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IDENTIFICATION OF SUSPECTED PALEOTSUNAMI DEPOSITS STUDY FROM KARAPYAK BEACH, PANGANDARAN AREA, WEST JAWA, INDONESIA
Get PDFIdentifying and determining paleotsunami deposits can be a vital tool for establishing the periodicity of earthquakes and their associated tsunami events beyond historical records. However, their deposits can be difficult to establish and to date. In this study, we used the characteristics of the 2006 Pangandaran tsunami deposit as a reference to identify paleotsunami deposits in Karapyak Beach, Pangandaran area, West Java, Indonesia. Similar to the 2006 Pangandaran tsunami deposit, the Karapyak Beach paleotsunami deposit is characterized by light brown loose sand materials overlying a dark brown paleosol layer with erosional contact. A thin layer of tsunami deposit, although varies in thickness, is locally found just above erosional contact. The deposit reveals non-laminated coarse grain size in the lower part that gradually changes into medium to fine sand in the upper part. The base of this lower part is rich with broken mollusc shells and corals. The mid to top of the lower part may contain several still-intact mollusc shells and corals, rock fragments, and anthropogenic products (roof tiles). Those types of fragments are absent in the upper part of this thin tsunami deposit. Grain size analysis shows a mixture of fine and coarse grains in the lower part of the 2006 tsunami deposits, as well as in the suspected paleotsunami deposits, suggesting an uprush of high energy flow during the sedimentation. The fining upward sequence above the mixed grain layers reflects a waning flow in pre-backwash deposition. Foraminifera analysis also shows a mixture of shallow and deep marine foraminifera in both recent tsunami and paleotsunami deposits. Based on the characteristics of the 2006 tsunami deposits, there are at least four paleotsunami deposits identified in Karapyak Beach, Pangandaran area
BIOZONA DELTA MAHAKAM MODERN BERDASARKAN KUMPULAN FORAMINIFERA BENTIK KECIL DAN POLEN KALIMANTAN TIMUR
No full textABSTRAKLokasi penelitian terletak di Delta Mahakam, Kalimantan Timur. Sebanyak 83 sampel sedimen diambil dari 3 bagian delta, yaitu Delta Plain, Delta Front dan Distributary Channel. Analisis foraminifera bentik kecil dan polen dilakukan dengan metode kuantitatif. Selanjutnya, Analisis kluster digunakan dalam penentuan biozona Delta Mahakam. Hasil penelitian menunjukkan Delta Mahakam terbagi menjadi 4 biozona, yaitu Biozona I (Polen palmae) terletak di Delta Plain, Biozona II (Foraminifera “A”) dan Biozona III (Foraminifera “B”) terletak di Delta Front. Sementara itu, Biozona IV (Polen non mangrove) terletak di Delta Plain, Delta Front dan Distributary Channel. Berdasarkan pola penyebaran biozona, Bagian Utara Delta Mahakam mempunyai biozona yang lebih beragam dibandingkan dengan bagian Selatan Delta Mahakam. Kata Kunci: Delta Mahakam, foraminifera bentik kecil, polen, biozona
ASSESSMENT OF POTENTIAL MARINE CURRENT ENERGY IN THE STRAITS OF THE LESSER SUNDA ISLANDS
Get PDFThe Lesser Sunda Islands extend from Bali to Timor and consist of two geologically distinct parts formed by a subduction system of oceanic crust along the Java-Timor Trench. The northern part which includes Bali, Lombok, Sumbawa, Flores, Wetar, Pantar and Alor, is volcanic in origin; whilst the southern part is non-volcanic, encompassing the islands of Sumba, Timor and Rote. The straits along the Lesser Sunda Islands are formed as a result of very complex geological processes and tectonics in this area. These straits are the most important cross-sections in the southern part of the Indonesian Throughflow (ITF), functioning as outlets for the mass flows of seawater from the Pacific Ocean to the Indian Ocean through the Flores and the Savu Seas. In these straits, relatively high current speeds are occurred, not only caused