late oligocene early miocene birth of the taklimakan desert as the world s second largest sand sea and one of the most important dust sources to the global aerosol system the formation of the taklimakan desert marks a major environmental event in central asia during the cenozoic determining when and how the desert formed holds the key to better understanding the tectonic climatic linkage in this critical region however the age of the taklimakan remains controversial with the dominant view being from 3 4 ma to 7 ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert in this study we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy we constrained the initial desertification to be late oligocene to early miocene between 26 7 ma and 22 6 ma we suggest that the taklimakan desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts both of which are closely linked to the tectonic uplift of the tibetan pamir plateau and tian shan which had reached a climatically sensitive threshold at this time

radionuclide migration in strongly fissured zones the sensitivity to some assumptions and parameters radionuclides escaping from a repository for high level nuclear waste in crystalline rock may eventually be carried by the flowing water in fissure zones in such zones the rock is broken into blocks of varying sizes and shapes also the water velocity may vary considerably in such zones a previously developed model which lumps the different blocks into a single pseudobody is tested by comparing it with an exact analytical solution which can account for the diffusion into blocks of any size distribution the approximate simplified model which is based on a numerical scheme and thus is more versatile gives errors which are small compared to the normal variation in observed block size distributions and other data a method for determining an average peclet number or dispersion length in a strongly varying velocity field is tested and found to give small errors compared to the present confidence limits in predicting dispersion data for large migration distance a simple criterion is proposed for defining the cutoff limit in the block size distribution below which the blocks can be modeled as if they were in equilibrium with the flowing water a simple sensitivity analysis shows that much can be gained if the confidencemore limits for block size distribution water flow rate dispersion data sorption data and matrix diffusion data can be narrowed down less

miocene volcaniclastic sequence within the xiyu formation from source to sink implications for drainage development and tectonic evolution in eastern pamir nw tibetan plateau

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

palynological evidence for the latest oligocene early miocene paleoelevation estimate in the lunpola basin central tibet uplift of the tibetan plateau is ultimately driven by the cenozoic collision between the indian and eurasian plates and their continued convergence one approach for studying the tibetan plateau uplift is to verify the paleoelevation changes from collision to present day this is important for understanding both the tectonics and the climatic effects the new high resolution palynological record of the uppermost oligocene to the lowest miocene strata from the lunpola basin indicates that the vegetation types during the latest oligocene earliest miocene were dominated by mixed coniferous broadleaved forests being different from the modern steppe vegetation by using the coexistence approach to the fossil pollen records after calibration the effects of temperature difference and the lapse rate a maximum paleoelevation of 3190 100 m asl was estimated in the lunpola basin in the latest oligocene earliest miocene being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

identifying eolian dust in the geological record abstract recognition of terrestrial dust in geological records is essential for reconstructing paleoenvironments and quantifying dust fluxes in the past however in contrast to eolian sands silt sized dust is difficult to recognize in pre quaternary records due to a lack of macroscopic features indicating eolian transport and mixing with alluvial sediments windblown dust deposits are commonly identified by comparing their sedimentological and petrological features with quaternary examples of dust known as loess here we review the characteristics of terrestrial dust deposits and conclude that most of these features are not exclusively windblown and may be formed by alluvial deposits as well we therefore synthesize a set of criteria which enable a reliable identification and quantification of dust while acknowledging potential contributions of alluvial components these methods include quartz grain surface morphology analysis to distinguish eolian and alluvial transport modes provenance studies to identify local and extrabasinal sources grain size shape end member modelling to quantify the various sedimentary contributions to the record and a basin scale stratigraphic approach to derive regional patterns and avoid interpretation of local phenomena we reassess the eocene to pliocene records of the chinese loess plateau and conclude that these strata represent both alluvial and eolian sediments deposited in extensive mudflat systems quaternary loess by contrast is almost exclusively composed of windblown dust the early pleistocene shift from mudflat to loess deposits is associated with a significant increase in accumulation rates likely due to increased dust production upwind overwhelming and blanketing the local mudflat systems in central china

indentation of the pamirs with respect to the northern margin of tibet constraints from the tarim basin sedimentary record the pamirs represent the indented westward continuation of the northern margin of the tibetan plateau dividing the tarim and tajik basins their evolution may be a key factor influencing aridification of the asian interior yet the tectonics of the pamir salient are poorly understood we present a provenance study of the aertashi section a paleogene to late neogene clastic succession deposited in the tarim basin to the north of the nw margin of tibet the west kunlun and to the east of the pamirs our detrital zircon u pb ages coupled with zircon fission track bulk rock sm nd and petrography data document changes in contributing source terranes during the oligocene to miocene which can be correlated to regional tectonics we propose a model for the evolution of the pamir and west kunlun wkl in which the wkl formed topography since at least 200 ma by 25 ma movement along the pamir bounding faults such as the kashgar yecheng transfer system had commenced marking the onset of pamir indentation into the tarim tajik basin this is coincident with basinward expansion of the northern wkl margin which changed the palaeodrainage pattern within the kunlun progressively cutting off the more southerly wkl sources from the tarim basin an abrupt change in the provenance and facies of sediments at aertashi has a maximum age of 14 ma this change records when the pamir indenter had propagated sufficiently far north that the north pamir was now located proximal to the aertashi region

late neogene loess deposition in southern tarim basin tectonic and palaeoenvironmental implications abstract uplift of the tibetan plateau during the late cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the kunlun and altyn mountains in the southern tarim basin early neogene sediments are characterised by sandstone siltstone and red mudstone representing floodplain to distal alluvial fan environments the early pliocene artux formation consists of medium grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone the late pliocene to early pleistocene xiyu formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits sedimentological investigation together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the xiyu and artux formations point to an aeolian origin suggesting desertic conditions in the tarim basin by the early pliocene the onset of aeolian sedimentation in the southern tarim basin coincided with uplift of the northern tibetan plateau inferred from the lithofacies change from fine grained mudstone and sandstone to coarse clasts tibetan plateau uplift resulted in the shift of sedimentary environments northwards into the southern tarim basin and could well have triggered the onset of full aridity in the taklimakan region as a whole

