Chinese loess 10Be records for the Jaramillo polarity subchron

Abstract

The Jaramillo subchron is a significant mark for Mid-Pleistocene magnetostratigraphic division and dating. However, there is a lack of sufficient discussion on this boundary compared to the well-studied Brunhes/Matuyama geomagnetic reversal. A controversy remains over the precise position of the Jaramillo polarity subchron in the Chinese loess records, which has definitely hampered efforts to establish an accurate Chinese loess chronological framework and to correlate this with marine oxygen isotope records. Here, we present a high-resolution loess ¹⁰Be record to trace the Jaramillo polarity subchron in the Xifeng loess section from the Chinese Loess Plateau. The results indicate that the upper and lower boundaries of the Jaramillo occurred approximately at 994 ± 2 ka and 1072 ± 4 ka, corresponding to marine isotope stage 28 (i.e., MIS 28) and MIS 31, respectively. These new ¹⁰Be tracing results are consistent with that of marine sediment records, but they are younger than the ages obtained from paleomagnetic measurements of the same loess sediments by ∼ 12 ka and ∼ 16 ka, respectively. This suggests that a complex process of remanent magnetism acquisition took place in the loess. We propose that the primary remanence obtained during the Jaramillo polarity subchron was overprinted by later magnetic signals resulting in delayed geomagnetic polarity boundaries.