the δ18o of primary and secondary waters in hydrous volcanic glass abstract we present analyses of phyllosilicates volcanic glass and a series of experiments and observations on the 18o of water extracted by rapid thermal pyrolysis at 1450 c using the tcea thermal conversion elemental analyzer the study includes the same hydrous glasses that were previously analyzed for their d values of extracted water seligman et al 2016 we utilize natural phyllosilicates where water is present as oh only natural magmatic and experimentally quenched glasses in which water occurs as h2om and oh and glasses that underwent low temperature secondary hydration by meteoric water almost completely as h2om our study documents that 1 thermal extraction and simultaneous pyrolysis of h2ot into co and h2 produces little or no exchange

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

how does floodplain width affect floodplain river ecology a preliminary exploration using simulations abstract hydraulic food chain models allow us to explore the linkages of river discharge regimes and river floodplain morphology to the structure and dynamics of modeled food webs physical conditions e g depth width velocity that vary with river discharge affect the performance birth growth feeding movement or death rates of organisms or trophic groups their performances in turn affect their impacts on food webs and ecosystems in channel and floodplain habitats here we explore the impact of floodplain width modeled as 1 10 and 40 the channel width on a food web with two energy sources detritus and vegetation invertebrates that consume these a size structured fish population which consumes invertebrates and in which larger fish cannibalize small fish and birds which feed on large fish hydraulic linkages to trophic dynamics are assumed to be mediated in three ways birds feed efficiently only in shallow water plant carrying capacity varies non linearly with water velocity and mobile and drifting organisms are diluted and concentrated with spillover of river discharge to the floodplain and its reconfinement to the channel aspects of this model are based on field observations of junk and bailey from the amazon of sparks from the mississippi and on our observations of the fly river in papua new guinea the model produced several counter intuitive results biomass of invertebrates and fish increased with floodplain width but much more rapidly from 1 to 10 floodplains than from 10 to 40 floodplains for birds maximum biomass occurred on the 10 floodplain initially high bird biomass on the 40 floodplain declined to extinction over time because although favorable fishing conditions shallow water were most prolonged on the widest floodplain this advantage was more than offset by the greater dilution of prey after spillover bird predation on large fish sometimes increased their biomass by reducing cannibalism and thereby increasing the abundance of small fish available to grow into the larger size class sensitivity analyses indicated that model results were relatively robust to variation in parameter values that we chose but much more exploration and calibration with field data are needed before we know how specific our results are to the structure and other assumptions of this model we share with others the opinion that progress towards understanding complex dynamic systems like floodplain river ecosystems requires frequent feedback between modeling and field observations and experimentation this understanding is crucial for river management and restoration organisms in real rivers have adapted to track and quickly exploit favorable conditions and to avoid or endure adverse conditions it is when we engineer away this environmental variability that we threaten the long term persistence of river adapted biota

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

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

paleobotanical evidence for high altitudes in nevada during the miocene leaf physiognomy provides estimates of environmental parameters including mean annual enthalpy which is a thermodynamic parameter of the atmosphere that varies with altitude analyses of 12 mid miocene floras from western nevada indicate that this part of the basin and range province stood 3 kilometers above sea level at 15 to 16 million years ago which is 1 to 1 5 kilometers higher than its present altitude much if not all of the collapse to present day altitudes seems to have been achieved by 13 million years ago the crust in much of this area has been extended and thinned throughout the past 40 to 50 million years and the isostatic balance of a thinning crust requires subsidence not uplift as suggested by previous paleobotanical work

light stable isotope systematics of large scale hydrologic regimes in california and nevada surface waters shallow groundwaters and precipitation samples were collected along three traverses which begin at the california coast and are oriented in an east west manner roughly parallel to the atmospheric flow path of meteoric water the hydrogen isotope compositions from short term precipitation records varied as much as 40 at one location and were not representative of the average annual isotopic composition of precipitation the hydrogen isotope ratios of surface waters and shallow groundwaters distinguish segments with isotopic variations that correlate with measured vertical fluxes of meteoric water one coastal segment appears to closely approximate an open system in which precipitation dominates over evapotranspiration most segments are described by rather regular variations in d 3 45 per 100 km which represent different degrees of closure of the hydrologic system caused by variable partitioning of precipitation between runoff and evapotranspiration all partially closed systems imply terrestrial recycling of water a simple model estimates this amount to be about 20 across northern and central california three segments representing the great basin show virtually no geographic variation and appear to represent isotopically closed systems

