windblown sand on venus the effect of high atmospheric density the high density of the venusian atmosphere significantly affects aeolian saltation transport and may also allow rapid alterations in the radar backscatter cross section of the surface saltation flux experiments were conducted under terrestrial and simulated venusian conditions to assess the effect of atmospheric density on aeolian transport of sediment total lane flux the vertical distribution of saltating particles and the average horizontal component of particle speed were measured and used to estimate the volumetric concentration of particles above the surface results show that so many particles are set into motion when wind speeds exceed a critical value that mid air collisions are a common result a condition termed choked saltation when choking occurs there is a reduction in the rate at which the total saltation flux increases with increasing wind speed at least in part due to a reduction in the mean horizontal speed of the particles choked saltation on venus may result in a reduction of the local aeolian erosion rate the obliteration of aeolian bedforms and rapid alteration of surface radar backscatter characteristics

windblown sand on venus preliminary results of laboratory simulations abstract small particles and winds of sufficient strength to move them have been detected from venera and pioneer venus data and suggest the existence of aeolian processes on venus the venus wind tunnel vwt was fabricated in order to investigate the behavior of windblown particles in a simulated venusian environment preliminary results show that sand size material is readily entrained at the wind speeds detected on venus and that saltating grains achieve velocities closely matching those of the wind measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from martian and terrestial simulations results are in general agreement with theory although certain discrepancies are apparent which may be attributed to experimental and or theoretical modeling procedures present findings enable a better understanding of venusian surface processes and suggest that aeolian processes are important in the geological evolution of venus

single quartz grain electron spin resonance esr dating of a contemporary desert surface deposit eastern desert egypt abstract signal resetting by sunlight prior to burial is a crucial assumption in electron spin resonance esr dating of sediments this resetting process is expected to be completed to a greater extent in arid than in fluvial environments the present paper investigates the natural and artificially irradiated signal intensity of ti related centres in single quartz grains collected from the desert surface eastern desert egypt in order to test this hypothesis the results suggest that in most grains both the ti li and ti h signal are completely reset to zero additive dose curves based on the sum of both ti centres show an anomaly in the low dose region possible causes for this behaviour are briefly discussed three fitting procedures are conducted and each of them shows a different palaeodose distribution with a rather large spread in d e values it is concluded that similar fossil deposits would be datable by single grain esr using q band measurements of the ti li or ti h signals in quartz

venus concentrations of radar reflective minerals by wind abstract areas of high radar reflectivity and low emissivity on venus may be covered with windblown material rich in fe and ti such as ilmenite a mineral common in some basaltic lava flows experiments under venus like conditions show that dense mineral grains become concentrated on the surfaces of windblown sediments when subjected to the low winds typical for venus

rate of wind abrasion on mars estimation of the rate of aeolian abrasion of rocks on mars requires knowledge of 1 particle flux 2 susceptibilities to abrasion of various rocks and 3 wind frequencies on mars fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the viking meteorology experiment assuming an abundant supply of sand sized particles estimated rates range up to 2 1 10 2 cm of abrasion per year in the vicinity of viking lander 1 this rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux the discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces we consider the primary reason to be related to the agents of abrasion either windblown grains are in very short supply or the grains are ineffective as agents of abrasion at least some sand sized 100 m grains appear to be present as inferred from both lander and orbiter observations high rates of abrasion occur for all experimental cases involving sands of quartz basalt or ash however previous studies have shown that sand is quickly comminuted to silt and clay sized grains in the martian aeolian regime experiments also show that these fine grains are electrostatically charged and bond together as sand sized aggregates laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand aggregates form a protective veneer on the target surface and can give rise to extremely low abrasion rates

dating of marine terrace sediments by esr tl and osl methods and their applicabilities abstract we present the results of a pilot study in which esr tl and optical dating are intercompared to assess their suitabilities for application to measurement of the uplift rates of the japanese islands samples used were known age marine ten ace sediments collected from three sites in central japan as a result of optical bleaching experiments it was found that the tl residual intensity was identified by uv lamp but we were not able to determine how the bleaching of the esr ti signal proceeded in antiquity esr tl and optical dating were performed using the ti signal the red tl emission and the uv emissions measured during stimulation by the waveband 500 40 nm respectively equivalent doses were estimated using the additive close method dose rates were calculated from radioisotope concentrations measured using neutron activation analysis it was found that variation in pore water content over time was of major significance in age determinations for these sediments on account of their history of deposition underwater with subsequent uplift and drainage it was concluded from the correspondence of ages estimated by tl and optical dating with geological expectation that the tl and optical dating methods are suitable for dating marine terrace sediments

