Identifying and dating buried micropodzols in Subatlantic polycyclic drift sands

Polycyclic soil sequences provide valuable archives of alternating unstable periods (sand drifting) and stable periods (soil formation) in NW-European coversand landscapes during the Subatlantic. Here we study six polycyclic soil sequences at the Weerterbergen (The Netherlands) to investigate how to read and interpret this geological archive. At each of the sites a micropodzol forms a clear stratigraphic marker between drift sand beds. We show that soil micromorphology is a practical method to distinguish geogenetic humic layers (containing redeposited organic material) from true pedogenic micropodzols. Optically stimulated luminescence dating of drift sand deposits above and below the micropodzols provides robust ages for periods of aeolian activity, and confines the timing and maximum duration of soil formation. We show that a pedogenic micropodzol was formed in many places in the study area around 1900 AD, and that the duration of this period of landscape stability differed between sites from decades to centuries. Radiocarbon dates, when carried out on soil organic matter, grossly overestimate the burial time of the micropodzols because the organic material in the micropodzols is a mix of geogenic particles and pedogenic carbon.