Applying portable OSL to obtain a detailed chronology of littoral sedimentary sequences from the northern shore of Lake Schweriner See, Germany

Holocene sedimentary sequences lacking organic remnants or containing redeposited organic material pose a challenge for detailed chronological investigations, as radiocarbon dating is unsuitable. Optically stimulated luminescence (OSL) can be used instead, but high-resolution OSL is costly. A more cost-effective and efficient approach involves the combination of low-resolution OSL dating with portable OSL (pOSL) profiling in 5–10 cm increments (e.g. Sanderson and Murphy, 2010; Brill et al. 2016). This method has been employed in the analysis of cored lacustrine sedimentary sequences from the northern shore of Lake Schweriner See, Germany.

In well-bleached Holocene sediments, quartz equivalent doses and portable post-infrared blue-light stimulated luminescence signals (further pOSL) from the polymineral fraction are linearly correlated (e.g. Brill et al., 2016). We used the obtained linear functions to estimate equivalent doses (D_es) in quartz for each pOSL signal. The dose rates were then interpolated between full OSL samples, and the ages were calculated by dividing the D_es by the corresponding dose rates. Finally, both the quartz full OSL ages and the ages derived from the pOSL signals were incorporated into a Bayesian age-depth model to obtain a continuous chronology.

The pOSL-to-D_e ratio is also a useful tool in the identification of incompletely bleached samples. Poorly bleached sediments exhibit a higher pOSL-to-D_e ratio in comparison to well bleached sediments because pOSL is a composite of signals from quartz and feldspars, which require a greater exposure time for complete bleaching than OSL from pure quartz (e.g. Murray et al., 2012). In the littoral sequences studied, elevated pOSL-to-D_e ratios were found to correspond with high quartz D_eoverdispersion (OD), which is another indicator of poor bleaching. One particular sample was observed to exhibit a high pOSL-to-D_e ratio yet low OD (15%), which may be attributed to distinct OSL sensitivity linked to a specific sediment source.

Our results demonstrate that the proposed approach suits littoral sediments and improves chronological frameworks for lacustrine sequences. A potential avenue for further refinement of age-depth models lies in the measurement of dose rates for all pOSL samples, as opposed to their estimation through interpolation.

References

Brill, D., Jankaew, K., & Brückner, H. (2016). Towards increasing the spatial resolution of luminescence chronologies – Portable luminescence reader measurements and standardized growth curves applied to a beach-ridge plain (Phra Thong, Thailand). Quaternary Geochronology, 36, 134–147.

Murray, A. S., Thomsen, K. J., Masuda, N., Buylaert, J.-P., & Jain, M. (2012). Identifying well-bleached quartz using the different bleaching rates of quartz and feldspar luminescence signals. Radiation Measurements, 47(9), 688–695.

Sanderson, D. C. W., & Murphy, S. (2010). Using simple portable OSL measurements and laboratory characterisation to help understand complex and heterogeneous sediment sequences for luminescence dating. Quaternary Geochronology, 5(2–3), 299–305.