esr dating in quaternary geology abstract electron spin resonance esr a relatively new dating technique was first suggested by zeller et al 1967 zeller 1968 and levy 1968 it has made substantial progress in frequent applications in the last few years esr dating is based on the direct measurement of the amount of radiation induced paramagnetic electrons trapped in crystal defects these free electrons were generated by alpha beta and gamma radiation of natural radioelements e g u th k and have accumulated in the minerals over geologic time the esr age is obtained by dividing the total amount of accumulated radiation dose archaeological dose ad by the dose per year annual dose this review comprises four major parts the principles of the method the determination of the archaeological dose ad the determination of the annual dose and a compilation of datable materials several questions remain the evaluation of the ad the determination of the annual dose and particularly with respect to the nature and stability of the electron traps used for dating

surface modification of venus as inferred from magellan observations of plains in sedna planitia clear stratigraphic relations can be discerned among volcanic flow units young flows exhibit sar specific cross section values similar to fresh terrestrial basalt flows whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows total degradation of 1 m depth over 0 6 b y is inferred for the sedna area from radar signatures impact crater abundances and ejecta superposition relations with respect to volcanic flow units analyses of parabolic ejecta deposits associated with the crater stuart imply that the material is typically centimeters in thickness a relatively small fraction 10 of venusian impact craters exhibit prominent parabolic ejecta deposits these craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years the inferred dispersal rate 10 3 m yr is too low to produce the degradation of flows at sedna planitia and it is concluded that the dominant flow modification process is in situ weathering in addition elevation dependent weathering is inferred in western ovda regio where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations the inferred rate of generation of high reflection coefficient materials is no more than 10 2 m yr based on the inability of aeolian activity to cover high reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high reflectivity surfaces at high elevations surface modification rates on venus are orders of magnitude lower than on earth venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on mars but are comparable to the estimated rate of weathering and erosion of martian bedrock low surface modification rates imply that it will be possible to determine regional scale age variations on venus based on the degree of preservation of volcanic landforms and microwave signatures

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

dunes and microdunes on venus why were so few found in the magellan data abstract a search through cycle 1 2 and 3 magellan radar data covering 98 of the surface of venus revealed very few dunes only two possible dune fields and several areas that may contain microdunes smaller than the resolution of the images 75 m were identified the aglaonice dune field was identified in the cycle 1 images by the specular returns characteristic of dune faces oriented perpendicular to the radar illumination cycle 1 and 2 data of the fortuna meshkenet dune field indicate that there has been no noticeable movement of the dunes over an 8 month period the dunes which are oriented both parallel and perpendicular to the radar illumination appear to be dark features on a brighter substrate bright and dark patches that were visible in either cycle 1 or 2 data but not both allowed identification of several regions in the southern part of venus that may contain microdunes the microdunes are associated with several parabolic crater deposits in the region and are probably similar to those formed in wind tunnel experiments under venus like conditions bragg scattering and or subpixel reflections from the near normal face on asymmetric microdunes may account for these bright and dark patches look angle effects and the lack of sufficient sand size particles seem to be the most likely reasons so few dunes were identified in magellan data insufficient wind speeds thinness of sand cover and difficulty in identifying isolated dunes may also be contributors to the scarcity of dunes

crater associated dark diffuse features on venus properties of surficial deposits and their evolution 1 in order to assess the nature of crater associated radar dark diffuse features ddfs on venus and to understand their formation and evolution we analyzed magellan radar roughness emissivity and reflectivity data in the vicinity of craters accompanied by these features following others we assumed that ddfs are deposits mantles of ejected material emplaced during formation of the impact crater the majority of radar dark parabolas the youngest ddfs are characterized by a smooth mantle atmosphere interface having low root mean square rms slopes on scales of 1 100 m as derived from magellan altimeter data older ddfs also often have areas with low rms slopes suggesting that the mantle rms slopes can be preserved for geologically long periods of time some parabolas and older ddfs have asymmetric small scale decimeter scale relief that is interpreted to be dunes that formed as a result of eolian processes this implies that the mantle material is mobile and can saltate under the influence of wind action on average aging of these features is accompanied by a decrease of mantle material dielectric permittivity the most efficient mechanism for parabola degradation seems to be the removal of mantle material from the site of initial deposition by subsequent winds we found a few examples of features that could be interpreted to be the result of in situ modification of the primary mantle

