THE INTERACTION OF CHANNELIZED TURBIDITY CURRENTS WITH A GROWING FOLD: A VIEW FROM THE SEASCAPE, OFFSHORE BRUNEI DARUSSALAM

Research focused on the interactions of rivers with growing topography has improved the understanding of key processes affecting landscape evolution. Unfortunately, difficulties associated with observing these interactions in the submarine setting have hampered the development of comparable advances for seascape evolution models. We present results defining the interactions of a submarine transport system with a growing shale-cored anticline. This study resolves the development of growth strata over the crest of the shale ridge using an industry-grade seismic volume from offshore Brunei Darussalam (NW Borneo). The shale ridge is located about 20 km down slope from the present-day edge of the continental-shelf in roughly 900 m of water. Its crest line runs for 18 km and is oriented perpendicular to the regional slope. Channels traverse the structure at roughly right-angles to the crest line. Subsurface mapping of the Quaternary section reveals that the entire structure is a site of net sediment deposition and defines a regional or background pattern of sedimentation that decreases gradually with distance from the shelf-slope break and is not affected by the local surface slope. Because of this pattern, sediment deposition on unchannelized segments of the anticline crest is similar to that immediately up and down dip, even though the surface slope can vary by as much as an order of magnitude. Local surface slope, however, is correlated with patterns of sediment deposition in the channels traversing the ridge. Local erosion is observed at highest surface slopes which are focused at the crest line position, producing knickpoints that are arrested at the ridge apex. Interestingly, channel gradients resulting in focused erosion are of similar magnitude to gradients found on the down slope side of the ridge at approximately 0.1 m/m. The focused erosion along channels demonstrates the importance of lateral confinement of flow in setting erosional and depositional trends. This system illustrates that dissected uplifting topography in the submarine setting is often the result of net depositional processes due to the low excess density of the currents relative to the surrounding ambient fluid and that the driving force for these currents comes from turbulently suspended sediment.