Ca/Mg比值对古环境的指示意义及其影响因素

Indicative Significance of Ca/Mg Ratio to Paleoenvironment and Its Influencing Factors

Ca/Mg比值作为古环境的判断指标已经得到广泛应用,但是由于其影响因素的多样性,导致其揭示的古气候意义还无法统一。本研究通过对济阳坳陷东营凹陷的坨712井、博16井、辛15井、梁28井、樊128井、樊31井的样品进行Ca、Mg元素的EDTA容量法分析,得出Ca/Mg比值对古环境的盐度、酸碱度具有指示作用,Ca/Mg比值与盐度和酸碱度均呈正相关,并分析了其影响因素;同时提出利用Ca/Mg比值进行相关研究时出现数值交叉或与所规定指标不相符的可能原因:(1)同一地区,同一时期的岩石,岩性发生了变化;(2)同一地区,相同岩性的岩石,不在同一层位;(3)同一地区,同一岩性的岩石,其母岩的来源不同。该研究为今后运用Ca/Mg比值恢复古环境和进行沉积相划分等研究工作提供了依据和参考。

Ca/Mg ratio has been widely used as a judgment index for the paleoenvironment. However, because of the diversity of its influencing factors, its paleoclimatic significance can not be unified. In this paper, samples from the wells of Tuo712, Bo16, Xin15. Liang28, Fan128, and Fan31 in Dongying sag of Jiyang depression were processed and analyzed by using EDTA volumetric method. The indicative function of Ca/Mg ratio on the salinity,acid-alkaline degree of paleoenvironment was obtained,indicating that there was a positive correlation between Ca/Mg ratio and salinity and acid-alkaline degree. The influence factors of Ca/Mg ratio were also analyzed. Possible reasons for the inconsistency between numerical cross and stipulated indexes Ca/Mg ratio was used for related researches were put forward as follows：the change of lithology of rocks in the same area during the same period,the different positions of rocks with the same lithology in the same area,and the different sources of parent rocks with the same lithology and of the same region. The research provides reference for further research of restoring the paleoenvironment and classi- fying sedimentary facies.