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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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MARINE GEOLOGICAL AND HYDRO OCEANOGRAPHIC DATA FOR SITE SEAPORT LOCATION SELECTION AT SAMPIT BAY AND ITS SURROUNDING, EAST KOTAWARINGIN, CENTRAL KALIMANTAN I Wayan Lugra
BULLETIN OF THE MARINE GEOLOGY Vol 30, No 1 (2015)
Publisher : Marine Geological Institute of Indonesia

Sampit Bay is one of many main gates to enter the Central Kalimantan Province, because there is Mentaya River Mouth as an access to the Sampit Harbour as a main port at its province. Until now, the Sampit Bay only used as anchored for big ships waiting turn to enter Sampit Port. The methods used are coastal characteristic mapping, seafloor surficial sediment sampling, grain size analyses, echosounding, and current measurement. Sampit bay has sandy coast, sand of sea floor surficial sediment, and gradation of sea floor morphology which is suitable for sea port location. On the other hand, the velocity of the surface and midle current in the bay ranging between 0.1-0.3 m/second which is dominated by south east direction. The mentioned velocity is under threshold for safety ship anchoraged. Beside that, most of the bay open to the wind from west and south west facing Java Sea, where the velocity ranging from 5-13 m/second which is included into weak catagories. Location is recommended to be sea port candidate in the south of Ujung Pandaran.Keywords: Sampit Bay, port location, coastal characteritistic, sea floor surficial sediment, current velocity. Teluk Sampit adalah salah satu gerbang utama memasuki Propinsi Kalimantan Tengah, karena tempat bermuaranya Sungai Mentaya yang merupakan akses menuju ke pelabuhan Sampit sebagai pelabuhan utama di provinsi tersebut. Selama ini teluk Sampit hanya digunakan sebagai tempat lego jangkar kapal-kapal besar yang menunggu giliran untuk berlabuh di Pelabuhan Sampit. Metode yang digunakan adalah pemetaan karakteristik pantai, pengambilan contoh sedimen permukaan dasar laut, analisis besar butir, pemeruman, dan pengukuran arus. Teluk Sampit memiliki jenis pantai berpasir dan sedimen permukaan dasar laut pasir serta morfologi dasar laut yang bergradasi cukup layak untuk lokasi pelabuhan. Disamping itu kecepatan arus permukaan dan menengah di teluk tersebut berkisar antara 0,1-0,3 meter/detik dengan arah dominan ke arah tenggara, dimana kecepatan arus tersebut masih dibawah ambang batas untuk keamanan kapal berlabuh. Disamping itu, sebagian besar teluk tersebut terbuka terhadap hembusan angin arah barat dan tenggara yang berhadapan dengan laut Jawa dimana kecepatan angin yang bertiup antara 5-13 meter/detik dan termasuk dalam katagori lemah. Lokasi yang paling layak untuk lokasi pelabuhan adalah sebelah selatan Ujung Banaran. Kata kunci: Teluk Sampit, lokasi pelabuhan, karakteristik pantai, sedimen permukaan dasar laut, kecepatan arus.

SAND DISTRIBUTION MODELING OF MIDDLE MIOCENE RESERVOIR OF â€œEAST TARAKAN A FIELDâ€ IN EASTERN PART OF TARAKAN ISLAND, EAST KALIMANTAN Priatin Hadi Widjaja; D. Noeradi
BULLETIN OF THE MARINE GEOLOGY Vol 26, No 2 (2011)
Publisher : Marine Geological Institute of Indonesia

