Estimation of eroded overburden and its tectonic significance of the third Member of Shahejie Formation in extreme southwest Jiyang Depression

Key words:  Jiyang Depression  the third Member of Shahejie Formation  eroded overburden estimation  stratigraphical paleo-thickness  depocenter

Abstract:

Using the physical geography and drilling well data, the eroded and original overbudens during the third Member of Shahejie Formation (Es₃) in extreme southwest Jiyang Depression were estimated with a series of methods such as stratigraphic correlation, porosity fitting and the principle and methods of basin modeling. The tectonic subsidence and the extension coefficient were then calculated, and the character of sedimentation and its main controlling factor were discussed. The results are as follows. First, the depocenter is NE-SW trending as a whole, but is locally nearly south-north trending during Es₃ stage in the extreme southwest Jiyang Depression. Second, the extensional level is not uniform:the center is stronger and it weakens toward northwest and southeast. The extension is controlled by NW-SE trending stress field in general, and by south-north trending locally resulting from the slip of the basement faults. Lastly, the spatial distribution of the depocenter in Jiyang Depression has gone through the progressive development from east-west trending in the early stage, the coexistence of nearby east-west and north-east trending in the middle stage, and north-east trending finally during Es₃ stage. The whole system is however controlled mainly by NW-SE trending extensional stress field.