On the presence of Upper Paleocene rocks in the foreland succession at Cabo Nariz, Tierra del Fuego, Chile: geology and new palynological and U-Pb data.

Abstract

On the west coast of Tierra del Fuego, south of Cabo Nariz, in Chile, Upper Cretaceous to Paleocene sedirnentary successions of the Magallanes foreland basin crop out. The presence of dinoflagellate cysts, as well as radiometric U-Pb SHRIMP dating of detrital zircons, indicate that this succession ranges from the Campanian to Thanetian (Late Paleocene) in age. The base of the exposed sedimentary succession comprises siltstones of externa! platform facies (Cerro Cuchilla Formation), which are thrust over the Cabo Nariz Beds. The latter formation is divided into two members: a lower siltstone-dominated turbidite facies member andan upper mernber of sandstone-dominated turbidites, with sandstone and conglomerate channel facies. The presence of dinocysts in the Cerro Cuchilla Formation suggests a late Campanian to early Danian age. The fossil content in the Cabo Nariz Beds indicate a Selandian (Middle Paleocene) depositional age in accordance with the detrital zircon ages which pro vide a maximum possible Campanian age (76.5±0.7 Ma), and very close to the Thanetian (Late Paleocene) (57.6±1 Ma) depositional ages for the lower and upper member, respectively. The sedimentary succession ofCabo Nariz Beds, is interpreted as a north-northwest prograding submarine fan of middle to Late Paleocene age. It is considered to represent the deposition of detritus derived from an uplifting orogen located to the south. The detrital zircon age spectra suggest that there was a period oflow intensity ofmagmatic activity in the source area around the K-T boundary.