Descripción: The geomorphologic analysis of the study area led to distinguish some formations not considered in previous geological research, as well as to explain the characteristics of the present relief. Thirteen principal geomorphic units produced by different geomorphic processes are recognized. Their variety and incidence through the time are expressed in the glacial morphogenesis concentrated in the western part of the Cordillera del Viento, in the volcanic landscape that predominates in the northern and eastern sectors (calderas, volcanoes, lava flows), in the structural control that defines the morphology of the fluvial process in the central zone and a firstly recognized important landslide to the north of Tricao Malal. As a result of the methodology employed two geological units of different age in the western part of the Tromen-Waile volcanic field were distinguished, which were initially interpreted as a single formation. A limited but consistent structural analysis of the region is also included.

Descripción: An environmental magnetic study of mainly fluvial "postpampean sediments" assigned to the Lujan Formation (Luján, Buenos Aires Province, Argentina) was carried out. The results obtained suggest a depletion of detrital ferromagnetic minerals during the pedogenetic processes. A characteristic magnetic signal can be distinguished in Holocene paleosols and soils of both eolian and fluvial "post-Pampean sediments" (Fm. Luján and Fm. La Postrera . This signal is analogous to that determined in loessic Pampean sediments assigned to the Buenos Aires Formation. It is inferred that the depletion of detrital ferromagnetic minerals is a general process in the Chacopampean area. This process may be associated with the genesis of a superparamagnetic fraction (SP), which could indicate dry periods during the climatic event. The depletion could also be associated with the genesis of a high coercitivy fraction, analogous with those determined in paleosols in the Pampean loess.

Descripción: A process of stream piracy caused by the active retrograde erosion of Limay Chico stream - a tributary of Limay river- is described. It is located in the southern part of headwaters of the Alicurá drainage basin, tributary of Collon Cura river. It is supposed that the increment of the headward erosion is related to the postglacial climatic conditions and a coetaneous deepening of the Limay river channel, a process expressed by modern and lower erosion terraces. Moreover the retrograde erosion was enhanced by the special location of the Limay Chico valley along an important line of structural weakness, the Limay Chico fault. The fluvial capture and the consequent diversion of the Alicurá basin upper part showed previous favorable conditions: 1) the topographic lower disposition of Limay Chico stream and their base level; 2) its steeper slope and the location of Limay Chico valley along a zone of structural and litologicalk weakness; 3) transverse arrangement of the Alicurá river's headwaters; 4) its gentle slope and location of their basin and base level at a topographic higher level. Several wind gaps were recognized and were interpreted two probable elbows of capture and barbed pattern. Also the increment of discharge of Limay Chico stream caused in their basin local phenomena of static rejuvenation. It is suppose a close genetic relation between the landslides observed along the steep fault scarp promoted by the Limay Chico Fault and the postglacial climatic change and the local erosional deepening of Limay Chico valley. The slumps characterized by the coalescence of their scan, generated the irregular and ruged landscape of the western side of Limay Chico valley. On the eastern valley slope the slumps reach minor expression. Longitudinal profils and slopes of the analized streams are included.

Descripción: Considering the high concentration of rock avalanches in the northern part of the Neuquén province of Argentina (36°-38°S and 70°-71°W) and their association with lacustrine basins forming natural dams, their catastrophic collapse seems not to be such a common process as could be expected for these cases. The present work depicts the area immediately affected by the outburst flood corresponding to the Navarrete dam catastrophic collapse (175 × 106 m3), through a sedimentological analysis, generated since the arroyo Colorado was blocked due to a rock avalanche deposit during not well constrained postglacial times. The outburst flood dispersion is initially inferred based on morphological criteria and then determined from a sedimentological analysis of its matrix. Furthermore, the matrix is compared to that of the fluvial terraces, which have been sampled along the arroyo Colorado. This comparison shows that even though differences among them are not so significant through most of the study area, matrix frequency starts to be distinctive from the most distant point of sampling.