The discovery well with initial name â€œEast Tarakan A-1â€ was drilled in February 2007 to a total vertical depth of 10,000 feet and encountered gas reservoir in Middle Miocene-age sands with deltaic sediment facies. The Field is structurally high, faulted to the Mengatal producing zones. This sandstone is hydrocarbon producer in most of onshore fields of Tarakan Island. â€œEast Tarakan Aâ€ Field has been suppported with 19 (nineteen) 2D Seismic data. There are three wells i.e: East Tarakan A-1, A2b and A3 with several logs data, mud log and biostratigraphic data. The study aims are firstly to built 3D structural model from time and depth structural maps based on seismic interpretation and well log analysis, secondly to create 3D properties model especially volume shale (V-shale) to get sand distribution. The sand distribution model is supported by 3D structural model, petrophysical analysis and seismic attributes as well as geo-statistic method. Based on petrophysical analysis and wells correlation, sand reservoir interval of Middle Miocene (Meliat Fm) can be devided into two zones respectively top to bottom; zone-1 dan zone-2. RMS Amplitude analysis has been used to help constrain the sand distribution. Sand distribution with two zones indicates that sand distribution of zone-1 and zone-2 are generally located in distributary channel delta. NTG Distribution model of zone-1 and zone-2 indicates that reservoir zone distributed in distributary sand with trend of west to east. NTG of zone-1 is relatively better reservoir than the zone-2. Keywords: Tarakan, Middle Miocene, V-shale, sand distribution, 3D model, NTG Sumur penemuan dengan nama inisial â€œEast Tarakan Aâ€ telah dibor pada Februari 2007 dengan total kedalaman 10.000 kaki dan dijumpai reservoir gas pada lapisan pasir berumur Miosen Tengah dengan fasies sedimen delta. Lapangan gas ini berupa struktur tinggian dan patahan bersebelahan dengan zona produksi Lapangan Mengatal. Batupasir sebagai batuan reservoir merupakan lapisan utama penghasil hidrokarbon di lapangan onshore di Pulau Tarakan. Lapangan â€œEast Tarakan Aâ€ didukung oleh data 19 penampang seismik 2D. Terdapat pula tiga sumur pemboran yaitu Tarakan A-1, A-2b dan A3 dengan beberapa data log sumur, mud log dan biostratigrafi. Studi ini dilakukan dengan maksud dan tujuan, pertama, membuat model stuktur geologi 3-dimensi dari peta struktur waktu dan kedalaman berdasarkan interpretasi seismic, analisis log sumur. Kedua, menghasilkan property model khususnya volume serpih (V-sh) untuk akhirnya memperoleh distribusi pasir. Model sebaran pasir didukung dengan model struktur 3D, analisis petrofisika dan atribut seismik serta metode geo-statistik. Based on petrophysical analysis and wells correlation, sand reservoir interval of Middle Miocene (Meliat Fm) can be devided into two zones respectively top to bottom; zone-1 dan zone-2. RMS Amplitude analysis has been used to help constrain the sand distribution. Sand distribution with two zones indicates that sand distribution of zone-1 and zone-2 are generally located in distributary channel delta. NTG Distribution model of zone-1 and zone-2 indicates that reservoir zone distributed in distributary sand with trend of west to east. NTG of zone-1 is relatively better reservoir than the zone-2. Berdasarkan pada analisis petrofisika dan korelasi antar sumur pemboran, lapisan reservoir pasir Miosen Tengah (Formasi Meliat) dibagi menjadi dua zona yaitu Zona-1 di bagian atas dan zona-2 di bawahnya. Analisis amplituda RMS pada data seismik digunakan untuk membantu penyebaran sedimen pasir. Sebaran pasir dengan dua zona menunjukkan secara umum keterdapatan pasir di area distributary channel delta. Model distribusi NTG (net to gross) pada zona-1 dan zona-2 memperlihatkan area reservoir berada di bagian pasir pada distributary channel dengan arah barat ke timur. NTG pada zona-1 relatif lebih baik daripada zona-2. Kata kunci: Tarakan, Miosen Tengah, V-serpih, sebaran pasir, NTG

STRUCTURAL GEOLOGICAL CONTROL ON THE MINERALIZATION ON TABUAN ISLAND,SEMANGKO BAY, SOUTH SUMATERA, INDONESIA Hananto Kurnio; Ulrich Schwarz Schampera
BULLETIN OF THE MARINE GEOLOGY Vol 23, No 1 (2008)
Publisher : Marine Geological Institute of Indonesia

