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

c4 expansion in the central inner mongolia during the latest miocene and early pliocene abstract the emergence of c4 photosynthesis in plants as a significant component of terrestrial ecosystems is thought to be an adaptive response to changes in atmospheric co 2 concentration and or climate during neogene times and has had a profound effect on the global terrestrial biosphere although expansion of c4 grasses in the latest miocene and pliocene has been widely documented around the world the spatial and temporal variations in the c4 expansion are still not well understood and its driving mechanisms remain a contentious issue here we present the results of carbon and oxygen isotope analyses of fossil and modern mammalian tooth enamel samples from the central inner mongolia our samples represent a diverse group of herbivorous mammals including deer elephants rhinos horses and giraffes ranging in age from the late oligocene to modern the 13 c values of 91 tooth enamel samples of early late miocene age or older with the exception of two 13 ma rhino samples 7 8 and 7 6 and one 8 5 ma suspected rhino sample 7 6 were all less than 8 0 vpdb indicating that there were no c4 grasses present in their diets and thus probably few or no c4 grasses in the ecosystems of the central inner mongolia prior to 8 ma however 12 out of 26 tooth enamel samples of younger ages 7 5 ma to 3 9 ma have 13 c values higher than 8 0 up to 2 4 indicating that herbivores in the area had variable diets ranging from pure c3 to mixed c3 c4 vegetation during that time interval the presence of c4 grasses in herbivores diets up to 76 c4 suggests that c4 grasses were a significant component of the local ecosystems in the latest miocene and early pliocene consistent with the hypothesis of a global factor as the driving mechanism of the late miocene c4 expansion today c3 grasses dominate grasslands in the central inner mongolia area the retreat of c4 grasses from this area after the early pliocene may have been driven by regional climate change associated with tectonic processes in central asia as well as global climate change

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

late cretaceous tectonic switch from a western pacific to an andean type continental margin evolution in east asia and a foreland basin development in ne china the early cretaceous structure of ne china was a result of slab rollback driven extensional tectonics characteristic of western pacific type continental margins oblique docking of a microcontinent along the asian active margin in the early late cretaceous induced a compressional stress regime that brought about an andean type continental margin development partitioning of contractional transpressional strain across ne china produced a retroarc foreland basin system comprising from east to west an orogenic wedge a foredeep songliao basin a forebulge great xing an range and a back bulge depozone hailar and erlian basins a sub circular lacustrine depozone in the pre existing songliao basin evolved into a nne trending depocentre near the forebulge and acquired a westward flowing fluvial deltaic drainage system during the campanian development of this retroarc foreland basin system signals a significant tectonic switch from a western pacific type to an andean type continental margin evolution in the geological history of east asia this article is protected by copyright all rights reserved

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

nd and sr isotope systematics of miocene to holocene volcanic rocks from southwest japan volcanism since the opening of the japan sea isotope nd and sr and geochemical data for twelve volcanic rocks from the shimane oki san in region of southwest japan give some insight into the miocene recent volcanic history of southern japan since rifting from the asian mainland the oldest rocks examined dolerites and ushikiri formation were erupted during the opening of the japan sea at about 15 ma and comprise arc tholeiites derived from a depleted source end 0 esr 0 interpreted in terms of a depleted mantle source modified by a slab derived fluid volcanics of oki dozen island in the japan sea are alkalic derived from an enriched mantle plume isotopically distinct from nearly oki dogo island eruption of the calc alkaline wakurayama andesite early pliocene and both arc and within plate type basalts 1 ma show that magmas were tapped from a variety of sources taking into account plate tectonics and seismic data the subduction influence until the quaternary was the pacific plate with philippines sea plate subduction affecting quaternary and younger volcanics

rapid exhumation at 8 ma on the liupan shan thrust fault from apatite fission track thermochronology implications for growth of the northeastern tibetan plateau margin abstract the liupan shan mountain is one of the outermost ranges in northeastern tibetan plateau the onset of its uplift provides insight on whether the plateau grew sequentially outward or broad areas of the plateau deformed simultaneously the apatite fission track method can be used to date rapid cooling as the result of unroofing of rocks in response to tectonically induced vertical motion fission track data from apatite in early cretaceous sedimentary strata exposed on the hanging wall of liupan shan thrust fault in northeastern tibet suggest that a late cenozoic rapid cooling events occurred at 7 3 8 2 ma or 8 ma this age apparently dates fault activity of the liupan shan thrust in response to northeastward growth of the tibetan plateau uplift and lateral growth which continues today numerous studies of the tibetan plateau suggest that the onset of deformation in eastern and northern margin of tibetan plateau occurred in the latest miocene

revisiting clay sized mineral and elemental records of the silicate weathering history in the northern tibetan plateau during the late cenozoic the role of aeolian dust

major element and ree compositions of pliocene sediments in southwest japan implications for paleoweathering and paleoclimate abstract the history of the east asian monsoon and the relationship between the development of the monsoon climate tectonics and global climate are complicated and controversial earlier studies have indicated that the east asian monsoon fluctuated in the asian interior during the pliocene thus the chemical weathering record in coastal regions of east asia can be the key to elucidating its evolution as well as the kuroshio current variability the present study clarifies the chemical weathering conditions in southwest japan based on the concentrations of major elements and rare earth elements rees in lacustrine muddy sediments the chemical weathering was moderate between 4 4 and 3 8 ma between 3 8 and 3 4 ma chemical weathering significantly intensified as indicated by the high values of the chemical index of alteration that reached a maximum of 98 as well as the high concentrations of rees and light rees against heavy rees and kaolinite rich clay mineral compositions despite the wide variation in source rock compositions and grain sizes the degree of chemical weathering remained moderate during the early pleistocene the intense chemical weathering on land in southwest japan from 3 8 to 3 4 ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the kuroshio current and the intensification of the east asian summer monsoon

