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

Abstract

A key event in the paleogeographic evolution of the Austral-Magallanes foreland basin was the Santonian–Maastrichtian continentalization, marked by the appearance of deltaic, fluvial and wetland sequences stacked on top of deep marine deposits. The expanding ecological niche was exploited by theropods and influenced the evolutionary history of dinosaurs. We present new detrital zircon U–Pb geochronological data across this littoral to continental depocenter, in order to provide insights of its age, geographical extension, source regions and geodynamic setting. Littoral sandstones from La Anita Formation yield Maximum Depositional Ages (MDA) between ~86–80 Ma (weighted mean ages), and ~79–78 Ma youngest zircons. Our results are in accordance with a Santonian–Campanian depositional age. The sequence continues with badlands and fluvial systems (Cerro Fortaleza and La Irene Formations), followed by meandering fluvial and lacustrine deposits (Chorrillo Formation). Transgressive marine facies topping the sequence (Calafate Formation) yield a preferred Maastrichtian 69 ± 2 Ma MDA from the youngest zircon. The provenance and tectonic analyses indicate that basin shallowing during Santonian–Campanian times was driven by advance of the orogenic front, which produced the shift from a foredeep setting to a wedge-top depozone. The unroofing of progressively deeper structural levels is registered in the basin fill, which suggests exhumation in the Basement domain during the Santonian–Maastrichtian.