Late Cenozoic genus Fupingopollenites development and its implications for the Asian summer monsoon evolution

摘要

An extinct palynomorph, Fupingopollenites, was used as the basis for a discussion of the late Cenozoic Asian summer monsoon (ASM) evolution and its possible driving forces. Based on the spatial and temporal variations in its percentages across Inner and East Asia, we found that Fupingopollenites mainly occurred in East Asia, with boundaries to the NE of ca. 42 degrees N, 135 degrees E and NW of ca. 36 degrees N, 103 degrees E during the Early Miocene (ca. 23-17 Ma). This region enlarged westwards, reaching the eastern Qaidam Basin (ca. 36 degrees N, 97.5 degrees E) during the Middle Miocene (ca. 17-11 Ma), before noticeably retreating to a region bounded to the NW at ca. 33 degrees N, 105 degrees E during ca. 11-5.3 Ma. The region then shrank further in the Pliocene, with the NE boundary shrinking southwards to about 35 degrees N, 120 degrees E; the area then almost disappeared during the Pleistocene (2.6-0 Ma). The flourishing and subsequent extinction of Fupingopollenites is indicative of a narrow ecological amplitude with a critical dependence on habitat humidity and temperature (most likely mean annual precipitation (MAP) >1000 mm and mean annual temperature (MAT) >10 degrees C). Therefore, the Fupingopollenites geographic distribution can indicate the humid ASM evolution during the late Cenozoic, revealing that the strongest ASM period occurred during the Middle Miocene Climate Optimum (MMCO, similar to 17-14 Ma), after which the ASM weakened coincident with global cooling. We argue that the global cooling played a critical role in the ASM evolution, while the Tibetan Plateau uplifts made a relatively small contribution. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.