Riset Geologi dan Pertambangan最新文献

{"title":"FORAMINIFERA ASSEMBLAGES AS A MARKER OF MUD ERUPTION SOURCE IN CIUYAH, CINIRU – KUNINGAN, WEST JAVA","authors":"V. Isnaniawardhani, Faizal Muhamadsyah, A. Sudrajat","doi":"10.14203/RISETGEOTAM2018.V28.509","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.509","url":null,"abstract":"Mud eruptions that rise claystone to sandstone-size fragments, liquid, gas, and heat to the surface have been identified in Ciuyah, Ciniru District, Kuningan. Field observation and sampling were conducted on host rock as well as mud in Ciuyah. Forty-two planktic and forty-two benthic foraminiferal species were identified in rock samples; while 89.28% of them are recorded in mud samples. Foraminifera contained in claystone and sandstone of Pemali and Halang Formations reveals the age of Middle to Late Miocene. Based on their stratigraphic ranges, planktic foraminifera assemblages in mud represent four age-marker groups, there are: older than Zone N.10 / Middle Miocene (indicated by the appearance of Globorotalia archeomenardii), ranges of Zone N.11 – N.12 / Middle Miocene (marked by the appearance of Globorotalia fohsi lobata and Globorotalia praemenardii), ranges of Zone N.13–N.14 / Middle Miocene (Globorotalia siakensis and Globorotalia mayeri), and ranges of Zone N.15–N.17 / Late Miocene (Globorotalia acostaensis acostaensis and Neogloboquadrina dutertrei dutertrei). Benthic foraminifera can be grouped into outer neritic and bathyal typical assemblages. That several age-marker planktic foraminifera groups mixing and deep marine typical benthic occurrence in mud samples is produced by reworking process during turbidity sedimentation, as well as erosion and elution of base- and side-rock composed by Pemali and Halang Formations.Semburan lumpur yang membawa fragmen-fragmen berukuran batulempung hingga batupasir, cairan, gas dan panas ke permukaan telah teridentifikasi di Ciuyah, Kecamatan Ciniru, Kuningan. Observasi  lapangan dan pengambilan sampel dilakukan terhadap batuan induk serta lumpur di Ciuyah dan sekitarnya. Empat puluh dua spesies foraminifera planktik dan empat puluh dua spesies bentik teridentifikasi dalam sampel batuan; dengan 89,28% di antaranya terekam dalam sampel lumpur. Foraminifera yang terkandung dalam batulempung dan batupasir Formasi Pemali dan Halang menunjukkan umur Miosen Tengah hingga Akhir. Berdasarkan rentang stratigrafinya, kumpulan foraminifera planktik dalam lumpur menunjukkan empat kelompok penanda umur, yaitu: lebih tua dari Zona N.10 / Miosen Tengah (ditunjukkan oleh kehadiran Globorotalia archeomenardii), rentang Zona N.11 - N.12 / Miosen Tengah (ditandai oleh kehadiran Globorotalia fohsi lobata dan Globorotalia praemenardii), rentang Zona N.13 -N.14 / Miosen Tengah (Globorotalia siakensis dan Globorotalia mayeri), dan rentang Zona N.15 - N.17 / Miosen Akhir (Globorotalia acostaensis acostaensis dan Neogloboquadrina dutertrei dutertrei). Foraminifera bentik dapat dikelompokkan dalam kumpulan neritik luar dan batial. Beberapa kelompok penanda umur foraminifera planktik dan kehadiran bentik laut dalam pada lumpur dihasilkan oleh pengerjaan ulang selama sedimentasi turbidit, serta erosi dan elusi batuan dasar dan batuan samping yang tersusun oleh Formasi Pemali dan Halang.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"150 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82273439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NUMERICAL MODELLING APPLICATIONS ON FRACTURE PREDICTIONS: AN EXAMPLE FROM THE BLUE LIAS FORMATION IN KILVE, UK","authors":"A. Patria","doi":"10.14203/RISETGEOTAM2018.V28.801","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.801","url":null,"abstract":"Numerical modeling using Comsol Multiphysics, with Finite Element Method, has been carried out to study fracture initiation, linkage, and deflection of the Blue Lias Formation. Data were from outcrop observation where hydrofractures were well