Evolution of the landforms across which the Atacama Desert is draped, 20°-24°s latitude

JORDAN, T. E.; BLANCO, N.; FEDERICO MIGUEL DAVILA; HOKE, G.; MPODOZIS, C.; NESTER, P.; TOMLINSON, A.

Philadelphia

Congreso; Geological Society of America Annual Meeting and Exposition; 2006

The extreme environment of the Atacama Desert of northern Chile depends upon lack of precipitation and lack of water input by surface drainages. A major factor contributing to hyperaridity is the topographic barrier of the Andes, blocking eastern moisture. An exception to the lack of surface water is the Loa River. We explore the Cenozoic evolution of the topography and drainage of the Atacama core. The western Andean slope is the major landform feature of the Atacama Desert, dividing the ~1000 m elevation Central Depression (Tamarugal Basin) from the Western Cordillera at > 4000 m elevation. Long-wavelength rotation of strata reveals ~3000 m of relief generation across that slope since ~17 Ma, of which about ~1500 m occurred since 5 -10 Ma. A second major landform is the Pre-Andean Depression (Calama and Salar de Atacama basins), at ~2000 m elevation. The major morphologic differentiation of the Calama and Atacama basins resulted from Oligocene normal faulting, unusual regionally but the initiation event of the anomalously large catchment of today’s Loa River. The Calama  basin overfilled with sediment and changed from endorheiric to exorheic conditions during the Miocene, integrating the Loa catchment, whereas the Atacama basin persisted in an endorheic state.  Because the Miocene Loa catchment predated thousands of meters of Andean uplift and the Plio-Quaternary volcanic chain, the paleo-environmental characteristics of the Calama basin/Loa Mio-Pliocene deposits reveal the paleoclimate and catchment evolution of upland regions probably now located in the Altiplano plateau, which are not representative of Atacama Desert. In contrast, strata in the Atacama and Tamarugal basins reflect the environmental history of the Atacama desert.