the splash function for snow from wind tunnel measurements in wind transport of snow horizontal momentum is extracted from the mean wind o w and transfered to the snow grains upon colliding with the surface the grains can bounce and eject further grains in a process known as splashing how ecien tly the horizontal momentum is converted to vertical momentum in the splash process is the determining factor for mass transport rates this paper discusses wind tunnel experiments performed to calculate the splash function for snow particles the data is used to develop a new splash function particular care is taken to include correlations in the data such as between ejection velocity and ejection angle the new splash function includes these correlations and its parameters are related to physical properties of the bed and snow

long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

mid holocene climate in the south central andes humid or dry have concluded thatgenerally drier conditions prevailed we argue that wet conditions result in high er river discharge and erosion whereas accu mulation of fine materials in a steep valleyrequires overall decreased river flow and a low energy environment with dry conditions fine grained but permeable sediments that accumu late in the valley bottom may form local aqui fers and raise the groundwater table despite alarger cross section in the valley and reduceddischarge overall modern analogs show thatgroundwater tables in such wetlands are oftenself sustained very local and disconnectedfrom their surroundings and are thus difficult tointerpret in terms of climate conditions today the rivers in both the tula n and puripica valleysare erosive and have dissected the mid holo cene sediments down to bedrock typically sediments from between 14 and 9 ky b p aperiod of well documented extreme humidity are missing in these valleys because of strongerosion whereas as expected sediments fromthis humid period are present in fossil springcomplexes tilomonte springs figure 4 in

do swarms of migrating barchan dunes record paleoenvironmental changes a case study spanning the middle to late holocene in the pampa de jaguay southern peru swarms of barchan dunes are common in arid environments unlike immobile or slowly moving dunes whose stratigraphy can be used to reconstruct paleoenvironmental changes the high migration rate of barchans seems to prohibit their use as geoarchives in this paper a possible use of barchan swarms for paleoenvironmental reconstructions is presented the approach is based on dune migration in a case study based on 500 dunes in the pampa de jaguay aeolian transport corridor in coastal southern peru middle to late holocene changes in the supply of aeolian material are inferred from calculating the time of dune initiation at the coastline limitations posed by the assumptions underlying this approach are discussed

complex multiple cosmogenic nuclide concentration and histories in the arid rio lluta catchment northern chile terrestrial cosmogenic nuclide tcn concentrations measured in river sediments can be used to estimate catchment wide denudation rates by investigating multiple tcn the steadiness of sediment generation transport and depositional processes can be tested measurements of 10be 21ne and 26al from the hyper to semi arid rio lluta catchment northern chile yield average single denudation rates ranging from 12 to 75 m myr 1 throughout the catchment paired nuclide analysis reveals complex exposure histories for most of the samples and thus the single nuclide estimates do not exclusively represent catchment wide denudation rates the lower range of single nuclide denudation rates 12 17 m myr 1 established with the noble gas 21ne is in accordance with palaeodenudation rates derived from 21ne 10be and 26al 10be ratio analysis since this denudation rate range is measured throughout the system it is suggested that a headwater signal is transported downstream but modulated by a complex admixture of sediment that has been stored and buried at proximal hillslope or terrace deposits which are released during high discharge events that is best evidenced by the stable nuclide 21ne which preserves the nuclide concentration even during storage intervals the catchment wide single 21ne denudation rates and the palaeodenuation rates contrast with previous tcn derived erosion rates from bedrock exposures at hillslope interfluves by being at least one order of magnitude higher especially in the lower river course these results support earlier studies that identified a coupling of erosional processes in the western cordillera contrasting with decoupled processes in the western escarpment and in the coastal cordillera copyright 2008 john wiley sons ltd

possible liquid water origin for atacama desert mudflow and recent gully deposits on mars evidence of recent gully activity on mars has been reported based on the formation of new light toned deposits within the past decade the origin of which remains controversial analogous recent light toned gully features have formed by liquid water activity in the atacama desert on earth these terrestrial deposits leave no mineralogical trace of water activity but rather show an albedo difference due to particle size sorting within a fine grained mudflow therefore spectral differences indicating varying mineralogy between a recent gully deposit and the surrounding terrain may not be the most relevant criteria for detecting water flow in arid environments instead variation in particle size between the deposit and surrounding terrain is a possible discriminator to identify a water based flow we show that the atacama deposit is similar to the observed mars gully deposits and both are consistent with liquid water activity the light toned mars gully deposits could have formed from dry debris flows but a liquid water origin cannot be ruled out because not all liquid water flows leave hydrated minerals behind on the surface therefore the mars deposits could be remnant mudflows that formed on mars within the last decade

a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years the quaternary paleoclimate of the central andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region the exact timing duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another and there have been few opportunities to compare climatic records from the same proxy along environmental gradients vegetation histories from fossil rodent middens provide one such opportunity on the pacific slope of the andes we previously reported a vegetation history from the upper margin 2400 3000 m of the absolute desert in the central atacama desert of northern chile that record identified a distinct wet phase that peaked between 11 8 and 10 5 ka when steppe grasses and other upland elements expanded as much as 1000 m downslope and a secondary wet period during the middle to late holocene 7 1 3 5 ka the latter wet phase remains controversial and is not as readily apparent in our lowelevation midden record we thus sought to replicate both phases in a midden record from the mid elevations 3100 3300 m of the arid prepuna where slight precipitation increases would be amplified midden records from these elevations identify conditions wetter than today at 13 5 9 6 7 6 6 3 4 4 3 2 and possibly 1 8 1 2 ka dry phases occurred at 9 4 8 4 ka and possibly at ca 5 1 ka present floras and modern hyperarid conditions were established after 3 2 ka the records from the two elevational bands generally match with some important differences these differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert 2003 elsevier science b v all rights reserved

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

the origin of solutes within the groundwaters of a high andean aquifer abstract this paper investigates the origin of solutes within the groundwaters of the monturaqui negrillar tilopozo mnt aquifer system within the high andes of the atacama desert that discharges into the salar de atacama key questions include the relative significance of volcanic hydrothermal processes and evaporitic brine recycling over solute supply as well as the pathways of solute ingress to the mnt aquifer system groundwaters were analysed for elemental major minor and trace and isotopic 18o 2h 13c dic 34s so4 87sr 86sr constituents to which various hydrochemical and multivariate statistical methods have been applied groundwaters are all classified as thermal and show increasing temperatures 27 35 c and concentrations of hco3 4 4 10 4 mmol l 1 dissolved inorganic carbon dic with increasing proximity to volcano socompa resulting from an increasing mass flux of steam and magmatic co2 pco2 0 016 to 0 10 atm 13c co2 9 3 to 3 6 v pdb boiled off a deep hydrothermal reservoir superimposed upon this gradational and relatively smooth spatial increase in heat and mass flow is a sharp structurally controlled increase in tds 826 3632 mg l 1 and a concomitant change in 34s so4 0 79 to 4 9 v cdt and 87sr 86sr values 0 707375 0 706859 associated with the inflow of evaporitic solutes evaporitic inputs are chemically and isotopically distinct from localised secondary hydrothermally derived solutes with major minor and trace element data suggesting an origin within a highly oxidising alkaline evaporitic lake receiving dilute inflows enriched in volcanic fumarolic sulfur mineralisation probably from volcanoes socompa salin or pular that delimit the eastern topographic extent of the aquifer system the conceptual model presented in this paper proposes that basal leakage of evaporitic brines from active salar s within the high altiplano volcanic arc are actively entrained by sub regional groundwater flow and conveyed to the mnt aquifer system where they mix with solutes derived from localised secondary hydrothermal gas water rock interaction this work provides detail on the origin and processes controlling the solute composition of groundwater inflows to the salar de atacama within the volcanically active and hyperarid atacama desert and may be of significance to conceptual models of evaporitic brine evolution recycling of evaporitic brines and hydrothermalism in arid regions

isotopic evidence for the source of ca and s in soil gypsum anhydrite and calcite in the atacama desert chile abstract the origin of pedogenic salts in the atacama desert has long been debated possible salt sources include in situ weathering at the soil site local sources such as aerosols from the adjacent pacific ocean or salt encrusted playas salars and extra local atmospheric dust to identify the origin of ca and s in atacama soil salts we determined 34 s and 87 sr 86 sr values of soil gypsum anhydrite and 87 sr 86 sr values of soil calcite along three east west trending transects our results demonstrate the strong influence of marine aerosols on soil gypsum anhydrite development in areas where marine fog penetrates inland results from an east west transect located along a breach in the coastal cordillera show that most soils within 90 km of the coast and below 1300 m in elevation are influenced by marine aerosols and that soils within 50 km and below 800 m in elevation receive 50 of ca and s from marine aerosols 34 s values 14 and 87 sr 86 sr values 0 7083 in areas where the coastal cordillera is 1200 m in elevation however coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced most pedogenic salts from inland soils have 34 s values between 5 0 to 8 0 and 87 sr 86 sr ratios between 0 7070 and 0 7076 these values are similar to average 34 s and 87 sr 86 sr values of salts from local streams lakes and salars 5 4 2 34 s and 0 70749 0 00045 87 sr 86 sr in the andes and atacama suggesting extensive eolian reworking of salar salts onto the surrounding landscape ultimately salar salts are precipitated from evaporated ground water which has acquired its dissolved solutes from water rock interactions both high and low temperature along flowpaths from recharge areas in the andes therefore the main source for ca and s in gypsum anhydrite in non coastal soils is indirect and involves bedrock alteration not surficially on the hyperarid landscape but in the subsurface by ground water followed by eolian redistribution of ground water derived salar salts to soils the spatial distribution of high grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt supporting arguments for tropospheric nitrogen as the main source for soil nitrate

