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BULLETIN OF THE MARINE GEOLOGY

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Published by Marine Geological Institute of Indonesia

ISSN : 14106175 EISSN : 25278843 DOI : -

Core Subject : Science,

Earth & Planetary Sciences

Bulletin of the Marine Geology is a scientific journal of Marine geoscience that is published periodically, twice a year (June and December). The publication identification could be recognized on the ISSN 1410-6175 (print) and e-ISSN: 2527-8843 (on-line) twice a year (June & December) and it has been accredited by Lembaga Ilmu Pengetahuan Indonesia (Indonesian Institute of Sciences) by Decree Number: 818/E/2015. As an open access journal, thus all content are freely available without any charge to the user. Users are allowed to download, and distribute the full texts of the articles without permission from the publisher.

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Articles 173 Documents

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MINERAL CONTENT OF SURFICIAL SEDIMENT OF THE RANGSANG ISLAND AND ITS SURROUNDING AREA, MERANTI REGENCY, ARCHIPELAGO RIAU PROVINCE Deny Setiady; Ediar Usman
BULLETIN OF THE MARINE GEOLOGY Vol 30, No 2 (2015)
Publisher : Marine Geological Institute of Indonesia

According to the regulation No 4 of 2009 of Mineral and Coal Mining Management stated that the requirement of an inventory for mineral resources data was created to support the establishment of mining area. This study is intended to obtain mineral resources content and surficial sediment data, Geographically the study area belongs to Meranti Archipelago Regency, Riau Province. it is located between 102o00'00" - 103o 15'00" E and 00o35'00" - 01o28'00" N. Grain size analyses result show that surficial sediment in the study area consists of silt, silty sand and sand which is dominated by silt. Based on the mineral identification, some of the minerals such as quartz, cassiterite, magnetite, hematite, dolonite, biotite and zircon have been found. Silt distribution is very wide started from estuarine southeast part northen part of Rangsang Island toward southeast of rangsang island. Sandy silt only found at the southeast of Rangsang Island, while sand sediment is found at the south and southeast of Rangsang Island. The presence of silt and sand grains is influenced by moderate to strong currents and wave patterns, so that the silt and sand grains sediment was transported along coastal to offsore area, while the fine grained (clay - silt) are deposited in the valley at the western part of Rangsang Island.Keywords: mineral, surficial sediment, Rangsang Island Berdasarkan Undang Undang Nomor 4 tahun 2009 tentang Pengelolaan Pertambangan Mineral dan Batubara, disebutkan bahwa inventarisasi data sumber daya mineral diperlukan dalam rangka mendukung penetapan Wilayah Pertambangan (WP). Penelitian ini dimaksudkan untuk memperoleh data kandungan sumber daya mineral dan sedimen dasar laut. Daerah penelitian, secara geografis termasuk dalam Kabupaten Kepulauan Meranti, Provinsi Riau, dan terletak pada koordinat antara 102o00'00" - 103o15'00" BT dan 00o35'00" - 01o28'00" LU. Hasil analisis besar butir menunjukkan sedimen permukaan dasar laut di daerah penelitian terdiri atas lanau, lanau pasiran dan pasir yang didominasi oleh lanau. Berdasarkan identifikasi mineral pada sedimen permukaan dasar lautnya menunjukkan kehadiran mineral kasiterit, magnetit, hematit, dolomit, biotit, zirkon dan kuarsa. Penyebaran lanau sangat luas dimulai dari daerah estuari barat laut dan bagian utara Pulau Rangsang, hingga ke sebelah tenggara Pulau Rangsang. Lanau pasiran hanya terdapat di tenggara Pulau rangsang, sedangkan pasir hanya terdapat di daerah di bagian selatan - tenggara Pulau Rangsang. Adanya butiran lanau - pasir dipengaruhi oleh pola arus dan gelombang yang sedang sampai kuat, sehingga butiran berukuran lanau - pasir dapat terangkut ke arah lepas pantai, sedangkan butiran halus (lempung) mengendap di daerah lembah di bagian barat Pulau Rangsang. Kata kunci: mineral, sedimen permukaan dasar laut, Pulau Rangsang

