zircon u pb and hf isotopic constraints on the onset time of india asia collision the time of initial collision between india and asia has been extremely controversial despite the fact that it is vital to constraining the orogenesis and subsequent evolution of the himalayas and tibetan plateau here we report u pb and hf isotope analysis of detrital zircons from two principal foreland basins that is the sangdanlin and gyangze basins respectively in the western and central parts of southern tibet our data suggest that asian derived clastic sediments started contributing to sedimentation on the indian continental margin earlier than generally thought at 60 ma in both basins near the yarlung zangbo suture zone in southern tibet no evidence for the existence of an intra oceanic arc within the neotethys is observed we conclude that 60 ma can be used to constrain the onset time of the india asia collision at least in central tibet after this initial collision closure of the neotethys propagated both westward and eastward with the final closure occurring at 50 and 45 ma in northwestern and eastern himalayas respectively our conclusion differs significantly from the previous view that the india asia collision may have started in northwestern himalaya and propagated eastward with diachronous suturing

late miocene accelerated exhumation in the central tajik basin and implications for northward indention and lateral growth of the pamir abstract the tajik basin located at the west of the pamir is characterized by a series of thin skinned folds and thrusts within its interior constraining the onset of deformation of these structures is important both for illustrating basin inversion process and for understanding growth history of the adjacent pamir to date the timing of thrusting and folding within the tajik basin has not been well studied in this study we determined the timing of fault motion of the aruntau thrust in the central tajik basin by using apatite u th he thermochronometry apatite u th he age data of sandstone samples collected from the hanging wall of the aruntau thrust fault combined with thermal history simulation constrains the onset of rapid cooling of rock samples at ca 10 6 ma given the compressional tectonic regime we propose that the observed rapid cooling was caused by thrust induced exhumation and thus the cooling age of 10 6 ma approximately represents the timing of thrusting initiation integrated with previous studies we found that the late miocene tectonic deformation was not only circumscribed within the tajik basin but also occurred in the areas north and east of the pamir and within the pamir we suggest that the synchronously widespread tectonic deformation in the pamir tian shan convergence zone reflects the enhanced northward indentation and lateral growth of the pamir since the late miocene

old origin for an active mountain range geology and geochronology of the eastern hindu kush pakistan prior to accretion of the kohistan island arc during the late cretaceous and final suturing of india with asia at ca 50 ma the hindu kush mountains along the border of afghanistan and northwest pakistan were situated on the active southern margin of asia geology and geochronology of the eastern hindu kush range in pakistan demonstrate that localized crustal melting and leucogranite intrusion took place in the gharam chasma area at ca 24 ma more regionally developed and widespread deformation metamorphism and magmatism took place before collision between both india and the kohistan island arc with asia ca 195 ma u pb monazite ages on a deformed leucogranite dike from the upper lutkho valley indicate an early jurassic phase of crustal melting u pb monazite ages of 135 126 ma on a staurolite schist from near gharam chasma are interpreted as a minimum age for staurolite grade metamorphism within the tirich mir fault zone pegmatite dikes crosscut the staurolite schists u pb dating of uraninites from one of these pegmatite dikes reveals an age of 114 2 ma monazites from the same rock give ages of 125 121 ma possibly due to inheritance of older cores these jurassic early cretaceous constraints on metamorphism and magmatism relate to subduction and accretion processes perhaps including the suturing of the karakoram and hindu kush terranes along the tirich mir fault in general high temperature low pressure metamorphism and subduction related granitoid magmatism in the eastern hindu kush suggest a high thermal gradient in an active margin setting from early jurassic to cretaceous time

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

is the north atlantic oscillation a breaking wave abstract given the recent observational evidence that the positive negative phase of the north atlantic oscillation nao is the remnant of anticyclonic cyclonic wave breaking this study uses a multilevel primitive equation model to investigate important dynamical attributes of the above wave breaking behavior for this purpose a hierarchy of different basic states two and three dimensional and initial perturbations are used with the three dimensional climatological flow as the basic state it is found that initial perturbations located equatorward poleward and upstream of the climatological atlantic jet lead to wave breaking similar to that of the positive negative nao phase consistently analysis of observational data indeed shows that the pacific storm track is displaced equatorward poleward prior the onset of the positive negative nao phase this result suggests that the latitudinal position of the pacific storm track plays an important role for determining the phase of the nao sen

combining fiber optic dts cross hole ert and time lapse induction logging to characterize and monitor a coastal aquifer the characterization of saline water intrusion swi and its hydrodynamics is a key issue to understand submarine groundwater discharge sgd and manage groundwater resources in coastal areas to test and compare different methods of characterization and monitoring a new experimental site has been constructed in a coastal alluvial aquifer north of barcelona city catalonia spain the site is located between 30 and 90 m from the seashore and comprises 16 shallow piezometers organized in nests of three with depths ranging between 15 and 25 m and 4 solitary piezometers the objective of this paper is to combine different recently developed monitoring techniques to evaluate temporal variations in the aquifer hydrodynamics of the site at different spatial scales before and after the dry season of 2015 at the site scale fibre optic distributed temperature sensing fo dts for the first time applied to study swi and cross hole electrical resistivity tomography chert has been applied at the meter borehole scale electrical conductivity of the formation has been applied not only in a repeated manner time lapse but also for the first time at relatively high frequency 1 sample every 10 min chert has provided a better characterization of the seawater intrusion than electrical conductivity data obtained from piezometers the combination of techniques has allowed improving the understanding of the system by 1 characterizing the extent and shape of swi 2 differentiating two different dynamics in the aquifer and 3 identifying preferential flow paths over different time and spatial intervals future challenges and the application of these techniques in other areas are also discussed

cenozoic tectonic rotations in different parts of the ne pamir implications for the evolution of the arcuate orogen the pamir salient defining the nw end of the himalayan tibetan orogen is a prominent curved orogen as a response to the indian eurasian collision its evolution history is essential for understanding intracontinental tectonic processes in the context of continental collision in this study we carry out systematic paleomagnetic studies on four sections in different parts of the ne pamir to unravel the tectonic evolution of the curved orogen our new results from the oytag section suggest that the clockwise cw rotations of the eastern pamir salient mainly occurred in the oligocene 32 26 ma as a response to the northward indentation of the pamir salient and was dominated by large scale dextral strike slip faults since then additionally the final collision between pamir and sw tian shan in the latest miocene reactivated the dextral talas ferghana fault tff thus be responsible for the counter clockwise ccw rotations at ulugqat however the limited tectonic rotations of the keliyang and sanju sections can be explained by the dominant thrust faulting in the foreland of the west kunlun mountains combined with the existing paleomagnetic data around the pamir salient our results support a four stage evolution 1 a roughly linear orogen before the early eocene 2 symmetric rotations on both sides until the latest oligocene followed by 3 asymmetric geometries with continued radial thrusting on the western flank and large scale strike slip fault on the eastern flank and 4 final collision between the pamir salient and sw tian shan in the late miocene

