18 o values in a zoned vein quartz crystal are the result of disequilibrium partitioning between fluid and crystal within a single crystal vith well developed concentric and sector zoning delta 18 o values determined with laser extraction techniques on milligram to submilligram sized samples range from 4 7 parts per thousand to 7 3 parts per thousand core to rim variations within single growth sectors fluctuate by 2 6 parts per thousand whereas differences between adjacent sectors along the same growth zone can exceed 2 0 parts per thousand in contrast fluid inclusion homogenization temperatures and salinities are relatively constant and show no effect of grow th or sector zoning differences in delta 18 o values between sectors along the same growth zone cannot result from variations in the oxygen isotope composition of the fluid and strongly suggest disequilibrium partitioning of oxygen isotopes between fluid and the growing crystal the cause of this disequilibrium is believed to be due to differences in surface structure and or growth mechanisms between nonequivalent faces

sequence stratigraphic evolution and cyclicity of an ancient coastal desert system the pennsylvanian permian lower cutler beds paradox basin utah u s a abstract the lower cutler beds comprise a 200 m thick succession of at least 12 repeating cyclic packages of strata each 10 18 m thick that are of mixed eolian fluvial and shallow marine origin these accumulated during the latest pennsylvanian to early permian in the paradox foreland basin of southeast utah each depositional cycle comprises a lower unit composed of a bioclastic wackestone or a bioclastic sandy calcarenite facies both of shallow marine origin the upper units in each cycle are of nonmarine eolian dune and interdune and fluvial channel and floodplain origin the mixed nonmarine and shallow marine nature of the inferred paleoenvironments of the lower cutler beds is significant because the preserved expression of the nonmarine eolian and fluvial units in each cycle demonstrates an external climatic control on system development whereas the marine units in each cycle together with associated transgressive and regressive surfaces demonstrate repeated episodes of relative sea level change key stratigraphic surfaces have been traced from the continentally dominated northeastern portion of the basin into apparently contemporaneous shallow marine dominated sections in the southwest of the basin interdependent changes in both climate and relative sea level change are shown to have generated the preserved cycles which are interpreted to represent high frequency sequences that are bounded by erosional unconformities sequence boundaries and paraconformities diastems relative sea level lowstand was coincident with climatic aridity at which time exposure of a broad low relief coastal plain enabled the generation of a substantial eolian sediment supply that was available for transport by a paleowind aligned parallel to the trend of the paleocoastline resulting in dune field construction and accumulation along a coastal belt episodes of relative sea level rise were coincident with a transition to a more humid paleoclimate during which the eolian sediment supply was greatly reduced resulting in dune field deflation and associated expansion of the fluvial system across the deflated former dune field surface marine transgression occurred first in a series of estuarine embayments via the back flooding of broad but shallow fluvially incised valley systems later transgression culminated in marine incursion over the former low relief floodplain episodes of relative sea level highstand were coincident with maximum climatic humidity the high frequency sequences make up a composite sequence set which itself records a longer term relative sea level cycle at this larger scale a lowstand systems tract is recorded in the lower part of the studied lower cutler beds succession whereas a substantial transgressive systems tract is developed in the upper part a regionally extensive maximum flooding surface defines the top of the lower cutler beds the preserved thickness and number of high frequency cycles together with their relation to the long term subsidence trend of the paradox basin records a periodic switching of both climate and relative sea level the temporally linked nature of which demonstrates that glacio eustasy exerted a dominant control on the origin of the preserved succession the lower cutler beds preserve evidence for the linkage and feedback between combined climatic and eustatic allogenic controls on sedimentation and their role in generating high frequency milankovitch style cycles in mixed clastic carbonate successions

