the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols the depth to carbonate nodular bk horizon in soils d in cm is correlated with mean annual precipitation p in mm so that bk horizons are deep in subhumid regions but shallow in semiarid regions previous quantifications of this relationship are unchanged by this new compilation of 807 soils p 137 24 6 45 d 0 013 d 2 where r 2 0 52 and standard error s e 147 mm in most north american postglacial soils the bk horizon is thin and well defined whereas in monsoonal tropical soils of pakistan and kenya the bk horizon is thick and diffuse data from 675 modern soils define the relationship between the thickness of soil with nodules t in cm and mean annual range of precipitation m in mm difference between monthly means of wettest and driest months m 0 79 t 13 71 where r 2 0 58 and s e 22 mm the relationship between carbonate nodule size s in cm and soil age a in ka is quantified by 9 radiocarbon dated soils from las cruces new mexico a 3 92 s 0 34 where r 2 0 57 and s e 1 8 k y these transfer functions are applied to reconstructing paleoclimatic change from paleocene eocene paleosols of the north horn formation and flagstaff limestone of axhandle canyon utah the terminal paleocene spike of warmth recorded by fossil plants in nearby wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in utah

atmospheric pco2 since 60 ma from records of seawater ph calcium and primary carbonate mineralogy a 60 m y record of atmospheric p co2 has been refined from knowledge of 1 secular changes in the major ion composition of seawater particularly ca and mg and 2 oscillations in the mineralogy of primary oceanic carbonate sediments both factors have had a significant impact on the chemistry of the ocean carbonate buffer system calculated atmospheric p co2 oscillated between values of 100 300 ppm and to maxima of 1200 2500 ppm from 60 to 40 ma and varied between 100 and 300 ppm from 25 ma to the present the refined p co2 values are significantly lower than previous estimates made from seawater ph data where total dissolved inorganic carbon was assumed constant and more in line with modeling and stomatal index estimations of atmospheric p co2 for the tertiary

miocene sedimentary environment and climate change in the northwestern qaidam basin northeastern tibetan plateau facies biomarker and stable isotopic evidences abstract facies biomarker and stable isotopic records from the miocene lacustrine sediments in the northwestern qaidam basin were investigated to reconstruct the miocene sedimentary environment and climatic history three distinct facies can be recognized these include the following 1 gray black laminated mudstone and marlstone which represent a semi deep fresh to semi brackish lake environment 2 gray yellowish massive mudstone marlstone and siltstone and 3 yellowish massive sandstone which imply a shallow brackish lake environment the decreasing c 27 c 31 and c 27 c 29 c 31 c 33 values the increasing acl mean chain length values of n alkanes and the vertical evolution of sedimentary environments indicate the overall intensified aridity which is considered to be an integrated result of high elevation of the himalaya tibetan system retreat of the paratethys and global cooling high fluctuations of the 18 o values and primary dolomite contents reveal the hydrologically closed paleolake with intermittently open conditions in the study area during middle late miocene the qaidam basin is suggested to be hydrologically segmented based on the stable isotopic data comparison between the study area and the northeastern area the most negative end of the oscillations of the 18 o values indicating the minimal evaporation which likely represents the isotopic ratio of the meteoric water surprisingly conveys stability in the shang youshashan and shizigou formations and displays a positive 2 5 shift this significant shift was probably due to the climatic aridification and air mass changes around 10 8 ma rather than the global cooling

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

flexural subsidence by 29 ma on the ne edge of tibet from the magnetostratigraphy of linxia basin china abstract this study provides a detailed magnetostratigraphic record of subsidence in the linxia basin documenting a 27 myr long sedimentary record from the northeastern edge of the tibetan plateau deposition in the linxia basin began at 29 ma and continued nearly uninterruptedly until 1 7 ma increasing rates of subsidence between 29 and 6 ma in the linxia basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to late oligocene late miocene time by late miocene early pliocene time a decrease in subsidence rates in the linxia basin associated with thrust faulting and a 10 clockwise rotation in the basin indicates that the deformation front of the tibetan plateau had propagated into the currently deforming region northeast of the plateau

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

uniform permian 40ar 39ar detrital mica ages in the eastern qaidam basin nw china where is the source new single grain 40ar 39ar detrital white mica ages from the lulehe section at the eastern qaidam basin yield uniform permian ages between 250 3 and 279 3 ma throughout the whole cenozoic sequence this is inconsistent with the present hinterland which is composed of early palaeozoic metamorphic units with subordinate early palaeozoic and few permian granites the new data indicate that permian tectonic units are likely more widespread at the north eastern margin of the tibetan plateau as known at present particularly within the qilian mountains the preferred explanation is that the qaidam block represents a rigid indenter which indented during late tertiary times into early palaeozoic orogenic units this is consistent with recent findings of a nw trending sinistral permian ductile shear zone and a dextral nw trending tertiary fault system close to the north eastern margin of the qaidam basin

mid eocene alluvial lacustrine succession at gebel el goza el hamra shabrawet area ne eastern desert egypt facies analysis sequence stratigraphy and paleoclimatic implications abstract this study aims to provide the depositional facies sequence stratigraphic and paleoclimatic characteristics of the mid eocene bartonian continental succession exposed at gebel el goza el hamra shabrawet area ne eastern desert egypt the studied succession consists of siliciclastic rocks followed upward by carbonate rocks detailed field observation and petrographic investigation indicate accumulation in floodplain dominated alluvial and shallow lacustrine systems the floodplain dominated alluvial facies 45 m thick is composed mainly of carbonate nodules bearing mottled mudrock with subordinate sandstone and conglomerate beds the conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits the massive laminated planner cross bedded fine to medium grained sandstone bodies interlayered within mudstone reflect sheet flood deposits the mudrocks associated with paleosols represent distal floodplain deposits the shallow lacustrine facies 15 m thick is made up of an alternation of marlstone micritic limestone dolostone and mudrock beds with charophytes and small gastropods both the alluvial and lacustrine facies show evidence of macro and micro pedogenic features pollen assemblages stable 18 o and 13 c isotopes and paleopedogenic features reflect prevalence of arid to semi arid climatic conditions during the bartonian the sequence stratigraphic framework shows an overall fining upward depositional sequence consisting of low and high accommodation systems tracts last hast and is bounded by two sequence boundaries sb 1 sb 2 conglomerate and pebbly sandstone deposits braided channel and sheet flood deposits of the lower part of the alluvial facies reflect a last mudrock and silty claystone facies distal floodplain deposits of the upper part of alluvial facies and its overlying lacustrine facies correspond to a hast the last hast and sb were formed during different accommodation to sediment supply a s ratio phases the variation in a s ratios was mainly controlled by sea level change as well as by local tectonic subsidence and uplift of the basin coincident with the reactivation of the syrian arc system during the bartonian

