Publications

Tectonically, the Indonesia – Australia margin was relatively quiescent during the Late Cretaceous period. Following Jurassic to Early Cretaceous rifting event the Cretaceous was a period of thermal sag and passive margin cooling throughout the Barakan – Tanimbar (West Aru) area. The passive margin is characterised by the development of a large prograding wedge which thins toward the northwest. In some areas, this wedge is associated with the development of shelfal sands during the Late Cretaceous time. This paper aims to describe the depositional setting of the Late Cretaceous in the West Aru area using interpretation of 3D seismic tied to wells control. Seismically, the Late Cretaceous (Campanian – Maastrichtian) is clearly identified by a progradational package which trending from southeast toward northwest. Some slope channels, with SE – NW trend, are also identified in this interval. Shelf edges are interpreted through isopach and seismic attribute maps. Spectral decomposition and inversion of seismic data has supported the Shelf Edge Delta model by differentiating depositional environment between the shelf and slope. Isopach maps clearly show a shifting of depocenter towards the southern part of West Aru from Early to Middle Campanian time. Barakan-1 and Koba-1 wells in West Aru penetrated Late Cretaceous sands. Both wells encountered blocky sandstone with good reservoir quality, fine grained and well sorted. Those sands were deposited during Campanian – Maastritchian age. The Late Cretaceous sands are sitting on the delta top of the seismically identified clinoforms. Using seismic and well data, a Late Cretaceous Delta system has been clearly identified through progradational features developing from Campanian through Maastrichtian. The sedimentary process may be influenced by fluvial or wave processes. It remains uncertain whether the sediment source was coming from a high area to the east of West Aru or from the Goulburn Graben. Keywords: Late Cretaceous play, progradation, delta, 3D seismic, Campanian-Maastrihctian, K80.1 marker