THE PALEOGENE BASIN WITHIN THE KENDENG ZONE, CENTRAL JAVA ISLAND, AND IMPLICATIONS TO HYDROCARBON PROSPECTIVITY

摘要

A large part of the E-W trending Kendeng Zone of Central Java, is covered by Quaternary volcanic products with some windows of late Tertiary outcrops, especially in the northern part. The NE-SW structure found in the area is generally associated with a Paleogene basin and has been proven as the locus of hydrocarbon source-rock deposition (e.g. Central Deep). The regional gravity map of Central Java shows that the zone is a deep basin. The gravity map also indicates that the Kendeng Zone is dissected by a NE-SW structural lineament that can be interpreted as the southward prolongation of the Paleogene structural trend. Field observations have proven that in the southern part of Java, Paleogene outcrops are located along these lineaments (eg. Cimandiri, Luk Ulo, Nanggulan, and Bayat). Stratigraphic studies in some Paleogene outcrops in the southern part of Java revealed that a Paleogene basin was present in the southern part of the island.A series of sediment samples comprising Paleogene and Neogene intervals have been collected during this study. Detailed geochemical analyses have been performed on some selected sediments. The characteristics of the sediments from both stratigraphic intervals have therefore been defined. Several oil samples were available for this study. Most of the oil samples have experienced severe biodegradation. Even though the samples are biodegraded some detailed geochemical analyses, such as gas chromatography — mass spectrometry (GC-MS) and stable isotope analyses, were still conducted. The results indicate that there is relatively good correlation of the biomarkercharacteristics of the crude oils with those of the Mio-Pliocene Halang Formation. However, as the Halang Formation is not sufficiently mature to produce liquid hydrocarbons, the source of the crude oils is most possibly the Wungkal Formation (Paleogene) that has similar depositional environment to the Halang Formation but occurred in a deeper stratigraphic position.