miocene climate change on the chinese loess plateau possible links to the growth of the northern tibetan plateau and global cooling the evolution of the asian monsoon arid environmental system during the cenozoic was closely related to the growth of the himalayan tibetan plateau and global climate change however due to inconsistencies in paleoclimatic reconstructions and to various constraints on the timing of the growth of the tibetan plateau the relative impacts of regional uplift and global cooling on asian climate change remain controversial here we investigate the mineralogical composition of a miocene red clay deposit on the western chinese loess plateau in order to infer changes in chemical weathering and monsoon intensity variations of four mineralogical ratios chlorite quartz illite quartz calcite quartz and protodolomite quartz reveal that the summer monsoon intensity was relatively strong during the early miocene 23 5 18 5 ma weakened gradually until 9 5 ma and strengthened again in the late miocene we synthesized previously published thermochronological data from the northeastern tibetan plateau and surrounding mountains and the results suggest that two phases of the rapid growth of northern tibet occurred around 24 17 and 13 7 ma comparison of paleoclimatic proxies and thermochronological data suggests that the gradual weakening of the summer monsoon intensity from 18 5 to 9 5 ma paralleled global cooling whereas two intervals of strengthened monsoon in the early and late miocene were possibly related to the rapid growth of northern tibet our combination of paleoenvironmental proxies and thermochronological data reveals possible links between miocene asian monsoon evolution phased growth of the tibetan plateau and global climate change and confirms the interconnection of geodynamic and atmospheric processes in the geological past

late mesozoic cenozoic evolution of the sanjiang basin in ne china and its tectonic implications for the west pacific continental margin abstract this study uses new seismic reflection profiles and exploratory well data to analyze the structural characteristics and evolution of the sanjiang basin in eastern heilongjiang ne china the basin sequence was divided into six stratigraphic units representing discrete middle upper jurassic lower cretaceous upper cretaceous eocene oligocene miocene and quaternary phases of development the sanjiang basin initiated as a passive marginal rift flank to the southern mongol okhotsk ocean during the middle jurassic and primary basin growth was terminated by orogenic deformation related to the mongol okhotsk suture to the north and the accretion of the nadanhada terrane to the east middle upper jurassic strata are controlled by half graben structures active during this phase of basin growth and are limited largely to the west suibin sub basin the wider basin experienced renewed rifting and large scale sag caused by back arc extension along the eurasian continental margin in the early cretaceous terminating during the late cretaceous in a phase of intense compression at the contemporary andean type continental margin this produced a series of thrust folds through the lower and upper cretaceous successions and led to the development of a regional scale erosional unconformity minor subsequent cenozoic extension is attributed to back arc extension along the west pacific continental margin with eocene oligocene miocene and quaternary deposits unconformably overlying the mesozoic sequences in half graben and extensional fault demarcated depocenters most prominently in the east qianjin sub basin

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

isotopic constraints on intensified aridity in central asia around 12 ma abstract the relationship between central asian aridification and the evolution of the himalayan tibetan orogen remains elusive new isotopic data from pedogenic and lacustrine carbonates sampled from well dated neogene strata 15 7 1 8 ma in the northeastern qaidam basin of the northern tibetan plateau identify a positive shift of 2 5 in 18 o values from 12 ma to 10 7 ma high values were maintained until 3 3 ma when 18 o values drop by 1 the timing of the positive shift in 18 o values is remarkably consistent with isotopic records from a vast region along and within the northern tibetan plateau isotopic mineralogical petrologic and facies analyses suggest that diagenetic effects and detrital contamination are minimal the positive shift in 18 o values as well as high 13 c values from pedogenic carbonates which are suggestive of low soil respiration rates is interpreted to indicate intensified aridity in central asia ca 12 ma the recognition of intensified aridity is critical to understanding the climatic effects of the development of the himalayan tibetan orogen we attribute this climatic change in the central asia to 1 retreat of paratethys from central asia strengthening the seasonal contrast and resulting in the loss of a nearby moisture source 2 attainment of high elevations in the himalayas and south central tibet blocking moisture bearing air masses from the indian and pacific oceans and 3 enhanced isolation and outward growth of the northern tibetan plateau the negative shift around 3 3 ma might be related to the onset of northern hemisphere glaciation intensification of the east asia monsoon and or effects of orographic rain out

provenance of cenozoic sediments in the xining basin revealed by nd and pb isotopic evidence implications for tectonic uplift of the ne tibetan plateau

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

clay sized sediment provenance change in the northern okinawa trough since 22kyrbp and its paleoenvironmental implication provenances of clay sized terrigenous sediments and a comprehensive interpretation of their high resolution variations in the northern okinawa trough since the late last glaciation remain unclear especially in regard to the huanghe and taiwan derived matter grain size clay mineralogy typical elemental ratio oxygen isotope and ams c 14 dating of core pc 1 in the northern okinawa trough were investigated to trace clay sized sediment provenance and transport process and thus to recover their forcing mechanisms over the last 22 kyr variations in linear sedimentation rate grain size delta o 18 ti ca ratio and clay minerals can be clearly divided into three distinct intervals consistent with changes in sediment provenance that can be close related to sea level fluctuation evolution of the tsushima warm current as well as influence from the east asian monsoon climate evolution during the late last glaciation period interval 1 22 16 kyr bp when the tsushima warm current was absent in the east china sea the paleo huanghe mouth was situated close to the study area and thus the paleo huanghe could have played major role in sedimentation therein in interval 2 16 7 3 kyr bp global sea level rise led to gradually retreating of the paleo huanghe mouth and thus decreasing terrigenous sediment supply from it to the study area since 73 kyr bp interval 3 some clay minerals from taiwan might have been transported northward to the study area by the fully evolved tsushima warm current characterized by higher chlorite kaolinite ratios in contrast the decreasing influence of the huanghe derived sediments during the strengthening of the tsushima warm current periods was probably caused by the blocking effect of the tsushima warm current particularly chlorite kaolinite ratio and smectite content in the okinawa trough sediment might be good proxies for indicating the tsushima warm current related sedimentary environment c 2014 elsevier b v all rights reserved

history of asian eolian input to the sea of japan since 15 ma links to tibetan uplift or global cooling abstract we present high resolution analyses of clay mineral assemblages combined with analysis of sr nd pb isotopic compositions of the

