Andes Of Northwestern Argentina Research Articles

Image Texture as Quality Indicator for Optical DEM Generation: Geomorphic Applications in the Arid Central Andes

The generation of Digital Elevation Models (DEMs) through stereogrammetry of optical satellite images has gained great popularity across various disciplines. For the analysis of these DEMs, it is important to understand the influence of the input data and different processing steps and parameters employed during stereo correlation. Here, we explore the effects that image texture, as well as the use of different matching algorithms (Block Matching (BM) and More Global Matching (MGM)), can have on optical DEMs derived from the flexible, open-source Ames Stereo Pipeline. Our analysis relies on a ∼2700 km2 clip of a SPOT6 tristereo scene covering the hyperarid, vegetation-free Pocitos Basin and adjacent mountain ranges in the northwestern Argentine Andes. A large, perfectly flat salt pan (paleolake bed) that covers the center of this basin is characterized by strong contrasts in image texture, providing a unique opportunity to quantitatively study the relationship between image texture and DEM quality unaffected by topography. Our findings suggest that higher image texture, measured by panchromatic variance, leads to lower DEM uncertainty. This improvement continues up to ∼103 panchromatic variance, above which further improvements in DEM quality are independent of local image texture but instead may have sensor or geometric origins. Based on this behavior, we propose that image texture may serve as an important proxy of DEM quality prior to stereo correlation and can help to set adequate processing parameters. With respect to matching algorithms, we observe that MGM improves matching in low-texture areas and overall generates a smoother surface that still preserves complex, narrow (i.e., ridge and valley) features. Based on this sharper representation of the landscape, we conclude that MGM should be preferred for geomorphic applications relying on stereo-derived DEMs. However, we note that the correlation kernel selected for stereo-matching must be carefully chosen depending on local image texture, whereby larger kernels generate more accurate matches (less artifacts) at the cost of smoothing results. Overall, our analysis suggests a path forward for the processing and fusion of overlapping satellite images with suitable view-angle differences to improve final DEMs.

Physico-chemical and biological controls in a travertine system in the high Andes of northwestern Argentina

Unraveling the processes involved in travertines and tufa formation, and the textural and geochemical signatures they preserve, are relevant given their potential as world-class oil reservoirs and analogues for ancient microbial carbonates. This study yields insights into the processes controlling hydrochemistry, isotopic fractionation and carbonate precipitation within a travertine system located in the southern border of the Puna plateau (Argentina), at an active high-altitude volcano-tectonic setting. Geochemical and isotopic composition of hot spring waters, together with its physico-chemical parameters, are typical of deep-cycled meteoric waters with most of the CO2 provided by a magmatic source. Downstream CO2 degassing rises the pH and shifts carbonate chemical equilibrium providing the bulk conditions for CaCO3 precipitation. Precipitates occur mainly as aragonite near hot springs and calcite throughout the rest of the system (~1 km extent) in close association with cyanobacteria, diatoms and exopolymeric substances (EPS). Constructive morphologies and crystalline crusts develop where strong CO2 degassing occurs, driven by contrasting CO2 partial pressures between hot spring waters and the atmosphere, and also associated to incremental downstream turbulence (e.g., dams and waterfalls). Biological influence is preponderant within downstream calm pools by providing an EPS substrate suitable for calcite nucleation, contributing to clotted micrite textures. Downstream trend towards heavier isotopic compositions of waters and related carbonates is given by the preferential degassing and evaporation of lighter isotopes (12C and 16O) and enrichment of heavy isotopes (13C and 18O) in the carbonate phase. Nonequilibrium isotopic fractionation seems to relate with kinetically-controlled processes and pH changes along the system. This study highlights that, while at the macroscale physico-chemical processes control bulk water and carbonate chemistry, providing favorable conditions for carbonate precipitation, at the microscale microbial activity has some control, particularly on the development of carbonate microtextures.