eolian ripples as examples of self organization in geomorphological systems abstract ripples arise spontaneoulsy from sandy beds subjected to winds sufficient to cause the saltation of surficial grains while the initially fastest growing wavelengths are 4 6 times the mean hop length of grains impelled downwind by long trajectory high energy saltating grains the ripple wavelengths developed over long periods can be several times this numerical simulations based upon techniques pioneered by p k haff and coworkers reveal that a complex process of ripple coalescence is responsible for this evolution of the ripple field small fast moving ripples catch up with and are absorbed by larger slower forms each such merger resulting in a growth of the mean wavelength and a decline in the relative dispersion of the wavelengths an heuristic argument is presented which accounts for the fast initial growth and subsequent slowing of growth of the mean wavelength as the ripple field evolves ripple cross sectional shape appears to be controlled in large part by a distrianment function which represents the declining likelihood of a grain stopping on a surface as it slopes more steeply downwind that the resulting asymptotic wavelength in the simulations depends strongly upon impact angle supports sharp s 1963 suggestion that the length of the shadow zone plays an important role in controlling the final ripple wavelength

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

luminescence dating of interglacial coastal depositional systems recent developments and future avenues of research abstract luminescence dating offers new opportunities to explore the evolution of quaternary marine coastal facies and landforms this review highlights the main advances in luminescence geochronology of interglacial coastal sediments through the analysis of 547 luminescence ages most of which were published during the last decade the majority of these reported luminescence investigations have been carried out along passive margin coasts since the turn of the century the discovery of a normalization procedure known as single aliquot regeneration sar has drastically reduced data scatter and improved precision with the consequence that quartz sar optically stimulated luminescence osl has become the dating protocol of choice for the last interglacial lig period a more complex technique known as thermally transferred osl tt osl is presumably proposed for dating older interglacials of the mid pleistocene and beyond feldspar luminescence is increasingly being applied to dating pleistocene sea level high stands due to a much higher dose saturation level than quartz osl the use of feldspar irsl infrared stimulated luminescence is limited by the occurrence of variable but ubiquitous anomalous fading af following the advent of af correction methods several middle pleistocene sites have been amenable to dating albeit with significant related uncertainties recently new protocols involving the measurement of post ir irsl at elevated temperatures have yielded relatively coherent ages for interglacial sediments up to ca 300 ka quartz osl tt osl af corrected irsl and post ir irsl ages are generally correlated with periods of sea level high stands a few ages are reported from the early and middle part of the middle pleistocene as mis11 9 and more commonly mis7 high stands are documented in strongly uplifting active margin coasts however by far the most obvious age peak corresponds to the end of the lig the mis5e shoreline is probably the most studied and luminescence dated coastal feature of all as the chronology of the sea level markers is crucial to assess global eustatic sea level variations through the course of the last interglacial nevertheless the observed abundance of young 100 120 ka luminescence ages for presumed mis5e sediments may underline methodological issues and or reflect the higher preservation potential of late regressive sequences on the other hand the occurrence of geographically distant reports of mis5a high stand might reflect a true eustatic origin for this event age analysis supports the impression of general reliability of luminescence for the timing of former sea level high stands there is a clear need to address issues in dose rate variability in the phenomenology of fading in feldspar and in the behaviour of luminescence growth with dose both in laboratory and natural conditions these could be addressed and properly evaluated by dating different minerals as multiple or single grains with consequent variable internal dose rates more robust practices in the application of luminescence dating techniques could eventually constrain the age uncertainties to no better than 2 3 therefore the strength of luminescence as a dating tool is more in terms of its extended age range and the ubiquity of datable material

magellan initial analysis of venus surface modification initial magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes ejecta deposits extending up to 1000 kilometers to the west of several impact craters windblown deposits and features in areas where there are both obstacles and a source of particulate material and evidence for slow steady degradation by atmosphere surface interactions and mass movements

uplift histories of africa and australia from linear inverse modeling of drainage inventories this is the final version it first appeared at http onlinelibrary wiley com wol1 doi 10 1002 2014jf003297 abstract

