Late Miocene East Asian Summer Monsoon Evolution and the Aeolian Deposits Chronology of Jianzha Basin in the Northeastern Margin of the Tibetan Plateau

Jianzha Basin is located in the northeastern part of the Tibetan Plateau and contains a thick sequence of Cenozoic sediments which are crucial for investigating the growth of the Tibetan Plateau and the record of the evolution of the Asian inland arid environment. Magnetostratigraphic results show that Late Cenozoic sedimentary sequence from the Jianzha Basin has recorded a continuous geomagnetic polarity sequence from C5r.3r to C3r, the section spans the interval from 11.8-5.8 Ma in the Late Miocene. Based on the high precision paleomagnetic dating framework and frequency susceptibility index (χfd), the cycle stratigraphy of Jianzha Basin was studied, whose results show the χfd of the deposit sediment displays a significant periodic change at around 7.2 Ma, which the record reveals that the East Asian summer monsoon (EASM) is dominated by 41 ka obliquity period before ~7.2 Ma and controlled by 100 ka short eccentricity period after 7.2 Ma. Spectral analysis of oxygen isotope records of benthic foraminifera from the South China Sea shows strong short eccentricity period and weak obliquity period between ~5.8 and ~7.2 Ma, and strong obliquity period and weak short eccentricity period between ~7.2 and ~11.8 Ma, which is consistent with the spectral analysis of frequency susceptibility (χfd) from the Jianzha Basin. In addition, it is found that the EASM climatic transition from 100,000-year orbital period to 40,000-year obliquity period occurred around 7.2 Ma, which is similar to the climatic transition around 0.9 Ma in the Middle Pleistocene. Therefore, the climate change result will provide a new similar model for predicting future monsoon climate changes. This study was supported by the National Natural Science Foundation of China (Grants 42272221, 41772167); and supported by projects funded by the Second Tibetan Plateau Scientific Expedition (STEP) program (2019QZKK0704); and supported by the Central University Research Foundation, Chang’an University (Grants 300102272901).