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DIAGENETIC FEATURES OF PALEO LAGOONAL REEF OF TACIPI AREA, SOUTH CELEBES Andri Slamet Subandrio
BULLETIN OF THE MARINE GEOLOGY Vol 24, No 2 (2009)
Publisher : Marine Geological Institute of Indonesia

Limestone outcrops of the Tacipi area is an ideal carbonate platform part of Neogene East and West Sengkang Basin that are located in the south part of Sulawesi, precisely in western of Bone city. The limestones of this area, outcropping mainly on the north-south oriented hills such as Temapole, Anadara, Tamping, Lappa, etc., are the best reef example in the Tacipi area, as the reef itself, its debris and detritus can be distinguished in the field. Throughout the ridges and pinnacle in Tacipi field the limestones are predominantly homogenous boundstones on the top and detrital bioclastic packstones with local grainstones, and wackestones at the bottom. There are four major reef zonation indentified pacth reef, barrier reef, fore reef and lagoon. The extensive freshwater leaching of fossil fragments and calcareous cement give the preservation of biomouldic and vug pore spaces. Key words : limestones, reef, Tacipi Singkapan batugamping daerah Tacipi merupakan suatu paparan karbonat Neogen yang ideal di timur dan barat Cekungan Sengkan yang terletak di bagian selatan Sulawesi, tepatnya di sebelah barat kota Bone. Batugamping di daerah tersebut, terutama tersingkap berorientasi utara â€“ selatan sejajar gunung-gunung seperti di Tempole, Anadara, Tamping, Lappa dan lain-lain, merupakan contoh terumbu terbesar di daerah Tacipi, sebagai bagian dari terumbu, sisa-sisa dan runtuhannya dapat dibedakan di daerah tersebut. Sepanjang punggungan dan puncaknya di daerah Tacipi, batugamping merupakan bagian utama dari lapisan pengikat yang homogen di bagian atas dan detrital bioklastik koral terpilah buruk dengan lokal struktur butiran secara setempat, dan struktur bioklastik laut pada bagian bawah. Ada empat zonasi utama terumbu yang telah identifikasi sebagai karang gosong, karang penghalang, karang depan dan lagun. Air tawar yang luas terlarut dari pecahan fosil dan semen mengandung zat kapur memberikan pengawetan terhadap jejak-jejak kehidupan dan pori-pori. Kata kunci : batugamping, terumbu, Tacipi

BENTHIC FORAMINIFERA IN SOUTH WAIGEO WATERS, RAJA AMPAT, WEST PAPUA Suhartini M. Natsir; M. Subkhan
BULLETIN OF THE MARINE GEOLOGY Vol 27, No 1 (2012)
Publisher : Marine Geological Institute of Indonesia

Waigeo Island is one of four large islands of the Raja Ampat group, West Papua Province. This area lies in the heart of the coral triangle region as the most marine bio-diversity on Earth. Coral reef ecosystem of the Waigeo is a favorable habitat for various organisms including foraminifera. Foraminifera have been proven as useful indicator of water quality surrounding the coral reef environment since FORAM Index was formulated. It gives additional importance of foraminifera beside their common uses on micropalaeontology for petroleum industry and palaeoecology. Therefore, it is very important to obtain data of the benthic foraminifera from various coral reef environments in Indonesia, such as around Waigeo Island. Sediment samples of this study were collected from 12 sites in southern part off Waigeo Island, on July 2011. Observation on benthic foraminifera shows that the study area is dominated by symbiotic bearing benthic foraminifera, Amphistegina lessonii, belongs to Suborder Rotaliina. This occurrence increases the values of FORAM Index (FI) at certain sites. Generally, the values of FI from most sites are high (FI>4) that provide a good indication for reef growth or recovery. The values of FI less than 2 are found at RJ3 and RJ4 indicate stress environment for reef growth and they are dominated by opportunistic and heterotrophic functional groups of Elphidium and Quinqueloculina. Keywords: benthic foraminifera, high value FI, Waigeo Island, West Papua Pulau Waegio merupakan salah satu dari empat pulau besar di Kepulauan Raja Ampat, Provinsi Papua Barat. Wilayah in terletak di jantung segitiga terumbu karang sebagai pusat paling kaya keanekaragaman hayatinya di bumi. Ekosistem terumbu karang Waigeo merupakan habitat yang cocok bagi kehidupan berbagai organisme termasuk foraminifera. Foraminifera telah terbukti sebagai indikator kualitas air sekitar terumbu karang setelah diformulasikan Indeks FORAM. Dengan demikian foraminifera telah mempunyai kegunaan tambahan selain fungsi umum dalam bidang mikropaleontologi pada industri perminyakan dan paleoekologi. Oleh karena itu sangat penting untuk mendapatkan data foraminifera bentik dari ekosistem terumbu karang di wilayah Indonesia, seperti perairan Pulau Waigeo. Sampel sedimen untuk studi ini diambil di 12 titik lokasi sebelah selatan Pulau Waigeo pada bulan Juli 2011. Hasil pengamatan memperlihatkan bahwa daerah penelitian di dominasi foraminifera bentik yang bersimbose dengan terumbu karang, Amphistegina lessonii, anggota Subordo Rotaliina. Kehadirannya meningkatkan nilai FI dari titik lokasi tertentu. Sebagian besar titik lokasi mempunyai nilai FI>4 memberi indikasi bahwa kondisi perairannya kondusif untuk pertumbuhan karang yang terletak di ekosistem terumbu karang. Secara umum, nilai FI di sebagian besar titik lokasi tinggi (>4) yang member indikasi kondisi lingkungan bagus bagi pertumbuhan karang. Nilai FI rendah (