Mineralization have been discovered on Tabuan Island, Semangko Bay, South Sumatera, Indonesia. Tabuan Island belongs to the Neogene Sunda-Banda magmatic arc system. Tabuan Island is a tectonic horst structure which belongs to the subduction-related, magmatically active Barisan zone along the active continental margin of western Sumatera. Basaltic-andesitic volcanics of the late Oligocene to earliest Miocene Hulusimpang Formation are distributed in a broad zone along and subparallel to the regional Semangko Fault and are hosts for several epithermal-style auriferous deposits. The occurrence of hydrothermal mineralization was first suggested from seismic identification of small intrusive bodies which form elongated northwest-southeast ridges passing through the island. Surface sampling campaigns on the island revealed significant hydrothermal alteration and mineralization with pervasive occurrences of sulphide minerals. Detailed mineralogical and geochemical studies at the Federal Institute for Geoscience and Natural Resources show pronounced disseminations and vein-type mineralization. Mineralization shows moderate enrichments in Au, Ag, Zn, Pb, Cu, As, Sb, Ba, and Mn. The association of subaerial island arc volcanism and subvolcanic intrusive bodies, the regional extensional and strike-slip structural regime, and the occurrence of epithermal-style alteration and mineralization in the same volcanic sequence along the coastal zone of Semangko Bay and on Tabuan Island reveal the great potential of this region for epithermal type Au-Ag and base metal deposits. On Tabuan Island, delineation of structural blocks and fault systems suggests that normal faults and margins of grabens may have acted as fluid channelling structures. Key words: structural geology, mineralization, Tabuan Island, Semangko Bay

Sediment Characteristics of Mergui Basin, Andaman Sea based on Multi-proxy Analyses Rina Zuraida; Rainer Arief Troa; Marfasran Hendrizan; Luli Gustiantini; Eko Triarso
BULLETIN OF THE MARINE GEOLOGY Vol 32, No 2 (2017)
Publisher : Marine Geological Institute of Indonesia

This paper presents the characteristics of sediment from core BS-36 (6°55.85’ S and 96°7.48’ E, 1147.1 m water depth) that was acquired in the Mergui Basin, Andaman Sea. The analyses involved megascopic description, core scanning by multi-sensor core logger, and carbonate content measurement. The purpose of this study is to determine the physical and chemical characteristics of sediment to infer the depositional environment. The results show that this core can be divided into 5 lithologic units that represent various environmental conditions. The sedimentation of the bottom part, Units V and IV were inferred to be deposited in suboxic to anoxic bottom condition combined with high productivity and low precipitation. Unit III was deposited during high precipitation and oxic condition due to ocean ventilation. In the upper part, Units II and I occurred during higher precipitation, higher carbonate production and suboxic to anoxic condition.Keywords: sediment characteristics, Mergui Basin, Andaman Sea, suboxic, anoxic, oxic, carbonate content Makalah ini menyajikan karakteristik sedimen contoh inti BS-36 (6°55,85’ LS dan 96°7,48’ BT, kedalaman 1147,1 m) yang diambil di Cekungan Mergui, Laut Andaman. Metode analisis meliputi pemerian megaskopis contoh inti, pemindaian contoh inti dengan menggunakan multi-sensor core logger, dan pengukuran kandungan karbonat. Tujuan penelitian adalah untuk mengetahui karakteristik fisik dan kimiawi sedimen untuk menafsirkan kondisi lingkungan pengendapan. Hasil penelitian menunjukkan bahwa contoh inti ini dapat dibagi menjadi 5 unit litologi yang mewakili kondisi lingkungan yang berbeda. Pada bagian bawah sedimen, Unit V dan IV ditafsirkan sebagai hasil endapan pada kondisi suboksik hingga anoksik pada saat produktivitas tinggi dan curah hujan rendah. Unit III diendapkan pada saat curah hujan tinggi dan kondisi oksik yang diperkirakan berkaitan dengan ventilasi samudera. Pada bagian atas, Unit II dan I diendapkan pada saat curah hujan cukup tinggi dengan produksi karbonat yang cukup besar dan kondisi dasar laut suboksik hingga anoksik. Kata kunci: karakteristik sedimen, Cekungan Mergui, Laut Andaman, suboksik, anoksik, oksik, kandungan karbonat

