深海氧同位素第3阶段晚期长江三角洲古环境初步研究

A PRELIMINARY STUDY ON THE PALEOENVIRONMENT DURING MIS 3 IN THE CHANGJIANG DELTA REGION

深海氧同位素第 3阶段 (MIS 3)晚期 ,世界气候比较温湿 ,世界海平面比现代海平面低约 2 0～ 4 0m。但是在长江三角洲地区 ,出现了更新世以来的最大海侵。海侵沉积层在太湖渡村分布在海拔 - 2 .5～ - 12 .2 5m之间 ,属河口海湾沉积 ;在上海分布在海拔 - 32 .3～ - 72 .76m之间 ,属浅海沉积。对长江三角洲MIS 3海侵沉积层进行构造运动校正之后 ,长江三角洲MIS 3古海平面高程约为 - 10m左右 ,一般比世界海平面要高的多。文章认为MIS 3晚期长江三角洲古海平面偏高可能与古太湖湾潮涌、长江古洪水有关 ,海侵沉积层顶面偏高可能还与水力均衡作用有关。

In later marine isotope stage 3(MIS 3), the world climate was relatively wet and humid, and the world sea level was about 20～40m lower compared with the modern sea level. While in the Changjiang Delta region, the maximum transgression was emerged since the Later Pleistocene. The transgression sediments are located in the east 827 bore of Taihu distributed in the altitudes between -2.5m and -12.25m,and belong to estuary bay sediments. The transgression sediments in the Shanghai area are distributed in the altitudes between -32.3m and -72.76m, and belong to shallow sea sediments. In the YL17 bore in the Heqiao town located in the east of Gehu, the transgression sediments are distributed in the altitude between 4.6m and 25.4m, and belong to front Delta sediments. We adjust the tectonic movement about the transgression sediments stratum in later MIS 3 in the Changjiang Delta, and we conclude that the altitude of the ancient sea level in the Changjiang Delta region was about -10m in later MIS 3 according to the fossil complex in the sediments. However, it was higher than the world sea level which was under -20m in the same period. We argue that the reason why the ancient sea level in the Changjiang Delta region in later MIS 3 was higher might be related with the tide in the ancient Taihu bay and ancient flood of the Changjiang River, and the reason why the top of the transgression sediments was higher may relate to the hydraulic equilibrium.