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

late oligocene to early miocene humidity change recorded in terrestrial sequences in the ili basin south eastern kazakhstan central asia enhanced aridification of central asia driven by the combined effects of orogenic surface uplift paratethys retreat changes in atmospheric moisture transport and global cooling is one of the most prominent cenozoic climate change events of the northern hemisphere deciphering regional long term patterns of central asian hydrology is therefore a key element in understanding the role of northern hemisphere mid latitude drying in the global hydrological system this study characterizes long term palaeoenvironmental conditions between the late oligocene and early miocene in south eastern kazakhstan based on stable isotopes elemental geochemistry and laser ablation uranium lead geochronology from alluvial fluvial and pedogenic deposits sedimentary facies and geochemical weathering indices suggest an increased surface and ground water discharge fed by orographically enhanced precipitation in the tien shan hinterland in contrast pedogenic stable isotope data and elevated rates of magnesium fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification this study posits that pronounced surface uplift of the tien shan mountains during the oligocene miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems this article is protected by copyright all rights reserved

the role of the westerlies and orography in asian hydroclimate since the late oligocene interactions between midlatitude westerlies and the pamir tian shan mountains significantly impact hydroclimate patterns in central asia today and they played an important role in driving asian aridification during the cenozoic we show that distinct westeast hydroclimate differences were established over central asia during the late oligocene ca 25 ma as recorded by stable oxygen isotopic values of soil carbonates our climate simulations show that these differences are present when relief of the pamir tian shan is higher than 75 of modern elevation 3000 m integrated with geological evidence we suggest that a significant portion of the pamir tian shan orogen had reached elevations of 3 km and acted as a moisture barrier for the westerlies since ca 25 ma

cenozoic right slip faulting along the eastern margin of the pamir salient northwestern china the pamir salient defines the western end of the himalayan tibetan orogen and has overthrust the tarim tajik basin to the north by 300 km along a late cenozoic south dipping intracontinental subduction zone field mapping structural measurements and analysis of mesoscale structures along a 32 km long reach of the yarkand river document the tectonic evolution of the east flank of this salient between the north pamir to the west and the western kunlun shan to the east the study area is cut by a set of four north northwest striking steeply dipping brittle faults microstructures and asymmetric outcrop to map scale folds indicate right slip along these faults between these structures fault bounded panels of phanerozoic strata are deformed by en echelon folds with axes that trend more westerly than the adjacent faults consistent with dextral transpression the fault system described here extends for 350 km along the eastern flank of the pamir salient transpressional right slip along this set of faults here called the kashgar yecheng transfer system appears to have accommodated late cenozoic separation of the north pamir from the western kunlun shan during south directed intracontinental subduction beneath the leading edge of the pamir salient correlation of major faults suggests total slip along the kashgar yecheng transfer system is likely on the order of 280 km this offset estimate implies long term slip rates of 7 15 mm a along the kashgar yecheng transfer system when combined with previous sedimentologic stratigraphic and thermochronologic data that indicate deformation along the east flank of the pamir started between the late eocene and early miocene these results imply that the first order structures on the western and eastern flanks of the pamir are asymmetric previous work has shown that deformation in the west was accommodated by anticlockwise vertical axis rotation of the pamir over the eastern margin of the tajik basin this rotation is generally interpreted to reflect northwest directed radial thrusting in contrast to the transpressional right slip transfer faulting on the east side reported here

the interplay between climate and tectonics during the upward and outward growth of the qilian shan orogenic wedge northern tibetan plateau abstract mountains grow upward and outward when the accretion of material outpaces its removal mountain building is synergistically influenced by geodynamics internal structures crustal and lithospheric and climate the northward growth of the qilian shan which occupies a transition zone between the 4500 m high central tibetan plateau and the adjacent

cenozoic episodic uplift and kinematic evolution between the pamir and southwestern tien shan abstract the pamir salient and southwestern tien shan belong to two different systems which collided due to the continuous northward drift of the indian plate during the cenozoic resulting in a shortening of 300 km the uplift history and kinematic evolution of the pamir southwestern tien shan remain unclear in this study we chose the 2025 m thick pakabulake formation in the east wuqia section at the southern most margin of the southwestern tien shan system to obtain a high resolution magnetostratigraphic record spanning 16 61 ma to 9 78 ma based on its high sedimentation rate stable ca e w paleocurrents and stable magnetic susceptibility values the nearby southwestern tien shan was inferred to have undergone stable uplift during this period of sedimentation combining our results with the previous low temperature thermochronology magnetostratigraphy and re calculated block rotations we conclude that four episodic uplift events occurred in the pamir southwestern tien shan during the cenozoic at times of 50 40 ma 35 16 ma 11 7 ma and

the provenance of taklamakan desert sand sand migration in the vast taklamakan desert within the tarim basin xinjiang uyghur autonomous region pr china is governed by two competing transport agents wind and water which work in diametrically opposed directions net aeolian transport is from northeast to south while fluvial transport occurs from the south to the north and then west to east at the northern rim due to a gradual northward slope of the underlying topography we here present the first comprehensive provenance study of taklamakan desert sand with the aim to characterise the interplay of these two transport mechanisms and their roles in the formation of the sand sea and to consider the potential of the tarim basin as a contributing source to the chinese loess plateau clp our dataset comprises 39 aeolian and fluvial samples which were characterised by detrital zircon u pb geochronology heavy mineral and bulk petrography analyses although the inter sample differences of all three datasets are subtle a multivariate statistical analysis using multidimensional scaling mds clearly shows that tarim desert sand is most similar in composition to rivers draining the kunlun shan south and the pamirs west and is distinctly different from sediment sources in the tian shan north a small set of samples from the junggar basin north of the tian shan yields different detrital compositions and age spectra than anywhere in the tarim basin indicating that aeolian sediment exchange between the two basins is minimal although river transport dominates delivery of sand into the tarim basin wind remobilises and reworks the sediment in the central sand sea characteristic signatures of main rivers can be traced from entrance into the basin to the terminus of the tarim river and those crossing the desert from the south to north can seasonally bypass sediment through the sand sea smaller ephemeral rivers from the kunlun shan end in the desert and discharge their sediment there both river run off and wind intensity are strongly seasonal their respective transport strength and opposing directions maintain the taklamakan in its position and topography