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

step wise change of asian interior climate preceding the eocene oligocene transition eot abstract understanding the global climate change from greenhouse to icehouse conditions at the eocene oligocene transition eot 34 million years ago requires climatic records from oceanic as well as continental realms of the key late eocene doubthouse period preceding this switch here we report integrated stratigraphic results from well dated late eocene continental mudflat to saline lake paleoenvironments of the xining basin northeastern tibetan plateau western china recording regional and global change cyclostratigraphic analysis strongly suggests continuous dominance of the 41 kyr obliquity cycle in the whole late eocene interval down to the base of polarity chron c18n 2n at 39 ma with additional input of the 100 kyr eccentricity cycle up to the base of chron c13r at 34 7 ma this might imply that high latitude climates dominated the area long before the eot probably related to incipient ice volume fluctuations furthermore our results reveal two paleoenvironmental deterioration steps preceding the eocene oligocene transition the first step occurs in the top of chron c17n 1n at 36 6 ma this age closely corresponds to 1 the high altitude pollen appearance in chron c16 2r at 36 4 ma in the same section 2 the recently dated final retreat of the tarim sea in western china and 3 a shift from precession to obliquity dominance in the atlantic ocean this near co occurrence suggests global change at this time we hypothesize this change is related to an increase in incipient ice sheet volume leading to passing threshold conditions for the high altitude pollen appearance and tarim sea retreat finally leading to decreased moisture availability in the xining basin at the second step in the base of chron c13r at 34 7 ma a substantial increase in clastic sedimentation rates is observed this might relate to increased climate variability preceding the greenhouse to icehouse transition at the eot that prevented landscapes to attain equilibrium configurations

the middle eocene to early miocene integrated sedimentary record in the qaidam basin and its implications for paleoclimate and early tibetan plateau uplift detailed analysis of whole rock geochemistry clay minerals sedimentary color and pollen in the dahonggou section northeast of the qaidam basin are investigated and the results suggest an intense weathering in the source area during the middle eocene 48 5 40 5 ma indicating a warm and humid condition the distinct decrease of chemical weathering degree in source regions began at 40 5 ma which is in agreement with the distinct decrease in redness of sedimentary sequences and the disappearance of thermophilic elements in pollen records this 40 5 ma cooling event extent demonstrated evidence for an intensification of central asian aridification which could be attributed to attainment of high elevations in southern central tibet and retreat of the paratethys from central asia in the late eocene reducing moisture transport to the qaidam basin

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

the andean type gangdese mountains paleoelevation record from the paleocene eocene linzhou basin abstract paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the cenozoic uplift of the himalayas and the tibetan plateau this paper presents new oxygen and carbon isotopic compositions from well dated tertiary paleosols lacustrine calcareous carbonates and marls from the nianbo 60 54 ma and upper pana formations 51 48 ma of the linzizong group in the linzhou penbo basin the sediments of the nianbo formation which are 180 m thick were deposited in alluvial fans braided rivers fan deltas and on nearshore to offshore lacustrine settings whereas those of the upper pana formation are 100 m thick and are comprised predominantly of proximal alluvial fan and braided river deposits correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment it is confirmed that the 18 o c and 13 c c values from nianbo and pana formations have not yet been reset by late stage diagenesis based on petrographic examination oxygen isotope of the fossil ostracodes and tectonic deformation of strata the paleoelevations are reconstructed using the corrected most negative paleosurface water 18 o psw values these imply that the linzhou area had attained an elevation of 4500 400 m during the period of the indo asian collision i e achieved a near present elevation and may form an andean type mountain range stretching the gangdese arc before collision the gangdese mountains probably maintained high elevations since at least the paleocene and could play a crucial role in the climate change in the interior of the tibetan plateau during the early cenozoic the paleogeomorphic scenario of the eocene tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin

cenozoic environmental evolution of the qaidam basin and its implications for the uplift of the tibetan plateau and the drying of central asia abstract a complete cenozoic pollen sequence of the qaidam basin has been constructed with absolute age control the cenozoic environmental evolution of the qaidam basin and its implications for the uplift of the tibetan plateau and the drying of central asia during the cenozoic era is discussed based on the interpretation of the pollen sequence the commencement of eolian deposition in central china and the change of climatic distribution pattern of china the results suggest that in the qaidam basin relatively dry climates prevailed in the eocene oligocene and pliocene pleistocene these dry periods resulted from the effects of a subtropical high pressure zone and the uplift of the surrounding mountains and the tibetan plateau respectively about a 600 km northward drift of western china has probably occurred during the late cenozoic resulting in the eocene oligocene arid climate belt twisting about six degrees of latitude the tibetan plateau reached probably 1500 m elevation by the latest miocene 8 5 ma not as high as it was thought previously the cenozoic environmental evolution of northwest china does not support the idea that the retreat of the paratethys sea played an important role in the late cenozoic drying of central asia at least not in northwest china

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

pollen evidence for an eocene to miocene elevation of central southern tibet predating the rise of the high himalaya quantifying the elevation history of the 2000 km wide tibetan plateau to an average elevation of 5 km is important for understanding key aspects of cenozoic global climate change collision tectonics and the evolution of the asian monsoon yet quantitative measures of cenozoic surface height change across tibet remain few and are sometimes contradictory here we report the first exploratory application of a modified co existence approach coa using previously published fossil pollen records to reconstruct quantitatively the cenozoic minimum palaeoaltitudes of gangdise nyainqentanglha area of the tibetan plateau gcm simulations were used to adjust eocene and miocene raw coa values for secular climate change and changes in palaeolatitude this modelled correction increased the coa derived altitudes by 895 96 m to give a minimum overall eocene altitude of 3295 3495 m the miocene correction factor of 481 25 m gave an overall minimum altitude estimate of 3000 3150 m for the holocene coa returns four equally likely elevations of 4800 4950 m 3800 3900 m 3000 3100 m and 2900 3000 m the first of these is indistinguishable from the present day regional average while the others suggest significant upslope pollen transport both the eocene and miocene palynologically derived height estimates are consistent with suggestions of significant core plateau elevation by the eocene but are likely to underestimate the true palaeoelevation due to pre himalayan upslope pollen transport

