iron oxide characteristics of the chinese loess red clay sequences and their implications for the evolution of the east asian summer monsoon since the late oligocene abstract the most significant climatic change in east asia involved the formation and evolution of the coupled monsoon arid environmental system during the cenozoic which was dynamically linked to global cooling and the growth of the qinghai tibet plateau however our understanding of monsoon evolution since the late oligocene remains controversial due to differences in the interpretation of various environmental proxies from loess archives in this study the composition and relative abundance of pedogenic iron oxides of two eolian sequences from the lingtai section and the zhuanglang drill core were investigated using rock magnetic optical spectroscopy and geochemical analyses the results indicate that while the composition of iron oxides in the mio pliocene red clay and quaternary loess paleosol sequences is similar the concentrations of magnetite maghemite hematite and goethite are quite different between loess paleosol and red clay the combination of magnetic proxies magnetic susceptibility fed fet and color a values reveals that precipitation and temperature played varying roles in driving pedogenesis and chemical weathering since the late oligocene during the late oligocene to early miocene the occurrence of relatively strong pedogenesis and chemical weathering was likely the result of high temperatures rather than high precipitation the east asian summer monsoon intensified during the middle miocene climate optimum 16 5 14 5 ma in response to global climatic warming subsequently during the middle to late miocene the monsoon intensity gradually weakened due to global cooling after 8 ma the summer monsoon strengthened substantially and reached a maximum during 4 5 2 6 ma possibly as a result of the uplift of the northeastern margin of the qinghai tibetan plateau during the late miocene the monsoon intensity then commenced a decreasing trend in the early pleistocene but then strengthened again after 1 0 ma

fluvial and aeolian interaction under permafrost conditions weichselian late pleniglacial twente eastern netherlands abstract close interaction between fluvial and aeolian deposition led to the formation of a distinct fluvio aeolian depositional environment in river valleys in the netherlands during the last glacial maximum we describe three sections illustrating this sedimentary environment the primary sedimentary structures and periglacial phenomena document the dynamic interaction between fluvial aeolian and periglacial processes the rivers were ephemeral in nature with alternating fluvial and aeolian deposition in overbank environments within the sections successive levels of frost cracks ice wedge casts soil wedges and cryoturbations are found the sections demonstrate that not all these levels of periglacial structures indicate climatic oscillations but are caused by lateral migration of fluvial activity however one large cryoturbation level truncated by a gravel lag the beuningen gravel bed is evidence of widespread permafrost degradation induced by climatic warming between ca 16 and 22 ka this climatic warming is followed by a significant increase of aeolian activity

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

putting the younger dryas cold event into context abstract the younger dryas event is by far the best studied of the millennial scale cold snaps of glacial time yet its origin remains a subject of debate the long held scenario that the younger dryas was a one time outlier triggered by a flood of water stored in proglacial lake agassiz has fallen from favor due to lack of a clear geomorphic signature at the correct time and place on the landscape the recent suggestion that the younger dryas was triggered by the impact of a comet has not gained traction instead evidence from chinese stalagmites suggests that rather than being a freak occurrence the younger dryas is an integral part of the deglacial sequence of events that produced the last termination on a global scale

linear dune pattern variability in the vicinity of dry valleys in the southwest kalahari linear sand dunes in the southwest kalahari dunefield have been widely observed to change pattern size and orientation in the vicinity of river valleys yet few explanations for this change have been put forward this paper identifies and describes four main associations between dunes and valleys which occur in the southwest kalahari i dunes which adjoin the valley on both sides with no discernible change in pattern or orientation ii dunes which adjoin the valley and change pattern iii dunes which adjoin the upwind valley flank but not the downwind side iv dune free zones on both sides of the valley the two main factors which influence the evolution of these associations are identified as the effect of the valley upon sediment supply and the effect of the valley upon wind regime our current state of knowledge about the potential geomorphological effects of these two variables is evaluated with reference to each association described

distribution of rare earth elements in surface sediments of the western gulf of thailand constraints from sedimentology and mineralogy abstract to understand the modern sedimentation and land sea interaction processes in the asian margin seas we analyze rare earth element contents ree i e la ce pr nd sm eu gd tb dy ho er tm yb lu and grain sizes detrital minerals from 158 surface sediment samples collected from the western gulf of thailand got the results reveal that the ree contents ranged from 25 42 g g to 201 21 g g with an average value of 137 21 g g and that the got is characterized by higher accumulations of lree relative to hree together with negative eu anomalies based on the spatial distribution characteristics of ree contents ce and eu the western got can be classified into three geochemical provinces the province i covers the northern and northwestern coastal zones of the got including the entire upper got its coarse size fraction and distribution pattern of hornblende and quartz dominated minerals caused ree contents to be the lowest and these sediments were mainly derived from the rivers around the upper got including the chao praya river and the kea klong river the province ii is located in the central got and has the highest ree concentrations due to finer sediment composition and higher contents of zircon authigenic pyrite and biogenetic limestone the province ii has two accumulation centers around samui island and koh chang island with ree spatial distribution influenced by the seasonal setting and mixed derived from multiple provenances around the got the province is located in the lower got close to malaysia the sediment type in this region is similar to that of province i except for different detrital mineral compositions especially the presence of siderite that is responsible for higher ree contents the sediments in this region exhibits similar distribution patterns to those of terrestrial materials from the malaysian peninsula such as that from the kelantan river the transportation processes of sediments in this region are mainly controlled by the coastal current

