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The bleaching limits of IRSL signals at various stimulation temperatures and their potential inference of the pre-burial light exposure duration
Infrared Stimulated Luminescence (IRSL) techniques are being increasingly used for dating sedimentary feldspars in the middle to late Quaternary. By employing several subsequent stimulations at increasing temperatures, a series of post-IR IRSL (pIRIR) signals with different characteristics (stability and bleachability) can be obtained for an individual sample. It has been experimentally demonstrated that higher-temperature pIRIR signals are more stable, but they tend to exhibit larger residual doses up to few tens of Gy, potentially causing severe age overestimation in young samples. In this study we conducted comprehensive bleaching experiments of IRSL and pIRIR signals using a loess sample from China, and demonstrated that non-bleachable components in the IR (and possibly pIRIR) signals do exist. The level of such non-bleachable signal shows clearly positive correlation with preheat/stimulation temperature, which further supports the notion that lower temperature pIRIR are advantageous to date young samples and sediments especially from difficult-to-bleach environments. These results display a potential in constrain the pre-burial light exposure history of sediment utilizing multiple feldspar post-IR IRSL (pIRIR) signals. For the studied loess sample, we infer that prior to its last burial, the sample has received an equivalent of >264 h exposure to the SOL2 simulator (more than 2,000 h of natural daylight).
K-feldspar pIRIR150 dating of the Late Pleistocene sediments in the NW Khangai Mountains (Mongolia) using a standardized dose-response curve approach
K-feldspar luminescence dating has been widely applied to constrain the timing of Quaternary sedimentation in different environments. However, the measurements are time-consuming. Meanwhile, anomalous fading and partial bleaching are the two potential problems inducing dating uncertainty. In this study, sand-size K-feldspar grains extracted from 32 luminescence samples from the northern slope of the Khangai Mountains, Mongolia, were dated using the post-infrared (IR) infrared stimulated luminescence protocol (pIRIR150. subscript shows the second stimulation temperature). The standardized dose-response curves (sDRCs) for luminescence dating, which could improve the measurement efficiency, were constructed. The K-feldspar luminescence chronology has been established after careful investigations of fading correction and bleaching degree of the signals. The sDRCs and individual DRC yield consistent ages, indicating that sDRCs are applicable for luminescence dating with an improvement in measurement efficiency. The fading corrected ages using the two fading correction models are generally in agreement. Based on age comparisons between the radiocarbon dates, the fading corrected pIRIR150 and IR50 ages, the pIRIR150 signal was not fully bleached for several samples. In contrast, some IR50 ages were overestimated due to fading over-correction. The investigated profiles have documented the sedimentary information since the last deglaciation.
Multi-method study of the Middle Pleistocene loess-palaeosol sequence of Köndringen, SW Germany
Loess-palaeosol sequences (LPSs) remain poorly investigated in the southern part of the Upper Rhine Graben but represent an important element to understand the environmental context controlling sediment dynamics in the area. A multi-method approach applied to the LPS at Köndringen reveals that its formation occurred during several glacial-interglacial cycles. Field observations, as well as colour, grain size, magnetic susceptibility, organic carbon, and carbonate content measured in three profiles at 5 cm resolution, provide detailed stratigraphical information. Only minor parts of the LPS are made up of loess sediment, whereas the major parts are polygenetic palaeosols and pedosediments of varying development that are partly intersected, testifying to a complex local geomorphic evolution. The geochronological framework is based on 10 cm resolution infrared-stimulated luminescence (IRSL) screening combined with 18 multi-elevated-temperature post-IR IRSL ages. The luminescence ages indicate that two polygenetic, truncated Luvisols formed during marine isotope stages (MISs) 9(-7?) and MIS 5e, whereas unaltered loess units correspond to the last glacial (MISs 5d-2) and MIS 8. The channel-like structure containing the two truncated Luvisols cuts into > 2 m thick pedosediments apparently deposited during MIS 12. At the bottom of the LPS, a horizon with massive carbonate concretions (loess dolls) occurs, which may correspond to at least one older interglacial.