Study On Prehistoric Flood Events As Indicated By Sedimentary Records From Chenghu Lake (Suzhou)

According to the analysis of grain size, magnetic parameters, active iron, organic matter, foraminifera and other palaeoenvironmental indicators of SC5 core from the ancient lake bottom of Chenghu in Suzhou, combining AMS 14C dating of SC4 nearby, this paper tries to discover some features of Taihu plain's sedimentary environment during early and middle Holocene. Preliminary conclusions are follows:First, SC5 core is where the ancient lake depression formed late last glacial eolian deposits (hard clay) as substrate, recorded in the middle Holocene (about 7000aBP～6000aBP) of the sedimentary history.6800aBP～6300aBP for the Holocene megathermal maximum period to development of peat deposits is dominantly; before and after the deposition are the main freshwater lakes, which in general is a freshwater lake plain environment.Second,3.50～0m is the middle Holocene deposits, formed in 7000aBP 6000aBP (14C, uncorrected). Holocene transgression in the area is confined to the paleo-channel SC1 core area. SC5 core's mid-Holocene sedimentary environment through Freshwater lake-Swamp-Lake evolution can be divided into:7000～6400aBP, the lake accumulation, with the lake sediment, lake water level shallow; 6400aBP about the formation of lake sediment environment; 6400～6200aBP, the formation of 50cm thick accumulation of peat, for the shallow water marsh environment; Basin Flood occurred in about 6200aBP.From 6200aBP to 6000aBP, a shallow lake formed.Third, after the Holocene megathermal maximum period.(about 6200aBP), there may be a high incidence of floods, sediment thickness of 10cm. Sediments thicken significantly, a number of magnetic parameters (χ, SIRM,χarm, HIRM,χarm/χ, SIRM/χ) abnormal high mark the formation of fresh water lake of Taihu Lake plain.