Paleogeomorphologic features and their controls on sandbody distribution on basin margin during Late Paleozoic Era and significance for petroleum exploration, Hangjinqi area, Ordos Basin

The paleogeomorphology in the Hangjinqi area of the Ordos Basin during the Late Paleozoic was restored by establishing a high-resolution sequence stratigraphy framework based on seismic data. The paleogeomorphologic features and their controls on sandbody distribution were discussed. When the Carboniferous Taiyuan Formation to the first member of Permain Shihezi Formation deposited, the study area featured by two distinct uplifts and three depressions from east to west. Vertically, three evolution periods were identified. In the first period, incised valleys developed and were overlapped and filled from the Taiyuan Formation to the first member of Shanxi Formation. In the second period, uplifts and depressions were inherited and gradually filled from the second member of Shanxi Formation to the first member of Shihezi Formation. In the last period, paleogeo-morphology was gentle and flat from the second to the third member of Shihezi Formation. Different periods of geomorphological evolution controlled the sandbody structure evolution. At the first period, the Taiyuan Formation distributed in the southern of Boerjianghaizi fault, which indicates the influence of the fault. Sand transported from the incised valleys in the north to deposit in the depressions in the south. Aggradational sandbodies deposited in the incised valleys and depressions. In the second period, the paleogeomorphology gradually became more and more flat, and faults showed weak controls on sandbody distribution. Sandbodies were contiguous with a certain degree of lateral oscillation. The inherited three depressions were the main distribution area of sandbodies. In the final period, sources retreated northward, and the paleogeomorphology was flat which formed the structure of mudstone-enclosed isolated sandbodies characterized by lateral isolation.