Palynological evidence for the Mid-Miocene Climatic Optimum recorded in Cenozoic sediments of the Tian Shan Range, northwestern China

Thick Cenozoic deposits were shed into the foreland basin of the Tian Shan Range, providing great potential for understanding the relationship between tectonic history and paleoclimatic changes. In the present study, we compiled a pollen record for the interval 26.5–2.6 Ma based on a palynological analysis of a latest Oligocene–Pliocene stratigraphic sequence in the northern foreland basin of the Tian Shan. Our results indicate that a remarkable warm climate occurred at ca. 18–15 Ma ago, corresponding to the Mid-Miocene Climatic Optimum, while a change to an arid climate occurred at 6 Ma, marked by an increase in the drought-tolerant herb taxa Artemisia and Chenopodiaceae. This latter change was coincident with the late Cenozoic climatic deterioration recorded at high latitudes in the Northern Hemisphere. These inferred climatic events are further supported by the results of principal component analysis of the pollen data, such records are important archives in reconstructing the paleoclimate of the Asian interior.