the oligo miocene qom formation iran evidence for an early burdigalian restriction of the tethyan seaway and closure of its iranian gateways in the central iranian esfahan sirjan and qom basins sedimentation of the oligo miocene qom formation took place on extensive mixed carbonate siliciclastic ramps during this time both basins were positioned at the eurasian margin of the tethyan seaway which connected the western and eastern regions of the tethys ocean at least until the late burdigalian during the so called terminal tethyan event the tethyan seaway was then closed due to the collision of the african arabian and iranian eurasian plates facies analysis of the sedimentary record of both basins indicates paleoenvironments ranging from terrestrial to open marine settings including mangrove restricted inner shelf lagoon seagrass meadow reefal and deeper offshore environments recognition of eight depositional sequences and elaboration of an integrated biostratigraphic framework calcareous nannoplankton planktic and larger benthic foraminifers gastropods and pectinids allow us to construct a basin spanning stratigraphy the assignment of the recognized sea level lowstands to the ru 3 to bur 3 lowstands of the global sea level curve enables a comparison with time equivalent sections from the zagros basin which was part of the african arabian plate on the opposing southern margin of the tethyan seaway the so calibrated sections display restrictions of the tethyan seaway and interruption of the south iranian gateways between the qom basin and the proto indopacific in relation to ongoing plate collision during the early burdigalian

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

spatial and temporal variation of summer precipitation over the eastern tibetan plateau and the north atlantic oscillation abstract the interannual variability of summer precipitation over the eastern tibetan plateau etp was examined in relation to the northern hemisphere macroscale circulation patterns during the period 1961 90 summer precipitation data for 66 stations located above 2000 m msl are used in the analysis using principal component analysis it is found that the dominant spatial pattern of interannual variability of the summer precipitation is a seesaw structure between the southern and northern parts of etp correlation analysis shows that this pattern of precipitation anomalies is closely associated with the north atlantic oscillation nao further analysis based on midtropospheric geopotential height and wind data suggests the upstream zonal flow variation associated with the nao pattern as the major mechanism linking the regional precipitation fluctuation to macroscale circulation conditions during the summers of low nao index values the westerly winds between 40 and 50 n from the eastern atlantic to

mountains and arid climates of middle latitudes simulations from a global climate model with and without orography have been used to investigate the role of mountains in maintaining extensive arid climates in middle latitudes of the northern hemisphere dry climates similar to those observed were simulated over central asia and western interior north america in the experiment with mountains whereas relatively moist climates were simulated in these areas in the absence of orography the experiments suggest that these interior regions are dry because general subsidence and relatively infrequent storm development occur upstream of orographically induced stationary wave troughs downstream of these troughs precipitation bearing storms develop frequently in association with strong jet streams in contrast both atmospheric circulation and precipitation were more zonally symmetric in the experiment without mountains in addition orography reduces the moisture transport into the continental interiors from nearby oceanic sources the relative soil wetness of these regions in the experiment without mountains is consistent with paleoclimatic evidence of less aridity during the late tertiary before substantial uplift of the rocky mountains and tibetan plateau is believed to have occurred

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

a miocene to pleistocene climate and elevation record of the sierra nevada california orographic precipitation of pacific sourced moisture creates a rain shadow across the central part of the sierra nevada california that contrasts with the southern part of the range where seasonal monsoonal precipitation sourced to the south obscures this rain shadow effect orographic rainout systematically lowers the hydrogen isotope composition of precipitation dppt and therefore dppt reflects a measure of the magnitude of the rain shadow hydrogen isotope compositions of volcanic glass dglass hydrated at the earth s surface provide a unique opportunity to track the elevation and precipitation history of the sierra nevada and adjacent basin and range province analysis of 67 well dated volcanic glass samples from widespread volcanic ash fall deposits located from the pacific coast to the basin and range province demonstrates that between 0 6 and 12 1 ma the hydrogen isotope compositions of meteoric water displayed a large 40 decrease from the windward to the leeward side of the central sierra nevada consistent with the existence of a rain shadow of modern magnitude over that time evidence for a miocene to recent rain shadow of constant magnitude and systematic changes in the longitudinal climate and precipitation patterns strongly suggest that the modern first order topographic elements of the sierra nevada characterized the landscape over at least the last 12 million years

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

hydrogen isotopes in eocene river gravels and paleoelevation of the sierra nevada we determine paleoelevation of the sierra nevada california by tracking the effect of topography on precipitation as recorded in hydrogen isotopes of kaolinite exposed in gold bearing river deposits from the eocene yuba river the data compared with the modern isotopic composition of precipitation show that about 40 to 50 million years ago the sierra nevada stood tall 2200 meters a result in conflict with proposed young surface uplift by tectonic and climatic forcing but consistent with the sierra nevada representing the edge of a pre eocene continental plateau

