甘肃兰州—民和盆地中铺地区下白垩统河口群沉积特征及其盆地分析意义

Sedimentary characteristics and their basin analysis significance of the Lower Cretaceous Hekou Group in Zhongpu area of Lanzhou-Minhe Basin,Gansu Province

甘肃兰州—民和盆地是中国西部典型的陆内断陷沉积盆地,该盆地发育的下白垩统河口群是一套以红褐色为主的碎屑岩地层。依据野外调查,以盆地分析方法为手段,从地层、沉积相、物源和古水流等方面入手对盆地东南部的中铺地区河口群进行了沉积环境的系统分析。通过对研究区内河口群沉积相、沉积构造和沉积序列的研究,认为整套地层垂向上发育有冲积扇相—辫状河相—曲流河相沉积,并进一步划分出若干微相;同时结合该地区的物源和古水流分析认为,早白垩世研究区内的物源主要来自南部的祁连山多旋回造山带; 盆地内的下白垩统河口群在不同地区呈现出不同特点,并以此建立了兰州—民和盆地早白垩世古地理格局及盆地演化模式。

Lanzhou-Minhe Basin is a typically intracontinental rift basin in western China.The Lower Cretaceous Hekou Group is a set of red brown based clastic rock formations.On the basis of field investigations,by means of basin analysis method,this article has a systematic analysis of the Hekou Group in the Zhongpu area of southeastern basin on the stratigraphy,sedimentary facies,provenance and palaeocurrent.The analysis result of sedimentary facies,sedimentary structures and sedimentary sequence of the Hekou Group indicates the vertical development of alluvial fan-braided river-meandering river facies and several microfacies.Meanwhile,the region of provenance and palaeocurrent research indicates that the provenance in this region mainly was the south Qilian Mountains polycyclic orogenic belt during the Early Cretaceous. It is concluded that the Hekou Group in different regions shows different characteristics in the Early Cretaceous,based on which, the Lanzhou-Minhe Basin palaeogeographic pattern and basin evolution model are established.