缅甸Twintaung玛珥湖碳酸盐年纹层及100年来微区原位元素分析  

Carbonate varves and minor element variations during the past 100 years in Maar Lake Twintaung, Myanmar

作　　者：孙青[1] 单雅冰 SEIN Kyaing 苏有亮[3] 朱庆增[3] 旺罗[3] 孙继敏[3] 顾兆炎[3] 储国强[3] 

机构地区：[1]国家地质实验测试中心,北京100037 [2]Myanmar Geosciences Society,Yangon,Myanmar [3]中国科学院地质与地球物理研究所,新生代地质与环境重点实验室,北京100029

出　　处：《科学通报》2015年第11期1038-1047,共10页Chinese Science Bulletin

基　　金：国家自然科学基金(41371219,41272198);中国科学院战略性先导科技专项(XDB03020000)资助

摘　　要：报道了缅甸蒙育瓦地区发现的5个玛珥湖,通过对这些玛珥湖的纹层研究,发现深度最大的Twintaung玛珥湖发育了碳酸盐年纹层,纹层层偶由厚度约为50～400？m的碳酸盐微层以及厚度100～600μm的碎屑-有机质层组成,其中碳酸盐微层是鉴定年纹层的重要标志.Twintaung玛珥湖年纹层的形成与缅甸蒙育瓦地区特殊的气候环境密切相关,每年12～4月为“干-热季”,降水少、蒸发高、湖水过饱和,导致方解石微晶生成;同时,每年干旱季节也是蓝藻Spirulina的繁盛时期,藻类繁盛需要消耗大量的CO_2,也促使碳酸盐生成.5～11月为“湿-热季”,降水较多,形成碎屑、有机质混合层.独立的核素测年（137Cs,210Pb）数据与纹层计数基本一致,证明了纹层的年季特征.为了理解元素指标的气候意义,我们运用同步辐射原位分析方法获得高分辨率元素数据,并与气象观测记录对比.通过主成分分析及与气象记录的对比,认为第一主成分主要包括岩石成因的元素（K,Ti,Fe,Cu,Zn,Rb和Zr等）,可能主要与物理化学风化作用、降水以及粉尘输入有关,影响因素复杂;第二主成分主要包括元素Ca和Sr,主要赋存于碳酸盐颗粒中,可能主要与蒸发-降水关联.气候干旱时期,湖水中Ca离子呈过饱和,促使碳酸盐沉淀.缅甸Twintaung玛珥湖碳酸盐年纹层沉积中Ca元素可能是高分辨率古气候变化研究的重要替代指标.We report on maar lakes and lacustrine carbonate varves in Myanmar. Carbonate varves are well developed in maar lake Twin Taung, the deepest of five maar lakes in Myanmar. Lamination consists of light and brown-colored laminate couplets in thin sections. A light- colored layer is composed mainly of calcite crystals with thickness 50-400 μm, and a dark-colored layer consists of other organic and siliceous matter. Climatic conditions in the study region are determined by the Indian monsoon and have a pronounced rainfall seasonality. The dry and hot season is between December and April, and warm and humid conditions prevail in summer and autumn. These characteristics are key to varve formation. In the dry and hot season, calcite crystals form with less precipitation and strong evaporation, whereas clastic and organic matter are deposited during the warm and humid season. An independent chronology derived from 137Cs and 21~pb shows good agreement with counted laminations. To compare with instrumental data, synchrotron radiation X-ray fluorescence measurement was used for extracting minor element datasets with high resolution. Based on principal component analysis and comparison between elemental variation and regional rainfall data, we interpret the elemental data in terms of climate variables such as precipitation and temperature. The first component includes lithogenic elements such as K, Ti, Fe, Cu, Zn, Rb and Zr, and might be controlled by various factors such as physical and chemical weathering processes, rainfall, and dust input. The second component, calcium and strontium, might be principally regulated by the balance between evaporation and precipitation. During drought periods, the calcium ion might supersaturate, causing carbonate calcite precipitation from the water column. Our preliminary result suggests that elements Ca and Sr in the annually laminated sediment might be useful indicators for studying paleoclimatic change at high resolution.

关 键 词：玛珥湖 碳酸盐年纹层 热带 同步辐射原位元素 分析 

分 类 号：P343.3[天文地球—水文科学] P532[天文地球—地球物理学]