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

accelerated mass flux to the arabian sea during the middle to late miocene possible links between orogenic uplift and the strengthening of the south asian monsoon are best examined in the arabian sea where the erosional flux is not dominated by the high himalaya as in the bengal fan but is controlled by tibet the karakoram and the hindu kush the erosional flux from these mountains into a basin where the monsoon is well dated allows a direct comparison of erosional tectonic and climatic processes new seismic data from the proximal indus fan permit the thickest part of this system to be dated for the first time through correlation to drilling sites after converting time sections to depth and then accounting for sediment compaction the data show a two to threefold increase in mass flux to the upper fan and continental shelf peaking during the middle miocene 16 11 ma and falling from the late miocene to the present increased sedimentation rates are accompanied by the growth of channel levee complexes high sediment flux does not correlate with monsoonal strengthening at 8 5 ma but follows uplift of the murray ridge uplift in tibet and the karakoram after 20 ma and the start of transpression along the karakoram fault at 18 ma 20 km of erosion

large scale erosional response of se asia to monsoon evolution reconstructed from sedimentary records of the song hong yinggehai and qiongdongnan basins south china sea

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

a high resolution record of rare earth element compositional changes from the mud deposit on the inner shelf of the east china sea implications for paleoenvironmental changes abstract a paleoenvironmental reconstruction of the east china sea ecs is presented using rare earth element ree analysis of sediments from core mz02 which was retrieved from the inner continental shelf s mud area the analytic results show that the total rees in the fine sediment vary between 137 76 g g and 231 53 g g with an average value of 187 69 g g obvious changes were found during the process of sedimentation by comparing with the ree compositions from the potential provenances the ratios of la sm ucc and gd yb ucc revealed that the sediments were mainly derived from river detrital outputs of the changjiang yangtze river minjiang and mountainous rivers from western taiwan island the contributions of terrestrial materials from these three main provenances were controlled by sea level change and the taiwan warm current twc chinese coastal current ccc system which is mainly driven by the east asian monsoon the high sedimentation rate during the transgression period between the late pleistocene and early holocene 13000 9800 a b p was caused by a well proportioned mixed provenance from changjiang western taiwanese rivers and minjiang sediments due to the lower sea level and the location of the foreshore nearshore face because of the stronger sediment reworking and erosion at the shelf edge during the early holocene 9800 7300 a b p the strengthening summer east asian monsoon transported the minjiang and western taiwanese river material northeastward and it became the main sediment source for fine sediments in the shallow sea region of the ecs while the changjiang provided a relatively minor amount of detrital sediment to the shelf the increasing strength of the twc might have played an important role in sediment dispersal and deposition on the ecs inner shelf during the period 7300 3500 a b p thus mountainous river material became the dominant sediment on the shelf of the ecs furthermore the results indicate that the east asian monsoon and the weakening of the twc were linked to an abrupt increase in changjiang derived terrigenous detritus material since 3500 a b p the source and sink pattern during this period is consistent with the modern sedimentation environment

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

reduced himalayan sediment production 8 myr ago despite an intensified monsoon uplift of the tibetan plateau about 7 8 myr ago1 2 may have been responsible3 5 for the apparent intensification of the asian monsoon 6 10 around that time increases in the oceanic 87sr 86sr ratio during the neogene period have been attributed11 12 to increased erosion from the himalayan orogen it has been suggested that the monsoonal intensification may have enhanced overall erosion rates in the region5 13 if this were the case sediment accumulation rates would have increased in the surrounding basins at this time here we present a reanalysis of stratigraphic data from the indo gangetic foreland and the bengal fan which demonstrates that both of these basins experienced a decline in sediment accumulation rates 8 myr ago thus it seems that monsoonal intensification was accompanied by a decrease in mechanical weathering this decrease could be due to reduced tectonic activity decreased himalayan glaciation or slope stabilization from dense plant cover

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

age and composition of dikes in southern tibet new constraints on the timing of east west extension and its relationship to postcollisional volcanism controversy exists over whether east west extension in southern tibet is related to plateau uplift or to the accommodation of plate boundary forces relationships between the onset of extension plateau uplift and the thermal state of the lithosphere are critical to this debate we present new data on postcollisional north south trending dikes in southern tibet their ages range from 18 3 2 7 ma to 13 3 0 8 ma and define the onset of regional east west extension in southern tibet dikes are compositionally indistinguishable from postcollisional lavas in southern tibet being either ultrapotassic having a source in the subcontinental lithospheric mantle or calc alkaline with a dominantly crustal origin the ultrapotassic dikes demonstrate that east west extension and subcontinental lithospheric mantle derived magmatism were temporally and spatially linked supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning thus the onset of extension by 18 3 2 7 ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces this places a new age limitation on the attainment of high elevation in southern tibet with implications for models that relate cenozoic monsoon intensification to plateau uplift

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

rapid fluvial incision and headward erosion by the yellow river along the jinshaan gorge during the past 1 2 ma as a result of tectonic extension abstract in north china the ordos block located northeast of the tibetan plateau is regarded as a stable craton surrounded by the yinchuan graben to the west the hetao graben to the north and the fenwei graben to the southeast the major tectonic structure around this block in the cenozoic reflects intensive extension as a response to the eastward extrusion of the tibetan plateau intermittent downcutting by the yellow river starting from the planation surface level on the ordos block and penetrating the bedrock resulted in the formation of the jinshaan gorge a series of well preserved fluvial terraces was identified along this gorge providing new insight into the far field effect of the eastward extrusion of the tibetan plateau magnetostratigraphic records from the planation surface and uppermost terrace suggest that this gorge has been entrenched over its total length in the period from 3 7 to 1 2 ma a preliminary explanation is proposed here for the morphological evolution of the yellow river in the jinshaan gorge on the basis of terrace correlation between seventeen geomorphic sections multiwave headward erosion initiated by the yellow river along this gorge has been reconstructed this process may be attributed to the lowering of the base level the fenwei graben this graben has been formed during the cenozoic as the tibetan plateau extruded eastwards resulting in accelerated ground subsidence a combined approach of magnetostratigraphy pedostratigraphy and optically stimulated luminescence osl was adopted to establish a new geochronology for terraces in the gorge at 1 2 ma 1 1 ma 787 ka 412 ka 245 ka 128 ka 29 ka and 11 ka these ages provide an excellent framework for calculating the extension within the fenwei graben the average incision rate appears to be enhanced significantly since 412 ka indicating a rapid extension within the fenwei graben during this time