dune and dune field development on padre island texas with implications for interdune deposition and water table controlled accumulation abstract portions of the back island dune fields on padre island texas undergo seasonal destructive and constructive phases in which they are reduced to a nearly planar surface during the winter and then reform during the spring and summer initial depositional sites for dry sand that we observed were associated with roughness elements that caused a lowering of the transport capacity of the flow bedforms develop through a series of morphologic and dynamic stages 1 irregular patches of dry sand 2 wind ripple protodunes with leeward flow expansion 3 grainfall protodunes with a range from leeward flow expansion to flow separation 4 barchan dunes with grainflow and 5 crescentic ridges that characterize the mature field the survival and further development of protodunes and dunes is f vored by increased size a more advanced stage of development unidirectional and moderate wind and a plentiful sand supply these factors can be viewed as the result of the interrelationship of aspects of eolian transport the nature of leeward secondary airflow patterns and sand supply dune field ordering occurs by repeated merging splitting cannibalization and lateral linking of dunes on padre island and other areas of dunes that we studied flow conditions across portions of interdune flats favor the transport of dry loose sand from interdune flats onto the dunes so that dunes grow at the expense of interdune flats dry surface deposits are therefore unlikely to accumulate on interdune flats but rather to characterize interdune depressions that may represent the minimum d stance to which an interdune flat can be closed otherwise accumulations on interdune flats most commonly should be formed on wet or damp surfaces or occur associated with some mechanism that protects the deposits from deflation padre island dune fields represent a type of eolian system where accumulations of dunes and interdune flats occur during periods of a water table rise with bypassing and deflation occurring as the water table becomes static or falls respectively

preservation of pre vegetational mixed fluvio aeolian deposits in a humid climatic setting an example from the middle proterozoic eriksfjord formation southwest greenland abstract sedimentological studies of a 30 m thick coastal cliff section within the middle proterozoic eriksfjord formation in western south greenland reveals three distinct types of fluvial sand sheet deposits that reflect perennial streams type i semi perennial streams type ii and ephemeral flash floods type iii perennial river sand sheets are characterised by co sets of medium scale trough cross beds interbedded with isolated medium and large scale high angle tabular cross beds indications of desiccation or subaerial exposure are absent semi perennial fluvial sand sheets consist predominantly of low angle cross beds interbedded with isolated sets of high angle tabular cross beds with common reactivation surfaces horizontal lamination and climbing ripple lamination form subordinate structures associated with the sand sheets are adhesion structures and 0 05 0 4 m thick sets of wind ripple lamination indicating periods of subaerial exposure and aeolian reworking high energy ephemeral flash flood sand sheets consist almost exclusively of planar parallel lamination and climbing ripple lamination with some isolated sets of low angle cross bedding scouring and internal truncation surfaces are common the three types of sand sheets are considered to reflect deposition under changing climatic conditions varying from humid to arid or semi arid aeolian deposits are preserved within the sand sheets showing characteristics of dominantly perennial flow punctuated by shorter periods of desiccation type ii while sand sheets showing features typical of arid and or semi arid flow conditions type iii contain no preserved aeolian deposits this selective preservation is interpreted to be a result of the combined effect of groundwater table level and fluvial style which in turn are inferred to have been controlled by the climatic regime the deposits show that during pre vegetational times the preservation of aeolian deposits under certain conditions may be more optimal in fluvial systems formed in a humid climate than in fluvial systems formed under semi arid or arid circumstances the occurrence of aeolian deposits within a precambrian succession of fluvial deposits therefore need not be an indication of the most arid environmental conditions

a stratigraphic model to account for complexity in aeolian dune and interdune successions wet aeolian systems in which the water table or its capillary fringe are in contact with the accumulation surface such that moisture influences sedimentation are well known from modern aeolian systems and several ancient preserved successions are recognized from outcrop one common mechanism by which accumulation of wet aeolian system deposits occurs is via a progressive rise in the relative water table level that is coincident with ongoing dune and interdune migration the angle of dune climb being determined by the ratio between the rate of relative water table rise and the rate of downwind migration of the bedforms accumulations of wet aeolian system deposits tend to be characterized by units of climbing dune strata separated by units of damp or wet interdune strata for simple geometric configurations where the size of the dune and interdune units the rate of bedform migration and the rate of aggradation all remain constant over space and time the resulting accumulation has a simple architecture characterized by sets of uniform thickness inclined at a constant angle however the dynamic nature of most aeolian dune systems means that such simple configurations are unlikely in nature the complexity inherent in these systems is accounted for here by a numerical model in which key controlling parameters including dune and interdune wavelength and spacing migration rate and aggradation rate are allowed to vary systematically both spatially from a dune field centre to its margin and temporally in response to changes in sediment availability or water table level the range of synthetic stratigraphic architectures generated by the model accounts for all the best known examples of aeolian dune and interdune stratigraphic configurations documented from the stratigraphic record modelling results have enabled the erection of a scheme for the classification of dune system type whereby the many elaborate stratal architectures known to exist in nature can effectively be accounted for by only four parameters that are allowed to vary over space and time dune and interdune wavelength and spacing rate of bedform migration and rate of accumulation results have applied implications including the modelling of reservoir heterogeneity and the prediction of fluid flow pathways of hydrocarbons water co2 and contaminants in subsurface reservoirs and aquifers in which low permeability interdune units might act as baffles or barriers

