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KARAKTERISTIK PETROLOGI KOMPLEKS INTRUSI KECAMATAN CIKALONGKULON KABUPATEN CIANJUR JAWA BARAT Firmansyah, Fahmi; Nugroho, Rio Priandri
JGE (Jurnal Geofisika Eksplorasi) Vol 10, No 2 (2024)
Publisher : Engineering Faculty Universitas Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.23960/jge.v10i2.394

Abstract

Penelitian tentang karakteristik batuan beku dapat berkontribusi pada penelitian lanjut tentang potensi sumber daya lainnya yang terkait dengan fenomena magmatisme, khususnya di lokasi yang memiliki sejarah magmatisme cukup panjang seperti di bagian barat Pulau Jawa. Studi karakteristik petrologi batuan beku pada penelitian ini dilakukan dengan menggunakan sampel yang diperoleh dari Cikalongkulon, Cianjur, Jawa Barat; sebuah lokasi dengan kompleks tubuh intrusi yang membentang hampir Barat-Timur. Dilakukan pengamatan lapangan dan petrografi guna menghasilkan sintesis terkait interaksi antaran tubuh batuan beku dan batuan samping di daerah penelitian. Dari observasi didapati bahwa terdapat metasomatisme yang terjadi akibat proses intrusi andesit terhadap batuan samping. Proses ini terjadi pada rentang suhu 270-320°C yang ditandai oleh kemunculan mineral sekunder berupa klorit, serisit, kalsit, kuarsa, dan epidot. Keberadaan metasomatisme ini juga mengindikasikan bahwa umur tubuh intrusi andesit harus lebih muda dari Miosen Tengah, berbeda dari interpretasi awal pada Peta Geologi Lembar Cianjur yang menempatkan tubuh batuan beku lebih tua dari batuan sedimen di sekitarnya.
Flow dynamics of unsteady pyroclastic density currents (PDC) from Sunda ignimbrite, West Java, Indonesia Ramadhan, Ilmi; Angkasa, Syahreza Saidina; Nugroho, Rio Priandri
Bulletin of Scientific Contribution Vol 19, No 2 (2021): Bulletins of Scientific Contribution : Geology
Publisher : Fakultas Teknik Geologi Universitas Padjadjaran

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24198/bsc.v19i2.35272

Abstract

Sunda Volcano is the one of several volcanoes in Indonesia which produced ignimbrite deposit from caldera forming eruption. Depending on the volume and considerable thickness of the deposits, Sunda ignimbrite might has been deposited with a variety of flow mechanisms. Heterogeneous deposition mechanism will heavily controlled by numerous parameters such as velocity, rheology, types of flow-boundary zone, or pre-existing topographic influence. According to the deposition parameters, Pleistocene Sunda ignimbrite transportation and deposition mechanisms are still unclear. Here we show detailed observations of each facies and the Unconformity Bounded Stratigraphic Units (UBSU) approach to determine the flow sub-units and flow mechanism of the Sunda ignimbrite. Overall, we found that Sunda ignimbrite consists of five different facies. Forestepping stacking pattern from Sunda ignimbrites also observed from stratigraphic correlation indicates that energy instability occurred during transport and deposition in the PDC. Waxing energy of PDC which occured is caused by the development of granular-flow and fluid-escape dominated flow-boundary zone at the base and body of emplaced PDC. Our results demonstrate how Sunda ignimbrite emplacement mechanism can be affects by pre-existing topography which developed during the effusive eruption of Sunda Volcano. Furthermore, we also found that Sunda ignimbrite deposition has been changed the topography into the gentler relief due to this forestepping pattern of each ignimbrite units. The study of Sunda ignimbrite facies can reveal suitable hazard mitigation and also use to characterize heterogenity in groundwater aquifers and geothermal reservoirs. Moreover, detailed facies analysis and UBSU could give us informations on how explosive eruption at 0.205 M.a take places on the southern flank of Sunda Volcano.
KARAKTERISTIK PETROLOGI KOMPLEKS INTRUSI KECAMATAN CIKALONGKULON KABUPATEN CIANJUR JAWA BARAT Firmansyah, Fahmi; Nugroho, Rio Priandri
JGE (Jurnal Geofisika Eksplorasi) Vol. 10 No. 2 (2024)
Publisher : Engineering Faculty Universitas Lampung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.23960/jge.v10i2.394

