Stratigraphy of the Upper Cretaceous-Paleocene from Thetis Bay, Fuegian Andes, Argentina: tectonic and paleobiologic events.

Abstract

The stratigraphic evolution of marine, Upper Cretaceous-Paleocene rocks within the inner fold belt of the foreland Austral-Malvinas basins is studied at the eastern tip of the Fuegian Andes. At Thetis Bay, the stratigraphic column includes three Formations: 1) Bahía Thetis, dark mudstone, tuff, turbidite sandstone, and resedimented conglomerate with late Campanian-?early Maastrichtian ammonites and foraminifera; 2) Policarpo, bioturbated, tuffaceous, sandy mudstone with Maastrichtian ammonites, foraminifera, and dinocysts in its lower-mid parts, and Danian dinocysts in its upper part; and 3) Tres Amigos (new name), conglomerate, sandstone and mudstone, with austral Paleocene dinocysts and foraminifera. Together with Santonian-lower Campanian strata, at Buen Suceso Bay, Maastrichtian to basal mid-Eocene strata, at caleta Falsa de Policarpo-Río Bueno, and lower to upper Eocene strata, at Cape Campo del Medio we erect a relatively complete Santonian to upper Eocene, composite stratigraphic column that records significant tectonic and paleobiologic events. Based on paleontologic dating and tectonic inferences on conglomerate bodies and unconformities, the age of three main pulses of Andean uplift are constrained within the late Campanian-?early Maastrichtian; mid-late Paleocene; and basal mid Eocene, respectively. The last record of inoceramid bivalves is in the early Campanian but most likely the extinction event could be indirectly recorded by the marked change from late Campanian-?early Maastrichtian disoxic-anoxic to late Maastrichtian oxic bottom conditions.