orbital scale evolution of the indian summer monsoon since 1 2 ma evidence from clay mineral records at iodp expedition 355 site u1456 in the eastern arabian sea abstract clay mineral assemblages at international ocean discovery program expedition 355 site u1456 drilled in the eastern arabian sea have been investigated to reveal the sediment provenances and reconstruct the erosion weathering patterns in the western himalaya and indian subcontinent thus constraining the evolution of the indian summer monsoon and its forcing mechanism since 1 2 ma the clay mineral assemblages at site u1456 mainly comprise smectite with an average value of 59 and illite with an average value of 33 with chlorite with an average value of 5 and kaolinite with an average value of 3 as minor constituents in terms of sediment provenance our results indicate that illite and chlorite are predominantly derived from the indus river which originates from the western himalaya and karakoram while smectite is primarily sourced from the narmada river and tapti river in the deccan traps with a non negligible contribution from the indus river in some cases variations in smectite illite chlorite ratio are ultimately controlled by the indian summer monsoon which is characterized by approximate glacial interglacial cyclicity showing higher values i e enhanced chemical weathering during interglacial periods in addition a major shift in smectite illite chlorite ratio at 0 9 ma is correlated to the mid pleistocene transition 1 2 0 9 ma both the marine isotope stage 13 event 533 478 ka and the mid brunhes event 430 ka are also recorded in the clay mineral proxies based on the spectral analysis smectite illite chlorite ratio displays a transition from nonprimary periodicity 29 kyr to strong eccentricity 100 kyr and precession 22 kyr periodicities at approximately 0 9 ma which corresponds to the mid pleistocene transition our study indicates that the variability of the indian summer monsoon at orbital timescales is controlled by high latitude i e ice volume and low latitude i e summer insolation processes

vertical and horizontal distribution of sedimentary facies and hydromorphic paleosols around paleo lake in the pliocene sediments in southwest japan abstract the collaborative study between descriptive paleopedology and sedimentology for the pliocene sediments in southwest japan clarified the paleo groundwater table at lake margins and the change of the paleoclimatic conditions in the coastal region of eastern asia during the pliocene period 3 4 ma some hydromorphic paleosols were formed in the proximal floodplain and the natural levee which are generally located in a high topographic position and these paleosols finally reached a similar maturity to ultisol and inceptisol the vertical variation of the sedimentary facies suggests the increased sedimentation rates and increased volume of sediment supply during this period the stratigraphic distribution of the hydromorphic paleosols in the pliocene formation implies the rising of the paleo groundwater table and to become considerably fluctuating of the paleo groundwater table the temporal change in weathering conditions implies that precipitation increased during the middle pliocene warm period

sea level control on the submarine fan architecture in a deepwater sequence of the niger delta basin abstract submarine fan architecture has long been considered much complicated as controlled by both allogenic and autogenic mechanisms however to which extent the allogenic sea level change controls the submarine fan architecture is still unclear this study uses integrated 3 d seismic well log and core data to characterize the submarine fan architecture in a deepwater sequence of the niger delta basin correlation of the timing of architecture units to high frequency sea level curve helps to investigate the sea level control on architecture distribution and evolution of submarine fan systems the studied sequence is a 3rd order sequence that formed during 12 5 10 5 ma and contains a lowstand systems tract lst and a transgressive highstand systems tract tst hst we find that the lst develops a single channel system that is terminated by a lobe system whereas the tst hst develops two mutually incised channel systems and mudflow deposits which are distinct from the conventional condensed sections and interpreted to result from the repeated 4th order sea level cycles during the tst hst of the 3rd order sequence single submarine fan systems which last for 0 3 0 6 myr are assumed to form in response to single 4th order sea level cycles since they are well correlated with each other each single submarine fan system contains several vertically stacked complex sets which are well correlated with 5th order sea level cycles that last for 0 1 0 2 myr suggesting their potential genetic links different complex sets in a single submarine fan system exhibit variable architectural features which are interpreted to result from the evolution of gravity flow types as the 4th order sea level fluctuates thus for the niger system at time scales 0 1 myr the allogenic sea level change is considered to have played a major role in controlling the submarine fan architecture at the scale of submarine fan systems and complex sets whereas autogenic effects on the submarine fan architecture may increase and become dominant on time scales

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

origin and development of artemisia asteraceae in asia and its implications for the uplift history of the tibetan plateau a review abstract the spatial and temporal evolution of artemisia and its relationship with the tibetan plateau tp uplift are examined by summarizing pollen data from 122 sites across china the pollen morphological data reveal that artemisia may have originated from the arid semiarid middle latitudes of asia in the late eocene and spread west and east in the oligocene as the result of early uplift of the tibetan plateau and the global cooling during the miocene artemisia reached the southeastern part of the tp and became common in the western tp due to the high elevation in these regions at the same time the asian monsoon prevented the spread of artemisia to the southern part of the tp since the pliocene especially in the pleistocene artemisia distribution was very similar to its current distribution which indicates that the topography of the tp and the paleoenvironmental conditions in the east asia became more like today thus the cenozoic origin and evolution of artemisia in the asia was strongly influenced by the uplift of the tp global cooling as well as monsoon development

late mio pliocene chemical weathering of the yulong porphyry cu deposit in the eastern tibetan plateau constrained by goethite u th he dating implication for asian summer monsoon abstract chemical weathering has provided a potentially important feedback between tectonic forcing and climate evolution of the asian continent although precise constraints on the timing and history of weathering are only variably documented here we use goethite u th he and 4 he 3 he geochronology to constrain the timing and rates of chemical weathering at the yulong porphyry cu deposit on the eastern tibetan plateau goethite grains have u th he ages ranging from 6 73 0 51 to 0 53 0 04 ma that correlate with independent paleoclimatic proxies inferred from supergene mn oxides and loess deposits under variable tectonic regimes and vegetation zones over the southeastern asia this correlation indicates that regional climatic conditions especially monsoonal precipitation controlled chemical weathering and goethite precipitation in a vast area of southeastern asia the goethite ages suggest that the asian summer monsoon was relatively strong from 7 to 4 6 ma but weakened between 4 6 and 4 ma and then significantly intensified from 4 to 2 ma the precipitation ages of goethites collected along a 100 m thick weathering profile decrease with depth and indicate a downward propagation of the weathering front at rates of 53 5 10 8 and 4 8 0 6 m ma during the intervals of 7 4 4 2 and 2 0 7 ma respectively the rapid propagation of weathering front during 4 2 ma was caused by abrupt lowering of the water table which was possibly related to local surface uplift or reorganization of the river systems in southeastern tibet during this period

climatic control on rapid exhumation along the southern himalayan front abstract along the southern himalayan front shf areas with concentrated precipitation coincide with rapid exhumation as indicated by young mineral cooling ages twenty new young 80 of the annual precipitation aft cooling ages reveal a coincidence between rapid erosion and exhumation that is focused in a 50 70 km wide sector of the himalaya rather than encompassing the entire orogen assuming simplified constant exhumation rates the rocks of two age vs elevation transects were exhumed at 1 4 0 2 and 1 1 0 4 mm a with an average cooling rate of 40 50 c ma during pliocene quarternary time following other recently published hypotheses regarding the relation between tectonics and climate in the himalaya we suggest that this concentrated loss of material was accommodated by motion along a back stepping thrust to the south and a normal fault zone to the north as part of an extruding wedge climatically controlled erosional processes focus on this wedge and suggest that climatically controlled surface processes determine tectonic deformation in the internal part of the himalaya

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

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

advent of strong south asian monsoon by 20 million years ago abstractthe monsoonal paleoclimate of india has been critical for understanding the tectonic history of himalayan and tibetan uplift over the past 60 my monsoonal circulation in deep time has been inferred from variation in stable isotopes of tooth enamel diatom blooms and dust influx in the indian ocean and the advent of c4 grasses but these proxies are compromised by temperature biotic and source effects our study uses a proxy of carbonate distribution within paleosol profiles to infer appearance of monsoonal circulation of modern strength in the himachal pradesh segment of the himalayan foreland by at least 20 my ago cued to high himalayan deformation and ongoing tibetan plateau uplift and retreat of the paratethys sea paleosol records also demonstrate declining chemical weathering with himalayan and tibetan uplift which was a force for global warming rather than cooling over the past 20 my

