Variation in middle-late Miocene sedimentation rates in the northern South China Sea and its regional geological implications

Abstract A complex suite of geological information from deep-sea drilling cores can provide insights into the Cenozoic evolution of the South China Sea (SCS). Therefore, the thick sediment sequence, obtained during International Ocean Discovery Program (IODP) Expedition 368 at Site U1501 in the northern SCS, provides excellent materials to investigate the paleoceanographic and geological evolution. The generally well-preserved calcareous nannofossil assemblages allowed us to establish a high-resolution biostratigraphic framework, and revealed dramatic fluctuations in sedimentation rates during the middle Miocene through earliest Pliocene (ca. 15–5 Ma). The sedimentation rate was high during the middle Miocene, decreased dramatically before the middle/late Miocene boundary and essentially ceased afterwards, with resumption of deposition close to the late Miocene/Pliocene boundary. Sediment source analysis with diffuse reflectance spectra shows that biogenic carbonate accounts for approximately half of the bulk sediments and that the dilution effect by terrigenous sediments partially controlled the carbonate content, whereas the high sedimentation rates were fueled by both sources during the middle Miocene. The apparent 1.5-Myr-long hiatus (10.5–9 Ma) corresponds to the globally distributed “carbonate crash”, which was truncated in this region by the regionally important Dongsha Movement. The accompanying decrease in carbonate content and terrigenous materials may indicate decreased biogenic carbonate export to deep waters during the carbonate crash, possibly resulting from the progressive constriction of the Indonesian Seaway. The restricted distribution of Discoaster hamatus at this site suggests that the Dongsha Movement commenced at 9.5 Ma, younger than previously proposed.