Palaeoclimate and palaeoenvironmental evolution during the late Pliocene (3.04-2.88 Ma) based on pollen records from the Yinchuan Basin, Northwest China

摘要

The late Pliocene is considered the key period of transition to the Quaternary glaciations. In this paper, we present pollen records from the PL02 borehole of the Yinchuan Basin, which is located in Northwest China and has a favourable sedimentary environment for the 3.04-2.88 Ma period, to explore changes in palaeovegetation and palaeoclimate. The results showed that the vegetation in the basin was dominated by typical steppe from 3.04 to 3.01 Ma, indicating that the climate was warm and humid; from 3.01 to 2.93 Ma, the vegetation was dominated by desert steppe, and the climate gradually became drier; after 2.97 Ma, the degree of drought intensified; and from 2.93 to 2.88 Ma, the vegetation was dominated by typical steppe, and the climate became relatively humid. At approximately 2.93 Ma, the percentage and concentration of pollen from broadleaved trees and the Artemisia to Chenopodiaceae (A/C) ratio increased rapidly, indicating that the climate had suddenly become humid, which may have been related to the strengthening of the East Asian summer monsoon (EASM) caused by the final closure of the Panama Seaway. At approximately 2.90 Ma, broadleaved pollen decreased rapidly, suggesting that the climate rapidly became cold, which may indicate the onset and expansion of the Northern Hemisphere ice sheets. We suggest that climate change in the Yinchuan Basin is closely related to global environmental changes and has global characteristics.