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

asian dust from land to sea processes history and effect from modern observation to geological records production transport and deposition of aeolian dust from land to sea closely interact with regional environment and global climate this special issue addresses transport of aeolian dust from the asian inland to the loess plateau and north pacific ocean and their possible links to oceanic ecosystem global climate and even human activity over various timescales the papers in this volume are multidisciplinary in nature and include sedimentology mineralogy geochemistry environmental magnetism and climate modelling on multi timescales from interannual glacial interglacial to tectonic timescales based on modern observation geological records and modelling this special issue offers new insights especially into aeolian provenance dynamics controls on dust production a novel marine aeolian proxy as well as long term aeolian input to the marginal basins of ne asia and its influence on oceanic productivity this issue provides a good example for future comprehensive studies of source to sink processes of asian dust from land to sea

astronomical forcing of terrestrial climate recorded in the pleistocene of the western tarim basin nw china abstract astronomically forced variations of climate are well documented in lacustrine and marine settings however few studies have examined astronomical forced cycles within quaternary fluvial fan successions to explore whether milankovitch cyclicity might also be present in fluvial fan successions we carried out high resolution gamma ray gr from downhole logging magnetic susceptibility ms rb sr and total organic carbon toc analysis of a core from an 800 m borehole kt11 from the kashgar region in the western tarim basin china spectral analyses of the gr ms and rb sr data reveal cycles with 70 m 30 m and 14 m wavelengths these pertain to relative variations in grain size electron spin resonance esr dating and magnetostratigraphy imply that the cored interval spans the past 1 1 myr this age span constraint coupled with the comparison of the ratios of these cycle wavelengths to expected ratios of milankovitch frequencies suggests that these cycles represent 100 kyr short eccentricity 40 kyr obliquity and 20 kyr precession frequencies respectively we constructed an astronomical time scale ats spanning the past 1 13 myr using the 100 kyr short eccentricity period the average accumulation rate is about 70 cm kyr for this 800 m core succession and the evolutive spectrum emphasizes that long term sedimentation rates were stable we also applied correlation coefficient coco analysis to identify the astronomical forcing thus we conclude that orbitally forced climate change was the main driver of stratigraphic alternations between sand and clay rich intervals in the kashgar region during maxima of the 100 kyr short eccentricity cycles which correspond to interglacial intervals more chemical weathering and increased seasonal runoff delivered a larger amount of relatively coarser grained sediments to the fluvial fan in the kashgar region and vice versa the mid pleistocene transition mpt at ca 0 9 to 0 65 ma is also well recorded in our gr and rb sr data and is characterized by a shift in dominant cycle period from 41 kyr obliquity to 100 kyr eccentricity after 0 65 ma the average toc content decreases whilst rb sr values increase which suggests that there was an increase in regional aridity of the kashgar region in the western tarim basin following the mpt this regional change is synchronous with the trend toward aridification observed throughout central asia

new paleomagnetic constraints on syntectonic growth strata in the western qaidam basin ne tibetan plateau abstract accompanied by crustal shortening and mountain uplift caused by the large magnitude south north directed shortening under the collision between india and eurasia syntectonic growth strata in the western qaidam basin document important information about intense intracontinental deformation of the ne tibetan plateau to better address the development of the qaidam basin and the propagation of the growth strata associated with multiple tectonic uplifts of the tibetan plateau we conducted a detailed paleomagnetic study on the late neogene fluvio lacustrine sedimentary sequence exposed at two outcrop sections and a drill core in the western qaidam basin and integrated the results with previous magnetostratigraphic studies based on well determined ages of the centers and limbs of the two anticlines we found an episodic late cenozoic crustal shortening in the center of the western qaidam basin as evidenced by syntectonic offlap growth strata deposited beginning at 3 2 ma combined with data from sedimentary facies and seismic profiles we suggest that offlap growth strata progressively became younger from southwest to northeast in the center of the western qaidam basin due to strong basinward propagation of the eastern kunlun fault and quick short lived pulses of multiple tectonic uplifts of the ne tibetan plateau

palaeomagnetic and palaeoenvironmental study of two parallel sections of late cenozoic strata in the central taklimakan desert implications for the desertification of the tarim basin abstract due to marine recession and stepwise uplift of the tibetan plateau during the cenozoic era an extremely arid environment and large deserts developed progressively in the interior of asia the tarim basin is a typical region that experienced this type of palaeoenvironmental evolution in this study we apply high resolution palaeomagnetic dating esr dating and palaeoenvironmental reconstruction to two parallel sections from an almost 1000 m thick sequence of terrestrial sediments in the central tarim basin in order to characterize and date the process of drying and desertification our results indicate that the western tarim basin started to accumulate terrestrial sediments in a dry land environment at the latest by 4 2 ma and that the initial desert was formed by 3 4 ma from fluvial sands originating from the tibetan plateau when the climate became particularly dry in the interior of asia due to the uplift of the tibetan plateau variations of the stratum properties including colour index and magnetic susceptibility indicate that the aridification trend was significantly intensified at 2 6 ma coincident with the onset of the northern hemisphere glaciations and consequently forming the present desert regime

spatial and altitudinal variations in the magnetic properties of eolian deposits in the northern tibetan plateau and its adjacent regions implications for delineating the climatic boundary abstract delineating the climatic boundary i e of precipitation and temperature in the northern tibetan plateau and along its margins is important for understanding the dynamics of global atmospheric circulation and the processes of dust production in central asia to date however meteorological data are scarce for this vast region which limits our understanding of regional climatic patterns and past climatic changes in eurasia in the present study we use a synthesis of both new and published rock magnetic data from the late pliocene the last glacial interglacial cycle and modern eolian sediments to identify the climatic boundary in the northern tibetan plateau and its adjacent areas the results demonstrate that eolian deposits under different environmental scenarios exhibit a clear contrast in the type and grain size distribution of magnetic minerals with the transition from humid to arid climatic regimes a gradual shift from magnetic minerals of predominantly pedogenic origin to predominantly detrital origin can be observed in the surface soils the spatial and altitudinal variations in the magnetic properties of surface soils reveal a distinct boundary of pedogenic intensity in the eastern qilian mountains the western pamir plateau and the northern tianshan mountains the inferred variations in pedogenic intensity combined with analysis of the available meteorological data demonstrate that the pedogenic boundary represents a critical climatic boundary between sub humid to semi arid and arid regions in the northern tibetan plateau and the adjacent regions stronger pedogenesis occurs in surface soils at higher altitudes on the windward side of the major mountains of the northern tibetan plateau supporting the conclusion that precipitation rather than temperature exerts the dominant effect on the magnetic enhancement of surface soils in addition a comparison of several late pliocene pleistocene and last glacial interglacial loess red clay sequences suggests that the modern spatial pattern of the climatic gradients in the northeastern tibetan plateau and the adjacent regions has been maintained since at least the late pliocene or early pleistocene moreover the results demonstrate that during the warm and humid interglacial periods a steepened rainfall gradient occurred in the northern tibetan plateau and its adjacent regions in the future detailed rock magnetic investigations of eolian deposits or surface soils could provide new insights into the dynamics of atmospheric circulation and the natural boundary conditions for paleoclimate modeling in the northern tibetan plateau

