Lithofacies Paleogeography of Majiagou Age of Ordovician in Ordos Basin

Key words: 
• single factor /
• land platform /
• dolomitic flat /
• bank /
• open sea

Abstract: Based on the study of stratigraphy and quantitative Sedimentology of eachfundamental sections,according to the “Single Factor Analysis and Comprehensive Mapping Method”,various single factor maps and quantitative lithofacies paleogeography maps of the Majiagou Age,i.e.Majiagou Age 1, Majiagou Age 2,Majiagou Age 3,Majiagou Age 4,Majiagou Age 5 and Majiagou Age 6 of Ordovician in Ordos,have been is studied and mapped.In these lithofacies paleogeography maps,the determination of paleogeographical units is based on quantitative single factor data.The features of the lithofacies paleogeograph of the Majiagou Age 1, Majiagou Age 3 and Majiagou Age 5 are similar,which can be summerized as “outside lands there were flats,in flats there were lagoons,outside flats there were open seas”and “in lagoons there were gypsum and salt”.The features of the lithofacies paleogeograph of the Majiagou Age 2,Majiagou Age 4 and Majiagou Aeg 6 are also similar,which can be summerized as “outside lands there were flats,outside flats there were open seas,in open seas there were banks,outside open seas there were troughs ”.Briefly,during the Majiagou Age there underwent three transgression-regression cycles.The reservoirs of the North Shaanxi Gas Field are the dolostones of the dolomitic flats in Majiagou 5,and the potential reservoirs will be the dolostones of the banks in Majiagou 4. Therefore,the study of the lithofacies paleogeography of Majiagou Age in Ordos has important significance in both geological theory and production.