Holocene oyster reefs: spatial and temporal distribution and sea level indicators in Bohai Bay

Based on studies of the Holocene buried and living oyster reefs on the Oyster Reef Plain and its adjacent shallow sea area of northwest Bohai Bay, this paper has reexamined the sedimentary significance and chronology of the data related to the oyeter reefs, and further collated the formation period as well as top and bottom altitudes of each reef group. The newly discovered oldest (the late Early Holocene) reef group, i.e., Group Pre-Ⅰ-1, was added to the originally determined nine reef-groups. Also, newly discovered reefs at the Binhai Lake and the airport area are tentatively assigned to the Reef Ⅴ as its subgrouop Ⅴ-1. Leveling for top altitude fluctuations in Dawuzhuang and other two reef sites indicates that the maximum fluctuation of the reef-top is ±0.7m, which is used as the vertical error range. The investigation of the altitude of LISL (the last irregular sandy/silty lamina) above the reef-top in five reef sites, including Beihuaidian reef, reveals that the average thickness between the reef top and the LISL is approximately 1.6m, which is the maximum vertically accreting thickness given by the local accommodation space between the MSL and MHW. It serves as evidence verifying a conclusion that the reef top corresponds to the msl. Thus, the reef top used as the sea level indicator is defined, i.e., the vertical range by adding ±0.7m to the reef top corresponds to the MSL.