ANALYSIS OF EROSION AND SEDIMENTATION PATTERNS USING SOFTWARE OF MIKE 21 HDFM-MT IN THE KAPUAS MURUNG RIVER MOUTH CENTRAL KALIMANTAN PROVINCE Franto Novico; Yusuf Adam Priohandono
BULLETIN OF THE MARINE GEOLOGY Vol 27, No 1 (2012)
Publisher : Marine Geological Institute of Indonesia

The public transportation system along the Kapuas River, Central Kalimantan are highly depend on water transportation. Natural condition gives high distribution to the smoothness of the vessel traffic along the Kapuas Murung River. The local government has planned to build specific port for stock pile at the Batanjung which would face with natural phenomena of sedimentation and erosion at a river mouth. Erosion and sedimentation could be predicted not only by field observing but it is also needed hypotheses using software analysis. Hydrodynamics and transport sediment models by Mike 21 HDFM-MT software will be applied to describe the position of sedimentations and erosions at a river mouth. Model is assumed by two different river conditions, wet and dry seasons. Based on two types of conditions the model would also describe the river flow and sediment transport at spring and neap periods. Tidal fluctuations and a river current as field observation data would be verified with the result of model simulations. Based on field observation and simulation results could be known the verification of tidal has an 89.74% correlation while the river current correlation has 43.6%. Moreover, based on the simulation the sediment patterns in flood period have a larger area than ebb period. Furthermore, the erosion patterns dominantly occur during wet and dry season within ebb period. Water depths and sediment patterns should be considered by the vessels that will use the navigation channel at a river mouth. Keywords: Kapuas Murung River, software Mike 21 HDFM-MT, erosion and sedimentation pattern Penduduk yang berada di sepanjang Sungai Kapuas sangat bergantung pada transportasi air. Kelancaran lalu lintas kapal di sepanjang Sungai Kapuas Murung sangat tergantung dengan kondisi alam yang terjadi. Rencana pemerintah daerah yang akan membangun pelabuhan khusus batubara di Batanjung akan berhadapan dengan fenomena alam yang umum terjadi di muara sungai yaitu sedimentasi dan erosi. Prediksi akan terjadinya sedimentasi dan erosi tidak hanya ditunjang pengamatan lapangan namun juga perlu dilakukan dengan melakukan hipotesa menggunakan bantuan analisis software. Penelitian ini akan menggambarkan posisi sedimentasi dan erosi di sekitar muara dengan pemodelan hidrodinamika dan transport sedimen yang menggunakan Software MIKE 21 HDFM-MT. Model dibuat dengan mengasumsikan kondisi sungai pada saat musim hujan dan musim kemarau. Berdasarkan dua kondisi tersebut model akan menggambarkan sebaran arus dan sebaran sedimen untuk periode bulan baru dan perbani. Data lapangan pasang surut dan kecepatan arus akan diverifikasi ke hasil simulasi model. Berdasarkan data hasil pengukuran lapangan dan data hasil simulasi model maka dapat diketahui bahwa verifikasi nilai pasang surut menunjukkan korelasi sebesar 89.74% sedangkan verifikasi nilai arus sebesar 43.6%. Selanjutnya dari hasil simulasi didapatkan bahwa pada saat pasang, gambaran posisi sedimentasi banyak terdapat pada bagian timur muara sungai dengan penyebaran cukup luas sedangkan pada kondisi surut area lebih sedikit. Selanjutnya gambaran daerah yang tererosi banyak terjadi pada saat air surut baik untuk musim hujan maupun kemarau. Kapal yang akan menggunakan muara sebagai alur pelayaran harus mempertimbangkan kondisi kedalaman air yang ada dan juga pola sedimentasi yang terjadi. Kata kunci: Sungai Kapuas Murung, software Mike 21FM HD-MT, erosi dan pola sedimentasi

