simulation of modern and middle cretaceous marine δ18o with an ocean atmosphere general circulation model 1 we have developed a coupled ocean atmosphere general circulation model the genesis mom model with the ability to transport and fractionate water isotopes in the ocean and atmosphere the model is used to predict modern and cretaceous precipitation and seawater 18o the model reproduces the large scale modern day isotopic distribution in the zonal mean the difference between simulated and observed seawater 18o is within 0 2 in the low and middle latitudes and within 1 at high latitudes in comparison to modern simulated cretaceous surface seawater 18o is systematically depleted by 0 3 at low and middle latitudes these differences are attributed to equilibrium fractionation during surface evaporation at low latitudes and an increased partitioning of 18o from the surface into the deep ocean due to intermediate and deep water formation in subtropical basins in the cretaceous we also find that regional seawater 18o is significantly influenced by the paleobathymetry and the resolution of oceanic gateways boundary conditions that are not well known for the past our simulation of cretaceous seawater 18o has major implications for oxygen isotope paleothermometry we conclude that conventional assumptions of past seawater 18o may lead to an overestimate of cretaceous sea surface temperatures especially at middle and high latitudes

history of upwelling in the tropical eastern pacific and the paleogeography of the isthmus of panama article i nfo today there is a tight knit relationship between the elevation of the central american isthmus and the ocean ographic conditions of the tropical eastern pacific where the elevation drops below 500 m low level wind jets pass seasonally from the atlantic to the pacific driving coastal upwelling in the tropical eastern pacific this paper determines if seasonal upwelling was present in five pliocene and pleistocene fossiliferous sites on the pacific coast of the burica region of the isthmus of panama using two independent approaches that compare bryozoan morphology and whole community composition of fossiliferous localities with material from upwelling and non upwelling modern localities no definitive evidence of seasonal upwelling exists in the pliocene implying non analogous oceanographic conditions because of continued interoceanic connection prior to the closure of the isthmus of panama conversely data from three mid pleistocene sites reveal robust evidence of strong seasonal upwelling suggesting that the elevat ion of the isthmus must have been sufficiently low to permit wind jets to form a low elevation isthmus of panama may have persisted until as recently as the mid pleistocene

stable isotope paleoaltimetry and the evolution of landscapes and life abstract reconstructing topography of our planet not only advances our knowledge of the geodynamic processes that shape the earth s surface equally important it adds a key element towards understanding long term continental moisture transport atmospheric circulation and the distribution of biomes and biodiversity stable isotope paleoaltimetry exploits systematic decreases in the oxygen 18o or hydrogen d isotopic composition of precipitation along a mountain front when the interaction of topography and advected moist air masses induces orographic precipitation these changes in 18o or d can be recovered from the geologic record and recent geochemical and modeling advances allow a broad range of proxy materials to be evaluated over the last 10 yr stable isotope paleoaltimetry has witnessed rapidly expanding research activities and has produced a broad array of fascinating tectonic and geomorphologic studies many of which have concentrated on determining the elevation history of continental plateau regions these single site studies have greatly expanded what used to be very sparse global paleoaltimetric data the challenge now lies in disentangling the surface uplift component from the impact of climate change on 18o and d in precipitation the robustness of stable isotope paleoaltimetry can be enhanced when high elevation 18o or d data are referenced against low elevation sites that track climate modulated sea level 18o or d of precipitation through time approach analysis of central andean paleosols documents that differences in 18o of soil carbonate between the subandean foreland and the bolivian altiplano are small between 11 and 7 ma but rise rapidly to ca 2 9 after 7 ma corroborating the magnitude of late miocene change in 18o on the altiplano future advances in stable isotope paleoaltimetry will greatly benefit from addressing four key challenges 1 identifying topographically induced changes in atmospheric circulation and associated teleconnections in the global climate system that affect 18o or d of precipitation 2 evaluating on a case by case basis if temporal and spatial changes in isotope lapse rates influence interpretations of paleoelevation 3 interfacing with phylogenetic techniques to evaluate competing hypotheses with respect to the timing of surface uplift and the diversification of lineages 4 characterizing feedbacks between changes in surface elevation and atmospheric circulation as these are likely to be equally important to the diversification of lineages than changes in surface elevation alone tackling these challenges will benefit from the accelerating pace of improved data model comparisons and rapidly evolving geochemical techniques for reconstructing precipitation patterns most importantly stable isotope paleoaltimetry has the potential to develop into a truly interdisciplinary field if innovative tectonic paleoclimatic and evolutionary biology phylogenetic approaches are integrated into a common research framework it therefore opens new avenues to study the long term evolution of landscapes and life

comment on revised paleoaltimetry data show low tibetan plateau elevation during the eocene botsyun et al research articles 1 march 2019 eaaq1436 have suggested that the tibetan plateau was low substantially less than 3000 meters during the eocene based on a comparison of oxygen isotope proxy data with isotope enabled climate model simulations however we contend that their conclusions are flawed as the result of a number of failings of both the modeling and the data comparison

refinement of eocene lapse rates fossil leaf altimetry and north american cordilleran surface elevation estimates abstract estimates of continental paleoelevation using proxy methods are essential for understanding the geodynamic climatic and geomorphoric evolution of ancient orogens fossil leaf paleoaltimetry one of the few quantitative proxy approaches uses fossil leaf traits to quantify differences in temperature or moist enthalpy between coeval coastal and inland sites along latitudes these environmental differences are converted to elevation differences using their rates of change with elevation lapse rate here we evaluate the uncertainty associated with this method using the eocene north american cordillera as a case study to do so we develop a series of paleoclimate simulations for the early 55 49 ma and middle eocene 49 40 ma period using a range of elevation scenarios for the western north american cordillera simulated eocene lapse rates over western north america are 5 c km and 9 8 kj km close to moist adiabatic rates but significantly different from modern rates further using linear lapse rates underestimates high altitude 3 km temperature variability and loss of moist enthalpy induced by non linear circulation changes in response to increasing surface elevation ignoring these changes leads to kilometer scale biases in elevation estimates in addition to these biases we demonstrate that previous elevation estimates of the western cordillera are affected by local climate variability at coastal fossil leaf sites of up to 8 c in temperature and 20 kj in moist enthalpy a factor which further contributes to elevation overestimates of 1 km for early eocene floras located in the laramide foreland basins and underestimates of 1 km for late middle eocene floras in the southern cordillera we suggest a new approach for estimating past elevations by comparing proxy reconstructions directly with simulated distributions of temperature and moist enthalpy under a range of elevation scenarios using this method we estimate mean elevations for the north american cordillera of 2 km using proxy temperatures and 3 km using proxy moist enthalpy this discrepancy is likely related to an inconsistency between the proxy data for temperature and moist enthalpy the combination of temperature and moist enthalpy estimates implies a warm and dry environment which is inconsistent with geological evidence for humid conditions our study emphasizes that lapse rates in warm climate were likely much different than today s and highlights the advantages of using climate models to understand past climate states and regional circulation patterns to derive more accurate paleoelevation estimates using proxy temperature and moist enthalpy

a comment on rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere by c n garzione et al earth planet sci lett 241 2006 543 556

modern and long term evaporation of central andes surface waters suggests paleo archives underestimate neogene elevations abstract central andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude 2 km miocene to modern surface uplift however the isotopic relationships between precipitation surface waters and soil waters upon which these reconstructions are based remain poorly constrained for both past and in many cases modern conditions we quantify the relationships between central andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples 18o and d collected between april 2009 and october 2012 the isotopic compositions of stream waters match precipitation along the eastern flank in contrast altiplano surface waters possess a lower d 18o slope 4 59 vs 8 for meteoric waters not observed in precipitation which signals heavy isotope evaporative enrichment in surface waters paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout andean uplift and that conditions may have been more evaporative when the andes were lower thus more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central andean plateau proxy materials likely overstate miocene to present surface uplift we propose altiplano paleoelevations of 1 2 km at 24 5 ma 1 5 2 9 km by 11 45 ma and modern elevations by 6 ma based on the lightest isotopic compositions observed in altiplano proxy materials which are least likely to be influenced by evaporation these constraints limit total late miocene to modern uplift to

