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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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Perbandingan karakteristik lingkungan pengendapan, batuan sumber, dan diagenesis Formasi Lakat di lereng timur laut dengan Formasi Talangakar di tenggara Pegunungan Tigapuluh, Jambi Rachmat Heryanto
Indonesian Journal on Geoscience Vol 1, No 4 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no4.20061The Central Sumatera Basin and the Jambi Subbasin is separated by the Tigapuluh High. During Late Oligocene – Middle Miocene, the Lakat Formation was deposited in fl uvial, fl ood plain associated with swamp, and tidal environments, whereas the Jambi Subbasin was occupied by the deposition of the Talangakar Formation in fl uvial and deltaic environments. The provenance of both formations was derived from the Tigapuluh and Barisan Mountain Highs. Diagenesis stage of the Talangakar Formation is higher (Mesogenetic mature B) than that of the Lakat Formation (Mesogenetic immature). This is because the Talangakar Formation was deposited within an unstable basin formed by horst, and graben structures which were still active during the deposition of the formation. On the other hand, the Lakat Formation was deposited in a more stable basin.

Karakteristik kimiawi air danau kawah Gunung Api Kelud, Jawa Timur pasca letusan tahun 1990 Eka Kadarsetia; Sofyan Primulyana; Pretina Sitinjak; Ugan Boyson Saing
Indonesian Journal on Geoscience Vol 1, No 4 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no4.20062Kelud is a strato type volcano characterized by phreatomagmatic and magmatic eruptions. Since last eruption in 1990, the volcano has showed no-more signifi cant volcanism. Currently, there is an opened westward crater lake as a remained eruption crater containing meteoric water and volcanic gases condensate generated from subsurface.Analysis result of lake water exhibits that its chemical composition was fl uctuated due to an infl uence of factors such as seasons, rates of volcanism activity and reactivity of internal chemical elements within the lake water.The volume of lake water increases during the wet season and experiences dilution to make declination of chemical components within the water. Temperature of the lake water increases as well as volcanic intensity, simultaneously to make addition of dissolved chemical compounds and elements such as SO , Cl, B, and F and creates acidic water. Fumarole/solfatara released anykind of gases, such as H O, CO , CO, HCl, SO , H S, HF, H , HBr, NH , CH , H BO , and N . Moreover interaction of andesitic rock and acidic water apparently produces ionic source of Na, K, Ca. Mg, Fe, Al including trace elements such as Zn, Li, Sr, As, Rb, Cr, Pb, Ti, Ni, Cu, Ce, and Be.The composition of crater lake water of the Kelud volcano is included into an immature water category with HCO . The fl uctuation of element, compound and gas contents within the lake water with their depletion trend during the period of 1990 – 2005 may be related to decreasing of volcanism activity in the duration of 1990 post-eruption.

Peningkatan kegiatan Gunung Api Tangkubanparahu Jawa Barat pada bulan April 2005 Isya Nurrahmat Dana; Eka Kadarsetia; Sofyan Primulyana; Muhammad Hendrasto; Asnawir Nasution
Indonesian Journal on Geoscience Vol 1, No 4 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no4.20063Tangkubanparahu is an active strato volcano located in West Java lying about 30 km to the north of Bandung City. Its crest is 2084 m above the sea level. In order to gain a better understanding on volcanism and magmatism of this volcano, various research and monitoring have been carried out, such as geochemistry and geophysics. Chemical composition of volcanic gases collected from the Ratu Crater (950 C in 1994, 1997, 1998 ratio of CO /H S, CO /H , and H /Ar, is suggested to indicate the presence of a fast fl uid movement and 2005, shows that the gas is hydrous with the main component of H O, CO , H S and small amount SO ; where CO content is higher than (SO + H S). The gas composition showing high of value from the depth before condensed at the shallow surface water area. Hotspring from the Domas Crater contains a high concentration of SO , low of Cl and absence of H CO . The high sulphate content is suggested to be originated from the volcanic gases, especially hydrogen sulphide oxydated near the surface, that then the gas infl uenced chemical composition due to shallow water.Continuous seismic monitoring uses one permanent station, while the other methods like Electric Distance Measurement (EDM), Global Positioning System (GPS) and Seismometer have been installed temporary. From geophysical evidence on April 2005 activity, some valuable information can be obtained. Hypocenter is located at the depth less than 2 km beneath an area between the Ratu and Domas Craters, while pressure source of deformation is below Domas Crater. Some low frequency volcanoquakes is possibly caused by volcanic gases released from the reservoir.

