Andean South Research Articles

Community Technical Identity among Potters in the Talina Valley, South Andean Bolivia

ABSTRACT This article explores the relationship between individual and community craft practices and technical identity. We examine the initial phases of the pottery production process, specifically the acquisition and processing of raw materials by women potters in the Indigenous and rural community of Chipihuayco in the Talina Valley, southern Bolivia. To unravel these dynamics, we employ a comprehensive approach that combines ethnographic and petrographic data. Ethnographic data provide insight into the collective and personal decision-making processes involved in ceramic production. Additionally, petrographic data allow us to investigate less visible aspects that shape technological practices, such as the mineralogical properties of raw materials and recipes. This study documents a strong association between the selection and processing of raw materials and a shared technical identity, which is embedded in broader cultural values and ritual practices.

Pre-hispanic wetland irrigation and metallurgy in the South Andean Altiplano (Intersalar Region, Bolivia, XIVth and XVth century CE)

The high-altitude Andean Altiplano has been subject to abrupt climate changes during the Holocene. The resulting impact on the hydrological cycle has obliged ancient societies to adapt and develop strategies to face droughts and sustain agropastoral activities. Here, we present the results of archaeological prospections together with the biogeochemical characterization of a well-dated core collected at Saitoco wetland in the arid southern Altiplano (Intersalar Region, Bolivia). Archaeological survey allowed the mapping of a network of channels collecting water from the surrounding mountains to the wetland, and the presence of small copper mines and metallurgical installations. Traces and major element concentrations and accumulation rates, together with elemental and isotopic characterization of organic matter (OM) (i.e., Corg and δ13Corg) in the wetland core have been used to document the evolution of the landscape in relation to climatic and anthropogenic pressure. While OM, bromine (Br), selenium (Se) and mercury (Hg) data were used to assess the variability of precipitations during the Late Holocene (4.2 ka BP to the present), local and regional mining activities have been reconstructed through the variations of lead (Pb), copper (Cu), and antimony (Sb). Our results show an abrupt change in OM composition during the 14th and 15th century CE, characterized by an abrupt shift in δ13Corg synchronous with a rise in Br, Se and Hg, testifying for the waterlogging of the wetland during a known arid period in the region. This change is attributed to anthropogenic transformation of the landscape through the irrigation of the wetland by channeling streams from the surrounding mountains. At the same time, a mining pollution signal was recorded supporting local Cu mining and metallurgy. The mining signal then reached its maximum values during the Inca and Colonial periods, which matches with reported enhanced mining activities in the region. From the colonial era onward, the wetland progressively dried up, likely resulting from the abandonment of the site. Through the combination of a biogeochemical record and archaeological prospections, this study provides evidences that societies of the arid Intersalar region have transformed their landscape and developed wetland irrigation and mining during the arid 14th and 15th century CE Period.

Evolutionary radiation of mid-Holocene lanceolate points from the highlands of the South Central Andes

Through phylogenetic reconstruction this work  analyzes the  diversification of  lanceolate points of the South Central Andes   which began in the early Holocene and spanned the entire mid- Holocene. Based on a regional-scale data, we   discuss the links between the increasing mid-Holocene risk conditions, the patterns of diversification of point lineages, demographic change and animal resources consumption. We distinguish a first instance of greater diversity of points, a higher rate of innovation and less class longevity. These trends progressively stabilized, giving rise to a pattern of  less innovation, decreasing taxa diversity  and greater class longevity as well as an age-related extinction pattern. We show that as projectile points diversified,hunting efficiency increased along the mid-Holocene by the increased representation of  high-return fauna in the regional zooarchaeological record.  We suggest that this diversification of  lanceolate points was an adaptive evolutionary radiation which began with the increase in the rate of innovation for coping with the increasing risk of the beginning of mid-Holocene in the South Central Andes. From this we conclude that technological innovation was a prerequisite for the human specialization in camelid hunting and for the development of a highly economically efficient foraging strategy in the south Andean  highlands

The Escaramayu Complex: A Prehispanic Metallurgical Establishment in the South Andean Altiplano (Escara, Potosi, Bolivia), Ninth to Fifteenth Centuries AD

