关键词: 40ka以来, 海岸沙地, 古风成沙, 气候与环境演变, 海南岛

Abstract:

In this study, with the coastal sandy land of Hainan Island as the research object, the representative and high-resolution stratigraphic sections including Mudui, and Qiziwan sections etc. in the eastern and western coasts of Hainan Island were selected to investigate the climatic and environmental variations of the coastal sandy land in recent 40 ka. Based on the accurate OSL and TL dating the chronologic sequence was reconstructed. The studies on the proxy indicators such as the composition and grain-size parameters of aeolian sand, SC/D value and susceptibility etc. show that during the interstadial of last glaciation the climate was relatively warm, the sea level fell by -8~10 m, and an advancing river delta formed in the coastal plain, which exhibited an alternatively distributed pattern with wetland and sand dunes. During the last glacial maximum the climate was dry and cold, and the sea level in the north of South China Sea dropped to -155 m, the Hainan Island linked up with the surrounding continental shelf and formed a vast continent, large area and various shapes of ancient sand dunes formed on the continental shelf, many rows of ancient sand ridges (dunes) parallelly extended over the (today's) coastal sandy land and formed a continuous deposition together with ancient sand dunes of the continental shelf. By the end of the last glacial maximum (17~15ka B.P.) the climate turned warm and humid, the sea level in the north of South China Sea rose to -131 m. During the last deglaciation the climate was in a cold-warm fluctuation state and six rapid climatic variation events occurred. In the cold period ancient sand ridges (dunes) experienced aggradational development but in the warm period ancient sand ridges (dunes) experienced fixation and soil-forming processes. Since the Holocene the climate turned warm and experienced fluctuated changes and at about 8 ka the sea level of South China Sea rapidly rose and gradually the modern oceanic environment formed. Meanwhile secondary sand dunes developed on the coastal sandy land and experienced multiple semi-fixation, fixation, dune aggradation and reactivation changes. This shows the coastal sandy lands in Hainan Island and other regions of China or even the global coastal sandy land experienced similar evolution processes.

Key words: since 40 ka B.P., ancient aeolian sand, coastal sandy land, climatic and environmental evolution, Hainan Island