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

evidence for northeastern tibetan plateau uplift between 25 and 20 ma in the sedimentary archive of the xining basin northwestern china the growth history of the tibetan plateau provides a valuable natural laboratory to understand tectonic processes of the india asia collision and their impact on and interactions with asian and global climate change however both tibetan plateau growth and asian paleoenvironments are generally poorly documented in pre pliocene times and reflect limited temporal coverage for different parts of the plateau here we present magnetostratigraphic results from the xining basin at the ne margin of the tibetan plateau precisely dating the record between the earliest oligocene 33 ma to the middle miocene 16 ma the pattern of observed paleomagnetic polarity zones is unequivocally correlated to the geomagnetic polarity time scale gpts indicating relatively constant and low sediment accumulation rates 32 m myr except for a peculiar period of unstable accumulation between 25 3 and 19 7ma at the beginning of this interval a marked permanent increase in magnetite content of the sediments is observed and likely relates to a change in provenance we directly relate this unstable period of sediment accumulation and provenance change to the coeval exhumation recently reported by low temperature thermochronology from the laji shan range which subsequently formed the southernmargin of the xining basin evidence for ne tibet tectonismat 25 20 ma can be associated with widespread deformation over the entire himalayan tibetan orogen at this time which may be linked to the coeval appearance of monsoon climate in eastern asia and the onset of central asian desertification

late miocene upward and outward growth of eastern tibet and decreasing monsoon rainfall over the northwestern indian subcontinent since 10 ma 1 many geologic observations suggest that the eastern portion of the tibetan plateau has expanded eastward and grown in height over the past 15 10 ma and other observations suggest that climate over the northwestern indian subcontinent nw india became more arid between 11 and 7 ma we suggest that they are linked higher terrain increased orographic precipitation over eastern tibet which diabatically heated the atmosphere there that heating then forced subsidence to the west via the mechanism proposed by rodwell and hoskins and subsidence suppressed rainfall simple gill model calculations for a heat source displaced from the equator show such subsidence and a regression of july august outgoing long wave radiation olr over southeastern tibet with rainfall shows a negative relationship between eastern tibet and nw india consistent with the proposed link between growth of eastern tibet and diminished south asian monsoon rainfall over the northwestern indian subcontinent

sedimentation induced burial of subsea pipelines observations from field data and laboratory experiments abstract sediment transport induced changes to the embedment of three 26 km long sections of subsea pipeline are analysed and subsequently explained using model scale experiments rather than the scour and scour induced sinking and sagging traditionally thought to dominate post lay pipeline spanning and embedment change the change for these pipelines is shown to be caused by sedimentation the pipelines traverse a range of metocean and soil conditions the variation in embedment correlates well with the variation in metocean conditions with most change occurring in an area where multidirectional high velocity short duration flows associated with internal waves propagate at near perpendicular angles to the pipeline to understand the mechanism driving these changes a series of model scale tests in o tube flumes have been completed under flow conditions mimicking those recorded in the field good agreement is found between the field and laboratory results both in terms of the process timescale and the post sedimentation profile the consistency of the embedment changes between the pipelines their correlation with metocean conditions and the ability to replicate these changes in model scale tests suggests that such changes can be accounted for in more effective pipeline design spans are relatively rare along the pipelines but where they do occur fish rather than scour are shown to be the principal agent of span formation

generalized time scale for wave induced backfilling beneath submarine pipelines abstract this paper presents 25 new laboratory experiments involving the wave induced backfilling of wave induced scour holes beneath submarine pipelines so called wave to wave backfilling scenarios the experiments complement the previous 8 wave to wave backfilling experiments of fredsoe et al as well as recent current to wave backfilling experiments of bayraktar et al it is found that the wave induced backfilling time scale is generally an order of magnitude larger than for scour and is relatively insensitive to the initial current or wave induced pre backfilling scour profile based on this the data sets involving wave induced backfilling are collectively analyzed resulting in a new generalized expression for estimating the wave induced backfilling time scale beneath pipelines in the live bed regime this expression accounts for primary dependence on the shields parameter as well as secondary dependence based on the difference between the estimated or known initial and expected final equilibrium scour depth due to the backfilling wave condition

