formation and stability of transverse and longitudinal sand dunes the shape of dunes depends on the history of wind regimes and sand availability in deserts exposed to winds from two different directions but with comparable magnitude dunes are found to be linear ridges which are either perpendicular or parallel to the mean wind direction depending on the angle between the two wind directions these dunes respectively observed for small and large angles between winds are called transverse and longitudinal dunes in both cases their large width hundreds of meters and evolution time scale years strongly limit the investigation of their dynamics and thus our understanding of such structures here we show that under water similar structures can be obtained but at much smaller space and time scales performing controlled experiments together with numerical simulations we highlight the physical mechanisms at play in the formation and long term evolution of these structures we show in particular that while longitudinal dunes are stable and extend in time transverse dunes are unstable they evolve into wavy ridges and eventually break into barchans if the sand supply is too low this fundamental difference is understood through the study of single sand piles and bars exposed to two winds in the case of a large angle between winds a sand pile grows a finger pointing in the average wind direction and transforms into a longitudinal dune such an elongation does not occur for a small angle where a sand pile evolves into a barchan these results explain the morphological differences between straight and long longitudinal dunes and sinuous transverse dunes while giving keys to infer the wind history or pattern state of development from the observation of dune shapes in the field

modeling the sar backscatter of linear dunes on earth and titan abstract we modeled the synthetic aperture radar sar response of linear dunes of the great sand sea in egypt using a single surface scattering term based on integral equation and physical optics models using multi frequency sir c x sar radar scenes and topography obtained from the shuttle radar topography mission srtm we were able to estimate reasonable values for the parameters describing the surface roughness of the dunes as the linear dunes of the great sand sea are relevant analogs for the linear dunes observed on titan by the cassini radar instrument these results were thus used as a starting point to simulate the radar response of titan s dunes as imaged by the radar instrument onboard the cassini spacecraft during the t8 flyby in october 2005 we show that a single surface scattering term is not sufficient to simulate the radar signal backscattered by the dunes on titan one has to add a diffuse scattering term indicating that titan s dunes are likely to have somewhat inhomogeneous internal structures related to porosity and or internal layering our results also indicate that the dunes on titan should be close to perfectly smooth possibly because of the formation of smaller ripples than on earth plus smoothing resulting from precipitation events

construction and evolution of submerged deltaic bodies on the high energy se african coastline the interplay between relative sea level and antecedent controls abstract this paper investigates the interplay between allocyclic controls and antecedent topography in the evolution of submerged coastal landforms including a back stepped delta using high resolution tools we examine the wave dominated thukela shelf and define the major seismic units key features identified comprise incised valleys scoured into bedrock that have overspilled to form lagoons at depths of 50 m these are in turn overlain by two prograding and backstepped sandy delta systems at 40 m and 32 m depth respectively the deltas interfinger with muddy prodelta deposits and are truncated by the holocene ravinement overlain by the contemporary prodelta of the thukela river system a bedrock high separates two physically separate strato morphological zones landward a sediment stripped steep and shallow nearshore zone and seaward a gentle zone downdip where the deltaic accumulations are sited delta development was favoured during sea level stillstands at 40 m and 32 m respectively the step back of the deltas corresponds to sharp increases in the rate of sea level rise associated with meltwater pulses the overall gentle palaeo bathymetric gradient has moderated erosion associated with rising sea level preserving a sandy back stepping delta and a draping mud clinoform submerged delta positioning relates to underlying incised valleys suggesting a synchronous transgressive evolution of the drainage and the delta incised valley network positioning is further governed by late pliocene aged growth faults in the basement rocks the geological framework has acted as a recurring primary control to the geomorphic evolution of the area partitioning accommodation for sediment accumulation and moderating the efficiency of ravinement

gravel bodies in the kumtagh desert and their geomorphological implications although developed in predominantly arid environments desert geomorphology sometimes bears information about past environmental change china s kumtagh desert has only recently been studied by researchers these investigations revealed the existence of several unique features compared with other chinese deserts including gravel bodies distributed in the northern part of the desert this paper summarizes the results of previous research in the region as well as information obtained from remote sensing and field investigations then discusses the geological background underlying quaternary geomorphology and the types development stages and geomorphological implications of the desert s gravel bodies four main types of gravel bodies and four developmental stages were identified it is suggested that the great elevation difference between the altyn tagh mountains and the kumtagh desert caused by uplift of the qinghai tibetan plateau constitutes the overall background for the development of gravel bodies but subsequent climatic events were the direct causes of their evolution the gravel bodies resulted from alluvial deposits on loose fine sediments mainly of aeolian origin that were subsequently subjected to wind erosion erosion cycles then progressively scattered these gravels to form gravel sheets the gravel bodies have three main geomorphological implications they record anomalous ancient climate events after the dune field formed and have little influence on the development of nearby seif dunes in the northeast demonstrate that the altyn tagh mountains are the main sediment source for the kumtagh desert and suggest that the evolution of the environment and geomorphology of the kumtagh desert have been influenced by neotectonic movements

provenance and transport process for interdune sands in the kumtagh sand sea northwest china abstract interdune areas are an important part of dune systems as they affect dune evolution and sand sea development however there has been little work on the provenance of interdune sediments our lack of knowledge of these sediments prevents a more complete understanding of sand sea formation and evolution in the present study we focused on the provenance of interdune sediments in the kumtagh sand sea based on their granular mineral and geochemical characteristics then further identified the spatial scope of the contribution of these sources to the interdune sediments and the associated transport mechanisms although sediment supply analysis suggested that the interdune sand may derive from the altyn tagh mountains beishan mountains and sanlongsha dune field the provenance signature based on the k rb and k ba ratios revealed that the ultimate sources were the altyn tagh mountains in the south and the beishan mountains in the north by plotting the identified provenance results on a map of the sand sea we found that the spatial scopes of contributions from these sources were separated at around 40 n however the existence of a fluvial load em1 and of reworked coarse particles em3 in the northern sand sea demonstrated that the interdune sands in this region were partly derived from the altyn tagh mountains in the south consequently by combining our results with the transport agents condition we concluded that the altyn tagh mountains supplied sediments to interdune areas by fluvial transport throughout the sand sea but that sediment in the northern sand sea was subsequently reworked and mixed with windblown sand originated from the beishan mountains

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

secondary flow deflection in the lee of transverse dunes with implications for dune morphodynamics and migration measurements of lee side airflow response from an extensive array of meteorological instruments combined with smoke and flow streamer visualization is used to examine the development and morphodynamic significance of the lee side separation vortex over closely spaced transverse dune ridges a differential deflection mechanism is presented that explains the three dimensional pattern of lee side airflow structure for a variety of incident flow angles these flow patterns produce reversed along dune and deflected surface flow vectors in the lee that are inferred to result in net lateral diversion of sand transport over one dune wavelength for incident angles as small as 10 from crest transverse i e 80 from the crest line this lateral displacement increases markedly with incident flow angle when expressed as the absolute value of the total deflection in degrees reversed and multi directional flow occurs for incident angles between 90 and 50 these results document the three dimensional nature of flow and sand transport over transverse dunes and provide empirical evidence for an oblique migration model copyright 2013 john wiley sons ltd

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

is there evidence for global scale forcing of southern hemisphere quaternary desert dune accumulation a quantitative method for testing hypotheses of dune system development luminescence dating of desert dune sediments has generated many hundreds of ages many used in reconstructions of quaternary environmental changes others in attempts to elucidate dune processes environmental and climatic interpretations of these records have proved problematic and it remains challenging to test hypotheses of the systematic response of dunefields to changes in external forcing in the past and to make predictions of the future we use a method that quantifies dune sediment accumulation to interpret dune luminescence age datasets rather than simply using the ages themselves as proxies of change the accumulation intensity method allows periods of dune sediment accumulation here over the timescale 102 105 years to be identified from compilations of dated sand sea stratigraphic sequences we apply this approach to two of the largest dune age datasets from southern africa and australia testing whether or not dunefield accumulation has co varied in the late quaternary and whether systematic relationships to external drivers at global hemispheric regional and local scales can be identified

domain size closure domains and the importance of magnetostriction in magnetite abstract previous micromagnetic calculations invoking magnetostatic exchange and crystalline anisotropy energies predict about an order of magnitude more domains in magnetite than have experimentally been observed domains observed on magnetite by the magneto optic kerr effect are of similar size as previously observed ones by the bitter technique simple but quite accurate domain calculations show that for rectangular parallelepipeds of magnetite it is the closure four domain configuration that should be of lowest energy for all multidomain grain sizes unless magnetostrictive energies are considered for the observed domain pattern it is shown that the domains themselves must carry significant magnetoelastic energies