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

sedimentation and preservation of the miocene atacama gravels in the pedernales chanaral area northern chile climatic or tectonic control in recent years longitudinal changes on the thin thick skinned tectonic styles of the central andes has been intensively discussed while other studies have considered the role of mass transfers on the unloading the orogen and on the stress regime along the plate interface arising from changes on the volume of sediment arriving into the peru chile trench the search for paleo climate records is therefore crucial for our understanding of the history of the central andes in this paper we focus on the atacama gravels an extensive blanket of miocene continental deposits filling a neogene paleo valley system along the southern atacama desert in northern chile an east west transect between pedernales and chanaral 26o30 s enabled us to carry out a sedimentological and tectonic study of the atacama gravels based on logging and field observations along the rio salado canyon new 39ar 40ar ages obtained on intercalated and overlying ignimbrites date the beginning of the atacama gravels sedimentation at around the oligocene miocene boundary and cessation of sedimentation in the late miocene thirteen lithofacies included within five facies associations a1 to a5 were identified depositional environments vary from proximal alluvial fan a1 a2 in the precordillera through ephemeral fluvial a3 a4 to distal playa lake a5 in the coastal cordillera no evidences of syn sedimentary deformation have been found showing that the change from sediment removal to sediment preservation cannot be explained by tectonic causes and climate change appears to be the dominant controlling factor of sediment preservation a progressive change from semi arid towards hyper arid climatic conditions during the miocene led to a reduction on the transport capacity of the fluvial system and sediment preservation along the paleovalley system formed during the oligocene

paleosurfaces paleoelevation and the mechanisms for the late miocene topographic development of the altiplano plateau abstract we construct a topographic datum across the central andes between 18 s and 22 s using extensive well preserved paleosurfaces that span the entire range this datum combined with estimates of topographic change from paleoaltimetry in the altiplano and geomorphic relief generation estimates from the plateau flanks allow us to reconstruct the paleo topography of the range at 10 ma using the 10 ma topography we explore which geophysical processes can create the observed topographic change over the

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

volcanic glass as a proxy for cenozoic elevation and climate in the cascade mountains oregon usa abstract after deposition volcanic glass hydrates with ambient water recording the average hydrogen isotope ratio d or 2h of local meteoric water during the hydration period previous researchers have used ancient glass d values to reconstruct paleotopography and paleoclimate while others have questioned the long term reliability of the proxy as a recorder of ancient meteoric water in this study we sampled volcanic glasses ranging in age 33 ma to 1 ma and local meteoric water converted to glass d values throughout the study area we propose a paleoenvironmental interpretation of volcanic glass results that resolves previously published isotopic data and agrees well with the petrologic structural and stratigraphic record namely the oregon cascades have been a significant topographic barrier since at least the mid miocene and likely as far back as the oligocene since reaching a topographic maximum during the eruption of columbia river flood basalts in the mid miocene surface elevations in oregon have decreased while the northern cascades in washington continue to rise

long term stability of hydrogen isotope ratios in hydrated volcanic glass abstract the advancement of conceptual and numerical geodynamic models necessitates quantitative orogen scale paleoelevation data felsic volcanic glasses which record the hydrogen isotope compositions d of meteoric water shortly after deposition provide several advantages as a paleoelevation proxy questions remain however about the reliability of this relatively new proxy including the effect of hydrofluoric hf acid abrasion in the preparation of glass shards for hydrogen isotope analysis and the stability of hydrogen isotope ratios in hydrated glass shards over geologic time 10 6 10 7 years hf acid abrasion of natural ancient glass shards results in systematic shifts in glass d values away from modern water d values to evaluate the effectiveness of hf acid abrasion we treated 70 150 m glass shards separated from various natural tephras with deuterium labeled water dlw d 18 205 for up to 400 days for all glasses this treatment resulted in elevated d values in comparison to untreated samples hf acid abrasion after dlw exposure however removed this effect and restored glass shards to their original untreated d values in samples older than 10 4 years hf acid abrasion removes hydrous alteration precipitates at the glass surface without measurably changing the d values of the underlying hydrated glass regardless of abrasion duration or glass composition additionally 45 34 ma glasses record d values that directly reflect their depositional environments as determined by stratigraphy glasses from tuffs deposited in demonstrably evaporative lacustrine environments have relatively high d values compared to glasses from contemporaneous tuffs deposited in nearby fluvial environments which have much lower d values the preservation of d values that systematically vary with original depositional environment despite 30 myr of post hydration exposure to the same meteoric water indicates that these volcanic glasses resisted measurable h isotope exchange on geologic timescales this research supports the use of natural felsic glass separates for paleoaltimetry and demonstrates the necessity of hf acid abrasion and glass shard isolation in sample preparation methods