POTENTIAL HAZARDS OF SEDIMENT IN KENDARI BAY, SOUTHEAST SULAWESI Nur Adi Kristanto; Yogi Noviadi; Purnomo Raharjo
BULLETIN OF THE MARINE GEOLOGY Vol 23, No 1 (2008)
Publisher : Marine Geological Institute of Indonesia

Kendari bay is located in front of Kendari city. There are two harbors in the inner part of bay which very important to support economic activities such as shipping and passenger transportation. The result of coastal characteristic mapping and physical oceanography survey show various coastal morphology, vegetation, weathering processes, sedimentation, currents, and water depth and sea floor morphology. Kendari bay is an enclosed bay; the area is wide in the inner part and narrow in mouth of bay (outlet), the morphology look like a bottleâ€™s neck. Numerous mouth rivers are concentrate around the bay. The rivers load material from land since erosion on land is intensive enough. There is indication that sediment supplies from land trough river mouth not equivalent with outlet capacity. Sediment load is trapped in the inner bay caused the outlet morphology. So high sediment rate play an important role in the process of shallow of water depth in Kendari bay. This condition make the Kendari bay is a prone area of sediment hazard due to height rate of sedimentary process. Therefore, to anticipate the hazards, precaution should be taken related to the Kendari bay as the center of activities in southeast of Sulawesi. The further survey is needed such as marine geotechnique and on land environmental to collect data, which can be used as database for development planning. Key words: Potential hazard, sediment, Kendari Bay Teluk Kendari terletak di bagian depan kota Kendari. Di bagian dalam teluk terdapat 2 pelabuhan yang sangat penting untuk menunjang kegiatan ekonomi seperti perikanan dan transportasi. Hasil pemetaan karakteristik pantai dan penyelidikan oseanografi memperlihatkan kondisi morfologi pantai, vegetasi, proses pelapukan, sedimentasi, arus, kedalaman air laut dan morfologi dasar laut. Teluk Kendari merupakan teluk tertutup yang lebar di bagian dalamnya dan sempit di bagian mulutnya dimana morfologinya terlihat seperti lehar botol. Beberapa mulut sungai terkosentrasi di sekitar teluk. Sungai bermuatan material dari daratan selama erosi didaratan cukup intensif. Hal ini mencerminkan indikasi suplai sedimen dari darat melalui muara sungai tidak sama dengan kapasitas pengeluaran. Muatan sedimen terperangkap di bagian dalam teluk dan menyebabkan terbentuknya morfologi cerobong. Tingginya muatan sedimen merupakan proses yang penting terjadinya pendangkalan di Teluk Kendari Kondisi tersebut menyebabkan Teluk Kendari cenderung merupakan daerah yang akan mengalami bahaya pendangkalan akibat tingginya proses sedimentasi. Oleh karena itu untuk menanggulagi bahaya tersebut, harus dilakukan pencegahan karena Teluk Kendari merupakan pusat kegiatan di Sulawesi Tenggara. Penelitian selanjutnya seperti pengumpulan data geoteknik kelautan dan lingkungan sangat diperlukan untuk dijadikan data dasar untuk rencana pengembangan.