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

the global climate response to lowering surface orography of antarctica and the importance of atmosphere ocean coupling abstracta global climate model is used to study the effect of flattening the orography of the antarctic ice sheet on climate a general result is that the antarctic continent and the atmosphere aloft warm while there is modest cooling globally the large local warming over antarctica leads to increased outgoing longwave radiation which drives anomalous southward energy transport toward the continent and cooling elsewhere atmosphere and ocean both anomalously transport energy southward in the southern hemisphere near antarctica poleward energy and momentum transport by baroclinic eddies strengthens anomalous southward cross equatorial energy transport is associated with a northward shift in the intertropical convergence zone in the ocean anomalous southward energy transport arises from a slowdown of the upper cell of the oceanic meridional overturning circulation and a weakening of the horizontal ocean gyres causing sea ice in the northern hemisphere to expand and the arctic to cool comparison wi

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

stratigraphy and geochemistry of pillow basalts within the ophiolitic melange of the izmir ankara erzincan suture zone implications for the geotectonic character of the northern branch of neotethys the izmir ankara erzincan suture zone of turkey is a broad zone of ophiolitic melange containing numerous fragmented blocks ranging in age from triassic to cretaceous stratigraphic sequences for various melange units are compared together with the geochemistry of associated basaltic pillow lavas of cretaceous age a review of geochemical data for the pillow lavas demonstrate a a dominant group of alkalic basalts with enriched incompatible elements variable zr y and zr nb ratios and b a range of tholeiitic basalts with slightly depleted to mildly enriched normalized rare earth patterns la yb n 0 4 3 0 and generally low zr y ratios the alkalic basalts can be chemically matched to pacific ocean seamounts although the close association of red radiolarites and cherts suggests that many basalts represent the margins of such structures rather than the main seamount edifice nd sr isotope data are typical for ocean island basalts and represent an admixture of a dominant em 1 source and a depleted morb like source enhanced 18o compositions are a consequence of submarine alteration and not crustal contamination tholeiitic compositions have affinities with both n and e type morb although most are probably representative of tholeiitic ocean islands overall the basalts are mainly representative of structures built on the ocean floor rather than the oceanic crust itself being scraped off the subducting crust and preserved in the melange of the accretionary wedge

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

late neogene environmental changes in the central himalaya related to tectonic uplift and orbital forcing the linkage between tectonic forces and climate evolution remains a matter of much debate and speculation here we present high resolution oxygen and carbon isotope data from an ancient lake basin in the central himalaya these data together with sedimentologic evidence reveal major changes in drainage systems and depositional settings at 7 2 5 5 and 3 2 ma these environmental changes appear to be driven by regional scale tectonics the oxygen isotope record also reveals alternating wet and dry climates with periodicities of 24 and 100 kyr that were likely controlled by orbital forcing paleo temperatures estimated using a fossil based oxygen isotope paleo thermometer are 21 6 ca t 7 ma which is 19 6 c higher than the present day mean annual temperature in the same area the much warmer environment inferred here is consistent with fossil mammalian and pollen assemblages and sediment clay mineralogy as well as carbon isotope data from fossil tooth enamels and paleosol carbonates the estimated temperature difference would require the study area to have been raised by 2 2 5 km since 7 ma to its current elevation of 4100 4500 m above sea level this result can be interpreted as either indicating the presence of a low altitude intermountain basin in the hanging wall of the already formed main central thrust or a protracted development of a north trending rift basin that has experienced changes in drainage system and depositional environment through time

modern precipitation δ18o and trajectory analysis over the himalaya tibet orogen from echam5 wiso simulations variations in oxygen isotope ratios 18o measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time in areas of extreme topography such as the tibetan plateau the interpretation of 18o has proven challenging this study investigates the climate controls on temporal daily and 6 h intervals and spatial variations in present day precipitation 18o 18op across the tibetan plateau using a 30 year record produced from the european centre hamburg echam5 wiso global atmospheric general circulation model gcm results indicate spatial and temporal agreement between model predicted 18op and observations large daily 18op variations of 25 to 5 occur over the tibetan plateau throughout the 30 simulation years along with interannual 18op variations of 2 analysis of extreme daily 18op indicates that extreme low values coincide with extreme highs in precipitation amount during the summer monsoon vapor transport from the north and southwest of the plateau generally corresponds with high 18op whereas vapor transport from the indian ocean corresponds with average to low 18op thus vapor source variations are one important cause of the spatial temporal differences in 18op comparison of gcm and rayleigh distillation model rdm predicted 18op indicates a modest agreement for the himalaya region averaged over 86 94 e confirming application of the simpler rdm approach for estimating 18op lapse rates across himalaya

stable isotope variations δ18o and δd in modern waters across the andean plateau abstract environmental parameters that influence the isotopic composition of meteoric water 18o and d are well characterized up the windward side of mountains where orographic precipitation results in a predictable relationship between the isotopic composition of precipitation and elevation the topographic and climatic evolution of the andean plateau and surrounding regions has been studied extensively by exploiting this relationship through the use of paleowater proxies however interpretation on the plateau itself is challenged by a poor understanding of processes that fractionate isotopes during vapor transport and rainout and by the relative contribution of unique moisture sources here we present an extensive dataset of modern surface water samples for the northern andean plateau and surrounding regions to elucidate patterns and causes of isotope fractionation in this continental environment these data show a progressive increase in 18o of stream water west of the eastern cordillera 1 70 km almost identical to the rate observed across the tibetan plateau attributed to a larger fraction of recycled water in precipitation and or increased evaporative enrichment downwind this may lead to underestimates of paleoelevation particularly for sites deep into the rainshadow of the eastern cordilleran crest that said elevation is a primary control on the isotopic composition of surface waters across the entire andean plateau and its flanks when considering the most negative 18o values highlighting the need for sufficiently large datasets to distinguish minimally evaporated samples there is a general increase in 18o on the plateau from north to south concomitant with an increase in aridity and decrease in convective moistening amount effect lastly stable isotope and seasonal precipitation patterns suggest easterlies provide the vast majority of moisture that falls as precipitation across the andean plateau and western cordillera from peru to northern bolivia 13 to 20 latitude with pacific derived moisture contributing a minor amount at low elevations near the coast

early cenozoic uplift of the puna plateau central andes based on stable isotope paleoaltimetry of hydrated volcanic glass uplift of the central andes is largely thought to have occurred during the past 10 m y based on paleoaltimetry studies from the altiplano of bolivia however the spatio temporal uplift history may not be uniform across the central andes we present new stable isotopic results from the salar de antofalla salina del fraile and arizaro basin on the puna plateau 24 26 s of northwestern argentina samples of volcanic glass give d paleowater values and modeled paleoelevations that indicate an elevated 4 km puna plateau since ca 36 ma with limited

increased sediment accumulation rates and climatic forcing in the central andes during the late miocene new zircon u pb ages from six volcanic ashes in the subandean foothills provide for the first time well constrained depositional ages of the late cenozoic strata in this region the radiometric ages indicate 12 4 0 5 ma 7 93 0 26 ma and 5 94 0 20 ma depositional ages for the bases of yecua tariquia and guandacay formations respectively we used these zircon ages to determine the accumulation rates of the late cenozoic foreland sediments in the subandes our results show a fourfold increase from 130 to 628 m m y in sediment accumulation rates between ca 7 9 and 6 ma during the deposition of andean derived coarsening and thickening upward sandstone dominated tariquia strata this increased accumulation rate correlates well with monsoon intensification and climate variability in south america which was accompanied by the development of fluvial megafan paleodrainage networks in the central andes this correlation suggests that climate may have been an important factor between the late miocene and pliocene

