A STUDY OF DEPOSITIONAL RATE IN THE NORTH CHINA PLAIN DURING THE PAST 40000 YEARS, BASED ON 14 C DATING DATA FROM A LARGE WEALTH OF SAMPLES
基于大样本14 C测年资料的 华北平原沉积速率研究*

The North China Plain is an area where much research in Quaternary geology has been done and a large number of 14C dating data is available from published materials. Extracting information of plain sediment depositional rate from these data and then studying the temporal variation of depositional rate in relation with varying natural conditions and human activities is an issue of great importance. Using 14C dating data from 456 locations in the North China Plain, average depositional rate (RT) for the period from the year when the sample was deposited to present has been calculated, and the temporal variation in RT are plotted. The resulting curve shows an increasing trend in the past 40000 years. The upper envelop line of the scattering points is used to reflect the maximum values of RT, which is referred to as RT,max. This index reflects the deposition of the lower Yellow River Plain, the main body of the North China Plain. The fitted upper envelop line indicates 4 breaks, occurring in the time of 10000aB.P., 5000aB.P., 3000aB.P., and 1400aB.P., respectively. The 4 breaks divide the fitted line into 5 straight-line segments, representing 5 stages of plain sediment accumulation in the past 40000 years. The slope of the 4 segments increases, reflecting the accelerating process in the plain deposition. An explanation has been given to the formative cause of the 4 breaks. Stages 1, 2, and 3 occurred due to natural environmental changes, and stages 4 and 5 was due to the joint influence of both natural and human factors. Information has been extracted from 456 samples for estimating the average depositional rate of the whole North China Plain during a period of 40000 years, which has been calculated as 0.9mm/a, and thus, the total sediment thickness in the past 40000 years has been estimated as 36m in the plain.