Universidad Nacional Autonoma de Mexico, Mexico

Calcareous nannofossil assemblages from land sections of the Japanese Islands and DSDP Holes in the equatorial to high latitude regions of the Pacific Ocean were analyzed in an effort to reconstruct their late Pliocene paleobiogeography. While the late Pliocene assemblages in the equatorial to middle latitude regions are comprised primarily of discoasters, both the high latitude and Japan Sea samples record an abrupt change from a Reticulofenestra-Dictyococcite assemblage to a Coccolithus pelagicus assemblage at 2.75 Ma. The northernmost boundary of the Discoaster assemblage moved southward in the East China Sea (western Pacific Ocean) at that time. These changes in the calcareous nannofossil paleobiogeography indicate the strong influence of heavy glaciation in high latitude to arctic regions of the Pacific Ocean. This also correlates with the final closure of the Central American seaway at 2.75 Ma.