active flexural slip faulting a study from the pamir tian shan convergent zone nw china the flexural slip fault fsf a type of secondary fault generated by bed parallel slip occurs commonly and plays an important role in accommodating fold growth although the kinematics and mechanics of fsfs are well studied relatively few field observations or geometric models explore its geomorphic expression in the pamir tian shan convergent zone nw china suites of well preserved fsf scarps displace fluvial terraces in the mingyaole and wulagen folds integrating interpretations of google earth images detailed geologic and geomorphic mapping and differential gps measurements of terrace surfaces we summarize geomorphic features that typify these faults and create kinematic models of active flexural slip faulting our study indicates the following i fsf scarps commonly occur near synclinal hinges irrespective of whether a the dip direction of beds on either side of the hinge is unidirectional or in opposite directions b the hinge is migrating or fixed or c the hinge shape is narrow and angular or wide and curved ii active fsfs are likely to produce higher scarps on steeper beds whereas lower or no topographic scarps typify gentler beds iii tilt angles of the terrace surface displaced above fsfs progressively decrease farther away from the hinge with abrupt changes in slope coinciding with fsf scarps the changes in tilt angle and scarp height have a predictable geometric relationship iv active fsfs can accommodate a significant fraction of total slip and play a significant role in folding deformation v active fsfs may be used to assess seismic hazards associated with active folds and associated blind thrusts

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

kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

magnetic susceptibility anisotropy strain and progressive deformation in permian sediments from the maritime alps france abstract the relationships among magnetic susceptibility anisotropy finite strain and progressive deformation have been studied in permian red shales and slates of the maritime alps southeastern france these rocks contain deformed reduction spots which serve as finite strain indicators the magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements the magnetic fabric changes progressively from oblate to prolate and back to oblate as deformation increases the quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined they differ between the less and more deformed areas perhaps due to a change in deformation mechanism accompanying an increase in metamorphism the relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control

detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

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

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

an integrated ams structural palaeo and rock magnetic study of eocene marine marls from the jaca pamplona basin pyrenees n spain new insights into the timing of magnetic fabric acquisition in weakly deformed mudrocks

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

paleomagnetic and geochronological constraints on the post collisional northward convergence of the southwest tian shan nw china a combined paleomagnetic and geochronological study is reported of paleogene basalt lavas and an intercalated red bed succession comprising a minimum of 14 basalt flows and 10 red bed horizons in the tuoyun basin of the southwest tian shan range china two basalt matrix samples yield 40 ar 39 ar isochron ages of 58 5f1 3 ma 2r mswd 0 9 and 60 4f1 3 ma 2r mswd 1 7 these compare well with a previously published k ar dilution age of 61 7f2 3 ma for comparable paleogene basalts and confirm that the younger pulse of magmatism in this basin is represented by both intrusive and extrusive activity demagnetization and component analysis identify a stable characteristic remanence chrm with predominantly reversed polarity following removal of secondary remanence by peak demagnetization steps below 250 350 8c or 5 mt rock magnetic analysis identifies pseudo single domain magnetite or titanomagnetite as carriers the stable chrm passes a fold test it was probably acquired at the time of lava emplacement results from the bulk of the collection imply that paleomagnetic data from the upper and lower 115 ma basalt series in the tuoyun basin are not distinguishable at the 95 significance level and indicate that this tectonic domain remained essentially stationary with respect to the earth s spin axis for 50 ma prior to onset of the india asia collision in early eocene times it is therefore probable that no paleomagnetically detectable crustal shortening occurred in the southwest tian shan prior to collision paleomagnetic data sets from the tuoyun basin also show that little or no paleolatitude difference is present between the tian shan and the reference latitude of eurasia at 60 ma this supports previous evidence suggesting that central asian blocks in the vicinity of the tian shan are unlikely to have experienced appreciable northward convergence relative to eurasia since onset of the india asia collision and initiation of the himalaya d 2005 elsevier b v all rights reserved

