Latest Olduvai short-lived reversal episodes recorded in Chinese loess

摘要

A duplicate high-resolution magnetic record was obtained from two parallel loess sections separated by about 300 m near Baoji city, southern Chinese Loess Plateau. This reveals at least eight short-lived reversed polarity episodes in the uppermost part of the Olduvai normal polarity subchronozone. Rock magnetic experiments and anisotropy of low-field magnetic susceptibility confirm that the multiple occurrence of short-lived reversals is not due to rock-magnetic and/or sedimentary causes. Assuming a constant accumulation rate within the Olduvai subchron, the short episode zone was estimated to span about 24–30 ka and 24–31 ka for the two sections, respectively. The duration of each short episode ranges from about 0.3 ka to 2.1 ka. The present results together with previous worldwide observations show that the occurrence of numerous short reversals is peculiar to the latest Olduvai subchron. The geodynamo may have been in an anomalous state at that time.