Sedimentological and ichnological analyses of the continental to marginal-marine Centenario Formation (Cretaceous), Neuquén Basin, Argentina: Reservoir implications

The upper Valanginian – lower Aptian Centenario Formation is a significant producer of oil and gas in the Neuquén Basin, western Argentina. This formation is located exclusively in the subsurface of the eastern and northeastern Neuquén Basin, and is 450–1000 m thick. The Centenario Formation laterally interfingers with the Agrio Formation. Previous studies addressing the paleogeographic history of the Centenario Formation are scarce, and a comprehensive geological model has yet to be put forward. The current study scrutinizes the Centenario Formation, especially its lower member, within the northeastern Neuquén Basin. The study area includes the Cerro Hamaca Oeste, Señal Cerro Bayo, and Volcán Auca Mahuida oilfields operated by Yacimientos Petrolíferos Fiscales (YPF). Sedimentological and ichnological core data, geophysical well logs, and petrographic thin sections have been utilized to construct a geological model. Eleven sedimentary facies and three facies associations have been identified from the core dataset, providing insights into the paleoenvironmental settings and their stresses on infaunal colonization. Basin-margin deposits from the northeastern part of the study region were formed in continental environments, comprising ephemeral fluvial channel complexes and floodplains, and are ichnologically represented by rare Skolithos and common rhizoliths. The central part of the study area is interpreted as recording deposition in ephemeral lakes, river-dominated lake deltas, and coastal lagoons and sabkhas, and is represented by a combination of stressed expressions of both the Skolithos and Scoyenia Ichnofacies. River-dominated, storm-influenced delta deposits are located towards the southwestern limit of the study area, and are ichnologically represented by the Skolithos and depauperate Cruziana Ichnofacies. Deltaic deposits gradually transition into the basinal facies of the Agrio Formation to the west. Overall sedimentologic characteristics suggest semi-arid to arid climatic conditions during deposition.