Geology and depositional environment of the sambipitu formation in the Bunder Area, Gunung Kidul Regency, Indonesia

Yogyakarta situated in the Central Java and the city is located only 30km from Merapi volcano area. The study area is located at the Bunder, Patuk Village, Gunung Kidul Regency,Special Provine of Yogyakarta, Indonesia. The geology, sedimentary structure and sedimentary facies need to be updated for the accuracy information and data of geology in Bunder area especially in determine their depositional environment. The objective of this study is to update a geological map of the area with scale of 1:25,000, to determine the deposition environment of the Sambipitu formation and also to analyse the sedimentary facies in the study area. The methods used in this study consist of two parts. The first is making lithostratigraphic columns from the combination observation of field work and laboratory .Second, petrographic observations from the rock sample to determine the composition of the constituent facies and lithological..At the upper part of the study area, it occurred pyroclastic-epiclastic rock and the alternation between sandstone with claystone, tuffaceous sandstone -siltstone with fragment tuff and limestone. The alternation of packestones and wackestones with marls also can be found in the Bunder area at the lower part of the study area.Based on the previous stratigraphic measurement data and analysis of association ichnofossil groups, the interpretation depositional environment from Lower Sambipitu Formation to Upper Sambipitu Formation shows the fluctuation of seawater level due to transgression and regression process in submarine fan.