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Review of Submarine Landslides in the Eastern Indonesia Region
Get PDFhis paper reviews submarine landslide potential in the eastern Indonesia by analyzing published and recently acquired bathymetric data and interpreting seismic reflection data. This review aims to study and invent hazards that might affect seafloor infrastructure construction such as optic cables, especially in the eastern Indonesia Region. The hazards were also recognized as source of tsunamis such as Palu Bay 2018 and Babi Island north of Flores Island in 1992. On the other hand, submarine landslide is a common process of basin fill sedimentation in the region. As blessed with many active volcanoes, it has 130 of total the world 400, Indonesia should aware of tsunami induced by volcanoes especially the ones closed to the sea. There are five active volcanoes frequently produce tsunami in historical times: Anak Krakatau, Sunda Strait; Makian, Maluku Province; Sangihe, Sulawesi; Teon and Nila, Banda Sea; and Iliwerung, Lembata Island, east Lesser Sunda Islands.Key words: submarine landslide, volcanic tsunami, seafloor infrastructure, eastern Indonesia Makalah ini menelaah potensi langsoran dasar laut di wilayah Timur Indonesia melalui analisis publikasi dan data batimetri yang baru diambil serta penafsiran data seismic refleksi. Tinjauan longsoran dasar laut dimaksudkan untuk mempelajari dan menginventarisasi bencana yang mungkin bisa mempengaruhi pembangunan infrastruktur dasar laut seperti halnya kabel optic, terutama di wilayah Timur Indonesia. Bencana tersebut telah dikenal sebagai sumber beberapa tsunami seperti Teluk Palu 2018 dan Pulau Babi utara Lombok di tahun 1992. Sebaliknya, longsoran dasar laut merupakan proses sedimentasi pengisian cekungan yang biasa terjadi di wilayah tersebut. Dikarunia akan gunungapi terbanyak di dunia, sebab memiliki 130 dari 400 dunia, Indonesia harus menyadari bahaya tsunami yang ditimbulkan oleh aktivitas gunungapi terutama yang dekat laut. Terdapat lima gunungapi aktif yang sering menghasilkan tsunami dalam sejarah: Anak Krakatau, Selat Sunda; Makian, Provinsi Maluku; Sangihe, Sulawesi; Teon dan Nila, Laut Banda; dan Iliwerung, Pulau Lembata, Nusa Tenggara Timur.Kata kunci: longsoran dasar laut, tsunami gunungapi, infrastruktur dasar laut, Wilayah Indonesia Timu
Inhibition Effects of Jakarta Bay Sediments to the Growth of Marine Diatom (Chaetoceros Gracilis)
Get PDFJakarta Bay coastal ecosystem is known suffered from water pollution and habitat degradation. Solid and fluid waste from households and several industrial areas flow and ended up in the bay. Ecotoxicological studies are needed to assess the effects of pollutant on marine organism, including phytoplankton as the primary producer. Therefore chemical analysis and toxicity test were performed to investigate the impact of Jakarta Bay Sediments to marine diatoms Chaetoceros gracilis. Heavy metals concentration especially Cu, Pb, Cd, and Hg in the sediments were lower than in previous studies. It could be related to the stricter environmental regulations which started enforced at the end of 1990s. Meanwhile, PAH and pesticide were higher than in previous studies. Increasing activities and maritime traffic in surrounding area of Tanjung Priok Port area and most likely comes from other adjacent harbors (Muara Baru, Muara Angke, and Marina Ancol harbor) and the massive usage of the pesticide compound in the households of the Jakarta City area were suspected to be the reasons. Estuaries area and locations <10 km were identified and predicted would produce harmful effects since the concentration of Zn and Hg in those area exceeded Probable Effects Level (PEL) of Sediment Quality Guidelines (SQG). The growth responses of Chaetoceros gracilis were varied greatly. Most of the sites (24 from 31 sites) showed inhibition effects on the growth of diatoms, ranged from 1.75-35.33 % (17.75±9.59 %) relative to control, with the highest inhibition value was at Cengkareng Drain estuary (M2). The relationship between the concentration of contaminants and the inhibition response could not be clearly explained, however, there is an assumption that low concentrations of some heavy metals were suspected to give adverse effects on diatom’s growth.Keywords: sediment, toxicity, marine diatoms, Chaetoceros gracilis, Jakarta BayEkosistem Teluk Jakarta dikenal mengalami pencemaran air dan degradasi habitat. Limbah cair dan padat berasal dari perumahan dan industri mengalir dan berakhir di teluk tersebut. Kajian ekotoksikologi diperlukan untuk mengetahui pengaruh pencemar terhadap organisme laut termasuk fitoplankton sebagai produsen primer. Analisis kimia dan uji toksisitas dilakukan untuk mengetahui dampak sedimen Teluk Jakarta terhadap diatom laut Chaetoceros gracilis. Konsentrasi logam berat terutama Cu, Pb, Cd, dan Hg dalam sedimen lebih rendah dari penelitian sebelumnya. Hal tersebut berkaitan dengan peraturan lingkungan ketat yang mulai diberlakukan pada akhir 1990-an. Namun demikian, konsentrasi PAH dan pestisida lebih tinggi dari penelitian sebelumnya. Hal tersebut diduga kuat akibat dari peningkatan aktivitas dan lalu lintas maritim di daerah sekitar Pelabuhan Tanjung Priok, juga kemungkinan besar berasal dari pelabuhan lain yang berdekatan (Muara Baru, Muara Angke, dan pelabuhan Marina Ancol) serta akibat penggunaan besar-besaran senyawa pestisida kegiatan rumah tangga di wilayah Kota Jakarta. Daerah dan lokasi estuaria <10 km diidentifikasi dan diprediksi akan menghasilkan efek berbahaya karena konsentrasi Zn dan Hg di area tersebut melebihi Probable Effects Level (PEL) dari Pedoman Kualitas Sedimen (SQG). Respon pertumbuhan diatom laut Chaetoceros gracilis sangat bervariasi. Sebagian besar stasiun (24 dari 31 stasiun) menunjukkan efek penghambatan pada pertumbuhan diatom, berkisar antara 1,75-35,33% (17,75 ± 9,59%) relatif terhadap kontrol, dengan nilai penghambatan tertinggi di muara Sungai Cengkareng (M2). Hubungan antara konsentrasi kontaminan dan respon penghambatan tidak dapat dijelaskan dengan lebih pasti namun terdapat asumsi konsentrasi rendah dari beberapa logam berat diduga memberikan efek buruk pada pertumbuhan diatom.Kata Kunci: sedimen, toksisitas, diatom laut, Chaetoceros gracilis, Teluk Jakart
KETEBALAN ENDAPAN SEDIMEN PASIR LAUT BERDASARKAN DATA SEISMIK DANGKAL SALURAN TUNGGAL DI PERAIRAN TAKALAR, SELAT MAKASSAR
Get PDFKetebalan dan jenis sedimen dasar laut di suatu lokasi penelitian dapat diketahui dari pengambilan data geologi permukaan dan bawah permukaan dasar laut. Metoda yang digunakan untuk mendapatkan data tersebut di atas antara lain geofisika laut (batimetri, seismik refleksi), geologi (pengambilan contoh sedimen dasar laut). Kegiatan penelitian ini berada di perairan Selat Makassar, di muara sungai sekitar pantai Takalar sebagai sumber sedimen pasir ke arah lepas pantai. Sumber sedimen pasir tersebut diketahui dari hasil pengamatan di lapangan ternyata dipengaruhi oleh energi gelombang, arus sejajar pantai (longshore current) dan arus pasang surut (tidal current). Data geologi bawah permukaan (sub bottom profiling) didapat dengan menganalisa rekaman seismik pantul dangkal untuk mengetahui ketebalan dan luasan sebaran sedimen pasir. Dari analisis data tersebut dilakukan pendekatan perhitungan secara kualitatif sehingga diketahui deposit endapan pasir dengan luas area kurang lebih 9,764 km², dengan asumsi ketebalan rata-rata 3,84 meter maka deposit kurang lebih 224 juta meter³.Kata Kunci : Seismik refleksi, sedimen pasiran, Takalar, Selat Makasar The thickness and type of seabed sediments at a research location can be known from surface and subsurface