The Late Cretaceous Orogenic System: Early Inversion of the Neuquén Basin and Associated Synorogenic Deposits (35º–38º S)

Abstract

The first regional tectonic uplift was registered in the Neuquén Basin atca. 100 Ma, resulting in the inception of the first foreland basin of the Andes at these latitudes. The infill of this foreland basin is represented by the nonmarine deposits of the Neuquén Group, characterized by the presence of growth strata and fold-thrust belt detrital derivation, typical of wedge-top depozones. The presence of a longlasting hiatus and angular unconformities in structures west of the wedge-top area indicate that these constituted the main detrital source areas of the Late Cretaceous foreland basin. These structures were uplifted by tectonic inversion of pre-existing normal faults, a mechanism that was also responsible for isolated basement block uplifts detected in the foredeep depozone. The regional unconformity between the synorogenic deposits of the Neuquén Group and the back-bulge deposits of the Bajada del Agrio Group represents the migration of the forebulge, which constituted another important detrital source of the foreland basin during its mature phase. An active fold-thrust belt, disconnected basement block uplifts and the identification ofthe typical depozones of present foreland basins provide a complete picture of the Late Cretaceous orogenic system responsible for the early inversion of the Neuquén Basin.