Distributary Drainage Systems in La Huerta Range, Western Pampean Ranges, San Juan, Argentina

Transversal drainage systems in the southern portion of the Bermejo intermontane basin -San Juan province, Argentina- are organized in five main rivers that reach the longitudinal Rio Bermejo valley. Geomorphological and sedimentological survey of the western piedmont of the La Huerta range shows that there is a north-south trend change of drainage basin morphometry and facies architecture. Facies distribution of the Las Chacras river, in the northern portion of the piedmont, fits with the classical alluvial fan model, with a divergent net of channels from the fan apex. In the middle portion of the piedmont (the Arenal and Puquial rivers), also alluvial fan facies are present with eolian interaction, triggering disconnection of mid fan facies from distal facies. In the southern portion of the piedmont, drainage system flows parallel to axial drainage system (Bermejo River). Facies architecture is different from those observed in the northern portion. In the Canada River, flows keep channelized until its distal portion in mid to high sinuosity channels that deposit alternate and scroll bars. In the distal portion, main channel diverge in a distributary net of channels that develops a fan-shaped deposit characterized by terminal splays and eolian dunes. Facies distribution allow considering the La Canada River as a distributive fluvial system. The last system under study is the Los Palos River which frequently disappears because it has a permeable substratum and deposit mostly terminal splays. The Los Palos River is interpreted as a flood-out system.