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

excitation of high frequency surface waves with long duration in the valley of mexico during the 1985 michoacan earthquake ms 8 1 large amplitude seismograms with extremely long duration were recorded in the lake bed zone of mexico city we interpret high frequency seismic wave fields in the three geotechnical zones the hill the transition and the lake bed zones in the valley of mexico on the basis of a systematic analysis for borehole strong motion recordings we make identification of wave types for real seismograms first amplitude ratios between surface and underground seismograms indicate that predominant periods of the surface seismograms are largely controlled by the wave field incident into surficial layers in the valley of mexico we interpret recorded surface waves as fundamental mode love waves excited in the mexican volcanic belt by calculating theoretical amplification for different scale structures second according to a cross correlation analysis the hill and transition seismograms are mostly surface waves in the lake bed zone while early portions are noisy body waves late portions are mostly surface waves third using two kinds of surface arrays with different station intervals we investigate high frequency surface wave propagation in the lake bed zone the wave propagation is very complicated depending upon the time section and the frequency band finally on the basis of a statistical time series model with an information criterion we separate s and surface wave portions from lake bed seismograms surface waves are dominant and are recognized even in the early time section thus high frequency surface waves with long duration in the valley of mexico are excited by the mexican volcanic belt

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

controls on the erosion of cenozoic asia and the flux of clastic sediment to the ocean rates of continental erosion may be reconstructed from variations in the rate of accumulation of clastic sediment most of which lies offshore global rates of marine sedimentation are usually considered to have reached a maximum after 3 4 ma driven by enhanced erosion in a variable glacial interglacial climate however a new compilation of seismic data from the marginal seas of asia now shows that only the red river reached its historic peak after 4 ma sediment flux from asia first peaked in the early middle miocene 24 11 ma well before the initiation of a glacial climate indicating that rock uplift and especially precipitation are the key controls on erosion at least over long periods of geologic time reconstructions of weathering in east asia show that faster erosion correlates with more humid warm climates in the early middle miocene changing to less erosive drier climates after 14 ma when antarctic glaciation begins average rates of sedimentation on most east asian continental margins since 1 8 ma are 5 6 times less than the modern fluvial flux implying that the flux to the oceans varies sharply on short timescales and is not always buffered over timescales of 10 4 yr by storage in flood plains

the structure and rate of late miocene expansion of c4 plants evidence from lateral variation in stable isotopes in paleosols of the siwalik group northern pakistan this study uses stable isotope variation within individual mio pliocene paleosols to investigate subkilometer scale phytogeography of late miocene vegetation change in southeast asia between ca 8 1 and 5 ma a time interval that coincides with dramatic global vegetation change we examine trends through time in the distribution of low latitude grasses c4 plants and forest c3 plants on indo gangetic floodplains using carbon 13c and oxygen isotopic 18o values in buried soil carbonates in siwalik series sediments exposed in the rohtas anticline north central pakistan revised high resolution magnetostratigraphy and a new 40ar 39ar date provide improved age control for the 2020 m rohtas section carbon isotope results capture lateral variability of c3 versus c4 plants at five stratigraphic levels r11 8 0 ma r15 6 74 6 78 ma r23 5 78 ma r29 4 8 4 9 ma and upper boundary tuff ubt 2 4 ma using detailed sampling of paleosols traceable laterally over hundreds of meters paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments channel fill crevassesplay and floodplain environments 13c results show that near the beginning 8 0 ma and after 4 0 ma the period of major ecological change vegetation was homogeneously c3 or c4 respectively regardless of paleo landscape position in the intervening period there is a wide range of values overall with c4 grasses first invading the drier portions of the system floodplain surfaces and c3 plants persisting in moister settings such as topographically lower channel swales although abrupt on a geologic timescale changes in abundance of c4 plants are modest 2 per 100 000 yr compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the quaternary earlier research documented a sharply defined c3 to c4 transition in pakistan between 8 1 and 5 0 ma based on vertical sampling but this higher resolution study reveals a more gradual transition between 8 0 and 4 5 ma in which c3 and c4 plants occupied different subenvironments of the siwalik alluvial plain 18o values as well as 13c values of soil carbonate increase up section at rohtas similar to isotope trends in other paleosol records from the region spatially however there is no correlation between 13c and 18o values at most stratigraphic levels this implies that the changes in soil hydrology brought about by the shift from forest to grassland i e an increase in average soil evaporation did not produce the shift through time in 18o values we interpret the trend toward heavier soil carbonate 18o values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 ma

forced regression across the marine to continental transition in jammu sub basin implication to the oligo miocene unconformity in the himalayan foreland abstract similar to the other sub basins marine to continental transition in jammu foreland also shows the presence of a characteristic greenish gray quartz arenite unit locally termed as white sandstone unit process based sedimentological and sequence stratigraphic work carried out across this white sandstone unit suggest that this unit was deposited in a shoreface settings during a forced regression the sharp base of the white sandstone unit represents a surf diastem a kind of regressive surface of marine erosion and does not signify a 10 myr unconformity the gradational top of the unit showing various degree of exposure and soil development has been interpreted as type 1 sequence boundary the white sandstone unit present along the entire stretch of the western sub himalaya also shows forced regressive nature in the subathu sub basin situated 350 km se of jammu so the forced regression across the marine to continental transition in the entire western himalayan foreland is a regional phenomena and not a local one contrary to the earlier works which proposed the presence of an unconformity spanning 10 myr encompassing the oligo miocene period the present study showed that the unconformity if present is of small duration possibly spanning

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

muscovite 40ar 39ar ages help reveal the neogene tectonic evolution of the southern annapurna range central nepal we present new muscovite 40 ar 39 ar ages from thirteen greater himalayan rocks and one lesser himalayan rock collected from four north trending transects across the southern annapurna range combining the new data with previously published ages leads to the following new insight into the tectonic development of the southern annapurna muscovite cooling ages from greater himalayan rocks are c 16 10 ma in the western annapurna and c 6 2 ma in the eastern annapurna revealing a decrease of 4 14 ma from west to east similarly the muscovite cooling age from one lesser himalayan rock in the west is c 7 ma and ages from several samples in the east are c 5 2 ma indicating a decline of 2 5 ma towards the east earlier cooling in the western annapurna can be explained by along strike differences in the geometry of the frontal ramp on the underlying thrust that carries these greater and lesser himalayan rocks and or by a ne striking fault that cut these rocks in greater himalayan rocks from the modi river valley one sample yielded muscovite 40 ar 39 ar ages of 18 0 0 7 and 16 2 0 5 ma for grain sizes of approximately 750 and 200 m respectively in contrast a sample collected 200 m structurally lower produced ages of 12 6 0 2 and 9 9 0 1 ma for these two grain sizes the north dipping bhanuwa fault has been proposed between these samples with different authors arguing for normal or thrust sense motion our newfound pattern of an older muscovite 40 ar 39 ar age pair in the hanging wall supports arguments for the existence of the bhanuwa fault and suggests normal sense motion

thermochronology quantifying exhumation history of the wudang complex in the south qinling orogenic belt central china the wudang complex located in the central part of south qinling has been inferred to be a segment of the yangtze craton involved in the orogen in this study the cooling exhumation history of the wudang complex is revealed through combined published geochronology data and new apatite fission track results three rapid exhumation episodes related to relevant geodynamic events have been identified previous 40 ar 39 ar and u th he data indicate that the most significant exhumation induced by the collision between the north and south china blocks occurred from c 237 to 220 ma after long term subsidence and sedimentation of the passive continental margin the second exhumation event related to the long distance effect of the pacific subduction occurred during the period from c 126 to 90 ma following the late cretaceous eocene peneplanation stage the final late cenozoic exhumation since c 15 ma may be attributed to the combined effect of the eastward growth of the tibetan plateau uplift and the asian monsoon