geological data collection. The methods used to obtain the above data include marine geophysics (bathymetry, seismic reflection), geology (sampling of sea floor sediments). This research activity was located in the Makassar Strait waters, at the mouth of the river around the Takalar coast as a source of sand sediment towards the offshore. The source of the sand sediment known from observations in the field was influenced by wave energy, longshore currents and tidal currents. Sub-bottom profiling is obtained by analyzing shallow reflected seismic records to determine the thickness and sand deposition distribution. From the analysis of the data the qualitative calculation approach is carried out so that it is known that the deposition of sand deposits with an area of approximately 9,764 km², assuming an average thickness of 3,84 meters, the deposit reserves of approximately 224 million meters³. Keyword : seismic reflection, sandy sediment, Takalar, Makasar strai
ESTIMASI TRANSPOR SEDIMEN DI PERAIRAN KECAMATAN BREBES, JAWA TENGAH BERDASARKAN LAJU SEDIMENTASI DAN PENDEKATAN MODEL NUMERIK
Get PDFErosi dan akresi telah menjadi masalah utama di perairan Kecamatan Brebes. Perubahan pesisir yang sangat dinamis dipicu oleh faktor hidro-oseanografi yang mengendalikan mekanisme transpor sedimen yang terjadi baik di muara maupun diwilayah pantai. Tujuan dari penelitian ini adalah untuk mengetahui tingkat rata-rata laju sedimentasi dan transpor sedimen yang terjadi di kawasan pantai Kecamatan Brebes. Pengambilan data laju sedimentasi menggunakan sediment trap yang kemudian dianalisis secara statistik. Perhitungan total transportasi sedimen dan distribusi vertikal suspensi sedimen dilakukan dengan pendekatan model numerik. Nilai laju sedimentasi berkisar antara 0,243 – 22,724 g.m-2.hari-1 dimana laju tertinggi berada di hulu sungai Pemali, Sungai Pemuda dan hilir sungai Pemali. Nilai sortasi sedimen menunjukkan nilai 1,1 – 1,59 (pemilahan buruk). Nilai skewness (Ski) berkisar antara 0,21 – 0,46 (dominan menceng sangat halus). Nilai kurtosis berkisar antara 1,79 – 4,45 (sangat runcing). Total transportasi sedimen sebesar 43,88 x 10-5 m3/s dan distribusi vertikal konsentrasi sedimen tersuspensi berkisar antara 1-176 mg/L (pasang) dan 3-198 mg/L (surut) dimana transpor sedimen sangat dipengaruhi oleh kondisi oseanografi (gelombang, pasang surut, dan arus sepanjang pantai). Pada saat tinggi gelombang pecah meningkat maka transpor sedimen yang terjadi juga semakin intens termasuk mekanisme erosi dan sedimentasi yang terjadi di dasar perairan.Kata kunci: Laju sedimentasi, model numerik, transpor sedimen, perairan BrebesErosion and accretion has become the main issues in Brebes Sub-District waters. Coastal changes which are very dynamic are triggered by hydro-oceanography factors controlling sediment transport mechanism occurred both in the estuary and coastal area. This study aims to determine the average of sedimentation rate and the sediment transport depiction in Brebes Sub-District coast. Sedimentation rate data collection was done using cylinder sediment trap which was then analyzed statistically. Total transport sediment and suspended sediment vertical distribution were calculated employing numerical model approach. The value of sedimentation rate ranged from 0.243 – 22.724 g.m-2.day-1 in which the highest value was observed upstream Pemali River, Pemuda River, and downstream Pemali River. Sediment sortation ranged from 1.1 – 1.59 (poorly sorted). Skewness (Ski) value ranged from 0.21 – 0.46 (very fine skewed). Kurtosis value ranged from 1.79 – 4.45 (very leptokurtic). Total sediment transport reached 43.88 x 10-5 m3/s and vertical distribution of suspended sediment ranged from 1-176 mg/L (flood) and 3-198 mg/L (ebb) respectively wherein the sediment transport is strongly controlled by the oceanography conditions (waves, tidal, and longshore current). When the breaking wave crest enhanced, the sediment transport occurs intensely including erosion and sedimentation in the bottom of water. Keywords: Sedimentation rate, numerical model, sediment transport, Brebes water
