late miocene environmental change in nepal and the northern indian subcontinent stable isotopic evidence from paleosols neogene sediments belonging to the siwalik group crop out in the himalayan foothills along the length of southern nepal carbon and oxygen isotopic analyses of siwalik paleosols from four long siwalik sections record major ecological changes over the past 11 m y the carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca 7 0 ma marking the displacement of largely c3 vegetation probably semi deciduous forest by c4 grasslands by the beginning of the pliocene all the flood plains of major rivers in this region were dominated by monsoonal grasslands the floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest miocene a similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of pakistan and in terrigenous organic matter from the bengal fan showing that the floral shift was probably continentwide the latest miocene also witnessed an average change of 4 in the oxygen isotopic composition of soil carbonate as observed previously in pakistan the reasons for this are unclear if not diagenetic a major environmental change is indicated perhaps related to that driving the carbon isotopic shift recently described pollen and leaf fossils from the surai khola section show that evergreen forest was gradually displaced by semi deciduous and dry deciduous forest between 11 and 6 ma the gradual nature of this floral shift which culminated in the rapid expansion of c4 grasses starting 7 0 m y ago is difficult to explain by a decrease in atmospheric pco2 alone cerling et al 1993 but fits well with a gradual onset of monsoonal conditions in the late miocene in the northern indian subcontinent himalayan uplift driving both monsoonal intensification and consumption of co2 through weathering may be the common cause behind major late miocene environmental change globally however the decline of effective moisture associated with monsoon development has probably slowed not increased the rate of consumption of co2 by chemical weathering of himalayan sediments

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

magnetostratigraphic and rock magnetic study of the neogene upper yaha section kuche depression tarim basin implications to formation of the xiyu conglomerate formation nw china 1 magnetostratigraphic study of 251 horizons through the younger yaha succession in the kuche depression of the tarim basin nw china lying beneath a massive regionally extensive xiyu conglomerate formation identifies nine reversed and eight normal polarity chrons correlating with the geomagnetic polarity time scale to show that deposition spanned the interval 5 3 to 1 7 ma sedimentation rates fell episodically from 49 to 24 cm kyr as neotectonic deformation in the southern tian shan thrust belt became focused on two major anticlines with the northern qiulitage anticline being initiated at 5 5 ma and developing a northern hinged limb that embraces the basal part of the studied section rock magnetic parameters show multiple signatures of lithologic change deformation burial diagenesis and climate with the latter identifying an early pliocene warm humid interval followed by cooling and desertification after 2 6 ma diachronous commencement of xiyu conglomerate deposition ranged from mid miocene in the north of the southern flank of the tian shan to pleistocene in the south advancing as a clastic wedge derived from the uplifted range front to the north this southward progradation was not climatically controlled although climatic effects may have modulated deposition during the pleistocene uplift in the tian shan at 16 15 ma correlates with rapid increase in sedimentation rate and episodic increases occurred subsequently until the initiation of the qiulitage anticline reduced rates since 5 0 ma contrast with increases more commonly recorded in foreland basins and have been controlled by accelerated growth of this regional structure counterbalancing uplift of the mountain front to the north

late miocene pleistocene evolution of india eurasia convergence partitioning between the bhutan himalaya and the shillong plateau new evidences from foreland basin deposits along the dungsam chu section eastern bhutan the shillong plateau is a unique basement cored uplift in the foreland of the eastern himalaya that accommodates part of the india eurasia convergence since the late miocene it was uplifted in the late pliocene to 1600 m potentially inducing regional climatic perturbations by orographically condensing part of the indian summer monsoon ism precipitations along its southern flank as such the eastern himalaya shillong plateau ism is suited to investigate effects of tectonics climate and erosion in a mountain range broken foreland system this study focuses on a 2200 m thick sedimentary section of the siwalik group strategically located in the lee of the shillong plateau along the dungsam chu at the front of the eastern bhutan himalaya we have performed magnetostratigraphy constrained by vitrinite reflectance and detrital apatite fission track dating combined with sedimentological and palynological analyses we show that 1 the section was deposited between 7 and 1 ma in a marginal marine deltaic transitioning into continental environment after 5 ma 2 depositional environments and paleoclimate were humid with no major change during the depositional period indicating that the orographic effect of the shillong plateau had an unexpected limited impact on the paleoclimate of the bhutanese foothills and 3 the diminution of the flexural subsidence in the basin and or of the detrital input from the range is attributable to a slowdown of the displacement rates along the main boundary thrust in eastern bhutan during the latest miocene pleistocene in response to increasing partitioning of the india eurasia convergence into the active faults bounding the shillong plateau

pollen ostracod and stable isotope records of palaeoenvironment and climate upper miocene and pliocene of the cankiri basin central anatolia turkey abstract an integrated stratigraphic study of neogene lacustrine succession in the cankiri basin central anatolia combining pollen analysis biostratigraphy and isotope analysis records variations in vegetation and depositional environment the palynological analysis of the upper miocene interval of the studied section reveals the existence of a coniferous forest this flora reflects warm temperate humid climatic conditions the pollen changes observed at the onset of the pliocene are related to climatic changes in the early pliocene the vegetation changed to a mixed coniferous forest dominated by meso microthermic trees cedrus and cathaya with a widespread herbaceous understory poaceae sparcely interspersed with open areas occupied by asteraceae whereas abies and deciduous trees quercus carya juglans ulmus carpinus acer etc are represented by lower percentages this flora reflects a warm temperate relatively arid climate reflecting the global warm climate of the early pliocene the fluctuations in abundance of tsuga may represent fluctuations in temperature climate analysis using the coexistence approach ca shows the presence of precipitation oscillations within the pliocene the identified ostracod assemblage indicates a dominance of fresh water conditions during the early late miocene and of brackish water conditions during the late late miocene while minor salinity oscillation is present throughout the section the 18 o sulfate and 87 sr 86 sr isotopic ratios of non marine gypsum are indistinguishable from the marine evaporites this suggests recycling of older marine evaporites which is also supported by intense replacement of ostracods by gypsum

the late neogene 87sr 86sr record of lowland himalayan rivers fossil shells and paleosol carbonate from ancestral himalayan river deposits provide a 87 sr 86 sr record of lowland himalayan river water during the late neogene reconstructed 87 sr 86 sr river values increased sharply in the late miocene probably marking the beginning of exhumation of high 87 sr 86 sr metalimestones more in the central than in the western himalayas these results imply that the marine 87 sr 86 sr record may not be a proxy for silicate weathering or consumption of atmospheric co 2 resulting from that weathering

