LUMINESCENCE DATING OF AN ANCIENT WALLED SETTLEMENT IN ORKHON VALLEY, MONGOLIA

Bemmann J,Munkhbayar L,Saran S,Tengis S

doi:10.5564/pmas.v57i4.918

Abstract

We investigated the potential of the optically stimulated luminescence (OSL) method to date young (<1000 years) samples collected in the Orkhon Valley Cultural Landscape, Mongolia. Quartz showed an infrared signal; therefore the post-IR OSL method was applied to small aliquots which are considered proxies for single grain measurements. Statistical analysis of the dose distribution produced CAM De of 5.14±0.10 Gy and over dispersion of 47.5%, and MAM De of 3.7±0.6 Gy. Since no partial bleaching was suspected, the analysis of signal composition was done and the fast quartz post-IR OSL lead to De of 4.9±0.2 Gy. Based on the quartz fast component and CAM De we propose the new chronology of ancient construction at 785±80 AD, rather than 906-1125 AD as suggested by archaeological evidence. However, the MAM age is in good agreement with independent age control for construction of the ramparts suggesting the date of reconstruction, collapse or reuse for the square walled enclosure MOR3 during 1090±80AD.

Highlights

The luminescence technique [2] is based on the fact that many naturally occurring minerals, including quartz and feldspar are able to act as dosimeters for the amount of ionizing radiation they are exposed to
This assumption appears to be the case with ceramics and bricks during the firing process; fired clay brick samples were successfully dated by the thermoluminescence (TL), optically stimulated luminescence (OSL) and post-infrared stimulated techniques [21], [24], [20]; using different brick samples they were able to reconstruct the construction of the palatial complex, the palace and the city walls in Karakorum - the ancient capital of the Mongol Empire
De results The methodology is far more advanced and better understood for quartz in comparison to feldspar and tends to give reliable estimates, several studies dealing with OSL quartz dating reported problems with low luminescence efficiency observed most commonly in young samples [17]

Summary

Introduction

The luminescence technique [2] is based on the fact that many naturally occurring minerals, including quartz and feldspar are able to act as dosimeters for the amount of ionizing radiation they are exposed to. A quartz fast component [4] is the signal used for De evaluation using the single aliquot regenerative-¬dose protocol by [25]. Coarse grains (150μm) 2mm aliquots were prepared for OSL and post-IR OSL luminescence measurements.

Results

Conclusion