luminescence dating of sand loess sequences and response of mu us and otindag sand fields north china to climatic changes the sand loess transition zone in north china is sensitive to climate change and is an ideal place to investigate past environmental changes however past climate change at millennial centennial timescales in this region has not been well reconstructed because of limited numerical dating alternations of sandy loam soils with aeolian sand layers in the mu us and otindag sand fields which lie along the sand loess transition zone indicate multiple intervals of dune activity and stability this change is probably a response to variations of the east asian monsoon climate during the late quaternary the single aliquot regeneration sar optically stimulated luminescence osl dating protocol which has been successfully applied to aeolian deposits worldwide is applied to these two sand fields in this study the osl ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale sections in both sand fields contain aeolian sand beds recording millennial scale episodes of dry climate and widespread dune activation including episodes at about the same time as heinrich event 5 and the younger dryas in the north atlantic region these results demonstrate the potential of aeolian sediments in semi arid north china to record millennial scale climatic events and also suggest that dry wet climate variation at the desert margin in china may be linked to climatic change elsewhere in the northern hemisphere through atmospheric circulation this article was published online on 27 november 2008 an error was subsequently identified this notice is included in the online and print versions to indicate that both have been corrected 16 december 2008 copyright 2008 john wiley sons ltd

holocene erosion triggered by climate change in the central loess plateau of china abstract understanding changes in holocene erosion is essential for predicting soil erosion in the future however the quantitative response of natural erosion to holocene climate change is limited for the loess plateau of china in this study two soil profiles were investigated on the luochuan and yanchang sites in the central loess plateau of china and four climate indicators i e magnetic susceptibility calcium carbonate content total organic carbon content and clay content

the geomorphology and evolution of aeolian landforms within a river valley in a semi humid environment a case study from mainling valley qinghai tibet plateau abstract this paper systematically analyzes a valley s aeolian landforms in a semi humid region and presents a model of its contemporary evolution mainling valley of the yarlung zangbo river on the qinghai tibet plateau was chosen as the case study for the analysis of morphometric characteristics and the evolution sequence of aeolian landforms via field data and remote sensing images the aeolian landforms were primarily composed of aeolian sand belts on river terraces and dunes sheets on hillside slopes three types of aeolian sand belts were identified based on their dune types in type i belts an erosive air stream combined with relatively high vegetation cover 10 produced sparsely distributed parabolic dunes with a high variability of dune heights in type ii belts the continual reworking by the erosive air stream in combination with low vegetation cover 3 formed more densely distributed barchans and transitional dunes with a moderate variability of dune heights and in type iii belts the gradual evolution from an erosive sand laden air stream to a saturated sand laden air stream in combination with low vegetation cover 2 produced the densest crescentic dunefields but with the least variability in dune heights dune sizes increase dune shapes become uniform and dune distribution becomes close from type i to iii belts lateral linking and merging of the dunes were also observed within the belts together this evidence indicates that an evolution sequence may exist aeolian dunefields in the belt appear to evolve from embryonic parabolic dunefields to adolescent barchan dunefields and subsequently to mature compound crescentic dunefields as the aeolian sand belt evolves into the mature stage sand accumulations at the foot of the mountain valley can be steps for sand accumulation on valley side slopes

climate changes of the northeastern tibetan plateau since the late glaciation inferred from clay mineralogy of sediments in kuhai lake a high resolution study of clay mineralogy has been carried out on a sediment core recovered from kuhai lake in order to investigate climatic and environmental changes in the northeastern tibetan plateau since the late glacial period clay mineralogy reveals significant changes in sedimentary sources and hydrolysis conditions in the kuhai lake catchment area before 14 9 cal ka bp the predominance of illite and relatively high amount of kaolinite derived mainly from the reworking of sedimentary rocks imply unstable cold arid conditions and significant glacier cover that prevented from weathering of metamorphic and mafic rocks in the high relief of the catchment between 14 9 and 5 4 cal ka bp an increase in smectite and chlorite contents associated with relatively low values of the illite chemistry index indicate that clay minerals derived from the weathering of metamorphic and volcanic rocks in the highlands of the catchment area such modifications were triggered by a melting of glaciers in the lake s catchment during the bolling allerod interstadial followed by an intensification of monsoon precipitations in the early holocene around 10 0 cal ka bp both processes are responsible for significant physical erosion in the highlands together with an efficient transport of smectite and chlorite from areas of high relief to the lake after 5 4 cal ka bp lower smectite and chlorite proportions associated with a predominance of al rich illite and kaolinite indicate a return to relatively dry conditions and a lowering of physical erosion in the drainage basin comparison between clay mineralogy and pollen records indicates that variations in weathering intensity in the kuhai lake catchment area and changes in its surrounding vegetation are synchronous demonstrating the large potential of clay mineralogical analysis to trace climate change of the tibetan plateau

enormous ganges brahmaputra sediment discharge during strengthened early holocene monsoon rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development however little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes in this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early holocene monsoon development of the ganges brahmaputra river delta began ca 11000 yr b p when rising sea level flooded the bengal basin thereby trapping most of the river s discharge on the inner margin chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin which provide a minimum estimate of the river s past sediment load results reveal that 5 1012 m3 of sediment was stored in the bengal basin from ca 11000 to 7000 yr b p which corresponds to a mean load of 2 3 109 t yr in comparison modern sediment load of the ganges brahmaputra is 1 109 t yr ranking it first among the world s rivers and underscoring the significance of a two fold increase sustained over 4 k y furthermore the timing of immense discharge in the early holocene strongly suggests its relation to a stronger than present southwest monsoon in south asia similar patterns of high monsoon related sediment discharge have been noted throughout the tropics and subtropics suggesting a widespread fluviosedimentary response the potential magnitude of which is showcased by the ganges brahmaputra system