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

the impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation the late cenozoic was a time of global cooling increased aridity and expansion of grasslands in the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes understand terrestrial paleoclimate and to determine the surface history of mountain belts the 18o values of these records in general increase from the mid miocene to the recent we suggest that these records record an increase in aridity and expansion of grasslands in midlatitude continental regions we use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate the role of vapor recycling and transpiration by different plant functional types this analysis shows that increased vapor recycling associated with grassland expansion along with biomechanistic changes in transpiration by grasses themselves conspires to lower the horizontal gradient in the 18o of atmospheric vapor as an air mass moves into continental interiors the resulting signal at a given inland site is an increase in 18o of precipitation with the expansion of grasslands and increasing aridity matching the general observed trend in terrestrial cenozoic 18o records there are limits to the isotopic effect that are induced by vapor recycling which we refer to here as a hydrostat in the modern climate this hydrostatic limit occurs at approximately the boundary between forest and grassland ecosystems

a new rossby wave breaking interpretation of the north atlantic oscillation this paper proposes the hypothesis that the low frequency variability of the north atlantic oscillation nao arises as a result of variations in the occurrence of upper level rossby wave breaking events over the north atlantic these events lead to synoptic situations similar to midlatitude blocking that are referred to as high latitude blocking episodes a positive nao is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic unblocked situation a negative nao is a description of periods in which episodes occur frequently a similar but weaker relationship exists between wave breaking over the pacific and the west pacific pattern evidence is given to support this hypothesis by using a two dimensional potential vorticity based index to identify wave breaking at various latitudes this is applied to northern hemisphere winter data from the 40 yr ecmwf re analysis era 40 and the events identified are then related to the nao certain dynamical precursors are identified that appear to increase the likelihood of wave breaking these suggest mechanisms by which variability in the tropical pacific and in the stratosphere could affect the nao

magnetostratigraphic data on neogene growth folding in the foreland basin of the southern tianshan mountains the tianshan range is one of the longest and highest mountain belts in central asia stretching east west for 2500 km uplift of this late paleozoic orogenic belt resulted from intracontinental deformation caused by the collision of the indian and eurasian plates during the cenozoic era to constrain the timing of cenozoic tectonic deformation of the tianshan range we analyzed the magnetostratigraphy of 3780 m thick neogene deposits from the kuqa foreland basin of southern tianshan the geometry measurements and magnetic fabric data show that syntectonic growth strata began to accumulate at 6 5 ma ago indicating that crustal shortening initiated in the latest miocene the increase in sedimentation rate and an abrupt change of the magnetic fabric parameters also occurred at 6 5 ma accompanied by onset of syntectonic growth strata the latest miocene crustal shortening is a signifi cant tectonic event in the foreland basin of the southern tianshan range in response to the india eurasia collision

late eocene palaeogeography of the proto paratethys sea in central asia nw china southern kyrgyzstan and sw tajikistan

cenozoic crustal shortening between the pamir and tien shan and a reconstruction of the pamir tien shan transition zone for the cretaceous and palaeogene the magnitude of the late cenozoic crustal shortening during convergence of the pamir and tien shan was determined using a contemporary pattern consisting of facies zones palaeomagnetic data regarding the rotation of tectonic units and data on the structure of the tadjik depression by late cenozoic cretaceous and palaeogene facies zones were cut by the vakhsh trans alay overthrust and darvaz strike slip faults and a significant part of the cretaceous palaeogene tadjik basin was overthrust by the pamir massif the sediments of easternmost part of the basin are preserved in the tarim depression the facies zones of the southern slope of the afghan tadjik basin were deformed and moved northward a pattern of facies zones indicates a convergence between the pamir and tien shan over a distance of 300 400 km a number of cross sections through the tadjik depression were used to establish the structure before folding a rotation of tectonic units indicated by structural data conforms to the angles of rotation as determined in palaeomagnetic studies the data suggest 300 km of convergence between the pamir and tien shan stratigraphic lithological structural and palaeomagnetic data formed the basis for the construction of the palinspastically restored palaeogeographic and sedimentologic environments for the tadjik shallow sea basin which was situated between the pamir and tien shan before their convergence in the late cenozoic the maps were constructed for the eight stratigraphic levels of the cretaceous and palaeogene the tadjik sea was a bay in the enormous turan sea in the early aptian this bay was located in what is now the afghan tadjik basin in late cretaceous the eastern shore of the bay lay 600 700 km further eastward and in the eocene marine environments extended even further eastward but after the rupelian continental environments occupied all of this region 2000 elsevier science b v all rights reserved

direct stratigraphic dating of india asia collision onset at the selandian middle paleocene 59 1 ma the collision of india with asia had a profound influence on cenozoic topography oceanography climate and faunal turnover however estimates of the time of the initial collision when indian continental crust arrived at the transhimalayan trench remain highly controversial here we use radiolarian and nannofossil biostratigraphy coupled with detrital zircon geochronology to constrain firmly the time when asian derived detritus was first deposited onto india in the classical sangdanlin section of the central himalaya which preserves the best paleocene stratigraphic record of the distal edge of the indian continental rise deep sea turbidites of quartzarenite composition and indian provenance are replaced upsection by turbidites of volcano plutoniclastic composition and asian provenance this sharp transition occurs above abyssal cherts yielding radiolaria of paleogene radiolarian zones rp 4 6 and below abyssal cherts containing radiolaria of zone rp6 and calcareous shales with nannofossils of the paleocene calcareous nannofossil zone cnp 7 constraining the age of collision onset to within the middle paleocene selandian the youngest u pb ages yielded by detrital zircons in the oldest asia derived turbidites indicate a maximum depositional age of 58 1 0 9 ma collision onset is thus mutually constrained by biostratigraphy and detrital zircon chronostratigraphy as 59 1 ma this age is both more accurate and more precise than those previously obtained from the stratigraphic record of the northwestern himalaya and suggests that within the resolution power of current methods the india asia initial collision took place quasi synchronously in the western and central himalaya

central asian moisture modulated by proto paratethys sea incursions since the early eocene abstract the establishment and evolution of the asian monsoons and arid interior have been linked to uplift of the tibetan plateau retreat of the inland proto paratethys sea and global cooling during the cenozoic however the respective role of these driving mechanisms remains poorly constrained this is partly due to a lack of continental records covering the key eocene epoch marked by the onset of tibetan plateau uplift proto paratethys sea incursions and long term global cooling in this study we reconstruct paleoenvironments in the xining basin ne tibet to show a long term drying of the asian continental interior from the early eocene to the oligocene superimposed on this trend are three alternations between arid mudflat and wetter saline lake intervals which are interpreted to reflect atmospheric moisture fluctuations in the basin we date these fluctuations using magnetostratigraphy and the radiometric age of an intercalated tuff layer the first saline lake interval is tentatively constrained to the late paleocene early eocene the other two are firmly dated between 46 ma top magnetochron c21n and 41 ma base c18r and between 40 ma base c18n and 37 ma top c17n remarkably these phases correlate in time with highstands of the proto paratethys sea this strongly suggests that these sea incursions enhanced westerly moisture supply as far inland as the xining basin we conclude that the proto paratethys sea constituted a key driver of asian climate and should be considered in model and proxy interpretations