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

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

japan sea opening history and mechanism a synthesis the respective tectonic effects of back arc spreading and continental collision in asia are considered either as two independent processes or as closely interrelated extrusion tectonics assumes that the opening of the south china sea and the left lateral motion along the red river fault are geometrically linked in a pull apart manner this model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated in the case of the japan sea we can show without ambiguity that back arc opening was controlled by large intracontinental strike slip faults which can be easily understood as effects of the india asia collision far from the indenter the japan sea opened in the early miocene in a broad pull apart zone between two major dextral strike slip shear zones the first one extends from north sakhalin to central japan along 2000 km it has accommodated about 400 km of finite displacement deformation along it varies from dextral transpression in the north to dextral transtension in the south the second is between korea and sw japan and has accommodated a smaller displacement of about 200 km the extensional domain in between lies in the back arc region of japan distributed stretching of the arc crust resulted in the formation of most of the japan sea while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the japan basin the first oceanic crust was formed in a small triangle based on the eastern shear zone and spreading propagated westward inside the pull apart region timing of oceanic crust formation of formation of the dextral shear zones and of block rotation in between as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history this evolution is discussed by comparison to other manifestations of the arc and back arc activity such as the history of sedimentation and volcanism the paper then suggests that the collision of india can have tectonic consequences as far north as japan and sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion

cretaceous anomalous subsidence and its response to dynamic topography in the songliao basin northeast china to understand the formation mechanisms and evolution of the songliao basin we applied backstripping and strain rate inversion methods to 20 wells and reinterpret two seismic sections in the songliao basin the obtained data were used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of this area the predicted post rift subsidence based on the uniform stretching model that followed earlier lithospheric thinning events was much lower than the subsidence provided by backstripping the anomalous subsidence during the post rift stage was between 200 m and 800 m in the songliao basin and the depocenter of anomalous subsidence moved eastward between ca 110 and 80 ma before returning to the west between ca 80 and 65 ma regional variations in the subsidence rates suggest a possible deficit in the negative buoyancy mantle loading that is induced by the sinking slab beneath the songliao basin in addition the anomalous post rift subsidence was primarily driven by downward drag pressure from the subducting western izanagi slab and asthenospheric mantle flow beneath the songliao basin the basement rifting in the songliao basin during the early cretaceous and the normal faulting that occurred during the post rift stage resulted in a secondary contribution to the anomalous post rift subsidence unlike the songliao basin several early cretaceous rift basins south of the yanshan belt were only filled during the syn rift subsidence and the anomalous post rift uplift of the yanshan belt was driven by deep mantle flow

depositional history and indian summer monsoon controls on the silicate weathering of sediment transported to the eastern arabian sea geochemical records from iodp site u1456 since 3 8 ma

the provenance of sediments in the gulf of lions western mediterranean sea in this study we undertook a reconnaissance study of sediments provenance in the gulf of lions focusing over the last 16 ka we used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing sediments samples were selected both onshore and offshore from the western eastern and central part of the gulf of lions we analyzed bulk sediments coarse and fine silt and clay fractions elemental and nd isotope compositions appeared to differ from one grain size fraction to another one these are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the nd isotope compositions our results indicate that sediments in the gulf of lions mainly originated from the rhone river watershed although a contribution of saharan dust is seen in one sample influence of pyrenean small rivers is minor in these samples some sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions

cretaceous and paleogene granitoid suites of the sikhote alin area far east russia geochemistry and tectonic implications abstract the mesozoic and cenozoic geological history of ne asia comprises alternating episodes of subduction or transform strike slip movement of the oceanic plate along the continental margin of eurasia this sequence resulted in the regular generation of granitoid suites that are characterized by different ages compositions and tectonic settings the hauterivian aptian orogenic stage of the sikhote alin associated with the strike slip displacement of the early paleozoic continental blocks the successive deformation of the jurassic and early cretaceous terranes and the injection of the earliest s type granitoids during late albian the area underwent syn strike slip compression caused by collision with the aptian island arc and resulted in the injection of voluminous magmas of calc alkaline magnesian s and i type and alkali calcic ferroan a type granitoids into syn faulting compressional and extensional basins respectively northwestward to westward movement of the izanagi plate resulted in the initiation of frontal subduction of the paleo pacific plate during the cenomanian maastrichtian in turn this resulted in the generation of plateau forming ignimbrites and their intrusive analogs formed from metaluminous i type felsic magmas paleocene eocene magmatism in the sikhote alin area commenced after the termination of subduction in a rifting regime related to strike slip movement of the oceanic plate relative to the continent the break off of the subducted plate and the injection of oceanic asthenospheric material into the subcontinental lithosphere resulted in the eruption of lamproites and fayalite rhyolites and coeval intrusions of gabbro and alkali feldspar granites type the a type granitic rocks and coeval gabbro monzonites are considered to be reliable indicators of the transform continental margin geodynamic settings

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

emplacement ages geochemical and sr nd hf isotopic characterization of mesozoic to early cenozoic granitoids of the sikhote alin orogenic belt russian far east crustal growth and regional tectonic evolution abstract the sikhote alin range of the russian far east is an important accretionary orogen of the western pacific orogenic belt in order to study the formation and tectonic evolution of the orogen we performed zircon u pb dating as well as geochemical and sr nd hf isotopic analyses on 24 granitoid samples from various massifs in the primorye and khabarovsk regions the zircon dating revealed that the granitoids were emplaced from 131 to 56 ma cretaceous to paleogene in the primorye region granitoids in the coastal sikhote alin intruded the cretaceous taukha accretionary terrane from ca 90 to 56 ma whereas those along the central sikhote alin fault zone intruded the jurassic samarka accretionary terrane during ca 110 75 ma the oldest monzogranite 131 ma was emplaced in the lermontovka area of the nw primorye region granitoid massifs along the central sikhote alin fault zone in the khabarovsk region formed from 109 to 58 ma thus the most important tectonothermal events in the sikhote alin orogen took place in the cretaceous geochemical analysis indicates that most samples are i type granitoids they have initial 87sr 86sr ratios ranging from 0 7040 to 0 7083 and initial nd isotopic ratios expressed as end t values from 3 0 to 5 0 mostly 0 to 5 the data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies including the subducted accretionary complex hidden paleozoic proterozoic basement rocks based on whole rock nd isotopic data we estimated variable proportions 36 77 of juvenile component mantle derived basaltic rocks in the generation of the granitic magmas furthermore zircon hf isotopic data ehf t 0 to 15 indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation the quasi continuous magmatism in the sikhote alin orogen suggests that the paleo pacific plate subduction was very active in the late cretaceous the apparently regular progression of granitic intrusion ages from 80 to 56 ma in the taukha terrane may reflect oblique underflow of the paleo pacific plate beneath the eurasian continental margin subduction was not only manifested by granitic intrusion but also by abundant silicic volcanism the late cretaceous paleo pacific plate motion probably changed from parallel or sub parallel to oblique relative to the continental margin of the sikhote alin leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks late cretaceous rapid sea floor spreading at ca 100 ma induced highly active subduction and led to voluminous magmatism in the entire circum pacific realm finally the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between sikhote alin and sw japan