TYPES AND DISTRIBUTION OF CORAL REEF ON THE KARIMATA COAST, WEST KALIMANTAN Noor C.D. Aryanto; Yani Permanawati
BULLETIN OF THE MARINE GEOLOGY Vol 24, No 1 (2009)
Publisher : Marine Geological Institute of Indonesia

The identification of quality and condition of the coral reef in the study areas will support the biological diversity and it frequently contains a valuable assortment of natural resources, conservation of marine biota. The environmental problem particularly on the coastal area needs a more comprehensive management due to the complexity of the rapidly growth. Karimata Archipelago geographically is located between 108o40' - 109o10' E and 1o25' - 1o50' S and administratively belongs to the Ketapang Regency (approximate 100 km west side of Ketapang). In the study area, the growth of coral reef is dominated by non-Acropora type arised between the depths 3-15m. The condition is somewhat good to good. Karimata Archipelago consist of two big islands they are Karimata Island (Studied area) and Serutu Island and also some other isles, with the topography from low land to high land having the height of about 1030 meters from sea level. Keywords: Coral reef, Karimata coast, West Kalimantan. Identifikasi kualitas dan kondisi terumbu karang di daerah penelitian dapat menopang keanekaragaman biologi yang pada akhirnya dapat berperan sebagai kawasan konservasi biota laut. Masalah kepekaan lingkungan khususnya di wilayah pantai dan pesisir memerlukan penanganan yang lebih komperhensif, karena kawasan ini relatif lebih kompleks selain perkembangannya yang demikian pesat. Gugusan kepulauan Karimata secara geografi menempati posisi 108o40' - 109o10' BT and 1o25' - 1o50' LS dan secara administrasi masuk dalam Kabupaten Ketapang (lebih-kurang berjarak 100 km ke arah barat dari Ketapang). Di lokasi telitian, keberadaan terumbu karangnya didominasi oleh jenis non-Acropora yang tumbuh baik pada kedalaman antara 3 hingga 15 m. Terumbu karang yang dijumpai dengan kondisi agak baik hingga baik. Kepulauan Karimata terdiri dari 2 pulau besar, P. Karimata di mana lokasi studi terletak dan P.Serutu dan beberapa pulau-pulau kecil dengan topografi dari dataran rendah hingga dataran tinggi (1030 m) di atas permukaan laut. Kata kunci:Terumbu karang, Pantai Karimata, Kalimantan Barat.

SUPPRESSING DIFFRACTION EFFECT USING KIRCHHOFF PRE-STACK TIME MIGRATION ON 2D SEISMIC MULTICHANNEL DATA AT FLORES SEA Tumpal Benhard Nainggolan; Subarsyah Subarsyah
BULLETIN OF THE MARINE GEOLOGY Vol 29, No 2 (2014)
Publisher : Marine Geological Institute of Indonesia