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

the age of the taklimakan desert the taklimakan desert is located in the foreland basin of the tibetan plateau we report here the results of stratigraphic investigations of a 1626 meter thick sequence with interbedded wind blown silt from the southern marginal taklimakan desert because the studied section is located downwind of the desert the eolian silt accumulation is closely linked to desert formation our new evidence indicates that shifting sand dunes prevailed in the tarim basin by at least 5 3 million years ago as they do today we attribute this event to late cenozoic climatic deterioration as well as to changes in atmospheric circulation induced by tibetan plateau uplift

sensitivity of eurasian climate to surface uplift of the tibetan plateau experiments with climate models are used to illustrate how earth s climate could be expected to change if surface uplift occurred the experiments contrast two climate simulations one with all continents at sea level and one with present day mountains and plateaus the simulations in the eurasia sector show that surface uplift increased elevation produces marked increases in the intensity of summer and winter monsoons of asia with development of wetter climates to the south and east of the tibetan plateau and drier climates to the north and west of the plateau there is a general cooling in northern polar latitudes comparison of simulations from two different models shows that the magnitude of the simulated changes depends upon how the models calculate the land surface hydrology and the ocean temperature the simulated changes produced by surface uplift agree in a general way with many geologic indicators of late cenozoic climate change the results suggest that surface uplift of mountains and platea

confirmation of a late miocene subchron c4n 2n 1r from the eastern qaidam basin in the ne tibetan plateau

late cenozoic fire enhancement response to aridification in mid latitude asia evidence from microcharcoal records fire provides an important indicator of paleoclimatic change however little information relating to late cenozoic fire history has been gathered in mid latitude asia including inner asia and east asia a key region for understanding the development of the arid monsoon climate system as well as the driving forces behind it here we first report the records of microcharcoal concentrations mc covering the holocene 10 0 ica and late pleistocene 0 8 0 ma which we use to analyze the fire activity patterns at an orbital time scale then we compile the late cenozoic mc record to investigate the long term fire history by analyzing four cores from the yangtze river delta yrd area east asia representing 8 0 ma and three sites in inner asia representing 18 2 ma the results show that the i mc remained higher during the relatively dry late holocene glacial stages than that during the humid middle holocene interglacial stages at individual sites ii mc increased with time in both inner asia and east asia after 18 and 8 ma respectively and iii mc always remained higher in the dry inner asia than in the contemporaneous wet east asia all these characteristics imply that late cenozoic fire occurrence in mid latitude asia experienced a gradual increasing trend along with the global temperature ice volume change and indicates a continuous aridification trend across mid latitude asia the global cooling rather than the tibetan plateau uplift might have played a key role in this observed trend c 2016 elsevier ltd all rights reserved

geologic offsets across the northern karakorum fault implications for its role and terrane correlations in the western himalayan tibetan orogen abstract while the 1000 km long karakorum right slip fault is one of the most prominent structures in the himalayan tibetan orogen considerable disagreement exists as to the total magnitude of offset across the fault and the role it has played in accommodating convergence between india and asia using satellite images i have correlated a well defined carbonate unit the late triassic early jurassic aghil formation across the northern portion of the karakorum fault from the southwest pamir to the tianshuihai terrane of western tibet the northern and southern exposure limits of the aghil formation have 149 167 km of separation which i interpret to represent the magnitude of displacement on the northern karakorum fault these values overlap with estimates correlating the bangong nujiang and shyok sutures across the central karakorum fault and maximum offsets of the miocene baltoro granite and rule out correlations of the bangong nujiang suture and the rushan pshart suture the displacement yields a geologic slip rate of 10 8 1 3 mm yr using an initiation age of 14 7 1 ma or 6 89 0 8 mm yr with an initiation age of 23 1 ma this result supports previous work showing limited offset across the karakorum fault and indicates that the fault that has not accommodated either large magnitudes i e 100 s of km of eastward lateral extrusion of tibet or hundreds of kilometers of offset between terranes of the western and central portions of the orogenic belt

timing cause and impact of the late eocene stepwise sea retreat from the tarim basin west china abstract a vast shallow epicontinental sea extended across eurasia and was well connected to the western tethys before it retreated westward and became isolated as the paratethys sea however the palaeogeography and the timing of this westward retreat are too poorly constrained to determine potential wider environmental impacts let alone understanding underlying mechanisms of the retreat such as global eustasy and tectonism associated with the indo asia collision here an improved chronostratigraphic and palaeogeographic framework is provided for the onset of the proto paratethys sea retreat at its easternmost extent in the tarim basin in western china is provided five different third order sea level cycles can be recognised from the cretaceous palaeogene sedimentary record in the tarim basin of which the last two stepped successively westwards as the sea retreated after the maximum third incursion new biostratigraphic data from the fourth and fifth incursions at the westernmost margin of the tarim basin are compared to our recent integrated bio magneto stratigraphic results on the fourth incursion near the palaeodepocentre in the south western part of the basin while the fourth incursion extended throughout the basin and retreated at 41 ma base c18r the last and fifth incursion is restricted to the westernmost margin and its marine deposits are assigned a latest bartonian early priabonian age from 38 0 to 36 7 ma near top c17n 2n to base c16n 2n similar to the fourth the fossil assemblages of the fifth incursion are indicative of shallow marine near shore conditions and their widespread distribution across eurasia suggests that the marine connection to the western tethys was maintained the lack of diachronicity of the fourth incursion between the studied sections across the southwest tarim basin suggests that the sea entered and withdrew relatively rapidly as can be expected in the case of eustatic control on a shallow epicontinental basin however the westward palaeogeographic step between the fourth and fifth incursions separated by several millions of years rather suggests the combined long term effect of tectonism possibly associated with early uplift of the pamir kunlun shan thrust belt the fourth and fifth regressions are time equivalent with significant aridification steps recorded in the asian interior thus supporting climate modelling results showing that the stepwise sea retreat from central asia amplified the aridification of the asian interior

oceanic style subduction controls late cenozoic deformation of the northern pamir orogen abstract the northern part of the pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent continent collision such zones are the least understood type of plate boundaries because modern examples are few and of limited access and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes in the pamir it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate bounding main pamir thrust mpt which forms the principal northern mountain and deformation front of the pamir however the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the mpt experienced relatively minor amounts of late cenozoic exhumation the pamir orogen as a whole is an integral part of the overriding plate in a subduction system while the remnant basin to the north constitutes the downgoing plate with the bulk of the convergence accommodated by underthrusting herein we demonstrate that the observed deformation of the upper and lower plates within the pamir alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback subduction erosion subduction accretion and marginal slab tear faults we suggest that the curvature of the north pamir is genetically linked to the short width and rollback of the south dipping alai slab northward motion indentation of the pamir is accommodated by crustal processes related to this rollback the onset of south dipping subduction is tentatively linked to intense pamir contraction following break off of the north dipping indian slab beneath the karakoram