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

deciphering relationships between the nicobar and bengal submarine fans indian ocean abstract the nicobar fan and bengal fans can be considered as the eastern and western parts respectively of the largest submarine fan system in the world this study presents the integrated results of petrographic and provenance studies from the nicobar fan and evaluates these in the context of controls on sedimentation both fans were predominantly supplied by himalaya derived material from the main tectono stratigraphic sequences as well as the gangdese arc a lack of volcanic material in the nicobar fan rules out sources from the sumatra magmatic arc overall the petrographic data shows a progressive decrease in sedimentary detritus and corresponding increase of higher grade metamorphic detritus up section changes in sediment provenance and exhumation rates in the himalaya are seen to track changes in sediment accumulation rates high sediment accumulation rates in the bengal fan occurred at 13 5 8 3 ma and in the nicobar fan from 9 5 5 ma both fans show peak accumulation rates at 9 5 8 3 ma but with the nicobar fan being about twice as high and both record a sharp drop from 5 5 5 2 ma that coincided with a change in river drainage associated with the brahmaputra river diverting west of the uplifting shillong plateau at 5 ma the nicobar fan was supplied by an eastern drainage route that finally closed at 2 ma when sediment accumulation rates in the nicobar fan significantly decreased sediment provenance record these changes in routing whereby bengal fan deposits include granitoid sources from the namche barwa massif in the eastern syntaxis that are not seen in the nicobar fan likely due to a more localised eastern drainage that included material from the indo burman wedge prior to 3 ma source exhumation rates were rapid and constant and the short lag time rules out significant intermediate storage and mixing in terms of climate versus tectonic controls tectonically driven changes in the river network have had most influence on fan sedimentation

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

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

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

a new type of pyroclastic deposit on the moon containing fe spinel and chromite 1 we present details of the identification of sites that show an absorption band at visible wavelengths and a strong 2 m band using the selene spectral profiler all the sites exhibiting the visible feature are found on the regional dark mantle deposit dmd at sinus aestuum all the instances of the visible feature show a strong 2 m band suggestive of fe and cr rich spinels which are different from previously detected mg rich spinel since no visible feature is observed in other dmds the dmd at sinus aestuum is unique on the moon the occurrence trend of the spinels at sinus aestuum is also different from that of the mg rich spinels which are associated with impact structures this may suggest that the spinel at sinus aestuum is a different origin from that of the mg rich spinel

glacial interglacial variation in catchment weathering and erosion paces the indian summer monsoon during the pleistocene abstract silicate weathering via co2 consumption is considered to regulate the long term climate change discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate however owing to the paucity of well dated and continuous records of weathering and erosion the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial interglacial climate remain elusive geochemical analysis of a 666 m core from the heqing basin a paleolake situated at the southeastern margin of the tibetan plateau demonstrates silicate versus carbonate weathering and erosion changes under indian summer monsoon ism conditions spanning the entire pleistocene via respective tracing between rb sr and al na ratios the rb sr record is interpreted as reflecting a competition between clayey silicate origin rb versus carbonate origin sr fluxes whereas al na ratio is a balance between weathering and erosion of silicate minerals both pacing the glacial interglacial cycles of the ism during interglacials strong silicate weathering intensity reflected by low al na values is mainly controlled by warmer temperatures with the reduced variability during 1 82 0 92 ma recalling the pacing of the arabian sea surface temperature amplitudes within glacials the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval in conclusion the heqing rb sr and al na records reveal the sensitivity of catchment weathering and erosion to ism changes over glacial interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials

cambrian to triassic geodynamic evolution of central qiangtang tibet abstract central qiangtang is a tectonic melange between the northern qiangtang terrane nqt and the southern qiangtang terrane sqt and it preserves a complete cambrian to triassic geological record related to tethyan evolution e g high pressure metamorphic rocks and ophiolites thus this region is the key to understanding the geodynamic processes that occurred during the dispersion of gondwana and the accretion of laurussia given previous studies on sedimentary paleomagnetic and seismic records this paper presents an integrated interpretation of ophiolites magmatism metamorphism and tectonism and reconstructs the cambrian triassic tectonic evolution of central qiangtang as described below 1 following the neoproterozoic early cambrian pan african orogeny and associated postcollisional extension the southward subduction of the proto tethys oceanic plate produced andean type magmatism along the northern margin of gondwana a back arc basin between the nqt and sqt further opened during the late cambrian early ordovician accompanying with trench retreat and overriding plate extension resulting from slab rollback 2 with the middle ordovician late silurian successive incorporation of micro continental terranes e g qaidam kunlun and tarim terranes into the northern margin of gondwana the back arc basin closed through subduction polarity reversal from southward to northward 3 during the late devonian early carboniferous the southward subduction of an oceanic plate to the north of the nqt separated the nqt and sqt through back arc extension consequently the nqt drifted northward rapidly and the back arc basin gradually evolved into a mature ocean basin i e longmu co shuanghu paleo tethys ocean lspto 4 subsequently a late carboniferous early permian continent continent collision between the nqt and the south china block scb resulted in the northward subduction of the lspto and the ongoing subduction probably induced the opening of a back arc basin between the nqt and the scb during the late permian 5 finally diachronous collision between the nqt and sqt closed the lspto during the early middle triassic and the termination of the collisional orogenic event was evidenced by strong late triassic magmatism related to postcollisional extension in the qiangtang block in this paper we propose that the opening and closure of back arc basins controlled the cambrian triassic tectonic evolution of central qiangtang which provides significant insights into the dispersion of gondwana and the accretion of laurussia

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

early oligocene paleosols of the dagshai formation india a record of the oldest tropical weathering in the himalayan foreland abstract this study reports paleopedological features of the fossil soils that formed during the earliest phase of continental sedimentation in the himalayan foreland the fluvial sequence of the dagshai formation 31 6 3 9 ma to 30 3 3 9 ma exposed along the koshaliya river nw himalaya contains four pedofacies named pedofacies a d of ferruginous paleosol sequences contained within overbank sediments the dagshai formation unconformably overlies the marine subathu formation pedofacies a consists of 3 4 well developed ferruginous paleosols overlain by gray sandstone beds pedofacies b d are marked by a progressive decrease in pedogenesis these paleosols occur as 0 5 m to 1 5 m thick bw bt btk bk bss horizons that are marked by extensive development of rhizoliths pedogenic carbonate and iron rich clay pedofeatures that correspond to modern entisols inceptisols alfisols and vertisols based on early oligocene paleogeographic position of the northward drifting indian plate it is inferred that these paleosols were formed at 18 n paleolatitude in the dagshai sub basin in the himalayan foreland micromorphology geochemical analyses weathering indices and stable isotope composition of paleosols indicate tropical climate paleoprecipitation of 947 1256 mm and paleotemperature of 25 c with an initial phase of monsoonal conditions during pedogenesis these paleoclimatic conditions favored c3 paleovegetation immediately after the transition from greenhouse to icehouse conditions

onset timing and slip history of the teton fault wyoming a multidisciplinary reevaluation the dramatic relief of the teton range in northwestern wyoming results from motion along the teton normal fault new apatite u th he ahe and fission track aft ages of samples collected in the footwall yield fundamental constraints on contrasting models of teton fault activity and consequent relative footwall uplift low elevation samples in the immediate footwall of the fault range from 12 5 to 6 5 ma ahe ages of samples from subvertical transects range from 57 8 to 6 5 ma rendezvous 54 0 to 6 8 ma grand and 20 5 to 7 1 ma moran with all three transects yielding an expected trend of decreasing age with decreasing elevation aft ages obtained from the three transects range from 55 4 to 45 7 ma rendezvous 43 2 to 13 3 ma grand and 38 0 to 11 7 ma moran inverse thermal history modeling indicates that the onset of relatively rapid cooling as a proxy for relative footwall uplift initiated first in the northern part of the range 15 13 ma and then migrated south as fault displacement continued 7 ma to present at rendezvous thus this work suggests that although the teton fault likely initiated due to basin and range extension this structure remains active normal fault displacement models also suggest a minimum of 6 km displacement for footwall uplift of 2 km if evaluated in the context of established normal fault length displacement relationships this yields a length of 180 km substantially longer than current estimates of teton fault length and putting the northern end of the fault well into and potentially beyond the bounds of yellowstone national park

