The Neogene to Quaternary evolution of the Neuquén Andes broken foreland forced by tectonic, climatic and surface processes (southern Central Andes)

Abstract

The Andes offer a distinctive example of the intricate interplay among climate, tectonics, and surface processes. This is exemplified by the mountain range's north-south orientation, which contrasts with the prevailing east-west wind direction. This interplay controls the uplift evolution of the broken foreland and thus the sediment transfer and erosion from mountain ranges to their forelands. The Neuquén Andes is a peculiar segment of the southern Central Andes, registering dramatic North-South variabilities in elevation, climate, and tectonic intensities established during the Neogene and Quaternary. In this study, we aimed to identify the tectono-stratigraphic evidence of the Neogene to Quaternary evolution of paleo-environments and drainage networks in the intramountainous basin of Pampa de Agua Amarga in the broken foreland of the southern Neuquén Andes of Argentina.Starting with a non-depositional and/or erosional phase during the Paleogene, the Pampa de Agua Amarga Basin underwent several phases of syn-orogenic sedimentation in the late Oligocene to early Miocene. The basin gradually shifted from a lacustrine to an alluvial depositional environment, with alluvial deposits becoming dominant in the mid-Miocene and fluvial deposits dominating in the Pliocene. A significant event occurred during the late Pliocene to early Pleistocene when coarse fluvial deposits were deposited, marking the last aggradation phase. In the early Pleistocene, the onset of incision triggered the drainage system to cut through the downstream topographic barrier. The excavation of the basin was abrupt, as evidenced by a mid-Pleistocene stepped fluvial terrace and alluvial fan that filled a large canyon across the southern end of the downstream topographic barrier.The study confirms the regional trend that Miocene basin infill is related to dry climate and high tectonic uplift, which overwhelmed the erosive power of the drainage network. The lowering of tectonic uplift intensity in the southern Neuquén Basin during the Plio-Pleistocene, along with sudden fluctuations in the global colder and wetter climate, ultimately led to the excavation of the intramountainous basin. The Westerlies Wind Belts generate high precipitation rates in the southern Neuquén Andean Cordillera, feeding the Negro River catchment in the retroarc Andean broken foreland. Consequently, the erosive power of the Negro River catchment overcame the declining tectonic uplift, causing significant erosion of the entire broken foreland and Cordillera of the southern Neuquén Andes. Conversely, more intense tectonic uplifts in the northern Neuquén Andes built a more effective orographic barriers that limited precipitation rates of both the Westerlies Wind Belt and South America Summer Monsoon, and preserved the intramountainous basins and mountain interior from erosion.