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

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 species. 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 assemblage 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 Yangzhou.