Depositional history and origin of porosity in a Miocene carbonate platform of Central Luconia, offshore Sarawak

Abstract

Recently acquired 3-D seismic reflection data, wireline logs and selected core samples were used to reconstruct the growth history of the platform as well as the sequence of diagenetic events and origin of porosity. Platform growth started by coalescence of isolated patch reefs. Growth history includes phase of progradation, backstepping and collapse of the platform flanks. The most pronounced seismic reflectors in the platform correspond to flooding events (transgressive systems tracts), occasionally preceded by lowstands. Platform growth was terminated by gradual submergence (drowning) indicated by smooth, concentric seismic reflections forming a convex mound. Syndepositionallow-offset normal faults controlled the geometry of the platform and triggered large landslides that can be seismically traced about 5,000 ft (1.5 km) in the basin. Three different processes have significantly contributed to porosity in the carbonate rocks: selective leaching during exposure, dolomitization and leaching during deep burial, probably related to warm fluids rising from depth. Quantitatively, the last group is the most important. As most of the carbonate porosity formed by carbonate dissolution under deep burial, the slide masses and related turbidites may contain highly porous rocks in the basins between platforms. These bodies can be separated by the platforms where their upslope ends are enveloped in clay-rich hemipelagic sediment. In other places, the porous slides and turbidites may establish connections between neighbouring platforms.