THE INFLUENCE OF COASTAL CONDITIONS TO TSUNAMI INUNDATION OF BIMA BAY, WEST NUSA TENGGARA Yudhicara Yudhicara; Rahayu Robiana
BULLETIN OF THE MARINE GEOLOGY Vol 29, No 1 (2014)
Publisher : Marine Geological Institute of Indonesia

Area along the coast that includes the territorial waters of the Bima Bay, West Nusa Tenggara, is prone to tsunamis, evidenced by the historical tsunamis record in 1815 due to the volcanic eruption of Tambora, 1818, 1836 and 1992 caused by earthquakes associated with tectonic system in the north of the island of Sumbawa, and 1892 were sourced from a distant source. Based on the coastal characteristics, the research area was divided into four types of beaches, namely: Steep rocky beach; Coastal walled plain; Flat coastal mangroves; and Flat sandy beaches. According to the lateral measurement, houses were built in the plains with a minimum height difference of 0.04 m at Rababuntu beach and a maximum of 22.63 m in New Asakota area. The settlement closest distance to the coastline is 10.3 m in Rababuntu, while the farthest extent is at Kawananta 194.58 m from the shoreline. The local bathymetry range between 1 and 42.5 m, where the inside of the very shallow waters of the Bay of Bima, gradually steeper at the mouth of the bay to the open sea. This conditions will influence the wave when entering the bay. It will come with large enough speed at the mouth of the bay, spread along the coastal waters of the eastern and continue spreading to all parts with the diminishing velocity, but the height increasing when it reaches shallow water, especially in the waters of the western Gulf of Bima. Several factors can affect the amount of risk that would be caused by the tsunami, in the research area include are: (1) The research area is located in an enclosed bay; (2) The local sea floor depths around the bay is relatively shallow waters; (3) Coastal characteristics of the research area is dominated by a gently sloping beach morphology with low relief, especially in the area of ??Bajo, Rababuntu and Bontokape and other beaches in the city of Bima; (4) Residential location very close to the shoreline; (5) Minimal vegetation cover; and (6) The presence of the artificial protective are inadequate. Based on tsunami modeling using the 1992 Flores earthquake parameter which is placed perpendicular to the research area obtain the maximum tsunami height around 4-5 m at Sowa and Kolo, near to the mouth of Bima Bay, while the minimum is at Kalaki, about 0,2 m which is at the inner bay. Keywords: Tsunami, coastal characteristics, bathymetry, factors influenced to tsunami inundation. Lokasi di sepanjang pantai yang mencakup wilayah Perairan Teluk Bima, Nusa Tenggara Barat, rentan terhadap tsunami, dibuktikan oleh catatan sejarah tsunami tahun 1815 karena letusan gunung berapi Tambora, 1818, 1836 dan 1992 disebabkan oleh gempa bumi yang terkait dengan tektonik sistem di bagian utara pulau Sumbawa, dan 1892 yang bersumber dari sumber yang jauh. Berdasarkan karakteristik pantai, daerah penelitian dibagi menjadi empat jenis pantai, yaitu: Pantai terjal berbatu; Pantai datar berdinding; Pantai datar berbakau; dan Pantai datar berpasir. Berdasarkan hasil pengukuran kemiringan pantai secara lateral, rumah dibangun di dataran pantai dengan perbedaan ketinggian minimal 0,04 m di Rababuntu dan maksimal 22,63 m di daerah Asakota Baru. Jarak terdekat bangunan terhadap garis pantai adalah 10.3 m di Rababuntu, sedangkan jarak terjauh adalah di Kawananta 194,58 m dari garis pantai. Rentang batimetri di perairan Teluk Bima berkisar antara 1 dan 42,5 m. Bagian dalam Perairan Teluk Bima sangat dangkal, secara bertahap makin alam dan curam di mulut teluk hingga ke laut terbuka. Kondisi ini akan mempengaruhi gelombang ketika memasuki Teluk. Gelombang akan datang dengan kecepatan yang cukup besar di mulut teluk, tersebar di sepanjang perairan pantai timur dan terus menyebar ke seluruh bagian dengan kecepatan berkurang, namun ketinggian meningkat saat mencapai perairan dangkal, terutama di perairan barat Teluk Bima. Beberapa faktor yang dapat mempengaruhi jumlah risiko yang akan disebabkan oleh tsunami, di daerah penelitian meliputi: (1) Daerah penelitian terletak di teluk tertutup; (2) Kedalaman dasar laut di sekitar Teluk adalah perairan yang relatif dangkal; (3) Karakteristik Pantai daerah penelitian didominasi oleh pantai morfologi landai dengan relief rendah, terutama di daerah Bajo, Rababuntu dan Bontokape dan pantai-pantai lainnya di Kota Bima; (4) Lokasi perumahan sangat dekat dengan garis pantai; (5) Minimalnya vegetasi penutup; dan (6) Keberadaan pelindung buatan tidak memadai. Kata Kunci: Tsunami, karakteristik pantai, batimetri, faktor yang mempengaruhi landaan gelombang tsunami.

