Abstract We report δ13C, δ18O, δ34S records coupled with elemental, pyrite morphology, and fluid inclusion data spanning the Cherry Valley Member in the Middle Devonian Marcellus shale from two cores located across a depth gradient in the Appalachian basin. The goal of the study was to evaluate the diagenetic and redox history of this carbonate-interbedded layer within a prominent shale gas system. Three lithological units were identified in the Cherry Valley Member: a nodular clay-rich marlstone lower unit, a fossiliferous limestone middle unit, and a calcareous mudstone upper unit. Low δ13C and δ18O values of the carbonate matrix display a mixing trend among marine carbonate, authigenic carbonate, and late stage diagenetic cementation. The petrology of barite nodules and associated δ34Sbarite values suggest that a shoaling sulfate-methane transition zone created by methane advection contributed to the nodule growth and pyritization. Along with other early and late diagenetic processes, this mechanism provided the main carbonate source for the lower unit due to elevated rates of aerobic methane oxidation. The δ34Spyrite values, U and Mo contents, and pyrite framboid size distributions together constrain the redox history of the Cherry Valley Member. An anoxic-euxinic marine environment rather than a fully oxygenated environment continued through the lower unit in areas with deeper paleo-bathymetry until it was interrupted by an episode of dysoxia during the deposition of the middle unit. Basin-scale anoxia was then renewed during a subsequent 3rd order sea level rise in the upper unit. The entire Cherry Valley Member was ultimately altered by warm burial fluid interaction through vertically distributed veins. The combined body of evidence indicates that the duration and spatial distribution of oxygenated marine conditions during the deposition of Cherry Valley Member within the Marcellus Formation may have been overestimated.

中文翻译：

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中泥盆统Marcellus组樱桃谷段成岩成因及沉积历史

摘要 我们报告了 δ13C、δ18O、δ34S 记录以及元素、黄铁矿形态和流体包裹体数据，这些数据跨越阿巴拉契亚盆地中跨深度梯度的两个岩心，横跨中泥盆统 Marcellus 页岩 Cherry Valley 段。该研究的目的是评估重要页岩气系统中这个碳酸盐岩互层的成岩和氧化还原历史。在樱桃谷段确定了三个岩性单元：一个富含结节粘土的泥灰岩下层单元、一个含化石的石灰岩中层单元和一个钙质泥岩上层单元。碳酸盐基质的低δ13C和δ18O值显示出海相碳酸盐、自生碳酸盐和晚期成岩胶结作用之间的混合趋势。重晶石结核的岩石学和相关的 δ34Sbarite 值表明，由甲烷平流形成的浅滩硫酸盐-甲烷过渡带促成了结核的生长和黄铁矿化。连同其他早期和晚期成岩过程，由于有氧甲烷氧化速率升高，这种机制为下部单元提供了主要的碳酸盐来源。δ34Spyrite 值、U 和 Mo 含量以及黄铁矿小枝形尺寸分布共同限制了樱桃谷成员的氧化还原历史。在古水深测量较深的区域，缺氧 - 富氧海洋环境而不是完全氧化的环境继续通过下部单元，直到它在中间单元沉积期间被缺氧事件中断。在随后的第三级海平面上升期间，盆地尺度的缺氧被更新。整个樱桃谷段最终通过垂直分布的静脉通过温暖的埋藏流体相互作用而改变。综合证据表明，马塞勒斯组内樱桃谷段沉积期间含氧海洋条件的持续时间和空间分布可能被高估了。