长江三峡地区的夷平面在宜昌地区白垩纪—第四纪沉积物中的反映

摘要

通过对湖北宜昌地区白垩纪—第四纪沉积演化的研究,发现存在3个明显的沉积旋回,每个旋回由下部颗粒粗大的砾石层和上部颗粒较细小的粉砂-泥质层组成.3个沉积旋回对应了宜昌以西三峡地区3期构造演化旋回,同时反映了三峡地区3期夷平面的存在.结合前人研究结果、古生物化石和对第四系善溪窑组的测年数据,认为3期夷平面形成时代分别为:鄂西期夷平面形成于白垩纪晚期—古近纪的始新世,山原期夷平面形成于上新世—早更新世初,云梦期夷平面形成于早更新世末—中更新世早期.%There are three major depositional cycles recognized in the Cretaceous to Quaternary deposits in the Yichang region, Hubei. Each cycle is composed of the gravel beds in the lower part and silt and mud beds in the upper part. These depositional cycles are interpreted to be the responses to the three phases of tectonic evolution and three phases of planation surfaces in the Three Yangtze Gorges areas west of Yichang. Referenced to the previous data, organic fossils and age determinations for the Quaternary Shanxiyao Formation, the planation surfaces cited above were dated at the Late Cretaceous-Eocene for the Exian planation surfaces, the Pliocene -beginning of the early Pleistocene for the Shanyuanian planation surfaces, and the end of the early Pleistocene-the early stage of the middle Pleistocene for the Yunmengian planation surfaces, respectively.