middle miocene reorganization of deformation along the northeastern tibetan plateau temporal variations in the orientation of cenozoic range growth in northeastern tibet define two modes by which india asia convergence was accommodated thermochronological age elevation transects from the hanging walls of two major thrust fault systems reveal diachronous miocene exhumation of the laji jishi shan in northeastern tibet whereas accelerated growth of the wnw trending eastern laji shan began ca 22 ma rapid growth of the adjacent north trending jishi shan did not commence until ca 13 ma this change in thrust fault orientation refl ects a middle miocene change in the kinematic style of plateau growth from long standing nne ssw contraction that mimicked the plate convergence direction to the inclusion of new structures accommodating east west motion this kinematic shift in northeastern tibet coincides with expansion of the plateau margin in southeastern tibet the onset of normal faulting in central tibet and accelerated shortening in northern tibet together these phenomena suggest a plateau wide reorganization of deformation

the modern foreland basin system adjacent to the central andes regional variations in sediment thickness internal structures average elevation and bouguer gravity define a four component foreland basin system adjacent to the central andes in the most proximal part of the foreland basin system the eastern subandean zone and westernmost chaco plain 1 3 km of cenozoic deposits overlies active folds and thrusts of the frontal andean orogenic wedge these wedge top deposits pass cratonward into a foredeep depozone containing a 3 4 km thick sedimentary prism that tapers toward and locally pinches out against a broad wavelength forebulge in the central eastern chaco plain the forebulge is underlain by precambrian mesozoic rocks and is largely covered by a thin veneer of quaternary alluvium east of the forebulge a thin 0 5 km saucer shaped accumulation of sediment beneath the pantanal wetland represents a back bulge depozone ancient counterparts of these four depozones can be identified in the central andes suggesting that modern basin architecture is the result of continuous eastward migration of the coupled orogenic wedge and foreland basin system since the late cretaceous paleocene

changes in environment and provenance within the changjiang yangtze river delta during pliocene to pleistocene transition abstract this study investigates heavy mineral assemblages in sediments of the modern changjiang delta yangtze river and the quaternary pliocene q n boundary strata within the delta area with the aim of deciphering changes in sediment provenance and the depositional environment during the pliocene to pleistocene transition major heavy mineral assemblages in the modern changjiang sediments originate from their provenance rocks while the distribution of unstable amphibole ultrastable zircon tourmaline and rutile and altered minerals limonite leucoxene are closely related to the climate and the hydrodynamic environment within the catchment the ratio of a certain unstable mineral amphibole to an altered mineral limonite is considered to be a sensitive indicator of the chemical weathering intensity that is largely affected by climate conditions heavy mineral data of core sediments reveal distinctly different environments and provenances between the upper quaternary and lower pliocene sedimentary strata in the changjiang delta the pliocene sediments are characterized by abnormally high contents of limonite 42 leucoxene 8 and zircon 15 but an extremely low amphibole content 5 enrichment of zircon is indicated from the mid lower changjiang catchment where granitoid rocks are widely distributed the strong enrichment of altered minerals and the considerable great loss of unstable minerals suggest that pliocene weathering was much stronger than it is nowadays in contrast high contents of amphibole garnet and pyroxene and the low stable mineral content in the quaternary strata indicate that sediment provenances may have extended to the upper changjiang catchment which underwent weak chemical weathering these results imply that changjiang as a large river system might have drained the east china s continental margin prior to the q n transition the distinct heavy mineral assemblages found at the q n boundary in the changjiang delta are indicative of a drastic environment with provenance changes in response to intensive neotectonics it is thus inferred that sensitive heavy mineral indices can be used to indicate the q n boundary in the changjiang delta where reliable geochronological proxies have rarely reached an agreement

clay sedimentation in the japan sea since the early miocene influence of source rock and hydrothermal activity abstract x ray diffraction analyses have been carried out on 128 samples of miocene to quaternary sediments from odp sites 794 795 and 797 some clay fractions of samples from site 797 have also been studied for rare earth elements and by nd isotopic analyses these three sites display similar lithological and clay assemblages with dominant chlorite illite and smectite showing that the sedimentation was homogeneous throughout the whole japan sea basin three mineralogical zones are recognized the first zone lower miocene sandy clay of sites 794 and 797 is mainly composed of chlorite resulting from hydrothermal transformation of arc derived smectite due to sill injections during the initial oceanic spreading stage the second zone lower miocene to lower pliocene siliceous claystone and diatomaceous silty clay is dominated by arc derived smectite the abundance of this mineral decreases upwards while illite and chlorite increase this trend reflects a change of detrital source from an eastern arc derived source ndt 3 3 variable lree enrichment to a western continental crust source nd t shale like ree patterns climatic modifications in the current dynamics are proposed as a cause for this change the third zone upper pliocene to recent silty clay with minor diatom oozes is characterized at site 797 by increasing amounts of illite and chlorite this reflects a more and more important western supply which is assumed to be related to tectonic rejuvenations of the asian margin or climatic modifications affecting the alteration conditions or the current dynamics at sites 794 and 795 the more or less sharp supply of chlorite seems to be driven by the incipient subduction zone on the eastern margin of the japan sea

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

new magnetostratigraphic and pedostratigraphic investigations of loess deposits in north east china and their implications for regional environmental change during the mid pleistocene climatic transition little is known about the long term climatic evolution of north eastern ne china because well preserved terrestrial paleoenvironmental archives are scarce in this vast region the extensive loess deposits in the chifeng region are the thickest and most complete loess paleosol sequence in ne china and have significant potential for reconstructing the paleoclimate of the region here we present new high resolution magnetostratigraphic results from two loess paleosol sections in the chifeng region the sanbahuo sbh and toudaojingzi tdjz sections the results demonstrate that both sections record the brunhes normal polarity chron and the upper portion of the matuyama reversed polarity chron based on these new results the base of the tdjz loess sequence is dated at ca 1 22 ma representing the oldest known loess deposits in ne china the initiation of loess accumulation in ne china was roughly synchronous with the large expansion of the eurasian loess belt during the late early pleistocene 1 2 0 7 ma probably reflecting a widespread intensification of aridity in northern mid latitudes we suggest that global cooling during the mid pleistocene climatic transition led to increased aridity and more favorable conditions for promoting the availability of silt for entrainment transport and deposition

