IPA14-G-086 PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Thirty-Eighth Annual Convention & Exhibition, May 2014 DEVELOPMENT OF THE SORONG FAULT ZONE NORTH OF MISOOL

The part of Sorong Fault Zone studied here is located to the north of Misool between Obi and Batanta. The fault zone cuts an Early Miocene collision suture between the Philippine Sea Plate and the northern Australian margin. Its complex geometry and tectonic history are important for hydrocarbon exploration and to the south of the fault zone are the major oil fields of the Salawati Basin in the Bird’s Head region of Papua. 2D seismic and multibeam seafloor bathymetry data demonstrate the characteristics of the fault zone and basins in the subsurface and at the surface. Three major fault strands of the Sorong Fault Zone are identified: the E–W striking Molucca-Sorong Fault to the north, the NE–SW striking North SulaSorong Fault in the middle and NE–SW striking North Misool-Sorong Fault to the south. These faults separate basinal areas which formed by different mechanisms, and as a result have different geomorphological, stratigraphic and structural characteristics. There are significant difficulties in correlating between the basinal areas which have different basement types. An intriguing feature of the fault zone is the variation in seabed expression of different segments. The western Sorong Fault Zone was active very recently although there is currently little seismic activity. There is evidence of both transpression and transtension at different places along the sinistral strike-slip system area. The Kofiau Basin has several features suggesting it could be the northern part of the Salawati Basin displaced to the west on the Molucca-Sorong Fault during the Pliocene. * Royal Holloway, University of London INTRODUCTION The Sorong Fault (Visser and Hermes, 1962; Pieters et al., 1983) is part of a left-lateral strike-slip zone which extends from eastern Papua, across the northern part of the Bird’s Head of New Guinea (Froidevaux, 1978; Hall et al., 1995; Satyana and Herawati, 2011) and continues west of the Bird’s Head which broadly marks the southern boundary of the Molucca Sea and Philippine Sea plates and the northern boundary of Australian Plate (Hall et al., 1995). Westward movement of the Pacific, Caroline and Philippine Sea plates relative to Australian continental crust (Hall, 1996, 2002) caused the left-lateral strike-slip zone (Froidevaux, 1978; Satyana and Herawati, 2011; Riadini et al., 2009) to develop along a suture produced during Paleogene collision of the Philippine-Halmahera arcs and the Australian margin (Ali and Hall, 1995; Hall et al., 1995; Hall, 1996, 2002). The initiation of the Sorong Fault system at ~25 Ma is based on geochronological and paleomagnetic data (Ali and Hall, 1995; Hall et al., 1995) from several islands located close to and north of the northern fault strand. The timing of displacement on the Sorong Fault from the northern Bird’s Head to as far west as Misool Island is still debated. Movements are suggested to have occurred in the Pliocene (Froidevaux, 1978; Gibson-Robinson et al., 1990; Decker et al., 2009; Satyana and Herawati, 2011) or the Miocene (Riadini et al, 2009). The geometry of the Sorong Fault Zone to the west of the Bird’s Head is not well known. Extending west of the Bird's Head, there are several PlioceneRecent left-lateral splays of the Sorong Fault (Figure 1). Hamilton (1979) named two splays of the Sorong Fault Zone the Molucca-Sorong Fault and the North Sula-Sorong Fault, while Letouzey et al. (1983) identified a third southern splay as the North Misool-Sorong Fault and referred to the zone between the two southern splays as the North BuruSalawati Tectonized Zone. Recently acquired seismic and multibeam data provided the opportunity to study this region in more detail.