Marine transgression since the MIS3 stage on the northwest coast of Bohai Bay, China

Since Late Pleistocene, there have been three marine transgression in the coastal area of Bohai Bay. Different scholars have explored the marine transgression sedimentary evolution and sea level change in the western and southern coasts of Bohai Bay by analyzing borehole sediment and ancient coastal relics. There is a lack of systematic research on the borehole sediment characteristics of Late Pleistocene Marine transgression in the northwestern coast of Bohai Bay. Based on the study of chronology, sedimentology and microbody paleontology of several boreholes in the northwest coast of Bohai Bay, this paper established the standard stratigraphic sequence, chronological framework and micropalaeontological assemblage zone of 40 meters to light of different tectonic units in the research area. There are two stages of transgression in the study area since MIS3 stage. The transgression age of MIS3 stage was 35210~37658 cal. a BP and that of MIS1 stage was 7050~11310 cal. a BP. Due to the influence of palaeoclimate change, palaeogeomorphology and neotectonic movement, the spatial distribution and lithofacies paleogeographic characteristics of transgressive strata in the two periods are obviously different. The scale of transgression in MIS1 stage is larger than that in MIS3 stage. It was lagoon sedimentary system in MIS1 stage and it was tidal flat-estuarine sand bar sedimentary system in MIS3 stage.