by the ITF but also due to its geometry, the influence of tidal flow, and monsoonal currents.Site study and ocean current measurement were conducted by using an echosounder, a pair of Acoustic Doppler Current Profilers (ADCP), and other supporting equipment. In general, the average of most ocean current speeds is less than 1.5 m/s with a duration flow of 8 -12 hours a day, and the maximum speed reaches up to 3 m/s. The tidal types in almost all the straits are mixed semidiurnal tides, in which two high waters and two low waters occur twice a day, with the high and low tides differ in height.The Lesser Sunda Straits were selected as the potential sites for ocean current power plant because their current speeds are relatively high and their characteristics are more predictable compared with other straits from other regions. Based on the results of bathymetry survey and current characteristics from the deployed ADCP at a fixed (stationary) location on the seabed, the best location for the current power turbines is at the depth of 15-30 m where the seabed gently sloping
SEBARAN SEDIMEN BERDASARKAN ANALISIS PARAMETER UKURAN BUTIR DI PERAIRAN MUARA SUNGAI SAMBAS KALIMANTAN BARAT
No full textStudi tentang sebaran sedimen dasar laut ini dilakukan dengan tujuan untuk mengetahui persentase nilai fraksi, jenis dan parameter statistik ukuran butir. Penelitian ini dilakukan pada bulan Maret – April 2021 di perairan muara Sambas, Kecamatan Pemangkat, Kalimantan Barat. Hasil persentase fraksi sedimen dasar laut dari pasir di lokasi ini diperoleh nilai rata-rata sebesar 23,11 %, lanau 63,33 % dan lempung 13,56 %. Dari hasil tersebut secara keseluruhan didapatkan sebaran jenis sedimen dasar di perairan ini didominasi oleh lanau. Berdasarkan parameter ukuran butir sedimen dasar diperoleh nilai ukuran butir rata-rata (Mz) berkisar antara 1,04 – 2,47. Hasil tersebut menunjukkan bahwa pemusatan sedimen di lokasi penelitian berada pada klasifikasi pasir halus (fine sand) dan pasir sedang (medium sand). Kemudian nilai sortasi yang diperoleh dari seluruh stasiun berkisar antara 0,93 - 1,50 dengan klasifikasi terpilah sedang (moderately sorted) dan terpilah buruk (poorly sorted), nilai skewnes berkisar antara 0,54 – 1,45 dengan klasifikasi condong sangat halus dan nilai kurtosis pada setiap stasiun berkisar antara 0,61 – 1,17 dengan klasifikasi platycuric, mesokurtic, very platykuric dan leptokurtic
INTERPRETASI GEOLOGI CEKUNGAN BERAU - PAPUA DAN SEKITARNYA, BERDASARKAN ANALISIS DATA GAYABERAT
Get PDFCekungan Berau merupakan cekungan yang mempunyai potensi menghasilkan hidrokarbon seperti halnya cekungan Bintuni dan Salawati. Penelitian yang telah dilakukan pada cekungan ini umumnya membahas studi tektonik dan stratigrafi regional serta geokimia. Analisis mengenai pola sub-cekungan dan konfigurasi batuan dasar belum pernah dilakukan pada daerah ini. Pada eksplorasi hidrokarbon, informasi mengenai tebal sedimen pola struktur dan pola tinggian diperlukan sebagai informasi awal dalam memetakan keberadaan deposenter yang ditindaklanjuti dengan survei lebih detail menggunakan metode seismik sehingga penelitian ini penting dilakukan. Penelitian ini dilakukan untuk mengestimasi keberadaan sub-cekungan sedimen, mengidentifikasi pola struktur geologi, dan konfigurasi batuan dasar pada cekungan Berau berdasarkan analisis data gayaberat. Metode yang dilakukan yaitu dengan menganalisis data gayaberat menggunakan analisis spektral, filter polinomial, dan pemodelan 2D. Hasil analisis spektral menunjukkan bahwa ketebalan batuan sedimen rata-rata diperkirakan 3.38 Km, orde yang dipilih dari hasil filter polinomial yaitu orde 6 yang digunakan untuk menentukan anomali regional dan residual. Sub-cekungan yang didelineasai berdasarkan hasil anomali residual gayaberat yaitu sebanyak 6 sub-cekungan sedimen, sedangkan pola struktur yang teridentifikasi yaitu berupa pola tinggian, graben, dan patahan/sesar. Hasil