2D seismic multichannel survey has been carried out by Marine Geological Institute of Indonesia to interpret imaging and sub-surface geological information in the Flores Sea. Seismic data processing starts from pre-processing until migration stage. Migration is an important stage in the seismic processing, because at this stage the effects of diffraction and oblique reflectors caused by fault, salt domes, wedging, etc. will be repositioned to the actual points. One example of diffraction effects can be seen on the seismic section of a conventional stacking that have not migrated, i.e. resulting in an apparent bowtie reflector. Geologists find difficulties in interpreting geological information from diffracted seismic section, so it needs further processing to overcome the effects. By using Kirchhoff method and carried out during the Pre-Stack Time Migration (PSTM), this method turns out to produce migrated seismic section which is much better than conventional stacked one. This is due to the Kirchhoff method suppressed the identified diffraction effects, so that the geologist can interpret geological structure of the resulting migrated seismic section of the Flores Sea. Keywords : 2D seismic multichannel, diffraction, Pre-Stack Time Migration (PSTM), Kirchhoff method. A Survei seismik 2D multichannel dilaksanakan oleh Marine Geological Institute of Indonesia untuk mengetahui gambaran serta informasi geologi bawah permukaan Laut Flores. Pengolahan data seismik dimulai dari pre-processing sampai tahap migration. Tahap migration merupakan tahap terpenting dalam pengolahan data seismik, oleh karena pada tahap ini efek difraksi dan reflektor miring yang diakibatkan oleh sesar, kubah garam, pembajian, dan lain-lain akan dikembalikan pada keadaan sebenarnya. Salah satu contoh adanya efek difraksi bisa dilihat pada penampang stacking konvensional yaitu â€œbowtieâ€ yang mengakibatkan terjadinya reflektor semu pada penampang seismik. Efek difraksi â€œbowtieâ€ sangat menyulitkan para peneliti dalam memperoleh informasi geologi, sehingga perlu adanya proses lebih lanjut untuk mengatasi efek tersebut. Salah satu metode migrasi yang berkembang saat ini yaitu metode Kirchhoff dan dilakukan pada saat Pre-Stack Time Migration (PSTM), menunjukkan hasil penampang jauh lebih baik daripada penampang stacking konvensional. Hal ini terjadi karena pada metode Kirchhoff Pre-Stack Time Migration, efek difraksi tersebut ditekan lebih awal sehingga penampang yang dihasilkan mampu menggambarkan struktur geologi permukaan Laut Flores Sea. Kata kunci : seismik 2D multikanal, difraksi, Pre-Stack Time Migration (PSTM), metode Kirchhoff.

THE INFLUENCE OF SEA-LEVEL CHANGES ON SEA-BOTTOM MORPHOLOGY OF SINGKAWANG WATERS WEST KALIMANTAN BASED ON ANALYSES OF BATHYMETRIC AND SEISMIC DATA Hananto Kurnio; Noor C.D. Aryanto
BULLETIN OF THE MARINE GEOLOGY Vol 26, No 2 (2011)
Publisher : Marine Geological Institute of Indonesia

