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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.

Arjuna Subject : -

Articles 796 Documents

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Hotwater Geochemistry for Interpreting The Condition of Geothermal Reservoir, Dieng Plateau Case, Banjarnegara-Wonosobo Regency, Central Java Yuris Ramadhan; K. Channel; N. R. Herdianita
Indonesian Journal on Geoscience Vol 8, No 2 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i2.158The researched area, located in the Dieng Plateau, is included into the Holocene Dieng Volcanic Rock Unit. The regional structure in this area is originated from the major caldera with local fault having orientation of SE - NW. Surface manifestations found in the researched area are hot springs located in Bitingan, Sileri, Siglagah, Pulosari, Kaliputih, and Sikidang. Fumaroles occur in Candradimuka and Pagerkandang and mud pools are located in Sileri and Sikidang craters. Temperatures of the hot springs ranges from 43 C to 61 C, pH of 6 - 7, and their conductivity are of 38-78 MeV. The type of hotwater is a mixture of bicarbonate, sulfate, and chloride sulfate deriving from condensation of steam. Based on a relative composition of Cl-Li-B, the hot water is originated from four different reservoirs with different rock associations, while their reservoir temperatures vary from 225 C to 300 C.

Magma Supply System at Batur Volcano Inferred from Volcano-Tectonic Earthquakes and Their Focal Mechanism Sri Hidayati; C. Sulaeman
Indonesian Journal on Geoscience Vol 8, No 2 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i2.159The Volcano-Tectonic (VT) earthquakes occurring during September - November 2009 were analyzed. The result shows that the epicentres aligning in NE- SW direction coincided with the weak zone of Batur Volcano Complex. The focal zone is located at the depth around 1.5 - 5.5 km beneath the summit. Migration of magma was detected by ground deformation measured by GPS and focal mechanism. Mechanism of VT earthquake shows mostly normal fault types during the swarm in November 2009.

Salinity Pattern in Semarang Coastal City: An Overview Novi Rahmawati; M. A. Marfai
Indonesian Journal on Geoscience Vol 8, No 2 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i2.160Semarang Coastal City is one of cities in Indonesia which has experienced a long-term salt intrusion. Land subsidence and groundwater exploitation were identified as main factors accelerated salt intrusion in this area. Extended salt intrusion into the land from year to year cannot be neglected. Salinity pattern and land use affected by this intrusion must be identified. Salinity pattern could be identified by electrical conductance content. The purposes of this research are: a) to define spatial electrical conductance map from 1995 to 2008 and b) to identify salinity pattern in each land use. Primary data set of electrical conductance measurement in 2004 and 2008 was performed. Secondary data set of electrical conductance was collected in 1995 and 2000. Electrical conductance mapping was assigned by point interpolation using GIS Environment. Land use classification was interpreted from topographical map and IKONOS using GIS Environment. Field check of land use was also done in the study area. Geologically, the area setting consists of Damar, Kalibiuk, and Breccias Formations, where the Damar Formation is the recharge source for groundwater in Semarang City. Based on the result, it can be concluded that the salinity content in groundwater increased from 1995-2008. In 1995, there was only 2.4% of brackish groundwater in Semarang Coastal City, but in 2008, most of area in that region was classified as saline. Land use conversion into built up area increased from 1998 to 2008. The area intruded by salt water increased within 1995, 2004, and 2008 periods. About 68 % of the area contained brackish water and most of the area were built up area in 1995. In 2004, no fresh groundwater found in Semarang Coastal City and the area of brackish groundwater reached 77% and about 23% was saline groundwater which 82% of the built up area included brackish groundwater. In 2008, approximately 55% of Semarang Coastal City was occupied by saline groundwater. About 51% of groundwater built up area was saline.

Seasonal Mean Variability of Coral-based Sea Surface Salinity from Simeulue, Mentawai, Bunaken, and Bali Sri Yudawati Cahyarini
Indonesian Journal on Geoscience Vol 8, No 3 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i3.161Sea surface salinity is an important parameter in a climate study. Coral δ18O records δ18O seawater and sea surface temperature (SST). While, coral Sr/Ca records SST only commonly used in a paleoclimate study to reconstruct SST. Thus, paired coral δ18O and Sr/Ca can be used to reconstruct δ18O seawater. δ18O seawater and SSS is linearly correlated, thus reconstructed δ18O seawater further is used to reconstruct sea surface salinity (SSS). Instead of using coral Sr/Ca as SST recorder, paired model (grid) or measured SST data is used to reconstruct SSS. In this study, paired coral δ18O and grid SST data are presented to reconstruct SSS from several different locations across Indonesian sea i.e Simeulue, Mentawai, Bunaken, and Bali. Coral-based SSS reconstructions from those locations are then compared to the grid SSS in the seasonal mean scale. The result shows that annual mean variation of salinity for period of 1958-2008 in Mentawai and Simeulue is 33.25 psu and 33.26 psu respectively, while in Bunaken and Bali is 34.03 psu and 33.47 psu respectively. Correlation coefficient between coral salinity and salinity from model data in the seasonal/monthly mean scale is high i.e R = 0.62 - 0.83. Based on the monthly mean data, corals in the studied area strongly record SSS variation in the monthly or seasonal mean scale. In Mentawai and Simeulue waters, SSS variation is influenced strongly by monsoon. While, in addition to the monsoon, ocean advection also affects seasonal variability of SSS in the Bunaken and Bali waters.

