青藏高原东北缘寺口子盆地新生代沉积演化及其构造意义

宁夏固原寺口子盆地发育巨厚的新生代地层,这些地层记录了青藏高原东北部的沉积演化特征和构造演变历史。根据剖面沉积物粒度特征、沉积结构和构造、沉积层序,识别出20种岩相、5种沉积相类型。结合前人对寺口子剖面的古地磁测年,分析研究盆地的沉积演化特征以及对构造的响应表明:20.1 Ma盆地以缓慢的坳陷沉降开始演化,直至1.2 Ma遭受破坏。在此期间青藏高原东北部经历了6.4 Ma、4.6 Ma和1.2 Ma这3次明显的构造挤压隆升运动,其中约6.4 Ma的构造运动是青藏高原向东北部扩展首次影响到海原—六盘山断裂以东地区。从盆地的形成和沉积演化过程来看,马东山山前断裂的逆冲推覆,导致了寺口子盆地的强烈变形和构造降升,并且最终成为青藏高原的最新组成部分。

Cenozoic sedimentary evolution of the Sikouzi Basin on the northeastern margin of the Qinghai-Tibetan Plateau and its tectonic significance

The Sikouzi Basin,located near Guyan in Ningxia Hui autonomous region,deposited the huge thick layer of Cenozoic strata,which document the characteristics of sedimentary evolvement and history of tectonic deformation. Based on analyzes of grain size,sedimentary structures and sedimentary sequence,twenty lithofacies and five sedimentary environments are recognized. By correlating previous magnetic straitigraphic result and our present analysis of sedimentary evolution and its response to tectonics,we suggest that the basin was slowly depressed before 20.1 Ma and was deformed in 1.2 Ma. Between 20.1 Ma and 1.2 Ma,three tectonic uplift events took place in the northeast of Qinghai-Tibet Plateau. They happened in the 6.4 Ma, 4.6 Ma and 1.2 Ma. Basin stratigraphy shows that the tectonic uplift at 6.4 Ma is the first time that growing of the northeastern Qinghai-Tibet Plateau affected the east region of Haiyuan-Liupan Shan faulting. Both the style of development and the evolution of the Sikouzi Basin uncover that the Late Cenozoic thrusting of the Madong Shan front fault system led to the following evolution pattern. The Sikouzi Basin was strongly deformed and uplifted,and then most of the basin was merged into marginal plateau and consequently became the newest part of the Qinghai-Tibet Plateau.