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

influence of andean uplift on climate and paleoaltimetry estimates article i nfo article history recent elevation reconstructions of the andean plateau suggest a rapid 2 5 1 0 km rise of the central andes between 10 and 6 ma this rapid rise has been attributed to a catastrophic removal of a dense lithospheric mantle root beneath the andes however these findings are based on the assumption that climate did not change during deposition of paleoaltimetry proxies here we evaluate south american climate change due to andean uplift and its influence on interpretations of plateau elevation from climate sensitive paleoaltimetry data a series of experiments are presented using the regcm3 regional general circulation model rcm to characterize changes in andean precipitation amount surface temperature and wind direction vapor source as a function of changing plateau elevation results indicate that south american and andean climate changed significantly in response to plateau growth more specifically rising of the plateau results in up to a 900 mm increase in rainy season december january february precipitation over the plateau plateau uplift also results in a decrease in non adiabatic surface temperature of up to 6 5 c in addition to adiabatic cooling directly related to elevation change through the lapse rate finally the prevailing wind direction and the vapor source for precipitation switches from the south pacific ocean to the equatorial atlantic as plateau elevation increases above of its present day elevation taken together these changes in paleoclimate would have substantially depleted the oxygen isotopic concentration of paleoprecipitation through the cenozoic unless this climatic effect is taken into consideration paleoaltimetry reconstructions based on stable isotope methods may overestimate the rapid rise of the andes by up to several kilometers we conclude that some or all of the apparent rapid rise of the andean plateau from paleoaltimetry data could be an artifact of large changes in paleoclimate

capture of high altitude precipitation by a low altitude eocene lake western u s sedimentary facies of the eocene green river formation refl ect a rapid increase in water supply to lake gosiute ca 49 ma marked by a stratigraphic fi ll to spill surface deposits below this surface constitute repetitive lacustrine expansion desiccation cycles whereas those above consist of continuous profundal lacustrine mudstone grading upward into volcaniclastic deltaic sandstone above the fi ll to spill surface calcitic mudstone 18 o decreases from 26 to 20 over an interval representing 100 k y we interpret this shift to have resulted from capture of a foreland river or rivers that drained higher topography north of lake gosiute most likely in north central idaho accurate paleoelevation estimates derived from stable isotopic records in intermontane basins thus may require detailed knowledge of regional drainage systems

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

carbonate oxygen isotope paleoaltimetry evaluating the effect of diagenesis on paleoelevation estimates for the tibetan plateau carbonate oxygen isotope paleoaltimetry is based on analysis of the d 18 o value of carbonate precipitated from surface water deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters which reflect paleoelevation this study provides examples from southern east central and northeastern tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates the most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary such as aragonitic shell material in rocks that do not contain shell material we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates where the potential effects of diagenesis are subtle or ambiguous we have evaluated the fidelity of the carbonate record from systematic trends in c and o isotopes that agree with other interpretations of paleoenvironment such as high frequency covariance in c and o that corresponds with changes in the mg concentration of carbonates using these strategies we have determined that diagenesis has not affected the isotopic composition of carbonates in the late miocene pliocene thakkhola graben in southern tibet and the oligocene to pliocene linxia basin in northeastern tibet in the case of paleogene basins in east central tibet however ambiguity in data precludes the determination of diagenetic effects d 2004 elsevier b v all rights reserved

from tectonically to erosionally controlled development of the himalayan orogen whether variations in the spatial distribution of erosion influ ence the location style and magnitude of deformation within the himalayan orogen is a matter of debate we report new 40 ar 39 ar white mica and apatite fission track aft ages that measure the vertical component of exhumation rates along an 120 km wide ne sw transect spanning the greater sutlej region of northwest india the 40 ar 39 ar data indicate that first the high himalayan crystalline units cooled below their closing temperature during the early to middle miocene subsequently lesser himalayan crys talline nappes cooled rapidly indicating southward propagation of the orogen during late miocene to pliocene time the aft data in contrast imply synchronous exhumation of a ne sw oriented 80 3 40 km region spanning both crystalline nappes during the pliocene quaternary the locus of pronounced exhumation de fined by the aft data correlates with a region of high precipita tion discharge and sediment flux rates during the holocene this correlation suggests that although tectonic processes exerted the dominant control on the denudation pattern before and until the middle miocene erosion may have been the most important factor since the pliocene

the effects of orography on midlatitude northern hemisphere dry climates abstract the role of mountains in maintaining extensive midlatitude arid regions in the northern hemisphere was investigated using simulations from the gfdl global climate model with and without orography in the integration with mountains dry climates were simulated over central asia and the interior of north america in good agreement with the observed climate in contrast moist climates were simulated in the same regions in the integration without mountains during all season but summer large amplitude stationary waves occur in response to the tibetan plateau and rocky mountains the midlatitude dry regions are located upstream of the troughs of these waves where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited in summer this mechanism contributes to the dryness of interior north america as a stationary wave trough remains east of the rockies but is not effective in eurasia due to seasonal changes in the atmospheric circulation the dryness

