RECORD OF SEA-LEVEL CHANGES ON A STRUCTURALLY ACTIVE MARGIN, OFFSHORE BRUNEI, NW BORNEO: IMPLICATIONS FOR RESERVOIR AND SEAL DISTRIBUTION AND STRATIGRAPHIC TRAP FORMATION

The NW Borneo margin, offshore Brunei Darussalam, is characterised by high subsidence-rates (overall 1 km/MA over the last 14 MA; up to 6 km/MA locally) combined with large-scale, and rapid, syndepositional deformation driven by delta-loading and regional tectonics. Deformation includes extensional (regional and counter-regional), contractional, and strike-slip structures. Effects of eustatically driven variations in the Cainozoic sea levels, which are readily recognised in the stratigraphic records of many passive margins, including the neighbouring Sarawak-basin segment of the NW Borneo margin, have been subdued, or overwritten, by the subsidence signal on the Brunei margin. High rates of background subsidence have imposed limits on the duration of SL lowstands, while inversely amplifying the effects of eustacy-driven SL rises. This study is chiefly concerned with periods of eustatic SL lowstands, and with the imprint of subsidence-variations in space and time on the eustatic SL signal.