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

tectonic evolution of the northeastern pamir constraints from the northern portion of the cenozoic kongur shan extensional system western china the late cenozoic kongur shan extensional system lies along the northeastern margin of the pamir at the western end of the himalayan tibetan orogen accommodating east west extension in the pamir at the northern end of the extensional system the kongur shan normal fault juxtaposes medium to high grade metamorphic rocks in both its hanging wall and footwall which record several mesozoic to cenozoic tectonic events schists within the hanging wall preserve a buchan metamorphic sequence dated as late triassic to early jurassic 230 200 ma from monazite inclusions in garnet metamorphic ages overlap with u pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the paleo tethys ocean the northern portion of the footwall of the extensional system exposes an upper amphibolite facies unit 650 c 8 kbar which structurally overlies a lowgrade metagraywacke unit the high grade unit records late early cretaceous crustal thickening at ca 125 110 ma followed by emplacement over the low grade metagraywacke along a north northeast directed thrust prior to ca 100 ma together these results indicate signifi cant middle cretaceous crustal thickening and shortening in the northern pamir prior to the indo asian collision a third late miocene ca 9 ma amphibolite facies metamorphic event 650 700 c 8 kbar is recorded in footwall gneisses of the kongur shan massif north of the kongur shan massif rapid cooling in the footwall beginning at 7 8 ma is interpreted to date the initiation of exhumation along the kongur shan normal fault a minimum of 34 km of east west extension is inferred along the kongur shan massif based on the magnitude of exhumation since the late miocene 29 km and the present dip of the kongur shan normal fault 40 field observations and interpretation of satellite images along the southernmost segment of the kongur shan extensional system indicate that the magnitude of late cenozoic east west extension decreases signifi cantly toward the south this observation is inconsistent with models in which east west extension in the pamir is driven by northward propagation of the right slip karakoram fault suggesting instead that extension is driven by vertical extrusion due to topographic collapse radial thrusting along the main pamir thrust or oroclinal bending of the entire pamir region

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

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

sedimentology and evaporite genesis in a holocene continental sabkha playa basin bristol dry lake california bristol dry lake a 155 km2 continental sabkha playa basin in the mojave desert of south eastern california is filled with at least 300 m of interbedded terrigenous clastics gypsum anhydrite and halite evaporite facies conform approximately to a bull s eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite transects through bristol dry lake from the alluvial fan to the centre of the playa reveal 1 crudely bedded alluvial fan clastics interfingering with 2 playa margin sand flat and wadi sand and silt followed by 3 gypsum anhydrite chaotic mud halite and clay of the saline mud flat and 4 salt pan halite beds terrigenous clastics were deposited in bristol dry lake by sheetflow and by suspension settling from ponded floodwater some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin thin nodular like beds of anhydrite and several types of gypsum occur across most of the playa giant hopper shaped halite cubes are suspended in saline mud flat facies suggesting that they grew displacively in brine soaked sediment just below the surface thick beds 4 m of halite in the playa centre may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods intense evaporation and brine level lowering and capillary discharge of brines the stratigraphy in the playa centre is cyclic an ideal cycle consists of 1 chaotic mud halite at the base overlain by 2 green to red clay with abundant giant hoppers and at the top 3 red clay gypsum and anhydrite with flaser to wavy bedded sand and silt this type of cycle probably records a gradual progradation of mud flat facies over salt pans bristol dry lake sediments are nearly identical to some of the permian evaporites of the permian basin region u s a and they can serve as modern analogues for ancient sabkha facies analysis

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

proterozoic mesozoic history of the central asian orogenic belt in the tajik and southwestern kyrgyz tian shan u pb 40ar 39ar and fission track geochronology and geochemistry of granitoids multimethod geochronology u pb zircon 40 ar 39 ar hornblende biotite feldspar apatite fission track on granitoids gneisses and cenozoic intramontane basin clastics of the gissar alai ranges south tian shan collisional belt west of the talas fergana fault elucidates a history of neoproterozoic magmatism late paleozoic magmatism and metamorphism and mesozoic cenozoic thermal reactivation zircon core and grain interior u pb ages of ca 2 7 2 4 2 2 1 7 1 1 0 85 and 0 85 0 74 ga tie the early evolution of the gissar alai ranges to that of the tarim craton at least part of the gissar range crystalline basement the garm massif shows u pb zircon crystallization ages of ca 661 552 ma median ca 609 ma again suggesting a tarim craton connection tarim collided with the middle tian shan block at ca 310 305 ma completing the protracted formation of the south tian shan collisional belt the massive gissar range granitoids intruded later ca 305 270 ma contemporaneous with peak barrovian type metamorphism in the garm massif rocks major and trace element compositions suggest that the gissar granitoid melts have continental arc affinity zircon e hf and whole rock e nd values of 2 1 to 6 9 and 2 7 to 7 2 respectively and hf isotope crustal model and nd isotope depleted mantle model ages of ca 1 0 1 2 and ca 1 1 2 2 ga respectively suggest significant input of precambrian crust in the gissar granitoid and garm orthogneiss melts consistent with the u pb ages of inherited and detrital zircons the distinct ca 661 552 ma garm gneiss crystallization ages and the ca 1 0 2 2 ga model ages and the lack of 2 4 3 4 ga model ages tie the garm gneisses and the reworked crust of the gissar range to the northern rim the kuqa and kolar sections of the tarim craton suggesting a united karakum tarim craton although about contemporaneous with widespread postcollisional magmatism in the entire tian shan the large volume and short duration of the gissar range magmatism including crustal thickening and prograde metamorphism during tarim craton middle tian shan block collision and formation and closure of an oceanic back arc basin the gissar basin indicate its origin in a distinct setting combined this likely resulted in midcrustal melting and upper crustal batholith emplacement mafic dikes and pipes intruded at ca 256 238 ma median ca 241 ma the source region of the parental melts was within the asthenospheric mantle the simplest interpretation for these basanites is that they were part of the tarim flood basalt province this would extend this province westward from the tarim craton into the southwestern tian shan and imply that the relatively short lived flood basalt event ca 290 270 ma was followed by much less voluminous but longer lasting hotspot magmatism the 40 ar 39 ar and detrital apatite fission track dates outline post gissar alai range granitoid emplacement cooling cimmerian collision events at the southern margin of asia late cretaceous crustal extension and local magmatism and early cenozoic shortening and burial in the far field of the india asia collision

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

magnetostratigraphy and rock magnetism of the neogene kuitun he section northwest china implications for late cenozoic uplift of the tianshan mountains in order to better constrain the tectonic evolution of central asia under the influence of the india asia collision we carried out a magnetostratigraphic study at the kuitun he section on the northern flank of the tianshan range northwest china a total of 801 samples were collected from a 1559 m thick section which is composed mainly of fluvio lacustrine sandstone and conglomerate stepwise thermal and alternating field demagnetization isolated a linear magnetization component that decays univectorally toward the origin and likely represents a primary magnetization principally carried by magnetite from this component 29 magnetic polarity intervals were identified they correlate between 3 1 and 10 5 ma with the reference magnetic polarity time scale indicating a relatively constant sedimentation rate with an average of 0 21 0 01 mm year we also performed a suite of rock magnetic experiments designed to track time transgressive changes in the sedimentary record from the rock magnetic parameters together with the constant sedimentation rate we conclude that the tianshan mountains were actively uplifting by 10 5 ma

