Santonian-Campanian continentalization in the Austral-Magallanes basin: regional correlation, provenance and geodynamic setting

Abstract

The initiation of the foreland stage in the Austral-Magallanes basin, which is indicated by the appearance of the fi rst sand-dominated and conglomeratic sequences with provenance sources from the South Patagonian Andes, presents two relevant characteristics. First, the initiation of the foreland basin stage was diachronous: Aptian in the northern depocenter (~46-49º), and Albian to Cenomanian in the central and southern depocenters (~50-51º and ~51-53º). A second striking fact is that the onset of synorogenic sedimentation was represented by littoral to fl uvial sequences in a restricted northern continental depocenter (Río Belgrano and Río Tarde Formations), but south of 50º, basal synorogenic sedimentation is represented by marine, sandy turbiditic layers (Lago Viedma, Cerro Toro and Punta Barrosa Formations). The ensuing Cretaceous evolution of the Austral-Magallanes foreland basin system also presents contrasting histories. The northern depocenter was inverted and exhumed during basins inversion in a Cenomanian advance of the orogenic front, and constituted an elevated sector as shown by a conspicuous Upper Cretaceous-Paleocene hiatus; a striking diff erence when the hiatus is compared with the ~5000 m thick Upper Cretaceous deposits south of Lago Viedma.