Abstract:

By analyzing the characteristics of major element oxides and their ratios in the sediment of the Shagou section in the Gonghe Basin， combined with the photoluminescence dating， we studied the environmental evolution of the early Late Pleistocene in Gonghe Basin. The results show that： （1） From the bottom to the top of the section， the SiO₂ content and Na/K ratio generally show the characteristic of "one valley and two peaks"， with an overall increasing trend. The high values all appear in the fine sand layer， indicating a cold and dry climate. The low values appear in the silt layer， indicating a warm and humid climate. （2） From the bottom to the top of the section， the CaO， MgO contents， and CIA ratio generally show a change characteristic of "one peak and two valleys"， with an overall decreasing trend. The high values all appear in the silt layer， indicating a warm and humid climate. The low values appear in the fine sand layer， indicating a cold and dry climate. （3） The climate of the Gonghe Basin has three obvious cool/dry-warm/humid fluctuations between 90-70 ka. Those fluctuations are divided into three stages. MIS 5b （91.5-89.4 ka） stage is the low water level period of the ancient Gonghe Lake that the climate develops from warm to cool-dry； MIS 5a （89.4-80.1 ka） stage is the high water level period of lakes with warm and humid climate； and MIS 4 （80.1-70.1 ka） stage is the shrinking period of lakes with cold and dry lakes.

Key words: Gonghe Basin, major element oxides, lacustrine sediment, environmental evolution