Late paleozoic high-constructive deltaic sequences from northwestern Patagonia, Argentine Republic

Abstract

Clastic deposits belonging to the Río Genoa Formation (Tepuel Group) have been studied in the southeastern area of the Tepuel-Genoa Basin. On the basis of detailed stratigraphic sections made in several localities along the Río Genoa Valley and neighboring areas, differen facies and subenvironments of a deltaic complex have been recognized and interpreted. These facies include upper delta plain (distributary channels, levees, and interdistributary bays), lower delta plain (mouth bars and delta front), and open sea (prodelta and platforms) deposits. The interpretation and evolution of the delta complex is also based on a cyclicity analysis (first-order Markovian chain) as well as on paleocurrents studies that allowed recognition of constructive and abandonment phases corresponding to a lobate delta model. Many of the facies mentioned contain abundant fossil plant and marine invertebrate remains, which were used for ecologic and biostratigraphic interpretations. Finally, the regional study of the lithofacies was related to tectosedimentary aspects of the Tepuel-Genoa Basin. In this regard, the delta progradation onto shallow marine deposits (Mojón de Hierro Formation) was due to a rising source area since latest Carboniferous time. Sedimentation was also controlled by “stillstand” sea conditions that were interrupted at least twice by high sea stages during Early Permian times.