Erosion or age overestimation? – the Urluia loess-palaeosol sequence

Abstract

Aeolian deposits, such as loess, are considered the ideal material for luminescence dating. However, recent studies have revealed problematic discrepancies between different grain size fractions of quartz (e.g., Timar-Gabor, 2015). Nevertheless, the emergence of the pIRIR protocol (e.g., Thiel et al. 2011) gives us another useful tool for the investigation of loess-paleosol sequences, especially in higher dose ranges. This poster presents the luminescence investigation of 13 fine grain samples from the Urluia loess-palaeosol sequence in the Lower Danube Basin in eastern Romania.

Polymineral samples were dated with the pIR50IR290 protocol and equivalent doses range from ~80 to ~620Gy. For the lower dose range two fine grain quartz ages confirm the pIRIR chronology (following the SAR protocol, Murray and Wintle, 2000, 2003), but for the higher dose range no quartz sample delivered reliable results as no preheat plateaus could be achieved. The investigations included preheat plateau and dose recovery tests for the quartz fractions and prior IR stimulation temperature tests, dose recovery tests and residual dose measurements for the polymineral fraction. All residual doses are <8Gy after bleaching for 24h in a solar simulator.

The performance of the luminescence data speaks for a reliable chronology, however, resulting ages do not confirm the existing stratigraphy: in the depth of 7-8.5m equivalent doses increase by ~150Gy (~60ka), indicating either a strong erosional event or an age overestimation. Equivalent doses show only minor increase in the lower part of the profile, which might indicate that the signal is approaching saturation, at least for the two lowermost samples. No indicators for erosion in the stratigraphy or within other investigated proxy data are visible and it still remains unclear where the discrepancy in expected ages and measured results comes from.

Murray AS, Wintle AG (2003), Radiation Measurements 37: 377-381.
Murray AS, Wintle AG (2000), Radiation Measurements 32: 57-73.
Thiel C, Buylert J-P, Murray AS, Terhorst B, Hofer I, Tsukamoto S, Frechen M (2011), Quaternary International 234: 23-31.
Timar-Gabor A, Constantin D, Marković, SB, Jain M (2015), Quaternary International 388: 168-176.

Resources

• UKlum_Urluia_CB_final.pdf

Bibliography

Bösken, J., Klasen, N., Zeeden, C., Obreht, I., Markovic, S., Veres, D., Hambach, U., Lehmkuhl, F. (2016): Erosion or age overestimation? – the Urluia loess-palaeosol sequence. UK Luminescence and ESR meeting 2016, 11th-13th July 2016, Liverpool, Great Britain.