Abstract

A succession of quartz-rich fluvial sandstones and siltstones derived from a mainly rhyolitic source and minor metamorphic rocks, located to the west, represent the first Upper Paleocene-Early Eocene deposits described in Chilean eastern central Patagonian Cordillera (46 degrees 45 'S). This unit, exposed 25 km south of Chile Chico, south of lago General Carrera, is here defined as the Ligorio Marquez Formation. It overlies with an angular unconformity Lower Cretaceous shallow marine sedimentary rocks (Cerro Colorado Formation) and subaerial tuffs that have yielded K-Ar dates of 128, 125 and 123 Ma (Flamencos Tuffs, of the Divisadero Group). The Ligorio Marquez Formation includes flora indicative of a tropical/subtropical climate, and its deposition took place during the initial part of the Late Paleocene-Early Eocene Cenozoic optimum. The underlying Lower Cretaceous units exhibit folding and faulting, implying a pre-Paleocene-Lower Eocene contractional tectonism. Overlying Oligocene-Miocene marine and continental facies in the same ar ea exhibit thrusts and normal faults indicative of post-Lower Miocene contractional tectonism. (C) 2000 Elsevier Science Ltd. All rights reserved.