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

ice push disturbances in high boreal and subarctic lakeshore ecosystems since ad 1830 northern quebec canada ice scars on lakeshore trees were surveyed on the islands of two large lakes in northern quebec clearwater lake 1270 km2 and bienville lake 900 km2 respectively at the southern edge of the subarctic and at the northern limit of the boreal zones correspondence of ice scar chronologies with hydrological and climatological instrumental registers indicated that shore ice pushes are due to lake floods in the ad 1930s a shift in the flood regimes occurred in the high boreal ice push activity was much more frequent prior to 1930 than in the subarctic major regional ice pushes occurred in ad 1854 1903 1914 1936 1947 1954 1959 60 1970 and 1979 prior to 1930 local major events were concentrated south of the subarctic zone but the situation inverted after 1930 a northward shift in the average position of the arctic front is postulated as having been the driving force of local hydrologic regimes that allowed ice disturbances to occur especially a in controlling the amount of snowfall ice scars

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

tectonic predesign of mass movements with examples from the chinese himalaya abstract the genesis of landslides has traditionally been ascribed essentially to exogenic nontectonic causes thus it has generally been assumed that progressive erosion oversteepens slopes until they become unstable and collapse by forming slides the specific triggers in each case would be exogenic influences such as for instance an extreme weather period this paper shows that in practically all cases of mass movements endogenic processes are also of fundamental importance in the first place a landscape responds as a complex open system existing in a quasi stationary state at the edge of chaos in which an endogenic input and exogenic outflow of mass and energy occur this quasi stationary state can become unstable resulting in landslides in the second place a direct predesign is present because of endogenic causes viz by a former or the present geotectonic stress field thus some common notable contentions regarding the origin of landslides are shown to be false a better understanding of the mechanisms for landslide genesis is illuminated using examples from the chinese mountain ranges at the east end of the himalayas in these particular cases the orientations of mass movements are directly controlled predesigned by the present day local tectonic stress

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

thermoluminescence dating of dunes at cape st lambert east kimberleys northwestern australia abstract quaternary lithostraigraphic units in coastal dunes have been dated in the dune field at cape st lambert near the mouth of the berkeley river in the east kimberley region northwestern australia using coarse fraction thermoluminescence tl dating twelve tl dates were measured four main chronostratigraphic units were identified the oldest dunes appear to have been produced from offshore deposits reworked by rising sea level about 5000 years ago two sequences of younger stable dunes derive from the river mouth sediments of the berkeley river and date to about 3000 years ago and 1600 years ago respectively the presently active dunes appear to have been initiated within the last 1000 years a period of increased climatic variability from 3000 yrs b p to the present appears to be responsible for most of the late holocene units identified at cape st lambert

palynological evidence for vegetation development and climatic change in the sub himalayan zone neogene central nepal abstract a palynological study on miocene pleistocene sediments exposed at surai khola in central nepal yields new information on vegetation and climate change over the last 11 5 ma our results show that during the late middle miocene to early late miocene 11 5 8 ma lower siwalik the himalayan foothills and the gangetic floodplain of nepal were mainly forested with subtropical to temperate broad leafed b l taxa e g quercus lithocarpus castanopsis alnus and tropical forest taxa respectively grasses were present at the time but were not abundant between the early to late late miocene 8 6 5 ma lower middle siwalik grassland replaced subtropical and temperate b l forest this change may be related to disturbance of the vegetation on the slopes due to uplift perhaps enhanced by intensification of the monsoon between late late miocene to pliocene early pleistocene 6 5 potamogeton and better preservation of all specimens enhanced seasonal flooding in the system during the pliocene 5 5 3 5 ma top middle siwalik may have produced local lacustrine conditions on the overbanks evidenced by an abundance of algae spirogyra and pteridophytes in the pollen assemblages evidence of climatic cooling between 6 5 5 ma ago is indicated by the onset of steppe taxa decrease of tropical forest taxa and disappearance of certain dipterocarpaceae pollen assemblages from the surai khola section suggest complex vegetation changes of which the shift to c 4 grass dominance was only one global climatic cooling the intensification of the monsoon and the late miocene uplift may all have contributed to the phytogeography in the sub himalayan zone

neogene foreland basin deposits erosional unroofing and the kinematic history of the himalayan fold thrust belt western nepal sedimentological and provenance data from the lower miocene pliocene dumri formation and siwalik group in western nepal provide new information about the timing of thrust faulting and the links between erosional unroofing of the himalaya and the cenozoic 87 sr 86 sr record of the ocean in western nepal the dumri formation is an 750 1300 m thick fluvial sandstone and overbank mudstone unit the siwalik group is 4200 m thick and consists of a lower member 850 m of 2 12 m thick fluvial channel sandstones and oxidized calcareous paleosols a middle member 2400 m of very thick 20 m channel sandstones and mainly organic rich histosols and an upper member 1000 m composed of gravelly braided river deposits paleocurrent data indicate that middle miocene pliocene rivers in western nepal flowed southward transverse to the thrust belt throughout deposition of the siwalik group no evidence was found for an axial fluvial trunk system i e the paleo ganges river in siwalik group sandstones a major increase in fluvial channel size is recorded by the transition from lower to middle siwalik members at 10 8 ma probably in response to an increase in seasonal discharge modal petrographic data from sandstones in the dumri formation and the siwalik group manifest an upsection enrichment in potassium feldspar carbonate lithic fragments and high grade metamorphic minerals modal petrographic analyses of modern river sands provide some control on potential source terranes for the miocene pliocene sandstones the dumri formation was most likely derived from erosion of sedimentary and low grade metasedimentary rocks in the tibetan tethyan himalayan zone during early miocene emplacement of the main central thrust the presence in dumri sandstones of plagioclase grains suggests exposure of crystalline rocks of the greater himalayan zone perhaps in response to tectonic unroofing by extensional detachment faults of the south tibetan detachment system during deposition of the lower siwalik group 15 11 ma emplacement of the dadeldhura thrust sheet one of the synformal crystalline thrust sheets of the southern himalaya on top of the dumri formation supplied abundant metasedimentary lithic fragments to the foreland basin a steady supply of plagioclase grains and high grade minerals was maintained by deeper erosion into the main central thrust sheet from 11 ma to the present k feldspar sand increased steadily suggesting that granitic source rocks became widely exposed during deposition of the upper part of the lower siwalik group this provenance change was caused by erosion of passively uplifted granites and granitic orthogneisses in the dadeldhura thrust sheet above a large duplex in the lesser himalayan rocks since the onset of deposition of the conglomeratic upper siwalik group 4 5 ma fault slip in this duplex has been fed updip and southward into the main boundary and main frontal thrust systems we obtained 113 u pb ages on detrital zircons from modern rivers and siwalik group sandstones that cluster at 460 530 ma 850 1200 ma 1 8 2 0 ga and 2 5 ga an abundance of cambrian ordovician grains in the siwalik group suggests sources of siwalik detritus in the granites of the dadeldhura thrust sheet and possibly the greater himalayan orthogneisses the older ages are consistent with sources in the greater and lesser himalayan zones an overall upsection increase in zircons older than 1 7 ga suggests increasing aerial exposure of lesser himalayan rocks none of the detrital zircons even in the modern river samples yielded a cenozoic age that might suggest derivation from the cenozoic greater himalayan leucogranites but this may be attributable to the inheritance problems that characterize the u pb geochronology of the leucogranites when compared with recent studies of the 87 sr 86 sr composition of paleosol carbonate nodules and detrital carbonate in paleosols from the siwalik group the provenance data suggest that erosion and weathering of metamorphosed carbonate rocks in the lesser himalayan zone and cambrian ordovician granitic rocks of the crystalline thrust sheets in central and eastern nepal may have played a significant role in elevating the 87 sr 86 sr ratio of middle miocene synorogenic sediments in the indo gangetic foreland basin and the bengal fan as well as global seawater