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

relationships among climate erosion topography and delamination in the andes a numerical modeling investigation cordilleran orogenic systems such as the andes are controlled by shortening rates climatically controlled erosion rates and in some cases eclogite production and delamination all of these processes are coupled however making it diffi cult to uniquely determine the relative importance of each process and the feedbacks among them in this paper we develop a massbalanced numerical model that couples an actively shortening orogen and crustal root with eclogite production delamination and climatically controlled erosion the model provides a fi rst order quantifi cation of the sources shortening and sinks erosion and eclogite production and delamination of crustal volume during the cenozoic in the andes as a function of latitude and time given reasonable estimates for the rates of eclogite production and the threshold size of the eclogitic root required for delamination the model suggests that in the central andes between 5 s and 32 s the orogen has grown to a suffi cient height to produce and maintain eclogite which in turn has promoted delamination in the lower crust and mantle in this region climatically controlled erosion rates infl uence the size of the orogen through two separate mechanisms by exporting mass via surface processes and by controlling the lithostatic pressure in the lower crust which modulates the rates of eclogite production and or delamination to the north and south of the central andes relatively low shortening rates and high precipitation and erosion rates have slowed eclogite production such that delamination likely has not occurred during the cenozoic

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

an abrupt decrease in southern hemisphere terrestrial temperature during the eocene oligocene transition abstract earth s climate transitioned from the greenhouse conditions of the eocene to the icehouse of the oligocene 34 million years ago global cooling was triggered by a decrease in atmospheric pco2 and is associated with the first appearance of large permanent ice sheets on antarctica the eocene oligocene transition eot is marked by a large two step increase in the 18 o of benthic foraminifera reflecting a combination of cooler global temperatures and continental ice growth we measured the hydrogen isotope composition of hydrated volcanic glasses deposited in patagonia during the eot to reconstruct stable isotope hydrology and associated changes in temperature during this critical climate transition these data show changes in stable hydrogen isotope ratios that are consistent with patagonian terrestrial mean annual temperature decreasing by 5 c during the eot before returning to 2 c below pre eot values by the early oligocene this is approximately synchronous with northern hemisphere cooling during the eot and indicates close coupling of temperature and atmospheric pco2

organic matter maturation under the influence of a deep intrusive heat source a natural experiment for quantitation of hydrocarbon generation and expulsion from a petroleum source rock toarcian shale northern germany four shallow boreholes were drilled in the hils syncline northern germany in order to determine quantitatively the amount of hydrocarbons generated and expelled during maturation of a typical kerogen type ii bearing source rock the holes penetrated the carbonceous lias shales posidonia shale lower toarcian and part of the adjacent dogger and lias mudstones the maturity of the organic matter in the cores recovered ranges from immature 0 48 r0 to overmature 1 45 r0 due to location of the hils syncline in the vicinity of the vlotho massif which is deep seated intrusive body facies variations of the lias within the short geographical distances in the study area are negligible organic matter mass balance calculations were based on detailed organic geochemical analyses of residual material in the lias shales kerogen bitumen etc and on the evidence of a uniform initial composition of these sediments in the study area dead carbon determinations supported this latter criterion but were not used as a parameter in the calculations about 50 of the initial kerogen was transformed into oil gas and inorganic compounds during the vitrinite reflectance increase from 0 48 to 0 88 ro and only marginally more during the maturity increase from 0 88 to 1 45 ro only a small portion of the generated material remained in the source rock even at a relatively early stage of generation 0 68 ro expulsion efficiency of oil plus gas reached a value of 86 at the end of the main generation stage 0 88 ro

