intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

valles marineris dune sediment provenance and pathways abstract although low albedo sand is a prevalent component of the martian surface sources and pathways of the sands are uncertain as one of the principal present day martian sediment sinks the valles marineris vm rift system hosts a diversity of dune field populations associated with a variety of landforms that serve as potential sediment sources including spur and gully walls interior layered deposits ilds and landslides here we test the hypothesis that vm dune fields are largely derived from a variety of local and regional intra rift sediment sources results show several dune fields are superposed on ancient wall massifs and ilds that are topographically isolated from extra rift sand sources spectral analysis of dune sand reveals compositional heterogeneity at the basinal dune field and dune scales arguing for discrete relatively unmixed sediment sources in coprates and melas chasmata mapping is consistent with the principle sand source for dunes being noachian aged upper and lower wall materials composed of primary igneous minerals and glasses some of which show evidence for alteration in contrast dune fields in capri juventae and ganges chasmata show evidence for partial sediment derivation from adjacent early hesperian aged hydrated sulfate bearing ild units this finding indicates that these ilds act as secondary sand sources dunes containing soft secondary minerals e g monohydrated sulfate are unlikely to have been derived from distant sources due to the physical weathering of sand grains during transport isolated extra rift dune fields sand sheets and sand patches are located on the plateaus surrounding vm and the adjoining areas but do not form interconnected networks of sand pathways into the rift if past wind regimes with respect to directionality and seasonality were consistent with more recent regimes inferred from morphological analysis i e dune slip faces wind streaks and were sufficient in strength and duration small dune populations within aurorae chaos and north of eastern vm might have resulted from extended sand pathways into vm however we favor local and regional derivation of dune sand from a variety of intra rift lithologic sources for most cases dune sand sources and the mechanism by which the sand is liberated are discussed in the context of findings described herein but are broadly applicable to analysis of sediment production elsewhere on mars

detectability of minerals on desert alluvial fans using reflectance spectra we analyzed the visible and near infrared reflectance spectra of soil samples collected from desert alluvial and colluvial surfaces in the cuprite mining district nevada these surfaces are downslope from hydrothermally altered volcanic rocks that contain spectrally characteristic minerals such as alunite and kaolinite coarse fractions of the soils on the alluvial fans are mineralogically variable and express the upslope lithologies fine fractions are remarkably similar mineralogically and spectrally in all samples because of dilution of local mineral components by regionally derived windblown dust theoretical models for spectral mixing and for particle size effects were used to model the observed spectral variations diagnostic mineral absorption bands in the spectra of fan materials were enhanced by computationally removing the spectrum of the homogenous fine soil component detection limits for minerals were found to be controlled by the sensitivity of the instrument the spectral contrast between the mineral and the background and the relative brightnesses of the mineral and the background these results show that spectral mixing models are useful for analyzing data with high spectral resolution obtained by field and aircraft spectrometers

inconsistent magnetic polarities between greigite and pyrrhotite magnetite bearing marine sediments from the tsailiao chi section southwestern taiwan abstract to establish a magnetobiostratigraphy for a 620 m thick middle to late pleistocene mudstone sequence in the lower gutingkeng formation of the tsailiao chi tlc section in southwestern taiwan we conducted paleomagnetic and mineral magnetic measurements together with sediment granulometry and calcareous nannofossil identification paleomagnetic samples from 65 sites revealed two types of thermal demagnetization 25 400 c behavior 1 single component stable characteristic remanence in magnetite and pyrrhotite dominated samples type s and 2 abrupt changes in polarity when samples with significant greigite concentrations were heated above 320 340 c type c the characteristic polarities derived from type s samples and from magnetite dominated type c samples obtained above 340 c are consistent with those determined from nannofossil biostratigraphy this implies that the nrm carried by magnetite and pyrrhotite is reliable the essentially antiparallel remanence components in type c samples below 340 c are attributed to greigite the almost antiparallel direction could have resulted from delayed formation of greigite but in this case the different direction of this component must have resulted from variable remanence lock in times alternatively the opposite polarities may result from self reversal which warrants further investigation pyrrhotite and greigite may have both formed authigenically but there is no clear explanation for the observed differences in direction

