Redox state and salinity are fundamental properties of watermasses, and in modern environments, detailed analysis of spatial variability in redox and salinity is possible through direct measurement. Watermass reconstruction is difficult in deep-time systems, however, because the sedimentary record of ancient watermasses is often incomplete or difficult to access on spatial scales large enough to permit basin-scale reconstruction. During the Middle Devonian to Early Mississippian periods, the Appalachian Basin of eastern North America was characterized by a variably restricted watermass, leading to extensive deposition of organic-rich black shale associated with the regional development of bottom-water anoxia. Watermass reconstruction during deposition of these units has previously been attempted, but only on small spatial scales, with most studies focused on trace element proxies applied to individual study sections. Here, we focus instead on a broader geographic reconstruction of watermasses in the Lower Mississippian (Tournaisian) Sunbury Shale and present a new geochemical dataset that spans five drill cores across a basin transect from northeastern Ohio to southern Kentucky (USA). Iron speciation and trace metal abundances reveal a strong paleoredox gradient that can be related to water depth and basin hydrography. In the northeastern-most core of Ohio, iron speciation reveals largely ambiguous redox conditions; however, oxic conditions are potentially indicated by very low total organic carbon and trace metal contents. These oxygenated conditions were likely related to proximity to the Catskill deltaic wedge complex that fed freshwater into the basin and lowered the position of the regional pycnocline. In contrast, in central and southern Ohio, paleoredox indicators reveal the development of ferruginous conditions associated with rapid deepening to the south into the central axis of the Appalachian Basin. Further to the south in Kentucky, our data reveal dominantly euxinic conditions, which developed as environments shoaled towards the basin-bounding Cumberland Sill. We also investigated paleosalinity across the Appalachian Basin using strontium/barium (Sr/Ba) ratios. Our data reveal a subtle paleosalinity gradient from low-brackish (i.e., close to freshwater) conditions close to the Catskill Delta complex to increasingly brackish conditions to the southwest. This trend was disrupted by large paleosalinity variation across a shallow mixing zone in the southwestern-most core. Lastly, strong enrichments of redox-sensitive trace metals in both ferruginous and euxinic environments are parsimoniously attributed to the operation of an iron-manganese particulate shuttle that continuously supplied oxide-sensitive metals to the Appalachian Basin. Ultimately, this study is among the first to present detailed watermass reconstruction in an ancient epeiric sea using both redox and salinity proxies applied over a large lateral transect. We suggest that a similar approach may be useful in other deep-time systems of geobiological, paleoclimatic, and paleoceanographic significance.

氧化还原状态和盐度是水质的基本属性，在现代环境中，可以通过直接测量来详细分析氧化还原和盐度的空间变异性。但是，在深层系统中很难进行水质重建，因为古代水质的沉积记录通常是不完整的，或者难以在足够大的空间尺度上获取以允许盆地规模的重建。在中泥盆纪至密西西比初期，北美东部的阿巴拉契亚盆地的水质变化有限，导致富含有机质的黑色页岩大量沉积，与底水缺氧区域性发展有关。以前曾尝试过在这些单元沉积过程中进行水质重建，但仅在较小的空间尺度上进行，大多数研究都将重点放在适用于各个研究部分的微量元素代理上。在这里，我们将注意力集中在下密西西比（突尼斯）桑伯里页岩的水质更广泛的地理重建上，并提出一个新的地球化学数据集，该数据集横跨从俄亥俄州东北部到肯塔基州南部（美国）的一个盆地样带的五个钻芯。铁的形态和痕量金属的丰度显示出很强的古氧化层梯度，这可能与水深和盆地水文学有关。在俄亥俄州最东北的核心地带，铁形态揭示了主要的歧义氧化还原条件。但是，总有机碳和痕量金属的含量极低可能表明有氧条件。这些含氧条件可能与靠近卡茨基尔三角洲楔形物的复杂性有关，后者将淡水注入盆地并降低了区域比索克林的位置。相反，在俄亥俄中部和南部，古氧化还原指标显示出与南部迅速向阿巴拉契亚盆地中心轴加深有关的铁质条件的发展。在肯塔基州以南的地方，我们的数据显示出主要为富油酸的环境，这种环境是随着环境向着以盆地为界的坎伯兰郡基石（Sumberland Shill）浅滩发展而形成的。我们还使用锶/钡（Sr / Ba）比研究了整个阿巴拉契亚盆地的古碱度。我们的数据显示，从靠近卡茨基尔三角洲综合体的低咸度（即接近淡水）条件到西南部日益咸淡的条件，微弱的古地理梯度。在西南最核心的一个浅层混合带中，较大的古盐度变化扰乱了这一趋势。最后，在铁质和富氧环境中氧化还原敏感性痕量金属的大量富集归因于铁锰颗粒梭的运行，该梭不断向阿巴拉契亚盆地供应氧化物敏感性金属。最终，该研究是最早使用远侧横断面上的氧化还原和盐度代理对古代表观海域进行详细水质重建的研究之一。我们建议类似的方法可能在其他具有地质生物学，古气候和古海洋学意义的深层系统中有用。在铁质和富余环境中，氧化还原敏感的痕量金属的大量富集可归因于铁锰颗粒梭的运行，该梭不断向阿巴拉契亚盆地供应氧化物敏感的金属。最终，该研究是最早使用远侧横断面上的氧化还原和盐度代理对古代表观海域进行详细水质重建的研究之一。我们建议类似的方法可能在其他具有地质生物学，古气候和古海洋学意义的深层系统中有用。在铁质和富余环境中，氧化还原敏感的痕量金属的大量富集可归因于铁锰颗粒梭的运行，该梭不断向阿巴拉契亚盆地供应氧化物敏感的金属。最终，该研究是最早使用远侧横断面上的氧化还原和盐度代理对古代表观海域进行详细水质重建的研究之一。我们建议类似的方法可能在其他具有地质生物学，古气候和古海洋学意义的深层系统中有用。这项研究是最早使用远侧横断面上的氧化还原和盐度代理在古代表观海域进行详细水质重建的研究之一。我们建议类似的方法可能在其他具有地质生物学，古气候和古海洋学意义的深层系统中有用。这项研究是最早使用远侧横断面上的氧化还原和盐度代理在古代表观海域进行详细水质重建的研究之一。我们建议类似的方法可能在其他具有地质生物学，古气候和古海洋学意义的深层系统中有用。