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

fluid flow through carbonate platforms as evidence for deep seated reservoirs in northwest australia fluid flow features in carbonate platforms of the outer browse basin northwest australia are investigated using 3d seismic and borehole data during the cenozoic the study area evolved from a carbonate ramp to a rimmed platform with isolated carbonate build ups as such it played a key role in focusing fluid on their buoyant flow to the surface statistical analyses of direct hydrocarbon indicators show fluid flow to be focused in elevated areas i e the greater is the focusing of fluid the larger is the carbonate platform or isolated build up locally karst systems created regions of enhanced permeability through the evolving carbonate stratigraphy karstified horizons are located on the top of carbonate build ups and platform clinoforms as fluid buoyantly concentrates and diffuses up into topographic highs in turn the putative migration of gas and fluid generated hypogenic karst systems enhancing permeability in otherwise lower permeability rock based on the interpreted data we suggest a pivotal relationship between the presence of carbonate build ups and karsts in the browse basin and hydrocarbon accumulations at depth areas of elevated topography focus sub surface fluid enhancing the permeability of carbonate successions in turn focused fluid flow can lead to the generation of methanogenic carbonates promoting the growth of isolated build ups and leading to further generation of elevated features this grants the identification of similar features on seismic data from northwest australia and other equatorial margins in the world as a valid proxy for the recognition of hydrocarbon accumulations below thick carbonate successions

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

fossil murine rodents as ancient monsoon indicators of the indian subcontinent abstract the ecomorphological aspects of murine rodent dentition were analyzed by comparing the relationship between fossils and their extant counterparts another aspect explored is the broad correlation of species richness vs rainfall and temperature data of an area integration of these results has provided a broad picture of the monsoonal conditions rainfall temperature and vegetation prevailing during the late middle miocene to late miocene 13 6 4 ma and pliocene 5 1 8 ma times in the northwestern part of the indian subcontinent terminal pleistocene kurnool cave murine fauna also provides some clues regarding the past climatic conditions in this part of andhra pradesh the results indicate that the late miocene possibly had monsoonal conditions quite different from that of the present day as none of the extant taxa cluster with the late miocene taxa the northwestern part of the indian subcontinent received rainfall between 1000 and 2000 mm in the early pliocene 5 4 ma and that in the late pliocene was between 2000 and 4000 mm late pliocene diversity of murine rodents reflects the existence of a diverse spectrum of ecological niches mainly open grassland savanna conditions interspersed with dry wet deciduous and semi evergreen forests terminal pleistocene around kurnool caves andhra pradesh was relatively drier compared to the pliocene with rainfall ranging between 600 and 1000 mm

late miocene and pliocene large land mammals and climatic changes in eurasia the fossil teeth of land mammals offer a powerful tool to map the regional details of past climate change in the terrestrial realm we use meanplant eaterhypsodonty molarcrownheight oflateneogenemammallocalitiestomaplatemioceneandpliocenepalaeoprecipitation on the eurasian continent and with higher temporal resolution in europe the results show that the mid latitude drying in eurasia affected thecentral parts ofthecontinentfirst and thatthedrying of western europeafter about7 8maseemstohavecoincidedroughlyintimewith a return to more humid conditions in eastern asia with a return to a drier east and more humid west in the pliocene within europe the hypsodonty based palaeoprecipitation maps suggest that the sequence from mn 9 to mn 12 ca 11 1 6 8 ma was dominated by an east west continental marine humidity gradient which gradually intensified and with a shift of dryer conditions eastwards in mn 12 ca 7 5ma thiswaspartlyoverlainfrommn13onwardsbyanorth southorientedgradient whichpersistedatleasttotheendofthepliocene the maps for both the earliest late miocene mn 9 ca 11 1 9 7 ma and the earliest pliocene mn 14 ca 4 9 4 2 ma show very low regional differentiation possibly suggesting perturbed phases in the evolution of the mammal communities analysis of hypsodonty and dietary structure of the mammalian plant eater community in europe during the entire interval shows that the miocene pliocene boundary was marked by a strong decrease in mesodont species and mixed feeders and an increase in brachydont species and omnivores in this view the shift in the latest miocene from east west to partly north south polarised hypsodonty patterns corresponds mainly to an increase in hypsodont species and grazers it seems probable that the east west gradient was primarily driven by precipitation while the north south gradient would also have been strongly influenced by temperature related effects of humidity

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

paleoclimatic fluctuations inferred from leaf wax n alkane records in central tibet in the late oligocene to early miocene abstract climatic variations and their forcing mechanisms in tibet are highly significant for understanding the environmental effects of the tibetan plateau through its controlling on atmospheric circulation here we present new leaf wax n alkanes from cenozoic lacustrine sediments in the lunpola basin of central tibet to constrain long term paleoclimatic changes our results suggest that the paleoclimate from the late oligocene to early miocene was generally stable but tending slightly towards cold dry from 25 5 to 23 2 ma followed by a trend towards warm humid between 23 2 and 21 7 ma and finally by a more arid and highly oscillating climate after 21 7 ma our results compare favorably with the proxies of marine 18o records which suggests that the general long term trend since the late oligocene has been a response to global temperature variations moreover spectral analysis of 13c31 and 2h31 data reveals that relative humidity exhibits 400 kyr cycles controlled mainly by periodic changes in global ice volumes

late cenozoic uplift in southern asia and the american west rationale for general circulation modeling experiments geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late cenozoic especially in the last 10 m y regions of major uplift include the tibetan plateau and himalayan mountains of southern asia and the sierra nevada colorado plateau basin and range rocky mountains and high plains of the american west uplift occurred at a scale large enough to affect regional and global climate in a number of ways several of which we evaluate by general circulation model experiments in accompanying papers