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

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

rans based simulation of turbulent wave boundary layer and sheet flow sediment transport processes abstract a numerical model coupling the horizontal component of the incompressible reynolds averaged navier stokes rans equations with two equation k turbulence closure is presented and used to simulate a variety of turbulent wave boundary layer processes the hydrodynamic model is additionally coupled with bed and suspended load descriptions the latter based on an unsteady turbulent diffusion equation for simulation of sheet flow sediment transport processes in addition to standard features common within such rans based approaches the present model includes 1 hindered settling velocities at high suspended sediment concentrations 2 turbulence suppression due to density gradients in the water sand mixture 3 boundary layer streaming due to convective terms and 4 converging diverging effects due to a sloping bed the present model therefore provides a framework for simultaneous inclusion of a number of local factors important within cross shore wave boundary layer and sediment transport dynamics the hydrodynamic model is validated for both hydraulically smooth and rough conditions based on wave friction factor diagrams and boundary layer streaming profiles with the results in excellent agreement with experimental and or previous numerical work the sediment transport model is likewise validated against oscillatory tunnel experiments involving both velocity skewed and acceleration skewed flows as well as against measurements beneath real progressive waves model capabilities are exploited to investigate the importance of boundary layer streaming effects on sediment transport in selected velocity skewed conditions for the medium sand grain conditions considered the model results suggest that streaming effects can enhance onshore sediment transport rates by as much as a factor of two moreover for fine sand conditions streaming and related convective effects are demonstrated to potentially reverse the direction of net transport i e from offshore to onshore relative that predicted in oscillatory tunnel conditions the developed model is implemented within the popular matlab environment and hence may be attractive for both research and educational purposes

experimental and numerical study of wave induced backfilling beneath submarine pipelines abstract this paper presents results of complementary experimental and numerical studies involving wave induced backfilling of current generated scour holes beneath submarine pipelines the laboratory experiments are conducted in a wave plus current flume utilizing laser doppler anemometry to measure velocities synchronized flow visualizations using digital image technology along with live bed scour and backfilling measurements each experiment is based on a two stage process 1 initial scour induced by a pure current followed by 2 backfilling induced by pure waves either regular or irregular the time series of scour depths are closely monitored through video recordings systematic analysis of these has resulted in a closed form expression for the backfilling time scale which is demonstrated to be a full order of magnitude greater than the well known time scale of scour with both governed primarily by the shields parameter the developed expression is strictly valid for the current to wave backfilling scenarios considered while likely serving as an upper limit for more general wave induced backfilling circumstances the experiments are complemented by similar backfilling simulations utilizing a fully coupled hydrodynamic and morphodynamic cfd model the numerical simulations demonstrate the ability of the model to predict backfilling towards expected equilibrium scour depths based on the new wave climate with time scales reasonably in line with experimental expectations

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

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

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

paleogene high elevations in the qiangtang terrane central tibetan plateau abstract the timing of uplift of the tibetan plateau remains controversial with estimates varying from eocene to more recent than pliocene in particular the paleoaltimetry of the qiangtang terrane on the central tibetan plateau is completely unknown here we present new stable isotope results of fluvial lacustrine carbonate cement pedogenic carbonate and marl from the kangtuo and suonahu formations deposited between 51 and 28 ma in the heihuling bamaoqiongzong area of the northern qiangtang terrane the lithofacies associations indicate that the kangtuo formation was deposited in alluvial fan and fluvial floodplain environments and the suonahu formation was deposited in near shore lacustrine playa lake and channelized fluvial environments carbon and oxygen isotope values coupled with the sedimentary facies interpretations point to evaporation and low respiration rates in the eocene oligocene paleosols suggesting an arid climate in the high qiangtang area at the time the 18opsw values of paleo surface water reconstructed from the lowest i e the least evaporated 18oc pdb values of the unaltered authigenic carbonates are used to make the minimum estimates of the average paleoelevation of the drainage basin the paleoelevation of the northern qiangtang terrane is reconstructed as above 5000 m by at least the middle oligocene 28 ma similar to the present elevation in this area the aridity and the positive shift in oxygen isotope values of surface waters in our study area may suggest that the high lhasa terrane established by the middle oligocene blocked the northward transport of tropical moisture maintenance of high elevation 5000 m from at least the oligocene to the present suggests that the qiangtang crust was already thickened by that time and that underthrusting of india beneath asia since then has continued to provide additional material while at the same time driving asian lower crust eastward by crustal flow

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

the impact of regional uplift of the tibetan plateau on the asian monsoon climate abstract the climatic effect of tibetan plateau tp uplift is a hot topic in paleoclimate research in this paper the results of a set of numerical simulations are reported to analyze the impact of regional tp uplift on the asian monsoon climate the focus is on the impact of the regional uplift in the west and east parts on south asian summer monsoon as well as the impact of regional uplift on east asian winter monsoon the results show that the uplifts of the himalaya and the central southern tp have little effect on summer precipitation increasing over south asia whereas the further uplifts of the tp in the west and east parts including the uplifts of both the eastern and western tp have important effects on the strengthening of the south asian summer monsoon the uplift of the eastern tp leads to low level cyclonic circulation anomalies appearing in the bay of bengal accompanied by anomalous upward movement and in turn precipitation markedly increases in the bay of bengal whereas the uplift of the western tp produces low level cyclonic circulation anomalies around the uplifted region and intensifies the moisture transport from the tropical ocean and thus precipitation further increases in south asia especially in the northern arabian sea the strengthened summer monsoon in south asia is coupled with the intensification in diabatic heating and moisture convergence for the east asian winter monsoon the intensification of winter monsoon winds is related more to the regional uplifts than the uplift of the whole tp the uplifts of the central southern tp the northern tp and other northern topography have greater effects on the strengthening of the winter monsoon winds

