Sedimentary Processes And Mechanism Of The Mud Areas On The China Sea Continental Shelf During The Middle To Late Holocene

The China marginal sea has a large number of mud areas,which have the advantages of high sedimentary rate,wide material sources and rich environmental information.It is very sensitive to sea level and climate change and can be used as an excellent information carrier of climate and environmental change.The sedimentary process in the mud area and the records of East Asian Monsoon(EAM)recovered by proxy of sediments are the research hotpots.However,it remains to be confirmed whether the East Asian Summer Monsoon(EASM)or the East Asian Winter Monsoon(EAWM)is the dominant factor controlling the sedimentary processes.The relationship between EASM and EAWM and its influencing factors during the Holocene have also been the focus of discussion.Four cores named B60(from the central mud area of the Bohai Sea),HS2(from the central mud area of the South Yellow Sea),S04-2(from the inner-shelf mud area of the East China Sea)and ZN4-2(from the mud area of the Beibu Gulf)were studied on geochronology and sedimentology.The chronology was built employed the ²¹⁰Pb and AMS¹⁴C dating.The sedimentary characteristics were revealed by analyses of grain size,diffuse spectral reflectance(DSR)and X-Ray Fluorescence(XRF)measurements.In this study,the sedimentary processes and characteristics of mud areas were analyzed and compared,and made comparative analyses by using proxies of climatic and environmental recovered from mud areas.The proxies of EAM and YSWC were extracted and the evolution of them were analyzed,the relationships between EASM and EAWM were explored.The main conclusions are drawn as follow:1.The sediments of B60 core were generally stable and phased variation were showed in the parameters.The process of sediment in the central mud area of the BS was mainly controlled by the YSWC during 1450?1050 a BP and 650?90 a BP,and dominated by the EASM during 1050?650 a BP and since 90 a BP.The parameters of grain size and contents of major and trace elements in sediment of HS2 core were obviously divided into four stages,but the proxies of color reflectance is relatively stable.The evolution of sediment in the central mud area of the SYS since 6000 a BP could be divided into four stages:during 6000?4600 a BP,3200?2200 a BP and since 2200 a BP,the sedimentary process was controlled by the EASM with stable hydrodynamic conditions and single material source;during 4600?3200 a BP,the process was mainly controlled by the EAWM.During the Holocene,the characteristics of grain size in the sediment of S04-2 core have changed significantly,the contents of some major and trace elements and color reflectance parameters have changes periodically,and other proxies are relatively stable.The evolution of sediment in the inner-shelf mud area of the ECS since 6300 a BP could be divided into four stages:during 6300?4600 a BP and since 2200 a BP,the sedimentary process was controlled by the EASM;during 4600?3200 a BP,the process was mainly controlled by the EAWM.Since 5500,the parameters of grain size in sediment of ZN4-2 core have fluctuated widely,and the contents of major and trace elements and color reflectance have changed suddenly in different layers.2.EASM variability reflected by sediments in core B60 was divided into four stages that corresponded well with historical records.There has been a negative correlation between the EASM and YSWC since 1500 a BP,and the correlation was controlled by the winter Arctic Oscillation(w AO).When the index of w AO increased in winter,there was a negative correlation between EASM and YSWC;on the contrary,there was a positive correlation between them.The intensity of both the EASM and EAWM showed a fluctuating trend of decrease after approximately 6000 a BP.The evolutionary history of the EASM and EAWM showed a similar downward trend at the millennial timescale;however,on the centennial timescale,their relationship was mostly anti-correlated.It was established that negative correlation between the EASM and the EAWM is controlled by strong solar radiation.The records from ECS showed negative correlation between EASM and EAWM since2500 a BP and before 7500 a BP,while positive correlation during 7500?2500 a BP.The records of EASM and Indian Summer Monsoon(ISM)from ZN4-2 core in the muddy area of Beibu Gulf showed a similar weakening trend on the millennium,while on the centennial scale,most of them showed negative correlation.3.The EASM is the main controlling factor in the sedimentary process of the mud area in the continental shelf,and the role of the EAWM is second to the EASM,which only plays a controlling role in some periods.The records of EASM recovered from core B60 showed that there was an increasing trend before 650 a BP and a decreasing trend after 650 a BP;however,the records recovered from core HS2showed an increasing trend since 1500 a BP.Records of EASM from core HS2 and ZN4-2 have generally trend in recent 6000 years,but were not consistent with that extracted from S04-2.The records of YSWC recovered from core B60 were in good agreement with the EAWM records recovered from core HS2 and S04-2.These reasons of difference may be caused by chronological deviation and the difference of formation and mechanism of different mud area,and the most important one is the difference of sediment source.