Magnetostratigraphy of the Neogene Sikouzi section at Guyuan, Ningxia, China

The thick, widely distributed lacustrine sediments in northern China may have recorded abundant information on the Asian monsoon evolution during the Late Cenozoic. However, reconstruction of such a history with these materials has been hampered by the paucity of reliable chronological constraints. In this study, systematic paleomagnetic measurements were conducted on a well-exposed, 2880-m thick fluviolacustrine sequence on the east side of the Liupan Mountains, a relatively monsoon-sensitive region. Correlation of the resultant magnetic polarity column to the Geomagnetic Polarity Timescale (GPTS) suggests that this sequence spans a time interval of 20.13–0.07 Ma and is generally continuous. The reliability of this correlation was further supported by three lines of independent evidence: i.e. Hipparion fossils, pollen assemblages and color changes of the sediments. Measurements of redness of the sedimentary succession suggest a remarkable decrease in air temperature over northern China, which may be closely associated with the global Mid-Miocene cooling caused by the extension of the Antarctic ice sheets. This event may have had an important influence on the evolution of the Asian monsoon circulation.