我国河流输沙对海岸和大陆架沉积的影响

我国现代海岸跨越构造沉降带和隆起带。据统计,在沉降带海岸入海的河流,其输沙量占我国人海河流输沙总量的90%以上,而在隆起带沿岸入海者,其输入量不足10%。沉降带沿岸以潮坪沉积为主,并出现巨厚的第四系沉积层;隆起带沿岸主要为海滩砂砾质沉积及与之相伴生的风成沉积,只在大河细粒物质沿岸运移所及之处,才形成潮坪沉积,且第四纪沉积层较薄,原地沉积物呈斑块状分布。东海和南海所接受的河流输沙量较少,异地沉积虽占据相当的范围,但原地沉积分布较广,并构成连续的沉积带。大河输沙通过海洋因素的搬运而沉积于相邻的小河口内,并构成堆积体,这是通过海、河泥沙交换,河流沉积物影响海岸沉积的另一个重要途径。在我国沿岸尚未发现主要由大陆架直接来沙产生的河口海岸沉积体。

Influence of Discharge Load in China on Coastal and Continental Shelf Sedimentation

The coastline of China is across uplift and subsidence areas. By account of52 major rivers flowing into seas of China, more than 90% suspended load dis-charges into the coastal zones in subsidence areas, and less than 10% in upliftareas. In the zones of subsidence areas there are tidal flat deposits and Quaternarybeds with great thickness, but in that of uplift areas beach sand and gravel de-velop and Quaternary deposits are very thin, and the tidal flat deposits may bewildly formed only where fine-grain sediments coming from great rivers and trans-porting along coast reach. In Bohai and Huanghai Seas the autochthonous sedi-ments are broadly distributed and spotted with allochthonous sediments becauseof huge suspended load contributed by rivers. However, in the East and SouthChina Seas the sediments contributed by rivers appear relatively limited, whileautochthonous ones develop wildly and construct continuous belts, The sedimentsfrom big rivers, which are carried with sea factors, settle down in small river mouths and build up sedimentary bodies. This is, one of the important ways thatthe discharge load influences on coast sedimentation by exchanging sediments coming from nearshore zones and rivers. On the coasts of China there rehave not been found sedimentary bodies in river mouths, which consist mainly of sandsdirectly from shelves.