Subsidence of the northern South China Sea and formation of the Bashi Strait in the latest Miocene: Paleoceanographic evidences from 9-Myr high resolution benthic foraminiferal δ18O and δ13C records

Abstract

We present astronomically tuned high time resolution (3–4kyr) benthic foraminiferal δ18O and δ13C records between 9Ma and 5Ma from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS). We found that the late Miocene ocean carbon shift (LMOCS) which was linked with the late Miocene/early Pliocene “Biogenic Bloom” also occurred in the northern and southern SCS. A marked deep-water δ13C gradient as much as ~1.0‰ of the northern and southern SCS was observed between 6.5Ma and 5.9Ma, which was probably caused by the significant difference in paleoproductivity between the northern and southern SCS. The deep δ13C gradient was likely produced by rapid tectonic subsidence in the northern SCS at ~6.0Ma and the final formation of the Bashi Strait at ~6.5Ma. A reversed benthic δ13C gradient of the northern and southern SCS was also observed between 1.2Ma and 0.35Ma, which was probably caused by the consecutive closures of the interarc water gates within the Bashi strait at ~3.0Ma and ~1.2Ma. Closures of the interarc water gates within the Bashi strait at ~3.0Ma and ~1.2Ma further semi-enclosed the SCS basin and made the paleoproductivity the major factor influencing the deep water δ13C, leading to the reversed deep water δ13C gradient of the northern and southern SCS between 1.2Ma and 0.35Ma.