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

a 100 ma bimodal composite dyke complex in the jiamusi block ne china an indication for lithospheric extension driven by paleo pacific roll back abstract a 125 m wide bimodal composite dyke complex consisting of rhyolite and dolerite dykes was emplaced into cretaceous volcanic strata of the songmuhe formation in the jiamusi block of ne china the dolerite dykes are sub vertical strike north south and intruded into both the country rocks and rhyolite dykes soon after the latter solidified shrimp zircon u pb dating shows that the rhyolite dykes were emplaced at 100 2 ma and the dolerite dykes were also most likely emplaced at 100 2 ma the rhyolite is characterized by enrichment in large ion lithophile elements lile and light rare earth elements lree and depletion in high field strength elements hfse it shows a significant negative eu anomaly and has e nd t values ranging from 0 49 to 1 66 and two groups of initial 87 sr 86 sr ratios at 0 7045 and 0 7061 the rhyolite displays the compositional signature of peraluminous ferroan granitoid indicating it was derived by either differentiation of basalt and or low pressure partial melting of crust the dolerite is also characterized by enrichment in lile and lree and depletion in hfse it has a weak negative eu anomaly and has e nd t 1 22 to 3 26 and 87 sr 86 sr i 0 7057 0 7074 the dolerite originated from partial melting of lithospheric mantle which was affected by subducted oceanic crust and experienced different amounts of crustal contamination such bimodal dyke complexes are an important indicator of crustal extension under the influence of mantle processes thus the dyke complex in the jiamusi block indicates mid cretaceous intra plate extension in ne china related to the subduction of the paleo pacific plate along the eastern eurasian continental margin when compared with mesozoic bimodal magmatism further to the west our new data support a temporal eastward migration of magmatism over a distance 1000 km from 160 ma to 100 ma this was most likely associated with roll back of the paleo pacific plate and consequent upwelling of asthenospheric mantle

orbital time scale records of asian eolian dust from the sea of japan since the early pliocene abstract a high resolution potassium content record of sediments from integrated ocean drilling program iodp site u1422 drilled in the northern sea of japan was employed to yield an astronomical timescale for this 205 m thick sedimentary archive the k content was quantified using the natural gamma radiation ngr data routinely measured on dv joides resolution the u1422 k wt series shows an increasing trend with time which parallels the growth of north hemisphere ice sheets since 4 ma as revealed by the global benthic foraminifer s oxygen isotope stack lr04 we propose that k content variations reflect changes in the relative contributions of asian eolian dust and volcanic weathering products in response to changes in global ice volume using the shipboard age model constrained by palaeomagnetism and nanofossils datums we tuned the u1422 k content variations to the lr04 stack our tuned age model for site u1422 goes back to 3 9 ma the studied record indicates that asian dust generation is enhanced during periods of global cooling the synchronous variations between the u1422 k record and the lr04 stack also suggest that global cooling played a dominant role in promoting the central asian aridification since 3 9 ma while the uplift of tibetan plateau plays a secondary role considering many disagreements still exists between the timing and amplitude of the qinghai tibetan uplift and the evolution of central asian aridity since the early pliocene

the late jurassic to present evolution of the andean margin drivers and the geological record 1 uncommonly long lived subduction and variable plate geometry along the south american andean plate margin resulted in diverse relationships between magmatic flux and extensional and contractional deformation as recorded by the overriding continental plate convergence velocities absolute overriding plate velocities and subducting slab ages were resolved along the trench from 170 ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions deformation style and magmatic features in the overriding plate key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors extensional back arc basins involving mafic oceanic crust developed only when the overriding plate velocity of south america was directed away from the trench and the modeled age of the subducting slab was older than 50 myr the development of fold and thrust belts and uplift of major plateaus was accompanied by trench normal convergence velocities in excess of 4 cm yr parameters investigated in this study revealed no correlation with the timing of major magmatic events nor was any correlation observed with the structural style of fold and thrust belts

history of yellow river and yangtze river delivering sediment to the yellow sea since 3 5 ma tectonic or climate forcing abstract reconstructing the plio pleistocene sedimentary history of the yellow sea is important for understanding the long term influence of the yellow river huanghe and or yangtze river changjiang on the asian marginal seas and to further constrain any links between river development regional paleoenvironmental change tectonic deformation and or global climate change here we present the first high resolution clay mineral record combined with sr nd isotopic compositions from a 300 m long sediment core recovered in the western south yellow sea our study suggests that large scale transgression in the yellow sea occurred after 0 8 ma possibly related to tectonic subsidence of eastern china coast and the min zhe uplift in contrast the sedimentary environment of bohai and yellow seas was mainly dominated by fluvial lacustrine deposits at 3 5 0 8 ma provenance analysis suggests a major change in sediment provenance from the yangtze river to the yellow river at 0 8 ma which corresponds to the timing of the final integration of the yellow river in its present form at the same time the major channels of the yangtze river migrated from the south yellow sea to the modern yangtze river delta due to the subsidence of east china coast the consistence in timing of the provenance transition and large scale regional marine transgression suggests that tectonic deformation rather than climate change is the first order control on the evolution of the yellow and yangtze rivers and sedimentary environmental change in the bohai and yellow seas

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

late miocene intensified tectonic uplift and climatic aridification on the northeastern tibetan plateau evidence from clay mineralogical and geochemical records in the xining basin

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

evolving sources of eolian detritus on the chinese loess plateau since early miocene tectonic and climatic controls abstract the thick deposits of eolian dust on the chinese loess plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations here we report a 22 ma long nd and sr isotopic records of the eolian sources decreasing e nd values and increasing 86 sr 87 sr ratios of the eolian deposits has been observed from early miocene to about 7 ma which indicates growing material contribution from qilian mountains relative to the gobi altay mountains the source shift during 22 7 ma is interpreted to reflect the erosional response of the qilian mountains to its surface uplift between 7 ma and 1 2 ma the results show relative constant nd and sr isotopic compositions of the eolian deposits and thus suggest a constant source contribution between qilian mountains and gobi altay mountains synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution since 1 2 ma nd and sr isotopic records indicate that the relative debris input from qilian mountains drops rapidly as large scale topographic changes would not be expected in such a short time period the source shift since 1 2 ma might be by the differing erosional responses in qilian mountains and gobi altay mountains to the development of full glacial climate after the middle pleistocene transition this work shows that combined nd and sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