AbstractArchaeological research carried out in the altiplano locale of Escaramayu (in the community of Escara, Potosí, Bolivia), revealed a prehispanic metallurgical establishment (ninth to fifteenth centuries AD) for the extractive processing of copper ores and, to a lesser extent, lead-silver ore exploited at the nearby Pulacayo mine. The number and variety of metallurgical equipment identified in this establishment for smelting metallic ore and for refining the metal indicate a deep level of technological experience and experimentation among the resident Escaramayu metalworkers during the Middle Horizon (MH) and Late Intermediate periods (LIP). In Escaramayu we find the first known antecedents of Andean wind furnaces (wayras) and a model of a prehispanic reverberatory furnace that was widely used in the southern Andean altiplano during the colonial period.

Soporte tela, pigmentos y moldura como manifestaciones de identidad cultural. Un estudio desde el cuadro San Francisco niño reparte el pan a los pobres (Cusco – Chile, ca. 1668–1684)

This article highlights the importance of applying material and technical studies to the pictorial heritage of Cusco, especially in situations where written accounts of the resources and creative processes involved in its production are limited. Through the analysis of samples of the physical order of the painting San Francisco distributing bread to the poor as a child, exhibited in the Museo Colonial de San Francisco in Santiago de Chile, the material iconological method was used to identify links with the European pictorial tradition and South Andean contributions and inventions. From this specific study, a way is presented by which a series of laboratory examinations focused on recognising the techniques and materials used in viceregal painting can provide valuable information about the context and society that gave them form and meaning.

Cenozoic exhumation history at the core of the Andes at 31.5°S revealed by apatite fission track thermochronology

The Andes at ~31°-32°S lie above the Chilean-Pampean flat slab zone (~27–33°S), where several morphostructural units developed resulting in a large orogenic width. The core of the Andes is composed of the La Ramada fold-and-thrust belt in Principal Cordillera and the basement blocks of Frontal Cordillera. While rock uplift of these blocks has been broadly constrained to the middle Miocene based on structural and provenance studies, thermochronologic approaches with the potential to directly constrain the timing and amount of exhumation have not been exploited until recently. Apatite fission track data from a ~1 km vertical profile collected within the Carboniferous Pico Los Sapos Batholith in the High Andes at 31.5°S places some constraints on the thermal evolution of the region since the Paleocene. The age-elevation profile combined with inverse thermal modeling and previous AHe thermochronology, indicates an episodic cooling/exhumation history. Rocks cooled rapidly in the early Cenozoic (ca. 65-55 Ma), followed by a period of relative thermal and tectonic stability when residence in an apatite partial annealing zone (PAZ) from at least ~52 Ma to ca.15 Ma, followed by final rapid cooling beginning ca. 15 Ma. We interpret early Cenozoic and middle Miocene rapid cooling events as to be related to erosional exhumation during Andean contractional phases, associated with thrust activity along the Mondaquita Fault. The age-elevation profile is partially duplicated, with upper samples being offset ~500 m due to back-thrusting since the late Miocene. The preservation of part of an exhumed PAZ indicates 3–5 km of exhumation since the onset of rapid cooling/exhumation at ~15 Ma. Although evidence for an early Cenozoic compressional phase in the High Andes at this latitude is scarce, the occurrence of a regional K-T (~65 Ma) unconformity supports our results. The Eocene Inca phase, registered north of 30°S, on the other hand, is not shown in our thermochronological data, suggesting that this tectonic phase did not affect the core of the Andes south of this latitude. Independent geological evidence both from the hinterland (structural, geochemical and thermochronological analyses) and foreland (provenance studies) corroborate our findings of a middle Miocene deformational event in the core of the Andes at 31.5°S.

Abstract B123: The genetic tone of prostate cancer risk linked to ancestry: Do we know all about genetic admixture, cancer, and ancestry?

