Paleogene Basin Evolution in Southern Patagonia as a Result of Plate Dynamics and Global Sea Level Changes

Abstract The Paleogene stratigraphic record of the Austral‐Magallanes foreland basin (southern Patagonia) reflects a complex interplay between Andean orogenesis, plate kinematics, and global climate shifts. We present 17 new detrital zircon U‐Pb geochronology data and one tuff U‐Pb age from Cenozoic strata exposed in the Río Turbio region (∼51.5°S). Our data constrain three depositional stages—the Cerro Dorotea (∼65–59 Ma), Río Turbio (∼47–35 Ma), and Río Guillermo (∼26–21 Ma) formations—bounded by two protracted hiatuses. Combined with previously published data, this new geochronologic data set allows us to characterize periods of arc activity based on zircon production periods, revealing a continuous active arc throughout the Cretaceous followed by a volcanic lull between 60 and 50 Ma. By integrating the refined stratigraphy with arc and back‐arc magmatic records, updated plate kinematic models, and global sea‐level curves, we identify the primary drivers of foreland basin evolution and, in particular, the processes that generated basin‐scale unconformities. We interpret the first regional unconformity, expressed as a Paleocene–Eocene hiatus, as the stratigraphic response to the subduction of the Farallon–Aluk mid‐ocean ridge. This ridge‐trench collision induced regional lithospheric uplift, the abrupt cessation of arc magmatism, and contemporaneous intraplate volcanism. In contrast, the subsequent Oligocene hiatus, which developed during a period of tectonic quiescence, can be attributed to a major eustatic sea‐level fall.