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

late neogene aridification and wind patterns in the asian interior insight from the grain size of eolian deposits in altun shan northern tibetan plateau abstract a well preserved and continuous neogene red clay deposit the caihonggou section was recently discovered in the eastern xorkol basin in the altun shan area at the northern margin of the tibetan plateau we report detailed grain size analyses for the caihonggou red clay and also for the shilou red clay section of the chinese loess plateau in east central china although the grain sizes are similar and can be modeled as two component mixtures the temporal variation of grain size and the proportions of grain size components are very different between the caihonggou and shilou sections indicating that their transportation and deposition processes and or source areas were completely different the fine component of the caihonggou red clay was transported by high level westerlies whereas the coarser particles were carried by lower level westerlies coming from the taklimakan desert as indicated also by previous detrital zircon provenance analysis a range of grain size parameters for the caihonggou section indicate that since about 8 ma and particularly between 8 and 6 ma the westerly winds strengthened and the aridity of the asian interior increased

formation and evolution of gobi desert in central and eastern asia abstract although the development of gobi desert in central and eastern asia has greatly affected the regional and even the global climate its precise origin and evolution have yet to be determined the three preconditions for the formation of gobi desert are i a dry climate ii basin landforms and iii abundant sediment production in this study we present a synthesis of both new and published data on the formation and evolution of gobi desert in central and eastern asia we conclude that the combined effects of mountain building the mid latitude westerly circulation and changes in the asian monsoon accompanied by global cooling were principally responsible for the formation of modern gobi desert landscapes in central and eastern asia during the late pliocene the arid climate in central and parts of eastern asia probably developed in the early cenozoic from 50 ma related events included the collision of the indian and asian plates the closure and complete retreat of the paratethys ocean from central asia and the growth of the himalayas and the tibetan plateau in the eocene through late miocene which blocked the water vapor supply and intensified the aridification of the asian interior superimposed on the topographic changes was the process of stepwise global cooling since the early oligocene and in particular since the late miocene which controlled the formation and evolution of the gobi desert landscape global cooling weakened the asian monsoon circulation strengthened the westerly circulation and enhanced physical weathering processes in mountain areas which together promoted both the aridification of the asian interior and sediment production these processes finally resulted in the establishment of the modern gobi desert landscape in the late pliocene we estimate that the modern gobi desert landscape was formed at 2 6 ma and was the result of the stepwise evolution of asian topography and climate during the cenozoic dominated by asian tectonic deformation and uplift and the evolution of asian monsoon climate and the westerly circulation forced by global temperature change

refuting the evidence for an earlier birth of the taklimakan desert in a recent issue of pnas zheng et al 1 report a late oligocene early miocene age of the taklimakan desert in northwest china their age was based on 40ar 39ar dating of biotites and u pb dating of zircons from layers within the xiyu formation which they interpreted as volcanic ash this chronology effectively extends the formation of the taklimakan desert from 5 ma as recently reported from outcrop 2 and high resolution borehole data 3 to 27 ma 1

controlling factors on a paleo lake oxygen isotope record yammouneh lebanon since the last glacial maximum abstract late quaternary paleoclimatic changes in the levant are difficult to extract from carbonate oxygen isotope records partly because the factors controlling the terrestrial 18 o signals are not fully understood in this region characterized by sharp climatic gradients here we address this purpose by presenting the first 14 c dated isotope record from the northern levant the record is based on oxygen isotopes from ostracod shells from lacustrine palustrine deposits accumulated in a small karstic hydrologically open basin yammouneh located on the eastern flank of mount lebanon we have first constructed a composite isotopic record obtained from three different ostracod taxa this yields an oxygen isotope record of ostracods ost related to the most widespread species ilyocypris inermis and converted to 18 o values coeval with calcite precipitated in equilibrium c with the lake water l as with other records from the mediterranean region the yammouneh profile shows maximum and minimum c values during the lgm and the early holocene respectively and a slight late holocene increase in order to discuss the potential causes of the observed 18 o values fluctuations e g changes in the isotopic composition of the moisture source temperature precipitation minus evaporation p e balance or atmospheric circulation we tentatively reconstruct the lake water isotope composition by correcting the c values for lake water temperature using regional paleotemperature estimates inferred l values were then corrected for the isotopic composition of the eastern mediterranean sea surface water the moisture source derived from planktonic foraminifera 18 o values corrected for alkenone based sea surface temperature our study suggests that holocene l fluctuations are primarily linked to changes in the sea surface water composition source effect amplified by enhanced inland rainfall during the early holocene during the lgm low l values at yammouneh are likely due to the ground temperature effect on the rainfall isotope composition possibly associated with a steeper altitudinal thermal gradient inland and with changes in air mass trajectories over the mediterranean sea

changes in tibetan plateau latitude as an important factor for understanding east asian climate since the eocene a modeling study abstract previous climate modeling studies suggest that the surface uplift of the himalaya tibetan plateau tp is a crucial parameter for the onset and intensification of the east asian monsoon during the cenozoic most of these studies have only considered the himalaya tp in its present location between 26 n and 40 n despite numerous recent geophysical studies that reconstruct the himalaya tp 10 or more of latitude to the south during the early paleogene we have designed a series of climate simulations to explore the sensitivity of east asian climate to the latitude of the himalaya tp our simulations suggest that the east asian climate strongly depends on the latitude of the himalaya tp surface uplift of a proto himalaya tp in the subtropics intensifies aridity throughout inland asia north of 40 n and enhances precipitation over east asia in contrast the rise of a proto himalaya tp in the tropics only slightly intensifies aridity in inland asia north of 40 n and slightly increases precipitation in east asia importantly this climate sensitivity to the latitudinal position of the himalaya tp is non linear particularly for precipitation across east asia the simulated precipitation patterns across east asia are significantly different between our scenarios in which a proto plateau is situated between 11 n and 25 n and between 20 n and 33 n but they are similar when the plateau translates northward from between 20 n and 33 n to its modern position our simulations when interpreted in the context of climate proxy data from central asia support geophysically based paleogeographic reconstructions in which the southern margin of a modern elevation proto himalaya tp was located at 20 n or further north in the eocene

