Grain size and magnetic susceptibility characteristics of Bei’an loess in northern Songnen Plain and their palaeoenvironmental significance

The Bei’an is located in the northern part of the Songnen Plain, and there has been little research on its loess formation and palaeoenvironment. This study provides a comprehensive analysis of the AMS14C, OSL, magnetic susceptibility, grain size characteristics, and lithological features of the Bei’an loess. The results show that the Bei’an loess roughly corresponds to the Guxiangtun Formation and upper part of the Harbin Formation. It exhibits low magnetic susceptibility values without any clear cyclical characteristics. The grain size frequency curve shows a unimodal distribution, indicating a sandy loam composition that differs from typical loess found in the eastern part of the Songnen Plain. However, Kd values, discriminant functions, and grain size plots (C-M, L-M, A-M charts) indicate that it does exhibit characteristics consistent with aeolian deposits. It is concluded that the Bei’an loess primarily represents aeolian deposition with secondary transportation and modification by rivers and mudflows. This suggests that during the late Pleistocene period in northern Songnen Plain was characterized by a dry-cold glacial environment. This study on Bei’an loess provides fundamental data for analyzing material sources for loess in northern Songnen Plain and holds significant importance for understanding the formation of loess in this region as well as beyond.