paleolake salinity evolution in the qaidam basin ne tibetan plateau between 42 and 29 ma links to global cooling and paratethys sea incursions abstract climate change in the asian interior during the early cenozoic remains poorly constrained due to difficulties in distinguishing the impacts of global cooling the early uplift of the tibetan plateau and the retreat of the paratethys a quantitative estimation of paleolake salinity enables a better understanding of the regional hydrological cycle and contemporaneous climate change here we present a quantitative record of paleolake salinity in the qaidam basin between 42 and 29 ma using detailed mineralogical investigations and clay boron content data this paleolake salinity record generally covers a tectonically less active period in the asian interior characterized by continuous global cooling the abrupt eocene oligocene climate transition and the paratethys transgression regression cycles thus offering an opportunity to explore the roles of global cooling and the paratethys retreat in regulating the regional hydrological cycle the results of two boron derived paleosalimeters equivalent boron and couch s salinity collectively indicate a two stage paleolake salinity evolution from an oligohaline mesohaline environment in the middle late eocene 42 34 ma to a mesosaline environment in the early oligocene 34 29 ma this transition is also supported by qualitative chloride based and ostracod based paleosalinity estimates in the qaidam basin our quantitative paleolake reconstruction between 42 and 29 ma in the qaidam basin yields a generally good match with the hydroclimate change in the neighboring xining basin thus indicating a comparable regional drying trend the synchronous changes in quantitative paleolake salinity and silicate weathering processes derived from the illite weathering index and chlorite content in the studied section suggest climate control of silicate weathering global cooling is speculated to have been the first order driving factor in regulating long term climatic evolution and weathering responses in the asian interior between 42 and 29 ma superimposed on this trend the paratethys transgression regression cycles served as an important factor regulating wet dry fluctuations in the asian interior between 42 and 34 ma

diachronous seawater retreat from the southwestern margin of the tarim basin in the late eocene in contrast to the present hyper arid inland basin surrounded by the high mountains of central asia the western tarim basin was once connected with the tajik basin at least in the late eocene when an epicontinental sea extended from the western tarim basin to europe western tarim is a key site for studying the retreat of seawater which was likely caused by the northward indentation of the pamir arc and facilitated by the climatic cooling and eustatic sea level change in the cenozoic here we present a new magnetostratigraphic record from the tarim basin that provides evidence of diachronous seawater retreat from its southwestern margin we studied about 1360 m of well exposed eocene oligocene strata at keliyang in the folded foreland of the west kunlun orogen until now the age of the strata has only been minimally constrained by the presence of late mid eocene marine fossils our biostratigraphic and magnetostratigraphic results demonstrate that the age of the sedimentary sequence ranges from 46 ma to 26 ma mid eocene to late oligocene and the seawater retreat at keliyang took place at 40 ma considering the stepwise northward indentation and uplift of the pamir orogen together with the other previous results we propose that seawater retreat from the southwestern margin of the tarim basin was diachronous in the late eocene ranging from 47 ma to 40 ma the regional indentation uplift and erosion of the pamir orogen played the dominant and important role in controlling the seawater retreat from the southwestern margin of the tarim basin

the paleoaltimetry of tibet an isotopic perspective stable isotopes provide a valuable perspective on the timing of elevation change of the tibetan plateau we begin our paper by looking in depth at isotopic patterns in modern tibet we show that the 18 o value of surface waters decreases systematically up the himalayan front in central nepal by about 2 8 km in agreement with the patterns documented and modeled by previous research on the tibetan plateau itself there is no apparent correlation between elevation and the 18 o value of flowing surface waters both surface waters and soil carbonates display a northward increase in 18 o values of about 1 5 north of the himalayan crest even though elevation increases modestly the isotopic increase with latitude reduces the isotope elevation gradient for water in the northernmost plateau to 1 to 2 km carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau temperature estimates from clumped isotope 47 analyses of modern soil carbonates significantly exceed mean annual air t and modeled maximum summer soil temperatures by 15 8 2 8 and 9 7 2 5 c respectively similarly elevated temperatures best account for the 18 o values observed in modern soil and lake carbonates we recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude corrected isotopic values with one notable exception our revised model produces paleoelevation estimates very close to previous estimates the exception is the reconstruction from late eocene age deposits at xoh xil for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed therefore there is no evidence for northward progression through time of tibetan elevation change instead the available but admittedly very scanty evidence suggests that much of tibet attained its modern elevation by the mid eocene a truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across tibet especially in the center and north and for 15 ma

cenozoic uplift exhumation and deformation in the north kuqa depression china as constrained by u th he thermochronometry placing spatial and temporal constraints on deformation uplift and exhumation using thermochronology methods can shed light on cenozoic orogenic evolution in the kuqa foreland new apatite u th he and previously published apatite fission track thermochronology are combined with vitrinite reflectance data and modeling to compile a low temperature multi stage thermal history of tectonic uplift thrust and exhumation a rapid uplift and exhumation event originated in south tianshan during the eocene 46 ma with systematic younging of mean apatite u th he ages from north to south from the margin towards the interior uplift and exhumation south edge of the biyoulebaoguzi anticline in the northern monocline belt at 36 ma with more than 3400 m of stratum denuded subsequently deformation and uplift south edge of the biyoulebaoguzi anticline in the northern monocline belt at 36 ma with more than 3400 m of stratum denuded subsequently deformation and uplift extended to the northern edge of kelasu yiqikelike at 10 ma and then at 6 ma the kanyaken anticline formed and uplifted resulting in 3000 3700 m of overburden erosion the data support sequential southward propagating deformation and uplift inferred exhumation in the north kuqa depression during the cenozoic probably as a result of the collision of india with asia far to the south of the tianshan

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

what drives the north atlantic oscillation s temperature anomaly pattern part ii a decomposition of the surface downward longwave radiation anomalies abstractradiative transfer calculations are conducted to determine the contribution of temperature and water vapor anomalies toward the surface clear sky downward longwave radiation dlr anomalies

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

tectonic significance of 24 ma crustal melting in the eastern hindu kush pakistan northward directed subduction has continued beneath the hindu kush from the mesozoic when the region formed part of the southern margin of asia until today the kohistan arc was accreted at ca 100 ma followed by the indian plate at 54 50 ma after the india asia collision a regional crustal melting event occurred at ca 25 21 ma to the east of the hindu kush in the karakoram range producing the baltoro pluton in the eastern hindu kush range most of the granitoids appear to be subduction related plutons that predate the india asia collision however the gharam chasma pluton is a two mica garnet tourmaline leucogranite that has intruded into staurolite grade schists and sillimanite k feldspar grade migmatites u pb ages on monazite xenotime and uraninite from undeformed samples of the gharam chasma pluton and a leucogranite dike that crosscuts the migmatites indicate that crustal melting occurred at ca 24 ma synchronous with the baltoro melting event this age also provides an upper limit on the age of the regional staurolite grade metamorphism in the eastern hindu kush

the winter midlatitude arctic interaction effects of north atlantic sst and high latitude blocking on arctic sea ice and eurasian cooling in this paper the effects of eurasian circulation patterns such as high latitude european blocking heb and ural blocking ub events on winter sea ice concentration sic in the barents kara seas bks and eurasian cooling is examined to differentiate the different roles of heb and ub in association with positive north atlantic oscillation nao events a particular focus is on the sic variability resulting from the effect of sea surface temperature sst near the gulf stream extension gse region through to the position change of eurasian blocking it is found that the sst shows a dipole pattern with a positive negative anomaly to the south north of the gse while the high sst in bks plays a major role in the bks sic decline the strengthening of north atlantic westerly winds associated with the sst dipole tends to promote long lived ub and heb events associated with nao to further reduce the bks sic while heb and ub depend on the prior bks warming and ub requires stronger north atlantic westerly winds than heb during ub warm moist air from the gse can reach the bks to enhance downward infrared radiation ir via increased northward transport produced by the nao ub relay the downward ir is weak during heb as the moisture is transported mainly into the western part of bks even though the nao heb relay still operates thus ub leads to more pronounced bks sea ice declines than under heb although the latter still significantly contributes to the sic loss it is also found that the central eastern asian cooling occurring during ub is related to an intense widespread sic decline in bks prior to the ub onset whereas the european cooling during heb is linked to a small sic decline in the western part of bks