In the history of Quaternary geology, global climate changes influenced worldwide sea-level variations. On this study, these phenomena are tried to be assessed through sea-bottom morphology changes using bathymetric and seismic strata box data obtained during field survey in Singkawang Waters, West Kalimantan. Sea-level changes in this area are referred to global variations that had been studied by many researchers. Maximal depth attained during bathymetry mapping was -52 meters which take place as a depression between Lemukutan and Penata Besar Islands. General depths are - 30 m; thus, morphology reconstruction was done for sea-level positions - 10 m, - 20 m, and - 30 m from mean sea level. At the study area, sea-level dropped more than -30 m was only occurred in sea bottom morphology of isolated depressions. These isolated depressions are assumed as paleo-lakes which occurred throughout Sunda Land by some authors. The study also shows that sea-level history in Singkawangâ€™s area span from approximately 10,000 years ago or Holocene time to Recent. During low sea-levels, the sea-bottom morphology was characterized by more extension of Singkawang land, formations of narrow straits between islands and developments of paleo-lakes assumed as fresh water lakes in the past. These events, based on Vorisâ€™s Diagram, occurred about 10,200 up to 8,300 years ago. On the other hand, marine clays appeared on coastal area of Singkawang. These might be evidence of sea-level rise in this area. About + 5m sea-level rise flooded this area approximately 4,200 years ago. Influences of sea-level changes to subbottom geological conditions were also assessed. The assessment was carried out by analyzing shallow seismic reflection records by using strata box. The records demonstrated that subsurface geology were characterized by truncation reflector configurations interpreted as fluvial environments. Keywords : sea-level changes, sea-bottom morphology, bathymetry, strata box, Singkawang Waters, West Kalimantan. Dalam sejarah geologi Kuarter, perubahan iklim global mempengaruhi variasi permukaan laut di seluruh dunia. Pada kajian ini fenomena tersebut dicoba dipelajari melalui perubahan morfologi dasar laut menggunakan data batimetri dan seismik pantul dangkal yang diperoleh selama survei lapangan di Perairan Singkawang, Kalimantan Barat. Perubahan muka laut di daerah ini mengacu pada variasi global yang telah dikaji oleh beberapa peneliti. Kedalaman tertinggi yang diperoleh selama pemetaan batimetri adalah 52 meter, yaitu berupa suatu daerah depresi antara Pulau Lemukutan dan Penata Besar. Umumnya kedalaman adalah -30 m; sehingga, rekonstruksi morfologi dilakukan pada posisi muka laut - 10 m, - 20 m, dan -30 m dari muka laut rata-rata. Di daerah kajian, muka laut turun lebih dari - 30 m hanya terjadi dalam morfologi dasar laut yang berupa daerah-daerah depresi yang terisolasi. Morfologi depresi terisolasi ini diduga sebagai danau purba oleh beberapa penulis yang terdapat pada Daratan Sunda. Kajian ini juga menunjukkan bahwa sejarah muka laut di daerah Singkawang mulai dari sekitar 10.000 tahun lalu (Holosen) hingga saat ini (Resen). Selama turunnya muka laut, morfologi dasar laut dicirikan oleh semakin meluasnya daratan Singkawang, terbentuknya beberapa selat sempit dan berkembangnya danau-danau purba yang diduga sebagai danau air tawar di masa lalu. Peristiwa tersebut, berdasarkan diagram umur terhadap muka laut Voris, terjadi sekitar 10.200 hingga 8.300 tahun lalu. Sementara itu, keterdapatan lempung endapan laut dari data pemboran pantai di Singkawang merupakan bukti naiknya muka laut di daerah ini. Kenaikan muka laut sekitar + 5 m telah menggenangi daerah ini kira-kira 4.200 tahun lalu. Tulisan ini juga membahas tentang pengaruh perubahan muka laut terhadap kondisi geologi bawah dasar laut. Kajian dilaksanakan dengan menganalisa rekaman seismik pantul dangkal. Rekaman menunjukkan bahwa geologi bawah dasar laut dicirikan oleh konfigurasi reflektor â€™toreh dan isiâ€™ atau truncation yang ditafsirkan sebagai lingkungan fluvial. Kata kunci : perubahan muka laut, morfologi dasar laut, batimetri, strata box, Perairan Singkawang, Kalimantan Barat.

FIELD CORRELATION BETWEEN PRECIPITATION-EL NINO RELATED VARIATION AND CORAL ?18O Sri Yudawati Cahyarini; B. Suwargadi
BULLETIN OF THE MARINE GEOLOGY Vol 22, No 1 (2007)
Publisher : Marine Geological Institute of Indonesia

Coral ?18O from Maudulung-Indonesia was analyzed using Finnigan MAT 251. Using statistical analysis from KNMI database is obtained that the seasonal mean field correlation between coral ? 18OSOI shows strong correlation during October. Field correlation of precipitation-coral ? 18O shows opposite pattern between eastern Pacific and western Pacific during strong El Nino event. Keywords: coral ?18O, field correlation, El NiÃ±o, Maudulung Sumba. Kandungan ?18O dalam koral dari wilayah Maudulung, Sumba, dianalisis dengan menggunakan Finnigan MAT 251. Korelasi spasial antara ?18O dengan SOI dalam skala musiman tinggi selama bulan Oktober. Korelasi spasial ini dilakukan dengan menggunakan fasilitas analisa statistik dalam database KNMI. Korelasi spasial antara presipitasi- coral ?18O menunjukkan pola-pola yang berlawanan antara wilayah timur dan barat Pasifi selama El NiÃ±o. Kata kunci: Koral ?18O, korelasi spasial, El NiÃ±o, Maudulung Sumba.

