Study On The Paleolimnological Evolution And Holocene Transgression In The Chenghu Region Of Suzhou, Jiangsu Province, China

This paper takes Suzhou Chenghu as the research object, focusing on the paleo-limnological formation and evolution at Suzhou Chenghu and the Holocene transgression revealed by sedimentary records at the background of the climate and sea level changes at Holocene. Through a comprehensive analysis of the mud hole sediments of lithological depression at SC4, AMS14C dating, magnetic susceptibility, grain size, foraminifera, organic carbon isotope, TOC/N and organic matter, combined with historical documents and integrating the research of other drillings at Chenghu in Suzhou, the following preliminary conclusions were obtained in this paper:1. Since the Holocene, the paleo-limnological sedimentary environment has experienced the evolution of the following three main stages at Chenghu:The first stage:The depositional environment dominated by river (valley) erosion at the early Holocene (ten thousand～7.0kaBP). With the incised and expansion of valley system, the hard clay plains formed at the last glacial period developed numerous terraces and valley landscapes, which suggested that the paleo-limnological formed during this period.The second stage:the middle Holocene (7.0～5.8kaBP) sedimentary environment dominated by accumulation and the average deposition rate increased with about 0.39cm/a. The paleo-limnological and paleo-channel were filled quickly.And the paleo-limnological experienced the evolution of from the exposed surface to marsh-marsh-affected by sea water-disturbance by the river;The third stage:in the late Holocene (5.8kaBP～Present), the sedimentary environment was the erosion and the sedimentary was missing. Later, Chenghu formed and is evoluting, and the hard clay plain and the paleo-limnological were evolved into a part of the lake's bottom and the average deposition rate was low.2.Study on foraminifera confirmed that there is a transgression event occurred at the region during the Holocene. The time of Holocene transgression was in the mid-Holocene (the equivalent of Zhenjiang transgression), basic consisted with previous researches based on the microfossil analysis.The analysis shows that the scale and the scope of the middle Holocene transgression are relatively small and the transgression strata only exists in the east and west of Chenghu valley and the low-lying lake areas. Combined with organic carbon isotope analysis of SC4 and pollen analysis of SC1, mid-Holocene transgression occurred in the Holocene high temperature phase.3. Since the mid-Holocene, the west Chenghu quagmire was low-lying and was not conducive to human existence but a large number of Neolithic settlement sites were found near the paleo-limnological, and this should be related to the surface environment and this not only conducive to hunting and fishing but also to farming. And the Xixu archaeological settlement sites in the branch of Wusong River into the Chenghu-east side of Xixu Pu River with the relatively high-lying lake's beach and the lake's bottom.All of those show that the migration and proliferation of cultural sites can be explained by the Holocene sea-level changes and coastline changes to some extent.