mid and late holocene limnogeology of laguna del negro francisco northern chile and its palaeoclimatic implications lacustrine sediments from the high elevation endorheic saline lake negro francisco 27 28 s 69 14 w 4125 m provide a detailed mid and late holocene environmental history of the southern chilean altiplano mineralogy chemical composition and sedimentary facies analyses of the deposits confirm the regional significance of mid holocene aridity between 6000 and 3800 bp precipitation rates were signifi cantly lower than the c 250 mm yr 1 of today fully arid conditions were interrupted by short term moist spells with an average return period of about 200 years effective moisture increased after 3800 bp and peaked between 3000 and 2600 bp and between 2200 and 1800 bp in two phases with conditions more humid than today comparison with regional palaeodata suggest that these two late holocene humid spells were most likely related to pacific moisture sources salinity levels increased again in laguna del negro francisco after 1800 bp the onset of modern climatic conditions was a stepwise nonlinear proce

cenozoic stratigraphy and basin tectonics of the andes mountains 20 28 south latitude clastic sedimentary basins have evolved during the past 40 m y in the central andes lat 20 28 s in response to shifting patterns of magmatism and deformation the distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the north american rocky mountains during the late cretaceous and early cenozoic petroleum exploration has focused on zones underlying the upper cenozoic strata along the eastern margin of the andes mountain belt between about 40 and 25 ma a nonmarine basin extended across the region that is now the andes mountains between about 25 and 10 ma the western part of the former basin became the site of a volcanic arc sediment accumulation continued in the east where marine intercalations demonstrate the low elevation of the basin after 10 ma the volcanic arc remained active and locally widened and crustal shortening caused regionally important thrust and reverse faulted ranges during the past 10 m y up to 4 000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains meanwhile in the interior of the mountains over 4 000 m of fine grained strata and evaporites accumulated in local depocenters

geochronology of epithermal au ag mineralization magmatic hydrothermal alteration and supergene weathering in the el penon district northern chile the el penon epithermal gold silver deposit region ii chile comprises multiple epithermal veins which contain a geologic resource measured indicated inferred of 7 million oz moz au and 199 moz ag the size combined with bonanza au grades makes it the most important precious metal deposit in the paleocene metallogenic belt of northern chile quartz adularia carbonate veins are hosted in paleocene and early eocene mafic to felsic volcanic rocks that are hydrothermally altered up to 100s of meters from mineralized veins late cretaceous and eocene intermediate composition intrusive rocks also occur in the district and locally preserve alteration associated with magmatic hydrothermal systems that are not related to precious metals mineralization of the el penon deposit timing of hydrothermal activity in the district and age and duration of weathering are constrained by ages for vein adularia hypogene alunite and supergene alunite determined by ar 39 ar 40 step heating experiments adularias from the three largest veins of the el penon deposit are dated at 52 to 53 ma 40 ar 39 ar indicating formation 1 to 3 m y later than host rhyolite domes magmatic hydrothermal quartz alunite alteration spatially associated with late cretaceous and eocene intermediate composition intrusive rocks is dated at 73 to 65 and 50 to 49 ma respectively supergene alunite dates from the el penon district indicate that weathering within a semiarid to arid climate occurred from 23 to 17 ma prior to the onset of hyperaridity

alluvial fan and playa sedimentation in an andean arid closed basin the pacencia group antofagasta province chile the mid tertiary pacencia group comprises over 2 km of continental sediments it was deposited in a half graben basin thought to have been active since early tertiary times conglomerates along the western basin margin were deposited as longitudinal bars rare transverse bars and channel fills with subsidiary debris flows all in a distal fan pebbly braided stream environment no proximal fan sediments are exposed petrographic and palaeocurrent analysis indicates these sediments were derived from cretaceous and possibly jurassic source areas to the northwest to the east within the basin a succession of sands silts muds thick evaporites and rare carbonates were deposited in playa sub environments saliferous muds central salt pan are overlain by interbedded red mudstones and thin high energy ribbon and sheet sands marginal dry mudflat and sandflat certain sand bodies carry stratiform cui agi au mineralization lakes existed at various stages and were fed by permanent fluvial systems the playa sediments were derived from crystalline source areas to the east proximal fan facies and sediment sources are now buried under the volcanic andes

lithofacies and cyclicity of mohilla evaporite basins on the rifted margin of the levant in the late triassic makhtesh ramon southern israel marine connected basins with evaporites occur beneath most extensional continental margins that originated at low latitudes and often are of major economic significance cyclicity in the evaporite lithofacies reflects the degree of restriction of the basin overprinted by sea level changes and caused by structural movements in the barrier region whether by fault block rotation footwall uplift or hanging wall subsidence in both extensional and compressional basins the upper triassic evaporites of the ramon section in southern israel model cyclic sedimentation in such environments the mohilla formation is a carbonate evaporate siliciclastic succession of carnian age that fills a chain of basins extending along the levant margin from southern israel to jordan and syria the basins developed in half grabens adjacent to normal faults that formed during a period of regional extension evaporites of this formation are well exposed in outcrops at makhtesh ramon the southernmost of these basins the m2 member of the mohilla formation is composed of 42 sub metre cycles of alternating dolostone gypsum and calcareous shales field and microfacies analysis showed these cycles to conform mostly to restricted shallow and marginal marine environments spatially limited by the uplifted shoulders of the half graben systems a total of 10 facies types belonging to six depositional environments have been identified from stacking patterns and analysis of bed to bed change cycles can be categorized into three groupings i low frequency exposure to exposure cycles that developed under eustatic or climate control ii high frequency deepening shallowing upward cycles characterized by gradual transitions due to short term sea level or runoff event oscillations possibly referable to orbital forcing and iii high frequency shallowing upward cycles characterized by abrupt transitions attributable to sporadic tectonic events affecting accommodation space or barrier effectiveness the way facies and cycling of the sedimentary environments was deciphered in the mohilla evaporite basin can be used to unravel the genesis of many other evaporite basins with barriers of tectonic origin

holocene lacustrine deposition in the atacama altiplano facies models climate and tectonic forcing abstract we investigate the holocene sedimentary infilling of two high altitude 4000 m a s l lacustrine basins in the subtropical regions of the atacama altiplano central andes northern chile that today contain permanent shallow saline lakes laguna del negro francisco 27 s and laguna miscanti 23 s laguna miscanti was surveyed with multi frequency high resolution seismic techniques and sediment cores were retrieved from offshore areas of both lakes because of the geological location of these lacustrine basins within the active andean convergent margin and the presence of present and past climatic gradients in the altiplano our detailed sedimentologic mineralogic and geochemical study evaluates tectonic volcanic and climatic controls on lacustrine sedimentation in an arid environment both lakes originated by tectonic and volcanic activity during the pleistocene tectonic control of basin dynamics was clearly exerted during the early stages increased subsidence was responsible for alluvial fan activity in the laguna miscanti basin prior to the establishment of the lake and the negro francisco basin changed from exorheic to endorheic hydrogeologic conditions needed to maintain the two perennial saline lakes are largely controlled by the basins tectonic history the evolution of laguna del negro francisco comprises four successive stages 1 perennial saline carbonate sulfate lake 2 saline pan saline lake complex with a carbonate sulfate brine 3 a perennial brackish stage with high macrophyte chara productivity and mostly calcite formation and 4 a residual stage with halite precipitation the depositional history recorded in the miscanti core illustrates the evolution from an aragonite producing ephemeral saline lake to a macrophyte dominated perennial brackish lake with an aragonite saline pan saline lake complex and a calcite producing perennial brackish lake as intermediate stages the hydrologic budget of the lakes is a direct response to effective moisture precipitation evaporation fluctuations and therefore climate variability has played a major role in chemical composition and lake level changes climate forcing has controlled the depositional history of the lakes during the holocene our study illustrates different responses of lake systems to external climatic forcing especially with respect to cyclicity threshold dynamics and the importance of sedimentary recycling the main sedimentary sequences in both lakes correspond to cycles of increasing and decreasing effective moisture however this cyclicity is characterized by abrupt change rather than gradual evolution threshold dynamics modulated limnogeological changes and caused a stepwise evolution of the lacustrine systems laguna miscanti and laguna del negro francisco sedimentary sequences provide depositional models for small topographically closed brackish to saline lakes that developed on active margins and evolved under fluctuating but generally arid climatic conditions

