民丰洼陷断层活动性及其对层序的控制作用

Fault Activities and Their Controls on Depositional Sequences in Minfeng Sub-Sag

民丰洼陷发育了两套断裂体系:北部的陈南断层和中部的民丰断裂带。首先通过地层去压实校正使地层厚度恢复到沉积时期的厚度,然后根据地层古厚度计算出陈南断层和民丰主断层不同时期的落差和生长指数。研究表明,陈南断层在沙三段沉积早、中期活动强烈,到沙三段沉积晚期、沙二段沉积期活动性降低;而民丰主断层在沙三段沉积早、中期还未形成,到沙三段沉积晚期开始形成。由于两条断层活动的差异性,民丰洼陷沙三段下、沙三段中地层厚度北厚南薄,呈楔状;沙三段上、沙二段地层厚度北薄南厚,呈反楔状。地层厚度的变化特征表明,断层的活动性控制了该区层序的发育。

Two sets of fault systems are found in Minfeng sub-sag. One is Chennan fault in the north, and the other is Minfeng fault belt in the middle. This paper studies these two faults by covering their original depositional thickness from formation de-compaction correction, followed by calculating the fault throw and the growth index of these two faults in different periods. The study shows the faults activities： for Chennan fault, it was active strongly from the early Es3 to the middle Es3, and active lightly from the late Es3 to the Es2; for Minfeng fault, it was not formed during the early and middle Es3 until the late Es3. Such differences of the fault activity resulted in strata thickness of the lower and middle Es3 in Minfeng sub-sag assuming wedge shape with the thick in the north and the thin in the south, while the upper Es3 to the Es2 assuming thin in north and thick in south. These features indicate it is the faults activities that control the development of depositional sequence in this area.