Reservoir Characterization Using Acoustic Impedance Inversion and Multi-Attribute Analysis in Nias Waters, North Sumatra
Get PDFSeismic method is one of the most frequently applied geophysical methods in the process of oil and gas exploration. This research is conducted in Nias Waters, North Sumatra using one line 2D post-stack time migration seismic section and two wells data. Reservoir characterization is carried out to obtain physical parameters of rocks affected by fluid and rock lithology. Seismic inversion is used as a technique to create acoustic impedance distribution using seismic data as input and well data as control. As final product, multi-attribute analysis is applied to integrate of inversion results with seismic data to determine the lateral distribution of other parameters contained in well data. In this research, multi-attribute analysis is used to determine the distribution of NPHI as a validation of hydrocarbon source rocks. In that area, there is a gas hydrocarbon prospect in limestone lithology in depth around 1450 ms. Based on the results of sensitivity analysis, cross-plot between acoustic impedance and NPHI are sensitive in separating rock lithology, the target rock in the form of limestone has physical characteristics in the form of acoustic impedance values in the range of 20,000-49,000 ((ft/s)*(g/cc)) and NPHI values in the range of 5-35 %. While the results of the cross-plot between the acoustic impedance and resistivity are able to separate fluid-containing rocks with resistivity values in the range about 18-30 ohmm. The result of acoustic impedance inversion using the model based method shows the potential for hydrocarbons in the well FYR-1 with acoustic impedance in the range 21,469-22,881 ((ft/s)*(gr/cc))
Identification of Quaternary Sediments and the Existence of Biogenic Gas Sources in the Topang Delta, Meranti, Riau
Get PDFDelta Topang, located in Topang Island, Riau Province is known to have the potential of biogenic gas. This research was conducted to identify the Quaternary sediment and the existence of biogenic gas reservoar. In this research has been conducted 75 points of surface geoelectrical measurements (38 points in Parit Jawa and 37 points in Parit Bintang) and 2 points of core drilling (BH-1 in Parit Jawa and BH-2 in Parit Bintang). Total Organic Carbon was also carried out on 10 samples (5 samples from each drilling core). Based on resistivity value of geoelectrical measurements from all points, in general are determined 2 sediment types, very fine sediment (silt and clay) and fine sand. We discussed in detail only point 11 representing Parit Jawa region and point 39 representing Parit Bintang Village. Both in point 11 and point 39, very fine sediment was identified from the surface down to 59 m and 58.5 m respectively, mostly dominated by hydrous clay. Below these, very fine sediment is identified as fine sand. Core drilling BH-1 and BH-2 (40 m length each) composed of thick layer of hydrous clay from the core surface down to bottom part, intercalated with thin layers of silt and fine sand. We considered fine sand found at depths between 24 to > 90 m (from all geoelectrical measurement points) as the closure of biogenic gas. At Parit Jawa biogenic gas closures are found at 2 locations, which are in south west and north east measurement area. At Parit Bintang biogenic gas closures are found at 3 location which are one in south and two in north measurement area. Total organic carbon analyzed from BH-1 indicate the highest percentage at 26-27 m depth with percentage 