This paper discusses the results of a study of calcareous nannofossils in 144 selected field
samples collected from four formations, namely, Aksitero, Moriones, Malinta and Tarlac, exposed on the western part of Tarlac Province in Central Luzon basin, and attempts to interpret the biostratigraphy of the area based on the said group of fossils. A total of 96 species belonging to 24 genera have been identified and plotted on calcareous nannofossil charts. A brief discussion on the nannofloral characteristics of the formations is given, and a tentative zonation scheme for the study ·area has been prepared and correlated to existing nannofossil and planktonic foraminiferal zonations.

The investigation has revealed that the sequence of calcareous nannofossil markers in the western part of the basin is similar to those that are found in some local areas and other parts of the world. Except for the absence of few important indices which probably is the result of paleoenvironmental exclusion and/or preservational factors, diagnostic species and  nannofossil assemblages characteristic of deep, open-marine environment are present in the basin. A total of eleven nannofossil zones of Martini (1971) within the Upper Oligocene to Upper Miocene have been recognized in the area of study.