Abstract:
Using seismic reflection profiles and drilling data, this study determined the types and styles of inverted structures in the Tabei Sag, Erlian Basin. Accordingly, this study explored the genetic mechanisms of the inverted structures and their relationships with sandstone-hosted uranium mines. The results indicate that the eastern and western parts of the Tabei Sag experienced different degrees of normal and inverted tectonism. As a result, the eastern part exhibits typical inverted structural styles. In contrast, in the western part, the Saihan Formation on the hanging wall of inverted fault F
1 in the Bayanwula and Manglai area was uplifted and almost completely eroded, with the original geometries of inverted structures being destroyed. During the late depositional stage of the Early Cretaceous Saihan Formation (113~98.9 Ma) and from the Late Cretaceous to the Early Paleocene (66~42 Ma), the subduction direction of the Paleo-Pacific Plate shifted from NW to NWW. This change altered the stress regime in the Tabei Sag from extension to compressional inversion, leading to the formation of a series of compressional and compressional-torsional structures. Consequently, the Saihan Formation and the Upper Cretaceous strata were uplifted and eroded, resulting in the formation of regional angular unconformities. The structural inversion transformed the sedimentary system of the Saihan Formation in the Tabei Sag from lacustrine to fluvial facies. Meanwhile, it caused differential uplift and uneven erosion of the Saihan Formation and its overburden, leading to the formation of erosion windows. This facilitated the infiltration and migration of uranium- and oxygen-bearing fluids toward deep parts. These processes controlled the morphologies and development of interlayer oxidation zones, thereby promoting the enrichment of uranium deposits.