Regional tectonics, differential subsidence, and sediment dispersal patterns: implications for sediment flux to the southern South China Sea and regional filling of sedimentary Basins during Pliocene to the Recent time

Abstract

The Nam Con Son, Malay, and West Natuna basins, located offshore of SE Vietnam and Peninsular Malaysia, initially formed during Eocene(?)-Oligocene rifting, and underwent inversion during Miocene time. Following cessation of tectonic activity at the end of Miocene time, these basins were subjected to spatially and temporally variable tectonic subsidence, which affected regional sediment dispersal patterns and paleogeographic evolution. This study focused on the complex interactions between regional tectonic deformation, differential subsidence across the southern South China Sea (SCS), evolving drainage networks, and sediment dispersal systems, which influenced filling of basins across the southwestern SCS during Pliocene to Recent time. The amount of tectonic subsidence across the Sunda Shelf has varied over long wavelengths (>500 km). The Nam Con Son Basin (NCSB) has experienced more subsidence than the Malay and West Natuna basins during Pliocene to Recent time. Miocene inversion in these basins may be responsible for differential subsidence. These differences in regional subsidence allowed the Malay and West Natuna basins to become overfilled during Pliocene to Recent time, while the NCSB is still underfilled and continues to receive sediments that bypass the Malay and West Natuna basins. Local basement highs such as the Natuna Arch, Khorat Platform, and Con Son High were sediment sources while they were emergent during eustatic lowstands, especially during Paleogene time, when the adjacent basins were underfilled. Major rivers that drained large parts of SE Asia have become progressively more important as sediment suppliers to the southern SCS during Neogene time. The paleo-Mekong River began to rapidly prograde into the NCSB during late Miocene time. A second depositional system added large volumes of sediment to the southern NCSB beginning in Pliocene time, after the Malay and West Natuna basins were effectively filled, and sediments were able to bypass these basins. Paleogeographic reconstructions of Pliocene to Recent time show fluvial and shelf environments progressively shifted eastward across the Sunda Shelf. Sediment transport systems such as fluvial and submarine channels were identified across the entire study area and the spatial and temporal evolution of these channel networks is critical for understanding sediment dispersal across the Sunda Shelf.