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

compact reconnaissance imaging spectrometer for mars observations of northern martian latitudes in summer 1 this paper brings together initial results obtained of the high northern latitudes in mars years 28 and 29 between october 2006 and october 2008 these measurements confirm many previous models and shed new light on the nature of polar surface materials particularly in intermediate albedo units of the polar layered deposits many of which are found to be ice rich we identify hydrated non ice materials present in many low albedo troughs as well as in the circumpolar erg that was previously associated with gypsum we identify icy outlier deposits that may be related to subsurface thermophysical properties and permafrost new observations of the gypsum rich dune material constrain models for its formation and distribution intrinsic properties of ice content and grain size are found to be independent of the albedo of fine layered units and may provide a novel method for stratigraphic identification and correlation

variation in grain size and morphology of an inland parabolic dune during the incipient phase of stabilization in the hobq desert china abstract a significant increase in rainfall in the summer of 2012 on the southern fringe of the hobq desert inner mongolia resulted in the vegetation and thus stability of dunes in this area our research focuses on a typical parabolic dune which was active in 2011 and became stabilized after vegetation colonization topographic surveys and surface sediment analysis of the morphology and surface sands of the parabolic dune indicate that decreasing mean grain size and sorting values better sorting slightly more positive skewness and increasing kurtosis occurred over the dune surface during the incipient phase of stabilization there was a strong relationship between grain size sorting and dune mobility surface sand from the stabilized dune was generally finer and better sorted than at the same location when the dune was active during 2011 2012 the dune head had moved eastwards by approximately 2 3 m while its two arms expanded outward by approximately 3 2 m the height of the dune decreased and the dune became larger with a decreasing volume once anchored 2013 2014 the overall morphology and the grain size and sorting characteristics of the dune became more constant and quite different than when the dune was active

wide distribution and glacial origin of polar gypsum on mars the north polar cap of mars is associated with different kinds of superficial sediments including the circumpolar dune field interior dune fields and sedimentary veneers scattered over the ice cap in order to resolve the mineralogical composition and the regional distribution of these sediments we processed omega and crism hyperspectral data with an original method based on spectral derivation we find that gypsum is present in all areas where undefined hydrated minerals had been previously detected including superficial sedimentary veneers covering the north polar cap interior dune fields and the whole circumpolar dune field morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap the source of superficial sedimentary veneers is the dust that was previously contained in the upper part of the ice cap the ice rich north polar layered deposits npld this gypsum bearing dust was released on south facing slopes of spiral troughs and arcuate scarps by ice ablation controlled by katabatic winds by the analysis of all associations of erosional scarps and dune fields over the north polar cap we also demonstrate that the polar dunes are composed of sand sized particles that were previously contained in the sediment rich basal unit bu corresponding to the lower part of the ice cap these particles contain gypsum and were released from the bu by regressive ablation of ice at marginal scarps that border the north polar cap and by vertical ablation of ice on olympia planum from a reconstruction of wind streamlines over and around the ice cap we infer that katabatic winds descending from the polar high and rotating around the north polar cap control the release of these gypsum bearing particles by ice ablation and the redistribution of these particles in the circumpolar dune field 2011 elsevier b v

discrimination of active and inactive sand from remote sensing kelso dunes mojave desert california abstract landsat tm images field data and laboratory reflectance spectra were examined for the kelso dunes mojave desert california to assess the use of visible and near infrared vnir remote sensing data to discriminate aeolian sand populations on the basis of spectral brightness results show that areas of inactive sand have a larger percentage of dark fine grained materials compared to those composed of active sand ehich contain less dark fines and a higher percentage of quartz sand size grains both areas are spectrally distinct in the vnir suggesting that vnir spectral data can be used to discriminate active and inactive sand populations in the mojave desert analysis of laboratory spectra was complicated by the presence of magnetite in the active sands which decreases their laboratory reflectance values to those of inactive sands for this application comparison of tm and laboratory spectra suggests that less than 35 vegetation cover does not influence the tm spectra

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

parabolic dune development modes according to shape at the southern fringes of the hobq desert inner mongolia china since the 1970s parabolic dunes at the southern fringe of the hobq desert inner mongolia china have exhibited many different shapes v shaped u shaped and palmate each with a unique mode of development in the study area parabolic dunes are mainly distributed in regions a b and c with an intermittent river running from the south to the north we used high resolution remote sensing images from 1970 to 2014 and rtk gps measurements to study the development modes of different dune shapes the modes are characterized by the relationship between the intermittent river and dunes formation of the incipient dune patterns the predominant source supply of dunes and the primary formation of different shapes v shaped u shaped and palmate most parabolic dunes in region a are v shaped and closer to the bank of the river the original barchans in this region exhibit disconnected arms behavior with the sand blown out of the riverbed through gullies the nebkhas on the disconnected arms acquire the external sand source through the fertile island effect thereby developing into triangular sand patches and further developing into v shaped parabolic dunes most parabolic dunes in regions b and c are palmate the residual dunes cut by the re channelization of river from transverse dune fields on the west bank are the main sand source of region b the parabolic dunes in region c are the original barchans having then been transformed the stoss slopes of v shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape the dune crest of v shaped parabolic dune is the deposition area which forms the arc shaped sand ridge their two arms are non parallel the lateral airflow of the arms jointly transport sand to the middle part of dunes resulting in a narrower triangle that gradually becomes v shaped palmate parabolic dunes have a steeper stoss slope and height the dune crest of the palmate parabolic dune is the erosion area which forms a long and narrow trough between nebkhas by the funnelling effect this process forces sand towards lee slopes which transform from concave original barchans into convex ultimately resulting in the formation of palmate parabolic dunes