pemodelan 2D menunjukkan bahwa batuan dasar pada cekungan Berau yaitu batuan metamorfik dengan nilai rapat massa sebesar 2.8 gr/cc, lapisan di atasnya di interpretasikan sebagai batuan sedimen berumur PraTersier dengan nilai rapat massa 2.5 gr/cc, di atas batuan PraTersier di interpretasikan sebagai batuan sedimen berumur Paleogen dengan nilai densitas sebesar 2.3 gr/cc, lapisan yang paling atas diinterpretasikan sebagai batuan sedimen berumur Neogen dengan nilai rapat massa sebesar 2.4 gr/cc. Berdasarkan hasil analisis gayaberat menunjukkan bahwa Cekungan Berau mempunyai lapisan batuan sedimen yang cukup tebal dan beberapa struktur tinggian yang diduga sebagai tempat migrasi hidrokarbon yang menarik untuk diteliti lebih lanjut untuk mengetahui keberadaan hidrokarbon.Kata Kunci : Gayaberat, Analisis Spektral, Polinomial, Pemodelan 2D, Cekungan Berau, Papua BaratBerau Basin is one of basin that potential to produce hydrocarbons like Bintuni and Salawati Basin. Research that has been carried out in these basins is generally tectonic and stratigraphic regional and geochemical studies. Analysis of sub-basin patterns and basement configurations haven’t been done in these area. In hydrocarbon exploration, information about sediment thickness, structure lineament and basement hight patterns is needed as initial information to mapping the depocenter existence which is followed by a more detailed survey such as seismic methods, so that this study is important to do. The research was conducted to delineate sediment sub-basin, to identify geological structure patterns, and basement configuration in the Berau basin based on gravity data analysis. The method used by analyzing gravity data by using spectral analysis, polynomial filtering and 2D forward modeling. The spectral analysis result showed that the average thickness of sedimentary rocks estimated 3.38 Km. The polynomial order chosen from the results of the polynomial filter is order 6 which is used to determine regional and residual anomalies. The sub-basins were delineated based on the results of gravity residual anomalies were 6 sediment sub-basins, while the structural patterns identified are basement height, graben, and fault. The 2D modeling results show that the basement of the basin is metamorphic rock with a mass density value of 2.8 gr/cc, the upper layer of the basement is interpreted as PraTersier sedimentary rock with a mass density value of 2.5 gr/cc, on PraTersier rocks is interpreted as Paleogene sedimentary rocks with a density value of 2.3 gr/cc, the top layer is interpreted as a Neogene sedimentary rock with a mass density value of 2.4 gr/cc. Based on the results of gravity analysis shows that the Berau Basin has a thick layer of sedimentary rocks and some basement height structures that are suspected as places of migration of hydrocarbons which are interesting to be explored further to determine the presence of hydrocarbons.Keywords : Gravity, Spektral Analysis, Polynomial, 2D Modeling, Berau Basin, West Papu
Study of Granitoid Distribution at Toboali Waters, Bangka Belitung Province: Seismic data interpretation approach
Get PDFBangka Island is one of the islands in Indonesia which is traversed by Southeast Asia granitoid belt. This belt stretches from Burma (Myanmar) to Bangka Belitung. This granitoid has potential as a source rock of mineral that carrying tin and rare earth element. At present, mapping of granitoid rocks to the waters area is rarely published, so acoustic basement mapping is necessary to do in order to determine the distribution of granitoids in Toboali waters. The research method used is a single channel seismic with an energy source of 300 joules. The sound source uses a single plate boomer, so it has a high enough resolution but the penetration is not deep enough. Acoustic basement in Toboali waters varies in depth from 15 - 75 ms or getting deeper south. When