The elevation gradient of small mammals richness and abundance in the dry Andes of northwestern Argentina

In this research we explore elevation gradient of small mammal diversity on the arid slopes of the Andes in northwestern Argentina. We evaluated the influence of climatic and environmental factors on species richness and abundance across two altitudinal transects between 2700 and 4700 m. We used canonical correspondence analysis, multiple regressions (GLM's), and variation partitioning analysis to evaluate the primary productivity, environmental heterogeneity, and climate as drivers of species diversity. The general trend indicates a greater diversity towards high elevation with an abrupt decrease towards the summit. The most remarkable pattern was the coincident distribution of the maximum values for both, abundance and richness at the same altitude (3700 m). The species richness showed a flattened distribution with the maximum values between 3200 and 3700 m and a small peak at 4200 m. We found that the joint effects of environmental heterogeneity with productivity explained most of the variation for richness and abundance (86.5%, 63.2% respectively). These results highlight the complexity of the mountain environments in desert areas while emphasizing the importance of these habitats for the maintenance of biological diversity. Our results constitute an important tool for the conservation of small mammals diversity in these mountain arid environments.

Assessing the impact of climate change on threatened endemic vascular plants of Argentina

Biodiversity loss due to climate change is one of the most critical current environmental problems. Global warming is causing substantial species-range shifts and local extirpations, especially for species with restricted distribution ranges. Studies of impact of the climate change on species ranges and environmental suitability have become a fundamental tool for evaluating conservation strategies. However, one important limitation of these approaches is that only species with an adequate number of spatially distinct occurrence records can be modelled, generally excluding threatened rare species from the analyses, a situation referred to as the ‘rare species modelling paradox’. To overcome this limitation, we analysed the effect of climate change on the richness of threatened endemic plants of Argentina employing a macroecological modelling approach, using three different modelling techniques (generalized linear mixed models – GLMM, generalized additive models – GAM, and boosted regression trees – BRT), four general circulation models, two representative CO2 concentration pathways (RCPs), and two time periods (2050 and 2070). We identified grid cells with the greatest decline in numbers of threatened endemics, determined species composition in these cells and characterized their vulnerability using three indices. A loss of species richness is observed in ca 83% of the cells, and both protected areas and hotspots of threatened species show significant decrease in future species richness. We identified 32 most affected cells under future climatic projections, including a total of 370 threatened endemic species and exhibiting high beta diversity values (high dissimilarity) among most of the cells. Cells with the highest vulnerability were located along the Central Andes of northwestern Argentina, along the Southern Andean Yungas, High Monte and Central Andean Puna ecoregions, and including a total of 118 threatened endemics (15% of those registered for Argentina) with greater representation of Asteraceae, Apocynaceae, Cactaceae and Iridaceae. However, coverage of protected area network is less than 5% for each of these cells. Our results highlight the urgent need for both in situ and ex situ conservation policies and strategies for the vascular flora of Argentina.

Identification of Debris‐Flow Channels Using High‐Resolution Topographic Data: A Case Study in the Quebrada del Toro, NW Argentina

AbstractResolving Earth's surface at the meter scale is essential for an improved understanding of the dynamics of mass‐movement processes. In this study, we explore the applicability and potential of digital elevation models (DEMs) derived from stereophotogrammetry to detect debris‐flow channels in the Quebrada del Toro in the northwestern Argentine Andes. Our analysis relies on a high‐resolution (3 m) DEM created from SPOT‐7 tri‐stereo satellite data. We carefully validated DEM quality with ∼6,000 differential GPS points and identified optimal parameters for DEM generation in high‐relief terrain. After multiple processing steps, we achieved an accuracy of 0.051 ± 1.915 m (1σ) using n = 3,139 control points with cm precision. Previous studies have used the drainage area and slope framework to identify topographic signatures of debris flows within a catchment. We built upon this and investigated individual river‐channel segments using connected‐component (CC) analysis on meter‐scale topographic data. We define CC as segments of similar slope along the channel profile. Based on seven manually identified debris‐flow catchments, we developed a debris‐flow similarity index using component length and mean channel‐segment slope and identified channel segments that have likely been shaped by debris flows. The presented approach has the potential to resolve intra‐catchment variability of transport processes, allows to constrain the extent of debris‐flow channels more precisely than slope‐area analysis, and highlights the versatility of combined space‐ and field‐based observations for natural‐hazard assessments.

