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Bulletin of Geology
Published by Institut Teknologi Bandung
ISSN : 25800752     EISSN : 25800752     DOI : 10.5614/bull.geol.
Core Subject : Science, Engineering,
Earth & Planetary Sciences Energy Engineering
Bulletin of Geology is a research-based periodical scientific open access journal published by Faculty of Earth Sciences and Technology, Institut Teknologi Bandung (ITB). The published article in Bulletin of Geology covers all geoscience and technology fields including Geology, Geophysics, Geodesy, Meteorology, Oceanography, Petroleum, Mining, and Geography. The submitted abstract must be written in English and Bahasa Indonesia, but the article content is English or Bahasa Indonesia.
Arjuna Subject : Ilmu Bumi dan Planet (semua kategori) - Geologi
Articles 100 Documents
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POTENSI PENGAYAAN TIMAH PRIMER DAN SEKUNDER SERTA UNSUR TANAH JARANG DI DAERAH SIMPANG PESAK, KABUPATEN BELITUNG TIMUR Yan Rizal
Bulletin of Geology Vol 5 No 3 (2021): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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Abstract Enrichment studies for primary and secondary tin and rare earth elements were carried out in the Simpang Pesak area, East Belitung Regency which is located at the coordinates of UTM 823865 - 827977 mE and 9653722 - 9658725 mS. This study was conducted to determine potential areas for primary and secondary tin content and rare earths in plaser deposits and granite source rock. The analysis was carried out on primary data taken directly in the field, in the form of rock samples and plaser sediment samples. Plaser sample analysis was carried out on three grain size fractions, namely fraction # 48 (297-354 μm), fraction # 100 (149 μm) and fraction -100 (<149 μm). Geochemical analysis using X-Ray Fluorescence (XRF) Portable on rock samples and plaser sediment concentrates to be carried out the levels of lead and rare earth elements. Univariate statistical analysis was performed to determine the limit value of elemental anomalies. Grain Counting Analysis (GCA) was also carried out on samples of plaser sediment to see the minerals contained in these deposits. Rare earth elements found in the study area include yttrium, cerium, and lanthanum. High levels of lead are in the southern part and some in the middle of the study area. High grade rare earth elements are well known in the central part of the study area. Tin and rare earth anomalies are enriched in the morphology of river steps with ancient alluvial plaser types. The factors that influence the anomaly area are ordering process, source rock, and morphology. Further exploration started from the west to the southeast towards the north towards the granite hills in the study area.
MULTIPARAMETER LAND SUBSIDENCE VULNERABILITY ASSESSMENT THROUGH SATELLITE IMAGERY, GIS, AND SPATIAL DATA INTEGRATION Sinatrya Diko Prayudi
Bulletin of Geology Vol 7 No 4 (2023): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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Land subsidence is a substantial issue today, particularly in some regions where it has the ability to interrupt future development, halt the process, and even modify the development plan. In general, this study focuses on updating current knowledge on land subsidence and performing risk assessments using a case study in Semarang City, Central Java, where land subsidence is a serious problem. Several satellite imageries, such as Sentinel-1 and Sentinel-2, are used as databases in this work, with various target analysis and Geographic Information Systems (GIS) methods used to handle and alter the data. Sentinel-1's radar data, along with the displacement analysis approach of Differential Interferometry Synthetic Aperture Radar (DInSAR), is primarily used to provide a snapshot of the present state of land subsidence under this area in 2022. The result demonstrates the variation of vertical displacement values ranging from -7.7 to 6.65 cm with subsidence spread mostly in the northern region, using two datasets with 60-day intervals between January and March. Using a combination of the Normalize Difference Vegetation Index (NDVI) and the Normalize Difference Built-in Index (NDBI) to create Built-up Index (BU) data, the Sentinel-2 data with optical-based images was then used to map the human-made feature and expansions, notably buildings. Each piece of information considered multiparameter was afterwards overlapped to build a vulnerability map, while also considering the geological dataset and validated by ground verification. This finding will be presented to the section of the city that can help support the city's future growth in terms of its vulnerability to land subsidence dangers.