migration modification and merging in aeolian systems and the significance of the depositional mechanisms in permian and triassic dune sands of europe and north america abstract the main depositional mechanisms acting in aeolian systems can be assessed in two different and independent ways first by the internal anatomical approach with analysis of the cross stratification fabric and second by the external morphological approach with study of shape and surface features of dunes anatomical investigations of various ancient aeolian systems in the permian and triassic of europe and north america and an extensive literature review concerning both internal anatomy and external morphology of ancient and modern dunes reveal three main depositional mechanisms operating in aeolian systems migration modification and merging migration comprises downwind movement of isolated dunes or trains of aeolian bedforms under predominantly constant wind direction the orientation of the interset surfaces partially depends on the angular relationship between the path of bedform climb and the depositional surface and also on subsidence simple systems are characterized by successive dunes of similar size whereas compound systems originate by superimposition of smaller aeolian bedforms on larger dunes or draas compound migration gives rise to the hierarchy of diastems modification comprises overprinting of existing dunes by winds coming from directions other than those that govern migration of the original aeolian bedforms the anatomical elements representing modification include both intrasets and extensive intersets depending on duration and on the scale of the changes of the winds simple modification comprises occasional origin of either only cross dipping erosional boundaries or both diastems and intraset laminae oriented in different directions a special case of modification is the creation of intrasets dipping in the same direction as the foreset inclination comprising either reactivation or relaxation surfaces depending on whether the foreset slope is steepened or lowered in angle complex modification takes place under repeatedly alternating winds of changing effectiveness small scale modification comprises minor alterations of existing dune types and medium scale modification is characterized by conversion of primary aeolian bedforms into secondary dune types small scale and medium scale modification take place during short term to smaller scale long term changes of effective wind direction large scale modification originates by large scale long term changes accompanied by a certain subsidence which result in burial of the older dunes by a younger train of aeolian bedforms within the same sand sea migrating obliquely to perpendicularly to the former wind direction very large scale modification is induced by very large scale long term changes which result int deflationary erosion of older dune fields and subsequent superimposition of a new sand sea on top of the eroded remnants of the former erg merging comprises coalescing of bedforms with only negligible erosion during burial of the first bedform by subsequent dunes merging is induced mainly when migration of dunes is stopped by a morphological barrier or ceases as a consequence of weakening winds merging further occurs during coalescence of numerous isolated barchans in rows to parallel wavy barchanoid ridges as a consequence of increasing availability of sand the main depositional mechanism in compound systems is migration of hierarchically superimposed bedforms with subordinate modification under predominantly unidirectional winds in complex systems migration modification and merging take place in different amounts under unidirectional bidirectional and multidirectional winds depending on direction and strength of both earlier and subsequent winds complex systems are either charcterized by mainly migration with subordinate modification or by considerable modification with either conversion or dissection of older dunes the effects of migration modification and merging are discussed in the light of both internal anatomy of ancient cross stratification fabrics and external morphology of recent dunes a classification of dune types based on these mechanisms divides the aeolian bedforms into primary secondary and tertiary types primary dunes originate by simple or compound migration with minor modification and comprise mainly transverse dunes secondary dunes originate by complex interaction of migration and modification or even predominantly by modification with the best examples being longitudinal dunes tertiary dunes form by merging of transverse and longitudinal elements with varying amounts of migration and modification and are mainly represented by star dunes the results of various anatomical case studies of ancient aeolianites indicate that simple migration was the dominant mechanism for construction of ergs in the northern hemisphere in permian and triassic times

