Sedimentary facies and its evolution of the Upper Palaeozoic in Zizhou area of Ordos Basin
Ma Yao1, Li Wenhou1, Wang Ruogu2, Pang Jungang3, Wu Yue3
1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069;
2. Research Institute of Yanchang Petroleum, Xi'an 710075;
3. School of Earth Sciences and Engineering, Xi'an Shiyou University, Xi'an 710065
On the basis of the analysis on a large number of drilling core observation, combined with regional geological background of Ordos Basin, the study uses the signal features such as lithology, palaeontology, sedimentary structure, grain size analysis, the geochemical characteristics to identify the sedimentary environment of each periods of Late Paleozoic in Zizhou area of Ordos Basin and summarize the evolution rules. There are five sedimentary systems in the study area of Late Paleozoic which are barrier coast system, shelf sedimentary system, meandering river delta sedimentary system, braided river delta sedimentary system and lacustrine sedimentary system. The sedimentary evolution is divided into two stages. The study focuses on sedimentary environment of Shanxi Formation and He 8 Member of Shihezi Formation. Shanxi Formation in Zizhou area deposits on the underwater environment. It is controlled by meandering river delta. There is short-term sea flooding only in the south part of study area. The study area is in fresh water environment in the early stage of Shihezi. It is controlled by braided river delta. The climate is changed from warm and humid to semi-arid and arid during Late Paleozoic. Sedimentary system is from marine and transitional to continental.