Abstract: The ages and sedimentation rates of the Xiaganchaigou and Shangganchaigou formations in the Hongsanhan section at the northwestern margin of the Qaidam basin were determined by high-resolution magnetostratigraphy. The results revealed that increased sedimentation rates occurred around 36 Ma due to the influence of a short tectonic movement in the Qaidam basin. India-Eurasia collision at 60 - 40 Ma resulted in strong reactivation of the Altyn Tagh fault, which was closely related to the formation of mountains at the northwestern margin of the Qaidam basin. The correlation between the Eocene-Oligocene boundary global cooling event and information of the detailed lithofacies, sandstone composition and stable isotopes of the sediments in this section suggests that the sediments in the area record this Eocene-Oligocene boundary global cooling event.