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

intensification of the asian monsoon and a chemical weathering event in the late miocene early pliocene implications for late neogene climate change several sedimentary geochemical and isotopic records indicate that the hypothesized intensification of the asian monsoon at about 8 ma triggered a physical and chemical weathering event in the himalayan tibetan plateau records of sediment input and clay composition from the northern indian ocean reveal clear weathering changes in the plateau at this time and ge si ratios of opaline silica as well as biogenic sedimentation rates indicate that increased dissolved element fluxes from this weathering event had an oceanwide effect it is likely that weathering intensity also increased in the andes and amazon basin in this interval as well perhaps the most important impact of this weathering event was to increase the net flux of the biolimiting nutrient phosphorus to the ocean as evidenced by a peak in phosphorus accumulation rates at this time the temporary increase in nutrient inputs to the ocean triggered increased oceanic productivity and organic carbon burial recorded in carbon isotopic records and paleooxygen concentrations the net result of this weathering event may have been an increase in the rate of drawdown of atmospheric co2 through the late miocene early pliocene via direct silicate weathering reactions and increased burial of organic carbon in the ocean this increased rate of atmospheric co2 drawdown may have destabilized the climate system by the late pliocene thus initiating a period of intense cooling and ice buildup leading to the present

in search of the late miocene early pliocene biogenic bloom in the atlantic ocean ocean drilling program sites 982 925 and 1088 1 we reconstruct paleoproductivity at three sites in the atlantic ocean ocean drilling program sites 982 925 and 1088 to investigate the presence and extent of the late miocene to early pliocene biogenic bloom from 9 to 3 ma our approach involves construction of multiple records including benthic foraminiferal and caco3 accumulation rates uvigerina counts dissolution proxies and geochemical tracers for biogenic and detrital fluxes this time interval also contains the so called late miocene carbon isotope shift a well known decrease in benthic foraminiferal 13c values we find that the timing of paleoproductivity maxima differs among the three sites at site 982 north atlantic benthic foraminifera and caco3 accumulation were both at a maximum at 5 ma with smaller peaks at 6 ma the paleoproductivity maximum was centered earlier 6 6 6 0 ma in the tropical atlantic site 925 in the south atlantic site 1088 paleoproductivity increased even earlier between 8 2 ma and 6 2 ma and remained relatively high until 5 4 ma we note that there is some overlap between the interval of maximum productivity between sites 925 and 1088 as well as the minor productivity increase at site 982 we conclude that the paleoproductivity results support hypotheses aiming to place the biogenic bloom into a global context of enhanced productivity in addition we find that at all three sites the 13c shift is accompanied by carbonate dissolution this observation is consistent with published studies that have sought a relationship between the late miocene carbon isotope shift and carbonate preservation

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

alluvial pollen on the north china plain abstract mordern alluvial pollen varies with geomorphic setting and depositional facies in sediments of the yellow hutuo and luan rivers and in baiyangdian and hengshuihu lakes most of the arboreal pollen is derived from the mountains whereas most of the nonarboreal pollen is derived from the plain itself alluvium dominated bypinuspollen andselaginellaspores was deposited during a flood hydrodynamic sorting of alluvial pollen exists in the sediments of floodplain central bar natural levees and point bar in reconstructing the ancient vegetation and past climate based on pollen in alluvium it is important to consider sedimentary facies and geomorphologic setting

uplift driven climate change at 12 ma a long δ18o record from the ne margin of the tibetan plateau carbonates from fluvial and lacustrine sediments were sampled from multiple measured sections in the linxia basin of western china based on textural and mineralogical evidence lacustrine carbonates are primary precipitates from lake water a 29 million year record of the oxygen isotope composition of meteoric water is inferred from the n 18 o values of these carbonates this inference is based on the most negative n 18 o values in the lake carbonates which represent lake waters that have experienced the least evaporative enrichment carbonate n 18 o values a proxy for rainfall n 18 o are v310 5x throughout the interval of 29 12 ma at 12 ma there is a shift to 39x a value that remains into the pliocene this implies a major reorganization of atmospheric circulation patterns and a shift to more arid conditions at the ne margin of the tibetan plateau with the post 12 ma system similar to that of today the 12 ma event may represent the time at which the tibetan plateau achieves sufficient elevation to block the penetration of moisture from the indian ocean or south pacific into western china the period of greatest aridity is from 9 6 to 8 2 ma a time interval which agrees well with other climate records 2003 elsevier b v all rights reserved

sensitivity of eurasian climate to surface uplift of the tibetan plateau experiments with climate models are used to illustrate how earth s climate could be expected to change if surface uplift occurred the experiments contrast two climate simulations one with all continents at sea level and one with present day mountains and plateaus the simulations in the eurasia sector show that surface uplift increased elevation produces marked increases in the intensity of summer and winter monsoons of asia with development of wetter climates to the south and east of the tibetan plateau and drier climates to the north and west of the plateau there is a general cooling in northern polar latitudes comparison of simulations from two different models shows that the magnitude of the simulated changes depends upon how the models calculate the land surface hydrology and the ocean temperature the simulated changes produced by surface uplift agree in a general way with many geologic indicators of late cenozoic climate change the results suggest that surface uplift of mountains and platea

eocene early miocene foreland basin development and the history of himalayan thrusting western and central nepal sedimentologic petrographic and u pb detrital zircon ages from middle eocene through early miocene sedimentary rocks in the lesser himalayan zone of western and central nepal indicate that a peripheral foreland basin system had developed in the eastern himalayan collision zone by middle eocene time the shallow marine eocene bhainskati formation accumulated in a back bulge depozone between a southward migrating forebulge and the indian craton migration of the forebulge through this region during eocene oligocene time produced a regional unconformity that spans 15 20 myr by early miocene time the forebulge unconformity was onlapped by the distal fringes of the southward migrating foredeep depozone represented by fluvial deposits of the dumri formation continued southward migration of the foredeep during the neogene accommodated the fluvial siwalik group light mineral provenance data and u pb detrital zircon ages suggest that the bhainskati was derived partly from tethyan sedimentary rocks of the tibetan himalayan zone during initial growth of the himalayan fold thrust belt the dumri was derived from metasedimentary and crystalline rocks of the greater himalayan zone during emplacement of the main central thrust and contemporaneous tectonic unroofing by normal faulting along the south tibetan detachment system the lesser himalayan crystalline thrust sheets were emplaced soon after deposition of the dumri formation 15 10 ma paleocurrent and lithofacies data from the dumri formation indicate deposition by west southwestward flowing rivers that drained into the indus portion of the himalayan foreland basin system during the early miocene thick channel sandstones in the lower dumri may represent the early miocene counterpart of the modern ganges river eastward diversion of the ganges drainage system to near its present location had occurred by 15 ma as the high standing aravalli range on the northern indian shield approached the front of the fold thrust belt assuming reasonable values for the flexural rigidity of indian lithosphere the time span of the forebulge unconformity yields a velocity of 14 33 mm yr for the southward migration of the fold thrust belt relative to india this range of values is consistent with neogene and present day estimates and suggests that only one third to one half of india eurasia convergence has been accommodated by shortening in the himalayan fold thrust belt since the onset of collision

