Late Silurian Hypersaline Seas in the Michigan Basin and Their Impact on Ancient and Modern Groundwater

大约4亿年前，密歇根盆地地区高盐海水的存在与上志留纪厚盐层的沉积有关，与附近中志留纪烃储集层的古含盐地下水堵塞孔隙有关，也可能与极含盐和富金属的现代地下水盐水的发育有关。为了确定古咸海是否是孤立的，其表面远低于周围海洋的水平，将分析内部和外部碳酸盐单元的主要稳定碳和氧同位素比率。碳同位素特征将用于推断咸海的深度，氧同位素特征将用于推断咸海的区域范围和蒸发状态。通过对捕获古流体的显微测温分析，揭示了中志留统油气储层中古含盐地下水的存在，揭示了古流体的形成温度、总盐度和阳离子含量。最后，通过重建位于整个密歇根盆地地区的中志留世碳酸盐岩的晚期流体历史，将验证最近的咸水海水演化为现代盐水的理论。通过分析这些岩石中的氧同位素趋势和流体包裹体的化学成分，可以记录盐水开发的时间和盆地盐水流出盆地的程度。该项目将通过获取设备、岩石样本和学生参与高年级这些主题的发展，使本科教学受益。

The presence of hypersaline ocean water in the Michigan Basin region approximately 400 million years ago can be tied to the deposition of thick upper Silurian salt sequences, to the plugging of porosity by ancient saline groundwater in nearby middle Silurian hydrocarbon reservoirs, and perhaps to the development of extremely saline and metal-rich modern groundwater brines. In order to determine whether the ancient saline sea was isolated, with its surface well below the level of surrounding seas, both internal and external carbonate units will be analyzed for primary stable carbon and oxygen isotopic ratios. Carbon isotopic signatures will be used to deduce the depth of the saline sea whereas oxygen isotopic signatures will be used to deduce its regional extent and evaporation state. The presence of ancient saline groundwaters in middle Silurian hydrocarbon reservoirs will be documented by microthermometric analysis of trapped ancient fluids, which can reveal their temperature of formation, total salinity and cation content. Finally, the recent theory that saline seawater evolved into modern brines will be tested by reconstructing the late fluid history of middle Silurian carbonates located throughout the Michigan basin region. Both the timing of brine development and the extent to which basinal brines traveled out of the basin will be documented by analyzing both oxygen isotopic trends and the chemistries of fluid inclusions trapped in these rocks. The project will benefit undergraduate instruction through acquisition of equipment, rock samples and involvement of students in development of senior these topics.