Study On Lithofacies Paleogeography Of Ordovician Majiagou Formation, Southeast Ordos Basin

Southeast Ordos Basin is form Yan’an to Chunhua, Ordovician Majiagou Formation development of thicker gypsum rock layers. Based on the research of Ordovician Majiagou Formation the expanding characteristic of stratum, sequence stratigraphy and sedimentary facies, study Majiagou Formation each layers lithofacies Paleogeography, The research provides a scientific basis for Northern Shaanxi Ordovician salt basin potash resources exploration.Ordovician Majiagou Formation is widely distributed in Southeast Ordos Basin,it is divided six lithologic section from Majiagou Age1 to Majiagou Age6. The “L”centeal paleo-uplift have important control action to Ordovician sedimentary evolution. Nothern shaanxi sunken Majiagou Formation development most complete and deposit the thickest, among them O1m55 is the most important salt deposition period,it can be divided into 10 section.Carbonate sediments dominated in southeast Ordos Basin Ordovician Majiagou Formation, and three sedimentary facies type were identified, they were evaporated platform, restricted platform and open platform. Majiagou Age1, Majiagou Age3 and Majiagou Age5 the climate is hot, mainly consist restricted platform and evaporative platform, the development of gypsum-halite lake, dolomitic flat and dolomitic flat contain gypsum.Majiagou Age2 and Majiagou Age4 the climate is humid, mainly consist open platform, the development of limestone flat and dolomitic flat contain limestone.According to the theory and research of sequence stratigraphy, Ordos Basin Southeast Ordovician Majiagou Formation has occurred three third-order sea-level change cycle, and identified the 3 sequences can be recognized during this interval.Southeast Ordos Basin Ordovician Majiagou Formation gypsum-halite lake development in Majiagou Age1, Majiagou Age3 and Majiagou Age5. Majiagou Age1’gypsum-halite lake is largest,Shanan15 and Yitan1 is secondary depositional center.In the Majiagou Age1 shanan139 is secondary depositional center of gypsum-halite lake. In the Majiagou Age1 gypsum-halite lake is gradually shrink, shanan15 andshanan139 is secondary depositional center, Yan126 well area is smaller secondary depositional center of gypsum-halite lake. Fugu4-Fugu5-Yan170-Yan144 such as well area development gypsum-salt layer of O1m54 and O1m55, but is smaller and imminent demise.Based on the research of study area Majiagou Formation’s lithofacies paleogeography,identified each depositional period’secondary depositional center of gypsum-halite lake and gypsum-salt layer characteristics,provides a guide for Southeast Ordos Basin potash resources exploration.