Palynological evidence for late Miocene stepwise aridification on the northeastern Tibetan Plateau

Jia Liu,Xi Yan Ye,Chun Hui Song,Ting Jiang Peng,Zheng Chuang Hui,Hao Yu,Ji Jun Li

doi:10.5194/cp-12-1473-2016

Abstract

Abstract. Holding a climatically and geologically key position both regionally and globally, the northeastern Tibetan Plateau provides a natural laboratory for illustrating the interactions between tectonic activity and the evolution of the Asian interior aridification. Determining when and how the late Miocene climate evolved on the northeastern Tibetan Plateau may help us better understand the relationships among tectonic uplift, global cooling and ecosystem evolution. Previous paleoenvironmental research has focused on the western Longzhong Basin. Late Miocene aridification data derived from pollen now require corroborative evidence from the eastern Longzhong Basin. Here, we present a late Miocene pollen record from the Tianshui Basin in the eastern Longzhong Basin. Our results show that a general trend toward dry climate was superimposed by stepwise aridification: a temperate forest with a rather humid climate existed in the basin between 11.4 and 10.1 Ma, followed by a temperate open forest environment with a less humid climate between 10.1 and 7.4 Ma, then giving way to an open temperate forest–steppe environment with a relatively arid climate between 7.4 and 6.4 Ma. The vegetation succession demonstrates that the aridification of the Asian interior occurred after ∼ 7–8 Ma, which is confirmed by other evidence from Asia. Furthermore, the aridification trend on the northeastern Tibetan Plateau parallels the global cooling of the late Miocene; the stepwise vegetation succession is consistent with the major uplift of the northeastern Tibetan Plateau during this time. These integrated environmental proxies indicate that the long-term global cooling and the Tibetan Plateau uplift caused the late Miocene aridification of the Asian interior.

Highlights

As the latter stage of the global Cenozoic cooling, the Neogene was a critical period for northern hemispheric aridification, especially for the marked aridification of the Asian interior
The tectonic uplift of the Tibetan Plateau (TP), global cooling and land–sea distributions have been suggested as the major drivers (An et al, 2001; Gupta et al, 2004; Kutzbach et al, 1993; Liu and Yin, 2002; Miao et al, 2012; Molnar et al, 2010)
The late Cenozoic basins, located at the northeast TP, document the environmental changes associated with tectonic uplift and global cooling

Summary

Introduction

As the latter stage of the global Cenozoic cooling, the Neogene was a critical period for northern hemispheric aridification, especially for the marked aridification of the Asian interior. Establishing when, and how, this process of aridification began and evolved is vital for elucidating the interactions among tectonic uplift, global cooling and ecosystem evolution. There is compelling evidence for the aridification of the Asian interior, there is no consensus concerning its evolution and driving mechanisms. Previous researchers have suggested that the aridification of the Asian interior began in the late Miocene, based on biological and isotopic evidence (Andersson and Werdelin, 2005; Cerling et al, 1997; Dettman et al, 2001; Eronen et al, 2012; Quade et al, 1989; Wang and Deng, 2005; Zhang et al, 2012).

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