PALEO-CHANNELS OF SINGKAWANG WATERS WEST KALIMANTAN AND ITS RELATION TO THE OCCURRENCES OF SUB-SEABOTTOM GOLD PLACERS BASED ON STRATA BOX SEISMIC RECORD ANALYSES Hananto Kurnio; Noor C.D. Aryanto
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 2 (2010)
Publisher : Marine Geological Institute of Indonesia

Strata box seismic records were used to analyze sub-seabottom paleochannels in Singkawang Waters, West Kalimantan. Based on the analyses, it can be identified the distribution and patterns of paleochannels. Paleo channel at northern part of study area interpreted as a continuation of Recent coastal rivers; and at the southern part, the pattern radiates surround the cone-shaped morphology of islands, especially Kabung and Lemukutan Islands. Paleochannels of the study area belong to northwest Sunda Shelf systems that terminated to the South China Sea. A study on sequence stratigraphy was carried out to better understanding sedimentary sequences in the paleochannels. This study is also capable of identifying placer deposits within the channels. Based on criterias of gold placer occurrence such as existence of primary gold sources, intense chemical and physical weathering to liberate gold grains from their source rocks of Sintang Intrusive. Gravity transportation that involved water media, stable bed rock and surface conditions, caused offshore area of Singkawang fulfill requirements for gold placer accumulations. Chemical and physical whethering proccesses from Oligocene to Recent, approximately 36 million, might be found accumulation of gold placer on the seafloor. Based on grain size analyses, the study area consisted of sand 43.4%, silt 54.3% and clay 2.3%. Petrographic examination of the sample shows gold grains about 0.2%. Keywords: paleochannels, strata box seismic records, gold placer. Rekaman seismik strata box digunakan untuk menganalisa sungai purba bawah permukaan di Perairan Singkawang, Kalimantan Barat. Berdasarkan hasil analisis data strata box dapat diidentifikasi sebaran dan pola sungai purba. Sungai purba di bagian utara daerah penelitian ditafsirkan sebagai kelanjutan sungai sekarang, dan di selatan sungainya berpola memancar yang berasal dari pulau-pulau bermorfologi kerucut, seperti Pulau Kabung dan Lemukutan. Sungai purba daerah penelitian termasuk pada sistem sungai purba Paparan Sunda barat laut berakhir di Laut Cina Selatan. Suatu kajian sekuen stratigrafi dilaksanakan untuk lebih memahami sekuen-sekuen sedimen dalam sungai purba. Kajian ini juga mampu mengidentifikasi endapan-endapan plaser dalam alur tersebut. Berdasarkan kriteria pembentukan emas plaser atau letakan, seperti terdapatnya sumber emas primer, pelapukan kimia dan fisika yang sangat intensif untuk membebaskan butiran-butiran emas dari batuan induknya yaitu Batuan Terobosan Sintang. Transportasi gaya berat yang melibatkan media air, kondisi batuan dasar dan permukaan yang stabil, membuat daerah lepas pantai Singkawang memenuhi kriteria untuk akumulasi emas letakan. Proses pelapukan kimia dan fisika mulai dari Oligosen hingga Resen, sekitar 36 juta tahun memungkinkan dijumpainya akumulasi emas letakan di dasar laut. Berdasarkan hasil analisa besar butir daerah penelitian terdiri dari pasir 43,4%, lanau 54,3% dan lempung 2,3 %. Uji petrogafi menunjukan kandungan emas sekitar 0,2%. Kata kunci: sungai purba, rekaman seismik strata box, emas letakan.