dune dammed paleovalleys of the nebraska sand hills intrinsic versus climatic controls on the accumulation of lake and marsh sediments although running water is the dominant geomorphic agent on earth eolian processes can gain ascendancy in regions where the climate is arid vegetation is sparse and abundant sand is available for transport with climate change the boundaries between fluvial dominated and eolian dominated areas may shift although there have been few reports in the north american literature of river systems blocked by dune sand our work in the nebraska sand hills provides evidence of multiple episodes of such blockage events during prolonged arid intervals in latest pleistocene and middle holocene time eolian dune sand blocked two large valley systems in western nebraska these blockages raised the water table of the high plains aquifer as much as 25 m over an area of 7000 km2 and created over one thousand lakes wetlands far removed from the discharge points of the buried paleovalley system are strongly alkaline exceeding 250 000 mg l total dissolved solids tds relatively fresh 280 mg l tds flow through lakes are present at the distal end of the system where the gradient of the water table is steep and the cross section of the buried valley is large anomalously thick marsh and lake sediments accumulated in deep paleovalleys upstream of dune dams near the southern margin of the sand hills our cores and radiocarbon dates from blue and crescent lakes reveal their histories to be quite distinct from adjacent swan lake these differences are best explained by multiple blockage events our work explains why lakes are most abundant in the driest part of the sand hills it also provides another line of evidence for major dune activity in the sand hills region during holocene time and shows that factors other than regional climate specifically location height and hydraulic conductivity of dune dams can control the rise and fall of the ground water table and the chemistry of lakes

geochemistry of coeval mesozoic plutonic and volcanic suites in hong kong middle jurassic to lower cretaceous intermediate to silicic plutonic and volcanic rocks of hong kong record a transition from calc alkaline through high k calc alkaline to transitional shoshonitic compositions with time close spatial and temporal associations among comagmatic volcanic plutonic pairs indicate that magmatism occurred in discrete episodes mostly of less than one million years duration synchronous high k calc alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction related to an extension related tectonic setting geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources the earliest mantle derived magmas interacted strongly with a dominantly archaean crustal protolith younger magmas show evidence for interaction with a dominantly proterozoic crustal protolith the strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources this interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

optical dating of dune sands in the northeastern deserts of china abstract optical dating has been used to obtain the ages of fossil stabilized sand dunes from four sections in the northeastern deserts of china our results indicate that the optically stimulated luminescence ages of the four sections correlate well even though the samples were collected from different deserts about 600 km apart our results also indicate that active dune formation in this region lasted from the last glacial maximum to about 10 ka and that the warm climate of the holocene was interrupted by a cold dry dune formation episode about 3 5 1 7 ka the holocene optimum in this region is between 10 and 3 6 ka and a later warm humid dune stabilization phase lasted from at least 1 6 to 1 0 ka the youngest age on the uppermost sand unit yielded an age of only 40 yr supporting the previous argument that the existence of modern active eolian sands in the regions with a mean annual precipitation of up to 450 mm is not mainly due to drought but to extensive land cultivation over historic time from the luminescence properties of the quartz grains it is hypothesized that the sands in most of the sections are probably derived from more than one source with a minor source of quartz having a different thermal history before deposition

late quaternary lake level fluctuations in the mababe depression middle kalahari palaeolakes and the role of zambezi inflows abstract a systematic drilling and optical dating programme on middle kalahari beach ridge relict shoreline sediments has enabled the identification of multiple episodes of lake high stands of an extensive palaeolake system at the terminus of the okavango delta northern botswana this paper presents 23 ages from the mababe depression and establishes four shoreline construction phases in the late quaternary coeval with other sub basin lake high stands lake ngami these synchronous lake phases result from a coalescence of the sub basins into a unified palaeolake lake thamalakane covering an area of 32 000 km2 six additional ages are also presented from the chobe enclave to the north of the basin where shoreline ridges were emplaced at the same time as lake thamalakane phases this suggests that increased flow in the chobe and zambezi system significantly contributed to the middle kalahari lake phases in both the post glacial and holocene periods the integration of these new data and their compatibility with other regional and tropical palaeo archives is discussed in the light of understanding quaternary climate drivers within the kalahari

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

effects of sedimentary sorting on neodymium isotopes in deep sea turbidites the study of neodymium model ages of sedimentary rocks has added considerably to our understanding of crustal growth and evolution so far however the possible effects of various sedimentary processes on nd isotope distributions have not been fully evaluated here we present nd isotope data for a series of sand mud pairs in modern deep sea turbidites from different tectonic settings which show that sands and muds commonly have significantly different nd isotope compositions that in only some cases are associated with differences in sm nd ratio differences are as great as 7 ndunits corresponding to nd model ages that differ by up to 0 44 gyr and may be explained by separation or unmixing of components from different sources during sedimentary transport and sorting for one sample heavy mineral fraction ation may be indicated these results have implications for studies of nd model ages in sedimentary rocks and for the interpretation of provenance from sedimentary petrography and geochemistry

volume balance of erosional loss and sediment deposition related to himalayan uplifts the volume of sediment in the foreland basins deltas and fans which are a consequence of the collision of india and asia appears to require the removal of a vertical section c 35km high if the sediments were entirely derived from the himalaya it is argued that this is implausible and that it is likely that the himalayan hinterland e g karakoram and tibet was an important source of sediment prior to c 20 ma when significant himalayan uplift commenced

comparison of quartz osl protocols using lateglacial and holocene dune sands from brandenburg germany abstract we present the results obtained using various different protocols in the quartz optically stimulated luminescence dating of a late glacial and holocene aeolian dune sequence near eberswalde north of berlin germany the allerod finow palaeosol and the laacher see tephra layer serve as chronostratigraphic markers and further independent age control is provided by eight 14 c ages the application of the single aliquot regenerative dose protocol using blue light stimulation and the multiple aliquot regenerative dose and additive dose protocols using broad band blue and green light stimulation are discussed a comparison of radionuclide analyses using high resolution gamma spectrometry and neutron activation analysis is also presented it is concluded that the two dosimetry methods give indistinguishable results although the gamma spectrometry data are more precise in contrast the single aliquot regenerative dose protocol is between 2 and 10 times more precise than the multiple aliquot protocols and systematic differences in performance are also observed the uncertainties in the dosimetry calculations are the largest contributor to the overall age uncertainties the accuracy of the resulting ages is considered very satisfactory when tested against the independent age controls over the entire age range from the present to 15 ka

