Elemental geochemical characteristics of Lower—Middle Permian mudstones in Taikang Uplift, southern North China Basin: implications for the FOUR-PALEO conditions

Abstract

The paleo-sedimentary environment can be restored qualitatively or semiqualitatively using elements or combinations of elements that are sensitive to the depositional environment. Through the analysis and testing of the main elements, trace elements and rare earth elements of twenty-one Lower—Middle Permian coal-bearing strata mudstone samples in Taikang Uplift, southern North China Basin, this study explored the FOUR-PALEO conditions (paleo-water depth, paleo-redox conditions, paleoclimate and paleo-provenance). The La and Co contents indicate that the water depth of the northern margin of the southern North China Basin became gradually shallower during the Lower—Middle Permian period. According to the U/Th, Uau, V/Cr, Ni/Co and V/Sc ratios, it is known that this section of the basin is in an oxidizing environment, and the oxidation is gradually enhanced from the Taiyuan Formation to the Lower Shihezi Formation. Paleoclimate from bivariate plot diagrams of C-value and Sr/Cu versus Ga/Rb shows that the Taikang Uplift was characterized by a warm and arid climate during the depositional period of Permian Taiyuan Formation and a warm and humid climate during the Lower Shihezi Formation and shows that the depositional period of Permian Shanxi Formation was in a transitional period of humid and arid. CIA, PIA, ICV, Th/U and K/Rb reflect the tectonic settings of the source area. From the Taiyuan Formation to the Lower Shihezi Formation, the CIA and PIA gradually increase, and the ICV gradually decreases, indicating enhanced chemical weathering and the transition from arid to humid in the source area, the arid and humid frequent change in the Taiyuan Formation, and a sudden climate change in the Shanxi Formation. Additionally, the provenance discriminant function, Zr/Sc-Th/Sr, REEs ratios, Th versus Hf-Co, Hf versus La/Th and ZREE vs. La/Yb indicate that the type of provenance is associated with magmatic differentiation. Moreover, discriminant diagrams, consisting of K2O/Na2O versus SiO2, La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10, suggest that the mudstones of Lower-Middle Permian were deposited in active continental margin tectonic settings.