Stratigraphic Evolution of the Northern Magallanes-Austral Basin, Argentine Patagonia

Abstract

The Late Cretaceous to Neogene Magallanes-Austral Basin of southern Patagonia provides a unique opportunity to study a well-preserved and well-exposed axially drained (N to S), elongate retroarc foreland basin built on attenuated continental crust. Whereas the stratigraphy of the Magallanes (southern) sector of the basin, including the deep-water Punta Barossa, Cerro Toro, and Tres Pasos Formations and the shallow-marine to deltaic Dorotea Formation, is well studied, the complicated deep- to shallow-marine stratigraphy in the Austral (northern) sector of the basin, including the Alta Vista, La Anita, Cerro Fortaleza, La Irene, Calafate, Lago Viedma and Puesto El Alamo Formations, remains relatively unexamined. We delineate, date and interpret this shallow water stratigraphy in an effort to correlate Austral units to their Magallanes counterparts and provide a more comprehensive basin history with a focus on tectonic controls. Preliminary results from detrital zircon geochronology, strontium isotope stratigraphy and detailed sedimentology suggest that the Alta Vista, La Anita, La Irene and Cerro Fortaleza Formations are Santonian to Maastrichtian in age and represent a failure-dominated slope to storm-influenced shelf and peripheral terrestrial sequence broadly equivalent to the Tres Pasos and Dorotea Formations, whereas the Puesto El Alamo Formation is Turonian to Coniacian in age and represents shallow-marine equivalents to the older Punta Barossa to Cerro Toro Formations. Additionally, there is likely an angular unconformity, previously unrecognized in outcrop, between the La Irene and Calafate Formations and equivalent stratigraphy to the north, suggesting that the Calafate Formation is equivalent to Cenozoic Magallanes stratigraphy.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016