A short, reverse polarity interval within the Jaramillo subchron: Evidence from the Jingbian section, northern Chinese Loess Plateau

Abstract

A high‐resolution paleomagnetic and rock magnetic investigation supported by scanning electron microscopy observations, X‐ray diffraction determinations, and anisotropy of magnetic susceptibility analyses has been carried out on a loess‐paleosol sequence from Jingbian (37.4°N, 108.8°E), at the northern extremity of the Chinese Loess Plateau. The results indicate that the magnetic assemblage is dominated by pseudo‐single‐domain magnetite with associated maghemite and traces of a higher‐coercivity phase, probably hematite. The Brunhes‐Matuyama and upper Jaramillo transitions have been carefully documented and a record of a short reverse polarity interval (SRI), entirely within the Jaramillo normal polarity subchron, has been obtained. The duration of the SRI, recorded over a stratigraphic interval of 48 cm, is 10.1 kyr (29 kyr if the polarity transitions are included). These results seem to exclude that rock magnetic variations are adversely affecting the recording process and compel us to reconsider the Jaramillo subchron as characterized by a pair of normal polarity intervals interrupted by a short reverse polarity interval.