Potential Feedbacks Between Tectonics, Climate, and Sediment Accumulation in a Neogene-Quaternary Intermontane Basin on the Margin of the Puna Plateau, Quebrada de Humahuaca, NW Argentina

Abstract:

Feedbacks between tectonics, climate, and sediment storage or removal in intermontane basins have the potential to modulate plateau growth. Previous studies suggest that the lithostatic load of thick sedimentary basin fills promotes the propagation of deformation into the foreland, whereas the removal of large volumes of sediment results in thrusting stepping back into the hinterland. To investigate these feedbacks, we reconstruct the Neogene-Quaternary deformational and sedimentary history of the northern Humahuaca basin, an intermontane basin on margin of the Puna Plateau. The timing of faulting, folding, sediment accumulation, and unconformities is constrained by U-Pb zircon dating of volcanic ashes interbedded with the sedimentary fill. As in the southern Humahuaca basin, the transition from westerly-derived sandstone and conglomeratic foreland basin deposits (Maimará Fm.) to predominately conglomeratic intermontane basin fills with variable provenance occurred at 4.3 Ma and is interpreted to result from uplift of the eastern basin-bounding ranges. In the northern Humahuaca basin, however, this transition is punctuated by two unconformities between 5 - 3.8 Ma. Between 4.3 - 2.5 Ma, the basin fill was dominated by rounded pebble-cobble conglomerates. Around 2.5 Ma, these conglomerates gave way to the fine-grained deposits of the Uquía Fm. and sediment-accumulation rates increased from 200-400 m/Myr to >500 m/Myr. This interval of fine-grained deposition and high sediment-accumulation rates may reflect a period of basin isolation and severed fluvial connectivity with the foreland related to increased aridity as a result of uplift of the eastern ranges. The transition back to conglomerates occurs at 2.2 Ma in the southern part of the northern Humahuaca basin and sometime between 2.1 and 1.3 Ma in the north. An unconformity exists between 2 Ma and 1 Ma strata. Thrust faults on the west side of the basin were active from >4.3 Ma to <3 Ma. Thrusts in the center of the basin were active sometime after 2 Ma and the easternmost thrust in the basin was likely active after 1.3 Ma. This timing suggests that rapid sediment accumulation between 2.5 - 2 Ma may have suppressed faulting in the center of the basin, whereas the removal of some of this sediment (i.e., the unconformity between 2 - 1 Ma) promoted intrabasin faulting.