裂陷盆地洼槽演化规律研究——以歧口凹陷西部为例

Sag evolution in muti-phase rifts: Case study on the Paleogene of Qikou Depression

裂陷盆地中洼槽的演化规律对疑灶的分布及生绘能力具有明显控制作用。歧口凹陷在古近纪经历了两期两向的裂陷活动,洼槽结构较为复杂,裂陷I幕,在N W-SE向伸展作用下,形成了多个NE-NNE向洼槽;至裂陷U幕,受N・S向伸展作用,NE-NNE向断层活动性逐渐减弱,NE-NNE向洼槽开始萎缩。本文基于控洼断层的空间组合样式及传播方式、洼槽内层序界面的接触关系,建立洼槽演化的3种模式;结合典型地震剖面、地层厚度图、控洼断层断距一距离曲线等相关证据,识别出歧口凹陷洼槽的演化规律。其中,歧南洼槽属于“生长连接型洼槽演化模式”,板桥洼槽属于“固定长度型洼槽演化模式”,而歧北洼槽属于“侧列叠覆型洼槽演化模式”。

In multi-phase rift basin, the evolution of sag plays a significant role in controlling the distribution and hydrocarbon generation ability of source kitchens. Qikou Depression experienced two periods of rifting in the Paleogene, so sag structure is very complex. In rift Ⅰ phase, under the NW-SE extension, several NE?NNE sags were formed. In rift Ⅱ phase, the activity of NE-NNE fault was gradually weakened by the N-S extension, while the E-W orientation fault played a main role in the depression. In this paper, we established three models of the sag evolution, based on the spatial combination style and propagation mechanism of main fault, interpretation of seismic reflection terminations, then we used typical seismic profiles, formation thickness maps, throw-distance curves and other relevant evidence to identify the evolution of Qikou Depression. Results indicate that Qinan Sag belongs to the “sag evolution controlled by isolated fault model”, Banqiao Sag belongs to the “sag evolution controlled by coherent fault model”, and Qibei Sag belongs to the “sag evolution controlled by overlay fault model”.