elevation or alteration evaluation of isotopic constraints on paleoaltitudes surrounding the eocene green river basin low oxygen isotope values 16 relative to peedee belemnite standard obtained from microbial carbonates of the green river formation have been interpreted as evidence for snowmelt and high elevations surrounding this early eocene lake basin however low values from microbial precipitates could also represent a diagenetic overprint we investigate these alternate hypotheses by measuring the oxygen isotope composition of altered and unaltered freshwater bivalves from the basin we analyzed subannual samples from 3 individuals and bulk samples from 54 individuals subannual samples exhibit clear seasonal fluctuations in oxygen isotope values these fluctuations are large enough to require seasonal shifts in temperature and or the oxygen isotope value of the lake water however the lowest value of any unaltered sample either bulk or high resolution corresponds to lake water 18 o of 12 relative to standard mean ocean water and is not low enough to require the addition of snowmelt to the lake a few bulk samples exhibit very low oxygen isotope values which would seem to suggest snowmelt however these samples also show clear evidence of calcite in x ray diffraction patterns demonstrating the presence of diagenetic precipitates given that 1 diagenetic alteration is a plausible explanation of very low 18 o values 2 alteration has not been examined in microbial carbonates and 3 unaltered aragonitic bivalves provide no independent evidence for low 18 o values for lake waters we conclude that robust isotopic evidence for high elevations surrounding the green river basin during the eocene is currently lacking

fine tuning of age integrating magnetostratigraphy radiocarbon dating and carbonate cyclicity example of lacustrine sediments from heqing basin yunnan china covering the past 1 myr abstract high resolution magnetostratigraphy wavelength spectra of carbonate cyclicities and ams radiocarbon dating are integrated to establish an optimum age model for a 168 m long drill core of lacustrine sediments from heqing basin yunnan province southwestern china a 14c age of 51 62 2 42 1 85 kyr bp is obtained at a depth of 7 3 m remanent magnetization is carried by maghemite and partly in addition by magnetite both showing the same direction the polarity sequence clearly reveals the brunhes matuyama b m boundary at 141 5 m blake event is found between 16 3 and 17 5 m and the upper boundary of jaramillo is indicated at 167 0 m carbonate content and magnetic susceptibility were used for spectral analysis fourier analysis was done on the depth section for sliding windows with different window lengths the spectra within the range of window centers 30 140 m show a dominant long wavelength which changes from about 18 5 m in the lower part 65 m depth to about 14 5 m in the upper part

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

climatic and ecologic changes during miocene surface uplift in the southern patagonian andes abstract the up to 4 km high southern patagonian andes form a pronounced topographic barrier to atmospheric circulation in the southern hemisphere westerlies and cause one of the most drastic orographic rain shadows on earth geologic data imply that this climatic pattern has been established or significantly enhanced during miocene surface uplift of this andean segment we report evidence for important climatic and ecologic changes in the eastern foreland of the patagonian andes that appear to be the result of this uplift to provide constraints on miocene plant ecosystems and precipitation in the eastern leeward foreland of the patagonian andes we determined carbon and oxygen isotope values of pedogenic carbonate nodules from a 500 m thick section of the continental santa cruz formation the age of these deposits was constrained by ar ar dating of intercalated tuffs which range from 22 to 14 ma at 16 5 ma the 13 c values increase by 3 the 18 o values decrease by 2 and the scatter in the oxygen isotope data increases significantly we interpret these changes as the consequence of 1 km surface uplift in this andean segment from the 18 o values and increased aridity to its east from the 13 c values and the increased scatter in the 18 o values sediments overlying the santa cruz formation are very limited in extent and volume and dominated by coarse conglomerates related to pleistocene and older glaciations it thus seems that by 14 ma deposition in the eastern foreland of the southern patagonian andes had essentially ceased as the result of rain shadow formation

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

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

climatic forcing of asymmetric orogenic evolution in the eastern cordillera of colombia new apatite fission track data paleoelevation estimates from paleobotany and recently acquired geological data from the eastern cordillera of colombia document the onset of increased exhumation rates in the northeastern andes at ca 3 ma the eastern cordillera forms an efficient orographic barrier that intercepts moisture laden winds sourced in the amazon lowlands leading to high rainfall and erosion gradients across the eastern flank of the range in contrast the drier leeward western flank is characterized by lower rates of deformation and exhumation in light of the geological evolution of the eastern cordillera the combination of these data sets suggests that the orographic barrier reached a critical elevation between ca 6 and ca 3 ma which ultimately led to protracted yet more focused erosion along the eastern flank sequentially restored structural cross sections across the eastern flank of the eastern cordillera indicate that shortening rates also have increased during the past 3 ma from fission track and structural cross section balancing we infer that accelerated exhumation led to increasing tectonic rates on the eastern flank creating a pronounced topographic and structural asymmetry in the eastern cordillera the tectonic and climatic evolution of this orogen thus makes it a prime example of the importance of climatic forcing on tectonic processes

onset of convective rainfall during gradual late miocene rise of the central andes a decrease in the ratio of 18o to 16o 18o of sedimentary carbonate from the bolivian altiplano has been interpreted to indicate rapid surface uplift of the late miocene andean plateau ap here we report on paleoclimate simulations of andean surface uplift with an atmospheric general circulation model gcm that tracks oxygen isotopes in vapor the gcm predicts changes in atmospheric circulation and rainfall that influence ap isotopic source and amount effects on eastern ap slopes summer convective precipitation increases by up to 6 millimeters per day 500 for plateau elevations that are greater than about 2000 meters high precipitation rates enhance the isotope amount effect leading to a decrease in precipitation 18o at high elevations and an increase in 18o lapse rate our results indicate that late miocene 18o depletion reflects initiation and intensification of convective rainfall

