87Sr/86Sr early Oligocene age for the Río Foyel Formation, Río Negro, Argentina

GRIFFIN, M.; CASADÍO, S.; PARRAS, A.; FELDMANN, R.; SCHWEITZER, C.

Diamante, Entre Ríos

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2004

Asociación Paleontológica Argentina

The age and stratigraphic relations of marine rocks exposed south of lake Nahuel Huapi (Río Negro) have been matter of debate. Part of these rocks are included in the Río Foyel Formation, which is well exposed along the banks of the Foyel River. The section includes alternate beds of massive shale with concretions and subordinate sandstones. These rocks yielded an abundant and diverse fauna near the top of the succession. Among other taxa present are the coral Flabellum sp.; the brachiopod Terebratella sp.; the bivalves Panopea nucleus (Ihering), Dosinia sp., Neilo bicarinata (Ljungner), Nucula sp., Atrina sp., Brachidontes sp., Zygochlamys sp., and Cucullaea cf. C. schilleri (Ljungner); the gastropods Turritella sp. and Fusinus sp.; the echinoderm ?Schizaster sp.; and the decapods Munida casadioi (Schweitzer and Feldmann), Callianopsis australis Casadío et al., Proterocarinus corsolini Casadío et al., Trichopeltarion levis Casadío et al., Baricarcinus mariae Casadío et al., and Asthenognathus microspinus Casadío et al. Workers studying the mollusks assigned an Eocene age to the Río Foyel Formation. However, foraminifers and pollen content suggest an early middle Oligocene age. The 87Sr/86Sr presented here was performed on a shell of ?Ostrea sp. collected near the base of the section exposed along the right bank of the river. The rate obtained was 0.707959, yielding an early Oligocene age (30.65 Ma), coincident with the available micropaleontological information