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

ophiolites synthetic seismograms and oceanic crustal structure 2 a comparison of synthetic seismograms of the samail ophiolite oman and the rose refraction data from the east pacific rise synthetic seismograms for the samail ophiolite computed using the full reflectivity technique are used to test the hypothesis that this ophiolite complex can serve as a prototype for young oceanic crust if so then this ophiolite complex can be compared with the older 45 m y bay of islands boi ophiolite to develop an aging model for oceanic crust synthetics for this young emplacement age 5 8 m y ophiolite are compared with ocean bottom hydrophone data from 0 5 and 4 5 m y age crust obtained during the rivera ocean seismic experiment second arrival phases from reflected refractions from one ophiolite velocity depth model and data from 4 5 m y age crust are in excellent agreement this agreement suggests that the samail ophiolite is a good working model for young oceanic crust earlier work has shown that the boi ophiolite is a good prototype for mature oceanic crust the boi ophiolite data also suggest that alteration of the lower oceanic crust and upper mantle is limited we use the petrologic and geochemical properties of the samail and boi ophiolites to develop a two stage model for crustal aging that directly limits alteration of the lower crust and upper mantle materials

cenozoic ostracoda and palaeoenvironments of the northeastern tarim basin western china abstract the paleogene rocks of the northeastern tarim basin in western china are composed mainly of reddish gypsum bearing coarse grained sediments and fossils are rare within these clastic facies however since the onset of the himalayan orogeny in the miocene continuous uplift of the tianshan mountains resulted in the rapid subsidence and appearance of a shallow lake environment as a result of this ostracods are widespread in the late cenozoic rocks of the tarim basin the brackish water ostracod cyprideis thrived from the mid to late miocene gypsum bearing sand and mud sediments were also deposited widely in the shallow brackish water lake environments this situation is similar to that of the qaidam basin which lies to the south of the altun mountains from the pliocene onwards the rates of subsidence and sedimentation increased the resulting regression of the lake led to disappearance of ostracods from a large part of the basin to the north of the kuqa depression the tianshan mountains underwent continuous uplift during the late himalayan orogeny as a result the quaternary lake deposits have a much greater extent than those of the pliocene and extend even further southward than those of the miocene consequently the brackish water ostracod cyprideis became dominant again during the quaternary from the end of the early pleistocene to present in this area an abundant and high diversity fauna of fresh to brackish water ostracods appeared alongside abundant cyprideis this situation is similar to that of the southern qaidam basin to the north of kunlun mountains the quaternary assemblages mainly consist of cyprideis torosa candoniella lactea candona neglecta candona arcina cypridopsis vidua limnocythere inopinata cypris subglobosa ilyocypris gibba ilyocypris biplicata eucypris inflata candoniella albicans darwinula sp and stenocypris sp under the extremely arid climate in the tarim basin freshwater originated mainly from snow melt this suggests that the tianshan mountains to the north were uplifted rapidly to above the snow line during the last million years the evolution of the ostracod assemblages indicates that the late himalayan orogeny not only controlled the deposition of biota assemblages but also took an important role in the hydrocarbon accumulation and migration

fe co3 oh in goethite from a mid latitude north american oxisol estimate of atmospheric co2 concentration in the early eocene climatic optimum abstract measured mole fractions x and 13c values of the fe co3 oh component in pedogenic goethite from a mid latitude oxisol of early eocene age 52 ma b p range from 0 0014 to 0 0064 and 20 1 to 15 4 respectively these values of x imply that concentrations of co2 gas in the paleosol were 7400 to 34 000 ppm 13c and 1 x are correlated and define a linear soil co2 diffusive mixing line with a positive slope such positive slopes are characteristic of mixing of two isotopically distinct co2 endmembers atmospheric co2 and co2 from oxidation of soil organic matter from the intercept of the mixing line it is calculated that the 13c value of organic matter in the ancient soil was 28 0 the magnitude of the slope implies an early eocene atmospheric co2 concentration of 2700 ppm a simple model for forest soils suggests that a canopy effect may cause atmospheric co2 concentrations deduced from pedogenic minerals to underestimate the actual concentrations of atmospheric co2 if a significant forest canopy were present at the time of formation of pedogenic goethite in the ione fm the concentration of 2700 ppm calculated for atmospheric co2 could be slightly low but the underestimate is expected to be

lower eocene alluvial paleosols pedogenic development stratigraphic relationships and paleosol landscape associations abstract two kinds of cumulative floodplain paleosols red and grey paleosols formed on overbank deposits of the willwood formation in the sand coulee area of the bighorn basin wyoming although both kinds experienced down profile iron movement due to seasonal saturation of a clay rich a horizon the red paleosols were better drained and their b horizons were rubified various redoximorphic features indicate that the grey paleosols were poorly drained the red paleosols show progressive increases in the degree of profile development away from an associated channel sandstone a paleosol landscape relationship termed pedofacies by bown and kraus 1987 although the grey paleosols show relatively systematic changes in hydromorphy consistent pedofacies changes were not recognized furthermore no lateral relationship between the red and grey paleosols was observed these features suggest that because of the retarding effects of poor drainage on soil weathering poorly drained soils are not amenable to pedofacies modelling and that the landscape associations of well drained and poorly drained soils may be difficult to document without unusually extensive exposures results of this study also show that the pedofacies model is limited by sediment accumulation rates and the kind of fine grained facies on which paleosols developed although readily observable in sand coulee pedofacies are difficult to recognize in the elk creek area where accumulation rates were approximately half as rapid as in sand coulee the attainment of steady state conditions is believed to have obscured pedofacies in the elk creek area finally pedofacies are only developed on true overbank deposits which in the willwood formation and probably many other ancient alluvial sequences make up only a fraction of the fine grained deposits only immature soils formed on the remainder of the fine grained facies because they were deposited very rapidly as a result of channel avulsion