STUDI GEOMEKANIKA DAN NILAI KEGETASAN UNTUK EVALUASI POTENSI GAS SERPIH FORMASI BATU KELAU CEKUNGAN KUTAI Daniel Radityo; Benyamin Sapiie; Yusup Iskandar
Bulletin of Geology Vol 3 No 1 (2019): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/bull.geol.2019.3.1.4

Abstract

Gas serpih merupakan gas yang terbentuk di batuan induk berupa serpih dan berperan sebagai reservoir. Akumulasi gas serpih terjadi dikarenakan batuan tersebut memiliki nilai porositas dan permeabilitas yang rendah. Gas serpih memerlukan kajian geomekanika, geokimia, dan petrografi formasi sebagai batuan induk dan batuan reservoir. Penelitian ini memiliki tujuan untuk menjelaskan proses karakterisasi fasies serpih Formasi Batu Kelau berdasarkan perbedaan kondisi geologi, geomekanika, dan geokimia; dan memberikan informasi tentang kriteria perekahan buatan yang sesuai untuk dapat mendistribusikan gas pada setiap fasies serpih Formasi Batu Kelau. Penelitian dilakukan pada Formasi Batu Kelau di Cekungan Kutai, Provinsi Kalimantan Timur. Penelitian ini menggunakan data lapangan, data log sumur, data seismik, dan data geokimia. Data log sumur diolah kemudian menghasilkan data petrofisika serpih, geomekanik, dan geokimia. Data lapangan dan XRD dilakukan untuk mendukung data log sumur sebagai korelasi stratigrafi. Kemudian dilakukan penarikan horizon Formasi Batu Kelau dengan strukturnya pada interpretasi seismik. Hasil interpretasi seismik menghasilkan Peta Stuktur Kedalaman, Peta Ketebalan dan Peta Paleogeografi umur Eosen Akhir Formasi Batu Kelau. Peta Kandungan Serpih, Peta Fasies Serpih, Peta Indeks Kegetasan, dan Peta Distribusi TOC di dapat dari hasil proses petrofisika. Data TOC, BI, dan kandungan serpih kemudian digabungkan sehingga dapat dibuat Peta Potensi Gas Serpih Formasi Batu Kelau. Proses petrofisika terbagi menjadi 3 tahap berupa petrofisika properti serpih yang membahas kandungan serpih, kandungan mineral, porositas, permeabilitas, saturasi air; petrofisika geomekanik yang membahas UCS, nisbah poisson, modulus elastisitas, indeks kegetasan dan petrofisika geokimia yang membahas TOC metode Passey. Penentuan Indeks kegetasan mengunakan metode indeks kegetasan rata-rata dengan menggunakan parameter nisbah poisson dan modulus elastisitas. Perhitungan TOC metode Passey membutuhkan log resistivitas dan sonik. Hasil petrofisika properti sepih, petrofisika geomekanik, dan petrofisika geokimia digabungkan dan kemudian di analisis. Kata kunci: Formasi Batu Kelau, gas serpih, geokimia, geomekanika, indeks kegetasan
EFEK AKURASI DAN GEOMETRIK SISTEM TINGGI DIGITAL ELEVATION MODEL (DEM) TERHADAP PEMODELAN BAHAYA BANJIR ROB DI JAKARTA Firman Juliandri; Heri Andreas; Dhota Pradipta
Bulletin of Geology Vol 6 No 2 (2022): Bulletin of Geology Special Issue: International Seminar on Earth Sciences and Te
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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The research aims to analyze the effect of DEM for accuracy and geometric height systems in regard with the results of tidal flood hazard modeling in Jakarta by comparing the modeling results from several DEM data that have different accuracy and by comparing the modeling results between global geoid datum and local datum refer to sea-level height. The high-accuracy DEM LiDAR model was used as a baseline to measure the accuracy between models. The DEMNAS-based model exhibits the result in the flooded area closest to the DEM LiDAR-based model with a ratio of 97%. The open-access Model i.e., DEM SRTM (30 m), DEM TanDEM-X (60 m), and DEM AW3D (30 m), shows a flooded area ratio about 5% - 48% with respect to DEM LiDAR-based model. The comparison between the model indicated a positive correlation between the vertical accuracy and spatial resolution of DEM with the accuracy of the tidal flood hazard model in Jakarta. Model using global geoid datum EGM2008 shows an inundated area less than 30% with respect to the inundated area from model using the Highest Astronomical Tide (HAT) tidal datum. The model validation shows the HAT tidal datum have optimum accuracy. Moreover, the HAT model provides a clear result that shows actual inundation points compared to other vertical datums. Furthermore, the comparisons between these models have been carried out to analyze the effect of model accuracy in regard to the results of the tidal flood risk assessment. The effect of low-accuracy DEM-based model exhibit the number of exposed populations about 2.2 – 54.0 and value of economic loss about 1.9 – 37.6 less times than the risk assessment using DEM LiDAR-based model.
