Cenozoic Sedimentary Basins Of Southern Ningxia - Structural Features And Its Evolution

Widespread Cainozoic groups found in the north Ningxia are now unlike a basin because of intensive reformation. They are located where the East Structural domain meets the West, an important area that has been attracting a lot studies. However, misled by the current structures, the former investigators did’t regarded the relic stratum as a reformed basin. Armed by the thought of studying reformed basins when investigating this area(South-Ningxia Basin), we can get the original face of the basin, and a better understanding about the uplifting Tibet Plateau and the reformation of The Ordos basin.This study starts from reformed South-Ningxia basin, with a lot of exploring about out crops and collecting documents abundantly. The original face of the basin will be reconstructed according to a compositive study about the horizontal distribution, variation in thickness and the deposit-structural features of the stratum, as well as all of reformatting elements including intensity, steps and variance the whole basin.It is considered that the South-Ningxia Basin began to subside at an approximate time from early-Eocene to early-Oligocene owing to the faulted depression that gave birth to several absolute rift-sags with one or both sides controlled by normal fault. Faulted depression lasted to early-Miocene when the lake basin peaked. Therefore, South-Ningxia Basin is a rifted basin.Combining tatistics and analysis of the Cenozoic folds’elements and their relation to main faults in South-Ningxia Basin with current GPS data and geologic bodies’ dislocation distance, it is estimated that the NW shrinkage and strike-slip amount during late deformation in its south part was about11.4-14.7km and the SSE strike-slip amount in its north part was about4km while the NE shrinkage was little. The original pattern of South-Ningxia Basin can be resumed by vector homing of current basin’s pattern in the direction of above displacement.South-Ningxia Basin and other peripheral fault basins of Ordos had synchronous rifting, which all were as a portion of Ordos Basin’s late reformation and had nothing to do with the extrusion expansion of Tibetan Plateau. This extrusion expansion didn’t spread to South-Ningxia Basin until late Miocene and resulted in the extinction due to tectonic inversion and late reformation of South-Ningxia Basin.