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

cenozoic tectonic and paleoenvironmental evolution of northwestern china evidence from two deep boreholes in the jartai basin abstract to study the cenozoic tectonic and paleoenvironmental evolution of northwestern china we drilled two deep boreholes jlt1 and jlt2 in the jartai basin magnetostratigraphy stratigraphy studies were conducted to establish a chronological framework sedimentary facies were reconstructed using lithology geophysical logs gamma ray gr and resistivity r and measurements of grain size sediment color l a and b and magnetic susceptibility and its frequency dependence the stratigraphic sequence of borehole jlt2 is similar to that of paleogene sediments in basins along the northeastern tibetan plateau which may be the result of the far field effect of the uplift of the tibetan plateau during the paleocene via faulting activity the results of borehole jlt1 indicate that the basin was occupied by alternating desert lacustrine and alluvial fan environments since ca 6 7 ma during ca 6 7 3 6 ma alternations of aeolian sand and lacustrine facies may reflect climatic cooling and drying and at that time the area may have been an important sediment source for the aeolian red clay of the loess plateau during ca 3 6 2 1 ma alluvial fan development also reflected the uplift of the northeastern tibetan plateau and the area acted as a source region for dust supplied to the loess plateau and the shanxi graben the alternations of aeolian sand and lacustrine deposits since ca 2 1 ma may have resulted from glacial interglacial variations of the east asian monsoon since ca 1 7 ma lacustrine deposition developed because of the enormous discharge of the yellow river into the jartai basin a tectonic movement at ca 0 8 ma is reflected by lacustrine red clay at the top of borehole jlt1 after the mid pleistocene transition the modern landscape of the jartai basin and its adjacent regions were formed

tectonic evolution of the pamir recorded in the western tarim basin china sedimentologic and magnetostratigraphic analyses of the aertashi section the northward indentation of the pamir salient into the tarim basin at the western syntaxis of the india asia collision zone is the focus of controversial models linking lithospheric to surface and atmospheric processes here we report on tectonic events recorded in the most complete and best dated sedimentary sequences from the western tarim basin flanking the eastern pamir the aertashi section based on sedimentologic provenance and magnetostratigraphic analyses increased tectonic subsidence and a shift from marine to continental fluvio deltaic deposition at 41 ma indicate that far field deformation from the south started to affect the tarim region a sediment accumulation hiatus from 24 3 to 21 6 ma followed by deposition of proximal conglomerates is linked to fault propagation into the tarim basin from 21 6 to 15 0 ma increasing accumulation rates of fining upward clastics is interpreted as the expression of a major dextral transtensional system linking the kunlun to the tian shan ahead of the northward pamir indentation at 15 0 ma the appearance of north pamir sourced conglomerates followed at 11 ma by central pamir sourced volcanics coincides with a shift to e w compression clockwise vertical axis rotations and the onset of growth strata associated with the activation of the local east vergent qimugen thrust wedge together this enables us to interpret that pamir indentation into tarim had started by 24 3 ma reached the study location by 15 0 ma and had passed it by 11 ma providing kinematic constraints on proposed tectonic models involving intracontinental subduction and delamination

exhumation history of the west kunlun mountains northwestern tibet evidence for a long lived rejuvenated orogen abstract how and when the northwestern tibetan plateau originated and developed upon pre existing crustal and topographic features is not well understood to address this question we present an integrated analysis of detrital zircon u pb and fission track double dating of cenozoic synorogenic sediments from the kekeya and sanju sections in the southwestern tarim basin these data help establishing a new chronostratigraphic framework for the sanju section and confirm a recent revision of the chronostratigraphy at kekeya detrital zircon fission track ages present prominent triassic early jurassic 250 170 ma and early cretaceous 130 100 ma static age peaks and paleocene early miocene 60 21 ma to eocene late miocene 39 7 ma moving age peaks representing source exhumation triassic early jurassic static peak ages document unroofing of the kunlun terrane probably related to the subduction of paleotethys oceanic lithosphere in combination with the occurrence of synorogenic sediments on both flanks of the kunlun terrane these data suggest that an ancient west kunlun range had emerged above sea level by triassic early jurassic times early cretaceous fission track peak ages are interpreted to document exhumation related to thrusting along the tam karaul fault kinematically correlated to the main pamir thrust further west widespread middle late mesozoic crustal shortening and thickening likely enhanced the early mesozoic topography paleocene early eocene fission track peak ages are presumably partially reset limited regional exhumation indicates that the early cenozoic topographic and crustal pattern of the west kunlun may be largely preserved from the middle late mesozoic the main pamir tam karaul thrust belt could be a first order tectonic feature bounding the northwestern margin of the middle late mesozoic to early cenozoic tibetan plateau toward the tarim basin late oligocene early miocene steady exhumation at a rate of 0 9 km myr is likely related to initial thrusting of the tiklik fault and reactivation of the tam karaul thrust thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the west kunlun orogen at this time this episode of exhumation and uplift associated with magmatism across western tibet is compatible with a double sided lithospheric wedge model primarily driven by breakoff of the indian crustal slab accelerated exhumation of the mountain front at a rate of 1 1 km myr since 15 ma supports active compressional deformation at the margins of the northwestern tibetan plateau we thus propose that the west kunlun mountains are a long lived topographic unit dating back to triassic early jurassic times and have experienced middle late mesozoic to early cenozoic rejuvenation and late oligocene miocene expansion

iodine 129 chronological study of brines from an ordovician paleokarst reservoir in the lunnan oilfield tarim basin abstract previous studies have shown that brines in an ordovician paleokarst reservoir of the lunnan oilfield in the tarim basin china are the product of mixing of paleo evaporated seawater in the east with paleometeoric waters in the west in order to put time constraints on the brine and related hydrocarbons in this field 10 brine samples were collected for which the iodine concentrations and 129 i i ratios were measured and discussed the iodine concentration 3 70 31 2 mg l and the 129 i i ratio 189 897 10 15 show that the iodine in the paleoseawater and meteoric water mw had different origins and 129 i characteristics the paleoseawater has a high iodine content 31 mg l indicating that iodine was introduced into the reservoir along with thermally generated hydrocarbons possibly in the cretaceous from the caohu sag in the eastern area based on consideration of all possible origins of iodine and 129 i in the brines it is suggested that the meteoric water maintained its initial iodine content 0 01 mg l and 129 i i ratio 1500 10 15 whereas the iodine enriched paloseawater ipsw exhibited a secular 129 i equilibrium n sq 39 atom l as a result of fissiogenic 129 i input in the reservoir over a long period of time the model of brine evolution developed on that basis confirmed that meteoric water entered the reservoir in the miocene at about 10 ma and partially mixed with the iodine enriched paleoseawater the movement of meteoric water was facilitated by faults created during the himalayan orogeny then became more dense after dissolving paleogene halite and infiltrated into the reservoir at high pressure the iodine and 129 i concentration in the brine contains information about the path and history of the fluid in the reservoir this may be useful in oil exploration since the movement of water was to some extent related to hydrocarbon migration