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

role of the westerlies in central asia climate over the cenozoic abstract there remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in central asia over the cenozoic tibetan plateau uplift variable monsoonal strength paratethys retreat and reduced moisture transport from the north atlantic have all been hypothesized to drive aridity in central asia distinguishing between these mechanisms requires knowledge of moisture transport pathways to central asia through time presently central asia receives recycled high 18 o moisture that has been transported across eurasia by the westerlies while southern tibet receives low 18 o moisture distilled by passage over the himalaya here we reconstruct the spatial distribution of oxygen isotopes in precipitation since the early eocene using a compilation of 18 o data from 2750 sedimentary carbonate samples across asia the spatial distribution of paleo precipitation 18 o remains remarkably similar through time with low 18 o values in the lee of the himalaya in southern tibet constant high 18 o values in central asia and intermediate values on the central plateau despite independent evidence for substantial changes in both topography and climate through time these results suggest that a long standing topographic feature has continuously blocked southerly moisture and subsequent progressive uplift of the tibetan plateau has had little impact on central asian climate in turn southerly monsoonal moisture has never persistently extended northward of the central plateau as a result the westerlies have remained the dominant moisture source in central asia since at least the early eocene therefore sedimentary aridity indicators in central asia such as loess deposition are controlled by the trans eurasian westerly moisture flux rather than tibetan plateau uplift

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

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

avulsion deposits in lower eocene alluvial rocks bighorn basin wyoming abstract eocene alluvial rocks in the northern bighorn basin can be subdivided into three major kinds fine grained deposits on which cumulative paleosols developed lithologically heterogeneous packages associated with immature paleosols and major sheet sandstone bodies the heterogeneous packages which alternate vertically with the cumulative paleosols are dominated by fine grained deposits and also contain ribbon sandstone bodies and thin 1 m sheet sandstone bodies most ribbon sandstones are less than 3 m thick and are more common in the middle and upper parts of the packages cut and fill deposits with fine grained fills are locally important because the lithologic packages are readily apparent in the field because of the immature or simple paleosols developed on the fine grain d facies they are referred to as simple paleosol packages the major sheet sandstones were deposited by meandering trunk rivers and locally overlie and truncate the other deposits contrary to classical models of meandering streams only a portion of the fine grained rocks in the study area were deposited by overbank flooding of a trunk channel on the basis of their stratigraphic position and few ribbon sandstones the upper parts of some simple paleosol packages are interpreted as ancient levee deposits associated with a trunk channel farther from the trunk channel overbank floods deposited alluvium on which the cumulative paleosols formed the greater parts of the simple paleosol packages including their fine grained deposits were deposited rapidly during channel avulsion ribbon sandstone bodies represent ancient splay channels on the avulsion belt simple paleosol packages in the willwood formation support the contention of smith et al 1989 that n many meandering river systems a significant portion of the fine grained deposits were deposited as the trunk channel avulsed deposits that resemble the simple paleosol packages may provide a means of recognizing avulsion episodes in other alluvial sequences

calibration of the clumped isotope geothermometer in soil carbonate in wyoming and nebraska usa implications for paleoelevation and paleoclimate reconstruction abstract recent work has shown that soil carbonates typically form as the soil dries after seasonal rainfall and therefore record seasonal aspects of climate rather than mean annual conditions because soil carbonate formation is closely related to the timing of local rainfall and drying it is necessary to understand the formation seasonality and temperature and soil water o 18 values recorded in modern soil carbonate before accurate estimates of stable isotope based paleoelevation and paleoclimate can be made here we study carbonate clumped isotope 47 and oxygen isotope o 18 compositions of modern soil carbonates and seasonal variations of soil moisture and temperature of nearby climate stations in wyoming and western nebraska usa to understand the seasonality of soil carbonate formation in semi arid to arid temperate montane settings we find that soil carbonate clumped isotope temperatures t 47 are 3 5 c higher than mean summer air temperature and are similar to or higher than average summer soil temperature at depths 40 cm soil moisture dramatically decreases in early summer following the cessation of spring rains and snowmelt and shows only brief increases after major mid late summer rain events soil water o 18 values calculated using carbonate o 18 and t 47 values are similar to the o 18 values of local mean summer precipitation these lines of evidence suggest that soil carbonates in our study area formed during times of soil dewatering in early summer and after major summer storm events in mid late summer and in or near equilibrium with mean summer precipitation o 18 values t 47 values of modern soil carbonates are inversely correlated with elevation with a lapse rate 4 0 c km similar to the modern air and soil temperature lapse rates calculated soil water o 18 values also are inversely correlated with elevation with a lapse rate of 3 7 km sample elevations can be reconstructed using both t 47 values and calculated soil water o 18 values between 900 m and 2600 m in our studied area with an accuracy of 0 5 km or less however o 18 values of precipitation and soil water reflect the complex interaction of climatic environmental and topographic conditions prior to carbonate formation whereas t 47 values may be influenced by site specific conditions we suggest that both soil carbonate t 47 values and calculated soil water o 18 values should be used to corroborate paleoelevation reconstruction and the seasonal nature of soil carbonate formation should be considered when soil carbonate t 47 values and o 18 values are applied for paleoclimate reconstruction

the clumped isotope geothermometer in soil and paleosol carbonate we studied both modern soils and buried paleosols in order to understand the relationship of temperature t c 47 estimated from clumped isotope compositions 47 of soil carbonates to actual surface and burial temperatures carbonates from modern soils with differing rainfall seasonality were sampled from arizona nevada tibet pakistan and india t c 47 obtained from these soils shows that soil carbonate forms in the warmest months of the year in the late morning to afternoon and probably in response to intense soil dewatering t c 47 obtained from modern soil carbonate ranges from 10 8 to 39 5 c on average t c 47 exceeds mean annual temperature by 10 15 c due to summertime bias in soil carbonate formation and to summertime ground heating by incident solar radiation secondary controls on t c 47 are soil depth and shading site mean annual air temperature maat across a broad range 0 30 c of site temperatures is highly correlated with t c 47 from soils following the equation maat c 1 20 t c 47 0 21 72 r 2 0 92 where t c 47 0 is the effective air temperature at the site estimated from t c 47 the effective air temperature represents the air temperature required to account for the t c 47 at each site after consideration of variations in t c 47 with soil depth and ground heating the highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from t c 47 in paleosol carbonate assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites t c 47 0 decreases systematically with elevation gain in the himalaya following the equation elevation m 229 t c 47 0 9300 r 2 0 95 assuming that temperature varied similarly with elevation in the past this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates we also measured t c 47 from long sequences of deeply buried 5 km paleosol carbonate in the himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition we found that paleosol carbonate faithfully records plausible soil t c 47 down to 2 5 4 km burial depth or 90 125 c deeper than this and above this temperature t c 47 in paleosol carbonate is reset to temperatures 40 c we observe 40 c as the upper limit for t c 47 in modern soils from soil depths 25 cm and therefore that t c 47 40 c obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present or non primary temperatures produced by resetting during diagenesis if representative this limits the use of t c 47 to reconstruct ancient surface temperature to modestly buried 3 4 km paleosol carbonates despite diagenetic resetting of 47 values 18 o and 13 c values of the same deeply buried paleosol carbonate appear unaltered we conclude that solid state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open system exchange of paleosol carbonate with significant quantities of water or other phases