the cenozoic climatic and topographic evolution of the western north american cordillera herein we present oxygen isotope records from cretaceous to recent terrestrial sediments in the western north american cordillera the purpose of this analysis is to use oxygen isotope records to understand the coupled surface elevation and climate histories of this region through the cenozoic to do this we constructed 18o maps of surface waters for time intervals that trace the development of topography of western north america these maps are based on 4861 oxygen isotope analyses from both published 4478 and new 383 data we determined the 18o values of surface waters using paleotemperatures derived previously from floral assemblages and the appropriate isotope fractionation factors these data suggest that in the late cretaceous to early eocene the sevier hinterland formed a plateau of unknown height around 50 ma a topographic wave developed in british columbia and eastern washington that swept southward reaching northeastern nevada at 40 to 38 ma and southern nevada 23 ma this southward encroachment of an eocene plateau sweep caused reorganization of drainage patterns such that the intraforeland basins of wyoming and utah drainages extended deep within the sevier hinterland as the wave swept southward the landscape within the sevier hinterland developed into a rugged and high mountain range with the hypsometric mean elevation of 4 km and relief of 1 5 km this eocene highland was bordered on the west by a high sierra nevada ramp and on the east by the intraforeland basins that captured water draining these growing highlands the spatial and temporal evolution of this highland correlates with the timing of volcanism and extension these observations support tectonic models that call for north to south removal of the farallon slab or piecemeal removal of mantle lithosphere the isotopic data show that prior to growth of this highland the north american monsoon nam penetrated much farther north in the paleocene eocene than today the combined effects of global cooling increasing latitudinal temperature gradients and the generation of the orographic barrier created by the growing north to south highland produced a southward migration of the nam front by the oligocene the hydrologic regime that we observe today was in place it has been modified since then as a result of basin and range extension and collapse of the highlands in the mid miocene this collapse allowed the nam to penetrate farther north into the great basin of nevada and utah

a mid cretaceous change from fast to slow exhumation of the western chinese altai mountains a climate driven exhumation signal abstract the chinese altai mountains in western china are bound by cenozoic transpressional strike slip faults many of which show quaternary activity to better understand how mesozoic cenozoic deformation has affected the history of exhumation and uplift of the chinese altai mountains we collected paleozoic granitoid samples for apatite fission track and apatite u th sm he thermochronology central apatite fission track ages for n 6 samples range from 68 to 104 ma whereas apatite u th sm he ages range from 56 to 272 ma for n 23 samples n 80 individual analyses across four transects in the western chinese altai our results indicate fast cooling during the late early cretaceous followed by slow cooling since thermal modeling results suggests

nonuniform surface uplift of the andean plateau revealed by deuterium isotopes in miocene volcanic glass from southern peru abstract proposals for rapid late miocene surface uplift driven by large scale lithospheric removal beneath the central andean plateau have been based largely on temperature sensitive paleoaltimeters both the magnitude and mechanism of this proposed pulse of uplift have been challenged first climatic general circulation models support protracted uplift with predicted temperature and isotopic shifts enhanced by attainment of threshold elevations second tectonic models in which surface elevations are compensated by regional contraction and crustal thickening question the need for lithospheric removal and predict broadly coeval uplift of the entire plateau we present hydrogen isotope data using a novel temperature insensitive volcanic glass proxy from continuous well dated lower to middle miocene basin fill in the western cordillera of the northern plateau that show a rapid decrease in d values 62 8 at 19 16 ma with extremely negative values continuing into the pliocene we propose that the basin reached its current elevation by 16 ma 6 myr earlier than proposed for the central plateau the rapid decrease in d values is consistent with punctuated surface uplift of 2 2 3 7 km between 19 and 16 ma whereas the 3 7 km upper estimate assumes a static climate similar to modern the 2 2 km lower estimate conservatively incorporates modeled changes in the isotopic composition of precipitation associated with elevation change comparison of these results to existing paleoelevation estimates from the andean plateau facilitates a tentative reconstruction of earliest middle miocene paleotopography showing a central depression with flanking hinterland and thrust belt highlands this apparent pattern of nonuniform plateau uplift contradicts shortening proportional topographic growth over tens of myr we propose that temporally and spatially irregular surface uplift may be linked to pronounced local variability in crustal shortening and or piecemeal removal of dense mantle lithosphere insofar as these irregularities reflect the scale of heterogeneity for surface uplift processes available paleoelevation estimates point to a principal uplift mechanism that varies over relatively short

tectonic evolution of the central andean plateau and implications for the growth of plateaus current end member models for the geodynamic evolution of orogenic plateaus predict a slow and steady rise during crustal shortening and ablative subduction i e continuous removal of the lower lithosphere or b rapid surface uplift following shortening which is associated with punctuated removal of dense lower lithosphere and or lower crustal flow this review integrates results from recent studies of the modern lithospheric structure geologic evolution and surface uplift history of the central andean plateau to evaluate the geodynamic processes involved in forming it comparison of the timing magnitude and distribution of shortening and surface uplift in combination with other geologic evidence highlights the pulsed nature of plateau growth we discuss specific regions and time periods that show evidence for end member geodynamic processes including middle late miocene surface uplift of the southern eastern cordillera and altiplano associated with shortening and ablative subduction latest

a late miocene subtropical dry flora from the northern altiplano bolivia abstract a variety of evidence suggests that the altiplano of the central andes the second highest and largest plateau on earth underwent significant uplift in the late miocene pliocene the most important datum supporting recent uplift is a collection of the 10 66 0 06 ma jakokkota flora from west central bolivia which implies a paleoelevation no more than 1600 1200 m today the site has an elevation of almost 4000 m in order to test the reliability of this estimate the present study analyzes a new collection of the jakokkota flora from a lacustrine unit that is 0 2 0 5 myr younger than the previously analyzed collection from a fluvial unit climate estimates based on leaf morphology for the two collections are statistically indistinguishable the combined flora has a mean annual temperature of 21 5 2 0 c and a mean annual precipitation of 550 180 mm the similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them nor a significant bias in the leaf morphology due to differing taphonomic processes the climate estimate for the combined flora thus presents a representative picture of the late miocene climate of the northern altiplano if one assumes that the climate of the tropics has not changed significantly since the late miocene as is suggested by marine isotopic data then the paleoclimate of the jakokkota flora implies a paleoelevation of 1160 600 m thus the jakokkota flora supports the hypothesis of a young age for the altiplano

extensional basin evolution in the cordillera blanca peru stratigraphic and isotopic records of detachment faulting and orogenic collapse in the andean hinterland 1 sedimentologic provenance oxygen isotope and 40ar 39ar results provide insights into late cenozoic evolution of an extensional hinterland basin in the peruvian andes the 5 6 5 km cordillera blanca composes the glaciated footwall of a low angle normal fault parallel to active contractional structures in the andean fold thrust belt the 200 km long wsw dipping 19 36 cordillera blanca detachment fault accommodated 12 15 km of dip slip displacement inducing subsidence of the hanging wall supradetachment basin which is filled by 1300 m of conglomerate sandstone siltstone and limited carbonate of the upper miocene pliocene lloclla formation lithofacies associations are attributed to lacustrine fan delta to proximal stream dominated alluvial fan sedimentation provenance data record footwall unroofing of jurassic through miocene volcanic and sedimentary rocks during nw directed axial dispersal of sediment provenance data record the appearance of footwall derived granite clasts from the upper miocene cordillera blanca batholith and a change to transverse wsw directed transport variations in the character and preservation of basin fill suggest along strike propagation of the fault through time initial extension and subsidence is constrained to the latest miocene by an 40ar 39ar biotite age of 5 4 0 1 ma for a basal tuff in the lloclla formation estimation of paleolake water composition shows very negative 18o vsmow values 13 6 to 18 2 indicating that high elevations comparable to modern were already attained in the cordillera blanca during earliest normal faulting and basin evolution these results lend support to models suggesting that substantial shortening crustal thickening and surface uplift were necessary precursor conditions for the generation of the cordillera blanca detachment fault

andean elevation control on tropical pacific climate and enso late cenozoic marine proxy data record a long term transition in the tropical pacific from el nino like conditions with reduced zonal sea surface temperature sst gradient deepened thermocline and reduced upwelling in the eastern equatorial pacific eep to conditions similar to modern this transition coincides with kilometer scale uplift of the central andes to understand whether the rise of the andes contributed to tropical pacific climate evolution we performed experiments with the national center for atmospheric research s community climate system model version 4 to quantify changes in tropical pacific climate and el nino southern oscillation as a function of andean elevations our results demonstrate that uplift increases the equatorial east west sst gradient and walker circulation the rise of the andes from 1 to 3 km increases the sst gradient by 0 8 c and walker circulation by 60 due to strengthened radiative cooling by enhanced low cloud formation in the eep this cooling effect is largest in the southeastern tropical pacific and accounts for about one half of the reconstructed sst cooling along the peru coast the uplift also strengthens upwelling north of the eep consistent with documented increases in biological productivity in this region and decreases the frequency of el nino southern oscillation and the number of strong el nino events simulated responses to andean uplift are generally consistent with the late cenozoic proxy records but too small in magnitude taken together our results indicate that andean uplift was likely one of the multiple factors that contributed to the long term evolution of both the mean climate state and the interannual variability in the tropical pacific

