第四紀後期における年代軸の決定と問題点 Geochronology in the Late Quaternary and Relating Problems
To reconstruct environmental changes in the late Quaternary, accurate dating is the most important. The framework of the late Quaternary chronology is based on magnetostratigraphy due to the reversal of geomagnetic polarity and oxygen isotope stratigraphy of foraminifera in marine sediments, which has been considered to be driven by astronomical forcing of solar energy reaching to the Earth, that is, the Milancovitch cycle. For dating during the past several tens of thouthands of years including the Last Glacial Period and the Holocene, radiocarbon dating is the most useful method. Recent developement of accelerator mass spectrometry (AMS) has realized precise dating by using mg amounts of carbon and AMS systems have been introduced widely. Basic concepts and methods of radiocarbon dating, especially on AMS radiocarbon dating, are reviewed and problems relating calibration of measured radiocarbon ages to calender ages are discussed.