Publications

The Northeast Java Basin is known as a mature Cenozoic basin. This understanding has caused the current exploration targets of the basin to be Cenozoic sediments only. As a result, the source rock in the basin is believed to be from Cenozoic sediments only, particularly the Ngimbang Formation, which was formed during the middle Eocene to Early Oligocene syn-rifting. This is true for most areas in the basin that Ngimbang carbonaceous shales sourced the Northeast Java oils. However, based on biomarkers, some oils from Kangean area show different characters. The oils show stronger marine character and reducing conditions although mixed with general characteristics of terrestrial and oxidizing source rocks. The Kangean oils also show very low oleanane and sterane indexes, indicating that the source of oils could be Cretaceous in age. The presence of Alisporites sp., an index taxa of the Lower Cretaceous age in the sediments analyzed, is another strong indication that there is a Cretaceous source in the area. Recent tectonic reconstruction of this area shows the possible presence of a Northern Gondwanaland-derived micro-continent underlying the Northeast Java Basin, including the Kangean Area. During the drifting, syn-drifting Lower Cretaceous marine sediments were deposited on the micro-continent. Recently acquired seismic data in this area show the presence of these Mesozoic sediments. The micro-continent existed under the eastern part of the Northeast Java Basin in mid-Cretaceous time. Burial sediments of and tectonics during the Cenozoic have matured the Lower Cretaceous source, generated oils and trapped in some structures in the Kangean area. The knowledge that we have an actively generating Lower Cretaceous source in the Northeast Java Basin will drive exploration in this area not only to the Cenozoic targets, but also to the new Mesozoic targets.