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

origin and development of theater headed valleys in the atacama desert northern chile morphological analogs to martian valley networks abstract understanding planetary landforms including the theater headed valleys box canyons of mars usually depends on interpreting geological processes from remote sensing data without ground based corroboration here we investigate the origin and development of two mars analog theater headed valleys in the hyperarid atacama desert of northern chile previous workers attributed these valleys to groundwater sapping based on remote imaging topography and publications on the local geology we evaluate groundwater sapping and alternative hypotheses using field observations of characteristic features strength measurements of strata exposed in headscarps and estimates of ephemeral flood discharges within the valleys the headscarps lack evidence of recent or active seepage weathering such as spring discharge salt weathering alcoves or vegetation their welded tuff caprocks have compressive strengths multiple times those of the underlying epiclastic strata flood discharge estimates of cubic meters to tens of cubic meters per second derived using the manning equation are consistent with the size of transported clasts and show that the ephemeral streams are geomorphically effective even in the modern hyperarid climate we interpret that headscarp retreat in the quebrada de quisma is due to ephemeral flood erosion of weak miocene epiclastic strata beneath a strong welded tuff with erosion of the tuff facilitated by vertical jointing the quebrada de humayani headscarp is interpreted as the scar of a giant landslide maintained against substantial later degradation by similar strong over weak stratigraphy this work suggests that theater headed valleys on earth and mars should not be attributed by default to groundwater sapping as other processes with lithologic and structural influences can form theater headscarps

upper triassic to lower cretaceous continental and coastal saline lake evaporites inthe atacama region of northern chile evaporites within upper triassic to lower cretaceous sequences in the atacama region of northern chile are interpreted as the deposits of continental and coastal saline lakes halite casts and finely laminated calcareous evaporites intercalated with alluvial and fluvial sediments are probably playa lake deposits these continental evaporites have been recognized in upper triassic alluvial sediments cifuncho formation in upper triassic lower jurassic braided river deposits basal unit of the pan de azucar formation and within a sequence of lower cretaceous aeolian alluvial and playa lake mudflat sediments quebrada monardes formation lower cretaceous evaporites between marine limestones lautaro formation and continental redbeds quebrada monardes formation were probably deposited in coastal saline lagoons produced during a regionally extensive marine regression these sequences and other similar successions in northern chile provide a record of almost continuous evaporite deposition and hence of arid to semi arid conditions since upper triassic times these conditions were primarily the result of a constant latitudinal position within the subtropical zone a contributary factor was the geographical position of the area initially on the west coast of gondwanaland and subsequently on the coast of south america with cold northward flowing ocean currents and offshore winds

palynology of the last interglacial glacial cycle in midlatitudes of southern chile abstract pollen and spores in stratigraphic sections located between 40 and 42 s range in age from the holocene through much of the llanquihue glaciation to the last interglaciation chronology of the stratigraphy derives from some 35 14c ages and the age relations of llanquihue drift and related deposits q mode rotated principal components analysis of four key pollen records covering the last interglacial glacial cycle resulted in four leading components nothofagus dombeyi type gramineae weinmannia fitzroya type and myrtaceae analysis emphasizes interaction between the first two components loadings of gramineae during the interglaciation are high unlike the holocene weinmannia fitzroya type loadings prominent in the holocene are negligible during the interglaciation n dombeyi type is the primary component during llanquihue glaciation it becomes modified by increases of gramineae sometime after 31 000 and before 14 000 yr b p and of myrtaceae later the myrtaceae with weinmannia fitzroya type also registers some activity around 42 000 yr b p fluctuations in the belt of westerly winds reflecting changing meteorological conditions in polar latitudes are suggested by these data with the belt located farther south than it is today interglacial climate was much drier and warmer than during the holocene more northerly displacement of the belt obtained when climate was colder during llanquihue glaciation evidence from comparable latitudes in the southern hemisphere points toward a synchrony of major climatic events indicating harmonious fluctuations in the position of the westerlies

re evaluation of mid holocene deposits at quebrada puripica northern chile duringthe middle holocene 8 3 ka wetland deposits accumulated in areas with emerg ent water tables in the central atacama desert 22 24 s producinga stratig raphic unit unit c that can be mapped and correlated across different basins and geomorphic settings wherever mapped unit c is located between 6 and 30 m above modern wetlands and includes thick sequences of diatomite and organic mats the origin depositional environment and paleoclimatic significance of unit c is controversial and currently under debate grosjean science 292 2001 2391a suggests the unit developed under a regime of falling lake and ground water levels whereas evidence presented here suggests that unit c formed during a period of rising ground water levels and increased vegetation cover the debate is embedded in broader discussions about geomorphic processes in ground water fed streams as well as the history and forcingof climate variability in the central andes the central atacama and andes are remote with few opportunities for different researchers to examine the same site one exception is a sequence of mid holocene deposits at the confluence of quebrada seca and r o puripica in northern chile 23 s grosjean et al quat res 48 1997 239 246 initially suggested the deposits accumulated in temporary lake basins which formed when recurringdebris flows from a side canyon quebrada seca dammed the main channel r o puripica duringa period of drought and reduced stream flow upon our visit to the site we found evidence that clearly demonstrates the deposits were not formed in temporary lakes but rather were deposited in a wetland environment disagreement remains about the climatic interpretation of wetland deposits grosjean science 292 2001 2391a now suggests that local ground water levels rise and wetland deposits aggrade in deep canyon systems such as r o puripica when stream power and channel erosion is reduced duringprolong ed dry spells however sedimentological evidence and the presence of unit c in many depositional environments not just deep canyons indicate that it formed during a period of higher regional ground water levels that were sustained by enhanced precipitation and recharge in the high andes 2003 elsevier science b v all rights reserved

episodic eolian deposition in the past ca 50 000years in the alto ilo dune field southern peru abstract the alto ilo dune field in the coastal desert of southern peru is located at the edge of the atacama desert and is one of the driest landscapes on earth a stratigraphic sequence of eolian sands paleosols and debris flow deposits are identified in this dune field spanning the past 55 ka we infer that eolian deposition is preceded by an increase in sediment supply from local alluvial fans that are upwind of the alto ilo dune field and thus reflects periods of relative hydrologic excess eolian sediment supply may increase also with the concomitant fall in sea level providing an additional foreland source area for eolian particles the presence of paleosols indicate millennial scale periods of locally wetter conditions possibly associated with spread of lomas vegetation fed from coastal fog sources debris flows reflect significant rainfall events possibly associated with enso variability the chronology is provided by optically stimulated luminescence using multiple aliquot regeneration protocols which reveal four major eolian depositional episodes at ca 55 to 45 ka 38 to 27 ka 22 to 16 ka and 12 ka eolian deposition in the late pleistocene dominates the record and is generally coincident with metrics of hydrologic excess from the peruvian andes and the altiplano which appears to translate into enhanced sediment availability on the coast a significant period of soil development between 18 and 13 ka is consistent with timing of central andean pluvial event and indicates widespread wet conditions the holocene record of eolian deposition is sparse reflecting limited alluvial fan sources and decreasing particle availability upwind with the rise in postglacial sea level

chronology of exotic mineralization at el salvador chile by 40ar 39ar dating of copper wad and supergene alunite exotic copper mineralization is a complex hydrochemical process linking supergene enrichment lateral copper transport and precipitation of copper oxide minerals in the drainage network of a porphyry copper deposit at the el salvador porphyry copper deposit in northern chile the majority of the exotic ore comprised a mixture of copper bearing manganese oxyhydrates termed copper wad x ray diffraction scanning electron microscopy and electron probe microanalysis show that the copper wad is composed of copper bearing cryptomelane k1 2 mn3 mn4 8o16 x h2o and birnessite k0 33 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mn 7 3 9 end document o14 7h2o structures these natural occurrences within the exotic ore provide the opportunity to directly date the formation of these deposits using recent advances in 40ar 39ar geochronology of supergene k mn oxides formed by weathering a suite of copper bearing cryptomelane and birnessite samples from exotic deposits within the el salvador district were characterized and dated by 40ar 39ar laser step heating supergene alunite kal3 so4 2 oh 6 found in paleospring feeder systems leading from the source zones of copper outward to the exotic mineralization was dated to independently constrain the age of exotic ore formation although the ar retentivity of the layered birnessite structure has been questioned by others the ar retentivity of these samples is thought to be a function of their natural preservation and limited postcrystallization ground water interaction in the hyperarid atacama desert the 40ar 39ar analytical results show that ar and or k losses after crystallization excess 40ar and 39ar recoil do not pose significant problems therefore in the context of exotic copper deposits within hyperarid environments this dating method is applicable to both cryptomelane and birnessite within copper wad the 40ar 39ar dating of exotic mineralization at el salvador indicates that supergene and exotic mineralization processes were active at 35 ma about 5 m y after the emplacement of hydrothermal mineralization and continued until the middle miocene the majority of exotic mineralization extends from the oligocene miocene 24 ma boundary through the middle miocene 11 ma and relates to supergene fluid emanating in multiple directions from the source of copper in indio muerto which represents a topographic high above the exotic deposits one reconnaissance date of exotic mineralization at the chuquicamata porphyry copper deposit yielded an age of 17 03 0 03 ma coincident with the known supergene alunite dates for this deposit reconnaissance dating at exotica mina sur and el abra proved problematic due to the presence of contaminant silicate minerals within the copper wad ages derived here for exotic mineralization are similar to the known supergene ages throughout northern chile the dates indicate that supergene exotic mineralization began at the eocene oligocene boundary and continued through the oligocene eventually ceasing in the middle miocene due to desiccation of the atacama desert a series of 10 cm thick supergene alunite veins were microsampled across their widths and dated to address the kinetics of alunite vein growth apparent growth rates of the veins vary from 71 to 100 mm m y in the horizontal direction to 24 mm m y in the vertical presumably caused by differences in pressure regimes due to their orientation

integrated analysis for constraining palaeoclimatic and volcanic influences on clay mineral assemblages in orogenic basins palaeogene andean foreland northwestern argentina abstract variations in clay mineral assemblages in ancient continental deposits are frequently used to reconstruct past climate changes in active settings volcanic events can supply highly labile volcaniclastic material which can easily be transformed into smectite via diagenesis which can produce a noticeable footprint in clay mineral assemblages southern central andean foreland deposits are appropriate case studies to ascertain whether the climatic signal was preserved in the clay assemblages of their fine grained sediments as tectonic uplift volcanism and sedimentation have been interacting since the cretaceous we have studied a 1400 m thick coarsening upward palaeogene succession of the tin tin basin northern calchaqui valley argentina applying x ray diffraction xrd electron microscopy and detailed sedimentary facies analysis with the aim of comparing tendencies in the vertical fluctuations of clay minerals with evidence from sedimentological facies illite muscovite plus smectite account for 78 to 100 of the clay minerals in the fine fraction with kaolinite and chlorite in subordinate amounts the vertical variation of sedimentary settings from an overbank lacustrine domain to fluvial braided plains and an aeolian dune field suggests a gradual increase in aridity upsection however smectite abundances do not show a gradual decreasing trend compatible with progressively lower hydrolyzing conditions their relative abundances vary widely throughout the section depicting pulse like abrupt fluctuations despite the absence of field evidence for volcanic influence several indications of volcanic and volcaniclastic material have been found under scanning electron microscopy sem in levels with high smectite abundances from the middle to the top of the succession they include quartz crystals showing embayments and skeletal forms with smectite filling the voids microcrystalline silica as well as heulandite crystals in close association with authigenic smectite the xrd analyses of these levels evidence well crystallized smectite which is characteristic of a volcaniclastic origin therefore the increase in smectite abundance in these beds reflects a significant volcaniclastic contribution which is also evidenced by a centimetre thick ash layer topward in the sequence the only smectite rich level near the base of the tin tin section also contains well crystallized smectite associated with heulandite thus probably evidencing volcaniclastic input we infer that most of the smectite in these sediments formed during early diagenesis probably through the dissolution of labile tuffaceous material textural and morphological analysis by sem is essential to determine whether clay mineral assemblages could be interpreted in terms of palaeoclimate