optical dating of holocene sediments from a variety of geomorphic settings using single grains of quartz this paper presents an improved method for the optical dating of holocene sediments from a variety of geomorphic settings we have measured the equivalent dose de in individual grains of quartz using green laser light for optical stimulation and have simulated the de distributions for multiple grain synthetic aliquots using the single grain data for 12 samples of known independent age we show that application of a minimum age model to the single grain and small 10 grain aliquot de data provides the most accurate estimate of the burial dose for nine of the samples examined 3 aeolian 5 fluvial and 1 marine the weighted mean de as obtained using the central age model gives rise to burial age overestimates of up to a factor of 10 for these nine samples whether single grains small aliquots or large 100 grain aliquots are used for the other three samples two aeolian and one fluvial application of either the minimum age model or the central age model to the single grain small aliquot and large aliquot de data yields burial ages in accord with the independent age control we infer that these three samples were well bleached at the time of deposition these results show that heterogeneous bleaching of the optical dating signal is commonplace in nature and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition we also show that grains sensitive to infrared ir stimulation can give rise to low de values which will result in significant underestimation of the burial dose and hence of the age of deposition we demonstrate that use of a modified single aliquot regenerative dose protocol incorporating ir stimulation prior to green light stimulation deals effectively with contamination by ir sensitive grains we conclude that application of the modified protocol to single grains or small aliquots of quartz using the lowest de population to estimate the burial dose is the best means of obtaining reliable ages for holocene sediments from a wide range of depositional environments d 2003 elsevier b v all rights reserved

chemical weathering and provenance evolution of holocene recent sediments from the western indus shelf northern arabian sea inferred from physical and mineralogical properties abstract we present a multi proxy mineral record based on x ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western indus shelf in order to reconstruct changing weathering intensities sediment transport and provenance variations since 13 ka core indus 10 is located northwest of the indus canyon and exhibits fluctuations in smectite illite chlorite ratios that correlate with monsoon intensity higher smectite illite chlorite and lower illite crystallinity normally associated with stronger weathering peaked during the early mid holocene the period of maximum summer monsoon hematite goethite and magnetic susceptibility do not show clear co variation although they both increase at indus 10 after 10 ka as the monsoon weakened at indus 23 located on a clinoform just west of the canyon hematite goethite increased during a period of monsoon strengthening from 10 to 8 ka consistent with increased seasonality and or reworking of sediment deposited prior to or during the glacial maximum after 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite goethite which we attribute to widespread cultivation of the floodplain triggering reworking especially after 200 years ago over holocene timescales sediment composition and mineralogy in two localities on the high energy shelf were controlled by varying degrees of reworking as well as climatically modulated chemical weathering

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

magnetostratigraphy and sedimentology of the jingchuan red clay section and correlation of the tertiary eolian red clay sediments of the chinese loess plateau a 325 m thick loess and red clay sequence was recently discovered at jingchuan which is situated about 45 km north of the previously studied lingtai section in the middle part of the chinese loess plateau the jingchuan section is composed of 199 m of pleistocene loess and 126 m of tertiary red clay deposits paleomagnetic studies show that the jingchuan red clay has a basal age of at least 7 7 ma which represents the oldest red clay deposits presently known in the loess plateau field observations and grain size analyses both suggest an eolian origin of the red clay thus extending available records of the eolian deposits in the loess plateau from about 7 0 ma to 7 7 ma correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late cenozoic red clay records in the loess plateau have a general continuous nature thereby providing potential for deriving long term climatic evolution signals from this eolian loess and red clay sequence

aeolian activity in the south margin of the tengger desert in northern china since the late glacial period revealed by luminescence chronology abstract aeolian sediments from deserts in northern china have been widely used in the study of aeolian sedimentology and its dynamic association with past climate conditions the tengger desert the fourth largest desert in china is sensitive to the waxing and waning of the asian monsoonal system previous attempts to date aeolian deposits in the tengger desert concentrated solely on local scales and only a limited number of dates have subsequently been made available accordingly past sand dune activity in this desert remains poorly understood the aim of this study was to conduct a detailed historical investigation of aeolian activity in this region since the late glacial period and potential forcing mechanisms that governed the desert s evolution for this purpose we collected and dated eighteen samples from different geological sections along a west east transect in the desert s southern margin using optically stimulated luminescence osl our results in combination with previous aeolian sediment chronologies show that sand dune accumulation occurred before 10 ka sandy loess developed between 10 and 6 ka when sand dunes stabilized as a result of increased effective moisture levels and sand dunes again mobilized from 3 ka onwards as a result of increased aridity findings indicate that aeolian activity at the southern margin of the tengger desert was closely associated with asian monsoon circulation moreover the transition between mobilization and stabilization of sand dunes demonstrates the significance of effective moisture which is influenced by both monsoon precipitation and local convection and evaporation effects interacting together to control aeolian activity