history of asian eolian input to the west philippine sea over the last one million years the eolian component in pacific ocean sediments has been recognized as providing a direct link between the continental loess and marine delta o 18 climate records over orbital timescales since 500 ka here we extend this eolian record over the past one million years we constructed high resolution clay mineral stratigraphies based on delta o 18 chronology in sediments from the international marine past global change images core md06 3050 from the west philippine sea in order to trace the sources of clay minerals and reconstruct proxy records of past changes in the asian eolian input to the basin since 1 0 ma the clay mineral assemblage in core md06 3050 mainly consists of smectite similar to 65 and illite similar to 25 with minor kaolinite similar to 5 and chlorite similar to 5 provenance analysis suggests that smectite was derived mainly from the weathering of volcanic rocks on luzon island whereas illite chlorite and kaolinite were mainly transported as eolian dust by the east asian winter monsoon from central asia illite smectite values in core md06 3050 are generally higher and more variable during glacial periods and lower during interglacials suggesting that higher eolian input to the west philippine sea generally co varied with east asian winter monsoon intensity and more aridity in continental asia since 1 0 ma spectral analysis further reveals the close link between the extent of high latitude glaciation east asian winter monsoon intensity and eolian input to the west philippine sea at eccentricity 100 ka obliquity 41 ka and precession 23 ka bands since 1 0 ma c 2012 elsevier b v all rights reserved

low temperature thermochronometry along the kunlun and haiyuan faults ne tibetan plateau evidence for kinematic change during late stage orogenesis the tibetan plateau is a prime example of a collisional orogen with widespread strike slip faults whose age and tectonic significance remain controversial we present new low temperature thermochronometry to date periods of exhumation associated with kunlun and haiyuan faulting two major strike slip faults within the northeastern margin of tibet apatite and zircon u th he and apatite fission track ages which record exhumation from 2 to 6 km crustal depths provide minimum bounds on fault timing results from kunlun samples show increased exhumation rates along the western fault segment at circa 12 8 ma with a possible earlier phase of motion from 30 20 ma along the central fault segment at circa 20 15 ma and along the eastern fault segment at circa 8 5 ma combined with previous studies our results suggest that motion along the haiyuan fault may have occurred as early as 15 ma along the western central fault segment before initiating at least by 10 8 ma along the eastern fault tip we relate an 250 km wide zone of transpressional shear to synchronous kunlun and haiyuan fault motion and suggest that the present day configuration of active faults along the northeastern margin of tibet was likely established since middle miocene time we interpret the onset of transpression to relate to the progressive confinement of tibet against rigid crustal blocks to the north and expansion of crustal thickening to the east during the later stages of orogen development

paleoceanographic evolution of the japan sea abstract multidisciplinary studies on nearly continuous hemipelagic sequences recovered from the deeper parts of the japan sea during odp leg 127 128 in 1989 yielded new information on the paleoceanographic conditions of the sea since its establishment as a deep marginal basin of significant size approximately at 20 ma by synthesizing these new information on surface and bottom water conditions ccd biogenic silica accumulation and paleogeog raphy it is possible to reconstruct changes in paleo ocean circulation within the sea it is also possible to specify the ultimate cause of such changes by comparing their timing and nature with those of global paleoceanographic as well as local tectonic events the result of our synthesis suggests that the japan sea has been responding to the high frequency changes of global surface conditions in very sensitive manner throughout its history however the mode of its response changed from time to time the changes in response mode have been strongly influenced by such factors as sill depth position of channels and the degree of closure of the sea which were controlled either by local tectonism or global eustatic sea level changes

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

late miocene quaternary rapid stepwise uplift of the ne tibetan plateau and its effects on climatic and environmental changes abstract the way in which the ne tibetan plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the tibetan plateau and the development of the present geomorphology and climate of central and east asia this paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings the dating of late cenozoic basin sediments and the tectonic geomorphology of the ne tibetan plateau demonstrates that the rapid persistent rise of this plateau began 8 1 ma followed by stepwise accelerated rise at 3 6 ma 2 6 ma 1 8 1 7 ma 1 2 0 6 ma and 0 15 ma the yellow river basin developed at 1 7 ma and evolved to its present pattern through stepwise backward expansion toward its source area in response to the stepwise uplift of the plateau high resolution multi climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the east asian winter monsoon and drying of the asian interior coupled with the episodic tectonic uplift since 8 ma and later also with the global cooling since 3 2 ma suggesting a major role for tectonic forcing of the cooling

chemical weathering in luzon philippines from clay mineralogy and major element geochemistry of river sediments clay mineralogy and major element geochemistry of 35 surface sediment samples collected in 21 major to moderate rivers of luzon philippines are used to evaluate the present chemical weathering process the clay mineral assemblage consists mainly of smectite average 86 with minor kaolinite 9 and chlorite 5 and very scarce illite 1 and does not show strong island wide differences the major element results of both bulk and clay fraction sediments indicate that the formation of clay minerals is accompanied by leaching of ca and na first and of fe and mn thereafter during the chemical weathering process a low moderate chemical weathering degree of bulk sediments and a moderate intensive degree of clay fraction sediments are obtained in luzon rivers based on proxies of chemical index of alteration cia and smectite crystallinity it is suggested that the majority of andesitic basaltic volcanic and sedimentary rocks along with the tectonically active geological setting and sub tropical east asian monsoon climate are responsible for the predominance of smectite in the clay mineral assemblage

paleoclimate change since the miocene inferred from clay mineral records of the jiuquan basin nw china abstract global cooling and the uplift of the tibetan plateau have long been considered the crucial controls of the climate change in inland asia since the cenozoic however which of these factors has played the leading role is unknown to understand climate change and the controlling factors in inland asia here we present new records of clay mineralogy and trace elements of clay fractions from the neogene sedimentary sequence in the jiuquan basin of the northeastern tibetan plateau the clay mineral records reveal four stages of paleoclimate changes from ca 24 ma to 17 ma the low total smectite and smectite i s mixed layers kaolinite illite chlorite and high illite contents suggest weak chemical weathering and hence arid climatic conditions for ca 17 14 ma the high total smectite and total smectite kaolinite illite chlorite and low illite contents suggest strong chemical weathering indicating a change in climate from cold and dry to warm and humid there was no palygorskite during this warm and humid period from ca 14 ma to 8 ma the low total smectite content high illite content and the appearance of palygorskite indicate that the climate turned to cold and dry since 8 ma low total smectite as well as high illite and chlorite contents suggest a colder and drier period the records of clay mineralogy illustrate that the jiuquan basin has experienced increasing aridity since ca 14 ma synchronous with the inland asian aridification given the synchroneity with the global cooling we suggest that the climate evolution in the jiuquan basin from the late oligocene to middle late miocene was mainly controlled by global climate change since the late miocene the uplift of the tibetan plateau and global cooling have significantly influenced the decreasing temperature and humidity of the jiuquan basin the uplift of tibetan plateau may intensify the aridity by blocking moisture from reaching the jiuquan basin