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

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

erosion profiles due to particles entrained by wind application of an eolian sediment transport model erosion by impacts of particles entrained in the wind scales with the kinetic energy of impacting grains a recent model of eolian sediment transport permits calculation of expected erosion patterns in objects of simple geometry the modeling of vertical erosion profiles in turn provides an exacting test of the transport model realistic distributions of liftoff velocities for saltating grains give rise to kinetic energy flux profiles characterized by a strong maximum as much as 1 4 m above the bed during strong winds kinetic energy flux due to suspended grains also peaks above the bed the height and strength of the maxima depend very strongly on the grain size distribution as grain size diminishes increased particle deflection by the air flow around an obstacle reduces delivery of kinetic energy to the surface for both saltating and suspended grains kinetic energy flux scales with the fifth power of the wind shear velocity erosion profiles in man made obstacles are well modeled with only slight modification of the saltation model to account for the relatively high elasticity of actual deflationary surfaces lending considerable support for the model the modeling also elucidates several aspects of ventifaction as small ventifacts 1 2 m in diameter and the lower portions of larger ones are predominantly eroded by saltating grains upwind surface irregularities are quickly damped leading to facets that dip upwind and sharply truncate lee surfaces sandblasting by suspended grains dominates along the upper portions of large ventifacts where grain paths are partially deflected by the obstacle and may lead to radially symmetrical flutes and grooves

esr in the 21st century from buried valleys and deserts to the deep ocean and tectonic uplift abstract electron spin resonance esr dating can date many materials including hydroxyapatite in enamel and some fish scales aragonite and calcite in corals molluscs some travertine and calcrete and quartz from ash fluvial deposits and some flint dating studies using these materials have numerous potential applications in many varied quaternary settings esr dating uses signals resulting from trapped charges created by radiation in crystalline solids ages are calculated by comparing the accumulated radiation dose in the dating sample with the internal and external radiation dose rates produced by natural radiation in and around the sample and produced by cosmic radiation when compared to other dating techniques age agreement has been excellent for teeth corals molluscs and quartz recent improvements have included using a more complex modelling technique to calculate the cosmic dose rates and more detailed modelling techniques for dealing with variable external dose rates methods in development include using quartz from buried fluvial valleys to date geomorphic surfaces and using the signals in barnacles and benthic foraminifera for dating fossils or their associated sediment new chronometer applications recently developed include using coral and mollusc dates to build sealevel curves and to monitor volcanic activity and tectonic uplift using tooth and mollusc dates to assess water availability in deserts and using isochron data to assess u uptake processes into teeth when coupled with other geochemical and geomorphological techniques esr can provide the chronometric control to build paleoclimatic and other paleoenvironmental records many other applications are possible from heating studies for artefacts to dating sulphates and other minerals on distant planets

the surface of venus as revealed by the venera landings part ii observations of the panoramic photographs transmitted by veneras 13 and 14 indicate that many visible rock units are layered and that at least a portion of the fine material could be the result of in situ geomorphic disintegration chemical and material property experiments indicate that the chemical composition of the material at the landing sites is essentially basaltic that the bearing strength is minimal a few kilograms per square centimetre or a few hundred kilopascals that the density is less than 1 5 g cm 3 that the porosity is very high 50 and that the electrical resistivity is very low the discussion on the possible geological nature of the surface of venus presented in part i florensky and others 1977a is extended in light of these new data six possible origins of the rock units were discussed 1 surface lava extrusion 2 igneous intrusion later exposed by erosion 3 pyroclastic fall 4 impact ejection and lithification 5 sedimentary deposits lithified at depth and later exposed by erosion and 6 surface metamorphism due to unique venusian surface conditions it is concluded that although none of the above hypotheses can be conclusively proven or disproven hypothesis 6 is to be advanced to the forefront this is suggested by 1 the low density and low bearing strength 2 the presence of layering 3 the possible presence of sedimentary structures in the rock units such as cross bedding and ripple marks 4 the low electrical resistivity which may indicate chemical alterations of surface material and 5 the albedo of the loose fine material which is lower than the albedo of the rock units this again suggests chemical alterations within the context of this hypothesis the rock units are sedimentary or sedimentary volcanic lithification occurred in the past due to surface chemical effects the rock units analogous with a similar terrestrial phenomenon can be referred to as duricrusts with the understanding that the venusian process is completely different from the terrestrial process presently the rock units are undergoing disintegration indicating that changes have occurred in the surface conditions at the landing sites