71.6%. From BH-2 the highest value is indicated at 33-34 m depth with percentage 78.0%. From all this information it is known that the formation of biogenic gas from the abundance of TOC is in the layers of hydrous clay and clay where is in an anaerobic sulfate-reduction environment.Keyword: Quartenary sediment, biogenic gas, surface geoelectrical measurement, core drilling, total organic carbonDelta Topang, yang terletak di Pulau Topang, Distrik Rangsang, Kabupaten Meranti, Provinsi Riau pada diketahui memiliki potensi keberadaan gas biogenik. Penelitian ini dilakukan untuk Identifikasi Sedimen Kuarter dan keberadaan sumber gas biogenik. Pada penelitian ini telah dilakukan 75 titik pengukuran geolistrik permukaan (38 titik di Parit Jawa dan 37 titik di Parit Bintang). Pemboran inti dilakukan di dua lokasi antara lain BH-1 di Parit Jawa dan BH-2 di Parit Bintang. Analisa total karbon organik juga dilakukan pada 10 sampel (5 sampel dari setiap inti pemboran). Berdasarkan nilai resisitivitas pengukuran geolistrik dari semua titik, secara umum ditentukan 2 jenis sedimen, adalah sedimen yang sangat halus (lanau dan lempung jenuh air) dan pasir halus. Dalam makalah ini dibahas secara rinci hanya titik 11 yang mewakili Desa Parit Jawa dan titik 39 yang mewakili Desa Parit Bintang. Baik di Point 11 dan Point 39, sedimen yang sangat halus diidentifikasi dari permukaan hingga kedalaman 59 m dan kedalaman 58,5 m, yang didominasi oleh lempung jenuh air, di bawah sedimen yang sangat halus ini diidentifikasi sebagai pasir halus. Hasil pemboran inti BH-1 dan BH-2 (masing-masing 40 m) terdiri dari lapisan tebal lempung jenuh air dari permukaan, ke bagian bawah merupakan lapisan lanau dan pasir halus. Dari pengukuran geolistrik diperoleh pasir halus yang ditemukan pada kedalaman antara 24 m hingga lebih dari 90 m adalah sumber gas biogenik. Di Parit Jawa, sumber gas biogenik ditemukan di 2 lokasi, yaitu di barat daya dan timur laut daerah pengukuran. Di Parit Bintang sumber gas biogenik ditemukan di 3 lokasi yaitu satu di selatan dan dua di daerah pengukuran utara. Total karbon organik yang dianalisis dari BH-1 menunjukkan persentase tertinggi pada kedalaman 26-27 m dengan persentase 71,6%. Dari BH-2 nilai tertinggi ditunjukkan pada kedalaman 33-34 m dengan persentase 78,0%. Dari semua informasi ini diketahui bahwa pembentukan gas biogenik dari kelimpahan TOC, berada di lapisan lempung dan lempung jenuh air di mana berada dalam lingkungan reduksi sulfat anaerob.Kata kunci: Sedimen Kuarter, gas biogenik, pengukuran geolistrik permukaan, pemboran inti, total organic carbo
INDIKASI LEMBAH PURBA SEBAGAI WADAH MINERAL PLASER DAN UNSUR TANAH JARANG DI PERAIRAN TANJUNG BERIKAT DAN SEKITARNYA, BANGKA TENGAH, BANGKA BELITUNG
Get PDFSecara regional daerah Bangka merupakan bagian dari Jalur Granit Utama Pembawa Timah. Daratan nya ditandai oleh intrusi Granit Klabat yang merupakan batuan penting sumber endapan plaser. Untuk mengetahui lembah purba maka dilakukan perekaman seismik saluran tunggal. Daerah penelitian secara administratif merupakan bagian dari wilayah Kabupaten Bangka Tengah, Propinsi Bangka Belitung. Perairan Tanjung Berikat dan sekitarnya dicirikan oleh kelerengan dasar laut rata-curam dengan kedalaman terukur antara 0-45 meter. Interpretasi seismik saluran tunggal menunjukkan stratigrafi seismik dari muda ke tua yaitu Runtunan A, Runtunan B, intrusi, dan Runtunan C sebagai dasar akustik. Ketebalan sedimen Runtunan A antara 5-30 meter dari permukaan dasar laut. Lembah purba memanjang cukup lebar dan dalam pada Runtunan B yang diduga sebagai fasies pengisian lembah berupa onlap fill. Fasies ini memiliki internal reflektor bebas pantulan-kaotik yang ditafsirkan sebagai wadah mineral plaser dan mineral ikutan pembawa unsur tanah jarang. Endapan plaser diperkirakan merupakan hasil pengerjaan ulang batuan