Syn-rift stratigraphy (Upper Triassic-Lower Jurassic) of the Neuquén Basin at the Sierra de Chacaico, Neuquén, Argentina.

Abstract

The sierra de Chacaico (Neuquén, Argentina) is one of the most important localities to study the Upper Triassic-Lower Jurassic syn-rift sequence of the Neuquén Basin. Structural and sedimentological analyses have been carried out in order to depict the stratigraphic evolution of the infill. The syn-rift sequence evolved in a volcano-sedimentary environment. For the entire column, three sections have been recognized. The lowest section is composed of basic to intermediate volcanic rocks associated with coarse-grained volcaniclastic deposits. The middle section is dominated by pyroclastic flow and fall deposits closely associated with volcaniclastic sandstones and minor conglomerates. Lacustrine carbonates and basaltic lavas were recognized at the top of the middle section. The upper section is characterized by coarse-grained conglomerates and breccias and pyroclastic fall and flow deposits. The whole area formed a unique depocentre during syn-rift evolution, its margins trending E-W/ENE-WSW. The southern margin acted as the main active border of the trough, where the thickest section was deposited. The syn-rift depocentre was inverted during later tectonic events leading to the generation of a complex pattern of anticlines and reverse faults. Some of these anticlines were formed by the inversion of oblique trending (north-east) normal faults suggesting the presence of internal steps within the depocentre. The structural and stratigraphic pattern observed at sierra de Chacaico is similar to the main framework of the Huincul high, one of the most prominent tectonic elements of the southern Neuquén Basin.