Tidally-influenced fluvial channel systems from the Miocene Malay Basin, Malaysia: Evidence from core facies and seismic geomorphological analyses

Abstract

The interpretation of tidal influence in a depositional system or stratigraphic interval buried deep in the subsurface is mainly based on sedimentary structures, fossils and trace fossils preserved in conventional cores. Studies of modern tidal depositional settings have shown that certain geomorphological features can be used as reliable tidal indicators. In this study we present evidence of tidal influence associated with Miocene channels in the Malay Basin, based on an integrated analysis of sedimentary facies from cores, well logs and high-quality 3D seismic data. Six facies associations identified in cores were interpreted as inter-distributary bay/offshore, tidal flat, subaqueous delta platform/prodelta, tide-influenced channel/bar, mouth bar, and mangrove/overbank deposits. Evidence for tidal influence include rhythmites, thick heterolithic successions, mud drapes, abundant bidirectional current indicators and the presence of an impoverished marine trace fossil assemblage. Channels identified in 3D seismic show unique geomorphological features indicative of tidal influence in the depositional system, such as flaring channel mouths, cuspate meanders, high-sinuosity, as well as dendritic and parallel channel networks comprising several orders of dead-end and through-flowing tributary channels. Identification of tidal geomorphological features in 3D seismic may help in predicting channel fill lithology in the subsurface, and in better planning of hydrocarbon exploration and development in basins with paralic channel-bearing reservoirs.