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

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

holocene environmental changes in the central inner mongolia based on single aliquot quartz optical dating and multi proxy study of dune sands abstract alternating units of dune sands and paleosols in the central inner mongolia imply multiple episodes of dune building and stabilization in response to the waxing and waning of the east asian monsoon such eolian deposits were dated by using the single aliquot quartz optical dating method combined with the multi proxy study on the deposits the past environmental changes during the holocene have been reconstructed our results indicate that widespread eolian sand mobilization occurred in the studied region during the beginning of the early holocene from 11 5 ka to 9 ka the climate became warm and humid during the period between 9 ka and 5 6 ka holocene optimum after 5 6 ka the region again became arid as inferred from dune building however the environmental changes during the late holocene have been affected by both climate and human impacts and the presence of desert environment in such semiarid region is not only the result of climatic drought of the late holocene but also related to poor land use practices

clay mineral assemblages in the northern south china sea implications for east asian monsoon evolution over the past 2 million years abstract clay mineral assemblages at odp site 1146 in the northern south china sea are used to investigate sediment source and transport processes and to evaluate the evolution of the east asian monsoon over the past 2 myr clay minerals consist mainly of illite 22 43 and smectite 12 48 with associated chlorite 10 30 kaolinite 2 18 and random mixed layer clays 5 22 hydrodynamic and mineralogical studies indicate that illite and chlorite sources include taiwan and the yangtze river that smectite and mixed layer clays originate predominantly from luzon and indonesia and that kaolinite is primarily derived from the pearl river mineral assemblages indicate strong glacial interglacial cyclicity with high illite chlorite and kaolinite content during glacials and high smectite and mixed layer clay content during interglacials during interglacials summer enhanced monsoon southwesterly currents transport more smectite and mixed layer clays to site 1146 whereas during glacials enhanced winter monsoon northerly currents transport more illite and chlorite from taiwan and the yangtze river the ratio smectite mixed layers illite chlorite was adopted as a proxy for east asian monsoon variability higher ratios indicate strengthened summer monsoon winds and weakened winter monsoon winds during interglacials in contrast lower ratios indicate a strongly intensified winter monsoon and weakened summer monsoon during glacials spectral analysis indicates the mineral ratio was dominantly forced by monsoon variability prior to the development of large scale glaciation at 1 2 myr and by both monsoon variability and the effects of changing sea level in the interval 1 2 myr to present

palaeoclimatic and palaeoenvironmental implications of late pleistocene aeolian sand in the jin shaan gorges of the yellow river valley revealed by luminescence chronology river valleys are critical water gas rock interactions zone where close interaction between fluvial and aeolian deposition are a pronounced feature in arid semi arid and semi humid environments

nd and sr isotope geochemistry of plutonic rocks from hong kong implications for granite petrogenesis regional structure and crustal evolution abstract combined nd and sr isotope data allow the plutonic rocks of hong kong to be grouped into three ne trending domains those of zone 1 in the northwestern part of the territory have nd t 87 sr 86 sr 0 0 71 the plutonic rocks in the central zone 2 exhibit a broad spectrum of isotope characteristics with nd t values of 4 2 to 7 0 tdm between 1 30 and 1 51 ga and 87 sr 86 sr 0 ratios in the range 0 7061 0 7102 granites of zone 3 in the southeastern part of the territory display relatively homogeneous isotope signatures with nd t between 5 5 and 6 5 and 87 sr 86 sr 0 ratios in the range 0 7067 0 7109 tdm model ages are between 1 39 and 1 47 ga the contrasting isotope signatures between zone 1 granites and those in zones 2 and 3 suggest there are inherent differences in the source regions and point to the existence of a basement terrane boundary in this part of southeast china the presence of a deep crustal discontinuity transecting hong kong would also account for the distribution and compositional variation of the granites and the dominant northeast structural control on dyke emplacement the variation in isotope signatures and tdm model ages observed in the hong kong rocks are consistent with a model involving the progressive interaction of mantle derived melts with two distinct crustal sources during a transition from compressional to extensional tectonics the boundary between these two crustal sources is marked by zone 2 in which isotope characteristics are more variable and a stronger mantle influence is preserved

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

eolian inputs of lead to the north pacific we evaluate the importance of natural eolian pb to the dissolved oceanic pb budget by measuring the isotopic composition of pb in 35 holocene and late quaternary sediment samples from the north pacific and in 10 samples of chinese loess when the pacific is divided into sediments provinces based on published end and sedimentological data pb from the central north pacific tends to be the most radiogenic and homogeneous due to the dominance of eolian chinese loess lead from the marginal north pacific and the sparsely sampled regions south of 5 n are less radiogenic and more variable owing to hemipelagic inputs from various volcanic arcs and older continental crust located around the pacific rim 208pb 204pb ratios provide the most distinctive provenance information due to the relatively high ratios in chinese loess the chinese loess samples come from 3 localities and span up to 2 myr of time acetic acid leachate bulk loess and loess silicate fractions were analyzed separately leachate pb is considerably less radiogenic than silicate pb the isotopic composition of the silicate component closely matches the sediment data from the central north pacific confirming the dominance of eolian loess in this region we divided up a suite of published hydrogenous pb isotope data from the pacific ocean according to their locations within the three independently defined sediment provinces these data define three distinct fields differentiated primarily by their 206pb 204pb ratios which increase going from the central to southern to marginal provinces this relationship with sediment province strongly suggests that natural eolian and probably hemipelagic inputs significantly impact the seawater pb budget direct support for the dominance of eolian chinese loess in the central north pacific dissolved pb budget comes from the close match between loess leachate pb and the central province hydrogenous pb data eolian inputs are likely to dominate local seawater pb budgets only where eolian pb fluxes are high relative to hemipelagic pb fluxes and where the flux of pb carried by deep water advection is low

a time slice approach to the history of cenozoic sedimentation in the indian ocean abstract results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which represent snap shots of the changing patterns of sediment accumulation in the indian ocean through the cenozoic the maps clearly delineate the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeography tectonics paleocirculation and or climate paleogene sediment accumulation rates were generally low with significant accumulation in only limited areas suggesting weak ocean circulation and stable well stratified conditions by contrast the vigorous thermohaline circulation of the neogene resulted in substantial widespread sedimentation accumulation rates were generally high and displayed a wide range of values following rapid growth of the east antarctic ice sheet in the mid miocene carbonate sedimentation has been progressively restricted to the shallow ridges and plateaus of the western indian ocean but accumulates there with locally high rates the link between tectonics and terrigenous sedimentation is exemplified by the major deep sea fans off east africa zambezi fan and india indus and bengal fans which developed in response to uplift and erosion beginning in late oligocene time in the east african rift system and the himalayas respectively although maps from only five widely spaced times are shown the methodology is such that a continuous series of maps at intervals as close as 1 m y can readily be generated ultimately the combination of such time slice maps with the results of detailed time series studies will provide a powerful tool for understanding past oceanic environments

