internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

developing a framework of quaternary dune accumulation in the northern rub al khali arabia located at the crossroads between africa and eurasia arabia occupies a pivotal position for human migration and dispersal during the late pleistocene deducing the timing of humid and arid phases is critical to understanding when the rub al khali desert acted as a barrier to human movement and settlement recent geological mapping in the northern part of the rub al khali has enabled the quaternary history of the region to be put into a regional stratigraphical framework in addition to the active dunes two significant palaeodune sequences have been identified dating of key sections has enabled a chronology of dune accretion and stabilisation to be determined in addition previously published optically stimulated luminescence osl dates have been put in their proper stratigraphical context from which a record of late pleistocene dune activity can be constructed the results indicate the record of dune activity in the northern rub al khali is preservation limited and is synchronous with humid events driven by the incursion of the indian ocean monsoon

a record of holocene climate change from lake geochemical analyses in southeastern arabia lacustrine sediments from southeastern arabia reveal variations in lake level corresponding to changes in the strength and duration of indian ocean monsoon iom summer rainfall and winter cyclonic rainfall the late glacial holocene transition of the region was characterised by the development of mega linear dunes these dunes became stabilised and vegetated during the early holocene and interdunal lakes formed in response to the incursion of the iom at approximately 8500 cal yr bp with the development of c3 dominated savanna grasslands the iom weakened ca 6000 cal yr bp with the onset of regional aridity aeolian sedimentation and dune reactivation and accretion despite this reduction in precipitation the lake was maintained by winter dominated rainfall there was a shift to drier adapted c4 grasslands across the dune field lake sediment geochemical analyses record precipitation minima at 8200 5000 and 4200 cal yr bp that coincide with bond events in the north atlantic a number of these events correspond with changes in cultural periods suggesting that climate was a key mechanism affecting human occupation and exploitation of this region

isotopic evidence for early to mid cretaceous ocean temperature variability abstract stable isotopic measurements have been made on planktonic and benthic foraminifera of early to mid cretaceous early albian cenomanian age from dsdp site 463 located in the pacific ocean the degree of alteration of the foraminifera has been assessed through the application of scanning electron microscopy the oxygen isotope data support the view that during the cenomanian globigerine foraminifera such as the genus hedbergella inhabited near surface waters whilst the flattened keeled morphotypes lived deeper within the water column the carbon isotope data reveal a more complex pattern as the 13 c values from planktonic species essentially show a large overlap which is interpreted in terms of a weak 13 c gradient existing in the upper part of the ocean in contrast the oxygen isotope data from planktonic foraminifera from the late albian display no discernible depth stratification pattern and the 13 c data also show a large overlap of values indicative of a complete disruption of the upper part of the thermocline a relatively low surface to bottom water temperature gradient within the early middle albian part of the succession may reflect a well mixed ocean inferred cool ocean temperatures and or high salinities for the early albian may reflect increased oceanic poleward heat transport an increase in temperature and or decrease in salinity in the cenomanian suggests a reduction of the poleward heat flux promoting the build up of limited polar ice during this period of tropical warmth

evaluation of simple geochemical indicators of aeolian sand provenance late quaternary dune fields of north america revisited abstract dune fields of quaternary age occupy large areas of the world s arid and semiarid regions despite this there has been surprisingly little work done on understanding dune sediment provenance in part because many techniques are time consuming prone to operator error experimental highly specialized expensive or require sophisticated instrumentation provenance of dune sand using k rb and k ba values in k feldspar in aeolian sands of the arid and semiarid regions of north america is tested here results indicate that k rb and k ba can distinguish different river sands that are sediment sources for dunes and dune fields themselves have distinctive k rb and k ba compositions over the basin and range and great plains regions of north america the hypothesized sediment sources of dune fields are reviewed and assessed using k rb and k ba values in dune sands and in hypothesized source sediments in some cases the origins of dunes assessed in this manner are consistent with previous studies and in others dune fields are found to have a more complex origin than previously thought use of k rb and k ba for provenance studies is a robust method that is inexpensive rapid and highly reproducible it exploits one of the most common minerals found in dune sand k feldspar the method avoids the problem of using simple concentrations of key elements that may be subject to interpretative bias due to changes in mineralogical maturity of quaternary dune fields that occur over time

latest pleistocene and holocene dune construction at the north eastern edge of the rub al khali united arab emirates abstract optical dating of two dune pro les developed in linear dunes in ras alkhaimah united arab emirates has been used to establish the timing and rateof dune accretion one section at awa was over 17 m high while that at idhnwas over 40 m high the awa dune appears to have accumulated very rapidly 10 000 years ago with a vertical accumulation rate of about 3ae3mka 1 theidhn dune appears to have accumulated over the past 1000 years with 20 m ofsediment accumulating in a time period of about 270 years the awa dunemay have accumulated in response to the transgression of the persian gulf byrising sea levels in late pleistocene and holocene times the idhn dune mayhave accumulated rapidly because of intensi ed human activity a short livedclimatic event or because it may periodically be reactivated after erosion by uvial action at its base keywords linear dune optical dating rub al khali sand accumulation introductionthere remains some uncertainty surrounding thestyle and timing of deposition of large aeoliandunes with authors supporting both gradual andpunctuated models of dune development for adiscussion see thomas 1997 this divergence ofopinion results from both the general absence ofdating control within dunes in most studies anddif culties in gaining exposures within some ofthe larger dune bedforms the purpose of thispaper is to establish a chronology of dunedevelopment for two thick 10 m dune sectionsexcavated within large complex linear dunesfrom within the rub al khali near ras alkhaimah in the north of the united arabemirates fig 1 the sites were selected becauseof the availability of thick fresh sections inrecently excavated moist sand with an area of around 600 000 km

