LATE MIOCENE CALCAREOUS NANNOFOSSILS AND BIOSTRATIGRAPHY OF THE SW TUMACO ONSHORE BASIN (COLOMBIAN PACIFIC)

A semiquantitative biostratigraphic study of calcareous nannofossils for three upper Miocene stratigraphic sections on the Pacific coast of Colombia (SW of the Tumaco onshore basin) is presented. To stablish the biochronology of the recovered nannofossils assemblages, standar biozones and previous recognized bioevents were identified and compared with other studies (e.g. ODP Leg 138, ODP Leg 165). A total of six bioevents were reconigzed, including the first record or lower occurrence (LO) of Amaurolithus primus, Reticulofenestra rotaria, Amaurolithus delicatus, Amaurolithus amplificus and Amaurolithus tricorniculatus, and the last record or highest occurrence (HO) of Reticulofenestra rotaria. Results suggest that the sections comprise a Tortonian to Messinian time interval, corresponding to the NN11a - NN11b biozones of Martini (1971) and CN9a - CN9b of Okada and Bukry (1980). Keywords: Calcareous nannofossils, Biostratigraphy, Late Miocene, Tumaco basin onshore.