First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation: insights on Late Cretaceous marine deposition in central Chile

Abstract

Upper Cretaceous marine rocks crop out along the Pacific coast of central and south-central Chile between 33° and 37°S. These strata constitute an important reference for the Upper Cretaceous of South America due to their diverse fossil fauna and flora. The type unit of these deposits is the Quiriquina Formation, near Concepción. This unit is considered Maastrichtian in age based on ammonites. Upper Cretaceous marine strata from other localities of central and south-central Chile are largely unstudied and their biostratigraphic ages are not precisely known. We present the first radiometric dating (U-Pb on detrital zircons) for Upper Cretaceous marine strata of the Chilean forearc at Punta Topocalma that indicates a probable depositional age of 71.9+0.9 Ma (latest Campanian-earliest Maastrichtian). Provenance analysis indicates that the source of sediments of the Punta Topocalma Formation was plutonic and volcano-sedimentary rocks from the Coastal Cordillera and the Central Depression of central Chile. The Lo Valle Formation, a volcano-sedimentary unit in the Central Depression, recorded deposition of the Upper Cretaceous volcanic arc that was coeval with marine sedimentation in the Topocalma area.