Abstract Background: Epidemiologic studies have shown a correlation between a population genetic makeup and prostate cancer (PCa) risk. Specifically, African ancestry has been linked to PCa genetic risk. Furthermore, genome-wide association studies in European and Caucasian racial/ethnic populations have shown around 80 different genetic risk variants. Therefore, it is paramount to estimate the generalizability of these variants in other populations. As such, the Colombian population would be an ideal scenario to assess the generalizability of these genomic findings. Colombian is a highly admixed population shaped from Native Americans mixed with Europeans and African populations in different times since the European colonization. We hypothesized that perhaps we could design PCa risk models that could predict the genetic risk vs. the genetic admixture variation in our population; thus, the genetic risk will be dependent of the degree of genetic admixture found in a specific subpopulation. Study Design: We propose to analyze epidemiologic data from the Colombian National Information Registry, using cancer incidence and mortality. We will investigate the cancer registries of four different Colombian cities: Manizales (Andes center region), Bucaramanga (west region), Pasto (Andes south region), and Barranquilla (Caribbean north region). Each of these cities has a characteristic genetic heterogeneity due to their geographical position, as well as the population composition. Andean regions, such as Pasto, have historically more Native American ethnicities, while the Caribbean region is more greatly influenced by African populations. We propose two biologic questions: 1. What is the molecular epidemiology of prostate cancer in Andean and Caribbean populations of Colombia and their association with prostate cancer risk? 2. What is the molecular epidemiology of prostate cancer in Andean and Caribbean populations of Colombia and their association with prostate cancer survival? Relevance: The capacity to identify PCa risk populations in developing countries will allow us to design public health strategies that focus on these populations, in order to implement policies for PCa prevention and early detection. It is paramount to understand the generalizability of genetic risk variants in other populations, such as the Colombian population. We propose to investigate the relationship between PCa genetic risk and the degree of genetic admixture found in different Colombian specific populations (Andes, Central and Caribbean). Potential findings could help us to categorize subpopulations within a main population. Currently, we label a population as “Latino” and are consequently labeling the entire population as one category. It will be important to acknowledge the heterogeneity of admixed populations in future studies. Citation Format: Víctor Flórez, Jorge Vélez, Oscar M. Vidal. The genetic tone of prostate cancer risk linked to ancestry: Do we know all about genetic admixture, cancer, and ancestry? [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr B123.

Exotic Pinus radiata Plantations do not Increase Andes Hantavirus Prevalence in Rodents.

Andes south virus (ANDV) is the etiologic agent of hantavirus cardiopulmonary syndrome (HCPS) in Chile and southern Argentina. Farm and forestry workers have been identified as a group at high risk of acquiring HCPS caused by ANDV due to their close exposure to rodents or their secretions in rural areas. Therefore, investigation on the effect of landscape composition on ANDV in wild rodents becomes relevant for disease prevention and control. In this study, we analyzed the influence of Monterey pine (Pinus radiata) plantations, an important monoculture in the global forest industry, on small mammal assemblage and on ANDV seroprevalence and abundance of seropositive rodents from central Chile. Small mammals were sampled seasonally during 2years in native forests, adult pine plantations and young pine plantations. A total of 1630 samples from seven rodent species were analyzed for antibody detection. ANDV seroprevalence and abundance of seropositive rodents were significantly higher in the native forest compared to pine plantations. Furthermore, Monterey pine plantations decrease the abundance and relative abundance of Oligoryzomys longicaudatus (the principal reservoir of ANDV) and do not change sex ratio and distribution of age classes of this rodent species, which are variables that are important for ANDV transmission. Our findings indicate that Monterey pine plantations would not pose a higher risk of human exposure to ANDV compared to the temperate native forest. Our results can be useful for hantavirus risks assessment in human-dominated areas where ANDV is endemic.