ANALYSES OF FORAMINIFERS MICROFAUNA AS ENVIRONMENTAL BIOINDICATORS IN KOTOK BESAR, KOTOK KECIL AND KARANG BONGKOK ISLANDS, KEPULAUAN SERIBU, DKI JAKARTA PROVINCE Nazar Nurdin; Luli Gustiantini
BULLETIN OF THE MARINE GEOLOGY Vol 29, No 1 (2014)
Publisher : Marine Geological Institute of Indonesia

Kepulauan Seribu is a well-known destination of marine tourism in Indonesia. Inevitably, the place has been affected by human activities. Hence it is important to preserve and conserve the area so as it is still suitable for reef community to grow and develop. One of the methods to evaluate the feasibility for reef environment is calculated by FoRAM Index (FI) values. Benthic foraminifera as a tool for environmental bioindicators were collected from 15 marine surface sediment samples in the vicinity areas of Kotok Besar, Kotok Kecil and Karang Bongkok islands in Kepulauan Seribu to assess the FI values. Approximately 20 genera of benthic foraminifera were found in the study area. The genera are dominated by Amphistegina and Calcarina along with Operculina, Quinqueloculina, Peneroplis, and Discorbis. The finding signifies reef flat environment as the dominant morphology, although the presence of fore slope is also observed particularly at the western part of Kotok Besar island. The assemblages of Operculina and Quinqueloculina suggest that the abundance of benthic foraminifera is influenced not only by the morphology of seafloor, but also by tidal current and terrestrial influence. The FI formula using foraminifers found in the study area results values above 4, thus the area can be reviewed as a decent environment for reef growth and development. Keywords: benthic foraminifera; bioindicator; FoRAM Index; coral community; seafloor morphology Kepulauan Seribu terkenal sebagai tujuan wisata laut di Indonesia, sehingga dapat dipastikan tempat ini dipengaruhi oleh aktifitas manusia. Oleh sebab itu sangat penting untuk menjaga dan melindungi kelestarian lingkungannya sehingga tetap cocok bagi komunitas karang untuk hidup dan berkembang. Salah satu metode untuk mengevaluasi kelayakan lingkungan terumbu adalah dengan menghitung nilai FoRAM Index (FI). Untuk analisis ini, foraminifera bentik dikoleksi dari 15 sampel sedimen permukaan laut dari daerah sekitar Pulau Kotok Besar, Kotok Kecil dan Pulau Karang Bongkok di Kepulauan Seribu. Hasil penelitian menunjukkan sekitar 20 genera foraminifera bentik yang ditemukan di daerah penelitian. Foraminifera didominasi oleh Amphistegina dan Calcarina, sedangkan jenis lain yang juga cukup berlimpah adalah Operculina, Quinqueloculina, Peneroplis, dan Discorbis. Hal ini menunjukkan lokasi penelitian memiliki jenis morfologi rataan karang sebagai morfologi dominan, walaupun kehadiran lereng karang (fore slope) juga teramati terutama pada bagian barat pulau Kotok Besar. Distribusi kelimpahan Operculina dan Quinqueloculina menunjukkan bahwa kelimpahan foraminifera bentik selain dipengaruhi oleh morfologi dasar laut juga dipengaruhi oleh pasang surut dan pengaruh terestrial. Hasil perhitungan FI berdasarkan foraminifera di wilayah penelitian menunjukkan nilai FI > 4 sehingga daerah ini dapat ditinjau sebagai lingkungan yang layak untuk pertumbuhan karang dan perkembangannya. Kata kunci: foraminifera bentik; bioindikator; FoRAM Index; komunitas koral; morfologi dasar laut