intraformational redistribution of selected trace elements in the posidonia shale hils syncline nw germany caused by the thermal influence of the vlotho massif selected samples of nw german posidonia shale hils syncline area were separated into five fractions bitumen kerogen pyrite carbonates silicates and chemically analyzed for trace element concentration using icp oes analyses in immature posidonia shale 0 53 ro co cu mo ni and zn occur mainly in the kerogen and pyrite fractions in mature posidonia shale 1 45 ro these trace elements are mainly fixed in the silicate fractions we postulate a thermally induced intraformational redistribution of co cu mo ni and zn caused by heat from a deep seated igneous intrusion the vlotho massif

response of meteoric δ18o to surface uplift implications for cenozoic andean plateau growth abstract the timing and magnitude of surface uplift provide important constraints on geodynamic models of orogen formation oxygen isotope 18 o and mass 47 isotopolog 47 compositions from terrestrial carbonate sediments have been used with modern isotope and temperature lapse rates to infer past surface elevations of the andes however these paleoaltimetry interpretations are contentious because variations in the oxygen isotope composition in meteoric water 18 o p are caused by changes in elevation orographic and regional climate here we use a limited domain isotope tracking general circulation model to simulate changes in 18 o p and isotopic lapse rates in response to andean surface uplift and to re evaluate 18 o and 47 changes in late miocene carbonates previously associated with rapid andean growth results indicate that andean surface uplift leads to changes in low level atmospheric circulation and an increase in precipitation along the eastern andean flank which influences isotopic source and amount effects simulated changes in andean 18 o p are not systematic with an increase in surface elevation but are instead a function of orographic thresholds that abruptly change regional climate a 18 o p decrease of 5 over the central andes and an increase in isotopic lapse rates up to 0 8 km 1 coincide with andean surface uplift from 75 to 100 of modern elevation these changes in the isotopic signature could account for the entire 3 4 18 o depletion in late miocene carbonate nodules and suggest an andean paleoelevation of 3000 m 75 of modern elevations before 10 ma

water in volcanic glass from volcanic degassing to secondary hydration abstract volcanic glass is deposited with trace amounts 0 1 0 6 wt of undegassed magmatic water dissolved in the glass after deposition meteoric water penetrates into the glass structure mostly as molecular h2o due to the lower d values of non tropical meteoric waters and the 30 offset between volcanic glass and environmental water during hydration secondary water imparts lighter hydrogen isotopic values during secondary hydration up to a saturation concentration of 3 4 wt h2o we analyzed compositionally and globally diverse volcanic glass from 0 to 10 ka for their d and h2ot across different climatic zones and thus different d of precipitation on a thermal conversion elemental analyzer tcea furnace attached to a mass spectrometer we find that tephrachronologically coeval rhyolite glass is hydrated faster than basaltic glass and in the majority of glasses an increase in age and total water content leads to a decrease in d while a few equatorial glasses have little change in d we compute a magmatic water correction based on our non hydrated glasses and calculate an average 103ln glass water for our hydrated felsic glasses of 33 which is similar to the 103ln glass water determined by friedman et al 1993a of 34 we also determine a smaller average 103ln glass water for all our mafic glasses of 23 we compare the d values of water extracted from our glasses to local meteoric waters following the inclusion of a 33 103ln glass water we find that following a correction for residual magmatic water based on an average d and wt h2ot of recently erupted ashes from our study the d value of water extracted from hydrated volcanic glass is on average within 4 of local meteoric water to better understand the difference in hydration rates of mafic and felsic glasses we imaged 6 tephra clasts ranging in age and chemical composition with bse by fei sem down to a submicron resolution mafic tephra have more bubbles per unit area 25 77 mm 2 than felsic tephra 736 mm 2 and thicker average bubble walls 0 07 mm than felsic tephra 0 02 mm we use a simplified diffusion model to quantify the hydration rate of vesicular glass as a function of the diffusivity of water and the average bubble wall thickness based on fits to our hydration rate data we estimate the initial low temperature diffusivity at 0 1 wt h2ot in volcanic glass mafic and felsic to be on the order of 10 3 to 10 4 m2 year and find that differences in hydration rates between mafic and felsic tephra can be attributed primarily to differences in vesicularity although slightly slower hydration of basalt cannot be precluded we also observe no consistent temporal difference in secondary meteoric water uptake in wet versus dry and hot versus cold climates

