南海东北部九龙峡谷上游支谷沉积地貌空间变化及控制因素分析

Spatial variation and controlling factors of sedimentary geomorphology in the tributary valleys of Jiulong submarine canyon,northeastern South China Sea

海底峡谷是陆源碎屑物和有机质进入深海的重要通道,也是开展海洋沉积学等交叉学科研究的热点区域。但受限于观测技术和分辨率,已有研究主要关注峡谷宏观沉积地貌演变和间歇性重力流沉积研究,极少报道内潮汐等常态动力及其塑造的沉积地貌。本文基于遥控潜水器(Remotely-Operated Vehicle,ROV)高清视频资料和船载多波束测深数据,定量分析了九龙峡谷上游支谷宏观形貌特征及谷底沙纹和沙丘分布规律。结果发现谷底普遍发育厘米级沙纹和米级沙丘等地貌,形态多样但空间分布具有规律性。沙纹波长和波高向下游总体呈减小趋势,是受谷底坡度变小、沉积物变细和内潮流速减弱等的共同控制;支谷汇流处有利于沙丘发育,可能是汇流导致谷内落潮流得到加强后有利于底形扩展。研究结果可增进对海底峡谷内潮汐沉积地貌形成机制的理解,并为古代内潮汐沉积相解释提供依据。

Submarine canyons are important conduits for terrigenous sediments and organic matter to enter the deep sea,and they are also hot spots for cross-disciplinary research on marine sedimentology and other disciplines.However,due to the limitations of observation technology and resolution,existing studies mainly focus on the evolution of macroscale sedimentary landforms and intermittent gravity flow sedimentation,and rarely report the constant dynamics such as internal tides and the sedimentary landforms shaped by them.Based on the high-resolution video data of Remotely-Operated Vehicle(ROV)and shipborne multibeam sounding data,this paper quantitatively analyzes the macro-topographic characteristics of the upstream tributaries of Jiulong Canyon and the distribution patterns of sand ripples and dunes at the bottom of the tributary valleys.The wavelength and wave height of ripples generally decrease downstream,which is controlled by the downstream decrease of valley bottom slope,finning sediments and weakening internal tidal flows.The confluence of tributaries is favorable for the development of larger bedforms,which may be due to the strengthening of ebbing internal tidal flows caused by the confluence.Our findings can improve the understanding of the formation mechanism of tidal sedimentary landforms in submarine canyons,and provide a basis for the interpretation of ancient internal tidal sedimentary facies.