reappraisal of miocene eolian deposition in tianshui basin china based on an investigation of stratigraphy and provenance eolian deposition in china is intimately related to asian desertification the fine grained sediments in the cenozoic basins along the northeastern tibetan plateau are increasingly reported as eolian deposits due to their loess like characteristics thus extending the onset time of asian desertification from the late miocene to the early miocene however the basin scale stratigraphic correlation and geographic origin of these fine grained sediments remain poorly investigated limiting any interpretation of the transportation and paleoclimatic conditions responsible for their emplacement this study combines analyses of detrital zircon u pb geochronology and heavy mineral assemblages to present the first comprehensive stratigraphic and provenance study of miocene sediments in the tianshui basin in northeastern tibet comparison of results from 64 sand sized and silt sized samples from various sedimentary beds across the basin reveals that the main stratigraphic packages can be correlated basin wide confirming that the silt sized sediments were a natural part of the basin fill statistical visualizations of the large data set from northern and western china clearly shows that the west qinling mountains are the main source of the tianshui basin silts contribution estimates corroborate this conclusion and eliminate the likelihood of substantial contributions from other mountains and drylands moreover the significant differences between the tianshui basin silts and the chinese loess plateau red clay are reflected by their heavy mineral compositions and euhedral zircon u pb ages these provenance analyses strongly contradict the previous assumption of desert origin for the tianshui basin silts moreover the northward transport of the tianshui basin silts conflicts with the prevailing dust pathway driven by the asian westerlies and winter monsoons which do not support the eolian interpretation for their formation consequently we suggest that the miocene tianshui basin silts cannot be used as an indicator of extensive desertification in contrast with the suggestions of previous studies this proposal undermines the corresponding hypothesis of an early miocene onset of asian interior desertification and further raises questions about the validity of prevalent paleoclimatic interpretations drawn from fine grained basin sediments

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

late holocene dune mobilization in the horqin dunefield of northern china abstract the late holocene environmental change and its relationship with climate and human activities in the horqin dunefield of northern china are poorly understood in the current study we presented a new reconstruction of late holocene dune mobilization in the horqin dunefield based on 68 quartz osl ages from 25 dune sections and interpretations of historical documents these sections were selected from a variety of different geomorphological units across the studied region the results show that at least four phases of dune mobilization were distinguished during the last 2000 years in horqin dunefield corresponding to 400 700 ce 1200 ce 1800 ce and after 1900 ce respectively by comparison with other well dated paleoclimate records and analysis on human activity records we infer that the cold arid climate caused the dune mobilization around 400 700 ce dune mobilization around 1200 ce can be attributed to the combinative impacts of cold climate and extensive human activities increasing human activities play a dominate role in the latest two phases of dune mobilization at around 1800 ce and after 1900 ce even though the climate warming and drying in 20th century may also contribute to the last phase of dune mobilization

seismotectonic range front segmentation and mountain belt growth in the pamir alai region kyrgyzstan india eurasia collision zone the trans alai range along the northern perimeter of the pamir region of kyrgyzstan is at the northern edge of the india eurasia collision zone the range defines a section of main pamir thrust which is divided into eastern central and western segments that record differential absorption of plate convergence the 50 km long east west striking central fault segment of the main pamir thrust has dip slip thrust fault offsets with a minimum holocene dip slip rate of 6 mm yr and is linked to the other segments via northwest striking dextral transfer the western transfer faults are well characterized geomorphically and the westernmost records the predominant transition to north vergent thrusting along the western segment via north vergent low angle thrust faults rooted in a steeply south dipping dextral shear zone in contrast the eastern segment deformation is widely distributed and geomorphically less evident but the transfer also takes place in a structurally complex zone asymmetric offset of a regionally correlated terrace geomorphic zonation and the distribution of historic earthquakes suggest that the central segment is mechanically linked with the western segment but not with the eastern segment the progressive closure of the alai valley by the northward advance of thrusting exemplifies the annihilation of an intramontane basin if the high surface uplift rates implied by these geologic observations have been maintained for the last few million years they attest to the high level of tectonic activity and the recency of construction of the trans alai range

high resolution magnetostratigraphic study of the paleogene neogene strata in the northern qaidam basin implications for the growth of the northeastern tibetan plateau abstract the cenozoic terrestrial intermontane qaidam basin on the northeastern edge of the tibetan plateau contains 12 km of sedimentary rocks that potentially document the accommodation of india asia convergence and the growth of the plateau the chronology remains incomplete hindering cross basin correlation between lithostratigraphic units and their further interpretation here we present a high resolution magnetostratigraphy spanning 5 km of paleogene neogene sequence at dahonggou in the northern qaidam basin based on correlation with the geomagnetic polarity time scale gpts we have dated the section to being between 52 and 7 ma the bottom conglomeratic unit ranging from 52 ma to 44 ma was deposited in high energy environments e g alluvial fan or braided river reflecting the earliest deformation and uplift of the basin bounding qilian shan fold thrust belt in response to india asia collision in addition we identified two major increases in sedimentation rate at 25 16 ma and after 9 5 ma and three phases of lesser increases at 52 44 ma 38 33 ma and 14 6 12 0 ma these increases in sedimentation rate are consistent with regional thermochronology and basin analysis studies which revealed enhanced motion on basin bounding thrust faults we argue that these accelerated sedimentation rates indicate pulsed tectonism in the northeastern tibetan plateau the pulse at 25 16 ma may further relate to phases of strong rainfall linked to an intense monsoon at that time

what enhanced the aridity in eocene asian inland global cooling or early tibetan plateau uplift abstract geological evidence shows that the asian inland environment experienced enhanced aridity from the early to the late eocene this enhanced eocene aridity in the asian inland was related to combined impacts from global cooling topographic uplift and land sea reorganization however the primary cause of the enhanced eocene aridity in this region is still under debate and varies between global cooling and early tibetan plateau uplift to distinguish between the importance of these factors we evaluate the climatic impacts of these factors from a modeling point of view consistent with geological evidence our simulations support the observed enhanced eocene aridity in the asian inland both global cooling induced by atmospheric co2 decrease and topographic uplift contributed to intensified asian inland aridity while land sea redistribution did not the uplift of the central tibetan plateau during the early stage of the india asia collision is emphasized more to be responsible for the long term asian inland aridification during the eocene playing at least an equally important role as the global cooling induced by decrease in atmospheric co2