STRUCTURAL CONTROL RELATED WITH MEDIUM-TO-VERY HIGH Au GRADE AT PIT B EAST AND B WEST, TUJUH BUKIT MINE, EAST JAVA Ilham Aji Dermawan; Andri Slamet Subandrio; Alfend Rudyawan; Arya Dwi Sanjaya; Rama Maharief; Krisma Anditya; Rizfan Hasnur; Muchamad Satya Muttaqien; Cicih Larasati Widya Fitri; Andi Pahlevi; Dedy Daulay; Agus Purwanto; Adi Adriansyah Sjoekri
Bulletin of Geology Vol 4 No 1 (2020): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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Tujuh Bukit generally consists of Late Oligocene – Middle Miocene volcanic and volcaniclastic Batuampar Formation. After tectonomagmatism took place at Pliocene, this stratigraphic unit altered and became a host rock for Pliocene economic mineralization. The research area located in open pit mining at Pit B East and B West. Both pits have an extensive area of ± 700 x 500 m2, projected on ± 9045100 – 9045600 mN and ± 174400 – 175100 mE UTM WGS 1984 zone 50S coordinate system. This research discusses structural control as the main role of alteration characteristics and Au high sulfidation epithermal mineralization system forming in open pit mining at Pit B East and B West, Tujuh Bukit mine. Main developed structural are Pliocene strike-slip system, relatively NW-SE and N-S orientation, with NNW-SSE principal stress following pure shear model. There is also relatively NW-SE normal fault and ENE-WSW thrust fault. All of these faults in the regional scale are NNW-SSE compressive tectonic compensation within one tectonic period. The strike-slip system resulting in normal fault and ridge zones within releasing stepover, releasing bend, and restraining bend structural geometry. Strike-slip faults in Pit B East and B West are the smallest strike-slip system within Tujuh Bukit regional scale. Developed structural geology representing recent tectonic of Java. Based on the field observation, core drilling, ASD instrument scanning, and petrographic analysis, the alteration unit divided into five, there are quartz, quartz-alunite, quartz-kaolinite, kaolinite-montmorillonite-chlorite, and kaolinite-montmorillonite alteration unit. Based on field and mineragraphic observation, there found ore minerals such as pyrite, chalcopyrite, covellite, bornite, tetrahedrite, azurite, malachite, hematite, and goethite. All these minerals generally found associated with silicification alteration, such as quartz, quartz-alunite, and quartz-kaolinite alteration unit. Development of medium to very high-grade mineralization within silicification alteration unit generally took place in normal fault zones caused by the strike-slip system on the releasing bend (can be found on the bending line of BE 2 and BE 3 Fault) and releasing stepover geometry (on the area between BE 1-BE 2 Fault, the area between BW 2-BW 3 Fault, and the area between BW 5-BW 6-BW 7 Fault), and BW 4 normal fault which parallel to the principal stress on a regional scale.