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

mapping the geochemistry of the northern rub al khali using multispectral remote sensing techniques spatial variations in sand sea geochemistry relate to mixing of different sediment sources and to variations in weathering due to problems of accessibility adequate spatial coverage cannot be achieved using field surveys alone however maps of geochemical composition produced from remotely sensed data can be calibrated against limited field data and the results extrapolated over large inaccessible areas this technique is applied to part of the rub al khali in the northern united arab emirates trend surface analysis of the results suggests that the sand sea at this location can be modelled as an east west mixing zone of two spectral components terrestrial reddened quartz sands and marine carbonate sands optical dating of these sediments suggests that dune emplacement occurred rapidly around 10 ka bp when sea level was rising rapidly the spatial distribution of mineralogical components suggests that this phase of dune emplacement resulted from coastal dune sands being driven inland during marine transgression thereby becoming mixed with rubified terrestrial sands copyright 2001 john wiley sons ltd

mapping the iron oxide content of dune sands namib sand sea namibia using landsat thematic mapper data abstract a linear mixture model was applied to landsat thematic mapper data to map iron oxide content over the northern part of the namib sand sea namibia field samples were collected to calibrate the remotely sensed iron oxide proportions to dithionite extractable fe in mg g 1 the in situ proportions correlating strongly with the remotely sensed estimates r 0 91 the results reveal a region of high fe oxide concentration in the east an area of low fe oxide concentration in the west separated by a mixing zone we interpret this to indicate that there is more than one sand source contributing to the sand sea

geomorphological and palaeoenvironmental investigations in the southeastern arabian gulf region and the implication for the archaeology of the region abstract during the late quaternary the climate of arabia has fluctuated between periods of higher rainfall and fluvial activity dominated by the influence of the indian ocean monsoon iom and drier arid conditions under the influence of the westerlies this has left a rich legacy of landforms from which temporal and spatial patterns of environmental change are reconstructed the coastal desert region of the southeastern arabian gulf has been a focal point for human settlement since 8000 cal yr bp the region is strategically located on an important trade route between two cradles of civilization namely mesopotamia and the indus changes in the evolution and modification of this landscape under varying climatic conditions have influenced humans living in and exploiting this landscape for food and water raw materials and trade routes in this study geomorphological and palaeoenvironmental investigations are integrated to provide a framework of environmental change for the late glacial and early mid holocene periods against which the archaeology of the area can be set the late glacial and earliest holocene was characterised by intense aridity and accumulation of mega linear dunes driven by the shamal winds in the arabian gulf region this continued into the earliest part of the holocene whilst southern arabia was under the influence of the iom the monsoon rains migrated into the gulf region between 8500 6000 cal bp during this time semi nomadic herders occupied this region and grazing their animals in a landscape covered with c3 savanna grassland the neolithic peoples also practised hunting and fishing and the collection of shellfish was an important activity pottery shows links with mesopotamia at this time from 6000 cal bp the iom retreated south and rainfall was derived from winterly westerly sources under drier conditions a switch occurred to a sparser cover of c4 grasses from 4500 cal bp the climate became much drier with the development of stronger westerly summer shamal winds and the reactivation of dunes across the region an intense arid period occurred at 4100 bp which corresponds with major drought conditions in mesopotamia and the indus region which led to major changes in society this event occurs at a major transition in the arabian gulf bronze age archaeological record with a decline in population and trade the last 4000 yr has largely been characterised by arid conditions similar to those found in the region today

investigation of the effect of surface heterogeneity and topography on the radiation environment of palmer station antarctica with a hybrid 3 d radiative transfer model we have developed and used a monte carlo radiative transfer code to investigate how surface topography and heterogeneous snow ice distributions affect the downwelling irradiance at palmer station antarctica 64 76 s 64 07 w the monte carlo calculations treat a three dimensional 3 d atmospheric volume which extends from the surface to 100 km altitude and has a 20 km 20 km footprint on the southwest coast of anvers island the radiative transfer calculations include the effects of molecular absorption rayleigh scattering and clouds the surface interaction is modeled explicitly the trajectories of reflected photons are computed from stochastic bidirectional directional reflectance functions and their paths are traced through multiple interactions with complex surface features computed results for a range of cloud optical depth solar zenith angle and surface albedo are presented comparisons of the 3 d model calculations to plane parallel model predictions show that the effective albedo which characterizes a given ice distribution is affected by regions surprisingly far from the point of interest under low clouds zcloud 1 km surface irradiance measurements over a snow surface are significantly affected by the dark ocean surface more than 7 km away for the opposite case of irradiance observations over ocean the effect of a distant snow surface is not significant at ranges greater than 2 or 3 km since the radius of influence depends on atmospheric transmission and surface albedo the effective albedo varies spectrally neglect of this nonlocal albedo effect may significantly degrade the accuracy of radiation diagnostics that depend on spectral intensity ratios