observed. Three models were set up to understand how fractures initiated, linked and arrested. The Young’s modulus of shales (Esh) was set with the value of 1 GPa, 5 GPa, and 10 GPa. The fluid excess pressure was applied with the value of 5 MPa, 10 MPa, and 15 MPa. The Young’s modulus of the limestone (Elst) was a constant at 10 GPa. The first model showed how the overburden induces fracture initiation. The results indicated that tensile stress concentrated only within limestone and favour to form fractures. The second model was about linking of fractures. The result explained that shear stress was dominantly concentrated in limestone layers. Previous hydrofractures possibly linked up forming shear fractures and en-echelon fractures. The third model was run to understand fracture propagation and deflection. The result was that tensile stress concentrated at the hydrofracture tips close to the contacts between limestone and shale. Hydrofractures were deflected, and in some places, hydrofractures were likely started to propagate through shale.Permodelan numerik dengan Comsol Multiphysics berdasarkan metode Elemen Terbatas  dilakukan untuk mempelajari inisiasi, hubungan, dan defleksi rekahan Formasi Blue Lias. Data berasal dari observasi singkapan dimana hydrofracture teramati. Tiga model dibuat untuk memahami bagaimana rekahan terinisiasi, terhubung, terambatkan dan terhenti. Modulus Young’s batulempung (Esh) diatur dengan nilai 1 GPa, 5GPa, dan 10 GPa. Tekanan kelebihan cairan (fluid excess pressure) yang diterapkan sebesar 5 MPa, 10 MPa, dan 15 MPa. Modulus Young’s batugamping (Elst) konstan sebesar 10 GPa. Model pertama menunjukkan bagaimana pembebanan mempengaruhi inisiasi rekahan. Hasil perhitungan menunjukkan bahwa tekanan tarik terkonsentrasi hanya pada lapisan batugamping dan memungkinkan terbentuknya rekahan. Model kedua mengenai hubungan rekahan. Model menunjukkan bahwa tekanan geser terkonsentrasi pada lapisan batugamping secara dominan. Hydrofracture yang telah ada akan terhubung membentuk rekahan geser and rekahan en-echelon. Model ketiga dihitung untuk memahami perambatan dan defleksi rekahan. Hasilnya menunjukkan bahwa tekanan tarik terkonsentrasi pada ujung hydrofracture dekat kontak lapisan batugamping dan batulempung. Hydrofracture terdefleksi dan pada beberapa titik mulai merambat menembus batulempung.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"1 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88475658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MODEL SISTEM PANAS BUMI LAPANGAN KARAHA - TALAGA BODAS BERDASARKAN INVERSI 2D DATA MAGNETOTELLURIK","authors":"Ilham Arisbaya, Aldinofrizal Aldinofrizal, Yayat Sudrajat, Eddy. Z Gaffar, Asep Harja","doi":"10.14203/RISETGEOTAM2018.V28.989","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.989","url":null,"abstract":"Daerah Karaha-Talaga Bodas, yang terletak di kawasan Utara Gunung Galunggung, Tasikmalaya diduga memiliki prospek panas bumi, dengan adanya manifestasi permukaan berupa fumarol dan mata air panas. Metode Magnetotelurik (MT) diaplikasikan untuk mengidentifikasi struktur resistivitas bawah permukaan yang terkait dengan sistem panas bumi. Pengolahan data MT dilakukan melalui beberapa tahap, yaitu transformasi  Fourier , seleksi  crosspower , analisis rotasi, analisis kontak vertikal dan inversi dengan hasil akhir berupa model sebaran 2D. Hasil pengolahan data menunjukan adanya lapisan konduktif dengan nilai resistivitas 1-10 Ohm.m, yang diduga berperan sebagai lapisan penudung. Zona reservoir berupa daerah dengan nilai resistivitas 10-100 Ohm.m. Nilai resistivitas yang lebih besar dari 100 Ohm.m berkorelasi dengan batuan beku yang biasa dianggap sebagai sumber panas. Interpretasi hasil pengolahan data MT diintegrasikan dengan informasi geologi untuk mendapatkan gambaran sistem Panas Bumi Karaha-Talaga Bodas . The area of Karaha-Talaga Bodas, at the north of Mount Galunggung, Tasikmalaya, was expected to have