doi:10.16186/j.cnki.1673-9787.2020060030

Received:2020/06/11

Revised:2020/07/28

Published:2022/05/15

Protolith restoration and its geological significance of the aluminiferous rock series of the Benxi Formation in the Yanlong area,Western Henan

LIU Enfa1, CAO Gaoshe2, XING Zhou2, SUN Fengyu2, DU Xin1, ZHOU Hongchun1, CHEN Yongcai1

1.The Fourth Geological Exploration Institute，Henan Geology and Mineral Bureau，Zhengzhou 450001，Henan，China，Henan Polytechnic University，Jiaozuo  454000，Henan， China;2.Institute of Resources & Environment，Henan Polytechnic University，Jiaozuo  454000 ， Henan，China

Abstract:The aluminiferous rock series of the late Carboniferous-early Permian Benxi Formation， as the base of the Upper Paleozoic in North China Block， are of great geological significance once their original rocks are restored. For this purpose， the borehole ZK0008 ， located at the Yanshi-Longmen region （ abbreviated as the Yanlong area） in southern North China Block， was selected to determine the mineral compositions and their existing status，and the elemental contents and their vertical change of the aluminiferous rock series，by means of X-ray diffraction , scanning electron microscopy with energy spectrum, as well as geochemical analysis. On these ba- ses , mineral genesis and the mechanism behind vertical mineral variation were analyzed, then the original rocks of the aluminiferous rock series were restored, and their geological significance was discussed. The results showed that the aluminiferous rock series of the Benxi Formation in the Yanlong area are mainly formed by diaspore and clay minerals, mostly cryptocrystalline aggregates. Inactive elements mainly exist in the pisolitic bauxite , whereas the active ones are mainly concentrated in the aluminous mudstones. Vertical variation in mineral compositions in the aluminiferous series was proposed to result from different degrees of ferrallitization with low maturity of the original siltstones, which mainly consisted of fine feldspar and/or lithoclasts from the North Qinling Orogenic Belt. During the original rocks of the Benxi Formation were deposited, rapid transgression might have made sea level reach the piedmont area of the North Qinling Orogenic Belt,and subsequently slow regression might have resulted in the diffusion of the feldspar and/or lithoclasts far from the source area. The o- riginal sediments of the Benxi Formation,once exposed to the surface , would have experienced rapid ferralliti- zation under humid , hot, and rainy climate conditions. Frequent sea-level fluctuations might have led to the superposition of several ferrallitization profiles , forming the aluminiferous rock series of the Benxi Formation eventually.

 Key words:Benxi Formation;aluminiferous rock series;original rock;North China Block;Western Henan

豫西偃龙地区本溪组含铝岩系的原岩恢复及其地质意义_刘恩法.pdf