Provenance analysis for surface sediments in different depositional environments of the middle-south Okinawa Trough

In this paper, surface sediments taken from three different depositional environments, i.e. the outer continental shelf, slope, and trough, of the middle-south Okinawa Trough were analyzed for rare earth elements (REE). The results suggest that the REE distribution patterns of the surface sediments from the continental slope and the Okinawa Trough are quite similar to those from Taiwan. The discrimination plot of La/Sm-Gd/Yb also shows that the surface sediments from continental slope and the Okinawa Trough are mainly located in the diagram close to the provenance end of Taiwan, further supporting the conclusion that the surface sediments of the continental slope and the Okinawa Trough are doubtlessly sourced from Taiwan. The obvious loss of heavy REE in the sediments of the outer continental shelf is consistent with the source of continental river sediments. In order to recognize the source of surface sediments in the outer shelf sedimentary area, the heavy mineral compositions of these sediments were analyzed. The results show that the heavy mineral assemblages of the outer continental shelf sediments are mainly composed of common hornblende, epidote, garnet, limonite, similar to the source composition of the Changjiang river. The outer continental shelf sediments are lack of zircon, mica, and magnetite, typical heavy minerals found in Taiwan, Huanghe river, and Minjiang river sediments respectively, which suggests that Taiwan, Yellow River, and the coast of Zhejiang and Fujian are not the main contributors to the outer continental shelf sediments. According to the results of previous dating data, the sediments of the outer shelf are relatively old, suggesting that the outer shelf sediments should be formed by the rework of the palaeo-Changjiang river materials by the modern circulation system of the East China Sea.