Deformation history of the Puna plateau, Central Andes of northwestern Argentina

Two tectonic shortening events created the first-order structural characteristics of the Puna plateau: one in the Paleozoic and a second during the Andean Orogeny in the Cenozoic. To constrain the structural characteristics and timing of Andean deformation in the Puna plateau, we focus on differentiating these two shortening events and provide cooling ages (apatite fission track and apatite (U–Th)/He) to determine the amount of Andean exhumation on the hanging-wall of major Cenozoic faults. Two contrasting expressions of shortening are documented. In Ordovician strata, strain requires four stages: folding, flattening through cleavage formation, low-angle faulting and local distributed shear. In the Mesozoic and Cenozoic strata, shortening is expressed as reverse faults, fault-propagation folds and dipping panels. Dissimilarities reflect different P-T conditions and amount of strain, as structures in the Ordovician rocks require higher temperatures and strain than Andean structures in the Mesozoic and Cenozoic strata. Furthermore, local Cretaceous AFT cooling ages in pervasively cleaved Ordovician rocks reveal these rocks did not reach temperatures compatible with cleavage formation during the Andean event. Lastly, our data show a middle Eocene to Oligocene exhumation history that supports an overall continuous development of the Andean thrust belt in the Puna plateau since the early Cenozoic.

Taxonomic novelties in Myrosmodes (Orchidaceae) from the northwestern Argentine Andes

Myrosmodes noemiae (Orchidaceae), a new species from the Puna biome in the high northwestern Argentine Andes, is described and illustrated. This species is currently known from a single population; its habitat, a distribution map, and a key to distinguish it from other species of Myrosmodes growing in the Andean region are presented. In addition, we present an updated distribution of M. gymnandra, clarify the holotype of M. nubigena, and designate a lectotype for Altensteinia paludosa, the basionym of Myrosmodes paludosa.

A series of confusing measurements in the search for water

A mine development in the high Andes of north-western Argentina requires a supply of fresh water for various uses, the largest being mineral processing. Complementary survey techniques in a gravel ...

Dispersion, colonization and phenotypic structure of prehistoric human populations of the Andes of North-Western Argentina.

In this article we study the phenotypic structure, biological relationships and evolutionary factors that acted on the biological diversity observed in the prehistoric groups that inhabited Northwest Argentina (NWA). The collections used belong to different subareas and periods of the development of this region. In this study 15 metric traits of the skull were used. To achieve the proposed objective, models derived from population genetics, multivariate statistical analysis, geo-referenced map and phenotypic correlation between geographical and biological distances were applied. The total genetic divergence (FST) is 16% and within subregions it varies between 2% and 10%. The correlation (r) between geographic and phenotypic distances among all samples in NWA is 0.3 and within subregions it varies between -0.16 (Quebrada de Humahuaca) and 0.7 (Puna de Jujuy). The analysis of georeferenced data indicates two phenotypic gradients in NWA. The results show a varied evolutionary scenario, characterized by an important population structure produced by a set of evolutionary factors (genetic isolation, non-random mating, effective size and different rates of genetic interaction between subpopulations).

Recent climate warming and the Varas rock glacier activity, Cordillera Oriental, Central Andes of Argentina

