Characteristics of Semilir Formation in Relationship With the Period of Volcanic Activity

Abstract

The Semilir Formation in the Baturagung area is a tipelocation of the Semilir Formation that is physiographically located on the part of the Southern Mountains Zone. Its spread extends from the western part of Imogiri, DIY, in the middle of Mt. Baturagung, to the eastern end of Mt. Gajahmungkur height. The Semilir Formation in the research area is aligned under Nglanggeran Formation and above Kebo-Butak Formation. The arrangement of rocks Semilir Formation in the basin of the Southern Mountains of Java is still seen from the standpoint of stratigraphy-sedimentology. The rock formation mainly consists of alternating breccia, sandstone, and claystone. Where the rock unit consists of tuff, tufflapilli, and pumice breccia, with generally rich in volcanic glass and quartz. These characteristics are related to volcano activities. This phenomenon is interesting to be studied further in order to reveal the volcano activities at that time that plays a role in the Semilir Formation. This study was studied from the perspective of stratigraphy-sedimentology and volcanology by measuring a detailed measurement of stratigraphy in order to obtain a sequence of lithologic variations of its constituent rocks. Detailed stratigraphic measurements that are characteristic of the Semilir Formation in connection with the periodization of volcanic eruptions in the South Mountain Basin indicate that there were 84 units of volcanic eruptions in 14 periods lie on the older volcanic rock succession. The location of this research is Semilir, Baturagung, Nglipar, Gunung Kidul, approximately south of Klaten, Central Java.