Abstract
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.
Highlights
En los valles intermontanos se reconocen diferentes ambientes sedimentarios que se organizan en dos grandes sistemas de drenaje
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
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)
Summary
En los valles intermontanos se reconocen diferentes ambientes sedimentarios que se organizan en dos grandes sistemas de drenaje. Sea cual sea la definición, estos sistemas se caracterizan por estar alejados del frente montañoso, desarrollarse en piedemontes de baja pendiente, estar dominados por procesos sedimentarios fluidos, presentar un patrón distributivo en planta, decrecer la profundidad, ancho e interconectividad de los canales aguas abajo, y tener una topografía convexa y lobulada (Friend, 1978; Nichols y Fisher, 2007; Hartley et al, 2010). Y siguiendo el principio del uniformismo, es más probable que las condiciones depositacionales hayan sido similares y que su ausencia en la bibliografía se deba a una falta de reconocimiento de los mismos en el registro, confundiéndolos con sistemas aluviales o fluviales clásicos. Para su caracterización se realizó un estudio geomorfológico y sedimentológico de detalle, con el fin de describir los diferentes procesos de cada subambiente a lo largo y ancho de todo el sistema
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