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

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

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

a 4 gyr shock age for a martian meteorite and implications for the cratering history of mars analyses of meteorites that originated on mars provide important insights into the geological and atmospheric evolution of the planet such analyses have hitherto been restricted to relatively young martian rocks1 the oldest martian meteorites have an age of approximately 1 3 billion years but the recently recognized2 martian meteorite allan hills 84001 which is distinct from the other martian meteorites2 4 shows evidence for a much older age5 6 here we report an analysis of the shock alteration history of this meteorite based on argon isotope dating from which we derive a shock age of 4 0 0 1 billion years the age and geological history of this meteorite suggest that it came from the heavily cratered noachian age terrains of mars s southern hemisphere and it may thus provide an absolute chronology for this region of the planet independent of that inferred from the cratering record the shock age of the meteorite also coincides with that of the so called lunar cataclysm a relatively short period during which many of the craters on the moon are believed to have formed supporting the idea7 that intense bombardment was widespread throughout the inner solar system between 3 9 and 4 1 billion years ago

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

late cenozoic slip on the talas ferghana fault the tien shan central asia although cenozoic crustal shortening and thickening by thrust faulting have built the present tien shan active right lateral shear on the northwest trending talas ferghana fault appears to be the most rapid localized deformation in the belt ephemeral stream valleys have been offset right laterally tens of metres new and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average holocene slip rate at 18 localities uncertainties allow 14 upper bounds to overlap the range of 8 16 mm yr and 95 confidence limits on such bounds at 11 sites are entirely within this range we infer that the rate of 10 mm yr is not simply an upper bound but applies to the late holocene epoch although the bounds on rates permit more rapid slip in the northwest than the southeast they do not place a useful constraint on variations in slip rate along the fault offsets of paleozoic facies boundaries imply a total right lateral shear of 180 250 km but early cretaceous sedimentary rock appears to have been offset only 60 10 km published paleomagnetic declinations of cretaceous miocene rock demonstrate 20 30 of counterclockwise rotation of the ferghana valley which lies just west of the talas ferghana fault with respect to stable parts of eurasia and 20 11 with respect to the central tien shan east of the fault these declinations are consistent with a maximum northwestward translation of 70 210 km of the ferghana valley at the talas ferghana fault and therefore with a similar maximum horizontal shortening across the chatkal ranges which lie between the ferghana valley and the kazakh platform estimates of crustal thickness beneath the chatkal ranges however permit only 60 100 km of cenozoic shortening if 100 km of slip on the talas ferghana fault accumulated at a constant rate of 10 mm yr it would imply an initiation of slip more recently than ca 10 ma long after india collided with the rest of eurasia

a paleomagnetic study of tertiary formations from the kyrgyz tien shan and its tectonic implications as part of a general investigation of cenozoic deformation in central asia we studied the paleomagnetism of tertiary red beds and lava flows from intermontane basins in the tien shan region of kyrgyzstan we collected 532 cores and hand samples from 78 sites at 12 localities and progressively demagnetized them thermally or with alternating fields for most sites there are magnetic components with unblocking temperatures higher than 600 c we infer that the magnetic carriers are mainly hematite and magnetite for most localities the high temperature component appears to predate tectonic folding for all localities mean inclinations are shallower than expected from apparent polar wander paths inclination anomalies range from 16 5 for the issyk kul basin to 26 7 for the fergana basin if due to changes in latitude these anomalies imply at least 2000 km of northward displacement of the tien shan during the tertiary for which there is no tectonic evidence we thus consider that the paleomagnetic reference directions cannot be directly compared with our tertiary data we explored other possible reasons for this anomaly which has also been reported from other parts of the alpine belt but we could not find a satisfactory explanation absolute rotations cannot be accurately determined because of problems with the reference direction nevertheless the mean declination for the fergana basin lies counterclockwise by 20 11 from the mean declination of the issyk kul basin this result is consistent with the counterclockwise rotation inferred for the fergana basin from the pattern of cenozoic faults and folds it suggests a cenozoic right lateral displacement of 110 60 km on the talas fergana fault

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

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

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

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

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

slip partitioning in the northeast pamir tian shan convergence zone abstract based on a detailed analysis of satellite imagery combined with field geologic and geomorphic observations we have mapped late cenozoic folds and faults in the northeastern pamir tian shan convergence zone it is a unique example to understand intracontinental ongoing mountain building within india eurasia collision system in the front of northeastern pamir our investigations reveal that the nw wnw trending folds display a right stepping en echelon pattern and nw wnw striking faults are mainly characterized by south dipping thrusts with an extensive dextral strike slip component drainage systems across the active faults show a systematic right lateral offset in contrast structural style of the ene trending fold and thrust belts are predominated by south north directed shortening southwest of the tian shan our results also infer that oblique thrusting accommodates as long term dextral slip rate of ca 4 0 mm yr during the late cenozoic time north of the pamir topographic front tectono stratigraphic evidence suggests that the tectonic deformation was initiated at ca 3 5 ma in the study area we suggest that intracontinental mountain building in the pamir tian shan convergence zone should be attributed to the crustal shortening caused by folding and thrusting as well as block rotation related to strike slip faulting within the india eurasia collision system