Temporal and Spatial Distribution of Heavy Metal in Sediment of Urban Coastal Waters: A Case Study in Jakarta Bay, Indonesia Fitri Budiyanto; Lestari Lestari
BULLETIN OF THE MARINE GEOLOGY Vol 32, No 1 (2017)
Publisher : Marine Geological Institute of Indonesia

Heavy metals, hazardous chemical substances, increase in marine environment due to anthropogenic discharges. However, due to the hydrodynamic of the marine system these metals could vary both temporal and spatial distribution of metals in Jakarta Bay. This study was to reveal the temporal and spatial distribution of metals in sediment over the bay and to assess the environmental condition. Sediment samples were collected in11 stations of March (transitional season) and June(dry season)2013. The result showed that the concentration of heavy metals varied spatially, in which elevated concentration occurred adjacent terrestrial indicating the enrichment of metal-anthropogenic source, but insignificant temporarily.Keywords: heavy metals, spatial distribution, temporal distribution, anthropogenic activities, Jakarta Bay. Logam berat merupakan bahan berbahaya yang tersebar di lingkungan laut karena pengaruh aktifitas antropogenik. Akan tetapi, logam berat ini dapat terdistribusi secara temporal ataupun spasial di Teluk Jakarta akibat sistem hidrodinamika laut. Tujuan dari penelitian ini adalah untuk mengetahui distribusi spasial dan temporal logam berat dalam sedimen dan untuk menilai kondisi lingkungan teluk. Sedimen diambil dari 11 stasiun pada bulan Maret (musim transisi) dan Juni (musim kering) tahun 2013. Hasil penelitian menunjukkan bahwa distribusi spasial logam berat bervariasi, dimana konsentrasinya meningkat di lokasi dekat daratan yang mengindikasikan tingginya sumber logam-antropogenik namun secara temporal tidak signifikan.Kata kunci: logam berat, distribusi spasial, distribusi temporal, kegiatan antropogenik, Teluk Jakarta.

Shallow Gas Features Based on Interpretation of Bottom Profilling Records at Topang Delta, Meranti Regency, Riau Province Purnomo Raharjo; Andrian Willyan Djaja; Ediar Usman
BULLETIN OF THE MARINE GEOLOGY Vol 31, No 1 (2016)
Publisher : Marine Geological Institute of Indonesia

One of the tasks in conducting a renewable energy research is finding a shallow gas contained commonly in river deltas. The location chosen is in Topang Delta,, Meranti District, Riau Province in 2015. The research was conducted by using sub-bottom profiling (SBP) method. Biogenic gas indications could be observed in the SBP records in the forms of free reflector, acoustic plumes and acoustic blanket. The shallow biogenic gas at research area is trapped in A and B sequences. Sequence A is characterized by plume gas and acoustic blanket, while B-type biogenic gas is showed by free-reflector feature of 10-15 meters depth. Sediment which does not have porocity such as old clay is required environment for anaerobic bacteria as catalyst in the formation of biogenic gas to be evolved. Old clay sediment is potential as a biogenic gas source rock afterwards migrated to a layer of sand as a reservoir rock. Some parts of biogenic gas does not appear to the surface because there have been traped in cap rock in form of young clay sediment.Keywords: Topang Delta, Biogenic Gas, free reflector, acoustic plumes, acoustic blanket Salah satu tugas dalam melakukan penelitian energi terbarukan adalah pecarian gas dangkal yang biasa terdapat di delta-delta sungai. Lokasi yang terpilih adalah di delta TopangÂ Kabupaten Kepulauan Meranti, Provinsi Riau pada tahun 2015. Penelitian yang dilakukan salah satunya menggunakan metoda sub bottom profilling (SBP). Indikasi gas biogenik tampak dalam rekaman subbottom profilling berupa reflektor bebas pantul, terobosan gas dan selimut akustik. Keterdapatan gas biogenik dangkal di lokasi penelitian terjebak dalam sekuen sedimen A dan B. Sekuen A dicirikan dengan kenampakan berupa terobosan gas dan selimut akustik, sedangkan biogenik gas tipe-B dicirikan dengan kehadiran reflektor bebas pantul dengan ketebalan 10-15 meter. Sedimen yang tidak memiliki porositas seperti lempung tua merupakan lingkungan yang dimungkinkan untuk bakteri anaerobik sebagai katalisator dalam pembentukan gas biogenik. Endapan lempung tua berpotensi sebagai batuan sumber biogenik gas kemudian bermigrasi ke lapisan sedimen pasir sebagai tempat tersimpannya gas biogenik. Sebagian gas biogenik tidak dapat muncul ke permukaan hingga lapisan atas karena terjebak dalam lapisan sedimen penutup berupa lempung muda.Kata Kunci : Delta Topang, Gas Biogenik, bebas pantul, terobosan gas, selimut akustik