geochronology of the baye mn oxide deposit southern yunnan plateau implications for the late miocene to pleistocene paleoclimatic conditions and topographic evolution 40ar 39ar laser incremental heating analyses of supergene k mn oxides from weathering profiles at the baye mn deposit southern yunnan plateau sw china were carried out to place constraints on the timing of weathering and derive insights into local paleoclimatic and landscape evolution weathering profiles in the baye mn mine are dominated by 20 30 m thick saprolites which are locally covered by unconsolidated alluvial deposits we analyzed 70 grains from 35 hand samples collected from four sites located at distinct elevations in most cases different grains from the same hand sample and different samples from the same site have reproducible 40ar 39ar plateau ages the plateau ages of individual grains are also consistent with the respective isochron integrated and ideogram ages this age consistency attests to the reliability of the geochronological results as numerical constraints on the formation and evolution of these weathering profiles sixty four grains from 32 hand samples collected from weathering profiles at four sites a to d yield well defined plateau or pseudoplateau ages ranging from 2 98 0 07 to 0 16 ma 2 the age results show that mn oxides become progressively younger towards lower elevations samples collected from the highest elevation site 1855 m a s l have the oldest ages at 2 98 0 07 to 2 83 0 13 ma samples from intermediate elevations 1821 to 1815 m a s l yield ages ranging from 2 91 0 10 to 2 08 0 11 ma and those from the lowest sites 1768 to 1753 m a s l are younger than 1 25 0 08 ma the age versus elevation relationship indicates fast downward propagation of weathering front since the late pliocene and permits estimating the weathering rates at 3 3 3 8 6 6 1 2 and 11 1 1 9 m myr 1 during the time periods of 2 98 2 83 2 91 2 08 and 1 25 to 0 16 ma respectively the average river incision rates estimated from the surface exposed ages range from 235 10 to 416 19 m myr 1 during the past 3 million years the incision rate calculated from minimum exposed ages at sites b d is 33 2 m myr 1 for the time period of 2 91 1 25 ma which is consistent with the slow incision of streams on the ridges over the yunnan plateau since the early pleistocene three mn oxide pebbles contained in the alluvial deposits overlying the saprolite dominated weathering profiles at the two highest sites provided additional information on the timing of weathering four grains from two pebbles yield plateau ages of 6 32 0 19 to 5 27 0 10 ma whereas the other two grains from the third pebble indicate the minimum formation ages of 8 2 0 4 and 9 3 0 3 ma these ages confirm the existence of older weathering profiles now dismantled in the region manganese oxide 40ar 39ar ages of the baye deposit when combined with results from other localities indicate that lateritic weathering and supergene mn enrichment and by inference warm and humid climates conducive to intense weathering have prevailed over the plateau since the middle to late miocene the climatic conditions inferred from the weathering geochronology are consistent with multiple independent marine and terrestrial sedimentary and paleontological records confirming that supergene mn oxides can be used as a useful proxy for past climate age clusters of mn oxides at 2 9 2 4 1 2 0 8 and 0 6 0 4 ma are broadly coincident with and thus likely reflect intensification events of the indian summer monsoon that brings moisture and abundant precipitation to the yunnan plateau these clusters also coincide with the periods of significant surface uplift in the yunnan plateau demonstrating a causal link between topographic evolution plateau uplift and intensification of the monsoonal climate

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

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

the evolution of miocene climates in north china preliminary results of quantitative reconstructions from plant fossil records the miocene climate evolution in north china is preliminarily discussed by means of comparisons in seven climate parameters quantitatively reconstructed by the coexistence approach on 34 selected macro and microfloras over north china the miocene temperatures show no great difference in the western and eastern part of north china temperature fluctuations particularly in mean annual temperature are found within floras from several sites the fluctuation pattern from a climate optimum in the mid miocene to cooling decline in the late miocene is generally consistent with the global trend of miocene temperature change the reconstructed precipitation from all the sites studied shows much wetter conditions in north china during the miocene than at present which corroborates the results from paleoprecipitation proxy of fossil mammals like the situation in paleo temperature the miocene precipitation from north china shows no distinct difference between the western and eastern regions it is suggested that north china particularly in the western part was by no means under an arid or semi arid environment during the miocene north china is an ideal region for study of the impact of the east asian monsoon system however the pattern of precipitation change derived from the monsoon index msh and mean annual precipitation map shows contradictory results therefore there appears no definite conclusion on when the east asian summer monsoon intensified possible reasons for inconsistency in temperature and precipitation changes are discussed directions of future work to improve the resolution of climate evolution are also pointed out c 2010 elsevier b v all rights reserved

insights into the early tibetan plateau from u th he thermochronology the central songpan ganzi belt located on the eastern margin of the tibetan plateau has a similar high elevation and low relief to parts of central tibet thermochronological studies from the central tibetan plateau reveal a history of slow exhumation rates 1 since 45ma however the exhumation history of the central songpan ganzi belt is unknown to address this we conducted an apatite and zircon u th he thermochronology study of bedrock samples collected across the central songpan ganzi belt and into central parts of the tibetan plateau zircon u th he ages range from 54 2 7 5 to 146 5 10 0ma and the majority of apatite u th he ages fall between 74 7 19 0 and 35 7 9 4ma thermal history models of these data show rapid cooling in the late mesozoic and much slower cooling diagnostic of low rates of erosion throughout most of the cenozoic the late mesozoic rapid cooling is consistent with the existence of significant topography and relief at least in some parts of the songpan ganzi belt at that time we find no evidence for a regional miocene acceleration in erosion although three samples from the headwaters of the salween and mekong rivers gave younger ahe ages between 15 and 16ma that reflect an acceleration in river incision supplementary material laser ablation inductively coupled plasma mass spectrometry zircon u pb data from central and eastern tibet are available at www geolsoc org uk sup18647

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

crustal architecture and moho topography beneath the eastern indian and bangladesh margins new insights on rift evolution and the continent ocean boundary the thick sedimentary cover 18 km along the eastern continental margin of india ecmi and over the bay of bengal has hindered understanding of the mechanisms of rifting that operated on the eastern indian and bangladesh margins analysis of multichannel seismic reflection data together with 3d gravity inversion and 2d gravity forward modelling illuminates basement configuration crustal thickness and moho topography thereby revealing the modes of rift evolution and the location of the continent ocean boundary cob along these margins the basement particularly in the shelf and slope regions of eastern peninsular india is traversed by nearly coast perpendicular graben and their seaward continuity is delineated up to 125 km from the coastline three different types of continental margin are present along the ecmi 1 sheared rift on the southern segment of the ecmi up to 14 n latitude offshore the southern granulite terrain 2 hyper extended rift in the central segment between 14 n and 17 n offshore the dharwar craton and 3 hypo extended rift on the northern segment between 17 n and 20 n offshore the eastern ghats mobile belt the graben terminations crustal thickness and moho topography of both the ecmi and offshore bengal basin clearly suggest that the cob runs nearly parallel to the coastline of peninsular india but takes an orthogonal turn offshore in the bengal basin and connects the palaeo continental shelf and the rajmahal sylhet line onshore in the bengal basin crustal thickness 8 10 km and depth to the moho discontinuity 28 km beneath the bangladesh margin are unusual because the crustal thickness increased through interaction of the kerguelen plume with the existing oceanic lithosphere the moho deepened largely due to the load of the bengal fan sediments the absence of rifted crustal blocks on the bangladesh margin and the continuity of the cob into the onshore bengal basin together imply that the present bangladesh region was under marine conditions at least until the beginning of bengal fan sedimentation i e no less than 23 ma