chassigny and the nakhlites carbon bearing components and their relationship to martian environmental conditions abstract the carbon and nitrogen inventories of chassigny and the nakhlites have been investigated by low resolution 100 c temperature increment stepped combustion in addition the contents and isotopic compositions of carbonate minerals have been assessed by the use of an acid dissolution technique low temperature carbon i e that which combusts below 500 c appears to be from two different sources one component is present in variable quantities 300 700 ppm and has 13 c 26 consistent with identification as terrestrial organic contamination the other is isotopically light with 13 c ca 36 which is unusual for normal sources of terrestrial contamination curiously the latter material is present in each sample in similar concentrations 45 15 ppm since this level of carbon is too high to be ascribed to a system blank it is considered that this component is probably indigenous to the meteorites the low temperature of release of the isotopically light carbonaceous material is testimony to its highly labile nature it is evidently organic material of some description the accompanying low temperature nitrogen also appears to be distributed between two components one with 15 n of ca 6 5 to 2 4 the other with 15 n 4 but it is not yet possible to establish relationships between the nitrogen and carbon components released below 500 c the meteorites investigated were found to contain 2 5 30 ppm carbon as carbonate with 13 c between 5 and 11 and 18 o between 23 and 29 variation in 13 c and 18 o of the carbonates indicates either a change in conditions during formation of the carbonate minerals or that there may be two distinct carbon sources magmatic species which are released on combustion at temperatures above 700 c apparently have an isotopically light carbon isotopic composition between 30 and 20 and are associated with light nitrogen 15 n superimposed on the magmatic species is a release of spallogenically produced isotopically heavy nitrogen seen most clearly in chassigny there is no evidence in any of the samples analysed for trapped martian atmospheric gases

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

paleomagnetism of miocene sediments from the turfan basin northwest china no significant vertical axis rotation during neotectonic compression within the tian shan range central asia abstract paleomagnetic results are reported from 377 samples of miocene red sediments in the turfan basin of east tian shan northwest china thermal demagnetization for most specimens isolates a low temperature component that groups around the present geomagnetic field a high temperature characteristic component is isolated from four localities and interpreted as primary remanent magnetization from apparent pre folding origin and positive reversal test as for previous results obtained from tertiary rocks in central asia the magnetic inclination is significantly shallower than the reference field computed from the eurasian apw path at 10 and 20 ma magnetic susceptibility measured in 324 specimens exhibits low anisotropy of less than 1 05 for 80 of the sample the low anisotropy degrees ams shape and orientations suggest that the studied rocks are unlikely to have undergone significant strain during compaction or tectonism we argue that the shallow inclination is likely to result from an initially shallow detrital remanent magnetization comparison of the paleomagnetic declination from eurasia north china and tarim suggests that the turfan basin has been subjected to little or no vertical axis rotation since the miocene together with paleomagnetic declinations on both sides of the talas ferghana fault we propose that the tian shan to the east of the talas ferghana fault has remained relatively stationary with respect to adjacent blocks since the miocene