palaeoenvironments palaeogeography and physiography of a large shallow muddy ramp late cenomanian turonian kaskapau formation western canada foreland basin the kaskapau formation spans late cenomanian to middle turonian time and was deposited on a low gradient shallow storm dominated muddy ramp dense well log control coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km2 the studied portion of the kaskapau formation is a mudstone dominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant regional flooding surfaces permit mapping of 28 allomembers each of which represent an average of ca 125 kyr more than 200 km from shore calcareous silty claystone predominates whereas 100 to 200 km offshore mudstone and siltstone predominate from about 30 to 100 km offshore centimetre bedded very fine sandstone and mudstone record along shelf sse directed storm generated geostrophic flows five to thirty kilometres from shore decimetre bedded hummocky cross stratified fine sandstone and mudstone record strongly oscillatory wave dominated flows whereas some gutter casts indicate shore oblique apparently mostly unidirectional geostrophic flows nearshore facies are dominated by swaley cross stratified or intensely bioturbated clean fine sandstone interpreted as recording respectively areas strongly and weakly affected by discharge from distributary mouths shoreface sandstones grade locally into river mouth conglomerates and sandstones including conglomerate channel fills up to 15 m thick locally brackish lagoonal shelly mudstones are present on the extreme western margin of the basin there is no evidence for clinoform stratification which indicates that the kaskapau sea floor had extremely low relief lacked a shelf slope break and was probably nowhere more than a few tens of metres deep the absence of clinoforms probably indicates a long term balance between rates of accommodation and sediment supply mud is interpreted to have been transported 250 km offshore in a sea bed nepheloid layer repeatedly re suspended by storms fine grained sediment accumulated up to a mud accommodation envelope perhaps only 20 to 40 m deep continuous re working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the accommodation envelope being deposited in areas of higher accommodation further down the transport path the facies distributions and stratal geometry of the kaskapau shelf strongly suggest that sedimentary facies especially grain size were related to distance from shore not to water depth as a result the 100 to 300 m depth interpreted from calcareous claystone facies for the more central parts of the interior seaway might be a significant overestimate

sequence development of a latest devonian tournaisian distally steepened mixed carbonate siliciclastic ramp canning basin australia abstract the sequence development and evolution of latest devonian earliest carboniferous fairfield group in the canning basin have been established through integration of detailed sedimentological analysis of core petrophysical data existing biostratigraphic data and new seismic interpretations the fairfield group on the lennard shelf was deposited on a mixed carbonate siliciclastic distally steepened ramp with a broad inner ramp narrow mid ramp and steepened outer ramp the majority of facies associations fa1 fa8 were formed in intertidal shallow subtidal conditions in proximal to distal inner ramp including siliciclastic tidal flats fa1 carbonate intertidal flats fa2 tidal flats and channels fa3 lagoons fa4 fa5 and shallow subtidal fa6 backshoal fa7 and fore shoal areas fa8 bioclastic muddy sandstone fa9 and bioclastic mudstone fa10 are the dominant mid ramp facies recognition of turbiditic facies of middle to lower slope of the outer ramp fa11 fa13 led to the identification of a distally steepened ramp antecedent topography exerted a significant control on platform morphology and the development of the widespread inner ramp facies on the lennard shelf a sequence stratigraphic analysis reveals that the fairfield group ramp deposits consists of four third order sequences s1 s4 that were largely deposited during sea level highstands hst characterized by progradational trends and dominant shallow subtidal inner ramp facies associations transgressive systems tracts tst are well developed in s1 and s3 and have a retrogradational facies pattern with dominant deep subtidal mid outer ramp facies associations lowstand systems tracts characterized by lowstand wedges and turbiditic facies are identified in the lower parts of s2 and s3 coarse and fine grained siliciclastic facies are mixed with carbonate facies as a result of coeval deposition on the inner and mid ramp and reciprocal deposition on the outer ramp a temporal variation in the types of carbonate grains and the amount of siliciclastic facies from the mixed peloidal skeletal carbonate siliciclastic ramp in s1 and s2 to the mixed skeletal carbonate siliciclastic ramp in s3 and a siliciclastic dominated ramp in s4 is interpreted as the change from a greenhouse to an icehouse state

fault control on depositional systems and sequence stratigraphic architecture in a multiphase rifted lacustrine basin a case study from the paleogene of the central bohai bay basin northeast china abstract the stratigraphic evolution of rift basins is complicated by out of phase displacement on boundary and intrabasinal faults and this analysis of paleogene strata in the central bohai bay basin of eastern china exemplifies this conundrum the spatial and temporal distribution of depositional systems and sequences in the central bohai bay basin are evaluated by using seismic reflection data in conjunction with drill cores and well logs three second order composite sequence boundaries are identified on seismic profiles on the basis of truncations below and onlap relationships above and by abrupt changes abrupt changes in gamma ray values on well logs composite sequences are comprised of third order sequences identified as distinctive seismic packages variations in thickness and distribution of third order sequences are consistent with out of phase displacement of boundary and intrabasinal faults which resulted in migration of depocenters in space and time a range of depositional systems are recognized including fan delta braid delta river delta sublacustrine fan and shallow and deep lacustrine during rift climax stages lowstand fan deltas developed on the hanging wall adjacent boundary faults to the north braid deltas on the footwall ramps to the south and sublacustrine fans in the central basin following transgression highstand braid deltas prograded from the north and south whereas river deltas during the late stages of basin fill both tectonic activity and climate were important controls on accommodation and the balance between sediment supply and accommodation determined the sedimentary architectures faulting uplift and erosion as well as fault block rotation controlled the formation of sequence boundaries and sequence geometries whereas variations in sediment flux can be attributed to climate changes high quality reservoirs are associated with deltaic channel fill and sublacustrine fan sandstones intrabasinal faults provided pathways for oil migration whereas prodeltaic lacustrine mudstones are source rocks as well as seals this study demonstrates that the spatial and temporal distribution of deposystems in rift basins in general requires an understanding of the history of boundary and intrabasinal faults within these compartmentalized basins

retrieving sand dune movements using sub pixel correlation of multi temporal optical remote sensing imagery northwest sinai peninsula egypt sand dune movements pose potential hazards against various land use activities in egypt to avoid or to minimize the hazards associated with sand dunes it is critical to determine their rates and patterns of migration at high accuracy and over wide spatial coverage this is however a real challenge using field work and traditional remote sensing approaches the co registration of optically sensed images and correlation cosi corr complements traditional approaches to provide accurate measurements at wide spatial coverage applying the cosi corr technique to two spot 4 panchromatic images acquired above north sinai we measured lateral migration of 6 0 to 19 4 m yr with an average of 7 7 m yr and 9 3 to 15 0 m yr with an average of 11 9 m yr for the whole barchans dune areas and a selected sample of barchan dunes respectively we also detected that the lateral movements along the crest lines of linear dunes ranged from 4 0 to 20 1 m yr with an average of 6 8 m yr for the whole area occupied by linear dunes for a selected linear dune within the study area the lateral migration of peaks and saddles along the crest lines ranged from 5 5 to 16 7 m yr with an average of 12 4 m yr the lateral migration of both barchans dunes and linear dunes showed high spatial variability validation of these results against the previously measured migration rates indicated high degree of accuracy of the technique in addition the displacement field produced from the correlation indicated that the direction of sand dune movements occurred towards the east and southeast which is well aligned with the previously determined sand dune drifting potentials

modeling microwave backscatter and thermal emission from linear dune fields application to titan we present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional physical roughness subsurface porosity heterogeneity and geometrical slope orientation properties this model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross section and emissivity compared to cassini concurrent radar and radiometry data acquired from october 2004 to june 2011 over titan s dune fields it provides clues to understand variations among dune regions on the largest saturn s moon in particular it brings a formal support to the idea first advanced in le gall et al le gall a janssen m a wye l c hayes a g radebaugh j savage c zebker h lorenz r d lunine j i kirk r l lopes r m c wall s callahan p stofan e r farr t and the cassini radar team 2011 icarus 213 608 624 that the size of the interdune valleys relative to that of the dunes varies across titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover i e bedrock contribution or degree of compaction heterogeneity of the sand cover the fensal and belet dune fields in particular are quite different in terms of these properties the comparison between the model and cassini data also reveals the potential presence of structures possibly small superposed dunes oriented perpendicular to the dune crests in the aztlan region

dunes on the skeleton coast namibia south west africa geomorphology and grain size relationships simple and locally compound transverse and barchanoid dunes dominate the 2000 km2 skeleton coast dunefield in northwestern namibia south west africa dune height and spacing are closely correlated r 0 89 and decrease across the dunefield from southwest to northeast with an accompanying change from transverse to barchanoid ridges and ultimately barchans the dunes are aligned transverse to the dominant strong south and south southwest onshore winds alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune forming winds to swing to the right over the dunes but resume their original direction beyond grain size and sorting vary at three scales the dune the dune landscape and through the dunefield overall the sands derived from three localities by deflation from beaches supplied by vigorous longshore drift become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing a statistically significant relationship r 0 65 was established between dune spacing and the phi grain size of the coarser fraction of the dune sands demonstrating the importance of the protective effects of coarse grains and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

tertiary sea level movements around southern africa sedimentological micropaleontological and seismic profiling data elucidate the history of tertiary sea level movements around southern africa these new data show that landward movement of the sea began in early paleocene time and continued into the early eocene the sea probably reached its maximum paleocene height during the early eocene and is today represented by outcrops up to at least 204 m and probably as high as 360 m above modern sea level a brief regressive pulse occurred during the middle eocene with renewed transgression in the late eocene a major regression followed probably spanning all of oligocene and early miocene times this regression exposed much of the continental shelf and is clearly represented on seismic reflection profiles by a widespread unconformity the major neogene transgression began in the middle miocene and probably reached its greatest extent in the late miocene or early pliocene the overall middle miocene to early pliocene transgression was interrupted by a brie