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

understanding himalayan erosion and the significance of the nicobar fan a holistic view of the bengal nicobar fan system requires sampling the full sedimentary section of the nicobar fan which was achieved for the first time by international ocean discovery program iodp expedition 362 west of north sumatra we identified a distinct rise in sediment accumulation rate sar beginning 9 5 ma and reaching 250 350 m myr in the 9 5 2 ma interval which equal or far exceed rates on the bengal fan at similar latitudes this marked rise in sar and a constant himalayan derived provenance necessitates a major restructuring of sediment routing in the bengal nicobar submarine fan this coincides with the inversion of the eastern himalayan shillong plateau and encroachment of the west propagating indo burmese wedge which reduced continental accommodation space and increased sediment supply directly to the fan our results challenge a commonly held view that changes in sediment flux seen in the bengal nicobar submarine fan were caused by discrete tectonic or climatic events acting on the himalayan tibetan plateau instead an interplay of tectonic and climatic processes caused the fan system to develop by punctuated changes rather than gradual progradation

oligocene miocene 28 13 ma climato tectonic evolution of the northeastern qinghai tibetan plateau evidenced by mineralogical and geochemical records of the xunhua basin abstract changes in sediment composition in the xunhua basin provide insights into the climatic and tectonic evolution of the northeastern qinghai tibetan plateau during the oligocene and miocene here we analyzed the clay mineralogy i e the proportions of smectite illite and chlorite and clay indicators bulk mineral composition i e the amounts of calcite quartz gypsum k feldspar plagioclase dolomite and halite and trace element indicators i e rb sr and ba sr ratios of sediments deposited from 28 to 13 ma in the xunhua basin to reveal the climate and or provenance changes the results suggest that significant changes in sediment provenance occurred at 25 1 ma and 21 6 ma caused respectively by initial uplift and accelerated uplift of the laji shan the xunhua basin experienced warm and humid conditions at 28 0 25 1 ma cool and dry conditions at 25 1 21 6 ma and somewhat warmer and wetter conditions at 21 6 19 2 ma followed by aridification in two steps at 19 2 ma and 13 9 ma the climate cooling event at 25 1 ma corresponds temporally to a major phase of uplift of central tibet relatively warmer and wetter conditions during the early miocene 21 6 19 2 ma are considered to record the influence of the asian summer monsoon and accelerated uplift of the laji shan the shift toward more arid conditions on the northeastern qinghai tibetan plateau at 19 2 13 9 ma was probably driven by uplift of the tibetan plateau and further aridification since 13 9 ma may reflect a weakening of the east asian summer monsoon and global climatic cooling

apatite fission track evidence for miocene denudation history in the gangdese conglomerate belt and yarlung tsangpo river implications for the evolution of southern tibet abstract low temperature thermochronology is used widely in the tibet plateau uplift some researches however have defined the time of rapid denudation as simply rock uplift and have neglected the fact that the rock denudation recorded by fission track ft data was controlled by both surface incision and rock uplift the incision of the yarlung zangbo river had a significant influence on uplift history inversion in southern tibet this paper simulated the bedrock denudation and river incision histories using apatite fission track aft data sampled from the gangdese conglomerate belt which is located in the middle of southern tibet and analyzed the geological meaning of the aft age of each sample the results showed the following 1 in the early miocene 22 16 ma both the value of the denudation rate and the incision rate were high 0 56 mm yr and 0 24 mm yr 2 in the middle late miocene the incision rate 0 12 mm yr was similar to the denudation rate 0 09 0 11 mm yr 3 the historical model between river incision and bedrock denudation revealed a significant difference in the denudation rate during the period ca 8 6 ma combining these data with previously published thermochronological ages and synthesizing these ages with regional geological we arrived at the following conclusions 1 in the early miocene the denudation event probably was caused by a combined result of indian plate rollback and the incision of the yarlung zangbo river 2 in the middle late miocene the denudation rate was consistent with the incision rate which suggested that the denudation episode was caused by climate change associated with asian monsoon intensification 3 after 8 ma the stable and slow incision rate indicated that regional drastic uplift had ceased the paleo elevation of the research area had approached and even exceeded the present day elevation in the late miocene

geochemistry and isotopic study of southern bay of bengal sediments implications for provenance and paleoenvironment during the middle miocene abstract the bay of bengal bob the largest bay in the world is known to receive large amounts of fresh water and suspended particulate matter from different sources the sediments deposited in the bay serve as a repository for paleoenviromental reconstruction studies the miocene epoch is an important interval in geologic time as it is marked by major climatic events that controlled ocean productivity redox conditions and provenance of sediments however limited work has been carried out to establish paleoenviromental changes and provenance of sediments during the miocene here we present detailed geochemical and radiogenic sr nd isotopic results from predominantly middle miocene sediments of ocean drilling program odp site 758a located in the southern bob lat 5 23 n long 90 21 e water depth 2925 m to understand paleoredox conditions paleoproductivity and provenance the results suggest that these sediments are strongly linked to climatically modulated surface processes that affected the region the distribution of redox sensitive element proxies u v cr at interval 17 8 ma points to an oxic depositional environment the major trace and rare earth elements distribution supports prevalence of the indian summer monsoon ism at 12 10 ma productivity proxies babio porg show a decreasing trend during colder events east antarctic ice sheet expansion eais and advent of late miocene cooling lmc events the trace and rare earth element concentrations are generally low except at intervals where glass shards were found the 87sr 86sr and end 0 values indicate that the sediments belong to the high himalayan sedimentary series hhss throughout the middle miocene however prior to initiation of the ism these sediments underwent meteoric alteration in the lowlands before deposition in the bob our records suggest that sediments at odp site 758a may have been introduced into the bob through the irrawaddy yarlung tsangpo drainage system during the entire period of this study the irrawaddy yarlung tsangpo system drained the indus tsangpo suture zone southern tibet the eastern himalayas and the arakan coast before debouching in the bob

thermobarometric and40ar 39ar geochronologic constraints on eohimalayan metamorphism in the dinggye area southern tibet mineral assemblages in the dinggye area of southern tibet 28 n 88 e provide new insights regarding the poorly understood eohimalayan metamorphic event in the eastern himalayan orogen major element partitioning thermobarometry of pelitic rocks indicates temperatures of 750 830 k at depths of 14 3 km consistent with the presence of kyanite sillimanite and andalusite schists in the area laser and resistance furnace40ar 39ar analyses of hornblendes from intercalated amphibolites yield closure ages of 25 ma overlap between the probable range of ar closure temperatures for these hornblendes and the metamorphic temperatures estimated through thermobarometry suggests that eohimalayan metamorphism in the dinggye area occurred in late oligocene time no more than about 10 million years before the main or neohimalayan phase of metamorphism in early to middle miocene time muscovite biotite and k feldspar40ar 39ar ages indicate an important episode of rapid cooling between 16 and 13 ma which is interpreted as a signature of tectonic denudation related to movement on n dipping extensional structures of the south tibetan detachment system

x ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 myr in the southern south china sea with benthic foraminiferal d 18 o reveal that phases of the east asian summer monsoon abruptly changed by more than 90 at 4 0 ma 2 75 ma 1 0 ma and 0 6 ma relative to global ice volume at the obliquity and the precession bands over the past 5 myr strong 400 kyr and 100 kyr cycles in the k al and ti al records consistently exist over the past 5 myr particularly these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65 n indicating an eccentricity forcing of the east asian summer monsoon the chemical weathering recorded in the elemental records of odp site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity the obliquity and the precession bands over the late pliocene and pleistocene

correlation of himalayan exhumation rates and asian monsoon intensity although most data suggest that the india eurasia continental collision began 45 55 myr ago the architecture of the himalayan tibetan orogen is dominated by deformational structures developed in the neogene period 23 myr ago the stratigraphic record and thermochronometric data indicate that erosion of the himalaya intensified as this constructional phase began and reached a peak around 15 myr ago it remained high until 10 5 myr ago and subsequently slowed gradually to 3 5 myr ago but then began to increase once again in the late pliocene and pleistocene epochs here we present weathering records from the south china sea bay of bengal and arabian sea that permit asian monsoon climate to be reconstructed back to the earliest neogene these indicate a correlation between the rate of himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 myr we interpret this correlation as indicating dynamic coupling between neogene climate and both erosion and deformation in the himalaya although the india eurasia collision initiated 50 myr ago major deformation and exhumation of the himalaya did not begin until the early neogene 23 myr ago this coincides with the increased intensity of the asian monsoons as indicated by weathering records from the south china sea bay of bengal and arabian sea and hints at a dynamic coupling between climate and both erosion and deformation in the himalaya