oxygen isotopes of marine mollusc shells record eocene elevation change in the pyrenees abstract constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate tectonics retroactions here we use oxygen stable isotope record on oyster shells preserved in marine foreland deposits to examine the past elevation of the pyrenees during the eocene our approach is based on the comparison with the paris basin an intracratonic basin not influenced by orogenic growth the finding of a shift of 1 5 between 49 and 41 ma indicating more negative 18oc in the south pyrenean foreland is interpreted to reflect the inflow of river water sourced from higher elevation in the pyrenees to test this and provide paleoelevation estimate we adopt a morphologic hydrological model accounting for the hypsometry of drainage basin our best fitting model shows that the pyrenees rose up to 2000 m this indicates that the pyrenees reached high elevation in the eocene thus providing new critical constraints on their long term orogenic development 18o of marine mollusc shells are proved potentially attractive for paleoelevation studies especially for mountain belts where elevated continental surfaces have not been preserved

development and response of a coupled catchment fan system under changing tectonic and climatic forcing sediment fans are a potentially useful and underexploited recorder of earth s climatic and tectonic history but historical observations have led to conflicting views on the importance of tectonic climatic and lithologic variables in controlling fan morphology and deposition a one dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates a transport limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation rock uplift rate is spatially variable across the model space increasing the fault slip rate or decreasing the precipitation rate leads to an increase in fan slope temporary back stepping of the fan toe and a pronounced angular unconformity conversely a decrease in slip rate or an increase in precipitation rate results in a decrease in fan slope and progradation and eventual stabilization of the fan toe once perturbed the system evolves toward a new equilibrium state with time constants of 0 5 to 2 myr these response times are insensitive to slip rate but are strongly dependent on precipitation rate variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate precipitation rate system size and catchment lithology this parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables

synchronous deformation on orogenic plateau margins insights from the arabia eurasia collision abstract the temporal and spatial distribution of deformation during the early phases of plateau formation is poorly known the iranian plateau is developing in response to arabia eurasia convergence and is a potential analog to the early phases of tibetan plateau deformation previous studies document the onset of the iranian plateau growth based on the kinematic history of the zagros to the south and the alborz mountains to the north here we present new detrital apatite fission track aft data from 13 modern rivers of the talesh mountains northwestern iranian plateau these mountains lie immediately south west of the rigid south caspian block a total of 1233 single grain cooling ages were measured and range between 185 and 4 ma deconvolution of grain age data documents three main phases of exhumation including the oligocene 30 23 ma early to middle miocene 18 12 ma and early pliocene 5 ma comparison between cooling ages from the talesh mountains and elsewhere across the iranian plateau indicates widespread plateau formation in the oligocene earlier than previously suggested for the northwestern plateau margin these results highlight deformation on both the northern and southern margins of the plateau over almost the entire history of iranian plateau formation a similar pattern of synchronous deformation on the north northeastern and southern margins of the tibetan plateau has recently been documented and highlights the significance of rigid basement blocks focusing far field deformation for both plateaus

rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere abstract the oxygen isotopic compositions of carbonates deposited in the northern altiplano demonstrate a rapid change in late miocene time which we attribute to an increase in elevation rainfall samples over an elevation transect adjacent to the altiplano of northern bolivia display a systematic decrease in mean annual 18 o values and define a local 18 o vs altitude gradient r gonfiantini m a roche j c olivry j c fontes g m zuppi the altitude effect on the isotopic composition of tropical rains chem geol 181 2001 147 167 which we apply to paleo meteoric water values determined from carbonates age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of 2 5 to 3 5 km occurred between 10 3 ma and 6 8 0 4 ma when the altiplano rose to its current elevation only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity this change coincides with an 30 decrease in the rate of convergence between the south america and nazca plates and the propagation of deformation into the eastern subandean zone which we infer to have resulted from the increase in the force per unit length applied by the elevated andean plateau to the surrounding lowlands

climate change in response to orographic barrier uplift paleosol and stable isotope evidence from the late neogene santa maria basin northwestern argentina the late cenozoic history of the santa maria basin in the northeastern sierras pampeanas records the far reaching climatic consequences of the development of orographic barriers to atlantic derived moisture the evolution of climate and ecosystems is coupled with the uplift of basement blocks west and east of the basin to their present elevations of 4000 5500 m the climatic and ecological history of the basin for the past 12 m y was reconstructed from paleosol characteristics and carbon and oxygen isotopes of pedogenic material a fluvial environment succeeded the final marine regression after ca 12 ma paleosols with illuvial clay and calcic nodules indicate a seasonally dry climate between ca 9 and 7 ma paleosols formed under conditions of episodic waterlogging as shown by organic matter preservation and variegated colors after ca 7 ma pedogenesis occurred under enhanced drainage due to tectonic steepening of the eastern basin margin this can be related to westward thrusting of the eastern basin bounding sierra aconquija and cumbres calchaquies calcic and silicic rhizoliths and authigenic clay point to persistent wet dry seasonality carbon isotope values document the spread of c 4 plants between ca 5 and 3 ma carbon isotopes show an increase in c 3 plants this is likely a consequence of uplift of the sierra de quilmes to the west resulting in a transitory episode of orographic precipitation within the santa maria basin aridification of the valley occurred between ca 3 and 2 5 ma and was related to creation of high topography to the east development of thick calcretes suggests that the present semiarid conditions were established by the end of pliocene time carbon isotopes show that the quaternary vegetation was c 4 plant dominated and oxygen isotopes attest to intense soil water evaporation

