Characteristics Of Detrital Minerals And Their Significance Of Provenance In Core EC2005 Located In Mud Sedimentary Area Of The Inner Shelf Of East China Sea

The heavy minerals in the sediments of core EC2005,located in the southern center of mud area in the inner shelf of East C hina Sea,were identified and analyzed for their significance of provenances and environments since 17.3Ka BP.The results show that:(1)in grade 0.063—0.25 mm and 0.031—0.063 mm,the dominant minerals are flaky minerals,magnetite,amphibole,epidote,dolomite,pyroxene,typical metamorphic minerals,altered minerals,rock fragments and authigenic,which are accounted for more than 96.00% of the total number of heavy minerals,but varied in sediments of core EC2005,the high content of heavy minerals appears in the horizon with rich authigenic pyrite contents.(2)In neurogen,because fine grained minerals are more sensitive to the change of hydrodynamic force,and the fine grained minerals' physical and chemical character became more important in the process of transportation and deposition increases in sediments of grade 0.031—0.063 mm,the difference between grade 0.063—0.25 mm and 0.031—0.063 mm is obvious in both the average levels and contents of vertical change.Compared to the content of heavy minerals in the grade 0.063 — 0.25 mm,the sediments in grade 0.031 — 0.063 mm containing more amphibole,tourmaline,sp hene,epidote,dolomite,apatite,olivine and augite,less flaky mineral and authigenic pyrite,the distinction of the other heavy minerals is not obvious.The dominant component in sediments of grade >0.25 mm is authigenic pyrite,autogenetic gypsum,bioclastic and plant debris,which changes obvious,concentrates and has its instruction of environment.According to the distribution of heavy minerals in different graded sediments,the sediments in core EC2005 can be divided into five sections(?—? in ascending order).Combining with the minerals' character in different graded sediments,the parameters of the grain size in sediments,the geochemical elements,AMS14 C dating and the sea level data in the west Pacific Ocean,the analysis results of hydrodynamic conditions and provenances shows that: Since the Last Deglaciation Periods,the tendency of hydrodynamic force was weak(17.3-15.6Ka BP)– strong(16.4-15.6Ka BP)– less strong(15.6-13.5Ka BP)– very weak(13.5-13.1Ka BP)– strong(13.1-12.3Ka BP)– weak(12.3-0Ka BP).With the sea level rising steadily,the environment changed into the low-energy anoxic neritic condition,during 12.3—4.7Ka BP,on the whole,the upwelling developed,then became weaker and the coastal current developed in the period of 4.7—0Ka BP.Although the hydrodynamic force changed vary,on the whole,the sedimentary provenance changed little,the main sedimentary provenance was the Yangtze River,in addition,the sediments in core EC2005 were also influenced by the materials carried by the river in Zhejiang province,especially during 13.1-17.3Ka BP,the date of heavy minerals in the sediments of the core EC2005 reflect the strong source signal from the Yangtze River.