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

aeolian dune field development in a water table controlled system skeiđararsandur southern iceland aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on skei ararsandur southern iceland the largest aeolian dune complex on the sandur covers an area of 80 km2 and is characterized by four distinct landform types i spatially isolated aeolian dunes ii extensive areas of damp and wet flooded interdune flat with small fluvial channels iii small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small predominantly damp interdune corridors and iv larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain the morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune interdune and fluvial processes that operate coevally on the sandur surface the geometry scale orientation and facies composition of sets of strata in the cores of the aeolian dunes and their relationship to adjoining interdune strata have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation construction pattern of migration style of accumulation and nature of preservation seasonal and longer term flooding induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds most of the dunes are currently undergoing active construction and migration and although sediment availability is limited because of the high water table substantial aeolian transport must occur especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century sediment compaction induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long term preservation wet dry and stabilizing aeolian system types all co exist on skei ararsandur and the dunes are variously undergoing coeval construction accumulation bypass stabilization and destruction as a result of interactions between localized factors

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

giant stromatolites and a supersurface in the navajo sandstone capitol reef national park utah at capitol reef national park utah 5 m high stromatolites are present locally on interdune carbonate lenses in the early jurassic navajo sandstone the stromatolites display both finely laminated and fenestral internal fabrics and grew along south facing interdune margins these stromatolites formed during a high water table episode engendered by a dune dammed paleodrainage in a stabilized navajo erg these stromatolites and the thick interdune section associated with them suggest a hiatus in erg accumulation and the presence of a super bounding surface

eolian fluvial interaction in the page sandstone middle jurassic in south central utah usa a case study of erg margin processes abstract channel and lens shaped deposits of non eolian red sandstone are enclosed within the eolian leche e member of the page sandstone in south central utah detailed analysis of lithology and geometry and regional correlation of the red sandstone deposits suggests that the channel shaped scours and in filling deposits were formed by ephemeral stream processes in contrast to earlier interpretations that suggested a marine estuarine origin we hypothesize that ephemeral streams transporting volcanic debris flowed toward the north and northeast along the western edge of the page erg local avulsion possibly caused by eolian damming of an adjacent drainage led to stream flow into low areas of the page erg entrainment of loose eolian sand combined with fluid loss via infiltration led to a rapid increase in sediment fluid ratio during flow events initially resulting in sandy debris flow deposition subsequent floods entrained less material from the underlying more cohesive debris flow deposits had a lower sediment water ratio and hence left deposits containing some evidence of flow turbulence eventually stream drainage avulsed again probably back to a more northerly course into the carmel sea fluvial deposition within the erg ceased and eolian deposits covered the now intercalated fluvial complex

aeolian dune and wet interdune sedimentation in the middle proterozoic dala sandstone sweden abstract the middle proterozoic dala sandstone covers an extensive area in west central sweden and the adjacent parts of norway but it is poorly exposed however a series of quarries in the lower part of the sandstone provides good exposures that allow an interpretation of the environment of deposition in this part of the unit only two facies have been distinguished facies a an aeolian dune facies and facies b a wet interdune facies facies a consists of large scale cross stratified sandstone in which cross stratified sets are up to almost 4 m thick while the maximum foreset dip is 25 sandflow and subcritically climbing translatent strata have been recognized in this facies but the identification of grainfall strata is uncertain penecontemporaneous folding and brecciation of cross strata has taken place locally facies b which was deposited simultaneously with facies a consists of sandstone with thin mud laminae an irregular wavy structure and numerous wave rippled and mud cracked surfaces the increasing proportion of facies b relative to facies a passing up the stratigraphic section may herald an approaching coastline lack of recognition rather than preservational bias is thought to be the reason for the apparent scarcity of aeolianites in the precambrian

