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Potensi sumber daya geologi di daerah Cekungan Bandung dan sekitarnya Bronto, Sutikno; Hartono, Udi
Indonesian Journal on Geoscience Vol 1, No 1 (2006)
Publisher : Geological Agency

DOI:Â 10.17014/ijog.vol1no1.20062aGeologically, Bandung Basin and the surrounding area comprise volcanic rocks; therefore, originally the geological resources, such as energy, environmental geology and mineral were generated from past volcanic activities. Energy resources having been utilized or in the exploration stage are water energy (Saguling Electrical Hydro Power) and geothermal energy (Darajat, Kamojang, Wayang-Windu and Patuha Geothermal Fields). Potency of hydrocarbon energy is considered due to the presence of Tertiary sedimentary rocks under Bandung volcanic rocks. Environmental resources include water, soil, land, and natural panorama that mostly are already used for living, tourism, industry etc. Mineral resources cover metals and non metals. Mineral explorations, particularly for gold, have been conducted in the southern Bandung area. Recently, Center for Geological Survey itself has found a new mineral resource in the northern Bandung, i.e. Cupunagara Village, Cisalak Sub-Regency, Subang Regency - West Jawa. Â Â

Fasies gunung api dan aplikasinya Bronto, Sutikno
Indonesian Journal on Geoscience Vol 1, No 2 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no2.20061Based on the nature and rock association, a composite volcanic cone can be divided into central facies, proximal facies, medial facies and distal facies. Physiographically, those begin from central eruption at the summit, going down to upper slope, lower slope, and foot plain in the surrounding area. Central facies is characterized by the presence of subvolcanic intrusions, lava domes, and hydrothermally altered rocks. Proximal facies consists of alternating lava fl ows and pyroclastic breccias. Medial fasies mainly is composed of pyroclastic breccias, laharic breccias, and conglomerates. Whereas, distal facies is dominated by fi ne-grained epiclastic rocks having sand to clay size. Tuff can be widely distributed from proximal to distal facies due to its fi ne grain and lightness. Methodological approachs for classifi cation of volcanic facies in Tertiary and older rocks are remote sensing and geomorphology, volcanic stratigraphy, physical volcanology, structural geology, and petrology-geochemistry. This volcanic facies division is useful for supporting new discovery on energy and mineral resources, environmental geology, and geologic hazard mitigation. Â

Stratigrafi gunung api daerah Bandung Selatan, Jawa Barat Bronto, Sutikno; Koswara, Achnan; Lumbanbatu, Kaspar
Indonesian Journal on Geoscience Vol 1, No 2 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no2.20064The aim of this volcano stratigraphic study is to understand the historic relationship of each volcanoes in the South Bandung area. Methods used in this study are landsat analyses, fi eldwork, petrographic studies, and radiometric dating. Physiographically, South Bandung is composed of mountaineous area, hilly area, and high plain of Pangalengan and Bandung itself. Based on volcanic stratigraphy, volcanic rocks there are divided into eleven rock units, nine of them are identifi ed their volcanic sources, having Pliocene to Quaternary ages. The presence of subsurface Miocene volcanic rocks supports the super imposed volcanisms from Tertiary to Quaternary in this area. Mineral resources of sulphide metals are found in the central facies of Soreang, Kuda, and Dogdog volcanoes. Whereas, geologic hazards covering tectonic earthquakes, volcanic eruptions, and landslides also threaten this area. Mineral explorations and hazard mitigations are necessary to the presence of mineral resources and geologic hazard potential. Â

Perkembangan Geologi pada Kuarter Awal sampai Masa Sejarah di Dataran Yogyakarta Mulyaningsih, Sri; Sampurno, Sampurno; Zaim, Yahdi; Puradimaja, Deny Juanda; Bronto, Sutikno; Siregar, Darwin Alijasa
Indonesian Journal on Geoscience Vol 1, No 2 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no2.20065The uplift of Southern Mountains in Early Pleistocene has formed the Yogyakarta Basin. In this basin, the Merapi volcanic activity has been developing. Based on 14C dating in cinder deposits exposed at Cepogo, the volcanic activity took place since Â±42 ka. While on the basis of K/Ar dating in andesitic lava at Bibi Volcano, the activity took place since 0.67 ma. The high in the south and the appearance of Merapi volcanic dome in the north had caused a fl at valley. The southern part of the valley is bounded by the Southern Mountains and the western part is bounded by the West Progo Mountains. In the present time, the lithology of the areas which are interpreted as a palaeo-valley is composed of black clay deposits. This black clay is a contact between the basement rocks and Merapi volcanic deposits. The black clay deposits exposed in the Progo River (Kasihan) has been developed since Â±16.59 to 0.47 ka, while in the Opak River (Watuadeg) 6210 y BP. Younger black clay deposits intersecting with lahars are also exposed at the Winongo River and have an age of 310 y BP. The age data of volcanic stratigraphy shows that Merapi activities had taken place since Â±6210 up to Â±310 years ago. Â

