Paula Santi Malnis, Carina E. Colombi, Natalia Rodríguez Posatini, Luis M. Rothis, Carlos O. Limarino
2 018
AndGeo vol.45 no.2 Santiago mayo 2018
En los últimos 10 años nuevos modelos sedimentarios para cuencas intermontanas ponen en discusión la dinámica depositacional clásicamente considerada (dominio de abanicos aluviales y grandes sistemas fluviales) para estas cuencas, tal es el caso de los Sistemas Fluviales Distributivos (SFD). Con el fin de comprender los procesos sedimentarios formadores de los SFD, en este trabajo se discuten los distintos subambientes sedimentarios del arroyo Papagayos y su terminación como un SFD. Para ello se analizan los subambientes sedimentarios del arroyo Papagayos teniendo en cuenta los diferentes elementos arquitecturales que lo conforman, como respuesta a las características morfométricas de su cuenca de drenaje, la interacción del clima en las cabeceras y en el valle, y las características geomorfológicas del piedemonte y del valle en el que se inserta, ubicado en el antepaís fracturado andino. El análisis sedimentológico y geomorfológico realizado en el arroyo Papagayos permite diferenciar cuatro zonas a lo largo de su recorrido: una proximal en donde se desarrolla un sistema fluvial entrelazado de carga gravosa y arenosa; una media caracterizada por un sistema fluvial anastomosado-anabranching arenoso y gravoso; una distal en donde se desarrolla un sistema fluvial distal efímero de carga arenosa de alta sinuosidad, con importante interacción eólica; y una de transición que correspondería a la faja litoral de la salina de Mascasín. Por otra parte, se observó que entre los procesos sedimentarios reconocidos en estos ambientes los flujos densos, especialmente los flujos cohesivos de barro, constituyen uno de los mecanismos más importantes de depositación en la llanura de inundación. Los procesos sedimentarios reconocidos a lo largo del arroyo Papagayos, y descritos en este trabajo, permiten no solo caracterizar mejor a los SFD de clima árido sino también facilitar su reconocimiento en ambientes antiguos.
Sedimentological characterization of a Distributive Fluvial System of arid climates: arroyo Papagayos, eastern piedmont of La Huerta-Las Imanas Ranges, San Juan, Argentina.
Recent studies proposed that distributive fluvial systems (DFS) occupy a great proportion in modern continental sedimentary basins, challenging classical sedimentary models proposed for similar ancient basin. Because of this, arises the importance of studying modern DFS with the aim of obtaining facial models to apply them in ancient deposits. In this paper, we analyze and discuss the sedimentary environments included in the modern deposits of the Arroyo Papagayos, Western Pampean Ranges, San Juan province, interpreted as a Distributive Fluvial System (DFS). We perform the study of the Papagayos creek by describing different architectural elements, which characterize the sub-environments organized in four zones from the mountain front to the distal playa lake. A low sinuosity gravelly-sandy bed braided fluvial system, characterizes the proximal zone. A medial to high sinuosity sandy-gravelly anastomosed-anabranching fluvial system describes the medial zone, where floodplain aggradation is domain by crevasse splays accretion. At this point, 10 km far from the mountain front, the deposits starts to develop a cone shaped morphology. A higher sinuosity flashy ephemeral meandering sandy-muddy fluvial system with eolian interaction defines the distal zone, where the main channel of the system disappears by low gradient of the topography and infiltration depositing muddy terminal splays. Finally, eolian dune and wet interdune deposits characterizes the fourth zone, interpreted as a transitional area between the DFS and the saline playa lake. A particular feature observed along the DFS system is that mudflows are the main sedimentary process in the floodplain, probably as the result of the combination of the seasonal arid climate and the Arroyo Papagayos drainage basin morphometry and the low gradient of the topography. The sedimentary process and environments recognized along the Arroyo Papagayos will allow a better understanding of arid DFS depositional dynamics as well as, to identify them in the geological record. Lastly, high aggrading conditions for DFS development will response to climate interaction between upland catchment area (semiarid) and valley (arid), drainage basin morphometry, smooth piedmont gradient and high tectonic subsidence of the basin, located in the Andean broken foreland.
Recent studies proposed that distributive fluvial systems (DFS) occupy a great proportion in modern continental sedimentary basins, challenging classical sedimentary models proposed for similar ancient basin. Because of this, arises the importance of studying modern DFS with the aim of obtaining facial models to apply them in ancient deposits. In this paper, we analyze and discuss the sedimentary environments included in the modern deposits of the Arroyo Papagayos, Western Pampean Ranges, San Juan province, interpreted as a Distributive Fluvial System (DFS). We perform the study of the Papagayos creek by describing different architectural elements, which characterize the sub-environments organized in four zones from the mountain front to the distal playa lake. A low sinuosity gravelly-sandy bed braided fluvial system, characterizes the proximal zone. A medial to high sinuosity sandy-gravelly anastomosed-anabranching fluvial system describes the medial zone, where floodplain aggradation is domain by crevasse splays accretion. At this point, 10 km far from the mountain front, the deposits starts to develop a cone shaped morphology. A higher sinuosity flashy ephemeral meandering sandy-muddy fluvial system with eolian interaction defines the distal zone, where the main channel of the system disappears by low gradient of the topography and infiltration depositing muddy terminal splays. Finally, eolian dune and wet interdune deposits characterizes the fourth zone, interpreted as a transitional area between the DFS and the saline playa lake. A particular feature observed along the DFS system is that mudflows are the main sedimentary process in the floodplain, probably as the result of the combination of the seasonal arid climate and the Arroyo Papagayos drainage basin morphometry and the low gradient of the topography. The sedimentary process and environments recognized along the Arroyo Papagayos will allow a better understanding of arid DFS depositional dynamics as well as, to identify them in the geological record. Lastly, high aggrading conditions for DFS development will response to climate interaction between upland catchment area (semiarid) and valley (arid), drainage basin morphometry, smooth piedmont gradient and high tectonic subsidence of the basin, located in the Andean broken foreland.
https://scielo.conicyt.cl/scielo.php?pid=S0718-71062018000200186&script=sci_arttext&tlng=en
