Flood and earthquake disturbance of ²¹⁰Pb geochronology (Lake Anterne, NW Alps)

Abstract

Dating recent lake sediment records yielding disturbed 210 Pb profiles has been a problem of wide interest in palaeoclimatic and palaeoseismic studies over the last few centuries. When applied to an alpine lake sedimentary record, a high‐resolution sedimentological study reveals that the 210 Pb profile is disturbed by the occurrence of single‐event deposits triggered by two different mechanisms: flood events deposits and gravity reworking. Removing disturbed layers from the 210 Pb profile yields a logarithmic depth–activity relationship. Using a simple 210 Pb decay model (CFCS) provides an assessment of mean accumulation rate of `continuous sedimentation', as opposed to `event‐linked sedimentation'. The correlation of the thickest four gravity‐reworked deposits with historically known earthquakes permits both validation and refinement of the age–depth relationship. This refinement highlights variations in accumulation rate consistent with post‐Little Ice Age climatic variations.