Paleochannel distribution, delta development and paleoenvironment evolution in Bohai Bay since the Late Pleistocene

The Bohai Bay and its coastal area are one of the most attractive hotspots for the studies of marine geology and Quaternary geology in China. Although many achievements have been made, some fundamental geological questions still remain unsolved. For example, did the Yellow River flow through Bohai Bay during the Late Pleistocene? How was the multi-stage delta lobes of the Yellow River Delta distribute in the Bohai Bay? Those questions have been attracting great attentions from marine geologists in China. Based upon ~2000 km seismic profile data, two ~30m-length boreholes (BHZK2017-1 and BHZK2017-2) in Bohai Bay during 2016-2017, numerous AMS ¹⁴C and OSL dating results and previous achievements of seismic profiles and boreholes, the stratigraphic sequences was divided into four seismic units (SU1-SU4) and six sedimentary units (DU1-DU6) in descending order, namely prodelta, tidal flat, floodplain, river channel, land-sea interaction facies and lacustrine/marsh facies, respectively. The general stratigraphic framework and sedimentary evolution of Bohai Bay since the Late Pleistocene were accordingly analyzed. It is revealed that the Yellow River likely flowed from near the East-West to the central basin of the Bohai Sea through the northern part of the Bohai Bay during 21.8-9 cal ka BP. Moreover, four subaqueous delta lobes distributed from the northwest to the south of the Bohai Bay since the Holocene were formed during 1400 AD-present, 1048-1128 AD, 700 BC-11 AD and 1855-present, respectively. Two northern subaqueous delta lobes were mainly related to the Haihe River, and the other two southern delta lobes were likely to be the Qikou superlobe and the modern Yellow River Delta superlobe respectively. The studies upon the sedimentary evolutions, paleochannel development and the subaqueous delta distribution since the Late Pleistocene would be conducive to the layout of coastal engineering programs and the mitigation of geological hazards in Bohai Bay.