Nannofossil Diversity and Biostratigraphy of Kebo Butak Formation from Kalinampu Area, Bayat - Central Java

The research location is part of the Kebo Butak Formation, where the outcrop is well-exposed in Kalinampu, Jarum Village, Bayat – Central Java. Nannofossil was prepared on 20 samples using gravity settling and observed under a light microscope with 1000x magnification. Nannofossil analysis of abundances and diversity in this area revealed 21 species and 7 genera. Biostratigraphic analysis showed that the Kebo Butak Formation in Kalinampu section can be divided into Furcatolithus predistentus Zone (CNO4/NP24), Sphenolithus ciperoensis Zone (CNO5/NP25), Shenolithus delphix Zone (CNO6/NP25) and Discoaster druggii Zone (CNM1/NN1). These results confirm that the Kebo Butak Formation age was deposited in a marine environment during the Late Oligocene (26.93 Ma) to Early Miocene (23.06 Ma).