palaeo drainage incised valley fills and transgressive systems tract sedimentation of the northern kwazulu natal continental shelf south africa sw indian ocean abstract two sequence boundaries are recognised in seismic data collected from the narrow northern kwazulu natal continental shelf these correspond to late cretaceous and latest pleistocene last glacial maximum lgm periods of sea level fall where fluvial incision into the shelf resulted in several incised valleys having formed in both examples the ensuing transgressive valley fills document an evolution from fluvially dominant sedimentation to classic backbarrier estuarine conditions central estuary basin sedimentation is most prominent within each fill and is separated from the underlying fluvial sediments by bayline ravinement processes tidal ravinement surfaces separate the upper estuarine sequences from barrier and shoreface deposition most easily observed in the latest pleistocene holocene valley fills where a holocene unconsolidated sediment wedge overlies the estuarine fill the wedge itself is characterised by two packages of sediment separated by a regionally occurring wave shoreface transgressive ravinement surface which crops out as a semi indurated shell hash in the mid to outer shelf late cretaceous examples are capped by deposits exhibiting oblique parallel to wavy reflectors interpreted as increasingly energetic deposits analogous to flood tide deltaic sedimentation valley incision and fill are linked to two onshore coastal lake systems lake sibaya and lake st lucia and appear to be the product of barrier breaching and fluvial re adjustment to baseline shifting of these systems during forced regression lake st lucia exhibits a composite palaeo drainage channel where both sequence boundaries merge within the lake margins lake sibaya has two distinct palaeo channels for each sequence boundary episode a late cretaceous channel which fed a small incised valley within which a modern day submarine canyon is located the other an lgm channel directed in towards the head of wright canyon the subsequent input of sediment causing this canyon to breach furthest into the shelf than any other canyon in the area offshore of lake st lucia the most proximal portions of the associated leven canyon occupy the mid shelf and are underlain by lake st lucia palaeo drainage channels of lgm age where erosion along the initial lgm palaeo channel has occurred freshwater exchange between the shelf and the fringing lake system has resulted in the development of sinuous features of leven canyon which have eroded in a downslope fluvial like manner thus occupying palaeo drainage lows as erosive flows were entrained models proposed here indicate that 1 the limited accommodation space offered by a narrow continental shelf may allow for a greater preservation potential of wave dominated estuarine facies 2 the seismic expression of these fills may vary yet still satisfy similar sedimentological conditions and 3 antecedent valley topography increases the preservation potential of these valley fills by providing a preferred space in which to re incise and then fill during sea level rise

effects of the magnus and saffman forces on the saltation trajectories of sand grain abstract saltating sand grains are the primary component of airborne sand and account for 75 of all sand transport flux the saltation height and horizontal distance traveled by sand grains are key factors in sand control engineering in addition to gravity and aerodynamic drag the magnus and saffman forces also play important roles in saltation to quantify the magnitudes of these forces in saltation we used high speed multi flash photography to observe the movement of saltating sand grains in a wind tunnel this proved to be an efficient technique for determining the movement and rotational velocities of grains of natural sand with grain sizes ranging from 0 2 to 0 3 mm and shear velocities u of 0 67 0 83 and 0 87 m s 1 the rotational speed of saltating sand grains varied between 200 and 800 rev s 1 mean clockwise and anticlockwise rotational speeds were nearly identical and both increased with increasing saltation height with saltation heights divided into 1 cm intervals the rotational speeds followed a lorentzian distribution calculations based on a saltation model showed that the maximum increases in saltation height and in horizontal distance due to the magnus force were 10 2 and 24 9 respectively the rate of increase of both parameters increased with increasing lift off angle the maximum increases in saltation height and horizontal distance of sand grains caused by the saffman force were only 4 6 and 3 7 respectively

sedimentary architecture of an ancient linear megadune barremian neuquen basin insights into the long term development and evolution of aeolian linear bedforms linear aeolian bedforms are the most abundant bedform type in modern earth sand seas and are very common in our solar system despite their abundance the long term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood the aims of this paper are to study the exposed record of an ancient linear megadune in order to discuss the factors that impact the development and sedimentary architecture of aeolian linear bedforms the outcrops of the ancient troncoso sand sea barremian neuquen basin argentina provide a unique opportunity to access a preserved megadune record with an external body geometry that unequivocally confirms its linear morphology architectural analysis of the bedform record reveals significant differences for several aspects of cross stratified set bodies and bounding surfaces and allows for the identification of three architectural complexes insights from deterministic models analysis of set body relative chronology and distribution suggest that complexes result from distinctive phases in bedform development it also clearly shows that the megadune s construction was achieved by expansion from a core where the oldest deposits are located and that its development was characterized by sustained growth and strong longitudinal dynamics factors that impact the development and architecture of linear bedforms are identified discussed and compared to bedforms of transverse dynamics finally a scheme of expected styles of sedimentary architecture for linear bedforms is presented this case study shows how growth can be a critical factor conditioning linear bedform architecture and indicates how the preservation of certain styles of sedimentary architecture in the geological record may not be as unusual as previously thought

sedimentation on the narrow 8km wide oceanic current influenced continental shelf off durban kwazulu natal south africa abstract the narrow transform margin of southeast africa and its associated sedimentological and hydrodynamic setting differs to other documented continental margins the durban bluff continental shelf is extremely narrow and steep 8 km wide with a gradient ranging from 2 to 8 characterised by a wave and oceanic current dominated regime seismic sequence boundary 2 developed during the last interglacial regression spans the entire shelf separating the holocene sediment wedge seismic unit h from underlying pleistocene deposits a wave ravinement surface marks the holocene transgression comprising a pavement lag of well sorted gravels and bioclastics overlain by inshore reef derived carbonate rich sediments and offshore by quartzose mid shelf sands the shelf sands represent the transgressive holocene to modern sediment wedge forming a seaward thinning unit stacked against the pleistocene blood reef aeolianite beachrock substrate the sediment wedge is dynamic and constantly redistributed by currents associated with the durban eddy inshore of the agulhas current and bottom surge associated with high swells and marine storm events these have been instrumental in shaping large scale shoreface attached and detached sand ridges the presence of mud lenses in the vicinity of blood reef represents deposition from turbid flood waters with preservation facilitated by the morphology of the durban bluff and blood reef palynological results reflecting the local subtropical vegetation and recently introduced neophytes together with radiocarbon dates provide a very recent age for this sediment supporting a terrestrial origin and deposition from a single large flood event

lateral migration thermoluminescence chronology and colour variation of longitudinal dunes near birdsville in the simpson desert central australia the longitudinal dunes of the simpson desert in the vicinity of birdsville have been reworked largely during the holocene from dunes deposited up to 80000 years ago or earlier the widespread asymmetry of these roughly northward trending dunes with steeper eastern faces and more gentle western faces supports wind rose data showing sand transporting winds from the southwest obliquely intersecting the dunes while this suggests a change in the wind pattern since the dune field was oriented it does not indicate that the dunes are necessarily shifting leeward eastward as a consequence it is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated relatively well vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind a condition that probably prevails in wetter regions and during episodes of relatively humid climate in contrast in very dry areas or during arid phases sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side thereby causing the dunes to shift eastward despite evidence that longitudinal dune crests can shift laterally to some extent the dunes in the western part of the simpson desert have not migrated either westward or eastward more than 100m or so from their pleistocene cores aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age

reproducibility and utility of dune luminescence chronologies abstract optically stimulated luminescence osl dating of dune deposits has increasingly been used as a tool to investigate the response of aeolian systems to environmental change amalgamation of individual dune accumulation chronologies has been employed in order to distinguish regional from local geomorphic responses to change however advances in dating have produced chronologies of increasing complexity in particular questions regarding the interpretation of dune ages have been raised including over the most appropriate method to evaluate the significance of suites of osl ages when local noisy and discontinuous records are combined in this paper these issues are reviewed and the reproducibility of dune chronologies is assessed osl ages from two cores sampled from the same dune in the northeast rub al khali united arab emirates are presented and compared alongside an analysis of previously published dune ages dated to within the last 30 ka distinct periods of aeolian activity and preservation are identified which can be tied to regional climatic and environmental changes this case study is used to address fundamental questions that are persistently asked of dune dating studies including the appropriate spatial scale over which to infer environmental and climatic change based on dune chronologies whether chronological hiatuses can be interpreted how to most appropriately combine and display datasets and the relationship between geomorphic and palaeoclimatic signals chronological profiles reflect localised responses to environmental variability and climatic forcing and amalgamation of datasets with consideration of sampling resolution is required otherwise local factors are always likely to dominate using net accumulation rates to display ages may provide an informative approach of analysing and presenting dune osl chronologies less susceptible to biases resulting from insufficient sampling resolution

