The oil and gas resources in Yan’an area of Ordos Basin are abundant, and Benxi Formation is one of the important exploration intervals. However, its sedimentary environment is complex, and the distribution of sand bodies and sedimentary evolution characteristics are not clear, which restricts the process of natural gas exploration and development in this area. Therefore, strengthening the study of geology of Benxi Formation in Yan’an area, especially the study of sequence stratigraphy, sedimentary characteristics and evolution, will provide favorable theoretical support for paleogeographic reconstruction, oil and gas exploration and development in this area. Based on the theories of high-resolution sequence stratigraphy, sedimentary petrology, logging geology and sedimentology, the stratigraphic and sedimentary characteristics of the late Paleozoic Benxi Formation in Yan’an area of Ordos Basin were studied, and the sequence stratigraphic unit division, isochronous stratigraphic framework, sedimentary facies types and evolution process were determined. The results show that in terms of sequence stratigraphy, one long-term base-level cycle, two medium-term base-level cycles and multiple short-term cycles can be identified in Benxi Formation. In terms of sedimentary facies types, 12 types of lithofacies and 7 lithofacies combinations were identified. According to this, it is considered that tidal flat and barrier island-lagoon sedimentary facies were developed in Benxi Formation in Yan’an area, and sedimentary microfacies such as tidal channel, sand flat, mixed flat, mud flat, peat flat, barrier island and lagoon sediments were identified. In terms of sedimentary facies distribution, tidal flat deposits are mainly developed in the southwest and south, and barrier island-lagoon deposits are mainly developed in the northeast and north. The sedimentary patterns of Ben 1 section and Ben 2 section are basically consistent.

The middle-Jurassic Yan’an Formation in Ordos Basin is a set of coal-bearing clastic strata influenced by multiple source systems of the peripheral orogenic belt after the lag effect of the Indosinian movement. The coal and oil-gas resources show great exploration potential. This paper investigates the provenance analysis based on the characteristics of light minerals, heavy minerals, paleo-flow, major, trace and rare earth elements. And the characteristics of source-to-sink system of Yan’an Formation in Ordos Basin are studied based on previous research results. The result shows that the Yan ’an Formation in Ordos Basin is influenced by four source-to-sink systems from Yinshan ancient land in the north, Alxa ancient land in the northwest, Qilian ancient land in the southwest and north Qinling orogenic belt in the south. This paper deepens the understanding of paleogeographic pattern on the basis of source-to-sink system partition: on the basis of the ravines crossbar landform in the pre-Jurassic period, the Yan’an Formation was influenced by the difference of weathering, denudation-transport and deposition processes in four different ancient terrigenous source areas. Yan’an Formation formed continental coal-bearing clastic rock deposits with Yan’an in the middle-Jiyuan in the southeast as the depositional center. Alluvial fan-braided river-meander river-delta-lake deposition changes from basin margin to catchment area in an orderly manner. The northwestern and northern source-to-sink system has the largest sedimentary scale. And it is the focus of basin exploration. It is concluded that the results have theoretical and practical significance for further understanding of various reservoir characteristics and reservoir prediction under the influence of different provenance systems.