Nanofósiles calcáreos de la Formación Agrio (Cretácico Inferior) en el sector sudoccidental de la Cuenca Neuquina, Argentina

calcareous nannofossil assemblages recorded in marine rocks of the lower cretaceous agrio formation in the southern neuquén basin are presented here. the cerro birrete (39o 16.456′s and 70o 5.94′o), barda cerro marucho (39o 26.685′s and 70o 13.015′o) and cerro marucho section (39o 26.443′s and 70o 13.21′o) are analized, being recognized 33 taxa, between them, the reliable markers are: clepsilithus maculosus rutledge and bown, eiffellithus striatus (black) applegate and bergen, eiffellithus windii applegate and bergen, nannoconus bucheri br？nnimann, nannoconus circularis déres and achéritéguy. the nannofossil association, of late valanginian-hauterivian age, allow to date of the agrio formation in the area and correlate it with others situated in different localities of the basin.