petrology of fe mg carpholite bearing metasediments from ne oman abstract fe mg carpholite occurs in metasediments of tectonically disrupted basement shelf and foreland basin units that structurally underlie the semail ophiolite in ne oman in the lower grade structurally higher units fe rich carpholite coexists with paragonite quartz illite kaolinite and chlorite whereas in deeper units fe mg carpholite occurs with pyrophyllite sudoite phengite and or chloritoid mineral compositions in these units indicate that chlorite is more magnesian than coexisting fe mg carpholite at low temperatures and pressures but at higher metamorphic grades xmg decreases in the order sudoite carpholite chlorite chloritoid this suggests a reversal in fe mg partitioning between fe mg carpholite and chlorite at temperatures below or close to those of the breakdown of kaolinite quartz to pyrophyllite and at xmg 0 35 phase relations and mineral equilibria indicate that the p t conditions of formation of the fe mg carpholite bearing rocks of ne oman range from 280 315 c 3 6 kbar for the structurally highest units to 325 440 c 6 9 5 kbar for the deepest units indicating a systematic down section increase in metamorphic grade textural relations in these rocks interpreted in the context of pertinent equilibria are consistent with the clockwise p t paths previously constrained for these units from petrological studies of interlayered isofacial mafic rocks

spectral signs of aeolian activity around a sand dune belt in northern algeria abstract dune color has been used to investigate the provenance stabilization and age of the sand here we look for signs of aeolian activity in the colors of a sand dune belt in northern algeria on the one hand visible and near infrared spectral analyses of satellite images and laboratory samples showed reddish yellowish and whitish sands depending on the amount of gypsum particles and fe oxides coating quartz grains specifically the dithionite extractable fe content was related to a redness index calculated from remote sensing data and the abundance of hematite estimated in the second derivative of the kubelka munk function paralleled the cielab hue angle of sand samples on the other hand a spatiotemporal analysis showed that the reddish sand had undergone a continuous remobilization and dispersion throughout the area reaching two large salt flats sabkhas with seasonal water yellowish and whitish sands appeared as patches on the periphery of these sabkhas and along the dune belt exhibiting percussion marks and dissolution pits on the surface of quartz grains taken together the results suggest that the reddish sand partially loses its fe oxide coatings by mechanical abrasion in the entrainment and reductive dissolution in the sabkhas during waterlogging becoming yellowish the periodic reactivation by wind of reddish and yellowish grains together with whitish gypsum particles formed by evaporation as the sabkhas dry up may explain the sorting of grains according to their mineralogy and size along the sand dune belt resulting in striking color changes accordingly color reflects sand movements and chemical processes taking place in this dune system

sedimentological and geochemical interpretation of a transgressive sequence the late cretaceous qahlah formation in the western oman mountains united arab emirates abstract the stratigraphic and palaeogeomorphologic conditions of the qahlah formation deposition in the united arab emirates are related to the geotectonic evolution of the western oman mountains during the late cretaceous the qahlah formation ranges from a few metres to more than 70 m in thickness it is the first sedimentary deposit to onlap the obducted semail ophiolite which was subjected to extensive weathering in a tropical environment during the maastrichtian erosion accompanied the transgression of the maastrichtian sea across the region the sedimentary sequence can be divided into four facies ophiolitic breccia ophiolitic conglomerate lateritic ferruginous silstone and lithic sandstone these sediments were probably formed in a shallow marine to beach setting adjacent to a retreating cliff line of the ophiolite a comparative analysis of the principal chemical and mineralogical components of the different facies indicates a genetic relationship between them the nickel content 0 85 1 1 16 wt in the laterite facies is of economic interest as a low grade ore provided that larger reserves can be identified

combining digital elevation data srtm aster high resolution satellite imagery quickbird and gis for geomorphological mapping a multi component case study on mediterranean karst in central crete abstract remote sensing data have become more and more popular for geomorphological investigations because their steadily increasing level of detail and accessibility opens up new potentials in this context this paper examines the application and quality of digital elevation models srtm and aster dems high resolution satellite imagery quickbird and gis techniques for the detection and mapping of karst landforms mainly enclosed depressions at different scales in the ida mountains of central crete besides discussing methodological issues and evaluating suitability potentials we conducted an exemplary case study based on spatial analysis of the regional karst morphology different input datasets and processing methods are applied gis based analysis land cover classification raster calculations etc in order to carry out an area wide surveying and mapping of karst depressions the findings are supported and validated by auxiliary field studies due to the level of detail and occasional data errors an exclusive use of satellite imagery or digital elevation models for automatic karst landform detection performs insufficiently our results demonstrate that mapping karst features through remote sensing is significantly dependent on scale of interest existing environmental conditions and data quality a semi automatic data integration approach on the basis of digital datasets generated by combined satellite image processing and dem analysis yields the best results especially when indirect karst indicating variables like iron oxide rich sediments are included as detection criteria the multi component application presented in this paper provides a time saving and effective tool for meso to macro scale object detection and extensive study areas however the potential of fully automated karst feature mapping still needs to be explored in future work concerning the spatial dimension of karstification in central crete the gis based results allow differentiating further geomorphological characteristics e g by indicating a significant altitudinal change of karst forms within the study area size and shape of depressions dolines uvalas and poljes vary considerably due to the geological setting climatic impacts neotectonics and elevation