the sensitivity of hillslope bedrock erosion to precipitation decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem hillslope erosion rates are well known to respond to changes in hillslope boundary conditions e g channel incision rates through their dependence on soil thickness and precipitation is an important control on soil formation surprisingly though compilations of hillslope denudation rates suggest little precipitation sensitivity to isolate the effects of precipitation and boundary condition we measured rates of soil production from bedrock and described soils on hillslopes along a semi arid to hyperarid precipitation gradient in northern chile in each climate zone hillslopes with contrasting boundary conditions actively incising channels versus non eroding landforms were studied channel incision rates which ultimately drive hillslope erosion varied with precipitation rather than tectonic setting throughout the study area these precipitation dependent incision rates are mirrored on the hillslopes where erosion shifts from relatively fast and biologically driven to extremely slow and salt driven as precipitation decreases contrary to studies in humid regions bedrock erosion rates increase with precipitation following a power law from 1 m ma 1 in the hyperarid region to 40 m ma 1 in the semi arid region the effect of boundary condition on soil thickness was observed in all climate zones thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels but the difference in bedrock erosion rates between the hillslopes within a climate region slower erosion rates on hillslopes with stable boundaries decreased as precipitation decreased the biotic abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases copyright 2010 john wiley sons ltd

the tropezon cu mo au deposit northern chile the missing link between iocg and porphyry copper systems this study has been supported by the project cicyt feder cgl2006 0378 of the spanish government and by internal funds of the igme

pattern and rate of erosion inferred from inca agricultural terraces in arid southern peru abstract earthworks of assumed age and their initial and current morphologies provide an ideal basis for developing and testing models for long term landform erosion inca agricultural terraces abandoned at 1532 a d in the drylands of southern peru may be used to document morphological changes since the abandonment the objective of this research is to determine the erosion pattern and process to estimate the erosion rate the development of rills and channels on the inca agricultural terraces is evidence for erosion by wash processes on slopes where the anchoring effect of vegetation is absent and loose material is available for removal the pattern and amount of erosion from 1532 2005 a d is estimated by comparing elevation models of the observed morphology and reconstructed models of the original morphology of the inca terraces the results show that in areas of sediment accumulation surface elevation increased up to 0 5 m elevation lowering on the terrace treads was 0 7 m at maximum and a temporally and spatially averaged lowering rate was 0 094 mm yr 1 this gives insights about how the rate of erosion occurs on currently disturbed lands in arid environments where soil resources are scarce and lands are prone to desertification

isotopic characterization of late neogene travertine deposits at barrancas blancas in the eastern atacama desert chile abstract here we explore the potential of spring related surface and subsurface carbonates as an archive of paleoenvironmental change at barrancas blancas located in the broadest and driest sector of the atacama desert at 24 5 s from these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past 11 5 ma u pb dates from the carbonates both surface and subsurface demonstrate that springs have discharged at this location over much of the last 11 5 ma attesting to the exceptional geomorphic stability of the central atacama many of the sampled vein systems line vertical fissures and formed within the aquifer before groundwater discharged at the surface carbonates in such circumstances should not undergo off gassing and kinetic fractionation prior to formation simplifying the interpretation of their isotopic composition oxygen isotopic compositions of carbonates are generally high 5 vpdb and using paleospring water temperatures of 3 13 c reconstructed from clumped isotopes point to strongly up to 50 evaporated water isotope values like those associated with the hyperarid core of the atacama desert today carbon isotopic compositions are also high 3 pdb reflecting a recharge area essentially devoid of plants and dominated by volcanic co 2 as is the case today our isotopic results are very similar to those from the calama basin to the north suggesting that the western face of the andes between 21 and 25 s has been highly evaporative and nearly plantless when these springs discharged over the last 11 5 ma the spring carbonates at barrancas blancas strongly resemble those found at devils hole and furnace creek in death valley usa and as such warrant further exploration as potential archives of climate change

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

stable isotopic composition of soil calcite o c and gypsum s overlying cu deposits in the atacama desert chile implications for mineral exploration salt sources and paleoenvironmental reconstruction abstract soils overlying two porphyry cu deposits spence gaby sur and the pampa del tamarugal atacama desert northern chile were collected in order to investigate the extent to which saline groundwaters influence soil chemistry in regions with thick miocene and younger sediment cover soil carbonate calcite was analyzed for c and o isotopes and pedogenic gypsum for s isotopes soil calcite is present in all soils at the spence deposit but increases volumetrically above two fracture zones that cut the miocene gravels including gravels that overlie the deposit the c isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the spence deposit all 13 c vpdb values fall within a narrow range 1 40 4 23 consistent with the carbonate having formed in equilibrium with atmospheric co 2 however 18 o vpdb for carbonate over both fracture zones is statistically different from carbonate elsewhere average 18 o vpdb 0 82 vs 2 23 respectively suggesting involvement of groundwater in their formation the composition of soils at the tamarugal anomaly has been most strongly affected by earthquake related surface flooding and evaporation of groundwater 13 c vpdb values 4 28 to 2 04 are interpreted to be a mixture of dissolved inorganic c dic from groundwater and atmospheric co 2 at the spence deposit soils only rarely contain sufficient so 4 for s isotope analysis the so 4 bearing soils occur only above the fracture zones in the gravel results are uniform 3 7 4 9 34 s cdt which is near the middle of the range for so 4 in groundwater 0 9 7 3 sulfur in soils at the gaby sur deposit 3 8 6 1 34 s cdt is dominated by gypsum which primarily occurs on the flanks and tops of hills suggesting deposition from so 4 rich fogs sulfate in gaby sur deposit gypsum is possibly derived by condensation of airborne so 4 from volcanic so 2 from the nearby andes at the gaby sur deposit and tamarugal anomaly pedogenic stable isotopes cannot distinguish between s from porphyry or redeposited so 4 from interior salars the three sites studied have had different histories of salt accumulation and display variable influence of groundwater which is interpreted to have been forced to the surface during earthquakes the clear accumulation of salts associated with fractures at the spence deposit and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process the interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism

climatic and geomorphic interactions on alluvial fans in the atacama desert chile abstract alluvial fan surfaces in the atacama desert of northern chile preserve evidence of recent precipitation driven surface flows determining the hydrologic characteristics of these flows is important for understanding the effects of rare yet significant storms in the region flow reconstruction runoff analysis and comparison with climatological data yield surface activation recurrence intervals of 1 20 years for three small fans and their associated catchments proximal to iquique and antofagasta chile modeled discharges provide minimum constraints on the precipitation rates required to resurface fans in the hyper arid region and suggest that relatively short lived and intense precipitation events 1 3 h 4 mm h 1 are capable of producing surface flows that mobilize and transport the largest grains found in channelized portions of the fan surface the results of this study provide an indication of the ability of a particular storm event i e precipitation rate to activate a geomorphic surface and contribute to our understanding of the controls on surface evolution in hyper arid environments

andean coastal uplift and active tectonics in southern peru 10be surface exposure dating of differentially uplifted marine terrace sequences san juan de marcona 15 4 s article i nfo along the san juan de marcona bay of southern peru two spectacular sequences of preserved marine terraces record net quaternary uplift previous geomorphic analysis of these paleo shorelines has revealed evidence of upper plate deformation and regional uplift however in the absence of a robust absolute dating method these studies contain substantial uncertainties concerning the numerical dating of these marine markers and thus the corresponding calculated surface uplift rates however field mapping surveying the neotectonic features and 10 be dating of abraded surfaces contained within two sequences of marine terraces along this margin should allow for the robust calculation of pleistocene uplift rates the san juan de marcona bay lies on the southern flank of the subducting and south migrating aseismic nazca ridge where the maximum rates of coastal uplift are expected in this locality we measure high uplift rates ranging from 0 4 m ka to 0 9 m ka during the pleistocene margin parallel normal faults displace several marine terraces and influence the development of bays thereby contributing to the configuration of paleo and present day coastlines the faults have relatively low slip rates b0 1 m ka over 400 ka and have been inactive for the last 80 ka the presence and activity of these normal faults can be directly linked to subduction zone processes with the release and accommodation of short term coseismic compression during megathrust subduction zone events in contrast the regional permanent uplift is probably controlled by post seismic and or interseismic strain accumulation over longer time scales due to inelastic behavior of the upper plate since at least the latest pliocene the san juan de marcona area has experienced long term regional tectonic uplift that has increased since about 800 ka due to the southward migration of the subducting nazca ridge based on migration velocity and geometry of the ridge the influence of the nazca ridge on the uplift of the forearc should account for 0 4 m ka within 145 km south of the ridge axis hence most of the post 400 ka mean uplift rate of the san juan de marcona area could be explained by the nazca ridge subduction

using remote sensing to quantify aeolian transport and estimate the age of the terminal dune field dunas pampa blanca in southern peru abstract aeolian dunes are widely used to reconstruct paleoenvironmental conditions however terminal dune fields ergs in the coastal desert of southern peru where information regarding quaternary paleoenvironmental conditions is very limited have until now not been used for paleoenvironmental reconstructions and the time depth of their accumulation is unknown here different estimates are derived to constrain the time depth recorded in the dunas pampa blanca a terminal dune field in coastal southern peru dune field age is calculated using the volume of the dunas pampa blanca and i recent aeolian transport rate in migrating transverse dunes feeding the dunas pampa blanca derived from digital processing of sequential landsat and quickbird images and ii limitations posed by recent fluvial sediment supply to the source of aeolian transport the resulting maximum age estimate of 70 8 ka from aeolian transport compares with a minimum age estimate of 4 75 ka from sediment supply however a minimum age estimate of 110 450 ka is deduced from the tectonic and topographic evolution of the region this discrepancy contradicts the hypothesis of late quaternary stability in the peruvian coastal desert and indicates that recent conditions of aeolian sediment supply and transport are not representative for the late quaternary

