Lithofacies Paleogeography and Sedimentary Environment in Ordovician Majiagou Formation, Eastern Ordos Basin
SHI Ji-An, SHAO Yi, ZHANG Shun-Cun, FU Cui-Qin, BAI Hai-Feng, MA Tie-Long, TUN Zhi-Xiong
1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China; 2．Graduate University of Chinese Academy of Sciences, Beijing 100049, China; 3.China Petrochemical Co.Ltd.Shenqli Oilfiecd Branch shengli Oil Extraction Factory,Dongying 257051,China;4. Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi′an 710016, China)>
Ordos Basin is a major hydrocarbon\|bearing basin in China and the Ordovician carbonate rock preserved plenty of natural gas resources. Majiagou Formation occurs widely around the whole basin, in which Member 1, Member 3 and Member 5 are composed dominantly of dolomite, anhydrite and salt rock, to a lesser extent, limestone; while Member 2, Member 4 and Member 6 are mainly limestone and dolomite. Using methods of sedimentary and geochemistry, this paper analyzed the sedimentary environment in the Majiagou Formation. It suggests that Member 1, Member 3 and Member 5 are characterized by a dry and hot climate as well as fall of the sea level. The area of Well Longtan 1 in the eastern basin is abundant of platform evaporites with the depositional anhydrite and salt rock, surrounded by a suite of dolomite intercalated by the thin layers of anhydrite from the anhydrite\|dolomite platform sediment. It deposits muddy dolomite, dolomitic limestone and fine\|grained dolomite in the limestone-dolomite platform and restricted sea. During the stage of Member 2 and Member 4 in Majiagou Formation, the climate is wet and hot with rising sea level. The study region presents limestone with little dolomite in the open sea environment; but the margin area is the restricted sea settings with interbeding dolomite and limestone. The sedimentary model has been built in Majiagou Formation and the lithofacies paleogeography map has been plotted for each Member in Majiagou Formation.
SHI Ji-An, SHAO Yi, ZHANG Shun-Cun, FU Cui-Qin, BAI Hai-Feng, MA Tie-Long, TUN Zhi-Xiong. Lithofacies Paleogeography and Sedimentary Environment in Ordovician Majiagou Formation, Eastern Ordos Basin[J]. Nature Gas GeoScience, 2009, 20(3): 316-324.