色度学方法的深时研究:以藏南贡扎剖面白垩系赛诺曼/土仑阶为例

The deep-time research by chromatometry:An example from the Cenomanian to Turonian Stages of the Cretaceous,Gongza section,Southern Tibet

色度学方法在揭示未固结或半固结沉积物沉积时的古气候方面有着良好的应用,但成岩或成岩后演化对原岩成分的改造使得其在已成岩岩石中的应用还不多。文中以藏南定日贡扎剖面白垩系晚赛诺曼阶到早土仑阶的98件岩石样品为研究对象,应用色度学方法,并结合镜下观察和主量元素分析,得到以下的主要结论:(1)对样品的CIE1976L*a*b*色度空间分析显示,L*与a*的变化趋势呈镜像对称,通过快速傅里叶变换可识别出半周期分别为9.2m和1.8m的两个主周期;而L*与b*的变化趋势大致相同。(2)色度指标与主量元素的相关性分析表明,L*值与碳酸盐含量正向相关,b*值可能主要与Mn元素含量相关,L*和b*可以对古海洋化学条件做出一些制约;a*受粘土矿物含量制约,反映了古气候的变化。

Chromatic methods have been well used in paleoclimate research for unconsolidated or semi-consolidated sediments.However,few researches based on these methods have been reported from diagenetic rocks,since their primary compositions and colors may be altered in the process of diagenesis and post-diagenesis.Thus,the deep-time research by means of chromatometry is still open to question.Ninety-eight Cretaceous rock samples collected from the Gongza Section,Tingri,southern Tibet,were studied using chromatic methods,together with microscopic observations and major elements analysis.Main conclusions were drawn as follows.（1） In the CIE1976 L a b color space,the variation trends of L and a,with mirror symmetry,indicate two main semi-periods of 9.2 m and 1.8 m obtained by Fast Fourier Transformation;while L and b values show similar variation trends.（2） Correlation analysis between chromatic indices and major elements suggests that L value has a positive correlation with the content of carbonate,b value is mainly influenced by manganese content,and together they can put some constraints on the chemical change of paleo-ocean;whereas a value is largely controlled by the content of clay minerals,which reflects paleoclimatic changes.