Comparison of luminescence dating methods on lake sediments from a small catchment: Example from Lake Yogo, Japan

Abstract

When applying luminescence dating to sediment deposited in aquatic environments, a key issue for accurate age determination is resetting of acquired luminescence in sediment by surface exposure (bleaching) before burial. The time needed for bleaching is known to vary among the signals used in three methods: optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), and post-infrared IRSL (pIRIR). A comparison of luminescence ages from these different signals is therefore useful to assess whether a sample was fully bleached before burial. In a comparison of OSL, IRSL50/225 and pIRIR225 ages of eight samples of fine-grained sediment from a 294-cm-long sediment core from Lake Yogo, a small-catchment lake in central Japan, the IRSL50/225 and pIRIR225 ages were much older than the OSL ages. The IRSL50/225 residual signals were close to zero, and the difference between pIRIR225 and OSL signals was much larger than the pIRIR225 residual signals. Thus, IRSL50/225 and pIRIR225 signals were not completely bleached, which we attribute to the short sediment transport distance in this small catchment. Five corrected bulk radiocarbon (14C) ages agreed with the OSL ages, except for two intervals in which OSL ages were about 500 and 1,900 years older than the corrected 14C ages. These discrepancies are attributable to incomplete bleaching related to sediment transport, whereas the rest of the OSL ages show no evidence of incomplete bleaching. This study shows that even in samples in which the pIRIR225 and IRSL50/225 signals are not well-bleached, OSL dating yields accurate age estimates because of the faster bleaching rate.