an experimental study of aeolian structures on venus experiments to simulate the formation of aeolian bed forms on venus show that a high density atmosphere produces small transverse bed forms with dimensionless similarities to terrestrial dunes but with both dimensional and behavioral similarities to subaqueous current ripples their development is influenced by wind speed particle size and atmospheric density although aeolian bed forms should be observed at all elevations on venus their optimum expression is compatible with the lowest elevations where atmospheric pressure is greatest their development is relatively unhindered by the presence of dense grains the lack of sorting in source sediment from which they form or the addition of cohesive dust small 10 cm bed forms are efficient in sorting materials either by density or particle size bed forms developed in the limited size of the wind tunnel are probably representative of small bed forms on venus considerations suggest that bed forms on venus may grow to larger sizes discovery of dune fields on magellan images of venus support this prediction

microdunes and other aeolian bedforms on venus wind tunnel simulations abstract previous studies confirm that sand can be entrained at the wind velocities recorded on venus present results describe bedforms produced in the venus wind tunnel vwt simulating the average venusian environment even at the low wind speeds measured on venus dunelike structures form in fine grained quartz sands particles 50 200 m in diameter the dunelike structures referred to as microdunes are considered to be true dunes analogous to those on earth because they have 1 slip faces 2 a lack of particle size sorting 3 a low ratio of saltation path length to dune length and 4 internal cross bedding the microdunes typically produced in the vwt are 9 cm long and 0 75 cm high it is proposed that there may be fields of microdunes on venus that are capable of very fast rates of migration and that they may grow into features much larger than those observed in the vwt however neither dunes nor other types of features develop above a wind speed of 1 5 m sec at this wind speed the bed is flat and featureless thus it is predicted that relatively short periods of higher winds may destroy microdunes and other small bedforms which could account for the sparsity of definitive aeolian features observed in venera images some apparent cross bedding observed in venera images however could represent preserved aeolian structures

optical dating of river terrace sediments from kanto plains japan abstract optical dating of river terrace sediments has been carried out in a test of the methodology for luminescence age determination of river terrace formation over the last 100 ka in this study samples were collected at river terraces whose ages were estimated by marker tephra geochronology and from a recent riverbed in the kanto plain japan samples from the recent riverbed show a weak osl signal only and gave young ages samples of river terrace sediments for optical dating were collected systematically from the section of about 8 m at the wall of a gravel quarry the optical ages found corresponded well with those estimated by the age of the marker tephras for samples deeper than 2 5 m however the samples from the ground surface to 2 5 m exhibited considerable scatter in the growth curves and gave a wide range of ages all significantly exceeding expectation this was attributed to the mixing of different age sediments by inundation and or human activities analyses of osl from single grains of quartz confirmed that these sediments were composed of grains having a wide range of palaeodoses consistent with such mixing

large scale patterns of eolian sediment transport on venus predictions for magellan the atmosphere of venus is likely to exert a major influence on the surface arecibo and venera 15 16 observations of the population of impact craters with bright halos give direct evidence of surface modification on the scale of centimeters to smooth the surface on time scales of 50 250 my both chemical and mechanical modifications probably occur diurnal winds in the planetary boundary layer can transport particles using boundary layer theory including the effects of topography surface stresses and resulting transport and deposition of sand size particles are calculated regional slopes are sites of largest surface stresses sand will be generally transported downhill although there is a preferential net transport from east to west in the same direction as the atmospheric superrotation it is predicted here that streaks may be seen in the magellan radar images which will indicate directions of net eolian transport on the surface of venus

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

towards single grain esr dating of sedimentary quartz first results abstract in optically stimulated luminescence dating apparent ages of individual grains are thought to reflect a wide distribution of initial bleaching levels in hard to bleach sediments although having a larger age range up to 1 ma and beyond this approach has not been used yet in electron spin resonance esr dating here we report on the first results of esr measurements on single sedimentary quartz grains initial bleaching levels are evaluated for two different river meuse deposits in limburg ne belgium measurements were done with a q band esr spectrometer on transparent quartz grains of sufficiently large diameter 0 5 0 7 mm single crystal esr properties were used to identify different esr active centres in about 50 of the selected grains an al and or ti li signal was detected and the latter has been selected for further measurements artificial bleaching experiments show a strong signal decrease with uv light exposure after gamma ray irradiation a number of different signal intensity vs artificial dose curves could be observed exponential growth exponential saturation linear with inflexion points and unclear ones many grains show increasing esr signals with doses up to 1000 gy suggesting that the age range could be extended over 1 ma covering the middle pleistocene and part of the early pleistocene accumulated doses of individual grains were calculated using the additive dose method the results show a large dose distribution of individual grains for both deposits it is concluded that insufficiently bleached grains can be detected using single grain esr measurements of sedimentary quartz in a fluvial environment

