Bone diagenesis in Iron Age Siberia: a histological and microtomographic study of Tunnug 1 (Russia, 2nd-4th c. CE)

The Siberian site of Tunnug 1, located in the Uyuk Valley (Tuva Republic, Russia), encompasses an Early Scythian burial mound (9th century BCE) and a peripheral cemetery attributed to the Kokel culture (2nd-4th centuries CE). Situated within a permafrost-affected environment, the site offers an opportunity to investigate bone preservation under long-term freeze-thaw cycle conditions and explore the relationship between funerary treatment and bone diagenesis. This study presents a combined histological and microtomographic analysis of 76 bone samples from 71 individuals across 36 burials. Transmitted light microscopy, scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) were employed to document biological, chemical and physical degradation. Bone preservation was evaluated through three approaches: the traditional Oxford Histological Index (OHI), quantitative image analysis and assessment of (micro)cracking. The results revealed moderate bone preservation (OHI 2-4). Biological degradation in the form of Microscopical Focal Destruction (MFD) and chemical alteration were identified in six individuals. Enlarged canaliculi were observed in every bone sample. Microcracks were present in all individuals, visible exclusively under SEM. No clear diagenetic signatures linked to specific funerary practices were identified, though variations in preservation suggest a possible influence of burial depth. The distinct impact of permafrost and long-term freeze-thaw cycles on bone microstructure could not be isolated, underscoring the multifactorial nature of diagenesis. This study highlights the complementary value of combining multiple analytical methods assessing bone diagenesis and emphasises the need for continued experimental research into the effects of freezing environments on human remains.