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

temporal constraints and pulsed late cenozoic deformation during the structural disruption of the active kashi foreland northwest china 1 in response to the ongoing indo asian collision structural deformation has encroached into the tian shan foreland in western china since the early miocene in order to reconstruct a detailed history of foreland deformation along the southern margin of the tian shan we have synthesized extensive mapping analysis of seismic sections magnetostratigraphy of the foreland fill and associated growth strata apatite fission track dating changes in sediment accumulation rates and geodetic surveys of deformed fluvial terraces across an area exceeding 6500 km2 that spans the kashi foreland in the northwestern tarim basin we use these data to place temporal constraints on individual structures that delineate at least 4 distinct stages of deformation stage 1 involved initial uplift of hinterland structures beginning at 20 25 ma stage 2 began at 16 3 ma when the basement involved deformation front stepped south to the kashi basin thrust that bounds the foredeep strata stage 3 occurred from 13 5 to 4 ma as the deformation front migrated south in episodic steps above thin skinned detachment and ramp flat folding finally stage 4 began after 4 ma with growth of the keketamu anticline followed by rapid southward migration of the deformation front to the atushi and then kashi detachment anticlines on the basis of the deformed tertiary strata and available seismic data calculations of the minimum magnitude of shortening yield totals ranging from 10 to 32 km since the early miocene of which 7 12 km occurred since 4 ma although average shortening rates since 16 3 ma were 0 8 1 3 mm a rates were faster from 16 3 to 13 5 ma 1 1 3 2 mm a after which they decreased to 0 5 mm a between 13 5 and 4 ma before increasing to 2 2 2 7 mm a after 4 ma similarly the rate of southward propagation of the deformation front was initially 3 7 mm a for the first 10 ma of basin development slowed to 1 5 mm a between 13 5 and 4 ma and increased to more than 10 mm a since 4 ma these changes in shortening and structural migration rates over time suggest that the loci of orogenic deformation shifted in and out of the foreland during the neogene surveyed stream terraces suggest that although most current deformation is located along the southern front of the foreland modest deformation and shortening continue in the hinterland structural style within the foreland has also changed over time from imbricate thrust faults with hanging wall folds along the northern margin to ramp flat faults and detachment folds along the southern margin where the basement rocks are previously deformed such as in the hinterland of the kashi foreland thick skinned fault ramps and related fault propagation folds dominate the structural style as syntectonic sedimentation within the foreland produced thick subhorizontal stratigraphy the structural style evolved to detachment and fault bend folding above these footwall flats within the neogene strata

paleomagnetic constraints on neotectonic deformation in the kashi depression of the western tarim basin nw china a paleomagnetic study is reported of eocene to pliocene formations from the kashi depression which aims to constrain the pattern of neotectonic deformation within the western sector of the tarim basin in northwest china with the exception of pliocene specimens from one locality east kulukeqiati which show large within site mean variations in declination most sites from five sampled formations yield well grouped characteristic remanent magnetizations and positive fold tests and are of probable post depositional detrital origin first order consistency of paleomagnetic results from a range of rock ages and localities demonstrates that only small inter locational vertical axis rotation has occurred here and indicates that the kashi depression is decoupled from the remainder of tarim to the east and has behaved as a quasi rigid block which has rotated by 20 30 counterclockwise relative to eurasia and north china since the late pliocene the crustal scale talas ferghana fault cuts the tian shan and meets the kashi depression in the region immediately to the northwest of the study region and we find no paleomagnetic evidence for differential rotations to suggest that this fault zone extends southwards across the kashi depression to link with the north pamir thrust fault nptf instead we argue that the southern extension of this zone is a transform orogen junction with southward motion of the eastern wall accommodated by southward thrusting at the margins of the south tian shan and the tarim basin we propose that dextral transpression around the margins of the crustal block incorporating the kashi depression was responsible for the contrasting amounts of thrusting on the nptf in the southwest and the south tian shan thrust fault in the north extensive evidence for neotectonism in the bordering zones of this block as well as some paleomagnetic evidence from low unblocking temperature components indicates that the deformation produced by block rotation is ongoing

calcium carbonate and sulfate of possible extraterrestrial origin in the eeta 79001 meteorite abstract two varieties of ca carbonate were found in a total of three interior 2 cm depth samples of glass inclusions from the shergottite meteorite elephant moraine antarctica a79001 two of the samples including the largest deposit around a vug near the center of the meteorite 8 cm depth contained veins of granular calcite with significant magnesium avg atomic mg mg ca 0 14 0 15 and phosphorus avg atomic p ca 0 04 either as mg calcite with dissolved p or as calcite with very finely intergrown mg bearing phosphate the second variety which occurred in a third sample with a previously documented high concentration of trapped gases consisted of disseminated 10 20 m anhedral grains of nearly pure caco3 and was intimately associated with laths and needles of ca sulfate possibly gypsum the coexisting carbonate and sulfate appeared to be partially decrepitated relict grains that were trapped during rapid solidification of quench textured pyroxene and glass for at least the latter occurrence textural relationships clearly indicate a pre terrestrial origin for the salts all evidence considered it is probable that both varieties of cacarbonate and the ca sulfate formed on a planetary body probably mars before the meteorite fell on earth