middle miocene pedological record of monsoonal climate from nw himalaya jammu kashmir state india abstract the lower siwalik subgroup represented by the dodenal kamlial formation and ramnagar members chinji formation is well exposed at ramnagar district udhampur jammu kashmir state the ramnagar member consists of an alternating sequence of silt and mudstone formed under crevasse splay and flood plain environments of deposition argillisol and gleysol soils are developed on the ramnagar member deposits argillisols formed under well drained conditions at high levels whereas gleysols formed under poorly drained conditions at low levels of the palaeo landscape geochemical and micromorphological studies of the ramnagar member palaeosols suggest formation under wet and humid climatic conditions early uplift of the tibetan plateau himalaya resulted in a contemporaneous change in precipitation and monsoonal climate conditions within the indian region beginning in middle miocene

sediment volume and mass beneath the bay of bengal rates of sediment accumulation and the amount of sedimentary fill in depocenters lying downstream of erosion in the himalayas and tibet can provide some insight into tectonics and geological history the objective of this paper is to put on record the best estimates which are possible with existing data of the volume and mass of sediments sedimentary rock and metasedimentary rock beneath the sea floor of the bay of bengal the sedimentary section in the bay of bengal is divided into two parts 1 eocene through holocene sediments and sedimentary rocks which post date the initial india asia collision volume 12 5 106 km3 mass 2 88 1016 t this is most of the bengal fan including its eastern lobe the nicobar fan plus some of the outer bengal delta 2 early cretaceous through paleocene pre collision sedimentary and metasedimentary rocks volume 4 36 106 km3 mass 1 13 to 1 18 1016 t these are interpreted as continental rise and pelagic deposits

a rb sr record of the weathering response to environmental changes in westerly winds across the tarim basin in the late miocene to the early pleistocene the long term record of lacustrine deposits in the tarim basin seems to provide a record of climate influenced by westerly winds to characterize the evolution of westerly winds we analyzed concentrations of rb v zn sc and sr for the drill core ls2 from lop nor in the eastern tarim basin the rb sr ratio in lacustrine deposits depends primarily on the sr element activity during weathering after the influence of source provenance has been removed we assume that with such a correction the rb sr ratio is controlled by precipitation which depends on moisture transport by westerly winds to the tarim basin the rb sr ratio displays a large amplitude oscillation that generally follows a pattern similar to that of pollen and ostracod assemblages which support the inference that rainfall amount affects the rb sr ratio and in turn suggests that it may serve as an index of precipitation that was transported by westerly wind all these climatic proxies obviously changed since the late miocene suggesting stronger aridification that may be attributed to a latitudinal shift in westerly winds since the late miocene a southward migration of westerly winds which then transported more moisture to the southern and eastern parts of the tibetan plateau agrees with modeling results and the geological record during that time this event may be causally related to the expansion of the northern hemisphere ice and or regional tectonic uplift of high mountains around the tarim basin

plateau uplift forcing climate change around 8 6 ma on the northeastern tibetan plateau evidence from an integrated sedimentary sr record abstract the uplift of the northern tibetan plateau tp has long been regarded as one of major factors accounting for both the enhanced process of aridification recorded in central asia and the shifts in the asian monsoonal circulations that are known to have occurred at approximately 8 ma until now there have been few sedimentary records reported on which can directly and in an integrated fashion shed light on the region s tectonic and climate regimes this can be largely attributed to the fact that the influence exerted by the presence of source materials and subsequent sedimentary sorting in this tectonically active region would be likely to bias significantly any paleoclimatic interpretation of silicate derived proxies based on detailed investigations of strontium sr distributions revealed by multi step leaching in a fluvial sequence from the linxia basin which includes paleosols we reconstructed the long term late miocene regional climatic and environmental changes likely to have occurred on the northeastern tp from 12 1 to 5 2 ma we investigated sr related proxies in two typical paleosol profiles to constrain sr mobility in paleosol weathering and thus to further prompt the interpretation of sr related proxies along the whole section we would suggest that carbonate derived sr concentrations and sr ca ratios are suitable proxies for tracing regional climate change associated with weathering and pedogenesis together they exhibit weakened chemical weathering intensity and pedogenesis at 8 6 ma the concomitant appearance of immature sediments through poor sedimentary sorting revealed by silicate derived rb sr 87 sr 86 sr and eu anomaly eu eu alongside a sharp increase in sedimentation rates noted at this time suggests that it was indeed tectonic uplift that principally controlled the dramatic climatic and environmental changes this multi proxy record of concomitant tectonic uplift and climate change in the linxia basin provides direct geological evidence for uplift driven climate change in the northeastern tp region

climate driven sediment aggradation and incision since the late pleistocene in the nw himalaya india abstract deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution in the kangra basin northwest sub himalaya india upper pleistocene to holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr to evaluate the potential influence of climate change on these fluctuations we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives new surface exposure dating of six terrace levels with in situ cosmogenic 10be indicates the onset of incision phases two terrace surfaces from the highest level t1 sculpted into the oldest preserved alluvial fan af1 date back to 53 4 3 2 ka and 43 0 2 7 ka 1 t2 surfaces sculpted into the remnants of af1 have exposure ages of 18 6 1 2 ka and 15 3 0 9 ka while terraces sculpted into the upper pleistocene holocene fan af2 provide ages of 9 3 0 4 ka t3 7 1 0 4 ka t4 5 2 0 4 ka t5 and 3 6 0 2 ka t6 together with previously published osl ages yielding the timing of aggradation we find a correlation between variations in sediment transport with oxygen isotope records from regions affected by the indian summer monsoon during periods of increased monsoon intensity and post last glacial maximum glacial retreat aggradation occurred in the kangra basin likely due to high sediment flux whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision

evidence for provenance change in deep sea sediments of the bengal fan a 7 million year record from iodp u1444a abstract previously published geochemical and mineralogical data have revealed conflicting views on the provenance of the deep sea sediments in the bengal fan here we report results of a study for a 330 m sequence consisting of both turbitide and semi pelagic sediments recovered at the site u1444a during the iodp 353 expedition a novel technique using the optically and thermally stimulated luminescence osl and tl signatures from quartz and k feldspar has been employed to characterise the mineral compositions of the sediments we show that the quartz luminescence sensitivity clearly differentiates the four sedimentary units there is a distinct increase of quartz luminescence sensitivity in unit 2 during the time interval of 3 5 0 5 ma analyses of the luminescence signal components in quartz and the ratio of the k feldspar and quartz also point to a change in unit 2 relative to the other three units we interpret such changes in the mineralogical compositions through the sequence as reflecting a change in the provenance over the last 7 million years in the western bengal fan we attribute the quartz with enhanced luminescence sensitivity in unit 2 to the contribution from the sources associated with indian rivers we infer that the delivery of the sediments from indian peninsula to iodp site u1444a is facilitated by a weakening in the turbidite deposition which is dominated by weathering products from the himalayas we speculate that the relatively high elevation of the 85 e ridge may act against the flow through and the associated deposition of turbidity current originated from the himalayas

