贺兰山中段米钵山组沉积特征及其意义

Sedimentary characteristics and their significance of Miboshan formation in the middle section of the Helan mountains

贺兰山中段中、上奥陶统米钵山组,在整个区域地层中占有重要地位,它是贺兰山南北向构造形成的重要标志。其地层明显区别于相邻地台区的沉积,对探讨贺兰山早古生代的构造格局及岩相古地理尤为重要。但对米钵山组沉积环境多有争论,观点各不相同。本文对该区米钵山组沉积特征、沉积层序、沉积岩相和古地理环境进行了分析研究,并划分为碎屑流、浊流和正常深水沉积三种类型,推断贺兰山南北向构造在加里东中期开始形成,并延续到白垩纪的新认识。

Distributed in the middle section of the Helan mountains, the strata of Miboshan formation of the middle and upper Ordovician occupy a significant position in the regional stratigraphic sequence and is the most important mark indicating the formation of northsouth trending tectonics in the region of the Helan mountains. The strata in the region are obviously different from the sediments in its adjacent platform, which is very important for discussion on the tectonic framework and lithofacies palaeogeography of the Helan mountains during the early Paleozoic. In addition, at present, there are many controversies on the sedimentary environment of Miboshan formation. This paper studies on sedimentary characteristics, sedi- mentary sequence, sedimentary lithofacies and palaeogeographic environment of the Miboshan formation, and divides the strata into three types, namely＇ clastic flows, turbidite flow and normal deep water sediments. Finally, it makes a new understanding that the north-south trending tectonics in the Helan mountains started from the middle period of Caledonian and lasted to Cretaceous.