230Th/234U dating of Holocene mollusk shells from Jeju Island, Korea, by multiple collectors inductively coupled plasma mass spectrometry

The Th-230/U-234 ages of fossil mollusk shells collected from the Sinyangri and Hamori Formations, the youngest stratigraphic units on Jeju Island, Korea, were estimated using multiple collectors inductively coupled plasma mass spectrometry. Seven aragonite shells yielded Th-230/U-234 ages ranging from 3434 +/- 40 yr to 4980 +/- 33 yr (2 sigma), in concordance with radiocarbon ages for samples containing little Th-232. Our data suggest that the Th-230/U-234 method can be a potentially useful tool for dating Holocene mollusks, provided that there is no evidence for severe recrystallization, cementation, and considerable amount of common thorium. An early uptake of uranium immediately after burial and subsequent maintenance of closed system for uranium and thorium can be assumed for our mollusk samples. This study, together with previous radiocarbon and optical dating results, demonstrates that the Hamori Formation where human footprints were recently discovered deposited during the middle Holocene.