esr dating of aeolian sand near tennant creek northern territory australia abstract electron spin resonance esr dating of aeolian sand in the northern territory of australia was carried out using the al centres in quartz grains as part of an attempt to date prehistoric faulting associated with the 1988 tennant creek earthquakes our experiments on optical bleaching of esr electron spin resonance signals show that sunlight does not completely bleach the esr signal from the al centre of quartz grains in this aeolian sand the total doses were determined from the acquired esr signal intensity however a correction to compensate for partial bleaching and the resultant inherited residual esr signal has to be carried out by using this technique the esr age estimates an increase with depth which suggests that nearly complete optical bleaching has occurred through this slice of geologic time for age estimates younger than 50 ka the esr ages are in generally good agreement with independently determined tl thermoluminescence data beyond 50 ka the esr ages are systematically older than the tl ages the oldest esr age estimate of 160 0 5 9 ka is from a sample at 228 cm depth and esr results from the vertical samplings yield an apparent sedimentation rate of 2 6 cm ka

thermoluminescence dating of sediments abstract the potential for using the thermoluminescence behaviour of sediments for dating them was first recognized by soviet scientists g v morozov and v n shelkoplyas and for over a decade their tl dates obtained from a variety of sediments have appeared in the soviet literature since 1977 tl sediment dates have been published by six additional groups using a variety of methods in this review we describe the principles of tl dating the various methods used and contrast tl dating of sediments with the now well accepted tl dating of pottery we conclude that while tl dating has the potential to solve many sedimentary problems more fundamental research needs to be carried out before such dates should be accepted a set of criteria for acceptable dates is proposed

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

esr studies on bleached sedimentary quartz abstract some esr signals in quartz are reported to be bleachable by sunlight and so they promise to be useful for dating sediments grun 1989 the ge signal in quartz is the only one that shows bleaching effects with uv light in short time scales hours therefore we used quartz samples from the sites of mauer homo erectus heidelbergensis samples from a borehole in the neckar valley entensee ladenburg near heidelberg and samples from a pegmatite for basic studies on the ge signal the results show that with our standard sample preparation procedure for quartz separation using red light as for tl samples the natural ge signal is not detectable but rises clearly with gamma irradiation several experiments for examination of the stability and sensitivity of the ge centre in quartz were carried out for comparison with the behaviour of the ge signal we measured the al signal as well our experiments show that the al signal is bleachable in long time scales weeks the behaviour on bleaching irradiation and thermal annealing is very complicated as the al centre is a hole centre it possibly interacts with several electron centres in the quartz and so the processes are of higher order

venera 13 and venera 14 sedimentary rocks on venus venera 13 and venera 14 transmitted almost complete panoramic views of their landing sites analyses of the photographs show the presence of rock formations undergoing geomorphic degradation the formations display ripple marks thin layering differential erosion and curvilinear fracturings some of them are interpreted as lithified clastic sediments the lithification could have taken place at depth or at the surface resulting in a type of duricrust the origin of the sediments is unknown but could be aeolian volcanic or related to impacts or to turbidity currents

an investigation of the effect of sunlight on the esr spectra of quartz centres implications for dating abstract the behaviour of esr signals due to titanium and aluminium centres in quartz sand on exposure to sunlight has been investigated samples of sand were recovered from cores taken off the coast of southeast australia at forster tuncurry and at an inland lake lake george naturally irradiated samples and also samples which were annealed and then artificially irradiated with gamma rays were used the esr signal due to titanium centres shows promise for dating the last exposure to sunlight of quartz grains

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

adhesion and abrasion of surface materials in the venusian aeolian environment in laboratory simulations of the venusian environment rock and mineral target surfaces struck by aeolian particles develop a thin layer of accretionary material derived from the particles attrition debris accretion may be in part a manifestation of cold welding a process well known in engineering where bonding occurs between metals at a tribological interface accretion on geological materials was found to occur at all venusian surface temperatures and for all types of materials tested first order variations in the amount deposited by particles are related to relative attrition susceptibilities second order variations relate to properties of the particle target interface variations in accretion volume are apparently independent of mineral chemistry and are only weakly dependent on crystallography the results suggest that accretion should be a fairly universal phenomenon in areas of venus subject to aeolian activity