The Termination of the Olduvai Subchron at Lingtai, Chinese Loess Plateau: Geomagnetic Field Behavior or Complex Remanence Acquisition?

Abstract

We present a detailed investigation of the geomagnetic polarity transition that terminated the Olduvai subchron as recorded by loess/paleosol sediments at Lingtai in the central Chinese Loess Plateau (CLP). The polarity transition occurs within loess layer L25, where mineral magnetic parameters show considerable variations and sedimentation rate changes occur. The magnetic record obtained after thermal cleaning exhibits more than twenty apparent polarity flips, most of which occur within a stratigraphic distance corresponding to no more than ∼15,000 years. We argue that these results do not represent the actual behavior of the geomagnetic field. Instead, we propose that the combined effect of detrital and pedogenic remanences—which almost always co-exist on the central CLP—are responsible. These cause significant, lithologically-controlled, delays in the acquisition of the total remanence. In effect, the sediments act as a filter that generates noisy magnetic output from possibly simple input. We conclude that loess/paleosol sediments from the central CLP are poor candidates for tracking short-term geomagnetic field behavior such as polarity transitions, geomagnetic excursions and paleosecular variation.