Contrasting Climates at Both Sides of the Andes in Argentina and Chile

The prominent Andes cordillera induces significant differences in climates between its eastern and western slopes. These climatic differences are largely reflected by contrasting vegetation and ice coverages but remain poorly documented. This study quantifies the abrupt changes of precipitation and cloud properties at both sides of the Andes south of 20°S by using surface daily precipitation and satellite (CloudSat and MODIS) data during the 2006-2016 period. Results show that the precipitation changes drastically and precipitating clouds can be of very different nature on each side of the Andes. In the tropical Andes (20°S-25°S), precipitation normally falls from a sole layer of thick stratiform and convective precipitating clouds during the warm semester, but the annual mean accumulation is about 10-100 times larger on the eastern than on the western slopes. A sole layer of low stratus clouds dominates over the Pacific coast, occasionally producing light rains, whereas high, thin, and non-precipitating clouds dominate most of the time over the continent. In the subtropical Andes (25°S-35°S), annual mean precipitation is similar on both sides, however, it falls from convective and stratiform precipitating clouds in the warm semester on the eastern slopes, and from stratiform precipitating clouds in the cold semester, mostly as frozen particles, on the western slopes. These different features on both slopes denote a climatic transition between the tropics and extratropics. In the extratropical Andes (south of 35°S), stratiform cloud types produces precipitation on both sides during all the year, but the annual mean precipitation and cloud frequency are enhanced on the western slopes and strongly reduced on the eastern slopes of the Andes. Cloud frequencies are higher than in the subtropics and evenly distributed as single- or multi-layers of low, middle and high clouds. Frozen particles become important in precipitating clouds over the mountains and on the lee side. These findings demonstrate the significant influence of the Andes cordillera on the climate all along southwestern South America, and constitute an excellent example of how the simple dependence of climate on latitude can be substantially altered by the topography.

Typification of names and nomenclatural notes on the South Andean and Patagonian species of Polygala Linnaeus (Polygalaceae)

As part of an ongoing revision of the genus Polygala, several names of the South Andean and Patagonian species in need of nomenclatural and taxonomic study were identified. 13 lectotypes have been designated for accepted names, synonyms and a dubious taxon.

An Updated Multi-Temporal Glacier Inventory for the Patagonian Andes With Changes Between the Little Ice Age and 2016

We present a satellite-derived glacier inventory for the whole Patagonian Andes south of 45.5°S and Tierra del Fuego including recent changes. Landsat TM/ETM+ and OLI satellite scenes were used to detect changes in the glacierized area between 1986, 2005 and 2016 for all of the 11.209 inventoried glaciers using a semi-automated procedure. Additionally we used geomorphological evidence, such as moraines and trimlines to determine the glacierized area during the Little Ice Age for almost 90% of the total glacierized area. Within the last ~150 years the glacierized area was reduced from 28.091±890 km2 to 22.636±905 km2, marking an absolute area loss of 5.455±1.269 km2 (19.4%). For the whole study region, the annual area decrease was moderate until 1986 with 0.10±0.04% a-1. Afterwards the area reduction increased, reaching annual values of 0.33±0.28% a-1and 0.25±0.5% a-1 for the periods of 1986-2005 and 2005-2016, respectively. There is a high variability of change rates throughout the Patagonian Andes. Small glaciers, especially in the north of the Northern Patagonian Icefield (NPI) and between the latter and the Southern Patagonian Icefield (SPI) had over all periods the highest rates of shrinkage, exceeding 0.92±1.22% a-1 during 2005-2016. In the mountain range of the Cordillera Darwin (CD), and also accounting for small ice fields south of 52°S, highest rates of shrinkage occurred during 1986-2005, reaching values up to 5.6±4.2% a-1, but decreased during the 2005-2016 period. Across the Andean main crest, the eastern parts of the NPI, SPI and adjoined glaciers had in absolute values the highest area reduction exceeding 2.145±482 km2 since the LIA. Large calving glaciers show a smaller relative decrease rate compared to land-terminating glaciers but account for the most absolute area loss. In general, glacier shrinkage is dependent on latitude, the initial glacier area, the environment of the glacial tongue (calving or non-calving glaciers) and in parts by glacial aspect.

The American species of the genus Glaucolepis Braun, 1917 (Neotrifurcula van Nieukerken, syn. nov.) (Lepidoptera: Nepticulidae).

We provide diagnostic characters for the genus Glaucolepis Braun, re-examine the type series of the type species of the North American G. saccharella Braun, describe two new species from Chile and Argentina (G. flagellata Remeikis & Stonis, sp. nov. and G. pseudoflagellata Remeikis & Stonis, sp. nov.), and provide the first photographic documentation of the central Andean G. aerifica (Meyrick). We synonymize Neotrifurcula van Nieukerken, 2016, syn. nov. with Glaucolepis and provide one new combination for the south Andean G. gielisorum (van Nieukerken, 2016), comb. nov. All species treated in the paper are illustrated with drawings and (or) photographs of the adults and genitalia.

