Abstract Kerogen in organic-rich rocks contains trace amounts of lithium (Li) that has been overlooked as a contributor to the global Li geochemical cycle. This study examined a variety of coals where kerogen is concentrated (>50% organic carbon) and hydrocarbon source rocks of different ages, depositional environments and thermal maturity to determine their range of Li isotopic compositions (δ7Li‰) and factors that influence their compositions. Using Secondary Ion Mass Spectrometry (SIMS), we analyzed 22 coals and 4 hydrocarbon source rocks (Types I, II, III), to determine the δ7Li of kerogen in situ, without chemical isolation of phases that can alter their original isotopic compositions. The δ7Li values of the coals surveyed are distinctly isotopically light ( NanoSIMS isotopic maps of the Lower Bakken Shale, and SIMS measurements of the Green River Shale show isotopically light Li associated with C-dominated areas, and heavier δ7Li with Si-dominated areas of the hydrocarbon source rocks. We conclude that kerogen is a source of isotopically light Li that contributes to fluids during thermal maturation and hydrocarbon generation. Kerogen may be a significant contributor of Li to pore fluids and its distinctly light Li isotopic composition relative to other terrestrial waters and minerals could provide a tracer of organic inputs to the global geochemical cycle.

中文翻译：

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美国煤和烃源岩的锂同位素组成：碳氢化合物的潜在示踪剂

摘要 富含有机物岩石中的干酪根含有微量的锂 (Li)，而锂 (Li) 是全球锂地球化学循环的一个贡献者。本研究检查了干酪根集中的各种煤（>50% 有机碳）和不同年龄、沉积环境和热成熟度的烃源岩，以确定它们的锂同位素组成 (δ7Li‰) 范围和影响其组成的因素。我们使用二次离子质谱法 (SIMS) 分析了 22 种煤和 4 种烃源岩（I、II、III 型），以原位确定干酪根的 δ7Li，而无需对可能改变其原始同位素组成的相进行化学分离。所调查煤的 δ7Li 值明显具有同位素轻（下巴肯页岩的 NanoSIMS 同位素图，Green River 页岩的 SIMS 和 SIMS 测量显示同位素轻的 Li 与碳为主的区域相关，而较重的 δ7Li 与烃源岩的 Si 为主的区域相关。我们得出结论，干酪根是同位素轻锂的来源，在热成熟和碳氢化合物生成过程中对流体有贡献。干酪根可能是孔隙流体中锂的重要贡献者，其相对于其他陆地水和矿物质的明显轻的锂同位素组成可以为全球地球化学循环提供有机输入的示踪剂。