NEW LAND ACCRETION FROM 2000-2003 AT SEGARA ANAKAN LAGOON, SOUTH COAST OF WEST AND CENTRAL JAVA I Wayan Lugra; Deny Setiady
BULLETIN OF THE MARINE GEOLOGY Vol 27, No 2 (2012)
Publisher : Marine Geological Institute of Indonesia

Segara Anakan Lagoon is an unique lagoon , where a lot of rivers enter into the lagoon such as Citanduy, Cibeureum, Cijolang, Cikawung and Ciseel Rivers. These rivers bring the sediment materials from upstream to the lagoon areas and resisted by Nusa Kambangan Island. The rate of sediment transportation every year occurred continuously and significantly. Its caused the creation of new land at eastern part of Segara Anakan Lagoon was about 376.69 hectares which is located at Cilacap District, while in the western part is about 15,78 hectares which is located at Ciamis District. Since 1999 to 2003 land accretion at Segara Anakan Lagoon was about 392.47 hectares with the rate of accretion around 78.50 hectares/year. In 1999 the area of the Segara Anakan Lagoon approximately 1,595 hectares. Based on the averages of rate land accretion, its predicted that in the middle of the 2019 whole of Segara Anakan will be land. The study had been done in 2003 by using hand drilling up to 2 meters depth, grab sampler and GPS Garmin 250 Map. The hand drilling result at accretion area, show that at eastern part of study area is composed of silt and cly, while at Nusawere Bay and Solok Jero is characterized by fine to coarse sand. Keywords : sediment materials, accretion area, and Segara Anakan Segara Anakan merupakan sebuah laguna yang unik dimana banyak sungai yang bermuara di perairan tersebut seperti Citanduy, Cibeureum Cimuntur, Cijolang, Cikawung, dan Ciseel. Sungai-sungi tersebut membawa material sedimen dari daerah aliran hulu ke kawasan laguna yang tertahan oleh Pulau Nusa Kambangan. Transportasi sedimen berlangsung terus menerus dengan laju pertambahan dari tahun ke tahun cenderung meningkat secara signifikan. Akibatnya terjadi pertambahan daratan di perairan Segara Anakan bagian timur sekitar 376,69 hektar yang termasuk wilayah Kabupaten Cilacap dan di bagian barat sekitar 15,78 hektar yang terletak di wilayah Kabupaten Ciamis. Sejak 1999 â€“ 2003, total luas pertambahan daratan di perairan Segara Anakan sekitar 392,47 hektar dengan perkiraan laju pertambahan daratan sekitar 78,50 hektar/tahun. Tahun 1999 luas Perairan Segara Anakan kurang lebih 1.595 hektar. Berdasarkan laju pertambahan daratan rata-rata tersebut, maka diperkirakan pada pertengahan tahun 2019 Perairan Segara Anakan seluruhnya menjadi daratan. Pada tahun 2003, telah dilakukan penelitian dengan menggunakan bor tangan sampai kedalaman 2 meter, pemercontoh comot dan GPS Garmin 250 Map. Hasil pemboran di lokasi pertambahan daratan tersebut menunjukkan di bagian timur tersusun dari lanau dan lempung, sedangkan di Teluk Nusawere dan Solok Jero disusun oleh pasir berbutir halus sampai sangat kasar. Kata kunci : material sedimen, pertambahan daratan, dan Segara Anakan

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