南海北部双峰南陆坡区的构造层序及沉积充填过程

利用高分辨率二维地震反射剖面及钻井资料,对南海北部双峰南陆坡区的构造层序及沉积充填特征进行了研究。根据地震不整合界面、构造发育特征及地层组合情况,将研究区地层从下至上划分为下、中、上三个构造层序。研究分析表明,构造活动、海盆扩张、相对海平面变化、火山活动及物源供给等因素在不同阶段因时而异地共同控制着各构造层序的沉积充填过程及演化。下构造层(Tg-T6)形成于一系列的半地堑结构断陷盆地,在湖泊相的沉积环境下,沉积体系受同沉积断裂控制明显,发育了冲积扇-扇三角洲-半深湖相沉积;中构造层(T6-T4)形成于西北次海盆扩张沉降构造背景,在陆坡缓慢沉降和火山喷发的双重影响下,造就了陆坡区特殊的几何形态结构,影响着沉积体系的发育,陆坡区中上部为浅海陆架边缘三角洲沉积,在陆坡区则以斜坡扇等相关沉积为主;上构造层(T4-T0)形成于相对海平面总体上升、西北次海盆由缓慢进入相对快速的沉降阶段,沉积作用受控于物质供应充分程度和深水作用,发育了以深水水道和滑塌体为沉积特征的深水沉积体系。

TECTONIC SEQUENCE AND ITS SEDIMENTARY FILLING PROCESS OF THE SHUANGFENGNAN SLOPE IN NORTHERN SOUTH CHINA SEA

Based on high-resolution seismic profile and well logging data, tectonic sequence and its depositional characteristics of the ShuangFengNan slope in northern South China Sea was studied. The stratigraphy sequence can be divided into three tectonic sequences:upper tectonic sequence、middle tectonic sequence and lower tectonic sequence in studied areas, according to the seismic reflect unconformity、the structural development characteristics and the stratigraphic assemblage characteristics. The results show that the factors, such as tectonism、spreading of the basin、changing of relative sea level、volcanic activity、provenance supply et al., controlled the sedimentary filling process and its evolution of the each tectonic sequence commonly in different stages. The lower tectonic sequence(Tg-T6) deposited in the lacustrine sedimentary environment, the depositional system was dominated by the major syndepositional faults obviously, it has developed the depositional systems of alluvial fan-fan delta-semi-deep lake mainly; The middle tectonic sequence(T6-T4) deposited under the tectonic background of the slow subsidence stage of the northwest sub-basin, under the influence of the slope subsidence and the eruption of the volcano, it created a special slope geometry structure, which were the main controlling factors for the developing of the depositional systems. it has developed the depositional system of the shelf-margin delta in up-midland, deepwater slope fan and related depositional system in the studied slope area. The upper tectonic sequence (T4-T0) deposited under the background of the relative sea level rising and the rapid subsidence stage of the northwest sub-basin. The sedimentation was mainly controlled by the supply of source and the deep-water deposition, it has developed the deep water depositional which characterized by the deepwater channel and the slump body.