DOI: 10.1594/pangaea.877342
title: OSL age determination of the Batagay thaw slump, Northeastern Siberia, link to file in Microsoft Excel format

description: We describe the stratigraphical, cryolithological: and geochronological characteristics of a permafrost sequence near Batagay in the Siberian Yana Highlands, the interior of the Sakha Republic (Yakutia), Russia. The recently formed Batagay mega-thaw slump exposes permafrost deposits to a depth of up to 80m and gives insight into a climate record close to Verkhoyansk, which has the most severe continental climate in the Northern Hemisphere. The lower part of the permafrost exposure was sampled for optically stimulated luminescence (OSL) dating. Two samples were taken in the form of cores from unfrozen but observably undisturbed deposits at the outer margin of thermokarst mounds. The tubes were sealed with opaque tape and transported to the OSL laboratory of TU Bergakademie Freiberg, Germany. One separate sediment sample was taken for high-purity germanium (HPGe) low-level gamma spectrometry in order to determine the radionuclide concentration required for dose rate calculations. OSL samples were treated under subdued red light. The outer 2 cm material layer was removed to retrieve only the inner core part that was not exposed to any light during sampling. The outer material was used for in situ water content measurements. The inner core part was processed for quartz and feldspar separation. Quartz procedures yielded sufficient material in the 90-160 µm as well as in the 63-100 µm fractions, while Krich feldspar yielded only sufficient quantities for one sample in the 63-100 µm fraction. The chemical mineral separation and cleaning included the removal of carbonates (HCl 10 %) and organics (H2O2 30 %). The feldspar was separated from quartz using feldspar flotation (HF 0.2 %, pH 2.4- 2.7, and dodecylamine). Subsequently, the density separation was performed to enrich K feldspars (2.53-2.58 g cm-3) and quartz (2.62-2.67 g cm-3). Quartz extracts were etched (HF 40 %) to remove the outer 10 µm of individual grains. After a final sieving, homogeneous sub-samples (aliquots) of quartz and K-feldspar extracts were prepared as a monograin layer on aluminium discs within a 2mm diameter. OSL and infrared stimulated luminescence (IRSL) measurements were performed using a Risø TL/OSL Reader DA-20 equipped with a 90 Sr beta irradiation source (4.95 Gy min-1). Feldspar signal stimulation was performed at 870 nm with infrared diodes (125 °C for 100 s) and the emission was collected through a 410 nm optical interference filter to cut off scattered light from stimulation and was detected with a photomultiplier tube. For quartz, blue LEDs of 470 nm were used for signal stimulation (125 °C for 100 s) and detection using a U 340 Hoya optical filter. Preheat and cut-heat temperatures were set to 240 and 200 °C, respectively. The measurement sequence followed the single-aliquot regenerative-dose (SAR) protocol, including tests of dose recycling, recuperation, and correction for sensitivity changes. Appropriate measurement conditions were evaluated and adjusted based on preheat and dose-recovery tests. Processing of measured data and statistical analyses were performed using the software Analyst v4.31.7 and the R package "Luminescence" for statistical computing. Sets of 10-40 equivalent doses for individual samples and grain size fractions were analyzed for skewness and data scatter. To address sediment mixing that potentially affects permafrost sediments, age modelling was based on the central age model (CAM).