LITOSTRATIGRAPHIC AND SEDIMENTOLOGICAL SIGNIFICANTS OF DEEPENING MARINE SEDIMENTS OF THE SAMBIPITU FORMATION GUNUNG KIDUL RESIDENCE, YOGYAKARTA Surono Surono; Asep Permana
BULLETIN OF THE MARINE GEOLOGY Vol 26, No 1 (2011)
Publisher : Marine Geological Institute of Indonesia

Sambipitu Formation in the Southern Mountains plays an important role due to its stratigraphic position, between syn-volcanism and post- volcanism periods. The formation widely distributes along the southern slope of the Baturagung Mountains, Gunung Kidul Residence, Yogyakarta Province. Stratigraphically, the Sambipitu Formation is conformably underlain by dominated unit of volcanic breccias of the Nglanggran Formation, and conformably overlain by dominated unit of marl of the Oyo Formation. Based on detail section along the river of Ngalang, the Sambipitu Formation can be divided into Lower and Upper Members. The Lower Member is dominated by sandstone and siltstone, which is alternated by breccias. The Upper Member is dominated by siltstone and mudstone, which is intercalated by sandstone, marl and conglomerate. The Lower Member was deposited on an environment influenced by tidal current, which was highly affected by gravity flows of volcanic material. This deposition environment was getting deeper to be an inner shelf, where the Upper Member was deposited. Furthermore, based on Rock-eval pyrolysis, TOC value of the Sambipitu Formation ranges from 0.08% to 0.43%, whilst the PY (potential yield) value less than 0.15 mg HC/g rock. Thus, on the basis of those two parameters, the Sambipitu Formation is included into oil prone source rock potential of poor category. Moreover, Tmax value of the Sambipitu Formation ranges from 226Â°C - 335Â°C, with the HI (hydrogen Index) value varies from 0 â€“ 12. It indicates that this formation contains kerogen Type III. Therefore, the organic thermal maturation based on plotting of Tmax vs HI, this formation falls into an immature category. Key word: Lithostratigraphy, volcanic material, tidal flat, inner shelf, and Sambipitu Formation. Formasi Sambipitu memegang peran penting karena posisi stratigrafinya yang terletak diantara perioda volkanisme dan pasca volkanisme. Formasi ini tersebar luas di lereng selatan Pegunungan Baturagung, Kabupaten Gunung Kidul, Provinsi Daerah Istimewa Yogyakarta. Formasi Sambipitu menindih selaras Formasi Nglanggran dan ditindih selaras oleh Formasi Oyo. Berdasarkan penampang stratigrafi rinci sepanjang Sungai Ngalang, Formasi Sambipitu dapat dibagi menjadi: Anggota Bawah dan Anggota Atas. Anggota Bawah didominasi oleh perselingan batupasir dan batulanau, dengan sisipani breksi gunung api. Sedangkan Anggota Atas didominasi oleh batulanau dan batulumpur dengan sisipan batupasir dan konglomerat. Anggota Bawah diendapkan di lingkungan paparan pasang-surut yang dipengaruhi oleh pengendapan material gunung api. Paparan pasang-surut itu semakin dalam menjadi paparan dalam dimana diendapkan Anggota Atas. Berdasarkan analisis Rock-eval pirolisis, nilai kandungan karbon total (TOC) serpih Formasi Sambipitu berkisar 0,08% â€“ 0,43%, sedangkan Potential yield (kandungan cairan hidrokarbon) kurang dari 0,15 mg HC/g batuan. Berdasarkan dua parameter tersebut diatas, formasi tersebut termasuk kedalam kategori oil prone source rock, dengan kategori buruk (poor). Formasi Sambipitu mempunyai nilai temperatur maksimum (Tmax) antara 226Â°C - 335Â°C, dengan nilai HI (Hydrogen Index) kurang dari 12, menunjukkan formasi ini memiliki kerogen tipe III. Berdasarkan diagram temperatur maksimum (Tmax) terhadap nilai indeks hidrogen (HI) bahan organik, kematangan organik dari formasi ini termasuk ke dalam tingkat belum matang. Kata kunci: Litostratigrafi, material volkanik, paparan pasang-surut, paparan dalam, dan Formasi Sambipitu.