late miocene climate variability and surface elevation in the central andes abstract temporal and spatial variations in topography and oxygen stable isotope ratios in precipitation in the central andes have stimulated widespread discussion about the competing roles of mantle and crustal processes and their feedbacks with global scale climatic change in uplifting and shaping the central andes in general one of the major obstacles in assessing the relative contributions of long term 10 5 10 6 a tectonic processes and precipitation as a proxy for climate to the uplift history of the andean orogen is the lack of integrated data sets that record late miocene patterns of uplift and climate radiogenic 87 sr 86 sr sedimentologic and stable isotope 18 o data from subandean foreland deposits of the chaco basin bolivia show a rapid 18 o and 87 sr 86 sr values at 8 5 ma that we interpret to reflect a change in precipitation patterns along the eastern cordillera and the subandean fold thrust belt in agreement with 13 c studies on paleosol carbonates we attribute this change to a southward deflection of the south american low level jet llj that currently exerts the dominant control over the seasonality and amount of precipitation along the eastern flanks of the andes deflection of the llj occurred most likely as the combined effects of readjustment of relief and topography within the eastern cordillera at 20 22 s and possibly associated surface uplift of the altiplano contemporaneous rapid positive shifts in 18 o and 87 sr 86 sr of pedogenic carbonate in fluvial foreland deposits are consistent with a transition to more seasonal precipitation conditions and critical threshold elevations being attained that affected south american atmospheric circulation patterns a four fold increase in sedimentation rates in the foreland together with a shift to strongly radiogenic 87 sr 86 sr ratios in paleo river water and sediment load as well as river incision into the well preserved san juan del oro paleo surface directly reflects a rapid change in moisture distribution along the eastern flank of the central andes at 8 5 ma and associated rearrangement of the drainage systems collectively the data presented here strongly suggest that between 12 and 8 ma the amount oxygen isotopic composition spatial distribution and seasonality of precipitation along the eastern flank of the bolivian andes changed dramatically which in turn require changes in trans andean moisture flux and isotopic composition of precipitation on the uplifting plateau region

geographic and temporal patterns in the late neogene 12 3 ma aridification of europe the use of small mammals as paleoprecipitation proxies abstract present day relations between small mammal community structure and rainfall are used to predict late neogene 12 3 ma precipitation patterns in europe and anatolia new proxy methods are developed which include regressions of mean annual and minimum monthly precipitation on diet invertivory index and locomotion habitat arboreality index a series of precipitation maps and a set of regional precipitation curves through time at 1 myr resolution are presented precipitation curves at a higher temporal resolution are constructed for the region of central spain the miocene results show the existence between 12 and 9 ma of a large wet 800 1200 mm yr zone extending from northern spain to the ukraine and characterized by the whole year penetration of large amounts of moisture far into the continent between 10 9 and 5 ma this european temperate wet zone etwz shrinks and or moves northward resulting in diachronous aridification a coeval northward migration of the subtropical high pressure zone shpz is hypothesized which is also consistent with the predicted onset of seasonal summer dryness between 10 and 8 ma the maximum extension of the etwz at 12 9 ma temporally correlates with northern hemisphere cooling suggesting that climate zonation rather than the global amount of atmospheric moisture controlled european climate at this time the main aridification at 9 8 ma could best be explained by a northward extension shifting of the subtropical high pressure zone and a transition towards less zonal circulation processes which ultimately could have been triggered by uplift of the tibetan plateau a temporary increase of precipitation at 7 6 ma is associated with renewed global cooling the lowest precipitation values less than 400 mm yr occur during the pliocene in southern and eastern europe uplift in eastern europe carpathians shrinking of the paratethys could well explain the aridification in this area and the associated sharpening of east west precipitation gradients across the continent

general circulation model simulation of the δ18o content of continental precipitation in the middle cretaceous a model proxy comparison we use the genesis atmospheric general circulation model gcm with water isotopic transport and fractionation capabilities to quantify the influence of atmospheric co 2 sea level and elevation of the western cordillera on the 18 o of middle cretaceous precipitation the model predicts a systematic increase of nearly 3 in the 18 o of north american precipitation due to warming associated with an increase in co 2 from 2 to 12 times pre industrial levels in contrast the specification of lowstand conditions and a high ancestral western cordillera reduces the 18 o of north american precipitation locally by as much as 6 and 8 we compare the simulated 18 o of precipitation with the 18 o of paleosol siderite spherules and find good agreement only when the model includes lowstand conditions and a high ancestral western cordillera our results imply either that cretaceous high latitude paleosol 18 o was influenced by orographic precipitation and the western interior seaway or that the gcm9s hydrological cycle is deficient at high p co 2 additional paleosol data are needed to resolve this issue

