西北冰洋北风海盆的碎屑流沉积

Debris flows deposition in the Northwind Basin,western Arctic Ocean

极地区域大陆边缘广泛发育水下碎屑流沉积,其中很多是冰川成因,是冰盖到达陆架边缘的产物。位于北冰洋楚科奇陆缘的北风海盆,其西侧陆缘已识别出大量碎屑流事件,而对北风海盆内部碎屑流的研究却几乎没有开展。该文利用高分辨率的浅地层剖面数据,勾勒出了北风海盆上部地层的碎屑流平面展布,且进行了期次划分;并结合周边的大型冰川线理(MSGL)的分布及走向,对所有识别出的碎屑流进行了成因推断。结果表明研究区内的碎屑流主要分布在西部次海盆的西南斜坡和中北部斜坡、东部次海盆的东南部以及部分海山/陡崖之下,其来源包括周边陆架、海脊高地和盆内海山。绝大多数碎屑流与MSGL伴生存在,推测为冰川成因,其中以西南斜坡最为发育,发现了超过9期的冰川碎屑流事件,代表了在其西南的冰蚀槽(宽水深槽)内曾发生超过9次的冰流事件,这一数据远大于前人所推测的冰流事件次数(3~5次)。同时也发现部分碎屑流邻近的海山/高地上不发育MSGL等冰川触地地貌,推测其为非冰川成因,邻近区域的冰盖/冰架触地或构造活动所引发的震动可能是这类碎屑流的触发因素。

Subaqueous debris flows are widely developed on polar continental margins,many of which are glacigenic,representing the products of ice sheets reaching the shelf edge.In the western Arctic Ocean,a large number of debris flows have been identified at the continental margin west of the Northwind Basin,however research on debris flows within this basin has hardly been carried out.In this study,the distribution of debris flows was outlined and their formation ages were determined using the high-resolution sub-bottom profiler data.Then the mega-scale glacial lineations(MSGL)was used as the judgment indicators to infer the origin of these debris flows.It is found that the debris flows in the study area are mainly distributed on the southwestern and northern-central slope of the western sub-basin,in the southeastern part of the eastern sub-basin,and on the slopes of some seamounts and cliffs.They are from the surrounding continental shelf,ridges and seamounts.Most debris flows coexist with MSGL and are presumed to be glacigenic.More than 9 glacigenic debris flows have been found on the southwestern slope,which may indicate more than 9 ice streams advances through the Broad Bathymetric Trough.The number of ice streams advances are much more than the previous speculation(3-5).There are also some debris flows with no ice-grounding landforms(e.g.MSGL)have been found in the nearby seamounts and are presumed to be non-glacigenic.The shock caused by the grounding of the ice sheets/shelves in the nearby area or tectonic movement may be the trigger factors for this kind of debris flows.