Identification and OSL ages of the Second Marine Bed in Bore-hole QX02 along the western coast of Bohai Bay

Alternation of marine and terrestrial sediments from Core QX02 along the western coast of Bohai Bay was recognized using lithological characteristics and quantity of benthic foraminifera analysis. Timing of the second marine bed, 11.4m thick, corresponding to a relative sea level of -26.83~-15.43m, was determined by both AMS ¹⁴C and OSL dating methods. The AMS ¹⁴C dates demonstrated that the second marine bed was deposited during the early Marine Isotope Stage 3 and even earlier. D_e distribution of typical sediments from the second marine bed was over-dispersed, and two distinct populations could be observed, which yielded a young age range of 51.9~39.9ka, and an old age range of 83.5~62.6ka, respectively. According to the principle of OSL dating, the old fraction obtained from D_e distribution was limited by the poorly bleaching and, in turn, the fraction of relative young ages was commonly adopted. However, it is plausible to have a clue from the cluster of the older ages that there would be an original sedimentary process and a corresponding timing of marine transgression.