IDENTIFICATION OF HARD ROCK BASED ON SHALLOW SEISMIC INTERPRETATION AND SPT TEST FOR FOUNDATION OF BRIDGE AT BALANG ISLAND, BALIKPAPAN BAY, EAST KALIMANTAN Ediar Usman; Kris Budiono
BULLETIN OF THE MARINE GEOLOGY Vol 26, No 1 (2011)
Publisher : Marine Geological Institute of Indonesia

The study area is located in Balikpapan Bay, the connecting waters between Pancur village at the southwest and Balang Island at the northeast. The objective of study is to know the engineering properties of rock as a foundation groundwork of bridge. Result of seismic reflection interpretation profiles in the survey area indicates that the seismic sequences can be divided into two sequences, those are sequence A and B. Sequence A lies at the upper part, which is characterized by concordance, parallel, wavy and hummocky reflectors. Sequence B is characterized by mounded, chaotic and free reflectors. Sediment thickness obtained from seismic profiles show that Quaternary sediment is about 1.56 to 4.89 meters, while harder substrate thickness ranging between 7.03 and 21.60 meters. While, based on core drilling data, hard rock started to appear between 3 and 4 meters below seafloor with Standard Penetration Test (SPT) between 32 and 34 blows as Tertiary sediments. Based on field observation and correlated with geological map of Balang Island, Balikpapan Sheet, the hard rock proposed for base of bridge foundation is Balang Island Formation (Middle Miocene) that consist of claystone, sandstone and coal layers that have been deformated and start to form fold as anticline. The seismic record show that, the hard rock is interpreted as B sequence that underlain by Quaternary sediments. Key words: seismic, drilling, Quaternary sediment, hard rock, bridge foundation, Balang Island Daerah penelitian terletak di Teluk Balikpapan, merupakan perairan penghubung antara desa Pancur di bagian baratdaya dan Pulau Balang di bagian timurlaut. Tujuan penelitian in untuk mengetahui sifat keteknikan batuan keras sebagai tapak jembatan. Hasil interpretasi rekaman seismik di lokasi penelitian menunjukkan bahwa sekuen sedimen dapat dibagi menjadi dua yaitu Sekuen A dan B. Sekuen A terletak di bagian atas dengan ciri reflektor selaras, sejajar, bergelombang terputus-putus dan perlapisan terputus-putus. Bagian paling bawah adalah Sekuen B dicirikan oleh bentuk reflektor berbukit-bukit kecil, berbintik-bintik kacau tidak beraturan dan makin ke bawah dicirikan oleh bebas pantul. Hasil perhitungan ketebalan sedimen pada penampang seismik diperoleh ketebalan sedimen Kuarter antara 1,56 - 4,89 meter dan kedalaman batuan keras berkisar antara 7,03 â€“ 21,60 meter. Sedangkan berdasarkan data pemboran, batuan keras mulai muncul pada kedalaman 3 - 4 meter di bawah dasar laut dengan SPT antara 32 â€“ 34 sebagai sedimen Tersier. Berdasarkan pengamatan di lapangan dan dikorelasikan dengan peta geologi P. Balang, Lembar Balikpapan, batuan keras yang diusulkan sebagai dasar tapak jembatan adalah Formasi Pulau Balang (Miosen Tengah) yang terdiri atas batulempung, batupasir and batubara yang sudah mengalami deformasi dan mulai terlipat membentuk antiklin. Pada penampang seismik, batuan keras tersebut adalah Sekuen B yang ditutupi oleh sedimen Kuarter. Kata kunci: seismik, pemboran, sedimen Kuarter, batuan keras, tapak jembatan, Pulau Balang.

