Stratigraphic Variations And Structural of Autobreccia: Implications Of Edaphic Potential in The Merapi-Ranti Volcanic Transition Zone, Geopark Ijen

¹ Departemen Geografi, Fakultas Ilmu Sosial, Universitas Negeri Malang, Jalan Semarang No. 5, Malang, East Java
³ Geology Geopark Ijen, Jalan Gajah Mada, Banyuwangi, East Java

^* Corresponding author: melatijuliarahma.fis@um.ac.id

Abstract

The transition zone between the Merapi Formation and the Ranti Formation in Kalibendo, Ijen Geopark, provides information in the form of rock outcrops that are used as parameters to understand and reconstruct geological phenomena in the past. The main problem in this study is the lack of clear stratigraphic information regarding the boundary between the two formations on geological maps and in previous studies. This study aims to reveal the stratigraphic sequence, identify autobreccia structures, and assess the edaphic implications in the Merapi–Ranti transition zone. This study uses a systematic method in the form of field observations and edaphic potential analysis as well as reconstructing geological phenomena and their potential for the surrounding environment. Based on rock outcrops at the research site, the stratigraphic sequence shows lava rocks from the Merapi Formation stacked on lava rocks from the Ranti Formation, indicating sequential formation. The discovery of autobreccia structures between the two formations is evidence of the interaction between molten lava from the Ranti Volcano and lava that had solidified from the Merapi Volcano. In addition, the diversity of rock and mineral structures is an indicator in reconstructing geological phenomena. Mineral diversity also correlates with edaphic potential, where soil resulting from the weathering of volcanic rocks is rich in minerals that can release nutrients, contributing to the formation of soil with high cation exchange capacity (CEC) that has long been utilized by the Osing ethnic for agriculture.