Studi Fasies dan Elemen Arsitektur Formasi Ranggam Di Daerah Belo Laut, Kabupaten Bangka Barat Yan Rizal; Elvira Risyeu Nur Annisa
Bulletin of Geology Vol 5 No 2 (2021): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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Abstrak Pulau Bangka merupakan salah satu daerah dengan potensi timah dan mineral ikutan timah yang besar. Potensi timah danmineral ikutan timah dijumpai sebagai endapan primer dan endapan plaser. Endapan plaser di pulau Bangka dikelompokkan sebagai endapan undak sungai Purba dan Formasi Ranggam. Formasi Ranggam merupakan endapan sedimen sungai yang berumur Tersier. Formasi Ranggam tersusun atas 9 litofasies, yaitu Fasies Konglomerat Pasiran (SG), Batupasir Halus (FS),Batupasir Konglomeratan (GS), Batulanau Tufan (TSL), Batupasir Silang-siur Planar (S-p), Batupasir Konglomeratan Gradasi Terbalik (SG-i), Batulempung (CL), Batulempung – Batupasir (CLS), Batupasir Tufan (TS). Berdasarkan pada Elemenarsitekturnya Formasi Ranggam diendapkan dalam lingkungan sungai sebagai endapan channel fill, floodplain, natural levee,dan crevasse splay. Kata kunci: Bangka, Formasi Ranggam, Litofasies, Elemen Arsitektur Abstract Bangka Island is one of the areas with a large potential for tin and tin associated minerals. The potential for tin and lead associated minerals is found as primary deposits and plaser deposits. Plaser deposits on the island of Bangka are grouped as deposits of the ancient river steps and the Ranggam Formation. The Ranggam Formation is a Tertiary river sediment deposit. The Ranggam Formation is composed of 9 lithofacies, namely the Facies of the Pasiran Conglomerate (SG), Fine Sandstone (FS), Conglomerate Sandstone (GS), Tufan Silicate Sandstone (TSL), Planar Cross-sectional Sandstone (Sp), Reverse Gradation Conglomerate Sandstone (SG-i ), Claystone (CL), Claystone - Sandstone (CLS), Tuffan Sandstone (TS). Based on its architectural elements, the Ranggam Formation is deposited in a river environment as channel fill, floodplain, natural levee, and crevasse splay deposits. Keywords: Bangka, Ranggam Formation, Litofasies, Architectural Elements
ANALISIS KESTABILAN LERENG BATUAN MENGGUNAKAN STUDI PERBANDINGAN KLASIFIKASI MASSA BATUAN RMR, RMI, DAN GSI PADA POTENSI LONGSORAN GULING DI DAERAH CIPATAT, KABUPATEN BANDUNG BARAT, JAWA BARAT Hasan Tri Atmojo
Bulletin of Geology Vol 7 No 3 (2023): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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Pada analisis kestabilan lereng batuan diperlukan penentuan massa batuan dari sebuah lereng. Untuk mendapatkan nilai massa batuan tersebut diperlukan uji parameter yang menyangkut karakteristik dan kondisi diskontinuitasnya. Pada penelitian ini digunakan studi perbandingan klasifikasi massa batuan terhadap lereng batuan, yaitu klasifikasi Geological Strength Index (GSI) dan Rock Mass Rating (RMR) dengan objek penelitian pada lereng batuan yang berada di Tebing Bancana, Daerah Cipatat, Kabupaten Bandung Barat, Provinsi Jawa Barat. Lokasi tersebut berada pada morfologi bentuk lereng terjal dengan litologi dominan berupa batugamping yang memiliki potensi longsoran guling. Tujuan dari studi perbandingan ini yaitu untuk menentukan dan mengevaluasi metode yang tepat untuk analisis kestabilan lereng berdasarkan nilai properti keteteknikan beserta nilai faktor keamanan yang dihasilkan. Metode klasifikasi massa batuan tersebut dianalisis menggunakan metode kesetimbangan batas dari peranti lunak Roctopple. Hasil analisis dari batugamping kalkarenit yang berada di Tebing Bancana memiliki nilai properti keteknikan klasifikasi massa batuan RMR yang lebih besar meliputi kohesi, sudut geser dalam, dan modulus deformasi berdampak pada nilai faktor keamanan dari lereng cenderung lebih besar dari metode GSI. Berdasarkan hasil analisis kinematik, lereng batuan memiliki potensi longsoran guling. Faktor keamanan yang diperoleh dengan menggunakan metode kesetimbangan batas menghasilkan nilai 0,95 dengan probabilitas longsoran 59,7%. Uji sensitivitas yang dilakukan terhadap pengaruh longsoran guling di sini didapatkan bahwa faktor yang paling berpengaruh pada longsoran guling di antaranya kohesi (toppling joints), sudut geser dalam (toppling joints), kemiringan (toppling joints), tinggi lereng, dan sudut kemiringan lereng. Kata kunci: Klasifikasi massa batuan, kestabilan lereng, longsoran guling, metode kesetimbangan batas
