基于微区LIBS菊石化石中钙元素分布的研究

Study on the Distribution of Ca Elements in Ammonite Stones Based on Micro LIBS

化石的研究可帮助科学家了解生物的演化进程,并帮助地质学家确定地层年代等地质信息,其中不同年代地层地质元素的变化是地质研究的热门课题。为研究不同年代地层地质元素的变化,搭建了一套微区LIBS实验系统,研究菊石化石中Ca元素的分布情况。采用非对称最小二乘法去除光谱数据的基线,并确定了最优的拟合参数。采用平均值归一化算法以减小光谱强度的相对标准偏差,多元线性回归算法计算模型的回归方程。首先,通过前期实验确定微区LIBS实验系统的最佳测试参数:激光波长为1064nm,激光脉冲频率为30Hz,光谱仪采集延时为700ns。其次,选取12块经过定量标定的天然岩石样品,从中随机抽取9块样品(闪长岩、闪长玢岩、辉长辉绿岩、粗玄岩、碱长粗面岩、角闪闪长岩、黑色浮岩、斑状角闪石花岗岩、玄武玻璃)作为测试集,其余3块样品(辉石闪长岩、辉石岩、斜长花岗岩)作为预测集。选取CaⅡ393.186nm,CaⅠ422.856nm,CaⅠ445.572nm,CaⅡ559.031nm,CaⅠ616.61nm五个特征峰的谱线强度作为自变量,测试样品的实际Ca元素含量为因变量,利用多元线性回归算法建立Ca元素的定量分析模型,经预测集检验后得平均预测精度为92.9%。对表面经打磨的菊石化石进行5×5点阵扫描,得到一系列原子光谱数据。根据Ca元素的定量分析模型,计算后得到菊石化石Ca元素的横向分布图,其横向分辨率优于100μm。作为纵向对比,选取每个测试点的第6,11和16组光谱数据进行处理,分别得到Ca元素的横向分布图。对比可以得到菊石化石Ca元素的纵向分布情况,结果表明菊石化石在平面和空间内均呈现不均匀分布的状态,推测实验所选取的菊石化石在形成的过程中所处周围地层地质的元素及其含量是动态变化的。菊石化石不仅可以作为判定地层年代的证据,还可以通过对菊石化石的元素分布及含量的研究推测该化石所处地层的元素信息。研究工作对于浅海地层地质的演变、环境的变化具有一定指导意义。

The research on fossils can help scientists understand the biological evolution and judge the stratigraphic age. The change of geological elements in diffe rent ages is a popular topic in geological research. In order to study the changes of geological elements in different ages, we used Micro LIBS to study the element distribution in the ammonite stones. The asymmetric least squares method is used to remove the baseline of the spectral data, and we determine the optimal fitting parameters. The average normalization algorithm is used to reduce the relative standard deviation, and the multiple linear regression algorithm is used to calculate the regression equation of this model. First, the optimal expe rimental parameters were determined by preliminary experiments: the wavelength of laser is 1 064 nm, the frequency of laser pulse is 30 Hz, and the acquisitio n delay is 700 ns. Secondly, 12 pieces of rocks whose contents were already kno wn were selected, 9 samples were randomly extracted for testing, and the remaini ng 3 samples were for predicting. CaⅡ 393.186 nm, CaⅠ 422.856 nm, Ca Ⅰ 445.572 nm , CaⅡ 559.031 nm and CaⅠ 616.61 nm were selected to establish the quantit at ive analysis model of Ca element with a prediction accuracy of 92.9%. Then, a 5×5 area was scanned to get a series of atomic spectrum data. According to th e quantitative analysis model of Ca element, the lateral distribution map of Ca element can be got, and its horizontal resolution is better than 100μm. Finally, the 6th, 11th, and 16th spectra data of each test point were selected for pr ocessing to get a lateral distribution map of Ca elements. The longitudinal dist ribution of Ca element in ammonite stones can be got by comparison. The Ammonite can not only be used as evidence to judge the age of the bottom layer, but als o the elemental information of the bottom layer of the fossil can be inferred by studying the element distribution and content of Ammonite. This research ha s guiding significance for the evolution of the geology of shallow sea stratum a nd environmental changes.