Stratigraphy and diagenesis of the Cambrian sandstone aquifer in northeastern Wisconsin

Author / Creator

Hischke, Tyler J., author

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Physical

Summary

The Cambrian-Ordovician aquifer of northeastern Wisconsin is utilized by domestic and high capacity wells. Although Cambrian strata have been studied extensively in southern and western Wisconsin, ...

The Cambrian-Ordovician aquifer of northeastern Wisconsin is utilized by domestic and high capacity wells. Although Cambrian strata have been studied extensively in southern and western Wisconsin, exposures are limited east of the Wisconsin Arch where the strata are broadly divided into the Elk Mound, Tunnel City, and Trempealeau Groups. Previous research in northeast Wisconsin has focused on Ordovician and younger strata, with little attention given to Cambrian rocks, despite their stratigraphic and hydrologic importance. Geogenic contaminants include radium, arsenic and associated heavy metals, strontium, and fluoride, which are dependent on aquifer rock chemistry. This study presents the first major investigation of the stratigraphy and petrography of the Cambrian rocks in northeastern Wisconsin, utilizing available outcrops and drill cores, as well as selected geologic logs and sets of well cuttings. Petrographic analysis was performed using thin-section and scanning electron microscopy of samples collected from outcrops, drill cores, and well cuttings. The Eau Claire Formation is a confining unit in the Elk Mound Group throughout much of southern and western Wisconsin, but is apparently absent in the study area. Because of this, it is recommended that the group name be used in reference to Elk Mound Group sandstones in northeastern Wisconsin. The Cambrian strata are predominantly mature quartz arenites, with arkosic and glauconitic arenites recognized in parts of the Tunnel City Group. Abundant dolomite is observed in sections of the Trempealeau and Tunnel City Groups. The authigenic mineralogy of these sandstones is complex. K-feldspar is abundant as overgrowths and authigenic cements. Carbonate cements include calcite, dolomite, ferroan dolomite, and minor ankerite. Sulfide mineralization includes pyrite/marcasite, chalcopyrite, and sphalerite. Sulfate cements include gypsum, celestine, and barite. Diagenetic kaolinite, illite, and glauconite are also observed, as well as authigenic titania minerals. This is the first comprehensive survey of the Cambrian strata in northeastern Wisconsin, and demonstrates the complex nature of both the stratigraphy and mineralogy of these rocks. This study provides information that may aid in future groundwater management efforts, as well as research of the geologic history in the area.

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