南黄海盆地碳酸盐岩碳氧同位素特征及意义

Characteristics of carbon and oxygen isotopes of carbonate rocks in South Yellow Sea Basin and their implication

对南黄海盆地碳酸盐岩烃源岩(P1q-T1q)进行了碳氧同位素测定及孢粉相等分析,研究海相碳酸盐岩有效烃源岩的形成和控制因素。通过对样品δ13C与δ18O相关性等的分析,发现碳氧同位素组成基本保留了原始海洋的同位素组成。栖霞组δ13C相对青龙组偏重,预示着较高的生物生产力,更有利于烃源岩的发育。栖霞组δ13C以均值为基准可以划分为3个演化阶段,并与孢粉相的变化相对应,表明不同层段烃源岩发育具有差异性。WX5-ST1井青龙组δ13CPDB(均值3.83‰)明显比CZ24-1-1井(均值-1.34‰)的偏重,并与高无定形孢粉相相对应,表明同一层段不同区域烃源岩形成也具有差异性。对比碳氧同位素和孢粉相资料,发现生物生产力与保存条件有效的匹配是烃源岩发育的有利层段。

Based on the analyses of carbon and oxygen isotope composition and palynofacies of carbonate source rocks （Pl q-Tlq） from the South Yellow Sea Basin, the formation and controlling factors of effective source rocks of marine facies were studied. The correlation between δ13C and δ18O indicated that the carbon and oxygen car- bon isotope compositions were similar to those in original ocean. The δ13CpDB values in Plq were heavier than those in Tl q, indicating for higher biological productivity, which was favorable for source rock generation. Based on mean value, the δ13CPDB values of Plq were divided into 3 evolution stages corresponding to the changes of pa- lynofacies, indicating that the formation of source rocks varied among different layers. The δ13CpDB values in Plq from well WX5-ST1 were 3.83‰ in average, obviously heavier than those from well CZ24-1 - 1 （ - 1.34%v in average）. It corresponded to the high content of amorphous organic matter, and proved the differences of source rock formation among different regions in the same layer. The comparison of carbon and oxygen isotopes and pa- lynofacies showed that the effective matching of biological for source rock formation. productivity and preservation condition was favorable for source rock formation.