Mineralogical and Geochemical Discrimination of the Occurrence and Genesis of Palygorskite in Eocene Sediments on the Northeastern Tibetan Plateau

Abstract

Palygorskite is a widely used indicator of semiarid to arid environments in paleoclimate studies. In this study, we present detailed mineralogical and geochemical investigations exploring the genesis of palygorskite found in Eocene fluvial sediment in the northern Qaidam Basin on the northeastern Tibetan Plateau. The presence of two types of palygorskite is revealed, based on their crystallinity characteristics and distinctive rare earth element (REE) patterns in the coexisting clay fraction. Well‐crystallized palygorskite samples are characterized by remarkably negative Ce anomalies and obvious middle rare earth element enrichment. Poorly crystallized palygorskite samples generally exhibit positive Ce anomalies and less pronounced middle rare earth element enrichment, which resemble those of nonpalygorskite‐bearing clay samples. Given the presence of an overall oxidized fluvial sedimentary environment, we attribute the well‐crystallized palygorskite (which has textures comprising long, interwoven fibers) to direct precipitation (i.e., neoformation) occurring within a reducing environment during early/postdepositional processes while the poorly crystallized palygorskite (which is characterized by short, club‐shaped single crystals) originates as catchment‐delivered detritus. These poorly crystallized palygorskites occur mostly in 49.5–47.0 Ma and are accompanied by decreasing kaolinite content, increasing chlorite content, and abundant xerophytic spore‐pollen from the Qaidam Basin, and its neighboring Xining Basin. Collectively, these evidences suggest that a less humid climate followed after the Early Eocene Climate Optimum.

Mineralogical Evolution of the Cretaceous Strata in the Songliao Basin, Northeastern China: Implications for Thermal History and Paleoenvironmental Evolution

“…In sedimentary processes, bulk mineralogical composition of sediments is controlled by lithology in provenance, climate condition, differentiation in transport and deposition, etc. For example, warmer and wetter climates induce chemical weathering of micas and feldspars, which triggers the formation of clay minerals [27,28]. After sediments get buried, diagenetic processes may alter the original mineralogical composition.…”

Early‐Middle Eocene Hydroclimate Variations Recorded by Environmental Magnetism in the Linxia Basin, NE Tibetan Plateau

“…In contrast, the preservation of early Cenozoic terrestrial sequences in this region is poor; only a few middle Eocene paleoenvironmental records exist in the Xorkol Basin (J. X. Li et al., 2018), the Xining Basin (Fang et al., 2015; Fang, Galy, et al., 2019; Z. He et al., 2019; Long et al., 2011; Meijer et al., 2021; Sayem et al., 2018), and the Qaidam Basin (Fang, Galy, et al., 2019; Song et al., 2018; M. Wu et al., 2021; Ye et al., 2018). There are different mechanisms to interpret the environmental changes in the NE Tibetan Plateau, based on these paleoenvironmental records, which have relatively low resolution.…”

“…He et al, 2019;Long et al, 2011;Meijer et al, 2021;Sayem et al, 2018), and the Qaidam Basin (Fang, Galy, et al, 2019;Song et al, 2018;M. Wu et al, 2021;Ye et al, 2018). There are different mechanisms to interpret the environmental changes in the NE Tibetan Plateau, based on these paleoenvironmental records, which have relatively low resolution.…”