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

loss of metals from pelites during regional metamorphism in aluminous metapelites the ratio h2o k2o decreases with increasing metamorphic grade and degree of reaction this ratio is a very practical indicator for the progress of the mineral reconstitution during progressive metamorphism with decreasing values of the ratio h2o k2o the cu concentration and the following element ratios also decrease either continuously or in stepwise fashion tl k2o ba k2o pb k2o bi k2o hg k2o sr na2o zn fe2 mg cd fe2 mg rb k2o remains approximately constant in the aluminous metapelites of the damara orogen in namibia the following losses occur between the biotite isograd and anatexis 61 cu 20 tl 34 ba 59 pb 86 bi 46 hg 30 sr 25 zn 31 cd thus the potential of regional metamorphism to form hydrothermal deposits in the low grade environment should not be neglected

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

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in toarcian source rocks of different maturities abstract this study is part of a comprehensive research program on the generation and migration of petroleum from the organic rich posidonia shale lower toarcian jurassic of the hils syncline northern germany four cores of the complete posidonia shale with varying amounts of underlying pliensbachian and overlying aalenian mudstones provided the sample base depending upon their distance from a presumed subjacent heat source the vlotho massif the cores display progressive levels of increasing thermal maturation with r 0 values 0 48 0 68 0 88 and 1 45 which span the limits of the oil generation window primary stratigraphic lithologic and petrographic attributes of the four sections are all very similar each includes a lower marlstone member about 5 m thick overlain by 11 31 m of calcareous clay shale clay minerals calcite pyrite kerogen and quartz are the principal constituents thus there is no evidence that depositional conditions of the posidonia shale varied significantly over the sampled area the omnipresence of framboidal pyrite clearly formed from the activity of sulphate reducing bacteria at or near the depositional interface is strong evidence that uniform reducing anoxic conditions were persistent at all localities this conclusion supports the assumption that initially each section was identical in overall properties and that significant differences observed in geochemistry organic macerals and other properties are directly related to the variable levels of thermal maturation kerogen from the least mature section r o 0 48 is type ii and composed of alginite a alginite b liptodetrinite bituminite and some terrestrial sporinite vitrinite and inertinite macerals with increasing maturation the alginite macerals exhibit a progressive change in morphology and fluorescence properties alginite of the least mature section displays a strong green fluorescence at 0 68 r o alginite macerals exhibit yellow orange fluorescence and are structurally well preserved although geochemical data indicate generation and loss of large amounts of oil at 0 88 r o hydrocarbon generation is almost complete and few primary alginites remain they have been transformed into secondary liptinites designated as metaalginite which have similar fluorescence colours at the highest maturation level 1 45 r o metaalginites are only weakly fluorescent with a shift toward red colours calcite and or bitumen filled bedding plane micro and macrofractures occur exclusively in the organic rich posidonia shale at maturity levels of 0 68 r o and above such features are totally absent in the immature posidonia section and in the adjacent organic poor mudstones this observation indicates that the fractures developed in direct response to overpressuring i e pore pressure exceeding lithologic load related to oil and gas generation in the source rock the fractures undoubtedly provided important expulsion conduits for generated products

cenozoic tectonic and topographic evolution of the northern sierra nevada california through stable isotope paleoaltimetry in volcanic glass we determine the paleoelevation of the northern sierra nevada california in the oligocene based on hydrogen stable isotope compositions of meteoric water preserved within volcanic glass from ignimbrites sampled across the range a 48 decrease in the isotopic composition of hydrated glass from ignimbrites located near paleosea level to ignimbrites 100 km to the east refl ects the effect of ancient high topography on precipitation these data show that 31 28 ma ago the northern sierra nevada had a steep western gradient and elevations similar to the present this study placed in the context of other paleoaltimetry studies suggests that the range was a high topographic feature throughout the cenozoic and that the majority of uplift occurred in the late cretaceous to early cenozoic much earlier than some studies have proposed

