Sedimentary record of Mesozoic intracontinental deformation in the south Ordos Basin, China

In general, intracontinental basins are nearly symmetric in geometry, lack of deformation, quite large in area, and overall subsidence curves are exponential in shape, showing relatively slow, long-lived, and continuous but decreasing subsidence rates. However, some examples from China, Africa, and Australia, including the Ordos basin, the subject of this dissertation, are similar to those of North America in that they are large, very long-lived basins, but differ in that they tend to be asymmetric, have episodic subsidence histories, and are often surrounded by zones of strong intracontinental deformation.; In order to understand what mechanisms cause the difference between Ordos Basin and those North American examples, how this long-lived basin evolved over time, I chose the south Ordos Basin as my research area. In addition, I was also interested in understanding the sedimentary response to intracontinental deformation during the Mesozoic, in particular during deposition of the Yanchang Formation during Triassic time.; Two active deformation belts---the Qinling orogenc belt to the south and Liupanshan thrust belt to the west---control the evolution of the south Ordos Basin during the Mesozoic time. Sandstone petrology and U-Pb detrital zircon geochronology was used to identify provenance, reconstruct paleogeography, and document the relative time of basin margin deformation belts.; The southwestern Ordos Basin shows broadly similar compositions with southern area. Most samples fall on the edge of the recycled orogeny provenance and the framework-mineral grains are relatively enriched in Qm and depleted in P compared with samples from the South Ordos Basin. Samples from the western Ordos Basin have relatively low percentages of feldspar and high percentages of lithic fragments compared to samples from the south and southwest. All data clearly fall within the recycled orogeny provenance, which indicate that southern source areas are less important towards the north along the western Ordos Basin. Besides the major framework grains, some minor components also reflect a change in provenance change through time. Abundance of carbonate grains in both the south and southwest Ordos Basin increase dramatically upper section. This likely reflects progressive erosion of thrusted sheets composed of continental shelf deposits of early Paleozoic age.; Two samples (one from the south and one from the southwest) were collected from the well-exposed Yanchang Formation and 258 detrital zircon grains in total were analyzed. Three major broad age population groups---240-490Ma, 1.8-2.0Ga, and 2.2-2.8Ga---characterize the detrital zircon grains of the Yanchang Formation. The two oldest population groups match well with ages of grains present in the basement rocks found in the North China block, most likely recycled from Paleozoic strata along the south and southwestern basin margins. The young ages can be subdivided into three distinctive age groups: 240-300Ma, 300-400Ma, and 400-490Ma. Both areas share some common sources with 240-300Ma age grains, the signature of detrital zircon grains derived from the Qilian-Qaidam terrane to the west. In addition, some locally derived sources also involved in both areas.; This provenance link suggests that probably there are some drainage systems bringing sediment from the western margin of the basin across to the south in addition to local sediment delivery systems when the Triassic Yanchang Formation was deposited. It also provides evidence of uplift and erosion of Qinling orogenic belt and the western Liupanshan thrust belt, and supports the interpretation that both deformation belts had formed and were shedding sediment into basin by the Triassic Yanchang Formation time.; Regional and detailed subsidence analyses in the south Ordos Basin show that there are at least two phases of rapid subsidence in the southern Ordos Basin---an early Paleozoic episode and an early Mesozoic episode. In general, the subsi...