Identifikasi Ketebalan Sedimen Dolina Karst Menggunakan Metode Tahanan Jenis Konfigurasi Wenner-Schlumberger di Desa Sekar, Pacitan

Nawangsari, Putri (2020) Identifikasi Ketebalan Sedimen Dolina Karst Menggunakan Metode Tahanan Jenis Konfigurasi Wenner-Schlumberger di Desa Sekar, Pacitan. Undergraduate thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Dolina merupakan cekungan yang berada pada sela antar bukit di wilayah karst yang memiliki sedimen lebih tebal dari daerah sekitarnya. Dolina menjadi indikator adanya pelarutan yang signifikan akibat adanya manifestasi seperti rongga di dalam tanah atau batuan. Ketebalan sedimen yang dimaksud dalam penelitian adalah lapisan lunak yang berasal dari pelarutan batuan di sekitar dolina dan terendapkan di area dolina maupun hasil pelarutan batuan dasar yang disebabkan oleh air yang menembus melalui celah batuan secara terus-menerus. Sedangkan batuan dasar yang dimaksud adalah lapisan batuan yang memiliki nilai resistivitas lebih besar dan kontras resistivitasnya terlihat cukup jauh dengan lapisan sedimen. Metode geolistrik resistivitas 2D dapat digunakan untuk menggambarkan kondisi bawah permukaan secara lateral dan vertikal sehingga digunakan dalam penelitian ini. Konfigurasi yang digunakan adalah Konfigurasi Wenner-Schlumberger. Ketebalan sedimen dapat diidentifikasi dari kontras resistivitas batuan yang dapat dilihat dari penampang hasil inversi. Penelitian dilakukan di dolina sekitar Luweng Dawung, Desa Sekar, Pacitan. Terdapat 4 lintasan pengukuran yang sejajar, dengan panjang lintasan 140 m, 145 m, 145 m, dan 155 m dominan berarah barat laut-tenggara. Data hasil pengukuran di lapangan diolah dengan perangkat lunak Res2dinv. Berdasarkan geologi regional, daerah penelitian termasuk ke dalam Formasi Wonosari yang tersusun atas dominan batuan karbonat terumbu. Pada penampang hasil inversi setiap lintasan terlihat persebaran nilai resistivitas yang menunjukkan litologi daerah penelitian. Nilai resistivitas di bawah 20 Ωm diinterpretasi sebagai tanah penutup dolina atau disebut sedimen dan nilai resistivitas di atas 20 Ωm diinterpretasi sebagai batuan karbonat terumbu atau disebut bedrock. Selain itu, nilai resistivitas antara 10-20 Ωm diinterpretasi sebagai rongga penuh air yang letaknya berada di antara batuan karbonat terumbu. Ketebalan sedimen pada lintasan NWG-1 sebesar 25 m, NWG-2 sebesar 16 m, NWG-3 sebesar 17 m, dan NWG-4 sebesar 20 m. Hubungan ketebalan antar lintasan dapat diperoleh jika data mencakup wilayah yang lebih luas ============================================================================================ Dolina is a basin between the hills in the karst region which has thicker sediments than the surrounding area. Dolina is an indicator of significant dissolution due to manifestations such as cavities in the soil or rocks. The thickness of the sediment referred to in this study is the soft layer that originates from the dissolution of rocks around the dolina and is deposited in the dolina area as well as the results of the dissolution of bedrock caused by water that penetrates through the rock gap continuously. While the bedrock is a rock layer that has a greater resistivity value and the resistivity contrast looks quite far from the sedimentary layer. 2D resistivity geoelectric method can be used to deliniate subsurface conditions laterally and vertically so that it is used in this study. The configuration used is Wenner-Schlumberger Configuration. Sediment thickness can be identified from the contrast of rock resistivity which can be seen from the cross section of the inversion results. The study was conducted in dolina around Luweng Dawung, Sekar Village, Pacitan. There are 4 parallel lines, with a length of 140 m, 145 m, 145 m, and 155 m dominantly directed northwest-southeast. Data from measurements in the field are processed with Res2dinv software. Based on regional geology, the study area is in Wonosari Formation which is composed of dominant reef limestone. In the cross section of the inversion results for each line, it is seen that the resistivity value distribution shows the lithology of the study area. Resistivity values below 20 Ωm are interpreted as soil cover dolina or called sediment and resistivity values above 20 Ωm are interpreted as reef limestone or called bedrock. In addition, resistivity values between 10-20 Ωm are interpreted as cavities full of water that are located between reef limestone. The thickness of the sediment in NWG-1 is 25 m, NWG-2 is 16 m, NWG-3 is 17 m, and NWG-4 is 20 m. Thickness relationships between lines can be obtained if the data covers a wider area.

Item Type: Thesis (Undergraduate)
Uncontrolled Keywords: Dolina, Karst, Wenner-Schlumberger
Subjects: G Geography. Anthropology. Recreation > GB Physical geography > GB600 Karst conservation.
Q Science > QE Geology > QE571 Sedimentation and deposition. Sediment transport.
T Technology > T Technology (General)
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Faculty of Civil Engineering and Planning > Geophysics Engineering > 33201-(S1) Undergraduate Thesis
Depositing User: Putri Nawangsari
Date Deposited: 11 Aug 2020 03:42
Last Modified: 11 Aug 2020 03:42
URI: http://repository.its.ac.id/id/eprint/77412

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