Middle Miocene Climate Marked Changes Preserved in saline lake: Qiadam Basin, China

Abstract:

Middle Miocene climate represents an abrupt and dramatic instance of global warming and cooling. High-resolution proxy records have been widely used to investigate the Neogene climatic evolution in different geographical settings, revealing the macroscopic climatic representation of Middle Miocene climate is consistent around the world. However, the scale of these records is still too large to only show the detailed Middle Miocene Climate changes. Consequently, what roles Tibet Plateau uplift and Global Cooling played for long-term aridification started from Mid-Miocene in inland Asia, the largest mid-latitude arid zone in the Northern Hemisphere, is still remains controversy. In addition, there are few evidences from terrestrial deposits of Mid-Miocene in inland Asia because of depositional hiatuses, and these evidences are nearly all from profile but intense long-term erosion may affect it. Our context conducted the high-resolution carbon and oxygen stable isotopes, proxy indexes including CIA and Sr/Cu, together with detailed petrologic investigation to meticulously depict sedimentary succession of mid-Miocene 400M continuous coring section of JS2 well located in the hinderland of Qaidam Basin. The result shows that the climate change was a gradually drying trend during the mid-Miocene in Qiadam basin instead of a sharp aridification. The fine-grained mixed sediments with intermittent deposition of algal/oolitic limestone interlayers may represent the Mid-Miocene Climatic Optimum (MMCO), while the fine-grained mixed sediments with intermittent deposition of dolomite interlayers may indicate the beginning of Middle Miocene Climate Transition (MMCT). During the MMCO, the Qiadam lake underwent cyclic changes of lake's expansion stage and slow shrinkage stage. During the MMCT, the lacustrine basin underwent cyclic changes of lake's expansion stage and rapid shrinkage stage. The decreased atmospheric precipitation and the increased evaporation are the main factors of this climate marked change, while the winter monsoon strengthening and the summer monsoon weakening caused by global cooling is the mainly driving mechanism. Qinghai-Tibet Plateau uplift may be not the mainly driving mechanism of Middle Miocene climate marked change. However, its relatively low elevation during the Middle Miocene may have contributed to formation of the MMCO event in inland Asia.