KARAKTERISTIK FASIES ENDAPAN TURBIDIT FORMASI HALANG DAERAH PAMRIYAN DAN SEKITARNYA, JAWA TENGAH

Abstract

ABSTRAK: Daerah penelitian secara administratif terletak di desa Pamriyan dan sekitarnya, Kecamatan Pituruh, Purworejo, Jawa Tengah. Pada daerah penelitian ditemukan keunikan sebaran batuan sedimen laut dalam pada Formasi Halang. Formasi Halang merupakan salah satu Formasi di Cekungan Serayu Selatan dengan endapan seri sikuen turbidit berumur Miosen Akhir hingga Pliosen Awal yang terbentuk di lingkungan laut dalam pada zona neritik luar hingga Batial Bawah. Dengan demikian, hal ini menarik peneliti untuk melakukan analisis mengenai fasies endapan sedimen turbidit laut dalam di beberapa aliran sungai daerah penelitian. Pengambilan data dilakukan dengan metode stratigrafi terukur yang kemudian dilakukan analisis sehingga menghasilkan data dan pembahasan dalam aspek stratigrafi berupa kolom stratigrafi terperinci untuk mengidentifikasi lithofacies, interpretasi proses dan interpretasi lingkungan pengendapan. Pada lintasan pertama diendapkan pada submarine fan system bagian proximal channel on inner fan dicirikan oleh litologi breksi fragmen aneka bahan dan fragmen satu bahan dengan struktur perlapisan hingga masif, channel portion of suprafan lobes on mid fan dicirikan oleh batupasir dengan struktur masif, batupasir perlapisan tebal dengan sisipan batulanau dan distal inner fan channel levee yang dicirikan oleh perselingan batupasir halus hingga sangat halus dengan batulanau. Pada lintasan kedua dicirikan dengan litologi breksi aneka bahan dengan struktur perlapisan dan masif yang diendapkan pada bagian proximal channel on inner fan, litologi batupasir halus sampai sedang dengan struktur masif, perlapisan dan graded bedding diendapkan pada channel portion of suprafan lobes on mid fan dan litologi perselingan batulanau dan batupasir halus dengan struktur perlapisan diendapkan pada bagian distal inner fan channel fan leeve pada submarine fan system. Pada lintasan ketiga daerah penelitian diendapkan pada bagian channel portion of suprafan lobes on mid fan dengan litologi batupasir halus sampai sedang dengan struktur masif dan litologi batulanau dengan struktur perlapisan yang diendapkan pada bagian distal inner fan channel fan leeve.

Kata Kunci: Endapan turbidite, Fasies, Laut dalam, Formasi Halang.

Abstract: The research area is administratively located in Pamriyan village and its surroundings, Pituruh Subdistrict, Purworejo, Central Java. In the study area, it was found that the distribution of deep marine sedimentary rocks in the Halang Formation was unique. The Halang Formation is one of the Formations in the South Serayu Basin with series of turbidite series deposits of the Late Miocene to Early Pliocene age which formed in the deep marine environment in the outer neritic zone to the Lower Batial. Thus, this attracts the researcher to conduct an analysis of the facies of deep sea turbidite sediment deposits in several river flows in the study area. Data was collected using a measured stratigraphic method which was then analyzed to produce data and discussion in the stratigraphic aspect in the form of a detailed stratigraphic column to identify lithofacies, process interpretation and interpretation of the depositional environment. In the first path deposited on the submarine fan system, the proximal channel on the inner fan is characterized by the lithology of the breccias of various material fragments and the fragments of one material with a massive layer structure, the channel portion of suprafan lobes on mid fan characterized by massive sandstones, thick layer sandstones with siltstone insertion and distal inner fan channel levee characterized by the alternation of fine to very fine sandstones with siltstone. The second path is characterized by breccia lithology of various materials with layering and massive structures deposited on the proximal channel on the inner fan, fine to moderate sandstone lithology with massive structures, layers and graded bedding deposited on the channel portion of suprafan lobes on mid fan and interchanging lithology. siltstone and fine sandstones with a layering structure are deposited on the distal part of the inner fan channel fan leeve in the submarine fan system. In the third path, the study area was deposited on the channel portion of the suprafan lobes on the mid fan with fine to moderate sandstone lithology with massive structures and siltstone lithology with the layer structure deposited on the distal part of the inner fan channel fan leeve.

Key words: Turbidite deposits, Facies, Deep Sea, Halang Formation.