Estratigrafía del Cretácico Superior en el flanco occidental de los Andes a los 35°S, Chile Central

Abstract

In this contribution, we report the preliminary results of a geological study, supported by radiometric age determinations (LA-ICP-MS in zircon crystal), for establishing the Upper Cretaceous stratigraphic frame of the study region. The latter correlates and nearby localities. Two units record the time from considered: (1) the Plan de los Yeuques Fm, a mainly volcanic, explosive and effusive, continental series of at least 2.200 m in thickness with an early Campanian-Danian age (63,4-75 Ma) and (2) the BRCU, a clastic continental series, of at least 230 m in thickness, with an early Campanian maximum depositional age (81, 5 Ma). The contact relation between these units is apparently concordant, but according to the radiometric dating, they could be separated by a maximum of a 6 m. y. depositional hiatus. Altogether, they cover the full age range of the upper Late Cretaceous and constitute a record of the margin evolution during this period. This is complementary to the stratigraphic units of similar age in the Argentinean flank of the Andes as the upper portion of the Neuquén Group, the lower portion of the Malargüe Group, and other Late Cretaceous igneous units that occur dispersed south of 37°S.