Menelusuri kebenaran letusan Gunung Merapi 1006 Supriati Dwi Andreastuti; Chris Newhall; Joko Dwiyanto
Indonesian Journal on Geoscience Vol 1, No 4 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no4.20064Until now, the large eruption of Merapi in 1006 is believed to take place although the truth is still debatable. Previous investigation proposed that the ”pralaya” of the Ancient Mataram Kingdom in 928 Saka (1006) was due to a volcanic activity. Bemmelen also inferred that impact of the eruption had destroyed and covered the Mendut and Borobudur Temples and dammed the Progo River. However, if the “pralaya” was caused by Merapi eruption, why the deposit that correlates to the the eruption is not recognized. If so, the eruption that covered the temples should have been very large, and left deposits around Merapi and of course easy to find. Historically, the “pralaya“ mentioned in the Pucangan Inscription did not happen in 1006, but in 1016 or 1017. However the “pralaya“ was caused by the attack of King Wurawari, not by the Merapi eruption. According to the history of Merapi eruptions, 11 large eruptions have occurred since 3000 years ago. However, none of those fi t with 1006 eruption. Except the large eruption (VEI 3-4), that produced Selo tephra, dated 1112 ± 73 years BP (765-911).

Klasifikasi gunung api aktif Indonesia, studi kasus dari beberapa letusan gunung api dalam sejarah Indyo Pratomo
Indonesian Journal on Geoscience Vol 1, No 4 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no4.20065Indonesia is well known as a volcanic country, where more than 30% out of all the world volcanoes occupied this region. Volcanic region is generally densely populated, because of their soil fertility and other land use. Based on their historical eruptions noted since and before 1600 A.D., the Indonesian active volcanoes are regrouped in to A type (79 volcanoes), which were defi ned as volcanoes erupted since 1600 A.D., B type (29 volcanoes) erupted before 1600 A.D., and C type (21 volcanoes) are solfatar fi elds (Bemmelen, 1949; van Padang 1951; Kusumadinata, 1979). Studies on parts of the Indonesian active volcanoes, show different eruptive characters, which are generally related to hazard potentials. A new classifi cation of Indonesian active volcanoes was proposed based on the combination of their physical properties, morphology, volcanic structure and eruptive styles to the eight differents types, those are Tambora (caldera formation), Merapi (lava dome), Agung (open crater), Papandayan (sector failure), Batur (post-caldera activities), Sangeangapi (lava fl ows) and Anak Krakatau types (volcano islands and submarine volcano). This classification would be make a better understanding to different characteristics of Indonesian active volcanoes, for the volcanic hazard and mitigation and also for the applied volcanological researches.

Evolusi pengendapan sedimen Kuarter di daerah utara Air Musi, Kota Palembang - Sumatera Selatan Herman Moechtar
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no1.20071In the studied area, the sedimentary Quaternary facies consists of fl uvial channel separated by fl oodbasin, swamp, and fl oodplain deposits. Changes in channel style from channel 1, 2, and to 3 are interpreted as the result of a change in the type of river discharge from low to high sinuosity channels. Vertical changes in the character of these fl uvial channels can be related to changes in humidity. The lateral and vertical succession of the fl oodbasin and swamp environments shows evidence of decreasing and increasing of these facies. They are the result of changes in climate. Vertical changes of the Quaternary deposit successions can be related to changes in climate. It is concluded that the subinterval facies I.a to I.c as form of channel 2 and fl oodplain facies (subinterval facies I.b) refl ects a continuosly increase in climate from minimum to climatic maximum. Whereas, from the subinterval facies I.c to II.c during deposition of the subinterval facies II.b by the occurrence of fl oodbasin facies 2, the humid climate decreased from climatic maximum to minimum. Probably, this can be called as astrostratigraphy or orbital stratigraphy.

Hydrothermal system of the Papandayan Volcano, West Java, Indonesia and its geochemistry evolution of thermal water after the November 2002 eruption Agnes Mazot; Alain Bernard; Igan Supriatman Sutawidjaja
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no1.20072Papandayan is a strato volcano situated in West Java, Indonesia. After the last magmatic eruptionin 1772, only few phreatic explosions have been occurring. At the present time, the activity is centeredin the northeast crater manifested by the presence of fumaroles and hot springs. In November 2002an explosive eruption occurred and ejected ash and altered rocks. Study of the altered rocks revealedthat an advanced argillic alteration took place in the hydrothermal system by an interaction betweenacid fl uids and rocks. Four zones of alteration have been formed as a limited extension along faults oracross permeable structures at different levels beneath the active crater of the volcano.Two types of acid fl uids are distinguished in the crater of the Papandayan Volcano: (1) acidsulphate-chloride water with pH values between 1.6 and 4.6, and (2) acid sulphate water with pHvalues between 1.2 and 2.5. The samples collected after the eruption revealed an increase in the SO4/Cl and Mg / Cl ratios. This evolution is likely explained by an increase in the neutralization of acidfl uids which tends to show that water-rock interactions were more signifi cant after the eruption. Thechanges in chemistry observed in 2003 were the consequence of the opening of new fractures whereunaltered or less altered volcanic rocks were in contact with the ascending acid water. The high δ34Svalues (9-17‰) observed in the acid sulphate-chloride water before the November 2002 eruptionsuggest that dissolved sulphates were mainly formed by the disproportionation of magmatic SO2. Onthe other hand, the low δ34S values (-0.3-7 ‰) observed in acid sulphate-chloride water sampled afterthe eruption suggest that the origin of dissolved sulphates for these waters is the surfi cial oxidation ofhydrogen sulphide.

