OSL and radiocarbon dating of a core from the Bohai Sea in China and implication for Late Quaternary transgression pattern

The Bohai Sea is a semi-enclosed continental shelf sea in northern China. Three transgression layers have been identified from the Late Quaternary strata in the western Bohai Sea and the coastal regions, which provide critical information on Late Quaternary sea-level fluctuations and landscape development. The three transgression layers were previously assigned to Marine Isotope Stage (MIS) 1 (transgression 1, T1), MIS 3 (T2) and MIS 5 (T3), respectively, mainly based on C-14 dating. However, this chronological framework aroused an enigma that the regional sea level in MIS 3 was even higher than that of MIS 5, conflicting with the context of global sealevel pattern. In order to clarify this issue, here quartz optically stimulated luminescence (OSL) dating (four samples) was used to constrain the T2 chronology of borehole TJC-1 from the western Bohai Sea. Radiocarbon samples (eight) of peaty sediments were also measured for reference and comparison. All the four OSL samples showed saturation ages of >80 ka, suggesting that the T2 layer should have formed at least in MIS 5, instead of in MIS 3. Radiocarbon ages in T2 should have been severely underestimated, with a saturation age range of 22-30 cal ka BP, similar to all the previous published radiocarbon ages. The renewed OSL chronological framework for Late Quaternary transgressions in the western Bohai Sea is in better compliance with the history of global sealevel change.

Automated summary

This study aims to clarify the chronology of Late Quaternary transgression layers in the western Bohai Sea, in order to address the discrepancy between the traditional chronological framework and the global sea-level change pattern. By using quartz optically stimulated luminescence (OSL) and radiocarbon dating, the study shows that the previous assignment of the transgression layer to MIS 3 was severely underestimated, and the actual age should be attributed to MIS 5.