The chronology of a sediment core from incised valley of the Yangtze River delta: Comparative OSL and AMS C-14 dating
The chronology of a sediment core from incised valley of the Yangtze River delta: Comparative OSL and AMS C-14 dating
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长江三角洲下切河谷沉积物岩心的年代学：比较 OSL 和 AMS C-14 测年
DOI：
10.1016/j.margeo.2017.11.008
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发表时间：
2018
期刊：
影响因子：
2.9
通讯作者：
Hutchinson Simon M.
中科院分区：
文献类型：
--
作者：
Nian Xiaomei;Zhang Weiguo;Wang Zhanghua;Sun Qianli;Chen Jing;Chen Zhongyuan;Hutchinson Simon M.
光激发发光（OSL）测年法在三角洲沉积物测年中得到了越来越多的应用，然而，它的应用可能受到不完全漂白问题的阻碍。为了解决这一问题，我们首次在长三角地区对单粒盐声分析方法进行了试验。在三角洲切割河谷的50.8 m沉积物岩心中共获得8个OSL和14个AMS14C样品。从8个岩心OSL样品中提取的石英，首先用中（45-63 μm）和粗（90-125 μm或150-180 μm）分数进行小多晶等分测量，以测试其各自年龄的内部一致性。结果表明，5个中粒石英样品中有4个漂白效果良好。相比之下，粗粒石英样品除2个三角洲前缘相样品外，表现出较差的白化作用。使用单粒OSL技术进一步分析了5个粗粒石英OSL样品。只有0.5-0.7%的谷物通过了拒收标准。单粒OSL定年适用于受不完全漂白影响的粗粒沉积物的年龄测定。然而，它消耗了大量的仪器时间。采用中心和最小年龄模型（CAM和MAM）计算样品的埋葬年龄；MAM时代最适合地层层序。对于中粒或粗粒石英，建议采用小等分来有效识别不完全漂白。AMS14C测年与OSL测年对比表明，14c测年比OSL测年早1 ~ 3ka。根据OSL年龄，岩心SD在10-8 ka和最后2 ka经历了快速积累。前者与全新世早期海平面的快速上升有关，而后者主要是由于沉积物中心向岩心地点迁移，而不是完全由人类活动引起的沉积物量增加。
Optically stimulated luminescence (OSL) dating has gained increased use in dating deltatic deposits, however, its application can be hindered by the problem of incomplete bleaching. To address this limitation, we test the single-grain OSL method for the first time in the Yangtze River delta. A total of eight OSL and 14 AMS14C samples were obtained from a 50.8 m long sediment core from the incised valley of the delta. Quartz extracted from eight OSL samples from the core was first measured with small multi-grain aliquots using medium- (45–63 μm) and coarse-grained (90–125 μm or 150–180 μm) fractions to test the internal consistency of their respective ages. The results showed that four of five medium-grained quartz samples appeared to be well bleached. In contrast, the coarse-grained quartz samples revealed poor bleaching, except for two samples from the delta front facies. Five coarse-grained quartz OSL samples were further analyzed using a single-grain OSL technique. Only 0.5–0.7% of the grains passed the rejection criteria. Single-grain OSL dating is appropriate for age determination of coarse-grained sediments which have been affected by incomplete bleaching. However, it consumes a lot of instrument time. Central and minimum age models (CAM and MAM) were used to calculate the burial age of the samples; MAM ages fit best in the stratigraphic sequence. Small aliquots are recommended as effective in identifying incomplete bleaching for medium- or coarse-grained quartz. A comparison of AMS14C dates and OSL ages shows that14C values are 1–3 ka older than OSL ages. According to the OSL ages, core SD experienced rapid accumulation 10–8 ka and in the last 2 ka. The former is linked to rapid sea-level rise in early Holocene, while the latter is primarily due to the migration of depo-center towards the core site, rather than entirely increased sediment delivery caused by human activities.