Okinawa Trough During The Late Quaternary Sedimentary Characteristics And Their Provenance And Environmental Significance

The composition and distribution of the grain size, minerals and elements for surface sediments from the north and south Okinawa Trough are investigated. Based on the result, the sources of the sediments are analysed, and the soure indications of some groups of element are given. Based on the distribution of grain size, minerals and elements for two core sediments, combined with the distribution of the oxygen isotopic ratios, the relationship between the sedimentary records and their paleo-environmental indications are investigated. The sediments from the shelf and slope of the north and south Okinawa Trough are similar to the residual sediments. The sediments are mainly composed of terrestrial debris, biogenicial debris, clay minerals and autogenous deposits. In the north Okinawa Trough. the sandy sediments from the shelf and slope mainly derived from the residual sediments of the Yellow River during the ice age, in present envieronment, the sediments are rebuilded by the biogenic and autogenous deposits. The fine-grained sediments from the area to the south of the Chejudo islands mainly derived from the shelf residual deposits. Some of the fine-grained sediments in the residual sediments redeposit in the role of the Huanghai Sea warm current and the Huanghai Sea coastal current. The sediments from the trough of the north Okinawa Trough mainly derived from the volcanic activity. There are a lot of volcanic glass, augite, hypersthene and magnetite in the area. The sediments of the south Okinawa Trough mainly derived from the Yangtz River. In addition, there are some marine biogenic and autogenous deposits. According to the distribution of elements, the sediments of the continental shelf in the Okinawa Trough are mainly composed of terrigenous composition, such as Si02, and biogenic compositions, such as CaO and Sr. The biogenic deposits dilute the terrigenous deposits. The elements, such as Fe203 and P205, rich in the slope, where is influenced by the Kuroshio. Some elements, such as A1203~ K20~ Cu Zn.. Co.. Ni and Cr, mainly hosted in the fine-grained sediment, rich in the trough. Based on the result of the R-model factors analyses, the elements are devided into different groups, combined with the minerals distributions, every elements group are given a different source indication. The 6 18Q ratio of planktonic foraminifera for two core sediments from the north (core Y 127) and the south(core EO 17) Okinawa Trough are analysed. Stratigraphic correlation of oxygen isotopic ratios show that the 6 ISQ ratio record the change of the paleo- environment of the Okinawa Trough. The higher the 6 I8~ ratio, the colder the weather is, and vice versa. The weather becomes warm at about I 2ka BP, and then there is a short cold stage at about 1 Oka BP. According to the change of elements in the stratigraphy, most of the elements recorded the event of Holocene warming, and only several elements recorded the YD event. The volcanic activity plays a very important role on the composition of the sediments and the sedimentatry environment in the Okinawa Trough. According to the oxygen isotopic stratigraphy, There exit two large-scale volcanic activity records from 8.Oka BP to now. Only in the north...