Petrography and geochemistry of sandstones from the Middle Jurassic Zhiluo Formation in the northern margin, Ordos Basin: Implications for provenance, tectonic setting, paleoweathering, paleoclimate, and sandstone-type uranium mineralization

Xiaoneng Luo ^1* Suping Peng ² Ziying Li ¹ Feng He ¹ Xide Li ¹ Zilong Zhang ¹

• ¹ Beijing Research Institute of Uranium Geology, Beijing, China
• ² China University of Mining and Technology, Beijing, Beijing, China

Key words: element geochemistry; provenance analysis; middle Jurassic sandstone; paleoenvironment; ordos basin used petrological, geochemical, U-Pb zircon dating, and heavy mineral analysis approaches to answer the provenance problem of the Zhiluo Formation in the basin's northern region. However, the controversy over the Jurassic in the northern Ordos Basin mainly lies in the unclear relationship between provenance and uranium source. Is uranium source from a uranium rich rock mass in the erosion source area? Alternatively, is it the activation and migration of uranium in the rock of the target layer itself? Or is this due to the influx of deep high-uranium fluids? Therefore, it is necessary to conduct in-depth research on Jurassic provenance in this area and explore the development of the prototype basin. Provenance is the link between the sedimentary basins and orogenic belts. Conducting provenance analysis on sedimentary basins helps to understand their sedimentary filling and structural evolution and is an important means of reconstructing paleogeographic environments and restoring the interaction between basin mountain systems. At present, there are relatively few systematic source analyses of the Jurassic system in the northern Ordos Basin, and the source analysis methods are relatively single, lacking a comprehensive regional systematic source study that combines multiple methods. The geochemical characteristics of sediments are controlled by the composition of the source rocks and influenced by chemical weathering processes. The climatic conditions of the source area determine the intensity of chemical weathering. Therefore, the geochemical characteristics of sedimentary rocks can serve as indicators of source rock features, geochemical weathering processes, and palaeoclimatic reconstruction. Despite the aforementioned results, there has been no previous discussion of the sources of clastic rocks in the Zhiluo Formation, palaeotectonic setting, palaeoclimate, palaeo-weathering, or paleogeography of their source rocks. This research seeks to elucidate the origin of the sandstones from the Zhiluo Formation while also redefining the tectonic context, paleoclimate, and paleoweathering conditions of their source rocks. To fulfil these objectives, a comprehensive mineralogical-geochemical study was conducted on the sandstones of the Zhiluo Formation.