uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains drummond c n wilkinson b h lohmann k c and smith g r 1993 effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains palaeogeogr palaeoclimatol palaeoecol 101 67 79 oxygen isotopic compositions of upper miocene 9 2 m y lacustrine limestone from northwestern wyoming range from 21 5 to 35 2 0 pdb and are the lightest yet reported for a non marine carbonate sequence these values require that lake water was greatly depleted in 180 relative to modern meteoric precipitation and indicate that most inflow was sourced as meltwater from glaciers in the adjacent gros ventre range assessment of climatic factors influencing the isotopic composition of global meteoric water indicates either that nearly all of miocene precipitation in the southern rocky mountains was derived from large lake systems in the snake river plain and northern great basin to the west or that gros ventre catchment elevations were up to 2300 m higher than at present because erosion rates in modern alpine regions suggest that subaerial denudation could only account for up to 1200 m of post miocene elevation reduction any additional lowering must reflect the influence of post laramide epeirogeny during basin and range extensional tectonism lacustrine isotopic data therefore provide boundary conditions on the timing and magnitude of changes in late cenozoic paleoclimate topography hydrology and tectonism in the western wyoming portion of the rocky mountains

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

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

simulations of warm tropical conditions with application to middle pliocene atmospheres during the early and mid pliocene the period from 5 to 3 million years ago approximately the earth is believed to have been significantly warmer than it is today but the reasons for the higher temperatures are unclear this paper explores the impact of recent findings that suggest that at that time cold surface waters were absent from the tropical and subtropical oceanic upwelling zones el nino was in effect a perennial rather than intermittent phenomenon and sea surface temperatures in low latitudes were essentially independent of longitude when these conditions are specified as the lower boundary condition for an atmospheric gcm we find that the trade winds along the equator and hence the walker circulation collapse the low level stratus clouds in low latitudes diminish greatly thus reducing the albedo of the earth the atmospheric concentration of water vapor increases and enhanced latent heat release due to stronger evaporation warms up the tropical atmosphere particularly between 40 s and 20 n moreover teleconnection patterns from the pacific induce a warming over north america that is enhanced by surface albedo feedback a process that may have helped to maintain this region ice free before 3 ma the results presented here indicate that the suggested absence of cold surface waters from the tropical and subtropical oceanic upwelling zones could have contributed significantly to the pliocene warmth

topographic development of the southern alps recorded by the isotopic composition of authigenic clay minerals south island new zealand abstract the southern alps are developing as a consequence of oblique collision between the pacific and australian plates the southern alps lie on the west side of the south island of new zealand and create a massive rain shadow where greater than 12 m year of rain falls on the west coast and semiarid conditions exist to the east the rain out effect across the mountains causes precipitation west of the southern alps to have d and 18 o values averaging 30 and 5 5 whereas precipitation in the rain shadow to the east is isotopically lighter d 72 and 18 o 9 8 such large differences in the isotopic composition of precipitation would not have existed prior to the development of significant topography we have examined the topographic evolution of the southern alps using oxygen isotope analyses of authigenic kaolinites formed in the rain shadow to the east of the mountains between the cretaceous low topography and the pleistocene changes in the isotopic composition of authigenic clay minerals forming in equilibrium with meteoric water in the stratigraphic sequence record the development of southern alps topography and the resultant rain shadow our oxygen isotope analyses of authigenic kaolinites show a 5 6 decrease in the early pliocene from 18 2 in older rocks to 12 3 in younger rocks in addition smectite is abundant in all samples from the late miocene to recent but is conspicuously absent in most older rocks suggesting a change to a generally drier climate roughly coincident with the isotopic shift in kaolinites this method may be useful in unraveling timing of development of mountain belts elsewhere in the world

neogene climate change and uplift in the atacama desert chile the relationship between andean uplift and extreme desiccation of the west coast of south america is important for understanding the interplay between climate and tectonics in the central andes yet it is poorly understood here we use soil morphological char acteristics salt chemistry and mass independent fractionation anomalies 17 o values in dated paleosols to reconstruct a middle miocene climatic transition from semiaridity to extreme hyperaridity in the atacama desert paleosols along the southeastern margin of the calama basin change from calcic vertisols with root traces slickensides and gleyed horizons to an extremely mature salic gypsisol with pedogenic nitrate we interpret this transition which occurred between 19 and 13 ma to represent a change in precipitation from 200 mm yr to 20 mm yr this drastic reduction in precipitation likely resulted from uplift of the central andes to elevations 2 km the uplift blocked moisture from the south american summer monsoon from entering the atacama the mid miocene gyp sisol with pedogenic nitrate is located at elevations between 2900 and 3400 m in the cal ama basin significantly higher than modern nitrate soils which occur below 2500 m modern and quaternary soils in this elevation zone contain soil carbonate and lack ped ogenic gypsum and nitrate we infer that 900 m of local surface uplift over the past 10 m y displaced these nitrate paleosols relative to modern nitrate soils and caused a return to wetter conditions in the calama basin by decreasing local air temperatures and creating an orographic barrier to pacific air masses

