全新世以来里下河地区古地理演变

里下河地区是苏北平原的重要组成部分，全新世以来，本区古地理环境经历了巨大的变化。据作者研究，大致可分为三个阶段：早全新世，本区受海侵影响，7－6kaB.P．左右海侵达到高峰，整个里下河地区成为一个大的浅水海湾；中全新世，海面相对稳定，长江、淮河等河流挟带大量泥沙入海，古海湾被岸外砂堤所包围，形成泻湖；晚全新世，海岸东迁，古泻湖演变为湖泊沼泽，在人类活动与黄河夺淮的影响下，本区逐渐演变为里下河平原。

Palaeogeographic Changes of the Lixiahe District Since the Holocene

The Lixiahe District contributes an important part to the North Jiangsu Plain since the Holocene, this district has undergone great palaeogeographic changes. According to the investigation and research done by the author,these changes have been fulfilled roughly through three stages. During the Early Holocene, this district had been transgressed. The transgression had reached its height during the period of 7ka-6ka B.P. The whole district had been reduced into a huge bay.ln the Middle Holocene,the sea level had remained relatively steadiness. However, some rivers such as the Yangtze River and the Huaihe River had carried a great guantity of sand to the sea to form an offshore bar which surrounded the old bay, and a lagoon come into being. As the Late Holocene opened, the seashore began to move eastward. The old lagoon became lakes and marshlands.As a result of human activities and the influences done by the Yellow River when it flew into the Huaihe River, this district has been gradually changed into the Lixiahe Plain.