*4.2. The Underground City Form of Kaifeng Since the Warring States*

From the analysis results of the grain size, black carbon, and element cycles, the four cores: JM, SZ, YZ and ML were divided-out into 15, 14, 14 and 16 comprehensive cycles respectively (Figure 10). Combined with chronological data, historical documents and archaeological data, the chronological framework of each sedimentary cycle since the Warring States Period can be established.