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

landform evolution in the arid northern united arab emirates impacts of tectonics sea level changes and climate abstract the interaction of wind and water may well be the key influence on the modern geomorphology of the arid regions of the world and has had a strong influence on long term landscape evolution in these areas this is the case for the landforms of the northern united arab emirates where aeolian landforms in the west lie on alluvial deposits and are adjacent to fluvial landforms in the east even within the aeolian forms there is evidence of modern and past water activity modern river flow is rare and largely confined to the mountains however rivers and alluvial activity were more important during certain periods in the past this study describes the landforms of the northern emirates ne and relates their form and evolution to alternating periods of arid and humid climates the study was initially carried out to provide a background for the soil survey of the ne details of landform character and materials were explored during the survey which involved detailed site and soil descriptions at 10 020 auger and geoprobe sites 2 m depth 200 backhoe pits 2 m depth and 150 drill observations 10 m depth the main landforms identified in the study area are the hajar mountains alluvial plains fans plains and wadis dunes ridges sand veneer rising dunes and coastal forms the influence of uplift and tilting of the hajar mountains during the miocene and more recently is considered sea level changes in the arabian gulf are also important the impacts of past climate change on the evolution of landforms is discussed and related to alternating periods of arid and wet climates the north westerly shamal wind is primarily responsible for the formation and continued evolution of the dune fields seen in the ne today

sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the uae a case study from ar rub al khali abstract the umm az zimul al wijan area is located in the southeastern part of the uae and covers about 1600 km 2 it is bounded to the east by the oman mountains and to the south and west by the extensive dune area of ar rub al khali field investigation revealed the common occurrence of parallel to sub parallel sand ridges with a general east west orientation also present but less frequent are barchan barchanoid and star dunes interdune areas are classified into four types that include dolomite mixed ancient sabkha and ophiolitic rock fragments mixed sand sheet and ophiolitic rock fragments and recent sabkha the textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size moderately to very well sorted positively skewed and mesokurtic quartz grains are mainly subrounded to subangular the similarity in roundness properties in different dune types in the eastern province of the uae seems not to be influenced by dune form based on the heavy mineral suites and the angularity of quartz grains it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the oman mountains acidic rocks of iran and from the coastal area

sources of iron oxides in reddish brown soil profiles from calcarenites in southern spain abstract we studied the distribution with depth of the different forms of iron in two reddish brown rubified soils developed on hematite free calcarenites in the province of cordoba southern spain hematite appeared in significant amounts in the a and b horizons of the soils and seemed to have originated mainly from the weathering of the fe bearing clay minerals smectites because of their low contents of fe both the non clay fraction and the carbonate of the parent material contributed little to fe oxide formation the distribution with depth of goethite in the clay fractions suggested that part of the initial goethite had been lost and might have been altered to hematite

the petrogenesis of leucogranitic dykes intruding the northern semail ophiolite united arab emirates field relationships geochemistry and sr nd isotope systematics the khawr fakkan block of the semail ophiolite united arab emirates exhibits a suite of 10 100 m scale metaluminous to peraluminous granitic intrusions ranging from cordierite andalusite biotite monzogranites to garnet tourmaline leucogranites which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros structural constraints suggest that the subduction of continental sedimentary material beneath the hot proto ophiolite in an intra oceanic arc environment led to granulite facies metamorphism at the subduction front and the generation of granitic melts which were emplaced up to the level of the ophiolite moho compositions indicate the analysed granitoids were largely minimum melts that crystallised at variable a h2o and pressures of 3 to 5 kbar the lile sr rb and ba covariation modelling suggests that the granitoids formed largely by the dehydration melting of muscovite rich metasediments initial 87sr 86sr ratios of analysed dykes vary between 0 710 and 0 706 at initial nd values of between 6 3 and 0 5 cogenetic units of a composite sill from ra s dadnah yield a sm nd isochron age of 98 8 9 5 ma mswd 1 18 geochemical and isotopic characteristics of the analysed granitic intrusions indicate that the subducted continental material was derived from oceanic trench fill haybi complex sediments preserved as greenschist asimah area to granulite facies bani hamid area ophiolitic metamorphic sole terranes the sr nd isotope systematics suggest that hybrid granitic melts were derived from pre magmatic mixing of two contrasting subduction zone sources