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

climate model sensitivity to atmospheric co2 levels in the early middle paleogene this study examines the sensitivity of the slab ocean version of the national center for atmospheric research climate system model with revised eocene geography orography and vegetation to changing carbon dioxide co2 levels we compare model results with temperature proxies from the geologic record for the early middle paleogene we ran three modeling experiments with co2 levels at 500 1000 and 2000 ppm and all with atmospheric methane levels of 3 5 ppm surface temperatures in the two higher co2 scenarios are warmer than those of the 500 ppm scenario the largest warming with increasing co2 occurred in the high latitudes particularly in the northern hemisphere during the wintertime compared to the 500 ppm case arctic wintertime temperatures increased by 10 c for the 1000 ppm scenario and 20 c for the 2000 ppm scenario the 1000 and 2000 ppm scenarios produced mean annual and cold month mean temperatures in mid and high latitudes that are much more compatible with the climate interpretations from eocene flora especially for data from the southern hemisphere tropical sea surface temperatures ssts in the 2000 ppm scenario however are still 4 c higher than the warmest temperatures inferred from proxy data the better match between temperatures in the high co2 modeling scenario and high latitude climate interpretations is consistent with the idea that the co2 levels during the eocene were high at least 3 4 times the pre industrial value of 280 ppm but the discrepancies in the tropics suggest that sst estimates from proxies are too low or that the models lack some tropical cooling mechanism that was important at this time

high resolution magnetostratigraphy of the neogene huaitoutala section in the eastern qaidam basin on the ne tibetan plateau qinghai province china and its implication on tectonic uplift of the ne tibetan plateau abstract the closed inland qaidam basin in the ne tibetan plateau contains possibly the world s thickest 12 000 m continuous sequence of cenozoic fluviolacustrine sedimentary rocks this sequence contains considerable information on the history of tibetan uplift and associated climatic change however work within qaidam basin has been held back by a paucity of precise time constraints on this sequence here we report on a detailed paleomagnetic study of the well exposed 4570 m huaitoutala section along the keluke anticline in the northeastern qaidam basin where three distinct faunas were recovered and identified from the middle miocene through pliocene constrained by these faunal ages the observed thirty three pairs of normal and reversed polarity zones can be readily correlated with chrons 2n 5br of the gpts this study assigns the age of the section to the interval between ca 15 7 ma to 1 8 ma in addition the widely used stratigraphic units the xia youshashan shang youshashan the shizigou and qigequan formations were formed at 15 3 ma 15 3 8 1 ma 8 1 2 5 ma and

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

anatomy and evolution of a lower cretaceous alluvial plain sedimentology and palaeosols in the upper blairmore group south western alberta canada the lower cretaceous albian upper blairmore group is part of a thick clastic wedge that formed adjacent to the rising cordillera in south western alberta regional transgressive intervals are superimposed on the overall regressive succession alluvial conglomerates sandstones and mudstones were deposited in east north eastward draining fluvial systems orientated transverse to the basin axis five facies associations have been identified igneous pebble conglomerate thick sandstone interbedded lenticular sandstone and mudstone thick mudstone with thin sandstone interlayers and fossiliferous sandstone and mudstone the facies associations are interpreted as gravelly fluvial channels sandy fluvial channels sand dominated floodplains mud dominated floodplains and marine shoreline deposits respectively five types of palaeosols are recognized in the upper blairmore group based on lithology the presence of pedogenic features clay coatings root traces ferruginous nodules slickensides carbonate nodules and degree of horizonization the regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution in source proximal areas palaeosol development was inhibited by high rates of sedimentation in source distal locations poor drainage resulting from high watertables low topography and lower rates of sedimentation also inhibited palaeosol development the best developed palaeosols containing bt horizons occur in intermediate alluvial plain positions tectonic hinge zone where the floodplains were most stable due to a balance between sedimentation erosion and subsidence rates extrapolating from the upper blairmore group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis at the hinge zone soil development is controlled primarily by climate and tectonics and their effect on sediment supply whereas closer to the palaeoshoreline relative sea level fluctuations resulting in poor drainage may have a more significant influence

magnetostratigraphy of cenozoic deposits in the western qaidam basin and its implication for the surface uplift of the northeastern margin of the tibetan plateau abstract thick cenozoic deposits in the northwestern qaidam basin record erosion of the altyn tagh and high terrain west of that basin and presumably the concurrent growth of the northeastern tibetan plateau a detailed magnetostratigraphic study of the huatugou section northwestern qaidam basin reveals that this section spans the period from 30 to 11 ma magnetostratigraphic and sedimentological studies indicate that the accumulation rate abruptly increased near 15 ma the acceleration in sedimentation rate suggests enhanced tectonic deformation in the qaidam basin since 15 ma that may have begun simultaneously with accelerated deformation along the altyn tagh kunlun and haiyuan faults which contributed to the growth history of the qaidam basin and its surroundings since 15 ma

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

climatic and tectonic uplift evolution since 7 ma in gyirong basin southwestern tibet plateau clay mineral evidence climate evolution associated with the uplift in gyirong southern margin of the tibetan plateau was investigated based on the clay mineralogy of the gyirong sediments using x ray diffraction and scanning electron microscopy methods the chlorite illite kaolinite smectite ratio and the illite crystallinity index suggest the trend of paleoclimate evolution in gyirong basin during 7 1 7 ma bp with a warm and humid climate in 7 0 5 8 ma a relative cool and dry climate in 5 8 5 5 ma a relative warm and humid climate in 5 5 2 5 ma and a much warmer climate in 2 5 1 7 ma respectively the fluctuating kaolinite smectite index and calcite content and the frequent occurrence of gypsum in the episode of 6 7 5 5 ma suggest intense climatic fluctuations between humid and more seasonal humid conditions five peaks exhibit at 5 8 4 9 4 3 3 6 and 2 5 ma in the curves of illite and chlorite content and illite crystallinity the intense uplift and tectonic forced cooling at 5 8 and 4 3 ma were indicated by the high illite crystallinity index and illite and chlorite content a remarkable increase in illite and chlorite content associated with only little increase in illite crystallinity at 3 6 ma indicates a rapid uplift but no significant climate change and a sharp increase in illite crystallinity while small change in illite and chlorite content at 2 5 ma suggests that no remarkable relief was produced by the uplift which may take place in the whole south tibet plateau while cooling at 4 9 ma is probably a record of the global climate cooling

hot or not impact of seasonally variable soil carbonate formation on paleotemperature and o isotope records from clumped isotope thermometry quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of earth surface temperature and soil water composition from paleosols pedogenic carbonates typically have been assumed to form at mean annual temperature but recent work suggests warm season bias in carbonate formation could impact the interpretation of d 18 o values and carbonate

