Abstract:
The evolution of the Asian monsoon since the late Miocene is discussed based on a comprehensive comparison of the loess-red clay deposits in the Chinese Loess Plateau, eolian flux in the Northwest Pacific Ocean, and Foraminifera fossils in the South China Sea and Arabian Sea. Wind-blown sediments accumulated over a wide area in the Chinese Loess Plateau around 8 Ma, when the Indian Monsoon was formed (or greatly enhanced), and around 3.5 Ma. The low abundance of planktonic Foraminifera Globigerinoides sacculifer and G. ruber and the high abundance of Neogloboquadrina at approximately 8 Ma at ODP Site 1146 in the South China Sea indicate that the ocean's surface temperature decreased and oceanic productivity increased, which indicates an increase in the East Asian winter monsoon winds. The high abundance of eolian dust in the North Pacific Ocean revealed by ODP Site 885/886 indicates an increase in widespread aridity in the Asian interior. The sediment flux increased in the Indian Ocean since 11 Ma, with peak flux at 9-8 Ma, which is due to the uplift of the Himalayas. When the uplift reached sufficient height, the arid area expanded in Central Asia and a large amount of dust was transported eastwards to North China and the North Pacific. Further rapid uplift of the entire Tibetan Plateau at 3.6 Ma, indicated by a thick gravel bed on the north flank of the Plateau, resulted in further aridity in the basins of central and eastern Asia, enhancement of the East Asian monsoon, and strong terrigenous sedimentation in both the South China Sea and the Indian Ocean in the late Pliocene.