Abstract We describe a new effort to date hydrothermal silica sinter deposits (geyserite) from the Upper Geyser Basin of Yellowstone National Park using 14C of co-deposited organic matter, U-series and cosmogenic 10Be methods. A majority of the samples were collected from stratigraphic sections, mainly at Riverside, Giant, and Castle Geysers. Ages obtained from 41 14C analyses range from modern to 12.1 cal ka BP. Nearly all the 14C ages show inconsistencies with their stratigraphic positions, and several replicate 14C analyses from the same sample result in significantly different ages. The δ13C values of the organic material in the sinter range from −26.6‰ to −12.7‰. The more enriched values are attributed to microbial fixation of dissolved inorganic carbon (DIC), which has heavier δ13C values and is 14C-depleted relative to atmospheric CO2, leading to an apparent older age. U-series analyses on 4 samples yielded ages between 2.2 and 7.4 ka. Large 230Th/U age uncertainties in the sinter, due to low uranium concentrations along with elevated 232Th and associated initial 230Th, make these ages imprecise for use on Holocene deposits. A single cosmogenic 10Be exposure age of 596 ± 18 ka is considerably older than the age of underlying rhyolite and is thus unreliable. This apparent old age results from contamination by meteoric 10Be trapped in the opal that overprints the very small amount of cosmogenic 10Be. By presenting the problems we encountered and discussing their probable cause, this paper highlights the difficulty in obtaining reliable, high-precision geochronological data necessary to use sinter deposits as paleoenvironmental and paleo-hydrothermal archives.

中文翻译：

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测年硅烧结矿（间歇泉）：一个警示故事

摘要 我们描述了使用 14C 共沉积有机物、U 系列和宇宙成因 10Be 方法对来自黄石国家公园上间歇泉盆地的热液二氧化硅烧结矿床（间歇泉）进行测年的新努力。大多数样品是从地层剖面收集的，主要是在 Riverside、Giant 和 Castle Geysers。从 41 14C 分析中获得的年龄范围从现代到 12.1 cal ka BP。几乎所有的 14C 年代都显示出与其地层位置不一致的情况，并且对同一样本的多次重复 14C 分析导致了显着不同的年代。烧结体中有机材料的δ13C值在-26.6‰至-12.7‰范围内。更丰富的值归因于溶解无机碳 (DIC) 的微生物固定，它具有更重的 δ13C 值并且相对于大气 CO2 消耗了 14C，导致明显的老年。对 4 个样本的 U 系列分析得出的年龄介于 2.2 和 7.4 ka 之间。由于铀浓度低以及 232Th 和相关的初始 230Th 升高，烧结矿中 230Th/U 年龄的不确定性很大，这使得这些年龄在用于全新世矿床时不精确。596 ± 18 ka 的单个宇宙成因 10Be 暴露年龄比下伏流纹岩的年龄大得多，因此不可靠。这种明显的老化是由于蛋白石中的流星 10Be 污染造成的，蛋白石覆盖了非常少量的宇宙生成 10Be。通过介绍我们遇到的问题并讨论它们的可能原因，本文强调了获得可靠、高精度的地质年代学数据的困难，这些数据必须将烧结矿床用作古环境和古热液档案。