experimental deformation of synthetic magnetite bearing calcite sandstones effects on remanence bulk magnetic properties and magnetic anisotropy we have quantified effects of experimental deformation on the magnetic properties of a set of synthetic calcite sandstone samples containing magnetite the deformation was carried out in a microcomputer controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10 5 s 1 most samples were deformed under dry conditions but a few were deformed with a pore fluid present the samples deformed under dry conditions required substantially higher differential stresses macroscopically ductile shortening strains of up to 25 produced the following irreversible changes in magnetic properties 1 increased bulk coercivity remanence coercivity and mean anhysteretic remanence susceptibility 2 decreased mean low field susceptibility 3 decreases in the component of remanence parallel to shortening 4 smaller decreases for most samples in the component normal to shortening resulting in a net rotation of the remanence away from the shortening axis 5 larger decreases in the normal component in a few samples resulting in a net rotation of the remanence towards the shortening axis 6 increased magnetic anisotropy and 7 increased deformation of initial magnetic ellipsoids a comparison of data for samples deformed under dry and wet conditions higher and lower differential stresses respectively indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain i e rotation and displacement of particles whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress

linear dunes on titan extensive dunes produced by wind transport of sand sized particles are common on earth and are also seen on mars and venus saturn9s moon titan is now shown to have similar dunes

antecedent geologic control on nearshore morphological development the wave dominated high sediment supply shoreface of southern namibia abstract the inner continental shelf nearshore zone and adjacent onland coastal strip of southern namibia has been mapped using airborne electromagnetic and magnetic techniques providing for the first time in the area a continuous onshore offshore geophysical dataset in addition the inner continental shelf and nearshore zones of this vigorous wave dominated coastline were mapped inshore of a pervasive acoustic blanketing layer using multibeam bathymetry singlebeam bathymetry and boomer sub bottom profiling systems in water depths between 3 and 55 m we use an integrated iterative approach to the interpretation of these brand new datasets to map the structural framework of the late proterozoic age bedrock of the area beneath thick holocene sand cover and show how despite the vigorous wave regime and high sediment supply from the orange river this framework acts as a recurring primary control to the area s geomorphic evolution the bedrock morphology is divided into three main zones that are constrained by nnw striking and coast parallel faults a southern zone characterised by both relatively shallow bedrock depth and shallow bedrock slope is bounded in the north by a dextral strike slip fault system this basement promontory is the primary control on the shallow low gradient seafloor in the southern zone strike slip movement on the fault shifted the bedrock to the north both down and inshore relative to the shallow basement promontory to the south however in this central zone both the seafloor and seafloor gradient remain shallow sediment accumulation in this area is explained by two processes firstly the relative downward movement of the bedrock has resulted in the creation of relatively more accommodation space and sediment delivery begins to overprint the underlying bedrock framework smoothing the general seafloor gradient in the central zone secondly this central zone directly north of the basement promontory has existed in a swell shadow as long lived sw directed wave energy has continually been refracted around the palaeo promontory promoting natural accretion of sediment within the lee of this feature a fault related inflection point on the modern coastline marks a change in coastline orientation from nw to slightly more north striking and the start of the northernmost bedrock zone here the shallow wide low relief seafloor zone transitions to a wider nearshore high relief zone that mimics the underlying uniformly steepening nearshore bedrock profile the combination of the uniform coast normal basement gradient with the fault related inflection changes the nearshore response to incoming wave energy in the northern zone waves approach at a slightly more oblique angle due to the fault controlled coastline orientation and reinforce an already vigorous longshore drift regime that is responsible for the steeper and deeper nearshore profile underpinned by the underlying steep basement topography the steep antecedent topography also limits the amount by which the seafloor can aggrade and subsequently adjust its slope an imbalance between the sediment supply and the large volume of accommodation space thus exists that cannot be overcome given the context of the vigorous longshore drift the continual inheritance of the underlying bedrock slope in the nearshore is further revealed with the unchanging slope of the reflectors that match the present day nearshore seafloor gradient we suggest that the geologic framework control remains a critical factor in nearshore beach system development even in an area of high sediment supply and high wave energy conditions

implications of dune pattern analysis for titan s surface history abstract analysis of large scale morphological parameters can reveal the reaction of dunes to changes in atmospheric and sedimentary conditions over 7000 dune width and 7000 dune spacing measurements were obtained for linear dunes in regions across saturn s moon titan from images t21 t23 t28 t44 and t48 collected by the synthetic aperture radar sar aboard the cassini spacecraft in order to reconstruct the aeolian surface history of titan dunes in the five study areas are all linear in form with a mean width of 1 3 km and mean crest spacing of 2 7 km similar to dunes in the african saharan and namib deserts on earth at the resolution of cassini sar the dunes have the morphology of large linear dunes and they lack evidence for features of compound or complex dunes the large size spacing and uniform morphology are all indicators that titan s dunes are mature features in that they have grown toward a steady state for a long period of time dune width decreases to the north perhaps from increased sediment stabilization caused by a net transport of moisture from south to north or from increased maturity in dunes to the south cumulative probability plots of dune parameters measured at different locations across titan indicate there is a single population of intermediate to large sized dunes on titan this suggests that unlike analogous dunes in the namib and agneitir sand seas dune forming conditions that generated the current set of dunes were stable and active long enough to erase any evidence of past conditions

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

temporal observations of a linear sand dune in the simpson desert central australia testing models for dune formation on planetary surfaces linear dunes are the most common dune form found on planetary surfaces yet questions remain about their formation temporal observations of a linear dune located in the simpson desert of central australia were made to monitor dune movement and to test competing hypotheses regarding linear dune formation our observations were collected on three separate occasions from 2006 to 2014 rebar stakes were placed in a gridded pattern so that multiple measurements of sand thickness gps surveys and photographs could be taken at the same locations over time we observed widespread reworking of sand on and around the dune crest with sand accumulation locally exceeding a meter between surveys overall the height of the dune crest increased by several centimeters we also observed fluctuations in the sand cover in the adjacent swales that often exceeded 2 3 cm between surveys yet we did not observe any appreciable changes in the position of the dune s downwind terminus weather data indicate that the effective sand transporting winds in the simpson are widely unimodal net sediment flux resultant drift direction is toward the north northwest locally at an oblique angle to dune orientation collectively our results suggest that the linear dune is actively maintained by vertical accretion the implications from our observations are that linear dunes on other planetary surfaces could form in wind regimes that are widely unimodal even where the resultant drift direction is locally oblique to dune orientation in particular such findings may provide support for global circulation models of titan

exploring morphology layering and formation history of linear terrestrial dunes from radar observations implications for titan abstract understanding the morphology and internal layering of large aeolian dune fields through radar observations can provide unique insights into the climatic and geophysical conditions that led to their formation in this study we perform a large scale characterization of the morphology and internal layering of linear dunes in hyper arid areas on earth through utilizing multiple complementary radar datasets sir c imaging srtm interferometry derived elevations and radar sounding or ground penetrating radar gpr linear dune fields in the egyptian desert are of special interest due to their significance as planetary analogs to dunes on mars and saturn s largest moon titan satellite radar imagery and elevation data of the region show significant variance in the geomorphology of different dune fields in egypt in addition gpr probing of the first few meters suggests different inner settings in the layering of dunes of different ages in eastern and western egypt reflecting different paleo climatic regimes that led to their formation furthermore our radiometric analysis suggests that dunes with different inner layering arrangement also exhibit different radar backscatter returns as a function of their heights for relatively younger dunes with a homogeneous inner structure like the ones in eastern egypt in the qattaniya dune field we observe that sigma0 does not change as a function of the dune height for relatively older dunes in western egypt like the great sand sea northern siwa and southern dune fields we observed a linear correlation between sigma0 and the dune height thus surface properties of dunes like morphology and backscatter variation with height are related to inner characteristics like arrangement of internal layering relative ages and can be used to infer their depositional history linear dunes discovered in the equatorial regions of titan by the cassini huygens mission are morphologically very similar to these linear dune fields in the egyptian sahara hence assessing the variability of morphology and radar backscatter properties of titan s dunes as a function of their heights can help constrain the ambiguities associated with their internal structure and formation history and provide insights into titan s paleo wind regimes

analysis of large aeolian wind blown bedforms using the shuttle radar topography mission srtm digital elevation data abstract dry land areas cover large parts of the land masses of earth of these a large portion is mantled by aeolian wind blown deposits and subjected to aeolian process i e the transport of sand or dust by wind one of the most prominent morphologies created by wind driven deposits are dunes and in their larger form draas or mega dunes these mega dunes tend to be widely spaced very large often forming a base on which smaller dunes form producing a compound dune pattern in february 2000 the shuttle radar topography mission onboard the space shuttle endeavour flew an interferometric radar system whose objective was to create a dem of nearly all earth land masses in this paper dem data from the c band 90 m data set and the x band 30 m data set were used to map and characterize the height and spacing of the large sand seas ergs on earth only the larger forms of dunes could be mapped reliably the dune spacing and heights extracted from the srtm dems tended to be in overall agreement with those reported in the literature in a comparison between the x band and the c band data it was found that the x band data are more sensitive to the smaller scale undulations on the compound dunes and better revealed the full height of the dunes

formation of the highest sand dunes on earth characterization of dune morphology has historically been based on relationships between dune forms and wind regimes with dune height shown to be sensitive to atmospheric boundary layer depth sand availability and sediment properties while these parameters have been used in numerical simulations to model the occurrences of some types of dunes they cannot alone explain the great diversity in form and size seen on earth and on other solar system bodies here we present results from our studies of dune formation in the badain jaran desert in western china where earth s tallest dunes occur we measured the variability of the dune morphology in this desert on the basis of landsat etm data and we detected the bedrock landforms beneath the aeolian sands by applying gravity methods wind records from stations at the periphery of the desert and srtm topographical data were examined also to augment the interpretation our studies demonstrate that in addition to average wind parameters dune height is highly sensitive to local geology subsurface characteristics and topography and interactions between changing climate conditions and aeolian and fluvial processes these additional factors need to be considered in the interpretation and simulation of dunes on earth we anticipate that analysis of anomalous dune heights like those seen in the badain jaran may also provide critical information on subsurface characteristics and environmental conditions on earth and on other planetary bodies

