A combined approach of obsidian provenance analysis and hydration dating supports the validity of archaeostratigraphy: A case from the Tachikarushunai V site Loc. C, Hokkaido, Japan

• Archaeostratigraphic integrity along slope is evaluated by obsidian hydration dates. • Obsidian provenance analysis is used to choose samples for hydration dating. • Microscopic observations on hydration rims show surfaces are partially eroded. • Internal rim measurements show a time difference between stratigraphic units. • Difference in estimated dates supports the archaeostratigraphic integrity. While the principle of stratigraphic superposition in archaeostratigraphy provides a basis for determining the chronological order of archaeological assemblages, the chronological interpretation of artifacts in slope settings, often disturbed by periglacial processes, hinges on the integrity of archaeological assemblages. Accordingly, the present study evaluates the integrity of lithic assemblages from the upper and lower units of the Tachikarushunai V site Loc. C (Tachikarushunai V-C) in a slope setting in northeastern Hokkaido, Japan, by examining the hydration dates of geochemically sourced obsidian artifacts. Although the distributions of surface rim measurements were not significantly different, we estimated more reliable dates from the inner rims, as surface erosion implied by pits observed on the obsidian surfaces. Based on these inner rim measurements, we observed a chronometric difference between the upper and lower assemblages (upper: 13,260 years ago, lower: 26,802 years ago), thus supporting the integrity of the archaeostratigraphy of Tachikarushunai V-C. Moreover, the technological difference between the upper and lower assemblages of Tachikarushunai V-C (upper: wedge-shaped microblade technology with the Yubetsu method, lower: flake production technology with some blades) is consistent with the reported dates from comparable Upper Paleolithic assemblages in Hokkaido and neighboring Beringian assemblages, particularly those associated with microblade technology.