Characterizing the geogenic background of the Midwest: a detailed mineralogical and geochemical investigation of a glacial till in southwestern Ohio
Characterizing the geogenic background of the Midwest: a detailed mineralogical and geochemical investigation of a glacial till in southwestern Ohio
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DOI：
10.1007/s12665-020-8890-z
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发表时间：
2020-03-21
影响因子：
2.8
通讯作者：
Krekeler, Mark P. S.
中科院分区：
文献类型：
--
作者：
Barnes, Matthew;McLeod, Claire L.;Krekeler, Mark P. S.
俄亥俄州有着几十年来工业污染的悠久历史。对这种污染的来源和影响的科学调查越来越普遍，特别是在该州的西南地区，最近的研究重点是在空气，城市土壤和沉积物质量以及水生环境的背景下进行。在这些和未来的污染调查中，一个关键的支持问题是了解天然地质物质的贡献和背景浓度。从俄亥俄州西南部巴特勒县的一个公众可访问的地点--佩弗公园采集的冰碛物样品进行了详细的研究，以表征其矿物学和地球化学性质。取样的冰碛物是威斯康星州冰川作用的结果，代表了该地区广泛的冰川漂移，是量化背景地质环境的理想目标。使用ICP-OES和ICP-MS表征样品的元素丰度，同时使用粉末X射线衍射、透射电子显微镜、X射线计算机断层扫描和反射光谱研究矿物学。化学上，直到采样类似于地球的散装大陆地壳的特点轻稀土（LREE）富集和亏损中/重稀土签名。在分析的39种次要和微量元素中，74%（n = 29）在20个采样点之间的变化小于10 ppm，并且在10种主要元素氧化物中，存在< 3重量%。%的变化，其中a <lwt.观察到七种主要元素氧化物的%变化。所有标准偏差（以2 sigma报告）均< 1。粉末XRD检测到的主要矿物包括伊利石、白云石（ripidolite）、石英、方解石、白云石和长石矿物，以及少量的角闪石，这与体相化学的推断一致。选定的样品上的X射线计算机断层扫描突出了相对于颗粒尺寸的五个数量级的变化，这是明显偏向细颗粒尺寸。伴随的反射光谱特征由来自高粘土矿物的特征（例如，伊利石）和碳酸盐含量，与从与辛辛那提拱和加拿大古代结晶大陆基底相关的区域广泛的奥陶纪地层推断的源材料一致。通过多种分析技术，证明了俄亥俄州西南部的Peffer Park冰碛物的成分变化非常小，并且高度代表了美国这一地区的地质背景。因此，这里报告的特点证明其使用和应用广泛的环境参考材料的中西部。
The state of Ohio has a long history of industrial pollution over numerous decades. Scientific investigations of the sources and impacts of this pollution are becoming increasingly common, particularly in the southwest region of the state, with a strong focus of recent studies being carried out within the context of air, urban soil and sediment quality, and aquatic environments. A key supporting issue in these, and future pollution investigations, is understanding the contribution from, and background concentrations of, natural geogenic materials. A glacial till sampled from Peffer Park, a publicly accessible site in Butler County southwest Ohio, was studied in detail to characterize its mineralogical and geochemical properties. The till sampled, a result of Wisconsin-aged glaciation, represents the regionally extensive glacial drift across the region and is the ideal candidate for targeting in efforts to quantify the background, geogenic environment. Samples were characterized for their elemental abundances using ICP-OES and ICP-MS, while mineralogy was investigated using powder X-ray diffraction, transmission electron microscopy, X-ray computed tomography, and reflective spectroscopy. Chemically, the till sampled is akin to the Earth's bulk continental crust with characteristic light REE (LREE) enrichment and depleted middle/heavy REE signatures. Of the 39 minor and trace elements analyzed, 74% (n = 29) vary by less than 10 ppm between the 20 sites sampled, and of the ten major element oxides, there is a < 3 wt. % variation with a < 1 wt. % variation observed for seven of the major element oxides. All standard deviations (reported at 2 sigma) are < 1. Major minerals detected by powder XRD include illite, chlorite (ripidolite), quartz, calcite, dolomite and feldspar minerals with lesser amounts of amphibole, consistent with inferences from bulk chemistry. X-ray computed tomography on a selected sample highlights five orders of magnitude variation with respect to particle size, which is demonstrably skewed toward fine particle size. Accompanying reflective spectral features are dominated by signatures from the high clay mineral (e.g., illite) and carbonate contents, consistent with inferred source materials from the regionally extensive Ordovician stratigraphy associated with the Cincinnati Arch and the ancient crystalline continental basement of Canada. Through a wide variety of analytical techniques, it is demonstrated that the Peffer Park till of southwest Ohio has a remarkably low variation in composition and is highly representative of the geogenic background of this region of the USA. Its characteristics reported here therefore justify its use and application as a broad environmental reference material for the Midwest.