黄河三角洲利津超级叶瓣时空范围的再认识

黄河三角洲是世界著名的河流三角洲之一。自有学者首次系统地提出黄河三角洲全新世10期超级叶瓣的时空分布范围后,这一观点近30年来未见明显的改进。借助渤海湾南岸研究区获得的4个20～30 m钻孔地层资料和相应的AMS14C测年数据,以及前人部分钻孔的研究成果,本文对黄河三角洲利津超级叶瓣的沉积演化框架和时空分布特征进行了重新厘定:研究区全新世沉积环境由早期的河道和泛滥平原沉积,逐渐向海侵过程中盐沼、潮坪和浅海相演化。海平面上升速率减缓之后三角洲开始发育并逐步成陆,直至最后被陆相沉积所覆盖。黄河下游古河道在9000-8000 cal a BP左右可能在黄骅南部入海;大约8000 cal a BP之后,黄河主河道南迁到滨州—惠民一带,并在7000-5500 cal a BP之间发育利津超级叶瓣;利津超级叶瓣的北界可能在马山子和阳信一界,而南界在郭井子和弥河之间;约5500 cal a BP之后,黄河下游古河道可能重新过黄骅入海,于5500-3500 cal a BP左右形成黄骅超级叶瓣;约3500 cal a BP之后,黄河古河道北迁至天津,直至～700 BC左右主流河道入海口再次南迁至河北岐口附近。

Rethinking the spatio-temporal distribution of Lijin superlobe in the Yellow River Delta

The Yellow River Delta is one of the most famous river deltas in the world. Since Xue and Cheng (1989) first systematically proposed the spatio-temporal distribution of ten Holocene superlobes in the delta, this hypothesis remains unchanged in the last three decades. To redefine the characteristics of sedimentary evolution and spatial-temporal distribution of Lijin superlobe in the Yellow River Delta, 4 boreholes with a length of 20-30 m were obtained in the coastal plain of South Bohai Bay. Combined with the achievements of previous boreholes in the study area, the stratigraphical data and AMS¹⁴C dating results in these boreholes revealed that the river channel and flooding plain dominated the study area in the early Holocene. It turned to be saltmarsh, tidal flat and shallow sea environments in the chronological order when the Holocene transgression reached the study area. Delta progradation began as the sea level decelerated, and was finally capped by the terrestrial sediments in this area. The ancient river channel of the Yellow River might enter the sea by the southern area of Huanghua during 9000-8000 cal a BP. After ~8000 cal a BP, the main river channel shifted southward between Binzhou and Huiming, which led to the development of Lijin superlobe from 7000 cal a BP to 5500 cal a BP. The northern boundary of Lijin superlobe may link Mashanzi with Yangxin while the southern one was located between Guojingzi and Mihe River. The ancient Yellow River mouth might return to Huanghua after ~5500 cal a BP and formed the Huanghua superlobe ranging from 5500 cal a BP to 3500 cal a BP. The Yellow River changed its main course to Tianjin earlier than 3500 cal a BP and might turn back to Qikou in Hebei province after ~700 BC.