orographic precipitation isotopic ratios in stratified atmospheric flows implications for paleoelevation studies an idealized fully nonlinear atmospheric model was used to evaluate the effects of stratified atmospheric flows on orographic precipitation isotopic ratios with the aim of improving the foundation for interpreting proxy records used for paleoelevation studies orographic precipitation isotopic ratios can be understood in terms of two nondimensional parameters the flow parameter nh u where n is the moist brunt vaisala frequency a measure of atmospheric stratification h is the large scale relief and u is the upstream horizontal wind speed perpendicular to the orogen and the horizontal aspect ratio the ratio of the along strike length of the orogen to its across strike width existing rayleigh condensation models for paleoaltimetry studies are only strictly applicable when nh u 0 much of the time high values of both nh u and favor precipitation upstream of the terrain leading to isotopic ratios that are more depleted than predicted by the rayleigh model high nh u and low favor low level deflection of winds around the terrain which substantially reduces lifting and condensation leading to precipitation isotopic ratios in that are less depleted than predicted by the simple rayleigh model changes in climate or the horizontal terrain aspect ratio can change precipitation isotopic ratios at least as much as changes in surface elevation and surface uplift need not always affect precipitation isotopic ratios suggesting that proxy records must be interpreted within a broad context of climate variability and landscape evolution

timing of seawater retreat from proto paratethys sedimentary provenance and tectonic rotations in the late eocene early oligocene in the tajik basin central asia abstract the tajik basin is now located to the west of the pamirs but it formerly connected with the tarim basin occupied by a large epicontinental sea proto paratethys sea once extended from europe to central asia however the northward indentation and collision of the pamirs into the tian shan separated the tajik and tarim basins creating manifold implications and consequences consequently timing of the final seawater retreat from the tajik basin is important for understanding the evolution of the proto paratethys sea the effect of the northward indentation of the pamirs on the sea regression and the influence of seawater retreat on the cenozoic aridification in the tajik basin here we present a multidisciplinary study of upper paleogene strata from the central tajik basin our results demonstrate that the final seawater retreat from the center of the tajik basin occurred at 38 6 ma which is earlier than a previous age of 37 4 ma from the northeastern tajik basin such a late eocene sea retreat was quasi simultaneous with that in the tarim basin this final marine regression was mainly a consequence of the northward indentation and growth of the pamirs which was an intracontinental response to the india asia collision our new detrital zircon ages indicate that the provenance of upper eocene lower oligocene strata was from the pamirs rather than tian shan implying that the reactivation of the tian shan was later than the early oligocene our paleomagnetic data indicate a 30 counterclockwise rotation of the central tajik basin that is much bigger than the previous estimate of 17 and we propose that such a counterclockwise rotation mostly occurred after the late miocene finally different from the previous reported aridfication at 39 ma or 37 ma our evidence demonstrates that drought intensified since the start of the oligocene at 34 ma being related to reduced water vapor transport to central asia caused by global cooling induced sea level drop the retreating paratethys sea and weakened sea surface evaporation

paleocene eocene foreland basin evolution in the himalaya of southern tibet and nepal implications for the age of initial india asia collision siliciclastic sedimentary rocks derived from the southern lhasa terrane sitting depositionally upon rocks of the northern indian passive continental margin provide an estimate of the age of initial contact between the continental parts of the indian and asian plates we report sedimentological sedimentary petrological and geochronological data from upper cretaceous paleocene strata in the sangdanlin section located along the southern flank of the indus yarlung suture zone in southern tibet this is probably the most proximal and therefore the oldest record of the india asia collision these strata were deposited by high density turbidity currents or concentrated density flows and suspension settling of pelagic biogenic debris in a deep marine setting an abrupt change from quartz arenitic to feldspatholithic sandstone compositions marks the transition from indian to asian sediment provenance the abrupt compositional change is accompanied by changes in u pb ages of detrital zircons diagnostic of a sediment provenance reversal from indian to asian sources the timing of the transition is bracketed between 60 ma and 58 5 0 6 ma by detrital zircon u pb ages and zircon u pb ages from a tuffaceous bed in the upper part of the section in the context of a palinspastically restored regional paleogeographic framework data from the sangdanlin section combined with previously published data from the northern tethyan himalaya and the frontal nepalese lesser himalaya and subhimalaya suggest that a flexural wave migrated 1300 km southward across what is now the himalayan thrust belt from paleocene time to the present

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

role of the westerlies in central asia climate over the cenozoic abstract there remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in central asia over the cenozoic tibetan plateau uplift variable monsoonal strength paratethys retreat and reduced moisture transport from the north atlantic have all been hypothesized to drive aridity in central asia distinguishing between these mechanisms requires knowledge of moisture transport pathways to central asia through time presently central asia receives recycled high 18 o moisture that has been transported across eurasia by the westerlies while southern tibet receives low 18 o moisture distilled by passage over the himalaya here we reconstruct the spatial distribution of oxygen isotopes in precipitation since the early eocene using a compilation of 18 o data from 2750 sedimentary carbonate samples across asia the spatial distribution of paleo precipitation 18 o remains remarkably similar through time with low 18 o values in the lee of the himalaya in southern tibet constant high 18 o values in central asia and intermediate values on the central plateau despite independent evidence for substantial changes in both topography and climate through time these results suggest that a long standing topographic feature has continuously blocked southerly moisture and subsequent progressive uplift of the tibetan plateau has had little impact on central asian climate in turn southerly monsoonal moisture has never persistently extended northward of the central plateau as a result the westerlies have remained the dominant moisture source in central asia since at least the early eocene therefore sedimentary aridity indicators in central asia such as loess deposition are controlled by the trans eurasian westerly moisture flux rather than tibetan plateau uplift

onset of aridification by 34 ma across the eocene oligocene transition in central asia cenozoic climate has changed markedly from a warm wet climate to the present cool dry glacial interglacial cycles the largest of these cooling steps is thought to have taken place across the eocene oligocene transition terrestrial airborne eolian loess is a direct result of land aridification therefore the prolonged formation of thick eolian loess deposits provides a key to aridification history in the geological past however the oldest eolian loess in the asian interior has been dated to only 25 22 ma here we present new sedimentological geochemical and magnetostratigraphic data from cenozoic sections in southwestern mongolia to show that the earliest eolian dust accumulation occurred by 34 ma 10 m y earlier than currently believed we suggest that this oldest eolian dust accumulation provides direct evidence for enhanced aridification across the eocene oligocene transition in central asia this is explicable by reduced moisture transport caused by prevailing westerlies during retreat of the neotethys ocean these climatic changes were related to the changing regional plate configuration as well as to global cooling and ice sheet growth in antarctica

two modes of appearance of the odden ice tongue in the greenland sea the odden ice tongue of the greenland sea normally forms locally in winter as frazil pancake ice allowing for high positive salt fluxes during freezing that leads to open ocean convection we report that another type of odden can develop usually late in the season and is composed of old ice advected through the east greenland current and by the jan mayen current this type causes the introduction of more meltwater that stabilizes the water column enhances productivity and affects the carbon cycle in the region the history of oddens is reviewed and our results indicate that from 1978 through 1997 the first type occurred almost every year except in 1984 1994 and 1995 while the second type has been observed to occur in 1987 and 1996

