Abstract: The middle and deep evaporites-bearing strata in the Ordos Basin are highlighted for exploration and development of continental salt resources in China. On the basis of previous studies, the sequence stratigraphy of the middle Ordovician Majiagou Formation was studied by using seismic data, well logging data and Vail classical sequence stratigraphy theory. Tectonic movement and sea level change, and well seismic combination technology were adopted in the study. The development controls of the evaporite series stratigraphy were further explored. Results show that the Majiagou Formation is divided into 1 second-order sequence, 3 third-order sequences and 8 fourth-order sequences. Based on the study of regional tectonic features and sedimentary facies, and in combination with the distribution of evaportie strata of the Majiagou Formation, it is considered that the second order sequence (structural sequence) and the third order sequence (sedimentary sequence) jointly affect the planar and vertical development of evaporite strata. Sedimentation (third order sequence) controls the formation of the original salt bodies. Tectonism (second order sequence) controls the formation of the original salt basin, and destorys, transforms and regulates the formation of the salt strata. The study of the sequence stratigraphy development and geological significance of evaporites-bearing strata can provide direction and basis for further exploration and development of middle and deep salt deposits in marine basins.

Key words: Ordos Basin, salt basin of northern Shaanxi, Ordovician, Majiagou Formation, sequence