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

paleodiet in northern chile through the holocene extremely heavy δ15n values in dental calculus suggest a guano derived signature abstract dental calculus extracted from the teeth of 28 prehistoric human skeletons from coastal and valley archaeological sites in northern chile that date from the archaic period 2300 bc to the late intermediate period ad 1476 was analyzed for stable isotope 15 n 13 c compositions 15 n compositions were extremely heavy 17 8 to 33 1 but comparable to some studies using conventional human biomaterials hair nail muscle at other prehistoric sites in northern chile there was a negative correlation between 15 n and 13 c for coastal sites but a positive correlation for valley sites results for the valley sites point to a diet that was influenced by marine resources throughout all time periods the unusually heavy 15 n values for the coastal sites require a dietary component with a 15 n composition significantly heavier than that of marine resources the hyper aridity at the study area mean annual rainfall of 0 5 0 6 mm year is a likely contributing factor to the production of heavy 15 n values but is unlikely to account for the heaviest 15 n values 30 one possible explanation for the heaviest 15 n values is that dietary components were impacted by isotopically heavy guano which is abundant in the region guano may have been used as a fertilizer during crop cultivation at the onset of the formative period continuing through the historic period after spanish contact the indirect impact of guano from abundant bird habitats in the region may have influenced wild foodstuffs harvested throughout the pre agricultural period results provide support for the utility of dental calculus as a proxy for obtaining stable carbon and nitrogen isotope signatures for use in paleodietary studies

timing and nature of alluvial fan development along the chajnantor plateau northern chile abstract alluvial systems in the atacama desert provide a unique opportunity to elucidate the sedimentary response to climate variability particularly changes in precipitation in hyperarid environments alluvial fans along the eastern margin of the salar de atacama adjacent to the chajnantor plateau in the atacama desert of northern chile provide an archive of climate modulated sediment transfer and erosion at an extreme of earth s climate three regional alluvial fan surfaces qf1 oldest to qf3 youngest were mapped along the western flank of the chajnantor plateau the alluvial fans were examined with geomorphic and terrestrial cosmogenic 36 cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment alluvial fans in the study area are comprised of hyperconcentrated flow and boulder rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes alluvial fan surfaces yield exposure ages that range from 49 6 4 4 to 194 12 ka while debris flow boulders yield exposure ages ranging from 12 4 2 1 to 229 53 ka cosmogenic 36 cl exposure ages indicate that abandonment of alluvial fan surfaces qf1 qf2 and qf3 date to 175 22 6 ka mis 6 134 5 9 18 ka mis 6 and 20 07 6 26 ka mis 2 respectively a 36 cl concentration depth profile through alluvial fan qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation 6 m in ca 25 kyr followed by surface abandonment ca 180 200 ka our data support a strong climatic control on alluvial fan evolution in the region and we propose that the alluvial fans along the margins of the salar de atacama form according to the humid model of fan formation

the depositional environments and tectonic development of a mesozoic intra arc basin atacama region chile a thick succession of continental redbeds was deposited in a 50 km wide intra arc basin on the andean active continental margin in the atacama region of northern chile during early cretaceous times upper jurassic to early cretaceous marine limestones were buried by the seaward progradation of a succession of coastal dunes saline lakes and sandflats aeolian dune fields migrating towards the east across these coastal plains became stabilized by the growth of vegetation interdune alluvial areas between the sand dunes and dune fields developed into extensive alluvial braid plains which were in turn superimposed by alluvial fans these fans were inundated by a regionally extensive saline lake produced by tectonic or volcanic damming of the sedimentary basin this lake dried up leaving a large area of playa lake mudflats the climate was warm and semi arid with a low and seasonal rainfall parts of the area supported a substantial vegetation of woody plants together with a vertebrate fauna of dinosaurs pterosaurs and crocodiles the continental redbeds were derived from a volcanic source and were deposited on continental crust in a deep but narrow north south elongated fault bounded graben this extensional basin formed in an intra arc setting within an active andesitic volcanic chain upwards coarsening sedimentary successions were the product of uplift of the fault bounded margins of the basin

surface evolution of salt encrusted playas under extreme and continued dryness miocene continental saltpans are scattered in the central valley of the atacama desert one of the driest regions on earth these evaporitic deposits are hydrologically inactive and are detached from groundwater brines or aquifers the surface of the saltpans also known as salars comprises desiccation polygons commonly with nodular salt structures along their sides the morphology and bulk mineralogy of salt polygons differs between and within salars and the shape and internal structure of salt nodules varies between different polygon types based on field observation and mineralogy and crystallography data we generated a conceptual model for the genesis and evolution of these surface features whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders in addition frequent but less intense deliquescence events further drive the evolution of salt nodules resulting in a characteristic internal structure that includes laminations and changes in porosity and crystal morphologies as a result and despite the extreme dryness the surfaces of fossil salars are dynamic on timescales of several years to decades in response to daily cycles in atmospheric moisture and also to rare and meager rainfall events we propose that fossil salars in the atacama desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness

zebra stripes in the atacama desert revisited granular fingering as a mechanism for zebra stripe formation abstract although a number of studies have pointed out the remarkable slowness of earth surface processes in the atacama desert process mechanisms under such extremely limited water availability are poorly understood and process rates remain unknown this paper revisits the discussion on the formation of the prominent atacama specific hillslope zebra stone stripes previously interpreted to result from palaeo overland flow owen et al 2013 compared to this study our data document different stripe characteristics with regard to stripe form and orientation as well as sorting and bedding patterns of stripe confining surface gravel units we found a remarkable form concordance between zebra stripes and deposits from experiments on segregation induced granular fingering hence we propose a combination of seismic shaking and instantaneous dry granular free surface flows as the key mechanism for zebra stripe formation our findings underline the potential significance of seismicity in shaping atacama landscapes which bear important analogies to extra terrestrial surfaces

paleohydrology of the laguna lejia north chilean altiplano and climatic implications for late glacial times paleoenvironmental and sedimentological data from laguna lejia 23 30 s 67 42 w 4325 m in the high altiplano of the chilean atacama desert indicate that climatic conditions during late glacial times were significantly wetter than today a water and energy budget model was used to simulate climatic scenarios that would have resulted in the observed changes in the water levels water surfaces water volumes and salinity during the time interval different climatic scenarios for the laguna lejia catchment include precipitation increases of over 100 up to 400 500 mm yr today 200 mm yr to account for the late glacial lake levels with shorelines 15 25 m higher than at present and a lake surface of 9 11 km2 compared to the present 2 km2 during the lake maximum about 13 500 11 300 yr b p finely laminated sediments consisting of mg calcite diatoms and sometimes gypsum were deposited the paleoenvironmental evidence indicates that north easterly wind direction prevailed and the summer rainfall resulted from a seasonal poleward shift of the tropical circulation the lake history of laguna lejia is representative for the altiplano area between 21 and 24 s

age of supergene oxidation and enrichment in the chilean porphyry copper province twenty five samples of supergene alunite collected from deeply developed supergene profiles in porphyry copper deposits and prospects between latitudes 20 degrees and 27 degrees s in northern chile yield k ar ages ranging from about 34 to 14 ma therefore supergene oxidation and enrichment processes were active from the early oligocene to the middle miocene a minimum of 20 m y supergene activity at individual deposits lasted for at least 0 4 to 6 2 m y the early oligocene supergene activity affected deposits in the paleocene porphyry copper belt whereas early and middle miocene supergene processes are documented in the early cretaceous paleocene and late eocene to early oligocene porphyry copper belts middle miocene oxidation also affected the oldest epithermal gold silver deposits in the maricunga belt farther east supergene activity commenced no less than 11 m y after generation of each porphyry copper deposit because of the time required to unroof the copper bearing parts of the system supergene activity throughout northern chile ceased at approximately 14 ma the geologic features of deposits and prospects and their morphotectonic positions present latitudes and present elevations display no obvious correlations with the supergene chronology exploration for major cumulative enrichment blankets should not be carried out either beneath thick sequences of piedmont gravels or ignimbrites of oligocene through middle miocene age unless their accumulation is demonstrably late in the documented history of supergene activity or in porphyry copper provinces such as those of central chile and northwestern argentina which formed after approximately 14 ma the uplift responsible for efficient cumulative copper enrichment is difficult to correlate convincingly with the brief pulses of compressive tectonism postulated for northern chile and contiguous areas unless their effects were much more prolonged intensifying aridity is confirmed as the likely reason for the cessation of supergene activity in northern chile and tectonic uplift was its most probable cause however more fundamental global controls producing a period of chemical weathering followed by worldwide dessication also may have played a role

