Processes of oscillatory basin filling and excavation in a tectonically active orogen:Quebrada del Toro Basin,NW Argentina

摘要

Intramontane basins may act as important sediment storage areas,serve as recorders of the history of deformation,record syntectonic deposition,and document the evolution of climatic conditions during deposition.We document the timing,cyclicky,and processes that led to the filling and reexcavation of the intramontane Quebrada del Toro basin in NW Argentina.Geomorphic and geologic observations indicate that the basin was filled with sediment that has been subsequently excavated at least two times in the last ~8 m.y.The last filling and excavation cycle occurred within the last 0.98 m.y.and has led to the deposition and removal of ~61.4 km~3 of material from the basin,leading to a basin-wide averaged minimum denudation rate of 0.16 mm/yr.Aggradation within the basin took place due to channel steepening of the downstream fluvial system that connects the intramontane basin to the foreland.This portion of the fluvial system is actively incising through an uplifting bedrock zone.We use observations within the Toro to test a quasi-physically based model of channel aggradation behind a rising base level that rises due to downstream channel steepening.Our work shows that the bedrock incision rate constant required to reproduce conditions observed within the Toro basin is consistent with values measured independently in similar rock types.Therefore,in intramontane basins that experience similar processes of filling and evacuation,this model may be used to assess the relative importance of tectonic rock uplift,bedrock resistance to fluvial incision,and climate in determining the geomorphic and sedimentologic history of these basins.