Recent studies have revealed that in high-altitude mountain environments the global warming trend over the last few decades tends to be strongly amplified. However, few attempts have been made to monitor the possible effects of such climate changes on high-altitude rock glaciers. In this paper, we provide a geomorphic analysis of the Varas rock glacier, and present the first observations of rock glacier temperature (air and ground) and surface velocities in the Andes of northwestern Argentina. A network of 30 boulders was monitored every year between 2012 and 2016 using a differential Global Positioning System. Over the observational period, the Varas active rock glacier registered velocities between 125 and 5 cm/yr, except for four boulders which did not shift. Over the five years of monitoring, the mean annual air and ground (at 5 and 50 cm depth) temperature remained above 0 °C. A long-term instrumental weather dataset (106 years), located ∼130 km from the Varas rock glacier, at La Quiaca station, reveals a warming trend of 0.8 °C during the last century, with a steep increase during the last two and half decades. The warming trend recorded in the region may have produced or facilitated the inactivity of the more-exposed sectors of the Varas active rock glacier. However, there also may be a delay in the relatively slow and full response of rock glaciers to the last few decades of warming. Finally, the observations allow us to propose a formation sequence in the Varas rock glacier valley, since postglacial time.

Three new mosses records from the Andes of northwestern Argentina.

Two mosses are newly reported for Argentina based on recent collections from Saltaprovince: Aligrimmia peruviana R.S. Williams and Conostomum cleistocarpum Herzog. Hitherto, they were considered endemic to Bolivia and Peru, respectively. In addition, Crossidium squamiferum (Viv.) Jur., a species distributed in Europe, North America, Mexico, Asia, North Africa, and Macaronesia, is here reported for the first time in South America.

Outlining the thermal posdepositional evolution of the Ordovician successions of northwestern Argentina by clay mineral analysis, chlorite geothermometry and Kübler index.

The thermal post-depositional evolution of metapelitic and metavolcanic rocks of the upper Cambrian-Ordovician succession in the Central Andes of northwestern Argentina, was estimated through X ray diffraction of clay mineral analysis, Kubler Index (KI), SEM-EDS study of selected samples and chlorite geothermometry. The study area comprise five representative regions in Puna and Cordillera Oriental, namely at Sierra de Santa Victoria (Nazareno and Santa Victoria river areas), Cordon de los Siete Hermanos (Yavi), Sierra de Rinconada and Sierra de Cochinoca-Escaya. The paleotemperatures obtained with the chlorite geothermometer, in coincidence with KI values, show an E-W trend from diagenesis/low anchizone in the eastern flank of Sierra de Santa Victoria, to high anchizone/epizone in the Puna, with intermediate values in the western flank of Sierra de Santa Victoria. This trend, in conjunction with the development of slaty cleavage in the Ordovician rocks from Yavi, Sierra de Cochinoca-Escaya and western localities coincide with the limits proposed for the “Ocloyic deformation belt”. The common occurrence of kaolinite in the slates and the metavolcanic rocks of Sierra de Cochinoca-Escaya, coupled with the substitution of chlorite by interstratified lower-temperature phases in most of these rocks and the occurrence of jarosite in a metadacite, indicate presence of hydrothermal fluids with high H+/cations ratios, producing acid type alteration (Utada, 1980), at temperatures between 100 and ~300 °C. The hydrothermal alteration should have been subsequent to the maximum burial and the attainment of epizonal metamorphism, and was very probably related with the posthumous activity of the Ordovician volcanic arc. The widespread occurrence of retrograde diagenesis products (smectite, kaolinite, as well as interstratified Chl/Sm and Chl/Vrm phases) in the anchizonal/epizonal metapelites of Sierra de Cochinoca-Escaya and Sierra de Rinconada constitute, up to our knowledge, the first report of an extensive hydrothermal activity affecting not only the metavolcanic rocks but also the Lower Ordovician sediments of northern Puna.

Peopling of the high Andes of northwestern Argentina

The goal of this presentation is to review the current evidence in order to model the early peopling of the highlands of Northwestern Argentina. Paleoenvironmental evidence of the late Pleistocene and early Holocene is thoroughly reviewed in order to set the stage of the process of human settlement of the Puna region of Argentina. I will analyze chronological evidence and the archaeological record –especially the archaeofaunas- of early hunter-gatherer occupations dated between 10,500 and 9000 BP (12,500 to 10,000 cal. BP). Finally, I discuss specific cultural and environmental aspects related to the dispersion and human colonization of the highland plateau.

