Neogene stratigraphic relationships within the Nam Con Son Basin, offshore Vietnam resulting from tectonics, eustasy, and sediment flux



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The South China Sea is a region of significant importance in terms of the records of SE Asian tectonics, including Tibetan Plateau uplift, and the onset and evolution of the East Asian monsoon. The Mekong River has been a dominant sediment source since at least late Miocene time and has headwaters on the eastern Tibetan Plateau. Understanding the Pliocene to Recent stratigraphy of the paleo-Mekong Delta and associated shelf-edge deposits aids in understanding changes in accommodation, sea level, and sediment supply. This record might then be useful in interpreting the longterm history of basin evolution in the Nam Con Son Basin. Nine sequence boundaries and associated sequences are recognized along the late Miocene to latest Pleistocene shelf in the East Nam Con Son Basin. Age constraints were assigned to key stratigraphic horizons by correlating sequence boundaries with published sea level curves. Accommodation in the study area is controlled by shelf -edge compaction, rift-related thermal subsidence, non-rift-related anomalous subsidence,Two primary sources supplied sediment to the southwestern South China Sea during Pliocene to Recent time and likely include the paleo-Mekong Delta and a fluviodeltaic system originating from the Sunda Shelf, such as the Molengraaff River. Changes in thickness, area, and location of Pliocene to Recent shelf-edge delta deposits reflect changes in accommodation and sediment supply over time, as well as progradation of the shelf edge during Pliocene to Recent time and avulsion of the shelf edge delta. Anomalous subsidence of LGM shelf edge deposits is estimated at approximately 40-50 m deeper than expected. The current depth of the LGM deltaic wedge may indicate renewed rapid tectonic subsidence during the last 18,000 yrs, possible compaction effects or a combination of these. eustatic change, and shelf edge faulting.