Stratigraphic analysis of the Lotena Formation (upper Callovian-lower Oxfordian) in central Neuquen Basin, Argentina.

Abstract

Integration of outcrop and subsurface information. A stratigraphic, palaeoenvironmental and sequence stratigraphic analysis of the Lotena Formation (upper Callovian-lower Oxfordian) is presented for an area of 2.500 km2 in the central portion of the Neuquen Basin (36°40’ y 37°10’S). Three distinctive intervals were defined for the Lotena Formation in the study area, termed here La Estrechura, El Pichanal and El Vado members. The La Estrechura Member is composed of marine deposits accumulated in a tidally-influenced setting for the western and southern parts of the study area. In the central and northern sectors, the La Estrechura Member was deposited in a fluvially-dominated deltaic system controlled by hyperpycnal flows. The El Pichanal Member is characterized by continental sediments accumulated in ephemeral fluvial and aeolian settings. Coarse-grained fluvial deposits are more abundant in the northeastern sector, while participation of fine-grained fluvial facies and aeolian sandy deposits increase towards the southwest. The El Vado Member lies on top of both the La Estrechura and El Pichanal members and represent a drastic change in accumulation conditions. This unit records transition from siliciclastic to mixed (siliciclastic-carbonatic) deposits developed in a wave-dominated, open marine system. The El Vado Member is overlain by carbonatic deposits of the La Manga Formation. The basal boundary of the Lotena Formation indicates a regional regressive event and it is here interpreted as a sequence boundary. The siliciclastic deposits of the La Estrechura and El Pichanal members constitute a higher-order sequence accumulated under important sediment supply and moderate accommodation creation. The lower boundary of the El Vado Member is considered as a regional transgressive surface, and its record is associated with the complete flooding of this part of the basin, together with a decrease in the rate at with terrigenous material was delivered to the basin. The transgressive trend registered for the Lotena Formation is reverted, in this area, with the development of the carbonate system of the La Manga Formation.