Phylogenetic relationships and generic re‐arrangements in “South Andean Loasas” (Loasaceae)

AbstractLoasaceae, a mostly American group, is one of the largest families of Cornales. In spite of considerable progress over the last 20 years, the relationships of some clades remain controversial, especially in the “South Andean Loasas” (SAL—Blumenbachia, Caiophora, Loasa, Scyphanthus). The present study addresses the phylogenetic relationships in SAL employing four plastid markers (rps16, trnL‐trnF, trnS‐trnG, matK) and ITS and aims at resolving the systematics and evolution of the group. Sequences obtained from a total of 59 SAL species (ca. 70% of the total, representing all lineages in the group) and 25 outgroup taxa were analysed using maximum likelihood and Bayesian inference approaches. ML best and BI strict consensus trees showed no significant differences in their topologies. Our results confirm that two species of Loasa ser. Malesherbioideae are not part of the SAL clade, but should be included in Presliophytum, a result which is here formalized. Blumenbachia (including sect. Angulatae and sect. Gripidea) is confirmed as a monophylum with high support. Loasa has to be redefined and restricted to a clade including only ser. Deserticolae, ser. Floribundae, ser. Loasa and ser. Macrospermae. Scyphanthus and Caiophora both are each monophyla and sister groups, but with two clades of Loasa as successive sister groups: (((Caiophora+Scyphanthus)+Loasa ser. Pinnatae)+(L. ser. Volubiles+L. ser. Acaules)) in a very well‐supported clade. Accordingly, Caiophora, Loasa ser. Pinnatae, L. ser. Volubiles, L. ser. Acaules and Scyphanthus could be included into a single genus, with Scyphanthus taking priority over Caiophora, creating a fairly heterogenous genus of ca. 52 species and requiring 50 new names. Alternatively, the clades Loasa ser. Pinnatae and L. ser. Volubiles + ser. Acaules can be removed into new segregate genera, which is here argued for and which requires the creation of only 16 new names. The new genus names and some of the new combinations are here formalized.

Species limits and morphometric and environmental variation within the South Andean and Patagonian Mulinum spinosum species-group (Apiaceae-Azorelloideae)

Delimiting species is an important, but frequently difficult aspect of systematics that should be addressed using data from multiple sources. Here we combine morphometric analyses and environmental characteristics to delimit species in the South Andean and Patagonian taxonomically difficult species-group composed by Mulinum spinosum, M. echinus and M. leptacanthum (Apiaceae-Azorelloideae). Molecular phylogenies have shown that these three species form part of a polytomy together with other Mulinum species, and therefore these data are not useful for their delimitation. We include measurements of 25 morphometric variables from 163 herbarium specimens and perform univariate and multivariate principal component analysis (PCA) and discriminant analysis (DA) to establish the limits amongst the three mostly sympatric, morphologically similar, and phylogenetically unresolved species. We also use 19 bioclimatic and three geographic variables from localities of the specimens to infer environmental characteristics of the taxa and test their relation with morphological variation. Morphological evidence supports the inclusion of M. echinus within the morphologically and climatically variable M. spinosum, and rejects its recognition as a distinct taxon at any rank. On the contrary, M. leptacanthum is considered a morphologically distinct species, generally restricted to high altitude areas of the southern Andes with a cooler and wetter climate. Within the widespread M. spinosum, environmental gradients of precipitation and temperature relate to morphological gradients (e.g., in leaf and inflorescence sizes, in leaf acicularity, and in fruit-wing width). These last results showed that the large morphological variation in vegetative and reproductive characteristics of this species that grows in arid and semiarid habitats are related to regional climatic gradients that have probably been important in the evolution of this species' plasticity, diversification, and differentiation.