The Study of Seafloor Tin Placer Resources of Quaternary Sediment at Toboali Waters, South Bangka Muhammad Zulfikar; Noor CD Aryanto
BULLETIN OF THE MARINE GEOLOGY Vol 31, No 2 (2016)
Publisher : Marine Geological Institute of Indonesia

Bangka Island has primary and secondary tin deposit. However, along the history of tin mining has been done the primary tin deposit domination is less than secondary tin deposit. Secondary tin deposit is formed from Granitic S-type source rock weathering and then transported by gravity. After that, Cassiterite mineral (SnO2) accumulates and forms a placer deposit in the study area. The thickness of sediment cover at Toboali Waters is quite diverse, with a range between 5-20 milliseconds, by knowing the quarter sediment thickness using seismic data interpretation results, is expected to give an idea about tin placer deposit potential in Toboali waters. Based on the Isochron map shows patterns of quaternary sediment thickening to the southwest, south and southeast of Bangka Island.Keywords: Quaternary sediment, placer deposit, isochron map, Toboali WatersPulau Bangka memiliki endapan timah primer dan endapan timah sekunder. Namun, sepanjang sejarah penambangan timah yang telah dilakukan endapan timah primer tidak mendominasi jika dibandingkan dengan endapan timah sekunder. Pembentukan endapan timah sekunder berawal dari pelapukan batuan Granit tipe-S yang kemudian mengalami transportasi akibat adanya gravitasi. Setelah itu, mineral kasiterit (SnO2) terakumulasi dan membentuk endapan plaser di daerah penelitian. Ketebalan sedimen penutup di Perairan Toboali berkisar antara 5-20 milidetik, dengan mengetahui ketebalan sedimen kuarter berdasarkan interpretasi data hasil rekaman seismik diharapkan dapat memberikan gambaran tentang potensi endapan timah placer di Perairan Toboali. Berdasarkan atas peta isokron, memperlihatkan bahwa pola penebalan sedimen kuater ke arah baratdaya, selatan dan tenggara Pulau Bangka.Kata kunci : Sedimen kuarter, endapan placer, peta isokron, Perairan Toboali

CHARACTERISTIC OF SHALE GAS RESERVOIR USING LMR (LAMBDA-MU-RHO) INVERSION: CASE STUDY BARNETT SHALE, FORT WORTH BASIN TEXAS, USA Hagayudha Timotius; Yulinar Firdaus
BULLETIN OF THE MARINE GEOLOGY Vol 28, No 1 (2013)
Publisher : Marine Geological Institute of Indonesia