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

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

impacts of andean uplift on the humboldt current system a climate model sensitivity study 1 using both an atmospheric global circulation model and a regional oceanic model we assess the impact of the andes uplift on the humboldt current system hcs with three topographic scenarios for the andes we show that the uplift played a crucial role in shaping the lower troposphere dynamics over the pacific ocean and in turn affected the physical characteristics of the system our results show that the uplift has triggered a marked southward shift of the hcs changing the latitudinal position of coastal upwelling areas as well as the strength of the south pacific gyre our oceanic modeling experiments show that the latitudinal pattern of sea surface temperatures is dramatically modified with reduced andes with anomalies reaching up to 3 c we discuss the feedbacks of these changes on south american climate as well as the potential onset of an altitudinal threshold that would have had triggered these changes

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

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

amazon plant diversity and climate through the cenozoic abstract the modern amazon lowlands date from the mid cenozoic when the andean orogeny defined an eastward or northward draining basin of immense size as the andean orogeny continued throughout the neogene and quaternary periods this system approached a steady state with andean flanks eroding to fill subsiding basins along the andean foreland followed by secondary erosion of sediments and transport in rivers across 3000 km to the atlantic ocean pollen data suggest that tropical forests were established on these lowlands at least by the end of the miocene with many modern amazon genera already present such antiquity is consistent with hypotheses that explain high diversity of modern amazon forests as the result of prolonged existence and minimal disturbance or extinction these museum models for amazon diversity came to be challenged by the paradigm of ice age aridity with its claim that the forests of the amazon lowlands were fragmented with each glacial advance into more or less tiny isolates called refugia separated by grass dominated communities like savanna for the latest pleistocene the arid amazon with forest refugia model can be tested by pollen analysis of lake sediments interpretation of amazon pollen data requires recognition both of the vast diversity of pollen types and an understanding of the dispersal of zoophilous pollen in the amazon amazon pollen analysis has been codified into a pollen atlas and this work used to review the available pollen data within the huge expanse of the amazon basin only three lacustrine records long enough and continuous enough to test this model have been published those from lake pata the carajas plateau and the amazon fan the review suggests community stability from all three data sets with no evidence for forest fragmentation in the amazon lowlands the principal response of amazon forest communities to climatic change is in the relative abundance of the more sensitive taxa particularly in response to interglacial warming a summary of geomorphological phenomena finds no evidence for glacial age aridity other than marginal reductions in precipitation within forest cover the amazon historical record is incomplete in time as well as in space there being essentially no paleobotanical data for much of the cenozoic particularly for the early pleistocene the data so far available however suggest stability and continuity of the forest cover over the vast amazon lowlands throughout the cenozoic as the circumstance in which the high amazon plant diversity evolved

plume separation by transient thermohaline convection in porous media research on thermohaline convection in porous media has borrowed heavily from the field of viscous liquid thermohaline convection transient thermohaline convection in porous media differs dramatically from that in viscous liquids because of thermal retardation the effects of thermal retardation are well known in geothermal reservoir engineering for forced convection processes such as liquid reinjection thermal retardation causes heat to move at approximately the darcy velocity while solute moves at the pore velocity the difference in transport of heat and solute makes transient thermohaline convection in porous media double advective rather than double diffusive for upward moving plumes dense solute is advected in front of the thermal plume and creates a density lid for downward moving plumes the dense solute plume separates from the thermal plume

