The Characteristics And Provenance Of The Sediment In The Southern East China Sea During The Last Glacial Age

As a result of the sea-level drop at the Last Glacial Maximum in the late Quaternary, the distribution of the land and sea in the eastern China continent changed a lot. The studies to exhibit the sedimentary source in the East China Sea during the last glacial age are of great significance to reveal the hydrologic situation of paleo-continent and paleo-ocean, climate change and environmental evolution. The upper layer sediment of core Q43 in the outshelf of the southern East China Sea shows that it is the regressive sequence of littoral facies to offshore facies and of representative significance. The sediments in the core are weakly weathered, lightly abraded and bad sorted, they have the same feature as river sediment, which is derived from near source and did not experience seriously transformation by ocean. Due to the rate of insufficient sediment supply the sedimentation rate is low. Under the hydrodynamitic condition in the outshelf heavy minerals are enriched to a certain extent. They are of horablede-epidote assemblage and contain some authigene ( pyrite and glauconite ). The content of stable mineral is small and mineral maturity index ( TRZG/HP ) is low. Based on studies of detrital minerals it is unraveled that the coarse-grained sediments are of single and stable source and have the same trait as intermediate-acidic granite and metamorphites. Beneath the relic sand of the outer shelf there is high grade of valuable heavy mineral sand ( for example ilmenite ) reaching the II anomaly order of marine placers and it is of potential resource prospects. Clay minerals are of illite, chlorite, kaolinite and smectite assemlblage. The content of illite is very high and its crystallinity index is high too, which indicate the cool and arid climate condition in the time of sediment conformation.The elemental geochemistry characteristics indicate that elements abundance is controlled seriously by grain size of sediment. The element content in the fine-grainedfraction ( <0.063mm) of the core is great. The correlation coefficient between the elements in the coarse-grained is high, which indicate that the coarse-grained sediments derived from the same provenance. The elements vertical distribution in the core is not only related to the host minerals, but also closely to sedimentary environment. Ratios of some selected element can indicate the change of source and the change of environment with time. Chondrite normalized REE distribution patterns for the core Q43 are comparable to those of the sediment of Changjiang River and Huanghe River delta. The geochemical characteristics of the sediment between the late Pleistocene and modern in Changjiang River and Huanghe River are different, but their similarity is quite remarkable which suggested that the two great rivers are of stable sedimentary sources. Comparison of the characteristic parameters of immobile elements, such as REE, Sc, Th, Ti etc and of the characteristics of sedimentology and mineralogy comes to a conclusion that the provenance of the sediment is different in the Last Glacial Maximum and in the sub-interglacial stage, and they have the traits of mixed source. During the Last Glacial Maximum the sediment in the outshelf of the southern East China Sea was affected weakly by Changjiang River and they are probably derived from the coast mountains of Zhejiang-Fujian Province, which are near the southern East China Sea.The characteristics of the sediment from the Okinawa Trough are controlled by provenance. Some major and trace elements vs. Al scatter plots show clearly the evolution stage of the sedimentary supply to Okinawa Trough. The provenance of the sediment in middle Okinawa Trough during the Last Glacial Maximum is the shelf of the East China Sea. The characteristics of elemental geochemistry ascertain that the sediment was derived from the paleo-Changjiang River.