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

a multi proxy analysis of the holocene humid phase from the united arab emirates and its implications for southeast arabia s neolithic populations an early to mid holocene humid phase has been identified in various arabian geo archives although significant regional heterogeneity has been reported in the onset duration and stability of this period a multi proxy lake and dune record from wahalah in the united arab emirates uae documents significant variations in hydrology biological productivity and landscape stability during the first half of the holocene these data reveal that post last glacial maximum dune emplacement continued into the earliest part of the holocene with the onset of permanent lacustrine sedimentation at the site commencing 8 5 ka cal bp a long term shift towards more arid conditions is inferred between 7 8 and 5 9 ka cal bp with intermittent flooding of the basin and distinct phases of instability throughout the catchment area this transition is linked to the southwards migration of the intertropical convergence zone itcz and associated weakening of monsoon rains a peak in landscape instability is recorded between 5 9 and 5 3 ka cal bp and is marked by a pronounced increase in regional dune emplacement these variations are considered alongside the record of human settlement raising important questions about the interactions between population demographics climate and environment in southeast arabia during the neolithic

mineralogical characterization and transport pathways of dune sand using landsat tm data wahiba sand sea sultanate of oman sand samples and landsat imagery were used to characterize the spatial distribution of sand mineralogy and to evaluate potential sources and transport pathways of sediment in the wahiba sand sea in the sultanate of oman landsat tm data were useful in the geomorphic interpretation of a desert aeolian environment to distinguish the mineralogies found in the wahiba area and in extending the identification of sand mineralogy beyond the point specific grid produced from field sampling the wahiba sand sea has been previously divided into upper north and higher in elevation and lower south and lower in elevation portions based on dune morphology large scale spatial distributions of mineral composition follow a similar pattern to that of the geomorphic regions within the dune field field and landsat tm data suggests the upper wahiba is comprised of well mixed carbonate and quartz sand with some areas of significant mafic content surface sand in the eastern and western margins of the upper wahiba originate from the lower wahiba and from local wadis sand in the lower wahiba was likely derived from southern sabkhas and the coastal area and is quartz rich with isolated locations of carbonate rich sand we suggest that these carbonate rich patches in the lower wahiba were derived from reworked aeolianites lithofied sand dunes which underlie most of the sand sea and not directly from the coast as previously reported

measurements of erythemal irradiance near davis station antarctica effect of inhomogeneous surface albedo to examine effects of inhomogeneous surface albedo on uv irradiance measurements were taken near davis station 68 58 s 77 97 e east antarctica during november december 1997 data were collected in transects perpendicular to an ice water boundary while one instrument continuously measured at the ice edge irradiances along transects were normalised by coincident measurements at the ice edge systematic differences in downwelling irradiance near the ice edge were observed over the highly reflective surface and open water for cloudless conditions the relative change in irradiance reached limiting values of about 5 from the ice edge to a point 2 5 km over snow covered ice and about 5 from the ice edge to a point 2 5 km over water in overcast conditions higher relative changes were observed about 30 from the ice edge to a point 2 5 km over ice on 17 november 1997 with no sign of a constant relative change being reached

discrimination of iron alteration minerals in visible and near infrared reflectance data field and laboratory studies were conducted to relate the mineralogy of rock and soil samples containing hematite fe2o3 goethite feooh and jarosite kfe3 so4 2 oh 6 to their reflectance properties in visible and near infrared wavelengths field reflectance measurements of regolith containing one or more of these minerals were made in the goldfield nevada mining district with a four channel radiometer the mineralogy and reflectance properties of regolith samples collected from these field measurement sites were then determined by laboratory studies mossbauer spectroscopy was used to identify the iron minerals present and their relative proportions the reflectance spectra of samples containing hematite and goethite were characterized by a reflectance minimum near 900 nm the location of this minimum could be accounted for by the relative proportions of hematite and goethite present in the samples under certain conditions it may be feasible to estimate the relative proportions of hematite and goethite on the earth s surface by determining the location of this near infrared reflectance minimum in high spectral resolution remote sensing data in addition the field measurements suggest that the ratio of band passes at 852 and 982 nm may be used to distinguish qualitatively among hematite goethite and jarosite thus maps of the distribution of these minerals may be derived from scanner images acquired in those band passes

development of the gran desierto sand sea northwestern mexico three major eolian sand populations can be recognized in the gran desierto sand sea of northwestern mexico by using spectral data from the landsat thematic mapper in conjunction with textural and mineralogical studies of surface sands each sand population has distinct textural mineralogic and spectral properties that can be related to sand dune morphology and position with reference to source areas and transport paths of the sands the oldest eolian sediment in the sand sea was derived from the early to middle pleistocene colorado river that flowed through the area of the western gran desierto subsequent inputs of eolian sands came from the area of the present colorado river valley and the coast south of the sand sea the spatial and temporal pattern of eolian deposition in the region has been controlled by quaternary tectonic and climatic changes resulting in the episodic input and deposition of sand