longitudinal dunes can move sideways longitudinal dunes occur in all major sand areas in the world their dominant mode of migration or extension is considered to be either prevailing or resultant wind parallel the dunes extending downwind via accretion of the terminal nose in the qaidam pendi in northwest china a series of active longitudinal dunes extend downwind at 5 10 m yr 1 internal sedimentary structures examined in the dunes however display beds dipping in one direction rather than two opposed directions as is expected analysis of aerial photographs confirms that these dunes migrate laterally up to three metres per year whilst maintaining a symmetrical longitudinal dune morphology

transform continental margins part 2 a worldwide review we present a global inventory of transform continental margins based on both a worldwide comparison of continent ocean boundary identifications with oceanic fracture zones traces and a compilation of published regional studies this inventory increases the number of identified transform margins from 29 to 78 these margins represent 16 of continental margins in cumulative length and 31 of non convergent margins we include morphological data published upper crustal sections continent to ocean transition locations and published moho shape data in the new database this review confirms that continent to ocean transitions are sharper at transform margins than at divergent margins it also emphasizes the structural diversity of transform margins associated with one third of transform margins we define marginal plateaus as a new type of relief that corresponds to a flat but deep surface inside the continental slope and that may be inherited from crustal thinning prior to transform faulting transform margin initiation appears to be favoured along propagating oceans and within cold and thick lithospheres

mesozoic magnetic anomalies in the southern natal valley the recognition of mesozoic magnetic anomalies m0 m12 within the submarine natal valley south west indian ocean provides a further constraint on the relative motion between south america falkland plateau and africa during the early opening phase of west gondwanaland fig 1 colinear with m12 magnetic anomaly g ref 1 is delineated north of the south tugela ridge2 an acoustic basement high which is suspected to have been emplaced within continental crust immediately north of the continental oceanic crust boundary cob during the initial rifting phase starting from a revised west gondwana reconstruction3 and using palaeo poles of rotation1 3 the falkland plateau can be rotated into the natal valley superposing the corresponding georgia basin and natal valley magnetic anomalies this achieves an optimum continuity of inter continental structural lineaments3 by overlapping of an anomaly intermediate to m10 and m11 m10n4 this suggests that the natal valley cob is located between anomalies m10 and m11 implying that in this zone of south west gondwana seafloor spreading commenced at 125 myr

11 11 dune morphology and dynamics this chapter discusses the key types of sand dunes and how they can be classified and assesses the major controls on their development the processes of dune dynamics are reviewed leading to a discussion of the concept of equilibrium in solitary dune form recent advances in modeling are reviewed that show how interactions between dunes may result in equilibrium at the dune field scale rather than at the single dune scale

aeolian features on venus preliminary magellan results magellan synthetic aperture radar data reveal numerous surface features that are attributed to aeolian or wind processes wind streaks are the most common aeolian feature they consist of radar backscatter patterns that are high low or mixed in relation to the surface on which they occur a data base of more than 3400 wind streaks shows that low backscatter linear forms long narrow streaks are the most common and that most streaks occur between 17 s to 30 s and 5 n to 53 n on smooth plains moreover most streaks are associated with deposits from certain impact craters and some tectonically deformed terrains we infer that both of these geological settings provide fine particulate material that can be entrained by the low velocity winds on venus turbulence and wind patterns generated by the topographic features with which many streaks are associated can account for differences in particle distributions and in the patterns of the wind streaks thus some high backscatter streaks are considered to be zones that are swept free of sedimentary particles to expose rough bedrock other high backscatter streaks may be lag deposits of dense materials from which low density grains have been removed dense materials such as ilmenite or pyrite have dielectric properties that would produce high backscatter patterns wind streaks generally occur on slopes 2 and tend to be oriented toward the equator consistent with the hadley model of atmospheric circulation in addition to wind streaks other aeolian features on venus include yardangs and dune fields the aglaonice dune field centered at 25 s 340 e covers 1290 km 2 and is located in an ejecta flow channel from the aglaonice impact crater the meshkenet dune field located at 67 n 90 e covers 17 120 km 2 in a valley between ishtar terra and meshkenet tessera wind streaks associated with both dune fields suggest that the dunes are of transverse forms in which the dune crests are perpendicular to the prevailing winds dunes on venus signal the presence of sand size 60 to 2 000 m grains the possible yardangs are found at 9 n 60 5 e about 300 km southeast of the crater mead although most aeolian features are concentrated in smooth plains near the equator the occurrence of wind streaks is widespread and some have been found at all latitudes and elevations they demonstrate that aeolian processes operate widely on venus the intensity of wind erosion and deposits however varies with locality and is dependent on the wind regime and supply of particles

geomorphological patterns in a linear dune field and ages of the linear dunes in the northern kumtagh desert northwest china the unique linear dunes in the northern kumtagh desert of northwest china have inspired enthusiastic debate among aeolian geomorphologists over their origins and classification their uniqueness lies not only in their morphology but also in their geomorphological patterns in this paper the geomorphological patterns and ages of the linear dunes in the northern kumtagh desert are analyzed using the pattern analysis method that was recently adopted by geomorphologists the analysis suggests that these linear dunes have developed since 13 ka bp during the late part of the most recent deglaciation stage when the region s dry climate was favorable for dune formation the differences in dune construction time within this region result from the complex factors that control their formation and spatial variations in the local environment but these factors were not strong enough to prevent us from estimating the dune age recorded by the geomorphological patterns with acceptable precision it is also suggested that the pattern analysis method can be used to estimate dune ages in the absence of more reliable dating methods

grain size variations on a longitudinal dune and a barchan dune abstract the grain size characteristics of the sand upon two dunes a 40 m high longitudinal dune in the central namib desert and a 6 0 m high barchan in the jafurah sand sea of saudi arabia vary with position on the dunes on the longitudinal dune median grain size decreases sorting improves and the grain size distributions are less skewed and more normalized toward the crest though sand at the windward toe is distinct elsewhere on the dune the changes in grain size characteristics are gradual an abrupt change in grain size and sorting near the crest as described by bagnold 1941 pp 226 229 is not well represented on this dune coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest avalanching down slipfaces at the crest acts only as a supplementary grading mechanism on the barchan dune median grain size also decreases near the crest but sorting becomes poorer though the grain size distributions are more symmetric and more normalized the dune profile is a gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling grain size increases and sorting improves down the dune s slipface however this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion on both dunes height and morphology appear to influence significantly the grain size characteristics

environmental dynamics of a star dune abstract star dunes the largest aeolian bedforms in the sand seas of the world are usually distributed within specific geographical areas that have multi directional wind regimes however relatively few studies have focused on the environmental factors that impart such great volumes of sand to these dunes specifically verification of the developmental processes of star dunes through long term monitoring is scarce in this study by observing 3 d airflow fields and long term dune dynamics we demonstrate how topographic barriers which generate vertical airflow and local air circulation control the development of a star dune on mingsha mountain in dunhuang china results show that airflow stagnation and deflection caused by topography is one of the major mechanisms for the formation of star dunes in our study topographic barriers contribute to the development of intensive vertical airflow dominated by easterly winds this intensive vertical airflow is one of the main driving mechanisms of the upward growth of mega dunes vertical airflow is the strongest developed airflow reported in available data on aeolian geomorphology in addition star dunes are usually distributed in areas where the local air circulation is strong the results of long term dune dynamics verify that local air circulation which forms three wind directions with the regional wind regime contributes to the maintenance and development of star dunes our study indicates that complex mega dunes are products of topographic barriers which facilitate their recognition in aeolian geomorphology we introduce a new evolution pattern of star dunes under the influence of local environment and topographic barriers

growth styles of shelf margin clinoforms prediction of sand and sediment budget partitioning into and across the shelf abstract growth styles of shelf margin clinoforms are reliable but understudied predictors of sand and sediment budget partitioning into and across the shelf three discrete clinoform growth styles were recognized including 1 strongly progradational shelf margin clinoforms with low growth trajectory angles gct low aggradation to progradation ratios a p low clinoform heights hc and long clinoform length lc 2 mixed progradational and aggradational shelf margin clinoforms with moderate gct moderate a p intermediate hc and moderate lc and 3 strongly aggradational clinoforms with high gct high a p high hc and short lc in the south china sea dataset considered strongly progradational shelf margin clinoforms exhibit flat progradational and at times a mildly aggrading stacking patterns whereas mixed progradational and aggradational clinoforms display stacking patterns with significant progradation and aggradation strongly aggradational shelf margin clinoforms are dominated by aggradational stacking patterns each clinoform growth style therefore represents a specific stratal stacking pattern providing an important tool for approaching a model independent methodology in sequence stratigraphy in the study dataset strongly progradational and strongly aggradational shelf margin clinoforms are fronted by sand prone submarine fan systems with high sand shale ratios and mud dominated mass transport systems with low sand shale ratios respectively mixed progradational and aggradational clinoforms are associated with mixed sand mud submarine canyon systems with moderate sand shale ratios additionally strongly progradational clinoforms partitioned great volumes of sediment into deep water areas as reflected by high rates of shelf edge progradation and apparent toplap strongly aggradational clinoforms in contrast stored great volumes of sediment on the shelf itself as indicated by high rates of shelf edge aggradation and very thick clinoform topsets gct and hc therefore increase linearly with sediment volumes partitioned into the shelf but decrease linearly with sand and sediment budget partitioning into deep water areas given a constant sediment supply condition growth styles of shelf margin clinoforms are thus good predictors of source to sink sand and sediment volume partitioning into and across the shelf assisting greatly in developing a more dynamic stratigraphy