granitoid.Kata Kunci : Dasar laut, runtunan stratigrafi, lembah/alur Purba, endapan plaser, dan Perairan Tanjung Berikat dan Sekitarnya, Bangka-Belitung. Geologically regional, the Bangka area is part of the Main Tin Belt Granite. The mainland of the study area is characterized by Klabat Granite intrusion which is an important rock source of placer deposits. To find out the placer availability of deposits on Paleo channel it was carried out for the recording of single channel seismic data. The study area is administratively part of the area of Central Bangka, Bangka-Belitung Province. Tanjung Berikat waters and its vicinity are characterized by the slope of the flat sea floor to steep with a measured depth of 0-45 meters. Seismic interpretation shows seismic stratigraphic from young to old consisting of sequence A, sequence B, Intrusion, and sequence C as acoustic basement. Sediment thickness of sequence A between 5-30 meters from seafloor surface sediment. Paleo channel with an elongated shape that is wide enough and deep in sequence B is interpreted as a channel filling facies in the form of onlap fill. This facies is characterized by the free to chaotic reflector configuration which is interpreted as a place for mineral placer and accessory minerals which contain rare earth elements. The availability of placer deposits is interpreted as the result of reworking of granitoid source rock.Keywords: Sea floor, stratigraphic seismic, Paleo channel, placer deposits, and Tanjung Berikat waters and surrounding, Bangka-Belitung
DIVERSITAS DAN DISTRIBUSI FORAMINIFERA DI SELAT BENGGALA DAN SEKITARNYA, ACEH
Get PDFPenelitian foraminifera di sekitar Selat Benggala belum diketahui namun telah ada penelitian dari sekitar pulau-pulau kecil di laut lepas Aceh. Penelitian mengenai keragaman dan sebaran foraminifera di perairan tersebut penting dilakukan sebagai data awal untuk interpretasi lingkungan pengendapan terkait batimetri, oseanografi, ekologi, klimatologi purba dan lain-lain. Hasil identifikasi foraminifera di sekitar Selat Benggala diperoleh 19 spesies foraminifera plangtonik dan 43 spesies foraminifera bentik. Nilai rasio foraminifera plangtonik dan foraminifera bentik (rasio P/B) relatif bervariasi berkisar antara 0 dan 81,84%. Nilai nol dijumpai di tiga stasiun yang didominasi oleh Amphistegina, Calcarina dan Heterostegina penciri lingkungan terumbu karang. Nilai rasio PB tertinggi tidak dijumpai pada stasiun dengan kedalaman tertinggi (1485 m) namun di stasiun yang berdekatan dengan pantai barat Pulau Weh pada kedalaman 101 m. Hal ini kemungkinan berkaitan dengan pola arus setempat dan morfologi dasar laut (kemiringan lereng) sehingga terjadi akumulasi spesimen foraminifera plangtonik.Kata kunci: foraminifera, rasio P/B, kedalaman, Selat Benggala, Aceh.Foraminiferal study from Benggala Strait is unknown but it has been studied from surrounding small islands off Aceh. The study of diversity and distribution of foraminifera from the present study area is important as the initial data for the interpretation of the environmental deposition, paleo-bathymetry, paleo-oceanography, ecology, climatology and others. This study has identified 19 planktonic foraminifera and 43 species of benthic from Benggala Strait. The ratio of benthic and planktonic foraminifera (PB ratio) are varied between 0 and 81.84%. The zero value is found in three stations that dominated by Amphistegina, Calcarina, and Heterostegina associated with coral environment. The highest value of PB ratio is not found in the deepest depth (1485 m) but in a station that is close to western coast of Weh island with 101 m water depth. It may related to local current system and seafloor morphology (slope gradient) that accumulated specimens of planktonic foraminifera. Keywords: foraminifera, P/B ratio, water depth, Benggala Strait, Aceh
