一、引言上海地区巨厚的松散覆盖层底部有一层砾石层。许多研究长江三角洲新构造运动的学者,曾把该砾石层的存在作为地壳下沉的有力证据之一。袁复礼曾经指出:“上海地区覆盖层底部的砾石层中既有冰川形成的压扭石子,又有温暖气候的孢粉植物,值得仔 I. INTRODUCTION There is a layer of gravel in the bottom of the huge loose cover in Shanghai. Many scholars who studied the neotectonic movement in the Yangtze River Delta used the existence of this gravel layer as one of the strong evidences of crustal sinking. Yuan Fu-li once pointed out: "In the gravel layer at the bottom of the overburden area in Shanghai, there are not only the compression stones formed by glaciers but also the warm climate of pollen plants.