Local high relief at the southern margin of the Andean plateau by 9 Ma: evidence from ignimbritic valley fills and river incision

AbstractA valley‐filling ignimbrite re‐exposed through subsequent river incision at the southern margin of the Andean (Puna) plateau preserves pristine geological evidence of pre‐late Miocene palaeotopography in the north western Argentine Andes. Our new 40Ar/39Ar dating of the Las Papas Ignimbrites yields a plateau age of 9.24 ± 0.03 Ma, indicating valley‐relief and orographic‐barrier conditions comparable to the present‐day. A later infill of Plio–Pleistocene coarse conglomerates has been linked to wetter conditions, but resulted in no additional net incision of the Las Papas valley, considering that the base of the ignimbrite remains unexposed in the valley bottom. Our observations indicate that at least 550 m of local plateau margin relief (and likely >2 km) existed by 9 Ma at the southern Puna margin, which likely aided the efficiency of the orographic barrier to rainfall along the eastern and south eastern flanks of the Puna and causes aridity in the plateau interior.

Overview of the Inca Frozen Mummies From Mount Lullaillaco (Argentina)

Three frozen bodies belonging to a young woman and two infants were found at an elevation of 6.715 meters (22,100 ft.) above sea level, on the summit of volcano Llullaillaco, in the Andes of northwestern Argentina. The mummies were discovered (and recovered for ulterior preservation and study) during scientific excavations codirected by the author of this paper at the highest archaeological site in the world. The mummies belonged to children that were sacrificed five hundred years ago, under the rule of the Inca Empire, as part of a state-controlled ceremony known as capacocha. According to the historical sources written during the Hispanic conquest, the Inca human sacrifices were performed in response to natural catastrophes, the death of the Inca emperor, or to propitiate the mountain spirits that grant fertility. The selected children and the young acllas or “chosen women” were taken in processions to the highest summits of the Andes to be sacrificed. They were believed to become messengers into the world of the mountain deities and the spirits of the ancestors. Numerous interdisciplinary studies were conducted on the frozen mummies between 1999 and 2004, a time span during which the “Llullaillaco children” were preserved at the Catholic University of Salta (UCASAL). These studies included radiological evaluations by conventional X-rays and CT scans, which provided information about condition and pathology of the bones and internal organs; as well as dental studies oriented to the estimation of the ages of the three children at the time of death. Ancient DNA studies and hair analysis were also performed in cooperation with academic institutions in the United States and Europe, including the Institute of Bioscience at the George Mason University, the University of Bradford and the Laboratory of Biological Anthropology at the University of Copenhagen. In this paper we focus on the frozen bodies of mount Llullaillaco as objects for bioarchaeological and medical research, providing an overview on the paleopathology of the mummies that are among the best preserved known to date.

The role of climate in the accumulation of lithium-rich brine in the Central Andes

Lithium-rich brine within the sub-surface of the Salar del Hombre Muerto (SHM) salt pan in the Andes of northwestern Argentina has a chemical and isotopic composition which is consistent with Li derived from several sources: the modern halite saturated lagoon, Li-rich salts and brines formed recently, and dissolution of halite which precipitated from ancient saline lakes. SHM lies in the closed basin that includes part of the massive Cerro Galán caldera which is drained by the Río los Patos, which is responsible for 90% of surface runoff into the salar. The low Li isotope composition, +3.4‰, of this river is consistent with significant contributions of geothermal spring water. As water drains through the volcaniclastic deposits which cover a large proportion of the basin, Li removal, as indicated by decreasing Li/Na, occurs but without significant isotope fractionation. This indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than Li incorporation into octahedral structural sites of clays. These observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals, which jointly have allowed the Li resource to accumulate rapidly. Changes in climate on a multi-millennial time scale, specifically in the hydrologic budget, have resulted in solute accumulation rates that have been variable through time, and decoupled Li and Na fluxes. Inflow to the salar under modern conditions has high Li/Na (7.9×10−3 by wt) with δ7Li indistinguishable from basement rocks (−0.3‰ to +6.4‰), while under pluvial climate conditions the Li/Na of the saline lake was 40 times lower than the modern lagoon (0.1–0.3×10−3 compared to 10.6–13.4×10−3) with slightly higher δ7Li, +6.9‰ to +12.3‰, reflecting the uptake of 6Li into secondary minerals which formed under a wetter climate.

