This paper tackles this problem based upon a variety of sedimentological evidence, such as paleomicrofauna, pollen and spores, sediment grain size, sedimentary structure, heavy mineral content and ¹⁴C radio-carbon dates. These data were mainly, in conjunction with nearly 200 subsurface drilling cores available in this area, collected from seven newly drilled cores at Gou-ting, Gaoqiao and Shuanlin etc.