east central asian climate evolved with the northward migration of the high proto tibetan plateau the evolution of cenozoic climate patterns in asia has been linked to uplift of the tibetan plateau tp retreat of the paratethys sea and global cooling however less attention has been placed on the latitudinal change of the tp here we report new climate modeling to explore how modern climate changes as a function of topographic growth and spatial migration of the tp our results show that the northward displacement of the uplifted proto tp within the subtropics can significantly affect the wind and precipitation pattern over east central asia by compiling proxy based climatic records paleolatitudinal and paleoelevational evolution models of the proto tp and in comparison with previous modeling under a global paleogeography we suggest that the northward migration of the proto tp in the paleogene could have intensified the aridity in central asia but its influence on east asian precipitation and monsoonal circulation could be dependent on the paleogeography and other boundary conditions plain language summary the evolution of the asian monsoons and aridification of asia s interior are thought to be driven by tibetan himalayan uplift recent geological observations suggest that the uplifted proto tibetan plateau proto tp migrated northward in the subtropics since the early eocene and reached its present position by the latest oligocene we therefore simulated the effects of this process on east central asian climate our climate modeling shows the northward migration of the high proto tp from 21 29 degrees n to 29 37 degrees n can significantly change the present day wind and precipitation patterns over east central asia especially central asia become drier because of the displacement of the anomalous dry belt caused by large scale atmospheric subsidence we further suggest that forcing by the paleolatitudinal migration of the high proto tp within the subtropics from the eocene to the earliest miocene could have drove the central asian paleoclimate to dryer conditions but migration might not be the sole parameter that governed the east asian monsoon during the paleogene

provenance of neogene eolian red clay in the altun region of western china insights from upb detrital zircon age data aridity of the asian interior plays an important role in the accumulation of eolian deposits in both eastern monsoon regime and western china westerly wind regime a better understanding of the provenance of those eolian deposits loess and red clay will shed light on the history and mechanisms of asian aridification in eastern china decrease in grain size from northwest to southeast shows that the neogene red clay of the chinese loess plateau clp was derived from the desert and arid lands of northwestern china by the east asian winter monsoon however in western china outcrops are limited and this is an obstacle to studies of the spatial variation of the provenance of eolian deposits we use upb geochronology of detrital zircons to determine the provenance of the altun red clay a recently discovered and continuous eolian deposit in western china our comparison of detrital zircon age spectra for the altun red clay with those of potential source regions and with results for the coeval red clay of the clp indicates that 1 the main zircon age components of the altun red clay are very different from those of the red clay on the clp suggesting that these deposits were sourced from different areas and 2 the altun red clay was likely sourced from the taklamakan desert and transported via westerly winds

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

resolving eolian volcanogenic and authigenic components in pelagic sediment from the pacific ocean abstract we measured major and trace element concentrations in the operationally defined chemically extracted residual aluminosilicate component of sediment from ocean drilling program sites 1215 and 1256 in the central and eastern equatorial pacific ocean and found that this residual component contains volcanogenic and authigenic aluminosilicates in addition to inferred eolian material while the residual component younger than 20 ma from the central pacific odp site 1215 is similar compositionally to upper continental crust and suggests an increase in the delivery of asian dust material since 20 ma the residual in sediment older than 20 ma indicates significant amounts of volcanogenic and authigenic materials volcanogenic debris comprises as much as 40 of the residual between 23 40 ma which coincides with the mid tertiary ignimbrite flare up that occurred in much of western north america the residual component extracted from the 50 ma biogenic sediment reflects authigenic signatures seawater like negative cerium anomalies and elevated fe si ratios the previously interpreted increase in an andesitic detrital source in north pacific locations may instead be authigenic material presenting significant challenges for many paleoclimate proxies additionally in the eastern pacific odp site 1256 the residual component contains 70 of volcanogenic material most likely originating from central america and also includes refractory barite the ability to separately identify eolian volcanogenic and authigenic materials in the aluminosilicate component of pelagic sediment allows resolution respectively of the climatic geologic and chemical processes contributing to the paleoceanographic archive in this critical oceanic region

new evidence on the age of the taklimakan desert the taklimakan desert is the world s second largest shifting sand desert located in the rain shadow of the tibetan plateau the initiation of desert formation in the asian interior is one of the most prominent climate changes in the northern hemisphere during the cenozoic era dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted tibetan plateau here we report 1071 m thick neogene deposits with inter calated eolian dune sands from the only outcrop in the central taklimakan desert based on paleo magnetic measurements biostratigraphic age control and previous electron spin resonance dating results the oldest in situ eolian dune sands were confi rmed to be ca 7 ma much older than the previous reported wind blown siltstone from the southern edge of the taklimakan desert this new result indicates that desert conditions initiated ca 7 ma in the center of the tarim basin we attribute this event to the late cenozoic climatic deterioration and or to the rain shadow effect caused by late miocene uplift of the northern tibetan margin

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

environmental magnetic evidence for enhanced aridification in the tarim basin since 5 3 ma nw china abstract the tarim basin located in the rain shadow of high asia is an ideal basin for studying the long term aridification history and the interplay between climate and regional tectonics here we report new environmental magnetic records from the foreland basin of southern tian shan our new magnetic records together with the results of color parameters suggest that the paleoenvironment in the study area changed abruptly since 5 3 ma this result is consistent with other paleoclimatic records from different parts of the tarim basin suggesting a basin wide extreme aridification prevailed in the tarim basin since the beginning of the pliocene the long term cooling trend of the climate in the tarim basin since the late miocene was generally controlled by first order global climate however the extreme aridification since 5 3 ma was dominantly controlled by decreased moisture transport caused by the final collision between pamir and tian shan as a response to the northward displacement of the pamir salient

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

high and dry in central tibet during the late oligocene the time at which the tibetan plateau rose to its present high elevation remains controversial with estimates ranging from 40 ma to more recent than 7 ma new stable isotope analyses of modern and accurately dated ancient paleosol carbonate in the nima basin of central tibet point to an arid climate and high paleoelevation 4 5 5 km comparable to today s setting by 26 ma oxygen isotope values of ancient 26 ma soil carbonate are both very negative and indistinguishable after modest corrections for changes in global climate from the lowest least evaporated oxygen isotope values of modern soil carbonates in the area substantial enrichments in oxygen 18 in paleolacustrine carbonates as well as high carbon isotope values from paleosol carbonates indicate considerable lake evaporation and low soil respiration rates respectively and both are consistent with the present arid climate of the nima area blockage of tropical moisture by the himalaya and perhaps the gangdese shan probably has contributed strongly to the aridity and very negative oxygen isotope values of soil carbonate and surface water in the nima area since at least the late oligocene the maintenance of high elevation since at least 26 ma suggests that any flow of lower crust from beneath central tibet must have been balanced by coeval northward insertion of indian crust beneath the plateau