Geochemical characteristics and depositional environments of mudstones from the Triassic Zhifang Formation in the Tongchuan Area, southern Ordos Basin, China

Abstract

Significant sedimentary and tectonic information is preserved in the geochemical characteristics of the Middle Triassic Zhifang Formation in the southern Ordos Basin, North China. In this paper, elemental geochemical analysis is performed for 12 mudstone and siltstone samples from the Zhifang Formation of the Liangzhai River-Liulinchuan section of Tongchuan City, Shaanxi Province, with a major element analysis performed via X-ray fluorescence spectrometry, trace element and rare earth element (REE) analyses performed via inductively coupled plasma mass spectrometry (ICP-MS). The palaeoenvironment and tectonic backgrounds of the study section are also studied by analyzing the elements and elemental ratios sensitive to palaeoenvironmental conditions. The geochemical proxies, including the concentrations of U, and ratios of Fe 2 O 3 /FeO, U/Th, V/(V + Ni), V/Cr, and Ni/Co indicate that the depositional environment of the Zhifang Formation was likely an oxic-dysoxic condition without strong lake-water stratification. The oxic-dysoxic condition is interpreted as one of the key controlling factors for the poor development of source rocks in the Zhifang Formation, although this formation is dominated by black fine-grained sediments. Because of the Qinling orogenic belt, the geochemical characteristics reflect a tectonic background of the provenance area that was an active continental margin related to the continental island arc.

Geochemical characteristics, palaeoenvironment, and provenance of marine mudstone in Shanxi Formation of Huaibei Coalfield, southern North China Plate

“…The valence state of Ce and Eu changes when the environment changes, so the Ce anomaly (δCe) and Eu anomaly (δEu) can be used as indicators for determining the sedimentary environment (Li, Ju, et al, 2017;Wang, Chen, et al, 2020). The anomalies of Ce and Eu in all mudstone samples are between 1, with average values of 0.98 and 0.97, indicating an oxic-anoxic deposition environment.…”

“…For example, the solubility and valence state of some trace elements change with the redox state of the depositional environment (i.e., U, V, Mo, Cr, Co), and are referred to as the redox sensitive elements (RSE) (Fonseca, Mendonça Filho, Lézin, de Oliveira, & Duarte, 2020;Tribovillard, Algeo, Lyons, & Riboulleau, 2006). Therefore, we can use the geochemical indicators such as the correlation and ratio of major and trace elements, as well as the triangulation diagram, element distribution patterns and other geochemical methods to complete the inversion of its depositional environment and provide evidence for further research (Awan et al, 2020;Bhatia, 1983;El-Bialy, 2013;Jones & Manning, 1994;Wang, Chen, Liang, Chang, & Deng, 2020;Wang, He, Zhu, & Ding, 2020).…”

Geochemical Characteristics and Environmental Implications of Trace Elements of the Paleocene in the West Lishui Sag, East China Sea Basin

“…Paleoclimate studies can be carried out based on the existence of some characteristic rock markers and paleontological fossils contained in sedimentary rocks as well as geological methods such as paleomagnetism and carbon and oxygen isotopes [20][21][22]. This study mainly used the elemental ratio method to judge the paleoclimate of the Paleocene in the West Lishui Sag.…”

“…There are many methods to distinguish paleosalinity. For example, paleontology, geochemical methods of major and trace elements and the mass spectrometry of saturated hydrocarbons can be used to quantify water salinity [19,20,[45][46][47]. In this study, the elemental ratio method was used to analyze the paleosalinity in the West Depression of Lishui Sag.…”

Plant resilience and extinctions through the Permian to Middle Triassic on the North China Block: A multilevel diversity analysis of macrofossil records

“…The age of the Ermaying Formation is suggested to be Anisian, based on the vertebrate Sinokannemeyeria association and CA-TIMS U-Pb zircon dating (Liu et al, 2018). In Zhifang, Tongchuan City of Shaanxi Province, the Zhifang Formation was identified as coeval withthe Ermaying Formation (Wang et al, 2019). The correlation of other lithological units to the Liujiagou, Heshanggou and Ermaying formations is provided in Appendix 1.…”