evolution of grasses and grassland ecosystems the evolution and subsequent ecological expansion of grasses poaceae since the late cretaceous have resulted in the establishment of one of earth s dominant biomes the temperate and tropical grasslands at the expense of forests in the past decades several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation the data indicate that the development of grassland ecosystems on most continents was a multistage process involving the paleogene appearance of c3 and c4 open habitat grasses the mid late cenozoic spread of c3 grass dominated habitats and finally the late neogene expansion of c4 grasses at tropical subtropical latitudes the evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open habitat grasses in addition the timing of these evolutionary and ecological events varied between regions consequently region by region investigations using both direct plant fossil

recent terrigenous sedimentation in joseph bonaparte gulf northwestern australia abstract the southern part of the sahul shelf is an excellent example of a macro tidal carbonate clastic transition a distinct lobe of recent seaward fining sand sized material has prograded onto the shelf from the shallow southern part of joseph bonaparte gulf defining the path of bed load transport on the inner shelf while this is a dominantly calcareous shelf parts of the inner shelf are characterised by deep erosion in which relict sediments are excavated from the bed the mechanical destruction of both relict and contemporary biogenic material takes place feeding fine carbonate detrius into the transport stream and there is significant bypassing of recent terrigenous material the lobe of transported sediments in the joseph bonaparte gulf is carbonate rich and masks the significant input of recent terrigenous material

isotopic preservation of himalayan tibetan uplift denudation and climatic histories of two molasse deposits two distinctive molasse deposits within the indo asian collision zone have been investigated to help understand the post oligocene evolution of the himalaya and southern tibetan plateau the siwalik group predominantly fluvial sandstones and siltstones is widespread throughout the foothills of the himalaya from pakistan to eastern india paleomagnetic analysis of a measured section in the bakiya khola southeastern nepal constrains depositional ages t dep to between 10 8 and 4 9 ma the average accumulation rate during this interval was 0 4 0 5 mm yr 40 ar 39 ar dating of 126 detrital k feldspars from nine horizons in the bakiya khola section t dep 8 25 to 2 2 ma provide snapshots in time of the cooling ages exposed at the earth s surface in this drainage basin the minimum age in the spectra from seven of the nine horizons averages only 3 m y older than t dep indicating exceptionally rapid unroofing in the himalaya throughout that interval half of the grains fro

reconciling the intertropical convergence zone himalayan tibetan tectonics and the onset of the asian monsoon system abstract numerous climate proxies from across central south and east asia have yielded different ages for the start or intensification of a monsoon climate system common estimates include the early part of the early miocene 23 20 ma and the late miocene 11 8 ma in the early miocene the average position of the intertropical convergence zone itcz was likely to be the 2000 km closer to the himalaya than at present based on published data for the palaeolatitude of the central pacific itcz such that himalayan climate was marked by high precipitation but not necessarily seasonality here we propose that increased seasonality in the late miocene in the himalaya and neighbouring regions was a response to an increase in the distance between the itcz and the himalaya tibet such that the itcz was only brought northwards during the northern hemisphere summer each year this is essentially the pattern of the modern south asian monsoon system these climatic changes coincide with a switch from north south extensional shear on the northern side of the high himalaya thrusting on the main central thrust and rapid metamorphic exhumation to thrusts further south in the himalaya main boundary thrust and a reduction in high himalayan exhumation rates we speculate that the tectonic changes were at least in part a response to a reduction in precipitation over the high himalaya the himalayan thrust belt re organised to maintain a critical taper appropriate to a drier orogen the reduction in metamorphic exhumation after the early miocene would also have led to a reduction in the flux of metamorphic co2 to the atmosphere thereby promoting the global shift to a cooler climate in the mid miocene

late cenozoic genus fupingopollenites development and its implications for the asian summer monsoon evolution an extinct palynomorph fupingopollenites was used as the basis for a discussion of the late cenozoic asian summer monsoon asm evolution and its possible driving forces based on the spatial and temporal variations in its percentages across inner and east asia we found that fupingopollenites mainly occurred in east asia with boundaries to the ne of ca 42 degrees n 135 degrees e and nw of ca 36 degrees n 103 degrees e during the early miocene ca 23 17 ma this region enlarged westwards reaching the eastern qaidam basin ca 36 degrees n 97 5 degrees e during the middle miocene ca 17 11 ma before noticeably retreating to a region bounded to the nw at ca 33 degrees n 105 degrees e during ca 11 5 3 ma the region then shrank further in the pliocene with the ne boundary shrinking southwards to about 35 degrees n 120 degrees e the area then almost disappeared during the pleistocene 2 6 0 ma the flourishing and subsequent extinction of fupingopollenites is indicative of a narrow ecological amplitude with a critical dependence on habitat humidity and temperature most likely mean annual precipitation map 1000 mm and mean annual temperature mat 10 degrees c therefore the fupingopollenites geographic distribution can indicate the humid asm evolution during the late cenozoic revealing that the strongest asm period occurred during the middle miocene climate optimum mmco similar to 17 14 ma after which the asm weakened coincident with global cooling we argue that the global cooling played a critical role in the asm evolution while the tibetan plateau uplifts made a relatively small contribution c 2015 international association for gondwana research published by elsevier b v all rights reserved

east asian summer monsoon weakening after 7 5 ma evidence from combined planktonic foraminifera mg ca and δ18o odp site 1146 northern south china sea abstract the monsoon system represents one of the basic elements of global atmospheric circulation its evolution and variability over long periods of geologic time play a significant role in our understanding of global climate in this study we focus on the late miocene interval from 10 ma to 6 ma a period of postulated profound ecological and environmental shifts in east and south asia the combined approach of measuring planktonic foraminiferal mg ca ratios and stable oxygen isotopes from ocean drilling program odp site 1146 enabled us to reconstruct temperature independent seawater 18o i e proxy for sea surface salinity variations in order to reconstruct the hydrography in the northern south china sea located offshore the pearl zhujiang river or its predecessor the location of odp site 1146 is considered to provide a most sensitive record for detecting potential changes in freshwater input river run off as a result of changes in continental humidity and hence changes in east asian summer monsoon easm climate local seawater 18o reconstructions reveal that monsoon development during the late miocene can be regarded as an abrupt weakening in the easm around 7 5 ma we suggest that an easm weakening was most likely the driving force for decreasing aridity in east and south asia at 8 6 ma leading to widespread ecosystem changes in east and south asia

