Identifikasi Karakteristik Batupasir Formasi Arjosari Berdasarkan Analisis Petrologi dan Petrografi di Daerah Wonosidi dan Sekitarnya, Kabupaten Pacitan, Provinsi Jawa Timur
DOI:
https://doi.org/10.29303/goescienceed.v7i4.3412Keywords:
Sandstone, Arjosari Formation, Petrology, Petrography, Carbonate, Non-carbonate.Abstract
The Arjosari Formation is one of the rock units exposed in the Southern Mountains Zone of Java and is characterized by various lithologies, including sandstone with carbonate and non-carbonate characteristics. These differences reflect variations in sediment composition and depositional processes that are important to be further investigated. This study aims to identify the characteristics of sandstone from the Arjosari Formation based on petrological and petrographic analyses in the Wonosidi area and its surroundings, Pacitan Regency, East Java Province. The methods used in this study include field observations to determine the macroscopic characteristics of the rocks, rock sampling, and petrographic analysis using thin sections under a polarizing microscope at 40× magnification. The analysis was conducted descriptively and interpretatively by examining texture, grain size and shape, sorting, packing, mineral composition, matrix, cement, grain contacts, and porosity. The results show that the carbonate sandstone consists of quartz, calcite, and sedimentary lithic fragments, with clay and micrite as matrix and carbonate and clay as cement. Meanwhile, the non-carbonate sandstone is dominated by quartz, plagioclase, and sedimentary lithic fragments, with clay-dominated matrix and cement. Both sandstone types exhibit intergranular porosity and have undergone compaction and cementation processes. The occurrence of carbonate and non-carbonate sandstone within the same Arjosari Formation indicates variations in the supply of siliciclastic and carbonate materials during sedimentation. The results demonstrate that the integration of petrological and petrographic analyses provides a better understanding of the rock characteristics and the transportation, deposition, and diagenetic processes affecting the sandstone of the Arjosari Formation.
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