provenance weathering and erosion records in southern okinawa trough sediments since 28ka geochemical and sr nd pb isotopic evidences abstract geochemical and sr nd pb isotopic compositions of the detrital sediments from odp hole 1202b and taiwan rivers were measured in this study aiming to reveal changes in sediment provenance in the southern okinawa trough sot since 28 ka and to examine the weathering and sediment transport processes in response to monsoon climate variability large variations in sr nd pb isotopic ratios at 11 9 ka suggest changes in detrital sediment provenance in the sot from a dominance of the paleo changjiang yangtze river and or continental shelf sediment during the late deglaciation and to west taiwan rivers since 9 5 ka volcanic rocks and eastern taiwan sediments have not significantly contributed to the sot the large shift in sediment provenance during the early holocene marks a major change in oceanic circulation mainly caused by the intrusion of the kuroshio current into the trough clay mineral and geochemical proxies suggest that the taiwan derived sediments accumulated during the early mid holocene climate optimum ca 9 5 4 ka might be tightly related to the reworking of older altered sediments from terraces and floodplains rather than having experienced more intense silicate weathering than in the late holocene 4 0 ka overall silicate weathering in taiwan was greatly inhibited by accelerating sediment production and transfer from land to ocean caused by monsoon intensification in holocene our study illustrates that the radiogenic isotopic and geochemical compositions of fine grained detrital sediments are sensitive tools for fingerprinting sediment sources and for reconstructing changes in oceanic currents and monsoon climate in river dominated east asian continental margin

increasing terrigenous sediment supply from taiwan to the southern okinawa trough over the last 3000 years evidenced by srnd isotopes and geochemistry abstract high resolution sedimentary records reveal the patterns of weathering and erosion in response to climate change environmental variability and human activity here we present major and trace element data sr nd isotopic compositions and mass accumulation rates mars for the siliciclastic sediment fraction of a relatively high resolution sedimentary archive from the southern okinawa trough east china sea we reveal the sedimentary source to sink processes and the physical erosion and chemical weathering history of taiwan the sr nd isotopic data indicate that sediments were mainly sourced from northeastern and western taiwan rivers and thus the sedimentary records reflect the weathering and erosion conditions in this source region volcanic rocks aeolian dust and terrigenous sediment from rivers in mainland china and eastern taiwan have not significantly contributed to the deposits in the southern okinawa trough since ca 3000 cal yr bp multiple indices including the chemical index of alteration cia k al alk ti na and k na are used to identify variations in the intensity of regional scale chemical weathering the strength of the sediment input is estimated using the mar of the siliciclastic marsiliciclastic and the mar of ti marti the results suggest that the bedrock of small mountainous river systems in taiwan has experienced relatively stable and moderate chemical alteration and that the terrigenous sediment supply from taiwan to the southern okinawa trough has progressively increased since ca 3000 cal yr bp a comparison of these data with climate and human activity indicates that the increased input of terrigenous sediment was closely related to an intensification of rainfall in taiwan over the last 3000 years after ca 1500 cal yr bp a sustained increase in the terrigenous sediment input likely to be attributed to the combined effects of intensified heavy rainfall and human activity occurred intense physical erosion in taiwan s river basins has exerted a long term constraint on chemical weathering intensity the lack of evident link between silicate weathering and climate forcing in these catchments suggests that paleoclimate reconstruction based on sedimentary geochemical records offshore of taiwan rivers requires careful consideration

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

development of the east asian monsoon mineralogical and sedimentologic records in the northern south china sea since 20 ma we here reconstruct the past change of the east asian monsoon since 20 ma using samples from ocean drilling program odp site 1146 in the northern south china sea based on a multi proxy approach including a monomineralic quartz isolation procedure identification of clay minerals by x ray diffraction xrd and grain size analysis of isolated terrigenous materials terrigenous supply to odp site 1146 was dominated by changes in the strength of multiple sources and transport processes grain size data modeled by an end member modeling algorithm indicate that eolian dust from the and asian inland and fluvial input have contributed on average 20 and 80 of total terrigenous material to odp site 1146 respectively specifically about 40 53 of the total quartz feldspar and only 6 11 of the total clay is related to eolian supply at the study site detailed analysis of the sedimentary environment and clay minerals combined with previous studies shows that smectite originates mainly from luzon kaolinite from the pearl river and illite and chlorite from the pearl river taiwan and or the yangtze river the proportion and mass accumulation rate mar of the coarsest end member em1 interpreted as eolian dust ratios of illite chlorite smectite quartz feldspar and mean grain size of terrigenous materials at odp site 1146 were adopted as proxies for east asian monsoon evolution the consistent variation of these independent proxies since 20 ma shows three profound shifts in the intensity of east asian winter monsoon relative to summer monsoon as well as aridity of the asian continent occurred at similar to 15 ma similar to 8 ma and the youngest at about 3 ma in comparison the summer monsoon intensified contemporaneously with the winter monsoon at 3 ma the phased uplift of the himalaya tibetan plateau may have played a significant role in strengthening the asian monsoon at similar to 15 ma 8 ma and 3 ma c 2007 elsevier b v all rights reserved

