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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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Tectonostratigraphy and Structures of Eastern Seram Syaiful Bachri
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i2.118The eastern Seram is part of the Outer Banda Arc consisting of para-autochthonous and allochthonous units which are unconformably overlain by the autochthonous units. The para-autochthonous units are derived from the outer margin of the Australian NW Shelf. This sequence comprises Permian metamorphic rocks of the Kobipoto Complex and its cover of Triassic - Jurassic to Cretaceous - Tertiary age. The allochthonous unit, or the pre-collisional Banda fore-arc sequence was overthrusted onto the NW Shelf sequence. The sediments overlying unconformably the allochthonous and para-autochthonous units are referred to as autochthonous units. These autochthonous units comprise sediments deposited post-Neogen collisional event between the Australian Continent and the Banda subduction zone. Structures develop in the eastern Seram are thrust, normal faults, folds, and cleavages. The thrusts are verging to the northeast suggesting that the deformation occurred before Seram was rotated in an E-W direction.

Organic Geochemistry and Rock-Eval Pyrolysis of Eocene fine Sediments, East Ketungau Basin, West Kalimantan M.H. Hermiyanto Zajuli; Suyono Suyono
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i2.119Indonesia contains many Paleogene and Neogene basins which some of them have been proven to be a very prolific producer of oil and gas. A study on the result of Rock-Eval pyrolysis and biomarker undertaken on the Eocene Mandai Group was able to assess hydrocarbon potential of the Paleogene fine sediments in the frontier basin, especially West Kalimantan area. East Ketungau Basin is located in the western Kalimantan, bounded with Melawi Basin by the Semitau High in the south and West Ketungau Basin in the west. The Mandai Group was deposited in the East Ketungau Basin during Eocene, consisting of sandstone and mudstone facies. Mudstone facies comprises shale, claystone, and coal. Seven samples of Eocene fine sediments collected from East Ketungau Basin were analyzed by Rock-Eval pyrolisis and three samples for biomarker to evaluate their hydrocarbon potential. The Rock-Eval pyrolisis result of Mandai Group shows that TOC value of this facies ranges from 0.34 % to 5.16 %, Potential Yield (PY) between 0.06 and 4.78 mg HC/g rock, and Hydrogen Index (HI) from 12 to 89. Based on that result, the fine sediments of Mandai Group are included into a gas prone source rock potential with poor to fair categories. Moreover Tmax values vary from 426o C to 451o C. The Eocene fine sediments of Mandai Group fall under kerogen type III. Based on Tmax and biomarker analyses, the maturity of the sediments is situated within immature to mature level. The fine sediments of Mandai Group were deposited in a terrestrial to marine environment under anoxic to sub-oxic condition.

Magma Genesis in Kabanjahe Region Continental Margin Arc of Sumatra Bhakti H. HaraHap
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i2.120Volcanic rocks in Kabanjahe region, Karo Regency, North Sumatra Province, are products of old Toba Caldera, Sibayak Volcano, and Sipiso-piso Volcano. Rhyolitic tuff is the main lithology distributed over a large area in this region. Others are basaltic, basaltic andesitic, andesitic, dacitic, and rhyolitic lavas. Data show that the rock was originated from magma of a continental origin formed at a subduction zone environment. Petrogenetic modelling suggests that the range in composition was mainly controlled by a fractional crystallization of plagioclase, clinopyroxene, hornblende, and biotite. Harker’s variation diagram of major and trace elements show a continuous range that indicates they are cognate. The lava in this area belongs to a high-K, calc-alkaline series, with particular high Nb concentrations. The composition of these high-Nb lavas is more similar to those of intra plate basalts rather than those of calc-alkaline or arc-tholeiitic basalt. The high anomaly of Nb which is accompanied by high Th, Rb, and normative corundum suggests that the source may also be enriched in incompatible elements, a characteristic feature of alkali magmatism. The similarity of the trace element of volcanic rocks to the within-plate basalts indicates that the convecting mantle wedge above subducted slabs contains variable proportions of MORB-source and OIB-source components; fluids added were derived from the subducted slab. Hence, it is interpreted that the high Nb concentration of volcanic rocks from Kabanjahe region were generated from subduction modified OIB source components. Alternatively, a deep seated faulting conduit magma from the lower mantle resulted in the alkaline enrichment of the volcanics. This article performs a petrological aspect, especially based on geochemical analysis including major elements, trace elements, and rare earth elements. The results are plotted into a general and specific classification used in petrology.

