Magnetostratigraphy of the Dahonggou section, northern Qaidam Basin and its bearing on Cenozoic tectonic evolution of the Qilian Shan and Altyn Tagh Fault

The timing of uplift of the Tibet Plateau has a central role in the development of tectonic models for the Tibet Plateau and Cenozoic global climate change. A detailed magnetostratigraphic study of the Dahonggou section, northern Qaidam Basin, reveal that the section spans from ~ 34 to ~ 8.5 Ma and the ages of the Shang Ganchaigou, Xia Youshashan and Shang Youshashan formations are from > 34 to 22–20 Ma, 22–20 to 13 Ma and 13 to < 8.5 Ma, respectively. Variations in lithofacies, sedimentation rate and magnetic susceptibility (K) suggest that the southern Qilian Shan was tectonically inactive and didn't respond to the rapid slip on the Altyn Tagh Fault at 30 Ma. In contrast, the similar sedimentary records in the Dahonggou section, the Xishuigou section along the Altyn Tagh Fault, and even more localities along much of the Qilian range front imply that the Qilian Shan and the Altyn Tagh Fault were synchronously tectonically active at about 12 Ma. The lower K between ~ 12 Ma and ~ 8.5 Ma in the sediments of the Dahonggou section is interpreted to be due to long-distanced oxidation and sorting, which cause not only that magnetite was oxidated to hematite, but also that magnetic minerals are enriched in fine-grained sediments and coarse-grained sediments bear few magnetic mineral.