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

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

new constraints on the chronology magnitude and distribution of deformation within the central andean orocline 1 constructing an accurate kinematic model for crustal thickening in the central andes is hampered by the inability of 2 d balanced cross sections to resolve the 3 d displacement field within the poorly studied orocline core this study presents new structural and thermochronometer data from the orocline axis in the central andes that constrains the magnitude and timing of deformation through 1 a balanced cross section quantifying shortening perpendicular to strike 2 field observations that constrain translational displacements parallel to strike and 3 thermochronology that brackets the age of exhumation and deformation mapping results show that north directed right lateral motion has been accommodated on at least one major strike slip fault in the eastern cordillera ec shortening perpendicular to fault strike is 179km 41 for the ec and inter andean zone ia and 86km 39 for the sub andes sa apatite fission track cooling ages indicate rapid ec ia exhumation from 46 to 18ma and 15 to 0ma in the sa zircon and apatite u th he ages show that rapid exhumation began 10 5ma in the sa these results are integrated with existing paleomagnetic and gps rotation data in map view reconstructions to quantify the magnitude of translational faulting related to oroclinal bending the reconstructions suggest that at least 85km of north directed translational displacement has been accommodated within the orocline core orogen parallel displacement and vertical axis rotations have focused crustal thickening at the orocline core and facilitated development of a high elevation plateau suggesting a genetic link between large scale oroclines and plateaus

miocene paleotopography of the central alps abstract reconstructing surface elevation surface uplift and relief histories is fundamental to understanding the growth of mountain ranges to explore their topographic limits and relate these to the interplay between geodynamic and earth surface processes here we aim to quantify miocene paleoelevation of the central european alps through stable isotope paleoaltimetry the novelty of our approach which renders our analysis less sensitive to past climate change is that stable isotope proxies of identical age are analyzed from both the high internal parts of the alpine orogen and the adjacent foreland basin whereas the foreland basin was at or near sea level and traces the combined effects of upstream changes in rainfall amount and composition the high alpine site additionally records the effect of elevation on stable isotopes in precipitation we compare hydrogen isotopic ratios d in mica and chlorite that interacted with meteoric water along the simplon detachment a major normal fault that developed at high elevations with meteoric water compositions deduced from carbonate bearing paleosols of the north alpine foreland basin d values of muscovite 126 and chlorite 135 from the brittle hanging wall and of recrystallized muscovite 108 and biotite 140 from adjacent footwall mylonites provide unequivocal evidence for localized syntectonic meteoric water interaction along the simplon detachment detailed 40 ar 39 ar and fission track geochronology constrains the timing of isotopic exchange to ca 14 5 ma when the footwall mylonites passed through the ductile to brittle transition age equivalent oxygen isotope ratios 18 o measured within pedogenic carbonate from north alpine foreland paleosols that developed near miocene sea level serve as our low elevation point of reference 18 o values in these paleosols dated with ca 100 ka precision vary between 19 and 25 smow with average values of 20 at ca 14 5 ma using the relative differences between meteoric water compositions in the foreland basin and the high alpine simplon detachment our isotope data are consistent with a mid miocene minimum average elevation difference of 2350 700 500 m for the simplon region our results indicate that miocene alpine elevations were at least comparable to those of today and are likely to have acted as an important barrier to atlantic derived moisture transport into central europe and eurasia since that time

abrupt changes in the rate of andean plateau uplift from reversible jump markov chain monte carlo inversion of river profiles abstract knowledge of the rate of surface uplift of the central andean plateau provides important boundary conditions for regional geodynamic models and paleoclimate reconstructions here we present a fully nonlinear inverse method to extract the rock uplift history of the central andean plateau from the cotahuasi river and its tributaries our approach is based on an analytical solution to the stream power model that relates elevation to rock uplift history under the assumptions of constant climatic conditions in space and time and spatially invariant rock uplift we use a bayesian framework that allows us to quantify the full state of knowledge of model parameters i e uncertainties trade offs the erosional efficiency defines the landscape response time and this must be determined using independent data therefore using thermochronometric data from the cotahuasi ocona canyon which record rapid fluvial incision at 13 10 ma we calibrate our results to infer a rock uplift history for the north central andean plateau we infer a pulse of rock uplift between 25 and 10 ma at rates as high as 0 25 km my however the rock uplift rate inferred during this pulse is not as high as is predicted if the central andean plateau grew as a result of loss of unstable lithospheric mantle therefore our results are more consistent with models requiring gradual uplift of the central andean plateau

stable isotope composition of precipitation across the southern patagonian andes 1 a surface water and precipitation transect across the southern patagonian andes at 47 48 s was conducted to assess how mountains affect the isotopic composition of precipitation this westerly wind region derives its moisture that falls as precipitation from the pacific orographic uplift of air over the andes causes pseudoadiabatic cooling and orographic precipitation on the western side and a strong rain shadow on the eastern side of the mountains these processes also produce a profound isotopic rain shadow with 18o values 4 lower in the east compared to the west on the windward western side of the andes the isotope values of precipitation and surface waters show weak although systematic trends with elevation but a pronounced correlation with distance from the main source of moisture pacific ocean a rayleigh simulation of precipitation 18o values as a function of condensation altitude matches our data well suggesting that other processes such as mixing of water sources and postcondensation evaporation are negligible and that topography is the dominant control on the isotope ratio of precipitation in contrast isotope ratios of waters on the leeward eastern side of the southern patagonian andes vary neither with elevation nor with distance from the mountains consistent with much of the precipitation on the leeward side being derived from precipitation carried over the andes by winds thus paleoprecipitation isotopic composition on the leeward side of orogens in similar climatic settings single moisture source and cool climate yield useful estimates of the elevation of these orogens but not local elevation

the impact of topography on isotopes in precipitation across the central anatolian plateau turkey paleoelevation reconstructions of mountain belts and orogenic plateaus based on stable isotope climate and precipitation records benefit greatly from present day calibrations that relate the fractionation of hydrogen d and oxygen 18o isotopes in precipitation to orographic rainfall here we establish a first order template of d and 18o of modern meteoric waters across the central anatolian plateau cap and its bordering pontic and taurus mountains we identify key regions in the plateau interior and along the plateau margins that have the potential to reliably record topography related paleotemperature and paleoprecipitation changes as recovered from stable isotope paleosol fossil teeth or lipid proxy data based on d and 18o data of more than 480 surface water samples from small catchments and springs we characterize moisture sources affecting the net isotopic budget of precipitation over the cap and analyze how orographic rainout and plateau aridity shape modern patterns of d and 18o in precipitation the taurus mountains bordering the cap to the south act as a major orographic barrier for transport of predominantly winter moisture and exhibit isotopic lapse rates of approximately 20 km for d and 2 9 km for 18o across an elevation range of nearly 3000 m the pontic mountains at the northern margin of the cap force perennial moisture to ascend and condensate revealing lapse rates of 19 km for d and 2 6 km for 18o the difference in the predominant moisture source for the southern and northern margins of the cap north african versus atlantic air masses is manifested in systematic north south differences in near sea level meteoric water compositions of dn s 20 permil and 18on s 3 permil in a swath across the central part of the plateau stable isotope data from the semi arid plateau interior with rainfall as low as 300 to 500 mm yr and mean summer temperatures attaining 23 c provide clear evidence for an evaporative regime that drastically affects surface water and runoff compositions and results in a local meteoric water line for the plateau interior that follows d 4 0 18o 29 3 strongly evaporitic conditions contrast rainfall patterns along the plateau margins including their immediate leeward flanks where d and 18o elevation relationships are reliable predictors of modern topography