hourglass sector zoning in metamorphic tourmaline and resultant major and trace element fractionation a new type of sector zoning with an hourglass shape has been identified in metamorphic tourmalines that formed under a wide variety of physical and chemical conditions the two sectors in the c direction are not equivalent due to asymmetry in the crystal structure of tourmaline along the c axis the c sector is characterized by low concentrations of ti ca mg and na although al is high and has a pale commonly blue or pale green color conversely the c sector is low in mg and al and high in ca fe and ti the latter two causing the dark brown color of this sector the a sector has intermediate characteristics and probably approximates a sector free tourmaline thin sectioning of these sector zoned tourmalines perpendicular to the c axis can produce three types of apparent radial zoning patterns blue green cores dark brown cores or no distinct cores these apparent cores will further vary in relative diameter depending on the sectioning level furthermore core boundaries can be straight or ragged depending on whether the relative growth speeds for the different faces was constant or variable these textures have been used to argue for a prograde or detrital origin of tourmaline cores however sector zoning is a more appealing explanation for most of these textures and can further explain the textural resemblance among metamorphic tourmalines from highly variable bulk rock composition metamorphic history and mineral paragenesis the sector zoning that is described here develops by preferential uptake of elements on the r growth plane resulting from a combined effect of differences in surface charge and morphology of this plane in the c and c directions this leads to the preferential incorporation of more positively charged elements in the c direction and a preference for a vacant x site in the c direction because the compositional differences among the sectors are pronounced in both major and trace elements and in the same order of magnitude as growth zoning variability the presence of sector zoning must be established and taken into account when making inferences from tourmaline chemistry

complexities in eolian and marine interactions processes and eustatic controls on erg development abstract the interplay between eolian and marine realms includes process interactions cycles of transgression and regression and possible inland effects of marine coastal events process interactions are geologically common and most obvious where eolian and marine environments are adjacent these interactions include sediment exchange between the two environments the supply of marine ions to the erg for surface and near surface cementation and the control directly or indirectly of marine events on the sediment budget of an erg regression accompanied by erg progradation over marine deposits occurs with both onshore and offshore winds marine transgression of ergs varies from producing a planar marine scoured surface to a planar deflation surface that precedes the transgression to varying degrees of paleotopographic dune preservation and a variety of transitional facies the extent of paleotopographic dune preservation is largely a function of the energy level of the transgressing marine realm the rate of the transgression and potential for early dune cementation general correlations between ergs and global eustatic sea level and coastal onlap curves occur for coastal and near coastal cyclic erg sequences eustatic control of inland ergs exists to the extent that sea level controls in large measure the extent of the basin exposed to subaerial processes i e regional base level and probably to a lesser extent the sediment supply to the erg direct correlation of inland erg events to coastal onlap curves is dubious at present but an indirect relationship may exist

the nature and possible origin of mega dunes in liwa ar rub al khali uae abstract the liwa area is located in the south central part of the uae along the northeastern upwind margin of the ar rub al khali sand sea and covers about 3694 km 2 it has one type of dunes a mega barchan that is compound and complex in form characterized by the superimposition of smaller dunes due to the giant size of barchans interdune areas appear as closed depressions that vary in shape from irregular elongate triangular to circular or semi circular these depressions are mostly covered with small barchans or sabkha deposits with patches of gypcrete in their upper parts scattered flat top mounds are also observed in interdune areas the size of dunes in liwa is directly controlled by quaternary climatic changes multiple generations are superimposed on one another separated by calcretic horizons the climate during dune formation alternated between relatively arid to humid the dune sands are unimodal with a modal class of fine sand moderately to very well sorted and near symmetrical and mesokurtic quartz grains are mainly subrounded to subangular based on the heavy mineral suites the sand came mostly from the ultrabasic rocks that form the ophiolitic sequence of the oman mountains the acidic rocks of iran and from the arabian shield

