黄河三角洲GJ1孔晚第四纪地层层序及全新世沉积单元划分

The Late Quaternary Stratigraphic Sequence and Holocene Deposit Unit of GJ1 Borehole in the Huanghe(Yellow River)Delta

黄河三角洲作为自然河流体系形成的大型河控三角洲,研究其地层结构可更好地理解河控三角洲的层序框架、河流改道与海平面升降等。本文主要基于黄河三角洲上GJ1钻孔沉积物的粒度以及测年数据,结合前人成果,利用岩性地层学、年代地层学等方法,划分了GJ1钻孔的沉积相,重点是全新统。GJ1钻孔78m长的岩心,形成年代为60ka B.P.至今,沉积相自下而上依次为(1)三角洲-河流-三角洲沉积(49.2~78.0m);(2)河流沉积(45.9~49.2m);(3)滨海近岸-河流沉积(24.6~45.9m);(4)河流沉积(19.4~24.6m);(5)全新世河流-滨海-三角洲前缘-河流-分流间湾与河流沉积(19.4m以浅),其中4.5m以浅为1917—1926年期间黄河行水的河床及废弃河道沉积。此外本文尝试将粒度数据与全新世古气候变化记录进行对比,发现全新世相对冷期GJ1孔平均粒径较粗,在相对暖期平均粒径较细的整体特征。且可以识别出6 500~6 000cal yr B.P.,4 200~3 800cal yr B.P.,3 500~2 500cal yr B.P.三次明显的北半球冰盖扩张,两极变冷,赤道变干的气候事件。

The study of the stratigraphic structureof a large river-dominated delta formed by a natural river system is beneficial to understanding the delta sequence stratigraphy,river avulsion and sea-level rise.Using the data of grain-sizeand C-14 dating of a 78 mlong drilling core in the Huanghe（Yellow River）Delta,together with previous studies,we divided sedimentary facies of GJ1 borehole from the late Quaternary by methods of sequence stratigraphyand chronostratigraphy.The GJ1 core formed during about 60 ka B.P.to present.From below to top,the sedimentary faciesof GJ1 core are,（1）delta,fluvial and delta deposits at depth of 49.2~78.0 m.（2）fluvial sediment（45.9~49.2 m）,formed during MIS4 period.（3）coastal,nearshore and fluvial deposits（24.6~45.9 m）.（4）fluvial sediment（19.4~24.6 m）.（5）Holocene fluvial,coastal,delta front,interdistributary bayandfluvial deposits（above19.4 m）,including the riverbed during 1917-1926 and abandoned channel deposits above 4.5 m.In addition,this paper attempts to compare the grain size parameter with the Holocene climate change records,and we found that the average grain size of the GJ1 core is relatively coarsein the cold period and wise versa.And three period of＂cool poles,dry tropics＂events can be identified at 6 500~6 000 cal yr B.P.,4 200~3 800 cal yr B.P.and3 500~2 500 cal yrB.P.