Paleoenvironmental implication of magnetic measurements on sediment cores from Taihu Lake, east China

Abstract

本文以太湖沉积物为研究对象,试图在磁性测量的基础上,对太湖湖区四个样芯进行分层,建立样芯间层位对应联系,并结合孢粉、粒度、地球化学和有机质含量等分析测定,从沉积物样芯的磁参数曲线变化中提取该地区的环境变化信息。研究结果表明,由于该方法具有快速简便、经济易行、无破坏等优点,从而可能对样芯作连续测量,以提取高分辨率的环境变化信息。在湖泊沉积物的研究中有着独到的作用,可作为地球化学、孢粉、微体古生物、粒度等分析测试的辅助手段和先导。;Taihu Lake is a large shallow lake on the southern deltaic plain of the Yangtze River An irLerdiscipline study is carried out on about two-meter-long sediment cores taken from this lake to retrieve high resolution information on Holocene environmental change in Taihu Lake region. Mineral magnetic measurement, as the precursor, has been made on three cores from vvest Taihu Lake and one core from east Taihu Lake, which is used for sediment stratigraphy, bulk lithological classification and core-core correlation. These results are set alongside those derived from geochemical, pollen and granulometric analysis to reconstruct the environmental seccesses recorded in the radiocarbon dated sediment column. For cores TM2, TM3 and Wl-6 from west Taihu Lake, three distinctive stratigraphic horizons have been identified on the basis of the magnetic measurements and they are correlated among the cores. These divisions are coincident with the variation of pollen assemblages, indicating different climatic periods In the Yangtze River Delta. It is suggested that the low part of these cores is the early Holocene sediments, when the climate became wanmar sea level rose and Taihu Lake appeared as several small separated lakes. There is no stable continued deposit at west Taihu since the large lake formed in mid-Holocene as the result of current erosion. At east Taihu, the sediment column recorded some detailed information on palaeoenvironmental changes, as it is a relatively small and closed bay. The study shows that rof magnetic parameters in core EU 1 are mainly resulted from changes in particle size constitution, implying the shifts of sedimentary environment in response to the climatic changes.