Geology, lithology and deltaic sub-environments discrimination in the Upper Neocomian of the Río Mayo area, Northwestern sector of the San Jorge Basin The aim of this study is to analyze the geology of the Neocomian cycle focused in the upper section of Pozo Cerro Guadal Formation. The lithological characterization of this unit has been performed by core and cutting descriptions and the interpretation of well logs in order to recognize the existing lithofacies and the associated prograding successions. Considering a deltaic facies model it has been possible to associate the recognized lithofacies to their corresponding depositional environments. Paleogeographic maps have been generated from the facies successions ́analysis and the correlation of the defined prograding sequences. Within a tectonostratigraphic context, the paleogeographic and paleoenvironmental reconstruction are useful to explain the relative reservoir and non reservoir facies distribution in each deltaic environment. The understanding of this conceptual model intends to be a guide in the construction of a geocelular model. .