structural and geochronological evidence for the leading edge of the greater himalayan crystalline complex in the central nepal himalaya abstract the himalaya is commonly described as a three layer two fault stack namely a high grade crystalline core featuring an inverted metamorphic field gradient the greater himalayan crystalline complex ghc is separated from units above and below by shear zones the lesser himalayan sequence lhs underlies the ghc below the main central thrust and the tethyan himalayan sequence ths overlies it along the south tibet detachment however the southern main central thrust hanging wall consists of a lower unit dominated by a right way up metamorphic sequence of biotite garnet schists bhimphedi group and an upper unit with only anchizone metamorphism pulchauki group the bhimphedi group is commonly equated to the ghc while the pulchauki group is well correlated to the ths however no shear zone separates these units we present new structural and geochronological data along the boundary between the ghc and the bhimphedi group in the kathmandu region these data reveal an 200 m thick early middle miocene top north northeast shear zone that we term the galchi shear zone we correlate this shear zone to the south tibet detachment on the basis of lithological metamorphic structural and chronological criteria the galchi shear zone merges with the main central thrust to the south bounding the leading edge of the ghc this result combined with recent work in the western himalaya suggests that the locally preserved leading edge of the ghc is sub parallel to the arc of the orogen and the southern main central thrust hanging wall is dominated by ths rocks this orogenic architecture rules out wedge extrusion and channel flow focused denudation kinematic models for the himalayan orogen but is accommodated by tectonic wedging kinematic models including channel tunneling models with modified timing

tertiary structural evolution of the gangdese thrust system southeastern tibet structural and thermochronological investigations of southern tibet xizang suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost tibetan plateau since late oligocene two thrust systems are documented in this study the north dipping gangdese system gts and the younger south dipping renbu zedong system rzt west of lhasa the gangdese thrust juxtaposes the late cretaceous forearc basin deposits of the lhasa block the xigaze group over the tethyan sedimentary rocks of the indian plate whereas east of lhasa the fault juxtaposes the late cretaceous eocene andean type arc the gangdese batholith over tethyan sedimentary rocks near zedong 150 km southeast of lhasa the gangdese thrust is marked by a 200 m thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks a major south dipping backthrust in the hanging wall of the gangdese thrust puts the xigaze group over tertiary conglomerates and the gangdese plutonics north of xigaze and west of lhasa a lower age bound for the gangdese thrust of 18 3 0 5 ma is given by crosscutting relationships the timing of slip on the gangdese thrust is estimated to be 27 23 ma from 40 ar 39 ar thermochronology and a displacement of at least 46 9 km is indicated near zedong the age of the gangdese thrust gt is consistent with an upper age limit of 24 ma for the initiation of movement on the main central thrust in places the younger renbu zedong fault is thrust over the trace of the gt obscuring its exposure the rzt appears to have been active at circa 18 ma but had ceased movement by 8 1 ma the suture between india and asia has been complexly modified by development of the gts rzt and locally strike slip and normal fault systems

chemical erosion in the eastern himalaya major ion composition of the brahmaputra and δ13c of dissolved inorganic carbon abstract major ion composition of waters 13 c of its dic dissolved inorganic carbon and the clay mineral composition of bank sediments in the brahmaputra river system draining india and bangladesh have been measured to understand chemical weathering and erosion and the factors controlling these processes in the eastern himalaya the time series samples collected biweekly at guwahati from the brahmaputra mainstream were also analyzed for the major ion composition clay mineralogy and chemical index of alteration cia of sediments suggest that weathering intensity is relatively poor in comparison to that in the ganga basin this is attributed to higher runoff and associated physical erosion occurring in the brahmaputra basin the results of this study show for the first time spatial and temporal variations in chemical and silicate erosion rates in the brahmaputra basin the subbasins of the brahmaputra watershed exhibit chemical erosion rates varying by about an order of magnitude the eastern syntaxis basin dominates the erosion with a rate of 300 t km 2 y 1 one of the highest among the world river basins and comparable to those reported for some of the basaltic terrains in contrast the flat cold and relatively more arid tibetan basin undergoes much slower chemical erosion 40 t km 2 y 1 the abundance of total dissolved solids tds 102 203 mg l in the time series samples collected over a period of one year shows variations in accordance with the annual discharge except one of them cause for which is attributable to flash floods na na corrected for cyclic component shows a strong positive correlation with si indicating their common source silicate weathering estimates of silicate cations na sil k sil ca sil mg sil suggest that about half of the dissolved cations in the brahmaputra are derived from silicates a proportion higher than that for the ganga system the co 2 consumption rate due to silicate weathering in the brahmaputra watershed is 6 10 5 moles km 2 y 1 whereas that in the eastern syntaxis subbasin is 19 10 5 moles km 2 y 1 similar to the estimates for some of the basaltic terrains this study suggests that the eastern syntaxis basin of the brahmaputra is one of most intensely chemically eroding regions of the globe and that runoff and physical erosion are the controlling factors of chemical erosion in the eastern himalaya

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

co evolution of monsoonal precipitation in east asia and the tropical pacific enso system since 2 36 ma new insights from high resolution clay mineral records in the west philippine sea clay mineralogical analysis and scanning electron microscope sem analysis were performed on deep sea sediments cored on the benham rise core md06 3050 in order to reconstruct long term evolution of east asian summer monsoon easm rainfall in the period since 2 36 ma clay mineralogical variations are due to changes in the ratios of smectite which derive from weathering of volcanic rocks in luzon island during intervals of intensive monsoon rainfall and illite and chlorite rich dusts which are transported from east asia by winds associated with the east asian winter monsoon eawm since luzon is the main source of smectite to the benham rise long term consistent variations in the smectite illite chlorite ratio in core md06 3050 as well as odp site 1146 in the northern south china sea suggest that minor contributions of eolian dust played a role in the variability of this mineralogical ratio and indicate strengthening easm precipitation in se asia during time intervals from 2360 to 1900 kyr 1200 to 600 kyr and after 200 kyr the easm rainfall record displays a 30 kyr periodicity suggesting the influence of el nino southern oscillation enso these intervals of rainfall intensification on luzon island are coeval with a reduction in precipitation over central china and an increase in zonal sst gradient in the equatorial pacific ocean implying a reinforcement of la nina like conditions in contrast periods of reduced rainfall on luzon island are associated with higher precipitation in central china and a weakening zonal sst gradient in the equatorial pacific ocean thereby suggesting the development of dominant el nino like conditions our study therefore highlights for the first time a long term temporal and spatial co evolution of monsoonal precipitation in east asia and of the tropical pacific enso system over the past 2 36 ma

effects of grain size on the chemical weathering index a case study of neogene fluvial sediments in southwest japan abstract grain size variation of sediments and sedimentary rocks generally complicates the assessment of the degree of chemical weathering as measured by the chemical index of alteration cia value mineralogical and geochemical research was carried out on miocene and pliocene fluvial sediments in southwest japan in order to evaluate the effects of grain size on the degree of chemical weathering a strong positive linear trend is usually exhibited between al2o3 sio2 ratios and quartz intensities obtained by x ray powder diffraction suggesting that the al2o3 sio2 ratio may be suitable as a grain size index for semi consolidated and unconsolidated sediments most of the fine grained sediments for which al2o3 sio2 ratios are over 0 4 have higher cia values of over 90 in contrast coarse grained sediments for which al2o3 sio2 ratios are lower especially below 0 2 display a wide range of cia values the cia values for intermediate grain sized samples for which al2o3 sio2 ratios range from 0 2 to 0 4 reflect distinctive differences in the degree of chemical weathering between miocene and pliocene sediments within this range of al2o3 sio2 ratios the miocene sediments have higher cia values 86 98 than pliocene sediments 71 92 to compare the degree of chemical weathering among some sediments or sedimentary rocks with variable grain sizes it is desirable to evaluate with the al2o3 sio2 ratios limited to the intermediate grain size range