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

active tectonics of the turkish iranian plateau 1 this paper examines how active faulting in the turkey iran caucasus region accommodates the arabia eurasia collision and the velocity field observed by gps the overall shortening across the zone is in general spatially separated partitioned into right lateral strike slip in the turkish iranian plateau and thrusting in the greater caucasus a band of counterclockwise rotating nw se right lateral strike slip faults accommodates a nw se gradient in ne directed velocity relative to eurasia between the black and caspian seas a nnw sse band of previously unrecognized oblique normal faults is present on the turkey iran border we estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 2 ma at present rates this implies a reorganization of deformation in the collision zone at that time after the initial collision at 12 ma probably in response to mantle induced dynamic uplift

effects of mountain uplift on east asian summer climate investigated by a coupled atmosphere ocean gcm abstract to study the effects of progressive mountain uplift on east asian summer climate a series of coupled general circulation model cgcm experiments were performed eight different mountain heights were used 0 no mountain 20 40 60 80 100 control run 120 and 140 the land sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe systematic changes in precipitation pattern and circulation fields as well as sea surface temperature sst appeared with progressive mountain uplift in summertime precipitation area moves inland on the asian continent with mountain uplift while the pacific subtropical anticyclone and associated trade winds become stronger the mountain uplift resulted in an sst increase over the western tropical pacific and the maritime continent and an sst decrease over the western indian ocean and the central subtropical pacific there is a drastic change in the east asian circulations with the threshold value

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

numerical simulation of wave induced scour and backfilling processes beneath submarine pipelines abstract a fully coupled hydrodynamic morphodynamic numerical model is presented and utilized for the simulation of wave induced scour and backfilling processes beneath submarine pipelines the model is based on solutions to reynolds averaged navier stokes equations coupled with k turbulence closure with additional bed and suspended load descriptions forming the basis for sea bed morphology the morphological evolution is updated continuously rather than being based e g on period or other time averaging techniques simulations involving wave induced scour over the range of keulegan carpenter number 5 6 kc 30 demonstrate reasonable match with previous experiments both in terms of the equilibrium scour depth as well as the scour time scale wave induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger kc to new wave climates characterized by lower kc values the simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate in line with experimental expectations the simulated backfilling process is characterized by two stages 1 an initial re distribution phase involving re organization of sediments in the immediate vicinity of the pipeline potentially followed by 2 a more lengthy backfilling evolution toward equilibrium scour depth the simulated backfilling time scales are of the same order of magnitude as in experiments though the multi stage process complicates a more systematic characterization the simulated sequences of scour and backfilling achieved within the present work are estimated to represent temporal durations of up to approximately 12 h at full practical scales

numerical modeling of flow and scour at pipelines a numerical model for the description of fluid flow and suspended and bed load sediment transport is presented density effects are included in the momentum reynolds equations and in the turbulence kappa and epsilon equations changes in bed levels are calculated from sediment continuity and the finite element grid is adapted to the geometry the reynolds equations and the transport equation for suspended sediment are solved numerically using a taylor galerkin finite element method the flow at a surface mounted cylinder in a steady flow is predicted in good agreement with experiments periodic vortex shedding from a cylinder placed above a rigid bed is predicted in good agreement with laboratory experiments provided that sufficiently detailed grids approximately 5 000 nodes are used scour calculations are performed for a cylinder in a steady flow with its underside placed at the level of the original flat bed predicted scour at a pipeline in steady flow is in good agreement with laboratory measurements reported in the literature

formation and development of a breaker bar under regular waves part 1 model description and hydrodynamics abstract in this work a detailed hydrodynamic model is presented which is used for the study of cross shore sediment transport and morphodynamics in two dimensions the model is described in the framework of the generally unstructured finite volume method considerable emphasis is put on those subtleties in the morphological formulation which are required to achieve mass conservation for the amount of sediment in the bed and in suspension in this first part of two the hydrodynamic description over the cross shore profile is presented the model is validated against an experiment with detailed measurements of the free surface and turbulence over a fixed breaker bar profile a test matrix covering a large interval of the surf similarity parameter is simulated and the phase lag between the breakpoint and the initiation of the setup is described the relation of this phase lag to a cross shore delay in dissipation of organised energy into turbulence is described the relation of this phase lag to the distribution of the location of maxima in bed shear stresses and magnitude of the undertow is also described furthermore processes in the hydrodynamics which will have a smoothing effect on the mean cross shore sediment transport and morphodynamic response are considered all simulations are presented for regular waves and for values of the deep water surf similarity parameter 0 in the range from 0 08 to 1 19 i e covering both spilling and plunging breakers