Olduvai亚时以来南黄海沉积层序及古地理变迁

THE SEDIMENTARY SEQUENCE AND PALAEOGEOGRAPHIC CHANGES OF THE SOUTH YELLOW SEA SINCE THE OLDUVAI SUBCHRON

根据海侵层与陆相层相间的特点,Olduvai亚时以来南黄海沉积层序可划分为15个地层段,据相分析存在着7个海侵层和1个具海侵迹象的层位。主要海侵层都具备经典的海侵-海退相序列。陆架区古地理演变可分为4个时期:(1)1.70—0.50Ma,古长江河流平原和三角洲发育时期。Olduvai亚时期间,QC_2孔发现感潮河段河床沉积,河口在124°E附近。0.97—0.73Ma海侵期,在122.2°E以东形成了大型水下三角洲。在海退期陆架区是冲积平原。(2)0.50Ma—75ka,大规模海侵波动期。发育了HVI,HV,HIV3个海侵层,分别为0.50—0.30Ma,0.27—0.20Ma,127—75ka,海侵规模越到后期越大,在东南季风作用下增强了中国东部大陆的水汽来源。(3)75—l4ka,末次冰期低海面吋期。河流最大下切深度达—133m,古长江水系向北东方向经对马海峡和朝鲜海峡流入日本海。河间地形成受侵蚀的风化高地。岩芯中还记录了两个短期的相对高海面期,与末次冰期的两个间冰阶相当。(4)14ka以来“全新世海侵”及黄河-淮河三角洲发育时期。14ka之前海平面回升到—68m,11ka之前回升到—50m,并出现了海平面的停顿或轻微下降,与新仙女木事件吻合。黄河-淮河三角洲发育在HI海侵层上,可分出6期三角洲复合体。

According to the alternation of terrestrial beds and transgressive beds, the sedimentary sequence of the South Yellow Sea since the Olduvai subchron can be divided into 15 stratigraphical members. According to the facies analysis, there are 7 transgressive beds and one bed with transgression marks, and classical transgressive-regressive facies sequence aiso appears in the major transgressive beds.Palaeogeographic evolution in the shelf area involved 4 periods:(1) 1.70--0.5Ma B, P. was the stage for the development of the Palaeo-Yangtze River alluvial plain and delta. Tide influenced-river channel sediments formed during the Olduvai have been found in borehole QC2. The river mouth was located near 124°E. And during the transgressive stage from 0.97--0.73Ma B. P. to the east of 122.2°E, a largescale undersea delta was formed. In the regressive stage, the shelf area became an alluvial plain.(2) 0.50--0.75Ma B. P. was muiti-transgressive fluctuation stage during which 3 transgressive beds(HVI, HV, HIV) developed, being dated to be 0.50--0.30Ms B. P., 0.27--0.20Ma B. P. and 127--75Ka B. P. respectively, with the extent of transgression increasing gradually. Influenced by southeast monsoons, the eastern China continent began to have a larger moisture source.(3) 75--14Ka B. P. was the low sea-level stage during the last giaciat period. The downcutting depth of rivers was up to --133m. Palaeo-Yangtze River system flowed northeastwards into the Sea of Japan through the Tsushima and Korean straits. The interfluvial area became an eroded, weathered high land. In the rock cores, two short-lived, relatively high sea-level stages were recorded, corresponding to two interstades in the last glacial period.(4) The period since 14Ka B. P. is the stage for 'Holocene transgression' and the development of the Yellow. River-Huathe River delta. Before 14Ka the sea level rose to --68m. and before 11Ka to --50m, and the sea-level was once at a standstill or slightly got down, which is coincident with the Younger Dryas event. The Yellow River-Huaihe River delta developed on trans- gressive bed HI and consists of the superimpositions of 6 deltaic complexes.