late quaternary stratigraphy paleoclimate and neotectonism of the persian arabian gulf region abstract the last glacial deposits in the persian arabian gulf consist of a 22 000 year old paralic terrigenous sequence in the mesopotamia shelf the foredeep in front of the iranian zagros mountains and the northern side of the biaban shelf elsewhere the gulf and probably the biaban shelf were mantled by 30 000 year old carbonates comparison of 14 c data from foraminifera from the last glacial terrigenous unit in the foredeep off iran with curves published by hopley hopley d 1982 the geomorphology of the great barrier reef quaternary development of coral reefs wiley new york 453 pp and chapell et al chapell j omura a tezer e mcculloch m pandolfi j ota y pillans b 1996 reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records earth planet sci lett 141 227 236 indicates that the region may have experienced uplift during the last glacial whereas other geologic data indicate that the foredeep has had a history of continuous subsidence during the cenozoic a possible explanation for this discrepancy is that the foraminifera analyzed are not in place but were reworked into shallower water during the holocene transgression however the foraminifera analyzed do not display any evidence of wear indicating that such transport was limited a third alternative is that sea level during the last glacial was much higher than indicated by the curves of hopley and chapell et al at the peak of the last glaciation 21 000 to 20 000 years ago when sea level was 120 m lower than now the gulf was a waterless basin and deposition was negligible on the biaban shelf the holocene transgressive sequence resting unconformably on last glacial sediments consists of 14 000 year old carbonates a 11 000 year old terrigenous delta on the northern end of the biaban shelf and 11 000 10 000 year old intertidal tidal aragonite deposited in a dry climate on the northeast side of the gulf the last glacial sediments are covered by 10 000 to 7000 year old aragonite muds younging toward the northwest resting on the aragonites on the biaban shelf and on the northeast and northwest sides of the gulf are marls deposited under the present humid climate the southwest side of the gulf continued to be a site of carbonate deposition throughout the holocene comparison of ams 14 c measurements of the late holocene marls with the sea level curve of fairbanks fairbanks r g 1989 a 17 000 year glacio eustatic sea level record influence of glacial melting rates and the younger dryas event and deep ocean circulation nature 342 637 642 indicates that the axial zone of the gulf off iran experienced subsidence during the holocene this subsidence coupled with a rapid rise in sea level during a major glacial melt 9500 to 8500 years ago when global sea level rose from 50 to 28 m led to the replacement of marl with a shallow 8 25 m water fauna by a deep 50 m water one similar measurements and other geologic data indicate that the mesopotamia shelf and the mouth of the mesopotamian depression on the northwest side of the gulf underwent both subsidence and uplift during the cenozoic these vertical oscillations however were more subdued than those in the foredeep off iran the arabian shelf along the gulf s southwest side appears to have experienced minor uplift during the cenozoic

dissolution behaviour of fine grained magnetite and maghemite in the citrate bicarbonate dithionite extraction method mineral magnetic properties of soils and sediments are increasingly used as proxy parameters for environmental and palaeoclimate analysis to investigate which magnetic minerals contribute to the environmental signal in the samples chemical techniques such as the citrate bicarbonate dithionite cbd extraction method have been introduced in environmental magnetism studies this technique is assumed to distinguish lithogenic magnetite from pedogenic maghemite mineral content in soils and sediments unfortunately interpretation of the cbd extractions is not straightforward because the procedure is sometimes more suitable for distinction between grain size than for distinction between minerals the procedure of the cbd extraction technique was investigated to determine the influence of extraction temperature and iron oxide concentration on the dissolution behaviour of the samples synthetic samples were extracted at three different temperatures 60o 70o and 80oc at similar iron oxide concentration 5 wt and for three different concentrations 0 1 wt 1 wt and 5 wt at the same temperature 60oc our results show that a lower extraction temperature reduces the dissolution rate for all samples while decrease in iron oxide concentration increases the dissolution rate thus the parameters in the cbd procedure have a major influence on the dissolution behaviour of the samples in practice this means that when natural samples of differing iron oxide concentration are extracted with this technique the results of the extractions cannot be compared therefore the outcome of this type of extraction experiment can only be accurately interpreted when the effect of the procedure on the dissolution behaviour is taken into account 1999 elsevier science b v all rights reserved

spectral properties iron oxide content and provenance of namib dune sands this paper applies multispectral remote sensing techniques to map the fe oxide content over the entire namib sand sea spectrometric analysis is applied to field samples to identify the reflectance properties of the dune sands which enable remotely sensed fe oxide mapping the results indicate that the pattern of dune colour in the namib sand sea arises from the mixing of at least two distinct sources of sand a red component of high fe oxide content present as a coating on the sand grains which derives from the inland regions particularly from major embayments into the southern african escarpment and a yellow coastal component of low fe oxide content which is brought into the area by northward moving aeolian transport processes these major provenances are separated by a mixing zone between 20 km and 90 km from the coast throughout the entire length of the sand sea previous workers have also recognised a third fluvial provenance but the methodology applied here is not able to map this source as a distinct spectral component

