琼东南盆地中央峡谷体系东段形态-充填特征及其地质意义

Characteristics of Morphology and Infillings and the Geological Significances of the Central Canyon System in Eastern Qiongdongnan Basin

通过对琼东南盆地东部水深数据和高精度地震资料的综合分析,对盆地东段中央峡谷体系的形态特征和内部充填结构进行了详细的描述和刻画。研究结果显示:琼东南盆地中央峡谷体系东段呈NEE向分布于长昌凹陷中央,峡谷具有相对笔直的通道,较为狭窄,剖面上表现为明显的"V型"形态,两侧发育陡峭的峡谷侧壁;东段峡谷的内部充填沉积物由滞留沉积体、块体流-席状砂复合体、浊流沉积体和垮塌沉积体构成,垂向上显示出多期的形成演化过程。形态特征和充填结构表明,盆地东段峡谷主要受到该区域古地貌特征的影响和控制,形成于晚中新世早期的长条状负地形为中央峡谷的形成提供了有利的空间,限制了盆地东段峡谷的形态特征,该地貌特征将持续影响峡谷内部的沉积物输送和堆积样式。更新世以来充分的沉积物供给在陆架坡折处形成了大量的陆坡峡谷,沉积物以垂向输送的方式沿着坡降向下运移,在下陆坡位置形成现代深水扇,并被现今中央峡谷的头部区域所捕获,在地貌特征的限制下,沉积物将发生转向输送,沿着盆地东段峡谷的走向,自西向东发生轴向运移。盆地东段构造控制型峡谷是造成琼东南盆地东西部中央峡谷体系在形态和充填上具有明显差异的原因。研究区内3种不同的现代沉积物输送方式,对于更好地理解盆地西部沉积物运移和西段峡谷的形成过程也具有一定的指示和对比意义。

Based on the integrated analysis of the bathymetric data and high-resolution seismic data, the morphological features and internal structures of the Central Canyon System （CCS）in eastern Qiongdongnan basin （QDNB）have been described and dissected accurately.The result shows that the CCS in eastern QDNB was located in the central part of the Changchang depression with an NEE orientation,showing a narrow,straight course in the plan and symmetrical V-shaped morphology with steep flanks in seismic profiles.The infillings were considered as turbidite channel lag deposits,mass transport complex-sheet sands （MTC-sheet complex）with cake-layer geometry,turbidites,and collapse deposits.They showed a multiple evolutional processes.The distinct differences of the CCS between the western and eastern segments implied that the canyon in eastern QDNB was primarily controlled by the plaeo-morphological feature associated to the tectonic transformation around 1 1.6 Ma,which might form the axial sub-basin in the central part of Changchang depression seemed as the rudiment of the CCS, define the morphology,and influence the sediment transports and accumulation patterns.The canyon in eastern QDNB wasconsidered as a tectonic-dominated submarine canyon.During the Holocene period, the sufficient deposits could be discharged by the slope canyons at the lower slope,where the modern submarine fan developed.Then the deposits were captured by the head of modern central canyon,and further transported along the canyon from west to east.The three modern sediment transportation models in eastern QDNB,the vertical transportation along the slope from north to south,the veer motion transportation in the head area of modern central canyon dominated by the topography,and the axial transportation associated to the canyon orientation from west to east, would be helpful in understanding the deepwater sedimentary processes in QDNB and provide more evidence for the forming of the CCS.