The decreasing of fossil fuel reserves in the conventional reservoir has made geologists and geophysicists to explore alternative energy source that could answer energy needs in the future. Therefore the exploration of oil and gas that is still trapped in the source rock (shale) is needed, and one of them still developed in shale gas. The method of Amplitude Versus Offset (AVO) Inversion is used for Lambda-Mu-Rho attributes, that is expected to assess values of physical parameters of shale. Fort Worth Basin is chosen to be a study area because, the Barnett Shale Formation has proven contains of oil and gas. This study using synthetic seismic data, based on geological model and well log data obtained from Vermylen (2012). It is expected from the study of Barnett Shale that related to shale gas development could be applied. Keyword: Shale gas, Barnett Shale, Fort Worth Basin, AVO Inversion, Lambda-mu-rho attributes Penurunan cadangan bahan bakar fosil pada reservoar konvensional membuat ahli geologi dan geofisika mengeksplorasi sumber energi alternatif guna menjawab kebutuhan energi di masa depan. Oleh karena itu dibutuhkan eksplorasi minyak dan gas yang masih terperangkap dalam batuan induk (serpih), dan salah satunya yang dikembangkan saat ini adalah â€œshale gasâ€. Penggunaan metode inversi Amplitudo Versus Offset (AVO) untuk atribut Lambda-Mu-Rho diharapkan dapat menghasilkan nilai-nilai parameter â€œfisis shaleâ€. Cekungan Fort Worth dipilih sebagai lokasi penelitian ini karena terdapat Formasi â€œBarnett Shaleâ€ yang telah terbukti mengandung minyak dan gas. Penelitian ini menggunakan data seismik sintetik berdasarkan model geologi serta data sumur yang diperoleh dari Vermylen (2012). Diharapkan dari penelitian tentang Barnett Shale yang berkaitan dengan pengembangan shale gas dapat diaplikasikan. Kata kunci: â€œShale gasâ€, â€œBarnett Shaleâ€, Cekungan Fort Worth, Inversi AVO, atribut Lambda-Mu-Rho

HIGH PERCENTAGE OF RARE EARTH ELEMENT CONNECTION WITH THE ACCUMULATION SEDIMENT AS RESPONSE LONGSHORE CURRENTS IN THE BELITUNG WATERS Delyuzar Ilahude; Maman Surachman
BULLETIN OF THE MARINE GEOLOGY Vol 30, No 2 (2015)
Publisher : Marine Geological Institute of Indonesia

The study area is geographically located in the West coast of Belitung island at coordinates 105o48'00" - 106o06' 00" E and 06o46'00" - 06o50' 00" S. The beach and coastal area is influenced by wave energy from the West and North directions The purpose of this study is to analyze the relationship between the zone of sediment accumulation of empirical approaches on oceanography parameter containing rare earth elements. The approach used is to predict the shore wave energy using wave prediction curve deep waters to obtain the energy flux of the wave at each point of reference. Sediments containing rare earth elements tend to lead to the south as a result of the movement of longshore currents. Regional coastal area of the western part of the island of Belitung, especially in the southern part of the estuary of the river Tanjung Pandan is estimated to be a zone of sediment accumulation. The movement of sediment caused by wave energy from the north led to sedimentation evolved significantly in the south which is thought to contain rare earths minerals derived from land. This sedimentation process takes place on a seasonal basis, which allegedly took place in the west. The movement of sediment to the south of the mouth of the Cerucuk River it is predicted that rare earth elements were supplied from these rivers tend to settle in the southern part of the estuary Cerucuk throughout the year.Keywords: accumulation of sediment, longshore currents, rare earth elements offshore Belitung Lokasi daerah penelitian secara geografis terletak di pesisir pantai barat Pulau Belitung pada koordinat 105o48'00" - 106o06'00" BT dan 06o46'00" - 06o50'00"LS. Pesisir pantai termasuk pantai terbuka terhadap pengaruh energi gelombang dari arah barat dan utara. Tujuan dari penelitian ini untuk melakukan analisis hubungan antara zona akumulasi sedimen dari pendekatan empirik parameter osenografi dan kandungan unsur tanah jarang. Pendekatan yang digunakan yaitu dengan memprediksi energi gelombang pantai menggunakan kurva prediksi gelombang perairan dalam untuk memperoleh energi fluks gelombang pada setiap titik referensi. Pengendapan sedimen bermuatan unsur tanah jarang cenderung mengarah ke selatan sebagai akibat dari pergerakan arus sejajar pantai. Daerah kawasan pesisir bagian barat Pulau Belitung terutama di bagian selatan muara sungai Tanjung Pandan diperkirakan menjadi zona akumulasi sedimen. Pergerakan sedimen akibat dari energi gelombang dari arah utara menyebabkan adanya sedimentasi berkembang cukup signifikan di bagian selatan yang diduga bermuatan mineral unsur tanah jarang asal dari darat. Proses sedimentasi ini berlangsung secara musiman, yang kemungkinan berlangsung pada musim barat. Adanya pergerakan sedimen ke arah selatan dari muara Sungai Cerucuk maka diperkirakan unsur tanah jarang yang dipasok dari sungai tersebut cenderung mengendap di bagian selatan dari muara Sungai Cerucuk sepanjang tahun. Kata kunci: akumulasi sedimen, arus sejajar pantai, unsur tanah jarang lepas pantai Belitung