airflow and roughness characteristics over partially vegetated linear dunes in the southwest kalahari desert there is little understanding of the flow field surrounding semi vegetated linear dunes and predictions of dune mobility are hampered by a lack of empirical data concerning windflow in an attempt to characterize the near surface airflow upwind of and over partially vegetated linear dunes in the southwest kalahari desert this study presents measurements of vertical and horizontal wind velocity profiles across cross sectional transects of seven partially vegetated linear dunes vegetation surveys combined with velocity measurements from vertical arrays of cup anemometers placed up to 2 3 m above the ground surface were used to gain information concerning the modification of airflow structure caused by the intrusion of the dunes into the atmospheric boundary layer and to predict the variability of aerodynamic roughness z0 from interdune to crest the results suggest an acceleration of flow up the windward slopes of the dunes and as such the data correspond to classical theory concerning flow over low hills essentially jackson and hunt 1975 principles where the theory is incapable of explaining the airflow structure and acceleration characteristics this is explained in part by the presence of a spatially variable vegetation cover over the dunes the vegetation is important both in terms of the varying aerodynamic roughness z0 and problems concerning the definition of a zero plane displacement d it is considered that any attempts to characterize surface shear stress over the kalahari linear dunes in order to predict sand transport and dune mobility will be hampered by two problems these are the progressively non log linear nature of the velocity profiles over the dunes caused by flow acceleration and the production of thin near surface boundary layers caused by areally variable aerodynamic roughness as a result of the partially vegetated nature of the dunes

barchan dune asymmetry observations from mars and earth barchan dune asymmetry refers to the extension of one barchan limb downwind it is a common dune form on earth and also occurs on mars and titan a new classification of barchan limbs is presented where three types of limb morphology are identified linear kinked and beaded these along with other dune scale morphological signatures are used to identify three of the causes of barchan asymmetry on mars bi directional winds dune collision and the influence of inclined topography the potential for specific dune asymmetric morphologies to indicate aspects of the formative wind regime on planetary surfaces is shown for example the placement of dune limbs can indicate the general direction and relative strength of formative oblique winds an extreme barchan limb length may indicate a long duration oblique wind a kinked limb may be evidence of the passage of a storm beaded limbs may represent surface wave instabilities caused by an increase in wind energy parallel to the dune a preliminary application of these signatures finds evidence for bi modal winds on mars however these and other morphological signatures of wind direction and relative strength should be applied to planetary landforms with caution as more than one process e g bi modal winds and collision may be operating together or sequentially on the dunefield in addition analysis should be undertaken at the dunefield scale and not on individual dunes finally morphological data should be acquired from similar scale dunes within a dunefield in addition to bi modal wind regimes on mars the frequent parallel alignment of the extended barchan limb to the dune suggests that dune collision is also an important cause of asymmetry on mars some of the more complex dunefield patterns result from a combination of dune collision limb extension and merging with downwind dunes dune asymmetric form does not inhibit dune migration in the namib desert or on mars data from the namib suggest that dune migration rates are similar for symmetric and asymmetric dunes further modeling and field studies are needed to refine our understanding of the potential range of limb and dune morphologies that can result from specific asymmetry causes

linear dunes on titan and earth initial remote sensing comparisons thousands of dunes found in cassini radar images of the equatorial regions of titan a moon around saturn are similar in size and morphology to linear dunes on earth we present remote sensing images of terrestrial analogues to the dunes on titan obtained by landsat and radar both at considerably higher resolution than are available at titan that provide information about dune landforms and processes dunes are generally dark to radar indicating smooth surfaces and signal absorbing materials but at certain incidence angles dune surfaces can reflect the radar signal and lead to a bright return linear dunes on titan and earth diverge around topographic obstacles creating teardrop patterns that indicate mean direction of wind flow and sand transport when sand supply or wind conditions change in linear dune fields such as behind an obstacle or near the margin of the dune field dunes disappear change size and spacing or change dune type these comparisons of features on titan and earth provide a better understanding of the global sand transporting wind directions sand properties and supply and the nature of the underlying substrate on titan

secondary airflow and sediment transport in the lee of a reversing dune lee side windspeed and sediment transport were measured over a small 1 2 m transverse ridge in the silver peak dunefield west central nevada usa using an intensive array of 25 cup anemometers and seven total flux traps during crest transverse and transporting flow conditions u0 3crest 8 4 m s 1 windspeed near the surface of the lee slope averaged half 48 per cent that of crest speeds dimensionless speeds in the separation zone ranged from 0 2 to 0 8 that of the outer flow u12 along the boundary of the separation cell windspeed increased by 10 per cent of the crest speed before separation equilibrium of upper and lower wake regions was not observed by the documented eight dune heights suggesting that wake recovery may not occur over closely spaced dunes sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs this suggests that a significant amount c 70 95 per cent of sediment transported over the crest moved as fallout for this data set flux was approximately proportional to the cube of the near surface windspeed u0 3 and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection beyond the interdune transport direction progressed from oblique to crest transverse this indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest transverse flows regarding the grain size and sorting properties of transported sediment there was no significant difference in mean grain size over the dune although in general particles were finer and more poorly sorted in the lee copyright 1999 john wiley sons ltd

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

is there continental crust underneath the northern natal valley and the mozambique coastal plains 1 to draw conclusions about the crustal nature and history of the natal valley and the mozambique ridge systematic potential field data were obtained during the aistek iii cruise with r v pelagia in 2009 this paper presents and interprets the results of that expedition the new magnetic data reveal a pattern of linear magnetic spreading anomalies nw se trending in the southwestern part of the mozambique ridge and e w trending on its central part the ariel graben which separates the mozambique ridge from the northern natal valley is represented by a pronounced negative anomaly in the magnetic as well as the free air gravity field the northern natal valley bears a complicated pattern of anomalies with mainly sw ne trends in the northern natal valley no indications for a continent ocean boundary between continental crust in the north and oceanic crust in the south exist either in the free air gravity or in the magnetic field the magnetic wavelengths of the mozambique coastal plains are similar to those of the northern natal valley and the mozambique ridge particularly in the gravity data the mozambique coastal plains the northern natal valley and the mozambique ridge appear as one continuous geological province we interpret the region from the mateke sabi monocline in the north to the southwestern tip of the mozambique ridge as mainly being floored by thickened oceanic crust

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

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

solid sediment load history of the zambezi delta abstract we calculate the solid sediment load history of the zambezi river for the last 120 ma i e middle cretaceous recent times our starting point is a detailed grid of two dimensional seismic reflection profiles calibrated by well log information after conversion from two way travel time to depth we made simple assumptions about the compaction history in order to construct isochore maps of solid sediment load and yield as a function of geological time our results show that solid sediment load has varied by 1 order of magnitude over the last 120 ma there have been three periods of elevated flux the first period occurred in late cretaceous times 90 65 ma and was synchronous with the rapid denudation of southern africa recognised by for example apatite fission track modelling the second period occurred in oligocene times 34 24 ma during proposed rapid regional uplift of southern africa the youngest phase of elevated flux started in late miocene times 10 ma and has continued to increase rapidly through to the present day a large proportion of this increase can be attributed to a doubling of the size of the zambezi catchment during the pliocene at other times we suggest that load variations can be used to bound the uplift history of the region which encompasses the catchment finally changes in the shape of the zambezi delta through time suggest that the mozambique current which sweeps through the mozambique channel from northeast to southwest initiated at the start of the miocene

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

submarine canyons associated with alternating sediment starvation and shelf edge wedge development northern kwazulu natal continental margin south africa abstract multibeam bathymetry and high resolution boomer data reveal a shelf edge wedge embayed by numerous canyons on the currently sediment starved northern kwazulu natal continental margin submarine canyons in the southern portions of the study area may be differentiated from those in the north by the presence of an underlying erosive surface marked by palaeo depressions and a thinner shelf edge wedge canyons exhibit square interfluves in the mid slope slump and landslide failure surfaces in their walls and high amplitude chaotic reflectors interpreted as slump deposits infilling older thalwegs the shelf edge wedge architecture where it is embayed by canyons is progradational into the canyon axes and marked particularly in the north by block like features these are interpreted as syn depositional growth faults lenses comprising chaotic high amplitude reflector packages are common within the wedge and are interpreted as laterally discontinuous slump masses instability of the shelf edge wedge is considered the driving force for canyon inception initial failures generated downslope eroding sediment flows and submarine rills that evolved into their modern forms by retrogressive slumping when the rill walls became oversteepened continued delivery of sediment to the shelf edge wedge was contemporaneous with canyon widening and headward erosion mid slope canyon topography formed as the result of sandy turbidity currents that ignited downslope of these slump sources coupled with non aggradation of the adjoining interfluves differences in the thickness of the shelf edge wedge are the result of varying fluvial influences where larger rivers crossed the shelf during sea level lowstands the shelf edge wedge has been cannibalised this is more pronounced in areas with subsurface palaeo depressions that may have constrained the downslope eroding phase especially during lowstands where there were insignificant fluvial influences no subsurface depressions and a better preserved shelf edge wedge are apparent post dating the shelf edge wedge a protracted period of sediment starvation occurred halting canyon development and stunting more elaborate erosion patterns such as those of other margins

