WANG B Y，GAO C, DU Y J, et al. Soft-sediment deformation structures and their paleoseismic significance of the Yan'an Formation, Ordos Basin [J]. Journal of Henan Polytechnic University( Natural Science), doi: 10.16186/j.cnki.1673-9787. （ 2026030031  ）

doi: 10.16186/j.cnki.1673-9787.（ 2026030031   ）

Received： 2026-03-25

Revised： 2026-06-26

Online： 2026-08-10

Soft-sediment deformation structures and their paleoseismic significance of the Yan'an Formation, Ordos Basin (Online)

Wang Bianyang1, Gao Chao1, Du Yanjun2 Yang Zeguang1, He Bin1, Guo Rui1

1.Research Institute of Shaanxi Yanchang Petroleum (Group) Co., Ltd., Xi’an, 710065, Shaanxi, China;2.Jingbian Oil Production Plant, Yanchang Oilfield Co., Ltd., Yulin 718500, Shaanxi, China

Abstract: Objectives  To investigate the genesis mechanism of soft-sediment deformation in the Yan'an Formation in the southern part of the northern Shaanxi Slope, Ordos Basin, and its indicative significance for paleoseismic activity, as well as to analyze its predictive value for hydrocarbon reservoir distribution. Methods By combining outcrop profile measurement and detailed investigation, this study takes the complete Yan'an Formation outcrop along the Yan'an–Ansai area as the research object. Through systematic observation and description of the soft-sediment deformation horizons and small intraformational faults developed in the Yan-6, Yan-5, and Yan-4 strata, we analyze their regional distribution, sedimentary environment, and deformation structural characteristics. Based on the regional paleotectonic setting, fault characteristics, and previous research results, the genesis of the deformation is comprehensively determined. Furthermore, its indication for the distribution of deep-water sand bodies in the lake basin is analyzed, and oil and gas reservoir prediction is carried out. Results Three sets of soft-sediment deformation layers and two small-scale intrastratal faults were identified in the Yan 6, Yan 5, and Yan 4 members. The deformation structures are mainly liquefaction-induced features such as liquefied diapirs, liquefied convolute deformation, pillow structures, and liquefied breccias, with relatively wide distribution. Comprehensive analysis indicates that these deformations are closely related to three episodes of paleoseismic activity associated with the Episode II of the Yanshan Movement and are of in-situ origin. On this basis, based on the control mechanism of paleoseismic activity on lake basin bottom morphology and deep-water sand body distribution, favorable areas for deep-water sand bodies were delineated. Drilling verification in the Xiasiwan Oilfield confirmed industrial oil flow within the favorable areas, validating the reliability of the research findings. Conclusions The soft-sediment deformation in the Yan'an Formation is a direct response to the paleoseismic activity of the Episode II of the Yanshan Movement, and its development characteristics can provide important evidence for reconstructing paleoseismic events in the basin. Meanwhile, paleoseismic activity plays a significant role in controlling the distribution of deep-water sand bodies in the lake basin. The relevant research results have important theoretical guiding significance for the subsequent oil and gas exploration of the Yan'an Formation in the southern part of the northern Shaanxi Slope.

Keywords: Ordos Basin;  Yan’an Formation; SSDs; Paleoseismic activity