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

andean scale highlands in the late cretaceous cordillera of the north american western margin from the late jurassic through the cretaceous collision between the north american and farallon plates drove extensive thin skinned thrusting and crustal shortening that resulted in substantial relief in the north american cordillera the elevation history of this region is tightly linked to the tectonic climatic and landscape evolution of western north america but is not well constrained here we use an atmospheric general circulation model with integrated oxygen isotope tracers isocam3 to predict how isotope ratios of precipitation would change along the north american cordillera as the mean elevation of orogenic highlands increased from 1200 m to 3975 m with increases in mean elevation highland temperatures fall monsoonal circulation along the eastern front of the cordillera is enhanced and wet season generally spring and summer precipitation increases simulated oxygen isotopic ratios in that precipitation are compared to those obtained from geologic materials e g fossil bivalves authigenic minerals quantification of match between model and data derived 18o values suggests that during the late cretaceous the best approximation of regional paleoelevation in western north america is a large orogen on the scale of the modern andes mountains with a mean elevation approaching 4000 m and a north south extent of at least 15 of latitude

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

the iglesia basin in the southern central andes a record of backarc extension before wedge top deposition in a foreland basin abstract the iglesia basin hosts a key sedimentary archive of the evolution of the southern central andes this basin is classically interpreted as recording the transition from an outer to an inner wedge top piggyback basin depozone in the early bermejo foreland basin system in this study we reevaluate the tectonic evolution of the iglesia basin based on the interpretation of 2d seismic reflection data structural geology zircon u pb geochronology and provenance analysis we report an extensional event that initiated the basin opening our results indicate normal faulting development and synextensional deposition from the latest oligocene earliest miocene to middle miocene since the middle miocene extensional activity experienced a progressive decrease in changing to shortening and basin inversion between the middle late miocene the latter stage coincided with the full development of pampean flat slab subduction indicating maximum plate coupling at that time our findings challenge the idea of uninterrupted paleogene to neogene flexural subsidence related to the andean orogenic load in the backarc area therefore the results of this study have important consequences for the early evolution of the bermejo foreland basin and ultimately for the growth of the southern central andes

magmatic and metallogenetic episodes in the northern tin belt cordillera real bolivia new k ar determinations for granitoid rocks and ores from the northern bolivian segment ca 15 18 s of the central andean cordillera oriental eastern cordillera confirm that this region displays a remarkable repetition of magmatic activity and associated lithophile metal mineralization intrusion of monzogranites in part peraluminous and granodiorites took place in the mid to late triassic apparent age range 225 202 ma and late oligocene early miocene 28 4 ca 19 2 ma the two plutonic domains are juxtaposed with little or no areal overlap along an essentially linear belt defining the inner boundary of the central andean magmatic arc there is no conclusive evidence of granitoid intrusion during the intervening period although at least two centres of upper cretaceous basic intermediate hypabyssal volcanic rocks are known whereas the triassic episode simultaneously affected ca 200 km of the belt the oligocene miocene domain experienced a longitudinal southeastward migration of activity which in its later stages 22 19 ma coincided with the initiation of widespread volcanism and intrusion on the altiplano to the west of the granitoid belt

response to comment on rapid uplift of the altiplano revealed through 13 c 18 o bonds in paleosol carbonates clumped isotope thermometry measurements of carbonate samples deposited in the bolivian altiplano as early as 28 5 million years ago and buried up to 5000 meters deep exhibit no relationship between burial depth and apparent temperature and largely yield temperatures within error of plausible earth surface conditions these results counter the predictions of sempere et al and support our previous conclusions regarding the uplift of the altiplano

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

quantifying the role of paleoclimate and andean plateau uplift on river incision 1 river incision over geologic timescales can be a valuable indicator of regional surface uplift however extracting the timing of surface uplift relative to the onset of incision is complicated by changes in precipitation commensurate with topographic development evidence of large scale river incision on the flanks of the andean plateau has been cited in support of a rapid and recent surface uplift event recent climate modeling studies demonstrate large magnitudes of regional climate change associated with surface uplift of the andes which may have influenced river incision processes here we present an analysis of mid miocene 16 ma to present river incision of the southwest peruvian ocona river a monte carlo approach with 1 6 105 different simulations is used to explore the range of surface uplift and paleoclimate histories that are compatible with the modern river profile and geological constraints on the incision timing and magnitude a range of channel properties including the erodibility coefficient and erosion threshold are considered results indicate that deep canyon incision on the plateau flanks may not be as diagnostic of rapid surface uplift as previously thought more specifically the evolution of the ocona river is consistent with local plateau elevations of 1 3 km at 16 ma and either a steady or punctuated uplift of 1 5 3 5 km since then the range of acceptable uplift histories is sensitive to the long term magnitude and temporal evolution of precipitation similar paleoprecipitation changes are expected to have modified river profile evolution elsewhere in the andes

mean annual temperature estimation based on leaf morphology a test from tropical south america abstract are models that predict mean annual temperature mat from leaf morphology applicable globally fifteen models that predict mat from leaf morphology were tested on thirty floral samples from tropical south america to determine the degree to which models based on published data that are primarily from other regions are applicable to floras from tropical south america the models included are based on regional data from north america south america and asia of the fifteen models tested five are simple linear regressions six are multiple linear regressions two are canonical correspondence analyses and two are correspondence analyses followed by nearest neighbor analyses for the seven modern floras with mat 21 c every model overestimates mat for the 23 modern floras with mat 21 c all models produce variable results without a systematic error the range of average model errors is 2 7 7 3 c while the absolute extremes of error are 0 and 15 1 c average 95 predictive confidence intervals range from 1 6 to 6 9 c predicted mat falls within the published standard error of the model for 0 67 of the south american test floras evaluating the seven sites with mat 21 c separately from the 23 sites with mat 21 c shows that no equation accurately estimates mat of the majority of low temperature sites but that four equations accurately estimate 50 of high temperature sites the results suggest that at least for sites of unknown or high elevation mean annual temperature of fossil floras from tropical south america may be better predicted from models based on the leaf morphology of tropical south american floras

the influence of the andes mountains on the south american low level flow 1 a dry hydrostatic three dimensional primitive equation model is used to evaluate the mechanical effect of the andes mountains on the south american low level flow llf the model simulations reproduce the evolution of a baroclinic wave over the continent under winter and summer conditions in both seasons as a consequence of the interaction between the basic flow and the andes northerly llf was reproduced east of the andes which resembles the main characteristics of the observed flow moreover seasonal changes of cyclone activity have a significant impact on the location of maximum llf and its alignment which exhibits a nw se orientation during winter and more meridional orientation in the warm season

influence of the andes mountains on south american moisture transport convection and precipitation mountain ranges are known to have a first order control on mid latitude climate but previous studies have shown that the andes have little effect on the large scale circulation over south america we use a limited domain general circulation model regcm3 to evaluate the effect of the andes on regional scale atmospheric dynamics and precipitation we present experiments in which andean heights are specified at 250 m and 25 50 75 and 100 of their modern values our experiments indicate that the andes have a significant influence on moisture transport between the amazon basin and the central andes deep convective processes and precipitation over much of south america through mechanical forcing of the south american low level jet llj and topographic blocking of westerly flow from the pacific ocean when the andes are absent the llj is absent and moisture transport over the central andes is mainly northeastward as a result deep convection is suppressed and precipitation is low along the andes above 50 of the modern elevation a southward flowing llj develops along the eastern andean flanks and transports moisture from the tropics to the subtropics moisture drawn from the amazon basin provides the latent energy required to drive convection and precipitation along the andean front large northerly moisture flux and reduced low level convergence over the amazon basin leads to a reduction in precipitation over much of the basin our model results are largely consistent with proxy evidence of andean climate change and have implications for the timing and rate of andean surface uplift