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

provenance of tertiary sandstone in the northern qaidam basin northeastern tibetan plateau integration of framework petrography heavy mineral analysis and mineral chemistry abstract an exceptionally thick cenozoic sedimentary succession has developed in the qaidam basin of the northeastern tibetan plateau the provenance remains enigmatic thus more precise investigations are needed an integrated study of sandstone framework petrography heavy mineral analysis and mineral chemistry was adopted to perform provenance analysis of the tertiary sandstones in the northern qaidam basin no individual method exists that can provide comprehensive provenance interpretations on spatial and temporal variations based on three types of data three depositional areas can be distinguished sandstones of area a exhibit relatively high abundances of quartz garnet and zircon as well as relatively high textural maturity implying long distance sources multi composition garnets and tourmalines reveal derivations of metasedimentary rocks and intermediate acidic igneous rocks sandstones of area b are rich in metamorphic lithic fragments epidote and garnet a dominance of fe rich garnets with low mg low mn and variable ca contents and dravites demonstrates predominant derivation of metasedimentary rocks therefore the north qaidam and south qilian terranes are potential source areas for these two depositional areas additionally high metamorphic heavy mineral abundances in the upper formations imply increasing contributions of these two metamorphic belts during the tertiary tectonic uplift however sandstones of area c are characterized by relatively high abundances of feldspar igneous heavy minerals and high fe mn garnet which suggest a main source of igneous rocks the altun and qilian mountains are potential source regions furthermore increasing amounts of feldspar and igneous heavy minerals in the upper formations indicate a significant presence of igneous parent rocks which are most likely a response to the multi stage uplift events in the altun mountains since the early eocene

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

middle miocene to earliest pliocene sedimentological and geochemical records of climate change in the western qaidam basin on the ne tibetan plateau global cooling tibetan plateau uplift and the retreat of the para tethys sea have long been thought to be the key controls of the cenozoic climate change in the asian inland however due to the scarcity of long term palaeoclimate records it is not entirely clear which of these factors plays the major role here we present new sedimentological and geochemical proxy records toc carbonate so42 and cl from a 1040 m late cenozoic sedimentary sequence ca 17 to 5 0 ma from the western part of the qaidam basin the largest inland basin on the ne tibetan plateau geochemical records reveal an evident two stage change from ca 17 ma to 11 1 ma phase i the proxies show an upward decrease of carbonate content and toc concentration and a persistent increase in the concentration of the soluble anions so42 and cl even though superimposed high frequency fluctuations are evident from ca 11 1 ma to 5 0 ma phase ii the average concentrations of so42 and cl are higher than those from phase i and a sharp decrease in the carbonate content occurred the sedimentological and geochemical proxy records demonstrate that the qaidam basin has experienced increased aridity since ca 11 1 ma we suggest that the miocene global cooling exerted a significant influence on the drying of the qaidam basin by decreasing evaporation rates and water vapour concentrations in the atmosphere the mio pliocene episodic and persistent uplift of the ne tibetan plateau exerted an important influence superimposed upon this driving force while during ca 11 1 to 8 ma the rapid uplift of the altun shan might have played a key role in climate change of the qaidam basin c 2013 elsevier b v all rights reserved

paleoelevation reconstruction using pedogenic carbonates paleoelevation reconstruction using stable isotopes although a relatively new science is making a significant contribution to our understanding of the recent growth of the world s major orogens in this review we examine the use of both light stable isotopes of oxygen and the new clumped isotope 47 carbonate thermometer in carbonates from soils globally the oxygen isotopic composition 18 o of rainfall decreases on average by about 2 8 km of elevation gain this effect of elevation will in turn be archived in the 18 o value of soil carbonates and paleoelevation can be reconstructed provided 1 temperature of formation can be estimated 2 the effects of evaporation are small 3 the effects of climate change can be accounted for and 4 the isotopic composition of the carbonate is not diagenetically altered we review data from modern soils to evaluate some of these issues and find that evaporation commonly elevates 18 o values of carbonates in deserts an effect that would lead to underestimates of paleoelevation some assessment of paleoaridity using qualitative indicators or carbon isotopes from soil carbonate is therefore useful in evaluating the oxygen isotope based estimates of paleoelevation sampling from deep 50 cm in paleosols helps reduce the uncertainties arising from seasonal temperature fluctuations and from evaporation the new clumped isotope 47 carbonate thermometer expressed as 47 offers an independent and potentially very powerful approach to paleoelevation reconstruction in contrast to the use of 18 o values nothing need be known about the isotopic composition of water from which carbonate grew in order to estimate of temperature of carbonate formation from 47 values using assumed temperature lapse rates with elevation paleoelevations can thereby be reconstructed case studies from the andes and tibet show how these methods can be used alone or in combination to estimate paleoelevation in both cases the potential for diagenetic alteration of primary carbonate values first has to be assessed clear examples of both preservation and alteration of primary isotopic values are available from deposits of varying ages and burial histories 47 values constitute a relatively straightforward test since any temperature in excess of reasonable surface temperatures points to diagenetic alteration for 18 o values preservation of isotopic heterogeneity between different carbonate phases offers a check on diagenesis results of these case studies show that one area of south central tibet attained elevations comparable to today by the late oligocene whereas 2 7 0 4 km of uplift occurred in the bolivian altiplano during the late miocene

