Intensified aridity of the Asian interior recorded by the magnetism of red clay in Altun Shan, NE Tibetan Plateau

The aridity history of monsoon-dominated areas has previously been traced by high-resolution studies of the well-known loess and red clay sequences on the Chinese Loess Plateau. However, the aridity process further west in China and the differences from the monsoon regime are unclear because no continuous aeolian sequences have been found in those areas. Here we describe and interpret an 88.4-m-thick Neogene aeolian sequence containing 40 visually-defined, brownish-red clay and gray caliche nodule layers in the eastern Xorhol Basin, northeast of the Tibetan Plateau. Magnetostratigraphic results show that the sequence was deposited between ~ 13 and 2.6 Ma. The sequence can be divided into two parts with different climate conditions according to magnetic susceptibility (MS): the lower part (13-11.5 Ma) indicates a more changeable climate with higher MS values (average 15 × 10− 8 m3 kg− 1) dominated by magnetite; the upper part (10.3-2.6 Ma) reflects a drier climate with lower, stable MS values (average 9.5 × 10− 8 m3 kg −1) mainly arising from hematite. Our results indicate that the intensified aridity of the Asian interior started between 11.5 Ma and 10.3 Ma, when MS decreased significantly due to outward growth of the Tibetan Plateau at around 12 Ma, together with ongoing global cooling and regression of the Neotethys Ocean during the Cenozoic.