evidence from paleosols for low to moderate elevation of the india asia suture zone during mid cenozoic time the post collisional uplift history of the india asia suture zone in southern tibet is important for understanding the geodynamic conditions of the india asia collision and how it may have modified regional and global climate here we use stable isotope and major element analyses of paleosols preserved in the liuqu conglomerate to reconstruct india asia suture zone paleoclimate and paleoelevation paleosol carbonate 13c vienna peedee belemnite average values of 9 4 1 1 indicate that liuqu paleosols were well vegetated by c3 plants unlike thinly vegetated and arid modern tibet major element weathering indices show that these soils experienced significant collapse and loss of cations due to weathering of similar intensity to that in the wet low elevations of the neogene himalayan foreland age estimates for the liuqu vary but current evidence points to an early miocene age our evidence requires that the india asia suture zone experienced wet well vegetated conditions during liuqu conglomerate deposition geodynamically this implies that the suture zone was at relatively low elevation and was topographically open to monsoon moisture as late as 40 m y after the start of the india asian collision this challenges the idea that uplift of the india asia suture zone was monotonic and tied directly to crustal thickening

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

lateral variations in vegetation in the himalaya since the miocene and implications for climate evolution the himalaya has a major influence on global and regional climate in particular on the asian monsoon system the foreland basin of the himalaya contains a record of tectonics and paleoclimate since the miocene previous work on the evolution of vegetation and climate has focused on the central and western himalaya where a shift from c3 to c4 vegetation has been observed at 7 ma and linked to increased seasonality but the climatic evolution of the eastern part of the orogen is less well understood in order to track vegetation as a marker of monsoon intensity and seasonality we analyzed 13c 13c and 18o 18o values of soil carbonate and associated 13c 13c values of bulk organic carbon from previously dated sedimentary sections exposing the syn orogenic detrital dharamsala and siwalik groups in the west and for the first time the siwalik group in the east of the himalayan foreland basin sedimentary records span from 20 to 1 myr in the west joginder nagar jawalamukhi and haripur kolar sections and from 13 to 1 myr in the east kameng section respectively the presence of soil carbonate in the west and its absence in the east is a first indication of long term lateral climatic variation as soil carbonate requires seasonally arid conditions to develop 13c 13c values in soil carbonate show a shift from around 10 to 2 at 7 ma in the west which is confirmed by 13c 13c analyses on bulk organic carbon that show a shift from around 23 to 19 at the same time such a shift in isotopic values is likely to be associated with a change from c3 to c4 vegetation in contrast 13c 13c values of bulk organic carbon remain at 23 23 in the east thus our data show that the current east west variation in climate was established at 7 ma we propose that the regional change towards a more seasonal climate in the west is linked to a decrease of the influence of the westerlies delivering less winter precipitation to the western himalaya while the east remained annually humid due to its proximity to the monsoonal moisture source

east west extension and miocene environmental change in the southern tibetan plateau thakkhola graben central nepal east west extensional basins are distributed across the southern half of the tibetan plateau at an elevation of 4 km these basins have generated much interest because of their potential implications for the regional tectonics and force distribution in the plateau this study documents the sedimentology of the miocene pliocene thakkhola graben fill in order to reconstruct basin evolution and paleoenvironment analysis of depositional systems paleodrainage patterns and conglomerate clast provenance of the 1 km thick graben fill sets limits on the timing of activity of the basin bounding faults and the development of southward axial drainage in the basin during the deposition of the oldest basin fill tetang formation ca 11 9 6 ma probably in a restricted basin minor motion occurred on the basin bounding fault systems an angular unconformity separates the tetang and overlying thakkhola formations where this contact can be observed in the southern part of the basin southward axial drainage was established by ca 7 ma with the onset of deposition of the thakkhola formation several episodes of damming of this drainage system are recorded by widespread lacustrine deposits in the southern part of the basin facies distribution and the progressive rotation of strata in the thakkhola formation indicate that the dangardzong fault on the western edge of the basin was active at this time and drainage ponding may have been related to displacement on normal faults associated with the south tibetan detachment system to the south of thakkhola graben contrasts between deposits of the tetang and thakkhola formations provide evidence for environmental change in the basin in the tetang formation the abundance of lacustrine facies the pollen record and the absence of paleosol carbonate suggest that conditions were more humid than during subsequent deposition of the thakkhola formation environmental change in the thakkhola graben coincided with environmental change observed in the siwalik foreland basin sequence arabian sea and bay of bengal at ca 8 7 ma although this climate change event has been previously attributed to intensification of the asian monsoon in response to uplift of the tibetan plateau paleoaltimetry data indicate that this region had already attained a high elevation by ca 11 ma thus the thakkhola graben stratigraphic record suggests that uplift of the southern tibetan plateau and the onset of the asian monsoon as inferred from paleoclimatic indicators were not directly related in a simple way

sustained wood burial in the bengal fan over the last 19 my the ganges brahmaputra g b river system transports over a billion tons of sediment every year from the himalayan mountains to the bay of bengal and has built the world s largest active sedimentary deposit the bengal fan high sedimentation rates drive exceptional organic matter preservation that represents a long term sink for atmospheric co2 while much attention has been paid to organic rich fine sediments coarse sediments have generally been overlooked as a locus of organic carbon oc burial however international ocean discovery program expedition 354 recently discovered abundant woody debris millimeter to centimeter sized fragments preserved within the coarse sediment layers of turbidite beds recovered from 6 marine drill sites along a transect across the bengal fan 8 n 3 700 m water depth with recovery spanning 19 my analysis of bulk wood and lignin finds mostly lowland origins of wood delivered episodically in the last 5 my export included c4 plants implying that coarse woody lowland export continued after c4 grassland expansion albeit in reduced amounts substantial export of coarse woody debris in the last 1 my included one wood rich deposit 0 05 ma that encompassed coniferous wood transported from the headwaters in coarse layers we found on average 0 16 weight oc which is half the typical biospheric oc content of sediments exported by the modern g b rivers wood burial estimates are hampered by poor drilling recovery of sands however high magnitude low frequency wood export events are shown to be a key mechanism for c burial in turbidites

late miocene vegetation reconstruction with the caraib model abstract climatic outputs from the atmospheric general circulation model echam4 coupled to a mixed layer ocean model are used as inputs to the caraib global vegetation model to reconstruct the distribution of vegetation and the biosphere carbon stocks over the continents during the late miocene tortonian the results show significant changes in the geographical distribution of vegetation during the late miocene compared to the present with a reduction of desert areas and an expansion of tropical seasonal forests which reached temperate latitudes these changes in vegetation distribution are accompanied by a moderate increase of the total biosphere carbon stock by 159 gt sensitivity tests to atmospheric co 2 have also been performed with the vegetation model only i e while keeping constant all climatic variables to their reference tortonian state these tests point out the potential importance of co 2 fertilization both regarding vegetation distribution and biosphere carbon storage the impact of an atmospheric co 2 decrease from 280 to 200 ppmv or increase from 280 to 560 ppmv on the vegetation distribution appears to be at least as large as that of the climate change between the tortonian and the present while in terms of carbon storage the impact of atmospheric co 2 is far much larger than the climatic one although the actual response of vegetation to co 2 fertilization may be much smaller than its theoretical response in the model these results emphasize the need to consider atmospheric co 2 as an important parameter for palaeovegetation reconstructions

