Abstract:

The Qinghai Lake is the largest inland lake in China, and is sensitive to climate change. As an important type of shallow lake sediments, the distribution of beach bars reflects the paleoclimatic evolution of the Qinghai Lake. The southern part of the Qinghai Lake develops a large number of beach bars, which represents an ideal place for studying the beach bar distribution in the lake. Based on field cross-section (trenches and deep pits) investigation around Yilangjian, the beach bar distribution and sedimentary characteristics there were described in detail, and are compared with the reconstructed lake level change curve. It is found that the reconstructed lake-level change curve of the Qinghai Lake has significant control over the beach bar distribution, and the evolution of Qinghai Lake beach bar with the lake-level rise and fall since 18 ka is reconstructed, which comprises four stages: (1)During the warm and humid end Pleistocene, the lake level fluctuated between 3,197-3,202 m; (2) In the cold and dry period of the Holocene, the Qinghai Lake was almost dry; (3) In the warmest period of the Holocene, the lake-level was at its highest since the beginning of the Holocene; (4) During the cool and humid period of the Holocene, the lake level fell back to 3,200 m and accelerated down in the 2.5 ka. During the Late Pleistocene and Late Holocene, the lake level fluctuated for a long time around the altitude of 3,202 m. In this altitude range, a large-scale compound beach bar was formed. In the Early Holocene, the Qinghai Lake was at its lowest level and more loess and lagoon were developed. In the Middle Holocene, the lake level was at its highest, forming a series of monolithic beach bars furthest from the current lake level.

Key words: Qinghai Lake, lake level, beach bar, paleoclimate