Appendix S1

OSL dating provides an estimate of the time elapsed since luminescent minerals, such as quartz, were last exposed to sunlight (Huntley et al., 1985; Aitken, 1998; Lian and Roberts, 2006; Jacobs and Roberts, 2007). Buried grains are exposed to an ionizing radiation flux (the 'dose rate') from the surrounding sediments and from cosmic rays, resulting in the absorption of energy and storage of trapped charge. The corresponding 'equivalent dose' (De) can be estimated using the OSL signal, and the burial age then obtained by dividing the De by the environmental dose rate. Table S1 lists the data used to determine the dose rates, De values and burial ages of the two sediment samples collected from Aybut Auwal (AYB1-OSL1 and AYB1-OSL2).光释光测年（Optically Stimulated Luminescence Dating，OSL）可估算石英等发光矿物末次受日光照射以来所经历的时长（Huntley等，1985；Aitken，1998；Lian与Roberts，2006；Jacobs与Roberts，2007）。被埋藏的矿物颗粒会受到周围沉积物及宇宙射线产生的电离辐射通量（即“剂量率”）的照射，进而吸收能量并储存被俘获的电荷。利用OSL信号可估算对应的等效剂量（equivalent dose，De），随后通过将De除以环境剂量率即可求得埋藏年龄。附表S1列出了用于测定采自Aybut Auwal的两个沉积物样品（AYB1-OSL1与AYB1-OSL2）的剂量率、De值及埋藏年龄的相关数据。