The Identification of Land Subsidance by Levelling Measurement and GPR Data at Tanjung Emas Harbour, Semarang Purnomo Raharjo; Mira Yosi
BULLETIN OF THE MARINE GEOLOGY Vol 32, No 1 (2017)
Publisher : Marine Geological Institute of Indonesia

Recently, the main problem in Semarang City is flood. This area has low relief that consists of coastal alluvial deposits, swamp and marine sediments. The coastline is characterized by muddy, sandy, and rocky coasts, and mangrove coast. Ground Penetrating Radar (GPR) records, show that subsurface geological condition of northern part of Semarang is coastal alluvial deposit and in the south is volcanic rocks. The aims of this this research is to determine land subsidence by levelling measurement in 2005 in Tanjung Emas Harbour area built on 1995. During ten years, there are various land subsidance in this area: in Coaster Street (21 – 41 cm), container wharf (62 – 94 cm), north breakwater (64 – 79 cm), west breakwater (74 – 140 cm), east groin (76 – 89 cm), and stacking area ( 77 – 109 cm). According to this research, it is concluded that one reason causes of flooding in this area is land subsidence.Keywords : flood, land subsidence, levelling, Tanjung Emas Harbour, Semarang Permasalahan yang berkembang di Kota Semarang saat ini adalah terjadinya banjir. Kawasan ini berelief rendah yang disusun oleh endapan aluvial pantai, rawa dan sedimen laut. Karakteristik garis pantai dicirikan oleh pantai berlumpur, berpasir dan berbatuan, serta pantai berbakau. Rekaman Ground Penetrating Radar (GPR) menunjukkan kondisi geologi bawah permukaan utara kota Semarang merupakan endapan aluvial pantai dan bagian selatan disusun oleh batuan vulkanik. Tujuan penelitian ini adalah untuk mengetahui kondisi penurunan tanah melalui pengukuran sifatdatar yang dilakukan pada tahun 2005, di kawasan Pelabuhan Tanjung Emas yang dibangun pada tahun 1995. Dalam kurun waktu 10 tahun, diketahui bahwa terdapat variasi penurunan tanah di kawasan ini: ruas jalan Coaster (21-41 cm), di kawasan dermaga peti kemas (62-94 cm), pemecah gelombang sebelah utara (64-79 cm), pemecah gelombang sebelah barat (74-140 cm), penahan gelombang sebelah timur (76-89 cm), dan pelataran peti kemas (77-109 cm). Berdasarkan penelitian ini, maka dapat disimpulkan bahwa salahsatu penyebab banjir di kawasan ini adalah akibat penurunan tanah.Kata Kunci : banjir, penurunan tanah, sipatdatar, Pelabuhan Tanjung Emas, Semarang

HEAVY MINERALS IN PLACER DEPOSIT IN SINGKAWANG WATERS, WEST Kalimantan, RELATED TO FELSIC SOURCE ROCK OF ITS COASTAL AREA Deny Setiady; Noor C.D. Aryanto
BULLETIN OF THE MARINE GEOLOGY Vol 25, No 1 (2010)
Publisher : Marine Geological Institute of Indonesia

Placer deposits are physically accumulated by fluvial and marine processes in coastal area. Thirty six samples were selected from seventy seven samples of seafloor sediment of Singkawang waters. Those samples have been analyzed microscopically for heavy mineral contents. Based on this analysis, the heavy minerals can be divided into four groups: oxyde and hydroxyde, silicate, sulphide, and carbonate. The source of most heavy minerals in the study area is commonly formed by Felsic igneous rock and finally deposited on the seafloor sediments. Keywords: heavy minerals, placer deposit, felsic igneous rock, Singkawang Endapan letakan secara fisik umumnya terakumulasi oleh proses sungai dan laut. Sebanyak 36 contoh dipilih dari 77 contoh sedimen permukaan dasar laut di Perairan Singkawang. Contoh tersebut telah dilakukan analisis kandungan mineral berat secara mikroskopis. Berdasarkan hasil analisis mineral berat ini dapat dibedakan menjadi empat kelompok yaitu oksida dan hidroksida, silikat, sulfida, dan karbonat. Sebagian besar sumber mineral berat di daerah penelitian pada umumnya berasal dari batuan beku felsik yang akhirnya diendapkan di permukaan dasar laut. Kata kunci: mineral berat, endapan letakan, batuan beku felsik, Singkawang.

