Miocene foraminifera from the Neuquén Basin, Argentina: stratigraphic and paleoenvironmental implications

Carolina Náñez, Norberto Malumian


At the Bajada del Jagüel and Opaso sections, located in the Añelo low, Neuquén Basin, Argentina, the Maastrichtian to Danian mudstones of the Jagüel Formation, are overlain by a succession composed of coquinas very rich in ostreid remains, sandstones and mudstones. This succession has been usually referred to the Roca Formation, a Paleocene marine unit with its type section located about 120 km to the southeast. A contrasting interpretation proposed by the late 70s considered that the beds assigned to the Roca Formation in the Añelo low were actually the base of the overlying Barranca de los Loros Formation, of terrestrial paleoenvironment and Miocene age, and that their very abundant Paleocene invertebrate remains were reworked. As part of a monographic study of the foraminiferal family Elphidiidae from southern Argentina, the specimens recovered from a muddy horizon intercalated between the coquinas at the Opaso and Bajada del Jagüel sections, previously assigned to Protelphidium sp. cf. P. hofkeri Haynes, are reviewed and identified as Porosononion granosum (d'Orbigny). Porosononion granosum is one of the most common foraminiferal species of the shallow Paranense transgression, which covered large part of Argentina during the middle-late Miocene, and has been traditionally referred to as Protelphidium tuberculatum in Argentina. The occurrence of this species indicates that the fossiliferous coquinas, sandstones and mudstones overlying the Jagüel Formation at the Bajada del Jagüel and Opaso sections should not be assigned to the Roca Formation, but are related to the Miocene Paranense transgression, thus supporting the later stratigraphic interpretation. In the muddy horizon, Porosononion granosum constitutes a monospecific assemblage, and its paleoenvironment is interpreted as marginal marine or lacustrine. The elphidiid specimens from the Roca Formation at the Sierras Blancas area, ca. 12 km southwest from the Opaso section, remain identified as Protelphidium sp. cf. P. hofkeri. Both species, P. sp. cf. P. hofkeri and P. granosum, are described and illustrated and paleoenvironmental and paleogeographic features are discussed.


Elphidiidae; Neuquén Basin; Miocene; Paleocene; foraminifera; Argentina

How to cite this article Náñez, C., and Malumian, N., 2018, Miocene foraminifera from the Neuquén Basin, Argentina: stratigraphic and paleoenvironmental implications: Andean Geology, v. 46, no. 1, , doi: