Early Cretaceous terrestrial weathering in northern China: Relationship between paleoclimate change and the phased evolution of the Jehol Biota

摘要

The Jehol Biota from lower Cretaceous deposits in northern China provides an important record of terrestrial fauna and flora, including feathered dinosaurs and one of the earliest angiosperms. This biota underwent three development phases, with a relatively limited biodiversity in the early phase that rapidly diversified in the middle phase. This study analyzes the conditions of terrestrial paleoweathering during the lower Cretaceous as inferred from the geochemistry of mudstones, with the aim of assessing the role of paleoclimate change as a background factor that led to the phased evolution of the Jehol Biota. The analysis focuses on the Dabeigou and Dadianzi formations of Hebei Province, northern China, which record the early and middle phases of the Jehol Biota, respectively. These fluviolacustrine sequences can be lithologically divided into lower and upper units. Geochemical weathering indices (e.g., W, SREE [total amount of rare earth elements], and ΔW) show a significant increase from the lower to the upper unit, indicating enhanced weathering of the hinterland. Based on a comparison with the W values of recent soils that developed under various climates, the obtained increase in W can be interpreted as indicating temporal increases in temperature and humidity. Therefore, the increase in hinterland weathering from the lower to the upper unit was possibly induced by a shift in the paleoclimate to a more temperate and humid state. The timing of this change in paleoclimate closely coincides with a shift in the Jehol Biota to an evolved phase. Consequently, this preliminary result indicates that paleoclimate change in terrestrial regions of northern China might have contributed to the development of the Jehol Biota.