High-resolution OSL dating of the Costinesti section (Dobrogea, SE Romania) using fine and coarse quartz

摘要

Previous studies on the application of optically stimulated luminescence dating on quartz extracted from Romanian loess yielded inconsistent age estimates between different grain sizes. The present work reports a high-resolution SAR-OSL chronology for the L1 (MIS 2-4), S1 (MIS 5) and L2 (MIS 6) units of the loess-palaeosol profile from Costinesti, that contains at least five loess-palaeosol alternations and is located on the Black Sea Shore (Dobrogea, SE Romania). Analysis were performed on fine (4-11 μm) and coarse (63-90 μm) quartz grains extracted from 25 samples collected at very high resolution (10-20 cm). Luminescence investigations confirm the reliability of the SAR-OSL dating protocol previously applied to Romanian loess (preheat at 220 ℃ for 10 s, cutheat to 180 ℃ and elevated temperature OSL (ETOSL). The dose-response curve is best described by the sum of two saturating exponential functions. The results confirm the different saturation characteristics of fine and coarse grains of quartz, as reported in previous studies on loess sections in SE Romania. The equivalent doses obtained for coarse grains are higher than those obtained for fine grains, for all samples. The fine quartz OSL age estimates are significantly younger than the coarse quartz age results, as in the case of previous studies on the Mircea-Voda and Mostistea loess sections. Coarse quartz in samples collected from the upper part of S1 yielded ages of 94 ± 11 ka, 116 ± 11 ka and 120 ± 10 ka that do not seem to underestimate the true burial age. The same observation applies to the upper part of L2. Overall, from the luminescence results it can be concluded that the S1 palaeosol formed during the MIS 5, and the discrepancy observed on coarse and fine quartz OSL ages is a general feature of SE Romanian loess.