琼东南盆地华光凹陷大型海底重力滑动系统特征及其成因机制

Characteristics and Genetic Mechanism of a Large-Scale Submarine Gravity-Driven System in Huaguang Depression,Qiongdongnan Basin

海底重力滑动系统研究对认识海底斜坡稳定性和深水沉积过程具有重要意义.南海北部琼东南盆地华光凹陷上中新统及其以上地层中发育一个大型的自南向北滑动的海底重力滑动系统.利用区域二维地震资料,查明了该大型海底重力滑动系统的地震相和发育特征,探讨了其可能的形成原因.该海底重力滑动系统由伸展域、过渡域、收缩域、滑动面和软弱层等5个要素构成;其发育演化可划分为晚中新世前重力滑动、上新世同重力滑动和第四纪后重力滑动等3个阶段:前重力滑动为物质准备阶段,水道复合体沉积于半深海泥质斜坡之上,为重力滑动提供物质基础;同重力滑动为重力滑动系统发育的主体阶段,沉积物披盖在强烈变形而产生的地形上,同时也发生一定程度的变形;后重力滑动为重力滑动系统萎缩阶段,沉积物逐渐将重力滑动产生的凸凹地形填平,并继续沉积.斜坡地形和高沉积物供给是海底重力滑动系统发育的基础;基底断层活化和底辟作用可能是触发其发育的动力源.

The study on submarine gravity-driven system(SGDS) is of great significance to understand the stability of submarine slope and the deep-water sedimentary processes. A large-scale SGDS sliding from south to north developed in the upper Miocene and above strata in the Huaguang depression of the Qiongdongnan basin, northern margin of the South China Sea. Based on regional 2 D seismic data, in this paper it describes the characteristics of seismic facies and development of this large-scale SGDS and discusses its genetic mechanism. The development of the SGDS, composed of five elements including extensional domain,transitional domain, contractional domain, sliding surface and weak layer, could be divided into three stages as follows: the Late Miocene pre-gravity-sliding stage, the Pliocene syn-gravity-sliding stage, and the Quaternary post-gravity-sliding stage. During the fore-gravity-sliding stage, the channel complex was deposited on the bathyal argillaceous slope, and served on the material basis for gravity sliding. During the syn-gravity-sliding stage, which is the main stage of the SGDS development, the sediments were draped on the topography caused by intense deformation, and at the same time, there was also a certain degree of deformation. During the post-gravity-sliding stage, meaning the shrinking of the SGDS, the sediments gradually filled up the topography caused by gravity sliding and continued to deposit. It is indicated that the slope topography and high-speed sediment supply is the basis for the development of the SGDS, and the activation of basement faults and diapirism may be the trigger for its development.