New Insights from the Baraboo Hills

Hi WN@TL Fans,
My Grandpa Zinnen worked for the Burlington Route, and so I’ve been tuned to the double iron bars since I was a kid.  Railroads run on many things, but one you might not want to overlook is the ballast under the rails and between the ties.  We think of trains as running on iron or steel ribbons, but in another sense they run on an elastic bed of stones along a road that on occasion is cut through rock, and on other occasions is chiseled or blasted from the face of a cliff.  
We owe some of our geological insights to railroads. Mines for the coal and the iron ore provided practical probes deep into the Earth.  Road cuts exposed rock layers that had been hidden from view. The steam engine’s thirst for water fueled the search for aquifers as railroads extended across the Plains and deserts.
But it’s the ballast that leads us into this week’s story on Baraboo quartzite. Pink and pointed, Baraboo ballast gives a uniquely colorful roadbed, distinct from the drab dolomite stones under the Illinois Central tracks that circled my boyhood neighborhood. And the quartzite, unlike the dolomite, really is as old as the hills.
How is it that such old strata are on the surface in Sauk County and compose the Baraboo Hills and the basin of Devils Lake?
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 (<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.


Next week (April 3Matthew Edney from the History of Cartography Project will be here to talk about the Project and to delve into the deepest origins of the Start of the Chart— when and how humans began to map their worlds.  
Also next week, on April 5, we’ll have a Special Friday Nite Edition at the special time of 7:30 in the special location of the Auditorium at the Wisconsin Historical Society on Library Mall. Tamara Thomsen of the Historical Society will speak on “Days of Ore:  Solving the Mysteries of Wisconsin’s Forgotten Mining Culture.”
Tammy’s talk helps launch the three day UW Science Expeditions campus open house April 5-7.  It’s free and it’s for everybody.  I hope you’ll come explore some of the ~30 venues that will be open to welcome you to campus in two weekends and all year round.
Hope to see you soon at Wednesday Nite @ The Lab.
Thanks again!
Tom Zinnen
Biotechnology Center & Division of Extension