a geothermal prospect due to several surface manifestations of fumaroles and hot springs. The Magnetotelluric method (MT) was then applied in this area to identify the subsurface resistivity structure related to the geothermal system. The MT data processing included Fourier transform, crossover selection, rotation analysis, vertical contact analysis, and inversion, with the result of a 2D resistivity model. The resistivity model indicated the existence of a conductive layer with the resistivity value of 1-10 Ohm.m, which could be a caprock. The reservoir zone is the area with the resistivity value of 10-100 Ohm.m. The resistivity value greater than 100 Ohm.m correlates with the basement, that acted as the heat source. Interpretation of the MT model was then integrated with the geological information to get an overview of the Karaha-Talaga Bodas geothermal system.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"40 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88363347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"SEDIMENTARY FACIES AND HYDROCARBON RESERVOIR POTENTIAL OF SAND FLAT IN THE UPPER PART OF TAPAK FORMATION IN BANYUMAS AREA, CENTRAL JAVA","authors":"Y. Rizal, W. Santoso, A. Rudyawan, R. A. Tampubolon, Affan Arif Nurfarhan","doi":"10.14203/RISETGEOTAM2018.V28.835","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.835","url":null,"abstract":"The upper part of Tapak Formation in Kali Cimande consists of alternating sandstones, siltstone and mudstone. The alternating sequence showed a fining and thinning upward bedding pattern. The facies association of the alternation built up by sand flat facies, which characterized by medium sandstone, moderate sorted, with cross-lamination sedimentary structures and mostly on the top of sandstone layer found a bioturbation trace fossils (Skolithos). Mixed flat facies, which is characterized by an alternation of thin layered sandstones with mudstone and siltstone, with lenticular, wavy, and flaser sedimentary structures, contained many forms of bioturbation, such Planolites, Thallasinoides, Lockeia, and Ophiomorpha. Mud flat facies association, is characterized by a repeated of claystone with thin sandstone intercalation, where the ratio of clay content more than 95 % of the total layers, contained abundantly with trace fossil Lockeia. Upper Tapak Formation plays as moderate reservoir potential. The thick sandstone in sand flat facies with moderate to poorly sorted and moderate porosity is required to provide hydrocarbon flows in Banyumas Basin.Bagian atas Formasi Tapak di Kali Cimande terdiri dari perselingan batupasir-batulanau dan mudstone. Sekuen perselingan menunjukkan pola perlapisan menghalus dan menipis ke atas. Asosiasi fasies tersebut terdiri dari fasies sand flat, yang dicirikan oleh batu pasir sedang, pemilahan sedang, struktur sedimen silang-siur serta fosil jejak bioturbasi (Skolithos) pada bagian puncak kebanyakan lapisan batu pasir. Fasies mixed flat, dicirikan oleh perselingan batupasir berlapis tipis dengan mudstone dan batulanau, serta struktur sedimen lentikular, perlapisan bergelombang, dan flaser, mengandung banyak bioturbasi, seperti Planolites, Thallasinoides, Lockeia, serta Ophiomorpha. Asosiasi Fasies sand flat, dicirikan oleh perulangan batulempung dengan sisipan batupasir tipis, dengan kandungan lempung lebih dari 95% total lapisan, serta fosil jejak Lockeia yang melimpah. Formasi Tapak Atas berperan sebagai reservoir potensial sedang. Bagian batupasir tebal di fasies sand flat dengan pemilahan sedang hingga buruk dan porositas sedang diperlukan untuk menyediakan aliran hidrokarbon di Cekungan Banyumas.  ","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"1 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86355177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MIKROZONASI SEISMIK WILAYAH KOTA PADANG BERDASARKAN PENGUKURAN MIKROTREMOR","authors":"Adrin Tohari, Dadan Dani Wardhana","doi":"10.14203/RISETGEOTAM2018.V28.984","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.984","url":null,"abstract":"Peristiwa gempa bumi pada tanggal 30 September 2009, dengan skala intensitas VII-VIII, mengindikasikan bahwa wilayah Kota Padang rentan terhadap amplifikasi tanah. Makalah ini menyajikan hasil analisis rasio spektra H/V untuk menghasilkan mikrozonasi kerentanan amplifikasi berdasarkan pengukuran mikrotremor. Hasil analisis menunjukkan variasi nilai periode predominan dan faktor amplifikasi yang dipengaruhi oleh jenis lapisan tanah dan struktur bawah permukaan. Berdasarkan variasi nilai faktor amplifikasi, wilayah Kota Padang dapat diklasifikasikan menjadi 5 (lima) zonasi kerentanan amplifikasi. Kawasan perumahan kepadatan tinggi, perdagangan dan perkantoran di wilayah kecamatan Nanggalo, Padang Utara, Padang Barat dan Padang Selatan berada di zona kerentanan tinggi hingga sangat tinggi terhadap bahaya amplifikasi. Hasil zonasi ini sesuai dengan fakta-fakta kerusakan bangunan akibat fenomena amplifikasi yang terjadi pada gempa bumi 30 September 2009. The 30 September 2009 earthquake event with intensity VII to VIII (MMI scale) indicated that Padang City region is prone to soil amplification. This paper presents the results of H/V spectral ratio analysis to produce a microzonation map of amplification for Padang City based on microtremor measurement. The analysis of microtremor data shows that the predominant period and amplification factor of the soils are spatially varied and influenced by soil types and subsurface structure. On the basis of amplification factor, Padang City is classified into 5 (five) zones. High and very high susceptible zones are mainly concentrated in the very dense residential areas, trade and office areas, including the districts of Nanggalo, Padang Utara, Padang Barat, and Padang Selatan. The predicted amplification susceptibility zones are in a good agreement with the phenomena of building damages due to amplification during the 2009 earthquake.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"178 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89270771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"SEBARAN ALTERASI BATUAN BERDASARKAN RASIO Th/U DI TAPALANG, MAMUJU, SULAWESI BARAT","authors":"I. Sukadana, Frederikus Dian Indrastomo, Ngadenin Ngadenin","doi":"10.14203/RISETGEOTAM2018.V28.661","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.661","url":null,"abstract":"Kecamatan Tapalang, Mamuju, menjadi tujuan eksplorasi uranium dengan adanya radiasi tinggi terdeteksi pada batuan basaltik Formasi Adang. Diperlukan lokalisasi daerah-daerah dengan tingkat potensi kandungan uranium yang tinggi. Proses alterasi meningkatkan tingkat kelarutan uranium, sehingga kadar uranium berkurang dan terjadi pengkonsentrasian torium serta logam tanah jarang (REE) yang signifikan. Dengan asumsi bahwa alterasi berasosiasi dengan rasio Th/U, maka dilakukan penelitian untuk mengetahui sebaran alterasi batuan berdasarkan korelasinya terhadap rasio Th/U. Penelitian dilakukan dengan pengukuran radioaktivitas dan pengamatan alterasi di lapangan, kemudian dilengkapi  dengan analisis XRF dan analisis mineragrafi untuk mengetahui tingkat alterasi. Rasio Th/U pada batuan lava Tapalang yang masih relatif segar memiliki nilai 3-30, dan batuan yang telah teralterasi memiliki nilai 30 - >3000. Pengembangan eksplorasi torium dapat difokuskan pada daerah dengan alterasi lanjut, sedangkan eksplorasi uranium harus difokuskan pada daerah yang bersifat reduktif, yang memungkinkan terbentuknya cebakan uranium. Tapalang, Mamuju, is a destination for uranium exploration due to the high radiation detected in basaltic rocks of Adang Formation. Uranium potentials localization is required since uranium is not distributed evenly. An alteration process increases the level of uranium solubility, so that the uranium content is depleted and the concentration of thorium and rare earth elements (REE) are significantly high. This study objective was to find the distribution of rock alterations and their correlation to the ratio of Th/U in Tapalang Region. Research methods were combination of radioactivity measurement and alteration observation in the field, completed by XRF and mineragraphy analysis to measure the grade of alteration. The alteration product indicated that this area has been affected by hydrothermal alteration in the potassic zone. Th/U ratio of fresh Tapalang lava rocks has a value of 3-30, and alterated rocks have 30 - 3000 value. These values can be used to delineating alteration areas, which have high Th/U ratio (30 - >3000). The development of thorium exploration can be focused on advanced alteration areas, whereas uranium exploration should focus on reductive areas that allow for uranium deposited.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"03 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85971115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"HIDROGEOLOGI DAN POTENSI CADANGAN AIRTANAH DI DATARAN RENDAH INDRAMAYU","authors":"Rizka Maria, Anna Fadliah Rusydi, Hilda Lestiana, Sunarya Wibawa","doi":"10.14203/RISETGEOTAM2018.V28.803","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.803","url":null,"abstract":"Potensi airtanah pada suatu cekungan tidak terlepas dari kondisi hidrogeologi di wilayah itu sendiri. Cekungan airtanah Indramayu, yang berada di pesisir utara Jawa Barat, hingga kini belum diketahui secara pasti potensi cadangannya. Penelitian ini bertujuan untuk mengetahui potensi cadangan  air tanah berdasarkan rekonstruksi hidrogeologi data bor. Hasil interpretasi hidrogeologi menunjukkan bahwa litologi akuifer didominasi oleh endapan lempung dengan sisipan lanau, sedikit pasir halus di bagian atas, endapan lempung marin dengan sisipan lanau, dan pasir halus di bagian bawah. Hasil perhitungan menunjukkan prediksi cadangan airtanah yang cukup potensial. Nilai rata – rata potensi airtanah bebas adalah 65.213,8 m 3 /hari atau 0,754 m 3 /det. Nilai rata – rata potensi airtanah tertekan adalah 79.557,1 m 3 /hari atau 0,920 m 3 /det. Tetapi kualitas airtanah di wilayah Losarang – Lobener – Pasekan – Sindang sebagian besar payau dan memiliki nilai DHL yang tinggi, berkisar antara 4710 – 11400 µs/cm. The groundwater potential of a basin depends on the hydrogeology of the area. Indramayu groundwater basin is located at the north coast of Java Island. Its reserves potential was not identified despite its importance. The objective of this research was to understand the potential of groundwater reserves based on hydrogeological reconstruction from drilling data analysis. The results of the hydrogeology interpretation had indicated that the aquifers lithology are dominated by clay deposits with silt layering, slightly fine sand at the top, marine clay deposits with silt inserts, and fine sand at the bottom. The calculation results had indicated a good potential of groundwater reserves. The mean value of the unconfined groundwater is 65,213.8 m 3 /day or 0.754 m 3 /sec. The mean value of the confined groundwater is 79,557.1 m 3 /day or 0.920 m 3 /sec. However, groundwater supply potential is not supported by the quality. The groundwater in Losarang - Lobener – Pasekan-Sindang area is brackish and has a high DHL value (4710 – 11400 µs/cm).","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"13 5 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81367148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MODEL KERENTANAN GERAKAN TANAH WILAYAH KECAMATAN CILILIN MENGGUNAKAN TRIGRS","authors":"Erizky Ade Kurniawan, Adrin Tohari, Indra Permanajati","doi":"10.14203/RISETGEOTAM2018.V28.969","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.969","url":null,"abstract":"Upaya pengurangan risiko gerakan tanah memerlukan pengetahuan yang baik tentang karakteristik curah hujan yang dapat mempengaruhi kerentanan suatu daerah perbukitan terhadap