Geology and deposition of volcaniclastic in Nglanggeran formation at Patuk Area, Gunung Kidul, Yogyakarta, Indonesia

The research study was located at Patuk area, Gunung Kidul Indonesia, Yogyakarta, with coordinate of 7'49'17.67"S to 7°52'0.16"S for the latitude and 110°28115.17"E to 110°30'58.2"E for the longitude. The geological information of Patuk area must be updated for current usage as the latest geological map was in scale 1: 100 000, where the accuracy of the map is decrease because of the large scale. The first objective for the research is to produced geological map with scale of 1: 25 000. The geomorphology, the structural geology and the lithology unit of Patuk area was observed, measured and analyzed in order to produce geological map. The historical geology for Patuk area can be determined and explained based on the geological study. The research specification was made in study area, where the formation that was focused on is Nglanggeran Formation. The deposition and lithology unit of Nglanggeran Formation consist of volcaniclastic sediments. Therefore, the method is different from the method used in sedimentary rock. Lithology log of volcaniclastic sediments was made and analyzed, based on the rock fragment size and mineral composition. The petrographic analysis play important roles in both geological mapping and research specification as the dominant lithology for Nglanggeran Formation is volcanic rocks. The second and third objectives were achieved based on the analysis of the research specification. The facies analysis was made based on the lithology log where there were four type of different facies in Nglanggeran Formation in study area. The deposition environment was determined based on the facies analysis and lithology log. The depositional environment for Nglanggeran Formation in study area is submarine environment.