摘要
宇宙成因核素埋藏年龄法是继宇宙成因核素暴露年龄法之后发展起来的又一同位素定年法,这一方法主要应用于沉积物定年。宇宙成因核素埋藏年龄法的原理是:具有不同半衰期的成对宇宙成因核素浓度及比值会随时间而发生变化,这些变化可以表示成时间的函数。因此,通过测定石英中成对宇宙成因核素的含量,可以定量化沉积物的沉积时间。宇宙成因核素埋藏年龄法在实际应用中还存在几方面不确定性:测量误差、参数引入的误差以及与地质模型的差异所引入的误差,本文对这些不确定因素进行了讨论。在实际采样过程中,应注意采样点及地质背景尽可能符合地质模型;在样品处理过程中,应保证石英纯度以及选用^(10)Be含量尽可能低的铍载体。在最后,本文例举了宇宙成因核素埋藏年龄法在昔格达湖相沉积和大邑砾岩定年中的应用,以及^(26)Al-^(10)Be-^(21)Ne联合定年。可以期待,这一方法在中国将被广泛地用于研究大型河流演化、中国早期人类的演化历史、第四纪早期冰川发育以及与青藏高原演化相关的构造和沉积问题。
Cosmogenic nuclide burial dating is another isotopic dating technique developed after cosmogenic nuclide exposure age dating. This method is mainly used in dating Pliocene sediments. Cosmogenic nuclide burial dating relies on different decay constants for paired cosmogenic nuclides. The assumption behind the method is that quartz is exposed to cosmic rays on the Earth＇s surface for a period of time, acquiring certain amounts of cosmogenic nuclides. The quartz is then quickly buried and decay of cosmogenic nuclides becomes the predominant process. Currently the most widely used cosmogenic nuclide pairs are ^10Be and ^26Al. The concentrations of cosmogenic nuclides and their ratios are functions of deposition time, so that determination of concentrations of paired cosmogenic nuclides in quartz allows quantifying the deposition age of sediments where quartz is isolated. Several factors affect the precision of the cosmogenic nuclide burial dating method, e. g. errors associated with cosmogenic nuclide concentrations, uncertainties with decay constants and surface production rate ratio of paired cosmogenic nuclides, and differences from the assumed quickly, one-time burial and steady-state erosion model. These factors have been discussed in the paper. In application of the method, we should collect samples that fit the model best. Caves,road construction, tile production and sand transport sites provide good places for samples used for burial dating. Lab experiments should prepare pure quartz where the AI concentration is low, and use Be carriers containing ^10Be as less as possible. The paper also exemplifies the application of cosmogenic nuclide burial dating in understanding the formation of Xigeda sediments and the Dayi conglomerates. We can expect that the method will be widely used in China in the study of large river capture and evolution, the origin and development of early hominin, glaciations in the Early Quaternary, and other sedimentation and orogenic problems associated with the growth of the Tibetan Plateau.
出处
《第四纪研究》
CAS
CSCD
北大核心
2012年第3期388-393,共6页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41173067和41021063)资助
关键词
宇宙成因核素
埋藏年龄法
稳态侵蚀
沉积年代
地表地质过程
cosmogenic nuclide
burial dating
steady-state erosion
deposition age
geological surface process