gerakan tanah. Daerah perbukitan di Kecamatan Cililin di Kabupaten Bandung Barat merupakan salah satu wilayah yang sering mengalami bencana gerakan tanah pada waktu hujan lebat. Makalah ini menyajikan hasil pemodelan kestabilan lereng regional menggunakan Transient Rainfall Infiltration and Grid-based Regional Slope-stability analysis (TRIGRS) untuk mengkaji pengaruh karakteristik curah hujan terhadap tingkat kerentanan gerakan tanah di wilayah Kecamatan Cililin. Hasil pemodelan memperlihatkan lokasi-lokasi gerakan tanah pada umumnya terletak pada zona kerentanan gerakan tanah tinggi. Selain itu, luas zona kerentanan sangat tinggi dapat meningkat dua kali akibat kenaikan intensitas hujan. Pemodelan juga mengindikasikan bahwa zona kerentanan gerakan tanah dikontrol oleh faktor topografi dan geologi. Zona kerentanan gerakan tanah sangat tinggi cenderung terjadi pada wilayah dengan kondisi kemiringan terjal dan tersusun oleh satuan batuan vulkanik berumur Miosen Akhir yang mempunyai nilai kuat geser yang rendah. Sedangkan zona kerentanan rendah terasosiasi dengan wilayah lereng landai yang tersusun oleh satuan tufa batuapung dan batupasir tufan berumur Miosen Tengah yang mempunyai nilai kuat geser yang tinggi. Efforts to reduce the risk of a landslide require a good knowledge of the characteristics of rainfall on the susceptibility of a hilly area to landslides. The hilly area of Cililin Subdistrict in West Bandung Regency is one of the areas that often experience landslide disasters during heavy rainfalls. This paper presents the regional slope stability modeling using Transient Rainfall Infiltration and Grid-based Regional Slope-stability analysis (TRIGRS) to assess the effect of rainfall on the landslide susceptibility in Cililin Subdistrict. Results of modeling show that the locations of previous landslide incidents are generally located in the very high susceptibility zone. Besides, the areas of very high landslide susceptibility can increase twice due to the increase of rainfall intensity. The modeling also indicates that the landslide susceptibility of the area is mainly controlled by the topographical and geological factors. The high landslide susceptible zone is most likely to occur in the steep hilly areas made up of soils with low shear strength values which were originated from the Upper Miocene volcanic rocks. Whereas very gentle slope areas are made up of high shear strength soil originated from the Middle Miocene (pumice tuff and tuffaceous sandstone) that belongs to the low landslide susceptibility zone.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"44 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89361961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PALEONTOLOGY OF ACROPORA CORALS AND STANDARD FACIES BELT FROM UJUNGGENTENG AREA, WEST JAVA","authors":"W. Santoso, Y. Zaim, Y. Rizal","doi":"10.14203/RISETGEOTAM2018.V28.799","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.799","url":null,"abstract":"The detail taxonomy analysis was performed to classify Acropora corals in Ujunggenteng Area. The research area was selected because the continuously exposed Quaternary coralline limestones, indicated the high variation and wide distribution of coral fossils. Moreover, the facies changes and contacts with shoreface sediments were clearly observed in this area. Detail taxonomy based on morphological description can classify Acropora corals in Ujunggenteng area into four species: Acropora cervicornis, Acropora palifera, Acropora gemmifera, and Acropora humilis. The study of coral paleontology and the application of the presence of corals as a standard facies belt were still rarely performed in Indonesia. Previous studies classified the coralline limestone into one standard facies belt, which was the organic build- up standard facies belt. Another approach was required to capture many conditions of coral fossil occurrences; not only in build-up condition but also in