济阳坳陷下第三系颗石藻类化石的分布及与油气的关系

DISTRIBUTION OF PALEOGENE COCCOLITHOPHORIDS IN JIYANG DEPRESSION AND THEIR RELATIONSHIP WITH OIL AND GAS

系统研究了山东济阳坳陷下第三系颗石藻类化石的分布特征 ,发现该类化石平面分布广泛 ,在全坳陷的4个次级凹陷中均有分布 ,垂向上 ,主要分布在沙河街组一段和四段 ,含化石地层累积厚度近 10 0 m,颗石藻化石属种单一 ,主要为 Reticulofenestra bohaiensis,该类化石以零星和层状两种形式分布在钙质纹层页岩、泥岩和泥质白云岩中 ,通过与现代海洋沉积中颗石藻的分布特征相比较 ,得出济阳坳陷颗石藻化石纹层是藻类勃发的结果 ,该类勃发对于生油岩的形成起着重要的控制作用。另外 ,讨论了颗石藻与低熟原油生成的因果关系 ,并进一步在济阳坳陷进行了验证。

Coccolithophorids is widely distributed in the Paleogene sediments of Jiyang depression,Shandong Province.It was discovered in each subdepression of Jiyang depression which is made up of Dongying sag,Zhanhua sag,Chezhen sag and Huimin sag.In the stratigraphic column,it is mainly distributed in the first and fourth member of Shahejie Formation(Oligocene and Eocene respectively).The thickness of coccoliths bearing sequence can be up to 100 m. The coccolithophorids of Jiyang is characterized by its monospecies(only one species Reticulofenestra bohaiensis has been discovered).This species is very small,only 3～5μm.Most of them have a good preservation,but some are poorly preserved.Coccoliths may be scattered in the mudstone and dolomite,but they are preserved in the coccoliths laminae in the calcareous lamination shale. Comparing with the production and deposition processes of modern coccolithophorids in the ocean,we concluded that the coccoliths laminae are formed by algal blooms.As calcareous lamination shale is an important oil source rock,so algal blooms are a primary mechanism for the formation of oil source rocks. Geochemical analysis of coccoliths bearing oil source rocks demonstrated that these rocks have abundant organic matter and specific biomarker,and they may be contributed to the genesis of immature oil.In the paper,the relationship between the distribution of coccolithophorids and the immature oil has been discussed.