Magnetic properties of Holocene core ZK9 in the subaqueous Yangtze delta and their mechanisms and implications  

作　　者：Yan LIU Zhongfa HE Zhanghua WANG 

机构地区：[1]Department of Geography, East China Normal University, Shanghai 200062, China [2]Shanghai Geological Survey, Shanghai 200072, China [3]State Key Laboratory of Estuarine and Coastal Research, Shanghai 200062, China

出　　处：《Frontiers of Earth Science》2013年第3期331-340,共10页地球科学前沿（英文版）

基　　金：We are deeply indebted to Drs. Weiguo Zhang and Brian Finlayson who kindly reviewed the paper and provided constructive comments. This study is jointly supported by the National Natural Science Foundation of China （Grant No. 41176070）, the Ministry of Science and Technology, China （No. 2010RCDW05） and the Ministry of Land and Resources of China （No. 201211009）.

摘　　要：We measured the magnetic properties of core ZK9 from the subaqueous Yangtze delta to examine the mechanisms and possibility of using magnetic proxies for the sedimentary environmental evolution controlled by the Holocene sea level. The results showed that low values of most magnetic parameters occurred and pyrite formed in the estuarine sediments during c. 10.5-8.4 cal ka BE reflecting the predominant early diagenesis in a tidaldominated depositional environment when the sea level rose rapidly. Sharp increases in the values of χARM （susceptibility of Anhysteresis Remanent Magnetisation）, χARM/χ, χARM/SIRM （Saturation Isothermal Remnant Magnetisation） and HIRM （Hard Isothermal Remnant Magnetisation） occurred immediately above the transitional zone from estuarine to deltaic system of c. 8.4--5.9 cal ka BP, which imply accumulation of single-domain magnetite and anti-ferromagnetic minerals. These magnetic properties indicate the enhanced freshwater processes at the core site as a result of the relatively stable sea level and the associated delta progradation since c. 5.9 cal ka BP. Therefore, magnetic proxies Of χARM and HIRM are useful to identify the maximum flooding surface. In addition, the intertidal-subtidal sediment of c. 13.2-10.5 cal ka BP had high values of χ, SIRM and HIRM, reflecting the features of a coastal environment. The sharp decline of the above parameters from c. 10.5 cal ka BP indicates possibly an event of rapid sea level rise.We measured the magnetic properties of core ZK9 from the subaqueous Yangtze delta to examine the mechanisms and possibility of using magnetic proxies for the sedimentary environmental evolution controlled by the Holocene sea level. The results showed that low values of most magnetic parameters occurred and pyrite formed in the estuarine sediments during c. 10.5-8.4 cal ka BE reflecting the predominant early diagenesis in a tidaldominated depositional environment when the sea level rose rapidly. Sharp increases in the values of χARM （susceptibility of Anhysteresis Remanent Magnetisation）, χARM/χ, χARM/SIRM （Saturation Isothermal Remnant Magnetisation） and HIRM （Hard Isothermal Remnant Magnetisation） occurred immediately above the transitional zone from estuarine to deltaic system of c. 8.4--5.9 cal ka BP, which imply accumulation of single-domain magnetite and anti-ferromagnetic minerals. These magnetic properties indicate the enhanced freshwater processes at the core site as a result of the relatively stable sea level and the associated delta progradation since c. 5.9 cal ka BP. Therefore, magnetic proxies Of χARM and HIRM are useful to identify the maximum flooding surface. In addition, the intertidal-subtidal sediment of c. 13.2-10.5 cal ka BP had high values of χ, SIRM and HIRM, reflecting the features of a coastal environment. The sharp decline of the above parameters from c. 10.5 cal ka BP indicates possibly an event of rapid sea level rise.

关 键 词：magnetic properties early diagenesis maximum flooding surface sea level Yangtze delta HOLOCENE 

分 类 号：P737.121[天文地球—海洋地质] O482.5[天文地球—海洋科学]