Abstract:
The distribution of clay minerals in the sediments of ODP Site 1148 (Leg 184), located on the north slope of the South China Sea, where 32.8 Ma sediments were recovered, shows different characteristics between 32.8 and 15.5 Ma and since 15.5 Ma. From 32.8 to 15.5 Ma, the sediments were dominated by smectite, whose relative abundance was as high as 70 percent. In the last 15.5 Ma, the abundance of illite and chlorite increased gradually as smectite decreased. Thus, the evolution of clay minerals in the sediments can be divided into two stages. From 32.8 to 15.5 Ma is a tectonically controlled stage in which clay minerals recorded the spreading history of the South China Sea. The period since 15.5 Ma is a stage where climate controlled the distribution of clay minerals. In this climate-controlled stage, the distribution of clay minerals indicates that temperature decreased gradually, then dropped rapidly. This result is consistent with that of delta (super 18) O of benthic foraminifers.