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

the effect of surface slope on saltation threshold a new wind tunnel has been constructed to study the mass transport properties of wind blown sand this report on the first set of experiments in the new wind tunnel concerns the effect of slope on threshold friction speed the results of this series of static threshold experiments and one dynamic threshold experiment for a range of particle diameters and bed slope angles show that provided the effects of reynolds number variation and interparticle cohesive force are accounted for the static friction angle is independent of slope and close in value to the measured static angle of response

morphodynamic mechanisms for the formation of asymmetric barchans improvement of the bagnold and tsoar models asymmetric barchan dunes exhibit a marked asymmetry this morphology develops from the combined effects of two dominant winds with different directions and relative strengths and can be described based on bagnold s and tsoar s models in bagnold s model the limb nearest to the strongest wind extends and is sustained and enhanced by a gentler wind nearly parallel to the barchan tsoar s model expects that the limb farthest from the gentler wind extends in a manner similar to the evolution of seif dunes and that the limb closest to the gentler wind is eroded to know which model will emerge with variations of the wind we did some numerical simulations and found that there exists a critical angle between orientations of the two winds which decide the formation model of asymmetric barchans when the angle is greater than this critical value the effect of the bi directional winds agrees with tsoar s model when the angle is less than the critical value the evolution of the two horns contradicts tsoar s model and agrees with bagnold s model the critical value for this angle depends on the transport ratio of two winds

sedimentology and depositional architecture of a submarine delta fan complex in the durban basin south africa abstract the seismic stratigraphy evolution and depositional framework of a sheared passive margin the durban basin of south east africa are described based on single channel 2d seismic reflection data six seismic units a f are revealed separated by major sequence boundaries these are compared to well logs associated with the seismic data set internal seismic reflector geometries and sedimentology suggest a range of depositional regimes from syn rift to upper slope and outer shelf nearshore and continental facies are not preserved with episodic shelf and slope sedimentation related to periods of tectonic induced base level fall the sedimentary architecture shows a change from a structurally defined shelf shearing phase to shallow ramp and then terminal passive margin sedimentary shelf settings sedimentation occurred predominantly during normal regressive conditions with the basin dominated by the progradation of a constructional submarine delta tugela cone during sea level lowstands lst the earlier phases of sedimentation are tectonic controlled however later stages appear to be linked to global eustatic changes

anomalous palaeomagnetic directions in a mesozoic basaltic dyke arguments for fault induced remagnetization abstract anomalously steep palaeomagnetic directions from the central part of an 5 m wide basaltic dyke from fossilryggen east antarctica suggest a recent to late tertiary age for its remanent magnetization in conflict with k ar isotope ages of 162 4 and 217 3 ma obtained from the central and slickenside margins respectively three neighbouring basaltic intrusions carry stable magnetizations whose directions mean d 23 mean i 40 and pole position 38 n 40 e accord with previously obtained mesozoic results from lava flows in the vestfjella basalt province east antarctica rock magnetic properties do not discriminate between the different dykes and it is proposed that the anomalous directions represent spot readings of the geomagnetic field which arise from complete remagnetization during a period of faulting in recent to late tertiary times

pseudo feathery dunes in the kumtagh desert abstract the kumtagh desert is the last explored desert in china the unique patterns on aerial photographs and satellite images have led previous researchers to the conclusion that the kumtagh desert is the only place over the world where typical feathery dunes are developed and that some unique wind regimes are at work recent field investigation reveals that the feathery patterns in fact reflect the albedo contrasts between the seif dunes bright dune like drifts and the dark inter dune lag sediments the wind regime in the area containing the so called feathery dunes is typical of the regime that produces seif dunes that were considered to be shafts of the feathery dunes and the vanes of the feathery dunes are in fact bright dune like drifts with indistinct height from the surroundings rather than true transverse dunes further analysis indicates that the sediments of seif dunes dune like drifts and dark inter dune flats differ in grain size distribution mineralogy reflectance spectrum and particle micro morphology sediments that constitute seif dunes and dune like drifts are finer and poorly rounded contain relatively more quartz and hence have higher albedo while the sediments that constitute the dark inter dune flats are coarser and better rounded contain far less quartz but relatively more andesite and dacite and hence have lower albedo as a result what was originally perceived as unique feathery dunes are in fact only pseudo feathery dunes composed primarily of seif dunes this discovery also demonstrates that blowing sand drifts can form dune like patterns that remain visible for long periods of time it is important to distinguish between the patterns of true dunes and those of dune like drifts pseudo dunes that cause albedo contrasts in interpreting remote sensing images

early tectonic extension between the agulhas bank and the falkland plateau due to the rotation of the lafonia microplate abstract along the southeast african continental margin a deep sedimentary basin and marginal ridge bordering the agulhas fracture zone formed coevally with south american counterparts underlying the falkland plateau extension in both the southern outeniqua and the falkland basin is related to large angle 100 rotation of the lafonia falkland islands block in middle late jurassic times during attempted propagation of the proto indian ocean across the active circum pacific margin of gondwanaland in the early cretaceous the jurassic microplate boundaries were partly reactivated and partly transected by a right lateral shear along the 1200 km long falkland agulhas transform fault preceded by substantial vorticity of the surrounding crustal blocks this boundary segment separating the south american and african plates was probably generated by complex geodynamic interactions between oceanic plate subduction continental to back arc rift propagation and the impingement of deep mantle plumes on the lithosphere

preservation of interdraa and plinth deposits by the lateral migration of large linear draas lower permian yellow sands northeast england abstract the lower permian yellow sands are preserved as eight relatively wide draa ridges linear compound dunes separated by interdraa corridors at the base of the marl slate zechstein flat bedded interdraa and draa plinth deposits are a significant constituent of the deposits exposed in the draa ridges these sediments are composed of relatively coarse grained wind ripple strata and form up to 9 m thick tabular sand bodies interdraa deposits are generally the most coarse grained and are horizontally to sub horizontally stratified they are gradationally overlain by low angle draa plinth deposits with numerous low angle diastems the contact between draa plinth and overlying trough cross bedded draa centre deposits is frequently gradational but can also be characterized by deep aeolian scours each draa ridge contains two interdraa draa plinth draa centre units which record an early phase of lateral migration of the draa field followed by a second phase of vertical accretion

uplift history of a transform continental margin revealed by the stratigraphic record the case of the agulhas transform margin along the southern african plateau the south and southeast coast of southern africa from 28 s to 33 s forms a high elevated transform passive margin bounded to the east by the agulhas falkland fracture zone affz we analysed the stratigraphic record of the outeniqua and durban thekwini basins located on the african side of the affz to determine the evolution of these margins from the rifting stage to present day the goal was to reconstruct the strike slip evolution of the agulhas margin and the uplift of the inland high elevation south african plateau the agulhas transform passive margin results from four successive stages 1 rifting stage from late triassic to early cretaceous 200 134 ma punctuated by three successive rifting episodes related to the gondwana breakup 2 wrench stage 134 131 ma evidenced by strike and dip slip deformations increasing toward the affz 3 active transform margin stage 131 92 ma during which the falkland malvinas plateau drifts away along the affz with an uplift of the northeastern part of the outeniqua basin progressively migrating toward the west 4 thermal subsidence stage 92 0 ma marked by a major change in the configuration of the margin onset of the shelf break passive margin morphology two main periods of uplift were documented during the thermal subsidence stage of the agulhas margin 1 a 92 ma short lived margin scale uplift followed by a second one at 76 ma located along the outeniqua basin and 2 a long lasting uplift from 40 to 15 ma limited to the durban thekwini basin this suggests that the south african plateau is an old upper cretaceous relief 90 70 ma reactivated during late eocene to early miocene times 40 15 ma

spatial and temporal patterns of aeolian sediment transport on an inland parabolic dune bigstick sand hills saskatchewan canada abstract topographic changes from erosion pins and on site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation stabilized inland prairie dune field over two years the sediment budget calculated from digital elevation models shows that the total volume of erosion 9890 m 3 is greater than the amount of deposition 6990 m 3 indicating a net loss of 2900 m 3 of sediment or 29 of eroded sediment from the dune sediment erosion occurred mainly on the stoss slope 3600 m 3 36 of eroded sediment but also on the south 2100 m 3 21 and north sides of the dune head 1700 m 3 17 the blowouts along the arms 1740 m 3 18 and the crest 650 m 3 7 erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit 100 m 3 1 thus the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes 5500 m 3 80 coinciding with the southeasterly resultant transport direction for november 2004 05 the net loss of about 2900 m 3 29 may be attributed to sediment carried in suspension over and beyond the dune correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions e g vegetation cover ground freezing moisture buffer the relative importance of temperature and precipitation on rates of sediment transport conversely wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions seasonal effects produce a complex interaction between wind climate and surface conditions this leads to a dynamic range of threshold velocities which in turn causes spatial and temporal variations in transport limiting and supply limiting conditions collectively these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid to high latitude inland settings