grassland expansion as an instrument of hydrologic change in neogene western north america abstract the evapotranspiration et flux accounts for approximately two thirds of terrestrial precipitation worldwide and in grassland regions et is equivalent in magnitude to precipitation regional contributions to the terrestrial hydrologic budget however have been far from constant in the past as distribution of vegetation changed dramatically the rise of grass dominated ecosystems is one of the most profound paleoecological changes in the cenozoic why then would grassland expansion not feature prominently in the record of neogene hydrologic change despite numerous stable isotope paleoenvironmental studies in neogene north america the contributions of land cover change have been largely ignored we present a compilation of 16 oxygen isotope studies of pedogenic carbonate and smectite from western north america including 4 new records nearly all records from california the basin and range the rocky mountains and the great plains show increases in o 18 on the order of 2 6 in order to assess the role of et in the hydrologic cycle we developed an isotopic water vapor transport model wherein we manipulated et parameters along a specified air mass trajectory grasslands lead to o 18 of precipitation o p 18 values that are up to 5 greater than broadleaf and needleleaf vegetation at inland study sites these results demonstrate that changes in vegetation played a critical role in establishing the modern hydrologic regime in western north america we suggest that this isotopic increase is due to three primary reasons 1 increased evaporation and transpiration fluxes in grassland regions affect water balance 2 shallower rooting depths of grasses lead to the transpiration of soil water enriched in o 18 due to evaporation and 3 grasslands transpire o 18 rich waters during a shorter more punctuated growing season we argue that the observed isotope signals are indicative of a feedback mechanism wherein grasslands not only respond to regional and global climatic trends but also act as a driver of hydrologic change by enhancing seasonality and aridity grasslands transmit hydrologic disturbances downstream engineering climatic conditions favorable for their expansion

aridification in continental asia after the middle eocene climatic optimum meco global climate cooling from greenhouse to icehouse conditions occurred across an enigmatic transitional interval during the eocene epoch characterized by incipient polar ice sheet formation as well as short lived warming events of which the middle eocene climatic optimum meco is most noticeable understanding this critical period requires high resolution records that are being gathered in marine basins but are still lacking in the terrestrial realm here we provide a precisely dated terrestrial record crossing the meco time interval from the xining basin nw china we document a rapid aridification step and the onset of obliquity dominated climate cyclicity indicated by lithofacies and pollen records dated at 40 0 ma at the base of magnetochron c18n 2n this shift is concomitant within error with the meco peak warming in ocean drilling program site 1258 for which we reassessed the magnetostratigraphic age at 40 0 ma also at base of magnetochron c18n 2n the rapidity of the shift observed in the xining basin and the region wide aridification and monsoonal intensification reported around 40 ma suggests asian paleoenvironments were responding to global climate changes associated with the meco however the xining records show only the permanent shift but not the transient peak warming observed in marine meco records we thus relate this permanent aridification to occur during the post meco cooling we propose the mechanisms linking global climate to asian paleoenvironments may be eustatic fluctuations driving the stepwise retreat of the proto paratethys epicontinental sea or simply global cooling reducing moisture supply to the continental interior in any case eocene global climate cooling from greenhouse to icehouse conditions seem to have played a primary role in shaping asian paleoenvironments

rossby wave propagation from the arctic into the midlatitudes does it arise from in situ latent heating or a trans arctic wave train abstractthe relationship between latent heating over the greenland barents and kara seas gbks hereafter and rossby wave propagation between the arctic and midlatitudes is investigated using glo

analysis of saltwater upconing beneath a pumping well abstract aquifer systems that contain freshwater and saltwater are usually stratified with the more dense saltwater underlying the freshwater a groundwater well discharging from the freshwater zone causes the saltwater to move upwards towards the well this phenomenon is known as saltwater upconing two methods of analysis the sharp interface method and the fluid density dependent solute transport method are used to simulate saltwater upconing numerical experiments including comparisons of the two methods indicate 1 for low to moderate pumpages the 50 isochlor and sharp interface correlate well 2 the well can discharge significant concentrations of saltwater even though a stable cone according to the sharp interface method exists below the well screen 3 an almost linear relationship exists between the well discharge rate and the concentration of the discharge at low pumping rates that maintain a stable cone and 4 upconing is sensitive to transverse dispersivity whereas it is insensitive to longitudinal dispersivity a simulation of upconing at test site no 4 truro cape cod massachusetts indicates that the appropriate field value of transverse dispersivity is very small this supports the validity of the sharp interface assumption for analyzing the behavior of systems with thin saltwater freshwater transition zones

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

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

impact of diabatic heating over the tibetan plateau on subsidence over northeast asian arid region 1 the formation mechanism of the arid climate over northeast asia is investigated by a series of regional climate model experiments precipitation there is suppressed by a prominent regional scale subsidence during summertime an experiment without diabatic heating shows very gentle vertical motion there whereas the subsidence is prominent when diabatic heating by solar radiation is included in the model additionally the other experiments indicate that an artificial heating over the tibetan plateau enhances the subsidence over the arid area which is similar to the observed distribution these results suggest that the thermal effects of the plateau induce the prominent subsidence the mechanical effects of the topography such as stationary mountain waves are not a principal reason for the subsidence nor the arid climate the stationary rossby wave driven by the diabatic heating over the plateau tends to propagate northward during boreal summer since subtropical westerly jet locates north of the plateau

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

a stalagmite record of abrupt climate change and possible westerlies derived atmospheric precipitation during the penultimate glacial maximum in northern china abstract the geochemistry and petrography of a stalagmite from wanxiang cave in central china provide a paleoclimate record of the penultimate glacial maximum pgm suggesting unexpectedly abundant non monsoonal atmospheric precipitation at the nadir of the pgm eleven u th 230 th ages from 149 to 140 ka bp place the stalagmite in marine isotope stage 6b coincident with the greatest benthic marine 18 o calcite values of mis 6 carbon and oxygen stable isotope data measurements of layer specific width positions of surfaces of non deposition or dissolution changes in the character and thickness of seemingly annual layers changes in concentration of organic acids within the stalagmite s calcite and patterns in the mg concentration of that calcite all combine to give a coherent paleoclimate record these data suggest that the stalagmite represents a wetter period than before or after its growth with the wettest and coldest phase at 145 to 144 ka bp this extreme in climate yields a striking correlation with the lr04 stack of oxygen isotope records from marine benthic forams if the latter is subjected to a 4500 year chronological adjustment previously suggested by u th data from corals the timing of the wudu stalagmite s deposition combines with findings elsewhere to suggest that the pgm was the most extreme of later pleistocene glacial maxima petrography and u th age determinations suggest dramatic changes in climate during the pgm at the beginning 149 146 ka bp and end 143 140 ka bp of the stalagmite s growth abrupt century scale drying caused lengthy hiatuses as dripwater to the stalagmite diminished on the other hand delivery of water to the stalagmite during the wettest phase 145 144 ka bp caused dissolution of previous layers of the stalagmite enhanced atmospheric precipitation during the cold of a glacial maximum is unexpected because within the spectrum of holocene climate cooler conditions lessen the impact of the east asian monsoon changes in the character of stalagmite layers indeed suggest weakened to negligible influence of the east asian monsoon during the nadir of the pgm however data from the stalagmite are compatible with atmospheric precipitation from westerly winds that today reach only northwestern china but that may have been deflected southward in the pgm by southward migration of the siberian high this unexpected significance of the westerlies during the pgm may be a result of the hypothesized extreme nature of the pgm relative to other glacial maxima of the later pleistocene

