Diego Winocur

Se presentan los resultados del relevamiento del arte rupestre e improntas naturales asociado a rayos en el Área Natural Protegida Laguna del Diamante (Mendoza). Tras dificultades metodológicas iniciales para diferenciar marcas antrópicas y marcas naturales de rayos (fulguritas), se propone una clasificación que abarca los distintos tipos de improntas, lo que resulta de utilidad para futuros trabajos: fulguritas sin intervención antrópica, fulguritas con intervención antrópica o asociadas a sitios arqueológicos; petroglifos que emulan fulguritas. Además, se discuten las implicancias de este tipo de motivos asociados a la figura del rayo para las poblaciones prehispánicas que habitaron el área, como estrategia de sacralización y apropiación del paisaje, sobre todo en momentos tardíos.

The La Laja Hydrothermal System is located in a tectonically and seismically active area in the southern Central Andes, in the San Juan Province of Argentina. Here we present a geomorphological and geophysical characterization of this system, aimed at constructing geological-structural models to explain its origin, configuration, and main manifestations. The geomorphological analysis allowed the identification of travertine cones and terraces, mudflats, springs, and channels, geoforms that were studied using gravimetry, magnetometry, electrical tomography and audio-magnetotelluric methods. The combination of these techniques, which provide information at different depths and resolutions, together with surface geological data, made it possible to refine the interpretation and generate robust models at the sites of interest. Results suggest that the geothermal manifestations are distributed along a ~NE-SW structural zone, subparallel to the mountain front, and that their origin is tectonic. Two systems controlling the flow of thermal waters were identified: to the north, the El Museo Fault, where the structure acts as a conduit for hydrothermal fluid circulation; and another to the south, which involves a more complex tectonic deformation, including the development of faults, folds, and zones of weakness.

Este artículo presenta un estudio sobre los materiales líticos de sitios de superficie localizados en Ovejería Chica, valle del Cajón, Catamarca. Un primer paso consistió en la identificación de las materias primas utilizadas mediante el uso de cortes delgados y su posterior caracterización mineralógica. Como resultado se reconoció a la riolita, una roca volcánica, como el recurso de mayor uso en los distintos sectores, lo que constituye un hecho inédito, ya que no se había identificado esta materia prima en otros sitios del valle. Por otra parte, el análisis tecno-morfológico permitió reconstruir la secuencia de producción para ciertas materias primas, a la vez que discriminar la existencia de artefactos con filos múltiples. Se suma a esto la presencia de cabezales líticos cuyos diseños remiten a cronologías que van del Holoceno medio al tardío. A partir de estos datos es dable sostener que al menos dos de los sectores estudiados fueron espacios multipropósitos, utilizados para diferentes actividades, entre ellas la caza. Los resultados mencionados constituyen un aporte para la comprensión del rol que jugaron estos espacios a cielo abierto a nivel regional.

Se presentan resultados de estudios arqueológicos realizados sobre segmentos del ramal transversal más meridional del Qhapac Ñan. Se propone que este ramal, ubicado en el NO de la provincia de Mendoza (Argentina), tuvo derivaciones que lo conectaban con una red compleja de vías de circulación inter-cordillerana. El registro obtenido permite inferir que los Incas usaron, en forma simultánea, los pasos Cristo Redentor y de Navarro y que este último pudo ser parte de un camino ceremonial que llevaba al cerro Aconcagua, apu/waca principal de la región. Se plantea también que generaron y/o mantuvieron otros caminos con función logística y ritual sobre los valles de los ríos Tupungato y de Las Vacas. Con esta nueva información se consolida la posibilidad de que los Incas hayan aplicado preferentemente, en este sector del extremo sur del Tawantinsuyu, políticas de dominación de tipo ideológico que llevaron a una sacralización de los caminos cordilleranos y sus entornos.

On the northern slopes of Meseta Belgrano (MB), eastern foothills of Patagonian Andes in Argentina, complex of multiple overlapping rock avalanches and landslides can be found. Interpretation of remote-sensing data, field mapping, together with OSL dating of lacustrine sediments revealed that slope collapses evolved during last oscillations of the Patagonian Ice Sheet and after its retreat. The longest rock avalanche with ~11 km runout originated most likely before the last glacial advance following the LGM because it involves moraine deposits in part of the scarp area. We suppose, that the distal part of the rock avalanche body was subaqueous due to presence of a proglacial lake in Lago Pueyrredón Valley after LGM. The hummocky character of the distal body and its lithological composition coming from MB bedrock was preserved, but the deposit is discontinuous with straight east-west glacial lineations on the surface. We think this is result of erosion by the ice sheet approaching from East during post-LGM glacial fluctuations. Next pronounced landslide activity took place after ~17 ka BP, when at least three rock avalanches overlaid lacustrine sediments in a dropping proglacial lake. One of them, superimposing the above described older rock avalanche, evolved from the collapsed moraine deposit and created ~5 km long lobe with subaqueous radial distal part. In the proximal parts of the rock avalanches east from this form, bellow the slopes of MB, distinct large ridge-like forms are visible in topography. They are similar to moraine ridges preserved on the MB slopes in higher altitudes. They can be interpreted as lower-lying moraines, but this requires another pronounced ice-sheet oscillation after its final retreat, which was not documented in Patagonian Ice Sheet chronostratigraphy. Thus, we interpret them as Toreva blocks. Documentation and granulometric analysis of natural outcrops in rock avalanche bodies show that typical features, i.e. blocky, jigsaw and fragmented facies are present throughout the depth along whole travel distances of rock avalanches. Fragmented facies with jigsaw-fractured blocks and preserved original lithology sequence are most frequent. Sedimentary facies are very similar in all of the studied rock avalanches, which collapsed from bedrock MB slopes, regardless of their age or size.

Although ice retreat is widely considered to be an important factor in landslide origin, many links between deglaciation and slope instabilities are yet to be discovered. Here we focus on the origin and chronology of an exceptionally large landslides situated along the eastern margin of the former Patagonian Ice Sheet (PIS). Accumulations of the largest rock avalanches in the former PIS territory are concentrated in the Lago Pueyrredón valley at the eastern foothills of the Patagonian Andes in Argentina. Long-runout landslides have formed along the rims of sedimentary and volcanic mesetas, but also on the slopes of moraines from the Last Glacial Maximum. At least two rock avalanches have volumes greater than 1 km3 and many other landslide accumulations have volumes in the order of tens to hundreds of million m3. Using cross-cutting relationships with glacial and lacustrine sediments and using OSL and 14C dating, we found that the largest volume of landslides occurred between ~17 and ~11 ka BP. This period coincides with a phase of rapid PIS retreat, the greatest intensity of glacial isostatic uplift, and a fast dropping of the glacial lakes along the foothills of the Patagonian Andes. The position of paleoshorelines in the landslide bodies and, in many places, the presence of folded and thrusted lacustrine sediments at the contact with rock avalanche deposits indicate that the landslides collapsed directly into the glacial lake. Although landslides along the former glacial lobe of Lago Pueyrredón continue today, they are at least an order of magnitude smaller than the rock and debris avalanches that occurred before the drainage of the glacial lake around 10-11 ka BP. Numerical modeling results indicate that large postglacial landslides may have been triggered by a combination of rapid sequential glacial lake drawdowns and seismicity due to glacial isostatic adjustment. We conclude that in addition to direct links such as glacial oversteepening, debuttressing and permafrost degradation, the retreat of ice sheets and the subsequent formation of transient large glacial lakes can fundamentally alter slope stability, especially if the slopes are built by weak sedimentary and volcanic rocks.