Online Journal for E&P Geoscientists

Kaswandi, Achmad A.¹; Mahmuddin, Iskandarsyah ^*1; Suparno, Supriyanto ¹
(1) Geophysics-Physics, University of Indonesia`, Jakarta, Indonesia.

Jatibungkus is a region consisting of limestone rock. It is located above the Karangsambung formations (deep water formation), approximately 200 m eastward from the Karangsambung - Kebumen road. Jatibungkus hill is a giant slab of coral limestone. These rocks deposited in shallow marine environments and existence is estimated because there is a shift by gravity. On this hill was also found caves such as Langse west cave, Sikepul cave, and Silodong cave in the east. Many hypotheses said that Jatibungkus is a hill composed by rock melange. Thus it reinforce us that the formation doesn’t continue until the deeper subsurface. This observation has support the hypothesis by examining the location of depth contact between scaley clay with limestone rocks. We prove this by using a Ground Penetrating Radar (GPR) as our method. The transmitter uses a frequency of 40 MHz with a depth range of around 50 m. We took data as much as 4 lines, with a path length range of 37-120 m. The length of each path is influenced by the complex structure of field surface. The results indicate that the reflector is at a depth between 10-20 m below ground surface. Conclusions from the observation reinforce the notion that Jatibungkus is a melange rock with a specific depth of about 20 m.