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INDONESIA
IJOG : Indonesian Journal on Geoscience
Published by Geological Agency of Indonesia
ISSN : 23559314     EISSN : 23559306     DOI : -
Core Subject : Science,
Earth & Planetary Sciences
The spirit to improve the journal to be more credible is increasing, and in 2012 it invited earth scientists in East and Southeast Asia as well as some western countries to join the journal for the editor positions in the Indonesia Journal of Geology. This is also to realize our present goal to internationalize the journal, The Indonesian Journal on Geoscience, which is open for papers of geology, geophysics, geochemistry, geodetics, geography, and soil science. This new born journal is expected to be published three times a year. As an international publication, of course it must all be written in an international language, in this case English. This adds difficulties to the effort to obtain good papers in English to publish although the credit points that an author will get are much higher.
Arjuna Subject : -
Articles 814 Documents
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Pyrolysis Behaviour of Muara Enim Coals: The Influence of Temperature and Ranks Ulfa, Raden Maria; Esaki, Takehiro; Tambaria, Theodora Noely; Sugai, Yuichi
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.159-170

Abstract

Underground coal gasification (UCG) is a clean coal technology that converts coal in-situ into synthetic gas (syngas) through thermal and chemical reactions. Coal pyrolysis, a key reaction in UCG, initiates the thermal decomposition of coal, and influences gas yield and composition. This study examines the influences of pyrolysis temperature and coal rank on gas production using coal samples from The Muara Enim Formation, South Sumatra Basin. Four coal samples, ranging from lignite to bituminous rank, were pyrolyzed at 300, 400, 500, and 600° C under inert conditions. The results indicate that gas yield increases with temperature due to enhanced thermal decomposition. At lower temperatures (300 ̶ 400° C) CO2 dominates, particularly in lower-rank coals due to their higher oxygen content. At higher temperatures (500 ̶ 600° C) more CH4 and H2 productions become more prominent, particularly in higher-rank coals. CH4 generation is driven by the breakdown of aliphatic structures, while H2 production results from dehydrogenation and condensation of aromatic structures. Lower-rank coal produced higher gas at low temperatures, indicating greater suitability for UCG under such conditions. In contrast, higher-rank coals require elevated temperatures for effective decomposition due to their greater thermal stability. These findings provide valuable geochemical insights into the pyrolysis behaviour of Muara Enim coals and offer a scientific basis for optimizing UCG conditions to improve gas yield and quality.
A GIS Framework to Identify The Suitability Map to Utilize Sand Deposited Land in Dibru River Basin: Using AHP Method and MCDM Sonowal, Gulap; Thakuriah, Gitika; Saikia, Palash Moni
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.171-187

Abstract

The site suitability for utilizing sand deposited land is an important step towards sustainable development by adopting conservative measures. Soil is the most crucial for maintaining an environment and ecosystem which is helpful to sustaining all forms of life. The increasing action of sand deposition day to day has been one of the common issues all over the world, especially the country with high magnitude flood. The present study aim is to identify the sensitive area of the sand deposition within The Dibru River Basin. Multicriteria evaluation is carried out using Geographic Information System (GIS) techniques to help the choice makers in identifying the suitable site of sand deposition. Different layers which were considered for multicriteria evaluation are: sand deposition, geomorphology, soil capability, soil texture, and slope for identifying the vulnerable zone of sand deposition. Analytical Hierarchy Processes (AHP) are used for weighted sum to find the sensitive area of the sand deposition for land management using selected criteria. The site suitability map was classified into low, moderate, and high deposition zones. This paper will help policy makers for implementing the preventive measures to use the siltation zone into sustainable agriculture practise within The Dibru River Basin.
Gravity Data Analysis for Fault Identification and Earthquake Hypocentre Relocation Using Modified Joint Hypocentre Determination Method in Cianjur Area Divia Isyania Putri; Suwondo; Mohammad Iqbal Tawakal; Tati Zera; Sutrisno Sutrisno
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.297-312

Abstract

An earthquake with a magnitude of M 5.6 occurred in Cianjur, West Java, on November 21st, 2022, and left 321 people dead. This event raised concerns about the potential for aftershocks, necessitating an in-depth analysis to evaluate future seismic risk in Cianjur. This study aims to identify the type of fault that triggered the earthquake and to relocate the hypocentre in the Cianjur area. First horizontal derivative (FHD) and second vertical derivative (SVD) methods from gravity data were used for mapping the fault structure and the fault type. Fault location is represented by zero SVD and peak FHD to determine the type of fault; the maximum FHD and minimum SVD values were compared. The correlation results of FHD and SVD graphs obtained a fault line with a northwest to southeast direction on the Cugenang Fault and Cimandiri Fault line, with its movement direction from Pelabuhan Ratu with a shear fault type. The results of the relocation analysis show the existence of two identified alignment structures in the direction of north northeast ̶ south southeast (NNW ̶ SSE) and east northeast to west-southwest (WSW-ENE) which form a group on the trendline of the fault zone, as evidenced by the tectonic activity in the Cianjur area caused by the existence of a pair of mutually perpendicular horizontal faults (shear conjugate faults).
The The First Occurrence of Mafic Alkaline Rock (Lamproite) in The Mamuju District, West Sulawesi, Indonesia: Implications for The REE and Critical Elements Enrichment Fadlin Fadlin; Shaban Godang; Arifudin Idrus; Hill Gendoet Hartono; Januar Aziz Zaenurrohman; Raden Muhammad Asfaro; Wildan Nur Hamzah; Hernani Vitorino Nhatinombe
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.199-219

Abstract

Mafic alkaline igneous rocks, along with their weathering products, are a significant source of Rare Earth Elements (REEs) and critical elements. One of the mafic alkaline rock-related REE and critical element sources is lamproite. Various methods were utilized in this study, including optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy with Energy Dispersive Spectroscopy (SEM-EDS), as well as whole-rock geochemical analyses using X-ray fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry/Optical Emission Spectroscopy (ICP-MS/OES). Based on mineralogical observations, it has been confirmed that the dykes from West Sulawesi are orendite-type lamproite rocks. Sanidine, phlogopite, diopside, and aegirine are the main minerals found in these rocks, including apatite and oxide minerals as accessory minerals. The dykes' whole-rock geochemistry indicates an ultrapotassic nature with a K₂O/Na₂O ratio > 3. Lamproite dykes display an increase in the large ion lithophile elements (LILEs) and a decrease in Ti, Sr, and P, with minimal Eu anomalies. They also show an increase in the light rare earth elements (LREEs), ranging from 901 to 1558 ppm, and a significantly higher content of Zr (968-3083 ppm), Th (152-408 ppm), and U (30-37 ppm). The dykes are related to an orogenic lamproite that formed during post-collisional tectonic continental extension. It contained a significant amount of REE-Zr-Th-bearing minerals, such as apatite (La-Ce-Nd), zirconosilicate (Zr-Ce), and Ba-perovskite (Zr-Th-Ce-Tb). The enrichment of light rare earth elements (LREEs), thorium (Th), and zirconium (Zr) in these dykes can be attributed to both primary and secondary enrichment processes, such as metasomatism and hydrothermal alteration. This phenomenon is evidenced by mineral replacement textures or pseudomorphs, as well as a skeletal texture resulting from rapid cooling in a hydrothermal fluid environment. Therefore, understanding the formation of mafic alkaline rocks, especially lamproite, and their role in enriching REEs and critical elements is a crucial future scientific goal.
Combining Lithium Isotope Systematics, Stable Isotopes, and Major Elements as a Powerful Tool for Detection of the Slab-Dehydrated Fluids in Southwestern Japan Rofiqul Umam
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.393-407

Abstract

This research aims to obtain a very sensitive geochemical analysis method to detect the contribution of thermal water or slab-dehydrated fluids to the surface waters of the Arima hot spring water in southwestern Japan. In this study, four groundwater samples from the previous research in the form of lithium isotope systematics and chlorine were taken from the public baths of the Arima hot spring waters. In addition, fourteen Arima hot water samples in the form of stable isotope and major element data of fourteen Arima hot water samples from previous research were also used. The interpretation of lithium isotopes (δ7Li) and Cl/Li ratios shows that four groundwater samples in this study have a δ7Li < 5 ‰ and Cl/Li < 1,000 and are in the thermal water category. Meanwhile, thirteen Arima hot spring waters from the previous research do not have lithium isotope (δ7Li) data and might be able to be estimated based on Li > 0.1 lmg/l, Cl > 1,000 lmg/l, and Cl/Li < 1000 and are in the thermal water category. One of the Arima hot spring waters from the previous research is a mixing water category with fairly high Cl, namely 435 mg/l. The combinations of lithium isotope systematics, stable isotopes, and major elements might be useful as a powerful geochemical analysis for the detection of slab-dehydrated fluids.
Site Specific Seismic Ground Response Analysis of Major Ports in Odisha, South-Eastern Coastal Region of India: A Case Study Satyaprakash Mishra; Arjun Sil; Amit Kumar Das
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.329-354

Abstract

Ports are vital economic arteries for any nation, making the resilience of port infrastructure to seismic events a paramount concern. This study emphasizes the necessity of constructing port facilities capable of withstanding significant seismic forces, particularly peak ground acceleration (PGA), which is crucial for maintaining their operational integrity during earthquakes. The local soil characteristics significantly influence the seismic ground motion, thus emphasizing the necessity of site-specific seismic investigations to enhance the safety of these critical structures. This study addresses the urgent need for site-specific seismic ground response analysis (GRA) in three major port locations in Odisha, India, where local geophysical data is scarce. Using borelog data and empirical correlations, shear wave velocity (Vs) profiles were estimated from standard penetration test (SPT-N) values. The analysis classified the sites based on their average Vs values at a depth of 30 m (Vs 30), following the criteria set by the National Earthquake Hazards Reduction Program (NEHRP). These were employed within the DEEPSOIL software framework to perform one-dimensional equivalent linear GRA using three real ground motion records representative of stable continental regions. The analysis computed peak ground acceleration (PGA), amplification factors, response spectra, and Fourier amplitude ratios. Results reveal significant amplification effects, especially at Dhamara port due to soft marine clays, with surface PGA values nearly doubling compared to bedrock input. Results show that surface-level PGA values are amplified up to 1.8 times the bedrock values, with the highest amplification at Dhamara. Fundamental site periods ranged from 0.47 to 0.72 s, and in some period ranges, the site-specific spectra exceeded IS 1893:2016 code spectra, particularly for Site Class E. The findings aid in the design of earthquake-resistant structures in regions where direct site-specific data may not be readily available, facilitating better-informed engineering decisions to enhance the resilience of port infrastructure against earthquakes.
Petrology, Geochemistry, and Peak Pressure-Temperature Metamorphism of Pinoh Metamorphic Rocks in The Schwaner Mountains, Indonesia Nugroho Imam Setiawan; Agung Harijoko; Rahmadi Hidayat; I Gde Sukadana; Frederikus Dian Indrastomo; Isyqi
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.243-267

Abstract

The Pinoh Metamorphic Rocks in the Schwaner Mountains predominantly underwent contact metamorphism near a granitoid body, oriented E–W and NW–SE. The whole-rock geochemical analyses indicate that these metapelites are characterized by high Al₂O₃ (16.6–22.0 wt.%), moderate SiO₂ (60.0–67.7 wt.%), low CaO and Na₂O, and enrichment in large-ion lithophile elements relative to high field strength elements. Trace-element and REE patterns normalized to upper continental crust show LREE enrichment, negative Sr anomalies, and variable Zr contents, suggesting significant sedimentary recycling. Chemical weathering indices (CIA = 79–89; CIW = 89–99) and low ICV values (0.58–0.75) indicate compositionally mature pelitic to semipelitic protoliths. Provenance discrimination diagrams suggest derivation mainly from intermediate to felsic-igneous sources, with minor mafic contributions, deposited in an active continental margin to continental arc setting. Integrated petrographic, microstructural, mineral-chemical, thermobarometric, and phase equilibria analyses of samples from the Nanga Pinoh and Nanga Semalam areas reveal two main metamorphic events (M1 and M2). The M1 event formed the primary S1 foliation, whereas the M2 event is marked by the growth of andalusite porphyroblasts and the occurrence of spotted biotite. Garnet locally nucleated during late M1, but was chemically re-equilibrated during M2. Peak metamorphic conditions of the garnet–andalusite–biotite schist, estimated using garnet–biotite–andalusite–quartz (GBAQ) geothermobarometry and pseudosection modeling, yield P–T conditions of 525–586° C at 2.0–3.8 kbar, consistent with low-pressure, high-temperature Buchan-type contact metamorphism related to Cretaceous granitoid magmatism in The Schwaner Mountains.
Enhancing Seismic Hazard Preparation in Lampung, Sumatra: Improved Magnitude Conversion, Seismicity Smoothing, and Area Source Modeling Rizki Wulandari; Yudha Styawan; Chung-Han Chan
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.221-241

