EPISODIC EROSION DYNAMICS AFFECTING DEPOSITIONAL BASINS OF NORTHWEST ARGENTINA

The competition between uplift and erosion is important to the history of depositional basins of Northwest Argentina. Intermontaine basins fill as rising mountains slow sediment export, but uplift of mountains also empowers streams on the foreland side to incise toward the plateau. This feedback is important to understanding foreland basin depositional systems, because of the potential for pulses of sediment delivery when streams cut entirely through uplifts. The geomorphology of basins west of the Sierra Alta suggests different histories of filling and excavation. The Casa Grande Basin is drained by the Yacoraite River, but lacustrine deposits in the basin indicate that it was partially or completely closed at some point during the Neogene, likely because of the uplift of the Sierra Alta. GIS modeling of the volume of sediment eroded from the Casa Grande basin post basin fill suggest that the Yacoraite River transported more than twice the sediment in another tributary fan that currently bows the profile of the Rio Grande. Thus, when the Yacoraite River incised across the Sierra Alta the subsequent delivery of sediment was potentially great enough to alter the fluvial profiles and depositional history in the Rio Grande basin. Cross uplift streams demonstrate a variety of morphologies that show differing degrees of incision across mountain blocks of varying relief, and with changing effects on their neighboring basins through sediment erosion, transport, and deposition.