Constraints on the use of 137Cs as a time-marker to support CRS and SIT chronologies

CRS and SIT are two Pb-210-based models widely used in the radiometric dating of recent sediments. Pb-210 chronologies should be validated using at least one independent tracer, such as Cs-137. This paper demonstrates that simple methods based on the identification of Cs-137 fallout peaks cannot provide a definitive support for CRS and SIT chronologies. Two main arguments will support this assertion: Firstly, the Cs-137 time-marks cannot support a CRS or SIT chronology if the derived sedimentation rates cannot explain the whole Cs-137 activity profile without postulating mixing. Secondly, the support by the Cs-137 time-marks for a given CRS or SIT chronology cannot be considered as definitive if other dating models can equally explain the whole set of data, thereby producing a different chronology. Several case studies selected from the literature are used to support the present discussion. (C) 2003 Elsevier Ltd. All rights reserved.