Holocene environmental evolution in the Qinghai Lake area recorded by aeolian deposits

摘要

Aeolian deposits, widely distributed in the Qinghai Lake area, provide independently palaeoclimatic information. Herein we report the detailed investigation results of Gangcha (GC) and Reshui (RS) sections, located at the northern Qinghai Lake area. The chemical index of alteration (CIA) and Al2O3-(CaO*+Na2O)-K2O (A-CN-K) ternary diagram suggest that most of the sediments experienced the degree of weak and moderate chemical weathering. The study area had undergone the great alternation between wet and dry climate, reflected by the variation of CIA values. The accumulation hiatus in the palaeosol layer was identified in the RS section. Our comprehensive results indicate that the relatively dry climate conditions and strong aeolian activity occurred from 11.0 to 7.5 ka in the Qinghai Lake area, in agreement with widespread aeolian sand deposits and loess deposits in the investigated aeolian sections. The middle Holocene (from 7.5 to 3.0 ka) was characterized by humid climate conditions and weak aeolian activity, supported by commonly developed palaeosol deposits in the Qinghai Lake area. After 3.0 ka, the aeolian activity was again strengthened due to drier climate conditions. The variations of summer insolation and the Asian monsoon may cause the increase or decrease of effective moisture, thereby result in the climate changes between dry and wet in the Qinghai Lake area.