thermal histories from the central alborz mountains northern iran implications for the spatial and temporal distribution of deformation in northern iran we integrate new and existing thermochronological geochronological and geologic data from the western and central alborz mountains of iran to better constrain the late cenozoic tectonic evolution of northern iran in the context of the arabia eurasia collision new data are presented for two granitic plutons north of the alborz range crest additional new apatite u th he data are also presented for volcanic intrusive and detrital apatite grains from two transects south of the range crest our most definitive results include zircon and apatite u th he and limited k feldspar 40 ar 39 ar thermal history data from the cretaceous ca 98 ma nusha pluton that reveal that the alborz basement underwent generally slow denudation 0 1 km m y as late as 12 ma with more accelerated exhumation 0 45 km m y that likely began shortly after 12 ma the lahijan pluton a late neoproterozoic cambrian basement exposure near the caspian shore records apatite u th he closure at 17 13 ma additional u th he results from detrital apatites sampled along two separate horizontal transects all consistently yielded latest miocene to pliocene apparent ages that imply that even supracrustal cover rocks within the alborz have undergone significant regionally extensive exhumation overall our data are consistent with 5 km of regionally extensive denudation since ca 12 ma the onset of rapid exhumation in the alborz at ca 12 ma appears to be consistent with other timing estimates that place the onset of the arabia eurasia collision between 14 and 10 ma

middle to late miocene middle eastern climate from stable oxygen and carbon isotope data southern alborz mountains n iran abstract the alborz mountains of northern iran intercept and divert the northern hemisphere westerlies carrying moisture from the mediterranean and black sea and form an orographic barrier to moisture sourced to the north in the caspian sea this implies that terrestrial deposits along the southern alborz mountains leeward side of northerly winds and windward side of westerlies with the respect to tibet and other mountainous terrain in the himalayan karakoram realm potentially track changes in past moisture and erosional regimes and mirror rainfall patterns here we present results of a stable isotope analysis and clay mineral study of the miocene ca 17 5 7 6 ma upper red formation in the foreland of the southern alborz mountains the changes recorded by stable oxygen and carbon isotope data from pedogenic and lacustrine palustrine carbonate in the southern alborz mountains suggest 1 an increase in aridity possibly related to the evolution of the alborz orographic rain shadow which became more efficient between 17 5 and 13 2 ma 2 a steady increase in precipitation between 13 2 and 10 3 ma with a significant increase in rainout along the southern slope of the alborz mountains between 11 and 10 3 ma possibly related to perturbations in atmospheric circulation pattern in the northern hemisphere as suggested by coeval wetter phases in southern europe and 3 a decrease in aridity from ca 9 6 to 7 6 ma possibly reflecting an increase in the seasonality of precipitation based on environmental and climatic changes observed across southern asia and india starting from ca 10 ma we speculate that the topographic evolution of the himalayan tibetan system might have affected the late miocene climate in middle east

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

rise and fall of the paratethys sea during the messinian salinity crisis abstract extremely thick evaporite units were deposited during the so called messinian salinity crisis msc 5 96 5 33 ma in a deep mediterranean basin that was progressively disconnected from the atlantic ocean a crucial but still poorly understood component in messinian evaporite models is the connectivity between mediterranean and paratethys i e the former black sea domain inadequate stratigraphic correlations and insufficient age control for paratethys sediments have so far hampered a thorough understanding of hydrological fluxes and paleoenvironmental changes here we present a new chronology for the eastern paratethys by integrating biostratigraphic and paleomagnetic data from mio pliocene sedimentary successions of romania and russia we show that a major flooding event from the mediterranean surged the paratethys basins at the maeotian pontian boundary 6 04 million years ago this indicates that sea level in both mediterranean and paratethys was high at the beginning of the msc we argue in favor of changes in paratethys mediterranean connectivity to initiate the msc in combination with elusive tectonic processes in the gibraltar arc a subsequent fall of paratethyan water level closely coincides to the mediterranean isolation event corresponding in age to the glacial cycles tg12 14 5 60 5 50 myr in the latest messinian a major climate change towards more humid conditions produced a positive hydrological balance and likely a transgression in the paratethys although our stratigraphic resolution cannot exclude a possible relation to the pliocene flooding of the mediterranean here

