Sedimentology and palaeoenvironmental evolution of the Patquía Formation (Permian), in the Sierra de Maz and cerro Bola, La Rioja Province, Argentina

Abstract

The sedimentological characteristics of the Patquía Formation in the Sierra de Maz and Cerro Bola areas were analyzed. Seven facies associations were recognized at four stratigraphical sections: Cerro Guandacol, La Cortadera, Cerro Noqués and Cerro Bola. Facies A is composed of agglomerates, breccias and conglomerates, deposited in small alluvial fans. Coarse sandstones and conglomerates of facies B were probably deposited in braided fluvial plains. Facies C comprises conglomerates and coarse sandstones from low to moderate sinuosity rivers. The most widespread association is facies D that consists of very coarse sandstones, fine sandstones, mudstones and tuffs. These rocks are interpreted as originating from high sinuosity channel migration across broad alluvial plains. Eolian sedimentation is registered in facies E composed of very fine to medium cross-bedded sandstones. Interbedded mudstones and fine sandstones (facies F) are interpreted as deposited in a shallow permanent lake dominated by clastic sedimentation. Facies G consists of white sandstone and pink mudstone, with minor proportions of large-scale, cross-bedded fine sandstone. It was deposited by low to moderate sinuosity fluvial systems on well-developed alluvial plains with isolated eolian dunes. Modal compositions of the sandstones revealed three petrofacies. The cuarzofeldica petrofacies represents the provenance of the Sierras Pampeanas basement. The cuarzofeldlítica petrofacies includes important amounts of acid and mesosilicic volcanic clasts related to the Permo-Triassic volcanic belt. The litomíxtica petrofacies shows high proportions of sedimentary and palaeovolcanic rock fragments from the Precordillera area. Stratigraphical analysis of the Patquía Formation allows recognition of two depositional sequences, SDi (lower) and SDs (upper). igraphical analysis of the Patquía Formation allows recognition of two depositional sequences, SDi (lower) and SDs (upper).