Characteristics of Clay Mineral in South China Sea since Oligocene and Its Significance
TANG Song SHAO Lei ZHAO Quan-hong (Key Laboratory of Marine Geology, Ministy of Education,Tongji University, Shanghai 200092)
The distribution of clay mineral in the sediments of ODP Leg 184 Site 1148, located on the north slope of the South China Sea and recovered 32.8Ma sediments,shows different character between 32.8-15.5 Ma and since 15.5-0Ma periods. In 32.8-15.5 Ma the sediments are dominated by smectite,whose relative abundance is as high as 70 percent,while the abundance of illite and chlorite increase gradually with the decrease of smectite into the last 15.5 Ma. Thus, the evolution of clay mineral in the sediments can be divided into two stages. 32.8-15.5 Ma is tectonic-controlled stage,in which the clay mineral record the speading history of South China Sea.Whereas the climate controlled the distribution of clay mineral since last 15.5 Ma.In this climate-controlled stage the distribution of clay mineral indicated that the temperature decreased gradually and droped rapidly at 3Ma.This result is well consistent with that of δ~ 18O of benthic foraminifera.