controls on spatial and temporal distribution of precambrian eolianites abstract inversely graded stratification generated by the migration of wind ripples and adhesion structures permit unequivocal identification of precambrian eolianites these criteria in combination with scale of cross beds angle of inclination of foresets geometry of depositional units and associated non eolian facies are used to discriminate between precambrian dune draa dune plinth sand sheet and interdune deposits that formed in inland and coastal settings based on an analysis of published literature fundamental conclusions can be drawn on the spatial and temporal distribution of precambrian eolianites the oldest reported eolianites are from the ca 2 1 ga deweras group in zimbabwe and hurwitz group in canada and numerous examples of eolianites are reported from the 1 8 ga and younger rock record lack of archean and early paleoproterozoic eolianites and their widespread development after 1 8 ga are examined with respect to absence of vegetation crustal growth and tectonic setting relative sea level fluctuations unfavorable atmospheric and or climatic change and non recognition the lack of pre 2 2 ga eolianites may be related to reworking by braided rivers combing across non vegetated floodplains reworking of coastal eolianites during transgression or their non recognition in the early precambrian record the temporal concentration of eolianites at 1 8 ga may best be related to the early stages of breakup and the assembly phases of supercontinents

thin eolianites interbedded within a fluvial and marine succession early proterozoic whitworth formation mount isa inlier australia abstract the early proterozoic whitworth formation in the mount isa inlier australia contains the oldest known thinly bedded eolian dune and amalgamated interdune deposits and records the complex interplay of eolian fluvial and marginal marine depositional processes the whitworth formation accumulated during the waning phases of rifting in a north south trending trough that began between 1808 and 1790 ma and ended before 1740 ma three eolian facies are recognized 1 cosets of cross strata 2 sets of horizontal to low angle strata and 3 isolated sets of cross strata facies el records preservation of dunes with low angles of climb without intervening interdune deposits sets of facies e2 are interpreted as either sand sheet preserved dune plinths or amalgamated interdune deposits facies e3 is encased in facies e2 and consists of lenses of cross strata with irregular tops this association of facies is comparable to recent gypsum dune and interdune deposits at white sands new mexico facies e3 reflects limited dune preservation during migration and accumulation at or near the groundwater table vertical change from amalgamated interdune deposits to dune without interdune deposits records dunefield initiation or lateral migration from a peripheral to a more centralized position within the dunefield increased sedimentation rates promoted preservation of dune deposits represented by facies e1 decreased sedimentation rate and possible limited sediment bypassing resulted in amalgamation of interdune deposits on the dunefield periphery eolian facies e1 and e2 are interbedded with ephemeral river deposits three ephemeral river facies are recognized 1 cosets of horizontal strata 2 cosets of horizontal strata and overlying trough cross beds and 3 cosets of medium scale trough cross beds ephemeral river facies f3 often are preserved in channels incised into eolian facies e3 associated marginal marine facies consist of 1 thin bedded arenites of intertidal to supratidal origin and 2 trough and tabular planar cross bed sets and cosets that resulted from migration of subaqueous dunes within a tide dominated subtidal setting interbedded fluvial and eolian deposits reflect either autogenic processes such as reworking of fluvial sands by eolian processes or incursion of a fluvial system into a dunefield related to allogenic processes such as climatic change dune deposits in the whitworth formation probably developed under arid to semi arid conditions as indicated by extensive ephemeral river deposits presence of evaporite pseudomorphs and absence of wet interdune deposits interbedded eolian fluvial and marginal marine deposits resulted from relative sea level fluctuations related to a combination of eustasy and intrabasinal tectonics

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

stratigraphic evolution of an aeolian erg margin system the permian cedar mesa sandstone se utah usa the permian cedar mesa sandstone of south east utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which in terms of palaeogeographic setting reflects a transition from a dry erg centre through a water table controlled aeolian dominated erg margin to an outer erg margin subject to periodic fluvial incursion the erg margin succession represents a wet aeolian system accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes and a range of dry damp and wet flooded interdune elements is recognized variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre locally interconnected damp and or wet interdune ponds in the aeolian dominated erg margin and fully interconnected fluvially flooded interdune corridors in the outer erg margin relationships between aeolian dune and interdune units indicate that dry damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration temporal variation in the rates of water table rise and bedform migration determined the angle of climb of the erg margin succession such that accumulation rates increased during periods of rapidly rising water table whereas sediment bypassing zero angle of climb occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table during these periods in the outer erg margin the expansion of fluvially flooded interdunes in front of non climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass flood supersurfaces a spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the cedar mesa erg margin succession