direction and timing of uplift propagation in the peruvian andes deduced from molecular phylogenetics of highland biotaxa abstract physical paleoaltimetric methods are increasingly used to estimate the amount and timing of surface uplift in orogens because the rise of mountains creates new ecosystems and triggers evolutionary changes biological data may also be used to assess the development and timing of regional surface uplift here we apply this idea to the peruvian andes through a molecular phylogeographic and phylochronologic analysis of globodera pallida a potato parasite nematode that requires cool temperatures and thus thrives above 2 0 2 5 km in these tropical highlands the peruvian populations of this species exhibit a clear evolutionary pattern with deeper more ancient lineages occurring in andean southern peru and shallower younger lineages occurring progressively northwards genetically diverging g pallida populations thus progressively colonized highland areas as these were expanding northwards demonstrating that altitude in the peruvian andes was acquired longitudinally from south to north i e in the direction of decreasing orogenic volume this phylogeographic structure is recognized in other independent highland biotaxa and point to the central andean orocline cao as the region where high altitudes first emerged moreover molecular clocks relative to andean taxa including the potato tomato group consistently estimate that altitudes high enough to induce biotic radiation were first acquired in the early miocene after calibration by geological and biological tie points and intervals the phylogeny of g pallida is used as a molecular clock which estimates that the 2 0 2 5 km threshold elevation range was reached in the early miocene in southernmost peru in the middle and late miocene in the abancay segment nw southern peru and from the latest miocene in central and northern peru although uncertainties attached to phylochronologic ages are significantly larger than those derived from geochronological methods these results are fairly consistent with coeval geological phenomena along the peruvian andes they strongly suggest that orogenic volume initially developed in the cao during most of the miocene until a breakthrough in the latest miocene allowed the northward propagation of crustal thickening into central and northern peru possibly by ductile crustal flow from the cao such a combined phylogeographic and phylochronologic approach to regional uplift opens perspectives to estimate the direction s and timing of acquisition of altitude over other cenozoic orogens

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

andean uplift ocean cooling and atacama hyperaridity a climate modeling perspective abstract located along the west coast of subtropical south america the atacama desert features an extremely dry climate in sharp contrast with relatively wet conditions over the central andes and farther east the atacama s hyperaridity has been attributed to its subtropical location the cold waters over the adjacent southeast pacific ocean and the presence of the andes cordillera although geological evidence reveals less dry conditions in the remote past the timing of the arid to hyperarid transition is a matter of controversy several studies suggest that such transition occurred between 19 and 13 ma fostered by the concurrent uplift of the andes during the lower middle miocene other studies however suggest a much earlier 25 ma or later 2 1 ma transition associated with global or regional ocean cooling here we use plasim a simple global climate model to study the effect of the andean surface uplift and sea surface temperature changes upon atacama aridity in one set of experiments the continental topography was scaled by a factor ranging from 0 9 to 0 1 decreasing the height of the andes did not increase precipitation over the atacama region but rather decrease the precipitation over the central andes and the interior of the continent these results consistent with previous modeling studies suggest that the andean uplift was not an important ingredient in the onset of atacama hyperaridity even if both events overlapped in time a globally uniform sea surface warming does not result in a significant increase of precipitation over the atacama in contrast a regional warming over the subtropical southeast pacific very effectively increase precipitation along the west coast of south america by decreasing the subsidence and the dry advection at low levels it suggested that a reinforcement of the humboldt current since the late miocene and particularly during the pliocene pleistocene transition was crucial in the drying of the atacama desert that culminated with the present day hyperarid conditions

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

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

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

origin of the high plateau in the central andes bolivia south america the bolivian altiplano in the central andes of south america is part of the second largest high plateau on earth it is an elongate region of subdued relief 1 2 105 km2 and 4 km above sea level bounded by the eastern cordillera and volcanic arc western cordillera here the crust is up to 75 km thick we describe the cenozoic geological evolution of this region using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure crustal shortening and magmatic addition and locally sedimentation are the main mechanisms of cenozoic crustal thickening leading to nearly 4 km of surface uplift since the paleocene addition of mafic melts appears to be a first order mechanism of cenozoic crustal growth contributing 40 of the crustal thickening beneath the volcanic arc removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind arc mafic volcanism at 23 ma and 0 5 ma contributing to the surface uplift the altiplano originated as a sedimentary basin several hundred kilometers wide between the proto western cordillera and a narrow zone of uplift proto eastern cordillera farther east the latter zone formed by inversion of the center of a wide lacustrine or marine cretaceous paleocene basin close to sea level at 45 ma a thickness of 2 4 km of paleogene continental elastics accumulated in the proto altiplano basin subsequently in the oligocene we estimate that this region and the western margin of the eastern cordillera were technically shortened 22 65 km resulting in 9 km of average crustal thickening the altiplano basin was rejuvenated at 25 ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting eastern and western cordilleras between 25 and 5 ma folding and thrusting in the western margin of the eastern cordillera migrated westward into the center of the altiplano basin essentially terminating deposition except in local subbasins and accommodating 13 30 km of shortening and an estimated 7 km of average crustal thickening subsequently there has been strike slip deformation and limited local thrusting 5 km of shortening geomorphological and geochronological evidence for 1 5 2 km of surface uplift of this region since the late miocene suggests 14 km of lower crustal thickening beneath an essentially rigid lid and can be explained by 100 150 km of underthrusting of the brazilian shield and adjacent regions beneath the eastern margin of the central andes the present subdued relief in the altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin

