Cryptic post-depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility

Abstract

Our anisotropy of magnetic susceptibility (AMS) investigation of the Gold Hill Steps (GHS2) and Halfway House (HH3) loess and paleosol profiles in central Alaska confirms that post-depositional reworking of loess at Gold Hill Steps has taken place and, of greater importance, identifies the reworked depth intervals. In GHS2, the majority of the loess below 7.80 m depth has been reworked. The loess at the Halfway House site is, as stated in the literature, a predominantly undisturbed aeolian deposit. However, we have identified two intervals that have been reworked in HH3. We infer from the depth variation of the AMS orientation distribution at GHS2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations. Permafrost loess behaved (1) as impermeable layers focusing and channeling flow, most likely that of groundwater, and (2) as rigid bodies undergoing rotations and lateral translations. A modern analogue of focused flow by an impermeable layer is identified at HH3.