赣北黄茅潭近代湖泊^(137)Cs蓄积特点、SCP计数和事件性沉积及其对^(210)Pb计年的矫正  

^(137)CS BUILDUP, DATING, AND TUNING FOR THE RECENT LAKE SEDIMENT IN HUANGMAOTAN LAKE, JIANGXI, SOUTH CHINA

作　　者：冷雪 吴霜 王昕梅 陈莎 朱笑虹 蒋梅鑫[1] 贾玉连[1,2] 李晓峰[1] 缪君翔 王野乔 LENG Xue WU Shuang WANG Xin-Mei JIA Yu-Lian LI Xiao-Feng CHEN Sha ZHU Xiao-Hong JIANG Mei-Xin MIAO Jun-Xiang WANG Ye-Qiao(School of Environment and Geography, Jiangxi Normal University, Nanchang 330022, China Ministry of Education Key Laboratory of Poyang Lake Wetland and Watershed Research, Nanchang 330022, China)

机构地区：[1]江西师范大学地理与环境学院,南昌330022 [2]鄱阳湖湿地与流域研究教育部重点实验室,南昌330022

出　　处：《海洋与湖沼》2017年第5期944-951,共8页Oceanologia Et Limnologia Sinica

基　　金：江西省重大生态安全问题监控协同创新中心项目;JXS-EW-00号;国家自然科学基金项目;41262007号;鄱阳湖湿地与流域研究教育部重点实验室(江西师范大学)开放基金资助项目;ZK2013003号

摘　　要：对赣北黄茅潭近代湖泊沉积岩芯进行了^(137)Cs、^(210)Pb测试和SCP(球状碳粒)计数分析,阐述了^(137)Cs蓄积特征,结合SCP计数、粒度指标及降水记录厘定了一些事件性沉积层位。研究表明,1986年前后是沉积环境中^(137)Cs行为的转折点;在这之前,^(137)Cs以大气散落为主,其蓄积行为大致与降水存在正相关关系,在这之后,^(137)Cs以流域侵蚀为主,其蓄积行为与降水呈负相关关系。1953—1954年、1974—1975年、1998—1999年,流域降水丰沛,相应沉积层位^(137)Cs比活度低,这与流域强烈侵蚀稀释了进入湖泊的^(137)Cs有关。1963—1964年沉积层位^(137)Cs蓄积峰稳定而显著,与高通量的大气散落有关,也与当时降水量低,大雨、暴雨次数少,流域侵蚀强度低造成较低的沉积速率等密切相关,是可靠的定年时标。1986年存在同样的气候环境特点,其蓄积峰可能也是存在的,但需要进一步确认。基于^(210)Pb方法,利用多种计年模式计算了沉积岩芯的年代,发现与这些事件性沉积层位具有较大差异。研究认为,在长江中游这种降水高、流域侵蚀强度高的较为复杂的沉积环境中,^(210)Pb计年存在较大误差。复杂沉积环境中近代沉积的定年,有必要深度挖掘^(137)Cs环境行为,在全面阐述其蓄积特点的基础上,辅以SCP计数、粒度指标及降水等识别事件性沉积层位,矫正^(210)Pb计年,是精确建立近代沉积时标的必要方法。Profiles of ^（210）Pb and ^（137）Cs of two cores drilled from Huangmaotan Lake were rebuilt, and were compared and adjusted against those of SCP（spheroidal carbonaceous particle） counting, and grain size records. The lake is situated in North Jiangxi, China along the middle reach of the Changjiang（Yangtze） River, 5.1km^2 in full-water area, and 7.7km^2 in catchment area. The basements of the catchment area are composed of Triassic-Cretaceous-Tertiary muddy sandstones and conglomerates mostly in continental facies. The two cores, HMT-1 and HMT-3, were taken in center of the lake, 100 m apart, with a Dutch-made Beeker corer, 6cm cross, and 80 cm long. Several sedimentary events in 1953—1954, 1963—1964, 1974—1975, 1998—1999, respectively, were determined based on correlation of above-mentioned records to the annual rainfall and the annual days of heavy rain during 1952—2012. The age control for Core HMT-1 was reconstructed, which is largely different from sedimentary chronology of ^（210）Pb. We believe that this discrepancy was mainly resulted from ^（210）Pb dating. As the sedimentary environment in the middle reaches of Changjiang River is complicated as revealed in the Huangmaotan Lake, an event horizon settled from large flood could cause errors in ^（210）Pb dating. In addition, we found that year 1986 is the turning point of ^（137）Cs environmental activity in sediment of the Changjiang River catchment. Before 1986, correlation between rainfall and ^（137）Cs concentrations was overall positive, which is mainly due to atmospheric deposition during 1952—1986; and after 1986, it became overall negative during 1986—2010 as the hosting sediments were derived mostly from the river catchment areas. A typical peak of ^（137）Cs activity in 1963—1964 was found related to high atmospheric fallout and to low sedimentation due to small rainfall and less flooding. Therefore, the ^（137）Cs peak of 1963—1964 can be used as a reliable time maker horizon for recent sediments in

关 键 词：黄茅潭 江西 蓄积特点 137Cs 210Pb SCP(球状碳粒)计数 事件性沉积层位 

分 类 号：P736.4[天文地球—海洋地质]