Geological Structures Appearances and Its Relation to Mechanism of Arc-Continent Collision Northen Alor-Wetar Islands Subarsyah Subarsyah; Riza Rahardiawan
BULLETIN OF THE MARINE GEOLOGY Vol 31, No 2 (2016)
Publisher : Marine Geological Institute of Indonesia

Study area is located in South Banda Basin near the triple junction between Eurasian, Pacific and Indo-Australian Plates. This area is part of back-arc thrusting zone that evolved to compensate convergence between Australia Continent and Banda Arc. Based on seismic section in this area, geological structure analysis is characterized into three distinctive zones. There are Thrust Zone (TZ), Proto Thrust Zone (PTZ) and Normal Fault Zone (NFZ). TZ is defined by distribution of numerous of thrust fault, PTZ contains a blind zone or folds instead of thrust fault, and NFZ defined by distribution of numerous normal fault in the upper portion of seismic section. PTZ identified at several seismic section along the bending zone of oceanic crust. The appearances of bending zone will be easily understood by comprehend the driving mechanism of Australia Continent to the Northeast. The bending zone also related to geometry and tectonic stress of collision. Based on this mechanism it was clearly understood why the western end of study area was not identified the bending zone but it probably the initial process of bending. Contradictive to the western end, the eastern part was clearly shown the bending zone that assumed to have the biggest tectonic stress at this moment. Map of structural analysis also explain that PTZ getting narrow towards the west as the indicator of less of tectonic stress.Keywords: Arc-Continent Collision, Proto Thrust Zone, Wetar, Back arc Thrusting, Banda Sea. Lokasi penelitian berada pada Cekungan Banda Selatan sekitar area triple junction antara Lempeng Eurasia, Pasifik dan Indo-Australia.Daerah ini merupakan bagian dari zona back-arc thrusting yang berkembang sebagai kompensasi dari konvergensi antara kontinen Austalia dan Busur Banda.Berdasarkan penampang seismik di daerah ini analisis struktur geologi dikelompokan kedalam tiga zona. Tiga zona tersebut meliputi Thrust Zone (TZ), Proto Thrust Zone (PTZ) and Normal Fault Zone (NFZ). TZ didefinisikan oleh distribusi dari sejumlah sesar naik, PTZ mengandung sejumlah blind thrust atau lipatan pengganti sesar naik dan NFZ didefinisikan oleh distribusi dari sejumlah sesar normal pada bagian atas dari penampang seismik. PTZ teridentifikasi pada beberapa penampang seismic sepanjang zona bending dari lempeng oseanik. Kenampakan dari zona bending akan mudah dipahami dengan mengetahui mekanisme pergerakan dari kontinen Australia ke arah timurlaut. Zona ini umumnya berhubungan dengan bentuk geometri dan besaran dari tectonic stress dari tumbukan. Berdasarkan mekanisme ini dapat dipahami dengan jelas mengapa bagian ujung barat dari daerah penelitian tidak teridentifikasi zona bending. Kontradiktif terhadap ujung barat, ujung timur memperlihatkan zona bending yang sangat jelas yang diperkirakan mempunyai tectonic stress yang paling besar pada saat ini. Peta dari analisis struktur juga menjelaskan bahwa zona PTZ semakin ke arah barat semakin menyempit sebagai indicator dari berkurangnya tectonic stress.Kata Kunci: Tumbukan Busur-Kontinen, Proto Thrust Zone, Wetar, Back arc Thrusting, Banda Sea.

