Gauss‐Matuyama Polarity Transition Obtained from a Loess Section at Weinan, North‐Central China

Abstract

AbstractA record of Gauss‐Matuyama (G/M) geomagnetic polarity transition has been obtained from the loess section at Weinan, Shaanxi Province in China. Grain size and weathering intensity analyses demonstrate that a rather weak pedogenesis occurred when the oldest loess unit L33 was deposited. Rock‐magnetic and paleo‐magnetic investigations indicate that the remanent magnetization is mainly carried by magnetite and maghemite deposited as detrital grains. The record of the polarity transition based on characteristic remanent magnetization (ChRM) directions of the low coercivity magnetic phase comprises 33 transitional directions. A pre‐transitional excursion defined by 4 intermediate directions and lasting about 2.2 ± 0.13 ka appears to have occurred prior to the G/M polarity transition. Then, the record displays a N–S–N cycle with virtual geomagnetic poles (VGPs) locating principally on American and Eastern‐Asia longitudes. Finally, the reverse polarity is established with VGPs clusting in the Atlantic near southern Africa, in a manner reminiscent of the record of the G/M transition recently restudied at Searles Valley. However, significant differences still exist between the Weinan and Searles Valley records. Thus, the field configuration during this transition might be more complicated than one dominated by an equatorial dipole or low‐order zonal non‐dipole components. The total duration of the directional change for the G/M transition at Weinan, as derived from independent loess accumulation rates, is about 9.43 ± 0.64 ka.