Extensional Tectonic Regime of Garut Basin based on Magnetotelluric Analysis Lina Handayani; Kamtono Kamtono; D. D. Wardhana
Indonesian Journal on Geoscience Vol 8, No 3 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i3.162Garut Basin are is part of Bandung-Garut Greater Basin (Bandung Zone) characterized by a large basin surrounded by mountain ranges. Active volcanoes had distributed their material as pyroclastic deposits around the outer border of the zone and as lava flow deposit separating the two basins. Bouguer gravity anomaly data had also indicated the presence of several low anomaly closures at about the area of Bandung and Garut Basins that were surrounded by high gravity anomaly zones. Two magnetotelluric surveys were completed to acquire the subsurface model that might explain the tectonic evolution of studied area. The first stage was characterized sby the presence of horst - graben structures that might imply an extensional regime of the area. The next stage of evolutionwas indicated by the horizontal layering correlated to the relative non-active tectonic. In addition, a most recent structure that appeared near the surface might suggest a possible extension force as the current stage.

Directed Volcanic Blast as a Tragedy of October 26Th, 2010 at Merapi Volcano, Central Java Igan S. Sutawidjaja
Indonesian Journal on Geoscience Vol 8, No 3 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i3.163Merapi is an active strato volcano located in Central Java. This volcano is regarded as the most active and most dangerous volcano in Indonesia. Since the twentieth century, the activities have comprised mainly the effusive growth of viscous lava domes and lava tongues, with occasional gravitational collapses of parts of over-steepened domes producing pyroclastic flows, commonly defined as “Merapi-Type”. Since October 2010, however, explosive eruptions of a relatively large size have occurred to VEI 4, and some associated pyroclastic flows were larger and had farther reach than any produced on July 2006. These events may also be regarded as another type of eruptions for Merapi. On October26th, 2010 such event happened, even though it was not caused by pyroclastic flows of the dome collapses, about thirty people were killed including Mbah Marijan, known as the Merapi volcano's spiritual gatekeeper, who was found dead at his home approximately 4 km from the crater. The Yogyakarta Palace subsequently confirmed his death. This time the disaster was caused by a sudden directed blast that took place at 17:02 pm throughout Cangkringan, Kinahrejo Village, at the south flank of Merapi Volcano. The victims were the local people who did not predict the blast threatened their areas, because they believed that the pyroclastic flows from the dome collapses as long as they knew, did not threaten their areas, and pyroclastic flows would flow down following the Boyong River as the closest valley to their village. The blast swept an area about 8 km2, reaching about 5 km in distance, deposited thin ash, and toppled all trees to the south around the Kinahrejo and Pakem areas. The blast that reached Kinahrejo Village seemed to have moderate temperatures, because all trees facing the crater were not burnt. However, the victims were affected by dehydration and blanketed by fine ash.

Paleogene Sediment Character of Mountain Front Central Sumatra Basin P. A. Suandhi; M. Rozalli; W. Utomo; A. Budiman; A. Bachtiar
Indonesian Journal on Geoscience Vol 8, No 3 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i3.164The SE-NW trending Mountain Front of Central Sumatra Basin is located in the southern part of the basin. The Mountain Front is elongated parallel to the Bukit Barisan Mountain, extending from the Regencies of North Padang Lawas (Gunung Tua in the northwest), Rokan Hulu, Kampar, Kuantan Singingi, and Inderagiri Hulu Regency in the southeast. The Palaeogene sediments also represent potential exploration objectives in Central Sumatra Basin, especially in the mountain front area. Limited detailed Palaeogene sedimentology information cause difficulties in hydrocarbon exploration in this area. Latest age information and attractive sediment characters based on recent geological fieldwork (by chaining method) infer Palaeogene sediment potential of the area. The Palaeogene sedimentary rock of the mountain front is elongated from northwest to southeast. Thickness of the sedimentary unit varies between 240 - 900 m. Palynology samples collected recently indicate that the oldest sedimentary unit is Middle Eocene and the youngest one is Late Oligocene. This latest age information will certainly cause significant changes to the existing surface geological map of the mountain front area. Generally, the Palaeogene sediments of the mountain front area are syn-rift sediments. The lower part of the Palaeogene deposit consists of fluvial facies of alluvial fan and braided river facies sediments. The middle part consists of fluvial meandering facies, lacustrine delta facies, and turbidity lacustrine facies sediments. The upper part consists of fluvial braided facies and transitional marine facies sediments. Volcanism in the area is detected from the occurrence of volcanic material as lithic material and spotted bentonite layers in the middle part of the mountain front area. Late rifting phase is indicated by the presence of transitional marine facies in the upper part of the Palaeogene sediments.

