Geology and stratigraphy of the Upper Triassic in the area surrounding of Llancaqueo farm, Los Menucos, North Patagonian Massif (Río Negro)

Abstract

Two sets of volcano-sedimentary rocks of different ages, one of the Permian-Lower Triassic age corresponding to the Los Menucos Complex and a younger one of the Upper Triassic age, were identified in the Los Menucos region, in the northern sector of the North Patagonian Massif. The lithological, stratigraphic and sedimentological characteristics of the rocks assigned to the Upper Triassic crop out in a typical area located in the vicinity of Llancaqueo place, 6 km NE of Los Menucos, are presented. There a volcanic and volcaniclastic succession stands out, at least 378 meters thick, which is supported by angular and erosive unconformity on the rocks of the Los Menucos Complex. The lower part of the succession is characterized by deposits corresponding to alluvial fan systems, high-energy braided rivers and sinuous rivers with floodplain development, while the upper part is represented by a bimodal sin-sedimentary magmatism composed of basalt-andesitic lava flows and subvolcanic bodies and riodacitic ignimbrites. With the informal name of Sedimentitas y volcanitas Llancaqueo, it is proposed to separate the volcano-sedimentary sequence of the Llancaqueo-type area from the set of volcanic and sedimentary rocks belonging to the Los Menucos Complex. In the regional context, the Upper Triassic age and the lithological characteristics of the Llancaqueo sedimentites and volcanites, orients the search for regional correlations towards the pyroclastic, volcanic and epiclastic sequences that make up the Precuyano Cycle of the Neuquén Basin and their equivalents in the basing edges.