central andean crustal structure from receiver function analysis abstract the central andean plateau 15 27 s is a high plateau in excess of 3 km elevation associated with thickened crust along the western edge of the south america plate in the convergent margin between the subducting nazca plate and the brazilian craton we have calculated receiver functions using seismic data from a recent portable deployment of broadband seismometers in the bolivian orocline 12 21 s region and combined them with waveforms from 38 other stations in the region to investigate crustal thickness and crust and mantle structures results from the receiver functions provide a more detailed map of crustal thickness than previously existed and highlight mid crustal features that match well with prior studies the active volcanic arc and altiplano have thick crust with moho depths increasing from the central altiplano 65 km to the northern altiplano 75 km the eastern cordillera shows large along strike variations in crustal thickness along a densely sampled sw ne profile through the bolivian orocline there is a small region of thin crust beneath the high peaks of the cordillera real where the average elevations are near 4 km and the moho depth varies from 55 to 60 km implying the crust is undercompensated by 5 km in comparison a broader region of high elevations in the eastern cordillera to the southeast near 20 s has a deeper moho at 65 70 km and appears close to isostatic equilibrium at the moho assuming the modern day pattern of high precipitation on the flanks of the andean plateau has existed since the late miocene we suggest that climate induced exhumation can explain some of the variations in present day crustal structure across the bolivian orocline we also suggest that south of the orocline at 20 s the thicker and isostatically compensated crust is due to the absence of erosional exhumation and the occurrence of lithospheric delamination

uplift of the central andes of nw argentina associated with upper crustal shortening revealed by multiproxy isotopic analyses this study contributes to the uplift history of the andes which has received increasing attention in recent years because of its implications for geodynamic models and climate feedbacks shortening resulting in crustal thickening and removal of gravitationally unstable mantle lithosphere has been proposed to control deformation and uplift of cordillera type orogenic systems such as the puna plateau of the central andes and its eastern margin the eastern cordillera we present new clumped isotope 47 18o and 2 data from carbonate nodules marlstone spring deposits and volcanic ashes from the puna plateau and eastern cordillera of nw argentina when combined with other geological evidence our data indicate that the puna plateau was near its present elevation since at least 10 ma whereas the eastern cordillera rose 1 5 km between 14 and 7 ma this history of uplift correlates with active shortening in the eastern cordillera and with incorporation of a regional foreland into the propagating orogenic wedge our study suggests that the elevation of the puna plateau changed little during the miocene pliocene whereas the margin experienced significant uplift associated with active deformation and crustal thickening

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

rapid regional surface uplift of the northern altiplano plateau revealed by multiproxy paleoclimate reconstruction the central altiplano is inferred to have experienced 2 5 1km surface uplift between 10 and 6 ma while the southern altiplano experienced a similar magnitude of surface uplift that began earlier between 16 and 9 ma to properly constrain the along strike timing of the altiplano plateau surface uplift it is necessary to know how and when the northernmost part of the altiplano plateau evolved we reconstruct the paleoclimate and infer the corresponding paleoelevation from the miocene pliocene deposits of the descanso yauri basin 14 15 s in the northernmost part of the altiplano plateau using 4 different proxies including carbonate clumped isotope composition i e 47 values carbonate 18 o c leaf wax d wax and pollen assemblages from paleosol lacustrine and palustrine carbonates and organic rich sediments the isotopic signatures reflect past climate conditions of mean annual air temperature 47 and meteoric water isotope values 18 o c d wax our results show that the northernmost plateau remained at low elevation 0 9 0 8 to 2 1 0 9km until late miocene time 9 ma characterized by 15 c warmer than modern temperature mean annual air temperature of 23 4 c 2 low elevation vegetation and precipitation signature with reconstructed 18 o mw vsmow of 8 3 2 0 2 from carbonate 18 o c and 8 6 1 8 2 from leaf wax d wax modern elevations of 4 km were not reached until 5 4 1 0ma as indicated by a negative shift in d wax vsmow from 143 4 12 8 2 to 209 2 21 1 2 between 9 1 0 7 and 5 4 1 0ma the timing of surface uplift of the northernmost altiplano is consistent with the evidence for late miocene surface uplift of the central altiplano 16 19 s between 10 and 6 ma and indicates that regional scale uplift in the northern central plateau significantly postdates the onset of surface uplift in the southern altiplano 19 22 s between 16 and 9 ma these results are consistent with piecemeal removal of the lower dense lithosphere combined with possible lower middle crustal flow from south to north in the plateau acting as the main mechanisms for the formation of the altiplano plateau

early to middle miocene climate in the atacama desert of northern chile abstract the cenozoic paleoclimate of the atacama desert is not well known we examined 14 early to mid miocene paleosols exposed in the el tesoro mine near calama chile the paleosols developed on an aggrading alluvial fan system and lie above the mineralized gravel horizons that host a copper ore body soil forming conditions that oscillated between chemical weathering and clay production humid analogous to modern alfisols to environments favoring the accumulation of pedogenic carbonate arid to semi arid analogous to modern aridisols are indicated in contrast the region is presently hyperarid and soils accumulate sulfates chlorides and nitrates while total chemical analyses clearly show the accumulation of ca by the carbonate rich paleosols none of the soils exhibit significant losses of elements by leaching the 18 o values of the carbonates range from 8 79 to 3 16 vpdb the o isotope data when combined with published data from the region reveal a significant divergence in the o isotope composition of precipitation in the eastern and western margins of the andean plateau since the early miocene suggesting that simple interpretations of declining 18 o values of carbonate with increasing elevation may not be appropriate these paleosols clearly indicate that wetter conditions prevailed in what is now the atacama desert during the early to mid miocene

impacts of cenozoic global cooling surface uplift and an inland seaway on south american paleoclimate and precipitation δ18o stable isotope records of precipitation 18 o 18 o prec have been used as paleoclimate and paleoelevation archives of orogens however interpretation of these records is limited by knowledge of how 18 o prec responds to changes in global and regional climate during mountain building events in this study the influence of atmospheric co 2 levels the extent of the antarctic ice sheet changes in andean surface elevation and the presence of the south american inland seaway on climate and 18 o prec in south america are quantified using the genesis v3 atmospheric general circulation model with isotope tracking capabilities results are presented in the context of cenozoic south american climate and 18 o prec changes more specifically we find 1 precipitation rates in the andes are sensitive to andean surface elevation the seaway and to a lesser extent co 2 levels increasing andean elevations and the presence of a seaway both cause large increases in precipitation but in different parts of the andes the growth of the antarctic ice sheet is found to have a small influence on south american precipitation 2 the stable isotopic composition of precipitation is sensitive to all of the parameters investigated an increase in 18 o prec of up to 8 is found in simulations with higher atmospheric co 2 in agreement with previous studies 18 o prec decreases with increasing andean elevation by an amount greater than that predicted by the modern adiabatic lapse rate furthermore the presence of an inland seaway causes a decrease in 18 o prec of 1 8 in the northern and central andes the amount of depletion is dependent on the isotopic composition of the seaway simulations without the antarctic ice sheet result in 18 o prec that is 0 3 lower than the modern finally time specific simulations for the miocene and eocene show that 18 o prec has decreased during the cenozoic and that local geographical gradients of 18 o prec have increased particularly in regions of high modern elevation we demonstrate that in addition to andean uplift and associated climate change co 2 levels and an inland seaway are likely to have influenced 18 o carb records from south america consideration of these global and paleogeographic changes is necessary when interpreting paleoclimate or paleoelevation from stable isotope records of 18 o prec

