dietary reconstruction of miocene gomphotherium mammalia proboscidea from the great plains region usa based on the carbon isotope composition of tusk and molar enamel abstract the miocene of the great plains of north america has long been recognized as an interval of major ecological reorganization to reconstruct the dietary response of the proboscidean gomphotherium to miocene ecosystem change in the great plains we analyzed the carbon isotope composition of 185 serial samples of tusk enamel from 17 individuals and bulk samples of posterior molars from 15 individuals of gomphotherium from localities in the great plains ranging in age from the early barstovian land mammal age ca 15 ma to the early hemphillian land mammal age ca 8 ma sets of samples from each tusk were designed to encompass about 1 year of tusk growth based on cheek tooth morphology gomphotherium is thought to be a browser with a diet primarily of dicots the mean 13 c of all samples is 9 8 1 2 indicating that the diet of gomphotherium was dominated by c 3 biomass if gomphotherium habitually foraged on water stressed plants in arid habitats which would have 13 c values higher than the average composition for c 3 and c 4 plants then all but one individual in this study consumed less than 50 c 4 biomass the maximum percentage of c 4 in the diet would be much lower if food plants had average 13 c values or if gomphotherium foraged in closed canopy habitats differences in 13 c values between specimens from the southwestern us and the great plains as well as between some coeval specimens from nebraska suggest geographic differences in either diet or typical foraging habitat the data do not indicate a trend toward inclusion of more c 4 vegetation in the diet of gomphotherium during the miocene and none of the serially sampled tusks exhibit seasonally varying 13 c profiles for most of its history in north america gomphotherium was a c 3 browser or a mixed feeder with a preference for browse our results indicate that areas of wooded habitat sufficient to support herds of large bodied herbivores remained available in the great plains through the late miocene

late oligocene miocene mid latitude aridification and wind patterns in the asian interior the asian interior has the largest mid latitude arid zone in the northern hemisphere and so has become increasingly attractive for studying the initiation and the past extent of aridification in this zone given the enormousness of the asian interior it remains unclear how old and extensive the eolian deposits might have been and what wind regimes have been responsible for the formation of the mid latitude arid zone here we report new eolian records of widespread tertiary eolian deposits in a region far from the chinese loess plateau the giant junggar inland basin of northwestern china our results demonstrate that the earliest eolian deposition initiated ca 24 ma we interpret that the tertiary eolian dust in the junggar basin was transported by westerly winds possibly from areas in kazakhstan the dust differs from the airborne dust transported by winter monsoon winds from the deserts of mongolia and northern china that accumulated on the loess plateau these results further reveal that the climate pattern similar to that of the present has prevailed at least since the latest oligocene in central asia

an 11 ma old red clay sequence on the eastern chinese loess plateau abstract older red clay deposits on the chinese loess plateau contain information of early paleomonsoon evolution and tectonic history of the ordos platform and the tibetan plateau a well conserved eolian red clay sequence was recently discovered at shilou on the eastern chinese loess plateau paleomagnetic measurements demonstrate that polarity zones recorded in the shilou red clay profile correspond well with polarity zones between c2an 1n and c5n 2n of the gpts and the basal age of the study profile is approximately 11 0 ma field observation grain size frequency distribution and quartz grain morphology suggest a wind blown origin for this sequence this indicates that the eastern loess plateau began to accumulate dust deposits at 11 ma ago implying earlier establishment of the east asian paleomonsoon probably owing to uplifting of the tibetan plateau and ongoing global cooling it also demonstrates that the eastern loess plateau belonging to the ordos platform was slowly uplifted and suffered from erosion in the early neogene and has no conserved eolian deposits older than 11 ma as in the western chinese loess plateau

