TECTONICS, CLIMATE, AND LANDSCAPE EVOLUTION OF THE SOUTHERN-CENTRAL ANDES REVEALED BY LEAF WAX STABLE ISOTOPES
The PGB hosts folded sediments that span 9 to 2 Ma, and it has been an integral part of the Andean Plateau since at least 15 Ma. δDwax values in the PGB sediments record a decrease from -125 to -203 ‰ between 8.5 and 7.6 Ma, which coincides with the disappearance of red beds and evaporites. A similar, but less pronounced D-depletion from -107 to -144 ‰ is recorded by the Angastaco Basin sediments over the same time interval. We suggest that this regional signal may reflect the onset of moisture transport into this inherently dry region via the South American Low-Level Jet. Concurrently, δ13Cwax values on the plateau increased from -32.5 to -27.5 ‰ and reflect (eco) hydrological changes, while no such changes are observed in the Angastaco Basin. Subsequent folding of PGB strata documents continuous intrabasinal deformation until 2 Ma, with potential elevation gain within the plateau. δDwax values from the plateau increase from -218 to -152 ‰ over this time interval. Our observations suggest enhanced aridification in the plateau realm, whereas the Angastaco Basin and the eastern flank of the Andean Plateau transitioned into humid conditions, and subsequently back to semi-arid conditions and reduced moisture transport toward the orogen interior due to orographic barrier formation starting from ca. 6.5 Ma.