The effect of trace fossil to porosity and permeability of Halang Formation, Cipari area, Cilacap, Central Java

• Main Author: ARI SETIAJI - NIM : 22015013, ROMY
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/30669
• Institution: Institut Teknologi Bandung

<p align="justify">Diagenesis is one of the important things in sedimentary rock. One part of the sedimentary rock diagenesis is the process of reworking the grains by an organism, known as the bioturbation process, that produces trace fossils. As a result of the bioturbation process it affects the porosity and permeability of sedimentary rocks. However, research on the relationship between the presence of trace fossils with porosity and permeability is rare. In this research, the stratigraphic cross-section measurement on one section and the observation of trace fossil on the Halang Formation sandstone layer then analyzed porosity and permeability by using porosimetri of helium gas and petrography to determine the porosity and permeability and the minerals of the trace fossil. <br /> <br /> The result is a Cipari area composed by tuffaceous sandstones, sandstones, and claystone. Twelve types of trace fossils were identified, including Arenacolites, Bergaueria, Chondrites, Cylindrichnus, Ophiomorpha, Paleophycus, Planolites, Rhizocorallium, Scolicia, Skolithos, Thalasinoides, and Zoophycus. Based on the density of the trace fossils on each layer, the overlap between the trace fossils, and the original packing contained in each layer of the Halang Formation sandstone, can be divided into six bioturbation index: 0 (0%), index 1 (1-10%), index 2 (11-30%), index 3 (31-50%), index 4 (51-70%), index 5 (71-95), and index 6 (100%). 39 chip samples have been carried out porosity and permeability measurements using helium gas as test medium. The result is that the presence of trace fossils in sedimentary rocks can increase the porosity and decrease the permeability. Based on these observations, the factors that influence the porosity and permeability of a rock in relation to the presence of trace fossils are grain packing, mineralogy, and bioturbation index. <br /> <br /> Keywords: Halang Formation, Cipari, trace fossils, porosity, permeability.<p align="justify">