THE IMAGES OF SUBSURFACE TERTIARY â€“ QUARTENARY DEPOSITS BASED ON GROUND PENETRATING RADAR RECORDS OF SUBI KECIL ISLAND COAST, NATUNA DISTRICT, RIAU ARCHIPELAGO PROVINCE Kris Budiono
BULLETIN OF THE MARINE GEOLOGY Vol 28, No 1 (2013)
Publisher : Marine Geological Institute of Indonesia

Subsurface Tertiary to Quaternary deposits from coast of Subi Kecil Island, Natuna Distric, Riau Archipelago Province, were imaged with Ground Penetrating Radar (GPR). The GPR survey was carried out by using GSSI Surveyor III/20 with 270 MHz and 40 MHz of 3200 MLF antennas. GPR data were processed using software GSSIâ€™s RADAN for Windows NTâ„¢. The interpretation were done by using the radar facies as a groups of radar reflections. The GPR images of study area can be recoqnized in to several facies such as parallel, sub parallel, chaotic, oblique, mound and reflection-free. The calibration were done with geological data along the coast (cliff and outcrop). Unit A is the uppermost layer which is characterized by continous to non continous pararel reflection, srong reflector and high amplitude and is interpreted as alluvium deposits. Below the unit A is unit B which is characterized by non continous sub parallel, chaotic and mound reflector, strong reflector and high amplitude. Unit C and D (Mio-Oligocene) are overlain by unit A and B include chaotic, reflection-free and, locally, discontinuous parallel, oblique mound reflector radar facies, correlatable at the cliff face to massive sands, mostly representing near coastal deposits. These units are bounded by continuous, high amplitude reflections that can be easily correlatable throughout the GPR profiles, serving as important stratigraphic markers. The GPR survey may improve the reconstruction of the depositional environments through the recognition of massive and unconsolidated sand deposits within unit A and B (Holocene). The stratigraphic framework was also improved through the recognition of the discontinuity surface between Units C and D. Keywords: radar facies, stratigraphy, Tertiary to Quatenary, Subi Kecil Island Pencitraan endapan bawah permukaan Tersier sampai Kuarter di pantai Pulau Subi Kecil, Natuna, Propinsi Riau Kepulauan, telah dilakukan dengan â€œGround Penetrating Radar (GPR). Survey GPR dilakukan menggunakan SIR 20 GSSI dengan antenna 200 MHz, 40 MHz da MLF 3200. Data GPR diproses mengunakan perangkat lunak Radan GSSI untuk Window NTTM. Citra Radar di daerah penelitian dapat dibagi menjadi reflektor paralel, sub paralel, chaotik, oblik, undulasi dan bebas refleksi. Kalibrasi telah dilakukan dengan kondisi geologi sepanjang pantai (tebing dan singkapan batuan). Unit A merupakan lapisan paling atas, dicirikan oleh reflektor parallel yang menerus dan tidak menerus, reflektor kuat, amplitudo tinggi dan ditafsirkan sebagai endapan alluvium. Di bawah unit A adalah unit B yang dicirikan oleh reflektor sub paralel yang menerus sampai tidak menerus, chaotic, hiperbolik, dengan reflektor kuat dan amplitudo tinggi. Unit C dan D (Mio-Oligosen) ditutupi oleh unit B yang dicirikan oleh fasies reflektor chaotic, bebas reflektor, dan secara lokal pararel tidak menerus, miring dan hiperbolik, dapat dikorelasikan dengan pasir padat pada tebing sebagai endapan dekat pantai. Citra GPR memperlihatkan rekonstruksi lingkungan pengendapan melalui pengenalan pasir padat dan pasir lepas pada unit A dan B (Holosen). Kerangka stratigrafi akan lebih baik melalui pengenalan ketidak menerusan lapisan antara unit C dan D. Kata kunci: fasies radar, stratigrafi, Tersier sampai Kuarter, Pulau Subi Kecil

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