the surface albedo of the greenland ice sheet satellite derived and in situ measurements in the sondre stromfjord area during the 1991 melt season the temporal and spatial variation in the surface albedo of the greenland ice sheet during the ablation season of 1991 is investigated the study focuses on an area east of sondre stromfjord measuring 200 km by 200 km and centred at 67 5 n 48 13 w the analysis is based on satellite radiance measurements carried out by the advanced very high resolution radiometer avhrr the broad band albedo is estimated from the albedos in channel 1 visible and channel 2 near infrared the results are calibrated with the surface albedo of sea and dry snow satellite derived albedos are compared with gimex ground measurements at three stations there is a high degree of consistency in temporal variation at two of the three stations large systematic differences are attributed to albedo variations on subpixel scale in the course of the ablation season four zones appear each parallel to the ice edge it is proposed that these are in order of increasing altitude i clean and dry ice ii ice with surface water iii superimposed ice and iv snow an extensive description of these zones is given on the basis of the situation on 25 july 1991 zones i iii and iv reveal fairly constant albedos 0 46 0 65 and 0 75 on average whereas zone ii is characterised by an albedo minimum 0 34 survey of the western margin of the greenland ice sheet up to 71 n shows that the zonation occurs between 66 and 70 n

abrasion control on dune colour muleshoe dunes sw usa abstract the muleshoe dunes an east west trending dunefield on the border separating texas and new mexico consist of two distinct components a white carbonate rich component and an overlying pink quartz rich component the pink component exhibits significant spatial variation in redness the reddest sands in the western part of the dunefield decrease in redness towards the east this gradient is thought to result from abrasion of an iron rich red clay coating as the sediments were transported eastward by late quaternary aeolian processes the effects of aeolian abrasion on the spectral signature and surface texture of the sediments were examined using laboratory abrasion experiments changes in spectral reflectance of abrasion samples from the laboratory were compared to field samples that were abraded naturally because of sediment transport the changes resulting from increased time of abrasion are similar to those observed with increased distance downwind in the dunefield these results suggest that downwind abrasion can explain the pattern of dune colour in the muleshoe dunes although this does not preclude other possible causes

holocene vegetation dynamics in the northeastern rub al khali desert arabian peninsula a phytolith pollen and carbon isotope study the holocene vegetation history of the arabian peninsula is poorly understood with few palaeobotanical studies to date at awafi ras al khaimah uae a 3 3 m lake sediment sequence records the vegetation development for the period 8500 cal yr bp to 3000 cal yr bp 13 c isotope pollen and phytolith analyses indicate that c3 pooid grassland with a strong woody element existed during the early holocene between 8500 and 6000 cal yr bp and became replaced by mixed c3 and c4 grasses with a strong c4 panicoid tall grass element between 5900 and 5400 cal yr bp an intense arid event occurred at 4100 cal yr bp when the lake desiccated and was infilled by aeolian sand from 4100 cal yr bp the vegetation was dominated by c4 chloridoid types and cyperaceae suggesting an incomplete vegetation cover and aeolian dune reactivation owing to increased regio nal aridity these data outline the ecosystem dynamics and carbon cycling in response to palaeomon soon and north westerly variability during the holocene copyright 2004 john wiley sons ltd

a test of three dimensional radiative transfer simulation using the radiance signatures and contrasts at a high latitude coastal site 1 a three dimensional monte carlo radiation code is used to analyze surface observations of sky radiance at a high latitude coastal site observations were made at palmer station antarctica under uniform marine stratus clouds during both ice free and iced in ocean conditions the model results using actual snow ocean area coverage show good qualitative agreement with all sky images and high spectral resolution radiometer scans when viewing over the island toward the northeast observations and modeling indicate that sky radiance in the visible bands is up to a factor of two greater than for directions toward the southwest viewing out over open ocean owing to a decrease in snow reflectance at longer wavelengths modeled and observed radiance distributions in the near infrared tend to be much more symmetric results of the modeling study indicate that details of the snow brdf or island topography have a very small effect on model predictions in addition the model indicates that the angular distribution of sky radiance is fairly insensitive to cloud optical depth assumed homogeneous and is independent of cloud height as long as cloud layer thickness is not much larger than the cloud base height

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

speleothem based paleoclimate record from northern oman u th age dating and stable isotope measurements of speleothems from hoti cave in northern oman yield paleoclimate information from the region extending to 125 ka the results 1 provide further confirmation of an early holocene wet period in southern arabia extending from some time prior to 9 7 ka and ending at 6 2 ka 2 demonstrate a second period of wetness closely coinciding with the last interglacial period marine isotope stage mis 5e 3 indicate that during mis 5e southern arabia was considerably wetter than during the early holocene and 4 demonstrate that periods of increased monsoon wind strength based on data from marine sediments do not always coincide with evidence of greatly increased precipitation even from nearby continental areas

low latitude holocene hydroclimate derived from lake sediment flux and geochemistry this study investigates hydrological responses to climatic shifts using sediment flux data derived from two dated palaeolake records in south east arabia flux values are generally low during the early holocene humid period ehhp 9 0 6 4k cal a bp although several short lived pulses of increased detrital input are recorded the most prominent of which is dated between 8 3 and 7 9k cal a bp the ehhp is separated from the mid holocene humid period mhhp 5 0 4 3k cal a bp by a phase of increased sediment flux and aridity which began between 6 4 and 5 9k cal a bp and peaked between 5 2 and 5 0k cal a bp the termination of the mhhp is marked by a phase of high detrital sediment flux between 4 3 and 3 9k cal a bp while long term shifts in climate are most likely linked to changes in the summer position of the intertropical convergence zone and associated indian and african monsoon systems it is noted that the abrupt short term phases of aridity observed in both records are coeval with intervals of rapid climate change globally which triggered non linear widespread landscape reconfigurations throughout south east arabia

