渤海南岸6000年来的岸线演变

THE COASTLINE EVOLUTION ON THE SOUTH COAST OF THE BOHAI SEA SINCE 6ka B.P.

冰后期的海侵,淹没了渤海地区;大约在距今6000年左右,海侵达到最大范围。本文按照海相地层的分布,讨论了渤海南岸当时的海侵界线,又根据粉砂淤泥质海岸平均高潮线上发育的贝壳堤的位置,确定了尔后的几条古岸线。从而表明在该区6000年来的海岸淤长过程中,曾出现过海岸线的数次停顿,这与黄河三角洲河口的交替摆动有密切关系。从而为研究渤海南岸的全新世地质历史,黄河三角洲的发育和区内资源开发提供重要的依据。

The Holocen transgression made the Bohai area immerged by sea water and formed the presenr Bohai Sea.On the south coast of the Bohai Sea there is the Yellow River which is one of the longest rivers in the world.In carries 1.056Ⅹ109 tons of sediments into the sea each year.So it significantly affected the coastline evaluuon of this area.This paper discussed the relationship between coastline evolution and the Yellow River migrations.By tracing the Holocene marine sediments in the cores we found a smooth arched paleocoastline which differed heavily from the recent South Bohai Sea Coastline at about 6ka B.P..Neither the Yellow River delta nor Laizhou Bay existed then.We called it the Paleo-Bohai South Bay.Besides,there are four,chenier ridges on the South coast of the Bohai Sea which are paleocoastlines of different historical times.Based on 14C dating and archaeological method their ages are 5ka B.P.of chenier Ⅳ,3.5ka B.P.of Ⅲ,2ka B.P.of H1,1ka B.P.of H2 and 0.05ka B.P.of I respctively. The Yellow River migrated very often in history.There were two kinds of migtations: the large scale between Shandong and Jiangsu province and the small scale on the river delta area.When the Yellow River infused into the Bohai Sea the coastline accreted rapidly.After it had migrated the sediment supply decreased,the wave eroded the former coast,carried shells to the shore and built a chenier ridse gradually.The four chenier ridges were the results of the Yellow River migrations.The Yellow River frequently infused into the Bohai Sea from the south coast.So far it has built a land of 17500km2 since 6ka B.P The large delta separated the Laizhou Bay from the Paleo-Bohai South-Bay and left four chenier ridges on it Since 3 5ka B.P.the accretion rate of deltic coastline averaged some 20m/a