Sedimentation rate and geochemical characters of the lagoonal deposits in the Yongle Atoll, Xisha Islands

A gravity core, labeled as Core YLD01, was collected from the lagoon of the Yongle Atoll. AMS¹⁴C isotopic dating and geochemical analysis were carried out aiming to reveal the changes in sedimentation rate during Holocene as well as the vertical variation in major chemical elements with time. The AMS¹⁴C isotope dating suggests that the sedimentation rate in the lagoon of Yongle Atoll is about 0.778mm/a since the Holocene. Geochemical composition of the sediments indicated that CaO dominates the lagoonal deposits followed by MgO, and the others are all lower than 1 %. The major elements can be grouped into five categories. Both the CaCO₃ content and the ratio of MgO/Al₂O₃ are very high, indicating that the major source of sediments is from native organisms. Other source of materials from outside is very little. Compared the data with Late Holocene climatic change, the sedimentation rate of the lagoonal deposits was obviously increased with the rise of SST on the Yongle Atoll.