TECTONIC AND GEOLOGICAL STRUCTURES OF GUNUNG KROMONG, WEST JAVA, INDONESIA

The Gunung Kromong complex is a solitary hill which physiographically located within the Jakarta Coastal Plain Zone. The research is mainly formed of primary data from observations and measurements of all geological elements especially morphological aspects and geological structures to reveal the tectonic background and its relation to the oil seepage. Sedimentary rocks outcrops appear in the western part around the cement plant surrounded by well exposed of igneous rocks. Oil seepage, gas and hot springs are found in limestone which has high fracture intensity and at low elevation. The distribution of sedimentary rocks is not only controlled by the folds and fault structures but also influenced by the igneous rock intrusion. The alignment of the structure in West Palimanan is formed by steep slopes on dacite igneous rock which is concluded as fault scarp. There are found abundance of fault indications in the form of slickenside, fault breccias, millonites, drag folds and have high intensity of shear joint. The KRG-7, KRG-8 and KRG-9 observation points, a slickenside with the same plane was found but has different slicken line, each shows a thrust fault and normal faults. The direction of slickenside divided into 4 units of fault groups. The series of hills in the south of the Baribis Fault occur because of the lifting through the fold and the thrust faults mechanism. The thrust fault in the Gunung Kromong complex is the hanging wall section of the Baribis thrust fault, so that it belongs to the leading thrust system.