extended stratigraphy palynology and depositional environments record the initiation of the himalayan gyirong basin neogene china here we report new sedimentological and paleontological data from a 603 5 m thick neogene sequence woma section in the gyirong basin a basin induced by east west extension in the himalayas of southern tibet we document the conglomeratic danzengzhukang formation at the base of the section and the overlying finer grained woma formation that includes a hipparion fauna based on stratigraphic correlations and earlier thermochronology and magnetostratigraphic results we bracket the depositional age of this section between 10 8 ma and 1 7 ma lithology paleo current directions and provenance analysis together with palynological and paleontological data have revealed three depositional environments for the deposition of the studied section 1 alluvial fan to braided river environments with ese transport directions danzengzhukang formation 1 7 ma with increased denudation and wsw paleo currents was associated with a deciduous coniferous and broad leaved mixed forest that suggests an increase in climate variability our data indicate that the gyirong basin was under overall warm and humid conditions throughout most of its history in agreement with high resolution oxygen and carbon isotope data collected from the same section this issue we interpret our warm climate in the gyirong basin to reflect the prevalence of the monsoonal influence and the distal pollen sources to result from orographic effects

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

clay mineral assemblages in the zhaotong basin of southwestern china implications for the late miocene and pliocene evolution of the south asian monsoon abstract the characteristics of the evolution of the south asian monsoon during the late miocene through the pliocene are highly debated to obtain a better understanding we studied the clay mineral assemblages and the clay fraction content of a high quality sedimentary sequence borehole core zk1 spanning the interval of 8 8 2 62 ma in the zhaotong basin southwestern yunnan province on the southeastern margin of the tibetan plateau smectite kaolinite illite and vermiculite were the four main clay minerals identified and changes in their relative abundance reveal a distinct pattern of climate change during the study interval until the very late miocene kaolinite and smectite with a small amount of illite were dominant suggesting a relatively warm and humid climate from 6 2 to 2 8 ma smectite was dominant with a minor amount of kaolinite and illite indicating a relatively cool and humid climate and from 2 8 to 2 62 ma vermiculite hiv and illite were dominant with a minor amount of kaolinite indicating a relatively cold and humid climate the variation in clay mineral assemblages indicate substantial changes in the south asian monsoon in the zhaotong basin that promoted a change from a warm and humid climate in the late micoene to cool and humid climate in the very late miocene through pliocene followed by a gradual trend towards a cold and humid climate in the very late pliocene comparison with records from elsewhere indicates that the observed variations in the south asian monsoon were mainly controlled by global cooling rather than by tibetan plateau uplift

middle miocene small mammals from the siwalik group of northwestern india abstract the freshwater siwalik deposits of the himalayan foreland basin have long been known to yield prolific miocene pleistocene mammalian fauna overwhelming of this data comes from the siwalik sequence of pakistan where good palaeomagnetic control is available for various siwalik lithounits in contrast limited data on fossil mammals more so on small mammals is available from the indian side of the siwalik where even most of the siwalik formations lack palaeomagnetic and or radiometric calibration despite the fact that several fossil yielding localities are known in india since long in the present research work small mammals discovered from a lower siwalik locality near ramnagar town in jammu province jammu and kashmir state india are reported and their age implication is discussed the mammal fauna from the study area contains four species of rodents belonging to four subfamilies these include rhizomyinae represented by kanisamys indicus ctenodactylinae by sayimys sivalensis myomiminae by myomimus sp and xerinae by tamias urialis the recovered biotas improve our knowledge on the rodent diversity of the indian lower siwalik subgroup and contribute to further constrain the age of the fossiliferous horizon between 13 6 and 13 2 ma the new fauna suggests a humid forested palaeoecological setting

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

palynological evidence for late miocene pliocene vegetation evolution recorded in the red clay sequence of the central chinese loess plateau and implication for palaeoenvironmental change innorthernchina the late miocene pliocene redclay in the easternloess plateau fills a gapofclimate records between the wellknown loess soil sequences of the last 2 6 ma and the miocene loess soil sequences from the western loess plateau previous studies indicate that the red clay is also of wind blown origin covering the period from 7 8t o 2 6 ma the red clay therefore provides a good archive to reconstruct paleoecological succession and paleoclimate change in this study a palynological investigation was conducted on the late miocene pliocene red clay sequence at xifeng central loess plateau which provides new insights into the nature of the evolution of vegetation and climate change from 6 2 to 2 4 ma our results show that during this period the central loess plateau region was covered mainly by a steppe vegetation indicating long lasting dry climatic condition three vegetational zones were recognized during this period zone a 6 2 to 5 8 ma is characterized by a steppe ecosystem zone b 5 8 to 4 2 ma is characterized by a significant increase of temperate forest plants indicating a relatively humid regional climate zone c 4 2 to 2 4 ma indicates a typical steppe ecosystem the vegetation shift at about 4 5 3 7 ma when the temperate forest plants decrease the vegetation gradually changed to typical grassland and even to desert steppe this is interpreted to represent a drying event the uplift of the tibetan plateau at about 4 5 ma that resulted in the intensification of the monsoon reversal is thought to have playedanimportantroleinthissignificantecological change high latitude coolingmayhavepartiallycontributedtotheclimateshift during 4 5 to 3 7 ma in the loess plateau region and most likely was the driving force for the ecological shift at about 3 7 ma

