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

研究了长江三角洲及其周边地区陆域环境变化的幅度、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周边地区的沉积物岩芯进行了各种环境分析，积累了有助于阐明环境变化速率的基础数据。年龄的确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)。为了弄清太湖的古环境，对其进行了孢粉、硅藻、有孔虫、软体动物等化石分析、磁化率测定、土壤颜色测定、粒度分析和化学分析。根据以上分析结果，认为10000年前海水入侵太湖地区，可能是在晚更新世，从汉州湾开始的全新世早、中期太湖再次发生海侵。9000年前沉积速率较快，为1.8 mm/年，之后逐渐减慢至1.3 mm/年。5000~2000年前，湖泊水位快速下降或迅速浮现2~3次。硅藻和有孔虫分析总体上表现出相同的海侵和海退变化趋势，但在某些层位表现出不同的趋势，这可能表明不同生物对环境快速变化的响应时间不同。在本研究期间，主要检查了每个岩心的古环境数据，但不足以与分析岩心的结果进行对比。在不久的将来，整理大量的古环境资料，将有助于揭示太湖地区的环境演化过程，建立长江三角洲的环境演化模式。

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.