the paleoaltimetry of tibet an isotopic perspective stable isotopes provide a valuable perspective on the timing of elevation change of the tibetan plateau we begin our paper by looking in depth at isotopic patterns in modern tibet we show that the 18 o value of surface waters decreases systematically up the himalayan front in central nepal by about 2 8 km in agreement with the patterns documented and modeled by previous research on the tibetan plateau itself there is no apparent correlation between elevation and the 18 o value of flowing surface waters both surface waters and soil carbonates display a northward increase in 18 o values of about 1 5 north of the himalayan crest even though elevation increases modestly the isotopic increase with latitude reduces the isotope elevation gradient for water in the northernmost plateau to 1 to 2 km carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau temperature estimates from clumped isotope 47 analyses of modern soil carbonates significantly exceed mean annual air t and modeled maximum summer soil temperatures by 15 8 2 8 and 9 7 2 5 c respectively similarly elevated temperatures best account for the 18 o values observed in modern soil and lake carbonates we recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude corrected isotopic values with one notable exception our revised model produces paleoelevation estimates very close to previous estimates the exception is the reconstruction from late eocene age deposits at xoh xil for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed therefore there is no evidence for northward progression through time of tibetan elevation change instead the available but admittedly very scanty evidence suggests that much of tibet attained its modern elevation by the mid eocene a truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across tibet especially in the center and north and for 15 ma

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

atmospheric response to atlantic tropical instability waves in community atmosphere model version 3 1 tropical instability waves tiws are 20 to 40 day waves that appear along the sea surface temperature sst front of the equatorial cold tongues in this study we investigate the atmospheric planetary boundary layer response to tiw induced sst variations in the tropical atlantic ocean using community atmosphere model version 3 cam3 developed at the national center for atmospheric research and compare the model simulation with available satellite measurements cam3 is used to simulate the response to atlantic tiws with t85 and t42 horizontal resolutions forced with daily tropical rainfall measuring mission microwave imager tmi ssts and t85 horizontal resolution forced with weekly tmi and reynolds ssts all four runs exhibit an atmospheric response to the sst anomalies but the amplitude of the response is different in each case the model simulates winds convergence column integrated water vapor and precipitation perturbations associated with tiws that are similar in many respects to the satellite observations however the wind convergence and divergence anomalies in the satellite observations are located west of the sst anomalies in the cam3 simulations the wind convergence is more in phase with sst anomalies differences between the observations and the model simulations appear to be due to both differences in the boundary layer response and differences in the horizontal advection process

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

vertebrate paleontology biostratigraphy geochronology and paleoenvironment of qaidam basin in northern tibetan plateau abstract qaidam basin is the largest terrestrial basin of the tibetan plateau and has the most continuous sedimentary record in the cenozoic although constituting the first known fossil vertebrates of the tibetan plateau and discovered in early scientific expeditions in the 1930s mammalian fossils from qaidam basin have not played a significant role in studying the basin stratigraphy our explorations in the qaidam basin during the past 8 years have resulted in the first well documented collection of fossil vertebrates from there in addition to being the best organisms for terrestrial biostratigraphy in the cenozoic the new fossil vertebrates offer a unique window into the ancient biotas that chronicle the late cenozoic uplift of the plateau and associated environmental changes here we establish for the first time a faunal sequence of early oligocene to early pliocene age four mammalian faunas are recognized olongbuluk mammal fauna middle miocene tuosu mammal fauna early late miocene shengou mammal fauna early late miocene and huaitoutala mammal fauna early pliocene all four mammal faunas can be directly or indirectly tied to a paleomagnetic section in the olongbuluk huaitoutala area permitting robust calibration of the chronology of these faunas at least four fish faunas are also found lulehe fish fauna late early to early late oligocene shengou fish fauna early late miocene eboliang fish fauna late late miocene to early pliocene and yahu fish fauna early pliocene the fish faunas represent the only records of their respective times in the tibetan plateau and thus by themselves cannot be used for age determination however these fish faunas are either integrated into paleomagnetic sections or directly tied to mammal faunas of known ages permitting independent assessment of their chronology zoogeographically qaidam mammal faunas show increasing endemism through time presumably related to topographic barriers formed by the growth and uplift of the tibetan plateau and to climatic changes triggered by the same tectonic process fishes that were trapped in internally drained basins developed pachyostotic morphologies caused by hypersaline environments which are associated with the increasing aridity of the tibetan plateau since early pliocene

palaeoprecipitation record using o isotope studies of the himalayan foreland basin sediments nw india abstract the himalayan foreland basin sediments were deposited during a crucial time period in the himalayan orogeny this period in the tertiary has become major focus of research because of the large scale uplift of the himalayan range which has greatly modified the climate of the asian continent the present south asian monsoonal climate is believed to be a consequence of himalayan uplift during this period also the himalayan orogeny comprises a major regional tectonic event of the earth hence the study of these himalayan foreland basin sediments are not only significant in revealing the palaeoclimatic history of the asian continent but also paves a way for understanding of the effects of himalayan orogeny on global climate here we report a palaeoprecipitation history of the ramnagar sub basin since miocene times and its regional correlation to other sub basins of the himalayan mountain belt an attempt has been made to use oxygen isotope ratios of pedogenic carbonates in siwalik palaeosols as proxy palaeo recorders to deduce the palaeoclimatic history of the jammu region in the ramnagar sub basin for the first time a total of 141 pedogenic carbonates have been analyzed from three siwalik sections covering a lateral stretch of approximately 40 50km along strike the 18 o values vary from 12 31 to 5 89 and when plotted against age indicate that 18 o values on average become 2 enriched from the oldest to the youngest analyzed sediments except for largely depleted 18 o values around 10 ma 5 ma and 1 8 ma this 2 increase in calculated 18 o values could have been possible by an 3 c increase in mean annual air temperature conversely the largely negative 18 o values indicate periods of intense rainfall or stronger monsoonal conditions an increase of 2 6 in 18 o values has been found from the 10 ma rainfall event to that at 1 8 ma which indicates a reduction of 173 mm in rainfall intensity and amount hence precipitation reconstructions indicate a progressive increase in aridity from 12 ma to recent excluding a short term increases in rainfall or monsoon intensity at around 10 ma 5 ma and 1 8 ma this pattern of palaeoprecipitation change is similar to the changes documented in other sub basins of the himalayan mountain range further monsoon intensification at around 10 ma 5 ma and 1 8 ma is also observable in various other proxy records thereby suggesting the role of significant regional tectonism in the evolution and intensification of the present south asian monsoon climate our results indicate that from the mid miocene to recent except for the periods of largely depleted 18 o values the average 18 o value increased by 2 the general increase in average 18 o values from lower to upper siwalik sediments can be explained by changes in both continentality and latitude of the moisture source it seems likely that this long term increase in 18 o values was due to the uplift of the himalayas and the tibetan plateau in the north which acted as a barrier to the passage of airmasses from central asia in the north thereupon with time restricting the source of airmasses to the south from the indian ocean