temperature dependence of magnetic susceptibility in an argon environment implications for pedogenesis of chinese loess palaeosols summary temperature dependence of magnetic susceptibility t has been widely used to determine changes in mineralogy of natural samples during heat treatment we carried out integrated rock magnetic experiments to interpret the t curves of the chinese loess palaeosols in argon we used both raw materials and heated samples in addition we also investigated the magnetic properties of magnetic extracts and residues to quantify contributions from each fraction to the bulk magnetic properties for the heating curves the susceptibility loss 30 per cent between 300 400 c is caused by the inversion from pedogenic fine grained maghemite to haematite suggesting that the susceptibility loss can be used as a new concentration index of the pedogenic fine grained superparamagnetic sp particles in the chinese loess palaeosols unlike the warming curves the cooling curves are dominated by newly formed fine grained magnetites with a dominant size of 35 nm the onset for the new production of these fine grained magnetic particles occurs at 400 c it is interesting that the room temperature magnetic susceptibility ph of the samples heated after a 700 c run is independent of the degree of pedogenesis and saturates at approximately 33 35 10 7 m3 kg 1 indicating that the susceptibility enhancement is controlled only by the reduction of fe bearing aeolian minerals during heating it appears that the 700 c thermal treatment in argon could be in some sense an analogue to the pedogenic processes thus we predict that 33 35 10 7 m3 kg 1 is the maximum susceptibility that pedogenesis can generate for the last interglacial palaeosol unit s1 in practice ph would be useful to quantify the aeolian inputs to the chinese loess plateau

magnetochronology of the upper cenozoic strata in the southwestern chinese tian shan rates of pleistocene folding and thrusting abstract the southwestern chinese tian shan of central asia is an actively deforming part of the indian asian collision system paleomagnetic investigations of two plio pleistocene terrestrial successions provide the first detailed magnetostratigraphy for the upper cenozoic strata in this region paleomagnetic samples were collected from 358 sites within the atushi formation and xiyu formation across the atushi talanghe anticline near atushi thermal demagnetization behavior reversal and fold tests of paleomagnetic stability indicate that the characteristic remanence directions were acquired before tilting and folding of the strata a composite magnetostratigraphic section for this sequence correlates with the mammoth subchron to the jaramillo subchron between 3 3 and 1 07 myr of the geomagnetic polarity timescale of cande and kent j geophys res 100 1995 6093 6095 the mean declination 349 3 in the boguzihe section indicates a counterclockwise vertical axis rotation 11 2 during the past 1 4 myr the conglomeratic xiyu formation is time transgressive along its progradational contact with the underlying atushi formation across a map distance of 6 km the basal contact ranges from less than 1 0 myr in the ganhangou section to 1 9 myr in the boguzihe section to the southwest and to 2 8 myr on the northwest limb of the anticline northeastward lateral propagation and growth of the atushi talanghe anticline initiated at 1 4 myr in the boguzihe and 1 2 myr in the ganhangou the cross section in the boguzihe provides a conservative maximum estimate of shortening rate of 3 3 4 4 mm yr and uplift rate of 3 mm yr this rate represents about half of the geodetically determined shortening rate between the northern tarim basin and the kyrgyz tian shan wang et al acta seismol sin 22 2000 263 270 reiger et al earth planet sci lett 191 2001 157 165 during fold growth over the past 1 4 myr the crest of the atushi talanghe anticline eroded at an average rate of 2 6 2 7 mm yr

hinge migrated fold scarp model based on an analysis of bed geometry a study from the mingyaole anticline southern foreland of chinese tian shan 2015 american geophysical union all rights reserved fold scarps a type of geomorphic scarp formed by folding mechanisms of hinge migration or limb rotation serve to delineate both fault bend characteristics and folding histories which can in turn illuminate tectonic processes and seismic hazards associated with thrust systems because the subsurface geometry of folds is commonly difficult to determine existing fold scarp models which rely on both the fold type and its causative fault geometries remain uncertain with respect to the kinematic evolution of a given fold in this paper we develop a model to illustrate that irrespective of specific fold type and subsurface geometries fold scarp growth in the mechanism of hinge migration can be successfully reconstructed based on analyses of bed geometry this model reveals that the underlying bed dips and the ratio of hinge migration distance hinge width control the fold scarp shape and slope during initial growth ratio 1 the slope reaches a maximum which solely depends on underlying bed dips the scarp height however is independent of the hinge width and can be used to quantify folding magnitude application of our model to fold scarps in the mingyaole anticline in the southern foreland of chinese tian shan indicates that the modeled fold scarp geometry can roughly match with field observations the mingyaole shortening rate is estimated to be 5 0 mm a since 15ka such that this single fold has accommodated about half of the regional convergence during the holocene key points folding through curved hinges creates a distinctive fold scarp geometry scarp slope relies on ratio of hinge migration width but scarp height is not shortening rate of the mingyaole fold is estimated to be 5 0 mm a since 15 ka such that this single fold has accommodated about half of the regional convergence during the holocene

