SEDIMENT PROVENANCE AND PALEOENVIRONMENT RECORDS OF THE CENTRAL OKINAWA TROUGH FOR THE LAST 17 000YEARS

Based on the data of grain size and clay minerals coupled with precise AMS 14C dating,this paper deals with the provenance and paleoenvironment evolution of the Central Okinawa Trough for the last17000awith the samples from the Core OKI04.The results indicate that the terrigenous sediments in the Central Okinawa Trough are mainly from the East China Sea carried by both the large rivers from East China(the Yangtz River and Yellow River)and the small rivers from east and west Taiwan.The two major provenances have different contribution to the study area in different periods.During the period of 17~13.4ka,sediments were mainly from the large rivers in East China(the Yangtz River and Yellow River)and the small rivers in east and west Taiwan;In the period of 13.4~11.4ka,sediments from west Taiwan increased;in the period of 11.4~7.5ka,the influence of the Yangtz river and Yellow river increased;during the period of 7.5~5.5ka,the sediments in the study area were mainly affected by the Taiwan source;since 5.5ka,the sediments were mainly from East Taiwan and Yangtz River.Our study also reveals that Kaolinite was mainly from the large rivers in the Eeast China mainland.Besides,the environmentally sensitive grain-size populations suggests that the sediments were transported mainly in a suspended manner.The transportation of the suspended sediments from the main rivers in East China is related to the ocean circulations driven by the winter monsoon.In this study,kaolinite content is used as the indicator of the winter monsoon's evolution under the assumption that the provenance remains unchanged,and thus 5strengthened periods of winter monsoon were identified since 17 000ain the East China mainland.