Refining stratigraphyand tectonic history using detrital zirconmaximumdepositionalage: an example fromthe Cerro Fortaleza Formation,Austral Basin, southern Patagonia
Z.T. Sickmann, T.M. Schwartz and S.A. Graham
Journal name: Basin Research
Issue: Vol 30, No 4, August 2018 pp. 708 - 729
Info: Article, PDF ( 15.15Mb )
The north–south trending, Late Cretaceous to modern Magallanes–Austral foreland basin of southernmost Patagonia lacks a unified, radiometric, age-controlled stratigraphic framework. By simplifying the sedimentary fill of the basin to deep-marine, shallow-marine and terrestrial deposits, and combining 13 new U-Pb detrital zircon maximum depositional ages (DZ MDAs) with published DZ MDAs and U-Pb ash ages, we provide the first attempt at a unified, longitudinal stratigraphic framework constrained by radiometric age controls. We divide the foreland basin history into two phases, including (1) an initial Late Cretaceous shoaling upward phase and (2) a Cenozoic phase that overlies a Palaeogene unconformity. New DZ samples from the shallow-marine La Anita Formation, the terrestrial Cerro Fortaleza Formation and several previously unrecognized Cenozoic units provide necessary radiometric age controls for the end of the Late Cretaceous foreland phase and the magnitude of the Palaeogene unconformity in the Austral sector of the basin. These samples show that the La Anita and Cerro Fortaleza Formations have Campanian DZ MDAs, and that overlying Cenozoic strata have Eocene to Miocene DZ MDAs. By filling this data gap, we are able to provide a first attempt at constructing a basinwide, age-controlled stratigraphic framework for the Magallanes– Austral foreland basin. Results show southward progradation of shallow marine and terrestrial environments from the Santonian through the Maastrichtian, as well as a northward increase in the magnitude of the Palaeogene unconformity. Furthermore, our new age data significantly impact the chronology of fossil flora and dinosaur faunas in Patagonia.