| Research Abstract |
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.
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