viewed from the continuity of the acoustic basement, it is estimated that the granitoid is 7 km from the nearest coastline.Key words: single channel seismic, seismic interprtation, granitoid distribution, Toboali Waters, Bangka Belitung ProvincePulau Bangka merupakan salah satu pulau di Indonesia yang dilalui oleh jalur granitoid Asia Tenggara. Jalur ini membentang dari Burma (Myanmar) hingga Bangka Belitung. Granitoid ini memiliki potensi sebagai batuan sumber pembawa mineral timah dan unsur tanah jarang. Pada saat ini pemetaan batuan granitoid pada daerah perairan jarang dipublikasikan, sehingga pemetaan batuan dasar akustik perlu dilakukan dalam rangka mengetahui sebaran granitoid di Perairan Toboali. Metode penelitian yang digunakan yaitu seismik single channel dengan sumber energi yang dikeluarkan sebesar 300 joule. Sumber suaranya menggunakan boomer single plate, sehingga memiliki resolusi yang cukup tinggi akan tetapi penetrasinya tidak cukup dalam. Batuan dasar akustik di Perairan Toboali memiliki kedalaman bervariasi mulai dari 15 – 75 ms atau semakin ke selatan semakin dalam. Jika dilihat dari kemenerusan batuan dasar akustiknya diperkirakan granitoid tersebut berada 7 km dari garis pantai terdekat.Kata kunci: Seismik single channel, interpretasi seismik, distribusi granitoid, Perairan Toboali, Provinsi Bangka Belitun
Site Determination for OTEC Turbine Installation of 100 MW Capacity in North Bali Waters
Get PDFThis research was conducted to investigate a suitable location for the OTEC (Ocean Thermal Energy Conversion) pilot plant in North Bali. The investigation was done by calculating the theoretical potential of electric power output using the method of Uehara and Ikegami (1990) for closed cycle OTEC. OTEC power plants require a temperature difference between surface and bottom water layers at least 20°C. Temperature data were obtained from the HYCOM temperature model for a period of 9 years (2008 - 2017) at 4 points which were verified with field data taken in 2017 using KR Geomarin III. The results of field measurements show that the sea surface temperature (SST) in the study area ranges from 28 to 31°C while at depth of 800 m 5.75°C. ∆T values range from 22 to 25°C. Verification of modelling temperature and measurement temperature shows that the modeling results resemble the temperature of North Bali Waters. Analyses results for the four points showed that B-11, located in the Tedjakula area, has the largest electrical power output (71,109 MW). Thus, point B-11 is the best location for development of OTEC pilot plant in North Bali Waters.Keywords: sea water temperature, net power, OTEC closed cycle, North BaliPenelitian ini dilakukan untuk menentukan lokasi yang layak untuk pilot plant OTEC (Ocean Thermal Energy Conversion) di perairan Bali Utara. Penentuan dilakukan dengan menghitungpotensi teoritis output daya listrik menggunakan metoda Uehara dan Ikegami (1990) untuk OTEC siklus tertutup. Pembangkit listrik OTEC membutuhkan perbedaan suhu antara lapisan permukaan dan lapisan dalam sebesar 20°C atau lebih. Data suhu didapatkan dari model suhu HYCOM untuk jangka waktu 9 tahun (2008 – 2017) pada 4 titik yang diverifikasi dengan data lapangan yang diambil pada tahun 2017 dengan menggunakan KR Geomarin III. Hasil pengukuran lapangan menunjukaan bahwa suhu permukaan laut (SPL) daerah penelitian berkisar 28-31°C dan suhu air pada kedalaman 800 m adalah 5,75°C. Nilai ∆T berkisar 22-25°C. Verifikasi suhu hasil pemodelan dengan suhu hasil pengukuran menunjukkan bahwa suhu hasil pemodelan dapat mewakili suhu perairan Bali Utara. Hasil analisis yang dilakukan pada 4 titik menunjukkan bahwa titik B-11 yang terletak di daerah Tedjakula memberikan output daya listrik terbesar (71,109 MW). Titik B-11 merupakan lokasi terbaik untuk pengembangan pilot plant OTEC di perairan Bali Utara.Kata kunci: suhu air laut, daya listrik, OTEC siklus tertutup, Bali Utar
