An automated method for varve interpolation and its application to the Late Glacial chronology from Lake Suigetsu, Japan

The Lake Suigetsu sediment has been recognised for its potential to create a wholly terrestrial (i.e. non-reservoir-corrected) 14C calibration dataset, as it exhibits annual laminations (varves) for much of its depth and is rich in terrestrial leaf fossils, providing a record of atmospheric radiocarbon. Microscopic analysis revealed that the varve record is curtailed due to the incomplete formation or preservation of annual laminae, necessitating interpolation. The program for varve interpolation presented here analyses the seasonal layer distribution and automatically derives a sedimentation rate estimate, which is the basis for interpolation, and applies it to complement the original varve count. As the interpolation is automated it largely avoids subjectivity, which manual interpolation approaches often suffer from. Application to the Late Glacial chronology from Lake Suigetsu demonstrates the implementation and the limits of the method. To evaluate the reliability of the technique, the interpolation result is compared with the 14C chronology from Lake Suigetsu, calibrated with the tree-ring derived section of the IntCal09 calibration curve. The comparison shows that the accuracy of the interpolation result is well within the 68.2% probability range of the calibrated 14C dates and that it is therefore suitable for calibration beyond the present tree-ring limit.