Depositional architecture and evolution of basin-floor fan systems since the Late Miocene in the Northwest Sub-Basin, South China Sea

Abstract

The sediment budget of the Northwest Sub-basin, South China Sea since the Late Miocene (11.6 Ma, average thickness > 1000 m) accounts for more than two-thirds of the total infill since the initial ocean spreading of the sub-basin (32 Ma). The sediment sources and architectural pattern of these deposits, however, are poorly known. Using high-resolution 2D reflection seismic data with age constraint from IODP boreholes, we have documented two interdigitating basin-floor fan systems that developed since the Late Miocene. These were fed by two of the largest deep-water canyon systems worldwide, from the west (the Central Canyon/Xisha Trough) and the northeast (the Pearl River Canyon), as well as from smaller headless canyons and gullies across the surrounding slopes. Based on careful analysis of seismic facies, their geometry and occurrence, we identify the principal deep-water architectural elements, including the multi-scale channels, channel-levee complexes, lobes, sheets and drapes, mass-transport deposits, volcanic intrusions, turbidity-current sediment-wave fields, and a contourite drift/terrace.