a late eocene palynological record from the hoh xil basin northern tibetan plateau and its implications for stratigraphic age paleoclimate and paleoelevation abstract the hoh xil basin lying in the central tibetan plateau is key to understanding the cenozoic tectonics paleoelevation and paleoclimate changes that have occurred in the tibetan plateau since the collision of the indian and asian tectonic plates however the stratigraphic age and paleoelevation indicated by the sediments of the hoh xil basin remain hotly debated here we report on one palynological record from the tth c section extracted from the yaxicuo group the stratigraphic unit between the fenghuoshan and wudaoliang groups and analyze its implications for stratigraphic age paleoclimate and paleoelevation in the hoh xil basin the record shows that palynological taxa are mainly dominated by xerophytic ephedripites nitrariadites nitrariapollis and chenopodipollis with few ferns and conifers rich morphologies correspond well with those in the xia ganchaigou formation fm of the qaidam basin to the north palynological percentages are well correlated with the middle member of the xia ganchaigou fm in the qaidam basin as well as the lower member of the mahalagou fm in the xining basin to the northeast the ages of the middle member of the xia ganchaigou and lower member of the mahalagou fms from these two basins are both identical to the bartonian stage 40 37 ma of the late eocene according to their respective high resolution magnetostratigraphic dating this means that the age of the yaxicuo group at least covers the bartonian stage besides the qaidam and xining basins the palynological assemblages of the tth c section are also similar to those of three other sites the jiuquan tu ha and hetao basins indicating similarly arid climates dominated by a northwestern chinese subtropical high and a relatively low paleoelevation in the hoh xil basin mostly

qaidam basin paleosols reflect climate and weathering intensity on the northeastern tibetan plateau during the early eocene climatic optimum abstract as an important geological archive paleosols have been widely used in reconstruction of paleoenvironmental and paleoclimatic conditions in this study we undertook detailed analyses of the clay mineralogy and carbon and oxygen isotopic compositions of pedogenic carbonates in a series of 13 paleosol horizons within a fluvial section of the eocene 52 44 ma lulehe formation in the qaidam basin pedogenic smectite and illite smectite i s mixed layer minerals are the predominant clay minerals in the paleosols suggesting that the early eocene paleoclimate of the qaidam basin was strongly seasonal with warm wet summers the high levels of pedogenic smectite production and high atmospheric pco2 reconstructed from soil carbonate nodule 13c mean 7 1 0 8 are consistent with elevated temperatures during the early eocene climatic optimum eeco coeval paleosol carbonate nodules yield estimated paleo surface water compositions 18opsw of 7 9 to 6 0 vsmow which are significantly higher than the 18o value of modern summer precipitation in the qaidam basin the estimated temperature difference 5 0 c cooling implies uplift of the study area by nearly 1000 m to its current average elevation of 3000 m above sea level this paleoelevation estimate agrees with modern meteoric water isotopes of global network of isotopes in precipitation gnip sites in asia in the same elevation range

stable isotope evidence for topographic growth and basin segmentation implications for the evolution of the ne tibetan plateau lithologic magnetostratigraphic and stable isotope records from the neogene xunhua and linxia basins along the tibetan plateau9s northeastern margin suggest that topography in the intervening jishi shan mountain range began to develop between 16 and 11 ma perturbations to local climate patterns resulting from the evolution of local topography are tracked through comparison of stable isotope compositions of calcareous basin fill materials across the jishi shan similarity of isotopic compositions is interpreted to reflect the presence of integrated basins whereas distinct isotopic compositions reflect unique basin hydrologies divergent isotope trends develop between ca 16 and 11 ma and are indicative of hydrologic separation in the adjacent xunhua and linxia basins and increased aridity in the leeward xunhua basin the development of aridity in the lee of the growing topography along the plateau9s northeast margin highlights the importance of evaporative enrichment in this extremely continental setting and explains the presence of anomalously positive 18 o values in modern rainfall our findings add to a growing body of evidence for deformation along the plateau9s north and northeastern margins in the middle to late miocene

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

magnetostratigraphy of paleogene sediments from northern qaidam basin china implications for tectonic uplift and block rotation in northern tibetan plateau abstract we have carried out a detailed magnetostratigraphic study of tertiary sediments in the northern margin of the qaidam basin northern tibetan plateau a total of 400 paleomagnetic samples with an interval of about 2 m were collected from the shanggancaigou and xiagancaigou formations in the hongsanhan section stepwise thermal demagnetization was used to isolate the magnetic components in these samples a higher temperature component htc was separated between 300 and 680 c from most of samples positive fold and reversal tests suggest a primary origin for the htc a magnetic polarity sequence is established and then compared with the geomagnetic polarity time scale ostracoda assemblages and also a fission track age from an adjacent section suggest a tertiary age of the shanggancaigou and xiagancaigou formations in the hongsanhan area the magnetozones in the xiagancaigou formation may correspond to subchrons c16n c18 ranging from 40 to 35 5 ma mid eocene and the shanggancaikou formation to subchrons c8 2n c15 age from 35 5 to 26 5 ma late eocene to late mid oligocene the accumulation of sandy conglomerate and conglomerate layers on top of the shanggancaikou formation and an abrupt increase in sedimentation rates are probably resulted from the main uplift of the north qaidam at about 30 ma when compared with coeval directions expected from eurasia the mean declinations indicate a slight vertical axis rotation of the northern qaidam basin since the mid eocene sinistral shear strain may be concentrated on the altyn tagh fault atf

winter and summer temperatures of the early middle eocene of france from turritella δ18o profiles the mean annual range of temperature is from a climatological point of view at least as important as the mean annual temperature in order to examine intra annual temperature variations in the warm early cenozoic we have analyzed stable oxygen and carbon isotopes along the transect of growth on excellently preserved specimens of the gastropod turritella imbricataria and the bivalve venericardia imbricata from sedimentary rocks of early middle eocene age ca 46 ma in the paris basin turritella shell growth is fast throughout the year and the isotopic records give the first detailed information about early middle eocene seasonal variations the oxygen isotope profiles indicate winter temperatures of about 14 c and summer temperatures of up to 28 c i e a seasonality indistinguishable from the present situation but an annual temperature some 10 c higher our results contradict the opinion that the climate during this period was more equable than that of today