The Input Variation Of Detrital Sediments And Its Controlling Factors In The Bicol Shelf Since 150 Ka

The West Philippine Sea is one of the key areas for global sea-air and sea-land interactions,and it is also an important place of global material and energy exchange,so it plays an important role in the study of regional source-sink process and global climate change.The Philippine island arc is the main source area of deep sea detrital sediments in the West Philippine.However,there is still no systematic research on the sedimentary characteristics of the detrital sediments,so there is a lack of basic data for the comparative study of the prevenance.There is also a lack of clear understanding of the changes and control factors of the island arc material input to the deep sea.A high-quality sediment core was collected at MD06-3052 station of Bicol Shelf on the east side of Luzon Island during MD155 cruise of "International Ocean Global Past Climate Change(IMAGES)" in 2006,which provides a good material for the above problems.In this dissertation,the characteristics of mineral composition,grain size,radiogenic Sr and Nd isotopes of the detrital sediments are studied.The source and transport mode of the detrital sediments are analyzed,and the variation and controlling factors of the input of detrital material to the seaare discussed.Through the combination of X-ray diffraction analysis(XRD)and Tescan Integrated Mineral Analyser(TIMA),the main minerals identified in the normal marine sediments of Bicol Shelf include calcite,aragonite,tourmaline,plagioclase,quartz,and epidote.The mineral composition of the turbidite is similar to the normal marine sedimentary layer.The tephra layers are characterized by volcanic glass,but the content and shape of volcanic glass in different tephra layers are different.Aragonite and calcite in the study area are mainly biogenetic,while quartz,plagioclase and tourmaline represent terrigenous detrital components.Since 150 ka,the content of carbonate increased in interglacial period and decreased in glacial period,while the content of quartz,plagioclase,and tourmaline changed in the opposite direction,showing high in glacial period and low in interglacial period.The quartz/carbonate ratio has a trend of high in glacial period and low in interglacial period,indicating that the input of terrigenous detrital materials increased in glacial period and decreased in interglacial period.In core MD06-3052,the detrital material in the normal marine sedimentary layers is mainly composed of clay and silt,the sand content is relatively low,while the sand content in the tephra layers and turbidity current layers is significantly increased.Three endmembers(EM1,mode at 2 ?m),EM2 mode at 10 ?m,and EM3,mode at 45?m)were separated from the detrital components of the normal marine sedimentary layers by using the particle size parameterized end-member analysis method.According to the grain-size distribution of each end member,Sr and Nd isotopic compositions of different grain size(<4 ?m and >20 ?m)were analyzed.The results show that different detrital end members in the core MD06-3052 are mainly from the Philippine island arc.In addition,through the comparative analysis of the main and trace elements of the volcanic glass in the tephra layer,the results show that the volcanic ash of 18 ka(A1)and 76 ka(A3)in the core MD06-3052 originates from the eruption of Pinatubo volcano,and the volcanic ash of 103 ka(A4)comes from the eruption of andesitic-dacitic magma in the Bicol arc active area.Combined with the the source and grain size of the detritla sediments,the transport mode of each end member is further analyzed.Among them,the EM1 and EM2 are transported to the Bicol Shelf through the surface and bottom currents,respectively.The EM3 coarse-grained detritus is formed by the redeposition of the exposed island shelf detrital sediments in the low sea level period under the action of gravity flow.The trends of the total content of weathering detritus,the content of each detrital end member,and the the mass accumulation rate(MAR)of coarse detritus(EM2 and EM3)are the same,as that of global sea level,which is highin glacial low sea level periods(40?14 ka and 150?130 ka)and low in interglacial high sea level periods.However,the MAR of fine-grained EM1 detrital end member did not increase significantly at40?14 ka low sea level period.We argue that sea level change is the main factor controlling the coarse detritus input from Luzon Island to Bicol Shelf.During the glacial period,the sea level was greatly reduced,which made most parts of the island shelf exposed and became a new source area,which led to a significant reduction in the transportation distance of detrital material from the source to the sink system in the Philippine island arc,thus significantly increasing the input of coarse detritus to the research area.The input of fine-grained detrital end member is not only affected by sea level change,but also by ocean current and regional precipitation.