Structural Characteristics and Exploration Significance of the Lower Paleozoic Detachment Thrust Belt in the Eastern Ordos Basin

Utilizing 2D and 3D seismic data, a large-scale detachment thrust structure within the Lower Paleozoic Ordovician Majiagou Formation (O<sub>1</sub>m) has been identified west of Lishi in the eastern Ordos Basin. This study investigates the structural characteristics, spatial distribution, evolutionary stages, and exploration potential of this structure. The results indicate:<i> (1)</i> The Lower Paleozoic Lishi West Detachment Thrust Belt (DTB) in the eastern Ordos Basin margin is 5–10km wide, extends nearly north-south parallel to the Lishi Fault Zone, and has considerable strike length.<i> (2)</i> The main faults of the Lishi West DTB initiated in the Precambrian and subsequently underwent four major evolutionary stages: stable sedimentation in the Ordovician epicontinental sea; formation of the detachment thrust belt from the Late Ordovician to Late Carboniferous; stable sedimentation from the Late Carboniferous to Middle Jurassic; and compressional uplift from the Middle Jurassic to Cretaceous.<i> </i><i>(3)</i> The Lishi West DTB originated during the Caledonian period as a deep-seated structural weak zone. During the Yanshanian period, the eastern basin margin experienced westward compression, leading to regional tilting and uplift. Stress release along this pre-existing weak zone caused significant variations in formation dip angles and fault characteristics across the belt. This DTB is interpreted as the boundary separating the Jinxi Warp-Fold Belt and the Yishan Slope.<i> </i><i>(4)</i> The detachment thrust belt in the eastern margin plays a critical role in hydrocarbon accumulation and subsequent migration/readjustment. The area west of the belt is favorable for exploring various coal-measure hydrocarbon resources, including deep coalbed methane (CBM) and in-source to near-source tight gas. A series of positive structural traps with large aerial extent have developed within the O<sub>1</sub>m Formation along the Lishi West DTB, demonstrating high exploration potential.