Geology and depositional environment of Oyo formation in Ngalang Area, Gedangsari District, Gunung Kidul Regency, Yogyakarta, Indonesia.

This study is conducted at Ngalang area that is located at Gedangsari district of Gunung Kidul Regency in Yogyakarta Special Region, Indonesia. This research is concern with objectives to produce and update a geological map of a study area (5km X 5km) with smaller scale 1:25 000 as the data from preliminaries study lasted on 1992 with larger scale which is 1:100 000. This research paper also conducted to interpret a facies association data collected in geological mapping of depositional environment of Oyo Formation. Stratigraphically, the study area is consists of Sambipitu formation, Oyo formation and Wonosari formation which in early to late Miocene. Methodology used for this research are geological and geomorphological mapping, remote sensing (ArcGIS) interpretation and laboratory analysis. General geology of study area and basic petrology which also include picture and description of sample in thin section under microscope also presented in this research paper. Geomorphology map, lithology and stratigraphy unit of Sambipitu formation, Oyo formation and Wonosari formation were discussed in this paper. Macrofossils and microfossils found in the study area also presented in this paper and were used as an advantage in order to gain more information and contribute a detail data regarding Oyo formation in Ngalang area. The depositional environment of the Oyo Formation is interpreted to be in the middle to outer ramp of shallow marine environment. The parameters used in data interpretation are facies association and foraminifera fossils analysis presence in the carbonates rocks in study area.