In fluvial and deltaic environments, different grain-size fractions experience varying degrees of bleaching of OSL signals due to variations in hydrodynamics and depositional processes. This has led to ambiguity for selection of grain-size fraction suitable for OSL dating. Comparison of OSL results from multiple grain-size fractions is one approach to ensure the reliability of OSL ages. We determined the quartz OSL ages of four grain-size fractions from fine silt to sand, together with the single grain OSL sensitivity in a Holocene sediment core from the Yangtze delta. For samples from the lower part of the sediment succession (including tidal river, tidal trough fill, estuarine front, tidal sand and delta front facies), OSL ages determined for different grain-size fractions were generally mutually consistent within the age range of ~2–9 ka, implying minor portion of incompletely bleached grains in the sediment at the time of burial. In contrast, significant partial bleaching was observed for three samples from younger delta front facies deposited during 0.4–0.6 ka. In these three samples, fine-silt quartz OSL ages were overestimated by ~0.5–2.0 ka compared with ages of coarser fractions. Based on the investigation of quartz luminescence sensitivity, we suggest that the southward shift of the Yellow River and increasing erosion in the Yangtze River catchment have led to enhanced water turbidity, resulting in partial bleaching of the sediment and substantial overestimation of the quartz OSL ages of fine silt during 0.4–0.6 ka. Alternatively, the erosion of older deposits and their redeposition elsewhere could retain large residual OSL ages. Notably, fine-silt quartz provides reliable ages for the period of 9–2 ka, suggesting that there was a lower degree of water turbidity compared with that since 2 ka. Therefore, the degree of OSL age overestimation may provide an indication of changes in water turbidity and sedimentary environment. Overall, our findings highlight the complexity of OSL dating in delta environments, and that an understanding of sediment transport and depositional processes is critical for reliable OSL dating.

在河流和三角洲环境中，由于流体动力学和沉积过程的变化，不同粒度的部分经历了OSL信号漂白的程度不同。这导致选择适合OSL测年的粒度级分的模棱两可。比较多种晶粒度的OSL结果是确保OSL年龄可靠性的一种方法。我们确定了从细粉砂到沙的四个粒度级分的石英OSL年龄，以及长江三角洲全新世沉积岩心中单颗粒OSL的敏感性。对于沉积物序列下部的样品（包括潮汐河，潮汐槽填充物，河口前沿，潮汐砂和三角洲前沿相），针对不同粒度级分确定的OSL年龄在〜2年龄范围内通常相互一致。 – 9 ka，这意味着在埋葬时，沉积物中有少量的不完全漂白的谷物。相反，从0.4-0.6 ka沉积的较年轻三角洲前相的三个样品中观察到了明显的局部漂白。在这三个样品中，与较粗级分的年龄相比，粉砂石英OSL的年龄被高估了约0.5-2.0 ka。根据对石英发光敏感性的调查，我们认为黄河南移和长江流域的侵蚀增加导致水浊度增加，导致沉积物部分漂白，并严重高估了石英OSL年龄。在0.4–0.6 ka期间细粉沙。另外，较老的沉积物的侵蚀及其在其他地方的再沉积可能会保留大量的OSL残留年龄。值得注意的是 细粉石英提供9–2 ka的可靠年龄，这表明与2 ka以来相比，水浊度较低。因此，OSL年龄的高估程度可能提供水浊度和沉积环境变化的指示。总体而言，我们的发现强调了三角洲环境中OSL测年的复杂性，并且对沉积物迁移和沉积过程的理解对于可靠的OSL测年至关重要。