Subaerial and subaqueous deposition of loess: Experimental assessment of detrital remanent magnetization in Chinese loess

Abstract

Loess and intercalated paleosols on the Chinese Loess Plateau (CLP) are the most extensive and continuous terrestrial archive of geomagnetic and paleoclimate variations covering the last 2.6 Ma. A first-order time-frame has been established for these sequences using paleomagnetic polarity boundaries. Major inconsistencies between the positioning of the Matuyama/Brunhes polarity boundary in Chinese loess/paleosol sequences and marine records, previously accounted for by assuming magnetization lock-in depths in loess of up to 2–3 m, have recently been resolved using a paleoclimatic indicator insensitive to pedogenesis that does require any major post-depositional acquisition of a remanent magnetization. This resolved controversy accentuates the lack of an adequate understanding of how Chinese loess acquires and retains a stable remanent magnetization. We report on laboratory re-deposition experiments with subaerial and subaqueous simulations of natural loess to elucidate factors controlling the acquisition of magnetization in loess. Our work complements and extends recently published results from comparable laboratory experiments by Zhao and Roberts (2010). Our major finding is that a stable magnetization is acquired and retained after initial wetting of dry-deposited loess with no significant time lag, in general accord with recent findings.