Abstract

Penelitian tentang karakteristik batuan beku dapat berkontribusi pada penelitian lanjut tentang potensi sumber daya lainnya yang terkait dengan fenomena magmatisme, khususnya di lokasi yang memiliki sejarah magmatisme cukup panjang seperti di bagian barat Pulau Jawa. Studi karakteristik petrologi batuan beku pada penelitian ini dilakukan dengan menggunakan sampel yang diperoleh dari Cikalongkulon, Cianjur, Jawa Barat; sebuah lokasi dengan kompleks tubuh intrusi yang membentang hampir Barat-Timur. Dilakukan pengamatan lapangan dan petrografi guna menghasilkan sintesis terkait interaksi antaran tubuh batuan beku dan batuan samping di daerah penelitian. Dari observasi didapati bahwa terdapat metasomatisme yang terjadi akibat proses intrusi andesit terhadap batuan samping. Proses ini terjadi pada rentang suhu 270-320°C yang ditandai oleh kemunculan mineral sekunder berupa klorit, serisit, kalsit, kuarsa, dan epidot. Keberadaan metasomatisme ini juga mengindikasikan bahwa umur tubuh intrusi andesit harus lebih muda dari Miosen Tengah, berbeda dari interpretasi awal pada Peta Geologi Lembar Cianjur yang menempatkan tubuh batuan beku lebih tua dari batuan sedimen di sekitarnya.
Preliminary Result on Optimum Seed Generation Bandwidth for Object-Based Image Segmentation (OBIS) of Porphyritic Igneous Thin Sections Nugroho, Rio Priandri; Widjaya, Victoria Vania Blanca; Roviansah, Mohamad
Jurnal Geologi dan Sumberdaya Mineral Vol. 25 No. 1 (2024): JURNAL GEOLOGI DAN SUMBERDAYA MINERAL
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.33332/jgsm.geologi.v25i1.698

Abstract

Crystal size distribution (CSD) analysis is one of many methods for studying the crystallization history of magma. It involves labor-intensive digitation of all crystals, which may prolong the processing of large data sets. This study presents a preliminary result of Object-Based Image Segmentation (OBIS) as a semi-automatic approach in crystal digitation. Five data sets containing 9 photomicrographs of porphyritic igneous rock thin sections were processed using SAGA GIS. The procedure produced an optimum bandwidth equation of y = 38.455 ln(x) + 114, where x is the average size of sampled crystal in mm. Segmentation tests on another sample using the formula returned good and consistent results with important notes on sensitivity to textures which may result in crystal segment separation, such as fractures, veins, and sieve, as well as the inability to separate all groundmass crystals. Even though it shows good results, this formula only applies where the pixel-to-length conversion factor of 562.2 pixel/mm. Keywords: OBIS, SAGA GIS, Optimum bandwidth, Photomicrograph, Porphyritic igneous rock thin section.
Semi-Automatic Segmentation of Igneous Rocks Thin Section Using SAGA: Application on Crystal Size Distribution (SCD) Based Residence Time Approximation Tangkulung, Tria Jessica; Terok, Johanes Timoty Jeremi; Nugroho, Rio Priandri; Hidayat, Muh Nur
Journal of Geoscience, Engineering, Environment, and Technology Special Issue from The 2nd International Conference on Upstream Energy Technology and Digitalization
Publisher : UIR PRESS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.25299/jgeet.2025.10.1.1.24271

Abstract

Crystal Size Distribution (CSD) is a quantitative method used to assess magmatic processes such as cooling rates, crystallization durations, and crystal growth dynamics. Traditionally, mineral segmentation in CSD analysis is performed manually, which is labor-intensive, particularly for large datasets. This study investigates a semi-automatic segmentation approach to improve efficiency in analyzing thin sections of igneous rocks. The segmentation process is divided into two methods: semi-automatic segmentation using SAGA software and manual segmentation for validation. The analysis focuses on phenocrysts (>0.2 mm) and microphenocrysts (0.2–<0.02 mm), with images taken using a polarizing microscope at 4x magnification. While the semi-automatic method showed limitations due to the thin section texture and the inherent characteristics of the OBIA algorithm, it proved effective in estimating magma residence time with an average absolute error of 0.4 years. Additionally, the method demonstrated a mean regression gradient error of 79% for microphenocrysts and 55% for phenocrysts, supporting its application in magma dynamics interpretation. This approach enhances the practicality of CSD analysis, particularly in large datasets, and provides a valuable tool for studying crystallization processes in igneous rocks. However, direct application for interpreting magma dynamic should be done with caution.
Landslide Susceptibility Mapping Using Logistic Regression Methods in Bogor Regency Assyidiqi, Sutan Vasya; Roviansah, Mohamad; Sujaka, Muhammad 'Azza; Nugroho, Rio Priandri; Misbahudin
Journal of Geoscience, Engineering, Environment, and Technology Special Issue from The 2nd International Conference on Upstream Energy Technology and Digitalization
Publisher : UIR PRESS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.25299/jgeet.2025.10.1.1.24273

Abstract

Landslides are a recurrent hazard in Bogor Regency, where steep volcanic terrain, high rainfall, varied lithology, land-use changes and active faults contribute to slope instability. This study presents the first regency-wide landslide susceptibility model using Logistic Regression supported by field validation. A dataset of 220 landslide occurrences from 2017 to 2022 and multiple geospatial factors including rainfall, slope, lithology, landcover, and NDVI was analyzed using a 70:30 train–test split to generate coefficient weights, probability surfaces and a binary susceptibility map derived from ROC-AUC thresholds. Landcover shows the strongest positive influence on landslide occurrence, whereas NDVI has the strongest negative effect, reflecting the stabilizing role of vegetation. Fault proximity exhibits near-zero influence, likely due to inactive structures or limited spatial resolution. The model achieved 82 percent accuracy with an AUC of 0.86. Susceptibility clustering near historical data suggests possible inventory bias. Improving model reliability will require more evenly distributed landslide data and UAV-based mapping to detect vegetation-covered past landslides.