东营凹陷沙河街组沉积岩碳氧同位素组成的古环境记录

Carbon and Oxygen Isotope Characteristics and Palaeoenvironmental Implications of Lacustrine Carbonate Rocks from the Shahejie Formation in the Dongying Sag

分析了东营凹陷沙河街组沉积碳酸盐的碳氧同位素组成,结果显示,东营凹陷沙河街组沉积碳酸盐δ13CPDB值介于-2.45‰～+6.44‰之间,平均值为+2.43‰;δ18OPDB值介于-13.98‰～-5.68‰之间,平均值为-9.47‰。δ13CPDB、δ18OPDB之间具有良好的正相关性,指示沙河街组沉积时期,东营凹陷为相对封闭的湖泊环境。在纵向上,沙三段沉积碳酸盐碳氧同位素发生了负漂移,具有最低的δ18OPDB和δ13CPDB,而沙二段沉积碳酸盐具有最高的δ18OPDB和δ13CPDB。东营凹陷古近系湖泊沉积碳酸盐碳氧同位素组成的变化是沉积环境综合作用的结果,指示了区域古气候条件由沙四期的干旱气候,向沙三期的湿润气候转变,至沙二期,气候又经历了短暂的干热阶段。东营凹陷沙河街期的沉积环境特征直接控制了各阶段发育的泥质岩类型及其沉积有机质特征。

This study presents the carbon and oxygen isotope compositions of carbonate rocks from the Paleocene Shahejie Formation （Es） in the Dongying Sag.The result showed that the δ^13CPDB of the studied samples ranges from-2.45‰ to ＋6.44‰,with an average of ＋2.43‰;and the δ^18OPDB of the studied samples ranges from-13.98‰ to-5.68‰,with an average of-9.47‰.The good correlation between δ^13CPDB and δ^18OPDB indicates that the samples were deposited in a closed lacustrine environment.The samples from the second member of the Shahejie Formation （Es2） have the highest δ^13CPDB and δ^18OPDB values,while those from the third member of the Shahejie Formation （Es3） have the lowest δ^13CPDB and δ^18OPDB values.The carbon and oxygen isotope characteristics of the Shahejie Formation recorded changes in sedimentary environment during deposition in the Dongying Sag,suggesting a dry climate prevailing during the period of Es4,then shifting to a wet climate in the period of Es3,and a relatively hot and dry climate in the period of Es2.The sedimentary environment plays an important control in the development of source rocks.