spreading of red sea overflow waters in the indian ocean as a result of its remarkably high salinity and despite its small volume input remnants of red sea water rsw have been identified in the agulhas current over 6000 km distant of their source this provided the motivation to investigate the long term mean spreading of rsw throughout the indian ocean using a comprehensive set of observations taken from the national oceanographic data center archives and from the world ocean circulation experiment hydrographic program for the indian ocean after emerging from the gulf of aden into the arabian sea rsw spreads predominantly southwestward along the african continental slope as indicated by strongly inclined isohalines across the arabian sea there is some monsoon variability so that during the winter monsoon there is more rsw present in the gulf of aden and an intensification of southward spreading along the western boundary between 12 and 5 n elsewhere the intermediate depth salinity field of the indian ocean appears relatively stationary between 5 and 10 s in the region of the south equatorial current isohalines of the rsw layer become quasi zonal across the width of the indian ocean only dipping southward toward the western boundary west of 50 e south of here there is a strong tongue of rsw spreading southward through the mozambique channel and into the agulhas current these conclusions concur with previous localized investigations of intermediate water properties using a simple mixing model the percentage of rsw throughout the indian ocean was quantified it was found that the flux of salt into the gulf of aden from the red sea is similar to that estimated to cross 32 s in the agulhas current this result implies that all the rsw which is mixed into the interior of the indian ocean may eventually be exported at the western boundary furthermore it implies that rsw is the dominant component of the salt budget for the intermediate layer and that input from the indonesian seas and via diapycnic processes are small

formation and spreading of arabian sea high salinity water mass the formation and seasonal spreading of the arabian sea high salinity water ashsw mass were studied based on the monthly mean climatology of temperature and salinity in the arabian sea north of the equator and west of 80 e on a 2 2 grid the ashsw forms in the northern arabian sea during winter and spreads southward along a 24 sigma t surface against the prevailing weak zonal currents the eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of india during the southwest monsoon the northern part of the core shoals under the influence of the findlater jet while the southern part deepens throughout the year the southward extent of the ashsw is inhibited by the equatorial currents the atmospheric forcing that leads to the formation of ashsw was delineated using the monthly mean climatology of heat and freshwater fluxes monsoon winds dominate all the flux fields during summer june september while latent heat release during the relative calm of the winter november february monsoon driven by cool dry continental air from the north results in an increased density of the surface layer thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern arabian sea during winter and drive convective formation of ashsw

late miocene pleistocene aridification of asian inland revealed by geochemical records of lacustrine fan delta sediments from the western tarim basin nw china abstract continuous cenozoic deposits have accumulated in the tarim basin northwestern china and are crucial to investigating the aridification history of the asian interior which has long been thought to be linked with the growth of the tibetan plateau retreat of the para tethys sea and global cooling however less and poor climatic records from the region hinder our understanding of the questions above here we report continuous lithologic sedimentary color and geochemical caco3 and salt ions records from precisely dated late miocene early pleistocene sedimentary sequence from western tarim basin nw china they indicate that arid climate had prevailed within the basin at latest at ca 5 7 ma and gradually increased in degree until ca 3 7 ma between ca 3 7 and 2 1 ma a hydrologic event occurred which supplied more water from the tien shan after ca 2 1 ma the climate in the basin turned to hyper arid we attribute the stepwise drying of the asian inland since ca 5 7 ma to the late miocene pliocene episodic uplift of the tibetan plateau pamir and the tien shan and the connection of the pamir with the tien shan in remote response to the collision of india with asia

yunnan a refuge for trilophodont proboscideans during the late miocene aridification of east asia fossil elephantimorph proboscideans are very common in miocene faunas of east asia however their evolution and migration associated with ecological pressure have been studied little especially in china in the present article analyses of the dynamics of the elephantimorph genera of northern and southern china were performed the results indicate considerable depression of elephantimorph proboscidean diversity in northern china and continuous success of this group in the yunnan region southern china during the late miocene notably all trilophodont elephantimorph proboscideans were extinct by the end of the middle miocene in northern china and did not recover until the latest miocene however trilophodont and tetralophodont elephantimorph proboscideans coexisted throughout the late miocene in the yunnan region therefore we interpret the yunnan region as a late miocene refuge for proboscideans especially trilophodonts from severe aridity in northern china caused by uplift of the tibetan plateau and retreat of the paratethys sea further analysis of the dynamics of coexisting genera indicates that the components of elephantimorph proboscidean assemblages in northern china display patterns distinct from those of yunnan southeast asia and siwalik therefore ecological barriers between northern china and siwalik and between northern china and yunnan southeast asia are hypothesized to have existed by as early as the middle miocene the latter barrier occasionally opened e g at the boundary between the middle and late miocene and thus provided a pathway for the survival of trilophodont proboscideans escaping from ecological pressures in northern china

