松嫩平原南缘现代沉积物磁化率、粒度、色度特征及古气候环境意义

深入了解松嫩平原第四纪古气候演化过程，对本区黑土退化的气候影响因素研究有重要理论意义。选择松嫩平原南缘大黑山地垒长春—四平段郭家（GJ）、湾沟（WG）、平安屯（PA）、腰分水岭旁（YP）、西地（XD）、胡家甸（H）、肖家（XJ）7个现代沉积剖面进行磁化率、粒度和色度分析。结果显示：各剖面沉积物磁化率多表现为干燥时期较大、湿润时期较小、寒冷阶段较大、温暖适宜阶段较小的特点。颜色对磁化率影响较大，不同颜色砂或砂质黏土的磁化率从大到小依次为红褐色→浅黄色或灰绿色→灰黑色。碳酸盐岩或灰岩物源的存在，使沉积物色度和磁化率之间的关系相对复杂。磁化率会随沉积物粒度增大而增大，冻融风化和降雨增多导致沉积物粒度增大，使磁化率升高；但温暖适宜时期，磁化率受物源供给量的减小而减小。磁化率、粒度和色度三指标综合反映出研究区早更新世寒冷干燥→中更新世冷湿—暖湿—冷湿→晚更新世寒冷较湿润的古气候环境演化过程。

Characteristics of Magnetic Susceptibility,Grain Size and Chromaticity of Modern Sediments in the Southern Margin of Songnen Plain and Their Paleoclimate Environment Significance

A better understanding of the Quaternary paleoclimate process in Songnen plain is of great theoretical significance for the study of the climate-influencing factors on the black soil degradation in this area. Seven sediments sections were collected from Guojia (GJ), Wangou (WG), Pingantun (PA), Yaofenshuiling (YP), Xidi (XD), Hujiadian (H),and Xiaojia (XJ) in the Changchun-Siping segment of Daheishan horst, the south margin of Songnen plain. The magnetic susceptibility, grain size,and chromaticity analyses indicate that the magnetic susceptibility of sediments is mostly characterized by increasing during drying or cold period,and decreasing during wet or warmer period. The color has a great influence on the magnetic susceptibility. The magnetic susceptibility of reddish brown sand or sandy clay is higher than that of light yellow or grayish green sand or sandy clay; while the magnetic susceptibility of light yellow or grayish green sand or sandy clay is higher than that of grayish black sand or sandy clay. The presence of carbonate or limestone in the source area makes the relationship between sediment chromaticity and magnetic susceptibility relatively complex. On the studied profiles, the magnetic susceptibility increases with the increase of grain size. Freeze-thaw or rainy can increase the grain size, and cause high magnetic susceptibility, however, in a warmer period, the magnetic susceptibility is reduced by the decrease of source supply. The three indicators comprehensively reflect that the seven sections experienced a paleoclimate environment process of a cold and dry in Early Pleistocene, cold and wet-warm and wet-cold and dry in Middle Pleistocene, and cool and wet in Late Pleistocene.