clumped isotope evidence for diachronous surface cooling of the altiplano and pulsed surface uplift of the central andes spatially extensive paleoelevation records of the altiplano plateau are critical to determining the geodynamic mechanisms that formed and support high elevations over a broad area prior stable isotope data reveal a climate history for the northern bolivian altiplano that has been interpreted to show rapid surface uplift of 2 5 1 0 km between 10 and 6 ma this study applies clumped isotope paleothermometry to paleosol carbonates formed at both a low elevation site and temporally overlapping high elevation sites in the southern altiplano eastern cordillera during the middle to late miocene surface paleotemperature decreased by 14 c in the southern altiplano eastern cordillera relative to stable low elevation paleotemperatures implying surface elevation increase of 1 9 0 7 km between 16 and 13 ma and an additional 0 7 0 6 km between 13 and 9 ma both the large magnitude of surface temperature decrease and earlier onset 7 4 myr in the south as compared to the north suggest rapid elevation increase by piecemeal removal of lower lithosphere beneath the plateau and possible northward lower crustal flow

early cenozoic evolution of topography climate and stable isotopes in precipitation in the north american cordillera paleoelevation reconstructions of the north american cordillera in ferred from the oxygen delta 18o and hydrogen delta d isotope ratios of terrestrial paleoclimate proxy materials soils ashes lake sediments suggest rapid north to south migration of topography in the early cenozoic pre 49 ma to 28 ma the validation of this reconstruction relies on an accurate understanding of the delta 18op and the associated regional climate change in response to the uplift of the western north america here we study this response using a global climate model gcm with explicit delta 18op diagnostics echam5 wiso focusing on the isotopic effects of different types of precipitation vapor mixing recycling and moisture source and compare the response against estimates made using a rayleigh distillation models of moist adiabatic condensation rdm four experiments are performed with eocene topography inferred from terrestrial stable isotope paleoaltimetry records to investigate how southward propagation of topography affects regional climate temperature precipitation and circulation pattern and dela 18op over north america our experiments predict delta 18op patterns that are broadly consistent with maps of temporally binned proxy delta 18o and generally support an early cenozoic north to south propagation of high topogra phy in the north american cordillera they do not support the commonly made assumption that isotopic fractionation occurs primarily through rainout following rayleigh distillation nor the application of modern empirical delta 18op lapse rates to past environments in our gcm simulations precipitation processes and climate changes that are not captured by rdms substantially affect delta 18op these processes include shifts in local precipitation type between convective and large scale rain and between rain and snow intensification of low level vapor recycling particularly on leeward slopes develop ment of air mass mixing and changes in wind direction and moisture source each of these processes can have significant 2 influences on delta 18op that are comparable in magnitude to surface uplift of hundreds or even thousands of meters in many regions these processes fortuitously compensate each other explaining the apparent agreement between echam5 wiso and proxy delta 18o and more broadly between rdm estimates and observed delta 18o elevation relationships in some regions compensation is incomplete and as a result echam5 wiso delta 18op does not agree with estimates from the rdm in these regions including the interior of the northern cordillera and the eastern flank of the southern cordillera moderate adjustments of paleoelevations may be in order

k ar geochronology of the late cenozoic volcanic rocks of the cordillera occidental southernmost peru abstract twenty four k ar radiometric ages are presented for late cenozoic continental volcanic rocks of the cordillera occidental of southernmost peru lat 16 57 17 36 s rhyodacitic ignimbrite eruptions began in this transect during the late oligocene and continued episodically through the miocene the development of andesitic dacitic strato volcanoes was initiated in the pliocene and continues to the present the earliest ignimbrite flows 25 3 22 7 ma are intercalated in the upper coarsely elastic member of the moquegua formation and demonstrate that this sedimentary unit accumulated in a trough parallel to andean tectonic trends largely in the oligocene more voluminous ash flow eruptions prevailed in the early miocene 22 8 17 6 ma and formed the extensively preserved huaylillas formation this episode was coeval with a major phase of andean uplift and the pyroclastics overlie an erosional surface of regional extent incised into a paleogene volcano plutonic arc terrain an age span of 14 2 8 9 ma mid late miocene is indicated for the younger chuntacala formation which again comprises felsic ignimbrite flows largely restricted to valleys incised into the pre huaylillas formation lithologies and at lower altitudes an extensive aggradational elastic facies the youngest areally extensive ignimbrites constituting the sencca formation were extruded during the late miocene in the earliest pliocene the ignimbrites were succeeded by more voluminous calcalkaline intermediate flows which generated numerous large and small stratovolcanoes these range in age from 5 3 to 1 6 ma present day or holocene volcanism is restricted to several large stratovolcanoes which had begun their development during the pleistocene by 0 7 ma the late oligocene early miocene ca 22 23 ma reactivation of the volcanic arc coincided with a comparable increase in magmatic activity throughout much of the cordilleras occidental and oriental of the central andes

incision into the eastern andean plateau during pliocene cooling canyon incision into mountain topography is commonly used as a proxy for surface uplift driven by tectonic or geodynamic processes but climatic changes can also instigate incision the 1250 kilometer km long eastern margin of the andean plateau hosts a series of 1 5 to 2 5 km deep canyons that cross major deformation zones using u th he thermochronology we document a transition from miocene faulting to pliocene canyon incision across the northeastern plateau margin regionally widespread pliocene incision into the eastern plateau margin is concurrent with a shift in global climate from early pliocene warmth to late pliocene cooling enhanced moisture transport onto the andean plateau driven by sea surface temperature changes during cooling is the likely pacemaker for canyon incision

a geodynamic model linking cretaceous orogeny arc migration foreland dynamic subsidence and marine ingression in southern south america abstract this study synthesizes the tectonomagmatic evolution of the andes between 35 30 s to 48 s with the aim to spotlight early contractional phases on andean orogenic building and to analyze their potential driving processes we examine early tectonic stages of the different fold thrust belts that compose this andean segment additionally we analyzed the spatio temporal magmatic arc evolution as a proxy of dynamic changes in andean subduction during critical tectonic stages of orogenic construction this revision proposes a hypothesis related the existence of a continuous large scale flat subduction setting in cretaceous times with a similar size to the present largest flat slab setting on earth this potential process would have initiated diachronically in the late early cretaceous and achieved full development in late cretaceous to earliest paleocene times constructing a series of fold thrust belts on the retro arc zone from 35 30 s to 48 s moreover we assess major paleogeographic changes that took place during flat slab full development in maastrichtian danian times at this moment an enigmatic atlantic derived marine flooding covered the patagonian foreland reaching as far as the andean foothills based on flexural and dynamic topography analyses we suggest that focused dynamic subsidence at the edge of the flat slab may explain sudden marine ingression previously linked to continental tilting and orogenic loading during a high sea level global stage finally flat subduction destabilization could have triggered massive outpouring of synextensional intraplate volcanic rocks in southern south america and the arc retraction in late paleogene to early neogene times

climate change imprinting on stable isotopic compositions of high elevation meteoric water cloaks past surface elevations of major orogens stable isotope paleoaltimetry has been widely used to estimate cenozoic surface elevation of major orogens the influence of global climate change on stable isotope paleoaltimetry is uncertain with proposals that warming could cause either overestimates or underestimates of past surface elevations in this study we increase atmospheric p co 2 by two and four times in an isotope tracking atmospheric general circulation model to investigate the effect of global warming on oxygen isotopic compositions of precipitation 18 o p over the continents as in other climate models the response in the genesis version 3 model to global warming is an amplification of upper troposphere temperatures through enhanced infrared absorption and a reduction in the surface to upper level temperature gradient due to the temperature dependence of isotopic fractionation vapor 18 o 18 o v follows suit leading to a reduction in the surface to upper troposphere 18 o v gradient in regions of subsidence including the major orogens and deserts downward mixing of 18 o enriched vapor from the troposphere to the near surface further reduces the lapse rate of 18 o v as a consequence of these effects the isotopic composition of precipitation in high elevation regions including the tibetan plateau rocky mountains european alps and andean plateau increases by 3 6 relative to that at low elevations neglect of this climate effect on high elevation 18 o p has likely led to underestimates of the surface elevation of cenozoic orogens