evidence for early 12 7 ma eolian dust impact on river chemistry in the northeastern tibetan plateau abstract as one of the largest dust sources on the earth s surface dryland in central asia gives rise to thick eolian deposits over east asia e g the chinese loess plateau clp and significantly influences the regional hydrochemistry in the downwind drainage areas however the formation of thick eolian dust deposits requires not only climatic prerequisites for dust emission and transport but also climatic and topographic conditions favourable for deposition and accumulation the scarcity of widespread eolian deposition around the clp before 7 8 ma hinders a full understanding of the processes and mechanisms of central asian aridification the deposition of eolian dust also impacts the hydrogeochemistry of fluvial systems and the precipitation of authigenic phases in continental sedimentary systems could be an archive for studying eolian dust dynamics when pure eolian deposits are scarce here we present the ca mg sr concentrations and 87sr 86sr isotope compositions of bulk carbonates in a new fluvial sequence 12 7 4 8 ma of the xining basin the mg ca and sr ca ratios of the carbonate describe a power law relationship with a power coefficient of 0 8 lower than the coefficient characteristic of prior calcite precipitation pcp an input of eolian dust with the dissolution of mg rich carbonate is likely responsible for the deviation from a pure pcp process the bulk carbonates also show a general decrease of 87sr 86sr ratios from 12 7 to 4 8 ma with a transition around 8 6 ma revealed by lower sr mg ratios the comparison of these proxies to a previously reported fluvial section 12 2 5 1 ma in the linxia basin 200 km to the southeast shows that the 87sr 86sr ratios of the bulk carbonates and water soluble salts in the linxia basin are around 0 7098 which is 0 0018 lower than those in the xining basin before 8 6 ma but shows a significant rise between 8 6 and 7 0 ma the two basins share the same range of carbonate 87sr 86sr ratios when sediments are younger than 7 ma for the last 7 myrs the evolution of the 87sr 86sr ratios in bulk carbonates of fluvial sediments and pliocene quaternary eolian deposits found in the xining basin are similar to those in typical eolian red clays loess palaeosol sequences on the clp these results suggest a transition of the hydrochemical regime at 8 6 ma in the linxia basin from a catchment only influenced by the weathering of its bedrock to one significantly impacted by eolian dust input in the xining basin the carbonate elemental and 87sr 86sr ratios are consistent with a hydrochemistry more impacted by the presence of the eolian dust there the dust input occurred earlier at 12 7 ma though it has strengthened since 8 6 ma the eolian dust impact on fluvial systems in the xining basin was much earlier than in the linxia basin and also preceded the initial accumulation of widespread eolian red clays on the clp 7 8 ma suggesting a temporally propagating and spatially stepwise expansion of eolian dust delivery across the asian inland during the late cenozoic

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

nd isotopic study of precambrian basement of south korea evidence for early archean crust we carried out a sm nd isotopic reconnaissance study of south korea eight river sediments gave crustal residence ages t dm between 1 7 and 2 7 ga implying that on average the crust of south korea was formed in early to middle proterozoic time twenty six precambrian basement rocks yielded t dm between 1 4 and 3 8 ga more than half of them exceed 2 5 ga indicating that south korea has a long history of crustal evolution four of the samples have t dm from 3 2 to 3 8 ga suggesting the possibility that there may be ancient continental crust in korea having ages comparable to those of the oldest cratons in the world however these samples also have preferentially higher sm nd so their old ages could be artifacts thus requiring confirmation the large variation in t dm of south korea is reminiscent of that for the south china block however the existence of early archean ages better matches that of the north china block because the basement of south china was thought to be mostly proterozoic in age the recent discovery of rare archean basement rocks in the south china block may favor models that attempt to correlate south korea with south china

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

interpretation of changes in water level accompanying fault creep and implications for earthquake prediction quantitative calculations for the effect of a fault creep event on observations of changes in water level in wells provide an approach to the tectonic interpretation of these phenomena for the pore pressure field associated with an idealized creep event having an exponential displacement versus time curve an analytic expression has been obtained in terms of exponential integral functions the pore pressure versus time curves for observation points near the fault are pulselike a sharp pressure increase or decrease depending on the direction of propagation is followed by more gradual decay to the normal level after the creep event the time function of the water level change may be obtained by applying the filter derived by a g johnson and others to determine the influence of atmospheric pressure on water level to the analytic pore pressure versus time curves the resulting water level curves show a fairly rapid increase or decrease and then a very gradual return to normal the results of this analytic model do not reproduce the steplike changes in water level observed by johnson and others if the procedure used to obtain the water level from the pore pressure is correct these results suggest that steplike changes in water level are not produced by smoothly propagating creep events but by creep events that propagate discontinously by changes in the bulk properties of the region around the well or by some other mechanism in addition simplistic calculations show that significant pressure field variations and water level changes near the surface may be expected to accompany a propagating creep event on a buried fault water level changes of as much as several meters may be expected at the surface for a creep event having a dislocation amplitude of l m on a semi infinite dislocation surface extending downward from a depth of 10 km and propagating horizontally at a rate of 10 km day the maximum near surface effect should be observed at a horizontal distance from the fault about equal to the depth of the top of the dislocation surface these results are consistent with the observations made in china of large water level changes preceding large earthquakes if some sort of aseismic creep event at depth precedes these earthquakes

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

detrital zircon u pb geochronology and stratigraphy of the cretaceous sanjiang basin in ne china provenance record of an abrupt tectonic switch in the mode and nature of the ne asian continental margin evolution abstract the age spectra obtained from 505 spots of detrital zircon u pb ages of five representative sandstone samples from the sanjiang basin in ne china point to a significant change in its provenance during the coniacian santonian the predominant detrital source for the sanjiang basin during the early cretaceous was the zhangguangcai range magmatic belt and jiamusi block along its western and southern periphery whereas it changed in the late cretaceous to its eastern periphery the timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin the time interval of non deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early cretaceous and a contractional deformation episode in the late cretaceous the sanjiang basin evolved during this time window from a backarc to a foreland basin the migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late cretaceous marked the onset of regional scale shortening and surface uplift in the upper plate of a flat or very shallow dipping subduction zone the stratigraphic record the detrital source and geochronology of the basinal strata and the internal structure of the sanjiang basin present therefore an important record of a tectonic switch in the nature of continental margin evolution of northeast asia during the late mesozoic

increased seasonality and aridity drove the c4 plant expansion in central asia since the miocene pliocene boundary abstract continuous and high resolution records of the content mass accumulation rate mar and 13 c values of black carbon obtained from integrated ocean drilling program iodp site u1430 in the southwestern japan sea have been established and combined with previous results obtained from central asia the main objective of this work is to reconstruct the historical changes in vegetation types c3 c4 and to constrain the driving force of c4 plant expansion over the last 13 ma the stable carbon isotope value of black carbon 13 c bc shows a major shift since the miocene pliocene boundary 5 3 ma suggesting significant expansion of c4 plants in broad areas of central asia including the inland basins of northwestern china and the loess plateau however a decline in the content and mar of black carbon reveals the absence of any link between fire and c4 plant expansion in central asia due to the dramatic decrease in biomass under a drying regime on a global scale asynchronous expansion of c4 plants suggests that regional hydroclimatic change rather than decline in co 2 concentration was the most important factor to influence c4 expansion we propose that the increased seasonality and the enhanced long term aridity driven by the concurrent decline in winter westerly vapor and increase in east asian summer monsoon precipitation were the main driving forces of c4 plant expansion in broad areas of central asia variations in winter westerly moisture have played a significant role in changes of regional climate and vegetation in central asia since the late miocene