Establishing a Luminescence-Based Chronostratigraphy for the Last Glacial-Interglacial Cycle of the Loess-Palaeosol Sequence Achajur (Armenia)

Abstract

The loess-palaeosol section Achajur is part of the Sevkar loess area in north-eastern Armenia and comprises three prominent pedocomplexes with intercalated loess units, probably spanning at least three glacial-interglacial cycles. With its central position between the Black Sea and the Caspian Sea, the Sevkar loess area serves as important bridge between loess sections in southeastern Europe and Central Asia. Establishing a numerical chronology of the Achajur loess section enables correlation with other loess-palaeosol sections and a palaeoenvironmental reconstruction of the region. In this paper, we focus on the chronology of the last glacial-interglacial cycle using luminescence dating on fine grain (4–11 µm) material. We compare two post-IR-IRSL protocols on polymineral fine grain using different stimulation temperatures, in order to evaluate the influence of fading and potential unbleachable residuals on our samples. For a backup of the younger ages (<50 ka), we also applied a single aliquot protocol on the quartz fine grain fraction. The results indicate that the upper loess unit was deposited during MIS3 and 4, while MIS2 ages are not present. The underlying pedocomplex and loess unit fall into MIS5 and MIS6, respectively. This confirms that the loess was deposited during dry phases and pedocomplexes formed during wetter phases, as is also shown by comparison with other palaeoenvironmental proxies from the area.

Last glacial loess dynamics in the Southern Caucasus (NE-Armenia) and the phenomenon of missing loess deposition during MIS-2

“…S5 a,b. The applicability of the protocol was confirmed by dose recovery tests and comparison with quartz OSL ages for the younger samples (< 60 ka) 39 , 109 . For older samples, especially within the MIS6 loess layer, ages were underestimated, probably due to fading.…”

“…For older samples, especially within the MIS6 loess layer, ages were underestimated, probably due to fading. This was made evident by comparison with a tephra layer located in the lower part of the MIS6 loess, which was dated to 194.0 ± 8.5 ka 39 , and by laboratory fading tests 39 , 109 Since laboratory fading rates often appear overestimated, measured fading rates were subtracted by a fixed rate of 1%, in order to represent the laboratory artefact responsible for the overestimation. This reduced fading rate was applied with the correction approach of 110 .…”