The Miocene foreland basins of Northern Patagonia: sediment transfer systems from the Southern Andean to the Atlantic shelf

Abstract

Unravelling the effects of external controls on the stratigraphic record of a region, as well as the determination of how they impact in the dynamics of a sedimentary system is nowadays a critical gap to solve in geosciences. This issue is challenging because it not only involves the net depositional parts of the systems, but also, implies the understanding of the dynamic interplay between erosion, sediment transfer, and deposition as well as temporary storage, and long term preservation of the sediments, from source to sink.The Northern Patagonia has an extensive and superbly exposed Neogene Andean foreland sediment record extending from the foot of the Southern Andes to the Atlantic shelf. This sediment transfer system is strongly linked to the Neogene orogenic growth of the Andes and was synchronously associated with the development of a profuse magmatism, a major climate change from wet to dryer conditions, as well as important relative sea level changes. Based on a multidisciplinary approach, which includes new structural, stratigraphic, geomorphological and geochronological dataset together with previous surface and subsurface regional surveys, three Miocene sediment transfer systems that connected the Andes with the Atlantic Ocean through more than 600 km were reconstructed. From north to south (45?48°S) these transfer systems are: Collón Cura?North Patagonian basins system, Ñirihuau?Valdés basins system and Rio Mayo?San Jorge basins system (Fig.1).Stratigraphic correlations along the sediment transfer systems indicate a continuous sedimentary record during the Miocene for the Collón Cura?North Patagonian and the Río Mayo?San Jorge basins system. However for the Ñirihuau?Valdés system an important hiatus is registered in the distal zone during the middle Miocene (i.e., Rawson-Valdés Basin). This stratigraphic gap is interpreted as a consequence of middle-term sediment transient storage in the foreland region during the middle Miocene associated with block uplift and the configuration of closed-basins. Thus, during the Miocene sediment transfer systems functioned as both fully connected and unconnected systems between the Andes and the Atlantic Ocean. Finally, although more studies are needed to refine and improve the chronostratigraphic framework of the Miocene sediment transfer systems, early results of this work show some relevant issues related to the origin of environmental signals and their propagation through time and space.