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

rise of the andes the surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening leading to their gradual rise recent studies of the andes indicate that their elevation remained relatively stable for long periods tens of millions of years separated by rapid 1 to 4 million years changes of 1 5 kilometers or more periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable dense lower lithosphere after long term thickening of the crust and lithospheric mantle

mechanisms of eastern mediterranean rainfall variability abstract this paper presents a simple theory for the association between observed eastern mediterranean em rainfall anomalies and north atlantic na climate variability large scale na atmospheric mass rearrangements primarily a modulation of the icelandic low and the subtropical high pressure systems tend to extend beyond the na a particularly strong such teleconnection exists between the northern na and southern europe and the mediterranean basin pressure anomalies over greenland iceland are thus associated with reversed polarity anomalies centered over the northern adriatic affecting the entire mediterranean basin elevated greenland pressure is accompanied by an anomalous cyclone over the mediterranean and a mediterranean high pressure system is present when pressure over greenland is reduced in the em these anomalies result in anomalous southerlies during greenland highs and northerlies during greenland lows eastern mediterranean southerlies warm the em while northerlies cool locally b

changes in terrestrial ecosystem since 30 ma in east asia stable isotope evidence from black carbon in the south china sea a 30 m y stable isotopic record of marine deposited black carbon from regional ter restrial biomass burning from the northern south china sea reveals photosynthetic path way evolution for terrestrial ecosystems in the late cenozoic this record indicates that c3 plants negatively adjusted their isotopic discrimination and c 4 plants appeared grad ually as a component of land vegetation in east asia since the early miocene a long time before sudden c4 expansion occurred during the late miocene to the pliocene the changes in terrestrial ecosystems with time can be reasonably related to the evolution of east asian monsoons which are thought to have been induced by several intricate mechanisms during the late cenozoic and could contribute significantly to the post miocene marine carbonate isotope decline

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

late miocene washhouse climate in europe abstract we present two eight million year long proxy records of precipitation for southwest and central europe covering the middle to late miocene 5 3 13 ma at a temporal resolution of about 60 kyr and 150 kyr respectively the estimates of precipitation are based on the ecophysiological structure of herpetological assemblages amphibians and reptiles from 13 0 ma until about 9 ma both records show a similar trend evolving from a long dry period 13 11 ma into a washhouse climate 10 2 9 8 ma characterized by global warm conditions and several times more precipitation than present the transition from washhouse to a dryer climate between 9 7 and 9 5 ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the vallesian crisis which included the extinction of hominoids in western europe a second washhouse period 9 0 8 5 ma coeval with a global warm episode was unprecedentedly intense in southwest europe but less pronounced in central europe from 8 ma onward a divergence in the two precipitation records is observed with southwest europe staying wetter and central europe becoming dryer than present both precipitation records are combined into a common run off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental europe the run off curve shows a remarkable positive correlation with atlantic deep water temperatures from ceara rise by lear et al 2003 which are significantly higher up to 3 c during the two washhouse periods and show no other positive excursion of comparable magnitude we discuss potential links and the role of the coeval temporary restriction of the central american seaway on ocean and atmosphere circulation

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

comparison of a paleosol carbonate isotope record to other records of pliocene early pleistocene climate in the western united states paleoecological and paleoenvironmental interpretations of stable isotope composition of pedogenic carbonate collected from the pliocene early pleistocene st david formation in southeastern arizona united states correlate with other proxy records of paleoclimate in the western united states wetter and perhaps cooler conditions between 3 2 and 2 8 ma are associated with lacustrine highstands at tulelake and searles lake in california a general trend toward drier conditions in the late pliocene is also apparent in all records a protracted arid monsoonal climate in the early pleistocene implied by the soil isotope data from arizona is not as readily correlated to other climate records and is perhaps related to uplift in the southern cordillera soil carbonate isotope data provide relatively continuous paleoclimatic records from fluvial sequences that supplement lacustrine records together they provide a framework for interpreting pliocene climate

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

soils at the hyperarid margin the isotopic composition of soil carbonate from the atacama desert northern chile we evaluate the impact of exceptionally sparse plant cover 0 20 and rainfall 2 114 mm yr on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet the atacama desert in northern chile d 13 c and d 18 o values of carbonates from the atacama are the highest of any desert in the world d 13 c vpdb values from soil carbonate range from 8 2 at the wettest sites to 7 9 at the driest we measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of cerling 1984 earth planet sci lett 71 229 240 in which we assumed an exponential form of the soil co2 production function and relatively shallow 20 30 cm average production depths overall we find that respiration rates are the main predictor of the d 13 c value of soil carbonate in the atacama whereas the fraction c3 to c4 biomass at individual sites has a subordinate influence the high average d 13 c value 4 1 of carbonate from the driest study sites indicates it formed perhaps abiotically in the presence of pure atmospheric co2 d 18 o vpdb values from soil carbonate range from 5 9 at the wettest sites to 7 3 at the driest and show much less regular variation with elevation change than d 13 c values d 18 o values for soil carbonate predicted from local temperature and d 18 o values of rainfall values suggest that extreme 80 in some cases soil dewatering by evaporation occurs at most sites prior to carbonate formation the effects of evaporation compromise the use of d 18 o values from ancient soil carbonate to

