Berau Sub-basin is the southernmost onshore depocenter of the greater Tarakan Basin NE Kalimantan. This basin with respect to hydrocarbon exploration has not been explored quite well until now, compared to their neighbor Tarakan Sub-basin, although oil seeps and HC show in some penetrated wells within the Berau-Sub Basin indicate that there are complete and working petroleum systems. Therefore, more detailed and integrated geological work is needed. A review of satellite imagery, geological surface data, and geophysical data have been integrated to reinterpret Tertiary facies distribution in the basin and some models have also been presented to explain the tectonic evolution of the basin and the resulting depositional environment related to basin infilling which imply to the forming of petroleum system element.
The basin is generally located on a passive margin which was initiated simultaneously with the formation of Sulawesi Sea by rifting of North Sulawesi from East Kalimantan in the Middle Eocene. Early sedimentary fill of the depocentre happened during Middle Eocene to Early Oligocene in transgressive transition to marine condition. Kuching, Suikerbrood, and Sekatak Highs surrounding the basin are then suspected to be the main source deposit. The regression related to regional tectonic uplift of the western basin margin began in Late Oligocene and was followed by transgression period which resulted in increasing clastic input to the basin. Later, the Middle Miocene uplift created newly emergent area to the west and formed constructive delta that prograded relatively from west toward east. The most significant tectonic event was in the Late Miocene, which produced folds and reverse faults. Those events were mainly triggered by strike slip reactivation on the existing NE-SW and NW-SE basement fractures. Regressive style of sedimentation continued until Pleistocene. Tectonic uplift that occurred in Pleistocene was probably the last tectonic event recorded, bringing present day configuration of geological condition of Berau area.
Authors : Herning Dyah Kusuma Wijayanti, Sugeng Sapto Surjono, Soedarmono