Bivalvos dulceacuícolos de la formación Ñorquinco (Oligoceno), en la cuenca del río Percey, provincia del Chubut, Argentina

The bivalve fauna of Norquinco Formation, from the Percey river basin, Chubut Province, is composed of: Diplodon aff. colhuapiensis Ihering, Diplodon aff. pehuenchensis (Doello-Jurado) Parodiz and Diplodon aff. oponcitonis Pilsbry y Olsson. This is a typical fresh-water assemblage evidence which this together with the sedimentalogical characteristics, which are also described, indicates a continental depositional environment. Although the evidence fauna is not conclusive, the age of the formation would be oligocene to early miocene. This is concluded based on stratigraphical relations in Ibis area and regionally.