A new species of <i>Minuartia</i> (Caryophyllaceae) restricted to the high Andes of South America

A new apetalous species of Minuartia from the high Andes of northwestern Argentina, M. altoandina, is here described and illustrated. At first sight, M. altoandina is morphologically very similar to the European M. sedoides because of the absence of petals and ciliate leaf margin with narrow hyaline teeth; however, from a biogeographical point of view, it will probably be related to the North American M. rossii complex through the morphology of M. austromontana.

Brazilian marsupial frogs are diphyletic (Anura: Hemiphractidae: Gastrotheca)

Molecular phylogenetic analyses based on expanded taxonomic and geographic sampling support the monophyly of the marsupial frog genera (family Hemiphractidae), resolve six geographically circumscribed lineages within Gastrotheca, and, for the first time, reveal that two divergent lineages of Gastrotheca inhabit the Atlantic Coastal Forests of Brazil. Within Gastrotheca, the earliest diverging clade is confined to northeastern Brazil, whereas the three subsequent diverging lineages are restricted to northern Venezuela (G. walkeri), southeastern Brazil, and northwestern South America. All species in these clades inhabit humid forests at low to mid-elevations, and their life histories are characterized by lacking free-living tadpoles (i.e., direct development). Two derived clades inhabit the Andes, and both contain species with either direct development or tadpoles. One Andean clade of Gastrotheca ranges in the high Andes from Colombia to extreme northern Peru, whereas the other clade inhabits high elevations in the Andes of southern Ecuador, Peru, and Bolivia, and lower elevations in the Andes of northwestern Argentina. The presence of two non-sister lineages on each side of the Amazon Basin suggests that vicariance across this central region played an important role in diversification within Gastrotheca.

Drainage and base-level adjustments during evolution of a late Pleistocene piggyback basin, Eastern Cordillera, Central Andes of northwestern Argentina

Fil: Gonzalez Bonorino, Gustavo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina. Universidad Tecnologica Nacional. Facultad Regional Rio Grande; Argentina

Spatiotemporal trends in erosion rates across a pronounced rainfall gradient: Examples from the southern Central Andes

The tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern Central Andes of northwestern Argentina cause strong contrasts in elevation, rainfall, and surface-process regimes. The climatic gradient in this region ranges from the wet, windward eastern flanks (~2m/yr rainfall) to progressively drier western basins and ranges (~0.1m/yr) bordering the arid Altiplano–Puna Plateau. In this study, we analyze the impact of spatiotemporal climatic gradients on surface erosion: First, we present 41 new catchment-mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns. Second, we re-evaluate paleoclimatic records from the Calchaquíes basin (66°W, 26°S), a large intermontane basin bordered by high (>4.5km) mountain ranges, to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late Pleistocene and Holocene. Three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time: (1) First-order spatial patterns of erosion rates can be explained by a simple specific stream power (SSP) approach. We explicitly account for discharge by routing high-resolution, satellite derived rainfall. This is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge. This relation indicates that erosion rates (ER) scale with ER~SSP1.4 on cosmogenic-nuclide time scales. (2) We identify an intrinsic channel-slope behavior in different climatic compartments. Channel slopes in dry areas (<0.25m/yr rainfall) are slightly steeper than in wet areas (>0.75m/yr) with equal drainage areas, thus compensating lower amounts of discharge with steeper slopes. (3) Erosion rates can vary by an order of magnitude between presently dry (~0.05mm/yr) and well-defined late Pleistocene humid (~0.5mm/yr) conditions within an intermontane basin. Overall, we document a strong climatic impact on erosion rates and channel slopes. We suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport, which is primarily responsible for maintaining the balance between surface uplift, erosion, sediment routing and transient storage in the orogen.