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

tertiary evolution of the western tarim basin northwest china a tectono sedimentary response to northward indentation of the pamir salient 1 this paper deals with the tertiary tectonic and sedimentary evolution of the western tarim basin based on an integrated stratigraphic sedimentary structural and tectonic analyses basin evolution is divided into three stages paleogene miocene and pliocene the western tarim basin was the easternmost part of the tethyan realm from late cretaceous to paleogene and marine sedimentation continued into the early miocene miocene development of the western tarim basin was chiefly governed by west kunlun right slip faulting and the simultaneous northward thrusting of the pamir salient and tianshuihai terrane yecheng subbasin developed as a pull apart basin owing to synchronous activity of the west kunlun and the shache yangdaman right slip faults hotan foreland basin formed in response to northward displacement of the tianshuihai terrane and another might have developed in front of the advancing pamir salient in the miocene basinward thrusting became predominant in the orogenic belts adjacent to the western tarim basin in the pliocene north directed displacement and uplift of the tiklik thrust terrane fragmented the preexisting hotan foreland basin and collision of the pamir with the southern tian shan deformational fronts caused complete destruction of the miocene pamir foreland basin eastward displacement of the qimugen fold thrust system led to flexural subsidence of the yecheng subbasin in the pliocene kashi subbasin developed as part of the southern tian shan foreland basin and was controlled by the eastern pamir as well a tectonic scenario is proposed to illustrate complicated interplay of the western tarim basin with its peripheral orogens in the tertiary

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

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

anisotropy of magnetic susceptibility ams records synsedimentary deformation kinematics at pico del aguila anticline pyrenees spain

neotectonic deformation in the southwestern tian shan western china evidence from paleomagnetic study of quaternary sediments from the mingyaole anticline

isotopic composition of carbonates in the snc meteorites allan hills 84001 and zagami we have measured the 13 c 12 c and 14 c 12 c ratios in co 2 released by acid etching of the meteorites zagami and allan hills 84001 we use the 14 c as a label to identify extraterrestrial carbonate phases as they will have a low 14 c 12 c ratio 4 modern terrestrial ratio compared to recent terrestrial material the new studies on allan hills 84001 confirm previous conclusions that the fe mg rich carbonate grains in this meteorite contain carbon with 13 c as high as 45 in contrast the carbon released from zagami is depleted in 13 c with 13 c as low as 20 we conclude that the isotopic composition of the carbon as carbonate released from acid etching of zagami is different from the carbonates observed in both allan hills 84001 and nakhla with the assumption that all of these meteorites sample the surface of mars we propose that the zagami carbonate samples a different carbon reservoir on this planet such as a magmatic source with this interpretation the high 13 c values of carbonate observed in allan hills 84001 and nakhla can be ascribed to a fractionated source compared with the originally light carbon a likely origin for this 13 c enriched component is an isotopically heavy martian atmosphere however given the possibility of biological activity involving allan hills carbonates we cannot exclude this as a source of the isotopic fractionation

equivalency of geologic and geodetic rates in contractional orogens new insights from the pamir frontal thrust across contractional orogens the equivalency between decadal convergence rates from geodetic gps data and geologic shortening rates at time scales of thousands or millions of years has rarely been documented here we present an example from the northern margin of chinese pamir where the main pamir thrust is tectonically quiescent and recent deformation is concentrated on the pamir frontal thrust pft based on dated and faulted fluvial terraces magnetostratigraphy and mapping the horizontal shortening rate of the pft is 6 7 mm a at time scales of both 18 4 ka and 0 35 ma comparable to the geodetic rate of 6 9 mm a across the same zone implying that modern geodetic rates are a reasonable proxy for geologic rates since 0 35 ma comparing this example with studies in other contractional orogens we conjecture that a match or mismatch of geologic geodetic rates typically depends on the time scale of observation fault geometry and fault mechanics 2012 by the american geophysical union