Mekanisme erupsi ignimbrit Kaldera Maninjau, Sumatera Barat Agung Pribadi; Eddy Mulyadi; Indyo Pratomo
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no1.20073Maninjau is a large collapsed caldera that was resulted from a large eruption of silicic pyroclastic material (220-250 km3), and was distributed to more than 75 km away from the source. Field observations have provided a good understanding to the eruptive mechanism of the Maninjau caldera formation, in respect to their stratigraphy, sedimentology and geochronology of the eruptive products. Two formations have been identifi ed, those are: the Maninjau Formation, comprising a sequence of ignimbrite and surge units erupted from the Maninjau Caldera, and the Malalak Formation as a prominent andesitic fall unit likely derived from the Singgalang - Tandikat Volcano that overlies the Maninjau Formation. The variable velocity of the fl ows suggests that the Maninjau eruption initiated by violent. The later phases of the eruption became more violent and associated with caldera collapse.

Gunung api maar di Semenanjung Muria Sutikno Bronto; Sri Mulyaningsih
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no1.20074Three maars are well identifi ed in the Muria Peninsula, i.e. Bambang Maar, Gunungrowo Maar, and Gembong Maar. The maars were formed by monogenetic volcanic eruptions due to the interaction between heat source (magma), groundwater and calcareous basement rocks. This interaction is able to produce very high pressure of gas and steam causing phreatic explosions, followed by phreatomagmatic- or even magmatic explosions and ended by a lava extrusion. Satellite image analyses have recognized twelve circular features, comprising Bambang Maar, Gunungrowo Maar, and Gembaong Maar. Phisiographically, these maars are characterized by circular depressions which are surrounded by hills that are gently sloping down away from the crater or having a radier pattern morphology. Outcrops and drilling core in the circular areas that are considered as volcanic maars are lava fl ows, pyroclastic breccias, lapillistones, and tuffs, located far away from the eruption centres of Muria and Genuk Volcanoes. One of the circular features, i.e. Jepara Circular Feature, is also supported by negative anomaly (<30 mgal) showing a circular pattern. In the future, a maar volcano could possibly erupt depending on the tectonic reactivity in the region.

Indikasi mineralisasi epitermal emas bersulfi da rendah, di Wilayah Kecamatan Bonjol, Kabupaten Pasaman, Sumatera Barat Hamdan Z. Abidin; Bhakti H. Harahap
Indonesian Journal on Geoscience Vol 2, No 1 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no1.20075Bonjol gold prospect, known as Old Dutch Gold mine, consists of several ore bodies (Malintang, Balimbing, Lubang Sempit, Lubang Belanda and Lubang Perak). The deposit hosts within the altered volcanic rocks known as Gunung Amas Formation of Early Miocene age (9.3 ± 0.4 - 11.9 ±1.0 Ma). This formation consists of various rock types such as rhyolitic tuff, volcanic breccia, dacitic tuffs and rhyolites. These rocks are moderate to strongly alter. Mineralogy of the deposit consists of gold and silver with minor pyrite, sphalerite and galena. Besides this, hematite, jarosite and manganese are also present as supergene minerals. Ore minerals are found within quartz veins ranging from few centimetres to tens of metres thick. The veins are characterized by crustiform, comb, vuggy, botroyidal, layering and bladed. Quartz is a dominant mineral as hydrothermal alteration in addition to illite, dickite, monmorillonite, kaolinite, chlorite, smectite, natrolite, nontronite, calcite, halloysite, palygorskite, muscovite, sepiolite, analcime, heulandite, clino-chlor, zircon, zoisite, laumontite, alunite, biotite and erionite. The presence of these secondary minerals could be classifi ed into prophylitic, argillic and advanced argillic types. Analytical result of gold–bearing quartz vein indicates higher content of gold (0.3%) and silver (400 ppm). In contrast, the content of sulphide minerals (Cu, Pb, and Zn) is very low (< 100 ppm). Combined geology, mineralogy, textures and alteration minerals, it is concluded that gold deposit in the area shows an indication of a low sulphidation epithermal type within Gunung Amas Formation.

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