Jurnal Sains dan Teknologi Lingkungan 18   Sismanto; Edy Hartantyo; Mochamad Nukman 

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).