Jurassic Uplift Along the Huincul Arch and Its Consequences in the Stratigraphy of the Cuyo and Lotena Groups. Neuquén Basin, Argentina

Abstract

Marine sedimentation in the Neuquen Basin started in the Early Jurassic with the accumulation of a progradational clastic system: the Cuyo Group. This sedimentary cycle begins with offshore shales of the Los Molles Formation, transitionally overlaid by shelfal to littoral sandstones and conglomerates of the Lajas Formation. According to the current stratigraphic schema, in the southern Neuquen Basin the Cuyo Group ends with continental red beds of the Challaco Formation, a unit interpreted as being the proximal equivalent of the Lajas Formation. Nevertheless, recent studies performed in the Picun Leufu area, complemented with regional stratigraphic evidence, suggest that the accumulation of these stratigraphic units is more likely related to a complex depositional scenario that involves tectonic activity during the Jurassic along the Huincul Arch. The uplift and exposure of Jurassic rocks along the Huincul Arch divided the basin into two sub-basins, each one having a different stratigraphy for the Middle-Late Jurassic time span. The stratigraphic analysis revealed that the red beds traditionally located at the top of the Cuyo Group in fact represent two different stratigraphic units separated by a regional unconformity. The lower unit (1) sharply overlies the Lajas Formation, corresponding to the Challaco Formation s.s. This unit was accumulated in a brackish lacustrine basin developed southward of the Huincul Arch (Picun Leufu Sub-basin). The upper unit (2) corresponds to the Bosque Petrificado Formation and is stratigraphically located at the base of the Lotena Group. The Bosque Petrificado Formation was accumulated in a fluvial to marine environment developed in the southern Neuquen Basin. Paleocurrent analysis suggests a sediment supply from the northeast, evidencing a local source of sediments related to an uplifted area. Recent biostratigraphic studies performed in the Bosque Petrificado and Lotena formations revealed an Early Callovian-Early Oxfordian age for these deposits.