琼东南盆地深水块体流构成及其沉积特征

Architecture and Characteristics of Mass Transport Deposits(MTDs) in Qiongdongnan Basin in Northern South China Sea

为了深化对琼东南盆地深水区沉积体系的认识,基于琼东南盆地深水区2D和3D地震资料,发现琼东南盆地深水区发育大量的块体流沉积.通过对块体流沉积进行精细刻画,识别出一些典型的块体流沉积特征:滑移体、陆坡陡崖、搬运块体、残余块体、挤压脊、逆冲断层以及块体流顶部的滞留沉积等.陡倾陆坡上块体流以杂乱反射为特征,地层变形剧烈,而宽缓陆坡上块体流以发育地层变形微弱的滑移体为特征,反映出陆坡角度对于块体流发育及其内部结构特征有明显的控制作用.大规模块体流沉积作为深海沉积的重要组成部分,对于深海沉积物的空间展布具有重要的控制作用:一方面,通过不规则顶面影响随后沉积物的输送通道和沉积体的内部结构;另一方面,对已沉积的地层产生直接的侵蚀作用,破坏原始沉积地层的内部结构,造成潜在储层中地质流体的逸散.因此,鉴于块体流对深水沉积体系重要的影响,有必要加强对块体流沉积的精细研究,以更好地指导深水油气勘探.

In order to understand the deepwater depositional system in Qiongdongnan basin better, this study interprets the deepwater depositional architectures based on the regional 2D and 3D seismic data and it is found that large-scale MTDs are well developed in Qiongdongnan basin. According to the detailed study on MTDs, typical elements have been identified such as slide, escarpment, transported blocks, remnant blocks, compression ridge, thrust fault and ponded depositon on the irregular top surface. The MTDs on the slope with steep angles are characterized by chaotic seismic facies with tense deformation, while those on the gentle-angle slope are characterized by the slide with less deformation, which indicates that the angle of the slope has obvious control effect on the development and internal architecture features of MTDs. Being regarded as an important part of deepwater deposition, MTDs have an important effect on the spatial distribution of sediment in deepwater. On the one hand, the irregular top surface of MTDs affects the distribution and internal architecture of succedent sediments; on the other hand, MTDs erodes the former strata directly and wrecks the internal structure of former strata. And also, the erosion can give rise to effusion of the fluid in potential reservoir. Hence, according to its important role in deepwater deposition system, it is necessary to further the elaborate study on the MTDs to make the deepwater exploration more efficiently.