Stratigraphic division of Quaternary strata and paleoenviroment analysis for Xinghua-Tongzhou region in the north flank of the Yangze River delta

Basing on measured drill cores selected from 5bore holes located respectively along Xinghua(ZK10)-Dongtai(ZK02)-Haian(ZK01)-Tongzhou(ZKA4)-Tongzhou(ZK03)section in the north flank of the Yangtze River delta,of which Xinghua and Dongtai belonging to the Dongtai Quaternary stratigraphic subregion and Haian,Tongzhou belonging to the Nantong Quaternary stratigraphic subregion,using lothostratigraphic,chronostrtigraphic and magnetostratigraphic analyses in combination with theory and method of sequence stratigraphy,apreliminary division of Quaternary strata in the studied area was made.The Quaternary strata of the two stratigraphic subregions can be divided into 4stratigraphic units,namely,Lower Pleistocene(QP1),Middle Pleistocene(QP2),Upper Pleistocene(QP3)and Holocene(Qh)from lower to upper.Quite different lithofacies and paleogeographic evolution characterisrics and shifting of ancient stream channels of the two stratigraphic subregions since Quaternary in the studied area were also discussed.Since Quaternary,the sediments of the Dongtai stratigraphic subregion in the north part of the studied area were mainly dominated by continental lacustrine facies sediments,while the sediments of the Nantong stratigraphic sudregion were doninated by continental lacustrine facies sediments in early Quaternary and marine-continental alternate facies sediments in middle-late Quaternaty.The shifting of ancient stream channels since Quaternary were occurred in the south part of Haian,the deep river-cut valleys were developed in Haian in middle-late pleistocene,and the ancient stream channels shifted southwards and approached the present site of the Yangtze River in the late stage of late pleistocene.