Dinamika pengendapan lahar permukaan pada alur-alur lembah di bagian selatan Gunung Api Merapi, Yogyakarta Mulyaningsih, Sri; Sampurno, Sampurno; Zaim, Yahdi; Puradimaja, Deny Juanda; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 1, No 3 (2006)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol1no3.20062Endapan aliran rombakan Gunung Api Merapi, yang lebih dikenal sebagai lahar, terbentuk dari hasil longsoran endapan awan panas yang dipicu oleh curah hujan yang sangat tinggi. Pada saat ini, endapan awan panas tersebut berasal dari guguran kubah lava. Material suspensi tersebut selanjutnya menuruni lereng dengan kecepatan yang tinggi, menghasilkan aliran turbulen. Aliran tersebut biasanya berkembang pada daerah dengan perbedaan morfologi berkemiringan lereng tinggi ke landai, atau yang sering dikenal sebagai daerah tekuk lereng. Studi ini didasarkan pada pengamatan dan pengukuran fragmen lahar yang berukuran besar di permukaan. Analisis meliputi arah penyirapan, bentuk, dan besar butir fragmen. Hasil penelitian mendapatkan model arah aliran fragmen besar lahar dari bagian atas aliran rombakan, yang membentuk âmodel punggung katakâ atau âmodel punggung gajahâ. Bagian depan katak atau gajah (kepala) yaitu arah aliran atau bagian depan aliran. Hasil penelitian juga menunjukkan bahwa model tersebut berlaku pada fragmen dengan diameter 90 cm atau lebih besar. Di daerah penelitian, fragmen dengan diameter 90 cm mencapai jarak hingga 22 km dari sumbernya. Hasil penelitian ini dapat digunakan sebagai model untuk menentukan arah aliran lahar (aliran rombakan) purba yang sumbernya belum diketahui. Â

Gunung api maar di Semenanjung Muria Bronto, Sutikno; Mulyaningsih, Sri
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. Â

Asal-usul Pembentukan Gunung Batur di daerah Wediombo, Gunungkidul, Yogyakarta Hartono, Gendoet; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 2, No 3 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no3.20073Physiographically, the Gunung Sewu Subzone is predominantly composed of limestone of the Wonosari Formation, but in Wediombo area volcanic rocks of the Wuni Formation is exposed. The Wediombo volcanic rocks contain lava flows and volcanic breccias associated with Batur intrusive rock, in which all the rocks have andesitic composition. The problem is whether the Wedi- ombo volcanic rocks originated from far distance area which then was intruded by local magma after its deposition, or it is an association of the Wediombo volcanic and the Batur intrusive rocks which both are the remnants of a paleovolcano in the area. To identify the central facies of the paleovolcano, the geological principle that âthe present is the key the pastâ is used as a geological approach.Wediombo area forms a high landscape showing an elevation of about 280 m above sea level with dips of the outer slopes 20 - 40%. The drainage pattern developing in the area fol- lows the existing circular structure to form subradial - radial patterns. The high landscape shows a circular structure with a diameter of less than 2 km and it opens to the Indian Ocean. Besides the Mount Batur intrusive rock, there are some other dikes which have been already hidrothermally altered, with some mineralization in the circular structure. Meanwhile, the outer slopes are composed of alternating lava flows and fragmental volcanic rocks of 22 - 25o in dip forming a concentric pattern. Petrologically, the Batur intrusive rock is light to dark grey in color, hypocrystalline porphyritic texture, with phenocryst ranges from 1.2 - 2.2 mm in size, subhedral-euhedral crystals, fine vesicular structures. The rock comprises plagioclase, pyroxene, hornblende and opaque minerals. Geochemically, the rock indicates an island arc tholeitic magma (SiO = 60.38 â 64.53 wt%, K O = 0.63 â 0.85 wt%). Those data indicate that the circular structure was the central facies and the outer slope was the proximal facies of the Wediombo paleovolcano in Gunungkidul Yogyakarta. Â

Genesis endapan aluvium Dataran Purworejo Jawa Tengah; Implikasinya terhadap sumber daya geologi Bronto, Sutikno
Indonesian Journal on Geoscience Vol 2, No 4 (2007)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol2no4.20072Purworejo is part of the Southern Central Jawa alluvial plain that is bordered by the South Sera- yu Mountains and Sumbing Volcano in the north, West Progo Mountains in the east, Indian Ocean in the south, and Kebumen-Banyumas plain in the west. This Purworejo plain comprises reworked allu- vial deposits, particularly from Tertiary volcanic rocks of the South Serayu and West Progo Mount- ains, and the Sumbing Quaternary Volcano. In the northern part older reworked material has formed Purworejo alluvial fan in the east and Kutoarjo alluvial fan in the west. Those alluvial fans developed from northeast side of studied area. The central part of Purworejo plain consists of older coastal alluvial deposits which have been covered by recent fluvial deposits that transported by Wawar River in the west, Jali River in the middle, and Bogowonto River in the east. The southern part of Purworejo plain, starting from the Lereng River until present coastal line is composed of younger alluvial coast- al deposits. It is suggested that groundwater resources are abundant under the Purworejo plain, and the young alluvial coastal deposits contain highly potential iron sand and associated minerals. Â