spatial and temporal variations in incised valley systems from the durban continental shelf kwazulu natal south africa abstract the evolution of several incised valley systems from the kwazulu natal shelf is compared over time these represent the shelf extension of the collective durban harbour drainage system and the mgeni mhlanga and mdloti rivers two main ages of incision are apparent early santonian cretaceous and late pleistocene holocene the early valleys formed by tectonic controls namely phases of higher frequency base level fall superimposed on lower frequency higher order transgression the results are complex networks of stacked compound valleys that have been exploited by some of the younger networks formed by glacio eustatic fall prior to the last glacial maximum lgm of 18 ka bp the valley fills have evolved from high energy basal fluvial deposits low energy central basin fines mixed energy estuarine mouth plug deposits clay rich flood deposits through capping sandy shoreface deposits the earliest fills are dominated by central basin deposits and were underfilled as a result of low gradient and limited sediment supply the more recent late pleistocene holocene fills have significantly thicker fluvial deposits as a result of increased gradient and stream competence during the later stages of valley and shelf evolution the youngest valleys show a situation of differential evolution along the valley length due to varying rates of sea level rise in the holocene initial rapid sea level rise caused drowning and overstepping of the outer segment of the incised valley whereas slower rates of sea level rise in the late holocene caused shoreface ravinement of the inner mid segments of the valley this differential exposure to accommodation has resulted in a sedimentological partitioning between tide dominated facies in the outer valley segment and river dominated facies in the inner segment cf cooper 2001

internal structure and surface geometry of longitudinal seif dunes abstract a mutual relationship exists between the morphology of longitudinal seif dunes and their dynamics and internal structure the basic mechanism of longitudinal dune movement results from the deflection of oblique wind flow into a longitudinal flow on the lee flank the magnitude of the longitudinal flow depends on the angle of the wind incidence with the crest line deposition occurs when this angle of incidence increases through meandering of the longitudinal dune crest line after heavy rain exposed the internal structure of the dune two kinds of depositional unit were found the main unit forms in the meandering area on both sides of the dune the other secondary unit is a narrow belt on both sides and parallel to the crest line the two units have different strikes because the laminae deposited on the dune are of the three primary stratification types climbing translatent strata sand flow cross strata and grainfall laminae the range of dips is wide 10 to 30 these dips accord with topographic profiles across the dune a model of the internal structure of a longitudinal dune has been developed from the field data the model shows the erosional and depositional areas along this linear dune

a revised fit of south america and south central africa abstract a new set of parameters for the total plate tectonic reconstruction of south america and south central africa is presented euler pole 46 75 n 32 65 w rotation angle 56 40 this fit is constrained by at least three pre drift tectonic features crossing from one continent to the other 1 the geophysically defined eastern and western boundaries of the submarine jurassic outeniqua basin south africa and the falkland plateau basin 2 the late precambrian transcurrent fault and mylonite belts of pernambuco brazil and foumban west africa and 3 the triassic northern tectonic front of the cape fold belt and the major morphological feature on the falkland plateau with which it is closely lined up isotopic ages of falkland plateau gneisses correspond to cape pluton and cape fold belt ages suggesting their palaeoposition was within the realm of the cape fold belt in addition the bathymetrically and geophysically defined northeastern apex of the falkland plateau fits into the re entrant angle defined on the south african margin by the steep southeast facing sheared agulhas margin and the southern face of the tugela cone simultaneously known precambrian outcrops in northeastern brazil and in the gulf of benin area of west africa are juxtaposed rather than overlapped reconstructions producing a closer fit of these cratonic areas are considered untenable

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

the late cretaceous to holocene sequence stratigraphy of a sheared passive upper continental margin northern kwazulu natal south africa abstract high resolution single channel seismic data reveal seven seismic units a g from the narrow and steep upper portions of the sheared passive continental margin of northern kwazulu natal several characteristic internal geometries are evident onlapping sheet like unit c aggradational progradational unit a and facies d3 and progradational unit b facies d1 2 and facies g1 on the basis of internal geometry and bounding unconformities lowstand units b facies d3 and lowermost unit g possible transgressive unit c highstand upper unit g and falling stage facies d1 and d2 systems tracts are delineated units e and f are not reconcilable due to acoustic opacity overall five incompletely preserved sequences are observed sequence one comprises unit a of suspected middle maastrichtian age separated from the overlying sequence by a subaerial unconformity surface sb1 units b and c form sequence two and span the late cretaceous late maastrichtian to mid late palaeocene two major hiatuses ensued angus and jimmy until mid pliocene times when unit d was deposited during shelf margin advance linked to hinterland uplift these falling stage systems tract deposits are separated from latest pliocene early pleistocene lowstand shelf edge deltaic deposits by a subaerial unconformity marking the deposition of sequence four facies d3 the age of unit e is uncertain unit f represents a series of shorelines formed during oxygen isotope stage ois 5a to 2 on the regressive and transgressive limbs preceding and following the last glacial maximum lgm the final partial sequence preserved is comprised of unit g formed during the ois 2 transgression to present mean sea level and subsequent development of the contemporary highstand wedge in terms of stratigraphic architecture this study shows an evolution from a ramp style margin with a poorly defined shelf break to that of a shelf break profile with a narrow and steep shelf in this respect the narrowness of this shelf cannot be accounted for by the inheritance of shearing effects rather the stratigraphic architecture reflects a period of slow and protracted subsidence with strong sediment dispersal later punctuated by hinterland uplift this formed the late pliocene shelf margin clinoforms of unit d and established the shelf break position at the offlap break of this wedge the resulting narrow shelf may play a significant role in the preservation of later sequences particularly in light of the continued uplift of the margin causing off shelf sediment bypass where tst and hst sequences may not be preserved this is reflected in the isolated preservation of shoreline and shallow marine deposits of the pleistocene units e and f

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

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

raked linear dunes in the kumtagh desert china abstract linear dunes are extensive in sand seas and dune fields around the world but they take a range of forms due to the complex factors that control their development raked linear dunes composed of primary ridges and subsidiary ridges that lie almost perpendicular to the primary ridges were recently identified in the northern part of china s kumtagh desert the primary ridges are typical linear dunes but the subsidiary ridges display vestiges of barchan dunes the subsidiary ridges are sufficiently short that they do not greatly affect the general appearance of the linear dunes however the raked linear dunes in the kumtagh desert have several unique characteristics that distinguish them from typical linear dunes these dunes develop in an environment that is deficient in available sediment and under a wind regime typical of linear dunes an environment with a high wind energy and a directional variability index rdp dp around 0 5 the raked linear dunes appear to have evolved from barchans following a modified form of tsoar s 1984 model barchans formed under a northern wind regime were modified by an eastern wind regime oriented at an oblique angle to the barchans the strengths of the two wind regimes are similar under these conditions the barchans became reoriented with the limbs farthest from the eastern winds extending to form subsidiary ridges and the limbs closest to the eastern winds forming the primary ridges which appear to form mainly from dune collisions

forced regressive and lowstand hudson paleo delta system latest pliocene growth of the outer new jersey shelf abstract interpretation of the latest pleistocene stratigraphy of the outer new jersey shelf has evolved over the last three decades with addition of new geological and geophysical data during the last decade new results have described and interpreted various depositional elements within the latest pleistocene that overlie the regional reflector known as the r horizon on the basis of observations made from detailed mapping of the r horizon and the overlying sediment wedge s using high resolution shallow seismic chirp data acquired in several phases between 2001 and 2006 we revise the depositional model for the offlapping multi clinothem sediment wedge on the latest pleistocene outer new jersey shelf as strike elongated lobes of a falling stage wave influenced delta system fed by a pre lgm paleo hudson river channel s that probably reached the late pleistocene shelf edge off new jersey this sediment wedge is composed of a series of prograding and offlapping clinothems of varying thickness within our data which does not extend to the basinward termination of the wedge we seldom observe preserved topsets of these clinothems parts of the foresets of some clinothems are also not preserved particularly in the proximal part of the wedge the sediment wedge is elongated in strike direction nne ssw which suggests along strike sediment movement and possible redistribution of sediment in that direction by ambient shore parallel currents our data do not record any time equivalent fluvial channels at the proximal end of the sediment wedge though there are channel features that cap and cut down into several of the clinothems that make up the wedge farther seaward we suggest that this can be explained in two possible ways 1 relatively large spatial separation between the prograding front of the delta system and the delta plain topset deposits as is very common under a falling stage sea level condition and 2 lack of preservation of the stratigraphic record of the delta plain channels because of the likely vigorous falling stage erosion of topsets during the fall of sea level and possibly also during the subsequent transgressive ravinement and flooding after the lgm the clinothems within the sediment wedge show systematic variation in thickness indicating a northward shift of the main depocenter this shift might also be an indication of gradual northward migration of the principal fluvial feeder such a possibility is supported by previously reported late pleistocene paleo hudson channel deposits south of the modern hudson shelf valley