Abstract
The research area is a part of South Serayu Mountain zone, specifically Bregada Kulon Progo. The Bregada Kulon Progo is a product of volcanic activity in the past, which can be seen by the volcanic rock called Old Andesite Formation. The end of the volcanic activity is characterized by the deposition of carbonate rocks which were part of Jonggrangan Formation and Sentolo Formation. The lower part of Sentolo Formation is composed by the mix of carbonate and volcanic materials. The research is carried out by two methods. The first is field method, which is implemented by geological mapping and rock sampling. The second is laboratory method, which is implemented by petrographic method. The petrographic method is implemented by making thin section of the rocks, then observing the thin section with polarization microscope to determine the composition of the rocks. The rock samples are mainly from the lower and middle part of Sentolo Formation, which probably still got the influence of volcanic activity. The benefit of the research is knowing the influence of volcanic activity in the carbonate rocks of Sentolo Formation. The presence of volcanic materials in the lower part of Sentolo Formation, can be predicted by two processes. First, the volcanic activity supplied those materials directly, and second, from the rework of the volcanic materials then mixed with carbonat materials of Sentolo Formation.
Highlights
1.1 BackgroundBregada Kulon Progo, the location of this research, is a part of the physiography of the Southern Mountains [1,5], based on other sources Bregada Kulon Progo belongs to the South Serayu Mountains [6]
Bregada Kulon Progo is the product of the volcanism activity during the Oligocene to Early Miocene
The volcanism activity produced the formation of volcanic deposition called Old Andesite Fomation (OAF)
Summary
Bregada Kulon Progo, the location of this research, is a part of the physiography of the Southern Mountains [1,5], based on other sources Bregada Kulon Progo belongs to the South Serayu Mountains [6]. Bregada Kulon Progo is the product of the volcanism activity during the Oligocene to Early Miocene. The volcanism activity produced the formation of volcanic deposition called Old Andesite Fomation (OAF). The end of volcanism activity is marked by the growth of reefs namely Jonggrangan Formation. The growth of reefs at Bregada Kulon Progo was followed by the deposition of clastic carbonate rocks called Sentolo Formation. The lower part of the Sentolo Formation is composed by a mixture of carbonate materials and volcanic materials. The presence of volcanic material at the bottom of Sentolo Formation leads to the presumption of volcanic activity which supply the volcanic material into Sentolo Formation or the existence of rework material from the old Andesite Formation which was deposited into the Sentolo Formation, resulting in a mixing on the lower part of Sentolo Formation. A study was conducted to study the lower and middle stratigraphy of Sentolo Formation, based on differences or variations in the composition of the formation
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