The Images of Subsurface Tertiary – Quartenary Deposits Based on Ground Penetrating Radar Records of Subi Kecil Island Coast, Natuna District, Riau Archipelago Province

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 GSSI’s RADAN for Windows NT™. 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 “Ground 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 Keci

Kajian Dinamika Pantai Selatan Banyuwangi Berdasarkan Hasil Penafsiran Citra Satelit Landsat Tm

Hasil kajian citra satelit Landsat Thematic Mapper (TM) menunjukkan daerah pantai selatan Banyuwangi mempunyai empat karakteristik dinamika pantai, yaitu daerah akresi, terjadi di muara Sungai Gonggo, Sungai Baru, dan Sungai Pergaul yang terjadi karena tingginya aliran (run off) dari sungai. Daerah abrasi terjadi di Teluk Grajagan yang terjadi karena adanya arus menerus dari laut sehingga sedimen dari Segoro Anakan tidak bisa diendapkan di daerah teluk dan hanya di muka sungai. Daerah abrasi dan akresi terdapat di teluk Rajegwesi dan Pancamaya yang mempunyai daerah akresi di muara sungai dan daerah abrasi di bagian sisi teluknya. Daerah stabil, terdapat di daerah-daerah yang menjorok ke laut dan sepanjang pantai Alas Purwo. Daerah akresi maupun abrasi umumnya terjadi di daerah topografi rendah, landai dan berupa aluvium, sedangkan daerah stabil terdapat pada daerah dengan topografi bertebing dan batuan penyusun berupa batuan keras. Kata kunci : sedimen, dinamika pantai, Landsat TM, pantai selatan Banyuwangi The result of the assesment of Landsat TM imageries show that the coastal area of south Banyuwangi have four coastal dynamic characteristics those are: accretion, abrasion, accretion and abrasion, and stable areas. Accretion area, is located in the river estuary of Gonggo, Baru, and Pergaul rivers that occur by run off from river. Abrasion area, is located in Grajagan Bay caused by continuous current from the sea so that the sediment from Segoro Anakan cannot precipitate in the bay area but only in the river mouth. Abrasion and accretion areas are located in Rajegwesi and Pancamaya Bays where the accretion area is in a river estuary but the abrasion area is in the side shares of the bay. Stable area is located in the peninsula area and along the Alas Purwo coast. Generally the accretion or abrasion areas were occurred in low relief topography and occupied by alluvium, whereas the stable area is characterized by the high relief topography consisting of hard rock. Key words: sediment, coastal dynamic, Landsat TM, south coast of Banyuwangi

Karakteristik Pantai Pulau Laut-sekatung (Salah Satu Pulau Terluar Nkri)

Pulau Laut-Sekatung adalah salah satu pulau terluar Negara Republik Indonesia yang berbatasan dengan perairan Malaysia Timur. Pulau ini terletak di laut Cina Selatan sebagai bagian dari Kepulauan Natuna dan secara administratif termasuk Provinsi Kepulauan Riau. Tujuan dari studi ini adalah untuk mengetahui karakteristik dan tipologi kawasan pantai berdasarkan metoda geologi dan geofisika kelautan seperti pemetaan geologi kawasan pantai, pengambilan contoh sedimen, serta data-data penunjang seperti pengamatan pasang surut, pengukuran arus dan batimetri. Berdasarkan metoda-metoda tersebut, kawasan pantai Pulau Laut dapat dibedakan 3 jenis yaitu, pantai berpasir, pantai berbatuan dan pantai berbakau. Pantai tipe I adalah pantai berpasir menempati bagian selatan dan timur daerah penelitian, merupakan pasir hasil metasedimen dan terumbu karang. Pantai tipe II adalah pantai berbakau, menempati bagian tenggara daerah penelitian dan merupakan endapan rawa dengan morfologi pedarataran. Pantai tipe III merupakan pantai berbatuan menempati bagian timur dan utara daerah penelitian, merupakan singkapan batuan metasedimen dan batuan beku berumur Kapur yang berasal dari Formasi Bunguran. Tipe pasang surut di perairan Pulau Laut-Sekatung adalah harian tunggal (diurnal tide). Morfologi dasar laut perairan pantai sebelah barat dan timur berbeda, dimana sebelah barat dari garis pantai morfologinya curam sedangkan sebelah timur morfologinya landai. Perubahan garis pantai dicirikan oleh erosi pantai dibagian barat dan akrasi dibagian timur. Kata kunci: Pulau Laut-Sekatung, pulau terluar, karakteristik pantai The Sekatung-Laut Island is one of the outer island of the Republic Indonesia which bordered with the East of Malaysia waters. This island is located in the South China Sea as part of Natuna island and administratively within the Province of Riau islands. The purpose of this study is to know the characteristic and typology of coastal area. To support this purpose, the geology and geophysical survey method such as coastal mapping, sediment sampling, tide, current and bathymetry measurement have been done. Based on these method, the coastal area of Sekatung-Sea island can be distinguished in to 3 type. Coastal type I is a sand coast which is located in the south and east of the island where sand material is derived from meta-sediment rock and coral reef. Coastal type II is a mangrove coast which is located in the south east of study area. This coast is characterized by swamp deposits, mangrove plantation and plain area. Coastal type III is a rocky coast. This coast is characterized by the steep cliff of Cretaceous meta-sediment and volcanic rock of Bungaran Formation. Tide characteristic of study area is diurnal tide and the maximum current velocity is about 1.6 meter/second and is dominated by north direction. The morphology of water coast at west coast is very steep and in the eastern part is very flat. The coast line change is characterized by the erosion in the eastern part and akrasi to sable coast in the western part. Key words: Laut-Sekatung island, outer island, coastal characteristi