late neogene evolution of the east asian monsoon revealed by terrestrial mollusk record in western chinese loess plateau from winter to summer dominated sub regime article i nfo more and more evidence indicates that the onset of the east asian ea monsoon can be traced back to the oligocene miocene boundary at about 23 ma however the process of its evolution is still less well known until now here we investigate its late neogene evolution by analyzing a terrestrial mollusk sequence from the chinese loess plateau clp covering the period between 7 1 and 3 5 ma considering the modern ecological requirements of these organisms we were able to define two groups of cold aridiphilous ca and thermo humidiphilous th species representing the ea winter and summer monsoon variations respectively as previously defined in the quaternary glacial interglacial cycles variations in these two groups indicate two different monsoon dominated periods during 7 1 3 5 ma first between 7 1 and 5 5 ma the ea winter monsoon with a 100 kyr periodicity was dominant second between 5 1 and 4 ma the ea summer monsoon dominated with a 41 kyr periodicity furthermore our mollusk record yields valuable evidence for a late miocene pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated associated with a periodicity transition from weak 100 kyr to 41 kyr the strengthened winter monsoon interval with a 100 kyr periodicity is coeval with orbital scale global ice volume changes in conjunction with the uplift of the tibetan plateau which probably reinforced the winter monsoon sub regime conversely closures of the panama and indonesian seaways associated with changes in obliquity between 5 1 and 4 ma are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency favoring heat and moisture transports between low and high latitudes to allow th mollusks to grow and develop in the clp

magnetostratigraphy of the xihe loess soil sequence and implication for late neogene deformation of the west qinling mountains summary theqinlingmountainrangeformsanimportantclimatebarrierbetweensouthernandnorthern china its western part referred to as the west qinling constitutes a unit of northeastern tibetan plateau the uplift history of qinling during the neogene is still a contentious issue magnetostratigraphic results from the 150 m thick xihe loess soil sequence nl vi located on the alluvial highlands surrounding an intermontane basin from the west qinling indicate 17 reverse and 17 normal magnetozones they are correlative with the interval from chron c5n to chron c2ar in the geomagnetic polarity timescale the age of the nl vi section can thus be palaeomagnetically constrained to a period from 10 5 to 4 2 ma the middle portion of the section has been affected intermittently by surface erosion processes as loess is sensitive to any erosion that may have been induced by substratum deformation and tectonic uplift this sequence indicates that the intermontane basin ridge pattern of the west qinling had already been formed by 10 5 ma thus providing suitable topographic conditions for aeolian deposition this timing is consistent with a significant deformation phase between 14 and 10 ma reported for the tibetan plateau meanwhile the complete preservation of the nl vi loess soil sequence precludes both intense deformation of the substrate and rapid uplift of the west qinling between 10 5 and 4 2 ma although the erosion affected portion of the nl vi section reflects some degree of tectonic instability from 8 3 to 6 9 ma the intensity must have been sufficiently weak to prevent the erosion of the aeolian deposits these further suggest that the late miocene growth of the tibetan plateau has not significantly affected the west qinling thus the studied nl vi aeolian sequence provides not only independent evidence for the uplift history of the west qinling within an accurate chronological framework but also provides new insights into the tectonic changes on the northeastern tibetan plateau

