PRELIMINARY ANALYSES BY SIMS ON TRACE COMPONENTS OF STALAGMITE MICROLAYERS AND THEIR CLIMATE SIGNIFICANCE
石笋微层物质组成的二次离子质谱初步分析及其气候意义

Speleothems can be a valuable high-resolution record of terrestrial paleoclimate,especially for the larest 2 000 years. Research has tended to focus on characteristics of microlayers formed along the growing axes of stalagmites and can be identified under microscopes. It has been supported that the microlayers almost are annual layers by TIMS-U series, AMS 14C and other dating methods.Since 1994, we have obtained many stalagmites from the East China. All stalagmite samples were cut along the growth axes, then 1mm tO 0.1mm polished section were made and observed under microscopes. Most of the deposits, especially the stalagmites in North China, contain microlayers. Bi-optical microlayers of the samples of stalagmites from Water Cave and Shihua Cave can be observed under transmitted light and fluorescent respectively, and so called transmitted-light microlayers and luminescent microlayers. Range of thickness for transmitted-light microlayers is 101 to 102 μm. The layer mostly has a white part at the bottom and a dark part on the top. Generally, the brightness of microlayer decreases gradually from the bottom to the top, and change abruptly to next microlayer. The luminescent intensity increases gradually from the lower to the upper part, and changes to next layer abruptly. These two kinds of microlayers are usually on the same location of the section. However, sometimes the numbers of the two types of the microlayers in same section are different.It seems that their causes are not the same. Under the transmitted light, the non-trallsparent dark matter can reflect and refraCt the normal light so the bosAnttedw-light microlayers are observed. The dark matter includes OM (organicmatter) and clay detritUs. Under the excitahon of fluorescent light OM can becomeluminescent such as the humic / fulvic acid, so the luwhnescent microlayers are aPPearing. OM usually is non-tfapsparent but some organic moleculars, with small and simple stwtLlres, can be transparent. In shoyt words, the dark matter in transmitted-light microlayers are not completely the luminescent OM. Secondary ion mass spectrometry (SIMS) can help in situ analysis with high spahal resoluhon and high measurement precision. To understand the sedimentary mechanism of hi-ophcal ndcrolayers in stalagmites, and find some proxies for climatic signal, we analyzed the componentS of the whcrolayer by TFS-2000 LMIG/TOF SIMS.5 points from the bottom tO top of a ndcrolayer have been measured for sample TS9701. T'he resultS are reported as the ratios of several positive secondary ions tO .40Ca. We found that there are more 24Mg, 88Sr and small moleculars of OM (organic matter) in the light part of the microlayer than the dark pat. HOwever, 56Fe and 138Ba are a little higher relahve to lighter part. Based on our resultS, we expect that the light part of ndcrolayer was formed in summef, and the dark part was formed in winter. In summer, because of a heavy rainfall and high temperatllre, there is a maximum co