Magnitude and Rate of Environmental Change -Example of Yangtze Delta During the last 20000 Years-

以长江三角洲及其周边地区为例，研究了该地区陆地环境变化的幅度和速率及其对全球环境变化的响应。对长江三角洲西南部太湖及其周边地区的沉积物柱样进行了各种环境分析，为阐明环境变化速率积累了基础资料。年龄测定是基于放射性碳测年和与日本群岛标准曲线相关的古地磁长期变化曲线（Hyodo等人，1993年）。为弄清太湖地区的古环境，通过对太湖地区的孢粉、硅藻、有孔虫、软体动物等化石分析，磁化率、土壤颜色的测定，粒度和化学成分的分析，认为太湖地区的古环境是在1万年前海水侵入的，全新世早、中期，太湖地区又发生了一次海侵。9000年前沉积速率较快，为1.8mm/年，9000年后沉积速率减慢，为1.3mm/年。在5000 ~ 2000年前，湖平面快速下降或快速出现的现象发生了2 ~ 3次，硅藻和有孔虫分析表明，海侵和海退的变化趋势大体一致，但在某些层位上表现出不同的趋势，这可能反映了生物群对环境快速变化的响应时间不同。主要对各岩心的古环境资料进行了核对，但对所分析的岩心结果进行对比还不够。在不久的将来，大量的古环境资料的整理，将使太湖地区的环境演变过程，建立长江三角洲的环境演变模式。

Magnitude and rate of environmental changes in terrestrial areas, and their response to the global environmental changes were investigated in the field of Yangtze Delta and its surroundings. Various kinds of environmental analyses were done for the sediment cores taken from Taihu Lake and the surrounding areas in the southwest part of Yangtze Delta, to accumulate fundamental data which are useful for clarifying the rate of environmental changes. Age determination is based on radiocarbon dating and paleomagnetic secular variation curves correlated with the standard curve of Japanese Islands (Hyodo et al., 1993). In order to make the paleoenvironments clear, fossil analyses such as pollen, diatom, foraminifer, and molluscs, measurement of magnetic susceptibility and soil color, and grain size and chemical analyses were performed.From the results of analyses mentioned above it is concluded that sea water invaded into Taihu Lake area before 10000 years ago, probably in the latest Pleistocene and sea transgression occurred again in Taihu in the early to middle Holocene from Hanzhou Bay. Sedimentation rate before 9000 years ago was rapid, 1.8 mm/year, but after that it was slowed down to 1.3 mm/year. From 5000 to 2000 years ago, quick lowering of lake level or rapid emergence happened two to three times.Diatom and foraminifer analyses showed the same changing trend of marine transgression and regression generally, however in some horizons they showed different trends, which possibly indicate the difference in response time to rapid environmental changes depending on biota.During this research term, paleoenvironmental data of each core were mainly checked, but it is not enough to correlate the results from cores analysed. In near future compiling a great amount of paleoenvironmental data obtained, will make the processes of environmental evolution in Taihu area and establish an evolution model in Yangtze Delta.