a new high precision furnace for paleomagnetic and paleointensity studies minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers although magnetic noise fields generated by heater currents in thermal demagnetizers have been noticed for a long time no satisfactory tests have been conducted to quantify their effects toward this end we have developed a new high precision thermal demagnetizer that greatly reduces the magnetic noise field we show the data quality generated by the new oven and the comparative results on several real samples that demonstrate the effects of the magnetic noise field due to heater currents the properties of the spurious magnetization emanating from the heater currents critically depend on the decay rate of amplitude and its waveform of electric power which is delivered to oven coils at the end of the heating stage of thermal demagnetization these results also illustrate the potential applications of this new instrument in paleomagnetism and paleointensity studies

transport and mixing of eolian sand from local sources resulting in variations in grain size in a gypsum dune field white sands new mexico usa abstract the white sands dune field new mexico usa provides a unique opportunity to study sources and eolian transport of sand end member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types textural differences between sources allow local transport paths to be deduced in total 1214 surface samples from 10 dunes and 2 downwind oriented transects were collected neither elevation on the dune lee or stoss location nor distance downwind correlated with mean grain size coarsest 10 d90 or sorting instead grain size distributions are controlled by mixing of locally sourced sand populations adjacent dunes can have different mean grain sizes resulting from different local source populations local within dune and between dune variability resulting from different sand sources dominates any larger scale trends across and within dunes four sand populations are identified based on microscopically observable differences in grain size shape and angularity each correlates with high loading of a different statistical factor derived from end member mixing analysis end member 1 em1 correlates with well sorted populations of finer grained equant rounded sands em2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes em3 is associated with samples of moderately to poorly sorted fine grained sand containing fine sand sized gypsum needles collected from areas of vegetated interdunes and em4 is associated with moderately well sorted coarse and very coarse grained sands collected from granule ripples these results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field rather than by dune scale or erg scale transport and sorting

early diagenesis of eolian dune and interdune sands at white sands new mexico abstract the degree of early diagenesis in eolian dune and interdune sands at white sands new mexico is largely a function of the relationship between sand location and the water table most active and vegetation stabilized dune sands are in the vadose zone whereas interdune sands are in the capillary fringe and phreatic zones crystallographically controlled dissolution of the framework gypsum grains results in elongate prismatic etch pits on sand grains from the capillary fringe and phreatic zones whereas dissolution of sand grains in the vadose zone is slight causing minute irregularities on grain surfaces vadose water percolating through the sand is manifest as meniscus layers consequently dune sands in the vadose zone are cemented mainly by meniscus shaped gypsum at grain contacts pendant cements formed on the lower margins of some sand grains cementation in the capillary fringe and the phreatic zone is more extensive than the vadose regardless of strata type typically well developed gypsum overgrowths form along the entire edge of a grain or may encompass the entire grain complex diagenetic histories are suggested by multiple overgrowths and several episodes of dissolution on single grains attesting to changing saturation levels with respect to gypsum in the shallow ground water these changes in saturation are possibly due to periods of dilution by meteoric recharge alternating with periods of concentration of ions and the formation of cement due to evaporation through the capillary fringe

