The Kinarut Sequence: A Model for Fan Deposition at the 10.6 Ma Sequence Boundary in Northwest Borneo Fold-Thrust Belt

Andrew Cullen, Alec Bray, Peter Osterloff, Mathew Choo, Boon-Teck Yong, Alex Huerlimann, and John Voon
Shell Malaysia Exploration and Production, Deepwater Exploration, Miri, Malaysia

As demonstrated by a string of discoveries over the preceding 3 years, the deepwater fold-thrust belt of NW Borneo has emerged as materially significant oil province during a phase of exploration largely un-calibrated by well data. Incorporation of new well results with prior studies enables refinement of the geological models for the pre-kinematic and syn-kinematic turbidite depositional systems of the basin. We present a depositional model for the “Kinarut Fan” that integrates biostratigraphy, lithostratigraphy, geochemical data, wireline data, and pressure analyses with regional mapping and seismic facies. The Upper Miocene Kinarut sequence generally pre-dates the onset of widespread deformation. Near the present-day shelf slope break the sequence overlies the Middle Miocene Kebabangan sands. Outboard, however, the Kinarut overlies an areally extensive mass transport complex that is interpreted as mass wasting of the shelf during the early stages of the 10.6 Ma sea level fall. The basal Kinarut sandstones tend to be massive and have a higher net to gross than overlying units. These sandstones, which have fair lateral continuity and fair vertical connectivity, are interpreted as amalgamated channels. The basal unit is overlain by a medium bedded vertically compartmentalized succession having excellent fine-scale lateral correlation that we interpret as dominated by unconfined sheet sands. The uppermost section consists of laminated thin beds interpreted as distal sheets sands that are ultimately capped by marine shale. On the basis of age, paleo-climate indicators, and stacking patterns, we interpret this succession as a lowstand systems tract at the TB3.1 sequence boundary that is progressively transgressed during the subsequent sea level rise.