17 / 2021-11-28 08:54:55

珠江口盆地西江凹陷裂陷期构造转换及其对沉积的意义

珠江口盆地；西江凹陷；古近纪；珠琼运动；区域应力；构造转换

研究表明珠江口盆地珠一坳陷在早始新世-早渐新世的裂陷期主要经历了珠琼运动Ⅰ幕和Ⅱ幕，发育文昌组和恩平组地层。西江凹陷位于珠一坳陷中部，凹陷内划分出西部西江主洼、东部西江36洼和番禺4洼3个次级洼陷。本文利用最新三维地震数据和解释成果，并结合有限钻井，对西江凹陷文昌组和恩平组的断裂活动、构造演化及沉积迁移等进行了系统分析。结果表明西江凹陷文昌组-恩平组沉积时期的构造转换表现为：1）控洼断裂走向为NE、NEE，后期开始发育近EW向断层；2）西江凹陷各次洼裂陷期以顺时针旋转的方式逐渐扩张；3）早文昌期各洼陷沉降中心偏北东，晚文昌期向南西迁移，东部两洼陷在早文昌期为统一湖盆；4）恩平期各次洼彼此相连，沉降中心继续向南西迁移，沉积地层西厚东薄；5）地震沉积相分布特征说明裂陷期的构造转换控制了沉积体系的迁移。断体系、洼陷结构及沉降中心的转换是区域构造运动的产物，是区域构造转换的响应。本文研究认为西江凹陷裂陷期的一系列构造转换是由于区域构造应力发生顺时针旋转造成的，区域应力由早文昌期的NW-SE向转为晚文昌期的NNW-SSE向，经历珠琼运动Ⅱ幕，在恩平期转为S-N向。番禺4洼是已证实的含油气洼陷，西江主洼和西江36洼勘探程度较低，本次研究关于断裂活动、构造演化和沉积迁移规律的认识对西江凹陷的勘探工作具有积极意义。

The study shows that the Zhuyi depression in the Pearl River Mouth Basin experienced acts I and II of zhuqiong Movement during the early Eocene-Early Oligocene rift, and developed the Wenchang Formation and Enping Formation strata. Xijiang depression is located in the central part of Zhuyi depression, which can be divided into three sub-sags: Xijiang Main Sub-sag in the west, Xijiang-36 Sub-sag and Panyu-4 Sub-sag in the east. Using the latest 3D seismic data and interpretation results, combined with limited drilling, this paper systematically analyzes the fault activity, tectonic evolution and sedimentary migration of the Wenchang and Enping formations in the Xijiang depression. The results show that the tectonic transformation of Wenchang and Enping Formations in Xijiang depression is as follows: 1) The depression-controlling fault strikes NE and NEE, and near EW-trending faults began to develop in the later period; 2) The Sub-sags in Xijiang depression gradually expand in clockwise rotation during the rifting period; 3) The subsidence centers of the sub-sags in the early Wenchang period were northeastward, and migrated to the southwest in the late Wenchang period, and the two eastern sags were unified lake basins in the early Wenchang period; During the Enping period, the sub-sags were connected to each other, the subsidence center continued to move to the southwest, and the sedimentary strata were thick in the west and thin in the east. 5) The distribution characteristics of seismic sedimentary facies indicate that the tectonic transformation during the rifting period controlled the migration of the sedimentary system. The transformation of fault system, sag structure and subsidence center is the product of regional tectonic movement and the response of regional tectonic transformation. In this paper, it is believed that a series of tectonic transformations during the rifting period of the Xijiang sag were caused by the clockwise rotation of regional tectonic stress, The regional stress changed from the NW-SE trend in the early Wenchang period to the NNW-SSE trend in the late Wenchang period, going through Act II of the Zhuqiong Movement, it was S-N during the Enping period. Panyu-4 Sub-sag is a proven hydrocarbon-bearing sag. The Xijiang Main Sub-sag and Xijiang-36 Sub-sag are relatively low in exploration. The understanding of fault activity, tectonic evolution and sedimentary migration in this study is of positive significance for the exploration of the Xijiang depression.