Potential Development of Hydrocarbon in Basement Reservoirs In Indonesia D. Sunarjanto; S. Widjaja
Indonesian Journal on Geoscience Vol 8, No 3 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i3.165Basement rocks, in particular igneous and metamorphic rocks are known to have porosity and permeability which should not be ignored. Primary porosity of basement rocks occurs as the result of rock formation. The porosity increases by the presence of cracks occurring as the result of tectonic processes (secondary porosity). Various efforts have been carried out to explore hydrocarbon in basement rocks. Some oil and gas fields proved that the basement rocks are as reservoirs which so far have provided oil and gas in significant amount. A review using previous research data, new data, and observation of igneous rocks in some fields has been done to see the development of exploration and basement reservoirs in Indonesia. A review on terminology of basement rock up till the identification of oil and gas exploration in basement rocks need to be based on the latest technology. An environmental approach is suggested to be applied as an alternative in analyzing the policy on oil and gas exploration development, especially in basement reservoirs.

Characteristics of Paleotsunami Sediments, A Case Study in Cilacap and Pangandaran Coastal Areas, Jawa, Indonesia Yudhicara Yudhicara; Y. Zaim; Y. Rizal; Aswan Aswan; R. Triyono; U. Setiyono; D. hartanto
Indonesian Journal on Geoscience Vol 8, No 4 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i4.166A paleotsunami study having been conducted in 2011 took two study cases in Cilacap and Pangandaran coastal areas. These two regions have been devastated by tsunami in the past and had the most severe damaged on 17 July 2006. Trenching, beach profiling, and sediment sampling had been carried out, and further analysis at the laboratory had been done, such as grain size and fossil analyses and dating. In Cilacap, an iron sand layer was found as a key bed suspected as a paleotsunami deposits due to the content of anthropogenic fragments. In Pangandaran, two layers of tsunami deposit candidates were found having thickness of 5 - 6 cm at the top as a 2006 tsunami deposit candidate, and 5 - 10 cm at the bottom as a paleotsunami deposit candidate. Both grain size and fossil analysis results could explain that Pangandaran’s sediments are tsunami deposits while Cilacap’s ones are assumed to be deposited by another process rather than a tsunami.

Interstratified Illite/Montmorillonite in Kamojang Geothermal Field, Indonesia D. F. Yudiantoro; E. suparka; S. Yuwono; I. Takashima; D. Ishiyama; Y. Kamah; J. Hutabarat
Indonesian Journal on Geoscience Vol 8, No 4 (2013)
Publisher : Geological Agency

DOI: 10.17014/ijog.v8i4.167Kamojang geothermal field located in West Java Province, falls under the Pangkalan Subregency, Bandung Regency. The researched area is a geothermal field located in the Quaternary volcanic caldera system of about 0.452 to 1.2 Ma. The volcanic activity generated hydrothermal fluids, interacting with rocks producing mineral alteration. The minerals formed in the areas of research are interstratified illite/montmorillonite (I/M). Analyses to identify interstratified I/M have been performed by X-ray diffraction using ethylene glycol, while the determination of the type and percentage of interstratified I/M was based on the calculation method of Watanabe. The methodology was applied on core and cutting samples from Wells KMJ-8, 9, 11, 13, 16, 23, 49, 51, and 54. The result of analysis of the samples shows that the type of clay is interstratified illite/montmorillonite and the minerals are formed at temperatures ranging from 180 to 220° C. The type of interstratified I/M in the studied area is S = 0 and S = 1. The percentage of illite type S = 0 is between 20 - 35% illite, whereas type S = 1 has about 45 - 72% illite. Along with the increasing depth, the percentage of illite is getting greater. This is consistent with the vertical distribution of temperature which increases according to the depth. This correlation results in an interpretation that the upflow zone of the geothermal reservoir is located in the centre of the Kamojang geothermal field.

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Ivan Ferdian

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Home Page

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Contact Name Ivan Ferdian

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Contact Name
Ivan Ferdian

Contact Email
ivan.ijgbg@gmail.com

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Journal Mail Official
ivan.ijgbg@gmail.com

Editorial Address
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Location
Kota bandung,

Jawa barat

INDONESIA