Chronologies of sedimentary changes in the south Bohai Sea, China: constraints from luminescence and radiocarbon dating

The alternation of terrestrial and marine deposits is an indicator of past environmental and sea-level changes. The age of deposition is usually dated by means of radiocarbon. However, radiocarbon dates of molluscan shells from coastal areas may be complicated by various sources of carbon, and problematic for deposits of 40–50 ka or older. Herein, we apply the Optically Stimulated Luminescence (OSL) dating method to date samples from terrestrial and marine/coastal sediments extracted from three cores in the south Bohai Sea, China. Multiple- and single-aliquot regenerative-dose procedures using OSL signals from fine-silt (4–11 μm), coarse-silt (38–63 μm) and fine-sand (63–90 or 90–125 μm) quartz were employed to determine the equivalent dose (D e). The results showed that: (i) OSL ages from quartz of different grain sizes and different protocols are consistent with each other; (ii) for Holocene samples, most of the radiocarbon dates agree well with OSL ages; (iii) for pre-Holocene samples, radiocarbon dates cluster at 40–50 14 C ka BP, whereas OSL ages are in stratigraphic order from 11 ka to 176 ka. Because of the self-consistency of the quartz OSL ages, the stratigraphic agreement in the three cores, and the clustering of the radiocarbon dates, we suggest that the quartz OSL ages are more reliable with respect to dating the samples from the south Bohai Sea. Finally, the four marine strata identified in the south Bohai Sea are likely to have formed during the Holocene, Marine Isotopic Stage (MIS) 3–5, MIS 6 and probably MIS 7, respectively.