Descripción: This thematic map describes the principal features of the landscape, a relative sequence of its geomorphic evolution, and arrives to important conclusions about its regional stratigrapby. The regional landscape is composed and polycyclic. The geoforms are related to different exogenous processes (glacial, fluvial and mass-wasting). An endogenous process (volcanism) formed the more distinctive features; a great tectonic-volcanic caldera and the preglacial Copahue stratovolcano. Some minor and youngest volcanic forms were formed during postglacial times. A previous fluvial cycle was replaced by glacial morphogenesis (valley glaciation) during the Quaternary, due a climatic intervention. A huge and very thick (500-800 m) ice-blister was lodged into the caldera. The ice-blister exceded the caldera's edges forming several glacial diffluences and giving an important and additional supply to neighbouring glacial valleys (Hualcupén and Trocoman), out of to the depression. The Pleistocene glaciation shows two local cycles of volcanic eruptions: pre- and post-glacial. The origin of many local lakes was related to glacial exharation. Others lakes have different genesis: by blocking slide, crater-lake and glacial exharation associated with important structural weakness (Caviahue Lake related to the Trapa-Trapa lineament or Caviahue graben). During postglacial times important rock-avalanches occurred in the Hualcupén valley: the Cajón Chico and Compul rock-avalanches were related to seismic shocks. Previously, their accumulations were interpreted as terminal moraines of a second glaciation. A fluvial rejuvenation phase was the consequence of a blocking of Agrio River by the Agrio volcanic flows, during the Holocene. After that, the river eroded this obstacle restablishing its previous base level. The Agrio cascade represents the upstream present position of the consequent rejuvenation wave. © 2005 Asociación Geológica Argentina.

Descripción: A rock-avalanche (named Las Cañas) was distinguished near the Potrero de Leyes rock-avalanche previously recognized in the southern Sierras Pampeanas. It is located on the western slope of the Sierra Grande de San Luis (San Luis Province), which is regarded as the range uplift front during the Andean tectonism. On account of its greater degradation than the Potrero de Leyes rock-avalanche, the deposits described here are considered to be older in age. Their morphometric attributes could be only roughly calculated, because fluvial erosion has removed a large portion of its initial shape and volume. The avalanche-related deposits form round-shaped hills, which can be distinguished from alluvial fan deposits by their higher altitude, photogeological signature and degree of degradation. Two fault sets have also modified its original surface configuration. It is considered that this phenomenon was also triggered by an earthquake. Hence, the recognition and analysis of these geomorphological processes provides a useful addition to palaeosismological analysis and is significant for an adequate evaluation of the the seismic hazard of this region. © 1998 Asociación Geológica Argentina.

Descripción: Landforms and soils in the Traful River Valley, Neuquén Province. The Andes Patagónicos Region is characterised by the presence of strong west-east bioclimatic, geomorphological and lithostratigraphical gradients, that controlled the genesis and geographical distribution of soils. In this contribution soil-landscape relationships in a sector of a transitional zone in the northern Andes Patagónicos are studied. The Traful River valley is located in Neuquén Province aproximately at 40°40′S and 71°15′W. Diverse geomorphological units were distinguished which were formed through glacial and fluvioglacial action, and partially modified in recent times by fluvial and eolian processes and by mass wasting. Holocen ashes and lapilli were deposited in different volcanic events and constitute the soils'main parent material. We recognize soils belong to three orders: entisols, mollisols and andisols. A strong gradient of variations in soils properties was observed. The Andisolization process decrease with distance from the Cordillera zone. © 1999 Asociación Geológica Argentina.

Descripción: In the right bank of the Arroyo Tapalqué (Salto de Piedra, Olavarría, Buenos Aires province) is a section through fluvial sediments of the Luján Formation (upper and lower members) and aeolian deposits of La Postrera Formation. A geological and geophysical study was carried out to determination the magnetic parameters of the sediments of both formations, in order to evaluate the environmental and climatic conditions at the time of deposition. Levels with high concentrations of ferromagnetic minerals are thought to be related to an increase in capacity of river transport probably due to higher rainfall. By contrast, a particular magnetic behaviour was detected in levels closely associated with pedogenetic processes (Suelo Puesto Callejón Viejo, SPCV, Suelo Puesto Berrondo, SPB and present soils). This behaviour is attributed to the partial dissolution of the ferromagnetic fraction (magnetic/titanomagnetite) and to possible formation of a high c oercitivity magnetic fraction (hematite?) as an associated process. These results are similar to those obtained for paleosols from the Buenos Aires Formation, probably because of parental material common to both. On the basis of present field and laboratory observations, together with previously available information, a detailed correlation is proposed between features observed in this section and palaeoclimatic fluctuations identified for Pleistocene/Holocene.