modeling grain size variations of aeolian gypsum deposits at white sands new mexico using aviris imagery abstract visible and near infrared vnir through short wavelength infrared swir 0 4 2 5 m aviris data along with laboratory spectral measurements and analyses of field samples were used to characterize grain size variations in aeolian gypsum deposits across barchan transverse parabolic and barchan dunes at white sands new mexico usa all field samples contained a mineralogy of 100 gypsum in order to document grain size variations at white sands surficial gypsum samples were collected along three transects parallel to the prevailing downwind direction grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621 m which were subjected to spectral measurements absorption band depths of the size fractions were determined after applying an automated continuum removal procedure to each spectrum then the relationship between absorption band depth and gypsum size fraction was established using a linear regression three software processing steps were carried out to measure the grain size variations of gypsum in the dune area using aviris data aviris mapping results field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits in contrast the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits based on laboratory estimates a representative barchan transverse dune transect 1 has a mean grain size of 1 16 449 m the error bar results show that the error ranges from 50 to 50 m mean grain size for a representative parabolic dune transect 2 is 1 51 352 m and 1 52 347 m for a representative barchan dune transect 3 t test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas the t test results also show that there are no significant differences between modeled and laboratory measured grain size values hyperspectral grain size modeling can help to determine dynamic processes shaping the formation of the dunes such as wind directions and the relative strengths of winds through time this has implications for studying such processes on other planetary landforms that have mineralogy with unique absorption bands in vnir swir hyperspectral data

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

analysis of linear dune sediment form relationships in the kalahari dune desert wilson s 1972a b hypothesis of grain size control of dune spacing is tested using data from linear dunes in the kalahari dune desert the results confirm wasson and hyde s 1983b rejection of the universal applicability of the theory though this does not discount relevance to other dune types factors pertaining to the rejection of the grain size theory in the kalahari are considered results also demonstrated that the height and spacing of linear dunes are related but only when values are grouped for blocks of dunes the gradient of the h s relationship differs between dunefields possibly because sand supply differences have an effect upon dune geometry

cretaceous geomagnetic paleointensities thellier experiments on pillow lavas and submarine basaltic glass from the ontong java plateau 1 we present new thellier paleointensity results on pillow lavas and pillow rim submarine basaltic glass sbg from 120 ma basalts erupted on the ontong java plateau all pillow lavas have suffered low temperature alteration and are unsuitable for thellier paleointensity experiments in contrast pillow rim sbg is virtually impermeable to seawater and therefore has suffered little or no low temperature alteration out of 21 selected sbg samples with magnetic moment larger than 10 10 am2 18 samples from 12 chilled sbg margins yielded paleointensity estimates of good technical quality rock magnetic measurements show the primary carrier of remanence is low ti titanomagnetite occurring in a continuous range of compositions starting from nearly pure magnetite as suggested by a recent study magnetic hysteresis parameters were monitored during the entire paleointensity experiment and a drastic change of parameters was observed above 400 440 c which is in accordance with the partial thermoremanent magnetization checks failing significantly above the same temperature we suggest that paleointensity estimates obtained below this critical temperature represent true determination of the paleomagnetic field strength for several pillow margins two to three samples were measured and in such cases the data agree well altogether we obtain reliable estimates from 12 sbg pillow rims yielding a mean paleointensity of 27 1 13 4 t and a corresponding virtual axial dipole moment of 5 8 2 8 1022 am2 this value is slightly higher than whole rock data from similar aged subaerial lava flows the paleosecular variation of the intensity estimates is slightly larger than previously reported for paleointensity determinations for the cretaceous normal superchron

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

a mechanism for the poleward propagation of zonal mean flow anomalies abstract observational studies have shown that tropospheric zonal mean flow anomalies frequently undergo quasi periodic poleward propagation a set of idealized numerical model runs is examined to investigate the physical mechanism behind this poleward propagation this study finds that the initiation of the poleward propagation is marked by the formation of negative zonal wind anomalies in the tropics these negative anomalies arise from meridional overturning breaking of waves that originate in midlatitudes this wave breaking homogenizes the potential vorticity pv within the region of negative zonal wind anomalies and also leads to the formation of positive zonal wind anomalies in the subtropics subsequent equatorward radiation of midlatitude waves is halted which results in wave breaking at the poleward end of the homogenized pv region this in turn generates new positive and negative zonal wind anomalies which enables a continuation of the poleward propagation the shielding of the homogenized

size frequency distribution of longitudinal dune rippled flank sands compared to that of slipface sands of various dune types rippled flanks of longitudinal dunes and the slip faces of various dune types can be distinguished granulometrically by comparing the top to bottom trend of changes of sorting in the sand population of each individual slope flank sands which are prone to sorting processes through migration of ripples alongslope are always better sorted upslope whereas slipface sands which are controlled by avalanche and grainfall of sands become better sorted downslope considering the absolute values of the bottom samples the sands of the slip faces are both better sorted and the size distribution more symmetrical than those of the rippled flanks applying this approach in investigating ancient sediments could improve palaeogeographical interpretations

comment on a new high precision furnace for paleomagnetic and paleointensity studies minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers by zhong zheng xixi zhao and chorng shern horng