SEQUENCE BIOSTRATIGRAPHY IN KANGEAN AREA, SUMENEP REGENCY, EAST JAVA BASIN

• Main Author: Nurmahdi, Naufal
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/75778
• Institution: Institut Teknologi Bandung

The Kangean Islands is located in Sumenep Regency, East Java Province. In the Kangean Area lies the East Java Basin, which is a hydrocarbon producer basin, so the development of oil and gas exploration activities becomes very important. A geological study of the exploration area is required for the development of oil and gas exploration activities in the area. The sequence biostratigraphy study that was conducted in this research is intended to study the geological setting of the Kangean area from time to time based on the sequence cycles. Therefore, this research presents some insights about the geology of the Kangean area based on sequence biostratigraphy. The sequence biostratigraphy started with biostratigraphy analysis to determine the biozonation, age, and depositional environment based on semiquantitative foraminifera microfossil distribution charts from three wells, which are I-1, J-2, and L-2. Lithology analysis was carried out to determine the lithology types of every formation based on rock sample descriptions that consist of ditch cuttings, sidewall core, and conventional core, as well as well logs such as gamma ray (GR) and spontaneous potential (SP). The analysis of the sequence framework is mainly based on biostratigraphy analysis results with the help of lithology analysis results to determine the sequence boundary (SB), lowstand system tract (LST), transgressive surface (TS), transgressive system tract (TST), maximum flooding surface (MFS), and highstand system tract (HST). The dating of those sequence components is also determined by using a dating model made from the datum of some selected foraminifera taxa that are known to have standard absolute dating. When those sequence components are already identified and dated, then sequence correlation can be executed to find out the lateral distribution and geological activities in each sequence. The analyses resulted in the conclusion that the interval of this research dates from the Late Oligocene up to the Late Pleistocene (N3 – N23), deposited on the upper bathyal up to the inner neritic environment. The formations that are present in the interval are the Prupuh Formation, Tuban Formation, Wonocolo Formation, Ledok Formation, Karren Formation, and Mundu Formation. There are 11 sequences, with 10 SB and 9 MFS. The sequence components that are known are SB-2 (19.1 mya), MFS-2 (18.5 mya), SB-3 (17.1 mya), MFS-3 (15.7 mya) SB-4 (14.3 mya), MFS-4 (13.6 mya), SB-5 (12 mya), MFS-5 (10.2 mya), SB-6 (8.6 mya), MFS-6 (7.9 mya), SB-7 (7 mya), MFS-7 (6.2 mya), SB-8 (4.7 mya), MFS-8 (3.5 mya), SB-9 (2.8 mya), MFS-9 (2.2 mya), SB-10 (2.1 mya), MFS-10 (1.9 mya), and SB-11 (0.9 mya). The result of sequence analysis and correlation shows the interpreted geological activity that happened in each sequence. Sequence 1 to Sequence 3 (Late Oligocene – Middle Miocene) shows that the Kangean area happened to be in the same geological setting, as evidenced by the limestone of the Prupuh Formation and claystone of the Tuban Formation that were found in every location. From Sequence 4 and the later (Middle Miocene – Late Pleistocene), the Kangean area separated into two different geological settings in the North and South, started by the presence of Karren Formation limestone that is exclusively found in the North. The separation of the Kangean area into two different geological settings is the result of the RMKS Fault Zone's activity and development.