Abstract
Radiocarbon (14C) ages were determined for dentine collagens of Naumann's elephant (Palaeoloxodon naumanni) and Yabe's giant deer (Sinomegaceros yabei) fossils recovered from the Late Pleistocene Nojiri-ko Formation distributed at the western area of Lake Nojiri, northern central Japan. 14C dating was conducted with a Tandetron accelerator mass spectrometer at the Dating and Materials Research Center, Nagoya University. Fossil samples were demineralized in a cellulose tube with HCI and separated into soluble and insoluble materials by centrifugation. The latter were heated at 90℃ in water and the filtrate was freeze-dried to obtain gelatinized collagen. The former was freeze-dried as soluble collagen. The values of C/N ratio and 14C age agreed well between the two types of collagens extracted from the same sample. 14C ages are classified into three groups: (a) Most molars of Naumann's elephant yielding apparently reasonable ages, which closely coincide with ages for wood fossils excavated from the same horizons; (b) Tusks of Naumann's elephant and antler of Yabe's giant deer fossils yielding ages younger than those for wood fossils; (c) A fow elephant molars yielding older ages. Specimens belonging to (a) and (c) are well-preserved and contain more than 1% gelatinized collagen with C/N ratios of around 3. 2. Specimens (c), however, are assumed to be reworked from lower beds. Specimens (b) may be contaminated from materials with younger carbon in the sediments. Radiocarbon dates obtained from (a) for the Nojiri-ko Formation range from 11,000 to 50,000 y. B. P. Comparison of these 14C ages with those formerly determined by the conventional β-rays counting technique shows that 14C ages obtained by both methods coincide with each other for ages younger than 23,000 y. B. P. However, our 14C ages older than 23,000 y. B. P. resulted in about 8,000 to 15.000 years older than ages obtained by the conventional methods.