transported condition. Therefore, another purpose of this study is to modify the standard facies belt with a different approach using coral taphonomy and sediment association.Analisis taksonomi secara detil dilakukan untuk mengklasifikasikan koral Acropora di daerah Ujunggenteng. Daerah penelitian dipilih karena tersingkapnya batugamping terumbu berumur Kuarter yang menerus, yang menunjukkan tingginya jumlah spesies dan distribusi fosil koral yang luas. Selain itu, perubahan fasies dan kontak dengan batupasir pantai dapat jelas diamati pada daerah ini. Taksonomi detil berdasarkan deskripsi morfologi dapat mengelompokkan koral Acropora di daerah Ujunggenteng menjadi empat spesies: Acropora cervicornis, Acropora palifera, Acropora gemmifera, dan Acropora humilis. Selain itu, studi mengenai paleontologi dan penggunaan kehadiran koral sebagai dasar pembagian sabuk standar fasies batugamping masih jarang dilakukan di Indonesia. Studi sebelumnya mengelompokkan batugamping terumbu menjadi satu sabuk standar fasies, yaitu organic build up. Pendekatan yang lain diperlukan untuk menjelaskan kondisi koral lainnya pada batugamping, tidak hanya dalam kondisi tumbuh, tetapi juga dalam kondisi tertransportasi. Oleh karena itu, penelitian ini bertujuan untuk memodifikasi sabuk standar fasies dengan pendekatan berbeda menggunakan tafonomi koral dan asosiasi sedimen. ","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"44 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87544294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PALEOBATIMETRI FORMASI JATILUHUR BERDASARKAN KUMPULAN FORAMINIFERA KECIL PADA LINTASAN SUNGAI CILEUNGSI, KABUPATEN BOGOR, JAWA BARAT","authors":"Lili Fauzielly, Lia Jurnaliah, Ria Fitriani","doi":"10.14203/RISETGEOTAM2018.V28.660","DOIUrl":"https://doi.org/10.14203/RISETGEOTAM2018.V28.660","url":null,"abstract":"Formasi Jatiluhur di sekitar Sungai Cileungsi merupakan lingkungan laut dangkal (zona neritik) berdasarkan dominasi foraminifera yang dikandungnya. Namun beberapa penelitian terdahulu menyatakan umur Formasi Jatiluhur yang bervariasi. Penelitian paleobatimetri berdasarkan kumpulan foraminifera kecil diharapkan dapat melengkapi kajian detil yang terkait dengan evolusi daerah ini selama Miosen. Pengambilan 30 sampel sedimen dilakukan secara sistematik pada satu lintasan di sepanjang Sungai Cileungsi. Hasil preparasi sampel sedimen dengan metode hidrogen peroksida menghasilkan 57301 individu foraminifera kecil yang terdiri dari 23276 individu foraminifera plangtonik dan 34025 foraminifera bentonik. Untuk mengetahui paleobatimetri, digunakan rasio foraminifera plangtonik dan foraminifera bentonik kecil.  Hasil  Rasio P/B berkisar antara 4,4 % - 74,0 % menunjukkan paleobatimetri Formasi Jatiluhur berkisar antara zona neritik dalam – zona batial atas. Jatiluhur Formation in the area of Cileungsi River was a shallow marine environment based on the foraminiferas domination. Several previous published papers had suggested age variation of the Jatiluhur Formation. Paleobatimetry study based on small foraminiferas was expected to complete the Miocene evolution analysis of the region. Thirty sediment samples were picked systematically in a section line along Cileungsi River. The hydrogen peroxide preparation of sediment samples produced 57301 small foraminifera. There were 23276 planktonic foraminiferas and 34025 benthic foraminiferas.  To understand the paleobathimetry of this research area, we calculated the ratio of planktonic foraminifera and benthic foraminifera (P/B ratio).  The P/B ratio is betweeen 4,4% and 74,0%.  The ratio suggests that the paleobathimetry of Jatiluhur Formation is Inner Neritic Zone - Upper Bathyal Zone.","PeriodicalId":41045,"journal":{"name":"Riset Geologi dan Pertambangan","volume":"24 1","pages":""},"PeriodicalIF":0.1,"publicationDate":"2018-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91267644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}