Magnetostratigraphy And Paleoclimatic Significance Of Miocene Sediment In Wushan Region

The Miocene is a key period in global climate change. There are symbolic events in the period, such as the formation of Asian paleomonsoon, the uplift of Tibetan Plateau and the significant change of ecology environment. Wushan region is located in the northeastern part of Tibetan Plateau, where is the convergence of three large physiographical regions. As a result, the site is sensitive to climate change. There are thick Miocene sediments which contain abundant information of Miocene climate change. The work is on the basis of fossil mammals and systematic sedimentary analysis work. We collected paleomagnetic samples in these strata, so we get the chronology of the basin. We also learn about the fluctuation of the Miocene climate change through magnetic susceptibility and sediment color analysis work. The research results are as follows:1. The chronology range of Nanyu section is 16.8-13.6Ma, and that of Jingwan section is 22.7-17.7Ma.2. The mineral compositions of Miocene sediment in Wushan region are mainly hematite, magnetite and maghemite through analyzing the thermal demagnetization curves.3. We contrast sediment color with the curves of South China Sea oxygen isotope, and the results show that the climate was cool and drought between 22.7 and 21.7 Ma. During the period of 21.7-19.1 Ma, the climate was warm and wet. Between 19.1 and 17.7Ma, the temperature was lower. During the period of 16.8-16.1 Ma, the climate was warmer and more drought. The climate changed to be warmer and wetter during the period of 16.1-14.5Ma. During the period of 14.5-11.3Ma, the climate tended to be cooler and more drought, followed by warmer climate between 11.25 and 10.2 Ma. The climate of the period of 10.2-8Ma was warmer and wetter than that of the period 8-6 Ma.4. The main reason for enhancement of magnetic susceptibility in Wushan region could be enhanced tectonic activity and aridification. Besides, sediment color seems to be a better climate proxy than magnetic susceptibility in Miocene climate change research.