Geochemical fingerprinting of basaltic glass in tephra deposits underlying the human footprints-bearing strata in Jeju Island, Korea: Provenance of tephra and age of the human footprints

Age of the human footprints in Sagyeri area, Jeju Island, Korea has been a subject of controversies since the discovery in 2004. This study reports a new basaltic tephra layer beneath the human footprints-bearing strata, and infers the source volcano of the tephra by comparing the major element composition of the glass and the componentry of accidental grains with those of the two nearby volcanic edifices (Songaksan volcano and Hyeongje Island) in addition to stratigraphic observations. Then we constrain the deposition age of the human footprints-bearing strata above the tephra layer, via revealing the eruption age of its source volcano. We found that the tephra layer at the footprints site is not only stratigraphically equivalent to the tephra rim beds of the Songaksan volcano but also compositionally identical to the glass in the major element content. Accidental quartz grains, which occur characteristically within the Songaksan Tuff, are also found in the tephra layer beneath the human footprints-bearing strata. These results suggest collectively that the tephra layer beneath the footprints-bearing strata was produced by the eruption of the Songaksan volcano. A set of new age data from the paleosol (C-14 age : ca. 3,600 yr BP) and the earthenware (OSL age : 5.5 +/- 0.7 ka) directly beneath the Songaksan tephra at a nearby archeological site, and from the shells (C-14 age : ca. 3,800 yr BP) from the lowermost tuff layer of the Songaksan tuff ring indicate that the human footprints-bearing strata, which accumulated above the tephra layer, are late Holocene strata that were deposited after the eruption of the Songaksan Volcano, ca. 3,800 yr BP. The significantly older ages of the organic matter in the bulk sediments at and near the footprints site (ca. 8,000 similar to 21,000 yr BP) are interpreted to be the results of the input of old terrestrial carbon material from the inland areas by reworking processes.