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

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

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

what drives the north atlantic oscillation s temperature anomaly pattern part i the growth and decay of the surface air temperature anomalies abstractcomposite analysis is used to examine the physical processes that drive the growth and decay of the surface air temperature anomaly pattern associated with the north atlantic oscillation n

what controlled mid late miocene long term aridification in central asia global cooling or tibetan plateau uplift a review abstract debate continues over whether global cooling or uplift of the tibetan plateau provided the first order driver for the aridification moisture levels of central asia throughout the mid late miocene between about 17 and 5 ma this review attempts to throw new light on the relations between the aridification and these two key factors this paper examines the evolution of miocene climate both moisture and temperature within five separate regions of eurasia to help understand the large scale controls of long term moisture in central asia the five regions include 1 europe 2 high latitude asia 3 the east asian monsoon region 4 the south asian monsoon region and 5 central asia itself because moisture reaching central asia has to firstly cross at least one of the other four regions temperature proxy data compiled from these five regions correlate with ocean temperatures from the global deep sea oxygen isotope records furthermore compiled moisture proxy data from the four regions surrounding central asia co vary and correlate with each other this can be explained by positive feedbacks between drying and cooling and supports the assumption that global cooling provides a dominant driving factor for the drying of eurasia global cooling reduces the amount of water vapor held in the atmosphere and thereby can cause terrestrial drying however in central asia the moisture evolution shows less similarity with its surroundings the uplift of the tibetan plateau including the tianshan mountains could provide a possible explanation for this difference the changing topography resulting from uplift events over time and space strongly influenced the moisture patterns in central asia during miocene times future research on the spatial timing and amplitude of tibetan plateau uplift should be useful to understand the moisture processes in central asia during the miocene

use of temperature logs in coal seam gas reservoirs application to the sydney basin australia this study examines the relationship between borehole temperature logs and gas distribution in coal seams both spatially and with depth temperature logs are often utilized in hydrogeology to monitor groundwater flow which can introduce methanogenic consortia into coal seams resulting in the generation and accumulation of coal seam gases areas of hydraulic connectivity characterized by open cleats and fractures provide a pathway for the meteoric influx whereas tight mineralized sections of strata prohibit vertical flow and have the potential to trap coal seam gases or to limit the influx of methanogens and the generation of secondary biogenic methane the combination of these concepts raises the possibility of utilizing temperature logs for mapping coal seam gas distributions and assisting exploration activities wireline temperature logs are inexpensive to obtain as part of any exploration production or monitoring program but provide information pertaining to flow regimes and in situ geological environments a case study is presented from the sydney basin of australia to demonstrate the types of analyses and interpretations relating to coal seam gas distribution that may be gleaned from temperature log datasets

evaluations of the saltwater groundwater interface from borehole temperature in a coastal region an interface between saltwater and groundwater was evaluated by monitoring the vertical groundwater temperature profiles the temperature gradients were found to be constant below certain depths in boreholes however the gradients decreased above the depths and the temperature profiles were convex in a coastal region the depth to change in the vertical thermal gradient indicates a hydrological boundary where upward groundwater flow exists above the boundary and no water flow exists below the boundary estimated depths to the interface between saltwater and fresh water using groundwater temperature agreed well with the depths calculated by traditional methods using groundwater potentials and with the results of the groundwater salinity results suggest that temperature may be an economical and reliable alternative to traditional methods

geologic controls of submarine groundwater discharge application of remote sensing to north lebanon typical of mediterranean countries the lebanese shoreline is well known for its littoral and offshore groundwater discharges the so called submarine springs the tectonic framework of the terrain explains its interruption by dense geologic structures i e fracturing faulting karstic routes as well as acute dips of rock strata seaward all of these structures serve as hydrologic agents transporting groundwater to the sea the study aims to locate these groundwater discharges and to interpret their geologic controls on land for this purpose two major lines of approach were followed the first is an airborne thermal infrared tir survey using radiometers to identify thermal anomalies thereby determining the exact location of submarine groundwater discharges sgds the second line of approach is the analysis of satellite images landsat 7etm to delineate the geologic features that govern the mechanism of water flow thereby determining their sources on land twenty seven major sgds were identified 10 of these being offshore springs the others littoral springs the springs show a large variety of discharge configurations and extents mainly parallel or perpendicular to the shoreline or rounded three major structural controls were identified to contribute to the transport of groundwater to the sea these are karstic galleries faults and tilted rock strata their contributions being 48 37 and 15 respectively the sgds associated with linear passageways i e karstic galleries and faults are connected with land aquifer formations several kilometers away from the shoreline moreover the presence of impervious rock formations at many localities along the coastline results in a confined hydrologic system promoting the flow of sgds into the sea

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

the middle eocene to early miocene integrated sedimentary record in the qaidam basin and its implications for paleoclimate and early tibetan plateau uplift detailed analysis of whole rock geochemistry clay minerals sedimentary color and pollen in the dahonggou section northeast of the qaidam basin are investigated and the results suggest an intense weathering in the source area during the middle eocene 48 5 40 5 ma indicating a warm and humid condition the distinct decrease of chemical weathering degree in source regions began at 40 5 ma which is in agreement with the distinct decrease in redness of sedimentary sequences and the disappearance of thermophilic elements in pollen records this 40 5 ma cooling event extent demonstrated evidence for an intensification of central asian aridification which could be attributed to attainment of high elevations in southern central tibet and retreat of the paratethys from central asia in the late eocene reducing moisture transport to the qaidam basin

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

asian monsoons and aridification response to paleogene sea retreat and neogene westerly shielding indicated by seasonality in paratethys oysters asian climate patterns characterised by highly seasonal monsoons and continentality are thought to originate in the eocene epoch 56 to 34 million years ago ma in response to global climate tibetan plateau uplift and the disappearance of the giant proto paratethys sea formerly extending over eurasia the influence of this sea on asian climate has hitherto not been constrained by proxy records despite being recognised as a major driver by climate models we report here strongly seasonal records preserved in annual lamina of eocene oysters from the proto paratethys with sedimentological and numerical data showing that monsoons were not dampened by the sea and that aridification was modulated by westerly moisture sourced from the sea hot and arid summers despite the presence of the sea suggest a strong anticyclonic zone at central asian latitudes and an orographic effect from the emerging tibetan plateau westerly moisture precipitating during cold and wetter winters appear to have decreased in two steps first in response to the late eocene 34 37 ma sea retreat second by the orogeny of the tian shan and pamir ranges shielding the westerlies after 25 ma paleogene sea retreat and neogene westerly shielding thus provide two successive mechanisms forcing coeval asian desertification and biotic crises

water temperature and conductivity variability as indicators of groundwater behaviour in complex aquifer systems in the south east of spain groundwater temperature and electrical conductivity logs were applied in this study to gain an understanding of the hydrogeological behaviour of a complex system this system compartmentalized by a large number of fractures which may even cause geothermal anomalies is that of the campo de dalias in the south east of the iberian peninsula in addition to this complexity one must consider the different levels with aquifer properties and their varying lithologies which in some cases are in direct contact with the sea vertical sections based upon the various logs allow lateral correlation to be made between the anomalies detected and provide information on the existence of both ascending and descending vertical flows and the inflow of sea water into the system analysis of environmental isotopes 18o and d indicate the areas of recharge with the greatest flow velocity no seasonal variation in the isotopes was observed which suggests that the residence time of the groundwater in the aquifer is several years radiocarbon dating gave estimates of generally long residence times although in some sectors it is possible to detect the current recharge based on its tritium content from rainwater infiltration or seawater intrusion copyright 2002 john wiley sons ltd