Determination of petrophysical properties of sedimentary rocks by optical methods

Petrophysical properties of rocks (thermal diffusivity and conductivity, porosity and density) as well as the correlation between them are of great importance for many geoscientific applications. The porosity of the reservoir rocks and their permeability are the most fundamental physical properties with respect to the storage and transmission of fluids, mainly oil characterization. Accurate knowledge of these parameters for any hydrocarbon reservoir is required for efficient development, management, and prediction of future performance of the oilfield. Thus, the porosity and permeability, as well as the chemical composition must be quantified as precisely as possible. This should be done along with the thermal properties, density, conductivity, diffusivity and effusivity that are intimately related with them. For this reason, photothermal Beam Deflection Spectrometry (BDS) technique for determination of materials' thermal properties together with other methods such as Energy Dispersive X-ray Scanning Electron Microscopy (SEM-EDX) for determining the chemical composition and sample structure, as well as optical microscopy to determine the particles size, were applied for characterization of sedimentary rocks. The rocks were obtained from the Andes south flank in the Venezuela's western basin. The validation of BDS applicability for determination of petrophysical properties of three sedimentary rocks of different texture and composition (all from Late Cretaceous associated with the Luna, Capacho and Colón-Mito Juan geological formations) was performed. The rocks' thermal properties were correlated to the microstructures and chemical composition of the examined samples.

Notas sobre el catolicismo social cusqueño: El canónigo Isaías Vargas y sus Apuntes críticos sobre asuntos indigenistas

The objective of the article is to make known the social thought of Father Isaias Vargas Bueno in the context of the Peruvian indigenist debate during the first half of the twen­tieth century. As a canon of Cusco and a close collaborator of Bishop Pedro Farfan, an important part of his pastoral work was linked to the study of the problems of the rural world in the Andean south and to the development of a persevering activism in favor of the native rights for more than four de­cades. Vargas participated in a social-Christian current that, being critical of the Marxism and the liberalism, raised a set of reformist proposals to benefit the indigenous population.

Habitats of ancient hunter-gatherers in the Puna: Resilience and discontinuities during the Holocene

Hunting groups are closely linked to the environments in which they live, especially in the deserts. This paper explores the relationship between people and desert environments in the long term using key concepts such as resilience, refugia and habitat loss. A thorough paleoenvironmental analysis was conducted to improve our understanding about continuities and discontinuities in the archaeological record of the South Andean highlands. This allowed us to test ideas about the availability of adequate human habitats during the Holocene. Cultural archives such as archaeofauna and lithic technology are employed to illustrate and discuss methodological perspectives for the identification and description of resilient human habitats in arid landscapes in the South Andean Puna.

Evaluating the effects of pollinator-mediated interactions using pollen transfer networks: evidence of widespread facilitation in south Andean plant communities.

Information about the relative importance of competitive or facilitative pollinator-mediated interactions in a multi-species context is limited. We studied interspecific pollen transfer (IPT) networks to evaluate quantity and quality effects of pollinator sharing among plant species on three high-Andean communities at 1600, 1800 and 2000m a.s.l. To estimate the sign of the effects (positive, neutral or negative), the relation between conspecific and heterospecific pollen deposited on stigmas was analysed with GLMMs. Network analyses showed that communities were characterised by the presence of pollen hub-donors and receptors. We inferred that facilitative and neutral pollinator-mediated interactions among plants prevailed over competition. Thus, the benefits from pollinator sharing seem to outweigh the costs (i.e. heterospecific deposition and conspecific pollen loss). The largest proportion of facilitated species was found at the highest elevation community, suggesting that under unfavourable conditions for the pollination service and at lower plant densities facilitation can be more common.

Caracterización de las arenas y arcillas minerales de los depósitos de canal y planicie de inundación del río Portuguesa, Venezuela

