Study On The Sedimentary Records Of Late Quaternary Transgression In The Chenghu Lake Region Of Suzhou, Jiangsu Province, China

There is a wide and deep valley in the bottom of Chenghu Lake, it may be a part of channel of Taihu basin to the sea. Sediments in the paleo-channel of Chenghu Lake may become good archives of environmental evolution since the Late Quaternary. In 2006, we drilled a 14 meters long core named SC1 ( 31°14′42.9″N, 120°49′12.1″E ). Based on the analyses of AMS¹⁴C, grain size, magnetic susceptibility, sporo-pollen, foraminifera and lithology of SC1 core from Chenghu Lake, with the help of the history of literature, this paper discusses evolutions of climate, sea-level and sedimentary environment since the Late Quaternary. Through these analyzing and researching some conclusions were reached and acquired:First, Twice transgressive cases since the Late Quaternary. There are two marine invasion events in the Chenghu Lake area since the Late Quaternary. One is Gehu transgression during the Late Pleistocene and the other is Zhenjiang transgression in the Mid-Holocene, periods of these two marine invasion events coincide with the previous research results. Gehu transgression is much stronger than Zhenjiang transgression. The Holocene marine invasion layer is only situated in the east of Chenghu Lake and the western low-lying areas. The two marine invasion events are all occurred during the warm-wet or hot-wet period, sea-level changes controlled by paleoclimate affected the sedimentary environment of the Yangtze River delta since the Late Quaternary.Second, The study also revealed a series of salt water intrusions after Zhenjiang transgression in the Mid-Holocene. There are more than a dozen times salt water intrusions after the Mid-Holocene. So it is proved that there are many small-scale transgression in this area except large-scale transgression of the Mid-Holocene.Third, Evolution of sedimentary environment since the Late Quaternary. During the Late Pleistocene, they indicate a thick layer of coarser grained fluvial deposits. During the last ice age, fluvial-lake sediments are prevailed. In the Early Holocene, they indicate a layer of small silt and clay-silt of fluvial deposits, partly shallow coastal deposits. During the Mid-Holocene, they indicate a layer of coastal and shallow deposits. Since the Late Holocene this area has not been affected by the seawater, it indicates a lake-to-sea channel, the upper layer shows a layer of lake and marsh deposits in the coastal plain.Fourth, Holocene transgression and human activities. Since the Mid-Holocene, there is a low-lying land in the west of Xixupu estuary, settlement sites are all located on the east side of the ancient channel. The pervasion and migration of cultural sites are controlled by the sea level and coastline of the Holocene.