Geology and depositional environment semilir formation of Hargomulyo Area, Gedangsari, Yogyakarta, Indonesia

Geological map of the Surakarta-Giritontro Quadrangles, Java scaled of 1:100,000 produced in 1997 and not updated since then. The pervious data are might change in term of geomorphology and new outcrop which might expose in the study. Thus this research is to update the geological map of study area scaled 1:25 000, to determine the facies characteristics and to interpret the depositional environment of Semilir Formation in Yogyakarta, Indonesia. The research was conducted by field studies and lab analysis involving traversing and thin section. Data was interpreted by using lithological section for Semilir Formation. The research area over all consists of six lithology unit namely tuff, tuffaceous sandstone, green tuff, tuff breccia, lapilli and andesite breccia All these rock aged from Late Oligicene-Early Miocene. Semilir Formation was form during volcanism period, mostly dominated by tuff breccia, lapilli, tuff and volcanic sandstone aged Early Miocene. Semilir Formation are separated into five facies and it has deep marine depositional environment. It form at underwater submarine fan at inner fan.