xeropreservation of functionalized lipid biomarkers in hyperarid soils in the atacama desert our understanding of long term organic matter preservation comes mostly from studies in aquatic systems in contrast taphonomic processes in extremely dry environments are relatively understudied and are poorly understood we investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the yungay region of the atacama desert lipids from seven soil horizons in a 2 5 m vertical profile were extracted and analyzed using gc ms and lc ms diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth deeper clay units contain fossil organic matter radiocarbon dead that has been protected from rainwater since the onset of hyperaridity we show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains this indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between 40 000 and 2 million years ago the exceptional structural preservation of biomarkers is likely due to the long term hyperaridity that has minimized microbial and enzymatic activity a taphonomic process we term xeropreservation i e preservation by drying the degree of biomarker preservation allowed us to reconstruct major changes in ecology in the yungay region that reflect a shift in hydrological regime from wet to dry since the early quaternary our results suggest that hyperarid environments which comprise 7 5 of the continental landmass could represent a rich and relatively unexplored source of paleobiological information on earth

supergene enrichment of copper deposits since the onset of modern hyperaridity in the atacama desert chile supergene enrichment of cu deposits in the atacama desert has played a critical role in making this the prime cu producing province of the world previously this has been believed to have occurred exclusively over a long period from the middle eocene to the late miocene which ended when climatic conditions changed from arid to hyperarid here we report u series disequilibrium ages in atacamite bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the atacama desert 230th 234u ages of gypsum intergrown with atacamite in supergene veins from cu deposits cluster at 240 ka chuquicamata 130 ka mantos blancos spence and 80 ka mantos de la luna michilla when coupled with previous data these results indicate that supergene enrichment of cu deposits did not cease after the onset of hyperaridity we propose that supergene enrichment in the atacama region developed in two main stages the main phase caused by downward circulation of meteoric waters in a semi arid setting was active from 45 until 9 ma with a last pulse ca 5 ma in the southern atacama desert during this phase atacamite bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water this was followed by a second stage starting at 2 1 5 ma and continuing until at least the late pleistocene when deep formation waters derived from the basement passed up through and modified the pre existing supergene cu oxide minerals atacamite has then been preserved in the prevailing hyperarid climate

evaluating the life expectancy of a desert pavement abstract this paper integrates prior scholarship on desert pavements with a case study of pavements on stream terraces in the sonoran desert to analyze the processes and site conditions that facilitate the survival of ancient desert pavements this synthesis identifies vital factors key factors and site specific factors promoting pavement stability hyperaridity is the vital factor in pavements surviving for 106 years or more aided by minimal bioturbation and clast size reduction three key factors aid in pavements surviving for 104 to 105 years accumulation of allochthonous dust underneath pavement cobbles a flat topography and a lack of headward retreating swales or gullies a unified explanation for pavement longevity however did not emerge from a literature review because a variety of site specific factors can also promote pavement antiquity including resistant bedrock beneath the pavement disk shaped cobbles to promote dust accumulation and microclimatological and ecological reasons for minimal bioturbation both key and site specific explanations for pavement longevity apply well to a case study of pavements on stream terraces in the sonoran desert central arizona the buildup of cosmogenic 10be and in situ 14c optically stimulated luminescence and varnish microlamination ages reveal stable pavements range in age between 30 and 332 ka with conditions for longevity including flat surface topography pavements underlain by consolidated granitic bedrock a lack of headward retreating gullies and swales 87sr 86sr analyses indicating the infiltration of allochthonous dust floating disk shaped pavement cobbles and a quartzite lithology resistant to disintegration however 10be ages also indicate evidence for the instability of desert pavements on stream terraces underlain by unconsolidated playa clays and unconsolidated fanglomerate these weaker materials allowed the growth of headward retreating swales that in turn promoted exposure of newer gravels by surface erosion

exploring for deeply covered mineral deposits formation of geochemical anomalies in northern chile by earthquake induced surface flooding of mineralized groundwaters northern chile is a major producer of copper from porphyry deposits most ores worked to date were exposed near the surface exploration is now focused on deposits along a basement unconformity buried under piedmont gravels deposited by ca 10 ma two recent discoveries the spence and gaby sur deposits are covered by gravel soils above these deposits have anomalies for elements present in saline mineralized groundwaters the anomalies occur above fracture zones in the gravels believed to represent the upward propagation of basement faults that guided emplacement of the porphyries we propose that during earthquakes in this seismically active region there was pumping of saline basement waters up the faults and fracture zones entraining mineralized groundwaters from the deposits after surface flooding and evaporation elements were redistributed by infrequent rains sampling shows that surface active cations such as cu 2 1 were adsorbed and retained in the top few centimeters of soil whereas nacl and porphyry indicator elements that dissolve as anions se re and as are not adsorbed and are removed to 40 cm depth given the 10 m y interval since the gravels were deposited and the hyperarid climate of the atacama desert anomalies may have formed by repeated episodes of seismically induced flooding company geochemical surveys show that such features are numerous in northern chile producing linear zones of saline soils plus other constituents of local groundwaters e g b and i where faults controlling these features intersect mineralization elements specific to the mineralization are also present saline zones may be outlined in the field by measuring the conductivity of soil plus water slurries sampling for full geochemical analyses can be limited to areas so defined anomalies may be generated along fault lines in other seismically active wetter climates but only for elements that are adsorbed on soil minerals although the context of the study is mineral exploration the process may be relevant to the formation of geochemical features of environmental interest above major faults

slow long term exhumation of the west central andean plate boundary chile we present a regional analysis of new low temperature thermochronometer ages from the central andean fore arc to provide insights into the exhumation history of the western andean margin to derive exhumation rates over 10 million year timescales 38 new apatite and zircon u th he ages were analyzed along six 500 km long near equal elevation coast parallel transects in the coastal cordillera cc and higher elevation precordillera pc of the northern chilean andes between latitudes 18 5 s and 22 5 s these transects were augmented with age elevation profiles where possible results are synthesized with previously published thermochronometric data corroborating a previously observed trenchward increase in cooling ages in peru and northern chile one dimensional thermal kinematic modeling of all available multichronometer equal elevation samples reveals mean exhumation rates of 0 2 km myr since 50 ma in the pc and 100 ma in the cc regression of pseudovertical age elevation transects in the cc yields comparable rates of 0 05 to 0 12 km myr between 40 and 80 ma differences between the long term mean 1 d rates and shorter term age elevation derived rates indicate low variability in the exhumation history modeling results suggest similar background exhumation rates in the cc and pc younger ages in the pc are largely a function of increased heat flow and consequently an elevated geothermal gradient near the arc slow exhumation rates are suggestive of semiarid conditions across the region since at least the eocene and deformation and development of the andean fore arc around this time

cortlandt beemerville magmatic belt a probable late taconian alkalic cross trend in the central appalachians a belt of alkalic to alkalic calcic pipes lamprophyres and intrusive complexes of probable late ordovician age extends from the peach lake croton falls area of westchester county new york about 100 km s80 w to beemerville new jersey the rocks are intruded across a taconic dynamothermal belt ranging from sillimanite grade on the east to chlorite grade on the west foliated middle ordovician and older rocks containing slaty cleavage or coarser grained metamorphic fabrics are crosscut by dikes that are posttectonic to late syntectonic relative to the taconian dynamothermal events analysis of thrust faults and fold structures within this belt suggests that this cross grain belt of alkalic to weakly alkalic rocks intruded steeply dipping brittle fractures trending n40 to 50 w n35 to 60 e and n70 to 80 e and along more ductile zones trending n20 to n70 e this plutonic activity was restricted to a discrete east west belt the clear posttectonic to syntectonic nature of the dikes and the spatial and temporal association with ordovician tectonism suggest that magmatic activity may be related to fracturing of mantle rock at the junction of two salients of taconic age that intersect in the new york recess the tectonic setting of the intrusive belt is unusual because it is associated in space and time with compressional tectonics of the taconic orogeny rather than with extensional rifting

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

late quaternary hydroclimatology of a hyper arid andean watershed climate change floods and hydrologic responses to the el nino southern oscillation in the atacama desert abstract although certain characteristics of the el nino southern oscillation enso are well known on contemporary timescales less is known about the magnitude frequency relationships of this atmospheric phenomenon on longer timescales or its relationship to widespread flooding especially in its core zone along the sub tropical andes where la nina or el nino episodes control regional hydroclimatology using a combination of stratigraphic evidence geochronologic dating 14c and osl stable isotope analyses and water geochemistry along the rio moquegua in the northern fringes of the atacama desert we assemble a paleoflood chronology for mainstem and tributary sections for the past ca 20 ka and ascertain the variation in enso frequency and magnitude because of the inherent watershed structure and regional hydroclimatology mid valley tributaries of the rio moquegua only flood during el nino episodes and thus provide an important proxy of extreme el ninos while mainstem stratigraphy records both la nina and el nino episodes el nino floods appear to have been pronounced during the late pleistocene and up to at least the younger dryas 12 000 cal yr bp while stratigraphic evidence of large el nino floods is lacking in tributary systems during the mid holocene flood stratigraphy in a 2 ka 7 m high terrace along the mainstem indicates an increased frequency and magnitude of large floods between ca 700 and 1610 ad as compared to the period from ca 160 bce to 700 ad with mega ninos occurring ca 1330 ad and ca 1650 ad water geochemistry and radiocarbon dating indicate that at least two major aquifers exist with wells and springs in the mid valley dating to 710 and 3100 14c yr bp respectively while water from a spring in the headwaters dates to 10 320 14c yr bp this range in dates suggests that groundwater flow in the mid valley is neither fossil water nor exclusively recharged from local precipitation while the older date for headwater sections suggests a more fossil groundwater source and lack of contemporary recharge the 18o similarity between groundwater in the mid valley and the regional meteoric water line mwl suggests a pacific moisture source and the role of el nino precipitation in recharging local aquifers thus el ninos and pacific sourced moisture are an important component of the regional hydroclimatology and the variation in enso frequency and intensity has significant social and hydrologic repercussions in these hyper arid settings

