Abstract: AMS ¹⁴C dating revealed that initiation timing of the four buried oyster reefs, Lingtou, Zengkouhe, Biaokou and Airport Logistic Center, 3~20km apart from each other, was different but the reef building-up at the four sites were almost simultaneously finished by accumulation of the thick muddy sediments at 4.2~4.0ka cal BP or so, which coincided with the ‘4.2ka event’. Furthermore, oxygen isotope study of the endogenic carbonate mud taken from the interior of the articulated oyster shells and the overlying muddy sediments in Zengkouhe and Lingtou profiles and pollen analysis from the same sampling positions were carried out. Both results indicate that the local climate condition tended to be cold and dry during the period of 4.5~4.3ka cal BP and then began to ameliorate in 4.3~4.2ka cal BP. The authors hold that this climate fluctuation was probably a response to the ‘4.2ka event’ in the study area.