testing the analytical protocols and calibration of volcanic glass for the reconstruction of hydrogen isotopes in paleoprecipitation in this study we investigate the foundations of the hydrated volcanic glass paleoelevation paleoenvironment proxy by testing 1 the sensitivity of volcanic glass d values to laboratory procedures 2 the reliability of young glass reconstructions of observed meteoric water values and 3 the paleoenvironmental reconstructions based on volcanic glass in comparison to those of other proxies volcanic glass d values are insensitive to variations in laboratory pretreatments displaying no signifi cant shift in d values with variations in duration of drying rinsing the temperature at which glass is dried or with the grain size that is analyzed however clay adhering to the glass particles may skew d results by 10 and hf acid pretreatment can cause signifi cant isotopic shifts parent water d values calculated from young 0 3 ma glass d values are in close accord with modern surface water d values across 3000 m of elevation in the central andes combined glass d values pedogenic carbonate 18 o values and clumped isotope paleothermometry from the 16 3 ma los cristales tuff provide a key test of resistance to resetting of d values in ancient glass hydration layers these proxies indicate hydrated volcanic glass preserves its stable isotopic information over geologic time and that the climatic patterns of the high and dry puna plateau were already in place by 16 3 ma

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

surface uplift and convective rainfall along the southern central andes angastaco basin nw argentina stable isotopic and sedimentary records from the orogenic puna plateau of nw argentina and adjacent intermontane basins to the east furnish a unique late cenozoic record of range uplift and ensuing paleoenvironmental change in the south central andes today focused precipitation in this region occurs along the eastern windward flanks of the eastern cordillera and sierras pampeanas ranges while the orogen interior constitutes high elevation regions with increasingly arid conditions in a westward direction as in many mountain belts such hydrologic and topographic gradients are commonly mirrored by a systematic relationship between the oxygen and hydrogen stable isotope ratios of meteoric water and elevation the glass fraction of isotopically datable volcanic ash intercalated in sedimentary sequences constitutes an environmental proxy that retains a signal of the hydrogen isotopic composition of ancient precipitation this isotopic composition thus helps to elucidate the combined climatic and tectonic processes associated with topographic growth which ultimately controls the spatial patterns of precipitation in mountain belts however between 25 5 and 27 s present day river based hydrogen isotope lapse rates are very low possibly due to deep convective seasonal storms that dominate runoff if not accounted for the effects of such conditions on moisture availability in the past may lead to misinterpretations of proxy records of rainfall here we present hydrogen isotope data of volcanic glass dg extracted from 34 volcanic ash layers in different sedimentary basins of the eastern cordillera and the sierras pampeanas combined with previously published dg records and our refined u pb and u th he zircon geochronology on 17 tuff samples we demonstrate hydrogen isotope variations associated with paleoenvironmental change in the angastaco basin which evolved from a contiguous foreland to a fault bounded intermontane basin during the late mio pliocene we unravel the environmental impact of mio pliocene topographic growth and associated orographic effects on long term hydrogen isotope records of rainfall in the south central andes and potentially identify temporal variations in regional isotopic lapse rates that may also apply to other regions with similar topographic boundary conditions

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

large scale drainage capture and surface uplift in eastern tibet sw china before 24 ma inferred from sediments of the hanoi basin vietnam current models of drainage evolution suggest that the non dendritic patterns seen in rivers in se asia reflect progressive capture of headwaters away from the red river during and as a result of surface uplift of eastern asia mass balancing of eroded and deposited rock volumes demonstrates that the red river catchment must have been much larger in the past in addition the nd isotope composition of sediments from the hanoi basin vietnam interpreted as paleo red river sediments shows rapid change during the oligocene before similar to 24 ma we interpret this change to reflect large scale drainage capture away from the red river possibly involving loss of the middle yangtze river reorganization was triggered by regional tilting of the region towards the east this study constrains initial surface uplift in eastern tibet and southwestern china to be no later than 24 ma well before major surface uplift and gorge incision after 13 ma

