Provenance and Depositional Environment of the Pliocene Sandstones from the Erlian Basin, North China

Abstract

The Erlian Basin is a Mesozoic–Cenozoic rift basin with a large thick Pliocene sandstones deposit, which has important oil, gas, and uranium resources exploration potential. The paleo-sedimentary environment plays an important role in controlling the development of mineral resource. However, provenance and depositional environment of the Pliocene sandstones remain enigmatic. To address it, this study reports the whole rock geochemical compositions of sandstones from the Youqi and Siziwangqi regions to reflect the paleo-sedimentary environment. The Youqi sandstones are classified as litharenite-arkose, whereas the Siziwangqi sandstones exhibit a graywacke affinity. Furthermore, both the Youqi and Siziwangqi sandstones exhibit low CIA, PIA, ICV, and Th/U values, suggesting that their source rocks were of great maturation and experienced low to moderate chemical weathering processes. The Ni/Co, U/Th, and Ce/Ce* values in these sandstones range from 0.4 to 5.9, 0.20 to 0.37, and 0.80 to 1.09, respectively, indicating that these sandstones were formed in an oxygen-rich depositional environment. Additionally, interelement ratios such as Sr/Cu, SiO₂/Al₂O₃, and Rb/Sr suggest a hot and arid paleoclimate during the deposition of these sandstones. Tectonic discrimination diagrams reveal a continental arc environment for the studied sandstones, Combining regional structural background, implying that the Erlian Basin was influenced by both Himalayan and the Pacific-Ocean-surrounding tectonism during the Pliocene period.