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

regional impact of an elevated heat source the zagros plateau of iran the authors propose that a heat driven circulation from the zagros plateau has a significant impact on the climate of the middle east plain mep especially summertime winds air temperature and aridity this proposal is examined in numerical experiments with a regional climate model simulations in which the zagros plateau was assigned a highly reflective snowlike albedo neutralized the heat driven circulation and produced an extra summertime warming of 1 2 c in the mep measured relative to a control simulation and to the records of the ncep ncar reanalysis project this effect was largest in midsummer when heating on the plateau was greatest additionally simulations with high albedo on the zagros showed reduced subsidence and enhanced precipitation in the mep these sensitivities are interesting because the zagros plateau lies downwind of the mep analysis of model results indicates that the sensitivity of the upwind subsidence region to zagros albedo can be understood as a linear atmospheric response to plateau heating communicated upwind by a steady heat driven circulation that influences the thermodynamic balance of the atmosphere this regional phenomenon adds to the large scale subsidence patterns established by the hadley circulation and the asian monsoon observed patterns of vertical motion in the middle east then are a combined product of zagros induced subsidence and hemispheric scale circulations

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

palaeo altimetry of the late eocene to miocene lunpola basin central tibet the elevation history of the tibetan plateau provides direct insight into the tectonic processes associated with continent continent collisions here we present oxygen isotope based estimates of the palaeo altimetry of late eocene and younger deposits of the lunpola basin in the centre of the plateau which indicate that the surface of tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years we conclude that crustal but not mantle thickening models combined with plate kinematic solutions of india asia convergence are compatible with palaeo elevation estimates across the tibetan plateau

possible regional tectonic controls on mammalian evolution in western north america abstract previous work has suggested that tectonically active regions act as speciation pumps for mammals and plant species but little is known about how fast or widespread tectonism must be in order to directly influence evolution here we use oxygen and hydrogen isotopic data from miocene sedimentary deposits to characterize the topographic evolution of the southern columbia plateau snake river plain and northern rocky mountain regions during the yellowstone hotspot passage with the ultimate goal of understanding whether topographic changes caused by the hotspot influenced mammalian evolution within those regions we conducted oxygen isotope analyses of 130 samples of lacustrine and paleosol carbonate from miocene stratigraphic sections that span much of the northern rocky mountain region and combined these data with previously published isotopic records collectively these isotopic data show that caldera formation associated with the yellowstone hotspot has modified regional topography and rearranged drainages along the track of the hotspot and that the hotspot has left a topographic depression in its wake we explore the extent to which these topographic changes influenced or are decoupled from diversity changes exhibited by the local mammal faunas and conclude that the passage of the hotspot and consequent surface uplift created rainshadows in the lee of high elevation calderas and or generated large volumes of volcanic materials influencing soils and vegetation collectively that may explain a possible rise in mammal diversity in the cp srp region at 14 ma coincident with a drop in diversity in the nrm it is still unclear however how different taphonomic pathways and sample standardization problems are influencing apparent diversity peaks at this temporal and geographic resolution

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

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

topographic and tectonic evolution of mountain belts controlled by salt thickness and rift architecture the role of the heterogeneous rheological architecture of rifted margins in the building of mountain belts has challenged our view of how a collisional orogen formed we show using two dimensional numerical experiments of collision built by the inversion of rifted margins that a weak pre extensional evaporitic layer delays the growth of topography and the onset of syn orogenic sedimentary record in foreland basins in tectonic models lacking a weak decollement layer the orogen grows by progressive accretion of basement thrusts with a 2 km thick salt layer the orogen develops an antiformal stack in the deep crust that is kinematically connected to a shallow thin skin thrust belt in the foreland as observed in many orogens a 5 km thick weak layer leads to the quasi absence of topography and widespread salt tectonics and obliterates thrusts propagation while promoting crust and mantle underthrusting during convergence the preservation of a marine seaway emphasizes that collision may involve a significant period of submarine continental accretion which duration is controlled by the thickness of the weak decollement layer from these experiments we infer that the thicker the salt layer the longer the delay between the onset of far field shortening and the formation of the orogen our study explains first order features recognized in many orogens controlled by variable salt thickness and extension

provenance evolution of oligocene pliocene foreland deposits in the dezful embayment to constrain central zagros exhumation history this paper presents a detailed provenance analysis of the 6 5 km thick oligocene pliocene foreland succession in the north dezful embayment in zagros iran using petrography geochemistry and palaeoflow analysis we determined three provenance shifts during the exhumation of the zagros orogen above the ahwaz sandstones sourced from the arabian craton a sharp decrease in sio2 al2o3 zr sc th sc th co and th cr within the gachsaran fm and the appearance of first cycle sands derived from metamorphic and volcanic rocks at the base of the aghajari fm characterize the onset of exhumation rising topography and denudation of the zagros orogenic system during the latest oligocene and constitute the first shift the second shift in the middle aghajari fm is marked by a distinct increase in radiolarian cherts and compatible incompatible elements indicating the exhumation of neotethyan radiolarite ophiolite allochthonous slices in the high zagros zone during the tortonian c 9 ma large quantities of carbonate clasts derived from the nearby growing izeh zone anticlines characterize the messinian c 7 ma bakhtyari conglomerates marking the third shift in conclusion a detailed hands on provenance analysis of the clastic sedimentary sequences in the north dezful embayment enabled us to determine catchment areas and shifts hitherto unstudied thus contributing to the exhumation history of the central zagros orogenic system supplementary material details of the petrography and geochemistry results are available at https doi org 10 6084 m9 figshare c 4905558