SEDIMENTOLOGICAL PROPERTIES OF THE 2010 MENTAWAI TSUNAMI DEPOSIT Yudhicara Yudhicara; Andrian Ibrahim
BULLETIN OF THE MARINE GEOLOGY Vol 27, No 2 (2012)
Publisher : Marine Geological Institute of Indonesia

Post tsunami survey of the October 25, 2010, Mentawai tsunami, has been carried out by a collaboration team of Indonesian-German scientists from 20 to 28 November 2010. One activity of the researches were investigation on tsunami deposits along the coast following the event that devastated the islands of Sipora, North Pagai and South Pagai. Sedimentological properties of Mentawai tsunami deposit were explained by this study, from both megascopic and laboratory result. In general, beaches along the study area are underlying by a stretch of reef limestone, sediments mostly composed of white sand while grey sand was found only at Malakopa. Tsunami sediments were taken from 20 locations, start from Betumonga at Sipora Island until Sibaru-baru Island at the southern tip of the study area. The thickness of tsunami deposits are ranged between 1.5 and 22 cm, which are generally composed of fine to coarse sand in irregular boundaries with the underlying soil. Based on grain size analysis, variation of sedimentological properties of tsunami deposits range between phi=-0,5793 and phi=3,3180 or very coarse to very fine sand. Tsunami deposits mostly have multiple layers which described their transport processes, run up at the bottom and back wash at the top. Structural sediments such as graded bedding of fining upward, parallel lamination and soil clast were found. The grain size distribution curves show two types of mode peak, unimodal and multimodal which are indication of different sorting condition representing the source materials. While segment grain size accumulative plot generally shows domination of dilatation and traction transport mechanism rather than suspension. In general, very rare fossils were found from Mentawai tsunami deposit, but those findings gave information on how depth tsunami start to scour the seafloor and transport it landward, such as an abundance of Sponge spicule was found which indicate shallow water environments (20-100 m seafloor depth). Keywords: 2010 Mentawai tsunami, tsunami deposit, grain size analysis, fossils identification. Survei pasca-tsunami Mentawai 25 Oktober 2010, telah dilakukan oleh Tim gabungan Indonesia-Jerman pada tanggal 20 - 28 November 2010. Salah satunya adalah melakukan identifikasi endapan tsunami yang ditemukan di sepanjang pantai yang terlanda tsunami di Pulau Sipora, Pagai Utara dan Pagai Selatan. Berdasarkan hasil penelitian baik megaskopik maupun analisis laboratorium, dalam tulisan ini dapat dijelaskan mengenai sifat-sifat sedimentologi dari endapan tsunami Mentawai. Secara umum litologi penyusun pantai di daerah penelitian disusun oleh hamparan batugamping terumbu, sebagian disusun oleh pasir berwarna putih, sedangkan di Malakopa tersusun oleh endapan pasir pantai berwarna abu-abu. Berdasarkan hasil analisis laboratorium, diperoleh variasi sifat sedimentologi, seperti kisaran ukuran butir endapan tsunami antara -0,5793 phi dan 3,3180 phi, yaitu pasir sangat kasar hingga sangat halus. Endapan tsunami umumnya memiliki beberapa lapis yang menunjukkan adanya proses transportasi, seperti saat air naik (run up) di lapisan bagian bawah dan surut di bagian atas, yang ditunjukkan dengan adanya perbedaan ukuran butir. Struktur sedimen ditemukan seperti adanya perubahan besar butir secara berangsur menghalus ke bagian atas, perlapisan sejajar dan fragmen tanah yang terperangkap dalam sedimen. Kurva distribusi ukuran butir memperlihatkan dua jenis model puncak, yaitu unimodal dan multimodal yang memperlihatkan kondisi pemilahan yang berbeda yang menunjukkan kondisi sumber material endapan tsunami, sedangkan grafik akumulasi ukuran butir umumnya memperlihatkan dominasi mekanisme transportasi dilatasi dan traksi daripada suspensi. Secara umum fosil yang terkandung dalam endapan tsunami Mentawai sangat jarang, namun sedikit banyak telah memberikan informasi seberapa dalam gelombang tsunami mulai menggerus lantai samudera dan memindahkannya ke darat, misalnya dengan ditemukannya fosil bentonik Sponge spicule yang melimpah, menunjukkan asal lingkungan laut dangkal dengan kedalaman laut 20-100 m. Kata kunci: Tsunami Mentawai 2010, endapan tsunami, analisis besar butir, identifikasi fosil.

