热带玛珥湖沉积物的磁组构特征及对湖水动力条件的指示  

MAGNETIC FABRICS OF MAAR LAKE SEDIMENTS IN TROPICAL SOUTHERN CHINA RECORD HYDRODYNAMIC PROCESS

作　　者：杨小强[1,2] 苏志华[1] 阳杰[3] 黄文娅[1] 

机构地区：[1]中山大学地球科学系,广州510275 [2]中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安710075 [3]国家海洋局南海环境监测中心,广州510300

出　　处：《第四纪研究》2012年第4期795-802,共8页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41072264);中央高校基本科研业务费专项资金项目(批准号:3161316);中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金项目(批准号:SKLLQG1016)共同资助

摘　　要：热带玛珥湖湖水动力条件的变化,是反映区域有效降雨量的重要指标,为探测有效降雨的时空分布特征及其机制提供了良好的基础素材。对位于雷琼半岛的双池岭和湖光岩两个玛珥湖进行沉积物磁组构的分析,结果表明尽管湖泊沉积物磁面理发育、磁线理值很小,玛珥湖的水动力条件比较微弱,但各向异性度P和水流速度函数Fs呈现向上递减的长期趋势,与湖泊草本植物孢粉含量向上增加、有机碳含量减低、沉积物颜色从黑褐色向青灰色过渡的特征一致,反映了大约9cal.kaB.P.以来,华南区域有效降雨最逐渐增加、湖水平面上升的过程。这种变化的机理可能是当夏季风减弱时,热带辐合带(ITCZ)南移、ENSO活动加强的结果。Regional net precipitation variations may be evaluated using the hydrodynamic conditions and the fluctuations of the tropical maar lake level. In this paper, the magnetic fabric of sediments from two maar lakes, Shuangchiling （19°56.6＇N,110°ll.4＇E）and Huguangyan（21°09＇N,110°17＇E）in tropical Southern China was studied to show the hydrodynamic variations of lakes since 9cal. kaB. P. The composite sediment profile ca. 16m in length of Shuangchiling lake was compiled from a 16m-long core and a 8m deep well, and the profile ca. 5m in length of Huguangyan Lake was obtained from three Livingstone piston cores collected in ca. 10m water depth. Cubic plastic boxes（ 1.9×l. 9×l. 9cm3） were continuously sampled at ca. 2cm intervals on two profiles to measure the anisotropy of magnetic susceptibility. The radio-carbon chronology of the Huguangyan profile was adjusted to the time scale of the Shuangchiling profile based on the paleosecular variation correlation between two lakes. The results show that the magnetic fabric properties of two lakes have the similar pattern and the consistent driving force. The minimum susceptibility axes（Kmi.） are close to the vertical, perpendicular to the bedding plane, and tightly grouped,whereas the inclinations of the maximum axes（Kin,x） are very shallow,indicating an original sedimentary magnetic fabric that has been undisturbed since deposition in weak hydrodynamic condition. The values of the anisotropy degree of susceptibility（P）of two lakes are all less than 1.08 （with a mean value 1.023 in Shuangchiling Lake and 1. 012 in Huguangyan Lake,respectively）, and show a long-term up-section decreasing trend with three significant sub-stages in the intervals 9. 0 - 5.6cal. kaB. P. ,5.6 - 2. 5cal. kaB. P. and posterior to 2. 5cal. kaB. P. respectively, which agrees well with the oxygen isotope variations of the stalagmite and ENSO activities in the tropical area. This behavior, coupled with the increasing Non-AP（ arboreal pollen）fraction ,fining grai

关 键 词：玛珥湖 磁组构 有效降雨量 全新世 

分 类 号：I318.41[文学—其他各国文学] P941.78[天文地球—自然地理学]