Luminescence dating of mortar and terracotta from a Royal Tomb at Ulaankhermiin Shoroon Bumbagar, Mongolia

Abstract

The spectacular royal tomb “Ulaankhermiin Shoroon Bumbagar” was discovered in Bulgan province, Mongolia, in 2011. Excavation of the site revealed its internal structure; a slope of 42 meters in length leading down to the underground mausoleum at a depth of 7 m below the ground. Archaeological investigations provided the site with an independent age control suggesting the construction date of the Royal tomb to the last quarter of the VII century.

In this study, we directly date different materials from the site, such as terracotta figurines, mortar and host sediment, using infrared-stimulated (IR₅₀) and postinfrared infrared stimulated (pIRIR) luminescence techniques. The most accurate estimate of 670 ± 70AD and 550 ± 110AD was obtained for terracotta figurines using IR₅₀ and pIRIR on aliquots of 4–11 µm polymineral grains. By comparison, sand-sized quartz single grain measurements on the embedded sediment yielded normal equivalent dose (D_e) distributions with a few outliers, justifying the use of the central age model (CAM) for age calculation, and yielded construction dating to the 780 ± 140AD. Finally, sand-sized quartz single grain measurements on wall mortar revealed incomplete bleaching of grains, requiring detailed analysis using statistical approaches; from this we identified the most well bleached population age of 740 ± 130AD, using the lowest 5%. The luminescence ages are in general agreement with the historically expected age.

Statement of significance The archaeological site at Ulaankhermiin Shoroon Bumbagar, Mongolia (with an independent age control) offers a great opportunity to apply luminescence dating methods, such as pIRIR on 4–11 µm polymineral fine grains, and single grain measurements on 200–250 µm quartz grains, to various materials, such as terracotta figurines, mortar-like limestone which covered the walls and embedded sediment in order to test the accuracy of optically stimulated luminescence (OSL) dating techniques. Compared to all other datable archaeological materials, mortar has the advantage of being intentionally manufactured at each stage of construction, since it cannot be recycled. However, dating of the well bleached grains of mortar, which provided the greatest challenge in this study, was achieved using the lowest 5% estimate, yielding an age of 740 ± 130AD. pIRIR on heated polymineral (feldspar-bearing) fine grain aliquots from terracotta figurines was tested, yielding IR₅₀ and pIRIR₁₈₀ dates in agreement with the CAM estimate from the host sediment.

Cite this article Solongo, S., Ochir, A., Tengis, S., Fitzsimmons, K., and Hublin, J.-J. Luminescence dating of mortar and terracotta from a Royal Tomb at Ulaankhermiin Shoroon Bumbagar, Mongolia. STAR 2015; 1(2), STAR2015122054892315Y.0000000004

Data availability The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are contained within the paper.