Chronostratigraphic and geomorphologic challenges of last glacial loess in Poland in the light of new luminescence ages
Authors: Zöller Ludwig , Fischer Manfred , Jary Zdzisław , Antoine Pierre , Krawczyk Marcin 
Published: April 2022

Abstract. The aim of this study is to check the validity of luminescence ages obtained
from last glacial–interglacial Polish loess palaeosol sequences (LPSs) by
several established current protocols, with respect to sound
geomorphological and chronostratigraphic interpretations. We report 38 new
optically stimulated luminescence (OSL) ages from fine-grained (4–11 µm) quartz separates extracted from four loess palaeosol sequences in Poland, measured in the Bayreuth
Luminescence Laboratory, Germany. The investigated sections are situated in
Lower Silesia in the southwest (Zaprężyn, Trzebnica Hills, and Biały Kościół, Strzelin Hills), the Sandomierz Upland (Złota) in central Poland, and the Volhynian Upland (Tyszowce) in the east, allowing for regional
comparison. From one Silesian section (Biały Kościół) 12 new post-infrared
infrared stimulated luminescence (pIRIR) ages are presented in addition to the quartz ages of identical sample
material. The obtained ages are compared to already published independently
elaborated middle-grain (45–63 µm) and coarse-grain (90–125 µm) quartz ages and pIRIR ages from fine grains produced in the Gliwice
Luminescence Laboratory (Poland). This comparison shows that in many cases
the middle- and coarse-grain quartz ages underestimate the fine-grain quartz
ages, but a general rule has not been able to be established so far, likely due to
different geological origin of the quartz grains. Even fine-grain quartz
ages ≥∼ 50 ka may be underestimated with respect to
lithostratigraphic expectations. For pIRIR ages, however, no evidence for
age underestimates has been found in the studied sections, but they are more easily prone to age overestimates due to unknown residual doses at
deposition in a periglacial environment. Basic agreement between the luminescence-based chronologies elaborated in
the two involved laboratories can be stated for the first time in contrast
to other previous studies. The observed age differences are, however,
critical for the accurate time bracketing of geomorphologic and
pedostratigraphic features such as ice wedging, thermokarst erosion events,
and interstadial soil formations and for their attribution to marine
isotope stages. Alternative interpretations are discussed including possible
periglacial mirroring of pre-LGM ice advances (Ristinge and Klintholm
advances) in the southwestern Baltic Sea area. The uncertainty in
luminescence ages from pre-Holocene loess due to fossil ice during
permafrost conditions is the major systematic error source which will be
addressed but at present is far from an unambiguous solution. The present
study focuses on a complex of interstadial soils now labelled L1SS1 and on
harsh periglacial climate afterwards and before, yielding some unexpected
results for the timing of ice wedging and thermokarst processes. In order
not to leave the users alone with the decision about the most credible
dating, the suggested way forwards is to simultaneously apply various
luminescence dating protocols including different quartz grain sizes and
pIRIR from fine polymineral grains, as an honest approach to reliable time
bracketing of geomorphological processes and stratigraphic events under debate.
A refinement of this approach remains challenging as far as the sole
reliable dating protocol is not ensured.