FASIES DAN LINGKUNGAN PENGENDAPAN FORMASI GADING DI RANTAUTIJANG, PUGUNG, TANGGAMUS

Abstract

Lampung area has a basin, namely the Lampung Intermountain Basin which has the potential as a hydrocarbon system (Amin et al., 1994). The composition of the basin consists of various types of sedimentary rocks formed through sedimentation processes in different environments (Pettijohn et al., 1987). There is a group of sedimentary rocks exposed in the Bukit Barisan Strip, namely the Gading Formation (Amin et al., 1994). The Gading Formation has the same characteristics as the Talang Akar Formation which is used as a hydrocarbon reserve. In the Gading Formation there is sandstone lithology that has the potential as a reservoir rock. Analysis of Facies Association and depositional environment is an important part of oil and gas exploration, to provide information on the distribution and geological characteristics of oil and gas reserves in an area. Walker and James (1992) explained that facies is a rock body with several specific characteristics or characteristics that can be determined from lithology, biological structure, and sedimentary structure that show different facies aspects from other rock bodies, whether below, above, or around it. Facies association is a combination of two or more facies that form a rock body with a certain size. The research is located in the Rantautijang area, Pugung District, Tanggamus Regency, Lampung Province. The research uses a megascopic texture and lithology structure analysis method and stratigraphic cross-section measurements with a facies analysis approach, facies associations and determination of depositional environments. Stratigraphic cross-section measurements were carried out on the Gading Formation on the banks of the Way Tebu River. From the results of the research that has been carried out, namely the Facies in the Gading Formation are fine sandstone, conglomerate, medium sandstone, silt with a laminated structure, clay with a laminated structure, lensed shale, sandstone with a load cast structure. The channel fill facies association is composed of fine sandstone facies, conglomerate, medium sandstone and sandstone with a load cast structure. The floodplain facies association consists of laminated silt facies, laminated clay and lensed shale. The depositional environment is fluvial because it consists of fine and coarse material that is deposited.