The Late Cretaceous-Cenozoic transgressions in Patagonia and the Fuegian Andes: Foraminifera, palaeoecology, and palaeogeography

Abstract

In southernmost South America, several ephemeral Atlantic transgressions flooded the Patagonian Platform: in the Maastrichtian-Danian, late Mid-Eocene, Late Oligocene-Early Miocene, and Middle Miocene; only in the Fuegian Andes did marine conditions remain continuously from the Maastrichtian up to the Middle Miocene. In the Maastrichtian, the calcareous foraminiferal benthic assemblages contain endemic species, and most of them disappear in the Cretaceous-Palaeogene transition. The Palaeocene carries the extinct cosmopolitan Midway type assemblage with few endemic taxa such as Buliminella isabelleana, and the genera Antarcticella and Boltovskoyella. The Palaeocene/Eocene turnover gives room to assemblages of modern and marked Austral aspect: Elphidiidae dominates in shallow environments, including genera endemic to high and mid-high southern latitudes such as Cribrorotalia. The Late Middle Eocene transgression is characterized by large nodosarids in the Fuegian area and the spreading of Elphidium saginatum. The Late Oligocene transgression is of limited extension and shallow waters, with abundant Buccella and the conspicuous genus Discorotalia. The Early Miocene transgression carries the extinct and typical Antarctic genus Ammoelphidiella and witnesses the origin of the modern Patagonian coastal assemblage, characterized by its pauperism and the dominance of the genus Buccella. The Middle Miocene transgression covers mainly northern Argentina. Considering that the late Middle Eocene and Middle Miocene transgressions are coeval with relative climatic optima, and in comparison with assemblages at similar palaeolatitudes elsewhere in the Southern Hemisphere, the absence of larger foraminifera or thermophilic forms in the Patagonian and Fuegian assemblages is outstanding.