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引用本文:江俊,ALAA Salem,赖晓鹤,张卫国,LESZEK Marks,FABIAN Welc,徐立辰,陈静,陈中原,孙千里.湖泊沉积物磁学特征指示的埃及Faiyum盆地全新世以来的环境演变.湖泊科学,2016,28(6):1391-1403. DOI:10.18307/2016.0625
JIANG Jun,ALAA Salem,LAI Xiaohe,ZHANG Weiguo,LESZEK Marks,FABIAN Welc,XU Lichen,CHEN Jing,CHEN Zhongyuan,SUN Qianli.Sediment magnetism of Faiyum basin (Egypt) and its implications for the Holocene environment change. J. Lake Sci.2016,28(6):1391-1403. DOI:10.18307/2016.0625
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湖泊沉积物磁学特征指示的埃及Faiyum盆地全新世以来的环境演变
江俊1, ALAA Salem2, 赖晓鹤1, 张卫国1, LESZEK Marks3, FABIAN Welc4, 徐立辰1, 陈静1, 陈中原1, 孙千里1
1.华东师范大学河口海岸学国家重点实验室, 上海 200062;2.Department of Geology, Faculty of Science, Kafrelsheikh University, Egypt;3.Faculty of Geology, University of Warsaw, Poland;4.Institute of Archaeology, Wyszynski University in Warsaw, Poland
摘要:
利用埃及北部Faiyum盆地获得的高取芯率沉积物岩芯,进行沉积物多种磁性参数的测量,结合有机碳、介形虫、粒度等分析,在AMS14C加速器测年的基础上,建立全新世以来湖泊沉积物磁性特征变化的时间序列.结果表明,粒度效应以及沉积后的各种次生作用对沉积物的磁性特征没有明显的影响,磁性变化主要反映了沉积物不同来源组成的相对变化.全新世前沉积物磁性较弱,主要含不完全反铁磁性矿物,与周边沙漠的物质相似,结合其粒度特征,沉积物来源应以近源物质为主.全新世早中期(约105.4 ka BP)沉积物磁性变化相对稳定,有机质含量也较高,指示了来自尼罗河较为稳定的物质供应;而大约5.4 ka BP尤其最近约4.2 ka BP以来,磁性的明显变化反映了流域降水减少情况下,来自青尼河物质贡献的相对增加;最近约2.0 ka BP以来沉积物的磁性变化,则更多地与盆地人类活动的强化有关.总体而言,Faiyum盆地全新世以来的环境演变主要受控于全新世以来尼罗河与盆地的水力学联系.即:全新世前盆地未与尼罗河连通时,沉积物主要来源于周边沙漠的风成物质;而受全新世早-中期来流域季风降水增加的影响,泛滥的尼罗河为盆地提供了相对稳定的物质供应,湖泊也处于高湖面;全新世晚期以来,随着流域干旱化的加剧,尼罗河与盆地的连通性开始减弱,来自高磁性的青尼罗河物质贡献开始相对增加.最近约2.0 ka BP以来,虽然仍有人工运河连接尼罗河与盆地,但沉积物磁性的显著变化更多地反映了盆地人类活动的不断强化.
关键词:  Faiyum盆地  环境磁学  全新世  湖泊沉积  尼罗河
DOI:10.18307/2016.0625
分类号:
基金项目:国家自然科学基金项目(41272194)和波兰科学基金项目(DEC-2012/05/B/ST10/00558)联合资助.
Sediment magnetism of Faiyum basin (Egypt) and its implications for the Holocene environment change
JIANG Jun1, ALAA Salem2, LAI Xiaohe1, ZHANG Weiguo1, LESZEK Marks3, FABIAN Welc4, XU Lichen1, CHEN Jing1, CHEN Zhongyuan1, SUN Qianli1
1.State Key Laboratory of Estuary and Coastal Research, East China Normal University, Shanghai 200062, P. R. China;2.Department of Geology, Faculty of Science, Kafrelsheikh University, Egypt;3.Faculty of Geology, University of Warsaw, Poland;4.Institute of Archaeology, Wyszynski University in Warsaw, Poland
Abstract:
Sediment magnetism, integrated with organic carbon, grain-size and ostracods analyses were conducted on a sediment core (FA-1) retrieved from Faiyum basin, north Egypt. The time sequences of sediment magnetism were established on the AMS14C-dated chronology. The result showed that grain-size and secondary alternation had minor effects on the characteristics of the sediment magnetism, and changes in sediment magnetism basically reflected the relative proportion of different sources contributing to the basin. Prior to the Holocene, weak sediment magnetism featured by incomplete antiferro magnetic minerals, together with the grain-size distribution similar to the surrounding desert deposits, indicating an aeolianorigin. The sediment magnetism kept relatively stable with high organic content during the early-to-middle Holocene at ca. 10-5.4 ka BP, suggesting the stable material inputs to the basin from the Nile. The last ca. 5.4 ka BP especially since the last ca. 4.2 ka BP, evident variations in sediment magnetism indicated the increasing contribution of material from the Blue Nile when rainfall declined in the Nile catchment.Of note, the change of sediment magnetism since the last ca. 2.0 ka BP largely exhibited the intensified human involves.Briefly, the environment settings of Faiyum basin since the Holocene were controlled by the hydrological linkage between the basin and the Nile.The sediment was primarily of Aeolianorigin when no hydrological connection occurred between the basin and the Nile prior to the Holocene.During the early-to-middle Holocene (ca.10-5.4 ka BP), the sediment source in the lake basin was mainly of fluvial origin when the Nile drained into the basin, largely driven by intensified monsoon activities in the Africa.With weakening hydrological linkage with the Nilein the late Holocene from declining monsoon rainfall, the basin was fed by relatively more magnetic materials from the Blue Nile.The rapid increase in sediment magnetism in the last ca. 2.0 ka BP had recorded the accelerated basin soil erosion by increasing human activities such as reclamation and farming rather than natural forcing.
Key words:  Faiyum basin  sediment magnetism  the Holocene  lacustrine sediment  the Nile
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