The collision between the India plate and the Eurasian plate formed the Qinghai-Tibet Plateau, known as the "Roof of the World." The formation and growth of the plateau have had a profound impact on the tectonic pattern, surface morphology, and climate evolution of the Eurasian continent. Currently, there have been many studies on the growth process and geomorphic evolution of the Qinghai-Tibet Plateau, but there are still different views and weak research on the climatic response in its surrounding areas. The northeastern margin of the Qinghai-Tibet Plateau is the most advanced area where the plateau is expanding towards the northeast. Since the Cenozoic, a large number of sedimentary basins have developed in this area. Although it has undergone strong transformations in the late Cenozoic, the residual stratigraphy with complete sequence and huge thickness in this area provides an important carrier for understanding the ancient environment and climate evolution of this region. In this context, this study focuses on the Ningnan Basin in the northeastern margin of the Qinghai-Tibet Plateau. By analyzing the geochemical characteristics of the detrital rocks in the basin from the Paleogene to Neogene, the study can reveal important information on the climate conditions, paleosalinity, paleowater depth, and redox environment of this region, thus restoring the characteristics of paleoenvironmental changes during the major evolutionary period in this region. At the same time, combined with regional geological data, the study further explores the relationship between climate change and the uplift of the Qinghai-Tibet Plateau in the northeastern margin.
In this study, 44 detrital rock samples were collected from the Sikouzi Formation to the Ganhegou Formation in the Ningnan Basin, and systematic elemental geochemical characteristic analysis was conducted. Combined with other research results in the area, such as paleobiological fossils, magnetic stratigraphy age, and stratigraphic division, the paleoenvironment and paleoclimate of the Cenozoic in the Ningnan Basin were reconstructed, and the following research results and understandings were obtained:
(1) The provenance area of the Cenozoic in the Ningnan Basin experienced weak weathering, and the rock in the provenance area was mainly composed of felsic rocks.
(2) From the Sikouzi Period to the Ganhegou Period, the main environment was oxidizing, but there were also short-lived reducing environments. Overall, all four periods had moderate to strong hydrodynamic environments.
(3) The Sikouzi Formation and Ganhegou Formation were deposited in a freshwater sedimentary environment, while the Zhangenbu Formation and Qingshuiying Formation were mainly deposited in a saltwater sedimentary environment.
(4) The Sikouzi Formation is dominated by a humid climate, the early Qingshuiying Formation was humid and gradually became arid, and the Zhangenbu Formation and Ganhegou Formation were mainly arid climates.
(5) At a larger scale, after the Himalayan movement about 23 million years ago, the geological response of the climate in the surrounding areas of the northeastern margin of the Qinghai-Tibet Plateau, such as Chaidamu, Lanzhou, Xining, and the Ningnan Basin studied in this paper, all recorded a transition from a humid to arid climate. The strong tectonic movement that appeared in the northeastern margin of the Qinghai-Tibet Plateau about 8 million years ago further intensified the aridification of this region and caused intense transformations in the Ningnan Basin. These changes are closely related to the uplift of the Qinghai-Tibet Plateau.
谷歌
火狐
