High-Resolution Eocene Magnetostratigraphy of the Xijigou Section: Implications for the Infilling Process of Xining Basin, Northeastern Tibetan Plateau

Abstract

The Eocene was the initial stage of the Cenozoic global climatic transition from greenhouse to icehouse conditions. Our understanding of the Eocene climate is based mainly on marine records, and comparison of marine and terrestrial climate records of the Eocene has revealed inconsistencies. Thus, there is a need for more continuous, high-resolution Eocene sedimentary records from land. Xining Basin in the northeastern Tibetan Plateau contains a sequence of well-exposed and complete Eocene strata. Extending previous research, we have conducted a new high-resolution lithostratigraphic and magnetostratigraphic study of the Xijigou section in Xining Basin. The results indicate that the Xijigou section spans the interval from ~34.2 to 53 Ma, representing an average sediment accumulation rate of ~1.4 cm/kyr. The basal ages of the Mahalagou and Honggou Formations are ~39.9 and ~52.4 Ma, respectively. A comparison of all available Eocene sedimentary records from Xining Basin indicates that the strata deposited during ~53–35 Ma developed conformably and are well correlated over space. We conclude that sediment deposition was not affected by large-scale tectonic activity at the time and rather was controlled by the global climate. After ~35 Ma, the sediment accumulation rate increased to ~4 cm/kyr, which may reflect the far-field influence of the India-Eurasia collision on Xining Basin.