Abstract: Buried oyster reefs are widely distributed over the coastal areas in the northwest of the Bohai Bay. Within the reef bodies, besides normally built-up sediment layers, there are some horizontal layers, which are mostly composed of debris of oyster shells and muddy materials. Various views exist with regard to the causes of these horizontal layers. One disagreement is concerned with whether or not the oyster hiatus presented in the reef body over the region reflects change in the coast environmental conditions in relation to sea-level, climate and storm characteristics. Some researchers have argued that the deposition rate or mechanical factors such as collapse of the reef body in response to overloading plays a role. In this study, we present the evidence from field investigations for the deposition patterns on the Xiaomiaohong living oyster reef, which is located in the vicinity of a tidal channel on the southern Jiangsu coast, to interpret the possible controlling factors on the formation of the horizontal layers in the Dawuzhuang buried oyster reefs in the Bohai Bay.
The results indicate that the horizontal layers with a spatially limited distribution pattern, as revealed in the vertical section in the Bohai Bay buried reefs, share the same characteristics as the present day patterns on the top of the living oyster reef on the Jiangsu coast. These horizontal layers are not correlated with local climate changes; rather, they might have been formed by localized high energy hydrodynamic conditions during the reef building-up, as is the case for the Xiaomiaohong living reef. However, in the present environment of the Xiaomiaohong living reef, there are no horizontal layers that are continuously distributed over a large area; such layers, however, are present in the Bohai Bay reefs. Further research is required to understand the processes for the formation of this type of horizontal layers. The vertical sequence of buried reefs records the processes during reef building-up, in addition to paleo-environmental changes.