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首页> 外文期刊>Quaternary geochronology >Testing the applicability of vacuum-encapsulated ~(40)Ar/~(39)Ar geochronology to pedogenic palygorskite and sepiolite
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Testing the applicability of vacuum-encapsulated ~(40)Ar/~(39)Ar geochronology to pedogenic palygorskite and sepiolite

机译：测试真空包裹〜（40）Ar /〜（39）Ar地质年代学对成岩坡缕石和海泡石的适用性

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摘要

The difficulty of isolating intact, mineralogically pure pedogenic crystals from cemented soil is one of the most significant obstacles to quantifying rates of soil formation, geomorphic processes, and climate change in arid regions.We evaluate the applicability of vacuum encapsulated ~(40)Ar/~(39)Ar geochronology to pedogenic palygorskite and sepiolite extracted from the 4 to 5 Ma, extant Mormon Mesa petrocalcic soilgeomorphic surface of southern Nevada, and from the 780 ka to 2 Ma Jornada Experimental Range La Mesa soil-geomorphic surface near Las Cruces, New Mexico. Selective dissolution of cements using NaOAc and Tiron, accompanied by particle size fractionation, was used to isolate the pedogenic Mgphyllosilicates. Scanning electron microscopy, inductively-coupled plasma spectrometry, X-ray diffraction, gas chromatograph mass spectrometry, and Ar isotope analysis were used to determine whether extraction impacted palygorskite/sepiolite suitability for ~(40)Ar/~(39)Ar geochronology. We found no adverse morphological or mineralogical effects, but meaningful ages could not be obtained due to small amounts of old, detrital phyllosilicates in the samples. While the potential of pedogenic palygorskite and/or sepiolite for geochronology now seems limited, results from this study may prove relevant for samples from other, non-pedogenic surface environments. It is hoped that this work will encourage further research towards successful ~(40)Ar/~(39)Ar geochronology of pedogenic phyllosilicates, as well as inform future geochemical or isotopic studies of individual pedogenic mineral species.
机译：从胶结土壤中分离完整的，矿物学上纯的成岩晶体的困难是量化干旱地区土壤形成，地貌过程和气候变化速率的最大障碍之一。我们评估了真空包裹〜（40）Ar /的适用性〜（39）从内华达州南部4-5 Ma的现存Mormon Mesa岩石钙质土壤地貌表面以及780 ka至2 Ma的乔丹达实验范围La Mesa土壤-地貌表面提取的成岩坡缕石和海泡石的Ar年代学，新墨西哥。使用NaOAc和Tiron选择性溶解水泥，并进行粒度分级分离，以分离成岩剂状的硅酸盐。扫描电子显微镜，电感耦合等离子体光谱，X射线衍射，气相色谱质谱和Ar同位素分析被用于确定萃取是否影响坡缕石/海泡石对〜（40）Ar /〜（39）Ar地质年代的适用性。我们没有发现不利的形态或矿物学影响，但由于样品中少量的旧碎屑层状硅酸盐而无法获得有意义的年龄。虽然成岩坡缕石和/或海泡石在地质年代学方面的潜力现在似乎很有限，但这项研究的结果可能证明与其他非成岩地表环境的样品有关。希望这项工作将鼓励对成岩层状硅酸盐成功的〜（40）Ar /〜（39）Ar地质年代学进行进一步的研究，并为将来的各个成岩矿物种类的地球化学或同位素研究提供信息。

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