IMPACTS OF MARINE SAND MINING ACTIVITIES TO THE COMMUNITY OF LONTAR VILLAGE, SERANG - BANTEN Semeidi Husrin; Joko Prihantono; Hadi Softyan
BULLETIN OF THE MARINE GEOLOGY Vol 29, No 2 (2014)
Publisher : Marine Geological Institute of Indonesia

Marine sand mining activities in Lontar Village have been started legally since 2003 and temporarily halted in 2013. The locals blamed the activities for severe environmental destruction in almost every corner of the village such as low productivity ofaquaculture, coastal erosion, and habitat loss. This paper has an objective to provide preliminary data and analyses for environmental impact assessment of marine sand mining in Serang (Lontar Village). Field investigations were carried out in June 2014 to collect primary data such as bathymetrical data and water quality parameters in the region to understand the environmental conditions after 10 years of marine sand mining activities as well as the characteristicsof local oceanography. Extensive interview with the locals were also conducted to collect information about the socio-economic conditions of the village. Field findings showed that LontarVillage have experienced critical environmental problems such as coastal erosion, high turbidiy and loss of marine lives. Moreover, we also found that the abandoned aquaculture fields have also been converted as sand mining quarries. Recommendations to reduce further environmental damage in Lontar Village are proposed considering both socio-economy and physical aspects. Keywords:sand mining, Lontar village, environmental damage, erosion Aktifitas penambangan pasir laut di Kampung Lontar telah dimulai secara legal sejak 2003 dan telah berhenti untuk sementara tahun 2013. Keberatan penduduk setempat terhadap aktifitas penambangan tersebut adalah disebabkan oleh adanya gangguan lingkungan di hampir setiap sudut perkampungan seperti rendahnya produktifitas budidaya perikanan, erosi pantai dan hilangnya. berbagai aneka ragam habitat. Tujuan penelitian ini adalah untuk mendapatkan data awal dan analisis terhadap pengaruh lingkungan akibat aktifitas penambangan pasir laut. Penyelidikan lapangan telah dilaksanakan pada bulan Juni 2014 yaitu untuk mengumpukan data sekunder seperti batimetri dan parameter kualitas air di kawasan tersebut. Penelitian ini adalah untuk mengeahui kondisi lingkungan setelah 10 tahun aktifitas penambangan pasir laut, begitu juga karakteristik oseanografi daerah tersebut. Wawancara intensif dengan penduduk lokal telah dilakukan juga untuk mengumpulkan informasi tentang kondisi sosial ekonomi perkampungan tersebut. Temuan lapangan menunjukkan bahwa perkampungan Lontar mengalami masalah lingkungan yang kritis seperti proses erosi pantai, kekeruhan yang tinggi, dan hilangnya kehidupan laut. Lebih lanjut lagi penelitian ini telah menemukan bahwa sekumpulan ladang budidaya perairan telah beralih menjadi tambang pasir. Saran untuk memperkecil kerusakan lingkungan lebih jauh di Perkampungan Lontar, diusulkan pertimbangan aspek sosial ekonomi dan aspek fisik. Kata kunci : tambang pasir, Perkampungan Lontar, kerusakan lingkungan, erosi.

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