Chengwei Hu

Eolian sediments are extensively distributed across the Earth’s surface, and their formation is intricately linked to climate change, tectonic activity, and topographic features. Consequently, the investigation of eolian sediments bears great geological significance. The northwest region of China is renowned for hosting the most extensive and thickest Late Miocene–Pliocene red clay deposits globally. Nonetheless, scholars have yet to reach a consensus regarding the precise formation processes of these red clays. The identification of the source region of the red clays is crucial for comprehending their formation mechanism. The correlation of zircon U-Pb age spectra is a frequently utilized method for determining the provenance of eolian sediments. In this study, we compared the previously published zircon U-Pb ages (n = 12,918) of the Late Miocene–Pliocene red clays in the Ordos Plateau with those from the potential provenance regions (n = 24,280). The analysis, supported by the tectonic and climatic background of the region, revealed that the Late Miocene–Pliocene red clay in the Ordos Plateau originates predominantly from the Yellow and Wei rivers, with a minor contribution from the weathering of bedrock in the western North China Craton. The transport of these detrital materials by the East Asian winter monsoon is impeded by the presence of the Qinling and Taihang Shan, resulting in their deposition on the flat surface of the Ordos Plateau. This development of red clay is consistent with the proximal accumulation model, illustrating how the hydrosphere, atmosphere, and lithosphere interacted to shape the red clay deposits during the Late Miocene and Pliocene periods in the Ordos Plateau.

The Qinling Shan is located between the North China Craton and the South China Block. Not only is investigating the exhumation process of the Qinling Shan beneficial for comprehending the tectonic collision history of mainland China but also for enhancing our understanding of the development of the Yellow and Yangtze Rivers. Previous studies have predominantly focused on bedrock analysis in the Qinling Shan. However, modern fluvial detrital samples offer a more extensive range of thermal history information. Therefore, we gathered modern fluvial debris samples from the Hanjiang River, which is the largest river in the South Qinling Shan. Subsequently, we conducted apatite fission-track analysis using the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method. A total of 214 valid track ages were obtained, with an age distribution ranging from 9.5 to 334.0 Ma. The Density Plotter software was employed to decompose the data and generate four prominent age peaks: 185, 103, 69, 35, and 12 Ma. The exhumation events of the Early Jurassic (185 Ma) and Cretaceous (103–69 Ma) in the Southern Qinling Shan were strongly influenced by the collision between the South China Block and the North China Craton, as well as the subduction of the West Pacific Plate, respectively. The far-field effect of the collision between the Indian Plate and the southern Asian continent influenced the exhumation of the South Qinling Shan during the Late Eocene (35 Ma) and Middle Miocene (12 Ma), respectively. In conjunction with the reported findings, we comprehensively analyzed the geological implications of the Mesozoic and Cenozoic exhumations of the Qinling Shan. The Qinling Shan emerged as a watershed between the Ordos and Sichuan Basins in the early Mesozoic and Cenozoic, respectively. However, the exhumation and expansion of the Tibetan Plateau has forced the Yangtze River to flow eastward, resulting in its encounter with the South Qinling Shan in the late Cenozoic. The exhumation of the Qinling Shan has resulted in fault depression in the southern Ordos Basin. This geological process has also contributed to the widespread arid climatic conditions in the basin. During the Miocene, the Yellow River experienced limited connectivity due to a combination of structural and climatic factors. As a result, the Qinling Shan served as an obstacle, dividing the connected southern Yangtze River from the northern segment of the Yellow River during the late Cenozoic era.