Estimation Of The Provenance And Flux Of The Sediments In The Okinawa Trough Using Quantitative Analysis Since Late 40 Ka

Deeply study on changes of marine environment, provenance and flux of the sediments during the glaciation-interglaciation climatic cycle is a highlight field of the paleoceanography studies in the Okinawa Trough.Based on detailed analysis for grain-size distributions, AMS¹⁴C dating, element and Sr-Nd isotopes compositions in the sediments of four cores that collected from the Okinawa Trough, the present thesis focus on the volcanic eruption events and terrigenous flux changes and its' response to the climatic evolution since the late 40 kaBP. There are several mathematical methods have been selected for data processing, such as Q-mode factor analysis for element content, end-member modeling for grain-size data, quantitative partition of mixed sediments using Sr and Nd isotopes composition, etc. The studies indicate that the main sources of siliciclastic detritus in the sediments of the Okinawa Trough are terrigenous materials from the China mainland and volcanic substances (volcanic glass and pumice). In addition, the proportion of aeolian detritus in the bulk sediments is not as high as expected. According to the grain-size distribution of siliciclastic detritus, the fraction of the terrigenous detritus with sedimentary environment sensitivities in the Okinawa Trough is identified and has the mode at about 7.81 μ m even various sediments sources and environmental characteristics are associated with different part of the Okinawa Trough. Which may provide evidence for 'terrigenous materials of the Okinawa Trough are mainly transported by the rivers of China'. As a result, the terrigenous flux in the sediments of Okinawa Trough is controlled not only by sea-level fluctuations, but also by palaeoclimatic changes in source region.Terrigenous supply in marine sediments is a function of interaction between land and ocean in response to climatic and oceanographic changes. At the middle Okinawa Trough, terrigenous flux since 35 cal. kaBP was calculated using Sr and Nd isotopes compositions in the sediments of Core DGKS9603. The results demonstrate that the terrigenous flux is higher in cool period than in warm period. The clay-size terrigenous detritus supplied by Yangtze River and East Asia winter monsoon also higher in the last glaciation maximum (LGM) while terrigenous flux is high and changes smoothly. But in the last deglaciation period, which has high sea-level rise speed, the terrigenous flux is higher than in the LGM suggests that there is a interactional connection between sea-level fluctuations and palaeoclimatic changes in source region during the process of controlling the terrigenous materials input into the middle Okinawa Trough.The volcanic materials imprint in the sediments of Holocene stratum indicates that volcanoes around the Okinawa Trough are more active in warm climate period. There arethree widespread volcanic eruptions occurred in Kyushu Island and Okinawa Trough and formed several volcanic tephra layers in the sea bottom sediments of the Okinawa Trough since the isotope stage 3. Changes of SiOz, Na20 and Zr contents in the sediments are good indicators for changes of volcanic materials input. The horizons of these three volcanic tephra layers in cores from the north and middle Okinawa Trough have homologous sedimentary ages. The eruptive ages of three volcanoes are 7563 ^ 25000 and 42000 cal. a BP and corresponding to K-Ah. AT and Okinawa I volcanic eruption event respectively. Compared with the K-Ah and AT tephra layers, great variation of grain-size distribution in the sediments of Okinawa I tephra demonstrates that Okinawa I tephra has different source against the former two tephra.Two end members, which are considered as good indicators for sediments sources, are extracted from the <63 U m fraction of the total grain-size distribution of siliciclatic detritus by grain-size end member modeling method. For the uppermost part (0-225em) of Core DGKS9603, the terrigenous flux in sediments is also calculated based on end member modeling software. The same trend is shown by the changes of terrigenous flux in sediments of DGKS9603 when calculated by grain-size end member modeling method and quantitative partition of mixed sediments using Sr and Nd isotopes composition. Which means that the grain-size end member modeling method is effective in sediment sources identification when it be used in the Okinawa Trough.The mixture rates of terrigenous and volcanic materials in the clay-size sediments of Core 155 are obtained by quantitative partition formula using Sr-Nd isotopes data. According to the results, the mixture rates of clay-size terrigenous detritus in sediments are decreasing with the depth decreasing during the isotope stage 1, on the contrary, the mixture rates of clay-size volcanic materials are increasing. In the isotope 3, the mixture situations in the sediments are conversely with the isotope stage 1. During the isotope 2, clay-size sediments are almost composed of terrigenous detritus. Compared with the grain-size characteristics of the bulk siliciclatic detritus in the sediments of Core 155. the changes of the mixture rates of clay-size volcanic detritus imply that the volcanic materials have different influence on clay-size sediments with different distance to the crater.The abruptly cooling events, such as Younger Dryas and Heinrich events, were identified from many cores at the Okinawa Trough. During the LGM. terrigenous flux in sediments are nearly invariable in Core DGKS9603 imply that there was no influence of thermohaline circulation changes in the Okinawa Trough during the episodes of H1 and H2 events. But the terrigenous flux in sediments is decreasing rapidly during the episodes of YD and H3 events may indicates that the occun-ence of these abruptly cooling events can speedup the decreasing trend of terrigenous flux which is controlled by sea-level changes in the Okinawa Trough during warm climatic period.