The Lithofacies Palaeogeography and Control of the Reservoirs in Middle Ordovician Ma5_4~1 Submember in Western Jingbian Tableland

摘要

The major rock types of Ordovician Majiagou Formation Ma5_4~1 Submember in western Jingbian Tableland include muddy dolomite, gypsum-bearing dolomite, gypsum dolomite, limy dolomite, and muddy powder crystal dolomite. This paper is based on the theory of sedimentary petrology and with the methodology of comprehensive mapping by using single factors to analyze multiple factors.Using stratum thickness, the content of gypsum and penecontemporaneous dolomite as single factors, we studied the lithofacies palaeogeography in Ma5_4~1 Submember.The results show that Ma5_4~1 is generally a set of sedimentation from supratidal limited evaporation environment and in the period of sea level decline with shallow water. The sedimentary microfacies are mainly composed of gypsum- bearing dolomitic flat and gypsum dolomitic flat ,dolomitic gypsum flat comes second. Wo combined the area's regional geological background with lithofacies palaeogeography to construct the limited evaporation tidal flat sedimentation maps of Ma5_4~1 Submember. Meanwhile,the control of reservoirs was studied. We thought that gypsum-bearing dolomitic flats and dolomitic flats provide a foundation for the development of large-area reservoirs.