杭州湾地区末次冰盛期第一硬质黏土层粒度特征及其环境意义

对于沉积物粒度分布特征的研究是衡量沉积介质能量,判别沉积地理环境和水动力条件的最基本方法之一。对杭州湾地区河姆渡钻孔的末次冰盛期第一硬质黏土层样品进行系统的粒度分析,并与典型黄土、古土壤、下蜀土及河流相、湖相样品进行对比后发现,该层位样品所显示的粒度分布特征与湖相沉积物极为相似,而与下蜀土及河流相沉积物有所差别。从粒度分布的角度推断,该区第一硬质黏土层的沉积环境为河湖相。

GRAIN-SIZE CHARACTERISTICS OF THE FIRST HARD CLAY AND THEIR ENVIRONMENTAL IMPLICATIONS DURING THE LAST GLACIAL MAXIMUM IN THE HANGZHOU BAY REGION

Several layers of dark green-yellowish brown hard clay in the Yangtze delta can be used as mark layers in the stratigraphy correlation due to their typical characteristics and widespread distribution.Among them,the first hard clay is considered as the boundary between Pleistocene and Holocene,and also the bearing course in engineering geology.The deposition of the FHC(first hard clay) has long been the focus of argument of whether aeolian or aqueous,fluvial or lacustrine. Grain size is the most fundamental physical property of sediment,and grain-size analysis draws statistical indexes and geological information from miscellaneous data of those individual samples.Through systematical analysis of the FHC samples of Hemudu core in the Hangzhou Bay region and comparisons of grain-size distributions of Xiashu Loess,typical loess and paleosol from Mangshan and Duanjiapo profiles,and from fluvial and lacustrine facies samples,it is found that the grain-size characteristics of the FHC samples are very close to those of the lacustrine samples,while the Xiashu Loess and typical paleosol show similarity to some extent.The FHC deposition in Hemudu core in the Hangzhou Bay region occurred in fluvial-lacustrine facies with its parent material coming from fluvial flood-plain during the Last Glacial Maximum.