Tectonostratigraphic evolution of the Obi Basin, North Maluku, Indonesia, with implications for petroleum exploration potential

The Obi Basin, one of the frontier basins in Eastern Indonesia, is classified as an oceanic basin and is believed to have poor petroleum potential. However, our tectonostratigraphic study reveals a thick sedimentary succession with indications of an active petroleum system. The Sorong Fault, which traverses the basin, significantly impacts the basin development, sedimentary infilling, petroleum generation, and migration pathways. Four rock sequences in Obi Basin were defined using seismic and geological data. Sequence-1 comprises Paleogene volcaniclastic of Anggai River Formation, deposited during the subduction of the Australian Plate beneath the Philippine Sea Plate, with older metamorphic and ophiolitic rocks. Subsequent collision in the Early Miocene led to basin uplifting and deposition of Sequence-2 (Fluk limestone and shale). The Middle Miocene eastward subduction of the Molucca Sea beneath Halmahera ended the Sequence-2, marked by volcaniclastics and shallow marine deposits of the Guyuti and Woi Formations. Afterward, Pliocene Halmahera-Sangihe arc collision caused major uplift, leading to rapid deposition of Sequence-3 (South Obi volcaniclastic and Anggai carbonate). A subsequent down-wrapping due to isostasy initiates the deposition of Quaternary turbidites of Sequence-4. In terms of the petroleum system, Sequence-1 is considered an economic basement, while Sequence-2 is identified as a mature source rock. Sequences-2, 3, and 4 exhibit interbedded coarse and fine sediments, which have the potential to be both reservoir and seal rocks. The movement of the Sorong Fault coincided with subduction in the Molucca Sea, creating four-way dip closure anticlines that serve as a structural trap.