Stratigraphic division of NB5 core in the Yangtze delta area and its environmental change information

Located in the west beach of Pacific Ocean and the mouth area of Yangtze River, the Yangtze delta area is doubly affected by the sea and the regional big river. Therefore, the sedimentary environment is very complex. The NB5 hole is in the north of Yangtze delta area. The NB5 hole at Xiting Town of Nantong City was drilled 362 m deep with 354m thickness of Quaternary strata. According to testing results of paleomagnetism, ¹⁴C and ESR of NB5 core, analyzing the lithological character, and a comparison with other cores in this area or nearby areas, the strata were divided and the environment evolution since the Quaternary was investigated. The result indicates that the bottom of Holocence is at about 46 m, the top of middle Pleistocene is at about 163 m, the top of lower Pleistocene is at about 240 m, and the bottom of lower Pleistocene is at about 354 m. There are five marine face layers in the core which are located 2-47 m and 125-163 m. they are the 1^st transgression layer (Zhenjiang transgression) and the 3^rd transgression layer (Kunshan transgression), because there exist remarkable different lithological characteristics and magnetic susceptibilities above 163 m and below 163 m in the core. The authors hold that the Gonghe movement that occurred in late middle Pleistocene might have affected the environment of this area greatly so that the main river flowed through this area.