云南梅树村剖面磷块岩底部过渡层碳、氧同位素研究

The Study of Carbon and Oxygen Isotopes from Transitional Beds at the Bottom of Phosphorites in Meishueun Section, Yunnan

摘要:

为了解梅树村剖面中谊村段底部白云质磷块岩与下伏小歪头山段含磷白云岩接触界面上下沉积环境及其演变,过去曾从宏观地质特征、岩石化学成分、微量元素、重砂矿物及生物化石等方面进行过综合研究。其成果表明,两岩性段界面上下呈渐变过渡关系,其沉积环境由潮间相向潮间—潮下高能相过渡。由于界面上下均为高能环境,二者间有时出现水下冲刷现象(罗惠麟等1982.1984)。本文试图通过碳、氧稳定同位素研究,获得更多信息。

Abstract:

Based on the study of the characteristics of stable isotopes of carbon and oxygen from dolomite in phosphatic dolostone and dolomitic phosphorite samples successively collected from the strata above or below the boundary between the Xiaowaitoushan and Zhongyicun members in Meishucun section, the δ¹³C values have been determined within the range from -1.65 to -2.42‰, indicating that the rocks are ascribed to marine sedimentary carbonate rocks. The increasing tendency of δ¹²C values for the samples from bottom to top shows that there is a conformable gradational contact between the two lithologic members, in general agreement with the results on the study of petrology, petrography and palaeontology of Meishucun section made by the previous workers. The δ¹⁸ O values range between -7.08 and -7.67‰, similar to the average δ¹⁸O values of seven Cambrian dolomite samples (-7.9‰) determined by Veizer and Hoets (1976), thus providing another evidence for the determination of the stratigraphic ages for the boundary of Meishucun section.