Waduk Parangjoho dan Songputri: Alternatif Sumber Erupsi Formasi Semilir di daerah Eromoko, Kabupaten Wonogiri, Jawa Tengah Bronto, Sutikno; Mulyaningsih, Sri; Hartono, G.; Astuti, B.
Indonesian Journal on Geoscience Vol 4, No 2 (2009)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol4no2.20091The Semilir Formation was typically originated from products of a very explosive volcanic activity, i.e. breccias, lapillistones, and tuffs containing abundant pumice. It has a light grey to white colour and high silica andesite to dacite in composition, mainly rich in volcanic glass and quartz. Sedimentary structures of these volcanic rocks are massive, grading, planar bedding, and cross-bedding to antidunes, with grain size varies from ash (â¤ 2 mm) to lapilli (2 â 64 mm) to bomb and block (> 64 mm). The formation is widely distributed from the west side (Pleret and Piyungan areas, Bantul Regency, Special Province of Yogyakarta) until Eromoko area in the east (Wonogiri Regency, Jawa Tengah Province). Stratigraphically, the Semilir Formation underlies the Nglanggeran Formation, and overlies the Mandalika Formation in the eastern part and Kebo-Butak Formation in the western part. Geomorphological- and lithological analyses of the Semilir Formation in areas of Parangjoho and Song- putri Dams, Eromoko Sub-regency, Wonogiri Regency indicate that the two depressions were alternatively volcanic sources of the Semilir Formation in the Eromoko area. This is proved by the presence of co-ignimbrite breccias(co-ignimbrite lag fall deposits), that descriptively they are polymict breccias. This rock is characterized by a mixing of pumice and various hard rock fragments that primarily are juvenile materials (volcanic blocks, bombs), accessory-, and accidental rock fragments set in pumice-rich volcanic ash and lapilli sizes. The accessory materials came from older volcanic rocks, whereas the accidental ones were originated from basement rocks. During a caldera forming event or a destruction period of an older composite volcanic cone(s), all older rocks resting above the magma chamber were ejected to the surface by a very high magmatic pressure. Since they were heavier than the juvenile material, most accessory and accidental rock fragments were left (lag fall) in caldera rim behind the ash and pumice flow. In the dam areas of Parangjoho and Songputri, the lag fall fragments consisting of andesite, pyroxene andesite, dacite, and pumice, being 10 â 150 cm in diameter are set in pumice-rich lapilli tuffs. Some of the rock fragments are volcanic blocks and bombs, while the older rocks are angular to very angular shape, having prismatic jointing or jigsaw-crack structures. The eruptions in the Parangjoho and Songputri craters were controlled by north-south trending fractures, and they resemble to the Katmaian caldera explosion type. Â

Analisis stratigrafi awal kegiatan Gunung Api Gajahdangak di daerah Bulu, Sukoharjo; Implikasinya terhadap stratigrafi batuan gunung api di Pegunungan Selatan, Jawa Tengah Hartono, Hill Gendoet; Bronto, Sutikno
Indonesian Journal on Geoscience Vol 4, No 3 (2009)
Publisher : Geological Agency

http://dx.doi.org/10.17014/ijog.vol4no3.20091Generally, Tertiary volcanisms in the Southern Mountains, Central Jawa were started with the formation of pillow lavas having basalt to basaltic andesite in composition. This initial stage volcanism developed into a Â construction period of composite volcanoes that consist of alternating basaltic to andesitic lava flows, breccias, and tuffs. The construction period could be followed by a destructive phase, producing pumice-rich pyroclastic breccias, lapillistones, and tuffs of high silica andesite to dacite, or even rhyolite in composition. A stratigraphic measuring section at Bulu area, Sukoharjo Regency, presents an alternat- ing fine-grained andesitic volcaniclastic material and some limestones, with the total thickness is 143.33 m. The thickness of bedded volcaniclastic material tends to be thickening upward from 35 m until 90 m. The grain size of the volcaniclastic material also tends to be coarsening upward from clay size through silt and fine sand to coarse sand and granules. Paleontological analysis on fossils contained in the lime- stone gives an age of Early Miocene (N7 - N9). The volcaniclastic rocks is conformably overlain by the Mandalika Formation, comprising alternating andesitic breccias, lavas, and tuffs. These data imply that the fine-grained volcaniclastic material is an initial product of the construction period of Gajahdangak Volcano in the area, that formed the Mandalika Formation. This Formation is overlain by the Semilir Formation, composed of pumice-rich pyroclastic breccias and tuffs with dacitic composition. This as- sociated volcanic rock reflects a product of a caldera explosion or a destructive phase. Based on the characteristics of lithology of volcanic products from the initial stage, to a construction and destruction period, and compiled age data, the Southern Mountains represent formal volcanic rock units that are able to be divided into many formations. Â

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