Jurnal Sains dan Teknologi Lingkungan

1. 18  Sismanto; Edy Hartantyo; Mochamad Nukman  Jurnal Sains dan Teknologi Lingkungan The major fold is trending east-west and other fold, it might an older old, is trending to the northeast-southwest. A complex folded formation occurs at the east and the western part at the geologiocal map of Banyumas Sheet, in the middle part is dominated by a single fold (Asikin, et al., 1992). The anticline along Prapagan to Gunung Wetan is bisected by faults system. The anticline across Jeruklegi has a low limb dip at the north and a slightly forming a recumbent form. This structure folded Tapak Formation of Early Pliocene age, which indicates the age of deformation is Middle- Late Pliocene or Plio-Pliotocene (Asikin, et al., 1992). The fault system at the study area is thrust, strike slip and normal fault. The thrust faults occur at the west and eastern part of Geological Map Sheet, trending to the east –west. The south block is the hanging wall. This thrust is bisected by strike slip fault. The fault system at the west is covered by alluvium deposit and the trace obviously appear along K. Jambuhandap which the Halang Fm. is crop out (Asikin, et al., 1992). The tectonic and basin development at Cilacap Area is strongly related to the Eurasia and Australian plate subduction since Cretaceous time (Early Tertiary age) (Asikin, et al., 1992). 2. Method The survey were performed by geoelectrical (resistivity) method i.e., Schlumberger sounding configuration. The lay out is about 500 m by McOhm resistivity meter. The resistivity method is a non-destructive survey to know the resistivity distribution of the soil vertically. The procedure is by injecting DC electrical current into the ground, and then measures the voltage on the surface by double potential electrodes at in line position. The comprehensive theory and method are described in Telford, et al., (1976). The processing and the modeling use Progress 3.0. 3. Results Local Geological Information The oldest rock in this area is sandy siltstone which mainly crop out at the eastern part of Camping Park. The sandy sandstone is in form of (1-10) cm layer, interbedded siltstone and sandstone which is intensively fractured. The porosity of this lithology is considered good and suitable for water reservoir; whereas the siltstone acts as its cap rock. The physical properties of sandy siltstone are conductive (low resistivity).