Reconstructing Middle-Late Miocene Bottom Water Mass Properties in the Northern South China Sea: Insights from Benthic Foraminifera

    There is a close relationship between the face of benthic foraminifera and water masses. Benthic foraminifera are sensitive to changes in seawater temperature, nutrients, and dissolved oxygen, making them a good material for reconstructing paleoceanographic environments, and thus are frequently used as indicators of the sedimentary environments. An alternation of brownish gray to greenish gray (“red-green”) intervals was observed at IODP Expedition 368 Site U1502 in the northern South China Sea. In this study, we analyzed benthic foraminiferal assemblages in sediments from two sections of Hole U1502A to reconstruct changes in bottom water mass properties in the northern South China Sea during the Middle-Late Miocene.
    Abundant benthic foraminifera were found in both sections, with higher abundance in the Late Miocene section (10R1W) than in the Middle Miocene section (29R5W-30R6W). Among them, a total of 78 genera and 225 species of benthic foraminifera were identified, and both sections were dominated by Epistominella exigua, Nuttallides umbonifera, Globocassidulina subglobosa, Gyroidinoides orbicularis ,and Oridorsalis umbonata，indicating a long-term deep-sea environment.
    Additionally, significant variations in the abundance of Uvigerina peregrina and Bulimina alazanensis were found in the two sections. The abundance of U. peregrina was much higher than that of B. alazanensis in the Middle Miocene section, whereas in the Late Miocene section, the abundance of U. peregrina decreased dramatically while that of B. alazanensis increased significantly. Since B. alazanensis occupied the same niche in the South Pacific deep water as U. peregrina in the North Pacific, this may suggest that the northern South China Sea was influenced by alternating deep water masses originating from the North Pacific to the South Pacific during the Middle-Late Miocene.

    This work is supported by the CAS Strategic Priority Project (XDB XDB26000000) and the National Natural Science Foundation of China (Grants 41776073).