description of a very dense meteorite collection area in western atacama insight into the long term composition of the meteorite flux to earth we describe the geological morphological and climatic settings of two new meteorite collections from atacama chile the el m edano collection was recovered by systematic on foot search in el m edano and caleta el cobre dense collection areas and is composed of 213 meteorites before pairing 142 after pairing the private collection has been recovered by car by three private hunters and consists of 213 meteorites similar to other hot desert finds and contrary to the falls and antarctica finds both collections show an overabundance of h chondrites a recovery density can be calculated only for the el m edano collection and gives 251 and 168 meteorites larger than 10 g km a2 before and after pairing respectively it is by far the densest collection area described in hot deserts the atacama desert is known to have been hyperarid for a long period of time and based on cosmic ray exposure ages on the order of 1 10 ma to have been stable over a period of time of several million years such a high meteorite concentration might be explained invoking either a yet unclear concentration mechanism possibly related to downslope creeping or a previously underestimated meteorite flux in previous studies or an average terrestrial age over 2 myr this last hypothesis is supported by the high weathering grade of meteorites and by the common terrestrial fragmentation with fragments scattered over a few meters of recovered meteorites

the relationships between sedimentary structures transport directions and dune types in mesozoic aeolian sandstones atacama region chile extensive occurrences of upper jurassic to lower cretaceous aeolian sandstones form part of a thick sequence of terrigenous red beds in northern chile these sediments accumulated in a n s elongated intermontane back arc basin on the landward side of an active volcanic chain this volcanic chain which was produced by subduction beneath the continental margin provided the source of almost all the clastic sediments the aeolian sands formed isolated dune fields covering only part of the depositional basin at any one time cosets of cross bedded sandstone up to 40 m thick represent the deposits of linear draas cross bedded sets which average between 0 5 and 1 m in thickness were produced by the migration of small dunes down and along the gentle lee slopes of the draas the majority of foreset laminations in the cross bedded sets are thin parallel and persistent they are the product of the lateral migration of dunes which developed oblique to the prevailing winds foreset laminations dip at low angles averaging 19 well below the angle of repose of dry sand most of the laminations originated by tractional processes rather than by grainflow avalanching or grainfall this conclusion indicates that the dunes were gently undulating with no slip faces the orientation of the direction of maximum dip of foreset laminations does not provide a reliable indicator of the palaeowind direction although individual sets or cosets commonly show a unidirectional pattern significant variations have been recorded between sets of the same age at nearby locations and vertically between one coset and the next variations in vertical sections were produced by the superimposition of draas with different orientations

late pliocene age for the atacama desert implications for the desertification of western south america the atacama desert forms one of the major hyperarid deserts of the world previous studies suggest that desertification commenced at 14 ma during global climate desiccation sedimentologic data from middle miocene to upper pliocene successions in the modern atacama desert indicate that a semiarid climate persisted from 8 to 3 ma punctuated by a phase of increased aridity at ca 6 ma as such hyperaridity did not commence until the late pliocene implications are 1 that the rain shadow generated by the andean cordillera has had a minor influence on climate change and 2 that the upwelling north flowing cold humboldt current although important in establishing the generally arid climate of western south america did not control the shift to hyperaridity the formation of the hyperarid atacama desert in the late pliocene accompanied the development of the current phase of aridification in the sahara and namib deserts and is attributed to a phase of global climate cooling

late quaternary paleohydrology of the central atacama desert lat 22 24 s chile in northern chile precipitation in the high andes 3500 m recharges groundwater systems that flow down the pacific slope and feed large aquifers in the hyperarid atacama desert wetlands which are often found along the base of the andes mark locations where the water table intersects the land surface at these locations paleo wetland deposits which are present as terraces between 3 and 20 m above modern wetlands record past water table heights along the andean front and are used to reconstruct changes in groundwater discharge paleo wetland deposits in the central atacama desert lat 22 24 s record an episode 15 4 9 ka of high water tables followed by an episode 8 3 ka of moderately high water tables elevated water tables result from increased groundwater discharge and ultimately from enhanced recharge in the andes the concordance of results from three separate hydrologic systems suggests that changes in groundwater discharge and recharge are regional and reflect climatic fluctuations this interpretation is supported by close agreement with other paleoclimatic records in the region the periods of greater groundwater discharge were separated by episodes 9 8 and 3 0 ka of significant groundwater lowering and stream incision implying greatly diminished discharge the central atacama and andes lat 22 24 s receive precipitation mainly from moist air masses transported from the amazon basin by the south american summer monsoon sasm increases in groundwater recharge are therefore thought to reflect an increase in the frequency and or moisture content of sasm air masses crossing the andes fluctuations in sasm precipitation have previously been linked to summer insolation in the southern hemisphere the wettest period in the central atacama 15 4 9 ka however coincides with a minimum in austral summer insolation at 10 ka suggesting that regional summer insolation is not a dominant influence on the sasm instead intensification of the sasm may be linked to extraregional forcings such as the walker circulation

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

andean uplift and climate change sedimentological data indicate that a semi arid arid climate prevailed across the central andes from 15 ma to 4 ma between 4 and 3 ma a switch to hyperaridity occurred along the western margin of south america palaeoaltitude data suggest that a substantial proto central andean mountain range was in place between 15 and 9 ma these data support the idea that the andean rain shadow existed by 15 ma and that it reinforced the pre existing climatic regime rather than changing it the change to hyperaridity in western south america is attributed to a combination of global climate cooling and enhanced upwelling of the humboldt current generated by closure of the central american seaway between 3 5 and 3 ma and not to the andean rain shadow

small scale lobate hillslope features on mars a comparative 3d morphological study with terrestrial solifluction lobes and zebra stripe lobes abstract small scale lobes ssl observed at the surface of mars are thought to be the result of solifluction hence their existence has important implications for our understanding of recent climate history the distribution of thaw liquids and its geomorphic effects as water is believed not to have been recently stable at the martian surface these small scale lobes are limited to sloping terrains and often occur alongside polygonal patterned ground attesting to the presence of ice in the environment in this study we perform a comparative 3d morphometric analysis of the lobes on mars with terrestrial analogues we use data from high resolution imaging science experiment hirise camera in order to create digital terrain models dtms on mars at 1 m pix for the terrestrial analogues we use dtms and orthophotos from five periglacial environments with solifluction lobes and from one site with lobate features found in the atacama desert the lobate features in the atacama desert are found within features called zebra stripes which are apparently unique to the atacama and are now generally accepted to be the result of seismic shaking we show that ssl on mars overlap morphometrically with terrestrial solifluction lobes and are less similar to zebra stripe lobes the majority of martian ssl occur below the angle of repose which demonstrates that a dry fall mechanism cannot be responsible for their formation and that lubrication of the subsurface is required we found that martian ssl only occur on slopes greater than 10 a constraint not observed for terrestrial solifluction lobes nor zebra stripe lobes in atacama we hypothesise that this apparent constraint does not result from the lowered gravity on mars but instead from differing soil properties and or thermal regime between mars and earth which affects the slope at which creep can initiate we cannot rule out a role of co2 sublimation in lobe formation based on our terrestrial measurements

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

the densest meteorite collection area in hot deserts the san juan meteorite field atacama desert chile we describe the geological morphological and climatic setting of the san juan meteorite collection area in the central depression of the atacama desert chile our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3 88 km 2 area the recovery density is in the range 9 12 falls km 2 depending on pairing making it the densest among meteorite collection areas in hot deserts this high meteorite concentration is linked to the long standing hyperaridity of the area the stability of the surface pebbles ma and very low erosion rates of surface pebbles approximately 30 cm ma 1 maximum the san juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka and limited weathering compared with other dense collection areas in hot desert chemical weathering in san juan is slow and mainly controlled by the initial porosity of meteorites as in the antarctic and other hot deserts there is an overabundance of h chondrites and a shortage of ll chondrites compared with the modern falls population suggesting a recent few ka change in the composition of the meteorite flux to earth

supergene oxidation of epithermal gold silver mineralization in the deseado massif patagonia argentina response to subduction of the chile ridge radiometric ages for supergene alunite and jarosite effectively date the oxidation of former concentrations of pyrite and any associated sulfide minerals these k bearing sulfate minerals formed under low ph conditions are uncommon supergene products in low sulfidation epithermal deposits because of the general paucity of pyrite for acid generation for this reason the age of supergene oxidation locally to depths of 200 m or more in the epithermal au ag deposits of the deseado massif located in the extra andean foreland of patagonia southern argentina has remained unknown although theoretically the oxidation could have taken place anytime between the late jurassic when the au ag mineralization formed and pleistocene k ar ages for alunite and jarosite from two widely separated and unusually pyritic ag bearing hydrothermal breccias lejano and libanesa show it to have been mid miocene 13 8 1 8 ma this is the time when the deseado massif underwent appreciable regional scale tectonic uplift and valley incision following 140 myr during which the region was topographically subdued and the site of either fluvio lacustrine or shallow marine sedimentation the uplift combined with increasing aridity due to the orographic rain shadow caused by growth of the patagonian andes to the west and enhanced by global cooling would have depressed regional groundwater tables thereby promoting the supergene sulfide oxidation the mid miocene uplift appears to have been triggered by development of a slab tear and slab window beneath the deseado massif during early stages of subduction of the chile oceanic ridge spreading center at the pacific margin supergene sulfide oxidation in both the deseado massif and atacama desert of northern chile was the result of cenozoic uplift during progressive aridification although the causes of these phenomena were radically different however when the supergene oxidation was taking place in the deseado massif up to 30 myr of supergene activity in the atacama desert were coming to an end because of the onset of hyperaridity

zebra stripes in the atacama desert fossil evidence of overland flow abstract some hillslopes in the hyperarid region of the atacama desert in northern chile have surface clasts organized into distinct contour parallel bands separated by bare soil we call the bands zebra stripes due to the contrast between the darkly varnished clasts and the light colored salt rich soil gravel that comprises the zebra stripes is sorted such that the coarsest clasts are at the downslope front and fine progressively upslope how and when the zebra stripes formed are perplexing questions particularly in a region experiencing prolonged hyperaridity using googleearth satellite imagery and field observations we report the first quantitative and qualitative observations of zebra stripes in order to test hypotheses of the mechanisms and timing of their formation we consider soil shrink swell seismic shaking and overland flow as possible formation mechanisms and find that overland flow is the most likely based on cosmogenic 10 be concentrations in surface clasts salt deposition rates from the atmosphere and content in the soils we propose that the salt rich soils began accumulating 10 6 y ago and the zebra stripes formed 10 3 10 4 y at the latest the zebra stripe pattern has been preserved due to the self stabilization of the clasts within the stripes and the continued absence of life which would disturb the surface as seen at a wetter site to the south we conclude that the occurrence of zebra stripes is diagnostic of a set of distinct characteristics of local and or regional precipitation soil hillslope form and bedrock type

