再论东濮凹陷沙三段成盐模式

Revisiting salt-forming models in the third member of Shahejie Formation in Dongpu Depression

关键词:  东濮凹陷  沙三段  盐岩序列  氯同位素  盐岩成因

Key words:  Dongpu Depression  the third member of Shahejie Formation  salt rock sequence  Cl isotope  origin of salt rock

摘要:

依据井点X衍射矿物和氯同位素垂向分布资料,分析东濮凹陷盐岩垂向序列,并结合咸水蒸发实验和盐湖钻孔资料分析盐岩沉积及保存过程,研究东濮凹陷沙三段成盐模式。结果表明:浅水蒸发成盐过程中保持有足够的水深,为盐下有机质的保存提供便利,浅水盐岩与油页岩及黄铁矿伴生不矛盾;淡水的注入是影响垂向盐韵律组成的关键因素,注入量少时可能引起氯同位素的变化,随着注入量的增大可能引起盐韵律中氯化物乃至硫化物的缺失;凹陷满盆含砂、控边断层上盘缺少粗碎屑的现象可能是边界断层长期小规模活动造成的,东濮凹陷沙三段盐岩更有可能是浅水蒸发成因。

Abstract:

Based on mineral X diffraction and the vertical distribution of chlorine isotopes, vertical sequences in Dongpu Depression and deposition and preservation processes of salt rock were analyzed combining the experiments of saline water evaporation and the salt lake drill data. The salt-forming models in Dongpu Depression from the deep-rooted mechanism were developed. Results suggest that,organic preservation may be facilitated with sufficient water depth during evaporation of salt-forming process in shallow water. Salt rock in shadow water may form with oil shale and pyrite. The volume of injected freshwater is the main factor to affect the vertical salt rhythmic deposition:it may cause the Cl isotope to vary when the injection is small, but with rising volume, chloride even sulfide may become deficient. The sandstone in Dongpu depression and the deficiency of coarse clastic in the hanging wall were caused by activities in bordered fault at small scales. Salt-forming in shadow water is most likely responsible for salt rock in the third member of Shahejie Formation.