the giant tortoise aldabrachelys and its bearing on the biogeography and dispersal of terrestrial biota in the western indian ocean abstract the evolution of species of giant tortoises and the nature of processes governing their dispersal in the western indian ocean have been matters of interest for some time historical records indicate that these animals were once widely distributed in the region from madagascar to the seychelles in the north and to the mascarene islands in the south new data on the status of aldabrachelys and related or supposed species and controversies regarding genetic diversity and distribution have prompted an evaluation of the islands and submerged banks in the region that during the later cenozoic might have provided refuges and or stepping stones for the spread of populations in what is now open ocean given the apparent stability of the crust in much of the area for at least the quaternary period sea level driven by climatic change and transport by ocean currents appear to be the principle factors controlling the access not only of populations of giant tortoises but also other terrestrial biota to potential refuge areas in the region the distributions of living and fossil tortoise communities are discussed four types of terrestrial oceanic refuges for migrants have been identified at the present day with the exception of aldabra high limestone islands offer only relatively small areas for colonization and all would have been drowned during interglacial sea level high stands although they have the potential for some increases in land area during the early stages of transitions to low stand as sea level fell significantly they would have become waterless pinnacles only generally accessible to organisms capable of flight volcanic islands have the same general limitations but may have remained as smaller entities when sea level was higher than at present but providing only limited land access and restricted vegetation low islands and sand cays typically of more recent origin could not have existed during periods of high sea levels but many are situated on extensive submerged banks that would have formed relatively large land areas when sea level was low major banks most of which are regarded as fragments of continental crust are currently submerged but during glacial periods would together have offered land areas in excess of 130 000 km2 providing a diverse range of terrestrial environments and vegetation access to all of these was nevertheless restricted by the distribution of ocean currents the only plausible natural means of dispersal which probably varied during glacial interludes but also by the abilities of the animals to survive long periods adrift in the ocean the distribution of these tortoises in both the fossil record and historical data provides a model for the dispersal of other terrestrial biota in the region although the present distribution and genetic characteristics of the tortoises probably reflects recent human intervention

circulation and water properties of the southwest indian ocean spring 1987 abstract the results obtrained during a cruise in the south western indian ocean from south africa to mauritius in september 1987 are presented temperature salinity oxygen and nutrients were measured at 70 ctd station 20 nautical miles apart the data perspective is enhanced by noaa satellite infrared imagery and geosat altimetry the major features encountered on the cruise were two intense cyclonic eddies in the vicinity of the mozambique ridge and the mozambique basin and which seemed to form part of the broader western boundary region of the southern indian ocean evidence was found of a significant equatoward flux at the madagascar ridge which provided input of water from higher latitudes the passage of north atlantic deep water was constrained by the bottom topography south of the madagascar ridge and this led to a reduction of its salinity and oxygen concentration the positive correlation between the ctd results and the altimetry enabled the identification tracking and description of a number of eddies in the region the transition zone of these eddies from east of madagascar to the african continent was identified and so was the apparent closure of the southern entrance of the mozambique channel to migrating eddies

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

magnetostratigraphy of the xiaolongtan formation bearing lufengpithecus keiyuanensis in yunnan southwestern china constraint on the initiation time of the southern segment of the xianshuihe xiaojiang fault the late cenozoic extensional basins in yunnan province southwestern china which are kinematically linked with the regional strike slip faults can provide meaningful constraints on the fault activity history and tectonic evolution of the southeast margin of the tibetan plateau semtp and further on the geodynamic evolution of the tibetan plateau however this has been severely impeded by the lack of precise age constraints on the timing of fault activity to better constrain the timing of fault activity and the tectonic rotation of semtp we undertook a high resolution magnetostratigraphic study on the xiaolongtan formation in the xiaolongtan basin which is located at the southern tip of the xianshuihe xiaojiang fault and is well known by the presence of hominoid lufengpithecus keiyuanensis rock magnetic experiments indicate that magnetite is the main remanence carrier correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and biostratigraphic data our correlation suggests that the xiaolongtan formation sedimentary sequence spans from chron c5ar 1r to chron c5n 2n which indicates that the age of the xiaolongtan formation ranges from 10 ma to 12 7 ma and that the ages of the two sedimentary layers possibly bearing the hominoid l keiyuanensis are 11 6 ma or 12 5 ma the basal age of the sediments is 12 7 ma which indicates that the activation of the southern xianshuihe xiaojiang fault was initiated at this time the overall mean paleomagnetic direction d 353 2 i 34 2 95 2 1 n 166 documents a counter clockwise vertical axis rotation of 8 3 with respect to eurasia which is the response to the activity of the left lateral xianshuihe xiaojiang fault