glacial interglacial temperature variations in soreq cave speleothems as recorded by clumped isotope thermometry clumped isotope thermometry is based on analyzing mass 47 in co2 extracted from carbonates and uses the tracer mass 47 anomaly 47 47 is defined as the deviation of r47 from that expected for a random distribution of isotopologues and reflects a temperature dependent preference of 13c and 18o to create a bond with each other in co2 or in the carbonate lattice being an internal characteristic of the carbonate mineral it is independent of the isotopic composition of the water in which equilibrium precipitation of the carbonate occurs and can therefore be used to independently determine carbonate growth temperatures this work provides a first examination of the applicability of clumped isotopes thermometry to reconstructing the growth temperatures of speleothems by examining the glacial interglacial variations of the 47 values of speleothem carbonates from soreq cave israel the results indicate that the last glacial maximum temperatures were 6 7 c colder than modern day temperature and a sample at 56 ky bp was 3 c colder than the modern early holocene temperatures were slightly above modern day and late holocene temperatures were slightly below modern day these temperature variations are similar to those previously estimated for eastern mediterranean sea surface water cave water was 18o depleted in the holocene compared to modern day by 0 6 1 and 1 1 more enriched in the last glacial maximum comparison of these cave water 18o values with fluid inclusion d values indicated a late holocene d excess value within the range of modern rainfall implying not vert similar45 relative humidity last glacial maximum and early holocene d excess values were significantly lower suggesting relative humidity of not vert similar60 and not vert similar70 respectively the temperatures reported in this study were empirically corrected for a non equilibrium artifact observed in a modern speleothem the similarity of the temperature variations obtained here to other independent records in the region suggests that the 47 temperature calibration slope observed in inorganic synthetic calcite and marine organisms may also be applied in speleothems but the offset observed in modern temperature suggests that the intercept is different so that a separate calibration is needed for accurate absolute temperature reconstruction using speleothem clumped isotopes similar examination of additional caves would be necessary to determine whether such empirical correction can be generally applied or is it a unique characteristic of soreq cave

microfabric mineralogy and early diagenetic history of the whitby mudstone formation toarcian cleveland basin u k the whitby mudstone formation in northeast england contains three shale facies normal restricted and bituminous which have previously been differentiated on the basis of sedimentary structures and faunal assemblages this paper shows that the three facies can also be differentiated by mineralogical geochemical and microtextural criteria determined using bsem edxra xrd and xrf the bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite calcite and dolomite the weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite the normal facies shales are very weakly laminated and contain siderite in addition to pyrite the geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon rich sulphidic carbon poor sulphidic and very carbon poor sulphidic respectively

rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates the elevation of earth s surface is among the most difficult environmental variables to reconstruct from the geological record here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters constrained by measurements of abundances of 13 c 18 o bonds in soil carbonates we use this approach to show that the altiplano plateau in the bolivian andes rose at an average rate of 1 03 0 12 millimeters per year between 10 3 and 6 7 million years ago this rate is consistent with the removal of dense lower crust and or lithospheric mantle as the cause of elevation gain

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

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

evidence for the development of the andean rain shadow from a neogene isotopic record in the atacama desert chile abstract varying ages from triassic to pliocene have been proposed for the onset of hyperaridity in the atacama desert the exact timing for the initiation of hyperaridity is critical for determining potential causes which range from regional effects of global cooling to andean uplift above elevations conducive to extreme rain shadows analysis of the stable isotopic composition of lower miocene quaternary 21 0 015 ma palustrine and lacustrine carbonates in the calama basin reveals extreme changes in their oxygen and carbon isotopic composition during the miocene limestone 18 o values increased by 5 from middle to late miocene ranging from 5 5 at 12 ma to 1 at 6 ma carbon isotopic values increase by 9 over the neogene from average values of 3 at 21 ma to 3 at 12 ma and reaching a maximum of 6 at 5 ma the increase in oxygen isotopic values occurred over a time span in which the catchment area of the basin experienced significant uplift causing the 18 o value of precipitation to become more negative we attribute the shift towards higher 18 o values to enhanced evaporative enrichment both of soil water or snow prior to infiltration and within shallow lakes or wetlands prior to carbonate precipitation the large increase in 13 c values was likely caused by a transition from a vegetated landscape influenced primarily by soil respired co 2 to a landscape largely devoid of vegetation and influenced by atmospheric and volcanic co 2 isotopic values of palustrine carbonates therefore indicate that hyperaridity commenced in the calama basin during the middle to late miocene in agreement with other paleoclimatic records from the basin the cause for the onset of this climate change is thought to be due to the development of a strong andean rain shadow associated with the uplift of the andes to mean elevations 2 km