Calculation of the sediment budget in the South China Sea abyssal basin lacks constraints from drilling data and reinterpretation of seismic data. On the basis of six multichannel seismic profiles across the Southwest Sub-basin (SWSB) and the drilling data from International Ocean Discovery Program Expedition 349, we divided the Cenozoic sediments into four sedimentary units. The sedimentary budget of the abyssal basin at different geological times was calculated. The previous works in the Mekong continental shelf and slope areas were integrated to calculate the sediment budget of the whole SWSB. Our researches show that the sediment budget in the SWSB increased during the Palaeogene and reached its first peak because of intensified erosion, which might have resulted from the continued uplift of the Tibetan Plateau and accelerated southeastward extrusion of the Indo-China Peninsula. Since the Late Miocene, the sediment budget was mainly influenced by the East Asia monsoon, that is, the intensified winter monsoon decreased the sediment budget of the entire area during the Late Miocene, whereas the strengthened summer monsoon increased the sediment budget during the Pliocene and reached a peak during the Pleistocene. The sediment budgets of the Mekong continental shelf, the Mekong continental slope, and the abyssal basin have distinct characteristics, relating to the infilling sequence of the terrestrial sediments in different regions. The sediment provenance of the SWSB was mainly from the Indo-China Peninsula, the Nansha area, and the Palawan before the Late Miocene. After that time, sediments were mainly transported from the modern Mekong River.

We calculated the sedimentary budget of the Northwest Sub-basin (NWSB), South China Sea for different geological times based on interpretations of four multichannel seismic profiles across the basin with constraints from International Ocean Discovery Program (IODP) Expeditions 367 and 368 drilling results. Sedimentation was generally dominated by regional tectonic events and climate change, but complicated by local tectonic events and geographic position, which resulted in a specific sedimentary budget in the NWSB compared with other marginal basins and the Southwest Sub-basin. The sedimentation rate was relatively low following the opening of the NWSB but increased gradually during the Middle Miocene, corresponding to the uplift of the Tibetan Plateau and the Asian monsoon. It reached its peak in the Late Miocene, corresponding to uplift of the Dongsha Island region that caused intensive bypass of eroded sediments from the Baiyun Sag into the abyssal basin, and reduced again during the Pliocene because of sediment storage on the wide northern continental shelf area compared to the abyssal basin during a period of high-stand sea level. Increase in sedimentation during the Pleistocene suggests that continental erosion and sediment transport to the abyssal basin were enhanced by an intensified Asian summer monsoon and glacial-interglacial climate fluctuations. Since the opening of the NWSB, the primary sediment provenance has been from southern China, with minor contributions from the Red River, Hainan Island, as well as local uplifts on the continental shelf.