双断湖盆沉积特征及其控制因素研究——以孤北洼陷沙四上亚段为例

Sedimentary characteristics and its controlling factors of double-fault lacustrine basin:a case study of the upper 4th member of Shahejie formation in Gubei depression

为了探讨双断湖盆的沉积充填特征、控制因素及其与单断湖盆的差异,本文充分利用岩心、粒度、地震、测录井等资料,以孤北洼陷沙四上亚段沉积期为研究对象,以沙河街组构造演化分析为基础,对其进行了系统的研究.认为研究区沙河街组构造演化可分为4个期次:Ek-Esx4为隆起形成前期;Ess4为隆起初始形成期;Esx3为隆起完全形成期;Esz3至今为继承性发育期.主要发育扇三角洲、三角洲以及湖相,不发育大面积的滩坝沉积;扇三角洲位于洼陷短轴两侧的陡坡带;三角洲发育在长轴方向的缓坡带.研究结果表明:沉积体系展布主要受到两条边界断层的控制:活动强弱控制相类型;速率差异控制发育位置;古地貌控制延伸方向.相比于单断湖盆,双断湖盆沉积充填更为复杂,具有沉积相展布较为对称,长轴方向牵引流沉积占主导、相变慢,短轴方向重力流沉积比重加大,相变快的特点.

This article aims to discuss the sedimentary characteristics of double-fault lacustrine basin,its controlling factors,as well as the differences between double-fault and single-fault lacustrine basins.Making full use of the cores,granularity,seismic and logging data,based on the analysis of tectonic evolution of Shahejie formation,the Ess4 sedimentary period of Gubei depression was studied systematically in the paper.The tectonic evolution of Shahejie formation in the research area can be divided into four periods：Ek—Esx4,the period before uplift forming;Ess4,the period that uplift formed initially;Esx3,the period that uplift formed completely;Esz3—now,the period that uplift developed inheritedly.The research area develops three sedimentary facies including fan delta,delta and lake but no large area of beach and bar;the fan delta develops in the steep slope belt at both sides of short axis;the delta develops in the gentle slope belt at both sides of long axis.The results show that the distribution of sedimentary systems is mainly controlled by the activity of two boundary faults：the strength of the fault activity controls the sedimentary types;the differences of activity rate controls the development location;the ancient landform controls the extending direction.Compared with singlefault lacustrine basin,the sedimentary filling of double-fault lacustrine basin is more complicated.Its development of sedimentary facies is more symmetrical.The traction flow deposition dominates in the long axis direction with slow facies changes,while in the short axis direction the proportion of gravity flow deposition becomes larger with fast facies variation.