OLIGOCENE-MIOCENE CHRONOSTRATIGRAPHY DEDUCED FROM CALCAREOUS NANNOFOSSIL IN TUBAN AREA, NORTH EAST JAVA BASIN Salsabila Reno, Rendy, Dewi Syavitri, Risma Amalia
Trisakti University
Abstract
Calcareous nannofossil biostratigraphy from 125 rock samples of wells SR-1 and SR-2 in the Tuban area, East Java were analyzed to reconstruct the chronostratigraphy of the north East Java Basin. These two wells are located in the Rembang Zone and the lithological unit is part of the Kujung and Ngimbang Formation. This research aims to determine the age of the SR-1 and SR-2 wells, the timing of unconformity, and determine the chronostratigraphic framework of the depositional history of the study area. The samples for this study were prepared using the smear slide method and a polarized microscope was used for the determination of the calcareous nannofossils assemblages, especially the distribution of index species. Based on biostratigraphic analysis, the age of the lithological unit in SR-1 is NP23-NP24 of early-late Oligocene and for SR-2 is NP23-NN4 of early Oligocene to early Miocene. The unconformity is only detected in SR-2, characterized by missing NN1 and NN2. The interpretation of the chronostratigraphic chart confirms that the oldest known deposition process in the area starts from NP23-NP25, in which the transgressive period due to the global sea level change rises during the ^Late Oligocene Warmth Event^. After that, an unconformity occurred at the NN1-NN2 caused by the Mi-1 Glaciation in the transition of the Oligo-Miocene Epoch. The deposition resumed at NN3-NN4 of the early Miocene during the transgressive period during the Mid-Miocene Climatic Optimum. This research hopefully can be useful and contribute to oil and gas exploration studies, as well as be used as a reference for biostratigraphy for further study.
Keywords: North East Java Basin, Calcareous Nannofossil, Biostratigraphy, Chronostratigraphy
