Sedimentary environment changes of the Ningshao Plain since the later stage of the Late Pleistocene: Evidence from palynology and stable organic carbon isotopes

Abstract

A 45.3-m long core was collected from near the Hemudu civilization site (Luojiang county, Zhejiang Province; 29°59.064′N, 121°21.754′E), which is located in the Ningshao plain on the southern margin of Hangzhou Bay. The core, named the HMD Core, was divided into seven lithological layers with clay and silt as the main lithological components. The sporopollen assemblages of this core combined with TOC/TN and stable organic carbon isotope (δ13CTOC) analysis revealed the sedimentary environmental changes since the later part of the Late Pleistocene in the Ningshao plain. The study area changed from terrestrial fluvial-flood plain facies before Marine Isotope Stage (MIS) 3 to shore plain during transgression in MIS3, and became a freshwater lake during regression at the time of the Last Glacial Maximum (LGM). The area started to become a semi-salt lake influenced by sea water during 15,900–5000 cal. BP, in which time period the lake was deeper and the climate became gradually warmer. Later the seawater withdrew, the lake began desalinating, and then became swampy and accumulated peat until 1000 cal. BP. After that, the area became dry land. The results also indicate that the sediments of the core are of endogenous organic origin and the δ13CTOC value was controlled by change in the concentration of atmospheric CO2, and thus was a response to global changes.