rapid early miocene acceleration of uplift in the gangdese belt xizang southern tibet and its bearing on accommodation mechanisms of the india asia collision abstract five samples from a biotite hornblende granodiorite phase of the 42 5 ma quxu pluton gangdese batholith southern tibet have been collected at 250 m vertical intervals biotite from these rocks yields monotonically decreasing40ar 39ar isochron ages with decreasing elevation of 26 8 0 2 23 3 0 5 19 7 0 3 18 4 0 4 and17 8 0 1ma tc 335 c coexisting k feldspars have virtually identical minimum apparent40ar 39ar ages of 17 0 0 4ma tc 285 c these data indicate parts of southern tibet experienced a pulse of uplift in the early miocene with the rate of uplift rising from 0 07 to 4 4 mm year in the interval 20 to 17 ma an apatite fission track age of 9 9 0 9ma from this locality constrains the average uplift rate at this site to about 0 81 mm year between 17 and 9 9 ma and 0 30 mm year from 9 9 ma to present k feldspar from the dagze granite 30 km to the east near lhasa yields a minimum apparent40ar 39ar age of 35 9 0 9ma tc 227 c which indicates an average uplift rate there of 0 21 mm year since then the marked pulse of uplift of the quxu granodiorite and the difference in uplift history between the dagze and quxu plutons suggests southern tibet has experienced discrete pulses of uplift variable in both space and time these data are not consistent with models which require a large proportion of uplift of the tibetan plateau to have occurred in the last 2 ma the data support the suggestion that convergence between india and asia was largely accommodated by tectonic escape during the opening of the south china sea 32 to 17 ma ago and permit distributed shortening as a mechanism for crustal thickening and uplift of this part of the tibetan plateau subsequent to 20 ma

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

petrogenetic implications of neodymium isotope data from the kohistan batholith north pakistan neodymium data are presented for five granitoid trondhjemite granite and leucogranite plutonic units from the kohistan batholith aged 102 ma to 29 ma these have present day l43 nd 144 nd ratios of between 0 512980 and 0 512734 calculated initial 143 nd 144 nd ratios of between 0 512861 and 0 512705 and nd values of between 6 91 and 2 04 there is a decrease in nd with time which is inversely correlative with a similar increase in sr three plutonic units matum das gilgit and shirot formed from a source enriched in sm and depleted in rb or radiogenic sr relative to bulk earth whilst a fourth unit the indus confluence acid sheets is only slightly enriched in radiogenic sr these four units define a temporal trend from the least evolved matum das pluton to the most evolved indus confluence acid sheets this trend was produced as a result of subducting oceanic sediment or seawater altered oceanic crust which melted or dehydrated and increasingly modified the isotopic composition of an original mantle protolith situated above the subducting plate the data preclude any significant input to the magmatism from ancient crust new data presented here together with other published data indicate an immature metavolcanic crustal source for the matum das pluton and a plutonic basement crustal source for the indus confluence acid sheets these crustally derived units retain a mantle isotopic signature indicating that the geochemical signature of kohistan evolved by remobilization of recently formed arc crust in addition to new inputs of mantle derived magma a fifth plutonic unit the parri acid sheets shows a clear compositional break from the other units being significantly enriched in radiogenic sr and nd with respect to bulk earth the source to the parri acid sheets is interpreted as metasedimentary rocks with a high rb sr ratio and a crustal residence time of c 70 ma

productivity and continental denudation history from the south china sea since the late miocene late miocene recent micropaleontological and geochemical records from ocean drilling program odp site 1143 in the southern south china sea scs indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling a high export production event a biogenic bloom event occurred in the southern scs between 12 and 6 ma during this period high ratios of smectite illite chlorite smectite quartz and al k indicate a high weathering intensity of the asian continent possibly due to the intensification of the east asian summer monsoon easm which may have increased the net flux of nutrients to the ocean both directly through terrestrial input and indirectly through upwelling activity a drop in ba ti al ti and ca ti values around 6 ma may indicate a lowering of productivity possibly due to the large consumption of sea surface nutrients by the biogenic bloom alternatively it may indicate a shift in terrigenous input source area at about 5 4 ma a decrease in weathering intensity as indicated by a sudden decrease in the values of smectite illite chlorite smectite quartz and al k might have led to a sudden decrease of terrestrial nutrient input to the scs we suggest that the biogenic bloom ended when nutrients in surface waters were exhausted because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the easm as a result radiolarians were absent in the studied area between similar to 6 and 3 2 ma at similar to 3 2 ma radiolarians began to recover possibly because the start of northern hemispheric glaciation and the rapid uplift of the tibet plateau led to intensification of the east asian monsoon after the mid pleistocene climate transition at 0 9 ma the abundance and mass accumulation rates of radiolarians increased probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon crown copyright c 2009 published by elsevier b v all rights reserved

