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INDONESIA
Indonesian Journal on Geoscience
ISSN : 23559314     EISSN : 23559306     DOI : -
Core Subject : Science,
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 5 Documents
Search results for , issue " Vol 6, No 2 (2011)" : 5 Documents clear
Magma Genesis in Kabanjahe Region Continental Margin Arc of Sumatra HaraHap, Bhakti H.
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1147.59 KB) | DOI: 10.17014/ijog.6.2.105-127

Abstract

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

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1816.031 KB) | DOI: 10.17014/ijog.6.2.95-104

Abstract

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

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (638.117 KB) | DOI: 10.17014/ijog.6.2.85-93

Abstract

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.
Fossilization Type of Elephas hysudrindicus from Blora on the Basis of Petrographic and Scanning Electron Microscopic Analyses Herman, Danny Z.
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (494.633 KB) | DOI: 10.17014/ijog.6.2.75-84

Abstract

DOI: 10.17014/ijog.v6i2.117Either fossils of the hominid or vertebrate have long been known from terraces along the Solo River in Central and East Java. Most terraces consist of andesitic sand to andesitic tuffaceous sand with either gravelpebble or conglomerate and some of them contain vertebrate fossils. It is in this place, an ancient elephant fossil named Elephas hysudrindicus was discovered in 2009. This fossil was discovered at an abandoned sand quarry of Sunggun area, Medalem Village, Kradenan Subregency, Blora Regency which and can be mentioned as a great event for the Geological Museum. It was said as a phenomenal discovery, because the fossil was found within the terrace with condition of nearly complete skeleton of an individual elephant. Some bone fragments of Elephas hysudrindicus fossil is treated as rock specimens because a number of minerals fill in either pore spaces or cavities or cracks within bones, and such infilling minerals can be observed in cut sections of the bones. Main goals of the study are to determine the distribution and type of minerals within the bones, interpret environment of deposition, and identify fossilization type. The methodology used in this study consists of petrographic and Scanning Electron Microscopic (SEM) analyses. Based on the petrographical observation, some bone specimens of Elephas hysudrindicus fossil are characterized by fibrous and porous feature with cracks occuring locally. Whilst, examination with SEM shows that the bone specimens are apparently composed of collophane or massive cryptocrystalline variety of apatite as the principal component of fossil bone, having physical characteristic of spheroidal structure and cavities of 100 to 1500 micron (μ) in diameter. Most cavities and pore spaces are predominantly filled in by either authigenic crystals of rhombohedral calcite and lesser pseudohexagonal kaolinite with either slightly minerals of manganese oxide or iron oxide or ilmenite, including oxidized kaolinite and calcium iron silicate. Impregnation during diagenesis may be the most appropriate expression for fossilization process of the Elephas hysudrindicus. It is indicated by the existing authigenic minerals within the bones cavities, pore spaces, and cracks which are possibly due to precipitation of mineralized fluids originated from groundwater within the terrace.
The Characteristics of Lahar in Merapi Volcano, Central Java as the Indicator of the Explosivity during Holocene Sudradjat, Adjat; Syafri, Ildrem; Paripurno, E. T.
Indonesian Journal on Geoscience Vol 6, No 2 (2011)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1903.942 KB) | DOI: 10.17014/ijog.6.2.69-74

Abstract

DOI: 10.17014/ijog.v6i2.116Merapi Volcano in Central Java has been the most active volcano during Holocene time. As a strato volcano, Merapi exhibits alternating volcanic activities of effusive and explosive characters and self destruction. The explosivity index has evolved during the last ten thousand years. The effusive activities were characterized by the occurrence of lava flows, the development of lava dome, and the production of the “nuee ardente d’avalanche” called Merapi type. The explosive stage is frequently accompanied by the occurence of pyroclastic flows. The present investigation is attempted to reveal the relationship between the characteristics of lahar and the evolution of the activity of Merapi Volcano. The quantitative analysis was focused on the size and shape of the lahar components particularly that of pumice as the main indicators in 73 measured stratigraphic columns of lahar deposits. In addition, the main chemical element rim structures of hornblende identified in lahar components indicate the different lahar units. There are five lahar units and five groups of Merapi activities which can be distinguished. It can be concluded that the characteristics of lahar reflect the evolution of the activities in the past. The risk analyses of Merapi Volcano therefore can be enlarged to cover the possible hazard based on the lahar characteristics.

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