Study on the buried oyster reefs and environmental changes with the underlying muddy sediments on the Northwest Coast of Bohai Bay

The Electric Conductivity of Stirred Clayey sediments into Water (EC), pH values and micropalaeontological studies of the underlying muddy sediments of the buried oyster reefs in Dawuzhuang and Airport sites, northwest coastal plain of Bohai Bay revealed a difference of the depositional environments of the underlying mud units in two sites. In Dawuzhuang, from the underlying to the overlying muds, environment changed from subtidal to the lower intertidal zone, which presented a falling tendency of relative sea level. However, the underlying mud in Airport site occurred in the intertidal and changed upwards to the reef body as being lagoonal environment. These indicate that the relative sea level fall resulted in intertidal environment in Dawuzhuang and a change from the open intertidal to relatively isolated intertidal lagoon environment in Airport site as a diatom thriving as well during the mid-Holocene all form the important reasons for the oyster reef development.