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

evolution of the south asian monsoon wind system since the late middle miocene abstract the evolution and timing of the inception of the south asian monsoon sam has been one of the most debated climatic mysteries amongst climate workers the himalaya tibetan plateau htp complex has been implicated as the main driver for sam circulation however there are intense debates as to whether there was a critical elevation of the htp complex that drove the sam and at what time such a critical elevation was attained also the role of the htp complex in driving the sam has been questioned in recent climate model studies the model simulation suggests a major intensification of the sam as early as 30 ma whereas marine records from the arabian sea indicate a major strengthening of the south asian summer or southwest monsoon winds between 10 and 8 ma the continental vegetation on the other hand captured a major transition from c 3 to c 4 type during 8 7 ma but whether this change was local or global and whether this transition was driven by monsoonal precipitation is not unanimously accepted our new record from ocean drilling program holes located off the oman margin and on the owen ridge western arabian sea shows appearance of monsoon wind proxy planktic foraminifer globigerina bulloides a significant increase in total organic carbon and a negative shift in stable carbon isotope record of benthic foraminifera at 12 9 ma these proxies indicate that present day south asian monsoon wind system began to develop during the late middle miocene 12 9 ma and summer monsoon was in its full strength in the late miocene 7 ma from 11 to 7 ma the summer monsoon was weaker when winter monsoon was stronger

the late miocene paleoenvironment of afghanistan as inferred from dental microwear in artiodactyls abstract dental microwear of late miocene artiodactyls from afghanistan can yield information on paleodiet and thus inferences can be drawn about their paleoenvironment the molayan locality lies at the border between the greek iranian and siwalik bioprovinces knowledge of the paleoenvironment will further our understanding of the faunal exchanges between these two provinces during the late miocene ninety nine specimens of seven bovid and one giraffid species are considered the number and diversity of the samples provide objective data which enable the reconstruction of the paleoenvironment prostrepsiceros aff vinayaki and sporadotragus tadzhikistanicus have similar dental microwear pattern which suggests a meal by meal mixed feeding diet phronetragus aff secondus gazella sp and the giraffid palaeotragus cf rouenii can only be characterized as mixed feeders in a general sense dorcadoxa porrecticornis was an obligate grazer and the two species of tragoportax were variable grazers the analysis also brings out clear similarities between extinct grazers and equus przewalskii which is a c3 grazer isotopic evidence from previous studies supports the microwear data comparisons with data from the late miocene of the potwar plateau suggest strong environmental differences with the afghan locality when brought together this disparate evidence about diet suggests an open and dry environment composed mainly of c3 grasses and evergreen bushes during the late miocene in afghanistan

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

the expansion of c4 grasses and global change in the late miocene stable isotope evidence from the americas j3c values in paleosols and fossil teeth have been used to document the expansion of c plants in south asia africa and north america during the late miocene however the exact timing and rate of expansion of c vegetation is unclear outside the old world because of a lack of high resolution records we present a high resolution record from northwest argentina in which the s13c values of soil carbonate rise above a threshold of 8 0 suggesting the presence of c plants starting at 7 3 6 7 ma sr3c values of fossil teeth from well dated sections in south and north america display a concomitant increase of c plants in the diets of large herbivores these results show that the late miocene expansion of c plants was global but occurred at different rates in each region while it is has been suggested that declining pc0 levels during the late neogene caused c plant expansion climate change such as an increase in summer dominated rainfall regimes globally is an alternative explanation the 6 0 soil carbonate records from south asia east africa and now also northwest argentina all show an increase of at least 3 4 in the late neogene either the result of climate change or of greater evaporation in average grassland soils

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

late cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the tian shan mountains 1 the folded neogene deposits in the northern foreland basin of the tian shan mountains provide important information about tectonic history and environmental changes of northwestern china on the basis of lithostratigraphic and magnetostratigraphic evidence we develop a new chronology for the previous studied kuitun he section our palynological study on the late miocene pliocene sediment of the dushanzi section yields new information about vegetation and climate change during the period of 8 7 2 58 ma the results indicate that steppe taxa artemisia and chenopodiaceae were generally dominant in the studied areas between 8 7 and 2 58 ma implying that a dry climate has occurred in the inland basins of northwestern china at least since 8 7 ma ago although the general climate pattern indicated by our palynological results displays to some extent of drought a warm and humid phase occurred at 5 8 3 9 ma ago this climatic optimum is comparable with the other records from the chinese loess plateau central japan the sub himalayan zone and the marine eustatic sea level rise implying this seems to be at least a regional climatic optimum

new evidence on the age of the taklimakan desert the taklimakan desert is the world s second largest shifting sand desert located in the rain shadow of the tibetan plateau the initiation of desert formation in the asian interior is one of the most prominent climate changes in the northern hemisphere during the cenozoic era dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted tibetan plateau here we report 1071 m thick neogene deposits with inter calated eolian dune sands from the only outcrop in the central taklimakan desert based on paleo magnetic measurements biostratigraphic age control and previous electron spin resonance dating results the oldest in situ eolian dune sands were confi rmed to be ca 7 ma much older than the previous reported wind blown siltstone from the southern edge of the taklimakan desert this new result indicates that desert conditions initiated ca 7 ma in the center of the tarim basin we attribute this event to the late cenozoic climatic deterioration and or to the rain shadow effect caused by late miocene uplift of the northern tibetan margin

evidence of continuous asian summer monsoon weakening as a response to global cooling over the last 8 ma abstract the asian summer monsoon asm is the dominant climate system of south and east asia however the history of monsoon intensification and the driving forces behind it are controversial wind blown sediments in mid latitude east asia and fluvial derived sediments in the northern south china sea imply contrasting asm patterns during the late cenozoic here we use pollen records from the southwest south china sea international ocean discovery program iodp site u1433 to reconstruct the asm evolution in low latitude southeast asia a slow increase in herbaceous plants since 8 ma indicates a persistent weakening of precipitation in indochina which is dominated by the asm this signal is closely associated with a consistent coniferous plant record indicating a continuous cooling trend that correlates well with sea surface temperature sst decrease in the west pacific ocean we propose that the monsoon weakening resulted in as much as a 25 reduction in precipitation over the past 8 ma in response to the northern hemisphere glaciation global cooling with some of the increase in conifers being linked to uplift of the vietnamese central highland and the se flank of the tibetan plateau in yunnan and northern vietnam

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr

formation of a rain shadow o and h stable isotope records in authigenic clays from the siwalik group in eastern bhutan we measure the oxygen and hydrogen stable isotope composition of authigenic clays from himalayan foreland sediments siwalik group and from present day small stream waters in eastern bhutan to explore the impact of uplift of the shillong plateau on rain shadow formation over the himalayan foothills stable isotope data from authigenic clay minerals 2 m suggest the presence of three paleoclimatic periods during deposition of the siwalik group between 7 and 1 ma the mean 18o value in paleometeoric waters which were in equilibrium with clay minerals is 2 5 lower than in modern meteoric and stream waters at the elevation of the foreland basin we discuss the factors that could have changed the isotopic composition of water over time and we conclude that a the most likely and significant cause for the increase in meteoric water 18o values over time is the amount effect specifically a decrease in mean annual precipitation b the change in mean annual precipitation over the foreland basin and foothills of the himalaya is the result of orographic effect caused by the shillong plateau s uplift the critical elevation of the shillong plateau required to induce significant orographic precipitation was attained after 1 2 ma c by applying scale analysis we estimate that the mean annual precipitation over the foreland basin of the eastern bhutan himalayas has decreased by a factor of 1 7 2 5 over the last 1 3 million years 2018 american geophysical union all rights reserved