Radiocarbon dating and the reconstruction of late Quaternary sea-level changes in Hong Kong

Abstract

Radiocarbon dating is used widely for the reconstruction of late Quaternary sea-level changes. In the present study, eight case studies in Hong Kong have been chosen to highlight the difficulty in obtaining reliable radiocarbon dates. Pre-Holocene radiocarbon dates exceeding about 8100 yr BP have been found to show a young age bias. A shell sample dated by two separate radiocarbon laboratories gave last interstadial ages differing by almost 9500 years while an oxygen-isotope stage 5e age was obtained using uranium-series dating. Other evidence including stratigraphy has shown that only the last interglacial age is acceptable. The young age bias is attributed mainly to the post-depositional introduction of 'young' carbon into the sample. For the reconstruction of sea-level changes, it is essential to select samples immediately above the base of the Holocene transgressive unit in offshore boreholes and excavations to satisfy the criteria of rapid burial. These samples should preferably include mud, plant matter and shells to facilitate interpretation. Furthermore, as many samples as possible from a range of water depths down to about 130 m below the present sea level should be dated to reduce error introduced by counting statistics so the true signal of sea-level changes can be reflected.