Geología y estratigrafía del Triásico superior en la zona aledaña al puesto Llancaqueo, Los Menucos, Macizo Nordpatagónico, Río Negro.

Abstract

Two sets of volcano-sedimentary rocks of different ages, one of the Permian-Early Triassic age corresponding to the Los Menucos Complex and another of probable Late Triassic age, were identified in the Los Menucos region, in the northern sector of the North Patagonian Massif. The lithological, stratigraphical and sedimentological characteristics of the provisionally assigned to the Upper Triassic rocks which crop out in the vicinity of Llancaqueo farm, 6 km towards the NE of Los Menucos, were presented. There is a volcanic and volcaniclastic succession with at least 368 m thick, which overlies an angular and erosive unconformity developed on the Los Menucos Complex. The lower section of the succession is characterized by deposits corresponding to alluvial fan systems, high-energy braided rivers and sinuous rivers with floodplains; while the upper section is represented by a sin-sedimentary magmatism composed of mesosilicic to basic lava flows associated with subvolcanic bodies, and riodacitic ignimbrites. The informal denomination of sucesión volcano-sedimentaria Llancaqueo was proposed to separate the volcano-sedimentary sequence of the Llancaqueo-type area from the rocks belonging to the Los Menucos Complex. In a regional context, the possible Upper Triassic age and the lithological characteristics of the sucesión volcano-sedimentaria Llancaqueo, suggest the search of correlations with the pyroclastic, volcanic and epiclastic sequences belonging to the Precuyano Cycle, or lateral equivalent within the Neuquén Basin.