Testing post-IR-IRSL dating on Armenian loess-palaeosol sections against independent age control

Abstract

Loess-palaeosol sections (LPS) in northern Armenia exhibit at least three alternating loess and pedocomplex units, indicative of an environment changing between erosional/depositional and stable conditions. The LPS they are located in a central key position between loess in Europe, central Asia and the Russian/Ukrainian Plains. Since an accurate chronology is crucial for any palaeoenvironmental reconstruction and correlation with other proxy records, we establish a post-IR-IRSL chronology for two loess sections in the Sevkar loess area and compare it with independent age control. This is mainly based on an 40 Ar/ 39 Ar age of a tephra encountered in the L-2 loess layer from the penultimate glacial, which is dated to 194.0 ± 8.5 ka. Further checks on the accuracy are provided by the expected stratigraphy and comparison with other palaeoenvironmental records. The comparison indicates that a fading correction is necessary for the older samples within the L-2 loess layer but when correcting for fading with fading rates measured in the laboratory, the ages are clearly overestimated. Therefore, it is tentatively suggested using a reduced fading rate by subtracting a fixed percentage of the measured fading rate as surrogate for a laboratory artefact. In our study, we reduce all fading rates by 1%/decade and yield fading corrected pIRIR ages which are in agreement with the independent age control. The resulting chronology reaches down to at least MIS8 and shows that loess deposition in northern Armenia occurred during global cold phases, whereas global warm phases are associated with landscape stability and soil formation.