Non-marine Paleogene sequences, Salta Group, Northwest Argentina

Deposits of Paleogene age form the culmination of the distensive basin developed from Lower Cretaceous up to Eocene times in North west A rgentina. The rift development shows a regional extension, and includes part of the sedimentation which occurred contemporaneously in Bolivia, Paraguay and Chile. During development of the sag basin, three depositional sequences were laid down. These were the Mealla, Maíz Gordo and Lumbrera Formations, which make up the Santa Bárbara Subgroup of the Salta Group. These units present similar sedimentological characteristics, which gives this period a cyclic arrangement . The sedimentary distribution and the arrangement of facies point to a closed basin, with alluvial sedimentation toward its borders, and the formation of lakes in its central area. Each unit shows a particular pattern of river systems, from perennial sand-gravel bed braided streams to fine-grained meandering streams, and pattern of the lake originated there. It is recognized that each lacustrine basin started to develop under shallow conditions in an arid climate, and then evolved to deeper lakes, which reached stratification of the water mass. The paleontologic content, especially the palinomorphs, records these fluctuating climatic changes, from arid situations to more humid conditions

Controls on intermontane basin filling, isolation and incision on the margin of the Puna Plateau, NW Argentina (similar to 23 degrees S)

Intermontane basins are illuminating stratigraphic archives of uplift, denudation and environmental conditions within the heart of actively growing mountain ranges. Commonly, however, it is difficult to determine from the sedimentary record of an individual basin whether basin formation, aggradation and dissection were controlled primarily by climatic, tectonic or lithological changes and whether these drivers were local or regional in nature. By comparing the onset of deposition, sediment-accumulation rates, incision, deformation, changes in fluvial connectivity and sediment provenance in two interrelated intermontane basins, we can identify diverse controls on basin evolution. Here, we focus on the Casa Grande basin and the adjacent Humahuaca basin along the eastern margin of the Puna Plateau in northwest Argentina. Underpinning this analysis is the robust temporal framework provided by U-Pb geochronology of multiple volcanic ashes and our new magnetostratigraphical record in the Humahuaca basin. Between 3.8 and 0.8 Ma, similar to 120 m of fluvial and lacustrine sediments accumulated in the Casa Grande basin as the rate of uplift of the Sierra Alta, the bounding range to its east, outpaced fluvial incision by the Rio Yacoraite, which presently flows eastward across the range into the Humahuaca basin. Detrital zircon provenance analysis indicates a progressive loss of fluvial connectivity from the Casa Grande basin to the downstream Humahuaca basin between 3 and 2.1 Ma, resulting in the isolation of the Casa Grande basin from 2.1 Ma to \u3c 1.7 Ma. This episode of basin isolation is attributed to aridification due to the uplift of the ranges to the east. Enhanced aridity decreased sediment supply to the Casa Grande basin to the point that aggradation could no longer keep pace with the rate of the surface uplift at the outlet of the basin. Synchronous events in the Casa Grande and Humahuaca basins suggest that both the initial onset of deposition above unconformities at similar to 3.8 Ma and the re-establishment of fluvial connectivity at similar to 0.8 Ma were controlled by climatic and/or tectonic changes affecting both basins. Reintegration of the fluvial network allowed subsequent incision in the Humahuaca basin to propagate upstream into the Casa Grande basin

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

Nous présentons une description synthétique de plusieurs fronts chevauchants ayant contrôlé les dépôts synorogéniques de la formation Piquete (d'âge plio-pléistocène) dans une partie du bassin d'avant-pays néogène du N.O. argentin (vallées de Lerma et Metan). (Résumé d'auteur

Géodynamique andine : résumés étendus = Andean geodynamics : extended abstracts

La déformation d'avant-pays le long du front est des Andes est de trois types : plissements et chevauchements de type "thin-skinned", chevauchements de type "thick-skinned", et chevauchements d'avant-pays du type de celui des Sierras Pampeanas. A l'échelle de l'orogène, un contrôle du développement des différents styles structuraux par des discontinuités préexistantes, stratigraphiques ou structurales, est plus net qu'un lien direct avec la géométrie de la subduction de la plaque Nazca. (Résumé d'auteur

Géodynamique andine : résumé étendus = Andean geodynamics : extended abstracts

Nous décrivons le contexte tectonique et la distribution régionale des bassins tertiaires développés dans les Andes centrales argentines (22°-36° latitude Sud) à l'époque post-incaïque (Eocène précoce) et pré-diaguite (Pliocène tardif-Pléistocène précoce). (Résumé d'auteur