Herwin Tiranda , Robert Hall

The area of the Offshore NW Sulawesi lies between eastern Sundaland (Borneo) and the North Arm of Sulawesi. Possible influences on the basins include Paleogene rifting in the Celebes Sea and Makassar Strait, Neogene subsidence and uplift in Borneo, late Neogene subduction at the present-day North Sulawesi Trench, and displacements related to the Palu-Koro Fault. This study presents the results of structural and stratigraphic framework of the Offshore NW Sulawesi based on interpretation of 2D seismic surveys offshore and multibeam bathymetry. In this study, the Offshore NW Sulawesi region is divided into three parts: the Deepwater Tarakan Basin in the NW, the Muara Sub-basin in the west, and separated from these by the Palu-Koro Fault, the North Sulawesi Fold-Thrust Belt in the east. There is no continuation of the left-lateral strike-slip Palu-Koro Fault to the adjacent area of Borneo via the Muara Sub-basin and Deepwater Tarakan Basin. Both basins developed after extension began in the Middle Eocene associated with oceanic spreading in the Celebes Sea. Since then, sediment was fed to the basins from the east and south, with several episodes of subsidence, particularly during Early Miocene in the Muara Sub-basin. Rapid prograding shelves from eastern Borneo are linked to regional inversion and uplift on land since the Middle Miocene and led to gravity-driven movement in the Deepwater Tarakan Basin which formed toe-thrust faults in the latest Miocene. Deformation in the North Sulawesi Fold-Thrust Belt is interpreted to have occurred in the latest Miocene or Pliocene to present-day with subduction of Celebes Sea at the North Sulawesi Trench and movement on the Palu-Koro Fault.