The record of mid-Holocene maximum landward marine transgression in the west coast of Bohai Bay, China

This study used benthic foraminifera, diatom, total organic carbon, organic carbon isotope ratios, C/N ratios, and grain-size data from three AMS14C dated cores collected from the western coastal lowland of Bohai Bay, China, to elucidate the coastal response to relative sea-level change during the Holocene. A layer of peaty clay overlaying early Holocene terrestrial sediment was dated to 8400–8000 cal BP, and the peaty material in the sediment suggests possible vegetation cover before the mid-Holocene marine inundation in the study area. Sedimentary facies and changes in diatom and foraminifera assemblages suggest a five-stage marine transgression–regression history. During the first stage from 8000 to 7855 cal BP, the study area was inundated primarily by freshwater swamp. During the second stage from 7855 to 6000 cal BP the study area was under brackish water influence. In the third stage from c. 6000 to 5750 cal BP, the study area experienced marine influences, and by this time the Holocene transgression reached its maximum landward location and height. This was followed by a period of regression since c. 5750 cal BP. During the last 4000 years, the study area was influenced by freshwater and became a floodplain environment. Thus, this study reveals that the most landward position of the Holocene marine transgression was situated somewhere between the coring locations of DC01 and QX01, which is about 80 km inland from the present shoreline. This means the west coast of the Bay has advanced at an average speed of c. 13 m/a since the mid Holocene. The relative sea level around 6000 cal BP was at − 2.64 ± 0.1 m.