Multi-method luminescence investigations on quartz grains of different sizes extracted from a loess section in Southeast Romania interbedding the Campanian Ignimbrite ash layer

Abstract

Abstract:In this study we present luminescence investigations of four samples of loess bracketing the Campanian Ignimbrite/Y5 tephra at the Rasova-Valea cu Pietre site, on the eastern bank of the Danube River, southeastern Romania. Investigations involved SAR-OSL dating on aliquots of fine (4-11 μm) and medium-grained (63-90 μm) quartz, as well as single grain analyses on 125-180 μm quartz. Luminescence dating results coupled with glass-shard chemical fingerprinting assign the depositional age and origin of the ash layer to that of the Campanian Ignimbrite/Y5 tephra, dated elsewhere using 40 Ar/ 39 Ar to 39.28 ± 0.11 ka. Fine-grained (4-11 μm) quartz SAR-OSL analyses yielded ages of 44.4 ± 4.5 ka below the ash, and 41.4 ± 4.2 ka above the ash layer. Single grain analysis on coarse-grained quartz, however, demonstrates that coarse material from these samples exhibits low sensitivity and responds poorly to internal checks of the SAR protocol in comparison with the finer sediment. This observation highlights the need for more extensive investigations into the luminescence properties of quartz as well as into the origin of quartz contributions from different primary sources in the Lower Danube loess steppe.

On the importance of grain size in luminescence dating using quartz

“…The good agreement of the ages obtained using different grain sizes of quartz in the low dose range increases our confidence in the accuracy of the SAR-OSL ages for samples with equivalent doses of about 100 Gy or less, as further confirmed by comparison with independent age control provided through tephrochronology (Constantin et al, 2012;Anechitei-Deacu et al, 2014) or radiocarbon dating (Trandafir et al, 2015). On the other hand, the age discrepancy of SAR-OSL ages previously reported for Romanian and Serbian loess for ages beyond~40 ka (equivalent doses >~100 Gy) was also found to be characteristic of Chinese loess.…”

Danube loess stratigraphy — Towards a pan-European loess stratigraphic model

“…2012; Timar-Gabor et al, 2011, 2012Timar-Gabor and Wintle, 2013); it has been suggested that this may reflect variations in depositional processes and source sediment of the different size fractions (Anechitei-Deacu et al, 2014) but at present the cause of these discrepancies is unclear. At present, the most reliable quartz OSL dating results for Danubian loess appear to derive from finegrained material, for ages up to ca.…”

“…At present, the most reliable quartz OSL dating results for Danubian loess appear to derive from finegrained material, for ages up to ca. 70 ka , and loess sections in Romania have been successfully dated within these limitations (Anechitei-Deacu et al, 2014;Constantin et al, 2012Fitzsimmons et al, 2013Fitzsimmons and Hambach, 2014), alongside sections in Serbia (Schmidt et al, 2010, Stevens et al, 2011. However, studies employing quartz OSL in Hungary have sometimes met with poor quartz luminescence properties such as low signals and reproducibility, although reliable ages may be obtained (Schatz et al, 2012).…”

“…2014; Stevens et al, 2011;Thiel et al, 2011;Timar-Gabor et al, 2011;Schmidt et al, 2010;TimarGabor and Wintle, 2013;Fitzisimmons and Hambach, 2014;Zöller et al, 2014). These developments in luminescence dating have been reviewed elsewhere (e.g.…”

“…Veres et al, 2013a;Fitzsimmons et al, 2013;Anechitei-Deacu et al, 2014;Constantin et al, 2012;Wacha and Frechen, 2011). The lower Danubian loess represents one of the few regions in Eastern Europe which can be used to test the accuracy of luminescence dating techniques, although species specific AMS 14 C dating of small gastropod shells may also prove important for younger deposits (Pigati et al, 2013).…”