DISTRIBUSI CHANNEL STEPNESS INDEX ZONA SESAR CIMANDIRI UNTUK IDENTIFIKASI JALUR SESAR AKTIF Rahmat Indrajati
Bulletin of Geology Vol 2 No 2 (2018): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/bull.geol.2018.2.2.2

Abstract

Zona Sesar Cimandiri dapat dilihat dari data citra satelit berupa kelurusan punggungan dan lembah dari teluk Pelabuhanratu, Kabupaten Sukabumi hingga Padalarang, Kabupaten Bandung. Sesar Cimandiri merupakan sesar aktif, karena terdapat gempabumi dangkal di sekitar sesar dan mengalami pergerakan horizontal berdasarkan pengamatan GPS. Gempabumi yang terjadi jarang melebihi magnitudo 6 Mw sehingga morfologi sesar tidak terlalu terlihat, sehingga jalur sesar aktif sulit didentifikasi. Perhitungan channel stepness index merupakan salah satu metode untuk mengenali sesar aktif dari profil sungai. Profil sungai yang dianalisa di sepanjang zona Sesar Cimandiri menunjukkan nilai ksn > 100 m0.9 merupakan nilai pada zona sesar aktif. Jalur sesar yang diperoleh adalah segmen Mekarasih, Cibatu, Tanjungsari dan Gandasoli. Jalur sesar diperoleh dari kompilasi data distribusi nilai channel stepness index, sejarah gempa, data seismisitas dan morfologi.
1D GEOMECHANICAL MODELING AND CRITICALLY-STRESSED FRACTURES ANALYSIS IN NATURALLY FRACTURED RESERVOIR, MUARA LABOH GEOTHERMAL FIELD, WEST SUMATRA, INDONESIA Taufik Al Amin; Marino Christiano Baroek; Sonny Santana; Benyamin Sapiie; Indra Gunawan
Bulletin of Geology Vol 6 No 1 (2022): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

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The effectiveness of geological structures to promote fluid flow is influenced by both geometric factors of the structural context and the local stress field. Multiple investigations have demonstrated that critically stressed fractures/faults promote dilatation and slip at flow-friendly zones. One-dimensional (1D) geomechanics and critically-stressed fractures analyses are carried out in one of the development well, ML-2, in Muara Laboh geothermal field, West Sumatra, Indonesia. The main purpose of this study is to establish the permeability pattern on fractures/faults and its relationship to the present-day in-situ stress. The analyses utilize wellbore data consisting of borehole images, gamma-ray (GR), shear and compressional sonic logs, pressure and temperature survey, and drilling data. Geomechanical modeling applies empirical stress estimation to log data and pressure test results, which is calibrated by stress polygon and the occurrence of wellbore failures. Linearized Mohr-Coulomb failure envelopes and failure criteria are used to determine the critically-stressed fractures. The 1D geomechanics model result shows that the in-situ stress regime in ML-2 well predominantly is strike-slip and the maximum horizontal stress direction is about N60°E, following far-field field stress direction. Critically-stressed fractures are more likely to happen in the NNE-SSW direction and its reciprocal. The high intensity of critically-stressed fractures tends to be associated with productive interval/feed zones.
GEOLOGI DAN SUMBERDAYA BATUBARA DAERAH SATIUNG – KUALA KUAYAN DAN SEKITARNYA, KABUPATEN KOTAWARINGIN TIMUR, PROVINSI KALIMANTAN TENGAH Yan Rizal; Muhammad Agung Akrom Fahmi; Hamzal Imanul Haq
Bulletin of Geology Vol 3 No 3 (2019): Bulletin of Geology
Publisher : Fakultas Ilmu dan Teknologi Kebumian (FITB), Institut Teknologi Bandung (ITB)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/bull.geol.2019.3.3.2

Abstract

Geological mapping on a scale of 1:25.000 was held in Satiung – Kuala Kuayan and its surrounding, East Kotawaringin, CentralKalimantan. The goal of this study is to identify the geological setting and coal potential in the research area. Primary data used in this research obtained from field observation and field data collection, such as outcrop data and drilling data. The stratigraphy of research area is divided into three unofficial units from the oldest to the youngest: Basement (Mesozoic), Dahor Formation (Pliocene – Pleistocene) and Alluvial. Coal quality of the study area shows lignite to sub-bituminous rank, with total resources is 291.737.730,9 Ton (measured 95.928.991,0 Ton and indicated 195.808.739,9 Ton).

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