Elemental geochemical characteristics and geological significance of Majiagou Formation, eastern Ordos Basin

Rock type and the distribution of major and trace elements of the Ordovician Majiagou Formation in the eastern Ordos Basin were used to elucidate the sedimentary environment and the origin of the sediments. The results showed that the main rock types in the Majiagou Formation are carbonate and evaporite rocks. The CaO and MgO contents are high and vary widely. SiO₂, Al₂O₃, Fe₂O₃, K₂O, Ti₂O and other major representatives of a terrigenous component have low contents, indicating marine facies deposits. The average contents of Sr and U in the trace elements are slightly enriched compared with the upper crust, and the average contents of Ba, Rb, Zn, and Cr are lower than those in the upper crust, indicating a poor terrigenous supply. The distribution curves of Mgo/Cao, Rb/Sr, Sr/Cu and Sr/Ba ratios indicated that the Majiagou Formation was deposited in a marine environment under a dry and warm climate accompanying a dry-wet climate evolution. During the O₂m₂, O₂m₄ and O₂m₅ stages, there was a brief transition from dry-hot climate to relatively humid climate.