PALINSPASTIC RECONSTRUCTION OF GEOLOGICAL STRUCTURES AT KALI LUTUT AND ITS SURROUNDINGS, KENDAL-TEMANGGUNG, JAWA TENGAH

• Main Author: Adha, Ikhwannur
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/37085
• Institution: Institut Teknologi Bandung

Kali Lutut is a location for special rocks series outcrop that called Lutut Beds, which are composed of sandstones and limestones with abundant quartz minerals and fragment of various types of rocks such as metamorphic rocks, volcanic rocks, basement rocks, and carbon fragment. Van Bemmelen classified this rocks series into North Serayu Basin, while Thanden et al., classified into Kendeng Basin. There is also Cipluk Oil Field in study area that can support subsurface data. This research was conducted to reconstruct the geological structure condition in Kali Lutut and its surroundings. The purpose of this study is to know geological structures characteristics, deformation evolutions, and paleogeography conditions, also its implication to hydrocarbon existence in Kali Lutut and its surroundings will be known. This research is generally based on field data evaluation combined with seismic data. Field data is obtained through direct investigation to determine geological conditions of the study area and rock sampling. Based on field data, petrographic analysis, and fossil analysis combined with straightness analysis and geological structure analysis, a geological map of study area was produced. Geological cross section is made based on geological map and seismic interpretations carried out by dip-domain method to describe subsurface conditions of the study area. Three geological cross sections have been made to carry out palinspastic reconstruction with balance cross-section method based on the flexural-slip model. It is also reconstructed in fence diagram to see topographic changes in each deformation. Stratigraphy of Kali Lutut and its surroundings consist of Basement, Pelang Formation, Kerek Formation that intruded by Andesite Intrusion, Penyatan Formation, Kaligetas Formation, Damar Formation, and Alluvium. Geological structures of study area can be classified into three groups based on its occurrences. They are normal fault group, thrust fault and fold group, and strike-slip fault group. Characteristic of thrust fault is fault-propagation fold that forming imbrication thrust fault. Thrust fault have east-west orientation with detachment between Kerek Formation-Basement Rock and Pelang Formation boundary in four to five kilometers depth. Based on reconstruction, study area have three deformations. First deformation was occurred on Basement Rock and extensionally in Eocene-Oligocene. Its strain is 4,2 - 9,4% extension. Second deformation was occurred in Late Miocene-Pliocene on Kerek Formation and shortening. Its strain is 29,6 - 44,5% shortening. Third deformation was occurred in Pliocene-Pleistocene and strike-slip fault formed in younger formation. Reconstruction show geometry of study area when Kerek Formation deposited was basinward to the south. Hydrocarbon are found in the west area of study area. It is part of Cipluk Oil Field and abandoned. Based on reconstruction, thrust fault is hydrocarbon migration path and formed anticline that can be structural trap in several area. Based on restoration and constant geothermal gradient approach, it show Kerek Formation and Pelang Formation reach maturity since Late Miocene. But last study of source rock from hydrocarbon sample show Kerek Formation and Pelang Formation which are deposited on deep marine, is not its source rock. Source rock of study area interpreted from outside.