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

groundwater sapping origin for the giant quebradas of northern chile northernmost chile is home to a well preserved disequilibrium landscape of great antiquity contrasting drainage patterns are developed on the western slope of the altiplano plateau the oldest of these patterns is a now relict parallel patterned drainage network in places a younger pattern comprising a series of deeply incised canyons or quebradas crosscuts the older parallel patterned network these canyons show strong evidence of a groundwater sapping origin we hypothesize that the initiation of the canyon network resulted from changes in the hydrological regime related to a drying out of climate of the forearc and to the uplift of the altiplano plateau

more than ten million years of hyper aridity recorded in the atacama gravels abstract the atacama desert s hyper aridity is closely linked to the development of world class copper and nitrate iodine ores and to regional tectonics and global paleoclimate changes in the cenozoic era the timing when the hyper aridity commenced remains controversial with proposed ages ranging from late oligocene to pleistocene in this study we provide an independent constraint on the initiation of atacama hyper aridity utilizing a 100 m deep profile within the atacama gravels and underneath porphyry copper deposit in spence northern chile the overall high concentration of sulfate up to 10 wt and a multimodal distribution of water soluble salt sulfates chlorides and nitrates indicate multiple generations of sedimentation and salt accumulation events under semi arid to hyper arid climate conditions the multiple sulfate isotope compositions 17o 18o 34s of the upper section 15 0 to 34 5 m are close to those of modern hyperarid surface sulfates while the lower section 34 5 to 65 m displays a depth dependent isotope trend that is best interpreted as marking a period of climate change from semi arid to hyper arid when these data are combined with new chronological 40ar 39ar dates obtained from a volcanic ash layer at depth of 28 0 m our results show that hyper arid condition in the atacama desert was prevailing at least prior to 9 47 ma and may go back as old as the middle miocene

giant evaporite belts of the neogene central andes large volumes of continental evaporites accumulated within the central andes during neogene uplift of the altiplano puna plateau and development of the andean volcanic arc halite and gypsum are dominant minerals along with local and economically important borates playa conditions have existed since ca 15 ma halite and borate deposition has occurred for the past 7 to 8 m y evaporites formed in salar environments e g playa lakes and are characterized by complex mineral assemblages occurrence zonation and geochemistry evaporite deposition was controlled by volcanism geothermal activity closed drainage and climate these andean deposits and their controls differ from evaporites in other continental and marine environments

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

an inventory of cryospheric landforms in the arid diagonal of south america high central andes atacama region chile abstract an integral glacial and periglacial inventory of the cryosphere in the atacama region in chile was carried out to estimate the amount of frozen water reserves in this arid to hyper arid region the inventory was carried out with medium to high spatial resolution satellite images and resulted in a total of 168 908 ha of landforms with significant ice content in one of the most fragile andean ecosystems the semi arid hyper arid zones this study shows an integral mapping of the cryosphere including glaciers and ice bearing periglacial landforms the different ice landforms in the atacama region shows a progressive change in the landforms containing ice responding to the northwards increase of aridity upon entry to the south american hyper arid axis the main change observed is that uncovered glaciers are not present north of 26 5 s being replaced by creeping permafrost landforms uncovered glaciers may produce more water annually compared to other ice bearing landforms but they only represent 2 7 of the cryospheric area however cryoforms containing a mixture of ice sediment and rock fragments could be more important as water reserves because of their large extensions that cover c 97 of the total area of ice bearing landforms mapped it also shows that the water supply potential of ice bearing periglacial landforms could be much higher than that of the glaciers in arid zones the comparison with the previous inventory of 1987 suggests a reduction of 34 of uncovered glaciers which is consistent with the aridization process observed in almost all of northern chile these findings reinforce the fact that glaciers and other types of permanent ice bearing landforms need to be inventoried together if the objective is to provide the society with a realistic view of the distribution of the cryospheric hydrological resources in desert regions

the origin of the magnetic record in eocene miocene coarse grained sediments deposited in hyper arid arid conditions examples from the atacama desert abstract magnetic proxies for paleoclimate are tools widely used to understand climate variability yet current proxies focus on loess derived soils in humid to temperate climate zones whereas coarse grained sediments in arid hyperarid climate zones remain poorly investigated to test the potential paleoclimatic environmental significance of the magnetic record of coarse grained sediments deposited in a region with a mean annual precipitation map

neogene evaporites in desert volcanic environments atacama desert northern chile the upper miocene and pliocene evaporite deposits of the atacama desert of northern chile hilaricos and soledad formations are among the few nonmarine evaporites in which aridity not only formed the deposits but has also preserved them almost unaltered under near surface conditions these deposits are largely composed of displacive ca sulphate and halite together with minor amounts of glauberite thenardite and polyhalite however at the base and top of these deposits there are also beds of gypsum crystal pseudomorphs that originally formed as free growth forms within shallow brine bodies rather than as displacive sediments the halite is present as interstitial cement displacive cubes and shallow water bottom growth chevron crusts most of the calcium sulphate is presently anhydrite pseudomorphous after gypsum that was the primary depositional sulphate mineral the secondary anhydrite formed under early diagenetic conditions after slight burial some metres resulting from the effect of strongly evolved pore brines the anhydrite has been preserved without rehydration during late diagenetic and exhumation stages on account of the arid environment of the atacama desert both the hilaricos and the soledad formations contain geochemical markers indicating that these neogene evaporites had a largely non marine origin bromine content in the halite is very low few p p m indicating neither a sedimentological relation with sea water nor the likelihood of direct recycling of prior marine halites moreover the d 34 s of sulphates 4ae5 to 9 also reflects a non marine origin with a strong volcanic influence although some recycling of mesozoic marine sulphates cannot be ruled out d 34 s of dissolved sulphate from hot springs and streams in the area commonly displays positive values 2 to 10 leaching of oxidized sulphur and chlorine compounds from volcanoes and epithermal ore bodies very common in the associated drainage areas have been the main contribution to the accumulation of evaporites the sedimentary and diagenetic evolution of the hilaricos and soledad evaporites based on lithofacies analysis provides information about the palaeohydrological conditions in the central depression of northern chile during the neogene in addition the diagenesis and exhumation history of these evaporites confirms the persistence of strongly arid conditions from late miocene until the present a final phase of tectonism took place permitting the internal drainage to change and open to the sea resulting in dissolution and removal of a significant portion of these deposits despite the extensive dissolution the remaining evaporites have undergone little late exhumational hydration

the origin and distribution of salts on alluvial fans in the atacama desert northern chile the atacama desert has been predominantly hyperarid since the middle miocene combined ionic and x ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in antofagasta province northern chile differences between the fans were largely due to the effect of local factors on salt input secondary redistribution and deposit preservation thus carbonate was notable in the high andes fan c and pre cordillera fan b whereas in the central valley fan a greater qualities of the more soluble salts chlorides and nitrates probably reflect the higher level of aridity and an oceanic source the camanchaca calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin evidence from the pre cordillera fan b however suggests that salt input may have been episodic related to changes in conditions within the general aridity and possibly to stone pavement and soil development calcium sulphate sources range from an input in andean precipitation and the camanchaca to abundant regional evaporite deposits it is probable however that products of andean volcanism constitute the dominant primary source of calcium sulphate and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater surface flow and the wind 1997 john wiley sons ltd

evidence of a microbial community associated with rock varnish at yungay atacama desert chile 1 rock varnish is a very slow growing nanostratigraphic coating consisting of approximately 70 fine grained clay and 30 iron and manganese oxides that forms on the surfaces of rocks in arid and semiarid climates the microbial diversity associated with rock varnish collected from the hyperarid yungay region of the atacama desert was investigated using culture independent biomolecular methods and an adenosine triphosphate atp assay the extraction of dna from rock varnish collected at yungay a region in which little to no dna has been extracted from the surface soil 1 cm to date indicates that rock varnish may provide a niche habitat for microbial life where water is essentially absent the clone library constructed suggests the presence of numerous phylogenetically distinct microorganisms ranging in diversity from cyanobacterial to a proteobacteria lineages the findings also show that only a few micrometers of varnish material are enough to shelter microbes like chroococcidiopsis spp from the intense ultraviolet radiation present in the atacama desert whether or not microorganisms are involved in its nucleation and or growth rock varnish appears to provide a microhabitat resembling cryptoendolithic communities seen on a larger scale

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

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of