Portuguesa river floodplain is one of the largest systems in the region of central western Venezuelan llanos. This sub-Orinoco River basin covers an area of 59 500km2 which means about 6.5% of the country. The basin includes two tectonic provinces, and the river and its tributaries flow through a geological mosaic composed of rocks different ages and mineralogical composition. The interest of this paper is to examine the mineralogical composition of sands and clays in the former and present sediments of the lower basin of the river and document the relationship between the mineralogy of river sediment source area and climate variations in this region during the Late Quaternary. Most of the tributaries of the Portuguese river transport sediments from the southern and southeastern ranges of the Andes and the Interior cordillera from the Caribbean range; other small rivers originate and transport sediments from the floodplain and from the oldest foothill terraces. The methodology consisted of collecting ancient sediments deposited in the floodplain and the current channel. For this study, 40 samples of sands associated with different pools of load current bed Portuguesa River and 23 samples of clay from the oldest sediments were collected; by core drilling on bar meanders and paleomeanders in the flood plain of the river. The sand fraction was separated by dry sieving and clays by the Bouyoucos (1962) method with some modifications. Mineralogical analyzes of both fractions was determined by X-ray diffraction for the case of sand the analysis was performed only on whole sample and clays were subjected to three treatments (total, ethylene glycol and heated sample at 550°) to detecting the presence of swelling clays. The results indicate that the sands are mainly composed of quartz, forming mature sand or quartz-arenites with lesser amounts of minerals such as chlorite, muscovite, calcite and albite, among others. Which identified peaks in the diffractograms quartz infer high crystallinity of quartz (3.3°) and a peak of lower intensity (4.2°). Meanwhile, in the clay fraction 13 crystalline mineral phases were determined mainly predominating well crystallized quartz (3.3°) and the well-crystallized kaolin (7.1°), illite (10 A°) and muscovite (5.0 A°). The origin of the sands is mainly related with the physical-mechanical disintegration of the rocks of the Venezuelan South Andean Cordillera orogen and the Caribbean range during arid climatic conditions that prevailed at the end of the Late Pleistocene and factors such as transport distance, residence time, pedogenesis, chemical weathering intensity and the source area. One detrital origin for quartz, illite and muscovite reported in the clay fraction, the origin of minerals kaolinite can be inherited from older or soil deposits associated with these fluvial sediments is postulated. However, as kaolinite and montmorillonite, vermiculite, neoformation may have originated from the chemical change experienced by the mica and feldspar, associated with wetter weather conditions, environment and intensely washed acidity conditions that characterize this tropical region. The influence of climate highlighted in the mineralogical evolution of sedimentary deposits reported in this study and suggests that the sediments were deposited from the Early to Late Holocene, under conditions similar to today's most humid tropical climate. It is concluded that the origin and composition of the sands and clays analyzed mainly show a close relationship with the source area of the sediments and factors such as the distance of sediment transport, the residence time in the channel and floodplain, the intensity of chemical weathering and climatic conditions that prevailed during the Late Pleistocene-Holocene.

Reconstructing streamflow variation of the Baker River from tree-rings in Northern Patagonia since 1765

Summary The understanding of the long-term variation of large rivers streamflow with a high economic and social relevance is necessary in order to improve the planning and management of water resources in different regions of the world. The Baker River has the highest mean discharge of those draining both slopes of the Andes South of 20°S and it is among the six rivers with the highest mean streamflow in the Pacific domain of South America (1100 m 3 s −1 at its outlet). It drains an international basin of 29,000 km 2 shared by Chile and Argentina and has a high ecologic and economic value including conservation, tourism, recreational fishing, and projected hydropower. This study reconstructs the austral summer – early fall (January–April) streamflow for the Baker River from Nothofagus pumilio tree-rings for the period 1765–2004. Summer streamflow represents 45.2% of the annual discharge. The regression model for the period (1961–2004) explains 54% of the variance of the Baker River streamflow ( R 2 adj = 0.54). The most significant temporal pattern in the record is the sustained decline since the 1980s ( τ = −0.633, p = 1.0144 ∗ 10 −5 for the 1985–2004 period), which is unprecedented since 1765. The Correlation of the Baker streamflow with the November–April observed Southern Annular Mode (SAM) is significant (1961–2004, r = −0.55, p r = −0.41, p Future research should consider the development of new tree-ring reconstructions to increase the geographic range and to cover the last 1000 or more years using long-lived species (e.g. Fitzroya cupressoides and Pilgerodendron uviferum ). Expanding the network and quality of instrumental weather, streamflow and other monitoring stations as well as the study and modeling of the complex hydrological processes in the Baker basin are necessary. This should be the basis for planning, policy design and decision making regarding water resources in the Baker basin.