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

paleomagnetic evidence for cenozoic block rotations in the tadjik depression central asia this paper presents results of a paleomagnetic study of oligo miocene red beds of the tadjik depression in central asia we sampled about 530 cores at 69 sites and six localities across the depression and along the western border of the pamirs samples were thermally demagnetized and high temperature components appear to predate folding of upper tertiary age throughout the depression paleomagnetic inclinations are consistent with those observed on the stable turan platform at the western margin of the depression however they are shallower by about 30 than the inclination predicted from the reference apparent polar wander path this appears to indicate a 23 difference in latitude which is incompatible with paleogeographic reconstructions for the tertiary a sound interpretation of this anomaly would require a better constrained tertiary paleomagnetic reference for asia inside the tadjik depression paleomagnetic declinations are all significantly rotated counterclockwise with respect to those measured on the turan platform the eastern part of the depression is a domain of large rotation 52 13 to 46 15 whereas smaller amounts of rotation have occurred in the western part 27 14 to 14 15 the similarity between tertiary and cretaceous data available for the area shows that rotations have occurred since the miocene little or no paleomagnetic rotations are observed in the ranges bordering the northern and western parts of the depression paleomagnetic and structural data suggest that block rotations in the tadjik depression are associated with indentation of the pamirs into stable asia at a larger scale observed rotations are compatible with a model of regional sinistral wrenching along a strip running from the gulf of oman to lake baikal

geothermal measurements in a deep well at regina saskatchewan abstract the university of regina geothermal project was designed to demonstrate the use of moderate temperature geothermal resources from sedimentary aquifers in heating large buildings the first well was drilled on the campus of the university of regina in the winter of 1979 hydraulic potentials show that individual aquifers of the basal clastic unit are not in direct hydraulic connection and temperature measurements show that flow is occurring in the open hole apparent terrestrial heat flow varies vertically in the upper clastic unit showing either cross formational water flow or errors in the measurement of thermal conductivity of shales a reasonably uniform heat flow of 51 mw m 2 in the carbonate evaporite unit may represent the terrestrial heat flow from the basement but this cannot be demonstrated with certainty

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 growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

reconstructing the paleotopography of mountain belts from the isotopic composition of authigenic minerals the paleorelief of mountain belts can be estimated from the 18 o value of authigenic minerals development of relief during mountain building often creates lee side rain shadows in which precipitation is depleted in 18 o and d the magnitude of this rain shadow effect is strongly correlated to relief a compilation of 18 o data from surface waters throughout the globe shows a linear relationship between net elevation change and 18 o r 2 0 79 through the use of this relationship we investigated the timing and magnitude of elevation change in the southern alps of new zealand and the sierra nevada of california the 18 o values of kaolinites from new zealand show an 6 decrease in the early pliocene that corresponds to an 2 km elevation change in the southern alps the 18 o of smectites from the sierra nevada show little change since 16 ma suggesting that these mountains have been a long standing topographic feature

volcanic and tectonic controls of lacustrine and alluvial sedimentation in the stephanian coal bearing sequence of the malpas sort basin catalonian pyrenees the infill of a small variscan basin shows a complex succession of lacustrine and alluvial sediments whose pattern of distribution through time appears to have changed in response to contemporaneous volcanism following initial deposition of pyroclastic breccias and extrusion of lavas small lakes were established on the floor of the basin their infills were probably locally controlled by relief on top of the lavas but the pattern was disrupted by phases of mass movement from the basin margin which emplaced debris flows and a sedimentary melange containing large blocks of limestone and led to extensive soft sediment deformation this complex sequence of events culminated in the emplacement of a widespread ash flow bed an alluvial plain established during a period of rather uniform subsidence was rapidly drowned to give an extensive lake whose progradational infill led to re establishment of an alluvial plain the deposition of a widespread airfall tuff coincided with the onset of differential subsidence during which major channel sandstones were stacked in association with poorly drained palaeosols in the east of the area whilst a mudstone dominated sequence characterized by well drained palaeosols developed in the west a return to more uniform subsidence appears to have coincided with the cessation of volcanic activity

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

a mechanism and simple dynamical model of the north atlantic oscillation and annular modes a simple dynamical model is presented for the basic spatial and temporal structure of the large scale modes of intraseasonal variability and associated variations in the zonal index such variability in the extratropical atmosphere is known to be represented by fairly well defined patterns and among the most prominent are the north atlantic oscillation nao and a more zonally symmetric pattern known as an annular mode which is most pronounced in the southern hemisphere these patterns may be produced by the momentum fluxes associated with large scale midlatitude stirring such as that provided by baroclinic eddies it is shown how such stirring as represented by a simple stochastic forcing in a barotropic model leads to a variability in the zonal flow via a variability in the eddy momentum flux convergence and to patterns similar to those observed typically the leading modes of variability may be characterized as a mixture of wobbles in the zonal jet position and pulses in the zonal jet strength if the stochastic forcing is statistically zonally uniform then the resulting patterns of variability as represented by empirical orthogonal functions are almost zonally uniform and the pressure pattern is dipolar in the meridional direction resembling an annular mode if the forcing is enhanced in a zonally localized region thus mimicking the effects of a storm track over the ocean then the resulting variability pattern is zonally localized resembling the north atlantic oscillation this suggests that the north atlantic oscillation and annular modes are produced by the same mechanism and are manifestations of the same phenomenon the time scale of variability of the patterns is longer than the decorrelation time scale of the stochastic forcing because of the temporal integration of the forcing by the equations of motion limited by the effects of nonlinear dynamics and friction for reasonable parameters these produce a decorrelation time of the order of 5 10 days the model also produces some long term 100 days or longer variability without imposing such variability via the external parameters except insofar as it is contained in the nearly white stochastic forcing

rain shadow development during the growth of mountain ranges an atmospheric dynamics perspective 1 an idealized atmospheric model is used to explore the links between climate and topography in the development of orographic rain shadows during orogenesis the atmospheric dynamics theory of density stratified fluid flow over topography is used to interpret the results the controlling nondimensional parameter is nh u where n is the brunt vaisala frequency a measure of atmospheric stability h is the terrain relief and u is the initial horizontal wind speed rain shadow development is found to be a nonlinear and nonunique function of both topography and atmospheric state indicating that geological records of orographic aridity cannot be interpreted in terms of relief alone when upstream topography exceeds nh u 1 during surface uplift downstream orographic precipitation vanishes and downstream orographic cloud mass decreases by as much as 90 upstream blocking of air flow can generate a forward projecting rain shadow in which a relatively low ridge nh u 1 may be decoupled from the atmospheric flow by a zone of flow stagnation extending upstream of the high terrain such an effect may occur if the valley separating the two ranges is narrower than the length scale of flow stagnation in the model configuration used here lateral widening of a relatively low nh u 1 range increases downstream cloud mass by up to a factor of 3 these results help to refine interpretations of climate tectonic interactions in shaping the geological record of the sierra nevada and andes

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e