江苏南通市四甲镇全新世以来有孔虫动物群的发现及其地质意义

Identification of Holocene foraminifera assemblages in Sijia Town of Nantong City, Jiangsu Province, and its geological significance

对江苏省南通市四甲镇CSJA6钻孔上部近43m的沉积物岩心进行了沉积学、年代学研究和有孔虫鉴定及组合划分，发现41属77种（含8个未定种）有孔虫。根据有孔虫动物群的垂直分布特征与AMS^14C年龄，初步建立了时间被部分标定的全新世有孔虫化石组合，自上而下为Ammonia beccarii vars.-Cribrononion subincertum Asano组合、Ammonia beccarii vars.-Globiger-inira glutinata组合和Ammonia beccarii vars.-Elphidium magellanicum组合。组合2、3带的时间界线约为8.1ka cal BP，组合3带的下界至少是10ka cal BP。这3个组合带的特征与以珠海、上海地区为代表的中国东部沿海平原全新世有孔虫组合相似。若将前人全新世海侵的14C年龄做进一步的校正，并结合本文钻孔研究成果可初步推测，在8.5-8ka cal BP时长江三角洲地区达到最大海侵，形成以镇江、扬州为顶点的长江巨大河口湾。

Drill hole CSJA6, located in Sijia Town of Nantong City in Jiangsu Province, was studied for its sedimentary framework, AMS^14C chronology and foraminifera fauna of the upper 43m core sediments. Based on thorough identification and combinational division, the authors have revealed that the foraminifera fauna of this part consists of 41 genera and 77 species, including 8 undefined spe-cies. According to the vertical distribution characteristics of the forams and AMS 14C dating, three assemblages were distinguished from top to bottom as Ammonia beccarii vars.-Cribrononion subincertuma assemblage, Ammonia beccarii vars.-Globigerinira glutinata assem-blage and Ammonia beccarii vars.-Elphidium magellanicum assemblage, of which the chrono-boundaries are partially determined as 8.1ka cal BP for Assemblages 2 and 3, whereas the lower boundary of Assemblage 3 is at least 10ka cal BP. General characteristics of such three assemblages are similar to the features of forams fauna found from China＇s coastal plains, represented by Zhuhai and Shanghai areas. Based on the aforementioned conclusion, in combination with necessary calibration of previously obtained non-calibrated 14C ages, the authors have arrived at a preliminary inference that the marine transgression in the working area reached its maximum range during ca. 8.5-8ka cal BP and created a super Yangtze River estuary heading towards its vertex in Zhenjiang and Yangz hou.