sedimentology based reconstructions of paleoclimate changes in the central andes in response to the uplift of the andes arica region between 19 and 21 s latitude northern chile we focus on the sedimentological record of the middle miocene to modern deposits in the andes of northern chile between 19 and 21 s these sediments deposited at the western escarpment of the central depression indicate successively more moisture on the western margin of the altiplano and the western cordillera where the sources are at the pacific coast 20 ma old exposure ages and salic gypsisols reflect an existing and ongoing hyperarid climate we interpret the increased divergence of climates between the coast and the altiplano as consequence of the andean rise to elevations higher than approximately 2 500 m a s l when the topography of the altiplano was sufficiently high and areally extensive to attract atlantic moisture accordingly the inferred general increase in run off was closely coupled with the uplift of the andes if the steady rise model applies in case that the rapid rise model for andean uplift is correct the inferred changes in sediment transport would have occurred independently of uplift requiring an alternative yet unknown driver

comment on rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates based on stable isotope measurements ghosh et al reports 27 january 2006 p 511 concluded that the bolivian altiplano uplifted 3 to 4 kilometers between 10 3 and 6 7 million years ago as a result of gravitational loss of dense lithosphere this result stands at odds with current geological knowledge of the central andes and we propose a test for the reliability of the paleoaltimetry method

fully coupled approach to modeling shallow water flow sediment transport and bed evolution in rivers 1 our ability to predict complex environmental fluid flow and transport hinges on accurate and efficient simulations of multiple physical phenomenon operating simultaneously over a wide range of spatial and temporal scales including overbank floods coastal storm surge events drying and wetting bed conditions and simultaneous bed form evolution this research implements a fully coupled strategy for solving shallow water hydrodynamics sediment transport and morphological bed evolution in rivers and floodplains pihm hydro and applies the model to field and laboratory experiments that cover a wide range of spatial and temporal scales the model uses a standard upwind finite volume method and roe s approximate riemann solver for unstructured grids a multidimensional linear reconstruction and slope limiter are implemented achieving second order spatial accuracy model efficiency and stability are treated using an explicit implicit method for temporal discretization with operator splitting laboratory and field scale experiments were compiled where coupled processes across a range of scales were observed and where higher order spatial and temporal accuracy might be needed for accurate and efficient solutions these experiments demonstrate the ability of the fully coupled strategy in capturing dynamics of field scale flood waves and small scale drying wetting processes

fluid dynamics driving saline water in the north east german basin in several areas of the north german basin saline water comes close to or even reaches the surface available data from wells indicate that brine stratification is under unstable conditions in the deeper underground in order to analyse the possible transport mechanisms 3d thermohaline simulations have been carried out for two different scenarios the 3d regional model 230 330 km indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands in addition a smaller scale model 10 10 km has been constructed with a grid resolution accounting for possible convective flow the results indicate that convective flow may play a dominant role in areas with minor topography in summary the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces

the formation and evolution of layered structures in porous media horizontally layered structures can develop in porous or partially molten environments such as magma chambers the early earth s mantle and hydrothermal systems we have studied the generation and evolution of these horizontally layered structures in a rigid porous medium by heating a compositionally stably stratified fluid from below growth of a convective layer through entrainment the formation of a vertical density interface on top of this layer and destabilization of the next layer are closely coupled it is shown that the growth of the first convective layer stops once the thermal equilibrium is reached since heat solute transfer across the thin density interfaces becomes purely diffusive dispersive the separately convecting layers can persist on a compositionally dispersive timescale while the number of layers that develop is determined by the magnitude of the thermal rayleigh number the final height of a newly formed layer is inversely proportional to the buoyancy ratio two dynamical mechanisms which lead to sudden interface disappearance determine the vertical layer scales rather than the initial evolution toward the thermal equilibrium finally the results are discussed with respect to the above mentioned geophysical scenarios

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

spatial temporal changes in andean plateau climate and elevation from stable isotopes of mammal teeth abstract paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern andean plateau on the order of 2 5 1 km occurred between 10 3 and 6 4 ma independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau this study focuses on teeth from modern and extinct mammal taxa including notoungulates pyrotheres and litopterns spanning 29 ma to present collected from the altiplano and eastern cordillera of bolivia 16 2 s to 21 4 s and lowland brazil tooth enamel of large water dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing previous studies have shown that the 18o of modern precipitation and surface waters decrease systematically with increasing elevations across the central andes our results from high elevation sites between 3600 and 4100 m show substantially more positive 18o values for late oligocene tooth samples compared to