Sea Surface Temperature Reconstruction Period 1993 - 2007 Based on Content Analysis of Coral Sr/Ca from the Region Labuan Bajo, Simeulue Island Sri Yudawati Cahyarini
Indonesian Journal on Geoscience Vol 6, No 3 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i3.121Sea surface temperature (SST) is one of the important parameters for (paleo) climate studies. The long time series of SST data are required to understand more the climate change. Coral geochemical proxy such as Sr/Ca overcomes this problem. Coral can provide long time series of climate data continuously from present till hundreds years ago, even fossil (dead) coral can do it till thousand years ago. In this study, Sr/Ca content of Porites coral within 10 m deep from Labuan Bajo, Simeulue Island was analyzed to reconstruct SST. Coral Sr/Ca shows a strong correlation with local SST in seasonal scale as well as in the annual mean scale. Reconstructed SST data show that the monsoon between 1993 2007 strongly influence the SST variation in the Simeulue region. It supposed that the seasonal variation signal strongly influence local SST than the annual mean signal such as El Nino.

Mechanism of High Frequency Shallow Earthquake Source in Mount Soputan, North Sulawesi Yasa Suparman; E. Kriswati; Y. E. Pamitro
Indonesian Journal on Geoscience Vol 6, No 3 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i3.122Moment tensor analysis had been conducted to understand the source mechanism of earthquakes in Soputan Volcano during October - November 2010 period. The record shows shallow earthquakes with frequency about 5 - 9 Hz. Polarity distribution of P-wave first onset indicates that the recorded earthquakes are predominated by earthquakes where almost at all stations have the same direction of P-wave first motions, and earthquakes with upward first motions.In this article, the source mechanism is described as the second derivative of moment tensor, approached with first motion amplitude inversion of P-wave at some seismic stations. The result of moment tensor decomposition are predominated by earthquakes with big percentage in ISO and CLVD component. Focal mechanism shows that the recorded earthquakes have the same strike in northeast-southwest direction with dip about 400 - 600. The sources of the high frequency shallow earthquakes are in the form of tensile-shear cracks or a combination between crack and tensile faulting.

Simulation of Groundwater Flow, Denpasar-Tabanan Groundwater Basin, Bali Province Heryadi Tirtomihardjo; T. Setiawan
Indonesian Journal on Geoscience Vol 6, No 3 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i3.123Due to the complex structure of the aquifer systems and its hydrogeological units related with the space in which groundwater occurs, groundwater flows were calculated in three-dimensional method (3D Calculation). The geometrical descritization and iteration procedures were based on an integrated finite difference method. In this paper, all figures and graphs represent the results of the calibrated model. Hence, the model results were simulated by using the actual input data which were calibrated during the simulation runs. Groundwater flow simulation of the model area of the Denpasar-Tabanan Groundwater Basin (Denpasar-Tabanan GB) comprises steady state run, transient runs using groundwater abstraction in the period of 1989 (Qabs-1989) and period of 2009 (Qabs-2009), and prognosis run as well. Simulation results show, in general, the differences of calculated groundwater heads and observed groundwater heads at steady and transient states (Qabs-1989 and Qabs-2009) are relatively small. So, the groundwater heads situation simulated by the prognosis run (scenario Qabs-2012) are considerably valid and can properly be used for controlling the plan of groundwater utilization in Denpasar-Tabanan GB.

Baseflow Separation of the Bribin River Upstream in Gilap Cave Flowage, Sewu Mountain Karst, Gunung Kidul, Yogyakarta T. N. Adji
Indonesian Journal on Geoscience Vol 6, No 3 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i3.124Baseflow of karst underground river is a dependable flow to recharge the underground flow within dry seasons. This research was conducted in Gilap Cave, located in the upper course of Bribin River. This location has a premeditated point for sustainable karst water along the Bribin River. The main objective of this study was to separate the components of Gilap underground river flow, with the intention on defining the proportion of baseflow component during the period of measurements. A water level data logger was installed during the period between 1 May 2006 and 31 March 2007 to determine the variation of water level during the dry season, rainy season, and when the prevalence of flood events. Subsequently, several times of discharge measurements at the time of high, medium, and low water level were carried out to define stage-discharge rating curve. Then, baseflow separation was conducted using automated baseflow separation by a digital filtering method. A digital filter value was obtained from a constant recession analysis of flood events all over the year, correlated with Maximum Baseflow Indices Value (BFImax) within karst aquifers. The result shows that during one year, 41 flood events occured in the Gilap Cave with digital filtering value of 0.996. In addition, the calculation of baseflow percentage performs that the overall value of the ratio is close to a number of around 80%. Meanwhile, the percentages within flood events vary between the range of 45-75%. From these figures, it generally confirms that flow from small fracture is still dominant to recharge dependable flow within the upper stream of Bribin River, especially in the dry season.

