Stratigraphy and sedimentary environments during the Late Quaternary, in the Eastern Bohai Sea (North China Platform)

Abstract

The Bohai Sea is a shallow sea at the east coast of China. It communicates with the Yellow Sea through a narrow strait. During and since the Late Pleistocene, the Bohai Sea has been a filled subsiding basin submitted to successive regressive-transgressive cycles. In the East Bohai Sea, a number of finger-shaped ridges are present near the strait, where tidal currents are dominant. Very-high resolution seismic reflection data have been interpreted relative to sedimentological data provided by a formerly drilled borehole.Seven seismic units are identified and correlated with the following events: units U7-U6 with the Bohai relative sea level rise (65,000–53,000 yr B.P.) and a relative sea level fall (53,000–39,000 yr B.P.); unit U5 with the Xianxian relative sea level rise (39,000–22,000 yr B.P.); unit U4 with the period of the late Würm glaciation (22,000–15,000 yr B.P.); units U3-U2 with the transitional period from the end of the Pleistocene to the beginning of the Holocene (15,000–9000 yr B.P.); and unit U1 with the Holocene (Huanghua) marine intrusion in the Bohai Sea (since 9000 yr B.P.).In the Bohai Sea, formation of the tidal ridges is probably due to a substantial increase in tidal-current velocities during the late Holocene rise of sea level. Constriction due to the strait amplifies the tidal process, so that the sediments of the late Holocene transgressive sequence have been remodeled as tidal ridge.