Geochronological features of the buried ancient sand ridge in Yangkou port, Jiangshu, and their paleoenvironmental significance

During the last glaciation(MIS Ⅱ stage), the Yangkou port area in Rudong County, Jiangsu Province was developed with the Upper Most Hard Clay. This area, since the early Hologence, had been subjected to erosion, with tidal channels developed locally in this area. Since the middle Holocene, the study area was dominated by tidal-and-flat deposits under the effect of the maximum transgression(around 7 000 a B.P.). At the high sea level period(5 220 a B.P.), most of the study area was submerged in the sea. With the sea level falling, north of the Yangkou port developed a series of ancient radial sand ridges, which belongs to a sedimentary system of coastal tidal flat-tidal sand ridges. Based on the sedimentary features, four-period buried tidal sand ridges have been recognized. Stratigraphic AMS ¹⁴C ages indicate that these ancient tidal sand ridges formed separately from 5 200 a B.P. to 1 000 a B.P., reflecting the active evolution process of the ancient tidal sand ridges under the effect of tidal dynamics.