Abstract:

Laohetou profile is located in the west of Baiyangdian depression. A 610 centimeter-deep sediment profile was studied in this paper. The AMS ¹⁴C measured data revealed that the sediment profile deposited since 25.5 cal ka BP. Combined with chronological data, grain size characteristics, susceptibility and sedimentary characteristics, the evolutionary process and environment features during the past 25.5cal ka BP were reconstructed. Results showed that there were seven stages as following. 25.5-20.9 cal ka BP(610-515 cm) is a fluvial facies and wind accumulation period; in 20.9-10.7 cal ka BP (515-388 cm), fluvial action is weakened, and wind accumulation may be strengthened; in 10.7-8.6 cal ka BP (388-335 cm), precipitation increases and  water accumulates, lakes expanding during this stage; 8.6-7.2 cal ka BP (335-299 cm) is a wind accumulation period; 7.2-3.2 cal ka BP(299-200 cm) is a lacustrine facies period; 3.2-1.3 cal ka BP(200-110 cm)is a fluvial facies period; from 1.3 cal ka BP to now(110-0 cm)，the precipitation decreases, but fluvial function is still obvious.

Key words: grain size characteristic, magnetic susceptibility, environmental evolution, Baiyangdian, Hebei Province