WN@TL - The Precambrian Geology of the Baraboo Hills. Esther Stewart. 2019.03.27

This week (March 27) Esther Stewart of the Wisconsin Geologic & Natural History Survey shares her newest insights into some of Wisconsin’s oldest rocks. The title of her presentation is "The Precambrian Geology of the Baraboo Hills." It’s a story of reading the deep-time sedimentary record and how old mine records and outcrops reveal a history of ancient rivers, oceans, and faulting in Wisconsin. Here’s how Esther describes her talk: "The Paleoproterozoic (less than 1.7 billion-years old) Baraboo Quartzite is present in the Baraboo Hills, Wisconsin, USA. It is one of several isolated quartzite outcrops across the southern Lake Superior region known as the Baraboo interval quartzites, and these rocks record a history of sedimentary basin development and regional deformation along the south-central Laurentian margin. "New Precambrian geologic mapping focused on the core of the Baraboo syncline, Sauk County combined with regional subsurface bedrock geologic mapping of Dodge County, WI refines the regional Precambrian stratigraphy of southern Wisconsin, which has allowed identification and mapping of regional faults. "Development of new geologic maps and cross-sections of southern Wisconsin’s Paleozoic and Precambrian bedrock geology involves field mapping, outcrop characterization, collection of new bedrock drill core, and discovery and integration of historic mining maps, drill records, and drill core. Revision of Precambrian stratigraphy and structure provides new constraint on the age and depositional setting of a young (less than 1.8 Ga) iron formation, which has implications for interpretations related to protracted ocean oxygenation and the evolution of life. Of more immediate practicality, mapping demonstrates that Paleozoic fold axes overlie Precambrian faults." About the Speaker: Esther Stewart has served as Precambrian geologist for the Wisconsin Geological and Natural History Survey since 2013. Prior to that, she worked as a petroleum geologist for several years in Houston, Texas. She holds a master’s degree from Idaho State University.