Investigation Of Ground Penetrating Radar For Detection Of Road Subsidence Northcoast Of Jakarta, Indonesia

A survey of Ground Penetrating Radar (GPR) was conducted in the coastal zone of northern part of Jakarta, Indonesia. The purpose of this survey was to provide the subsurface of coastal Quaternary sedimentary features and stratigraphy disturbances associated with induce post road subsidence 2009. The possibility of subsurface lithology disturbance shown by the GPR record. This record resulted from GPR methods using SIR system 20 GSSI, 270 MHz and 400 MHz and MLF 3200 transducer. The method is a promising tool for resolving changes of physical properties in subsurface lithology condition at the natural scale due to composition changes of physical properties.The reflection data resulted that GPR can distinguish between image the basic geometry forms such as lithology , structure geology , soil and subsurface utilities condition Keywords: Quaternary geology, Jakarta subsidence northern road 2009, Ground Penetrating Radar Penyelidikan “Ground Penerating Radar†(GPR) telah dilaksanakan di kawasan pantai utara Jakarta Utara, Indonesia. Tujuan dari penyelidikan GPR ini adalah untuk melihat kondisi sedimen Kuarter bawah permukaan dan gangguan stratigrafi sehubungan dengan penurunan jalan raya pada tahun 2009. Kemungkinan gangguan terhadap litologi bawah permukaan terlihat pada rekaman GPR. Hasil rekaman metoda GPR mempergunakan model SIR 20 GSSI, transduser 270MHz, 400 MHz dan MLF 3200

Karakteristik dan Distribusi Lumpur Sidoarjo Sepanjang Sungai, Estuari dan Perairan Porong

Semburan lumpur Sidoarjo (Lusi) di daerah Porong menambah fungsi Sungai Porong menjadi sarana untuk mengalirkan lumpur ke arah laut, karena kemampuan tanggul – tanggul penghalang di sekitar lokasi semburan sangat terbatas. Kondisi ini berdampak pula terhadap terbawanya lumpur lapindo ke perairan Porong. Penelitian ini bermaksud untuk mengetahui sebaran sedimen di sungai, muara dan perairan sekitar Porong terutama yang bersumber dari luapan lumpur Sidoarjo. Materi yang digunakan dalam penelitian ini adalah sebanyak 30 sampel sedimen hasil sampling yang diambil di lokasi sungai – muara sungai Porong dan 30 sampel sedimen permukaan dasar laut di perairan sekitar muara sungai Porong. Distribusi umum sebaran sedimen di perairan Porong menunjukkan sedimen lumpur ditemukan di pinggir sungai dan sedimen pasir ditemukan di bagian tengah sungai. Distribusi umum sedimen dasar perairan di sekitar muara Porong berupa pasir, lempung dan lempung lanau pasiran. Hasil analisis mikroskopik dan SEM menunjukkan bahwa sedimen yang berasal dari luapan lumpur Sidoarjo ditemukan di sepanjang aliran Sungai Porong sampai muara, namun belum ditemukan di perairan luar sekitar muara Porong. Sedimen Lusi yang sampai ke muara Porong berukuran butir sampai 2,5 mikron. Deskripsi megaskopis menunjukkan sedimen Lusi pasir - kerikil umumnya berbentuk pipih (halus– agak halus). Hasil SEM menunjukkan bahwa sedimen yang berasal dari lumpur Sidoarjo umumnya seragam dan didominasi berupa smectite. Berbeda dengan sedimen sungai, hasil SEM yang diperoleh dari sampel laut yang menunjukkan sedimennya beragam, berupa montmorilonite, kaolinite dan illite. Kata Kunci : Sedimen, Porong, lumpur Sidoarjo The Sidoarjo mudflow in the Porong area increases the functions of Porong River as media to drain the muds towards the sea, because the ability of embankments in the area as a barrier is very limited. This condition intends to determine the presence and distribution of sediment in rivers, estuaries and waters originating from the Lusi mudflow. The materials used in this study are the sediment sampling results as many as 30 samples taken from the river and off the river mouth and 30 samples of sea surface sediments in the surrounding waters. General distribution of sediments in the Porong River shows the form of mud sediments are generally found in the riverside and sandy sediment found in the middle of the river, while the distribution of sediments in waters Porong form of sand, clay and sandy silt clay. The results of microscopic and SEM analysis showed that the sediments derived from the Lusi mudflow found along Porong River till estuaries, but they have not reach surrounding water of Porong estuary. The Lusi sediment that reached the estuary Porong sized to 2.5 micron. General megascopic description show the shape of the Lusi sediment as sand-gravel is a flat-shaped (rounded - sub rounded). SEM results showed that the sediments derived from the Lusi is generally uniform and dominated by smectite. In contrast to stream sediments, the SEM results obtained from marine sediment samples show a variety of sediments, in the form of montmorillonite, caolinite and illite. Key words: Sediment, Porong, Sidoarjo, Mud Overflow (Lusi