a stable isotope record of late cenozoic surface uplift of southern alaska abstract although the timing of an acceleration in late cenozoic exhumation of southern alaska is reasonably well constrained as beginning 5 6 ma the surface uplift history of this region remains poorly understood to assess the extent of surface uplift relative to rapid exhumation we developed a stable isotope record using the hydrogen isotope composition d of paleo meteoric water over the last 7 ma from interior basins of alaska and yukon territory our record which is derived from authigenic clays dclay in silicic tephras documents a 50 60 increase in d values from the late miocene 6 7 ma through the plio pleistocene transition 2 3 ma followed by near constant values over at least the last 2 ma although this enrichment trend is opposite that of a rayleigh distillation model typically associated with surface uplift we suggest that it is consistent with indirect effects of surface uplift on interior alaska including changes in aridity moisture source and seasonality of moisture we conclude that the dclay record documents the creation of a topographic barrier and the associated changes to the climate of interior alaska and yukon territory

elevation dependent changes in n alkane δd and soil gdgts across the south central andes abstract surface uplift of large plateaus may significantly influence regional climate and more specifically precipitation patterns and temperature sometimes complicating paleoaltimetry interpretations thus understanding the topographic evolution of tectonically active mountain belts benefits from continued development of reliable proxies to reduce uncertainties in paleoaltimetry reconstructions lipid biomarker based proxies provide a novel approach to stable isotope paleoaltimetry and complement authigenic or pedogenic mineral proxy materials in particular outside semi arid climate zones where soil carbonates are not abundant but soil organic matter has a high preservation potential here we present d values of soil derived n alkanes and mean annual air temperature mat estimates based on branched glycerol dialkyl glycerol tetraether brgdgt distributions to assess their potential for paleoelevation reconstructions in the southern central andes we analyzed soil samples across two environmental and hydrological gradients that include a hillslope 26 28 s and a valley 22 24 s transect on the windward flanks of central andean eastern cordillera in nw argentina our results show that present day n alkane d values and brgdgt based mat estimates are both linearly related with elevation and in good agreement with present day climate conditions soil n alkanes show a d lapse rate d of 1 64 100 m r 2 0 91 p 0 01 at the hillslope transect within the range of d lapse rates from precipitation and surface waters in other tropical regions in the andes like the eastern cordillera in colombia and bolivia and the equatorial and peruvian andes brgdgt derived soil temperatures are similar to monitored winter temperatures in the region and show a lapse rate of t 0 51 c 100 m r 2 0 91 p 0 01 comparable with lapse rates from in situ soil temperature measurements satellite derived land surface temperatures at this transect and weather stations from the eastern cordillera at similar latitude as a result of an increasing leeward sampling position along the valley transect lapse rates are biased towards lower values and display higher scatter d 0 95 100 m r 2 0 76 p 0 01 and t 0 19 c 100 m r 2 0 48 p 0 05 despite this higher complexity they are in line with lapse rates from stream water samples and in situ soil temperature measurements along the same transect our results demonstrate that both soil n alkane d values and mat reconstructions based on brgdgts distributions from the hillslope transect d 1 64 100 m r 2 0 91 p 0 01 and t 0 51 c 100 m r 2 0 91 p 0 01 track the direct effects of orography on precipitation and temperature and hence the combined effects of local and regional hydrology as well as elevation

canyon incision chronology based on ignimbrite stratigraphy and cut and fill sediment sequences in sw peru documents intermittent uplift of the western central andes abstract based on an 40ar 39ar and u pb based chronostratigraphy of ignimbrite sheets and the geomorphological features of watersheds river profiles and slope deposits in the ocona cotahuasi maran ocm and colca valleys of southwest peru we reconstruct the valley incision history of the western central andes over the last c 25 myr we further document the pleistocene and holocene evolution of deep valleys on the basis of 14 10be surface exposure ages obtained on debris avalanche deposits and river straths the data suggest that uplift was gradual over the past 25 myr but accelerated after c 9 ma valley incision started around 11 9 ma and accelerated between 5 and 4 ma incision was followed by several pulses of valley cut and fill after 2 3 ma evidence presented suggest that the post 5 ma sequence of accelerated canyon incision probably resulted from a combination of drainage piracy from the cordilleran drainage divide towards the altiplano accentuated flexural tilting of the western cordillera towards the se and increased rainfall on the altiplano after late miocene uplift of the eastern cordillera the valley deepening and slope steepening driven by tectonic uplift gave rise to large occurrences of rockslope failure the collapsed rock masses periodically obstructed the canyons thus causing abrupt changes in local base levels and interfering with the steadiness of fluvial incision as a result channel aggradation has prevailed in the lower gradient u shaped pacific rim canyons whereas re incision through landslide deposits has occurred more rapidly across the steeper v shaped upper valleys existing canyon knickpoints are currently arrested at the boundary between the plutonic bedrock and widespread outcrops of middle miocene ignimbritic caprock where groundwater sapping favouring rock collapse may be the dominant process driving headward erosion

tectonostratigraphic evolution of the upper cretaceous cenozoic central anatolian basins an integrated study of diachronous ocean basin closure and continental collision

large along strike variations in the onset of subandean exhumation implications for central andean orogenic growth abstract plate tectonics drives mountain building in general but the space time pattern and style of deformation is influenced by how climate geodynamics and basement structure modify the orogenic wedge growth of the subandean thrust belt which lies at the boundary between the arid high elevation central andean plateau and its humid low elevation eastern foreland figures prominently into debates of orogenic wedge evolution we integrate new apatite and zircon u th he thermochronometer data with previously published apatite fission track data from samples collected along four subandean structural cross sections in bolivia between 15 and 20 s we interpret cooling ages vs structural depth to indicate the onset of subandean exhumation and signify the forward propagation of deformation we find that subandean growth is diachronous south 11 3 ma vs north 6 2 ma of the bolivian orocline and that subandean exhumation magnitudes vary by more than a factor of two similar north south contrasts are present in foreland deposition hinterland erosion and paleoclimate these observations both corroborate diachronous orogenic growth and illuminate potential propagation mechanisms of particular interest is an abrupt shift to cooler more arid conditions in the altiplano hinterland that is diachronous in southern bolivia 16 13 ma vs northern bolivia 10 7 ma and precedes the timing of subandean propagation in each region others have interpreted the paleoclimate shift to reflect either rapid surface uplift due to lithosphere removal or an abrupt change in climate dynamics once orographic threshold elevations were exceeded these mechanisms are not mutually exclusive and both would drive forward propagation of the orogenic wedge by augmenting the hinterland backstop either through surface uplift or spatially variable erosion in summary we suggest that diachronous subandean exhumation was driven by piecemeal hinterland uplift orography and the outward propagation of deformation

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

linking orography climate and exhumation across the central andes quantifying interactions between uplift climate deformation and exhumation remains difficult in many cases due to a paucity of data relevant to all processes we synthesize new and existing data to understand the orogen scale orographic changes across the central andes bolivia we use a regional climate model and geo thermochronologic data to identify the correlations between changes in precipitation due to surface uplift and spatiotemporal patterns of deformation and erosional exhumation mean orographic rainfall patterns do not reach near present day gradients and values until the topography grows to 75 modern elevations new fission track data near the orocline apex indicate that rapid exhumation moved eastward beginning in the eastern cordillera ca 50 15 ma the interandean zone ca 18 6 ma and in the subandes ca 7 3 ma throughout bolivia exhumation is consistent with deformation until ca 15 11 ma after which the pattern corresponds better with the increased rainfall toward modern values these linked observations suggest that ca 15 11 ma regional elevations reached threshold values 75 modern necessary to generate near present day enhanced rainfall gradients these gradients have resulted in variable exhumation implied by the structural level of rocks exposed across the thrust belt and confirmed by fission tracks in apatite the main insight is that the climate induced middle miocene recent exhumation varies over scales of a few hundred kilometers across bolivia and implies that high mean rainfall 3 m yr and long time scales 10 m y may be necessary for climate to induce orographically driven exhumation patterns recorded by fission tracks

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

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable