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IJOG : Indonesian Journal on Geoscience

IJOG
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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.

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Articles 796 Documents

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Indonesian Landforms and Plate Tectonics Verstappen, Herman Th.
Indonesian Journal on Geoscience Vol 5, No 3 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i3.103The horizontal configuration and vertical dimension of the landforms occurring in the tectonically unstable parts of Indonesia were resulted in the first place from plate tectonics. Most of them date from the Quaternary and endogenous forces are ongoing. Three major plates â the northward moving Indo-Australian Plate, the south-eastward moving SE-Asian Plate and the westward moving Pacific Plate - meet at a plate triple-junction situated in the south of New Guineaâs Birdâs Head. The narrow North-Moluccan plate is interposed between the Asia and Pacific. It tapers out northward in the Philippine Mobile Belt and is gradually disappearing. The greatest relief amplitudes occur near the plate boundaries: deep ocean trenches are associated with subduction zones and mountain ranges with collision belts. The landforms of the more stable areas of the plates date back to a more remote past and, where emerged, have a more subdued relief that is in the first place related to the resistance of the rocks to humid tropical weathering Rising mountain ranges and emerging island arcs are subjected to rapid humid-tropical river erosions and mass movements. The erosion products accumulate in adjacent sedimentary basins where their increasing weight causes subsidence by gravity and isostatic compensations. Living and raised coral reefs, volcanoes, and fault scarps are important geomorphic indicators of active plate tectonics. Compartmental faults may strongly affect island arcs stretching perpendicular to the plate movement. This is the case on Java. Transcurrent faults and related pull-apart basins are a leading factor where plates meet at an angle, such as on Sumatra. The most complicated situation exists near the triple-junction and in the Moluccas. Modern research methods, such as GPS measurements of plate movements and absolute dating of volcanic outbursts and raised coral reefs are important tools. The mega-landforms resulting from the collision of India with the Asian continent, around 50.0 my. ago, and the final collision of Australia with the Pacific, about 5.0 my. ago, also had an important impact on geomorphologic processes and the natural environment of SE-Asia through changes of the monsoonal wind system in the region and of the oceanic thermo-haline circulation in eastern Indonesia between the Pacific and the Indian ocean. In addition the landforms of the region were, of course, affected by the Quaternary global climatic fluctuations and sea level changes.

Mekanisme Gempa Vulkanik Gunung Talang Pasca Gempa Tektonik Mentawai Tahun 2007-2009, Sumatra Barat Kriswati, Estu; Pamitro, Y. E.; Basuki, A.
Indonesian Journal on Geoscience Vol 5, No 3 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i3.104The Mentawai tectonic earthquake (magnitude 6.8 on the Richter Scale) on April 10, 2005 is assumed to trigger Talang volcanic activity that caused an eruption on April 12, 2005. Information on the source mechanism of volcanic earthquakes after the tectonic earthquake is expected to answer question of âDo tectonic earthquakes around the Talang Volcano trigger its volcanic activities?â Epicenter distribution of the volcanic earthquakes between 2007 and 2009 shows a southeast â northwest pattern with dextral strike-slip fault and normal fault mechanisms. The data show that earthquake activities at the Talang Volcano were dominated by local structure movements influenced by regional tectonic movements. Between 2007 and 2009, there were three process stages related to magnitude 6 or larger tectonic earthquakes around the Talang Volcano. First stage was a period before August 16, 2009. In this stage, volcanic fluids rose to the shallower chamber beneath the Talang Volcano. Second stage was a compressional stage and formation of a reverse fault influenced by Mentawai tectonic earthquake on August 16, 2009 and activation of a fault that intersects the Volcano. The third stage was a compresional stage and formation of a reverse fault influenced by Padang tectonic earthquake on September 30, 2009. In this stage, area fracturing was intensified, thereby the fracturing became more intensive. As the result, the accumulated volume and pressure of several tectonic earthquakes were released that caused an increase of eruption column soon after the tectonic earthquake.

Physical Disintegration Characterization of Mudrocks Subjected to Slaking Exposure and Immersion Tests Sadisun, Imam A.; Bandono, Bandono; Shimada, H.; Ichinose, M.; Matsui, K.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.105In order to gain insights into the detailed physical disintegration characteristics of various types of mudrock, a series of static slaking exposure and immersion tests were carefully carried out in this study. The intent of this paper is to exhaustively describe and discuss the results of the tests, including slaking mechanism, mode and rate/intensity. In general, it can be obviously identified that there are significant different susceptibilities of each mudrock tested to slake-disintegration. These differences can not only be identified from the results of slaking exposure test but also from slaking immersion test. It seems that there is also an agreement in both testing results, which show that the most resistant mudrock to slaking was Ikeshima shales, and was comparatively, followed by Ombilin siltstones, Tanjung Enim mudstones-claystones, and Subang claystones as the worst slaking characteristic. The detailed differences in fundamental characteristics of physical disintegration characteristics will further widely be discussed in this paper.

Geochemical and Thermodinamic Modeling of Segara Anak Lake and the 2009 Eruption of Rinjani Volcano, Lombok, Indonesia Solikhin, Akhmad; Kunrat, S. I.; Bernard, A.; Barbier, B.; Campion, R.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.106Rinjani is the second highest volcano in Indonesia with an elevation of 3726 m above sea level. TheÂ steep and highest cone of Rinjani consists mainly of loose pyroclastic ejecta and contains a crater with aÂ few solfataras. The West of this cone is Segara Anak caldera. The western side of the caldera is occupiedÂ by a 230 m deep lake, covering an area of 11 kmÂ² and its volume was (before the 2009 eruption) estimatedÂ 1.02 km3. This is probably the largest hot volcanic lake in the world.The lake water is neutral (pH: 7-8) andÂ its chemistry dominated by chlorides and sulfates with a relatively high TDS (Total Dissolved Solids: 2640Â mg/l). This unusual TDS as well as the lake surface temperatures (20 - 22Â°C) well above ambient temperaturesÂ (14 - 15Â°C) for this altitude, reflect a strong input of hydrothermal fluids. Numerous hot springs are locatedÂ along the shore at the foot of Barujari volcanic cone. Bathymetric profiles show also several areas withÂ columns of gas bubbles escaping from the lake floor indicating a significant discharge of CO gas into theÂ lake. The mass and energy balance model of Rinjani Crater Lake produce total heat lost value on the averageÂ of 1700 MW. Most of the heating periods of the lake occurred when the heat released by the surface ofÂ the lake to the atmosphere was lower than the heat supplied from the hydrothermal system. Peaks of heatÂ losses correspond to period of strong winds. Crater lake monitoring can provide a basic information aboutÂ deep magmatic activity and surface processes that occur in the volcano. The monitoring also contributes toÂ predict the next eruption in order to improve mitigation of volcanic eruption. Precursory signals of the MayÂ 2009 eruption can be seen from significant changes in the temperature and chemistry of some of the hotÂ springs, the increase of Fe concentrations in spring #54, chemical plume of low pH and dissolved oxygen,Â acidification of Segara Anak Lake, and increasing of lake surface temperatures. The new lava flow fromÂ May - August 2009 eruption covers an area of 650,000 m2. The shoreline was significantly modified by theÂ entry of lava into Segara Anak Lake. The area of the lake is reduced by 460,000 m2.

Geothermal Prospect Selection Using Analytical Hierarchy Process (AHP): A Case Study in Sulawesi Island, Indonesia Suryantini, Suryantini; Wibowo, H.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.107Analytical Hierarchy Process (AHP) is a Multi Criterion Decision Making (MCDM) Technique. It can handle any complex, multicriterion, and multiperson problems. In AHP, the problems are decomposed into a hierarchically structure and are given the weights according to its importance. Thus, the strength with which one alternative dominates another with respect to a given criterion can be identified. The output is a priority ranking indicating the overall preference for each decision alternative. This paper describes the application of AHP to select a geothermal prospect in Sulawesi Island to be developed in the near future. The alternatives consist of three geothermal prospects. i.e., Suwawa, Pulu, and Marana. Three major criteria are used and applied into those three prospects: Geoscience, Infrastructure, and Social-culture aspects. Under each of these major criteria, there are several subcriteria. Geoscience criterion which consists of Resources, Geothermal System, and Geological Risk Subcriteria is given the highest weight with the assumption that if resources are large and can be developed commercially, then there is no reason not to be exploited; the technology and other infrastructure aspects are no longer an obstacle. The result shows that Suwawa Prospect is the best option to be developed in the near future. The second option or rank is Marana Prospect, and the third is Pulu Prospect. This result is in agreement with the future plan of the development of Sulawesi Island. If the regulation and plan of development were suddenly changed, the goal of this AHP might not be appropriate anymore, and the second or third option might replace the first rank. The benefits of using AHP are (1) the facts and reasons behind the decision are well documented, (2) able to handle quantitative and qualitative inputs, (3) able to accommodate environmental, social and other influences, and (4) able to handle subjective judgments of individuals. Lessons learned from AHP application for geothermal prospect selection could be extended into multi criterion decision making at a group level.

Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, Pangalengan, West Java Subandrio, Andri S.; Basuki, N. I.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.108The Bunikasih vein system in the Pangalengan district of West Java is a low-sulfidation, adularia sericiteÂ epithermal gold deposit. It is hosted by Late Miocene andesitic volcanic and volcanoclastic rocksÂ occurring in the south western margin of Malabar Volcano complex. Gold ore and alteration minerals related to deposition of gold in Bunikasih deposits superimposed on Late Tertiary-Quaternary andesiticÂ formation that were altered and mineralized by some hydrothermal events. The veins consist almostÂ entirely of quartz, with small amounts of adularia, bladed calcite, pyrite, and gold. Gold ore shoots areÂ vertically restricted and are more continuous horizontally. The veins display complex and multi episodicÂ filling with texture characteristics of open space precipitation such us colloform, lattice bladed, crustiformÂ banding, vugs, breccia, and cockade and comb texture. The presence of bladed calcite and silicaÂ pseudomorph after bladed calcite suggests that the hydrothermal fluids boiled. In the Cibaliung sectionÂ of the area, anomalous gold is related to veins trending northeast - southwest, milky quartz with darkÂ grey to black manganese staining is found intermittently for a length of about 800m. The mineralizedÂ andesite ore bodies exhibit broad alteration patterns adjacent to mineralization, passing from fresh rockÂ into anargillic, chlorite zone, and then sericite-silica close to mineralization. An argillic assemblageÂ composed of kaolinite with fine-grained pyrite bulb is present in the upper portions and surrounding ofÂ the quartz vein system. The veins range from centimeter to meter in size. Of 24 vein samples collected,Â gold averages up to 0.3 grams per tone ("g/t"), to a high of 24.6 g/t. The Bunikasih epithermal goldÂ deposit was mined by people for more than 10 years, mainly for the gold ore.

The Evolution of Gajahmungkur Paleovolcano, Wonogiri, Central Java, as A Reference to Revize the Terminology of âOld Andesite Formationâ Syafri, Ildrem; Sudradjat, A.; Sulaksana, Nana; Hartono, G.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.109Gajahmungkur is a Tertiary paleovolcano located in Wonogiri Regency, Central Java. The volcanic product of this volcano are widely distributed and composed of important elements of the stratigraphic sequence in the Southern Mountain area. The volcanic products so far have been simply classified as âOld Andesite Formationâ which apparently is not in line with the stratigraphic code and the Indonesian Stratigraphic Code. The description of paleovolcano therefore might contribute to the revision of the âOld Andesite Formationâ. The evolution of Gajahmungkur paleovolcano commenced with the formation of a submarine volcano, and then at the second phase a composite volcano emerged above sea level forming a volcano island. The third phase was the self destruction resulting in a formation of a caldera. Pumiceous components dominated the products. At the fourth phase, the activities began to decline producing more basaltic rocks. The statistical analysis of the interrelation between various physical properties of the clastic rocks leads to the identification of volcanic facies and the location of the paleovolcano vent.

Macroscopic, Microscopic, and Paleo-depositional Features of selected Coals in Arahan, Banjarsari, Subanjeriji, and South Banko Regions, South Sumatra Suwarna, Nana; Kusumahbrata, Y.
Indonesian Journal on Geoscience Vol 5, No 4 (2010)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v5i4.110The Arahan, Banjarsari, Subanjeriji, and Banko Regions, parts of the Bukit Asam coalfield, isÂ situated in the Lematang Depression of South Palembang Sub-basin, South Sumatera Basin. Twenty twoÂ fresh outcrop and subcrop samples of Seam B, A, Benuang, Enim, and Jelawatan of the Mio-PlioceneÂ Muaraenim coals have been analyzed macroscopically and microscopically, to assess the characteristicsÂ and depositional environment of the coal present. On the basis of lithotype analysis, accompanied byÂ organic-petrological and SEM analyses, the coal seams of the Muaraenim Formation show variations inÂ the predominance of some macerals, indicating successions of environmental changes. Petrographically,Â the dominant maceral group is vitrinite, present in high to very high values (69.4 â 97.4 %); whilst theÂ minor one is inertinite showing a low to moderate amount (0.4 â 22.0 %), followed by low to moderateÂ value of exinite (0.4 â 18.2 %). Vitrinite reflectance values are present in a low to moderate level,Â varying from 0.34 to 0.55 %, with one sample showing value of 0.59 %. Mineral matter dominated byÂ clay minerals, with minor pyrite and carbonate, displays a low degree (0.4 â 5.4 %), with one sampleÂ of 12.0 %. Organic facies study tends to indicate that the coals were deposited in a wet forest swamp toÂ limnic zone, within lower delta plain to transgressive area. This condition has supported the depositionalÂ setting interpreted from sedimentary facies associations that shows a shallow-water continental marginÂ sequence, varying from a fluvial to deltaic environment. The organic facies concept is thus applicableÂ in basin studies context and has potential to become an additional tool for interpretation of depositionalÂ environment.

Focal Mechanism and Parameter of Volcano-Tectonic Earthquake Source, in Mount Guntur, West Java Hidayati, Sri; Suparman, Y.; Loeqman, A.
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v6i1.111Guntur Volcano in West Java is one of the most active volcanoes in Indonesia. The last eruption took place in 1847 and the volcanic activity has been dormant since then, however its seismicity is active. During the period of July to October 2009, the hypocenter distribution of VT earthquakes is mostly located at western flank of the volcano, beneath Guntur - Gandapura craters at the depth of less than 5 km. The depth pattern shows deeper to the northwest. The VT earthquakes deeper than 5 km were not found in this period. The focal mechanism of VT earthquakes are oblique normal fault, strike-slip fault and oblique reverse fault types. The mechanism of those earthquakes is not uniquely determined probably due to complicated structures at Guntur volcano complex area, which is aligned in NW-SE direction. T-axis of the oblique normal fault is trending in northwest - southeast direction similar to the structures found in the summit area of Gunung Guntur Volcano. Similarly, one of the strike-slip fault nodal line and P-axis of oblique reverse fault are also trending in northwest - southeast. Ploting of the earthquake source parameters (seismic moment, corner frequency, and stress drop) made to hypocenter distance shows no significant difference on those parameters between earthquakes at close and far distances to Kabuyutan station. It is probably due to the hypocenters are not concentrated in one zone. Meanwhile, the relationship between seismic moment (Mo) and seismic source radius (r) shows that for earthquakes with moment of smaller than 1018 dyne cm, the radius of the hypocenter is constant which is namely 60 m.

Turbidite Facies of the Halang Formation in Ajibarang Area, Central Java Praptisih, Praptisih; Kamtono, Kamtono
Indonesian Journal on Geoscience Vol 6, No 1 (2011)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.v6i1.112An understanding of deepwater turbidite sediments is very important mainly dealing with the determinationÂ of a reservoir geometry. The problem arising in the turbidite sediment geometry is very complex and varied,Â and its existence depends on how, when, and type of its environment. In Central Java, the broad turbiditeÂ sediment distribution of the Halang Formation is needed to be observed its facies association. This paperÂ will discuss the turbidite facies of Halang Formation in the Ajibarang area. The method used to analyzeÂ the turbidite facies is by measuring stratigraphic sections and observing the lithofacies characteristics toÂ reconstruct its depositional environment. The Halang Formation outcrop in the Ajibarang area is dominantlyÂ composed of alternating sandstone and claystone or marl. Based on the observation, the turbidite facies ofÂ Halang Formation, in the Ajibarang area, was deposited on a submarine fan system at the middle fan ofÂ suprafan lobes. Compiling with the previous studies, the source of the Halang Formation is indicated to beÂ derived from the south southwest.

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Ivan Ferdian

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Location
Kota bandung,

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