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

single grain heavy mineral provenance of garnet and amphibole in the surveyor fan and precursor sediments on the gulf of alaska abyssal plain implications for climate tectonic interactions in the st elias orogen abstract the st elias orogen formed as a result of the northwestward drift of the yakutat terrane along and final collision with the alaska margin in the miocene its exhumation coincided with changing glacial conditions that are considered to have strongly interacted with mountain building processes a significant part of the record of these tectonic climatic interactions is stored in sediments on the gulf of alaska abyssal plain including the surveyor fan our study examines temporal provenance changes of miocene through pleistocene sediments of the surveyor fan gulf of alaska to constrain the dynamics of exhumation and mass transfer from the evolving st elias orogen to the adjacent surveyor deep sea fan we present single grain geochemical data of amphibole and garnet and 40 ar 39 ar cooling ages of biotite and amphibole together with point counting data of heavy minerals from sands and silts from two sites in the distal and proximal fan drilled by iodp expedition 341 in 2013 sites u1417 and u1418 respectively a shift in heavy mineral composition during the miocene predating the onset of glaciation points to a tectonically induced change in erosion centers and sediment transport probably caused by the rise of the st elias mountains garnet and amphibole data suggest the chugach metamorphic complex is the main sediment source implying input to the surveyor fan from sources relatively far in the north during the miocene changing provenance signals from the miocene to pliocene suggest rising input from the lower grade metamorphic areas at the southern flanks of the orogen indicating the advance of glaciers to the tidewater line providing material from this flanking region higher input from the chugach metamorphic complex in all pleistocene sediments suggests the northern hemisphere glaciation at the plio pleistocene boundary caused erosion and sediment yield from the interior of the orogen climatic changes at the mid pleistocene transition did not cause significant changes in the provenance signal

sedimentology stratigraphy and architecture of the nicobar fan bengal nicobar fan system indian ocean results from international ocean discovery program expedition 362 drill sites in the southern bay of bengal at 3 degrees n 91 degrees e international ocean discovery program expedition 362 have sampled for the first time a complete section of the nicobar fan an

strong interannual variation of the indian summer monsoon in the late miocene the modern asian monsoon system exhibits strong interannual variation which has profound environmental and economical impacts it has been well documented that the mean asian monsoon state underwent significant changes in the late miocene 11 5 ma ago but how the interannual variability of the monsoon climate evolved during this period is still largely unknown in this study a long term simulation of the late miocene with a fully coupled atmosphere ocean general circulation model echam5 mpi om at t31l19 resolution is used to explore the interannual variation of the indian summer monsoon ism in the late miocene the regional climate model cosmo clm with a higher spatial resolution 1 1 is further employed to better characterize the spatial patterns of these variations our results show that although the mean ism circulation is weaker in the late miocene runs its interannual variation is as strong as or even stronger than at present and the dominant periods 2 6 2 7 years are shorter than at present 3 4 8 4 years it is noticed that while the extratropical influence on the ism variability is weaker than present a persistent el nino southern oscillation with stronger than present interannual variability is observed in our late miocene run this may have maintained a strong interannual variation of the ism with a shorter period in the late miocene our findings do not only improve our understanding of the asian monsoon evolution in the late miocene but also shed light on the future changes in the interannual variability of the ism

paleoclimatic estimation reveals a weak winter monsoon in southwestern china during the late miocene evidence from plant macrofossils the late miocene xianfeng flora of yunnan province southwestern china was chosen to reconstruct the paleoclimate and the intensity of the asian monsoon three available quantitative climate reconstruction methods from fossil plants i e leaf margin analysis lma the climate leaf analysis multivariate program clamp and the coexistence approach ca were used in this study mats mean annual temperatures resulting from these three approaches i e lma 17 2 2 38 degrees c clamp 15 43 1 25 degrees c ca 17 2 21 7 degrees c appear to have been higher than the present 14 9 degrees c suggesting a much warmer climate in the late miocene both the growing season precipitation gsp from clamp 1908 7 217 7 mm and mean annual precipitation map from ca 1206 0 1613 0 mm estimates are higher than modern values 1003 2 mm gsp and 1038 mm map respectively indicating a more humid climate during the late miocene by comparing these with climates reconstructed from neighboring late miocene floras we conclude that the general late miocene climate appears warmer and more humid than present conditions in southwestern china furthermore the evident differences in estimated monthly temperatures between the summer and winter and precipitations between the humid and dry seasons indicate the existence of seasonality though not as strong as that of today difference in precipitation of dry season indicates a marked strengthening in the winter monsoon since the late miocene a new monsoon intensity index has also been defined based on precipitation seasonality to investigate the intensity of the asian monsoon c 2012 elsevier b v all rights reserved

tectonic evolution of the himalayan thrust belt in western nepal implications for channel flow models we present a new geologic map of western nepal and three balanced regional cross sections in the himalayan thrust belt the minimum shortening between the south tibetan detachment and the main frontal thrust is 485 743 km and suggests that total himalayan shortening may exceed 900 km all rocks involved in the thrust belt are of upper crustal affinity implying that a comparable length of indian lower crust and mantle lithosphere was subducted beneath tibet major structural features are the subhimalayan thrust system lesser himalayan imbricate zone dadeldhura thrust sheet lesser himalayan duplex ramgarh thrust sheet main central thrust sheet and a north dipping normal sense shear zone possibly related to the south tibetan detachment these structures are continuous along the entire nepalese portion of the himalayan thrust belt new 40 ar 39 ar ages from the ramgarh thrust zone greater himalayan rocks and the lower part of the tethyan sequence support a kinematic model in which major thrust systems in nepal propagated southward from early miocene time onward the geometry and kinematic history of the thrust belt in western nepal are not compatible with recent models for southward ductile extrusion of greater himalayan rocks in a mid crustal channel instead the thrust belt in western nepal behaved like a typical forward propagating thrust system involving unmetamorphosed brittlely deformed rocks in its frontal part and ductilely deformed higher grade metamorphic rocks in its hinterland region although our results do not support published versions of the channel flow model they provide additional geological and geo chronological data that will assist future attempts to develop geodynamic models for the himalayan tibetan orogenic system

geochemical and nd isotopic variations in sediments of the south china sea a response to cenozoic tectonism in se asia secular variations in geochemistry and nd isotopic data have been documented in sediment samples at odp site 1148 in the south china sea major and trace elements show significant changes at ca 29 5 ma and 26 23 ma whereas ond values show a single change at ca 26 23 ma increases in al ti al k rb sr and la lu ratios and a decrease in the th la ratio of the sediments beginning at 29 5 ma are consistent with more intense chemical weathering in the source region the abrupt change in nd isotopes and geochemistry at ca 26 23 ma coincides with a major discontinuity in the sedimentology and physical properties of the sediments implying a drastic change in sedimentary provenance and environment at the drill site comparison of the nd isotopes of sediments from major rivers flowing into the south china sea suggests that pre 27 ma sediments were dominantly derived from a southwestern provenance indochina sunda shelf and possibly northwestern borneo whereas post 23 ma sediments were derived from a northern provenance south china this change in provenance from southwest to north was largely caused by ridge jumping during seafloor spreading of the south china sea associated with a southwestward expansion of the ocean basin crust and a global rise in sea level thus the geochemical and nd isotopic changes in the sediments at odp site 1148 are interpreted as a response to a major plate reorganization in se asia at ca 25 ma b 2003 elsevier science b v all rights reserved

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

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

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

late cenozoic sporopollen records in the yangtze river delta east china and implications for east asian summer monsoon evolution abstract the late cenozoic east asian summer monsoon easm is generally linked with the tibetan plateau uplift and or global cooling in this study four cores zk004 zk005 sz03 and sz04 consisting of fluvial lacustrine deposits spanning the period of 8 0 0 ma were obtained from the yangtze river delta east china for sporopollen analysis to investigate trends in the easm evolution and its driving forces the results show that high percentages of arboreal taxa such as fagaceae ulmaceae juglandaceae taxaceae taxodiaceae liquidambar anacardiaceae rutaceae etc represent a relatively warm and humid climate between 8 0 and 2 6 ma the herb dominated vegetation poceae asteraceae cyperaceae etc is linked with a relatively cold and dry climate after 2 6 ma the compiled thermophilic percentages and ap arbors nap non arbors ratios of these four cores which show that the long term cooling and drying trends are similar to the global cooling since 8 0 ma imply that the easm experienced long term weakening coincident with the global cooling however over this super long time scale the thermophilic percentages and ap nap ratios have remained at roughly stable levels since 2 6 ma possibly due to the effects of the tibetan plateau uplifts