active sand seas and the formation of desert loess abstract loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains 20 80 m that serve as an important archive of information on quaternary climate change despite the intensive research during the past century on desert loess formation its origin remains poorly understood and is still a fundamental problem in sedimentology the ongoing debate is focused on the first stage of loess formation the production of coarse silt quartz grains although laboratory experiments indicate the potential of dunes with their abundant quartz sand grains as a primary source for generating coarse silt grains this concept has been generally rejected because field based evidence of abrasion from sand grains eolian abrasion is scarce here we have adopted a global view of the sand sea loess association and examine in detail several well known late pleistocene loess regions in different subtropical deserts africa the middle east and arabia this analysis demonstrates that all these loess regions are located downwind of adjacent sand seas together with evidence of mineralogical similarity between the loess and the sand dunes and the contemporaneous deposition of the loess and movement of the dunes these observations suggest that sand seas are an important source for desert loess because there is only limited silt storage in sand dunes we postulate that the silt grains comprising most of the loess are not reworked from the dunes but are generated probably through active eolian abrasion of the sand grains under past climates characterized by intensified winds as a result the role of sand dunes and eolian abrasion in the formation of desert loess may be more important than previously thought

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

shoreline reconstructions for the persian gulf since the last glacial maximum abstract sea level change in the persian gulf since the time of the last maximum glaciation at about 18 000 yr bp is predicted to exhibit considerable spatial variability because of the response of the earth to glacial unloading of the distant ice sheets and to the meltwater loading of the gulf itself and the adjacent ocean models for these glacio hydro isostatic effects have been compared with observations of sea level change and palaeoshoreline reconstructions of the gulf have been made from the peak of the glaciation until about 14 000 yr bp the gulf is free of marine influence out to the edge of the biaban shelf by 14 000 yr bp the strait of hormuz had opened up as a narrow waterway and by about 12 500 years ago the marine incursion into the central basin had started the western basin flooded about 1000 years later momentary stillstands may have occurred during the gulf flooding phase at about 11 300 and 10 500 yr bp the present shorelines was reached shortly before 6000 yr ago and exceeded as relative sea level rose 1 2 m above its present level inundating the low lying areas of lower mesopotamia these reconstructions have implications for models of the evolution of the euphrates tigris karun delta as well as for the movements of people and the timing of the earliest settlements in lower mesopotamia for example the early gulf floor would have provided a natural route for people moving westwards from regions to the east of iran from the late palaeolithic to early neolithic

dune whitening and inter dune freshwater ponds in ne brazil the changes in color of sand dunes from white to yellow or red is often interpreted to signify their age or their source materials in this study we demonstrate the effect seasonal inter dune freshwater ponds have on the bleaching of the color of sand dunes by iron reduction in the anaerobic conditions they create by combining spectral measurements of field samples of dune sand together with the analysis of satellite images covering three dune fields in ne brazil lencois maranhenses jericoacoara and canoa quebrada we demonstrate its existence in the field in areas where ponds cover 41 of the dune field as in lencois maranhenses an almost total bleaching in the color of the sand occurs after which the dunes remain white with no relation to distance from the coastline in areas with less ponds e g jericoacoara or canoa quebrada dune whitening is less active and there are areas where dune rubification occurs as this process may have occurred in other dune fields during past climate conditions that may have been different from current ones interpretations of dunes age based on their color should be handled with care

calcareous dunes of the united arab emirates and noah s flood the postglacial reflooding of the persian arabian gulf abstract aeolian dunes cover most of the united arab emirates and a large part of the eastern arabian peninsula although these sands as well as older aeolianites are largely composed of quartz there is a high percentage of detrital carbonate in them south of the persian arabian gulf for more than 40 km this percentage decreases inland these carbonate grains consist mainly of marine bioclastic fragments and calcareous ooids and were derived from the floor of the persian gulf which was exposed during low sea level of the last glacial period the postglacial rise in sea level rapidly reflooded the floor of the persian gulf cutting off the source for these aeolian sediments between 12 and 6 ka the sea transgressed more than 1000 km inundating the extended route of the tigris euphrates river and forcing people living on the exposed floor of the gulf to abandon their settlements because of the varying rate of eustatic sea level rise these waters at times flooded across the flat floor of the persian gulf at more than a kilometer per year we proposed that the stories of a great flood recorded in the bible as noah s flood and in babylonian history on clay tablets excavated in the tigris euphrates delta as the epic of gilgamesh are a record of this rapid postglacial flooding of the floor of the persian gulf

cretaceous plate tectonic reconstructions abstract plate tectonic reconstructions for each cretaceous stage are produced as base maps for cretaceous paleogeography and for oceanic and continental data both geologic and geophysical data are utilized to determine the relative rotations of cretaceous plates with respect to north america a sea floor spreading history is generated from the relative rotations this history is consistent with data from the deep sea drilling project paleolatitude lines are derived using average paleomagnetic pole positions these reconstructions are significantly more comprehensive than previous global reconstructions although there are still many areas which remain controversial