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

late weichselian fluvio aeolian sediments and holocene drift sands of the classic type locality in twente e netherlands a high resolution dating study using optically stimulated luminescence abstract the late weichselian and holocene fluvio aeolian sands of the type locality lutterzand in the e netherlands have been the focus of many palaeoclimatic palaeoenvironmental and geochronological studies in the present study an accurate and detailed chronological framework has been established using radiocarbon and optically stimulated luminescence dating additionally the sedimentological characteristics of the fluvio aeolian and aeolian sequences have been reinvestigated four main phases of fluvio aeolian sedimentation have been differentiated in the lutterzand sections consistent with the late pleniglacial the pre allerod lateglacial the late dryas and the late holocene from at least 25 2 1 9 ka up to 19 9 1 6 ka the area was marked by a transition from fluvial to aeolian deposition under continuous permafrost conditions older coversand i the beuningen gravel bed is considered as the lithostratigraphic marker for permafrost degradation shallow channelling and aeolian deflation associated with the formation of a desert pavement localised fluvial sedimentation in shallow channels took place in two phases a first from 20 ka to 23 ka and a second at around 16 ka the desert pavement formed in between 16 ka and 14 ka but probably shortly after 16 ka the aeolian sediments overlying the beuningen gravel bed were deposited as sand sheets and low dunes and yielded ages between 15 8 1 4 ka and 12 2 0 9 ka although the osl ages seem to point to fairly continuous coversand sedimentation during the lateglacial the intercalated usselo soil allows distinguishing a pre allerod phase resulting in the older coversand ii and the younger coversand i between 15 8 1 4 ka and 12 3 1 0 ka from a post allerod phase with deposition of the younger coversand ii between 13 6 1 1 ka and 12 2 0 9 ka during the major part of the holocene podzol soil formation occurred in the top of the aeolian sediments probably due to human activities local erosion of the upper part of the lateglacial sequences and redeposition took place these drift sands were dated between 0 40 0 04 ka and 0 20 0 02 ka

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

clay mineral distribution in surface sediments of the northeastern south china sea and surrounding fluvial drainage basins source and transport clay mineralogy of surface samples throughout the northeastern south china sea scs and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine grained sediments three characteristic end members in clay mineral compositions were observed from three major provenances respectively major kaolinite and moderate illite and chlorite from the pearl river predominant illite and chlorite from taiwan and principal smectite from the luzon arc system the transport of four clay mineral species in the northeastern scs is influenced by various mechanisms smectite derived from the luzon arc system is transported mainly by surface current with significant influence of the kuroshio intrusion illite and chlorite from taiwan are mainly carried by deep water current while kaolinite from the pearl river is affected obviously by the westward guangdong coastal current and longshore current a westerly tongue shaped distribution of high contents of illite and chlorite mainly from taiwan on the eastern shelf may result from the westward guangdong coastal current during the winter the results suggest that clay mineral assemblages in the northeastern scs are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features the implication of clay minerals for proxies of the late quaternary east asian monsoon evolution is realized through both the provenance supply and current transport processes c 2010 elsevier b v all rights reserved

pleistocene glaciation of the king valley western tasmania australia abstract analysis of the geomorphology geology and palynology of deposits in the king valley permits the identification of four glaciations and two interglaciations and has led to a revision of the pleistocene stratigraphy of the west coast range the oldest late cenozoic deposits in the valley appear to predate glaciation contain extinct pollen types and are probably of late tertiary age overlying deposits of the linda glaciation show intense chemical weathering and have a reversed detrital remanent magnetization indicating deposition before 730 000 yr b p the highly weathered tills are conformably overlain by organic deposits of the regency interglaciation which show a transition from montane scrub rainforest to lowland temperate rainforest deposits formed during the later moore glaciation record advances of the king glacier and glaciers from the west coast range a pollen bearing fluvial deposit records an interstade during this glaciation on the basis of weathering rinds amino acid dating and palaeomagnetism the deposits are estimated to have formed between 730 000 and 390 000 yr b p the moore glaciation deposits are overlain by sediments of the henty glaciation which are believed to predate 130 000 yr b p these deposits record multiple advances of the king glacier and the development of a large lake during an interstade deposits of the subsequent pieman interglaciation consist of organic fine sands and silts that record a lowland scrub rainforest deposits of the last margaret glaciation are restricted to small areas in the northern part of the valley although the most recent ice advance culminated after 19 000 yr b p evidence of older deposits of the margaret glaciation suggests that an early last glaciation ice advance may have occurred when combined with earlier studies the recent work in the king valley has provided one of the more complete records of pleistocene glaciation in the southern hemisphere comparison of the deposits with the record of glaciation in southern south america and westland new zealand suggests some similarities exist between pre last glaciation events and indicates that glacial events in southern hemisphere middle latitude areas were synchronous during the last glaciation

nyainqentanglha shear zone a late miocene extensional detachment in the southern tibetan plateau a major low angle ductile shear zone containing s c mylonites involves metamorphosed granitic rocks at the southeastern edge of the nyainqentanglha mountain range southern tibet prominent triangular facet geomorphology is developed by valley erosion of the detachment surface defined by the top of the southeast dipping mylonitec shear zone kinematic criteria consistently indicate a top to southeast sense of shear the ductile shearing deformation is inferred from isotopic cooling ages to have occurred during the interval 11 5 ma late miocene we interpret the shear zone as a regional extensional detachment its development indicates when the extensional tectonics in this area started which in turn may mark the time when the maximum sustainable surface elevation and perhaps crustal thickness was reached in southern tibet

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

displacement along the red river fault constrained by extension estimates and plate reconstructions significant e w extension and or compression must have been generated by displacements along the red river fault rrf since its curvature does not match a small circle centered at the euler pole for the indochina south china plate pair the amount of extension perpendicular to the rrf offshore vietnam depends on the magnitude of left lateral displacement along the rrf in general the larger the left lateral displacement along the fault the smaller the amount of e w extension all purely strike slip models of the opening of the south china sea that assume large displacements 250 km along the rrf encounter major problems because they imply little extension or even considerable shortening offshore east vietnam this is inconsistent with the presence of large elongated basins offshore vietnam using a plate tectonic model we compare continental extension values implied by different magnitudes of displacement along the rrf with crustal stretching estimates derived from 2 d profiles modeled from gravity data we utilize 2 d gravity forward models to restore the extended continental margin crust to its original position prior to extension we find that substantial amounts of extension for offshore vietnam can only be modeled assuming moderate displacements along the rrf compatible with the presence of a southward subducting proto south china sea the total amount of ene wsw extension offshore northern vietnam constrained by our 2 d gravity profiles and gravity inversion increases southward from 36 to 89 km along the yinggehai basin these values of ene wsw extension are consistent with 250 km of left lateral displacement along the rrf