Meso-Cenozoic Structural Characteristics And Its Evolution And Reformation In Weibei Area

Weibei area is located in the south of Ordos basin, where different tectonic units converge. It has undergone multi-stage tectonic activities and intense post-reformation in the Mesozoic and the Cenozoic, which caused its structural characteristics complicated and the Mesozoic strata denudated incompletely or completely.Directing by the principle of "overall, dynamic, comprehensive", differentiate of structural phase, analysis of structural characteristics and estimation of erosion thickness are done. Furthermore, Meso-Cenozoic structural evolution and post-reformation in Weibei area are discussed.According to structural sequences, deformation characteristics, stratigraphic contact relations, coarse clastic rocks and the data of fission track, the Mesozoic and Cenozoic in Weibei area can be divided into evolution phase and post-reformation phase by the end of early Cretaceous. Evolution phase can also be divided into four stages which are according with four significant structural events. And the post-reformation period since late Cretaceous also has four stages. The structural features of main deformational stages were introduced and summarized.By synthetically using the trend thickness method, interval travel time method and restriction of survival strata and so forth, the erosion thickness of main deformational stages were estimated scientifically. The estimate result of erosion thickness between Yanchang and Yanan period shows that the original thicknesses of Yanchang formation obviously thicken toward the south. Combining with the lithological characteristic, the boundary of Yanchang formation should be far from the south of Weibei area. The erosion between Yanan period and Zhiluo period in Weibei area is stronger in east and west than in central, and its maximum is 240m. The erosion after late Cretaceous period is the most intense and its thickness can reach 5000m at most. The volume is approximate 22562km~3. Accompanied by the development of Weihe basin, the erosion gradually enhanced. By comprehensively analyzing sedimentary evolution, the source of deposition in early Cretaceous, and the data of fission track, it was shown that Weibei uplift began to develope since late Cretaceous and its fast uplift was closely correlated to the faulting of Weihe basin. The edge of Weibei area has the characteristics of fault-block tilting and different erosions, which result in the today's structural features in Weibei area.In the end, according to structural characteristics, sedimentary characteristics, estimation of erosion thickness, development process of Weibei uplift, settlement characteristics of Weibei basin, and regional tectonic setting, the structural evolution and reformation of Weibei area in Meso-Cenozoic are discussed preliminary.