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

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

controls on the stratigraphic development of the triassic fundy basin nova scotia implications for the tectonostratigraphic evolution of triassic atlantic rift basins abstract the late triassic synrift succession of the minas sub basin bay of fundy nova scotia includes a fluvio alluvial fan dominated unit lower and middle wolfville formation a transitional fluvio playa unit upper wolfville formation and an upper playa dominated package blomidon formation we describe the facies development in the 240 m thick upper wolfville formation examine vertical facies stacking patterns and develop a depositional model for this succession the unit comprises channelized and unconfined fluvial deposits interbedded with aeolian and playa sediments that grade upward into playa deposits the succession comprises progradational and retrogradational fluvial packages and thin aggradational playa claystones comparison with 11 other atlantic margin continental triassic rift basins allows an assessment of the controls that govern rift basin development the transition from fluvial to playa or lacustrine conditions occurs in all basins at different times the lack of synchronicity indicates that global climate change was not a controlling factor we suggest that the fluvial to lacustrine or playa transition was due to a decrease in source area relief related to a decline in regional tectonic activity and that the basin was hydrologically closed throughout sedimentation this tectonostratigraphic model may be appropriate for other triassic basins developed along the atlantic margin

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism

shallow marine and coastal eolian quartz arenites in the neoarchean palaeoproterozoic karutola formation dongargarh volcano sedimentary succession central india abstract the neoarchean palaeoproterozoic karutola formation a 200 m thick supermature quartz arenite occurs interlayered between two thick units of intermediate to basic volcanic rocks of the dongargarh group despite metamorphism and deformation detrital texture and sedimentary structures are well preserved allowing detailed process based facies analysis the facies recognised include 1 inner shelf 2 shoreface 3 delta mouth lower delta plain 4 tidal flat and 5 foreshore backshore a coastal sand sheet dominated by adhesion structures and consisting of alternating eolian and foreshore aqueous deposits records eolian processes operative in the karutola coastal area textural characteristics hint at a significant eolian contribution to the shallow marine sand overall palaeocurrent indicates a nw se shoreline trend with hinterland to the west of the present outcrop belt a surface indicating an abrupt increase in the water depth divides the formation into two units the lower part encloses inner shelf to foreshore backshore deposits and the upper part of the succession records deposition from the shoreface to lower deltaplain environment a tidal flat sandstone mudstone unit is developed only in the north western end of the study area a granite gneiss source terrain cropping out to the west and a hot humid climate appears to have supplied the abundant quartz sand to the karutola shoreline and the sand population attained textural maturity through eolian and aqueous reworking it is postulated that the aqueous eolian interaction inferred for the karutola sand should be common in sandy depositional environments that lacked land vegetation

distinctions and uses of stratification types in the interpretation of eolian sand abstract eolian and subaqueous cross strata cannot be distinguished reliably by many commonly cited criteria they can however generally be distinguished by the characteristics of their component types of stratification which represent processes of sorting and transport of the grain population on dunes eolian dune stratification types consist of grainflow cross strata grainfall laminae and wind ripple generated climbing translatent strata some of these types especially translatent strata have characteristics unique to the eolian realm these same stratification types are found to compose some ancient cross strata and their occurrence confirms the eolian interpretations of pans of the entrada jurassic navajo triassic jurassic and galesville cambrian formations a well as revealing emergent islands in the curtis formation jurassic previously considered to be totally marine in origin stratification types show a characteristic distribution on modern eolian dunes and differ in their relative abundances and structure on dunes of differing size and kind these same relations allow some estimates of the type shape and original height of ancient dune deposits as well as influencing the occurrences of surface features such as tracks and tipple forms the geological record of stratification types and other dune features is greatly affected however by the extent of the post depositional truncation of dunes

sedimentology and development of parabolic dunes grande prairie dune field alberta the grande prairie dune field in northwest central alberta is composed of parabolic and dome dunes presently inactive but which had developed under westerly winds two parabolic dune types are rec