Engineering Geological Characteristics of the Residual Soil, Lower Quaternary Sediments in Kertajati Region, Majalengka, West Java Untung Sudarsono; G. Hasibuan
Indonesian Journal on Geoscience Vol 6, No 3 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i3.125Only few engineering geological researches on residual soil have been conducted in Indonesia, whereas many infrastructure projects take place on undulating area and mountainous area which are composed of residual soils. The paper discusses residual soil characteristics of the Lower Quaternary sediment (Qos) in Kertajati area, Majalengka. The methodology of the research consists of engineering geological mapping, in situ test using 2.5 ton penetrometer, sampling and laboratory test for index properties, Atterberg limits, grain size analysis, and strength tests. Field test analysis data show that the thickness of residual soil resting on the basement rock in the study area varies from 2.40 - 14.20 m. Upwards, it comprises sands, silts, and clays, respectively. Laboratory analysis data indicate that the residual soil is dominated by fine-grained fraction, composed of high plastic clay (CH). Relationship among engineering geological parameters was analysed using linear regression and tested using statistic method t-test to find real correlation among variables within 95 - 90% significance level.. Based on the test, there are real positive correlation with 19 degree of freedom and 5% and 10% level of significance are found in between plasticity indexes (IP) and liquid limits (LL), between plasticity indexes (IP) and clay contents (C), between specific gravities (G ) and clay contents (C). The real negative correlation with nine degree of freedom and 5% and 10% level of significance occurs in between cohesion (c) dengan friction angle (φ). Corelation between degree of saturation (G ) and clay contents (C) with 19 degree of freedom is found in 10% level of significance.

Geology and Characteristics of Pb-Zn-Cu-Ag Skarn Deposit at Ruwai, Lamandau Regency, Central Kalimantan Arifudin Idrus; L. D. Setijadji; F. Thamba
Indonesian Journal on Geoscience Vol 6, No 4 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i4.126This study is dealing with geology and characteristics of mineralogy, geochemistry, and physicochemical conditions of hydrothermal fluid responsible for the formation of skarn Pb-Zn-Cu-Ag deposit at Ruwai, Lamandau Regency, Central Kalimantan. The formation of Ruwai skarn is genetically associated with calcareous rocks consisting of limestone and siltstone (derived from marl?) controlled by NNE-SSW-trending strike slip faults. It is localized along N 70° E-trending thrust fault, which also acts as the contact zone between sedimentary and volcanic rocks in the area. The Ruwai skarn is mineralogically characterized by prograde alteration comprising garnet (andradite) and clino-pyroxene (wollastonite), and retrograde alteration composed of epidote, chlorite, calcite, and sericite. Ore mineralization is typified by sphalerite, galena, and chalcopyrite, formed at early retrograde stage. Galena is typically enriched in silver up to 0.45 wt % and bismuth of about 1 wt %. No Ag-sulphides are identified within the ore body. Geochemically, SiO is enriched and CaO is depleted in limestone, consistent with silicic alteration (quartz and calc-silicate) and decarbonatization of the wallrock. The measured resources of the deposit are 2,297,185 tonnes at average grades of 14.98 % Zn, 6.44% Pb, 2.49 % Cu, and 370.87 g/t Ag. Ruwai skarn orebody was originated at moderate temperatures of 250 - 266 °C and low salinity of 0.3 - 0.5 wt.% NaCl eq. The late retrograde stage was formed at low temperature of 190 - 220 °C and low salinity of ~0.35 wt.% NaCl eq., which was influenced by meteoric water incursion at the late stage of the Ruwai Pb-Zn-Cu-Ag skarn formation.

Regression-Correlation of Petrophysical Inter-Parameter of Igneous Rocks and Limestone from Kulonprogo Mountain Region, Yogyakarta Special Region Sigit Maryanto; R. Hasan
Indonesian Journal on Geoscience Vol 6, No 4 (2011)
Publisher : Geological Agency

DOI: 10.17014/ijog.v6i4.127Laboratory test of complete petrophysic parameters encompasing water absorption, compressive strength, Los Angeles abrasive strength, Rudellof abrasive strength, and wear resistance with Na2SO4 has been carried out for igneous and carbonate rocks taken from Kulonprogo Mountains region. Statistical verification of the data exhibits variation of correlation coefficients among parameters ranging from medium to very high value. The values of petrophysic test results are determined by the rock types. The result of this study is useful to estimate the accuracy of values of each parameter test result in Geological Survey Institute Laboratory using regression formula representing each relationship.

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Contact Name Ivan Ferdian

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Contact Name
Ivan Ferdian

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ivan.ijgbg@gmail.com

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Journal Mail Official
ivan.ijgbg@gmail.com

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Location
Kota bandung,

Jawa barat

INDONESIA