Study On Magnetostratigraphy And Tectonics Of Ningnan Basin Group

The Ningnan Basin Group, mainly located at the south of Ningxia province, is the sediment after the late reformation without basin shape. The spread scope generally refers to the Tertiary strata that are massively uncovered and distributed to the south of the Yin Chuan basin. Most of the strata is red, scattered and ruleless. It has important significance for its special status of geography and tectonics. The residual basin adheres to the southwest of the Mesozoic Ordos basin to the east and the northeastern horn of the Tibet Plateau to the west, which correspond with the Cenozoic faulted basins in the neighboring area of the Ordos basin from afar, and is the most immediate response to the uplift of Tibetan plateau. Hence, the study on the formation, evolution and disappear of the Ningnan Basin Group is crucial and irreplaceable to the Cenozoic reformation and the regional geodynamic environment of the Ordos Basin, the recovery of original Mesozoic basin, the oil-gas exploration in this area, and the uplift of Tibetan plateau.Many predecessors make exploratory research on the Cenozoic in Ningnan area, but the age their studied is limited, so the work is exploratory and very simple, rarely concerning formation, evolution and late reformation of the basin, especially the regional geodynamic environment and tectonic attribute of the Cenozoic basin. There are a series of problems should be resolved, still.Through high-resolution test about three typical sections and 80 days' field reconnaissance, the current distribution and tectonic characters of the Tertiary and Neozoic and the contact relation between each other are all explored.Based on the high-resolution sampling at the distance of 0.3-0.5m and systematic heating demagnetization, the regional magnetic sequence composed of 15 normal zones and 14 reversed zones is put forward. From the magnetic result, it is shown that the first sediment of Cenozoic Sikouzi Formation is in the range from 47.906Ma to 29.401MaB.R. In addition, many fission tracks on Ordos Basin and its neighboring tectonic units are analyzed. Combining with the spore-pollen findings and sections, tectonics and evolution of the Cenozoic Ningnan Basin Groups are discussed. In combination with the age, strata features and tectonic attribute of the other Cenozoic faulted basins around Ordos Basin, the evolution and response relationship between Ordos Basin and its neighboring basins are also discussed. The uplift period of the surrounding mountains and the reverse time of the east and west of Ordos Basin is worked out. It is revealed that the Ordos Basin have a very well response to its Cenozoic ambient faulted basins which are ordered and begins with the part of Hetao basin and Weihei basin, and the next is all the Ordos' neighboring basins.