Late Cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the Tian Shan Mountains

[1] The folded Neogene deposits in the northern foreland basin of the Tian Shan Mountains provide important information about tectonic history and environmental changes of northwestern China. On the basis of lithostratigraphic and magnetostratigraphic evidence, we develop a new chronology for the previous studied Kuitun He section. Our palynological study on the late Miocene - Pliocene sediment of the Dushanzi section yields new information about vegetation and climate change during the period of 8.7 - 2.58 Ma. The results indicate that steppe taxa ( Artemisia and Chenopodiaceae) were generally dominant in the studied areas between 8.7 and 2.58 Ma, implying that a dry climate has occurred in the inland basins of northwestern China at least since 8.7 Ma ago. Although the general climate pattern indicated by our palynological results displays to some extent of drought, a warm and humid phase occurred at 5.8 - 3.9 Ma ago. This climatic optimum is comparable with the other records from the Chinese Loess Plateau, central Japan, the Sub-Himalayan Zone, and the marine eustatic sea level rise, implying this seems to be, at least, a regional climatic optimum.