Tectonic and climatic evolution of the Angastaco Basin (25°-26°S, eastern Cordillera, NW Argentina)

The aim of this thesis is to explore the effects of climate and tectonics on late Cenozoic Payogastilla Group sedimentation in the Angastaco Basin in order to understand the foreland basin evolution in NW Argentina. This is accomplished via sedimentology, geochronology, stable isotope geochemistry, and thermochronology. Lithofacies analysis along measured stratigraphic sections documents a fine-grained, fluvial-lacustrine environment for the late Miocene Palo Pintado Fm. and a coarse-grained, braided-fluvial environment for the Pliocene San Felipe Fm. Provenance data document the evolution of basin sources from southwest and west during deposition of the Palo Pintado and lower San Felipe fms. to east during deposition of the upper San Felipe Fm.. U-Pb zircon geochronology constrains the transition between the two formation to &sim5.2 Ma and the first deposition of sediment derived from the present-day orographic barrier to &sim4 Ma.delta13C values from pedogenic carbonate nodules range from -15.4&permil to -10.2&permil for the Palo Pintado Fm. and from -9.5&permil to -8.2&permil for the San Felipe Fm., which can be best explained by increased, sustained aridity since &sim5 Ma. The a18O values range from -9.6&permil to -5.9&permil for the Palo Pintado Fm. and from -6.1&permil to -5.2&permil for the San Felipe Fm., corroborating this interpretation. The shift toward more arid conditions correlates with a significant increase in grain size and depositional environment an no significant change in sedimentation rate. Since aridity precedes the development of an orographic effect, I interpret the grain size increase and change in depositional environment in the Angastaco Basin since &sim5 Ma to be a response of the sedimentary system to aridification resulting from regional climate change.I propose that the drainage geometry, when combined with provenance data, sheds insight regarding the distinct foreland basin depozones in which Payogastilla Group formations were deposited. Sandstone provenance data support an interpretation of a regional foreland disrupted by basement uplifts through time. The Quebrada de los Colorados Fm. was deposited in the distal to proximal foredeep. By mid-Angastaco Fm., the Angastaco Basin was within a wedge-top depozone. The axial geometry of the Angastaco Basin drainage during Palo Pintado Fm. deposition, paralleling the Cerro Negro Range, combined with decreased subsidence, suggests an overfilled fluvial-lacustrine (Carroll and Bohacs, 1999) piggyback stage. By &sim4 Ma, with the uplift of the Sierra de los Colorados Range, the Angastaco Basin became a structurally isolated basin, with thick-skinned reverse-fault bounded ranges to the west and east.