Abstract

This work improves seismic hazard evaluation for the Lampung region in Sumatra by tackling the precision in magnitude conversion, attenuation of seismicity, and area-source modelling. Considering the variety magnitude. The magnitude conversion equations were initially validated using scales from historical earthquake data. And, if required, enhanced to guarantee their dependability for the area. Utilizing maximum likelihood estimation Maximum Likelihood Estimation (MLE) and ordinary. Ordinary least squares (OLS) regression was employed to compute parameters for frequency-magnitude distributions. Facilitating a comprehensive comparison that acknowledges OLS's sporadically superior alignment with observed data. Gaussian distribution smoothing was utilized diverse bandwidths (25, 50, 75, and 100 km) to illustrate spatial seismicity patterns, disclosing a distance of 50 kilometers. Bandwidth provides the most consistent model performance, especially in terms of accuracy in the Molchan illustration. The area skill score (ASS) validates the superior forecasting capacity of the smoothed seismicity models. Using bandwidths of 25, 50, and 75 kilometers producing competitive outcomes. Furthermore, the region was partitioned into discrete seismic zones predicated on fault characteristics and seismicity density, further augmenting localized hazard assessments. This is polished. multi-method approach encompassing magnitude conversion, spatial smoothing, and area-specific analysis. Modelling offers a comprehensive framework for seismic hazard preparedness in Lampung, providing useful insights for infrastructure strategic planning and disaster mitigation.
Backshore Sand Infiltration Characterization for The Sustainable Waterfront City Tourism Development at Balikpapan Bay, Indonesia Totok Sulistyo; Sari Bahagiarti Kusumayudha; Tedy Agung Cahyadi; Reza Adhi Fajar; Mariatul Kiptiah; Desak Made Ristia Kartika
Indonesian Journal on Geoscience Vol. 13 No. 2 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.2.313-328

Abstract

The researched area is the waterfront city of Balikpapan City, where the east and south coast areas have been developed as tourist destinations. The east coastline has an attractive view with its extensive sand deposits, geologically known as quaternary alluvium deposits (QA). On the south coastline, sands are spotted and have a limited spread with a steeper slope. The infiltration rate measurement and sampling were conducted in fifteen locations on the east coast and ten locations on the south coast to assess the water inundation potential on coastal sand. The field observation of water inundation after rain was also conducted to locate the inundation areas. The subtraction of two satellite images was also conducted for validation. Actual sand infiltration rates of the east and south coasts range from relatively slow to very fast. The impact of slow to medium infiltration is the surface water inundation that disturbs the function of the coastal sand as a place for tourist activities. Based on the overall infiltration, the East Coast has greater vulnerability to water inundation than the South Coast. The implication of such a condition without proper engineering treatment in the long term will reduce tourist visits. As a consequence, the revenue will decrease, and cause negative multiplier effects on the economy of local inhabitants. Scientific findings will contribute to the geoscience knowledge; the origin of the sand deposits determines the differences in the physical characteristics of the east and south coast sands. The source of the south coastline sand is the Tertiary Miocene Balikpapan Formation (Tmbp). Meanwhile, the source of the east coastline sands is the Tertiary Pliocene Kampungbaru Formation (Tpkb).
A Comprehensive Evaluation of Sandstone Reservoirs: A Methodological Study on The Impact of High Chlorite Content Thanh Tung Nguyen; Hoang Anh Nguyen; Thuan Van Nguyen; Triet Le Minh; Quang Tuan Nguyen
Indonesian Journal on Geoscience Vol. 13 No. 3 (2026)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.13.3.373-392

Abstract

Chlorite-bearing sandstone reservoirs often pose challenges in hydrocarbon zone interpretation due to their dual effects: porosity preservation and pore-throat blockage at depth. For a better understanding, this study integrates multiple methodologies, including mineralogical analysis of core samples and petrophysical logging, to classify and to assess the influence of high chlorite content on reservoir quality; a comprehensive well log interpretation approaches and machine learning (ML) to water saturation estimation in chlorite-affected intervals. Based on porosity and permeability measurements, thin-section analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as special core analysis (SCAL), the morphologies of chlorite are mainly grain-coating, rosetted boxwork, and floccules. Furthermore, the reservoirs are classified into four groups according to chlorite impact levels. Classes 1 and 2 exhibit minimal chlorite influence, whereas classes 3 and 4 show a significant chlorite effect. Notably, class 4 demonstrates lower permeability than class 3, despite higher porosity and a stronger impact of chlorite due to pore-throat blockage by abundant chlorite floccules. Water saturation analysis reveals that in high-chlorite zones, the dual-water model provides more accurate results than Archie’s equation, whereas in low-chlorite intervals, both methods yield comparable outcomes. Additionally, ML-based predictions using the state-of-the-art LightGBM tool on well-log data exhibit strong alignment with core analysis and empirical calculations, with R²= 0.8804 and RMSE = 0.0572. These findings significantly enhance water saturation estimation in chlorite-impacted reservoirs and demonstrate broad applicability for assessing chlorite distribution in wells with limited core data or well log datasets.

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