THERMOLUMINESCENCE DATING OF THE ORKUTSAY LOESS SECTION IN TASHKENT REGION, UZBEKISTAN, CENTRAL-ASIA

The chronology of loess in Central Asia was investigated by means of t hermoluminescence dating (TL) in the 1970s, when age estimates ranging from 20 ka to over 800 ka were taken as providing an absolute chronol ogy. This has caused major misinterpretation of Central Asian loess st ratigraphy and palaeoclimatic reconstruction. We present a new TL stud y of a loess section at Orkutsay in the Tashkent Region, Uzbekistan. N ine samples spreading over a large stratigraphic interval yield appare nt TL ages ranging from 20 ka to 134 ka. We interpret our TL results w ith reference to recent TL dating studies of loess from other regions. We consider most of our TL age estimates obtained by the regeneration method to be underestimated. A single TL date of 92.8 ka obtained by the total bleach method for loess just below the first pedocomplex (PC I) of the last interglacial is also significantly younger than expecte d. We attribute the underestimation to sensitivity change induced by t he laboratory optical bleach and instability of the TL signal. We conc lude that the current TL techniques as employed in this study cannot p rovide a reliable absolute chronology for the sequence below PC1 and c annot provide even a relative chronology for the loess below PC2. For the Orkutsay section the dating limit is around 130 ka. The results of this study suggest that the previous Central Asian loess chronology b ased on early TL studies is not valid.