Publications

The aim of this paper is to highlight the contribution of conventional core data in the development of sequence stratigraphic models, and to illustrate this with a cored interval from the Middle Miocene Upper Cibulakan Formation (Main interval) of the Offshore Northtwest Java (ONWJ) Basin, Indonesia.The Main intenral of the ONWJ Basin comprises up to 1500 ft of interbedded shales, sandstones, siltstones and limestones deposited in an overall paralic setting under transgressive conditions within a wholly marine depositional environment. A 75 0 foot low invasion core in the U-1 1 well provides almost continuous core coverage through the upper Main interval on the ",U", structure. This core provides the database for this paper.A characteristic of the Main interval is the organization of sandstones into 50-1 00 ft. thick packages separated by thicker sections (up to 250 ft.) of tuffaceous, grcy-green, full!- marine shales. These sandstone packages reflect the abrupt introduction of coarse clastic material into a relatively quiescent marine setting b?, the relyorking of delta front sands at times of relative lowstand. Firm grounds at the basal contact imply an episode of subaqueous erosion prior to deposition of thc sandstone. The complex stacking of sandstones and mudstones within the package reflects the interplay between largely autocyclic processes (e.g. lobe si\,itching), subtle trariations in basin topograph?,. sediment supply and relative sea level fluctuations. Regionally extensive limestones at the top of the sandstone packages reflect sedimentation during the ",maximum flooding", event, and are regionally correlatable throughout the study area.Many other sequence stratigraphic interpretations have been developed in basins with well defined shelf margins. However, such a shelf-slope break is not observed in these middle Miocene deposits. In addition, evidence for the development of marine shoreface sequences or surfaces of subaerial exposure are rare. This paper highlights the importance of a detailed sedimentological description of conventional core to aid the development of a (sequence) stratigraphic framework.The important emphasis of this approach is on the recognition of facies associations, along with their associated bounding surfaces. This information can then be supplemented with other geological data (e.g. biostratigraphy), and bc integrated with well log and seismic data to fully implement exploration and development efforts in these fully marine depositional environments.