Sedimentation Dynamics of the Lower Part of Sentolo Formation at Niten Stream Traverse, Girimulyo, West Progo

Previous geologists showed that Sentolo Formation was interfingering with Jonggrangan Formation and both of them laid unconformably on Old Andesite Formation. The aim of this study is a deeper understanding of the sedimentation dynamics of Sentolo Formation in order to know its stratigraphic relationship to Old Andesite Formation. Petrographic analysis was used to describe the microfacies. Paleontological analysis was used to know the age and sedimentation environment. Stratigraphic measurement of Sentolo Formation in the section of Niten Stream traverse showed that Sentolo Formation was sedimented on the basin environment (SMF3/FZ1; SMF2/FZ1), deep shelf margin (SMF3/FZ3) to foreslope (SMF4/FZ4). The paleontological data indicate that these sedimentary rocks was depositing during Early Miocene until the beginning of Middle Miocene (N6 – N9). Sedimentary rock succession is generally dominated by layered limestone with tuff sandstones that develop well in the lower – middle layer. It indicates that the dynamic of basin sedimentation which formed during that period was influenced by volcanic activity that gradually weakened and caused the basin relatively quiet, producing thick limestone.