燕山地区中元古界碳酸盐岩碳、氧同位素特征及其环境意义

Carbon and Oxygen Isotope Characteristics and Its Environmental Significance of the Mesoproterozoic Carbonate Rocks in Yanshan Region

燕山地区中元古界高于庄组-雾迷山组主要为海相碳酸盐岩潮坪相沉积,按潮汐作用可划分为潮上带、潮间带和潮下带3个沉积相带。对研究区112件碳酸盐岩碳、氧同位素样品进行了测试和原始性验证,认为其原始组分保存良好。并根据地质统计学原理,探讨不同沉积相带碳、氧同位素的分布规律,结果表明:δ13C值变化范围为-2.2‰～1.6‰,均值为-0.1‰;δ18O值在-9‰～2.3‰之间变化,均值为-5.53‰。进一步对不同沉积相带主要分布区间进行统计,得出潮上带δ13C值为-1.5‰～-0.5‰,δ18O值为-6‰～-4‰,Z值(古盐度)为120～125;潮间带δ13C值为-0.5‰～1‰,δ18O值为-8‰～-4‰,Z值为123～127;潮下带δ13C值为0～1.5‰。分析认为:沉积环境从潮上带→潮间带→潮下带,δ13C值、Z值呈升高趋势,δ18O值呈降低趋势。δ13C值主要受有机碳氧化与有机碳的埋藏速率因素影响;δ18O值主要受海平面升降变化影响,与之呈负相关关系;Z值同时反映碳、氧同位素组成,且更受碳同位素的影响。

Mesoproterozoic Gaoyuzhuang-Wumishan Formation in Yanshan Region were mainly marine carbonate tidal-flat facies and could be divided into supratidal zone,intertidal zone and subtidal of three sedimentary facies according to the tidal effects.Through 112 pieces of samples of carbonate and oxygen isotope were tested and the original validation was carried out.It is considered that their original components are well-preserved.And in accordance with the principles of geostatistics,the distribution of the different sedimentary facies of carbon and oxygen isotope is studied.The results indicate that the δ13C value changes are between-2.2 ‰ and 1.6 ‰,and the average value is-0.1 ‰;the δ18O values are from-9 ‰ to 2.3 ‰,and the average value is-5.53 ‰.After statistics are further made on the main distribution law of different sedimentary facies,the result shows that the δ13C value is from-1.5 ‰ to-0.5 ‰,the δ18O value is from-6 ‰ to-4 ‰,and the Z value is from 120 to 125;the δ13C value is from-0.5 ‰ to 1 ‰,the δ18O value is from-8 ‰ to-4 ‰,and the Z value is from 123 to 127 in the intertidal zone;the δ13C value is from 0‰ to 1.5 ‰ in the subtidal zone.Analysis shows that the δ13C and Z value are tended to increase and the δ18O value decreases in the depositional environment which is from the supratidal zone-intertidal-subtidal zone.The δ13C value is mainly affected by oxidation of organic carbon and organic carbon burial rate factors;the δ18O value is mainly affected by the sea-level change which is negatively correlated with carbon isotope;the Z values reflect the carbon and oxygen isotopic composition,and are more affected by carbon isotope.