an examination of the dietary habits of platybelodon grangeri from the linxia basin of china evidence from dental microwear of molar teeth and tusks the paleodiet of shovel tusked gomphotheres from the upper middle miocene hujialiang formation of the linxia basin gansu province china was assessed via molar microwear analysis of dental enamel both adults and an ontogenetic series of individuals of platybelodon grangeri with assigned dental ages estimated via comparison of eruption and wear to that of extant elephants were analyzed mandibular tusks were also examined for microscopic scars to test a long standing hypothesis that p grangeri used its mandibular tusks to shovel substrate results show a consistent browsing signal throughout all of the age classes studied evenso scratch numbers are higher and scratch widths are greater in older individuals indicating that coarser browse was consumed in older versus younger individuals results are more similar to those of the extant forest elephant loxodonta cyclotis than to other extant forms loxodonta africana and elephas maximus mandibular tusk microwear is very fine and inconsistent with the usage of lower tusks to shovel aquatic or terrestrial substrates and more consistent with stripping vegetation than as shoveling agents

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

chronological sequence and subdivision of chinese neogene mammalian faunas six land mammal ages are recognized for the neogene of east asia the ages are based upon updated large and small mammal faunas and replace or redefine the land mammal stages erected by li et al 1984 comparisons and correlations are made to faunas in europe northern and southern asia and north america in addition methods of utilizing mammalian faunal data to define and recognize geochronologic ages are discussed

physical and biochemical aspects of the flow across the mascarene plateau in the indian ocean this paper presents results from a detailed hydrographic survey of the mascarene plateau and surrounding area undertaken by the rrs charles darwin in june july 2002 we examine how the westward flowing south equatorial current sec crosses the plateau and how the structure of the flow determines the supply of nutrients to the surface waters we find that the flow of the sec across the plateau is highly dependent on the complex structure of the banks which make up the plateau and that a large part of the flow is channelled between the saya de malha and nazareth banks furthermore the sec forms a sharp boundary between subtropical water masses from further south which are low in nutrients and waters from further north which are relatively nutrient rich overall the sec delivers relatively high levels of nutrients to the near surface waters of the central and northern regions of the plateau compared with the southern regions of the plateau this is partly due to uplifting of density surfaces through ekman suction on the northern side of the sec and partly due to the higher levels of nutrients on those density surfaces on the northern side of the sec this may drive increased production of phytoplankton in these areas which would in turn be expected to fuel increased abundances of zooplankton and higher levels of the food chain

north atlantic warming during global cooling at the end of the cretaceous differences in regional responses to climate fluctuations are well documented on short time scales e g el nino southern oscillation but with the exception of latitudinal temperature gradients regional patterns are seldom considered in discussions of ancient greenhouse climates contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years this paper shows that the north atlantic warmed by as much as 6 c 1 5 decrease in 18o values of planktic foraminifera during the maastrichtian global cooling interval we suggest that warming was the result of the importation of heat from the south atlantic decreasing north atlantic 18o values are also associated with increasing gradients in planktic 13c values suggesting increasing surface water stratification and a correlated strengthening of the north atlantic polar front if correct this conclusion predicts arctic cooling during the late maastrichtian beyond implications for the maastrichtian these data demonstrate that climate does not behave as if there is a simple global thermostat even on geologic time scales

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

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes