Prelude to the extinction: Revision of the Achchagyi-Allaikha and Berelyokh mass accumulations of mammoth

The little known Achchagyi-Allaikha mass assemblage of mammoths and the well-known Berelyokh site (Lower Indigirka River, Arctic Siberia) were studied. Detailed study of the Achchagyi-Allaikha site provided ample data concerning its geology, stratigraphy, taphonomy, and the gender-age structure of the taphocoenosis. The Achchagyi-Allaikha assemblage included redeposited bones from numerous young (not less than 21) and some adult female mammoths, with limited quantities of Bison, Equus and Rangifer bones. Collagen from mammoth bones preserved at the Achchagyi-Allaikha site (n = 6) was radiocarbon-dated at 12,490 ± 80 to 12,400 ± 60 BP. At the Berelyokh site, eight mammoth bones were radiocarbon-dated at 12,720 ± 100 to 11,900 ± 50 BP, one bison bone was dated at 12,380 ± 150 BP, and one mammoth bone dated at 36,500 ± 1000 (redeposited bone included in younger sediments). The mass accumulations are synchronous and are similar in their mode of formation. The assemblage of mammoths in the Achchagyi-Allaikha and Berelyokh sites resulted from simultaneous deaths of a large number of animals (probably herd-family groups) in one or several seasons. It is very probable that the deposits in both cases were not of cultural origin. The formation of the burials is a direct consequence of short but strong climatic warming (Bølling Oscillation) that resulted in many unfavorable environmental conditions. Among these, the increase of snow cover and stronger spring floods were very notable. Bølling warming is a model of the large-scale Holocene event. Mass death of mammoths during the Bølling phase was a prelude to their final extinction.